title: Radical-scavenging activity of melatonin, either alone or in combination with vitamin E, ascorbate or 2-mercaptoethanol as co-antioxidants, using the induction period method.
abstract: BACKGROUND
  Melatonin shows antioxidant/prooxidant activity but its mechanism of action remains unknown.
  
  
  METHODS
  The radical-scavenging activity of melatonin and various melatonin/co-antioxidant mixtures in a 1:1 molar ratio was evaluated in terms of the length of the induction period (IP) for polymerization of methyl methacrylate (MMA), initiated by thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) or by benzoyl peroxide (BPO) under nearly anaerobic conditions, which was monitored by differential scanning calorimetry (DSC).
  
  
  RESULTS
  The observed IP (A) for a pinoline, L-ascorbyl 2,6-dibutyrate (ASDB), vitamin E (alpha-, beta-, gamma- or delta-T) or 2-mercaptoethanol (2ME) mixture was compared with the calculated total sum of IP (melatonin+each co-antioxidant) (B). For both the AIBN and BPO systems, the A/B for the melatonin/ASDB, beta-T, gamma-T or delta-T mixture was 0.3-0.7, whereas that for the melatonin/2ME mixture was approximately 1. For the AIBN system, the A/B for the melatonin/alpha-T or pinoline mixture was 0.7-0.8. By contrast, for the BPO system, that for the melatonin/alpha-T or pinoline mixture was approximately 1.
  
  
  CONCLUSIONS
  The prooxidant effect of the melatonin/ascorbate or vitamin E mixtures induced by radical-oxidizing activity may help to explain the anticancer activity of melatonin in biological systems.
authors.affiliation: Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Kanda-surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kadoma
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Fujisawa
mesh_terms: D001205:Ascorbic Acid / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D001585:Benzoyl Peroxide / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D016166:Free Radical Scavengers / Q000737:chemistry / Q000494:pharmacology*; D005609:Free Radicals / Q000037:antagonists & inhibitors* / Q000737:chemistry; D015227:Lipid Peroxidation; D008550:Melatonin / Q000737:chemistry / Q000494:pharmacology*; D008623:Mercaptoethanol / Q000494:pharmacology; D020366:Methylmethacrylate / Q000737:chemistry; D009570:Nitriles / Q000737:chemistry; D058105:Polymerization; D013876:Thiophenes / Q000737:chemistry; D014810:Vitamin E / Q000737:chemistry / Q000494:pharmacology
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D009570:Nitriles; D013876:Thiophenes; C019101:alpha-terthienyl; D014810:Vitamin E; D020366:Methylmethacrylate; D008623:Mercaptoethanol; C004526:azobis(isobutyronitrile); D008550:Melatonin; D001205:Ascorbic Acid; D001585:Benzoyl Peroxide