Marshall K A, Reiter R J, Poeggeler B, Aruoma O I, Halliwell B
Neurodegenerative Disease Research Centre, Pharmacology Group, University of London King's College, UK.
Free Radic Biol Med. 1996;21(3):307-15. doi: 10.1016/0891-5849(96)00046-9.
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.
褪黑素作为“时差反应”和失眠的一种治疗方法，其推广力度日益加大，并且有人提出它在体内可作为一种抗氧化剂。本文对褪黑素的抗氧化和潜在促氧化活性进行了体外研究。褪黑素能够以足够的速率清除次氯酸（HOCl），从而保护过氧化氢酶不被该分子灭活。褪黑素还能阻止HOCl对5-硫代-2-硝基苯甲酸的氧化。褪黑素可降低牛脑磷脂的过氧化反应，计算得出的IC50为（210±2.3）微摩尔。相比之下，同样能清除HOCl的血清素在降低磷脂过氧化反应方面更有效（IC50为15±5微摩尔）。两种化合物与三氯甲基过氧自由基（CCl3O2）反应的速率常数分别为（2.7±0.2）×108和（1.2±0.1）×108M-1·s-1。褪黑素不能清除超氧阴离子自由基，对博来霉素铁系统造成的DNA损伤仅有微弱的保护作用。相比之下，血清素在博来霉素铁系统中是弱促氧化剂，而在Fe(3+)-EDTA/H2O-脱氧核糖系统中是强促氧化剂。由于溶解性限制，无法在该系统中检测褪黑素。我们的数据表明，褪黑素仅具有有限的直接抗氧化活性。
