Oxidative Stress on Human Cells in the Presence of Nano-Sized Titanium Dioxide (original) (raw)

Nanosized TiO 2 (nanoTiO 2) is one of the most widely used nanomaterials, with applications ranging from paints, self-cleaning coatings, pharmaceuticals, to food and cosmetics. In spite of this massive use of nanoTiO 2 , its biological activity and toxicity remains subject of the intense debate. In particular, there is still considerable uncertainty in the current understanding of the relationship between physico-chemical parameters of nanoTiO 2 , such as crystalline phase, size, aspect ratio, surface properties, surface defects and surface chemistry and its potential toxicological effects. Motivated by this general problem, this thesis provides a multidisciplinary experimental insight into to the toxicity and photo-toxicity of various forms of nanoTiO 2. Firstly, since all of the widely accepted models of nanoTiO 2 toxicity involve reactive oxygen species (ROS), electron spin resonance (ESR) in combination with spintrapping was used to measure ROS formation efficiency for the two most industrially important polymorphs of TiO 2 , anatase and rutile. The study was performed in an unprecedentedly broad range of particle sizes: 3.8 nm to 150 nm and 5 nm to 215 nm, for anatase and rutile nanoTiO 2 , respectively. Moreover, the photocatalytic and toxic properties of custom-made anatase-based TiO 2 nanowires (with a diameter of 35 nm and a length of 0.5-1 μm) were characterized for the first time. For pure anatase nanoTiO 2 , the maximum ROS generation efficacy was found for nanoparticle sizes in the range of 25-30 nm. The ROS generation efficacy of the custom-made TiO 2 nanowires was ca. 30% lower, being close to that of the commercial anatase nanoTiO 2 with primary grain sizes of 5.3 nm. Secondly, this thesis addressed challenging, complex and still poorly understood processes occurring when nanoTiO 2 particles are brought into contact with living cells. In particular, the comparative nanotoxicity study towards human melanoma Lu1205 and WM793 cell lines was performed for three selected nanomaterials: the custom-made anatase-based TiO 2 nanowires, the commercial anatase nanoTiO 2 with a primary particle size of 5.3 nm and similar in vitro ROS formation efficacy, and the industrial photocatalytic standard, P25 Degussa (a formulation consisting of 80% anatase and 20% rutile, with primary grain sizes of 25 nm). This comparative nanotoxicity study was performed using very low concentrations of nanoTiO 2 (2-2.5 μg/mL), considerably lower than that applied in the majority of previous ex vivo cell culture studies.