title: Quantitation of [5-14CH3]-(2R, 4'R, 8'R)-α-tocopherol in humans.
abstract: Half-lives of α-tocopherol in plasma have been reported as 2-3 d, whereas the Elgin Study required >2 y to deplete α-tocopherol, so gaps exist in our quantitative understanding of human α-tocopherol metabolism. Therefore, 6 men and 6 women aged 27 ± 6 y (mean ± SD) ingested 1.81 nmol, 3.70 kBq of [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol. The levels of (14)C in blood plasma and washed RBC were monitored frequently from 0 to 460 d while the levels of (14)C in urine and feces were monitored from 0 to 21 d. Total fecal elimination (fecal + metabolic fecal) was 23.24 ± 5.81% of the (14)C dose, so feces over urine was the major route of elimination of the ingested [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol, consistent with prior estimates. The half-life of α-tocopherol varied in plasma and RBC according to the duration of study. The minute dose coupled with frequent monitoring over 460 d and 21 d for blood, urine, and feces ensured the [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol (the tracer) had the chance to fully mix with the endogenous [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol (the tracee). The (14)C levels in neither plasma nor RBC had returned to baseline by d 460, indicating that the t(1/2) of [5-CH(3)]-(2R, 4'R, 8'R)-α-tocopherol in human blood was longer than prior estimates.
authors.affiliation: Department of Nutrition, University of California, Davis, CA 95616, USA.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Chuang
authors.forename: Hosea D
authors.initials: HD
authors.lastname: Matel
authors.forename: Krishnan P
authors.initials: KP
authors.lastname: Nambiar
authors.forename: Seung-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: James G
authors.initials: JG
authors.lastname: Fadel
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Holstege
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Clifford
mesh_terms: D000328:Adult; D002250:Carbon Radioisotopes; D005243:Feces / Q000737:chemistry; D006207:Half-Life; D006801:Humans; D024502:alpha-Tocopherol / Q000032:analysis* / Q000097:blood / Q000652:urine
chemical_list: D002250:Carbon Radioisotopes; D024502:alpha-Tocopherol