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SARCOPENIA IN PRIMARY CARE: SCREENING, DIAGNOSIS, MANAGEMENT

 

S. Crosignani1, C. Sedini1, R. Calvani2, E. Marzetti2, M. Cesari3

 
1. Fellowship in Geriatrics and Gerontology, University of Milan, Milan, Italy; 2. Fondazione Policlinico Universitario “Agostino Gemelli” IRCCS, Catholic University of the Sacred Heart Rome, Italy; 3. IRCCS Istituti Clinici Scientifici Maugeri, University of Milan, Milan, Italy
Corresponding author: Silvia Crosignani, MD, Email: silvia.crosignani@unimi.it

J Frailty Aging 2020;in press
Published online December 7, 2020, http://dx.doi.org/10.14283/jfa.2020.63


Abstract

Detection of sarcopenia in primary care is a first and essential step in community-dwelling older adults before implementing preventive interventions against the onset of disabling conditions. In fact, leaving this condition undiagnosed and untreated can impact on the individual’s quality of life and function, as well as on healthcare costs. This article summarizes the many instruments today available for promoting an earlier and prompter detection of sarcopenia in primary care, combining insights about its clinical management. Primary care physicians may indeed play a crucial role in the identification of individuals exposed to the risk of sarcopenia or already presenting this condition. To confirm the suspected diagnosis, several possible techniques may be advocated, but it is important that strategies are specifically calibrated to the needs, priorities and resources of the setting where the evaluation is conducted. To tackle sarcopenia, nutritional counselling and physical activity programs are today the two main interventions to be proposed. Multicomponent and personalized exercise programs can (and should) be prescribed by primary care physicians, taking advantage of validated programs ad hoc designed for this purpose (e.g., the Vivifrail protocol). It is possible that, in the next future, new pharmacological treatments may become available for tackling the skeletal muscle decline. These will probably find application in those individuals non-responding to lifestyle interventions.

Key words: Skeletal muscle, aging, geriatrics, physical function, muscle strength.


 

Introduction

“Sarcopenia” is a term referred to the progressive loss of skeletal muscle mass typically occurring with advancing age, as defined by Irwin Rosenberg in 1989 (1). Since then, the term has been used to more broadly embrace the age-related skeletal muscle decline, including both decrease in mass as well as reduction in strength and performance. To date, several definitions of sarcopenia have been proposed in the literature, and different consensus articles have tried to operationally frame this condition. Unfortunately, despite the fact that sarcopenia has even received a specific ICD-10 code in October 2016 (2), there is still no agreement in the scientific community about the gold standard definition to adopt for capturing this condition (3). Table 1 presents the most widely used definitions of sarcopenia currently available in the literature.

Table 1
Main definitions of sarcopenia

 

Sarcopenia still represents an underdiagnosed condition in daily practice, leaving untreated many cases amenable of interventions. Given the aging of the population, it is important that primary care physicians become familiar with the management of this condition for multiple reasons:
1) Detecting sarcopenia should be part of the routine visit due to the simplicity of the necessary tools and for the limited time required;
2) Sarcopenia is considered a reversible condition and can be contrasted by correct nutrition advices and personalized physical activity programs (4, 5);
3) Interventions directed against geriatric conditions, such as sarcopenia, are usually developed with long-term objectives (6), thus likely to involve the co-management by the primary care physician;
4) The management of a clinical condition, especially at advanced age, is strongly facilitated when the primary care physician (the one who best knows the clinical characteristics and behaviours of the patient) plays an active role;
5) Tackling sarcopenia is of primary importance in the community, where the vicious cycle of disability may still be amenable of reversion;
6) Recognizing sarcopenia in primary care may improve the design of the optimal care plan for the older person.

The present article is aimed at summarizing available evidence about the diagnosis and therapeutic process that can be activated for sarcopenia in primary care. The available diagnostic tools to recognize and quantify sarcopenia will be critically discussed. In particular, it will be considered that the operational definition of sarcopenia in primary care should be balanced to the limited availability of resources and time in this specific setting.

 

Prevalence, clinical relevance and costs

According to the World Health Organization (WHO), in 2050 there will be at least 2 billion persons aged 65 years or older, compared to the current 600 million. The increasing life expectancy is a worldwide demographic phenomenon, parallel to the growing number of persons affected by age-related chronic conditions (including sarcopenia).
In the absence of a gold standard for capturing sarcopenia, the estimate of its prevalence remains quite variable. Furthermore, the prevalence of sarcopenia is also highly influenced by the studied population and the setting where the condition is looked for, thus limiting the availability of single and reliable estimates. Nevertheless, a relatively robust evaluation of the phenomenon sets the prevalence of sarcopenia to be between 8.4% and 27.6% in community-dwelling older persons (7, 8), 14-33% in long-term care residents and 10% in acute hospital care population (9).
Sarcopenia is more likely to be present in men than in women and tends to increase with advancing age. Asians, persons with low body mass index, and those with low education represent other groups of people at higher risk of sarcopenia (7).
Sarcopenia has been associated with many negative health-related outcomes, including disability, poor physical function, falls, fractures, loss of independence, hospitalizations, institutionalization, and mortality. In patients with several comorbidities and clinical conditions (e.g., patients with cancer or undergoing surgery), sarcopenia has shown to represent a negative prognostic factor (10, 11).
Analyses conducted on Third National Health and Nutrition Examination Survey (NHANES III) database have calculated the direct costs of sarcopenia. Sarcopenia was found to cost about$18,5 billion ($10.8 billion in men, $7.7 billion in women) per year in the United States, and it represented about 1.5% of total direct health care costs calculated in the year 2000 (12). Reducing the prevalence of sarcopenia by 10% would result in about $1.1 billion savings per year. And this without considering the indirect costs of sarcopenia, such as the loss of productivity for the individual as well as for the eventual caregivers(12).Another example of how burdensome is sarcopenia for public health is brought by a Portuguese study showing that sarcopenia is independently related to hospitalization costs, independently of age. Sarcopenia was responsible for adding €884 per patient (95% confidence interval [95%CI] €295-€1,476) to hospital care costs, that represents a 58.5% increase. Again, these figures are likely underestimating the economic burden of sarcopenia because not taking into account the indirect costs (13).
In order to adequately tackle sarcopenia and prevent its detrimental consequences (for both the individual and the healthcare system), it is mandatory to design and implement an effective plan of action. In fact, it is important to preventively track sarcopenia when it is still reversible, and before its vicious cycle might cause the onset of frailty and disability.In this context, it is noteworthy that not everyone with sarcopenia is disable, but the condition substantially increases the risk of disability (14). Not surprisingly, sarcopenia is frequently considered as a condition to target for avoiding the most negative consequences of the disabling process. At the same time, the positioning of sarcopenia at the initial phases of physical dysfunction automatically indicates this as a condition of special interest for primary care professionals. In other words, the detection of sarcopenia (or, at least, the suspicion of it) in primary care might promote the implementation of successful interventions when the person is still independently living in the community.

 

Screening

It is recommended that adults aged 65 years and older should be screened annually for sarcopenia, or after the occurrence of major health events (falls, hospitalization).
It is also advisable screening older adults on the occasion of the first consultation or, for instance, at annual health check-up or flu vaccination appointments (15).
For the screening of sarcopenia in primary care, several instruments and methodologies have been developed over the years. It is generally recommended that the presence of sarcopenia should be suspected in every individual aged 65 years or older, presenting signs or symptoms suggestive of skeletal muscle impairment (3). A recent consensus paper promoting the identification and management of sarcopenia in primary care has proposed the so-called “Red Flag Method”(3) (Table 2). The purpose of this method is to generate alerts about those physical manifestations typically caused by sarcopenia that can be 1) reported by the subject, or 2) evaluated by the physician during the clinical assessment. In other words, the Red Flag Method may represent a sort of checklist for supporting the physician at the identification of several neglected signs, symptoms and conditions behind which sarcopenia might be hidden(3). The pedagogical value of the method should also be acknowledged. In fact, healthcare professionals may find in it a way for being trained at the clinical manifestation of sarcopenia, becoming more familiar with it, and introducing the process in the daily routine.

Table 2
The“red flag” method, SARC-F, and other instruments for the assessment of sarcopenia in the primary care setting

BIA: Body Impedance Analysis; DXA: Dual-energy X-ray Absorptiometry; CT: computed tomography; MRI: magnetic resonance imaging; SPPB test: Short Physical Performance Battery test; TUG: Time Up and Go.

 

Alternatives to formal/structured assessments might also be found in actions made by the individual during the clinical contact. For example, hints about the possible presence of sarcopenia might be provided by the strength of the individual’s handshake, his/her walking speed from the waiting room to the office, or observing how the person sits down and stands up from the chair.
If the Red Flag Method is based on a relatively long list of items to consider in the identification of possible sarcopenia, John Morley recently developed an ad hoc instrument (i.e., the SARC-F questionnaire) for a more rapid screening of the condition(16). SARC-F is the acronym of Strength, Assistance in walking, Rise from a chair, Climb stairs, and Falls. Each of these items receives a score ranging between 0 (absence of the sign) and 2 (inability or severe issue). A total score equal to or higher than 4 points is predictive of sarcopenia and poor health-related outcomes. The SARC-F can be used to identify individuals in the need of a more detailed and careful assessment of sarcopenia, and potentially lead to a more in-depth analysis of the case through the comprehensive geriatric assessment. Interestingly, in the revised version of the European recommendations for the definition and diagnosis of sarcopenia, designed by the European Working Group on Sarcopenia in Older People (EWGSOP), the use of SARC-F is suggested for the early identification of individuals amenable of further evaluation (17). This choice is motivated by the low sensitivity and high specificity of the instrument (17, 18).
Another opportunity for promoting the inclusion of the sarcopenia assessment in primary care can be found in a wider use of anthropometry. Although they would be useful to assess the body composition, the most commonly considered imaging methods might be unfeasible in primary care. Anthropometry (i.e., the measurement of body mass index, waist circumference, calf circumference, mid-upper arm circumference, and/or skinfold thickness) may provide easily applicable, inexpensive, and non-invasive techniques for identifying individuals at risk of presenting low muscle mass (19, 20). Recently, the Yubi-Wakka (finger-ring)test has also been proposed in this context. This is a simple self-screening method to quickly assess sarcopenia, comparing the calf circumference with the ring generated by the individual’s fingers (21).Table 2 lists several methods to be considered for the screening of sarcopenia in primary care.

 

Diagnosis

As mentioned, a gold standard definition to diagnose sarcopenia is today not yet available. In general, the available recommendations coming from different panels of experts and task forces tend to indicate the need of combining a quantitative dimension (capturing the skeletal muscle mass) and a qualitative one (assessing the skeletal muscle function). Whereas the assessments of skeletal muscle strength and/or physical performance are relatively easy to be conducted, the body composition evaluation might be challenging in the primary care setting. In fact, general practitioners may not have easy/immediate access to the suggested methodologies for measuring the skeletal muscle mass, or (at best) may have to rely on suboptimal techniques. For this reason, the accurate diagnosis of sarcopenia is likely to require the referral to specialized centres, where the dual energy X-ray absorptiometry (DXA) or other (more sophisticated) techniques (e.g., magnetic resonance imaging or computerized tomography) are available. At best, the quantification of the skeletal muscle mass in primary care might be estimated using the bioelectrical impedance analysis (BIA). This technique is inexpensive, easy to use, and readily reproducible, although its results might be inaccurate, especially in the presence of certain clinical conditions (e.g., in the presence of fluid retention).
Nevertheless, a lot can still be done in primary care to detect the sarcopenia condition. The identification of individuals with sarcopenia might also start by measuring some neglected signs or symptoms of muscular poor health, for example by formally and routinely testing muscle strength/performance. In this context, the routine adoption of the handgrip strength is widely recommended and relatively easy to implement in primary care and represents a cornerstone parameter for the diagnosis of sarcopenia (22–24). In case a dynamometer is not available, the Chair Stand Test can be a valid and reliable alternative for measuring the muscle strength (17).
It is likely that, in the next future, novel methodologies will be developed for supporting Physician to diagnose sarcopenia. One of themost promising ones is represented by the deuterated creatine (D3-creatine) dilution method, which is able to provide a direct quantification of the individual’s muscle mass via the ingestion of deuterium-marked creatine and is the only technique providing a direct and unbiased estimate of muscle mass.
Although its use is currently limited to the research setting(19), this method has relevant potential for diffusion in primary care because 1) based on the simple administration of a pill and a urine analysis (to be performed after 24-48 hours), and 2) overcoming the need of the above-mentioned diagnostic tools for body composition assessment.

 

Management

Primary care physicians may play a crucial role in the identification of individuals exposed to the risk of sarcopenia or already presenting this condition. They may preventively act providing recommendations for managing reversible risk factors (e.g., sedentary behavior, unhealthy diet) and eventually referring them to specialists for further evaluation.
To date, no pharmacological agent is available for the treatment of sarcopenia, but several molecules (at different stages of development) are in the pipelines of pharmaceutical industries. Thus, physical activity and nutritional interventions currently represent the basis of the clinical management of sarcopenia(25,26). Unfortunately, there is still a general lack of knowledge among healthcare professionals for correctly prescribing personalized interventions of physical activity and/or healthy diet.

Physical activity

The design ofa person-tailored physical activity program for tackling sarcopenia is not easy, especially if considering 1) the clinical complexity of older persons presenting this condition, and 2) the lack of adequate training that healthcare professionals may receive for this task during the curriculum of traditional study. Nevertheless, the beneficial effects that a physical exercise program may exert in frail and/or sarcopenic individuals is very well documented (27).
In general, multicomponent/combined exercise programs including aerobic activities, resistance training, and flexibility exercises are recommended. These should be proposed by primary care physicians to frail and/or sedentary community-dwelling persons as part of clinical routine (15). In this context, the material produced by VIVIFRAIL project is important to be mentioned (28). VIVIFRAIL was designed to provide support to primary care physicians in the prescription of personalized programs of physical activity. The program is based on a preliminary assessment of the individual’s physical performance, muscle strength, balance, and risk of falls. The results of such evaluation are then used to design an intervention that is tailored to the individual’s capacities and deficits. Importantly, VIVIFRAIL is designed for empowering the individual at monitoring his/her progresses (29). The VIVIFRAIL material is available at the project website (www.vivifrail.eu), and an app has also been developed for supporting the individual and the healthcare professionals.
Another project to be mentioned for its potential of reshaping the management of sarcopenia is “The Sarcopenia and Physical fRailty IN older people: multi-componenT Treatment strategies” (SPRINTT) study(30). This project, funded by the Innovative Medicines Initiative (IMI), is aimed to developing an operational definition of sarcopenia that might be acceptable by regulatory agencies. The project includes a randomized control trial designed to test the effects of a multidomain lifestyle intervention (mainly based on physical activity and nutritional counselling) on a condition combining physical frailty and sarcopenia. Interestingly, the target condition was theoretically framed in order to mirror the nosological conditions that are traditionally object of observation by regulatory agencies. The developed operational definition has been preliminarily endorsed by the European Medicines Agency before the beginning of the SPRINTT randomized controlled trial. At the end of the trial, investigators will be in the position of 1) estimating the prevalence of the novel condition in the general population, 2) ascertain the reversibility of the condition after implementation of lifestyle changes promoting healthy ageing, and 3) identify a subgroup of individuals resistant to the beneficial effects of physical activity and healthy diet. In particular, this latter point is of special interest because paving the way towards the profiling of future candidates to pharmacological interventions against sarcopenia (31).

Nutrition

Malnutrition is a condition due to a protein or other nutrient imbalance, responsible for negative effects on body composition, physical function, and clinical outcome. It plays a key role in the pathogenesis of sarcopenia and fragility. It is necessary to recognize malnutrition early in older adults to plan nutritional programs aimed at improving the outcome (32).
In hospital settings Nutrition Risk Screening-2002 (NRS-2002) or Malnutrition Universal Screening Tool (MUST) are used for the screening of malnutrition whereas Mini Nutritional Assessment (MNA) is considered the gold standard for the older adults hospitalized or in an outpatient setting. In the subject at risk of malnutrition, the evaluation of the nutritional status must be carried out.
These screening tools help to have a patient-centered approach, provide adequate nutritional advice, and monitoring nutritional status over time (33, 34).
An example of malnutrition prevention is the “Health Enhancement Program (HEP)”, a randomized trial with robust results. After an initial assessment conducted by a trained staff of each participant’s health and functional status, a personalized plan was carried out to counteract disability risk factors. The program consists in motivational strategies to promote behavioral changes in depression, poor nutrition, and a sedentary lifestyle. At one year follow up, compared with enrollment, a reduction of risk factors was registered (35).
An attempt of intervention in frail older adults in a clinical setting is the program of the Geriatric Frailty Clinic (G. F. C.) at the Gerontopole of Toulouse. Older adults, considered as frail by their General Practitioner, underwent a multidisciplinary evaluation at the G.F.C where the team members proposed a Personalized Prevention Plan (PPP); in case of malnutrition, detected by the MNA, a nutritionist was asked for improve dietary intake with specific recommendations. A follow-up, consisted of a nurse call after one month and three months, was organized to determine the intervention’s efficacy. After one year the Geriatrician reassessed the patient’s improvements with a multidisciplinary evaluation (36).
Recently, two consensus papers (promoted by the European Society for Clinical Nutrition and Metabolism and the PROT-AGE study group) agreed that people aged 65 years or older require a higher intake of proteins compared to what usually recommended for activating muscle protein synthesis and maintaining muscle health. Therefore, both groups recommended the assumption of at least 1–1.2 g of proteins/kg/day in older persons, pushing even higher this minimum threshold in the presence of catabolic or muscle wasting conditions (37, 38).
About the quality of proteins, essential amino acids (EAAs; in particular leucine) are recognized as providing an important anabolic stimulus. In fact, leucine is able to increase muscle protein synthesis in older people, as also confirmed in a recent meta-analysis. In fact, its consumption has been found to be directly correlated with muscle mass in healthy older people (39).
β-hydroxy β-methylbutyrate (HMB) is one of the metabolites of leucine that is able to exert anabolic effects. HMB is frequently used by athletes to improve their physical performance and has also showed promising results in improving muscle mass and strength in older adults. When applied to bed resting older people, HMB stimulated muscle mass preservation. HBM supplementation combined with exercise seems to promote the regenerative capacity of skeletal muscles (25).
For what concerns vitamin D, its supplementation is surely useful for correcting states of insufficiency or deficiency (40, 41). Nevertheless, no evidence supports its use in individuals with normal vitamin D concentrations for improving muscle health.

Drugs

No drugs are currently registered for use in the treatment of sarcopenia, and no pharmacological intervention can be accepted as first-line therapy of sarcopenia (15). However, several new molecules are currently under study at various stages of development. It is noteworthy the special interest devoted by regulatory agencies in this field. Both the Food and Drugs Administration and the European Medicines Agency are paving the way for structuring pharmacological research on this topic.
Despite the urgency of the problem, the development of pharmaceutical therapies for sarcopenia and frailty has lagged, in part because of the lack of consensus definitions for the two conditions. In 2015,an experts’ group gathered during the International Conference on Frailty and Sarcopenia Research (ICSFR) to discuss challenges related to drugs designed to the target the biology of frailty and sarcopenia (8).
Based on the available evidence, myostatin antagonists, like Bimagrumab, may be promising candidates to treat people with low lean muscle mass, in particular people older than 70 years. Bimagrumab is a monoclonal antibody that blocks the binding of myostatin to activin, thus blocking its negative regulation of muscle growth (42). Young men treated with a single dose of Bimagrumab may experience an increase in muscle mass similar to that induced by 12 week of high-intensity resistance training(43,44), while sedentary adults may receive a benefit equivalent to 9 months of jogging 12-20 miles per week (45).
Researchers are also focused on selective androgen receptor modulators (SARMs). These are a class of androgen receptor ligands that increase low lean muscle mass by binding to the androgen receptor in muscles. Different molecules have already undergone phase I, II and III trials, but at the moment longer studies are required to demonstrate the long-term safety and the efficacy of these drugs (8).
Inflammatory modulators, such as those acting on the tumour necrosis factor-α (TNFα) and interleukin-1 (IL1), are also under study. Systemic inflammation and the increasing of TNFα and IL1 in blood lead to muscle atrophy (46). Inflammatory modulators could limit the reduction of skeletal muscle by reducing pro-inflammatory cytokines.

 

Conclusions

Sarcopenia is the age-related progressive decline of skeletal muscle. It is a common age-related condition, and has a relevant impact on the person’s quality of life and functioning, as well as on healthcare costs.
Primary care physicians may play a pivotal role in the identification of the risk of sarcopenia in the aged population. Indeed, the primary care physician may detect the early manifestations of this condition and lead to its fast diagnosis and care. In this framework, multiple instruments have been developed for promoting the detection of sarcopenia in primary care. Once sarcopenia is identified, a comprehensive assessment of the individual may lead to person-tailored interventions based on nutritional counselling and physical activity programs. In the next future, the availability of pharmacological therapies could be able to prevent the skeletal muscle decline in those individuals resistant to the benefits of healthy lifestyle prescriptions.

 

Conflicts of Interest: Matteo Cesari received honoraria from Nestlé for presentations at scientific meetings and as member of scientific advisory boards. No other conflict of interest declared by the Authors.

 

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SERUM VITAMIN D AND AGE-RELATED MUSCLE LOSS IN AFRO-CARIBBEAN MEN: THE IMPORTANCE OF AGE AND DIABETIC STATUS

 

J. Hwang1, J.M. Zmuda1, A.L. Kuipers1, C.H. Bunker1, A.J. Santanasto1, V.W. Wheeler2, I. Miljkovic1

 

1. Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA, USA; 2. Tobago Health Studies Office, Scarborough, Tobago, Trinidad & Tobago
Corresponding author: Iva Miljkovic, MD, PhD, FAHA, Associate professor, Department of Epidemiology, University of Pittsburgh, A524 Crabtree Hall, 130 DeSoto Street, Pittsburgh, PA 15261, Phone: 412-624-7325, E-mail: miljkovici@edc.pitt.edu
J Frailty Aging 2019;in press
Published online November 29, 2018, http://dx.doi.org/10.14283/jfa.2018.40

 


Abstract

Background: Prospective studies examining the potential association of vitamin D with age-related muscle loss have shown inconsistent results. Objective: To examine the association between baseline serum 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)2D), and prospective change in lean mass with aging in African ancestry population. We also determined if associations were modulated by age and diabetes mellitus (DM). Design: Prospective observational cohort study. Setting: Data were collected from a random sub-sample of 574 men, participants of the Tobago Bone Health Study (TBHS). Participants: 574 Afro-Caribbean men, aged 43+ years (mean age: 59.1 ± 10.5), who were randomly selected as the participants in both the baseline and the follow-up visits. Measurements: Baseline fasting serum 25(OH)D was measured using liquid chromatography mass spectrometry (LC-MS/MS), and and 1,25(OH)2D was measured using radioimmunosassay (RIA). Changes in dual-energy X-ray absorptiometry (DXA)-measured appendicular lean mass (ALM), and total body lean mass (TBLM) were measured over an average of 6.0 ± 0.5 years. The associations of 25(OH)D and 1,25(OH)2D with ALM and TBLM were assessed by multiple linear regression model after adjusting for potential confounders. Results: When stratifying all men into two groups by age, greater baseline 25(OH)D and 1,25(OH)2D levels were associated with smaller losses of ALM and TBLM in older (age 60+ years) but not in younger (age 43 – 59 years) men. When stratifying by DM status, the associations of 25(OH)D and 1,25(OH)2D with declines in ALM and TBLM were statistically significant only in prediabetic, but not among normal glycemic or diabetic men. Conclusion: Higher endogenous vitamin D concentrations are associated with less lean mass loss with aging among older and prediabetic Afro-Caribbean men independent of potential confounders. Our findings raise a possibility that maintaining high serum vitamin D level might be important for musculoskeletal health in elderly and prediabetic African ancestry men.

Key words: Lean mass loss, skeletal muscle, aging, diabetes, sarcopenia;


 

Introduction

Age-related muscle loss and associated physical function impairment are strongly related to decreased quality of life and increased physical disability, morbidity and mortality in later life (1). Thus, preserving muscle mass in the elderly is of public health importance. In recent years, increasing attention has been drawn to the potential beneficial role of vitamin D on preserving skeletal muscle mass with aging, despite conflicting results have been reported in several prospective studies. In a study by Visser et al., vitamin D deficiency (25(OH)D < 20 ng/mL) in both men and women aged 55-85 years old was associated with increased risk of sarcopenia more than two times than those who had sufficient serum 25(OH)D levels (2). Similarly, a study by Liu et al. also suggested that lower 25(OH)D was associated with greater appendicular lean mass loss in Chinese aged 50-70 years old (3). Recently, Hirani et al. reported that those who were in the lowest quartile of serum 25(OH)D level (25(OH)D < 40 nmol/L) and 1,25(OH)2D (< 62 pmol/L) had roughly twice the risk of sarcopenia of those with highest quartile during a 5-year follow-up in Australians aged ≥ 70 years old (4). In contrast, Scott et al. reported that baseline 25(OH)D level was not associated with change in appendicular lean mass over an average of 2.6 years in Caucasian aged 50-79 years (5). Chan et al. also found non-significant association over 4 years in Chinese population aged 65 and older (6). The majority of research on this topic has been conducted in Caucasian and Asian individuals, no prospective study was conducted in African ancestry population.
Afro-Caribbeans are known to have lower prevalence of vitamin D deficiency compared to African Americans and Caucasians, possibly due to the difference in geographic location, sunlight exposure, and lifestyles (7,8). Although low vitamin D level has often been associated with increased risk of insulin resistance and diabetes mellitus (9), the Afro-Caribbean populations have, paradoxically, high burden of diabetes mellitus (DM), possibly due, in part, to different characteristics of skeletal muscle, such as different rate of muscular fat infiltration and/or distinct composition of muscle fibers (10-12). Because DM may further exacerbate muscle loss in older adults (13), this population may be at higher risk of age-related muscle loss. However, little is known to what extent their high level of vitamin D and their high burden of DM impact the association of vitamin D with age-related skeletal muscle loss in Afro-Caribbean populations.
In the present study, we investigated the association of the baseline serum levels of 25(OH)D and 1,25(OH)2D, a biologically active form of 25(OH)D, with longitudinal changes in lean mass over an average of six years in Afro-Caribbean men aged 43 and older. Further, because advancing age and DM may alter vitamin D levels and are associated with an accelerated loss of lean mass with aging, we also tested if associations depend on age, or the presence of prediabetes or DM.

