The treatment of mice with 5 mg/kg nano-TiO2 for 60 days did not change the levels of ROS such as O2−, H2O2, nitric oxide (NO), and MDA (Fig. ​(Fig.6),6), or the mRNA levels of SOD, CAT, GSHPx, MT, GST, HSP70, P53, and TF genes in liver tissues (Fig. ​(Fig.7).7). Treatment of mice with 10 or 50 mg/kg nano-TiO2 for 60 days resulted in significant increases in the levels of O2−, H2O2, NO, and MDA (Fig. ​(Fig.6),6), decreases in the mRNA levels of SOD, CAT, MT, GST, HSP70, P53, TF, and GSHPx genes, and increases in the mRNA levels of CYP1A genes in the liver of mice (Fig. ​(Fig.7).7). The results showed that high doses of nano-TiO2-induced oxidative stress and changes in the expression of protective genes in the liver of exposed mice.

We further evaluated brain toxicity of nano-TiO2. We first examined the ratios of brain/body weight in the mice exposed to nano-TiO2 (i.p. for 14 days). Low doses (5, 10, 50 mg/kg) did not change the ratios of brain/body weight, and higher doses (100, 150, 200 mg/kg) significantly decreased the ratios of brain/body weight in a dose-dependent manner (Fig. ​(Fig.2).2). The concentration of Ti in the brain tissues was significantly increased in a dose-dependent manner (Fig. ​(Fig.11).