Hyodeoxycholic acid alleviates non-alcoholic fatty liver disease through modulating the gut-liver axis

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.

Gut‑liver axis in liver disease: From basic science to clinical treatment (Review)

Incidence of a number of liver diseases has increased. Gut microbiota serves a role in the pathogenesis of hepatitis, cirrhosis and liver cancer. Gut microbiota is considered 'a new virtual metabolic organ'. The interaction between the gut microbiota and liver is termed the gut‑liver axis. The gut‑liver axis provides a novel research direction for mechanism of liver disease development. The present review discusses the role of the gut‑liver axis and how this can be targeted by novel treatments for common liver diseases.

Pharmacodynamic material basis of licorice and mechanisms of modulating bile acid metabolism and gut microbiota in cisplatin-induced liver injury based on LC-MS and network pharmacology analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Cisplatin (CP), a widely used antineoplastic agent, is a leading cause of drug-induced liver injury (DILI) due to its hepatotoxic effects. Licorice (GC), an established remedy in traditional Chinese medicine (TCM), has shown promise in addressing liver diseases and DILI. Nonetheless, the specific active components and underlying mechanisms of GC in mitigating CP-induced liver injury remain inadequately investigated.

AIM OF THE STUDY

This study examined the active components and efficacy of GC in addressing CP-induced hepatotoxicity, focusing on its mechanisms related to bile acid metabolism and gut microbiota regulation.

MATERIALS AND METHODS

Utilizing a CP-induced rat liver injury model, this study evaluated changes in liver coefficient, liver function indices, and pathological morphology while assessing the efficacy of GC for both prevention and treatment of CP-induced liver injury. Subsequently, UPLC-Q-TOF-MS qualitatively analyzed GC's blood-entering components, elucidating its pharmacodynamic material basis. Network pharmacology analysis identified potential pathways and targets of GC's blood components in relation to CP-induced liver injury. Furthermore, metabolomics and 16S rRNA sequencing were employed to clarify the pharmacodynamic mechanisms of GC in modulating bile acid metabolism and gut microbiota, offering insights into its preventive and therapeutic roles.

RESULTS

The pharmacodynamic results revealed that GC significantly reduced liver function biomarkers and improved pathological changes in liver tissue. UPLC-Q-TOF-MS analysis identified 16 blood-entering components as potential pharmacodynamic agents of GC for preventing and treating CP-induced liver injury. Network pharmacology analysis suggested a link between GC's efficacy and the bile acid metabolic pathway. Furthermore, metabolomics analysis, immunoblotting, and 16S rRNA sequencing demonstrated that GC regulated bile acid metabolites in both liver and feces, enhanced FXR and BSEP expressions in the liver, and decreased CYP27A1 expression. Additionally, GC mitigated CP-induced intestinal dysbiosis by altering the abundance of gut microbiota.

CONCLUSIONS

UPLC-Q-TOF-MS performed a qualitative analysis of 16 blood-entering components linked to GC, providing a basis for further exploration of the pharmacodynamic material underpinning GC. The protective role of GC in CP-induced liver injury appears connected to enhanced bile acid metabolism and restoration of gut microbiota balance.

Ramulus Mori (Sangzhi) alkaloids ameliorate high-fat diet induced obesity in rats by modulating gut microbiota and bile acid metabolism

Objective

The objective of this study is to investigate the ability of Ramulus Mori (Sangzhi) alkaloid tablets (SZ-A) to ameliorate obesity and lipid metabolism disorders in rats subjected to a high-fat diet (HFD) through metagenomics, untargeted lipidomics, targeted metabolism of bile acid (BA), and BA pathways, providing a novel perspective on the management of metabolic disorders.

Methods

In this research, HFD-fed rats were concurrently administered SZ-A orally. We measured changes in body weight (BW), blood lipid profiles, and liver function to assess therapeutic effects. Liver lipid status was visualized through H&E and Oil Red O. Gut microbiota composition was elucidated using metagenomics. The LC-MS-targeted metabolomics approach was utilized to define the fecal BA profiles. Furthermore, the lipid metabolomics of adipose tissue samples was investigated using an LC-MS analysis platform. The expression levels of the BA receptor were determined by western blotting. Additionally, serum insulin (INS), glucagon-like peptide-1 (GLP-1), and inflammatory cytokines were quantified using an ELISA kit. The integrity of the colonic epithelial barrier was assessed using immunofluorescence.

Results

SZ-A notably decreased BW and blood lipid levels in obese rats while also alleviating liver injury. Additionally, SZ-A reduced the serum levels of leptin (LEP), INS, and GLP-1, indicating its potential to modulate key metabolic hormones. Most notably, SZ-A substantially improved gut microbiota composition. Specifically, it reshaped the gut microbiota structure in HFD-fed rats by increasing the relative abundance of beneficial bacteria, such as Bacteroides, while decreasing the populations of potentially harmful bacteria, such as Dorea and Blautia. At the BA level, SZ-A decreased the levels of harmful BAs, including hyodeoxycholic acid (HDCA), deoxycholic acid (DCA), 12-keto lithocholic acid (12-KLCA), lithocholic acid (LCA), and muricholic acid (MDCA). Between the model group and SZ-A, 258 differentially abundant metabolites were detected, with 72 upregulated and 186 downregulated. Furthermore, these BAs are implicated in the activation of the FXR-FGF15 and TGR5-GLP-1 pathways in the intestine. This activation helps to alleviate HFD-fed intestinal inflammation and restore intestinal barrier damage by modulating inflammatory cytokines and bolstering the intestinal barrier's capabilities.

Conclusions

Our findings indicate that SZ-A effectively modulates BW, serum lipid profiles, and liver function in HFD-fed rats. Moreover, SZ-A exerts a positive influence on inflammatory cytokines, thereby mitigating inflammation and promoting the restoration of the intestinal barrier. Significantly, our research indicates that adjusting the gut microbiome and BA levels could serve as an effective approach for both preventing and treating obesity and related metabolic dyslipidemia.

Metabolomics at the cutting edge of risk prediction of MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major public health threat globally. Management of patients afflicted with MASLD and research in this domain are limited by the lack of robust well-established non-invasive biomarkers for diagnosis, prognostication, and monitoring. The circulating metabolome reflects both the systemic metabo-inflammatory milieu and changes in the liver in affected individuals. In this review we summarize the available literature on changes in the different components of the metabolome in MASLD with a focus on changes that are linked to the presence of underlying steatohepatitis, severity of disease activity, and fibrosis stage. We further summarize the existing literature around biomarker panels that are derived from interrogation of the metabolome. Their relevance to disease biology and utility in practice are also discussed. We further highlight potential direction for future studies particularly to ensure they are fit for purpose and suitable for widespread use.

Metabolic disorders, inter-organ crosstalk, and inflammation in the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents a global health concern, affecting over 30 % of adults. It is a principal driver in the development of cirrhosis and hepatocellular carcinoma. The complex pathogenesis of MASLD involves an excessive accumulation of lipids, subsequently disrupting lipid metabolism and prompting inflammation within the liver. This review synthesizes the recent research progress in understanding the mechanisms contributing to MASLD progression, with particular emphasis on metabolic disorders and interorgan crosstalk. We highlight the molecular mechanisms linked to these factors and explore their potential as novel targets for pharmacological intervention. The insights gleaned from this article have important implications for both the prevention and therapeutic management of MASLD.

Tryptophan Ameliorates Metabolic Syndrome by Inhibiting Intestinal Farnesoid X Receptor Signaling: The Role of Gut Microbiota-Bile Acid Crosstalk

Background and Aims: Metabolic syndrome (MS) is a progressive metabolic disease characterized by obesity and multiple metabolic disorders. Tryptophan (Trp) is an essential amino acid, and its metabolism is linked to numerous physiological functions and diseases. However, the mechanisms by which Trp affects MS are not fully understood. Methods and Results: In this study, experiments involving a high-fat diet (HFD) and fecal microbiota transplantation (FMT) were conducted to investigate the role of Trp in regulating metabolic disorders. In a mouse model, Trp supplementation inhibited intestinal farnesoid X receptor (FXR) signaling and promoted hepatic bile acid (BA) synthesis and excretion, accompanied by elevated levels of conjugated BAs and the ratio of non-12-OH to 12-OH BAs in hepatic and fecal BA profiles. As Trp alters the gut microbiota and the abundance of bile salt hydrolase (BSH)-enriched microbes, we collected fresh feces from Trp-supplemented mice and performed FMT and sterile fecal filtrate (SFF) inoculations in HFD-treated mice. FMT and SFF not only displayed lipid-lowering properties but also inhibited intestinal FXR signaling and increased hepatic BA synthesis. This suggests that the gut microbiota play a beneficial role in improving BA metabolism through Trp. Furthermore, fexaramine (a gut-specific FXR agonist) reversed the therapeutic effects of Trp, suggesting that Trp acts through the FXR signaling pathway. Finally, validation in a finishing pig model revealed that Trp improved lipid metabolism, enlarged the hepatic BA pool, and altered numerous glycerophospholipid molecules in the hepatic lipid profile. Conclusion: Our studies suggest that Trp inhibits intestinal FXR signaling mediated by the gut microbiota-BA crosstalk, which in turn promotes hepatic BA synthesis, thereby ameliorating MS.

