alpha-tocopherol affects the urinary and biliary excretion of 2,7,8-trimethyl-2(2 '-carboxyethyl)-6-hydroxychroman, gamma-tocopherol metabolite, in rats

摘要

In this study, we investigated a change in the excretory content of 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (gamma -CEHC), a gamma -tocopherol (gamma -Toc) metabolite, in rat urine and bile by using a new high-performance liquid chromatography-electrochemical detection (HPLC-ECD) method. In this determination, CEHC [alpha- and gamma -CEHC, where alpha -CEHC = 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman] in the biological specimens were treated with 3 N methanolic HCl to hydrolyze conjugates and to promote esterification. The methylated samples were extracted by n-hexane/water (1:2). The analyses of the methyl esters of alpha -CEHC and gamma -CEHC were performed by an HPLC-ECD using an ODS-3 column at 35 degreesC. The mobile phase was acetonitrile/water (45:55, vol/vol) containing 50 mM sodium perchlorate. After rat urine and bile samples, respectively, were methylated as described above, methylated biliary metabolites were identified by liquid chromatography-mass spectrometry as methyl esters of gamma -CEHC. Furthermore, we examined the differences in the excretion of gamma -CEHC between rat urine and bile after an oral administration of gamma -Toc or alpha- + gamma -Toc by the above HPLC method. In the gamma -Toc group, each vitamin E-deficient rat was given 0.5 mt of a stripped corn oil preparation containing 10 mg of gamma -Toc, In the alpha- + gamma -Toc group, the rat was given 10 mg of alpha -Toe and 10 mg of gamma -Toc. The content of gamma -CEHC in rat urine from the alpha- + gamma -Toc group was increased more in comparison to the gamma -Toc group at 18-36 h after oral administration. Moreover, the content of gamma -CEHC in rat bile in the alpha- + gamma -Toc group was increased more in comparison to the gamma -Toc group at 6-18 h after oral administration. Therefore, we have suggested that gamma -CEHC was shifted mainly to urinary excretion after gamma -CEHC had been excreted into the bile. Furthermore, we assume that alpha -Toe may affect the metabolism of gamma -Toc to gamma -CEHC in the body. [References: 12]