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 degrees C. 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 mL 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-Toc 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-Toc may affect the metabolism of gamma-Toc to gamma-CEHC in the body.
We previously showed that alpha- and gamma-tocotrienols accumulate in adipose tissue and skin but not in plasma or other tissues of rats fed a tocotrienol-rich fraction extracted from palm oil containing alpha-tocopherol and alpha- and gamma-tocotrienols. To clarify the nature of tocotrienol metabolism, we studied the distribution of alpha- or gamma-tocotrienol in rats fed alpha- or gamma-tocotrienol without alpha-tocopherol, and the effect of alpha-tocopherol on their distribution. Wistar rats (4-wk-old) were fed a diet with 50 mg alpha-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 1, and a diet with 50 mg gamma-tocotrienol/kg alone or with 50 mg alpha-tocopherol/kg in expt. 2, for 8 wk. alpha-Tocotrienol was detected in various tissues and plasma of the rats fed alpha-tocotrienol alone, and the alpha-tocotrienol concentrations in those tissues and plasma decreased (P < 0.05) by the dietary alpha-tocopherol in the rats fed alpha-tocotrienol with alpha-tocopherol. However, gamma-tocotrienol preferentially accumulated in the adipose tissue and skin of the rats fed gamma-tocotrienol alone, and the dietary alpha-tocopherol failed either to decrease (P >/= 0.05) gamma-tocotrienol concentrations in the adipose tissue and skin or to increase (P >/= 0.05) in the urinary excretion of 2,7,8-trimethyl-2(2'-carboxymethyl)-6-hydroxycroman, a metabolite of gamma-tocotrienol, in the rats fed gamma-tocotrienol with alpha-tocopherol. These data suggest that alpha-tocopherol enhances the alpha-tocotrienol metabolism but not the gamma-tocotrienol metabolism in rats.
Method: a-Tocopherol and g-tocopherol are metabolized into 2,5,7,8-tetramethyl-2-(2 0 -carboxyethyl)-6-hydroxychroman (a-CEHC) and 2,7,8-trimethyl-2-(2 0 -carboxyethyl)-6-hydroxychroman (g-CEHC), respectively. We analyzed a-and g-CEHC concentrations in human serum and urine by high-performance liquid chromatography during administration of a-tocopherol. Fourteen healthy adult male volunteers received 1200 IU per day of RRR-a-tocopherol for 28 days. Blood and urine samples were obtained on days 0, 14, 28, and 56. Results: During a-tocopherol administration, the plasma g-tocopherol concentration decreased significantly, but there was marked elevation of the a-tocopherol concentration. Increased concentration of a-CEHC and g-CEHC in both serum and urine indicated the acceleration of vitamin E metabolism. Conclusion: High-dose administration of a-tocopherol caused an increase of g-tocopherol metabolism, which might have caused a decrease of the plasma g-tocopherol concentration.
Background: The bioavailability of g-tocopherol and metabolites of vitamin E after g-tocopherol administration is not well understood. We investigated the effect of g-tocopherol administration on the levels and metabolism of a-and g-tocopherol in healthy volunteers. Methods: We measured two metabolites of vitamin E (2,5,7,8-tetramethyl-2-(2 0 -carboxyethyl)-6-hydroxychroman (a-CEHC) and 2,7,8-trimethyl-2-(2 0 -carboxyethyl)-6-hydroxychroman (g-CEHC)) in plasma and urine by high-performance liquid chromatography with electrochemical detection (HPLC-ECD) during administration of g-tocopherol. Two groups of volunteers were enrolled. The g-tocopherol group received two g-tocopherol capsules (each containing 186.4 mg of g-tocopherol and 5 mg of a-tocopherol) for 28 days, while the control group received d-a-tocopherol at 5 mg/day, which was the same dose as that given to the g-tocopherol group. Blood and urine samples were obtained on days 0, 14, 28, 35, 42, and 56 after the initiation of g-tocopherol administration. Results: The plasma g-tocopherol concentration increased markedly during administration of g-tocopherol and the plasma g-CEHC concentration increased along with that of g-tocopherol. The plasma a-tocopherol concentration decreased significantly during g-tocopherol administration. The plasma concentration of a-CEHC decreased significantly and urinary excretion of a-CEHC tended to increase in the g-tocopherol group. Urinary sodium secretion was significantly increased at 1 week after the cessation of g-tocopherol administration, but there was no significant difference of urine volume between the two groups. Conclusion: Metabolism of a-tocopherol is accelerated and the plasma a-tocopherol concentration is decreased during g-tocopherol administration.
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