The activity of melatonin and related indoleamines against LOO? AND LO? free radicals depends on their functional groups and the assay system

FAGALI, N.; CATALÁ, A.

Londres

Congreso; 16th Society for Free Radical Research International (SFRRI) Biennial Meeting; 2012

International Society for Free Radical Research

Because of the great number of results obtained in very different assay systems, both in vitro and in vivo, the antioxidant activity of melatonin (MLT) is undeniable. However, its direct activity against low aggressive free radicals, as LOO? and LO?, remains under discussion. Accordingly, it was the main goal of the present work to study the antioxidant activity of MLT, N-acetylserotonin (NAS), 5-HO-tryptophan (5HO-TRP) and 5-methoxytryptamine (5MTP) in two different lipid systems with high content of polyunsaturated fatty acids (PUFAs): triglycerides (Tg) of fish oil dissolved in chloroform and sonicated liposomes (SL) made of retinal lipids in aqueous media. In the Tg-chloroform-system the peroxidation reaction was initiated by cumen hydroperoxide whereas SL were peroxidized with Fe2+. Both initiators generate breakdown of lipoperoxides previously formed with LOO? and LO? production. The techniques employed at the present work were: 1) chemiluminescence, 2) TBARS production, 3) DPPH assay, 4) determination of conjugated dienes production and 5) analysis of fatty acid profile by CG-MS. Butilated hydroxitoluene (BHT) was employed as a reference because of its well known antioxidant capacity. Our results showed that MLT and 5MTP were unable to protect PUFAs against lipid peroxidation in both systems, whereas NAS and 5HO-TRP were better antioxidants that BHT in the Tg-system but ineffective in the SL-system. We conclude that the antioxidant behaviour of MLT and structural analogues during lipid peroxidation depends not only on their functional groups but also on the assay system and could be better explained by the polar paradox theory.