 

Methods

Study Population

From 1997 to 2003, 3,170 predominantly Afro-Caribbean men aged 40 and older were recruited for population-based Tobago Bone Health Study (TBHS) on the island of Tobago, Trinidad & Tobago. Details of the study design have been previously published (14). Briefly, eligibility criteria included being ambulatory, non-institutionalized and not terminally ill. From 2004 to 2007 (baseline for the current analysis), 2,174 men in the original cohort completed a total body dual energy x-ray absorptiometry (DXA) scan. From 2010 to 2013 (follow-up for the current analysis), 1653 men (76% of participants at baseline visit) who had DXA measured returned for repeat DXA scans. After a follow-up exam was completed, we randomly selected 574 who came both visits to have serum 25-hydroxyvitamin D (25(OH)D) and 1,25 dihydroxyvitamin D (1,25(OH)2D) measured in fasting serum samples obtained at the baseline clinic visit, with average follow-up time of 6.0 years (range: 4.6 – 8.5 years). Men selected for 25(OH)D and 1,25(OH)2D measurement were similar to those not selected in terms of baseline age, height, weight, prevalence of DM and hypertension, and other characteristics. However, selected men had significantly higher rate of physical activity (66.7% vs 42.7%, P < 0.001), and lower rate of cancer (5% vs 9.2%, P = 0.001). The Institutional Review Boards of the University of Pittsburgh and the Tobago Ministry of Health and Social Services approved this study and all subjects gave written informed consents.

Baseline and Follow-up DXA scans (2004-2007, 2010-2013)

Lean mass was measured at baseline and follow-up exams by Hologic QDR-4500W scanner (Hologic, Bedford, MA, USA) (15) according to the manufacturer’s instructions. Scans were analyzed with QDR software version 8.26a. The annual percentage change in ALM and TBLM were calculated for each individual as [(follow-up – baseline)/baseline × 1/follow-up years].

Biochemical Measurements

We were able to measure 1,25(OH)2D levels in addition to 25(OH)D, which only one prospective study has been conducted to investigate its role in musculoskeletal health despite it is a biologically functional form of vitamin D (4). Blood samples were obtained in the morning by venipuncture after a 12-hour fast. Sterile red top (serum) tubes were allowed to stand at room temperature for a maximum of 20 minutes to clot before centrifugation. Serum was aliquoted into cryovials and immediately frozen at -80˚C. All samples remained frozen until assay. 25(OH)D was measured using liquid chromatography tandem mass spectrometry (LC-MS/MS) which is considered as a gold standard to measure 25(OH)D (16), and 1,25(OH)2D was measured by radioimmunoassay (RIA) (Diasorin) which is an accurate and validated method (17). The assay involves an extraction and purification step of vitamin D metabolites. The treated sample is assayed using a competitive RIA procedure based on a polyclonal antibody specific for both 25(OH)D and 1,25(OH)2D. The intra- and inter- assay coefficients of variation were 7% and 14%, respectively. Measurement of intact parathyroid hormone (iPTH) in serum was performed using a Scantobodies immunoradiometric assay (Santee, CA) at Columbia University (18). The inter- and intra-assay coefficients of variation were 8.4% and 5.6%, respectively.

Other Measurements

We administered questionnaires asking race/ethnicity, demographic characteristics, medical history, physical activity, and lifestyle habits. Moderate alcohol use was defined as having consumed 4 or more drinks per week in the past 12 months. Smoking was defined as self-reported current smoking. We considered that men were physically active if they reported “walking for exercise in the past 7 days”, because walking is the major mode of physical activity on the island (19). We measured body weight with lightweight clothing and without shoes in kilograms using a calibrated balance beam scale. Height was measured in centimeters using a wall-mounted height board without participants wearing shoes.

Medical Conditions

DM was defined as fasting serum glucose ≥ 126 mg/dL or currently taking anti-diabetic medication. Prediabetes was defined as a fasting serum glucose level of 100-125 mg/dL measured at baseline without being diagnosed with diabetes or taking antidiabetic medication. Hypertension was defined as a systolic blood pressure of ≥ 140 mmHg and/or diastolic blood pressure of ≥ 90 mmHg, or currently taking antihypertensive medication. A history of cancer was identified by self-reported physician’s diagnosis. Vitamin D deficiency was defined as serum 25(OH)D < 20 ng/mL, and insufficiency as 20 – 29 ng/mL (20).

Statistical analysis

Descriptive statistics, including mean and standard deviations, were calculated for all continuous variables. Multiple linear regression analyses were performed to assess the relationship of 25(OH)D and 1,25(OH)2D to annualized rates of change in ALM and TBLM. Potential confounders included baseline: age, height, weight, physical activity, smoking, alcohol intake, major comorbidities (diabetes, hypertension, and cancer), and iPTH levels, as well as, change in weight during follow-up. To examine the potential modulating impact of aging on the association, we stratified men into two groups: a younger (age 43 – 59) and older group (age 60+). In secondary analyses, we also examined the potential modulating role of DM on lean mass loss with aging by stratifying subjects into three categories: no diabetes (non-DM), prediabetes (pre-DM) and diabetes (DM). Multicollinearity was assessed by variance influence factor (VIF). For all significant associations, locally weighted scatter smoothing (lowess) plot was used to assess if there was any cut-off point. Statistical significance was defined using an alpha of P < 0.05 (two-sided). All analyses were performed by STATA/MP version 14 (StataCorp, College Station, TX).

 

Results

Association of baseline 25(OH)D and 1,25(OH)2D with annual rate of change in lean mass

Table 1 shows the general characteristics for all 574 men and for men stratified by age group (age 43-59 N = 297 versus age 60+ N = 277). Average 25(OH)D and 1,25(OH)2D levels were 33.90 ± 9.12 ng/mL and 104.38 ± 46.21 pg/mL, respectively. The prevalence of vitamin D deficiency and insufficiency were 3.8% and 33.1%, respectively. ALM declined by -0.81 ± 0.84 %/year, whereas TBLM declined by -0.78 ± 0.70 %/year. There were significant differences in body weight, alcohol consumption, DM, hypertension, serum iPTH level, annual change in ALM and TBLM, and 1,25(OH)2D between middle-aged men (aged 43 – 59) and older men (aged 60+) (p < 0.05 for all).

Table 1 General Characteristics of Afro-Caribbean Men

Table 1
General Characteristics of Afro-Caribbean Men

Abbreviations: iPTH, Intact parathyroid hormone, ALM, Appendicular lean mass, TBLM, Total body lean mass, 25(OH)D, 25 hydroxyvitamin D, 1,25(OH)2D, 1,25 dihydroxyvitamin D; Continuous variables are presented as mean value ± SD, and categorical variables are presented as frequency (percentage)

 

Table 2 shows the results of the multiple linear regression analyses to assess the relationship between each vitamin D and rate of change in lean mass. In all men and the middle-aged group, neither 25(OH)D nor 1,25(OH)2D were significantly associated with ALM or TBLM change during follow-up. However, among older men, 1 standard deviation (SD) greater baseline 25(OH)D was associated with a 10% lower rate of decline in TBLM (p = 0.010). Similarly, 1 SD greater baseline 1,25(OH)2D level was associated with a 16% lower rate of decline in ALM (p = 0.004) and a 12 % lower decline in TBLM (p = 0.005). 25(OH)D was borderline, but not significantly, associated with ALM loss in the older men (p = 0.068). Using the lowess regression plot, we did not visually find any cut-off points for both 25(OH)D and 1,25(OH)2D (data not shown).

Table 2 Associations of Baseline 25(OH)D and 1,25(OH)2D with Annual Percentage Change in ALM and TBLM by Age Category

Table 2
Associations of Baseline 25(OH)D and 1,25(OH)2D with Annual Percentage Change in ALM and TBLM by Age Category

Abbreviations: ALM, Appendicular lean mass, TBLM, Total body lean mass; Data presented are β coefficient (95% CI) for annual lean mass change per 1 SD difference in vitamin D (95% CI); All models were adjusted for covariates: age, height, weight, physical activity, smoking, alcohol intake, major comorbidities (diabetes, hypertension, and cancer), and iPTH levels, as well as, change in weight during follow-up

 

Association of baseline 25(OH)D and 1,25(OH)2D with annual change in ALM and TBLM by diabetes status

Because DM has been associated with accelerated loss of lean mass with aging (12), we examined the association between baseline vitamin D metabolites levels and lean mass change in strata of DM status (non-DM, pre-DM, and DM; Table 3). Men with DM were significantly older, more obese, but lost more weight over-time than non-diabetic men (p ≤ 0.001 for all). However, the difference in lean mass change between non-diabetic men and diabetic men lost statistical significance after adjusting for age and body weight (data not shown). The association of greater baseline 25(OH)D and 1,25(OH)2D with lower rate of decline in ALM and TBLM was only significant in the pre-DM group, but not in non-DM or DM groups. (Table 4). From the lowess regression plot, we did not visually identify any cut-off points for both 25(OH)D and 1,25(OH)2D (data not shown).

Table 3 Characteristics of Afro-Caribbean Men at Baseline by Diabetes Status

Table 3
Characteristics of Afro-Caribbean Men at Baseline by Diabetes Status

Abbreviations: iPTH, Intact parathyroid hormone, ALM, Appendicular lean mass, TBLM, Total body lean mass, 25(OH)D, 25 hydroxyvitamin D3, 1,25(OH)2D, 1,25 dihydroxyvitamin D3; Continuous variables are presented as mean value ± SD, and categorical variables are presented as frequency and percentage; P-values were determined using tests for linear trend across the groups

Table 4 Associations of Baseline 25(OH)D and 1,25(OH)2D with Annual Percentage Change in ALM and TBLM by DM Status

Table 4
Associations of Baseline 25(OH)D and 1,25(OH)2D with Annual Percentage Change in ALM and TBLM by DM Status

Abbreviations: Non-DM, Non-diabetes mellitus, Pre-DM. Pre-diabetes mellitus, DM, Diabetes mellitus, ALM, Appendicular lean mass, TBLM, Total body lean mass; 25(OH)D, 25 hydroxyvitamin D3, 1,25(OH)2D, 1,25 dihydroxyvitamin D3; Data presented are β coefficient (95% CI) for annual lean mass change per 1 SD difference in vitamin D; All models were adjusted for covariates: age, height, weight, physical activity, smoking, alcohol intake, major comorbidities (hypertension, and cancer), and iPTH levels, as well as, change in weight during follow-up

 

Discussion

In the present study, we found that higher serum 25(OH)D and 1,25(OH)2D levels are independently associated with lower rate of age-related lean mass loss in older Afro-Caribbean men. Our findings related to endogenous vitamin D and lean masses are in line with some (2-4), but not all (5, 6), previous prospective studies on this topic. This discrepancy may be due to the difference in methodology to measure variables and/or population characteristics. Our studied population is entirely African ancestry, which we thus far found no prospective study on the topic conducted in African ancestry population, and found only one cross-sectional study with meaningfully high proportion of non-Caucasian men (21). Although this study reported that no association was found between serum vitamin D and muscle mass, due to the difference in study design, geographic location, and demographic characteristics, this finding may not be comparable to our study.
The men in the TBHS had a much lower prevalence of vitamin D deficiency (3.8%) than studied populations in the most previous prospective studies (9.6 – 53.7%) (2-5). One study investigated Chinese people who had relatively low prevalence of vitamin D deficiency (5.9%) (6), but unlike the current study, no association was found between appendicular lean mass and baseline 25(OH)D over 4.5 years. In contrast, Liu et al. reported significant association between serum 25(OH)D and appendicular lean mass in older Chinese population with relatively high vitamin D deficiency (53.7%) (3). Based on the two studies conducted in Chinese population, the author suggested that threshold level of 25(OH)D from which 25(OH)D has a preventive effect on muscle mass might exist. However, we did not find any threshold effect for either 25(OH)D or 1,25(OH)2D levels in the associations with a change in lean mass. Whether the difference in race/ethnicity and/or lifestyles affect these inconclusive results is unclear.
In addition, we found that the association between serum vitamin D and lean mass change was dependent on DM status such that the beneficial effect was only significant in those with prediabetes versus normal glycemia or DM. Given that antidiabetic medication has a protective effect on muscle mass (22), we postulate that the treatment effect may be masking the association between serum vitamin D and lean mass loss in the DM group. Although most analyses in the previous studies adjusted for diabetes with other covariates, to our knowledge, no study was conducted in diabetic or prediabetic individuals including cross-sectional studies. Our finding suggests that whereas the relationship between serum vitamin D and lean mass loss is unclear in younger or non-diabetic African ancestry men, it may become linear in those who are old or who have insulin resistance. This may be of clinical importance because individuals with insulin resistance have been shown to be at particularly high risk of age-related muscle mass loss (13).
We found that 1,25(OH)2D, a hormonally active form of 25(OH)D, was associated with age-related changes in lean mass to a similar extent as 25(OH)D. It has been suggested that these metabolites may have distinct effects on the muscle, with 1,25(OH)2D being correlated with muscle strength, versus 25(OH)D linked to muscle efficiency and muscle-specific gene expression (23). With regards to muscle mass, only two previous studies investigated the effect of 1,25(OH)2D. While Hirani et al. suggested that the effect of 1,25(OH)2D was similar with 25(OH)D with regards to the risk of sarcopenia (4), a cross-sectional study conducted by Marantes et al. reported a significant association of 1,25(OH)2D with muscle mass and power, but not for 25(OH)D (24). However, in our study, the effects of 25(OH)D and 1,25(OH)2D on lean mass were largely similar. Thus, potential differences in the effects of vitamin D metabolites on muscle mass and function should be clarified in future studies.
Several potential mechanisms have been proposed to explain the beneficial effects of vitamin D on age-related skeletal muscle loss. Vitamin D may regulate insulin sensitivity in skeletal muscle (25), possibly by upregulating insulin receptors expression (26), and enhancing the insulin signaling pathway (27). Vitamin D may alter the serum levels of muscle growth factors and atrophy markers as reported in an animal study (28). Furthermore, it has been suggested that vitamin D may directly contribute to myoblast proliferation and differentiation in animal (29), and human cells (30) by regulating gene transcription via vitamin D receptor (VDR) signaling pathway.
Our study has potential several limitations. First, although our study was longitudinal, our observational study design does not enable us to definitely confirm a causal relationship between serum vitamin D and lean mass changes. Second, our sample included only Afro-Caribbean men; thus, our findings may not be applicable to women or other racial/ethnic groups. A previous study reported that although the effect modification by sex was not detected in the association between serum vitamin D and muscle mass change, the degree of muscle mass loss was greater in men than women in Chinese population, suggesting the difference in sex-specific hormonal status between men and women may play a role in the association (3). Thus, the potential effect of sex, as well as, of sex-specific hormones in the association should be clarified in future studies. Third, we were not able to examine the potential modulating effect of nutritional status and sunlight exposure due to limited data in the TBHS. Fourth, the random selection of men to have vitamin D measured was performed after the follow-up visits were completed. Although we tested for baseline differences between the men selected versus those not selected for vitamin D measurement, and found them to be largely similar, we detected significant differences in the prevalence of cancer and the level of physical activity. Thus, it is possible that a survival bias remained at play in the observed associations. Finally, our data collection completed by 2013, which can be considered to be old. However, we believe that the trend we observed among Tobagonian Afro-Caribbean men would remain to date, unless a considerable change in their nutrition, lifestyle or weather on the island occurred. Despite our study limitations, the current study has a number of unique strengths ands add to the current literature on vitamin D and lean mass loss with aging. First, our study is the first longitudinal study that we are aware of that focuses on serum vitamin D and lean mass changes with aging in African ancestry individuals. Additionally, we were able to examine the individual relationships between 25(OH)D and its hormonally active form, 1,25(OH)2D, with age-related changes in lean mass. Finally, our relatively large sample size enabled us to have enough statistical power to stratify total sample to subgroups to assess potential modulating effect of both age and DM status.
In conclusion, we found that greater serum 25(OH)D and 1,25(OH)2D levels were independently associated with lower age-related loss of lean muscle mass in older and prediabetic Afro-Caribbean men. Our findings suggest that maintaining high serum vitamin D level may be important in musculoskeletal health, particularly in the elderly and those who have insulin resistance. Further studies are needed to better understand the association between vitamin D and skeletal muscle aging.

 

Funding: This research was supported, in part, by funding or in-kind services from the Division of Health and Social Services and Tobago House of Assembly, and by grants R01-AR049747 and R01-DK097084 from the National Institute of Health (NIH).
Conflict of Interest: None.

 

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24.    Marantes I, Achenbach SJ, Atkinson EJ, Khosla S, Melton LJ 3rd, Amin S. Is vitamin D a determinant of muscle mass and strength? J Bone Miner Res 2011;26(12):2860-2871.
25.    Grammatiki M, Rapti E, Karras S, Ajjan RA, Kotsa K. Vitamin D and diabetes mellitus: Causal or casual association? Rev Endocr Metab Disord 2017;18(2):227-241.
26.    Dunlop TW, Vaisanen S, Frank C, Molnar F, Sinkkonen L, Carlberg C. The human peroxisome proliferator-activated receptor delta gene is a primary target of 1alpha,25-dihydroxyvitamin D3 and its nuclear receptor. J Mol Biol 2005;349(2):248-260.
27.    Barazzoni R, Short KR, Asmann Y, Coenen-Schimke JM, Robinson MM, Nair KS. Insulin fails to enhance mTOR phosphorylation, mitochondrial protein synthesis, and ATP production in human skeletal muscle without amino acid replacement. Am J Physiol Endocrinol Metab 2012;303(9):E1117-1125.
28.    Girgis CM, Cha KM, Houweling PJ, et al. Vitamin D receptor ablation and vitamin D deficiency result in reduced grip strength, altered muscle fibers, and increased myostatin in mice. Calcif Tissue Int 2015;97(6):602-610.
29.    Girgis CM, Clifton-Bligh RJ, Mokbel N, Cheng K, Gunton JE. Vitamin D signaling regulates proliferation, differentiation, and myotube size in C2C12 skeletal muscle cells. Endocrinology 2014;155(2):347-357.
30.    Olsson K, Saini A, Stromberg A, et al. Evidence for Vitamin D Receptor Expression and Direct Effects of 1alpha,25(OH)2D3 in Human Skeletal Muscle Precursor Cells. Endocrinology 2016;157(1):98-111.

DEVELOPMENT OF PHARMACOTHERAPIES FOR THE TREATMENT OF SARCOPENIA

 

D. Rooks, R. Roubenoff

 

The Department of Musculoskeletal Translational Medicine at the Novartis Institutes for BioMedical Research, 220 Massachusetts Avenue, Cambridge, MA 02139, USA and Novartis Campus, Basel, Switzerland
Corresponding author: Daniel Rooks, The Department of Musculoskeletal Translational Medicine at the Novartis Institutes for BioMedical Research, 220 Massachusetts Avenue, Cambridge, MA 02139, USA, daniel.rooks@novartis.com
J Frailty Aging 2019;in press
Published online April 30, 2019, http://dx.doi.org/10.14283/jfa.2019.11

 


Abstract

Sarcopenia, the associated loss of skeletal muscle mass and strength and impaired physical function seen with aging, is a growing, global public health challenge in need of accepted, proven treatments that address the needs of a broad range of older adults. While exercise, primarily resistance training, and increased dietary protein have been shown to delay and even reverse losses in muscle mass, strength and physical function seen with aging, proven treatments that are accessible globally, cost effective and sustainable by patients are needed. While no drug has yet demonstrated the substantial safety and clinical value needed to be the first pharmacological therapy registered for muscle wasting or sarcopenia, the field is active. Several approaches to treating the muscle loss and subsequent functional decline are being studied in a variety of patient populations across every continent. We provide a review of the leading programs and approaches and available findings from recent studies. In addition, we briefly discuss several related issues needed to facilitate the development of a safe and efficacious pharmacotherapeutic that could be used as part of a treatment plan for older men and women with sarcopenia.

Key words: Sarcopenia, skeletal muscle, aging, functional impairment, pharmacotherapy.


 

Introduction

Sarcopenia is the age-associated loss of muscle mass and function that result in impaired muscle strength and power, adversely impacting an older persons’ functional capability. The results are typically seen as slowed walking speed and difficulty with basic movements of daily life such as rising from a seated position, climbing stairs and continuous walking. The physical consequences of sarcopenia put a person at risk for falls and fractures, hospitalization, loss of independent living and death (1, 2). The etiology of sarcopenia is a constellation of factors involving the aging neuromuscular machinery (motor unit number and efficiency, muscle architecture and orientation, fiber type distribution, excitation-contraction coupling), reduced anabolic hormone levels, muscle disuse, and inflammation, driven by environmental, genetic and behavioral factors, and is still being clarified (3-5). Even with a known etiology, the loss of muscle mass and function is commonly viewed as “normal aging” in many places. The rapid aging of societies and the increasing effectiveness of technology to engineer muscle work out of daily life, make sarcopenia a growing global public health concern that requires proven, accessible, cost effective and sustainable approaches to its prevention, delay, treatment and reversal (6-9).
Treatments for sarcopenia have focused mostly on extrinsic approaches such as exercise and diet, but recent scientific advances have brought greater attention to additional treatment options. There is a substantial body of literature demonstrating the benefits of exercise, primarily resistance training, and physical activity on muscle mass, strength and function in older adults of various levels of baseline physical function (10-14). These studies demonstrate the plasticity of the neuromotor system to adapt to external stress, even into the tenth decade of life, and the transfer of increased muscle function to the improvement of a person’s physical capacity (15-17). Similarly, data showing the efficacy of increased dietary protein and other nutrients to support healthy aging and the maintenance of physical function have led to revised dietary recommendations for protein and other nutrients in older people (18-20). Despite these advances and increased public awareness, the widespread adoption of increased exercise, physical activity or healthier eating by older adults generally has been insufficient (21-24). The topics of exercise and nutrition for improved health and function and as contributors to and potential treatment for sarcopenia in older adults have been reviewed recently (3, 25-27).
Advances in understanding of the biology associated with aging, muscle wasting and sarcopenia provide potential targets for drug discovery and are being pursued by the pharmaceutical and biotech industries and academia (28-30). This review briefly summarizes the definition of sarcopenia, commonly used assessments and preclinical studies and clinical trial findings of the more advanced drug development programs for the treatment of muscle wasting, including for sarcopenia. In addition, we discuss several related issues that are needed to facilitate the development of a safe and efficacious pharmacotherapeutic that could be used as part of a treatment plan for older men and women with sarcopenia.

 

Sarcopenia

In 1989, Irwin Rosenberg introduced the term “sarcopenia”, to describe the age-associated loss of skeletal muscle mass (31). In the past decade, the operational definition has evolved to include an estimate of total or appendicular muscle mass normalized to body size concurrent with impaired physical function, seen as muscle strength (e.g., isometric handgrip strength) and usual gait speed, with a focus on the individual’s quality of life and risk of adverse health events (32-36). Recently, the most widely referenced definition for sarcopenia was updated (37). Of note is the prioritization of muscle weakness as the primary determinant of the diagnosis, based on the view that strength is an important characteristic of the muscle disease, can be measured easily and reliably in the clinic, and is a better predictor of adverse health outcomes than low muscle mass. Low lean mass is used to confirm sarcopenia and distinguish it from other causes of muscle weakness, while gait speed and other measures of performance are used to indicate disease severity. Several cutoff points were modified and new ones added. In addition, age is acknowledged as one of many possible causes of sarcopenia and symptoms could begin before older age (37). Table 1 details the criteria and cutoffs for the various consensus statements. The most advanced operational definition of sarcopenia is being evaluated in the ongoing Innovative Medicines Initiative SPRINTT (Sarcopenia & Physical fRailty IN older people: multi-componenT Treatment strategies) study, which was approved by the European Medicines Agency (38). While no universal definition for sarcopenia exists, the consensus statements provide adequate guidance to identify a sufficiently homogeneous population of older adults with lower than average lean mass and reduced muscle function and physical performance.

