Ursodeoxycholic acid exerts farnesoid X receptor-antagonistic effects on bile acid and lipid metabolism in morbid obesity

How far are we from an approved drug for nonalcoholic steatohepatitis?

INTRODUCTION

Metabolic-associated fatty liver disease (MAFLD) previously known but still debatable, as nonalcoholic fatty liver disease (NAFLD) is one of the main causes of chronic liver disease and subsequent cirrhosis worldwide, accounting for around 30% of liver diseases. The change in its nomenclature has been brought about by the novel discoveries regarding its pathogenesis, in which metabolic dysfunction plays the most important role. It is widely known that for every disease, the treatment should always be targeted toward the underlying etiology and pathogenesis.

AREAS COVERED

MAFLD/NAFLD pathogenesis is heterogeneous, and includes multiple gene polymorphisms, presence of insulin resistance, as well as concomitant diseases that contribute to the disease onset and progression. As a result of this, even though lifestyle modification (owing to metabolic abnormalities) is the first line of treatment, multiple drugs have been tested to target each of the known pathways leading to MAFLD/NAFLD and progression of steatohepatitis. We aim to review the most relevant information regarding previous and ongoing research and recommendations regarding treatment of MAFLD/NAFLD.

EXPERT OPINION

Combination therapies associated to weight loss and exercise will be the optimal approach for these patients. It is important to evaluate each patient to select the specific combination according to patient characteristics.

Gut microbiome determines therapeutic effects of OCA on NAFLD by modulating bile acid metabolism

Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disease, had no approved pharmacological agents yet. Obeticholic acid (OCA), a novel bile acid derivative, was demonstrated to ameliorate NAFLD-related manifestations. Regarding the role of gut-liver axis in liver disease development, this study aimed to explore the potential role of gut microbiota in the treatment of OCA in NAFLD mice induced by the high-fat diet (HFD). Antibiotic-induced microbiome depletion (AIMD) and fecal microbiota transplantation (FMT) confirmed the critical role of gut microbiota in OCA treatment for NAFLD by effectively alleviating histopathological lesions and restoring liver function impaired by HFD. Metagenomic analysis indicated that OCA intervention in HFD mice remarkably increased the abundance of Akkermansia muciniphila, Bifidobacterium spp., Bacteroides spp., Alistipes spp., Lactobacillus spp., Streptococcus thermophilus, and Parasutterella excrementihominis. Targeted metabolomics analysis indicated that OCA could modulate host bile acids pool by reducing levels of serum hydrophobic cholic acid (CA) and chenodeoxycholic acid (CDCA), and increasing levels of serum-conjugated bile acids, such as taurodeoxycholic acid (TDCA) and tauroursodesoxycholic acid (TUDCA) in the HFD-fed mice. Strong correlations were observed between differentially abundant microbes and the shifted bile acids. Furthermore, bacteria enriched by OCA intervention exhibited much greater potential in encoding 7alpha-hydroxysteroid dehydrogenase (7α-HSDs) producing secondary bile acids rather than bile salt hydrolases (BSHs) mainly responsible for primary bile acid deconjugation. In conclusion, this study demonstrated that OCA intervention altered gut microbiota composition with specially enriched gut microbes modulating host bile acids, thus effectively alleviating NAFLD in the mice.

Serum FGF19 predicts outcomes of Kasai portoenterostomy in biliary atresia

BACKGROUND AND AIMS

Outcomes after Kasai portoenterostomy (KPE) for biliary atresia remain highly variable for unclear reasons. As reliable early biomarkers predicting KPE outcomes are lacking, we studied the prognostic value of FGF19.

APPROACH AND RESULTS

Serum and liver specimens, obtained from biliary atresia patients (N=87) at KPE or age-matched cholestatic controls (N=26) were included. Serum concentration of FGF19 and bile acids, liver mRNA expression of FGF19 , and key regulators of bile acid synthesis were related to KPE outcomes and liver histopathology. Immunohistochemistry and in situ hybridization were used for the localization of liver FGF19 expression. Serum levels (223 vs. 61 pg/mL, p <0.001) and liver mRNA expression of FGF19 were significantly increased in biliary atresia. Patients with unsuccessful KPE (419 vs. 145 pg/mL, p =0.047), and those subsequently underwent liver transplantation (410 vs. 99 pg/mL, p =0.007) had significantly increased serum, but not liver, FGF19, which localized mainly in hepatocytes. In Cox hazard modeling serum FGF19 <109 pg/mL predicted native liver survival (HR: 4.31, p <0.001) also among patients operated <60 days of age (HR: 8.77, p =0.004) or after successful KPE (HR: 6.76, p =0.01). Serum FGF19 correlated positively with increased serum primary bile acids ( R =0.41, p =0.004) and ductular reaction ( R =0.39, p =0.004).

CONCLUSIONS

Increased serum FGF19 at KPE predicted inferior long-term native liver survival in biliary atresia and was associated with unsuccessful KPE, elevated serum primary bile acids, and ductular reaction.

Bacillus cereus Alters Bile Acid Composition and Alleviates High-Carbohydrate Diet-Induced Hepatic Lipid Accumulation in Nile Tilapia (Oreochromis niloticus)

A high-carbohydrate diet (HCD) can induce excessive fat accumulation in fish, and intestinal microbiota are thought to play important roles in host metabolism. Whether and how intestinal bacteria alleviate the HCD-induced metabolic disorders in fish have attracted more attention. Bacillus cereus was isolated from the intestine content of Nile tilapia. The control diet, high-carbohydrate diet (HC), and HC supplemented with B. cereus Su1 (HCS) were used to feed juvenile Nile tilapia for 8 weeks. The results of the present study showed that B. cereus Su1 supplementation decreased the serum glucose, triglycerides (TG), and reduced hepatic lipid accumulation compared with the HC group. The intestinal bacterial composition analysis suggested that HCS elevated bacterial diversity and the enriched bacteria were closely related to bile acid (BA) metabolism. Higher bile salt hydrolase (BSH) activity was found in the HCS group and B-targeted metabolomic analysis revealed that HCS increased BA content in the intestine and liver compared with HC, including unconjugated BAs (CA and CDCA) and conjugated BAs (TCA, GCA, TCDCA, GCDCA, TDCA, and TUDCA). Furthermore, a high-carbohydrate diet supplemented with B. cereus Su1 significantly enhanced the protein expression of the BA receptor farnesoid X receptor in the liver and decreased significantly the expression level of lipid synthesis-related genes and proteins, while it had no significant effect on lipolysis-related genes and proteins. This study found that B. cereus Su1 altered the intestinal microbiota and bile acid content and composition to regulate the lipid metabolism, revealing the function of the crosstalk among probiotics, intestinal microbiota, and BAs in ameliorating lipid accumulation induced by a high-carbohydrate diet in fish.

Expanding the Library of 1,2,4-Oxadiazole Derivatives: Discovery of New Farnesoid X Receptor (FXR) Antagonists/Pregnane X Receptor (PXR) Agonists

Compounds featuring a 1,2,4-oxadiazole core have been recently identified as a new chemotype of farnesoid X receptor (FXR) antagonists. With the aim to expand this class of compounds and to understand the building blocks necessary to maintain the antagonistic activity, we describe herein the synthesis, the pharmacological evaluation, and the in vitro pharmacokinetic properties of a novel series of 1,2,4-oxadiazole derivatives decorated on the nitrogen of the piperidine ring with different N-alkyl and N-aryl side chains. In vitro pharmacological evaluation showed compounds 5 and 11 as the first examples of nonsteroidal dual FXR/Pregnane X receptor (PXR) modulators. In HepG2 cells, these compounds modulated PXR- and FXR-regulated genes, resulting in interesting leads in the treatment of inflammatory disorders. Moreover, molecular docking studies supported the experimental results, disclosing the ligand binding mode and allowing rationalization of the activities of compounds 5 and 11.

Defecation status, intestinal microbiota, and habitual diet are associated with the fecal bile acid composition: a cross-sectional study in community-dwelling young participants

PURPOSE

Bile acid (BA) metabolism by intestinal bacteria is associated with the risk of gastrointestinal diseases; additionally, its control has become a modern strategy for treating metabolic diseases. This cross-sectional study investigated the influence of defecation status, intestinal microbiota, and habitual diet on fecal BA composition in 67 community-dwelling young participants.

