Titanium dioxide particles phosphorylate histone H2AX independent of ROS production

With the rising use of nano-sized particles in nanotechnology, harmful effects of TiO2 particles which have been recognized as a safe material, are of increasing concern. In this study, we examined the genotoxicity of two different sized TiO2 particles in the lung adenocarcinoma epithelial cell line A549 based on the phosphorylation of histone H2AX (γ-H2AX), recently regarded as a sensitive marker for DNA damage. TiO2 particles generated γ-H2AX, which was more remarkable with the smaller particles. Flow cytometric analysis showed that the generation was independent of cell cycle phases and cells which incorporated larger amounts of TiO2 particles had more significant γ-H2AX. Although there are some reports that the incorporation of nanomaterials into cells generates reactive oxygen species (ROS), the level of ROS was low even if large amounts of TiO2 particles were taken-up. In addition, the generation of γ-H2AX by TiO2 particles was more significant than that after treatment with hydrogen peroxide. On the other hand, the generation of γ-H2AX was attenuated by coating the surface of TiO2 particles with bovine serum albumin. These results suggested that smaller TiO2 particles were easy to incorporate into cells and generated cell cycle phase-independent γ-H2AX, which was dependent on the condition of the TiO2 surface but not on the formation of ROS.

► TiO2 particles generated γ-H2AX, which was more remarkable with smaller particles.
► The generation of γ-H2AX was independent of cell cycle phases.
► ROS formation by TiO2 particles was not involved in the generation of γ-H2AX.
► The surface condition of TiO2 particles would be an important factor in the generation of γ-H2AX.