Synergistic effects of Ligilactobacillus salivarius Li01 and psyllium husk prevent mice from developing loperamide-induced constipation

Constipation is a gastrointestinal (GI) condition marked by difficulty in defecation, abdominal pain and distension, significantly impacting both physical and mental health. Ligilactobacillus salivarius Li01 (Li01) is a probiotic known to prevent constipation in mice, while psyllium husk (PSH) is a dietary fiber with high water retention, acting as an intestinal lubricant. This study investigates the effects of a combined treatment of Li01 and PSH on mice with loperamide-induced constipation. The combination treatment improved GI transit rates, increased the water content of feces, and regulated serum concentrations of GI hormones more effectively than either Li01 or PSH alone. The beneficial effects were linked to higher levels of butyric acid and a greater proportion of non-12-OH bile acids (BAs) in the GI tract. These protective effects were not influenced by changes in gut microbiota. Additionally, Li01 produced butyric acid and fermented PSH in vitro. Our findings suggest that the probiotic Li01 and the prebiotic PSH synergistically protect against constipation in mice, highlighting their potential as functional food components.

Metabolic Differences among Patients with Cirrhosis Using Q Exactive Hybrid Quadrupole Orbitrap Mass Spectrometry Technology

The hospitalization and mortality rates of patients gradually increase following the onset and progression of liver cirrhosis (LC). We aimed to help define clinical stage and better target interventions by detecting the expression of specific metabolites in patients with different stages of LC via Q Exactive hybrid quadrupole orbitrap mass spectrometry (UPLC-Q-Exactive) technology. This noninterventional observation case-control study involved 139 patients with LC or acute-on-chronic liver failure (ACLF) in a Chinese hospital between October 2022 and April 2023. Serum specimens were analyzed for multiple metabolite levels using UPLC-Q-Exactive. Data were processed to screen for differentially accumulated metabolites (DAMs). Short time-series expression miner (STEM) analysis and enrichment analysis were performed to assess cirrhosis progression biomarkers. Following univariate and multivariate analyses, a Venn diagram indicated nine significant DAMs in common among groups. STEM analysis showed 8'-hydroxyabscisic acid, HDCA, pyruvate-3-phosphate, indospicine, eplerenone, and DEHP as significant; their levels first peaked [Child-Turcotte-Pugh (CTP) class B peaked] and then decreased with CTP grade aggravation. Significant differences among 8'-hydroxyabscisic acid, eplerenone, and DEHP were observed among LC comorbidities and between subgroups. Therefore, serum levels of six DAMs may characterize metabolomic changes, determine the severity of LC, and predict the development of ACLF.

Medium chain triglycerides alleviate non-alcoholic fatty liver disease through bile acid-mediated FXR signaling pathway: A comparative study with common vegetable edible oils

With the global epidemic trend of obesity, non-alcoholic fatty liver disease (NAFLD) has become a significant cause of chronic liver disease, seriously affecting human health. Medium-chain triglycerides (MCT) with a fatty acid chain length varying between 6 and 10 carbon atoms (most sources from coconut and palm kernel oils), which exhibited activities to improve lipid metabolism, prevent cardiovascular diseases, and enhance immunity. However, the efficacy differences and potential mechanisms between MCT and traditional long-chain vegetable oils (palm oil, PA; high oleic peanut oil, OA) in obesity-induced NAFLD were still unclear. The present study treated obesity-induced NAFLD mice with different dietary lipids for 16 weeks. The results showed that MCT supplements significantly improved abnormal elevation of weight gain and blood lipids and reduced hepatic lipid accumulation to a greater extent than PA and OA. Furthermore, bile acid profiling results indicated that MCT significantly changed the composition of bile acids in the liver, reduced the concentrations of cholic acid (CA), deoxycholic acid (DCA), β-muricholic acid (β-MCA), and ursodeoxycholic acid (UDCA) and increased the concentrations of chenodeoxycholic Acid (CDCA), taurochenodeoxycholic acid （TCDCA), hyodeoxycholic acid (HDCA), and taurohyodeoxycholic acid (THDCA). Mechanistically, MCT supplement upregulated FXR signal and inhibited the expression of key genes for triglyceride synthesis in the liver, thereby reducing hepatic lipid accumulation. In summary, MCT exerted a superior effect on PA and OA in improving obesity-induced NAFLD. These results provided new evidence for the application of MCT in treating NAFLD.

Role of the histone deacetylase family in lipid metabolism: Structural specificity and functional diversity

Lipids play crucial roles in signal transduction. Lipid metabolism is associated with several transcriptional regulators, including peroxisome proliferator activated receptor γ, sterol regulatory element-binding protein 1, and acetyl-CoA carboxylase. In recent years, increasing evidence has suggested that members of the histone deacetylase (HDAC) family play key roles in lipid metabolism. However, the mechanisms by which each member of this family regulates lipid metabolism remain unclear. This review discusses the latest research on the roles played by HDACs in fat metabolism. The role of HDACs in obesity, diabetes, and atherosclerosis has also been discussed. In addition, the interaction of HDACs with the gut microbiome and circadian rhythm has been reviewed, and the future development trend in HDACs has been predicted, which may potentiate therapeutic application of targeted HDACs in related metabolic diseases.

Therapeutic potential of Parabacteroides distasonis in gastrointestinal and hepatic disease

Increasing evidences indicate that the gut microbiota is involved in the development and therapy of gastrointestinal and hepatic disease. Imbalance of gut microbiota occurs in the early stages of diseases, and maintaining the balance of the gut microbiota provides a new strategy for the treatment of diseases. It has been reported that Parabacteroides distasonis is associated with multiple diseases. As the next-generation probiotics, several studies have demonstrated its positive regulation on the gastrointestinal and hepatic disease, including inflammatory bowel disease, colorectal cancer, hepatic fibrosis, and fatty liver. The function of P. distasonis and its metabolites mainly affect host immune system, intestinal barrier function, and metabolic networks. Manipulation of P. distasonis with natural components lead to the protective effect on enterohepatic disease. In this review, the metabolic pathways regulated by P. distasonis are summarized to illustrate its active metabolites and their impact on host metabolism, the role and action mechanism in gastrointestinal and hepatic disease are discussed. More importantly, the natural components can be used to manipulate P. distasonis as treatment strategies, and the challenges and perspectives of P. distasonis in clinical applications are discussed.

Gut Bifidobacterium pseudocatenulatum protects against fat deposition by enhancing secondary bile acid biosynthesis

Gut microbiome is crucial for lipid metabolism in humans and animals. However, how specific gut microbiota and their associated metabolites impact fat deposition remains unclear. In this study, we demonstrated that the colonic microbiome of lean and obese pigs differentially contributes to fat deposition, as evidenced by colonic microbiota transplantation experiments. Notably, the higher abundance of Bifidobacterium pseudocatenulatum was significantly associated with lower backfat thickness in lean pigs. Microbial-derived lithocholic acid (LCA) species were also significantly enriched in lean pigs and positively correlated with the abundance of B. pseudocatenulatum. In a high-fat diet (HFD)-fed mice model, administration of live B. pseudocatenulatum decreased fat deposition and enhances colonic secondary bile acid biosynthesis. Importantly, pharmacological inhibition of the bile salt hydrolase (BSH), which mediates secondary bile acid biosynthesis, impaired the anti-fat deposition effect of B. pseudocatenulatum in antibiotic-pretreated, HFD-fed mice. Furthermore, dietary LCA also decreased fat deposition in HFD-fed rats and obese pig models. These findings provide mechanistic insights into the anti-fat deposition role of B. pseudocatenulatum and identify BSH as a potential target for preventing excessive fat deposition in humans and animals.

Bile acid disorders and intestinal barrier dysfunction are involved in the development of fatty liver in laying hens

The pathogenesis of fatty liver is highly intricate. The role of the gut-liver axis in the development of fatty liver has gained increasing recognition in recent years. This study was conducted to explore the role of bile acid signaling and gut barrier in the pathogenesis of fatty liver. A total of 100 "Jing Tint 6" laying hens, 56-week-old, were used and fed basal diets until 60 weeks of age. At the end of the experiment, thirty individuals were selected based on the degree of hepatic steatosis. The hens with minimal hepatic steatosis (< 5 %) were chosen as healthy controls, while those with severe steatosis (> 33 %) in the liver were classified as the fatty liver group. Laying hens with fatty liver and healthy controls showed significant differences in body weight, liver index, abdominal fat ratio, feed conversion ratio (FCR), albumin height, Haugh unit, and biochemical indexes. The results of bile acid metabolomics revealed a clear separation in hepatic bile acid profiles between the fatty liver group and healthy controls, and multiple secondary bile acids were decreased in the fatty liver group, indicating disordered bile acid metabolism. Additionally, the mRNA levels of farnesoid X receptor (FXR) and genes related to bile acid transport were significantly decreased in both the liver and terminal ileum of hens with fatty liver. Moreover, the laying hens with fatty liver exhibited significant decreases in ileal crypt depth, the number of goblet cells, and the mRNA expression of tight junction-related proteins, alongside a significant increase in ileal permeability. Collectively, these findings suggest that disordered bile acids, suppressed FXR-mediated signaling, and impaired intestinal barrier function are potential factors promoting the development of fatty liver. These insights indicate that regulating bile acids and enhancing intestinal barrier function may become new preventive and therapeutic strategies for fatty liver in the near future.

