alpha- and delta-tocopherol induce expression of hepatic alpha-tocopherol-transfer-protein mRNA.
alpha-Tocopherol transfer protein (alpha-TTP) supplements nascent very-low-density lipoprotein (VLDL) preferentially with alpha-tocopherol by selecting the alpha-isomers against other stereoisomers of tocopherol. It is exclusively expressed in liver. We investigated whether the expression of the hepatic alpha-TTP can be induced by dietary tocopherols. Vitamin E-depleted rats were fed with a diet containing alpha- and delta-tocopherol (ratio 1:3). The expression of alpha-TTP mRNA was measured in liver tissue. The ratio of tocopherol stereoisomers was determined in plasma, plasma lipoproteins and tissues to measure the metabolic action of alpha-TTP. Refeeding a diet containing either alpha- or delta-tocopherol, or both, caused a steady increase of the expression of alpha-TTP mRNA. In parallel the alpha/delta-tocopherol ratio increased in plasma, VLDL, high-density lipoprotein and low-density lipoprotein as well as in liver tissue, when the diet was fed containing both isomers. The alpha-tocopherol/delta-tocopherol ratio of heart, kidney, lung, lamellar bodies of lung and in lung lavage showed no or a comparatively low increase. The data show that both tocopherol isomers were able to induce alpha-TTP mRNA in rat liver and, thus, the ability of liver to select for the alpha-isomer. On the other hand, tocopherol depletion did not change the expression of hepatic alpha-TTP mRNA in the rat.
Fechner
H
H
Department of Neonatology, University Hospital Charité, Humboldt University, D-10098 Berlin, Federal Republic of Germany.
Schlame
M
M
Guthmann
F
F
Stevens
P A
PA
Rüstow
B
B
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics*; D004032:Diet; D015870:Gene Expression / Q000187:drug effects*; D008074:Lipoproteins / Q000097:blood; D008099:Liver / Q000378:metabolism*; D008168:Lung / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D013237:Stereoisomerism; D014810:Vitamin E / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D002352:Carrier Proteins; D008074:Lipoproteins; D012333:RNA, Messenger; C017763:alpha-tocopherol transfer protein; D014810:Vitamin E