The effect of melatonin and structural analogues on the lipid peroxidation of triglycerides enriched in ω-3 polyunsaturated fatty acids

The lipid peroxidation of triglycerides enriched in polyunsaturated fatty acids was investigated by photoemission techniques and the TBARS assay. Butylated hydroxytoluene, 5-OH-tryptophan and N-acetylserotonin inhibited light emission and TBARS formation in a concentration dependent manner. However, it was enhanced in the presence of melatonin and 5-methoxytryptamine and was dependent on its concentration. The total relative luminic units were found to be lower in those systems incubated in the presence of butylated hydroxytoluene, N-acetylserotonin or 5-OH-tryptophan; this decreased proportionally to the concentration of the compound tested. The order of inhibition was 5-OH-tryptophan > N-acetylserotonin > butylated hydroxytoluene with the following IC50 values: 0.65, 6.5 and 9.0 mM respectively. The free-radical scavenging activity of the indole derivatives was also analyzed by the DPPH method, and the results indicate that 5-OH-tryptophan, and N-acetylserotonin exhibited a dose-dependent free-radical scavenging ability at all of the tested concentrations. Thus, at 10 μM concentration a decrease of 84.71% and 73.50% of initial DPPH was observed, compared to 51.00% of BHT. Melatonin and 5-methoxytriptamine decreased the initial concentration of DPPH only 1.85% and 5.0%, respectively. The possible formation of N1-acetyl-N2 formyl-5-methoxykynuramine (AFMK) during lipid peroxidation of triglycerides enriched in PUFAs with cumene hydroperoxide in the presence of melatonin was also analyzed.