Role of the dissolved zinc ion and reactive oxygen species in cytotoxicity of ZnO nanoparticles

With large-scale production and wide application of nanoscale ZnO, its health hazard has attracted extensive worldwide attention. In this study, cytotoxicity of different sized and shaped ZnO nanoparticles in mouse macrophage Ana-1 was investigated. And contribution of dissolved Zn2+ and ROS in toxicity of ZnO particles was analyzed. The results indicated that ZnO particles manifested dose-dependent toxic effect on Ana-1 cells without size-dependence, and the particles shape may impact cytotoxicity of ZnO particles. When the concentration of dissolved Zn2+ tended to equilibrium in the complete cell medium, the zinc ion concentration was approximately 10 μg/ml, inducing about 50% cell death, which was close to the cytotoxicity of ZnCl2 (IC50 = 13.33 μg Zn/ml). The Zn2+ concentration had significant correlations with cell viability and LDH level induced by the supernatant of ZnO particle suspensions (incubation at 37 °C for 24 h). Thus, the dissolved Zn2+ played the main role in toxic effect of ZnO particles. Moreover, ROS generation assays demonstrated that ZnO particles produced intrinsically a small quantity of ROS, intracellular ROS was mainly produced after ZnO particles or the dissolved Zn2+ entered into the cells. Although intracellular ROS had significant correlations with cell viability and LDH induced by ZnO particles, intracellular ROS may not be a major factor in cytotoxicity of ZnO nanoparticles, but the cytotoxic response.