Safety, tolerability and pharmacodynamics of apical sodium-dependent bile acid transporter inhibition with volixibat in healthy adults and patients with type 2 diabetes mellitus: a randomised placebo-controlled trial

The current findings on the gut-liver axis and the molecular basis of NAFLD/NASH associated with gut microbiome dysbiosis

Recent research has highlighted the complex relationship between gut microbiota, metabolic pathways, and nonalcoholic fatty liver disease (NAFLD) progression. Gut dysbiosis, commonly observed in NAFLD patients, impairs intestinal permeability, leading to the translocation of bacterial products like lipopolysaccharides, short-chain fatty acids, and ethanol to the liver. These microbiome-associated mechanisms contribute to intestinal and hepatic inflammation, potentially advancing NAFLD to NASH. Dietary habits, particularly those rich in saturated fats and fructose, can modify the microbiome composition, leading to dysbiosis and fatty liver development. Metabolomic approaches have identified unique profiles in NASH patients, with specific metabolites like ethanol linked to disease progression. While bariatric surgery has shown promise in preventing NAFLD progression, the role of gut microbiome and metabolites in this improvement remains to be proven. Understanding these microbiome-related pathways may provide new diagnostic and therapeutic targets for NAFLD and NASH. A comprehensive review of current literature was conducted using multiple medical research databases, including PubMed, Scopus, Web of Science, Embase, Cochrane Library, ClinicalTrials.gov, ScienceDirect, Medline, ProQuest, and Google Scholar. The review focused on studies that examine the relationship between gut microbiota composition, metabolic pathways, and NAFLD progression. Key areas of interest included microbial dysbiosis, endotoxin production, and the influence of diet on gut microbiota. The analysis revealed that gut dysbiosis contributes to NAFLD through several mechanisms, diet significantly influences gut microbiota composition, which in turn affects liver function through the gut-liver axis. High-fat diets can lead to dysbiosis, altering microbial metabolic activities and promoting liver inflammation. Specifically, gut microbiota-mediated generation of saturated fatty acids, such as palmitic acid, can activate liver macrophages and increase TNF-α expression, contributing to NASH development. Different dietary components, including cholesterol, fiber, fat, and carbohydrates, can modulate the gut microbiome and influence NAFLD progression. This gut-liver axis plays a crucial role in maintaining immune homeostasis, with the liver responding to gut-derived bacteria by activating innate and adaptive immune responses. Microbial metabolites, such as bile acids, tryptophan catabolites, and branched-chain amino acids, regulate adipose tissue and intestinal homeostasis, contributing to NASH pathogenesis. Additionally, the microbiome of NASH patients shows an elevated capacity for alcohol production, suggesting similarities between alcoholic steatohepatitis and NASH. These findings indicate that targeting the gut microbiota may be a promising approach for NASH treatment and prevention. Recent research highlights the potential of targeting gut microbiota for managing nonalcoholic fatty liver disease (NAFLD). The gut-liver axis plays a crucial role in NAFLD pathophysiology, with dysbiosis contributing to disease progression. Various therapeutic approaches aimed at modulating gut microbiota have shown promise, including probiotics, prebiotics, synbiotics, fecal microbiota transplantation, and dietary interventions. Probiotics have demonstrated efficacy in human randomized controlled trials, while other interventions require further investigation in clinical settings. These microbiota-targeted therapies may improve NAFLD outcomes through multiple mechanisms, such as reducing inflammation and enhancing metabolic function. Although lifestyle modifications remain the primary recommendation for NAFLD management, microbiota-focused interventions offer a promising alternative for patients struggling to achieve weight loss targets.

Analysis of C4 Concentrations to Predict Impact of Patient-Reported Diarrhea Associated With the Ileal Bile Acid Transporter Inhibitor Linerixibat

Linerixibat, an ileal bile acid transporter (IBAT) inhibitor, is being evaluated for the treatment of pruritus in primary biliary cholangitis (PBC). Diarrhea is commonly reported with this drug class as IBAT inhibition redirects bile acids (BA) to the colon. Serum 7-alpha-hydroxy-4-cholesten-3-one (C4) measurement is a validated method to identify BA diarrhea. To inform dose selection, we characterized the relationship between linerixibat dose, C4 levels, and patient-reported bother on the gastrointestinal symptom rating scale (GSRS) diarrhea question. A kinetic-pharmacodynamic model was developed using data from five Phase 1/2 trials, to describe the effect of linerixibat dose (1-180 mg) and regimen (once/twice daily) on C4 concentrations over time. GSRS data from patients with PBC and pruritus in the Phase 2b GLIMMER study (NCT02966834) were used to develop a proportional odds model to predict the probability of a score of 1-7 (no-very severe discomfort) to the question "Have you been bothered by diarrhea during the past week?" in relation to linerixibat dose. The two models were linked to describe the linerixibat dose-C4-diarrhea bother relationship. Models were validated using graphical and numerical assessment and visual predictive checks. Linerixibat caused dose-dependent increases in C4 until saturation (~180 mg total daily dose). Increased C4 concentrations trended with increased GSRS diarrhea scores. Simulations demonstrated increases in moderate-to-very severe (≥ 4) diarrhea scores with increasing linerixibat dose. Increases in patient-reported diarrhea scores were linerixibat dose-dependent. Selecting an optimal dose that maximizes linerixibat's ability to improve pruritus while minimizing patient-reported diarrhea bother is important to support treatment adherence.

The burden of Alagille syndrome: uncovering the potential of emerging therapeutics - a comprehensive systematic literature review

Aim: Alagille syndrome (ALGS) is a rare, cholestatic multiorgan disease associated with bile duct paucity, leading to cholestasis. Clinical symptoms of cholestasis include debilitating pruritus, xanthomas, fat-soluble vitamin deficiencies, growth failure, renal disease and impaired health-related quality of life (HRQoL). The main objective was to review the current literature on the epidemiological, clinical, psychosocial and economic burden of ALGS in view of the development of ileal bile acid transporter (IBAT) inhibitors. Methods: Electronic literature databases were searched in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist. Results: 330 publications were screened, 119 were relevant: 11 randomized controlled trials (RCTs), 21 non-RCTs, 10 HRQoL studies, two studies assessing cost/resource use and 77 epidemiological studies across several databases through 31 July 2024. Studies confirm that patients with ALGS experience cardiac anomalies, impaired growth, renal disease, poor HRQoL, fat-soluble vitamin deficiencies and debilitating pruritus; until the approval of IBAT inhibitors for the treatment of cholestatic pruritus in patients with ALGS, supportive management was the standard of care. Conclusion: This review confirms the substantial clinical, economic and HRQoL burden associated with ALGS and consolidates current treatment evidence. Data from recent trials in ALGS demonstrate the potential impact of IBAT inhibitors to transform lives by improving cholestatic pruritus symptoms, HRQoL and native liver survival.

Exploring bile acid transporters as key players in cancer development and treatment: Evidence from preclinical and clinical studies

Bile acid transporters (BATs) are integral membrane proteins belonging to various families, such as solute carriers, organic anion transporters, and ATP-binding cassette families. These transporters play a crucial role in bile acid transportation within the portal and systemic circulations, with expression observed in tissues, including the liver, kidney, and small intestine. Bile acids serve as signaling molecules facilitating the absorption and reabsorption of fats and lipids. Dysregulation of bile acid concentration has been implicated in tumorigenesis, yet the role of BATs in this process remains underexplored. Emerging evidence suggests that BATs may modulate various stages of cancer progression, including initiation, development, proliferation, metastasis, and tumor microenvironment regulation. Targeting BATs using siRNAs, miRNAs, and small compound inhibitors in preclinical models and their polymorphisms are well-studied for transporters like BSEP, MDR1, MRP2, OATP1A2, etc., and have shed light on their involvement in tumorigenesis, particularly in cancers such as those affecting the liver and gastrointestinal tract. While BATs' role in diseases like Alagille syndrome, biliary atresia, and cirrhosis have been extensively studied, their implications in cancer warrant further investigation. This review highlights the expression and function of BATs in cancer development and emphasizes the potential of targeting these transporters as a novel therapeutic strategy for various malignancies.

Bile Acid Signaling in Metabolic and Inflammatory Diseases and Drug Development

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

Dan-shen Yin promotes bile acid metabolism and excretion to prevent atherosclerosis via activating FXR/BSEP signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Dan-shen Yin (DSY), a traditional prescription, has been demonstrated to be effective in decreasing hyperlipidemia and preventing atherosclerosis (AS), but its mechanism remains unknown. We hypothesized that DSY activates farnesoid X receptor (FXR) to promote bile acid metabolism and excretion, thereby alleviating AS.

AIM OF THE STUDY

This study was designed to explore whether DSY reduces liver lipid accumulation and prevents AS by activating FXR and increasing cholesterol metabolism and bile acid excretion.

MATERIALS AND METHODS

The comprehensive chemical characterization of DSY was analyzed by UHPLC-MS/MS. The AS models of ApoE-/- mice and SD rats was established by high-fat diet and high-fat diet combined with intraperitoneal injection of vitamin D3, respectively. The aortic plaque and pathological changes were used to evaluate AS. Lipid levels, H&E staining and oil red O staining were used to evaluate liver lipid accumulation. The cholesterol metabolism and bile acid excretion were evaluated by enzyme-linked immunosorbent assay, UPLC-QQQ/MS. In vitro, the lipid and FXR/bile salt export pump (BSEP) levels were evaluated by oil red O staining, real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting.

RESULTS

A total of 36 ingredients in DSY were identified by UPLC-MS/MS analysis. In vivo, high-dose DSY significantly inhibited aortic intimal thickening, improved arrangement disorder, tortuosity, and rupture of elastic fibers, decreased lipid levels, and reduced the number of fat vacuoles and lipid droplets in liver tissue in SD rats and ApoE-/- mice. Further studies found that high-dose DSY significantly reduced liver lipid and total bile acids levels, increased liver ursodeoxycholic acid (UDCA) and other non-conjugated bile acids levels, increased fecal total cholesterol (TC) levels, and augmented FXR, BSEP, cholesterol 7-alpha hydroxylase (CYP7A1), ATP binding cassette subfamily G5/G8 (ABCG5/8) expression levels, while decreasing ASBT expression levels. In vitro studies showed that DSY significantly reduced TC and TG levels, as well as lipid droplets, while also increasing the expression of ABCG5/8, FXR, and BSEP in both HepG2 and Nr1h4 knockdown HepG2 cells.

CONCLUSION

This study demonstrated that DSY promotes bile acid metabolism and excretion to prevent AS by activating FXR. For the prevent of AS and drug discovery provided experimental basis.

Inhibition of hepatic bile salt uptake by Bulevirtide reduces atherosclerosis in Oatp1a1-/-Ldlr-/- mice

Bile salts can strongly influence energy metabolism through systemic signaling, which can be enhanced by inhibiting the hepatic bile salt transporter Na+ taurocholate cotransporting polypeptide (NTCP), thereby delaying hepatic reuptake of bile salts to increase systemic bile salt levels. Bulevirtide is an NTCP inhibitor and was originally developed to prevent NTCP-mediated entry of Hepatitis B and D into hepatocytes. We previously demonstrated that NTCP inhibition lowers body weight, induces glucagon-like peptide-1 (GLP1) secretion, and lowers plasma cholesterol levels in murine obesity models. In humans, a genetic loss-of-function variant of NTCP has been associated with reduced plasma cholesterol levels. Here, we aimed to assess if Bulevirtide treatment attenuates atherosclerosis development by treating female Ldlr-/- mice with Bulevirtide or vehicle for 11 weeks. Since this did not result in the expected increase in plasma bile salt levels, we generated Oatp1a1-/-Ldlr-/- mice, an atherosclerosis-prone model with human-like hepatic bile salt uptake characteristics. These mice showed delayed plasma clearance of bile salts and elevated bile salt levels upon Bulevirtide treatment. At the study endpoint, Bulevirtide-treated female Oatp1a1-/-Ldlr-/- mice had reduced atherosclerotic lesion area in the aortic root that coincided with lowered plasma LDL-c levels, independent of intestinal cholesterol absorption. In conclusion, Bulevirtide, which is considered safe and is EMA-approved for the treatment of Hepatitis D, reduces atherosclerotic lesion area by reducing plasma LDL-c levels. We anticipate that its application may extend to atherosclerotic cardiovascular diseases, which warrants clinical trials.

Exposure of Ldlr-/- Mice to a PFAS Mixture and Outcomes Related to Circulating Lipids, Bile Acid Excretion, and the Intestinal Transporter ASBT

BACKGROUND

Previous epidemiological studies have repeatedly found per- and polyfluoroalkyl substances (PFAS) exposure associated with higher circulating cholesterol, one of the greatest risk factors for development of coronary artery disease. The main route of cholesterol catabolism is through its conversion to bile acids, which circulate between the liver and ileum via enterohepatic circulation. Patients with coronary artery disease have decreased bile acid excretion, indicating that PFAS-induced impacts on enterohepatic circulation may play a critical role in cardiovascular risk.

OBJECTIVES

Using a mouse model with high levels of low-density and very low-density lipoprotein (LDL and VLDL, respectively) cholesterol and aortic lesion development similar to humans, the present study investigated mechanisms linking exposure to a PFAS mixture with increased cholesterol.

METHODS

Male and female L d l r - / - mice were fed an atherogenic diet (Clinton/Cybulsky low fat, 0.15% cholesterol) and exposed to a mixture of 5 PFAS representing legacy, replacement, and emerging subtypes (i.e., PFOA, PFOS, PFHxS, PFNA, GenX), each at a concentration of 2 mg / L , for 7 wk. Blood was collected longitudinally for cholesterol measurements, and mass spectrometry was used to measure circulating and fecal bile acids. Transcriptomic analysis of ileal samples was performed via RNA sequencing.

