title: Kinetics and selectivity of mechanism-based inhibition of guinea pig hepatic and pulmonary cytochrome P450 by N-benzyl-1-aminobenzotriazole and N-alpha-methylbenzyl-1-aminobenzotriazole.
abstract: 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-1-aminobenzotriazole (BBT) and N-alpha-methylbenzyl-1-aminobenzotriazole (alpha MB) 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 (t1/2 = 13.2 vs. 155 min) for 0.1 microM alpha MB when compared with equimolar BBT. On the other hand, hepatic EROD inactivation was more rapid (t1/2 = 8.1 vs. 11 min) with 0.1 microM BBT, compared with equimolar alpha MB. Inactivation of pulmonary PROD activity was the most rapid and potent, with an apparent half-life for inactivation of t1/2 = 0.94 and 32.2 min for 0.025 microM alpha MB and BBT, respectively. Incubation of hepatic microsomes for 45 min in the presence of NADPH and 10 microM BBT or alpha MB 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 alpha MB, respectively), EROD (80% and 50%), and MROD (15% and 3%) activities was reversed to varying degrees. We conclude that BBT and alpha MB 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, alpha MB is relatively more potent and selective for guinea pig lung P4502B isozyme(s).
authors.affiliation: Department of Pharmacology and Toxicology, University of Western Ontario, London, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Sinal
authors.forename: J R
authors.initials: JR
authors.lastname: Bend
mesh_terms: D000818:Animals; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008168:Lung / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D009249:NADP / Q000378:metabolism; D010078:Oxazines / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology*
chemical_list: D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D007527:Isoenzymes; D010078:Oxazines; D014230:Triazoles; C067013:N-benzyl-1-aminobenzotriazole; C059849:alpha-methylbenzylaminobenzotriazole; D009249:NADP; C007649:ethoxyresorufin; C044943:pentoxyresorufin; D003577:Cytochrome P-450 Enzyme System; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2