Lipid peroxidation in small and large phospholipid unilamellar vesicles induced by water-soluble free radical sources

The susceptibility of small and large egg yolk phosphatidylcholine unilamel lar vesicles to Fe2+/histidine-Fe3+- and Fenton reagent (Fe2+-H2O2)-induced lipid peroxidation was evaluated by measuring the formation of thiobarbitu ric acid reactive substances (TBARS). It has been found that surface curvat ure or phospholipid packing exerts significant effect on the oxidative susc eptibility of the unsaturated lipid bilayers and the highly curved and loos ely packed small unilamellar vesicles (SUVs) exhibit much less resistance t o the oxidative stress induced by the water-soluble free radical sources. T he presence of lipid hydroperoxides in sonicated vesicles was excluded as t he cause for higher level of lipid peroxidation in the phospholipid SUVs. I nstead, the experimental results can be explained by the difference in abil ity of the water-soluble oxidants to penetrate the two types of lipid membr anes. This hypothesis is supported by data obtained from fluorescence lifet ime and quenching studies. (C) 2000 Academic Press.