Genotoxic effects of zinc oxide nanoparticles in nasal mucosa cells are antagonized by titanium dioxide nanoparticles

•ZnO-NP-induced toxicity is reduced by TiO2-NPs.•DNA repair capacity after ZnO-NP-induced DNA damage is enhanced by TiO2-NPs.•Interaction of zinc ions and TiO2-NPs may be the reason for toxicity antagonism. Titanium dioxide nanoparticles (TiO2-NPs) and zinc oxide nanoparticles (ZnO-NPs) are often used in sunscreens and other consumer products due to their photoprotective properties. However, concern exists regarding them possibly causing cyto- and genotoxic effects. The aim of this study was to assess cyto- and genotoxicity of these nanomaterials after single or combined exposure. For this purpose, a battery of cell culture test systems for human nasal mucosa (monolayer, air–liquid interface and mini organ culture) were exposed to 0.1–20μg/ml of TiO2- and ZnO-NPs alone and in combination. Cytotoxicity was measured by the MTT assay, and DNA damage and repair capacity were investigated using the comet assay. TiO2-NPs did not exhibit any cyto- or genotoxic potential within the tested concentrations. However, results of the study indicated cyto- and genotoxicity resulting from ZnO-NPs. The genotoxicity could be antagonized by TiO2-NPs. Furthermore, the DNA repair capacity after ZnO-NP-induced DNA damage was enhanced by TiO2-NPs. The adsorption of dissolved zinc ions onto TiO2-NPs is discussed as the major antagonistic mechanism. The combination of both metal oxide nanoparticles interferes with the genotoxicity of ZnO-NPs and should be discussed as a reasonable and safe alternative to the sole use of ZnO-NPs in consumer products.