"Nutraceuticals" in relation to human skeletal muscle and exercise

A randomised controlled trial assessing the potential of palmitoylethanolamide (PEA) to act as an adjuvant to resistance training in healthy adults: a study protocol

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) and analgesics are used frequently by athletes either prophylactically for the prevention of pain, or to accelerate recovery following an injury. However, these types of pain management strategies have been shown to inhibit signalling pathways (e.g., cyclooxygenase-2) that may hinder muscular adaptations such as hypertrophy and strength. Nutraceuticals such as palmitoylethanolamide (PEA) have analgesic properties that act via different mechanisms to NSAIDS/analgesics. Furthermore, PEA has been shown to have a positive effect on sleep and may contribute positively to muscle hypertrophy via PKB activation. Although PEA has not been widely studied in the athletic or recreationally active population, it may provide an alternative solution for pain management if it is found not to interfere with, or enhance training adaptations. Therefore, the study aim is to investigate the effects of daily PEA supplementation (Levagen + ®) with resistance training on lean body mass, strength, power and physical performance and outcomes of recovery (e.g., sleep) compared to placebo.

METHODS

This double-blind, randomised controlled study will take place over an 11-week period (including 8-weeks of progressive resistance training). Participants for this study will be 18-35 years old, healthy active adults that are not resistance trained. Participants will attend a familiarisation (week 0), pre-testing (week 1) and final-testing (week 11). At the pre-testing and final-testing weeks, total lean body mass (dual-energy X-ray absorptiometry; DXA), total mid-thigh cross sectional area (pQCT), maximal muscular strength (1 repetition maximum bench press, isometric mid-thigh pull) and power (countermovement jump and bench throw) will be assessed. Additionally, circulating inflammatory cytokines and anabolic hormones, sleep quality and quantity (ActiGraph), pain and subjective wellbeing (questionnaires) will also be examined.

DISCUSSION

This study is designed to investigate the effects that PEA may have on pre-to post intervention changes in total body and regional lean muscle mass, strength, power, sleep, subjective wellbeing, and pain associated with resistance training and menstruation compared with the placebo condition. Unlike other NSAIDs and analgesics, which may inhibit muscle protein synthesis and training adaptations, PEA which provides analgesia via alternative mechanisms may provide an alternative pain management solution. It is therefore important to determine if this analgesic compound interferes with or enhances training adaptations so that athletes and active individuals can make an informed decision on their pain management strategies.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR: ACTRN12621001726842p).

A proprietary blend of Sphaeranthus indicus flower head and Mangifera indica bark extracts increases muscle strength and enhances endurance in young male volunteers: a randomized, double-blinded, placebo-controlled trial

Background

The demand for safe and efficacious botanical formulations to increase muscle mass, strength, and stamina is increasing among athletes and the general population. The nutraceutical supplements of medicinal plant origin exert minimal health concern.

Objective

This randomized, double-blind, placebo-controlled study was aimed to evaluate the ergogenic potential of a proprietary, standardized formulation (LI12542F6) of Sphaeranthus indicus flower head and Mangifera indica stem bark extracts.

Methods

Forty male participants 18-40 years of age were assigned to receive either a placebo (n = 20) or 650 mg/day LI12542F6 (n = 20) for 56 days. All participants performed a fixed set of resistance exercises during the intervention. The primary endpoint was the change from baseline muscle strength, assessed by one-repetition maximum (1-RM) bench and leg presses, and handgrip strength. The secondary endpoints included cable pull-down repetitions, time to exhaustion on a treadmill, mid-upper arm circumference (MUAC), body composition using dual-energy x-ray absorptiometry (DEXA), and free testosterone and cortisol levels in serum.

Results

Fifty-six days supplementation of LI12542F6 significantly improved baseline bench press (P < 0.0001), leg press (P < 0.0001), handgrip strength (P < 0.0006), number of repetitions (P < 0.0001), and time to exhaustion (P < 0.0008), compared to placebo. Post-trial, the LI12542F6 group also showed significantly increased MUAC and improved body composition and serum hormone levels. The participants' hematology, clinical chemistry, and vital signs were within the normal range. No adverse events were observed.

Conclusion

This study demonstrates that LI12542F6 supplementation significantly increases muscle strength and size and improves endurance in healthy men. Also, LI12542F6 is well-tolerated by the participants.

Nutraceuticals and COVID-19: A mechanistic approach toward attenuating the disease complications

Nutraceuticals have emerged as potential compounds to attenuate the COVID-19 complications. Precisely, these food additives strengthen the overall COVID treatment and enhance the immunity of a person. Such compounds have been used at a large scale, in almost every household due to their better affordability and easy access. Therefore, current research is focused on developing newer advanced formulations from potential drug candidates including nutraceuticals with desirable properties viz, affordability, ease of availability, ease of administration, stability under room temperature, and potentially longer shelf-lives. As such, various nutraceutical-based products such as compounds could be promising agents for effectively managing COVID-19 symptoms and complications. Most importantly, regular consumption of such nutraceuticals has been shown to boost the immune system and prevent viral infections. Nutraceuticals such as vitamins, amino acids, flavonoids like curcumin, and probiotics have been studied for their role in the prevention of COVID-19 symptoms such as fever, pain, malaise, and dry cough. In this review, we have critically reviewed the potential of various nutraceutical-based therapeutics for the management of COVID-19. We searched the information relevant to our topic from search engines such as PubMed and Scopus using COVID-19, nutraceuticals, probiotics, and vitamins as a keyword. Any scientific literature published in a language other than English was excluded. PRACTICAL APPLICATIONS: Nutraceuticals possess both nutritional values and medicinal properties. They can aid in the prevention and treatment of diseases, as well as promote physical health and the immune system, normalizing body functions, and improving longevity. Recently, nutraceuticals such as probiotics, vitamins, polyunsaturated fatty acids, trace minerals, and medicinal plants have attracted considerable attention and are widely regarded as potential alternatives to current therapeutic options for the effective management of various diseases, including COVID-19.