Table 1 Summary of key published criteria and cut-offs for defining sarcopenia

Table 1
Summary of key published criteria and cut-offs for defining sarcopenia

ASMI –appendicular skeletal muscle index (appendicular lean mass (kg)/height (m2)) by dual X-ray absorptiometry; 6MWD – Six-minute walk distance; SPPB – Short Physical Performance Battery; TUG – Timed Up and Go test; FNIH – Foundation for the National Institutes of Health; BMI – body weight (kg)/height (m2);

 

Moving beyond aging as the primary cause of sarcopenia, cutoff points for these criteria are being applied to a broad range of populations. This use allows prevalence estimates to be established while considering racial, ethnic and geographical differences (36, 39-44).  Increasingly, the term sarcopenia has been used to describe the loss of skeletal muscle mass and function associated with various diseases (45). The range of illnesses include cancer (46), cirrhosis (47), chronic obstructive pulmonary diseases (48), peripheral arterial disease (49), post stroke (50), and heart failure (51), and in those undergoing organ transplant (52) and recovering from hip fracture (53).
Sarcopenia results in mobility disability in approximately 2-5% of older adults (54). Loss of skeletal muscle mass and strength are common consequences of many chronic diseases, of hospitalizations and bedrest, and of normal aging; and are strongly associated with morbidity, mobility impairment, loss of independence, lower quality of life and death (2, 54, 55, 56, 57). Currently, there is no standard, scalable treatment for this loss of skeletal muscle mass, strength, and function seen with aging or other causes.
Determining the occurrence of sarcopenia in a population depends on the definition used, the country or geographical region and the method of assessing lean body mass, a proxy for quantifying skeletal muscle (1, 40, 41, 58-60). Of the three criteria common among the definitions – quantity of muscle for body size, strength and gait speed – total or appendicular lean body mass has the greatest impact on prevalence (1, 61). Moreover, the method of body composition measurement – dual X-ray absorptiometry (DXA) or bioelectrical impedance analysis (BIA) – affects prevalence even further. Considering the differences between calculations and the range of ages in the various cohorts, current prevalence estimates of low muscle mass range from 1-29% in community-dwelling populations, 14-33% in long-term care populations and approximately 10% in acute care inpatients (1, 40, 41, 59, 60, 62).
In 2016, an ICD-10-CM (International Statistical Classification of Diseases and Related Health Problems, revision 10, clinical modifications) code was introduced for sarcopenia, which acknowledged it as a disease for the first time (63). Recommendations for clinical practice and clinical trials have promoted discussions and knowledge sharing to advance both areas important to developing a proven care plan for this growing patient population (8, 9, 64-66). A universally accepted definition for sarcopenia would facilitate the development of drug treatment for this patient population.

 

Clinical outcome assessments

No endpoint has been approved for the registration of a drug for sarcopenia or other muscle wasting condition, but health authorities are moving closer to accepting physical performance-based and patient-reported outcome assessments for use in drug trials (67-70). Several measures of physical performance have been validated in older adults (71, 72) and proposed as viable endpoints to assess intrinsic capacity as part of a comprehensive evaluation of health (9, 73, 74). Muscle strength, chair rise ability and gait speed assessment can predict mobility limitation (75-78) and their inclusion could move the field closer to universally accepted assessments of a person’s physical capability – the ultimate clinical goal.
The Short Physical Performance Battery (SPPB) is a series of tasks involving three domains of physical function – static balance, usual walking speed and rising from a chair – used globally to assess and quantify lower extremity function (79). Each section is scored 0-4 based on performance and summed for a total score of 0-12 with a minimum clinically important difference (MCID) of 1 point. Created and introduced in longitudinal aging studies in the United States in the 1970’s, a substantial body of literature on SPPB performance is available, documenting test-retest reliability (73); construct validity (79, 80); predictive validity for mortality (79, 81), incident disability (77, 82), institutionalization and hospitalization (73, 79), functional decline after hospital discharge (83); and sensitivity to clinically important change (72, 80, 84). The SPPB has been translated into multiple languages in Europe and Asia and has been administered throughout the world with no known serious adverse consequences. The SPPB has been used as the primary (85, 86) and key secondary (14) outcome in a number of randomized clinical trials involving lower extremity musculoskeletal function and mobility of older adults.
Gait speed or usual walking speed is easy to evaluate in both clinical and research environments, is commonly included in comprehensive geriatric care in many countries and has been called the “5th vital sign” (73, 74, 87, 88). There is a substantial body of epidemiological and intervention-based literature demonstrating a strong association between decreased gait speed (≥ 0.1 m/s) and future adverse physical, psychological and cognitive status, and health outcomes including falls, hospitalizations, mobility disability and death (89-91). Gait speeds of <0.8 m/s and <1.0 m/s over four meters have been recommended to identify older adults at increased risk of functional decline, mobility impairment and adverse health events (32, 34-36, 54, 58).
Skeletal muscle weakness is commonly seen with aging and a reduction in skeletal muscle mass, and correlates with mobility disability and other adverse health outcomes (12, 36, 92). Lower muscle strength, including when assessed by handgrip, is associated with higher risks for falling, chronic disease, impaired mobility and disability (57, 75, 93). Proposed in most consensus statements, grip strength is easy to administer, perform and interpret, does not require motor learning and is relatively inexpensive (32-35, 37, 76). However, as an isometric test, it is not necessarily a reflection of muscle function in the real world, but rather a somewhat artificial construct that gains measurement precision at the cost of direct applicability to daily functional activities. However, the recent focus on muscle weakness as a key characteristic of sarcopenia (37) makes it important to provide a clinic based tool; thus, isometric muscle strength assessed by handgrip dynamometry is being recommended more often.
Looking ahead, digital technologies such as wearable sensors, mobile applications and connected devices, that quantify mobility and other related behaviors and capabilities relevant to patients during daily life, will allow objective evidence to be used to better understand the impact a drug or other intervention has on patients’ quality of life (94, 95).
The identification of approved trial endpoints will guide drug development to use relevant assessments that can be compared across treatments (66-68, 96) and answer several critical questions: What is clinically important improvement in a patient with sarcopenia? What domains of physical function are important to patients’ quality of life? And, how much improvement in a given parameter is clinically meaningful? Until a standardized set of assessments are approved, established tests of physical function and associated MCIDs will be used in drug development trials. Findings from intervention trials in sarcopenia and from longitudinal studies where adults meeting the criteria for sarcopenia can be identified may provide a more accurate, clinically relevant MCID. Collaboration between health authorities, academia and industry will move the field closer to standardized clinical outcome assessments (70).

 

Drugs to counter muscle loss

In the past 10 years, significant efforts have been made in the area of developing a pharmacotherapeutic to treat age- and muscle-related loss of physical function.  These approaches include the potential expanded use of available drugs registered for other conditions (3, 97, 98), and to a greater extent the development of new molecular entities (Table 2).

Table 2 Overview of trials evaluating new drugs for sarcopenia and muscle wasting*

Table 2
Overview of trials evaluating new drugs for sarcopenia and muscle wasting*

* listed in clinicaltrials.gov as of 1 Jan 2019

 

The majority of first generation muscle drugs being developed act directly on the main defining characteristic of sarcopenia – the loss of muscle mass. However, drug-induced hypertrophy alone is insufficient as a treatment, unless it translates into an increase in muscle strength and improved patient function. The new field has explored various biological pathways and targets and numerous approaches, including small molecules and biologics. To date, results from trials have shown a range of measurable changes in muscle mass, with less success for improving muscle strength or patient physical function. Observed safety concerns or a lack of sufficient efficacy has thinned the early field of drug candidates; several are in phase II for efficacy and dose range finding.

 

Selective androgen receptor modulators

Selective androgen receptor modulators (SARMs) are a class of drug that controls the activity of the androgen receptor and are designed to selectively stimulate anabolic effects on skeletal muscle and other tissues (i.e., bone), without the adverse androgenic effects on liver, heart and prostate (99). SARMs have demonstrated efficacy in recovery of skeletal muscle in several preclinical models of muscle wasting, including corticosteroids and hypogonadism (99, 100). Clinically, results have shown moderate increases in lean body mass of adults with sarcopenia and in healthy older adults, without a concomitant increase in strength or improvement in physical function. In a cohort of 170 older women who met the definition of sarcopenia, 6-months’ exposure to MK-0773 (Merck, Kenilworth, New Jersey) resulted in a statistically significant increase of approximately 0.6 kg of appendicular lean body mass over placebo at 3- and 6-months, but did not improve muscle strength or physical performance (assessed by the SPPB, stair climb test and gait speed) compared to placebo (101).
In a 12-week study with 120 healthy men and women over the age of 60 years, 3 mg GTx-024 (enobosarm; GTx, Memphis, Tennessee) resulted in a statistically significant mean increase of 1.3 kg (~3%) of total lean body mass and decrease of 0.6 kg body fat (102). A corresponding statistical improvement in stair climb time observed in the GTx-024 group was not clinically meaningful. Both studies reported the drugs were well tolerated with a small number of adverse events, including elevated transaminase levels that resolved with discontinuation of the drug. Despite a positive proof of concept trial in women with stress urinary incontinence (NCT03241342), GTx-024 did not sufficiently improve outcomes in the extended study with that population (GTx-024; NCT03566290) (clinicaltrials.gov). Currently, SARMs are being evaluated for safety and efficacy in patients with hip fracture (VK5211/LGD-4033/ligandrol; NCT02578095), COPD (GSK2881078; NCT03359473), post radical prostatectomy for prostate cancer (LY2452473; NCT02499497) and in combination treatment for androgen receptor positive triple negative breast cancer (GTx-024; NCT02971761) (Table 2).

Table 3 Overview of active trials evaluating diet, exercise or combination interventions for sarcopenia and muscle wasting*

Table 3
Overview of active trials evaluating diet, exercise or combination interventions for sarcopenia and muscle wasting*

* listed in clinicaltrials.gov as of 1 Jan 2019; † HMB = β-Hydroxy β-Methylbutyrate

 

Myostatin, activin and ActRII pathway antagonists

The targets for new drugs that have received the most attention are those in the myostatin-activin pathway. Several members of the transforming growth factor beta (TGF-β) superfamily of secreted proteins, including myostatin (growth and differentiation factor 8; GDF8), activin A, and GDF11, negatively regulate skeletal muscle mass in animals and humans throughout the lifecycle (103-106). Ligand signaling occurs via activin receptors, which are heterodimers of a type I receptor (ALK4 or ALK5) and a type II receptor (ActRIIA or ActRIIB); the resulting signal is transduced and activates the Smad 2/3 pathway. These signals inhibit muscle protein synthesis and myocyte differentiation and proliferation (107, 108). The absence of any of these ligands in developing animals and humans results in a hypermuscular phenotype with an increased number and size of muscle fibers (107, 109, 110). Postpartum blockade of myostatin activity in animals and humans by either direct action on the ligand (111-115) or receptor antagonism (108, 109, 116, 117) is associated with varying degrees of muscle hypertrophy, and less frequently with clinically meaningful improvement in physical function (117).
Three approaches have been explored to drug this pathway. Initially, a soluble decoy ActRIIb receptor (ACE-031; Acceleron, Cambridge, MA) demonstrated a substantial increase in skeletal muscle mass through hypertrophy of both type I and II fibers in mice (118) and subsequently in thigh muscle volume in humans (119). The single ascending dose study was in effect a proof of concept demonstrating that the skeletal muscle effects seen in mice were translatable to humans. A single dose of ACE-031 in healthy postmenopausal women 45-75 years of age resulted in mean increases in thigh muscle volume (TMV) assessed via MRI of 3.7% and 5.3% over placebo at day 29 with 1 mg and 3 mg doses, respectively. A decrease in total fat mass (assessed by DXA) was seen in the 3 mg dose level. The mechanism of action of ACE-031 caused a reduction of follicle stimulating hormone (FSH) secretion through the inhibition of activin on stimulating FSH release. This effect on FSH is also seen with other drugs perturbing the myostatin-ActRII pathway. The ACE-031 program was stopped following the discontinuation of a study in boys with Duchenne’s muscular dystrophy due to the occurrence of epistaxis and telangiectasias (120), thought to be an effect of the drug on other members of the TGF- β superfamily (e.g., BMP9 and BMP10), rather than on activin or myostatin. A follow-up program using a similar approach (decoy receptor to myostatin, activins A and B and GDF-11) is examining the effectiveness of a recombinant fusion protein of modified human follistatin (ACE-083). However, rather than acting systemically, the antibody is designed to act locally and injected directly into a muscle. Studies in wild-type (121) and mdx mice (122) showed localized increases in muscle volume and isometric strength. The first in human study in healthy postmenopausal women showed peak volume increases of 14.5% and 8.9% in the rectus femoris and tibialis anterior muscles, respectively, with no changes in strength (123). ACE-083 is being studied in patients with facioscapulohumeral muscular dystrophy (NCT02927080) and Charcot–Marie–Tooth disease (NCT03124459). Also using a ligand trap approach, ACE-2494 is being studied in healthy volunteers (NCT03478319).
The second and most common approach to stimulating muscle growth via the myostatin-activin pathway has been by targeting the individual ligands, primarily myostatin. Early programs with the myostatin antibody MYO-029 (Wyeth, New York, NY) (124) and anti-myostatin peptibody AMG745 (Amgen; Thousand Oaks, CA) (125) showed an increase in skeletal muscle mass in preclinical studies, but were discontinued due to a lack of sufficient clinical efficacy. PF-06252616 (domagrozumab, Pfizer, New York, NY) a humanized anti-myostatin antibody and its murine analog mRK35, has shown to increase skeletal muscle mass and body weight in cynomolgous monkeys and mice, including the mdx mouse (115). Data from the first-in-human, single ascending and multiple dose study showed increases in total body lean mass by DXA of 2.50%, 5.38% and 3.33% at 15, 29 and 57 days, respectively, following a single 10 mg/kg dose (112). Notable lean mass changes were not seen with lower or higher dose levels. Three doses of 10 mg/kg resulted in a mean difference in thigh muscle volume assessed by MRI of 4.49% from placebo at Day 113 (NCT01616277). Phase II studies in Duchenne’s muscular dystrophy and limb girdle muscular dystrophy 2I are ongoing (NCT02310763; NCT02907619; NCT02841267).
LY2495655 (landogrozumab; Lilly, Indianapolis, IN), another humanized monoclonal antibody to myostatin, was evaluated in a group of 201 elderly men and women 75 years and older with a history of at least one fall in the past 12 months and low grip strength and chair rise performance (111). Following 24 weeks of chronic exposure, individuals receiving the antibody saw an increase in appendicular lean body mass (aLBM) of 0.43 kg compared to placebo (+0.303 kg vs. -0.123 kg). No clinically meaningful treatment-associated improvements were seen in muscle strength, usual gait speed or 6-minute walk distance. In a second study with a cohort of men and women ≥50 years of age who were scheduled for elective total hip arthroplasty due to osteoarthritis, 12 weeks of exposure to LY2495655 resulted in an increase in aLBM compared to placebo of less than 2.5% at 8 weeks of exposure (126). No meaningful difference in muscle strength, physical performance or self-reported measures of physical function compared to placebo was reported.
Taking a similar approach, REGN1033/SAR391786 (trevogrumab, Regeneron Pharmaceuticals Inc., Tarrytown, NY) is a human monoclonal antibody targeting myostatin. In vivo, REGN1033 demonstrated the ability to increase muscle size by increasing fiber cross-sectional area resulting in improved maximum isometric force production (strength) in young and aged mice (113). Dosing before and during hind-limb suspension (7-days) and during and after 14-days of casting or dexamethasone administration resulted in the prevention of muscle loss and enhanced recovery of muscle mass in mice compared to placebo. In addition, muscle hypertrophy and improved endurance running in old mice was observed without exercise training.  REGN1033 was evaluated for safety and efficacy in 253 sarcopenic older adults (NCT01963598) (127). Twelve weeks of exposure to three dose levels of REGN1033 (100 mg and 300 mg monthly and 300 mg every two weeks) resulted in increases in lean body mass with all doses (1.2%-1.8% vs. -0.5% PBO; p<0.05) and a decrease in total fat mass in the high dose (-2.67% vs. -0.08%) in men and women 70 years and older. Modest, inconsistent, non-significant improvements were seen in strength and function (127).
Activin A, another ligand that signals through the ActRII, has recently been proposed to have a greater effect on regulating muscle mass in primates than myostatin (113). In a recent phase I study (NCT02943239), 48 healthy postmenopausal women received a single dose of either placebo, the anti-myostatin antibody (REGN1033), an anti-activin antibody (REGN2477; garetosmab), or one of three dose levels of the combination of the two antibodies (128). Findings reported at the 2018 International Conference on Frailty and Sarcopenia Research showed that inhibiting the action of both myostatin and activin A with the two antibodies resulted in a dose dependent increase in TMV and aLBM. The group receiving the highest dose level of the combination treatment showed an increase from baseline at 8 weeks of 7.73% compared to 0.88%, 2.85% and 4.85% in the groups receiving placebo, REGN2477 and REGN1033, respectively. A reduction in total fat mass was also seen in the high dose combination group.
The above anti-myostatin antibodies work by blocking the interaction of mature myostatin with its receptor. Recently, a different approach was reported that uses human monoclonal antibodies to selectively bind to the precursor (pro- and latent) forms of myostatin inhibiting the proteolytic steps required for extracellular activation of the growth factor (129). Data with SRK-015 (Scholar Rock, Cambridge, MA) in a mouse model, reported a 27% increase in total cross sectional area and a 20% increase in mean cross sectional area of type IIB fibers of the plantar flexor. Given concurrently with dexamethasone, the antibody attenuated the drug-induced atrophy of skeletal muscle in the mice.
Receptor blockade is the third treatment strategy being explored to perturb the myostatin-ActRII pathway. BYM338 (bimagrumab, Novartis, Basel, Switzerland) is a human, monoclonal antibody to both ActRIIA and ActRIIB that prevents ligand binding to the receptor and promotes differentiation of human myoblasts by inhibiting downstream phosphorylation of Smad 2/3 (108). The affinity for both receptor types enhances the drug’s efficacy (109). Bimagrumab increased body weight and muscle size in mice by expanding myofiber cross section in slow, fast and mixed fiber type muscles in a dose dependent manner. The effectiveness of blocking all ligand activity at the ActRII vs. inhibiting myostatin alone was evaluated two ways in vivo. A mouse version of the bimagrumab antibody (CDD866) was compared to a myostatin inhibitor and resulted in greater increases in body weight (36% vs. 15%) due to muscle hypertrophy. Subsequently, CDD866 administration to both wild type and myostatin mutant mice, resulted in increased body weight, lean body mass and muscle weight in both groups, confirming that inhibiting multiple ligands of the ActRII with bimagrumab could induce greater hypertrophy than blocking myostatin alone (108). In addition, CDD866 prevented muscle loss and maintained isometric muscle strength in dexamethasone-induced atrophy (unpublished results).
In humans, bimagrumab has demonstrated consistent increases in total lean body mass and concomitant decreases of fat mass in healthy volunteers and those with insulin resistance (+1.6-2.0 kg LBM and -0.97 to -2.3 kg fat mass with 8-10 weeks of exposure) (129) and expedites the recovery of skeletal muscle volume following 14-days in a cast (116). Concomitant with the body composition changes in adults with insulin resistance, a single dose of bimagrumab resulted in a reduction of HbA1c (-0.21%) and improvement in insulin sensitivity of 20-40% (130). The mechanism of action of bimagrumab results in suppression of FSH secretion in women that is reversible with drug discontinuation (130). Other than FSH, exposure to bimagrumab results in no clinically relevant effects on the pituitary-gonadal or pituitary-adrenal axes in either men or women.
To date, the only trial with bimagrumab to see an increase in skeletal muscle mass translate to improved patient function was in a proof of concept study in older adults with sarcopenia. Participants administered bimagrumab, saw significant increases in TMV of 7.72% to 8.01% and total LBM of 5.2% to 6.0% (1.8 kg – 2.0 kg) with a corresponding decrease in total fat mass of -1.5 to -3.0 kg with 8 to 16 weeks of exposure. In patients with gait speeds <0.8 m/s at baseline, gains in lean mass seen with bimagrumab translated to clinically meaningful improvements in usual gait speed (+0.15 m/s) and six-minute walk distance (+82 m) over placebo at 16 weeks, with an improvement in distance walked (+66 m) seen at 24 weeks (117).  In patients with sporadic inclusion body myositis, an increase in muscle mass with bimagrumab treatment did not sufficiently improve patient function and the program was discontinued in this disease (NCT01925209; clinicaltrials.gov). Three phase II studies are ongoing in sarcopenia (NCT02333331), hip fracture recovery (NCT02152761) and obesity in type II diabetes (NCT03005288).

 

Other pharmacological approaches

CK-2127107 (reldesemtiv; Cytokinetics, San Francisco) is a selective fast skeletal muscle troponin activator (FSTA) designed to increase the force of contraction of type II (fast) muscle fibers. CK-2127107 and its predecessor (tirasemtiv; CK-2017357) act by increasing the sensitivity of fast skeletal muscle fibers to calcium by extending the time calcium is bound to the troponin complex, resulting in greater force production with submaximal nerve stimulation. This approach has been explored in several neuromuscular disease populations and is currently in phase 3 with tirasemtiv in patients with amyotrophic lateral sclerosis (ALS) (NCT02496767). Data on CK-2127107, a second generation FSTA, showed sufficient safety, tolerability, pharmacokinetics and initial pharmacodynamics in healthy volunteers (131) and is being studied in patients with spinal muscular atrophy (NCT02644668), ALS (NCT03160898), chronic obstructive pulmonary disease (NCT02662582) and in older adults with limited mobility (NCT03065959).
BIO101 (Sarconeos; Biophytis, Paris) is an oral medication based on the active ingredient 20-hydroxyecdysone (20E), which is an extract from the herb Stemmacantha carthamoides (Maral root). A phase II trial to evaluate safety and efficacy of six-months of exposure to BIO101 is ongoing in community-dwelling men and women with sarcopenia and sarcopenic obesity 65 years of age and older at risk for mobility disability (NCT03452488).

 

Conclusion

Sarcopenia is a growing socio-economic burden due to the ongoing demographic shift and the aging of most societies, with no viable treatment to meet the global need. While not yet successful in leading to an approved drug, significant progress has been made in the past 10 years to develop drugs for treating age- and muscle-related loss of physical function. The first generation of muscle drugs directly address the original defining characteristic of sarcopenia – the loss of muscle mass – with the expectation that a resulting muscle hypertrophy would translate to an increase in muscle strength and improved patient function. This translation of muscle mass to improved patient function remains the major challenge for current experimental drugs that target skeletal muscle anabolism. To date, results from trials have shown a range of measurable muscle hypertrophy, with limited success for improving muscle strength or patient physical function. The new field is exploring various pathways, targets and mechanisms of action based on the evolving science around skeletal muscle biology. Drug development focuses on new molecular entities and novel biology. While observed safety concerns or a lack of sufficient efficacy has thinned the early field, several drug candidates are in phase II to evaluate efficacy and dose range finding for numerous conditions with associated muscle wasting, including sarcopenia. The next generation of drugs to improve physical function will likely target muscle function directly, with less or no effect on muscle mass, which would align well with strength and patient function based diagnostic criteria for sarcopenia. Currently, available study findings hold out hope that phase III studies with drugs for the treatment of sarcopenia will begin within the next few years. As with the consensus statements defining sarcopenia, collaboration among drug development organizations and other industries, academic experts, patient advocacy groups, and health authorities will drive progress in the field of understanding the pathophysiology, medical and societal consequences and effective interventions for sarcopenia, including where a pharmacotherapeutic would be most beneficial to patients.

 

Conflict of interest: Both authors are full-time employees of Novartis Institutes for BioMedical Research.

 

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BIOMARKERS OF SARCOPENIA IN CLINICAL TRIALS RECOMMENDATIONS FROM THE INTERNATIONAL WORKING GROUP ON SARCOPENIA

 

M. CESARI1, R.A. FIELDING2, M. PAHOR3, B. GOODPASTER4, M. HELLERSTEIN5, G. ABELLAN VAN KAN1, S.D. ANKER6,7, S. RUTKOVE8, J.W. VRIJBLOED9, M. ISAAC10, Y. ROLLAND1, C. M’RINI11, M. AUBERTIN-LEHEUDRE12, J.M. CEDARBAUM13, M. ZAMBONI14, C.C. SIEBER15, D. LAURENT16, W.J. EVANS17, R. ROUBENOFF18, J.E. MORLEY19, B.VELLAS1 FOR THE INTERNATIONAL WORKING GROUP ON SARCOPENIA

 

1.  Institut du Vieillissement, Gérontopôle and INSERM Unit 1027, Université de Toulouse, Toulouse, France; 2. Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA; 3. Department of Aging and Geriatric Research, Institute on Aging, University of Florida, Gainesville, FL, USA; 4. Division of Endocrinology and Metabolism, University of Pittsburgh, Pittsburgh, PA, USA; 5. Department of Nutritional Sciences and Toxicology, University of California at Berkeley, San Francisco, CA, USA; 6. Department of Cardiology, Campus Virchow-Klinikum, Charité Universitätsmedizin Berlin, Germany; 7. Centre for Clinical and Basic Research, IRCCS San Raffaele, Rome, Italy; 8. Harvard Medical School, Boston, MA, USA; 9. Neurotune AG, Schlieren, Switzerland; 10. Human Medicine Special Areas, Scientific Advice Section, European Medicines Agency, London, UK; 11. Institut Mérieux, Lyon, France; 12. Départment de kinanthropologie, Université du Quebec, Montreal, Canada; 13. Clinical Research Operations, Neuroscience & Neuromuscular Disorders, Cytokinetics Inc., South San Francisco, CA, USA; 14. Department of Medicine, University of Verona, Verona, Italy; 15. Institute for Biomedicine of Aging, Friedrich-Alexander-University Erlangen-Nürnberg, Nürnberg, Germany; 16. Novartis Institutes for Biomedical Research, Basel, Switzerland; 17. Muscle Metabolism DPU, Metabolic Pathways CEDD, GlaxoSmithKline, Research Triangle Park, NC, USA; 18. Musculoskeletal Translational Medicine, Novartis Institutes for Biomedical Research, Cambridge, MA, USA; 19. University School of Medicine and GRECC, VA Medical Center, St. Louis, MO, USA.

