Nuclear receptors as drug targets in cholestatic liver diseases

Treatment in primary biliary cholangitis: Beyond ursodeoxycholic acid

Primary biliary cholangitis (PBC) is a rare cholestatic immune-mediated liver disease. The clinical course varies from mild to severe, with a substantial group of patients developing cirrhosis within a decade. These patients are at risk of hepatocellular carcinoma, decompensation and liver failure. First line Ursodeoxycholic acid (UDCA) treatment improves the cholestatic surrogate markers, and was recently associated with a favorable survival free of liver transplantation, even in case of an incomplete biochemical response. However, despite adequate UDCA therapy, patients remain at risk of liver disease progression. Therefore, on-treatment multifactor-based risk stratification is necessary to identify patients in need of additional therapy. This requires a personalized approach; especially as recent studies suggest that complete biochemical normalization as most stringent response criterion might be preferred in selected patients to optimize their outcome. Today, stricter biochemical goals might actually be reachable with the addition of farnesoid X receptor or peroxisome proliferator-activated receptor agonists, or, in highly-selected cases, use of corticosteroids. Randomized controlled trials showed improvements in the key biochemical surrogate markers with the addition of these drugs, which have also been associated with improved clinical outcome. Considering this evolving PBC landscape, with more versatile treatment options and treatment goals, this review recapitulates the recent insight in UDCA therapy, the selection of patients with a residual risk of liver disease progression and the results of the currently available second line treatment options.

The role of peroxisome proliferator-activated receptors in the regulation of bile acid metabolism

Bile acids are synthesized from cholesterol in the liver. Dysregulation of bile acid homeostasis, characterized by excessive accumulation in the liver, gallbladder and blood, can lead to hepatocellular damage and the development of cholestatic liver disease. Nuclear receptors play a crucial role in the control of bile acid metabolism by efficiently regulating bile acid synthesis and transport in the liver. Among these receptors, peroxisome proliferator-activated receptor (PPAR), a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily, controls the expression of genes involved in adipogenesis, lipid metabolism, inflammation and glucose homeostasis and has emerged as a potential therapeutic target for the treatment of the metabolic syndrome in the past two decades. Emerging evidence suggests that PPAR activation holds promise as a therapeutic target for cholestatic liver disease, as it affects both bile acid production and transport. This review provides a comprehensive overview of recent advances in elucidating the role of PPAR in the regulation of bile acid metabolism, highlighting the current position of PPAR agonists in the treatment of primary biliary cholangitis. By summarizing the specific regulatory effects of PPAR on bile acids, this review contributes to the exploration of novel therapeutic strategies for cholestatic liver diseases.

Discovery of the First Subnanomolar PPARα/δ Dual Agonist for the Treatment of Cholestatic Liver Diseases

Peroxisome proliferator-activator receptors α/δ (PPARα/δ) are considered as potential drug targets for cholestatic liver diseases (CLD) via ameliorating hepatic cholestasis, inflammation, and fibrosis. In this work, we developed a series of hydantoin derivatives as potent PPARα/δ dual agonists. Representative compound V1 exhibited PPARα/δ dual agonistic activity at the subnanomolar level (PPARα EC₅₀ = 0.7 nM; PPARδ EC₅₀ = 0.4 nM) and showed excellent selectivity over other related nuclear receptors. The crystal structure revealed the binding mode of V1 and PPARδ at 2.1 Å resolution. Importantly, V1 demonstrated excellent pharmacokinetic (PK) properties and a good safety profile. Notably, V1 showed potent anti-CLD and antifibrotic effects in preclinical models at very low doses (0.03 and 0.1 mg/kg). Collectively, this work provides a promising drug candidate for treating CLD and other hepatic fibrosis diseases.

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.

Advances in understanding of biliary atresia pathogenesis and progression - a riddle wrapped in a mystery inside an enigma

INTRODUCTION

Biliary atresia is a potentially fatal condition of the bile ducts - both intra- and extrahepatic, for which we have no cure. Though principally a cholestatic condition, much of its pathology stems from its tendency to aggressively induce liver fibrosis and ultimately cirrhosis, only partially restrained by the portoenterostomy.

AREAS COVERED

This review is based on the current literature exploring the heterogeneous nature of biliary atresia. Thus, there are various phenotypes or variants of biliary atresia, each potentially with different etiological backgrounds caused by a number of hypothetical pathological mechanisms thought to be important in the genesis of the condition. Search methodology: the review (Oct. - Nov. 2022) is based on a search of PubMed (NLM) using main keyword 'biliary atresia' with supplementary searches using 'fibrosis'; 'inflammation'; 'BASM'; 'genetics'; 'surgery'; 'experimental'; 'etiology'; 'virology'; 'cases'; and 'syndromes.'

EXPERT OPINION

Future developments will be made on matching clinical variants with a more distinct pathophysiological discrimination and those pathways linking the initial cholestatic phase of biliary atresia to the early stages of fibrosis.

Cholestasis: exploring the triangular relationship of gut microbiota-bile acid-cholestasis and the potential probiotic strategies

Cholestasis is a condition characterized by the abnormal production or excretion of bile, and it can be induced by a variety of causes, the factors of which are extremely complex. Although great progress has been made in understanding cholestasis pathogenesis, the specific mechanisms remain unclear. Therefore, it is important to understand and distinguish cholestasis from different etiologies, which will also provide indispensable theoretical support for the development of corresponding therapeutic drugs. At present, the treatment of cholestasis mainly involves several bile acids (BAs) and their derivatives, most of which are in the clinical stage of development. Multiple lines of evidence indicate that ecological disorders of the gut microbiota are strongly related to the occurrence of cholestasis, in which BAs also play a pivotal role. Recent studies indicate that probiotics seem to have certain effects on cholestasis, but further confirmation from clinical trials is required. This paper reviews the etiology of and therapeutic strategies for cholestasis; summarizes the similarities and differences in inducement, symptoms, and mechanisms of related diseases; and provides information about the latest pharmacological therapies currently available and those under research for cholestasis. We also reviewed the highly intertwined relationship between gut microbiota-BA-cholestasis, revealing the potential role and possible mechanism of probiotics in the treatment of cholestasis.

The Farnesoid X Receptor as a Master Regulator of Hepatotoxicity

The nuclear receptor farnesoid X receptor (FXR, NR1H4) is a bile acid (BA) sensor that links the enterohepatic circuit that regulates BA metabolism and elimination to systemic lipid homeostasis. Furthermore, FXR represents a real guardian of the hepatic function, preserving, in a multifactorial fashion, the integrity and function of hepatocytes from chronic and acute insults. This review summarizes how FXR modulates the expression of pathway-specific as well as polyspecific transporters and enzymes, thereby acting at the interface of BA, lipid and drug metabolism, and influencing the onset and progression of hepatotoxicity of varying etiopathogeneses. Furthermore, this review article provides an overview of the advances and the clinical development of FXR agonists in the treatment of liver diseases.

Novel Therapies in Primary Biliary Cholangitis: What Is in the Pipeline?

Primary biliary cholangitis is a chronic autoimmune disease characterized by inflammation and the progressive destruction of small intrahepatic bile ducts. Current first-line treatment includes ursodeoxycholic acid; however, a significant number of patients have an inadequate response to therapy. These patients are at risk of liver failure requiring liver transplantation and experience a poor quality of life due to refractory symptoms. This manuscript aims to shed light on the current and prospective treatment options that may slow disease progression and improve these patients' symptoms.

miRNA and miRNA target genes in intervention effect of Zhuyu pill on cholestatic rat model

ETHNOPHARMACOLOGICAL RELEVANCE

Zhuyu pill (ZYP), an effective prescription of traditional Chinese medicine, is composed of Coptis chinensis Franch. and Tetradium ruticarpum (A. Jussieu) T. G. Hartley and has shown potential anticholestatic effects. However, its mechanism of action in treating cholestasis remains unclear. Since post-transcriptional control of mRNA by micro-RNAs (miRNAs) represents an important mechanism of gene regulation, it is promising to explore this in relation to ZYP and cholestasis.

