GLUTATHIONE-DEPENDENT AND GLUTATHIONE-S-TRANSFERASE-DEPENDENT OXIDATIVE DESULFURATION OF THE THIONE XENOBIOTIC DIETHYLDITHIOCARBAMATE METHYL-ESTER

Oxidative desulfuration of diethyldithiocarbamate methyl ester (DDTC-M e), a thione xenobiotic and a metabolite of disulfiram, was studied, U sing a rat liver microsomal incubation system, DDTC-Me was oxidized at the thionosulfur group, forming DDTC-Me sulfine. Only minimal desulfu ration of DDTC-Me to S-methyl-N,N-diethylthiolcarbamate (DETC-Me) occu rred. Desulfuration of DDTC-Me increased 4-fold when the microsomal in cubation was supplemented with reduced glutathione (GSH) and increased 8-fold when both GSH and glutathione-S-transferase (EC 2.5.1.18) were added. Similar results were obtained using a simplified system contai ning DDTC-Me sulfine, GSH, and glutathione-S-transferase. This suggest ed that DDTC-Me sulfine is a stable intermediate formed before DDTC-Me is desulfurated to DETC-Me. This unprecedented desulfuration process can be explained as follows. GSH attacks the oxithiirane isomer of DDT C-Me sulfine, resulting in ring opening followed by loss of glutathion e hydrodisulfide, which is reduced by GSH to oxidized glutathione and H2S. GSH can also reduce DDTC-Me sulfine to DDTC-Me. This mechanism is supported by in vitro studies. An approximately 1:1 stoichiometry was observed for the formation of H2S and DETC-Me. A 1:1 stoichiometry wa s also observed for the consumption of DDTC-Me sulfine, formation of D ETC-Me plus DDTC-Me, and formation of oxidized glutathione. Glutathion e hydrodisulfide was trapped by derivatization in situ using 4-vinylpy ridine. Oxidative desulfuration of a series of dithiocarbamate esters also followed a similar mechanism.