| Abstract |
Dietary lipids and fat-soluble micronutrients are solubilized in mixed micelles and absorbed in the small intestine. Based on an assumption that cholesterol and other fat-soluble molecules share a number of transport mechanisms and the fact that Niemann-Pick C1-like 1 (NPC1L1) is critical for intestinal cholesterol absorption, we hypothesized that some fat-soluble molecules may be transported by NPC1L1. To investigate this hypothesis, we compared the cellular uptake and inhibitory effects of ezetimibe, the molecular target of which is NPC1L1, between cholesterol and some fat-soluble molecules using rat NPC1L1-overexpressing Caco-2 cells. The in vitro analysis suggested that NPC1L1 mediates the uptake of alpha-tocopherol (vitamin E) in an ezetimibe-sensitive manner as well as the uptake of cholesterol but does not mediate the uptake of retinol (vitamin A) or cyclosporin A. To confirm the ezetimibe-sensitive uptake of alpha-tocopherol in vivo, we performed an in vivo absorption study using rats and the results suggested a physiologically significant role of NPC1L1-mediated alpha-tocopherol absorption. Furthermore, using human NPC1L1 overexpression system, we demonstrated that both cholesterol and alpha-tocopherol uptake was also significantly increased by the overexpression of human NPC1L1 and ezetimibe inhibited their uptake. Mutual inhibition studies of cholesterol and alpha-tocopherol in human NPC1L1-mediated uptake revealed the inhibitory effect of cholesterol and the stimulatory effect of alpha-tocopherol on the NPC1L1-mediated transport of both substrates. The present data suggest, for the first time, that NPC1L1 has the ability to transport alpha-tocopherol and that ezetimibe is able to inhibit the intestinal absorption of alpha-tocopherol.
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