Therapeutic approaches for muscle wasting disorders

Exploring the Association between Elevated Anxiety Symptoms and Low Skeletal Muscle Mass among Asymptomatic Adults: A Population-Based Study in Republic of Korea

Individuals with mental health problems are at higher risk of musculoskeletal diseases. However, the association between low muscle mass (LMM) and anxiety symptoms remains uninvestigated. This cross-sectional study enrolled 174,262 adults (73,833 women, 100,429 men), aged 18 to 89, who completed the anxiety scale and body composition analyses. Using bio-electrical impedance analysis, skeletal muscle mass index (SMI) was calculated based on appendicular skeletal muscle mass (ASM) (kg)/height (m2). LMM was defined as SMI < 7.0 kg/m2 in men and <5.4 kg/m2 in women. Anxiety symptoms were screened using the Clinical Useful Anxiety Outcome Scale (CUXOS) with cut-off scores of 20, 30, and 40. Multivariable logistic regression analyses were performed. LMM prevalence was 20.17% in women, 3.86% in men (p < 0.001). The prevalence of anxiety symptoms in LMM group decreased from mild (CUXOS > 20: women, 32.74%, men, 21.17%) to moderate (CUXOS > 30: 13.34%, 7.32%), to severe anxiety symptoms (CUXOS > 40: 4.00%, 1.73%). In multivariable-adjusted models, LMM was associated with mild (aOR (95% confidence interval)), women, 1.13 (1.08-1.17); men, 1.17 (1.08-1.27)), moderate (1.17 (1.11-1.24); 1.35 (1.19-1.53) and severe anxiety symptoms (1.18 (1.07-1.3), 1.36 (1.06-1.74)), demonstrating an increased risk of ORs with escalating anxiety severity. LMM was independently associated with a higher prevalence of anxiety symptoms.

Organs in orbit: how tissue chip technology benefits from microgravity, a perspective

Tissue chips have become one of the most potent research tools in the biomedical field. In contrast to conventional research methods, such as 2D cell culture and animal models, tissue chips more directly represent human physiological systems. This allows researchers to study therapeutic outcomes to a high degree of similarity to actual human subjects. Additionally, as rocket technology has advanced and become more accessible, researchers are using the unique properties offered by microgravity to meet specific challenges of modeling tissues on Earth; these include large organoids with sophisticated structures and models to better study aging and disease. This perspective explores the manufacturing and research applications of microgravity tissue chip technology, specifically investigating the musculoskeletal, cardiovascular, and nervous systems.

Naringenin improves muscle endurance via activation of the Sp1-ERRγ transcriptional axis

Skeletal muscle function declines in the aging process or disease; however, until now, skeletal muscle has remained one of the organs most undertreated with medication. In this study, naringenin (NAR) was found to build muscle endurance in wild-type mice of different ages by increasing oxidative myofiber numbers and aerobic metabolism, and it ameliorates muscle dysfunction in mdx mice. The transcription factor Sp1 was identified as a direct target of NAR and was shown to mediate the function of NAR on muscle. Moreover, the binding site of NAR on Sp1 was further validated as GLN-110. NAR enhances the binding of Sp1 to the CCCTGCCCTC sequence of the Esrrg promoter by promoting Sp1 phosphorylation, thus upregulating Esrrg expression. The identification of the Sp1-ERRγ transcriptional axis is of great significance in basic muscle research, and this function of NAR has potential implications for the improvement of muscle function and the prevention of muscle atrophy.

Physiology of Stretch-Mediated Hypertrophy and Strength Increases: A Narrative Review

Increasing muscle strength and cross-sectional area is of crucial importance to improve or maintain physical function in musculoskeletal rehabilitation and sports performance. Decreases in muscular performance are experienced in phases of reduced physical activity or immobilization. These decrements highlight the need for alternative, easily accessible training regimens for a sedentary population to improve rehabilitation and injury prevention routines. Commonly, muscle hypertrophy and strength increases are associated with resistance training, typically performed in a training facility. Mechanical tension, which is usually induced with resistance machines and devices, is known to be an important factor that stimulates the underlying signaling pathways to enhance protein synthesis. Findings from animal studies suggest an alternative means to induce mechanical tension to enhance protein synthesis, and therefore muscle hypertrophy by inducing high-volume stretching. Thus, this narrative review discusses mechanical tension-induced physiological adaptations and their impact on muscle hypertrophy and strength gains. Furthermore, research addressing stretch-induced hypertrophy is critically analyzed. Derived from animal research, the stretching literature exploring the impact of static stretching on morphological and functional adaptations was reviewed and critically discussed. No studies have investigated the underlying physiological mechanisms in humans yet, and thus the underlying mechanisms remain speculative and must be discussed in the light of animal research. However, studies that reported functional and morphological increases in humans commonly used stretching durations of > 30 min per session of the plantar flexors, indicating the importance of high stretching volume, if the aim is to increase muscle mass and maximum strength. Therefore, the practical applicability seems limited to settings without access to resistance training (e.g., in an immobilized state at the start of rehabilitation), as resistance training seems to be more time efficient. Nevertheless, further research is needed to generate evidence in different human populations (athletes, sedentary individuals, and rehabilitation patients) and to quantify stretching intensity.

Investigating the Combined Effects of Mechanical Stress and Nutrition on Muscle Hypertrophic Signals Using Contractile 3D-Engineered Muscle (3D-EM)

Since 3D-EM closely resembles in vivo muscles, the aim of this study was to investigate the effects of exercise (electrical pulse stimulation (EPS)) and nutrition (maca), which contains triterpenes, on muscle hypertrophy by using 3D-EM for the first time. The 3D-EM was composed of C2C12 cells and type 1 collagen gel, was differentiated for 14 days, and was divided into four groups: control, maca, EPS, and maca + EPS. The medium was replaced every two days before each EPS intervention, and the concentration of maca in the culture solution was 1 mg/mL. The intervention conditions of the EPS were 30 V, 1 Hz, and 2 ms (24 h on, 24 h off, for one week). The expression levels of proteins were examined by Western blotting. The intervention of maca and EPS upregulated the expression of MHC-fast/slow (both p < 0.05) compared with the control group, and the addition of maca had no effect on the phosphorylation of mTOR (p = 0.287) but increased the AMPK phosphorylation (p = 0.001). These findings suggest that intervention with maca and EPS has a positive effect on muscle hypertrophy, which has a positive impact on sarcopenia. However, the underlying mechanisms remain to be further explored.

Swimming exercise and nano-l-arginine supplementation improve oxidative capacity and some autophagy-related genes in the soleus muscle of aging rats

The present research aims to evaluate the effect of swimming exercise and chitosan-coated l-arginine on mitochondrial oxidation, BCL2 Interacting Protein 3 (Bnip3), NIP-like protein × (Nix), B-cell lymphoma-extra-large (Bcl-xL) and autophagy-related protein light chain 3(LC3) expression in soleus muscle of aging rats. In this experimental research, 25 male Wistar rats were assigned into five groups randomly: young, old, old + Nano l-arginine (Nano L-a), old + exercise (Ex), and old + Nano l-arginine (Nano L-a) + exercise (Ex) (n = 5 in each). They performed a swimming exercise program five days a week for six weeks. To determine the relative strength for rats before and after performing these interventions, the 1repetition maximum (1RM) test was done as a pre and post-test. The exercise program started with 20 min and after four sessions, gradually increased to 60 min and this time was maintained until the completion of the training period. l-arginine coated with chitosan nanoparticles was given to the rats in the l-arginine-supplemented group via gavage at a dosage of 500 mg/kg/day, five days a week, for six weeks. Additionally, the rats in all groups were fed a normal diet (2.87 kcal/g and 15 % energy from fat). Upon the completion of the protocol implementation, the rats were sacrificed and the soleus muscle was fixed and frozen to determine hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC), gene expression analysis, levels of reactive oxygen species (ROS), and total antioxidant capacity (TAC). The results from the present research indicated that swimming exercise and Nano l-arginine improve the strength and histology of muscle tissue in old rats (p < 0.05). Aging significantly increased the expression of Nix and Bnip3 (p < 0.05) and reduced the Bcl-xL gene expression (p < 0.05). The expression of LC3 protein also increased with aging (p < 0.05). Therapeutic interventions, such as combined treatment (old + Nano L-a + Ex) for old animals, reduced the amount of this protein in soleus muscle (p < 0.05). The ROS values also showed a significant reduction only in the old + Nano L-a + Ex group compared to the old group. Moreover, TAC values show a significant decrease in the old and old + Ex groups in comparison to the young group. The use of arginine supplement, especially in nano form, along with swimming exercise seems to reduce the oxidative damage to the elderly muscle tissue, which has a positive effect on the structure and function of the soleus muscle. Since these interventions only had a significant effect on LC3 protein, further studies with more diverse measurement methods for autophagy are suggested.

