Bile acid transporters and regulatory nuclear receptors in the liver and beyond

Compensatory Transition of Bile Acid Metabolism from Fecal Disposition of Secondary Bile Acids to Urinary Excretion of Primary Bile Acids Underlies Rifampicin-Induced Cholestasis in Beagle Dogs

Drug induced cholestasis (DIC) is complexly associated with dysbiosis of the host-gut microbial cometabolism of bile acids (BAs). Murine animals are not suitable for transitional studies because the murine BA metabolism is quite different from human metabolism. In this work, the rifampicin (RFP) induced cholestasis was established in beagle dogs that have a humanlike BA profile to disclose how RFP affects the host-gut microbial cometabolism of BAs. The daily excretion of BA metabolites in urine and feces was extensively analyzed during cholestasis by quantitative BA profiling along the primary-secondary-tertiary axis. Oral midazolam clearance was also acquired to monitor the RFP-induced enterohepatic CYP3A activities because CYP3A is exclusively responsible for the tertiary oxidation of hydrophobic secondary BAs. RFP treatments caused a compensatory transition of the BA metabolism from the fecal disposition of secondary BAs to the urinary excretion of primary BAs in dogs, resulting in an infantile BA metabolism pattern recently disclosed in newborns. However, the tertiary BAs consistently constituted limitedly in the daily BA excretion, indicating that the detoxification role of the CYP3A catalyzed tertiary BA metabolism was not as strong as expected in this model. Multiple host-gut microbial factors might have contributed to the transition of the BA metabolism, such as inhibition of BA transporters, induction of liver-kidney interplaying detoxification mechanisms, and elimination of gut bacteria responsible for secondary BA production. Transitional studies involving more cholestatic drugs in preclinical animals with a humanlike BA profile and DIC patients may pave the way for understanding the complex mechanism of DIC in the era of metagenomics.

The function of zebrafish gpbar1 in antiviral response and lipid metabolism

G protein-coupled bile acids receptor 1 (GPBAR1 or TGR5) has been widely studied as a metabolic regulator involved in bile acids synthesis, glucose metabolism and energy homeostasis. Several recent studies have shown that mammalian GPBAR1 is also involved in antiviral innate immune responses. However, the functions of piscine GPBAR1 in antibacterial or antiviral immune responses and lipid metabolism remain unclear. In the present study, we report the functional characterization of zebrafish gpbar1. Similar to mammalian GPBAR1, zebrafish gpbar1 contains similar domain composition, shows a dose-dependent activation by bile acids including INT777, LCA, DCA, CDCA and CA, and can be induced by viral infection. Compared with corresponding control groups, a significant antiviral activity against spring viremia of carp virus (SVCV) infection was observed in ZF4 cells overexpressing zebrafish gpbar1 with INT777 treatment, but not in ZF4 cells overexpressing zebrafish gpbar1 without INT777 treatment. The activation of zebrafish gpbar1 had no significant antibacterial effect against Edwardsiella piscicida infection in ZF4 cells in vitro. Transcriptome analysis revealed that zebrafish gpbar1 activation played a crucial role in activating RLR signaling pathway and inducing the production of ISGs, but not for bile acid biosynthesis and transportation. The co-occurrence analysis for antiviral-related and bile acids metabolism-related DEGs suggested a strong interaction among 2 bile acid receptors (gpbar1 and nr1h4), slco2b1 and the antiviral DEGs. The lipidomic analysis showed that zebrafish gpbar1 activation in ZF4 cells resulted a change of glycerophospholipids, but none of bile acids nor their derivatives, which were different from mammalian GPBAR1. All together, these results firstly demonstrate the conserved antiviral role of gpbar1 and its function in regulating glycerophospholipids metabolism in teleost.

Ursodeoxycholic acid improves pregnancy outcome in patients with intrahepatic cholestasis during pregnancy: A protocol for systematic review and meta-analysis

BACKGROUND

Intrahepatic cholestasis of pregnancy (ICP) is a common complication in the third trimester of pregnancy, which may result in premature delivery, fetal distress, stillbirth, and other adverse pregnancy outcomes. Ursodeoxycholic acid (UDCA) is a first-line treatment for ICP and has been controversial in improving adverse pregnancy outcomes. The purpose of this protocol is to systematically evaluate the effect of UDCA on pregnancy outcomes in patients with intrahepatic cholestasis during pregnancy.

METHODS

To search the databases PubMed, Embase, Web of Science, the Cochrane Library, CNKI, WanFang, VIP, CBMDIsc by computer, then to include randomized controlled clinical studies on UDCA for treatment of intrahepatic cholestasis during pregnancy from the establishment of the database to October 1, 2020. Two researchers independently extract and evaluate the data of the included studies, and meta-analysis is conducted on the included literatures using RevMan5.3 software.

RESULTS

This protocol evaluates the outcome of UDCA in improving ICP by incidence of postpartum hemorrhage in pregnant women preterm birth rates meconium contamination rate in amniotic fluid incidence of fetal distress scale of newborns scoring <7 in 5-min Apgar incidence of neonatal admission to neonatal intensive care unit.

CONCLUSION

This protocol will provide an evidence-based basis for clinical use of UDCA in the treatment of intrahepatic cholestasis during pregnancy.

ETHICS AND DISSEMINATION

Private information from individuals will not be published. This systematic review also does not involve endangering participant rights. Ethical approval was not required. The results may be published in a peer-reviewed journal or disseminated at relevant conferences.

OSF REGISTRATION NUMBER

DOI 10.17605 / OSF.IO / BE67H.

Chronic Alcohol Consumption Increased Bile Acid Levels in Enterohepatic Circulation and Reduced Efficacy of Irinotecan

AIMS

To investigate the effect of ethanol intake on the whole enterohepatic circulation (EHC) of bile acids (BAs) and, more importantly, on pharmacokinetics of irinotecan.

METHODS

The present study utilized a mouse model administered by gavage with 0 (control), 240 mg/100 g (30%, v/v) and 390 mg/100 g (50%, v/v) ethanol for 6 weeks, followed by BA profiles in the whole EHC (including liver, gallbladder, intestine and plasma) and colon using ultra-high performance liquid chromatography with tandem mass spectrometry analysis. Pharmacokinetic parameters of irinotecan were measured after administration of irinotecan (i.v. 5 mg/kg) on alcohol-treated mice.

RESULTS

The results showed that compared with the control group, concentrations of most free-BAs, total amount of the three main forms of BAs (free-BA, taurine-BA and glycine-BA) and total BAs (TBAs) in 50% ethanol intake group were significantly increased, which are mostly attributed to the augmentation of free-BAs and taurine-BAs. Additionally, the TBAs in liver and gallbladder and the BA pool were markedly increased in the 30% ethanol intake group. Importantly, ethanol intake upregulated the expression of BA-related enzymes (Cyp7a1, Cyp27a1, Cyp8b1 and Baat) and transporters (Bsep, Mrp2, P-gp and Asbt) and downregulated the expression of transporter Ntcp and nuclear receptor Fxr in the liver and ileum, respectively. Additionally, 50% ethanol intake caused fairly distinct liver injury. Furthermore, the AUC0-24 h of irinotecan and SN38 were significantly reduced but their clearance was significantly increased in the disrupted EHC of BA by 50% ethanol intake.

CONCLUSIONS

The present study demonstrated that ethanol intake altered the expression of BA-related synthetases and transporters. The BA levels, especially the toxic BAs (chenodeoxycholic acid, deoxycholic acid and lithocholic acid), in the whole EHC were significantly increased by ethanol intake, which may provide a potential explanation to illuminate the pathogenesis of alcoholic liver injury. Most importantly, chronic ethanol consumption had a significant impact on the pharmacokinetics (AUC0-24 h and clearance) of irinotecan and SN38; hence colon cancer patients with chronic alcohol consumption treated with irinotecan deserve our close attention.

Pharmacophore modeling and virtual screening studies for discovery of novel farnesoid X receptor (FXR) agonists

Farnesoid X receptor (FXR) agonists would be considered as an important therapeutic strategy for several chronic liver and metabolic diseases. Here we have employed an integrated virtual screening by combining ligand-based pharmacophore mapping and molecular docking to identify novel nonsteroidal FXR agonists. Eighteen compounds were selected for in vitro FXR agonistic activity assay, and results showed five compounds exhibiting promising FXR agonistic activity. Among these compounds, compounds F4 and F17 were the most remarkable in vitro activity by using homogeneous time resolved fluorescence (HTRF) assay and the full-length FXR reporter gene assay in HepG2 cells. Real-time PCR assay was performed to measure the expression of FXR target genes. Compounds F4 and F17 increased small heterodimer partner (SHP), in turn, suppress mRNA levels of cholesterol 7-alpha-hydroxylase (CYP7A1). The obtained compounds F4 and F17 from this study may be potential leads for developing novel FXR agonists in the treatment of metabolic diseases.

