Transport of vitamin E by differentiated Caco-2 cells

Abstract

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. Vitamin E uptake was initially rapid and then reached saturation. Subcellular localization revealed that vitamin E primarily accumulated in microsomal membranes. Oleic acid (OA) treatment, which induces chylomicron assembly and secretion, decreased microsomal membrane-bound vitamin E in a time-dependent manner. To study secretion, differentiated Caco-2 cells were pulse-labeled with vitamin E and chased in the presence and absence of OA. In the absence of OA, vitamin E was associated with intestinal high density lipoprotein (I-HDL), whereas OAtreated cells secreted vitamin E with I-HDL and chylomicrons. No extracellular transfer of vitamin E between these lipoproteins was observed. Glyburide, an antagonist of ABCA1, partially inhibited its secretion with I-HDL, whereas plasma HDL increased vitamin E efflux. An antagonist of microsomal triglyceride transfer protein, brefeldin A, and monensin specifically inhibited vitamin E secretion with chylomicrons. These studies indicate that vitamin E taken up by Caco-2 cells is stored in the microsomal membranes and secreted with chylomicrons and I-HDL. Transport via I-HDL might contribute to vitamin E absorption in patients with abetalipoproteinemia receiving large oral doses of the vitamin. Vitamin E is a major lipid-soluble antioxidant and is an essential nutrient for normal growth and development. Its deficiency results in neurological dysfunction, muscular weakness, and reproductive failure (1-3). Although a diet rich in vegetable oils and whole grains is a sufficient source of vitamin E in normal people (4), deficiency can result because of lipid malabsorption syndromes such as abetalipoproteinemia, a disease in which apolipoprotein B (apoB)-containing lipoproteins (chylomicrons, very low density lipoproteins, and low density lipoproteins) are absent in the plasma (1, 2). High oral doses of vitamin E ameliorate the deficiency and normalize plasma and adipose tissue levels of the vitamin in these patients (5). The mechanisms involved in vitamin E absorption in the absence of apoB-lipoprotein assembly are not known.Current knowledge of intestinal vitamin E absorption is based on human and animal studies involving oral or intraduodenal administration of vitamin E followed by lymph and plasma analysis (1-3, 6-9). Vitamin E uptake by the intestinal cells is believed to be less efficient than that of other fat-soluble vitamins. In most studies, z20-50% of dietary vitamin E is believed to be absorbed (4, 10). In contrast, z80% of dietary vitamin A is absorbed in 24 h...

Intestinal lipid absorption

“…Vitamin E absorption from the intestine is thought to occur predominantly through the secretion of chylomicrons into the lymphatic system. Consistent with this hypothesis is the observation that vitamin E absorption is dependent on the availability of oleic acid for triglyceride synthesis and chylomicron assembly and is inhibited by MTP inhibitors (7). The importance of alternative pathways for vitamin E absorption has also been suggested by the observation that symptoms of vitamin E deficiency are ameliorated after treatment with high doses of vitamin E in patients deficient in chylomicrons.…”

“…The uptake of vitamin E from the intestine has traditionally been assumed to be a simple process of passive diffusion. However, in a study in Caco-2 cells, it was shown to be a rapid, saturable, temperature-dependent process (7). Recent studies suggest that SR-BI plays a role in vitamin E absorption (154).…”

Vitamine E et physiologie du tissu adipeux

“…Ce processus implique la MTP (microsomal triglycerides transfert protein ; (Anwar et al, 2007)). En cas de faible apport alimentaire de lipides ne permettant pas la secretion de chylomicrons, une partie de la vitamine E sembleêtre excretee dans les HDL d'origine intestinale par un transporteur de la famille des ATP binding cassettes : ABCA1 (Anwar et al, 2006, Reboul et al, 2010. La vitamine E restant dans les chylomicrons residuels, c'est-a-dire celle qui n'a pas ete echangee avec d'autres lipoproteines ou distribuee aux tissus peripheriques lors de la lipolyse par les lipases endotheliales, est captee par le foie.…”

Mechanism of hypertriglyceridemia in CTP:phosphoethanolamine cytidylyltransferase-deficient mice

“…3D ) and the relative change in TAG and DAG ( Fig. 3E ) were 1.8-2.3-fold higher in the intestinal mucosa of Pcyt2 +/ Ϫ mice compared with littermate controls, demonstrating that in addition to (CM L ), small chylomicrons (CM SM ), and the VLDL-like chylomicron particles (CM VLDL) was performed as previously described (28)(29)(30). Media or enterocyte protein homogenates were mixed with 2 ml of 1.006 g/ml-density solution containing 0.57 g/ml KBr, to obtain a fi nal density of 1.10 g/ml.…”