CYP8B1 downregulation mediates the metabolic effects of vertical sleeve gastrectomy in mice.

BACKGROUND AND AIMS: Although the benefits of vertical sleeve gastrectomy (VSG) surgery are well known, the molecular mechanisms by which VSG alleviates obesity and its complications remain unclear. We aim to determine the role of CYP8B1 (cytochrome P450, family 8, subfamily B, polypeptide 1) in mediating the metabolic benefits of VSG. APPROACH AND RESULTS: We found that expression of CYP8B1, a key enzyme in controlling the 12α-hydroxylated (12α-OH) bile acid (BA) to non-12α-OH BA ratio, was strongly downregulated after VSG. Using genetic mouse models of CYP8B1 overexpression, knockdown, and knockout, we demonstrated that overexpression of CYP8B1 dampened the metabolic improvements associated with VSG. In contrast, short hairpin RNA-mediated CYP8B1 knockdown improved metabolism similar to those observed after VSG. Cyp8b1 deficiency diminished the metabolic effects of VSG. Further, VSG-induced alterations to the 12α-OH/non-12α-OH BA ratio in the BA pool depended on CYP8B1 expression level. Consequently, intestinal lipid absorption was restricted, and the gut microbiota (GM) profile was altered. Fecal microbiota transplantation from wild type-VSG mice (vs. fecal microbiota transplantation from wild-type-sham mice) improved metabolism in recipient mice, while there were no differences between mice that received fecal microbiota transplantation from knockout-sham and knockout-VSG mice. CONCLUSIONS: CYP8B1 is a critical downstream target of VSG. Modulation of BA composition and gut microbiota profile by targeting CYP8B1 may provide novel insight into the development of therapies that noninvasively mimic bariatric surgery to treat obesity and its complications.

Pyridine-containing substrate analogs are restricted from accessing the human cytochrome P450 8B1 active site by tryptophan 281.

The human oxysterol 12α-hydroxylase cytochrome P450 8B1 (CYP8B1) is a validated drug target for both type 2 diabetes and nonalcoholic fatty liver disease, but effective selective inhibitors are not yet available. Herein, steroidal substrate-mimicking compounds with a pyridine ring appended to the C12 site of metabolism were designed as inhibitors, synthesized, and evaluated in terms of their functional and structural interactions with CYP8B1. While the pyridine nitrogen was intended to coordinate the CYP8B1 active site heme iron, none of these compounds elicited shifts in the CYP8B1 Soret absorbance consistent with this type of interaction. However, when CYP8B1 was cocrystallized with the pyridine-containing compound with the 3-keto-Δ4 steroid backbone most similar to the endogenous substrate, it was apparent that this ligand was bound in a channel leading to the active site, instead of near the heme iron. Inspection of this structure suggested that tryptophan 281 directly above the heme might restrict active site binding of potential inhibitors with this design. This hypothesis was supported when a CYP8B1 W281F mutation did allow all three compounds to coordinate the heme iron as designed. These results indicated that the design of next-generation CYP8B1 inhibitors should be compatible with the low-ceiling tryptophan immediately above the heme iron.

The structure and characterization of human cytochrome P450 8B1 supports future drug design for nonalcoholic fatty liver disease and diabetes.

Human cytochrome P450 8B1 (CYP8B1) is involved in conversion of cholesterol to bile acids. It hydroxylates the steroid ring at C12 to ultimately produce the bile acid cholic acid. Studies implicated this enzyme as a good drug target for nonalcoholic fatty liver disease and type 2 diabetes, but there are no selective inhibitors known for this enzyme and no structures to guide inhibitor development. Herein, the human CYP8B1 protein was generated and used to identify and characterize interactions with a series of azole inhibitors, which tend to be poorly selective P450 inhibitors. Structurally related miconazole, econazole, and tioconazole bound with submicromolar dissociation constants and were effective inhibitors of the native reaction. CYP8B was cocrystallized with S-tioconazole to yield the first X-ray structure. This inhibitor bound in the active site with its azole nitrogen coordinating the heme iron, consistent with inhibitor binding and inhibition assay data. Additionally, the CYP8B1 active site was compared with similar P450 enzymes to identify features that may facilitate the design of more selective inhibitors. Selective inhibitors should promote a better understanding of the role of CYP8B1 inhibition in normal physiology and disease states and provide a possible treatment for nonalcoholic fatty liver disease and type 2 diabetes.