AIM OF THE STUDY

To confirm the anticholestatic effect of ZYP and to explore its potential biological mechanism.

MATERIALS AND METHODS

In this study, a cholestasis rat model was induced by α-naphthyl-isothiocyanate (ANIT, 50 mg/kg) and treated with ZYP (low dose: 0.6 g/kg, high dose: 1.2 g/kg). Serum biochemistry indices and liver histopathology were used to evaluate the model and efficacy, and miRNA sequencing was used to measure differences in miRNA expression in the liver between the control, model, low-dose ZYP, and high-dose ZYP groups. To verify the accuracy of sequencing results and explore the potential anti-cholestasis mechanism of ZYP, RT-PCR was used to identify differentially expressed miRNAs and their target genes.

RESULTS

Both high- and low-dose ZYP exhibited significant anticholestatic effects, with the high-dose showing better effects than low-dose ZYP. Additionally, four differentially expressed miRNAs, rno-miR-147, rno-miR-20b-5p, rno-miR-29b-3p, and rno-miR-3586-3p, were found to be upregulated in cholestasis and downregulated after ZYP intervention. Eight target genes of the above miRNAs, including ABCG8, CLOCK, PLEC, SLC4A2, NEB, ADAMTS12, TTN and FAM174B were inhibited in cholestatic rats, exhibiting up-regulated expression tendencies after ZYP intervention, and the expression tendencies were significant negatively correlated with serum biochemical indices.

CONCLUSIONS

ZYP can significantly reduce liver biochemical indices and improve liver tissue damage in cholestasis rats through the regulation of miRNA expression in the liver, producing a positive regulatory effect on bile excretion-related genes.

Metabolomic Analysis Reveals the Therapeutic Effects of MBT1805, a Novel Pan-Peroxisome Proliferator-Activated Receptor Agonist, on α-Naphthylisothiocyanate-Induced Cholestasis in Mice

Background and Aims: Therapeutic drugs that are used to treat cholestatic liver disease are limited; however, the results of clinical trials on primary biliary cholangitis treatment targeting peroxisome proliferator-activated receptors (PPARs) are encouraging. In this study, we aimed to identify the effects of MBT1805, a novel balanced PPARα/γ/δ agonist, on cholestasis induced by α-naphthylisothiocyanate (ANIT) and elucidate the underlying mechanisms through untargeted and bile acid-targeted metabolomic analysis.

Methods: Levels of serum biochemical indicators (transaminase, aspartate transaminase, alkaline phosphatase, and total bilirubin) and liver histopathology were analyzed to evaluate the therapeutic effects of MBT1805 on ANIT-induced cholestasis in C57BL/6 mice. Untargeted and bile acid-targeted metabolomic analysis of liver tissues was performed using ultrahigh-performance liquid chromatography-triple quadrupole mass spectrometry (UPLC-MC/MC). qRT-PCR and Western blot analysis were carried out to measure the expression of key enzymes and transporters regulating bile acid synthesis, biotransformation, and transport.

Results: MBT1805 significantly improved abnormal levels of liver biochemical indicators and gallbladder enlargement induced by ANIT. Histopathological analysis showed that MBT1805 effectively relieved ANIT-induced necrosis, vacuolation, and inflammatory infiltration. Untargeted metabolomic analysis identified 27 metabolites that were involved in the primary biliary acid biosynthesis pathway. In addition, bile acid-targeted metabolomics showed that MBT1805 could alleviate the abnormal bile acid content and composition induced by ANIT. Furthermore, qRT-PCR and Western blot results confirmed that MBT1805 could effectively regulate bile acid synthesis, biotransformation, and transport which helps relieve cholestasis.

Conclusions: MBT1805 is a potential candidate drug for cholestasis, with a balanced PPARα/γ/δ activation effect.

Predicting Target Genes of San-Huang-Chai-Zhu Formula in Treating ANIT-Induced Acute Intrahepatic Cholestasis Rat Model via Bioinformatics Analysis Combined with Experimental Validation

Background

San-Huang-Chai-Zhu formula (SHCZF) has been used to improve cholestasis for many years. This study aims to predict the possible gene targets of SHCZF in treating acute intrahepatic cholestasis (AIC) in rats.

Materials and Methods

Eighteen SD rats were randomly assigned to the normal group, ANIT group, and ANIT + SHCZF group. Alpha-naphthylisothiocyanate (ANIT) was used to induce AIC. Serum biochemical indexes were detected in each group. After treatment, the livers were collected and used to extract RNA. The library was constructed by TruSeq RNA, sequenced by Illumina, and analyzed by various bioinformatics methods. qRT-PCR was used to verify the target genes related to the efficacy of SHCZF.

Results

Serum ALT, AST, ALP, and TBIL were significantly higher in the ANIT group than in the normal group. Serum ALT and AST levels in the ANIT + SHCZF group were substantially lower than those in the ANIT group. A total of 354 intersected genes were screened by expression level correlation and PCA analysis, GO and KEGG pathway enrichment analysis, and WGCNA and STEM analysis. Then, 4 overlapping genes were found by pathway/BP/gene network construction. SHCZF reversed the downregulation of expression of CYP4A1 and HACL1 and the upregulation of expression of DBI and F11R induced by ANIT. In addition, the qRT-PCR result showed that mRNA expression of CYP4A1, HACL1, and F11R genes in the liver was consistent with the prediction result of bioinformatics analysis.

Conclusion

CYP4A1, HACL1, and F11R are genes related to the occurrence of ANIT-induced AIC in rats and may be considered as targets of SHCZF for the treatment of AIC.

Feedback Signaling between Cholangiopathies, Ductular Reaction, and Non-Alcoholic Fatty Liver Disease

Fatty liver diseases, such as non-alcoholic fatty liver disease (NAFLD), are global health disparities, particularly in the United States, as a result of cultural eating habits and lifestyle. Pathological studies on NAFLD have been mostly focused on hepatocytes and other inflammatory cell types; however, the impact of other biliary epithelial cells (i.e., cholangiocytes) in the promotion of NAFLD is growing. This review article will discuss how cholestatic injury and cholangiocyte activity/ductular reaction influence NAFLD progression. Furthermore, this review will provide informative details regarding the fundamental properties of cholangiocytes and bile acid signaling that can influence NAFLD. Lastly, studies relating to the pathogenesis of NAFLD, cholangiopathies, and ductular reaction will be analyzed to help gain insight for potential therapies.

The Role of Vitamin K in Cholestatic Liver Disease

Vitamin K (VK) is a ligand of the pregnane X receptor (PXR), which plays a critical role in the detoxification of xenobiotics and metabolism of bile acids. VK₁ may reduce the risk of death in patients with chronic liver failure. VK deficiency is associated with intrahepatic cholestasis, and is already being used as a drug for cholestasis-induced liver fibrosis in China. In Japan, to treat osteoporosis in patients with primary biliary cholangitis, VK₂ formulations are prescribed, along with vitamin D₃. Animal studies have revealed that after bile duct ligation-induced cholestasis, PXR knockout mice manifested more hepatic damage than wild-type mice. Ligand-mediated activation of PXR improves biochemical parameters. Rifampicin is a well-known human PXR ligand that has been used to treat intractable pruritus in severe cholestasis. In addition to its anti-cholestatic properties, PXR has anti-fibrotic and anti-inflammatory effects. However, because of the scarcity of animal studies, the mechanism of the effect of VK on cholestasis-related liver disease has not yet been revealed. Moreover, the application of VK in cholestasis-related diseases is controversial. Considering this background, the present review focuses on the effect of VK in cholestasis-related diseases, emphasizing its function as a modulator of PXR.