Multi-omics joint analysis reveals that the Miao medicine Yindanxinnaotong formula attenuates non-alcoholic fatty liver disease

BACKGROUD

Non-alcoholic fatty liver disease (NAFLD) is a growing chronic liver disease worldwide, and no effective agent is approved yet for this condition. Traditional Chinese Medicine (TCM), which has been practiced for thousands of years in China and other Asian countries, is considered an important source for identifying novel medicines for various diseases. Miao medicine Yindanxinnaotong formula (YDX) is a classical TCM for the treatment of hyperlipidemia disease by reducing blood lipid content, while the role of YDX have not been clarified in NAFLD.

PURPOSE

To investigate the protective effect of YDX on NAFLD in mice induced by high fat diet (HFD) and clarify the potential mechanism.

METHODS

NAFLD mice model was constructed by receiving HFD for 10-week period with or without YDX administration. Lipid profiles, biochemical indicators, and histopathological staining were performed to evaluate the extent of hepatic lipid accumulation and hepatic steatosis. 16S rRNA sequencing was used to determine the gut microbial composition. Serum metabolomics was further used to investigate the changes in plasma biomarkers for NAFLD-associated by UPLC-Q-TOF/MS analysis. Subsequently, liver transcriptomics was employed to identify differentially expressed genes and explore regulatory pathways. Then, lipid metabolism-related proteins and inflammation factors were examined by Western blot and ELISA.

RESULTS

YDX reduced body weight gain, liver index and inflammatory cytokines levels, along with improved hepatic steatosis, serum lipid profile, sensitivity to insulin and also tolerance to glucose, and enhanced oxidative defense system in HFD-induced mice. Also, YDX remarkedly affected gut microbiota diversity and community richness and decreased the ratio of Firmicutes/Bacteroidetes. Meanwhile, YDX also reduced the production of harmful lipid metabolites in the sera of NAFLD mice, such as LPC(18:0), LPC(18:1) and carnitine. Notably, consistent with liver transcriptomics results, YDX downregulated the expression of proteins implicated in de novo lipid synthesis (Srebp-1c, Acaca, Fasn, Scd-1, and Cd36) and pro-inflammatory cytokines (IL-6 and TNF-α), and increased the expression of proteins-related fatty acid β-oxidation (Ampkα, Ppar-α, and Cpt-1) in the liver by activating Ampk pathway.

CONCLUSION

YDX is promisingly an effective therapy for preventing NAFLD by modulating the Ampk pathway, inhibiting gut microbiota disorder, and reducing the production of harmful lipid metabolites.

Ileal microbial microbiome and its secondary bile acids modulate susceptibility to nonalcoholic steatohepatitis in dairy goats

BACKGROUND

Liver damage from nonalcoholic steatohepatitis (NASH) presents a significant challenge to the health and productivity of ruminants. However, the regulatory mechanisms behind variations in NASH susceptibility remain unclear. The gut‒liver axis, particularly the enterohepatic circulation of bile acids (BAs), plays a crucial role in regulating the liver diseases. Since the ileum is the primary site for BAs reabsorption and return to the liver, we analysed the ileal metagenome and metabolome, liver and serum metabolome, and liver single-nuclei transcriptome of NASH-resistant and susceptible goats together with a mice validation model to explore how ileal microbial BAs metabolism affects liver metabolism and immunity, uncovering the key mechanisms behind varied NASH pathogenesis in dairy goats.

RESULTS

In NASH goats, increased total cholesterol (TC), triglyceride (TG), and primary BAs and decreased secondary BAs in the liver and serum promoted hepatic fat accumulation. Increased ileal Escherichia coli, Erysipelotrichaceae bacterium and Streptococcus pneumoniae as well as proinflammatory compounds damaged ileal histological morphology, and increased ileal permeability contributes to liver inflammation. In NASH-tolerance (NASH-T) goats, increased ursodeoxycholic acid (UDCA), isodeoxycholic acid (isoDCA) and isolithocholic acid (isoLCA) in the liver, serum and ileal contents were attributed to ileal secondary BAs-producing bacteria (Clostridium, Bifidobacterium and Lactobacillus) and key microbial genes encoding enzymes. Meanwhile, decreased T-helper 17 (TH17) cells and increased regulatory T (Treg) cells proportion were identified in both liver and ileum of NASH-T goats. To further validate whether these key BAs affected the progression of NASH by regulating the proliferation of TH17 and Treg cells, the oral administration of bacterial UDCA, isoDCA and isoLCA to a high-fat diet-induced NASH mouse model confirmed the amelioration of NASH through the TH17 cell differentiation/IL-17 signalling/PPAR signalling pathway by these bacterial secondary BAs.

CONCLUSION

This study revealed the roles of ileal microbiome and its secondary BAs in resilience and susceptibility to NASH by affecting the hepatic Treg and TH17 cells proportion in dairy goats. Bacterial UDCA, isoDCA and isoLCA were demonstrated to alleviate NASH and could be novel postbiotics to modulate and improve the liver health in ruminants. Video Abstract.

Gut microbiota and bile acids: Metabolic interactions and impacts on diabetic kidney disease

The intestinal microbiota comprises approximately 1013-1014 species of bacteria and plays a crucial role in host metabolism by facilitating various chemical reactions. Secondary bile acids (BAs) are key metabolites produced by gut microbiota.Initially synthesized by the liver, BA undergoes structural modifications through the activity of various intestinal microbiota enzymes, including eukaryotic, bacterial, and archaeal enzymes. These modified BA then activate specific receptors that regulate multiple metabolic pathways in the host, such as lipid and glucose metabolism, energy balance, inflammatory response, and cell proliferation and death. Recent attention has been given to intestinal flora disorders in diabetic kidney disease (DKD), where activation of BA receptors has shown promise in alleviating diabetic kidney damage by modulating renal lipid metabolism and mitochondrial production. Imbalances in the intestinal flora can influence the progression of DKD through the regulation of bile acid and its receptor pathways. This review aims to propose a mechanism involving the gut-BA-diabetes and nephropathy axes with the goal of optimizing new strategies for treating DKD.

A novel selenoglycoside compound GlcSeCys alleviates diets-induced obesity and metabolic dysfunctions with the modulation of Galectin-1 and selenoproteins

Selenium, an essential trace element in human, has been shown to play protective roles in obesity and metabolic disorders despite insufficient understanding of mechanisms. Moreover, it's well known that biological actions of selenium compounds differed greatly due to divergent chemical forms. Selenoglycoside is a type of organoselenium compounds with excellent hydrophilicity, but biological activity of which in vivo are almost unknown. We have designed and synthesized Se-β-d-glucopyranosyl-D-selenocysteine, a novel selenoglycoside compound named GlcSeCys. Herein, GlcSeCys was given to high fat high cholesterol (HFHC) fed mice to determine its actions as well as relevant molecular mechanisms using transcriptome and multiple molecular biological methods. It was revealed that GlcSeCys displayed pronounced anti-obesity effect and significantly alleviated hyperglycemia, hyperinsulinemia along with hepatic steatosis in HFHC diets-induced mice. Mechanistically, GlcSeCys was found to inhibit lipogenesis, lipid uptake and inflammation in liver, along with attenuation of Galectin-1 and induction of selenoprotein S (SELENOS). With regard to adipose tissues, GlcSeCys ameliorated hypertrophy of adipocytes, suppressed lipids biosynthesis and stimulated WAT browning along with abrogated WAT inflammation activation, which were in line with repression of Galectin-1 and increase of GPx3. Collectively, our results uncovered, for the first time, that selenoglycoside compound GlcSeCys possessed excellent protective effects against obesity and metabolic disorders, and the mechanisms were correlated with modulation of Galectin-1 and selenoproteins, shedding lights upon molecular biology of selenium and novel therapeutic for obesity and relevant metabolic disorders.

Biological functions and pharmacological behaviors of bile acids in metabolic diseases

BACKGROUND

Bile acids, synthesized endogenously from cholesterol, play a central role in metabolic regulation within the enterohepatic circulatory system. Traditionally known as emulsifying agents that facilitate the intestinal absorption of vitamins and lipids, recent research reveals their function as multifaceted signal modulators involved in various physiological processes. These molecules are now recognized as key regulators of chronic metabolic diseases and immune dysfunction. Despite progress in understanding their roles, their structural diversity and the specific functions of individual bile acids remain underexplored.

AIM OF REVIEW

This study categorizes the bile acids based on their chemical structures and their roles as signaling molecules in physiological processes. It consolidates current knowledge and provides a comprehensive overview of the current research. The review also includes natural and semisynthetic variants that have demonstrated potential in regulating metabolic processes in animal models or clinical contexts.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bile acids circulate primarily within the enterohepatic circulation, where they help maintain a healthy digestive system. Disruptions in their balance are linked to metabolic disorders, hepatobiliary diseases and intestinal inflammation. Through receptor-mediated pathways, bile acids influence the progression of metabolic diseases by regulating glucose and lipid metabolism, immune function, and energy expenditure. This review aims to provide a comprehensive, systematic foundation to for understanding their physiological roles and supporting future therapeutic developments for metabolic and inflammatory diseases.

