Toxicology 215 (2005) 234–244 Chronic ethanol exposure downregulates hepatic expression of pregnane X receptor and P450 3A11 in female ICR mice Jian-Ping Wang a , De-Xiang Xu a,b,∗ , Mei-Fang Sun a , Yuan-Hua Chen a , Hua Wang a , Wei Wei b a Department of Toxicology, Anhui Medical University, Meishan Road, Hefei, Anhui Province 230032, PR China b Institute of Clinical Pharmacology, Anhui Medical University, Hefei, Anhui Province 230032, PR China Received 11 June 2005; received in revised form 8 July 2005; accepted 11 July 2005 Available online 26 August 2005 Abstract Pregnane X receptor (PXR) is a nuclear receptor that regulates cytochrome P450 3A (CYP3A) gene transcription in a ligand- dependent manner. Ethanol has been reported to be either an inducer or an inhibitor of CYP3A expression. In this study, we investigated the effects of chronic ethanol exposure on PXR and P450 3A11 gene expression in mouse liver. Female ICR mice were administered by gavage with different doses (1000, 2000 and 4000 mg/kg) of ethanol for up to 5 weeks. Hepatic PXR and P450 3A11 mRNA levels were measured using RT-PCR. Erythromycin N-demethylase (ERND) activity was used as an indicator of CYP3A protein expression. Results showed that chronic ethanol exposure markedly decreased hepatic PXR and P450 3A11 mRNA levels. Consistent with downregulation of P450 3A11 mRNA, chronic ethanol exposure significantly decreased ERND activity in a dose-dependent manner. Additional experiment showed that chronic ethanol exposure significantly increased plasma endotoxin level and hepatic CD14 and TLR-4 mRNA expression, all of which were blocked by elimination of Gram-negative bacteria and endotoxin with antibiotics. Correspondingly, pretreatment with antibiotics reversed the downregulation of PXR and P450 3A11 mRNA expression and ERND activity in mouse liver. Furthermore, the downregulation of hepatic PXR and P450 3A11 mRNA expression was significantly attenuated in mice pretreated with GdCl 3 , a selective Kupffer cell toxicant. GdCl 3 pretreatment also significantly attenuated chronically ethanol-induced decrease in ERND activity. These results indicated that activation of Kupffer cells by gut-derived endotoxin contributes to downregulation of hepatic PXR and P450 3A11 expression during chronic alcohol intoxication. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Ethanol; Endotoxin; Pregnane X receptor; Cytochrome P450 3A; Kupffer cells 1. Introduction The cytochrome P450 3A (CYP3A) is a member of the cytochrome P-450 monooxygenase superfamily, ∗ Corresponding author. Tel.: +86 551 5161170. E-mail address: xudex@mail.hf.ah.cn (D.-X. Xu). which accounts for 25–35% of the total cytochrome P450 present in adult human or rat liver (Wrighton et al., 2000). CYP3A enzymes are responsible for the oxidative metabolism of numerous clinically used drugs, including psychotropic, cardiac, analgesic, hor- monal, immunosuppressant, antineoplastic and antihis- taminic agents (Thummel and Wilkinson, 1998). Hepatic CYP3A expression is highly regulated by development, 0300-483X/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.tox.2005.07.005