Blood glucose-lowering activity of protocatechuic acid is mediated by inhibiting a-glucosidase

α-Glucosidase inhibitors are effective in controlling postprandial hyperglycemia,which play crucial roles in the management of type 2 diabetes.Protocatechuic acid(PCA)is one of phenolic acids existing not only in various plant foods but also as a major microbial metabolite of dietary anthocyanins in the large colon.The present study investigated the inhibitory mechanism of PCA on a-glucosidase in vitro and examined its effect on postprandial blood glucose levels in vivo.Results from in vitro experiments demonstrated that PCA was a mix-type inhibitor of a-glucosidase.Driven by hydrogen bonds and van der Waals interactions,PCA reversibly bound withα-glucosidase to form a stable a-glucosidase-PCA complex in a spontaneous manner.The computational simulation found that PCA could insert into the active cavity of a-glucosidase and establish hydrogen bonds with catalytic amino acid residues.PCA binding aroused the steric hindrance for substrates to enter active sites and caused the structural changes of interacted catalytic amino acid residues.PCA also exhibited postprandial hypoglycemic capacity in diabetic mice.This study may provide the theoretical basis for the application of PCA as an active ingredient of functional foods in dietary management of diabetes.

Suppression of postprandial blood glucose elevation by buckwheat(Fagpopyrum esculentum) albumin hydrolysate and identification of the peptide responsible to the function

The objective of this study is to evaluate the suppressive effect of buckwheat-albumin hydrolysate on postprandial hyperglycemia and identify the peptide responsible to the function. Buckwheat-albumin hydrolysate was prepared by using digestive enzymes and was orally administered to rats together with soluble starch. The blood was taken from the tail vein up to 90 min after oral administration to measure blood-glucose and plasma-insulin levels. The peptide with α-amylase inhibitory activity was purified from the buckwheathydrolysate by gel-filtration chromatography, α-amylase affinity chromatography, and high performance liquid chromatography(HPLC). The amino-acid sequence of the peptide was identified by a protein sequencer and was compared with that in the buckwheat-genome database. Buckwheat-albumin hydrolysate significantly suppressed the elevation of blood glucose level 15 min after starch administration. The amino-acid sequence of the peptide with α-amylase inhibitory activity was YVEPDCGNLGCCYHC in the parental protein of molecular mass 17.8 k Da and theoretical pI 4.77. The amino-acid sequence, molecular weight, and pI of the parental protein in buckwheat albumin were different from those of α-amylase inhibitor in wheat albumin. This study suggests that the novel α-amylase inhibitor identified in buckwheat albumin is a potential candidate for a functional food material to suppress postprandial blood glucose elevation.

Carbohydrate Intake Is Correlated with the Glycated Albumin to Glycated Hemoglobin Ratio in Drug-Naive Patients with Type 2 Diabetes

Background: The glycated albumin (GA) to HbA1c ratio (GA/HbA1c ratio) has been reported to reflect postprandial hyperglycemia. Carbohydrate is the primary dietary macronutrient that causes postprandial hyperglycemia. Thus, we investigated whether carbohydrate intake was associated with the GA/HbA1c ratio in patients with type 2 diabetes. Methods: Daily energy intake and carbohydrate intake were estimated in twenty-two patients with type 2 diabetes who received no pharmacological therapy (18 men and 4 women, age 53 ± 11 years old). The energy index and the carbohydrate index were defined as the ratio of daily energy intake to body weight and daily carbohydrate intake to body weight, respectively. Results: The energy index was significantly correlated with the GA/HbA1c ratio (r = 0.451, p = 0.035), but not with fasting plasma glucose (FPG), HbA1c and GA. The carbohydrate index was significantly correlated with GA (r = 0.461, p = 0.031) and the GA/HbA1c ratio (r = 0.554, p = 0.007), but not with FPG and HbA1c. Multivariate analysis revealed that the carbohydrate index was independently associated with the GA/HbA1c ratio (β = 0.397, p = 0.046). Conclusions: The carbohydrate index was significantly correlated with GA and the GA/HbA1c ratio in the patients with type 2 diabetes. These results suggest that carbohydrate intake may be associated with the GA/HbA1c ratio through postprandial hyperglycemia.