Exercise-acclimated microbiota improves skeletal muscle metabolism via circulating bile acid deconjugation

The Role of Fermentable Fibre on Endurance Exercise Capacity: A Randomised Crossover Trial of Inulin Supplementation

Manipulation of the mouse gut microbiome has been shown to increase gut-derived short-chain fatty acids and improve exercise capacity. Associations between exercise performance and gut microbiome composition and metabolites have also been identified in human studies. Yet there is little direct evidence that prebiotics are able to increase acetate production and improve exercise capacity in human participants. We conducted a randomised controlled cross-over trial with 21 healthy and active males (35.0 ± 6.9 years; 24.4 ± 2.7 kg/m2) to investigate the effect of 15 g of inulin (prebiotic) on exercise performance (15 km cycle time trial), compared to placebo. Time to completion of a 15 km time trial was the primary outcome, while plasma acetate concentration and markers of inulin fermentation (breath H2 concentration) and muscle oxygenation were measured to explore potential mechanisms of action. Time to complete the 15 km time trial was not affected by inulin mean difference between inulin and placebo trials: (-10.37 s, 95% CI [-150.8, 130.1 s], p = 0.884). The marker of inulin fermentation (H2 concentration increase from baseline) was significantly higher in inulin compared to placebo condition (+42.61 ppm, 95% CI [30.04, 55.19], p = 0.001 and +31.13 ppm, 95% CI [3.73, 58.51], p = 0.029, respectively), but plasma acetate concentration did not differ between conditions. Likewise, markers of muscle oxygenation were not different between inulin and placebo. Our current results do not support the acute use of prebiotics to improve exercise performance in adults. Possible explanations for the absence of ergogenic effects may be that the timing between prebiotic ingestion and exercise was too short to allow for complete fermentation into acetate, participants were in a fasted rather than a fed state, or that the single dose of supplement was insufficient. These factors, together with advanced methods (stable isotope studies) should be investigated in a follow-up study to elucidate the fate and role of colonic-derived acetate during exercise.

Exercise, Diet, and Brain Health: From the Perspective of Gut Microbiota Regulation

The existing body of evidence has highlighted gut microbiota as a versatile regulator of body wellness affecting not only multiple physiological metabolisms but also the function of remote organs. Emerging studies revealed a reciprocal relationship between physical exercise and intestinal microbiota, suggesting that physical exercise could enhance gut health, including regulating intestinal barrier integrity, increasing microbial diversity, and promoting beneficial microbial metabolism. Furthermore, the beneficial outcomes of exercise on the intestine may also promote brain health through the gut-brain axis. Diet is an important factor in boosting exercise performance and also greatly impacts the structure of gut microbiota. Abundant research has reported that diet alongside exercise could exert beneficial effects on metabolism, immune regulation, and the neuropsychiatric system. In this paper, we used a narrative review, primarily searching PubMed, Web of Science, and Elsevier, to review the existing research on how moderate-intensity exercise promotes gut health, and we introduced the effects of exercise on the nervous system through the gut-brain axis. We also proposed dietary strategies targeting the regulation of gut microbiota to provide guidelines for boosting brain health. This review highlights that moderate exercise and a healthy diet promote gut and brain health.

Atypical gut microbial ecosystem from athletes with very high exercise capacity improves insulin sensitivity and muscle glycogen store in mice

Although the gut microbiota is known to act as a bridge between dietary nutrients and the body's energy needs, the interactions between the gut microbiota, host energy metabolism, and exercise capacity remain uncertain. Here, we characterized the gut microbiota ecosystem in a cohort of healthy normo-weight humans with highly heterogeneous aerobic exercise capacities and closely related body composition and food habits. While our data support the idea that the bacterial ecosystem appears to be modestly altered between individuals with low-to-high exercise capacities and close food habits, we report that gut bacterial α diversity, density, and functional richness are significantly reduced in athletes with very high exercise capacity. By using fecal microbiota transplantation, we report that the engraftment of gut microbiota from athletes with very high exercise capacity improves insulin sensitivity and muscle glycogen stores into transplanted mice, which highlights promising therapeutic perspectives in fecal transplantation from human donors selected based on exercise capacity traits.

