The Biological Foundations of Sarcopenia: Established and Promising Markers

Impact of sarcopenia on variceal rebleeding in patients after endoscopic therapy: a multicenter retrospective cohort study based on propensity score matching

BACKGROUND

Sarcopenia is a common complication of liver cirrhosis and can be used for predicting dismal prognostic outcomes. This study aimed to evaluate the role of sarcopenia in rebleeding and mortality of liver cirrhosis patients after endoscopic therapy.

METHODS

The liver cirrhosis patients who received endoscopic treatment were enrolled. Propensity score matching (PSM) was used to overcome selection bias. Two-year rebleeding episodes and mortality after endoscopic therapy were recorded.

RESULTS

A total of 109 (32.4%) sarcopenia patients were reported. Before PSM, the frequency of rebleeding was significantly higher in the sarcopenia group relative to the non-sarcopenia group (41.3% vs. 15.9%, p < 0.001). Moreover, the multivariable analysis revealed that sarcopenia (p < 0.001, HR:2.596, 95% CI 1.591-4.237) was independently associated with a 2-year rebleeding episode. After PSM, the sarcopenia group exhibited an increased rebleeding rate as compared with non-sarcopenia group (44.4% vs. 15.3%, p < 0.001). According to multivariable analysis, sarcopenia (p < 0.001, HR:3.490, 95% CI 1.756-6.938) was identified as a significant predictor for 2-year rebleeding.

CONCLUSION

Sarcopenia was significantly associated with a high 2-year rebleeding rate in liver cirrhosis patients after endoscopic treatment. Therefore, the precise evaluation of a patient's nutritional status, including sarcopenia becomes mandatory before endoscopic treatment.

Postabsorptive and postprandial myofibrillar protein synthesis rates at rest and after resistance exercise in women with postmenopause

Feeding and resistance exercise stimulate myofibrillar protein synthesis (MPS) rates in healthy adults. This anabolic characterization of "healthy adults" has been namely focused on males. Therefore, the purpose of this study was to examine the temporal responses of MPS and anabolic signaling to resistance exercise alone or combined with the ingestion of protein in postmenopausal females and compare postabsorptive rates with young females. Sixteen females [60 ± 7 yr; body mass index (BMI) = 26 ± 12 kg·m-2] completed an acute bout of unilateral resistance exercise before consuming either: a fortified whey protein supplement (WHEY) or water. Participants received primed continuous infusions of L-[ring-13C6]phenylalanine with bilateral muscle biopsies before and after treatment ingestion at 2 h and 4 h in nonexercised and exercised legs. Resistance exercise transiently increased MPS above baseline at 0-2 h in the water condition (P = 0.007). Feeding after resistance exercise resulted in a late phase (2-4 h) increase in MPS in the WHEY condition (P = 0.005). In both conditions, resistance exercise did not enhance the cumulative (0-4 h) MPS response. In the nonexercised leg, MPS did not differ at 0-2 h, 2-4 h, or 0-4 h of the measurement periods (all, P > 0.05). Likewise, there were no changes in the phosphorylation of p70S6K, AMPKα, or total and phosphorylated yes-associated protein on Ser127. Finally, postabsorptive MPS was lower in premenopausal versus postmenopausal females (P = 0.023). Our results demonstrate that resistance exercise-induced changes in MPS are temporally regulated, but do not result in greater cumulative (0-4 h) MPS in postmenopausal women.NEW & NOTEWORTHY An adequate quality and quantity of skeletal muscle is relevant to support physical performance and metabolic health. Muscle protein synthesis (MPS) is an established remodeling marker, which can be hypertrophic or nonhypertrophic. Importantly, protein ingestion and resistance exercise are two strategies that support healthy muscle by stimulating MPS. Our study shows postmenopause modulates baseline MPS that may diminish the MPS response to the fundamental anabolic stimuli of protein ingestion and resistance exercise in older females.

Associations between life's essential 8 and sarcopenia in US adults: a cross-sectional analysis

Cardiovascular disease (CVD) is closely associated with sarcopenia. We aimed to examine the relationship between Life's Essential 8 (LE8) and the incidence of sarcopenia among adults in the United States. In this study, a cross-sectional analysis was conducted using data from the National Health and Nutrition Examination Survey from 2013 to 2018 and included 5999 adult participants. LE8 score was categorized into low (< 49), moderate (49-79), and high CVH (≥ 79) groups and consisted of health behavior score and health factor score based on American Heart Association definitions. Sarcopenia was defined according to The Foundation for the National Institutes of Health Sarcopenia Project. Multivariate logistic regressions, restricted cubic spline regressions, and subgroup analyses were used to assess the association between LE8 and sarcopenia. LE8 and its subscales score were negatively associated with the incidence of sarcopenia in US adults.

Epigenetic Aging Is Associated With Measures of Midlife Muscle Volume and Attenuation in CARDIA Study

BACKGROUND

GrimAge acceleration (GAA), an epigenetic marker that represents physiologic aging, is associated with age-related diseases including cancer and cardiovascular diseases. However, the associations between GAA and muscle mass and function are unknown.

METHODS

We estimated measures of GAA in 1 118 Black and White participants from the Coronary Artery Risk Development in Young Adults (CARDIA) Study at exam years (Y) 15 (2000-2001) and 20 (2005-2006). Abdominal muscle composition was measured using CT scans at the Y25 (2010-2011) visit. We used multivariate regression models to examine associations of GAA estimates with muscle imaging measurements.

RESULTS

In the CARDIA study, each 1-year higher GAA was associated with an average 1.1% (95% confidence interval [CI]: 0.6%, 1.5%) higher intermuscular adipose tissue (IMAT) volume for abdominal muscles. Each 1-year higher GAA was associated with an average -0.089 Hounsfield unit (HU; 95% CI: -0.146, -0.032) lower lean muscle attenuation and an average -0.049 HU (95% CI: -0.092, -0.007) lower IMAT attenuation for abdominal muscles. Stratified analyses showed that GAA was more strongly associated with higher abdominal muscle IMAT volume in females and significantly associated with lower lean muscle attenuation for White participants only.

CONCLUSIONS

Higher GAA is associated with higher abdominal muscle IMAT volume and lower lean muscle attenuation in a midlife population.

