Photo-irradiated titanium dioxide catalyzes site specific DNA damage via generation of hydrogen peroxide.
Titanium dioxide (TiO2) is a potential photosensitizer for photodynamic therapy. In this study, the mechanism of DNA damage catalyzed by photo-irradiated TiO2 was examined using [32P]-5'-end-labeled DNA fragments obtained from human genes. Photo-irradiated TiO2 (anatase and rutile) caused DNA cleavage frequently at the guanine residue in the presence of Cu(II) after E. coli formamidopyrimidine-DNA glycosylase treatment, and the thymine residue was also cleaved after piperidine treatment. Catalase, SOD and bathocuproine, a chelator of Cu(I), inhibited the DNA damage, suggesting the involvement of hydrogen peroxide, superoxide and Cu(I). The photocatalytic generation of Cu(I) from Cu(II) was decreased by the addition of SOD. These findings suggest that the inhibitory effect of SOD on DNA damage is due to the inhibition of the reduction of Cu(II) by superoxide. We also measured the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, and showed that anatase is more active than rutile. On the other hand, high concentration of anatase caused DNA damage in the absence of Cu(II). Typical free hydroxyl radical scavengers, such as ethanol, mannnitol, sodium formate and DMSO, inhibited the copper-independent DNA photodamage by anatase. In conclusion, photo-irradiated TiO2 particles catalyze the copper-mediated site-specific DNA damage via the formation of hydrogen peroxide rather than that of a free hydroxyl radical. This DNA-damaging mechanism may participate in the phototoxicity of TiO2.
Department of Radiation Chemistry, Life Science Research Center, Mie University, Edobashi 2-174, Tsu Mie 514-8507, Japan.
Kazutaka
K
Hirakawa
Masafumi
M
Mori
Mami
M
Yoshida
Shinji
S
Oikawa
Shosuke
S
Kawanishi
D002374:Catalase / Q000494:pharmacology; D003300:Copper / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects*; D043382:DNA-Formamidopyrimidine Glycosylase / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D016166:Free Radical Scavengers / Q000494:pharmacology; D011905:Genes, ras / Q000235:genetics; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D017665:Hydroxyl Radical / Q000378:metabolism; D008027:Light; D010618:Phenanthrolines / Q000494:pharmacology; D017319:Photosensitizing Agents / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D014025:Titanium / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D014874:Water Pollutants, Chemical
D019941:Cyclin-Dependent Kinase Inhibitor p16; D016166:Free Radical Scavengers; D010618:Phenanthrolines; D017319:Photosensitizing Agents; D016159:Tumor Suppressor Protein p53; D014874:Water Pollutants, Chemical; D013481:Superoxides; C009495:titanium dioxide; D017665:Hydroxyl Radical; D003300:Copper; C002478:bathocuproine; D006861:Hydrogen Peroxide; D014025:Titanium; D002374:Catalase; D013482:Superoxide Dismutase; D043382:DNA-Formamidopyrimidine Glycosylase