The role of CYP3A4 in the biotransformation of bile acids and therapeutic implication for cholestasis

Unveiling the Pharmacological Mechanisms of Davidiin's Anti-Diabetic Efficacy in Streptozotocin-Treated Rats: A Comprehensive Analysis of Serum Metabolome

Background

Polygonum capitatum Buch.-Ham. ex D. Don (P. capitatum), a traditional herb used in Miao medicine, is renowned for its heart-clearing properties. Davidiin, the primary bioactive component (approximately 1%), has been used to treat various conditions, including diabetes. Given its wide range of effects and the diverse biomolecular pathways involved in diabetes, there is a crucial need to study how davidiin interacts with these pathways to better understand its anti-diabetic properties.

Materials and Methods

Diabetic rats were induced using a high-fat diet and streptozotocin (STZ) administered intraperitoneally at 35 mg/kg. Out of these, 24 rats with blood glucose levels ≥ 11.1 mmol/L and fasting blood glucose levels ≥ 7.0 mmol/L were selected for three experimental groups. These groups were then treated with either metformin (gavage, 140 mg/kg) or davidiin (gavage, 90 mg/kg) for four weeks. After the treatment period, we measured body weight, blood glucose levels, and conducted untargeted metabolic profiling using UPLC-QTOF-MS.

Results

Davidiin has been shown to effectively treat diabetes by reducing blood glucose levels from 30.2 ± 2.6 mmol/L to 25.1 ± 2.4 mmol/L (P < 0.05). This effect appears stronger than that of metformin, which lowered glucose levels to 26.5 ± 2.6 mmol/L. The primary outcomes of serum metabolomics are significant changes in lipid and lipid-like molecular profiles. Firstly, davidiin may affect phosphatide metabolism by increasing levels of phosphatidylinositol and sphingosine-1-phosphate. Secondly, davidiin could influence cholesterol metabolism by reducing levels of glycocholic acid and glycochenodeoxycholic acid. Lastly, davidiin might impact steroid hormone metabolism by increasing hepoxilin B3 levels and decreasing prostaglandins.

Conclusion

Our study demonstrates that davidiin modulates various lipid-related metabolic pathways to exert its anti-diabetic effects. These findings offer the first detailed metabolic profile of davidiin's action mechanism, contributing valuable insights to the field of Traditional Chinese Medicine in the context of diabetes treatment.

Research progress regarding CYP3A gene family in gastric cancer

Cytochrome P450 family 3 subfamily A (CYP3A), a major member of cytochrome P450 (CYP) family, is one of the most important drug metabolizing enzymes in human. CYP3A includes 4 gene subtypes (CYP3A4, CYP3A5, CYP3A7, and CYP3A43), which is involved in 60% of drug metabolism in the human. It is not only widely distributed in normal tissues, but also significantly overexpressed in various tumor tissues. Recently, CYP3A has attracted great attention due to its involvement in the progression from chronic atrophic gastritis to gastric cancer, as well as the differential metabolism and resistance of chemotherapeutic drugs. Targeting CYP3A gene mediated-prodrug provides new ideas for the treatment of gastric cancer and is expected to become a new target for the diagnosis and treatment of gastric cancer.

A multi-omics study to investigate the progression of the Correa pathway in gastric mucosa in the context of cirrhosis

BACKGROUND

Patients with liver cirrhosis (LC) are prone to gastric mucosa damage. We investigated the alterations of gastric mucosa in LC patients and their possible mechanisms through multi-omics.

RESULTS

We observed significant gastric mucosa microbial dysbiosis in LC subjects. Gastric mucosal microbiomes of LC patients contained a higher relative abundance of Streptococcus, Neisseria, Prevotella, Veillonella, and Porphyromonas, as well as a decreased abundance in Helicobacter and Achromobacter, than control subjects. The LC patients had higher levels of bile acids (BAs) and long-chain acylcarnitines (long-chain ACs) in serum. The gastric mucosal microbiomes were associated with serum levels of BAs and long-chain ACs. Transcriptome analyses of gastric mucosa revealed an upregulation of endothelial cell specific molecule 1, serpin family E member 1, mucin 2, caudal type homeobox 2, retinol binding protein 2, and defensin alpha 5 in LC group. Besides, the bile secretion signaling pathway was significantly upregulated in the LC group.

CONCLUSIONS

The alterations in the gastric mucosal microbiome and transcriptome of LC patients were identified. The impaired energy metabolism in gastric mucosal cells and bile acids might aggravate the inflammation of gastric mucosa and even exacerbate the Correa's cascade process. The gastric mucosal cells might reduce bile acid toxicity by bile acid efflux and detoxification.

TRIAL REGISTRATION

ChiCTR2100051070.

Multi‑omics‑based analysis of the regulatory mechanism of gypenosides on bile acids in hypercholesterolemic mice

Gynostemma pentaphyllum is a traditional medicine used by ethnic minorities in southwest China and gypenosides are currently recognized as essential components of the pharmacological substances of Gynostemma pentaphyllum, which are effective in regulating metabolic syndrome, especially in improving hepatic metabolic disorders. The present study randomly divided C57BL/6J male mice into the normal diet control group (ND), high-fat diet modeling group (HFD) and gypenosides group (GP). Liquid chromatography-mass spectrometry (UPLC-MS) was applied to quantify bile acids in the liver, bile and serum of mice in ND, HFD and GP groups. Liver proteins were extracted for trypsin hydrolysis and analyzed quantitatively using UPLC-MS + MS/MS (timsTOF Pro 2). Total mouse liver RNA was extracted from ND, HFD and GP groups respectively, cDNA sequencing libraries constructed and sequenced using BGISEQ-500 sequencing platform. The expression of key genes Fxr, Shp, Cyp7a1, Cyp8b1, and Abab11 was detected by RT-qPCR. The results showed that gypenosides accelerated free bile acid synthesis by promoting the expression of bile acid synthase CYP7A1 and CYP8B1 genes and proteins and accelerating the secretion of conjugated bile acids from the liver to the bile ducts. GP inhibited the bile acid transporters solute carrier organic anion transporter family member (SLCO) 1A1 and SLCO1A4, reducing the reabsorption of free bile acids and accelerating the excretion of free bile acids from the blood to the kidneys. It also promoted the metabolic enzyme CYP3A11, which accelerated the metabolism and clearance of bile acids, thus maintaining the balance of the bile acid internal environment.

Pharmacometabolomics of trabectedin in metastatic soft tissue sarcoma patients

Objective: Trabectedin is an anti-cancer drug commonly used for the treatment of patients with metastatic soft tissue sarcoma (mSTS). Despite its recognized efficacy, significant variability in pharmacological response has been observed among mSTS patients. To address this issue, this pharmacometabolomics study aimed to identify pre-dose plasma metabolomics signatures that can explain individual variations in trabectedin pharmacokinetics and overall clinical response to treatment. Methods: In this study, 40 mSTS patients treated with trabectedin administered by 24 h-intravenous infusion at a dose of 1.5 mg/m2 were enrolled. The patients' baseline plasma metabolomics profiles, which included derivatives of amino acids and bile acids, were analyzed using multiple reaction monitoring LC-MS/MS together with their pharmacokinetics profile of trabectedin. Multivariate Partial least squares regression and univariate statistical analyses were utilized to identify correlations between baseline metabolite concentrations and trabectedin pharmacokinetics, while Partial Least Squares-Discriminant Analysis was employed to evaluate associations with clinical response. Results: The multiple regression model, derived from the correlation between the AUC of trabectedin and pre-dose metabolomics, exhibited the best performance by incorporating cystathionine, hemoglobin, taurocholic acid, citrulline, and the phenylalanine/tyrosine ratio. This model demonstrated a bias of 4.6% and a precision of 17.4% in predicting drug AUC, effectively accounting for up to 70% of the inter-individual pharmacokinetic variability. Through the use of Partial least squares-Discriminant Analysis, cystathionine and hemoglobin were identified as specific metabolic signatures that effectively distinguish patients with stable disease from those with progressive disease. Conclusions: The findings from this study provide compelling evidence to support the utilization of pre-dose metabolomics in uncovering the underlying causes of pharmacokinetic variability of trabectedin, as well as facilitating the identification of patients who are most likely to benefit from this treatment.

The Farnesoid X Receptor as a Master Regulator of Hepatotoxicity

The nuclear receptor farnesoid X receptor (FXR, NR1H4) is a bile acid (BA) sensor that links the enterohepatic circuit that regulates BA metabolism and elimination to systemic lipid homeostasis. Furthermore, FXR represents a real guardian of the hepatic function, preserving, in a multifactorial fashion, the integrity and function of hepatocytes from chronic and acute insults. This review summarizes how FXR modulates the expression of pathway-specific as well as polyspecific transporters and enzymes, thereby acting at the interface of BA, lipid and drug metabolism, and influencing the onset and progression of hepatotoxicity of varying etiopathogeneses. Furthermore, this review article provides an overview of the advances and the clinical development of FXR agonists in the treatment of liver diseases.

Plasma metabolomic profiling reveals factors associated with dose-adjusted trough concentration of tacrolimus in liver transplant recipients

Inter- and intrapatient variability of tacrolimus exposure is a vital prognostic risk factor for the clinical outcome of liver transplantation. New factors or biomarkers characterizing tacrolimus disposition is essential for optimal dose prediction in recipients of liver transplant. The aim of the study was to identify potential plasma metabolites associated with the dose-adjusted trough concentration of tacrolimus in liver transplant recipients by using a global metabolomic approach. A total of 693 plasma samples were collected from 137 liver transplant recipients receiving tacrolimus and regular therapeutic drug monitoring. Untargeted metabolomic analysis was performed by ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry. Univariate and multivariate analyses with a mixed linear model were conducted, and the results showed that the dose-adjusted tacrolimus trough concentration was associated with 31 endogenous metabolites, including medium- and long-chain acylcarnitines such as stearoylcarnitine (β = 0.222, p = 0.001), microbiota-derived uremic retention solutes such as indolelactic acid (β = 0.194, p = 0.007), bile acids such as taurohyodeoxycholic acid (β = -0.056, p = 0.002), and steroid hormones such as testosterone (β = 0.099, p = 0.001). A multiple linear mixed model including 11 metabolites and clinical information was established with a suitable predictive performance (correlation coefficient based on fixed effects = 0.64 and correlation coefficient based on fixed and random effects = 0.78). These data demonstrated that microbiota-derived uremic retention solutes, bile acids, steroid hormones, and medium- and long-chain acylcarnitines were the main metabolites associated with the dose-adjusted trough concentration of tacrolimus in liver transplant recipients.

PPARα: A potential therapeutic target of cholestasis

The accumulation of bile acids in the liver leads to the development of cholestasis and hepatocyte injury. Nuclear receptors control the synthesis and transport of bile acids in the liver. Among them, the farnesoid X receptor (FXR) is the most common receptor studied in treating cholestasis. The activation of this receptor can reduce the amount of bile acid synthesis and decrease the bile acid content in the liver, alleviating cholestasis. Ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) have a FXR excitatory effect, but the unresponsiveness of some patients and the side effect of pruritus seriously affect the results of UDCA or OCA treatment. The activator of peroxisome proliferator-activated receptor alpha (PPARα) has emerged as a new target for controlling the synthesis and transport of bile acids during cholestasis. Moreover, the anti-inflammatory effect of PPARα can effectively reduce cholestatic liver injury, thereby improving patients’ physiological status. Here, we will focus on the function of PPARα and its involvement in the regulation of bile acid transport and metabolism. In addition, the anti-inflammatory effects of PPARα will be discussed in some detail. Finally, we will discuss the application of PPARα agonists for cholestatic liver disorders.