Insulin Prevents Hypercholesterolemia by Suppressing 12α-Hydroxylated Bile Acids.

BACKGROUND: The risk of cardiovascular disease in type 1 diabetes remains extremely high, despite marked advances in blood glucose control and even the widespread use of cholesterol synthesis inhibitors. Thus, a deeper understanding of insulin regulation of cholesterol metabolism, and its disruption in type 1 diabetes, could reveal better treatment strategies. METHODS: To define the mechanisms by which insulin controls plasma cholesterol levels, we knocked down the insulin receptor, FoxO1, and the key bile acid synthesis enzyme, CYP8B1. We measured bile acid composition, cholesterol absorption, and plasma cholesterol. In parallel, we measured markers of cholesterol absorption and synthesis in humans with type 1 diabetes treated with ezetimibe and simvastatin in a double-blind crossover study. RESULTS: Mice with hepatic deletion of the insulin receptor showed marked increases in 12α-hydroxylated bile acids, cholesterol absorption, and plasma cholesterol. This phenotype was entirely reversed by hepatic deletion of FoxO1. FoxO1 is inhibited by insulin and required for the production of 12α-hydroxylated bile acids, which promote intestinal cholesterol absorption and suppress hepatic cholesterol synthesis. Knockdown of Cyp8b1 normalized 12α-hydroxylated bile acid levels and completely prevented hypercholesterolemia in mice with hepatic deletion of the insulin receptor (n=5-30), as well as mouse models of type 1 diabetes (n=5-22). In parallel, the cholesterol absorption inhibitor, ezetimibe, normalized cholesterol absorption and low-density lipoprotein cholesterol in patients with type 1 diabetes as well as, or better than, the cholesterol synthesis inhibitor, simvastatin (n=20). CONCLUSIONS: Insulin, by inhibiting FoxO1 in the liver, reduces 12α-hydroxylated bile acids, cholesterol absorption, and plasma cholesterol levels. Thus, type 1 diabetes leads to a unique set of derangements in cholesterol metabolism, with increased absorption rather than synthesis. These derangements are reversed by ezetimibe, but not statins, which are currently the first line of lipid-lowering treatment in type 1 diabetes. Taken together, these data suggest that a personalized approach to lipid lowering in type 1 diabetes may be more effective and highlight the need for further studies specifically in this group of patients.

Gut microbiota depletion aggravates bile acid-induced liver pathology in mice with a human-like bile acid composition.

Cyp2c70-deficient mice have a human-like bile acid (BA) composition due to their inability to convert chenodeoxycholic acid (CDCA) into rodent-specific muricholic acids (MCAs). However, the hydrophobic BA composition in these animals is associated with liver pathology. Although Cyp2c70-ablation has been shown to alter gut microbiome composition, the impact of gut bacteria on liver pathology in Cyp2c70-/- mice remains to be established. Therefore, we treated young-adult male and female wild-type (WT) and Cyp2c70-/- mice with antibiotics (AB) with broad specificity to deplete the gut microbiota and assessed the consequences on BA metabolism and liver pathology. Female Cyp2c70-/- mice did not tolerate AB treatment, necessitating premature termination of the experiment. Male Cyp2c70-/- mice did tolerate AB but showed markedly augmented liver pathology after 6 weeks of treatment. Dramatic downregulation of hepatic Cyp8b1 expression (-99%) caused a reduction in the proportions of 12α-hydroxylated BAs in the circulating BA pools of AB-treated male Cyp2c70-/- mice. Interestingly, the resulting increased BA hydrophobicity strongly correlated with various indicators of liver pathology. Moreover, genetic inactivation of Cyp8b1 in livers of male Cyp2c70-/- mice increased liver pathology, while addition of ursodeoxycholic acid to the diet prevented weight loss and liver pathology in AB-treated female Cyp2c70-/- mice. In conclusion, depletion of gut microbiota in Cyp2c70-/- mice aggravates liver pathology at least in part by increasing the hydrophobicity of the circulating BA pool. These findings highlight that the potential implications of AB administration to cholestatic patients should be evaluated in a systematic manner.

