title: Alloxan acts as a prooxidant only under reducing conditions: influence of melatonin.
abstract: Depending on the availability of suitable reducing agents, alloxan can be either a prooxidant or an antioxidant. Alloxan and its reduced derivative, dialuric acid, act as a redox couple, driven by reduced glutathione (GSH) or L-cysteine, generating in vitro in the presence of oxygen, both superoxide radical and hydrogen peroxide. The production of superoxide radicals was shown by the appearance of lucigenin chemiluminescence (CL) as well as by the generation of formazan from nitroblue tetrazolium (NBT). The lucigenin CL as well as the NBT reduction was inhibited by superoxide dismutase and partially by catalase. Melatonin inhibited alloxan-mediated CL. In contrast, in the absence of reducing agents, alloxan is a scavenger of superoxide radicals formed by other reactions. Because of the high content of reducing compounds in the cell (e.g. glutathione), it is suggested that alloxan acts in vivo mainly as a generator of reactive oxygen species.
authors.affiliation: Institute of Pathophysiology, Martin Luther University, Halle-Wittenberg, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Brömme
authors.forename: H
authors.initials: H
authors.lastname: Ebelt
authors.forename: D
authors.initials: D
authors.lastname: Peschke
authors.forename: E
authors.initials: E
authors.lastname: Peschke
mesh_terms: D000496:Alloxan / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000633:toxicity; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D003124:Colorimetry; D016166:Free Radical Scavengers / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects; D008163:Luminescent Measurements; D008550:Melatonin / Q000494:pharmacology*; D009580:Nitroblue Tetrazolium; D016877:Oxidants / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017382:Reactive Oxygen Species; D013481:Superoxides / Q000378:metabolism
chemical_list: D000975:Antioxidants; D016166:Free Radical Scavengers; D007093:Imidazoles; D016877:Oxidants; D017382:Reactive Oxygen Species; D013481:Superoxides; D009580:Nitroblue Tetrazolium; C021286:alloxanic acid; D000496:Alloxan; D006861:Hydrogen Peroxide; D005978:Glutathione; D008550:Melatonin