Valproate and Short-Chain Fatty Acids Activate Transcription of the Human Vitamin D Receptor Gene through a Proximal GC-Rich DNA Region Containing Two Putative Sp1 Binding Sites

The vitamin D receptor (VDR) mediates 1,25-dihydroxyvitamin D3 pleiotropic biological actions through transcription regulation of target genes. The expression levels of this ligand-activated nuclear receptor are regulated by multiple mechanisms both at transcriptional and post-transcriptional levels. Vitamin D3 is the natural VDR activator, but other molecules and signaling pathways have also been reported to regulate VDR expression and activity. In this study, we identify valproic acid (VPA) and natural short-chain fatty acids (SCFAs) as novel transcriptional activators of the human VDR (hVDR) gene. We further report a comprehensive characterization of VPA/SCFA-responsive elements in the 5' regulatory region of the hVDR gene. Two alternative promoter DNA regions (of 2.4 and 3.8 kb), as well as subsequent deletion fragments, were cloned in pGL4-LUC reporter vector. Transfection of these constructs in HepG2 and human Upcyte hepatocytes followed by reporter assays demonstrated that a region of 107 bp (from -107 to -1) upstream of the transcription start site in exon 1a is responsible for most of the increase in transcriptional activity in response to VPA/SCFAs. This short DNA region is GC-rich, does not contain an apparent TATA box, and includes two bona fide binding sites for the transcription factor Sp1. Our results substantiate the hypothesis that VPA and SCFAs facilitate the activity of Sp1 on novel Sp1 responsive elements in the hVDR gene, thus promoting VDR upregulation and signaling. Elevated hepatic VDR levels have been associated with liver steatosis and, therefore, our results may have clinical relevance in epileptic pediatric patients on VPA therapy. Our results could also be suggestive of VDR upregulation by SCFAs produced by gut microbiota.

Crosstalk of hepatocyte nuclear factor 4a and glucocorticoid receptor in the regulation of lipid metabolism in mice fed a high-fat-high-sugar diet

Background

Hepatocyte nuclear factor 4α (HNF4α) and glucocorticoid receptor (GR), master regulators of liver metabolism, are down-regulated in fatty liver diseases. The present study aimed to elucidate the role of down-regulation of HNF4α and GR in fatty liver and hyperlipidemia.

Methods

Adult mice with liver-specific heterozygote (HET) and knockout (KO) of HNF4α or GR were fed a high-fat-high-sugar diet (HFHS) for 15 days. Alterations in hepatic and circulating lipids were determined with analytical kits, and changes in hepatic mRNA and protein expression in these mice were quantified by real-time PCR and Western blotting. Serum and hepatic levels of bile acids were quantified by LC-MS/MS. The roles of HNF4α and GR in regulating hepatic gene expression were determined using luciferase reporter assays.

Results

Compared to HFHS-fed wildtype mice, HNF4α HET mice had down-regulation of lipid catabolic genes, induction of lipogenic genes, and increased hepatic and blood levels of lipids, whereas HNF4α KO mice had fatty liver but mild hypolipidemia, down-regulation of lipid-efflux genes, and induction of genes for uptake, synthesis, and storage of lipids. Serum levels of chenodeoxycholic acid and deoxycholic acid tended to be decreased in the HNF4α HET mice but dramatically increased in the HNF4α KO mice, which was associated with marked down-regulation of cytochrome P450 7a1, the rate-limiting enzyme for bile acid synthesis. Hepatic mRNA and protein expression of sterol-regulatory-element-binding protein-1 (SREBP-1), a master lipogenic regulator, was induced in HFHS-fed HNF4α HET mice. In reporter assays, HNF4α cooperated with the corepressor small heterodimer partner to potently inhibit the transactivation of mouse and human SREBP-1C promoter by liver X receptor. Hepatic nuclear GR proteins tended to be decreased in the HNF4α KO mice. HFHS-fed mice with liver-specific KO of GR had increased hepatic lipids and induction of SREBP-1C and PPARγ, which was associated with a marked decrease in hepatic levels of HNF4α proteins in these mice. In reporter assays, GR and HNF4α synergistically/additively induced lipid catabolic genes.

Conclusions

induction of lipid catabolic genes and suppression of lipogenic genes by HNF4α and GR may mediate the early resistance to HFHS-induced fatty liver and hyperlipidemia.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01654-6.

Dietary Inhibitors of CYP3A4 Are Revealed Using Virtual Screening by Using a New Deep-Learning Classifier

CYP3A4 is the main human enzyme responsible for phase I metabolism of dietary compounds, prescribed drugs and xenobiotics, steroid hormones, and bile acids. The inhibition of CYP3A4 activity might impair physiological mechanisms, including the endocrine system and response to drug admission. Here, we aimed to discover new CYP3A4 inhibitors from food and dietary supplements. A deep-learning model was built that classifies compounds as either an inhibitor or noninhibitor, with a high specificity of 0.997. We used this classifier to virtually screen ∼60,000 dietary compounds. Of the 115 identified potential inhibitors, only 31 were previously suggested. Many herbals, as predicted here, might cause impaired metabolism of drugs, and endogenous hormones and bile acids. Additionally, by applying Lipinski's rules of five, 17 compounds were also classified as potential intestine local inhibitors. New CYP3A4 inhibitors predicted by the model, bilobetin and picropodophyllin, were assayed in vitro.

Lithocholic Acid Activates Mas-Related G Protein-Coupled Receptors, Contributing to Itch in Mice

The present study focused on lithocholic acid (LCA), a secondary bile acid that contributes to cholestatic pruritus. Although recent studies have found that LCA acts on MAS-related G protein-coupled receptor family member X4 (MRGPRX4) in humans, it is unclear which subtypes of MRGPRs are activated by LCA in mice since there is no precise ortholog of human MRGPRX4 in the mouse genome. Using calcium imaging, we found that LCA could activate mouse Mrgpra1 when transiently expressed in HEK293T cells. Moreover, LCA similarly activates mouse Mrgprb2. Importantly, LCA-induced responses showed dose-dependent effects through Mrgpra1 and Mrgprb2. Moreover, treatment with QWF (an antagonist of Mrgpra1 and Mrgprb2), YM254890 (Gα_q inhibitor), and U73122 (an inhibitor of phospholipase C) significantly suppressed the LCA-induced responses, implying that the LCA-induced responses are indeed mediated by Mrgpra1 and Mrgprb2. Furthermore, LCA activated primary cultures of mouse sensory neurons and peritoneal mast cells, suggesting that Mrgpra1 and Mrgprb2 contribute to LCA-induced pruritus. However, acute injection of LCA did not induce noticeable differences in scratching behavior, implying that the pruritogenic role of LCA may be marginal in non-cholestatic conditions. In summary, the present study identified for the first time that LCA can activate Mrgpra1 and Mrgprb2. The current findings provide further insight into the similarities and differences between human and mouse MRGPR families, paving a way to understand the complex roles of these pruriceptors.