METHODS

Feces were collected for intestinal microbiota and BA analyses; data about defecation status and dietary habits were collected using the Bristol stool form scales and a brief-type self-administered diet history questionnaire, respectively. The participants were categorized into four clusters based on their fecal BA composition, according to cluster analysis, and tertiles based on deoxycholic acid (DCA) and lithocholic acid (LCA) levels.

RESULTS

The high primary BA (priBA) cluster with high fecal cholic acid (CA) and chenodeoxycholic acid (CDCA) levels had the highest frequency of normal feces, whereas the second BA (secBA) cluster with high levels of fecal DCA and LCA had the lowest. Alternately, the high-priBA cluster had a distinct intestinal microbiota, with higher Clostridium subcluster XIVa and lower Clostridium cluster IV and Bacteroides. The low-secBA cluster with low fecal DCA and LCA levels had the lowest animal fat intake. Nevertheless, the insoluble fiber intake of the high-priBA cluster was significantly higher than that of the high-secBA cluster.

CONCLUSION

High fecal CA and CDCA levels were associated with distinct intestinal microbiota. Conversely, high levels of cytotoxic DCA and LCA were associated with increased animal fat intake and decreased frequency of normal feces and insoluble fiber intake.

CLINICAL TRIAL REGISTRY

University Hospital Medical Information Network (UMIN) Center system (UMIN000045639); date of registration: 15/11/2019.

Gut Microbial Metabolites on Host Immune Responses in Health and Disease

Intestinal microorganisms interact with various immune cells and are involved in gut homeostasis and immune regulation. Although many studies have discussed the roles of the microorganisms themselves, interest in the effector function of their metabolites is increasing. The metabolic processes of these molecules provide important clues to the existence and function of gut microbes. The interrelationship between metabolites and T lymphocytes in particular plays a significant role in adaptive immune functions. Our current review focuses on 3 groups of metabolites: short-chain fatty acids, bile acids metabolites, and polyamines. We collated the findings of several studies on the transformation and production of these metabolites by gut microbes and explained their immunological roles. Specifically, we summarized the reports on changes in mucosal immune homeostasis represented by the Tregs and Th17 cells balance. The relationship between specific metabolites and diseases was also analyzed through latest studies. Thus, this review highlights microbial metabolites as the hidden treasure having potential diagnostic markers and therapeutic targets through a comprehensive understanding of the gut-immune interaction.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

The regulatory effects of second-generation antipsychotics on lipid metabolism: Potential mechanisms mediated by the gut microbiota and therapeutic implications

Second-generation antipsychotics (SGAs) are the mainstay of treatment for schizophrenia and other neuropsychiatric diseases but cause a high risk of disruption to lipid metabolism, which is an intractable therapeutic challenge worldwide. Although the exact mechanisms underlying this lipid disturbance are complex, an increasing body of evidence has suggested the involvement of the gut microbiota in SGA-induced lipid dysregulation since SGA treatment may alter the abundance and composition of the intestinal microflora. The subsequent effects involve the generation of different categories of signaling molecules by gut microbes such as endogenous cannabinoids, cholesterol, short-chain fatty acids (SCFAs), bile acids (BAs), and gut hormones that regulate lipid metabolism. On the one hand, these signaling molecules can directly activate the vagus nerve or be transported into the brain to influence appetite via the gut-brain axis. On the other hand, these molecules can also regulate related lipid metabolism via peripheral signaling pathways. Interestingly, therapeutic strategies directly targeting the gut microbiota and related metabolites seem to have promising efficacy in the treatment of SGA-induced lipid disturbances. Thus, this review provides a comprehensive understanding of how SGAs can induce disturbances in lipid metabolism by altering the gut microbiota.

Maternal Exercise Protects Male Offspring From Maternal Diet-Programmed Nonalcoholic Fatty Liver Disease Progression

Maternal obesity programs the risk for development of nonalcoholic fatty liver disease (NAFLD) in offspring. Maternal exercise is a potential intervention to prevent developmentally programmed phenotypes. We hypothesized that maternal exercise would protect from progression of NAFLD in offspring previously exposed to a maternal obesogenic diet. Female mice were fed chow (CON) or high fat, fructose, cholesterol (HFFC) and bred with lean males. A subset had an exercise wheel introduced 4 weeks after starting the diet to allow for voluntary exercise. The offspring were weaned to the HFFC diet for 7 weeks to induce NAFLD. Serum, adipose, and liver tissue were collected for metabolic, histologic, and gene expression analyses. Cecal contents were collected for 16S sequencing. Global metabolomics was performed on liver. Female mice fed the HFFC diet had increased body weight prior to adding an exercise wheel. Female mice fed the HFFC diet had an increase in exercise distance relative to CON during the preconception period. Exercise distance was similar between groups during pregnancy and lactation. CON-active and HFFC-active offspring exhibited decreased inflammation compared with offspring from sedentary dams. Fibrosis increased in offspring from HFFC-sedentary dams compared with CON-sedentary. Offspring from exercised HFFC dams exhibited less fibrosis than offspring from sedentary HFFC dams. While maternal diet significantly affected the microbiome of offspring, the effect of maternal exercise was minimal. Metabolomics analysis revealed shifts in multiple metabolites including several involved in bile acid, 1-carbon, histidine, and acylcarnitine metabolism. This study provides preclinical evidence that maternal exercise is a potential approach to prevent developmentally programmed liver disease progression in offspring.

Glycoursodeoxycholic acid regulates bile acids level and alters gut microbiota and glycolipid metabolism to attenuate diabetes

Accumulating evidence suggests that the bile acid regulates type 2 diabetes mellitus (T2DM) through gut microbiota-host interactions. However, the mechanisms underlying such interactions have been unclear. Here, we found that glycoursodeoxycholic acid (GUDCA) positively regulates gut microbiota by altering bile acid metabolism. GUDCA in mice resulted in higher taurolithocholic acid (TLCA) level and Bacteroides vulgatus abundance. Together, these changes resulted in the activation of the adipose G-protein-coupled bile acid receptor, GPBAR1 (TGR5) and upregulated expression of uncoupling protein UCP-1, resulting in elevation of white adipose tissue thermogenesis. The anti-T2DM effects of GUDCA are linked with the regulation of the bile acid and gut microbiota composition. This study suggests that altering bile acid metabolism, modifying the gut microbiota may be of value for the treatment of T2DM.

Benefits of Huang Lian mediated by gut microbiota on HFD/STZ-induced type 2 diabetes mellitus in mice

BACKGROUND

Huang Lian (HL), one of the traditional Chinese medicines (TCMs) that contains multiple active components including berberine (BBR), has been used to treat symptoms associated with diabetes for thousands of years. Compared to the monomer of BBR, HL exerts a better glucose-lowering activity and plays different roles in regulating gut microbiota. However, it remains unclear what role the gut microbiota plays in the anti-diabetic activity of HL.

METHODS

In this study, a type 2 diabetes mellitus (T2DM) mouse model was induced with a six-week high-fat diet (HFD) and a one-time injection of streptozotocin (STZ, 75 mg/kg). One group of these mice was administrated HL (50 mg/kg) through oral gavage two weeks after HFD feeding commenced and continued for four weeks; the other mice were given distilled water as disease control. Comprehensive analyses of physiological indices related to glycolipid metabolism, gut microbiota, untargeted metabolome, and hepatic genes expression, function prediction by PICRUSt2 were performed to identify potential mechanism.

RESULTS

We found that HL, in addition to decreasing body fat accumulation, effectively improved insulin resistance by stimulating the hepatic insulin-mediated signaling pathway. In comparison with the control group, HL treatment constructed a distinct gut microbiota and bile acid (BA) profile. The HL-treated microbiota was dominated by bacteria belonging to Bacteroides and the Clostridium innocuum group, which were associated with BA metabolism. Based on the correlation analysis, the altered BAs were closely correlated with the improvement of T2DM-related markers.

