Casein glycomacropeptide‐derived peptide IPPKKNQDKTE ameliorates high glucose‐induced insulin resistance in HepG2 cells via activation of AMPK signaling

Scope Recently , casein glycomacropeptide (GMP)‐derived peptide was found to possess potent antioxidant and anti‐inflammatory activities. In this study, the improvement effects and underlying molecular mechanisms of GMP‐derived peptide on hepatic insulin resistance were investigated. Methods and results The peptide IPPKKNQDKTE was identified from GMP papain hydrolysates by LC‐ESI‐MS/MS. Effects of IPPKKNQDKTE on glucose metabolism and expression levels of the hepatic insulin signaling proteins in high glucose‐induced insulin‐resistant HepG2 cells were evaluated. Results showed that IPPKKNQDKTE dose‐dependently increased glucose uptake and intracellular glycogen in insulin‐resistant HepG2 cells without affecting cell viability. IPPKKNQDKTE increased the phosphorylation of Akt and GSK3β and decreased the expression levels of p‐GS, G6Pase and PEPCK. These IPPKKNQDKTE‐mediated protection effects were reversed by PI3K/Akt inhibitor LY294002, showing the mediatory role of PI3K/Akt. Moreover, treatment with IPPKKNQDKTE reduced IRS‐1 Ser307 phosphorylation and increased phosphorylation of AMPK. Knockdown AMPK using siRNA in HepG2 cells increased Ser307 phosphorylation of IRS‐1 and reduced Akt phosphorylation in IPPKKNQDKTE‐treated insulin‐resistant cells. Conclusion IPPKKNQDKTE prevents high glucose‐induced insulin resistance in HepG2 cells by modulating the IRS‐1/PI3K/Akt signaling pathway through AMPK activation, indicating that IPPKKNQDKTE plays a potential role in the prevention and treatment of hepatic insulin resistance and type 2 diabetes.