Identification of novel peptides from goat milk casein that ameliorate high-glucose-induced insulin resistance in HepG2 cells.

In this study, we investigated the effect of goat milk casein hydrolysates on glucose consumption rate, intracellular glycogen concentration, and mRNA expression of gluconeogenesis-related genes, including phosphoenolpyruvate carboxykinase 1 (PCK1) and glucose-6-phosphatase catalytic subunit (G6PC), in insulin-resistant HepG2 cells. From the obtained hydrolysates, we also purified and characterized novel peptides that ameliorated high-glucose-induced insulin resistance in HepG2 cells. The 3-h hydrolysate caused the highest glucose consumption rate in insulin-resistant HepG2 cells. It also showed positive effects on promoting intracellular glycogenesis and reducing mRNA expression of PCK1 and G6PC. We separated the obtained hydrolysates into 3 fractions (F1, F2, and F3) by gel filtration chromatography; we further purified F1 using reversed-phase HPLC and identified peptides using liquid chromatography-tandem mass spectrometry. The bioactive peptides identified were SDIPNPIGSE (α-casein, f195-204), NPWDQVKR (α-casein, f123-130), SLSSSEESITH (β-casein, f30-40), and QEPVLGPVRGPFP (β-casein, f207-219). Our findings indicated that specific bioactive peptides from goat milk casein hydrolysates ameliorated insulin resistance in HepG2 cells that had been treated with high glucose. This is a first step toward determining whether goat milk casein hydrolysates can be used as food ingredients to ameliorate insulin resistance.