Complement component C3 is associated with body composition parameters and sarcopenia in community-dwelling older adults: a cross-sectional study in Japan

BACKGROUND

Chronic inflammation is a factor in the pathogenesis of sarcopenia, which is characterized by low muscle mass and reduced strength. Complement C3 is important in the management of the immune network system. This study seeks to determine the relationship between serum C3 levels and body composition and sarcopenia-related status in community-dwelling older adults.

METHODS

Study participants were 269 older adults living in rural Japan. A bioelectrical impedance analysis device was used to measure body composition parameters including body mass index (BMI), body fat percentage, waist-hip-ratio, and appendicular skeletal muscle mass index (SMI). Muscle function was measured by handgrip strength and 6-m walking speed. The correlation coefficients for C3 level and measurements were calculated using Pearson correlation analysis. Participants were categorized into normal, pre-sarcopenia, dynapenia, or sarcopenia groups. Sarcopenia was defined according to 2019 Asian Working Group for Sarcopenia definition, dynapenia was defined as low muscle function without low muscle mass, and pre-sarcopenia was defined as the presence of low muscle mass only. The C3 threshold score for sarcopenia status was evaluated by receiver operating characteristic curve (ROC) analysis.

RESULTS

Significant positive correlations were found between C3 and BMI, body fat percentage, and waist-hip ratio in both sexes, and further positive correlations with SMI were found in women. The relationship with body fat percentage was particularly strong. Body composition measurements (BMI, body fat percentage, and waist- hip ratio) and C3 levels were lowest in the sarcopenia group compared with the others. ROC analysis showed that the significant threshold of C3 for discriminating between the normal and sarcopenia groups was 105 mg/dL. Multiple logistic regression analysis showed that participants with C3 < 105 mg/dL had an odds ratio of 3.27 (95% confidence interval, 1.49-7.18) for sarcopenia adjusted by sex, age and body fat percentage.

CONCLUSION

C3 levels are suggested to be related to body composition and pathophysiological functions of sarcopenia. C3 is expected to become a useful biomarker for sarcopenia, for predicting the onset of the disease and for predicting the effectiveness of interventions.

Association Between Dietary Fiber Intake and Low Muscle Strength Among Korean Adults

The health benefits of dietary fiber are widely recognized, but its impact on muscle health remains unclear. Therefore, this study aimed to elucidate the relationship between dietary fiber intake and muscle strength through a cross-sectional analysis of data from the Korea National Health and Examination Survey (KNHANES). Data from a single 24-h dietary recall and handgrip strength tests of 10,883 younger adults aged 19 to 64 years and 3,961 older adults aged ≥ 65 years were analyzed. Low muscle strength was defined as handgrip strength < 28 kg for men and < 18 kg for women. Multivariable linear and logistic regression analyses were conducted to determine the association of dietary fiber intake with muscle strength. Approximately 43% of Korean adults met the recommended intake of dietary fiber, and those with higher dietary fiber consumption also had higher total energy and protein intake. After adjusting for confounding variables, dietary fiber intake was found to be positively associated with maximal handgrip strength in younger women aged 19 to 64 years (β = 0.015; standard error [SE] = 0.006) and older men aged ≥ 65 years (β = 0.035; SE = 0.014). For older women aged ≥ 65 years, those in the lowest quartile of dietary fiber intake had a higher risk of low muscle strength than those in the highest quartile after adjustment of confounders (odds ratio 1.709; 95% confidence interval 1.130-2.585). These results suggest that adequate dietary fiber intake may reduce the risk of sarcopenia in older Korean women.

Thyroarytenoid Oxidative Metabolism and Synaptic Signaling Dysregulation in the Female Pink1-/- Rat

OBJECTIVES AND HYPOTHESIS

Vocal dysfunction, including hypophonia, in Parkinson disease (PD) manifests in the prodromal period and significantly impacts an individual's quality of life. Data from human studies suggest that pathology leading to vocal deficits may be structurally related to the larynx and its function. The Pink1-/- rat is a translational model used to study pathogenesis in the context of early-stage mitochondrial dysfunction. The primary objective of this work was to identify differentially expressed genes in the thyroarytenoid muscle and examine the dysregulated biological pathways in the female rat.

METHODS

RNA sequencing was used to determine thyroarytenoid (TA) muscle gene expression in adult female Pink1-/- rats compared with controls. A bioinformatic approach and the ENRICHR gene analysis tool were used to compare the sequencing dataset with biological pathways and processes, disease relationships, and drug-repurposing compounds. Weighted Gene Co-expression Network Analysis was used to construct biological network modules. The data were compared with a previously published dataset in male rats.

RESULTS

Significant upregulated pathways in female Pink1-/- rats included fatty acid oxidation and muscle contraction, synaptic transmission, and neuromuscular processes. Downregulated pathways included anterograde transsynaptic signaling, chemical synaptic transmission, and ion release. Several drug treatment options including cetuximab, fluoxetine, and resveratrol are hypothesized to reverse observed genetic dysregulation.

CONCLUSIONS

Data presented here are useful for identifying biological pathways that may underlie the mechanisms of peripheral dysfunction including neuromuscular synaptic transmission to the TA muscle. These experimental biomarkers have the potential to be targeted as sites for improving the treatment for hypophonia in early-stage PD.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:3412-3421, 2023.

U-Shaped Association of Standardized Serum 25-Hydroxyvitamin D with Risk of Low Muscle Mass: A Population-Based Cross-Sectional Study

Background

In the United States (U.S.) general population, the association between standardized serum 25-hydroxyvitamin D (25(OH)D) concentration and risk of low muscle mass (LMM) remains unclear. Our research aimed to determine whether or not there was a relationship between serum 25(OH)D concentration and risk of LMM.

Methods

We analyzed the cross-sectional data of the US population that participated in the National Health and Nutrition Examination Survey between 2011 and 2014. The relationship between serum 25(OH)D concentration and LMM risk was evaluated using restricted cubic spline (RCS) with multivariate logistic regression model and subgroup analysis.

Results

In all, we included 10,256 people in our analysis. The RCS plot demonstrated a U-shaped relationship between serum 25(OH)D concentration and risk of LMM (P for nonlinearity <0.05). At a Vitamin D concentration of 38.5 nmol/L, LMM risk was at its lowest. Based on analyses stratified by age, sex, hypertension, and diabetes mellitus (DM), serum 25(OH)D concentration and risk of LMM were U-curve correlated for those age 40 or older, male, with hypertension, or without DM. However, LMM risk was positively related to serum 25(OH)D concentration in those younger than age 40 or in women.