The Combined Oral Stable Isotope Assessment of Muscle (COSIAM) reveals D-3 creatine derived muscle mass as a standout cross-sectional biomarker of muscle physiology vitality in older age

Validated diagnostics of skeletal muscle vitality could benefit clinical and basic science in terms of mechanistic insights and in determining the efficacy of interventions, e.g. exercise/pharmaceuticals/nutrients. We recently developed a Combined Oral Assessment of Muscle (COSIAM) that can be used to simultaneously quantify whole-body muscle mass (WBMM), muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Here, we aimed to establish, in a cross-sectional fashion, links between COSIAM parameters and established aspects of muscle function. We recruited 37 healthy older adults (male (M):female (F) (21/16); 72 ± 5 y)) into a 3-day trial. Subjects consumed D₃-creatine (D₃-Cr dilution to assess WBMM), D₂O (MPS by incorporation of alanine) and D₃-3-methylhistidine (D₃-MH dilution to assess MPB). A biopsy at day 3 was used to determine MPS, and blood/urine samples were collected to determine D₃-Cr/D₃-MH dilution for WBMM and MPB. Physiological measures of muscle mass (e.g. DXA/ultrasound) and function (e.g. handgrip strength, maximum voluntary contraction (MVC), one-repetition maximum (1-RM)) were ascertained. A stepwise linear regression approach was used to address links between facets of COSIAM (MPS, MPB, WBMM) and muscle physiology. Despite expected differences in muscle mass, there were no significant differences in MPS or MPB between sexes. WBMM as measured using D₃-Cr positively correlated with DXA-derived lean body mass (LBM) and appendicular LBM (ABLM). Stepwise linear regression was used to assess which combination of MPS, MPB, D₃-Cr and absolute synthesis rate (ASR) best predicted physiological measures of muscle health in these older adults. D₃-Cr WBMM alone was the best predictor of handgrip, 1RM and MVC, and outperformed more traditional measures of muscle mass by DXA. The COSIAM approach substantiates D₃-Cr as a robust biomarker of multiple muscle physiology health biomarkers. Future work using COSIAM should focus upon how and which parameters it can inform upon in relation to disease progression and the efficacy of interventions.

A 12-Week Randomized Double-Blind Placebo-Controlled Clinical Trial, Evaluating the Effect of Supplementation with a Spinach Extract on Skeletal Muscle Fitness in Adults Older Than 50 Years of Age

The aim of a 12-week randomized double-blind placebo-controlled study was to assess the effect of daily supplementation with a natural extract of Spinacia oleracea L. (4 × 500 mg capsules/day; total 2 g per day) combined with a moderate-intensity training program (1 h session/3 times a week) on skeletal muscle fitness in adults over 50 years of age. Muscle strength assessed by isokinetic and isometric dynamometry improved significantly in the experimental (n = 23) and the placebo (n = 22) groups, but the magnitude of improvement was higher in the experimental group, with between-group differences in almost all variables, including isokinetic at 60° s⁻¹ in knee extension, peak torque (p < 0.007); total work per repetition maximum (p < 0.009); isokinetic at 180°s⁻¹ in knee extension, peak torque (p < 0.002); total work (p < 0.007); total work per repetition maximum (p < 0.005); average power (p < 0.027); isometric in knee extension, peak torque (p < 0.005); and average peak torque (p < 0.002). Similar findings were observed for muscle quality. Changes in quality of life (SF-36) were not found, except for improvements in the role physical (p < 0.023) and role emotional (p < 0.001) domains, likely as a result of the physical training sessions. A nutritional survey did not revealed changes in dietary habits. No adverse events were recorded. In subjects over 50 years of age, moderate-intensity strength training combined with daily supplementation for 12 weeks with a natural extract of Spinacia oleracea L. improved muscle-related variables and muscle quality. Maintaining muscle health is a key component of healthy aging.

Preventing c2c12 muscular cells damage combining magnesium and potassium with vitamin D3 and curcumin

Background and aim

Physical activity is defined as any bodily movement produced by skeletal muscles which causes energy consumption; moderate and constant physical activity is known to be beneficial and to slow the muscle loss process associated with aging. The aim of the present study was to test, in an in vitro exercise model, the biological effects of a new formulation composed of magnesium and potassium combined with vitamin D and curcumin created to support muscle activity and to prevent hypercontraction damage.

Experimental procedure

C2C12 cells were treated with vitamin D, buffered magnesium bisglycinate, curcumin, and potassium citrate. Cell viability, morpho-functional changes, calcium and magnesium movements, and the main kinases involved in glucose uptake were analyzed. The glycogen level and lactate were also evaluated.

Results and conclusion

Important results about a positive effect on mitochondrial activity, ATP production, oxygen consumption and in the physiological differentiation of C2C12 cells were obtained. Further experiments were performed under conditions that mimic the biological aspects of strenuous exercise. The combination of magnesium, vitamin D3, curcumin, and potassium citrate revealed beneficial effects on skeletal muscle cells under physiological conditions as well as while mimicking intense activity. In particular, in an in vitro model, they were able to control the hypercontraction, restoring ion fluxes, reducing inflammation signaling and supporting the main mechanism involved on aerobic activity. Our results have indicated for the first time that this new combination could be considered as a new nutraceutical formulation to improve physical performance and muscle recovery.

Maslinic acid activates mTORC1 and human TGR5 and induces skeletal muscle hypertrophy

Maslinic acid, a naturally occurring pentacyclic triterpene in more than 30 plants (including olives), reportedly increases human muscle mass and muscle strength; however, the underlying molecular mechanism remains unknown. C57BL/6J mice were fed a standard diet or supplemented with 0.27% maslinic acid for 4 weeks, and their skeletal muscle mass was measured. Mice that consumed maslinic acid displayed significant increases in gastrocnemius and soleus muscle mass. Cultured mouse-C2C12 skeletal muscle cells were treated with mammalian target of rapamycin complex 1 (mTORC1) or protein kinase b (Akt) inhibitor, and protein synthesis was quantified. Maslinic acid accelerated protein synthesis via mTORC1 activation independent of Akt. Furthermore, maslinic acid activated human Takeda G protein-coupled receptor 5 (TGR5) more strongly than mouse TGR5, augmenting the expression of several genes related to muscular hypertrophy. Maslinic acid activated mTORC1 and human TGR5, implying its contribution to human muscular hypertrophy through these effects.