SEW2871 attenuates ANIT-induced hepatotoxicity by protecting liver barrier function via sphingosine 1-phosphate receptor-1-mediated AMPK signaling pathway

Cholestatic liver injury, a group of diseases characterized with dysregulated bile acid (BA) homeostasis, was partly resulted from BA circulation disorders, which is commonly associated with the damage of hepatocyte barrier function. However, the underlying hepatocyte barrier-protective molecular mechanisms of cholestatic liver injury remain poorly understood. Interestingly, recent studies have shown that sphingosine-1-phosphate (S1P) participated in the process of cholestasis by activating its G protein-coupled receptors S1PRs, regaining the integrity of hepatocyte tight junctions (TJs). Here, we showed that SEW2871, a selective agonist of sphingosine-1-phosphate receptor 1(S1PR1), alleviated ANIT-induced TJs damage in 3D-cultured mice primary hepatocytes. Molecular mechanism studies indicated that AMPK signaling pathways was involved in TJs protection of SEW2871 in ANIT-induced hepatobiliary barrier function deficiency. AMPK antagonist compound C (CC) and agonist AICAR were all used to further identify the important role of AMPK signaling pathway in SEW2871's TJs protection of ANIT-treated mice primary hepatocytes. The in vivo data showed that SEW2871 ameliorated ANIT-induced cholestatic hepatotoxicity. Further protection mechanism research demonstrated that SEW2871 not only regained hepatocyte TJs by the upregulated S1PR1 via AMPK signaling pathway, but also recovered hepatobiliary barrier function deficiency, which was verified by the restored BA homeostasis by using of high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). These results revealed that the increased expression of S1PR1 induced by SEW2871 could ameliorate ANIT-induced cholestatic liver injury through improving liver barrier function via AMPK signaling and subsequently reversed the disrupted BA homeostasis. Our study provided strong evidence that S1PR1 may be a promising therapeutic approach for treating intrahepatic cholestatic liver injury. Graphical abstract.

Scientific Evidence for the Treatment of Children with Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastro-intestinal disorders which significantly impacts the quality of life of affected children. Abdominal pain improved by defecation, associated with a change in stool form and frequency, represents its specific clinical marker. Even if a number of potential patho-physiological mechanisms have been described, the exact underlying etiology of IBS is so far unclear. Likewise, no optimal treatment has ever been found neither for adult nor for pediatric patients. Current therapeutic options include drugs, dietary interventions and biopsychosocial therapies. The present review aims at evaluating the scientific evidence supporting the efficacy of these treatments for children with IBS.

Physiologically inspired culture medium prolongs the lifetime and insulin sensitivity of human hepatocytes in micropatterned co-cultures

Given significant species-specific differences in liver functions, cultures of primary human hepatocytes (PHHs) are useful for assessing drug metabolism and to mitigate the risk of drug-induced hepatotoxicity in humans. While significant advances have been made to keep PHHs highly functional for 2-4 weeks in vitro, especially upon co-culture with both liver- and non-liver-derived non-parenchymal cells (NPCs), the functional lifespan of PHHs is 200-400 days in vivo. Therefore, it is desirable to determine culture conditions that can further prolong PHHs functions in vitro for modeling chronic drug exposure, disease pathogenesis, and to provide flexibility to the end-user for staggering drug incubations across multiple culture batches. Most PHH culture platforms utilize supraphysiologic levels of glucose and insulin and bovine-derived serum when including NPCs, which can alter PHH functions. Therefore, here we developed a culture medium containing physiologic levels of glucose (5 mM), insulin (500 pM), and human serum (10 % v/v) and tested its effects on micropatterned co-cultures (MPCCs) in which PHHs are organized onto collagen domains of empirically optimized dimensions and surrounded by 3T3-J2 murine fibroblasts that express liver-like molecules and induce higher PHH functions than liver-derived NPCs. Our physiologically-inspired culture medium allowed better retention of PHH morphology, polarity, and functions (albumin and urea, cytochrome-P450 activities, and sensitivity to insulin-mediated inhibition of gluconeogenesis) for up to 10 weeks relative to the traditional medium. Finally, PHHs in the physiologic medium displayed clinically-relevant responses to prototypical drugs for hepatoxicity and cytochrome-P450 induction. Ultimately, our physiologic culture medium could find broader utility for the continued development of PHH-NPC co-cultures for drug development, investigating the effects of patient-derived sera on PHH functions and disease phenotypes, and for use in cell-based therapies.

The role of serum bile acid profile in differentiation between nonalcoholic fatty liver disease and chronic viral hepatitis

Background

Bile acids are essential organic molecules synthesized from cholesterol in the liver. They have been utilized as indicators of hepatobiliary impairment because synthesis of BAs and their metabolism are influenced by liver diseases. We aimed to investigate the role of serum bile acid level and composition in differentiation between nonalcoholic fatty liver disease (NAFLD) and chronic viral hepatitis. An ultra-performance liquid chromatography coupled with mass spectrometry assay was used to measure the serum level of 14 bile acids in chronic viral hepatitis and NAFLD patients beside normal healthy control subjects.

Results

The mean serum levels of 11 out of the 14 bile acids (two primary, six conjugated, and three secondary) were significantly higher in viral hepatitis compared to control. Only 4 bile acids [2 primary, one glycine conjugated (GCDCA), and one secondary (LCA)] had statistically significant increase in their mean serum bile acid level in NAFLD compared to control. Comparing viral hepatitis group against NAFLD group revealed that the mean serum levels of five conjugated and one secondary bile acid (DCA) were significantly higher in viral hepatitis group. Receiver operating characteristic (ROC) curve analysis revealed that LCA had the best diagnostic performance for viral hepatitis followed by TCA and GCDCA. ROC curve for the combined three parameters had better sensitivity and specificity (70.55% and 94.87% respectively).

Conclusion

BA compositions including primary, secondary, and conjugated ones could differentiate between chronic viral hepatitis and NAFLD patients, and they might be potential distinguishing biomarkers for this purpose.

Gut Microbiota, Peroxisome Proliferator-Activated Receptors, and Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. HCC incidence rate is sixth and mortality is fourth worldwide. However, HCC pathogenesis and molecular mechanisms remain unclear. The incidence of HCC is associated with genetic, environmental, and metabolic factors. The role of gut microbiota in the pathogenesis of HCC has attracted researchers' attention because of anatomical and functional interactions between liver and intestine. Studies have demonstrated the involvement of gut microbiota in the development of HCC and chronic liver diseases, such as alcoholic liver disease (ALD), nonalcoholic fatty liver disease (NAFLD), and liver cirrhosis. Peroxisome proliferator-activated receptors (PPARs) are a group of receptors with diverse biological functions. Natural and synthetic PPAR agonists show potential for treatment of NAFLD, liver fibrosis, and HCC. Recent studies have demonstrated that PPARs take part in gut microbiota inhabitation and adaptation. This manuscript reviews the role of gut microbiota in the development of HCC and precancerous diseases, the role of PPARs in modulation of gut microbiota and HCC, and potential of gut microbiota for HCC diagnosis and treatment.

Inulin Supplementation Disturbs Hepatic Cholesterol and Bile Acid Metabolism Independent from Housing Temperature

Dietary fibers are fermented by gut bacteria into the major short chain fatty acids (SCFAs) acetate, propionate, and butyrate. Generally, fiber-rich diets are believed to improve metabolic health. However, recent studies suggest that long-term supplementation with fibers causes changes in hepatic bile acid metabolism, hepatocyte damage, and hepatocellular cancer in dysbiotic mice. Alterations in hepatic bile acid metabolism have also been reported after cold-induced activation of brown adipose tissue. Here, we aim to investigate the effects of short-term dietary inulin supplementation on liver cholesterol and bile acid metabolism in control and cold housed specific pathogen free wild type (WT) mice. We found that short-term inulin feeding lowered plasma cholesterol levels and provoked cholestasis and mild liver damage in WT mice. Of note, inulin feeding caused marked perturbations in bile acid metabolism, which were aggravated by cold treatment. Our studies indicate that even relatively short periods of inulin consumption in mice with an intact gut microbiome have detrimental effects on liver metabolism and function.

Metabolomics research on the hepatoprotective effect of cultured bear bile powder in α-naphthylisothiocyanate-induced cholestatic mice

Natural bear bile powder (NBBP) is a famous traditional medicine and has been widely used in clinic. However, access to the sources of bear bile is restricted; hence, it is essential to discover new substitutes for NBBP. Cultured bear bile powder (CBBP) is transformed from chicken bile and contains main ingredients as to NBBP. In the present study, the effect and potential mechanism of action of CBBP on cholestatic liver injury in-naphthylisothiocyanate (ANIT)-induced mouse model was explored using metabolomics. CBBP treatment ameliorated impaired hepatic dysfunction and tissue damage that induced by ANIT. Metabolomics showed there were 28 different metabolites induced by ANIT as compared with control mice, and 18 of which was reversed by CBBP. Pathway analysis revealed that those 18 metabolites are mainly involved in bile acid (BA) biosynthesis and D-glutamine and D-glutamate metabolism. Further LC-MS/MS analysis showed that CBBP and NBBP both reduced serum and liver levels of BAs, but increased their biliary levels. Additionally, CBBP and NBBP upregulated expression of BA efflux transporters, Mrp2, Mrp3, and Mrp4, and metabolic enzymes, Cyp2b10 and Ugt1a1 of liver tissue of cholestatic mice, increased the BA excretion and metabolism. Moreover, CBBP and NBBP treatment upregulated GCLc/GCLm expression, and restored glutathione metabolism. In conclusion, the protective effects of CBBP against cholestatic liver injury were similar to those of NBBP. Mechanistically, both CBBP and NBBP reversed the disruption in homeostasis of BAs and glutathione, alleviating damage to hepatocytes.

Open-label phase II study evaluating safety and efficacy of the non-steroidal farnesoid X receptor agonist PX-104 in non-alcoholic fatty liver disease

Background

The PX-104 is an oral non-steroidal agonist for the farnesoid X receptor (FXR), a key regulator of bile acid (BA), glucose and lipid homeostasis.

Aims and methods

This single center, proof of concept study evaluated the efficacy, safety and tolerability of PX-104 in non-diabetic NAFLD patients. 12 individuals were treated daily with 5 mg of PX-104 orally for 4 weeks. Serum liver enzymes, insulin sensitivity by clamp like index (CLIX) and hepatic fat by proton ¹H‑MRS, MRI-PDFF and CAP were assessed. Hepatic energy metabolism and Kupffer cell function were evaluated by phosphorus ³¹P‑MRS and superparamagnetic iron oxide MRI (SPIO-MRI). Other readouts included serum lipids and markers of BA metabolism/signaling besides fecal microbiome and BA analysis.

