Radiation-Induced Apoptosis in Thymocytes: Inhibition by Diethyldithiocarbamate and Zinc

Apoptosis is a process of physiological cell death characterized by DNA fragmentation, chromatin condensation, loss of membrane asymmetry, mitochondrial alterations and cell lethality. In the present study, apoptosis induced in thymocytes by γ irradiation is evaluated by flow cytometry, by a diphenylamine colorimetric method and by gel electrophoresis. Treatment of thymocytes with diethyldithiocarbamate or zinc shows that these compounds can inhibit radiation-induced apoptosis. Moreover, a synergistic effect is observed by using combinations of both compounds: ZnSO4 potentiates the effect of diethyldithiocarbamate at concentrations at which the compounds used separately show a low efficacy. A study of kinetics shows that addition of 1 μM diethyldithiocarbamate + 50 μM ZnSO4 (the most efficient combination) after irradiation can decrease DNA fragmentation even when it is added 2-3 h after irradiation. However, 1 μM diethyldithiocarbamate + 50 μM ZnSO4 cannot prevent the radiation-induced loss of membrane asymmetry and the decrease in alteration of the mitochondrial membrane as measured by binding of merocyanine 540 and uptake of rhodamine 123, respectively.