CONCLUSION

These results indicated that the anti-diabetic activity of HL was achieved, at least partly, by regulating the structure of the gut microbiota and the composition of BAs.

Interventions for non-alcoholic liver disease: a gut microbial metabolites perspective

Over the past two decades, non-alcoholic fatty liver disease (NAFLD) has become a leading burden of hepatocellular carcinoma and liver transplantation. Although the exact pathogenesis of NAFLD has not been fully elucidated, recent hypotheses placed more emphasis on the crucial role of the gut microbiome and its derivatives. Reportedly, microbial metabolites such as short-chain fatty acids, amino acid metabolites (indole and its derivatives), bile acids (BAs), trimethylamine N-oxide (TMAO), and endogenous ethanol exhibit sophisticated bioactive properties. These molecules regulate host lipid, glucose, and BAs metabolic homeostasis via modulating nutrient absorption, energy expenditure, inflammation, and the neuroendocrine axis. Consequently, a broad range of research has studied the therapeutic effects of microbiota-derived metabolites. In this review, we explore the interaction of microbial products and NAFLD. We also discuss the regulatory role of existing NAFLD therapies on metabolite levels and investigate the potential of targeting those metabolites to relieve NAFLD.

Intratracheal exposure to polyhexamethylene guanidine phosphate disrupts coordinate regulation of FXR-SHP-mediated cholesterol and bile acid homeostasis in mouse liver

A public health crisis in the form of a significant incidence of fatal pulmonary disease caused by repeated use of humidifier disinfectants containing polyhexamethylene guanidine phosphate (PHMG) recently arose in Korea. Although the mechanisms of pulmonary fibrosis following respiratory exposure to PHMG are well described, distant-organ effect has not been reported. In this study, we investigated whether intratracheal administration of PHMG affects liver pathophysiology and metabolism. Our PHMG mouse model showed a significant decrease in liver cholesterol level. An mRNA-seq analysis of liver samples revealed an alteration in the gene expression associated with cholesterol biosynthesis and metabolism to bile acids. The expression of genes involved in cholesterol synthesis was decreased in a real-time PCR analysis. To our surprise, we found that the coordinate regulation of cholesterol and bile acid homeostasis was completely disrupted. Despite the decreased cholesterol synthesis and low bile acid levels, the farnesoid X receptor/small heterodimer partner pathway, which controls negative feedback of bile acid synthesis, was activated in PHMG mice. As a consequence, gene expression of Cyp7a1 and Cyp7b1, the rate-limiting enzymes of the classical and alternative pathways of bile acid synthesis, was significantly downregulated. Notably, the changes in gene expression were corroborated by the hepatic concentrations of the bile acids. These results suggest that respiratory exposure to PHMG could cause cholestatic liver injury by disrupting the physiological regulation of hepatic cholesterol and bile acid homeostasis.

Role of bile acids in overweight and obese children and adolescents

Bile acids (BAs) are amphipathic molecules synthetized in the liver. They are primarily involved in the digestion of nutrients. Apart from their role in dietary lipid absorption, BAs have progressively emerged as key regulators of systemic metabolism and inflammation. In the last decade, it became evident that BAs are particularly important for the regulation of glucose, lipid, and energy metabolism. Indeed, the interest in role of BA in metabolism homeostasis is further increased due to the global public health increase in obesity and related complications and a large number of research postulating that there is a close mutual relationship between BA and metabolic disorders. This strong relationship seems to derive from the role of BAs as signaling molecules involved in the regulation of a wide spectrum of metabolic pathways. These actions are mediated by different receptors, particularly nuclear farnesoid X receptor (FXR) and Takeda G protein coupled receptor 5 (TGR5), which are probably the major effectors of BA actions. These receptors activate transcriptional networks and signaling cascades controlling the expression and activity of genes involved in BA, lipid and carbohydrate metabolism, energy expenditure, and inflammation. The large correlation between BAs and metabolic disorders offers the possibility that modulation of BAs could be used as a therapeutic approach for the treatment of metabolic diseases, including obesity itself. The aim of this review is to describe the main physiological and metabolic actions of BA, focusing on its signaling pathways, which are important in the regulation of metabolism and might provide new BA -based treatments for metabolic diseases.

Non-alcoholic fatty liver disease and type 2 diabetes mellitus: general approaches to the choice of therapy

Currently, there is a growing interest in one of the most common diseases in hepatology non-alcoholic fatty liver disease (NAFLD). There is evidence that approximately 75% of cases of NAFLD occur against the background of obesity, dyslipidemia or type 2 diabetes mellitus (T2DM). At the present stage, a persistent pathophysiological interaction between NAFLD and T2DM has been demonstrated. Insulin resistance is one of the main pathogenetic causes of the development of T2DM and NAFLD. At the same time, it is necessary to highlight the role of the intestinal microbiota and epigenome in the manifestation and progression of NAFLD. Therefore, treatment approaches should be comprehensive. Diet therapy should be aimed at calorie restriction. However, in real clinical practice, phisicians face a low commitment to appropriate and long-term dietary recommendations necessary for weight loss. At the same time, use of dietary fibers, which are part of the preparation Mucofalk, helps to slow down the passage of food through the digestive tract, increase the saturation period. Use of a low-calorie diet with a significant fat restriction may increase the risk of gallstones. Ursodeoxycholic acid preparations (Ursofalk) can be recommended for the prevention of cholelithiasis. Considering the role of intestinal microflora in the pathogenesis of NAFLD, it is necessary to correct dysbiotic changes as well as basic pharmacotherapy. Thus, a comprehensive approach to the management of patients with NAFLD and T2DM should be aimed not only at therapy, but also at the prevention of associated metabolic disorders.

Gut-liver axis: Pathophysiological concepts and clinical implications

Bidirectional crosstalk along the gut-liver axis controls gastrointestinal health and disease and exploits environmental and host mediators. Nutrients, microbial antigens, metabolites, and bile acids regulate metabolism and immune responses in the gut and liver, which reciprocally shape microbial community structure and function. Perturbation of such host-microbe interactions is observed in a variety of experimental liver diseases and is facilitated by an impaired intestinal barrier, which is fueling hepatic inflammation and disease progression. Clinical evidence describes perturbation of the gut-liver crosstalk in non-alcoholic fatty liver disease, alcoholic liver disease, and primary sclerosing cholangitis. In liver cirrhosis, a common sequela of these diseases, the intestinal microbiota and microbial pathogen-associated molecular patterns constitute liver inflammation and clinical complications, such as hepatic encephalopathy. Understanding the intricate metabolic interplay between the gut and liver in health and disease opens an avenue for targeted therapies in the future, which is probed in controlled clinical trials.

Suppression of bile acid synthesis as a tipping point in the disease course of primary sclerosing cholangitis

Background & Aims

Farnesoid X receptor (FXR) agonists and fibroblast growth factor 19 (FGF19) analogues suppress bile acid synthesis and are being investigated for their potential therapeutic efficacy in cholestatic liver diseases. We investigated whether bile acid synthesis associated with outcomes in 2 independent populations of people with primary sclerosing cholangitis (PSC) not receiving such therapy.

Methods

Concentrations of individual bile acids and 7α-hydroxy-4-cholesten-3-one (C4) were measured in blood samples from 330 patients with PSC attending tertiary care hospitals in the discovery and validation cohorts and from 100 healthy donors. We used a predefined multivariable Cox proportional hazards model to evaluate the prognostic value of C4 to predict liver transplantation-free survival and evaluated its performance in the validation cohort.

Results

The bile acid synthesis marker C4 was negatively associated with total bile acids. Patients with fully suppressed bile acid synthesis had strongly elevated total bile acids and short liver transplantation-free survival. In multivariable models, a 50% reduction in C4 corresponded to increased hazards for liver transplantation or death in both the discovery (adjusted hazard ratio [HR] = 1.24, 95% CI 1.06–1.43) and validation (adjusted HR = 1.23, 95% CI 1.03–1.47) cohorts. Adding C4 to established risk scores added value to predict future events, and predicted survival probabilities were well calibrated externally. There was no discernible impact of ursodeoxycholic acid treatment on bile acid synthesis.

