Fibroblast growth factor 15 functions as an enterohepatic signal to regulate bile acid homeostasis

Farnesoid X receptor activation alleviates hepatic encephalopathy by improving hepatic ammonia metabolism in murine models

BACKGROUND

Hepatic encephalopathy (HE) is a mental and neurological complication induced by acute or chronic hepatic failure. Emerging evidence indicates that the farnesoid X receptor (FXR), a multifunctional nuclear receptor and transcription factor, plays a pivotal role in regulating the expression of key genes associated with ammonia metabolism. However, the effect of FXR activation on HE has remained largely uncharted.

METHODS

We established mouse models of HE by intraperitoneal injection of thioacetamide (TAA) and partial hepatectomy (PHx). Subsequently, we administered obeticholic acid (OCA) to activate FXR and investigated its effects on HE through comprehensive biochemical, biological, histological and behavioral analysis. Additionally, in vitro experiments were conducted to examine the impact of FXR activation on ammonia stress.

FINDINGS

In the animal model of HE, activation of FXR upregulated the expression of key enzymes involved in ammonia metabolism pathway within the liver, thereby enhancing urea cycle functionality, reducing plasma ammonia levels, and mitigating liver injury. Furthermore, FXR activation significantly improved behavioral activities in mice and mitigated inflammation in the brain. Finally, our findings demonstrated that activating FXR could enhance ammonia metabolism and ammonia tolerance of C3A cells.

INTERPRETATION

Our data provide novel evidence demonstrating that the activation of FXR by OCA exerts regulatory control over the expression of enzymes involved in ammonia metabolism, thereby effectively alleviating HE. Consequently, FXR could emerge as a promising novel target for HE treatment.

FUNDING

This study was supported by the National Natural Science Foundation of China No: 81970726 (to W-D Chen), and Henan Provincial Key Project of Medical Science and Technology Research No: SBGJ202102215 (to WL Ye).

Hepatic and intestinal tissue-specific Fxr deficiency alters bile acid homeostasis in female mice

Farnesoid X receptor (FXR), predominantly expressed in the liver and intestine, plays a crucial role in regulating bile acid (BA) metabolism. However, the specific contributions of FXR in different tissues to BA homeostasis remain unclear. To elucidate the comprehensive roles of FXR, we developed a novel double tissue-specific knockout (KO) mouse model of Fxr in both liver and intestine (FxrΔL/ΔIN). Notably, FxrΔL/ΔIN mice exhibited significantly increased BA levels in the serum and liver, which were consistent with Fxr whole body KO mice (Fxr-/-). However, FxrΔL mice only showed elevated hepatic BA concentration, whereas FxrΔIN displayed remarkably increased BA concentration in feces. Fxr deletion increased the BA synthesis genes mRNA level, such as Cyp7a1 and Cyp8b1, but reduced the expression of FXR downstream target genes Shp and Fgf15. These findings provide a valuable model to underscore the pivotal functions of tissue-specific FXR in maintaining BA homeostasis. Moreover, these insights facilitate the development of FXR-targeted therapeutic strategies for the BA dysregulation disease treatment.NEW & NOTEWORTHY We successfully developed a double tissue-specific Fxr knockout (DKO) mouse model, which provides a novel tool for investigation of FXR functions in the liver and intestine. Unlike whole body KO, the DKO model excludes the FXR impact on other tissues. FxrΔL/ΔIN mice exhibited significantly increased BA levels in the serum and liver, which were consistent with Fxr-/- mice. We established a powerful tool for therapeutic strategies for bile acid metabolism disorders associated with FXR.

Multicomponent parenteral lipid emulsions do not prevent liver injury in neonatal pigs with obstructive cholestasis

Biliary atresia (BA) is a pediatric liver disease that often necessitates parenteral nutrition (PN) to support growth due to impaired liver function. While soy-based lipid emulsions (SLE) are commonly used in PN, they may contribute to cholestatic liver injury. In contrast, mixed lipid emulsions (MLE) show promise in preventing cholestasis in infants without BA, potentially by restoring bile flow. However, their effectiveness in patients of complete bile duct obstruction, as seen in BA, remains uncertain. To explore the potential benefits of MLE in BA, we utilized a neonatal pig model of bile duct ligation (BDL). Pigs underwent either BDL or sham surgery and were subsequently fed either MLE or SLE via PN, or enterally with formula. The MLE-BDL pigs exhibited significantly greater weight gain compared with those fed SLE or formula enterally. Additionally, MLE-BDL pigs showed higher serum bile acid and γ-glutamyl transferase concentrations compared with SLE-BDL pigs. However, no significant differences in liver injury, assessed by ductular reaction or fibrosis, were observed between MLE- and SLE-BDL pigs. Based on weight gain alone, MLE may be a superior lipid emulsion for use in neonates with obstructive cholestasis.

Fexaramine as the intestine-specific farnesoid X receptor agonist: A promising agent to treat obesity and metabolic disorders

Fexaramine, a gut-restricted farnesoid X receptor (FXR) agonist, promotes glucose and lipid homeostasis, improves insulin sensitivity, promotes white adipose tissue browning, and stimulates nonshivering thermogenesis. Enhancement in energy expenditure due to an increase in amount of energy burned by brown and 'beige' adipocytes results in subsequent weight loss. Fexaramine is poorly absorbed into circulation when delivered orally, which limits systemic FXR activation and toxicity. An increase in β3-adrenoceptor signaling, activation of Takeda G protein-coupled receptor 5/glucagon-like peptide-1 (TGR5/GLP-1) signaling, and induction of fibroblast growth factor (FGF)-19/FGF-15 play crucial roles in fexaramine metabolic actions. Intestinal FXR activation is a promising, potentially safe approach for treating obesity and metabolic syndrome.

Clostridium butyricum protects the ileal barrier in mice by regulating the farnesoid X receptor signaling pathway

BACKGROUND

The intestinal barrier has an important role in maintaining homeostasis. The aim of this study was to determine the protective effect of Clostridium butyricum (CBM) on small intestinal barrier damage in mice and the role of farnesoid X receptor (FXR) in regulating the intestinal barrier by C. butyricum.

METHODS AND RESULTS

A model of small intestinal injury induced by dextran sulfate sodium (DSS) was constructed to detect repair of intestinal barrier damage after feeding with C. butyricum. In the DSS model group, expression of the tight junction protein (TJP) was significantly decreased and expression of inflammatory factors was significantly increased. TJP expression was significantly increased and inflammatory factor expression was significantly decreased after C. butyricum feeding, which indicated that intestinal barrier function was repaired. In addition, inhibition of FXR expression as well as the downstream signaling pathways were demonstrated in the DSS model group. FXR and its downstream signaling pathways were significantly upregulated after feeding with C. butyricum. Then, intestinal barrier function was evaluated by constructing an intestinal-specific FXR knockout (KO) DSS model in mice. Suppression of TJP and upregulated expression of inflammatory factors were detected in the KO DSS group but there was no significant difference in the expression of TJP and inflammatory factors after C. butyricum feeding. Furthermore, there was no significant difference in FXR downstream signaling pathway expression after C. butyricum feeding compared to the KO DSS group. C. butyricum supernatants (CSs) upregulated the FXR signaling pathways in vitro. CSs did not activate the FXR signaling pathway when FXR was suppressed.

CONCLUSIONS

C. butyricum supplementation effectively ameliorated DSS-induced intestinal barrier disruption. C. butyricum may have a protective effect on the small intestine through the FXR signaling pathway.

FGF21 reverses MASH through coordinated actions on the CNS and liver

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive form, metabolic dysfunction-associated steatohepatitis (MASH), represent a growing public health burden with limited therapeutic options. Recent studies have revealed that fibroblast growth factor 21 (FGF21)-based analogs can significantly improve MASH, but the mechanisms for this effect are not well understood. Here, we demonstrate that the beneficial metabolic effects of FGF21 to reverse MASH are mediated through distinct mechanisms to independently lower hepatic triglyceride and cholesterol levels. Specifically, FGF21 signaling directly to glutamatergic neurons in the central nervous system (CNS) stimulates hepatic triglyceride reduction and reversal of fibrosis, whereas FGF21 signaling directly to hepatocytes is necessary and sufficient to reduce hepatic cholesterol levels in mice. Mechanistically, we show that FGF21 acts in the CNS to increase sympathetic nerve activity to the liver, which suppresses hepatic de novo lipogenesis. These results provide critical insights into a promising pharmacological target to treat MASH.

The functions of gut microbiota-mediated bile acid metabolism in intestinal immunity

BACKGROUND

Bile acids, derived from cholesterol in the liver, consist a steroidal core. Primary bile acids and secondary bile acids metabolized by the gut microbiota make up the bile acid pool, which modulate nuclear hormone receptors to regulate immunity. Disruptions in the crosstalk between bile acids and the gut flora are intimately associated with the development and course of gastrointestinal inflammation.

AIM OF REVIEW

This review provides an extensive summary of bile acid production, transport and metabolism. It also delves into the impact of bile acid metabolism on the body and explores the involvement of bile acid-microbiota interactions in various disease states. Furthermore, the potential of targeting bile acid signaling as a means to prevent and treat inflammatory bowel disease is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, we primarily address the functions of bile acid-microbiota crosstalk in diseases. Firstly, we summarize bile acid signalling and the factors influencing bile acid metabolism, with highlighting the immune function of microbially conjugated bile acids and the unique roles of different receptors. Subsequently, we emphasize the vital role of bile acids in maintaining a healthy gut microbiota and regulating the intestinal barrier function, energy metabolism and immunity. Finally, we explore differences of bile acid metabolism in different disease states, offering new perspectives on restoring the host's health and the gastrointestinal ecosystem by targeting the gut microbiota-bile acid-bile acid receptor axis.

