Strong Antihyperglycemic Effects of Water-Soluble Fraction of Brazilian Propolis and Its Bioactive Constituent, 3,4,5-Tri-O-caffeoylquinic Acid

Abstract

To clarify the suppression of postprandial blood glucose rise via α-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 IC₅₀ value of 24 μM. In addition, the noncompetitive inhibition power apparently increased with the number of caffeoyl groups bound to quinic acid.