Hepatic uptake of conjugated bile acids is mediated by both sodium taurocholate cotransporting polypeptide and organic anion transporting polypeptides and modulated by intestinal sensing of plasma bile acid levels in mice

Hepatitis B and D virus entry

Hepatitis B virus (HBV) entry is the initial step of viral infection, leading to the formation of covalently closed circular DNA, which is a molecular reservoir of viral persistence and a key obstacle for HBV cure. The restricted entry of HBV into specific cell types determines the nature of HBV, which has a narrow host range in tissues and species. Hepatitis D virus (HDV) shares viral surface antigens with HBV and thus follows a similar entry mechanism at its early stages. In late 2012, sodium taurocholate cotransporting polypeptide was discovered as an HBV and HDV entry receptor. Since then, the mechanisms of HBV and HDV entry have been extensively analysed. These analyses have expanded our understanding of HBV and HDV host tropism and have provided new strategies for the development of antiviral agents. Notably, the structures of sodium taurocholate cotransporting polypeptide and its interaction with the 2-48 amino acid region of viral preS1 have been recently solved. These findings will stimulate further entry studies. In this Review, we summarize current understanding of HBV and HDV entry and future perspectives.

Psoraleae Fructus affects the livers of normal and ulcerative colitis rats differently by altering bile acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Psoraleae Fructus (PF), the dried mature fruit of the leguminous plant Psoralea corylifolia L., is often used as a nutraceutical and to treat ulcerative colitis (UC). However, recently there have been reports of PF-induced liver injury.

AIM OF THE STUDY

To investigate the difference and mechanism of hepatotoxicity between normal and UC rats oral administration with PF, and clarify the relationship between PF risk and disease status.

MATERIALS AND METHODS

PF water extracts (at the human equivalent dosage and 8-fold greater; 0.7 and 5.6 g/kg/day, respectively) were given to normal and UC rats for 4 weeks, and the general behaviors and colonic mucosal conditions were observed. The liver injury and its mechanism were studied by blood biochemistry, coagulation time, liver hematoxylin and eosin (H&E) staining, bile acids (BAs) metabolism, transcriptome analysis, quantitative real-time polymerase chain reaction (qRT‒PCR) and western blot (WB)experiments.

RESULTS

Normal rats receiving 5.6 g/kg PF water extract showed significantly increased serum levels of total bilirubin (TBIL) and total bile acids (TBA), significantly prolonged activated partial thromboplastin time (APTT), prothrombin time (PT) and thromboplastin time (TT), and slightly swollen hepatocytes, and obvious hepatobiliary hyperplasia. These liver injuries may be related to disordered BAs metabolism: the levels of farnesoid x receptor (FXR) and sulfotransferase family 2A member 1/2 (SULT2a1/a2) were down-regulated, whereas the levels of microsomal epoxide hydrolase (mEH), organic anion transporting polypeptide (OATP) and multidrug resistance-associated protein 3 (MRP3) were up-regulated, leading to liver and blood UnconBA and GlycineBA accumulation. However, at the same dose, UC model rats exhibited no obvious liver damage.

CONCLUSION

Normal rats, but not UC rats, displayed signs of liver injury in response to 5.6 g/kg PF water extract administration. Therefore, we recommend that healthy individuals should be aware of the potential risks associated with PF, and other patients should take PF according to their physician's guidance.

Anti-HBV activity of (R)-gentiandiol, a metabolite of Swertiamarin, in transgenic mice: Insights from non-targeted serum metabolomics

Swertiamarin, a predominant component in many traditional Chinese swertia herbs, shows significant anti-HBV activity clinically. (R)-gentiandiol and (S)-gentiandiol are the metabolites of swertiamarin in vivo. In this study, HBsAg, HBeAg and HBV-DNA were determined in liver tissue of HBV-transgenic C57BL/6NCrl mice to analyze anti-HBV activities of swertiamarin, (R)-gentiandiol and (S)-gentiandiol. It was found that HBsAg, HBeAg and HBV-DNA levels were significantly reduced in a dose-dependent manner when (R)-gentiandiol was administered at 1.5, 3 and 6 mg/kg. However, (S)-gentiandiol showed no anti-HBV activity at all. In addition, we also performed untargeted metabolomics to discover biomarkers and metabolic pathways of swertiamarin and (R)-gentiandiol in HBV-transgenic C57BL/6NCrl mice. A total of 15 candidate biomarkers were obtained. Meanwhile, the metabolic disorders including 8 metabolic pathways, such as taurine and hypotaurine metabolism were explored. Taurine and hypotaurine metabolism was the primary pathway for (R)-gentiandiol to regulate HBV-transgenic C57BL/6NCrl mice. It is the first time to clarify real active anti-HBV metabolites of swertiamarin, which can offer more insights into anti-HBV activities of swertia herbs, and bring novel ideas for new drug development in anti-HBV herbs.

Sanye tablet regulates gut microbiota and bile acid metabolism to attenuate hepatic steatosis

ETHNOPHARMACOLOGICAL RELEVANCE

Sanye Tablet (SYT), a patent traditional Chinese prescription, is commonly used in treating type 2 diabetes mellitus and hyperlipidemia. Both clinical and animal studies suggest that SYT effectively regulates lipid metabolism. However, its mode of action on hepatic steatosis has yet to be fully elucidated.

AIM OF STUDY

This study investigates the lipid-regulating effects and underlying mechanism of SYT in high-fat diet (HFD)-induced hepatic steatosis mice.

MATERIAL AND METHODS

The inhibitory effects of SYT on developing hepatic steatosis were investigated in HFD-fed C57BL/6N mice. Biochemical markers, including total cholesterol (TC) and triglycerides (TG), were measured using specific kits. Hepatic histological alterations were determined by Hematoxylin and Eosin (H&E) and Oil Red O staining. Hepatic, fecal, and systemic bile acids (BAs) profiles were detected by UPLC-MS. mRNA and protein levels of BAs synthesis-related enzymes and critical nodes of farnesoid X receptor (FXR)/fibroblast growth factor 15 (FGF15)/fibroblast growth factor receptor 4 (FGFR4) signaling were detected. Fecal microbial composition was analyzed by 16S rRNA gene sequencing and the antimicrobial activity of SYT was further evaluated in vitro.

RESULTS

SYT alleviated HFD-induced hepatic steatosis by decreasing TG and TC levels, relieving hepatocyte ballooning, and promoting hepatic BAs synthesis. Moreover, SYT significantly increased the levels of taurine-conjugated BAs in the liver and feces, which in turn inhibited the FXR/FGF15/FGFR4 signaling. Consequently, the hepatic BAs synthesis-related enzyme expression was promoted to reduce lipid accumulation. Notably, SYT remodeled the gut microbiota composition of HFD-fed mice, especially inhibiting the growth of bile salt hydrolase (BSH)-producing bacteria, such as Lactobacillus murinus, Lactobacillus johnsonii, and Enterococcus faecalis.

CONCLUSION

The findings illustrated that SYT prevented hepatic steatosis by improving hepatic lipid accumulation, which is reflected in modulating the gut-liver axis. SYT corrects BAs profile, restores perturbed FXR/FGF15/FGFR4 signaling and promotes hepatic BAs synthesis, which is associated with modulation on certain BSH-producing bacteria.

Sodium taurocholate co-transporting polypeptide deficiency attenuates acetaminophen-induced hepatotoxicity via regulating expression of drug metabolism enzymes in mice

Acetaminophen (APAP) overdose can induce liver injury and is generally accompanied by disruption of bile acid homeostasis. Physiologically, sodium taurocholate co-transporting polypeptide (NTCP) participates in the uptake of bile acids from portal blood into hepatocytes to maintain enterohepatic recirculation but its role in APAP-induced hepatotoxicity is unclear. Wild-type (WT) C57BL/6J and NTCP knockout (KO) mice were injected with 400mg/kg APAP and liver injury was evaluated by serum biochemical markers and histologic evaluation. RNA-seq analysis was performed to evaluate the liver gene expression profiles in APAP-treated mice. Compared with WT mice, the exposure to APAP overdose caused liver dysfunction, oxidative stress, inflammation and cell death, which were ameliorated by NTCP deficiency. APAP detoxification, metabolism, and elimination were significantly accelerated by the upregulation of UDP-glucuronosyltransferase (Ugt1a1, Ugt1a6 and Ugt1a9), sulfotransferase (Sult1a1 and Sult2a1) and bile acid efflux transporters (Abcc2/3/4) in NTCP KO mice compared with WT mice. Interestingly, APAP-induced hepatotoxicity was ameliorated using Irbesartan and Ezetimibe (NTCP inhibitors). In conclusion, NTCP deficiency attenuates APAP-induced hepatotoxicity by enhancing the metabolism and elimination of APAP. NTCP inhibitors protect against APAP-induced hepatotoxicity and thus are a potential therapeutic option.

