Investigation of antihyperglycaemic activity of banana (Musa sp. Var. Nanjangud rasa bale) flower in normal and diabetic rats

Background: The vital enzymes of starch digestion and absorption are intestinal α-glucosidases and their inhibition improves postprandial hyperglycaemia, constituting an effective mode of therapy in diabetes. Objectives: The present study was designed to assess the inhibitory potential of ethanol extract of banana flower (EF) on mammalian α-glucosidases and its pharmacological effects on postprandial hyperglycaemia in normal and alloxan-induced diabetic rats. Materials and Methods: EF was evaluated for its inhibitory potential and mode of inhibition on mammalian α-glucosidases. Further, the role of EF and its constituents Umbelliferone (C1) and Lupeol (C2) on glucose uptake using isolated rat hemi-diaphragm and insulinotropic activity using RINm5F (rat insulinoma) cell lines were determined. The phytocomponents in EF were also evaluated using GC-MS. Results: EF illustrated a dose-dependent inhibition for rat intestinal sucrase, maltase and p-nitrophenyl-α-D-glucopyranoside (pNPG) hydrolysis (IC₅₀ values: 18.76±0.22, 25.54±0.10 and 76.42±1.12 μg/ml, respectively) and the mode of inhibition was non-competitive with low Ki values. Oral administration (100-200 mg/kg b.wt.) of EF significantly improved the maltose/glucose-induced postprandial hyperglycaemia in normal and alloxan-induced diabetic rats. EF, C1 and C2 exhibited stimulation of glucose uptake and a dose-dependent glucose-induced insulin secretion at both 4.5 and 16.7 mM glucose concentrations. Further, GC-MS analysis revealed significant levels of steroids (25.61%), diazoprogesterone (21.31%), sesquiterpene (11.78%) and other phytocomponents. Conclusion: EF inhibited α-glucosidases besides promoting glucose uptake and insulin secretion, resulting in antihyperglycaemic effect determining EF as a potent anti-diabetic agent.