RESULTS

After 7 wk of PFAS exposure, average circulating PFAS levels were measured at 21.6, 20.1, 31.2, 23.5, and 1.5 μ g / mL in PFAS-exposed females and 12.9, 9.7, 23, 14.3, and 1.7 μ g / mL in PFAS-exposed males for PFOA, PFOS, PFHxS, PFNA, and GenX, respectively. Total circulating cholesterol levels were higher in PFAS-exposed mice after 7 wk (352 mg / dL vs. 415 mg / dL in female mice and 392 mg / dL vs. 488 mg / dL in male mice exposed to vehicle or PFAS, respectively). Total circulating bile acid levels were higher in PFAS-exposed mice (2,978  pg / μ L vs. 8,496  pg / μ L in female mice and 1,960  pg / μ L vs. 4,452  pg / μ L in male mice exposed to vehicle or PFAS, respectively). In addition, total fecal bile acid levels were lower in PFAS-exposed mice (1,797  ng / mg vs. 682  ng / mg in females and 1,622  ng / mg vs. 670  ng / mg in males exposed to vehicle or PFAS, respectively). In the ileum, expression levels of the apical sodium-dependent bile acid transporter (ASBT) were higher in PFAS-exposed mice.

DISCUSSION

Mice exposed to a PFAS mixture displayed higher circulating cholesterol and bile acids perhaps due to impacts on enterohepatic circulation. This study implicates PFAS-mediated effects at the site of the ileum as a possible critical mediator of increased cardiovascular risk following PFAS exposure. https://doi.org/10.1289/EHP14339.

Lupeol improves bile acid metabolism and metabolic dysfunction-associated steatotic liver disease in mice via FXR signaling pathway and gut-liver axis

Metabolic dysfunction-associated steatotic liver disease (MASLD) has a multifactorial and complex pathogenesis. Notably, the disorder of Bile acid (BA) metabolism and lipid metabolism-induced lipotoxicity are the main risk factors of MASLD. Lupeol, traditional regional medicine from Xinjiang, has a long history of use for its anti-inflammatory, anti-tumor, and immune-modulating properties. Recent research suggests its potential as a therapeutic option for MASLD due to its proposed binding capacity to the nuclear BA receptor, Farnesoid X receptor (FXR), hence could represent a therapeutic option for MASLD. In this study, a natural triterpenoid drug lupeol improved BA metabolism and MASLD in mice through the FXR signaling pathway and the gut-liver axis. Furthermore, lupeol effectively restored gut healthiness and improved intestinal immunity, barrier integrity, and inflammation, as indicated by the reconstructed gut flora. Compared with fenofibrate (Feno), lupeol treatment significantly reduced weight gain, fat deposition, and liver injury, decreased serum total cholesterol (TC) and triglyceride (TG) levels, and alleviated hepatic steatosis and liver inflammation. BA analysis showed that lupeol treatment accelerated BA efflux and decreased uptake of BA by increasing hepatic FXR and bile salt export pump (BSEP) expression. Gut microbiota alterations could be related to enhanced fecal BA excretion in lupeol-treated mice. Therefore, consumption of lupeol may prevent HFD-induced MASLD and BA accumulation, possibly via the FXR signaling pathway and regulating the gut microbiota.

Sodium/bile acid co-transporter inhibitors currently in preclinical or early clinical development for the treatment of primary biliary cholangitis

INTRODUCTION

Pruritus is common and often undertreated in patients with primary biliary cholangitis (PBC). Existing treatments largely have an aging and low-quality evidence base, and studies included only small numbers of patients. More recent data that has added to our understanding of pruritus treatments has often come from clinical trials where itching was a secondary outcome measure in a trial designed primarily to assess disease-modifying agents. This area represents an unmet clinical need in the management of PBC.

AREAS COVERED

In this manuscript, we first summarize the proposed mechanisms for PBC-related pruritus and the current treatment paradigm. We then present an appraisal of the existing pre-clinical and clinical evidence for the use of ileal bile acid transporter inhibitors (IBATis) for this indication in PBC patients.

EXPERT OPINION

Evidence for the efficacy of IBATis is promising but limited by the currently available volume of data. Furthermore, larger clinical trials with long-term data on efficacy, safety and tolerability are needed to confirm the role of using IBATis in clinical practice and their place on the itch treatment ladder. Additional focus should also be given to exploring the disease-modifying potential of IBATis in PBC.

Novel preclinical developments of the primary sclerosing cholangitis treatment landscape

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease associated with inflammation, fibrosis, and destruction of intra- and extrahepatic bile ducts. Despite substantial recent advances in our understanding of PSC, the only proven treatment of PSC is liver transplantation. There is an urgent unmet need to find medical therapies for this disorder.

AREAS COVERED

Multiple drugs are currently under evaluation as therapeutic options for this disease. This article summarizes the literature on the various novel therapeutic options that have been investigated and are currently under development for the treatment of PSC.

EXPERT OPINION

In the next decade, more than one drug will likely be approved for the treatment of the disease, and we will be looking at combination therapies for the optimal management of the disease.

Research progress on the relationship between bile acid metabolism and type 2 diabetes mellitus

Bile acids, which are steroid molecules originating from cholesterol and synthesized in the liver, play a pivotal role in regulating glucose metabolism and maintaining energy balance. Upon release into the intestine alongside bile, they activate various nuclear and membrane receptors, influencing crucial processes. These bile acids have emerged as significant contributors to managing type 2 diabetes mellitus, a complex clinical syndrome primarily driven by insulin resistance. Bile acids substantially lower blood glucose levels through multiple pathways: BA-FXR-SHP, BA-FXR-FGFR15/19, BA-TGR5-GLP-1, and BA-TGR5-cAMP. They also impact blood glucose regulation by influencing intestinal flora, endoplasmic reticulum stress, and bitter taste receptors. Collectively, these regulatory mechanisms enhance insulin sensitivity, stimulate insulin secretion, and boost energy expenditure. This review aims to comprehensively explore the interplay between bile acid metabolism and T2DM, focusing on primary regulatory pathways. By examining the latest advancements in our understanding of these interactions, we aim to illuminate potential therapeutic strategies and identify areas for future research. Additionally, this review critically assesses current research limitations to contribute to the effective management of T2DM.

Safety, tolerability, and efficacy of maralixibat in adults with primary sclerosing cholangitis: Open-label pilot study

BACKGROUND

Primary sclerosing cholangitis (PSC) is frequently associated with pruritus, which significantly impairs quality of life. Maralixibat is a selective ileal bile acid transporter (IBAT) inhibitor that lowers circulating bile acid (BA) levels and reduces pruritus in cholestatic liver diseases. This is the first proof-of-concept study of IBAT inhibition in PSC.

METHODS

This open-label study evaluated the safety and tolerability of maralixibat ≤10 mg/d for 14 weeks in adults with PSC. Measures of pruritus, biomarkers of BA synthesis, cholestasis, and liver function were also assessed.