A metabolomic-based study on disturbance of bile acids metabolism induced by intratracheal instillation of nickel oxide nanoparticles in rats

Nickel oxide nanoparticles (Nano NiO) evoke hepatotoxicity, while whether it affects the hepatic metabolism remains unclear. The aim of this study was to explore the differential metabolites and their metabolic pathways in rat serum and to further verify the potential mechanism of bile acids' (BAs) metabolism dysregulation after Nano NiO exposure. Sixteen male Wistar rats were intratracheally instilled with Nano NiO (0.24 mg/kg body weight) twice a week for 9 weeks. Liquid chromatography/mass spectrometry was applied to filter the differentially expressed metabolites in rat serum. Western blot was employed to detect the protein contents. Twenty-one differential metabolites that associated with BAs, lipid and phospholipid metabolism pathways were identified in rat serum after Nano NiO exposure. Decreased cholic acid and deoxycholic acid implied that the BAs metabolism was disturbed. The nickel content increased in liver after Nano NiO exposure. The protein expression of cholesterol 7α-hydroxylase (CYP7A1) was down-regulated, and the bile salt export pump was up-regulated after Nano NiO administration in rat liver. Moreover, dehydroepiandrosterone sulphotransferase (SULT2A1) and cytochrome P450 (CYP) 3A4 were elevated in the exposure group. In conclusion, Nano NiO might trigger the disturbances of BAs, lipid and phospholipid metabolism pathways in rats. The diminished serum BAs induced by Nano NiO might be related to the down-regulation of synthetase and to the overexpression of transmembrane protein and detoxification enzymes in BAs metabolism.

The 1β-Hydroxy-Deoxycholic Acid to Deoxycholic Acid Urinary Metabolic Ratio: Toward a Phenotyping of CYP3A Using an Endogenous Marker?

In this study, we assessed the potential use of the 1β-hydroxy-deoxycholic acid (1β-OH-DCA) to deoxycholic acid (DCA) urinary metabolic ratio (UMR) as a CYP3A metric in ten male healthy volunteers. Midazolam (MDZ) 1 mg was administered orally at three sessions: alone (control session), after pre-treatment with fluvoxamine 50 mg (12 h and 2 h prior to MDZ administration), and voriconazole 400 mg (2 h before MDZ administration) (inhibition session), and after a 7-day pre-treatment with the inducer rifampicin 600 mg (induction session). The 1β-OH-DCA/DCA UMR was measured at each session, and correlations with MDZ metrics were established. At baseline, the 1β-OH-DCA/DCA UMR correlated significantly with oral MDZ clearance (r = 0.652, p = 0.041) and C_max (r = -0.652, p = 0.041). In addition, the modulation of CYP3A was reflected in the 1β-OH-DCA/DCA UMR after the intake of rifampicin (induction ratio = 11.4, p < 0.01). During the inhibition session, a non-significant 22% decrease in 1β-OH-DCA/DCA was observed (p = 0.275). This result could be explained by the short duration of CYP3A inhibitors intake fixed in our clinical trial. Additional studies, particularly involving CYP3A inhibition for a longer period and larger sample sizes, are needed to confirm the 1β-OH-DCA/DCA metric as a suitable CYP3A biomarker.

Overview of bile acid signaling in the cardiovascular system

Bile acids (BAs) are classically known to play a vital role in the metabolism of lipids and in absorption. It is now well established that BAs act as signaling molecules, activating different receptors (such as farnesoid X receptor, vitamin D receptor, Takeda G-protein-coupled receptor 5, sphingosine-1-phosphate, muscarinic receptors, and big potassium channels) and participating in the regulation of energy homeostasis and lipid and glucose metabolism. In addition, increased BAs can impair cardiovascular function in liver cirrhosis. Approximately 50% of patients with cirrhosis develop cirrhotic cardiomyopathy. Exposure to high concentrations of hydrophobic BAs has been shown to be related to adverse effects with respect to vascular tension, endothelial function, arrhythmias, coronary atherosclerotic heart disease, and heart failure. The BAs in the serum BA pool have relevant through their hydrophobicity, and the lipophilic BAs are more harmful to the heart. Interestingly, ursodeoxycholic acid is a hydrophilic BA, and it is used as a therapeutic drug to reverse and protect the harmful cardiac effects caused by hydrophobic elevated BAs. In order to elucidate the mechanism of BAs and cardiovascular function, abundant experiments have been conducted in vitro and in vivo. The aim of this review was to explore the mechanism of BAs in the cardiovascular system.

Pharmacokinetics of CamSA, a potential prophylactic compound against Clostridioides difficile infections

Clostridioides difficile infections (CDI) are the leading cause of nosocomial antibiotic-associated diarrhea. C. difficile produces dormant spores that serve as infectious agents. Bile salts in the gastrointestinal tract signal spores to germinate into toxin-producing cells. As spore germination is required for CDI onset, anti-germination compounds may serve as prophylactics. CamSA, a synthetic bile salt, was previously shown to inhibit C. difficile spore germination in vitro and in vivo. Unexpectedly, a single dose of CamSA was sufficient to offer multi-day protection from CDI in mice without any observable toxicity. To study this intriguing protection pattern, we examined the pharmacokinetic parameters of CamSA. CamSA was stable to the gut of antibiotic-treated mice but was extensively degraded by the microbiota of non-antibiotic-treated animals. Our data also suggest that CamSA's systemic absorption is minimal since it is retained primarily in the intestinal lumen and liver. CamSA shows weak interactions with CYP3A4, a P450 hepatic isozyme involved in drug metabolism and bile salt modification. Like other bile salts, CamSA seems to undergo enterohepatic circulation. We hypothesize that the cycling of CamSA between the liver and intestines serves as a slow-release mechanism that allows CamSA to be retained in the gastrointestinal tract for days. This model explains how a single CamSA dose can prevent murine CDI even though spores are present in the animal's intestine for up to four days post-challenge.

