Evaluation of the antioxidant effect of melatonin by flow injection analysis-luminol chemiluminescence

• Published in: Pharmacological research Vol. 48; no. 4; pp. 361 - 367
• Main Authors: Sariahmetoglu, M, Wheatley, R.A, Çakýcý, Ý, Kanzýk, Ý, Townshend, A
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.10.2003
• Subjects: Antioxidant; Antioxidants - chemistry; Antioxidants - pharmacology; Chemiluminescence; FIA; Flow Injection Analysis - methods; Hydrogen Peroxide - chemistry; Hydrogen Peroxide - metabolism; Hydroxyl Radical - chemistry; Hydroxyl Radical - metabolism; Luminescent Measurements; Luminol - chemistry; Melatonin; Melatonin - chemistry; Melatonin - pharmacology; Peroxynitrous Acid - chemistry; Peroxynitrous Acid - metabolism; Reperfusion; Serotonin - chemistry; Serotonin - pharmacology; Sodium Hypochlorite - chemistry; Sodium Hypochlorite - metabolism; Solutions; Superoxides - chemistry; Superoxides - metabolism; Tryptophan - chemistry; Tryptophan - pharmacology; Water; Melatonin; Chemiluminescence; Reperfusion; Antioxidant; FIA
• ISSN: 1043-6618; 1096-1186
• DOI: 10.1016/S1043-6618(03)00177-4

The antioxidant effect of melatonin was evaluated by using a flow injection analysis chemiluminescence (FIA-CL) method to measure alone its direct antioxidant behaviour in aqueous solutions. Inhibition by melatonin, dl-tryptophan or serotonin (5-hydroxytryptamine, 5-HT) of the steady CL emissions of various oxidants with luminol was measured. Log IC 50 values of melatonin were calculated: −2.6±0.1 M for superoxide (O 2 −), −3.0±0.02 M, for hydrogen peroxide (H 2O 2), −4.7±0.04 M, for hypochlorous anion ( −OCl), −2.8±0.1 M, for hydoxyl ( OH) and −2.0±0.03 M, for peroxynitrite (ONOO −). Thus melatonin exerted a limited direct antioxidant activity towards reactive oxygen species (ROS) in aqueous solutions, broadly comparable to that of tryptophan, but less than that of serotonin and of major antioxidants such as ascorbic acid. This suggests that where the benefits of melatonin are correctly attributed to antioxidant behaviour, this is mediated largely through antioxidant enzymes. The pharmacological implications are discussed.