RESULTS

Of 27 enrolled participants, 85.2% completed treatment. Gastrointestinal treatment-emergent adverse events (TEAEs) occurred in 81.5%, with diarrhea in 51.9%. TEAEs were mostly mild or moderate (63.0%); 1 serious TEAE (cholangitis) was considered treatment related. Mean serum BA (sBA) levels decreased by 16.7% (-14.84 µmol/L; 95% CI, -27.25 to -2.43; p = 0.0043) by week 14/early termination (ET). In participants with baseline sBA levels above normal (n = 18), mean sBA decreased by 40.0% (-22.3 µmol/L, 95% CI, -40.38 to -4.3; p = 0.004) by week 14/ET. Liver enzyme elevations were not significant; however, increases of unknown clinical significance in conjugated bilirubin levels were observed. ItchRO weekly sum scores decreased from baseline to week 14/ET by 8.4% (p = 0.0495), by 12.6% (p = 0.0275) in 18 participants with pruritus at baseline, and by 70% (p = 0.0078) in 8 participants with ItchRO daily average score ≥3 at baseline.

CONCLUSIONS

Maralixibat was associated with reduced sBA levels in adults with PSC. In participants with more severe baseline pruritus, pruritus improved significantly from baseline. TEAEs were mostly gastrointestinal related. These results support further investigation of IBAT inhibitors for adults with PSC-associated pruritus. ClinicalTrials.gov: NCT02061540.

Increased expression of glucagon-like peptide-1 and cystic fibrosis transmembrane conductance regulator in the ileum and colon in mouse treated with metformin

Metformin, an oral medication, is prescribed to patients with type 2 diabetes mellitus. Although the efficacy, safety, and low economic burden of metformin on patients have long been recognized, approximately 5% of the patients treated with this drug develop severe diarrhea and discontinue the treatment. We previously reported that 1,000 mg·kg^-1·day^-1 of metformin induced diarrhea in diabetic obese (db/db) mice and wood creosote (traditional medication for diarrhea) ameliorated the symptoms. In this study, we attempted to elucidate the molecular mechanisms by which metformin induces diarrhea. Cystic fibrosis transmembrane conductance regulator (CFTR) is a key ion (chloride) channel in cyclic adenosine monophosphate (cAMP)-induced diarrhea. Metformin treatment increased bile flow (bile acids and bilirubin) in the ileum of mice. In addition, the treatment was accompanied by an increase in mRNA and protein levels of CFTR in the mucosa of the ileum and colon in both wild-type (C57BL/6J) and db/db mice. Glucagon-like peptide-1 (GLP-1), as well as cholic acid, induces CFTR mRNA expression in human colon carcinoma Caco-2 cells through cAMP signaling. Although wood creosote (10 mg/kg) ameliorated diarrhea symptoms, it did not alter the mRNA levels of Glp-1 or Cftr. Similar to overeating, metformin upregulated GLP-1 and CFTR expression, which may have contributed to diarrhea symptoms in mice. Although we could not identify db/db mouse-specific factors associated with metformin-induced diarrhea, these factors may modulate colon function. Wood creosote may not interact with these factors but ameliorates diarrhea symptoms.

Biological tuners to reshape the bile acid pool for therapeutic purposes in non-alcoholic fatty liver disease

Bile acids synthesized within the hepatocytes are transformed by gut microorganisms and reabsorbed into the portal circulation. During their enterohepatic cycling, bile acids act as signaling molecules by interacting with receptors to regulate pathways involved in many physiological processes. The bile acid pool, composed of a variety of bile acid species, has been shown to be altered in diseases, hence contributing to disease pathogenesis. Thus, understanding the changes in bile acid pool size and composition in pathological processes will help to elaborate effective pharmacological treatments. Five crucial steps along the enterohepatic cycle shape the bile acid pool size and composition, offering five possible targets for therapeutic intervention. In this review, we provide an insight on the strategies to modulate the bile acid pool, and then we discuss the potential benefits in non-alcoholic fatty liver disease.

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

Cholestatic Itch: Our Current Understanding of Pathophysiology and Treatments

Hepatic pruritus is common in liver conditions, including cholestasis and nonalcoholic fatty liver disease. The pruritus can be severe enough to diminish sleep and decrease quality of life. The pathophysiology likely involves many molecules and receptors, including bile acids, bilirubin, lysophosphatidic acid (LPA), endogenous opioids, and serotonin. Recent advances suggest a significant role of Mas-related G protein-coupled receptor X4 (MRGPRX4) and autotaxin/LPA as key players in cholestatic pruritus. Further research is needed to develop increasingly targeted therapies with greater efficacy, especially given that many patients report itch refractory to various treatments. Cholestyramine was the only US FDA-approved drug for cholestatic pruritus until recent approval of ileal bile acid transporter (IBAT) inhibitors for use in the pediatric cholestatic conditions, progressive familial intrahepatic cholestasis and Alagille syndrome. Both medications decrease the bile acid pool. IBAT inhibitors are under investigation for broader use, and targeting LPA receptors and MRGPR4 are additional attractive options.

Bile Acid Sequestrants for Hypercholesterolemia Treatment Using Sustainable Biopolymers: Recent Advances and Future Perspectives

Bile acids, the endogenous steroid nucleus containing signaling molecules, are responsible for the regulation of multiple metabolic processes, including lipoprotein and glucose metabolism to maintain homeostasis. Within our body, they are directly produced from their immediate precursors, cholesterol C (low-density lipoprotein C, LDL-C), through the enzymatic catabolic process mediated by 7-α-hydroxylase (CYP7A1). Bile acid sequestrants (BASs) or amphiphilic resins that are nonabsorbable to the human body (being complex high molecular weight polymers/electrolytes) are one of the classes of drugs used to treat hypercholesterolemia (a high plasma cholesterol level) or dyslipidemia (lipid abnormalities in the body); thus, they have been used clinically for more than 50 years with strong safety profiles as demonstrated by the Lipid Research Council-Cardiovascular Primary Prevention Trial (LRC-CPPT). They reduce plasma LDL-C and can slightly increase high-density lipoprotein C (HDL-C) levels, whereas many of the recent clinical studies have demonstrated that they can reduce glucose levels in patients with type 2 diabetes mellitus (T2DM). However, due to higher daily dosage requirements, lower efficacy in LDL-C reduction, and concomitant drug malabsorption, research to develop an "ideal" BAS from sustainable or natural sources with better LDL-C lowering efficacy and glucose regulations and lower side effects is being pursued. This Review discusses some recent developments and their corresponding efficacies as bile removal or LDL-C reduction of natural biopolymer (polysaccharide)-based compounds.

Contributions of bile acids to gastrointestinal physiology as receptor agonists and modifiers of ion channels

Bile acids (BAs) are known to be important regulators of intestinal motility and epithelial fluid and electrolyte transport. Over the past two decades, significant advances in identifying and characterizing the receptors, transporters, and ion channels targeted by BAs have led to exciting new insights into the molecular mechanisms involved in these processes. Our appreciation of BAs, their receptors, and BA-modulated ion channels as potential targets for the development of new approaches to treat intestinal motility and transport disorders is increasing. In the current review, we aim to summarize recent advances in our knowledge of the different BA receptors and BA-modulated ion channels present in the gastrointestinal system. We discuss how they regulate motility and epithelial transport, their roles in pathogenesis, and their therapeutic potential in a range of gastrointestinal diseases.

Si-Wu-Tang ameliorates fibrotic liver injury via modulating intestinal microbiota and bile acid homeostasis

Background

Fibrotic liver injury is a progressive scarring event, which may permanently affect liver function and progress into devastating end-stage liver diseases due to the absence of effective therapies. Si-Wu-Tang (SWT), a traditional Chinese medicine formula used in clinic to treat gynecological disorders for centuries, has been investigated in recent preliminary findings for its role in alleviating chronic liver diseases. Here we aim to elucidate the therapeutic effects and possible mechanisms of SWT against fibrotic liver injury.

Methods

UHPLC-MS/MS was performed to investigate the chemical characterization of SWT. After intragastrically administered with carbon tetrachloride (CCl₄) every 3 days for 1-week, C57BL/6 mice were orally administered with SWT (5.2, 10.4 and 20.8 g/kg) once daily for 3 weeks along with CCl₄ challenge. Liver function was determined by the measurement of serum biomarkers, hematoxylin and eosin (H&E) and Masson’s trichrome staining. Intestinal inflammatory infiltration and the disruption of intestinal barrier were examined by H&E and E-cadherin immunohistochemical staining. The microbial composition of intestinal content was determined by 16S rRNA sequencing. Serum bile acids (BAs) profiling was analyzed by LC–MS/MS. Simultaneously, the expression of genes of interest was determined by qPCR and western blot.

Results

SWT exhibited remarkable therapeutic effects on CCl₄-induced liver fibrosis, as indicated by improved collagen accumulation in livers, intestinal barrier injury and hepatic and intestinal inflammatory response. Results of 16S rRNA sequencing revealed that SWT treatment strikingly restructured intestinal microbiota in fibrotic mice by increasing the relative abundances of Bacteroides and Lachnoclostridium and decreasing the relative abundances of Alistipes and Rikenellaceae. UHPLC-MS/MS data suggested that SWT altered the composition of BAs in circulation as evidenced by increased unconjugated BAs like cholic acid and chenodeoxycholic acid but decreased conjugated BAs including taurocholic acid and taurodeoxycholic acid, compared to that in CCl₄ mice. Notably, SWT efficiently improved the imbalance of BA homeostasis in livers caused by CCl₄ via activating farnesoid X receptor (FXR)-fibroblast growth factor 15 enterohepatic and FXR-small heterodimer partner hepatic pathways.

Conclusion

SWT decreased inflammatory response, reconstructed gut microbiota-mediated BA homeostasis as well as activated FXR pathways, which eventually protected against CCl₄-induced fibrotic liver injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00524-0.

Gut-restricted apical sodium-dependent bile acid transporter inhibitor attenuates alcohol-induced liver steatosis and injury in mice

BACKGROUND

Recent studies have shown that human and experimental alcohol-related liver disease (ALD) is robustly associated with dysregulation of bile acid homeostasis, which may in turn modulate disease severity. Pharmacological agents targeting bile acid metabolism and signaling may be potential therapeutics for ALD.

METHODS

The potential beneficial effects of a gut-restricted apical sodium-dependent bile acid transporter (ASBT) inhibitor were studied in a chronic-plus-binge ALD mouse model.

RESULTS

Blocking intestinal bile acid reabsorption by the gut-restricted ASBT inhibitor GSK2330672 attenuated hepatic steatosis and liver injury in a chronic-plus-binge ALD mouse model. Alcohol feeding is associated with intestinal bile acid accumulation but paradoxically impaired ileal farnesoid × receptor (FXR) function, and repressed hepatic cholesterol 7α-hydrolase (CYP7A1) expression despite decreased hepatic small heterodimer partner (SHP) and ileal fibroblast growth factor 15 (FGF15) expression. ASBT inhibitor treatment decreased intestinal bile acid accumulation and increased hepatic CYP7A1 expression, but further decreased ileal FXR activity. Alcohol feeding induces serum bile acid concentration that strongly correlates with a liver injury marker. However, alcohol-induced serum bile acid elevation is not due to intrahepatic bile acid accumulation but is strongly and positively associated with hepatic multidrug resistance-associated protein 3 (MRP4) and MRP4 induction but poorly associated with sodium-taurocholate cotransporting peptide (NTCP) expression. ASBT inhibitor treatment decreases serum bile acid concentration without affecting hepatocyte basolateral bile acid uptake and efflux transporters.

CONCLUSION

ASBT inhibitor treatment corrects alcohol-induced bile acid dysregulation and attenuates liver injury in experimental ALD.

Drugs for Non-alcoholic Steatohepatitis (NASH): Quest for the Holy Grail

Nonalcoholic fatty liver disease (NAFLD) is a global epidemic that is likely to become the most common cause of chronic liver disease in the next decade, worldwide. Though numerous drugs have been evaluated in clinical trials, most of them have returned inconclusive results and shown poorly-tolerated adverse effects. None of the drugs have been approved by the Food and Drug Administration for treating biopsy-proven non-alcoholic steatohepatitis (NASH). Vitamin E and pioglitazone have been extensively used in treatment of biopsy-proven nondiabetic NASH patients. Although some amelioration of inflammation has been seen, these drugs did not improve the fibrosis component of NASH. Therefore, dietary modification and weight reduction have remained the cornerstone of treatment of NASH; moreover, they have shown to improve histological activity as well as fibrosis. The search for an ideal drug or 'Holy Grail' within this landscape of possible agents continues, as weight reduction is achieved only in less than 10% of patients. In this current review, we summarize the drugs for NASH which are under investigation, and we provide a critical analysis of their up-to-date results and outcomes.

A Novel Fluorescence-Based Method to Evaluate Ileal Apical Sodium-Dependent Bile Acid Transporter ASBT

This study aimed to demonstrate usefulness of the fluorophore-labeled bile acid derivative, N-(24-[7-(4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole)]amino-3α,7α,12α-trihydroxy-27-nor-5β-cholestan-26-oyl)-2'-aminoethane sulfonate (tauro-nor-THCA-24-DBD) as a substrate of apical sodium-dependent bile acid transporter (ASBT, SLC10A2), which is expressed at distal ileum for reabsorption of bile acids and to find a novel fluorescence-based method to evaluate ASBT activity. In HPLC analysis, chromatogram of tauro-nor-THCA-24-DBD showed double peaks: R- and S-isomers of the compound. When ASBT was expressed in Xenopus laevis oocytes, their uptakes were higher than those by control oocytes, demonstrating both are transported by ASBT. Therefore, results were analyzed separately as peak 1, peak 2 and sum of them. Concentration dependent uptake of tauro-nor-THCA-24-DBD in ASBT-expressing oocytes was saturable with Km 122 μM and Vmax 1.49 pmol/oocyte/30 min for peak 1, 30.7 μM and 1.34 pmol/oocyte/30 min for peak 2, and 40.6 μM and 2.36 pmol/oocyte/30 min for sum, respectively. These uptakes were decreased in the presence of taurocholic acid and in the Na⁺ free condition. Furthermore, in Caco-2 cells, tauro-nor-THCA-24-DBD uptake was also Na⁺-dependent and saturable. Additionally, these uptakes were decreased by elobixibat, a selective ASBT inhibitor. Accordingly, it was concluded that tauro-nor-THCA-24-DBD is a substrate of ASBT and useful to evaluate the intestinal ASBT transport activity.

