FIGURE 6-5 RRR-α-Tocopherol is preferentially resecreted by the liver and distributed to circulating lipoproteins. NOTE: HDL = high-density lipoprotein; LDL = low-density lipoprotein; VLDL = very low-density lipoprotein.

SOURCE: Adapted from Traber (1999).

In three people with ataxia and vitamin E deficiency (AVED) secondary to a defect in the α-TTP gene (Cavalier et al., 1998), the half-lives for both RRR- and SRR-α-tocopherols were approximately 13 hours (Traber et al., 1994b). These studies demonstrate that RRR- and SRR-α-tocopherols in the AVED patients disappear at the same rate as SRR-α-tocopherol in the control subjects. This suggests that α-TTP, which is defective in the AVED patients, is responsible for the longer half-life of RRR-α-tocopherol in the control subjects. It was estimated that resecretion of RRR-α-tocopherol by the liver in the control subjects resulted in the daily replacement of nearly all of the circulating RRR-α-tocopherol. Thus, the liver maintains plasma RRR-α-tocopherol concentrations by a continuous resecretion process. In contrast, other forms of vitamin E (e.g., SRR-α- and γ-tocopherols) are not resecreted into the plasma.


Oxidation Products. α-Tocopherol can be oxidized to the tocopheroxyl radical—one-electron oxidation product—which can be reduced back to the unoxidized form by reducing agents such as vitamin C. Further oxidation of the tocopheroxyl radical forms

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement