Combinatorial targeting of G-protein-coupled bile acid receptor 1 and cysteinyl leukotriene receptor 1 reveals a mechanistic role for bile acids and leukotrienes in drug-induced liver injury.

BACKGROUND AND AIM: Drug-induced liver injury (DILI) is a common disorder that involves both direct liver cell toxicity and immune activation. The bile acid receptor, G-protein-coupled bile acid receptor 1 (GPBAR1; Takeda G-protein-coupled receptor 5 [TGR5]), and cysteinyl leukotriene receptor (CYSLTR) 1 are G-protein-coupled receptors activated by bile acids and leukotrienes, exerting opposite effects on cell-to-cell adhesion, inflammation, and immune cell activation. To investigate whether GPBAR1 and CYSLTR1 mutually interact in the development of DILI, we developed an orally active small molecule, CHIN117, that functions as a GPBAR1 agonist and CYSLTR1 antagonist. APPROACH AND RESULTS: RNA-sequencing analysis of liver explants showed that acetaminophen (APAP) intoxication positively modulates the leukotriene pathway, CYSLTR1, 5-lipoxygenase, and 5-lipoxygenase activating protein, whereas GPBAR1 gene expression was unchanged. In mice, acute liver injury induced by orally dosing APAP (500 mg/kg) was severely exacerbated by Gpbar1 gene ablation and attenuated by anti-Cysltr1 small interfering RNA pretreatment. Therapeutic dosing of wild-type mice with CHIN117 reversed the liver damage caused by APAP and modulated up to 1300 genes, including 38 chemokines and receptors, that were not shared by dosing mice with a selective GPBAR1 agonist or CYSLTR1 antagonist. Coexpression of the two receptors was detected in liver sinusoidal endothelial cells (LSECs), monocytes, and Kupffer cells, whereas combinatorial modulation of CYSLTR1 and GPBAR1 potently reversed LSEC/monocyte interactions. CHIN117 reversed liver damage and liver fibrosis in mice administered CCl 4 . CONCLUSIONS: By genetic and pharmacological approaches, we demonstrated that GPBAR1 and CYSLTR1 mutually interact in the development of DILI. A combinatorial approach designed to activate GPBAR1 while inhibiting CYSLTR1 reverses liver injury in models of DILI.

Development of dual GPBAR1 agonist and RORγt inverse agonist for the treatment of inflammatory bowel diseases.

Inflammatory bowel diseases (IBD), including Crohn's disease and ulcerative colitis, are chronic disorders characterized by dysregulated immune response and persistent inflammation. Recent studies suggest that bile acid receptors, particularly GPBAR1, and the transcription factor RORγt play critical roles in modulating intestinal inflammation. This study evaluates the therapeutic potential of PBT002, a dual GPBAR1 agonist and RORγt inverse agonist, in IBD models. The effects of PBT002 were assessed through in vitro and in vivo experiments. Macrophages and T lymphocytes obtained from the buffy coat were exposed to PBT002 to evaluate its immunomodulatory activity. The beneficial effects in vivo were evaluated in mouse models of colitis induced by TNBS, DSS or DSS + IL-23 using also a Gpbar1 knock-out male mice. PBT002 exhibited an EC50 of 1.2 µM for GPBAR1 and an IC50 of 2.8 µM for RORγt. In in vitro, PBT002 modulated macrophage polarization towards an anti-inflammatory M2 phenotype and reduced Th17 cell markers while increasing Treg markers. In the TNBS-induced colitis model, PBT002 reduced weight loss, CDAI, and colon damage, while it modulated cytokine gene expression towards an anti-inflammatory profile. In GPBAR1-/-, the anti-inflammatory effects of PBT002 were attenuated, indicating partial GPBAR1 dependence. RNA sequencing revealed significant modulation of inflammatory pathways by PBT002. In DSS+IL-23 induced colitis, PBT002 mitigated disease exacerbation, reducing pro-inflammatory cytokine levels and immune cell infiltration. In conclusion, PBT002, a GPBAR1 agonist and RORγt inverse agonist, modulates both the innate and adaptive immune responses to reduce inflammation and disease severity in models of IBD.

Atorvastatin protects against liver and vascular damage in a model of diet induced steatohepatitis by resetting FXR and GPBAR1 signaling.

