title: Hydrogen peroxide is responsible for UVA-induced DNA damage measured by alkaline comet assay in HaCaT keratinocytes.
abstract: We investigated the role of different reactive oxygen species (ROS) in ultraviolet A (UVA)-induced DNA damage in a human keratinocyte cell line, HaCaT. UVA irradiation increased the intracellular levels of hydrogen peroxide (H2O2), detected by a fluorescent probe carboxydichlorodihydrofluorescein, and caused oxidative DNA damage, single strand-breaks and alkali-labile sites, measured by alkaline single cell gel electrophoresis (comet assay). Superoxide anion (O2*-) was a likely substrate for H2O2 production since diethyldithiocarbamate (DDC), a superoxide dismutase blocker, decreased the level of intracellular H2O2. Hydrogen peroxide was shown to play a central role in DNA damage. Increasing the intracellular levels of H2O2 with aminotriazole (AT) (a catalase blocker) and buthionine sulfoximine (BSO) (an inhibitor of glutathione synthesis) potentiated the UVA-induced DNA damage. Exogenous H2O2 was also able to induce DNA damage. Since H2O2 alone is not able to damage DNA directly, we investigated the significance of the H2O2-derived hydroxyl radical (*OH). Addition of FeSO4, that stimulates *OH formation from H2O2 (Fenton reaction) resulted in a twofold increase of DNA-damage. Desferrioxamine, an iron chelator that blocks the Fenton reaction, prevented UVA-induced DNA damage. We also employed a panel of less specific antioxidants and enzyme modulators. Sodium selenite (Na-Se) present in glutathione peroxidase and thioredoxin reductase and addition of glutathione (GSH) prevented DNA-damage. Tocopherol potently prevented UVA-and H2O2-induced DNA damage and reduced intracellular H2O2 -levels. Ascorbic acid reduced H2O2 production, but only partly prevented DNA damage. Singlet oxygen (1O2) did not seem to play an important role in the UVA-induced DNA-damage since the specific 1O2 scavenger sodium azide (NaN3) and the less specific 1O2 scavenger beta-carotene did not markedly prevent either DNA-damage or H2O2 production. In conclusion the conversion of H2O2 to *OH appears to be the most important step in UVA-induced generation of strand breaks and alkali-labile sites and the bulk H2O2 appears to originate from O2*- generated by UVA irradiation.
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark. ap02@bbh.hosp.dk
authors.forename: A B
authors.initials: AB
authors.lastname: Petersen
authors.forename: R
authors.initials: R
authors.lastname: Gniadecki
authors.forename: J
authors.initials: J
authors.lastname: Vicanova
authors.forename: T
authors.initials: T
authors.lastname: Thorn
authors.forename: H C
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D002460:Cell Line; D020552:Comet Assay; D004249:DNA Damage; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism* / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide