Excessive adipose tissue infiltration in skeletal muscle in individuals with obesity, diabetes mellitus, and peripheral neuropathy: association with performance and function

Comparative analysis of SARC-F-EBM, Ishii test, and six other screening tools for sarcopenia in Chinese community-dwelling older adults: a cross-sectional diagnostic study

To assess the relative performance of simple screening methods for sarcopenia in Chinese community-dwelling older adults. Data of older adults aged ≥ 60 were collected through a cross-sectional investigation. Sarcopenia was defined according to the Asian Working Group for Sarcopenia 2019 criteria. The accuracy of screening methods was evaluated using sensitivity, specificity, receiver operating characteristic (ROC) curves and area under the ROC curves (AUC). The AUC value greater than 0.8 represented the good screening ability. A total of 918 older adults (44.3% men, mean age 70.4 ± 6.5 years) were included in this study. The overall prevalence rates of possible sarcopenia, confirmed sarcopenia, and severe sarcopenia were 59.5%, 12.8%, and 5.9%, respectively. In men, the SARC-F-EBM and Ishii tests indicated good screening capabilities for confirmed sarcopenia, with an AUC of 0.81 (95% CI: 0.77-0.85) and 0.80 (95% CI: 0.76-0.84), respectively. In women, the highest AUC was also achieved using the SARC-F-EBM at 0.79 (95% CI: 0.75-0.82), followed by the Ishii test at 0.77 (95% CI: 0.74-0.81), showing the moderate efficacy. A ranking diagram showed that SARC-F-EBM was most likely to be considered the best method for diagnosing sarcopenia in terms of AUC and sensitivity, regardless of sex. We recommend the SARC-F-EBM for sarcopenia screening in community-dwelling Chinese older adults when respondents are able to answer the questionnaire accurately; otherwise, the Ishii test consisting entirely of objective measures could be used.

Interactions between muscle volume and body mass index on brain structure in the UK Biobank

Background

Low skeletal muscle volume may increase dementia risk through mechanisms affecting brain structure. However, it is unclear whether this relationship exists outside of sarcopenia and/or varies by other factors. We aimed to study the interplay between skeletal muscle volume and factors, such as age, sex, and body mass index (BMI), in explaining brain structure at midlife in a cohort without sarcopenia.

Methods

We used abdominal and brain magnetic resonance imaging (MRI) data from a population-based cohort enrolled in the UK Biobank. The following measures were derived: thigh fat-free muscle volume (FFMV), total brain volume (TBV), gray matter volume (GMV), white matter volume (WMV), total hippocampal volume (THV), and white matter hyperintensity volume (WMHV). Participants below sex-based grip strength thresholds suggesting probable sarcopenia were excluded. Linear regression analysis was used to study the interaction or mediation effects of age, sex, and BMI on the associations between FFMV and brain volumes.

Results

Data were available for 20,353 participants (median age 64 years, 53% female). We found interactions between thigh FFMV, BMI, and age (all p < 0.05). Greater thigh FFMV was associated with better brain volumes in those aged <64 years with normal (TBV: β = 2.0 ml/L, p = 0.004; GMV: β = 0.8 ml/L, p = 0.04; WMV: β = 1.1 ml/L, p = 0.006; WMHV: β = -0.2 ml/L, p = 3.7 × 10-5) or low BMI (TBV: β = 21.2 ml/L, p = 0.003; WMV: β = 13.3 ml/L, p = 0.002, WMHV: β = -1.1 ml/L, p = 0.04).

Conclusion

Greater thigh muscle volume correlates with better brain volumes at midlife in people without sarcopenia, but this relationship weakens with greater age and BMI. Further study is required to investigate the underlying mechanisms to understand which components of body composition are potentially modifiable risk factors for dementia.

Body mass index-adjusted calf circumference is associated with mortality in hospitalized older patients with excess weight

OBJECTIVES

Given the innovative nature of the method, our study aimed to assess the prognostic significance of body mass index (BMI)-adjusted calf circumference (CC) in older patients who are hospitalized.

METHODS

This was a unique analysis as part of other cohorts comprising general hospitalized patients aged 60 years or older of both sexes. Only patients with excess weight (BMI ≥ 25 kg/m2) were included. CC was adjusted by reducing 3, 7, or 12 cm for BMI (in kg/m2) within 25-29.9, 30-39.9, and ≥40 kg/m2, respectively. CC was considered low if ≤ 34 cm for males and ≤ 33 cm for females. Clinical outcomes included prolonged length of hospital stay (LOS) and mortality.

RESULTS

A total of 222 patients were included. After BMI adjustments, 72.1% of the patients were reclassified from a normal CC category to a low CC category. The frequency of low CC increased from 33.8% to 81.9% following BMI adjustments. Among those reclassified to the low CC, 11 died, compared to only 2 patients in the group that maintained a normal CC classification. BMI-adjusted CC was inversely associated with mortality (HR adjusted 0.84, 95% CI 0.73 to 0.95), but not with prolonged LOS.

CONCLUSIONS

Our novel study highlights the prognostic value of BMI-adjusted CC. As an anthropometric marker of muscle mass, it proved to be a predictor of mortality in older patients with high BMI. This adjustment is further important because it may help to better detect low muscle mass in these patients where such conditions might be masked.

Reduced Cervical Muscle Fat Infiltrate Is Associated with Self-Reported Recovery from Chronic Idiopathic Neck Pain Over Six Months: A Magnetic Resonance Imaging Longitudinal Cohort Study

Background: It is unclear why neck pain persists or resolves, making assessment and management decisions challenging. Muscle composition, particularly muscle fat infiltrate (MFI), is related to neck pain, but it is unknown whether MFI changes with recovery following targeted interventions. Methods: We compared muscle composition quantified from fat-water magnetic resonance images from the C3 to T1 vertebrae in individuals with and without chronic idiopathic neck pain at two times 6 months apart. Those with neck pain received six weeks of intervention (physiotherapy or chiropractic) after their baseline MRI; at 6 months, they were classified as recovered (≥3 on the 11-point Global Rating of Change scale) or not recovered. Results: At 6 months, both asymptomatic and recovered individuals had decreased MFI compared to baseline (asymptomatic estimated marginal mean difference -1.6% 95%; CI -1.9, -1.4; recovered -1.6; -1.8, -1.4; p < 0.001) whereas those classified as not recovered had increased MFI compared to baseline (0.4; 0.1, 0.7; p = 0.014), independent of age, sex and body mass index. Conclusions: It appears MFI decreases with recovery from neck pain but increases when neck pain persists. The relationship between cervical MFI and neck pain suggests MFI may inform diagnosis, theragnosis and prognosis in individuals with neck pain. Future development of a clinical test for MFI may assist in identifying patients who will benefit from targeted muscle intervention, improving outcomes.

Quantification of volumetric thigh and paravertebral muscle fat content: comparison of quantitative Dixon (Q-Dixon) magnetic resonance imaging (MRI) with high-speed T2-corrected multiecho MR spectroscopy

Background

Muscle fat infiltration (MFI) is increasingly recognized as a critical factor influencing muscle function and metabolic health. Accurate quantification of MFI is essential for diagnosing and monitoring various muscular and metabolic disorders. Quantitative Dixon (Q-Dixon) magnetic resonance imaging (MRI) and high-speed T2-corrected multi-echo (HISTO) magnetic resonance spectroscopy (MRS) are both advanced imaging techniques that offer potential for detailed assessment of MFI. However, the validity and reliability of these methods in measuring volumetric changes in muscle composition, particularly in both thigh and paravertebral muscles, have not been thoroughly compared. This study aims to validate volumetric measurements using Q-Dixon MRI against HISTO MRS in thigh and paravertebral muscles, taking into account the heterogeneity of MFI.

Methods

A retrospective study was conducted with 54 subjects [mean age, 60 years; 38 male (M)/16 female (F)] for thigh muscle and 56 subjects (mean age, 50 years; 22 M/34 F) for paravertebral muscle assessment using a 3-Tesla MRI. The proton density fat fraction (PDFF) was measured with Q-Dixon MRI and HISTO MRS within the upper-middle part of quadriceps femoris and paravertebral muscles at L4/5 level in volumes-of-interest (VOIs). The corresponding volumetric Q-Dixon freehand VOI PDFF was measured. Scatterplots, Bland-Altman plots, Spearman correlation coefficients, and Wilcoxon signed rank test with Bonferroni correction were employed. The Kruskal-Wallis H tests followed by Bonferroni-corrected post hoc tests were analyzed to compare parameter differences with visual MFI grades.

Results

Q-Dixon cubic VOI PDFF correlated positively with HISTO MRS PDFF in thigh (r=0.96, P<0.001) and paravertebral groups (r=0.98, P<0.001), with insignificant differences (P=0.29, 0.82, respectively). Both PDFF values from cubic VOIs in Q-Dixon and HISTO MRS differed from the freehand Q-Dixon PDFF (all P<0.001). Only for <5% HISTO MRS PDFF, there was a difference between HISTO MRS PDFF and Q-Dixon cubic VOI PDFF (P=0.002).

Conclusions

Volumetric Q-Dixon cubic VOI PDFF exhibited good correlation and consistency with HISTO MRS PDFF for quantitative fat assessment in thigh and paravertebral muscles except for muscles with fat fraction <5%, and the Q-Dixon freehand VOI PDFF offers a more comprehensive assessment of the actual MFI compared to cubic VOI.

Fatty infiltration of gastrocnemius-soleus muscle complex: Considerations for myosteatosis rehabilitation

Although previous studies have reported fatty infiltration of the gastrocnemius-soleus complex, little is known about the volumetric distribution and patterns of fatty infiltration. The purpose of this anatomical study was to document and quantify the frequency, distribution, and pattern of fatty infiltration of the gastrocnemius-soleus complex. One hundred formalin-embalmed specimens (mean age 78.1 ± 12.3 years; 48F/52M) were serially dissected to document the frequency, distribution, and pattern of fatty infiltration in the medial and lateral heads of gastrocnemius and soleus muscles. Fatty infiltration was found in 23% of specimens, 13 unilaterally (8F/5M) and 10 (5M/5F) bilaterally. The fatty infiltration process was observed to begin medially from the medial aspect of the medial head of gastrocnemius and medial margin of soleus and then progressed laterally throughout the medial head of gastrocnemius and the marginal, anterior, and posterior soleus. The lateral head of gastrocnemius remained primarily muscular in all specimens. Microscopically, the pattern of infiltration was demonstrated as intramuscular with intact aponeuroses, and septa. The remaining endo-, peri-, and epimysium preserved the overall contour of the gastrocnemius-soleus complex, even in cases of significant fatty replacement. Since the external contour of the calf is preserved, the presence of fatty infiltration may be underdiagnosed in the clinic without imaging. Myosteatosis is associated with gait and balance challenges in the elderly, which can impact quality of life and result in increased risk of falling. The findings of the study have implications in the rehabilitation management of elderly patients with sarcopenia and myosteatosis.

Intermuscular adipose tissue accumulation is associated with higher tissue sodium in healthy individuals

BACKGROUND AND AIMS

High tissue sodium accumulation and intermuscular adipose tissue (IMAT) are associated with aging, type 2 diabetes, and chronic kidney disease. In this study, we aim to investigate whether high lower-extremity tissue sodium accumulation relates to IMAT quantity and whether systemic inflammatory mediators and adipocytokines contribute to such association.

METHODS

Tissue sodium content and IMAT accumulation (percentage of IMAT area to muscle area) were measured in 83 healthy individuals using sodium imaging (23Na-MRI) and proton (1H-MRI) imaging of the calf. Insulin sensitivity was assessed by glucose disposal rate (GDR) measured with the hyperinsulinemic-euglycemic clamp.

RESULTS

Median (interquartile range) muscle and skin sodium contents were 16.6 (14.9, 19.0) and 12.6 (10.9, 16.7) mmol/L, respectively. Median IMAT was 3.69 (2.80, 5.37) %. In models adjusted for age, sex, BMI, GDR, adiponectin, and high-sensitivity C-reactive protein, increasing tissue sodium content was significantly associated with higher IMAT quantity (p = 0.018 and 0.032 for muscle and skin tissue sodium, respectively). In subgroup analysis stratified by sex, skin sodium was significantly associated with IMAT only among men. In interaction analysis, the association between skin sodium and IMAT was greater with increasing levels of high-sensitivity C-reactive protein and interleukin-6 (p for interaction = 0.022 and 0.006, respectively).

CONCLUSIONS

Leg muscle and skin sodium are associated with IMAT quantity among healthy individuals. The relationship between skin sodium and IMAT may be mediated by systemic inflammation.

Use of computed tomography to identify muscle quality subgroups, spatial mapping, and preliminary relationships to function in those with diabetic peripheral neuropathy

BACKGROUND

Decreased muscle volume and increased muscle-associated adipose tissue (MAAT, sum of intra and inter-muscular adipose tissue) of the foot intrinsic muscle compartment are associated with deformity, decreased function, and increased risk of ulceration and amputation in those with diabetic peripheral neuropathy (DPN).

RESEARCH QUESTION

What is the muscle quality (normal, abnormal muscle, and adipose volumes) of the DPN foot intrinsic compartment, how does it change over time, and is muscle quality related to gait and foot function?

METHODS

Computed tomography was performed on the intrinsic foot muscle compartment of 45 subjects with DPN (mean age: 67.2 ± 6.4 years) at baseline and 3.6 years. Images were processed to obtain volumes of MAAT, highly abnormal, mildly abnormal, and normal muscle. For each category, annual rates of change were calculated. Paired t-tests compared baseline and follow-up. Foot function during gait was assessed using 3D motion analysis and the Foot and Ankle Ability Measure. Correlations between muscle compartment and foot function during gait were analyzed using Pearson's correlations.

RESULTS

Total muscle volume decreased, driven by a loss of normal muscle and mildly abnormal muscle (p<0.05). MAAT and the adipose-muscle ratio increased. At baseline, 51.5% of the compartment was abnormal muscle or MAAT, increasing to 55.0% at follow-up. Decreased total muscle volume correlated with greater midfoot collapse during gait (r = -0.40, p = 0.02). Greater volumes of highly abnormal muscle correlated with a lower FAAM score (r = -0.33, p = 0.03).

SIGNIFICANCE

Muscle volume loss may progress in parallel with MAAT accumulation, impacting contractile performance in individuals with DPN. Only 48.5% of the DPN intrinsic foot muscle compartment consists of normal muscle and greater abnormal muscle is associated with worse foot function. These changes identify an important target for rehabilitative intervention to slow or prevent muscle deterioration and poor foot outcomes.

Impaired skeletal muscle regeneration in diabetes: From cellular and molecular mechanisms to novel treatments

Diabetes represents a major public health concern with a considerable impact on human life and healthcare expenditures. It is now well established that diabetes is characterized by a severe skeletal muscle pathology that limits functional capacity and quality of life. Increasing evidence indicates that diabetes is also one of the most prevalent disorders characterized by impaired skeletal muscle regeneration, yet underlying mechanisms and therapeutic treatments remain poorly established. In this review, we describe the cellular and molecular alterations currently known to occur during skeletal muscle regeneration in people with diabetes and animal models of diabetes, including its associated comorbidities, e.g., obesity, hyperinsulinemia, and insulin resistance. We describe the role of myogenic and non-myogenic cell types on muscle regeneration in conditions with or without diabetes. Therapies for skeletal muscle regeneration and gaps in our knowledge are also discussed, while proposing future directions for the field.

Comprehensive review on lipid metabolism and RNA methylation: Biological mechanisms, perspectives and challenges

Adipose tissue plays a crucial role in maintaining energy balance, regulating hormones, and promoting metabolic health. To address disorders related to obesity and develop effective therapies, it is essential to have a deep understanding of adipose tissue biology. In recent years, RNA methylation has emerged as a significant epigenetic modification involved in various cellular functions and metabolic pathways. Particularly in the realm of adipogenesis and lipid metabolism, extensive research is ongoing to uncover the mechanisms and functional importance of RNA methylation. Increasing evidence suggests that RNA methylation plays a regulatory role in adipocyte development, metabolism, and lipid utilization across different organs. This comprehensive review aims to provide an overview of common RNA methylation modifications, their occurrences, and regulatory mechanisms, focusing specifically on their intricate connections to fat metabolism. Additionally, we discuss the research methodologies used in studying RNA methylation and highlight relevant databases that can aid researchers in this rapidly advancing field.

Prevalence of low calf circumference in hospitalized patients classified by raw or body mass index-adjusted values

BACKGROUND

Adiposity can influence the estimation of muscle mass using calf circumference (CC) and underestimate the frequency of low CC. An adjustment for CC using body mass index (BMI) was proposed to reduce this effect. We aimed to compare the low CC frequency in hospitalized patients when considering raw and BMI-adjusted values and explore data by sex, age, and race (white and non-white).

METHODS

Secondary analysis from two cohort studies conducted with adult hospitalized patients using BMI and CC data collected in the first 72 h after hospital admission. We classified low CC by two approaches: (1) raw CC; (2) BMI-adjusted CC for patients with BMI ≥ 25. Cutoff values for low CC were ≤34 cm (men) and ≤33 cm (women).

RESULTS

Among 1272 patients (54.1 ± 15.3 years old; 51.7% women; 82.1% White race), low CC frequency was 30.6% and low BMI-adjusted CC was 68.9%. For all elevated BMI categories, the low CC frequency was higher when considering BMI-adjusted values (P < 0.001). Low CC was more frequent (P < 0.001) in older adults (38.7% by raw; 79.1% by BMI-adjusted value) than in younger adults (27.6% by raw; 65.2% by BMI-adjusted value) and it was not associated with race. Low CC by raw values was more frequent in men than in women (35.0% versus 26.4%; P = 0.001), but did not differ between sexes when classified by BMI-adjusted values (70.7% versus 67.1%; P = 0.184).

CONCLUSION

Low CC BMI adjusted was 2.2 times more frequent in comparison with raw CC values, and it was identified in >60% of patients with BMI ≥ 25.

Studying intramuscular fat deposition and muscle regeneration: insights from a comparative analysis of mouse strains, injury models, and sex differences

Intramuscular fat (IMAT) infiltration, pathological adipose tissue that accumulates between muscle fibers, is a shared hallmark in a diverse set of diseases including muscular dystrophies and diabetes, spinal cord and rotator cuff injuries, as well as sarcopenia. While the mouse has been an invaluable preclinical model to study skeletal muscle diseases, they are also resistant to IMAT formation. To better understand this pathological feature, an adequate pre-clinical model that recapitulates human disease is necessary. To address this gap, we conducted a comprehensive in-depth comparison between three widely used mouse strains: C57BL/6J, 129S1/SvlmJ and CD1. We evaluated the impact of strain, sex and injury type on IMAT formation, myofiber regeneration and fibrosis. We confirm and extend previous findings that a Glycerol (GLY) injury causes significantly more IMAT and fibrosis compared to Cardiotoxin (CTX). Additionally, females form more IMAT than males after a GLY injury, independent of strain. Of all strains, C57BL/6J mice, both females and males, are the most resistant to IMAT formation. In regard to injury-induced fibrosis, we found that the 129S strain formed the least amount of scar tissue. Surprisingly, C57BL/6J of both sexes demonstrated complete myofiber regeneration, while both CD1 and 129S1/SvlmJ strains still displayed smaller myofibers 21 days post injury. In addition, our data indicate that myofiber regeneration is negatively correlated with IMAT and fibrosis. Combined, our results demonstrate that careful consideration and exploration are needed to determine which injury type, mouse model/strain and sex to utilize as preclinical model especially for modeling IMAT formation.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Association of Calf Circumference with Clinical and Biochemical Markers in Older Adults with COVID-19 Admitted at Intensive Care Unit: A Retrospective Cross-Sectional Study

BACKGROUND

COVID-19 is an infectious disease characterized by a severe catabolic and inflammatory state, leading to loss of muscle mass. The assessment of muscle mass can be useful to identify nutritional risk and assist in early management, especially in older adults who have high nutritional risks. The aim of this study was to evaluate the association of calf circumference (CC) with clinical and biochemical markers and mortality in older adults with COVID-19 admitted to the intensive care unit (ICU).

