Dual farnesoid X receptor/TGR5 agonist INT-767 reduces liver injury in the Mdr2-/- (Abcb4-/-) mouse cholangiopathy model by promoting biliary HCO⁻₃ output

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of INT-787, a Novel Farnesoid X Receptor Agonist, in Healthy Volunteers: A Phase 1 Trial

Aberrant farnesoid X receptor (FXR) signaling is implicated in cholestatic, inflammatory, and fibrotic liver diseases. In preclinical/clinical studies, semisynthetic bile acid-derived FXR agonists markedly improved hepatic function in various conditions. INT-787, a novel hydrophilic semisynthetic bile acid FXR agonist, has demonstrated a reduction in inflammatory and fibrotic markers and regulation of bile acid/lipid metabolism. This first-in-human, randomized, placebo-controlled phase 1 study assessed the safety, tolerability, pharmacokinetics, and pharmacodynamics of INT-787 and its equipotent metabolites in healthy volunteers by evaluating single ascending doses (SAD), multiple ascending doses (MAD), and food effect. Participants (n = 130) across all study portions were similar in age, race, and body mass index. In the SAD and MAD portions, the maximum plasma concentration (Cmax) and area under the curve (AUC) for total INT-787 generally increased with dose. In the Food Effect portion, the mean Cmax of total INT-787 was almost 2-fold higher under fasted conditions compared with fed conditions; AUC0-inf was unchanged. Steady state for total INT-787 was reached by Day 7. In cohorts receiving ≥ 50 mg doses, the half-life of total INT-787 ranged from 21 to 55 h. INT-787 metabolites exhibited increased concentrations after mealtimes despite morning dosing, consistent with endogenous bile acid behavior. Following single and multiple doses of INT-787, decreases in C4 and increases in FGF-19 levels were observed. Single and multiple oral doses were generally well tolerated; 4 adverse events of mild, transient pruritus not requiring interventions were reported at higher doses. These results warrant further investigation of INT-787 in patients with liver-related disorders.

Transcription factors, metabolic dysfunction-associated fatty liver disease, and therapeutic implications

Metabolic dysfunction-associated fatty liver disease (MAFLD) encompasses a spectrum of liver diseases ranging from metabolic dysfunction-associated fatty liver to metabolic dysfunction-associated steatohepatitis, which may progress to liver cirrhosis and hepatocellular carcinoma. Several mechanisms, including obesity, insulin resistance, dyslipidemia, inflammation, apoptosis, mitochondrial dysfunction, and reactive oxygen species, have been proposed to underlie the progression of MAFLD. Transcription factors are proteins that specifically bind to DNA sequences to regulate the transcription of target genes. Numerous transcription factors regulate MAFLD by modulating the transcription of genes involved in steatosis, inflammation, apoptosis, and fibrosis. Here, we review the pathological factors associated with MAFLD, with a particular emphasis on the transcription factors that contribute to the progression of MAFLD and their therapeutic implications.

Restoring FXR expression as a novel treatment strategy in liver cancer and other liver disorders

INTRODUCTION

Liver cancer is a leading cause of cancer-associated mortality and is often linked to preexisting liver conditions. Emerging research demonstrates FXR dysregulation, particularly its reduced expression, in the pathogenesis of liver diseases, including inflammation, fibrosis, cholestatic disorders, metabolic dysregulation, and liver cancer. Therefore, this review explores the role of FXR and its agonists in mitigating these conditions.

AREAS COVERED

This article summarizes FXR's involvement in liver disorders, primarily emphasizing on hepatic neoplasms, and examines the potential of FXR agonists in restoring FXR activity in liver diseases, thereby preventing their progression to liver cancer. The information presented is drawn from existing preclinical and clinical studies specific to each liver disorder, sourced from PubMed.

EXPERT OPINION

It is well established that FXR expression is downregulated in liver disorders, contributing to disease progression. Notably, FXR agonists have demonstrated therapeutic potential in ameliorating liver diseases, including hepatocellular carcinoma. We believe that activating or restoring FXR expression with agonists offers significant promise for the treatment of liver cancer and other liver conditions. Therefore, FXR modulation by agonists, particularly in combination with other therapeutic agents, could lead to more targeted treatments, improving efficacy while reducing side effects.

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic biliary inflammation associated with periductular fibrosis of the intrahepatic and extrahepatic bile ducts leading to strictures, bacterial cholangitis, decompensated liver disease and need for liver transplantation. This rare focal liver disease affects all races and ages, with a predominance of young males. There is an up to 88% association with inflammatory bowel disease. Although the aetiology is unknown and the pathophysiology is poorly understood, PSC is regarded as an autoimmune liver disease based on a strong immunogenetic background. Further, the associated risk for various malignancies, particularly cholangiocellular carcinoma, is also poorly understood. No medical therapy has been approved so far nor has been shown to improve transplant-free survival. However, ursodeoxycholic acid is widely used since it improves the biochemical parameters of cholestasis and is safe at low doses. MRI of the biliary tract is the primary imaging technology for diagnosis. Endoscopic interventions of the bile ducts should be limited to clinically relevant strictures for balloon dilatation, biopsy and brush cytology. End-stage liver disease with decompensation is an indication for liver transplantation with recurrent PSC in up to 38% of patients. Several novel therapeutic strategies are in various stages of development, including apical sodium-dependent bile acid transporter and ileal bile acid transporter inhibitors, integrin inhibitors, peroxisome proliferator-activated receptor agonists, CCL24 blockers, recombinant FGF19, CCR2/CCR5 inhibitors, farnesoid X receptor bile acid receptor agonists, and nor-ursodeoxycholic acid. Manipulation of the gut microbiome includes faecal microbiota transplantation. This article summarizes present knowledge and defines unmet medical needs to improve quality of life and survival.

Liver GPBAR1 Associates With Immune Dysfunction in Primary Sclerosing Cholangitis and Its Activation Attenuates Cholestasis in Abcb4-/- Mice

BACKGROUND AND AIMS

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterised by progressive biliary inflammation and fibrosis, leading to liver cirrhosis and cholangiocarcinoma. GPBAR1 (TGR5) is a G protein-coupled receptor for secondary bile acids. In this study, we have examined the therapeutic potential of BAR501, a selective GPBAR1 agonist in a PSC model.

METHODS

Single-cell analysis of healthy human liver samples and gene expression analysis of PSC liver samples were conducted. In vitro studies on a human cholangiocyte cell line (NHC), U937 and human hepatic stellate cells (hSteCs) were performed. Additionally, Abcb4-/- mice were treated with BAR501 for 12-24 weeks.

RESULTS

Single-cell analysis demonstrated that GPBAR1 is expressed by macrophages, NK cells, sinusoidal cells and to a lesser extent by cholangiocytes. Total liver expression of GPBAR1 increases in PSC patients compared to that in healthy controls and positively correlates with markers for monocytes and NK cells and cytokeratin 19. In vitro treatment of NHCs with BAR501 reversed the acquisition of a pro-inflammatory phenotype and the downregulation of GPBAR1 expression promoted by LPS in an NF-κB-dependent manner. Treating Abcb4-/- mice reduced bile duct inflammation and liver fibrosis and prevented the downregulation of GPBAR1 expression. Treating mice with BAR501 also modulated the bile acid pool composition and reduced the dysbiosis-associated gut permeability, and intestinal and systemic inflammation. Ex vivo experiments using conditioned media from BAR501-treated cholangiocytes mitigated the activation of macrophages.

