Transport of vitamin E by differentiated Caco-2 cells.

In hepatocytes, vitamin E is secreted via the efflux pathway and is believed to associate with apolipoprotein B (apoB)-lipoproteins extracellularly. The molecular mechanisms involved in the uptake, intracellular trafficking, and secretion of dietary vitamin E by the intestinal cells are unknown. We observed that low concentrations of Tween-40 were better for the solubilization and delivery of vitamin E to differentiated Caco-2 cells, whereas high concentrations of Tween-40 and sera inhibited this uptake.

Effect of vitamin E supplementation in patients with ataxia with vitamin E deficiency.

Ataxia with vitamin E (Vit E) defciency (AVED) is an autosomal recessive disorder caused by mutations of the alpha tocopherol transfer protein gene. The Friedreich ataxia phenotype is the most frequent clinical presentation. In AVED patients, serum Vit E levels are very low in the absence of intestinal malabsorption.

Localization of alpha-tocopherol transfer protein in the brains of patients with ataxia with vitamin E deficiency and other oxidative stress related neurodegenerative disorders.

Vitamin E (alpha-tocopherol) is an essential nutrient and an important antioxidant. Its plasma levels are dependent upon oral intake, absorption and transfer of the vitamin to a circulating lipoprotein. The latter step is controlled by alpha-tocopherol transfer protein (alpha-TTP), which is a 278 amino acid protein encoded on chromosome 8, known to be synthesized in the liver.

Vitamin E dose-response studies in humans with use of deuterated RRR-alpha-tocopherol.

Background: Supplemental vitamin E does not raise plasma alpha-tocopherol concentrations more than approximately 3-fold.

Objective: To elucidate the mechanism for the limitation in plasma alpha-tocopherol, we undertook human supplementation trials using incrementally increased doses of deuterated vitamin E.

Design: Plasma was obtained from 6 healthy, young adults (4 men and 2 women) during 3 sequential supplementation trials with doses of 15, 75, and 150 mg RRR-alpha-tocopheryl acetate labeled with deuterium (d3-RRR-alpha-tocopheryl acetate).

Human plasma and tissue alpha-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E.

We report a comparison of natural and synthetic vitamin E in humans using deuterium labeling to permit the two forms of vitamin E to be measured independently in plasma and tissues of each subject. Differences in natural and synthetic vitamin E concentrations were measured directly under equal dosage conditions using an equimolar mixture of deuterated RRR-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate. Two groups of five adults took 30 mg of the mixture as a single dose and as eight consecutive daily doses, respectively.

Ataxia with isolated vitamin E deficiency: heterogeneity of mutations and phenotypic variability in a large number of families.

Ataxia with vitamin E deficiency (AVED), or familial isolated vitamin E deficiency, is a rare autosomal recessive neurodegenerative disease characterized clinically by symptoms with often striking resemblance to those of Friedreich ataxia. We recently have demonstrated that AVED is caused by mutations in the gene for alpha-tocopherol transfer protein (alpha-TTP). We now have identified a total of 13 mutations in 27 families.

Dissociation of LPL and LDL: effects of lipoproteins and anti-apoB antibodies.

We have shown previously that the activity of lipoprotein lipase (LPL), the major enzyme responsible for hydrolysis of triglyceride contained in circulating lipoproteins, is associated with lipoproteins in postheparin plasma. In other studies, microtiter plate assays showed that LPL interaction with low density lipoprotein (LDL) and very low density lipoprotein (VLDL) was decreased by antibodies to apolipoprotein (apo)B. To test whether antibodies to apoB affected LPL-LDL association in solution, two types of assays were performed, gel filtration and coprecipitation.

Disruption of cholesterol 7alpha-hydroxylase gene in mice. II. Bile acid deficiency is overcome by induction of oxysterol 7alpha-hydroxylase.

Past experiments and current paradigms of cholesterol homeostasis suggest that cholesterol 7alpha-hydroxylase plays a crucial role in sterol metabolism by controlling the conversion of cholesterol into bile acids. Consistent with this conclusion, we show in the accompanying paper that mice deficient in cholesterol 7alpha-hydroxylase (Cyp7-/- mice) exhibit a complex phenotype consisting of abnormal lipid excretion, skin pathologies, and behavioral irregularities (Ishibashi, S., Schwarz, M.