Corresponding author: Matteo Cesari, MD, PhD, Institut du Vieillissement, Gerontopôle; Université de Toulouse. 37 Allées Jules Guesde, 31000 Toulouse, France. Phone: +33 (0)5 6114-5628; Fax: +33 (0)5 6114-5640; Email: macesari@gmail.com. Alternative address for correspondence: Roger Fielding, PhD, Jean Mayer USDA Human Nutrition Research Center on Aging; Tufts University. 711 Washington Street, 02111 Boston, MA, USA. Email: roger.fielding@tufts.edu

J Frailty Aging 2012;1(3):102-110
Published online February 16, 2012, http://dx.doi.org/10.14283/jfa.2012.17


Abstract

Sarcopenia, the age-related skeletal muscle decline, is associated with relevant clinical and socioeconomic negative outcomes in older persons. The study of this phenomenon and the development of preventive/therapeutic strategies represent public health priorities. The present document reports the results of a recent meeting of the International Working Group on Sarcopenia (a task force consisting of geriatricians and scientists from academia and industry) held on June 7-8, 2011 in Toulouse (France). The meeting was specifically focused at gaining knowledge on the currently available biomarkers (functional, biological, or imaging-related) that could be utilized in clinical trials of sarcopenia and considered the most reliable and promising to evaluate age-related modifications of skeletal muscle. Specific recommendations about the assessment of aging skeletal muscle in older people and the optimal methodological design of studies on sarcopenia were also discussed and finalized. Although the study of skeletal muscle decline is still in a very preliminary phase, the potential great benefits derived from a better understanding and treatment of this condition should encourage research on sarcopenia. However, the reasonable uncertainties (derived from exploring a novel field and the exponential acceleration of scientific progress) require the adoption of a cautious and comprehensive approach to the subject.

Key words: Biomarkers, sarcopenia, elderly, skeletal muscle, imaging, screening, follow-up, assessment, aging, consensus paper.

 

The present article is jointly published in the Journal of Frailty & Aging and in the Journal of Cachexia, Sarcopenia and Muscle


 

Introduction

One of the most recognized changes in body composition with senescence is the loss of skeletal muscle mass. This loss occurs even among physically active older persons and was originally termed «sarcopenia» for the Greek words «flesh» and «loss» (1). The age-related loss in skeletal muscle mass is associated with substantial social and economic costs and is characterized by impairments in strength, limitations in function, and ultimately physical disability and institutionalization (2-4). In consideration of the increased awareness of this syndrome and the continued rapid development of therapeutic strategies to slow or reverse sarcopenia, the International Working Group on Sarcopenia was convened to address issues related to the successful conduct of clinical trials in this area (5). This task force, consisting of geriatricians and scientists from academia and industry, met again in Toulouse, France in June of 2011, to discuss the current state of the art in the development of biomarkers to be utilized in clinical trials on sarcopenia. The purpose of this meeting was to gain an understanding of the currently available parameters that could be utilized in clinical trials of sarcopenia and to discuss future research needs in this area. Specific topics that were addressed include: review of current consensus definitions of sarcopenia, the importance of muscle performance and quality, biomarkers in other clinical states and chronic diseases, potential biomarkers for sarcopenia, applications in clinical trials, and recommendations for future studies.

Definition of sarcopenia

Since the advent of the term «sarcopenia» in 1989, there has been a dramatic increase in publications in this area and clinical interest in this condition (6). Originally described as the age-related decrease in skeletal muscle mass (7), until very recently there has been a lack of consensus on the operational definition of sarcopenia without clinically appropriate correlates for this syndrome. In the past two years, a number of academic societies have put forward operational definitions of sarcopenia (8-11). Although each consensus definition has some distinct features, there is general agreement among these groups on the definition of sarcopenia. A summary of consensus sarcopenia definitions is presented in Table 1. The characteristics of sarcopenia highlighted in these reports include: an objective measure of muscle or fat free mass using dual energy x-ray absorptiometry (DXA) or computed tomography (CT), a reliable measure of muscle strength, and/or an objective test of physical functioning. Although the sequence of events and specific recommendations differ somewhat, the general approaches proposed require that patients be identified with measured deficits in physical function for which sarcopenia may be the cause, and subsequently quantification of muscle strength and mass to definitively confirm the diagnosis.

Table 1 Summary of consensus sarcopenia definitions

Definition of biomarker

A biomarker is defined as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention”(12). Hence, biomarkers support the diagnosis, facilitate the tracking of changes over time, and help clinical and therapeutic decision-making processes. Taking this definition into account, the functional, biological, or imaging-related parameters considered in the present document will be hereby generally referred to with the term «biomarker».

There are currently numerous parameters that are potentially able to track the age-related skeletal muscle decline. Depending on the parameter chosen to define sarcopenia, different information might be obtained. Such variability depends on the specific characteristics of each parameter and the mechanisms measured by the parameter. The intrinsic (e.g., accuracy, specificity, sensitivity) and extrinsic (e.g., cost, availability, time to be performed) properties of each biomarker will largely drive its use in research trials, making it more suitable for screening, baseline evaluation, and/or definition of outcomes (Table 2).

Table 2 Possible biomarkers to be used in trials on sarcopenia

* The importance of all these biomarkers in the evaluation of sarcopenia will largely depend on the study hypotheses, the specific aims, and/or the target population. – : Not recommended for this use; + : may be of use, but severely limited; ++ : suitable for this use; +++ : recommended for this use

The use of biomarkers in a given study must be «fit for purpose». Thus, several different biomarkers may be required to support different aspects of the development of a therapeutic intervention. For example, biomarkers for detection and diagnosis may not be the same as those that ideally track disease progression. Likewise, for new therapeutic agents, a single assay may not suffice as a biomarker reflecting both target engagement and the pharmacodynamic effects of a drug.

Muscle quantity versus muscle quality

Although muscle mass can objectively define the presence of sarcopenia, several components of skeletal muscle function are not adequately captured by simply measuring mass or cross-sectional area. It is now clear that there is a certain degree of divergence between changes in muscle mass and alterations in muscle performance. The well-described decline in skeletal muscle mass in older adults is a critical determinant of age-related weakness, which is defined as a reduction in maximal voluntary joint torque or power. Yet, it is now clear that the relationship between force production capability and muscle size in older adults is less robust than it is in young people (13). Indeed, longitudinal studies have demonstrated that the age-related decline in muscle strength far exceeds the observed changes in muscle mass or size, particularly in weight-stable individuals (14, 15). Furthermore, longitudinal studies indicate that maintenance or even gain of muscle mass may not prevent weakness in older adults (15, 16). In addition, a number of age-related changes in force production capability is not readily explained by a reduction in muscle mass, including decreased specific force (force per cross sectional area) (17, 18) and slower rate of isometric force production (expressed relative to peak torque or to body weight) (19, 20). Furthermore, voluntary weight loss leads to reductions in muscle mass/size with no declines in muscle strength (21). It is also noteworthy that pharmacologic interventions that increase muscle mass/size do not necessarily improve voluntary strength. Similarly, physical activity interventions that increase muscle strength do not necessarily augment muscle size (22, 23). Noticeably, gains in muscle strength secondary to increased physical activity generally precede measurable changes in skeletal muscle mass/size.

The progressive muscle atrophy with aging is associated with a loss of overall muscle force and changes in force and power generation of the remaining muscle fibers (24). However, several additional physiological mechanisms that accompany the phenomenon of sarcopenia may directly influence muscle function and force production with advancing age. Recent evidence has shown that adipose tissue accumulation around and between muscle fibers concomitant with reductions in muscle cross-sectional area occurs with aging, and that this skeletal muscle attenuation is inversely associated with muscle performance (18, 25). Age-related changes in the nervous system may also play a substantial role in the decline in muscle power generation (26). These include loss of motor neurons and concomitant remodeling of motor units through collateral reinnervation (27), impairment of neuromuscular activation observed as decreased maximal motor unit firing rates (28-30) and uncoordinated patterns of intermuscular neural activation (31). Finally, changes in individual muscle fiber composition and intrinsic contractile properties may influence the decline in muscle force among older adults. For instance, cross-sectional observations suggest that reductions in muscle torque may be related to changes in fiber composition and, in particular, to the preferential atrophy of type II (fast-twitch) fibers with aging (32). Specific changes in the intrinsic ability of aged muscle to generate force have also been observed (33). Decreases in specific force (force normalized per cross sectional area) and unloaded shortening velocity in type I and IIA fibers have been reported in older males compared with young controls (32, 34). Conversely, recent longitudinal data have demonstrated that, despite reductions in whole muscle cross-sectional area, single muscle fiber contractile function is preserved with advancing age as existing fibers may compensate and partially correct these deficits, therefore maintaining optimal force-generating capacity (14).

Although precise and valid measures of muscle mass are important components of sarcopenia assessment, these gross measures of muscle size do not adequately account for the dynamic components (force, power, activation) of muscle function that are responsible for performing activities of daily living. Future trials on sarcopenia adopting clinically meaningful endpoints should evaluate these key biomarkers of muscle function through the use of state-of-the-art methodologies.

Quantitative assessment of sarcopenia

The bidimensional definition of sarcopenia simultaneously includes a functional parameter (i.e., muscle performance) and a quantitative index (i.e., muscle mass). Therefore, techniques aimed at capturing the objective amount of skeletal mucle mass are required. Multiple methodologies are currently available to accomplish this task (35).

DXA is the most commonly used imaging technique for several reasons. First of all, because it is commonly available in clinical and research settings, being relatively inexpensive, sufficiently precise, and well-accepted by older persons. Second, the initial operative definition of sarcopenia proposed by Baumgartner and colleagues (3) was based on appendicular lean mass measured by DXA. Later on, DXA was used to provide alternative definitions of sarcopenia based on the fat-adjusted residual method (36). Nevertheless, it cannot be ignored that the first operative definition is dated more than 10 years, and during this time several steps forward have been made in refining imaging techniques as well as understanding the sarcopenia phenomenon.

The identification of the “gold standard” for the quantitative evaluation of muscle mass in clinical trials (which is currently lacking) should be based on criteria of accuracy (i.e., the degree of conformity of a measure to a standard or a true value), precision (i.e., the degree of refinement with which an operation is performed or a measurement stated), reproducibility (i.e., the quality of being reproducible under the same operating conditions over a period of time, or by different operators), sensitivity to change (i.e., the degree of being modified by interventions), and accessibility (i.e., its usual availability in research and clinical centers).

DXA currently represents the more accessible technique for body composition assessment. It may accurately provide estimates of lean, fat, and bone tissues in the entire body or in specific regions. Moreover, it is inexpensive and quick to be performed. The radiation exposure associated with DXA is low and highly acceptable (about 1 mrem, a quantity similar to that of a 3-day background). The main limitations of this imaging approach reside in some analytical differences across manufacturers and models, and the risk of biased results due to the low differentiation between water and bone-free lean tissue.

CT accurately measures a direct physical property of the muscle (e.g., cross-sectional area and volume). It also allows the evaluation of muscle density (a parameter related to intramyocellular lipid deposits) as well as subcutaneous and intramuscular adipose tissue deposition. The radiation exposure associated with this technique is higher (i.e., about 15 mrem) than with DXA.

Magnetic resonance imaging (MRI) presents a high agreement with CT and provides similar measures. It does not involve radiation exposure, and also has the additional capacity of multiple slice acquisition, thus rendering 3D volumetric estimates. The lack of radiation exposure makes MRI the method of choice for many studies where ethics committee or national authority approval is more difficult to obtain for CT. The major limitations of this methodology reside in the higher technical complexity and costs, and in the inapplicability to subjects with older models of implanted metal devices (e.g., joint prostheses, pace-makers, etc.). Both CT and MRI may be limited in the ability to accomodate very obese individuals.

Finally, it needs to be emphasized that imaging provides information only about one of the two sarcopenia dimensions. As discussed earlier, changes in muscle function and quantity do not necessarily follow similar trajectories with aging (37). Therefore, interventions able to increase lean mass may not necessarily produce parallel gains in strength and vice versa (38). To overcome this issue and include the two components of sarcopenia in the same variable, it has been proposed to compute an index of skeletal muscle quality derived from the ratio between strength and mass (15, 39, 40).

One of the most recently developed techniques which might find larger application in the near future for the evaluation of sarcopenia is the electrical impedance myography (EIM) (41). This is a noninvasive, painless approach based on the surface application and measurement of a high-frequency, low-intensity electrical current applied to specific muscles. EIM detects changes in the conductivity and permittivity of skeletal muscle caused by alterations in muscle composition and structure. EIM is repeatable and sensitive to skeletal muscle changes in patients with amyotrophic lateral sclerosis (42). Moreover, its changes over time may also have clinical relevance as they are predictive of survival in animal models of amyotrophic lateral sclerosis (43). Finally, it is also noteworthy that the EIM phase shows a consistent inverse relationship with age (44).

An alternative method to measure skeletal muscle size is by ultrasonography. This technique has shown to be a valid (versus MRI-based measurements) and highly reliable way for assessing cross-sectional areas of large individual human muscles (45). It is particularly useful in mobility-impaired subjects who cannot easily be transported to scanners such as CT or MRI machines.

Also remarkable is the development of mass isotopomer distribution analysis based on the evaluation of protein and proteome synthesis rate obtained by heavy water labeling (46, 47). Although this technique can still be considered suitable mainly for research settings, its flexibility and the large amount of information it provides about a wide spectrum of proteins make it extremely promising.

Other techniques are also available to detect sarcopenia, but their limited validation, low accuracy, and difficult large-scale implementation discourage their use. For example, bioeletrical impedance analysis (BIA) is a popular, very simple and low-cost technique, but its results are far from being accurate. The BIA technique is based on the notion that tissues rich in water and electrolytes are less resistant to the electrical passage than adipose tissue. The BIA is therefore based on a single body resistance parameter (not a direct measure of skeletal muscle), and its results can be easily altered by fluid retention and health status in general. For these reasons, a recent consensus paper by the Society of Sarcopenia, Cachexia and Wasting Disorders has discouraged the use of BIA for the assessment of sarcopenia (9).

Definition of critical thresholds

There is still resistance to accept sarcopenia as a clinical condition despite its well-established relationship with major health-related negative events (in particular, mobility and physical disability) (8). This issue might (at least partly) be explained by the current lack of clinically relevant thresholds that distinguish normal from abnormal values of skeletal muscle mass.

Several approaches can be adopted to identify critical cut-points. A paradigmatic example potentially lending support to the operative definition of sarcopenia might be provided by the approach previously adopted to identify osteoporosis on the basis of bone mineral density. In fact, approaches that have been developed for bone and osteoporosis may serve well for skeletal muscle and sarcopenia. The clinical definition of a specific condition (which will consequently lead to the indication for treatment) might be based on:

1)    A parallel clinical diagnosis. For osteoporosis, diagnosis can be obtained by evaluating the presence of vertebral fractures or deformities at the X-ray examination. Vertebral fractures indicate decreased bone strength, regardless of bone mineral density. It is well-established that patients with vertebral fractures present an increased risk of new events, and therefore require treatment. This approach is legitimate and may well work, but may find some limitations when applied in primary prevention.

2)    A biological assessment. Given its well-established association with fracture risk, bone mineral density may represent the key parameter on which to rely to determine the presence or absence of osteoporosis. However, bone mineral density (like any other biological marker) exists as a continuous variable, does not present a clear threshold, and is parallel to gradients of risk. Although necessary to provide clinical relevance to biological markers, any categorization will lead to a loss of information and will inevitably introduce an “arbitrary” decision. For the definition of osteoporosis, the cut-off defining the disease was arbitrarily set by a committee which judged the -2.5 standard deviations at the T-score as an adequate match between risk and prevalence. One major problem with the bone definition that should not be repeated for sarcopenia is the inclusion of osteopenia. Osteopenia (defined by a bone mineral density T-score ranging between -1 and 2.5 SDs) encompasses about 50% of the female healthy population, and has led to confusion and concerns among policy-makers regarding the validity of a construct that cannot really be considered abnormal. An approach consistent with this model has also been adopted in the definition of other clinical conditions such as anemia (48).

3)    The risk of adverse clinical outcomes. The indication to treatment of a specific condition (e.g., osteoporosis) might be based on the evaluation of risk of events (i.e., fractures) resulting from the assessment of multiple factors (which may even not include bone mineral density) (49). This approach will not be exclusively based on the single evaluation of a (potentially inaccurate and/or arguable) biomarker, but on a more comprehensive screening and on cost-effectiveness analyses (e.g., treat if the 10-year risk is exceeding a critical threshold). With this rationale, the FRAX (50) and QFractureScores(51) algorithms were recently developed to guide osteoporosis treatment.

In summary, the presence of sarcopenia might be determined by 1) relying on a clinical diagnosis closely related to skeletal muscle decline (e.g., mobility disability) after exclusion of secondary causes, 2) a representative scientific committee identifying a critical threshold for a biological parameter directly representative of skeletal muscle health, and/or 3) developing a risk index to guide treatment.

Biological markers of sarcopenia

Given the syndromic nature of sarcopenia, intervention strategies aimed at preventing/treating its process might need to target multiple risk factors. In this context, several biological markers have been shown to be associated with skeletal muscle mass, strength and function, thus representing potential markers for the effect of the studied interventions. Such a list is quite long, and each biomarker identifies a specific mechanism contributing the age-related skeletal muscle decline, although they are not specific to muscle and many are likely to turn out to be only weakly associated with clinically relevant outcomes. The most common markers are inflammatory biomarkers [e.g., C-reactive protein (52, 53), interleukin-6 (52-54), and tumor necrosis factor-α (52, 54)], clinical parameters [e.g., hemoglobin (55, 56), serum albumin (57, 58), urinary creatinine (59)], hormones [e.g., dehydroepiandrosterone sulfate (60), testosterone (61), insulin-like growth factor-1 (62), and vitamin D (63-65)], products of oxidative damage [e.g., advanced glycation end-products (66), protein carbonyls (67, 68), and oxidized low-density lipoproteins (69)], or antioxidants [e.g., carotenoids (70, 71), and α-tocopherol (70)].

Other promising biomarkers have been identified in the last years and may represent useful parameters to more directly explore sarcopenia because they are closely related to skeletal muscle changes. For example, plasma concentrations of procollagen type III N-terminal peptide (P3NP) represent an interesting marker of skeletal muscle remodeling (72, 73). P3NP is a fragment released by the cleavage of procollagen type III to generate collagen III (a protein produced in soft connective tissues, skin, and muscle). Preliminary studies have also suggested an interesting role played by biomarkers specifically linked to the neuromuscular junction in evaluating skeletal muscle modifications (74, 75).

Clinical outcome measures of sarcopenia

Ultimately, the goal of clinical trials for sarcopenia treatments will require the evaluation of clinical benefit. In fact, clinical measures can also be considered as biomarkers as they reflect the impact of the pathological process of sarcopenia on the patient’s health. The assessment of measures of muscle strength (e.g., hand grip), muscle power (e.g., leg extension power), and physical performance [e.g., Short Physical Performance Battery (4) and gait speed tests] comprise important indices of the individual’s physical function. In addition, functional outcome measures will need to be developed in order to help understand the impact of any treatment-related quantitative gains in performance on the person’s daily life.

Recommendations

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Adoption of comprehensive operative definitions

The lack of a unique operative definition of sarcopenia and the numerous methodological issues could potentially hinder efforts to study sarcopenia and to develop effective treatments. Such difficulties should not hamper the process of exploring this syndrome which severely affects the health status of millions of older persons. The current ambiguities can be easily overcome by adopting flexible and comprehensive approaches in the design of studies, for example by avoiding reliance on a single parameter or technique to evaluate age-related skeletal muscle decline. The adoption of a variety of assessment approaches in combination is agreeable. Although this might lead to the risk of conflicting results (and increase the need of resources), it will serve to 1) capture different domains of the sarcopenia syndrome, 2) provide useful insights about the pathophysiological process underlying this phenomenon, and 3) facilitate the development and use of the findings in future and more definitive studies. In this context, it is noteworthy the lack of studies simultaneously testing different techniques measuring skeletal muscle (e.g., MRI, CT, DXA, etc) in relationship with clinically meaningful outcomes. Such studies might greatly help in the standardization of instruments and in the adoption of an univocal direction in the study of sarcopenia.

MRI and CT scan to be equally considered as “gold standard” imaging techniques

It is now clear that to be adequately assessed, the sarcopenia phenomenon cannot merely rely on the evaluation of the contractile part of skeletal muscle. The close relationship between lean mass and adipose tissue in determining age-related decline of skeletal muscle is evident (38, 76, 77). Therefore, techniques allowing the simultaneous evaluation of fat and muscle should be preferred. DXA, CT and MRI are the most important assessment instruments. CT and MRI should be considered the “gold standard” techniques. The balance of pros and cons for both CT and MRI does not allow a clear indication on which of the two should be preferred. Resources, instrument availability, and need of details will represent the factors guiding the investigator’s preference for one over the other. On the other hand, DXA should not be discarded, and still represents the instrument more likely to promote the “clinical relevance” of sarcopenia. For its characteristics, DXA may be an extremely interesting methodology to be used for preliminary screening. Moreover, its use in combination with either CT or MRI will help drive the research in the field towards more clinical aspects. While imaging and other biomarkers will be valuable tools for initial proof of concept studies, assessment tools for evaluating the effect of treatments on outcomes reflecting clinical benefit will be required to support eventual pivotal studies.

Adequate length of study

To evaluate the efficacy of a specific intervention on sarcopenia, it is necessary that the follow-up will be sufficiently long to allow the hypothesized modifications of biomarkers. Surely, not all biomarkers will be similarly influenced by the intervention. Such variations will depend on multiple factors, including the population characteristics, the type and strength of the tested intervention, and the sensibility of the biomarker to changes. However, six months have been generally indicated as the minimum timeframe to expect changes in imaging parameters.

Sarcopenia is a “work in progress”

The study of sarcopenia is still in its infancy, but we have clearly acknowledged the great potential benefits arising from the understanding and treatment of this condition at both person and population levels. Taking together the uncertainties of exploring a novel field with the exponential acceleration of scientific progress, it is currently difficult to provide long-lasting statements, recommendations, and guidelines. It is likely that what seems reasonable today will be confounded by several studies in the near future. For this reason, extreme caution is needed to avoid jeopardizing the future development of research in the field. It is important to consider the study of sarcopenia as a “work in progress”, always amenable to changes and redirections. After all, the first Phase II trials in this syndrome are just starting, and this is the appropriate time to raise doubts and pose questions. With time, a stronger foundation for sarcopenia research will be developed that will ultimately lead to larger scale and more definitive studies. In this context, it is critical that an ongoing dialogue be initiated and sustained amongst investigators with an interest in age-dependent decline of muscle.

Acknowledgements: Dr. Fielding’s contribution is based upon work supported by the US Department of Agriculture, under agreement No. 58-1950-7-707.

Members of the International Working Group on Sarcopenia: Gabor Abellan Van Kan, France; Sandrine Andrieu, France; Stefan D. Anker, Germany; Patricia Anthony, Switzerland; Christian Asbrand, Germany; Mylène Aubertin-Leheudre, Canada; Sebastien Barbart-Artigas, Canada; Olivier Benichou, France; Cécile Bonhomme, France; Pascale Borensztein, France; Denis Breuillé, Switzerland; Sergio Castro Henriquez, Chile; Jesse M. Cedarbaum, USA; Matteo Cesari, France; Patricia Chatelain, France; Wm. Cameron Chumlea, USA; Richard V. Clark, USA; Capucine De Meynard, France; William J. Evans, USA; Gary Fanjiang, USA; Luigi Ferrucci, USA; Roger A. Fielding, USA; Philippe Garnier, France; Sophie Gillette-Guyonnet, France; Bret Goodpaster, USA; Marie-Françoise Gros, France; Luis Miguel F. Gutierrez Robledo, Mexico; Marc Hellerstein, USA; Kelly Krohn, USA; Maria Isaac, United Kingdom; Didier Laurent, Switzerland; Menghua Luo, USA; Hélène Matheix-Fortunet, France; Inge Mohede, The Netherlands; John E. Morley, USA; Christine M’Rini, France; Ramon Navarro, France; Bruno Oesch, Switzerland; Reinhard Ommerborn, Germany; Marco Pahor, USA; Patrick Ritz, France; Yves Rolland, France; Daniel Rooks, USA; Ronnen Roubenoff, USA; Fariba Roughead, Switzerland; Seward Rutkove, USA; Cornel C. Sieber, Germany; Michèle Storrs-Malibat, France; Stephanie Studenski, USA; Yannis Tsouderos, France; Bruno Vellas, France; Sjors Verlaan, The Netherlands; Stephan Von Haehling, Germany; J. Willem Vrijbloed, Switzerland; Sander Wijers, The Netherlands; Mauro Zamboni, Italy.

Conflicts of interest: MC has received consultancy fees from Sanofi-Aventis and Pfizer; RAF is consultant with Merck, Eli Lilly, Cytokinetics, DMI, Kraft Foods, and Unilever; MH is stockholder, chairmen of scientific advisory board and consultant for KineMed, Inc.; SA is consultant with Brahms, Vifor, Professional Dietetics, PsiOxus, Takeda, receives research support from Vifor, BG Medicine, and has received fees for speaking at meetings from Brahms, Vifor; SR has equity in and receives consulting income from Convergence Medical Devices, Inc; WV is employee and shareholder of Neurotune AG; YR receives support from Lactalis, Lundbeck, Lilly, Nutricia, Servier, Cheisi, Ipsen, Novartis; JMC is employee and shareholder of Cytokinetics, Inc; MZ has received a fee from Abbot for a conference; DL and RR are employed by Novartis; WJE is employed by GlaxoSmithKline; JEM is consultant and stokeholder of Mattern Pharmaceuticals and consultant for Sanofi-Aventis; BV is consultant and member of Advisory Board with Novartis, Servier, Nestlè. MP, BG, GAVK, MI, CMR, MAL, CCS have no conflict of interest to declare.

Disclaimer: Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the Authors and do not necessarily reflect the position of the supporting organizations or agencies.

