Obeticholic Acid: An Update of Its Pharmacological Activities in Liver Disorders

Bile acids and their receptors in hepatic immunity

Similarly to conventional steroids, bile acids function as signaling molecules, acting on a family of membrane and nuclear receptors. The best-characterized bile acid-regulated receptors are the farnesoid X receptor, activated by primary bile acids, and the G-protein-coupled bile acid receptor 1 (also known as Takeda G protein-coupled receptor 5), which is activated by secondary bile acids, such as lithocholic acid (LCA) and deoxycholic acid. Both the farnesoid X receptor and G-protein-coupled bile acid receptor 1 are expressed in cells of innate immunity, monocytes/macrophages, and natural killer cells. Their activation in these cells provides counter-regulatory signals that are inhibitory in nature and attenuate inflammation. In recent years, however, it has been increasingly appreciated that bile acids biotransformations by intestinal microbiota result in the formation of chemically different secondary bile acids that potently regulate adaptive immunity. The 3-oxoLCA and isoalloLCA, two LCA derivatives, bind receptors such as the retinoic acid receptor-related orphan receptor gamma t (RORγt) and the vitamin D receptor (VDR) that are expressed only by lymphoid cells, extending the regulatory role of bile acids to T cells, including T-helper 17 cells and type 3 innate lymphoid cells (ILC3). In this novel conceptual framework, bile acids have emerged as one of the main components of the postbiota, the waste array of chemical mediators generated by the intestinal microbiota. Deciphering the interaction of these mediators with the immune system in the intestine and liver is a novel and fascinating area of bile acid renaissance.

Design, Synthesis, and Pharmacological Evaluation of Dual FXR-LIFR Modulators for the Treatment of Liver Fibrosis

Although multiple approaches have been suggested, treating mild-to-severe fibrosis in the context of metabolic dysfunction associated with liver disease (MASLD) remains a challenging area in drug discovery. Pathogenesis of liver fibrosis is multifactorial, and pathogenic mechanisms are deeply intertwined; thus, it is well accepted that future treatment requires the development of multitarget modulators. Harnessing the 3,4,5-trisubstituted isoxazole scaffold, previously described as a key moiety in Farnesoid X receptor (FXR) agonism, herein we report the discovery of a novel class of hybrid molecules endowed with dual activity toward FXR and the leukemia inhibitory factor receptor (LIFR). Up to 27 new derivatives were designed and synthesized. The pharmacological characterization of this series resulted in the identification of 3a as a potent FXR agonist and LIFR antagonist with excellent ADME properties. In vitro and in vivo characterization identified compound 3a as the first-in-class hybrid LIFR inhibitor and FXR agonist that protects against the development of acute liver fibrosis and inflammation.

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.

Discovery of 4-aminophenylacetamide derivatives as intestine-specific farnesoid X receptor antagonists for the potential treatment of nonalcoholic steatohepatitis

Farnesoid X receptor (FXR) plays a key role in bile acid homeostasis, inflammation, fibrosis, lipid and glucose metabolism and is emerging as a promising therapeutic target for nonalcoholic steatohepatitis (NASH). Emerging evidence suggested that intestine-specific FXR antagonists exhibited remarkable metabolic improvements and slowed NASH progression. In this study, we discovered several potent FXR antagonists using a multistage ligand- and structure-based virtual screening approach. Notably, compound V023-9340, which possesses a 4-aminophenylacetamide scaffold, emerged as the most potent FXR antagonist with an IC50 value of 4.27 μM. In vivo, V023-9340 demonstrated selective accumulation in the intestine, substantially ameliorating high-fat diet (HFD)-induced NASH in mice by mitigating hepatic steatosis and inflammation. Mechanistic studies revealed that V023-9340 strongly inhibited intestinal FXR while concurrently feedback-activated hepatic FXR. Further structure-activity relationship optimization employing V023-9340 has resulted in the synthesis of a more efficacious compound V02-8 with an IC50 value of 0.89 μM, which exhibited a 4.8-fold increase in FXR antagonistic activity compared to V023-9340. In summary, 4-aminophenylacetamide derivative V023-9340 represented a novel intestine-specific FXR antagonist and showed improved effects against HFD-induced NASH in mice, which may serve as a promising lead in discovering potential therapeutic drugs for NASH treatment.

The regulation of tissue-specific farnesoid X receptor on genes and diseases involved in bile acid homeostasis

Bile acids (BAs) facilitate the absorption of dietary lipids and vitamins and have also been identified as signaling molecules involved in regulating their own metabolism, glucose and lipid metabolism, as well as immunity. Disturbances in BA homeostasis are associated with various enterohepatic and metabolic diseases, such as cholestasis, nonalcoholic steatohepatitis, inflammatory bowel disease, and obesity. As a key regulator, the nuclear orphan receptor farnesoid X receptor (FXR, NR1H4) precisely regulates BA homeostasis by transcriptional regulation of genes involved in BA synthesis, metabolism, and enterohepatic circulation. FXR is widely regarded as the most potential therapeutic target. Obeticholic acid is the only FXR agonist approved to treat patients with primary biliary cholangitis, but its non-specific activation of systemic FXR also causes high-frequency side effects. In recent years, developing tissue-specific FXR-targeting drugs has become a research highlight. This article provides a comprehensive overview of the role of tissue-specific intestine/liver FXR in regulating genes involved in BA homeostasis and briefly discusses tissue-specific FXR as a therapeutic target for treating diseases. These findings provide the basis for the development of tissue-specific FXR modulators for the treatment of enterohepatic and metabolic diseases associated with BA dysfunction.

Development of bile acid activated receptors hybrid molecules for the treatment of inflammatory and metabolic disorders

The farnesoid-x-receptor (FXR) and the G protein bile acid activated receptor (GPBAR)1 are two bile acid activated receptors highly expressed in entero-hepatic, immune, adipose and cardiovascular tissues. FXR and GPBAR1 are clinically validated targets in the treatment of metabolic disorders and FXR agonists are currently trialled in patients with non-alcoholic steato-hepatitis (NASH). Results of these trials, however, have raised concerns over safety and efficacy of selective FXR ligands suggesting that the development of novel agent designed to impact on multiple targets might have utility in the treatment of complex, multigenic, disorders. Harnessing on FXR and GPBAR1 agonists, several novel hybrid molecules have been developed, including dual FXR and GPBAR1 agonists and antagonists, while exploiting the flexibility of FXR agonists toward other nuclear receptors, dual FXR and peroxisome proliferators-activated receptors (PPARs) and liver-X-receptors (LXRs) and Pregnane-X-receptor (PXR) agonists have been reported. In addition, modifications of FXR agonists has led to the discovery of dual FXR agonists and fatty acid binding protein (FABP)1 and Leukotriene B4 hydrolase (LTB4H) inhibitors. The GPBAR1 binding site has also proven flexible to accommodate hybrid molecules functioning as GPBAR1 agonist and cysteinyl leukotriene receptor (CYSLTR)1 antagonists, as well as dual GPBAR1 agonists and retinoid-related orphan receptor (ROR)γt antagonists, dual GPBAR1 agonist and LXR antagonists and dual GPBAR1 agonists endowed with inhibitory activity on dipeptidyl peptidase 4 (DPP4). In this review we have revised the current landscape of FXR and GPBAR1 based hybrid agents focusing on their utility in the treatment of metabolic associated liver disorders.

