Biodiscrimination of α‐tocopherol stereoisomers during intestinal absorption

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Abstract
Synthetic α-tocopherol (α-Toc) contains equal amounts of eight different stereoisomers, and the four stereoisomers with the 2R configuration are generally more active than their correspoding 2S-isomers. We investigated the biodiscrimination of α-Toc stereoisomers during intestinal absorptionin situ andin vitro. Intestinal absorption of α-Toc stereoisomers was examinedin situ in vitamin E-deficient rats with cannulated thoracic ducts. We found that the ratios of α-Toc stereoisomers in lymph of the all-rac-α-Toc group were the same as the administered α-Toc stereoisomers, and 2R-isomers occupied approximately 50% of absorbed α-Toc. The uptake of α-Toc stereoisomers also was measured using Caco-2 cells cultured on filter membranes. The concentration ofRRR-α-Toc in Caco-2 cells was not significnatly different from that ofSRR-α-Toc. Therefore, the discrimination of α-Toc stereoisomers does not occur during absorption in small intestine, suggesting the liver as a source for the biodiscrimination.