 

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PROCOLLAGEN TYPE III N-TERMINAL PEPTIDE (P3NP) AND LEAN MASS: A CROSS-SECTIONAL STUDY

 

S.D. BERRY1, V.S. RAMACHANDRAN2,5, P.M. CAWTHON3, P. GONA4,5, R.R. MCLEAN1, L.A. CUPPLES5,6, D.P. KIEL1

 

1. Hebrew SeniorLife, Institute for Aging Research & Harvard Medical School, 1200 Centre Street, Boston, MA 02131, USA; 2. Boston University School of Medicine, 671 Harrison Avenue, Harrison Court B06, Boston, MA 02118, USA; 3. California Pacific Medical Center Research Institute, Suite 5700, 185 Berry Street, San Francisco, CA 94107, USA; 4. University of Massachusetts Medical School, Dept. of Quantitative Health Sciences, 55 Lake Ave North Worchester, MA01655, USA; 5. Framingham Health Study, 73 Mt. Wayte Avenue, Framingham, MA 01702, USA; 6. Boston University School of Public Health, 715 Albany Street, Boston, MA 02118, USA

Corresponding Author: Sarah D. Berry, MD MPH; Hebrew SeniorLife, Institute for Aging Research & Harvard Medical School, 1200 Centre Street, Boston, MA 02131. Phone: +1 (617) 971-5355; Fax:  +1 (617) 971-5339; e-mail: doxycycline dosage for walking pneumonia doxycycline hyclate and alcohol sarahberry@hsl.harvard.edu.

J Frailty Aging 2013;2(3):129-134
Published online February 11, 2016, http://dx.doi.org/10.14283/jfa.2013.19


Abstract

Background: Procollagen type III N-terminal peptide (P3NP) is released during collagen synthesis in muscle. Increased circulating P3NP is a marker not only of muscle growth, but also of muscle repair and fibrosis.  Thus, P3NP may be a potential biomarker for sarcopenia. Objective: To determine the association between plasma P3NP and lean mass and strength. Design, Setting, and Participants: A cross-sectional study of men and women from the Framingham Offspring Study. Participants included a convenience sample of 687 members with a measure of plasma P3NP and lean mass, and 806 members with P3NP and quadriceps strength assessment. Measurements: Linear regression was used to estimate the association between total and appendicular lean mass and plasma P3NP, and quadriceps strength and P3NP. Results: Mean age was 58 years. Median plasma P3NP was similar in men (3.4 mg/L), premenopausal women (3.1 mg/L), and postmenopausal women (3.0 mg/L). In adjusted models, higher P3NP was associated with a modest decrease in total and appendicular lean mass in postmenopausal women [β= -0.13 unit P3NP/kg total lean mass; p=0.003]. A similar trend was found among premenopausal women, although results were not statistically significant [β=-0.10 unit P3NP/kg total lean mass; p=0.41]. No association between P3NP and lean mass was observed in men. P3NP was not associated with strength in men or women. Conclusion: Our results suggest that plasma P3NP might be a useful biomarker of muscle mass in postmenopausal women if longitudinal studies demonstrate that it has adequate sensitivity and specificity to predict muscle loss.

Key words: Procollagen type III N-terminal peptide, lean mass, sarcopenia, skeletal muscle, aging.


 

Introduction

Sarcopenia, which is characterized by reduced muscle mass and diminished muscle function (1, 2), is common among elderly persons (3). Although loss of lean mass may be a weak predictor of adverse health outcomes such as gait abnormalities and disability (4-7), muscle mass remains an important determinant of muscle function (8). Despite the clinical significance of age-related declines in muscle mass and function, the mechanisms for this phenomenon are not fully understood, and to date, there are no approved therapies to maintain or improve muscle mass in older adults. The discovery of methods to identify persons at risk for loss of lean mass is therefore critical as they may lead to improved therapeutic options.

A potential biomarker to identify elders at risk for sarcopenia is procollagen III N-terminal peptide (P3NP).  Procollagen type III is found abundantly in skeletal muscle and other soft tissues such as skin, and in negligible amounts in bone. During the late phases of collagen synthesis, the N-terminal end of procollagen  type III is cleaved releasing P3NP into the circulation (9). Thus, increased levels of P3NP have been observed during the normal increases in lean mass associated with puberty in adolescent boys and girls (10), as well as in response to endurance-type exercise in adult males (11).

High levels of P3NP have also been observed in pathologic conditions associated with abnormal collagen formation including congestive heart failure (12, 13), hypertension (14), coronary artery disease (15), and cirrhosis (16). In these diseases, it is postulated that inflammation leads to abnormal collagen synthesis and fibrosis of the associated soft tissues, which results in elevated P3NP levels (17). With aging, healthy muscle fibers are lost and there is denervation of existing muscle fibers resulting in loss of muscle mass (2, 18). There is also an increase in inflammatory cytokines within the muscle leading to the deposition of non-contractile fibers within the muscle unit and consequent impaired muscle function (18). Thus, we hypothesized that in otherwise healthy older adults, circulating P3NP concentrations would be inversely associated with lean mass and muscle strength.

To our knowledge, no prior studies have evaluated the association between lean body mass and P3NP in a cohort of older men and women. Therefore, we conducted a cross-sectional analysis to determine the association between plasma P3NP and lean mass (total and appendicular) in a convenience sample from the Framingham Offspring Study.  Because sarcopenia is a product of muscle size and muscle function, we also examined the cross-sectional association between plasma P3NP and quadriceps strength in the same cohort.

Methods

Study Population

The Framingham Offspring Cohort began in 1971 to examine familial clustering of cardiovascular disease (19), and it includes 5,124 adult children of the Framingham Original Cohort and the spouses of these children. Participants were followed every four years with comprehensive physical examinations and risk factor assessments. Of the 3,532 Offspring who were alive and attended the examination cycle clinic visit between the years 1995-1998, a sample of 943 participants with echocardiography were selected to examine echocardiographic characteristics associated with P3NP (Figure 1) (20). Participants were eligible provided they met one of the following four criterion by echocardiography:  1) end-diastolic left ventricular internal diameter (LVEDD) and wall thickness (LVWT) below their respective sex-specific medians (n=539);  2)LVEDD equal to or exceeding the sex-specific 90th percentiles (n=188); 3)LVWT equal to or exceeding the sex-specific 90th percentiles (n=195); or 4) both LVEDD and LVWT exceeding the sex-specific 90th percentiles (n=21). Participants with available plasma P3NP levels were younger (57.5 versus 59.3 years) and less likely to consume >3 alcoholic beverages/week (16.5 versus 23.9%) compared with participants without a measure of P3NP.

Of the 943 Offspring participants with measured plasma P3NP, 687 participants had lean mass measured and 806 participants had quadriceps strength measured during a Framingham Osteoporosis Study examination between 1996 and 2001. Participants with a measure of total lean mass or quadriceps strength were more likely to be women, have a lower BMI, and less likely to smoke, compared to participants without either measure.

Lean mass

Whole body dual x-ray absorptiometry (DXA) was performed using a Lunar DPX-L bone densitometer (LunarCorp; Madison, WI) as previously described (21). Lean mass (kg) was calculated as the difference in soft tissue mass and fat tissue mass (in grams) divided by 1000. Total lean mass included all body regions whereas appendicular lean mass was defined as the sum of lean mass in the arms and legs.

Isometric quadriceps strength: For quadriceps strength, the right leg was tested unless participants complained of pain or had recently undergone surgery, in which case the left leg was tested. Participants were asked to sit in a chair with their back supported, and the tested leg was flexed at 60 degrees. A hand-held dynamometer (Lafayette Instrument) was placed 6 cm above the lateral malleolus. Subjects were instructed to exert their maximum force against the dynamometer for 2 seconds. The measurement was repeated, and the greater of the two readings was included in the analyses.

P3NP

Fasting blood samples were drawn from participants while in a supine position. Samples were centrifuged, and plasma was frozen at –70 degrees C until assay. Plasma P3NP was measured using a radioimmunoassay (Amersham Pharmacia Biotech). All specimens were processed in duplicate, and the mean intra-assay coefficient of variation was 6%.

Other covariates

During the 1995-1998 Framingham clinic examination, weight was measured to the nearest pound without shoes, and height was measured to the nearest quarter-inch. These were used to calculate BMI (kg/m2). Smoking status (current versus other), alcohol consumption (total drinks/week), and hormone use (oral or patch versus none) were obtained by self report.

Indicators of cardiac muscle mass (LVEDD and LVWT), which were used to determine P3NP eligibility, were assessed by transthoracic echocardiography (Sonos 1000 Hewlett-Packard). We calculated LVEDD as the sum of interventricular septum (IVS) and posterior wall (PW) measurements. LVWT was estimated using a formula previously described by Devereux (22).

Ethics

This study was approved by the Institutional Review Boards of Hebrew SeniorLife and Boston University Medical Center and all participants signed a consent form. The authors have no financial conflicts of interest.

Statistics

We first described characteristics of participants by sex-specific quartiles of P3NP. ANOVA  was used to compare continuous characteristics across quartiles, and Chi-square tests to compare categorical characteristics. P3NP was not normally distributed (right skew), whereas the dependent variables, lean mass and quadriceps strength, were normally distributed. For this reason we considered P3NP as both a continuous and log transformed variable in subsequent analyses.

Using linear regression, we calculated the crude associations of P3NP (as the primary independent variables) with dependent variables of total and appendicular lean mass, and with quadriceps strength in men, premenopausal women, and postmenopausal women, separately. Resulting β coefficients reflect the unit (mg/L) or log unit association of P3NP per kg of lean mass or quadriceps strength. We then estimated the proportion of variation in lean mass explained by P3NP (R2). In multivariable analyses, age and BMI were retained in all models regardless of significance. Other covariates (i.e., smoking status, alcohol consumption, categorization of LVEDD and LVWT by echocardiogram, and for post-menopausal women, hormone use) were sequentially removed from the model using a backwards stepwise process if the association with lean mass was not significant at a level of p ≤0.10. We used SAS version 9.2 for all analyses.

Results

The mean age of participants was 57.6 years (standard deviation: 9.6 years), and 40.2% were men (Table 1). Mean P3NP was similar in men (3.9 mg/L) and in pre- and postmenopausal women (4.1 and 4.0 mg/L, respectively; however, there was a considerable range of values, particularly among postmenopausal women (0.02-53.3 mg/L).

 

Table 1 Characteristics (mean ± standard deviation, or percentage) of 806 Framingham Offspring participants in a study of plasma Procollagen Type III N-terminal peptide (P3NP) and muscle function, overall and by sex-specific plasma P3NP quartiles

* among 687 subjects with both a measure of P3NP and total body lean mass; † P for trend<0.01; ‡ P for trend<0.05

In postmenopausal women and men, higher P3NP levels were associated with older age (Table 2), as was BMI for all participants. In postmenopausal women, the lowest quartile of P3NP had the greatest proportion of hormone replacement users. Total and appendicular lean mass was lower with higher P3NP in premenopausal women, although this was not statistically significant. There was no association between P3NP quartiles and quadriceps strength in men or women.

Figure 1 Participants of the Framingham Offspring study who were included in the analysis of P3NP and lean mass, and P3NP and strength

Table 2 Unadjusted and adjusted* ß-regression coefficients† for the associations between plasma Procollagen Type III N-Terminal Peptide (P3NP) and total lean mass, appendicular lean mass, and quadriceps strength, by sex

* Covariates considered in the models included age, BMI, current smoking, current alcohol use, cardiac parameters (left ventricular end diastolic weight and diameter), and estrogen supplementation in post-menopausal women; † β-coefficients approximate association between plasma P3NP unit (mg/L) per kg of lean mass or strength£

In the unadjusted analyses, there was no association between plasma P3NP and total or appendicular lean mass in men (Figure 2: R2=0.00; Table 2: β-coefficient=-0.01 unit P3NP/ kg appendicular lean mass, p=0.90). Results were qualitatively similar after adjusting for age, BMI, smoking, alcohol use, and cardiac muscle mass (Table 2), and when we examined the association in older (age ≥65 years) and younger men separately (not shown). Plasma P3NP was inversely associated with total and appendicular lean mass in both premenopausal and postmenopausal women, although this association was only statistically significant in postmenopausal women (Figure 2: R2 for appendicular lean mass in postmenopausal women=0.02, p=0.01). Results were similar in the adjusted analyses (β-coefficient=-0.05 unit P3NP/kg appendicular lean mass, p=0.02).  Results were also similar after log-transformation of P3NP (Table 3), although the association between P3NP and appendicular lean mass was no longer statistically significant in postmenopausal women (β-coefficient=-0.25 log unit P3NP/kg appendicular lean mass, p=0.10).

Table 3 Unadjusted and adjusted* ß-regression coefficients† for the associations between log transformed plasma Procollagen Type III N-Terminal Peptide (P3NP) and total lean mass, appendicular lean mass, and quadriceps strength, by sex

* Covariates considered in the models included age, BMI, current smoking, current alcohol use, cardiac parameters (left ventricular end diastolic weight and diameter), and estrogen supplementation in post-menopausal women; † β-coefficients approximate association between plasma P3NP log unit (mg/L) per kg of lean mass or strength

There was no association between plasma P3NP and quadriceps strength in the crude or adjusted analyses in men or women (Table 2). In men, the multivariable adjusted β-coefficient for P3NP and quadriceps strength was 0.12 unit P3NP/kg strength (p=0.27), while in postmenopausal women there was an inverse relationship that did not reach statistical significance (β-coefficient =-0.05 unit P3NP/kg strength, p=0.44). Results were similar after log-transformation of P3NP (Table 3).

Figure 2 Cross-sectional association between plasma P3NP and total and appendicular lean mass in men (o), premenopausal women (Δ), and postmenopausal women (◊)

 

Discussion

To our knowledge, this is the first study to examine the cross-sectional association between plasma P3NP and lean mass in a study of both men and women. We found that higher levels of plasma P3NP were associated with a modest decrease in total and appendicular lean mass in postmenopausal women. P3NP was not associated with lean mass in men, nor was it associated with quadriceps strength in either sex.

In a clinical trial of 106 elderly community-dwelling men who received a GnRH agonist plus recombinant growth hormone or testosterone, Bhasin et al. found that early increases in P3NP were associated with greater gains in total and appendicular lean mass (23). In fact, using stepwise models the authors concluded that change in P3NP was a stronger predictor of change in total and appendicular lean mass as compared with age, serum testosterone, or IGF-1.

In our cross-sectional study, we found an inverse association between plasma P3NP and total and appendicular lean mass in women.  While our results may seem contradictory, there may be an explanation for our findings. In the study by Bhasin, subjects were given an anabolic agent stimulating the growth of lean mass. Because P3NP is released during periods of collagen synthesis, it is not surprising that greater increases in plasma P3NP were associated with greater gains in lean mass. Typically, however, aging adults do not receive anabolic agents nor do they experience rapid increases in muscle mass. In the absence of anabolic agents and during periods of muscle loss, P3NP may be elevated as a result of the abnormal inflammation and fibrosis of skeletal muscle.  There is some support for this hypothesis in animal models, where denervation and immobilization of rat muscle uncouples the regulation of collagen biosynthesis resulting in excess collagen formation in the endomysium and perimysium (24), the compartments where Type III collagen is found in the highest concentrations. Prospective studies are needed to validate this hypothesis and our findings.

Our finding that plasma P3NP was inversely associated with lean mass in postmenopausal women, but not in men, is intriguing. One possible explanation is that men tended to be younger than postmenopausal women. If younger men were maintaining lean mass without producing more collagen, inclusion of these younger men may have attenuated the overall association between P3NP and lean mass in men. However, when we examined the subgroup of men with ages above the median, we did not detect an inverse association between P3NP and lean mass. Alternatively, there may be some difference in sex hormones that attenuates the association between P3NP and lean mass in men. Our results do not support this hypothesis as the association was similar in pre- and postmenopausal women, and additional adjustment for estrogen use among postmenopausal women did not affect our estimates. Nevertheless, we did not examine other sex hormone effects, such as testosterone.  Further investigation on the sex-specific relationship between plasma P3NP and lean mass is warranted.

Higher levels of P3NP are not specific to collagen formation within skeletal muscle, and they may also be found in association with fibrosis of other connective tissues and organs containing type III collagen. Furthermore, P3NP is a general marker of collagen production, and our results suggest that it may not distinguish between healthy skeletal muscle growth and pathologic fibrosis of skeletal muscle.  A few male and female participants had markedly elevated plasma P3NP levels (Figure 2), suggesting very high production of Type III collagen in those persons. We found no obvious differences between the characteristics of participants with extreme P3NP and those with lower plasma P3NP levels. It is possible that these persons experienced an acute muscle injury, recently initiated exercise therapy, or had abnormal fibrosis of other organs containing Type III collagen.  We did not have detailed information on these factors to adjust in our models; however, regression estimates were similar when residual outliers were considered.

We found no cross-sectional association between P3NP and muscle strength. This again may relate to an inability of the assay to distinguish between healthy and diseased collagen formation within skeletal muscle. Future prospective longitudinal studies of older adults are needed to determine if P3NP predicts changes in lean mass and strength.

There are several limitations to our study. First our study utilized a single measure of P3NP as a predictor of lean mass. On average, plasma P3NP was measured 1.9 years before the measure of lean mass was ascertained (range 0 days to 5.4 years). P3NP levels are believed to stay relatively constant throughout healthy adulthood (11).  Even in the study by Bhasin et al, which utilized anabolic agents, a steady state of P3NP was observed within 8 weeks of drug administration (23). Thus, multiple measures of P3NP or a simultaneous measure of P3NP with lean mass is unlikely to have changed our results.  Second, participants were comprised of a convenience sample within the Framingham Offspring Study. Eligible participants were more likely to be younger women with healthy characteristics (lower BMI, less smokers, and less excess alcohol), and this may have limited our ability to find an association between lean mass and plasma P3NP, particularly in men.  Third, our analysis is cross-sectional, and we are unable to determine if P3NP is associated with loss of muscle mass in men and women.  Future studies should consider whether elevated serum P3NP predicts persons at risk for muscle loss, and thus, are good candidates for intervention.  Finally, our study was performed in a cohort of Caucasian Americans, and these findings may not be generalizable to other groups.

Because sarcopenia is common and associated with poor outcomes in the elderly population, it is important that new biomarkers associated with muscle mass be discovered in an effort to improve diagnostic and treatment options (25). Our study suggests that plasma P3NP could potentially be a useful biomarker of muscle mass in postmenopausal women if it is found to have adequate sensitivity and specificity for muscle turnover in larger, future studies. Prospective studies of plasma P3NP and changes in muscle mass are needed to confirm this association and to understand why circulating P3NP might be more strongly associated with lean mass in women than in men.

Acknowledgements: This work was funded by a grant from NIAMS/NIA R01 AR/AG 41398 and Framingham Heart Study, (NHLBI/NIH Contract #N01-HC-25195 and RO1 HL67288), a grant from the NIA K23 AG033204, and from the Men’s Associates from Hebrew SeniorLife.  These analyses were presented in part as a poster at the 2010 annual meeting for the American Society for Bone and Mineral Research in Toronto, Ontario on October 15, 2010.

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KLOTHO, FGF21 AND FGF23: NOVEL PATHWAYS TO MUSCULOSKELETAL HEALTH?

 

B. BARTALI1, R.D. SEMBA2, A.B. ARAUJO1

1. New England Research Institutes, Department of Epidemiology, Watertown, MA; 2. Johns Hopkins University School of Medicine, Baltimore

Corresponding Author: Benedetta Bartali, PhD, New England Research Institutes, 9 Galen Street Watertown, MA 02472 USA, Phone: +1(617) 972-3350, FAX: +1 (617) 673-9514, email: bbartali@neriscience.com

J Frailty Aging 2013;2(4):179-183
Published online February 10, 2016, http://dx.doi.org/10.14283/jfa.2013.26


Abstract

Bone mineral density, muscle mass and physical function reach their peak between the second and fourth decade of life and then decline steadily with aging. The crucial question is: what factors contribute to or modulate this decline? The aim of this mini-review is to propose a theoretical framework for the potential role of emerging biomarkers such as klotho, fibroblast growth factors (FGF)21 and FGF23 on musculoskeletal health, with a particular focus on decline in muscle mass and function, and calls for future research to examine this proposed link. The identification of new physiological mechanisms underlying these declines may open a potentially important avenue for the development of novel intervention strategies aimed at preventing or reducing their potentially detrimental consequences.

Key words: Klotho, fibroblast growth factors, aging, skeletal muscle.


 

Musculoskeletal Changes with Aging and their Implications

Bone loss and the decline in muscle mass, strength and physical function that occur with aging are major risk factors for the development of adverse outcomes, including falls (1, 2), mobility limitation (3) and recurrent hospitalization (4), and often represent the early stage of a continuum leading to disability and dependency (3, 5, 6). Considering the projected demographic transition, with an estimate of 19% of Americans being 65 or older in 2030 (7), these aging-related conditions will dramatically increase in the next years, as well as their medical and health care costs (8, 9). Therefore, the identification of factors contributing to the exacerbation and progression of bone/muscle loss and functional decline represent an important public health concern, and a crucial step for the development of primary and secondary prevention strategies.

Bone mineral density, muscle mass and physical function reach their peak between the second and fourth decade of life and then decline steadily with aging (10-12). The crucial question is: what factors contribute to or modulate this decline? It is well-known that the level of physical activity is reduced with advanced age and that muscle disuse plays an important role in bone loss and the decline in muscle mass and physical function (13, 14). However, it has been shown that even highly active older persons, including master swimmers and athletes, still have significantly lower muscle mass and strength than their younger counterparts (15), suggesting that other factors contribute to this aging-related process.

The aim of this mini-review is to propose a theoretical framework for the potential role of emerging biomarkers such as klotho, fibroblast growth factors (FGF)21 and FGF23, on musculoskeletal health, with a particular focus on decline in muscle mass and function, and calls for future research to examine this proposed link. The identification of new physiological mechanisms underlying these declines may open a potentially important avenue for the development of novel intervention strategies aimed at preventing or reducing their potentially detrimental consequences.

Klotho, FGF21 and FGF23: Metabolism and Clinical Phenotypes

Klotho is a recently discovered protein (16) that was named after the Greek goddess, Klotho, who spins the thread of life. It is mainly expressed in the distal renal tubule and the choroidplexus in the brain (16) and is composed of a very short (10 amino acids) intracellular domain, a transmembrane, and a large extracellular domain which can act as a circulating hormone (17). It is released into the extracellular space and can be detected in sera (18). There are two forms of klotho protein: membrane klotho and secreted klotho.

Membrane klotho functions as a receptor for FGF21 and FGF23 and is required for their metabolic activity (19, 20). Because of the lack of a heparin-binding domain, these FGFs can leave the tissues of origin and serve as circulating hormones (21).

Secreted klotho functions as a humoral factor with a number of activities, including lowering intracellular oxidative stress and regulation of ion channel and transport (22, 23). Experimental studies have shown that klotho extends lifespan by 19-31% when overexpressed (24) and causes a phenotype of premature aging, including muscle atrophy and muscle weakness (16, 25), when its expression is disrupted. Furthermore, klotho deficient mice are osteopenic (16, 26) with low bone turnover, resulting in a decreased cortical bone thickness of femur, tibia and vertebrae by 20-40% when compared with wild-type mice (27). Although the underlying factors contributing to this premature aging phenomenon are unclear, putative mechanisms are its role in repressing insulin/IGF1 signaling through FGF21 (24), lowering intracellular oxidative stress (22) and regulating phosphate and calcium homeostasis through FGF23 (24, 28).

FGF21 is a recently discovered endocrine factor that is emerging as a regulator of glucose and lipid metabolism. It is mostly expressed in the liver but also in the pancreas, white adipose tissue and muscle (29, 30). FGF21 expression in the liver is primarily induced by prolonged fasting through peroxisome proliferator-activated receptor (PPAR)-α activation and in white adipose tissue by feeding through activation of PPAR-y, a master transcriptional regulator of adipogenesis (31). The preferred receptor for FGF21 (FGFR1c) is abundantly expressed in adipose tissue (19, 20, 32) where FGF21-regulated genes are involved in lipogenesis, lipolysis, and fatty acid oxidation (33, 34). When administered to rodents and monkeys with obesity and diabetes, recombinant FGF21 causes weight loss, and reduces plasma glucose, triglycerides, insulin resistance, and hepatic steatosis (33, 35, 36). Experimental studies suggest that FGF21 also regulates skeletal homeostasis, by potentiating PPAR-y activity and inhibiting osteoblastogenesis (37). However, little is known on the functional role of FGF21 in humans, where its role in glucose metabolism is controversial (38-43).

FGF23 was first identified in the ventrolateral thalamic nucleus of the brain in mice (44) and its importance was discovered when its mutation lead to the development of autosomal dominant hypophosphatemic rickets (ADHR) (45). FGF23 is a bone-derived hormone that acts on the kidney to modulate bone mineralization by regulating phosphate excretion, and the synthesis of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and parathyroid hormone (PTH)(46). In particular, when phosphate is in excess, FGF23 acts on kidney to promote phosphate excretion into urine. FGF23 also reduces serum 1,25-(OH)2D3 levels to suppress phosphate absorption from intestine. Thus, FGF23 functions as a hormone that induces negative phosphate balance (47, 48) and it has been shown to play a causative role in the development of several hypophosphatemic rickets/osteomalacia. Furthermore, FGF23 functions as an inhibiting factor of PTH synthesis (49, 50) and has been associated with PTH levels in humans as well (51). Mice knock-out for FGF23 show a clinical phenotype resembling aging, including growth retardation, skin atrophy, decreased bone density and decreased longevity (46). Patients with hypophosphatemic rickets/osteomalacia often report muscle weakness and bone pain that severely affects their daily life activities (52).

 

Novel Pathways to Musculoskeletal Health?

FGF21 and FGF23 share common structural and biological features (53) and both require klotho to bind their cognate FGF receptors and exert their biological activities (19, 54). Therefore, they likely act systemically and synergistically and may affect musculoskeletal health through different pathways. For example, klotho contributes to phosphate and calcium homeostasis (28) by affecting FGF23 (54), which is considered a putative cornerstone for bone mineralization, and also FGF21 might contribute to skeletal homeostasis not only in mice (37) but also in humans.

