Association of lithocholic acid with skeletal muscle hypertrophy through TGR5-IGF-1 and skeletal muscle mass in cultured mouse myotubes, chronic liver disease rats and humans

The microbiota-derived bile acid taurodeoxycholic acid improves hepatic cholesterol levels in mice with cancer cachexia

Alterations in bile acid profile and pathways contribute to hepatic inflammation in cancer cachexia, a syndrome worsening the prognosis of cancer patients. As the gut microbiota impinges on host metabolism through bile acids, the current study aimed to explore the functional contribution of gut microbial dysbiosis to bile acid dysmetabolism and associated disorders in cancer cachexia. Using three mouse models of cancer cachexia (the C26, MC38 and HCT116 models), we evidenced a reduction in the hepatic levels of several secondary bile acids, mainly taurodeoxycholic (TDCA). This reduction in hepatic TDCA occurred before the appearance of cachexia. Longitudinal analysis of the gut microbiota pinpointed an ASV, identified as Xylanibacter rodentium, as a bacterium potentially involved in the reduced production of TDCA. Coherently, stable isotope-based experiments highlighted a robust decrease in the microbial 7α-dehydroxylation (7α-DH) activity with no changes in the bile salt hydrolase (BSH) activity in cachectic mice. This approach also highlighted a reduced microbial 7α-hydroxysteroid dehydrogenase (7α-HSDH) and 12α-hydroxysteroid dehydrogenase (12α-HSDH) activities in these mice. The contribution of the lower production of TDCA to cancer cachexia was explored in vitro and in vivo. In vitro, TDCA prevented myotube atrophy, whereas in vivo hepatic whole transcriptome analysis revealed that TDCA administration to cachectic mice improved the unfolded protein response and cholesterol homeostasis pathways. Coherently, TDCA administration reversed hepatic cholesterol accumulation in these mice. Altogether, this work highlights the contribution of the gut microbiota to bile acid dysmetabolism and the therapeutic interest of the secondary bile acid TDCA for hepatic cholesterol homeostasis in the context of cancer cachexia. Such discovery may prove instrumental in the understanding of other metabolic diseases characterized by microbial dysbiosis. More broadly, our work demonstrates the interest and relevance of microbial activity measurements using stable isotopes, an approach currently underused in the microbiome field.

Crosstalk Between Bile Acids and Intestinal Epithelium: Multidimensional Roles of Farnesoid X Receptor and Takeda G Protein Receptor 5

Bile acids and their corresponding intestinal epithelial receptors, the farnesoid X receptor (FXR), the G protein-coupled bile acid receptor (TGR5), play crucial roles in the physiological and pathological processes of intestinal epithelial cells. These acids and receptors are involved in the regulation of intestinal absorption, signal transduction, cellular proliferation and repair, cellular senescence, energy metabolism, and the modulation of gut microbiota. A comprehensive literature search was conducted using PubMed, employing keywords such as bile acid, bile acid receptor, FXR (nr1h4), TGR5 (gpbar1), intestinal epithelial cells, proliferation, differentiation, senescence, energy metabolism, gut microbiota, inflammatory bowel disease (IBD), colorectal cancer (CRC), and irritable bowel syndrome (IBS), with a focus on publications available in English. This review examines the diverse effects of bile acid signaling and bile receptor pathways on the proliferation, differentiation, senescence, and energy metabolism of intestinal epithelial cells. Additionally, it explores the interactions between bile acids, their receptors, and the microbiota, as well as the implications of these interactions for host health, particularly in relation to prevalent intestinal diseases. Finally, the review highlights the importance of developing highly specific ligands for FXR and TGR5 receptors in the context of metabolic and intestinal disorders.

The Molecular Pathogenesis of Sarcopenia/Frailty in Cirrhosis

Cirrhosis is an important cause of morbidity and death in patients with chronic liver disease. It can be divided into compensatory and decompensated stages. During the decompensation period, complications such as esophageal and gastric varices hemorrhage, hepatic encephalopathy, infection, and hepatorenal syndrome are often incurred, which has a high mortality rate and leverages huge economic burden on society, healthcare resources, and individuals. Sarcopenia and frailty are common in patients with cirrhosis. The pathogenesis of sarcopenia and frailty in the context of cirrhosis is complicated and multifactorial, including overwhelming systemic inflammation, imbalance of muscle protein metabolism, malnutrition, endocrine and metabolic dysfunctions, intestinal microecological disorders, lack of physical exercise, and other aspects. Notably, accumulating evidence implicates that many patients experience sarcopenia/frailty even before the onset of liver cirrhosis. In this regard, the magnitude of liver fibrosis is closely linked to the progression of sarcopenia with reciprocal impact. In conclusion, this review article will shed light on the pathogenesis of cirrhosis complicated with sarcopenia/frailty, aimed at facilitating early diagnosis and effective management.