Bile acid signaling in skeletal muscle homeostasis: from molecular mechanisms to clinical applications

The intricate relationship between bile acid metabolism and skeletal muscle function has emerged as a crucial area of research in metabolic health. This review synthesizes current evidence highlighting the fundamental role of bile acids as key signaling molecules in muscle homeostasis and their therapeutic potential in muscle-related disorders. Recent advances in molecular biology and metabolomics have revealed that bile acids, beyond their classical role in lipid absorption, function as essential regulators of muscle mass and function through multiple signaling pathways, particularly via the nuclear receptor FXR and membrane receptor TGR5. Clinical studies have demonstrated significant associations between altered bile acid profiles and muscle wasting conditions, while experimental evidence has elucidated the underlying mechanisms linking bile acid signaling to muscle protein synthesis, energy metabolism, and regeneration capacity. We critically examine the emerging therapeutic strategies targeting bile acid pathways, including receptor-specific agonists, microbiome modulators, and personalized interventions based on individual bile acid profiles. Additionally, we discuss novel diagnostic approaches utilizing bile acid-based biomarkers and their potential in early detection and monitoring of muscle disorders. This review also addresses current challenges in standardization and clinical translation while highlighting promising future directions in this rapidly evolving field. Understanding the bile acid-muscle axis may provide new opportunities for developing targeted therapies for age-related muscle loss and metabolic diseases.

Exercise, the Gut Microbiome and Gastrointestinal Diseases: Therapeutic Impact and Molecular Mechanisms

The benefits of regular physical activity (PA) on disease prevention and treatment outcomes have been recognized for centuries. However, only recently has interorgan communication triggered by the release of "myokines" from contracting skeletal muscles emerged as a putative mechanism by which exercise confers protection against numerous disease states. Cross-talk between active skeletal muscles and the gut microbiota reveal how regular PA boosts host immunity, facilitates a more diverse gut microbiome and functional metabolome, and plays a positive role in energy homeostasis and metabolic regulation. In contrast, and despite the large interindividual variation in the human gut microbiome, reduced microbial diversity has been implicated in several diseases of the gastrointestinal (GI) tract, systemic immune diseases, and cancers. Although prolonged, intense, weight-bearing exercise conducted in extreme conditions can increase intestinal permeability, compromising gut-barrier function and resulting in both upper and lower GI symptoms, these are transient and benign. Accordingly, the gut microbiome has become an attractive target for modulating many of the positive effects of regular PA on GI health and disease, although the precise dose of exercise required to induce favourable changes in the microbiome and enhance host immunity is currently unknown. Future efforts should concentrate on gaining a deeper understanding of the factors involved in exercise-gut interactions through the generation of functional 'omics readouts (ie, metatranscriptomics, metaproteomics, and metabolomics) that have the potential to identify functional traits of the microbiome that are linked to host health and disease states, and validating these interactions in experimental and preclinical systems. A greater understanding of how PA interacts with the GI tract and the microbiome may enable targeted therapeutic strategies to be developed for individuals and populations at risk for a variety of GI diseases.

The Role of Myokines in Liver Diseases

Myokine is a general term for hormones, peptides, and other substances secreted by skeletal muscle. Myokine has attracted much attention in recent years as a key substance for understanding the mechanism of "exercise and health". Skeletal muscle accounts for about 40% of the total human weight and is now recognized as an endocrine organ that produces myokines, which have physiological activity. Representative myokines include IL-6, myostatin, irisin, brain-derived neurotropic factor, fibroblast growth factor-21, and decorin. On the other hand, sarcopenia, defined by quantitative and qualitative loss of skeletal muscle, is a condition that has received much attention in recent years because of its close correlation with prognosis. In patients with chronic liver disease (CLD), sarcopenia is a common complication. Mechanisms underlying sarcopenia in CLD patients have been reported to involve protein-energy malnutrition, which is characteristic of patients with cirrhosis, signaling involved in protein synthesis and degradation, myokines such as myostatin and decorin, the ubiquitin-proteasome pathway, sex hormones such as testosterone, dysbiosis, and insulin resistance, etc., in addition to aging. Each of these pathological conditions is thought to be intricately related to each other, leading to sarcopenia. This review will summarize the relationship between CLD and myokines.

The Bile Acid Metabolism of Intestinal Microorganisms Mediates the Effect of Different Protein Sources on Muscle Protein Deposition in Procambarus clarkii

The most economically important trait of the Procambarus clarkii is meat quality. Protein deposition is essential in muscle growth and nutritional quality formation. The effects and potential mechanisms of feed protein sources on crustaceans' muscle protein deposition have not been elucidated. This study established an all-animal protein source (AP) and an all-plant protein source group (PP), with a feeding period of 8 weeks (four replicates per group, 45 individuals per replicate). The results demonstrated that muscle protein deposition, muscle fiber diameter, and hardness were significantly higher in the PP group (p < 0.05). The transcript levels of genes involved in protein synthesis were notably upregulated, while those of protein hydrolysis and negative regulators of myogenesis notably downregulated in PP group (p < 0.05). Furthermore, protein sources shaped differential intestinal microbiota composition and microbial metabolites profiles, as evidenced by a significant decrease in g_Bacteroides (p = 0.030), and a significant increase in taurochenodeoxycholic acid (TCDCA) in PP group (p = 0.027). A significant correlation was further established by Pearson correlation analysis between the g_Bacteroides, TCDCA, and genes involved in the MSTN-mediated protein deposition pathway (p < 0.05). In vitro anaerobic fermentation confirmed the ability of the two groups of intestinal flora to metabolically produce differential TCDCA (p = 0.038). Our results demonstrated that the 'Bacteroides-TCDCA-MSTN' axis may mediate the effects of different protein sources on muscle development and protein deposition in P. clarkii, which was anticipated to represent a novel target for the muscle quality modulation in crustaceans.