Yes-associated protein regulates the hepatoprotective effect of vitamin D receptor activation through promoting adaptive bile duct remodeling in cholestatic mice

Mounting clinical evidence has revealed that the vitamin D receptor (VDR) is associated with cholestatic liver injury, although the functions of VDR in this condition remain largely unexplored. Here, we investigated the effects of VDR activation on bile duct ligation (BDL) mice, and the underlying mechanisms were further investigated. A low-calcemic VDR agonist, paricalcitol (PAL, 200 ng/kg), was intraperitoneally injected into BDL mice every other day for 5 days or 28 days. Liver histology, liver function indicators, cholangiocyte proliferation, fibrosis scores, and inflammation were evaluated. Mice treated with PAL were rescued from the decreased survival rate induced by BDL and liver damage was reduced. Mechanistically, PAL promoted cholangiocyte proliferation, which was likely conducive to proliferating bile duct maturation and increased branching of bile ducts. PAL treatment also increased the expression of Yes-associated protein (YAP) and its target protein epithelial cell adhesion molecule (EpCam) and decreased the level of inactive cytoplasmic phosphorylated YAP. YAP knockdown abrogated PAL-induced primary bile duct epithelial cell proliferation, confirmed with YAP inhibitor administration. In addition, BDL-induced liver fibrosis and inflammatory cell infiltration were reduced by PAL treatment at both day 5 and day 28 post-BDL. In conclusion, VDR activation mitigates cholestatic liver injury by promoting adaptive bile duct remodeling through cholangiocytic YAP upregulation. Because PAL is an approved clinical drug, it may be useful for treatment of cholestatic liver disease. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

iTRAQ-based quantitative proteomics analysis of the hepatoprotective effect of melatonin on ANIT-induced cholestasis in rats

The therapeutic effects of melatonin on cholestatic liver injury have received widespread attention recently. The aim of the present study was to investigate the mechanisms of the anti-cholestatic effects of melatonin against α-naphthyl isothiocyanate (ANIT)-induced liver injury in rats and to screen for potential biomarkers of cholestasis through isobaric tags for relative and absolute quantitation (iTRAQ) proteomics. Rats orally received melatonin (100 mg/kg body weight) or an equivalent volume of 0.25% carboxymethyl cellulose sodium salt 12 h after intraperitoneal injection of ANIT (75 mg/kg) and were subsequently sacrificed at 36 h after injection. Liver biochemical indices were determined and liver tissue samples were stained using hematoxylin-eosin staining, followed by iTRAQ quantitative proteomics to identify potential underlying therapeutic mechanisms and biomarkers. The results suggested that the expression levels of alanine transaminase, aspartate aminotransferase, total bilirubin and direct bilirubin were reduced in the rats treated with melatonin. Histopathological observation indicated that melatonin was effective in the treatment of ANIT-induced cholestasis. iTRAQ proteomics results suggested that melatonin-mediated reduction in ANIT-induced cholestasis may be associated with enhanced antioxidant function and relieving abnormal fatty acid metabolism. According to pathway enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes, the major metabolic pathways for the metabolism of melatonin are fatty acid degradation, the peroxisome proliferator-activated receptor signaling pathway, fatty acid metabolism, chemical carcinogenesis, carbon metabolism, pyruvate metabolism, fatty acid biosynthesis and retinol metabolism, as well as drug metabolism via cytochrome P450. Malate dehydrogenase 1 and glutathione S-transferase Yb-3 may serve as potential targets in the treatment of ANIT-induced cholestasis with melatonin.

Tectorigenin alleviates intrahepatic cholestasis by inhibiting hepatic inflammation and bile accumulation via activation of PPARγ

BACKGROUND AND PURPOSE

Increasing evidence suggests that human cholestasis is closely associated with the accumulation and activation of hepatic macrophages. Research indicates that activation of PPARγ exerts liver protective effects in cholestatic liver disease (CLD), particularly by ameliorating inflammation and fibrosis, thus limiting disease progression. However, existing PPARγ agonists, such as troglitazone and rosiglitazone, have significant side effects that prevent their clinical application in the treatment of CLD. In this study, we found that tectorigenin alleviates intrahepatic cholestasis in mice by activating PPARγ.

EXPERIMENTAL APPROACH

Wild-type mice were intragastrically administered α-naphthylisothiocyanate (ANIT) or fed a diet containing 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) to simultaneously establish an experimental model of intrahepatic cholestasis and tectorigenin intervention, followed by determination of intrahepatic cholestasis and the mechanisms involved. In addition, PPARγ-deficient mice were administered ANIT and/or tectorigenin to determine whether tectorigenin exerts its liver protective effect by activating PPARγ.

KEY RESULTS

Treatment with tectorigenin alleviated intrahepatic cholestasis by inhibiting the recruitment and activation of hepatic macrophages and by promoting the expression of bile transporters via activation of PPARγ. Furthermore, tectorigenin increased expression of the bile salt export pump (BSEP) through enhanced PPARγ binding to the BSEP promoter. In PPARγ-deficient mice, the hepatoprotective effect of tectorigenin during cholestasis was blocked.

CONCLUSION AND IMPLICATIONS

In conclusion, tectorigenin reduced the recruitment and activation of hepatic macrophages and enhanced the export of bile acids by activating PPARγ. Taken together, our results suggest that tectorigenin is a candidate compound for cholestasis treatment.

Metabolic Profiling of Bile Acids in the Urine of Patients with Alcohol-Associated Liver Disease

Bile acids (BAs) play important functions in the development of alcohol-associated liver disease (ALD). In the current study, urine BA concentrations in 38 patients with well-described alcohol-associated hepatitis (AH) as characterized by Model for End-Stage Liver Disease (MELD), 8 patients with alcohol-use disorder (AUD), and 19 healthy controls (HCs) were analyzed using liquid chromatography-mass spectrometry. Forty-three BAs were identified, and 22 BAs had significant changes in their abundance levels in patients with AH. The potential associations of clinical data were compared to candidate BAs in this pilot proof-of-concept study. MELD score showed positive correlations with several conjugated BAs and negative correlations with certain unconjugated BAs; taurine-conjugated chenodeoxycholic acid (CDCA) and MELD score showed the highest association. Cholic acid, CDCA, and apocholic acid had nonsignificant abundance changes in patients with nonsevere ALD compared to HCs but were significantly increased in those with severe AH. Receiver operating characteristic analysis showed that the differences in these three compounds were sufficiently large to distinguish severe AH from nonsevere ALD. Notably, the abundance levels of primary BAs were significantly increased while most of the secondary BAs were markedly decreased in AH compared to AUD. Most importantly, the amount of total BAs and the ratio of primary to secondary BAs increased while the ratio of unconjugated to conjugated BAs decreased as disease severity increased. Conclusion: Abundance changes of specific BAs are closely correlated with the severity of AH in this pilot study. Urine BAs (individually or as a group) could be potential noninvasive laboratory biomarkers for detecting early stage ALD and may have prognostic value in AH morbidity.

Xanthohumol ameliorates Diet-Induced Liver Dysfunction via Farnesoid X Receptor-Dependent and Independent Signaling

The farnesoid X receptor (FXR) plays a critical role in the regulation of lipid and bile acid (BA) homeostasis. Hepatic FXR loss results in lipid and BA accumulation, and progression from hepatic steatosis to nonalcoholic steatohepatitis (NASH). This study aimed to evaluate the effects of xanthohumol (XN), a hop-derived compound mitigating metabolic syndrome, on liver damage induced by diet and FXR deficiency in mice. Wild-type (WT) and liver-specific FXR-null mice (FXR^Liver−/−) were fed a high-fat diet (HFD) containing XN or the vehicle formation followed by histological characterization, lipid, BA and gene profiling. HFD supplemented with XN resulted in amelioration of hepatic steatosis and decreased BA concentrations in FXR^Liver−/− mice, the effect being stronger in male mice. XN induced the constitutive androstane receptor (CAR), pregnane X receptor (PXR) and glucocorticoid receptor (GR) gene expression in the liver of FXR^Liver−/− mice. These findings suggest that activation of BA detoxification pathways represents the predominant mechanism for controlling hydrophobic BA concentrations in FXR^Liver−/− mice. Collectively, these data indicated sex-dependent relationship between FXR, lipids and BAs, and suggest that XN ameliorates HFD-induced liver dysfunction via FXR-dependent and independent signaling.

Schisandrol B promotes liver enlargement via activation of PXR and YAP pathways in mice

BACKGROUND

Schisandrol B (SolB) is one of the bioactive components from a traditional Chinese medicine Schisandra chinensis or Schisandra sphenanthera. It has been demonstrated that SolB exerts hepatoprotective effects against drug-induced liver injury and promotes liver regeneration. It was found that SolB can induce hepatomegaly but the involved mechanisms remain unknown.

PURPOSE

This study aimed to explore the mechanisms involved in SolB-induced hepatomegaly.

METHODS

Male C57BL/6 mice were injected intraperitoneally with SolB (100 mg/kg) for 5 days. Serum and liver samples were collected for biochemical and histological analyses. The mechanisms of SolB were investigated by qRT-PCR and western blot analyses, luciferase reporter gene assays and immunofluorescence.

RESULTS

SolB significantly increased hepatocyte size and proliferation, and then promoted liver enlargement without liver injury and inflammation. SolB transactivated human PXR, activated PXR in mice and upregulated hepatic expression of its downstream proteins, such as CYP3A11, CYP2B10 and UGT1A1. SolB also significantly enhanced nuclear translocation of PXR and YAP in human cell lines. YAP signal pathway was activated by SolB in mice.

CONCLUSION

These findings demonstrated that SolB can significantly induce liver enlargement, which is associated with the activation of PXR and YAP pathways.

Recent developments in diagnostics and treatment of neonatal cholestasis

Neonatal cholestasis is characterized by conjugated hyperbilirubinemia in the newborn and young infant and is a sign common to over 100 hepatobiliary and/or metabolic disorders. A timely evaluation for its etiology is critical in order to quickly identify treatable causes such as biliary atresia, many of which benefit from early therapy. An expanding group of molecularly defined disorders involving bile formation, canalicular transporters, tight junction proteins and inborn errors of metabolism are being continuously discovered because of advances in genetic testing and bioinformatics. The advent of next generation sequencing has transformed our ability to test for multiple genes and whole exome or whole genome sequencing within days to weeks, enabling rapid and affordable molecular diagnosis for disorders that cannot be directly diagnosed from standard blood tests or liver biopsy. Thus, our diagnostic algorithms for neonatal cholestasis are undergoing transformation, moving genetic sequencing to earlier in the evaluation pathway once biliary atresia, "red flag" disorders and treatable disorders are excluded. Current therapies focus on promoting bile flow, reducing pruritus, ensuring optimal nutrition, and monitoring for complications, without addressing the underlying cause of cholestasis in most instances. Our improved understanding of bile formation and the enterohepatic circulation of bile acids has led to emerging therapies for cholestasis which require appropriate pediatric clinical trials. Despite these advances, the cause and optimal therapy for biliary atresia remain elusive. The goals of this review are to outline the etiologies, diagnostic pathways and current and emerging management strategies for neonatal cholestasis.

Dysregulation of Circulating FGF19 and Bile Acids in Primary Biliary Cholangitis-Autoimmune Hepatitis Overlap Syndrome

Background

Primary biliary cholangitis-autoimmune hepatitis overlap syndrome (PBC-AIH OS), which exhibits features between autoimmune hepatitis and cholestasis, is a common condition and usually shows a progressive course toward cirrhosis and liver failure without adequate treatment. Synthesis of bile acids (BAs) plays an important role in liver injury in cholestasis, and the process is regulated by fibroblast growth factor 19 (FGF19). The overall role of circulating FGF19 in BA synthesis and PBC-AIH OS requires further investigation.

Methods

We analyzed BA synthesis and correlated clinical parameters with serum BAs and FGF19 in 35 patients with PBC-AIH OS. Serum concentrations of 7alpha-hydroxycholest-4-en-3-one (C4) were used to quantify the synthesis of BA directly.

Results

Serum FGF19 levels were higher, while C4 levels were substantially lower in PBC-AIH OS patients than those in healthy controls. Circulating FGF19 levels strongly correlated with C4 (r = −0.695, p < 0.0001), direct bilirubin (r = 0.598, p = 0.0001), and total bile acids (r = 0.595, p = 0.002). Moreover, circulating FGF19 levels strongly correlated with the model for end-stage liver disease score (r = 0.574, p = 0.0005) and Mayo risk score (r = 0.578, p = 0.001).

Conclusions

Serum FGF19 is significantly increased in patients with PBC-AIH OS, while BA synthesis is suppressed. Circulating FGF19 primarily controls the regulation of BA synthesis in response to cholestasis and under cholestatic conditions. Therefore, modulation of circulating FGF19 could provide a promising targeted therapy for patients with PBC-AIH OS.

Ronda O, Verkade HJ, Stojakovic T, Scharnagl H, Habib A, Zimmermann R, Lotersztajn S, Trauner M. Monoacylglycerol Lipase Inhibition Protects From Liver Injury in Mouse Models of Sclerosing Cholangitis

BACKGROUND AND AIMS

Monoacylglycerol lipase (MGL) is the last enzymatic step in triglyceride degradation, hydrolyzing monoglycerides into glycerol and fatty acids (FAs) and converting 2-arachidonoylglycerol into arachidonic acid, thus providing ligands for nuclear receptors as key regulators of hepatic bile acid (BA)/lipid metabolism and inflammation. We aimed to explore the role of MGL in the development of cholestatic liver and bile duct injury in mouse models of sclerosing cholangitis, a disease so far lacking effective pharmacological therapy.

APPROACH AND RESULTS

To this aim we analyzed the effects of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding to induce sclerosing cholangitis in wild-type (WT) and knockout (MGL-/- ) mice and tested pharmacological inhibition with JZL184 in the multidrug resistance protein 2 knockout (Mdr2-/- ) mouse model of sclerosing cholangitis. Cholestatic liver injury and fibrosis were assessed by serum biochemistry, liver histology, gene expression, and western blot characterization of BA and FA synthesis/transport. Moreover, intestinal FAs and fecal microbiome were analyzed. Transfection and silencing were performed in Caco2 cells. MGL-/- mice were protected from DDC-induced biliary fibrosis and inflammation with reduced serum liver enzymes and increased FA/BA metabolism and β-oxidation. Notably, pharmacological (JZL184) inhibition of MGL ameliorated cholestatic injury in DDC-fed WT mice and protected Mdr2-/- mice from spontaneous liver injury, with improved liver enzymes, inflammation, and biliary fibrosis. In vitro experiments confirmed that silencing of MGL decreases prostaglandin E2 accumulation in the intestine and up-regulates peroxisome proliferator-activated receptors alpha and gamma activity, thus reducing inflammation.

CONCLUSIONS

Collectively, our study unravels MGL as a metabolic target, demonstrating that MGL inhibition may be considered as potential therapy for sclerosing cholangitis.

Quantitative proteomics analysis of Fructus Psoraleae-induced hepatotoxicity in rats

Fructus Psoraleae, which is commonly consumed for the treatment of osteoporosis, bone fracture, and leucoderma, induces liver injury. This study investigated the pathogenesis of the ethanol extract of Fructus Psoraleae (EEFP)-induced liver injury in rats. EEFP (1.35, 1.80, and 2.25 g·kg^-1) was administrated to Sprague Dawley (SD) rats for 30 d. We measured liver chemistries, histopathology, and quantitative isobaric tags for relative and absolute quantitation (iTRAQ)-based protein profiling. EEFP demonstrated parameters suggestive of liver injury with changes in bile secretion, bile flow rate, and liver histopathology. iTRAQ analysis showed that a total of 4042 proteins were expressed in liver tissues of EEFP-treated and untreated rats. Among these proteins, 81 were upregulated and 32 were downregulated in the treatment group. KEGG pathway analysis showed that the drug metabolic pathways of cytochrome P450, glutathione metabolism, glycerolipid metabolism, and bile secretion were enriched with differentially expressed proteins. The expression of key proteins related to the farnesoid X receptor (FXR), i.e., the peroxisome proliferators-activated receptor alpha (PPAR-α), were downregulated, and multidrug resistance-associated protein 3 (MRP3) was upregulated in the EEFP-treated rats. Our results provide evidence that EEFP may induce hepatotoxicity through various pathways. Furthermore, our study demonstrates changes in protein regulation using iTRAQ quantitative proteomics analysis.