The Role of Mitochondrial Enzymes, Succinate-Coupled Signaling Pathways and Mitochondrial Ultrastructure in the Formation of Urgent Adaptation to Acute Hypoxia in the Myocardium

The effect of a single one-hour exposure to three modes of hypobaric hypoxia (HBH) differed in the content of O₂ in inhaled air (FiO₂-14%, 10%, 8%) in the development of mitochondrial-dependent adaptive processes in the myocardium was studied in vivo. The following parameters have been examined: (a) an urgent reaction of catalytic subunits of mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX2, ATP5A) in the myocardium as an indicator of the state of the respiratory chain electron transport function; (b) an urgent activation of signaling pathways dependent on GPR91, HIF-1α and VEGF, allowing us to assess their role in the formation of urgent mechanisms of adaptation to hypoxia in the myocardium; (c) changes in the ultrastructure of three subpopulations of myocardial mitochondria under these conditions. The studies were conducted on two rat phenotypes: rats with low resistance (LR) and high resistance (HR) to hypoxia. The adaptive and compensatory role of the mitochondrial complex II (MC II) in maintaining the electron transport and energy function of the myocardium in a wide range of reduced O₂ concentrations in the initial period of hypoxic exposure has been established. The features of urgent reciprocal regulatory interaction of NAD- and FAD-dependent oxidation pathways in myocardial mitochondria under these conditions have been revealed. The data indicating the participation of GPR91, HIF-1a and VEGF in this process have been obtained. The ultrastructure of the mitochondrial subpopulations in the myocardium of LR and HR rats differed in normoxic conditions and reacted differently to hypoxia of varying severity. The parameters studied together are highly informative indicators of the quality of cardiac activity and metabolic biomarkers of urgent adaptation in various hypoxic conditions.

Sex differences in systemic bone and muscle loss following femur fracture in mice

Fracture induces systemic bone loss in mice and humans, and a first (index) fracture increases the risk of future fracture at any skeletal site more in men than women. The etiology of this sex difference is unknown, but fracture may induces a greater systemic bone loss response in men. Also sex differences in systemic muscle loss after fracture have not been examined. We investigated sex differences in systemic bone and muscle loss after transverse femur fracture in 3-month-old male and female C57BL/6 J mice. Whole-body and regional bone mineral content and density (BMC and BMD), trabecular and cortical bone microstructure, muscle contractile force, muscle mass, and muscle fiber size were quantified at multiple time points postfracture. Serum concentrations of inflammatory cytokines (IL-1β, IL-6, and TNF-α) were measured 1-day postfracture. One day postfracture, IL-6 and Il-1B were elevated in fracture mice of both sexes, but TNF-α was only elevated in male fracture mice. Fracture reduced BMC, BMD, and trabecular bone microstructural properties in both sexes 2 weeks postfracture, but declines were greater in males. Muscle contractile force, mass, and fiber size decreased primarily in the fractured limb at 2 weeks postfracture and females showed a trend toward greater muscle loss. Bone and muscle properties recovered by 6 weeks postfracture. Overall, postfracture systemic bone loss is greater in men, which may contribute to sex differences in subsequent fracture risk. In both sexes, muscle loss is primarily confined to the injured limb and fracture may induce greater inflammation in males.

Phytochemical‑rich herbal formula ATG‑125 protects against sucrose‑induced gastrocnemius muscle atrophy by rescuing Akt signaling and improving mitochondrial dysfunction in young adult mice

The antioxidant capability of herbal remedies has attracted widespread attention, but their molecular mechanisms in a muscle atrophy model have not been explored. The aim of the present study was to compare the bioactivity of sucrose challenged mice following treatment with ATG‑125. Here, through a combination of transcriptomic and biomedical analysis, herbal formula ATG‑125, a phytochemical‑rich formula, was identified as a protective factor against muscle atrophy in sucrose challenged mice. Gene ontology (GO) identified differentially expressed genes that were primarily enriched in the 'negative regulation of proteolysis', 'cellular amino acid metabolic process', 'lipoprotein particle' and 'cell cycle', all of which were associated with the ATG‑125‑mediated prevention of muscle atrophy, particularly with regard to mitochondrial biogenesis. In skeletal muscle, a set of mitochondrial‑related genes, including angiopoietin‑like 4, nicotinamide riboside kinase 2 (Nmrk2), pyruvate dehydrogenase lipoamide kinase isozyme 4, Asc‑type amino acid transporter 1 and mitochondrial uncoupling protein 3 (Ucp3) were markedly upregulated following ATG‑125 intervention. An increase in Nmrk2 and Ucp3 expression were noted after ATG‑125 treatment, in parallel with upregulation of the 'nicotinate and nicotinamide metabolism' pathway, as determined using the Kyoto Encyclopedia of Genes and Genomes (KEGG). Furthermore, KEGG pathway analysis revealed the downregulation of 'complement and coagulation cascades', 'cholesterol metabolism', 'biosynthesis of amino acids' and 'PPAR signaling pathway', which were associated with the downregulation of serine (or cysteine) peptidase inhibitor clade A member (Serpina)3, Serpina1b, Serpina1d, Serpina1e, apolipoprotein (Apo)a1 and Apoa2, all of which were cardiovascular and diabetes‑associated risk factors and were regulated by ATG‑125. In addition, ATG‑125 treatment resulted in downregulated mRNA expression levels of ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2, troponin‑I1, troponin‑C1 and troponin‑T1 in young adult gastrocnemius muscle compared with the sucrose group. Nuclear factor‑κB‑hypoxia inducible factor‑1α‑TGFβ receptor type‑II‑vascular endothelial growth factor staining indicated that ATG‑125 decreased sucrose‑induced chronic inflammation. ATG‑125 was sufficient to prevent muscle atrophy, and this protective effect may be mediated through upregulation of AKT phosphorylation, upregulating the insulin growth factor‑1R‑insulin receptor substrate‑PI3K‑AKT pathway, which in turn resulted in a forkhead box O‑dependent decrease in protein degradation pathways, including regulation of atrogin1 and E3 ubiquitin‑protein ligase TRIM63. Peroxisome‑proliferator activated receptor γ coactivator 1α (PGC1α) was decreased in young adult mice challenged with sucrose. ATG‑125 treatment significantly increased PGC1α and significantly increased UCP‑1,2,3 expression levels, which suggested ATG‑125 poised the mitochondria for uncoupling of respiration. This effect is consistent with the increased SIRT1 levels and may explain an increase in mitochondria biogenesis. Taken together, the present study showed that ATG‑125, as an integrator of protein synthesis and degradative pathways, prevented muscle wasting.

Role of Age-Related Mitochondrial Dysfunction in Sarcopenia

Skeletal muscle aging is associated with a significant loss of skeletal muscle strength and power (i.e., dynapenia), muscle mass and quality of life, a phenomenon known as sarcopenia. This condition affects nearly one-third of the older population and is one of the main factors leading to negative health outcomes in geriatric patients. Notwithstanding the exact mechanisms responsible for sarcopenia are not fully understood, mitochondria have emerged as one of the central regulators of sarcopenia. In fact, there is a wide consensus on the assumption that the loss of mitochondrial integrity in myocytes is the main factor leading to muscle degeneration. Mitochondria are also key players in senescence. It has been largely proven that the modulation of mitochondrial functions can induce the death of senescent cells and that removal of senescent cells improves musculoskeletal health, quality, and function. In this review, the crosstalk among mitochondria, cellular senescence, and sarcopenia will be discussed with the aim to elucidate the role that the musculoskeletal cellular senescence may play in the onset of sarcopenia through the mediation of mitochondria.

Pharmaceutical and personal care product residues in a macrophyte pond-constructed wetland treating wastewater from a university campus: Presence, removal and ecological risk assessment

Pharmaceuticals and personal care products (PPCPs) constitute a group of chemicals of concern because of their potential toxicity when reaching aquatic environments. Wastewaters are one of the main pathways of introduction into the environment of the chemical compounds used in PPCPs because, in most cases, wastewater treatment facilities are not 100% efficient in their removal. This problem is accentuated in rural zones and isolated communities where conventional treatment systems are too expensive to build and operate. Waste-stabilization ponds and constructed wetlands (CWs) are natural wastewater treatment systems which are used to improve the quality of sewage from small communities because of their low cost and easy maintenance. There is growing interest in combining the two technologies to make a more robust system, taking into account their respective strengths and weaknesses. In this work, a combined macrophyte pond-CW system was evaluated for the presence at three sampling points (influent, pond effluent and CW effluent) of fifteen steroid hormones and six benzotriazole ultraviolet stabilizers (BUVSs). None of the targeted BUVS compounds were detected in either the influent or effluent, probably because of the particular characteristics of the population served by the wastewater system. In contrast, eight different steroid hormone compounds were detected at concentrations ranging from 17.3 to 247.7 ng·L^-1 in influent samples and from 8.1 to 22.1 ng·L^-1 in final effluent samples. The pond-CW system showed high elimination rates of steroid hormone residues with average removal efficiencies of over 77%. This efficacy was confirmed in the ecological risk assessment evaluation that was performed. Final effluents showed a low ecological risk associated with steroid hormones in contrast to the medium-high ecological risks found in the influent samples.

