Mechanism-Based Inactivation of Hepatic Ethoxyresorufin O-Dealkylation Activity by Naturally Occurring Coumarins

Several naturally occurring coumarins contained in the human diet have been found to be effective inhibitors and inactivators of murine hepatic ethoxyresorufin O-dealkylase (EROD) and pentoxyresorufin O-dealkylase in vitro [Cai, Y., Bennett, D., Nair, R. V., Ceska, O., Ashwood-Smith, M., and DiGiovanni, J. (1993) Chem. Res. Toxicol. 6, 872−879]. In the present study, these same coumarins decreased the content of cytochrome P450 (P450) in either 3-methylcholanthrene (MC)- or phenobarbital-induced murine hepatic microsomes but did not have a major effect on heme content. Detailed in vitro studies with [14C]coriandrin, which selectively inhibits and inactivates P450 1A1-mediated EROD activity, demonstrated that it covalently bound, in a preferential manner, to hepatic microsomal protein from MC-pretreated mice. A linear relationship was observed between covalent binding and loss of EROD activity. The inclusion of electrophile trapping agents in the incubations significantly inhibited the covalent binding of ...