Treatment of Sarcopenia with Bimagrumab: Results from a Phase II, Randomized, Controlled, Proof-of-Concept Study

Advancements in Drug Delivery Systems for the Treatment of Sarcopenia: An Updated Overview

Since sarcopenia is a progressive condition that leads to decreased muscle mass and function, especially in elderly people, it is a public health problem that requires attention from researchers. This review aims to highlight drug delivery systems that have a high and efficient therapeutic potential for sarcopenia. Current as well as future research needs to consider the barriers encountered in the realization of delivery systems, such as the route of administration, the interaction of the systems with the aggressive environment of the human body, the efficient delivery and loading of the systems with therapeutic agents, and the targeted delivery of therapeutic agents into the muscle tissue without creating undesirable adverse effects. Thus, this paper sets the framework of existing drug delivery possibilities for the treatment of sarcopenia, serving as an inception point for future interdisciplinary studies.

Therapeutic applications and challenges in myostatin inhibition for enhanced skeletal muscle mass and functions

Myostatin, a potent negative regulator of skeletal muscle mass, has garnered significant attention as a therapeutic target for muscle dystrophies. Despite extensive research and promising preclinical results, clinical trials targeting myostatin inhibition in muscle dystrophies have failed to yield substantial improvements in muscle function or fitness in patients. This review details the mechanisms behind myostatin's function and the various inhibitors that have been tested preclinically and clinically. It also examines the challenges encountered in clinical translation, including issues with drug specificity, differences in serum myostatin concentrations between animal models and humans, and the necessity of neural input for functional improvements. Additionally, we explore promising avenues of research beyond muscle dystrophies, particularly in the treatment of metabolic syndromes and orthopedic disorders. Insights from these alternative applications suggest that myostatin inhibition may hold the potential for addressing a broader range of pathologies, providing new directions for therapeutic development.

Emerging Targets and Treatments for Sarcopenia: A Narrative Review

BACKGROUND

Sarcopenia is characterized by the progressive loss of skeletal muscle mass, strength, and function, significantly impacting overall health and quality of life in older adults. This narrative review explores emerging targets and potential treatments for sarcopenia, aiming to provide a comprehensive overview of current and prospective interventions.

METHODS

The review synthesizes current literature on sarcopenia treatment, focusing on recent advancements in muscle regeneration, mitochondrial function, nutritional strategies, and the muscle-microbiome axis. Additionally, pharmacological and lifestyle interventions targeting anabolic resistance and neuromuscular junction integrity are discussed.

RESULTS

Resistance training and adequate protein intake remain the cornerstone of sarcopenia management. Emerging strategies include targeting muscle regeneration through myosatellite cell activation, signaling pathways, and chronic inflammation control. Gene editing, stem cell therapy, and microRNA modulation show promise in enhancing muscle repair. Addressing mitochondrial dysfunction through interventions aimed at improving biogenesis, ATP production, and reducing oxidative stress is also highlighted. Nutritional strategies such as leucine supplementation and anti-inflammatory nutrients, along with dietary modifications and probiotics targeting the muscle-microbiome interplay, are discussed as potential treatment options. Hydration and muscle-water balance are emphasized as critical in maintaining muscle health in older adults.

CONCLUSIONS

A combination of resistance training, nutrition, and emerging therapeutic interventions holds potential to significantly improve muscle function and overall health in the aging population. This review provides a detailed exploration of both established and novel approaches for the prevention and management of sarcopenia, highlighting the need for further research to optimize these strategies.

Effect of Bimagrumab on body composition: a systematic review and meta-analysis

BACKGROUND

Sarcopenia, a condition marked by progressive muscle mass and function decline, presents significant challenges in aging populations and those with chronic illnesses. Current standard treatments such as dietary interventions and exercise programs are often unsustainable. There is increasing interest in pharmacological interventions like bimagrumab, a monoclonal antibody that promotes muscle hypertrophy by inhibiting muscle atrophy ligands. Bimagrumab has shown effectiveness in various conditions, including sarcopenia.

AIM

The primary objective of this meta-analysis is to evaluate the impact of bimagrumab treatment on both physical performance and body composition among patients diagnosed with sarcopenia.

MATERIALS AND METHODS

This meta-analysis follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We systematically searched PubMed, Ovid/Medline, Web of Science, and the Cochrane Library databases up to June 2024 using appropriate Medical Subject Headings (MeSH) terms and keywords related to bimagrumab and sarcopenia. Eligible studies were randomized controlled trials (RCTs) that assessed the effects of bimagrumab on physical performance (e.g., muscle strength, gait speed, six-minute walk distance) and body composition (e.g., muscle volume, fat-free body mass, fat body mass) in patients with sarcopenia. Data extraction was independently performed by two reviewers using a standardized form, with discrepancies resolved through discussion or consultation with a third reviewer.

RESULTS

From an initial search yielding 46 records, we screened titles, abstracts, and full texts to include seven RCTs in our meta-analysis. Bimagrumab treatment significantly increased thigh muscle volume (mean difference [MD] 5.29%, 95% confidence interval [CI] 4.08% to 6.50%, P < 0.001; moderate heterogeneity χ2 = 6.41, I2 = 38%, P = 0.17) and fat-free body mass (MD 1.90 kg, 95% CI 1.57 kg to 2.23 kg, P < 0.001; moderate heterogeneity χ2 = 8.60, I2 = 30%, P = 0.20), while decreasing fat body mass compared to placebo (MD - 4.55 kg, 95% CI - 5.08 kg to - 4.01 kg, P < 0.001; substantial heterogeneity χ2 = 27.44, I2 = 89%, P < 0.001). However, no significant improvement was observed in muscle strength or physical performance measures such as gait speed and six-minute walk distance with bimagrumab treatment, except among participants with slower baseline walking speeds or distances.

DISCUSSION AND CONCLUSION

This meta-analysis provides valuable insights into the effects of bimagrumab on sarcopenic patients, highlighting its significant improvements in body composition parameters but limited impact on functional outcomes. The observed heterogeneity in outcomes across studies underscores the need for cautious interpretation, considering variations in study populations, treatment durations, and outcome assessments. While bimagrumab shows promise as a safe pharmacological intervention for enhancing muscle mass and reducing fat mass in sarcopenia, its minimal effects on muscle strength and broader physical performance suggest potential limitations in translating body composition improvements into functional gains. Further research is needed to clarify its long-term efficacy, optimal dosing regimens, and potential benefits for specific subgroups of sarcopenic patients.

Skeletal muscle dysfunction with advancing age

As a result of advances in medical treatments and associated policy over the last century, life expectancy has risen substantially and continues to increase globally. However, the disconnect between lifespan and 'health span' (the length of time spent in a healthy, disease-free state) has also increased, with skeletal muscle being a substantial contributor to this. Biological ageing is accompanied by declines in both skeletal muscle mass and function, termed sarcopenia. The mechanisms underpinning sarcopenia are multifactorial and are known to include marked alterations in muscle protein turnover and adaptations to the neural input to muscle. However, to date, the relative contribution of each factor remains largely unexplored. Specifically, muscle protein synthetic responses to key anabolic stimuli are blunted with advancing age, whilst alterations to neural components, spanning from the motor cortex and motoneuron excitability to the neuromuscular junction, may explain the greater magnitude of function losses when compared with mass. The consequences of these losses can be devastating for individuals, their support networks, and healthcare services; with clear detrimental impacts on both clinical (e.g., mortality, frailty, and post-treatment complications) and societal (e.g., independence maintenance) outcomes. Whether declines in muscle quantity and quality are an inevitable component of ageing remains to be completely understood. Nevertheless, strategies to mitigate these declines are of vital importance to improve the health span of older adults. This review aims to provide an overview of the declines in skeletal muscle mass and function with advancing age, describes the wide-ranging implications of these declines, and finally suggests strategies to mitigate them, including the merits of emerging pharmaceutical agents.