Bifidobacterium pseudolongum-Derived Bile Acid from Dietary Carvacrol and Thymol Supplementation Attenuates Colitis via cGMP-PKG-mTORC1 Pathway

Carvacrol and thymol (CAT) have been widely recognized for their antimicrobial and anti-inflammatory properties, yet their specific effects on colitis and the mechanisms involved remain insufficiently understood. This study establishes a causative link between CAT administration and colitis mitigation, primarily through the enhancement of Bifidobacterium pseudolongum abundance in the colon. This increase promotes the production of secondary bile acids, particularly hyodeoxycholic acid (HDCA) and 12-ketodeoxycholic acid (12-KCAC), which exert anti-inflammatory effects. Notably, CAT does not alleviate colitis symptoms in germ-free mice, indicating the necessity of gut microbiota. This research uncovers a novel regulatory mechanism where HDCA and 12-KCAC inhibit colonic inflammation by reducing the expression of transmembrane guanylate cyclase 1A in the colonic epithelium. This downregulation elevates intracellular Ca2+ and cGMP levels, activating protein kinase G (PKG). Activated PKG subsequently suppresses the mTOR signaling pathway, thereby ameliorating dextran sulfate sodium (DSS)-induced colonic damage. These findings highlight potential metabolites and therapeutic targets for preventing and treating colitis. Bifidobacterium pseudolongum, HDCA, and 12-KCAC emerge as promising candidates for therapeutic interventions in colitis and related disorders characterized by impaired tight junction function.

Melatonin Ameliorates Cadmium-Induced Liver Fibrosis Via Modulating Gut Microbiota and Bile Acid Metabolism

Cadmium (Cd) is a widespread environmental contaminant with high toxicity to human health. Melatonin has been shown to improve Cd-induced liver damage. However, its mechanism has not yet been elucidated. In this study, we aimed to investigate the effects of melatonin on Cd-induced liver damage and fibrosis. A combination of 16S rRNA gene sequencing and mass spectrometry-based metabolomics was adopted to investigate changes in the gut microbiome and its metabolites on the regulation of melatonin in Cd-induced liver injury and fibrosis of mice. Further, nonabsorbable antibiotics, a fecal microbiota transplantation (FMT) program and intestine-specific farnesoid X receptor (FXR) knockout mice were employed to explore the mechanism of melatonin (MT) on liver injury and fibrosis in Cd treated mice. MT significantly improved hepatic inflammation, bile duct hyperplasia, liver damage, and liver fibrosis, with a notable decrease in liver bile acid levels in Cd-exposed mice. MT treatment remodeled the gut microbiota, improved gut barrier function, and reduced the production of gut-derived lipopolysaccharide (LPS). MT significantly decreased the intestinal tauro-β-muricholic acid levels, which are known as FXR antagonists. Notably, MT prominently activated the intestinal FXR signaling, subsequently inhibiting liver bile acid synthesis and decreasing hepatic inflammation in Cd-exposed mice. However, MT could not ameliorate Cd-induced liver damage and fibrosis in Abx-treated mice. Conversely, MT still exerted a protective effect on Cd-induced liver damage and fibrosis in FMT mice. Interestingly, MT failed to reverse liver damage and fibrosis in Cd-exposed intestinal epithelial cell-specific FXR gene knockout mice, indicating that intestinal FXR signaling mediated the protective effect of MT treatment. MT improves Cd-induced liver damage and fibrosis through reshaping the intestinal flora, activating the intestinal FXR-mediated suppression of liver bile acid synthesis and reducing LPS leakage in mice.

Intermittent Fasting Improves Insulin Resistance by Modulating the Gut Microbiota and Bile Acid Metabolism in Diet-Induced Obesity

SCOPE

Adipose tissue macrophages (ATMs) are crucial in the pathogenesis of insulin resistance (IR). Intermittent fasting (IF) is an effective intervention for obesity. However, the underlying mechanism by which IF improves IR remains unclear.

METHODS AND RESULTS

Male C57BL/6J mice are fed chow-diet and high-fat diet (HFD) for 12 weeks, then is randomized into ad libitum feeding or every other day fasting for 8 weeks. Markers of ATMs and expression of uncoupling protein 1 (UCP-1) are determined. Gut microbiota and bile acids (BAs) are profiled using 16S rRNA sequencing and targeted metabolomics analysis. Results indicate that IF improves IR in HFD-induced obesity. IF decreases ATM infiltration, pro-inflammatory M1 gene expression, and promotes white adipose tissue (WAT) browning by elevating UCP-1 expression. IF restructures microbiota composition, significantly expanding the abundance of Verrucomicrobia particularly Akkermansia muciniphila, with the decrease of that of Firmicutes. IF increases the level of total BAs and alters the composition of BAs with higher proportion of 12α-hydroxylated (12α-OH) BAs. The changes in these BAs are correlated with differential bacteria.

CONCLUSION

The findings indicate that IF improves IR partially mediated by the interplay between restructured gut microbiota and BAs metabolism, which has implications for the dietary management in obesity.

FXR activation remodels hepatic and intestinal transcriptional landscapes in metabolic dysfunction-associated steatohepatitis

The escalating obesity epidemic and aging population have propelled metabolic dysfunction-associated steatohepatitis (MASH) to the forefront of public health concerns. The activation of FXR shows promise to combat MASH and its detrimental consequences. However, the specific alterations within the MASH-related transcriptional network remain elusive, hindering the development of more precise and effective therapeutic strategies. Through a comprehensive analysis of liver RNA-seq data from human and mouse MASH samples, we identified central perturbations within the MASH-associated transcriptional network, including disrupted cellular metabolism and mitochondrial function, decreased tissue repair capability, and increased inflammation and fibrosis. By employing integrated transcriptome profiling of diverse FXR agonists-treated mice, FXR liver-specific knockout mice, and open-source human datasets, we determined that hepatic FXR activation effectively ameliorated MASH by reversing the dysregulated metabolic and inflammatory networks implicated in MASH pathogenesis. This mitigation encompassed resolving fibrosis and reducing immune infiltration. By understanding the core regulatory network of FXR, which is directly correlated with disease severity and treatment response, we identified approximately one-third of the patients who could potentially benefit from FXR agonist therapy. A similar analysis involving intestinal RNA-seq data from FXR agonists-treated mice and FXR intestine-specific knockout mice revealed that intestinal FXR activation attenuates intestinal inflammation, and has promise in attenuating hepatic inflammation and fibrosis. Collectively, our study uncovers the intricate pathophysiological features of MASH at a transcriptional level and highlights the complex interplay between FXR activation and both MASH progression and regression. These findings contribute to precise drug development, utilization, and efficacy evaluation, ultimately aiming to improve patient outcomes.

Hoxa5 alleviates adipose tissue metabolic distortions in high-fat diet mice associated with a reduction in MERC

BACKGROUND

Mitochondria-endoplasmic reticulum membrane contact (MERC) is an important mode of intercellular organelle communication and plays a crucial role in adipose tissue metabolism. Functionality of Hoxa5 is an important transcription factor involved in adipose tissue fate determination and metabolic regulation, but the relationship between Hoxa5 and MERC is not well understood.

RESULTS

In our study, we established an obesity model mouse by high-fat diet (HFD), induced the alteration of Hoxa5 expression by adenoviral transfection, and explored the effect of Hoxa5 on MERC dysfunction and metabolic distortions of adipose tissue with the help of transmission electron microscopy, calcium ion probe staining, and other detection means. The results showed Hoxa5 was able to reduce MERC production, alleviate endoplasmic reticulum stress (ERS) and calcium over-transport, and affect cGAS-STING-mediated innate immune response affecting adipose tissue energy metabolism, as well as affect the AKT-IP3R pathway to alleviate insulin resistance and ameliorate metabolic distortions in adipose tissue of mice.

CONCLUSIONS

Our results suggest that Hoxa5 can ameliorate high-fat diet-induced MERC overproduction and related functional abnormalities, in which finding is expected to provide new ideas for the improvement of obesity-related metabolic distortions.

Zhi-Kang-Yin formula attenuates high-fat diet-induced metabolic disorders through modulating gut microbiota-bile acids axis in mice

BACKGROUND

Metabolic disorders have become one of the global medical problems. Due to the complexity of its pathogenesis, there is still no effective treatment. Bile acids (BAs) and gut microbiota (GM) have been proved to be closely related to host metabolism, which could be important targets for metabolic disorders. Zhi-Kang-Yin (ZKY) is a traditional Chinese medicine (TCM) formula developed by the research team according to theory of TCM and has been shown to improve metabolism in clinic. However, the underlying mechanisms are unclear.

AIM OF THE STUDY

This study aimed to investigate the potential mechanisms of the beneficial effect of ZKY on metabolism.

METHODS

High-fat diet (HFD)-fed mice were treated with and without ZKY. The glucose and lipid metabolism-related indexes were measured. BA profile, GM composition and hepatic transcriptome were then investigated to analyze the changes of BAs, GM, and hepatic gene expression. Moreover, the relationship between GM and BAs was identified with functional gene quantification and ex vivo fermentation experiment.

