DNA damage caused by metal nanoparticles: involvement of oxidative stress and activation of ATM.

Nanotechnology is a fast growing emerging field, the benefits of which are widely publicized. Our current knowledge of the health effects of metal nanoparticles such as nanosized cobalt (Nano-Co) and titanium dioxide (Nano-TiO(2)) is limited but suggests that metal nanoparticles may exert more adverse pulmonary effects as compared with standard-sized particles. To investigate metal nanoparticle-induced genotoxic effects and the potential underlying mechanisms, human lung epithelial A549 cells were exposed to Nano-Co and Nano-TiO(2). Our results showed that exposure of A549 cells to Nano-Co caused reactive oxygen species (ROS) generation that was abolished by pretreatment of cells with ROS inhibitors or scavengers, such as catalase and N-acetyl-L(+)-cysteine (NAC). However, exposure of A549 cells to Nano-TiO(2) did not cause ROS generation. Nano-Co caused DNA damage in A549 cells, which was reflected by an increase in length, width, and DNA content of the comet tail by the Comet assay. Exposure of A549 cells to Nano-Co also caused a dose- and a time-response increased expression of phosphorylated histone H2AX (γ-H2AX), Rad51, and phosphorylated p53. These effects were significantly attenuated when A549 cells were pretreated with catalase or NAC. Nano-TiO(2) did not show these effects. These results suggest that oxidative stress may be involved in Nano-Co-induced DNA damage. To further investigate the pathways involved in the Nano-Co-induced DNA damage, we measured the phosphorylation of ataxia telangiectasia mutant (ATM). Our results showed that phosphorylation of ATM was increased when A549 cells were exposed to Nano-Co, and this effect was attenuated when cells were pretreated with catalase or NAC. Pretreatment of A549 cells with an ATM specific inhibitor, KU55933, significantly abolished Nano-Co-induced DNA damage. Furthermore, pretreatment of A549 cells with ROS scavengers, such as catalase and NAC, significantly abolished Nano-Co-induced increased expression of phosphorylated ATM. Taken together, oxidative stress and ATM activation are involved in Nano-Co-induced DNA damage. These findings have important implications for understanding the potential health effects of metal nanoparticle exposure.