EFFECTS OF MELATONIN ON LIPID-PEROXIDATION INDUCED BY OXYGEN RADICALS

We here report the activity of the neurohormone melatonin (MLT) as a s cavenger of free radicals in two different experimental models: (a) li noleic acid peroxidation initiated by different free radical-generatin g systems and (b) a multilamellar vesicle system composed of dilinoleo ylphosphatidylcholine. In system (a) linoleic acid peroxidation, induc ed by either the water-soluble initiator 2,2'-azobis (2-amidinopropane ) dihydrochloride(ABAP) or Fe2+-EDTA addition to 2.6 mM linoleic acid dispersed in SDS-phosphate buffer, was evaluated as the formation of c onjugated dienes, measured spectrophotometrically at 236 nm. MLT did n ot reduce the rate of peroxidation induced by ABAP, but did reduce, in a concentration-dependent fashion, the rate of the reaction activated by Fe2+-EDTA. In system (b) multilamellar vesicles were used as the s ubstrate for lipid peroxidation, initiated by Fe2+-EDTA and determined by means of malonaldehyde (MDA) and 4-hydroxyalkenal (4-HDA) content. MLT was found to be slightly more effective in system (b) than in the dispersed linoleic acid system (see a). These results show that MLT i nhibits lipid damage induced by oxygen free radicals. However, MLT is only about one one-hundredth as effective an antioxidant as vitamin E in the micelles system.