Effect of citrulline on muscle protein turnover in an in vitro model of muscle catabolism

OBJECTIVE

Muscle net catabolism, as seen after severe trauma or sepsis or in postoperative situations, is mediated by hormones (e.g., cortisol) and proinflammatory cytokines (e.g., tumor necrosis factor alpha [TNF-α]). Specific amino acids may be able to limit this muscle mass loss. Citrulline (CIT) stimulates muscle protein synthesis in various situations, but little data exist on hypercatabolic situations and the effects on protein breakdown are unknown. Our aim was to assess the effect of CIT on protein turnover in an in vitro model of muscle hypercatabolism.

METHODS

Myotubes derived from C2C12 myoblasts were treated with 150 nM dexamethasone (DEX), 10 ng/mL TNF-α, or 0.006% ethanol (as control [CON]) for 24 h. Subsequently, myotubes were incubated with or without 5 mM CIT for 6 h. Muscle protein synthesis rate was evaluated by the surface sensing of translation method and by l-[3,5-³H]tyrosine (Tyr) incorporation. The muscle protein breakdown rate was evaluated from Tyr release into culture medium. CIT action was analyzed by non-parametric Kruskal-Wallis and Mann-Whitney tests.

RESULTS

CIT treatment significantly increased protein synthesis rates compared with the DEX or TNF-α group (surface sensing of translation method; DEX + CIT versus DEX; P = 0.03 and TNF-α+CIT versus TNF-α; P = 0.05) and significantly decreased protein breakdown rate in the CON and DEX groups (CON + CIT versus CON; P = 0.05 and DEX + CIT versus DEX; P = 0.05).

CONCLUSIONS

CIT treatment regulated muscle protein turnover in an in vitro model of muscle net catabolism. Exploring the underlying mechanisms would also be of interest.

Denervation drives skeletal muscle atrophy and induces mitochondrial dysfunction, mitophagy and apoptosis via miR-142a-5p/MFN1 axis

Rationale: Peripheral nerve injury is common in clinic, which leads to severe atrophy and dysfunction of the denervated muscles, but the underlying mechanism is not fully understood. Recent studies advanced the causative role of mitochondrial dysfunction in muscle atrophy, while the upstream triggers remained unclear. Methods: In the present study, Atrophy of gastrocnemius and tibialis anterior (TA) were evaluated in mice sciatic nerve transection model. Transmission electron microscopy (TEM) was then used to observe the microstructure of atrophic gastrocnemius and mitochondria. Subsequently, small RNA sequencing, luciferase reporter assay and Electrophoretic Mobility Shift (EMSA) were performed to explore the potential signaling pathway involved in skeletal muscle atrophy. The effects of the corresponding pathway on mitochondrial function, mitophagy, apoptosis and muscle atrophy were further determined in C2C12 cells and denervated gastrocnemius. Results: Gastrocnemius and TA atrophied rapidly after denervation. Obvious decrease of mitochondria number and activation of mitophagy was further observed in atrophic gastrocnemius. Further, miR-142a-5p/ mitofusin-1 (MFN1) axis was confirmed to be activated in denervated gastrocnemius, which disrupted the tubular mitochondrial network, and induced mitochondrial dysfunction, mitophagy and apoptosis. Furthermore, the atrophy of gastrocnemius induced by denervation was relieved through targeting miR-142a-5p/MFN1 axis. Conclusions: Collectively, our data revealed that miR-142a-5p was able to function as an important regulator of denervation-induced skeletal muscle atrophy by inducing mitochondrial dysfunction, mitophagy, and apoptosis via targeting MFN1. Our findings provide new insights into the mechanism of skeletal muscle atrophy following denervation and propose a viable target for therapeutic intervention in individuals suffering from muscle atrophy after peripheral nerve injury.

Wheel running predicts resilience to tumors in old mice

Aging intervention studies are hampered by the lack of predictive measures for determination of individuals at risk of age-associated chronic disease. Assessment of physical resilience could be informative in this regard, especially for age-related diseases such as cancer. Voluntary wheel running is a mildly stressful physical activity that is easily quantifiable in the mouse but has not been studied as a predictor of resistance to tumor invasiveness with increasing age. Male C57BL/6 mice in cohorts of 4, 12, 20, and 28 months of age were allowed access to a slanted in-cage running wheel for 3 days. Three months later, mice were injected subcutaneously with B16 melanoma tumor cells and followed for two weeks before harvesting. No relation was observed between running distance and tumor burden in the 4-month age group. The 12-month age group showed a trend, and the 20- and 28-month age groups showed a negative correlation (P < 0.05) between running distance and tumor burden. Mice in the 20-month age group that ran longer distances had lower tumor invasive scores compared to mice in the same age group that ran shorter distances. In conclusion, short term exercise capability could be a marker for resilience to cancer, and possibly other age-related disease conditions, in mice.

Change of skeletal muscle mass in patients with pheochromocytoma

The effects of catecholamine excess due to pheochromocytoma on body composition, including skeletal muscle mass, are unknown. Here, we investigated the effects of catecholamine metabolites on body composition in subjects with pheochromocytoma. After body compositions using bioelectrical impedance analysis, urinary metanephrine (UM), and urinary normetanephrine (UNM) were measured in 16 patients with pheochromocytoma and 224 patients with nonfunctioning adrenal incidentaloma (NFAI), we compared skeletal muscle mass and fat mass (FM) between the two groups. After adjustments for confounders, UM (β = - 0.171, P = 0.006) and UNM (β = - 0.249, P < 0.001) levels were correlated inversely with skeletal muscle mass index (SMI), but not FM or percentage FM (pFM), in all subjects. Patients with pheochromocytoma had lower ASM by 7.7% (P = 0.022) and SMI by 6.6% (P = 0.001) than patients with NFAI. Conversely, FM and pFM were not statistically different between the two groups. The odds ratio for low skeletal muscle mass in the presence of pheochromocytoma was 10.33 (95% confidence interval, 2.65-40.22). Our results indicate that patients with pheochromocytoma have a reduced skeletal muscle mass and suggest that catecholamine excess has adverse effects on skeletal muscle metabolism.

Citrulline and muscle protein homeostasis in three different models of hypercatabolism

Supplementation of enteral nutrition (EN) by specific amino acids (AAs) has been proposed to prevent muscle protein loss in intensive care unit (ICU) patients. Citrulline (Cit), which has been shown to stimulate muscle protein synthesis in other situations, may be of interest in this setting. Our aim was to assess the effect of Cit in three catabolic models relevant to critical illness: endotoxemia (LPS), traumatic brain injury (TBI), and TBI with infectious complications (TBI-Ec), which are characterized by different alterations in protein homeostasis. Fifty-eight male Sprague-Dawley rats (200-220 g) were randomized to receive a standard diet ad libitum (CON, n = 9) or to undergo catabolic injuries on day 0 (D0, n = 49), and EN (Sondalis HP energy® 290 kcal/kg/d) from day 1 (D1) combined with Cit (2 g/kg/d) or isonitrogenous non-essential AAs (NEAAs) until day 3 (D3). Endotoxemia was induced by IP injection of LPS from E. coli (3 mg/kg), TBI by hydraulic percussion, and infectious complications (TBI-Ec) by administration of luminescent E. coli on D1. Nitrogen balance (ΔN) and 3-methylhistidine (3-MHis) were measured daily. Muscle protein synthesis (MPS, measured by the SUnSET method) and mTORC1 activation (S6K-1 and 4E-BP1 phosphorylation) were measured on D3 2 h after the arrest of enteral nutrition in soleus, extensor digitorum longus (EDL), gastrocnemius and tibialis muscles. ΔN was lower (p < 0.001) in all three models of injury compared with basal and CON from D1 to D3, and more negative in the LPS-CIT (p < 0.05) than in the LPS group. The 3-MHis/creatinine ratio was significantly increased on D1 in all groups compared with CON, and on D2 only in the LPS and TBI groups (p < 0.0001, LPS and TBI vs. CON). MPS was similar in all groups in soleus and tibialis but significantly higher in EDL in LPS-CIT [LPS-CIT: 4.5 ± 1.7 (mean ± SD) vs. CON: 2.3 ± 1.2; and vs. LPS-NEAA: 3.1 ± 2.3] and in gastrocnemius (LPS-CIT vs. CON; p = 0.05). S6K-1 phosphorylation in the EDL was also higher in LPS-CIT vs. CON (LPS-CIT: 0.94 ± 0.51 CON: 0.42 ± 0.28), but not in gastrocnemius. IL-6 plasma level was significantly higher in all the catabolic groups vs. CON (p < 0.005) with no difference between treatments (Cit or NEAAs). In conclusion, the TBI model showed only a rise in muscle proteolysis, whereas the LPS model displayed a rise in both protein synthesis and proteolysis. Secondly, our results show that the Cit effect varies according to the type of injury and to the muscle under study. The stimulation of MPS rate and the mTOR pathway in LPS-treated rats contrasts with degraded ΔN, suggesting that the Cit effect on protein metabolism in critically ill rats is limited at the whole-body level.