Atorvastatin protects against liver and vascular damage in a model of diet induced steatohepatitis by resetting FXR and GPBAR1 signaling.

Farnesoid-x-receptor (FXR) agonists, currently trialed in patients with non-alcoholic steatosis (NAFLD), worsen the pro-atherogenic lipid profile and might require a comedication with statin. Here we report that mice feed a high fat/high cholesterol diet (HFD) are protected from developing a pro-atherogenic lipid profile because their ability to dispose cholesterol through bile acids. This protective mechanism is mediated by suppression of FXR signaling in the liver by muricholic acids (MCAs) generated in mice from chenodeoxycholic acid (CDCA). In contrast to CDCA, MCAs are FXR antagonists and promote a CYP7A1-dependent increase of bile acids synthesis. In mice feed a HFD, the treatment with obeticholic acid, a clinical stage FXR agonist, failed to improve the liver histopathology while reduced Cyp7a1 and Cyp8b1 genes expression and bile acids synthesis and excretion. In contrast, treating mice with atorvastatin mitigated liver and vascular injury caused by the HFD while increased the bile acids synthesis and excretion. Atorvastatin increased the percentage of 7α-dehydroxylase expressing bacteria in the intestine promoting the formation of deoxycholic acid and litocholic acid, two GPBAR1 agonists, along with the expression of GPBAR1-regulated genes in the white adipose tissue and colon. In conclusion, present results highlight the central role of bile acids in regulating lipid and cholesterol metabolism in response to atorvastatin and provide explanations for limited efficacy of FXR agonists in the treatment of NAFLD.

Hepatocyte Nuclear Factor 4α Prevents the Steatosis-to-NASH Progression by Regulating p53 and Bile Acid Signaling (in mice).

BACKGROUND AND AIMS: Hepatocyte nuclear factor 4α (HNF4α) is highly enriched in the liver, but its role in the progression of nonalcoholic liver steatosis (NAFL) to NASH has not been elucidated. In this study, we investigated the effect of gain or loss of HNF4α function on the development and progression of NAFLD in mice. APPROACH AND RESULTS: Overexpression of human HNF4α protected against high-fat/cholesterol/fructose (HFCF) diet-induced steatohepatitis, whereas loss of Hnf4α had opposite effects. HNF4α prevented hepatic triglyceride accumulation by promoting hepatic triglyceride lipolysis, fatty acid oxidation, and VLDL secretion. Furthermore, HNF4α suppressed the progression of NAFL to NASH. Overexpression of human HNF4α inhibited HFCF diet-induced steatohepatitis in control mice but not in hepatocyte-specific p53-/- mice. In HFCF diet-fed mice lacking hepatic Hnf4α, recapitulation of hepatic expression of HNF4α targets cholesterol 7α-hydroxylase and sterol 12α-hydroxylase and normalized hepatic triglyceride levels and attenuated steatohepatitis. CONCLUSIONS: The current study indicates that HNF4α protects against diet-induced development and progression of NAFLD by coordinating the regulation of lipolytic, p53, and bile acid signaling pathways. Targeting hepatic HNF4α may be useful for treatment of NASH.

Reabsorption of bile acids regulated by FXR-OATP1A2 is the main factor for the formation of cholesterol gallstone.

The purpose of this study was to demonstrate the aberrant metabolism of bile acids in patients with cholesterol gallstone and explore for its underlying mechanisms. The composition of bile acids collected from the patients with cholelithiasis and the control individuals was analyzed by LC-MS. The expression of genes regulating the metabolism of bile acids was quantitatively determined by real-time PCR or Western blot analysis. Cholesterol saturation index of patients with gallstone was significantly higher than that of the controls. The concentrations of taurodeoxycholic acid and taurolithocholic acid in the bile of patients were significantly higher than that of the controls. When compared with the controls, it was remarkable in the patients that the mRNA expression of farnesoid X receptor (FXR) was lower, whereas that of organic anion transporting polypeptide (OATP1A2) was higher. However, the expressions of both mRNA and protein of cytochrome P-450 family 8 subfamily B member 1 (CYP8B1) did not differ between the patients and the controls. Although the protein level of CYP8B1 was significantly lower in the subjects with single nucleotide polymorphism (SNP) rs3732860(G), the composition of bile acids and the ratio of CA to CDCA remained unaltered in the patients with different SNP genotype of CYP8B1. In conclusion, the axis of FXR-OATP1A2 that physiologically regulated the reabsorption of bile acids might play an important role in the composition of bile acids and the development of gallstone. CYP8B1 gene was irrelevant to the altered composition of bile acids in patients with gallstone.NEW & NOTEWORTHY For the first time, our results indicate that the axis of farnesoid X receptor-organic anion transporter polypeptide 1A2 that physiologically regulates the reabsorption of bile acids might play an important role in the regulation of the composition of bile acids and make contribution to the development of cholelithiasis.

Epistane, an anabolic steroid used for recreational purposes, causes cholestasis with elevated levels of cholic acid conjugates, by upregulating bile acid synthesis (CYP8B1) and cross-talking with nuclear receptors in human hepatocytes.

Anabolic-androgenic steroids are testosterone derivatives, used by body-builders to increase muscle mass. Epistane (EPI) is an orally administered 17α-alkylated testosterone derivative with 2a-3a epithio ring. We identified four individuals who, after EPI consumption, developed long-lasting cholestasis. The bile acid (BA) profile of three patients was characterized, as well the molecular mechanisms involved in this pathology. The serum BA pool was increased from 14 to 61-fold, basically on account of primary conjugated BA (cholic acid (CA) conjugates), whereas secondary BA were very low. In in vitro experiments with cultured human hepatocytes, EPI caused the accumulation of glycoCA in the medium. Moreover, as low as 0.01 µM EPI upregulated the expression of key BA synthesis genes (CYP7A1, by 65% and CYP8B1, by 67%) and BA transporters (NTCP, OSTA and BSEP), and downregulated FGF19. EPI increased the uptake/accumulation of a fluorescent BA analogue in hepatocytes by 50-70%. Results also evidenced, that 40 µM EPI trans-activated the nuclear receptors LXR and PXR. More importantly, 0.01 µM EPI activated AR in hepatocytes, leading to an increase in the expression of CYP8B1. In samples from a human liver bank, we proved that the expression of AR was positively correlated with that of CYP8B1 in men. Taken together, we conclude that EPI could cause cholestasis by inducing BA synthesis and favouring BA accumulation in hepatocytes, at least in part by AR activation. We anticipate that the large phenotypic variability of BA synthesis enzymes and transport genes in man provide a putative explanation for the idiosyncratic nature of EPI-induced cholestasis.

FXR agonist GW4064 improves liver and intestinal pathology and alters bile acid metabolism in rats undergoing small intestinal resection.

