RESUMO
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-alpha-rhamnoside, kaempferol 3-O-alpha-rhamnoside and quercetin 3-O-alpha-arabinoside an intermediate effect. The highest inhibitory activity was shown by quercetin 3-O-alpha-(2''-galloyl)rhamnoside and kaempferol 3-O-alpha-(2''galloyl)rhamnoside. None of the flavonoids mentioned above showed an inhibitory effect on the disrupted microsomal G-6-Pase. Quercetin 3-O-alpha-(2''-galloyl)rhamnoside and kaempferol 3-O-alpha-(2''-galloyl)rhamnoside exhibited the lowest IC50 of all the flavonoids assayed. Also, the phlorizin IC50 is reported.
Assuntos
Bauhinia , Inibidores Enzimáticos/farmacologia , Glucose-6-Fosfatase/antagonistas & inibidores , Hipoglicemiantes/farmacologia , Fitoterapia , Extratos Vegetais/farmacologia , Animais , Diabetes Mellitus/prevenção & controle , Inibidores Enzimáticos/administração & dosagem , Inibidores Enzimáticos/química , Inibidores Enzimáticos/uso terapêutico , Flavonoides/administração & dosagem , Flavonoides/farmacologia , Flavonoides/uso terapêutico , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/química , Hipoglicemiantes/uso terapêutico , Concentração Inibidora 50 , Microssomos Hepáticos/efeitos dos fármacos , Microssomos Hepáticos/enzimologia , Extratos Vegetais/administração & dosagem , Extratos Vegetais/química , Extratos Vegetais/uso terapêutico , Folhas de Planta , RatosRESUMO
In intact microsomes, quercetin 3-O-alpha-(2''-galloyl)rhamnoside (QGR) inhibits glucose-6-phosphatase (G-6-Pase) in a concentration-dependent manner. QGR increased the G-6-Pase K(m) for glucose-6-phosphate without change in the V(max). The flavonol did not change the kinetic parameters of disrupted microsomal G-6-Pase or intact or disrupted microsomal G-6-Pase pyrophosphatase (PPase) activity. This result allowed the conclusion that QGR competitively inhibits the glucose-6-phosphate (G-6-P) transporter (T1) without affecting the catalytic subunit or the phosphate/pyrophosphate transporter (T2) of the G-6-Pase system.QGR strongly inhibits the neoglucogenic capacity of rat liver slices incubated in a Krebs-Ringer bicarbonate buffer, supplemented with lactate and oleate saturated albumin. The QGR G-6-Pase inhibition might explain the decrease in the liver slice neoglucogenic capacity and, in turn, could reduce glucose levels in diabetic patients.