METHODS

A retrospective cross-sectional study was conducted in a public hospital. CC was adjusted for body mass index (BMI), reducing 3, 7, or 12 cm for a BMI of 25-29.9, 30-39.9, and ≥40 kg/m2, respectively, and classified as reduced when <33 cm for women and <34 cm for men. Pearson's correlation between BMI and CC was performed to assess the association between variables. Regression analysis was adjusted for sex, age, and BMI variables. Cox regression was used to assess survival related to CC.

RESULTS

A total of 208 older adults diagnosed with COVID-19 admitted to ICU were included, of which 84% (n = 176) were classified as having reduced CC. These patients were older, with lower BMI, higher nutritional risk, malnourished, and higher concentration of urea and urea-creatinine ratio (UCR) compared with the group with normal CC. There was an association between edematous patients at nutritional risk and malnourished with reduced CC in the Cox regression, either adjusted or not for confounding.

CONCLUSIONS

CC was not associated with severity, biochemical markers, or mortality in older adults with COVID-19 admitted to the ICU, but it was associated with moderately malnourished patients assessed by subjective global assessment (SGA).

Association of physical activity with fatty infiltration of muscles after total hip arthroplasty

OBJECTIVE

This study aimed to investigate the association between muscle density as an indicator of fatty infiltration of lower extremity muscles and physical activity (PA) after total hip arthroplasty (THA) and identify the patient characteristics with high postoperative PA.

METHODS

This study included 62 female patients who underwent THA for unilateral hip osteoarthritis. Muscle density of the gluteus maximus, gluteus medius, iliopsoas, and quadriceps muscles was measured using computed tomography (CT). PA was assessed using University of California, Los Angeles (UCLA) activity scores. CT and UCLA activity score were obtained before and 1 year after THA. The patients were divided into two groups, sufficient (score ≥ 6) and insufficient (score < 6) activity groups, based on their level of PA as determined by their UCLA activity score 1 year after THA. The association of PA with the amount of changes in muscle density was examined with Spearman's rank correlation coefficient. Logistic regression analysis was performed to identify postoperative factors determining PA at 1 year after THA.

RESULTS

Spearman's rank correlation coefficient showed a significantly positive association between recovery in PA and an increase in muscle density of the gluteus maximus, gluteus medius, iliopsoas, and quadriceps muscles. Additionally, logistic regression analysis confirmed that postoperative muscle densities of the gluteus maximus and quadriceps muscles were variables determining the PA 1 year after THA.

CONCLUSION

The findings of this study indicated that the improvement of fatty infiltration in lower limb muscles, especially in the gluteus maximus and quadriceps, is likely to promote the increase in postoperative PA.

The effects of myosteatosis on skeletal muscle function in older adults

Myosteatosis, or the infiltration of fatty deposits into skeletal muscle, occurs with advancing age and contributes to the health and functional decline of older adults. Myosteatosis and its inflammatory milieu play a larger role in adipose tissue dysfunction, muscle tissue dysfunction, and increased passive muscle stiffness. Combined with the age-related decline of sex hormones and development of anabolic resistance, myosteatosis also contributes to insulin resistance, impaired muscle mechanics, loss of force production from the muscle, and increased risk of chronic disease. Due to its highly inflammatory secretome and the downstream negative effects on muscle metabolism and mechanics, myosteatosis has become an area of interest for aging researchers and clinicians. Thus far, myosteatosis treatments have had limited success, as many lack the potency to completely rescue the metabolic and physical consequences of myosteatosis. Future research is encouraged for the development of reliable assessment methods for myosteatosis, as well as the continued exploration of pharmacological, nutritional, and exercise-related interventions that may lead to the success in attenuating myosteatosis and its clinical consequences within the aging population.

Gromwell (Lithospermum erythrorhizon) Attenuates High-Fat-Induced Skeletal Muscle Wasting by Increasing Protein Synthesis and Mitochondrial Biogenesis

Gromwell (Lithospermum erythrorhizon, LE) can mitigate obesity-induced skeletal muscle atrophy in C2C12 myotubes and high-fat diet (HFD)-induced obese mice. The purpose of this study was to investigate the anti-skeletal muscle atrophy effects of LE and the underlying molecular mechanism. C2C12 myotubes were pretreated with LE or shikonin, and active component of LE, for 24 h and then treated with 500 μM palmitic acid (PA) for an additional 24 h. Additionally, mice were fed a HFD for 8 weeks to induced obesity, and then fed either the same diet or a version containing 0.25% LE for 10 weeks. LE attenuated PA-induced myotubes atrophy in differentiated C2C12 myotubes. The supplementation of LE to obese mice significantly increased skeletal muscle weight, lean body mass, muscle strength, and exercise performance compared with those in the HFD group. LE supplementation not only suppressed obesity-induced skeletal muscle lipid accumulation, but also downregulated TNF-α and atrophic genes. LE increased protein synthesis in the skeletal muscle via the mTOR pathway. We observed LE induced increase of mitochondrial biogenesis and upregulation of oxidative phosphorylation related genes in the skeletal muscles. Furthermore, LE increased the expression of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha and the phosphorylation of adenosine monophosphate-activated protein kinase. Collectively, LE may be useful in ameliorating the detrimental effects of obesity-induced skeletal muscle atrophy through the increase of protein synthesis and mitochondrial biogenesis of skeletal muscle.

Does Obesity Affect the Rate of Force Development in Plantar Flexor Muscles among Older Adults?

The literature offers limited information on the effect of obesity on the rate of force development (RFD), a critical parameter for mobility in older adults. The objectives of this study were to explore the influence of obesity on the RFD in older adults and to examine the association between this neuromuscular parameter and walking speed. The participants (42 older adults) were classified into two groups: the control group (CG, n = 22; mean age = 81.13 ± 4.02 years; body mass index (BMI) = 25.13 ± 3.35 kg/m2), and the obese group (OG, n = 20; mean age = 77.71 ± 2.95 years; BMI = 34.46 ± 3.25 kg/m2). Walking speed (m/s) was measured using the 10 m walking test. Neuromuscular parameters of the plantar flexors were evaluated during a maximal voluntary contraction test using a dynamometer. The RFD was calculated from the linear slop of the force-time curve in the following two phases: from the onset of the contraction to 50 ms (RFD0-50) and from 100 to 200 ms (RFD100-200). The gait speed was lower in the OG compared to the CG (p < 0.001). The RFD50/100 and RFD100/200 were lower in the OG compared to the CG (p < 0.001). The RFD50/100 was found to be the predominant influencer on gait speed in the OG. In conclusion, obesity negatively impacts the RFD in older adults and RFD stands out as the primary factor among the studied parameters influencing gait speed.

SARC-F and modified versions using arm and calf circumference: Diagnostic performance for sarcopenia screening and the impact of obesity

AIM

SARC-F is limited by low sensitivity for sarcopenia identification. As surrogates of muscle mass, mid-arm circumference (MAC) and/or calf circumference have been proposed as additions to SARC-F to enhance sarcopenia identification. The aim of this study was to evaluate the diagnostic performance of SARC-F, SARC-CalF, SARC-F + MAC, and SARC-CalF + MAC in sarcopenia detection, and to assess the impact of obesity on their diagnostic performance.

METHODS

We studied 230 healthy non-frail community-dwelling older adults age >50 years. We performed receiver operating characteristic curve analysis for SARC-F, SARC-CalF, SARC-F + MAC and SARC-CalF + MAC against sarcopenia diagnosed by the Asian Working Group for Sarcopenia (AWGS) 2019 as the reference standard. Obesity was defined by high waist circumference (men ≥90 cm, women ≥80 cm). We performed subgroup analysis to compare between obese and non-obese groups.

RESULTS

The prevalence of sarcopenia was 27.0% by AWGS 2019. SARC-CalF + MAC had the best diagnostic performance (area under the curve [AUC] 0.74, 95% confidence interval [CI] 0.67-0.81; sensitivity 66.1%; specificity 69.1%), followed by SARC-CalF (AUC 0.70, 95% CI 0.62-0.78; sensitivity 21.0%; specificity 95.8%). SARC-F (AUC 0.57, 95% CI 0.49-0.66; sensitivity 0%; specificity 100%) performed significantly worsethan its modified versions (P < 0.05). There was higher accuracy of sarcopenia identification in obese compared with non-obese groups for SARC-F + MAC (AUC 0.75, 95% CI 0.65-0.85 vs. 0.58, 95% CI 0.46-0.70) and SARC-CalF + MAC (AUC 0.75, 95% CI 0.66-0.85 vs. 0.70, 95% CI 0.59-0.81).

CONCLUSIONS

The addition of arm circumference to SARC-CalF confers better diagnostic accuracy for sarcopenia identification, especially in the obese group. Thus, MAC may complement SARC-CalF for community screening of sarcopenia amongst healthy community-dwelling older adults by increasing sensitivity for the detection of sarcopenic obesity. Geriatr Gerontol Int 2024; 24: 182-188.

Population-scale skeletal muscle single-nucleus multi-omic profiling reveals extensive context specific genetic regulation

Skeletal muscle, the largest human organ by weight, is relevant to several polygenic metabolic traits and diseases including type 2 diabetes (T2D). Identifying genetic mechanisms underlying these traits requires pinpointing the relevant cell types, regulatory elements, target genes, and causal variants. Here, we used genetic multiplexing to generate population-scale single nucleus (sn) chromatin accessibility (snATAC-seq) and transcriptome (snRNA-seq) maps across 287 frozen human skeletal muscle biopsies representing 456,880 nuclei. We identified 13 cell types that collectively represented 983,155 ATAC summits. We integrated genetic variation to discover 6,866 expression quantitative trait loci (eQTL) and 100,928 chromatin accessibility QTL (caQTL) (5% FDR) across the five most abundant cell types, cataloging caQTL peaks that atlas-level snATAC maps often miss. We identified 1,973 eGenes colocalized with caQTL and used mediation analyses to construct causal directional maps for chromatin accessibility and gene expression. 3,378 genome-wide association study (GWAS) signals across 43 relevant traits colocalized with sn-e/caQTL, 52% in a cell-specific manner. 77% of GWAS signals colocalized with caQTL and not eQTL, highlighting the critical importance of population-scale chromatin profiling for GWAS functional studies. GWAS-caQTL colocalization showed distinct cell-specific regulatory paradigms. For example, a C2CD4A/B T2D GWAS signal colocalized with caQTL in muscle fibers and multiple chromatin loop models nominated VPS13C, a glucose uptake gene. Sequence of the caQTL peak overlapping caSNP rs7163757 showed allelic regulatory activity differences in a human myocyte cell line massively parallel reporter assay. These results illuminate the genetic regulatory architecture of human skeletal muscle at high-resolution epigenomic, transcriptomic, and cell state scales and serve as a template for population-scale multi-omic mapping in complex tissues and traits.

