In vitro Evaluation of Cellular Responses Induced by Al(OH)₃-treated Rutile TiO₂ anoparticles

Abstract

In many cases, nanoparticles have higher physical and chemical activities than fine particles. These activities are beneficial for industrial use; however, they may have biological effects resulting from properties such as high toxicity. Rutile titanium dioxide (TiO₂) is one of the most important metal oxide nanoparticles. It has been used not only for industrial purposes but also in cosmetics such as sunscreen. Compared to anatase TiO₂, cellular influences of rutile TiO₂ are not well understood. In the present study, we examined cells for examining the effects of cosmetic-grade Al(OH)₃-treated rutile TiO₂ nanoparticles. It has been suggested that metal ion release and the subsequent oxidative stress play an important role in the cytotoxicity of metal oxide nanoparticles. Therefore, we focused on the effect of released soluble metal and the induction of oxidative stress due to rutile TiO₂ nanoparticles. First, the properties of TiO₂ medium dispersion were detected. Rutile TiO₂ nanoparticles had strong protein adsorption ability. Titanium ion release from TiO₂ nanoparticles in the medium dispersion was not detected, and aluminum ions were found to be slightly released. Next, two kinds of cultured cells-human lung carcinoma A549 cells and human keratinocyte HaCaT cells-were exposed to stable TiO₂ medium dispersion. Cellular influences (oxidative stress, apoptosis, and colony formation) of the TiO₂ nanoparticles were small. These results suggest that metal ion release is the most important cytotoxic factor influencing the toxic activity of metal oxide nanoparticles. On the other hand, the cellular effect of adsorbed serum proteins is small. Therefore, cellular influences of Al(OH)₃-treated rutile TiO₂ nanoparticles that did not release metal ions are limited. The detection of metal ion release is essential for the evaluation of the cellular influence of metal oxide nanoparticles.