Evaluation of flavonoids from Bauhinia megalandra leaves as inhibitors of glucose-6-phosphatase system

From the methanol extract of Bauhinia megalandra fresh leaves, eight flavonoids were isolated and evaluated by rat liver microsomal glucose-6-phosphatase (G-6-Pase) bioassay, which might be a useful methodology for screening antihyperglycaemic substances. All the flavonoids assayed showed an inhibitory effect on the intact microsomal G-6-Pase: quercetin and kaempferol exhibited the lowest effect; astilbin, quercetin 3-O-α-rhamnoside, kaempferol 3-O-α-rhamnoside and quercetin 3-O-α-arabinoside an intermediate effect. The highest inhibitory activity was shown by quercetin 3-O-α-(2″-galloyl)rhamnoside and kaempferol 3-O-α-(2″galloyl)rhamnoside. None of the flavonoids mentioned above showed an inhibitory effect on the disrupted microsomal G-6-Pase. Quercetin 3-O-α-(2″-galloyl)rhamnoside and kaempferol 3-O-α-(2″-galloyl)rhamnoside exhibited the lowest IC50 of all the flavonoids assayed. Also, the phlorizin IC50 is reported. Copyright © 2005 John Wiley & Sons, Ltd.