Hyperoside modulates bile acid and fatty acid metabolism, presenting a potentially promising treatment for non-alcoholic fatty liver disease

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial chronic condition that requires a systematic approach for effective management. Multi-effect therapeutic drugs derived from traditional Chinese medicine are increasingly being recognized as promising alternatives for NAFLD intervention. Hyperoside, a natural flavone glycoside found in Cuscuta chinensis Lam, Forsythia suspensa, and Crataegus pinnatifida Bge, has been shown to effectively mitigate NAFLD in rats. However, the underlying mechanism through which hyperoside alleviates NAFLD remains unclear.

OBJECTIVE

This study aims to explore the specific mechanisms by which hyperoside intervenes in the progression of NAFLD.

METHODS

In this study, a high-fat diet was used to induce the NAFLD model in rats. An integrated analysis, including mass spectrometry-based lipidomics, TMT-based proteomics, 16S rRNA sequencing, and bile acid-targeted metabolomics, was employed to identify significantly altered metabolites and proteins. Western blotting, molecular docking, and isothermal titration calorimetry were conducted to analyze the direct targets of action.

RESULTS

The results indicate that hyperoside activates farnesoid X receptor (FXR), promoting fatty acid oxidation and the efflux of bile acids from the liver. Additionally, hyperoside inhibits hepatic ATP citrate lyase (ACLY) and works synergistically with activated FXR to suppress de novo lipogenesis. Hyperoside also inhibits intestinal microbes linked to bile-salt hydrolase (BSH) activity, which enhances the production of ileal bile acids (BAs), particularly conjugated BAs, thus reducing the liver toxicity of endogenous BAs.

CONCLUSION

Our findings suggest that hyperoside alleviates NAFLD by modulating fatty acid and bile acid metabolism through FXR and ACLY, suggesting its potential as a multi-effect candidate drug for the treatment of NAFLD.

Fibroblast growth factor receptor signaling in metabolic dysfunction-associated fatty liver disease: Pathogenesis and therapeutic targets

Metabolic dysfunction-associated fatty liver disease (MAFLD) has emerged as a significant hepatic manifestation of metabolic syndrome, with its prevalence increasing globally alongside the epidemics of obesity and diabetes. MAFLD represents a continuum of liver damage, spanning from uncomplicated steatosis to metabolic dysfunction-associated steatohepatitis (MASH). This condition can advance to more severe outcomes, including fibrosis and cirrhosis. Fibroblast growth factor receptors (FGFRs) are a family of four receptor tyrosine kinases (FGFR1-4) that interact with both paracrine and endocrine fibroblast growth factors (FGFs). This interaction activates the phosphorylation of tyrosine kinase residues, thereby triggering downstream signaling pathways, including RAS-MAPK, JAK-STAT, PI3K-AKT, and PLCγ. In the context of MAFLD, paracrine FGF-FGFR signaling is predominantly biased toward the development of liver fibrosis and carcinogenesis. In contrast, endocrine FGF-FGFR signaling is primarily biased toward regulating the metabolism of bile acids, carbohydrates, lipids, and phosphate, as well as maintaining the overall balance of energy metabolism in the body. The interplay between these biased signaling pathways significantly influences the progression of MAFLD. This review explores the critical functions of FGFR signaling in MAFLD from three perspectives: first, it examines the primary roles of FGFRs relative to their structure; second, it summarizes FGFR signaling in hepatic lipid metabolism, elucidating mechanisms underlying the occurrence and progression of MAFLD; finally, it highlights recent advancements in drug development aimed at targeting FGFR signaling for the treatment of MAFLD and its associated diseases.

Pathophysiological underpinnings of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is emerging as the leading cause of chronic liver disease worldwide, reflecting the global epidemics of obesity, metabolic syndrome, and type 2 diabetes. Beyond its strong association with excess adiposity, MASLD encompasses a heterogeneous population that includes individuals with normal body weight ("lean MASLD") highlighting the complexity of its pathogenesis. This disease results from a complex interplay between genetic susceptibility, epigenetic modifications, and environmental factors, which converge to disrupt metabolic homeostasis. Adipose tissue dysfunction and insulin resistance trigger an overflow of lipids to the liver, leading to mitochondrial dysfunction, oxidative stress, and hepatocellular injury. These processes promote hepatic inflammation and fibrogenesis, driven by cross talk among hepatocytes, immune cells, and hepatic stellate cells, with key contributions from gut-liver axis perturbations. Recent advances have unraveled pivotal molecular pathways, such as transforming growth factor-β signaling, Notch-induced osteopontin, and sphingosine kinase 1-mediated responses, that orchestrate fibrogenic activation. Understanding these interconnected mechanisms is crucial for developing targeted therapies. This review integrates current knowledge on the pathophysiology of MASLD, emphasizing emerging concepts such as lean metabolic dysfunction-associated steatohepatitis (MASH), epigenetic alterations, hepatic extracellular vesicles, and the relevance of extrahepatic signals. It also discusses novel therapeutic strategies under investigation, aiming to provide a comprehensive and structured overview of the evolving MASLD landscape for both basic scientists and clinicians.

Tailoring obeticholic acid activity by iridium(III) complex conjugation to develop a farnesoid X receptor probe

INTRODUCTION

The farnesoid X receptor (FXR) is a crucial regulator in the intestine, maintaining bile acid homeostasis. Inhibiting intestinal FXR shows promise in managing inflammatory bowel and liver diseases by reducing bile acid accumulation. Additionally, changes in FXR expression could serve as a potential biomarker for intestinal diseases. Therefore, developing an imaging probe for FXR holds significant potential for the early detection, simultaneous treatment, and monitoring of FXR-related diseases.

OBJECTIVES

The study aimed to develop a bioimaging probe for FXR by conjugating obeticholic acid (OCA), an FXR agonist, to an iridium(III) complex, and to investigate its application for targeting FXR in intestinal cells.

METHODS

OCA was conjugated to an iridium(III) complex to generate the novel complex 1. The effect of complex 1 on FXR activity, nuclear translocation, and downstream targets was investigated in intestinal epithelial cells using various biochemical and cellular assays. Additionally, the photophysical properties of complex 1 were assessed for FXR imaging.

RESULTS

Complex 1 retained the desirable photophysical properties for monitoring FXR in intestinal cells while reversing OCA's activity from agonistic to antagonistic. It disrupted FXR-RXR heterodimerization, inhibited FXR nuclear translocation, and downregulated downstream targets responsible for bile acid absorption, transport, and metabolism in intestinal epithelial cells.

CONCLUSION

The study successfully developed an imaging probe and modulator of FXR by conjugating OCA to an iridium(III) complex. Complex 1 retained the favorable photophysical properties of the iridium(III) complex, while reversing OCA's activity from agonistic to antagonistic. The findings highlight the exciting application of using metals to tailor the activity of nuclear receptor modulators in living systems.

Synergistic action of cilnidipine and bexarotene in mitigating cholestatic liver damage: role of FXR signaling cascade

Cholestasis, a condition characterized by impaired bile flow, can lead to severe liver damage if left untreated. Current therapeutic options are limited, necessitating the development of novel treatment strategies. This study investigated the synergistic action of cilnidipine, a calcium channel blocker, and bexarotene, a retinoid X receptor (RXR) agonist, in mitigating cholestatic liver damage induced by alpha-naphthyl isothiocyanate (ANIT) in rats. The study aimed to elucidate the role of the farnesoid X receptor (FXR) signaling cascade in the protective effects of the combined treatment. Rats were divided into three groups: a negative control group, an ANIT-treated group, and a group pretreated with cilnidipine and bexarotene before ANIT administration. Biochemical markers of liver function, oxidative stress, and inflammation were assessed, along with histological examination of liver tissue. The expression of genes related to the FXR signaling pathway was also evaluated using quantitative polymerase chain reaction (qPCR). The results demonstrated that pretreatment with cilnidipine and bexarotene significantly attenuated ANIT-induced cholestatic liver damage, as evidenced by improved liver function markers, reduced oxidative stress and inflammation, and ameliorated histological changes. Furthermore, the combined treatment upregulated the expression of FXR and its target genes, suggesting that the protective effects may be mediated through the activation of the FXR signaling cascade. These findings highlight the potential of cilnidipine and bexarotene as a novel therapeutic approach for the management of cholestatic liver disorders and provide insights into the underlying molecular mechanisms involving the FXR signaling pathway.

Lactococcus petauri LZys1 modulates gut microbiota, diminishes ileal FXR-FGF15 signaling, and regulates hepatic function

Recent studies have indicated that Lactococcus petauri LZys1 (L. petauri LZys1), isolated from healthy human feces, exhibits a promising probiotic profile in vitro. However, its impact on the physiological status of the host in vivo remains uncertain. The objective of our study was to investigate the effects and mechanisms of orally administering L. petauri LZys1 on gut microbiota and liver function in mice. We administered L. petauri LZys1 through daily oral gavage to C57BL/6 male mice. Subsequently, we analyzed changes in gut microbiota composition using 16S rRNA sequencing and quantified alterations in hepatic-intestinal bile acid (BA) profile. Serum biochemical parameters were assessed to evaluate liver function. Our findings revealed that L. petauri LZys1 led to an increase in body weight, liver mass, and serum aminotransferase levels. Oral administration altered the gut microbiota composition, resulting in reduced diversity and abundance of intestinal bacteria. Additionally, the profiles of BAs were suppressed across organs, associated with the downregulation of the ileum's farnesoid X receptor (FXR)/fibroblast growth factor 15 (FGF15) signaling pathway. The decrease in circulating FGF15 mediated the downregulation of hepatic fibroblast growth factor receptor 4 (FGFR4)/FXR, disrupting BA metabolism and fatty acid oxidation. Our findings suggest that L. petauri LZys1 may impact liver function by influencing the gut microbiota-mediated ileal FXR-FGF15 axis and inhibiting hepatic bile acid metabolism.