The main functions of FGF23 signaling in the kidney are the reduction of 1,25(OH)2D3 synthesis and of renal tubular phosphate reabsorption (55). Consequently, FGF23 is directly involved in the regulation of the active form of vitamin D and of serum phosphate levels. Extracellular phosphate is necessary to allow mineralization of bone matrix, while intracellular phosphate plays an important role in energy stores and production (e.g. in the form of phosphocreatine and ATP) (77), which are needed for muscles to function. Consequently, klotho and FGF23 may play an important role not only in bone mineralization but also in the maintenance of muscle mass and function given their interplay with vitamin D and the critical role of phosphate in energy (ATP) and protein production. In line with this hypothesis, a number of studies have shown that low levels of vitamin D are associated with decline in muscle mass (56), muscle strength (57) and physical function (58, 59). Furthermore, skeletal muscle is a major user of ATP (60) to power the movement of the myosin heads and to allow muscle contractions. Interestingly, experimental studies have shown that injections of FGF23 antibodies increased serum phosphate and 1,25-(OH)2D3 levels as well as grip strength and spontaneous movements in hypophosphatemic mice (61).

FGF21 may play a role in muscle mass and function with its involvement in energy metabolism as well. Indeed, during starvation and intense physical activity the levels of FGF21 increase through the PPAR-α pathway in order to enhance energy production (ketogenesis) and utilization (oxidation) of free fatty acids. Chau et al. (62) demonstrated that FGF21 regulates energy homeostasis in adipocytes through activation of adenosine monophosphate (AMP)-activated protein kinase, sirtuin 1, and PPAR g co-activator-1a leading to enhanced mitochondrial function and oxidative capacity. FGF21 also causes growth hormone resistance, and therefore, plays a key role in orchestrating the adaptive starvation response (21). Finally, circulating levels of FGF21 are positively associated with insulin resistance (43, 63) and with type II diabetes (64), conditions associated with musculoskeletal-related outcomes (65, 66).

 

Figure 1 Simplified conceptual framework

 

Additional potential pathways that may link these novel biomarkers with musculoskeletal health are their involvement in the regulation of systemic inflammation and oxidative stress, as these conditions are associated with decline in muscle mass and strength (67-70). Indeed, Lee et al. recently showed that FGF21 plays a role in inhibiting the activation of the transcription factor nuclear factor-kappa B (NF-kB) (71), the master regulator of inflammation that can be activated in skeletal muscle cells under inflammatory conditions (72). Finally, NF-kB activation is tightly linked to increased oxidative stress, which alters the balance between protein synthesis and degradation and, consequently, may affect the rate of protein degradation in skeletal muscle (73, 74). Interestingly, klotho has been shown to be a cytoprotective protein that defends against oxidative stress (75) and, in turn, may contribute to reduce protein degradation and muscle loss. Therefore, as simplified in the conceptual framework (figure), these novel biomarkers may play a role in musculoskeletal health through different mechanisms, and are likely to function in an interaction network rather than in an additive fashion.  However, despite this strong theoretical basis, there is a gap in the current scientific knowledge on the effect of klotho, FGF21 and FGF23 on muscle mass and function in humans. Indeed, there are only two studies in humans published to date on this topic, and they show that one standard deviation increase in plasma klotho was significantly associated with muscle strength (β=1.20, standard error=0.35, p=0.0009)(76) and with reduced risk of developing Activities of Daily Living disability (odds ratio=0.57, 95% confidence interval=0.35-0.93) (77) in Italian older persons. In conclusion, this mini-review provides a theoretical basis for the potential role of these emerging biomarkers on musculoskeletal health, with a particular focus on muscle mass and function. This could represent an interesting opportunity for the development of novel intervention strategies aimed at reducing muscle and functional decline with aging and their detrimental consequences.

 

Acknowledgements: This work was supported by NIH awards R01AG020727 and R01AG027012 from the National Institute on Aging, and R01HL111271 from the National Heart, Lung and Blood Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of NIA, NHLBI or NIH.

 

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A PILOT STUDY OF AGE-RELATED CHANGES IN THE SPHINGOLIPID COMPOSITION OF THE RAT SARCOPLASMIC RETICULUM

D.W. RUSS1,2, M. NAKAZAWA2,3, I.M. BOYD1

1. Laboratory for Integrative Muscle Biology, Division of Physical Therapy, Ohio University, Athens, OH USA; 2. Ohio Musculoskeletal & Neurological Institute (OMNI), Heritage College of Osteopathic Medicine, Athens, OH USA; 3. Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Athens, OH USA.

Corresponding author: David W. Russ, PT, Ph.D. Associate Professor, School of Rehabilitation & Communication Sciences, Division of Physical Therapy, Ohio University, W279 Grover Center, Athens, OH  45701, Phone: 740-566-0022, Fax: 740-593-0293, Email: russd@ohio.edu

J Frailty Aging 2015;4(4):166-172
Published online October 15, 2015, http://dx.doi.org/10.14283/jfa.2015.73


Abstract

Background: Muscle strength declines more rapidly than muscle size, manifesting as a loss of muscle quality. One putative contributor to this impairment of muscle quality is impaired sarcoplasmic reticulum (SR) function. Objectives: The principal objective of this study was to characterize the sphingolipid composition of the SR in adult and aging rat muscles. A secondary, exploratory objective was to test for associations between SR sphingolipids and SR function (i.e., Ca2+ release). Design: Using an animal model, the objectives were evaluated in a pre-clinical, cross-sectional study. Setting: Data were collected in an academic research laboratory. Participants: Medial gastrocnemius muscles of adult (n=8; 7-8 months) and aged (n=8; 24-25 months), male F344/BN hybrid rats were processed to extract SR. Measurements: Sphingolipids in the SR were measured using tandem mass spectrometry. Fatty acid concentrations within the major sphingolipid classes were evaluated via Principal Component Analysis (PCA). In a subset of samples, SR Ca2+ release rates were determined using fluorometric methods, and associations with specific (based on results of PCA) fatty acid concentrations were evaluated. Results: Aging SR showed an overall decline in the ratio of unsaturated to saturated fatty acids. Age-specific differences were observed for hexosylceramide and ceramide-1-phosphate. Within subset of samples with SR Ca2+ release data, a significant negative association between Ca2+ release and C1P18:0 and trends for positive associations with hexCER24:0 and 24:1 were observed. Conclusions: These preliminary, pre-clinical data suggest that changes in SR sphingolipids may play a role in age-related impairment of muscle function. Further work is needed to explore this hypothesis, as SR sphingolipids may prove a fruitful target for interventions, be they physical (i.e., exercise), nutritional or pharmacological..

Key words: Skeletal muscle, sarcopenia, ceramide, muscle quality, calcium.


Introduction

Increasing age is typically accompanied by changes in various structural and functional characteristics of skeletal muscle. The most obvious examples of these are loss of muscle cell number and size (1) and impaired force production (2), respectively. These two phenomena are clearly related, but the loss of force production typically exceeds the loss of muscle mass (2, 3), suggesting that impairment of contractile function, independent of changes in muscle size, accompanies old age. This loss of force production per unit muscle size is often described as a loss of muscle quality (4).

Identifying the mechanisms contributing to age-related loss of muscle quality is of marked importance for promoting healthy aging. Simply maintaining or increasing the size of aging muscles has does not consistently improve force production (5), and  loss of muscle force production (i.e., weakness) negatively influences several aspects of physical function (6, 7) and even predicts mortality (8). Among the mechanisms suggested to contribute to age-related loss of muscle quality is impaired excitation-contraction coupling (E-CC) (3, 9, 10). This complex process converts the neural signal for muscle activation (muscle action potential) into muscle contraction through a series of biophysical steps, and is critical to optimal muscular force production and maintenance of muscle quality. We (10), and others (11), have reported age-related reductions in SR Ca2+ release, a critical step in E-CC, in experiments on isolated SR vesicles. Although some investigators have attributed declines in SR function with aging to decreased expression of the SR Ca2+-release channel (Ryanodine Receptor; RYR) (9), we (10), and others (3, 12), have found no age-related decline in expression. It has also been suggested that impairment of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), which returns myoplasmic Ca2+ to the SR, disrupts the normal Ca2+ release process with aging (13). However, we have found that Ca2+ release can be impaired in aging muscle, even when SERCA function is preserved (10, 14, 15).

In contrast to investigations of SR-associated proteins, little study has been made of the effect of aging on the SR itself. As an abundant specialized form of endoplasmic reticulum (ER) (16), the SR is membranous in nature, making the lipid composition of the membrane a potential target of age-related modifications. The predominant lipids of the SR are the phospholipids phosphatidylcholine and phosphatidylethanolamine, though sphingomyelin and some glycosphingolipids are also present (17, 18). Cholesterol and phosphatidylethanolamine, but not phosphatidylcholine (the most abundant class of phospholipid), increase in the SR with old age, demonstrating age-related modifications of the SR membrane (19). Our previous studies have found changes in protein profiles consistent with altered sphingolipid metabolism (e.g., increases in serine palmitoyltransferase and sphingomyelinase expression) that occur in conjunction with impaired muscle quality and SR Ca2+-release (15, 20). These changes suggest that age-related changes in sphingolipids, particularly an increase in ceramide, could accompany the changes in phospholipids. Ceramide lies at a key hub in the sphingolipid synthesis pathway (Figure 1a), is known to be a potent, active signaling molecule (21) and has been linked to membrane repair (22). As we have observed that content of dysferlin, another membrane repair protein, is elevated in the aging SR (14), it is not unreasonable to think that aging muscles could promote ceramide production to maintain SR integrity. If such changes in lipid metabolism do occur in the SR, they could contribute to impaired E-CC. It has been demonstrated that the function of integral membrane proteins (such as RYR and SERCA) is influenced by the fatty acid composition of the membranes in which they are situated (23).

Methods

Animals and Ethical Approval

Adult (n=8; 7-8 months) and aged (n=8; 24-25 months), male F344/BN hybrid rats, representing an age of ~60% maximum lifespan (24), and one at which locomotor deficits have been observed (25), were used in the contractile experiments. All animals were housed in an environmentally controlled facility (12–12 h light–dark cycle, 22°C), and had ad libitum access to standard rat chow (Prolab RMH 3000; calories provided by proteins, fats and carbohydrates:  26, 15, and 59%, respectively) and water. Animal use and all procedures were approved by the Ohio University Institutional Animal Care and Use Committee, and the “Principles of laboratory animal care“ (NIH publication No. 86-23, revised 1985), were followed throughout the study. 

Sarcoplasmic Reticulum Isolation  

Frozen muscle portions (~400 mg) were processed to isolate SR vesicles, as described by Lees and Williams (26). Briefly, muscle tissue was minced and homogenized in ice-cold buffer (20 mM HEPES, 250 mM sucrose, 0.2% sodium azide, 0.2 mM PMSF, and 1 mM EDTA (pH 7.0) via three 15-s bursts at 10,000 rpm. The resulting homogenates were centrifuged at 8,000 g for 15 min at 4°C. Potassium chloride was added to the supernatant at a final concentration of 600 mM. The samples were incubated on ice, with gentle shaking, for 1 h, then centrifuged at 43,000 g for 120 min. The resulting pellet (purified SR vesicles) was resuspended in storage buffer (homogenizing buffer containing 300 mM sucrose and 150 mM KCl) and frozen in liquid N2. These SR samples were then shipped on dry ice to Metabolon (West Sacramento, CA) for subsequent sphingolipid analyses.

Sphingolipid Analysis

The SR lipids were analyzed using the TrueMass Ceramides Panel. Briefly, deuterium-labeled internal standards were added to SR samples, and the mixture was solubilized in methanol followed by a crash extraction. A bilayer was formed with the addition of KCl in water, and the organic layer was removed and concentrated under nitrogen. The extract was spin filtered and split into 2 injections: ceramides and sphingosines. The extract was injected onto an Agilent C8 column connected to an Agilent 1290 Infinity LC and ABI 4000 QTRAP. The analytes were ionized via positive electrospray and the mass spectrometer was operated in the tandem MS mode. The absolute concentration of each sphingolipid was determined by comparing the peak to that of the relevant internal standard. The concentration and fatty acid composition (14:0, 16:0, 18:0, 18:1, 20:0, 20:1, 22:0, 22:1, 24:0, 24:1, 26:0, 26:1) of: ceramide (CER), dihydroceramide (DHC), ceramide-1-phosphate (C1P), hexosylceramide (hexCER) and lactosylceramide (lacCER), were determined as well as 3-keto-sphingasine (3SA), sphingosine (SP), sphingosine-1-phosphate (S1P), sphinganine (SA) and sphinganine-1-phosphate (SA1P).  Molar concentrations were expressed as pmoles/g sample wet weight.

Sarcoplasmic Reticulum Calcium Release

In a subset of the animals (5 adult; 4 aged) used for the present analyses, we had SR Ca2+ release data from the contralateral MG muscle. In these instances, a portion of the muscle was homogenized fresh, as previously described (10, 14), to produce a homogenate fraction suitable for testing of Ca2+ handling. Kinetics of Ca2+ release were assessed as we have described elsewhere (15), using 400 g of sample protein, the ratiometric Ca2+-indicator dye Fura-2 and 4-chloro-m-cresol (4-CMC) to selectively activate the RYR (10). Assays were conducted in duplicate and the peak rates of Ca2+ release were expressed relative to sample total protein content.

Statistical Analyses

The total abundance of each sphingolipid class was characterized by descriptive statistics, as was the relative (%) content of each fatty acid species within a sphingolipid class. To determine whether the aging altered lipid profiles, principal component analysis (PCA) was applied to each lipid class separately (CER, SM, C1P, DHC, hexCER, and lacCER) as well as all classes together after each variable had been z-transformed to have the same mean and variance. Because there were up to 6 missing values in 13 of the 71 variables, we applied a special version of PCA (27) that iteratively approximates the data by solving one PC at a time (recursively subtracted empirical orthogonal functions). The number of PCs to be retained was determined by inspecting a scree plot. Afterwards, the Man-Whitney U (MWU) test was used evaluate age-related differences for each retained PC. All tests were performed 2-tailed at the 5% significance level.

Following the PCA analyses, we tested for age differences in those species identified by in PCA as having PC loadings ≥0.3 in components where a trend (p ≤0.10) for an effect of age was identified. Because only single fatty acid species were associated with 3SA, SP, S1P, SA and SA1P, we tested these metabolites for an effect of age using un-paired t-tests. We also conducted Spearman correlational analyses between SR Ca2+ release and those fatty-acid species identified by the PCA as capturing the age difference in the retained PCs.

Results

Sphingolipid Content

For each sphingolipid class, all of the fatty acid species were summed within each age group and the percent of the total determined to provide a picture of overall sphingolipid content.  By far, the most abundant sphingolipid observed in the SR was SM, with very low abundance seen for DHC, lacCER, C1P, SP and SA (Figure 1B). We also determined the fold change in aged vs. adult SR within each sphingolipid class (Figure 1C). At this crude level of classification, a significant decrease in hexCER and trend for an increase in C1P were observed in the aged muscles. In addition, we compared the ratio of the total unsaturated:saturated fatty acid species, and found that it was signficantly (p=0.046) lower in the SR from aged rats (Figure 1D). To better explore potential differences related to specific fatty acid species, we subsequently conducted PCA.

Figure 1 Sphingolipid Classes: A) Schematic of sphingolipid synthetic pathway; B) Relative content of each sphingolipid class within each age group; C) Fold change in aged vs. adult SR within each lipid class; D) Ratio of total monounsaturated:saturated fatty acids. * = significantly different from adult; †= trend for difference from adult (p=0.088)

Principal Component Analyses

All Sphingolipid Classes (Scaled): Ten PCs accounted for 90% of the variance in all lipid classes (Table). Unlike applying PCA to each lipid class separately, no lipid had PC loading exceeding ±0.3. The age difference was marginally significant in PCs1 and 7 (p-values=0.08).

CER: PCA indicated that the first PC accounted for more than 98% of the variance in this lipid class (Table), and this component was predominantly influenced by CER18:0 (Figure 2). That is, only CER18:0  had a PC loading whose absolute value was greater than 0.3. The age groups did not differ in this component (Table 1).

Table 1 Results of Principal Component Analyses (N=16)

PC = principal component, Y = young mice (n=8), O = old mice (n=8); p-values based on the Mann-Whittney-U test; *p<0.05, †p<0.1

 

SM: The first two PCs accounted for more than 93% of the variance in this lipid class (Table 1). The first component was predominantly influenced by SM18:0, while the second was influenced by SM24:1, SM24:0, and SM22:0 (Figure 2). While these components did not reflect the age difference (p-values>0.2), the age groups significantly differed in PC4 (p=0.05, Table 1). In this component, SM24:1 and SM20:0 contributed negatively, while SM24:0 did so positively (Figure 2, PC4).

Figure 2 Loadings of Principal Components (PCs) applied to: A) all lipid classes together (scaled); B) CER; C) SM; D) C1P; E) DHC; F) hexCER; and G) laCER. The black dashed lines indicate the cutoff values of ±0.3. Black dots indicate |loadings|>0.3 while grey dots indicate |loadings|≤0.3

C1P: The first two PCs accounted for more than 99% of the variance in this lipid class (Table 1). Both components were influenced by C1P20:0 and C1P18:0 (Figure 3). Neither component reflected the age difference (p-values >0.1, Table 1).

Figure 3 SR Calcium Release: A) Mean (+SE) peak rate of Ca2+ release from adult and aged muscles. * = significantly different from adult. B) Correlation between C1P18:0 and SR Ca2+ release (P = 0.025, see text for details). C) Correlation between hexCER24:0 and SR Ca2+ release (p=0.088, see text for details). D) Correlation between hexCER24:1 and SR Ca2+ release (p=0.099), see text for details

DHC: The first two PCs accounted for more than 97% of the variance in this lipid class (Table 1). Both components were influenced by DHC24:0, DHC20:0, and DHC18:0). DHC24:1 also contributed to forming PC1. Neither component reflected the age difference (p-values >0.2, Table 1).

hexCER: The first PC accounted for nearly 97% of the variance in this lipid class (Table 1). This component was influenced by HEXCER24:1, HEXCER24:0 and HEXCER22:1  and captured the age difference (p=0.04, Table 1). Similarly, PC2 captured the age difference (p=0.04), even though it was not selected by a scree test.

lacCER: The first two PCs accounted for 93.3% and 6.3% of the variance in this lipid class, respectively (Table 1). The first component was predominantly influenced by lacCER24:0, whereas the second component was influenced by lacCER18:0, and also by lacCER24:0 and lacCER24:1 to a lesser degree. Neither component captured the age difference (p-values >0.2, Table 1).

Sphingosines & Sphinganines

As there was only one fatty acid species observed for SP & S1P(18:1), and SA & SA1P (18:0), we did not conduct PCA on these lipids. None of them exhibited any age-related differences, nor did the ratios of the phosphorylated to unphosphorylated forms (data not shown).

SR Calcium Release

In the subset of samples for which data were available (5 adult, 4 aged), there was a significant reduction of SR Ca2+ release with age (p=0.05). Of note, a significant negative association between SR Ca2+ release and C1P18:0 was present (r=-0.733; p=0.025), as were trends for positive associations between SR Ca2+ release and hexCER24:0 and hexCER24:1 (r=0.600, p=0.088 and r=0.583, p=0.099, respectively; Figure 3B-D).

Discussion

This pilot study examined age-related changes in the sphingolipid composition of the SR in a mixed, though predominantly fast, skeletal muscle. The motivation for this study stemmed from several factors: 1) impaired SR function has been linked to reduced force in models of skeletal muscle fatigue and injury, 2) aging muscles that exhibit reduced muscle quality have also been found to exhibit impaired SR function, 3) different organelles exhibit different membrane compositions and may respond differently to aging, 4) the functionality of integral membrane proteins can be influenced by the composition of the membranes in which they are situated, 5) our previous findings suggest that aging muscle exhibit a protein expression profile consistent with altered sphingolipid metabolism (i.e., increased ceramide) and 6) ceramide has been associated with stress and membrane injury/repair.

The results of the lipomic analyses indicate that SM is far more abundant than the other sphingolipids in skeletal muscle SR, though it represents a fairly small fraction of total SR membrane lipids when compared to the predominant phospholipid classes (18). When considering entire classes (i.e., summing all fatty acid species within a class), age-specific differences were found for hexCER and C1P. In addition, aging was associated with a decline in the ratio of unsaturated to saturated fatty acids (all unsaturated fatty acids in the sphingolipids studied were mono-unsaturated). A PCA of all lipid classes and fatty acid species found that 10 PCs could account for >90% of the variance, though no specific fatty acid species within any PC appeared to significantly influence that component.  Some modest effects of age were present in PC1 (27.6% of variance) and PC7 (4.3% of variance).

To gain further insight in to the potential effects of age suggested by the PCA of all lipid classes, we conducted further PCAs on the fatty acid species within each class. For each class, 1-2 PCs accounted for ≥95% of the variance. In general, saturated fatty acids appeared to be the main drivers of these PCs, except within hexCER, in which 24:1 and 22:1 significantly influenced the PCs. Age differences were captured within hexCER (PC1 & 2) and C1P (PC1).  As we had SR Ca2+ release in a subset of the animals used in the present study, we performed correlational analyses of the factors that influenced those PCs that captured an age difference. Within these limited data, a significant negative association between Ca2+ release and C1P18:0 and trends for positive associations with hexCER24:0 and 24:1 were observed. As C1P tended to increase, and hexCER to decrease, with age these findings are consistent with the age-related decline in SR Ca2+ release seen here and in our previous studies (10, 14, 15).

Our initial hypothesis that increased age would be associated with increased SR CER content was not supported by comparisons of total sphingolipid class, nor by PCA of fatty acid species within CER. However the two sphingolipid classes that showed the greatest age differences, hexCER and C1P, exhibited significant (r=-0.506; p=0.046 and r=-0.768; p=0.001, respectively) associations with total CER content.  Interestingly, the negative and positive associations of hexCER and C1P are consistent with the respective age-related decreases and increases in these classes (Figure 1C).  Also of note, the unsaturated:saturated fatty acid ratio, which exhibited a decline with aging, was positively associated (r=0.675; p=0.008) with hexCER content.

As is typical of pilot investigations of this sort, the sample size is quite small and the findings are largely descriptive in nature. Nevertheless, the data here suggest that the composition of the SR membrane, and sphingolipids in particular could be a potential target for therapeutic interventions to enhance muscle strength and quality. The fact that the greatest age differences occurred opposite directions in hexCER and C1P, which represent divergent downstream products of ceramide metabolism, suggests several possible mechanisms that could be at work. Gangliosides, which are downstream products of hexCER and lacCER metabolism, are known to act in a variety of signaling transduction pathways (28). In addition, it has been shown that certain gangliosides can alter Ca2+ flux in skeletal muscle SR (29). However, while that study demonstrates the potential for CER and gangliosides to affect SR Ca2+ release, it evaluated Ca2+ movement through the dihydropyridine receptor, whereas the RYR is the principal site of Ca2+ release during muscle contraction.  It could be that increased ceramide metabolism with aging upregulates both hexCER and C1P synthesis, but the hexCER is preferentially utilized to generate gangliosides, while the C1P accumulates. The significant positive association between C1P and CER suggests this might be the case. Alternatively, aging could be associated with preferential activation of the ceramide kinase versus the glucosylceramide synthase pathway, and thus diminish the hexCER available for gangliosides. Future studies that incorporate measurements of ganglioside content may help clarify these hypotheses.

To our knowledge, this is the first study to present data of this kind. Despite the limitations of this pilot study, the results suggest that aging alters the composition of the SR membrane. This could have important implications for SR function and contractility in aging muscle. Additional studies are needed to determine if experimental alterations of the SR membrane can enhance function of the aging SR, and more importantly, muscle force production. Based on the present results, possible targets could include stimulation of glucosylceramide synthase or inhibition of ceramide kinase.

Acknowledgements: The authors thank Dr. Tracy Shafizadeh of Metabolon (West Sacramento, CA) for overseeing the lipid analyses and assistance with Figure 1.

Conflict of Interest: None of the authors is aware of any conflict of interest regarding any aspect of the work reported here.  Portions of these data have been presented in abstract form at the 2015 International Conference on Frailty & Sarcopenia Research, Boston, MA USA.

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8. Fanzani A, Zanola A, Faggi F et al. Implications for the mammalian sialidases in the physiopathology of skeletal muscle. Skeletal Muscle. 2012;2(1):23.

9. Gustavsson M, Traaseth NJ, Veglia G. Activating and deactivating roles of lipid bilayers on the Ca(2+)-ATPase/phospholamban complex. Biochemistry. 2011;50(47):10367-74.

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11. Krainev AG, Ferrington DA, Williams TD, Squier TC, Bigelow DJ. Adaptive changes in lipid composition of skeletal sarcoplasmic reticulum membranes associated with aging. Biochim Biophys Acta. 1995;1235(2):406-18.

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14. Metter EJ, Talbot LA, Schrager M, Conwit R. Skeletal muscle strength as a predictor of all-cause mortality in healthy men. J Gerontol A Biol Sci Med Sci. 2002;57(10):B359-65.

15. Muthing J, Maurer U, Neumann U, Kniep B, Weber-Schurholz S. Glycosphingolipids of skeletal muscle: I. Subcellular distribution of neutral glycosphingolipids and gangliosides in rabbit skeletal muscle. Carbohydrate Research. 1998;307(1-2):135-45.

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17. Renganathan M, Delbono O. Caloric restriction prevents age-related decline in skeletal muscle dihydropyridine receptor and ryanodine receptor expression. FEBS Lett. 1998;434(3):346-50.

18. Russ DW, Boyd IM, McCoy KM, McCorkle KW. Muscle-specificity of age-related changes in markers of autophagy and sphingolipid metabolism. Biogerontology. 2015.