Conclusions

Bile acid accumulation-associated suppression of bile acid synthesis was apparent in patients with advanced PSC and associated with reduced transplantation-free survival. In a subset of the patients, bile acid synthesis was likely suppressed beyond a tipping point at which any further pharmacological suppression may be futile. Implications for patient stratification and inclusion criteria for clinical trials in PSC warrant further investigation.

Lay summary

We show, by measuring the level of the metabolite C4 in the blood from patients with primary sclerosing cholangitis (PSC), that low production of bile acids in the liver predicts a more rapid progression to severe disease. Many people with PSC appear to have fully suppressed bile acid production, and both established and new drugs that aim to reduce bile acid production may therefore be futile for them. We propose C4 as a test to find those likely to respond to these treatments.

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The bile acid synthesis marker C4 associated negatively with bile acid levels in patients with PSC.

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Suppression of bile acid synthesis was likely nearly complete in advanced PSC.

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UDCA treatment contributed significantly to total circulating bile acids but did not appear to affect bile acid synthesis.

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Attempts to inhibit bile acid synthesis in patients with low C4 may be futile, and such drugs may be contraindicated.

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Patients with PSC and low circulating C4 had shorter liver transplantation-free survival in two independent cohorts.

Hepatic thyroid hormone signalling modulates glucose homeostasis through the regulation of GLP-1 production via bile acid-mediated FXR antagonism

Thyroid hormones (TH) regulate systemic glucose metabolism through incompletely understood mechanisms. Here, we show that improved glucose metabolism in hypothyroid mice after T3 treatment is accompanied with increased glucagon-like peptide-1 (GLP-1) production and insulin secretion, while co-treatment with a GLP-1 receptor antagonist attenuates the effects of T3 on insulin and glucose levels. By using mice lacking hepatic TH receptor β (TRβ) and a liver-specific TRβ-selective agonist, we demonstrate that TRβ-mediated hepatic TH signalling is required for both the regulation of GLP-1 production and the insulinotropic and glucose-lowering effects of T3. Moreover, administration of a liver-targeted TRβ-selective agonist increases GLP-1 and insulin levels and alleviates hyperglycemia in diet-induced obesity. Mechanistically, T3 suppresses Cyp8b1 expression, resulting in increased the levels of Farnesoid X receptor (FXR)-antagonistic bile acids, thereby potentiating GLP-1 production and insulin secretion by repressing intestinal FXR signalling. T3 correlates with both plasma GLP-1 and fecal FXR-antagonistic bile acid levels in people with normal thyroid function. Thus, our study reveals a role for hepatic TH signalling in glucose homeostasis through the regulation of GLP-1 production via bile acid-mediated FXR antagonism.

Modulatory role of gut microbiota in cholesterol and glucose metabolism: Potential implications for atherosclerotic cardiovascular disease Atherosclerosis

Accumulating evidence suggests an important role of gut microbiota in physiological processes of host metabolism as well as cardiometabolic disease. Recent advances in metagenomic and metabolomic research have led to discoveries of novel pathways in which intestinal microbial metabolism of dietary nutrients is linked to metabolic profiles and cardiovascular disease risk. A number of metaorganismal circuits have been identified by microbiota transplantation studies and experimental models using germ-free rodents. Many of these pathways involve gut microbiota-related bioactive metabolites that impact host metabolism, in particular lipid and glucose homeostasis, partly via specific host receptors. In this review, we summarize the current knowledge of how the gut microbiome can impact cardiometabolic phenotypes and provide an overview of recent advances of gut microbiome research. Finally, the potential of modulating intestinal microbiota composition and/or targeting microbiota-related pathways for novel preventive and therapeutic strategies in cardiometabolic and cardiovascular diseases will be discussed.

Olive- and Coconut-Oil-Enriched Diets Decreased Secondary Bile Acids and Regulated Metabolic and Transcriptomic Markers of Brain Injury in the Frontal Cortexes of NAFLD Pigs

The objective of this study was to investigate the effect of dietary fatty acid (FA) saturation and carbon chain length on brain bile acid (BA) metabolism and neuronal number in a pig model of pediatric NAFLD. Thirty 20-day-old Iberian pigs, pair-housed in pens, were randomly assigned to receive one of three hypercaloric diets for 10 weeks: (1) lard-enriched (LAR; n = 5 pens), (2) olive-oil-enriched (OLI, n = 5), and (3) coconut-oil-enriched (COC; n = 5). Pig behavior and activity were analyzed throughout the study. All animals were euthanized on week 10 and frontal cortex (FC) samples were collected for immunohistochemistry, metabolomic, and transcriptomic analyses. Data were analyzed by multivariate and univariate statistics. No differences were observed in relative brain weight, neuronal number, or cognitive functioning between diets. Pig activity and FC levels of neuroprotective secondary BAs and betaine decreased in the COC and OLI groups compared with LAR, and paralleled the severity of NAFLD. In addition, OLI-fed pigs showed downregulation of genes involved in neurotransmission, synaptic transmission, and nervous tissue development. Similarly, COC-fed pigs showed upregulation of neurogenesis and myelin repair genes, which caused the accumulation of medium-chain acylcarnitines in brain tissue. In conclusion, our results indicate that secondary BA levels in the FCs of NAFLD pigs are affected by dietary FA composition and are associated with metabolic and transcriptomic markers of brain injury. Dietary interventions that aim to replace saturated FAs by medium-chain or monounsaturated FAs in high-fat hypercaloric diets may have a negative effect on brain health in NAFLD patients.

Duodenal-jejunal bypass reduces serum ceramides via inhibiting intestinal bile acid-farnesoid X receptor pathway

BACKGROUND

Bile acids play an important role in the amelioration of type 2 diabetes following duodenal-jejunal bypass (DJB). Serum bile acids are elevated postoperatively. However, the clinical relevance is not known. Bile acids in the peripheral circulation reflect the amount of bile acids in the gut. Therefore, a further investigation of luminal bile acids following DJB is of great significance.

AIM

To investigate changes of luminal bile acids following DJB.

METHODS

Salicylhydroxamic acid (SHAM), DJB, and DJB with oral chenodeoxycholic acid (CDCA) supplementation were performed in a high-fat-diet/streptozotocin-induced diabetic rat model. Body weight, energy intake, oral glucose tolerance test, luminal bile acids, serum ceramides and intestinal ceramide synthesis were analyzed at week 12 postoperatively.

RESULTS

Compared to SHAM, DJB achieved rapid and durable improvement in glucose tolerance and led to increased total luminal bile acid concentrations with preferentially increased proportion of farnesoid X receptor (FXR) - inhibitory bile acids within the common limb. Intestinal ceramide synthesis was repressed with decreased serum ceramides, and this phenomenon could be partially antagonized by luminal supplementation of FXR activating bile acid CDCA.

CONCLUSION

DJB significantly changes luminal bile acid composition with increased proportion FXR-inhibitory bile acids and reduces serum ceramide levels. There observations suggest a novel mechanism of bile acids in metabolic regulation after DJB.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

Recent advances on FXR-targeting therapeutics

The bile acid receptor FXR has emerged as a bona fide drug target for chronic cholestatic and metabolic liver diseases, ahead of all non-alcoholic fatty liver disease (NAFLD). FXR is highly expressed in the liver and intestine and activation at both sites differentially contributes to its desired metabolic effects. Unrestricted FXR activation, however, also comes along with undesired effects such as a pro-atherogenic lipid profile, pruritus and hepatocellular toxicity under certain conditions. Several pre-clinical studies have confirmed the potency of FXR activation for cholestatic and metabolic liver diseases, but overall it remains still open whether selective activation of intestinal FXR is advantageous over pan-FXR activation and whether restricted or modulated FXR activation can limit some of the side effects. Even more, FXR antagonist also bear the potential as intestinal-selective drugs in NAFLD models. In this review we will discuss the molecular prerequisites for FXR activation, pan-FXR activation and intestinal FXR in/activation from a therapeutic point of view, different steroidal and non-steroidal FXR agonists, ways to restrict FXR activation and finally what we have learned from pre-clinical models and clinical trials with different FXR therapeutics.