FXR and NASH: an avenue for tissue-specific regulation

NASH is within the spectrum of NAFLD, a liver condition encompassing liver steatosis, inflammation, hepatocyte injury, and fibrosis. The prevalence of NASH-induced cirrhosis is rapidly rising and has become the leading indicator for liver transplantation in the US. There is no Food and Drug Administration (FDA)-approved pharmacological intervention for NASH. The farnesoid X receptor (FXR) is essential in regulating bile acid homeostasis, and dysregulation of bile acids has been implicated in the pathogenesis of NASH. As a result, modulators of FXR that show desirable effects in mitigating key characteristics of NASH have been developed as promising therapeutic approaches. However, global FXR activation causes adverse effects such as cholesterol homeostasis imbalance and pruritus. The development of targeted FXR modulation is necessary for ideal NASH therapeutics, but information regarding tissue-specific and cell-specific FXR functionality is limited. In this review, we highlight FXR activation in the regulation of bile acid homeostasis and NASH development, examine the current literature on tissue-specific regulation of nuclear receptors, and speculate on how FXR regulation will be beneficial in the treatment of NASH.

FXR agonists for colorectal and liver cancers, as a stand-alone or in combination therapy

Farnesoid X receptor (FXR, NR1H4) is generally considered as a tumor suppressor of colorectal and liver cancers. The interaction between FXR, bile acids (BAs) and gut microbiota is closely associated with an increased risk of colorectal and liver cancers. Increasing evidence shows that FXR agonists may be potential therapeutic agents for colorectal and liver cancers. However, FXR agonists alone do not produce the desired results due to the complicated pathogenesis and single therapeutic mechanism, which suggests that effective treatments will require a multimodal approach. Based on the principle of improvingefficacy andreducingside effects, combination therapy is currently receiving considerable attention. In this review, colorectal and liver cancers are grouped together to discuss the effects of FXR agonists alone or in combination for combating the two cancers. We hope that this review will provide a theoretical basis for the clinical application of novel FXR agonists or combination with FXR agonists against colorectal and liver cancers.

Repurposing FDA-approved drugs as FXR agonists: a structure based in silico pharmacological study

Farnesoid X receptor (FXR) modulates the expression of genes involved in lipid and carbohydrate homeostasis and inflammatory processes. This nuclear receptor is likely a tumor suppressor in several cancers, but its molecular mechanism of suppression is still under study. Several studies reported that FXR agonism increases the survival of colorectal, biliary tract, and liver cancer patients. In addition, FXR expression was shown to be down-regulated in many diseases such as obesity, irritable bowel syndrome, glomerular inflammation, diabetes, proteinuria, and ulcerative colitis. Therefore, development of novel FXR agonists may have significant potential in the prevention and treatment of these diseases. In this scenario, computer-aided drug design procedures can be resourcefully applied for the rapid identification of promising drug candidates. In the present study, we applied the molecular docking method in conjunction with molecular dynamics (MD) simulations to find out potential agonists for FXR based on structural similarity with the drug that is currently used as FXR agonist, obeticholic acid. Our results showed that alvimopan and montelukast could be used as potent FXR activators and outperform the binding affinity of obeticholic acid by forming stable conformation with the protein in silico. However, further investigational studies and validations of the selected drugs are essential to figure out their suitability for preclinical and clinical trials.

Machine learning- and structure-based discovery of a novel chemotype as FXR agonists for potential treatment of nonalcoholic fatty liver disease

Farnesoid X receptor (FXR) is a promising target for drug discovery against nonalcoholic fatty liver disease (NAFLD). However, no FXR agonist has been approved for NAFLD so far. The R & D of FXR agonists are somewhat hindered by the lack of effective and safe chemotypes. To this end, we developed a multi-stage computational workflow to screen the Specs and ChemDiv chemical library for FXR agonists, which consisted of machine learning (ML)-based classifiers, shape-based and electrostatic-based models, a FRED-based molecular docking protocol, an ADMET prediction protocol and substructure search. As a result, we identified a novel chemotype that has never been reported before, with compound XJ02862 (ChemDiv ID: Y020-6413) as the representative. By designing an asymmetric synthesis strategy, we were able to prepare four isomers of compound XJ02862. Interestingly, one of the isomers, 2-((S)-1-((2S,4R)-2-methyl-4-(phenylamino)-3,4-dihydroquinolin-1(2H)-yl)-1-oxopropan-2-yl)hexahydro-1H-isoindole-1,3(2H)-dione (XJ02862-S2), showed potent FXR agonistic activity in HEK293T cells. The molecular docking, molecular dynamics simulations and site-directed mutagenesis suggested the hydrogen bond between compound XJ02862-S2 and HIS294 of FXR is essential for ligand binding. We further demonstrated that compound XJ02862-S2 had no agonistic effect on TGR5. Further biological experiments have shown that compound XJ02862-S2 could ameliorate hypercholesterolemia, hepatic steatosis, hyperglycemia, insulin resistance (IR) in high-fat-diet induced obese (DIO) mice. In term of molecular mechanism, compound XJ02862-S2 regulates the expression of FXR downstream genes involved in lipogenesis, cholesterol transport and bile acid biosynthesis and transport. Taken together, we have discovered a novel chemotype as potent FXR agonists for NAFLD by computational modeling, chemical synthesis and biological evaluation.

