Ginsenoside Rg1 ameliorates palmitic acid-induced insulin resistance in HepG2 cells in association with modulating Akt and JNK activity.

Abstract

Hepatic insulin resistance can be induced by excess dietary intake of saturated fat. Ginsenoside Rg1 (GRg1), the major active ginsenoside enriched in tonic food ginseng, was reported to help alleviate liver diseases. In the present study, GRg1 was evaluated for its impact on palmitic acid (PA)-induced hepatic insulin resistance model in vitro. Insulin resistance in HepG2 cells was induced by 0.5 mM PA exposure for 24 h and then the effect of GRg1 on cellular glucose consumption was measured. Expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphate (G6Pase) were analyzed by Western blot and quantitative real-time polymerase chain reaction. Activation of protein kinases and transcript factor was analyzed by measuring protein phosphorylation. The influence of GRg1 on reactive oxygen species (ROS) production in HepG2 was also examined. GRg1 reversed PA-induced decrease in glucose consumption of HepG2 cells by downregulating gluconeogenesis genes G6pase and PEPCK. GRg1 increased Akt activation but inhibited JNK activation in PA-challenged HepG2 cells. Cellular ROS level was elevated in insulin-resistant HepG2 cells but was reduced by GRg1. Together these findings indicate that GRg1 protects against hepatic insulin resistance via preserving insulin signaling sensitivity and is a promising alternative medicine.