KINETICS AND SELECTIVITY OF MECHANISM-BASED INHIBITION OF GUINEA-PIG HEPATIC AND PULMONARY CYTOCHROME-P450 BY N-BENZYL-1-AMINOBENZOTRIAZOLEAND N-ALPHA-METHYLBENZYL-1-AMINOBENZOTRIAZOLE

The time dependence for mechanism-based inactivation of cytochrome P45 0 (P450)-dependent 7-pentoxyresorufin O-depentylation (PROD), 7-ethoxy resorufin O-deethylation (EROD), and 7-methoxyresorufin O-demethylatio n (MROD) activities by N-benzyl-1 -aminobenzotriazole (BBT) and N-alph a-methylbenzyl-1-amino-benzotriazole (alpha MB) was investigated in he patic and pulmonary microsomes from phenobarbital-treated guinea pigs, in the presence of NADPH, both compounds inhibited P450-dependent cat alytic activity in a time- and concentration-dependent manner. Inactiv ation of hepatic PROD activity was more rapid (t(1/2) = 13.2 vs. 155 m in) for 0.1 mu M alpha MB when compared with equimolar BET. On the oth er hand, hepatic EROD inactivation was more rapid (t(1/2) = 8.1 vs, 11 min) with 0.1 mu M BBT, compared with equimolar alpha MB. inactivatio n of pulmonary PROD activity was the most rapid and potent, with an ap parent half-life for inactivation of t(1/2) = 0.94 and 32.2 min for 0. 025 mu M alpha MB and BBT, respectively. Incubation of hepatic microso mes for 45 min in the presence of NADPH and 10 mu M BBT or alpha MB re sulted in >90% inhibition of PROD, EROD, and MROD activities, After wa shing by repeated sedimentation and resuspension, inhibition of PROD ( 78%; 93% for BBT and alpha MB, respectively), EROD (80% and 50%), and MROD (15% and 3%) activities was reversed to varying degrees. We concl ude that BET and alpha MB are rapidly metabolized to products that inh ibit individual P450 isozymes by both mechanism-based (P4502B and P450 1A1) and reversible (P4501A2) mechanisms, Of the two inhibitors, alpha MB is relatively more potent and selective for guinea pig lung P4502B isozyme(s).