CONCLUSIONS

Our study provides evidence for the therapeutic potential of selective GPBAR1 agonists in intestinal inflammation-associated cholestasis, warranting the evaluation of BAR501 in PSC patients.

From Pathophysiology to Practice: Evolving Pharmacological Therapies, Clinical Complications, and Pharmacogenetic Considerations in Portal Hypertension

Background: Portal hypertension is a major complication of chronic liver diseases, leading to serious issues such as esophageal variceal bleeding. The increase in portal vein pressure is driven by both an organic component and a functional component, including tonic contraction of hepatic stellate cells. These processes result in a pathological rise in intrahepatic vascular resistance, stemming from partial impairment of hepatic microcirculation, which is further exacerbated by abnormalities in extrahepatic vessels, including increased portal blood flow. Objectives: This review aims to provide a comprehensive overview of the evolving pharmacological therapies for portal hypertension, with consideration and discussion of pathophysiological mechanisms, clinical complications, and pharmacogenetic considerations, highlighting potential directions for future research. Methods: A review of recent literature was performed to evaluate current knowledge and potential therapeutic strategies in portal hypertension. Results: For over 35 years, non-selective beta-blockers have been the cornerstone therapy for portal hypertension by reducing portal vein inflow as an extrahepatic target, effectively preventing decompensation and variceal hemorrhages. However, since not all patients exhibit an adequate response to non-selective beta-blockers (NSBBs), and some may not tolerate NSBBs, alternative or adjunctive therapies that enhance the effects of NSBBs on portal pressure are being investigated in preclinical and early clinical studies. Conclusions: A better understanding of pharmacogenetic factors and pathophysiological mechanisms could lead to more individualized and effective treatments for portal hypertension. These insights highlight potential directions for future research.

Bile acid metabolism and signalling in liver disease

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

Aberrant basement membrane production by HSCs in MASLD is attenuated by the bile acid analog INT-767

BACKGROUND

The farnesoid X receptor (FXR) is a leading therapeutic target for metabolic dysfunction-associated steatohepatitis (MASH)-related fibrosis. INT-767, a potent FXR agonist, has shown promise in preclinical models. We aimed to define the mechanisms of INT-767 activity in experimental MASH and dissect cellular and molecular targets of FXR agonism in human disease.

METHODS

Leptin-deficient ob/ob mice were fed a MASH-inducing diet for 15 weeks before the study started. After baseline liver biopsy and stratification, mice were allocated to INT-767 (10 mg/kg/d) or vehicle treatment for 8 weeks, either alongside an ongoing MASH diet (progression) or following conversion to normal chow (reversal). Effects on extracellular matrix remodeling were analyzed histologically and by RNA-sequencing. Serum fibrosis biomarkers were measured longitudinally. Human liver samples were investigated using bulk and single-cell RNA-sequencing, histology, and cell culture assays.

RESULTS

INT-767 treatment was antifibrotic during MASH progression but not reversal, attenuating the accumulation of type I collagen and basement membrane proteins (type IV collagen and laminin). Circulating levels of PRO-C4, a type IV collagen formation marker, were reduced by INT-767 treatment and correlated with fibrosis. Expression of basement membrane constituents also correlated with fibrosis severity and adverse clinical outcomes in human MASH. Single-cell RNA-sequencing analysis of mouse and human livers, and immunofluorescence staining colocalized FXR and basement membrane expression to myofibroblasts within the fibrotic niche. Treatment of culture-activated primary human HSCs with INT-767 decreased expression of basement membrane components.

CONCLUSIONS

These findings highlight the importance of basement membrane remodeling in MASH pathobiology and as a source of circulating biomarkers. Basement membrane deposition by activated HSCs is abrogated by INT-767 treatment and measurement of basement membrane molecules should be included when determining the therapeutic efficacy of FXR agonists.

Cardiovascular Disease May Be Triggered by Gut Microbiota, Microbial Metabolites, Gut Wall Reactions, and Inflammation

Cardiovascular disease (CVD) may be inherited, as recently shown with the identification of single nucleotide polymorphisms (SNPs or "snips") on a 250 kb DNA fragment that encodes 92 proteins associated with CVD. CVD is also triggered by microbial dysbiosis, microbial metabolites, metabolic disorders, and inflammatory intestinal epithelial cells (IECs). The epithelial cellular adhesion molecule (Ep-CAM) and trefoil factor 3 (TFF3) peptide keeps the gut wall intact and healthy. Variations in Ep-CAM levels are directly linked to changes in the gut microbiome. Leptin, plasminogen activator inhibitor 1 (PAI1), and alpha-1 acid glycoprotein 1 (AGP1) are associated with obesity and may be used as biomarkers. Although contactin 1 (CNTN1) is also associated with obesity and adiposity, it regulates the bacterial metabolism of tryptophan (Trp) and thus appetite. A decrease in CNTN1 may serve as an early warning of CVD. Short-chain fatty acids (SCFAs) produced by gut microbiota inhibit pro-inflammatory cytokines and damage vascular integrity. Trimethylamine N-oxide (TMAO), produced by gut microbiota, activates inflammatory Nod-like receptors (NLRs) such as Nod-like receptor protein 3 (NLRP3), which increase platelet formation. Mutations in the elastin gene (ELN) cause supra valvular aortic stenosis (SVAS), defined as the thickening of the arterial wall. Many of the genes expressed by human cells are regulated by gut microbiota. The identification of new molecular markers is crucial for the prevention of CVD and the development of new therapeutic strategies. This review summarizes the causes of CVD and identifies possible CVD markers.

Central role for cholangiocyte pathobiology in cholestatic liver diseases

Cholangiopathies comprise a spectrum of chronic intrahepatic and extrahepatic biliary tract disorders culminating in progressive cholestatic liver injury, fibrosis, and often cirrhosis and its sequela. Treatment for these diseases is limited, and collectively, they are one of the therapeutic "black boxes" in clinical hepatology. The etiopathogenesis of the cholangiopathies likely includes disease-specific mediators but also common cellular and molecular events driving disease progression (eg, cholestatic fibrogenesis, inflammation, and duct damage). The common pathways involve cholangiocytes, the epithelial cells lining the intrahepatic and extrahepatic bile ducts, which are central to the pathogenesis of these disorders. Current information suggests that cholangiocytes function as a signaling "hub" in biliary tract-associated injury. Herein, we review the pivotal role of cholangiocytes in cholestatic fibrogenesis, focusing on the crosstalk between cholangiocytes and portal fibroblasts and HSCs. The proclivity of these cells to undergo a senescence-associated secretory phenotype, which is proinflammatory and profibrogenic, and the intrinsic intracellular activation pathways resulting in the secretion of cytokines and chemokines are reviewed. The crosstalk between cholangiocytes and cells of the innate (neutrophils and macrophages) and adaptive (T cells and B cells) immune systems is also examined in detail. The information will help consolidate information on this topic and guide further research and potential therapeutic strategies for these diseases.

