Farnesoid X receptor agonists in biliary tract disease

Fecal Bile Acids in Canine Chronic Liver Disease: Results from 46 Dogs

The concentrations of fecal and serum bile acids (BAs) are known to be altered in human patients with chronic liver diseases (CLDs), especially those with biliary tract involvement (BTD). Scarce literature is available regarding fecal BA modifications during canine CLDs. This study aimed to evaluate fecal BAs in canine CLDs according to different clinical and clinicopathological variables. Forty-six dogs were enrolled. Canine feces were analyzed by HPLC. Cholic Acid (CA), Chenodeoxycholic Acid (CDCA), Ursodeoxycholic Acid (UDCA), Deoxycholic Acid (DCA), and Lithocholic Acid (LCA) were measured, and primary BAs (CA + CDCA), secondary BAs (UDCA + DCA + LCA), and the primary/secondary (P/S) ratio were calculated. Primary BAs (p < 0.0001), CA (p = 0.0003), CDCA (p = 0.003), the P/S ratio (p = 0.002), and total BAs (p = 0.005) were significatively higher in BTD dogs (n = 18) compared to in non-BTD dogs (n = 28). Fecal secondary BAs did not statistically differ between BTD and non-BTD dogs. Gastrointestinal clinical signs (p = 0.028) and diarrhea (p = 0.03) were significantly more prevalent in BTD dogs compared to in non-BTD dogs, supporting the hypothesis of some pathological mechanisms assimilable to bile acid diarrhea (BAD). Our results could reflect imbalances of the fecal BA metabolism in dogs with CLDs. Further studies involving gut microbiome and metabolomic assessment are needed to better understand the possible clinical implications of BA metabolism disruption and their potential role in canine CLDs.

Role of Gut Microbial Metabolites in the Pathogenesis of Primary Liver Cancers

Hepatobiliary malignancies, which include hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), are the sixth most common cancers and the third leading cause of cancer-related death worldwide. Hepatic carcinogenesis is highly stimulated by chronic inflammation, defined as fibrosis deposition, and an aberrant imbalance between liver necrosis and nodular regeneration. In this context, the gut-liver axis and gut microbiota have demonstrated a critical role in the pathogenesis of HCC, as dysbiosis and altered intestinal permeability promote bacterial translocation, leading to chronic liver inflammation and tumorigenesis through several pathways. A few data exist on the role of the gut microbiota or bacteria resident in the biliary tract in the pathogenesis of CCA, and some microbial metabolites, such as choline and bile acids, seem to show an association. In this review, we analyze the impact of the gut microbiota and its metabolites on HCC and CCA development and the role of gut dysbiosis as a biomarker of hepatobiliary cancer risk and of response during anti-tumor therapy. We also discuss the future application of gut microbiota in hepatobiliary cancer management.

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.

Primary biliary cholangitis: molecular pathogenesis perspectives and therapeutic potential of natural products

Primary biliary cirrhosis (PBC) is a chronic cholestatic immune liver disease characterized by persistent cholestasis, interlobular bile duct damage, portal inflammation, liver fibrosis, eventual cirrhosis, and death. Existing clinical and animal studies have made a good progress in bile acid metabolism, intestinal flora disorder inflammatory response, bile duct cell damage, and autoimmune response mechanisms. However, the pathogenesis of PBC has not been clearly elucidated. We focus on the pathological mechanism and new drug research and development of PBC in clinical and laboratory in the recent 20 years, to discuss the latest understanding of the pathological mechanism, treatment options, and drug discovery of PBC. Current clinical treatment mode and symptomatic drug support obviously cannot meet the urgent demand of patients with PBC, especially for the patients who do not respond to the current treatment drugs. New treatment methods are urgently needed. Drug candidates targeting reported targets or signals of PBC are emerging, albeit with some success and some failure. Single-target drugs cannot achieve ideal clinical efficacy. Multitarget drugs are the trend of future research and development of PBC drugs.

Characteristics and Inpatient Outcomes of Primary Biliary Cholangitis and Autoimmune Hepatitis Overlap Syndrome

BACKGROUND AND AIMS

Primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH) are hepatobiliary diseases of presumed immune-mediated origin that have been shown to overlap. The aim of this retrospective trial was to use national data to examine the characteristics and outcomes of patients hospitalized with overlapping PBC and AIH (PBC/AIH).

METHODS

The National Inpatient Sample was used to identify hospitalized adult patients with PBC, AIH, and PBC/AIH from 2010 to 2014 by International Classification of Diseases-Ninth Edition Revision codes; patients with hepatitis B virus and hepatitis C virus infection were excluded. Primary outcomes measures were in-hospital outcomes that included mortality, respiratory failure, septic shock, length of stay, and total hospital charges. Secondary outcomes were the clinical characteristics of PBC/AIH, including the comorbid extrahepatic autoimmune disease pattern and complications of cirrhosis.

RESULTS

A total of 3,478 patients with PBC/AIH were included in the study. PBC/AIH was associated with higher rates of Sjögren's syndrome (p<0.001; p<0.001), lower rates of Crohn's disease (p<0.05; p<0.05), and higher rates of cirrhosis-related complications when compared to PBC or AIH alone. There were similar rates of mortality between the PBC/AIH, PBC, and AIH groups. The PBC/AIH group had higher rates of septic shock when compared to the PBC group (p<0.05) and AIH group (p<0.05) after adjusting for possible confounders.

CONCLUSIONS

PBC/AIH is associated with a lower rate of Crohn's disease, a higher rate of Sjögren's syndrome, higher rates of cirrhosis-related complications, and significantly increased risk of septic shock compared to PBC and AIH individually.

Mechanism of Hydrophobic Bile Acid-Induced Hepatocyte Injury and Drug Discovery

Cholestatic liver disease is caused by the obstruction of bile synthesis, transport, and excretion in or outside the liver by a variety of reasons. Long-term persistent cholestasis in the liver can trigger inflammation, necrosis, or apoptosis of hepatocytes. Bile acid nuclear receptors have received the most attention for the treatment of cholestasis, while the drug development for bile acid nuclear receptors has made considerable progress. However, the targets regulated by bile acid receptor drugs are limited. Thus, as anticipated, intervention in the expression of bile acid nuclear receptors alone will not yield satisfactory clinical results. Therefore, this review comprehensively summarized the literature related to cholestasis, analyzed the molecular mechanism that bile acid damages cells, and status of drug development. It is hoped that this review will provide some reference for the research and development of drugs for cholestasis treatment in the future.

