Vitamin E regulatory mechanisms.
Dietary and supplemental vitamin E is absorbed and delivered to the liver, but of the various antioxidants with vitamin E activity, only alpha-tocopherol is preferentially recognized by the alpha-tocopherol transfer protein (alpha-TTP) and is transferred to plasma, while the other vitamin E forms (e.g., gamma-tocopherol or tocotrienols) are removed from the circulation. Hepatic alpha-TTP is required to maintain plasma and tissue alpha-tocopherol concentrations. The liver is the master regulator of the body's vitamin E levels in that it not only controls alpha-tocopherol concentrations, but also appears to be the major site of vitamin E metabolism and excretion. Vitamin Es are metabolized similarly to xenobiotics; they are initially omega-oxidized by cytochrome P450s, undergo several rounds of beta-oxidation, and then are conjugated and excreted. As a result of these various mechanisms, liver alpha-tocopherol and other vitamin E concentrations are closely regulated; thus, any potential adverse vitamin E effects are limited.
Traber
Maret G
MG
Department of Nutrition and Exercise Science, Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA. maret.traber@oregonstate.edu
D000975:Antioxidants / Q000008:administration & dosage / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D014810:Vitamin E / Q000008:administration & dosage / Q000502:physiology*; D014811:Vitamin E Deficiency / Q000378:metabolism* / Q000517:prevention & control
D000975:Antioxidants; D002352:Carrier Proteins; D014810:Vitamin E