Age-dependent skeletal muscle transcriptome response to bed rest-induced atrophy

Short-term muscle disuse induces significant muscle loss in older adults and in some reports may be more accelerated with aging. Identifying muscle transcriptional events in response to bed rest may help identify therapeutic targets to offset muscle loss. Therefore, we compared the muscle transcriptome between young and older adults after bed rest and identified candidate targets related to changes in muscle loss. RNA was sequenced (HiSeq, Illumina; DESeq, R) from muscle biopsies obtained from young [ n = 9; 23 yr (SD 3)] and older [ n = 18; 68 yr (SD 6)] adults before and after 5-day bed rest. Significantly altered pathways in both young and old subjects relating to mechanosensing and cell adhesion (Actin Cytoskeleton Signaling, ILK Signaling, RhoA Signaling, and Integrin Signaling) were altered (activation z score) to a greater extent in old subjects. Hepatic Fibrosis/Hepatic Stellate Cell Activation was the top regulated pathway significantly altered only in the old. Fifty-one differentially regulated genes were only altered in the young after bed rest and resembled a gene expression profile like that in the old at baseline. Inflammation and muscle wasting genes (CXCL2, GADD45A) were uniquely increased in the old after bed rest, and the macrophage gene MAFB decreased in the old and correlated with the change in leg lean mass. In summary, skeletal muscle dysregulation during bed rest in the old may be driven by alterations in molecules related to fibrosis, inflammation, and cell adhesion. This information may aid in the development of mechanistic-based therapies to combat muscle atrophy during short-term disuse. NEW & NOTEWORTHY Using RNA sequencing and bioinformatics approaches, we identified that older adult skeletal muscle was characterized by dysregulated pathways associated with fibrosis, inflammation (upregulated), and cell adhesion and mechanosensing (downregulated) pathways, with a subset of genes differentially regulated in old and young muscle after bed rest that may describe predisposition to muscle loss. Unique upregulated genes only expressed in old muscle after bed rest indicated increased inflammation and muscle wasting (CXCL2, GADD45A) and decreased MAFB correlated with the change in leg lean mass.

Oral creatine supplementation attenuates muscle loss caused by limb immobilization: a systematic review

Abstract Introduction: Recent studies have pointing creatine supplementation as a promising therapeutic alterna- tive in several diseases, especially myopathies and neurodegenerative disorder. Objective: elucidate the role of creatine supplementation on deleterious effect caused by limb immobilization in humans and rats. Methods: Analyzed articles were searched by three online databases, PubMed, SportDicus e Scielo. After a review and analysis, the studies were included in this review articles on effect of creatine supplementation on skeletal muscle in humans and rat, before, during and after a period of limb immobilization. Results: Studies analyzed demonstrated positive points in use of creatine supplementation as a therapeutic tool to mitigating the deleterious effects of limb immobilization, in humans and rat. Conclusion: The dataset of this literature review allows us to conclude that creatine supplementation may reduce muscle loss and/or assist in the recovery of muscle atrophy caused by immobilization and disuse in rats and humans. Also, we note that further research with better methodological rigor is needed to clarify the mechanisms by which creatine support the recovery of muscle atrophy. Moreover, these effects are positive and promising in the field of muscle rehabilitation, especially after member’s immobilization.

Divergent effects of resistance training and anabolic steroid on the postsynaptic region of different skeletal muscles of aged rats

This study aimed to analyze the effects of resistance training associated with testosterone administration in the neuromuscular junction (NMJ) postsynaptic region of different skeletal muscle types of aged rats. Wistar rats were divided into: SEI - 20-months-old control, SEF - 24-months-old control, T - 20-months-old with testosterone, S - 20-months-old resistance trained and ST - 20-months-old with resistance training associated with testosterone propionate. All groups were submitted to familiarization and maximum load carrying testing (MLCT). The MLCT was applied before and after the resistance training (RT) period. RT (6-8×/session with progressive loads of 50 to 100%, 3×/week and 120s interval) was performed in ladder climbing for 15weeks. The administration of testosterone propionate was performed 2×/week (10mg/kg/body weight). After euthanize, soleus and plantaris muscles were removed and prepared for histochemistry and cytofluorescence. T, S and ST significantly increased their maximum carrying load capacity compared to SEI and SEF (p<0.05). For soleus postsynaptic region, ST had lower total and stained area than SEF (p<0.05). For plantaris, the postsynaptic component of T was statistically larger than SEI (p<0.05). For soleus histochemistry, T, S and ST groups showed the same magnitude of type I myofibers hypertrophy, thus statistically different from SEI and SEF (p<0.05). The cross-sectional area of the type IIa myofibers of the ST was larger than SEF (p<0.05). The volume density of type I myofibers show to be lower in ST than SEI (p<0.05). As for type IIa myofibers, ST increased Vv [type IIa] compared to SEI and SEF (p<0.05). For plantaris, T significantly hypertrophied type I myofibers compared to SEI and SEF (p<0.05). S and ST demonstrated significant increases of type I myofibers compared to SEI and SEF (p<0.05). As for type IIx myofibers, both S and ST showed myofibers larger than SEI (p<0.05). However, only the ST had significant difference compared to SEF (p<0.05). In conclusion, both therapies, alone or combined, have little effect on the morphology of the NMJ postsynaptic region of distinct muscles. Moreover, the three therapies are potentially stimulating for strength gains and muscle hypertrophy.

Effects of Strength Training and Anabolic Steroid in the Peripheral Nerve and Skeletal Muscle Morphology of Aged Rats

Thirty male 20-month-old Wistar rats were divided into groups: IC—initial control (n = 6), FC—final control (n = 6), AC—anabolic hormone control (n = 6), ST—strength trained (n = 6) and STA—strength trained with anabolic hormone (n = 6). All groups were submitted to adaptation, familiarization and maximum load carrying test (MLCT). Strength training (6–8×/session with loads of 50%–100% MLCT, 3×/week and pause of 120 s) was performed in ladder climbing (LC) for 15 weeks. The administration of testosterone propionate (TP) was performed 2×/week (10 mg/kg) in animals in the AC and STA groups. After the experimental period, animals were euthanized and the tibial nerve and plantaris muscle removed and prepared for electron transmission and histochemistry. To compare the groups we used one-way ANOVA (post hoc Bonferroni), student’s t-tests for pre vs. post (dependent and independent variables) comparisons and significance level set at p ≤ 0.05. The following significant results were found: (a) aging decreased the number of myelinated axon fibers; (b) use of isolated TP increased the diameter of myelinated fibers, along with increased thickness of myelin sheath; (c) ST increased area of myelinated and unmyelinated fibers, together with the myelin sheath. These changes made it possible to increase the area occupied by myelinated fibers keeping their quantity and also reduce the interstitial space; and (d) association of anabolic steroid and ST increased the area of unmyelinated axons and thickness of the myelin sheath. Compared to ST, both strategies have similar results. However, Schwann cells increased significantly only in this strategy.

FoxO3a suppression and VPS34 activity are essential to anti-atrophic effects of leucine in skeletal muscle

Our aim is to gain insight into the mechanisms underlying the anti-atrophic effects of leucine, namely, the way that this amino acid can restrain the up-regulation of MuRF1 and Mafbx/Atrogin-1 in muscle atrophy. Male rats received dietary leucine supplementation for 1-3 days, during which time their hind limbs were immobilized. Our results showed that leucine inhibited Forkhead Box O3 (FoxO3a) translocation to cell nuclei. In addition, leucine was able to reverse the expected reduction of FoXO3a ubiquitination caused by immobilization. Unexpectedly, leucine promoted these effects independently of the Class I PI3K/Akt pathway. Vacuolar protein sorting 34 (VPS34; a Class III PI3K) was strongly localized in nuclei after immobilization and leucine supplementation was able to prevent this effect. In experiments on cultured primary myotubes, dexamethasone led to the localization of VPS34 in the nucleus. In addition, the pharmacological inhibition of VPS34 blocked VPS34 nuclear localization and impaired the protective effect of leucine upon myotube trophicity. Finally, the pharmacological inhibition of VPS34 in primary myotubes prevented the protective effects of leucine upon MuRF1 and Mafbx/Atrogin-1 gene expression. Autophagy-related target genes were not responsive to leucine. Thus, we demonstrate that the anti-atrophic effect of leucine is dependent upon FoxO3a suppression and VPS34 activity.

STRENGTH TRAINING AND ANABOLIC STEROID DO NOT AFFECT MUSCLE CAPILLARIZATION OF MIDDLE-AGED RATS

ABSTRACT Introduction: It is generally accepted that the capillary network decreases with advancing age. The combined effect of resistance training (RT) and testosterone still needs to be elucidated. Objective: This study aimed to measure capillary profile of different skeletal muscles of middle-aged rats undergoing RT and administration of exogenous testosterone. Methods: Wistar rats were divided into five experimental groups: control with 13-month-old rats (SC), control with 16-month-old rats (SE), aged rats + anabolic agent (SA), aged rats + RT (T), and aged rats + RT + anabolic agent (TA). Results: For soleus, the SE group presented a decrease in the percentage of capillaries in comparison to SC group. SA, T, and TA groups had increased capillary volume in comparison to SC. As for the extensor digitorum longus (EDL), SA, T, and TA groups demonstrated lower capillary volume and numeric density in comparison to SC and SE. The EDL of the T and TA groups presented 70% less capillaries than soleus. The numerical and volumetric density and capillary ratio by muscle fiber were not statistically altered by any intervention. The cross-sectional area (CSA) of the soleus of the SA, T and TA groups was statistically different from SC group. The soleus CSA was greater in the TA and T groups than in the SC, SE and SA groups, and the EDL CSA was greater in the TA compared to all other groups. The TA group had greater values than the SE, SA, and T groups. Conclusion: The type of intervention used did not affect any variables measured in the capillary profile. However, the use of anabolic steroid and/or RT showed a tendency to decrease the density of capillaries in the EDL.

BGP-15 Improves Aspects of the Dystrophic Pathology in mdx and dko Mice with Differing Efficacies in Heart and Skeletal Muscle

Duchenne muscular dystrophy is a severe and progressive striated muscle wasting disorder that leads to premature death from respiratory and/or cardiac failure. We have previously shown that treatment of young dystrophic mdx and dystrophin/utrophin null (dko) mice with BGP-15, a coinducer of heat shock protein 72, ameliorated the dystrophic pathology. We therefore tested the hypothesis that later-stage BGP-15 treatment would similarly benefit older mdx and dko mice when the dystrophic pathology was already well established. Later stage treatment of mdx or dko mice with BGP-15 did not improve maximal force of tibialis anterior (TA) muscles (in situ) or diaphragm muscle strips (in vitro). However, collagen deposition (fibrosis) was reduced in TA muscles of BGP-15-treated dko mice but unchanged in TA muscles of treated mdx mice and diaphragm of treated mdx and dko mice. We also examined whether BGP-15 treatment could ameliorate aspects of the cardiac pathology, and in young dko mice it reduced collagen deposition and improved both membrane integrity and systolic function. These results confirm BGP-15's ability to improve aspects of the dystrophic pathology but with differing efficacies in heart and skeletal muscles at different stages of the disease progression. These findings support a role for BGP-15 among a suite of pharmacological therapies for Duchenne muscular dystrophy and related disorders.

Daily consumption of tea catechins improves aerobic capacity in healthy male adults: a randomized double-blind, placebo-controlled, crossover trial

Our previous studies demonstrated that dietary supplementation with tea catechins combined with exercise improved endurance capacity in mice. This study aimed to demonstrate the effect of daily tea catechin consumption on aerobic capacity in humans. Sixteen Japanese non-athlete male subjects (aged 25-47 years) took 500 mL of a test beverage with or without tea catechins (570 mg) daily for 8 weeks and attended a training program twice a week. Aerobic capacity was evaluated by indirect calorimetry and near-infrared spectroscopy during graded cycle exercise. Catechin beverage consumption was associated with a significantly higher ventilation threshold during exercise and a higher recovery rate of oxygenated hemoglobin and myoglobin levels after graded cycle exercise when compared to subjects receiving the placebo beverage. These results indicate that daily consumption of tea catechins increases aerobic capacity when combined with semiweekly light exercise, which may be due to increased skeletal muscle aerobic capacity.

Age-related functional changes and susceptibility to eccentric contraction-induced damage in skeletal muscle cell

Depending upon external loading conditions, skeletal muscles can either shorten, lengthen, or remain at a fixed length as they produce force. Fixed-end or isometric contractions stabilize joints and allow muscles to act as active struts during locomotion. Active muscles dissipate energy when they are lengthened by an external force that exceeds their current force producing capacity. These unaccustomed eccentric activities often lead to muscle weakness, soreness, and inflammation. During aging, the ability to produce force under these conditions is reduced and appears to be due to not only reductions in muscle mass but also to alterations in the basic mechanisms of contraction. These alterations include impairments in the excitation–contraction process, and the action of the cross-bridges. Also, it is well known that age-related skeletal muscle atrophy is characterized by a preferential atrophy of fast fibers, and increased susceptibility to fast muscle fiber when aged muscles are exposed to eccentric contraction followed by the impaired recovery process has been reported. Taken together, the selective loss of fast muscle fiber in aged muscle could be affected by eccentric-induced muscle damage, which has significant implication to identify the etiology of the age-related functional changes. Therefore, in this review the alteration of age-related muscle function and its impact to/of eccentric induced muscle damage and recovery will be addressed in detail.

Lessons from mammalian hibernators: molecular insights into striated muscle plasticity and remodeling

Striated muscle shows an amazing ability to adapt its structural apparatus based on contractile activity, loading conditions, fuel supply, or environmental factors. Studies with mammalian hibernators have identified a variety of molecular pathways which are strategically regulated and allow animals to endure multiple stresses associated with the hibernating season. Of particular interest is the observation that hibernators show little skeletal muscle atrophy despite the profound metabolic rate depression and mechanical unloading that they experience during long weeks of torpor. Additionally, the cardiac muscle of hibernators must adjust to low temperature and reduced perfusion, while the strength of contraction increases in order to pump cold, viscous blood. Consequently, hibernators hold a wealth of knowledge as it pertains to understanding the natural capacity of myocytes to alter structural, contractile and metabolic properties in response to environmental stimuli. The present review outlines the molecular and biochemical mechanisms which play a role in muscular atrophy, hypertrophy, and remodeling. In this capacity, four main networks are highlighted: (1) antioxidant defenses, (2) the regulation of structural, contractile and metabolic proteins, (3) ubiquitin proteosomal machinery, and (4) macroautophagy pathways. Subsequently, we discuss the role of transcription factors nuclear factor (erythroid-derived 2)-like 2 (Nrf2), Myocyte enhancer factor 2 (MEF2), and Forkhead box (FOXO) and their associated posttranslational modifications as it pertains to regulating each of these networks. Finally, we propose that comparing and contrasting these concepts to data collected from model organisms able to withstand dramatic changes in muscular function without injury will allow researchers to delineate physiological versus pathological responses.

α-Lipoic Acids Promote the Protein Synthesis of C2C12 Myotubes by the TLR2/PI3K Signaling Pathway

Skeletal muscle protein turnover is regulated by endocrine hormones, nutrients, and inflammation. α-Lipoic acid (ALA) plays an important role in energy homeostasis. Therefore, the aim of this study was to investigate the effects of ALA on protein synthesis in skeletal muscles and reveal the underlying mechanism. ALA (25 μM) significantly increased the protein synthesis and phosphorylation of Akt, mTOR, and S6 in C2C12 myotubes with attenuated phosphorylation of AMPK, Ikkα/β, and eIF2α. Intraperitoneal injection of 50 mg/kg ALA also produced the same results in mouse gastrocnemius. Both the PI3K (LY294002) and mTOR (rapamycin) inhibitors abolished the effects of ALA on protein synthesis in the C2C12 myotubes. However, AICAR (AMPK agonist) failed to block the activation of mTOR and S6 by ALA. ALA increased TLR2 and MyD88 mRNA expression in the C2C12 myotubes. TLR2 knockdown by siRNA almost eliminated the effects of ALA on protein synthesis and the Akt/mTOR pathway in the C2C12 myotubes. Immunoprecipitation data showed that ALA enhanced the p85 subunit of PI3K binding to MyD88. These findings indicate that ALA induces protein synthesis and the PI3K/Akt signaling pathway by TLR2.

