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. 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 OA-treated 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.
Anwar
Kamran
K
Department of Anatomy, State University of New York Downstate Medical Center, Brooklyn, NY, USA.
Kayden
Herbert J
HJ
Hussain
M Mahmood
MM
D001054:Apolipoproteins A / Q000378:metabolism; D001692:Biological Transport; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology; D002454:Cell Differentiation; D002788:Cholesterol Esters / Q000378:metabolism; D002914:Chylomicrons / Q000378:metabolism / Q000502:physiology; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology; D008075:Lipoproteins, HDL / Q000378:metabolism; D008954:Models, Biological; D015398:Signal Transduction / Q000502:physiology; D014810:Vitamin E / Q000378:metabolism* / Q000493:pharmacokinetics
D001054:Apolipoproteins A; D002352:Carrier Proteins; D002788:Cholesterol Esters; D002914:Chylomicrons; D008075:Lipoproteins, HDL; C106092:microsomal triglyceride transfer protein; D014810:Vitamin E