INHIBITION OF ADRENAL CYTOCHROMES P450 BY 1-AMINOBENZOTRIAZOLE IN-VITRO

Studies were done to determine the effects of a P450 suicide inhibitor , 1-aminobenzotriazole (ABT), on adrenal steroid and xenobiolic metabo lism. Incubation of guinea pig adrenal microsomes with ABT plus an NAD PH-generating system caused a time-dependent decline in total P450 con centrations. The maximal decrease in P450 levels was approximately 35% and was accompanied by an equimolar decrease in heme content. Western blot analyses indicated that ABT had no effect on P450 apoprotein lev els. Benzphetamine (BZ) N-demethylase and benzo[a]pyrene (BP) hydroxyl ase activities were inhibited almost completely by microsomal incubati ons with ABT. In contrast, neither steroid 17 alpha-hydroxylase nor 21 -hydroxylase activity was affected by ABT. The steroid-induced type I spectral change in adrenal microsomes also was not affected by ABT, wh ereas that induced by BZ was eliminated. Similar studies with adrenal mitochondria indicated that ABT had no effect on mitochondrial P450 co ncentrations or on mitochondrial steroid metabolism. The results demon strate that the in vitro actions of ABT on adrenal cytochromes P450 ar e highly selective for those isozymes that catalyze xenobiotic metabol ism. Therefore, ABT should serve as a useful probe for further charact erization of adrenal xenobiotic-metabolizing P450 isozymes.