Icaritin requires Phosphatidylinositol 3 kinase (PI3K)/Akt signaling to counteract skeletal muscle atrophy following mechanical unloading

Counteracting muscle atrophy induced by mechanical unloading/inactivity is of great clinical need and challenge. A therapeutic agent that could counteract muscle atrophy following mechanical unloading in safety is desired. This study showed that natural product Icaritin (ICT) could increase the phosphorylation level of Phosphatidylinositol 3 kinase (PI3K) at p110 catalytic subunit and promote PI3K/Akt signaling markers in C2C12 cells. This study further showed that the high dose ICT treatment could significantly attenuate the decreases in the phosphorylation level of PI3K at p110 catalytic subunit and its downstream markers related to protein synthesis, and inhibit the increases in protein degradation markers at mRNA and protein levels in rat soleus muscle following 28-day hindlimb unloading. In addition, the decreases in soleus muscle mass, muscle fiber cross-sectional area, twitch force, specific force, contraction time and half relaxation time could be significantly attenuated by the high dose ICT treatment. The low dose ICT treatment could moderately attenuate the above changes induced by unloading. Wortmannin, a specific inhibitor of PI3K at p110 catalytic subunit, could abolish the above effects of ICT in vitro and in vivo, indicating that PI3K/Akt signaling could be required by ICT to counteract skeletal muscle atrophy following mechanical unloading.

L-Citrulline Protects Skeletal Muscle Cells from Cachectic Stimuli through an iNOS-Dependent Mechanism

Dietary L-citrulline is thought to modulate muscle protein turnover by increasing L-arginine availability. To date, the direct effects of increased L-citrulline concentrations in muscle have been completely neglected. Therefore, we determined the role of L-citrulline in regulating cell size during catabolic conditions by depriving mature C2C12 myotubes of growth factors (serum free; SF) or growth factors and nutrients (HEPES buffered saline; HBS). Cells were treated with L-citrulline or equimolar concentrations of L-arginine (positive control) or L-alanine (negative control) and changes in cell size and protein turnover were assessed. In myotubes incubated in HBS or SF media, L-citrulline improved rates of protein synthesis (HBS: +63%, SF: +37%) and myotube diameter (HBS: +18%, SF: +29%). L-citrulline treatment substantially increased iNOS mRNA expression (SF: 350%, HBS: 750%). The general NOS inhibitor L-NAME and the iNOS specific inhibitor aminoguanidine prevented these effects in both models. Depriving myotubes in SF media of L-arginine or L-leucine, exacerbated wasting which was not attenuated by L-citrulline. The increased iNOS mRNA expression was temporally associated with increases in mRNA of the endogenous antioxidants SOD1, SOD3 and catalase. Furthermore, L-citrulline prevented inflammation (LPS) and oxidative stress (H₂O₂) induced muscle cell wasting. In conclusion, we demonstrate a novel direct protective effect of L-citrulline on skeletal muscle cell size independent of L-arginine that is mediated through induction of the inducible NOS (iNOS) isoform. This discovery of a nutritional modulator of iNOS mRNA expression in skeletal muscle cells could have substantial implications for the treatment of muscle wasting conditions.

Low molecular weight guluronate prevents TNF-α-induced oxidative damage and mitochondrial dysfunction in C2C12 skeletal muscle cells

Muscle wasting is associated with a variety of chronic or inflammatory disorders. Evidence suggests that inflammatory cytokines play a vital role in muscle inflammatory pathology and this may result in oxidative damage and mitochondrial dysfunction in skeletal muscle. In our study, we used microwave degradation to prepare a water-soluble low molecular weight guluronate (LMG) of 3000 Da from Fucus vesiculosus obtained from Canada, the Atlantic Ocean. We demonstrated the structural characteristics, using HPLC, FTIR and NMR of LMG and investigated its effects on oxidative damage and mitochondrial dysfunction in C2C12 skeletal muscle cells induced by tumor necrosis factor alpha (TNF-α), a cell inflammatory cytokine. The results indicated that LMG could alleviate mitochondrial reactive oxygen species (ROS) production, increase the activities of antioxidant enzymes (GSH and SOD), promote mitochondrial membrane potential (MMP) and upregulate the expression of mitochondrial respiratory chain protein in TNF-α-induced C2C12 cells. LMG supplement also increased the mitochondrial DNA copy number and mitochondrial biogenesis related genes in TNF-α-induced C2C12 cells. LMG may exert these protective effects through the nuclear factor kappa B (NF-κB) signaling pathway. These suggest that LMG is capable of protecting TNF-α-induced C2C12 cells against oxidative damage and mitochondrial dysfunction.

Citrulline does not prevent skeletal muscle wasting or weakness in limb-casted mice

BACKGROUND

Increasing arginine (Arg) availability reduces atrophy in cultured skeletal muscle cells. Supplementation with its metabolic precursor citrulline (Cit) is more effective at improving skeletal muscle Arg concentrations.

OBJECTIVE

We tested the hypothesis that Cit supplementation would attenuate skeletal muscle atrophy and loss of function during hindlimb immobilization in mice.

METHODS

Male C57BL/6JArc mice underwent 14 d of unilateral hindlimb immobilization/plaster casting and were supplemented with ~0.81 g Cit · kg⁻¹ · d⁻¹ (CIT group) or Ala (ALA group) mixed into their food. The uncasted contralateral limb (internal control) and an uncasted group (CON) served as controls. Muscle atrophy was evaluated with mass, fiber area, and in situ muscle function.

RESULTS

Tibialis anterior (TA) muscle mass [ALA: 37.6 ± 0.92 mg; CIT: 38.3 ± 1.25 mg] and peak tetanic force (ALA: 1150 ± 38.5 mN; CIT: 1150 ± 52.0 mN) were lower (P < 0.001) in the ALA (53.9 ± 0.42 mg) and CIT (1760 ± 28.5 mN) groups than in the CON group. No difference was found between ALA and CIT groups for TA mass, fiber area, or peak force. The mRNA expression of the nitric oxide synthase 2, inducible (Nos2; ~15-fold) and B-cell chronic lymphoid leukemia/lymphoma 2/adenovirus E1B 19 kDa interacting protein 3 (Bnip3; ~17-fold) genes and the ratio of microtubule-associated protein light chain 3BII to 3BI (LC3BII:LC3BI) (50.5% ± 17.7%) were higher (P < 0.05) in the ALA group than in the CON group, suggesting increased autophagy. In the CIT group, Bnip3 mRNA was lower (-70%; P < 0.05) and Nos2 mRNA tended to be lower (-45%; P = 0.05) than in the ALA group, whereas LC3BII:LC3BI was not different from the CON group.

CONCLUSIONS

Cit treatment of male mice did not affect therapeutically relevant outcome measures such as skeletal muscle mass and peak muscle force after 14 d of hindlimb immobilization.

Daily consumption of milk fat globule membrane plus habitual exercise improves physical performance in healthy middle-aged adults

Our recent studies demonstrated that habitual exercise plus dietary supplementation with milk fat globule membrane (MFGM) improved endurance capacity and muscle function by stimulating neuromuscular development in mice. The aim of this study was to investigate the efficacy of dietary MFGM supplementation plus habitual exercise on the physical performance of middle-aged Japanese adults in a pilot randomized, double-blind, placebo-controlled trial. Forty-four subjects (men, n = 22; women, n = 22) were randomly assigned into two groups: one received placebo tablets (placebo group, n = 22 [men, n = 11; women, n = 11]), while the other received MFGM tablets (MFGM group, n = 22 [men, n = 11; women, n = 11]). The subjects ingested either MFGM (1 g/day) or placebo (1 g/day of whole milk powder) tablets every day for the 10-week study period and engaged in an exercise training program twice per week. A physical function test was performed at baseline and at 5 and 10 weeks. A significant group-by-time interaction was found for the side step test, muscle cross-sectional area (CSA), and muscle fiber conduction velocity (MFCV). In the placebo group, there were no significant intragroup differences. In the MFGM group, side step score and muscle CSA were significantly greater at 10 weeks compared to the baseline, and MFCV was significantly higher than that in the placebo group at 10 weeks. The changes in percentage of the side step score, muscle CSA, and MFCV in the MFGM group were significantly higher than in the placebo group at 10 weeks. These results suggest that daily MFGM ingestion combined with regular exercise might enhance physical performance such as agility in middle-aged adults.

Supplementation with Pfaffia glomerata (Sprengel) Pedersen does not affect androgenic-anabolic parameters in male rats

ETHNOPHARMACOLOGICAL RELEVANCE

Paffia spp (Amaranthacea) has a widespread use of in Brazil as a possible hormonal supplement and a substitute of Panax ginseng, although information on its reproductive effects is missing.

