Interaction of tocopherol with peroxyl radicals does not lead to the formation of lipid hydroperoxides in liposomes.

alpha-Tocopherol (alpha-TOH) is thought to act as a lipid-soluble antioxidant by scavenging the chain-carrying lipid peroxyl radical (LOO.), giving rise to alpha-TO. and LOOH. The aim of the present work is to test the possibility that alpha-TOH may also exert a protective action by converting LOO. into the parent, unoxidized lipid molecule (LH) with concomitant formation of O2- and T+O. To assess the relative contribution of the two pathways, the amounts of products accumulating were measured, i.e. LOOH and O2-, under conditions where lipid peroxidation was initiated at linear rates by the UV light-induced decomposition of AIBN. The overall conclusion of the study is based on the observation that significant amounts of O2- were produced, whereas the delta LOOH/delta alpha-TOH was considerably smaller than 1.0. A mechanism of one or two-electron oxidation of TOH is considered; according to it the phospholipid primary structure is restored (LOO.-->LH, breaking of the C-->O bond). This leads to the oxygen or superoxide anion-radical release accordingly.