Farnesoid-x-receptor (FXR) agonists, currently trialed in patients with non-alcoholic steatosis (NAFLD), worsen the pro-atherogenic lipid profile and might require a comedication with statin. Here we report that mice feed a high fat/high cholesterol diet (HFD) are protected from developing a pro-atherogenic lipid profile because their ability to dispose cholesterol through bile acids. This protective mechanism is mediated by suppression of FXR signaling in the liver by muricholic acids (MCAs) generated in mice from chenodeoxycholic acid (CDCA). In contrast to CDCA, MCAs are FXR antagonists and promote a CYP7A1-dependent increase of bile acids synthesis. In mice feed a HFD, the treatment with obeticholic acid, a clinical stage FXR agonist, failed to improve the liver histopathology while reduced Cyp7a1 and Cyp8b1 genes expression and bile acids synthesis and excretion. In contrast, treating mice with atorvastatin mitigated liver and vascular injury caused by the HFD while increased the bile acids synthesis and excretion. Atorvastatin increased the percentage of 7α-dehydroxylase expressing bacteria in the intestine promoting the formation of deoxycholic acid and litocholic acid, two GPBAR1 agonists, along with the expression of GPBAR1-regulated genes in the white adipose tissue and colon. In conclusion, present results highlight the central role of bile acids in regulating lipid and cholesterol metabolism in response to atorvastatin and provide explanations for limited efficacy of FXR agonists in the treatment of NAFLD.

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

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

The bile acid activated receptors GPBAR1 and FXR exert antagonistic effects on autophagy.

Autophagy is a highly conserved catabolic process activated by fasting and caloric restriction. FXR, a receptor for primary bile acids, reverses the activity of cAMP-response element binding protein (CREB) on autophagy-related genes (Atg)s and terminates autophagy in the fed state. GPBAR1, a receptor for secondary bile acids, exerts its genomic effects via cAMP-CREB pathway. By genetic and pharmacological approaches, we have obtained evidence that GPBAR1 functions as a positive modulator of autophagy in liver and white adipose tissue (WAT) in fasting. Mechanistically, we found that Gpbar1-/- mice lack the expression of Cyp2c70 a gene essential for generation of muricholic acids which are FXR antagonists, and have an FXR-biased bile acid pool. Because FXR represses autophagy, Gpbar1-/- mice show a defective regulation of autophagy in fasting. BAR501, a selective GPBAR1 agonist, induces autophagy in fed mice. Defective regulation of autophagy in Gpbar1-/- could be reversed by FXR antagonism, while repression of autophagy by feeding was partially abrogated by FXR gene ablation, and FXR activation repressed Atgs in the fast state. BAR501 reversed the negative regulatory effects of feeding and FXR agonism on autophagy and promoted the recruitment of CREB to a CRE on the LC3 promoter. In mice exposed to chronic high caloric intake, GPBAR1 agonism ameliorated insulin sensitivity and induced Atgs expression in the liver and WAT. In summary, GPBAR1 is required for positive regulation of autophagy in fasting and its ligands reverse the repressive effects exerted on liver and WAT autophagy flow by FXR in fed.

Discovery of Bile Acid Derivatives as Potent ACE2 Activators by Virtual Screening and Essential Dynamics.

The angiotensin-converting enzyme II (ACE2) is a key molecular player in the regulation of vessel contraction, inflammation, and reduction of oxidative stress. In addition, ACE2 has assumed a prominent role in the fight against the COVID-19 pandemic-causing virus SARS-CoV-2, as it is the very first receptor in the host of the viral spike protein. The binding of the spike protein to ACE2 triggers a cascade of events that eventually leads the virus to enter the host cell and initiate its life cycle. At the same time, SARS-CoV-2 infection downregulates ACE2 expression especially in the lung, altering the biochemical signals regulated by the enzyme and contributing to the poor clinical prognosis characterizing the late stage of the COVID-19 disease. Despite its important biological role, a very limited number of ACE2 activators are known. Here, using a combined in silico and experimental approach, we show that ursodeoxycholic acid (UDCA) derivatives work as ACE2 activators. In detail, we have identified two potent ACE2 ligands, BAR107 and BAR708, through a docking virtual screening campaign and elucidated their mechanism of action from essential dynamics of the enzyme observed during microsecond molecular dynamics calculations. The in silico results were confirmed by in vitro pharmacological assays with the newly identified compounds showing ACE2 activity comparable to that of DIZE, the most potent ACE2 activator known so far. Our work provides structural insight into ACE2/ligand-binding interaction useful for the design of compounds with therapeutic potential against SARS-CoV-2 infection, inflammation, and other ACE2-related diseases.

