One of the most widely used nanomaterials at present is zinc oxide (ZnO) nanoparticles (NP), with multiple applications in cosmetic, technological industry and, recently, also in biomedicine. This widespread use means that humans are increasingly being exposed to these NP, raising concerns about how this could affect health. Despite being one of the most studied NP from a toxicological point of view, much remains unknown about how they may affect specific cell types, such as glial cells, and their mechanism of action. The aim of this work was to evaluate the effects on cell viability caused by exposure to ZnO NP in the human glioblastoma A172 cell line, and the role of Zn²⁺ in the observed effects. ZnO NP were characterised, and cellular uptake was assessed by flow cytometry. The effects on cell viability were assessed by MTT assay. To determine the role of Zn²⁺ ions in the observed effects, we analysed their release from ZnO NP by flame atomic absorption spectrometry. Then, cells were treated with zinc sulphate at concentrations that equal the amount of Zn²⁺ ions released by the tested concentrations of ZnO NP. Exposure to ZnO NP induced a significant decrease in cell viability depending on the dose and treatment duration. The ability of ZnO NP to release Zn²⁺ ions into the medium in a concentration-dependent manner was confirmed; however, the their presence was not responsible, at least entirely, for the observed cytotoxic effects. These results provide information about the toxic potential of ZnO NP in human glial cells and the involvement of Zn²⁺ ions released in the observed effects.

Funding: Ministry of Science and Innovation: MCIN/AEI/10.13039/501100011033 (Grant PID2020-114908GA-I00), Xunta de Galicia (ED431B 2022/16 and ED481A 2019/003), CICA-Disrupting Project 2021SEM‐B2, and Ministry of Education, Culture and Sport [BEAGAL18/00142 to V.V.].