Introduction: Because of the increased production and application of manufactured Nano-TiO₂ in the past several years, it is important to investigate its potential hazards. TiO₂ is classified by IARC as a possible human carcinogen; however, the potential mechanism of carcinogenesis has not been studied clearly. The present study aimed to investigate the mechanism of DNA damage in rat lung and extra-pulmonary organs caused by TiO₂ nanoparticles.
Methods: In the present study, SD  rats were exposed to Nano-TiO₂ by intratracheal injection at a dose of 0, 0.2, or 1 g/kg body weight. The titanium levels in tissues were detected by ICP-MS. Western blot was used to detect the protein expression levels. The DNA damage and oxidative stress were detected by comet assay and ROS, MDA, SOD , and GSH-Px  levels, respectively.
Results: The titanium levels of the 1 g/kg group on day-3 and day-7 were significantly increased in liver and kidney as well as significantly decreased in lung compared to day-1. ROS and MDA levels were statistically increased, whereas SOD  and GSH-Px  levels were statistically decreased in tissues of rats in dose-dependent manners after Nano-TiO₂ treatment. PI3K , p-AKT /AKT , and p-FOXO3a /FOXO3a  in lung, liver, and kidney activated in dose-dependent manners. The levels of DNA damage in liver, kidney, and lung in each Nano-TiO₂ treatment group were significantly increased and could not recover within 7 days. GADD45α , ChK2 , and XRCC1  in liver, kidney, and lung of rats exposed to Nano-TiO₂ statistically increased, which triggered DNA repair.
Conclusion: This work demonstrated that Ti could deposit in lung and enter extra-pulmonary organs of rats and cause oxidative stress, then trigger DNA damage through activating the PI3K-AKT-FOXO3a  pathway and then promoting GADD45α , ChK2 , and XRCC1  to process the DNA repair.
Keywords: Nano-TiO₂, DNA damage, PI3K/AKT/FOXO3a signaling pathway, DNA repair, GADD45α/ChK2/XRCC1 signaling pathway