The choleretic role of tauroursodeoxycholic acid exacerbates alpha-naphthylisothiocyanate induced cholestatic liver injury through the FXR/BSEP pathway

The aim of this study was to determine the effect of tauroursodeoxycholic acid (TUDCA) on the alpha-naphthylisothiocyanate (ANIT)-induced model of cholestasis in mice. Wild-type and farnesoid X receptor (FXR)-deficient (Fxr^-/- ) mice were used to generate cholestasis models by gavage with ANIT. Obeticholic acid (OCA) was used as a positive control. In wild-type mice, treatment with TUDCA for 7 days resulted in a dramatic increase in serum levels of alanine aminotransferase (ALT), with aggravation of bile infarcts and hepatocyte necrosis with ANIT-induction. TUDCA activated FXR to upregulate the expression of bile salt export pump (BSEP), increasing bile acids (BAs)-dependent bile flow, but aggravating cholestatic liver injury when bile ducts were obstructed resulting from ANIT. In contrast, TUDCA improved the liver pathology and decreased serum ALT and alkaline phosphatase (ALP) levels in ANIT-induced Fxr^-/- mice. Furthermore, TUDCA inhibited the expression of cleaved caspase-3 and reduced the area of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining in the model mice. TUDCA also upregulated anion exchanger 2 (AE2) protein expression, protecting cholangiocytes against excessive toxic BAs. Our results showed that TUDCA aggravated cholestatic liver injury via the FXR/BSEP pathway when bile ducts were obstructed, although TUDCA inhibited apoptotic activity and protected cholangiocytes against excessive toxic BAs.

Gut Microbial Metabolites on Host Immune Responses in Health and Disease

Intestinal microorganisms interact with various immune cells and are involved in gut homeostasis and immune regulation. Although many studies have discussed the roles of the microorganisms themselves, interest in the effector function of their metabolites is increasing. The metabolic processes of these molecules provide important clues to the existence and function of gut microbes. The interrelationship between metabolites and T lymphocytes in particular plays a significant role in adaptive immune functions. Our current review focuses on 3 groups of metabolites: short-chain fatty acids, bile acids metabolites, and polyamines. We collated the findings of several studies on the transformation and production of these metabolites by gut microbes and explained their immunological roles. Specifically, we summarized the reports on changes in mucosal immune homeostasis represented by the Tregs and Th17 cells balance. The relationship between specific metabolites and diseases was also analyzed through latest studies. Thus, this review highlights microbial metabolites as the hidden treasure having potential diagnostic markers and therapeutic targets through a comprehensive understanding of the gut-immune interaction.

A perspective study of the possible impact of obeticholic acid against SARS-CoV-2 infection

The causative agent of CoV disease 2019 is a new coronavirus CoV type 2, affecting the respiratory tract with severe manifestations (SARS-CoV-2). Covid-19 is mainly symptomless, with slight indications in about 85% of the affected cases. Many efforts were done to face this pandemic by testing different drugs and agents to make treatment protocols in different countries. However, the use of these proposed drugs is associated with the development of adverse events. Remarkably, the successive development of SARS-CoV-2 variants which could affect persons even they were vaccinated, prerequisite wide search to find efficient and safe agents to face SARS-CoV-2 infection. Obeticholic acid (OCA), which has anti-inflammatory effects, may efficiently treat Covid-19. Thus, the goal of this perspective study is to focus on the possible medicinal effectiveness in managing Covid-19. OCA is a powerful farnesoid X receptor (FXR) agonist possessing marked antiviral and anti-inflammatory effects. FXR is dysregulated in Covid-19 resulting in hyper-inflammation with concurrent occurrence of hypercytokinemia. Interestingly, OCA inhibits the reaction between this virus and angiotensin-converting enzyme type 2 (ACE2) receptors. FXR agonists control the expression of ACE2 and the inflammatory signaling pathways in this respiratory syndrome, which weakens the effects of Covid-19 disease and accompanied complications. Taken together, FXR agonists like OCA may reveal both direct and indirect impacts in the modulation of immune reaction in SARS-CoV-2 conditions. It is highly recommended to perform many investigations regarding different phases of the discovery of new drugs.

Combinatorial therapy with BAR502 and UDCA resets FXR and GPBAR1 signaling and reverses liver histopathology in a model of NASH

Non-alcoholic steatosis (NAFLD) and steatohepatitis (NASH) are two highly prevalent human disorders for which therapy remains suboptimal. Bile acids are signaling molecules acting on two main receptors the Farnesoid-x-receptor (FXR) and G protein coupled receptor GPB AR1. Clinical trials have shown that FXR agonism might result in side effects along with lack of efficacy in restoring liver histopathology. For these reasons a multi-targets therapy combined FXR agonists with agent targeting additional molecular mechanisms might have improved efficacy over selective FXR agonists. In the present study we have compared the effects of BAR502, a dual FXR/GPBAR1 ligand) alone or in combination with ursodeoxycholic acid (UDCA) in a model of NAFLD/NASH induced by feeding mice with a Western diet for 10 weeks. The results demonstrated that while BAR502 and UDCA partially protected against liver damage caused by Western diet, the combination of the two, reversed the pro-atherogenic lipid profile and completely reversed the histopathology damage, attenuating liver steatosis, ballooning, inflammation and fibrosis. Additionally, while both agents increased insulin sensitivity and bile acid signaling, the combination of the two, modulated up top 85 genes in comparison of mice feed a Western diet, strongly reducing expression of inflammatory markers such as chemokines and cytokines. Additionally, the combination of the two agents redirected the bile acid metabolism toward bile acid species that are GPBAR1 agonist while reduced liver bile acid content and increased fecal excretion. Together, these data, highlight the potential role for a combinatorial therapy based on BAR502 and UDCA in treating of NAFLD.

Asiatic acid alleviates liver fibrosis via multiple signaling pathways based on integrated network pharmacology and lipidomics

Liver fibrosis is characterized by the abnormal deposition of the extracellular matrix with a severe inflammatory response and/or metabolic disorder. Asiatic acid (AA), a natural compound derived from Centella asiatica, exhibited potent anti-fibrosis effects. This investigation first confirmed the anti-fibrosis effects of AA in TGF-β-LX-2 cells and CCl₄-induced liver fibrosis mice, and then sought to elucidate a novel mechanism of action by integrating network pharmacology and lipidomics. Network pharmacology was used to find potential targets of AA, while lipidomics was used to identify differential metabolites between fibrosis and recovered cohorts. AA could suppress hepatic stellate cell activation in vitro and improve liver fibrosis in vivo. Network pharmacology unveiled the genes involved in pathways in cancer, peroxisome proliferators-activated receptors signaling pathway, and arachidonic acid metabolism pathway. Furthermore, five key genes were found in the both human and mouse databases, indicating that arachidonic acid metabolism was important. Changes in lyso-phosphocholine (22:5), prostaglandin F2α, and other related lipid metabolites also suggested the involvement of arachidonic acid metabolism the anti-fibrotic effect. In summary, our integrated strategies demonstrated that AA targeted multiple targets and impeded the progression of liver fibrosis by ameliorating arachidonic acid metabolism.

