6533b7d2fe1ef96bd125defa

RESEARCH PRODUCT

[37] Interactions between vitamin A and vitamin E in liposomes and in biological contexts

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Publisher Summary This chapter discusses the interactions between vitamin A and vitamin E in liposomes. The chapter reviews several studies carried out by incorporating a variable proportion of all- trans -retinol and α-tocopherol in soybean phosphatidylcholine liposomes. It discusses the antioxidant effectiveness of all- trans - retinol in retinal membranes, whether deprived of endogenous α-tocopherol. In the experiments discussed in the chapter, synergistic effects between all- trans -retinal and α -tocopherol are evident in chemical bilayer as well as in natural membranes. In addition, when all- trans -retinol and α –tocopherol are allowed to act in combination, consumption of both antioxidants during the lipid peroxidation is delayed. Despite evidence for reciprocal protective effects, the mechanisms underlying these interactions remain puzzling in some respects. Consumption kinetics does not show regeneration mechanisms for any of the antioxidants. Because vitamin A easily undergoes autoxidation, an antioxidant protection of all- trans -retinol by α-tocopherol could lead to the enhancement of antioxidant activity of all- trans -retinol. Nevertheless, if some α-tocopherol serves to prevent autoxidation of all- trans -retinol, it would also be expected to be consumed more rapidly in the presence of all- trans -retinol excess, which is in contrast with the experimental evidence. In the light of the complex antioxidant mechanism of retinol, a possibility is that the antioxidant protection by α-tocopherol results in a much more effective activity of all- trans -retinol so that it can strongly compete with α-tocopherol for the scavenging of peroxyl radicals. This could finally preserve the membrane lipid and α-tocopherol itself.