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KMID : 0381019960290101157
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Korean Journal of Nutrition
1996 Volume.29 No. 10 p.1157 ~ p.1157
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Vitamin E Kinetics, Lipoprotein Transport and Requirements
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Traber, Maret G.
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Abstract
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New techniques of molecular biology and use of stable isotopes have led to new insights in the regulation of plasma vitamin E. During intestinal absorption and chylomicron secretion in humans following oral administration of deuterium labeled toopherols, all the forms of vitamin E appeared similarly in plasma and distributed to all the circulating lipoproteins. Subsequently, the plasma was preferentially enriched in RRR-cc-tocopherol as a result of VLDL catabolism. A kinetic model of plasma vitamin E transport in humans using deuterium labeled stereoisomers of a-tocopherol(RRR- and SRR-, natural and synthetic forms of vitamin E, respectively) demonstrated that RRR-atocopherol is preferentially re-turned to the plasma from the liver, accounting fornearly 1 pool of a-tocopherol per day. The hepatic atocopherol transfer protein(aTTP) transfers atocopherol, which suggests that it is responsible for the incorporation of RRR-atocopherol into VLDL. Defects in the aTTP gene are associated with a characteristic syndrome, ataxia with vitamin E deficiency, AVED. Studies in AVED patients using deuterated tocopherols demonstrated that they have difficulty maintaining plasma RRR-atocopherol concentrations not as a result of impaired absorption, but as a result of impaired incorporation into VLDL. The importance of aTTP in maintaining normal plasma vitamin E concentrations. will be discussed. In addition, the implications for vitamin E supplementation in normal humans will be addressed.
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