Effects Of Quercetin On Cholesterol Metabolism In Rat Hepatocytes Cultured In High Lipid Environment

ObjectiveTo determine the effects of quercetin on cholesterol metabolism, cell viability in BRL cells and the potential mechanisms at cellular and molecular levels involved in order to provide theoretical and experimental basis for better understanding the effects of quercetin, as well as its possible applications.Methods1.Preparation of high lipid serum:Wistar rats were fed by gavage a high lipid emulsion for 1 week. At the end of the experiment, blood samples were collected under sterile condition and serum were separated by centrifugation.2. Preparation of culture medium supplemented with high lipid serum:we tested the content of cholesterol in serum to determine whether the high lipid serum was prepared successfully, and then 10% high lipid serum was added into culture medium to compose a high lipid serum culture medium.3. Selection of quercetin concentration:BRL cells were treated with different concentrations (0,5,10, and 20 μmol/L) of quercetin in the media containing 10% normal fetal bovine serum for 24 h, and then switched to the high lipid culture medium with same quercetin concentrations for 48 h. The media and cells were collected for biochemical analysis. Meanwhile, the viability of cells was measured.4. On the basis of the experiments above, we further investigated the effects of quercetin on cholesterol metabolism in BRL cells. The expressions of the mRNA and protein, as well as the activity of important enzymes in cholesterol metabolism were determined.Results1. After the high lipid emulsion was administrated for 1 week, the contents of serum TC, FCH and LDL-C were significantly increased compared with the baseline.2. After 24 h culture, the contents of TC, FCH and LDL-C in the medium were obviously higher in high lipid serum group than in normal serum control. Compared with the cells cultured in normal medium, the contents of intracellular TC and FCH were increased significantly after cultured in high lipid serum media for 48 h.3. The viability of cells was significantly decreased after the treatment of 20μmol/L quercetin as compared to the cells in other groups. The activity of LDH showed no obvious difference among different groups. Compared with 0 and 5 μmol/L quercetin groups, the apoptosis rate of the cells treated with 20μmol/L quercetin was significantly increased. Therefore, we chose 10μmol/L as the suitable concentration of quercetin for the following investigation.4. Compared with 0 μmol/L quercetin group, the contents of TC, FCH and CE in other quercetin groups were decreased, whereas the content of LDL-C was not changed significantly. The contents of extracellular TC,FCH and CE in 10 and 20μmol/L quercetin groups were significantly decreased as compared to the 0 μmol/L quercetin group. Meanwhile, a decreased trend in the contents of intracellular TC and FCH were noted, but without significant difference. The CE content showed no significant change.5.The expressions of mRNA and protein, as well as the activity of HMGCR, were significantly decreased as compared to the control group, while the expressions of mRNA and protein of LDLR, SREBP-2, ABCA1 and LXRa were significantly increased after 10μmol/L quercetin treatment.ConclusionIt is concluded that quercetin at the concentration of 10μmol/L has a significant impact on cholesterol metabolism in rat hepatocytes. It was showed that 10μmol/L quercetin could significantly decrease the expressions of mRNA, protein and the activity of HMGCR. Moreover, the expressions of mRNA and protein of LDLR and SREBP2 (an upstream regulatory factor of LDLR) were significantly reduced. The expressions of the mRNA and protein of ABCA1 and its upstream regulatory factor LXRa were significantly increased.