Biliary fibrosis is an important but neglected pathological feature in hepatobiliary disorders: from molecular mechanisms to clinical implications

Fibrosis resulting from pathological repair secondary to recurrent or persistent tissue damage often leads to organ failure and mortality. Biliary fibrosis is a crucial but easily neglected pathological feature in hepatobiliary disorders, which may promote the development and progression of benign and malignant biliary diseases through pathological healing mechanisms secondary to biliary tract injuries. Elucidating the etiology and pathogenesis of biliary fibrosis is beneficial to the prevention and treatment of biliary diseases. In this review, we emphasized the importance of biliary fibrosis in cholangiopathies and summarized the clinical manifestations, epidemiology, and aberrant cellular composition involving the biliary ductules, cholangiocytes, immune system, fibroblasts, and the microbiome. We also focused on pivotal signaling pathways and offered insights into ongoing clinical trials and proposing a strategic approach for managing biliary fibrosis-related cholangiopathies. This review will offer a comprehensive perspective on biliary fibrosis and provide an important reference for future mechanism research and innovative therapy to prevent or reverse fibrosis.

Patented Farnesoid X receptor modulators: a review (2019 - present)

INTRODUCTION

The Farnesoid X receptor (FXR) is a key transcription factor that is involved in the bile acid signaling network. The modulation of the FXR activity influences glucose and lipid homeostasis, reduces obesity and insulin resistance, as well as it regulates the pathogenesis of inflammatory and metabolic disorders. FXR ligands have therefore emerged in drug discovery as promising therapeutic agents for the prevention and treatment of gastrointestinal and liver diseases, including cancer.

AREAS COVERED

Recent advances in the field of FXR modulators are reviewed, with a particular attention on patent applications filed in the past 5 years related to both the discovery and development of FXR targeting drugs.

EXPERT OPINION

FXR agonists have proven their efficacy and safety in humans and have shown a significant potential as clinical agents to treat metabolic and inflammatory associated conditions. However, several challenges, including adverse events such as pruritus, remain to be solved. Current studies aim to gain insights into the pathophysiological mechanisms by which FXR regulates metabolism and inflammation in terms of tissue/organ/isoform-specificity, post-translational modifications and coregulatory proteins, on the route of novel, improved FXR modulators.

Targeting Farnesoid X Receptor in Tumor and the Tumor Microenvironment: Implication for Therapy

The farnesoid-X receptor (FXR), a member of the nuclear hormone receptor superfamily, can be activated by bile acids (BAs). BAs binding to FXR activates BA signaling which is important for maintaining BA homeostasis. FXR is differentially expressed in human organs and exists in immune cells. The dysregulation of FXR is associated with a wide range of diseases including metabolic disorders, inflammatory diseases, immune disorders, and malignant neoplasm. Recent studies have demonstrated that FXR influences tumor cell progression and development through regulating oncogenic and tumor-suppressive pathways, and, moreover, it affects the tumor microenvironment (TME) by modulating TME components. These characteristics provide a new perspective on the FXR-targeted therapeutic strategy in cancer. In this review, we have summarized the recent research data on the functions of FXR in solid tumors and its influence on the TME, and discussed the mechanisms underlying the distinct function of FXR in various types of tumors. Additionally, the impacts on the TME by other BA receptors such as takeda G protein-coupled receptor 5 (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic receptors (CHRM2 and CHRM3), have been depicted. Finally, the effects of FXR agonists/antagonists in a combination therapy with PD1/PD-L1 immune checkpoint inhibitors and other anti-cancer drugs have been addressed.

Obeticholic acid treatment of mice to promote fertilization and reproduction

Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, has been demonstrated to ameliorate the histopathological characteristics of liver damage. Nonetheless, the systemic safety profile of OCA with regard to reproduction and development remains poorly understood. In the present study, we conducted a dose-response experiment by administering OCA at doses of 5 mg/kg, 10 mg/kg, or 20 mg/kg through tube feeding to investigate its effect on reproductive development and fertilization rate in both male and female mice. Furthermore, we evaluated the levels of protein and mitochondrial function in the placenta through western blot, qPCR, and scanning electron microscopy. The results showed that 10 mg/kg and 20 mg/kg OCA doses significantly reduced the rate of placental implantation (P < 0.05). Also, OCA increased maternal body weight. In addition, OCA increased levels of FXR and TGR5 and produced changes in oxidative stress levels (P < 0.05). Mitochondrial activity result found that 10 mg/kg and 20 mg/kg of OCA significantly reduced the mitophagy autosomes/nucleus compared with the normal control group (P < 0.05). What is more, there was no significant difference in sperm count after OCA intervention in either C57BL/10 mice or BALB/c mice. Overall, we demonstrated that OCA treatment protected against placental implantation by suppressing placental oxidative stress and mitochondrial activity.

Non-steroidal FXR agonist cilofexor improves cholestatic liver injury in the Mdr2-/- mouse model of sclerosing cholangitis

Background & Aims

The nuclear receptor farnesoid X receptor (FXR) is a key regulator of hepatic bile acid (BA) and lipid metabolism, inflammation and fibrosis. Here, we aimed to explore the potential of cilofexor (GS-9674), a non-steroidal FXR agonist, as a therapeutic approach for counteracting features of cholestatic liver injury by evaluating its efficacy and mechanisms in the Mdr2/Abcb4 knockout (-/-) mouse model of sclerosing cholangitis.

Methods

FVB/N wild-type and Mdr2-/- or BALB/c wild-type and Mdr2-/- mice were treated with 0, 10, 30 or 90 mg/kg cilofexor by gavage every 24 h for 10 weeks. Serum biochemistry, gene expression profile, hydroxyproline content, and picrosirius red and F4/80 immunostaining, were investigated. Bile flow, biliary bicarbonate and BA output, and hepatic BA profile, were assessed.

Results

Cilofexor treatment improved serum levels of aspartate aminotransferase, alkaline phosphatase as well as BAs in Mdr2-/- animals. Hepatic fibrosis was improved, as reflected by the reduced picrosirius red-positive area and hydroxyproline content in liver sections of cilofexor-treated Mdr2-/- mice. Intrahepatic BA concentrations were lowered in cilofexor-treated Mdr2-/- mice, while hepatobiliary bile flow and bicarbonate output were increased.

Conclusion

Collectively the current data show that cilofexor treatment improves cholestatic liver injury and decreases hepatic fibrosis in the Mdr2-/- mouse model of sclerosing cholangitis.

Impact and implications

Treatment with cilofexor, a non-steroidal farnesoid X receptor (FXR) agonist, improved histological features of sclerosing cholangitis, cholestasis and hepatic fibrosis in the Mdr2-/- mouse model. These findings indicate, that pharmacological stimulation of intestinal FXR-mediated gut-liver signaling, via fibroblast growth factor 15 (thereby reducing bile acid synthesis), may be sufficient to attenuate cholestatic liver injury in the Mdr2-/- mouse model of sclerosing cholangitis, thus arguing for potential therapeutic properties of cilofexor in cholestatic liver diseases.

INT-767-A Dual Farnesoid-X Receptor (FXR) and Takeda G Protein-Coupled Receptor-5 (TGR5) Agonist Improves Survival in Rats and Attenuates Intestinal Ischemia Reperfusion Injury

Intestinal ischemia is a potentially catastrophic emergency, with a high rate of morbidity and mortality. Currently, no specific pharmacological treatments are available. Previous work demonstrated that pre-treatment with obeticholic acid (OCA) protected against ischemia reperfusion injury (IRI). Recently, a more potent and water-soluble version has been synthesized: Intercept 767 (INT-767). The aim of this study was to investigate if intravenous treatment with INT-767 can improve outcomes after IRI. In a validated rat model of IRI (60 min ischemia + 60 min reperfusion), three groups were investigated (n = 6/group): (i) sham: surgery without ischemia; (ii) IRI + vehicle; and (iii) IRI + INT-767. The vehicle (0.9% NaCl) or INT-767 (10 mg/kg) were administered intravenously 15 min after start of ischemia. Endpoints were 7-day survival, serum injury markers (L-lactate and I-FABP), histology (Park-Chiu and villus length), permeability (transepithelial electrical resistance and endotoxin translocation), and cytokine expression. Untreated, IRI was uniformly lethal by provoking severe inflammation and structural damage, leading to translocation and sepsis. INT-767 treatment significantly improved survival by reducing inflammation and preserving intestinal structural integrity. This study demonstrates that treatment with INT-767 15 min after onset of intestinal ischemia significantly decreases IRI and improves survival. The ability to administer INT-767 intravenously greatly enhances its clinical potential.

