Kigelia africana fruit fractions inhibit in vitro alpha-glucosidase activity: a potential natural alpha-glucosidase inhibitor

Abstract

Background: Diabetes affects 75% of people in low-income countries, where conventional drugs like metformin are available, but newer drugs like alpha-glucosidase inhibitors are not accessible to most Southern African patients.

Aim: To evaluate the α-glucosidase and α-amylase inhibitory activities of fractionated aqueous extracts of Kigelia africana fruit (KAFE) and their phytochemical fingerprints using gas chromatography-mass spectrometry (GC-MS).

Materials and methods: We studied K. africana fruit fractions' inhibitory effects on alpha-glucosidase and alpha-amylase using bioassay-guided fractionation, and analyzed their phytochemical profiles with GC-MS.

Key findings: Both the aqueous extract and ethyl acetate fraction of the aqueous extract exhibited a low dose-dependent inhibition of alpha-amylase activity (p < 0.0001). At a concentration of 500 μg/mL, the aqueous extract caused an alpha-glucosidase inhibition of 64.10 ± 2.7%, with an estimated IC50 of 193.7 μg/mL, while the ethyl acetate fraction had an inhibition of 89.82 ± 0.8% and an estimated IC50 of 10.41 μg/mL. The subfraction G, which had the highest alpha-glucosidase inhibitory activity at 85.10 ± 0.7%, had significantly lower activity than the ethyl acetate fraction. The most bioactive fraction was found to contain 11"(2-cyclopenten-1-yl) undecanoic acid, ( +)- and cyclopentane undecanoic acid as well as the indole alkaloids Akuammilan-17-ol-10-methoxy, N-nitroso-2-methyl-oxazolidine and epoxide Oxirane2.2″ -(1.4-butanediyl) bis-.

Conclusion: The K. africana fruit fraction demonstrated significant alpha-glucosidase inhibitory activity, while its alpha-amylase inhibitory activity was limited. This study suggests a potential natural alpha-glucosidase inhibitor and phytocompounds that could serve as leads for developing antidiabetic agents.

Keywords: Kigelia africana fruit fractions; Alpha-amylase inhibition; Alpha-glucosidase inhibition; Diabetes; Gas Chromatography- mass spectrometry; Phytochemistry.

Fig. 1

Percentage (%) inhibition of alpha-amylase by Aqueous extract and Ethyl acetate fraction. Data points determined via ANOVA represent the mean ± SD of quadruplicates. ** (p < 0.0001) compared to Acarbose 500µM

Fig. 2

Percentage (%) inhibition of alpha-glucosidase by Kigelia aqueous crude extract and Ethyl acetate fraction (*) shows a significantly higher % inhibition of ethyl acetate fractions compared to Kigelia aqueous crude extracts at the same concentrations (p < 0.0001)

Fig. 3

% inhibition of alpha-glucosidase enzyme by Kigelia subfractions *(p < 0.0001) statistically significant difference of % inhibition among fractions

Fig. 4

GC–MS chromatogram of subfraction F. The numbers indicated in the spectrogram correspond with the peaks of compounds indicated in Table 1 below

Fig. 5

GC–MS chromatogram for sub-fraction G. The numbers indicated in the spectrogram correspond with the peaks of compounds indicated in Table 2 below

Fig. 6

GC–MS chromatogram for sub-fraction H. The numbers indicated in the spectrogram correspond with the peaks of compounds indicated in Table 3 below

Fig. 7

GC–MS chromatogram for sub-fraction J. The numbers indicated in the spectrogram correspond with the peaks of compounds indicated in Table 4 below