Translocation of apolipoprotein B across the endoplasmic reticulum is blocked in abetalipoproteinemia.

Abetalipoproteinemia (ABL) is an autosomal recessive disease characterized by the inability of the liver and intestine to secrete apolipoprotein B (apoB). Mutations in the microsomal triglyceride transfer protein (MTP) gene, but not the apoB gene, are responsible for the ABL phenotype. It is not clear how loss of MTP in ABL patients leads to a complete, but specific, block in the secretion of apoB.

A novel function for apolipoprotein B: lipoprotein synthesis in the yolk sac is critical for maternal-fetal lipid transport in mice.

Apolipoprotein (apo) B, the principal structural component necessary for the synthesis and secretion of triglyceride-rich lipoproteins by the intestine and liver, is highly expressed in the yolk sac visceral endoderm of mammals, although its function in this tissue has been hitherto unclear. Disruption of the apoB gene in mice results in embryonic lethality (approximately 9.5 - 10.

Lipoproteins containing apolipoprotein B isolated from patients with abetalipoproteinemia and homozygous hypobetalipoproteinemia: identification and characterization.

Abetalipoproteinemia (ABL) and homozygous hypobetalipoproteinemia (HBL) are inherited disorders which are classically characterized by progressive retinal and spinocerebellar disease, fat-soluble vitamin deficiency, and absence of apolipoprotein (apo) B from the plasma. Using immunoaffinity chromatography with an anti-apo B antiserum, we isolated apo B-containing lipoprotein (LpB) particles from the plasma of 4 ABL and 2 HBL patients. The LpB particles were characterized and compared with low density lipoprotein (LDL) and LpB isolated from normal plasma.

Human alpha-tocopherol transfer protein: cDNA cloning, expression and chromosomal localization.

alpha-Tocopherol transfer protein (alpha TTP), which specifically binds this vitamin and enhances its transfer between separate membranes, was previously isolated from rat liver cytosol. In the current study we demonstrated the presence of alpha TTP in human liver by isolating its cDNA from a human liver cDNA library. The cDNA for human alpha TTP predicts 278 amino acids with a calculated molecular mass of 31,749, and the sequence exhibits 94% similarity with rat alpha TTP at the amino acid level.

Ataxia with isolated vitamin E deficiency is caused by mutations in the alpha-tocopherol transfer protein.

Ataxia with isolated vitamin E deficiency (AVED) is an autosomal recessive neurodegenerative disease which maps to chromosome 8q13. AVED patients have an impaired ability to incorporate alpha-tocopherol into lipoproteins secreted by the liver, a function putatively attributable to the alpha-tocopherol transfer protein (alpha-TTP). Here we report the identification of three frame-shift mutations in the alpha TTP gene.

Exencephaly and hydrocephaly in mice with targeted modification of the apolipoprotein B (Apob) gene.

Apolipoprotein B (apoB) is a key structural component of several lipoproteins. These lipoproteins transport cholesterol, lipids, and vitamin E in the circulation. Humans that produce truncated forms of apoB have low plasma concentrations of apoB, beta-lipoproteins, cholesterol, and often vitamin E.

Human plasma vitamin E kinetics demonstrate rapid recycling of plasma RRR-alpha-tocopherol.

A kinetic model of vitamin E transport in humans is described using data from our studies with deuterium-labeled stereoisomers of alpha-tocopherol (RRR- and SRR-). In normal subjects, both alpha-tocopherols are present at similar concentrations in chylomicrons, but by 24 hr, RRR-alpha-tocopherol is at higher plasma concentrations because RRR-alpha-tocopherol is preferentially incorporated into very low density lipoproteins, which are then secreted into plasma. In three nondiscriminator patients with familial isolated vitamin E deficiency, the fractional disappearance rates (mean +/- SD) of deuterium-labeled RRR- and SRR-alpha-tocopherols in plasma were 1.

beta-Carotene transport in human lipoproteins. Comparisons with a-tocopherol.

The purpose of this study was to investigate the temporal relationships of the transport of beta-carotene in human lipoproteins. We administered 60 mg beta-carotene with breakfast to nine fasting subjects, then blood samples were collected at intervals of up to 75 h, lipoproteins were isolated, and beta-carotene was quantitated. beta-Carotene concentrations in chylomicrons and very low density lipoproteins (VLDL) peaked at 6 and 9 h, respectively.

