Nano Titanium Dioxide Induces the Generation of ROS and Potential Damage in HaCaT Cells Under UVA Irradiation

Nano titanium dioxide (nano-TiO₂) is frequently used in cosmetics, especially in sunscreen. Nano-TiO₂ has been reported to be an efficient photocatalyst, which is able to produce reactive oxygen species (ROS) under UVA irradiation. However, the effects and mechanisms of skin toxicity caused by nano-TiO₂ remain unclear. In this study, we explored the cytotoxicity and oxidative stress induced by nano-TiO₂ under UVA irradiation with different crystal forms (anatase, rutile and anatase/rutile) and sizes (4 nm, 10 nm, 21 nm, 25 nm, 60 nm) in human keratinocyte HaCaT cells. Intracellular distribution of nano-TiO₂, cell viability, intracellular reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP), super oxide dismutase (SOD) activity and Malondialdehyde (MDA) content were measured. The results showed that nano-TiO₂ (10–200 g/ml) significantly reduced cell viability in a dose-dependent manner in HaCaT cells. The cell viability was 76.9%, 60.2%, and 44.1% following nano-TiO₂ (4 nm), nano-TiO₂ (10 nm) and P25 treatment at the concentration of 200 g/ml, respectively (P < 0.01). Nano-TiO₂ induced ROS resulted in oxidative stress in these cells by reducing SOD and increasing MDA levels. The MMP of the cells was decreased significantly (P < 0.01) while the apoptosis rate was increased. Anatase and amorphous forms of nano-TiO₂ showed higher cytotoxicity than the rutile form. The results indicated that nano-TiO₂ could induce the generation of ROS and damage HaCaT cells under UVA irradiation.