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Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver.

ABSTRACT: Activation of Constitutive Androstane Receptor (CAR) protects against bile acid (BA)-induced liver injury. This study was performed to determine the effect of CAR activation on bile flow, BA profile, as well as expression of BA synthesis and transport genes. Synthetic CAR ligand 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) was administered to mice for 4 days. BAs were quantified by UPLC-MS/MS (ultraperformance liquid chromatography-tandem mass spectrometry). CAR activation decreases total BAs in livers of male (49%) and female mice (26%), largely attributable to decreases of the 12?-hydroxylated BA taurocholic acid (T-CA) (males (M) 65%, females (F) 45%). Bile flow in both sexes was increased by CAR activation, and the increases were BA-independent. CAR activation did not alter biliary excretion of total BAs, but overall BA composition changed. Excretion of muricholic (6-hydroxylated) BAs was increased in males (101%), and the 12?-OH proportion of biliary BAs was decreased in both males (37%) and females (28%). The decrease of T-CA in livers of males and females correlates with the decreased mRNA of the sterol 12?-hydroxylase Cyp8b1 in males (71%) and females (54%). As a response to restore BAs to physiologic concentrations in liver, mRNA of Cyp7a1 is upregulated following TCPOBOP (males 185%, females 132%). In ilea, mRNA of the negative feedback regulator Fgf15 was unaltered by CAR activation, indicating biliary BA excretion was sufficient to maintain concentrations of total BAs in the small intestine. In summary, the effects of CAR activation on BAs in male and female mice are quite similar, with a marked decrease in the major BA T-CA in the liver.

SUBMITTER: Lickteig AJ

PROVIDER: S-EPMC4880140 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver.

Lickteig Andrew J AJ Csanaky Iván L IL Pratt-Hyatt Matthew M Klaassen Curtis D CD

Toxicological sciences : an official journal of the Society of Toxicology 20160316 2

Activation of Constitutive Androstane Receptor (CAR) protects against bile acid (BA)-induced liver injury. This study was performed to determine the effect of CAR activation on bile flow, BA profile, as well as expression of BA synthesis and transport genes. Synthetic CAR ligand 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) was administered to mice for 4 days. BAs were quantified by UPLC-MS/MS (ultraperformance liquid chromatography-tandem mass spectrometry). CAR activation decreases tot ...[more]

PMID: 26984780

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Project description:The constitutive androstane receptor (CAR) is a xenosensing nuclear receptor and regulator of cytochrome P450s (CYPs). However, the role of CAR as a basal regulator of CYP expression nor its role in sexually dimorphic responses have been thoroughly studied. We investigated basal regulation and sexually dimorphic regulation and induction by the potent CAR activator TCPOBOP and the moderate CAR activator Nonylphenol (NP). NP is an environmental estrogen and one of the most commonly found environmental toxicants in Europe and the United States. Previous studies have demonstrated that NP induces several CYPs in a sexually dimorphic manner, however the role of CAR in regulating NP-mediated sexually dimorphic P450 expression and induction has not been elucidated. Therefore, wild-type and CAR-null male and female mice were treated with honey as a carrier, NP, or TCPOBOP and CYP expression monitored by QPCR and Western blotting. CAR basally regulates the expression of Cyp2c29, Cyp2b13, and potentially Cyp2b10 as demonstrated by QPCR. Furthermore, we observed a shift in the testosterone 6alpha/15alpha-hydroxylase ratio in untreated CAR-null female mice to the male pattern, which indicates an alteration in androgen status and suggests a role for androgens as CAR inverse agonists. Xenobiotic-treatments with NP and TCPOBOP induced Cyp2b10, Cyp2c29, and Cyp3a11 in a CAR-mediated fashion; however NP only induced these CYPs in females and TCPOBOP induced these CYPs in both males and females. Interestingly, Cyp2a4, was only induced in wild-type male mice by TCPOBOP suggesting Cyp2a4 induction is not sensitive to CAR-mediated induction in females. Overall, TCPOBOP and NP show similar CYP induction profiles in females, but widely different profiles in males potentially related to lower sensitivity of males to either indirect or moderate CAR activators such as NP. In summary, CAR regulates the basal and chemically inducible expression of several sexually dimorphic xenobiotic metabolizing P450s in a manner that varies depending on the ligand.

Dataset Information

Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver.

Publications

Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver.

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