Radiation-induced peroxidation and fragmentation of lipids in a model membrane

Purpose : To ascertain the possibility of fragmentation processes in lipid membranes when acted upon with γ-radiation under various conditions, and to evaluate fragmentation processes quantitatively in comparison with the lipid peroxidation processes. Materials and methods : Phospholipids as components of multilamellar liposomes exposed to 137 Cs γ-rays at dose-rates of 0.06 and 0.33 Gy s -1 in the dose range 0-18 kGy. Peroxidation products were determined spectrophotometrically and fragmentation products were analysed using thin-layer chromatography and GLC methods. Results : Phosphatidylglycerol containing unsaturated fatty acid residues and free hydroxyl groups underwent both peroxidation and fragmentation when its aqueous dispersions were treated with ionizing radiation. γ-Radiolysis of multilamellar liposomes led to the formation of peroxidation products, as well as phosphatidic acid and hydroxyacetone, fragmentation products of the initial lipid. Comparable radiation-chemical yields of conjugated-diene products and phosphatidic acid indicate that the probabilities of oxidation and fragmentation processes to occur are approximately equal in this case. In contrast to lipid peroxidation, lipid fragmentation is not accelerated but suppressed by oxygen and appears to be a prevailing process in de-aerated solutions. The phosphatidic acid formed as a result of phosphatidylglycerol fragmentation can intensify the lipid peroxidation. Conclusions : Treatment of lipid membranes with ionizing radiation leads to the destructive processes within both hydrophobic and hydrophilic moiety of lipids.