Nutritional composition and proteomic analysis of soft-shelled turtle (Pelodiscus sinensis) egg and identification of oligopeptides with alpha-glucosidase inhibitory activity

This study aimed to explore nutritional compositions and proteomics of soft-shelled turtle (SST) egg, as well as identify potential antidiabetic oligopeptides with α-glucosidase inhibitory property. Results revealed that SST egg is a promising source of highly nutritious proteins and minerals (54.64% and 5.81% of dry matter, respectively). Further proteomic analysis showed SST egg proteins contained at least 9 protein families, such as transferrin/iron binding protein and immunoregulation-related protein. Hydrolysis by different enzymes, especially papain, remarkably increased α-glucosidase inhibitory activity and scavenging activity for ABTS, DPPH, hydroxyl and oxygen radicals of SST egg proteins. Peptides from papain hydrolysate were fractionated using ultrafiltration followed by reverse phase chromatography, and 16 peptides were identified in the most active fraction by LC-QTOF-MS/MS. Molecular docking revealed that 14 of these peptides could easily dock into the substrate-binding pocket and/or inhibitor binding sites of α-glucosidase with the docking score below -150 kcal/mol, indicating their potential α-glucosidase inhibitory properties. The five most abundant oligopeptides with potent interaction with α-glucosidase were further synthesized, and oligopeptides HNKPEVEVR, ARDASVLK and SGTLLHK strongly inhibited the activity of α-glucosidase (IC₅₀ of 56, 195 and 289 µmol/L, respectively). Therefore, oligopeptides from enzymatic hydrolysate of SST egg protein exhibit potential antidiabetic activity, making it a promising functional food ingredient.

Principles of stable isotope research - with special reference to protein metabolism

The key to understanding the mechanisms regulating disease stems from the ability to accurately quantify the dynamic nature of the metabolism underlying the physiological and pathological changes occurring as a result of the disease. Stable isotope tracer technologies have been at the forefront of this for almost 80 years now, and through a combination of both intense theoretical and technological development over these decades, it is now possible to utilise stable isotope tracers to investigate the complexities of in vivo human metabolism from a whole body perspective, down to the regulation of sub-nanometer cellular components (i.e organelles, nucleotides and individual proteins). This review therefore aims to highlight; 1) the advances made in these stable isotope tracer approaches - with special reference given to their role in understanding the nutritional regulation of protein metabolism, 2) some considerations required for the appropriate application of these stable isotope techniques to study protein metabolism, 3) and finally how new stable isotopes approaches and instrument/technical developments will help to deliver greater clinical insight in the near future.

Metabolic flux analysis of branched-chain amino and keto acids (BCAA, BCKA) and β-hydroxy β-methylbutyric acid across multiple organs in the pig

Branched-chain amino acids (BCAA) and their metabolites the branched-chain keto acids (BCKA) and β-hydroxy β-methylbutyric acid (HMB) are involved in the regulation of key signaling pathways in the anabolic response to a meal. However, their (inter)organ kinetics remain unclear. Therefore, branched-chain amino acids (BCAA) [leucine (Leu), valine (Val), isoleucine (Ile)], BCKA [α-ketoisocaproic acid (KIC), 3-methyl-2-oxovaleric acid (KMV), 2-oxoisovalerate (KIV)], and HMB across organ net fluxes were measured. In multi-catheterized pigs (n = 12, ±25 kg), net fluxes across liver, portal drained viscera (PDV), kidney, and hindquarter (HQ, muscle compartment) were measured before and 4 h after bolus feeding of a complete meal (30% daily intake) in conscious state. Arterial and venous plasma were collected and concentrations were measured by LC- or GC-MS/MS. Data are expressed as mean [95% CI] and significance (P < 0.05) from zero by the Wilcoxon Signed Rank Test. In the postabsorptive state (in nmol/kg body wt/min), the kidney takes up HMB (3.2[1.3,5.0]) . BCKA is taken up by PDV (144[13,216]) but no release by other organs. In the postprandial state, the total net fluxes over 4 h (in µmol/kg body wt/4 h) showed a release of all BCKA by HQ (46.2[34.2,58.2]), KIC by the PDV (12.3[7.0,17.6]), and KIV by the kidney (10.0[2.3,178]). HMB was released by the liver (0.76[0.49,1.0]). All BCKA were taken up by the liver (200[133,268]). Substantial differences are present in (inter)organ metabolism and transport among the BCAA and its metabolites BCKA and HMB. The presented data in a translation animal model are relevant for the future development of optimized clinical nutrition.NEW & NOTEWORTHY Branched-chain amino acids (BCAA) and their metabolites the branched-chain keto acids (BCKA) and β-hydroxy β-methylbutyric acid (HMB) are involved in the regulation of key signaling pathways in the anabolic response to a meal. Substantial differences are present in (inter)organ metabolism and transport among the BCAA and its metabolites BCKA and HMB. The presented data in a translation animal model are relevant for the future development of optimized clinical nutrition.

How to Overcome Anabolic Resistance in Dialysis-Treated Patients?

A current hypothesis is that dialysis-treated patients are "anabolic resistant" i. e., their muscle protein synthesis (MPS) response to anabolic stimuli is blunted, an effect which leads to muscle wasting and poor physical performance in aging and in several chronic diseases. The importance of maintaining muscle mass and MPS is often neglected in dialysis-treated patients; better than to describe mechanisms leading to energy-protein wasting, the aim of this narrative review is to suggest possible strategies to overcome anabolic resistance in this patient's category. Food intake, in particular dietary protein, and physical activity, are the two major anabolic stimuli. Unfortunately, dialysis patients are often aged and have a sedentary behavior, all conditions which per se may induce a state of "anabolic resistance." In addition, patients on dialysis are exposed to amino acid or protein deprivation during the dialysis sessions. Unfortunately, the optimal amount and formula of protein/amino acid composition in supplements to maximixe MPS is still unknown in dialysis patients. In young healthy subjects, 20 g whey protein maximally stimulate MPS. However, recent observations suggest that dialysis patients need greater amounts of proteins than healthy subjects to maximally stimulate MPS. Since unneccesary amounts of amino acids could stimulate ureagenesis, toxins and acid production, it is urgent to obtain information on the optimal dose of proteins or amino acids/ketoacids to maximize MPS in this patients' population. In the meantime, the issue of maintaining muscle mass and function in dialysis-treated CKD patients needs not to be overlooked by the kidney community.

Nutraceuticals and Exercise against Muscle Wasting during Cancer Cachexia

Cancer cachexia (CC) is a debilitating multifactorial syndrome, involving progressive deterioration and functional impairment of skeletal muscles. It affects about 80% of patients with advanced cancer and causes premature death. No causal therapy is available against CC. In the last few decades, our understanding of the mechanisms contributing to muscle wasting during cancer has markedly increased. Both inflammation and oxidative stress (OS) alter anabolic and catabolic signaling pathways mostly culminating with muscle depletion. Several preclinical studies have emphasized the beneficial roles of several classes of nutraceuticals and modes of physical exercise, but their efficacy in CC patients remains scant. The route of nutraceutical administration is critical to increase its bioavailability and achieve the desired anti-cachexia effects. Accumulating evidence suggests that a single therapy may not be enough, and a bimodal intervention (nutraceuticals plus exercise) may be a more effective treatment for CC. This review focuses on the current state of the field on the role of inflammation and OS in the pathogenesis of muscle atrophy during CC, and how nutraceuticals and physical activity may act synergistically to limit muscle wasting and dysfunction.