Mortality associated with liver disease has been observed in patients with short bowel syndrome (SBS); however, its mechanism remains unclear, but bile acid (BA) dysmetabolism has been proposed as a possible cause. The farnesoid X receptor (FXR) is the key regulator of BA synthesis. Here, we showed that, in a rat model of short bowel resection associated with liver disease (SBR-ALD), the BA composition of hepatic tissues reflected a larger proportion of primary and secondary unconjugated BAs, whereas that of the colon contents and serum showed an increased ratio of secondary unconjugated BAs. Both hepatic and intestinal regulation of BA synthesis was characterized by a blunted hepatic FXR activation response. The mRNA expression levels of cholesterol 7a-hydroxylase (CYP7A1), sterol 12a-hydroxylase (CYP8B1), and sterol 27 hydroxylase (CYP27A1), the key enzymes in BA synthesis, were upregulated. After intervention with the FXR agonist GW4064, both the liver histology and serum transaminase activity were improved, which demonstrated the attenuation of SBR-ALD. The BA compositions of hepatic tissue, the colon contents, and serum recovered and were closer to those of the sham group. The expression levels of hepatic FXR increased, and its target genes were activated. Consistent with this, the expression levels of CYP7A1, CYP8B1, and CYP27A1 were downregulated. Ileum tissue FXR and its target genes were slightly elevated. This study showed that the FXR agonist GW4064 could correct BA dysmetabolism to alleviate hepatotoxicity in SBR animals. GW4064 intervention resulted in a decrease in fecal bile excretion and elevated plasma/hepatic conjugated BA levels. GW4064 increased the reabsorption of conjugated BAs by inducing apical sodium-dependent bile salt transporter expression in the ileum. Concomitantly, FXR activation in the presence of GW4064 decreased BA production by repressing the expression of key synthetases, including CYP7A1, CYP8B1, and CYP27A1. These findings provide a clinical research direction for the prevention of liver disease in patients with SBS.NEW & NOTEWORTHY This study assessed the impact of treatment with GW4064, a farnesoid X receptor agonist, on the development of short bowel resection (SBR) associated with liver disease in a rat model of SBR. GW4064 was able to correct bile acid dysmetabolism and alleviate hepatotoxicity in SBR animals.

Signatures of Relaxed Selection in the CYP8B1 Gene of Birds and Mammals.

The CYP8B1 gene is known to catalyse reactions that determine the ratio of primary bile salts and the loss of this gene has recently been linked to lack of cholic acid in the bile of naked-mole rats, elephants and manatees using forward genomics approaches. We screened the CYP8B1 gene sequence of more than 200 species and test for relaxation of selection along each terminal branch. The need for retaining a functional copy of the CYP8B1 gene is established by the presence of a conserved open reading frame across most species screened in this study. Interestingly, the dietary switch from bovid to cetacean species is accompanied by an exceptional ten amino acid extension at the C-terminal end through a single base frame-shift deletion. We also verify that the coding frame disrupting mutations previously reported in the elephant are correct, are shared by extinct Elephantimorpha species and coincide with the dietary switch to herbivory. Relaxation of selection in the CYP8B1 gene of the wombat (Vombatus ursinus) also corresponds to drastic change in diet. In summary, our forward genomics-based screen of bird and mammal species identifies recurrent changes in the selection landscape of the CYP8B1 gene concomitant with a change in dietary lipid content.

Conversion of chenodeoxycholic acid to cholic acid by human CYP8B1.

The human cytochrome P450 enzyme CYP8B1 is a crucial regulator of the balance of cholic acid (CA) and chenodeoxycholic acid (CDCA) in the liver. It was previously shown to catalyze the conversion of 7α-hydroxycholest-4-en-3-one, a CDCA precursor, to 7α,12α-dihydroxycholest-4-en-3-one, which is an intermediate of CA biosynthesis. In this study we demonstrate that CYP8B1 can also convert CDCA itself to CA. We also show that five derivatives of luciferin are metabolized by CYP8B1 and established a rapid and convenient inhibitor test system. In this way we were able to identify four new CYP8B1 inhibitors, which are aminobenzotriazole, exemestane, ketoconazole and letrozole.

Therapeutic modulation of the bile acid pool by Cyp8b1 knockdown protects against nonalcoholic fatty liver disease in mice.