Robustness testing and optimization of an adverse outcome pathway on cholestatic liver injury

Adverse outcome pathways (AOPs) have been recently introduced as tools to map the mechanisms underlying toxic events relevant for chemical risk assessment. AOPs particularly depict the linkage between a molecular initiating event and an adverse outcome through a number of intermediate key events. An AOP has been previously introduced for cholestatic liver injury. The objective of this study was to test the robustness of this AOP for different types of cholestatic insult and the in vitro to in vivo extrapolation. For this purpose, in vitro samples from human hepatoma HepaRG cell cultures were exposed to cholestatic drugs (i.e. intrahepatic cholestasis), while in vivo samples were obtained from livers of cholestatic mice (i.e. extrahepatic cholestasis). The occurrence of cholestasis in vitro was confirmed through analysis of bile transporter functionality and bile acid analysis. Transcriptomic analysis revealed inflammation and oxidative stress as key events in both types of cholestatic liver injury. Major transcriptional differences between intrahepatic and extrahepatic cholestatic liver insults were observed at the level of cell death and metabolism. Novel key events identified by pathway analysis included endoplasmic reticulum stress in intrahepatic cholestasis, and autophagy and necroptosis in both intrahepatic as extrahepatic cholestasis. This study demonstrates that AOPs constitute dynamic tools that should be frequently updated with new input information.

Picroside II protects against cholestatic liver injury possibly through activation of farnesoid X receptor

BACKGROUD

Cholestasis, accompanied by the accumulation of bile acids in body, may ultimately cause liver failure and cirrhosis. There have been limited therapies for cholesteric disorders. Therefore, development of appropriate therapeutic drugs for cholestasis is required. Picroside II is a bioactive component isolated from Picrorhiza scrophulariiflora Pennell, its mechanistic contributions to the anti-cholestasis effect have not been fully elucidated, especially the role of picroside II on bile acid homeostasis via nuclear receptors remains unclear.

PURPOSE

This study was designed to investigate the hepatoprotective effect of picroside II against alpha-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury and elucidate the mechanisms in vivo and in vitro.

METHODS

The ANIT-induced cholestatic mouse model was used with or without picroside II treatment. Serum and bile biochemical indicators, as well as liver histopathological changes were examined. siRNA, Dual-luciferase reporter, quantitative real-time PCR and Western blot assay were used to demonstrate the farnesoid X receptor (FXR) pathway in the anti-cholestasis effects of picroside II in vivo and in vitro.

RESULTS

Picroside II exerted hepatoprotective effect against ANIT-induced cholestasis by impaired hepatic function and tissue damage. Picroside II increased bile acid efflux transporter bile salt export pump (Bsep), uptake transporter sodium taurocholate cotransporting polypeptide (Ntcp), and bile acid metabolizing enzymes sulfate transferase 2a1 (Sult2a1) and UDP-glucuronosyltransferase 1a1 (Ugt1a1), whereas decreased the bile acid synthesis enzymes cholesterol 7α-hydroxylase (Cyp7a1) and oxysterol 12α-hydroxylase (Cyp8b1). In addition, expression of FXR and the target gene Bsep was increased, whereas aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor alpha (PPARα) and their corresponding target genes were not significantly influenced by picroside II under cholestatic conditions. Furthermore, regulation of transporters and enzymes involved in bile acid homeostasis by picroside II were abrogated by FXR silencing in mouse primary cultured hepatocytes. Dual-luciferase reporter assay performed in HepG2 cells demonstrated FXR activation by picroside II.

CONCLUSION

Our findings demonstrate that picroside II exerts protective effect on ANIT-induced cholestasis possibly through FXR activation that regulates the transporters and enzymes involved in bile acid homeostasis. Picroside II might be an effective approach for the prevention and treatment of cholestatic liver diseases.

Emerging therapies in primary sclerosing cholangitis: pathophysiological basis and clinical opportunities

Primary sclerosing cholangitis (PSC) is a progressive liver disease, histologically characterized by inflammation and fibrosis of the bile ducts, and clinically leading to multi-focal biliary strictures and with time cirrhosis and liver failure. Patients bear a significant risk of cholangiocarcinoma and colorectal cancer, and frequently have concomitant inflammatory bowel disease and autoimmune disease manifestations. To date, no medical therapy has proven significant impact on clinical outcomes and most patients ultimately need liver transplantation. Several treatment strategies have failed in the past and whilst prescription of ursodeoxycholic acid (UDCA) prevails, controversy regarding benefits remains. Lack of statistical power, slow and variable disease progression, lack of surrogate biomarkers for disease severity and other challenges in trial design serve as critical obstacles in the development of effective therapy. Advances in our understanding of PSC pathogenesis and biliary physiology over recent years has however led to a surge of clinical trials targeting various mechanistic compartments and currently raising hopes for imminent changes in patient management. Here, in light of pathophysiology, we outline and critically evaluate emerging treatment strategies in PSC, as tested in recent or ongoing phase II and III trials, stratified per a triad of targets of nuclear and membrane receptors regulating bile acid metabolism, immune modulators, and effects on the gut microbiome. Furthermore, we revisit the UDCA trials of the past and critically discuss relevant aspects of clinical trial design, including how the choice of endpoints, alkaline phosphatase in particular, may affect the future path to novel, effective PSC therapeutics.

Cholestatic liver diseases: An era of emerging therapies

Recently the field of cholestasis has expanded enormously reflecting an improved understanding of the molecular mechanisms underlying bile secretion and its perturbation in chronic cholestatic disease. Novel anti-cholestatic therapeutic options have been developed for patients not favorably responding to ursodeoxycholic acid (UDCA), the current standard treatment for cholestatic liver disease. Important novel treatment targets now also include nuclear receptors involved in bile acid (BA) homoeostasis like farnesoid X receptor and G protein-coupled receptors e.g., the G-protein-coupled BA receptor “transmembrane G coupled receptor 5”. Fibroblast growth factor-19 and enterohepatic BA transporters also deserve attention as additional drug targets as does the potential treatment agent norUDCA. In this review, we discuss recent and future promising therapeutic agents and their potential molecular mechanisms in cholestatic liver disorders.

Effects of Absence of Constitutive Androstane Receptor (CAR) on Bile Acid Homeostasis in Male and Female Mice

Accumulation of BAs in hepatocytes has a role in liver disease and also in drug-induced liver injury. The Constitutive Androstane Receptor (CAR) has been shown to protect against BA-induced liver injury. The polymorphism of CAR has recently been shown to modify the pharmacokinetics and pharmacodynamics of various drugs. Thus it was hypothesized that polymorphism of CAR may also influence BA homeostasis. Using CAR-null and WT mice, this study modeled the potential consequences of CAR polymorphism on BA homeostasis. Our previous study showed that chemical activation of CAR decreases the total BA concentrations in livers of mice. Surprisingly the absence of CAR also decreased the BA concentrations in livers of mice, but to a lesser extent than in CAR-activated mice. Neither CAR activation nor elimination of CAR altered the biliary excretion of total BAs, but CAR activation increased the proportion of 6-OH BAs (TMCA), whereas the lack of CAR increased the excretion of TCA, TCDCA and TDCA. Serum BA concentrations did not parallel the decrease in BA concentrations in the liver in either the mice after CAR activation or mice lacking CAR. Gene expression of BA synthesis, transporter and regulator genes were mainly similar in livers of CAR-null and WT mice. In summary, CAR activation decreases primarily the 12-OH BA concentrations in liver, whereas lack of CAR decreases the concentrations of 6-OH BAs in liver. In bile, CAR activation increases the biliary excretion of 6-OH BAs, whereas absence of CAR increases the biliary excretion of 12-OH BAs and TCDCA.