The Bile Acid Receptor GPBAR1 Modulates CCL2/CCR2 Signaling at the Liver Sinusoidal/Macrophage Interface and Reverses Acetaminophen-Induced Liver Toxicity.

Drug-induced liver injury caused by acetaminophen (acetyl-para-aminophenol [APAP]) is the main cause of acute liver failure and liver transplantation in several Western countries. Whereas direct toxicity exerted by APAP metabolites is a key determinant for early hepatocytes injury, the recruitment of cells of innate immunity exerts a mechanistic role in disease progression, determining the clinical outcomes. GPBAR1 is a G protein-coupled receptor for secondary bile acids placed at the interface between liver sinusoidal cells and innate immunity. In this report, using genetic and pharmacological approaches, we demonstrate that whereas Gpbar1 gene deletion worsens the severity of liver injury, its pharmacological activation by 6ß-ethyl-3a,7b-dihydroxy-5b-cholan-24-ol rescues mice from liver injury caused by APAP. This protective effect was supported by a robust attenuation of liver recruitment of monocyte-derived macrophages and their repolarization toward an anti-inflammatory phenotype. Macrophage depletion by gadolinium chloride pretreatment abrogated disease development, whereas their reconstitution by spleen-derived macrophage transplantation restored the sensitivity to APAP in a GPBAR1-dependent manner. RNA sequencing analyses demonstrated that GPBAR1 agonism modulated the expression of multiple pathways, including the chemokine CCL2 and its receptor, CCR2. Treating wild-type mice with an anti-CCL2 mAb attenuated the severity of liver injury. We demonstrated that negative regulation of CCL2 production by GPBAR1 agonism was promoter dependent and involved FOXO1. In conclusion, we have shown that GPBAR1 is an upstream modulator of CCL2/CCR2 axis at the sinusoidal cell/macrophage interface, providing a novel target in the treatment of liver damage caused by APAP.

Bile Acid Signaling in Inflammatory Bowel Diseases.

Bile acids are a group of chemically different steroids generated at the host/microbial interface. Indeed, while primary bile acids are the end-product of cholesterol breakdown in the host liver, secondary bile acids are the products of microbial metabolism. Primary and secondary bile acids along with their oxo derivatives have been identified as signaling molecules acting on a family of cell membrane and nuclear receptors collectively known as "bile acid-activated receptors." Members of this group of receptors are highly expressed throughout the gastrointestinal tract and mediate the bilateral communications of the intestinal microbiota with the host immune system. The expression and function of bile acid-activated receptors FXR, GPBAR1, PXR, VDR, and RORγt are highly dependent on the structure of the intestinal microbiota and negatively regulated by intestinal inflammation. Studies from gene ablated mice have demonstrated that FXR and GPBAR1 are essential to maintain a tolerogenic phenotype in the intestine, and their ablation promotes the polarization of intestinal T cells and macrophages toward a pro-inflammatory phenotype. RORγt inhibition by oxo-bile acids is essential to constrain Th17 polarization of intestinal lymphocytes. Gene-wide association studies and functional characterizations suggest a potential role for impaired bile acid signaling in development inflammatory bowel diseases (IBD). In this review, we will focus on how bile acids and their receptors mediate communications of intestinal microbiota with the intestinal immune system, describing dynamic changes of bile acid metabolism in IBD and the potential therapeutic application of targeting bile acid signaling in these disorders.

Agonism for the bile acid receptor GPBAR1 reverses liver and vascular damage in a mouse model of steatohepatitis.

Nonalcoholic steatohepatitis (NASH) is associated with an increased risk of developing cardiovascular complications and mortality, suggesting that treatment of NASH might benefit from combined approaches that target the liver and the cardiovascular components of NASH. Using genetic and pharmacologic approaches, we show that G protein-coupled bile acid-activated receptor 1 (GPBAR1) agonism reverses liver and vascular damage in mouse models of NASH. NASH is associated with accelerated vascular inflammation representing an independent risk factor for development of cardiovascular diseases and cardiovascular-related mortality. GPBAR1, also known as TGR5, is a G protein-coupled receptor for secondary bile acids that reduces inflammation and promotes energy expenditure. Using genetic and pharmacologic approaches, we investigated whether GPBAR1 agonism by 6ß-ethyl-3α,7ß-dihydroxy-5ß-cholan-24-ol (BAR501) reverses liver and vascular damage induced by exposure to a diet enriched in fat and fructose (HFD-F). Treating HFD-F mice with BAR501 reversed liver injury and promoted the browning of white adipose tissue in a Gpbar1-dependent manner. Feeding HFD-F resulted in vascular damage, as shown by the increased aorta intima-media thickness and increased expression of inflammatory genes (IL-6,TNF-α, iNOS, and F4/80) and adhesion molecules (VCAM, intercellular adhesion molecule-1, and endothelial selectin) in the aorta, while reducing the expression of genes involved in NO and hydrogen sulfide generation, severely altering vasomotor activities of aortic rings in an ex vivo assay. BAR501 reversed this pattern in a Gpbar1-dependent manner, highlighting a potential role for GPBAR1 agonism in treating the liver and vascular component of NASH.-Carino, A., Marchianò, S., Biagioli, M., Bucci, M., Vellecco, V., Brancaleone, V., Fiorucci, C., Zampella, A., Monti, M. C., Distrutti, E., Fiorucci, S. Agonism for the bile acid receptor GPBAR1 reverses liver and vascular damage in a mouse model of steatohepatitis.

