Objectives: 

Oxidative damage to lipids and proteins produces structural changes in cell membranes that disrupt molecular motion altering many cellular functions. Our aim was to investigate the antioxidant ability of the immediate precursor of melatonin in the metabolic pathway of tryptophan, N-acetyl-serotonin (NAS), assessing its capacity to inhibit the rigidity induced by iron and ascorbic acid on cell membranes isolated from rat liver

Materials: 

Hepatic membranes (0,5 mg protein/mL) were obtained by differential centrifugation from Sprague-Dawley male rats weighing 200-240 g and incubated with or without NAS (0.01; 0.05; 0.1; 0.3; 1 mM) in a shaking bath at 37°C for 120 min. Lipid and protein oxidation were induced by adding 0,1 mM FeCl3 and 0,1 mM ascorbic acid and incubating at 37°C for 120 min. The reaction was stopped by adding 2 mM EDTA. Membrane fluidity was monitored by fluorescence polarization of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluene sulfonate. Malonaldehyde (MDA) + 4-hydroxyalkenals (4-HDA) concentrations and carbonyl protein contents were estimated as indices of oxidative damage to lipids and proteins respectively. Statistical comparisons among experimental groups were performed using student's paired t-test with a level of significance of p<0.05.

Results: 

After oxidative damage membrane fluidity decreased, whereas MDA+4-HDA concentrations and protein carbonylation increased. The abilities of NAS to inhibit membrane rigidity, and lipid and protein oxidation by 50% (IC50), were 0.12, 0.15, and 0.16 mM respectively.

Conclusions: 

These results suggest that the protective role of NAS in preserving optimal levels of fluidity of the biological membranes may be related to its ability to reduce lipid and protein oxidation.