Effect of a Flaxseed Lignan Intervention on Circulating Bile Acids in a Placebo-Controlled Randomized, Crossover Trial

Plant lignans and their microbial metabolites, e.g., enterolactone (ENL), may affect bile acid (BA) metabolism through interaction with hepatic receptors. We evaluated the effects of a flaxseed lignan extract (50 mg/day secoisolariciresinol diglucoside) compared to a placebo for 60 days each on plasma BA concentrations in 46 healthy men and women (20-45 years) using samples from a completed randomized, crossover intervention. Twenty BA species were measured in fasting plasma using LC-MS. ENL was measured in 24-h urines by GC-MS. We tested for (a) effects of the intervention on BA concentrations overall and stratified by ENL excretion; and (b) cross-sectional associations between plasma BA and ENL. We also explored the overlap in bacterial metabolism at the genus level and conducted in vitro anaerobic incubations of stool with lignan substrate to identify genes that are enriched in response to lignan metabolism. There were no intervention effects, overall or stratified by ENL at FDR < 0.05. In the cross-sectional analysis, irrespective of treatment, five secondary BAs were associated with ENL excretion (FDR < 0.05). In vitro analyses showed positive associations between ENL production and bacterial gene expression of the bile acid-inducible gene cluster and hydroxysteroid dehydrogenases. These data suggest overlap in community bacterial metabolism of secondary BA and ENL.

Impairment of bile acid metabolism by perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in human HepaRG hepatoma cells

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are man-made chemicals that are used for the fabrication of many products with water- and dirt-repellent properties. The toxicological potential of both substances is currently under debate. In a recent Scientific Opinion, the European Food Safety Authority (EFSA) has identified increased serum total cholesterol levels in humans as one major critical effect being associated with exposure to PFOA or PFOS. In animal studies, both substances induced a decrease of serum cholesterol levels, and the underlying molecular mechanism(s) for these opposed effects are unclear so far. In the present study, we examined the impact of PFOA and PFOS on cholesterol homoeostasis in the human HepaRG cell line as a model for human hepatocytes. Cholesterol levels in HepaRG cells were not affected by PFOA or PFOS, but both substances strongly decreased synthesis of a number of bile acids. The expression of numerous genes whose products are involved in synthesis, metabolism and transport of cholesterol and bile acids was strongly affected by PFOA and PFOS at concentrations above 10 µM. Notably, both substances led to a strong decrease of CYP7A1, the key enzyme catalyzing the rate-limiting step in the synthesis of bile acids from cholesterol, both at the protein level and at the level of gene expression. Moreover, both substances led to a dilatation of bile canaliculi that are formed by differentiated HepaRG cells in vitro. Similar morphological changes are known to be induced by cholestatic agents in vivo. Thus, the strong impact of PFOA and PFOS on bile acid synthesis and bile canalicular morphology in our in vitro experiments may allow the notion that both substances have a cholestatic potential that is connected to the observed increased serum cholesterol levels in humans in epidemiological studies.

Rifampicin, not vitamin E, suppresses parenteral nutrition-associated liver disease development through the pregnane X receptor pathway in piglets

Infants receiving long-term parenteral nutrition (PN) develop PN-associated liver disease (PNALD). We previously (Ng K et al. JPEN J Parenter Enteral Nutr 40: 656-671, 2016. doi:10.1177/0148607114567900.) showed that PN containing soy-based lipid supplemented with vitamin E (α-tocopherol) prevents the development of PNALD. We hypothesize that this occurs via vitamin E activation of pregnane X receptor (PXR)-mediated pathways involved in bile acid metabolism. Neonatal piglets received PN for 14 days containing Intralipid (IL; soy-based lipid emulsion), IL supplemented with 12.6 mg·kg^-1·day^-1 vitamin E (VITE), or IL with 10 mg·kg^-1·day^-1 Rifadin IV (RIF), a PXR agonist. Pigs treated with IL and VITE, but not RIF, developed cholestasis and hyperbilirubinemia, markers of liver disease. The hepatic PXR target genes CYP3A29 and UGT1A6 increased during RIF treatment. RIF also modestly increased metabolism of chenodeoxycholic acid to the more hydrophilic bile acid hyocholic acid. Serum fibroblast growth factor (FGF)-19, a key regulator in suppressing hepatic bile acid synthesis, significantly increased in the RIF group. We conclude rifampicin modified markers of PNALD development by increased metabolism of bile acids and potentially suppressed bile acid synthesis. Vitamin E was ineffective at high lipid doses in preventing PNALD.NEW & NOTEWORTHY Intravenous vitamin E and rifampicin were administered to neonatal piglets receiving parenteral nutrition to determine their efficacy in reducing the progression of parenteral nutrition-associated liver disease (PNALD). Rifampicin increased serum FGF-19 concentrations and synthesis of the bile acid hyocholic acid which led to a reduction of PNALD parameters at 2 wk of administration. This result has potential clinical implications for the use of rifampicin as a safe and inexpensive treatment for short-term development of PNALD.

The influence of biological sex and sex hormones on bile acid synthesis and cholesterol homeostasis

Obesity and elevated serum lipids are associated with a threefold increase in the risk of developing atherosclerosis, a condition that underlies stroke, myocardial infarction, and sudden cardiac death. Strategies that aim to reduce serum cholesterol through modulation of liver enzymes have been successful in decreasing the risk of developing atherosclerosis and reducing mortality. Statins, which inhibit cholesterol biosynthesis in the liver, are considered among the most successful compounds developed for the treatment of cardiovascular disease. However, recent debate surrounding their effectiveness and safety prompts consideration of alternative cholesterol-lowering therapies, including increasing cholesterol catabolism through bile acid (BA) synthesis. Targeting the enzymes that convert cholesterol to BAs represents a promising alternative to other cholesterol-lowering approaches that treat atherosclerosis as well as fatty liver diseases and diabetes mellitus. Compounds that modify the activity of these pathways have been developed; however, there remains a lack of consideration of biological sex. This is necessary in light of strong evidence for sexual dimorphisms not only in the incidence and progression of the diseases they influence but also in the expression and activity of the proteins affected and in the manner in which men and women respond to drugs that modify lipid handling in the liver. A thorough understanding of the enzymes involved in cholesterol catabolism and modulation by biological sex is necessary to maximize their therapeutic potential.

Impact of CYP3A4*1G Polymorphism on Fentanyl Analgesia Assessed by Analgesia Nociception Index in Chinese Patients Undergoing Hysteroscopy

Background:

The clinical efficacy of fentanyl for pain control differs greatly across individuals. The purpose of this study was to investigate the impact of CYP3A4*1G polymorphism including wild-type homozygote (CYP3A4*1/*1, GG), mutant heterozygote (CYP3A4*1/*1G, GA), and mutant homozygote (CYP3A4*1G/*1G, AA) on fentanyl analgesia in Chinese patients undergoing hysteroscopy by the assessment of analgesia nociception index (ANI).