Duodenal fluid analysis is an excellent differential diagnosis method of diseases with enterohepatic circulation disturbance

Enterohepatic circulation is essential for maintaining a constant bile acid concentration. Diseases with enterohepatic circulation disturbances are usually difficult to diagnose definitively without the time-consuming and expensive genetic tests. This study analyzed and compared duodenal fluid in patients with biliary atresia (BA), familial intrahepatic cholestasis 2 (FIC2), and sodium taurocholate cotransporting polypeptide (NTCP) deficiency. This study aimed to assess the diagnostic value of duodenal fluid analysis in patients with enterohepatic circulation disturbance. This study retrospectively analyzed data from 18 patients with BA, 13 patients with FIC2, and 15 patients with NTCP deficiency. All patients completed the duodenal tube tests before receiving treatment for cholestasis. The patients were intubated through the right nasal cavity to the middle or lower duodenum, as confirmed by radiography. 3-5 mL of duodenal fluid was collected at last. Clinical presentations, laboratory data, genetic data, and so forth were collected for the analysis. Among the 3 types of diseases, levels of total bile acid (TBA), total bilirubin (TB), direct bilirubin (DB), and gamma-glutamyl transpeptidase (GGT) in duodenal fluid showed significant differences (P < .01). Compared with the same indications in duodenal fluid, levels of TBA and GGT in serum did not show significant differences between patients with FIC2 and NTCP deficiency (P > .05). Duodenal TBA/serum TBA ratio, duodenal TB/serum TB ratio, duodenal DB/serum DB ratio, and duodenal GGT/serum GGT ratio also showed significant differences between patients with BA and NTCP deficiency, between patients with FIC2 and NTCP deficiency (P < .01). For diagnosis of BA, increased GGT and absent TB, DB, and TBAs had a sensitivity of 100%, 100%, 100%, and 100%, a specificity of 86.1%, 100%, 97.2%, and 97.2%. Duodenal tube tests have been used for the diagnosis of BA for over 10 years. Our findings support the duodenal fluid analysis as a tool for prompt timely diagnosis of BA. This study also indicates that the test is a useful diagnostic method with high accuracy for other diseases with enterohepatic circulation disturbance.

SLC10A5 deficiency causes hypercholanemia

BACKGROUND AND AIMS

Solute Carrier Family 10 Member 5 (SLC10A5) is a member of SLC10, comprising transporters of bile acids, steroidal hormones, and other substrates, but its function remains unclear. The aim of the current investigation was to clarify its function in the metabolism of bile acid and hypercholanemia.

APPROACH AND RESULTS

Whole-exome sequencing and Sanger sequencing were used to identify and confirm the variant in the subjects of hypercholanemia. CRISPR/Cas9-mediated genome engineering was used to establish the knockout and point mutation mice. Primary mouse hepatocytes were isolated, and cell lines were cultured. SLC10A5 was silenced by siRNA and overexpressed by wild-type and mutant plasmids. The fluorescent bile acid derivative was used for the bile acid uptake assay. Bile acids were assessed with ultra-performance liquid chromatography tandem mass spectrometry. A heterozygous variant SLC10A5 : c.994_995del (p.D332X) was identified in subjects with elevated total bile acid or altered bile acid profiles. Bile acids were increased in the serum and liver of knockout and point mutation mice. The expressions of FXR and SHP, regulators involved in the negative feedback of bile acid synthesis, were downregulated, while the bile acid synthesis genes CYP7A1 and CYP8B1 were upregulated in both gene-edited mice. Both the wild and mutant SLC10A5 proteins were localized on the plasma membrane. Knockdown, knockout, or targeted mutation of SLC10A5 led to the inhibition of bile acid uptake by cell lines and primary mouse hepatocytes.

CONCLUSION

SLC10A5 is involved in the uptake of bile acid, and its deficiency causes hypercholanemia.

Rapid quantification of murine bile acids using liquid chromatography-tandem mass spectrometry

Interest in bile acids (BAs) is growing due to their emerging role as signaling molecules and their association with various diseases such as colon cancer and metabolic syndrome. Analyzing BAs requires chromatographic separation of isomers, often with long run times, which hinders BA analysis in large studies. Here, we present a high-throughput method based on liquid chromatography-tandem mass spectrometry to quantify BAs in mouse samples. After acidic protein precipitation in the presence of a comprehensive mixture of stable isotope-labeled internal standards (SIL-ISs), BAs are separated on a biphenyl column by gradient elution at basic pH. Quantification is performed using a six-point calibration curve. Except for the separation of β- and ω-muricholic acid (MCA) species, a rapid separation of 27 BA species was achieved in a run time of 6.5 min. Plasma quality controls (QCs) were used to evaluate intra- and inter-day precision. The CV was less than 10% for most BA species and exceeded 20% only for glycohyodeoxycholic (GHDCA) and taurohyodeoxycholic acid (THDCA) due to the lack of a corresponding SIL-IS. The limit of quantification (LoQ) was tested using diluted QCs and was found to be compromised for some BA species as a result of insufficient isotopic purity of the SIL-IS, leading to significant interference with the respective analyte. Finally, we tested the mouse sample material requirements for plasma, bile, and liver samples and determined BA concentrations in C57/BL6N wild-type mice. In conclusion, the LC-MS/MS method presented here permits a rapid and reproducible quantification of the major murine BAs.

Getting in the zone: Metabolite transport across liver zones

The liver has many functions including the regulation of nutrient and metabolite levels in the systemic circulation through efficient transport into and out of hepatocytes. To sustain these functions, hepatocytes display large functional heterogeneity. This heterogeneity is reflected by zonation of metabolic processes that take place in different zones of the liver lobule, where nutrient-rich blood enters the liver in the periportal zone and flows through the mid-zone prior to drainage by a central vein in the pericentral zone. Metabolite transport plays a pivotal role in the division of labor across liver zones, being either transport into the hepatocyte or transport between hepatocytes through the blood. Signaling pathways that regulate zonation, such as Wnt/β-catenin, have been shown to play a causal role in the development of metabolic dysfunction-associated steatohepatitis (MASH) progression, but the (patho)physiological regulation of metabolite transport remains enigmatic. Despite the practical challenges to separately study individual liver zones, technological advancements in the recent years have greatly improved insight in spatially divided metabolite transport. This review summarizes the theories behind the regulation of zonation, diurnal rhythms and their effect on metabolic zonation, contemporary techniques used to study zonation and current technological challenges, and discusses the current view on spatial and temporal metabolite transport.

Validation of NBD-coupled taurocholic acid for intravital analysis of bile acid transport in liver and kidney of mice

Fluorophore-coupled bile acids (BA) represent an important tool for intravital analysis of BA flux in animal models of cholestatic diseases. However, addition of a fluorophore to a BA may alter transport properties. We developed and validated a 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole-coupled taurocholic acid (3β-NBD-TCA) as a probe for intravital analysis of BA homeostasis. We compared transport of 3β-NBD-TCA to [3H]-TCA in HEK293 cells stably expressing the mouse hepatic or renal BA carriers mNtcp or mAsbt, respectively. We also studied distribution kinetics intravitally in livers and kidneys of anesthetized wildtype and mOatp1a/1b cluster knockout mice (OatpKO) with and without administration of the Ntcp inhibitor Myrcludex B and the ASBT inhibitor AS0369. In vitro, 3β-NBD-TCA and [3H]-TCA showed comparable concentration- and time-dependent transport via mNtcp and mAsbt as well as similar inhibition kinetics for Myrcludex B and AS0369. Intravital analysis in the livers of wildtype and OatpKO mice revealed contribution of both mNtcp and mOatp1a/1b in the 3β-NBD-TCA uptake from the sinusoidal blood into hepatocytes. Combined deletion of mOatp1a/1b and inhibition of mNtcp by Myrcludex B blocked the uptake of 3β-NBD-TCA from sinusoidal blood into hepatocytes. This led to an increase of 3β-NBD-TCA signal in the systemic circulation including renal capillaries, followed by strong enrichment in a subpopulation of proximal renal tubular epithelial cells (TEC). The enrichment of 3β-NBD-TCA in TEC was strongly reduced by the systemic ASBT inhibitor AS0369. NBD-coupled TCA has similar transport kinetics as [3H]-TCA and can be used as a tool to study hepatorenal BA transport. See also the graphical abstract(Fig. 1).

