Putative role of intracellular Zn2+ release during oxidative stress: a trigger to restore cellular thiol content that is decreased by oxidative stress

Although the ability of zinc to retard the oxidative process has been recognized for many years, zinc itself has been reported to induce oxidative stress. In order to give some insights into elucidating the role of intracellular Zn2+ in cells suffering from oxidative stress, the effects of N-ethylmaleimide (NEM) and ZnCl2 on cellular thiol content and intracellular Zn2+ concentration were studied by use of 5-chloromethylfluorescein diacetate (5-CMF-DA) and FluoZin-3 pentaacetoxymethyl ester (FluoZin-3-AM) in rat thymocytes. The treatment of cells with NEM attenuated 5-CMF fluorescence and augmented FluoZin-3 fluorescence in a dose-dependent manner. These NEM-induced phenomena were observed under external Zn2+-free conditions. Results suggest that NEM decreases cellular thiol content and induces intracellular Zn2+ release. Micromolar ZnCl2 dose-dependently augmented both FluoZin-3 and 5-CMF fluorescences, suggesting that the elevation of intracellular Zn2+ concentration increases cellular thiol content. Taken together, it is hypothesized that intracellular Zn2+ release during oxidative stress is a trigger to restore cellular thiol content that is decreased by oxidative stress.