Picroside II protects against cholestatic liver injury possibly through activation of farnesoid X receptor

BackgroudCholestasis, accompanied by the accumulation of bile acids in body, may ultimately cause liver failure and cirrhosis. There have been limited therapies for cholesteric disorders. Therefore, development of appropriate therapeutic drugs for cholestasis is required. Picroside II is a bioactive component isolated from Picrorhiza scrophulariiflora Pennell, its mechanistic contributions to the anti-cholestasis effect have not been fully elucidated, especially the role of picroside II on bile acid homeostasis via nuclear receptors remains unclear.PurposeThis study was designed to investigate the hepatoprotective effect of picroside II against alpha-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury and elucidate the mechanisms in vivo and in vitro.MethodsThe ANIT-induced cholestatic mouse model was used with or without picroside II treatment. Serum and bile biochemical indicators, as well as liver histopathological changes were examined. siRNA, Dual-luciferase reporter, quantitative real-time PCR and Western blot assay were used to demonstrate the farnesoid X receptor (FXR) pathway in the anti-cholestasis effects of picroside II in vivo and in vitro.ResultsPicroside II exerted hepatoprotective effect against ANIT-induced cholestasis by impaired hepatic function and tissue damage. Picroside II increased bile acid efflux transporter bile salt export pump (Bsep), uptake transporter sodium taurocholate cotransporting polypeptide (Ntcp), and bile acid metabolizing enzymes sulfate transferase 2a1 (Sult2a1) and UDP-glucuronosyltransferase 1a1 (Ugt1a1), whereas decreased the bile acid synthesis enzymes cholesterol 7α-hydroxylase (Cyp7a1) and oxysterol 12α-hydroxylase (Cyp8b1). In addition, expression of FXR and the target gene Bsep was increased, whereas aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor alpha (PPARα) and their corresponding target genes were not significantly influenced by picroside II under cholestatic conditions. Furthermore, regulation of transporters and enzymes involved in bile acid homeostasis by picroside II were abrogated by FXR silencing in mouse primary cultured hepatocytes. Dual-luciferase reporter assay performed in HepG2 cells demonstrated FXR activation by picroside II.ConclusionOur findings demonstrate that picroside II exerts protective effect on ANIT-induced cholestasis possibly through FXR activation that regulates the transporters and enzymes involved in bile acid homeostasis. Picroside II might be an effective approach for the prevention and treatment of cholestatic liver diseases.     

Activation of farnesoid X receptor attenuates hepatic injury in a murine model of alcoholic liver disease

Alcoholic liver disease (ALD) is a common cause of advanced liver disease, and considered as a major risk factor of morbidity and mortality worldwide. Hepatic cholestasis is a pathophysiological feature observed in all stages of ALD. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily, and plays an essential role in the regulation of bile acid, lipid and glucose homeostasis. However, the role of FXR in the pathogenesis and progression of ALD remains largely unknown. Mice were fed Lieber-DeCarli ethanol diet or an isocaloric control diet. We used a specific agonist of FXR WAY-362450 to study the effect of pharmacological activation of FXR in alcoholic liver disease. In this study, we demonstrated that FXR activity was impaired by chronic ethanol ingestion in a murine model of ALD. Activation of FXR by specific agonist WAY-362450 protected mice from the development of ALD. We also found that WAY-362450 treatment rescued FXR activity, suppressed ethanol-induced Cyp2e1 up-regulation and attenuated oxidative stress in liver. Our results highlight a key role of FXR in the modulation of ALD development, and propose specific FXR agonists for the treatment of ALD patients.     

Metabolomics study of the hepatoprotective effect of Phellinus igniarius in chronic ethanol-induced liver injury mice using UPLC-Q/TOF-MS combined with ingenuity pathway analysis

