Assessing the Cytotoxicity of TiO 2-x Nanoparticles with a Different Ti 3+ (Ti 2+ )/Ti 4+ Ratio.

Titanium dioxide (TiO ₂ ) nanoparticles are promising biomedical agents characterized by good biocompatibility. In this study, we explored the cytotoxicity of TiO _2-x nanoparticles with a different Ti ³⁺ (Ti ²⁺ )/Ti ⁴⁺ ratio and analyzed the efficiency of eryptosis indices as a tool in nanotoxicology. Two types of TiO _2-x nanoparticles (NPs) were synthesized by the hydrolysis of titanium alkoxide varying the nitric acid content in the hydrolysis mixture. Transmission electron microscopy (TEM) images show that 1-TiO _2-x and 2-TiO _2-x NPs are 5 nm in size, whereas X-ray photoelectron spectroscopy (XPS) reveals different Ti ³⁺ (Ti ²⁺ )/Ti ⁴⁺ ratios in the crystal lattices of synthesized NPs. 1-TiO _2-x nanoparticles contained 54% Ti ⁴⁺ , 38% Ti ³⁺ , and 8% Ti ²⁺ , while the relative amount of Ti ⁴⁺ and Ti ³⁺ in the crystal lattice of 2-TiO _2-x nanoparticles was 63% and 37%, respectively. Cell viability and cell motility induced by TiO _2-x nanoparticles were investigated on primary fibroblast cultures. Eryptosis modulation by the nanoparticles along with cell death mechanisms was studied on rat erythrocytes. We report that both TiO _2-x nanoparticles do not decrease the viability of fibroblasts simultaneously stimulating cell migration. Data from in vitro studies on erythrocytes indicate that TiO _2-x nanoparticles trigger eryptosis via ROS- (1-TiO _2-x ) and Ca ²⁺ -mediated mechanisms (both TiO _2-x nanoparticles) suggesting that evaluation of eryptosis parameters is a more sensitive nanotoxicological approach for TiO _2-x nanoparticles than cultured fibroblast assays. TiO _2-x nanoparticles are characterized by low toxicity against fibroblasts, but they induce eryptosis, which is shown to be a promising tool for nanotoxicity screening. The Ti ³⁺ (Ti ²⁺ )/Ti ⁴⁺ ratio at least partly determines the cytotoxicity mechanisms for TiO _2-x nanoparticles.
(© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)