Lipid peroxidation inhibited by monoamines.

We investigated the inhibition of lipid peroxidation by monoamines. We found that monoamines, including dopa, dopamine, adrenaline and serotonin, strongly inhibited lipid peroxidation induced by 2,2'-azobis-(2-amidinopropane)-dihydrochroride (AAPH). In contrast, lipid peroxidation induced by 2,2'-azobis-(2,4-dimethylvaleronitrile) was not effectively inhibited by the monoamines. Degradation of R-phycoerythrin induced by AAPH was strongly prevented by these monoamines, suggesting that monoamines scavenge peroxyl radicals in the buffer and on the surface of membrane lipid layers. Methoxy derivatives of dihydroxyphenylacetic acid and 5-methoxytryptophan produced little inhibition of lipid peroxidation induced by AAPH, suggesting that hydroxy groups of monoamines donate protons to peroxyl radicals to prevent lipid peroxidation. However, the monoamines did not sharply inhibit lipid peroxidation induced by ascorbate-ADP-Fe3+ and t-butylhydroperoxide-Fe2+. Lipid peroxidation predominantly proceeding by peroxyl radicals in these reaction systems seems unlikely.