The Bile Acid Receptor GPBAR1 Regulates the M1/M2 Phenotype of Intestinal Macrophages and Activation of GPBAR1 Rescues Mice from Murine Colitis.

GPBAR1 (TGR5 or M-BAR) is a G protein-coupled receptor for secondary bile acids that is highly expressed in monocytes/macrophages. In this study, we aimed to determine the role of GPBAR1 in mediating leukocyte trafficking in chemically induced models of colitis and investigate the therapeutic potential of BAR501, a small molecule agonist for GPBAR1. These studies demonstrated that GPBAR1 gene ablation enhanced the recruitment of classically activated macrophages in the colonic lamina propria and worsened the severity of inflammation. In contrast, GPBAR1 activation by BAR501 reversed intestinal inflammation in the trinitrobenzenesulfonic acid and oxazolone models by reducing the trafficking of Ly6C+ monocytes from blood to intestinal mucosa. Exposure to BAR501 shifted intestinal macrophages from a classically activated (CD11b+, CCR7+, F4/80-) to an alternatively activated (CD11b+, CCR7-, F4/80+) phenotype, reduced the expression of inflammatory genes (TNF-α, IFN-γ, IL-1ß, IL-6, and CCL2 mRNAs), and attenuated the wasting syndrome and severity of colitis (≈70% reduction in the Colitis Disease Activity Index). The protective effect was lost in Gpbar1-/- mice. Exposure to BAR501 increased the colonic expression of IL-10 and TGF-ß mRNAs and the percentage of CD4+/Foxp3+ cells. The beneficial effects of BAR501 were lost in Il-10-/- mice. In a macrophage cell line, regulation of IL-10 by BAR501 was GPBAR1 dependent and was mediated by the recruitment of CREB to its responsive element in the IL-10 promoter. In conclusion, GPBAR1 is expressed in circulating monocytes and colonic macrophages, and its activation promotes a IL-10-dependent shift toward an alternatively activated phenotype. The targeting of GPBAR1 may offer therapeutic options in inflammatory bowel diseases.

Wnt/ß-Catenin Signaling Induces Integrin α4ß1 in T Cells and Promotes a Progressive Neuroinflammatory Disease in Mice.

The mechanisms leading to autoimmune and inflammatory diseases in the CNS have not been elucidated. The environmental triggers of the aberrant presence of CD4+ T cells in the CNS are not known. In this article, we report that abnormal ß-catenin expression in T cells drives a fatal neuroinflammatory disease in mice that is characterized by CNS infiltration of T cells, glial activation, and progressive loss of motor function. We show that enhanced ß-catenin expression in T cells leads to aberrant and Th1-biased T cell activation, enhanced expression of integrin α4ß1, and infiltration of activated T cells into the spinal cord, without affecting regulatory T cell function. Importantly, expression of ß-catenin in mature naive T cells was sufficient to drive integrin α4ß1 expression and CNS migration, whereas pharmacologic inhibition of integrin α4ß1 reduced the abnormal T cell presence in the CNS of ß-catenin-expressing mice. Together, these results implicate deregulation of the Wnt/ß-catenin pathway in CNS inflammation and suggest novel therapeutic strategies for neuroinflammatory disorders.

Signaling from Intestine to the Host: How Bile Acids Regulate Intestinal and Liver Immunity.