The Culprit Behind HBV-Infected Hepatocytes: NTCP

Hepatitis B virus (HBV) is a globally prevalent human DNA virus responsible for over 250 million cases of chronic liver infections, leading to conditions such as liver inflammation, cirrhosis and hepatocellular carcinoma (HCC). Sodium taurocholate co-transporting polypeptide (NTCP) is a transmembrane protein highly expressed in human hepatocytes and functions as a bile acid (BA) transporter. NTCP has been identified as the receptor that HBV and its satellite virus, hepatitis delta virus (HDV), use to enter hepatocytes. HBV entry into hepatocytes is tightly regulated by various signaling pathways, and NTCP plays an important role as the initial stage of HBV infection. NTCP acts as an initiation signal, causing metabolic changes in hepatocytes and facilitating the entry of HBV into hepatocytes. Thus, a comprehensive understanding of NTCP's role is crucial. In this review, we will examine the regulatory mechanisms governing HBV pre-S1 binding to liver membrane NTCP, the role of NTCP in HBV internalization, and the transcriptional and translational regulation of NTCP expression. Additionally, we will discuss clinical drugs targeting NTCP, including combination therapies involving NTCP inhibitors, and consider the safety of NTCP as a therapeutic target.

Structural basis for hepatitis B virus restriction by a viral receptor homologue

Macaque restricts hepatitis B virus (HBV) infection because its receptor homologue, NTCP (mNTCP), cannot bind preS1 on viral surface. To reveal how mNTCP loses the viral receptor function, we here solve the cryo-electron microscopy structure of mNTCP. Superposing on the human NTCP (hNTCP)-preS1 complex structure shows that Arg158 of mNTCP causes steric clash to prevent preS1 from embedding onto the bile acid tunnel of NTCP. Cell-based mutation analysis confirms that only Gly158 permitted preS1 binding, in contrast to robust bile acid transport among mutations. As the second determinant, Asn86 on the extracellular surface of mNTCP shows less capacity to restrain preS1 from dynamic fluctuation than Lys86 of hNTCP, resulting in unstable preS1 binding. Additionally, presence of long-chain conjugated-bile acids in the tunnel induces steric hindrance with preS1 through their tailed-chain. This study presents structural basis in which multiple sites in mNTCP constitute a molecular barrier to strictly restrict HBV.

Bile Acid Signaling in Metabolic and Inflammatory Diseases and Drug Development

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 biliary secretion of lipids, endogenous metabolites, and xenobiotics. In intestine, bile acids facilitate the digestion and absorption of dietary lipids and fat-soluble vitamins. Through activation of nuclear receptors and G protein-coupled receptors and interaction with gut microbiome, bile acids critically regulate host metabolism and innate and adaptive immunity and are involved in the pathogenesis of cholestasis, metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, type-2 diabetes, and inflammatory bowel diseases. Bile acids and their derivatives have been developed as potential therapeutic agents for treating chronic metabolic and inflammatory liver diseases and gastrointestinal disorders. SIGNIFICANCE STATEMENT: Bile acids facilitate biliary cholesterol solubilization and dietary lipid absorption, regulate host metabolism and immunity, and modulate gut microbiome. Targeting bile acid metabolism and signaling holds promise for treating metabolic and inflammatory diseases.

Dynamic pattern of postprandial bile acids in paediatric non-alcoholic fatty liver disease

BACKGROUND

Dysregulation of bile acids (BAs), as important signalling molecules in regulating lipid and glucose metabolism, contributes to the development of non-alcoholic fatty liver disease (NAFLD). However, static BA profiles during fasting may obscure certain pathogenetic aspects. In this study, we investigate the dynamic alterations of BAs in response to an oral glucose tolerance test (OGTT) among children with NAFLD.

METHODS

We recruited 230 subjects, including children with overweight/obesity, or complicated with NAFLD, and healthy controls. Serum BAs, 7-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor 19 (FGF19) were quantified during OGTT. Clinical markers related to liver function, lipid metabolism and glucose metabolism were assessed at baseline or during OGTT.

FINDINGS

Conjugated BAs increased while unconjugated ones decreased after glucose uptake. Most BAs were blunted in response to glucose in NAFLD (p > .05); only glycine and taurine-conjugated chenodeoxycholic acid (CDCA) and cholic acid (CA) were responsive (p < .05). Primary BAs were significantly increased while secondary BAs were decreased in NAFLD. C4 and FGF19 were significantly increased while their ratio FGF19/C4 ratio was decreased in NAFLD. The dynamic pattern of CDCA and taurine-conjugated hyocholic acid (THCA) species was closely correlated with glucose (correlation coefficient r = .175 and -.233, p < .05), insulin (r = .327 and -.236, p < .05) and c-peptide (r = .318 and -.238, p < .05). Among which, CDCA was positively associated with liver fat content in NAFLD (r = .438, p < .05). Additionally, glycochenodeoxycholic acid (GCDCA), CDCA and THCA were potential biomarkers to discriminate paediatric NAFLD from healthy controls and children with obesity.

INTERPRETATION

This study provides novel insights into the dynamics of BAs during OGTT in paediatric NAFLD. The observed variations in CDCA and HCA species were associated with liver dysfunction, dyslipidaemia and dysglycaemia, highlighting their potential roles as promising diagnostic and therapeutic targets in NAFLD.

Tauroursodeoxycholic Acid Improves Nonalcoholic Fatty Liver Disease by Regulating Gut Microbiota and Bile Acid Metabolism

Tauroursodeoxycholic acid (TUDCA) is a synthetic bile salt that has demonstrated efficacy in the management of hepatobiliary disorders. However, its specific mechanism of action in preventing and treating nonalcoholic fatty liver disease (NAFLD) remains incompletely understood. This research revealed that TUDCA treatment can reduce obesity and hepatic lipid buildup, enhance intestinal barrier function and microbial balance, and increase the presence of Allobaculum and Bifidobacterium in NAFLD mouse models. TUDCA can influence the activity of farnesoid X receptor (FXR) and cholesterol 7α-hydroxylase (CYP7A1), resulting in higher hepatic bile acid levels and increased expression of sodium taurocholate cotransporting polypeptide (NTCP), leading to elevated concentrations of liver-bound bile acids in mice. Furthermore, TUDCA can inhibit the expression of FXR and fatty acid transport protein 5 (FATP5), thereby reducing fatty acid absorption and hepatic lipid accumulation. This investigation provides new insights into the potential of TUDCA for preventing and treating NAFLD.

Inhibition of hepatic bile salt uptake by Bulevirtide reduces atherosclerosis in Oatp1a1-/-Ldlr-/- mice

Bile salts can strongly influence energy metabolism through systemic signaling, which can be enhanced by inhibiting the hepatic bile salt transporter Na+ taurocholate cotransporting polypeptide (NTCP), thereby delaying hepatic reuptake of bile salts to increase systemic bile salt levels. Bulevirtide is an NTCP inhibitor and was originally developed to prevent NTCP-mediated entry of Hepatitis B and D into hepatocytes. We previously demonstrated that NTCP inhibition lowers body weight, induces glucagon-like peptide-1 (GLP1) secretion, and lowers plasma cholesterol levels in murine obesity models. In humans, a genetic loss-of-function variant of NTCP has been associated with reduced plasma cholesterol levels. Here, we aimed to assess if Bulevirtide treatment attenuates atherosclerosis development by treating female Ldlr-/- mice with Bulevirtide or vehicle for 11 weeks. Since this did not result in the expected increase in plasma bile salt levels, we generated Oatp1a1-/-Ldlr-/- mice, an atherosclerosis-prone model with human-like hepatic bile salt uptake characteristics. These mice showed delayed plasma clearance of bile salts and elevated bile salt levels upon Bulevirtide treatment. At the study endpoint, Bulevirtide-treated female Oatp1a1-/-Ldlr-/- mice had reduced atherosclerotic lesion area in the aortic root that coincided with lowered plasma LDL-c levels, independent of intestinal cholesterol absorption. In conclusion, Bulevirtide, which is considered safe and is EMA-approved for the treatment of Hepatitis D, reduces atherosclerotic lesion area by reducing plasma LDL-c levels. We anticipate that its application may extend to atherosclerotic cardiovascular diseases, which warrants clinical trials.