IMPORTANCE

This work elucidated the impact of L. petauri LZys1 on host gut microbiota metabolism and hepatic physiological metabolism. We observed that L. petauri LZys1 administration induced liver weight gain and biochemical parameters changes, in addition to a altered gut microbiota and suppressed bile acid (BA) profiles. Furthermore, we propose that changes in liver status are related to the enterohepatic farnesoid X receptor-fibroblast growth factor axis, which alters bile acid metabolism and disrupts liver function. The above findings suggest that attention should be paid to the effect of probiotics on liver function.

Gut-Microbiota-Driven Lipid Metabolism: Mechanisms and Applications in Swine Production

Background/Objectives: The gut microbiota plays a pivotal role in host physiology through metabolite production, with lipids serving as essential biomolecules for cellular structure, metabolism, and signaling. This review aims to elucidate the interactions between gut microbiota and lipid metabolism and their implications for enhancing swine production. Methods: We systematically analyzed current literature on microbial lipid metabolism, focusing on mechanistic studies on microbiota-lipid interactions, key regulatory pathways in microbial lipid metabolism, and multi-omics evidence (metagenomic/metabolomic) from swine models. Results: This review outlines the structural and functional roles of lipids in bacterial membranes and examines the influence of gut microbiota on the metabolism of key lipid classes, including cholesterol, bile acids, choline, sphingolipids, and fatty acids. Additionally, we explore the potential applications of microbial lipid metabolism in enhancing swine production performance. Conclusions: Our analysis establishes a scientific framework for microbiota-based strategies to optimize lipid metabolism. The findings highlight potential interventions to improve livestock productivity through targeted manipulation of gut microbial communities.

Gut Microbiota and Its Metabolite Taurine-β-Muricholic Acid Contribute to Antimony- and/or Copper-Induced Liver Inflammation

Antimony and copper can contaminate vegetables and enter the human body through the digestive tract, inducing severe and extensive biotoxicity. However, the role of bile acids (BAs) in the pathogenesis of liver inflammation by antimony or copper has not been elucidated. Our results indicated that antimony and/or copper induced liver inflammation, causing the disruption of gut microbiota, with the down-regulation of probiotics and up-regulation of harmful bacteria closely correlated to liver inflammation. Targeted metabolomics of BAs showed that antimony and/or copper significantly up-regulated the levels of taurine-β-muricholic acid (T-β-MCA) in serum and liver, which was due to the reduction of Lactobacillus spp. A farnesoid X receptor (FXR) antagonist, T-β-MCA inhibited the FXR-SHP pathway in liver and FXR-FGF15 pathway in ileum, thereby promoting the transcription of cholesterol 7-alpha hydroxylase (CYP7A1) and increasing total bile acid concentrations, ultimately leading to liver inflammation. These findings provide new insights into the underlying mechanisms of antimony- and/or copper-induced liver inflammation.

Activation of gut FXR improves the metabolism of bile acids, intestinal barrier, and microbiota under cholestatic condition caused by GCDCA in mice

Abnormal bile acid (BA) metabolism is involved in liver fibrosis. In a previous study, we discovered that the hydrophobic BA glycochenodeoxycholate (GCDCA) induced liver fibrosis and that GW4064, an agonist of farnesoid X receptor (FXR), alleviated liver fibrosis caused by GCDCA. However, the impacts of GCDCA on liver BAs, gut BAs, the intestinal barrier, and the gut microbiota are unclear, and obtaining this information would provide additional information into the role of GCDCA in the development of liver fibrosis. In the present study, ultra-performance liquid chromatography‒tandem mass spectrometry revealed that mice administered GCDCA by gavage had higher levels of total and primary liver BAs than those in the control group, and a significant reduction in primary liver BAs was observed in the GCDCA + GW4064 group compared with those in the GCDCA group. Compared with those in the control group, the mice administered GCDCA by gavage had greater levels of total and primary BAs in the gut, especially T-alpha-MCA and T-beta-MCA, and no significant differences in the terminal ileum were observed between the GCDCA and GCDCA + GW4064 groups. Immunohistochemistry indicated that GCDCA administration inhibited gut FXR and FGF15 expression, whereas GW4064 activated gut FXR and promoted FGF15 expression. Moreover, immunohistochemistry revealed that GCDCA administration decreased mucin2, claudin-1, occludin, and ZO-1 expression, whereas GW4064 restored their expression. 16S rDNA sequencing revealed that the alpha diversity of the microbiota did not significantly differ among the three groups, but differences in the beta diversity of the microbiota were observed among the three groups. At the phylum level, GCDCA significantly disturbed the gut microbiota, as indicated by reductions in Desulfobacterota, Bacteroidota, and Actinobacteria in the GCDCA group compared with those in the control group. However, significantly increased abundances of Proteobacteria, Cyanobacteria, and Patescibacteria were noted in the GCDCA group compared with the control group. GW4064 administration significantly improved the microbiota structure at the phylum level. The efficacy of GW4064 was also observed at the genus level. Correlation analyses revealed fewer relationships between the gut microbiota and gut BAs, whereas the gut microbiota was more closely related to liver BAs in the GCDCA and GW4064 intervention groups. Together, GCDCA induced cholestasis and disturbed BA metabolism in the gut and liver, as well as the intestinal barrier and structure of the gut microbiota. Activation of gut FXR improved intestinal barrier injury and alleviated BA metabolism dysfunction and dysbacteriosis caused by GCDCA under cholestatic conditions.

IMPORTANCE

Glycochenodeoxycholate (GCDCA) is a hydrophobic bile acid (BA) in humans and is highly increased in the serum and stool of liver fibrosis patients. However, the effects of GCDCA were not comprehensively investigated in the process of liver bile acid metabolism, gut microbiota, and intestinal barrier. It was reported that GCDCA can promote liver fibrosis via the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway in mice, and gut farnesoid X receptor activation alleviated the fibrosis caused by GCDCA in our previous study. Gut microbiota is also responsible for BA metabolism; meanwhile, BA metabolism may also exert an effect on the intestinal barrier. Nowadays, the comprehensive understanding of gut microbiota and intestinal barrier in relation to BA disorder was still insufficient. Current study further investigated the role of GCDCA in BA metabolism, gut microbiota, and intestinal barrier to help understand the effects of GCDCA in liver fibrosis, which may provide intervention methods for liver fibrosis caused by dysregulation of BA metabolism.

Alterations in intestinal bile acid transport provide a therapeutic target in patients with post-bariatric hypoglycaemia

While Roux-en-Y gastric bypass is an effective treatment for obesity and type 2 diabetes, up to one-third of patients develop post-bariatric hypoglycaemia (PBH). Individuals with PBH exhibit increased postprandial secretion of the intestinal hormone fibroblast growth factor 19 (FGF19, Fgf15 in mice). However, the underlying mechanisms contributing to PBH remain uncertain. Here we demonstrate that faecal and plasma bile acid (BA) profiles are significantly altered in postoperative individuals with PBH versus those without hypoglycaemia. Furthermore, altered BAs in PBH induce FGF19 secretion in intestinal cells in a manner dependent on the apical sodium-dependent BA transporter (ASBT). We demonstrate that ASBT inhibition reduces Fgf15 expression and increases postprandial glucose in hypoglycaemic mice. Our data suggest that dysregulation of luminal BA profiles and transport may contribute to PBH and provide proof of concept that ASBT inhibition could be developed as a new therapeutic strategy for PBH.

Farnesoid X Receptor Regulated Sepsis-Induced Abnormal Bile Acid Metabolism via the Fibroblast Growth Factor 15/Fibroblast Growth Factor Receptor 4 Pathway

OBJECTIVE

The study aims to investigate the mechanism of Farnesoid X receptor (FXR) activation in sepsis-induced abnormal bile acid metabolism and the metabolism status of each bile acid type.

METHODS

The sepsis mouse model was developed via lipopolysaccharide intraperitoneal injection and confirmed via hematoxylin and eosin (H&E) staining. FXR agonist activated the FXR/fibroblast growth factor (FGF)15/FGFR pathway via quantitative real-time polymerase chain reaction and Western blot. Consequently, metabolomics and bioinformatics analysis were conducted to identify the alterations in each kind of bile acid content following FXR agonist/inhibitor intervention.

RESULTS

The H&E staining indicated that FXR activation alleviates the liver injury of the sepsis mouse model. The increased FGF15 and FXFR expression levels and decreased CYP7A1 demonstrated FXR/FGF15/FGFR pathway activation following FXR agonist treatment. Furthermore, total bile acid, interleukin (IL)-6, and tumor necrosis factor-α concentrations were downregulated after FXR activation, whereas IL-10 concentration was upregulated, indicating the alleviated effect of FXR agonist in sepsis. Consequently, metabolomics and bioinformatics analysis determined that T-a-MCA were downregulated in both FXR agonist and inhibitor groups, whereas six bile acid types were altered in the control group.

CONCLUSION

FXR activation was crucial in alleviating sepsis-induced hepatic injury and cholestasis through the FGF15/FGFR signaling pathway, and FXR may act as a potential preventive and intervention target of sepsis.

Inhibition of ATGL alleviates MASH via impaired PPARα signalling that favours hydrophilic bile acid composition in mice

BACKGROUND & AIMS

Adipose triglyceride lipase (ATGL) is an attractive therapeutic target in insulin resistance and metabolic dysfunction-associated steatotic liver disease (MASLD). This study investigated the effects of pharmacological ATGL inhibition on the development of metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis in mice.

METHODS

Streptozotocin-injected male mice were fed a high-fat diet to induce MASH. Mice receiving the ATGL inhibitor atglistatin (ATGLi) were compared to controls using liver histology, lipidomics, metabolomics, 16s rRNA, and RNA sequencing. Human ileal organoids, HepG2 cells, and Caco2 cells treated with the human ATGL inhibitor NG-497, HepG2 ATGL knockdown cells, gel-shift, and luciferase assays were analysed for mechanistic insights. We validated the benefits of ATGLi on steatohepatitis and fibrosis in a low-methionine choline-deficient mouse model.

RESULTS

ATGLi improved serum liver enzymes, hepatic lipid content, and histological liver injury. Mechanistically, ATGLi attenuated PPARα signalling, favouring hydrophilic bile acid (BA) synthesis with increased Cyp7a1, Cyp27a1, Cyp2c70, and reduced Cyp8b1 expression. Additionally, reduced intestinal Cd36 and Abca1, along with increased Abcg5 expression, were consistent with reduced levels of hepatic triacylglycerol species containing polyunsaturated fatty acids, like linoleic acid, as well as reduced cholesterol levels in the liver and plasma. Similar changes in gene expression associated with PPARα signalling and intestinal lipid transport were observed in ileal organoids treated with NG-497. Furthermore, HepG2 ATGL knockdown cells revealed reduced expression of PPARα target genes and upregulation of genes involved in hydrophilic BA synthesis, consistent with reduced PPARα binding and luciferase activity in the presence of the ATGL inhibitors.

CONCLUSIONS

Inhibition of ATGL attenuates PPARα signalling, translating into hydrophilic BA composition, interfering with dietary lipid absorption, and improving metabolic disturbances. Validation with NG-497 opens a new therapeutic perspective for MASLD.

IMPACT AND IMPLICATIONS

Despite the recent approval of drugs novel mechanistic insights and pathophysiology-oriented therapeutic options for MASLD (metabolic dysfunction-associated steatotic liver disease) are still urgently needed. Herein, we show that pharmacological inhibition of ATGL, the key enzyme in lipid hydrolysis, using atglistatin (ATGLi), improves MASH (metabolic dysfunction-associated steatohepatitis), fibrosis, and key features of metabolic dysfunction in mouse models of MASH and liver fibrosis. Mechanistically, we demonstrated that attenuation of PPARα signalling in the liver and gut favours hydrophilic bile acid composition, ultimately interfering with dietary lipid absorption. One of the drawbacks of ATGLi is its lack of efficacy against human ATGL, thus limiting its clinical applicability. Against this backdrop, we could show that ATGL inhibition using the human inhibitor NG-497 in human primary ileum-derived organoids, Caco2 cells, and HepG2 cells translated into therapeutic mechanisms similar to ATGLi. Collectively, these findings reveal a possible new avenue for MASLD treatment.

Central FGF19 signaling enhances energy homeostasis and adipose tissue thermogenesis through sympathetic activation in obese mice

Fibroblast growth factor 19 (FGF19) signaling in the brain is associated with body weight loss, reduced food intake, and improved glycemic control in obese mice through unclear mechanisms. Here, we investigated the effects of central FGF19 administration on peripheral tissues, focusing on adipose tissue and its contributions to body weight loss. Using single-cell RNA sequencing of the adult murine hypothalamus, we found that FGF19 has the potential to target multiple cell populations, including astrocytes-tanycytes, microglia, neurons, and oligodendrocytes. Central delivery of FGF19 decreased body weight gain and ameliorated glucose-insulin homeostasis in diet-induced obese (DIO) mice. These results were accompanied by increased energy expenditure and reduced peripheric inflammation. Notably, these effects were attributable to the increased activity of thermogenic adipocytes, as upregulated thermogenic markers in brown and inguinal adipose tissue and improved cold tolerance were induced by central FGF19. However, under blunted sympathetic activity, the described effects were abolished. Moreover, cold exposure induced upregulation of FGF19 receptors and coreceptors specifically in the hypothalamus, suggesting a critical metabolic adaptation for thermoregulation and energy homeostasis. Our findings indicate that central FGF19 signaling improves energy homeostasis in DIO mice, at least in part, by stimulating sympathetic activity and adipose tissue thermogenesis. These findings highlight FGF19's potential as a therapeutic target for obesity and metabolic disorders.NEW & NOTEWORTHY Although most studies associate central fibroblast growth factor 19 (FGF19) with reduced food intake, our findings highlight its role in enhancing thermogenesis in white and brown adipose tissues through sympathetic activation. Central FGF19 not only regulates feeding but also drives peripheral adaptations critical for energy homeostasis and body weight control under obesogenic conditions. These insights underscore the significance of top-down mechanisms in FGF19 action and its therapeutic potential for combating obesity.

Disentangling the nutrition-microbiota liaison in inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is a set of chronic intestinal inflammatory disorders affecting the gastrointestinal (GI) tract. Beside compromised intestinal barrier function and immune hyperactivation, a common IBD feature is dysbiosis, characterized by a reduction of some strains of Firmicutes, Bacteroidetes, Actinobacteria and an increase in Proteobacteria and pathobionts. Emerging evidence points to diet and nutrition-dependent gut microbiota (GM) modulation, as etiopathogenetic factors and adjuvant therapies in IBD. Currently, no nutritional regimen shows universal efficacy, and advice are controversial, especially those involving restrictive diets potentially resulting in malnutrition. This review provides an overview of the role of macronutrients, dietary protocols and GM modulation in IBD patients. A Western-like diet contributes to an aberrant mucosal immune response to commensal bacteria and impairment of the intestinal barrier integrity, thereby triggering intestinal inflammation. Conversely, a Mediterranean nutritional pattern appears to be one of the most beneficial dietetic regimens able to restore the host intestinal physiology, by promoting eubiosis and preserving the intestinal barrier and immune function, which in turn create a virtuous cycle improving patient adherence to the pattern. Further clinical studies are warranted, to corroborate current IBD nutritional guidelines, and develop more accurate models to move forward precision nutrition and ameliorate patients' quality of life.

Targeting Bile-Acid Metabolism: Nutritional and Microbial Approaches to Alleviate Ulcerative Colitis

Ulcerative colitis (UC) is a chronic inflammatory disease affecting the colorectum, posing a significant global health burden. Recent studies highlight the critical role of gut microbiota and its metabolites, particularly bile acids (BAs), in UC's pathogenesis. The relationship between BAs and gut microbiota is bidirectional: microbiota influence BA composition, while BAs regulate microbiota diversity and activity through receptors like Farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5). Targeting bile-acid metabolism to reshape gut microbiota presents a promising therapeutic strategy for UC. This review examines the classification and synthesis of BAs, their interactions with gut microbiota, and the potential of nutritional and microbial interventions. By focusing on these therapies, we aim to offer innovative approaches for effective UC management.

Bile acids and their receptors in hepatic immunity

Similarly to conventional steroids, bile acids function as signaling molecules, acting on a family of membrane and nuclear receptors. The best-characterized bile acid-regulated receptors are the farnesoid X receptor, activated by primary bile acids, and the G-protein-coupled bile acid receptor 1 (also known as Takeda G protein-coupled receptor 5), which is activated by secondary bile acids, such as lithocholic acid (LCA) and deoxycholic acid. Both the farnesoid X receptor and G-protein-coupled bile acid receptor 1 are expressed in cells of innate immunity, monocytes/macrophages, and natural killer cells. Their activation in these cells provides counter-regulatory signals that are inhibitory in nature and attenuate inflammation. In recent years, however, it has been increasingly appreciated that bile acids biotransformations by intestinal microbiota result in the formation of chemically different secondary bile acids that potently regulate adaptive immunity. The 3-oxoLCA and isoalloLCA, two LCA derivatives, bind receptors such as the retinoic acid receptor-related orphan receptor gamma t (RORγt) and the vitamin D receptor (VDR) that are expressed only by lymphoid cells, extending the regulatory role of bile acids to T cells, including T-helper 17 cells and type 3 innate lymphoid cells (ILC3). In this novel conceptual framework, bile acids have emerged as one of the main components of the postbiota, the waste array of chemical mediators generated by the intestinal microbiota. Deciphering the interaction of these mediators with the immune system in the intestine and liver is a novel and fascinating area of bile acid renaissance.

Emerging role of bile acids in colorectal liver metastasis: From molecular mechanism to clinical significance (Review)

Liver metastasis is the leading cause of colorectal cancer (CRC)‑related mortality. Microbiota dysbiosis serves a role in the pathogenesis of colorectal liver metastases. Bile acids (BAs), cholesterol metabolites synthesized by intestinal bacteria, contribute to the metastatic cascade of CRC, encompassing colorectal invasion, migration, angiogenesis, anoikis resistance and the establishment of a hepatic pre‑metastatic niche. BAs impact inflammation and modulate the immune landscape within the tumor microenvironment by activating signaling pathways, which are used by tumor cells to facilitate metastasis. Given the widespread distribution of BA‑activated receptors in both tumor and immune cells, strategies aimed at restoring BA homeostasis and blocking metastasis‑associated signaling are of importance in cancer therapy. The present study summarizes the specific role of BAs in each step of colorectal liver metastasis, elucidating the association between BA and CRC progression to highlight the potential of BAs as predictive biomarkers for colorectal liver metastasis and their therapeutic potential in developing novel treatment strategies.

Emerging mechanisms of organ crosstalk: The role of oxylipins

There is growing interest in the role of oxylipins in the pathophysiology of several diseases. This is accompanied by a limited but evolving evidence base describing augmented oxylipin concentrations in a range of complications including cardiovascular disease, obesity, liver disease and neurological disorders. Despite this, literature describing oxylipin profiles in blood and multiple organs is inconsistent and the mechanisms by which these profiles are altered, and the relationships between localised tissue and circulating oxylipins are poorly understood. Inflammation and immune response associated with disease requires communication across organs and physiological systems. For example, inflammation and comorbidities associated with obesity extend beyond the adipose tissue and affect the vascular, hepatobiliary and digestive systems amongst others. Communication between organs and physiological systems is implicated in the progression of disease as well as the maintenance of homeostasis. There is emerging evidence for the role of oxylipins as a mechanism of communication in organ crosstalk but the role of these in orchestrating multiple organ and system responses is poorly understood. Herein, we review evidence to support and describe the role of oxylipins in organ crosstalk via the cardiosplenic and gut-link axis. In addition, we review emerging mechanisms of oxylipin regulation, the gut microbiome and modification using nutritional intervention. Finally, we describe future perspectives for addressing challenges in measurement and interpretation of oxylipin research with focus on the host genome as a modifier of oxylipin profiles and response to dietary lipid intervention.

Branched-chain amino acids promote hepatic Cyp7a1 expression and bile acid synthesis via suppressing FGF21-ERK pathway

Branched-chain amino acids (BCAAs) including leucine, isoleucine and valine have been linked with metabolic and cardiovascular diseases. BCAAs homeostasis is tightly controlled by their catabolic pathway. BCKA dehydrogenase (BCKD) complex is the rate-limiting step for BCAA catabolism. Mitochondrial phosphatase 2C (PP2Cm) dephosphorylates the BCKD E1alpha subunit and activates BCKD complex. Deficiency of PP2Cm impairs BCAA catabolism, leading to higher plasma BCAA concentrations. Emerging evidence shows that bile acids are key regulators of glucose, lipid and energy metabolism. In this study, we investigated whether a direct link existed between BCAAs and bile acids metabolism. Wild-type mice were fed with normal-BCAA or high-BCAA diet, while PP2Cm deficiency mice were fed with normal chow for 14 weeks. The mice were fasted for 6 h before tissue harvest to exclude metabolic changes due to immediate food intake. We showed that the bile acids in tissues and feces were significantly elevated in wild-type mice fed with high-BCAA diet as well as in PP2Cm deficiency mice fed with normal chow. These mice displayed significantly increased expression of cholesterol 7 alpha-hydroxylase (CYP7A1), the rate-limiting enzyme of bile acid synthesis in liver, and 7α-hydroxy-4-cholesten-3-one (C4), a freely diffusible metabolite downstream of CYP7A1 in plasma. BCAAs induced Cyp7a1 expression in cultured hepatocytes. In mouse liver and cultured hepatocytes, we demonstrated that elevated BCAAs inhibited fibroblast growth factor 21 (FGF21) expression and ERK signaling pathway. Direct inhibition of ERK by U0126 (800 nM) markedly induced Cyp7a1 expression in cultured hepatocytes. Moreover, the induced Cyp7a1 expression and inhibitory effects of BCAAs on ERK signaling pathway were abolished by treatment with recombinant FGF21 protein in mouse liver and cultured hepatocytes. Collectively, this study demonstrates a direct link between BCAAs and bile acid synthesis. BCAAs promotes Cyp7a1 expression and bile acid synthesis in liver via inhibiting FGF21-ERK signaling pathway. BCAAs-regulated bile acid synthesis and homeostasis may contribute to developing novel therapeutic strategies for the treatment of metabolic disorders.

Ultrasonographic assessment of gastric and gallbladder dynamics in human health and disease

The diagnosis of functional disorders of the upper gastrointestinal tract relies on clinical evaluation after exclusion of most frequent organic diseases. Diagnostic techniques contribute to better characterization of disease, choice of specific therapy, and follow-up. Functional ultrasonography was introduced in the early '80 s for the non-invasive study of gastric and gallbladder emptying without ionizing radiation, during fasting and postprandially. This technique detects dysfunctional motility in several gastrointestinal and systemic conditions, and can be used along with the assessment of real-time satiety and gastrointestinal symptoms after food ingestion, and dosing of hormones involved in the modulation of gastrointestinal and metabolic homeostasis. Functional ultrasonography has been increasingly used to explore the gastrointestinal pathophysiology, the gut-brain interaction, the effects of drugs (such as antidiabetics), the response to specific dietary and feeding patterns, and to support the development of nutraceuticals. In this evolving scenario, ultrasonography stands as a widely available, highly sustainable, non-invasive, repeatable, safe and low-cost tool, as compared with more expensive, less sustainable or still scarcely standardized procedures to study gastric and gallbladder motility as scintigraphy, wireless motility capsule tests, 13C breath tests, or magnetic resonance imaging. Functional ultrasonography not only provides reliable data in experimental protocols, but also in the assessment of clinical conditions as dyspeptic symptoms, diabetes, gastroenteric and neurological diseases, critical illness, and as a benchmark to evaluate the gastrointestinal effects of innovative drugs.

Role of Protein Regulators of Cholesterol Homeostasis in Immune Modulation and Cancer Pathophysiology

Cholesterol metabolism and homeostasis have emerged as important factors governing various aspects of cancer biology. Clinical associations between circulating cholesterol and poor prognosis or use of cholesterol-lowering medication and improved prognosis have been noted for several different solid tumors. Mechanistically, cholesterol has many different direct and indirect effects on cancer cells themselves but is also critically involved in shaping the function of other cells of the tumor microenvironment, especially immune cells. There are 2 major feedback loops regulating cholesterol homeostasis. Here we highlight the major proteins involved in the so-called oxysterol-bile acid feedback loop and discuss how each has been implicated in cancer biology. We focus on roles within the immune system with implications for cancer. Given that many of these proteins are enzymes or nuclear receptors, both of which are amenable to small molecule intervention, we posit that this axis may represent a promising area for therapeutic intervention.

Expression of Bile Acid Receptors and Transporters Along the Intestine of Patients With Type 2 Diabetes and Controls

CONTEXT

The enterohepatic circulation of bile acids depends on intestinal absorption by bile acid transporters and activation of bile acid receptors, which stimulates secretion of hormones regulating glucose and lipid metabolism and appetite. Distribution of bile acid transporters and receptors in the human gut and their potential involvement in type 2 diabetes (T2D) pathophysiology remain unknown.

OBJECTIVE

We explored the expression of genes involved in bile acid metabolism throughout the intestines of patients with T2D and matched healthy controls.

METHODS

Intestinal mucosa biopsies sampled along the intestinal tract in 12 individuals with T2D and 12 healthy controls underwent messenger RNA (mRNA) sequencing. We report expression profiles of apical sodium-dependent bile acid transporter (ASBT), organic solute transporter (OST) α/β, farnesoid X receptor (FXR), Takeda G receptor 5 (TGR5), fibroblast growth factor 19 (FGF19), and FGF receptor 4 (FGFR4).

RESULTS

Expression of ASBT and OSTα/β was evident in the duodenum of both groups with increasing levels through the small intestine, and no (ASBT) or decreasing levels (OSTα/β) through the large intestine. The FXR expression pattern followed that of OSTα/β whereas FGFR4 was evenly expressed through the intestines. Negligible levels of TGR5 and FGF19 were evident. Patients with T2D exhibited lower levels of FGF19, FXR, ASBT, and OSTα/β mRNAs compared with healthy controls, although the differences were not statistically significant after adjusting for multiple testing.

CONCLUSION

We demonstrate distinct expression patterns of bile acid transporters and receptors through the intestinal tract with signs of reduced ASBT, OSTα/β, FXR, and FGF19 mRNAs in T2D.

Host metabolism balances microbial regulation of bile acid signalling

Metabolites derived from the intestinal microbiota, including bile acids (BA), extensively modulate vertebrate physiology, including development1, metabolism2-4, immune responses5-7 and cognitive function8. However, to what extent host responses balance the physiological effects of microbiota-derived metabolites remains unclear9,10. Here, using untargeted metabolomics of mouse tissues, we identified a family of BA-methylcysteamine (BA-MCY) conjugates that are abundant in the intestine and dependent on vanin 1 (VNN1), a pantetheinase highly expressed in intestinal tissues. This host-dependent MCY conjugation inverts BA function in the hepatobiliary system. Whereas microbiota-derived free BAs function as agonists of the farnesoid X receptor (FXR) and negatively regulate BA production, BA-MCYs act as potent antagonists of FXR and promote expression of BA biosynthesis genes in vivo. Supplementation with stable-isotope-labelled BA-MCY increased BA production in an FXR-dependent manner, and BA-MCY supplementation in a mouse model of hypercholesteraemia decreased lipid accumulation in the liver, consistent with BA-MCYs acting as intestinal FXR antagonists. The levels of BA-MCY were reduced in microbiota-deficient mice and restored by transplantation of human faecal microbiota. Dietary intervention with inulin fibre further increased levels of both free BAs and BA-MCY levels, indicating that BA-MCY production by the host is regulated by levels of microbiota-derived free BAs. We further show that diverse BA-MCYs are also present in human serum. Together, our results indicate that BA-MCY conjugation by the host balances host-dependent and microbiota-dependent metabolic pathways that regulate FXR-dependent physiology.

Hepatocyte-Derived FGF1 Alleviates Isoniazid and Rifampicin-Induced Liver Injury by Regulating HNF4α-Mediated Bile Acids Synthesis

Isoniazid and rifampicin co-therapy are the main causes of anti-tuberculosis drug-induced liver injury (ATB-DILI) and acute liver failure, seriously threatening human health. However, its pathophysiology is not fully elucidated. Growing evidences have shown that fibroblast growth factors (FGFs) play a critical role in diverse aspects of liver pathophysiology. The aim of this study is to investigate the role of FGFs in the pathogenesis of isoniazid (INH) and rifampicin (RIF)-induced liver injury. Through systematic screening, this study finds that hepatic FGF1 expression is significantly downregulated in both mouse model and human patients challenged with INH and RIF. Hepatocyte-specific Fgf1 deficiency exacerbates INH and RIF-induced liver injury resulted from elevated bile acids (BAs) synthases and aberrant BAs accumulation. Conversely, pharmacological administration of the non-mitogenic FGF1 analog - FGF1ΔHBS significantly alleviated INH and RIF-induced liver injury via restoring BAs homeostasis. Mechanically, FGF1 repressed hepatocyte nuclear factor 4α (Hnf4α) transcription via activating FGF receptor 4 (FGFR4)-ERK1/2 signaling pathway, thus reducing BAs synthase. The findings demonstrate hepatic FGF1 functions as a negative regulator of BAs biosynthesis to protect against INH and RIF-induced liver injury via normalizing hepatic BAs homeostasis, providing novel mechanistic insights into the pathogenesis of ATB-DILI and potential therapeutic strategies for treatment of ATB-DILI.

