Protective effect of indoleamines on in vitro ascorbate‐Fe²⁺dependent lipid peroxidation of rod outer segment membranes of bovine retina

Abstract

: Rod outer segment membranes (ROS) are highly vulnerable to autooxidation because of their high content of long chain polyunsaturated fatty acids (PUFAs). Melatonin and N‐acetylserotonin are indoleamines synthesized in the pineal gland, retina and other tissues. These compounds are free radical scavengers and indirect antioxidants because of their stimulatory effect on antioxidative enzymes. We compared the in vitro protective effect of melatonin and N‐acetylserotonin on the ascorbate‐Fe2+ induced lipid peroxidation of PUFAs located in ROS membranes. This process was measured by chemiluminescence and fatty acid composition of total lipids of ROS. We assayed increasing concentrations of melatonin (0–10 mm) and N‐acetylserotonin (0–2 mm). In both cases the total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of either melatonin or N‐acetylserotonin; this decreased proportional to the concentration of the indole. Thus, 10 mm melatonin and 2 mm N‐acetylserotonin produced a reduction of 51 ± 6 and 100% in the total chemiluminescene (lipid peroxidation), respectively. We also noticed a PUFAs protection: the docosahexaenoic acid content decreased considerably when the membranes were submitted to oxidative damage. This reduction was from 37.6 ± 2.1% in the native membranes to 6.2 ± 0.8% in those which were peroxidized. These changes were less pronounced in treated ROS membranes; as an example in the presence of 10 mm melatonin or 2 mm N‐acetylserotonin we observed a content preservation of 22:6 n‐3 (23.6 ± 1.2 and 39.1 ± 1.2% respectively). The concentration of each compound required to inhibit 50% of the lipid peroxidation (IC50) was 9.82 mm for melatonin and 0.43 mm for N‐acetylserotonin, respectively. N‐acetylserotonin shows a protective effect about 20 times higher than that of melatonin.

The Ability of Melatonin to Counteract Lipid Peroxidation in Biological Membranes

“…The concentration of each compound required to inhibit 50% of the lipid peroxidation (IC50) was 9.82 mM for melatonin and 0.43 mM for Nacetylserotonin, respectively. Nacetyl serotonin showed a protective effect about 20 times higher than that of melatonin; [94] significance of this apparent difference remains unknown; however, caution is needed when interpreting these results since the role of N-acetyl serotonin as an in vivo antioxidant remains essentially uninvestigated. We have shown that the indoleamines melatonin and N-acetyl serotonin protects rat liver microsomes against lipid peroxidation induced by ascorbate-Fe 2+ in a concentrationdependent manner.…”

N-Acetyl-Serotonin Protects HepG2 Cells from Oxidative Stress Injury Induced by Hydrogen Peroxide

“…Leaden and Catalá [67] and García et al [68] found that NAS strengthened biological membranes against oxidative stress, which may be related to its ability to reduce lipid peroxidation. Additional studies have shown that NAS also exerts protective effects against peroxidative damage of neurons [69–71], lung epithelial cells [72], erythrocytes [73], testicular cells [74], retinal cells [75, 76], and lymphocytes [77]. The data imply that the antioxidant effect of NAS is independent of melatonin and stronger than that of melatonin [76, 78].…”

Recent Developments of Melatonin Related Antioxidant Compounds

“…This compound is a free radical scavenger and indirect antioxidant because of its stimulatory effect on antioxidative enzymes like MLT. Comparison of the in vitro protective effect of MLT and N-acetylserotonin on the ascorbate-Fe 2+ induced lipid peroxidation of PUFAs located in ROS membranes [58] showed that the protective effect of N-acetylserotonin against ascorbate-Fe 2+ -induced oxidative damage was approximately 20 times higher than that of MLT. MLT and tryptophan derivatives such as N-acetylserotonin possess free radical scavenging activity.…”