The role of botanical triterpenoids and steroids in bile acid metabolism, transport, and signaling: Pharmacological and toxicological implications

Bile acids (BAs) are synthesized by the host liver from cholesterol and are delivered to the intestine, where they undergo further metabolism by gut microbes and circulate between the liver and intestines through various transporters. They serve to emulsify dietary lipids and act as signaling molecules, regulating the host's metabolism and immune homeostasis through specific receptors. Therefore, disruptions in BA metabolism, transport, and signaling are closely associated with cholestasis, metabolic disorders, autoimmune diseases, and others. Botanical triterpenoids and steroids share structural similarities with BAs, and they have been found to modulate BA metabolism, transport, and signaling, potentially exerting pharmacological or toxicological effects. Here, we have updated the research progress on BA, with a particular emphasis on new-found microbial BAs. Additionally, the latest advancements in targeting BA metabolism and signaling for disease treatment are highlighted. Subsequently, the roles of botanical triterpenoids in BA metabolism, transport, and signaling are examined, analyzing their potential pharmacological, toxicological, or drug interaction effects through these mechanisms. Finally, a research paradigm is proposed that utilizes the gut microbiota as a link to interpret the role of these important natural products in BA signaling.

Expression of hepatic genes involved in bile acid metabolism in dairy cows with fatty liver

Bile acids are cholesterol-derived molecules that are primarily produced in the liver. In nonruminants with fatty liver, overproduction of bile acids is associated with liver injury. During the transition period, fatty liver is a metabolic disorder that can affect up to 50% of high-producing dairy cows. The purpose of this study was to provide a comprehensive evaluation on hepatic bile acid metabolism in dairy cows with fatty liver by assessing expression changes of genes involved in bile acid synthesis, export and uptake. The serum activities of aspartate aminotransferase, alanine aminotransferase and glutamate dehydrogenase and concentration of total bile acids were all greater, whereas serum concentration of total cholesterol was lower in cows with fatty liver than in healthy cows. Content of total bile acids was higher but total cholesterol was slightly lower in liver tissues from fatty liver cows than from healthy cows. The hepatic mRNA abundance of cholesterol 7a-hydroxylase (CYP7A1), hydroxy-delta-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 7 (HSD3B7) and sterol 12α-hydroxylase (CYP8B1), enzymes involved in the classic pathway of bile acid synthesis, was higher in fatty liver cows than in healthy cows. Compared with healthy cows, the hepatic mRNA abundance of alternative bile acid synthesis pathway-related genes sterol 27-hydroxylase (CYP27A1) and oxysterol 7α-hydroxylase (CYP7B1) did not differ in cows with fatty liver. The protein and mRNA abundance of bile acid transporter bile salt efflux pump (BSEP) were lower in the liver of dairy cow with fatty liver. Compared with healthy cows, the hepatic mRNA abundance of bile acid transporters solute carrier family 51 subunit α (SLC51A), ATP binding cassette subfamily C member 1 (ABCC1) and 3 (ABCC3) was greater in cows with fatty liver, whereas the solute carrier family 51 subunit β (SLC51B) did not differ. The expression of genes involved in bile acid uptake, including solute carrier family 10 member 1 (NTCP), solute carrier organic anion transporter family member 1A2 (SLCO1A2) and 2B1 (SLCO2B1) was upregulated in dairy cows with fatty liver. Furthermore, the hepatic protein and mRNA abundance of bile acid metabolism regulators farnesoid X receptor (FXR) and small heterodimer partner (SHP) were lower in cows with fatty liver than in healthy cows. Overall, these data suggest that inhibition of FXR signaling pathway may lead to the increased bile acid synthesis and uptake and decreased secretion of bile acids from hepatocytes to the bile, which elevates hepatic bile acids content in dairy cows with fatty liver. As the hepatotoxicity of bile acids has been demonstrated on nonruminant hepatocytes, it is likely that the liver injury is induced by increased hepatic bile acids content in dairy cows with fatty liver.

Progress in Biomarkers Related to Biliary Atresia

Biliary atresia (BA) is a congenital cholestatic disease that can seriously damage children's liver function. It is one of the main reasons for liver transplantation in children. Early diagnosis of BA is crucial to the prognosis of patients, but there is still a lack of reliable non-invasive diagnostic methods. Additionally, as some children are in urgent need of liver transplantation, evaluating the stage of liver fibrosis and postoperative native liver survival in children with BA using a straightforward, efficient, and less traumatic method is a major focus of doctors. In recent years, an increasing number of BA-related biomarkers have been identified and have shown great potential in the following three aspects of clinical practice: diagnosis, evaluation of the stage of liver fibrosis, and prediction of native liver survival. This review focuses on the pathophysiological function and clinical application of three novel BA-related biomarkers, namely MMP-7, FGF-19, and M2BPGi. Furthermore, progress in well-known biomarkers of BA such as gamma-glutamyltransferase, circulating cytokines, and other potential biomarkers is discussed, aiming to provide a reference for clinical practice.

The role of peroxisome proliferator-activated receptors in the regulation of bile acid metabolism

Bile acids are synthesized from cholesterol in the liver. Dysregulation of bile acid homeostasis, characterized by excessive accumulation in the liver, gallbladder and blood, can lead to hepatocellular damage and the development of cholestatic liver disease. Nuclear receptors play a crucial role in the control of bile acid metabolism by efficiently regulating bile acid synthesis and transport in the liver. Among these receptors, peroxisome proliferator-activated receptor (PPAR), a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily, controls the expression of genes involved in adipogenesis, lipid metabolism, inflammation and glucose homeostasis and has emerged as a potential therapeutic target for the treatment of the metabolic syndrome in the past two decades. Emerging evidence suggests that PPAR activation holds promise as a therapeutic target for cholestatic liver disease, as it affects both bile acid production and transport. This review provides a comprehensive overview of recent advances in elucidating the role of PPAR in the regulation of bile acid metabolism, highlighting the current position of PPAR agonists in the treatment of primary biliary cholangitis. By summarizing the specific regulatory effects of PPAR on bile acids, this review contributes to the exploration of novel therapeutic strategies for cholestatic liver diseases.

Development of novel liver-targeting glucocorticoid prodrugs

Background

Glucocorticoids (GCs) are widely used in the treatment of inflammatory liver diseases and sepsis, but GC's various side effects on extrahepatic tissues limit their clinical benefits. Liver-targeting GC therapy may have multiple advantages over systemic GC therapy. The purpose of this study was to develop novel liver-targeting GC prodrugs as improved treatment for inflammatory liver diseases and sepsis.

Methods

A hydrophilic linker or an ultra-hydrophilic zwitterionic linker carboxylic betaine (CB) was used to bridge cholic acid (CA) and dexamethasone (DEX) to generate transporter-dependent liver-targeting GC prodrugs CA-DEX and the highly hydrophilic CA-CB-DEX. The efficacy of liver-targeting DEX prodrugs and DEX were determined in primary human hepatocytes (PHH), macrophages, human whole blood, and/or mice with sepsis induced by cecal ligation and puncture.

Results

CA-DEX was moderately water soluble, whereas CA-CB-DEX was highly water soluble. CA-CB-DEX and CA-DEX displayed highly transporter-dependent activities in reporter assays. Data mining found marked dysregulation of many GR-target genes important for lipid catabolism, cytoprotection, and inflammation in patients with severe alcoholic hepatitis. These key GR-target genes were similarly and rapidly (within 6 h) induced or down-regulated by CA-CB-DEX and DEX in PHH. CA-CB-DEX had much weaker inhibitory effects than DEX on endotoxin-induced cytokines in mouse macrophages and human whole blood. In contrast, CA-CB-DEX exerted more potent anti-inflammatory effects than DEX in livers of septic mice.

Conclusions

CA-CB-DEX demonstrated good hepatocyte-selectivity in vitro and better anti-inflammatory effects in vivo. Further test of CA-CB-DEX as a novel liver-targeting GC prodrug for inflammatory liver diseases and sepsis is warranted.

Role of sodium taurocholate cotransporting polypeptide (NTCP) in HBV-induced hepatitis: Opportunities for developing novel therapeutics

Hepatitis B is an infectious disease caused by the HBV virus. It presents a significant challenge for treatment due to its chronic nature and the potential for developing severe complications, including hepatocirrhosis and hepatocellular carcinoma. These complications not only cause physical and psychological distress to patients but also impose substantial economic and social burdens on both individuals and society as a whole. The internalization of HBV relies on endocytosis and necessitates the involvement of various proteins, including heparin sulfate proteoglycans, epidermal growth factor receptors, and NTCP. Among these proteins, NTCP is pivotal in HBV internalization and is primarily located in the liver's basement membrane. As a transporter of bile acids, NTCP also serves as a receptor facilitating HBV entry into cells. Numerous molecules have been identified to thwart HBV infection by stifling NTCP activity, although only a handful exhibit low IC50 values. In this systematic review, our primary focus dwells on the structure and regulation of NTCP, as well as the mechanism involved in HBV internalization. We underscore recent drug breakthroughs that specifically target NTCP to combat HBV infection. By shedding light on these advances, this review contributes novel insights into developing effective anti-HBV medications.

