title: Rice protein hydrolysates stimulate GLP-1 secretion, reduce GLP-1 degradation, and lower the glycemic response in rats.
abstract: Rice has historically been consumed in Asia as a major source of carbohydrates, however, little is known regarding the functional roles of rice proteins as dietary factors. In the present study, we investigated whether peptides derived from rice proteins could stimulate GLP-1 secretion, which results in reducing glycemia via the incretin effect in normal rats. Hydrolysates were prepared from the protein fraction of rice endosperm or rice bran, and the effects of these hydrolysates on GLP-1 secretion were examined in a murine enteroendocrine cell line GLUTag. Plasma was collected after oral administration of the rice protein hydrolysates, under anesthesia, or during glucose tolerance tests in rats. In anesthetized rats, plasma dipeptidyl peptidase-IV (DPP-IV) activity was measured after ileal administration of the rice protein hydrolysates. GLP-1 secretion from GLUTag cells was potently stimulated by the rice protein hydrolysates, especially by the peptic digest of rice endosperm protein (REPH) and that of rice bran protein (RBPH). Oral administration of REPH or RBPH elevated plasma GLP-1 concentrations, which resulted in the reduction of glycemia under the intraperitoneal glucose tolerance test. In addition, the plasma DPP-IV activity was attenuated after ileal administration of REPH or RBPH, which resulted in a higher ratio of intact (active) GLP-1 to total GLP-1 in the plasma. These results demonstrate that rice proteins exert potent stimulatory effects on GLP-1 secretion, which could contribute to the reduction of postprandial glycemia. The inhibitory effect of these peptides on the plasma DPP-IV activity may potentiate the incretin effect of GLP-1.
authors.affiliation: Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Tohru
authors.initials: T
authors.lastname: Hira
authors.forename: Daisuke
authors.initials: D
authors.lastname: Inoue
authors.forename: Yukikazu
authors.initials: Y
authors.lastname: Harada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Mikio
authors.initials: M
authors.lastname: Fujii
authors.forename: Motoni
authors.initials: M
authors.lastname: Kadowaki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hara
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000097:blood; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D005951:Glucose Tolerance Test; D007082:Ileum / Q000378:metabolism; D054795:Incretins / Q000378:metabolism; D008297:Male; D051379:Mice; D012275:Oryza / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000008:administration & dosage* / Q000737:chemistry; D011492:Protein Hydrolysates / Q000008:administration & dosage* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D001786:Blood Glucose; D054795:Incretins; D010940:Plant Proteins; D011492:Protein Hydrolysates; D052216:Glucagon-Like Peptide 1; D018819:Dipeptidyl Peptidase 4