Titanium dioxide (tio2) is a polymorphic solid with a local structure in which Ti is coordinated to about 5 oxygen atoms. It is distinguished from crystalline forms in which Ti coordinates to 6 oxygen atoms, including rutile and brookite.
TiO2 is used as a coating and for other industrial purposes, primarily in the production of titanium nitrate (TiN), which is an acid that is used to remove nitrous oxide from combustion power plant exhaust gases. It is also used for antibacterial applications under UV light irradiation.
A number of in vitro and in vivo studies indicate that TiO2 NPs may cause certain reproductive and developmental toxicities, mainly due to the generation of ROS and oxidative stress. Various cell lines have been used to determine the genotoxic effects of TiO2 NPs, with a number of different cellular pathways being implicated.
Molecular mechanisms of toxicity:
In vitro studies have shown that TiO2 NPs can induce apoptosis via both the caspase-8/Bid and the p38/JNK pathways. However, TiO2 NPs can induce cytotoxicity in some cell lines through a mitochondrial apoptosis pathway independent of the caspase-8/Bid pathway.
In a study on mice, TiO2 NPs were taken up by human red blood cells without phagocytosis and endocytosis, which is not a common cellular uptake mechanism for particles. Since erythrocytes do not have phagocytic receptors, diffusion and adhesive interactions may play an important role in this cellular uptake of TiO2 NPs.