title: Inactivation of primary antioxidant enzymes in mouse keratinocytes by photodynamically generated singlet oxygen.
abstract: Cellular antioxidant enzymes protect against damage caused by exposure to endogenous or exogenous prooxidants. Singlet oxygen ((1)O(2)) is a reactive form of oxygen that can be produced in vivo either in normal and pathophysiologic conditions or by photosensitizing chemicals, as during photodynamic treatment. We hypothesized that photodynamically generated (1)O(2) would decrease the enzymatic activities of cellular antioxidants. To test this hypothesis, we treated cultured mouse epidermal keratinocytes with the photosensitizer Photofrin plus visible light to produce (1)O(2), and then measured CuZnSOD, MnSOD, and catalase activities with both ingel and spectrophotometric enzyme activity assays. Our results demonstrated that the enzymatic activities of cellular CuZnSOD, MnSOD, and catalase were significantly decreased after keratinocytes were treated with Photofrin plus visible light. By contrast, the enzymatic activities of cellular CuZnSOD, MnSOD, and catalase were unaffected in control cells treated with Photofrin only or visible light only. Despite the decreased levels of enzymatic activities, the protein levels of all three primary antioxidant enzymes remained constant after photodynamic treatment, as determined by Western blotting. L-Histidine, a (1)O(2) quencher, protected against the inactivation of cellular CuZnSOD, MnSOD, and catalase enzymes induced by photodynamically generated (1)O(2). The conclusion from these experiments is that the primary cellular antioxidant enzymes CuZnSOD, MnSOD, and catalase can be inactivated by photodynamically generated (1)O(2) in nucleated mammalian cells. These findings may be useful in the future development of antineoplastic adjuvant therapies that use photodynamic generation of (1)O(2) to inactivate antioxidant defenses with a goal of sensitizing tumor cells to prooxidant-generating drugs.
authors.affiliation: Free Radical and Radiation Biology Graduate Program, Department of Radiation Oncology, The University of Iowa, Iowa City, 52242, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Luo
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.forename: Yuping
authors.initials: Y
authors.lastname: Zhang
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Spitz
authors.forename: Garry R
authors.initials: GR
authors.lastname: Buettner
authors.forename: Larry W
authors.initials: LW
authors.lastname: Oberley
authors.forename: Frederick E
authors.initials: FE
authors.lastname: Domann
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism*; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects; D017323:Dihematoporphyrin Ether / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015603:Keratinocytes / Q000201:enzymology* / Q000528:radiation effects; D008027:Light; D051379:Mice; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D026082:Singlet Oxygen / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000975:Antioxidants; D017319:Photosensitizing Agents; D026082:Singlet Oxygen; D017323:Dihematoporphyrin Ether; D002374:Catalase; D013482:Superoxide Dismutase