Titanium dioxide nanoparticles trigger p53-mediated damage response in peripheral blood lymphocytes

Titanium dioxide nanoparticles (nano-TiO₂) are widely used as a photocatalyst in air and water remediation. These nanoparticles are known to induce toxicity; however, their cytotoxic mechanism is not fully understood. In this study, we investigated the underlying mechanism of nano-TiO₂-induced cytotoxicity in peripheral blood lymphocytes. We examined the genotoxic effects of nano-TiO₂ in lymphocytes using alkaline single-cell gel electrophoresis (Comet) and cytokinesis-block micronucleus (CBMN) assays. Lymphocytes treated with nano-TiO₂ showed significantly increased micronucleus formation and DNA breakage. Western-blot analysis to identify proteins involved in the p53-mediated response to DNA damage revealed the accumulation of p53 and activation of DNA damage checkpoint kinases in nano-TiO₂-treated lymphocytes. However, p21 and bax, downstream targets of p53, were not affected, indicating that nano-TiO₂ does not stimulate transactivational activity of p53. The generation of reactive oxygen species (ROS) in nano-TiO₂-treated cells was also observed, andN-acetylcysteine (NAC) supplementation inhibited the level of nano-TiO₂-induced DNA damage. Given that ROS-induced DNA damage leads to p53 activation in the DNA damage response, our results suggest that nano-TiO₂ induces ROS generation in lymphocytes, thereby activating p53-mediated DNA damage checkpoint signals. Environ. Mol. Mutagen., 2008.