AIM OF THE STUDY

To evaluated possible anabolic-androgenic or anti-androgenic effects of Pfaffia glomerata (PG) extract using intact eight-months-old male rats and pre-pubertal castrated rats.

MATERIALS AND METHODS

Three different dose levels of PG (8.5, 30 and 85 mg/kg/day) were administered to eight-months-old rats for 28 days or to castrated males for 7 days (Hershberger assay). In the experiment with intact animals, 24h fecal samples were collected for quantification of fecal metabolites of androgens throughout treatment. At the end of the treatment period, animals were euthanized for evaluation of serum testosterone, reproductive organ weights, number of spermatids per testis, diameter of seminiferous tubules and cross-sectional area of soleus muscle fibers. In the Hershberber assay, androgenic or anti-androgenic effects were evaluated by the weights of androgen-dependent tissues: ventral prostate, seminal vesicle, glans penis and levator ani muscle/bulbocavernosus muscle.

RESULTS

No effects were observed in the concentrations of fecal metabolites of androgens monitored during the treatment of intact eight-months-old rats. Moreover, at the end of treatment, no changes were seen in any of the investigated parameters. In the Hershberger assay, the PG extract did not induce androgenic or anti-androgenic effects at the dose levels tested. Significant effects were only observed in animals treated with testosterone and testosterone plus flutamide, which were used as positive controls for androgenicity and anti-androgenicity, respectively.

CONCLUSIONS

At the dose levels tested, PG extract does not induce anabolic-androgenic or anti-androgenic effects in rats.

Pharmacology of manipulating lean body mass

Dysfunction and wasting of skeletal muscle as a consequence of illness decreases the length and quality of life. Currently, there are few, if any, effective treatments available to address these conditions. Hence, the existence of this unmet medical need has fuelled large scientific efforts. Fortunately, these efforts have shown many of the underlying mechanisms adversely affecting skeletal muscle health. With increased understanding have come breakthrough disease-specific and broad spectrum interventions, some progressing through clinical development. The present review focuses its attention on the role of the antagonistic process regulating skeletal muscle mass before branching into prospective promising therapeutic targets and interventions. Special attention is given to therapies in development against cancer cachexia and Duchenne muscular dystrophy before closing remarks on design and conceptualization of future therapies are presented to the reader.

Serum C1q as a novel biomarker of sarcopenia in older adults

Aging-induced elevation in C1q secretion activates the Wnt signaling pathway in muscles, leading to the development of muscle fibrosis. However, the association between serum C1q level and muscle mass and strength remains unclear in humans. The aim of the study was to elucidate whether serum C1q level is associated with aging- and resistance training-induced changes in muscle mass and strength. First, in a cross-sectional study, we investigated the association between serum C1q level and muscle mass and strength in 131 healthy subjects, aged 20-81 yr. Second, in an intervention study, we examined the association between the effects of serum C1q level and muscle mass and strength on 12 wk resistance training in 11 healthy older adults (60-81 yr). In the cross-sectional study, serum C1q level increased with aging and was negatively correlated with muscle mass and strength. Furthermore, 12 wk resistance training in older adults reduced the age-associated elevation in serum C1q levels. The training effect of serum C1q level significantly correlated with the change in the cross-sectional area of the thigh (r = -0.703; P < 0.01). Serum C1q level may reflect loss of muscle mass; therefore, C1q may be a novel biomarker of sarcopenia.

Arginine protects muscle cells from wasting in vitro in an mTORC1-dependent and NO-independent manner

Amino acids are potent regulators of muscle protein synthesis and breakdown and have received considerable attention for the treatment of muscle wasting conditions. Arginine is critically involved in numerous physiological functions including providing substrate for the production of creatine, urea and nitric oxide (NO) and in the synthesis of new proteins. However, little is known about the direct effects of arginine on skeletal muscle protein synthesis during catabolic conditions. The aims of this study were to determine whether exogenous arginine could protect skeletal muscle cells from wasting directly and whether this effect was dependent on production of NO and/or activation of the rapamycin-sensitive mechanistic target of rapamycin complex 1 (mTORC1) signalling pathway. To explore these aims, we deprived mature C2C12 myotubes from nutrients and growth factors by incubating them in HEPES buffered saline with arginine or equimolar concentrations of alanine (control). Our results show that arginine: increased the ratio of phosphorylated to total mTOR (146 %), S6 (40 %) and 4EBP1 (69 %); increased protein synthesis (69 %) during the first hour of treatment; and increased myotube diameter by ~15 %. Experiments using the NO synthase inhibitor L-NG-Nitroarginine Methyl Ester showed a NO-independent protection from muscle wasting. On the other hand, the mTORC1 inhibitor rapamycin prevented increases in phosphorylated S6, protein synthesis and myotube diameter. The activation of mTORC1 and protein synthesis by arginine was not associated with changes in the phosphorylation status of Akt, but rather increased the expression of the amino acid-sensitive type III PI3-kinase Vps34 signalling protein. These data support a direct role for arginine in the regulation of mTORC1 in skeletal muscle.

Gut barrier dysfunction and microbial translocation in cancer cachexia: a new therapeutic target

Purpose of Review

Cachexia is a complex metabolic syndrome characterized by skeletal muscle and adipose tissue loss and is frequently associated with emaciation, anorexia, systemic inflammation, and metabolic dysfunction. Lack of a clear understanding of the cause of cancer cachexia has impeded progress in identifying effective therapeutic agents. This review summarizes recent publications on the role of gut barrier function, intestinal microbiota, and inflammation in the etiology of cancer cachexia and new therapeutic interventions that may benefit treatment strategies.

Recent Findings

Significant advances have been made in understanding the composition and metabolic capabilities of the intestinal microbiota and its impact on gut barrier function with implications for certain inflammatory-based diseases. Recent studies reported associations between intestinal permeability and endotoxemia with development of cancer cachexia and other metabolic disorders. Improvements in intestinal function and weight gain along with decreased inflammation have been reported for potential therapeutic agents such as eicosapentaenoic acid, immunoglobulin isolates, and probiotics.

Summary

Continued progress in the scientific understanding of the complex interplay between the intestinal microbiota, gut barrier function, and host inflammatory responses will uncover new therapeutic targets to help avoid the serious metabolic alterations associated with cachexia.

Functional β-adrenoceptors are important for early muscle regeneration in mice through effects on myoblast proliferation and differentiation

Muscles can be injured in different ways and the trauma and subsequent loss of function and physical capacity can impact significantly on the lives of patients through physical impairments and compromised quality of life. The relative success of muscle repair after injury will largely determine the extent of functional recovery. Unfortunately, regenerative processes are often slow and incomplete, and so developing novel strategies to enhance muscle regeneration is important. While the capacity to enhance muscle repair by stimulating β₂-adrenoceptors (β-ARs) using β₂-AR agonists (β₂-agonists) has been demonstrated previously, the exact role β-ARs play in regulating the regenerative process remains unclear. To investigate β-AR-mediated signaling in muscle regeneration after myotoxic damage, we examined the regenerative capacity of tibialis anterior and extensor digitorum longus muscles from mice lacking either β₁-AR (β₁-KO) and/or β₂-ARs (β₂-KO), testing the hypothesis that muscles from mice lacking the β₂-AR would exhibit impaired functional regeneration after damage compared with muscles from β₁-KO or β₁/β₂-AR null (β₁/β₂-KO) KO mice. At 7 days post-injury, regenerating muscles from β₁/β₂-KO mice produced less force than those of controls but muscles from β₁-KO or β₂-KO mice did not exhibit any delay in functional restoration. Compared with controls, β₁/β₂-KO mice exhibited an enhanced inflammatory response to injury, which delayed early muscle regeneration, but an enhanced myoblast proliferation later during regeneration ensured a similar functional recovery (to controls) by 14 days post-injury. This apparent redundancy in the β-AR signaling pathway was unexpected and may have important implications for manipulating β-AR signaling to improve the rate, extent and efficacy of muscle regeneration to enhance functional recovery after injury.

Dexamethasone-induced autophagy mediates muscle atrophy through mitochondrial clearance

Glucocorticoids, such as dexamethasone, enhance protein breakdown via ubiquitin-proteasome system. However, the role of autophagy in organelle and protein turnover in the glucocorticoid-dependent atrophy program remains unknown. Here, we show that dexamethasone stimulates an early activation of autophagy in L6 myotubes depending on protein kinase, AMPK, and glucocorticoid receptor activity. Dexamethasone increases expression of several autophagy genes, including ATG5, LC3, BECN1, and SQSTM1 and triggers AMPK-dependent mitochondrial fragmentation associated with increased DNM1L protein levels. This process is required for mitophagy induced by dexamethasone. Inhibition of mitochondrial fragmentation by Mdivi-1 results in disrupted dexamethasone-induced autophagy/mitophagy. Furthermore, Mdivi-1 increases the expression of genes associated with the atrophy program, suggesting that mitophagy may serve as part of the quality control process in dexamethasone-treated L6 myotubes. Collectively, these data suggest a novel role for dexamethasone-induced autophagy/mitophagy in the regulation of the muscle atrophy program.