Bile acid-based therapies for non-alcoholic steatohepatitis and alcoholic liver disease

Bile acids are synthesized from cholesterol only in hepatocytes. Bile acids circulating in the enterohepatic system act as physiological detergent molecules to help solubilize biliary cholesterol and emulsify dietary lipids and fat-soluble vitamins in small intestine. Bile acids are signaling molecules that activate nuclear receptor farnesoid X receptor (FXR) and cell surface G protein-coupled receptor TGR5. FXR critically regulates bile acid homeostasis by mediating bile acid feedback inhibition of hepatic bile acid synthesis. In addition, bile acid-activated cellular signaling pathways regulate metabolic homeostasis, immunity, and cell proliferation in various metabolically active organs. In the small and large intestine, gut bacterial enzymes modify primary bile acids to generate secondary bile acids to help shape the bile acid pool composition and subsequent biological effects. In turn, bile acids exhibit anti-microbial properties and modulate gut microbiota to influence host metabolism and immunity. Currently, bile acid-based therapies including systemic and intestine-restricted FXR agonists, TGR5 agonists, fibroblast growth factor 19 analogue, intestine FXR antagonists, and intestine apical sodium-bile acid transporter (ASBT) inhibitors have been developed as promising treatments for non-alcoholic steatohepatitis (NASH). These pharmacological agents improved metabolic and inflammatory disorders via distinct mechanisms of action that are subjects of extensive research interest. More recently, human and experimental alcoholic liver disease (ALD) has been associated with disrupted bile acid homeostasis. In additional, new findings showed that targeting bile acid metabolism and signaling may be promising therapeutic approaches for treating ALD.

Mechanism of Hydrophobic Bile Acid-Induced Hepatocyte Injury and Drug Discovery

Cholestatic liver disease is caused by the obstruction of bile synthesis, transport, and excretion in or outside the liver by a variety of reasons. Long-term persistent cholestasis in the liver can trigger inflammation, necrosis, or apoptosis of hepatocytes. Bile acid nuclear receptors have received the most attention for the treatment of cholestasis, while the drug development for bile acid nuclear receptors has made considerable progress. However, the targets regulated by bile acid receptor drugs are limited. Thus, as anticipated, intervention in the expression of bile acid nuclear receptors alone will not yield satisfactory clinical results. Therefore, this review comprehensively summarized the literature related to cholestasis, analyzed the molecular mechanism that bile acid damages cells, and status of drug development. It is hoped that this review will provide some reference for the research and development of drugs for cholestasis treatment in the future.

The Role of Parenteral Lipids in the Development of Hepatic Dysfunction and Hepatic Steatosis in a Mouse Model of Total Parenteral Nutrition

Parenteral nutrition-associated liver disease, a common and life-threating complication among people who require long-term parenteral nutrition, has been associated with abnormal liver function, cholestasis, steatosis and fibrosis. Intravenous soybean lipids may be associated with the development of liver disease. We therefore examined whether different doses of parenteral lipids would affect the development of liver disease, and further investigated the possible pathogenesis of it. C57BL/6J mice with a central catheter placed in the right jugular vein were divided into three groups. The control group received normal mouse chow with intravenous normal saline; The lipids group received parenteral nutrition solution (0.14 g lipids per day); the H-lipids group received parenteral nutrition solution with twice the amount of lipids (0.3 g lipids per day). Changes in body weight, serum biochemical parameters, liver histology and farnesoid X receptor gene expression in the liver were assessed. The values of serum direct bilirubin, total bilirubin and cholesterol were markedly increased in the H-lipids group at day 7. The predominant histologic finding in the H-lipids group was steatosis, and the steatosis score in the H-lipids group was much higher than in the other two groups at either day 5 or day 7. Hepatic expression of farnesoid X receptor mRNA decreased after 7 d of parenteral nutrition. High doses of parenteral lipids are more likely to develop liver disease in a mouse model of parenteral nutrition. Farnesoid X receptor may play a key role in the development of parenteral nutrition-associated liver disease.

Rethinking Bile Acid Metabolism and Signaling for Type 2 Diabetes Treatment

PURPOSE OF REVIEW

Herein, we review the role of FXR and TGR5 in the regulation of hepatic bile acid metabolism, with a focus on how our understanding of bile acid metabolic regulation by these receptors has evolved in recent years and how this improved understanding may facilitate targeting bile acids for type 2 diabetes treatment.

RECENT FINDINGS

Bile acid profile is a key regulator of metabolic homeostasis. Inhibition of expression of the enzyme that is required for cholic acid synthesis and thus determines bile acid profile, Cyp8b1, may be an effective target for type 2 diabetes treatment. FXR and, more recently, TGR5 have been shown to regulate bile acid metabolism and Cyp8b1 expression and, therefore, may provide a mechanism with which to target bile acid profile for type 2 diabetes treatment. Inhibition of Cyp8b1 expression is a promising therapeutic modality for type 2 diabetes; however, further work is needed to fully understand the pathways regulating Cyp8b1 expression.

Discovery of glycocholic acid and taurochenodeoxycholic acid as phenotypic biomarkers in cholangiocarcinoma

Although several biomarkers can be used to distinguish cholangiocarcinoma (CCA) from healthy controls, differentiating the disease from benign biliary disease (BBD) or pancreatic cancer (PC) is a challenge. CCA biomarkers are associated with low specificity or have not been validated in relation to the biological effects of CCA. In this study, we quantitatively analyzed 15 biliary bile acids in CCA (n = 30), BBD (n = 57) and PC (n = 17) patients and discovered glycocholic acid (GCA) and taurochenodeoxycholic acid (TCDCA) as specific CCA biomarkers. Firstly, we showed that the average concentration of total biliary bile acids in CCA patients was quantitatively less than in other patient groups. In addition, the average composition ratio of primary bile acids and conjugated bile acids in CCA patients was the highest in all patient groups. The average composition ratio of GCA (35.6%) in CCA patients was significantly higher than in other patient groups. Conversely, the average composition ratio of TCDCA (13.8%) in CCA patients was significantly lower in all patient groups. To verify the biological effects of GCA and TCDCA, we analyzed the gene expression of bile acid receptors associated with the development of CCA in a CCA cell line. The gene expression of transmembrane G protein coupled receptor (TGR5) and sphingosine 1-phosphate receptor 2 (S1PR2) in CCA cells treated with GCA was 8.6-fold and 3.4-fold higher compared with control (untreated with bile acids), respectively. Gene expression of TGR5 and S1PR2 in TCDCA-treated cells was not significantly different from the control. Taken together, our study identified GCA and TCDCA as phenotype-specific biomarkers for CCA.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

