Investigation of the Efficacy and Chemical Composition of Selected Traditional Medicines Used to Treat Onchocerciasis and Schistosomiasis in Ghana

Abstract

In this study, two traditional medicines used to treat schistosomiasis (NTD-B4) and onchocerciasis (NTD-O4) in Ghana, were investigated to substantiate their claimed efficacy and to isolate the bioactive ingredients through bioassay-guided fractionation. Crude extracts of these remedies were prepared by successive extraction with DCM and methanol via cold percolation. Biological activities of the resulting crude extracts were evaluated in in vitro anti-schistosomal and anti-onchocercal assays against Schistosoma mansoni and Onchocerca ochengi, respectively. Further, the samples were screened for antitrypanosomal activity against Trypanosoma brucei brucei. NTD-B4-DCM exhibited 100% and 78.4 ± 2.8% inhibition effect against the schistosomula and adult worms of S. mansoni, respectively. The recorded IC50 value was 30.5 μg/mL. NTD-O4-DCM was not active against its target disease, onchocerciasis. It showed a percentage inhibition of 25%, 100 ± 0%, and 28.8 ± 0.0% against the microfilaria, adult male, and adult female worms of O. ochengi, respectively. Both extracts, however, showed promising activity against T. brucei brucei (IC50=5.63 ± 0.8 μg/mL for NTD-B4-DCM, and 8.69 ± 1.55 μg/mL for NTD-O4-DCM). Following the promising outcome of the antitrypanosomal assay, the crude extracts were selected for bioassay-guided fractionation. Fractionation of NTD-B4-DCM and subsequent isolation of bioactive compounds led to the identification of an eupatoriochromene-rich oil (42.6%) via GC-MS, which was 1.3-fold (IC50 <0.0977 μg/mL) more active than the standard antitrypanosomal drug, diminazene aceturate (IC50 = 0.13 μg/mL). Fractionation and isolation of bioactive compounds from NTD-O4-DCM also led to the identification of oil Dr/F-1/E-1/ML, with favorable activity (IC50= 1.51 ± 0.65 μg/mL), which precipitated a white flaky solid which was proposed to be hexyl 9-oxo-decanoate via the acquired 1D and 2D-NMR data.