Determination of TiO₂, ZrO₂, and Al₂O ₃ nanoparticles on genotoxic responses in human peripheral blood lymphocytes and cultured embyronic kidney cells

In this study a genotoxic evaluation of titanium dioxide (TiO₂, 2.3 nm), zirconium oxide (ZrO₂, 6 nm), aluminum oxide (Al ₂O₃, 16.7 nm) nanoparticles (NP) and their ionic forms was conducted using human peripheral blood lymphocytes and cultured human embryonic kidney (HEK293) cells by means of a modified alkaline comet assay with/without the formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease III (Endo III) enzymes. Modifications to the comet assay by using lesion-specific endonucleases, such as Endo III and Fpg, detect DNA bases with oxidative damage. Both human peripheral blood lymphocytes and cultured embryonic kidney cells were incubated with TiO₂, ZrO₂, or Al₂O ₃ NP at concentrations of 1, 10, or 100 μg/ml. Our results showed no significant induction in DNA damage by the comet assay with/without the Endo III and Fpg enzymes at all concentrations of ZrO₂ and Al ₂O₃. In the case of TiO₂ NP only the highest concentration of 100 μg/ml significantly induced a genotoxic response. Data thus indicate that both ZrO₂ and Al₂O₃ NP were not genotoxic in our system and in the case of TiO₂ the lowest-observed-adverse-effect level (LOAEL) for genotoxicity was 100 μg/ml. Evidence indicates that these metallic NP are considered safe in light of the fact that no genotoxicity was noted with ZrO₂ and Al ₂O₃ and that the highest TiO₂ concentration is not environmentally relevant.