title: Evaluation of the antioxidant activity of melatonin in vitro.
abstract: Melatonin is being increasingly promoted as a treatment for "jet lag" and insomnia and has been suggested to act as an antioxidant in vivo. The antioxidant and potential pro-oxidant activities of melatonin were investigated in vitro. Melatonin was able to scavenge hypochlorous acid (HOCl) at a rate sufficient to protect catalase against inactivation by this molecule. Melatonin could also prevent the oxidation of 5-thio-2-nitrobenzoic acid by HOCl. Melatonin decreased the peroxidation of ox-brain phospholipids with a calculated IC50 of (210 +/- 2.3) microM. In contrast, serotonin which also scavenged HOCl, was much more effective in decreasing phospholipid peroxidation (IC50 15 +/- 5 microM). Both compounds reacted with trichloromethylperoxyl radical (CCl3O2) with rate constants of (2.7 +/- 0.2) x 10(8) and (1.2 +/- 0.1) x 10(8)M-1 s- respectively. Melatonin did not scavenge superoxide radical and weakly protected DNA against damage by the ferric bleomycin system. By contrast serotonin was weakly pro-oxidant in the ferric-bleomycin system and strongly pro-oxidant in the Fe(3+)-EDTA/H2O-deoxyribose system. Solubility restrictions precluded examination of melatonin in this system. Our data show that melatonin exerts only limited direct antioxidant activities.
authors.affiliation: Neurodegenerative Disease Research Centre, Pharmacology Group, University of London King's College, UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Marshall
authors.forename: R J
authors.initials: RJ
authors.lastname: Reiter
authors.forename: B
authors.initials: B
authors.lastname: Poeggeler
authors.forename: O I
authors.initials: OI
authors.lastname: Aruoma
authors.forename: B
authors.initials: B
authors.lastname: Halliwell
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001761:Bleomycin / Q000031:analogs & derivatives / Q000494:pharmacology; D001921:Brain / Q000378:metabolism; D002374:Catalase / Q000037:antagonists & inhibitors; D002417:Cattle; D004249:DNA Damage; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D006997:Hypochlorous Acid / Q000378:metabolism / Q000494:pharmacology; D015227:Lipid Peroxidation / Q000187:drug effects; D008550:Melatonin / Q000494:pharmacology*; D009579:Nitrobenzoates / Q000378:metabolism; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D013053:Spectrophotometry; D013438:Sulfhydryl Compounds; D013481:Superoxides / Q000378:metabolism
chemical_list: D000975:Antioxidants; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D009579:Nitrobenzoates; D010545:Peroxides; D010743:Phospholipids; D013438:Sulfhydryl Compounds; C023503:iron bleomycin; D001761:Bleomycin; D013481:Superoxides; C011136:thionitrobenzoic acid; C049375:perhydroxyl radical; D012701:Serotonin; D006997:Hypochlorous Acid; D002374:Catalase; D008550:Melatonin