The role of plasmalogens in the photoreactivity of human retinal lipid extracts of different age groups

Purpose: Plasmalogens (PLs) constitute a specific subclass of phospholipids characterized by a vinyl-ether bond in SN-1 position of the glycerol backbone and account for 10% of total phospholipids in the retina, where are considered as sacrificial antioxidants. PLs above 50% of other phospholipids present in the retina contain polyunsaturated fatty acid (PUFA) chain in SN-2 position. In this work we analyzed the influence of PLs on of phospholipids naturally occurring in the human retina (SRL) in a model system and in retinal pigment epithelium cells in vitro. Methods: Lipid composition of human retinal extracts (RLE) has been determined by GC and LC/MS analysis. RLE and SRL with and without PLS were oxidized in the dark in liposomes equilibrated with air at 37°C. Blue-light induced photoreactivity of the oxidized lipid samples was measured in model systems and in ARPE-19 cells in vitro using time-resolved singlet oxygen phosphorescence at 1270nm, electron paramagnetic resonance (EPR) -oximetry, EPR-spin trapping and electrochemical detection of cholesterol hydroperoxides.Results: Human RLE are very sensitive to oxidation despite the presence of endogenous hydrophobic antioxidants. Both oxidised RLE and SRL generate singlet oxygen and superoxide anion upon irradiation with blue light. The observed photoreactivity of lipids extracted from human retinas increases with age of the donor. It also becomes more pronounced with autooxidation in case of both RLE and SRL.Conclusions: Our results indicate that plasmalogens mediate photoreactivity of retinal lipids in a complex way. It is detected by an increase in the photouptake of oxygen and decreased yields of singlet oxygen photogeneration by oxidized phospholipids