Therapeutic mechanisms and beneficial effects of non-antidiabetic drugs in chronic liver diseases

The global burden of chronic liver disease (CLD) is substantial. Due to the limited indication of and accessibility to antiviral therapy in viral hepatitis and lack of effective pharmacological treatment in nonalcoholic fatty liver disease, the beneficial effects of antidiabetics and non-antidiabetics in clinical practice have been continuously investigated in patients with CLD. In this narrative review, we focused on non-antidiabetic drugs, including ursodeoxycholic acid, silymarin, dimethyl4,4'-dimethoxy-5,6,5',6'-dimethylenedixoybiphenyl-2,2'-dicarboxylate, L-ornithine L-aspartate, branched chain amino acids, statin, probiotics, vitamin E, and aspirin, and summarized their beneficial effects in CLD. Based on the antioxidant, anti-inflammatory properties, and regulatory functions in glucose or lipid metabolism, several non-antidiabetic drugs have shown beneficial effects in improving liver histology, aminotransferase level, and metabolic parameters and reducing risks of hepatocellular carcinoma and mortality, without significant safety concerns, in patients with CLD. Although the effect as the centerpiece management in patients with CLD is not robust, the use of these non-antidiabetic drugs might be potentially beneficial as an adjuvant or combined treatment strategy.

Theabrownin and Poria cocos Polysaccharide Improve Lipid Metabolism via Modulation of Bile Acid and Fatty Acid Metabolism

Nonalcoholic fatty liver disease (NAFLD) is prevalent worldwide, while no pharmaceutical treatment has been approved. Natural herbs are promising for their amelioration effect on lipid metabolism. Theabrownin (TB) and Poria cocos polysaccharide (PCP) have been reported to have effect on hyperlipidemia and diabetes. Here, we compared the effect of individual TB or PCP and the combination of TB and PCP (TB + PCP) on NAFLD phenotypes and the alteration of metabolism in the mice with high-fat diet. The results showed that TB, PCP, and TB + PCP reduced serum and hepatic lipid levels, among which TB + PCP was the most effective. Serum metabolomic profile and liver mRNA analyses revealed that the treatments altered metabolic pathways involved in fatty acid metabolism, bile acid metabolism, and tricarboxylic acid cycle, which was also most significant in the TB + PCP group. This study demonstrated that TB, PCP, especially the combination of TB and PCP could be potential therapeutic formula for NAFLD that promoted lipid utilization and inhibited lipid synthesis and absorption.

Schisandrin B mitigates hepatic steatosis and promotes fatty acid oxidation by inducing autophagy through AMPK/mTOR signaling pathway

BACKGROUND

Schisandrin B (Sch B), which inhibits hepatic steatosis caused by non-alcoholic fatty liver disease (NAFLD), is one of the most active dibenzocyclooctadienes isolated from Schisandra chinensis (Turcz.) Baill with various pharmacological activities. In this study, the role of Sch B-induced autophagy in lipid-lowering activities of Sch B was examined and the underlying mechanisms were elucidated.

METHODS

Free fatty acid (FFA)-stimulated HepG2 cells and mouse primary hepatocytes (MPHs) and high-fat diet (HFD)-fed mice were used as NAFLD models. The role of Sch B-induced autophagy in lipid-lowering effects of Sch B was assessed using ATG5/TFEB-deficient cells and 3-methyladenine (3-MA)-treated hepatocytes and mice.

RESULTS

Sch B simultaneously active autophagy through AMPK/mTOR pathway and decreased the number of lipid droplets in FFA-treated HepG2 cells and MPHs. Additionally, siATG5/siTFEB transfection or 3-MA treatment mitigated Sch B-induced autophagy and activation of fatty acid oxidation (FAO) and ketogenesis in FFA-treated HepG2 cells and MPHs. Sch B markedly decreased hepatic lipid content and activated the autophagy through AMPK/mTOR pathway in HFD-fed mice. However, the activities of Sch B were suppressed upon 3-MA treatment. Sch B upregulated the expression of key enzymes involved in FAO and ketogenesis, which was mitigated upon 3-MA treatment. Moreover, changes in hepatic lipid components and amino acids may be related to the Sch B-induced autophagy pathway.

CONCLUSION

These results suggested that Sch B inhibited hepatic steatosis and promoted FAO by activation of autophagy through AMPK/mTOR pathway. Our study provides novel insights into the hepatic lipophagic activity of Sch B and its potential application in the management of NAFLD.

Metabolites of Gut Microbiota and Possible Implication in Development of Diabetes Mellitus

Diabetes mellitus is characterized by having a disorder of glucose metabolism. The types of diabetes mellitus include type 1 diabetes mellitus, type 2 diabetes mellitus, gestational diabetes mellitus, and other specific types of diabetes mellitus. Many risk factors contribute to diabetes mellitus mainly including genetics, environment, obesity, and diet. In the recent years, gut microbiota has been shown to be linked to the development of diabetes. It has been reported that the gut microbiota composition of diabetic patients is different from that of healthy people. Although the mechanism behind the abnormality remains to be explored, most hypotheses focus on the inflammation response and leaky gut in relation to the changes in production of endotoxins and metabolites derived from the intestinal flora. Consequently, the above-mentioned abnormalities trigger a series of metabolic changes, gradually leading to development of hyperglycemia, insulin resistance, and diabetes. This review is (i) to summarize the differences in gut microbiota between diabetic patients and healthy people, (ii) to discuss the underlying mechanism(s) by which how lipopolysaccharide, diet, and metabolites of the gut microbiota affect diabetes, and (iii) to provide a new insight in the prevention and treatment of diabetes.

Discovery of farnesoid X receptor and its role in bile acid metabolism

In 1995, the nuclear hormone orphan receptor farnesoid X receptor (FXR, NR1H4) was identified as a farnesol receptor expressed mainly in liver, kidney, and adrenal gland of rats. In 1999, bile acids were identified as endogenous FXR ligands. Subsequently, FXR target genes involved in the regulation of hepatic bile acid synthesis, secretion, and intestinal re-absorption were identified. FXR signaling was proposed as a mechanism of feedback regulation of the rate-limiting enzyme for bile acid synthesis, cholesterol 7⍺-hydroxylase (CYP7A1). The primary bile acids synthesized in the liver are transformed to secondary bile acids by the gut microbiota. The gut-to-liver axis plays a critical role in the regulation of bile acid synthesis, composition and circulating bile acid pool size, which in turn regulates glucose, lipid, and energy metabolism. Dysregulation of bile acid metabolism and FXR signaling in the gut-to-liver axis contributes to metabolic diseases including obesity, diabetes, and non-alcoholic fatty liver disease. This review will cover the discovery of FXR as a bile acid sensor in the regulation of bile acid metabolism and as a metabolic regulator of lipid, glucose, and energy homeostasis. It will also provide an update of FXR functions in the gut-to-liver axis and the drug therapies targeting bile acids and FXR for the treatment of liver metabolic diseases.

Bile Acids Transporters of Enterohepatic Circulation for Targeted Drug Delivery

Bile acids (BAs) are important steroidal molecules with a rapidly growing span of applications across a variety of fields such as supramolecular chemistry, pharmacy, and biomedicine. This work provides a systematic review on their transport processes within the enterohepatic circulation and related processes. The focus is laid on the description of specific or less-specific BA transport proteins and their localization. Initially, the reader is provided with essential information about BAs′ properties, their systemic flow, metabolism, and functions. Later, the transport processes are described in detail and schematically illustrated, moving step by step from the liver via bile ducts to the gallbladder, small intestine, and colon; this description is accompanied by descriptions of major proteins known to be involved in BA transport. Spillage of BAs into systemic circulation and urine excretion are also discussed. Finally, the review also points out some of the less-studied areas of the enterohepatic circulation, which can be crucial for the development of BA-related drugs, prodrugs, and drug carrier systems.

Alteration of Bile Acids and Omega-6 PUFAs Are Correlated With the Progression and Prognosis of Drug-Induced Liver Injury

Background & Aims

Drug-induced liver injury (DILI) is one of the leading causes of liver failure with some of the patients progressed to chronic DILI. The mechanisms underlying the severity and chronicity of DILI are poorly elucidated and the biomarkers are limited. Metabolites and gut microbiota played a crucial role in the development of various liver diseases. Herein, a systematic analysis of serum metabolites and gut microbiota was performed in DILI patients, aiming to identify metabolites correlated with the progression and clinical prognosis of DILI.

