DITHIOCARBAMATE TOXICITY TOWARD THYMOCYTES INVOLVES THEIR COPPER-CATALYZED CONVERSION TO THIURAM DISULFIDES, WHICH OXIDIZE GLUTATHIONE IN AREDOX CYCLE WITHOUT THE RELEASE OF REACTIVE OXYGEN SPECIES

We have reported previously that diethyldithiocarbamate (DDC) and pyrr olidine dithiocarbamate (PDTC) induce apoptosis in rat thymocytes. Apo ptosis was shown to be dependent upon the transport of external Cu ion s into the cells and was accompanied by the oxidation of intracellular glutathione, indicating the inducement of pro-oxidative conditions (C . S. I. Nobel, M. Kimland, B. Lind, S. Orrenius, and A. F. G. Slater, J. Biol. Chem. 270, 26202-26208, 1995). In the present investigation w e have examined the chemical reactions underlying these effects. Evide nce is presented to suggest that dithiocarbamates undergo oxidation by Cu-II ions, resulting in formation of the corresponding thiuram disul fides, which are then reduced by glutathione, thereby generating the p arent dithiocarbamate and oxidized glutathione (glutathione disulfide) . Although DDC and PDTC were found to partially stabilize Cu-I ions, l imited redox cycling of the metal ion was evident. Redox cycling did n ot, how ever, result in the release of reactive oxygen species, which are believed to be scavenged in situ by the dithiocarbamate, DDC and P DTC were, in fact, shown to prevent copper-dependent hydroxyl radical formation and DNA fragmentation in model reaction systems. The thiuram disulfide disulfiram (DSF) was found to induce glutathione oxidation, DNA fragmentation, and cell killing more potently than its parent dit hiocarbamate, DDC. Of particular importance was the finding that, comp ared with DDC, the actions of DSF were less prone to inhibition by the removal of external copper ions with a chelating agent. This observat ion is consistent with our proposed mechanism of dithiocarbamate toxic ity, which involves their copper-catalyzed conversion to cytotoxic thi uram disulfides. (C) 1998 Academic Press.