Background: Reverse cholesterol transport (RCT) is an important cardioprotective mechanism and the decrease in cholesterol efflux can result in the dyslipidemia. Although liraglutide, a glucagon like peptide-1 analogue, has mainly impacted blood glucose, recent data has also suggested a beneficial effect on blood lipid. However, the exact mechanism by which liraglutide modulates lipid metabolism, especially its effect on RCT, remain undetermined. Hence, the aim of the present study was to investigate the potential impacts and potential underlying mechanisms of liraglutide on the cholesterol efflux in both db/db mice and HepG2 cells.
Methods: Six-week old db/db mice with high fat diet (HFD) and wild type mice were administered either liraglutide (200 μg/kg) or equivoluminal saline subcutaneously, twice daily for 8 weeks and body weight was measured every week. After the 8-week treatment, the blood was collected for lipid evaluation and liver was obtained from the mice for hematoxylin-eosin (HE) staining, red O staining and Western blotting. Cholesterol efflux was assessed by measuring the radioactivity in the plasma and feces after intraperitoneal injection of 3H-labeled cholesterol. HepG2 Cells were treated with different concentrations of glucose (0, 5, 25, and 50 mmol/L) with or without liraglutide (1000 nmol/L) for 24 h. The intracellular cholesterol efflux was detected by BODIPY-cholesterol fluorescence labeling. Real-time PCR or Western blotting was used to examine the expression levels of ABCA1, ABCG1 and SR-B1.
Results: Liraglutide significantly decreased blood glucose, serum total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C). It also reduced liver lipid deposition in db/db mice fed with HFD. Moreover, the movement of 3H-cholesterol from macrophages to plasma and feces was significantly enhanced in db/db mice fed with HFD after liraglutide adminstration. In vitro study, liraglutide could promote the cholesterol efflux of HepG2 cells under high glucose, and also increase the expression of ABCA1 by activating the ERK1/2 pathway.
Conclusions: Liraglutide could improve lipid metabolism and hepatic lipid accumulation in db/db mice fed with HFD by promoting reversal of cholesterol transport, which was associated with the up-regulation of ABCA1 mediated by the ERK1/2 phosphorylation.
Keywords: ABCA1; High glucose; High-fat diet; Liraglutide; Molecular mechanism; Reverse cholesterol transport; db/db mice.