Results

A significant decrease in ALT (p = 0.027; 1‑tailed) and GGT (p = 0.019) was observed, without changes in serum alkaline phosphatase or serum lipids. Insulin sensitivity improved in 92% of patients (p = 0.02). However, hepatic steatosis measured by PDFF-MRI, ¹H‑MRS and CAP besides extended serum lipoprotein and BA profiles did not change. NADPH/γATP ratios at ³¹P‑MRS significantly decreased (p = 0.022) possibly reflecting reduced hepatic inflammatory stress, but SPIO-MRI remained unchanged. Reduced preponderance of Coriobacteriaceae (p = 0.036) correlated with a relative reduction of total fecal BAs. There were no serious adverse events but short intervals of cardiac arrhythmia recorded in 2 patients led to termination of the study.

Conclusion

The non-steroidal FXR agonist PX-104 improved insulin sensitivity and liver enzymes after 4 weeks of treatment in non-diabetic NAFLD patients. Changes in fecal BAs and gut microbiota deserve more extensive investigations.

Electronic supplementary material

The online version of this article (10.1007/s00508-020-01735-5) contains supplementary material, which is available to authorized users.

The inhibition of hepatic Pxr-Oatp2 pathway mediating decreased hepatic uptake of rosuvastatin in rats with high-fat diet-induced obesity

PURPOSE

Obesity affecting drug pharmacokinetics results in the risk of the therapeutic failure or toxic side effects of drugs increasing. Unfortunately, the pharmacokinetic data in obese patients still lack for majority of drugs. Therefore, our study principally investigated the effect of obesity induced by high fat-diet (HFD) on the pharmacokinetics of rosuvastatin and explored the underlying mechanism via the hepatic pregnane X receptor (Pxr)- organic anion transporting polypeptide 2 (Oatp2) signaling pathway and multidrug resistance-associated protein 2 (Mrp2) in rats.

MAIN METHODS

Rats with obesity was induced by HFD for 4 weeks, and subsequently, the effect of obesity on the blood concentration, pharmacokinetic parameters and biliary excretion of rosuvastatin administrated intravenously and the hepatic uptake of rosuvastatin in the rat primary hepatocytes were evaluated. Additionally, in order to illuminate the underlying mechanism, the alterations of the mRNA expressions of Oatp2, Mrp2 and Pxr and the concentrations of lithocholic acid (LCA), glycine-LCA (GLCA) and taurine-LCA (TLCA) in liver were determined.

KEY FINDINGS

The blood concentration of rosuvastatin that has great relationship with the muscle toxicity increased in rats with HFD-induced obesity, which could be principally ascribed to the decreased hepatic uptake of rosuvastatin that was mainly resulted from the inhibition of hepatic Pxr-Oatp2 pathway.

SIGNIFICANCE

The decreased hepatic uptake of rosuvastatin causing the increase of the rosuvastatin concentration in blood under the condition of HFD-induced obesity provides a cue for clinicians to reduce the rosuvastatin dose for obese patients to avoid the occurrence risk of the muscle toxicity of rosuvastatin.

Inflammation Drives MicroRNAs to Limit Hepatocyte Bile Acid Transport in Murine Biliary Atresia

BACKGROUND

Biliary atresia (BA) is an inflammatory pediatric cholangiopathy with only surgical means for treatment. Many contributors to bile acid synthesis and transport have previously been reported to be downregulated in patients with BA; yet, the driving factors of the abnormal bile acid synthesis and transport in regard to BA have not been previously studied.

MATERIALS AND METHODS

Wild type or Ig-α^-/- mice were injected with salt solution (control) or rotavirus on day of life 0, and analyses were performed on day of life 14. The mRNA levels of bile acid transporters/nuclear receptors and liver microRNAs (miRNAs) were compared between groups. A mouse hepatocyte cell line was used to examine the effects of innate cytokines on miRNA levels and bile acid transporter/nuclear receptor expression and miRNAs on bile acid transporter/nuclear receptor expression.

RESULTS

BA mice had significantly increased mRNA expression of innate cytokines and miRNAs known to bind bile acid transporters/nuclear receptors (miRNAs -22-5p, -34a-5p, and -222-3p) and decreased mRNA expression of bile acid transporters and nuclear receptors. In vitro, TNF-α and IL-1β decreased BSEP and CYP7A1 while increasing miRNA-34a-5p and miRNA 222-3p. LXR, SHP, CYP7A1, NTCP, and MRP2 were decreased by miRNA-34a-5p, whereas miRNA-222-3p decreased NTCP and MRP4. TNF-α and IL-1β increased expression of miRNAs 34a-5p and 222-3p and these miRNAs then decrease expression of multiple bile acid transporters and nuclear receptors.

CONCLUSIONS

Loss of bile acid transporters increases hepatotoxicity via bile acid retention. Therapeutic agents that increase bile acid transport or nuclear receptor functioning should be investigated in BA.

Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging

Over the past two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

Urinary Bile Acid Profile of Newborns Born by Cesarean Section Is Characterized by Oxidative Metabolism of Primary Bile Acids: Limited Roles of Fetal-Specific CYP3A7 in Cholate Oxidations

This work aims to investigate how the bile acid metabolism of newborns differs from that of adults along the axis of primary, secondary, and tertiary bile acids (BAs). The total unconjugated BA profiles were quantitatively determined by enzyme digestion techniques in urine of 21 newborns born by cesarean section, 29 healthy parturient women, 30 healthy males, and 28 healthy nonpregnant females. As expected, because of a lack of developed gut microbiota, newborns exhibited poor metabolism of secondary BAs. Accordingly, the tertiary BAs contributed limitedly to the urinary excretion of BAs in newborns despite their tertiary-to-secondary ratios significantly increasing. As a result, the primary BAs of newborns underwent extensive oxidative metabolism, resulting in elevated urinary levels of some fetal-specific BAs, including 3-dehydroCA, 3β,7α,12α-trihydroxy-5β-cholan-24-oic acid, 3α,12-oxo-hydroxy-5β-cholan-24-oic acid, and nine tetrahydroxy-cholan-24-oic acids (Tetra-BAs). Parturient women had significantly elevated urinary levels of tertiary BAs and fetal-specific BAs compared with female control, indicating that they may be excreted into amniotic fluid for maternal disposition. An in vitro metabolism assay in infant liver microsomes showed that four Tetra-BAs and 3-dehydroCA were hydroxylated metabolites of cholate, glycocholate, and particularly taurocholate. However, the recombinant cytochrome P450 enzyme assay found that the fetal-specific CYP3A7 did not contribute to these oxidation metabolisms as much as expected compared with CYP3A4. In conclusion, newborns show a BA metabolism pattern predominated by primary BA oxidations due to immaturity of secondary BA metabolism. Translational studies following this finding may bring new ideas and strategies for both pediatric pharmacology and diagnosis and treatment of perinatal cholestasis-associated diseases. SIGNIFICANCE STATEMENT: The prenatal BA disposition is different from adults because of a lack of gut microbiota. However, how the BA metabolism of newborns differs from that of adults along the axis of primary, secondary, and tertiary BAs remains poorly defined. This work demonstrated that the urinary BA profiles of newborns born by cesarean section are characterized by oxidative metabolism of primary BAs, in which the fetal-specific CYP3A7 plays a limited role in the downstream oxidation metabolism of cholate.

Volixibat in adults with non-alcoholic steatohepatitis: 24-week interim analysis from a randomized, phase II study

BACKGROUND & AIMS

Volixibat is an inhibitor of the apical sodium-dependent bile acid transporter (ASBT) that has been hypothesized to improve non-alcoholic steatohepatitis (NASH) by blocking bile acid reuptake and stimulating hepatic bile acid production. We studied the safety, tolerability and efficacy of volixibat in patients with NASH.

METHODS

In this double-blind, phase II dose-finding study, adults with ≥5% steatosis and NASH without cirrhosis (N = 197) were randomized to receive volixibat (5, 10 or 20 mg) or placebo once daily for 48 weeks. The endpoints of a predefined interim analysis (n = 80), at week 24, were: ≥5% reduction in MRI-proton density fat fraction and ≥20% reduction in serum alanine aminotransferase levels. The primary endpoint was a ≥2-point reduction in non-alcoholic fatty liver disease activity score without worsening fibrosis at week 48.

RESULTS

Volixibat did not meet either interim endpoint; the study was terminated owing to lack of efficacy. In participants receiving any volixibat dose, mean serum 7-alpha-hydroxy-4-cholesten-3-one (C4; a biomarker of bile acid synthesis) increased from baseline to week 24 (+38.5 ng/ml [SD 53.18]), with concomitant decreases in serum total cholesterol (-14.5 mg/dl [SD 28.32]) and low-density lipoprotein cholesterol (-16.1 mg/dl [SD 25.31]). These changes were generally dose-dependent. On histological analysis, a greater proportion of participants receiving placebo (38.5%, n = 5/13) than volixibat (30.0%, n = 9/30) met the primary endpoint. Treatment-emergent adverse events (TEAEs) were mainly mild or moderate. No serious TEAEs were related to volixibat. Diarrhoea was the most common TEAE overall and the most common TEAE leading to discontinuation.

CONCLUSIONS

Increased serum C4 and decreased serum cholesterol levels provide evidence of target engagement. However, inhibition of ASBT by volixibat did not elicit a liver-related therapeutic benefit in adults with NASH.

LAY SUMMARY

A medicine called volixibat has previously been shown to reduce cholesterol levels in the blood. This study investigated whether volixibat could reduce the amount of fat in the liver and reduce liver injury in adults with an advanced form of non-alcoholic fatty liver disease. Volixibat did not reduce the amount of fat in the liver, nor did it have any other beneficial effect on liver injury. Participants in the study generally tolerated the side effects of volixibat and, as in previous studies, the main side effect was diarrhoea. These results show that volixibat is not an effective treatment for people with fatty liver disease.

