Inhibition of α-glucosidase by flavonoids of Cymbopogon citratus (DC) Stapf

Ethnopharmacological relevance: Leaves extracts from Cymbopogon citratus (DC) Stapf. are widely used in traditional medicine exhibiting several in vivo biological activities, including antidiabetic. Several flavonoids, including aglycones and glycosides, were reported in this plant and previous studies suggested that flavonoids may interact with targets related to diabetes. Aim of the study: Evaluated the hypoglycemic activity of C. citratus flavonoids through alpha-glucosidase inhibition and assess the structure-activity relationship using molecular docking studies. Material and methods: An infusion of C. citratus leaves and its flavonoid-rich fraction were prepared. Five flavonoids from this fraction were isolated and structurally characterized by UV spectral analysis with shift reagents, HPLC-PDA-ESI/MSn and H-1 NMR. The antidiabetic potential of C. citratus infusion, its flavonoid-rich fraction, glycosylated flavonoids and aglycones was evaluated trough the in vitro inhibition of yeast alpha-glucosi-dase. Posteriorly, molecular docking of the tested flavonoids was performed to investigate its possible interactions with the alpha-glucosidase pocket. Results: The infusion of C. citratus, its flavonoid-rich fraction, luteolin and five flavone glycosides namely, luteolin 6-C-beta-glucopyranoside (isoorientin), luteolin 7-O-neohesperidoside (ionicerin), luteolin 7-O-beta-glucopyranoside (cynaroside), Luteolin 2 ''-O-rhamnosyl-C-(6-deoxy-ribo-hexos-3-ulosyl) (cassiaoccidentalin B), luteolin 6-C-alpha-arabinofuranosil-(1 -> 2)-alpha-L-rhamnopyranoside (kurilesin A) showed higher inhibitory activity than the reference drug. This activity increased by the addition of a sugar moiety. However, the di-glycosides were less active than mono-glycosides. The docking studies showed interactions of sugar moieties and A or B rings with the catalytic pocket mainly through hydrogen bonds. Conclusions: Our results corroborate the potential of C. citratus as a medicinal plant for the treatment of diabetes and revealed that its flavonoid glycosides has hypoglycemic effect and can be explored as drug candidates to act as alpha-glucosidase inhibitors in the treatment of diabetes.