Methods

Various serum metabolites were quantitated using a metabolite array technology in this prospective study. Gut microbiome compositions and the expression profiles of liver genes were determined in patients with DILI and healthy controls.

Results

Metabolomic analysis revealed that bile acids (BAs) and polyunsaturated fatty acids (PUFAs) were closely related to DILI severity and chronicity respectively. The ratios of serum primary/secondary BAs and omega-6/omega-3 PUFAs were elevated in DILI patients. A model established by adrenic acid (AdA) and aspartic acid (Asp) exerts good performance for predicting the chronicity of DLIL. Hepatic transcriptome revealed enhanced expression of PUFA peroxidation and supressed expression of BA synthesis related genes in DILI patients. In addition, Lactic acid bacteria and BA converting bacteria were increased in gut of DILI patients. Besides, elevated serum malondialdehyde (MDA) and fibroblast growth factor 19 (FGF19) was observed in DILI patients.

Conclusion

BAs and PUFAs could be potent markers for the severity and chronicity of DILI respectively. The panel of AdA and Asp could be ideal predictive model for the risk of chronicity at the acute stage of DILI. Gut microbiota might act as a negative feedback mechanism to maintain the homeostasis of BAs and PUFAs via FGF19 signalling and PUFA saturation, respectively. Our study revealed novel biomarkers for severe and chronic DILI and provided new therapeutic targets for DILI.

Bile acid coordinates microbiota homeostasis and systemic immunometabolism in cardiometabolic diseases

Cardiometabolic disease (CMD), characterized with metabolic disorder triggered cardiovascular events, is a leading cause of death and disability. Metabolic disorders trigger chronic low-grade inflammation, and actually, a new concept of metaflammation has been proposed to define the state of metabolism connected with immunological adaptations. Amongst the continuously increased list of systemic metabolites in regulation of immune system, bile acids (BAs) represent a distinct class of metabolites implicated in the whole process of CMD development because of its multifaceted roles in shaping systemic immunometabolism. BAs can directly modulate the immune system by either boosting or inhibiting inflammatory responses via diverse mechanisms. Moreover, BAs are key determinants in maintaining the dynamic communication between the host and microbiota. Importantly, BAs via targeting Farnesoid X receptor (FXR) and diverse other nuclear receptors play key roles in regulating metabolic homeostasis of lipids, glucose, and amino acids. Moreover, BAs axis per se is susceptible to inflammatory and metabolic intervention, and thereby BAs axis may constitute a reciprocal regulatory loop in metaflammation. We thus propose that BAs axis represents a core coordinator in integrating systemic immunometabolism implicated in the process of CMD. We provide an updated summary and an intensive discussion about how BAs shape both the innate and adaptive immune system, and how BAs axis function as a core coordinator in integrating metabolic disorder to chronic inflammation in conditions of CMD.

Bile acid-gut microbiota crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction with an increasing prevalence, and its precise aetiology remains unclear. Gut microbiota dysbiosis has been found to be associated with IBS pathogenesis. In addition, a high incidence of bile acid diarrhoea and disturbed bile acid metabolism has been observed in IBS patients. The abundant microorganisms inhabited in human gut have essential functions in bile acid biotransformation, and can immensely affect the size and constitution of bile acid pool. Meanwhile, the alterations of bile acid profile can inversely interfere with the gut microbiota. This review discussed the role of intricate correlations between bile acids and gut microbiota in IBS pathogenesis and delineated the possible molecular mechanisms, mainly the signalling induced by farnesoid X receptor and transmembrane G protein-coupled receptor 5. Besides, some biomarkers for identifying bile acid diarrhoea in IBS population were listed, assisting the diagnosis and classification of IBS. Moreover, it also assessed some therapeutic strategies for IBS that regulate the bile acid-gut microbiota axis, such as dietary modulation, probiotics/prebiotics, faecal microbiota transplantation, and antibiotics. Collectively, this article illustrated the relationship between bile acids and gut microbiota in IBS pathophysiology and might offer some novel therapeutic options for IBS.

Dealkenylation of neoandrographolide, a phytochemical from Andrographis paniculata stimulates FXR (Farnesoid X Receptor) and enhances gallstone dissolution

FXR (Farnesoid X Receptor) is one of the nuclear receptors expressed in the liver performing a significant role in the maintenance of bile acid concentration. An imbalance of cholesterol and bile acid ratio due to any undefined reason could cause gallstone formation. Hence, this paper aims to screen phytochemicals that could maintain a requisite balance of cholesterol and bile acid by targeting FXR and thereby contributing to the dissolution of gallstone. Nineteen phytochemicals were selected and queried for Pa and Pi in the way2drug online server for hepatoprotective property, cholesterol synthesis and absorption inhibition property, and β-glucuronidase inhibiting activity. Cianidanol, neoandrographolide, cynarine, saponins, and tanins with satisfying stated properties were docked with the screened FXR (PDB ID- 1OSH) using HADDOCK server, followed by pharmacokinetics study utilizing SwissADME tool. Neoandrographolide fits best among the other selected literature-based phytochemicals with minor violation of 'Brenk's rule'. The violation was corrected with the removal of an alkene group in the provided ChemDraw space of SwissADME. This Dealkenylated compound was further docked with FXR. The promising response under the static condition of the Dealkenylated compound was analyzed for molecular dynamic simulation at physiological conditions for 100 ns. Dealkenylated Neoandrographolide (DN) exhibited hepatoprotective, cholesterol synthesis and absorption inhibition property, and β-glucuronidase inhibition activity with a superior binding score of -42.6+/-1.5 with FXR. The interaction of the FXR receptor and the DN showed exceptional stability at physiological conditions during MD simulation and fit for the ADME properties, therefore it could be a potent candidate to dissolve gallstones.Communicated by Ramaswamy H. Sarma.

Bile acid metabolism and FXR-mediated effects in human cholestatic liver disorders

Intrahepatic cholestasis is the main feature of a group of liver diseases that are characterized by hepatic and systemic accumulation of bile acids due to impaired excretion of bile, based on inflammation of intrahepatic and extrahepatic bile ducts or dysfunction of hepatobiliary transport proteins. The nuclear bile acid sensor farnesoid X receptor (FXR) is central for the regulation of bile acid turnover, including synthesis, hepatic excretion and intestinal and hepatic uptake. Several drugs targeting FXR have been developed for the treatment of cholestatic liver diseases, and so far one of them has been granted conditional approval. In this review, we will discuss the current knowledge and the clinical and experimental data available on agents affecting FXR and bile acid turnover.

Ursodesoxycholic acid is an FFA4 agonist and reduces hepatic steatosis via FFA4 signaling

Ursodeoxycholic acid (UDCA) is a safe bile acid effective in reducing hepatic steatosis in non-alcoholic fatty liver disease (NAFLD). However, the mechanism of action linked to this effect is poorly defined. In the present study, we identified that UDCA acted as a free fatty acid receptor 4 (FFA4) agonist with EC50 of 10.4 ± 0.7 μM, and its activity was determined by dynamic mass redistribution, fluorometric imaging plate reader, inositol monophosphate and bioluminescence resonance energy transfer assays. Moreover, UDCA showed FFA4 selectivity over eleven other G protein-coupled receptors. Real-Time PCR and immunocytochemistry analyses showed that FFA4 was abundantly expressed in human hepatocytes HuH-7 cells. In an in vitro model of NAFLD induced by oleic acid (OA), UDCA downregulated lipid accumulation in HuH-7 cells and suppressed sterol-regulatory element binding protein-1c (SREBP-1c) mRNA expression. This suppression of SREBP-1c was restored when FFA4 expression was knocked down in siRNA assay. In a mouse model of hepatic steatosis, db/db mice were exposed to a high-fat diet (HFD), and treatment of UDCA or docosahexaenoic acid (DHA, an endogenous FFA4 agonist) effectively prevented body weight gain and hepatic fat deposition and reduced triglyceride (TG) levels in serum and liver. This study not only identified a new skeleton of FFA4 agonists, but also demonstrated that FFA4 signal was accounting for the protective effects of UDCA in the NAFLD treatment.