CLINICAL TRIAL IDENTIFIER

NCT02787304.

Maternal glucose homeostasis is impaired in mouse models of gestational cholestasis

Women with intrahepatic cholestasis of pregnancy (ICP), a disorder characterised by raised serum bile acids, are at increased risk of developing gestational diabetes mellitus and have impaired glucose tolerance whilst cholestatic. FXR and TGR5 are modulators of glucose metabolism, and FXR activity is reduced in normal pregnancy, and further in ICP. We aimed to investigate the role of raised serum bile acids, FXR and TGR5 in gestational glucose metabolism using mouse models. Cholic acid feeding resulted in reduced pancreatic β-cell proliferation and increased apoptosis in pregnancy, without altering insulin sensitivity, suggesting that raised bile acids affect β-cell mass but are insufficient to impair glucose tolerance. Conversely, pregnant Fxr-/- and Tgr5-/- mice are glucose intolerant and have reduced insulin secretion in response to glucose challenge, and Fxr-/- mice are also insulin resistant. Furthermore, fecal bile acids are reduced in pregnant Fxr-/- mice. Lithocholic acid and deoxycholic acid, the principal ligands for TGR5, are decreased in particular. Therefore, we propose that raised serum bile acids and reduced FXR and TGR5 activity contribute to the altered glucose metabolism observed in ICP.

Probiotic Lactobacillus rhamnosus GG Prevents Liver Fibrosis Through Inhibiting Hepatic Bile Acid Synthesis and Enhancing Bile Acid Excretion in Mice

BACKGROUND AND AIMS

Cholestatic liver disease is characterized by gut dysbiosis and excessive toxic hepatic bile acids (BAs). Modification of gut microbiota and repression of BA synthesis are potential strategies for the treatment of cholestatic liver disease. The purpose of this study was to examine the effects and to understand the mechanisms of the probiotic Lactobacillus rhamnosus GG (LGG) on hepatic BA synthesis, liver injury, and fibrosis in bile duct ligation (BDL) and multidrug resistance protein 2 knockout (Mdr2-/- ) mice.

APPROACH AND RESULTS

Global and intestine-specific farnesoid X receptor (FXR) inhibitors were used to dissect the role of FXR. LGG treatment significantly attenuated liver inflammation, injury, and fibrosis with a significant reduction of hepatic BAs in BDL mice. Hepatic concentration of taurine-β-muricholic acid (T-βMCA), an FXR antagonist, was markedly increased in BDL mice and reduced in LGG-treated mice, while chenodeoxycholic acid, an FXR agonist, was decreased in BDL mice and normalized in LGG-treated mice. LGG treatment significantly increased the expression of serum and ileum fibroblast growth factor 15 (FGF-15) and subsequently reduced hepatic cholesterol 7α-hydroxylase and BA synthesis in BDL and Mdr2-/- mice. At the molecular level, these changes were reversed by global and intestine-specific FXR inhibitors in BDL mice. In addition, LGG treatment altered gut microbiota, which was associated with increased BA deconjugation and increased fecal and urine BA excretion in both BDL and Mdr2-/- mice. In vitro studies showed that LGG suppressed the inhibitory effect of T-βMCA on FXR and FGF-19 expression in Caco-2 cells.

CONCLUSION

LGG supplementation decreases hepatic BA by increasing intestinal FXR-FGF-15 signaling pathway-mediated suppression of BA de novo synthesis and enhances BA excretion, which prevents excessive BA-induced liver injury and fibrosis in mice.

Species Differences of Bile Acid Redox Metabolism: Tertiary Oxidation of Deoxycholate is Conserved in Preclinical Animals

It was recently disclosed that CYP3A is responsible for the tertiary stereoselective oxidations of deoxycholic acid (DCA), which becomes a continuum mechanism of the host-gut microbial cometabolism of bile acids (BAs) in humans. This work aims to investigate the species differences of BA redox metabolism and clarify whether the tertiary metabolism of DCA is a conserved pathway in preclinical animals. With quantitative determination of the total unconjugated BAs in urine and fecal samples of humans, dogs, rats, and mice, it was confirmed that the tertiary oxidized metabolites of DCA were found in all tested animals, whereas DCA and its oxidized metabolites disappeared in germ-free mice. The in vitro metabolism data of DCA and the other unconjugated BAs in liver microsomes of humans, monkeys, dogs, rats, and mice showed consistencies with the BA-profiling data, confirming that the tertiary oxidation of DCA is a conserved pathway. In liver microsomes of all tested animals, however, the oxidation activities toward DCA were far below the murine-specific 6β-oxidation activities toward chenodeoxycholic acid (CDCA), ursodeoxycholic acid, and lithocholic acid (LCA), and 7-oxidation activities toward murideoxycholic acid and hyodeoxycholic acid came from the 6-hydroxylation of LCA. These findings provided further explanations for why murine animals have significantly enhanced downstream metabolism of CDCA compared with humans. In conclusion, the species differences of BA redox metabolism disclosed in this work will be useful for the interspecies extrapolation of BA biology and toxicology in translational researches. SIGNIFICANCE STATEMENT: It is important to understand the species differences of bile acid metabolism when deciphering biological and hepatotoxicology findings from preclinical studies. However, the species differences of tertiary bile acids are poorly understood compared with primary and secondary bile acids. This work confirms that the tertiary oxidation of deoxycholic acid is conserved among preclinical animals and provides deeper understanding of how and why the downstream metabolism of chenodeoxycholic acid dominates that of cholic acid in murine animals compared with humans.

A Gilbert syndrome-associated haplotype protects against fatty liver disease in humanized transgenic mice

UDP-glucuronosyltransferases 1 A (UGT1A) enzymes are capable of detoxifying a broad range of endo- and xenobiotic compounds, which contributes to antioxidative effects, modulation of inflammation and cytoprotection. In the presence of low-function genetic UGT1A variants fibrosis development is increased in various diseases. This study aimed to examine the role of common UGT1A polymorphisms in NASH. Therefore, htgUGT1A-WT mice and htgUGT1A-SNP mice (carrying a common human haplotype present in 10% of the white population) were fed a high-fat Paigen diet for 24 weeks. Serum aminotransferase activities, hepatic triglycerides, fibrosis development and UGT1A expression were assessed. Microscopic examination revealed higher hepatic fat deposition and a significant induction of UGT1A gene expression in htgUGT1A-WT mice. In agreement with these observations, lower serum aminotransferase activities and lower expression levels of fibrosis-related genes were measured in htgUGT1A-SNP mice. This was accompanied by reduced PPARα protein levels in htgUGT1A-WT but not in SNP mice. Our data demonstrate a protective effect of a UGT1A SNP haplotype, leading to milder hepatic steatosis and NASH. Higher PPARα protein levels in animals with impaired UGT1A activity are the likely result of reduced glucuronidation of ligands involved in PPARα-mediated fatty acid oxidation and may lead to the observed protection in htgUGT1A-SNP mice.

The Systems Biology of Drug Metabolizing Enzymes and Transporters: Relevance to Quantitative Systems Pharmacology

Quantitative systems pharmacology (QSP) has emerged as a transformative science in drug discovery and development. It is now time to fully rethink the biological functions of drug metabolizing enzymes (DMEs) and transporters within the framework of QSP models. The large set of DME and transporter genes are generally considered from the perspective of the absorption, distribution, metabolism, and excretion (ADME) of drugs. However, there is a growing amount of data on the endogenous physiology of DMEs and transporters. Recent studies—including systems biology analyses of “omics” data as well as metabolomics studies—indicate that these enzymes and transporters, which are often among the most highly expressed genes in tissues like liver, kidney, and intestine, have coordinated roles in fundamental biological processes. Multispecific DMEs and transporters work together with oligospecific and monospecific ADME proteins in a large multiorgan remote sensing and signaling network. We use the Remote Sensing and Signaling Theory (RSST) to examine the roles of DMEs and transporters in intratissue, interorgan, and interorganismal communication via metabolites and signaling molecules. This RSST‐based view is applicable to bile acids, uric acid, eicosanoids, fatty acids, uremic toxins, and gut microbiome products, among other small organic molecules of physiological interest. Rooting this broader perspective of DMEs and transporters within QSP may facilitate an improved understanding of fundamental biology, physiologically based pharmacokinetics, and the prediction of drug toxicities based upon the interplay of these ADME proteins with key pathways in metabolism and signaling. The RSST‐based view should also enable more tailored pharmacotherapy in the setting of kidney disease, liver disease, metabolic syndrome, and diabetes. We further discuss the pharmaceutical and regulatory implications of this revised view through the lens of systems physiology.

Reused palm oil from frying pork or potato induced expression of cytochrome P450s and the SLCO1B1 transporter in HepG2 cells

Deep frying degrades the oil and generates harmful products. This study evaluated effects of reused palm oil (from frying pork or potato) on expression of cytochrome P450s (CYPs), the transporter (SLCO1B1), and lipid metabolism regulators; proliferator-activated receptors (PPAR) and sterol regulatory element binding protein (SREBP). Human hepatic carcinoma cell line (HepG2) cells were incubated with oleic acid (OA), new palm oil, or reused palm oils for 24 hr. Fatty acid accumulation was examined by Nile red staining. Total RNA was extracted, followed by RT/qPCR of the target genes. Fatty acid accumulation was significantly different between the new and the reused oils. Expression of CYP1A2, CYP2C19, CYP2E1, CYP3A4, CYP4A11, and SLCO1B1 was induced by reused oils. Expression of PPAR-α was strongly increased in all treatments while SREBP-1a and SREBP-1c were suppressed. Modification of CYPs, PPAR-α, and SLCO1B1 by palm oil might increase the risk of fatty acid accumulation with associated oxidative stress. Therefore, consumption of palm oil or reused oil should be limited. PRACTICAL APPLICATIONS: Deep frying degrades the oil and generates harmful products. This study evaluated effects of reused palm oil (from frying pork or potato) on expression of cytochrome P450s (CYPs), the transporter (SLCO1B1), and lipid metabolism regulators; PPAR and SREBP in HepG2 cells. Both of the reused oils-induced profiles of all CYP and SLCO1B1, but the new oil upregulated CYP2E1, CYP3A4, and CYP4A11. PPAR-α was induced while SREBP-1a and SREBP-1c were suppressed by all treatments. Inductions of CYPs with suppression of SREBP-1a and SREBP-1c might contribute to an increased risk of fatty acid accumulation. These findings revealed the impacts of reused palm oil on metabolism via CYPs which related to oxidative stress for further study. Hence, consumption of palm oil or reused cooking oil should be of concern.