RESULTS

ZKY reduced weight gain and lipid levels in both liver and serum, attenuated hepatic steatosis and improved glucose tolerance in HFD-fed mice. BA profile detection showed that ZKY changed the composition of BAs and increased the proportion of unconjugated BAs and non-12-OH BAs. Hepatic transcriptomic analysis revealed fatty acid metabolism and BA biosynthesis related pathways were regulated. In addition, ZKY significantly changed the structure of GM and upregulated the gene copy number of bacterial bile salt hydrolase. Meanwhile, ZKY directly promoted the growth of Bifidobacterium, which is a well-known bile salt hydrolase-producing genus. The ex vivo co-culture experiment with gut microbiota and BAs demonstrated that the changes of BAs profile in ZKY group were mediated by ZKY-shifted GM, which led to increased expression of genes associated with fatty acid degradation in the liver.

CONCLUSION

Our study indicated that the effect of ZKY on improving metabolism is associated with the modulation of GM-BAs axis, especially, by upregulating the abundance of bile salt hydrolase-expression bacteria and increasing the levels of unconjugated BAs. This study indicates that GM-BAs axis might be an important pathway for improving metabolic disorders by ZKY.

Bile Acid Signaling in Metabolic and Inflammatory Diseases and Drug Development

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates biliary secretion of lipids, endogenous metabolites, and xenobiotics. In intestine, bile acids facilitate the digestion and absorption of dietary lipids and fat-soluble vitamins. Through activation of nuclear receptors and G protein-coupled receptors and interaction with gut microbiome, bile acids critically regulate host metabolism and innate and adaptive immunity and are involved in the pathogenesis of cholestasis, metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, type-2 diabetes, and inflammatory bowel diseases. Bile acids and their derivatives have been developed as potential therapeutic agents for treating chronic metabolic and inflammatory liver diseases and gastrointestinal disorders. SIGNIFICANCE STATEMENT: Bile acids facilitate biliary cholesterol solubilization and dietary lipid absorption, regulate host metabolism and immunity, and modulate gut microbiome. Targeting bile acid metabolism and signaling holds promise for treating metabolic and inflammatory diseases.

What defines a healthy gut microbiome?

The understanding that changes in microbiome composition can influence chronic human diseases and the efficiency of therapies has driven efforts to develop microbiota-centred therapies such as first and next generation probiotics, prebiotics and postbiotics, microbiota editing and faecal microbiota transplantation. Central to microbiome research is understanding how disease impacts microbiome composition and vice versa, yet there is a problematic issue with the term 'dysbiosis', which broadly links microbial imbalances to various chronic illnesses without precision or definition. Another significant issue in microbiome discussions is defining 'healthy individuals' to ascertain what characterises a healthy microbiome. This involves questioning who represents the healthiest segment of our population-whether it is those free from illnesses, athletes at peak performance, individuals living healthily through regular exercise and good nutrition or even elderly adults or centenarians who have been tested by time and achieved remarkable healthy longevity.This review advocates for delineating 'what defines a healthy microbiome?' by considering a broader range of factors related to human health and environmental influences on the microbiota. A healthy microbiome is undoubtedly linked to gut health. Nevertheless, it is very difficult to pinpoint a universally accepted definition of 'gut health' due to the complexities of measuring gut functionality besides the microbiota composition. We must take into account individual variabilities, the influence of diet, lifestyle, host and environmental factors. Moreover, the challenge in distinguishing causation from correlation between gut microbiome and overall health is presented.The review also highlights the resource-heavy nature of comprehensive gut health assessments, which hinders their practicality and broad application. Finally, we call for continued research and a nuanced approach to better understand the intricate and evolving concept of gut health, emphasising the need for more precise and inclusive definitions and methodologies in studying the microbiome.

Refined diet consumption increases neuroinflammatory signalling through bile acid dysmetabolism

Over recent decades, dietary patterns have changed significantly due to the increasing availability of convenient, ultra-processed refined foods. Refined foods are commonly depleted of key bioactive compounds, which have been associated with several deleterious health conditions. As the gut microbiome can influence the brain through a bidirectional communication system known as the 'microbiota-gut-brain axis', the consumption of refined foods has the potential to affect cognitive health. In this study, multi-omics approaches were employed to assess the effect of a refined diet on the microbiota-gut-brain axis, with a particular focus on bile acid metabolism. Mice maintained on a refined low-fat diet (rLFD), consisting of high sucrose, processed carbohydrates and low fibre content, for eight weeks displayed significant gut microbial dysbiosis, as indicated by diminished alpha diversity metrics (p < 0.05) and altered beta diversity (p < 0.05) when compared to mice receiving a chow diet. Changes in gut microbiota composition paralleled modulation of the metabolome, including a significant reduction in short-chain fatty acids (acetate, propionate and n-butyrate; p < 0.001) and alterations in bile acid concentrations. Interestingly, the rLFD led to dysregulated bile acid concentrations across both the colon (p < 0.05) and the brain (p < 0.05) which coincided with altered neuroinflammatory gene expression. In particular, the concentration of TCA, TDCA and T-α-MCA was inversely correlated with the expression of NF-κB1, a key transcription factor in neuroinflammation. Overall, our results suggest a novel link between a refined low-fat diet and detrimental neuronal processes, likely in part through modulation of the microbiota-gut-brain axis and bile acid dysmetabolism.

Dynamic pattern of postprandial bile acids in paediatric non-alcoholic fatty liver disease

BACKGROUND

Dysregulation of bile acids (BAs), as important signalling molecules in regulating lipid and glucose metabolism, contributes to the development of non-alcoholic fatty liver disease (NAFLD). However, static BA profiles during fasting may obscure certain pathogenetic aspects. In this study, we investigate the dynamic alterations of BAs in response to an oral glucose tolerance test (OGTT) among children with NAFLD.

METHODS

We recruited 230 subjects, including children with overweight/obesity, or complicated with NAFLD, and healthy controls. Serum BAs, 7-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor 19 (FGF19) were quantified during OGTT. Clinical markers related to liver function, lipid metabolism and glucose metabolism were assessed at baseline or during OGTT.

FINDINGS

Conjugated BAs increased while unconjugated ones decreased after glucose uptake. Most BAs were blunted in response to glucose in NAFLD (p > .05); only glycine and taurine-conjugated chenodeoxycholic acid (CDCA) and cholic acid (CA) were responsive (p < .05). Primary BAs were significantly increased while secondary BAs were decreased in NAFLD. C4 and FGF19 were significantly increased while their ratio FGF19/C4 ratio was decreased in NAFLD. The dynamic pattern of CDCA and taurine-conjugated hyocholic acid (THCA) species was closely correlated with glucose (correlation coefficient r = .175 and -.233, p < .05), insulin (r = .327 and -.236, p < .05) and c-peptide (r = .318 and -.238, p < .05). Among which, CDCA was positively associated with liver fat content in NAFLD (r = .438, p < .05). Additionally, glycochenodeoxycholic acid (GCDCA), CDCA and THCA were potential biomarkers to discriminate paediatric NAFLD from healthy controls and children with obesity.

INTERPRETATION

This study provides novel insights into the dynamics of BAs during OGTT in paediatric NAFLD. The observed variations in CDCA and HCA species were associated with liver dysfunction, dyslipidaemia and dysglycaemia, highlighting their potential roles as promising diagnostic and therapeutic targets in NAFLD.

Novel microbial modifications of bile acids and their functional implications

This review outlines the recent discoveries of bile acids that have undergone novel microbial modifications, highlighting their biological roles and the profound implications for the development of innovative therapeutic strategies. The review aims to provide valuable insights and breakthroughs for future drug candidates in the expanding field of bile acid therapeutics.

Analysis of Serum Bile Acid Profile Characteristics and Identification of New Biomarkers in Lean Metabolic Dysfunction-Associated Fatty Liver Disease Based on LC-MS/MS

Objectives

Plasma bile acid (BA) has been widely studied as pathophysiological factors in chronic liver disease. But the changes of plasma BA level in lean metabolic dysfunction-associated fatty liver disease (MAFLD) remains unclear. Here, we clarified the BA metabolic characteristics of lean MAFLD and explored its significance and mechanism as a marker.

Methods

We employed ultra-performance liquid chromatography tandem mass spectrometry based on BA metabonomics to characterize circulating bile acid in lean MAFLD patients. Explore its significance as serum biomarkers by further cluster analysis, functional enrichment analysis, and serum concentration change analysis of differential BAs. Evaluation of diagnostic value of differential BAs by ROC analysis.

Results

A total of 65 BAs were detected and 17 BAs were identified which showed different expression in the lean-MAFLD group compared with the normal group. Functional annotation and enrichment analysis of KEGG and HMDB showed that differential BAs were mainly related to bile acid biosynthesis, bile secretion, cholesterol metabolism, and familial hypercholangitis, involving diseases including but not limited to cirrhosis, hepatocellular carcinoma, chronic active hepatitis, colorectal cancer, acute liver failure, and portal vein obstruction. ROC analysis displayed that the 6 BA metabolites (GCDCA-3S, GUDCA-3S, CDCA-3S, NCA, TCDCA, and HDCA) exhibited well differential diagnostic ability in discriminating between lean MAFLD patients and normal individuals with an area under the curve (AUC) ⩾0.85.

Conclusions

We delineated the characteristics of BA level in patients with lean MAFLD, and identified 6 potential plasma BA biomarkers of lean MAFLD.

