Glutathione Carbamoylation with S-Methyl N, N-diethylthiolcarbamate Sulfoxide and Sulfone : Mitochondrial Low Km Aldehyde Dehydrogenase Inhibition and Implications for Its Alcohol-Deterrent Action

Abstract

S-Methyl N, N-diethylthiolcarbamate sulfoxide (DETC-MeSO) and sulfone (DETC-MeSO 2) both inhibit rat liver low K m aldehyde dehydrogenase (ALDH 2) in vitro and in vivo (Nagendra et al., Biochem Pharmacol 47: 1465–1467, 1994). DETC-MeSO has been shown to be a metabolite of disulfiram, but DETC-MeSO 2 has not. Studies were carried out to further investigate the inhibition of ALDH 2 by DETC-MeSO and DETC-MeSO 2. In an in vitro system containing hydrogen peroxide and horseradish peroxidase, the rate of DETC-MeSO oxidation corresponded to the rate of DETC-MeSO 2 formation. Carbamoylation of GSH by both DETC-MeSO and DETC-MeSO 2 was observed in a rat liver S 9 fraction. Carbamoylation of GSH was not observed in the presence of N-methylmaleimide. In in vitro studies, DETC-MeSO and DETC-MeSO 2 were equipotent ALDH 2 inhibitors when solubilized mitochondria were used, but DETC-MeSO was approximately four times more potent than DETC-MeSO 2 in intact mitochondria. In studies with rats, the dose (i.p. or oral) required to inhibit 50% ALDH 2 ( ed 50) was 3.5 mg/kg for DETC-MeSO and approximately 35 mg/kg for DETC-MeSO 2, approximately a 10-fold difference. Furthermore, maximum ALDH 2 inhibition occurred 1 hr after DETC-MeSO administration, whereas maximal ALDH 2 inhibition occurred 8 hr after DETC-MeSO 2 dosing. DETC-MeSO is, therefore, not only a more potent ALDH 2 inhibitor than DETC-MeSO 2 in vivo, but also in vitro when intact mitochondria are utilized. The in vitro results thus support the in vivo findings. Since oxidation of DETC-MeSO can occur both enzymatically and non-enzymatically, it is possible that DETC-MeSO 2 is formed in vivo. DETC-MeSO 2, however, is not as effective as DETC-MeSO in inhibiting ALDH 2, probably because it has difficulty penetrating the mitochondrial membrane. Thus, even if DETC-MeSO 2 is formed in vivo from DETC-MeSO, it is the metabolite DETC-MeSO that is most likely responsible for the inhibition of ALDH 2 after disulfiram administration.