Novel insights regarding mechanisms for treatment of sarcopenia

High Serum AST/ALT Ratio and Low Serum INS*PA Product Are Risk Factors and Can Diagnose Sarcopenia in Middle-Aged and Older Adults

BACKGROUND

Sarcopenia is an age-related clinical condition and associated with an increased risk of adverse outcomes. However, to date, there is no global standard for the diagnosis of sarcopenia, and fewer serum biomarkers have been suggested for the diagnosis of sarcopenia. It is, thus, important that sarcopenia-related serological diagnostic markers be explored. The present study was based on the Asian Working Group on Sarcopenia 2019 (AWGS 2019) criteria to assess whether aspartate aminotransferase/alanine aminotransferase (AST/ALT) ratio and fasting insulin*prealbumin (INS*PA) product are diagnostic markers associated with sarcopenia in various ethnic groups in western China.

METHODS

This cross-sectional study included 4,099 adults (1,471 men and 2,628 women) from the West China Health and Aging Trend (WCHAT) study. The value of serum biomarkers was based on laboratory data. The accompanying metabolic disorders and the associated parameters were evaluated. Logistic regression analysis was used to explore the association between markers and sarcopenia. Receiver operating characteristic curve (ROC) analysis was used to evaluate the diagnostic efficacy of the test in differentiating sarcopenia.

RESULTS

Binary regression analysis showed that high serum AST/ALT (OR = 2.247) and adrenal cortisol (PTC, OR = 1.511), low serum INS*PA (OR = 2.970), free triiodothyronine (FT3, OR = 1.313), 25-OH-VitD (VitD, in male participants, OR = 1.817), and diastolic blood pressure (DBP, in female subjects, OR = 1.250) were independent risk factors for sarcopenia (P < 0.05). AST/ALT and INS*PA were not affected by metabolic factors and had better diagnostic efficacy for sarcopenia. The AUC of the INS*PA was the highest (0.705, 0.706, and 0.701, respectively, P < 0.05), followed by that of the AST/ALT (0.680, 0.675, and 0.695, respectively, P < 0.05). The AUC of the AST/ALT/(INS*PA)*10,000 used to diagnose sarcopenia was 0.727.

CONCLUSION

Among middle-aged and older adults of multiple ethnicities in western China, we found that higher AST/ALT and lower INS*PA levels are associated with an increased prevalence of sarcopenia. Since these serum biomarkers are inexpensive and can be obtained easily from biochemical routine, regular follow-up of AST/ALT and INS*PA may be an effective strategy in sarcopenia screening and management.

Prevalence of sarcopenia and its associated factors: the impact of muscle mass, gait speed, and handgrip strength reference values on reported frequencies

OBJECTIVES

Sarcopenia is a common treatable geriatric condition. The aim of this study was to estimate the prevalence of sarcopenia and its associated factors in community-dwelling elderly living in Rio de Janeiro, Brazil, and to discuss the impact of different muscle mass, handgrip strength and gait speed cut-off values on the reported frequency of sarcopenia.

METHODS

The health habits, functional capacity, and anthropometric measurements of 745 individuals aged ≥65 years from the Frailty in Brazilian Older People study were analyzed. The participants were classified into the following four groups: no sarcopenia, pre-sarcopenia, sarcopenia and severe sarcopenia. Univariate and multivariate regression analyses were performed. Muscle mass, handgrip strength and gait speed cut-off thresholds tailored to the sample and those proposed by the European Working Group on Sarcopenia in Older People were used to compare the prevalence rates of sarcopenia.

RESULTS

Seventy-three percent of the participants were female, 61.9% were Caucasian, and the mean age was 76.6 years. The prevalence rates of sarcopenia were 10.8% and 18% using the sample-tailored and European consensus cut-off values, respectively. Sarcopenia was associated with advanced age (OR: 37.2; CI95%12.35-112.48), Caucasian race (OR: 1.89; CI 95% 1.02-3.52), single marital status (OR:6; CI95% 2.2-16.39), low income (OR:3.64; CI 95% 1.58-8.39), and the presence of comorbidities (OR:3.26; CI 95%1.28-8.3).

CONCLUSION

In this study, the estimated prevalence of sarcopenia was similar to that reported in most studies after the tailored handgrip strength and gait speed cut-off values were adopted. A higher prevalence was observed when the cut-off values suggested by the European consensus were used. This indicates that the prevalence of sarcopenia must be estimated using population-specific reference values.

Sarcopenia

Sarcopenia refers to age-related muscle loss, defined using a combination of appendicular muscle mass, muscle strength, and physical performance measures. The pathogenesis depends on a balance between positive and negative regulators of muscle growth. Sarcopenia increases the risk for falls, fractures, dependency, use of hospital services, institutionalization, poor quality of life, and mortality. In clinical practice, brief screening tools, such as the 5-item SARC-F score, may be useful. Although pharmacologic treatments are actively being studied, the current mainstay consists of optimizing nutrition status, in particular protein and vitamin D status, and resistance exercises.

Discovery of Novel Small Molecules that Activate Satellite Cell Proliferation and Enhance Repair of Damaged Muscle

Skeletal muscle progenitor stem cells (referred to as satellite cells) represent the primary pool of stem cells in adult skeletal muscle responsible for the generation of new skeletal muscle in response to injury. Satellite cells derived from aged muscle display a significant reduction in regenerative capacity to form functional muscle. This decrease in functional recovery has been attributed to a decrease in proliferative capacity of satellite cells. Hence, agents that enhance the proliferative abilities of satellite cells may hold promise as therapies for a variety of pathological settings, including repair of injured muscle and age- or disease-associated muscle wasting. Through phenotypic screening of isolated murine satellite cells, we identified a series of 2,4-diaminopyrimidines (e.g., 2) that increased satellite cell proliferation. Importantly, compound 2 was effective in accelerating repair of damaged skeletal muscle in an in vivo mouse model of skeletal muscle injury. While these compounds were originally prepared as c-Jun N-terminal kinase 1 (JNK-1) inhibitors, structure-activity analyses indicated JNK-1 inhibition does not correlate with satellite cell activity. Screening against a broad panel of kinases did not result in identification of an obvious molecular target, so we conducted cell-based proteomics experiments in an attempt to identify the molecular target(s) responsible for the potentiation of the satellite cell proliferation. These data provide the foundation for future efforts to design improved small molecules as potential therapeutics for muscle repair and regeneration.