Evaluation of the antioxidant activity of melatonin in vitro

Karyn Ann Marshall, Russel J. Reiter, Burkhard Poeggeler, Okezie I. Aruoma, Barry Halliwell

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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) μM. In contrast, serotonin which also scavenged HOCl, was much more effective in decreasing phospholipid peroxidation (IC50 15 ± 5 μM). Both compounds reacted with trichloromethylperoxyl radical (CCl3O2) with rate constants of (2.7 ± 0.2) x 108 and (1.2 ± 0.1) x 108 M-1 s-1 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 Fe3+- EDTA/H2O2-deoxyribose system. Solubility restrictions precluded examination of melatonin in this system. Our data show that melatonin exerts only limited direct antioxidant activities.

Original languageEnglish (US)
Pages (from-to)307-315
Number of pages9
JournalFree Radical Biology and Medicine
Volume21
Issue number3
DOIs
StatePublished - Jan 1 1996

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Keywords

  • Melatonin
  • antioxidants
  • free radicals
  • lipid peroxidation
  • peroxyl radicals

ASJC Scopus subject areas

  • Biochemistry
  • Physiology (medical)

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