[The inhibitors of the apical sodium-dependent bile acid transporter (ASBT) as promising drugs]

Inhibition of the apical sodium-dependent bile acid transporter (ASBT, also known as IBAT - ileal bile acid transporter, SLC10A2) leads to disruption of the enterohepatic circulation of bile acids and their excretion with fecal masses. This is accompanied by cholesterol utilization for synthesis of new bile acids. ASBT inhibitors are promising drugs for the treatment of such diseases as non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, type 2 diabetes mellitus, necrotic enterocolitis, chronic constipation, atherosclerosis. To date the most known chemically synthesized inhibitors are: A3309, SHP626, A4250, 264W94, GSK2330672, SC-435. All of them are at different stages of clinical trials, which confirm the high efficacy and good tolerance of these inhibitors. Current trends in this field also include directed chemical synthesis of ASBT inhibitors, as well as their search among substances of plant origin.

Potential of ileal bile acid transporter inhibition as a therapeutic target in Alagille syndrome and progressive familial intrahepatic cholestasis

Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC) are rare, inherited cholestatic liver disorders that manifest in infants and children and are associated with impaired bile flow (ie cholestasis), pruritus and potentially fatal liver disease. There are no effective or approved pharmacologic treatments for these diseases (standard medical treatments are supportive only), and new, noninvasive options would be valuable. Typically, bile acids undergo biliary secretion and intestinal reabsorption (ie enterohepatic circulation). However, in these diseases, disrupted secretion of bile acids leads to their accumulation in the liver, which is thought to underlie pruritus and liver-damaging inflammation. One approach to reducing pathologic bile acid accumulation in the body is surgical biliary diversion, which interrupts the enterohepatic circulation (eg by diverting bile acids to an external stoma). These procedures can normalize serum bile acids, reduce pruritus and liver injury and improve quality of life. A novel, nonsurgical approach to interrupting the enterohepatic circulation is inhibition of the ileal bile acid transporter (IBAT), a key molecule in the enterohepatic circulation that reabsorbs bile acids from the intestine. IBAT inhibition has been shown to reduce serum bile acids and pruritus in trials of paediatric cholestatic liver diseases. This review explores the rationale of inhibition of the IBAT as a therapeutic target, describes IBAT inhibitors in development and summarizes the current data on interrupting the enterohepatic circulation as treatment for cholestatic liver diseases including ALGS and PFIC.

Volixibat in adults with non-alcoholic steatohepatitis: 24-week interim analysis from a randomized, phase II study

BACKGROUND & AIMS

Volixibat is an inhibitor of the apical sodium-dependent bile acid transporter (ASBT) that has been hypothesized to improve non-alcoholic steatohepatitis (NASH) by blocking bile acid reuptake and stimulating hepatic bile acid production. We studied the safety, tolerability and efficacy of volixibat in patients with NASH.

METHODS

In this double-blind, phase II dose-finding study, adults with ≥5% steatosis and NASH without cirrhosis (N = 197) were randomized to receive volixibat (5, 10 or 20 mg) or placebo once daily for 48 weeks. The endpoints of a predefined interim analysis (n = 80), at week 24, were: ≥5% reduction in MRI-proton density fat fraction and ≥20% reduction in serum alanine aminotransferase levels. The primary endpoint was a ≥2-point reduction in non-alcoholic fatty liver disease activity score without worsening fibrosis at week 48.

RESULTS

Volixibat did not meet either interim endpoint; the study was terminated owing to lack of efficacy. In participants receiving any volixibat dose, mean serum 7-alpha-hydroxy-4-cholesten-3-one (C4; a biomarker of bile acid synthesis) increased from baseline to week 24 (+38.5 ng/ml [SD 53.18]), with concomitant decreases in serum total cholesterol (-14.5 mg/dl [SD 28.32]) and low-density lipoprotein cholesterol (-16.1 mg/dl [SD 25.31]). These changes were generally dose-dependent. On histological analysis, a greater proportion of participants receiving placebo (38.5%, n = 5/13) than volixibat (30.0%, n = 9/30) met the primary endpoint. Treatment-emergent adverse events (TEAEs) were mainly mild or moderate. No serious TEAEs were related to volixibat. Diarrhoea was the most common TEAE overall and the most common TEAE leading to discontinuation.

CONCLUSIONS

Increased serum C4 and decreased serum cholesterol levels provide evidence of target engagement. However, inhibition of ASBT by volixibat did not elicit a liver-related therapeutic benefit in adults with NASH.

LAY SUMMARY

A medicine called volixibat has previously been shown to reduce cholesterol levels in the blood. This study investigated whether volixibat could reduce the amount of fat in the liver and reduce liver injury in adults with an advanced form of non-alcoholic fatty liver disease. Volixibat did not reduce the amount of fat in the liver, nor did it have any other beneficial effect on liver injury. Participants in the study generally tolerated the side effects of volixibat and, as in previous studies, the main side effect was diarrhoea. These results show that volixibat is not an effective treatment for people with fatty liver disease.

CLINICAL TRIAL IDENTIFIER

NCT02787304.

Apical sodium-dependent bile acid transporter, drug target for bile acid related diseases and delivery target for prodrugs: Current and future challenges

Apical Sodium-dependent Bile Acid Transporter (ASBT) actively reabsorbs bile acids (BAs) from the gut lumen. This process is a critical step in the enterohepatic circulation (EHC) of BAs and plays important roles in the homeostasis of BAs in the body. Therefore, ASBT is considered a favorite target for intervention to regulate the levels of BAs, cholesterol, lipid and glucose etc. In addition, ASBT is also a popular delivery target for developing prodrugs, due to its intestinal localization, high expression and high uptake capacity. In the past ten years, ASBT has been the focus by both academia and pharmaceutical industry as research targets not only for BA-related diseases but also for prodrug delivery. Numerous studies have been published and many candidate ASBT inhibitors are being developed. Here we review and summarize the current states of ASBT research with a focus on the therapeutic applications of ASBT as a target for therapy as well as a delivery target for prodrugs. The current and future challenges in ASBT research and outlook of drug developments are discussed.

An FGF15/19-TFEB regulatory loop controls hepatic cholesterol and bile acid homeostasis

Bile acid synthesis plays a key role in regulating whole body cholesterol homeostasis. Transcriptional factor EB (TFEB) is a nutrient and stress-sensing transcriptional factor that promotes lysosomal biogenesis. Here we report a role of TFEB in regulating hepatic bile acid synthesis. We show that TFEB induces cholesterol 7α-hydroxylase (CYP7A1) in human hepatocytes and mouse livers and prevents hepatic cholesterol accumulation and hypercholesterolemia in Western diet-fed mice. Furthermore, we find that cholesterol-induced lysosomal stress feed-forward activates TFEB via promoting TFEB nuclear translocation, while bile acid-induced fibroblast growth factor 19 (FGF19), acting via mTOR/ERK signaling and TFEB phosphorylation, feedback inhibits TFEB nuclear translocation in hepatocytes. Consistently, blocking intestinal bile acid uptake by an apical sodium-bile acid transporter (ASBT) inhibitor decreases ileal FGF15, enhances hepatic TFEB nuclear localization and improves cholesterol homeostasis in Western diet-fed mice. This study has identified a TFEB-mediated gut-liver signaling axis that regulates hepatic cholesterol and bile acid homeostasis.

