High sensitivity of testicular function to titanium nanoparticles

Titanium dioxide nanoparticles (TiNPs) present toxicity in organs such as the liver, lung, and intestine. The testis has also been reported as a target organ of TiNPs. We recently reported that TiNPs had no genotoxic effect in the liver and bone marrow, while showing clear testicular dysfunction. In this paper, therefore, we systematically compared the sensitivity of hepatic function using biochemical markers and testicular function against TiNPs. Male C57BL/6J mice were injected intravenously with TiNPs (Aeroxide-P25, at doses of 0.1, 1, 2, and 10 mg/kg body weight) once per week for 4 consecutive weeks. Mice were sacrificed three days after the last injection. Body weights, liver weights, and testicular-related organ weights were not found to be changed by TiNP treatment. Moreover, TiNPs caused no hepatic damage, as evaluated by alanine aminotransferase and aspartate aminotransferase indexes. The testicular function, however, was clearly impaired by TiNP treatment; reduction in two sperm motion parameters (motile percent and progressive percent) and sperm numbers in cauda epididymides was seen. We observed Ti accumulation in the liver but not in the testis, as well as no change in plasma levels of sex hormones related to spermatogenesis. Our findings indicate that the testis is highly sensitive to TiNPs, as compared to the liver. We believe that, when considering the biological effects of TiNPs, testicular function (especially motility ability) may be a sensitive indicator.