Research and development of drug delivery systems based on drug transporter and nano-formulation

In recent years, the continuous occurrence of multi-drug resistance in the clinic has made people pay more attention to the transporter. Changes in the expression and activity of transporters can cause corresponding changes in drug pharmacokinetics and pharmacodynamics. The drug-drug interactions (DDI) caused by transporters can seriously affect drug effectiveness and toxicity. In the development of pharmaceutical preparations, people have increasingly concerned about the effects and regulation of transporters in drug effects. To improve the targeting and physicochemical properties of drugs, the development of targeted agents is very rapid. Among them, novel nano-formulations are the best. With the continuous innovation and development of nano-formulation, its application has become more and more extensive. Nano-formulation has exerted certain advantages in the drug development based on transporters, and is also involved in the combination of targeted transporters. This review focuses on the application of novel nano-agents targeting transporters and the introduction of drug-transporter-based nano-formulations.

Gadoxetic acid-enhanced MR imaging for hepatocellular carcinoma: molecular and genetic background

Gadoxetic acid-enhanced magnetic resonance imaging (MRI) plays important roles in diagnosis of hepatic lesions because of its superiority in the detectability of small lesions, its differentiation ability, and its utility for the early diagnosis of hepatocellular carcinoma (HCC). In HCC, expression of organic anion transporting polypeptide (OATP) 1B3 correlates with the enhancement ratio in the hepatobiliary phase. Gadoxetic acid-enhanced MRI, an indirect molecular imaging method, reflects OATP1B3 expression in HCC. OATP1B3 expression gradually decreases from the dysplastic nodule stage to advanced HCC. Decreased expression is a sensitive marker of multistep hepatocarcinogenesis, especially in the early stages. Hypervascular HCCs commonly show hypointensity in the hepatobiliary phase corresponding to a decrease in OATP1B3; however, approximately 10% of HCCs show hyperintensity due to OATP1B3 overexpression. This hyperintense HCC shows less aggressive biological features and has a better prognosis than hypointense HCC. Hyperintense HCC can be classified into a genetic subtype of HCC with a mature hepatocyte-like molecular expression. OATP1B3 expression and the less aggressive nature of hyperintense HCC are regulated by the molecular interaction of β-catenin signaling and hepatocyte nuclear factor 4α, a tumor suppressor factor. Gadoxetic acid-enhanced MR imaging has the potential to be an imaging biomarker for HCC. KEY POINTS: • The hepatobiliary phase is a sensitive indirect indicator of organic anion transporting polypeptide1B3 (OATP1B3) expression in hepatocellular carcinoma (HCC). • The OATP1B3 expression, namely, enhancement in the hepatobiliary phase, decreases from the very early stage of hepatocarcinogenesis, contributing to early diagnosis of HCC. • HCC showing hyperintensity on the hepatobiliary phase is a peculiar genetic subtype of HCC with OATP1B3 overexpression, a less aggressive nature, and mature hepatocyte-like molecular/genetic features.

Mechanism of Asbt (Slc10a2)-related bile acid malabsorption in diarrhea after pelvic radiation

Background: Radiation is a mode of treatment for many pelvic malignancies, most of which originate in the gynecologic, gastrointestinal, and genitourinary systems. However, the healthy gut is unavoidably included in the irradiation volume, resulting in undesirable results that manifest as radiation-induced diarrhea (RID), which is the most common side effect of radiation therapy and significantly affects the patients' quality of life. This study aimed to investigate the potential mechanism of diarrhea after pelvic radiotherapy in rats based on the effect of radiation on bile acid homeostasis and sodium-dependent bile acid transporter (Asbt).Methods: In this experimental study, male Sprague-Dawley rats were divided into the following groups - pelvic irradiation, cholestyramine-concurrent radiation, and control groups. The rats in the pelvic irradiation group were irradiated in the pelvic region with 2 Gy per day for five consecutive days. The total bile acid (TBA) levels in the ileum, colon, and feces were measured using automatic biochemical analyzer, and the levels of individual bile acids were evaluated by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The mRNA and protein expression of Asbt in ileum were assessed by qRT-PCR and Western blot assay. The rats in the cholestyramine-concurrent radiation group were administered with cholestyramine, a bile acid-chelating resin, and concurrent radiation for 5 days. The body weight of rats was monitored daily, and the degree of diarrhea was scored.Results: Diarrhea was observed at 2 and 3 days post-pelvic radiation. The TBA levels were significantly decreased at 4 and 5 days post-radiation in the ileum (p < .01, p < .01) and increased at 4 and 5 days post-radiation in the colon (p < .05, p < .05). The fecal excretions of TBA were significantly increased at 3, 4, and 5 days post-radiation (p < .05). The levels of individual bile acids were significantly decreased in the ileum and increased in the colon and feces, post-radiation. The mRNA and protein expression of Asbt in the ileum gradually decreased with increasing days of pelvic radiation and significantly decreased at 3 and 5 days post-radiation, respectively. Furthermore, a significant decrease in body weight was observed post-pelvic radiation, and cholestyramine administration did not reverse the weight loss. However, the incidence of RID was decreased after administration of cholestyramine.Conclusions: Bile acid malabsorption is partially responsible for RID post-pelvic radiation in rats, and the potential mechanism is related to the downregulation of the ileal Asbt.

Primary biliary cholangitis: pathogenesis and therapeutic opportunities

Primary biliary cholangitis is a chronic, seropositive and female-predominant inflammatory and cholestatic liver disease, which has a variable rate of progression towards biliary cirrhosis. Substantial progress has been made in patient risk stratification with the goal of personalized care, including early adoption of next-generation therapy with licensed use of obeticholic acid or off-label fibrate derivatives for those with insufficient benefit from ursodeoxycholic acid, the current first-line drug. The disease biology spans genetic risk, epigenetic changes, dysregulated mucosal immunity and altered biliary epithelial cell function, all of which interact and arise in the context of ill-defined environmental triggers. A current focus of research on nuclear receptor pathway modulation that specifically and potently improves biliary excretion, reduces inflammation and attenuates fibrosis is redefining therapy. Patients are benefiting from pharmacological agonists of farnesoid X receptor and peroxisome proliferator-activated receptors. Immunotherapy remains a challenge, with a lack of target definition, pleiotropic immune pathways and an interplay between hepatic immune responses and cholestasis, wherein bile acid-induced inflammation and fibrosis are dominant clinically. The management of patient symptoms, particularly pruritus, is a notable goal reflected in the development of rational therapy with apical sodium-dependent bile acid transporter inhibitors.

Effects of supplemental dietary bile acids on growth, liver function and immunity of juvenile largemouth bass（Micropterus salmoides）fed high-starch diet

The present study was conducted to investigate the effects of bile acids (BAs) on the growth, liver function and immunity of the largemouth bass fed high-starch diet. The experiment set three isonitrogenous and isoenergetic semi-purified diets, LS: low-starch diet (5%), HS: high-starch diet (19%) and SB: high-starch diet with BAs (350 mg/kg diet). An 8-week feeding trial was conducted in largemouth bass of initial weight 23.69 ± 0.13 g. The results indicated that the weight gain (WG) and protein efficiency ratio (PER) of fish fed LS and SB were significantly higher than HS treatment. The superoxide dismutase (SOD) and catalase (CAT) activities of SB group were significantly increased, while malondialdehyde (MDA) content significantly reduced in liver compared with HS group. The activities of alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) and glucose contents in plasma of SB group were significantly lower than HS treatment, whereas the content of triglyceride (TG) and total cholesterol (TC) in plasma were significantly higher than HS treatment. Additionally, the plasma immunoglobulin count, lysozyme activity and the blood leukocyte count (WBC) in SB group were significantly higher than HS group. The results of paraffin section of liver showed the histopathological alterations were significantly reduced in the SB group compared to HS group. All in all, this study revealed that bile acids supplement could significantly improve growth performance, enhance liver function and immune ability, and alleviate stress responses of M. salmoides fed high-starch diet.

Conditional loss of geranylgeranyl diphosphate synthase alleviates acute obstructive cholestatic liver injury by regulating hepatic bile acid metabolism

Previous studies have suggested that metabolites in the mevalonate pathway are involved in hepatic bile acid metabolism, yet the details of this relationship remain unknown. In this study, we found that the hepatic farnesyl pyrophosphate (FPP) level and the ratio of FPP to geranylgeranyl pyrophosphate (GGPP) were increased in mice with acute obstructive cholestasis compared with mice that underwent a sham operation. In addition, the livers of the mice with acute obstructive cholestasis showed lower expression of geranylgeranyl diphosphate synthase (GGPPS), which synthesizes GGPP from FPP. When Ggps1 was conditionally deleted in the liver, amelioration of liver injury, as shown by downregulation of the hepatic inflammatory response and decreased hepatocellular apoptosis, was found after ligation of the common bile duct and cholecystectomy (BDLC). Subsequently, liquid chromatography/mass spectrometry analysis showed that knocking out Ggps1 decreased the levels of hepatic bile acids, including hydrophobic bile acids. Mechanistically, the disruption of Ggps1 increased the levels of hepatic FPP and its metabolite farnesol, thereby resulting in farnesoid X receptor (FXR) activation, which modulated hepatic bile acid metabolism and reduced hepatic bile acids. It was consistently indicated that digeranyl bisphosphonate, a specific inhibitor of GGPPS, and GW4064, an agonist of FXR, could also alleviate acute obstructive cholestatic liver injury in vivo. In general, GGPPS is critical for modulating acute obstructive cholestatic liver injury, and the inhibition of GGPPS ameliorates acute obstructive cholestatic liver injury by decreasing hepatic bile acids, which is possibly achieved through the activation of FXR-induced bile acid metabolism.

