Cyto- and genotoxicity of ultrafine TiO2 particles in cultured human lymphoblastoid cells

Titanium dioxide is frequently used in the production of paints, paper, plastics, welding rod-coating material, and cosmetics, because of its low toxicity. However, recent studies have shown that nano-sized or ultrafine TiO2 (UF-TiO2) (<100 nm in diameter) can generate pulmonary fibrosis and lung tumor in rats. Cytotoxicity induced by UF-TiO2 in rat lung alveolar macrophages was also observed. This generates great concern about the possible adverse effects of UF-TiO2 for humans. The cytotoxicity and genotoxicity of UF-TiO2 were investigated using the methyl tetrazolium cytotoxicity (MTT) assay, the population growth assay, the apoptosis assay by flow cytometry, the cytokinesis block micronucleus (CBMN) assay, the comet assay, and the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutation assay. WIL2-NS cells were incubated for 6, 24 and 48 h with 0, 26, 65 and 130 μg/ml UF-TiO2. Significant decreases in viability were seen in the MTT assay at higher doses; for example, 61, 7 and 2% relative viability at 130 μg/ml for 6, 24 and 48-h exposure (P < 0.01). A dose-dependent relationship was observed, while a time-dependent relationship was seen only at the highest dose (130 μg/ml) after exposure for 24 and 48 h. Treatment with 130 μg/ml UF-TiO2 induced approximately 2.5-fold increases in the frequency of micronucleated binucleated cells (P < 0.01). In addition, a significant reduction in the cytokinesis block proliferation index was observed by the CBMN assay (P < 0.05). In the comet assay, treatment with 65 μg/ml UF-TiO2 induced approximately 5-fold increases in olive tail moment (P < 0.05). In the HPRT mutation assay, treatment with 130 μg/ml UF-TiO2 induced approximately 2.5-fold increases in the mutation frequency (P < 0.05). The results of this study indicate that UF-TiO2 can cause genotoxicity and cytotoxicity in cultured human cells.