Insights of direct and indirect regulation of PXR through phosphorylation in fatty liver disease

The pregnane X receptor (PXR), a ligand-activated nuclear receptor, regulates the transcription of several genes that encode many enzymes and transporters related to drug metabolism. PXR also performs an important role as a physiological sensor in the modulation of endobiotic metabolism for hormones, bile acids, cholesterol, fatty acids, and glucose. Dysregulation of these PXR-mediated pathways is implicated in the progression of metabolic dysfunction-associated steatohepatitis (MASH), contributing to the complex interplay of factors involved in chronic liver disease development and exacerbation affecting millions worldwide. This review highlights the current knowledge of PXR expression and its role in endobiotic metabolism related to MASH development, which is associated with diverse causes and dire outcomes. This review focuses on elucidating the molecular pathways associated with PXR activation directly or indirectly and PXR interaction with other regulatory factors. Although there is still much to comprehend about the intricate details of these pathways, the conclusion is drawn that PXR exerts a crucial role in the pathological and physiological pathways of hepatic cellular processes, which holds promise as a potential pharmacological target for exploring novel therapeutic approaches for MASH treatment and/or prevention. SIGNIFICANCE STATEMENT: The pregnane X receptor (PXR) plays a fundamental role in regulating gene expression involved in xenobiotic and endobiotic metabolism. Dysregulation of PXR-mediated pathways is related to the development of metabolic dysfunction-associated steatohepatitis. The ligand-independent pathways regulating PXR hepatic functions through phosphorylation shed light on possible indirect molecular mechanisms and pathways that regulate PXR activity and function. Understanding these pathways may provide insight into new pharmaceutical interventions for metabolic dysfunction-associated steatohepatitis development.

Bile acid sequestrant inhibits gluconeogenesis via inducing hepatic cysteine dioxygenase type 1 to reduce cysteine availability

Bile acid sequestrants such as cholestyramine (ChTM) are gut-restricted bile acid-binding resins that block intestine bile acid absorption and attenuate hepatic bile acid signaling. Bile acid sequestrants induce hepatic bile acid synthesis to promote cholesterol catabolism and are cholesterol-lowering drugs. Bile acid sequestrants also reduce blood glucose in clinical trials and are approved drugs for treating hyperglycemia in type-2 diabetes. However, the mechanisms mediating the glucose-lowering effect of bile acid sequestrants are still incompletely understood. Here we showed that ChTM treatment decreased hepatic glucose production in Western diet-fed mice with paradoxically induced hepatic gluconeogenic genes. Cysteine dioxygenase type 1 (CDO1) mediates cysteine conversion to taurine and its expression is repressed by bile acids. We show that ChTM induced hepatic CDO1 and selectively reduced hepatic cysteine availability. Knockdown of liver CDO1 increased liver cysteine and glucose production in mice, whereas hepatocytes cultured in cystine-deficient medium showed reduced glucose production. By using dietary protein-restricted and cystine-modified Western diets that selectively alter hepatic cysteine availability, we found that reduced hepatic cysteine availability strongly inhibited glucose production in mice. Interestingly, chronic dietary protein restriction also prevented Western diet-induced obesity, which was fully reversed by restoring dietary cystine intake alone. Consistently, reduced cysteine availability dose-dependently inhibited adipogenesis in vitro. In conclusion, we report that the glucose-lowering effect of bile acid sequestrants is mediated by a CDO1-induced hepatic cysteine restriction mimetic effect. Furthermore, the anti-obesity effect of dietary protein restriction is largely mediated by reduced dietary cysteine intake.NEW & NOTEWORTHY Hepatic cysteine availability is a key driver of hepatic gluconeogenesis. Bile acid sequestrant inhibits gluconeogenesis by inducing CDO1-mediated cysteine catabolism to reduce cysteine availability. Dietary protein restriction causes hepatic cysteine deficiency without overall amino acid deficiency. The glucose-lowering effect of dietary protein restriction is largely mediated by lower dietary cysteine intake. The anti-obesity effect of chronic dietary protein restriction is largely mediated by lower dietary cysteine intake.

Simiao Wan attenuates high-fat diet-induced hyperlipidemia in mice by modulating the gut microbiota-bile acid axis

ETHNOPHARMACOLOGICAL RELEVANCE

Hyperlipidemia is a lipid metabolism disorder and a risk factor for obesity, diabetes, and coronary heart disease. It occurs mostly in the old adults; however, its incidence rate is increasing annually and there is a trend towards younger adults. Current clinical drugs for treating hyperlipidemia have multiple side effects. Therefore, it is necessary to develop safe and effective drugs from natural products to prevent and treat hyperlipidemia. Simiao Wan (SMW) is a classic Chinese medicine prescription first recorded in the Cheng Fang Bian Du of the Qing Dynasty. Studies have shown that SMW has excellent efficacy in metabolic diseases, which can effectively improve hyperlipidemia combined with other metabolic diseases. However, its underlying mechanism in hyperlipidemia treatment is yet to be clarified.

AIM OF THE STUDY

To investigate the hypolipidemic effect of SMW on hyperlipidemic mice and explore whether the gut microbiota-bile acid (BA) axis is the potential mechanism.

MATERIALS AND METHODS

A hyperlipidemic mouse model was established using a high-fat diet (HFD), and the hypolipidemic effect of SMW was detected in vivo. We performed 16S ribosomal RNA sequencing and BA metabolism analysis to explore the hypolipidemic mechanisms of SMW. Western blotting was conducted to detect the expression of proteins involved in the gut microbiota-BA axis to determine the potential lipid-lowering pathway.

RESULTS

Excessive obesity in hyperlipidemic mice was alleviated after 8 weeks of SMW treatment. The total cholesterol and low-density lipoprotein cholesterol levels decreased significantly, whereas high-density lipoprotein cholesterol levels increased. SMW also reduced hepatic lipid and inguinal white adipose tissue accumulation in HFD-induced hyperlipidemic mice. Furthermore, intestinal bile saline hydrolase (BSH) level, associated with BA excretion, decreased. Meanwhile, SMW decreased the abundance of BSH-enriched microbes in hyperlipidemic mice. SMW increased the intestinal conjugated-BAs contents in hyperlipidemic mice, especially tauro-β-muricholic acid and tauro-ursodeoxycholic acid, which are ileac farnesoid X receptor (FXR) antagonists. Inhibited intestinal FXR signaling with SMW was accompanied by a decreased expression of intestinal fibroblast growth factor 15 and the activation of hepatic FXR, which promoted hepatic cholesterol conversion to BA.

CONCLUSION

SMW indirectly attenuated HFD-induced hyperlipidemia in mice by regulating the gut microbiota-BA axis. Our results provide a pharmacological basis for SMW treating hyperlipidemia and suggest a new idea for developing lipid-lowering drugs.

Hepatic FXR-FGF4 is required for bile acid homeostasis via an FGFR4-LRH-1 signal node under cholestatic stress

Bile acid (BA) homeostasis is vital for various physiological processes, whereas its disruption underlies cholestasis. The farnesoid X receptor (FXR) is a master regulator of BA homeostasis via the ileal fibroblast growth factor (FGF)15/19 endocrine pathway, responding to postprandial or abnormal transintestinal BA flux. However, the de novo paracrine signal mediator of hepatic FXR, which governs the extent of BA synthesis within the liver in non-postprandial or intrahepatic cholestatic conditions, remains unknown. We identified hepatic Fgf4 as a direct FXR target that paracrinally signals to downregulate Cyp7a1 and Cyp8b1. The effect of FXR-FGF4 is mediated by an uncharted intracellular FGF receptor 4 (FGFR4)-LRH-1 signaling node. This liver-centric pathway acts as a first-line checkpoint for intrahepatic and transhepatic BA flux upstream of the peripheral FXR-FGF15/19 pathway, which together constitutes an integral hepatoenteric control mechanism that fine-tunes BA homeostasis, counteracting cholestasis and hepatobiliary damage. Our findings shed light on potential therapeutic strategies for cholestatic diseases.

High-fat/high-sucrose diet results in a high rate of MASH with HCC in a mouse model of human-like bile acid composition

BACKGROUND

Wild-type (WT) mice fed a conventional high-fat/high-sucrose diet (HFHSD) rarely develop metabolic dysfunction-associated steatohepatitis (MASH) with HCC. Because mouse bile acid (BA) is highly hydrophilic, we hypothesized that making it hydrophobic would lead to MASH with HCC.

METHODS

Eleven-week-old WT and Cyp2a12/Cyp2c70 double knockout (DKO) mice were divided into two groups, including one which was fed a normal chow diet, and one which was fed an HFHSD. Samples were collected after 15, 30, 47, and 58 weeks for histological, biochemical, and immunological analyses.

RESULTS

In the HFHSD group, body weight gain did not differ in WT versus DKO mice, although HFHSD-fed DKO mice exhibited markedly accelerated liver inflammation, fibrosis, and carcinogenesis. HFHSD upregulated lipogenesis and downregulated fatty acid oxidation in both WT and DKO mice, which increased liver lipid accumulation and lipotoxicity. However, the increase in reactive oxygen species production and carcinogenesis observed in DKO mice could not be explained by abnormal lipid metabolism alone. Regarding BA metabolism, DKO mice had a higher hydrophobicity index. They exhibited an age-associated increase in chenodeoxycholic acid (CDCA) levels because of CYP8B1 activity inhibition due to the farnesoid X receptor activation. HFHSD further downregulated CYP8B1, presumably by activating the Liver X receptor. Liver CDCA accumulation was associated with increased inflammation, reactive oxygen species production, and hepatocyte FGF15 induction. Moreover, in noncancerous liver tissues, HFHSD appeared to activate STAT3, an oncogenic transcription factor, which was enhanced by a CDCA-rich environment.

