Melatonin prevents oxidative damage to protein and lipid induced by ascorbate-Fe3+-EDTA: Comparison with glutathione and a-tocopherol
by Seok Joong Kim, Russel J. Reiter, Wenbo Qi, Dun-xian Tan & Javier Cabrera
melatonin, free radicals, protein oxidation, lipid peroxidation, liposome, a-tocopherol, glutathione
OBJECTIVES: The ability of melatonin to protect protein and lipid against oxidative damage induced by an ascorbate-Fe3+-EDTA (AFE) system which generates the hydroxyl radical was investigated using bovine serum albumin (BSA) and phosphatidylcholine (PC) liposomes, respectively, and compared with the protective effects of reduced glutathione and a-tocopherol. The comparison study was also performed using PC liposomes containing BSA.
METHODS: BSA, PC liposomes or their mixtures were exposed to the HO·-generating system of AFE composed of 0.1 mM EDTA-Fe3+ and 0.5 mM ascorbate in 0.1 M phosphate buffer, pH 7.4, at 37°C for 1 h. Oxidative damage of BSA was determined by measuring the carbonyl content and the fragmentation of protein by the reaction with dinitrophenylhydrazine (DNPH) and electrophoresis, respectively. Lipid peroxidation of PC liposomes was indicated by the quantity of malondialdehyde and 4-hydroxyalkenals.
RESULTS: Melatonin inhibited protein damage as indicated by the reduced formation of carbonyl groups and fragmentation of BSA by AFE as effectively as did glutathione while a-tocopherol was ineffective. Melatonin also prevented lipid peroxidation to the same extent as did a-tocopherol in PC liposomes.
CONCLUSION: Both BSA and PC lipid exposed to AFE are effectively protected by melatonin while hydrophilic glutathione and hydrophobic a-tocopherol are as effective as melatonin only in one target, i.e., BSA or PC lipid, respectively.