Age-related Muscle Fat Infiltration in Lung Screening Participants: Impact of Smoking Cessation

Rationale

Skeletal muscle fat infiltration progresses with aging and is worsened among individuals with a history of cigarette smoking. Many negative impacts of smoking on muscles are likely reversible with smoking cessation.

Objectives

To determine if the progression of skeletal muscle fat infiltration with aging is altered by smoking cessation among lung cancer screening participants.

Methods

This was a secondary analysis based on the National Lung Screening Trial. Skeletal muscle attenuation in Hounsfield unit (HU) was derived from the baseline and follow-up low-dose CT scans using a previously validated artificial intelligence algorithm. Lower attenuation indicates greater fatty infiltration. Linear mixed-effects models were constructed to evaluate the associations between smoking status and the muscle attenuation trajectory.

Measurements and Main Results

Of 19,019 included participants (age: 61 years, 5 [SD]; 11,290 males), 8,971 (47.2%) were actively smoking cigarettes. Accounting for body mass index, pack-years, percent emphysema, and other confounding factors, actively smoking predicted a lower attenuation in both males (β0 =-0.88 HU, P<.001) and females (β0 =-0.69 HU, P<.001), and an accelerated muscle attenuation decline-rate in males (β1=-0.08 HU/y, P<.05). Age-stratified analyses indicated that the accelerated muscle attenuation decline associated with smoking likely occurred at younger age, especially in females.

Conclusions

Among lung cancer screening participants, active cigarette smoking was associated with greater skeletal muscle fat infiltration in both males and females, and accelerated muscle adipose accumulation rate in males. These findings support the important role of smoking cessation in preserving muscle health.

The use of non-invasive imaging modalities for the assessment of skeletal muscle quantity and quality in people with HIV: A narrative review

BACKGROUND

People with HIV (PWH) are prone to mobility impairments and physical dysfunction, with the loss of skeletal muscle quantity and quality being a major contributor to the dysfunction. Assessment of skeletal muscle is an important component of care for this patient population for early intervention and treatment. The use of non-invasive imaging techniques to evaluate skeletal muscle, such as dual X-ray absorptiometry, computer tomography and magnetic resonance imaging, has increased in popularity in recent years.

PURPOSE

This narrative review synthesizes the use of these techniques and summarizes the associations between outcomes from these imaging modalities and physical function in PWH.

Lower Adherence to a Mediterranean Diet Is Associated with High Adiposity in Community-Dwelling Older Adults: Results from the Longevity Check-Up (Lookup) 7+ Project

High adiposity impacts health and quality of life in old age, owing to its association with multimorbidity, decreased physical performance, and frailty. Whether a high adherence to a Mediterranean diet (Medi-Diet) is associated with reduced body adiposity in older adults is unclear. The present study was conducted to assess the prevalence of high adiposity in a large sample of community-dwelling older adults. We also explored the relationship between whole-body adiposity estimated through relative fat mass (RFM) and Medi-Diet adherence. Data were obtained from the Longevity Check-up 7+ (Lookup7+) project database. RFM was estimated from anthropometric and personal parameters using a validated equation. RFM was categorized as high if ≥40% in women and ≥30% in men. Information on diet was collected using a food frequency questionnaire, while Medi-Diet adherence was assessed through a modified version of the Medi-Lite scoring system. Analyses were conducted in 2092 participants (mean age 73.1 ± 5.9 years; 53.4% women). Mean RFM was 39.6 ± 5.14% in women and 29.0 ± 3.6% in men. High adiposity was found in 971 (46.4%) participants and was more frequent in those with a low (54.2%) or moderate (46.4%) Medi-Diet adherence compared with the high-adherence group (39.7%, p < 0.001). Logistic regression indicated that older adults with high Medi-Diet adherence were less likely to have a high RFM. Other factors associated with a greater risk of having high adiposity were older age, female sex, and physical inactivity. Our findings support an association between healthy lifestyles, including a greater adherence to a Mediterranean-style diet, and lower body adiposity in older adults.

Fat infiltration of the posterior paraspinal muscles is inversely associated with the fat infiltration of the psoas muscle: a potential compensatory mechanism in the lumbar spine

BACKGROUND

The function of the paraspinal muscles and especially the psoas muscle in maintaining an upright posture is not fully understood. While usually considered solely as a hip flexor, the psoas muscle and its complex anatomy suggest that the muscle has other functions involved in stabilizing the lumbar spine. The aim of this study is to determine how the psoas muscle and the posterior paraspinal muscles (PPM; erector spinae and multifidus) interact with each other.

METHODS

A retrospective review including patients undergoing posterior lumbar fusion surgery between 2014 and 2021 at a tertiary care center was conducted. Patients with a preoperative lumbar magnetic resonance imaging (MRI) scan performed within 12 months prior to surgery were considered eligible. Exclusion criteria included previous spinal surgery at any level, lumbar scoliosis with a Cobb Angle > 20° and patients with incompatible MRIs. MRI-based quantitative assessments of the cross-sectional area (CSA), the functional cross-sectional area (fCSA) and the fat area (FAT) at L4 was conducted. The degree of fat infiltration (FI) was further calculated. FI thresholds for FIPPM were defined according to literature and patients were divided into two groups (< or ≥ 50% FIPPM).

RESULTS

One hundred ninetypatients (57.9% female) with a median age of 64.7 years and median BMI of 28.3 kg/m2 met the inclusion criteria and were analyzed. Patients with a FIPPM ≥ 50% had a significantly lower FI in the psoas muscle in both sexes. Furthermore, a significant inverse correlation was evident between FIPPM and FIPsoas for both sexes. A significant positive correlation between FATPPM and fCSAPsoas was also found for both sexes. No significant differences were found for both sexes in both FIPPM groups.

CONCLUSION

As the FIPPM increases, the FIPsoas decreases. Increased FI is a surrogate marker for a decrease in muscular strength. Since the psoas and the PPM both segmentally stabilize the lumbar spine, these results may be indicative of a potential compensatory mechanism. Due to the weakened PPM, the psoas may compensate for a loss in strength in order to stabilize the spine segmentally.

Adiposity is associated with widespread transcriptional changes and downregulation of longevity pathways in aged skeletal muscle

BACKGROUND

Amongst healthy older people, a number of correlates of impaired skeletal muscle mass and function have been defined. Although the prevalence of obesity is increasing markedly in this age group, information is sparse about the particular impacts of obesity on ageing skeletal muscle or the molecular mechanisms that underlie this and associated disease risk.

METHODS

Here, we examined genome-wide transcriptional changes using RNA sequencing in muscle biopsies from 40 older community-dwelling men from the Hertfordshire Sarcopenia Study with regard to obesity (body mass index [BMI] >30 kg/m2 , n = 7), overweight (BMI 25-30, n = 19), normal weight (BMI < 25, n = 14), and per cent and total fat mass. In addition, we used EPIC DNA methylation array data to investigate correlations between DNA methylation and gene expression in aged skeletal muscle tissue and investigated the relationship between genes within altered regulatory pathways and muscle histological parameters.

RESULTS

Individuals with obesity demonstrated a prominent modified transcriptional signature in muscle tissue, with a total of 542 differentially expressed genes associated with obesity (false discovery rate ≤0.05), of which 425 genes were upregulated when compared with normal weight. Upregulated genes were enriched in immune response (P = 3.18 × 10-41 ) and inflammation (leucocyte activation, P = 1.47 × 10-41 ; tumour necrosis factor, P = 2.75 × 10-15 ) signalling pathways and downregulated genes enriched in longevity (P = 1.5 × 10-3 ) and AMP-activated protein kinase (AMPK) (P = 4.5 × 10-3 ) signalling pathways. Furthermore, differentially expressed genes in both longevity and AMPK signalling pathways were associated with a change in DNA methylation, with a total of 256 and 360 significant cytosine-phosphate-guanine-gene correlations identified, respectively. Similar changes in the muscle transcriptome were observed with respect to per cent fat mass and total fat mass. Obesity was further associated with a significant increase in type II fast-fibre area (P = 0.026), of which key regulatory genes within both longevity and AMPK pathways were significantly associated.

CONCLUSIONS

We provide for the first time a global transcriptomic profile of skeletal muscle in older people with and without obesity, demonstrating modulation of key genes and pathways implicated in the regulation of muscle function, changes in DNA methylation associated with such pathways and associations between genes within the modified pathways implicated in muscle regulation and changes in muscle fibre type.

Obesity-Related Knee Osteoarthritis-Current Concepts

The knee is the joint most frequently involved in osteoarthritis and represents a significant contributor to patient morbidity and impaired functional status. Major risk factors include genetics, age, sex, mechanical load and obesity/metabolic syndrome. Recent studies highlighted the role of obesity and metabolic syndrome in the pathogenesis of knee osteoarthritis not simply through increased mechanical loading but the systemic effects of obesity-induced inflammation. The current concept of knee osteoarthritis is that of a 'whole joint disease', which highlights the involvement not only of articular cartilage but also the synovium, subchondral bone, ligaments and muscles. Obesity and metabolic syndrome are associated with higher levels of pro-inflammatory cytokines, increased production of adipokines with both protective and destructive effects on articular cartilage, an up-regulation of proteolytic enzymes such as matrix metalloproteinases and aggrecanases and an increase in free fatty acids and reactive oxygen species induced by dyslipidemia. These findings underscore that the adequate management of knee osteoarthritis needs to include an optimization of body weight and a beneficial mobility regimen. The possible introduction of pharmacological therapy targeting specific molecules involved in the pathogenesis of obesity-related osteoarthritis will likely also be considered in future therapeutic strategies, including personalized treatment approaches.