CONCLUSIONS

Here, we developed a new model of MASH with HCC using mice with human-like BA composition and found that HFHSD and elevated hepatic CDCA synergistically increased the risk of MASH with HCC.

Bile acid metabolism and signalling in liver disease

Bile acids (BAs) serve as signalling molecules, efficiently regulating their own metabolism and transport, as well as key aspects of lipid and glucose homeostasis. BAs shape the gut microbial flora and conversely are metabolised by microbiota. Disruption of BA transport, metabolism and physiological signalling functions contribute to the pathogenesis and progression of a wide range of liver diseases including cholestatic disorders and MASLD (metabolic dysfunction-associated steatotic liver disease), as well as hepatocellular and cholangiocellular carcinoma. Additionally, impaired BA signalling may also affect the intestine and kidney, thereby contributing to failure of gut integrity and driving the progression and complications of portal hypertension, cholemic nephropathy and the development of extrahepatic malignancies such as colorectal cancer. In this review, we will summarise recent advances in the understanding of BA signalling, metabolism and transport, focusing on transcriptional regulation and novel BA-focused therapeutic strategies for cholestatic and metabolic liver diseases.

Intestine-derived fibroblast growth factor 19 alleviates lipopolysaccharide-induced liver injury by regulating bile acid homeostasis and directly improving oxidative stress

Background

Cholestasis plays a critical role in sepsis-associated liver injury (SALI). Intestine-derived fibroblast growth factor 19 (FGF19) is a key regulator for bile acid homeostasis. However, the roles and underlying mechanisms of FGF19 in SALI are still unclear.

Methods

We conducted a case-control study that included 58 pediatric patients aged from 1 month to 14-years-old diagnosed with sepsis at Shanghai Children's Hospital from January to December 2018 and 30 healthy individuals. The serum FGF19 levels of these patients with sepsis were analyzed and compared with those of healthy controls. Recombinant human FGF19 was intravenously injected in mice once a day for 7 days at a dose of 0.1 mg/kg body weight before lipopolysaccharide (LPS) treatment. Liver bile acid profiles and the gene expression involved in bile acid homeostasis were investigated in the mice groups. Metabolomic data were further integrated and analyzed using Ingenuity Pathways Analysis (IPA) software. In the in vitro analysis using HepG2 cells, the influence of FGF19 pretreatment on reactive oxygen species (ROS) production and mitochondrial dysfunction was analyzed. Compound C (CC), an inhibitor of AMP-activated protein kinase (AMPK) activation, was used to confirm the roles of AMPK activation in FGF19-mediated hepatoprotective effects.

Results

Serum FGF19 levels were significantly lower in children with sepsis than in healthy controls (115 pg/mL vs. 79 pg/mL, P=0.03). Pre-administration of recombinant human FGF19 alleviated LPS-induced acute liver injury (ALI) and improved LPS-induced cholestasis in mice. Moreover, FGF19 directly reversed LPS-induced intracellular ROS generation and LPS-decreased mitochondrial membrane potential in vitro and in vivo, resulting in hepatoprotection against LPS-induced apoptosis. More importantly, the inhibition of AMPK activity partially blocked the protective effects of FGF19 against LPS-induced oxidative stress and mitochondrial dysfunction.

Conclusions

Intestine-derived FGF19 alleviates LPS-induced ALI via improving bile acid homeostasis and directly suppressing ROS production via activating the AMPK signaling pathway.

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.

Structure-guided discovery of bile acid derivatives for treating liver diseases without causing itch

Chronic itch is a debilitating symptom profoundly impacting the quality of life in patients with liver diseases like cholestasis. Activation of the human G-protein coupled receptor, MRGPRX4 (hX4), by bile acids (BAs) is implicated in promoting cholestasis itch. However, the detailed underlying mechanisms remain elusive. Here, we identified 3-sulfated BAs that are elevated in cholestatic patients with itch symptoms. We solved the cryo-EM structure of hX4-Gq in a complex with 3-phosphated deoxycholic acid (DCA-3P), a mimic of the endogenous 3-sulfated deoxycholic acid (DCA-3S). This structure revealed an unprecedented ligand-binding pocket in MRGPR family proteins, highlighting the crucial role of the 3-hydroxyl (3-OH) group on BAs in activating hX4. Guided by this structural information, we designed and developed compound 7 (C7), a BA derivative lacking the 3-OH. Notably, C7 effectively alleviates hepatic injury and fibrosis in liver disease models while significantly mitigating the itch side effects.

Investigating the Effects of Dietary Bile Acids on Production Performance and Lipid Metabolism in Late-Phase Laying Hens

Multiply adverse effects including declines in production performance and excessive fat deposition were noticed with the extension of the laying cycle in hens, which are pertinent to animal welfare and human food safety. This study aimed to investigate the effect of dietary supplementation of bile acids (BAs) on production performance and lipid metabolism in late-phase laying hens. A total of 144 70-week-old hens were distributed into three treatments with eight replicates per treatment, including the basal diet with 0 (Ctrl), 95.01 (Low-BA), and 189.99 mg/kg (High-BA) of porcine BAs, respectively. The test period was from 70 to 75 weeks. The supplementation of BAs did not significantly alter laying performance during the trial, whereas it increased (p < 0.05) the total follicles compared to the Ctrl diet. The eggs from the hens fed the BA diet exhibited increased (p > 0.05) relative weight of eggshell and yolk color than those that consumed the Ctrl diet. There were no significant changes following BA treatment regarding the serum lipid profile. Dietary BA treatment reduced the total triglyceride in livers to different extents, resulting in the decreased diameter and area of vacuoles in liver tissues. The low-dose BA treatment decreased the mRNA levels of fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD), while promoting the expression of lipoprotein lipase (LPL) compared to the Ctrl group (both p < 0.05). Of note, the expressions of farnesoid X receptor (FXR), apical sodium-dependent bile acid transporter (ASBT), and ileum bile acid-binding protein (IBABP) were notably downregulated (p < 0.05) by the low-dose BA treatment. Dietary BA treatment had no apparent effects on laying performance, whereas it increased the follicle frequency, eggshell weight, and yolk color. Moreover, a diet containing 95.01 mg/kg of BAs depressed ileal BA resorption and hepatic fatty deposition by reducing lipogenesis and promoting lipolysis, which may have a beneficial effect on the liver in late-phase layers.

Liver-gut axis signaling regulates circadian energy metabolism in shift workers

Circadian rhythm is critical to maintaining the whole-body metabolic homeostasis of an organism. Chronic disruption of circadian rhythm by shift work is an important risk factor for metabolic diseases. Fibroblast growth factor 15/19 (FGF15/19), a key component in the liver-gut axis, potently suppresses bile acid (BA) synthesis and improves insulin sensitivity. FGF15/19 emerges as a novel pharmaceutical target for prevention and treatment of metabolic diseases. The nicotinamide adenine dinucleotide (NAD+)-dependent sirtuin 1 (SIRT1) deacetylase plays an important role in the maintenance of hepatic homeostasis by linking hepatic metabolism to circadian rhythm. Here, our clinical study identified that circadian rhythmicity and levels of plasma FGF19 and BA profiling, and cellular NAD+-dependent SIRT1 signaling were disturbed in night shift (NS, n = 10) compared to day shift (DS, n = 12) nurses. Our in vitro data showed that recombinant FGF19 protein rescued cellular circadian rhythm disrupted by SIRT1 inhibitors. Furthermore, we determined the effect of FGF15 on circadian rhythm and hepatic metabolism in wild-type (WT), Fgf15 knockout (KO), and Fgf15 transgenic (TG) mice. The expressions of circadian-controlled genes (CCGs) involved in SIRT1 signaling, BA and lipid metabolism, and inflammation were disrupted in Fgf15 KO compared to WT and/or Fgf15 TG mice. Moreover, systemic FGF15 deficiency led to the circadian disturbance of NAD+-dependent SIRT1 signaling and significant reduction during nighttime in mice. These findings suggest that FGF15/19 regulates the circadian energy metabolism, which warrants further studies as a putative prognostic biomarker and pharmaceutical target for preventing against metabolic diseases associated with chronic shift work.

A developmental biliary lineage program cooperates with Wnt activation to promote cell proliferation in hepatoblastoma

Cancers evolve not only through the acquisition and clonal transmission of somatic mutations but also by epigenetic mechanisms that modify cell phenotype. Here, we use histology-guided and spatial transcriptomics to characterize hepatoblastoma, a childhood liver cancer that exhibits significant histologic and proliferative heterogeneity despite clonal activating mutations in the Wnt/β-catenin pathway. Highly proliferative regions with embryonal histology show high expression of Wnt target genes, the embryonic biliary transcription factor SOX4, and striking focal expression of the growth factor FGF19. In patient-derived tumoroids with constitutive Wnt activation, FGF19 is a required growth signal for FGF19-negative cells. Indeed, some tumoroids contain subsets of cells that endogenously express FGF19, downstream of Wnt/β-catenin and SOX4. Thus, the embryonic biliary lineage program cooperates with stabilized nuclear β-catenin, inducing FGF19 as a paracrine growth signal that promotes tumor cell proliferation, together with active Wnt signaling. In this pediatric cancer presumed to originate from a multipotent hepatobiliary progenitor, lineage-driven heterogeneity results in a functional growth advantage, a non-genetic mechanism whereby developmental lineage programs influence tumor evolution.

