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The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity.

ABSTRACT: The pregnane X receptor (PXR) is the molecular target for catatoxic steroids such as pregnenolone 16alpha-carbonitrile (PCN), which induce cytochrome P450 3A (CYP3A) expression and protect the body from harmful chemicals. In this study, we demonstrate that PXR is activated by the toxic bile acid lithocholic acid (LCA) and its 3-keto metabolite. Furthermore, we show that PXR regulates the expression of genes involved in the biosynthesis, transport, and metabolism of bile acids including cholesterol 7alpha-hydroxylase (Cyp7a1) and the Na(+)-independent organic anion transporter 2 (Oatp2). Finally, we demonstrate that activation of PXR protects against severe liver damage induced by LCA. Based on these data, we propose that PXR serves as a physiological sensor of LCA, and coordinately regulates gene expression to reduce the concentrations of this toxic bile acid. These findings suggest that PXR agonists may prove useful in the treatment of human cholestatic liver disease.

SUBMITTER: Staudinger JL

PROVIDER: S-EPMC30660 | biostudies-literature | 2001 Mar

REPOSITORIES: biostudies-literature

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The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity.

Staudinger J L JL Goodwin B B Jones S A SA Hawkins-Brown D D MacKenzie K I KI LaTour A A Liu Y Y Klaassen C D CD Brown K K KK Reinhard J J Willson T M TM Koller B H BH Kliewer S A SA

Proceedings of the National Academy of Sciences of the United States of America 20010301 6

The pregnane X receptor (PXR) is the molecular target for catatoxic steroids such as pregnenolone 16alpha-carbonitrile (PCN), which induce cytochrome P450 3A (CYP3A) expression and protect the body from harmful chemicals. In this study, we demonstrate that PXR is activated by the toxic bile acid lithocholic acid (LCA) and its 3-keto metabolite. Furthermore, we show that PXR regulates the expression of genes involved in the biosynthesis, transport, and metabolism of bile acids including cholester ...[more]

PMID: 11248085

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Project description:IntroductionCholestasis is characterized by accumulation of bile acids and inflammation, causing hepatocellular damage. Still, liver damage markers are highest in acute cholestasis and drop when this condition becomes chronic, indicating that hepatocytes adapt towards the hostile environment. This may be explained by a hormetic response in hepatocytes that limits cell death during cholestasis.AimTo investigate the mechanisms that underlie the hormetic response that protect hepatocytes against experimental cholestatic conditions.MethodsHepG2.rNtcp cells were preconditioned (24 h) with sub-apoptotic concentrations (0.1-50 ?M) of various bile acids, the superoxide donor menadione, TNF-? or the Farsenoid X Receptor agonist GW4064, followed by a challenge with the apoptosis-inducing bile acid glycochenodeoxycholic acid (GCDCA; 200 ?M for 4 h), menadione (50 ?M, 6 h) or cytokine mixture (CM; 6 h). Levels of apoptotic and necrotic cell death, mRNA expression of the bile salt export pump (ABCB11) and bile acid sensors, as well as intracellular GCDCA levels were analyzed.ResultsPreconditioning with the pro-apoptotic bile acids GCDCA, taurocholic acid, or the protective bile acids (tauro)ursodeoxycholic acid reduced GCDCA-induced caspase-3/7 activity in HepG2.rNtcp cells. Bile acid preconditioning did not induce significant levels of necrosis in GCDCA-challenged HepG2.rNtcp cells. In contrast, preconditioning with cholic acid, menadione or TNF-? potentiated GCDCA-induced apoptosis. GCDCA preconditioning specifically reduced GCDCA-induced cell death and not CM- or menadione-induced apoptosis. The hormetic effect of GCDCA preconditioning was concentration- and time-dependent. GCDCA-, CDCA- and GW4064- preconditioning enhanced ABCB11 mRNA levels, but in contrast to the bile acids, GW4064 did not significantly reduce GCDCA-induced caspase-3/7 activity. The GCDCA challenge strongly increased intracellular levels of this bile acid, which was not lowered by GCDCA-preconditioning.ConclusionsSub-toxic concentrations of bile acids in the range that occur under normal physiological conditions protect HepG2.rNtcp cells against GCDCA-induced apoptosis, which is independent of FXR-controlled changes in bile acid transport.

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The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity.

Publications

The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity.

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