Pathogenesis of biliary fibrosis

Chronic cholestatic liver diseases such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are associated with active hepatic fibrogenesis, and, ultimately, to the development of cirrhosis. However, the precise relationship between cholestasis, in its broad meaning, and liver tissue fibrosis is still poorly defined. Fibrogenesis is currently viewed as a dynamic process that appears strictly related to the extent and duration of parenchymal injury. This relationship is clearly evident in the presence of reiterative hepatocellular necrosis due to viral infection or alcohol abuse. It appears that "pure" intralobular intrahepatic cholestasis secondary to biliary secretory failure of the hepatocyte, in absence of hepatocellular damage, lobular inflammation and bile duct damage and/or proliferation, is not associated with marked and/or progressive liver tissue fibrosis. In contrast, marked and progressive liver tissue fibrosis always follows liver diseases characterized by chronic inflammatory bile duct damage as seen in PBC and PSC or chronic mechanical obstruction of the biliary tree. Overall, the fibrogenic process in these clinical conditions appears to be related to a more complex interaction between immune/inflammatory mechanisms, cytokine networks and the derangement of the homeostasis between epithelial and mesenchymal cells. The elucidation of these mechanisms is indeed crucial for the identification of potential diagnostic and therapeutic targets.

Targeting Bile Acid Receptors: Discovery of a Potent and Selective Farnesoid X Receptor Agonist as a New Lead in the Pharmacological Approach to Liver Diseases

Bile acid (BA) receptors represent well-defined targets for the development of novel therapeutic approaches to metabolic and inflammatory diseases. In the present study, we report the generation of novel C-3 modified 6-ethylcholane derivatives. The pharmacological characterization and molecular docking studies for the structure-activity rationalization, allowed the identification of 3β-azido-6α-ethyl-7α-hydroxy-5β-cholan-24-oic acid (compound 2), a potent and selective FXR agonist with a nanomolar potency in transactivation assay and high efficacy in the recruitment of SRC-1 co-activator peptide in Alfa Screen assay. In vitro, compound 2 was completely inactive towards common off-targets such as the nuclear receptors PPARα, PPARγ, LXRα, and LXRβ and the membrane G-coupled BA receptor, GPBAR1. This compound when administered in vivo exerts a robust FXR agonistic activity increasing the liver expression of FXR-target genes including SHP, BSEP, OSTα, and FGF21, while represses the expression of CYP7A1 gene that is negatively regulated by FXR. Collectively these effects result in a significant reshaping of BA pool in mouse. In summary, compound 2 represents a promising candidate for drug development in liver and metabolic disorders.

Target profiling analyses of bile acids in the evaluation of hepatoprotective effect of gentiopicroside on ANIT-induced cholestatic liver injury in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiopicroside (GPS), one of iridoid glucoside representatives, is the most potential active component in Gentiana rigescens Franch. ex Hemsl and Gentiana macrophylla Pall. These two herbs have been used to treat jaundice and other hepatic and billiary diseases in traditional Chinese medicine for thousands of years.

AIM OF THE STUDY

This study aimed to investigate the protective effects and mechanisms of GPS on α-naphthylisothiocyanate (ANIT) induced cholestatic liver injury in mice.

MATERIALS AND METHODS

Mice were treated with GPS (130mg/kg, ig) for 5 consecutive days. On the third day, mice were given a single dose of Alpha-naphthylisothiocyanate (75mg/kg, ig). Serum biochemical markers and individual bile acids in serum, liver, urine and feces were measured at different time points after ANIT administration. The expression of hepatic bile acid synthesis, uptake and transporter genes as well as ileum bile acid transporter genes were assayed.

RESULTS

In this study, ANIT exposure resulted in serious cholestasis with liver injury, which was demonstrated by dramatically increased serum levels of ALT, ALP, TBA and TBIL along with TCA CA, MCAs and TMCAs accumulation in both liver and serum. Furthermore, ANIT significantly decreased bile acid synthesis related gene expressions, and increased expression of bile acid transporters in liver. Continuous treatment with GPS attenuated ANIT-induced acute cholestasis as well as liver injury and correct the dyshomeostasis of bile acids induced by ANIT. Our data showed that GPS significantly upregulated the hepatic mRNA levels of synthesis enzymes (Cyp8b1 and Cyp27a1) and transporters (Mrp4 Mdr1 and Ost-β) as well as ileal bile acid circulation mediators (Asbt and Fgf15), accompanied by serum and hepatic bile acid levels decrease and further urinary and fecal bile acid levels increase.

CONCLUSION

GPS can change bile acids metabolism which highlights its importance in mitigating cholestasis, resulting in the marked decrease of intracellular bile acid pool back toward basal levels. And the protective mechanism was associated with regulation of bile acids-related transporters, but the potential mechanism warrants further investigation.

Navigation in bile acid chemical space: discovery of novel FXR and GPBAR1 ligands

Bile acids are signaling molecules interacting with nuclear receptors and membrane G-protein-coupled receptors. Among these receptors, the farnesoid X receptor (FXR) and the membrane G-coupled receptor (GPBAR1) have gained increasing consideration as druggable receptors and their exogenous dual regulation represents an attractive strategy in the treatment of enterohepatic and metabolic disorders. However, the therapeutic use of dual modulators could be associated to severe side effects and therefore the discovery of selective GPBAR1 and FXR agonists is an essential step in the medicinal chemistry optimization of bile acid scaffold. In this study, a new series of 6-ethylcholane derivatives modified on the tetracyclic core and on the side chain has been designed and synthesized and their in vitro activities on FXR and GPBAR1 were assayed. This speculation resulted in the identification of compound 7 as a potent and selective GPBAR1 agonist and of several derivatives showing potent dual agonistic activity.

