Abstract
Titanium dioxide (TiO2), also known as titanium (IV) oxide or anatase, is the naturally occurring oxide of titanium. It is also one of the most commercially used form. To date, no parameter has been set for the average ambient air concentration of TiO2 nanoparticles (NP) by any regulatory agency. Previously conducted studies had established these nanoparticles to be mainly non-cyto- and -genotoxic, although they had been found to generate free radicals both acellularly (specially through photocatalytic activity) and intracellularly. The present study determines the role of TiO2-NP (anatase, ∅ < 100 nm) using several parameters such as cyto- and genotoxicity, DNA-adduct formation and generation of free radicals following its uptake by human lung cells in vitro. For comparison, iron containing nanoparticles (hematite, Fe2O3, ∅ < 100 nm) were used. The results of this study showed that both types of NP were located in the cytosol near the nucleus. No particles were found inside the nucleus, in mitochondria or ribosomes. Human lung fibroblasts (IMR-90) were more sensitive regarding cyto- and genotoxic effects caused by the NP than human bronchial epithelial cells (BEAS-2B). In contrast to hematite NP, TiO2-NP did not induce DNA-breakage measured by the Comet-assay in both cell types. Generation of reactive oxygen species (ROS) was measured acellularly (without any photocatalytic activity) as well as intracellularly for both types of particles, however, the iron-containing NP needed special reducing conditions before pronounced radical generation. A high level of DNA adduct formation (8-OHdG) was observed in IMR-90 cells exposed to TiO2-NP, but not in cells exposed to hematite NP. Our study demonstrates different modes of action for TiO2- and Fe2O3-NP. Whereas TiO2-NP were able to generate elevated amounts of free radicals, which induced indirect genotoxicity mainly by DNA-adduct formation, Fe2O3-NP were clastogenic (induction of DNA-breakage) and required reducing conditions for radical formation.
Highlights
Titanium dioxide (TiO2) has several isoforms of which anatase is the most commercially used type
Physico-chemical characterization of nanoparticles (NP) electron dispersive X-ray analysis (EDX) spectral analysis of the particle surface chemical composition revealed that the TiO2 nanoparticles contained 56% titanium (Ti), 41% oxygen (O) and 3% carbon (C) elements, while Fe2O3-NP were purely composed of 78.7% iron (Fe) and 21.3% oxygen (O)
Zeta potential measurements revealed that TiO2-NP had a +48.8 mV charge and the average particle hydrodynamic diameter proved to be 91 nm
Summary
Titanium dioxide (TiO2) has several isoforms of which anatase is the most commercially used type. Occupational exposure to TiO2 nanoparticles can occur during manufacturing/use of these particles as pigments for paints, varnishes, enamels, lacquers and paper coatings to impart whiteness, opacity and brightness [2]. The surface charge is one of the major physical properties of the nanoparticles that play a major role in their industrial application. It can only be measured indirectly through the zeta potential which is a function of the surface charge of the particle or any adsorbed layer at the interface and the nature and composition of the surrounding medium in which the particle is suspended. The zeta potential gives no information on the elemental composition of the surface [3]
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