Conclusion

There is a U-shaped relationship between serum 25(OH)D concentration and the risk of LMM in the general U.S. population. Careful monitoring and appropriate Vitamin D supplementation might lessen the risk of LMM.

Inflammatory biomarkers at different stages of Sarcopenia in older women

In recent years, studies have found that Sarcopenia alters inflammatory biomarkers. However, the behavior of inflammatory biomarkers at different stages of Sarcopenia is not well understood. This study aimed to compare a broad panel of inflammatory biomarkers in older women at different stages of Sarcopenia. The study included 71 Brazilian community-dwelling older women. Muscle Strength was assessed by using handgrip strength (Jamar dynamometer). The Short Physical Performance Battery (SPPB) was performed to assess the physical performance, and body composition was assessed by DEXA. Sarcopenia was diagnosed and classified according to the EWGSOP2 criteria. Blood was drawn, and inflammatory biomarkers associated with Sarcopenia (IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, TNF, adiponectin, leptin, resistin, BDNF, sTNFr-1 and sTNFr-2) was analysed. After diagnosis and classification of sarcopenia, 45% of women did not present Sarcopenia (NS, N = 32), 23.9% were diagnosed with Sarcopenia Probable (SP, N = 17), 19,7% with Sarcopenia Confirmed (SC, N = 14), and 11.3% with Severe Sarcopenia (SS, N = 8). The analysis of inflammatory biomarkers revealed that the more advanced the stage of Sarcopenia, the higher the levels of BDNF, IL-8, sTNFr-1, and sTNFr-2. The assessment of BDNF, IL-8, sTNFr-1, and sTNFr-2 levels may be an adjuvant tool in diagnosis and severity classification of Sarcopenia in older Brazilian women.

Sarcopenia and Cognitive Decline in Older Adults: Targeting the Muscle-Brain Axis

Declines in physical performance and cognition are commonly observed in older adults. The geroscience paradigm posits that a set of processes and pathways shared among age-associated conditions may also serve as a molecular explanation for the complex pathophysiology of physical frailty, sarcopenia, and cognitive decline. Mitochondrial dysfunction, inflammation, metabolic alterations, declines in cellular stemness, and altered intracellular signaling have been observed in muscle aging. Neurological factors have also been included among the determinants of sarcopenia. Neuromuscular junctions (NMJs) are synapses bridging nervous and skeletal muscle systems with a relevant role in age-related musculoskeletal derangement. Patterns of circulating metabolic and neurotrophic factors have been associated with physical frailty and sarcopenia. These factors are mostly related to disarrangements in protein-to-energy conversion as well as reduced calorie and protein intake to sustain muscle mass. A link between sarcopenia and cognitive decline in older adults has also been described with a possible role for muscle-derived mediators (i.e., myokines) in mediating muscle-brain crosstalk. Herein, we discuss the main molecular mechanisms and factors involved in the muscle-brain axis and their possible implication in cognitive decline in older adults. An overview of current behavioral strategies that allegedly act on the muscle-brain axis is also provided.

C-terminal agrin fragment as a biomarker of muscle wasting and weakness: a narrative review

Ageing is accompanied by an inexorable loss of muscle mass and functionality and represents a major risk factor for numerous diseases such as cancer, diabetes and cardiovascular and pulmonary diseases. This progressive loss of muscle mass and function may also result in the insurgence of a clinical syndrome termed sarcopenia, exacerbated by inactivity and disease. Sarcopenia and muscle weakness yield the risk of falls and injuries, heavily impacting on health and social costs. Thus, screening, monitoring and prevention of conditions inducing muscle wasting and weakness are essential to improve life quality in the ageing modern society. To this aim, the reliability of easily accessible and non-invasive blood-derived biomarkers is being evaluated. C-terminal agrin fragment (CAF) has been widely investigated as a neuromuscular junction (NMJ)-related biomarker of muscle dysfunction. This narrative review summarizes and critically discusses, for the first time, the studies measuring CAF concentration in young and older, healthy and diseased individuals, cross-sectionally and in response to inactivity and physical exercise, providing possible explanations behind the discrepancies observed in the literature. To identify the studies investigating CAF in the above-mentioned conditions, all the publications found in PubMed, written in English and measuring this biomarker in blood from 2013 (when CAF was firstly measured in human serum) to 2022 were included in this review. CAF increases with age and in sarcopenic individuals when compared with age-matched, non-sarcopenic peers. In addition, CAF was found to be higher than controls in other muscle wasting conditions, such as diabetes, COPD, chronic heart failure and stroke, and in pancreatic and colorectal cancer cachectic patients. As agrin is also expressed in kidney glomeruli, chronic kidney disease and transplantation were shown to have a profound impact on CAF independently from muscle wasting. CAF concentration raises following inactivity and seems to be lowered or maintained by exercise training. Finally, CAF was reported to be cross-sectionally correlated to appendicular lean mass, handgrip and gait speed; whether longitudinal changes in CAF are associated with those in muscle mass or performance following physical exercise is still controversial. CAF seems a reliable marker to assess muscle wasting in ageing and disease, also correlating with measurements of appendicular lean mass and muscle function. Future research should aim at enlarging sample size and accurately reporting the medical history of each patient, to normalize for any condition, including chronic kidney disease, that may influence the circulating concentration of this biomarker.

Two-CyDye-Based 2D-DIGE Analysis of Aged Human Muscle Biopsy Specimens

The gradual loss of skeletal muscle mass during aging and associated decline in contractile strength can result in reduced fitness, frailty, and loss of independence. In order to better understand the molecular and cellular mechanisms that underlie sarcopenia of old age and the frailty syndrome, as well as identify novel therapeutic targets to treat age-related fiber wasting, it is crucial to develop a comprehensive biomarker signature of muscle aging. Fluorescence two-dimensional gel electrophoresis (2D-DIGE) in combination with sensitive mass spectrometry presents an ideal bioanalytical tool for biomarker discovery in biogerontology. This chapter outlines the application of the 2D-DIGE method for the comparative analysis of human biopsy specimens from middle-aged versus senescent individuals using a two-CyDye-based method.