Alterations in skeletal muscle morphology and mechanics in juvenile male Sprague Dawley rats exposed to a high-fat high-sucrose diet

Although once a health concern largely considered in adults, the obesity epidemic is now prevalent in pediatric populations. While detrimental effects on skeletal muscle function have been seen in adulthood, the effects of obesity on skeletal muscle function in childhood is not clearly understood. The purpose of this study was to determine if the consumption of a high-fat high-sucrose (HFS) diet, starting in the post-weaning period, leads to changes in skeletal muscle morphology and mechanics after 14 weeks on the HFS diet. Eighteen 3-week-old male CD-Sprague Dawley rats were randomly assigned to a HFS (C-HFS, n = 10) or standard chow diet (C-CHOW, n = 8). Outcome measures included: weekly energy intake, activity levels, oxygen consumption, body mass, body composition, metabolic profile, serum protein levels, and medial gastrocnemius gene expression, morphology, and mechanics. The main findings from this study were that C-HFS rats: (1) had a greater body mass and percent body fat than control rats; (2) showed early signs of metabolic syndrome; (3) demonstrated potential impairment in muscle remodeling; (4) produced lower relative muscle force; and (5) had a shift in the force-length relationship, indicating that the medial gastrocnemius had shorter muscle fiber lengths compared to those of C-CHOW rats. Based on the results of this study, we conclude that exposure to a HFS diet led to increased body mass, body fat percentage, and early signs of metabolic syndrome, resulting in functional deficits in MG of childhood rats.

Effects of free weight and body mass-based resistance training on thigh muscle size, strength and intramuscular fat in healthy young and middle-aged individuals

NEW FINDINGS

What is the central question of this study? How do free weight resistance training (RT) and body mass-based RT for 8 weeks compare for isometric muscular strength, muscle size and intramuscular fat (IMF) content in the quadriceps femoris? What is the main finding and its importance? Free weight and body mass-based RTs could induce muscle hypertrophy; however, decreased IMF content was observed following the body mass-based RT alone.

ABSTRACT

The objective of this study was to investigate the effects of free weight and body mass-based resistance training (RT) on muscle size and thigh intramuscular fat (IMF) in young and middle-aged individuals. Healthy individuals (aged 30-64 years) were assigned to either a free weight RT group (n = 21) or a body mass-based RT group (n = 16). Both groups performed whole-body resistance exercise twice a week for 8 weeks. Free weight resistance exercises (squats, bench press, deadlift, dumbbell rows and back range) involved 70% one repetition maximum, with three sets of 8-12 repetitions per exercise. The nine body mass-based resistance exercises (leg raise, squats, rear raise, overhead shoulder mobility exercise, rowing, dips, lunge, single-leg Romanian deadlifts and push-ups) included the maximum possible repetitions per session, which were performed in one or two sets. Mid-thigh magnetic resonance images using the two-point Dixon method were taken pre- and post-training. The muscle cross-sectional area (CSA) and IMF content in the quadriceps femoris were measured from the images. Both the groups showed significantly increased muscle CSA post-training (free weight RT group, P = 0.001; body mass-based RT group, P = 0.002). IMF content in the body mass-based RT group significantly decreased (P = 0.036) but did not significantly change in the free weight RT group (P = 0.076). These results suggest that the free weight and body mass-based RTs could induce muscle hypertrophy; however, in healthy young and middle-aged individuals, decreased IMF content was induced following the body mass-based RT alone.

Decellularization-Based Quantification of Skeletal Muscle Fatty Infiltration

Fatty infiltration is the accumulation of adipocytes between myofibers in skeletal muscle and is a prominent feature of many myopathies, metabolic disorders, and dystrophies. Clinically in human populations, fatty infiltration is assessed using noninvasive methods, including computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US). Although some studies have used CT or MRI to quantify fatty infiltration in mouse muscle, costs and insufficient spatial resolution remain challenging. Other small animal methods utilize histology to visualize individual adipocytes; however, this methodology suffers from sampling bias in heterogeneous pathology. This protocol describes the methodology to qualitatively view and quantitatively measure fatty infiltration comprehensively throughout intact mouse muscle and at the level of individual adipocytes using decellularization. The protocol is not limited to specific muscles or specific species and can be extended to human biopsy. Additionally, gross qualitative and quantitative assessments can be made with standard laboratory equipment for little cost, making this procedure more accessible across research laboratories.

Single-nucleus and bulk RNA sequencing reveal cellular and transcriptional mechanisms underlying lipid dynamics in high marbled pork

Pork is the most consumed meat in the world, and its quality is associated with human health. Intramuscular fat (IMF) deposition (also called marbling) is a key factor positively correlated with various quality traits and lipo-nutritional values of meat. However, the cell dynamics and transcriptional programs underlying lipid deposition in highly marbled meat are still unclear. Here, we used Laiwu pigs with high (HLW) or low (LLW) IMF contents to explore the cellular and transcriptional mechanisms underlying lipid deposition in highly-marbled pork by single-nucleus RNA sequencing (snRNA-seq) and bulk RNA sequencing. The HLW group had higher IMF contents but less drip loss than the LLW group. Lipidomics results revelled the changes of overall lipid classes composition (e.g., glycerolipids including triglycerides, diglycerides, and monoglycerides; sphingolipids including ceramides and monohexose ceramide significantly increased) between HLW and LLW groups. SnRNA-seq revealed nine distinct cell clusters, and the HLW group had a higher percentage of adipocytes (1.40% vs. 0.17%) than the LLW group. We identified 3 subpopulations of adipocytes, including PDE4D⁺/PDE7B⁺ (in HLW and LLW), DGAT2⁺/SCD⁺ (mostly in HLW) and FABP5⁺/SIAH1⁺ cells (mostly in HLW). Moreover, we showed that fibro/adipogenic progenitors could differentiate into IMF cells and contribute to 43.35% of adipocytes in mice. In addition, RNA-seq revealed different genes involved in lipid metabolism and fatty acid elongation. Our study provides new insights into the cellular and molecular signatures of marbling formation; such knowledge may facilitate the development of new strategies to increase IMF deposition and the lipo-nutritional quality of high marbled pork.

Increased adiposity is associated with altered skeletal muscle energetics

The objective of this pilot study was to characterize relationships between skeletal muscle energy metabolism and body composition in healthy adults with varied amounts and distribution of adipose tissue. In vivo muscle energetics were quantified using dynamic 31P magnetic resonance spectroscopy with knee extension exercise standardized to subject lean body mass. Spearman's correlation analysis examined relationships between muscle metabolism indices and measures of adiposity including body mass index (BMI), total body fat, and quadriceps intermuscular adipose tissue (IMAT). Post hoc partial correlations were examined controlling for additional body composition measures. Kruskal-Wallis tests with Dunn-Sidak post hoc comparisons evaluated group differences in energy metabolism based on body composition profiles (i.e., lean, normal-weight obese, and overweight-obese) and IMAT tertiles. BMI negatively correlated with end-exercise muscle pH after correcting for IMAT and total body fat (r = -0.46, P = 0.034). Total adiposity negatively correlated with maximum oxidative capacity after correcting for IMAT (r = -0.54, P = 0.013). IMAT positively correlated with muscle proton buffering capacity after correcting for total body fat (r = 0.53, P = 0.023). Body composition groups showed differences in end-exercise fall in [PCr] with normalized workload (P = 0.036; post hoc: overweight-obese < lean, P = 0.029) and maximum oxidative capacity (P = 0.021; post hoc: normal-weight obese < lean, P = 0.016). IMAT tertiles showed differences in end-exercise fall in [PCr] with normalized workload (P = 0.035; post hoc: 3rd < 1st, P = 0.047). Taken together, these results support increased adiposity is associated with reduced muscle energetic efficiency with more reliance on glycolysis, and when accompanied with reduced lean mass, is associated with reduced maximum oxidative capacity.NEW & NOTEWORTHY Skeletal muscle energy production is influenced by both lean body mass and adipose tissue but the effect of their distribution on energy metabolism is unclear. This study examined variations in quadriceps muscle energy metabolism in healthy adults with varied relative amounts of lean and adipose tissue. Results suggest increased adiposity is associated with reduced muscle energetic efficiency with more reliance on glycolysis, and when accompanied with reduced lean mass, is associated with reduced maximum oxidative capacity.

Levothyroxine use and longitudinal changes in thigh muscles in at-risk participants for knee osteoarthritis: preliminary analysis from Osteoarthritis Initiative cohort

BACKGROUND

We examined the association between levothyroxine use and longitudinal MRI biomarkers for thigh muscle mass and composition in at-risk participants for knee osteoarthritis (KOA) and their mediatory role in subsequent KOA incidence.

METHODS

Using the Osteoarthritis Initiative (OAI) data, we included the thighs and corresponding knees of participants at risk but without established radiographic KOA (baseline Kellgren-Lawrence grade (KL) < 2). Levothyroxine users were defined as self-reported use at all annual follow-up visits until the 4th year and were matched with levothyroxine non-users for potential confounders (KOA risk factors, comorbidities, and relevant medications covariates) using 1:2/3 propensity score (PS) matching. Using a previously developed and validated deep learning method for thigh segmentation, we assessed the association between levothyroxine use and 4-year longitudinal changes in muscle mass, including cross-sectional area (CSA) and muscle composition biomarkers including intra-MAT (within-muscle fat), contractile percentage (non-fat muscle CSA/total muscle CSA), and specific force (force per CSA). We further assessed whether levothyroxine use is associated with an 8-year risk of standard KOA radiographic (KL ≥ 2) and symptomatic incidence (incidence of radiographic KOA and pain on most of the days in the past 12 months). Finally, using a mediation analysis, we assessed whether the association between levothyroxine use and KOA incidence is mediated via muscle changes.

