ZnCl2 and vitamin C, known as antioxidants, differently potentiate the cytotoxicity of H2O2 in rat thymocytes : Cytometric analysis using forward and side scatters

The ‘antioxidant hypothesis’ proposes that antioxidant nutrients afford protection against chronic diseases by decreasing oxidative damages. The ability of zinc to retard oxidative processes has been recognized for many years. However, the application of ZnCl2 potentiates the cytotoxicity of H2O2. Thus, some antioxidants may be cytotoxic under certain oxidative conditions. Therefore, in this study, the effect of vitamin C, one of antioxidant nutrients, on the cells treated with H2O2 has been examined to see if vitamin C potentiates the cytotoxicity of H2O2. Experiments were carried out with flow cytometer and rat thymocytes. Vitamin C also potentiated the cytotoxicity of H2O2. The increase in cell lethality induced by the combination of H2O2 and ZnCl2 was associated with the increase in population of shrunken cells with increased intensity of side scatter. However, it was not the case for the combination of H2O2 and vitamin C. The profile of cytotoxicity induced by H2O2 and vitamin C was different from that by H2O2 and ZnCl2. It may be suggested that the effects of zinc and vitamin C varies from cytoprotective to cytotoxic, being dependent on the type of oxidative stress

NOR-3, a donor of nitric oxide, increases intracellular Zn²⁺ concentration and decreases cellular thiol content: A model experiment using rat thymocytes, FluoZin-3, and 5-chloromethylfluorescein

Our previous study showed that nitroprusside, a donor of nitric oxide (NO), increased intracellular Zn2+ concentration without affecting cellular content of glutathione (GSH) although it has been proposed that the cytotoxicity of NO is resulted from its interaction with glutathione and zinc. Nitroprusside releases not only NO but also cyanides (Fe(II)CN and Fe(III)CN), CN-, Fe2+, and Fe3+. Therefore, such decomposition products may mask NO-induced action on cellular GSH content. In this study, we used NOR-3 as a donor of NO to reveal the effects of NO on intracellular Zn2+ concentration and cellular GSH content in a cytometric manner with fluorescent probes, FluoZin-3-AM and 5-chloromethylfluorescein diacetate. NOR-3 at 1-3 mM significantly increased intracellular Zn2+ concentration and decreased cellular GSH content. After the removal of extracellular Zn2+ by diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA, a chelator for Zn2+), the increase in intracellular Zn2+ concentration by NOR-3 was still observed although DTPA significantly attenuated the increase in intracellular Zn2+ concentration by NOR-3. Results suggest an involvement of both intracellular Zn2+ release and increase in membrane Zn2+ permeability. It is likely that NO induces oxidative stress, leading to an increase in intracellular Zn2+ concentration