Immunomodulatory functions of FXR

The Farnesoid-x-receptor (FXR) is a bile acids sensor activated in humans by primary bile acids. FXR is mostly expressed in liver, intestine and adrenal glands but also by cells of innate immunity, including macrophages, liver resident macrophages, the Kupffer cells, natural killer cells and dendritic cells. In normal physiology and clinical disorders, cells of innate immunity mediate communications between liver, intestine and adipose tissues. In addition to FXR, the G protein coupled receptor (GPBAR1), that is mainly activated by secondary bile acids, whose expression largely overlaps FXR, modulates chemical communications from the intestinal microbiota and the host's immune system, integrating epithelial cells and immune cells in the entero-hepatic system, providing a mechanism for development of a tolerogenic state toward the intestinal microbiota. Disruption of FXR results in generalized inflammation and disrupted bile acids metabolism. While FXR agonism in preclinical models provides counter-regulatory signals that attenuate inflammation-driven immune dysfunction in a variety of liver and intestinal disease models, the clinical relevance of these mechanisms in the setting of FXR-related disorders remain poorly defined.

Hepatoprotective Effects of Glycyrrhetinic Acid on Lithocholic Acid-Induced Cholestatic Liver Injury Through Choleretic and Anti-Inflammatory Mechanisms

Cholestasis is a clinical syndrome triggered by the accumulation and aggregation of bile acids by subsequent inflammatory responses. The present study investigated the protective effect of glycyrrhetinic acid (GA) on the cholestatic liver injury induced by lithocholic acid (LCA) from both anti-inflammatory and choleretic mechanistic standpoints. Male C57BL/6 mice were treated with LCA twice daily for 4 days to induce intrahepatic cholestasis. GA (50 mg/kg) and pregnenolone 16α-carbonitrile (PCN, 45 mg/kg) were intraperitoneally injected 3 days before and throughout the administration of LCA, respectively. Plasma biochemical indexes were determined by assay kits, and hepatic bile acids were quantified by LC-MS/MS. Hematoxylin and eosin staining of liver sections was performed for pathological examination. Protein expression of the TLRs/NF-κB pathway and the mRNA levels of inflammatory cytokines and chemokines were examined by Western blotting and PCR, respectively. Finally, the hepatic expression of pregnane X receptor (PXR) and farnesoid X receptor (FXR) and their target genes encoding metabolic enzymes and transporters was evaluated. GA significantly reversed liver necrosis and decreased plasma ALT and ALP activity. Plasma total bile acids, total bilirubin, and hepatic bile acids were also remarkably preserved. More importantly, the recruitment of inflammatory cells to hepatic sinusoids was alleviated. Additionally, the protein expression of TLR2, TLR4, and p-NF-κBp65 and the mRNA expression of CCL2, CXCL2, IL-1β, IL-6, and TNF-α were significantly decreased. Moreover, GA significantly increased the expression of hepatic FXR and its target genes, including BSEP, MRP3, and MRP4. In conclusion, GA protects against LCA-induced cholestatic liver injury by inhibiting the TLR2/NF-κB pathway and upregulating hepatic FXR expression.

Rifaximin Ameliorates Non-alcoholic Steatohepatitis in Mice Through Regulating gut Microbiome-Related Bile Acids

Non-alcoholic steatohepatitis (NASH) is the progressive stage of non-alcoholic fatty liver disease (NAFLD). The non-absorbable antibiotic rifaximin has been used for treatment of irritable bowel syndrome, traveling diarrhea, and hepatic encephalopathy, but the efficacy of rifaximin in NASH patients remains controversial. This study investigated the effects and underlying mechanisms of rifaximin treatment in mice with methionine and choline deficient (MCD) diet-induced NASH. We found that rifaximin greatly ameliorated hepatic steatosis, lobular inflammation, and fibrogenesis in MCD-fed mice. Bacterial 16S rRNA sequencing revealed that the gut microbiome was significantly altered in MCD-fed mice. Rifaximin treatment enriched 13 amplicon sequence variants (ASVs) belonging to the groups Muribaculaceae, Parabacteroides, Coriobacteriaceae_UCG-002, uncultured Oscillospiraceae, Dubosiella, Rikenellaceae_RC9_gut_group, Mucispirillum, and uncultured Desulfovibrionaceae. However, rifaximin treatment also reduced seven ASVs in the groups Aerococcus, Oscillospiraceae, uncultured Ruminococcaceae, Bilophila, Muribaculaceae, Helicobacter, and Alistipes in MCD-fed mice. Bile acid-targeted metabolomic analysis indicated that the MCD diet resulted in accumulation of primary bile acids and deoxycholic acid (DCA) in the ileum. Rifaximin delivery reduced DCA levels in MCD-fed mice. Correlation analysis further showed that DCA levels were associated with differentially abundant ASVs modulated by rifaximin. In conclusion, rifaximin may ameliorate NASH by decreasing ileal DCA through alteration of the gut microbiome in MCD-fed mice. Rifaximin treatment may therefore be a promising approach for NASH therapy in humans.

Beyond lipids: Novel mechanisms for parenteral nutrition-associated liver disease

Parenteral nutrition (PN) is a therapy that delivers essential nutrients intravenously to patients who are unable to meet their nutrition requirements via standard enteral feeding. This methodology is often referred to as PN when accompanied by minimal or no enteral nutrition (EN). Although PN is lifesaving, significant complications can arise, such as intestinal failure-associated liver disease and gut-mucosal atrophy. The exact mechanism of injury remains ill defined. This review was designed to explore the available literature related to the drivers of injury mechanisms. The Farnesoid X receptor and fibroblast growth factor 19 signaling pathway seems to play an important role in gut-systemic signaling, and its alteration during PN provides insights into mechanistic links. Central line infections also play a key role in mediating PN-associated injury. Although lipid reduction strategies, as well as the use of multicomponent lipid emulsions and vitamin E, have shown promise, the cornerstone of preventing injury is the early establishment of EN.

