Bile acid receptor agonists in primary biliary cholangitis: Regulation of the cholangiocyte secretome and downstream T cell differentiation

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.

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.

Cholangiocyte organoids to study drug-induced injury

BACKGROUND

Drug induced bile duct injury is a frequently observed clinical problem leading to a wide range of pathological features. During the past decades, several agents have been identified with various postulated mechanisms of bile duct damage, however, mostly still poorly understood.

METHODS

Here, we investigated the mechanisms of chlorpromazine (CPZ) induced bile duct injury using advanced in vitro cholangiocyte cultures. Intrahepatic cholangiocyte organoids (ICOs) were driven into mature cholangiocyte like cells (CLCs), which were exposed to CPZ under cholestatic or non-cholestatic conditions through the addition of a bile acid cocktail.

RESULTS

CPZ caused loss of monolayer integrity by reducing expression levels of tight junction protein 1 (TJP1), E-cadherin 1 (CDH1) and lysyl oxidase homolog 2 (LOXL2). Loss of zonula occuludens-1 (ZO-1) and E-cadherin was confirmed by immunostaining after exposure to CPZ and rhodamine-123 leakage further confirmed disruption of the cholangiocyte barrier function. Furthermore, oxidative stress seemed to play a major role in the early damage response by CPZ. The drug also decreased expression of three main basolateral bile acid transporters, ABCC3 (ATP binding cassette subfamily C member 3), SLC51A/B (solute carrier family 51 subunit alpha/beta) and multidrug resistance transporter ABCB1 (ATP binding cassette subfamily B member 1), thereby contributing to bile acid accumulation. CPZ did not induce an inflammatory response by itself, but addition of TNFα revealed a synergistic effect.

CONCLUSION

These results show that ICOs present a model to identify toxic drugs affecting the bile ducts while providing mechanistic insights into hepatotoxicity.

Emerging Therapeutic Strategies in The Fight Against Primary Biliary Cholangitis

The liver has a vital role in many metabolic and regulatory processes in the body. Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is a chronic cholestatic autoimmune disease of the intrahepatic bile ducts associated with loss of tolerance to mitochondrial antigens. At this time there is no definitive cure for PBC; however, ursodeoxycholic acid (UDCA) has been shown to reduce injury when administered as the first line of treatment. Additional therapeutics can be given concurrently or as an alternative to UDCA to manage the symptoms and further curb disease progression. Currently, a liver transplant is the only potentially curative option when the patient has developed end-stage liver disease or intractable pruritus. This review aims to delineate the pathogenesis of primary biliary cholangitis and shed light on current therapeutic strategies in the treatment of PBC.

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.

Implications of gut microbiota in autoimmune liver diseases

Autoimmune liver diseases (AILD) are a group of immune-mediated liver inflammatory diseases with three major forms including autoimmune hepatitis (AIH), primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Interaction of both genetic and environmental factors leads to the breakdown of self-tolerance, hence resulting in hyper-responsive of autoantibodies and aggressive autoreactive immune cells. Genetic studies have identified dozens of risk loci associated with initiation and development of AILD. However, the role of exogenous factors remains unclear. Recently, both infectious and inflammatory diseases have been associated with microbiota, which colonizes multiple mucosal surfaces and participates in human physiological process and function in immune system, particularly influencing liver, and biliary system via gut-liver axis. Emerging evidence on the role of gut microbiota has expanded our knowledge of AILD in both pathogenesis and potential therapeutic targets, along with putative diagnosis biomarkers. Herein we review the relationship between host and gut microbiota, discuss their potential roles in disease onset and progression, and summarize the compositional and functional alterations of the microbiota in AILD. We also highlighted the microbiota-based therapeutics such as antibiotics and fecal microbiota transplantation (FMT).

