Role of Cyt-C/caspases-9,3, Bax/Bcl-2 and the FAS death receptor pathway in apoptosis induced by zinc oxide nanoparticles in human aortic endothelial cells and the protective effect by alpha-lipoic acid

• The toxicity has been ascribed to undissolved ZnO NPs form the culture solution.
• ZnO NPs localization in vesicles might suggest their role in mitochondrion.
• FAS death receptor and mitochondrial pathways are the major mechanisms of apoptosis induced by ZnO NPs.
• Oxidative stress played an important role in apoptosis, and LA completely abolished apoptosis.

Zinc oxide nanoparticles (ZnO NPs) are widely used in a variety of products used in daily life. However, their impact on human health has not been completely elucidated. This study was designed to investigate the cytotoxicity associated with ZnO NPs, the role of dissolution in the toxicity of ZnO NPs, the molecular mechanisms and mode of cell death induced by ZnO NPs in human aortic endothelial cells (HAECs), and the protective effects of the antioxidant alpha-lipoic acid (LA). ZnO NPs significantly reduced cell viability in a dose- and time-dependent manner, resulted in intracellular oxidative stress and cell membrane leakage when treated with doses of 8–50 μg/mL for 12 and 24 h in HAECs. The toxicity was produced by undissolved ZnO NPs but not dissolved Zn2+ and metal impurities. Exposure to ZnO NPs was found to induce apoptosis at 12 h and necrosis after 24 h. Apoptosis was confirmed using reactive oxygen species that triggered a decrease in mitochondria membrane potential, increase in Cyt-C release, activation of caspases 3 and caspases9 and increase in the ratio of Bax/Bcl-2. Futhermore, ZnO NPs could activate the Fas death receptor pathway. In addition, the antioxidant LA was able to protect HAECs from apoptosis induced by ZnO NPs.