BackgroundPhellinus igniarius (L.) Quèl as a potential medicinal mushroom possesses multiple biological activities including hepatoprotection, but the hepatoprotective mechanism is not clear.PurposeTo elucidate the hepatoprotective effect and potential target of P. igniarius.MethodsThe male C57BL/6 mice were fed with the Lieber–DeCarli diet containing alcohol or isocaloric maltose dextrin as control diet with or without P. igniarius decoction (PID) in the dosage of 0.65 g/kg and 2.6 g/kg. The levels of serum biomarkers were detected by an automatic biochemistry analyser. The histopathological changes of liver were observed by hematoxylin and eosin (H&E) staining. Ultra performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-Q/TOF-MS) was applied for investigating the dynamic changes of serum metabolites in chronic ethanol-induced liver injury mice and after treatment with PID. Ingenuity pathway analysis (IPA) was employed to identify the potential target of PID.ResultsPID could significantly reduce the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG) and total bile acid (TBA) in serum and improved hepatic steatosis and inflammation. In terms of metabolism, a total of 36 serum differential metabolites were identified, and PID intervention regulated 24 of them, involving the key metabolic pathways such as the biosynthesis of unsaturated fatty acids, primary bile acid biosynthesis, glycerophospholipid metabolism, fatty acids biosynthesis, ether lipid metabolism and arachidonic acid metabolism. On the mechanism, IPA showed that farnesol X receptor (FXR) was the major potential target for PID, and PID could improve chronic alcohol intake induced by the inhibition of mRNA expression of FXR in the liver and the activation of mRNA expression of FXR in the intestine in mice.ConclusionThe present study for the first time systematically illustrated the hepatoprotective effect of P. igniarius and preliminarily explored its potential target FXR. P. igniarius might be exploited as a promising therapeutic option for alcoholic liver injury.     

Dolomiaea souliei ethyl acetate extract protected against α-naphthylisothiocyanate-induced acute intrahepatic cholestasis through regulation of farnesoid x receptor-mediated bile acid metabolism

BackgroundCholestasis is characterized by accumulation of bile components in liver and systemic circulation. Restoration of bile acid homeostasis via activating farnesoid x receptor (FXR) is a promising strategy for the treatment of cholestasis. FXR-SHP (small heterodimer partner) axis plays an important role in maintaining bile acid homeostasis.PurposeTo investigate the anti-cholestasis effect of Dolomiaea souliei (Franch.) C.Shih (D. souliei) and clarify its underlying mechanism against α-naphthylisothiocyanate (ANIT) induced acute intrahepatic cholestasis.MethodsANIT-induced Sprague-Dawley rats were employed to investigate the anti-cholestasis effect of D. souliei ethyl acetate extract (DSE). Ursodeoxycholic acid (UDCA) was used as positive control. Bile flow and blood biochemical parameters were measured. Liver histopathological examination was conducted via hematoxylin-eosin staining. Western blot analysis was carried out to evaluate the protein levels related to bile acids metabolism and inflammation. The interactions between FXR and costunolide or dehydrocostus lactone, were conducted by molecular docking experiments. The effect of costunolide and dehydrocostus lactone on aspartate aminotransferase (AST), alanine aminotransferase (ALT) levels and FXR expression were also evaluated using guggulsterone-induced L02 cells.ResultsDSE could promote bile excretions and protect against ANIT-induced liver damage in cholestasis rats. Protein levels of FXR, SHP, Na⁺/taurocholate cotransporter (NTCP), bile salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2) were increased and the expressions of cholesterol 7α-hydroxylase (CYP7A1) and sterol 27-hydroxylase (CYP27A1) were decreased by DSE. Meanwhile, the anti-inflammatory factors, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6) were also significantly increased, and the pro-inflammatory factor, interleukin-10 (IL-10), was significantly decreased in rats of DSE groups. Molecular docking revealed that costunolide and dehydrocostus lactone could be well docked into the FXR protein molecule, and hydrophobic interactions played the main function. Costunolide could reverse the increased AST and ALT levels and increase the FXR expression in guggulsterone-induced L02 cells.ConclusionDSE had an anti-cholestasis effect by activating FXR-SHP axis, inhibiting synthesis of bile acid, and increasing bile secretion, together with inflammatory response and improving liver injury. Costunolide may be the main active component. This study provided a potential therapeutic mechanism for D. souliei as an anti-cholestasis medicine in the treatment of cholestasis liver diseases.     