Neonatal cholestasis: emerging molecular diagnostics and potential novel therapeutics

Neonatal cholestasis is a group of rare disorders of impaired bile flow characterized by conjugated hyperbilirubinaemia in the newborn and young infant. Neonatal cholestasis is never physiological but rather is a sign of hepatobiliary and/or metabolic disorders, some of which might be fatal if not identified and treated rapidly. A step-wise timely evaluation is essential to quickly identify those causes amenable to treatment and to offer accurate prognosis. The aetiology of neonatal cholestasis now includes an expanding group of molecularly defined entities with overlapping clinical presentations. In the past two decades, our understanding of the molecular basis of many of these cholestatic diseases has improved markedly. Simultaneous next-generation sequencing for multiple genes and whole-exome or whole-genome sequencing now enable rapid and affordable molecular diagnosis for many of these disorders that cannot be directly diagnosed from standard blood tests or liver biopsy. Unfortunately, despite these advances, the aetiology and optimal therapeutic approach of the most common of these disorders, biliary atresia, remain unclear. The goals of this Review are to discuss the aetiologies, algorithms for evaluation and current and emerging therapeutic options for neonatal cholestasis.

Mechanisms and in vitro models of drug-induced cholestasis

Cholestasis underlies one of the major manifestations of drug-induced liver injury. Drug-induced cholestatic liver toxicity is a complex process, as it can be triggered by a variety of factors that induce 2 types of biological responses, namely a deteriorative response, caused by bile acid accumulation, and an adaptive response, aimed at removing the accumulated bile acids. Several key events in both types of responses have been characterized in the past few years. In parallel, many efforts have focused on the development and further optimization of experimental cell culture models to predict the occurrence of drug-induced cholestatic liver toxicity in vivo. In this paper, a state-of-the-art overview of mechanisms and in vitro models of drug-induced cholestatic liver injury is provided.

Activation of constitutive androstane receptor inhibits intestinal CFTR-mediated chloride transport

Constitutive androstane receptor (CAR) belonging to the nuclear receptor superfamily plays an important role in the xenobiotic metabolism and disposition. It has been reported that CAR regulates the expression of the ATP-binding cassette (ABC) transporters in the intestine, such as multidrug resistance protein 1 (MDR1) and multidrug resistance-associated protein 2/3 (MRP2 and MRP3). In this study, we investigated the role of CAR in the regulation of cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride transport in T84 human colonic epithelial cells and mouse intestinal tissues. Treatments of T84 cell monolayers with specific CAR agonists (CITCO and phenytoin at concentrations of 1 μM and 5 μM, respectively) for 24 h decreased transepithelial Cl^- secretion in response to cAMP-dependent agonist. This inhibition was abolished by coincubation of CITCO with a CAR antagonist, CINPA1. We confirmed that an inhibitory effect of CAR agonists was not due to their cytotoxicity. Basolateral membrane permeabilization experiments also revealed that activation of CAR decreased apical Cl^- current stimulated by both CPT-cAMP and genistein (a direct CFTR activator). Such activation also reduced both mRNA and protein expression of CFTR. Furthermore, CITCO decreased cholera toxin (CT)-induced Cl^- secretion across T84 cell monolayers. In ICR mice, administration of TCPOBOP (3 mg/kgBW), a murine-specific CAR agonist, for 7 days produced significant decreases in CFTR mRNA and protein expressions in intestinal tissues. Interestingly, TCPOBOP also inhibited CT-induced intestinal fluid accumulation in mice. This is the first evidence showing that CFTR was downregulated by CAR activation in the intestine. Our findings suggest that CAR has potential as a new drug target for treatment of condition with hyperactivity/ hyperfunction of CFTR especially secretory diarrheas.

Mechanisms of Drug-Induced Cholestasis

Cholestasis can be defined as any situation of impaired bile secretion with concomitant accumulation of bile acids in the liver or in the systemic circulation. A variety of factors may evoke cholestasis, including genetic disorders, metabolic pathologies, infectious diseases, immunogenic stimuli, and drugs. Drug-induced cholestasis is a mechanistically complex process. At least three triggering factors of drug-induced cholestasis have been described, including effects on drug transporters, various hepatocellular changes, and altered bile canaliculi dynamics. These stimuli induce two cellular responses, each typified by a number of key events, namely a deteriorative response activated by bile acid accumulation and an adaptive response aimed at decreasing the uptake and increasing the export of bile acids into and from the liver, respectively. The mechanistic scenario of drug-induced cholestasis is described in this chapter.

Constitutive Androstane Receptor Differentially Regulates Bile Acid Homeostasis in Mouse Models of Intrahepatic Cholestasis

Bile acid (BA) homeostasis is tightly regulated by multiple transcription factors, including farnesoid X receptor (FXR) and small heterodimer partner (SHP). We previously reported that loss of the FXR/SHP axis causes severe intrahepatic cholestasis, similar to human progressive familial intrahepatic cholestasis type 5 (PFIC5). In this study, we found that constitutive androstane receptor (CAR) is endogenously activated in Fxr:Shp double knockout (DKO) mice. To test the hypothesis that CAR activation protects DKO mice from further liver damage, we generated Fxr;Shp;Car triple knockout (TKO) mice. In TKO mice, residual adenosine triphosphate (ATP) binding cassette, subfamily B member 11 (ABCB11; alias bile salt export pump [BSEP]) function and fecal BA excretion are completely impaired, resulting in severe hepatic and biliary damage due to excess BA overload. In addition, we discovered that pharmacologic CAR activation has different effects on intrahepatic cholestasis of different etiologies. In DKO mice, CAR agonist 1,4‐bis[2‐(3,5‐dichloropyridyloxy)]benzene (TCPOBOP; here on TC) treatment attenuated cholestatic liver injury, as expected. However, in the PFIC2 model Bsep knockout (BKO) mice, TC treatment exhibited opposite effects that reflect increased BA accumulation and liver injury. These contrasting results may be linked to differential regulation of systemic cholesterol homeostasis in DKO and BKO livers. TC treatment selectively up‐regulated hepatic cholesterol levels in BKO mice, supporting de novo BA synthesis. Conclusion: CAR activation in DKO mice is generally protective against cholestatic liver injury in these mice, which model PFIC5, but not in the PFIC2 model BKO mice. Our results emphasize the importance of the genetic and physiologic background when implementing targeted therapies to treat intrahepatic cholestasis.

Advances in drug-induced cholestasis: Clinical perspectives, potential mechanisms and in vitro systems

Despite growing research, drug-induced liver injury (DILI) remains a serious issue of increasing importance to the medical community that challenges health systems, pharmaceutical industries and drug regulatory agencies. Drug-induced cholestasis (DIC) represents a frequent manifestation of DILI in humans, which is characterised by an impaired canalicular bile flow resulting in a detrimental accumulation of bile constituents in blood and tissues. From a clinical point of view, cholestatic DILI generates a wide spectrum of presentations and can be a diagnostic challenge. The drug classes mostly associated with DIC are anti-infectious, anti-diabetic, anti-inflammatory, psychotropic and cardiovascular agents, steroids, and other miscellaneous drugs. The molecular mechanisms of DIC have been investigated since the 1980s but they remain debatable. It is recognised that altered expression and/or function of hepatobiliary membrane transporters underlies some forms of cholestasis, and this and other concomitant mechanisms are very likely in DIC. Deciphering these processes may pave the ways for diagnosis, prognosis and prevention, for which currently major gaps and caveats exist. In this review, we summarise recent advances in the field of DIC, including clinical aspects, the potential mechanisms postulated so far and the in vitro systems that can be useful to investigate and identify new cholestatic drugs.

Novel and emerging therapies for cholestatic liver diseases

While bile acids are important for both digestion and signalling, hydrophobic bile acids can be harmful, especially when in high concentrations. Mechanisms for the protection of cholangiocytes against bile acid cytotoxicity include negative feedback loops via farnesoid X nuclear receptor (FXR) activation, the bicarbonate umbrella, cholehepatic shunting and anti-inflammatory signalling, among others. By altering or overwhelming these defence mechanisms, cholestatic diseases such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) can further progress to biliary cirrhosis, end-stage liver disease and death or liver transplantation. While PBC is currently treated with ursodeoxycholic acid (UDCA) and obeticholic acid (OCA), many fail treatment, and we have yet to find an effective therapy for PSC. Novel therapies under evaluation target nuclear and surface receptors including FXR, transmembrane G-protein-coupled receptor 5 (TGR5), peroxisome proliferator-activated receptor (PPAR) and pregnane X receptor (PXR). Modulation of these receptors leads to altered bile composition, decreased cytotoxicity, decreased inflammation and improved metabolism. This review summarizes our current understanding of the role of bile acids in the pathophysiology of cholestatic liver diseases, presents the rationale for already approved medical therapies and discusses novel pharmacologic therapies under investigation.