Rifampicin induces clathrin-dependent endocytosis and ubiquitin-proteasome degradation of MRP2 via oxidative stress-activated PKC-ERK/JNK/p38 and PI3K signaling pathways in HepG2 cells

It was reported that antituberculosis medicines could induce liver damage via oxidative stress. In this study, we investigated the effects of rifampicin (RFP) on the membrane expression of multidrug resistance-associated protein 2 (MRP2) and the relationship between oxidative stress and RFP-induced endocytosis of MRP2 in HepG2 cells. We found that RFP (12.5–50 μM) dose-dependently decreased the expression and membrane localization of MRP2 in HepG2 cells without changing the messenger RNA level. RFP (50 μM) induced oxidative stress responses that further activated the PKC-ERK/JNK/p38 (protein kinase C-extracellular signal-regulated kinase/c-JUN N-terminal kinase/p38) and PI3K (phosphoinositide 3-kinase) signaling pathways in HepG2 cells. Pretreatment with glutathione reduced ethyl ester (2 mM) not only reversed the changes in oxidative stress indicators and signaling molecules but also diminished RFP-induced reduction in green fluorescence intensity of MRP2. We conducted co-immunoprecipitation assays and revealed that a direct interaction existed among MRP2, clathrin, and adaptor protein 2 (AP2) in HepG2 cells, and their expression was clearly affected by the changes in intracellular redox levels. Knockdown of clathrin or AP2 with small interfering RNA attenuated RFP-induced decreases of membrane and total MRP2. We further demonstrated that RFP markedly increased the ubiquitin–proteasome degradation of MRP2 in HepG2 cells, which was mediated by the E3 ubiquitin ligase GP78, but not HRD1 or TEB4. In conclusion, this study demonstrates that RFP-induced oxidative stress activates the PKC-ERK/JNK/p38 and PI3K signaling pathways that leads to clathrin-dependent endocytosis and ubiquitination of MRP2 in HepG2 cells, which provides new insight into the mechanism of RFP-induced cholestasis.

Chenodeoxycholic Acid Modulates Bile Acid Synthesis Independent of Fibroblast Growth Factor 19 in Primary Human Hepatocytes

Bile acids (BAs) are detergents essential for intestinal absorption of lipids. Disruption of BA homeostasis can lead to severe liver damage. BA metabolism is therefore under strict regulation by sophisticated feedback mechanisms. The hormone-like protein Fibroblast growth factor 19 (FGF19) is essential for maintaining BA homeostasis by down regulating BA synthesis. Here, the impact of both FGF19 and chenodeoxycholic acid (CDCA) on primary human hepatocytes was investigated and a possible autocrine/paracrine function of FGF19 in regulation of BA synthesis evaluated. Primary human hepatocytes were treated with CDCA, recombinant FGF19 or conditioned medium containing endogenously produced FGF19. RNA sequencing revealed that treatment with CDCA causes deregulation of transcripts involved in BA metabolism, whereas treatment with FGF19 had minor effects. CDCA increased FGF19 mRNA expression within 1 h. We detected secretion of the resulting FGF19 protein into medium, mimicking in vivo observations. Furthermore, medium enriched with endogenously produced FGF19 reduced BA synthesis by down regulating CYP7A1 gene expression. However, following knockdown of FGF19, CDCA still independently decreased BA synthesis, presumably through the regulatory protein small heterodimer partner (SHP). In summary, we show that in primary human hepatocytes CDCA regulates BA synthesis in an FGF19-independent manner.

Paracrine Fibroblast Growth Factor 1 Functions as Potent Therapeutic Agent for Intrahepatic Cholestasis by Downregulating Synthesis of Bile Acid

Endocrine fibroblast growth factor (FGF) 19 has been shown to be capable of maintaining bile acid (BA) homeostasis and thus hold promise to be a potential therapeutic agent for cholestasis liver disease. However, whether paracrine FGFs possess this BA regulatory activity remains to be determined. In our study, we identified that paracrine fibroblast growth factor 1 (FGF1) was selectively downregulated in the liver of alpha naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis mice, suggesting a pathological relevance of this paracrine FGF with abnormal BA metabolism. Therefore, we evaluated the effects of engineered FGF1 mutant - FGF1^ΔHBS on the metabolism of hepatic BA and found that this protein showed a more potent inhibitory effect of BA biosynthesis than FGF19 without any hepatic mitogenic activity. Moreover, the chronic administration of FGF1^ΔHBS protected liver against ANIT-induced injury by reducing hepatic BA accumulation. Taken together, these data suggest that FGF1^ΔHBS may function as a potent therapeutic agent for intrahepatic cholestasis liver disease.

Lignans from Schisandra sphenanthera protect against lithocholic acid-induced cholestasis by pregnane X receptor activation in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cholestasis is a clinical syndrome caused by toxic bile acid retention that will lead to serious liver diseases. Ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) are the only two FDA-approved drugs for its treatment. Thus, there is a clear need to develop new therapeutic approaches for cholestasis. Here, anti-cholestasis effects of the lignans from a traditional Chinese herbal medicine, Schisandra sphenanthera, were investigated as well as the involved mechanisms.

MATERIALS AND METHODS

Adult male C57BL/6J mice were randomly divided into 9 groups including the control group, LCA group, LCA with specific lignan treatment of Schisandrin A (SinA), Schisandrin B (SinB), Schisandrin C (SinC), Schisandrol A (SolA), Schisandrol B (SolB), Schisantherin A (StnA) and Schisantherin B (StnB), respectively. Mice were treated with each drug (qd) for 7 days, while the administration of lithocholic acid (LCA) (bid) was launched from the 4th day. Twelve hours after the last LCA injection, mice were sacrificed and samples were collected. Serum biochemical measurement and histological analysis were conducted. Metabolomics analysis of serum, liver, intestine and feces were performed to study the metabolic profile of bile acids. RT-qPCR and Western blot analysis were conducted to determine the hepatic expression of genes and proteins related to bile acid homeostasis. Dual-luciferase reporter gene assay was performed to investigate the transactivation effect of lignans on human pregnane X receptor (hPXR). RT-qPCR analysis was used to detect induction effects of lignans on hPXR-targeted genes in HepG2 cells.

RESULTS

Lignans including SinA, SinB, SinC, SolA, SolB, StnA, StnB were found to significantly protect against LCA-induced intrahepatic cholestasis, as evidenced by significant decrease in liver necrosis, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) activity. More importantly, serum total bile acids (TBA) and total bilirubin (Tbili) were also significantly reduced. Metabolomics analysis revealed these lignans accelerated the metabolism of bile acids and increased the bile acid efflux from liver into the intestine or feces. Gene analysis revealed these lignans induced the hepatic expressions of PXR-target genes such as Cyp3a11 and Ugt1a1. Luciferase reporter gene assays illustrated that these bioactive lignans can activate hPXR. Additionally, they can all upregulate hPXR-regulate genes such as CYP3A4, UGT1A1 and OATP2.

CONCLUSION

These results clearly demonstrated the lignans from Schisandra sphenanthera exert hepatoprotective effects against LCA-induced cholestasis by activation of PXR. These lignans may provide an effective approach for the prevention and treatment of cholestatic liver injury.

Liver Injury and Failure in Critical Illness

The frequency of acquired liver injury and failure in critical illness has been significantly increasing over recent decades. Currently, liver injury and failure are observed in up to 20% of patients in intensive care units and are associated with significantly increased morbidity and mortality. Secondary forms of liver injury in critical illness are divided primarily into cholestatic, hypoxic, or mixed forms. Therefore, sufficient knowledge of underlying alterations (e.g., hemodynamic, inflammatory, or drug induced) is key to a better understanding of clinical manifestations, prognostic implications, as well as diagnostic and therapeutic options of acquired liver injury and failure. This review provides a structured approach for the evaluation and treatment of acquired liver injury and failure in critically ill patients.

Serum Concentrations of 7α-hydroxy-4-cholesten-3-one Are Associated With Bile Acid Diarrhea in Patients With Crohn's Disease

BACKGROUND & AIMS

Patients with Crohn's disease (CD) often have bile acid diarrhea (BAD), due to bile acid malabsorption following ileal resection (IR). Bile acid malabsorption increases production of 7α-hydroxy-4-cholesten-3-one (C4), a bile acid precursor. We investigated relationships between serum concentrations of C4 and BAD in patients with CD.

METHODS

We collected demographic data, serum samples, and information on the presence of diarrhea (>3 liquid bowel movements/day), as well as clinical, endoscopic, and histologic scores from 26 patients with CD and IR, 21 patients with CD without IR, and 37 patients with ulcerative colitis (UC). We compared serum concentrations of C4 and fibroblast growth factor 19 (FGF19) between groups. We performed area under the receiver operating characteristic curve (AUROC) analysis to identify the optimal cutoff C4 concentrations for the diagnosis of diarrhea attributable to bile acid malabsorption (BAD), defined as diarrhea and a serum concentration of FGF19 <60 pg/mL.