Bile acid metabolism in type 2 diabetes mellitus

Type 2 diabetes mellitus is a complex disorder associated with insulin resistance and hyperinsulinaemia that is insufficient to maintain normal glucose metabolism. Changes in insulin signalling and insulin levels are thought to directly explain many of the metabolic abnormalities that occur in diabetes mellitus, such as impaired glucose disposal. However, molecules that are directly affected by abnormal insulin signalling might subsequently go on to cause secondary metabolic effects that contribute to the pathology of type 2 diabetes mellitus. In the past several years, evidence has linked insulin resistance with the concentration, composition and distribution of bile acids. As bile acids are known to regulate glucose metabolism, lipid metabolism and energy balance, these findings suggest that bile acids are potential mediators of metabolic distress in type 2 diabetes mellitus. In this Review, we highlight advances in our understanding of the complex regulation of bile acids during insulin resistance, as well as how bile acids contribute to metabolic control.

A Narrative Review on the Impact of Probiotic Supplementation on Muscle Development, Metabolic Regulation, and Fiber Traits Related to Meat Quality in Broiler Chickens

Public concern over drug resistance has led to governmental regulations banning the use of antibiotics as growth promoters, stimulating interest in developing complementary strategies to maintain animal production, mitigate infections, and enhance muscle characteristics and quality parameters, especially in meat-producing animals. Probiotics are recognized as a potential strategy for improving growth, primarily by promoting intestinal homeostasis. These microorganisms are suggested to modulate gut microbiota, preserving their ecosystem and influencing secondary metabolite production, which can directly or indirectly regulate skeletal muscle metabolism by influencing the expression of key muscle-related genes and the activity of various signaling factors. Several studies have documented the potential benefits of various strains of Bacillus, Enterococcus, and members of the Lactobacillaceae family on muscle characteristics. These studies have shown that probiotics not only modulated myogenic factors but also influenced proteins and enzymes involved in signaling pathways related to carbon metabolism, inflammatory response, mitochondrial dynamics, and antioxidant activity. These effects have been associated with improvements in meat quality parameters and enhanced growth performance. This manuscript seeks to present a brief overview of the impact of probiotic supplementation on muscle health and the quality of meat in broiler chickens.

Bile acids acting as a feeding signal and functional foods mimicking bile acid function

To elucidate the function of the bile acid-binding receptor TGR5 in skeletal muscle, we developed transgenic mice expressing human TGR5 in the skeletal muscle tissue. A significant increase in muscle mass was observed in these transgenic mice, whereas a decrease in muscle mass was observed in the TGR5-deficient mice. Following treadmill exercise, TGR5 gene expression increased in response to ER stress induced in skeletal muscle via an ER stress response motif present in its promoter region. Exercise and rapid postprandial elevation in blood bile acid concentrations can be considered the primary stimuli for the TGR5-mediated increase in skeletal muscle mass. We developed a scoring system to identify food ingredients with TGR5 agonist activity, and identified the citrus limonoid nomilin. Similar effects were observed for other triterpenoids in addition to nomilin. Cell culture and in vivo experiments demonstrated that these food factors increase protein synthesis and muscle mass.

Lithocholic acid phenocopies anti-ageing effects of calorie restriction

Calorie restriction (CR) is a dietary intervention used to promote health and longevity1,2. CR causes various metabolic changes in both the production and the circulation of metabolites1; however, it remains unclear which altered metabolites account for the physiological benefits of CR. Here we use metabolomics to analyse metabolites that exhibit changes in abundance during CR and perform subsequent functional validation. We show that lithocholic acid (LCA) is one of the metabolites that alone can recapitulate the effects of CR in mice. These effects include activation of AMP-activated protein kinase (AMPK), enhancement of muscle regeneration and rejuvenation of grip strength and running capacity. LCA also activates AMPK and induces life-extending and health-extending effects in Caenorhabditis elegans and Drosophila melanogaster. As C. elegans and D. melanogaster are not able to synthesize LCA, these results indicate that these animals are able to transmit the signalling effects of LCA once administered. Knockout of AMPK abrogates LCA-induced phenotypes in all the three animal models. Together, we identify that administration of the CR-mediated upregulated metabolite LCA alone can confer anti-ageing benefits to metazoans in an AMPK-dependent manner.

The role of bile acid metabolism in bone and muscle: from analytics to mechanisms

Osteoporosis and sarcopenia are both common age-related disorders that are associated with increased morbidity and mortality. Bone and muscle are metabolically very active tissues that require large amounts of energy. Bile acids (BAs), a group of liver-derived steroid compounds, are primarily known as emulsifiers that facilitate the resorption of dietary fat and lipids. In addition, they have pleiotropic metabolic functions in lipoprotein and glucose metabolism, inflammation, and intestinal bacterial growth. Through these effects, they are related to metabolic diseases, such as diabetes, hypertriglyceridemia, atherosclerosis, and nonalcoholic steatohepatitis. BAs mediate their metabolic effects through receptor dependent and receptor-independent mechanisms. Emerging evidence suggests that BAs are also involved in bone and muscle metabolism. Under normal circumstances, BAs support bone health by shifting the delicate equilibrium of bone turnover toward bone formation. In contrast, low or excessive amounts of BAs promote bone resorption. In cholestatic liver disease, BAs accumulate in the liver, reach toxic concentrations in the circulation, and thus may contribute to bone loss and muscle wasting. In addition, the measurement of BAs is in rapid evolution with modern mass spectrometry techniques that allow for the detection of a continuously growing number of BAs. This review provides a comprehensive overview of the biochemistry, physiology and measurement of bile acids. Furthermore, it summarizes the existing literature regarding their role in bone and muscle.

Oleanolic acid alleviate intestinal inflammation by inhibiting Takeda G-coupled protein receptor (TGR) 5 mediated cell apoptosis

Oleanolic acid (OA) is a bioactive compound present in plant-based foods known for its beneficial impact on gastrointestinal health, specifically in alleviating diarrhea. Nonetheless, the underlying mechanisms by which OA mitigates gut epithelial damage have yet to be elucidated. In this study, OA significantly markedly ameliorated adverse effects induced by Dextran Sulfate Sodium (DSS), including weight loss and epithelial morphological damage in a murine model. Remarkably, compared to normal mice, standalone administration of OA had no discernible impact on the animals. Concurrently, we identified a significant up-regulation in the expression levels of TGR5 and BAX in the intestines of DSS-exposed mice, coupled with a decline in Bcl2 expression. Correlation analyses revealed a robust association between TGR5 and BAX expression. Oral administration of OA efficaciously counteracted these alterations. To probe the role of TGR5 in cellular apoptosis, further, a lentivirus transfection approach was utilized to induce TGR5 overexpression in intestinal epithelial cells (IPEC-J2). RNA sequencing indicated that TGR5 overexpression significantly influenced biological processes, particularly in modulating cellular activation and intercellular adhesion, in contrast to the control group cells. Functional assays substantiated that TGR5 overexpression compromised cell viability and accelerated apoptosis. Notably, OA treatment in TGR5-overexpressed cells restored cell viability, suppressed TGR5 and BAX expression, and augmented Bcl2 expression. In sum, our data suggest that OA mitigates intestinal epithelial apoptosis and bolsters cellular proliferation by downregulating TGR5. This research provides valuable insights into the prospective utility of OA as a functional food supplement or adjunctive therapeutic agent for enhancing gastrointestinal health.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

Dietary bile acids improve breast muscle growth in chickens through FXR/IGF2 pathway

It is a common practice to provide fast-growing broilers with high-fat diets in the context of integrated farms in Northeast China. Therefore, fat digestion, absorption, and utilization efficiency are critical for broiler meat production. Bile acids (BA) promote fat digestion and absorption, but whether and how BA affects muscle growth in broilers remains unclear. In this study, 1-day-old broilers were fed diets containing varying levels of crude fat (low, medium, and high) with or without BA supplementation for 42 d. Chickens fed a high-fat diet supplemented with BA exhibited significantly (P < 0.05) higher body weight (BW) at 21 d and average daily gain (ADG) during the first 21 d compared to the other groups. Throughout the entire experiment, feed conversion rate (FCR) was significantly (P < 0.05) lower in the high-fat group without the addition of BA, which was further decreased (P < 0.05) with BA supplementation. The improved growth performance in the BA-supplemented high-fat group was associated with significantly (P < 0.05) higher lipase activity in the small intestine chyme, a decreased trend (P = 0.06) in abdominal fat ratio, and significantly (P < 0.05) higher breast muscle mass. Histological analysis revealed significant (P < 0.05) increases in myofiber diameter, cross-sectional area, and RNA and DNA concentrations in the breast muscle of BA-supplemented broilers on the high-fat diet. Additional histological analysis further revealed significant (P < 0.05) enhancements in myofiber diameter, cross-sectional area, and RNA and DNA concentrations within the breast muscles of broilers supplemented with BA and a high-fat diet. The increased insulin-like growth factor 2 (IGF2) in the breast muscle of broilers fed a BA-supplemented high-fat diet correlated with significantly (P < 0.05) increased farnesoid X factor (FXR) protein expression and binding to the IGF2 promoter. These results suggest that dietary BA supplementation improves FCR and breast muscle growth in broilers fed a high-fat diet, potentially through the FXR-mediated IGF2 pathway.