S-acylation modulates the function of the apical sodium-dependent bile acid transporter in human cells

The ileal apical sodium-dependent bile acid transporter (ASBT) is crucial for the enterohepatic circulation of bile acids. ASBT function is rapidly regulated by several posttranslational modifications. One reversible posttranslational modification is S-acylation, involving the covalent attachment of fatty acids to cysteine residues in proteins. However, whether S-acylation affects ASBT function and membrane expression has not been determined. Using the acyl resin-assisted capture method, we found that the majority of ASBT (∼80%) was S-acylated in ileal brush border membrane vesicles from human organ donors, as well as in HEK293 cells stably transfected with ASBT (2BT cells). Metabolic labeling with alkyne-palmitic acid (100 μm for 15 h) also showed that ASBT is S-acylated in 2BT cells. Incubation with the acyltransferase inhibitor 2-bromopalmitate (25 μm for 15 h) significantly reduced ASBT S-acylation, function, and levels on the plasma membrane. Treatment of 2BT cells with saturated palmitic acid (100 μm for 15 h) increased ASBT function, whereas treatment with unsaturated oleic acid significantly reduced ASBT function. Metabolic labeling with alkyne-oleic acid (100 μm for 15 h) revealed that oleic acid attaches to ASBT, suggesting that unsaturated fatty acids may decrease ASBT's function via a direct covalent interaction with ASBT. We also identified Cys-314 as a potential S-acylation site. In conclusion, these results provide evidence that S-acylation is involved in the modulation of ASBT function. These findings underscore the potential for unsaturated fatty acids to reduce ASBT function, which may be useful in disorders in which bile acid toxicity is implicated.

Intestinal microbiome and NAFLD: molecular insights and therapeutic perspectives

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of dysregulated lipid and glucose metabolism, which is often associated with obesity, dyslipidemia and insulin resistance. In view of the high morbidity and health risks of NAFLD, the lack of effective cure has drawn great attention. In recent years, a line of evidence has suggested a close linkage between the intestine and liver diseases such as NAFLD. We summarized the composition and characteristics of intestinal microbes and reviewed molecular insights into the intestinal microbiome in development and progression of NAFLD. Intestinal microbes mainly include bacteria, archaea, viruses and fungi, and the crosstalk between non-bacterial intestinal microbes and human liver diseases should be paid more attention. Intestinal microbiota imbalance may not only increase the intestinal permeability to gut microbes but also lead to liver exposure to harmful substances that promote hepatic lipogenesis and fibrosis. Furthermore, we focused on reviewing the latest "gut-liver axis"-targeting treatment, including the application of antibiotics, probiotics, prebiotics, synbiotics, farnesoid X receptor agonists, bile acid sequestrants, gut-derived hormones, adsorbents and fecal microbiota transplantation for NAFLD. In this review, we also discussed the potential mechanisms of "gut-liver axis" manipulation and efficacy of these therapeutic strategies for NAFLD treatment.

Intestinal Absorption of Bile Acids in Health and Disease

The intestinal reclamation of bile acids is crucial for the maintenance of their enterohepatic circulation. The majority of bile acids are actively absorbed via specific transport proteins that are highly expressed in the distal ileum. The uptake of bile acids by intestinal epithelial cells modulates the activation of cytosolic and membrane receptors such as the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (GPBAR1), which has a profound effect on hepatic synthesis of bile acids as well as glucose and lipid metabolism. Extensive research has focused on delineating the processes of bile acid absorption and determining the contribution of dysregulated ileal signaling in the development of intestinal and hepatic disorders. For example, a decrease in the levels of the bile acid-induced ileal hormone FGF15/19 is implicated in bile acid-induced diarrhea (BAD). Conversely, the increase in bile acid absorption with subsequent overload of bile acids could be involved in the pathophysiology of liver and metabolic disorders such as fatty liver diseases and type 2 diabetes mellitus. This review article will attempt to provide a comprehensive overview of the mechanisms involved in the intestinal handling of bile acids, the pathological implications of disrupted intestinal bile acid homeostasis, and the potential therapeutic targets for the treatment of bile acid-related disorders. Published 2020. Compr Physiol 10:21-56, 2020.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Apical sodium-dependent bile acid transporter inhibition with volixibat improves metabolic aspects and components of non-alcoholic steatohepatitis in Ldlr-/-.Leiden mice

Interruption of bile acid recirculation through inhibition of the apical sodium-dependent bile acid transporter (ASBT) is a promising strategy to alleviate hepatic cholesterol accumulation in non-alcoholic steatohepatitis (NASH), and improve the metabolic aspects of the disease. Potential disease-attenuating effects of the ASBT inhibitor volixibat (5, 15, and 30 mg/kg) were investigated in high-fat diet (HFD)-fed Ldlr-/-.Leiden mice over 24 weeks. Plasma and fecal bile acid levels, plasma insulin, lipids, and liver enzymes were monitored. Final analyses included liver histology, intrahepatic lipids, mesenteric white adipose tissue mass, and liver gene profiling. Consistent with its mechanism of action, volixibat significantly increased the total amount of bile acid in feces. At the highest dose, volixibat significantly attenuated the HFD-induced increase in hepatocyte hypertrophy, hepatic triglyceride and cholesteryl ester levels, and mesenteric white adipose tissue deposition. Non-alcoholic fatty liver disease activity score (NAS) was significantly lower in volixibat-treated mice than in the HFD controls. Gene profiling showed that volixibat reversed the inhibitory effect of the HFD on metabolic master regulators, including peroxisome proliferator-activated receptor-γ coactivator-1β, insulin receptor, and sterol regulatory element-binding transcription factor 2. Volixibat may have beneficial effects on physiological and metabolic aspects of NASH pathophysiology.

Recent advances in managing/understanding the metabolic syndrome

The metabolic syndrome (MetS) concept gathers in a single entity a set of metabolic abnormalities that have in common a close relationship with ectopic deposit of lipids, insulin resistance, and chronic low-grade inflammation. It is a valuable teaching tool to help health professionals to understand and integrate the consequences of lipotoxicity and the adverse metabolic consequences of insulin resistance. Also, it is useful to identify subjects with a high risk for having incident type 2 diabetes. Systems biology studies have gained a prominent role in understanding the interaction between adipose tissue dysfunction, insulin action, and the MetS traits and co-morbidities (that is, non-alcoholic steatohepatitis, or NASH). This approach may allow the identification of new therapeutic targets (that is, de novo lipogenesis inhibitors for NASH). Treatment targets on MetS are the adoption of a healthy lifestyle, weight loss, and the control of the co-morbidities (hyperglycemia, dyslipidemia, arterial hypertension, among others). The long-term goals are the prevention of type 2 diabetes, cardiovascular events, and other MetS-related outcomes. In the last few decades, new drugs derived from the identification of innovative treatment targets have come on the market. These drugs have positive effects on more than one MetS component (that is, hyperglycemia and weight control). New potential treatment targets are under study.

