The Structural Characterization And DPP4 Inhibition Of Oat Globulin Peptides

Dipeptidyl peptidase ? (DPP4) is a new target for the treatment of type 2 diabetes (T2D). We can regulate the postprandial glucose through controlling the activity of DPP4 to manage T2D. Recently, the bioactive peptides with DPP4 inhibition are interested in the treatment of T2D. Oat, buckwheat and highland barely are kinds of heath supporting foods, which have been considered to be benefit for the cardiovascular diseases in traditional China. Oat contains plenty of proteins, however its heath effect is not completely clear today. In this study, the DPP4 inhibition of peptides derived from oat, buckwheat and highland barely proteins were invegstigated firstly; Then, the structures of oat globulin peptides were identified, the docking modeling was then used to select DPP4 inhibitory peptides and the selected peptides were synthesized; Finally, the modulating effect of peptides on the expression of T2D targets including DPP4, GLP-1, ?-glucosidase and GLUTs were examined to determine whether the peptides could influence glucose conversion, uptake and incretin secretion in the intestinal cell system. For comparison, sitagliptin (STP), a synthesized drug that inhibits DPP4, was used as a positive control in the cell system.(1) The main protein fractions were extracted from oat (globulin and glutelin), buckwheat (albumin and glutelin), and highland barley (albumin and glutelin). Using the aforementioned simulated in vitro gastrointestinal digestion model, we found that the hydrolysates from oat, buckwheat, and highland barley flours have the DPP4 inhibitory activity. Among these three flours, the one with the highest inhibition upon DPP4 was oat flour (IC50.0.99 mg/mL); Oat globulin peptides in low molecular weight (MW< 3kDa) faction (OGb) showed IC50 at 2.04 mg/mL; Alcalase can release more potent DPP4 inhibitory peptides from proteins.(2) Thirty five peptides were identified from OGb by the liquid chromatography-mass spectroscopy (LC-ESI-MS/MS). These peptides have R' or 'K:as the C-terminal residue following tryptic digestion, and most were 7-14 amino acid residues in length. With the computationally docking,9 peptides can make tight bonding with the DPP4 active sites, and two of them were synthesized. After the DPP4 assay, the peptide LQAFEPLR (LQ8) has strong DPP4 inhibitory with IC50 at 103.5 ?M (0.1 mg/mL). While, EFLLAGNNK (EF9) was found to be a weak DPP4 inhibitor with exhibiting only up to 31% inhibition at 400?g/mL.(3) This study first confirmed the efficacy of oat peptides on DPP4 inhibition in the Caco-2 cell system. The cells were incubated with complete cell medium adding OGb. LQ8, and STP. and the results showed that DPP4 has lowest inhibition from 48 h incubation time. Further, we found that all the samples can down-regulate the expression of DPP4 and up-regulate the expression of GLP-1. However, they also can increase some other targets" expression, including a-glucosidase, GLUT2, and GLUT5 in the Caco-2 cells.This study showed that oat globulin peptide could be potentially utilized to treat T2D and manage postprandial hyperglycemia.