Oral Administration of Corn Zein Hydrolysate Stimulates GLP-1 and GIP Secretion and Improves Glucose Tolerance in Male Normal Rats and Goto-Kakizaki Rats

Abstract

We have previously demonstrated that ileal administration of the dietary protein hydrolysate prepared from corn zein (ZeinH) stimulated glucagon-like peptide-1 (GLP-1) secretion and attenuated hyperglycemia in rats. In this study, to examine whether oral administration of ZeinH improves glucose tolerance by stimulating GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) secretion, glucose tolerance tests were performed in normal Sprague-Dawley male rats and diabetic Goto-Kakizaki (GK) male rats. The test solution was gavaged before ip glucose injection in normal rats or gavaged together with glucose in GK rats. Blood samples were collected from the tail vein or by using the jugular catheter to measure glucose, insulin, GLP-1, and GIP levels. In the ip glucose tolerance test, oral administration of ZeinH (2 g/kg) significantly suppressed the glycemic response accompanied by an immediate increase in plasma GLP-1 and GIP levels in normal rats. In contrast, oral administration of another dietary peptide, meat hydrolysate, did not elicit a similar effect. The glucose-lowering effect of ZeinH was attenuated by a GLP-1 receptor antagonist or by a GIP receptor antagonist. Furthermore, oral ZeinH induced GLP-1 secretion and reduced glycemic response in GK rats under the oral glucose tolerance test. These results indicate that the oral administration of the dietary peptide ZeinH improves glucose tolerance in normal and diabetic rats by its incretin-releasing activity, namely, the incretinotropic effect.

Defining Conditions for Optimal Inhibition of Food Intake in Rats by a Grape-Seed Derived Proanthocyanidin Extract

“…with saline or Ex9 30 min before light offset and thereafter with intragastric water, gallic acid or GSPE 15 min before light offset. Chow intake was subsequently measured after it was reintroduced [29,30,31]. The Ex9 dose was studied previously to rule out any effect on food intake and to confirm its antagonistic effect on i.p.…”

Possible abilities of dietary factors to prevent and treat diabetes via the stimulation of glucagon‐like peptide‐1 secretion

“…Pioneering research on protein hydrolysates are being performed by the research group of Hira and Hara at Hokkaido University, which reported the GLP‐1 secretion‐enhancing effect and hyperglycemia‐suppressing effect of the hydrolysate of zein, a maize‐derived protein . Furthermore, GLP‐1 secretion‐promoting effects via mitogen‐activated protein kinase by meat protein hydrolysates have been reported.…”

“…Another research group also reported the GLP-1 secretion-enhancing effects of casein and proteins from codfish, egg, and wheat, as well as the stimulation of GLP-1 secretion by egg protein hydrolysate [18]. Pioneering research on protein hydrolysates are being performed by the research group of Hira and Hara at Hokkaido University, which reported the GLP-1 secretion-enhancing effect and hyperglycemia-suppressing effect of the hydrolysate of zein, a maize-derived protein [19][20][21]. Furthermore, GLP-1 secretion-promoting effects via mitogen-activated protein kinase by meat protein hydrolysates [22] have been reported.…”

Antioxidant and hypoglycaemic effects of tilapia skin collagen peptide in mice

“…Silk fibroin hydrolysate exhibited antidiabetic effects in a non-insulindependent diabetes mellitus mouse model (Do et al, 2012). Oral administration of corn zein hydrolysate was proved to improve glucose tolerance in normal and diabetic rats (Higuchi et al, 2013). Peptides from the macroalga Palmaria palmata were purified and exhibited dipeptidyl peptidase IV inhibitory effects, suggesting their potential as functional food ingredients in the prevention and management of type 2 diabetes (Harnedy et al, 2015).…”