TY - JOUR T1 - Repression of Phenobarbital-Dependent CYP2B1 mRNA Induction by Reactive Oxygen Species in Primary Rat Hepatocyte Cultures JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1402 LP - 1409 DO - 10.1124/mol.59.6.1402 VL - 59 IS - 6 AU - K. I. Hirsch-Ernst AU - K. Schlaefer AU - D. Bauer AU - A. F. Heder AU - G. F. Kahl Y1 - 2001/06/01 UR - http://molpharm.aspetjournals.org/content/59/6/1402.abstract N2 - Xenobiotic-metabolizing cytochrome P-450 (P-450) enzymes not only play a pivotal role in elimination of foreign compounds but also contribute to generation of toxic intermediates, including reactive oxygen species, that may elicit cellular damage if produced excessively. Expression of several xenobiotic-metabolizing P-450 enzymes is induced by phenobarbital (PB). Pronounced induction is observed for the rat CYP2B1 isoform. A primary rat hepatocyte culture system was used to investigate whether reactive oxygen species might modulate PB-dependent CYP2B1 induction. In cells cultivated for 3 days with 1.5 mM PB, substantial CYP2B1 mRNA induction was observed (100%). Addition of H2O2 or of the catalase inhibitor 3-amino-1,2,4-triazole (AT) to the medium repressed induction to approximately 30% (at 1 mM H2O2 and 2 mM AT, respectively). Accordingly, treatment of hepatocytes with PB and the glutathione precursor N-acetylcysteine (NAC) led to enhanced PB-dependent induction (to over 1000% at 10 mM NAC). In primary hepatocyte cultures transfected with aCYP2B1 promoter-luciferase construct containing approximately 2.7 kilobase pairs of the native CYP2B1promoter sequence, PB-dependent reporter gene activation was repressed by AT and stimulated by N-acetylcysteine. Furthermore, a 263-base pair CYP2B1 promoter fragment encompassing the phenobarbital-responsive enhancer module conferred suppression of PB-dependent luciferase expression by AT and activation by NAC in a heterologous SV40-promoter construct. In summary, these data demonstrate a regulatory mechanism that is dependent on the cellular redox status, which modulates CYP2B1 mRNA induction by PB on the transcriptional level, thus representing a feedback mechanism preventing further P-450–dependent production of reactive oxygen intermediates under oxidative stress. ER -