Dysregulation of serum bile acids and FGF19 in alcoholic hepatitis

BACKGROUND & AIMS

The degree of cholestasis is an important disease driver in alcoholic hepatitis, a severe clinical condition that needs new biomarkers and targeted therapies. We aimed to identify the largely unknown mechanisms and biomarkers linked to cholestasis in alcoholic hepatitis.

METHODS

Herein, we analyzed a well characterized cohort of patients with alcoholic hepatitis and correlated clinical and histological parameters and outcomes with serum bile acids and fibroblast growth factor 19 (FGF19), a major regulator of bile acid synthesis.

RESULTS

We found that total and conjugated bile acids were significantly increased in patients with alcoholic hepatitis compared with controls. Serum FGF19 levels were strongly increased and gene expression of FGF19 was induced in biliary epithelial cells and ductular cells of patients with alcoholic hepatitis. De novo bile acid synthesis (CYP7A1 gene expression and C4 serum levels) was significantly decreased in patients with alcoholic hepatitis. Importantly, total and conjugated bile acids correlated positively with FGF19 and with disease severity (model for end-stage liver disease score). FGF19 correlated best with conjugated cholic acid, and model for end-stage liver disease score best with taurine-conjugated chenodeoxycholic acid. Univariate analysis demonstrated significant associations between FGF19 and bilirubin as well as gamma glutamyl transferase, and negative correlations between FGF19 and fibrosis stage as well as polymorphonuclear leukocyte infiltration, in all patients with alcoholic hepatitis.

CONCLUSION

Serum FGF19 and bile acids are significantly increased in patients with alcoholic hepatitis, while de novo bile acid synthesis is suppressed. Modulation of bile acid metabolism or signaling could represent a promising target for treatment of alcoholic hepatitis in humans.

LAY SUMMARY

Understanding the underlying mechanisms that drive alcoholic hepatitis is important for the development of new biomarkers and targeted therapies. Herein, we describe a molecule that is increased in patients with alcoholic hepatitis. Modulating the molecular pathway of this molecule might lead to promising targets for the treatment of alcoholic hepatitis.

Predicting drug-induced cholestasis: preclinical models

INTRODUCTION

In almost 50% of patients with drug-induced liver injury (DILI), the bile flow from the liver to the duodenum is impaired, a condition known as cholestasis. However, this toxic response only appears in a small percentage of the treated patients (idiosyncrasy). Prediction of drug-induced cholestasis (DIC) is challenging and emerges as a safety issue that requires attention by professionals in clinical practice, regulatory authorities, pharmaceutical companies, and research institutions. Area covered: The current synopsis focuses on the state-of-the-art in preclinical models for cholestatic DILI prediction. These models differ in their goal, complexity, availability, and applicability, and can widely be classified in experimental animals and in vitro models. Expert opinion: Drugs are a growing cause of cholestasis, but the progress made in explaining mechanisms and differences in susceptibility is not growing at the same rate. We need reliable models able to recapitulate the features of DIC, particularly its idiosyncrasy. The homogeneity and the species-specific differences move animal models away from a fair predictability. However, in vitro human models are improving and getting closer to the real hepatocyte phenotype, and they will likely be the choice in the near future. Progress in this area will not only need reliable predictive models but also mechanistic insights.

Mathematical Models in the Description of Pregnane X Receptor (PXR)-Regulated Cytochrome P450 Enzyme Induction

The pregnane X receptor (PXR) is a drug/xenobiotic-activated transcription factor of crucial importance for major cytochrome P450 xenobiotic-metabolizing enzymes (CYP) expression and regulation in the liver and the intestine. One of the major target genes regulated by PXR is the cytochrome P450 enzyme (CYP3A4), which is the most important human drug-metabolizing enzyme. In addition, PXR is supposed to be involved both in basal and/or inducible expression of many other CYPs, such as CYP2B6, CYP2C8, 2C9 and 2C19, CYP3A5, CYP3A7, and CYP2A6. Interestingly, the dynamics of PXR-mediated target genes regulation has not been systematically studied and we have only a few mechanistic mathematical and biologically based models describing gene expression dynamics after PXR activation in cellular models. Furthermore, few indirect mathematical PKPD models for prediction of CYP3A metabolic activity in vivo have been built based on compartmental models with respect to drug–drug interactions or hormonal crosstalk. Importantly, several negative feedback loops have been described in PXR regulation. Although current mathematical models propose these adaptive mechanisms, a comprehensive mathematical model based on sufficient experimental data is still missing. In the current review, we summarize and compare these models and address some issues that should be considered for the improvement of PXR-mediated gene regulation modelling as well as for our better understanding of the quantitative and spatial dynamics of CYPs expression.

N-3 Polyunsaturated Fatty Acids Stimulate Bile Acid Detoxification in Human Cell Models

Cholestasis is characterized by the accumulation of toxic bile acids (BAs) in liver cells. The present study aimed to evaluate the effects of n-3 polyunsaturated fatty acids (n-3 PUFAs), such as docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, on BA homeostasis and toxicity in human cell models. The effects of EPA and/or DHA on the expression of genes involved in the maintenance of BA homeostasis were analyzed in human hepatoma (HepG2) and colon carcinoma (Caco-2) cells, as well as in primary culture of human intestinal (InEpC) and renal (RPTEC) cells. Extracellular BA species were quantified in culture media using LC-MS/MS. BA-induced toxicity was evaluated using caspase-3 and flow cytometry assays. Gene expression analyses of HepG2 cells reveal that n-3 PUFAs reduce the expression of genes involved in BA synthesis (CYP7A1, CYP27A1) and uptake (NTCP), while activating genes encoding metabolic enzymes (SULT2A1) and excretion transporters (MRP2, MRP3). N-3 PUFAs also generate a less toxic BA pool and prevent the BA-dependent activation of apoptosis in HepG2 cells. Conclusion. The present study reveals that n-3 PUFAs stimulate BA detoxification.

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.

Genetic loss of the muscarinic M3 receptor markedly alters bile formation and cholestatic liver injury in mice

AIM

Hepatic innervation represents a potentially underestimated regulator of liver function and regeneration. The muscarinic 3 receptor (M₃ -R) is the primary cholangiocyte receptor for the afferent parasympathetic innervation of bile ducts. We aimed to determine the specific role of the M₃ -R in bile formation and models for cholestatic liver disease in mice.

METHODS

We compared bile flow and composition in M₃ -R knock-out mice (M₃ -R^-/- ) and wild type littermates (WT). Furthermore, we compared liver inury of M₃ -R^-/- and WT mice after 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding, a well-characterized preclinical model of cholestatic liver disease. To analyze the possible role of the M₃ -R as a therapeutic target, we treated 4-week-old Mdr2^-/- mice, a preclinical model for sclerosing cholangitis, with the M₃ -R agonist bethanechol for 4 weeks.

RESULTS

M₃ -R^-/- mice showed significantly reduced bile flow compared to WT mice, most likely due to decreased biliary HCO₃^- secretion. However, even aged M₃ -R^-/- mice did not spontaneously develop liver injury or cholestasis. Challenging M₃ -R^-/- and WT littermates with DDC feeding showed substantially aggravated liver injury in M₃ -R^-/- mice. After 4 weeks bethanechol treatment, Mdr2^-/- mice showed less liver injury compared to controls.

CONCLUSION

Our experimental findings suggest that M₃ -R-signalling significantly influences bile formation. Loss of the M₃ -R increases susceptibility to cholestatic injury in DDC-fed mice. Since treatment of Mdr2^-/- mice with a M₃ -R agonist decreases liver injury, M3-R signaling may represent a therapeutic target in specific cholangiopathies.

