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Citrus flavonoids collectively dominate the α-amylase and α-glucosidase inhibitions

Abstract A series of citrus flavonoids were evaluated for α-amylase and α-glucosidase inhibitory activities in vitro. The inhibitory capacities of flavanone glycosides were greater than those of polymethoxy flavones for α-amylase. Naringin exhibited the most potent α-glucosidase inhibitory activity with IC50 0.55 μM and was about 196.83 times more active than acarbose. Poncirin led to a 43-fold improvement in α-amylase inhibition over acarbose. The double-reciprocal (Lineweaver-Burk) plot confirms a competitive inhibition mode towards α-amylase and α-glucosidase activities. The inhibition activity was significantly lowered when citrus flavonoids were pre-incubated with starch. The binding site for naringin, poncirin, hesperidin, tangeretin in α-amylase showed a polar contact numbers, respectively, of 47, 54, 51, and 44 more than that involving acarbose. The hydrogen bonds formed between nobilitin and the key residue of Lys506 of α-glucosidase, namely Asn475:N-A:Lys506:O, might provide its extra affinity when compared to tangeritin. These findings provided a strong and rational reason to establish the selected citrus flavonoids capability as a therapeutic target for postprandial hyperglycaemia modulation.