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24. Taylor MH, Losch M, Wenzel M, Schroter J. On the Sensitivity of Field Reconstruction and Prediction Using Empirical Orthogonal Functions Derived from Gappy Data. J Climate. 2013;26(22):9194-205.

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PHARMACOLOGICAL INTERVENTIONS IN FRAILTY AND SARCOPENIA: REPORT BY THE INTERNATIONAL CONFERENCE ON FRAILTY AND SARCOPENIA RESEARCH TASK FORCE

M. CESARI1,2, R. FIELDING3, O. BÉNICHOU4, R. BERNABEI5, S. BHASIN6, J.M. GURALNIK7, A. JETTE8, F. LANDI5, M. PAHOR9, L. RODRIGUEZ-MANAS10, Y. ROLLAND1,2, R. ROUBENOFF11, A.J. SINCLAIR12, S. STUDENSKI13, T. TRAVISON14, B. VELLAS1,2 ON BEHALF OF THE INTERNATIONAL CONFERENCE ON FRAILTY AND SARCOPENIA RESEARCH TASK FORCE

1. Gérontopôle, Centre Hospitalier Universitaire de Toulouse, Toulouse, France; 2. INSERM UMR1027, Université de Toulouse III Paul Sabatier, Toulouse, France; 3. Jean Mayer USDA, Human Nutrition Research Center, Boston, MA, USA; 4. Musculoskeletal Area, Eli Lilly & Co, Paris, France; 5. Department of Geriatrics, Neurosciences, and Orthopedics, Catholic University of the Sacred Heart, Roma, Italy; 6. Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA; 7. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA; 8. Health and Disability Research Institute, Boston University School of Public Health, Boston, MA, USA; 9. Department of Aging and Geriatric Research, University of Florida-Institute on Aging, Gainesville, FL, USA; 10. Servicio de Geriatria, Hospital Universitario de Getafe, Getafe, Spain; 11. Global Translational Medicine, Novartis Institutes for Biomedical Research, Basel, Switzerland; 12. Foundation for Diabetes Research in Older People, Luton, United Kingdom; 13. National Institute on Aging, Baltimore, MD, USA; 14. Institute for Aging Research, Hebrew SeniorLife, Boston, MA, USA

Corresponding author: Matteo Cesari, MD, PhD. Gérontopôle, Centre Hospitalier Universitaire de Toulouse; 37 Allées Jules Guesde, 31000 Toulouse, France. Phone: +33 (0)5 61145628; Fax: +33 (0)5 61145640; email: macesari@gmail.com

J Frailty Aging 2015;4(3):114-120
Published online June 25, 2015, http://dx.doi.org/10.14283/jfa.2015.64

Task Force members: Christian Asbrand (Frankfurt am Main, Germany), Olivier Benichou (Paris, France), Cynthia A Bens (Washington, DC, USA), Roberto Bernabei (Roma, Italy), Shalender Bhasin (Boston, MA, USA), Denis Breuillé (Lausanne, Switzerland), Andrea Buschiazzo (Martinez, Provincia de Buenos Aires, Argentina), Francesca Cerreta (London, United Kingdom), Matteo Cesari (Toulouse, France), Alfonso Cruz-Jentoft (Madrid, Spain), Susanna Del Signore (Paris, France), Stephen Donahue (Tarrytown, NY, USA), Roger Fielding (Boston, MA, USA), Francesco Landi (Roma, Italy), Juerg Gasser (Basel, Switzerland), Joerg Goldhahn (Basel, Switzerland), Jack M Guralnik (Baltimore, MD, USA), Michaela Hoehne (Lutry, Switzerland), Lori Janesko (Uniontown, PA, USA), Alan Jette (Boston, MA, USA), Makoto Kashiwa (Tokyo, Japan), Francesco Landi (Rome, Italy), Valerie Legrand (Nanterre, France), Fady Malik (San Francisco, CA, USA), Cecilia Marta (Bridgewater, NJ, USA), John Morley (St. Louis, MO, USA), Vikkie Mustad (Columbus, OH, USA), Marco Pahor (Gainesville, FL, USA), Suzette Pereira (Columbus, OH, USA), Leocadio Rodriguez-Manas (Getafe, Spain), Yves Rolland (Toulouse, France), Ronenn Roubenoff (Basel, Switzerland), Fariba Roughead (Minnetonka, MN, USA), Jonathan Sadeh (Bridgewater, NJ, USA), Antoni Salva (Barcelona, Spain), Brad Shumel (Tarrytown, NY, USA), Alan J Sinclair (Luton, United Kingdom), Stephanie Studenski (Baltimore, MD, USA), Richard Swanson (Tarrytown, NY), Min Tian (Columbus OH, USA), Thomas Travison, Boston, MA, USA), Estelle Trifilieff (Basel, Switzerland),  Bruno Vellas (Toulouse, France), Sjors Verlaan (Utrecht, The Netherlands), Sander Wijers (Utrecht, The Netherlands).


Abstract

Sarcopenia and frailty often co-exist and both have physical function impairment as a core component. Yet despite the urgency of the problem, the development of pharmaceutical therapies for sarcopenia and frailty has lagged, in part because of the lack of consensus definitions for the two conditions. A task force of clinical and basic researchers, leaders from the pharmaceutical and nutritional industries, and representatives from non-profit organizations was established in 2012 with the aim of addressing specific issues affecting research and clinical activities on frailty and sarcopenia. The task force came together on April 22, 2015 in Boston, Massachusetts, prior to the International Conference on Frailty and Sarcopenia Research (ICFSR). The theme of this meeting was to discuss challenges related to drugs designed to target the biology of frailty and sarcopenia as well as more general questions about designing efficient drug trials for these conditions. The present article reports the results of the task force’s deliberations based on available evidence and preliminary results of ongoing activities. Overall, the lack of a consensus definition for sarcopenia and frailty was felt as still present and severely limiting advancements in the field. However, agreement appears to be emerging that low mass alone provides insufficient clinical relevance if not combined with muscle weakness and/or functional impairment. In the next future, it will be important to build consensus on clinically meaningful functional outcomes and test/validate them in long-term observational studies. 

Key words: Clinical trial, methodology, prevention, disability, physical performance, skeletal muscle.


Introduction

Sarcopenia, the age-related loss of muscle mass and strength, represents an increasing public health risk as the world’s population ages at a rapid pace (1). Between 2000, and 2050, the United Nations predicts a doubling of the number of people over age 60 (2), and a recent analysis of prevalence studies concluded that sarcopenia prevalence ranges from 1-29% in community dwelling populations and 14-33% in long-term care populations (3).  Muscle weakness and impaired function that result from sarcopenia are also major components of the geriatric syndrome of frailty (4), thus sarcopenia and frailty are frequently studied in parallel, and indeed they both have physical function impairment as a core condition (5). Yet despite the urgency of the problem, developing treatments for sarcopenia and frailty has lagged, in part because of the lack of consensus definitions for the two conditions.

A task force of clinical and basic researchers, leaders from the pharmaceutical and nutritional industries, and representatives from non-profit organizations came together on April 22, 2015 in Boston, Massachusetts, prior to the International Conference on Frailty and Sarcopenia Research (ICSFR) to address issues that have slowed the development of new treatments. The increase in size of the Task Force since it was established in 2012 reflects the increasing recognition of the need for more effective ways of treating sarcopenia and frailty, as well as increased attention on the part of industry. This, the third meeting of the Task Force, discussed specific challenges related to drugs designed to target the underlying biology of sarcopenia as well as more general questions about designing efficient drug trials for these conditions.

Targeting the underlying biology of sarcopenia 

Research over the past fifteen years has revealed multiple complex and intersecting pathways involved in the regulation of muscle protein balance as well as many possible approaches to reverse muscle loss. Potential regulators include androgens, which act through androgen receptor/Wnt/beta-catenin signaling pathway; insulin and insulin growth factor 1 (IGF-1), which regulate protein synthesis and degradation through the PI3K/AKT pathway; myostatin, a powerful inhibitot of muscle growth, as well as other members of the transforming growth factor-β (TGF- β) superfamily, which act through SMAD signaling; and inflammatory modulators  including pro-inflammatory cytokines such as tumor necrosis factor-α and interleukin-1 (6). Compounds currently in development for the treatment of muscle wasting and sarcopenia are providing further insight into underlying mechanisms. Examples of two classes of these compounds follow.

Myostatin antagonists 

Bimagrumab is a monoclonal antibody that binds to type II activin receptors (ActRII), blocking the binding of myostatin, GDF11, and activin A. Binding of these ligands normally initiates a signaling cascade that results in decreased muscle growth 7. A single dose of bimagrumab increases muscle mass in healthy young men similar to that achieved with 12 week of high-intensity resistance training (8, 9), and in sedentary middle-aged adults, equivalent to that achieved with 9 months of jogging 12-20 miles per week (10).  It has also been shown to work in elderly people; and, in a single leg casted model in healthy young men, bimagrumab improved recovery from atrophy.

Novartis received breakthrough therapy approval for bimagrumab for the treatment of sporadic inclusion body myositis (sIBM) in 2013. In people with this rare muscle disease, a single dose of the drug resulted in an increase in 6-minute walking distance (6MWD) of 52 meters over placebo (11), providing the first evidence of a possible clinical benefit. Now the drug is being tested in people in their 70s with low lean muscle mass. Initial results suggest that a single dose of the drug is well tolerated and associated with an increase in appendicular lean mass (aLM) and handgrip strength (12). Interestingly, gait speed was improved only in those with poor results at the baseline 6MWD test, suggesting that frail people may respond best.

Selective Androgen Receptor Modulators (SARMs) 

Selective androgen receptor modulators (SARMs), a class of androgen receptor ligands that display tissue-selective activation of androgenic signaling, may have potential as function promoting therapies for a variety of conditions, including functional limitations associated with ageing and chronic diseases, osteoporosis, anemia, and hypogonadism, and for male contraception. Osteoporosis represents another component of the frailty syndrome and evidence suggests links between osteoporosis and sarcopenia (13).  Indeed, SARMs also have been shown to have favorable effects on bone mass and quality.

A number of steroidal and non-steroidal SARMs have undergone phase I, II and III trials. For instance, the non-steroidal SARM LGD-4033 has demonstrated preferential tissue selectivity for muscle compared to prostate. Moreover, a 21-day ascending dose study of LGD-4033 in healthy young men showed that the drug was well tolerated, had a favorable pharmacokinetic profile, and increased lean body mass and leg press strength (14).

Another SARM, MK-773, has undergone phase II studies in both men and women with sarcopenia. In one study of women age 65 or older with sarcopenia and frailty, treatment with MK-0773 produced statistically significant increases in LBM compared to placebo, but no significant improvement in strength or function. Both the treatment group and placebo group also received Vitamin D and protein supplementation (15). Other SARMs have also shown benefits in the treatment of muscle wasting associated with cancer, a condition known as cachexia (16, 17).

While SARMS appear to be safe and efficacious in increasing LBM and possibly strength and function, their effects on muscle mass and function at the doses that have been studied have been modest in comparison to the effects from treatment with supraphysiologic doses of testosterone (18).  It is possible that longer studies are needed to demonstrate functional improvements, but it is also likely that more potent and selective SARMs are needed, particularly compounds that are agonists on muscle and antagonists on prostate. The effects of androgens are augmented by functional exercise training (19), and it is possible that translation of muscle mass and strength gains induced by androgens into functional improvements may require functional exercise training. SARMs have generally well tolerated in short term trials. Larger trials of longer duration are needed to demonstrate the long-term safety and efficacy of SARMs in improving physical function and health outcomes.

Designing efficient drug trials for sarcopenia and frailty 

Despite the fact that both sarcopenia and frailty are highly prevalent in older populations, a high degree of heterogeneity and the absence of consensus diagnostic criteria makes the design and implementation of treatment trials extremely challenging. The Task Force addressed many of these issues at its first meeting in 2012 (20). Since then, there has been some progress to define what does and does not represent sarcopenia. In 2014, Anker et al proposed “muscle wasting disease” as a new disease classification which brings together the concepts of sarcopenia, frailty, muscle wasting, and cachexia (21). This framework distinguishes acute from chronic conditions; classifies according to etiology (e.g., due to aging or an underlying medical condition), and then classifies by disease severity and progression.

Defining the target population

Patients with frailty and sarcopenia usually present with multiple chronic diseases that contribute to physical, cognitive, and functional disability. In clinical trials, this large variability increases the uncertainty in possible drug effects by inflating the confidence intervals. However, attempting to control variability by using homogeneous but less representative study populations reduces the generalizability of the results of a trial.

Recent trials have taken two general approaches to targeting patients with sarcopenia: either assessing the degree of sarcopenia and selecting those who are more severely affected or those in the middle of the spectrum; or selecting patients with specific conditions that predispose them to sarcopenia, for example, hip fracture (22). In the Lifestyle Interventions and Independence for Elders (LIFE) study, sedentary older adults were stratified according to their score on the Short Physical Performance Battery (SPPB), excluding those with scores over 9, and oversampling those with scores of 7 or below (23). There was an overall benefit of the exercise intervention. Subgroup analysis showed that those with scores of 8 or 9 had little effect from the physical activity intervention, while a strong beneficial effect was seen in those with poorer function at baseline (scores of 7 or below). At the same time, those with lower SPPB scores are also in poorer health, resulting also in a higher rate of hospitalizations.

In terms of targeting specific conditions, the Aging in Motion (AIM) coalition (aginginmotion.org), which was established by the Alliance for Aging Research in 2011, has been working to obtain regulatory qualification for functional outcomes for clinical trials in specific conditions, including hip fracture, elective total hip arthroplasty, and hospital immobilization (Intensive Care Unit-Acquired Weakness, or ICUAW). The Task Force heard a report on one such study, a trial of LY2495655, a monoclonal antibody that targets myostatin in older individuals who were frequent fallers.  Other studies have targeted patients based on age, inactivity, or presence of frailty; and patients with COPD, diabetes, heart failure, and stroke. A goal of the AIM effort is to puch for regulatory recognition of functional outcomes by including those who are functionally limited.

Whether there is a generalizable way to target sarcopenia across these conditions remains a question. The International Working Group on Sarcopenia proposed targeting patients based on an assessment of physical functioning or weakness; considering patients who are non-ambulatory or who cannot rise from a chair unassisted; or an assessment of habitual gait speed, possibly in combination with a quantitative measurement of body composition of DXA (24). The Foundation for the National Institutes of Health (FNIH) Sarcopenia Project proposed a clinical strategy to identify subjects with muscle weakness and low muscle mass (Figure 1) (25). They went on to amass clinical data from over 26,000 individuals in nine studies to conduct a cross-sectional analysis and define normal/abnormal cut-points based on a logic that a clinician would use for differential diagnosis. For example, if a subject complains he or she has functional problems in getting out of a chair, the clinician might first test to see if muscle weakness is present and, if so, whether reduced lean body mass coexists.

Figure 1 Clinical paradigm for targeting subjects with sarcopenia (reproduced after authorization) (25)

Interestingly, gender seems to be extremely relevant at modifying the relationship between different body composition parameters and physical function (26). Muscle quality, i.e., the capacity of muscle to generate force, also appears to be important, pointing to the possible need to develop criteria for muscle quality as force per unit of mass. Further studies are also needed to clarify the relationship between mass, strength, and function in diverse populations.  One problem with existing data is that most of it has been obtained in high-income countries. Different screening criteria and measures may be needed in developing countries that may have limited access to imaging and other technologies.   

Outcome measures

Physical function as a primary outcome 

Measures of physical function, particularly walking measures, have typically been used in clinical trials of sarcopenia, since walking appears to be the best predictor of disability, hospitalization, mortality, and health care expenditure (27). Several measures of walking ability have been used, including the 400 meter walk (400-MWT), 6MWD, usual gait speed test, and the SPPB which also includes a gait speed subtest. The difficulty or incapability to walk a quarter of a mile or 400 meters is also the standard measure used by the U.S. Census Bureau to assess disability. For the 400-MWT, subjects are permitted to stop but not sit or receive assistance during the walk, although a cane is allowed; and must complete the course within 15 minutes. Ability to complete the test and the time required to do so have been shown to discriminate the risk for mortality, cardiovascular disease, mobility limitation, and disability in community dwelling older adults (28).

An advantage of the 400-MWT is that there are no safety exclusions; an individual may “fail” if he or she is unable to complete the test, but failure is the outcome, rather than missing data. It also has high test-retest reliability (29). This test can therefore be used as a primary outcome measure in an intervention trial, as it was in the LIFE study. The LIFE study randomized over 1,600 sedentary individuals between the ages of 70 and 89 years to a structured moderate intensity physical activity program or a health education program for an average period of 2.6 years (23). Importantly, the use of the 400-MWT as the primary outcome enabled adjudication of the outcome even if participants were unable to come to the lab for assessment. For the LIFE study, adjudication was based on the following outcomes:

– unable to complete 400 meter walk

– unable to walk 4 m or unable to complete 4 m walk test in 10 seconds or less, i.e., gait speed less than 0.4 m/sec

– self reported inability to walk across a room without assistance

– proxy report of inability to walk across a room without assistance

– medical record documentation of inability to walk across a room (bedbound, wheelchair bound, etc.)

Using this adjudication framework, the LIFE study was able to substantially increase the amount of available information for determining the absence/presence of the studied outcomes, even among individuals who were too sick or frail to come to the clinic. In a trial without such methods, such patients would be lost to follow up, resulting in a loss of power and potentially introducing bias into the interpretation of results.

The 6MWT has been used as an outcome measures in a number of other trials, for example the Testosterone Trials (T-TRIAL) (30, 31). Like the 400-MWT, the 6MWT is strongly predictive of mortality (32). Other performance measures, such as the SPPB also have high prognostic value. In the LIFE pilot study, the SPPB was shown to be not only a risk factor for future health outcomes, but modifiable as well (33). Each of the different assessment tools measures different characteristics, for example performance vs. endurance; and each defines a meaningful change differently (34).

The key questions addressed at the Task Force meeting were, which measure is more efficient and what sample size is needed to demonstrate efficacy using different measures. As discussed by Espeland et al. (35), the categorization of continuous outcomes usually reduces statistical power. However, a categorical variable may still more efficiently represent an underlying continuous commonality than continuous parameters that are less directly related. Thus, for example, in the LIFE-P, analyses showed that using the 400-MWT with a 20% effect size requires about 1,669 people for 80% power, compared to 5,178 subjects using the 4-meter walk test and 4,673 using the SPPB.

Physical measures such as DXA measures of aLM and leg extension strength may also be used as either primary or secondary outcome measures, but it is unlikely that a drug indication would ever be approved for these endpoints alone since they are not directly linked to how the subject feels of functions.

Other outcome measures

Multiple secondary outcomes are also typically used in clinical trials, including additional physical performance and functional measures; changes in body composition or size; changes in nutritional status; functional changes such as a reduction in the incidence of falls, fractures, or disability; cognitive and mood changes; quality of life and health care utilization measures; and mortality. Patient-reported outcomes (PROs) have also increasingly been used as secondary outcomes to provide clinically meaningful data.

Secondary outcomes may be selected to study events that may not be widely recognized as relevant or essential to the condition. They also include those leading to a better understanding of the clinical and functional reaction of the organism to the pharmacological/non-pharmacological intervention, including adverse events. Availability of resources and time, and burden to the subject also play roles in the selection of secondary outcomes. Events/conditions that are interesting to be evaluated but may lack sufficient power to be used as primary or secondary may be referred as tertiary or exploratory outcomes.

The biological background of the disease and the phase of the study, also drive the selection of secondary outcomes.  For example, secondary outcomes in early phase studies may be more focused on the kinetic and dynamic characteristics of the tested pharmacologic intervention, while in later phase studies, secondary outcomes may rather elucidate the interaction between the drug and organism as well as the clinical relevance.

Secondary outcomes may also be found embedded in the primary outcome. For example, a single measure of mobility such as the 400-MWT may provide information relevant to functional ability, such as the speed of completing the test, the number of stops during the conduct of the test, the speed variability, the average gait speed, etc. (36). As well, the SPPB can be deconstructed into its specific subtasks in order to obtain additional information beyond that provided by the overall score.

PROs for sarcopenia have started being incorporated into many studies of treatments for both sarcopenia and frailty. For example, in the bimagrumab studies described earlier, PROs have been included although the data have not yet been analyzed. Also in the FNIH Sarcopenia Project, a set of outcome measures have been proposed, including performance measures, PROs, health care utilization, serious injuries (e.g. fractures), and mortality. The investigators will then evaluate correlations of these measures with measures of lean mass, strength, and muscle quality. The exploration of a wide variety of secondary outcomes in this data set may provide important data regard the optimal design of future trials.

Many PROs have been proposed for measuring the frailty phenotype, yet the multidimensionality of the syndrome, as well as a serious and disturbing lack of consensus on the definition of frailty creates obvious challenges for scientific measurement. For example, Fried and colleagues have centered the definition of frailty around the cumulative effect of five criteria (largely focused on the physical aspect), while others adopted a more comprehensive approach including loss in psychological or social domains (37).

Even the five components of the frailty phenotype as defined by Fried and colleagues (38) are not included in many of the PRO measures that have been developed. Most of the measures discussed assess various physical components, while others address the psychological, cognitive, social, demographic, and health care utilization dimensions of frailty. The Irish Longitudinal Study on Aging, for example, included two multidimensional measures — the Self-Reported Frailty Index (SRFI) and the Test-Based Frailty Index (TBFI). The investigators found that prevalence estimates varied from 11% with the SRFI to 17% with the TBFI. Interestingly, women had a higher prevalence of frailty using the SRFI compared to a lower prevalence with the TBFI, suggesting that frailty PROs may mis-estimate the prevalence of frailty in community dwelling elders and obscure gender differences.

For trials of conditions such as sarcopenia and frailty in which definitions remain unclear, flexibility is essential in selecting secondary outcomes that will enable applying results across different settings and cross-checking them according to the current different definitions and possible developments in such a dynamic field of research. Outcome measures must be selected not only based on the type of drug being tested, but also based on a clear definition of the main outcome, baseline differences in the target population, the number of sites, and the experience and training of personnel at the sites. Moreover, trialists must take into account the impact of the intervention on the studied outcome measure, which might significantly affect the duration of the trial.

Biomarkers

There is a need for biomarkers of frailty and sarcopenia aimed at improving diagnostic performance, monitor the progression of the condition(s), predict outcomes, assess treatment response, and optimize the clinical decision making process. Biomarkers should also help us better understand the relationships between aging, frailty, sarcopenia, and disability.

A complex network of biological processes influence the development of sarcopenia and frailty, including physiologic changes in metabolism, muscle strength and power, hormones, inflammatory process, and insulin resistance, among others. For example, results from the Cardiovascular Healthy Study identified increases in components of the inflammation and coagulation systems in frail compared to non-frail community-dwelling adults (39).

FRAILOMIC (www.frailomic.org) is an initiative undertaken by a consortium of university and hospital-based research centers and the World Health Organization (WHO) to analyze multiple classical and non-classical blood-and urine-based laboratory biomarkers on samples collected from approximately 75,000 older individuals. In combination with clinical biomarkers collected from the same cohort, FRAILOMIC will identify through data mining combinations of no more than 5 biomarkers that can be used clinically for diagnosis and prognosis of disability as well as predicting the risk of frailty. Cohorts will be followed prospectively for at least 2.5 years in order to assess progression of frailty, and gender will be included in the analysis. Secondary objectives of the project include 1) assessing interactions between –omic based biomarkers and nutrition and physical exercise on the natural history of frailty, 2) testing whether the identified assessment are useful in special populations, such as people with diabetes, obesity, and cardiovascular disease; and 3) test the validity of existing frailty criteria.           

Novel designs

From a statistical and study design perspective, heterogeneity in the population of individuals with sarcopenia and frailty, as well as in possible interventions, treatment effectiveness and efficacy, and clinical meaningfulness across subpopulations, combine to make clinical trial design particularly challenging. Adaptive trials have been used in other disease areas such as oncology to deal with heterogeneity, since they enable modification of multiple design elements to increase the efficiency of a trial. For sarcopenia studies, adaptive approaches may use machine learning and simulation to tailor trials for individuals with specific risk profiles at the time of randomization, such as weakness or slow gait speed, particularly when there is a specific threshold that is predictive of a downstream outcome such as disability. Eligible participants can be stratified according to their risk profiles to various interventions.

Given the complexity of such designs, Berry et al have proposed the use of platform trial designs, an extension of adaptive trial design that enables the evaluation of multiple treatments in multiple subpopulations simultaneously (40).  The innovation comes from the ability to think of multiple types of trials within a single platform that handles multicomponent interventions and directly targets the effects of specific combination, enabling rapid identification of winning combinations and culling of non-efficacious arms. However, while tailoring and adapting may offer some benefits for trials of sarcopenia and frailty, unclear definitions of the conditions and at-risk populations remain obstacles to carefully consider.

Overcoming barriers to clinical trial participation

Despite the growing recognition among clinicians and scientists about the importance of frailty and sarcopenia, a lack of operational definitions for these conditions has limited their inclusion on national health policy agendas. Indeed, there have been no major studies examining the health economics of interventions for these conditions in well-defined populations. Added to this, although the vast majority of health care is delivered through primary care settings, most clinical research is carried out in specialist-oriented and hospital-based rather than primary care networks, and such research may have limited relevance to primary care processes and pathways.

A non-for-profit institute called the Foundation for Diabetes Research in Older People at Diabetes Frail (www.diabetesfrail.org) was established to address this discrepancy by focusing on primary care, where a wider number and more representative group of patients should be available for studies. The institute aims to convince primary care teams to collaborate in research studies and facilitate their involvement by creating infrastructure within primary care settings and care homes, and building the costs of primary care research into grant applications.

