Intestinal apolipoprotein B secretion is inhibited by the flavonoid quercetin: Potential role of microsomal triglyceride transfer protein and diacylglycerol acyltransferase |
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Authors: | Adele?Casaschi Qi?Wang Ka'ohimanu?Dang Alison?Richards Email author" target="_blank">Andre?TheriaultEmail author |
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Affiliation: | (1) Division of Medical Technology, John A. Burns School of Medicine, University of Hawaii at Manoa, 1960 East-West Road, Biomed C-206, 96822 Honolulu, Hawaii |
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Abstract: | Recent studies have yielded evidence that plant flavonoids reduce hepatic lipid and apolipoprotein B (apoB) secretion. However,
the possible role of flavonoids in regulating lipid and apoB secretion by the intestine has not been studied. The purpose
of our study was to examine the effects of quercetin, a common dietary flavonoid, on TAG and apoB secretion in a human intestinal
cell-line, CaCo-2. Differentiated postconfluent CaCo-2 cells grown on filters and pretreated with quercetin for 8 h were shown
by ELISA to inhibit basolateral apoB secretion in a dose-dependent manner. At 15 μM, the secretion of both apoB-100 and apoB-48
were inhibited similarly. This effect was shown to be specific, as quercetin did not affect the incorporation of 35S]methionine/cysteine into secreted TCA-precipitable proteins. To determine the mechanism underlying this inhibitory effect,
we examined two regulatory points: IAG availability and lipid transfer to the lipoprotein particle. Quercetin inhibited TAG
synthesis under both basal and lipid-rich conditions, indicating that lipid availability is a determining factor in the regulation
of apoB secretion by quercetin. The reduction was due at least in part to a decrease in diacylglycerol acyltransferase activity.
We next examined lipid transfer or lipidation of the lipoprotein particle by analyzing microsomal IAG transfer protein (MTP)
activity. Quercetin decreased MTP activity moderately. In summary, the data demonstrated that pharmacological concentrations
of quercetin are a potent inhibitor of intestinal apoB secretion and that reduced lipid availability and lipidation in the
lipoprotein assembly step are the mechanism for the suppression of apoB-containing lipoprotein secretion by quercetin in CaCo-2
cells. |
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