Effects of extracts and compounds from Cudrania tricuspidata leaves on alpha-glucosidase activity

To clarify the postprandial glucose suppression effect of the leaves of Cudrania. Tricuspidata Bureau (Moraceae; CT), the extracts of CT were evaluated for the inhibition on α-glucosidase in vitro. The results indicated that the concentrations which gave 50% inhibition (IC₅₀) of the aqueous extract and the ethanolic extract were 3.14 and 0.0345mg/mL compared to 0.419 mM of acarbose (a positive control). To identify the active compounds which are responsible for the inhibition on α-glucosidase, seventeen compounds (caffeic acid, p-coumaric acid, chlorogenic acid, cryptochlorogenic acid, protocatechuic acid, catechin, epicatechin, kaempferol, kaempferol 3-β-D-glucopyranoside, quercetin, quercitrin, isoquercitrin, rutin, resveratrol, oxyresveratrol, umbelliferone and isobavachalcone) were quantified by HPLC in CT extract, and were examined for the inhibition on α-glucosidase. The compounds in high contents were chlorogenic acid, 0.726, catechin 0.229, rutin 0.152, isobavachalcone 0.041, and caffeic acid 0.034% (w/w) in the ethanolic extract. The IC₅₀ values on α-glucosidase were kaemferol 0.0001, kaempferol 3-β-D-glucopyranoside 0.002, quercitrin 0.002, p-coumaric acid 0.004, and oxyresveratrol 0.005 mM. The result indicated that the compounds tested were responsible for the inhibitory activity of CT, although the content and the inhibitory potency was not linear. The study suggests that CT might suppress increase in postprandial glucose via the inhibitory effect on α-glucosidase. Acknowledged for KFRI and KRF (NRF-2010–0024475).