SELECTIVE-INHIBITION OF CYTOCHROME-P450 2E1 IN-VIVO AND IN-VITRO WITHTRANS-1,2-DICHLOROETHYLENE

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytoch rome P450 (P450) 2E1, on the catalytic activities and total content of hepatic P450 was determined in vivo and in vitro. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 h postdosing, and total P450 content and the activities of P450 1A 2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, P450 2E1, and P45 0 3A were determined. The lowest dose of DCE that yielded maximal inac tivation of P450 2E1 was found to be 100 mg/kg. Significant decreases in total content of P450 or the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, and P450 3A were not observed duri ng the 24 h following administration of DCE (100 mg/kg ip), but P450 2 E1 activity was diminished about 65% at 2 and 5 h after DCE treatment and returned to control levels at 24 h. Additionally, there was little or no significant effect on the activities of hepatic cytosolic alcoh ol dehydrogenase or mitochondrial or microsomal aldehyde dehydrogenase s 5 h postdosing. DCE showed the same selectivity for P450 inactivatio n in vitro, and P450 2E1 activity was inhibited by >80% without affect ing the other isozymes. However, DCE (5 mM) also proved to be a good c ompetitive inhibitor of the probe activities of P450 1A2 and P450 2C6. The in vivo inhibition of P450 2E1 was accompanied by decreases in th e levels of the immunoreactive protein, and an additional immunoreacti ve band appeared at ca. 30 kDa in the Western blot of microsomes from DCE-treated rats, possibly arising from proteolytic degradation of P45 0 2E1 protein after covalent modification by the inhibitor. DCE is an effective, relatively nontoxic inhibitor of P450 2E1 in vivo and in vi tro that has greater selectivity than other agents currently used.