Biodiscrimination of alpha-tocopherol stereoisomers in humans after oral administration.

We investigated changes in the concentrations of the stereoisomers of alpha-tocopherol in serum and lipoproteins in seven normal, healthy women aged 21-37 y who had received oral administration of natural and synthetic alpha-tocopheryl acetate. This study was conducted in three separate periods of 28 d each; there was a 3-mo washout period between each experimental period. During the first period the subjects were administered a daily dose of 100 mg RRR-alpha-tocopherol/d, whereas in the second and third periods 100 mg all-rac-alpha-tocopheryl acetate/d and 300 mg all-rac-alpha-tocopheryl acetate/d were given, respectively. Blood samples were collected 3 d before each treatment and 1, 3, 7, 14, and 28 d after treatment. alpha-Tocopherol stereoisomer concentrations in serum and lipoproteins (very-low-, low-, and high-density lipoproteins) were determined by the chiral HPLC method. The bioavailability of RRR-alpha-tocopherol was greater than that of all-rac-alpha-tocopheryl acetate. When bioavailability was estimated from the increase in the concentration of RRR- or all-rac-alpha-tocopherol in serum, bioavailability of RRR-alpha-tocopherol administered at 100 mg/d was not different from that of all-rac-alpha-tocopheryl acetate administered at 300 mg/d. 2R-Isomers and small amounts of 2S-isomers were detected in the serum lipoproteins of subjects administered all-rac-alpha-tocopheryl acetate.