Lost in translation: challenges of current pharmacotherapy for sarcopenia

A healthy lifespan relies on independent living, in which active skeletal muscle is a critical element. The cost of not recognizing and acting earlier on unhealthy or aging muscle could be detrimental, since muscular weakness is inversely associated with all-cause mortality. Sarcopenia is characterized by a decline in skeletal muscle mass and strength and is associated with aging. Exercise is the only effective therapy to delay sarcopenia development and improve muscle health in older adults. Although numerous interventions have been proposed to reduce sarcopenia, none has yet succeeded in clinical trials. This review evaluates the biological gap between recent clinical trials targeting sarcopenia and the preclinical studies on which they are based, and suggests an alternative approach to bridge the discrepancy.

Biological basis and treatment of frailty and sarcopenia

In an ageing society, the importance of maintaining healthy life expectancy has been emphasized. As a result of age-related decline in functional reserve, frailty is a state of increased vulnerability and susceptibility to adverse health outcomes with a serious impact on healthy life expectancy. The decline in skeletal muscle mass and function, also known as sarcopenia, is key in the development of physical frailty. Both frailty and sarcopenia are highly prevalent in patients not only with advanced age but also in patients with illnesses that exacerbate their progression like heart failure (HF), cancer, or dementia, with the prevalence of frailty and sarcopenia in HF patients reaching up to 50-75% and 19.5-47.3%, respectively, resulting in 1.5-3 times higher 1-year mortality. The biological mechanisms of frailty and sarcopenia are multifactorial, complex, and not yet fully elucidated, ranging from DNA damage, proteostasis impairment, and epigenetic changes to mitochondrial dysfunction, cellular senescence, and environmental factors, many of which are further linked to cardiac disease. Currently, there is no gold standard for the treatment of frailty and sarcopenia, however, growing evidence supports that a combination of exercise training and nutritional supplement improves skeletal muscle function and frailty, with a variety of other therapies being devised based on the underlying pathophysiology. In this review, we address the involvement of frailty and sarcopenia in cardiac disease and describe the latest insights into their biological mechanisms as well as the potential for intervention through exercise, diet, and specific therapies.

Molecular Pathways Governing the Termination of Liver Regeneration

The liver has the unique capacity to regenerate, and up to 70% of the liver can be removed without detrimental consequences to the organism. Liver regeneration is a complex process involving multiple signaling networks and organs. Liver regeneration proceeds through three phases: the initiation phase, the growth phase, and the termination phase. Termination of liver regeneration occurs when the liver reaches a liver-to-body weight that is required for homeostasis, the so-called "hepatostat." The initiation and growth phases have been the subject of many studies. The molecular pathways that govern the termination phase, however, remain to be fully elucidated. This review summarizes the pathways and molecules that signal the cessation of liver regrowth after partial hepatectomy and answers the question, "What factors drive the hepatostat?" SIGNIFICANCE STATEMENT: Unraveling the pathways underlying the cessation of liver regeneration enables the identification of druggable targets that will allow us to gain pharmacological control over liver regeneration. For these purposes, it would be useful to understand why the regenerative capacity of the liver is hampered under certain pathological circumstances so as to artificially modulate the regenerative processes (e.g., by blocking the cessation pathways) to improve clinical outcomes and safeguard the patient's life.

Advances in sarcopenia: mechanisms, therapeutic targets, and intervention strategies

Sarcopenia is a multifactorial condition characterized by loss of muscle mass. It poses significant health risks in older adults worldwide. Both pharmacological and non-pharmacological approaches are reported to address this disease. Certain dietary patterns, such as adequate energy intake and essential amino acids, have shown positive outcomes in preserving muscle function. Various medications, including myostatin inhibitors, growth hormones, and activin type II receptor inhibitors, have been evaluated for their effectiveness in managing sarcopenia. However, it is important to consider the variable efficacy and potential side effects associated with these treatments. There are currently no drugs approved by the Food and Drug Administration for sarcopenia. The ongoing research aims to develop more effective strategies in the future. Our review of research on disease mechanisms and drug development will be a valuable contribution to future research endeavors.

Muscle strength and non-alcoholic fatty liver disease/metabolic-associated fatty liver disease

This editorial comments on an article published in a recent issue of World Journal of Gastroenterology, entitled “Association of low muscle strength with metabolic dysfunction-associated fatty liver disease: A nationwide study”. We focused on the association between muscle strength and the incidence of non-alcoholic fatty liver disease (NAFLD) and metabolic-associated fatty liver disease (MAFLD), as well as the mechanisms underlying the correlation and related clinical applications. NAFLD, which is now redefined as MAFLD, is one of the most common chronic liver diseases globally with an increasing prevalence and is characterized by malnutrition, which may contribute to decreased muscle strength. Reduction of muscle strength reportedly has a pathogenesis similar to that of NAFLD/ MAFLD, including insulin resistance, inflammation, sedentary behavior, as well as insufficient vitamin D. Multiple studies have focused on the relationship between sarcopenia or muscle strength and NAFLD. However, studies investigating the relationship between muscle strength and MAFLD are limited. Owing to the shortage of specific medications for NAFLD/MAFLD treatment, early detection is essential. Furthermore, the relationship between muscle strength and NAFLD/MAFLD suggests that improvements in muscle strength may have an impact on disease prevention and may provide novel insights into treatments including dietary therapy, as well as tailored physical activity.

The Current Landscape of Pharmacotherapies for Sarcopenia

Sarcopenia is a skeletal muscle disorder characterized by progressive and generalized decline in muscle mass and function. Although it is mostly known as an age-related disorder, it can also occur secondary to systemic diseases such as malignancy or organ failure. It has demonstrated a significant relationship with adverse outcomes, e.g., falls, disabilities, and even mortality. Several breakthroughs have been made to find a pharmaceutical therapy for sarcopenia over the years, and some have come up with promising findings. Yet still no drug has been approved for its treatment. The key factor that makes finding an effective pharmacotherapy so challenging is the general paradigm of standalone/single diseases, traditionally adopted in medicine. Today, it is well known that sarcopenia is a complex disorder caused by multiple factors, e.g., imbalance in protein turnover, satellite cell and mitochondrial dysfunction, hormonal changes, low-grade inflammation, senescence, anorexia of aging, and behavioral factors such as low physical activity. Therefore, pharmaceuticals, either alone or combined, that exhibit multiple actions on these factors simultaneously will likely be the drug of choice to manage sarcopenia. Among various drug options explored throughout the years, testosterone still has the most cumulated evidence regarding its effects on muscle health and its safety. A mas receptor agonist, BIO101, stands out as a recent promising pharmaceutical. In addition to the conventional strategies (i.e., nutritional support and physical exercise), therapeutics with multiple targets of action or combination of multiple therapeutics with different targets/modes of action appear to promise greater benefit for the prevention and treatment of sarcopenia.

Bezafibrate attenuates immobilization-induced muscle atrophy in mice

Muscle atrophy due to fragility fractures or frailty worsens not only activity of daily living and healthy life expectancy, but decreases life expectancy. Although several therapeutic agents for muscle atrophy have been investigated, none is yet in clinical use. Here we report that bezafibrate, a drug used to treat hyperlipidemia, can reduce immobilization-induced muscle atrophy in mice. Specifically, we used a drug repositioning approach to screen 144 drugs already utilized clinically for their ability to inhibit serum starvation-induced elevation of Atrogin-1, a factor related to muscle atrophy, in myotubes in vitro. Two candidates were selected, and here we demonstrate that one of them, bezafibrate, significantly reduced muscle atrophy in an in vivo model of muscle atrophy induced by leg immobilization. In gastrocnemius muscle, immobilization reduced muscle weight by an average of ~ 17.2%, and bezafibrate treatment prevented ~ 40.5% of that atrophy. In vitro, bezafibrate significantly inhibited expression of the inflammatory cytokine Tnfa in lipopolysaccharide-stimulated RAW264.7 cells, a murine macrophage line. Finally, we show that expression of Tnfa and IL-1b is induced in gastrocnemius muscle in the leg immobilization model, an activity significantly antagonized by bezafibrate administration in vivo. We conclude that bezafibrate could serve as a therapeutic agent for immobilization-induced muscle atrophy.

Current and investigational medications for the treatment of sarcopenia

Sarcopenia, defined as the loss of muscle mass and function, is a widely prevalent and severe condition in older adults. Since 2016, it is recognized as a disease. Strength exercise training and nutritional support are the frontline treatment of sarcopenia, with no drug currently approved for this indication. However, new therapeutic options are emerging. In this review, we evidenced that only very few trials have focused on sarcopenia/sarcopenic patients. Most drug trials were performed in different clinical older populations (e.g., men with hypogonadism, post-menopausal women at risk for osteoporosis), and their efficacy were tested separately on the components of sarcopenia (muscle mass, muscle strength and physical performances). Results from trials testing the effects of Testosterone, Selective Androgen Receptor Modulators (SARMs), Estrogen, Dehydroepiandrosterone (DHEA), Insulin-like Growth Factor-1 (IGF-1), Growth Hormone (GH), GH Secretagogue (GHS), drug targeting Myostatin and Activin receptor pathway, Vitamin D, Angiotensin Converting Enzyme inhibitors (ACEi) and Angiotensin Receptor Blockers (ARBs), or β-blockers, were compiled. Although some drugs have been effective in improving muscle mass and/or strength, this was not translated into clinically relevant improvements on physical performance. Finally, some promising molecules investigated in on-going clinical trials and in pre-clinical phase were summarized, including apelin and irisin.

Ubiquitin-proteasome pathway in skeletal muscle atrophy

Skeletal muscles underpin myriad human activities, maintaining an intricate balance between protein synthesis and degradation crucial to muscle mass preservation. Historically, disruptions in this balance-where degradation overshadows synthesis-have marked the onset of muscle atrophy, a condition diminishing life quality and, in grave instances, imperiling life itself. While multiple protein degradation pathways exist-including the autophagy-lysosome, calcium-dependent calpain, and cysteine aspartate protease systems-the ubiquitin-proteasome pathway emerges as an especially cardinal avenue for intracellular protein degradation, wielding pronounced influence over the muscle atrophy trajectory. This paper ventures a panoramic view of predominant muscle atrophy types, accentuating the ubiquitin-proteasome pathway's role therein. Furthermore, by drawing from recent scholarly advancements, we draw associations between the ubiquitin-proteasome pathway and specific pathological conditions linked to muscle atrophy. Our exploration seeks to shed light on the ubiquitin-proteasome pathway's significance in skeletal muscle dynamics, aiming to pave the way for innovative therapeutic strategies against muscle atrophy and affiliated muscle disorders.

[GDF5: a therapeutic candidate for combating sarcopenia]

Sarcopenia is a complex age-related muscular disease affecting 10 to 16 % of people over 65 years old. It is characterized by excessive loss of muscle mass and strength. Despite a plethora of studies aimed at understanding the physiological mechanisms underlying this pathology, the pathophysiology of sarcopenia remains poorly understood. To date, there is no pharmacological treatment for this disease. In this context, our team develop therapeutic approaches based on the GDF5 protein to counteract the loss of muscle mass and function in various pathological conditions, including sarcopenia. After deciphering one of the molecular mechanisms governing GDF5 expression, we have demonstrated the therapeutic potential of this protein in the preservation of muscle mass and strength in aged mice.

Muscle-bone crosstalk via endocrine signals and potential targets for osteosarcopenia-related fracture

Background

Osteosarcopenia is a syndrome coexisting sarcopenia and osteopenia/osteoporosis, with a high fracture risk. Recently, skeletal muscle and bone have been recognized as endocrine organs capable of communication through secreting myokines and osteokines, respectively. With a deeper understanding of the muscle-bone crosstalk, these endocrine signals exhibit an important role in osteosarcopenia development and fracture healing.

Methods

This review summarizes the role of myokines and osteokines in the development and treatment of osteosarcopenia and fracture, and discusses their potential for osteosarcopenia-related fracture treatment.

Results

Several well-defined myokines (myostatin and irisin) and osteokines (RANKL and SOST) are found to not only regulate skeletal muscle and bone metabolism but also influence fracture healing processes. Systemic interventions targeting these biochemical signals has shown promising results in improving the mass and functions of skeletal muscle and bone, as well as accelerating fracture healing processes.

Conclusion

The regulation of muscle-bone crosstalk via biochemical signals presents a novel and promising strategy for treating osteosarcopenia and fracture by simultaneously enhancing bone and muscle anabolism. We propose that myostatin, irisin, RANKL, and SOST may serve as potential targets to treat fracture patients with osteosarcopenia.

The translational potential of this article

Osteosarcopenia is an emerging geriatric syndrome where sarcopenia and osteoporosis coexist, with high fracture risk, delayed fracture healing, and increased mortality. However, no pharmacological agent is available to treat fracture patients with osteosarcopenia. This review summarizes the role of several myokines and osteokines in the development and treatment of osteosacropenia and fracture, as well as discusses their potential as intervention targets for osteosarcopenia-related fracture, which provides a novel and promising strategy for future osteosarcopenia-related fracture treatment.

Sarcopenia and malignancies: epidemiology, clinical classification and implications

Sarcopenia is a progressive systemic skeletal muscle disorder characterized by a pathological decline in muscle strength, quantity, and quality, which frequently affects the elderly population. The majority of cancer patients are of advanced age. Patients may already have sarcopenia prior to cancer development, and those with cancer are prone to developing sarcopenia due to hypercatabolism, inflammation, reduced physical fitness, anorexia, adverse effects, and stress associated with anticancer therapy. Based on the timing, sarcopenia in patients with cancer can be categorized into three: pre-existing sarcopenia before the onset of cancer, sarcopenia related to cancer, and sarcopenia related to cancer treatment. Sarcopenia not only changes the body composition of patients with cancer but also increases the incidence of postoperative complications, reduces therapeutic efficacy, impairs quality of life, and results in shortened survival. Different therapeutic strategies are required to match the cancer status and physical condition of patients with different etiologies and stages of sarcopenia. Here, we present a comprehensive review of the epidemiology and diagnosis of sarcopenia in patients with cancer, elucidate the complex interactions between cancer and sarcopenia, and provide evidence-based strategies for sarcopenia management in these patients.

Evaluation of Associations of Growth Differentiation Factor-11, Growth Differentiation Factor-8, and Their Binding Proteins, Follistatin and Follistatin-Like Protein-3, With Measures of Skeletal Muscle Mass, Muscle Strength, and Physical Function in Older Adults

BACKGROUND

Based on studies from animal models, growth differentiation factor-11 (GDF-11) may have rejuvenating effects in humans. GDF-11 has high sequence homology with GDF-8 (also known as myostatin); follistatin and follistatin-like protein-3 (FSTL-3) are inhibitory proteins of both GDF-8 and GDF-11.

METHODS

Using highly specific liquid chromatography with tandem mass spectrometry assays for GDF-11 and GDF-8 and immunoassays for follistatin and FSTL-3, we quantified the association of these factors with muscle size, strength, and physical performance in 2 prospective cohort studies of community-dwelling older adults (Health, Aging, and Body Composition study [Health ABC] and Cardiovascular Health Study [CHS]).

RESULTS

GDF-8 levels were positively associated with thigh muscle cross-sectional area and density in Health ABC (data not available in CHS). GDF-8 levels were positively associated with lean mass (a surrogate of muscle mass) in Health ABC but not CHS, and grip strength in CHS but not Health ABC. FSTL-3 (and perhaps follistatin) was negatively associated with lean mass and had variable associations with other variables. In contrast, GDF-11 was not significantly associated with strength or performance.

CONCLUSIONS

GDF-8 and its binding proteins, follistatin and FSTL-3, may constitute a counterregulatory system (chalones) to restrain age-related loss of muscle mass and strength.

Relationships of GDF8 and 11 and Their Antagonists With Decline of Grip Strength Among Older Adults in the Baltimore Longitudinal Study of Aging

Although growth/differentiation factor 11 (GDF11), growth/differentiation factor 8 (GDF8), and their circulating antagonists, which include GDF11 and GDF8 propeptides, follistatin (FST), WAP, Follistatin/Kazal, Immunoglobulin, Kunitz And Netrin Domain Containing (WFIKKN)1, and WFIKKN2, have been shown to influence skeletal muscle and aging in mice, the relationship of these circulating factors with human phenotypes is less clear. This study aimed to characterize the relationship between plasma GDF8, GDF11, FST, WFIKKN1, and WFIKKN2 concentrations with the decline of grip strength in 534 adults, ≥65 years, who participated in the Baltimore Longitudinal Study of Aging and had grip strength measured over time. Plasma GDF8 and GDF11 mature proteins, GDF8 and GDF11 propeptides, FST (isoform FST315 and cleaved form FST303), WFIKKN1, and WFIKKN2 concentrations were measured using selected reaction monitoring-tandem mass spectrometry at baseline. Grip strength was measured at baseline and at follow-up visits (median follow-up 8.87 years). Mean (standard deviation) grip strength declined in men and women by -0.84 (2.45) and -0.60 (1.32) kg/year, respectively. Plasma GDF8 and GDF11 mature proteins, GDF8 and GDF11 propeptides, FST315, FST303, WFIKKN1, and WFIKKN2 concentrations were not independently predictive of the decline of grip strength in men or women in multivariable linear regression analyses that adjusted for potential confounders. In conclusion, circulating GDF8, GDF11, and their antagonists do not appear to influence the decline of grip strength in older men or women.

Adjuvant pharmacological strategies for the musculoskeletal system during long-term space missions

Despite 2 h of daily exercise training, muscle wasting and bone loss are still present after 6-month missions to the international space station. Some crew members lose bone much faster than others. In preparation for missions to the Moon and Mars, space agencies are therefore reviewing their countermeasure portfolios. Here, we discuss the potential of current pharmacological strategies. Bone loss in space is fuelled by bone resorption. Alendronate, an oral bisphosphonate, reduced bone losses in experimental bed rest and space. However, gastrointestinal side effects precluded its further utilization in space. Zoledronate (a potent bisphosphonate), denosumab (RANKL antagonist) and romosozumab (sclerostin antagonist) are all administered via injection. They effectively suppress bone resorption and are routinely prescribed against osteoporosis. Their serious adverse effects, namely, osteonecrosis of the jaw and atypical femur fractures occur very rarely when the usage is limited to 1 or 2 years. Hence, utilization of one of these compounds may outweigh the bone risks of space travelling, in particular in those with high bone resorption rates. Muscle wasting in space is likely due to hampered muscle protein synthesis. Even though this might theoretically be countered by the synthesis-boosting effects of anabolic steroids, the practical grounds for such recommendation are currently weak. Moreover, they reveal their full potential only when combined with an anabolic exercise stimulus, for example, via strength training. It therefore seems that a combination of exercise and pharmacological countermeasures should be considered for musculoskeletal health on the way to the Moon and Mars and back.

Role of nutrition in patients with coexisting chronic obstructive pulmonary disease and sarcopenia

Chronic obstructive pulmonary disease (COPD) is one of the most common chronic diseases in the elderly population and is characterized by persistent respiratory symptoms and airflow obstruction. During COPD progression, a variety of pulmonary and extrapulmonary complications develop, with sarcopenia being one of the most common extrapulmonary complications. Factors that contribute to the pathogenesis of coexisting COPD and sarcopenia include systemic inflammation, hypoxia, hypercapnia, oxidative stress, protein metabolic imbalance, and myocyte mitochondrial dysfunction. These factors, individually or in concert, affect muscle function, resulting in decreased muscle mass and strength. The occurrence of sarcopenia severely affects the quality of life of patients with COPD, resulting in increased readmission rates, longer hospital admission, and higher mortality. In recent years, studies have found that oral supplementation with protein, micronutrients, fat, or a combination of nutritional supplements can improve the muscle strength and physical performance of these patients; some studies have also elucidated the possible underlying mechanisms. This review aimed to elucidate the role of nutrition among patients with coexisting COPD and sarcopenia.

GDF8 Contributes to Liver Fibrogenesis and Concomitant Skeletal Muscle Wasting

Patients with end-stage liver disease exhibit progressive skeletal muscle atrophy, highlighting a negative crosstalk between the injured liver and muscle. Our study was to determine whether TGFβ ligands function as the mediators. Acute or chronic liver injury was induced by a single or repeated administration of carbon tetrachloride. Skeletal muscle injury and repair was induced by intramuscular injection of cardiotoxin. Activin type IIB receptor (ActRIIB) ligands and growth differentiation factor 8 (Gdf8) were neutralized with ActRIIB-Fc fusion protein and a Gdf8-specific antibody, respectively. We found that acute hepatic injury induced rapid and adverse responses in muscle, which was blunted by neutralizing ActRIIB ligands. Chronic liver injury caused muscle atrophy and repair defects, which were prevented or reversed by inactivating ActRIIB ligands. Furthermore, we found that pericentral hepatocytes produce excessive Gdf8 in injured mouse liver and cirrhotic human liver. Specific inactivation of Gdf8 prevented liver injury-induced muscle atrophy, similar to neutralization of ActRIIB ligands. Inhibition of Gdf8 also reversed muscle atrophy in a treatment paradigm following chronic liver injury. Direct injection of exogenous Gdf8 protein into muscle along with acute focal muscle injury recapitulated similar dysregulated muscle regeneration as that observed with liver injury. The results indicate that injured liver negatively communicate with the muscle largely via Gdf8. Unexpectedly, inactivation of Gdf8 simultaneously ameliorated liver fibrosis in mice following chronic liver injury. In vitro, Gdf8 induced human hepatic stellate (LX-2) cells to form a septa-like structure and stimulated expression of profibrotic factors. Our findings identified Gdf8 as a novel hepatomyokine contributing to injured liver-muscle negative crosstalk along with liver injury progression.

Lean nonalcoholic fatty liver disease and sarcopenia

Nonalcoholic fatty liver disease (NAFLD) has become one of the most common chronic liver diseases in the world. The risk factor for NAFLD is often considered to be obesity, but it can also occur in people with lean type, which is defined as lean NAFLD. Lean NAFLD is commonly associated with sarcopenia, a progressive loss of muscle quantity and quality. The pathological features of lean NAFLD such as visceral obesity, insulin resistance, and metabolic inflammation are inducers of sarcopenia, whereas loss of muscle mass and function further exacerbates ectopic fat accumulation and lean NAFLD. Therefore, we discussed the association of sarcopenia and lean NAFLD, summarized the underlying pathological mechanisms, and proposed potential strategies to reduce the risks of lean NAFLD and sarcopenia in this review.

Challenges and Future Prospects of Targeting Myostatin/Activin A Signaling to Treat Diseases of Muscle Loss and Metabolic Dysfunction

Over the past 25 years, considerable progress has been made in terms of elucidating the regulatory and signaling mechanisms underlying the control of skeletal muscle mass by myostatin and other secreted proteins belonging to the transforming growth factor-β superfamily. Preclinical studies demonstrating the potential benefits of targeting the activities of these ligands have fueled the development of numerous biologics capable of perturbing this signaling pathway and increasing muscle mass and function. These biologics have been tested in numerous clinical trials for a wide range of indications characterized by muscle loss and excess adiposity. Here, we review the results of these trials and discuss some of the challenges and future prospects for targeting this signaling pathway to treat muscle and metabolic diseases. Myostatin inhibitors may improve metabolic outcomes by increasing muscle mass, and metabolic disorders may be attractive potential indications for these molecules.

A Phase 1 study for safety and pharmacokinetics of BIO101 (20-hydroxyecdysone) in healthy young and older adults

BACKGROUND

Sarcopenia is an age-related skeletal muscle disorder characterized by loss of muscle mass and strength leading to mobility disability. 20-Hydroxyecdysone (20E) is a polyhydroxylated plant steroid that demonstrates pharmacological effects in many disease animal models including ageing/sarcopenia. BIO101 is a 20E purified investigational drug (≥97%) that previously demonstrated good toxicology profiles in rat and dog. BIO101 is evaluated in healthy young and older adults in a Phase 1 study.

METHODS

This study is a Single Ascending Dose (SAD) followed by a 14-day Multiple Ascending Dose (MAD). In SAD, BIO101 was administered orally to 16 young adults at doses from 100 to 1400 mg and to 8 older adults (age ≥65 years) at 1400 mg. In MAD, doses of 350 mg once daily (qd), 350 mg twice daily (bid) and 450 mg bid were administered to 10 older adults. The primary objective was to evaluate safety and pharmacokinetics (PK), including dosing of circulating metabolites. Pharmacodynamic effects were investigated with regard to myostatin, procollagen-III-amino-terminal propeptide (PIIINP), myoglobin, creatine-kinase Muscle Brain (CKMB), renin and aldosterone plasma/serum levels.

RESULTS

BIO101 showed a good safety profile with only mild to moderate adverse events and a satisfactory pharmacokinetic profile. In SAD, at 100 mg to 1400 mg, mean Cmax and areas under the curve increased less than dose-proportionally. Mean half-life was short (2.4-4.9 h), and mean renal clearance was comparable in all doses (4.05-5.05 L/h). Mean plasma exposure was slightly lower in older adults (22% lower for Cmax and 13%-15% lower for AUCs) compared with young subjects. In MAD, 350 and 450 mg bid led to a slight accumulation over 14 days (mean ratio of accumulation [Rac] of 1.31 in both cohorts). Reduction of biomarkers (myoglobin, CK-MB) mean serum levels (vs. baseline) was observed at 450 mg bid. Two major metabolites of 20E (14-deoxy-20-hydroxyecdysone and 14-deoxypoststerone) were identified and quantified.

CONCLUSIONS

BIO101 shows a good safety and pharmacokinetic profile that led to the selection of doses for the subsequent interventional clinical trials of Phase 2 in age-related sarcopenia (SARA-INT) and Phase 3 in Covid-19 (COVA).

Postprandial secretion of follistatin after gastric bypass surgery and sleeve gastrectomy

Follistatin is secreted from the liver and may regulate muscle growth and insulin sensitivity. Protein intake stimulates follistatin secretion, which may be mediated by increased glucagon in the context of low insulin concentrations. We investigated circulating follistatin after mixed-meals in two cohorts of patients who were part of previously published studies and had undergone bariatric surgery with either simultaneous assessment of amino acid absorption or administration of the GLP-1 receptor antagonist exendin-(9-39), which increased glucagon concentrations and impaired insulin secretion. Study 1 comprised obese matched subjects with previous Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery and unoperated controls who underwent 6-hour mixed-meal tests with intravenous and oral tracers including intrinsically labelled caseinate in the meal. Study 2 comprised obese subjects with previous RYGB who underwent two 5-hour mixed-meal tests with concomitant exendin-(9-39) or saline infusion. In study 1, the secretion of follistatin as well as the amino acid absorption was accelerated after RYGB compared with SG and controls, but the glucagon-to-C-peptide ratios did not differ between the groups. In study 2, exendin-(9-39) administration increased postprandial glucagon concentrations and lowered insulin secretion, whereas the concentration of follistatin was unchanged. In conclusion, postprandial follistatin secretion is accelerated in patients after RYGB which might be explained by an accelerated protein absorption rate rather than the glucagon-to-insulin ratio.

Pharmaceutical treatment of bone loss: From animal models and drug development to future treatment strategies

Animal models are fundamental to advance our knowledge of the underlying pathophysiology of bone loss and to study pharmaceutical countermeasures against it. The animal model of post-menopausal osteoporosis from ovariectomy is the most widely used preclinical approach to study skeletal deterioration. However, several other animal models exist, each with unique characteristics such as bone loss from disuse, lactation, glucocorticoid excess, or exposure to hypobaric hypoxia. The present review aimed to provide a comprehensive overview of these animal models to emphasize the importance and significance of investigating bone loss and pharmaceutical countermeasures from perspectives other than post-menopausal osteoporosis only. Hence, the pathophysiology and underlying cellular mechanisms involved in the various types of bone loss are different, and this might influence which prevention and treatment strategies are the most effective. In addition, the review sought to map the current landscape of pharmaceutical countermeasures against osteoporosis with an emphasis on how drug development has changed from being driven by clinical observations and enhancement or repurposing of existing drugs to today's use of targeted anti-bodies that are the result of advanced insights into the underlying molecular mechanisms of bone formation and resorption. Moreover, new treatment combinations or repurposing opportunities of already approved drugs with a focus on dabigatran, parathyroid hormone and abaloparatide, growth hormone, inhibitors of the activin signaling pathway, acetazolamide, zoledronate, and romosozumab are discussed. Despite the considerable progress in drug development, there is still a clear need to improve treatment strategies and develop new pharmaceuticals against various types of osteoporosis. The review also highlights that new treatment indications should be explored using multiple animal models of bone loss in order to ensure a broad representation of different types of skeletal deterioration instead of mainly focusing on primary osteoporosis from post-menopausal estrogen deficiency.

The elusive role of myostatin signaling for muscle regeneration and maintenance of muscle and bone homeostasis

Skeletal muscle is one of the leading frameworks of the musculo-skeletal system, which works in synergy with the bones. Long skeletal muscles provide stability and mobility to the human body and are primarily composed of proteins. Conversely, improper functioning of various skeletal muscles leads to diseases and disorders, namely, age-related muscle disorder called sarcopenia, a group of genetic muscle disorders such as muscular dystrophies, and severe muscle wasting in cancer known as cachexia. However, skeletal muscle has an excellent ability to undergo hypertrophy and enhanced functioning during sustained exercise over time. Indeed, these processes of skeletal muscle regeneration/hypertrophy, as well as degeneration and atrophy, involve an interplay of various signaling pathways. Myostatin is one such chemokine/myokine with a significant contribution to muscle regeneration or atrophy in multiple conditions. In this review, we try to put together the role and regulation of myostatin as a function of muscle regeneration extrapolated to multiple aspects of its molecular functions.

Sarcopenia as a Determinant of the Efficacy of Immune Checkpoint Inhibitors in Non-Small Cell Lung Cancer: A Meta-Analysis

OBJECTIVE

The impact of pre-immunotherapy sarcopenia in patients with non-small cell lung cancer (NSCLC) receiving immune checkpoint inhibitors (ICIs) is elusive. We performed a meta-analysis to investigate the association between sarcopenia and clinical outcomes of ICIs.

METHODS

PubMed, EMBASE, and the Cochrane Library were searched.

RESULTS

Thirteen clinical trials were selected. The 1,2-year overall survival rate was lower in the sarcopenia group (odds ratio (OR) = 2.44, 95% confidence interval (CI), 1.78-3.35, P < 0.00001; OR = 1.60, 95% CI, 1.08-2.37, P = 0.02), with I² = 34%, P = 0.15, and I² = 41%, P = 0.12. The 1,2-year progression-free survival (PFS) was the same (OR = 3.43, 95% CI, 1.86-6.33, P < 0.0001; OR = 2.06, 95% CI, 1.19-3.58, P < 0.0001), with I² = 31%, P = 0.17 and I²=31%, P = 0.17. Sarcopenia reduced the overall response rate (OR = 2.22, 95% CI, 1.01-4.84, P = 0.02), with I²= 56%, P = 0.02, and disease control rate (OR = 3.15, 95% CI, 2.10-4.72, P < 0.0001) with I² = 33%, P = 0.18.

CONCLUSION

Pre-immunotherapy sarcopenia was associated with poor clinical outcomes in patients with advanced NSCLC who received ICIs.

Proteome network analysis of skeletal muscle in lignan-enriched nutmeg extract-fed aged mice

Sarcopenia, characterized by reduced muscle mass and fiber number leading to muscular atrophy, has been associated with serious socioeconomic challenges among the elderly in developed countries. Therefore, preventing sarcopenia could be a promising strategy for achieving a healthy aging society. Nutmeg (Myristica fragrans) has been used as a spice to increase flavor and prevent putrefaction of food. Nutmeg contains various bioactive components that improve muscle activity. To determine the potential effect of lignan-enriched nutmeg extract (LNX) on sarcopenia, LNX (100 mg/kg body weight)-fed aged mice were subjected to forced exercise. Herein, aged (22-month-old) mice fed LNX for three weeks exhibited a shortened and thickened soleus muscle. The ratio of the soleus muscle mass (%) to body weight was significantly increased in LNX-fed aged mice. The relative increase in muscle mass in LNX-fed aged mice improved exercise activities, including rotarod, swimming, and grip strength test results. Proteome profiles of the soleus muscle of LNX-fed mice were used to analyze protein–protein interaction network. Several myosin heavy chain isoforms were found to interact with actin, ACTA1, which functions as a hub protein. Furthermore, the expression of myogenic proteins, such as MYH1, MYH4, and ACTA1, was dose-dependently increased in vivo. In result, our functional proteomic analysis revealed that feeding LNX restored muscle proteins in aged mice.

Myostatin: A Skeletal Muscle Chalone

Myostatin (GDF-8) was discovered 25 years ago as a new transforming growth factor-β family member that acts as a master regulator of skeletal muscle mass. Myostatin is made by skeletal myofibers, circulates in the blood, and acts back on myofibers to limit growth. Myostatin appears to have all of the salient properties of a chalone, which is a term proposed over a half century ago to describe hypothetical circulating, tissue-specific growth inhibitors that control tissue size. The elucidation of the molecular, cellular, and physiological mechanisms underlying myostatin activity suggests that myostatin functions as a negative feedback regulator of muscle mass and raises the question as to whether this type of chalone mechanism is unique to skeletal muscle or whether it also operates in other tissues.

Comparison of surgical complications after curative surgery in patients with oral cavity squamous cell carcinoma and sarcopenia

BACKGROUND

The study aims to clarify the association of sarcopenia with perioperative and postoperative complications in oral cavity squamous cell carcinoma (OCSCC) patients undergoing curative surgery and to understand the reasons causing the poor oncologic outcomes for OCSCC.

METHODS

We conducted a propensity score matching study to investigate the association of perioperative and postoperative outcomes in OCSCC patients with sarcopenia and without sarcopenia. A retrospective analysis of a large national data set from the Taiwan Cancer Registry Database was conducted. At least two claims for patients with a principal diagnosis of sarcopenia within the 12-month preoperative period were defined as the criteria for sarcopenia diagnosis (ICD-10-CM code M62.84). Sarcopenia was diagnosed through the measurement of low muscle strength and low muscle mass by any one of the patient's attending orthopaedic physician, rehabilitation physician, family medicine specialist or geriatrician. A multivariate logistic regression model was used to calculate the perioperative, and postoperative major complications.

RESULTS

Our final cohort included 16 293 patients with OCSCC (10 862 and 5 431 in the sarcopenia and nonsarcopenia groups, respectively) who were eligible for further analysis. The sarcopenia group was 10.40% female and 89.60% male, and the nonsarcopenia group was 9.74% female and 90.26% male. The mean age ± standard deviation (SD) were 56.44 ± 11.14 and 56.22 ± 11.29 for sarcopenia and nonsarcopenia groups. OCSCC patients with sarcopenia undergoing curative surgery had a significantly higher blood transfusion rate and volume; longer intensive care unit (ICU) stay, and hospital stay; higher postoperative 30-day mortality (adjusted odds ratio [aOR]: 1.12, 95% confidence interval [CI] [1.07, 1.56]) and rates of pneumonia (aOR: 1.34, 95% CI [1.20, 1.50]), acute renal failure (aOR: 1.45, 95% CI [1.12, 1.87]) and septicaemia (aOR: 1.29, 95% CI [1.15, 1.45]); higher postoperative first-year mortality (aOR: 1.18, 95% CI [1.13, 1.51]) and rates of pneumonia (aOR: 1.43, 95% CI [1.30, 1.56]), acute myocardial infarction (aOR: 1.52, 95% CI [1.06, 2.18]) and septicaemia (aOR: 1.29, 95% CI [1.15, 1.45]).

CONCLUSIONS

OCSCC patients with sarcopenia might exhibit more perioperative and surgical complications than those without sarcopenia.

Age-Related Dysfunction in Proteostasis and Cellular Quality Control in the Development of Sarcopenia

Sarcopenia is a debilitating skeletal muscle disease that accelerates in the last decades of life and is characterized by marked deficits in muscle strength, mass, quality, and metabolic health. The multifactorial causes of sarcopenia have proven difficult to treat and involve a complex interplay between environmental factors and intrinsic age-associated changes. It is generally accepted that sarcopenia results in a progressive loss of skeletal muscle function that exceeds the loss of mass, indicating that while loss of muscle mass is important, loss of muscle quality is the primary defect with advanced age. Furthermore, preclinical models have suggested that aged skeletal muscle exhibits defects in cellular quality control such as the degradation of damaged mitochondria. Recent evidence suggests that a dysregulation of proteostasis, an important regulator of cellular quality control, is a significant contributor to the aging-associated declines in muscle quality, function, and mass. Although skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) plays a critical role in cellular control, including skeletal muscle hypertrophy, paradoxically, sustained activation of mTORC1 recapitulates several characteristics of sarcopenia. Pharmaceutical inhibition of mTORC1 as well as caloric restriction significantly improves muscle quality in aged animals, however, the mechanisms controlling cellular proteostasis are not fully known. This information is important for developing effective therapeutic strategies that mitigate or prevent sarcopenia and associated disability. This review identifies recent and historical understanding of the molecular mechanisms of proteostasis driving age-associated muscle loss and suggests potential therapeutic interventions to slow or prevent sarcopenia.

Crosstalk between bone and muscle in chronic kidney disease

With increasing life expectancy, the related disorders of bone loss, metabolic dysregulation and sarcopenia have become major health threats to the elderly. Each of these conditions is prevalent in patients with chronic kidney disease (CKD), particularly in more advanced stages. Our current understanding of the bone-muscle interaction is beyond mechanical coupling, where bone and muscle have been identified as interrelated secretory organs, and regulation of both bone and muscle metabolism occurs through osteokines and myokines via autocrine, paracrine and endocrine systems. This review appraises the current knowledge regarding biochemical crosstalk between bone and muscle, and considers recent progress related to the role of osteokines and myokines in CKD, including modulatory effects of physical exercise and potential therapeutic targets to improve musculoskeletal health in CKD patients.

Pharmacokinetics and Pharmacodynamics of Bimagrumab (BYM338)

BACKGROUND

Bimagrumab is a human monoclonal antibody binding to the activin type II receptor with therapeutic potential in conditions of muscle wasting and obesity. This phase I study evaluated the pharmacokinetics (PK), pharmacodynamics (PD), and safety of various dose regimens of bimagrumab and routes of administration in healthy older adults.

METHODS

This was a randomized, double-blind, placebo-controlled, parallel-arm, multiple-dose study in older adult men and women (aged ≥ 70 years, body mass index [BMI] 18-34 kg/m²) with stable health and diet. The study comprised seven treatment groups (Cohorts 1-7). Participants received bimagrumab or placebo treatment every 4 weeks for three doses (Cohorts 1 [700 mg] and 2 [210 mg] intravenous infusion; Cohorts 3 [1500 mg] and 4 [525 mg] subcutaneous infusion), or every week for 12 doses (Cohorts 5 [300 mg], 6 [150 mg], and 7 [52.5 mg] subcutaneous bolus injection) and were followed up until week 20. Blood samples were collected for bimagrumab PK analysis. PD were assessed by dual energy X-ray absorptiometry to quantify the change from baseline in lean body mass (LBM) and fat body mass (FBM) compared with placebo. Safety was assessed throughout the study.

RESULTS

Eighty-four of 91 (92.3%) randomized participants (mean age 74.5 years; BMI 28.0 kg/m²) completed the study. Demographic characteristics were generally balanced across the groups. A target-mediated drug disposition profile was observed following both intravenous and subcutaneous administration. The absolute subcutaneous bioavailability was estimated at approximately 40%. LBM increased by 4-6% (1.5-2 kg) from baseline throughout the treatment period for intravenous and subcutaneous regimens, except for the 52.5 mg subcutaneous dose, which did not differ from placebo. Concurrently, there was a decrease in FBM (approximately 2-3 kg) for all intravenous and subcutaneous regimens. Bimagrumab was generally safe and well tolerated; adverse events were mostly mild to moderate in severity.

CONCLUSIONS

Dose levels of bimagrumab administered weekly subcutaneously resulted in PK profiles and PD effects comparable with monthly intravenous dosing, which supports the feasibility of the subcutaneous route of administration for bimagrumab for future clinical development.

Acetyl-L-carnitine Slows the Progression from Prefrailty to Frailty in Older Subjects: A Randomized Interventional Clinical Trial

BACKGROUND

Ageing is characterized by a gradual decline in body function, representing the clinical situation called "frailty". Prefrailty is the intermediate stage between frailty and robust condition. L-carnitine (LC) plays an important role in energy production from long-chain fatty acids in mitochondria, and its serum level is lower in prefrail and frail subjects.

OBJECTIVE

This study aims to evaluate the effect of Acetyl-L-carnitine (ALCAR) in pre-frail older patients.

METHODS

We scheduled 3 months of treatment and then 3 months of follow-up. A total of 92 subjects were selected from May, 2009 to July, 2017, in a randomized, observational, double-blind, placebo-controlled study. We scheduled 3 months of treatment and then 3 months of follow-up. ALCAR (oral 1.5 g/bis in die - BID) or placebo groups were used.

RESULTS

After the treatment, only the treated group displayed a decrease in C reactive protein (CRP) p < 0.001 and an increase in serum-free carnitine and acetylcarnitine (p < 0.05) in Mini-Mental state (MMSE) p < 0.0001 and 6-walking distance (p < 0.0001); ALCAR group vs. placebo group showed a decrease in HDL cholesterol and CRP (p < 0.01), an increase in MMSE score (p < 0.001) and in the 6-walking distance (p < 0.001).

CONCLUSIONS

ALCAR treatment delays the incidence and severity of onset of degenerative disorders of the elderly in prefrail subjects with improvement in memory and cognitive processes.

Functional capacity, sarcopenia, and bone health

Bone and muscle are recognised as interacting tissues, the so-called 'muscle-bone unit', in which these two tissues communicate to coordinate their development (chemically and metabolically), as well as their response to loading or injury. Musculoskeletal disorders of ageing, specifically osteoporosis and sarcopenia, are highly prevalent in older individuals. They signify a significant burden for older people affecting their mobility, confidence, and quality of life, as well as being a major cost to healthcare systems worldwide. This review considers the coexistence of osteoporosis and sarcopenia in individuals and describes risk factors, clinical consequences, approaches to management, and the link with functional capacity.

Pathogenesis of sarcopenia in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common pulmonary disease characterized by persistent respiratory symptoms and airflow obstruction. In addition to lung diseases, chronic obstructive pulmonary disease (COPD) is often associated with other organ diseases, and sarcopenia is one of the common diseases. In recent years, multiple factors have been proposed to influence muscle dysfunction in COPD patients, including systemic and local inflammation, oxidative stress, hypoxia, hypercapnia, protein synthesis, catabolic imbalance, nutritional changes, disuse, ageing, and the use of medications such as steroids. These factors alone or in combination can lead to a reduction in muscle mass and cross-sectional area, deterioration of muscle bioenergy metabolism, defects in muscle repair and regeneration mechanisms, apoptosis and other anatomical and/or functional pathological changes, resulting in a decrease in the muscle’s ability to work. This article reviews the research progress of possible pathogenesis of sarcopenia in COPD.

Inhibition of myostatin and related signaling pathways for the treatment of muscle atrophy in motor neuron diseases

Myostatin is a negative regulator of skeletal muscle growth secreted by skeletal myocytes. In the past years, myostatin inhibition sparked interest among the scientific community for its potential to enhance muscle growth and to reduce, or even prevent, muscle atrophy. These characteristics make it a promising target for the treatment of muscle atrophy in motor neuron diseases, namely, amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), which are rare neurological diseases, whereby the degeneration of motor neurons leads to progressive muscle loss and paralysis. These diseases carry a huge burden of morbidity and mortality but, despite this unfavorable scenario, several therapeutic advancements have been made in the past years. Indeed, a number of different curative therapies for SMA have been approved, leading to a revolution in the life expectancy and outcomes of SMA patients. Similarly, tofersen, an antisense oligonucleotide, is now undergoing clinical trial phase for use in ALS patients carrying the SOD1 mutation. However, these therapies are not able to completely halt or reverse progression of muscle damage. Recently, a trial evaluating apitegromab, a myostatin inhibitor, in SMA patients was started, following positive results from preclinical studies. In this context, myostatin inhibition could represent a useful strategy to tackle motor symptoms in these patients. The aim of this review is to describe the myostatin pathway and its role in motor neuron diseases, and to summarize and critically discuss preclinical and clinical studies of myostatin inhibitors in SMA and ALS. Then, we will highlight promises and pitfalls related to the use of myostatin inhibitors in the human setting, to aid the scientific community in the development of future clinical trials.

Development of ovarian tumour causes significant loss of muscle and adipose tissue: a novel mouse model for cancer cachexia study

BACKGROUND

Cancer-associated cachexia (CAC) is a complex syndrome of progressive muscle wasting and adipose loss with metabolic dysfunction, severely increasing the morbidity and mortality risk in cancer patients. However, there are limited studies focused on the underlying mechanisms of the progression of CAC due to the complexity of this syndrome and the lack of preclinical models that mimics its stagewise progression.

METHODS

We characterized the initiation and progression of CAC in transgenic female mice with ovarian tumours. We measured proposed CAC biomarkers (activin A, GDF15, IL-6, IL-1β, and TNF-α) in sera (n = 6) of this mouse model. The changes of activin A and GDF15 (n = 6) were correlated with the decline of bodyweight over time. Morphometry and signalling markers of muscle atrophy (n ≥ 6) and adipose tissue wasting (n ≥ 7) were assessed during CAC progression.

RESULTS

Cancer-associated cachexia symptoms of the transgenic mice model used in this study mimic the progression of CAC seen in humans, including drastic body weight loss, skeletal muscle atrophy, and adipose tissue wasting. Serum levels of two cachexia biomarkers, activin A and GDF15, increased significantly during cachexia progression (76-folds and 10-folds, respectively). Overactivation of proteolytic activity was detected in skeletal muscle through up-regulating muscle-specific E3 ligases Atrogin-1 and Murf-1 (16-folds and 14-folds, respectively) with decreasing cross-sectional area of muscle fibres (P < 0.001). Muscle wasting mechanisms related with p-p38 MAPK, FOXO3, and p-AMPKα were highly activated in concurrence with an elevation in serum activin A. Dramatic fat loss was also observed in this mouse model with decreased fat mass (n ≥ 6) and white adipocytes sizes (n = 6) (P < 0.0001). The adipose tissue wasting was based on thermogenesis, supported by the up-regulation of uncoupling protein 1 (UCP1). Fibrosis in adipose tissue was also observed in concurrence with adipose tissue loss (n ≥ 13) (p < 0.0001).

