Emodin lows NPC1L1-mediated cholesterol absorption as an uncompetitive inhibitor

Abstract

Emodin (EM) is one of the active components of the traditional Chinese medicine rhubarb, and there is evidence of its hypolipidemic activity, though the exact mechanism is unknown. NPC1L1 is a key protein in human cholesterol uptake that is primarily expressed in hepatocytes and gastrointestinal epithelial cells. Our findings suggest that rhodopsin inhibits cellular cholesterol uptake by influencing NPC1L1 cholesterol transport. The results showed that NBD-cholesterol uptake in human HepG2 cells was 27 %, 31.3 %, 33.6 %, 41.6 %, and 52.6 % of control after treatment with 100, 75, 50, 25, and 12.5 % M EM, respectively, compared to 50 % for 100 M Ezetimibe. Kinetic studies revealed that EM inhibited cellular uptake of cholesterol through anti-competitive inhibition. Furthermore, using confocal fluorescence quantification, we discovered that after cholesterol deprivation treatment reintroduced cholesterol supply, cholesterol uptake was significantly higher in HepG2 cells highly expressing NPC1L1 than in U2OS cells with low NPC1L1 expression. As a result, we hypothesize that EM may inhibit cholesterol uptake via NPC1L1 in human hepatocytes in an anti-competitive manner. Overall, as a dietary supplement or lipid-modifying drug, EM has the potential to lower cholesterol.