Secondary bile acids are associated with body lipid accumulation in obese pigs

The aim of this study was to investigate the reasons for the differences in lipid accumulation between lean and obese pigs. The bile acids with varying levels within two types of pigs were found and then in vitro experiments were conducted to identify whether these bile acids can directly affect lipid accumulation. Fourteen pigs, including seven lean and seven obese pigs with body weights of approximately 80 kg, were fed the same diet at an amount approximately equivalent to 3% of their respective body weights daily for 42 d. In vitro, 3T3-L1 preadipocytes were cultured in medium with high glucose levels and were differentiated into mature adipocytes using differentiation medium. Then, bile acids were added to mature adipocytes for 4 d. The results showed that there was a difference in body lipids levels and gut microbiota composition between obese and lean pigs (P < 0.05). According to the results of gut microbial function prediction, the bile acid biosynthesis in colonic digesta of obese pigs were different from that in lean pig. Sixty-five bile acids were further screened by metabolomics, of which 4 were upregulated (P < 0.05) and 2 were downregulated (P < 0.05) in obese pigs compared to lean pigs. The results of the correlation analysis demonstrated that chenodeoxycholic acid-3-β-D-glucuronide (CDCA-3Gln) and ω-muricholic acid (ω-MCA) had a negative correlation with abdominal fat weight and abdominal fat rate, while isoallolithocholic acid (IALCA) was positively associated with crude fat in the liver and abdominal fat rate. There was a positive correlation between loin muscle area and CDCA-3Gln and ω-MCA (P < 0.05), however, IALCA and 3-oxodeoxycholic acid (3-oxo-DCA) were negatively associated with loin eye muscle area (P < 0.05). Isoallolithocholic acid increased the gene expression of peroxisome proliferator-activated receptor gamma (PPARG) and the number of lipid droplets (P < 0.05), promoting the lipid storage when IALCA was added to 3T3-L1 mature adipocytes in vitro. In conclusion, the concentration of bile acids, especially gut microbiota related-secondary bile acids, in obese pigs was different from that in lean pigs, which may contribute to lipid accumulation within obese pigs.

Jujuboside A through YY1/CYP2E1 signaling alleviated type 2 diabetes-associated fatty liver disease by ameliorating hepatic lipid accumulation, inflammation, and oxidative stress

Non-alcoholic fatty liver disease (NAFLD) was a chronic complication of type 2 diabetes mellitus (T2DM), and this comorbid disease lacked therapeutic drugs. Semen Ziziphi Spinosae (SZS) was the seed of Ziziphus jujuba var. Spinosa (Bunge) Hu ex H.F. Chow, and it could alleviate the symptoms of T2DM patients. As a triterpene saponin, Jujuboside A (Ju A) was the main active substance isolated from SZS and could improve hyperglycemia of diabetic mice. However, it was still unknown whether Ju A has protective effects on T2DM-associated NAFLD. Our study showed that Ju A attenuated T2DM-associated liver damage by alleviating hepatic lipid accumulation, inflammatory response, and oxidative stress in the liver of db/db mice, and high glucose (HG) and free fatty acid (FFA) co-stimulated human hepatocellular carcinomas (HepG2) cells. Along with the improved hyperglycemia and liver injury, Ju A restrained Yin Yang 1 (YY1)/cytochrome P450 2E1 (CYP2E1) signaling in vivo and in vitro. YY1 overexpression intercepted the protective effects of Ju A on T2DM-induced liver injury via promoting hepatic lipid accumulation, inflammatory response, and oxidative stress. While, the blocking effect of YY1 overexpression on Ju A's hepatoprotective effect was counteracted by further treatment of CYP2E1 specific inhibitor diethyldithiocarbamate (DDC) in vitro. In-depth mechanism research showed that Ju A through YY1/CYP2E1 signaling promoted hepatic fatty acid β-oxidation, and inhibited inflammatory response and oxidative stress by activating peroxisome proliferator-activated receptor alpha (PPARα), leading to the improvement of T2DM-associated NAFLD. Ju A might be a potential agent in the treatment and health care of T2DM-associated liver disease, especially NAFLD.

Emerging chemophysiological diversity of gut microbiota metabolites

Human physiology is profoundly influenced by the gut microbiota, which generates a wide array of metabolites. These microbiota-derived compounds serve as signaling molecules, interacting with various cellular targets in the gastrointestinal tract and distant organs, thereby impacting our immune, metabolic, and neurobehavioral systems. Recent advancements have unveiled unique physiological functions of diverse metabolites derived from tryptophan (Trp) and bile acids (BAs). This review highlights the emerging chemophysiological diversity of these metabolites and discusses the role of chemical and biological tools in analyzing and therapeutically manipulating microbial metabolism and host targets, with the aim of bridging the chemical diversity with physiological complexity in host-microbe molecular interactions.

Ex vivo metabolism kinetics of primary to secondary bile acids via a physiologically relevant human faecal microbiota model

Bile acids (BA) are synthesized in the human liver and undergo metabolism by host gut bacteria. In diseased states, gut microbial dysbiosis may lead to high primary unconjugated BA concentrations and significant perturbations to secondary BA. Hence, it is important to understand the microbial-mediated formation kinetics of secondary bile acids using physiologically relevant ex vivo human faecal microbiota models. Here, we optimized an ex vivo human faecal microbiota model to recapitulate the metabolic kinetics of primary unconjugated BA and applied it to investigate the formation kinetics of novel secondary BA metabolites and their sequential pathways. We demonstrated (1) first-order depletion of primary BA, cholic acid (CA) and chenodeoxycholic acid (CDCA), under non-saturable conditions and (2) saturable Michaelis-Menten kinetics for secondary BA metabolite formation with increasing substrate concentration. Notably, relatively lower Michaelis constants (Km) were associated with the formation of deoxycholic acid (DCA, 14.3 μM) and lithocholic acid (LCA, 140 μM) versus 3-oxo CA (>1000 μM), 7-keto DCA (443 μM) and 7-keto LCA (>1000 μM), thereby recapitulating clinically observed saturation of 7α-dehydroxylation relative to oxidation of primary BA. Congruently, metagenomics revealed higher relative abundance of functional genes related to the oxidation pathway as compared to the 7α-dehydroxylation pathway. In addition, we demonstrated gut microbial-mediated hyocholic acid (HCA) and hyodeoxycholic acid (HDCA) formation from CDCA. In conclusion, we optimized a physiologically relevant ex vivo human faecal microbiota model to investigate gut microbial-mediated metabolism of primary BA and present a novel gut microbial-catalysed two-step pathway from CDCA to HCA and, subsequently, HDCA.

Interactions between Gut Microbiota and Natural Bioactive Polysaccharides in Metabolic Diseases: Review

The gut microbiota constitutes a complex ecosystem, comprising trillions of microbes that have co-evolved with their host over hundreds of millions of years. Over the past decade, a growing body of knowledge has underscored the intricate connections among diet, gut microbiota, and human health. Bioactive polysaccharides (BPs) from natural sources like medicinal plants, seaweeds, and fungi have diverse biological functions including antioxidant, immunoregulatory, and metabolic activities. Their effects are closely tied to the gut microbiota, which metabolizes BPs into health-influencing compounds. Understanding how BPs and gut microbiota interact is critical for harnessing their potential health benefits. This review provides an overview of the human gut microbiota, focusing on its role in metabolic diseases like obesity, type II diabetes mellitus, non-alcoholic fatty liver disease, and cardiovascular diseases. It explores the basic characteristics of several BPs and their impact on gut microbiota. Given their significance for human health, we summarize the biological functions of these BPs, particularly in terms of immunoregulatory activities, blood sugar, and hypolipidemic effect, thus providing a valuable reference for understanding the potential benefits of natural BPs in treating metabolic diseases. These properties make BPs promising agents for preventing and treating metabolic diseases. The comprehensive understanding of the mechanisms by which BPs exert their effects through gut microbiota opens new avenues for developing targeted therapies to improve metabolic health.

Chitosan-Stabilized Selenium Nanoparticles Alleviate High-Fat Diet-Induced Non-Alcoholic Fatty Liver Disease (NAFLD) by Modulating the Gut Barrier Function and Microbiota

Low molecular weight chitosan selenium nanoparticles (LCS-SeNPs), a biologically active compound derived from selenium polysaccharides, have demonstrated potential in addressing obesity. However, the mechanism through which LCS-SeNPs alleviate high-fat diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) remains unclear. Our results elucidated that LCS-SeNPs significantly inhibited fat accumulation and markedly improved the intestinal barrier by increasing mucus secretion from goblet cells. Moreover, LCS-SeNPs reshaped intestinal flora composition by increasing the abundance of mucus-associated microbiota (Bifidobacterium, Akkermansia, and Muribaculaceae_unclassified) and decreasing the abundance of obesity-contributed bacterium (Anaerotruncus, Lachnoclostridium, and Proteus). The modulation of intestinal microbiota by LCS-SeNPs influenced several metabolic pathways, including bile acid secretion, purine metabolites, and tryptophan derivation. Meanwhile, glycocholic acid and tauro-beta-muricholic acid were significantly reduced in the LCS-SeNP group. Our study suggests the crucial role of intestinal microbiota composition and metabolism, providing a new theoretical foundation for utilizing selenium polysaccharides in the intervention of HFD-induced NAFLD.

