Liposomes Containing α-Tocopherol and Ascorbate are Protected from an External Oxidant Stress

Abstract

The interaction between α-tocopherol and ascorbate in protecting membrane lipids from peroxidation was studied in unilamellar liposomes in which α-tocopherol was incorporated into the liposomal membrane, and ascorbate was trapped within the vesicles. Extravesi-cular ferricyanide was reduced by ascorbate-derived electrons, and this was enhanced by the presence of α-tocopherol in the lipid bilayer. When a water-soluble free radical initiator was added to the outside of liposomes, intravesicular ascorbate prevented oxidation of α-tocopherol, and this effect was associated with complete protection against peroxidation of membrane lipids. These results suggest that ascorbate-dependent recycling of α-tocopherol can protect biological membranes from peroxidation by oxidants originating across the membrane bilayer from ascorbate.