Vitamin E as an antioxidant in vitro and in vivo

Measurements of the absolute rate constants for the reaction with peroxyl radicals of alpha, beta, gamma and delta-tocopherol and several model compounds are described. The peroxyl radicals were obtained either by the autoxidation of styrene or by the flash photolysis of di-t-butyl ketone in an oxygen-saturated environment. The kinetic data are discussed in stereoelectronic terms. Vitamin E and total lipid-soluble, chain-breaking antioxidant concentrations in some normal and cancerous tissues have been measured. In human blood plasma and erythrocyte ghost membranes vitamin E is the major, and possibly the only, chain-breaking antioxidant. Lipid extracts of Novikoff ascites hepatoma cells contain considerably more vitamin E relative to lipid than do extracts of normal rat liver. These tumour lipids contain relatively fewer highly unsaturated fatty acids and are present at lower lipid/wet tissue ratios than the normal liver lipids. A number of unresolved problems relating to the action of vitamin E in vivo are discussed.