DITHIOCARBAMATES INDUCE APOPTOSIS IN THYMOCYTES BY RAISING THE INTRACELLULAR LEVEL OF REDOX-ACTIVE COPPER

Dithiocarbamates are metal-chelating compounds that can exert either p ro-oxidant or antioxidant effects in different situations, They have r ecently been found to potently inhibit apoptotic cell death, an activi ty attributed to their antioxidant action, However, when thymocytes we re exposed to pyrrolidine dithiocarbamate, an oxidation of the glutath ione pool occurred within 90 min, Longer incubation resulted in cell s hrinkage, chromatin fragmentation, glutathione depletion, and eventual cell lysis, which is typical of apoptosis in these cells, These chang es were inhibited by inclusion of non-permeable metal chelators in the incubation medium, suggesting that pyrrolidine dithiocarbamate exerts its toxic effect by transporting a redox-active metal into the cell. This was directly confirmed when sustained 8-fold elevations of intrac ellular copper were detected after addition of pyrrolidine dithiocarba mate. In agreement with this, supplementation of the incubation medium with submicromolar concentrations of copper significantly potentiated pyrrolidine dithiocarbamate toxicity, We conclude that pyrrolidine di thiocarbamate exerts a powerful pro oxidant effect on thymocytes due t o its ability to transport external redox-active copper into cells, Th e resulting increase in glutathione disulfide may also explain the tem porary anti-apoptotic activity of this compound described in other sys tems.