Chronic Ethanol Exposure Downregulates The Expressions Of Pregnane X Receptor And Its Target Gene Cyp3all In Mouse Liver

Objective To investigate the effects of chronic ethanol exposure on the expressions of PXR and Cyp3a11 mRNA and erythromycin N-demethylase (ERND) activity and to explore the role of bacterial endotoxin and Kupffer cells in chronic ethanol-induced downregulation of PXR and Cyp3a11.Methods To investigate the effects of chronic ethanol exposure on the expressions of PXR and its target gene Cyp3a11 in mouse liver, female ICR mice were administered by gavage with different doses (1,2 and 4 g/kg) of ethanol daily for five weeks. To investigate the role of bacterial endotoxin in chronic ethanol-induced downregulation of PXR and Cyp3a11, mice were pretreated with polymyxin B (150 mg/kg/day, po) plus neomycin (450 mg/kg/day, po) to prevent growth of intestinal bacteria. To determine the role of Kupffer cells in downregulation of PXR and Cyp3a11, mice were administered twice weekly with GdCl₃ (10 mg/kg, iv), a selective Kupffer cell toxicant, to inactivate Kupffer cells. Mouse livers were excised for total RNA extraction and microsome isolation. PXR and Cyp3a11 mRNA levels were measured using RT-PCR. ERND catalytic activity was measured using Nash method.Results Chronic ethanol exposure significantly inhibited the expressions of hepatic PXR and Cyp3a11 mRNA in a dose-dependent manner. Consistent with the downregulation of PXR and Cyp3a11 mRNA, chronic ethanol exposure also significantly decreased ERND activity. Treatment with antibiotics significantly decreased plasma endotoxin concentration and hepatic CD14 and TLR4 mRNA level.