Impact of Primary and Secondary Bile Acids on Clostridioides difficile Infection

Primary bile acids (BAs), synthesized from cholesterol in the liver, after their secretion with bile into the intestinal lumen, are transformed by gut microbiota to secondary BAs. As natural detergents, BAs play a key role in the digestion and absorption of lipids and liposoluble vitamins. However, they have also been recognized as important signaling molecules involved in numerous metabolic processes. The close bidirectional interactions between BAs and gut microbiota occur since BAs influence microbiota composition, whereas microbiota determines BA metabolism. In particular, it is well established that BAs modulate Clostridioides difficile life cycle in vivo. C. difficile is a cause of common nosocomial infections that have become a growing concern. The aim of this review is to summarize the current knowledge regarding the impact of BAs on the pathogenesis, prevention, and treatment of C. difficile infection.

Human menstrual blood-derived stem cell transplantation suppresses liver injury in DDC-induced chronic cholestasis

BACKGROUND

Cholestatic liver injury can lead to serious symptoms and prognoses in the clinic. Currently, an effective medical treatment is not available for cholestatic liver injury. Human menstrual blood-derived stem cells (MenSCs) are considered as an emerging treatment in various diseases. This study aimed to explore the treatment effect of MenSCs in cholestatic liver injury.

METHODS

The treatment effect of MenSCs on chronic cholestatic liver injury was verified in 3,5-diethoxycarbonyl-1,4-dihydroxychollidine (DDC)-induced C57/BL6 mice. Pathological, fibrosis area in the liver tissue and serum liver enzymes were tested. Proteomics and western blot were used to explore the related targets and molecular mechanisms. Adeno-associated virus (AAV) 9-infected mice were applied for verification.

RESULTS

MenSCs markedly improved the survival rate of the DDC-treated mice (60% vs. 100%), and decreased the mouse serum aspartate aminotransferase (AST) (169.4 vs. 108.0 U/L, p < 0.001), alanine aminotransferase (ALT) (279.0 vs. 228.9 U/L, p < 0.01), alkaline phosphatase (ALP) (45.6 vs. 10.6 U/L, p < 0.0001), direct bilirubin (DBIL) (108.3 vs. 14.0 μmol/L, p < 0.0001) and total bilirubin (TBIL) (179.2 vs. 43.3 μmol/L, p < 0.0001) levels as well as intrahepatic cholestasis, bile duct dilation and fibrotic areas (16.12 vs. 6.57%, p < 0.05). The results further indicated that MenSCs repaired the DDC-induced liver tight junction (TJ) pathway and bile transporter (OATP2, BSEP and NTCP1) injury, thereby inhibiting COL1A1, α-SMA and TGF-β1 activation by upregulating liver β-catenin expression.

CONCLUSIONS

MenSC transplantation could be an effective treatment method for cholestatic liver injury in mice. MenSCs may exhibit therapeutic effects by regulating β-catenin expression.

SU5, a new Auraptene analog with improved metabolic stability, ameliorates nonalcoholic fatty liver disease in methionine- and choline-deficient diet-fed db/db mice

Farnesoid X receptor (FXR) has been considered as a promising target for non-alcoholic steatohepatitis (NASH), while existing FXR agonists suffer from serious side effects. Thus, it is very necessary to identify novel FXR agonists with good safety. Auraptene (AUR) is a new FXR agonist with excellent safety and extensive pharmacological activities, while the lactone of AUR is vulnerable to esterolysis. In this study, the lactone of AUR was converted to metabolically stable amide moiety, and the obtained analog SU5 revealed comparable activity and better metabolic stability than that of AUR. In NASH model, SU5 showed stronger efficacy than AUR on fatty liver by up-regulating gene expressions related to FXR in vivo. Moreover, SU5 improved lipid metabolism by down-regulating the gene expressions of lipid synthesis, while up-regulating the gene expressions of fatty acid β-oxidation and triglyceride metabolism. Besides, the inflammation-related genes were significantly decreased in SU5 treated group. These positive results highlighted the pharmacological potential of SU5 for the treatment of NASH.

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.

Linking liver metabolic and vascular disease via bile acid signaling

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder affecting over one quarter of the global population. Liver fat accumulation in NAFLD is promoted by increased de novo lipogenesis leading to the development of a proatherosclerotic lipid profile and atherosclerotic cardiovascular disease (CVD). The CVD component of NAFLD is the main determinant of patient outcome. The farnesoid X receptor (FXR) and the G protein bile acid-activated receptor 1 (GPBAR1) are bile acid-activated receptors that modulate inflammation and lipid and glucose metabolism in the liver and CV system, and are thus potential therapeutic targets. We review bile acid signaling in liver, metabolic tissues, and the CV system, and we propose the development of dual FXR/GPBAR1 ligands, intestine-restricted FXR ligands, or statin combinations to limit side effects and effectively manage the liver and CV components of NAFLD.

miR-199a-5p inhibits the Expression of ABCB11 in Obstructive Cholestasis

ATP-binding cassette, subfamily B member 11 (ABCB11) is an efflux transporter for bile acids on the liver canalicular membrane. The expression of this transporter is reduced in cholestasis; however, the mechanisms contributing to this reduction are unclear. In this study, we sought to determine whether miR-199a-5p contributes to the depletion of ABCB11/Abcb11 in cholestasis in mice. In a microRNA (miRNA) screen of mouse liver after common bile duct ligation (CBDL), we found that miR-199a-5p was significantly upregulated by approximately fourfold. In silico analysis predicted that miR-199a-5p would target the 3′-untranslated region (3′-UTR) of ABCB11/Abcb11 mRNA. The expression of ABCB11-3′-UTR luciferase construct in Huh-7 cells was markedly inhibited by cotransfection of a miRNA-199a-5p mimic, which was reversed by an miRNA-199a-5p mimic inhibitor. We also show treatment of mice after CBDL with the potent nuclear receptor FXR agonist obeticholic acid (OCA) significantly increased Abcb11 mRNA and protein and decreased miR-199a-5p expression. Computational mapping revealed a well-conserved FXR-binding site (FXRE) in the promoter of the gene encoding miR-199a-5, termed miR199a-2. Electromobility shift, chromatin immunoprecipitation, and miR199a-2 promoter-luciferase assays confirmed that this binding site was functional. Finally, CBDL in mice led to depletion of nuclear repressor NcoR1 binding at the miR199a-2 promoter, which facilitates transcription of miR199a-2. In CBDL mice treated with OCA, NcoR1 recruitment to the miR199a-2 FXRE was maintained at levels found in sham-operated mice. In conclusion, we demonstrate that miR-199a-5p is involved in regulating ABCB11/Abcb11 expression, is aberrantly upregulated in obstructive cholestasis, and is downregulated by the FXR agonist OCA.