Discrimination between RRR- and all-racemic-alpha-tocopherols labeled with deuterium by patients with abetalipoproteinemia.

The ability to discriminate between stereoisomers of alpha-tocopherol was studied in five patients with abetalipoproteinemia (ABL) because an impairment in secretion of apolipoprotein B-containing lipoproteins might impede the normally enhanced plasma transport of RRR-alpha-tocopherol. An oral dose containing 3.7 g of each 2R, 4'R,8'R-alpha-[5-C2H3]tocopheryl acetate (d3RRR-alpha-tocopheryl acetate) and 2RS,4'RS,8'RS-alpha-[5,7-(C2H3)2]tocopheryl acetate (d6 all rac-alpha-tocopheryl acetate) was administered, then the labeled and unlabeled alpha-tocopherol contents of plasma and red blood cells from multiple blood samples obtained at selected times up to 72 h following the dose were quantitated.

Efficacy of water-soluble vitamin E in the treatment of vitamin E malabsorption in short-bowel syndrome.

A water-soluble form of vitamin E, tocopheryl succinate polyethylene glycol 1000 (TPGS), was used as an oral vitamin E supplement in a 71-y-old patient with severe fat malabsorption and vitamin E deficiency secondary to short-bowel syndrome. An absorption test with deuterium-labeled TPGS demonstrated that TPGS was absorbed and the released alpha-tocopherol was transported normally in lipoproteins. The disappearance portion of the deuterated alpha-tocopherol curves were parallel to those in control subjects, suggesting normal metabolic turnover of alpha-tocopherol.

Concomitant brainstem axonal dystrophy and necrotizing myopathy in vitamin E-deficient rats.

The purpose of this study was to simultaneously evaluate in rats the effects of vitamin E depletion on tissue alpha-tocopherol (alpha-T) concentrations, electrophysiologic measurements and histopathology. Rats (21-day-old male Wistar) were fed either vitamin E-deficient or supplemented (control) diets (n = 6/group) for 10, 16, and 61 weeks. At these times, electrophysiologic tests (electromyography, spinal and somatosensory evoked potentials, and motor nerve conduction velocity) were performed, the rats were killed and alpha-T concentrations of adipose tissue, sciatic nerve, and cervical and lumbar spinal cord were measured along with histopathologic evaluation of skeletal muscles and the nervous system.

Intestinal expression of human apolipoprotein A-IV in transgenic mice fails to influence dietary lipid absorption or feeding behavior.

Two transgenic mouse lines, expressing low or high amounts of human apo A-IV were created. In low and high expressor HuAIVTg mice on a chow diet, serum human apo A-IV levels were 6 and 25 times the normal human level and on a high fat diet, they were 12 and 77 times higher. Human apo A-IV was equally distributed between lipoprotein (mainly HDL) and lipid-free fractions.

Vitamin E deficiency in dogs does not alter preferential incorporation of RRR-alpha-tocopherol compared with all rac-alpha-tocopherol into plasma.

The plasma and lipoprotein transport of RRR and all rac-alpha-tocopherols, labeled with different amounts of deuterium [2R,4'R,8'R-alpha-[5-C2H3]tocopheryl acetate (d3RRR-alpha-tocopheryl acetate] and 2RS, 4'RS, 8'RS-alpha-[5,7-(C2H3)2]tocopheryl acetate (d6all rac-alpha-tocopheryl acetate), was studied in adult beagle dogs that had been fed a vitamin E-deficient (-E; two dogs) or supplemented (+E; two dogs) diet for two years. We set out to test the hypothesis that the activity of the hepatic tocopherol binding protein (which is thought to preferentially incorporate RRR-alpha-tocopherol into the plasma) is up-regulated by vitamin E deficiency. Labeled alpha-tocopherols increased and decreased similarly in plasma of both -E and +E dogs.

Alpha-tocopherol concentrations of the nervous system and selected tissues of adult dogs fed three levels of vitamin E.

The effects of dietary vitamin E levels on tissue alpha-tocopherol (alpha-T) concentrations in different parts of the nervous system are largely unknown. Therefore, we measured the alpha-T contents of nervous and other tissues obtained from beagle dogs fed for two years a vitamin E-deficient diet (-E, 0.05 +/- 0.