RESULTS

Patients with UC had a median serum C4 concentration of 11.8 ng/mL, whereas patients with CD and IR with ileitis (documented endoscopically) had a median concentration of 100.0 ng/mL (P compared to UC < .0001) and patients with CD and IR without ileitis had a median concentration of 51.6 ng/mL (P compared to UC < .001). Patients with CD without IR did not have a significantly higher median concentration of C4 than patients with UC (P = .71), regardless of ileitis (P = .34). When endoscopic findings were confirmed histologically, similar results were found to analyses using endoscopic findings alone. A higher proportion of patients with active UC had diarrhea (72.0% vs 0 patients with inactive UC; P < .001), but their median concentrations of C4 did not differ significantly from that of patients with inactive UC (12.1 ng/mL vs 9.7 ng/mL; P = .3). A cutoff concentration of C4 of 48.3 ng/mL or greater identified patients with diarrhea attributable to bile acid malabsorption with 90.9% sensitivity, 84.4% specificity, and an AUROC 0.94. A significantly higher proportion of patients with concentrations of C4 above this cutoff had BAD (50.0%) than below this cutoff (1.8%) (P < .001). When we analyzed only patients with diarrhea, a C4 cutoff of 48.3 ng/mL identified those with low FGF19 concentrations (<60 pg/mL) with 91% sensitivity and 95.5% specificity (AUROC, 0.99). Above this cutoff, 83.3% of patients had a serum concentration of FGF19 <60 pg/mL compared to 4.5% below this threshold (P < .0001). C4 concentrations correlated with the number of daily bowel movements (r = 0.41; P = .004) and correlated inversely with FGF19 concentrations (r = -0.72; P<.0001).

CONCLUSION

We observed significantly increased serum concentrations of C4 in patients with CD with IR, compared to patients with UC. A cutoff concentration of C4 above 48.3 ng/mL identifies patients with diarrhea likely attributable to bile acid malabsorption (BAD) with an AUROC value of 0.94. Increased serum levels of bile acid precursors identify patients with diarrhea and a low serum concentration of FGF19, and concentrations of C4 correlate with daily liquid bowel movements and correlate inversely with FGF19 concentrations. C4 may be a biomarker to identify patients with diarrhea attributable to bile acid malabsorption.

OATP1B3-1B7, a novel organic anion transporting polypeptide, is modulated by FXR ligands and transports bile acids

Organic anion transporting polypeptide (OATP) 1B3-1B7 (LST-3TM12) is a member of the OATP1B [solute carrier organic anion transporter (SLCO) 1B] family. This transporter is not only functional but also expressed in the membrane of the smooth endoplasmic reticulum of hepatocytes and enterocytes. OATP1B3-1B7 is a splice variant of SLCO1B3 in which the initial part is encoded by SLCO1B3, whereas the rest of the mRNA originates from the gene locus of SLCO1B7. In this study, we not only showed that SLCO1B3 and the mRNA encoding for OATP1B3-1B7 share the 5' untranslated region but also that silencing of an initial SLCO1B3 exon lowered the amount of SLCO1B3 and of SLCO1B7 mRNA in Huh-7 cells. To validate the assumption that both transcripts are regulated by the same promoter we tested the influence of the bile acid sensor farnesoid X receptor (FXR) on their transcription. Treatment of Huh-7 and HepaRG cells with activators of this known regulator of OATP1B3 not only increased SLCO1B3 but also OATP1B3-1B7 mRNA transcription. Applying a heterologous expression system, we showed that several bile acids interact with OATP1B3-1B7 and that taurocholic acid and lithocholic acid are OATP1B3-1B7 substrates. As OATP1B3-1B7 is located in the smooth endoplasmic reticulum, it may grant access to metabolizing enzymes. In accordance are our findings showing that the OATP1B3-1B7 inhibitor bromsulphthalein significantly reduced uptake of bile acids into human liver microsomes. Taken together, we report that OATP1B3-1B7 transcription can be modulated with FXR agonists and antagonists and that OATP1B3-1B7 transports bile acids.NEW & NOTEWORTHY Our study on the transcriptional regulation of the novel organic anion transporting polypeptide (OATP) 1B3-1B7 concludes that the promoter of solute carrier organic anion transporter (SLCO) 1B3 governs SLCO1B3-1B7 transcription. Moreover, the transcription of OATP1B3-1B7 can be modulated by farnesoid X receptor (FXR) agonists and antagonists. FXR is a major regulator in bile acid homeostasis that links OATP1B3-1B7 to this physiological function. Findings in transport studies with OATP1B3-1B7 suggest that this transporter interacts with the herein tested bile acids.

Multi-technique comparison of atherogenic and MCD NASH models highlights changes in sphingolipid metabolism

Lipotoxicity is a key player in the pathogenesis of nonalcoholic steatohepatitis (NASH), a progressive subtype of nonalcoholic fatty liver disease (NAFLD). In the present study, we combine histological, transcriptional and lipidomic approaches to dissociate common and specific alterations induced by two classical dietary NASH models (atherogenic (ATH) and methionine/choline deficient (MCD) diet) in C57BL/6J male mice. Despite a similar degree of steatosis, MCD-fed mice showed more pronounced liver damage and a worsened pro-inflammatory and pro-fibrogenic environment than ATH-fed mice. Regarding lipid metabolism, the ATH diet triggered hepatic counter regulatory mechanisms, while the MCD diet worsened liver lipid accumulation by a concomitant increase in lipid import and reduction in lipid export. Liver lipidomics revealed sphingolipid enrichment in both NASH models that was accompanied by an upregulation of the ceramide biosynthesis pathway and a significant rise in dihydroceramide levels. In contrast, the phospholipid composition was not substantially altered by the ATH diet, whereas the livers of MCD-fed mice presented a reduced phosphatidylcholine to phosphatidylethanolamine (PC/PE) ratio and a strong depletion in phospholipids containing the sum of 34-36 carbons in their fatty acid chains. Therefore, the assessment of liver damage at the histological and transcriptional level combined with a lipidomic analysis reveals sphingolipids as shared mediators in liver lipotoxicity and pathogenesis of NASH.

Cholestasis In Infants With Down Syndrome Is Not Due To Extrahepatic Biliary Atresia: A Ten-Year Single Egyptian Centre Experience

Purpose

We aimed to define the clinical presentations, course and outcome of cholestasis in infants with Down syndrome (trisomy 21) who presented to the Pediatric Hepatology Clinic, New Children Hospital, Cairo University, Egypt.

Methods

Retrospective analysis of data of cohort of infants with Down syndrome and cholestasis who followed up during 2005-2015.

Results

Among 779 infants with cholestasis who presented during 2005-2015, 61 (7.8%) had Down syndrome. Six dropped out. Among the 55 who followed-up for a mean duration +SD = 12.1 ± 16.7 months, none had extrahepatic biliary atresia (EHBA), 37 (63.3%) had neonatal hepatitis and 18 (32.7%) had non-syndromic paucity of intrahepatic biliary radicals. Fourteen (25.4%) had associated congenital heart disease. Only 35 (63.3%) cleared the jaundice. Twenty-nine (52.7%) received ursodeoxycholic acid (UDCA); of them, 13 cleared the jaundice, one improved, 14 progressed and one died, compared to 22 who cleared the jaundice of the 26 who did not receive UDCA. Only three of those who did not receive UDCA progressed and none died. UDCA carried a 3.4-fold risk of poor prognosis (p= 0.001). UDCA use was associated with more complications (p= 0.016) in those with Down syndrome and cholestasis.

Conclusion

We did not come across EHBA among neonates and infants with Down syndrome in 10 years. Non-syndromic paucity is associated with favorable outcome in infants with Down syndrome. UDCA use in cholestasis with Down syndrome is associated with poor outcome.

Metabolomic-transcriptomic landscape of 8-epidiosbulbin E acetate -a major diterpenoid lactone from Dioscorea bulbifera tuber induces hepatotoxicity

Studies have shown that 8-epidiosbulbin E acetate (EEA), a major diterpenoid lactone in the tuber of Dioscorea bulbifera, can induce hepatotoxicity in vivo. However, the underlying mechanisms remain unknown. Using the integrated transcriptomic and metabolomics method, in this study we investigated the global effect of EEA exposure on the transcriptomic and metabolomic profiles in mice. The abundance of 7131 genes and 42 metabolites in the liver, as well as 43 metabolites in the serum were altered. It should be noted that EEA mainly damaged hepatic cells through the aberrant regulation of multiple systems primarily including bile acid metabolism, and taurine and hypotaurine metabolism. In addition, an imbalance of bile acid metabolism was found to play a key pat in response to EEA-triggered hepatotoxicity. In summary, these findings contributed to understanding the underlying mechanisms of EEA hepatotoxicity.

Cardiovascular Risk Categories in Patients With Nonalcoholic Fatty Liver Disease and the Role of Low-Density Lipoprotein Cholesterol

Cardiovascular disease (CVD) is the leading cause of death in patients with nonalcoholic fatty liver disease (NAFLD). The current analysis expands the knowledge on atherogenic lipid profiles in NAFLD by modeling changes in low‐density lipoprotein cholesterol (LDL‐C) and total cholesterol (TC) in a prospectively enrolling real‐life study cohort to inform physicians on the cardiovascular (CV) event risk based on these changes. A total of 304 patients with histologically confirmed NAFLD were included (mean age, 52 years; equal sex distribution). Of these, 129 (42.4%) patients exhibited a NAFLD activity score ≥4 and 186 (61.2%) had at least intermediate fibrosis ≥F2. The median TC levels were 209 mg/dL (interquartile range [IQR], 183, 239), LDL‐C 131 mg/dL (IQR, 103, 152), and high‐density lipoprotein cholesterol (HDL‐C) 45 mg/dL (IQR, 38, 52). Only 16.9% of patients received lipid‐lowering therapy. According to the LDL/HDL ratio, 69 (23.7%) patients exhibited a high CV risk. The 10‐year CV event risk according to the Framingham risk score (FRS) was low in 91 (41.2%), intermediate in 59 (26.7%), and high in 71 (32.1%) patients and higher in the ≥F2 NAFLD population. A moderate increase in LDL‐C levels by 20 mg/dL led to a transition of 20% of patients into the high‐risk group when assessing the LDL/HDL ratio. According to the FRS, 6 (2.7%) patients moved from low to intermediate and 11 (4.9%) from intermediate to high CV risk. Conclusion: Patients with NAFLD exhibit a substantial CV event risk and are frequently undertreated with lipid‐lowering medication. Moderate increases in LDL‐C would result in worsening of the CV event risk in approximately 7.8% of all patients without a history of CVD.

