NOVEL URINARY METABOLITE OF ALPHA-TOCOPHEROL, 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 invol ve the opening of the chroman structure because of its oxidation to to copherylquinone. In contrast, we describe here ,8-tetramethyl-2(2'-car boxyethyl)-6-hydroxychroman (alpha-CEHC) as the major urinary metaboli te of alpha-tocopherol that appears in human urine after vitamin E sup plementation. It is formed directly from alpha-tocopherol without prev ious oxidative splitting of the chroman ring. The correlation of alpha -tocopherol intake, plasma alpha-tocopherol concentrations, and urinar y excretion of alpha-CEHC in human volunteers supplemented with RRR-al pha-tocopherol dosages ranging from 0 to 800 mg/d was examined. HPLC a nd gas chromatography-mass spectroscopy analysis revealed that alpha-C EHC was only excreted when a plasma threshold of 7-9 mu mol alpha-toco pherol/g total lipid was exceeded. This concentration was obtained by a daily intake of approximate to 50-150 mg alpha-tocopherol. We sugges t 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 o ptimum vitamin E intake.