The Effects of Taurocholic Acid on Biliary Damage and Liver Fibrosis Are Mediated by Calcitonin-Gene-Related Peptide Signaling

BACKGROUND & AIMS

Cholangiocytes are the target cells of liver diseases that are characterized by biliary senescence (evidenced by enhanced levels of senescence-associated secretory phenotype, SASP, e.g., TGF-β1), and liver inflammation and fibrosis accompanied by altered bile acid (BA) homeostasis. Taurocholic acid (TC) stimulates biliary hyperplasia by activation of 3',5'-cyclic cyclic adenosine monophosphate (cAMP) signaling, thereby preventing biliary damage (caused by cholinergic/adrenergic denervation) through enhanced liver angiogenesis. Also: (i) α-calcitonin gene-related peptide (α-CGRP, which activates the calcitonin receptor-like receptor, CRLR), stimulates biliary proliferation/senescence and liver fibrosis by enhanced biliary secretion of SASPs; and (ii) knock-out of α-CGRP reduces these phenotypes by decreased cAMP levels in cholestatic models. We aimed to demonstrate that TC effects on liver phenotypes are dependent on changes in the α-CGRP/CALCRL/cAMP/PKA/ERK1/2/TGF-β1/VEGF axis.

METHODS

Wild-type and α-CGRP-/- mice were fed with a control (BAC) or TC diet for 1 or 2 wk. We measured: (i) CGRP levels by both ELISA kits in serum and by qPCR in isolated cholangiocytes (CALCA gene for α-CGRP); (ii) CALCRL immunoreactivity by immunohistochemistry (IHC) in liver sections; (iii) liver histology, intrahepatic biliary mass, biliary senescence (by β-GAL staining and double immunofluorescence (IF) for p16/CK19), and liver fibrosis (by Red Sirius staining and double IF for collagen/CK19 in liver sections), as well as by qPCR for senescence markers in isolated cholangiocytes; and (iv) phosphorylation of PKA/ERK1/2, immunoreactivity of TGF-β1/TGF- βRI and angiogenic factors by IHC/immunofluorescence in liver sections and qPCR in isolated cholangiocytes. We measured changes in BA composition in total liver by liquid chromatography/mass spectrometry.

RESULTS

TC feeding increased CALCA expression, biliary damage, and liver inflammation and fibrosis, as well as phenotypes that were associated with enhanced immunoreactivity of the PKA/ERK1/2/TGF-β1/TGF-βRI/VEGF axis compared to BAC-fed mice and phenotypes that were reversed in α-CGRP-/- mice fed TC coupled with changes in hepatic BA composition.

CONCLUSION

Modulation of the TC/ α-CGRP/CALCRL/PKA/ERK1/2/TGF-β1/VEGF axis may be important in the management of cholangiopathies characterized by BA accumulation.

The Nuclear Receptor PXR in Chronic Liver Disease

Pregnane X receptor (PXR), a nuclear receptor known for modulating the transcription of drug metabolizing enzymes and transporters (DMETs), such as cytochrome P450 3A4 and P-glycoprotein, is functionally involved in chronic liver diseases of different etiologies. Furthermore, PXR activity relates to that of other NRs, such as constitutive androstane receptor (CAR), through a crosstalk that in turn orchestrates a complex network of responses. Thus, besides regulating DMETs, PXR signaling is involved in both liver damage progression and repair and in the neoplastic transition to hepatocellular carcinoma. We here summarize the present knowledge about PXR expression and function in chronic liver diseases characterized by different etiologies and clinical outcome, focusing on the molecular pathways involved in PXR activity. Although many molecular details of these finely tuned networks still need to be fully understood, we conclude that PXR and its modulation could represent a promising pharmacological target for the identification of novel therapeutical approaches to chronic liver diseases.

The Serum Proteome and Ursodeoxycholic Acid Response in Primary Biliary Cholangitis

BACKGROUND AND AIMS

Stratified therapy has entered clinical practice in primary biliary cholangitis (PBC), with routine use of second-line therapy in nonresponders to first-line therapy with ursodeoxycholic acid (UDCA). The mechanism for nonresponse to UDCA remains, however, unclear and we lack mechanistic serum markers. The UK-PBC study was established to explore the biological basis of UDCA nonresponse in PBC and identify markers to enhance treatment.

