Cytotoxicity and DNA damage in mouse macrophages exposed to silica nanoparticles

Silica (SiO₂) nanoparticles are being progressively applied in various applications, including cosmetics, food technology, and medical diagnostics. Although crystalline SiO₂ is a known carcinogen, the carcinogenicity of SiO₂ nanoparticles remains unclear. Here, we assessed the cytotoxic effects and DNA injury induced by exposure to various dosages of SiO₂ nanoparticles at 0-2400 mg/mL (0-3200 mg/mL microscale SiO₂ as positive control) for 24 h using RAW264.7 cells, followed by methyl tetrazolium (MTT) assay. Cells were also treated by 31.25, 125, and 500 mg/mL SiO₂ nanoparticles (500 mg/mL microscale SiO₂ as positive control) for 24 h and examined by single cell gel electrophoresis assay (SCEG) and flow cytometry. Outstanding dose-related decline in cell viability was observed with enhancing dosages of SiO₂ nanoparticles by MTT assay. The inhibitory concentration 50% of SiO₂ nanoparticles and microscale SiO₂ was 16690 and 5080 mg/mL, respectively. The comet rate (comet%), length of tail, the percentage in DNA tail (TDNA%) and olive tail moment (OTM) induced by SiO₂ nanoparticles were significantly increased in comparison with control and microscale SiO₂ at 500 mg/mL. 500 mg/mL SiO₂ nanoparticles and microscale SiO₂ caused a significant increase in apoptosis rate, decreased proliferation index and increased cell proportions in G₀/G₁ phases by contrast to the negative control (P < 0.05). This indicates that SiO₂ nanoparticles are more cytotoxic than microscale SiO₂ particles; they induce DNA injury, increase apoptosis, and decrease the proliferation index in RAW264.7 cells. DNA injury and apoptosis may be involved in reducing cell proliferation.