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 ef fects are associated with cytochrome P-450 (P450)dependent formation o f metabolite(s) that bind covalently to tissue macromolecules. Our goa l was to investigate effects of DCE on P450 in liver microsomes. Speci fic objectives were to examine 1) inactivation of P450 by DCE and to d etermine if during this inactivation the heme and/or apoprotein moieti es are destroyed and 2) isozyme-selective biotransformation of DCE by P450. Our results showed significant reduction of P450 content in reac tions containing DCE and microsomes from untreated (30%) or phenobarbi tal-treated (20%) mice. Maximal reduction (50%) of P450 was evoked by DCE in reactions catalyzed by microsomes from acetone-treated mice. Al terations in heme levels were not detected in any microsomal preparati on 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 c ontrol and phenobarbital-treated mice. DCE did not cause inhibition of 7-pentoxyresorufin-O-dealkylation in any microsomal preparation. Immu noinhibition with an anti-2E1 antibody abolished the observed inhibiti on of p-nitrophenol hydroxylation. Densitometric scanning of protein i mmunoblots using an anti-2E1 antibody revealed a 40% decrease in micro somes reacted with DCE, whereas no change was observed in immunoblots prepared with an anti-2B antibody. These results showed that 1) biotra nsformation of DCE is catalyzed by the 2E1 and not by the 2B enzyme an d 2) DCE inactivates P450 by destruction of the apoprotein rather than the heme moieties.