In vitro biotransformation of 1,1-dichloroethylene by hepatic cytochrome P-450 2E1 in mice.

1,1-Dichloroethylene (DCE) is hepatotoxic in mice and its cytotoxic effects are associated with cytochrome P-450 (P450)-dependent formation of metabolite(s) that bind covalently to tissue macromolecules. Our goal was to investigate effects of DCE on P450 in liver microsomes. Specific objectives were to examine 1) inactivation of P450 by DCE and to determine if during this inactivation the heme and/or apoprotein moieties are destroyed and 2) isozyme-selective biotransformation of DCE by P450. Our results showed significant reduction of P450 content in reactions containing DCE and microsomes from untreated (30%) or phenobarbital-treated (20%) mice. Maximal reduction (50%) of P450 was evoked by DCE in reactions catalyzed by microsomes from acetone-treated mice. Alterations in heme levels were not detected in any microsomal preparation incubated in the presence of DCE. Significant inhibition of p-nitro-phenol hydroxylation was found in microsomes incubated previously with DCE and was most pronounced in acetone-treated mice, as compared to control and phenobarbital-treated mice. DCE did not cause inhibition of 7-pentoxyresorufin-O-dealkylation in any microsomal preparation. Immunoinhibition with an anti-2E1 antibody abolished the observed inhibition of p-nitrophenol hydroxylation. Densitometric scanning of protein immunoblots using an anti-2E1 antibody revealed a 40% decrease in microsomes reacted with DCE, whereas no change was observed in immunoblots prepared with an anti-2B antibody. These results showed that 1) biotransformation of DCE is catalyzed by the 2E1 and not by the 2B enzyme and 2) DCE inactivates P450 by destruction of the apoprotein rather than the heme moieties.