Bile acid-mediated signaling in cholestatic liver diseases

Chronic cholestatic liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), are associated with bile stasis and gradually progress to fibrosis, cirrhosis, and liver failure, which requires liver transplantation. Although ursodeoxycholic acid is effective in slowing the disease progression of PBC, it has limited efficacy in PSC patients. It is challenging to develop effective therapeutic agents due to the limited understanding of disease pathogenesis. During the last decade, numerous studies have demonstrated that disruption of bile acid (BA) metabolism and intrahepatic circulation promotes the progression of cholestatic liver diseases. BAs not only play an essential role in nutrition absorption as detergents but also play an important role in regulating hepatic metabolism and modulating immune responses as key signaling molecules. Several excellent papers have recently reviewed the role of BAs in metabolic liver diseases. This review focuses on BA-mediated signaling in cholestatic liver disease.

Protective and aggressive bacterial subsets and metabolites modify hepatobiliary inflammation and fibrosis in a murine model of PSC

OBJECTIVE

Conflicting microbiota data exist for primary sclerosing cholangitis (PSC) and experimental models.

GOAL

define the function of complex resident microbes and their association relevant to PSC patients by studying germ-free (GF) and antibiotic-treated specific pathogen-free (SPF) multidrug-resistant 2 deficient (mdr2-/- ) mice and microbial profiles in PSC patient cohorts.

DESIGN

We measured weights, liver enzymes, RNA expression, histological, immunohistochemical and fibrotic biochemical parameters, faecal 16S rRNA gene profiling and metabolomic endpoints in gnotobiotic and antibiotic-treated SPF mdr2-/- mice and targeted metagenomic analysis in PSC patients.

RESULTS

GF mdr2-/- mice had 100% mortality by 8 weeks with increasing hepatic bile acid (BA) accumulation and cholestasis. Early SPF autologous stool transplantation rescued liver-related mortality. Inhibition of ileal BA transport attenuated antibiotic-accelerated liver disease and decreased total serum and hepatic BAs. Depletion of vancomycin-sensitive microbiota exaggerated hepatobiliary disease. Vancomycin selectively decreased Lachnospiraceae and short-chain fatty acids (SCFAs) but expanded Enterococcus and Enterobacteriaceae. Antibiotics increased Enterococcus faecalis and Escherichia coli liver translocation. Colonisation of GF mdr2-/- mice with translocated E. faecalis and E. coli strains accelerated hepatobiliary inflammation and mortality. Lachnospiraceae colonisation of antibiotic pretreated mdr2-/- mice reduced liver fibrosis, inflammation and translocation of pathobionts, and SCFA-producing Lachnospiraceae and purified SCFA decreased fibrosis. Faecal Lachnospiraceae negatively associated, and E. faecalis/ Enterobacteriaceae positively associated, with PSC patients' clinical severity by Mayo risk scores.

CONCLUSIONS

We identified novel functionally protective and detrimental resident bacterial species in mdr2-/- mice and PSC patients with associated clinical risk score. These insights may guide personalised targeted therapeutic interventions in PSC patients.

Biosensor-based active ingredient recognition system for screening TNF-α inhibitors from lotus leaves

Erhuangquzhi granules (EQG) have been clinically proven to be effective in nonalcoholic steatohepatitis (NASH) treatment. However, the active components and molecular mechanisms remain unknown. This study aimed to screen active components targeting tumor necrosis factor α (TNF-α) in EQG for the treatment of NASH by a surface plasmon resonance (SPR) biosensor-based active ingredient recognition system (SPR-AIRS). The amine-coupling method was used to immobilize recombinant TNF-α protein on an SPR chip, the specificity of the TNF-α-immobilized chip was validated, and nine medicinal herbs in EQG were prescreened. Nuciferine (NF), lirinidine (ID), and O-nornuciferine (NNF) from lotus leaves were found and identified as TNF-α ligands by UPLC‒MS/MS, and the affinity constants of NF, ID, and NNF to TNF-α were determined by SPR experiments (Kd = 61.19, 31.02, and 20.71 µM, respectively). NF, ID, and NNF inhibited TNF-α-induced apoptosis in L929 cells, the levels of secreted IL-6 and IL-1β were reduced, and the phosphorylation of IKKβ and IκB was inhibited in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. In conclusion, a class of new active small-molecule TNF-α inhibitors was discovered, which also provides a valuable reference for the material basis and mechanism of EQG action in NASH treatment.

Bile Acids and Biliary Fibrosis

Biliary fibrosis is the driving pathological process in cholangiopathies such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Cholangiopathies are also associated with cholestasis, which is the retention of biliary components, including bile acids, in the liver and blood. Cholestasis may worsen with biliary fibrosis. Furthermore, bile acid levels, composition and homeostasis are dysregulated in PBC and PSC. In fact, mounting data from animal models and human cholangiopathies suggest that bile acids play a crucial role in the pathogenesis and progression of biliary fibrosis. The identification of bile acid receptors has advanced our understanding of various signaling pathways involved in regulating cholangiocyte functions and the potential impact on biliary fibrosis. We will also briefly review recent findings linking these receptors with epigenetic regulatory mechanisms. Further detailed understanding of bile acid signaling in the pathogenesis of biliary fibrosis will uncover additional therapeutic avenues for cholangiopathies.

Primary biliary cholangitis as a roadmap for the development of novel treatments for cholestatic liver diseases†

The discovery of nuclear receptors and transporters has contributed to the development of new drugs for the treatment of cholestatic liver diseases. Particular progress has been made in the development of second-line therapies for PBC. These new drugs can be separated into compounds primarily targeting cholestasis, molecules targeting fibrogenesis and molecules with immune-mediated action. Finally, drugs aimed at symptom relief (pruritus and fatigue) are also under investigation. Obeticholic acid is currently the only approved second-line therapy for PBC. Drugs in the late phase of clinical development include peroxisome proliferator-activated receptor agonists, norursodeoxycholic acid and NADPH oxidase 1/4 inhibitors.

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.

