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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.

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Abbreviations

CEHC:

Carboxyethyl-hydroxychroman

α-CEHC:

2,5,7,8-tetramethyl-2(2′-carboxyethyl)-6-hydroxychroman

γ-CEHC:

2,7,8-trimethyl-2(2′-carboxyethyl)-6-hydroxychroman

CYP:

Cytochrome P450

α-TTP:

α-tocopherol transfer protein

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Acknowledgments

This work was supported in part by JSPS KAKENHI and a Sasakawa Scientific Research Grant from the Japan Science Society. We acknowledge a generous donation of vitamin E isoforms and CEHC from Eisai Food & Chemical and Eisai, respectively.

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Correspondence to Saiko Ikeda.

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Uchida, T., Nomura, S., Sakuma, E. et al. α-Tocopherol does not Accelerate Depletion of γ-Tocopherol and Tocotrienol or Excretion of their Metabolites in Rats. Lipids 48, 687–695 (2013). https://doi.org/10.1007/s11745-013-3796-0

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Keywords

  • Carboxyethyl-hydroxychroman
  • Catabolism
  • Rat
  • Tocopherol
  • Tocotrienol
  • Vitamin E