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

Abstract

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_S1-casein, f195-204), NPWDQVKR (α_S2-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.