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Abstract
BackgroundEndodesmia calophylloides and Hymenostegia afzelii belong to the Guttiferae and Caesalpiniaceae plant families with known uses in African ethno-medicine to treat malaria and several other diseases. This study aimed at identifying antiplasmodial natural products from selected crude extracts from H. afzelii and E. calophylloides and to assess their cytotoxicity.MethodsThe extracts from H. afzelii and E. calophylloides were subjected to bioassay-guided fractionation to identify antiplasmodial compounds. The hydroethanol and methanol stem bark crude extracts, fractions and isolated compounds were assessed for antiplasmodial activity against the chloroquine-sensitive 3D7 and multi-drug resistant Dd2 strains of Plasmodium falciparum using the SYBR green I fluorescence-based microdilution assay. Cytotoxicity of active extracts, fractions and compounds was determined on African green monkey normal kidney Vero and murine macrophage Raw 264.7 cell lines using the Resazurin-based viability assay.ResultsThe hydroethanolic extract of H. afzelii stem bark (HasbHE) and the methanolic extract of E. calophylloides stem bark (EcsbM) exhibited the highest potency against both Pf3D7 (EC50 values of 3.32 ± 0.15 μg/mL and 7.40 ± 0.19 μg/mL, respectively) and PfDd2 (EC50 of 3.08 ± 0.21 μg/mL and 7.48 ± 0.07 μg/mL, respectively) strains. Both extracts showed high selectivity toward Plasmodium parasites (SI > 13). The biological activity-guided fractionation led to the identification of five compounds (Compounds 1–5) from HasbHE and one compound (Compound 6) from EcsbM. Of these, Compound 1 corresponding to apigenin (EC50Pf3D7, of 19.01 ± 0.72 μM and EC50PfDd2 of 16.39 ± 0.52 μM), and Compound 6 corresponding to 3,3′-O-dimethylellagic acid (EC50Pf3D7 of 4.27 ± 0.05 μM and EC50PfDd2 of 1.36 ± 0.47 μM) displayed the highest antiplasmodial activities. Interestingly, both compounds exhibited negligible cytotoxicity against both Vero and Raw 264.7 cell lines with selectivity indices greater than 9.ConclusionsThis study led to the identification of two potent antiplasmodial natural compounds, 3,3′-O-dimethylellagic acid and apigenin that could serve as starting points for further antimalarial drug discovery.
Highlights
Endodesmia calophylloides and Hymenostegia afzelii belong to the Guttiferae and Caesalpiniaceae plant families with known uses in African ethno-medicine to treat malaria and several other diseases
This study led to the identification of two potent antiplasmodial natural compounds, 3,3′-Odimethylellagic acid and apigenin that could serve as starting points for further antimalarial drug discovery
The compounds were identified by comparing their Nuclear magnetic resonance spectroscopy (NMR) and Mass spectrometry (MS) data to those of previously reported compounds viz. apigenin (1) [23], afzelechin (2) [24], kaempferol
Summary
Endodesmia calophylloides and Hymenostegia afzelii belong to the Guttiferae and Caesalpiniaceae plant families with known uses in African ethno-medicine to treat malaria and several other diseases. Despite substantial global efforts towards its eradication, malaria remains a major public health problem, in sub-Saharan Africa. Several challenges exist in the chemotherapy of malaria, and include widespread resistance and the limited number of drug choices available to manage multidrugresistant parasite strains. To address these challenges, the antimalarial drug discovery pipeline should be continuously flushed-in with novel chemical scaffolds having promising features as starting points for new drugs development to combat malaria. One of the approaches to achieve this goal is to investigate herbal medicines and their derived secondary metabolites
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