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.

Gentamicin alleviates cholestatic liver injury by decreasing gut microbiota-associated bile salt hydrolase activity in rats

Intrahepatic cholestasis lacks effective therapeutic drugs. The gut microbiota-associated bile salt hydrolases (BSH) may be a potential therapeutic target. In this study, oral administration of gentamicin (GEN) decreased the serum and hepatic levels of total bile acid in 17α-ethynylestradiol (EE)-induced cholestatic male rats, significantly improved the serum levels of hepatic biomarkers and reversed the histopathological changes in the liver. In healthy male rats, the serum and hepatic levels of total bile acid were also decreased by GEN, the ratio of primary to secondary bile acids, and conjugated to unconjugated bile acids was significantly increased, and the urinary excretion of total bile acid was elevated. 16S rDNA sequencing of the ileal contents revealed that GEN treatment substantially reduced the abundance of Lactobacillus and Bacteroides both of which expressed BSH. Consistently, BSH activity analysis by the generation of d5-chenodeoxycholic acid from d5-taurochenodeoxycholic acid in situ showed BSH was significantly inhibited in the ileal contents of rats treated with GEN. This finding led to an increased proportion of hydrophilic conjugated bile acids and facilitated the urinary excretion of total bile acids, thereby decreasing serum and hepatic total bile acids and reversing liver injury related to cholestasis. Our results provide important evidence that BSH can be a potential drug target for treating cholestasis.

Serum FGF19 predicts outcomes of Kasai portoenterostomy in biliary atresia

BACKGROUND AND AIMS

Outcomes after Kasai portoenterostomy (KPE) for biliary atresia remain highly variable for unclear reasons. As reliable early biomarkers predicting KPE outcomes are lacking, we studied the prognostic value of FGF19.

APPROACH AND RESULTS

Serum and liver specimens, obtained from biliary atresia patients (N=87) at KPE or age-matched cholestatic controls (N=26) were included. Serum concentration of FGF19 and bile acids, liver mRNA expression of FGF19 , and key regulators of bile acid synthesis were related to KPE outcomes and liver histopathology. Immunohistochemistry and in situ hybridization were used for the localization of liver FGF19 expression. Serum levels (223 vs. 61 pg/mL, p <0.001) and liver mRNA expression of FGF19 were significantly increased in biliary atresia. Patients with unsuccessful KPE (419 vs. 145 pg/mL, p =0.047), and those subsequently underwent liver transplantation (410 vs. 99 pg/mL, p =0.007) had significantly increased serum, but not liver, FGF19, which localized mainly in hepatocytes. In Cox hazard modeling serum FGF19 <109 pg/mL predicted native liver survival (HR: 4.31, p <0.001) also among patients operated <60 days of age (HR: 8.77, p =0.004) or after successful KPE (HR: 6.76, p =0.01). Serum FGF19 correlated positively with increased serum primary bile acids ( R =0.41, p =0.004) and ductular reaction ( R =0.39, p =0.004).

CONCLUSIONS

Increased serum FGF19 at KPE predicted inferior long-term native liver survival in biliary atresia and was associated with unsuccessful KPE, elevated serum primary bile acids, and ductular reaction.

Active enterohepatic cycling is not required for the choleretic actions of 24-norUrsodeoxycholic acid in mice

The pronounced choleretic properties of 24-norUrsodeoxycholic acid (norUDCA) to induce bicarbonate-rich bile secretion have been attributed to its ability to undergo cholehepatic shunting. The goal of this study was to identify the mechanisms underlying the choleretic actions of norUDCA and the role of the bile acid transporters. Here, we show that the apical sodium-dependent bile acid transporter (ASBT), organic solute transporter-α (OSTα), and organic anion transporting polypeptide 1a/1b (OATP1a/1b) transporters are dispensable for the norUDCA stimulation of bile flow and biliary bicarbonate secretion. Chloride channels in biliary epithelial cells provide the driving force for biliary secretion. In mouse large cholangiocytes, norUDCA potently stimulated chloride currents that were blocked by siRNA silencing and pharmacological inhibition of calcium-activated chloride channel transmembrane member 16A (TMEM16A) but unaffected by ASBT inhibition. In agreement, blocking intestinal bile acid reabsorption by coadministration of an ASBT inhibitor or bile acid sequestrant did not impact norUDCA stimulation of bile flow in WT mice. The results indicate that these major bile acid transporters are not directly involved in the absorption, cholehepatic shunting, or choleretic actions of norUDCA. Additionally, the findings support further investigation of the therapeutic synergy between norUDCA and ASBT inhibitors or bile acid sequestrants for cholestatic liver disease.

Biological tuners to reshape the bile acid pool for therapeutic purposes in non-alcoholic fatty liver disease

Bile acids synthesized within the hepatocytes are transformed by gut microorganisms and reabsorbed into the portal circulation. During their enterohepatic cycling, bile acids act as signaling molecules by interacting with receptors to regulate pathways involved in many physiological processes. The bile acid pool, composed of a variety of bile acid species, has been shown to be altered in diseases, hence contributing to disease pathogenesis. Thus, understanding the changes in bile acid pool size and composition in pathological processes will help to elaborate effective pharmacological treatments. Five crucial steps along the enterohepatic cycle shape the bile acid pool size and composition, offering five possible targets for therapeutic intervention. In this review, we provide an insight on the strategies to modulate the bile acid pool, and then we discuss the potential benefits in non-alcoholic fatty liver disease.

Bile acids and their receptors in regulation of gut health and diseases

It is well established that bile acids play important roles in lipid metabolism. In recent decades, bile acids have also been shown to function as signaling molecules via interacting with various receptors. Bile acids circulate continuously through the enterohepatic circulation and go through microbial transformation by gut microbes, and thus bile acids metabolism has profound effects on the liver and intestinal tissues as well as the gut microbiota. Farnesoid X receptor and G protein-coupled bile acid receptor 1 are two pivotal bile acid receptors that highly expressed in the intestinal tissues, and they have emerged as pivotal regulators in bile acids metabolism, innate immunity and inflammatory responses. There is considerable interest in manipulating the metabolism of bile acids and the expression of bile acid receptors as this may be a promising strategy to regulate intestinal health and disease. This review aims to summarize the roles of bile acids and their receptors in regulation of gut health and diseases.

Evaluation of the drug-drug interaction potential of the novel hepatitis B and D virus entry inhibitor bulevirtide at OATP1B in healthy volunteers

Introduction: Bulevirtide is a first-in-class antiviral drug to treat chronic hepatitis B/D. We investigated the drug-drug interaction potential and pharmacokinetics of high-dose subcutaneous bulevirtide (5 mg twice daily) with organic anion transporting polypeptide 1B1 (OATP1B1) and cytochrome P450 (CYP) 3A4. Methods: This was a single-center, open-label, fixed-sequence drug-drug interaction trial in 19 healthy volunteers. Before and at bulevirtide steady state, participants ingested a single 40 mg dose of pravastatin. A midazolam microdose was applied to quantify CYP3A4 activity. Results: At bulevirtide steady state, pravastatin area under the concentration-time curve (AUC_0-∞) increased 1.32-fold (90% CI 1.08-1.61). The 5 mg bulevirtide twice-daily treatment resulted in a mean AUC_0-12 of 1210 h*ng/ml (95% CI 1040-1408) and remained essentially unchanged under the influence of pravastatin. CYP3A4 activity did not change to a clinically relevant extent. As expected, total bile acids increased substantially (35-fold) compared to baseline during bulevirtide treatment. All study medication was well tolerated. Discussion: The study demonstrated that high-dose bulevirtide inhibited OATP1B-mediated hepatic uptake of the marker substrate pravastatin but the extent is considered clinically not relevant. Changes in CYP3A4 activity were also not clinically relevant. In conclusion, this study suggests that OATP1B substrate drugs as well as CYP3A4 substrates may safely be used without dose adjustment in patients treated with bulevirtide. However, in patients using high statin doses and where concomitant factors potentially further increase statin exposure, caution may be required when using bulevirtide.

The Clinical Relevance and Immune Correlation of SLC10 Family Genes in Liver Cancer

Background and Aim

This study was aimed to reveal the clinical relevance and immune correlation of the SLC10 family genes in liver cancer.

Methods

A comprehensive bioinformatics analysis was utilized to determine the gene expression, genetic alterations, DNA methylation, clinical significance, survival association and immune correlation of seven SLC10 family genes in liver cancer. The multiplexed immunohistochemical technique was applied to determine the association between SLC10A3 protein expression and immune cells, and the correlation between SLC10A3 protein and immune checkpoints (PD1 and PD-L1) in a cohort of 32 individuals with liver cancer.