Urolithin A augments angiogenic pathways in skeletal muscle by bolstering NAD+ and SIRT1

Urolithin A (UA) is a natural compound that is known to improve muscle function. In this work we sought to evaluate the effect of UA on muscle angiogenesis and identify the underlying molecular mechanisms. C57BL/6 mice were administered with UA (10 mg/body weight) for 12–16 weeks. ATP levels and NAD⁺ levels were measured using in vivo ³¹P NMR and HPLC, respectively. UA significantly increased ATP and NAD⁺ levels in mice skeletal muscle. Unbiased transcriptomics analysis followed by Ingenuity Pathway Analysis (IPA) revealed upregulation of angiogenic pathways upon UA supplementation in murine muscle. The expression of the differentially regulated genes were validated using quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC). Angiogenic markers such as VEGFA and CDH5 which were blunted in skeletal muscles of 28 week old mice were found to be upregulated upon UA supplementation. Such augmentation of skeletal muscle vascularization was found to be bolstered via Silent information regulator 1 (SIRT1) and peroxisome proliferator-activated receptor-gamma coactivator-1-alpha (PGC-1α) pathway. Inhibition of SIRT1 by selisistat EX527 blunted UA-induced angiogenic markers in C2C12 cells. Thus this work provides maiden evidence demonstrating that UA supplementation bolsters skeletal muscle ATP and NAD⁺ levels causing upregulated angiogenic pathways via a SIRT1-PGC-1α pathway.

Sestrins in Physiological Stress Responses

Sestrins are a family of proteins that respond to a variety of environmental stresses, including genotoxic, oxidative, and nutritional stresses. Sestrins affect multiple signaling pathways: AMP-activated protein kinase, mammalian target of rapamycin complexes, insulin-AKT, and redox signaling pathways. By regulating these pathways, Sestrins are thought to help adapt to stressful environments and subsequently restore cell and tissue homeostasis. In this review, we describe how Sestrins mediate physiological stress responses in the context of nutritional and chemical stresses (liver), physical movement and exercise (skeletal muscle), and chemical, physical, and inflammatory injuries (heart). These findings also support the idea that Sestrins are a molecular mediator of hormesis, a paradoxical beneficial effect of low- or moderate-level stresses in living organisms.

Dietary protein, exercise, ageing and physical inactivity: interactive influences on skeletal muscle proteostasis

Dietary protein is a pre-requisite for the maintenance of skeletal muscle mass; stimulating increases in muscle protein synthesis (MPS), via essential amino acids (EAA), and attenuating muscle protein breakdown, via insulin. Muscles are receptive to the anabolic effects of dietary protein, and in particular the EAA leucine, for only a short period (i.e. about 2-3 h) in the rested state. Thereafter, MPS exhibits tachyphylaxis despite continued EAA availability and sustained mechanistic target of rapamycin complex 1 signalling. Other notable characteristics of this 'muscle full' phenomenon include: (i) it cannot be overcome by proximal intake of additional nutrient signals/substrates regulating MPS; meaning a refractory period exists before a next stimulation is possible, (ii) it is refractory to pharmacological/nutraceutical enhancement of muscle blood flow and thus is not induced by muscle hypo-perfusion, (iii) it manifests independently of whether protein intake occurs in a bolus or intermittent feeding pattern, and (iv) it does not appear to be dependent on protein dose per se. Instead, the main factor associated with altering muscle full is physical activity. For instance, when coupled to protein intake, resistance exercise delays the muscle full set-point to permit additional use of available EAA for MPS to promote muscle remodelling/growth. In contrast, ageing is associated with blunted MPS responses to protein/exercise (anabolic resistance), while physical inactivity (e.g. immobilisation) induces a premature muscle full, promoting muscle atrophy. It is crucial that in catabolic scenarios, anabolic strategies are sought to mitigate muscle decline. This review highlights regulatory protein turnover interactions by dietary protein, exercise, ageing and physical inactivity.

Animal, Plant, Collagen and Blended Dietary Proteins: Effects on Musculoskeletal Outcomes

Dietary protein is critical for the maintenance of musculoskeletal health, where appropriate intake (i.e., source, dose, timing) can mitigate declines in muscle and bone mass and/or function. Animal-derived protein is a potent anabolic source due to rapid digestion and absorption kinetics stimulating robust increases in muscle protein synthesis and promoting bone accretion and maintenance. However, global concerns surrounding environmental sustainability has led to an increasing interest in plant- and collagen-derived protein as alternative or adjunct dietary sources. This is despite the lower anabolic profile of plant and collagen protein due to the inferior essential amino acid profile (e.g., lower leucine content) and subordinate digestibility (versus animal). This review evaluates the efficacy of animal-, plant- and collagen-derived proteins in isolation, and as protein blends, for augmenting muscle and bone metabolism and health in the context of ageing, exercise and energy restriction.

Contemporary stable isotope tracer approaches: Insights into skeletal muscle metabolism in health and disease

NEW FINDINGS

What is the topic of this review? This review discusses the application of new stable isotope tracer techniques in understanding the control of skeletal muscle mass. What advances does it highlight? This review highlights current advances in stable isotope tracer techniques through their combination with high-throughput proteomics technologies.

ABSTRACT

Beyond its primary locomotory and key structural functions, skeletal muscle provides additional vital roles for maintenance of metabolic health, acting as a storage point for glucose and intramuscular lipids for energy production, alongside being the largest reservoir for amino acids in the body. Therefore, maintenance of muscle mass is key to the promotion of health and well-being across the lifespan and in several disease states. As such, when skeletal muscle is lost, in either clinical (cancer, organ failure etc.) or non-clinical (ageing, inactivity) situations, there are potentially devastating consequences attached, with robust links existing between muscle mass loss and mortality. Great efforts are being made to reverse or slow muscle mass declines in health and disease, through combinations of lifestyle changes and nutritional and/or pharmaceutical intervention. However, despite this comprehensive research effort, the underlying metabolic and molecular mechanisms have yet to be defined properly. However, with the rapid acceleration of analytical developments over recent years, the application of stable isotope tracers to the study of human muscle metabolism is providing unique insights into the mechanisms controlling skeletal muscle loss and allowing more targeted therapeutic strategies to be developed. The aim of this review is to highlight the technical breakthroughs in our understanding of muscle wasting in health and disease and how future directions and developments incorporating 'omics' with stable isotope tracers will allow for a more personalized and stratified therapeutic approach.

