Cytochrome P450 2E1/2A6-Selective Inhibition by Halogenated Anilines on Metabolic Activation of Dimethylnitrosamine in Human Liver Microsomes

Abstract

Nine halogenated anilines, consisting of di- and tri-substituted fluoro-, chloro-, and bromoanilines, were subjected to analysis of their cytochrome P450 (CYP) 2E1/2A6-selective inhibitory effects on metabolic activation of dimetylnitrosamine (DMN) in human liver microsomes. Inhibitory activities (IC₅₀) of these anilines on human recombinant CYP2E1 ranged from 8.0 to 549 μM. However, most of these anilines showed no remarkable inhibition of CYP1A2, while their IC₅₀ values on CYP2A6 ranged from 2.9 to 232 μM. The CYP2E1 selectivity of these anilines in terms of the ratio of the IC₅₀ values of these anilines on CYP2A6 to those on CYP2E1, ranged from 0.1- to 5.2-fold. Their CYP2E1 selectivity decreased in the following order: 3,4,5-trifluoroaniline (3,4,5-triF-A) > 3,5-diF-A >> 3,5-dichloroaniline (3,5-diCl-A) > 3,4-diCl-A > 2,6-diCl-A > 2,3,4-trichloroaniline (2,3,4-triCl-A) > 2,4,6-triCl-A > 2,6-dibromoaniline (2,6-diBr-A) > 3,4,5-triCl-A. The inhibitory effects of these anilines on metabolic activation of DMN were analyzed using human liver microsomes. The IC₅₀ values of these anilines on demethylation metabolism of DMN correlated with those of these anilines on CYP2E1. These results suggest that these halogenated anilines may be useful as indicators of CYP-selectivity involved in metabolic activation of nitrosamines.