Results

The expression of SLC10 family genes was different between normal liver tissues and malignant liver tissues. SLC10A5 showed the highest alteration rate (8%), followed by SLC10A3 (2.8%). Low expression of SLC10A1 was indicative of poor tumor grade and advanced tumor stage in liver cancer. Scatter plots uncovered that expression of SLC10A3 was inversely associated with SLC10A1 and SLC10A5 expression in liver cancer. The expression of SLC10A1 and SLC10A5 was strongly associated with their DNA methylation. SLC10A1 expression was a reliable genetic biomarker for the prediction of survival outcomes in liver cancer population. Expression of SLC10 family genes was remarkably linked with the abundance of most immune infiltrating cells in liver cancer, and SLC10A3 was the most significant member. The multiplexed immunohistochemical technique confirmed that there existed the significant correlations between SLC10A3 protein expression and CD4 T cells, CD20 B cells and the close association with PD-1 in the stromal area from malignant tissues.

Conclusion

The expressions of SLC10 family genes were different between normal liver tissues and malignant liver tissues, and they were correlated with each other in liver cancer. SLC10A1 possesses the most significant correlation with survival outcomes. SLC10A3 exhibited the most significant relationship with immune cells, as revealed by bioinformatics analysis and multispectral imaging technique.

Metabolic Effect of Blocking Sodium-Taurocholate Co-Transporting Polypeptide in Hypercholesterolemic Humans with a Twelve-Week Course of Bulevirtide-An Exploratory Phase I Clinical Trial

Bile acids (BA) play an important role in cholesterol metabolism and possess further beneficial metabolic effects as signalling molecules. Blocking the hepatocellular uptake of BA via sodium-taurocholate co-transporting polypeptide (NTCP) with the first-in-class drug bulevirtide, we expected to observe a decrease in plasma LDL cholesterol. In this exploratory phase I clinical trial, volunteers with LDL cholesterol > 130 mg/dL but without overt atherosclerotic disease were included. Thirteen participants received bulevirtide 5 mg/d subcutaneously for 12 weeks. The primary aim was to estimate the change in LDL cholesterol after 12 weeks. Secondary endpoints included changes in total cholesterol, HDL cholesterol, lipoprotein(a), inflammatory biomarkers, and glucose after 12 weeks. In addition, cardiac magnetic resonance imaging (CMR) was performed at four time points. BA were measured as biomarkers of the inhibition of hepatocellular uptake. After 12 weeks, LDL cholesterol decreased not statistically significantly by 19.6 mg/dL [−41.8; 2.85] (Hodges−Lehmann estimator with 95% confidence interval). HDL cholesterol showed a significant increase by 5.5 mg/dL [1.00; 10.50]. Lipoprotein(a) decreased by 1.87 mg/dL [−7.65; 0]. Inflammatory biomarkers, glucose, and cardiac function were unchanged. Pre-dose total BA increased nearly five-fold (from 2026 nmol/L ± 2158 (mean ± SD) at baseline to 9922 nmol/L ± 7357 after 12 weeks of treatment). Bulevirtide was generally well tolerated, with most adverse events being administration site reactions. The exploratory nature of the trial with a limited number of participants allows the estimation of potential effects, which are crucial for future pharmacological research on bile acid metabolism in humans.

Intrauterine growth retardation affects liver bile acid metabolism in growing pigs: effects associated with the changes of colonic bile acid derivatives

BACKGROUND

Intrauterine growth retardation (IUGR) is associated with severely impaired nutrient metabolism and intestinal development of pigs. Our previous study found that IUGR altered intestinal microbiota and metabolites in the colon. However, the consequences of IUGR on bile acid metabolism in pigs remained unclear. The present study aimed to investigate the bile acid metabolism in the liver and the profile of bile acid derivatives in the colon of growing pigs with IUGR using bile acid targeted metabolomics. Furthermore, we determined correlations between colonic microbiota composition and metabolites of IUGR and normal birth weight (NBW) pigs at different growth stages that were 7, 21, and 28-day-old, and the average body weight (BW) of 25, 50, and 100 kg of the NBW pigs.

RESULTS

The results showed that the plasma total bile acid concentration was higher (P < 0.05) at the 25 kg BW stage and tended to increase (P = 0.08) at 28-day-old in IUGR pigs. The hepatic gene expressions related to bile acid synthesis (CYP7A1, CYP27A1, and NTCP) were up-regulated (P < 0.05), and the genes related to glucose and lipid metabolism (ATGL, HSL, and PC) were down-regulated (P < 0.05) at the 25 kg BW stage in IUGR pigs when compared with the NBW group. Targeted metabolomics analysis showed that 29 bile acids and related compounds were detected in the colon of pigs. The colonic concentrations of dehydrolithocholic acid and apocholic acid were increased (P < 0.05), while isodeoxycholic acid and 6,7-diketolithocholic acid were decreased (P < 0.05) in IUGR pigs, when compared with the NBW pigs at the 25 kg BW stage. Moreover, Spearman's correlation analysis revealed that colonic Unclassified_[Mogibacteriaceae], Lachnospira, and Slackia abundances were negatively correlated (P < 0.05) with dehydrolithocholic acid, as well as the Unclassified_Clostridiaceae abundance with 6,7-diketolithocholic acid at the 25 kg BW stage.

CONCLUSIONS

These findings suggest that IUGR could affect bile acid and glucolipid metabolism in growing pigs, especially at the 25 kg BW stage, these effects being paralleled by a modification of bile acid derivatives concentrations in the colonic content. The plausible links between these modified parameters are discussed.

Repression of Organic Anion Transporting Polypeptide (OATP) 1B Expression and Increase of Plasma Coproporphyrin Level as Evidence for OATP1B Downregulation in Cynomolgus Monkeys Treated with Chenodeoxycholic Acid

Farnesoid X receptor (FXR) is a nuclear receptor known to markedly alter expression of major transporters and enzymes in the liver. However, its effects toward organic anion transporting polypeptides (OATP) 1B1 and 1B3 remain poorly characterized. Therefore, the present study was aimed at determining the effects of chenodeoxycholic acid (CDCA), a naturally occurring FXR agonist, on OATP1B expression in cynomolgus monkeys. Multiple administrations of 50 and 100 mg/kg of CDCA were first shown to significantly repress mRNA expression of SLCO1B1/3 approximately 60% to 80% in monkey livers. It also suppressed cytochrome P450 (CYP)7A1-mRNA and induced OSTα/β-mRNA, which are well known targets of FXR and determinants of bile acid homeostasis. CDCA concomitantly decreased OATP1B protein abundance by approximately 60% in monkey liver. In contrast, multiple doses of 15 mg/kg rifampin (RIF), a pregnane X receptor agonist, had no effect on hepatic OATP1B protein, although it induced the intestinal P-glycoprotein and MR2 proteins by ∼2-fold. Moreover, multiple doses of CDCA resulted in a steady ∼2- to 10-fold increase of the OATP1B biomarkers coproporphyrins (CPs) in the plasma samples collected prior to each CDCA dose. Additionally, 3.4- to 11.2-fold increases of CPI and CPIII areas under the curve were observed after multiple administrations compared with the single dose and vehicle administration dosing groups. Taken together, these data suggest that CDCA represses the expression of OATP1B1 and OATP1B3 in monkeys. Further investigation of OATP1B downregulation by FXR in humans is warranted, as such downregulation effects may be involved in bile acid homeostasis and potential drug interactions in man. SIGNIFICANCE STATEMENT: Using gene expression and proteomics tools, as well as endogenous biomarker data, for the first time, we have demonstrated that OATP1B expression was suppressed and its activity was reduced in the cynomolgus monkeys following oral administration of 50 and 100 mg/kg/day of chenodeoxycholic acid (CDCA), a Farnesoid X receptor agonist, for 8 days. These results lead to a better understanding of OATP1B downregulation by CDCA and its role on bile acid and drug disposition.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

Interruption of bile acid uptake by hepatocytes after acetaminophen overdose ameliorates hepatotoxicity

BACKGROUND & AIMS

Acetaminophen (APAP) overdose remains a frequent cause of acute liver failure, which is generally accompanied by increased levels of serum bile acids (BAs). However, the pathophysiological role of BAs remains elusive. Herein, we investigated the role of BAs in APAP-induced hepatotoxicity.

METHODS

We performed intravital imaging to investigate BA transport in mice, quantified endogenous BA concentrations in the serum of mice and patients with APAP overdose, analyzed liver tissue and bile by mass spectrometry and MALDI-mass spectrometry imaging, assessed the integrity of the blood-bile barrier and the role of oxidative stress by immunostaining of tight junction proteins and intravital imaging of fluorescent markers, identified the intracellular cytotoxic concentrations of BAs, and performed interventions to block BA uptake from blood into hepatocytes.