NRF2 Activation in Autophagy Defects Suppresses a Pharmacological Transactivation of the Nuclear Receptor FXR

NF-E2-related factor 2 (NRF2), an antioxidant transcription factor, is activated in autophagy-deficient mice due to the accumulations of p62/SQSTM1 and its subsequent interaction with Kelch-like-ECH-associated protein 1 (KEAP1), an adaptor component for Cullin3-based E3 ubiquitin ligase complex. Farnesoid x receptor (FXR/NR1H4) is a ligand-dependent transcription factor that belongs to the nuclear receptor superfamily. FXR plays an essential role in bile acid synthesis and enterohepatic circulation, affecting glucose and lipid metabolism. Obeticholic acid as a potent FXR agonist has been approved to treat primary biliary cholangitis and clinical trials for its use in the treatment of other liver diseases are underway. Here we show that NRF2 activation in autophagy defects impedes a transactivation of FXR. Liver-specific Atg7 knockout mice or a treatment of autophagy inhibitor showed decreased inductions of FXR target genes upon its synthetic agonists. Moreover, enforced NRF2 activations with small molecules potently decreased the pharmacological activation of FXR in cultured cells. Finally, we demonstrate that NRF2 activation by the treatment with the food antioxidant butylated hydroxyanisole is necessary and sufficient to inhibit the pharmacological activation of FXR in vivo. These results reveal a novel function of the basal autophagy-NRF2 axis for the regulation of FXR transactivation, and shed light on a potential therapeutic strategy in metabolic disease.

Transcriptional Regulation of Hepatic Autophagy by Nuclear Receptors

Autophagy is an adaptive self-eating process involved in degradation of various cellular components such as carbohydrates, lipids, proteins, and organelles. Its activity plays an essential role in tissue homeostasis and systemic metabolism in response to diverse challenges, including nutrient depletion, pathogen invasion, and accumulations of toxic materials. Therefore, autophagy dysfunctions are intimately associated with many human diseases such as cancer, neurodegeneration, obesity, diabetes, infection, and aging. Although its acute post-translational regulation is well described, recent studies have also shown that autophagy can be controlled at the transcriptional and post-transcriptional levels. Nuclear receptors (NRs) are in general ligand-dependent transcription factors consisting of 48 members in humans. These receptors extensively control transcription of a variety of genes involved in development, metabolism, and inflammation. In this review, we discuss the roles and mechanisms of NRs in an aspect of transcriptional regulation of hepatic autophagy, and how the NR-driven autophagy pathway can be harnessed to treat various liver diseases.

Changes in bile acid subtypes and long-term successful weight-loss in response to weight-loss diets: The POUNDS lost trial

BACKGROUND AND AIMS

Primary bile acids (BAs) are synthesized in the liver and secondary BAs result from intestinal microbial activity. Different subtypes of BAs may be involved in regulating adiposity and energy homeostasis. We examined how changes in circulating BA subtypes induced by weight-loss diets were associated with improvements in adiposity, regional fat deposition and energy metabolism among overweight and obese adults.

METHODS

The study included 551 subjects who participated in a 2-year weight-loss diet intervention trial. Circulating 14 BA subtypes (primary and secondary unconjugated BAs and their taurine-/glycine-conjugates) were measured at baseline and 6 months. Associations of changes in BAs with changes in weight, waist circumference, resting energy expenditure (REE), body fat composition and fat distribution were evaluated.

RESULTS

Greater decreases in primary BAs (cholate and chenodeoxycholate) and secondary BAs (deoxycholate and lithocholate) and their conjugates (except for glycolithocholate) were associated with more decreases in weight and waist circumference at 6 months (P_{-after-false-discovery-rate-correction} [P_FDR ] < .05). We found that changes in glycocholate and glycoursodeoxycholate were consistently associated with reductions of general and central adiposity, REE, whole-body fat and visceral adipose tissue (P_FDR  < .05). Further, the initial (6-month) changes in BA subtypes were differently predictive of successful weight loss over 2 years.

CONCLUSIONS

The decreases in primary and secondary BA subtypes after eating low-calorie weight-loss diets were significantly associated with improving adiposity, fat accumulation and energy metabolism, suggesting that specific BA subtypes would be predictive of long-term successful weight loss and individuals' response to the treatment of weight-loss diets.

The effect of Tauroursodeoxycholic acid (TUDCA) and gut microbiota on murine gallbladder stone formation

INTRODUCTION AND OBJECTIVES

The incidence of gallstone-related disease steadily increased in the last few years. Here, we aimed to investigate the effect of tauroursodeoxycholic acid¹ (TUDCA) on preventing cholesterol gallstones formation in high-fat fed (HFD) mice.

MATERIAL AND METHODS

Specific pathogen-free male C57Bl/6 mice were fed a lithogenic diet² (LD group) alone or in combination with TUDCA (5g/kg diet) for 8 weeks. Upon sacrifice, serum, gallbladder, liver and small intestine were collected and the formation of gallstones or crystals in the gallbladder was analyzed. Additionally, the intestinal microbiota, and bile acid composition, serum lipids and hepatic lipids were studied.

RESULTS

Cholesterol gallstones with cholesterol crystals formed in mice of the LD-fed group (15/15, 100%). However, only cholesterol crystals were found in three mice without the presence of any gallstone in the TUDCA-treated group. Both serum and hepatic total cholesterol levels in the TUDCA group were significantly decreased compared with the LD group. Concomitantly, mRNA expression of Abcg5 and Abcg8 was significantly lower in the liver of the TUDCA group whilst mRNA transcripts for Abcb11, Acat2, and Cyp27 were significantly increased compared with the LD group. Additionally, the gallbladder cholesterol saturation index (1.06±0.15) in the TUDCA group was significantly decreased compared with the LD group. Interestingly, the ratio of Firmicutes/Bacteroides in the TUDCA group was increased 3x fold.

CONCLUSIONS

TUDCA can inhibit the absorption and synthesis of lipids in the small intestine by improving the intestinal microbiota in HFD-fed mice, thus reducing gallstone formation.

Diammonium Glycyrrhizinate Ameliorates Obesity Through Modulation of Gut Microbiota-Conjugated BAs-FXR Signaling

Obesity is a worldwide epidemic metabolic disease. Gut microbiota dysbiosis and bile acids (BAs) metabolism disorder are closely related to obesity. Farnesoid X-activated receptor (FXR), served as a link between gut microbiota and BAs, is involved in maintaining metabolic homeostasis and regulating glucose and lipid metabolism. We previously reported that diammonium glycyrrhizinate (DG) could alter gut microbiota and prevent non-alcoholic fatty liver disease. However, it remains ambiguous how DG affects the gut microbiota to regulate host metabolism. In this present study, 16S rRNA Illumina NovaSeq and metabolomic analysis revealed that DG treatment suppressed microbes associated with bile-salt hydrolase (BSH) activity, which, in turn, increased the levels of taurine-conjugated BAs accompanied by inhibition of ileal FXR-FGF15 signaling. As a result, several obesity-related metabolism were improved, like lower serum glucose and insulin levels, increased insulin sensitivity, few hepatic steatosis and resistance to weight gain. Additionally, decreased level of serum lipopolysaccharide was observed, which contributed to a strengthened intestinal barrier. The effect of DG on weight loss was slightly enhanced in the antibiotics-treated obese mice. Collectively, the efficacy of DG in the treatment of obesity might depend on gut microbiota-conjugated BAs-FXR axis. Hence, it will provide a potential novel approach for the treatment of obesity.

Increased circulating butyrate and ursodeoxycholate during probiotic intervention in humans with type 2 diabetes

Background

An increasing body of evidence implicates the resident gut microbiota as playing a critical role in type 2 diabetes (T2D) pathogenesis. We previously reported significant improvement in postprandial glucose control in human participants with T2D following 12-week administration of a 5-strain novel probiotic formulation (‘WBF-011’) in a double-blind, randomized, placebo controlled setting (NCT03893422). While the clinical endpoints were encouraging, additional exploratory measurements were needed in order to link the motivating mechanistic hypothesis - increased short-chain fatty acids - with markers of disease.

