Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in the biological sciences. The increasing use of TiO₂ NPs increases the risk of humans and the environment being exposed to NPs. We previously showed that toll-like receptors (TLRs) play an important role in the interactions between NPs and cells. Our previous results indicated that TLR4 increased the DNA damage response induced by TiO₂ NPs, due to enhanced NP uptake into the cytoplasm, whereas TLR3 expression decreased the DNA damage response induced by TiO₂ NPs because of NP retention in the endosome. In this study, we explored the molecular mechanism of the DNA damage response induced by TiO₂ NPs using TLR3 or TLR4 transfected cells. We examined the effect of TLR3 or TLR4 over-expression on oxidative stress and the effect of DNA damage induced by TiO₂ NPs on gene expression levels.

Our results showed evidence for elevated oxidative stress, including the generation of reactive oxygen species (ROS), with increased hydrogen peroxide levels, decreased glutathione peroxidase, and reduced glutathione and activated caspase-3 levels in cells exposed for 48 h to 10 μg/ml TiO₂ NPs. These effects were enhanced by TLR4 and reduced by TLR3 over-expression. Seventeen genes related to DNA double-strand breaks and apoptosis were induced, particularly IP6K3 and ATM.

Our results indicated that TiO₂ NPs induced ROS, and the above molecules are implicated in the genotoxicity induced by TiO₂ NPs.