Bile acid-microbiota crosstalk in gastrointestinal inflammation and carcinogenesis

Emerging evidence points to a strong association between the gut microbiota and the risk, development and progression of gastrointestinal cancers such as colorectal cancer (CRC) and hepatocellular carcinoma (HCC). Bile acids, produced in the liver, are metabolized by enzymes derived from intestinal bacteria and are critically important for maintaining a healthy gut microbiota, balanced lipid and carbohydrate metabolism, insulin sensitivity and innate immunity. Given the complexity of bile acid signalling and the direct biochemical interactions between the gut microbiota and the host, a systems biology perspective is required to understand the liver-bile acid-microbiota axis and its role in gastrointestinal carcinogenesis to reverse the microbiota-mediated alterations in bile acid metabolism that occur in disease states. An examination of recent research progress in this area is urgently needed. In this Review, we discuss the mechanistic links between bile acids and gastrointestinal carcinogenesis in CRC and HCC, which involve two major bile acid-sensing receptors, farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (TGR5). We also highlight the strategies and cutting-edge technologies to target gut-microbiota-dependent alterations in bile acid metabolism in the context of cancer therapy.

Resveratrol modifies biliary secretion of cholephilic compounds in sham-operated and cholestatic rats

AIM

To investigate the effect of resveratrol on biliary secretion of cholephilic compounds in healthy and bile duct-obstructed rats.

METHODS

Resveratrol (RSV) or saline were administered to rats by daily oral gavage for 28 d after sham operation or reversible bile duct obstruction (BDO). Bile was collected 24 h after the last gavage during an intravenous bolus dose of the Mdr1/Mrp2 substrate azithromycin. Bile acids, glutathione and azithromycin were measured in bile to quantify their level of biliary secretion. Liver expression of enzymes and transporters relevant for bile production and biliary secretion of major bile constituents and drugs were analyzed at the mRNA and protein levels using qRT-PCR and Western blot analysis, respectively. The TR-FRET PXR Competitive Binding Assay kit was used to determine the agonism of RSV at the pregnane X receptor.

RESULTS

RSV increased bile flow in sham-operated rats due to increased biliary secretion of bile acids (BA) and glutathione. This effect was accompanied by the induction of the hepatic rate-limiting transporters for bile acids and glutathione, Bsep and Mrp2, respectively. RSV also induced Cyp7a1, an enzyme that is crucial for bile acid synthesis; Mrp4, a transporter important for BA secretion from hepatocytes to blood; and Mdr1, the major apical transporter for xenobiotics. The findings were supported by increased biliary secretion of azithromycin. The TR-FRET PXR competitive binding assay confirmed RSV as a weak agonist of the human nuclear receptor PXR, which is a transcriptional regulator of Mdr1/Mrp2. RSV demonstrated significant hepatoprotective properties against BDO-induced cirrhosis. RSV also reduced bile flow in BDO rats without any corresponding change in the levels of the transporters and enzymes involved in RSV-mediated hepatoprotection.

CONCLUSION

Resveratrol administration for 28 d has a distinct effect on bile flow and biliary secretion of cholephilic compounds in healthy and bile duct-obstructed rats.

Pregnane X receptor and constitutive androstane receptor modulate differently CYP3A-mediated metabolism in early- and late-stage cholestasis

AIM

To ascertain whether cholestasis affects the expression of two CYP3A isoforms (CYP3A1 and CYP3A2) and of pregnane X receptor (PXR) and constitutive androstane receptor (CAR).

METHODS

Cholestasis was induced by bile duct ligation in 16 male Wistar rats; whereas 8 sham-operated rats were used as controls. Severity of cholestasis was assessed on histological examination of liver sections, and serum concentrations of albumin, AST, ALT, GGT, ALPK and bilirubin. Gene and protein expressions of PXR, CAR, CYP3A1 and CYP3A2 were assessed by means of qRT-PCR and Western blot, respectively. Alterations in CYP3A activity were measured by calculating the kinetic parameters of 4-OH and 1’-OH-midazolam hydroxylation, marker reactions for CYP3A enzymes.

RESULTS

The mRNA and protein expression of CYP3A1 increased significantly in mild cholestasis (P < 0.01). At variance, mRNA and protein expression of CYP3A2 didn’t change in mild cholestasis, whereas the expression and activity of both CYP3A1 and CYP3A2 decreased dramatically when cholestasis became severe. Consistently with these observations, the nuclear expression of both PXR and CAR, which was measured because they both translocate into the cell nucleus after their activation, virtually disappeared in the late stage of cholestatic injury, after an initial increase. These results indicate that early- and late-stage cholestasis affects CYP3A-mediated drug metabolism differently, probably as consequence of the different activation of PXR and CAR.

CONCLUSION

Early- and late-stage cholestasis affects CYP3A-mediated drug metabolism differently. PXR and CAR might be targeted therapeutically to promote CYP3A-mediated liver detoxification.

Reduced triglyceride accumulation due to overactivation of farnesoid X receptor signaling contributes to impaired liver regeneration following 50% hepatectomy in extra‑cholestatic liver tissue

The aim of the present study was to investigate the role of triglyceride metabolism in the effect of obstructive cholestasis on liver regeneration following 50% partial hepatectomy (PH). Obstructive cholestatic rat models were achieved via ligation of the common bile duct (BDL). Following comparisons between hepatic pathological alterations with patients with perihilar cholangiocarcinoma, rats in the 7 day post‑BDL group were selected as the BDL model for subsequent experiments. Liver weight restoration, proliferating cell nuclear antigen labeling index, cytokine and growth factor expression levels, and hepatic triglyceride content were evaluated to analyze liver regeneration post‑PH within BDL and control group rats. The results of the present study revealed that obstructive cholestasis impaired liver mass restoration, which occurred via inhibition of early stage hepatocyte proliferation. In addition, reduced triglyceride content and inhibited expression of fatty acid β‑oxidation‑associated genes, peroxisome proliferator activated receptor α and carnitine palmitoyltransferase, were associated with an insufficient energy supply within the BDL group post‑PH. Notably, the expression levels of fatty acid synthesis‑associated genes, including sterol‑regulatory element‑binding protein‑1c, acetyl‑coA carboxylase 1 and fatty acid synthase were also reduced within the BDL group, which accounted for the reduced triglyceride content and fatty acid utilization. Further investigation revealed that overactivated farnesoid X receptor (FXR) signaling may inhibit fatty acid synthesis within BDL group rats. Collectively, the role of triglycerides in liver regeneration following PH in extra‑cholestatic livers was identified in the present study. Additionally, the results indicated that overactivated FXR signaling‑induced triglyceride reduction is associated with insufficient energy supply and therefore contributes to the extent of impairment of liver regeneration following PH within extra‑cholestatic livers.

Iron depletion induces hepatic secretion of biliary lipids and glutathione in rats

Iron depletion (ID) has been shown to induce the liver expression of Cyp7a1, the rate-limiting enzyme initiating conversion of cholesterol to bile acids (BA), although the effect on bile acids metabolism and bile production is unknown. Therefore, we investigated changes in bile secretion and BA synthesis during diet-induced iron depletion (ID) in rats. ID increased bile flow along with augmented biliary excretion of bile acids, glutathione, cholesterol and phospholipids. Accordingly, we found transcriptional upregulation of the Cyp7a1, Cyp8b1, and Cyp27a1 BA synthetic enzymes, as well as induction of the Abcg5/8 cholesterol transporters in ID rat livers. In contrast, intravenous infusion of ³H-taurocholate failed to elicit any difference in biliary secretion of this compound in the ID rats. This corresponded with unchanged expression of canalicular rate-limiting transporters for BA as well as glutathione. We also observed that ID substantially changed the spectrum of BA in bile and decreased plasma concentrations of BA and cholesterol. Experiments with differentiated human hepatic HepaRG cells confirmed human CYP7A1 orthologue upregulation resulting from reduced iron concentrations. Results employing a luciferase reporter gene assay suggest that the transcriptional activation of the CYP7A1 promoter under ID conditions works independent of farnesoid X (FXR), pregnane X (PXR) and liver X (LXRα) receptors activation. It can be concluded that this study characterizes the molecular mechanisms of modified bile production as well as cholesterol as along with BA homeostasis during ID. We propose complex upregulation of BA synthesis, and biliary cholesterol secretion as the key factors affected by ID.