Anti-Cholestatic Therapy with Obeticholic Acid Improves Short-Term Memory in Bile Duct-Ligated Mice

Patients with cholestatic liver disease, including those with primary biliary cholangitis, can experience symptoms of impaired cognition or brain fog. This phenomenon remains unexplained and is currently untreatable. Bile duct ligation (BDL) is an established rodent model of cholestasis. In addition to liver changes, BDL animals develop cognitive symptoms early in the disease process (before development of cirrhosis and/or liver failure). The cellular mechanisms underpinning these cognitive symptoms are poorly understood. Herein, the study explored the neurocognitive symptom manifestations, and tested potential therapies, in BDL mice, and used human neuronal cell cultures to explore translatability to humans. BDL animals exhibited short-term memory loss and showed reduced astrocyte coverage of the blood-brain barrier, destabilized hippocampal network activity, and neuronal senescence. Ursodeoxycholic acid (first-line therapy for most human cholestatic diseases) did not reverse symptomatic or mechanistic aspects. In contrast, obeticholic acid (OCA), a farnesoid X receptor agonist and second-line anti-cholestatic agent, normalized memory function, suppressed blood-brain barrier changes, prevented hippocampal network deficits, and reversed neuronal senescence. Co-culture of human neuronal cells with either BDL or human cholestatic patient serum induced cellular senescence and increased mitochondrial respiration, changes that were limited again by OCA. These findings provide new insights into the mechanism of cognitive symptoms in BDL animals, suggesting that OCA therapy or farnesoid X receptor agonism could be used to limit cholestasis-induced neuronal senescence.

The role of gut microbiota in liver regeneration

The liver has unique regeneration potential, which ensures the continuous dependence of the human body on hepatic functions. As the composition and function of gut microbiota has been gradually elucidated, the vital role of gut microbiota in liver regeneration through gut-liver axis has recently been accepted. In the process of liver regeneration, gut microbiota composition is changed. Moreover, gut microbiota can contribute to the regulation of the liver immune microenvironment, thereby modulating the release of inflammatory factors including IL-6, TNF-α, HGF, IFN-γ and TGF-β, which involve in different phases of liver regeneration. And previous research have demonstrated that through enterohepatic circulation, bile acids (BAs), lipopolysaccharide, short-chain fatty acids and other metabolites of gut microbiota associate with liver and may promote liver regeneration through various pathways. In this perspective, by summarizing gut microbiota-derived signaling pathways that promote liver regeneration, we unveil the role of gut microbiota in liver regeneration and provide feasible strategies to promote liver regeneration by altering gut microbiota composition.

Ginsenoside Rc, as an FXR activator, alleviates acetaminophen-induced hepatotoxicity via relieving inflammation and oxidative stress

Acetaminophen (APAP) intake leads to excessive NAPQI deposition, stimulating inflammatory and oxidative stress and causing fatal liver injury. However, the detailed molecular mechanism involved is unknown, and effective therapeutic approaches remain insufficient. In this study, we discovered that treatment with ginsenoside Rc can prevent the inflammatory response caused by APAP and oxidative stress in mouse primary hepatocytes (MPHs), along with the corresponding changes in related genes. Additionally, Ginsenoside Rc effectively alleviates APAP-induced cellular apoptosis and NAPQI accumulation in MPHs. In vivo, Ginsenoside Rc administration remarkably attenuates APAP-induced hepatotoxicity, repairing liver damage and improving survival. Moreover, Ginsenoside Rc treatment modulates genes involved in APAP metabolism, leading to a decrease in NAPQI and resulting in the alleviation of fatal oxidative stress and inflammatory response after APAP exposure, along with the expression of their related indicators. Furthermore, our RNA-seq and molecular docking analysis implies that FXR expression and FXR transcriptional activity are stimulated by Ginsenoside Rc treatment. Notably, due to the lack of FXR in mice and MPHs, ginsenoside Rc can no longer play its original protective role against hepatotoxicity and cell damage caused by APAP, and it is difficult to improve the corresponding survival rate and prevent hepatic apoptosis, NAPQI generation, fatal oxidative stress, and the inflammatory response induced by APAP and the expression of related genes. In summary, our results indicate that Ginsenoside Rc could act as an effective FXR activator and effectively regulate FXR-induced antioxidant stress and eliminate inflammation while also having an anti-apoptotic function.

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.

Ileal bile acid transporter inhibition in Cyp2c70 KO mice ameliorates cholestatic liver injury

Cyp2c70 is the liver enzyme in rodents responsible for synthesis of the primary 6-hydroxylated muricholate bile acid (BA) species. Cyp2c70 KO mice are devoid of protective, hydrophilic muricholic acids, leading to a more human-like BA composition and subsequent cholestatic liver injury. Pharmacological inhibition of the ileal BA transporter (IBAT) has been shown to be therapeutic in cholestatic models. Here, we aimed to determine if IBAT inhibition with SC-435 is protective in Cyp2c70 KO mice. As compared to WT mice, we found male and female Cyp2c70 KO mice exhibited increased levels of serum liver injury markers, and our evaluation of liver histology revealed increased hepatic inflammation, macrophage infiltration, and biliary cell proliferation. We demonstrate serum and histologic markers of liver damage were markedly reduced with SC-435 treatment. Additionally, we show hepatic gene expression in pathways related to immune cell activation and inflammation were significantly upregulated in Cyp2c70 KO mice and reduced to levels indistinguishable from WT with IBAT inhibition. In Cyp2c70 KO mice, the liver BA content was significantly increased, enriched in chenodeoxycholic acid, and more hydrophobic, exhibiting a hydrophobicity index value and red blood cell lysis properties similar to human liver BAs. Furthermore, we determined IBAT inhibition reduced the total hepatic BA levels but did not affect overall hydrophobicity of the liver BAs. These findings suggest that there may be a threshold in the liver for pathological accretion of hydrophobic BAs and reducing hepatic BA accumulation can be sufficient to alleviate liver injury, independent of BA pool hydrophobicity.

Development of 3α,7α-dihydroxy-6α-ethyl-24-nor-5β-cholan-23-sulfate sodium salt (INT-767): Process optimization, synthesis and characterization of metabolites

Herein we report our synthetic efforts in supporting the development of the bile alcohol sulfate INT-767, a FXR/TGR5 dual agonist with remarkable therapeutic potential for liver disorders. We describe the process development to a final route for large scale preparation and analogues synthesis. Key sequences include Grignard addition, a one-pot two-step shortening-reduction of the carboxylic side chain, and the final sulfation reaction. The necessity for additional steps such as the protection/deprotection of hydroxyl groups at the steroidal body was also evaluated for step-economy and formation of side-products. Critical bottlenecks such as the side chain degradation have been tackled using flow technology before scaling-up individual steps. The final synthetic route may be successfully employed to produce the amount of INT-767 required to support late-stage clinical development of the compound. Furthermore, potential metabolites have been synthesized, characterized and evaluated for their ability to modulate FXR and TGR5 receptors providing key reference standards for future drug investigations, as well as offering further insights into the structure-activity relationships of this class of compounds.

Targeting bile acid signaling for the treatment of liver diseases: From bench to bed

Liver diseases and related complications have become one of the leading causes of morbidity and mortality worldwide, yet effective medicine or approved treatment approach is still limited. Thus, novel therapy is urgently required to prevent or at least slow down the growing burden of liver transplantation or even death caused by malignant liver diseases. As the irreplaceable modulator of hepatic and intestinal signaling cascades, bile acids (BAs) play complex physiological as well as pathological roles in regulating energy and immune homeostasis in various liver diseases, including but not limited to metabolic diseases and cholangiopathies, making them highly attractive therapeutic targets. In the current review, recent progress in the research of enterohepatic circulation of BAs and potential therapeutic targets of BAs signaling, especially the development of currently available treatments, including agonizts of FXR and TGR5, analogs of FGF19, inhibitors of ASBT, and the regulation of gut microbiome through fecal microbiota transplantation were extensively summarized. Their protective effects, molecular mechanisms, and outcomes of clinical trials were highlighted. The structural features of these candidates and perspectives for their future development were further discussed. In conclusion, we believe that pharmacological therapies targeting BAs signaling represent promising and efficient strategies for the treatment of complex and multifactorial liver disorders.

Recent advances on FXR-targeting therapeutics

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

Role of bile acids and their receptors in gastrointestinal and hepatic pathophysiology

Bile acids (BAs) can regulate their own metabolism and transport as well as other key aspects of metabolic homeostasis via dedicated (nuclear and G protein-coupled) receptors. Disrupted BA transport and homeostasis results in the development of cholestatic disorders and contributes to a wide range of liver diseases, including nonalcoholic fatty liver disease and hepatocellular and cholangiocellular carcinoma. Furthermore, impaired BA homeostasis can also affect the intestine, contributing to the pathogenesis of irritable bowel syndrome, inflammatory bowel disease, and colorectal and oesophageal cancer. Here, we provide a summary of the role of BAs and their disrupted homeostasis in the development of gastrointestinal and hepatic disorders and present novel insights on how targeting BA pathways might contribute to novel treatment strategies for these disorders.

Bile acids and their receptors: modulators and therapeutic targets in liver inflammation

Bile acids participate in the intestinal emulsion, digestion, and absorption of lipids and fat-soluble vitamins. When present in high concentrations, as in cholestatic liver diseases, bile acids can damage cells and cause inflammation. After the discovery of bile acids receptors about two decades ago, bile acids are considered signaling molecules. Besides regulating bile acid, xenobiotic, and nutrient metabolism, bile acids and their receptors have shown immunomodulatory properties and have been proposed as therapeutic targets for inflammatory diseases of the liver. This review focuses on bile acid-related signaling pathways that affect inflammation in the liver and provides an overview of the preclinical and clinical applications of modulators of these pathways for the treatment of cholestatic and autoimmune liver diseases.

Molecular Basis of Bile Acid-FXR-FGF15/19 Signaling Axis

Bile acids (BAs) are a group of amphiphilic molecules consisting of a rigid steroid core attached to a hydroxyl group with a varying number, position, and orientation, and a hydrophilic side chain. While BAs act as detergents to solubilize lipophilic nutrients in the small intestine during digestion and absorption, they also act as hormones. Farnesoid X receptor (FXR) is a nuclear receptor that forms a heterodimer with retinoid X receptor α (RXRα), is activated by BAs in the enterohepatic circulation reabsorbed via transporters in the ileum and the colon, and plays a critical role in regulating gene expression involved in cholesterol, BA, and lipid metabolism in the liver. The FXR/RXRα heterodimer also exists in the distal ileum and regulates production of fibroblast growth factor (FGF) 15/FGF19, a hormone traveling via the enterohepatic circulation that activates hepatic FGF receptor 4 (FGFR4)-β-klotho receptor complex and regulates gene expression involved in cholesterol, BA, and lipid metabolism, as well as those regulating cell proliferation. Agonists for FXR and analogs for FGF15/19 are currently recognized as a promising therapeutic target for metabolic syndrome and cholestatic diseases.

Intercellular crosstalk of liver sinusoidal endothelial cells in liver fibrosis, cirrhosis and hepatocellular carcinoma

Intercellular crosstalk among various liver cells plays an important role in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Capillarization of liver sinusoidal endothelial cells (LSECs) precedes fibrosis and accumulating evidence suggests that the crosstalk between LSECs and other liver cells is critical in the development and progression of liver fibrosis. LSECs dysfunction, a key event in the progression from fibrosis to cirrhosis, and subsequently obstruction of hepatic sinuses and increased intrahepatic vascular resistance (IHVR) contribute to development of portal hypertension (PHT) and cirrhosis. More importantly, immunosuppressive tumor microenvironment (TME), which is closely related to the crosstalk between LSECs and immune liver cells like CD8+ T cells, promotes advances tumorigenesis, especially HCC. However, the connections within the crosstalk between LSECs and other liver cells during the progression from liver fibrosis to cirrhosis to HCC have yet to be discussed. In this review, we first summarize the current knowledge of how different crosstalk between LSECs and other liver cells, including hepatocytes, hepatic stellate cells (HSCs), macrophoges, immune cells in liver and extra cellular matrix (ECM) contribute to the physiological function and the progrssion from liver fibrosis to cirrhosis, or even to HCC. Then we examine current treatment strategies for LSECs crosstalk in liver fibrosis, cirrhosis and HCC.

Loss of luminal carbonic anhydrase XIV results in decreased biliary bicarbonate output, liver fibrosis, and cholangiocyte proliferation in mice

Carbonic anhydrase XIV (Car14) is highly expressed in the hepatocyte, with predominance in the canalicular membrane and its active site in the extracellular milieu. The aim of this study is to determine the physiological relevance of Car14 for biliary fluid and acid/base output, as well as its role in the maintenance of hepatocellular and cholangiocyte integrity. The common bile duct of anesthetized car14^-/- and car14^+/+ mice was cannulated and hepatic HCO₃^- output was measured by microtitration and bile flow gravimetrically before and during stimulation with intravenously applied tauroursodeoxycholic acid (TUDCA). Morphological alterations and hepatic damage were assessed histologically and immunohistochemically in liver tissue from 3- to 52-week-old car14^-/- and car14^+/+ mice, and gene and/or protein expression was measured for pro-inflammatory cytokines, fibrosis, and cholangiocyte markers. Biliary basal and more so TUDCA-stimulated HCO₃^- output were significantly reduced in car14^-/- mice of all age groups, whereas bile flow and hepatic and ductular morphology were normal at young age. Car14^-/- mice developed fibrotic and proliferative changes in the small bile ducts at advanced age, which was accompanied by a reduction in bile flow, and an upregulation of hepatic cytokeratin 19 mRNA and protein expression. Membrane-bound Car14 is essential for biliary HCO₃^- output, and its loss results in gradual development of small bile duct disease and hepatic fibrosis. Bile flow is not compromised in young adulthood, suggesting that Car14-deficient mice may be a model to study the protective role of biliary canalicular HCO₃^- against luminal noxi to the cholangiocyte.

Therapeutic Opportunities of GPBAR1 in Cholestatic Diseases

GPBAR1, a transmembrane G protein-coupled receptor for bile acids, is widely expressed in multiple tissues in humans and rodents. In recent years, GPBAR1 has been thought to play an important role in bile homeostasis, metabolism and inflammation. This review specifically focuses on the function of GPBAR1 in cholestatic liver disease and summarizes the various pathways through which GPBAR1 acts in cholestatic models. GPBAR1 mainly regulates cholestasis in a holistic system of liver-gallbladder-gut formation. In the state of cholestasis, the activation of GPBAR1 could regulate liver inflammation, induce cholangiocyte regeneration to maintain the integrity of the biliary tree, control the hydrophobicity of the bile acid pool and promote the secretion of bile HCO₃⁻. All these functions of GPBAR1 might be clear ways to protect against cholestatic diseases and liver injury. However, the characteristic of GPBAR1-mediated proliferation increases the risk of proliferation of cholangiocarcinoma in malignant transformed cholangiocytes. This dichotomous function of GPBAR1 limits its use in cholestasis. During disease treatment, simultaneous activation of GPBAR1 and FXR receptors often results in improved outcomes, and this strategy may become a crucial direction in the development of bile acid-activated receptors in the future.

