Effects Of Cereal Peptides On Type 1 Diabetes And The Mechanisms

Type 1 diabetes mellitus(T1D)is an autoimmune disease in which the insulin-producing pancreatic ?-cells are targeted and destroyed by infiltrating immunocytes,resulting in lifelong dependence on exogenous insulin.In recent years,rapid increases in the incidence of T1 D and its high fatality rate had become a great threat to people's health.Human diet has been proved to be an environmental factor for the initiation and progression of T1 D.Peptides derived from diet are well acknowledged for their immense potential for the functional food.Peptides are easy to be digested and absorbed,and have demonstrated anti-inflammation,antioxidant and enhancing immunity properties.T1 D is also an inflammatory disease.Anti-inflammatory peptides may be beneficial to prevent T1 D.Therefore,the effects of soybean peptide(SP),mung bean peptide(MP),corn peptide(CP),peptide purified from CP,wheat peptide(WP)and peptide isolated from WP on the onset and progression of T1 D were investigated in type 1 diabetic animals.The relationship between properties of indicated peptides and hypoglycemic effect was studied.Based on this,one hypoglycemic peptide was screened.The effects of SP,MP,CP and WP on the blood glucose in STZ-induced diabetic C57BL/6J mice were investigated.Both CP-treated and WP-treated mice exhibited markedly lower blood glucose compared with the diabetic control mice.In addition,islets of CP-and WP-treated mice were depauperate compared with untreated model mice.The hypoglycemic effect of CP and WP on T1 D was further confirmed using NOD mice as an animal model.CP significantly delayed the onset and decreased the incidence of T1 D in NOD mice,reduced the serum pro-inflammatory IL-6 level and pancreatic insulitis,and increased serum insulin concentration and area of pancreatic ? cells.While these anti-diabetic effects were not observed in the WP-treated NOD mice.To investigate whether CP counteract the pro-inflammatory effect of WP,a mixture of CP and WP were gavaged to NOD mice.The mixture of CP and WP delayed the onset and reduced the incidence of T1 D in NOD mice,significantly decreased serum IL-6 concentration,IL-6 gene expression in pancreas and pancreatic insulitis,and obviously increased the area of ? cells,IL-10 gene expression in pancreas,serum insulin content,histidine and serine levels in sera.These results suggested that the mixture of CP and WP protected against the development of T1 D.The first fraction of corn peptide(C1),the second fraction of corn peptide(C2),the first fraction of wheat peptide(W1)and the second fraction of wheat peptide(W2)were respectively isolated from CP and WP by Sephadex G-15.To investigate the hypoglycemic effect of C1,C2,W1 and W2,C1,C2,W1 and W2 were gavaged to NOD mice respectively.Compared with control NOD mice,C2 and W2 delayed the onset of T1 D in NOD mice,significantly decreased serum IL-6 level,and markedly enhanced serum insulin content.However,C1 and W1 had opposite effects.To predict the hypoglycemic role of peptide in vitro,the relationship of the hypoglycemic effects of SP,MP,CP,WP,C1,C2,W1 and W2 and their properties was declared.The physicochemical property,composition and content of amino acids of indicated peptides and their impact on the proliferation and function of ? cells in vitro and in vivo were investigated.The hypoglycemic effects of indiated peptides were line with content of arginine and leucine,and their anti-inflammatory ability in vitro.Phe-Leu(FL)and Leu-Lys(LK)were identified from both W2 and C2 using LC-MS/MS.The effects of FL and LK on proliferation and anti-inflammatory function in MIN-6 cells were investigated.Both FL and LK markedly increased the proliferation of MIN-6 cells.Then MIN-6 cells were treated by LPS or TNF-? to induce the pancreatic inflammation of ?-cells respectively,and we found both FL and LK significantly increased the cell proliferation.Moreover,LK effectively reduced the mRNA expression of IL-6 and TNF-?.However,FL had the opposite effect.These data indicated LK had anti-inflammatory effect in MIN-6 cells.To elucidate the mechanisms of hypoglycemic effect of indicated peptides,MIN-6 cells were used as an in vitro model.Following stimulation with LPS,the phosphorylation of P-38 activated,but this effect was aborted in the presence of exogenous CP.In addition,CP exposure also activated p-Akt(Ser 473)in LPS-stimulated MIN-6 cells,but p-Erk pathway activation was similar in all conditions.LK activated p-Akt(Ser 473)and inhibited p-p38 in MIN-6 cell under inflammatory conditions.LK also significantly downregulated cleaved caspase-3 and upregulated Bcl-2/Bax in LPS-stimulated MIN-6 cells.These results indicated that the hypoglycemic effects of CP may be involved in the combined action of activated p-Akt(Ser 473)and inhibited p-p38 by reducting the expression level of IL-6 under inflammatory conditions.In addition,LK may be a potential antidiabetic peptide.