Results

Here we report targeted and untargeted metabolomic measurements on fasting plasma (n = 104) collected at baseline and end of intervention. Butyrate and ursodeoxycholate increased among participants randomized to WBF-011, along with compelling trends between butyrate and glycated haemoglobin (HbA1c). In vitro monoculture experiments demonstrated that the formulation’s C. butyricum strain efficiently synthesizes ursodeoxycholate from the primary bile acid chenodeoxycholate during butyrogenic growth. Untargeted metabolomics also revealed coordinated decreases in intermediates of fatty acid oxidation and bilirubin, potential secondary signatures for metabolic improvement. Finally, improvement in HbA1c was limited almost entirely to participants not using sulfonylurea drugs. We show that these drugs can inhibit growth of formulation strains in vitro.

Conclusion

To our knowledge, this is the first description of an increase in circulating butyrate or ursodeoxycholate following a probiotic intervention in humans with T2D, adding support for the possibility of a targeted microbiome-based approach to assist in the management of T2D. The efficient synthesis of UDCA by C. butyricum is also likely of interest to investigators of its use as a probiotic in other disease settings. The potential for inhibitory interaction between sulfonylurea drugs and gut microbiota should be considered carefully in the design of future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02415-8.

Targeting gut microbial bile salt hydrolase (BSH) by diet supplements: new insights into dietary modulation of human health

Dietary supplements could modulate the abundance of BSH-producing bacteria to regulate the BSH enzyme activity, thereby change the BAs composition to regulate FXR signaling, which then regulate human health.

Novel therapeutic targets for cholestatic and fatty liver disease

Cholestatic and non-alcoholic fatty liver disease (NAFLD) share several key pathophysiological mechanisms which can be targeted by novel therapeutic concepts that are currently developed for both areas. Nuclear receptors (NRs) are ligand-activated transcriptional regulators of key metabolic processes including hepatic lipid and glucose metabolism, energy expenditure and bile acid (BA) homoeostasis, as well as inflammation, fibrosis and cellular proliferation. Dysregulation of these processes contributes to the pathogenesis and progression of cholestatic as well as fatty liver disease, placing NRs at the forefront of novel therapeutic approaches. This includes BA and fatty acid activated NRs such as farnesoid-X receptor (FXR) and peroxisome proliferator-activated receptors, respectively, for which high affinity therapeutic ligands targeting specific or multiple isoforms have been developed. Moreover, novel liver-specific ligands for thyroid hormone receptor beta 1 complete the spectrum of currently available NR-targeted drugs. Apart from FXR ligands, BA signalling can be targeted by mimetics of FXR-activated fibroblast growth factor 19, modulation of their enterohepatic circulation through uptake inhibitors in hepatocytes and enterocytes, as well as novel BA derivatives undergoing cholehepatic shunting (instead of enterohepatic circulation). Other therapeutic approaches more directly target inflammation and/or fibrosis as critical events of disease progression. Combination strategies synergistically targeting metabolic disturbances, inflammation and fibrosis may be ultimately necessary for successful treatment of these complex and multifactorial disorders.

A Current Understanding of Bile Acids in Chronic Liver Disease

Chronic liver disease (CLD) is one of the leading causes of disability-adjusted life years in many countries. A recent understanding of nuclear bile acid receptor pathways has increased focus on the impact of crosstalk between the gut, bile acids, and liver on liver pathology. While conventionally used in cholestatic disorders and to dissolve gallstones, the discovery of bile acids' influence on the gut microbiome and human metabolism offers a unique potential for their utility in early and advanced liver diseases because of diverse etiologies. Based on these findings, preclinical studies using bile acid-based molecules have shown encouraging results at addressing liver inflammation and fibrosis. Emerging data also suggest that bile acid profiles change distinctively across various causes of liver disease. We summarize the current knowledge and evidence related to bile acids in health and disease and discuss culminated and ongoing therapeutic trials of bile acid derivatives in CLD. In the near future, further evidence in this area might help clinicians better detect and manage liver diseases.

Ursodeoxycholic Acid Treatment Restores Gut Microbiota and Alleviates Liver Inflammation in Non-Alcoholic Steatohepatitic Mouse Model

Gut microbiota dysbiosis plays an important role in the progression of non-alcoholic fatty liver disease (NAFLD), and no approved drugs are available for NAFLD treatment. In this study, we aimed to explore the dynamic changes of gut microbiota at the different stages of NAFLD and determine whether ursodeoxycholic acid (UDCA) could improve liver histopathological features of non-alcoholic steatohepatitis (NASH) mice induced by a high-fat high-cholesterol (HFHC) diet and its impact on gut microbiota. 6-week-old male C57BL/6 mice were fed with a HFHC or normal diet for 12, 18, and 24 weeks, respectively, to simulate the different stages of NAFLD. 16s ribosomal RNA genes from mice fecal samples at the different time points were sequenced to evaluate the dynamic changes of the gut microbiota. Then, C57BL/6 mice were fed with a HFHC diet for 24 weeks to establish the NASH model. Different doses of UDCA were administered intragastrically for additional 4 weeks. Normal diet-fed mice were taken as control. Serum samples, liver, and intestine tissues were harvested for biochemical tests and histopathological examinations. 16s ribosomal RNA genes from mice fecal samples were sequenced to assess the structural changes of gut microbiota. HFHC diet-fed mice developed simple steatosis, steatohepatitis, and fibrosis at 12, 18, and 24 weeks, respectively. The profile of gut microbiota dynamically changed with the different stages of NAFLD. NASH mice had significantly higher abundance of Fecalibaculum, Coriobacteriaceae_UCG-002, and Enterorhabdus, and lower abundance of norank_f_Muribaculaceae, Bacteroides, and Alistipes, which were partially restored by UDCA treatment. UDCA treatment significantly attenuated hepatic inflammation of NASH mice as indicated by the sum of ballooning and lobular inflammation of the NALFD activity score (3.2 ± 0.8 vs 1.8 ± 0.8, p = 0.029), and partially restored gut microbiota dysbiosis, and increased the expression of Claudin-1 and ZO-1 in the intestine, but did not activate the suppressed Farnesoid X receptor signal pathway. Conclusions: The gut microbiota dynamically changes with the different stages of NAFLD. UDCA treatment (120 mg/kg) could partially restore gut microbiota, repair gut barrier integrity, and attenuate hepatic inflammation in the NASH mouse model.

Combined Analysis of the Effects of Exposure to Blue Light in Ducks Reveals a Reduction in Cholesterol Accumulation Through Changes in Methionine Metabolism and the Intestinal Microbiota

Monochromatic light is widely used in industry, medical treatment, and animal husbandry. Green-blue light has been found to stimulate the proliferation of satellite cells and the results of studies on the effects of blue light on poultry vary widely. It would be worthwhile to study the effect of blue light on poultry growth and how exposure to blue light affects metabolism and the intestinal microbiota. In this study, we irradiated Cherry Valley ducks with 460 nm wavelength light (blue light) for 3 weeks to explore the effects of blue light in comparison to those of white light (combined wavelength light) on animal growth and development. Our results showed that, under exposure to blue light, the body weight and average daily feed intake of ducks were decreased, but the leg muscle and relative length of the intestine were increased. Exposure to blue light chiefly enhanced the anti-inflammatory and antioxidant capacities of the animal and decreased lipid levels in serum and liver. Metabolomic analysis revealed that blue light heightened cysteine and methionine metabolism, and increased serum taurine and primary bile acid levels, as well as up-regulating the metabolites L-carnitine and glutamine. Treatment with blue light significantly increased the beta diversity of intestinal microbiota and the relative abundances of bile acid hydrolase-producing bacteria, especially Alistipes. These changes promote the synthesis of secondary bile acids to further enhance lipid metabolism in the host, thereby reducing cholesterol accumulation in ducks. These results should help us better understand the effects of exposure to blue light on metabolite levels and the intestinal microbiota, and suggest that it may be possible to use colored light to control the development of livestock and poultry.