Changes in beta-catenin expression and activation during progression of primary sclerosing cholangitis predict disease recurrence

Primary sclerosing cholangitis (PSC) is a rare, chronic, cholestatic liver disease characterized by progressive inflammation and fibrosis of the bile ducts. We have previously demonstrated the importance of Wnt/β-catenin signaling in mouse models of PSC. In this study, we wished to determine the clinical relevance of β-catenin localization in patient samples. In livers explanted from patients diagnosed with PSC, the majority (12/16; 75%) lacked β-catenin protein expression. Biopsies from patients post-transplant were classified as recurrent or non-recurrent based on pathology reports and then scored for β-catenin activation as a function of immunohistochemical localization. Despite lack of statistical significance, patients with recurrent primary disease (n = 11) had a greater percentage of samples with nuclear, transcriptionally active β-catenin (average 58.8%) than those with no recurrence (n = 10; 40.53%), while non-recurrence is correlated with β-catenin staining at the cell surface (average 52.63% for non-recurrent vs. 27.34% for recurrent), as determined by three different methods of analysis. β-catenin score and years-to-endpoint are both strongly associated with recurrence status (p = 0.017 and p = 0.00063, respectively). Finally, there was significant association between higher β-catenin score and increased alkaline phosphatase, a marker of biliary injury and disease progression. Thus, β-catenin expression and activation changes during the progression of PSC, and its localization may be a useful prognostic tool for predicting recurrence of this disease.

Downregulation of TGR5 (GPBAR1) in biliary epithelial cells contributes to the pathogenesis of sclerosing cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterized by chronic inflammation and progressive fibrosis of the biliary tree. The bile acid receptor TGR5 (GPBAR1) is found on biliary epithelial cells (BECs), where it promotes secretion, proliferation and tight junction integrity. Thus, we speculated that changes in TGR5-expression in BECs may contribute to PSC pathogenesis.

METHODS

TGR5-expression and -localization were analyzed in PSC livers and liver tissue, isolated bile ducts and BECs from Abcb4^-/-, Abcb4^-/-/Tgr5^Tg and ursodeoxycholic acid (UDCA)- or 24-norursodeoxycholic acid (norUDCA)-fed Abcb4^-/- mice. The effects of IL8/IL8 homologues on TGR5 mRNA and protein levels were studied. BEC gene expression was analyzed by single-cell transcriptomics (scRNA-seq) from distinct mouse models.

RESULTS

TGR5 mRNA expression and immunofluorescence staining intensity were reduced in BECs of PSC and Abcb4^-/- livers, in Abcb4^-/- extrahepatic bile ducts, but not in intrahepatic macrophages. No changes in TGR5 BEC fluorescence intensity were detected in liver tissue of other liver diseases, including primary biliary cholangitis. Incubation of BECs with IL8/IL8 homologues, but not with other cytokines, reduced TGR5 mRNA and protein levels. BECs from Abcb4^-/- mice had lower levels of phosphorylated Erk and higher expression levels of Icam1, Vcam1 and Tgfβ2. Overexpression of Tgr5 abolished the activated inflammatory phenotype characteristic of Abcb4^-/- BECs. NorUDCA-feeding restored TGR5-expression levels in BECs in Abcb4^-/- livers.

CONCLUSIONS

Reduced TGR5 levels in BECs from patients with PSC and Abcb4^-/- mice promote development of a reactive BEC phenotype, aggravate biliary injury and thus contribute to the pathogenesis of sclerosing cholangitis. Restoration of biliary TGR5-expression levels represents a previously unknown mechanism of action of norUDCA.

LAY SUMMARY

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease-associated with progressive inflammation of the bile duct, leading to fibrosis and end-stage liver disease. Bile acid (BA) toxicity may contribute to the development and disease progression of PSC. TGR5 is a membrane-bound receptor for BAs, which is found on bile ducts and protects bile ducts from BA toxicity. In this study, we show that TGR5 levels were reduced in bile ducts from PSC livers and in bile ducts from a genetic mouse model of PSC. Our investigations indicate that lower levels of TGR5 in bile ducts may contribute to PSC development and progression. Furthermore, treatment with norUDCA, a drug currently being tested in a phase III trial for PSC, restored TGR5 levels in biliary epithelial cells.

Farnesoid X receptor and fibroblast growth factor 15/19 as pharmacological targets

The farnesoid X receptor (FXR) is a nuclear receptor and transcriptional regulator activated by bile acids or synthetic FXR agonists. FXR is expressed highly in the liver and intestine where modulation of FXR critically regulates the expression of genes involved in cholesterol and bile acid homeostasis, hepatic gluconeogenesis/lipogenesis, and inflammation. We review the roles of FXR and one of its intestinal target genes, fibroblast growth factor (FGF) 15 in mice/FGF19 in humans, play in regulating these important pathways in health and diseases. The main purpose of this review is to review therapeutics that target bile acid signaling to treat non-alcoholic steatohepatitis (NASH), a stage of disease within the spectrum of non-alcoholic fatty liver disease (NAFLD) with a focus on current preclinical studies in mice and clinical research. NASH is a huge medical burden and characterized by hepatic steatosis, inflammation, and progressive development of liver fibrosis. However, there is currently no Food and Drug Administration approved treatment option for NASH. While there are multiple factors contributing to NASH pathophysiology, bile acid regulation is proposed to have a major role in NASH pathogenesis. Synthetic FXR agonists and FGF19 protein may be promising agents to treat NASH, with obeticholic acid (OCA), cilofexor, tropifexor, nidufexor, EDP-305, and NGM282 currently in phase II or III clinical trials of NASH. FXR antagonism has also emerged, and antagonists like ursodeoxycholic acid (UDCA) and glycine-beta-muricholic acid (Gly-MCA) are in pre-clinical stage development for NASH treatment. This mini review seeks to evaluate and organize the literature available on FXR ligands and pathways for the treatment of NASH.

Nuclear Receptors in Liver Fibrosis

Nuclear receptors are ligand-activated transcription factors that regulate gene expression of a variety of key molecular signals involved in liver fibrosis. The primary cellular driver of liver fibrogenesis are activated hepatic stellate cells. Different NRs regulate the hepatic expression of pro-inflammatory and pro-fibrogenic cytokines that promote the transformation of hepatic stellate cells into fibrogenic myofibroblasts. Importantly, nuclear receptors regulate gene expression circuits that promote hepatic fibrogenesis and/or allow liver fibrosis regression. In this review, we highlight the direct and indirect influence of nuclear receptors on liver fibrosis, with a focus on hepatic stellate cells, and discuss potential therapeutic effects of nuclear receptor modulation in regard to anti-fibrotic and anti-inflammatory effects. Further research on nuclear receptors-related signaling may lead to the clinical development of effective anti-fibrotic therapies for patients with liver disease.

Farnesoid X receptor (FXR): Structures and ligands

Farnesoid X receptor (FXR) is a bile acid activated nuclear receptor (BAR) and is mainly expressed in the liver and intestine. Upon ligand binding, FXR regulates key genes involved in the metabolic process of bile acid synthesis, transport and reabsorption and is also involved in the metabolism of carbohydrates and lipids. Because of its important functions, FXR is considered as a promising drug target for the therapy of bile acid-related liver diseases. With the approval of obeticholic acid (OCA) as the first small molecule to target FXR, many other small molecules are being evaluated in clinical trials. This review summarizes the structures of FXR, especially its ligand binding domain, and the development of small molecules (including agonists and antagonists) targeting FXR.