Methods:

A total of 200 gynecologic patients scheduled for elective hysteroscopy under general anesthesia at Peking University People's Hospital from May to December in 2017 were enrolled in this study. Venous blood was withdrawn for genotyping of CYP3A4*1G before operation. Fentanyl 1 μg/kg was administered preoperatively followed by target-controlled infusion of propofol for induction and maintenance. Intraoperative analgesic efficacy of fentanyl was assessed by ANI monitoring at T0 (entering room), T1 (cervical dilation), T2 (start of cervical aspiration), and T3 (end of cervical aspiration) time points. The duration of propofol infusion and total dosage of propofol were recorded as well.

Results:

The patients were divided into three groups according to CYP3A4*1G polymorphism, including 143 in GG group, 47 in GA group, and 10 in AA group. There was no significant difference in clinical demographics among three groups. The frequency of CYP3A4*1G variant alleles accounted for 16.8% and the distribution of variant alleles was consistent with Hardy–Weinberg equilibrium. Using a multilevel model, ANI values at T1 (63.81 ± 19.61), T2 (63.63 ± 17.82), and T3 (65.68 ± 17.79) were significantly lower than that at T0 (77.16 ± 12.93) in the study population (F = 23.50, P < 0.001), suggesting that higher levels of pain at T1, T2, and T3 than T0. Patients with GG genotype showed significantly lower ANI than those with GA or AA genotypes during hysteroscopy under the same dose of fentanyl.

Conclusion:

CYP3A4*1G polymorphism associated with the analgesic efficacy of intraoperative fentanyl in the patients undergoing hysteroscopy under general anesthesia.

Cell-printed 3D liver-on-a-chip possessing a liver microenvironment and biliary system

To overcome the drawbacks of in vitro liver testing during drug development, numerous liver-on-a-chip models have been developed. However, current liver-on-a-chip technologies are labor-intensive, lack extracellular matrix (ECM) essential for liver cells, and lack a biliary system essential for excreting bile acids, which contribute to intestinal digestion but are known to be toxic to hepatocytes. Therefore, fabrication methods for development of liver-on-a-chip models that overcome the above limitations are required. Cell-printing technology enables construction of complex 3D structures with multiple cell types and biomaterials. We used cell-printing to develop a 3D liver-on-a-chip with multiple cell types for co-culture of liver cells, liver decellularized ECM bioink for a 3D microenvironment, and vascular/biliary fluidic channels for creating vascular and biliary systems. A chip with a biliary fluidic channel induced better biliary system creation and liver-specific gene expression and functions compared to a chip without a biliary system. Further, the 3D liver-on-a-chip showed better functionalities than 2D or 3D cultures. The chip was evaluated using acetaminophen and it showed an effective drug response. In summary, our results demonstrate that the 3D liver-on-a-chip we developed is promising in vitro liver test platform for drug discovery.

Nuclear Receptor Metabolism of Bile Acids and Xenobiotics: A Coordinated Detoxification System with Impact on Health and Diseases

Structural and functional studies have provided numerous insights over the past years on how members of the nuclear hormone receptor superfamily tightly regulate the expression of drug-metabolizing enzymes and transporters. Besides the role of the farnesoid X receptor (FXR) in the transcriptional control of bile acid transport and metabolism, this review provides an overview on how this metabolic sensor prevents the accumulation of toxic byproducts derived from endogenous metabolites, as well as of exogenous chemicals, in coordination with the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Decrypting this network should provide cues to better understand how these metabolic nuclear receptors participate in physiologic and pathologic processes with potential validation as therapeutic targets in human disabilities and cancers.

The influences of cholecystectomy on the circadian rhythms of bile acids as well as the enterohepatic transporters and enzymes systems in mice

Bile acids (BAs), the most important endogenous and signaling molecules regulate the target transporters and enzymes at transcriptional level, participate in a wide variety of processes throughout the entire gastrointestinal tract to orchestrate homeostasis in vivo. BAs and their metabolism and transportation appear to follow the clear circadian rhythms, and they are recently proposed also as the potential chronobiological signals that can affect the molecular clock mechanism. Cholecystectomy are believed to affect the circadian rhythms of BAs and the relevant enterohepatic transporters and enzymes systems and their regulatory signaling pathways, for the reason that the circadian cycle of gallbladder filling and emptying play a pivotal role in controlling the flow of bile into the intestine and the enterohepatic circulation of BAs. Here, in the present study, the circadian rhythms about BAs concentration and composition and the mRNA expression of genes involved in BAs transportation, metabolism and regulation in liver and ileum of mice with or without gallbladder were evaluated. As a result, it has been found that, mice with gallbladder exhibited significant and distinct circadian oscillations in BAs concentration, mRNA expression of enterohepatic transporters and enzymes systems and farnesoid X receptor-mediated regulatory pathways both in liver and ileum during gallbladder emptying period (1:00 AM and 1:00 PM), despite food was restricted during these periods; the circadian rhythmicity of BAs pool and hepatic and ileal BAs diminished but the BAs composition had no significant alteration in liver and ileum after cholecystectomy as compared with sham-operated mice; in parallel to the alteration of BAs levels in liver and ileum after cholecystectomy, the day/night circadian oscillations in the mRNA expression of the relevant transporting and metabolic genes and the farnesoid X receptor signaling pathway-mediated “intestine-liver†regulatory axis also shifted. In conclusion, the BAs concentration and the corresponding genes exhibit significant circadian rhythms in mice with gallbladder, and the circadian oscillations of most of the investigation factors are flattened and altered following by cholecystectomy, which could mainly ascribe to the disappearance of the filling and emptying cycle of gallbladder and might result in pathological states or drug chronopharmacology alternation. We expect that this study would provide a cue for patients with cholecystectomy.