Primary bile acids (BAs) are generated in the liver as the end products of cholesterol catabolism; they are then conjugated and accumulated in the gallbladder. After a meal ingestion, BAs are reversed into the duodenum to facilitate the lipid absorption. At the intestinal level, the 95% of BAs are reabsorbed and redirected into enterohepatic circulation; indeed only a small amount of them are then subjected to chemical modifications by the intestinal microbiota, which plays a very important role in the generation of secondary bile acids and in regulating host's metabolism and activity of the immune system. Behind their role in nutrients absorption, bile acids act as signaling molecules, activating several receptors, known as bile acid-activated receptors (BARs), including the farnesoid-X-receptor (FXR) and the G protein-coupled bile acid receptor 1 (GPBAR1 or Takeda G-protein receptor 5). Both receptors appear to contribute to maintain the tolerogenic state of the liver and intestine immunity. In particular, FXR and GPBAR1 are highly expressed in cells of innate immunity including intestinal and liver macrophages, dendritic cells, and natural killer T cells. In this chapter, we provide an overview on mechanisms through which FXR and GPBAR1 modulate the signaling between microbiota and intestinal and liver innate immune system. This overview could help to explain beneficial effects exerted by GPBAR1 and FXR agonists in the treatment of metabolic and immuno-mediated diseases.

Future trends in the treatment of non-alcoholic steatohepatitis.

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

Disruption of TFGß-SMAD3 pathway by the nuclear receptor SHP mediates the antifibrotic activities of BAR704, a novel highly selective FXR ligand.

Liver fibrosis, a major health concern worldwide, results from abnormal collagen deposition by activated hepatic stellate cells (HSCs) in an injured liver. The farnesoid-x-receptor (FXR) is a bile acid sensor that counteracts HSCs transdifferentiation. While targeting FXR holds promise, 6-ethyl-CDCA known as obeticholic acid, the first in class of FXR ligands, causes side effects, partially because the lack of selectivity toward GPBAR1, a putative itching receptor. Here, we describe the 3-deoxy-6-ethyl derivative of CDCA, BAR704, as a highly selective steroidal FXR agonist. METHODS: Liver Fibrosis was induced in mice by carbon tetrachloride (CCl4). MAIN RESULTS: In transactivation assay BAR704 activated FXR with and EC50 of 967 nM while exerted no agonistic activity on other receptors including GPBAR1. In naïve mice, BAR704 modulated the expression of FXR target genes in the liver of wild type mice but not in FXR-/- mice. In cirrhotic mice, administration of BAR704, 15 mg/kg for 9 weeks, spared the liver biosynthetic activity (bilirubin and albumin plasma levels), reduced liver fibrosis score (Sirius red staining), expression of pro-fibrogenetic (Colα1α, TGFß and αSMA) and inflammatory genes (IL-1ß, TNFα) and portal pressure. From mechanistic stand point, we have found that exposure of LX2 cells, a human HSCs line, to BAR704 increased the transcription of the short heterodimer partner (SHP) and induced the binding of this nuclear receptor to SMAD3, thus abrogating the binding of phosho-SMAD3 to the TGFß promoter. CONCLUSIONS AND APPLICATIONS: BAR704 is a selective FXR agonist that reduces liver fibrosis by interfering with the TGFß-SMAD3 pathway in HSCs. Selective FXR agonists may represent an attractive strategy for the treatment of liver fibrosis.

Lack of glucocorticoid-induced leucine zipper (GILZ) deregulates B-cell survival and results in B-cell lymphocytosis in mice.

Glucocorticoids (GC) are widely used as antiinflammatory/immunosuppressive drugs and antitumor agents in several types of lymphoma and leukemia. Therapeutic doses of GC induce growth-suppressive and cytotoxic effects on various leukocytes including B cells. Molecular mechanisms of GC action include induction of GC target genes. Glucocorticoid-induced leucine zipper (GILZ) is a rapidly, potently, and invariably GC-induced gene. It mediates a number of GC effects, such as control of cell proliferation, differentiation, and apoptosis. Here we show that deletion of GILZ in mice leads to an accumulation of B lymphocytes in the bone marrow, blood, and lymphoid tissues. Gilz knockout (KO) mice develop a progressive nonlethal B lymphocytosis, with expansion of B220(+) cells in the bone marrow and in the periphery, dependent on increased B-cell survival. Decreased B-cell apoptosis in mice lacking GILZ correlates with increased NF-κB transcriptional activity and Bcl-2 expression. B cell-specific gilz KO mice confirmed that the effect of GILZ deletion is B-cell self-intrinsic. These results establish GILZ as an important regulator of B-cell survival and suggest that the deregulation of GILZ expression could be implicated in the pathogenesis of B-cell disorders.

