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Physiological functions of vitamin E and biodiscrimination of its stereoisomers.

Vitamin E is recognized as a fat-soluble antioxidant able to scavenge oxygen radicals and to quench singlet oxygen. Of 8 analogues of vitamin E alpha-tocopherol has the highest biological activity. In addition, all-rac-alpha-tocopherol 2R-stereoisomers are more active than their 2S-counterparts. To cast light on the significance of this in vivo, we investigated the discrimination and distribution of alpha-tocopherol stereoisomers in rats using chiral-HPLC. Alpha-tocopherol was found to be absorbed from the small intestine without discrimination. After transfer to the liver, however, 2R-isomers are preferentially secreted into VLDL. In this discrimination the alpha-tocopherol transfer protein functions as a key substance.