Role of oxidative stress, mitochondrial membrane potential, and calcium homeostasis in nickel sulfate-induced human lymphocyte death in vitro

When isolated human lymphocytes were treated in vitro with various concentrations of nickel sulfate (NiSO4) (0-4 mM) at 37 °C for 4 h, both concentration- and time-dependent effects of NiSO4 on lymphocyte death were observed. Increased generation of hydrogen peroxide, depletion of both nonprotein and protein sulfhydryl contents, and lipid peroxidation were induced by NiSO4. NiSO4-induced lymphocyte death was significantly prevented by pre-treatment with either catalase, or dimethylthiourea/mannitol, or deferoxamine, or excess glutathione/N-acetylcysteine. Cotreatment with cyclosporin A (a specific inhibitor of mitochondrial membrane potential) not only inhibited NiSO4-induced mitochondrial membrane potential, but also significantly prevented Ni compound-induced lymphocyte death. NiSO4-induced lymphocyte death was also significantly prevented by modulating intracellular calcium fluxes using both Ca2+ channel blockers and intracellular Ca2+ antagonist. Thus, the mechanism of NiSO4-induced activation of lymphocyte death signalling pathways involves not only the excess generation of different types of oxidative stress but also NiSO4-induced loss of mitochondrial membrane potential and destabilization of cellular calcium homeostasis as well.