Association of Micronutrients and Handgrip Strength in Korean Older Population: A Cross-Sectional Study

Sarcopenia is characterized by the loss of skeletal muscle mass, strength, and physical performance. Dynapenia and kratopenia are described as the loss of muscle strength and power. Nutritional intake status is one of the factors affecting the prevention of an age-related muscle decline such as sarcopenia, dynapenia, or kratopenia in older populations. This study aimed to investigate the association between the intake of micronutrients and handgrip strength in 1254 individuals (546 men and 708 women) of the Korean older population from the most recent dataset. They were analyzed and divided into two groups: a LHS group with low handgrip strength (<28 kg for men and <18 kg for women) and a normal group with normal handgrip strength. Logistic regression analysis was performed to estimate the odds ratios (ORs) and 95% confidence intervals (Cis) of the associations between micronutrient intakes and low handgrip strength in Korean older population by gender. Among micronutrients, insufficient potassium intake showed a significant association with low handgrip strength for men (OR: 3.159, 95% CI: 1.164−8.578) and women (OR: 2.793, 95% CI: 1.380−5.654) aged ≥65 years, respectively (p = 0.005 for men, p = 0.024 for women), as a result of adjusting for all confounding factors that could affect low handgrip strength. In conclusion, potassium intake among micronutrients in Korean older populations with low handgrip strength might need continuous monitoring for the intervention or prevention of dynapenia or sarcopenia.

Ranolazine Counteracts Strength Impairment and Oxidative Stress in Aged Sarcopenic Mice

Sarcopenia is defined as the loss of muscle mass associated with reduced strength leading to poor quality of life in elderly people. The decline of skeletal muscle performance is characterized by bioenergetic impairment and severe oxidative stress, and does not always strictly correlate with muscle mass loss. We chose to investigate the ability of the metabolic modulator Ranolazine to counteract skeletal muscle dysfunctions that occur with aging. For this purpose, we treated aged C57BL/6 mice with Ranolazine/vehicle for 14 days and collected the tibialis anterior and gastrocnemius muscles for histological and gene expression analyses, respectively. We found that Ranolazine treatment significantly increased the muscle strength of aged mice. At the histological level, we found an increase in centrally nucleated fibers associated with an up-regulation of genes encoding MyoD, Periostin and Osteopontin, thus suggesting a remodeling of the muscle even in the absence of physical exercise. Notably, these beneficial effects of Ranolazine were also accompanied by an up-regulation of antioxidant and mitochondrial genes as well as of NADH-dehydrogenase activity, together with a more efficient protection from oxidative damage in the skeletal muscle. These data indicate that the protection of muscle from oxidative stress by Ranolazine might represent a valuable approach to increase skeletal muscle strength in elderly populations.

Age-dependent impact of two exercise training regimens on genomic and metabolic remodeling in skeletal muscle and liver of male mice

Skeletal muscle adapts to different exercise training modalities with age; however, the impact of both variables at the systemic and tissue levels is not fully understood. Here, adult and old C57BL/6 male mice were assigned to one of three groups: sedentary, daily high-intensity intermittent training (HIIT), or moderate intensity continuous training (MICT) for 4 weeks, compatible with the older group's exercise capacity. Improvements in body composition, fasting blood glucose, and muscle strength were mostly observed in the MICT old group, while effects of HIIT training in adult and old animals was less clear. Skeletal muscle exhibited structural and functional adaptations to exercise training, as revealed by electron microscopy, OXPHOS assays, respirometry, and muscle protein biomarkers. Transcriptomics analysis of gastrocnemius muscle combined with liver and serum metabolomics unveiled an age-dependent metabolic remodeling in response to exercise training. These results support a tailored exercise prescription approach aimed at improving health and ameliorating age-associated loss of muscle strength and function in the elderly.

Relationship of Haptoglobin Phenotypes With Sarcopaenia in Patients With Congestive Heart Failure

BACKGROUND

Systemic inflammation in patients with chronic heart failure (CHF) contributes to age-related muscle loss or sarcopaenia. However, the relationship of plasma haptoglobin (Hp), an acute-phase reactant, with muscle and physical health in CHF is unknown.

METHODS

This study investigated the associations of plasma haptoglobin levels and phenotypes with handgrip strength (HGS), appendicular skeletal muscle index (ASMI) and physical capacity in healthy controls (n=67) and CHF patients (n=61) aged 55-73 years.

RESULTS

Patients with CHF had higher plasma Hp levels and higher proportions of Hp2-2 phenotype when compared with healthy controls. Plasma Hp2-1 and Hp2-2 levels were negatively associated with HGS and ASMI in healthy controls and CHF (both p<0.05). A negative association of plasma Hp2-2 with gait speed and plasma Hp2-1 with daily steps count was also found in CHF (p<0.05). Patients with Hp2 phenotype showed higher expressions of inflammation and oxidative stress markers, as well as low scores on quality of life parameters.

CONCLUSIONS

Circulating Hp may be a valuable biomarker for assessing muscle health and physical capacity in CHF.

Specific lysophosphatidylcholine and acylcarnitine related to sarcopenia and its components in older men

Background

Metabolic profiling may provide insights into the pathogenesis and identification of sarcopenia; however, data on the metabolic basis of sarcopenia and muscle-related parameters among older adults remain incompletely understood. This study aimed to identify the associations of metabolites with sarcopenia and its components, and to explore metabolic perturbations in older men, who have a higher prevalence of sarcopenia than women.

Methods

We simultaneously measured the concentrations of amino acids, carnitine, acylcarnitines, and lysophosphatidylcholines (LPCs) in serum samples from a cross-sectional study of 246 Chinese older men, using targeted metabolomics. Sarcopenia and its components, including skeletal muscle index (SMI), 6-m gait speed, and handgrip strength were assessed according to the algorithm of the Asian Working Group for Sarcopenia criteria. Associations were determined by univariate and multivariate analyses.

Results

Sixty-five (26.4%) older men with sarcopenia and 181 (73.6%) without sarcopenia were included in the study. The level of isovalerylcarnitine (C5) was associated with the presence of sarcopenia and SMI. Regarding the overlapped metabolites for muscle parameters, among ten metabolites associated with muscle mass, six metabolites including leucine, octanoyl-L-carnitine (C8), decanoyl-L-carnitine (C10), dodecanoyl-L-carnitine (C12) and tetradecanoyl-L-carnitine (C14), and LPC18:2 were associated with handgrip strength, and three of which (C12, C14, and LPC18:2) were also associated with gait speed. Specifically, tryptophan was positively associated and glycine was negatively associated with handgrip strength, while glutamate was positively correlated with gait speed. Isoleucine, branched chain amino acids, and LPC16:0 were positively associated with SMI. Moreover, the levels of LPC 16:0,18:2 and 18:0 contributed significantly to the model discriminating between older men with and without sarcopenia, whereas there were no significant associations for other amino acids, acylcarnitines, and LPC lipids.

Conclusions

These results showed that specific and overlapped metabolites are associated with sarcopenic parameters in older men. This study highlights the potential roles of acylcarnitines and LPCs in sarcopenia and its components, which may provide valuable information regarding the pathogenesis and management of sarcopenia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02953-4.

A neuromuscular perspective of sarcopenia pathogenesis: deciphering the signaling pathways involved

The escalation of life expectancy is accompanied by an increase in the prevalence of age-related conditions, such as sarcopenia. Sarcopenia, a muscle condition defined by low muscle strength, muscle quality or quantity, and physical performance, has a high prevalence among the elderly and is associated to increased mortality. The neuromuscular system has been emerging as a key contributor to sarcopenia pathogenesis. Indeed, the age-related degeneration of the neuromuscular junction (NMJ) function and structure may contribute to the loss of muscle strength and ultimately to the loss of muscle mass that characterize sarcopenia. The present mini-review discusses important signaling pathways involved in the function and maintenance of the NMJ, giving emphasis to the ones that might contribute to sarcopenia pathogenesis. Some conceivable biomarkers, such as C-terminal agrin fragment (CAF) and brain-derived neurotrophic factor (BDNF), and therapeutic targets, namely acetylcholine and calcitonin gene-related peptide (CGRP), can be retrieved, making way to future studies to validate their clinical use.

Association of urinary phthalate metabolites with sarcopenia in US adults: NHANES 1999-2006

Phthalates have been extensively detected in environmental and biological matrices. Exposure to phthalates is implicated in various human diseases. In this study, we conducted a cross-sectional study to determine whether urinary phthalate metabolite concentrations were correlated with prevalence of sarcopenia in US adult population. We included 3562 participants with detailed information on skeletal muscle mass and urinary phthalate metabolites based on National Health and Nutrition Examination Survey (NHANES) 1999-2006 data. A total of 7 main phthalate metabolites were analyzed in the urine sample of each participant. Appendicular skeletal muscle mass (ASM) was measured using dual-energy X-ray absorptiometry. Multivariable linear regression models were conducted following adjustment for multiple covariates. ASM adjusted by body mass index (ASM/BMI) was calculated, and sarcopenia was defined as the lowest quintile for ASM/BMI value. Compared with participants in quartile 1, those in quartile 2 of urinary mono-n-butyl phthalate (MnBP) and quartile 4 of urinary monobenzyl phthalate (MBzP) had decreased ASM/BMI. Urinary MnBP in quartile 4, as well as urinary MBzP in quartile 2, was shown to be significantly correlated with higher sarcopenia prevalence. In subgroup analysis, negative association of MBzP with ASM/BMI was observed in both males and females, while this negative association was only observed in males for MnBP. Females with higher urinary monoethyl phthalate (MEP) concentrations had higher sarcopenia risk. Taken together, the present study found several urinary phthalate metabolites were positively associated with sarcopenia prevalence in US adult population. These findings indicated phthalate exposure might be an important environmental risk factor contributing to sarcopenia development.

Association between plasma procollagen type III N-terminal peptide (P3NP) levels and physical performance in elderly men: The Korean Frailty and Aging Cohort Study (KFACS)

BACKGROUND

Physical performance decline associated with aging is clinically important in the development of disability in the older population. More recently, procollagen type III N-terminal peptide (P3NP) and synaptosomal-associated protein of 25 kDa (SNAP25) have been suggested as potential biomarkers for physical performance decline.

OBJECTIVE

The objective of this pilot study was to examine plasma P3NP and SNAP25 levels in relation to muscle mass, strength, and performance status, and to investigate the association of plasma P3NP and SNAP25 levels with sarcopenia components.

METHODS

Seventy-nine community-dwelling elderly men (mean age: 78.1 ± 3.5 years) were randomly selected and matched by age from the Korean Frailty and Aging Cohort Study. The sample was classified into the "normal," "low muscle mass only," "sarcopenia," and "low physical performance only" groups according to the criteria of the Asian Working Group for Sarcopenia 2019. Estimates and 95% confidence intervals (CIs) of log P3NP and log SNAP25 levels by muscle mass, strength, and performance status were obtained using a generalized linear model. Pearson correlations and multiple linear regression analyses were used to assess the association of log P3NP and log SNAP25 levels with appendicular skeletal muscle mass (ASM) index, handgrip strength, and physical performance.

RESULTS

Log P3NP levels tended to be associated with low physical performance compared with the normal group (estimate = 0.54; 95% CI = -0.05, 1.14; p = 0.072). Log P3NP levels were inversely associated with physical performance (short physical performance battery and five-times sit-to-stand test) after adjusting for potential confounders (all p < 0.05) and tended to have an inverse association with gait speed (p = 0.078). Log P3NP levels tended to have a positive correlation with the ASM index (r² = 0.042; p = 0.070), but not with handgrip strength (r² = 0.0009; p = 0.795). However, no significant association between plasma SNAP25 levels and physical performance was observed.

CONCLUSION

Plasma P3NP levels might be a potential biomarker for decreased physical performance in elderly men. Further studies with larger sample sizes are needed to confirm our findings.

Sarcopenia associates with SNAP-25 SNPs and a miRNAs profile which is modulated by structured rehabilitation treatment

Background

Sarcopenia is a loss of muscle mass and strength causing disability, morbidity, and mortality in older adults, which is characterized by alterations of the neuromuscular junctions (NMJs). SNAP-25 is essential for the maintenance of NMJ integrity, and the expression of this protein was shown to be modulated by the SNAP-25 rs363050 polymorphism and by a number of miRNAs.