SAR studies on FXR modulators led to the discovery of the first combined FXR antagonistic/TGR5 agonistic compound

BACKGROUND

Bile acids can serve as signaling molecules by activating the nuclear receptor FXR and the G-protein-coupled receptor TGR5 and both bile acid receptors are prominent experimental drug targets. Results/methodology: In this study we optimized the fatty acid mimetic compound pirinixic acid to a new scaffold with the aim to develop novel FXR modulatory compounds. After a multistep structure-activity optimization process, we discovered FXR agonistic compounds and the first dual FXR antagonistic and TGR5 agonistic compound 79a.

CONCLUSION

With this novel dual activity profile on both bile acid receptors 79a might be a valuable pharmalogical tool to further study the bile acid signaling network.

Insights on FXR selective modulation. Speculation on bile acid chemical space in the discovery of potent and selective agonists

Bile acids are the endogenous modulators of the nuclear receptor FXR and the membrane receptor GPBAR1. FXR represents a promising pharmacological target for the treatment of cholestatic liver disorders. Currently available semisynthetic bile acid derivatives cover the same chemical space of bile acids and therefore they are poorly selective toward BA receptors, increasing patient risk for adverse side effects. In this report, we have investigated around the structure of CDCA describing the synthesis and the in vitro and in vivo pharmacological characterization of a novel family of compounds modified on the steroidal tetracyclic core and on the side chain. Pharmacological characterization resulted in the identification of several potent and selective FXR agonists. These novel agents might add utility in the treatment of cholestatic disorders by potentially mitigating side effects linked to unwanted activation of GPBAR1.

Investigation on bile acid receptor regulators. Discovery of cholanoic acid derivatives with dual G-protein coupled bile acid receptor 1 (GPBAR1) antagonistic and farnesoid X receptor (FXR) modulatory activity

Bile acids, the end products of cholesterol metabolism, activate multiple mechanisms through the interaction with membrane G-protein coupled receptors including the bile acid receptor GPBAR1 and nuclear receptors such as the bile acid sensor, farnesoid X receptor (FXR). Even if dual FXR/GPBAR1 agonists are largely considered a novel opportunity in the treatment of several liver and metabolic diseases, selective targeting of one of these receptors represents an attractive therapeutic approach for a wide range of disorders in which dual modulation is associated to severe side effects. In the present study we have investigated around the structure of LCA generating a small library of cholane derivatives, endowed with dual FXR agonism/GPBAR1 antagonism. To the best of our knowledge, this is the first report of bile acid derivatives able to antagonize GPBAR1.

Oleanolic acid attenuates obstructive cholestasis in bile duct-ligated mice, possibly via activation of NRF2-MRPs and FXR antagonism

Obstructive cholestasis is characterized by impairment of hepatic canalicular bile efflux and there are no clinically effective drugs to cure except surgeries. Previously we revealed that oleanolic acid (OA) protected against lithocholic acid (LCA)-induced intrahepatic cholestasis in mice. Cholestasis caused by LCA is characterized by segmental bile duct obstruction, whether OA possesses the beneficial effect on completed obstructive cholestasis induced by bile duct ligation (BDL) remains unknown. In this study, we demonstrated that BDL-induced mice liver pathological change, and increase in serum levels of ALT, AST and ALP were all significantly reduced by OA (20 mg/kg, i.p.). Meanwhile, OA also lowered total bilirubin and total bile acids levels in serum, as well as total bile acids level in liver, in contrast, urinary total bile acids output was remarkably up-regulated by OA. Gene expression analysis showed that OA caused significant increased mRNA expression of MRP3 and MRP4 located at hepatic basolateral membrane, and restoration of MRP2 and BSEP located at hepatic cannalicular membrane. Furthermore, significant NRF2 protein accumulation in nucleus was also observed in OA treated mice. In mice primary cultured hepatocytes, the effects of OA on MRP2, MRP3 and MRP4 expression were directly proved to be mediated via NRF2 activation, and BSEP downregulation induced by OA was in part due to FXR antagonism. Luciferase assay performed in Hep G2 cells also illustrated that OA was a partial FXR antagonist. Taken together, we conclude that OA attenuates obstructive cholestasis in BDL mice, possibly via activation of NRF2-MRPs and FXR antagonism.

Impaired Itching Perception in Murine Models of Cholestasis Is Supported by Dysregulation of GPBAR1 Signaling

Background & Aims

In cholestatic syndromes, body accumulation of bile acids is thought to cause itching. However, the mechanisms supporting this effect remain elusive. Recently, GPBAR1 (TGR5) a G-protein coupled receptor has been shown to mediate itching caused by intradermal administration of DCA and LCA. 6α-ethyl-3α, 7α-dihydroxy-24-nor-5β-cholan-23-ol (BAR502) is a non-bile acid dual ligand for FXR and GPBAR1.

Methods

Cholestasis was induced in wild type and GPBAR1^-/- mice by administration of α-naphthyl-isothiocyanate (ANIT) or 17α-ethynylestradiol.

Results.

In naïve mice skin application of DCA, TLCA, 6-ECDCA, oleanolic and betulinic acid induces a GPBAR1 dependent pruritogenic response that could be desensitized by re-challenging the mice with the same GPBAR1 agonist. In wild type and GPBAR1^-/- mice cholestasis induced by ANIT fails to induce spontaneous itching and abrogates scratching behavior caused by intradermal administration of DCA. In this model, co-treatment with BAR502 increases survival, attenuates serum alkaline phosphatase levels and robustly modulates the liver expression of canonical FXR target genes including OSTα, BSEP, SHP and MDR1, without inducing pruritus. Betulinic acid, a selective GPBAR1 ligand, failed to rescue wild type and GPBAR1^-/- mice from ANIT cholestasis but did not induced itching. In the 17α-ethynylestradiol model BAR502 attenuates cholestasis and reshapes bile acid pool without inducing itching.

Conclusions

The itching response to intradermal injection of GPBAR1 agonists desensitizes rapidly and is deactivated in models of cholestasis, explain the lack of correlation between bile acids levels and itching severity in cholestatic syndromes. In models of non-obstructive cholestasis, BAR502 attenuates liver injury without causing itching.

