title: DNA damaging potential of photoactivated p25 titanium dioxide nanoparticles.
abstract: 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 nonphotoactivated TiO2 NPs kept in the dark can also induce DNA damage. In this work, we utilize stable isotope-dilution gas chromatography/tandem mass spectrometry to quantitatively characterize the levels and types of oxidatively generated base lesions in genomic DNA exposed to NIST 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 (0.5-50 μg/mL) do not lead to the formation of base lesions. However, when the same DNA is exposed to either visible light from 400 to 800 nm (energy dose of ∼14.5 kJ/m(2)) for 24 h or UVA light at 370 nm for 30 min (energy dose of ∼10 kJ/m(2)), 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 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; however, TiO2 NPs exposed to electromagnetic radiation within the visible portion of the light spectrum can induce the formation of DNA lesions. On the basis of these findings, comet assay processing of cells exposed to TiO2 should be performed in the dark to minimize potential artifacts from laboratory light.
authors.affiliation: Material Measurement Laboratory-Biosystems and Biomaterials Division, ‡Material Measurement Laboratory-Chemical Sciences Division, §Engineering Laboratory-Materials and Structural Systems Division, National Institute of Standards and Technology , 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.
authors.forename: Elijah J
authors.initials: EJ
authors.lastname: Petersen
authors.forename: Vytas
authors.initials: V
authors.lastname: Reipa
authors.forename: Stephanie S
authors.initials: SS
authors.lastname: Watson
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Stanley
authors.forename: Savelas A
authors.initials: SA
authors.lastname: Rabb
authors.forename: Bryant C
authors.initials: BC
authors.lastname: Nelson
mesh_terms: D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000737:chemistry*; D004249:DNA Damage / Q000187:drug effects* / Q000528:radiation effects; D003849:Deoxyguanosine / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D008401:Gas Chromatography-Mass Spectrometry; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism; D008027:Light; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D053719:Tandem Mass Spectrometry; D014025:Titanium / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: C009495:titanium dioxide; D017665:Hydroxyl Radical; D004247:DNA; C427203:calf thymus DNA; D014025:Titanium; D003849:Deoxyguanosine