Tissue distribution of vitamin E metabolites in rats after oral administration of tocopherol or tocotrienol.

Tomono Uchida, Saki Nomura, Tomio Ichikawa, Chisato Abe, Saiko Ikeda

Index: J. Nutr. Sci. Vitaminol. 57(5) , 326-32, (2011)

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Abstract

We previously found that 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (_CEHC), a metabolite of the vitamin E isoforms _-tocopherol or _-tocotrienol, accumulated in the rat small intestine. The aim of this study was to evaluate tissue distribution of vitamin E metabolites. A single dose of -tocopherol, _-tocopherol or a tocotrienol mixture containing - and _-tocotrienol was orally administered to rats. Total amounts of conjugated and unconjugated metabolites in the tissues were measured by HPLC with an electrochemical detector, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox) was used as an internal standard. Twenty-four hours later, the vitamin E isoforms were detected in most tissues and in the serum. However, 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (CEHC), a metabolite of -tocopherol or -tocotrienol, and _CEHC accumulated in the serum and in some tissues including the liver, small intestine and kidney. Administration of -tocopherol increased the _CEHC concentration in the small intestine, suggesting that -tocopherol enhances _-tocopherol catabolism. In contrast, ketoconazole, an inhibitor of cytochrome P450 (CYP)-dependent vitamin E catabolism, markedly decreased the _CEHC concentration. These data indicate that vitamin E metabolite accumulates not only in the liver but also in the small intestine and kidney. We conclude that some dietary vitamin E is catabolized to carboxyethyl-hydroxychroman in the small intestine and is secreted into the circulatory system.