Olea europaea Linn (Oleaceae) Fruit Pulp Extract Suppresses Sterol Regulatory Element-Binding Proteins-1c via AMP-Activated Protein Kinase Activation in Human Hepatic Cells

Purpose: To investigate the molecular mechanisms underlying the role of Olea europaea Linn (Oleaceae) fruit pulp extract (OPF) in the prevention of high glucose-induced lipid accumulation in human HepG2 hepatocytes. Methods: HepG2 cells were pretreated with various concentration of OPF (0, 10, 20, 40 and 80 μg/ml) and then treated with serum-free medium with normal glucose (5 mM) for 1 h, followed by exposure to high glucose (25 mM D-glucose) for 24 h. Cell viability and cytotoxicity parameters were measured using LDH and MTT assay while triglyceride and total cholesterol levels were evaluated using respective enzymatic reagent kits. Protein expressional levels were analyzed by Western blotting. Results: OPF did not influence the cell viability (up to 200 μg/ml) and showed any signs of cytotoxicity (up to 80 μg/ml). OPF significantly attenuated lipid accumulation in human HepG2 hepatocytes when exposed to high glucose (25 mM D-glucose) in a dose-dependently (p < 0.05, 0.01 and 0.001 at 20, 40 and 80 μg/ml concentrations, respectively). Nile red staining showed that 10, 20, 40 and 80 μg/ml concentrations of OPF reduced lipid accumulation by 25, 33.7 (p < 0.05), 43.7 (p < 0.01) and 52.5 % (p < 0.001), respectively. The increased levels of triglycerides and total cholesterol contents were also attenuated by OPF (p < 0.001 at 80 μg/ml). Further, OPF attenuated the expression of fatty acid synthase and sterol regulatory element-binding protein-1. Adenosine monophosphate-activated protein kinase was also activated by OPF treatment when exposed to high glucose (25 mM D-glucose) in human HepG2 hepatocytes. Conclusion: This study indicates that OPF has hypolipidemic effects by inhibiting lipid biosynthesis mediated via AMPK signaling. Thus, this extract can be potentially developed into an anti-obesity agent.