Methods

We analysed these parameters in a cohort of sarcopenic patients undergoing structured rehabilitation. The rs363050 genotype frequency distribution was analyzed in 177 sarcopenic patients and 181 healthy controls (HC). The concentration of seven miRNAs (miR-451a, miR-425-5p, miR155-5p, miR-421-3p, miR-495-3p, miR-744-5p and miR-93-5p), identified by mouse brain miRNome analysis to be differentially expressed in wild type compared to SNAP-25^± heterozygous mice, was analyzed as well by droplet digital PCR (ddPCR) in a subgroup of severe sarcopenic patients undergoing rehabilitation.

Results

The SNAP-25 rs363050 AA genotype was significantly more common in sarcopenic patients compared to HC (p_c = 0.01); miR-451a was significantly up-regulated in these patients before rehabilitation. Rehabilitation modified miRNAs expression, as miR-155-5p, miR-421-3p, miR-451a, miR-425-5p, miR-744-5p and miR-93-5p expression was significantly up-regulated (p < 0.01), whereas that of miR-495-3p was significantly down-regulated (p < 0.001) by rehabilitation. Notably, rehabilitation-associated improvement of the muscle-skeletal SPPB score was significantly associated with the reduction of miR-451a expression.

Conclusion

These results support the hypothesis of a role for SNAP-25 in sarcopenia and suggest SNAP-25-associated miRNAs as circulatory biomarkers of rehabilitative outcome for sarcopenia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02989-x.

Associations between elevated growth differentiation factor-15 and sarcopenia among community-dwelling older adults

BACKGROUND

Growth differentiation factor 15 (GDF-15) is associated with disease progression, mitochondrial dysfunction, and mortality. Elevated GDF-15 level was recently reported to be associated with poorer physical performance in healthy adults. However, the association between serum GDF-15 level and sarcopenia in community-dwelling older adults has not been well characterized.

METHODS

We conducted cross-sectional (n = 929) and two-year prospective analyses (n = 788) among participants aged 70-84 years enrolled in the Korean Frailty and Aging Cohort Study. Participants with an estimated glomerular filtration rate of <60 mL/min/1.73 m 2 were excluded. Appendicular lean mass was measured using dual-energy X-ray absorptiometry. Sarcopenia status was determined according to the Asian Working Group for Sarcopenia-2019 algorithm.

RESULTS

At baseline, 16.6% of the participants had sarcopenia. Median GDF-15 concentration was higher in the sarcopenic group than in the non-sarcopenic group (1221 pg/mL vs. 1019 pg/mL, p<0.001). In the multivariate analysis adjusted for cardiometabolic risk and biological factors, the highest GDF-15 tertile (≥1245 pg/mL) had an increased likelihood of sarcopenia (odds ratio, 1.96; 95% confidence interval, 1.16-3.33) than the lowest tertile (<885 pg/mL). During the two-year follow-up period, 67 (10.1%) individuals without sarcopenia at baseline developed sarcopenia. There were no significant associations between baseline serum GDF-15 levels and incident sarcopenia or its components (all p>0.05).

CONCLUSIONS

Elevated GDF-15 was associated with prevalent sarcopenia but not able to predict incident sarcopenia in the 2-year follow-up. Further studies are needed to explore the pathophysiological roles of GDF-15 in the development of sarcopenia.

Skeletal muscle-specific calpastatin overexpression mitigates muscle weakness in aging and extends life span

Calpain activation has been postulated as a potential contributor to the loss of muscle mass and function associated with both aging and disease, but limitations of previous experimental approaches have failed to completely examine this issue. We hypothesized that mice overexpressing calpastatin (CalpOX), an endogenous inhibitor of calpain, solely in skeletal muscle would show an amelioration of the aging muscle phenotype. We assessed four groups of mice (age in months): 1) young wild type (WT; 5.71 ± 0.43), 2) young CalpOX (5.6 ± 0.5), 3) old WT (25.81 ± 0.56), and 4) old CalpOX (25.91 ± 0.60) for diaphragm and limb muscle (extensor digitorum longus, EDL) force frequency relations. Aging significantly reduced diaphragm and EDL peak force in old WT mice, and decreased the force-time integral during a fatiguing protocol by 48% and 23% in aged WT diaphragm and EDL, respectively. In contrast, we found that CalpOX mice had significantly increased diaphragm and EDL peak force in old mice, similar to that observed in young mice. The impact of aging on the force-time integral during a fatiguing protocol was abolished in the diaphragm and EDL of old CalpOX animals. Surprisingly, we found that CalpOX had a significant impact on longevity, increasing median survival from 20.55 mo in WT mice to 24 mo in CalpOX mice (P = 0.0006).NEW & NOTEWORTHY This is the first study to investigate the role of calpastatin overexpression on skeletal muscle specific force in aging rodents. Muscle-specific overexpression of calpastatin, the endogenous calpain inhibitor, prevented aging-induced reductions in both EDL and diaphragm specific force and, remarkably, increased life span. These data suggest that diaphragm dysfunction in aging may be a major factor in determining longevity. Targeting the calpain/calpastatin pathway may elucidate novel therapies to combat skeletal muscle weakness in aging.

Characterization of the gut-liver-muscle axis in cirrhotic patients with sarcopenia

BACKGROUND & AIM

Sarcopenia is frequent in cirrhosis and is associated with unfavourable outcomes. The role of the gut-liver-muscle axis in this setting has been poorly investigated. The aim of this study was to identify gut microbiota, metabolic and inflammatory signatures associated with sarcopenia in cirrhotic patients.

METHODS

Fifty cirrhotic patients assessed for the presence of sarcopenia by the quantification of muscle mass and strength were compared with age- and sex-matched controls. A multiomic analysis, including gut microbiota composition and metabolomics, serum myokines and systemic and intestinal inflammatory mediators, was performed.

RESULTS

The gut microbiota of sarcopenic cirrhotic patients was poor in bacteria associated with physical function (Methanobrevibacter, Prevotella and Akkermansia), and was enriched in Eggerthella, a gut microbial marker of frailty. The abundance of potentially pathogenic bacteria, such as Klebsiella, was also increased, to the detriment of autochthonous ones. Sarcopenia was associated with elevated serum levels of pro-inflammatory mediators and of fibroblast growth factor 21 (FGF21) in cirrhotic patients. Gut microbiota metabolic pathways involved in amino acid, protein and branched-chain amino acid metabolism were up-regulated, in addition to ethanol, trimethylamine and dimethylamine production. Correlation networks and clusters of variables associated with sarcopenia were identified, including one centred on Klebsiella/ethanol/FGF21/Eggerthella/Prevotella.

