α- and δ-Tocopherol induce expression of hepatic α-tocopherol-transfer-protein mRNA

Abstract

α-Tocopherol transfer protein (α-TTP) supplements nascent very-low-density lipoprotein (VLDL) preferentially with α-tocopherol by selecting the α-isomers against other stereoisomers of tocopherol. It is exclusively expressed in liver. We investigated whether the expression of the hepatic α-TTP can be induced by dietary tocopherols. Vitamin E-depleted rats were fed with a diet containing α- and δ-tocopherol (ratio 1:3). The expression of α-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 α-TTP. Refeeding a diet containing either α- or δ-tocopherol, or both, caused a steady increase of the expression of α-TTP mRNA. In parallel the α/δ-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 α-tocopherol/δ-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 α-TTP mRNA in rat liver and, thus, the ability of liver to select for the α-isomer. On the other hand, tocopherol depletion did not change the expression of hepatic α-TTP mRNA in the rat.