Bile acid signaling in metabolic disease and drug therapy

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates hepatobiliary secretion of lipids, lipophilic metabolites, and xenobiotics. In the intestine, bile acids are essential for the absorption, transport, and metabolism of dietary fats and lipid-soluble vitamins. Extensive research in the last 2 decades has unveiled new functions of bile acids as signaling molecules and metabolic integrators. The bile acid-activated nuclear receptors farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, and G protein-coupled bile acid receptor play critical roles in the regulation of lipid, glucose, and energy metabolism, inflammation, and drug metabolism and detoxification. Bile acid synthesis exhibits a strong diurnal rhythm, which is entrained by fasting and refeeding as well as nutrient status and plays an important role for maintaining metabolic homeostasis. Recent research revealed an interaction of liver bile acids and gut microbiota in the regulation of liver metabolism. Circadian disturbance and altered gut microbiota contribute to the pathogenesis of liver diseases, inflammatory bowel diseases, nonalcoholic fatty liver disease, diabetes, and obesity. Bile acids and their derivatives are potential therapeutic agents for treating metabolic diseases of the liver.

Extending the structure-activity relationship of anthranilic acid derivatives as farnesoid X receptor modulators: development of a highly potent partial farnesoid X receptor agonist

The ligand activated transcription factor nuclear farnesoid X receptor (FXR) is involved as a regulator in many metabolic pathways including bile acid and glucose homeostasis. Therefore, pharmacological activation of FXR seems a valuable therapeutic approach for several conditions including metabolic diseases linked to insulin resistance, liver disorders such as primary biliary cirrhosis or nonalcoholic steatohepatitis, and certain forms of cancer. The available FXR agonists, however, activate the receptor to the full extent which might be disadvantageous over a longer time period. Hence, partial FXR activators are required for long-term treatment of metabolic disorders. We here report the SAR of anthranilic acid derivatives as FXR modulators and development, synthesis, and characterization of compound 51, which is a highly potent partial FXR agonist in a reporter gene assay with an EC50 value of 8 ± 3 nM and on mRNA level in liver cells.

Modification on ursodeoxycholic acid (UDCA) scaffold. discovery of bile acid derivatives as selective agonists of cell-surface G-protein coupled bile acid receptor 1 (GP-BAR1)

Bile acids are signaling molecules interacting with the nuclear receptor FXR and the G-protein coupled receptor 1 (GP-BAR1/TGR5). GP-BAR1 is a promising pharmacological target for the treatment of steatohepatitis, type 2 diabetes, and obesity. Endogenous bile acids and currently available semisynthetic bile acids are poorly selective toward GP-BAR1 and FXR. Thus, in the present study we have investigated around the structure of UDCA, a clinically used bile acid devoid of FXR agonist activity, to develop a large family of side chain modified 3α,7β-dihydroxyl cholanoids that selectively activate GP-BAR1. In vivo and in vitro pharmacological evaluation demonstrated that administration of compound 16 selectively increases the expression of pro-glucagon 1, a GP-BAR1 target, in the small intestine, while it had no effect on FXR target genes in the liver. Further, compound 16 results in a significant reshaping of bile acid pool in a rodent model of cholestasis. These data demonstrate that UDCA is a useful scaffold to generate novel and selective steroidal ligands for GP-BAR1.

Identification of trisubstituted-pyrazol carboxamide analogs as novel and potent antagonists of farnesoid X receptor

Farnesoid X receptor (FXR, NRIH4) plays a major role in the control of cholesterol metabolism. This suggests that antagonizing the transcriptional activity of FXR is a potential means to treat cholestasis and related metabolic disorders. Here we describe the synthesis, biological evaluation, and structure-activity relationship (SAR) studies of trisubstituted-pyrazol carboxamides as novel and potent FXR antagonists. One of these novel FXR antagonists, 4j has an IC50 of 7.5 nM in an FXR binding assay and 468.5 nM in a cell-based FXR antagonistic assay. Compound 4j has no detectable FXR agonistic activity or cytotoxicity. Notably, 4j is the most potent FXR antagonist identified to date; it has a promising in vitro profile and could serve as an excellent chemical tool to elucidate the biological function of FXR.

Obeticholic acid and budesonide for the treatment of primary biliary cirrhosis

INTRODUCTION

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease of adults. Treatments are needed when patients have incomplete response to ursodeoxycholic acid (UDCA).

AREAS COVERED

Discoveries of the key role played by bile acids (BAs) and nuclear receptors (NRs) in regulating liver and metabolic homeostasis have led to promising therapeutic approaches in liver diseases. A PubMed search for the recent literature on NRs in liver disease was conducted. In particular, obeticholic acid (OCA) is a farnesoid X receptor (FXR) agonist that has an important role in the enterohepatic circulation of BAs. Preliminary studies of OCA in patients with PBC have demonstrated marked biochemical improvement when administered in combination with UDCA and alone. Pruritus is the most common side effect, limiting treatment at higher doses. Budesonide is a glucocorticoid receptor/pregnane X receptor (PXR) agonist also involved in BA synthesis, metabolism and transport. Studies with budesonide have shown positive effects of short-term combination therapy in selected patients with early stage disease and overlapping features of autoimmune hepatitis.

EXPERT OPINION

Though larger studies are needed, preliminary results of agents targeting FXR and PXR have been encouraging, particularly in subsets of patients with PBC and may mark a new therapeutic era.

Role of nuclear receptor FXR in liver regeneration

Liver regeneration is a practical compensatory re-growth in response to the loss of hepatic tissue. The mechanism of liver regeneration is very complex and many cytokines, transcription factors and signaling pathways are involved in this process. The farnesoid X receptor (FXR) is a member of metabolic nuclear receptors of intracellular ligand-activated transcription factors and plays an important role in metabolism of bile acids, lipid and glucose. In addition, it has been recently reported that FXR is crucial for liver regeneration. FXR activation directly promotes liver regeneration by regulating hepatocyte proliferation and regulates synthesis and transport of bile acids to prevent the liver from injury by increased bile acids after hepatectomy. The metabolic regulation of FXR is beneficial to liver regeneration. This review focuses on the mechanism of FXR regulation of liver regeneration and targeted drugs.

