Member of Carrera del Investigador Científico, Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.
Lipid–protein modifications during ascorbate-Fe2+ peroxidation of photoreceptor membranes: protective effect of melatonin
Article first published online: 22 JUN 2006
Journal of Pineal Research
Volume 41, Issue 3, pages 201–210, October 2006
How to Cite
Guajardo, M. H., Terrasa, A. M. and Catalá, A. (2006), Lipid–protein modifications during ascorbate-Fe2+ peroxidation of photoreceptor membranes: protective effect of melatonin. Journal of Pineal Research, 41: 201–210. doi: 10.1111/j.1600-079X.2006.00352.x
- Issue published online: 22 JUN 2006
- Article first published online: 22 JUN 2006
- Received April 6, 2006; accepted May 14, 2006.
- lipid peroxidation;
- protein oxidation;
- rod outer segments
Abstract: The rod outer segment (ROSg) membranes are essentially lipoprotein complexes. Rhodopsin, the major integral protein of ROSg, is surrounded by phospholipids highly enriched in docosahexaenoic acid (22:6 n3). This fluid environment plays an important role for conformational changes after photo-activation. Thus, ROSg membranes are highly susceptible to oxidative damage. Melatonin synthesized in the pineal gland, retina and other tissues is a free radical scavenger. The principal aim of this work was to study the changes in the ROSg membranes isolated from bovine retina submitted to nonenzymatic lipid peroxidation (ascorbate-Fe2+ induced), during different time intervals (0–180 min). Oxidative stress was monitored by increase in the chemiluminescence and fatty acid alterations. In addition we studied the in vitro protective effect of 5 mm melatonin. The total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of melatonin. The docosahexaenoic acid content decreased considerably when the membranes were exposed to oxidative damage. This reduction was from 35.5 ± 2.9% in the native membranes to 12.65 ± 1.86% in those peroxidized during 180 min. In the presence of 5 mm melatonin we observed a content preservation of 22:6 n3 (23.85 ± 2.77%) at the same time of peroxidation. Simultaneously the alterations of membrane proteins under oxidative stress were studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Loss of protein sulfhydryl groups and increased incorporation of carbonyl groups were utilized as biomarkers of protein oxidation. In membranes exposed to Fe2+-ascorbate, we observed a decrease of protein thiols from 50.9 ± 3.38 in native membranes to 1.72 ± 2.81 nmol/mg of protein after 180 min of lipid peroxidation associated with increased incorporation of carbonyl groups into proteins from 7.20 ± 2.50 to 12.50 ± 1.12 nmol/mg of protein. In the SDS-PAGE we observed a decrease in the content of all the proteins, mainly rhodopsin, as a consequence of peroxidation. Melatonin, prevent both lipid peroxidation and protein oxidation.