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.