Bile acid metabolism and signaling

Bile acids are important physiological agents for intestinal nutrient absorption and biliary secretion of lipids, toxic metabolites, and xenobiotics. Bile acids also are signaling molecules and metabolic regulators that activate nuclear receptors and G protein-coupled receptor (GPCR) signaling to regulate hepatic lipid, glucose, and energy homeostasis and maintain metabolic homeostasis. Conversion of cholesterol to bile acids is critical for maintaining cholesterol homeostasis and preventing accumulation of cholesterol, triglycerides, and toxic metabolites, and injury in the liver and other organs. Enterohepatic circulation of bile acids from the liver to intestine and back to the liver plays a central role in nutrient absorption and distribution, and metabolic regulation and homeostasis. This physiological process is regulated by a complex membrane transport system in the liver and intestine regulated by nuclear receptors. Toxic bile acids may cause inflammation, apoptosis, and cell death. On the other hand, bile acid-activated nuclear and GPCR signaling protects against inflammation in liver, intestine, and macrophages. Disorders in bile acid metabolism cause cholestatic liver diseases, dyslipidemia, fatty liver diseases, cardiovascular diseases, and diabetes. Bile acids, bile acid derivatives, and bile acid sequestrants are therapeutic agents for treating chronic liver diseases, obesity, and diabetes in humans.

Role of nuclear receptors in lipid dysfunction and obesity-related diseases

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 12 meeting in San Diego, CA. The presentations discussed the roles of a number of nuclear receptors in regulating glucose and lipid homeostasis, the pathophysiology of obesity-related disease states, and the promise associated with targeting their activities to treat these diseases. While many of these receptors (in particular, constitutive androstane receptor and pregnane X receptor) and their target enzymes have been thought of as regulators of drug and xenobiotic metabolism, this symposium highlighted the advances made in our understanding of the endogenous functions of these receptors. Similarly, as we gain a better understanding of the mechanisms underlying bile acid signaling pathways in the regulation of body weight and glucose homeostasis, we see the importance of using complementary approaches to elucidate this fascinating network of pathways. The observation that some receptors, like the farnesoid X receptor, can function in a tissue-specific manner via well defined mechanisms has important clinical implications, particularly in the treatment of liver diseases. Finally, the novel findings that agents that selectively activate estrogen receptor β can effectively inhibit weight gain in a high-fat diet model of obesity identifies a new role for this member of the steroid superfamily. Taken together, the significant findings reported during this symposium illustrate the promise associated with targeting a number of nuclear receptors for the development of new therapies to treat obesity and other metabolic disorders.

Pathogenesis and treatment of parenteral nutrition-associated liver disease

BACKGROUND

Parenteral nutrition-associated liver disease (PNALD) has been common in patients who require long-term parenteral nutrition. PNALD develops in 40%-60% of infants on long-term parenteral nutrition compared with 15%-40% of adults on home parenteral nutrition for intestinal failure. The pathogenesis of PNALD is multifactorial and remains unclear. There is no specific treatment. Management strategies for its prevention and treatment depend on an understanding of many risk factors. This review aims to provide an update on the pathogenesis and treatment of this disease.

DATA SOURCES

A literature search was performed on the MEDLINE and Web of Science databases for articles published up to October 2011, using the keywords: parenteral nutrition associated liver disease, intestinal failure associated liver disease, lipid emulsions and fish oil. The available data reported in the relevant literatures were analyzed.

RESULTS

The literature search provided a huge amount of evidence about the pathogenesis and management strategies on PNALD. Currently, lack of enteral feeding, extended duration of parenteral nutrition, recurrent sepsis, and nutrient deficiency or excess may play important roles in the pathogenesis of PNALD. Recent studies found that phytosterols, present as contaminants in soy-based lipid emulsions, are also an important factor in the pathogenesis. Moreover, the treatment of PNALD is discussed.

CONCLUSIONS

The use of lipid emulsions, phytosterols in particular, is associated with PNALD. Management strategies for the prevention and treatment of PNALD include consideration of early enteral feeding, the use of specialized lipid emulsions such as fish oil emulsions, and isolated small bowel or combined liver and small bowel transplantation. A greater understanding of the pathogenesis of PNALD has led to promising interventions to prevent and treat this condition. Future work should aim to better understand the mechanisms of PNALD and the long-term outcomes of its treatment.

Scoparone potentiates transactivation of the bile salt export pump gene and this effect is enhanced by cytochrome P450 metabolism but abolished by a PKC inhibitor

BACKGROUND AND PURPOSE

Hyperbilirubinaemia and cholestasis are two major forms of liver abnormality. The Chinese herb Yin Chin has been used for thousands of years to treat liver dysfunctions. In mice, this herb and its principal ingredient scoparone were found to accelerate the clearance of bilirubin accompanied by the induction of uridine diphosphate-5'-glucuronosyltransferase-1A1 (UGT1A1), a bilirubin processing enzyme. The aim of this study was to determine whether scoparone induces the expression of human UGT1A1. In addition, the expression of the bile salt export pump (BSEP), a transporter of bile acids, was determined.

EXPERIMENTAL APPROACH

Primary human hepatocytes and hepatoma line Huh7 were treated with scoparone, chenodeoxycholic acid (CDCA) or both. The expression of UGT1A1 and BSEP mRNA was determined. The activation of the human BSEP promoter reporter by scoparone was determined in Huh7 cells by transient transfection and in mice by bioluminescent imaging. The metabolism of scoparone was investigated by recombinant CYP enzymes and pooled human liver microsomes.

KEY RESULTS

Scoparone did not enhance the expression of either human BSEP or, surprisingly, UGT1A1. However, scoparone significantly potentiated the expression of BSEP induced by CDCA. Consistent with this, scoparone potentiated the stimulant effect of CDCA on the human BSEP promoter. This potentiation was enhanced by co-transfection of cytochrome P4501A2 but abolished by the PKC inhibitor GF109203X.

CONCLUSIONS AND IMPLICATIONS

Scoparone and Yin Chin normalize liver function primarily by enhancing the secretion of bile acids, and this effect probably varies depending on the metabolic rate of scoparone.

