Short Preirradiation of TiO₂ Nanoparticles Increases Cytotoxicity on Human Lung Coculture System

Anatase titanium dioxide nanoparticles (TiO₂ NPs) are used in a large range of industrial applications mainly due to their photocatalytic properties. Before entering the lung, virtually all TiO₂ NPs are exposed to some UV light, and lung toxicity of TiO₂ NPs might be influenced by photoexcitation that is known to alter TiO₂ surface properties. Although the TiO₂ NPs toxicity has been extensively investigated, limited data are available regarding the toxicity of TiO₂ NPs that have been pre-exposed to UV light, and their impact on humans remains unknown. In this study, five types of TiO₂NPs with tailored physicochemical features were characterized and irradiated by UV for 30 min. Following irradiation, cytotoxicity, pro-inflammatory response, and oxidative stress on a human lung coculture system (A549 epithelial cells and macrophages differentiated from THP-1 cells) were assessed. The surface charge of all samples was less negative after UV irradiation of TiO₂ NPs, and the average aggregate size was slightly increased. A higher cytotoxic effect was observed for preirradiated TiO₂ NPs compared to nonirradiated samples. Preirradiation of TiO₂ NPs had no significant impact on the pro-inflammatory response and oxidative stress as shown by a similar production of IL-8, TNF-α, and reactive oxygen species.