Bioactivation of 1,1-dichloroethylene to its epoxide by CYP2E1 and CYP2F enzymes

1,1-Dichloroethylene (DCE) exposure to mice elicits lung toxicity that selectively targets bronchiolar Clara cells. The toxicity is mediated by DCE metabolites formed via cytochrome P450 metabolism. The primary metabolites formed are DCE epoxide, 2,2-dichloroacetaldehyde, and 2-chloroacetyl chloride. The major metabolite detected is 2-S-glutathionyl acetate [C], a putative conjugate of DCE epoxide with glutathione. In this investigation, studies were undertaken to test the hypothesis that CYP2E1 and CYP2F2 are involved in bioactivation of DCE to the epoxide in murine lung. We have developed a method using liquid chromatography/mass spectrometry (LC/MS) to evaluate the kinetics of the rates of production of conjugate [C] by recombinant CYP2E1 and CYP2F enzymes and lung microsomes. Concentration-dependent formation of conjugate [C] was found in incubations of DCE with recombinant CYP2E1 and CYP2F enzymes and lung microsomes from CD-1, wild-type (mixed 129/Sv and C57BL), and CYP2E1-null mice. Recombinant rat CYP2E1 exhibited greater affinity and catalytic efficiency for DCE metabolism than did recombinant human CYP2E1, mouse CYP2F2, goat CYP2F3 or rat CYP2F4. In the lung microsomal incubations, the rates of conjugate [ C] production were higher in CD-1 mice than in either wild-type or CYP2E1-null mice; the level of [ C] in CYP2E1-null mice was about 66% of that in wild-type mice. These results demonstrated that LC/MS analysis is a suitable method for detection and quantitation of conjugate [C], and that CYP2E1 and CYP2F2 catalyze the bioactivation of DCE to the epoxide in murine lung. The results also demonstrated that CYP2E1 is the high-affinity enzyme involved in DCE bioactivation.