Involvement of microRNAs in the regulation of muscle wasting during catabolic conditions

Loss of muscle proteins and the consequent weakness has important clinical consequences in diseases such as cancer, diabetes, chronic heart failure, and in aging. In fact, excessive proteolysis causes cachexia, accelerates disease progression, and worsens life expectancy. Muscle atrophy involves a common pattern of transcriptional changes in a small subset of genes named atrophy-related genes or atrogenes. Whether microRNAs play a role in the atrophy program and muscle loss is debated. To understand the involvement of miRNAs in atrophy we performed miRNA expression profiling of mouse muscles under wasting conditions such as fasting, denervation, diabetes, and cancer cachexia. We found that the miRNA signature is peculiar of each catabolic condition. We then focused on denervation and we revealed that changes in transcripts and microRNAs expression did not occur simultaneously but were shifted. Indeed, whereas transcriptional control of the atrophy-related genes peaks at 3 days, changes of miRNA expression maximized at 7 days after denervation. Among the different miRNAs, microRNA-206 and -21 were the most induced in denervated muscles. We characterized their pattern of expression and defined their role in muscle homeostasis. Indeed, in vivo gain and loss of function experiments revealed that miRNA-206 and miRNA-21 were sufficient and required for atrophy program. In silico and in vivo approaches identified transcription factor YY1 and the translational initiator factor eIF4E3 as downstream targets of these miRNAs. Thus miRNAs are important for fine-tuning the atrophy program and their modulation can be a novel potential therapeutic approach to counteract muscle loss and weakness in catabolic conditions.

Rasch analysis of the Edmonton Symptom Assessment System and research implications

BACKGROUND

Reliable and valid assessment of the disease burden across all forms of cancer is critical to the evaluation of treatment effectiveness and patient progress. The Edmonton Symptom Assessment System (esas) is used for routine evaluation of people attending for cancer care. In the present study, we used Rasch analysis to explore the measurement properties of the esas and to determine the effect of using Rasch-proposed interval-level esas scoring compared with traditional scoring when evaluating the effects of an exercise program for cancer survivors.

METHODS

Polytomous Rasch analysis (Andrich's rating-scale model) was applied to data from 26,645 esas questionnaires completed at the Juravinski Cancer Centre. The fit of the esas to the polytomous Rasch model was investigated, including evaluations of differential item functioning for sex, age, and disease group. The research implication was investigated by comparing the results of an observational research study previously analysed using a traditional approach with the results obtained by Rasch-proposed interval-level esas scoring.

RESULTS

The Rasch reliability index was 0.73, falling short of the desired 0.80-0.90 level. However, the esas was found to fit the Rasch model, including the criteria for uni-dimensional data. The analysis suggests that the current esas scoring system of 0-10 could be collapsed to a 6-point scale. Use of the Rasch-proposed interval-level scoring yielded results that were different from those calculated using summarized ordinal-level esas scores. Differential item functioning was not found for sex, age, or diagnosis groups.

CONCLUSIONS

The esas is a moderately reliable uni-dimensional measure of cancer disease burden and can provide interval-level scaling with Rasch-based scoring. Further, our study indicates that, compared with the traditional scoring metric, Rasch-based scoring could result in substantive changes to conclusions.

'From death, lead me to immortality' - mantra of ageing skeletal muscle

Skeletal muscle is a post-mitotic tissue maintained by repair and regeneration through a population of stem cell-like satellite cells. Following muscle injury, satellite cell proliferation is mediated by local signals ensuring sufficient progeny for tissue repair. Age–related changes in satellite cells as well as to the local and systemic environment potentially impact on the capacity of satellite cells to generate sufficient progeny in an ageing organism resulting in diminished regeneration. ‘Rejuvenation’ of satellite cell progeny and regenerative capacity by environmental stimuli effectors suggest that a subset of age-dependent satellite cell changes may be reversible. Epigenetic regulation of satellite stem cells that include DNA methylation and histone modifications which regulate gene expression are potential mechanisms for such reversible changes and have been shown to control organismal longevity. The area of health and ageing that is likely to benefit soonest from advances in the biology of adult stem cells is the emerging field of regenerative medicine. Further studies are needed to elucidate the mechanisms by which epigenetic modifications regulate satellite stem cell function and will require an increased understanding of stem-cell biology, the environment of the aged tissue and the interaction between the two.

Glycine administration attenuates skeletal muscle wasting in a mouse model of cancer cachexia

BACKGROUND AND AIMS

The non-essential amino acid, glycine, is often considered biologically neutral, but some studies indicate that it could be an effective anti-inflammatory agent. Since inflammation is central to the development of cancer cachexia, glycine supplementation represents a simple, safe and promising treatment. We tested the hypothesis that glycine supplementation reduces skeletal muscle inflammation and preserves muscle mass in tumor-bearing mice.

METHODS

To induce cachexia, CD2F1 mice received a subcutaneous injection of PBS (control, n = 12) or C26 tumor cells (n = 32) in accordance with the protocols developed by Murphy et al. [Murphy KT, Chee A, Trieu J, Naim T, Lynch GS. Importance of functional and metabolic impairments in the characterization of the C-26 murine model of cancer cachexia. Dis Models Mech 2012;5(4):533-545.]. Subcutaneous injections of glycine (n = 16) or PBS (n = 16) were administered daily for 21 days and at the conclusion of treatment, selected muscles, tumor and adipose tissue were collected and prepared for Real-Time RT-PCR or western blot analysis.

RESULTS

Glycine attenuated the loss of fat and muscle mass, blunted increases in markers of inflammation (F4/80, P = 0.01 & IL-6 mRNA, P = 0.01) and atrophic signaling (MuRF, P = 0.047; atrogin-1, P = 0.04; LC3B, P = 0.06 and; BNIP3, P = 0.10) and tended to attenuate the loss of body mass (P = 0.07), muscle function (P = 0.06), and oxidative stress (GSSG/GSH, P = 0.06 and DHE, P = 0.07) seen in tumor-bearing mice. Preliminary studies that compared the effect of glycine administration with isonitrogenous doses of alanine or citrulline showed that the observed protective effect was specific to glycine.

CONCLUSIONS

Glycine protects skeletal muscle from cancer-induced wasting and loss of function, reduces the oxidative and inflammatory burden, and reduces the expression of genes associated with muscle protein breakdown in cancer cachexia. Importantly, these effects were glycine specific.

Large-scale isolation of human skeletal muscle satellite cells from post-mortem tissue and development of quantitative assays to evaluate modulators of myogenesis

BACKGROUND

During aging, there is a decreased ability to maintain skeletal muscle mass and function (sarcopenia). Such changes in skeletal muscle are also co-morbidities of diseases including cancer, congestive heart failure and chronic obstructive pulmonary disease. The loss of muscle mass results in decreased strength and exercise tolerance and reduced ability to perform daily activities. Pharmacological agents addressing these pathologies could have significant clinical impact, but their identification requires understanding of mechanisms driving myotube formation (myogenesis) and atrophy and provision of relevant assays. The aim of this study was to develop robust in vitro methods to study human myogenesis.

METHODS

Satellite cells were isolated by digestion of post-mortem skeletal muscle and selection using anti-CD56 MicroBeads. CD56(+) cell-derived myotubes were quantified by high content imaging of myosin heavy chains. TaqMan-polymerase chain reaction arrays were used to quantify expression of 41 selected genes during differentiation. The effects of activin receptor agonists and tumour necrosis factor alpha (TNFα) on myogenesis and gene expression were characterised.

RESULTS

Large-scale isolation of CD56(+) cells enabled development of a quantitative myogenesis assay with maximal myotube formation 3 days after initiating differentiation. Gene expression analysis demonstrated expression of 19 genes changed substantially during myogenesis. TNFα and activin receptor agonists inhibited myogenesis and downregulated gene expression of muscle transcription factors, structural components and markers of oxidative phenotype, but only TNFα increased expression of pro-inflammatory markers.

CONCLUSIONS

We have developed methods for large-scale isolation of satellite cells from muscle and quantitative assays for studying human myogenesis. These systems may prove useful as part of a screening cascade designed to identify therapeutic agents for improving muscle function.