Inhibitory effect of banana (Musa sp. var. Nanjangud rasa bale) flower extract and its constituents Umbelliferone and Lupeol on α-glucosidase, aldose reductase and glycation at multiple stages

• Ethanol extract of banana flower (EF) inhibited α-glucosidase enzyme suggesting the presence of potential enzyme inhibiting compounds in the extract.
• Umbelliferone and Lupeol were isolated from EF for the first time and recognised to be novel scaffold for the design of non-competitive α- glucosidase inhibitors.
• EF and its constituents also exhibited beneficial effects against parameters associated with secondary complications of diabetes through inhibition of aldose reductase and glycation at multiple stages.

Postprandial hyperglycaemia is characterized as the earliest symptom of diabetes and its management attenuates several of the associated secondary complications. In this context, we investigated the role of ethanol extract of banana flower (EF) for its antihyperglycaemic effects. The EF showed a strong inhibition towards α-glucosidase and pancreatic amylase which play a vital role in clinical management of postprandial hyperglycaemia. The major active compounds present in EF were identified as Umbelliferone (C1) and Lupeol (C2) using various spectroscopic methods. C1 (IC50: 7.08 ± 0.17 μg/ml) and C2 (IC50: 7.18 ± 0.14 μg/ml) were found to inhibit α-glucosidase in a non-competitive mode of inhibition, with low Ki values. Further, in vitro glycation assays showed that EF and its compounds prevented each stage of protein glycation and formation of its intermediary compounds. EF, C1 and C2 also exhibited a potent inhibition on aldose reductase with IC50 values of 2.25 ± 0.29, 1.32 ± 0.22 & 1.53 ± 0.29 μg/ml respectively. Our results suggest that, the observed potential of EF in antihyperglycaemic activity via inhibition of α-glucosidase and in antidiabetogenic effect by inhibition of polyol pathway and protein glycation is more likely to be attributed to the presence of C1 and C2.