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THE EFFECT OF ISONIAZID ON CYP 2 E 1-AND CYP 4 A-MEDIATED HYDROXYLATION OF ARACHIDONIC ACID IN THE RAT LIVER AND KIDNEY

Cytochrome P450 (P450) bioactivation of arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) has been reported to be isoformand tissue-specific. To determine whether altered P450 expression affects the production of these metabolites, the formation of HETEs after isoniazid-mediated CYP2E1 induction was evaluated in the rat liver and kidney. Male Sprague-Dawley rats received isoniazid (200 mg/kg) or saline intraperitoneally once daily for 5 days. Chlorzoxazone, lauric acid, and arachidonic acid hydroxylation was measured in liver and kidney microsomes with and without preincubation with the specific CYP2E1 inhibitor, trans-1,2dichloroethylene (DCE). P450 isoform content and tissue HETE metabolite concentrations were also determined. Isoniazid increased CYP2E1 protein, and the 6-hydroxychlorzoxazone formation rate was increased by 2.7 0.3and 2.2 0.5-fold in liver and kidney, respectively. Formation of 19-HETE and 11-hydroxylauric acid was induced 2.3 0.6-fold and 2.2 0.4-fold in the liver, respectively, with no difference in the kidney. All of the induced activities were attenuated by DCE. An unanticipated decrease in liver CYP4A expression and in vitro 20-HETE formation rate was observed after isoniazid administration. Isoniazid decreased liver and kidney 20-HETE content to 34 10% and 15.6 5.3% of control, respectively, without significantly altering tissue 19-HETE concentration. Based on these findings, we conclude that under induced conditions, CYP2E1 is a primary enzyme involved in liver, but not kidney, formation of 19-HETE. In addition, formation of both CYP4A and 20-HETE is reduced in the liver by isoniazid. It was also demonstrated that tissue concentrations parallel in vitro inhibited formation rates for 20-HETE, but not the induced 19-HETE forma-