Bile Acids-Based Therapies for Primary Sclerosing Cholangitis: Current Landscape and Future Developments.

Primary sclerosing cholangitis (PSC) is a rare, chronic liver disease with no approved therapies. The ursodeoxycholic acid (UDCA) has been widely used, although there is no evidence that the use of UDCA delays the time to liver transplant or increases survival. Several candidate drugs are currently being developed. The largest group of these new agents is represented by FXR agonists, including obeticholic acid, cilofexor, and tropifexor. Other agents that target bile acid metabolism are ASTB/IBAP inhibitors and fibroblasts growth factor (FGF)19 analogues. Cholangiocytes, the epithelial bile duct cells, play a role in PSC development. Recent studies have revealed that these cells undergo a downregulation of GPBAR1 (TGR5), a bile acid receptor involved in bicarbonate secretion and immune regulation. Additional agents under evaluation are PPARs (elafibranor and seladelpar), anti-itching agents such as MAS-related G-protein-coupled receptors antagonists, and anti-fibrotic and immunosuppressive agents. Drugs targeting gut bacteria and bile acid pathways are also under investigation, given the strong link between PSC and gut microbiota.

Current Landscape and Evolving Therapies for Primary Biliary Cholangitis.

Primary Biliary Cholangitis (PBC) is a chronic autoimmune liver disorder characterized by progressive cholestatic that, if untreated, can progress to liver fibrosis, cirrhosis and liver decompensation requiring liver transplant. Although the pathogenesis of the disease is multifactorial, there is a consensus that individuals with a genetic predisposition develop the disease in the presence of specific environmental triggers. A dysbiosis of intestinal microbiota is increasingly considered among the potential pathogenic factors. Cholangiocytes, the epithelial cells lining the bile ducts, are the main target of a dysregulated immune response, and cholangiocytes senescence has been recognized as a driving mechanism, leading to impaired bile duct function, in disease progression. Bile acids are also recognized as playing an important role, both in disease development and therapy. Thus, while bile acid-based therapies, specifically ursodeoxycholic acid and obeticholic acid, have been the cornerstone of therapy in PBC, novel therapeutic approaches have been developed in recent years. In this review, we will examine published and ongoing clinical trials in PBC, including the recently approved peroxisome-proliferator-activated receptor (PPAR) agonist, elafibranor and seladelpar. These novel second-line therapies are expected to improve therapy in PBC and the development of personalized approaches.

Immunology of bile acids regulated receptors.

Bile acids are steroids formed at the interface of host metabolism and intestinal microbiota. While primary bile acids are generated in the liver from cholesterol metabolism, secondary bile acids represent the products of microbial enzymes. Close to 100 different enzymatic modifications of bile acids structures occur in the human intestine and clinically guided metagenomic and metabolomic analyses have led to the identification of an extraordinary number of novel metabolites. These chemical mediators make an essential contribution to the composition and function of the postbiota, participating to the bidirectional communications of the intestinal microbiota with the host and contributing to the architecture of intestinal-liver and -brain and -endocrine axes. Bile acids exert their function by binding to a group of cell membrane and nuclear receptors collectively known as bile acid-regulated receptors (BARRs), expressed in monocytes, tissue-resident macrophages, CD4+ T effector cells, including Th17, T regulatory cells, dendritic cells and type 3 of intestinal lymphoid cells and NKT cells, highlighting their role in immune regulation. In this review we report on how bile acids and their metabolitesmodulate the immune system in inflammations and cancers and could be exploiting for developing novel therapeutic approaches in these disorders.

BAR502/fibrate conjugates: synthesis, biological evaluation and metabolic profile.

BAR502, a bile acid analogue, is active as dual FXR/GPBAR1 agonist and represents a promising lead for the treatment of cholestasis and NASH. In this paper we report the synthesis and the biological evaluation of a library of hybrid compounds prepared by combining, through high-yield condensation reaction, some fibrates with BAR502.The activity of the new conjugates was evaluated towards FXR, GPBAR1 and PPARα receptors, employing transactivation or cofactor recruitment assays. Compound 1 resulted as the most promising of the series and was subjected to further pharmacological investigation, together with stability evaluation and cell permeation assessment. We have proved by LCMS analysis that compound 1 is hydrolyzed in mice releasing clofibric acid and BAR505, the oxidized metabolite of BAR502, endowed with retained dual FXR/GPBAR1 activity.