Rp. Lee et Pg. Forkert, IN-VITRO BIOTRANSFORMATION OF 1,1-DICHLOROETHYLENE BY HEPATIC CYTOCHROME-P-450 2E1 IN MICE, The Journal of pharmacology and experimental therapeutics, 270(1), 1994, pp. 371-376
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.