The DNA Damaging Potential of Photoactivated P25 Titanium Dioxide Nanoparticles
Elijah J. Petersen, Vytautas Reipa, Stephanie S. Watson, Deborah S. Jacobs, Savelas A. Rabb, Bryant C. Nelson
Titanium dioxide nanoparticles (TiO2 NPs) are found in numerous commercial and personal care products. Thus, it is necessary to understand and characterize their potential environmental health and safety risks. It is well known that photoactivated TiO2 NPs in aerated aqueous solutions can generate highly reactive hydroxyl radicals (OH) which can damage DNA. Surprisingly, recent in vitro studies utilizing the comet assay have shown that non-photoactivated TiO2 NPs kept in the dark can also induce DNA damage. In this work, we utilize high resolution, stable isotope-dilution gas chromatography/tandem mass spectrometry (GC/MS/MS) to quantitatively characterize the levels and types of oxidatively generated base lesions in genomic DNA exposed to National Institute of Standards and Technology Standard Reference Material TiO2 NPs (Degussa P25) under precisely controlled illumination conditions. We show that DNA samples incubated in the dark for 24 h with TiO2 NPs (concentrations ranging from 0.5 µg/mL to 50 µg/mL) does not lead to the formation of base lesions. However, when the same samples are exposed to either visible light from 400 nm to 800 nm (energy dose of 14.5 kJ/m2) for 24 h or UVA light at 370 nm for 30 min (energy dose of 10 kJ/m2), there is a significant formation of lesions at the 50 µg/mL dose for the visible light exposure and a significant formation of lesions at the 5 µg/mL and 50 µg/mL doses for the UVA light exposure. These findings suggest that commercial P25 TiO2 NPs do not have an inherent capacity to oxidatively damage DNA bases in the absence of sufficient photoactivation, yet electromagnetic radiation within the visible portion of the light spectrum can induce the formation of DNA lesions. Based on these findings, comet assay processing of cells exposed to TiO2 should be performed in the dark to minimize potential artefacts from laboratory light.