A potential role of GW4064 to inhibit gut bacterial overgrowth by activating FXR in suppression of ethanol-induced liver injury

Hepatic parenchymal and nonparenchymal cells are highly susceptible to ethanol and its metabolites, and excessive alcohol consumption results in damage to the liver. Ethanol induces an increased prevalence for bacterial overgrowth in the small intestine and translocation of endotoxin into the portal blood. Some studies have pointed to a role for activation of Kupffer cells by gut bacteria-derived endotoxin as a primary event in mechanisms of alcoholic liver injury (ALD). GW4064, a potent farnesoid X receptor (FXR) agonist, has been developed as a hepatoprotective agent, and has been used in animal models of a variety of liver diseases. At the same time, previous experimental results showed that BAs and GW4064 inhibit bacterial overgrowth in the small intestine. It is logical to postulate that GW4064 may control or alleviate the ethanol-induced liver injury through inhibiting gut bacterial overgrowth. GW4064 activates FXR, which induces the expression of several genes with potential functions in mucosal defense to prevent intestinal bacteria overgrowth and translocation into the circulation induced by ethanol, and then will alleviate ethanol-induced liver injury. The hypothesis will provide the brand-new direction that we may prevent and treat ALD by using GW4064 through activating FXR to control gut bacteria overgrowth.     

Coordinated induction of bile acid detoxification and alternative elimination in mice: role of FXR-regulated organic solute transporter-alpha/beta in the adaptive response to bile acids

The bile acid receptor farnesoid X receptor (FXR) is a key regulator of hepatic defense mechanisms against bile acids. A comprehensive study addressing the role of FXR in the coordinated regulation of adaptive mechanisms including biosynthesis, metabolism, and alternative export together with their functional significance is lacking. We therefore fed FXR knockout (FXR(-/-)) mice with cholic acid (CA) and ursodeoxycholic acid (UDCA). Bile acid synthesis and hydroxylation were assessed by real-time RT-PCR for cytochrome P-450 (Cyp)7a1, Cyp3a11, and Cyp2b10 and mass spectrometry-gas chromatography for determination of bile acid composition. Expression of the export systems multidrug resistance proteins (Mrp)4-6 in the liver and kidney and the recently identified basoalteral bile acid transporter, organic solute transporter (Ost-alpha/Ost-beta), in the liver, kidney, and intestine was also investigated. CA and UDCA repressed Cyp7a1 in FXR(+/+) mice and to lesser extents in FXR(-/-) mice and induced Cyp3a11 and Cyp2b10 independent of FXR. CA and UDCA were hydroxylated in both genotypes. CA induced Ost-alpha/Ost-beta in the liver, kidney, and ileum in FXR(+/+) but not FXR(-/-) mice, whereas UDCA had only minor effects. Mrp4 induction in the liver and kidney correlated with bile acid levels and was observed in UDCA-fed and CA-fed FXR(-/-) animals but not in CA-fed FXR(+/+) animals. Mrp5/6 remained unaffected by bile acid treatment. In conclusion, we identified Ost-alpha/Ost-beta as a novel FXR target. Absent Ost-alpha/Ost-beta induction in CA-fed FXR(-/-) animals may contribute to increased liver injury in these animals. The induction of bile acid hydroxylation and Mrp4 was independent of FXR but could not counteract liver toxicity sufficiently. Limited effects of UDCA on Ost-alpha/Ost-beta may jeopardize its therapeutic efficacy.     

Dehydrodiconiferyl alcohol,a lignan from Herpetospermum pedunculosum,alleviates cholestasis by activating pathways associated with the farnesoid X receptor

BackgroundIn our previous study, we demonstrated the hepatoprotective effect of Herpetospermum pedunculosum in cholestatic rats. A bioassay-guided study also led to the identification and isolation of a lignan, dihydrodiconiferyl alcohol (DA) from the seeds of H. pedunculosum.PurposeTo investigate whether DA could alleviate cholestasis and determine the mechanisms underlying such action.MethodsMale Sprague-Dawley (SD) rats were administered with DA (10, 20 or 40 mg/kg) intragastrically once daily for 7 days prior to treatment with α-naphthylisothiocyanate (ANIT) (60 mg/kg). We then evaluated the levels of a range of serum indicators, determined bile flow, and carried out histopathological analyses. Western blotting was then used to investigate the levels of inflammatory mediators and the Farnesoid X Receptor (FXR), proteins involved in the downstream biosynthesis of bile acids, and a range of transport proteins. Molecular docking was used to simulate the interaction between DA and FXR. Cell viability of human hepatocytes (L-02) cells was determined by MTT. Then, we treated guggulsterone-inhibited L-02 cells, Si-FXR L-02 cells, and FXR-overexpression cells with the FXR agonist GW4064 (6 μM) or DA (25, 50 and 100 μM) for 24 h before detecting gene and protein expression by RT-PCR and western blotting, respectively.ResultsDA significantly attenuated ANIT-induced cholestasis in SD rats by reducing liver function indicators in the serum, increasing bile flow, improving the recovery of histopathological injuries in the liver, and by alleviating pro-inflammatory cytokines in the liver. DA also increased the expression levels of FXR and altered the levels of downstream proteins in the liver tissues, thus indicating that DA might alleviate cholestasis by regulating the FXR. Molecular docking simulations predicted that DA was as an agonist of FXR. In vitro mechanical studies further showed that DA increased the mRNA and protein expression levels of FXR, Small Heterodimer Partner 1/2, Bile Salt Export Pump, Multidrug Resistance-associated Protein 2, and Na+/taurocholate Co-transporting Polypeptide, in both guggulsterone-inhibited and Si-FXR L-02 cells. Moreover, DA enhanced the mRNA and protein expression of FXR, and its downstream genes and proteins, in L-02 cells containing an FXR-overexpression plasmid.ConclusionDA may represent an effective agonist for FXR has significant therapeutic potential for the treatment of cholestatic liver injury.     

