Kinetics and selectivity of mechanism-based inhibition of guinea pig hepatic and pulmonary cytochrome P450 by N-benzyl-1-aminobenzotriazole and N- α-methylbenzyl-1-aminobenzotriazole

The time dependence for mechanism-based inactivation of cytochrome P450 (P450)-dependent 7-pentoxyresorufin O-depentylation (PROD), 7-ethoxyresorufin O-deethylation (EROD), and 7-methoxyresorufin O-demethylation (MROD) activities by N-benzyl-l-aminobenzotriazole (BBT) and N-α-methylbanzyl-l- aminobenzotriazole (αMB) was investigated In hepatic and pulmonary microsomes from phenobarbital-treated guinea pigs. In the presence of NADPH, both compounds inhibited P450-dependent catalytic activity in a time- and concentration-dependent manner, inactivation of hepatic PROD activity was more rapid (t 1/4 = 13.2 vs. 155 min) for 0.1 μM αMB when compared with equimolar BBT. On the other hand, hepatic EROD inactivation was more rapid (t 1/4 = 8.1 vs. 11 min) with 0.1 μM BBT, compared with equimolar αMB. Inactivation of pulmonary PROD activity was the most rapid and potent, with an apparent haft-life for inactivation of t 1/4 = 0.94 and 32.2 mln for 0.025 μM αMB and BBT, respectively. Incubation of hepatic microsomes for 45 min in the presence of NADPH and 10 μM BBT or αMB resulted in >90% inhibition of PROD, EROD, and MROD activities. After washing by repeated sedimentation and resuspension, inhibition of PROD {78%; 93% for BBT and αMB, respectively), EROD (80% and 50%), and MROD (15% and 3%) activities was reversed to varying degrees. We conclude that BBT and αMB are rapidly metabolized to products that inhibit individual P450 isozymes by both mechanism-based (P4502B and P4501A1) and reversible (P4501A2) mechanisms. Of the two inhibitors, αMB is relatively more potent and selective for guinea pig lung P4502B isozyme(s).