ABBREVIATIONS

Asbt: apical sodium-dependent bile acids transporter; AUC24h: area under the 24-hour BA concentration time curve; BAs: bile acids; Bsep: bile salt export pump; β-MCA: β-muricholic acid; CA: cholic acid; CDCA: chenodeoxycholic acid; Cyp3a11: cytochrome P450 3a11 (human CYP3A4); Cyp7a1: cholesterol 7α-hydroxylase cytochrome P450 7a1; DCA: deoxycholic acid; Fxr: farnesoid X receptor; Fgf15: fibroblast growth factor 15; G-: glycine conjugated bile acid; HDCA: hyodesoxycholic acid; LCA: lithocholic acid; Mrp2: multidrug resistance-associated protein 2; NDCA: demethylation deoxycholic acid; Ntcp: Na+-taurocholate co-transporting polypeptide; Oatp2: organic anion transporting polypeptide 2; Ostα/β: heterodimeric organic solute transporters alpha and beta; Shp: small heterodimer partner; T-: taurine conjugated bile acid; UDCA: ursodeoxycholic acid.

p53-mediated regulation of bile acid disposition attenuates cholic acid-induced cholestasis in mice

BACKGROUND AND PURPOSE

The tumour suppressor p53 is traditionally recognized as a surveillance molecule to preserve genome integrity. Recent studies have demonstrated that it contributes to metabolic diseases. Here, we investigated the role of p53 in the regulation of bile acid disposition and cholestasis.

EXPERIMENTAL APPROACH

The bile acid disposition-related gene expression profile affected by p53 activation was assessed in mouse primary hepatocytes with p53 depletion and in Trp53-null mice. Dual luciferase reporter assay was used to detect the transcriptional activities of target genes. Anticholestatic effects of p53 activator doxorubicin were investigated in a 0.5% cholic acid-fed mouse model of cholestasis. Changes in bile acids were evaluated using metabolomics analysis.

KEY RESULTS

Doxorubicin-mediated p53 activation induced Cyp2b10, Sult2a1 and Abcc2/3/4 expression in mice in vitro and in vivo. ABCC3 and CYP2B6 (human orthologue of Cyp2b10) were identified as direct p53 target genes. Doxorubicin attenuated cholic acid-induced cholestasis in mice, as demonstrated by shrunken gall bladder, decreased serum total bile acid and total bilirubin levels and alkaline phosphatase activity. Targeted metabolomics analysis revealed that doxorubicin enhanced the excretion of bile acid metabolites from serum and liver to intestine and faeces. Up-regulation of Cyp2b10, Sult2a1 and Abcc2/3/4 expression was further confirmed in cholestatic mice. Cholic acid-induced cholestatic injury was aggravated in p53-deficient mice and levels of bile acid in intestine and faeces were decreased.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest a novel role of p53 in promoting bile acid disposition and alleviating cholestatic syndrome, which provides a potential therapeutic target for cholestasis.

Chicken bile powder protects against α-naphthylisothiocyanate-induced cholestatic liver injury in mice

This study explored the effects of chicken bile powder (CBP), a 2000-year-old Chinese medicine, on α-naphthyl isothiocyanate (ANIT)-induced intrahepatic cholestasis in mice. CBP treatment for 14 days significantly ameliorated ANIT-induced changes in serum alanine aminotransferase, aspartate aminotransferase, bile acids, bilirubin, γ-glutamyl transpeptidase, alkaline phosphatase, and liver tissue morphology. Serum metabolomics showed changes in 24 metabolites in ANIT-exposed mice; 16 of these metabolites were reversed by CBP treatment via two main pathways (bile acid biosynthesis and arachidonic acid metabolism). Additionally, CBP administration markedly increased fecal and biliary bile acid excretion, and reduced total and hydrophobic bile acid levels in the livers of cholestatic mice. Moreover, CBP increased liver expression of bile acid efflux transporters and metabolic enzymes. It also attenuated ANIT-induced increases in hepatic nuclear factor-κB-mediated inflammatory signaling, and increased liver expression of the nuclear farnesoid X receptor (FXR) in cholestatic mice. CBP also activated FXR in vitro in HEK293T cells expressing mouse Na⁺-taurocholate cotransporting polypeptide. It did not ameliorate the ANIT-induced liver injuries in FXR-knockout mice. These results suggested that CBP provided protection from cholestatic liver injury by restoring bile acid homeostasis and reducing inflammation in a FXR-dependent manner.

Increased glycine-amidated hyocholic acid correlates to improved early weight loss after sleeve gastrectomy

BACKGROUND

Bile acids (BAs) are post-prandial hormones that play an important role in glucose and lipid homeostasis as well as energy expenditure. Total and glycine-amidated BAs increase after sleeve gastrectomy (SG) and correlate to improved metabolic disease. No specific bile acid subtype has been shown conclusively to mediate the weight loss effect. Therefore, the objective of this study was to prospectively evaluate the comprehensive changes in meal-stimulated BAs after SG and determine if a specific change in the BA profile correlates to the early weight loss response.

METHODS

Patients were prospectively enrolled at the University of Nebraska Medical Center who were undergoing a SG for treatment of morbid obesity. Primary and secondary plasma bile acids and their amidated (glycine, G-, or taurine, T-) subtypes were measured at fasting, 30 and 60 min after a liquid meal performed pre-op, and at 6 and 12 weeks post-op. Area under the curve (AUC) was calculated for the hour meal test for each bile acid subtype. BAs that were significantly increased post-op were correlated to body mass index (BMI) loss.

RESULTS

Total BA AUC was significantly increased at 6 (p < 0.01) and 12 weeks post-op (p < 0.01) compared to pre-operative values. The increase in total BA AUC was due to a statistically significant increase in G-BAs. Nine different BA AUC subtypes were significantly increased at both 6 and 12 weeks post-op. Increased total and G-chenodeoxycholic acid AUC was significantly correlated to the 6 week BMI loss (p = 0.03). Increased G-hyocholic acid was significantly correlated to increased weight loss at both 6 (p = 0.05) and 12 weeks (p = 0.006).

CONCLUSIONS

SG induced an early and persistent post-prandial surge in multiple bile acid subtypes. Increased G-hyocholic consistently correlated with greater early BMI loss. This study provides evidence for a role of BAs in the surgical weight loss response after SG.

