Abstract: Objective: To evaluate the improvement of blood glucose levels in type 2 diabetic rats using buckwheat hull extracts (BHEs) rich in flavonoids and to explore its possible mechanisms. Methods: The inhibitory effect of BHEs on α-glucosidase and α-amylase activities was evaluated in vitro, and the type of enzyme inhibition was determined by Lineweaver-Burk (L-B) analysis. Type 2 diabetic rat models were established with a high-fat diet and intraperitoneal injection of streptozotocin (STZ), and then the rats were randomly divided into control (without induction of diabetes mellitus, given distilled water), model group (given distilled water), positive control group (gavaged with metformin hydrochloride at 100 mg/(kg·d)), and low-, medium- and high-dose BHEs groups (50, 100 and 200 mg/(kg·d), respectively). The administration by gavage once a day last for 28 days. The body weight, fasting blood glucose (FBG), fasting serum insulin (FINS), fasting C-peptide and oral glucose tolerance test (OGTT) were determined during this period. Results: The inhibitory activity of BHEs on α-glucosidase-maltose system was dose dependent with a percentage inhibition of 41.12% at a concentration of 1 mg/mL. The data of enzyme kinetics showed the inhibition was competitive. In the model group, body weight was reduced by 33.1%, FBG was increased up to (17.85 ± 2.25) mmol/L as well as the levels of FINS and C peptide were reduced to 24.80% and 12.77%, respectively (P < 0.05), when compared with the normal control group. Compared with the model group, the BHEs groups showed a significant improvement in body weight loss after 28 days of invention, FBG levels in the medium- and high-dose groups were decreased by 39.4% and 48.2%, respectively, and the area under the curve (AUC) of OGTT was declined by 47.36% and 59.47%, respectively (P < 0.05). Compared with the model group, the middle- and high-dose groups improved the levels of FINS by 32.79% and 34.44% and C-peptide by 7.40% and 13.08%, respectively (P < 0.05). Conclusion: BHEs can improve blood glucose level in a dose-dependent manner in type 2 diabetes induced by STZ as α-glucosidase inhibitors, and simultaneously can repair islet β-cell function.

Key words: buckwheat hull extracts, α-glucosidase, diabetes mellitus type 2, blood glucose, insulin, C-peptide