Genetic ablation of aldehyde reductase (Akr1a) augments exercise endurance in mice via activation of the PGC-1α-involved pathway

AIMS

Aldehyde reductase (AKR1A) is involved in the synthesis of ascorbic acid (AsA) as well as the detoxification of aldehydes. AKR1A^-/- (KO) mice produce about 10% of the normal amounts of AsA compared to AKR1A^+/+ (WT) mice. We investigated physiologic roles of AKR1A in running using the KO mice.

MAIN METHODS

The KO mice were subjected to a treadmill test under either restricted AsA production or a sufficiency by supplementation and compared the results with those of WT mice. Contents of glucose, aspartate aminotransferase, AsA and free fatty acids in blood were measured. Glycogen contents were measured in the liver and skeletal muscle, and hepatic proteins were examined by immunoblot analyses.

KEY FINDINGS

Running performance was higher in the KO mice than the WT mice irrespective of the AsA status. After the exercise period, blood glucose levels were decreased in the WT mice but were preserved in the KO mice. Liver glycogen levels were also consistently preserved in the KO mice after exercise. Free fatty acid levels tended to be originally high in blood plasma compared to those of the WT mice and were increased to similar extent in them. A key regulator of energy metabolism, PGC-1α, and the products of downstream target genes that encode for glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphatase, were constitutively at high levels in the KO mice.

SIGNIFICANCE

The genetic ablation of AKR1A activates the PGC-1α pathway and spare glucose, which would consequently confer exercise endurance.

Red Ginseng Improves Exercise Endurance by Promoting Mitochondrial Biogenesis and Myoblast Differentiation

Red ginseng has been reported to elicit various therapeutic effects relevant to cancer, diabetes, neurodegenerative diseases, and inflammatory diseases. However, the effect of red ginseng on exercise endurance and skeletal muscle function remains unclear. Herein, we sought to investigate whether red ginseng could affect exercise endurance and examined its molecular mechanism. Mice were fed with red ginseng extract (RG) and undertook swimming exercises to determine the time to exhaustion. Animals fed with RG had significantly longer swimming endurance. RG treatment was also observed to enhance ATP production levels in myoblasts. RG increased mRNA expressions of mitochondrial biogenesis regulators, NRF-1, TFAM, and PGC-1α, which was accompanied by an elevation in mitochondrial DNA, suggesting an enhancement in mitochondrial energy-generating capacity. Importantly, RG treatment induced phosphorylation of p38 and AMPK and upregulated PGC1α expression in both myoblasts and in vivo muscle tissue. In addition, RG treatment also stimulated C2C12 myogenic differentiation. Our findings show that red ginseng improves exercise endurance, suggesting that it may have applications in supporting skeletal muscle function and exercise performance.

From skeletal muscle weakness to functional outcomes following critical illness: a translational biology perspective

Intensive care unit acquired weakness (ICUAW) is now a well-known entity complicating critical illness. It increases mortality and in the critical illness survivor it is associated with physical disability, substantially increased health resource utilisation and healthcare costs. Skeletal muscle wasting is a key driver of ICUAW and physical functional outcomes in both the short and long term. To date, there is no intervention that can universally and consistently prevent muscle loss during critical illness, or enhance its recovery following intensive care unit discharge, to improve physical function. Clinical trials of early mobilisation or exercise training, or enhanced nutritional support have generated inconsistent results and we have no effective pharmacological interventions. This review will delineate our current understanding of the mechanisms underpinning the development and persistence of skeletal muscle loss and dysfunction in the critically ill individual, highlighting recent discoveries and clinical observations, and utilisation of this knowledge in the development of novel therapeutics.

Effects of almond, dried grape and dried cranberry consumption on endurance exercise performance, recovery and psychomotor speed: protocol of a randomised controlled trial

Background

Foods rich in nutrients, such as nitrate, nitrite, L-arginine and polyphenols, can promote the synthesis of nitric oxide (NO), which may induce ergogenic effects on endurance exercise performance. Thus, consuming foods rich in these components, such as almonds, dried grapes and dried cranberries (AGC), may improve athletic performance. Additionally, the antioxidant properties of these foods may reduce oxidative damage induced by intense exercise, thus improving recovery and reducing fatigue from strenuous physical training. Improvements in NO synthesis may also promote cerebral blood flow, which may improve cognitive function.

Methods and analysis

Ninety-six trained male cyclists or triathletes will be randomised to consume ~2550 kJ of either a mixture of AGC or a comparator snack food (oat bar) for 4 weeks during an overreaching endurance training protocol comprised of a 2-week heavy training phase, followed by a 2-week taper. The primary outcome is endurance exercise performance (5 min time-trial performance) and secondary outcomes include markers of NO synthesis (plasma and urinary nitrites and nitrates), muscle damage (serum creatine kinase and lactate dehydrogenase), oxidative stress (F2-isoprostanes), endurance exercise function (exercise efficiency, submaximal oxygen consumption and substrate utilisation), markers of internal training load (subjective well-being, rating of perceived exertion, maximal rate of heart rate increase and peak heart rate) and psychomotor speed (choice reaction time).

Conclusion

This study will evaluate whether consuming AGC improves endurance exercise performance, recovery and psychomotor speed across an endurance training programme, and evaluate the mechanisms responsible for any improvement.

Trial registration number

ACTRN12618000360213.

The effect of acute oral phosphatidic acid ingestion on myofibrillar protein synthesis and intracellular signaling in older males

BACKGROUND

Age-related muscle loss (sarcopenia) may be driven by a diminished myofibrillar protein synthesis (MyoPS) response to anabolic stimuli (i.e. exercise and nutrition). Oral phosphatidic acid (PA) ingestion has been reported to stimulate resting muscle protein synthesis in rodents, and enhance resistance training-induced muscle remodelling in young humans.

PURPOSE

This study examined the effects of acute oral PA ingestion on resting and exercise-induced MyoPS rates in older individuals.

