Ding-Ping Bai, Xi-Feng Zhang, Guo-Liang Zhang, Yi-Fan Huang, Sangiliyandi Gurunathan

Zinc oxide nanoparticles (ZnO NPs) are frequently used in industrial products such as paint, surface coating, and cosmetics, and recently, they have been explored in biologic and biomedical applications. Therefore, this study was undertaken to investigate the effect of ZnO NPs on cytotoxicity, apoptosis, and autophagy in human ovarian cancer cells (SKOV3). ZnO NPs with a crystalline size of 20 nm were characterized with various analytical techniques, including ultraviolet-visible spectroscopy, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. The cytotoxicity, apoptosis, and autophagy were examined using a series of cellular assays. Exposure of cells to ZnO NPs resulted in a dose-dependent loss of cell viability, and the characteristic apoptotic features such as rounding and loss of adherence, enhanced reactive oxygen species generation, and loss of mitochondrial membrane potential were observed in the ZnO NP-treated cells. Furthermore, the cells treated with ZnO NPs showed significant double-strand DNA breaks, which are gained evidences from significant number of γ-H2AX and Rad51 expressed cells. ZnO NP-treated cells showed upregulation of p53 and LC3, indicating that ZnO NPs are able to upregulate apoptosis and autophagy. Finally, the Western blot analysis revealed upregulation of Bax, caspase-9, Rad51, γ-H2AX, p53, and LC3 and downregulation of Bcl-2. The study findings demonstrated that the ZnO NPs are able to induce significant cytotoxicity, apoptosis, and autophagy in human ovarian cells through reactive oxygen species generation and oxidative stress. Therefore, this study suggests that ZnO NPs are suitable and inherent anticancer agents due to their several favorable characteristic features including favorable band gap, electrostatic charge, surface chemistry, and potentiation of redox cycling cascades.