Comparison of toxicity between the different-type TiO₂ nanowires in vivo and in vitro.

In this study, we compared their toxicity in vivo and in vitro based on the physicochemical properties of three different types of TiO₂ nanowires, H₂Ti₃O₇ nanowires (1HTO), hydrothermal treatment (2HTO), and calcination (3HTO) of 1HTO. The surface of 1HTO was smooth, and the surface of 2HTO was much rougher. The negative charge on the surface increased in the order of 2HTO, 3HTO, and 1HTO, whereas the surface area increased in the order of 3HTO, 1HTO, and 2HTO. The lung is a main exposure route of nanoparticles. On day 28 after a single instillation (1 mg/kg), three nanowires induced a Th2-type inflammatory response together with the relative increase in CD4⁺ T cells, especially by 2HTO. In vitro, three TiO₂ nanowires (10 μg/ml) commonly induced the generation of cell debris in eight cell lines which may be the potential target organ of nanoparticles, especially by 2HTO. It seemed that the generation of cell debris coincides with the increase in autophagosome-like vacuoles in the cytosol. In further study using BEAS-2B cells originated from the lung, the protein amount from cells exposed to 2HTO decreased more clearly although the generation of reactive oxygen species (ROS) was less compared to 1HTO and 3HTO. Based on these results, we suggest that surface area may act as an important factor depends on the biological response by TiO₂ nanowires. Furthermore, the increase in autophagosome-like vacuoles may be an important cause of cell death by nanoparticles with ROS.