Developments in bile salt based therapies: A critical overview

Bile acids, amphipathic molecules known for their facilitating role in fat absorption, are also recognized as signalling molecules acting via nuclear and membrane receptors. Of the bile acid-activated receptors, the Farnesoid X Receptor (FXR) and the G protein-coupled bile acid receptor-1 (Gpbar1 or TGR5) have been studied most extensively. Bile acid signaling is critical in the regulation of bile acid metabolism itself, but it also plays a significant role in glucose, lipid and energy metabolism. Activation of FXR and TGR5 leads to reduced hepatic bile salt load, improved insulin sensitivity and glucose regulation, increased energy expenditure, and anti-inflammatory effects. These beneficial effects render bile acid signaling an interesting therapeutic target for the treatment of diseases such as cholestasis, non-alcoholic fatty liver disease, and diabetes. Here, we summarize recent findings on bile acid signaling and discuss potential and current limitations of bile acid receptor agonist and modulators of bile acid transport as future therapeutics for a wide-spectrum of diseases.

Ileal Bile Acid Transporter Inhibition for the Treatment of Chronic Constipation, Cholestatic Pruritus, and NASH

Bile acids are synthesized from cholesterol in the liver, excreted with bile into the duodenum, almost completely taken up again in the distal ileum and finally returned to the liver with portal blood in a process termed enterohepatic circulation. Bile acid synthesis, excretion, and reuptake are tightly regulated. The apical sodium-dependent bile acid transporter [ASBT; also known as ileal bile acid transporter (IBAT) and SLC10A2] is pivotal for the almost complete reabsorption of conjugated bile acids in the ileum. Dysfunctional IBAT may be the cause of bile acid diarrhea. Pharmacological IBAT inhibition results in an increased bile acid load in the colon and subsequently a lower bile acid pool, which is associated with improved liver histology in animal models of cholestatic liver disease and non-alcoholic steatohepatitis (NASH). In humans, IBAT inhibitors have been tested in clinical trials with widely different indications: in patients with idiopathic chronic constipation, an increased number of bowel movements was observed. In adult and pediatric cholestatic liver diseases with pruritus, various IBAT inhibitors showed potential to improve itching. Adverse events of IBAT inhibitors, based on their mode of action, are abdominal pain and diarrhea which might patients to withdraw from study medications. So far, no data are available of a study of IBAT inhibitors in patients with NASH. In this review we summarize the preclinical and most recent clinical studies with various IBAT inhibitors and discuss the difficulties that should be addressed in future studies.

Future trends in the treatment of non-alcoholic steatohepatitis

With an estimated prevalence of ≈25% in Western and Asian countries, non alcoholic fatty liver disease (NAFLD), caused by chronic excessive caloric intake, is the emerging as the most prevalent liver disorder worldwide. NAFLD exists in two clinical entities, non-alcoholic fatty liver disease (NAFL), a relative benign disease that carry on minimal risk of liver-related morbidity but significant risk of cardiovascular complications, and non-alcoholic steatohepatitis (NASH), a progressive liver disorder with a significant risk for development of liver-related morbidities and mortality. While, liver injury in NASH is contributed by lipid overload in hepatocytes, lipotoxicity, the main determinant of disease progression is an inflammation-driven fibrotic response. Here, we review the landscape of emerging pharmacological interventions in the treatment of NAFL and NASH. A consensus exists that, while treating the liver component of NASH requires development of novel pharmacological approaches, the future therapy of NASH needs to be tailored to the single patient and most likely will be a combination of agents acting on specific pathogenic mechanisms at different disease stage.

Bile acid regulation: A novel therapeutic strategy in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive fat deposition in the liver in the absence of significant alcohol consumption. Dysregulated bile acid (BA) metabolism is an important indicator in the pathology of NAFLD, which could progress into more severe forms of liver injury. Lipid metabolism, immune environment and intestinal bacteria are all affected by dysregulated BA metabolism directly, but the mechanisms remain unclear. Several drug candidates that target BA metabolism, either used alone or in combination with other agents, are currently under development for treatment of NAFLD. Here, we summarize the relationship of dysregulated BA metabolism and NAFLD, discuss the effects and mechanisms of dysregulated BAs-induced lipid metabolism disorder. Challenges in developing novel treatments are also discussed.

A randomised, double-blind, placebo-controlled phase 1 study of the safety, tolerability and pharmacodynamics of volixibat in overweight and obese but otherwise healthy adults: implications for treatment of non-alcoholic steatohepatitis

Background

Accumulation of toxic free cholesterol in hepatocytes may cause hepatic inflammation and fibrosis. Volixibat inhibits bile acid reuptake via the apical sodium bile acid transporter located on the luminal surface of the ileum. The resulting increase in bile acid synthesis from cholesterol could be beneficial in patients with non-alcoholic steatohepatitis. This adaptive dose-finding study investigated the safety, tolerability, pharmacodynamics, and pharmacokinetics of volixibat.

Methods

Overweight and obese adults were randomised 3:1 to double-blind volixibat or placebo, respectively, for 12 days. Volixibat was initiated at a once-daily dose of 20 mg, 40 mg or 80 mg. Based on the assessment of predefined safety events, volixibat dosing was either escalated or reduced. Other dose regimens (titrations and twice-daily dosing) were also evaluated. Assessments included safety, tolerability, stool hardness, faecal bile acid (FBA) excretion, and serum levels of 7α-hydroxy-4-cholesten-3-one (C4) and lipids.

Results

All 84 randomised participants (volixibat, 63; placebo, 21) completed the study, with no serious adverse events at doses of up to 80 mg per day (maximum assessed dose). The median number of daily bowel evacuations increased from 1 (range 0–4) to 2 (0–8) during volixibat treatment, and stool was looser with volixibat than placebo. Volixibat was minimally absorbed; serum levels were rarely quantifiable at any dose or sampling time point, thereby precluding pharmacokinetic analyses. Mean daily FBA excretion was 930.61 μmol (standard deviation [SD] 468.965) with volixibat and 224.75 μmol (195.403) with placebo; effects were maximal at volixibat doses ≥20 mg/day. Mean serum C4 concentrations at day 12 were 98.767 ng/mL (standard deviation, 61.5841) with volixibat and 16.497 ng/mL (12.9150) with placebo. Total and low-density lipoprotein cholesterol levels decreased in the volixibat group, with median changes of − 0.70 mmol/L (range − 2.8 to 0.4) and − 0.6990 mmol/L (− 3.341 to 0.570), respectively.

Conclusions

This study indicates that maximal inhibition of bile acid reabsorption, as assessed by FBA excretion, occurs at volixibat doses of ≥20 mg/day in obese and overweight adults, without appreciable change in gastrointestinal tolerability. These findings guided dose selection for an ongoing phase 2 study in patients with non-alcoholic steatohepatitis.

Trial registration

ClinicalTrials.gov identifier: NCT02287779 (registration first received 6 November 2014).

Electronic supplementary material

The online version of this article (10.1186/s40360-018-0200-y) contains supplementary material, which is available to authorized users.