Hydroxymethylvinyl ketone: a reactive Michael acceptor formed by the oxidation of 3-butene-1,2-diol by cDNA-expressed human cytochrome P450s and mouse, rat, and human liver microsomes.

Abstract

The metabolic fate of 3-butene-1,2-diol (BDD), a secondary metabolite of the industrial carcinogen, 1,3-butadiene, is unclear. The current study characterizes BDD oxidation to hydroxymethylvinyl ketone (HMVK), a reactive Michael acceptor. Because of its instability in aqueous medium, HMVK was trapped by conjugation with GSH, a reaction that occurred readily at physiological conditions (pH 7.4, 37 degrees C) to yield 1-hydroxy-2-keto-4-(S-glutathionyl)butane. The results show that BDD was oxidized to HMVK by mouse, rat, and human liver microsomes and by cDNA-expressed human cytochrome P450s. Eadie-Hofstee plots demonstrated biphasic kinetics of BDD oxidation with mouse and rat liver microsomes and one of three individual human liver microsomes; BDD oxidation by the other two human liver microsomal samples was best described by monophasic kinetics. Of the human P450 enzymes examined, only P450 2E1 exhibited activity at 1 mM BDD. P450 3A4 was capable of catalyzing the reaction at a high BDD (10 mM) concentration; P450 1A1, 1A2, 1B1, 2D6-Met, and 2D6-Val produced only trace amounts of HMVK-GSH whereas P450 2A6, 2C8, 2C9, and 4A11 had no detectable activity. Detection of HMVK or the HMVK-GSH conjugate was dependent on reaction time, protein, and BDD concentrations, and the presence of NADPH. Collectively, the results provide clear evidence for BDD bioactivation to yield HMVK. Because mouse, rat, and human liver microsomes exhibited K(m) values of 50-80 microM, the results also suggest that HMVK could be formed after rodent or human exposure to BDD or its parent compound, BD.