Farnesoid x receptor agonists: what they are and how they might be used in treating liver disease

The farnesoid X receptor (FXR) is a nuclear receptor expressed in the liver, small intestine, kidneys, and adrenals. In mouse liver, FXR is bound to thousands of genomic DNA binding sites. Conformational changes induced by bile acid binding to pre-bound FXR leads to increased expression of a variety of genes. These changes lead to decreased intracellular bile acid concentrations through multiple mechanisms including decreased bile acid synthesis from cholesterol, decreased hepatocellular uptake and increased secretion into bile. Activated FXR also modulates the expression of genes responsible for lipid and glucose metabolism. One of the other genes induced by activated FXR is a small heterodimeric partner (SHP), a protein that represses expression of specific genes. The effects of pharmacologically modulating FXR activation in humans is only beginning to be explored with the hopes of favorably altering lipid and glucose metabolism to address the vascular and metabolic complications of obesity and diabetes.

Discovery that theonellasterol a marine sponge sterol is a highly selective FXR antagonist that protects against liver injury in cholestasis

Background

The farnesoid-x-receptor (FXR) is a bile acid sensor expressed in the liver and gastrointestinal tract. Despite FXR ligands are under investigation for treatment of cholestasis, a biochemical condition occurring in a number of liver diseases for which available therapies are poorly effective, mice harboring a disrupted FXR are protected against liver injury caused by bile acid overload in rodent models of cholestasis. Theonellasterol is a 4-methylene-24-ethylsteroid isolated from the marine sponge Theonella swinhoei. Here, we have characterized the activity of this theonellasterol on FXR-regulated genes and biological functions.

Principal Findings

Interrogation of HepG2 cells, a human hepatocyte cell line, by microarray analysis and transactivation assay shows that theonellasterol is a selective FXR antagonist, devoid of any agonistic or antagonistic activity on a number of human nuclear receptors including the vitamin D receptor, PPARs, PXR, LXRs, progesterone, estrogen, glucorticoid and thyroid receptors, among others. Exposure of HepG2 cells to theonellasterol antagonizes the effect of natural and synthetic FXR agonists on FXR-regulated genes, including SHP, OSTα, BSEP and MRP4. A proof-of-concept study carried out to investigate whether FXR antagonism rescues mice from liver injury caused by the ligation of the common bile duct, a model of obstructive cholestasis, demonstrated that theonellasterol attenuates injury caused by bile duct ligation as measured by assessing serum alanine aminostrasferase levels and extent of liver necrosis at histopathology. Analysis of genes involved in bile acid uptake and excretion by hepatocytes revealed that theonellasterol increases the liver expression of MRP4, a basolateral transporter that is negatively regulated by FXR. Administering bile duct ligated mice with an FXR agonist failed to rescue from liver injury and downregulated the expression of MRP4.

Conclusions

FXR antagonism in vivo results in a positive modulation of MRP4 expression in the liver and is a feasible strategy to target obstructive cholestasis.

Conicasterol E, a small heterodimer partner sparing farnesoid X receptor modulator endowed with a pregnane X receptor agonistic activity, from the marine sponge Theonella swinhoei

We report the isolation and pharmacological characterization of conicasterol E isolated from the marine sponge Theonella swinhoei. Pharmacological characterization of this steroid in comparison to CDCA, a natural FXR ligand, and 6-ECDCA, a synthetic FXR agonist generated by an improved synthetic strategy, and rifaximin, a potent PXR agonist, demonstrated that conicasterol E is an FXR modulator endowed with PXR agonistic activity. Conicasterol E induces the expression of genes involved in bile acids detoxification without effect on the expression of small heterodimer partner (SHP), thus sparing the expression of genes involved in bile acids biosynthesis. The relative positioning in the ligand binding domain of FXR, explored through docking calculations, demonstrated a different spatial arrangement for conicasterol E and pointed to the presence of simultaneous and efficient interactions with the receptor. In summary, conicasterol E represents a FXR modulator and PXR agonist that might hold utility in treatment of liver disorders.

New insights on the pathogenesis of biliary cirrhosis provided by studies in FXR knockout mice

The nuclear bile acid receptor, farnesoid X receptor (FXR), may play a pivotal role in liver fibrosis. We tested the impact of genetic FXR ablation in four different mouse models. Hepatic fibrosis was induced in wild-type and FXR knock-out mice (FXR((-/-))) by CCl(4) intoxication, 3,5-diethoxycarbonyl-1,4-dihydrocollidine feeding, common bile duct ligation, or Schistosoma mansoni (S.m.)-infection. In addition, we determined nuclear receptor expression levels (FXR, pregnane X receptor (PXR), vitamin D receptor, constitutive androstane receptor (CAR), small heterodimer partner (SHP)) in mouse hepatic stellate cells (HSCs), portal myofibroblasts (MFBs), and human HSCs. Cell type-specific FXR protein expression was determined by immunohistochemistry in five mouse models and prototypic human fibrotic liver diseases. Expression of nuclear receptors was much lower in mouse and human HSCs/MFBs compared with total liver expression with the exception of vitamin D receptor. FXR protein was undetectable in mouse and human HSCs and MFBs. FXR loss had no effect in CCl(4)-intoxicated and S.m.-infected mice, but significantly decreased liver fibrosis of the biliary type (common bile duct ligation, 3,5-diethoxycarbonyl-1,4-dihydrocollidine). These data suggest that FXR loss significantly reduces fibrosis of the biliary type, but has no impact on non-cholestatic liver fibrosis. Since there is no FXR expression in HSCs and MFBs in liver fibrosis, our data indicate that these cells may not represent direct therapeutic targets for FXR ligands.