RESULTS

We included 1043 matched thighs/knees (266:777 levothyroxine users:non-users; average ± SD age: 61 ± 9 years, female/male: 4). Levothyroxine use was associated with decreased quadriceps CSAs (mean difference, 95%CI: - 16.06 mm2/year, - 26.70 to - 5.41) but not thigh muscles' composition (e.g., intra-MAT). Levothyroxine use was also associated with an increased 8-year risk of radiographic (hazard ratio (HR), 95%CI: 1.78, 1.15-2.75) and symptomatic KOA incidence (HR, 95%CI: 1.93, 1.19-3.13). Mediation analysis showed that a decrease in quadriceps mass (i.e., CSA) partially mediated the increased risk of KOA incidence associated with levothyroxine use.

CONCLUSIONS

Our exploratory analyses suggest that levothyroxine use may be associated with loss of quadriceps muscle mass, which may also partially mediate the increased risk of subsequent KOA incidence. Study interpretation should consider underlying thyroid function as a potential confounder or effect modifier. Therefore, future studies are warranted to investigate the underlying thyroid function biomarkers for longitudinal changes in the thigh muscles.

Profiling of N6-methyladenosine methylation in porcine longissimus dorsi muscle and unravelling the hub gene ADIPOQ promotes adipogenesis in an m6A-YTHDF1-dependent manner

BACKGROUND

Intramuscular fat (IMF) content is a critical indicator of pork quality, and abnormal IMF is also relevant to human disease as well as aging. Although N6-methyladenosine (m⁶A) RNA modification was recently found to regulate adipogenesis in porcine intramuscular fat, however, the underlying molecular mechanisms was still unclear.

RESULTS

In this work, we collected 20 longissimus dorsi muscle samples with high (average 3.95%) or low IMF content (average 1.22%) from a unique heterogenous swine population for m⁶A sequencing (m⁶A-seq). We discovered 70 genes show both differential RNA expression and m⁶A modification from high and low IMF group, including ADIPOQ and SFRP1, two hub genes inferred through gene co-expression analysis. Particularly, we observed ADIPOQ, which contains three m⁶A modification sites within 3' untranslated and protein coding region, could promote porcine intramuscular preadipocyte differentiation in an m⁶A-dependent manner. Furthermore, we found the YT521‑B homology domain family protein 1 (YTHDF1) could target and promote ADIPOQ mRNA translation.

CONCLUSIONS

Our study provided a comprehensive profiling of m⁶A methylation in porcine longissimus dorsi muscle and characterized the involvement of m⁶A epigenetic modification in the regulation of ADIPOQ mRNA on IMF deposition through an m⁶A-YTHDF1-dependent manner.

Mid-life cyclists preserve muscle mass and composition: a 3D MRI study

Physical activity and a healthy lifestyle are crucial factors for delaying and reducing the effects of sarcopenia. Cycling has gained popularity in the last decades among midlife men. While the cardiovascular benefits of cycling and other endurance exercises have been extensively proved, the potential benefits of lifelong aerobic exercise on muscle health have not been adequately studied. Our aim was to quantify the benefits of cycling in terms of muscle health in middle-aged men, using magnetic resonance imaging. We ran a cross-sectional study involving two groups of middle-aged male adults (mean age 49 years, range 30-65) that underwent Dixon MRI of the pelvis. The groups consisted of 28 physically inactive (PI) and 28 trained recreational cyclists. The latter had cycled more than 7000 km in the last year and have been training for 15 years on average, while the PI volunteers have not practiced sports for an average of 27 years. We processed the Dixon MRI scans by labelling and computing the fat fraction (FF), volume and lean volume of gluteus maximus (GMAX) and gluteus medius (GMED); and measuring the volume of subcutaneous adipose tissue (SAT). We found that the cyclists group had lower FF levels, a measure of intramuscular fat infiltration, compared to the PI group for GMAX (PI median FF 21.6%, cyclists median FF 14.8%, p < 0.01) and GMED (PI median FF 16.0%, cyclists median FF 11.4%, p < 0.01). Cyclists had also larger GMAX and GMED muscles than the PI group (p < 0.01), after normalizing it by body mass. Muscle mass and fat infiltration were strongly correlated with SAT volume. These results suggest that cycling could help preserve muscle mass and composition in middle-aged men. Although more research is needed to support these results, this study adds new evidence to support public health efforts to promote cycling.

Thigh and Calf Myosteatosis are Strongly Associated with Muscle and Physical Function in African Caribbean Men

BACKGROUND

African Caribbeans have higher levels of myosteatosis than other populations; however, little is known about the impact of myosteatosis on physical function in African Caribbeans. Herein, we examined the association between regional myosteatosis of the calf, thigh, and abdomen versus physical function in 850 African-Ancestry men aged 64.2 ± 8.9 (range 50-95) living on the Caribbean Island of Tobago.

METHODS

Myosteatosis was measured using computed tomography and included intermuscular adipose tissue (IMAT) and muscle density levels of the thigh, calf, psoas, and paraspinous muscles. Outcomes included grip strength, time to complete 5 chair-rises, and 4-meter gait speed. Associations were quantified using separate linear models for each myosteatosis depot and were adjusted for age, height, demographics, physical activity, and chronic diseases. Beta coefficients were presented per standard deviation of each myosteatosis depot.

RESULTS

Higher thigh IMAT was the only IMAT depot significantly associated with weaker grip strength (β = -1.3 ± 0.43 kg, p = .003). However, lower muscle density of all 4 muscle groups was associated with weaker grip strength (all p < .05). Calf and thigh myosteatosis (IMAT and muscle density) were significantly associated with both worse chair rise time and gait speed (all p < .05), whereas psoas IMAT and paraspinous muscle density were associated with gait speed.

CONCLUSION

Myosteatosis of the calf and thigh-but not the abdomen-were strongly associated with grip strength and performance measures of physical function in African Caribbean men. However, posterior abdominal myosteatosis may have some utility when abdominal images are all that are available.

Association of Computed Tomography Measures of Muscle and Adipose Tissue and Progressive Changes throughout Treatment with Clinical Endpoints in Patients with Advanced Lung Cancer Treated with Immune Checkpoint Inhibitors

To investigate the association between skeletal muscle mass and adiposity measures with disease-free progression (DFS) and overall survival (OS) in patients with advanced lung cancer receiving immunotherapy, we retrospectively analysed 97 patients (age: 67.5 ± 10.2 years) with lung cancer who were treated with immunotherapy between March 2014 and June 2019. From computed tomography scans, we assessed the radiological measures of skeletal muscle mass, and intramuscular, subcutaneous and visceral adipose tissue at the third lumbar vertebra. Patients were divided into two groups based on specific or median values at baseline and changes throughout treatment. A total number of 96 patients (99.0%) had disease progression (median of 11.3 months) and died (median of 15.4 months) during follow-up. Increases of 10% in intramuscular adipose tissue were significantly associated with DFS (HR: 0.60, 95% CI: 0.38 to 0.95) and OS (HR: 0.60, 95% CI: 0.37 to 0.95), while increases of 10% in subcutaneous adipose tissue were associated with DFS (HR: 0.59, 95% CI: 0.36 to 0.95). These results indicate that, although muscle mass and visceral adipose tissue were not associated with DFS or OS, changes in intramuscular and subcutaneous adipose tissue can predict immunotherapy clinical outcomes in patients with advanced lung cancer.

Mechanisms underlying altered neuromuscular function in people with DPN

Diabetes alters numerous physiological functions and can lead to disastrous consequences in the long term. Neuromuscular function is particularly affected and is impacted early, offering an opportunity to detect the onset of diabetes-related dysfunctions and follow the advancement of the disease. The role of physical training for counteracting the deleterious effects of diabetes is well accepted but at the same time, it appears difficult to reliably assess the effects of exercise on functional capacity in patients with diabetic peripheral neuropathy (DPN). In this paper, we will review the specific characteristics of various neuromuscular dysfunctions associated with diabetes according to the DPN presence or not, and their changes over time. We present several propositions regarding the onset of neuromuscular alterations in people with diabetes compared to people with DPN. It appears that motor unit loss and neuromuscular transmission impairment are among the main mechanisms explaining the considerable degradation of neuromuscular function in the transition from a diabetic to neuropathic state. Rate of force development and contractile properties could start to decrease with the onset of preferential type II fiber atrophy, commonly reported in people with DPN. Finally, M_max amplitude could decrease with neuromuscular fatigue only in people with DPN, reflecting the fatigue-related neuromuscular transmission impairment reported in people with DPN. In this review, we show that the different neuromuscular parameters are altered at different stages of diabetes, according to the presence of DPN or not. The precise evaluation of these parameters might participate in adapting the physical training prescription.

Effects of resistance training on body recomposition, muscular strength, and phase angle in older women with different fat mass levels

AIMS

The concomitant increase in skeletal muscle mass (SMM) and decrease in fat mass has been termed body recomposition. This study aimed to analyze the influence of pre-training levels of fat mass on body recomposition, muscular strength, and (phase angle) PhA after 24 weeks of resistance training (RT) in older women.

METHODS

Data from 99 older women (68.6 ± 5.7 years, 65.7 ± 8.6 kg, 155.1 ± 5.8 cm, 27.2 ± 3.1 kg/m²) was retrospectively analyzed. Participants were separated into tertiles according to the amount of fat mass at baseline as follows: low fat mass (L-FM, n = 33), moderate fat mass (M-FM, n = 33), and high fat mass (H-FM, n = 33). The participants underwent a RT program consisting of eight exercises, three sets per exercise, with a load between 8 and 15 RM, performed three times per week for 24 weeks. The SMM and fat mass were evaluated by dual-energy X-ray absorptiometry (DXA). Body recomposition was determined by the composite Z-score of changes in SMM and fat mass. One repetition maximum (1RM) tests in chest press, knee extension, and preacher curl were assessed to verify muscular strength. Bioimpedance was used to determine phase angle.

