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A feasibility study quantifying in vivo human alpha-tocopherol metabolism.
Andrew J Clifford1, Fabiana F de Moura, Charlene C Ho
1Department of Nutrition, University of California, Davis, Davis, CA 5616-8669, USA. ajclifford@ucdavis.edu
The American Journal of Clinical Nutrition
|December 13, 2006
Summary
Human vitamin E metabolism differs between RRR- and all-rac-alpha-tocopherol. The all-rac form is preferentially degraded and eliminated, while the RRR form has longer residence times and greater distribution, highlighting distinct metabolic pathways.
Area of Science:
- Biochemistry
- Human Metabolism
- Pharmacokinetics
Background:
- Human vitamin E (alpha-tocopherol) metabolism requires further quantification.
- Understanding the in vivo fate of different alpha-tocopherol isomers is crucial.
Purpose of the Study:
- To quantify and interpret the in vivo metabolism of RRR- and all-rac-alpha-tocopherol in an adult human.
- To compare the metabolic fate and disposition of the two major alpha-tocopherol stereoisomers.
Main Methods:
- Administration of radiolabeled RRR- and all-rac-alpha-tocopheryl acetate to a human subject.
- Measurement of tracer fate in plasma, lipoproteins, urine, and feces over time.
- Analysis and interpretation using kinetic modeling.
Main Results:
- Both RRR- and all-rac-alpha-tocopherol isomers were absorbed equally well (approx. 77.5%).
- Urine was the primary elimination route, with all-rac-alpha-tocopherol preferentially degraded and eliminated compared to RRR-alpha-tocopherol.
- RRR-alpha-tocopherol exhibited longer residence times in plasma and liver pools and a greater distribution volume than all-rac-alpha-tocopherol.
Conclusions:
- All-rac-alpha-tocopherol is preferentially degraded and eliminated via urine, the major route.
- RRR-alpha-tocopherol demonstrates longer residence times and a larger distribution in the body compared to the all-rac form.
- The liver contains two kinetically distinct alpha-tocopherol pools, suggesting complex regulatory mechanisms.
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