Conclusions

The lack of consensus definitions again arose during discussions at this Task Force meeting, as well as at previous meetings. At this point, while consensus on a definition of sarcopenia has still not been reached, agreement appears to be emerging that low mass alone provides insufficient clinical relevance if not combined with muscle weakness and/or functional impairment.

Pharmacologic and non-pharmacologic interventions for frailty and sarcopenia are nevertheless in development. The Task Force agreed on the need to build consensus on clinically meaningful functional outcomes in a more systematic manner, as well as on the need for long-term observational studies to test and validate these outcomes. In order to accomplish this, participants called for stakeholders to come together in a collaborative framework.

Conflicts of interest: Olivier Benichou is employee at Ely Lilli & Co. Roberto Bernabei is principal investigator of an Innovative Medicines Initiative (IMI)-funded project (including partners from the European Federation of Pharmaceutical Industries and Aassociations [EFPIA]). Shalender Bhasin has received research grants from NIA, NINR, Regeneron, Lilly, and Abbvie, which are administered by the Brigham and Women’s Hospital; he has served as a consultant for Abbvie, Regeneron, Sanofi, Lilly, and Viking. Matteo Cesari has received honoraria for presentations at scientific meetings and/or research fundings from Nestlé, Pfizer, Novartis and serves as workpackage leader in an IMI-funded project (including partners from EFPIA). Ronenn Roubenoff is employee at Novartis. The Gérontopôle (Chair Bruno Vellas) has received grant support from the PHRC, ANR, European Comission as well as: Abbvie, Affiris, Avid, BMS,  Eisai,  Elan, Envivo, Exhonit, Genentech, GSK, Ipsen, Lilly, Lundbeck, Médivation, MSD, Nutricia, Otsuka, Pharnext, Pfizer, Pierre-Fabre, Régénéron, Roche, Sanofi, Servier, TauRx Therapeutics, Wyeth. Bruno Vellas has served as consultant/advisor to Biogen, GSK,  Lilly, Lundbeck, Medivation, MSD, Nestlé, Nutricia,  Pfizer, Roche, Sanofi, Servier, TauRx Therapeutics, Novartis. The other authors have no conflict of interest to disclose.

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10. Durheim MT, Slentz CA, Bateman LA, Mabe SK, Kraus WE. Relationships between exercise-induced reductions in thigh intermuscular adipose tissue, changes in lipoprotein particle size, and visceral adiposity. Am J Physiol Endocrinol Metab. 2008;295(2):E407-E412.

11. Amato AA, Sivakumar K, Goyal N et al. Treatment of sporadic inclusion body myositis with bimagrumab. Neurology. 2014;83(24):2239-2246.

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15. Papanicolaou DA, Ather SN, Zhu H et al. A phase IIA randomized, placebo-controlled clinical trial to study the efficacy and safety of the selective androgen receptor modulator (SARM), MK-0773 in female participants with sarcopenia. J Nutr Health Aging. 2013;17(6):533-543.

16. Dalton JT, Taylor RP, Mohler ML, Steiner MS. Selective androgen receptor modulators for the prevention and treatment of muscle wasting associated with cancer. Curr Opin Support Palliat Care. 2013;7(4):345-351.

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20. Vellas B, Pahor M, Manini T et al. Designing Pharmaceutical Trials for Sarcopenia in Frail Older Adults: EU/US Task Force Recommendations. J Nutr Health Aging. 2013;17(7):612-618.

21. Anker SD, Coats AJ, Morley JE et al. Muscle wasting disease: a proposal for a new disease classification. J Cachexia Sarcopenia Muscle. 2014;5(1):1-3.

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24. Fielding RA, Vellas B, Evans WJ et al. Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology, and consequences. International working group on sarcopenia. J Am Med Dir Assoc. 2011;12(4):249-256.

25. Studenski SA, Peters KW, Alley DE et al. The FNIH Sarcopenia Project: Rationale, Study Description, Conference Recommendations, and Final Estimates. J Gerontol A Biol Sci Med Sci. 2014;69(5):547-558.

26. Cesari M, Rolland Y, Abellan Van Kan G, Bandinelli S, Vellas B, Ferrucci L. Sarcopenia-Related Parameters and Incident Disability in Older Persons: Results From the “Invecchiare in Chianti” Study. J Gerontol A Biol Sci Med Sci. 2015;70 (4):547-558.

27. Hardy SE, Kang Y, Studenski S, Degenholtz HB. Ability to walk 1/4 mile predicts subsequent disability, mortality, and health care costs. J Gen Intern Med. 2011;26(2):130-135.

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31. Cunningham GR, Stephens-Shields AJ, Rosen RC et al. Association of sex hormones with sexual function, vitality, and physical function of symptomatic older men with low testosterone levels at baseline in the testosterone trials. J Clin Endocrinol Metab. 2015;100(3):1146-1155.

32. Mutikainen S, Rantanen T, Alén M et al. Walking ability and all-cause mortality in older women. Int J Sports Med. 2011;32(3):216-222.

33. Pahor M, Blair SN, Espeland M et al. Effects of a physical activity intervention on measures of physical performance: Results of the lifestyle interventions and independence for Elders Pilot (LIFE-P) study. J Gerontol A Biol Sci Med Sci. 2006;61(11):1157-1165.

34. Perera S, Mody S, Woodman RC, Studenski S. Meaningful change and responsiveness in common physical performance measures in older adults. J Am Geriatr Soc. 2006;54(5):743-749.

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36. Vestergaard S, Patel KV, Bandinelli S, Ferrucci L, Guralnik JM. Characteristics of 400-meter walk test performance and subsequent mortality in older adults. Rejuvenation Res. 2009;12(3):177-184.

37. Walston J, Hadley E, Ferrucci L et al. Research agenda for frailty in older adults: toward a better understanding of physiology and etiology: summary from the American Geriatrics Society/National Institute on Aging Research Conference on Frailty in Older Adults. J Am Geriatr Soc. 2006;54(6):991-1001.

38. Fried LP, Tangen CM, Walston J et al. Frailty in older adults: evidence for a phenotype. J Gerontol A Biol Sci Med Sci. 2001;56(3):M146-M156.

39. Walston J, McBurnie MA, Newman AB et al. Frailty and activation of the inflammation and coagulation systems with and without clinical comorbidities: results from the Cardiovascular Health Study. Arch Intern Med. 2002;162(20):2333-2341.

40. Berry SM, Connor JT, Lewis RJ. The platform trial: an efficient strategy for evaluating multiple treatments. JAMA. 2015;313(16):1619-1620.

DESIGNING DRUG TRIALS FOR SARCOPENIA IN OLDER ADULTS WITH HIP FRACTURE – A TASK FORCE FROM THE INTERNATIONAL CONFERENCE ON FRAILTY AND SARCOPENIA RESEARCH (ICFSR)

B. VELLAS1,2, R. FIELDING3, R. MILLER4, Y. ROLLAND1, S. BHASIN5, J. MAGAZINER6, H. BISCHOFF-FERRARI7, ON BEHALF OF THE ICFSR TASK FORCE MEMBERS

 

1. Centre Hospitalier Universitaire de Toulouse, Toulouse, France; 2. Inserm UMR1027, Université de Toulouse, Toulouse, France; 3. Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA; 4. Muscle Metabolism Discovery Performance Unit, GlaxoSmithKline, Raleigh-Durham, NC, USA; 5. Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA; 6. Department of Epidemiology & Public Health Director, University of Maryland School of Medicine, Baltimore, MD, USA; 7. Department of Geriatrics and Aging Research, University of Zurich, Zurich, Switzerland

Corresponding author: Bruno Vellas, MD. Gérontopôle, CHU Toulouse; Service de Médecine Interne et Gérontologie Clinique. 170 Avenue de Casselardit, 31059 Toulouse, France. Phone: +33 (0)5 6177-6425; Fax: +33 (0)5 6177-6475. E-mail: vellas.b@chu-toulouse.fr

J Frailty Aging 2014;3(4):199-204
Published online December 9, 2014, http://dx.doi.org/10.14283/jfa.2014.24

 


Abstract

In May 2012, a Sarcopenia Consensus Summit was convened by the Foundation of the National Institutes of Health (FNIH), National Institute of Aging (NIA), and the U.S. Food and Drug Administration (FDA); and co-sponsored by five pharmaceutical companies. At this summit, sarcopenia experts from around the world worked to develop agreement on a working definition of sarcopenia, building on the work of previous efforts to generate a consensus. With the ultimate goal of improving function and independence in individuals with sarcopenia, the Task Force focused its attention on people at greatly increased risk of muscle atrophy as a consequence of hip fracture. The rationale for looking at this population is that since hip fracture is a recognized condition, there is a clear regulatory path forward for developing interventions. Moreover, patients with hip fracture may provide an appropriate population to advance understanding of sarcopenia, for example helping to define diagnostic criteria, develop biomarkers, understand the mechanisms that underlie the age-related loss of muscle mass and strength, and identify endpoints for clinical trials that are reliable, objective, and clinically meaningful. Task Force members agreed that progress in treating sarcopenia will require strengthening of partnerships between academia, industry, and government agencies, and across continents to reach consensus on diagnostic criteria, optimization of clinical trials design, and identification of improved treatment and preventive strategies. In this report, the main results of the Task Force discussion are presented.

Key words: Sarcopenia, hip fracture, clinical trials, skeletal muscle, aging.


Introduction

As people are living longer, sarcopenia – the age related loss of muscle mass and strength – is becoming increasingly prevalent as a cause of disability and loss of independence. Developing treatments for sarcopenia, however, faces challenges on multiple fronts. Some people consider sarcopenia a part of normal aging rather than a condition requiring intervention. In addition, regulatory and commercial paths for sarcopenia treatments are untrodden, in part because of the lack of consensus on a definition of sarcopenia. Defining sarcopenia as a recognized condition or a manifestation of a recognized condition, and developing diagnostic criteria for the condition are necessary prerequisites for gaining regulatory approval of therapeutic products for this condition.

In May 2012, a Sarcopenia Consensus Summit was convened by the Foundation of the National Institutes of Health (FNIH), National Institute of Aging (NIA), and the U.S. Food and Drug Administration (FDA); and co-sponsored by five pharmaceutical companies. At this summit, sarcopenia experts from around the world worked to develop agreement on a working definition of sarcopenia (1), building on the work of previous efforts to generate a consensus (2, 3). While progress was made towards developing a better understanding of sarcopenia, a consensus definition remains elusive.

Hip fracture is universally accepted as a recognized condition, and it is understood that pre-fracture and post- fracture muscle loss compromise functional capacity. Moreover, hip fracture increases risk of institutionalization (15-35% may be institutionalized), risk of falls, and mortality (18-33% die within 1 year). Thus, a task force of experts in sarcopenia met on March 12, 2014 in Barcelona, Spain, at the International Conference on Frailty and Sarcopenia Research (ICFSR) to explore whether using hip fracture as the diagnosed condition in drug trials could represent a path forward toward achieving regulatory approval for sarcopenia treatments in older adults. The Task Force was convened by the Global Aging Research Network (GARN), a collaboration of the International Association of Gerontology and Geriatrics (IAGG).

 

Change in body composition and function after hip fracture

The Baltimore Hip Studies (BHS) have been conducted for over 25 years with the goal of identifying, developing, and evaluating strategies to optimize recovery from hip fracture. Analysis of data from the BHS have shown significant decreases in total body mass, lean mass, and bone mineral density were observed 10 days to 2 months following hip fracture (4, 5). Sarcopenia, defined as appendicular lean mass normalized for height, was found in about 35% of women at baseline (3-10 days after hip fracture), increased to over 50% at 2 months, and increased further up to 12 months post- fracture (6). Patients also experience substantial functional consequences such that for patients functioning independently before fracture, a large percentage remain unable to climb 5 stairs, get in and out of the bath or on and off the toilet 12 months post-fracture (7). In another study testing the ability of subjects to walk 300 meters in 6 minutes, only 4% of hip- fracture patients were able to walk at this level at 2 months, and even by 12 months only 16% had achieved this level of mobility (8, 9).

Hip fracture is a multi-faced problem requiring multi-domain interventions with different strategies addressing different impairments at different stages of the recovery process. However, researchers are only beginning to understand the optimal way of treating patients at different stages (including preventive approaches pre-fracture).

 

Diagnostic criteria for sarcopenia in older adults with hip fracture

The loss of mobility imposed by hip fracture results in sarcopenia characterized by declining muscle mass, deficiencies in strength and power, functional limitations and eventually, disability. Different diagnostic criteria have been proposed for sarcopenia (2, 3, 10-12), but the field has yet to reach consensus on whether diagnosis should be based on muscle mass, strength, or functional limitations. In addition, the timing of the most inspired  diagnosis relative to the injury is important. Following an acute injury, pain and delirium can complicate the diagnostic process. If surgery has been performed, post- surgical recommendations for recovery may range from bed rest to varying periods of partial weight-bearing exercise. These different management strategies, as well as co-morbidities and limited mobility, particularly among the very old, also influence the ability to diagnose sarcopenia.

The prevalence of sarcopenia depends on how the condition is defined. For example, using Dual-Energy X-ray Absorptiometry (DXA) scanning to determine appendicular lean mass in 340 women 2-4 weeks following hip fracture, Di Monaco et al found that 58% were sarcopenic (13). In contrast, a study using bioelectrical impedance analysis (BIA) to calculate whole-body skeletal muscle mass in a hip fracture patients found that 71% were sarcopenic (14). Anthropometric measures (height, weight, sex) have also been used to predict muscle mass (15). Table 1 summarizes the advantages and disadvantages of different methods for diagnosing sarcopenia.

Task force members advocated for testing the various definitions of sarcopenia against an important endpoint, such as falls. Since functional measures are the most clinically relevant, basing a trial on muscle mass could be problematic; however, if muscle mass and functional measures prove to be equivalent predictors of falls, muscle mass could be considered a more reliable and objective endpoint.

Table 1: Methods for assessing sarcopenia in patients with hip fracture (modified from Rolland Y et al. Clin Geriatr Med 2011;27:423-47)

 

Targeting hip fracture patients for sarcopenia clinical trials

When to begin intervention depends on the goals of intervention. One argument in favor of intervening shortly after hip fracture occurs is that muscle loss may occur early after hip fracture. Comparing the fractured vs. non-fractured legs, at two months post-fracture the fractured leg shows less normal density muscle, more low-density muscle, and high intermuscular adipose tissue. In addition, the period of greatest risk for a subsequent fall and second fracture (16), as well as the greatest risk of mortality occurs close to the time of fracture (17). Thus, if the goal is to minimize muscle loss and reduce falls, intervention should begin early.

However, a recent home-based exercise intervention program (8) found that when subjects started the intervention about two months post-fracture, there was no significant difference between the intervention and control arms in terms of functional measures even 12 months post-fracture. In another study where a home-based exercise intervention program was started approximately 9 months post-fracture, there was a modest improvement in function 6 months following randomization (18). Thus if the aim is to demonstrate functional improvement, there may be a benefit from waiting until the period of high risk has passed. Later studies may also be more likely to involve home-based interventions.

Later studies would also be less likely to enroll subjects at high risk of adverse outcomes in the early stages. From the point of view of sponsors conducting a study, there is a fine balance between successful conduct of the study and generalizability. On the one hand, excluding subjects unlikely to benefit or at high risk of adverse events improves the likelihood of a successful trial. On the other hand there has recently been increased attention from regulatory agencies on the need to enroll representative populations (18). Thus, for example, in the Orwig study, only 19% of the 1276 patients identified were eligible for the study. Excluded were those with prefracture nursing home residency (24%), prefracture history of dementia (13%), cardiac disease (12%) or orthopedic hardware in the contralateral hip (10%). In only 15% of 1546 assessed subjects were enrolled. Many subjects refused to participate, died, or could not be reached by the study coordinators. Inclusion rates of only 15-19% raise doubts about the applicability of the results to real-life populations.

 

Trial design issues

The Task Force discussed various trial design issues that must be considered. These are summarized below:

Inpatient or outpatient study. This may vary depending on where the study will be conducted. In the United States, the typical length of hospital stay following hip fracture is about 5 days, followed by discharge to a rehabilitation facility; whereas in Europe patients typically are hospitalized longer.

Suggested inclusion criteria (Table 2).

  • moderate degree of ADL impairment and mobility limitation (e.g. difficulty or dependence in two or more basic, instrumental or mobility activities).
  • presence of the condition (i.e., hip fracture) using objective and precise measures. Need to operationalize the indication so that it can be ascertained accurately and reliably using both self-reported and performance based measures.
  • Residence in community or assisted living preferred since institutionalized patients tend to have more comorbidities.
  • Should sarcopenia be an eligibility criteria? Arguments for and against were presented;.

Table 2: Exemple of inclusion criteria for sarcopenia trials in patients with hip fracture

 

Suggested exclusion criteria:

  • Subjects who are unlikely to respond, will respond differently, or may be at risk of adverse events.
  • Subjects who were unable to walk without human assistance before fracture as well as those with limiting neuromuscular conditions that my affect mobility or physical function.
  • Severe cognitive deficits, severe depression, progressive neurologic disease or previous stroke.
  • Comorbid conditions that could affect response to treatment or compromise the safety of the treatment, e.g. cancer, anemia, terminal illness, end-stage renal disease requiring dialysis, some cardiovascular conditions such as recent myocardial infarction, acute coronary syndrome or stroke; organ dysfunction (with established cutoffs for relevant measures).
  • Marked obesity
  • Currently using other drugs that may affect drug metabolism or response.

 

Drug specific exclusions:

  • For trials of promyogenic drugs, there may be an increased risk of cardiovascular disease especially in older adults with multiple co-morbid conditions. Therefore, individuals with certain cardiovascular conditions or those at high risk of cardiovascular events may be excluded.
  • For trials of androgens and selective androgen receptor modulators (SARM) exclude those with conditions that may be affected by androgens (e.g., those with prostate cancer or breast cancer, or with elevated prostate specific antigen [PSA] or International prostate symptom score [IPSS] or hematocrit >50%, or untreated severe obstructive sleep apnea %), as well as those with conditions that may affect the response to androgens (20).

 

Questionable exclusions:

  • Osteoporosis and vitamin D deficiency occur are highly prevalent in hip fracture patients. Since Vitamin D may affect physical function especially at very low levels, consider excluding those with severe deficiency and replacing Vitamin D in others with a dose that would raise 25(OH)D into normal range, then monitor levels.

 

Timing of intervention following hip fracture. The suggestion was made to take a middle ground (4-12 weeks after fracture) since in first four weeks multiple medical and post- surgical issues may complicate recovery. Also, most patients are involved in rehab programs at this early stage.

Randomization and stratification. Randomization is necessary to ensure that groups are comparable at baseline and to reduce selection bias. However, hip fracture patients often have a high prevalence of co-morbidities, necessitating other allocation strategies to minimize the risk of imbalance between the treatment arms. Further, in multi-domain trials that combine pharmaceutical treatment with physical activity, decisions must be made whether to allow physical activity to distribute randomly or to control physical activity so that different drug treatment arms have a similar “dose” of physical activity. Controlling physical activity offers the advantage of smaller sample sizes but introduces numerous challenges with regard to implementation of the intervention and ensuring adherence to the program.

Trial duration. Shorter durations result in reduced costs and lower attrition; however, longer duration trials may be needed to acquire information about safety and efficacy. Trials of 6-12 months may provide the best trade-off. For example, trials of testosterone and exercise have shown improvements in muscle mass, strength, and function over a 6 month duration (20-23).

Efficacy outcomes – Primary outcome measures should assess an aspect of the condition that is clinically meaningful, can be measured safely, reproducibly, and precisely. These measures may be performance based or self-reported, each type with advantages and disadvantages (24). Therefore, inclusion of both types of measures would provide a more comprehensive assessment of efficacy.

  • Performance based measures should be aligned with self- reported measures and the subjects’ functional limitations and symptoms. For example, walking speed is an excellent integrated measure of physical function and mobility disability. It can be measured precisely and reproducibly, is responsive to intervention, predictive of health outcomes, and Minimal Clinically Important Differences (MCIDs) are known (25, 26). Gait speed measures can utilize a short or long walk and can also be incorporated into composite measures such as the Short Physical Performance Battery (SPPB) and Physical Functional Performance Test (PFP), as well as self-reported measures such as the Physical Functioning scale (PF-10). Self-reported measures can include specific questions that allow for dichotomous analysis.
  • Measures should have a plausible link to the mechanism of action. For example, promyogenic anabolic therapies are expected to result in increased muscle mass and strength, leading to improved physical function, increased independence, improved health perceptions, and improvements in other health-related outcomes. Therefore, trials of such drugs should include muscle mass and performance as outcomes, but will also need to show that the intervention results in meaningful improvement in patient’s life.
  • Maintaining independence is of primary importance in the lives of hip fracture patients. More than half of patients with hip fracture lose their ability to function independently, primarily because of mobility limitations. This often results in nursing home placement and also increases health care costs (7).
  • The Activity Measure for Post-Acute Care (AM-PAC) is a measure of disability in activities of daily living, mobility and social functioning. The MCID is known and is related to outcomes including mortality (18).
  • Other outcomes: pain, mood and affect, well-being, falls, fall-related injuries, hospitalizations, death
  • Biomarkers of muscle mass and strength are necessary and useful to power a trial, but insufficient to establish efficacy (7, 23, 27).

Imaging and biomarkers for sarcopenia trials in older adults with hip fracture

Biomarkers for sarcopenia are used not only diagnostically but also to track disease progression and response to therapy. As with their use in diagnosis, each method has advantages and disadvantages. For example, CT precisely measures direct physical properties of muscle but exposes patients to radiation. In an elderly individual, CT is likely to show loss of normal density muscle, increased low density muscle, increased myocellular lipid accumulation and intermuscular fat. MRI provides similar information and has the additional capacity for multiple slice acquisition, however it comes with a higher cost and higher subject burden. DXA assesses both bone and soft tissue density with high precision and reliability but is affected by hydration levels and does not allow for assessment of the fractured limb where the magnitude of muscle and strength loss may be greater than in the unfractured limb. Additional non-invasive measures, including ultrasound, bioelectrical impedance, assessment of serum metabolites (28) and genomic studies offer other approaches to assessing muscle mass, although so far, none of these assessments has the sensitivity to be used as a primary outcome in clinical trials.

Nonetheless, incorporating biomarkers into trials offers the potential to provide important information, e.g. to show target engagement in phase 1b trials; as well as validation of the approaches for use in future trials.

 

Intervention: treatment and prevention

The Task Force addressed whether trials should focus on prevention or treatment. For pro-myogenic drugs, a prevention trial would probably be unrealistic given the huge sample size required, the uncertainty about efficacy, and the lack of knowledge about long-term safety. Moreover, a prevention trial would require identification of individuals at risk, which is not at this point well defined. However, a treatment trial of a pro-myogencic drug in patients with hip fracture would provide a more favorable risk/benefit ratio. The primary endpoint could be, for example, improved function, with prevention of falls a secondary endpoint with functional significance. Similar endpoints have been incorporated into interventional studies discussed earlier, such as those conducted as part of the Baltimore Hip Studies.

Prevention trials are also underway. For example, DO-HEALTH is a clinical trial taking place in 7 European cities to determine whether combining exercise with vitamin D and omega-3 fatty acids will prevent disease in older age. Over 2,000 seniors have been enrolled, including subjects classified as pre-frail and those with a history of falls. The five primary endpoints include incidence of non-vertebral fractures and functional decline, as well as endpoints related to cardiovascular and brain health and immunity. All clinical endpoints are supported by biomarker studies.

 

Conclusions

With the ultimate goal of improving function and independence in individuals with sarcopenia, the Task Force focused its attention on people at greatly increased risk of muscle atrophy as a consequence of hip fracture. The rationale for looking at this population is that since hip fracture is a recognized condition, there is a clear regulatory path forward for developing interventions. Moreover, patients with hip fracture may provide an appropriate population to advance understanding of sarcopenia, for example helping to define diagnostic criteria, develop biomarkers, understand the mechanisms that underlie the age-related loss of muscle mass and strength, and identify endpoints for clinical trials that reliable, objective, and clinically meaningful.

Task Force members agreed that progress in treating sarcopenia will require strengthening of partnerships between academia, industry, and government agencies, and across continents to reach consensus on diagnostic criteria, optimization of clinical trials design, and identification of improved treatment and preventive strategies.

 

Acknowledgments: Members of the ICFSR Task Force: Gabor Abellan van Kan (Toulouse, France), Lisa J. Bain (Elverson, USA), Cécile Bonhomme (Torcé, France), Denis Breuillé (Lausanne, Switzerland), Francesca Cerreta (London, United Kingdom), Alfonso Cruz-Jentoft (Madrid, Spain), Dominique Dardevet (Ceyrat, France), Justine Davies (London, United Kingdom), Susanna Del Signore (Chilly Mazarin, France), Stephen Donahue (Tarrytown, USA), Philippe Guillet (Chilly Mazarin, France), Michaela Hoehne (Lutry, Switzerland), Makoto Kashiwa (Saitama, Japan), Valerie Legrand (Nanterre, France), Fady Malik (San Francisco, USA), Erwin Meijer (Schiphol Airport, The Netherlands), Marco Pahor (Gainesville, USA), Robert Pordy (Tarrytown, USA), Leocadio Rodriguez- Manas (Madrid, Spain), Daniel Rooks (Cambridge, USA), Fariba Roughead (Minnetonka, USA), Klaudius Siegfried (Langen, Germany), Alan J Sinclair (Bedfordshire, United Kingdom), Elisabeth Stöcklin (Wurmisweg, Switzerland), Laszlo Tanko (Basel, Switzerland), Sjors Verlaan (Schiphol Airport, The Netherlands), Sander Wijers (Wageningen, The Netherlands).

Conflicts of interests: The TF cost was financed by the ICFSR conference and registration fees

 

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