Zirconium dioxide nanoparticles induced cytotoxicity in rat cerebral cortical neurons and apoptosis in neuron-like N2a and PC12 cell lines.

During recent decades, the application of zirconium dioxide nanoparticles (ZrO₂-NP) has been expanded in various fields ranging from medicine to industry. It has been shown that ZrO₂-NP has the potential to cross the blood-brain barrier (BBB) and induce neurotoxicity. In the current study, we investigated the in vivo neurotoxicity, as well as, the cellular mechanism of ZrO₂-NP toxicity on two neuronal-like cell lines, PC12 and N2a. PC12 and N2a cells were exposed to increasing concentrations of ZrO₂-NP (0-2000 µg/ml) for 48 h. The apoptotic effect of ZrO₂-NP was determined using annexin V/propidium iodide double staining (by flow cytometry), and western blot analysis of relative apoptotic proteins, including caspase-3, caspase-9, bax, and bcl2. Based on our results, ZrO₂-NP at concentrations of 250-2000 μg/mL increased both early and late-stage apoptosis in a concentration-dependent manner. Moreover, the expressions of cleaved-caspase-3 and -9 proteins and the bax/bcl2 ratio were significantly increased. In addition, oral administration of ZrO₂-NP (50 mg/kg) to male Wistar rats for 28 days led to the loss of neuronal cells in the cerebral cortex. Taken together, our findings highlighted the role of apoptosis on cytotoxicity induced by ZrO₂-NP.