Helicobacter hepaticus Infection Promotes Hepatitis and Preneoplastic Foci in Farnesoid X Receptor (FXR) Deficient Mice

Farnesoid X receptor (FXR) is a nuclear receptor that regulates bile acid metabolism and transport. Mice lacking expression of FXR (FXR KO) have a high incidence of foci of cellular alterations (FCA) and liver tumors. Here, we report that Helicobacter hepaticus infection is necessary for the development of increased hepatitis scores and FCA in previously Helicobacter-free FXR KO mice. FXR KO and wild-type (WT) mice were sham-treated or orally inoculated with H. hepaticus. At 12 months post-infection, mice were euthanized and liver pathology, gene expression, and the cecal microbiome were analyzed. H. hepaticus induced significant increases hepatitis scores and FCA numbers in FXR KO mice (P<0.01 and P<0.05, respectively). H. hepaticus altered the beta diversity of cecal microbiome in both WT and FXR KO mice compared to uninfected mice (P<0.05). Significant upregulation of β-catenin, Rela, Slc10a1, Tlr2, Nos2, Vdr, and Cyp3a11 was observed in all FXR KO mice compared to controls (P<0.05). Importantly, H. hepaticus and FXR deficiency were necessary to significantly upregulate Cyp2b10 (P<0.01). FXR deficiency was also a potent modulator of the cecal microbiota, as observed by a strong decrease in alpha diversity. A significant decrease in Firmicutes, particularly members of the order Clostridiales, was observed in FXR KO mice (P<0.05 and FDR<5%, ANOVA). While FXR deficiency strongly affects expression of genes related to immunity and bile acid metabolism, as well as the composition of the microbiome; however, its deficiency was not able to produce significant histopathological changes in the absence of H. hepaticus infection.     

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

Background

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

Principal Findings

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

Conclusions

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

Selective PPARδ agonist seladelpar suppresses bile acid synthesis by reducing hepatocyte CYP7A1 via the fibroblast growth factor 21 signaling pathway

Peroxisome proliferator–activated receptor delta (PPARδ) agonists have been shown to exert beneficial effects in liver disease and reduce total bile acid levels. The mechanism(s) whereby PPARδ agonism reduces bile acid levels are, however, unknown, and therefore the aim of the present study was to investigate the molecular pathways responsible for reducing bile acid synthesis in hepatocytes, following treatment with the selective PPARδ agonist, seladelpar. We show that administration of seladelpar to WT mice repressed the liver expression of cholesterol 7 alpha-hydroxylase (Cyp7a1), the rate-limiting enzyme for bile acid synthesis, and decreased plasma 7α-hydroxy-4-cholesten-3-one (C4), a freely diffusible metabolite downstream of Cyp7a1. In primary mouse hepatocytes, seladelpar significantly reduced the expression of Cyp7a1 independent of the nuclear bile acid receptor, Farnesoid X receptor. In addition, seladelpar upregulated fibroblast growth factor 21 (Fgf21) in mouse liver, serum, and in cultured hepatocytes. We demonstrate that recombinant Fgf21 protein activated the c-Jun N-terminal kinase (JNK) signaling pathway and repressed Cyp7a1 gene expression in primary hepatocytes. The suppressive effect of seladelpar on Cyp7a1 expression was blocked by a JNK inhibitor as well as in the absence of Fgf21, indicating that Fgf21 plays an indispensable role in PPARδ-mediated downregulation of Cyp7a1. Finally, reduction of CYP7A1 expression by seladelpar was confirmed in primary human hepatocytes. In conclusion, we show that seladelpar reduces bile acid synthesis via an FGF21-dependent mechanism that signals at least partially through JNK to repress CYP7A1.     