RESULTS

Prior to the onset of cell death, APAP overdose causes massive oxidative stress in the pericentral lobular zone, which coincided with a breach of the blood-bile barrier. Consequently, BAs leak from the bile canaliculi into the sinusoidal blood, which is then followed by their uptake into hepatocytes via the basolateral membrane, their secretion into canaliculi and repeated cycling. This, what we termed 'futile cycling' of BAs, led to increased intracellular BA concentrations that were high enough to cause hepatocyte death. Importantly, however, the interruption of BA re-uptake by pharmacological NTCP blockage using Myrcludex B and Oatp knockout strongly reduced APAP-induced hepatotoxicity.

CONCLUSIONS

APAP overdose induces a breach of the blood-bile barrier which leads to futile BA cycling that causes hepatocyte death. Prevention of BA cycling may represent a therapeutic option after APAP intoxication.

LAY SUMMARY

Only one drug, N-acetylcysteine, is approved for the treatment of acetaminophen overdose and it is only effective when given within ∼8 hours after ingestion. We identified a mechanism by which acetaminophen overdose causes an increase in bile acid concentrations (to above toxic thresholds) in hepatocytes. Blocking this mechanism prevented acetaminophen-induced hepatotoxicity in mice and evidence from patients suggests that this therapy may be effective for longer periods after ingestion compared to N-acetylcysteine.

Sodium+/taurocholate cotransporting polypeptide as target therapy for liver fibrosis

OBJECTIVE

Sodium⁺/ taurocholate cotransporting polypeptide (NTCP) is a membrane transporter affecting the enterohepatic circulation of bile acids (BAs). We aimed to evaluate NTCP's roles in humans and animal models of liver fibrosis (LF).

DESIGN

Primary hepatic stellate cells (pHSCs) isolated from livers biopsies of patients with LF with different fibrosis grading were stained for NTCP. NTCP gene silencing, taurocholic acid (TCA), obeticholic acid (OCA), epigallocatechin gallate (EGCG) and HA-100 dihydrochloride (HA-100) were used as tools to modulate NTCP expression on human HSC line (LX2). BA trafficking/uptake were assessed extracellularly (LX2 culture medium) and intracellularly following treatment with/without NTCP neutralizing antibody. LF models of C57/BL6 mice of carbon tetrachloride (CCl₄) and leptin-deficient (Ob/Ob) fed with high-fat diet (Ob/Ob ^HFD ) were evaluated for pHSCs-NTCP expressions, metabolic and LF profiles following intraperitoneal injections of NTCP neutralizing antibody.

RESULTS

pHSCs from F3/F4-scored patients of LF exhibit threefold increased NTCP expressions compared with F0-scored patients (p<0.0001). Sorted-activated HSCs (LX2^αSMA+) showed high expressions of NTCP and high TCA uptake in vitro and triggered a further increase in their activations. This phenomenon was inhibited with NTCP small interfering RNA and the NTCP neutralizing antibody. Sorted LX2^NTCP+ (high alpha smooth muscle actin (αSMA)/high NTCP) cells showed high phosphorylated pathways of AKT/mTOR and protein kinase C (PKC) accompanied with a decrease in farnesoid X receptor expression. Moreover, LX2^NTCP+ cells treated with EGCG, OCA and PKC inhibitor HA-100 significantly decreased NTCP and αSMA. NTCP neutralizing antibody inhibited NTCP (less TCA uptake); it attenuated LF in both CCl₄ and Ob/Ob ^HFD animal models with ameliorated metabolic profile.

CONCLUSION

NTCP expression is linearly correlated with fibrosis severity. Modulated BA trafficking could be an important step in LF pathogenesis. Antagonising BA uptake may suggest a therapeutic strategy for preventing disease progression.

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

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

Bile acid detergency: permeability, inflammation, and effects of sulfation

Bile acids are amphipathic, detergent molecules. The detergent effects of di-α-hydroxy-bile acids are relevant to several colonic diseases. The aims were to review the concentrations of bile acids reaching the human colon in health and disease, the molecular structure of bile acids that determine detergent functions and the relationship to human diseases (neuroendocrine tumors, microscopic colitis, active celiac disease, and ulcerative colitis, Crohn's disease and ileal resection), the relationship to bacterial uptake into the mucosa, mucin depletion, and epithelial damage, the role of bile acids in mucosal inflammation and microscopic colitis, and the role of sulfation of bile salts in detoxification or prevention of the detergent effects of bile acids. The concentrations of bile acids reaching the human colon range from 2 to 10 mM; di-α-hydroxy bile acids are the only bile acids with detergent effects that include mucin depletion, mucosal damage, bacterial uptake, and microscopic inflammation that may be manifest in diseases associated with no overt inflammation of the mucosa, such as bile acid diarrhea, ileal diseases such as neuroendocrine tumors, ileal resection, and nonalcoholic steatohepatitis. Sulfation inactivates colonic secretion due to primary bile acids, but it may render secondary bile acids proinflammatory in the colon. Other evidence in preclinical models of inflammatory bowel disease (IBD) suggests reduced sulfation causes barrier dysfunction, inflammation, or carcinogenesis. These advances emphasize relevance and opportunities afforded by greater understanding of the chemistry and metabolism of bile acids, which stands to be further enhanced by research into the metabolic interactions of microbiota with bile acids.

Regulation of the HBV Entry Receptor NTCP and its Potential in Hepatitis B Treatment

Hepatitis B virus (HBV) is a globally prevalent human DNA virus responsible for more than 250 million cases of chronic liver infection, a condition that can lead to liver inflammation, cirrhosis, and hepatocellular carcinoma. Sodium taurocholate co-transporting polypeptide (NTCP), a transmembrane protein highly expressed in human hepatocytes and a mediator of bile acid transport, has been identified as the receptor responsible for the cellular entry of both HBV and its satellite, hepatitis delta virus (HDV). This has led to significant advances in our understanding of the HBV life cycle, especially the early steps of infection. HepG2-NTCP cells and human NTCP-expressing transgenic mice have been employed as the primary cell culture and animal models, respectively, for the study of HBV, and represent valuable approaches for investigating its basic biology and developing treatments for infection. However, the mechanisms involved in the regulation of NTCP transcription, translation, post-translational modification, and transport are still largely elusive. Improvements in our understanding of NTCP biology would likely facilitate the design of new therapeutic drugs for the prevention of the de novo infection of naïve hepatocytes. In this review, we provide critical findings regarding NTCP biology and discuss important questions that remain unanswered.

Molecular Regulation of Bile Acid Homeostasis

Bile acids have been known for decades to aid in the digestion and absorption of dietary fats and fat-soluble vitamins in the intestine. The development of gene knockout mice models and transgenic humanized mouse models have helped us understand other functions of bile acids, such as their role in modulating fat, glucose, and energy metabolism, and in the molecular regulation of the synthesis, transport, and homeostasis of bile acids. The G-protein coupled receptor TGR5 regulates the bile acid induced alterations of intermediary metabolism, whereas the nuclear receptor FXR regulates bile acid synthesis and homeostasis. However, this review indicates that unidentified factors in addition to FXR must exist to aid in the regulation of bile acid synthesis and homeostasis. SIGNIFICANCE STATEMENT: This review captures the present understanding of bile acid synthesis, the role of bile acid transporters in the enterohepatic circulation of bile acids, the role of the nuclear receptor FXR on the regulation of bile acid synthesis and bile acid transporters, and the importance of bile acids in activating GPCR signaling via TGR5 to modify intermediary metabolism. This information is useful for developing drugs for the treatment of various hepatic and intestinal diseases, as well as the metabolic syndrome.

Dihydroartemisinin improves hypercholesterolemia in ovariectomized mice via enhancing vectorial transport of cholesterol and bile acids from blood to bile

The increase of concentrations of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in the serum of postmenopausal women is the important risk factor of the high morbidity of cardiovascular diseases of old women worldwide. To test the anti-hypercholesterolemia function of dihydroartemisinin (DHA) in postmenopausal women, ovariectomized (OVX) mice were generated, and DHA were administrated to OVX mice for 4 weeks. The blood and liver tissues were collected for biochemical and histological tests respectively. The mRNA and protein expression levels of genes related to metabolism and transport of cholesterol, bile acid and fatty acid in the liver or ileum were checked through qPCR and western blot. DHA could significantly reduce the high concentrations of TC and LDL-C in the serum and the lipid accumulation in the liver of ovariectomized mice. The expression of ABCG5/8 was reduced in liver of OVX mice, and DHA could up-regulate the expression of them. Genes of transport proteins for bile salt transport from blood to bile, including Slc10a1, Slco1b2 and Abcb11, were also significantly up-regulated by DHA. DHA also down-regulated the expression of Slc10a2 in the ileum of OVX mice to reduce the absorption of bile salts. Genes required for fatty acid synthesis and uptake, such as Fasn and CD36, were reduced in the liver of OVX mice, and DHA administration could significantly up-regulate the expression of them. These results demonstrated that DHA could improve hypercholesterolemia in OVX mice through enhancing the vectorial transport of cholesterol and bile acid from blood to bile.

