Putative role of intracellular Zn(2+) 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 Zn(2+) in cells suffering from oxidative stress, the effects of N-ethylmaleimide (NEM) and ZnCl(2) on cellular thiol content and intracellular Zn(2+) 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 Zn(2+)-free conditions. Results suggest that NEM decreases cellular thiol content and induces intracellular Zn(2+) release. Micromolar ZnCl(2) dose-dependently augmented both FluoZin-3 and 5-CMF fluorescences, suggesting that the elevation of intracellular Zn(2+) concentration increases cellular thiol content. Taken together, it is hypothesized that intracellular Zn(2+) release during oxidative stress is a trigger to restore cellular thiol content that is decreased by oxidative stress.

Micromolar Zn(2+) potentiates the cytotoxic action of submicromolar econazole in rat thymocytes: possible disturbance of intracellular Ca(2+) and Zn(2+) homeostasis.

Econazole, one of imidazole antifungals, has been reported to exhibit an inhibitory action on Mycobacterium tuberculosis and its multidrug-resistant strains under in vitro and ex vivo conditions. There is a chemotherapeutic potential of econazole against tuberculosis. We have revealed that Zn(2+) at micromolar concentrations potentiates the cytotoxicity of imidazole antifungals by increasing membrane Zn(2+) permeability. It is reminiscent of a possibility that econazole exhibits harmful action on human in the presence of Zn(2+) at a physiological range when the agent is systemically administered. Because it is necessary to characterize the cytotoxic action of econazole in the presence of Zn(2+), we have cytometrically examined the effects of econazole, ZnCl(2), and their combination on rat thymocytes. ZnCl(2) at concentrations ranging from 1 microM to 30 microM significantly increased the lethality induced by 10 microM econazole in a concentration-dependent manner. Econazole at a sublethal concentration of 1 microM significantly augmented the intensity of side scatter in the presence of micromolar ZnCl(2), suggesting the change in an intracellular circumstance by the combination of econazole and ZnCl(2). Econazole at 0.3 microM or more in the presence of ZnCl(2) increased the intensity of Fluo-3 fluorescence, an indicator for intracellular Ca(2+). Furthermore, the intensity of FluoZin-3 fluorescence, an indicator for intracellular Zn(2+), was also augmented by econazole at 0.1 microM or more in the presence of ZnCl(2). Results suggest that the combination of submicromolar econazole with micromolar ZnCl(2) may increase the intracellular concentration of Ca(2+) and Zn(2+), leading to disturbance of intracellular Ca(2+) and Zn(2+) homeostasis that triggers cytotoxic action.