Cyclocarya paliurus extract attenuates hepatic lipid deposition in HepG2 cells by the lipophagy pathway

Abstract

Context: Cyclocarya paliurus (CP) (Batal.) Iljinsk (Cyclocaryaceae), a plant native to China, is the sole species in the genus Cyclocarya. Its leaves have been widely used as a remedy for hyperlipidaemia in traditional folk medicine. However, the mechanism underlying CP-induced lipolysis, especially in the liver, has not been entirely elucidated. Objective: This study investigates the effect of CP ethanol extract (CPE) on hepatic steatosis and the underlying molecular mechanisms involved. Materials and methods: The effect of CPE at concentrations of 0, 6.25, 12.5, 25, 50, and 100 μg/mL on the viability of HepG2 cells was examined using the cell counting kit-8 (CCK-8) assay after incubation for 24 h. CPE-induced changes in intracellular lipid content were assessed by measuring the absorbance of oil red O staining at 520 nm, and the possible underlying mechanisms were further studied using quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis, western blotting, immunofluorescence studies and transmission electron microscopy. Results: The half-maximal inhibitory concentration (IC50) of CPE in HepG2 cells was 97.27 μg/mL. Treatment with 50 μg/mL CPE increased lipid clearance, which was associated with increased autophagy in HepG2 cells. CPE-induced autophagy involved downregulation of phosphorylation level of mammalian target of rapamycin (0.87 ± 0.08 vs. 1.31 ± 0.10). Fluorescent double staining and electron microscopy images showed lipid deposits within autolysosomes, thereby confirming the abovementioned findings. Discussion and conclusions: CPE can induce hepatic fat clearance through the autophagy-lysosome pathway known as lipophagy. CPE has potential as a functional food.