Bile acids (BAs) are surfactant molecules that regulate the intestinal absorption of lipids. Thus, the modulation of BAs represents a potential therapy for nonalcoholic fatty liver disease (NAFLD), which is characterized by hepatic accumulation of fat and is a major cause of liver disease worldwide. Cyp8b1 is a critical modulator of the hydrophobicity index of the BA pool. As a therapeutic proof of concept, we aimed to determine the impact of Cyp8b1 inhibition in vivo on BA pool composition and as protection against NAFLD. Inhibition of Cyp8b1 expression in mice led to a remodeling of the BA pool, which altered its signaling properties and decreased intestinal fat absorption. In a model of cholesterol-induced NAFLD, Cyp8b1 knockdown significantly decreased steatosis and hepatic lipid content, which has been associated with an increase in fecal lipid and BA excretion. Moreover, inhibition of Cyp8b1 not only decreased hepatic lipid accumulation, but also resulted in the clearance of previously accumulated hepatic cholesterol, which led to a regression in hepatic steatosis. Taken together, our data demonstrate that Cyp8b1 inhibition is a viable therapeutic target of crucial interest for metabolic diseases, such as NAFLD.-Chevre, R., Trigueros-Motos, L., Castaño, D., Chua, T., Corlianò, M., Patankar, J. V., Sng, L., Sim, L., Juin, T. L., Carissimo, G., Ng, L. F. P., Yi, C. N. J., Eliathamby, C. C., Groen, A. K., Hayden, M. R., Singaraja, R. R. Therapeutic modulation of the bile acid pool by Cyp8b1 knockdown protects against nonalcoholic fatty liver disease in mice.

The Positive Effects of Grifola frondosa Heteropolysaccharide on NAFLD and Regulation of the Gut Microbiota.

: Non-alcoholic fatty liver disease (NAFLD) is a major public health problem in many countries. In this study, the ability of Grifola frondosa heteropolysaccharide (GFP) to ameliorate NAFLD was investigated in rats fed a high-fat diet (HFD). The molecular mechanisms modulating the expression of specific gene members related to lipid synthesis and conversion, cholesterol metabolism, and inflammation pathways were determined. The components of the intestinal microflora in rats were analyzed by high-throughput next-generation 16S rRNA gene sequencing. Supplementation with GFP significantly increased the proportions of Allobaculum, Bacteroides, and Bifidobacterium and decreased the proportions of Acetatifactor, Alistipes, Flavonifractor, Paraprevotella, and Oscillibacter. In addition, Alistipes, Flavonifractor, and Oscillibacter were shown to be significant cecal microbiota according to the Spearman's correlation test between the gut microbiota and biomedical assays (|r| > 0.7). Histological analysis and biomedical assays showed that GFP treatments could significantly protect against NAFLD. In addition, Alistipes, Flavonifractor, and Oscillibacter may play vital roles in the prevention of NAFLD. These results suggest that GFP could be used as a functional material to regulate the gut microbiota of NAFLD individuals.

TGR5 contributes to glucoregulatory improvements after vertical sleeve gastrectomy in mice.

OBJECTIVE: Vertical sleeve gastrectomy (VSG) produces high rates of type 2 diabetes remission; however, the mechanisms responsible remain incompletely defined. VSG increases circulating bile acid concentrations and bile acid signalling through TGR5 improves glucose homeostasis. Therefore, we investigated the role of TGR5 signalling in mediating the glucoregulatory benefits of VSG. DESIGN: VSG or sham surgery was performed in high-fat-fed male Tgr5+/+ (wild type) and Tgr5-/- (knockout) littermates. Sham-operated mice were fed ad libitum or food restricted to match their body weight to VSG-operated mice. Body weight, food intake, energy expenditure, insulin signalling and circulating bile acid profiles were measured and oral glucose tolerance testing, islet immunohistochemistry and gut microbial profiling were performed. RESULTS: VSG decreased food intake and body weight, increased energy expenditure and circulating bile acid concentrations, improved fasting glycaemia, glucose tolerance and glucose-stimulated insulin secretion, enhanced nutrient-stimulated glucagon-like peptide 1 secretion and produced favourable shifts in gut microbial populations in both genotypes. However, the body weight-independent improvements in fasting glycaemia, glucose tolerance, hepatic insulin signalling, hepatic inflammation and islet morphology after VSG were attenuated in Tgr5-/- relative to Tgr5+/+ mice. Furthermore, VSG produced metabolically favourable alterations in circulating bile acid profiles that were blunted in Tgr5-/- relative to Tgr5+/+ mice. TGR5-dependent regulation of hepatic Cyp8b1 expression may have contributed to TGR5-mediated shifts in the circulating bile acid pool after VSG. CONCLUSIONS: These results suggest that TGR5 contributes to the glucoregulatory benefits of VSG surgery by promoting metabolically favourable shifts in the circulating bile acid pool.

