Role of flavin-dependent monooxygenases and cytochrome P450 enzymes in the sulfoxidation of S-methyl N,N-diethylthiolcarbamate.
Disulfiram is bioactivated to S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), the metabolite proposed to be responsible for the action of disulfiram as an aldehyde dehydrogenase inhibitor. This bioactivation process includes a reduction, an S-methylation, and two successive oxidations. Sulfur-containing functional groups are substrates for cytochrome P450 enzymes or flavin-containing monooxygenases (FMO). In the present study, we investigated the contribution of these monooxygenases to the formation of DETC-MeSO from its immediate precursor S-methyl N,N-diethylthiolcarbamate (DETC-Me). Liver microsomes obtained from mature male rats were incubated with DETC-Me. The formation of DETC-MeSO was blocked completely by solubilization of the microsomes with the detergent Emulgen 911, or by the presence of the cytochrome P450 inhibitor 1-benzylimidazole. However, thermal-inactivation of FMO resulted in only a partial loss in DETC-MeSO formation. Liver microsomes from phenobarbital-treated rats showed a 4- to 5-fold increase in the rate of formation of DETC-MeSO, compared with controls. Liver microsomes from pyrazole-treated rats showed a 50% decrease in the sulfoxidation of DETC-Me compared with controls. In a purified reconstituted system, cytochrome P450 2B1 (CYP2B1) catalyzed the formation of DETC-MeSO at a rate of 51 nmol DETC-MeSO formed/min/nmol cytochrome P450. Antibodies to CYP2B1 caused a 60% inhibition of DETC-MeSO formation by liver microsomes from phenobarbital-treated rats. These results suggest that in male rat liver microsomes, cytochrome P450 plays a major role in catalyzing the sulfoxidation of DETC-Me, whereas FMO plays a minor role (< 10%). Also, in liver microsomes from phenobarbital-treated rats, CYP2B1 is the major catalyst for the sulfoxidation of DETC-Me.
Madan
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Department of Pharmacology and Toxicology, University of Kansas, Lawrence 66045.
Parkinson
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Faiman
M D
MD
D000818:Animals; D000906:Antibodies; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004221:Disulfiram / Q000493:pharmacokinetics; D004050:Ditiocarb / Q000031:analogs & derivatives / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013454:Sulfoxides / Q000378:metabolism*; D013859:Thiocarbamates / Q000378:metabolism*
D000906:Antibodies; D013454:Sulfoxides; D013859:Thiocarbamates; C073220:S-methyl N,N-diethylthiolcarbamate sulfoxide; C070631:S-methyl diethylthiocarbamate; D003577:Cytochrome P-450 Enzyme System; D004050:Ditiocarb; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming); D004221:Disulfiram