(E)-7-Ethylidene-lithocholic Acid (7-ELCA) Is a Potent Dual Farnesoid X Receptor (FXR) Antagonist and GPBAR1 Agonist Inhibiting FXR-Induced Gene Expression in Hepatocytes and Stimulating Glucagon-like Peptide-1 Secretion From Enteroendocrine Cells

Bile acids (BAs) are key signaling steroidal molecules that regulate glucose, lipid, and energy homeostasis via interactions with the farnesoid X receptor (FXR) and G-protein bile acid receptor 1 (GPBAR1). Extensive medicinal chemistry modifications of the BA scaffold led to the discovery of potent selective or dual FXR and GPBAR1 agonists. Herein, we discovered 7-ethylidene-lithocholic acid (7-ELCA) as a novel combined FXR antagonist/GPBAR1 agonist (IC₅₀ = 15 μM/EC₅₀ = 26 nM) with no off-target activation in a library of 7-alkyl substituted derivatives of BAs. 7-ELCA significantly suppressed the effect of the FXR agonist obeticholic acid in BSEP and SHP regulation in human hepatocytes. Importantly, 7-ELCA significantly stimulated the production of glucagon-like peptide-1 (GLP-1), an incretin with insulinotropic effect in postprandial glucose utilization, in intestinal enteroendocrine cells. We can suggest that 7-ELCA may be a prospective approach to the treatment of type II diabetes as the dual modulation of GPBAR1 and FXR has been supposed to be effective in the synergistic regulation of glucose homeostasis in the intestine.

Bile acid activated receptors: Integrating immune and metabolic regulation in non-alcoholic fatty liver disease

Bile acids are a family of atypical steroids generated at the interface of liver-intestinal microbiota acting on a ubiquitously expressed family of membrane and nuclear receptors known as bile acid activated receptors. The two best characterized receptors of this family are the nuclear receptor, farnesoid X receptor (FXR) and the G protein-coupled receptor, G protein-coupled bile acid receptor 1 (GPBAR1). FXR and GPBAR1 regulate major aspects of lipid and glucose metabolism, energy balance, autophagy and immunity and have emerged as potential pharmaceutical targets for the treatment of metabolic and inflammatory disorders. Clinical trials in non-alcoholic fatty liver disease (NAFLD), however, have shown that selective FXR agonists cause side effects while their efficacy is partial. Because FXR and GPBAR1 exert additive effects, dual FXR/GPBAR1 ligands have been developed for the treatment of metabolic disorders and are currently advanced to clinical trials. Here, we will review the role of FXR and GPBAR1 agonism in NAFLD and how the two receptors could be exploited to target multiple components of the disease.

Moderate Alcoholic Hepatitis

The natural history of moderate alcoholic hepatitis (AH) is not well known. It is a frequent disease with a probable underestimated incidence compared with its severe form. Among the different prognostic scores predicting short-term mortality in AH, MELD seems to be the most accurate. The mortality of moderate AH is 3% to 7% in the short to medium term and 13% to 20% at 1 year, mainly because of liver-related complications, including severe infections. Long-term abstinence is the main goal of the treatment. There is still need for the development of new therapies for AH, including the less severe forms.

Design, synthesis, and biological evaluation of novel FXR agonists based on auraptene

Farnesoid X receptor (FXR) has been considered as an attractive target for metabolic disorder and liver injury, while many current FXR agonists suffer from undesirable side effects, such as pruritus. Therefore, it is urgent to develop new structure types different from current FXR agonists. In this study, a series of structural optimizations were introduced to displace the unstable coumarin and geraniol scaffolds of auraptene (AUR), a novel and safe FXR agonist. All of these efforts led to the identification of compound 14, a potent FXR agonist with nearly fourfold higher activity than AUR. Molecular modeling study suggested that compound 14 fitted well with binding pocket, and formed the key ionic bond with His291 and Arg328. In acetaminophen-induced acute liver injury model, compound 14 exerts better therapeutic effect than that of AUR, which highlighting its pharmacological potential in the treatment of drug-induced liver injury.

The identification of farnesoid X receptor modulators as treatment options for nonalcoholic fatty liver disease

INTRODUCTION

The farnesoid-x-receptor (FXR) is a ubiquitously expressed nuclear receptor selectively activated by primary bile acids.

AREA COVERED

FXR is a validated pharmacological target. Herein, the authors review preclinical and clinical data supporting the development of FXR agonists in the treatment of nonalcoholic fatty liver disease.

EXPERT OPINION

Development of systemic FXR agonists to treat the metabolic liver disease has been proven challenging because the side effects associated with these agents including increased levels of cholesterol and LDL-c and reduced HDL-c raising concerns over their long-term cardiovascular safety. Additionally, pruritus has emerged as a common, although poorly explained, dose-related side effect with all FXR ligands, but is especially common with OCA. FXR agonists that are currently undergoing phase 2/3 trials are cilofexor, tropifexor, nidufexor and MET409. Some of these agents are currently being developed as combination therapies with other agents including cenicriviroc, a CCR2/CCR5 inhibitor, or firsocostat an acetyl CoA carboxylase inhibitor. Additional investigations are needed to evaluate the beneficial effects of combination of these agents with statins. It is expected that in the coming years, FXR agonists will be developed as a combination therapy to minimize side effects and increase likelihood of success by targeting different metabolic pathways.

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.

Differential roles of farnesoid X receptor (FXR) in modulating apoptosis in cancer cells

Cancer is one of the leading causes of mortality in the world. The conventional treatment strategies of cancer are surgery, radiation, and chemotherapy. However, in the advanced stage of the disease chemotherapy is the prime treatment and it is effective in only less than 10% of the patients. Therefore, there is an urgent need to find out novel therapeutic targets and delineate the mechanism of action of these targets for better management of this disease. Recent studies have shown that some of the proteins have differential role in different cancers. Therefore, it is pertinent that the targeting of these proteins should be based on the type of cancer. The nuclear receptor, FXR, is one of the vital proteins that regulate cell apoptosis. Besides, it also regulates other processes such as cell proliferation, angiogenesis, invasion, and migration. Studies suggest that the low or high expression of FXR is associated with the progression of carcinogenesis depending on the cancer types. Due to the diverse expression, it functions as both tumor suppressor and promoter. Previous studies suggest the overexpression of FXR in breast, lung, esophageal, and prostate cancer, which is related to poor survival and poor prognosis in patients. Therefore, targeting FXR with agonists and antagonists play different outcome in different cancers. Hence, this review describes the role of FXR in different cancers and the role of its inhibitors and activators for the prevention and treatment of various cancers.