Association of Serum Bile Acid Profile with Diet and Physical Activity Habits in Japanese Middle-Aged Men

BACKGROUND/OBJECTIVES

Circulating bile acid (BA) profiles change with lifestyle and are closely related to intestinal BA metabolisms such as deconjugation and conversion to secondary BAs. The composition of BA in the blood is involved in systemic nutrient metabolism and intestinal health. Herein, we explored the associations of lifestyle and physical fitness with the circulating BA profile of middle-aged men.

METHODS

Data of 147 male participants (aged 50-64 years; BMI < 26 kg/m2; no medication for diabetes or dyslipidemia) from the Japan Multi-Institutional Collaborative Cohort study were analyzed. Serum concentrations of 15 types of BAs were examined for associations with variables on dietary habits, physical-activity habits, and physical fitness.

RESULTS

Green tea intake was positively associated with the deconjugation ratio of total BAs (p = 0.028) and negatively associated with secondary BA levels (free deoxycholic acid [DCA] (p = 0.078), glyco-DCA (p = 0.048), and tauro-DCA (p = 0.037)). In contrast, physical activity was negatively associated with the deconjugation ratio (p = 0.029) and secondary BA levels (free DCA (p = 0.098), and free lithocholic acid (p = 0.009)). Grip strength was also negatively associated with secondary BA levels (tauro-DCA (p = 0.041)) but was not associated with the deconjugation ratio. Energy and fat intake and skeletal muscle mass were not associated with the deconjugation ratio or secondary BA levels.

CONCLUSIONS

The study findings suggest that lifestyle-associated changes in serum deconjugated and secondary BAs indicate improvements in nutrient metabolism and the intestinal environment.

Cholestyramine alleviates bone and muscle loss in irritable bowel syndrome via regulating bile acid metabolism

Irritable bowel syndrome (IBS) is a widespread gastrointestinal disorder known for its multifaceted pathogenesis and varied extraintestinal manifestations, yet its implications for bone and muscle health are underexplored. Recent studies suggest a link between IBS and musculoskeletal disorders, but a comprehensive understanding remains elusive, especially concerning the role of bile acids (BAs) in this context. This study aimed to elucidate the potential contribution of IBS to bone and muscle deterioration via alterations in gut microbiota and BA profiles, hypothesizing that cholestyramine could counteract these adverse effects. We employed a mouse model to characterize IBS and analysed its impact on bone and muscle health. Our results revealed that IBS promotes bone and muscle loss, accompanied by microbial dysbiosis and elevated BAs. Administering cholestyramine significantly mitigated these effects, highlighting its therapeutic potential. This research not only confirms the critical role of BAs and gut microbiota in IBS-associated bone and muscle loss but also demonstrates the efficacy of cholestyramine in ameliorating these conditions, thereby contributing significantly to the field's understanding and offering a promising avenue for treatment.

The changing metabolic landscape of bile acids - keys to metabolism and immune regulation

Bile acids regulate nutrient absorption and mitochondrial function, they establish and maintain gut microbial community composition and mediate inflammation, and they serve as signalling molecules that regulate appetite and energy homeostasis. The observation that there are hundreds of bile acids, especially many amidated bile acids, necessitates a revision of many of the classical descriptions of bile acids and bile acid enzyme functions. For example, bile salt hydrolases also have transferase activity. There are now hundreds of known modifications to bile acids and thousands of bile acid-associated genes, especially when including the microbiome, distributed throughout the human body (for example, there are >2,400 bile salt hydrolases alone). The fact that so much of our genetic and small-molecule repertoire, in both amount and diversity, is dedicated to bile acid function highlights the centrality of bile acids as key regulators of metabolism and immune homeostasis, which is, in large part, communicated via the gut microbiome.

Regulating bile acids signaling for NAFLD: molecular insights and novel therapeutic interventions

Nonalcoholic fatty liver disease (NAFLD) emerges as the most predominant cause of liver disease, tightly linked to metabolic dysfunction. Bile acids (BAs), initially synthesized from cholesterol in the liver, undergo further metabolism by gut bacteria. Increasingly acknowledged as critical modulators of metabolic processes, BAs have been implicated as important signaling molecules. In this review, we will focus on the mechanism of BAs signaling involved in glucose homeostasis, lipid metabolism, energy expenditure, and immune regulation and summarize their roles in the pathogenesis of NAFLD. Furthermore, gut microbiota dysbiosis plays a key role in the development of NAFLD, and the interactions between BAs and intestinal microbiota is elucidated. In addition, we also discuss potential therapeutic strategies for NAFLD, including drugs targeting BA receptors, modulation of intestinal microbiota, and metabolic surgery.

