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

Abstract

Titanium dioxide nanoparticles (nano‐TiO 2) 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‐TiO 2‐induced cytotoxicity in peripheral blood lymphocytes. We examined the genotoxic effects of nano‐TiO 2 in lymphocytes using alkaline single‐cell gel electrophoresis (Comet) and cytokinesis‐block micronucleus (CBMN) assays. Lymphocytes treated with nano‐TiO 2 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‐TiO 2‐treated lymphocytes. However, p21 and bax, downstream targets of p53, were not affected, indicating that nano‐TiO 2 does not stimulate transactivational activity of p53. The generation of reactive oxygen species (ROS) in nano‐TiO 2‐treated cells was also observed, and N‐acetylcysteine (NAC) supplementation inhibited the level of nano‐TiO 2‐induced DNA damage. Given that ROS‐induced DNA damage leads to p53 activation in the DNA damage response, our results suggest that nano‐TiO 2 induces ROS generation in lymphocytes, thereby activating p53‐mediated DNA damage checkpoint signals. Environ. Mol. Mutagen., 2008. © 2008 Wiley‐Liss, Inc.