Curcumin inhibits cholesterol uptake in Caco-2 cells by down-regulation of NPC1L1 expression

Caco-2 cells were cultured to confluence. The micelles composed of bile salt, monoolein, and 14C-cholesterol were prepared. We first incubated the cells with the micelles in the presence and absence of ezetimibe, the specific inhibitor of NPC1L1, to see whether the uptake of the cholesterol in the cells was mediated by NPC1L1. We then pretreated the cells with curcumin at different concentrations for 24 h followed by examination of the changes of cholesterol uptake in these curcumin-treated cells. Finally we determined whether curcumin affects the expression of NPC1L1 by both Western blot analysis and qPCR quantification.We found that the uptake of radioactive cholesterol in Caco-2 cells was inhibited by ezetimibe in a dose-dependent manner. The results indicate that the uptake of cholesterol in this study was mediated by NPC1L1. We then pretreated the cells with 25-100 μM curcumin for 24 h and found that such a treatment dose-dependently inhibited cholesterol uptake with 40% inhibition obtained by 100 μM curcumin. In addition, we found that the curcumin-induced inhibition of cholesterol uptake was associated with significant decrease in the levels of NPC1L1 protein and NPC1L1 mRNA, as analyzed by Western blot and qPCR, respectively.Curcumin inhibits cholesterol uptake through suppression of NPC1L1 expression in the intestinal cells.Elevated plasma cholesterol levels constitute a major risk factor for atherosclerosis and coronary heart diseases [1]. The levels of plasma cholesterol are influenced by de novo biosynthesis, absorption in the gut, and the removal of cholesterol from the blood [2]. The intestine plays a major role in regulating cholesterol homeostasis and about 36% reductions of plasma cholesterol could be achieved by total inhibition of cholesterol absorption [3]. Absorption of cholesterol is a multi-step process in which cholesterol is micellized by bile acids in the intestinal lumen, taken up by the enterocytes, assembled into lipoproteins, and transp