Bile Acids and the Potential Role in Primary Biliary Cirrhosis.

BACKGROUND: Bile acids (BAs) play a potential role in regulating the whole-body metabolic homeostasis via the interaction with gut microbiome and the signal transduction as messengers, which establish a link between the primary biliary cirrhosis (PBC) and gut microbiome in many aspects, particularly with regard to the immune system of the body. PBC, as a chronic cholestatic liver disease characterised by the destruction of small intrahepatic bile ducts, causes fibrosis and potential cirrhosis without efficient therapies. SUMMARY: Recent researches show BAs can induce the differentiation of hepatic stellate cells, suggesting that it may serve as a novel therapy to resist, even changeover the irreversible liver cirrhosis in PBC. Key Messages: In this review, we conclude and provide information on the possible mechanism of pleiotropic BAs in homeostasis of the gut microbiome and liver regeneration, and hope to broaden the therapy of PBC and promote the relevant drugs' development.

Protective Effects of Alisol B 23-Acetate Via Farnesoid X Receptor-Mediated Regulation of Transporters and Enzymes in Estrogen-Induced Cholestatic Liver Injury in Mice.

PURPOSE: To investigate protective effects of alisol B 23-acetate (AB23A) against hepatotoxity and cholestasis induced by 17α-ethinylestradiol (EE) in association with farnesoid X receptor (FXR) activation in vivo and in vitro. METHODS: The cholestatic liver injury model was established by subcutaneous injections of EE in C57BL/6 mice. Serum biomarkers, bile flow assay and H&E staining were used to identify the amelioration of cholestasis after AB23A treatment. Mice primary hepatocytes culture, gene silencing experiment, real-time PCR and Western blot assay were used to elucidate the mechanisms underlying AB23A hepatoprotection. RESULTS: AB23A treatment protected against liver injury induced by EE through increasing hepatic efflux and reducing uptake of bile acid via an induction in efflux transporters (Bsep and Mrp2) and an inhibition in hepatic uptake transporter (Ntcp) expression. AB23A also reduced bile acid synthesis through repressing Cyp7a1 and Cyp8b1, and increased bile acid metabolism through an induction in gene expression of Sult2a1. We further demonstrated that the changes in transporters and enzymes, as well as ameliorative liver histology in AB23A-treated mice were abrogated by FXR antagonist guggulsterone in vivo and were abrogated after FXR was silenced in vitro. CONCLUSIONS: AB23A produces protective effects against EE-induced cholestasis, due to FXR-mediated gene regulation.

Synergic hypocholesterolaemic effect of n-3 PUFA and oestrogen by modulation of hepatic cholesterol metabolism in female rats.

n-3 PUFA such as EPA and DHA as well as oestrogen have been reported to decrease blood levels of cholesterol, but their underlying mechanism is unclear. The purpose of this study was to determine the effects of the combination of n-3 PUFA supplementation and oestrogen injection on hepatic cholesterol metabolism. Rats were fed a modified AIN-93G diet with 0, 1 or 2 % n-3 PUFA (EPA+DHA) relative to the total energy intake for 12 weeks. Rats were surgically ovariectomised at week 8, and, after 1-week recovery, rats were injected with 17ß-oestradiol-3-benzoate (E2) or maize oil for the last 3 weeks. Supplementation with n-3 PUFA and E2 injection significantly increased the ratio of the hepatic expression of phosphorylated AMP activated protein kinase (p-AMPK):AMP activated protein kinase (AMPK) and decreased sterol regulatory element-binding protein-2, 3-hydroxy-3-methylglutaryl coenzyme A reductase and proprotein convertase subtilisin/kexin type 9. Supplementation with n-3 PUFA increased hepatic expression of cholesterol 7α-hydroxylase (CYP7A1), sterol 12α-hydroxylase (CYP8B1) and sterol 27-hydroxylase (CYP27A1); however, E2 injection decreased CYP7A1 and CYP8B1 but not CYP27A1. Additionally, E2 injection increased hepatic expression of oestrogen receptor-α and ß. In conclusion, n-3 PUFA supplementation and E2 injection had synergic hypocholesterolaemic effects by down-regulating hepatic cholesterol synthesis (n-3 PUFA and oestrogen) and up-regulating bile acid synthesis (n-3 PUFA) in ovariectomised rats.