Oleanolic acid promotes skeletal muscle fiber type transformation by activating TGR5-mediated CaN signaling pathway

In recent years, the impact of bile acids and their representative G protein-coupled bile acid receptor 1 Takeda-G-protein-receptor-5 (TGR5) signaling pathway on muscle function and metabolic health has gained considerable interest. Increasing the content of slow muscle fibers has been recognized as an effective strategy to improve metabolic health. Oleanolic acid (OA) is a naturally occurring triterpenoid compound derived from plants, which can activate TGR5. The aim of this study was to investigate the effect of OA and TGR5 on muscle fiber types and further explore the underlying TGR5-dependent mechanisms. In this study, mice were divided into three groups and dietary supplementation with 0, 50, or 100 mg/kg OA. In addition, C2C12 cells were treated with OA at concentrations of 0, 5, 10, and 20 µM. Our studies revealed that OA promoted the conversion of fast to slow muscle fibers. In addition, it was found that OA activated the TGR5-mediated calcineurin (CaN)/nuclear factor of activated T cells cytoplasmic 1 (NFATc1) signaling pathway. Further mechanistic investigations demonstrated that inhibiting TGR5 and CaN abolished the effects of OA on muscle fiber types transformation. In conclusion, this study found that OA promotes the transformation of fast muscle fibers to slow muscle fibers through the TGR5-mediated CaN/NFATc1 signaling pathway.

Bile Acids as Signaling Molecules: Role of Ursodeoxycholic Acid in Cholestatic Liver Disease

Ursodeoxycholic acid (UDCA) is a natural substance physiologically produced in the liver. Initially used to dissolve gallstones, it is now successfully used in treating primary biliary cirrhosis and as adjuvant therapy for various hepatobiliary cholestatic diseases. However, the mechanisms underlying its beneficial effects still need to be clarified. Evidence suggests three mechanisms of action for UDCA that could benefit humans with cholestatic liver disease (CLD): protection of cholangiocytes against hydrophobic bile acid (BA) cytotoxicity, stimulation of hepatobiliary excretion, and protection of hepatocytes against BA-induced apoptosis. These mechanisms may act individually or together to potentiate them. At the molecular level, it has been observed that UDCA can generate modifications in the transcription and translation of proteins essential in the transport of BA, correcting the deficit in BA secretion in CLD, in addition to activating signaling pathways to translocate these transporters to the sites where they should fulfill their function. Inhibition of BA-induced hepatocyte apoptosis may play a role in CLD, characterized by BA retention in the hepatocyte. Thus, different mechanisms of action contribute to the improvement after UDCA administration in CLD. On the other hand, the effects of UDCA on tissues that possess receptors that may interact with BAs in pathological contexts, such as skeletal muscle, are still unclear. This work aims to describe the main molecular mechanisms by which UDCA acts in the human body, emphasizing the interaction in tissues other than the liver.

Altered gut microbiome, bile acid composition and metabolome in sarcopenia in liver cirrhosis

BACKGROUND

Sarcopenia in liver cirrhosis is associated with low quality of life and high mortality risk. The pathogenesis has yet to be fully understood. We hypothesized that gut microbiome, bile acid (BA) composition and metabolites differ between cirrhotic patients with and without sarcopenia and contribute to pathogenesis.

METHODS

Cirrhotic patients with (n = 78) and without (n = 38) sarcopenia and non-cirrhotic controls with (n = 39) and without (n = 20) sarcopenia were included in this study. Faecal microbiome composition was studied by 16S rDNA sequencing, serum and faecal BA composition by ultra-high-performance liquid chromatography-tandem mass spectrometry, and metabolite composition in serum, faeces and urine by nuclear magnetic resonance.

