Cytotoxicity and genotoxicity of ultrafine crystalline SiO2 particulate in cultured human lymphoblastoid cells

Respirable crystalline silica has been classified as a human lung carcinogen. Ultrafine (diameter < 100 nm) silica particles may be important in carcinogenesis, although the mechanisms remain unclear. In the present study, WIL2-NS cells were incubated for 6, 24, and 48 hr with 0, 30, 60, and 120 pg/ml ultrafine crystalline SiO2 (UFSiO2). The cytotoxic and genotoxic effects caused by UF-SiO2 in cultured human cells were investigated via a set of bioassays. Significant closedependent decreases in percent cell viability were seen with increasing dose of UF-SiO2 in the methyl tetrazolium assay. Significant decreases were seen at 120 mu g/ml (58, 38, and 57% for 6, 24, and 48-hr exposure, respectively). During 4 days growth in the flasks, there was a slight recovery observed after washing off UF-SiO2 as measured by the population growth assay. Significant close- dependent reduction in the cytokinesis block proliferation index was observed by the cytokinesis block micronucleus assay. Treatment with 120 mu g/ml UF-SiO2 for 24 hr produced a fourfold increase in the frequency of micronucleated binucleated cells (MNBNC). The increase in MNBNC was close-clependent. The lowest dose that gave a statistically significant increase in MNBNC was 30 mu g/ml (24-hr treatment), which had cytotoxicity of less than 10%. There was no significant difference in DNA strand breakage as measured by the Comet assay. A significant increase in induced mutant frequency was found at 120 mu g/ml as detected by the hypoxanthine guanine phosphoribosyltransferase mutation assay. The results indicate that UF-SiO2 is cytotoxic and genotoxic in cultured human cells. Enviran.