Mechanisms Of Action Of Highland Barley Whole Grain On Hypoglycemic Activity

As one of the three major serious diseases in the world,the epidemic of diabetes mellitus(DM)is particularly severe.The intake of fruits,vegetables and whole grains in the diet is negatively correlated to the risk of chronic degenerative diseases such as DM,obesity and cardiovascular diseases,which may be ascribed to the additive and synergistic combinations of various phytochemicals especially phenolics,flavonoids and dietary fiber in plant foods.It has many advantages such as less toxic and adverse effects,high safety and low cost.Recently,the utilization of whole grains with low side reactions as an alternative method for the prophylaxis and treatment of DM has aroused great concern.Highland barley(Hordeum vulgare L.)is rich in phytochemicals especially phenolics,which exhibits a variety of biological activities.However,there are few reports on the systematical regulation mechanism of highland barley whole grain(BWG)on the disorders of glucose and lipid metabolism.Therefore,in the present study,the phenolic profiles and antioxidant activity of highland barley extract were analyzed at first,and then the hypoglycemic activity of BWG in vitro and the mechanisms of regulating the disorders of glucose and lipid metabolism in vivo were investigated via insulin resistance cell model IR-Hep G2 as well as db/db mouse model with the characteristics of diabetes and hyperlipidemia.The mechanisms of BWG on hypoglycemic and hypolipidemic activities were systematically explored through elucidating inflammation,oxidative stress,intestinal microbiota,glucose and lipid metabolism pathways and insulin signaling pathway.The main results obtained were as follows:(1)Phenolic profiles and antioxidant activity of highland barley extract: Highland barley extract was rich in phenolics and flavonoids,which partitioned in both free and bound forms.Results from high performance liquid chromatography-photodiode array detector(HPLC-PAD)showed that ferulic acid,naringin,catechin and quercetin were the dominant phenolics in highland barley,and the content of ferulic acid was more than 6 times of that of other phenolic compounds.Moreover,highland barley extract possessed strong antioxidant ability evaluated by oxygen radical absorbance capacity(ORAC),peroxyl radical scavenging capacity(PSC)and cellular antioxidant activity(CAA)assays,which might be attributed to the combination of free phenolics and bound phenolics.In addition,the types and contents of phenolics and their corresponding antioxidant activities were significantly different among different highland barley varieties.Correlation analysis showed that there was a positive correlation between antioxidant activity,phenolic content and phenolic profiles of highland barley extract.(2)In vitro hypoglycemic activity of highland barley extract: At the chemical level,highland barley extract inhibited the enzyme activities of α-amylase and α-glucosidase in a dose-dependent manner,further prohibited the conversion of starch and other polysaccharides into glucose to enter the blood circulation,and thus exhibited hypoglycemic capacity.Additionally,the inhibitory effects of highland barley bound phenolics among different varieties on the two enzymes were stronger than the corresponding free phenolics.At the cellular level,highland barley extract could prohibit gluconeogenesis and promote glycogen synthesis via modulating IRS-1/PI3K/Akt signaling pathway and GLUT4 translocation,thus down-regulating the gene expression and enzyme activities of G6 Pase and PEPCK,while up-regulating those of GSK3β,and ultimately,exerting hypoglycemic activity by regulation of glucose homeostasis in IR-Hep G2 cells.Furthermore,the synergistic combination of ferulic acid,naringin and catechin in highland barley extract could improve the utilization of peripheral glucose via further promoting glycogen synthesis of IR-Hep G2 cells,thus ameliorating insulin resistance,possessing hypoglycemic effect,as well as reducing the consumption of single drugs.(3)The regulatory mechanism of BWG on glucose metabolism in db/db mice was investigated via evaluating some indexes including inflammatory cytokines and the expression of glucose metabolism-related genes and proteins: BWG intervention for 8weeks reduced the levels of inflammatory factors in db/db mice,further inhibited the phosphorylation of serine in IRS-1 and activated IRS-1/PI3K/Akt insulin signaling pathway,thus decreased insulin resistance.Moreover,BWG could significantly increase the expression of mi RNA-26 a and mi RNA-451 in the insulin pathway,while down-regulate the expression of mi RNA-126 a and mi RNA-29 a,and then regulate m RNA expression at the posttranscriptional level.Furthermore,BWG exhibited hypoglycemic effect through up-regulating the expression of PI3 K protein,phosphorylation of Akt and GSK3β protein,and m RNA expression of IRS-1,PI3 K,Akt,GSK3β and FOXO1,further modulating the activities of G6 Pase,PEPCK,HK and GS,thus inhibiting hepatic gluconeogenesis,improving glycogen synthesis,as well as alleviating insulin resistance and glucose intolerance.(4)The regulatory mechanism of BWG on lipid metabolism in db/db mice was explored via assessing some indexes including cecal microbiota and the expression of lipid metabolism-related genes and proteins: BWG could alleviate oxidative stress and liver injury in db/db mice,and recover the dysbiosis of cecal microbiota by increment of Firmicutes/Bacteroidetes ratio and Alistipes abundance as well as diminution of Bacteroides and Desulfovibrionaceae abundances to regulate lipid metabolism-related genes.In addition,BWG down-regulated the expression levels of mi RNA-122,mi RNA-33,mi RNA-34 a and mi RNA-206 involved in fatty acid synthesis,further regulation of m RNA expression at the posttranscriptional level.Moreover,BWG could inhibit the m RNA and protein expression of SREBP-1c,FAS,and SCD1 in the liver of db/db mice,while up-regulate the m RNA expression of AMPKα and the ratio of pAMPKα/AMPKα,thus triggering the inhibition of fatty acid synthesis.In conclusion,BWG can maintain the dynamic homeostasis of glucose and lipid metabolism by regulating inflammation,oxidative stress,cecal microbiota,IRS-1/PI3K/Akt insulin pathway,AMPK/SREBP-1c/FAS fatty acid synthesis pathway and related mi RNAs,thus alleviating the symptoms of hyperglycemia and hyperlipidemia in db/db mice.