Aqueous extract of Annona macroprophyllata: a potential α-glucosidase inhibitor

Abstract

Annona genus contains plants used in folk medicine for the treatment of diabetes. In the present study, an aqueous extract prepared from Annona macroprophyllata (Annonaceae, also known as A. diversifolia) leaves was evaluated on both the activity of yeast α -glucosidase (an in vitro assay) and sucrose tolerance in Wistar rats. The results have shown that the aqueous extract from A. macroprophyllata inhibits the yeast α -glucosidase with an IC₅₀ = 1.18 mg/mL, in a competitive manner with a K(i) = 0.97 mg/mL, a similar value to that of acarbose (K(i) = 0.79 mg/mL). The inhibitory activity of A. macroprophyllata was reinforced by its antihyperglycemic effect, at doses of 100, 300, and 500 mg/kg in rats. Chromatographic analysis identified the flavonoids rutin and isoquercitrin in the most polar fractions of A. macroprophyllata crude extract, suggesting that these flavonoids are part of the active constituents in the plant. Our results support the use of A. macroprophyllata in Mexican folk medicine to control postprandial glycemia in people with diabetes mellitus, involving active constituents of flavonoid nature.

Figure 1

Structure of flavonoids rutin and isoquercitrin.

Figure 2

Lineweaver-Burk plots of α-glucosidase inhibition at different concentrations of (a) acarbose and (b) extract aqueous from A. macroprophyllata. 0.0 mg/mL (■), 0.2 mg/mL (⚫), 0.4 mg/mL (▲), 0.6 mg/mL (▼), 0.8 mg/mL (◂), 1.0 mg/mL (▸), 1.2 mg/mL (◆), 1.4 mg/mL (⬢).

Figure 3

Effects of the crude extract of the leaves of A. macroprophyllata on blood glucose levels in rats on the OSTT. Vehicle (■), acarbose 5 mg/kg (◂), extract A. macroprophyllata 100 mg/kg (⚫), extract A. macroprophyllata 300 mg/kg (▲), and extract A. macroprophyllata 500 mg/kg (▼). Each value is the mean ± SEM for 4 rats in each group. *P < 0.05 is significantly different. t-test for comparison with respect to negative control values at the same time. Baseline glycemia 77 mg/dL.