title: α-Tocopherol does not accelerate depletion of γ-tocopherol and tocotrienol or excretion of their metabolites in rats.
abstract: From an enzyme kinetic study using rat liver microsomes, α-tocopherol has been suggested to accelerate the other vitamin E catabolism by stimulating vitamin E ω-hydroxylation, the late limiting reaction of the vitamin E catabolic pathway. To test the effect of α-tocopherol on catabolism of the other vitamin E isoforms in vivo, we determined whether α-tocopherol accelerates depletion of γ-tocopherol and tocotrienol and excretion of their metabolites in rats. Male Wistar rats were fed a γ-tocopherol-rich diet for 6 weeks followed by a γ-tocopherol-free diet with or without α-tocopherol for 7 days. Intake of γ-tocopherol-free diets lowered γ-tocopherol concentrations in serum, liver, adrenal gland, small intestine, and heart, but there was no effect of dietary α-tocopherol on γ-tocopherol concentrations. The level of urinary excretion of γ-tocopherol metabolite was not affected by dietary α-tocopherol. Next, the effect of α-tocopherol on tocotrienol depletion was examined using rats fed a tocotrienol-rich diet for 6 weeks. Subsequent intake of a tocotrienol-free diet with or without α-tocopherol for 7 days depleted concentrations of α- and γ-tocotrienol in serum and tissues, which was accompanied by a decrease in the excretion of γ-tocotrienol metabolite. However, neither the tocotrienol concentration nor γ-tocotrienol metabolite excretion was affected by dietary α-tocopherol. These data showed that dietary α-tocopherol did not accelerate the depletion of γ-tocopherol and tocotrienol and their metabolite excretions, suggesting that the positive effect of α-tocopherol on vitamin E ω-hydroxylase is not sufficient to affect the other isoform concentrations in tissues.
authors.affiliation: Department of Home Economics, Aichi Gakusen University, Okazaki, Japan.
authors.forename: Tomono
authors.initials: T
authors.lastname: Uchida
authors.forename: Saki
authors.initials: S
authors.lastname: Nomura
authors.forename: Eri
authors.initials: E
authors.lastname: Sakuma
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Hanzawa
authors.forename: Saiko
authors.initials: S
authors.lastname: Ikeda
mesh_terms: D000284:Administration, Oral; D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D042926:Cytochrome P-450 CYP4A / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D024508:Tocotrienols / Q000008:administration & dosage / Q000097:blood* / Q000652:urine*; D024502:alpha-Tocopherol / Q000008:administration & dosage / Q000097:blood* / Q000652:urine*; D024504:gamma-Tocopherol / Q000008:administration & dosage / Q000097:blood* / Q000652:urine*
chemical_list: D024508:Tocotrienols; D024504:gamma-Tocopherol; D042926:Cytochrome P-450 CYP4A; D024502:alpha-Tocopherol