To clarify a postprandial glucose suppression effect of diacylated anthocyanin with alpha-glucosidase (AGH) inhibitory activity, a single oral administration study of it in male 8-week-old Sprague-Dawley rats was performed. The diacylated anthocyanin used in this study was peonidin 3-O-[2-O-(6-O-E-feruloyl-beta-D-glucopyranosyl)-6-O-E-caffeoyl-beta-D-glucopyranoside]-5-O-beta-D-glucopyranoside isolated from storage roots of the purple sweet potato (Ipomoea batatas cv. Ayamurasaki), which showed a potent maltase inhibitory activity with an IC(50) value of 200 microM preferable to sucrase inhibition. When the diacylated anthocyanin (100 mg/kg) was administered following maltose (2 g/kg), a maximal blood glucose level (BGL) at 30 min was significantly decreased by 16.5% (P < 0.01) compared to vehicle. A minimum 10 mg/kg dose of the anthocyanin was necessary for the suppression of glycemic rise, and the ED(20) (69 mg/kg) was estimated to be approximately 30-fold lower than that of the therapeutic drug acarbose (ED(20) = 2.2 mg/kg). A reduction of serum insulin secretion was also observed corresponding to the decrease in BGL. No significant change in BGL was observed when sucrose or glucose was ingested, suggesting that the anti-hyperglycemic effect of the anthocyanin was achieved by maltase inhibition, not by sucrase or glucose transport inhibition at the intestinal membrane.

To clarify the suppression of postprandial blood glucose rise via a a-glucosidase (AGH) inhibitory action by natural compounds, propolis was examined in this study. A single oral administration of propolis extract (50% methanol fraction on XAD-2 column chromatography) in Sprague-Dawley rats demonstrated a potent antihyperglycemic effect with the significant AUC 0-120 min reduction of 38% at a dose of 20 mg/kg compared to that of controls. Among the active compounds isolated from the fraction, 3,4,5-tri-caffeoylquinic acid was found to be a prominent candidate that exerts the effect and shows a strong maltase-specific inhibition with an IC 50 value of 24 m mM. In addition, the noncompetitive inhibition power apparently increased with the number of caffeoyl groups bound to quinic acid.

The suppressive effect on the postprandial blood glucose rise through -glucosidase (AGH) inhibition was investigated in this study in order to clarify an antihyperglycemic function of 6-O-caffeoylsophorose (CS) from diacylated anthocyanin. The administration of CS (100 mg/kg) following maltose (2 g/kg) to Sprague-Dawley rats resulted in the maximal blood glucose level after 30 min being significantly decreased by 11.1% compared to the control. A reduction in the serum insulin secretion was also observed in parallel to the decrease in blood glucose level. No blood glucose change was apparent when sucrose or glucose was ingested, suggesting that the antihyperglycemic effect of CS was achieved by maltase inhibition, rather than by sucrase or glucose transport inhibition. An AGH inhibitory assay demonstrated that the non-competitive maltase inhibition of CS was partly due to acylation by phenolic acid with sugar, the presence of hydroxyl groups in the aromatic ring, and the presence of an unsaturated alkyl chain in the acylated moiety.