Isotschimgine alleviates nonalcoholic steatohepatitis and fibrosis via FXR agonism in mice

Farnesoid X receptor (FXR) agonist obeticholic acid (OCA) has emerged as a potential therapy for nonalcoholic fatty liver disease (NAFLD). However, the side effects of OCA may limit its application in clinics. We identified previously that isotschimgine (ITG) is a non-steroidal FXR selective agonist and has potent therapeutic effects on NAFLD in mice. Here, we aimed to evaluate the therapeutic effects of ITG on nonalcoholic steatohepatitis (NASH) and fibrosis in mice. We used methionine and choline deficient (MCD) diet-induced NASH mice, bile duct ligation (BDL), and carbon tetrachloride (CCl₄ )-treated hepatic fibrosis mice to investigate the effects of ITG on NASH, fibrosis, and cholestatic liver injury. Our results showed that ITG improved steatosis and inflammation in the liver of MCD diet-fed mice, as well as alleviated fibrosis and inflammation in the liver of CCl₄ -treated mice. Furthermore, ITG attenuated serum bile acid levels, and reduced vacuolization, inflammatory infiltration, hepatic parenchymal necrosis, and collagen accumulation in the liver of BDL mice. Mechanistically, ITG increased the expression of FXR target genes. These data suggest that ITG is an FXR agonist and may be developed as a novel therapy for NASH, hepatic fibrosis, or primary biliary cholangitis.

Hepatobiliary acid-base homeostasis: Insights from analogous secretory epithelia

Many epithelia secrete bicarbonate-rich fluid to generate flow, alter viscosity, control pH and potentially protect luminal and intracellular structures from chemical stress. Bicarbonate is a key component of human bile and impaired biliary bicarbonate secretion is associated with liver damage. Major efforts have been undertaken to gain insight into acid-base homeostasis in cholangiocytes and more can be learned from analogous secretory epithelia. Extrahepatic examples include salivary and pancreatic duct cells, duodenocytes, airway and renal epithelial cells. The cellular machinery involved in acid-base homeostasis includes carbonic anhydrase enzymes, transporters of the solute carrier family, and intra- and extracellular pH sensors. This pH-regulatory system is orchestrated by protein-protein interactions, the establishment of an electrochemical gradient across the plasma membrane and bicarbonate sensing of the intra- and extracellular compartment. In this review, we discuss conserved principles identified in analogous secretory epithelia in the light of current knowledge on cholangiocyte physiology. We present a framework for cholangiocellular acid-base homeostasis supported by expression analysis of publicly available single-cell RNA sequencing datasets from human cholangiocytes, which provide insights into the molecular basis of pH homeostasis and dysregulation in the biliary system.

The gut microbiome-bile acid axis in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and is a leading cause of cancer-related deaths globally, with few effective therapeutic options. Bile acids (BAs) are synthesized from cholesterol in the liver and can be modulated by farnesoid X receptor (FXR) and G-protein coupled BA receptor 1 (GPBAR1/TGR5). Alterations in BAs can affect hepatic metabolic homeostasis and contribute to the pathogenesis of liver cancer. Increasing evidence points to the key role of bacterial microbiota in the promotion and development of liver cancer. They are also involved in the regulation of BA synthesis and metabolism. The purpose of this review is to integrate related articles involving gut microbiota, BAs and HCC, and review how the gut microbiota-BA signaling axis can possibly influence the development of HCC.

Enterohepatic circulation of bile acids and their emerging roles on glucolipid metabolism

Bile acids (BAs) are amphiphilic molecules with a nonpolar steroid carbon skeleton and a polar carboxylate side chain. Recently, BAs have aroused the attention of scholars due to their potential roles on metabolic diseases. As important endogenous ligands, BAs are wildly active in the enterohepatic circulation, during which microbiota play a significant role in promoting the hydrolysis and dehydroxylation of BAs. Besides, many pathways initiated by BAs including glucolipid metabolism and inflammation signaling pathways have been reported to regulate the host metabolism and maintain immune homeostasis. Herein, the characteristics on the enterohepatic circulation and metabolism of BAs are systematically summarized. Moreover, the regulation mechanism of the glucolipid metabolism by BAs is intensively discussed. Worthily, FXR and TGR5, which are involved in glucolipid metabolism, are the prime candidates for targeted therapies of chronic metabolic diseases such as diabetes and hypercholesterolemia.

Bile Acids and GPBAR-1: Dynamic Interaction Involving Genes, Environment and Gut Microbiome

Bile acids (BA) are amphiphilic molecules synthesized in the liver from cholesterol. BA undergo continuous enterohepatic recycling through intestinal biotransformation by gut microbiome and reabsorption into the portal tract for uptake by hepatocytes. BA are detergent molecules aiding the digestion and absorption of dietary fat and fat-soluble vitamins, but also act as important signaling molecules via the nuclear receptor, farnesoid X receptor (FXR), and the membrane-associated G protein-coupled bile acid receptor 1 (GPBAR-1) in the distal intestine, liver and extra hepatic tissues. The hydrophilic-hydrophobic balance of the BA pool is finely regulated to prevent BA overload and liver injury. By contrast, hydrophilic BA can be hepatoprotective. The ultimate effects of BA-mediated activation of GPBAR-1 is poorly understood, but this receptor may play a role in protecting the remnant liver and in maintaining biliary homeostasis. In addition, GPBAR-1 acts on pathways involved in inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity, and sinusoidal blood flow. Recent evidence suggests that environmental factors influence GPBAR-1 gene expression. Thus, targeting GPBAR-1 might improve liver protection, facilitating beneficial metabolic effects through primary prevention measures. Here, we discuss the complex pathways linked to BA effects, signaling properties of the GPBAR-1, mechanisms of liver damage, gene-environment interactions, and therapeutic aspects.

Knockout of the Tachykinin Receptor 1 in the Mdr2-/- (Abcb4-/-) Mouse Model of Primary Sclerosing Cholangitis Reduces Biliary Damage and Liver Fibrosis

Activation of the substance P (SP)/neurokinin 1 receptor (NK1R) axis triggers biliary damage/senescence and liver fibrosis in bile duct ligated and Mdr2-/- (alias Abcb4-/-) mice through enhanced transforming growth factor-β1 (TGF-β1) biliary secretion. Recent evidence indicates a role for miR-31 (MIR31) in TGF-β1-induced liver fibrosis. We aimed to define the role of the SP/NK1R/TGF-β1/miR-31 axis in regulating biliary proliferation and liver fibrosis during cholestasis. Thus, we generated a novel model with double knockout of Mdr2-/- and NK1R-/ (alias Tacr1-/-) to further address the role of the SP/NK1R axis during chronic cholestasis. In vivo studies were performed in the following 12-week-old male mice: (i) NK1R-/-; (ii) Mdr2-/-; and (iii) NK1R-/-/Mdr2-/- (Tacr1-/-/Abcb4-/-) and their corresponding wild-type controls. Liver tissues and cholangiocytes were collected, and liver damage, changes in biliary mass/senescence, and inflammation as well as liver fibrosis were evaluated by both immunohistochemistry in liver sections and real-time PCR. miR-31 expression was measured by real-time PCR in isolated cholangiocytes. Decreased ductular reaction, liver fibrosis, biliary senescence, and biliary inflammation were observed in NK1R-/-/Mdr2-/- mice compared with Mdr2-/- mice. Elevated expression of miR-31 was observed in Mdr2-/- mice, which was reduced in NK1R-/-/Mdr2-/- mice. Targeting the SP/NK1R and/or miR-31 may be a potential approach in treating human cholangiopathies, including primary sclerosing cholangitis.