CONCLUSIONS

Our novel preclinical CAC mouse model mimics human CAC phenotypes and serum biomarkers. The mouse model in this study showed proteolysis in muscle atrophy, browning in adipose tissue wasting, elevation of serum activin A and GDF15, and atrophy of pancreas and liver. This mouse line would be the best preclinical model to aid in clarifying molecular mediators of CAC and dissecting metabolic dysfunction and tissue atrophy during the progression of CAC.

A pas de deux of osteoporosis and sarcopenia: osteosarcopenia

The musculoskeletal conditions osteoporosis and sarcopenia are highly prevalent in older adults. Osteoporosis is characterized by low bone mass and microarchitectural deterioration of bone, whereas sarcopenia is identified by the loss of muscle strength, function and mass. Osteoporosis represents a major health problem contributing to millions of fractures worldwide on an annual basis, whereas sarcopenia is associated with a range of adverse physical and metabolic outcomes. They both affect physical and social function, confidence and quality of life as well as contributing to high health-care costs worldwide. Osteosarcopenia is the term given when both conditions occur concomitantly and it has been suggested that interactions between these two conditions may accelerate individual disease progression as co-existence of osteoporosis and sarcopenia is associated with higher morbidity from falls, fracture, disability as well as mortality. In this review, we will outline the epidemiology, pathogenesis and clinical consequences of osteosarcopenia and discuss available management strategies.

Factors mediating exercise-induced organ crosstalk

Exercise activates a plethora of metabolic and signalling pathways in skeletal muscle and other organs causing numerous systemic beneficial metabolic effects. Thus, regular exercise may ameliorate and prevent the development of several chronic metabolic diseases. Skeletal muscle is recognized as an important endocrine organ regulating systemic adaptations to exercise. Skeletal muscle may mediate crosstalk with other organs through the release of exercise-induced cytokines, peptides and proteins, termed myokines, into the circulation. Importantly, other tissues such as the liver and adipose tissue may also release cytokines and peptides in response to exercise. Hence, exercise-released molecules are collectively called exerkines. Moreover, extracellular vesicles (EVs), in the form of exosomes or microvesicles, may carry some of the signals involved in tissue crosstalk. This review focuses on the role of factors potentially mediating crosstalk between muscle and other tissues in response to exercise.

The Correlation of Serum Myostatin Levels with Gait Speed in Kidney Transplantation Recipients

The primary role of myostatin is to negatively regulate skeletal muscle growth. The gait speed is a noninvasive, reliable parameter that predicts cardiovascular risk and mortality. This study evaluated the relationship between serum myostatin concentrations and gait speeds in patients who had undergone kidney transplantation (KT). A total of 84 KT recipients were evaluated. A speed of less than 1.0 m/s was categorized into the low gait speed group. We measured serum myostatin concentrations with a commercial enzyme-linked immunosorbent assay. KT recipients in the low gait speed group had significantly older age, as well as higher body weight, body mass index (BMI), skeletal muscle index, serum triglyceride levels, glucose levels, and blood urea nitrogen levels, lower estimated glomerular filtration rates and serum myostatin levels, a higher percentage of steroid use, and a lower proportion of mycophenolate mofetil use. Multivariable logistic regression analysis revealed that lower myostatin levels and lower frequency of mycophenolate mofetil use were independently associated with low gait speed. In multivariable stepwise linear regression analysis, myostatin levels were positively correlated with gait speeds, and age and BMI were negatively correlated with gait speeds. In the study, serum myostatin levels were significantly lower in the low gait speed group. Subjects in the low gait speed group also had greater BMI and older age.

Myostatin: Basic biology to clinical application

Myostatin is a member of the transforming growth factor (TGF)-β superfamily. It is expressed by animal and human skeletal muscle cells where it limits muscle growth and promotes protein breakdown. Its effects are influenced by complex mechanisms including transcriptional and epigenetic regulation and modulation by extracellular binding proteins. Due to its actions in promoting muscle atrophy and cachexia, myostatin has been investigated as a promising therapeutic target to counteract muscle mass loss in experimental models and patients affected by different muscle-wasting conditions. Moreover, growing evidence indicates that myostatin, beyond to regulate skeletal muscle growth, may have a role in many physiologic and pathologic processes, such as obesity, insulin resistance, cardiovascular and chronic kidney disease. In this chapter, we review myostatin biology, including intracellular and extracellular regulatory pathways, and the role of myostatin in modulating physiologic processes, such as muscle growth and aging. Moreover, we discuss the most relevant experimental and clinical evidence supporting the extra-muscle effects of myostatin. Finally, we consider the main strategies developed and tested to inhibit myostatin in clinical trials and discuss the limits and future perspectives of the research on myostatin.

Matrigel 3D bioprinting of contractile human skeletal muscle models recapitulating exercise and pharmacological responses

A key to enhance the low translatability of preclinical drug discovery are in vitro human three-dimensional (3D) microphysiological systems (MPS). Here, we show a new method for automated engineering of 3D human skeletal muscle models in microplates and functional compound screening to address the lack of muscle wasting disease medication. To this end, we adapted our recently described 24-well plate 3D bioprinting platform with a printhead cooling system to allow microvalve-based drop-on-demand printing of cell-laden Matrigel containing primary human muscle precursor cells. Mini skeletal muscle models develop within a week exhibiting contractile, striated myofibers aligned between two attachment posts. As an in vitro exercise model, repeated high impact stimulation of contractions for 3 h by a custom-made electrical pulse stimulation (EPS) system for 24-well plates induced interleukin-6 myokine expression and Akt hypertrophy pathway activation. Furthermore, the known muscle stimulators caffeine and Tirasemtiv acutely increase EPS-induced contractile force of the models. This validated new human muscle MPS will benefit development of drugs against muscle wasting diseases. Moreover, our Matrigel 3D bioprinting platform will allow engineering of non-self-organizing complex human 3D MPS.

Alave-Furrer et al adapted their recently-developed 3D bioprinting platform to allow microvalve-based drop-on-demand printing of cell-laden Matrigel containing primary human muscle precursor cells. Their bioprinting platform recapitulated aspects of exercise and pharmacological responses and thus could aid the engineering of more complex 3D microphysiological systems.

Sarcopenia and Frailty: Challenges in Mainstream Nephrology Practice

Sarcopenia and frailty are prevalent in the chronic kidney disease (CKD) population. Sarcopenia is characterised by the loss of muscle mass and function, while frailty is defined as a multi-system impairment associated with increased vulnerability to stressors. There is substantial overlap between the 2 conditions, particularly with regards to physical aspects: low grip strength, gait speed and low muscle mass. Both sarcopenia and frailty have been associated with a wide range of adverse health outcomes. Although there is no recommended pharmacological treatment as yet, it is widely accepted that exercise training and nutritional supplementation are the key interventions to maintain skeletal muscle mass and strength. This review aims to present a comprehensive overview of sarcopenia and frailty in patients with CKD.

Advances in research on pharmacotherapy of sarcopenia

Sarcopenia is a comprehensive degenerative disease with the progressive loss of skeletal muscle mass with age, accompanied by the loss of muscle strength and muscle dysfunction. As a new type of senile syndrome, sarcopenia seriously threatens the health of the elderly. The first-line treatment for sarcopenia is exercise and nutritional supplements. However, pharmacotherapy will provide more reliable and sustainable interventions in geriatric medicine. Clinical trials of new drugs targeting multiple molecules are ongoing. This article focuses on the latest progress in pharmacotherapeutic approaches of sarcopenia in recent years by comprehensively reviewing the clinical outcomes of the existing and emerging pharmacotherapies as well as the molecular mechanisms underlying their therapeutic benefits and side effects.