Nickel oxide nanoparticles induce cytotoxicity, oxidative stress and apoptosis in cultured human cells that is abrogated by the dietary antioxidant curcumin

► NiO NP applications are accompanied by limited safety regulations & toxicity data. ► NiO NP-induced cytotoxicity and oxidative stress in HEp-2 and MCF-7 cells. ► NiO NP-induced caspapse-3 activation and DNA fragmentation in both types of cells. ► Curcumin attenuated NiO NP-induced cytotoxicity in both types of cells. ► Curcumin also ameliorated NiO NP-induced ROS & LPO generation and GSH depletion.