Cytochrome P-450-dependent bioactivation of 1,1-dichloroethylene to a reactive epoxide in human lung and liver microsomes.
We investigated the cytochrome P-450-dependent metabolism of 1, 1-dichloroethylene (DCE) by human lung and liver microsomes and compared the results from analogous experiments in mice. Metabolites were identified by HPLC analysis of their glutathione conjugates and/or hydrolyzed products and were detected by using [14C]DCE. The role of human CYP2E1 in the metabolic reactions was examined by comparing p-nitrophenol hydroxylase activities with levels of metabolites formed and by using the CYP2E1-selective inhibitor diallyl sulfone. The major products formed in microsomal incubations containing NADPH were the DCE-epoxide-derived glutathione conjugates 2-(S-glutathionyl)acetyl glutathione and 2-S-glutathionyl acetate. Lower levels of the acetal of 2,2-dichloroacetaldehyde were also detected. In lung samples from eight patients, the amounts of epoxide-derived conjugates formed ranged from 15.6 +/- 4.23 to 34.9 +/- 12.75 pmol/mg protein/min. The levels in murine lung were higher at 40.0 +/- 3.8 pmol/mg protein/min. In liver samples from five patients, conjugate levels ranged from 46.5 +/- 8.3 to 240.0 +/- 10. 5 pmol/mg protein/min, whereas levels in murine liver were 83.0 +/- 6.2 pmol/mg protein/min. Conjugate levels formed in human liver correlated with the relative levels of p-nitrophenol hydroxylase activity present, but this relationship was equivocal in human lung. Diallyl sulfone inhibited the formation of the glutathione conjugates (20-65%) in liver samples from all four patients, whereas only one of five human lung samples exhibited this inhibition (27%). These results demonstrated that the DCE-epoxide is a major metabolite formed by human microsomes and is mediated by CYP2E1 in liver and in some individuals in lung.
Dowsley
T F
TF
Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario, Canada.
Reid
K
K
Petsikas
D
D
Ulreich
J B
JB
Fisher
R L
RL
Forkert
P G
PG
D000293:Adolescent; D000328:Adult; D000368:Aged; D000498:Allyl Compounds / Q000494:pharmacology; D000818:Animals; D001711:Biotransformation; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004000:Dichloroethylenes / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000378:metabolism*; D005260:Female; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D007223:Infant; D008168:Lung / Q000201:enzymology*; D008297:Male; D051379:Mice; D008861:Microsomes / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D008875:Middle Aged; D013450:Sulfones / Q000494:pharmacology
D000498:Allyl Compounds; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D004000:Dichloroethylenes; D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D013450:Sulfones; C068327:diallyl sulfone; C029297:vinylidene chloride; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; D005978:Glutathione