Cytotoxicity and DNA-damage in Mouse Macrophage Exposed to Silica Nanoparticles

[Objective] In order to assess cytotoxic effects and DNA damage induced by exposure to different doses of silica nanoparticles, we conducted a study using Raw264.7 cells [Methods] RAW264.7 cells were exposured to silica nanoparticles at 0.24 mg/ml(0-32 mg/ml microscale SiO2 as positive control) for 24 h and analysed by MTT for cytotoxic effect evaluation. Cells were also exposed to 31.25, 125, 500 mu g/ml of silica nanoparticles(500 mu g/ml microscale SiO2) for 24 h and DNA single strand breaks were evaluated by Single Cell gel Electrophoresis (SCEG, Comet test), and apoptosis and cell cycle were analysed by flow cytometry. [Results] Significant dose-dependent decreases in percent cell viability were seen with increasing dose of silica nanoparticles in the methyl tetrazolium assay. The inhibitory concentration 50% (IC50) of silica nanoparticles and of microscale SiO2 was 16.69 and 5.08 mg/ml respectively. In DNA strand breakage as measured by the Comet assay, the rate of comet (comet%), tail length (TL), the percentage of DNA in the tail (TDNA%) and olive tail moment (OTM) induced by silica nanoparticles were significantly increased in comparison with microscale SiO2 at 500 mu g/ml (P<0.05). the rate of apoptosis cell caused by silica nanoparticles at 125, 500 mu g/ml was significantly higher than control group. There was no significant difference of apoptosis rate silica nanoparticles and microscale, SiO2 at 500 mu g/ml (P>0.05). Silica nanoparticles at 125,500 mu g/ml caused significant decreases of PI and increases (P<0.05) in the proportions of cells in G(0)/G(1) phases as compared with negative control PI and proportions cell in G(0)/G(1) and S phase caused by SiO2 nanoparticles and microscale SiO2 at dosage of 500 mu g/ml were no significant difference (P>0.05). [Conclusion] The results indicate that SiO2 nanoparticles are more cytotoxic than microscale SiO2 particles. SiO2 nanoparticles induce DNA injury, apoptosis increase, PI decrease in RAW264.7 cells. DNA injury and cell apoptosis may be involved in the reducing of cell proliferation.