Pulmonary CYP2E1 bioactivates 1,1-dichloroethylene in male and female mice.

Pulmonary cytotoxicity induced by 1,1-dichloroethylene (DCE) has been linked to the generation of reactive intermediates through a cytochrome P450-dependent pathway. In the present studies, our objectives were to investigate and compare cytochrome P450 isozyme-selective bioactivation of DCE in vitro in the lungs of male and female mice. Our results showed that CYP2E1-dependent p-nitrophenol hydroxylation was significantly higher in microsomes from female (0.45 +/- 0.01 nmol/mg protein/min) than from male (0.38 +/- 0.02 nmol/mg protein/min) mice. Lung microsomes from male mice incubated in the presence of an NADPH-generating system and increasing amounts of DCE (5-20 mM) exhibited corresponding decreases in p-nitrophenol hydroxylase activity (19%-50%); however, greater decreases (26%-70%) were observed in lung microsomes from female mice incubated under the same conditions. In contrast, alterations in CYP2B1-dependent 7-pentoxyresorufin O-dealkylation and CYP1A1-dependent 7-ethoxyresorufin O-dealkylation were not detected in any microsomal preparation incubated with DCE. Reaction with an anti-CYP2E1 antibody abolished the inhibition of p-nitrophenol hydroxylation by DCE. Protein immunoblotting revealed significant decreases in the intensity of the bands of microsomal samples incubated previously with DCE; in contrast, alterations in heme content were not evoked by reaction with DCE. Our results have demonstrated that CYP2E1, and not CYP2B1 or CYP1A1, mediated the bioactivation of DCE. Furthermore, this bioactivation occurred to a greater extent in lung microsomes from female than from male mice, which suggests that females may be at slightly greater risk for DCE-induced pneumotoxicity.