Mechanisms involved in vitamin E transport by primary enterocytes and in-vivo absorption

Kamran Anwar, Jahangir Iqbal, and M. Mahmood Hussain

Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, NY 11203

Corresponding Author: mhussain{at}downstate.edu

It is generally believed that vitamin E is absorbed along with chylomicrons. However, we previously reported that human colon carcinoma Caco-2 cells utilize dual pathways, apolipoprotein B-lipoproteins and high density lipoproteins (HDL), to transport vitamin E. Here, we used primary enterocytes and rodents to identify in vivo vitamin E absorption pathways. Uptake of [3H]-a-tocopherol by primary rat and mouse enterocytes increased with time and reached a maximum at 1 hour. In the absence of exogenous lipid supply, these cells secreted vitamin E with HDL. Lipids induced secretion of vitamin E with intermediate density lipoproteins and enterocytes supplemented with lipids and oleic acid secreted vitamin E with chylomicrons. The secretion of vitamin E with HDL was not affected by lipid supply, but was enhanced when incubated with HDL. MTP inhibition reduced vitamin E secretion with chylomicrons without affecting its secretion with HDL. Enterocytes from Mttp deficient mice also secreted less vitamin E with chylomicrons. In vivo absorption of [3H]-a-tocopherol by mice after P407 injection to inhibit lipoprotein lipase revealed that vitamin E was associated with triglyceride-rich lipoproteins and small HDL containing apolipoprotein B48 and apolipoprotein AI. These studies indicate that enterocytes utilize two pathways for vitamin E absorption. Absorption with chylomicrons is the major pathway of vitamin E absorption. The HDL pathway may be important when chylomicron assembly is defective and can be exploited to deliver vitamin E without increasing fat consumption.

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