RESULTS

Bacteroides fragilis, Blautia marseille, Sutterella spp. and Veillonella parvula were associated with cirrhotic patients with sarcopenia, whereas Bacteroides ovatus was more abundant in cirrhotic patients without sarcopenia. We observed significantly elevated secondary BAs, deoxycholic acid (DCA; P = 0.01) and lithocholic acid (LCA; P = 0.02), and the ratios of deoxycholic acid to cholic acid (DCA:CA; P = 0.04), lithocholic acid to chenodeoxycholic acid (LCA:CDCA; P = 0.03) and 12 alpha-hydroxylated to non-12 alpha-hydroxylated BAs (12-α-OH:non-12-α-OH BAs; P = 0.04) in serum of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia, indicating an enhanced transformation of primary to secondary BAs by the gut microbiome. CA (P = 0.02) and the ratios of CA:CDCA (P = 0.03) and total ursodeoxycholic acid to total secondary BAs (T-UDCA:total-sec-BAs, P = 0.03) were significantly reduced in the stool of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia. Also, valine and acetate were significantly reduced in the serum of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia (P = 0.01 and P = 0.03, respectively). Multivariate logistic regression further confirmed the association of B. ovatus (P = 0.01, odds ratio [OR]: 12.8, 95% confidence interval [CI]: 168.1; 2.2), the ratios of 12-α-OH:non-12-α-OH BAs (P = 0.03, OR: 2.54, 95% CI: 0.99; 6.55) and T-UDCA:total-sec-BAs (P = 0.04, OR: 0.25, 95% CI: 0.06; 0.98) in serum and stool CA:CDCA (P = 0.04, OR: 0.79, 95% CI: 0.62; 0.99), and serum valine (P = 0.04, OR: 1.00, 95% CI: 1.02; 1.00) with sarcopenia in cirrhosis after correcting for the severity of liver disease and sex.

CONCLUSIONS

Our study suggests a potential functional gut microbiome-host interaction linking sarcopenia with the altered gut microbiomes, BA profiles and amino acids pointing towards a potential mechanistic interplay in understanding sarcopenia pathogenesis.

Ursodeoxycholic acid induces sarcopenia associated with decreased protein synthesis and autophagic flux

BACKGROUND

Skeletal muscle generates force and movements and maintains posture. Under pathological conditions, muscle fibers suffer an imbalance in protein synthesis/degradation. This event causes muscle mass loss and decreased strength and muscle function, a syndrome known as sarcopenia. Recently, our laboratory described secondary sarcopenia in a chronic cholestatic liver disease (CCLD) mouse model. Interestingly, the administration of ursodeoxycholic acid (UDCA), a hydrophilic bile acid, is an effective therapy for cholestatic hepatic alterations. However, the effect of UDCA on skeletal muscle mass and functionality has never been evaluated, nor the possible involved mechanisms.

METHODS

We assessed the ability of UDCA to generate sarcopenia in C57BL6 mice and develop a sarcopenic-like phenotype in C₂C₁₂ myotubes and isolated muscle fibers. In mice, we measured muscle strength by a grip strength test, muscle mass by bioimpedance and mass for specific muscles, and physical function by a treadmill test. We also detected the fiber's diameter and content of sarcomeric proteins. In C₂C₁₂ myotubes and/or isolated muscle fibers, we determined the diameter and troponin I level to validate the cellular effect. Moreover, to evaluate possible mechanisms, we detected puromycin incorporation, p70S6K, and 4EBP1 to evaluate protein synthesis and ULK1, LC3 I, and II protein levels to determine autophagic flux. The mitophagosome-like structures were detected by transmission electron microscopy.

RESULTS

UDCA induced sarcopenia in healthy mice, evidenced by decreased strength, muscle mass, and physical function, with a decline in the fiber's diameter and the troponin I protein levels. In the C₂C₁₂ myotubes, we observed that UDCA caused a reduction in the diameter and content of MHC, troponin I, puromycin incorporation, and phosphorylated forms of p70S6K and 4EBP1. Further, we detected increased levels of phosphorylated ULK1, the LC3II/LC3I ratio, and the number of mitophagosome-like structures. These data suggest that UDCA induces a sarcopenic-like phenotype with decreased protein synthesis and autophagic flux.

CONCLUSIONS

Our results indicate that UDCA induces sarcopenia in mice and sarcopenic-like features in C₂C₁₂ myotubes and/or isolated muscle fibers concomitantly with decreased protein synthesis and alterations in autophagic flux.