APPROACH AND RESULTS

Discovery serum proteomics (Olink) with targeted multiplex validation were carried out in 526 subjects from the UK-PBC cohort and 97 healthy controls. In the discovery phase, untreated PBC patients (n = 68) exhibited an inflammatory proteome that is typically reduced in scale, but not resolved, with UDCA therapy (n = 416 treated patients). Nineteen proteins remained at a significant expression level (defined using stringent criteria) in UDCA-treated patients, six of them representing a tightly linked profile of chemokines (including CCL20, known to be released by biliary epithelial cells (BECs) undergoing senescence in PBC). All showed significant differential expression between UDCA responders and nonresponders in both the discovery and validation cohorts. A linear discriminant analysis, using serum levels of C-X-C motif chemokine ligand 11 and C-C motif chemokine ligand 20 as markers of responder status, indicated a high level of discrimination with an AUC of 0.91 (CI, 0.83-0.91).

CONCLUSIONS

UDCA under-response in PBC is characterized by elevation of serum chemokines potentially related to cellular senescence and was previously shown to be released by BECs in PBC, suggesting a potential role in the pathogenesis of high-risk disease. These also have potential for development as biomarkers for identification of high-risk disease, and their clinical utility as biomarkers should be evaluated further in prospective studies.

Primary Biliary Cholangitis and Bile Acid Farnesoid X Receptor Agonists

Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease characterized by the progressive destruction of the intrahepatic bile ducts. Currently, the first line drug for PBC is ursodeoxycholic acid (UDCA) characterized by anti-apoptotic, anti-inflammatory and protective actions on cholangiocytes. Despite its recognized therapeutic action, 30-40% of PBC patients only partially benefit from UDCA therapy. This has led to the identification of the role of the farnesoid x receptor (FXR) in cholestatic liver diseases and, consequently, to the development of obeticholic acid (OCA), a steroid FXR agonist that has been recently approved for the treatment of PBC. OCA though is not effective in all patients and can cause itch, which eventually induces treatment drop out. Therefore, the search for new therapeutic strategies for PBC has begun. This review, in addition to summarizing the current treatments for PBC, provides overview of the chemical characteristics of new steroid FXR agonist candidates that could represent a future perspective for the treatment of PBC.

Obeticholic acid-a new therapy in PBC and NASH

INTRODUCTION

Obeticholic acid (OCA) is a semi-synthetic hydrophobic bile acid (BA) analogue that is highly selective agonist of farnesoid X receptor (FXR), a key nuclear BA receptor, which induces expression of gut-derived hormones, in particular fibroblast growth factor 19. The resulting beneficial effects of OCA on glucose and lipid metabolism and particularly hepatic inflammation make it a candidate for the treatment of a variety of conditions including primary biliary cholangitis (PBC) and nonalcoholic steatohepatitis (NASH).

SOURCES OF DATA

In PBC patients who have not initially responded to ursodeoxycholic acid, OCA has been shown in double-blind controlled clinical trials to significantly reduce serum alkaline phosphatase. To date, OCA is the only therapy licensed by the FDA, EMA and endorsed by NICE as second line therapy for PBC.No medications are currently approved in Europe or the USA for the treatment of NASH.In recent clinical trials, OCA has been shown encouraging results by improving liver blood tests and reducing liver fibrosis with no worsening of NASH.

AREAS OF AGREEMENT

OCA is the established second line therapy for PBC in those patients who fail to adequately respond to ursodeoxycholic acid.

AREAS OF CONTROVERSY

The main side effects of OCA treatment in both PBC and NASH is that of dose-dependent pruritis which can lead to treatment discontinuation in ~1-10% of patients. In addition, OCA-treated patients may also exhibit (reversible) alterations in serum lipid levels; most notably a small decrease in high density lipoprotein cholesterol. It is not yet known whether these changes carry a long-term cardiovascular risk in NASH.In addition, the relatively high cost of OCA may limit its use in cash-limited health systems.

GROWING POINTS

Additional clinical trials are in progress to ascertain the long-term effects of OCA on survival in PBC and NASH.

AREAS TIMELY FOR DEVELOPING RESEARCH

New FXR agonists with a lower rate of side effects are being developed and trialed. Combination therapy with other agents may offer increased efficacy.