METHODS

Sixteen older males performed a bout of unilateral leg resistance exercise followed by oral ingestion of 750 mg of soy-derived PA or a rice-flour placebo (PL) over 60 min post-exercise. A primed-continuous infusion of l-[ring-¹³C₆]-phenylalanine with serial muscle biopsies was used to determine MyoPS at rest and between 0-150 and 150-300 min post-exercise.

RESULTS

Plasma [PA] concentrations were elevated above basal values from 180 to 300 min post-exercise in PA only (P = 0.02). Exercise increased MyoPS rates above basal values between 150 and 300 min post-exercise in PL (P = 0.001), but not PA (P = 0.83). Phosphorylation of p70S6K, rpS6, 4E-BP1 and Akt was elevated above basal levels in the exercised leg over 150-300 min post-exercise for PL only (P = 0.018, 0.007, 0.011 and 0.002, respectively), and were significantly greater than PA (P < 0.01 for all proteins). The effects of oral PA ingestion on proteolytic signaling markers were equivocal.

CONCLUSIONS

Acute oral phosphatidic acid ingestion appears to interfere with resistance exercise-induced intramuscular anabolic signaling and MyoPS in older males and, therefore, may not be a viable treatment to counteract sarcopenia. Clinicaltials.gov registration no: NCT03446924.

A modified diet does not ameliorate muscle pathology in a mouse model for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by a lack of dystrophin protein. Next to direct effects on the muscles, this has also metabolic consequences. The influence of nutrition on disease progression becomes more and more recognized. Protein intake by DMD patients may be insufficient to meet the increased demand of the constantly regenerating muscle fibers. This led to the hypothesis that improving protein uptake by the muscles could have therapeutic effects. The present study examined the effects of a modified diet, which composition might stimulate muscle growth, on disease pathology in the D2-mdx mouse model. D2-mdx males were fed with either a control diet or modified diet, containing high amounts of branched-chain amino acids, vitamin D3 and ursolic acid, for six weeks. Our study indicates that the modified diet could not ameliorate the muscle pathology. No effects on bodyweight or weight of individual muscles were observed. Neither did the diet affect severity of fibrosis or calcification of the muscles.

Supplements with purported effects on muscle mass and strength

PURPOSE

Several supplements are purported to promote muscle hypertrophy and strength gains in healthy subjects, or to prevent muscle wasting in atrophying situations (e.g., ageing or disuse periods). However, their effectiveness remains unclear.

METHODS

This review summarizes the available evidence on the beneficial impacts of several popular supplements on muscle mass or strength.

RESULTS

Among the supplements tested, nitrate and caffeine returned sufficient evidence supporting their acute beneficial effects on muscle strength, whereas the long-term consumption of creatine, protein and polyunsaturated fatty acids seems to consistently increase or preserve muscle mass and strength (evidence level A). On the other hand, mixed or unclear evidence was found for several popular supplements including branched-chain amino acids, adenosine triphosphate, citrulline, β-Hydroxy-β-methylbutyrate, minerals, most vitamins, phosphatidic acid or arginine (evidence level B), weak or scarce evidence was found for conjugated linoleic acid, glutamine, resveratrol, tribulus terrestris or ursolic acid (evidence level C), and no evidence was found for other supplements such as ornithine or α-ketoglutarate (evidence D). Of note, although most supplements appear to be safe when consumed at typical doses, some adverse events have been reported for some of them (e.g., caffeine, vitamins, α-ketoglutarate, tribulus terrestris, arginine) after large intakes, and there is insufficient evidence to determine the safety of many frequently used supplements (e.g., ornithine, conjugated linoleic acid, ursolic acid).

CONCLUSION

 In summary, despite their popularity, there is little evidence supporting the use of most supplements, and some of them have been even proven ineffective or potentially associated with adverse effects.

Contraction and nutrition interaction promotes anabolism in cachectic muscle

PURPOSE OF REVIEW

Cachexia is a disease-related multifactorial syndrome characterized by inflammation, massive muscle protein catabolism and carbohydrate and lipid metabolism disorder.Several studies tried to define the impact of either nutrition or physical exercise (single approach strategy) or their combination (multimodal approach strategy) on prevention and/or treatment of muscle wasting in cachectic patients.

RECENT FINDINGS

Single approach strategies (i.e. nutrition or physical exercise) have the potential of preventing and improving features of the cachexia syndrome possibly with a differential impact according to the underlying disease. Limited information is available on the beneficial effect of multimodal approach strategies.

SUMMARY

Multimodal approaches appear to be more effective than those based on single interventions in physiological condition and in cachectic patients with COPD or chronic kidney disease. Further studies, however, are required in cachexia induced by heart failure, cancer and critical illness.

The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans

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Loss of muscle mass with age is due to atrophy and loss of individual muscle fibres.

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Anabolic resistance is fundamental in age-related fibre atrophy.

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Fibre loss is associated with denervation and remodelling of motor units.

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The plasticity of both factors should be considered in future research.

Age-related loss of skeletal muscle mass and function, sarcopenia, is associated with physical frailty and increased risk of morbidity (chronic diseases), in addition to all-cause mortality. The loss of muscle mass occurs incipiently from middle-age (∼1%/year), and in severe instances can lead to a loss of ∼50% by the 8–9th decade of life. This review will focus on muscle deterioration with ageing and highlight the two underpinning mechanisms regulating declines in muscle mass and function: muscle fibre atrophy and muscle fibre loss (hypoplasia) – and their measurement. The mechanisms of muscle fibre atrophy in humans relate to imbalances in muscle protein synthesis (MPS) and breakdown (MPB); however, since there is limited evidence for basal alterations in muscle protein turnover, it would appear that “anabolic resistance” to fundamental environmental cues regulating diurnal muscle homeostasis (namely physical activity and nutrition), underlie age-related catabolic perturbations in muscle proteostasis. While the ‘upstream’ drivers of the desensitization of aged muscle to anabolic stimuli are poorly defined, they most likely relate to impaired efficiency of the conversion of nutritional/exercise stimuli into signalling impacting mRNA translation and proteolysis. Additionally, loss of muscle fibres has been shown in cadaveric studies using anatomical fibre counts, and from iEMG studies demonstrating motor unit loss, albeit with few molecular investigations of this in humans. We suggest that defining countermeasures against sarcopenia requires improved understandings of the co-ordinated regulation of muscle fibre atrophy and fibre loss, which are likely to be inextricably linked.

