Lipid-Lowering Activity of Oak Essential Oil and Its Effect on Lipid Metabolism of Caenorhabditis elegans

This study investigated the lipid-lowering activity and action mechanism of oak essential oil (OEO). OEO had strong in vitro lipid-lowering activity, and its half-maximal inhibitory concentration (IC₅₀) on pancreatic lipase, cholesterol esterase and α-glucosidase were (0.62 ± 0.05), (0.20 ± 0.04) and (0.63 ± 0.01) mg/mL, respectively. Enzymatic kinetics and fluorescence emission spectroscopy showed that the inhibition type of OEO on pancreatic lipase was reversible non-competitive inhibition, and the quenching type was static quenching. The in vivo lipid-lowering activity of OEO was also assessed using Caenorhabditis elegans as a model organism. It turned out that OEO increased lipid droplets with a diameter of 0–0.6 μm and decreased lipid droplets with a diameter of 1.2–1.8 μm in high-fat C. elegans; 20 μg/mL of OEO reduced the fat content and total triglyceride level of high-fat C. elegans by 26.46% and 21.35%, respectively. The results of real-time polymerase chain reaction (PCR) showed that OEO significantly up-regulated the relative expression levels of lipid hydrolysis genes (atgl-1 and hosl-1) and fatty acid beta oxidation genes (acs-2), and significantly down-regulated the relative expression levels of fat synthesis genes (fat-5, fat-6, fat-7 and sbp-1). This study indicates that OEO has lipid-lowering activity, providing data support for its application for the alleviation of obesity.