NTCP Deficiency Affects the Levels of Circulating Bile Acids and Induces Osteoporosis

BACKGROUND

The p.Ser267Phe mutation in the SLC10A1 gene can cause NTCP deficiency. However, the full clinical presentation of p.Ser267Phe homozygous individuals and its long-term consequences remain unclear. Hence, in the present study, we characterized the phenotypic characteristics of NTCP deficiency and evaluated its long-term prognosis.

METHODS

Ten NTCP p.Ser267Phe homozygous individuals were recruited and a comprehensive medical evaluation with a 5-year follow-up observation was performed. The phenotypic characteristics of NTCP deficiency were also demonstrated using an NTCP-global knockout mouse model.

RESULTS

During the 5-year follow-up observation of 10 NTCP p.Ser267Phe homozygous adults, we found that the most common phenotypic features of NTCP deficiency in adults were hypercholanemia, vitamin D deficiency, bone loss, and gallbladder abnormalities. The profile of bile acids (BAs) in the serum was significantly altered in these individuals and marked by both elevated proportion and concentration of primary and conjugated BAs. Moreover, the NTCP deficiency led to increased levels of serum BAs, decreased levels of vitamin D, and aggravated the osteoporotic phenotype induced by estrogen withdrawal in mice.

CONCLUSIONS

Both mice and humans with NTCP deficiency presented hypercholanemia and were more prone to vitamin D deficiency and aggravated osteoporotic phenotype. Therefore, we recommend monitoring the levels of BAs and vitamin D, bone density, and abdominal ultrasounds in individuals with NTCP deficiency.

Exposure to a mixture of legacy, alternative, and replacement per- and polyfluoroalkyl substances (PFAS) results in sex-dependent modulation of cholesterol metabolism and liver injury

BACKGROUND

Epidemiological studies have shown Per- and polyfluoroalkyl substances (PFAS) to be associated with diseases of dysregulated lipid and sterol homeostasis such as steatosis and cardiometabolic disorders. However, the majority of mechanistic studies rely on single chemical exposures instead of identifying mechanisms related to the toxicity of PFAS mixtures.

OBJECTIVES

The goal of the current study is to investigate mechanisms linking exposure to a PFAS mixture with alterations in lipid metabolism, including increased circulating cholesterol and bile acids.

METHODS

Male and female wild-type C57BL/6J mice were fed an atherogenic diet used in previous studies of pollutant-accelerated atherosclerosis and exposed to water containing a mixture of 5 PFAS representing legacy, replacement, and alternative subtypes (i.e., PFOA, PFOS, PFNA, PFHxS, and GenX), each at a concentration of 2 mg/L, for 12 weeks. Changes at the transcriptome and metabolome level were determined by RNA-seq and high-resolution mass spectrometry, respectively.

RESULTS

We observed increased circulating cholesterol, sterol metabolites, and bile acids due to PFAS exposure, with some sexual dimorphic effects. PFAS exposure increased hepatic injury, demonstrated by increased liver weight, hepatic inflammation, and plasma alanine aminotransferase levels. Females displayed increased lobular and portal inflammation compared to the male PFAS-exposed mice. Hepatic transcriptomics analysis revealed PFAS exposure modulated multiple metabolic pathways, including those related to sterols, bile acids, and acyl carnitines, with multiple sex-specific differences observed. Finally, we show that hepatic and circulating levels of PFOA were increased in exposed females compared to males, but this sexual dimorphism was not the same for other PFAS examined.

DISCUSSION

Exposure of mice to a mixture of PFAS results in PFAS-mediated modulation of cholesterol levels, possibly through disruption of enterohepatic circulation.

Functional characterization of Clonorchis sinensis sodium-bile acid co-transporter (CsSBAT) as a steroid sulfate transporter

Clonorchis sinensis (Cs) is a common trematode in Asian countries. Infection by Cs can result in many clinical symptoms. Here, a cDNA encoding a Cs apical sodium-dependent bile acid transporter (CsSBAT) was isolated from a Cs cDNA library, and functional characterization was performed using Xenopus laevis oocyte expression system. When expressed in Xenopus laevis oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate and dehydroepiandrosterone sulfate. No trans-uptake of carnitine, estradiol 17 β-D glucuronide, prostaglandin E₂, p-aminohippuric acid, α-ketoglutaric acid, and tetraethylammonium was observed. CsSBAT-mediated estrone sulfate uptake was in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04 μM for [³H]estrone sulfate. CsSBAT-mediated estrone sulfate uptake was strongly inhibited by sulfate conjugates but not glucuronide conjugates. These findings contribute to our understanding of CsSBAT transport properties and the cascade of estrogen metabolite movement in Cs.

Na+-Taurocholate Co-Transporting Polypeptide (NTCP) in Livers, Function, Expression Regulation, and Potential in Hepatitis B Treatment

Chronic hepatitis B virus (HBV) infection has become one of the leading causes of liver cirrhosis and hepatocellular carcinoma globally. The discovery of sodium taurocholate co-transporting polypeptide (NTCP), a solute carrier, as a key receptor for HBV and hepatitis D virus (HDV) has opened new avenues for HBV treatment. Additionally, it has led researchers to generate hepatoma cell lines (including HepG2-NTCP and Huh-7-NTCP) susceptible to HBV infection in vitro, hence, paving the way to develop and efficiently screen new and novel anti-HBV drugs. This review summarizes the history, function and critical findings regarding NTCP as a viral receptor for HBV/HDV, and it also discusses recently developed drugs targeting NTCP.

Bioactivity of Dietary Polyphenols: The Role in LDL-C Lowering

Cardiovascular diseases are the leading causes of the death around the world. An elevation of the low-density lipoprotein cholesterol (LDL-C) level is one of the most important risk factors for cardiovascular diseases. To achieve optimal plasma LDL-C levels, clinal therapies were investigated which targeted different metabolism pathways. However, some therapies also caused various adverse effects. Thus, there is a need for new treatment options and/or combination therapies to inhibit the LDL-C level. Dietary polyphenols have received much attention in the prevention of cardiovascular diseases due to their potential LDL-C lowering effects. However, the effectiveness and potential mechanisms of polyphenols in lowering LDL-C is not comprehensively summarized. This review focused on dietary polyphenols that could reduce LDL-C and their mechanisms of action. This review also discussed the limitations and suggestions regarding previous studies.

Review article: therapeutic aspects of bile acid signalling in the gut-liver axis

BACKGROUND

Bile acids are important endocrine modulators of intestinal and hepatic signalling cascades orchestrating critical pathophysiological processes in various liver diseases. Increasing knowledge on bile acid signalling has stimulated the development of synthetic ligands of nuclear bile acid receptors and other bile acid analogues.

AIM

This review summarises important aspects of bile acid-mediated crosstalk between the gut and the liver ("gut-liver axis") as well as recent findings from experimental and clinical studies.

METHODS

We performed a literature review on bile acid signalling, and therapeutic applications in chronic liver disease.

RESULTS

Intestinal and hepatic bile acid signalling pathways maintain bile acid homeostasis. Perturbations of bile acid-mediated gut-liver crosstalk dysregulate transcriptional networks involved in inflammation, fibrosis and endothelial dysfunction. Bile acids induce enterohepatic feedback signalling by the release of intestinal hormones, and regulate enterohepatic circulation. Importantly, bile acid signalling plays a central role in maintaining intestinal barrier integrity and antibacterial defense, which is particularly relevant in cirrhosis, where bacterial translocation has a profound impact on disease progression. The nuclear bile acid farnesoid X receptor (FXR) is a central intersection in bile acid signalling and has emerged as a relevant therapeutic target.

CONCLUSIONS

Experimental evidence suggests that bile acid signalling improves the intestinal barrier and protects against bacterial translocation in cirrhosis. FXR agonists have displayed efficacy for the treatment of cholestatic and metabolic liver disease in randomised controlled clinical trials. However, similar effects remain to be shown in advanced liver disease, particularly in patients with decompensated cirrhosis.