Cyclocarya paliurus triterpenoids suppress hepatic gluconeogenesis via AMPK-mediated cAMP/PKA/CREB pathway

Abnormal enhancement of hepatic gluconeogenesis is a vital mechanism of the pathogenesis of Type 2 diabetes mellitus (T2DM); thus, its suppression may present an efficient therapeutic strategy for T2DM. Cyclocarya paliurus (CP), a plant species native to China, has been reported to have anti-hyperglycemia activity. Our previous studies have revealed that Cyclocarya paliurus triterpenic acids (CPT) exert the favorable glucose-lowering activity, but the regulatory effect of CPT on hepatic gluconeogenesis is still unclarified.

This study aimed to investigate the potential role and mechanism of CPT in gluconeogenesis.

In this study, the ameliorative effect and underlying mechanism of CPT on gluconeogenesis were investigated: high-fat diet and streptozotocin-induced T2DM mice and glucagon-challenged mouse primary hepatocytes.

T2DM model mice with or without oral administration of CPT for 4 weeks were monitored for body weight, glucose and lipid metabolism. Hematoxylin and eosin staining was used to observe liver lipid deposition. Real-time PCR assays were performed to examine the mRNA expression of glucose-6-phosphate (G6Pase), and phosphoenolpyruvate carboxykinase (PEPCK), two key enzymes involved in liver gluconeogenesis. Western blotting was used to determine AMP-dependent protein kinase (AMPK) expression and induction of the glucagon signaling pathway. The possible mechanism of CPT on liver gluconeogenesis was further explored in glucagon-induced mouse primary hepatocytes.

In vivo and in vitro experiments revealed that CPT treatment significantly reduced fasting blood glucose, total cholesterol and triglyceride levels, and improved insulin resistance. Furthermore, CPT could obviously decreased the mRNA and protein expression of G6Pase and PEPCK, the cyclic AMP content, the phosphorylation level of protein kinase A and cyclic AMP response element-binding protein. But CPT promoted the phosphorylation of AMP-dependent protein kinase (AMPK) and activation of phosphodiesterase 4B. Mechanistically, intervention with Compound C (an AMPK inhibitor) partially blocked the suppressive effect of CPT on hepatic gluconeogenesis.

These findings suggested that CPT may inhibit hepatic gluconeogenesis against T2DM by activating AMPK.