Silk sericin has significantly hypoglycaemic effect in type 2 diabetic mice via anti-oxidation and anti-inflammation

The sericin protein from silk-processing waste added to the normal diet at 0.8% (g%) level was administered orally to type 2 diabetic (T2D) mice to investigate its hypoglycaemic effects and mechanism. The oral protein is in the form of silk sericin hydrolysate, obtained from a boiling treatment of 0.025% calcium hydroxide solution. The protein significantly decreased fasting blood glucose, fasting plasma insulin, and glycosylated serum protein levels; improved oral glucose tolerance and insulin tolerance, and enhanced antioxidative activities. The protein could ameliorate the pathological damage in pancreatic β-cells and the liver tissue. It enhanced the expression of key proteins and enzymes, including insulin receptor, insulin receptor substrate, PI3K, phosphorylated-AKT, hepatic kinase, GLUT4, glycogen synthase, GSK3β, GLK, PFK1, PKM2, and AMPKα, which are related to insulin metabolism and glycolysis. The protein also reduced the expression of G6Pase, PCK, and ACC, which are related to gluconeogenesis and lipid metabolism in the liver, and decreased the expression of TNF-α, IL-6, P65, and IKKβ related to inflammation. In general, sericin could maintain normal glucose levels and regulate insulin secretion, insulin and lipid metabolism, and inhibition of inflammation. Therefore, sericin protein could be developed into a novel functional health food with significantly hypoglycaemic effect.