Novel urinary metabolite of alpha-tocopherol, 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman, as an indicator of an adequate vitamin E supply?
Previously, the metabolism of alpha-tocopherol was considered to involve the opening of the chroman structure because of its oxidation to tocopherylquinone. In contrast, we describe here 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC) as the major urinary metabolite of alpha-tocopherol that appears in human urine after vitamin E supplementation. It is formed directly from alpha-tocopherol without previous oxidative splitting of the chroman ring. The correlation of alpha-tocopherol intake, plasma alpha-tocopherol concentrations, and urinary excretion of alpha-CEHC in human volunteers supplemented with RRR-alpha-tocopherol dosages ranging from 0 to 800 mg/d was examined. HPLC and gas chromatography-mass spectroscopy analysis revealed that alpha-CEHC was only excreted when a plasma threshold of 7-9 mumol alpha-tocopherol/g total lipid was exceeded. This concentration was obtained by a daily intake of approximately 50-150 mg alpha-tocopherol. We suggest that alpha-CEHC excretion indicates a saturated binding capacity of vitamin E in the plasma and thus may be considered to be a marker of optimum vitamin E intake.
D015415:Biomarkers; D002839:Chromans / Q000737:chemistry / Q000652:urine*; D004355:Drug Stability; D006801:Humans; D008297:Male; D011422:Propionates / Q000737:chemistry / Q000652:urine*; D014810:Vitamin E / Q000008:administration & dosage / Q000378:metabolism*
D015415:Biomarkers; D002839:Chromans; D011422:Propionates; D014810:Vitamin E; C084852:2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman