Beyond vitamin E supplementation: an alternative strategy to improve vitamin E status.
Vitamin E has many reported health effects and is recognized as the most important lipid-soluble, chain-breaking antioxidant in the body. Vitamin E has also been reported to play a regulatory role in cell signalling and gene expression. Epidemiological studies show that high blood concentrations of vitamin E are associated with a decreased risk of cardiovascular diseases and certain cancers. Yet, high doses of supplemental vitamin E have been associated with an elevated risk of heart failure and all-cause mortality. Therefore, establishing alternative strategies to improve vitamin E status without potentially increasing mortality risk may prove important for optimal nutrition. To identify dietary phenolic compounds capable of increasing blood and tissue concentrations of vitamin E, selected polyphenols were incorporated into standardized, semi-synthetic diets and fed to male Sprague-Dawley rats for 4 weeks. Blood plasma and liver tissue concentrations of alpha-T and gamma-Twere determined. The flavanols (+)-catechin and (-)-epicatechin, the flavonol quercetin, and the synthetic preservative butylated hydroxytoluene (BHT) markedly elevated the amount of alpha-T in plasma and liver. The sesame lignan sesamin and cereal alkylresorcinols substantially increased the concentrations of gamma-T, but not alpha-T, in the liver. Sesamin also increased gamma-T concentrations in plasma. In order to study the impact of selected polyphenols on the enzymatic degradation of vitamin E, HepG2 cells were incubated together with phenolic compounds in the presence of tocopherols and the formation of metabolites was determined. Sesamin, at concentrations as low as 2 microM, almost completely inhibited tocopherol side-chain degradation and cereal alkylresorcinols inhibited it, dose-dependently (5-20 microM), by 20-80%. BHT, quercetin, (-)-epicatechin, and (+)-catechin had no effect on tocopherol-omega-hydroxylase activity in HepG2 cells. In order to confirm the inhibition of gamma-T metabolism by sesame lignans in humans, sesame oil or corn oil muffins together with deuterium-labelled d6-alpha-Tand d2-gamma-Twere given to volunteers. Urine samples were collected for 72 h and analysed for deuterated and non-deuterated tocopherol metabolites. Consumption of sesame oil muffins significantly reduced the urinary excretion of d2-gamma-CEHC and total (sum of labelled and unlabelled) gamma-CEHC. Overall, the findings from these studies show that the tested dietary phenolic compounds increase vitamin E concentrations through different mechanisms and, thus, have the potential to improve vitamin E status without the use of vitamin E supplements.