A double-blind placebo controlled trial into the impacts of HMB supplementation and exercise on free-living muscle protein synthesis, muscle mass and function, in older adults

Age-related sarcopenia and dynapenia are associated with frailty and metabolic diseases. Resistance exercise training (RET) adjuvant to evidence-based nutritional intervention(s) have been shown as mitigating strategies. Given that β-hydroxy-β-methyl-butyrate (HMB) supplementation during RET improves lean body mass in younger humans, and that we have shown that HMB acutely stimulates muscle protein synthesis (MPS) and inhibits breakdown; we hypothesized that chronic supplementation of HMB free acid (HMB-FA) would enhance MPS and muscle mass/function in response to RET in older people.

We recruited 16 healthy older men (Placebo (PLA): 68.5 ± 1.0 y, HMB-FA: 67.8 ± 1.15 y) for a randomised double-blind-placebo controlled trial (HMB-FA 3 × 1 g/day vs. PLA) involving a 6-week unilateral progressive RET regime (6 × 8 repetitions, 75% 1-RM, 3 · wk⁻¹). Deuterium oxide (D₂O) dosing was performed over the first two weeks (0–2 wk) and last two weeks (4–6 wk) with bilateral vastus lateralis (VL) biopsies at 0–2 and 4–6 wk (each time 75 ± 2 min after a single bout of resistance exercise (RE)) for quantification of early and later MPS responses and post-RE myogenic gene expression. Thigh lean mass (TLM) was measured by DXA, VL thickness and architecture (fibre length and pennation angle) by ultrasound at 0/3/6 wk, and strength by knee extensor 1-RM testing and MVC by isokinetic dynamometry (approx. every 10 days).

RET induced strength increases (1-RM) in the exercised leg of both groups (398 ± 22N to 499 ± 30N HMB-FA vs. 396 ± 29N to 510 ± 43N PLA (both P < 0.05)). In addition, maximal voluntary contraction (MVC) also increased (179 ± 12 Nm to 203 ± 12 Nm HMB-FA vs. 185 ± 10 Nm to 217 ± 11 Nm PLA (both P < 0.05); with no group differences. VL muscle thickness increased significantly in the exercised leg in both groups, with no group differences. TLM (by DXA) rose to significance only in the HMB-FA group (by 5.8%–5734 ± 245 g p = 0.015 vs. 3.0% to 5644 ± 323 g P = 0.06 in PLA). MPS remained unchanged in the untrained legs (UT) 0–2 weeks being 1.06 ± 0.08%.d⁻¹ (HMB-FA) and 1.14 ± 0.09%.d⁻¹ (PLA), the trained legs (T) exhibited increased MPS in the HMB-FA group only at 0–2-weeks (1.39 ± 0.10%.d⁻¹, P < 0.05) compared with UT: but was not different at 4–6-weeks: 1.26 ± 0.05%.d⁻¹. However, there were no significant differences in MPS between the HMB-FA and PLA groups at any given time point and no significant treatment interaction observed. We also observed significant inductions of c-Myc gene expression following each acute RE bout, with no group differences. Further, there were no changes in any other muscle atrophy/hypertrophy or myogenic transcription factor genes we measured.

RET with adjuvant HMB-FA supplements in free-living healthy older men did not enhance muscle strength or mass greater than that of RET alone (PLA). That said, only HMB-FA increased TLM, supported by early increases in chronic MPS. As such, chronic HMB-FA supplementation may result in long term benefits in older males, however longer and larger studies may be needed to fully determine the potential effects of HMB-FA supplementation; translating to any functional benefit.

Implications on older women of age- and sex-related differences in activation patterns of shoulder muscles: A cross-sectional study

We conducted a cross-sectional study to assess differences in neuromotor attributes of shoulder muscles between age groups in both sexes and to better understand functional disorders in older women. Twenty young (20-42 years old), 20 middle-aged (43-67), and 20 older (> 68) adults participated in a comparative surface-electromyography study of five muscles. We identified age-related differences in women, especially in scapula stabilizer muscles. There was a tendency for both sexes of delayed onset times with increasing age, excepting the upper trapezius muscle in females. The results highlight the importance of understanding musculoskeletal aging in women to adequately guide physical therapeutic approaches.

The Effect of Diet on Improved Endurance in Male C57BL/6 Mice

The consumption of fruits and vegetables appears to help with maintaining an adequate level of exercise and improves endurance. However, the mechanisms that are involved in this process are not well understood. In the current study, the impact of diets enriched in fruits and vegetables (GrandFusion^®) on exercise endurance was examined in a mouse model. GrandFusion (GF) diets increased mitochondrial DNA and enzyme activity, while they also stimulated mitochondrial mRNA synthesis in vivo. GF diets increased both the mRNA expression of factors involved in mitochondrial biogenesis, peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), mitochondrial transcription factor A (Tfam), estrogen-related receptor alpha (ERRα), nuclear respiratory factor 1 (NRF-1), cytochrome c oxidase IV (COXIV) and ATP synthase (ATPsyn). Mice treated with GF diets showed an increase in running endurance, rotarod perseverance and grip strength when compared to controls who were on a regular diet. In addition, GF diets increased the protein expression of phosphorylated AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), PGC-1α and peroxisome proliferator-activated receptor delta (PPAR-δ), which was greater than exercise-related changes. Finally, GF reduced the expression of phosphorylated ribosomal protein S6 kinase 1 (p-S6K1) and decreased autophagy. These results demonstrate that GF diets enhance exercise endurance, which is mediated via mitochondrial biogenesis and function.

Twelve-week combined resistance and aerobic training confers greater benefits than aerobic training alone in nondialysis CKD

There is a growing consensus that patients with chronic kidney disease (CKD) should engage in regular exercise, but there is a lack of formal guidelines. In this report, we determined whether combined aerobic and resistance exercise would elicit superior physiological gains, in particular muscular strength, compared with aerobic training alone in nondialysis CKD. Nondialysis patients with CKD stages 3b–5 were randomly allocated to aerobic exercise {AE, n = 21; 9 men; median age 63 [interquartile range (IQR) 58–71] yr; median estimated glomerular filtration rate (eGFR) 24 (IQR 20–30) ml·min−1·1.73 m−2} or combined exercise [CE, n = 20, 9 men, median age 63 (IQR 51–69) yr, median eGFR 27 (IQR 22–32) ml·min−1·1.73 m−2], preceded by a 6-wk run-in control period. Patients then underwent 12 wk of supervised AE (treadmill, rowing, or cycling exercise) or CE training (as AE plus leg extension and leg press exercise) performed three times per week. Outcome assessments of knee extensor muscle strength, quadriceps muscle volume, exercise capacity, and central hemodynamics were performed at baseline, following the 6-wk control period, and at the end of the intervention. AE and CE resulted in significant increases in knee extensor strength of 16 ± 19% (mean ± SD; P = 0.001) and 48 ± 37% ( P < 0.001), respectively, which were greater after CE ( P = 0.02). AE and CE resulted in 5 ± 7% ( P = 0.04) and 9 ± 7% ( P < 0.001) increases in quadriceps volume, respectively ( P < 0.001), which were greater after CE ( P = 0.01). Both AE and CE increased distance walked in the incremental shuttle walk test [28 ± 44 m ( P = 0.01) and 32 ± 45 m ( P = 0.01), respectively]. In nondialysis CKD, the addition of resistance exercise to aerobic exercise confers greater increases in muscle mass and strength than aerobic exercise alone.

