Recent advances in vitamin E metabolism and deficiency.
Alpha-, beta-, gamma- and delta-tocopherol are present in many foods and are, in the absence of fat malabsorption, well absorbed from the gut. Their anti-oxidant property is well known and protects arteries and capillaries as well as blood lipids and nervous tissue against oxidative stress. In contrast to beta-, gamma- and delta-tocopherol, alpha-tocopherol is preferentially conserved by the discriminating action of the liver alpha-tocopherol transfer protein, which also maintains plasma alpha-tocopherol concentration within a range of 20 to 40 microM. In the circulation, alpha-tocopherol, in association with the transfer-protein, is assembled into the very low-density lipoprotein and low-density lipoprotein particles and released for use by the peripheral tissues. Recent data suggest that alpha-tocopherol is not only an anti-oxidant but also a regulator of gene expression through its binding to nuclear receptors. The precise mechanism of regulating gene expression, however, is still unknown. The four tocopherols are ultimately degraded by omega-oxidation and subsequent beta-oxidations followed by the elimination of the metabolites in the bile and in the urine. Patients with a defect of the alpha-tocopherol transfer protein are unable to maintain their alpha-tocopherol reserves and progressively lose tendon reflexes and have signs and symptoms of spinocerebellar ataxia while plasma vitamin E level drops below 2 microg/ml.
Department of Pediatrics, UZ Gasthuisberg, Herestraat 49, 3000, Leuven, Belgium. kindergeneeskunde@uz.kuleuven.ac.be
Ephrem
E
Eggermont
D000975:Antioxidants / Q000378:metabolism* / Q000494:pharmacology*; D003937:Diagnosis, Differential; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D009626:Terminology as Topic; D014810:Vitamin E / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D014811:Vitamin E Deficiency / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology*
D000975:Antioxidants; D014810:Vitamin E