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.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

Comparison of the Pharmacokinetics of Generic Versus Branded Obeticholic Acid in a Chinese Population: Effects of Food and Sex

The present study assessed the pharmacokinetics and bioequivalence of a single 10-mg dose of a generic and the branded formulation (Ocaliva) of obeticholic acid (OCA) in healthy Chinese subjects under fasting and fed conditions. The possible effects of food and sex on the pharmacokinetics of OCA and its 2 active metabolites (glyco-OCA and tauro-OCA) were evaluated. Plasma concentrations of OCA and its 2 active metabolites were measured by liquid chromatography-tandem mass spectrometry. The 90%CIs of the ratios of the test and reference formulations for C_max , AUC_0-t , and AUC_0-∞ of OCA, glyco-OCA, and tauro-OCA were contained entirely within the 80% to 125% range required for bioequivalence under fasting and fed conditions. Plasma exposure of OCA was 30% to 36% higher under fed compared with fasting conditions. Plasma exposure of OCA, glyco-OCA, and tauro-OCA was 39% to 66%, 22% to 58%, and 37% to 84% higher, respectively, in women compared with men under fasting and fed conditions. In conclusion, OCA was well tolerated in healthy Chinese subjects under fasting and fed conditions. The single 10-mg dose of a generic OCA formulation was bioequivalent to Ocaliva. Food and sex impacted the pharmacokinetics of OCA and/or its 2 active metabolites. Further studies are required to determine if these effects are clinically relevant.

Basic science to clinical trials in non-alcoholic fatty liver disease and alcohol-related liver disease: collaboration with industry

Non-alcoholic fatty liver disease (NAFLD) and alcohol-related liver disease (ALD) are highly prevalent forms of chronic liver diseases globally, associated with rising all-cause morbidity and mortality. While distinct diseases, NAFLD and ALD share several similarities; both can result in fatty liver disease, steatohepatitis, associated hepatic fibrosis and cirrhosis-related complications, including hepatocellular carcinoma (HCC). Our understanding of the pathophysiology and manifestations of these diseases has advanced significantly, which has established a new foundation to identify therapeutic targets and test new treatments. This review underscores emerging pathogenic pathways that establish a template for target identification and clinical trials. Success is critically dependent upon productive interactions between academic investigators and industry to address unmet therapeutic needs in NAFLD and ALD.

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.

Structural basis of tropifexor as a potent and selective agonist of farnesoid X receptor

Farnesoid X receptor (FXR) is considered as a potential target for the treatment of several liver disorders such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Tropifexor is a highly potent and non-steroidal FXR agonist that has progressed into phase II clinical trials in patients with PBC. The clinical trials demonstrate that tropifexor improved serum markers of patients with liver diseases and lower side effect such as pruritus that might be implicated with TGR5 activation. However, the molecular mechanism of the potency and selectivity of tropifexor remains unclear. In this study, the binding affinity of FXR and tropifexor is measured by isothermal titration calorimetry (ITC) assays. The crystal structure of the FXR/tropifexor complex is determined at 2.7 Å resolution to explain the molecular mechanism of tropifexor bound to FXR-LBD. Structural comparison with other FXR/agonists structures reveals the conformational change in the FXR/tropifexor structure. Moreover the structural superposition of TGR5/tropifexor indicates that the steric hindrance between tropifexor and TGR5 might be a possible explanation for the impotency arises of tropifexor to TGR5. Overall, our analyses might provide an insight into the molecular mechanism of tropifexor binding to FXR-LBD and account for the high selectivity of tropifexor for FXR versus TGR5.

An insight into primary biliary cholangitis and its recent advances in treatment: semi-synthetic analogs to combat ursodeoxycholic-acid resistance

INTRODUCTION

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease which on progression causes cirrhosis; various studies also suggested that several diseases can co-exist in patients. In existing depiction of disease PBC, apart from entire use of ursodeoxycholic acid (UDCA), several patients need to step forward to liver-transplantation or death due to resistance or non-responder with UDCA monotherapy.

AREAS COVERED

To overcome this non-respondent treatment, novel bile acid semi-synthetic analogs have been identified which shows their potency against for farnesoid X receptor and transmembrane G protein-coupled receptor-5 which are identified as target for many developing analogs which have desirable pharmacokinetic profiles.

EXPERT OPINION

A range of studies suggests that adding semisynthetic analogs in therapeutic regime improves liver biochemistries in patients with suboptimal response to UDCA. Thus, the aspire of this review is to abridge and compare therapeutic value and current markets affirm of various bile acids semi-synthetic analogs which certainly are having promising effects in PBC monotherapy or in pooled treatment with UDCA for PBC.

Obeticholic acid reduces biliary and hepatic matrix metalloproteinases activity in rat hepatic ischemia/reperfusion injury

Background

We have previously shown that obeticholic acid (OCA) upregulates the biliary excretion of asymmetric dimethylarginine (ADMA), an inhibitor of iNOS regulating the activity of matrix metalloproteinases (MMPs). Here, the effects of OCA on MMP-2 and MMP-9 activity in liver, bile and serum were evaluated after hepatic ischemia/reperfusion (I/R) injury.

Material and methods

Male Wistar rats (n = 20) were orally administered 10 mg/kg/day of OCA (5 days) and subjected to a 60-min ischemia and 60-min reperfusion. Bile, serum and tissue were collected for MMP-2 and MMP-9 activity quantification. The MMP regulator tissue reversion-inducing cysteine rich protein with Kazal motifs (RECK), tissue inhibitor of metalloproteinases (TIMPs), iNOS and biliary levels of LDH, γGT, glucose and ADMA were quantified.

Results

In the I/R group, OCA administration reduced MMP-2 and MMP-9 in liver, bile and serum. A downregulation of tissue RECK and TIMPs, observed under I/R, were recovered by OCA. Immunohistochemical staining of hepatic tissue demonstrated that RECK expression is mainly localized in both cholangiocytes and hepatocytes. Hepatic iNOS positively correlated with tissue MMP-2 and MMP-9 activity. Biliary levels of LDH, γGT and glucose were lower in I/R rats treated with OCA; in bile, MMP levels positively correlated with LDH and γGT.

Conclusion

Thus, OCA administration confers protection to cholangiocytes via downregulation of biliary MMPs in livers submitted to I/R. This event is associated with hepatic RECK- and TIMP-mediated MMP decrease.

Bile Acids and FXR: Novel Targets for Liver Diseases

Bile acids (BAs) are evolutionally conserved molecules synthesized in the liver from cholesterol and have been shown to be essential for lipid homeostasis. BAs regulate a variety of metabolic functions via modulating nuclear and membrane receptors. Farnesoid X receptor (FXR) is the most important nuclear receptor for maintaining BA homeostasis. FXR plays a tissue-specific role in suppressing BA synthesis and promoting BA enterohepatic circulation. Disruption of FXR in mice have been implicated in liver diseases commonly occurring in humans, including cholestasis, non-alcoholic fatty liver diseases, and hepatocellular carcinoma. Strategically targeting FXR activity has been rapidly used to develop novel therapies for the prevention and/or treatment of cholestasis and non-alcoholic steatohepatitis. This review provides an updated literature review on BA homeostasis and FXR modulator development.

3β-Isoobeticholic acid efficiently activates the farnesoid X receptor (FXR) due to its epimerization to 3α-epimer by hepatic metabolism

Bile acids (BAs) are important signaling molecules acting via the farnesoid X nuclear receptor (FXR) and the membrane G protein-coupled bile acid receptor 1 (GPBAR1). Besides deconjugation of BAs, the oxidoreductive enzymes of colonic bacteria and hepatocytes enable the conversion of BAs into their epimers or dehydrogenated forms. Obeticholic acid (OCA) is the first-in-class BA-derived FXR agonist approved for the treatment of primary biliary cholangitis. Herein, a library of OCA derivatives, including 7-keto, 6-ethylidene derivatives and 3β-epimers, was synthetized and investigated in terms of interactions with FXR and GPBAR1 in transaction assays and evaluated for FXR target genes expression in human hepatocytes and C57BL/6 mice. The derivatives were further subjected to cell-free analysis employing in silico molecular docking and a TR-FRET assay. The conversion of the 3βhydroxy epimer and its pharmacokinetics in mice were studied using LC-MS. We found that only the 3β-hydroxy epimer of OCA (3β-isoOCA) possesses significant activity to FXR in hepatic cells and mice. However, in a cell-free assay, 3β-isoOCA had about 9-times lower affinity to FXR than did OCA. We observed that 3β-isoOCA readily epimerizes to OCA in hepatocytes and murine liver. This conversion was significantly inhibited by the hydroxy-Δ⁵-steroid dehydrogenase inhibitor trilostane. In addition, we found that 3,7-dehydroobeticholic acid is a potent GPBAR1 agonist. We conclude that 3β-isoOCA significantly activates FXR due to its epimerization to the more active OCA by hepatic metabolism. Other modifications as well as epimerization on the C3/C7 positions and the introduction of 6-ethylidene in the CDCA scaffold abrogate FXR agonism and alleviate GPBAR1 activation.

Bile acid modulators for the treatment of nonalcoholic steatohepatitis (NASH)

INTRODUCTION

Nonalcoholic steatohepatitis (NASH) is a progressive form of nonalcoholic fatty liver disease (NAFLD) for which therapy is suboptimal. The farnesoid-X-receptor (FXR) and the G protein bile acid receptor (GPBAR)1 are two bile acid-activated receptors that exert regulatory effects on lipid, glucose, energy, and immune homeostasis. GPBAR1 and FXR ligands have shown efficacy in reversing steatohepatitis and fibrosis in preclinical models of NASH.

AREA COVERED

This article evaluates the efficacy and pitfalls of GPBAR1 and FXR-based therapies in the treatment of NASH. While there are no GPBAR1 agonist in clinical development, several FXR ligands have completed phase 2 and phase 3 trials in NASH. EDP305, tropifexor, cilofexor, nidufexor, TERN.101, Px-104, EYP001, MET409. Individual FXR agonists have shown variable efficacy in reversing liver steatohepatitis and fibrosis. Class-related, dose-dependent side effects: pruritus, increased plasma levels of cholesterol and LDLc, and reduction of HDL have been reported.

EXPERT OPINION

Efficacy of FXR agonists as stand-alone therapy is limited by dose-related side effects. Efficacy of combining an FXR agonist with statins, CCR2, and ACC inhibitors is currently investigated. Identification of patient subsets would allow development of patients tailored therapy using a combination of drugs acting on different molecular mechanisms.

Opposite effects of the FXR agonist obeticholic acid on Mafg and Nrf2 mediate the development of acute liver injury in rodent models of cholestasis

The farnesoid-X-receptor (FXR) is validated target in the cholestatic disorders treatment. Obeticholic acid (OCA), the first in class of FXR agonist approved for clinical use, causes side effects including acute liver decompensation when administered to cirrhotic patients with primary biliary cholangitis at higher than recommended doses. The V-Maf avian-musculoaponeurotic-fibrosarcoma-oncogene-homolog-G (Mafg) and nuclear factor-erythroid-2-related-factor-2 (Nrf2) mediates some of the downstream effects of FXR. In the present study we have investigated the role of FXR/MafG/NRF2 pathway in the development of liver toxicity caused by OCA in rodent models of cholestasis. Cholestasis was induced by bile duct ligation (BDL) or administration of α-naphtyl-isothiocyanate (ANIT) to male Wistar rats and FXR^-/- and FXR^+/+ mice. Treating BDL and ANIT rats with OCA exacerbated the severity of cholestasis, hepatocytes injury and severely downregulated the expression of basolateral transporters. In mice, genetic ablation FXR or its pharmacological inhibition by 3-(naphthalen-2-yl)-5-(piperidin-4-yl)-1,2,4-oxadiazole rescued from negative regulation of MRP4 and protected against liver injury caused by ANIT. By RNAseq analysis we found that FXR antagonism effectively reversed the transcription of over 2100 genes modulated by OCA/ANIT treatment, including Mafg and Nrf2 and their target genes Cyp7a1, Cyp8b1, Mat1a, Mat2a, Gss. Genetic and pharmacological Mafg inhibition by liver delivery of siRNA antisense or S-adenosylmethionine effectively rescued from damage caused by ANIT/OCA. In contrast, Nrf2 induction by sulforaphane was protective. CONCLUSIONS: Liver injury caused by FXR agonism in cholestasis is FXR-dependent and is reversed by FXR and Mafg antagonism or Nrf2 induction.

Pediatric Cholestasis: Epidemiology, Genetics, Diagnosis, and Current Management

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