Probiotic Lactobacillus rhamnosus GG prevents progesterone metabolite epiallaopregnanolone sulfate-induced hepatic bile acid accumulation and liver injury

Intrahepatic cholestasis of pregnancy (ICP) is gestation-specific liver disease associated with liver injury and increased serum and hepatic bile acids. Although the mechanism of ICP is still not fully understood, the reproductive hormones seem to play an important role. Recent studies show that a progesterone metabolite, epiallopregnanolone sulfate (PM5S), is supraphysiologically elevated in the serum of ICP patients, indicating it may play an etiology role in ICP. Bile acid homeostasis is controlled by multiple mechanisms including farnesoid X receptor (FXR)-mediated bile acid export and synthesis. It is known that cholic acid (CA), a primary bile acid, can activate FXR, which is inhibited by PM5S, an FXR antagonist. Here we employed a mouse model of concurrent exposure of CA and PM5S-induced liver injury and determined the effects of probiotic Lactobacillus rhamnosus GG (LGG) in the prevention of the bile acid disorders and liver injury. Mice challenged with CA + PM5S had significantly increased levels of serum and hepatic bile acids and bilirubin and liver enzyme. Pretreatment with LGG significantly reduced bile acid and bilirubin levels associated with reduced liver enzyme level and mRNA expression levels of pro-inflammatory cytokines. We also showed that the beneficial effects of LGG is likely mediated by hepatic FXR activation and bile salt export pump (BSEP) upregulation. In conclusion, our results provide a rationale for the application of probiotics in the management of ICP through gut microbiota-mediated FXR activation.

Protective effect of herbal medicine Huangqi decoction against chronic cholestatic liver injury by inhibiting bile acid-stimulated inflammation in DDC-induced mice

BACKGROUND

Huangqi decoction (HQD), a classic traditional herbal medicine, has been used for liver fibrosis, but its effect on intrahepatic chronic cholestatic liver injury remains unknown.

PURPOSE

In the present study, we investigated the hepatoprotective effect of HQD and the underlying molecular mechanisms in 3, 5-diethoxycarbonyl-1, 4-dihydroxychollidine (DDC)-induced chronic cholestatic mice.

METHODS

The DDC-induced cholestatic mice were administrated HQD for 4 or 8 weeks. Serum biochemistry and morphology were investigated. The serum and liver bile acid (BA) levels were detected by ultra performance liquid chromatography-tandem mass spectrometry. The liver expression of BA metabolizing enzymes and transporters, and inflammatory and fibrotic markers was measured by real-time polymerase chain reaction, western blotting, and immunohistochemistry.

RESULTS

HQD treatment for 4 or 8 weeks ameliorated DDC-induced liver injury by improving impaired hepatic function and tissue damage. HQD treatment for 8 weeks further decreased the liver expression of cytokeratin 19, tumor growth factor (TGF)-β, collagen I, and α-smooth muscle actin, and ameliorated ductular reaction and liver fibrosis. HQD markedly decreased the accumulation of serum and liver BA. The expression of BA-metabolizing enzymes, cytochrome P450 2b10 and UDP glucuronosyltransferase 1 A1, and multidrug resistance-associated protein 2, Mrp3, and Mrp4 involved in BA homeostasis was increased by 4 weeks of HQD treatment. The expression of BA uptake transporter Na⁺-taurocholate cotransporting polypeptide was decreased and that of Mrp4 was increased after 8 weeks of HQD treatment. Nuclear factor-E2-related factor-2 (Nrf2) was remarkably induced by HQD treatment. Additionally, HQD treatment for 8 weeks decreased the liver expression of inflammatory factors, interleukin (IL)-6, IL-1β, tumor necrosis factor-α, monocyte chemoattractant protein-1, and intracellular adhesion molecule-1. HQD suppressed the nuclear factor (NF)-κB pathway.

CONCLUSION

HQD protected mice against chronic cholestatic liver injury and biliary fibrosis, which may be associated with the induction of the Nrf2 pathway and inhibition of the NF-κB pathway, ameliorating BA-stimulated inflammation.

Transcriptome Profiling of Placenta through Pregnancy Reveals Dysregulation of Bile Acids Transport and Detoxification Function

Placenta performs the function of several adult organs for the fetus during intrauterine life. Because of the dramatic physiological and metabolic changes during pregnancy and the strong association between maternal metabolism and placental function, the possibility that variation in gene expression patterns during pregnancy might be linked to fetal health warrants investigation. Here, next-generation RNA sequencing was used to investigate the expression profile, including mRNAs and long non-coding RNAs (lncRNAs) of placentas on day 60 of gestation (G60), day 90 of gestation (G90), and on the farrowing day (L0) in pregnant swine. Bioinformatics analysis of differentially expressed mRNAs and lncRNAs consistently showed dysregulation of bile acids transport and detoxification as pregnancy progress. We found the differentially expressed mRNAs, particularly bile salt export pump (ABCB11), organic anion-transporting polypeptide 1A2 (OATP1A2), carbonic anhydrase II (CA2), Na⁺-HCO₃⁻ cotransporter (NBC1), and hydroxysteroid sulfotransferases (SULT2A1) play an important role in bile acids transport and sulfation in placentas during pregnancy. We also found the potential regulation role of ALDBSSCG0000000220 and XLOC_1301271 on placental SULT2A1. These findings have uncovered a previously unclear function and its genetic basis for bile acids metabolism in developing placentas and have important implications for exploring the potential physiological and pathological pathway to improve fetal outcomes.

Farnesoid X Receptor Activation by Obeticholic Acid Elevates Liver Low-Density Lipoprotein Receptor Expression by mRNA Stabilization and Reduces Plasma Low-Density Lipoprotein Cholesterol in Mice

Objective- The objective of this study was to determine whether and how activation of farnesoid X receptor (FXR) by obeticholic acid (OCA), a clinical FXR agonist, modulates liver low-density lipoprotein receptor (LDLR) expression under normolipidemic conditions. Approach and Results- Administration of OCA to chow-fed mice increased mRNA and protein levels of LDLR in the liver without affecting the sterol-regulatory element binding protein pathway. Profiling of known LDLR mRNA-binding proteins demonstrated that OCA treatment did not affect expressions of mRNA degradation factors hnRNPD (heterogeneous nuclear ribonucleoprotein D) or ZFP36L1 but increased the expression of Hu antigen R (HuR) an mRNA-stabilizing factor. Furthermore, inducing effects of OCA on LDLR and HuR expression were ablated in Fxr^-/- mice. To confirm the post-transcriptional mechanism, we used transgenic mice (albumin-luciferase-untranslated region) that express a human LDLR mRNA 3' untranslated region luciferase reporter gene in the liver. OCA treatment led to significant rises in hepatic bioluminescence signals, Luc-untranslated region chimeric mRNA levels, and endogenous LDLR protein abundance, which were accompanied by elevations of hepatic HuR mRNA and protein levels in OCA-treated transgenic mice. In vitro studies conducted in human primary hepatocytes and HepG2 cells demonstrated that FXR activation by OCA and other agonists elicited the same inducing effect on LDLR expression as in the liver of normolipidemic mice. Furthermore, depletion of HuR in HepG2 cells by short interfering RNA transfection abolished the inducing effect of OCA on LDLR expression. Conclusions- Our study is the first to demonstrate that FXR activation increases LDLR expression in liver tissue by a post-transcriptional regulatory mechanism involving LDLR mRNA-stabilizing factor HuR.

Ursodeoxycholic acid accelerates bile acid enterohepatic circulation

BACKGROUND AND PURPOSE

Ursodeoxycholic acid (UDCA) is the first-line treatment for primary biliary cholangitis, but its effects on the enterohepatic circulation of bile acid (BA) have been under-investigated. Therefore, we studied the influence of UDCA on BA enterohepatic circulation in vivo and the mechanisms by which UDCA affects the BA kinetics.

EXPERIMENTAL APPROACH

Mice were treated with UDCA and other BAs to observe changes in BA pool and BA transporters involved in enterohepatic circulation. Isotope dilution techniques and biochemical analyses were applied to study BA kinetics after oral administration of UDCA, and the mechanism involved.

KEY RESULTS

Oral administration of UDCA in mice reduced the overall BA pool and produced a unique BA profile with high-abundance conjugated UDCA species, including tauroursodeoxycholic acid (TUDCA) and GUDCA. We found increased expression of several main BA transporters in the ileum and liver. BA kinetic experiment showed that feeding UDCA shortened cycling time of BA and accelerated BA enterohepatic circulation. Additionally, we found evidence that the effect of UDCA administration on accelerating BA enterohepatic circulation was due to the inhibition of farnesoid X receptor (FXR) signalling in the ileum and FGF15/19 in the liver.

CONCLUSION AND IMPLICATIONS

Oral administration of UDCA produced a unique BA profile with high-abundance TUDCA and GUDCA and significantly accelerated BA enterohepatic circulation through the inhibition of intestinal FXR signalling and reduced level of FGF15/19, which in turn, induced the expression of BA transporters in the liver. These findings highlight a critical role for UDCA in maintaining the homeostasis of BA enterohepatic circulation in vivo.