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Identification of the Human P‐450 Enzymes Responsible for the Sulfoxidation and Thiono‐Oxidation of Diethyldithiocarbamate Methyl Ester: Role of P‐450 Enzymes in Disulfiram Bioactivation
Author(s) -
Madan Ajay,
Parkinson Andrew,
Faiman Morris D.
Publication year - 1998
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.1998.tb03901.x
Subject(s) - chemistry , disulfiram , enzyme , cyp3a4 , cyp3a , microsome , biochemistry , cytochrome p450 , cyp2b6 , cyp2a6 , sodium diethyldithiocarbamate , hydroxylation , stereochemistry , organic chemistry
Diethyldithiocarbamate methyl ester (DDTC‐Me) is a precursor to the formation of S ‐methyl‐ N,N ‐diethyliolcarbamate sulfoxide, the active metabolite proposed to be responsible for the alcohol deterrent effects of disulfiram. The present study investigated the role of human cytochrome P‐450 (CYP) enzymes in sulfoxidation and thiono‐oxidation of DDTC‐Me, intermediary steps in the activation of disulfiram. Several approaches were used in an attempt to delineate the particular P‐450 enzyme(s) involved in the sulfoxidation and thiono‐oxidation of DDTC‐Me. These approaches included the use of cDNA‐expressed human P‐450 enzymes, correlation analysis with sample‐to‐sample variation in human P‐450 enzymes in a bank of human liver microsomes, and chemical and antibody inhibition studies. Multiple human P‐450 enzymes (CYP3A4, CYPlA2, CYP2A6, and CYP2D6) catalyzed the sulfoxidation of DDTC‐Me, as determined with cDNA‐expressed enzymes. Several lines of evidence suggest that the sulfoxidation of DDTC‐Me by human liver microsomes is primarily catalyzed by CYP3A4/5, including (1) a high correlation between DDTC‐Me sulfoxidation and testosterone 6β‐hydroxylation; (2) increased DDTC‐Me sulfoxidation in the presence of α‐naphthoflavone, an activator of CYP3A enzymes; (3) inhibition of this reaction by inhibitors of CYP3A4/5 enzymes, such as troleandomycin and ketoconazole; and (4) inhibition of DDTC‐Mesulfoxidation by antibodies against CYP3A enzymes. On the other hand, several lines of evidence suggested that the thiono‐oxidation of DDTC‐Me by human liver microsomes is catalyzed in part by CYPlA2, CYP266, CYPPEl, and CYP3A4/5, including (1) these human P450 enzymes among others have the capacity to catalyze this reaction, as determined with cDNA‐expressed enzymes; (2) a high correlation between DDTC‐Me thiono‐oxidation and testosterone 6β‐hydroxylation, weak inhibition by ketoconazole, troleandomycin, and anti‐CYP3A antibodies suggested a minor role for CYP3A4; (3) a high correlation with immunoreactive CYP2B6 suggested involvement of this enzyme; (4) weak inhibition of DDTC‐Me thiono‐oxidation by furafylline and anti‐CYPlA antibody suggested involvement of CYPlA2, and (5) inhibition of DDTC‐Me thiono‐oxidation by DDTC and anti‐CYP2E antibodies suggested a role for CYP2E1. Collectively, these data suggested CYP3A4/5 enzymes are the major contributors to the sulfoxidation of DDTC‐Me by human liver microsomes, and CYPlA2, CYP2B6, CYP2E1, and CYP3A4/5 contribute toward DDTC‐Me thiono‐oxidation by human liver microsomes. This study, in conjunction with others (Madan et al., Drug Metab. Dispos. 23:1153–1162, 1995), may help explain the variability in disulfiram's effectiveness as an alcohol deterrent.