oa Genotoxicity Induced By Nanomaterials

Nanomaterials are useful for their characteristic properties and are commonly used in various fields. The assessment of genotoxicity and safety of nanomaterials are, therefore, of serious concern. So far, we have examined genotoxic effects of various nanomaterials, including fullerenes, kaolins, multi-wall carbon nanotubes and magnetite, using in vitro and in vivo assay systems. All of these nanomaterials significantly induced micronuclei and enhanced frequency of sister chromatid exchange in cultured mammalian cells. When ICR mice were intratracheally instilled with a single dose (0.2 mg/animal) of these nanomaterials, DNA damage of the lungs analyzed by Comet assay increased about two to three times that of the vehicle control. We also analyzed the formation of DNA adducts related to oxidative stress (8-oxo-2’-deoxyguanosine and heptanone etheno-deoxyribonucleosides) in lungs of mice exposed to nanomaterials using the stable-isotope dilution LC-MS/MS method. These DNA adduct levels were increased in the nanomaterial-treated mice compared with a vehicle control. Moreover, we examined in vivo mutagenicity of nanomaterials using gpt delta transgenic mice intratracheally-instilled with four consecutive doses of 0.2 mg per animal. All nanomaterials increased gpt mutant frequencies in the lungs of gpt delta transgenic mice. Mutation spectra analysis showed transversions were predominant, and among these, the G:C to C:G was commonly increased by these nanomaterials. Based on these observations, it is suggested that oxidative stress and inflammatory responses are probably involved in the genotoxicity induced by nanomaterials. To further clarify the mechanisms of genotoxicity by nanomaterials, comprehensive DNA adduct analysis (DNA adductome) is now being investigated for DNA samples derived from lungs of mice exposed to nanomaterials. On the other hand, the effects of atypical nanomaterials such as difference of surface structure on genotoxicity are not fully elucidated yet. In the present study, we investigated the DNA damaging potency of two types of kaolins by Comet assay, and found out that genotoxicity differs between two types of kaolins. We are now investigating the incorporation rate into mammalian cells, and reactive oxygen species generation of these kaolins.