蛹虫草虫草素对ANIT诱导胆汁淤积性肝损伤的保护作用

本研究探讨虫草素对α-萘异硫氰酸酯（ANIT）诱导胆汁淤积性肝损伤的改善作用及保护机制。首先建立ANIT诱导胆汁淤积性肝损伤模型,通过检测血生化指标、HE染色观察肝脏组织病理的情况评价虫草素的保肝作用,进一步通过Western blot和实时定量PCR技术分析胆汁酸合成、分解、转运以及炎症相关通路的变化。结果显示,与模型组相比,虫草素可以有效降低血清中总胆汁酸水平,改善肝功能,明显降低肝脏病理损伤和炎性细胞浸润。同时,虫草素激活胆汁酸核受体FXR,上调胆汁酸转运体NTCP、BSEP表达,缓解肝内的胆汁酸淤积情况。此外,虫草素还可通过调控NF-κB信号通路抑制肝脏IL-6和IL-1β表达。结果提示,虫草素对ANIT诱导的胆汁淤积模型小鼠肝损伤具有保护作用,其机制可能与其减少肝内胆汁淤积和抑制炎症有关。     

Ethyl acetate extract of herpetospermum pedunculosum alleviates α-naphthylisothiocyanate-induced cholestasis by activating the farnesoid x receptor and suppressing oxidative stress and inflammation in rats

BackgroundTraditionally, seeds of Herpetospermum pedunculosum were used to treat liver disease or cholepathy. Up to date, their protecting effect against cholestasis was remain unclarified.PurposeTo investigate the efficacy, possible mechanisms, and active constituents of the ethyl acetate extract from the seeds of Herpetospermum pedunculosum (HPEAE), studies were carried out using cholestasis rat model induced by α-naphthylisothiocyanate (ANIT).MethodsMale rats were intragastrically treated with HPEAE (100, 200 or 400 mg/kg) once a day for 7 days and were modeled with ANIT (60 mg/kg). The levels of serum indicators, bile flow, and histopathology were evaluated. Indices of oxidative stress and inflammatory mediators were detected using the enzyme-linked immunosorbent assay. Western blotting method was employed for analyzing the protein levels in the signal pathways of farnesoid X receptor (FXR), kelch ech associating protein 1/nuclear factor erythroid 2-related factor 2 (Keap1/Nrf2) and nuclear factor κB (NF-κB). The chemical compositions of HPEAE was analyzed by HPLC, and partially chemical components of HPEAE were identified by comparisons of their retention times with the standards. The FXR agonistic activity of the identified compounds was evaluated in l-02 cells induced by guggulsterone using a high-content screening system.ResultsThe cholestasis caused by ANIT can be significantly ameliorated by restoring the liver function indexes of alanine transaminase, aspartate transaminase, alkaline phosphatase, gamma-glutamyltransferase, total bilirubin, direct bilirubin and total bile acid, which are dose-dependent, as well as pathological liver injury and bile flow. Mechanical studies suggested that HPEAE can activate the expression of FXR and then up regulate its downstream proteins (multidrug resistance-associated protein 2, bile salt export pump and Na+/taurocholate cotransporting polypeptide). Moreover, the levels of the active oxygen index glutathione, superoxide dismutase, glutathione peroxidase, catalase and malondialdehyde were markedly restored by treatment with HPEAE. Western blotting further confirmed that HPEAE up regulated the expression of quinone oxidoreductase 1, heme oxygenase 1 and Keap1, lowered the expression of Nrf2 and reduced oxidative stress. HPEAE also up regulated P-glycoprotein 65, phosphorylated P-glycoprotein 65 and inhibitor of NF-κB kinase α expression, down regulated inhibitor of NF-κB (IκB), restored inflammatory mediator tumor necrosis factor-α, interleukin-1β (IL-1β), IL-6 and IL-10, and reduced inflammatory response. Fifteen compounds were identified (12 lignans and 3 coumarins). Among them, five lignans exhibited the significant FXR agonistic activity in vitro.ConclusionHPEAE may alleviate the cholestasis and liver injury caused by ANIT in rats by activating FXR, as well as suppressing the Keap1/Nrf2 and NF-κB signaling pathways and lignans may be its main active components.     

Abolished synthesis of cholic acid reduces atherosclerotic development in apolipoprotein E knockout mice

To investigate the effects of abolished cholic acid (CA) synthesis in the ApoE knockout model [apolipoprotein E (apoE) KO],a double-knockout (DKO) mouse model was created by crossbreeding Cyp8b1 knockout mice (Cyp8b1 KO), unable to synthesize the primary bile acid CA, with apoE KO mice. After 5 months of cholesterol feeding, the development of atherosclerotic plaques in the proximal aorta was 50% less in the DKO mice compared with the apoE KO mice. This effect was associated with reduced intestinal cholesterol absorption, decreased levels of apoB-containing lipoproteins in the plasma, enhanced bile acid synthesis, reduced hepatic cholesteryl esters, and decreased hepatic activity of ACAT2. The upregulation of Cyp7a1 in DKO mice seemed primarily caused by reduced expression of the intestinal peptide FGF15. Treatment of DKO mice with the farnesoid X receptor (FXR) agonist GW4064 did not alter the intestinal cholesterol absorption, suggesting that the action of CA in this process is confined mainly to formation of intraluminal micelles and less to its ability to activate the nuclear receptor FXR. Inhibition of CA synthesis may offer a therapeutic strategy for the treatment of hyperlipidemic conditions that lead to atherosclerosis.     

Regulation of human class I alcohol dehydrogenases by bile acids

Class I alcohol dehydrogenases (ADH1s) are the rate-limiting enzymes for ethanol and vitamin A (retinol) metabolism in the liver. Because previous studies have shown that human ADH1 enzymes may participate in bile acid metabolism, we investigated whether the bile acid-activated nuclear receptor farnesoid X receptor (FXR) regulates ADH1 genes. In human hepatocytes, both the endogenous FXR ligand chenodeoxycholic acid and synthetic FXR-specific agonist GW4064 increased ADH1 mRNA, protein, and activity. Moreover, overexpression of a constitutively active form of FXR induced ADH1A and ADH1B expression, whereas silencing of FXR abolished the effects of FXR agonists on ADH1 expression and activity. Transient transfection studies and electrophoretic mobility shift assays revealed functional FXR response elements in the ADH1A and ADH1B proximal promoters, thus indicating that both genes are direct targets of FXR. These findings provide the first evidence for direct connection of bile acid signaling and alcohol metabolism.     

Hepatic bile acid metabolism and expression of cytochrome P450 and related enzymes are altered in Bsep −/− mice

The bile salt export pump (BSEP/Bsep; gene symbol ABCB11/Abcb11) translocates bile salts across the hepatocyte canalicular membrane into bile in humans and mice. In humans, mutations in the ABCB11 gene cause a severe childhood liver disease known as progressive familial intrahepatic cholestasis type 2. Targeted inactivation of mouse Bsep produces milder persistent cholestasis due to detoxification of bile acids through hydroxylation and alternative transport pathways. The purpose of the present study was to determine whether functional expression of hepatic cytochrome P450 (CYP) and microsomal epoxide hydrolase (mEH) is altered by Bsep inactivation in mice and whether bile acids regulate CYP and mEH expression in Bsep ^?/? mice. CYP expression was determined by measuring protein levels of Cyp2b, Cyp2c and Cyp3a enzymes and CYP-mediated activities including lithocholic acid hydroxylation, testosterone hydroxylation and alkoxyresorufin O-dealkylation in hepatic microsomes prepared from female and male Bsep ^?/? mice fed a normal or cholic acid (CA)-enriched diet. The results indicated that hepatic lithocholic acid hydroxylation was catalyzed by Cyp3a/Cyp3a11 enzymes in Bsep ^?/? mice and that 3-ketocholanoic acid and murideoxycholic acid were major metabolites. CA feeding of Bsep ^?/? mice increased hepatic Cyp3a11 protein levels and Cyp3a11-mediated testosterone 2β-, 6β-, and 15β-hydroxylation activities, increased Cyp2b10 protein levels and Cyp2b10-mediated benzyloxyresorufin O-debenzylation activity, and elevated Cyp2c29 and mEH protein levels. We propose that bile acids upregulate expression of hepatic Cyp3a11, Cyp2b10, Cyp2c29 and mEH in Bsep ^?/? mice and that Cyp3a11 and multidrug resistance-1 P-glycoproteins (Mdr1a/1b) are vital components of two distinct pathways utilized by mouse hepatocytes to expel bile acids.