Bile Acid Composition and Transcriptome Analysis of the Liver and Small Intestine in Different Species

Bile, a crucial fluid produced continuously by the liver, plays an essential role in digestion within the small intestine. Beyond its primary function in lipid digestion, bile also acts as a pathway for the elimination of various endogenous and exogenous substances. There have been limited studies focusing on interspecies differences. This study offers a comprehensive analysis of bile acid (BA) composition and its correlation with gene expression patterns across six different species, including mammals and poultry, through combining Liquid Chromatography-Mass Spectrometry (LC-MS) and transcriptome sequencing. The BA profiles revealed distinct metabolite clusters: D-glucuronic acid (GLCA) and glycochenodeoxycholic acid (GCDCA) were predominant in mammals, while taurolithocholic acid (TLCA) and T-alpha-MCA were prevalent in poultry, highlighting species-specific BA compositions. Differentially abundant metabolites, particularly GDCA, glycohyodeoxycholic acid (GHDCA) and taurodeoxycholic acid (TDCA) showed significant variations across species, with pigs showing the highest BA content. Transcriptome analysis of the liver and small intestine tissues of 56 cDNA libraries across the six species revealed distinct mRNA expression patterns. These patterns clustered samples into broad categories based on tissue type and phylogenetic relationships. Furthermore, the correlation between gene expression and BA content was examined, identifying the top 20 genes with significant associations. These genes potentially serve as biomarkers for BA regulation.

Fluoride induces hepatointestinal damage and vitamin B2 mitigation by regulating IL-17A and Bifidobacterium in ileum

INTRODUCTION

Fluorosis is a global public health disease affecting more than 50 countries and 500 million people. Excessive fluoride damages the liver and intestines, yet the mechanisms and therapeutic approaches remain unclear.

OBJECTIVES

To explore the mechanisms by which fluoride-induced intestinal-hepatic damage and vitamin B2 alleviation.

METHODS

Fluoride and/or vitamin B2-treated IL-17A knockout and wild-type mouse models were established, the morphological and functional changes of liver and gut, total bile acid biosynthesis, metabolism, transport, and regulation of FXR-FGF15 signaling pathways were evaluated, the ileal microbiome was further analyzed by 16S rDNA sequence. Finally, Bifidobacterium supplementation mouse model was designed and re-examined the above indicators.

RESULTS

The results demonstrated that fluoride induced hepatointestinal injury and enterohepatic circulation disorder by altering the synthesis, transporters, and FXR-FGF15 pathway regulation of total bile acid. Importantly, the ileum was found to be the most sensitive and fluoride changed ileal microbiome particularly by reducing abundance of Bifidobacterium. While vitamin B2 supplementation attenuated fluoride-induced enterohepatic circulation dysfunction through IL-17A and ileal microbiome, Bifidobacterium supplementation also reversed fluoride-induced hepatointestinal injury.

CONCLUSION

Fluoride induces morphological and functional impairment of liver and gut tissues, as well as enterohepatic circulation disorder by altering total bile acid (TBA) synthesis, transporters, and FXR-FGF15 signaling regulation. Vitamin B2 attenuated fluoride-induced enterohepatic circulation disorder through IL-17A knockout and ileal microbiome regulation. The ileum was found to be the most sensitive to fluoride, leading to changes in ileal microbiome, particularly the reduction of Bifidobacterium. Furthermore, Bifidobacterium supplementation reversed fluoride-induced hepatointestinal injury. This study not only elucidates a novel mechanism by which fluoride causes hepatointestinal toxicity, but also provides a new physiological function of vitamin B2, which will be useful in the therapy of fluorosis and other hepatoenterological diseases.

The role of botanical triterpenoids and steroids in bile acid metabolism, transport, and signaling: Pharmacological and toxicological implications

Bile acids (BAs) are synthesized by the host liver from cholesterol and are delivered to the intestine, where they undergo further metabolism by gut microbes and circulate between the liver and intestines through various transporters. They serve to emulsify dietary lipids and act as signaling molecules, regulating the host's metabolism and immune homeostasis through specific receptors. Therefore, disruptions in BA metabolism, transport, and signaling are closely associated with cholestasis, metabolic disorders, autoimmune diseases, and others. Botanical triterpenoids and steroids share structural similarities with BAs, and they have been found to modulate BA metabolism, transport, and signaling, potentially exerting pharmacological or toxicological effects. Here, we have updated the research progress on BA, with a particular emphasis on new-found microbial BAs. Additionally, the latest advancements in targeting BA metabolism and signaling for disease treatment are highlighted. Subsequently, the roles of botanical triterpenoids in BA metabolism, transport, and signaling are examined, analyzing their potential pharmacological, toxicological, or drug interaction effects through these mechanisms. Finally, a research paradigm is proposed that utilizes the gut microbiota as a link to interpret the role of these important natural products in BA signaling.

Dietary sodium sulphate supplementation during mid-to-late gestation improves placental angiogenesis, bile acid metabolism, and serum amino acid concentrations of sows

Sulphate plays a vital role in the growth and development of the foetus. Sodium sulphate (Na2SO4) is utilised as a dietary protein nutrient factor and helps replenish sulphur elements in livestock and poultry. Therefore, this study aimed to investigate the effects of Na2SO4 supplementation in mid to late pregnancy on bile acid metabolism, amino acid metabolism, placental vascular development and antioxidant capacity of sows. At day 1 of gestation (G1), a total of twenty-six primiparous sows were carefully chosen and randomised into two groups: (1) control group, (2) Na2SO4 group (1.40 g/kg). Blood samples and placentas from sows were collected to measure biochemistry parameters, antioxidant indexes, placental vascular density, and indicators related to bile acid metabolism and amino acid concentrations, respectively. We found that dietary supplementation with Na2SO4 had a tendency for a reduction of incidence of stillborn at farrowing. Further observation showed that sows supplemented with Na2SO4 had decreased total bile acid level in cord blood, and increased placental gene expression of sulphotransferase and organic anion transport peptide. Na2SO4 supplementation increased catalase and total superoxide dismutase activity in cord blood, decreased placental malondialdehyde content, and enhanced placental protein expression of Sirtuin 1. Moreover, Na2SO4 consumption resulted in increased vascular density of placental stroma and elevated amino acid levels in sows and cord blood. Furthermore, maternal Na2SO4 consumption reduced serum urea concentrations of sows and umbilical cord blood at G114. In addition, dietary supplementation with Na2SO4 activated the protein expression of the placental mechanistic target of rapamycin complex 1. Collectively, these findings indicated that maternal supplementation with Na2SO4 during mid-to-late gestation elevated foetal survival via improving placental angiogenesis, bile acid metabolism and amino acid utilisation.

Hepatic protein phosphatase 1 regulatory subunit 3G alleviates obesity and liver steatosis by regulating the gut microbiota and bile acid metabolism

Intestinal dysbiosis and disrupted bile acid (BA) homeostasis are associated with obesity, but the precise mechanisms remain insufficiently explored. Hepatic protein phosphatase 1 regulatory subunit 3G (PPP1R3G) plays a pivotal role in regulating glycolipid metabolism; nevertheless, its obesity-combatting potency remains unclear. In this study, a substantial reduction was observed in serum PPP1R3G levels in high-body mass index (BMI) and high-fat diet (HFD)-exposed mice, establishing a positive correlation between PPP1R3G and non-12α-hydroxylated (non-12-OH) BA content. Additionally, hepatocyte-specific overexpression of Ppp1r3g (PPP1R3G HOE) mitigated HFD-induced obesity as evidenced by reduced weight, fat mass, and an improved serum lipid profile; hepatic steatosis alleviation was confirmed by normalized liver enzymes and histology. PPP1R3G HOE considerably impacted systemic BA homeostasis, which notably increased the non-12-OH BAs ratio, particularly lithocholic acid (LCA). 16S ribosomal DNA (16S rDNA) sequencing assay indicated that PPP1R3G HOE reversed HFD-induced gut dysbiosis by reducing the Firmicutes/Bacteroidetes ratio and Lactobacillus population, and elevating the relative abundance of Blautia, which exhibited a positive correlation with serum LCA levels. A fecal microbiome transplantation test confirmed that the anti-obesity effect of hepatic PPP1R3G was gut microbiota-dependent. Mechanistically, PPP1R3G HOE markedly suppressed hepatic cholesterol 7α-hydroxylase (CYP7A1) and sterol-12α-hydroxylase (CYP8B1), and concurrently upregulated oxysterol 7-α hydroxylase and G protein-coupled BA receptor 5 (TGR5) expression under HFD conditions. Furthermore, LCA administration significantly mitigated the HFD-induced obesity phenotype and elevated non-12-OH BA levels. These findings emphasize the significance of hepatic PPP1R3G in ameliorating diet-induced adiposity and hepatic steatosis through the gut microbiota-BA axis, which may serve as potential therapeutic targets for obesity-related disorders.

