| Tartary buckwheat has been considered as a kind of nutritional foods due to its high levels of proteins,vitamins,minerals,amino acids and flavonoids.Therefore,our study aimed to evaluate the antioxidant and hypoglycemic activities of tartary buckwheat flavonoids.In order to evaluate its activities more precisely and scientificly,in vitro gastrointestinal digestion model was considered.Firstly,tartary buckwheat flavonoids were subjected to in vitro simulated gastrointestinal digestion to produce tartary buckwheat flavonoids digest(TBFD),and then the antioxidant and hypoglycemic activities of tartary buckwheat flavonoids extract(TBFE)and TBFD were compared.The antioxidant activitiy was analyzed by in vitro antioxidant assays(DPPH,ABTS and FRAP assays)and cellular ROS assay,while the hypoglycemic activity was determined based on the inhibitory activity of a-glucosidase enzyme and cellular glucose consumption..Finally,in vivo antioxidant capacity and hypoglycemic effect of tartary buckwheat flavonoids were evaluated using db/db mice model.The main results were listed as follows:(1)Selection of tartary buckwheat varieties and optimization for tartary buckwheat flavonoids extractionThe flavonoid content of Yunnan tartary buckwheat was the highest among all the tested tartary buckwheat(Yunnan,Shandong,Shanxi,Guizhou and Shaanxi tartary buckwheat).Rutin and quercetin were the major compounds in Yunnan tartary buckwheat flavonoids,and the contents were 100 mg/g and 10 mg/g,respectively.Four factors including ethanol volume fraction,solid to liquid ratio,extraction time and temperature were optimized by response surface methodology(RSM)to obtain a maximum extraction rate of Yunnan tartary buckwheat flavonoids.According to our results,the optimum extraction conditions were as follows:the ethanol volume fraction of 54%,a solid to liquid ratio of 1:24 g/mL,extraction time lasting 62 min,and at an extraction temperature of 71 ?.Under the optimum extraction conditions,the theoretical flavonoid yield was 2.21%.The actual flavonoid yield was 2.20%with the relative error of 0.45%compared with the theoretical yield.These results indicated that the model can be used to predict the extraction yield of Yunnan tartary buckwheat flavonoids.(2)Effects of in vitro simulated gastrointestinal digestion on antioxidant and hypoglycemic activities of Yunnan tartary buckwheat flavonoids.After digestion,the contents of rutin and quercitrin were slightly decreased.Antioxidant activity of TBFE and TBFD were evaluated by ABTS and DPPH assays,the IC50 values of TBFE were 0.81 mg/mL and 0.18 mg/mL,respectively,while the IC50 of TBFD were 1.30 mg/mL and 0.61 mg/mL,respectively.The iron ion reduction abilities of TBFE and TBFD were 19.37 mg VC/g and 7.00 mg VC/g.These results revealed that both TBFE and TBFD exerted potent antioxidant capacity and the in vitro antioxidant capacity was decreased after digestion.?-glucosidase plays a key role in catalyzing carbohydrates to glucose,and decrease in its activity could prevent the carbohydrates metabolism and glucose uptake,,thus inhibiting the rise of postprandial blood glucose levels.Therefore,inhibiting a-glucosidase enzyme is an effective strategy in decreasing blood glucose levels.According a-glucosidase inhibitory results,both TBFE(IC50,0.31 mg/mL)and TBFD(IC50,0.42 mg/mL)showed potential inhibitory activity of a-glucosidase compared with acarbose(IC50,0.25 mg/mL),indicating that tartary buckwheat flavonoids could be considered as a natural a-glucosidase inhibitor against diabetes.Further cell studies demonstrated that TBFE and TBFD could significantly attenuate H2O2-inudced ROS generation.The fluorescence intensities of TBFE at concentrations of 50,100 ?g/mL was decreased to 125%and 134%compared with that of H2O2-treated group(its fluorescence intensity was 202%).The fluorescence intensity of TBFD at 100 ?g/mL was decreased to 129%.In addition,we have found that both TBFE and TBFD could increase glucose consumption in HepG2 cells.Compared with control group,10 ?g/mL of TBFE and TBFD increased the glucose consumption by 45.43%and 58.36%respectively.Further studies showed that tartary buckwheat flavonoids could significantly promote the glycogen synthesis in HepG2 cells.Compared with the control group,at 10 ?g/mL concentration both TBFE and TBFD significantly increased the glycogen synthesis(173%and 190%glycogen)compared with control group.These results indicated that TBFE and TBFD have the potent abilities to promote glucose consumption and glycogen synthesis in HepG2 cells.(3)Effect of tartary buckwheat flavonoids on db/db diabetic miceThe antioxidant and hypoglycemic effects of buckwheat flavonoids were investigated using db/db diabetic mouse model.The serum glucose levels in db/m and db/db mice were 7.5 mmol/L and 21.2 mmol/L,respectively.Interestingly,administration of tartary buckwheat flavonoids significantly reduced serum glucose level in db/db mice.In the present study,db/db diabetic mice were administrated with 200 and 400 mg/kg/day,respectively.200 and 400 mg/kg/day buckwheat flavonoids mitigated the hyperglycemic symptom(18.8 mmol/L and 15.3 mmol/L,respectively)in comparison with that in vehicle administrated db/db mice.In addition to the glucose level,tartary buckwheat flavonoids were found to ameliorate glucose intolerance and insulin resistance in db/db mice.Moreover,tartary buckwheat flavonoids significantly reduced serum biochemical parameters including ALT,AST and ALP,which reflectthe liver function in db/db mice.Buckwheat flavonoids treatment significantly reduced serum triglyceride(TG),total cholestrol(TC)and LDL-c levels.Administration of buckwheat flavonoid also reduced TC and malondialdehyde(MDA)content,improved the total antioxidant capacity(TAOC)and aspartate aminotransferase activity in liver tissue.Collectively,these results suggests that tartary buckwheat flavonoids could improve hyperglycemia,dislipidimia and hypocholesterolemia,which might have implication for prevention and treatment of diabetes mellitus and metabolic disorders. |
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