Toxicity assessment of six titanium dioxide nanoparticles in human epidermal keratinocytes

Purpose: The aim of this study was to evaluate and compare the toxicity of six different types of titanium dioxide (TiO₂) nanoparticles (NP) on human epidermal keratinocytes (HEK).

Materials and methods: Six TiO₂ NP (A (10 nm), A*(32 nm), B (27.5 nm), C (200 nm), C*(30-40 nm), and D*(200-400 nm)) were suspended in water or culture medium and characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). In addition, these NP were assayed with cell viability, cytokine release and cellular uptake in HEK.

Results: TiO₂NP did not change in shape in the culture medium when visualized by TEM. There was an increase in agglomeration with all TiO₂NP in the medium when measured by DLS. Since TiO₂NP interfered with the CellTiter 96®AQueous One and MTT assays but had a minimal effect on alamar Blue (aB). The aB viability assay was selected to assess all six types of TiO₂NP and sample B had a statistically significant decrease in viability at 0.4 mg/ml. A slight increase in TNF-α was noted in sample A*, C, and D* at as low as 0.05 mg/ml. Sample A* and B at certain concentrations showed an increase in Interleukin (IL)-6. IL-10 and IL-1β release for all TiO₂NP were noted around the detection limit with no significant changes compared to control. A statistically significant decrease in IL-8 was noted for all TiO₂NP at the highest concentrations due to the adsorption of IL-8 by TiO₂. All TiO₂NP were localized within cytoplasmic vacuoles of HEK and the element Ti was detected by energy-dispersive x-ray spectroscopy analysis.

Conclusions: Based on cell viability, only sample B was slightly cytotoxic to HEK and samples B and A* have the potential to cause inflammation indicated by an increase in IL-6.