Effects of Quercetin Nanoemulsion on Cholesterol Efflux and MicroRNA-33/34a Expression in the Liver of Mice Fed with a High-Cholesterol Diet

Abstract

Quercetin is a flavonoid widely present in plants; despite its beneficial physiological activity, it exhibits considerably low bioavailability. Nanoemulsion technology is used for improving the bioavailability of lipophilic phenolic compounds. This study aimed to investigate the potential effects of quercetin nanoemulsion (QN) on regulating the microRNA (miR)-33/34a pathway involved in cholesterol efflux in the liver of mice fed with a high-cholesterol (HC) diet. Subsequently, C57BL/6J mice were divided into four groups and fed a normal chow diet, HC diet supplemented with 1% cholesterol and 0.5% cholic acid, or HC diet supplemented with 0.05% QN or 0.1% QN for 6 weeks. Serum and hepatic lipid profiles were assayed using commercial enzymatic kits. Gene expression and miR levels were quantified using real-time quantitative reverse transcription polymerase chain reaction, and adenosine monophosphate-activated protein kinase (AMPK) activity was measured using an AMPK Kinase Assay kit. QN supplementation improved serum and liver lipid profiles. QN upregulated the mRNA levels of adenosine triphosphate (ATP)-binding cassette subfamily A1, ATP-binding cassette subfamily G1, and scavenger receptor class B type 1, which are related to cholesterol efflux. In the QN group, the hepatic AMPK activity increased, whereas miR-33, and miR-34a expression levels decreased. These results suggest that QN may enhance cholesterol efflux, at least partly through modulating AMPK activity and miR-33/34a expression in the liver.

Keywords: AMP-activated protein kinase; cholesterol; microRNAs; quercetin.

Fig. 1

Expression of genes related to cholesterol efflux in the liver of mice fed with normal chow (NC), high-cholesterol (HC), HC+0.05% QN (QNL), and HC+0.1% QN (QNH) diets for 6 weeks. The mRNA levels of adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1), ATP-binding cassette transporter G1 (ABCG1), and scavenger receptor class B type 1 (SR-B1) are measured using real-time quantitative reverse transcription polymerase chain reaction. Values are expressed as mean±SE (n=6). Different letters (a,b) indicate significant differences among the four groups (NC, HC, QNL, and QNH groups) at P<0.05. QN, quercetin nanoemulsion.

Fig. 2

Adenosine monophosphate-activated protein kinase (AMPK) activity in the liver of mice fed with normal chow (NC), high-cholesterol (HC), HC+0.05% QN (QNL), and HC+0.1% QN (QNH) diets for 6 weeks. Values are expressed as mean±SE (n=6). Different letters (a,b) indicate significant differences among the four groups (NC, HC, QNL, and QNH groups) at P<0.05. QN, quercetin nanoemulsion.

Fig. 3

microRNA (miR)-33 (A) and miR-34a (B) expression in the liver of mice fed with normal chow (NC), high-cholesterol (HC), HC+0.05% QN (QNL), and HC+0.1% QN (QNH) diets for 6 weeks. Values are expressed as mean±SE (n=6). Different letters (a-c) indicate significant differences among the four groups (NC, HC, QNL, and QNH groups) at P<0.05. QN, quercetin nanoemulsion.

Fig. 4

Schematic diagram showing possible mechanisms by which quercetin nanoemulsion (QN) regulates hepatic lipid metabolism and the microRNA (miR)-33/34a pathways. AMPK, adenosine monophosphate-activated protein kinase; ABCA1, adenosine triphosphate (ATP)-binding cassette transporter A1; ABCG1, ATP-binding cassette transporter G1; SR-B1, scavenger receptor class B type 1.