Antioxidant role of melatonin in lipid peroxidation of human LDL.
The antioxidant effect of melatonin on LDL oxidation was studied in vitro using either a thermolabile initiator or copper ions to induce lipid peroxidation. Loading of LDL with melatonin showed only weak protection against oxidative damage as compared to alpha-tocopherol. In the presence of high concentrations of melatonin (1000 mol/mol LDL) in the medium a clear protective effect was found during lag- and propagation phase, albeit weaker than after loading with alpha-tocopherol. It is concluded that melatonin is not incorporated into LDL in sufficient concentrations to prevent lipid peroxidation effectively. When melatonin is present in the incubation medium during oxidation, a partitioning equilibrium between aqueous and lipid phase is established. Only under these conditions can melatonin act as a chain breaking antioxidant. The concentrations required, however, are far beyond those found in human plasma. Therefore, the data in this study do not support a direct physiological relevance of melatonin as an antioxidant in lipid peroxidation processes.
Abuja
P M
PM
Institute of Biochemistry, University of Graz, Austria. peter.abuja@kfunigraz.ac.at
Liebmann
P
P
Hayn
M
M
Schauenstein
K
K
Esterbauer
H
H
D000578:Amidines / Q000494:pharmacology; D000975:Antioxidants; D015764:Bepridil / Q000031:analogs & derivatives; D001713:Biphenyl Compounds; D019327:Copper Sulfate / Q000494:pharmacology; D005609:Free Radicals; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects / Q000502:physiology*; D008077:Lipoproteins, LDL / Q000737:chemistry*; D008550:Melatonin / Q000502:physiology*; D010851:Picrates; D014810:Vitamin E / Q000494:pharmacology
D000578:Amidines; D000975:Antioxidants; D001713:Biphenyl Compounds; D005609:Free Radicals; D008077:Lipoproteins, LDL; D010851:Picrates; D014810:Vitamin E; C046728:2,2'-azobis(2-amidinopropane); D015764:Bepridil; C004931:1,1-diphenyl-2-picrylhydrazyl; D008550:Melatonin; D019327:Copper Sulfate