RESULTS

Results indicated that after the RT period, a greater positive body recomposition was observed in the L-FM group than in M-FM and H-FM groups. Moreover, all groups increased muscular strength and phase angle with no significant difference among groups (P > 0.05).

CONCLUSION

The present study results suggest that the initial amount of fat mass influences the body recomposition induced by RT in older women, with those with lower pre-training fat mass levels presenting higher levels of body recomposition. However, improvements in muscular strength and phase angle are not dependent on the amount of initial fat mass in older women.

Differences in motor unit behavior during isometric contractions in patients with diabetic peripheral neuropathy at various disease severities

The aim of this study was to determine whether HD-sEMG is sensitive to detecting changes in motor unit behavior amongst healthy adults and type 2 diabetes mellitus (T2DM) patients presenting diabetic peripheral neuropathy (DPN) at different levels. Healthy control subjects (CON, n = 8) and T2DM patients presenting no DPN symptoms (ABS, n = 8), moderate DPN (MOD, n = 18), and severe DPN (SEV, n = 12) performed isometric ankle dorsiflexion at 30 % maximum voluntary contraction while high-density surface EMG (HD-sEMG) was recorded from the tibialis anterior muscle. HD-sEMG signals were decomposed, providing estimates of discharge rate, motor unit conduction velocity (MUCV), and motor unit territory area (MUTA). As a result, the ABS group presented reduced MUCV compared to CON. The groups with diabetes presented significantly larger MUTA compared to the CON group (p < 0.01), and the SEV group presented a significantly lower discharge rate compared to CON and ABS (p < 0.01). In addition, the SEV group presented significantly higher CoV_force compared to CON and MOD. These results support the use of HD-SEMG as a method to detect peripheral and central changes related to DPN.

Defining reference values for body composition indices by magnetic resonance imaging in UK Biobank

BACKGROUND

Magnetic resonance imaging (MRI) is the gold standard for evaluating body composition. However, the reference ranges have not been established.

METHODS

Three lean tissue and seven adipose tissue parameters based on MRI data from the UK Biobank were used in this study. Participants with European ancestry and data on at least one parameter were screened. Age- and sex-specific percentile curves were generated using the lambda-mu-sigma method. Three levels of reference ranges were provided, which were equivalent to the mean ± 1 standard deviation (SD), 2 SDs and 2.5 SDs.

RESULTS

The final analysis set for each parameter ranged from 4842 to 14 148 participants (53.4%-56.6% women) with a median age of 61. For lean tissue parameters, compared with those at age 45, the median total lean tissue volume and total thigh fat-free muscle volume at age 70 were 2.83 and 1.73 L, and 3.02 and 1.51 L lower in men and women, respectively. The median weight-to-muscle ratios at age 45 were 0.51 and 0.83 kg/L lower compared with those at age 70 in men and women, respectively. Adipose tissue parameters showed inconsistent differences. In men, the median muscle fat infiltration, visceral adipose tissue (VAT) volume, total abdominal adipose tissue index and abdominal fat ratio were 1.48%, 0.32 L, 0.08 L/m² and 0.4 higher, and the median abdominal subcutaneous adipose tissue (ASAT) volume and total adipose tissue volume were 0.47 and 0.41 L lower, respectively, at age 70 than at age 45. The median total trunk fat volume was approximately 9.53 L at all ages. In women, the median muscle fat infiltration and VAT volume were 1.68% and 0.76 L higher, respectively, at age 70 than at age 45. The median ASAT volume, total adipose tissue volume, total trunk fat volume, total abdominal adipose tissue index and abdominal fat ratio were 0.35 L, 0.78 L, 1.12 L, 0.49 L/m² and 0.06 higher, respectively, at age 60 than at age 45. The medians of the former three parameters were 0.33 L, 0.14 L and 0.20 L lower, at age 70 than at age 60. The medians of the latter two parameters were approximately 3.64 L/m² and 0.55 at ages between 60 and 70.

CONCLUSIONS

We have established reference ranges for MRI-measured body composition parameters in a large community-dwelling population. These findings provide a more accurate assessment of abnormal adipose and muscle conditions.

MME+ fibro-adipogenic progenitors are the dominant adipogenic population during fatty infiltration in human skeletal muscle

Fatty infiltration, the ectopic deposition of adipose tissue within skeletal muscle, is mediated via the adipogenic differentiation of fibro-adipogenic progenitors (FAPs). We used single-nuclei and single-cell RNA sequencing to characterize FAP heterogeneity in patients with fatty infiltration. We identified an MME⁺ FAP subpopulation which, based on ex vivo characterization as well as transplantation experiments, exhibits high adipogenic potential. MME⁺ FAPs are characterized by low activity of WNT, known to control adipogenic commitment, and are refractory to the inhibitory role of WNT activators. Using preclinical models for muscle damage versus fatty infiltration, we show that many MME⁺ FAPs undergo apoptosis during muscle regeneration and differentiate into adipocytes under pathological conditions, leading to a reduction in their abundance. Finally, we utilized the varying fat infiltration levels in human hip muscles and found less MME⁺ FAPs in fatty infiltrated human muscle. Altogether, we have identified the dominant adipogenic FAP subpopulation in skeletal muscle.

Ankle flexor torque, size and density are differential determinants of distal tibia trabecular plate-rod morphometry and bone strength: The Ankle Quality Study

HYPOTHESIS

Greater peak torque and higher myotendinous density at the ankle are associated with a more plate-like architecture at the distal tibia.

METHODS

In this cross-sectional study, women and men ≥ 50 years old with no metal implants, reconstructive surgery, muscular dystrophies, or tendinopathies in any leg were recruited by convenience. Isometric ankle dorsi-plantar flexion and inversion-eversion peak torques were measured using dynamometry. HR-pQCT distal tibia scans were completed. Both assessments were completed on the same day on the non-dominant leg. Integral and trabecular vBMD were derived from standard analyses, failure load (FL) was obtained from finite element analysis, plate-specific parameters were computed from individual trabecula segmentation (ITS) analysis, myotendinous density (MyD) and volume fraction (MyV/TV) were computed from soft tissue analysis. pQCT scans of the 66 % mid-leg were performed (500 μm at 15 mm/s) to obtain muscle density (MD) and muscle cross-sectional area (MCSA).

STATISTICAL ANALYSIS

General linear models estimated how ankle muscle group torque and muscle size and density differentially related, both separately and together, to whole-bone properties (integral vBMD, FL) and trabecular morphometry (ITS plate parameters). Models were adjusted for age, sex, BMI, use of glucocorticoids, current osteoarthritis, and participation in moderate to vigorous recreational or sport activities.

RESULTS

Among 105 participants (77 % female, mean age: 63 (10) years, BMI: 25.8 (5.4) kg/m², 25 % with OA, 17 % fracture history, 42 % falls history), all torque measures, particularly ankle dorsiflexion and eversion, were correlates of plate-plate/rod junction density and failure load. However, muscle size and density measures were further associated with vBMD. The effect of greater ankle flexor-extensor torque on more connected bone was stronger when MyD was higher (interaction p < 0.001).

CONCLUSION

Strength of muscles around the ankle are correlates of plate-like trabeculae at the distal tibia, while leaner muscle and myotendinous tissues facilitates better quality bone for stronger ankle muscle torque.

Transitional Dynamics of Sarcopenia and Associations of Nutritional Indices with State Transitions in Chinese aged ≥ 50

OBJECTIVES

Sarcopenia's temporal profile can be regarded as a dynamic process with distinct states, in which malnutrition plays an important role. This study aimed to address two research gaps: sarcopenia's transitional dynamics and associations of nutritional indices with state transitions in community-dwelling Chinese adults aged 50 and older.

DESIGN

A prospective population-based cohort study.

SETTING

Community-based setting in western China.

PARTICIPANTS

The analytic sample included data from 1910 participants aged ≥ 50 in the West China Health and Aging Trend study between 2018-2022.

MEASUREMENTS

We defined three states: the initial normal state (normal muscle strength, physical performance and muscle mass), the worst sarcopenia state (low muscle mass plus low muscle strength and/or low physical performance) and the intermediate subclinical state (the other scenarios). The relevant measurement methods and cut-off points were based on the 2019 AWGS consensus. Using a continuous-time multistate Markov model, we calculated probabilities of transitions between different states over 1, 2 and 4 years; we also examined associations between nutritional indices and transitions, including body mass index (BMI), calf circumference (CC), mid-arm circumference (MAC), triceps skinfold thickness (TST), albumin (ALB), geriatric nutrition risk index (GNRI), vitamin D (VitD) and prealbumin (PA).

RESULTS

For individuals in the normal state, their probabilities of remaining stable versus progressing to a subclinical state were 53.4% versus 42.1% at 2 years, and 40.6% versus 49.0% at 4 years. In the subclinical population, their 2- and 4-year chances were 60.2% and 51.2% for maintaining this state, 11.8% and 16.2% for developing sarcopenia, 28.0% and 32.6% for reverting to normal. For sarcopenic individuals, the likelihood of staying stable versus retrogressing to the subclinical state were 67.0% versus 26.3% at 2 years, and 48.3% versus 36.3% at 4 years. Increased BMI, CC, MAC, TST, ALB, GNRI and PA correlated with reversion from the subclinical state, among which increased TST, ALB and PA were also paralleled with reversion from sarcopenia, while decreased BMI, CC, MAC, TST and GNRI were associated with progression to sarcopenia. VitD was not significantly associated with any transitions.

CONCLUSION

This study reveals how sarcopenia changes over time in a Chinese population. It also highlights the usefulness of simple and cost-effective nutritional status indices for indicating state transitions, which can help identify individuals at risk of sarcopenia and guide targeted interventions within the optimal time window.

A Skeletal Muscle-Centric View on Time-Restricted Feeding and Obesity under Various Metabolic Challenges in Humans and Animals

Nearly 50% of adults will suffer from obesity in the U.S. by 2030. High obesity rates can lead to high economic and healthcare burdens in addition to elevated mortality rates and reduced health span in patients. Emerging data demonstrate that obesity is a multifactorial complex disease with various etiologies including aging, a lifestyle of chronic high-fat diets (HFD), genetic predispositions, and circadian disruption. Time-restricted feeding/eating (TRF; TRE in humans) is an intervention demonstrated by studies to show promise as an effective alternative therapy for ameliorating the effects of obesity and metabolic disease. New studies have recently suggested that TRF/TRE modulates the skeletal muscle which plays a crucial role in metabolism historically observed to be impaired under obesity. Here we discuss recent findings regarding potential mechanisms underlying TRF's modulation of skeletal muscle function, metabolism, and structure which may shed light on future research related to TRF as a solution to obesity.

Influence of patient-specific factors when comparing multifidus fat infiltration between chronic low back pain patients and asymptomatic controls

Introduction

Many studies have attempted to link multifidus (MF) fat infiltration with muscle quality and chronic low back pain (cLBP), but there is no consensus on these relationships.

Methods

In this cross-sectional cohort study, 39 cLBP patients and 18 asymptomatic controls were included. The MF muscle was manually segmented at each lumbar disc level and fat fraction (FF) measurements were taken from the corresponding advanced imaging water-fat images. We assessed the distribution patterns of MF fat from L1L2 to L5S1 and compared these patterns between groups. The sample was stratified by age, sex, body mass index (BMI), subject-reported pain intensity (VAS), and subject-reported low back pain disability (oswestry disability index, ODI).

Results

Older patients had significantly different MF FF distribution patterns compared to older controls (p < 0.0001). Male patients had 34.8% higher mean lumbar spine MF FF compared to male controls (p = 0.0006), significantly different MF FF distribution patterns (p = 0.028), 53.7% higher mean MF FF measurements at L2L3 (p = 0.037), and 50.6% higher mean MF FF measurements at L3L4 (p = 0.041). Low BMI patients had 29.7% higher mean lumbar spine MF FF compared to low BMI controls (p = 0.0077). High BMI patients only had 4% higher mean lumbar spine MF FF compared to high BMI controls (p = 0.7933). However, high BMI patients had significantly different MF FF distribution patterns compared to high BMI controls (p = 0.0324). Low VAS patients did not significantly differ from the control cohort for any of our outcomes of interest; however, high VAS patients had 24.3% higher mean lumbar spine MF FF values (p = 0.0011), significantly different MF FF distribution patterns (p < 0.0001), 34.7% higher mean MF FF at L2L3 (p = 0.040), and 34.6% higher mean MF FF at L3L4 (p = 0.040) compared to the control cohort. Similar trends were observed for ODI.

Conclusions

This study suggests that when the presence of paraspinal muscle fat infiltration is not characteristic of an individual's age, sex, and BMI, it may be associated with lower back pain.

High-refined carbohydrate diet alters different metabolic functions in female rats

A diet containing refined carbohydrate (HCD) caused obesity and white adipose tissue (WAT) abnormalities, but it is unclear if HCD is linked with other metabolic dysfunctions in female models. Thus, we assessed whether HCD results in WAT, pancreas, liver, skeletal muscle (SM) and thyroid (TH) abnormalities in female rats. Female rats were fed with HCD for 15 days and metabolic morphophysiology, inflammation, oxidative stress (OS), and fibrosis markers were assessed. HCD rats presented large adipocytes, hyperleptinemia, and WAT OS. HCD caused irregular glucose metabolism, low insulin levels, and large pancreatic isle. Granulomas, reduced glycogen, and OS were observed in HCD livers. HCD caused hypertrophy and increased in glycogen in SM. HCD caused irregular TH morphophysiology, reduced colloid area and high T3 levels. In all selected tissues, inflammation and fibrosis were observed in HCD rats. Collectively, these data suggest that the HCD impairs metabolic function linked with irregularities in WAT, pancreas, liver, SM and TH in female rats.

Inflammaging: Implications in Sarcopenia

In a world in which life expectancy is increasing, understanding and promoting healthy aging becomes a contemporary demand. In the elderly, a sterile, chronic and low-grade systemic inflammation known as "inflammaging" is linked with many age-associated diseases. Considering sarcopenia as a loss of strength and mass of skeletal muscle related to aging, correlations between these two terms have been proposed. Better knowledge of the immune system players in skeletal muscle would help to elucidate their implications in sarcopenia. Characterizing the activators of damage sensors and the downstream effectors explains the inference with skeletal muscle performance. Sarcopenia has also been linked to chronic diseases such as diabetes, metabolic syndrome and obesity. Implications of inflammatory signals from these diseases negatively affect skeletal muscle. Autophagic mechanisms are closely related with the inflammasome, as autophagy eliminates stress signaling sent by damage organelles, but also acts with an immunomodulatory function affecting immune cells and cytokine release. The use of melatonin, an antioxidant, ROS scavenger and immune and autophagy modulator, or senotherapeutic compounds targeting senescent cells could represent strategies to counteract inflammation. This review aims to present the many factors regulating skeletal muscle inflammaging and their major implications in order to understand the molecular mechanisms involved in sarcopenia.

Impact of low skeletal muscle mass and quality on clinical outcomes in patients with head and neck cancer undergoing (chemo)radiation

The study aimed to explore the impact of low skeletal muscle mass and quality on survival outcomes and treatment tolerance in patients undergoing radical chemo-radiation therapy for head and neck cancer (HNC). This is significant given the growing interest in sarcopenia as a possible negative predictive/prognostic factor of disease progression and survival. From 2010 to 2017, 225 patients were included in the study. Pre-treatment computed tomography (CT) scans of HNC patients undergoing (chemo)radiation therapy were retrospectively reviewed. The skeletal muscle area, normalized for height to obtain the skeletal muscle index (SMI), the skeletal muscle density (SMD) and the intramuscular adipose tissue area (IMAT) were measured at the level of the L3 vertebra. Low SMD and low SMI were defined according to previously reported thresholds, while high IMAT was defined using population-specific cut-point analysis. SMI, SMD, and IMAT were also measured at the proximal thigh (PT) level and tested as continuous variables. Clinical morpho-functional parameters, baseline nutritional markers with a known or suspected impact on HNC treatment, clinical outcomes and sarcopenia were also collected. In multivariate analyses, adjusted by age, sex, stage, diabetes, body mass index (BMI), and weight loss, L3-SMI was not significantly associated with survival, while poor muscle quality was negatively associated with overall survival (OS) (HR = 1.88, 95% CI = 1.09-3.23, p = 0.022 and HR = 2.04, 95% CI = 1.27-3.27, p = 0.003, for low L3-SMD and high L3-IMAT, respectively), progression-free survival (PFS) (HR = 2.26, 95% CI = 1.39-3.66, p = 0.001 and HR = 1.97, 95% CI = 1.30-2.97, p = 0.001, for low L3-SMD and high L3-IMAT, respectively) and cancer-specific survival (CSS) (HR = 2.40, 95% CI = 1.28-4.51, p = 0.006 and HR = 1.81, 95% CI = 1.04-3.13, p = 0.034, for low L3-SMD and high L3-IMAT, respectively). Indices at the PT level, tested as continuous variables, showed that increasing PT-SMI and PT-SMD were significant protective factors for all survival outcomes (for OS: HR for one cm²/m² increase in PT-SMI 0.96; 95% CI = 0.94-0.98; p = 0.001 and HR for one HU increase in PT-SMD 0.90; 95% CI = 0.85-0.94; p < 0.001, respectively). PT-IMAT was a significant risk factor only in the case of CSS (HR for one cm² increase 1.02; 95% CI = 1.00-1.03; p = 0.046). In conclusion, pre-treatment low muscle quality is a strong prognostic indicator of death risk in patients affected by HNC and undergoing (chemo)radiotherapy with curative intent.

Individual Cofactors and Multisensory Contributions to the Postural Sway of Adults with Diabetes

To assess the interactions between individual cofactors and multisensory inputs on the postural sway of adults with type 2 diabetes and healthy subjects, 69 adults accepted to participate in the study (48 with/ 21 without diabetes). Assessments included neuro-otology (sinusoidal-rotation and unilateral-centrifugation), ophthalmology and physiatry evaluations, body mass index (BMI), physical activity, quadriceps strength, the ankle/brachial index and polypharmacy. Postural sway was recorded on hard/soft surface, either with eyes open/closed, or without/with 30° neck extension. The proportional differences from the baseline of each condition were analyzed using Multivariate and Multivariable analyses. Patients with polyneuropathy and no retinopathy showed visual dependence, while those with polyneuropathy and retinopathy showed adaptation. Across sensory challenges, the vestibulo-ocular gain at 1.28 Hz and the BMI were mainly related to changes in sway area, while the dynamic visual vertical was mainly related to changes in sway length. The ankle/brachial index was related to the effect of neck extension, with contributions from quadriceps strength/physical activity, polyneuropathy and polypharmacy. Across conditions, men showed less sway than women did. In conclusion, in adults with diabetes, sensory inputs and individual cofactors differently contribute to postural stability according to context. Rehabilitation programs for adults with diabetes may require an individualized approach.

In vitro skeletal muscle models for type 2 diabetes

Type 2 diabetes mellitus, a metabolic disorder characterized by abnormally elevated blood sugar, poses a growing social, economic, and medical burden worldwide. The skeletal muscle is the largest metabolic organ responsible for glucose homeostasis in the body, and its inability to properly uptake sugar often precedes type 2 diabetes. Although exercise is known to have preventative and therapeutic effects on type 2 diabetes, the underlying mechanism of these beneficial effects is largely unknown. Animal studies have been conducted to better understand the pathophysiology of type 2 diabetes and the positive effects of exercise on type 2 diabetes. However, the complexity of in vivo systems and the inability of animal models to fully capture human type 2 diabetes genetics and pathophysiology are two major limitations in these animal studies. Fortunately, in vitro models capable of recapitulating human genetics and physiology provide promising avenues to overcome these obstacles. This review summarizes current in vitro type 2 diabetes models with focuses on the skeletal muscle, interorgan crosstalk, and exercise. We discuss diabetes, its pathophysiology, common in vitro type 2 diabetes skeletal muscle models, interorgan crosstalk type 2 diabetes models, exercise benefits on type 2 diabetes, and in vitro type 2 diabetes models with exercise.