Muricholic bile acids are potent regulators of bile acid synthesis via a positive feedback mechanism.

OBJECTIVE: Bile acid (BA) synthesis is regulated by negative feedback end-product inhibition, initiated by farnesoid X receptors (FXRs) in liver and gut. Studies on cholic acid (CA)-free Cyp8b1(-/-) mice have concluded that CA is a potent suppressor of BA synthesis. Cyp8b1(-/-) mice have increased BA synthesis and an enlarged BA pool, a phenotype shared with bile-duct-ligated, antibiotics-administered and with germ-free mice. Studies on such mice have concluded BA synthesis is induced due to reduced hormonal signalling by fibroblast growth factor (FGF)15 from intestine to liver. A mutual finding in these models is that potent FXR-agonistic BAs are reduced. We hypothesized that the absence of the potent FXR agonist deoxycholic acid (DCA) may be important for the induction of BA synthesis in these situations. DESIGN: Two of these models were investigated, antibiotic treatment and Cyp8b1(-/-) mice and their combination. Secondary BA formation was inhibited by ampicillin (AMP) given to wild-type and Cyp8b1(-/-) mice. We then administered CA, chenodeoxycholic acid (CDCA) or DCA to AMP-treated Cyp8b1(-/-) mice. RESULTS: Our data show that the phenotype of AMP-treated wild-type mice resembles that of Cyp8b1(-/-) mice with fourfold induced Cyp7a1 expression, increased intestinal apical sodium-dependent BA transporter expression and increased hepatic BA levels. We also show that reductions in the FXR-agonistic BAs CDCA, CA, DCA or lithocholic acid cannot explain this phenotype; instead, it is likely due to increases in levels of α- and ß-muricholic BAs and ursodeoxycholic acid, three FXR-antagonistic BAs. CONCLUSIONS: Our findings reveal a potent positive feedback mechanism for regulation of BA synthesis in mice that appears to be sufficient without endocrine effects of FGF15 on Cyp7a1. This mechanism will be fundamental in understanding BA metabolism in both mice and humans.

Decreased bile-acid synthesis in livers of hepatocyte-conditional NADPH-cytochrome P450 reductase-null mice results in increased bile acids in serum.

NADPH-cytochrome P450 reductase (Cpr) is essential for the function of microsomal cytochrome P450 monooxygenases (P450), including those P450s involved in bile acid (BA) synthesis. Mice with hepatocyte-specific deletion of NADPH-cytochrome P450 reductase (H-Cpr-null) have been engineered to understand the in vivo function of hepatic P450s in the metabolism of xenobiotics and endogenous compounds. However, the impact of hepatic Cpr on BA homeostasis is not clear. The present study revealed that H-Cpr-null mice had a 60% decrease in total BA concentration in liver, whereas the total BA concentration in serum was almost doubled. The decreased level of cholic acid (CA) in both serum and livers of H-Cpr-null mice is likely due to diminished enzyme activity of Cyp8b1 that is essential for CA biosynthesis. Feedback mechanisms responsible for the reduced liver BA concentrations and/or increased serum BA concentrations in H-Cpr-null mice included the following: 1) enhanced alternative BA synthesis pathway, as evidenced by the fact that classic BA synthesis is diminished but chenodeoxycholic acid still increases in both serum and livers of H-Cpr-null mice; 2) inhibition of farnesoid X receptor activation, which increased the mRNA of Cyp7a1 and 8b1; 3) induction of intestinal BA transporters to facilitate BA absorption from the intestine to the circulation; 4) induction of hepatic multidrug resistance-associated protein transporters to increase BA efflux from the liver to blood; and 5) increased generation of secondary BAs. In summary, the present study reveals an important contribution of the alternative BA synthesis pathway and BA transporters in regulating BA concentrations in H-Cpr-null mice.