A Comprehensive Evaluation of Steroid Metabolism in Women with Intrahepatic Cholestasis of Pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a common liver disorder, mostly occurring in the third trimester. ICP is defined as an elevation of serum bile acids, typically accompanied by pruritus and elevated activities of liver aminotransferases. ICP is caused by impaired biliary lipid secretion, in which endogenous steroids may play a key role. Although ICP is benign for the pregnant woman, it may be harmful for the fetus. We evaluated the differences between maternal circulating steroids measured by RIA (17-hydroxypregnenolone and its sulfate, 17-hydroxyprogesterone, and cortisol) and GC-MS (additional steroids), hepatic aminotransferases and bilirubin in women with ICP (n = 15, total bile acids (TBA) >8 μM) and corresponding controls (n = 17). An age-adjusted linear model, receiver-operating characteristics (ROC), and multivariate regression (a method of orthogonal projections to latent structure, OPLS) were used for data evaluation. While aminotransferases, conjugates of pregnanediols, 17-hydroxypregnenolone and 5β-androstane-3α,17β-diol were higher in ICP patients, 20α-dihydropregnenolone, 16α-hydroxy-steroids, sulfated 17-oxo-C19-steroids, and 5β-reduced steroids were lower. The OPLS model including steroids measured by GC-MS and RIA showed 93.3% sensitivity and 100% specificity, while the model including steroids measured by GC-MS in a single sample aliquot showed 93.3% sensitivity and 94.1% specificity. A composite index including ratios of sulfated 3α/β-hydroxy-5α/β-androstane-17-ones to conjugated 5α/β-pregnane-3α/β, 20α-diols discriminated with 93.3% specificity and 81.3% sensitivity (ROC analysis). These new data demonstrating altered steroidogenesis in ICP patients offer more detailed pathophysiological insights into the role of steroids in the development of ICP.

Association between Circulating Vitamin D Metabolites and Fecal Bile Acid Concentrations

Although hydrophobic bile acids have been demonstrated to exhibit cytotoxic and carcinogenic effects in the colorectum, ursodeoxycholic acid (UDCA) has been investigated as a potential chemopreventive agent. Vitamin D has been shown to play a role in both bile acid metabolism and in the development of colorectal neoplasia. Using a cross-sectional design, we sought to determine whether baseline circulating concentrations of the vitamin D metabolites 25(OH)D and 1,25(OH)2D were associated with baseline fecal bile acid concentrations in a trial of UDCA for the prevention of colorectal adenoma recurrence. We also prospectively evaluated whether vitamin D metabolite concentrations modified the effect of UDCA on adenoma recurrence. After adjustment for age, sex, BMI, physical activity, and calcium intake, adequate concentrations of 25(OH)D (≥30 ng/mL) were statistically significantly associated with reduced odds for high levels of total [OR, 0.61; 95% confidence interval (CI), 0.38-0.97], and primary (OR, 0.61; 95% CI, 0.38-0.96) bile acids, as well as individually with chenodeoxycholic acid (OR, 0.39; 95% CI, 0.24-0.63) and cholic acid (OR, 0.56; 95% CI, 0.36-0.90). No significant associations were observed for 1,25(OH)2D and high versus low fecal bile acid concentrations. In addition, neither 25(OH)D nor 1,25(OH)2D modified the effect of UDCA on colorectal adenoma recurrence. In conclusion, this is the first study to demonstrate an inverse relationship between circulating levels of 25(OH)D and primary fecal bile acid concentrations. These results support prior data demonstrating that vitamin D plays a key role in bile acid metabolism, and suggest a potential mechanism of action for 25(OH)D in colorectal cancer prevention. Cancer Prev Res; 9(7); 589-97. ©2016 AACR.

Screening of Drug Metabolizing Enzymes for the Ginsenoside Compound K In Vitro: An Efficient Anti-Cancer Substance Originating from Panax Ginseng

Ginsenoside compound K (CK), a rare ginsenoside originating from Panax Ginseng, has been found to possess unique pharmacological activities specifically as anti-cancers. However, the role of cytochrome P450s (CYPs) in the metabolism of CK is unclear. In this study, we screened the CYPs for the metabolism of CK in vitro using human liver microsomes (HLMs) or human recombinant CYPs. The results showed that CK inhibited the enzyme activities of CYP2C9 and CYP3A4 in the HLMs. The K_m and V_max values of CK were 84.20±21.92 μM and 0.28±0.04 nmol/mg protein/min, respectively, for the HLMs; 34.63±10.48 μM and 0.45±0.05 nmol/nmol P450/min, respectively, for CYP2C9; and 27.03±5.04 μM and 0.68±0.04 nmol/nmol P450/min, respectively, for CYP3A4. The IC₅₀ values were 16.00 μM and 9.83 μM, and K_i values were 14.92 μM and 11.42μM for CYP2C9 and CYP3A4, respectively. Other human CYP isoforms, including CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP2C19, showed minimal or no effect on CK metabolism. The results suggested that CK was a substrate and also inhibitors for both CYP2C9 and CYP3A4. Patients using CK in combination with therapeutic drugs that are substrates of CYP2C9 and CYP3A4 for different reasons should be careful, although the inhibiting potency of CK is much poorer than that of enzyme-specific inhibitors.

Bile Acid Metabolism and Signaling in Cholestasis, Inflammation, and Cancer

Bile acids are synthesized from cholesterol in the liver. Some cytochrome P450 (CYP) enzymes play key roles in bile acid synthesis. Bile acids are physiological detergent molecules, so are highly cytotoxic. They undergo enterohepatic circulation and play important roles in generating bile flow and facilitating biliary secretion of endogenous metabolites and xenobiotics and intestinal absorption of dietary fats and lipid-soluble vitamins. Bile acid synthesis, transport, and pool size are therefore tightly regulated under physiological conditions. In cholestasis, impaired bile flow leads to accumulation of bile acids in the liver, causing hepatocyte and biliary injury and inflammation. Chronic cholestasis is associated with fibrosis, cirrhosis, and eventually liver failure. Chronic cholestasis also increases the risk of developing hepatocellular or cholangiocellular carcinomas. Extensive research in the last two decades has shown that bile acids act as signaling molecules that regulate various cellular processes. The bile acid-activated nuclear receptors are ligand-activated transcriptional factors that play critical roles in the regulation of bile acid, drug, and xenobiotic metabolism. In cholestasis, these bile acid-activated receptors regulate a network of genes involved in bile acid synthesis, conjugation, transport, and metabolism to alleviate bile acid-induced inflammation and injury. Additionally, bile acids are known to regulate cell growth and proliferation, and altered bile acid levels in diseased conditions have been implicated in liver injury/regeneration and tumorigenesis. We will cover the mechanisms that regulate bile acid homeostasis and detoxification during cholestasis, and the roles of bile acids in the initiation and regulation of hepatic inflammation, regeneration, and carcinogenesis.