Perfluorooctanoic acid (PFOA) and its alternative perfluorobutanoic acid (PFBA) alter hepatic bile acid profiles via different pathways

The disruption of per- and polyfluoroalkyl substances (PFASs) on bile acid (BA) homeostasis has raised public concerns, making the evaluation of their effects and underlying mechanisms a high priority. Although the use of perfluorooctanoic acid (PFOA) has been restricted, it remains a widespread legacy PFAS in the environment. Concurrently, the use of its prevalent short-chain alternative, perfluorobutanoic acid (PFBA), is increasing, yet the toxicity assessment of PFBA remains inadequate. In this study, C57BL/6N mice were exposed to PFOA and PFBA (0.4 or 10 mg/kg body weight) by gavage for 28 days. The results showed that both PFOA and PFBA significantly increased hepatic weight, although PFBA exhibited lower bioaccumulation than PFOA in the liver. Targeted metabolomics revealed that PFOA significantly decreased total BA levels and altered their composition. Conversely, PFBA, without significantly altering total BA levels, notably changed their composition, such as increasing the proportion of cholic acid. Further investigations using in vivo and in vitro assays suggested that PFOA inhibited the expression of Cyp7A1, a key BA synthetase, potentially via PPARα activation, thereby reducing BA levels. In contrast, PFBA enhanced Cyp7A1 expression, associated with the inhibition of intestinal Farnesoid X receptor-fibroblast growth factor 15 (FXR-FGF15) pathway. This study evaluated the differences in the BA-interfering effects of PFOA and PFBA and shed light on the potential mechanisms, which will provide new insights into the health risks of legacy PFASs and their alternatives.

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.

Impact of Sleeve Gastrectomy on Body Weight and Food Intake Regulation in Diet-Induced Obese Mice

The epidemic of obesity has increased worldwide and is associated with comorbidities such as diabetes and cardiovascular disease. In this context, strategies that modulate body weight and improve glycemic metabolism have increased, and bariatric surgeries such as Sleeve Gastrectomy (SG) have been highlighted in obesity treatment. However, the mechanism by which SG reduces body weight and improves glycemic control remains unknown. Thus, in this study, we aimed to evaluate food intake and the expression of hypothalamic genes involved with the regulation of this process in diet-induced obese mice submitted to SG. For this, we used C57BL/6 mice submitted to a 10-week high-fat diet protocol and submitted to SG. Food intake, fed and fasted glycemia, as well as hypothalamic anorexigenic and orexigenic gene expression were evaluated 4 weeks after the surgical procedure. First, we observed that SG reduces body weight (44.19 ± 0.47 HFD, 43.51 ± 0.71 HFD-SHAM, and 38.22 ± 1.31 HFD-SG), fasting glycemia (115.0 ± 4.60 HFD, 122.4 ± 3.48 HFD-SHAM, and 93.43 ± 4.67 HFD-SG), insulinemia (1.77 ± 0.15 HFD, 1.92 ± 0.27 HFD-SHAM, and 0.93 ± 0.05 HFD-SG), and leptinemia (5.86 ± 1.38 HFD, 6.44 ± 1.51 HFD-SHAM, and 1.43 ± 0.35 HFD-SG) in obese mice. Additionally, SG reduces food (5.15 ± 0.18 HFD, 5.49 ± 0.32, HFD-SHAM, and 3.28 ± 0.26 HFD-SG) and total (16.88 ± 0.88 HFD, 17.05 ± 0.42, HFD-SHAM, and 14.30 ± 0.73 HFD-SG) calorie intake without alterations in anorexigenic and orexigenic gene expression. In conclusion, these data indicate that SG improves obesity-associated alterations at least in part by a reduction in food intake. This effect is not associated with the canonical food intake pathway in the hypothalamus, indicating the involvement of non-canonical pathways in this process.

β-Klotho as novel therapeutic target in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): A narrative review

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) represents the most frequent cause of hepatic disorder, and its progressive form defined as Metabolic Dysfunction-Associated Steatohepatitis (MASH) contributes to the development of fibrosis/cirrhosis and hepatocellular carcinoma (HCC). Today effective therapeutic strategies addressing MASH-related comorbidities, inflammation, and fibrosis are needed. The fibroblast growth factor (FGF) 19 and 21 and their fibroblast growth factor receptor/β-Klotho (KLB) complexes have recently emerged as promising druggable targets for MASLD. However, less is known regarding the causative association between KLB activity and advanced stages of liver disease. In the present narrative review, we aimed to provide an up-to-date picture of the role of the KLB co-receptor in MASLD development and progression. We performed a detailed analysis of recently published preclinical and clinical data to decipher the molecular mechanisms underlying KLB function and to correlate the presence of inherited or acquired KLB aberrancies with the predisposition towards MASLD. Moreover, we described ongoing clinical trials evaluating the therapeutic approaches targeting FGF19-21/FGFR/KLB in patients with MASLD and discussed the challenges related to their use. We furtherly described that KLB exhibits protective effects against metabolic disorders by acting in an FGF-dependent and independent manner thus triggering the hypothesis that KLB soluble forms may play a critical role in preserving liver health. Therefore, targeting KLB may provide promising strategies for treating MASLD, as supported by experimental evidence and ongoing clinical trials.

Fibroblast growth factor 21 improves insulin sensitivity by modulating the bile acid-gut microbiota axis in type Ⅱ diabetic mice

BACKGROUND

Fibroblast growth factor 21 (FGF21) is an important regulator of glycolipid metabolism. However, whether the gut microbiota is related to the anti-diabetic and obesity effects of FGF21 remains unclear.

METHODS

Our research used KO/KO db/db male mice and streptozotocin (STZ)-induced to simulate the construction of two type II diabetic mellitus (T2DM) models, and detected impaired glucose tolerance in the model by using the ipGTT and ITT assays, and collected feces from the model mice for sequencing of the intestinal flora and the content of short-chain fatty acids. H＆E staining was used to detect changes in intestinal tissue, the serum levels of LPS and GLP-1 were detected by ELISA.

RESULTS

In this study, we found that FGF21 significantly improved insulin sensitivity, attenuated intestinal lesions, and decreased serum lipopolysaccharide (LPS) concentrations in T2DM mice. Moreover, FGF21 reshaped the gut microbiota and altered their metabolic pathways in T2DM mice, promoting the production of short-chain fatty acids (SCFAs) and the secretion of glucagon-like peptide 1 (GLP-1). Fecal transplantation experiments further confirmed that feces from FGF21-treated diabetic mice demonstrated similar effects as FGF21 in terms of anti-diabetic activity and regulation of gut microbiota dysbiosis. Additionally, the antibiotic depletion of gut microbiota abolished the beneficial effects of FGF21, including increased GLP-1 secretion and fecal SCFA concentration. Additionally, the FGF21 effects of ameliorating intestinal damage and suppressing plasma LPS secretion were suppressed. All these findings suggest that FGF21 prevents intestinal lesions by modifying the gut microbiota composition. Furthermore, FGF21 affected bile acid synthesis by inhibiting CYP7A1, the key enzyme of bile acid synthesis.

CONCLUSSION

Therefore, FGF21 enriched beneficial bacteria by preventing bile acid synthesis and stimulating the secretion of the intestinal hormone GLP-1 via the increased production of gut microbiota metabolites, thereby exerting its anti-diabetic effects.

Fibroblast Growth Factors in Cardiovascular Disease

Despite advancements in managing traditional cardiovascular risk factors, many cardiovascular diseases (CVDs) persist. Fibroblast growth factors (FGFs) have emerged as potential diagnostic markers and therapeutic targets for CVDs. FGF1, FGF2, and FGF4 are primarily used for therapeutic angiogenesis. Clinical applications are being explored based on animal studies using approaches such as recombinant protein administration and adenovirus-mediated gene delivery, targeting patients with coronary artery disease and lower extremity arterial disease. Although promising results have been observed in animal models and early-stage clinical trials, further studies are required to assess their therapeutic potential. The FGF19 subfamily, consisting of FGF19, FGF21, and FGF23, act via endocrine signaling in various organs. FGF19, primarily expressed in the small intestine, plays important roles in glucose, lipid, and bile acid metabolism and has therapeutic potential for metabolic disorders. FGF21, found in various tissues, improves glucose metabolism and insulin sensitivity, suggesting potential for treating obesity and diabetes. FGF23, primarily secreted by osteocytes, regulates vitamin D and phosphate metabolism and serves as an important biomarker for chronic kidney disease and CVDs. Thus, FGFs holds promise for both therapeutic and diagnostic applications in metabolic and cardiovascular diseases. Understanding the mechanisms of FGF may pave the way for novel strategies to prevent and manage CVDs, potentially addressing the limitations of current treatments. This review explores the roles of FGF1, FGF2, FGF4, and the FGF19 subfamily in maintaining cardiovascular health. Further research and clinical trials are crucial to fully understand the therapeutic potential of FGFs in managing cardiovascular health.

A primer on the pleiotropic endocrine fibroblast growth factor FGF19/FGF15

Fibroblast Growth Factor 19 (FGF19) is a member of the Fibroblast Growth Factor (FGF) family, known for its role in various cellular processes including embryonic development and metabolic regulation. FGF19 functions as an endocrine factor, influencing energy balance, bile acid synthesis, glucose and lipid metabolism, as well as cell proliferation. FGF19 has a conserved structure typical of FGFs but exhibits unique features. Unlike most FGFs, which act locally, FGF19 travels through the bloodstream to distant targets including the liver. Its interaction with the β-Klotho (KLB) co-receptor and FGF Receptor 4 (FGFR4) in hepatocytes or FGFR1c in extrahepatic tissues initiates signaling cascades crucial for its biological functions. Although the mouse ortholog, FGF15, diverges significantly from human FGF19 in protein sequence and receptor binding, studies of FGF15-deficient mice have led to a better understanding of the proteins' role in bile acid regulation, metabolism, and embryonic development. Overexpression studies in transgenic mice have further revealed roles in not only ameliorating metabolic diseases but also in promoting hepatocyte proliferation and tumorigenesis. This review summarizes the gene and protein structure of FGF19/15, its expression patterns, phenotypes in mutant models, and implication in human diseases, providing insights into potential therapeutic strategies targeting the FGF19 signaling pathway.