Acetate Alleviates Gut Microbiota Depletion-Induced Retardation of Skeletal Muscle Growth and Development in Young Mice

The normal growth and development of skeletal muscle is essential for the health of the body. The regulation of skeletal muscle by intestinal microorganisms and their metabolites has been continuously demonstrated. Acetate is the predominant short-chain fatty acids synthesized by gut microbiota through the fermentation of dietary fiber; however, the underlying molecular mechanisms governing the interaction between acetate and skeletal muscle during the rapid growth stage remains to be further elucidated. Herein, specific pathogen-free (SPF) mice, germ-free (GF) mice, and germ-free mice supplemented with sodium acetate (GS) were used to evaluate the effects of acetate on the skeletal muscle growth and development of young mice with gut microbiota deficiency. We found that the concentration of serum acetate, body mass gain, succinate dehydrogenase activity, and expression of the myogenesis maker gene of skeletal muscle in the GS group were higher than those in the GF group, following sodium acetate supplementation. Furthermore, the transcriptome analysis revealed that acetate activated the biological processes that regulate skeletal muscle growth and development in the GF group, which are otherwise inhibited due to a gut microbiota deficiency. The in vitro experiment showed that acetate up-regulated Gm16062 to promote skeletal muscle cell differentiation. Overall, our findings proved that acetate promotes skeletal muscle growth and development in young mice via increasing Gm16062 expression.

The underappreciated diversity of bile acid modifications

The repertoire of modifications to bile acids and related steroidal lipids by host and microbial metabolism remains incompletely characterized. To address this knowledge gap, we created a reusable resource of tandem mass spectrometry (MS/MS) spectra by filtering 1.2 billion publicly available MS/MS spectra for bile-acid-selective ion patterns. Thousands of modifications are distributed throughout animal and human bodies as well as microbial cultures. We employed this MS/MS library to identify polyamine bile amidates, prevalent in carnivores. They are present in humans, and their levels alter with a diet change from a Mediterranean to a typical American diet. This work highlights the existence of many more bile acid modifications than previously recognized and the value of leveraging public large-scale untargeted metabolomics data to discover metabolites. The availability of a modification-centric bile acid MS/MS library will inform future studies investigating bile acid roles in health and disease.

Gut Frailty: Its Concept and Pathogenesis

BACKGROUND

There is still a considerable gap between average life expectancy and healthy life expectancy in Japan. Recent research has revealed that gut frailty may be a worsening factor for various diseases, a cause of chronic inflammation, and a precursor to frailty.

SUMMARY

Among self-reported symptoms, constipation is particularly significant as one of the key symptoms of gut frailty. Studies have demonstrated that individuals with constipation have significantly lower survival rates and are also at a higher risk of developing various diseases such as chronic kidney disease, cardiovascular diseases, and neurodegenerative disorders like Parkinson's disease. Various molecular mechanisms could contribute to gut frailty, and the decrease in mucus secretion is an extremely early-stage pathology. Dysbiosis of gut microbiota has a major impact on many conditions associated with gut frailty. Prebiotics, probiotics, post-biotics, and fecal microbiota transplantation are under investigation as a treatment option for gut frailty.

KEY MESSAGE

Although the concept of gut frailty has not yet gained widespread recognition, we hope to propose more practical screening methods, diagnostic approaches, and specific interventions in the future.

Acetate and succinate benefit host muscle energetics as exercise-associated post-biotics

Recently, the gut microbiome has emerged as a potent modulator of exercise-induced systemic adaptation and appears to be crucial for mediating some of the benefits of exercise. This study builds upon previous evidence establishing a gut microbiome-skeletal muscle axis, identifying exercise-induced changes in microbiome composition. Metagenomics sequencing of fecal samples from non-exercise-trained controls or exercise-trained mice was conducted. Biodiversity indices indicated exercise training did not change alpha diversity. However, there were notable differences in beta-diversity between trained and untrained microbiomes. Exercise significantly increased the level of the bacterial species Muribaculaceae bacterium DSM 103720. Computation simulation of bacterial growth was used to predict metabolites that accumulate under in silico culture of exercise-responsive bacteria. We identified acetate and succinate as potential gut microbial metabolites that are produced by Muribaculaceae bacterium, which were then administered to mice during a period of mechanical overload-induced muscle hypertrophy. Although no differences were observed for the overall muscle growth response to succinate or acetate administration during the first 5 days of mechanical overload-induced hypertrophy, acetate and succinate increased skeletal muscle mitochondrial respiration. When given as post-biotics, succinate or acetate treatment may improve oxidative metabolism during muscle hypertrophy.