Biological Activity of Vitamin E Compounds and Natural Materials by the Resorption-Gestation Test, and Chemical Determination of the Vitamin E Activity in Foods and Feeds

Abstract

The biological activity of the tocopherols and tocotrienols has been re-examined by the rat resorption-gestation test. The following values have been obtained (with d,l-alpha-tocopheryl acetate = 100%): d-alpha-tocopherol 80%; d,l-alpha-tocopherol 59%; d-alpha-tocopheryl acetate 136%; d-alpha-tocotrienol 13%; d-beta-tocopherol 45%; d-beta-tocotrienol 4%; d-gamma-tocopherol 13%; d-delta-tocopherol less than 0.4%. The possibility of alpha- and gamma-tocopherol being synergists has been tested, but no significant effect was found. The antioxidants BHT and ethoxyquin were without effect on the utilization of alpha-tocopherol by the rat. After chemical determination of the tocopherols and tocotrienols in foods and mixed feeds, these biological activities were used to calculate the vitamin E activity. For two samples of margarine and two samples of mixed feed, the calculated value of the vitamin E activity after chemical determination of the tocopherols and tocotrienols was compared with the value found by direct bioassay, and reasonably good agreement was found. The authors suggest that determination of vitamin E in foods and feeds as a rule should be carried out as a chemical determination of the individual tocopherols and tocotrienols followed by a calculation of the vitamin E activity from the biological activity of the tocopherols and tocotrienols.

Complexity of vitamin E metabolism

“…As α-TOH fulfills all of these criteria best within the group of vitamin E forms, it binds efficiently to α-TTP into a deep cavity lined with hydrophobic residues [16] , while α-TTP does not readily bind [104] to or transfer γ-TOH [103] . Since the affinity of different vitamin E forms to α-TTP reflects the biological activity from rat resorption-gestations assays [94] , the hypothesis is supported that α-TTP is responsible for the discrimination of α-TOH. However, a current study from Grebenstein et al [105] raises the suggestion that the metabolism of vitamin E, but not α-TTP, is responsible for discrimination against mainly non-α-TOH forms, as α-TTP protects the side-chain of the different vitamin E forms from ω-hydroxylaseinduced degradation.…”

“…Since afamin has 18 predicted binding sites for vitamin E and shows binding affinity for both α-TOH and γ-TOH, it has been suggested to be an alternative vitamin E transporter in body fluids under conditions where the lipoprotein system is not sufficient for vitamin E transport [89] . Originally, vitamin E was discovered as a resorption-gestations factor in female rats [2,94] . Afamin was therefore suggested as playing a role in female fertility [92] , and indeed it has been shown to bind vitamin E and to increase in maternal serum during pregnancy [92] .…”

Mechanisms for the prevention of vitamin E excess

“…1 ) Almost immediately upon vitamin E's discovery in 1922 ( 12 ), these different forms of vitamin E were recognized to have differing biologic activities in rodents ( 13 ). Biologic activities were assessed by the various vitamin E forms to reverse defi ciency symptoms, specifi cally fetal resorption in vitamin E-defi cient pregnant rats ( 14 ). The different vitamin E forms are interconvertable by plants ( 15 ), but there is no convincing evidence that the same is true for animals.…”

Gamma-Tocopherol – An Underestimated Vitamin?

“…Results from animal experiments published 20-30 years ago and very recent data on Á-tocopherol suggest that this vitamer might have a special role that needs to be considered. The relative activity of Á-to ·-tocopherol in animal experiments (different criteria) or animal/human red blood cell hemolysis tests was 1-11% [12], 8-19% [13], 13% [14], 28% [8], 30% [15], 37% [16], 38% [5], and 67% [7]. The importance of Á-tocopherol is also highlighted in several recent human, animal, and cell line studies [17][18][19][20][21][22][23][24].…”