CONCLUSIONS

Alterations in the gut-liver-muscle axis are associated with sarcopenia in patients with cirrhosis. Detrimental but also compensatory functions are involved in this complex network.

Sarcopenia and homocysteine: is there a possible association in the elderly? A narrative review

BACKGROUND

Sarcopenia (SA) is a progressive skeletal muscle disorder, associated with increased risk of adverse outcomes, including falls, fractures, physical disability and mortality. Several risks factors may contribute to the development of SA in the elderly; among them, nutrition plays a key role in muscle health. The elderly are at risk of inadequate intake in terms of micronutrients affecting muscle homeostasis, such as B vitamins, related to homocysteine (Hcy) metabolism.

OBJECTIVES AND METHODS

This narrative review analysed the association between increased Hcy levels and SA, according to the criteria of the International Working Group on Sarcopenia, the European Working Group on Sarcopenia in Older People and the Asian Working Group for Sarcopenia. The authors focused not only on SA per se but also on exploring the association between increased Hcy levels and components of SA, including muscle mass, muscle strength and physical performance.

RESULTS

Results are inconsistent, except for muscle mass, showing no significant associations with Hcy levels.

CONCLUSIONS

Few and conflicting data emerged in this review on the association between SA and increased Hcy levels due to numerous differences between studies that change the significance of the association of Hcy and SA, as well as the muscle strength, muscle mass and physical performance. Furthermore, because the ageing process is not uniform in the population owing to differences in genetics, lifestyle and general health, chronological age fails to address the observed heterogeneity among the 'elderly' of the studies reported in this revision. Therefore, further studies are still needed.

Basic Science of Frailty-Biological Mechanisms of Age-Related Sarcopenia

Aging is associated with loss of function across organ systems, contributing to systemic frailty. Loss of skeletal muscle mass and function, in particular, is a major source of frailty in older adults, severely impacting quality of life. Some loss of muscle mass and strength with aging is inevitable, and sarcopenia, the severe loss of muscle mass with aging, is common. Sarcopenia is determined in part by genetics but can be modified by lifestyle choices. The pathophysiologic underpinnings of sarcopenia are complex and multifactorial. In this review, the causes of sarcopenia are surveyed at the systems, cell, subcellular, and molecular levels with emphasis on the interplay between these various causes of this degenerative disease process.

Methionine transsulfuration pathway is upregulated in long-lived humans

Available evidences point to methionine metabolism as a key target to study the molecular adaptive mechanisms underlying differences in longevity. The plasma methionine metabolic profile was determined using a LC-MS/MS platform to systematically define specific phenotypic patterns associated with genotypes of human extreme longevity (centenarians). Our findings demonstrate the presence of a specific plasma profile associated with human longevity characterized by an enhanced transsulfuration pathway and tricarboxylic acid (TCA) cycle intermediates, as well as a reduced content of specific amino acids. Furthermore, our work reveals that centenarians maintain a strongly correlated methionine metabolism, suggesting an improved network integrity, homeostasis and more tightly regulated metabolism. We have discovered a particular methionine signature related to the condition of extreme longevity, allowing the identification of potential mechanisms and biomarkers of healthy aging.

AChRs Degeneration at NMJ in Aging-Associated Sarcopenia-A Systematic Review

Sarcopenia is an aging process with a decline of skeletal muscle mass and function, which is a challenging public health problem with reduced quality of life in patients. The endplate, the post-synaptic part of the neuromuscular junction (NMJ), occupies 0.1% of the myofiber surface area only, but is composed of millions of acetylcholine receptors (AChRs) that are efficient in binding to acetylcholine (ACh) and triggering skeletal muscle contraction. This systematic review aims to examine aging-associated alterations of post-synaptic AChRs, including morphology, function and related gene expression. A systematic literature search was conducted in PubMed, Embase and Web of Science with relevant keywords by two independent reviewers. Original pre-clinical and clinical studies regarding AChRs changes during aging with available full text and written in English were included. Information was extracted from the included studies for further review. In total, 30 articles were included. Various parameters assessing AChRs alterations by radioassay, immunofluorescence, electrophysiology and mechanical test were reported. Endplate fragmentation and denervation were common in old skeletal muscles during aging. To ensure efficient NMJ transmission and force generation, type I or IIb muscle fibers tended to have increased ACh quanta releasing after electrical stimulations, while type IIa muscle fibers tended to have stronger binding between ACh and AChRs, but the overall function of AChRs was reduced during aging. Alterations of AChRs area depended on muscle type, species and the progress of muscle atrophy and type I muscles fibers tended to demonstrate enlarging AChRs areas. Myogenic regulator factors (MRFs) can regulate the expression of AChRs subunits, while decreased MRF4 may lead to expression changes of AChRs subunits during aging. Sarcoglycan-α can delay low-density lipoprotein receptor-related protein 4 (LRP4) degradation. This protein was increased in old muscles but still cannot suppress the degradation of LRP4. Investigating the role of these AChRs-related genes in the process of aging may provide a potential target to treat sarcopenia.

Biomarkers Profile of People With Sarcopenia: A Cross-sectional Analysis From UK Biobank

OBJECTIVE

This study aimed to characterize the biomarker profile of sarcopenic vs nonsarcopenic men and women, using the current European Working Group on Sarcopenia in Older People (EWGSOP2) definition in the UK Biobank study.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

A total of 396,707 (68.8% women, age 38 to 73) participants from UK Biobank.

MEASURES

Thirty-three biomarkers, standardized to sex-specific z-scores, were included in the analysis. Associations between these biomarkers and sarcopenia, defined using EWGSOP2 criteria, were examined using multiple linear regression.

RESULTS

Higher concentrations of rheumatoid factor, C-reactive protein, cystatin C, sex hormone-binding globulin, gamma-glutamyltransferase, alkaline phosphatase, and total protein, as well as lower concentrations of insulin-like growth factor-1, albumin, creatinine, sodium, and systolic blood pressure, were associated with sarcopenia in both men and women. However, some of the associations differed by sex. Sarcopenia was associated with higher concentrations of phosphate, lipoprotein A, and lower of diastolic blood pressure, HbA1c, urea, glucose, total bilirubin, and testosterone in women only, and with higher concentrations of high-density lipoprotein, aspartate aminotransferase, and direct bilirubin and lower values of apolipoprotein A, vitamin D, and apolipoprotein B in men only.

CONCLUSIONS AND IMPLICATIONS

Several biomarkers were associated with sarcopenia in men and women using the new EWGSOP2 statement. However, some of these associations and their magnitude differed between men and women. Considering the EWGSOP2 updated its statement on the definition of sarcopenia in 2019, this study enables us to update the study of the biomarkers profile of people with sarcopenia.

Corticospinal Control of Human Locomotion as a New Determinant of Age-Related Sarcopenia: An Exploratory Study

Sarcopenia is a muscle disease listed within the ICD-10 classification. Several operational definitions have been created for sarcopenia screening; however, an international consensus is lacking. The Centers for Disease Control and Prevention have recently recognized that sarcopenia detection requires improved diagnosis and screening measures. Mounting evidence hints towards changes in the corticospinal communication system where corticomuscular coherence (CMC) reflects an effective mechanism of corticospinal interaction. CMC can be assessed during locomotion by means of simultaneously measuring Electroencephalography (EEG) and Electromyography (EMG). The aim of this study was to perform sarcopenia screening in community-dwelling older adults and explore the possibility of using CMC assessed during gait to discriminate between sarcopenic and non-sarcopenic older adults. Receiver Operating Characteristic (ROC) curves showed high sensitivity, precision and accuracy of CMC assessed from EEG Cz sensor and EMG sensors located over Musculus Vastus Medialis [Cz-VM; AUC (95.0%CI): 0.98 (0.92-1.04), sensitivity: 1.00, 1-specificity: 0.89, p < 0.001] and with Musculus Biceps Femoris [Cz-BF; AUC (95.0%CI): 0.86 (0.68-1.03), sensitivity: 1.00, 1-specificity: 0.70, p < 0.001]. These muscles showed significant differences with large magnitude of effect between sarcopenic and non-sarcopenic older adults [Hedge's g (95.0%CI): 2.2 (1.3-3.1), p = 0.005 and Hedge's g (95.0%CI): 1.5 (0.7-2.2), p = 0.010; respectively]. The novelty of this exploratory investigation is the hint toward a novel possible determinant of age-related sarcopenia, derived from corticospinal control of locomotion and shown by the observed large differences in CMC when sarcopenic and non-sarcopenic older adults are compared. This, in turn, might represent in future a potential treatment target to counteract sarcopenia as well as a parameter to monitor the progression of the disease and/or the potential recovery following other treatment interventions.

The emerging role of skeletal muscle mitochondrial dynamics in exercise and ageing

Mitochondria are the hub for energy production within living cells. They can undergo morphological changes in response to nutrient availability and cellular stress. Here, we review how exercise chronically and acutely affects mitochondrial dynamics. Moreover, we discuss whether mitochondrial dysfunction observed in elderly subjects is due to the ageing process per se or due to the associated sedentary state. Finally, we study how endurance exercise can improve mitochondrial dynamics in older subjects, thereby improving their overall health and likely limiting muscle waste.

Targeting Age-Dependent Functional and Metabolic Decline of Human Skeletal Muscle: The Geroprotective Role of Exercise, Myokine IL-6, and Vitamin D

In the elderly, whole-body health largely relies on healthy skeletal muscle, which controls body stability, locomotion, and metabolic homeostasis. Age-related skeletal muscle structural/functional deterioration is associated with a higher risk of severe comorbid conditions and poorer outcomes, demanding major socioeconomic costs. Thus, the need for efficient so-called geroprotective strategies to improve resilience and ensure a good quality of life in older subjects is urgent. Skeletal muscle senescence and metabolic dysregulation share common cellular/intracellular mechanisms, potentially representing targets for intervention to preserve muscle integrity. Many factors converge in aging, and multifaceted approaches have been proposed as interventions, although they have often been inconclusive. Physical exercise can counteract aging and metabolic deficits, not only in maintaining tissue mass, but also by preserving tissue secretory function. Indeed, skeletal muscle is currently considered a proper secretory organ controlling distant organ functions through immunoactive regulatory small peptides called myokines. This review provides a current perspective on the main biomolecular mechanisms underlying age-dependent and metabolic deterioration of skeletal muscle, herein discussed as a secretory organ, the functional integrity of which largely depends on exercise and myokine release. In particular, muscle-derived interleukin (IL)-6 is discussed as a nutrient-level biosensor. Overall, exercise and vitamin D are addressed as optimal geroprotective strategies in view of their multi-target effects.

Regulatory role of exercise-induced autophagy for sarcopenia

Sarcopenia is an aging-related disease, described as the progressive reduction in mass and strength of skeletal muscle. Sarcopenia is typically characterized as the accumulation of damaged products due to an imbalance between protein synthesis and protein degradation. This imbalance between protein synthesis and degradation is attributed to impaired autophagic signal pathways. Sarcopenia can predispose elderly patients to several complications that may significantly impact patient quality of life. Recent evidence indicates that autophagy is required for the control of skeletal muscle mass under catabolic conditions and plays a crucial role in maintaining the homeostasis and integrity of skeletal muscle, specifically at appropriate level of autophagy. Exercise may be considered as a stress stimulus that can substantially modulate cellular signaling to promote metabolic adaptations. Appropriate exercise can induce autophagy or regulate the functional status of autophagy. Additionally, exercise-induced autophagy is the most effective treatment available in slowing down sarcopenia, improving mitochondrial quality, and the number of quiescent satellite cells, as a process that depends on basal autophagy. The molecular mechanisms underpinning the development of sarcopenia, however, remained largely unknown. In this narrative review, the current molecular mechanisms of sarcopenia are discussed from the perspective of exercise-induced autophagy and the effect of different exercise modalities on this response. This narrative review will aim to provide the references for developing scientific and optimal intervention strategies including exercise intervention for the prevention and treatment of sarcopenia through regulating autophagic signal pathways.