Arsenic exposure at environmentally relevant levels induced metabolic toxicity in development mice: Mechanistic insights from integrated transcriptome and metabolome

Emerging evidence has linked arsenic exposure and metabolic homeostasis, but the mechanism is incompletely understood, especially at relatively low concentrations. In this study, we used a mouse model to evaluate the health impacts and metabolic toxicity of arsenic exposure in drinking water at environmentally relevant levels (0.25 and 1.0 ppm). Our results indicated that arsenic damaged intestinal barrier and induced arsenic accumulation, oxidative stress, and pathological changes in the liver and illum. Interestingly, arsenic increased the hepatic triglyceride (TG) and total cholesterol (TC), while reduced serum TG and TC levels. The liver transcriptome found that arsenic exposure caused transcriptome perturbation and promoted hepatic lipid accumulation by regulating the exogenous fatty acids degradation and apolipoproteins related genes. The serum metabolomics identified 74 and 88 differential metabolites in 0.25 and 1.0 ppm, respectively. The KEGG disease and subcellular location analysis indicated that arsenic induced liver and intestinal diseases, and the mitochondrion might be the target organelle for arsenic-induced toxicity. Co-enrichment of transcriptome and metabolome identified 24 metabolites and 9 genes as metabolic toxicity biomarkers. Moreover, 40 male (20 nonalcoholic fatty liver disease (NAFLD) cases and 20 healthy controls) was further selected to validate our findings. Importantly, the significantly changed L-palmitoylcarnitine, 3-hydroxybutyric acid, 2-hydroxycaproic acid and 6 genes of Hadha, Acadl, Aldh3a2, Cpt1a, Cpt2, and Acox1 were found in the NAFLD cases. The results from integrated multi-omics and chemical-protein network analysis indicated that L-palmitoylcarnitine played a critical role in metabolic toxicity by regulating mitochondrial fatty acids β-oxidation genes (Cpt1a, Cpt2). In conclusion, these findings provided new clues for the metabolic toxicity of arsenic exposure at environmentally relevant levels, which involved in the late-life NAFLD development. Our results also contribute to understanding the human responses and phenotypic changes to this hazardous material exposure in the environment.

Dysregulated bile acid homeostasis: unveiling its role in metabolic diseases

Maintaining bile acid homeostasis is essential for metabolic health. Bile acid homeostasis encompasses a complex interplay between biosynthesis, conjugation, secretion, and reabsorption. Beyond their vital role in digestion and absorption of lipid-soluble nutrients, bile acids are pivotal in systemic metabolic regulation. Recent studies have linked bile acid dysregulation to the pathogenesis of metabolic diseases, including obesity, type 2 diabetes mellitus (T2DM), and metabolic dysfunction-associated steatotic liver disease (MASLD). Bile acids are essential signaling molecules that regulate many critical biological processes, including lipid metabolism, energy expenditure, insulin sensitivity, and glucose metabolism. Disruption in bile acid homeostasis contributes to metabolic disease via altered bile acid feedback mechanisms, hormonal dysregulation, interactions with the gut microbiota, and changes in the expression and function of bile acid transporters and receptors. This review summarized the essential molecular pathways and regulatory mechanisms through which bile acid dysregulation contributes to the pathogenesis and progression of obesity, T2DM, and MASLD. We aim to underscore the significance of bile acids as potential diagnostic markers and therapeutic agents in the context of metabolic diseases, providing insights into their application in translational medicine.

Chrysanthemum morifolium attenuates metabolic and alcohol-associated liver disease via gut microbiota and PPARα/γ activation

BACKGROUND

Metabolic and alcohol-associated liver disease (MetALD) shows a high prevalence rate in liver patients, but there is currently no effective treatment for MetALD. As a typical edible traditional Chinese medicinal herb, the anti-inflammatory, antioxidant, and hepatoprotective properties of water extract of Chrysanthemum morifolium Ramat. (WECM) has been demonstrated. However, its therapeutic effect on MetALD and the associated mechanisms remain unclear.

PURPOSE

To investigate the underlying mechanisms of WECM against MetALD.

METHODS

We constructed a MetALD rat model following a high-fat & high-sucrose plus alcohol diet (HFHSAD). MetALD rats were treated with WECM at 2.1, 4.2, and 8.4 g/kg/d for six weeks. Efficacy was determined, and pathways associated with WECM against MetALD were predicted through serum and hepatic biochemical marker measurement, histopathological section analysis, 16S rDNA sequencing of the gut microbiota and untargeted serum metabolomics analyses. Changes in genes and proteins in the peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ) signaling pathways were detected by RT‒PCR and Western blotting.

RESULTS

WECM treatment significantly attenuated hepatic steatosis, hyperlipidemia and markers of liver injury in MetALD rats. Moreover, WECM improved vascular endothelial function, hypertension, and systematic oxidative stress. Mechanistically, WECM treatment altered the overall structure of the gut microbiota through maintaining Firmicutes/Bacteroidota ratio and reducing harmful bacterial abundances such as Clostridium, Faecalibaculum, and Herminiimonas. Notably, WECM promoted 15-deoxy-△12, 14-prostaglandin J2 (15d-PGJ2) release and further activated the PPARγ to reduce serum TNF-α, IL-1β, and IL-6 levels. Additionally, WECM upregulated PPARα and downregulated the levels of CD36 and FABP4 to improve lipid metabolism.

CONCLUSION

Our findings provide the first evidence that WECM treatment significantly improved hepatic steatosis, oxidative stress and inflammation in MetALD rats by regulating the gut microbiota and activating the 15d-PGJ2/PPARγ and PPARα signaling pathway.

Ningxiang Pig-Derived Parabacteroides distasonis HNAU0205 Alleviates ETEC-Induced Intestinal Apoptosis, Oxidative Damage, and Inflammation in Piglets

Weaning is a critical stage in the growth and development of piglets, often inducing stress reactions. This study aims to investigate the effects of Parabacteroides distasonis (PBd) derived from Ningxiang pigs on growth performance, intestinal apoptosis, oxidative damage, and inflammation in ETEC-challenged weaned piglets. A total of 22 Duroc × Landrace × Yorkshire (DLY) piglets, 24 days old with similar body weights, were randomly divided into three groups: Control (n = 7), ETEC (n = 7), and PBd + ETEC (n = 8). The results show that, compared to the Control group, ETEC challenge led to decreased growth performance, reduced villus height in the duodenum and jejunum, increased crypt depth in the duodenum, a decreased villus-height-to-crypt-depth ratio, increased expression of apoptosis-related genes (Caspase-8 and Caspase-9), increased expression of oxidative damage-related genes (Nrf2, GSH-PX, mTOR, and Beclin1), increased expression of inflammation-related genes (Myd88, P65, TNF-α, and IL-6), and reduced the contents of SCFAs in the colonic chyme (acetate, propionate, butyrate, valerate, and total SCFAs). Compared to the ETEC group, the PBd + ETEC group alleviated the reduction in growth performance, mitigated intestinal morphological damage, and reduced the expression of the aforementioned apoptosis, oxidative damage, and inflammation-related genes with the increase in SCFAs. In conclusion, PBd derived from Ningxiang pigs effectively reduces ETEC-induced intestinal damage in weaned piglets, improves intestinal health, and increases the content of SCFAs in the colonic chyme, thereby enhancing growth performance.

Bile Acids as Emerging Players at the Intersection of Steatotic Liver Disease and Cardiovascular Diseases

Affecting approximately 25% of the global population, steatotic liver disease (SLD) poses a significant health concern. SLD ranges from simple steatosis to metabolic dysfunction-associated steatohepatitis and fibrosis with a risk of severe liver complications such as cirrhosis and hepatocellular carcinoma. SLD is associated with obesity, atherogenic dyslipidaemia, and insulin resistance, increasing cardiovascular risks. As such, identifying SLD is vital for cardiovascular disease (CVD) prevention and treatment. Bile acids (BAs) have critical roles in lipid digestion and are signalling molecules regulating glucose and lipid metabolism and influencing gut microbiota balance. BAs have been identified as critical mediators in cardiovascular health, influencing vascular tone, cholesterol homeostasis, and inflammatory responses. The cardio-protective or harmful effects of BAs depend on their concentration and composition in circulation. The effects of certain BAs occur through the activation of a group of receptors, which reduce atherosclerosis and modulate cardiac functions. Thus, manipulating BA receptors could offer new avenues for treating not only liver diseases but also CVDs linked to metabolic dysfunctions. In conclusion, this review discusses the intricate interplay between BAs, metabolic pathways, and hepatic and extrahepatic diseases. We also highlight the necessity for further research to improve our understanding of how modifying BA characteristics affects or ameliorates disease.

Toxicological evaluation of porcine bile powder in Kunming mice and Sprague-Dawley rats

Background: Porcine bile powder (PBP) is a traditional Chinese medicine that has been used for centuries in various therapeutic applications. However, PBP has not previously undergone comprehensive component analysis and not been evaluated for safety through standard in vivo toxicological studies. Methods: In our study, we characterized the component of PBP by liquid chromatography-mass spectrometry. The acute and subchronic oral toxicity, genotoxicity, and teratogenicity studies of PBP were designed and conducted in Kunming mice and Sprague-Dawley (SD) rats. Results: The chemical analysis of PBP showed that the main components of PBP were bile acids (BAs), especially glycochenodeoxycholic acid. There were no signs of toxicity observed in the acute oral test and the subchronic test. In the genotoxicity tests, no positive results were observed in the bacterial reverse mutation test. Additionally, in the mammalian micronucleus test and mouse spermatocyte chromosomal aberration test, no abnormal chromosomes were observed. In the teratogenicity test, no abnormal fetal development was observed. Conclusion: Our findings demonstrate that PBP, composed mainly of BAs, is non-toxic and safe based on the conditions tested in this study.

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

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.