Mechanism of the Inhibitory Action of Chestnut Astringent Skin Extract on Carbohydrate Absorption

Chestnut astringent skin (CAS) extract inhibited pancreatic α-amylase and intestinal α-glucosidase in a concentration-dependent manner with the 50% inhibition concentration (IC_<50>) for amylase, maltase and sucrase being 7.5, 650 and 390μg/mL, respectively. We have investigated the effect of CAS extract on carbohydrate absorption in normal rats. Oral administration of CAS extract to rats fed cornstarch (2g/kg body weight) significantly suppressed the increase of blood glucose levels and the area under the curve (AUC). Administration of CAS extract to rats fed maltose or sucrose delayed the increase of blood glucose level and slightly suppressed AUC, but not significantly. Administration of CAS extract to rats fed glucose did not affect the increase in blood glucose level or AUC. Similar results were observed with type-2 diabetic model rats (GK/jcl). To test the effect of CAS extract on diabetes, type 2 diabetic model mice (db/db mice) were fed a standard laboratory diet containing 1 or 2% CAS extract. CAS extract prevented increases in body weight and fasting blood glucose concentration. These data suggest that CAS extract has an anti-dia-betic function in type 2 diabetic mice that mainly functions through inhibition of α-amylase.