CYP2E1-dependent bioactivation of 1,1-dichloroethylene in murine lung: formation of reactive intermediates and glutathione conjugates.

We investigated the cytochrome P450-dependent metabolism of 1,1-dichloroethylene (DCE) in murine lung microsomal incubations. The metabolites were identified as their glutathione conjugates or hydrolyzed products, analyzed by HPLC and quantified with [14C]DCE. We determined the relative quantities of DICE metabolites formed in lung microsomal incubations and compared them to those produced in liver. Furthermore, we used antibody inhibition experiments to investigate the CYP2E1-dependent metabolism of DCE in lung. Our results demonstrated that reactive intermediates were generated from DCE in the lung microsomal incubations. The DCE epoxide (12.6 +/- 1.4 pmol/mg protein/min) was the major metabolite formed and was identified as two glutathione conjugates, 2-(S-glutathionyl) acetyl glutathione and 2-S-glutathionyl acetate. Lower levels of the acetal of 2,2-dichloroacetaldehyde (3.6 +/- 0.25 pmol/mg protein/min) were detected. The ratio of acetal to DCE epoxide was higher in lung (0.30 +/- 0.04) than in liver (0.12 +/- 0.02). Preincubation of microsomes with a CYP2E1-inhibitory monoclonal antibody resulted in a maximum inhibition of 50% in the formation of both the acetal and the glutathione conjugates derived from the DCE epoxide. These data demonstrated that lung CYP2E1 metabolizes DCE to reactive intermediates of which the DCE epoxide is both the major metabolite formed and an efficient scavenger of glutathione, implicating it as an important toxic species mediating DCE-induced lung cytotoxicity.