High expression of liver histone deacetylase 3 contributes to high-fat-diet-induced metabolic syndrome by suppressing the PPAR-γ and LXR-α-pathways in E3 rats

In the previous experiment, we found that there was a different response between E3 rats and DA.1U rats to high-fat-diet-induced metabolic syndrome (HFD-MetS). The aim of this study was to explore the cause and molecular mechanism of the genetic difference in susceptibility to metabolic syndrome in E3 rats as compared with DA.1U rats. Firstly, a 12-week HFD-MetS model in E3 and DA.1U rats was carried out and assessed. Then, the expression of key insulin signaling molecules, metabolic nuclear receptors, metabolic key enzymes and histone deacetylases (Hdacs) was determined by different methods. Finally, the effects of overexpression and disruption of Hdac3 on metabolic nuclear receptors were analyzed in CBRH-7919 cells and primarily-hepatic cells from DA.1U and E3 rats. We found that E3 rats were susceptible, while DA.1U rats were resisted to HFD-MetS. The expression of liver X receptor α,β (LXR-α,β), farnesoid X receptor (FXR), peroxisome proliferator activated receptor γ (PPAR-γ) and cholesterol 7α-hydroxylase (CYP7A1) increased markedly in DA.1U rat liver, whereas they decreased significantly in E3 rats. The expression of Hdac3 increased by HFD treatment in both E3 and DA.1U rat livers, but the constitutive Hdac3 expression was lower in DA.IU rat liver than in E3 rat liver. Importantly, overexpression of Hdac3 could downregulate the expression of LXR-α, PPAR-γ and CYP7A1 in both CBRH-7919 cells and primarily cultured hepatic cells from DA.IU rats. On the contrary, disruption of Hdac3 by shRNA upregulated the expression of LXR-α, PPAR-γ and CYP7A1 in both CBRH-7919 cells and primarily cultured hepatic cells from E3 rats. The results suggested that a high constitutive expression of Hdac3 inhibiting the expression of PPAR-γ, LXR-α and CYP7A1 in liver contributes to HFD-MetS in E3 rats.

TGR5: a novel target for weight maintenance and glucose metabolism

TGR5, an emerging G protein-coupled receptor, was identified as a membrane receptor for bile acids. The expression of TGR5 and its function are distinct from the previously identified nuclear bile acid receptor, farnesoid X receptor (FXR). These two bile acid receptors complement with each other for maintaining bile acid homeostasis and mediating bile acid signaling. Both receptors are also shown to play roles in regulating inflammation and glucose metabolism. An interesting finding for TGR5 is its role in energy metabolism. The discovery of TGR5 expression in brown adipocyte tissues (BATs) and the recent demonstration of BAT in adult human body suggest a potential approach to combat obesity by targeting TGR5 to increase thermogenesis. We summarize here the latest finding of TGR5 research, especially its role in energy metabolism and glucose homeostasis.

Fibrosis in autoimmune and cholestatic liver disease

Autoimmune and cholestatic liver disease account for a significant part of end-stage liver disease and are leading indications for liver transplantation. Especially cholestatic liver diseases (primary biliary cirrhosis and primary sclerosing cholangitis) appear to be different from other chronic liver diseases with regards to pathogenesis. Portal fibroblasts located in the connective tissue surrounding bile ducts appear to be different from hepatic stellate cells with regards to expression of marker proteins and response the profibrogenic and mitogenic stimuli. In addition there is increasing evidence for a cross talk between activated cholangiocytes and portal myofibroblasts. Several animal models have improved our understanding of the mechanisms underlying these chronic liver diseases. In the present review, we discuss the current concepts and ideas with regards to myofibroblastic cell populations, mechanisms of fibrosis, summarize characteristic histological findings and currently employed animal models of autoimmune and cholestatic liver disease.

Discovery of sulfated sterols from marine invertebrates as a new class of marine natural antagonists of farnesoid-X-receptor

We report the biochemical characterization of sulfated polyhydroxysterols isolated from marine invertebrates as potent antagonists of farnesoid-X-receptor (FXR), a ligand-regulated transcription factor involved in the regulation of lipid and glucose homeostasis in mammals. Molecular characterization of a library of sulfated polyhydroxysteroids resulted in the identification of a first FXR antagonist. In contrast to partial antagonists, this compound was endowed with an antagonistic activity on the expression of a subset of FXR-regulated genes in liver cells and abrogated the release of nuclear coreceptor from the promoter of these genes. The putative binding mode to FXR, obtained through docking calculations, suggested the crucial role played by the bent shape of the molecule as well as the presence of one hydroxyl group in its side chain. This compound is a major tool to explore the effect of FXR inhibition in pharmacological settings.

Missing link identified: GpBAR1 is a neuronal bile acid receptor

In addition to their classical functions in aiding the digestion and absorption of lipids, bile acids are increasingly gaining appreciation for their roles in regulating intestinal physiology. Bile acids are now widely considered as hormones that exert a wide range of physiological and pathophysiological effects both within and outside the gastrointestinal (GI) tract. The discovery of the bile acid receptor, GpBAR1, represented a major step forward in our understanding of how cells can sense and respond to bile acids. GpBAR1 is a cell surface G protein-coupled receptor expressed on adipose tissue and skeletal muscle where it has been found to be an important regulator of cellular metabolism. In a paper published in the current issue of Neurogastroenterology and Motility, Poole et al. investigated the expression and function of GpBAR1 in mouse intestine. They found the receptor to be expressed throughout the GI tract but predominantly on nerves within the myenteric and submucosal plexuses. Employing in vitro and in vivo techniques they demonstrated that activation of GpBAR1 by bile acids inhibits small and large intestinal motor function and delays intestinal transit. The effects of GpBAR1 activation are mediated through activation of cholinergic and nitrergic interneurons. The data reported by Poole et al. provides novel and exciting insights into how bile acids exert their actions in the intestine. This Editorial Viewpoint aims to further consider the potential physiological and pathophysiological implications of their findings.

Antidiabetic sulfonylureas modulate farnesoid X receptor activation and target gene transcription

Background: The sulfonylureas glibenclamide and glimepiride are oral antidiabetic drugs that stimulate insulin secretion by closing pancreatic ATP-dependent potassium channels. The farnesoid X receptor (FXR) is a ligand-activated transcription factor that regulates the expression of several target genes involved in bile acid metabolism and lipid and glucose homeostasis. Methods: In this study we investigated the potential effects of sulfonylureas on the signaling of FXR using a reporter-gene assay, real-time qPCR and computational methods such as molecular docking and molecular dynamic simulations. Results: We demonstrate that glibenclamide and glimepiride modulate FXR activation in a reporter-gene assay and induce FXR target genes in HepG2 cells. Within the docking experiments and molecular dynamics simulation, we found glibenclamide interacting with the ligand-binding domain of FXR and with helix 12. Conclusion: Glibenclamide and glimepiride are potential ligands of FXR and modulate activation and signaling.