Scavenging of reactive oxygen species by melatonin

• Published in: Biochimica et biophysica acta Vol. 1425; no. 3; pp. 469 - 477
• Main Authors: Zang, Lun-Yi, Cosma, Greg, Gardner, Henry, Vallyathan, Val
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 27.11.1998
• Subjects: Antioxidants - pharmacology; Cyclic N-Oxides - chemistry; Electron paramagnetic resonance; Electron Spin Resonance Spectroscopy; Free Radical Scavengers - pharmacology; Hydrogen peroxide; Hydrogen Peroxide - analysis; Hydroxyl radical; Hydroxyl Radical - analysis; Melatonin; Melatonin - pharmacology; Oxygen - analysis; Reactive Oxygen Species; Singlet Oxygen; Spin trapping; Superoxide radical; Superoxides - analysis; 1O 2, singlet oxygen; Melatonin; Hydrogen peroxide; EPR, electron paramagnetic resonance; Superoxide radical; Spin trapping; TEMPO, 2,2,6,6-tetramethylpiperidine oxide; OH, hydroxyl radical; DMSO, dimethylsulfoxide; HRP, horseradish peroxidase; Singlet oxygen; H 2O 2, hydrogen peroxide; RB, Rose bengal; AMK, N 1-acetyl- N 2-5-methoxykynuramine; Electron paramagnetic resonance; O ⋅− 2, superoxide anion radical; DMPO, 5,5-dimethyl-1-pyrroline- N-oxide; Hydroxyl radical; TEMP, 2,2,6,6-tetramethylpiperidine
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/S0304-4165(98)00099-3

The direct effects of the neurohormone melatonin on reactive oxygen species (ROS) were investigated. Melatonin was found to inhibit DMPO-O − 2 formation in a dose-dependent manner. At the level of 1.7±0.07 mM, melatonin caused 50% inhibition of EPR signal intensity of DMPO-O − 2during the reaction of xanthine and xanthine oxidase. The reaction rate constant of melatonin with O ⋅− 2 was found to be 1.25±0.07×10 3 M −1 s −1. However, melatonin (up to 1.2 mM) did not exhibit significant effect toward ⋅OH radical, produced by the Fenton reaction. In addition, we found no evidence for the formation of the melatonin indolyl cation radical that presumably precedes conversion of melatonin to its stable N 1-acetyl- N 2-5-methoxykynuramine (AMK) metabolite following sequential reactions of melatonin with O ⋅− 2 and ⋅OH. On the other hand, melatonin was capable of scavenging H 2O 2 in a dose-dependent manner with an IC 50=0.5±0.02 mM. The reaction rate constant of melatonin with H 2O 2 was found to be 2.52±0.19×10 5 M −1 s −1. Furthermore, melatonin was also found to inhibit 1O 2-dependent 2,2,6,6-tetramethylpiperidine oxide (TEMPO) radical formation during rose bengal photodynamic reaction. The results suggest that melatonin’s antioxidant properties, in part, may involve a direct effect on scavenging of ROS.