Can the critically ill patient generate sufficient energy to facilitate exercise in the ICU?

PURPOSE OF REVIEW

Trials of physical rehabilitation post critical illness have yet to deliver improved health-related quality of life in critical illness survivors. Muscle mass and strength are lost rapidly in critical illness and a proportion of patients continue to do so resulting in increased mortality and functional disability. Addressing this issue is therefore fundamental for recovery from critical illness.

RECENT FINDINGS

Altered mitochondrial function occurs in the critically ill and is likely to result in decreased adenosine tri-phosphate (ATP) production. Muscle contraction is a process that requires ATP. The metabolic demands of exercise are poorly understood in the ICU setting. Recent research has highlighted that there is significant heterogeneity in energy requirements between critically ill individuals undertaking the same functional activities, such as sit-to-stand. Nutrition in the critically ill is currently thought of in terms of carbohydrates, fat and protein. It may be that we need to consider nutrition in a more contextual manner such as energy generation or management of protein homeostasis.

SUMMARY

Current nutritional support practices in critically ill patients do not lead to improvements in physical and functional outcomes, and it may be that alternative methods of delivery or substrates are needed.

The potential for targeted rewriting of epigenetic marks in COPD as a new therapeutic approach

Chronic obstructive pulmonary disease (COPD) is an age and smoking related progressive, pulmonary disorder presenting with poorly reversible airflow limitation as a result of chronic bronchitis and emphysema. The prevalence, disease burden for the individual, and mortality of COPD continues to increase, whereas no effective treatment strategies are available. For many years now, a combination of bronchodilators and anti-inflammatory corticosteroids has been most widely used for therapeutic management of patients with persistent COPD. However, this approach has had disappointing results as a large number of COPD patients are corticosteroid resistant. In patients with COPD, there is emerging evidence showing aberrant expression of epigenetic marks such as DNA methylation, histone modifications and microRNAs in blood, sputum and lung tissue. Therefore, novel therapeutic approaches may exist using epigenetic therapy. This review aims to describe and summarize current knowledge of aberrant expression of epigenetic marks in COPD. In addition, tools available for restoration of epigenetic marks are described, as well as delivery mechanisms of epigenetic editors to cells. Targeting epigenetic marks might be a very promising tool for treatment and lung regeneration in COPD in the future.

Recent developments on the extraction and application of ursolic acid. A review

Ursolic acid (UA) is a pentacyclic triterpenoid widely found in herbs, leaves, flowers and fruits; update information on the major natural sources or agro-industrial wastes is presented. Traditional (maceration, Soxhlet and heat reflux) and modern (microwave-, ultrasound-, accelerated solvent- and supercritical fluid) extraction and purification technologies of UA, as well as some patented process, are summarized. The great interest in this bioactive compound is related to the beneficial effects in human health due to antioxidant, antimicrobial, anti-inflammatory, hepatoprotective, immunomodulatory, anti-tumor, chemopreventive, cardioprotective, antihyperlipidemic and hypoglycemic activities, and others. UA may augment the resistance of the skin barrier to irritants, prevent dry skin and could be suitable to develop antiaging products. The development of nanocrystals and nanoparticle-based drugs could reduce the side effects of high doses of UA in organisms, and increase its limited solubility and poor bioavailability of UA which limit the potential of this bioactive and the further applications. Commercial patented applications in relation to cosmetical and pharmaceutical uses of UA and its derivatives are surveyed.

Pharmacological targeting of exercise adaptations in skeletal muscle: Benefits and pitfalls

Exercise exerts significant effects on the prevention and treatment of many diseases. However, even though some of the key regulators of training adaptation in skeletal muscle have been identified, this biological program is still poorly understood. Accordingly, exercise-based pharmacological interventions for many muscle wasting diseases and also for pathologies that are triggered by a sedentary lifestyle remain scarce. The most efficacious compounds that induce muscle hypertrophy or endurance are hampered by severe side effects and are classified as doping. In contrast, dietary supplements with a higher safety margin exert milder outcomes. In recent years, the design of pharmacological agents that activate the training program, so-called "exercise mimetics", has been proposed, although the feasibility of such an approach is highly debated. In this review, the most recent insights into key regulatory factors and therapeutic approaches aimed at leveraging exercise adaptations are discussed.

Aging Gut Microbiota at the Cross-Road between Nutrition, Physical Frailty, and Sarcopenia: Is There a Gut-Muscle Axis?

Inadequate nutrition and physical inactivity are the mainstays of primary sarcopenia-physiopathology in older individuals. Gut microbiota composition is strongly dependent on both of these elements, and conversely, can also influence the host physiology by modulating systemic inflammation, anabolism, insulin sensitivity, and energy production. The bacterial metabolism of nutrients theoretically influences skeletal muscle cell functionality through producing mediators that drive all of these systemic effects. In this study, we review the scientific literature supporting the concept of the involvement of gut microbiota in primary sarcopenia physiopathology. First, we examine studies associating fecal microbiota alterations with physical frailty, i.e., the loss of muscle performance and normal muscle mass. Then, we consider studies exploring the effects of exercise on gut microbiota composition. Finally, we examine studies demonstrating the possible effects of mediators produced by gut microbiota on skeletal muscle, and intervention studies considering the effects of prebiotic or probiotic administration on muscle function. Even if there is no evidence of a distinct gut microbiota composition in older sarcopenic patients, we conclude that the literature supports the possible presence of a "gut-muscle axis", whereby gut microbiota may act as the mediator of the effects of nutrition on muscle cells.