Evaluating Antiplasmodial and Antimalarial Activities of Soybean (Glycine max) Seed Extracts on P. falciparum Parasite Cultures and P. berghei-Infected Mice

Background. Plasmodium parasite resistance to artemisinin-based combination therapies (ACTs) calls for development of new, affordable, safe, and effective antimalarial drugs. Studies conducted previously on soybean extracts have established that they possess antimicrobial, anti-inflammatory, anticancerous, and antioxidant properties. The activity of such extracts on Plasmodium parasites has not been potentially exploited. Objectives. The aim of this study was to determine the antiplasmodial activity of soybean extracts using Plasmodium falciparum cultures, followed by an in vivo evaluation of safety and antimalarial activity of the extracts in Plasmodium berghei ANKA strain-infected mice. Method. Aqueous, methanol, and peptide extracts of soybean seeds were prepared. An in vitro evaluation of the extracts for antiplasmodial activity was carried out using two P. falciparum strains: D6, a chloroquine-sensitive Sierra Leone 1 strain and W2, a chloroquine-resistant Indochina 1 strain. Following the in vitro assessment, two active extracts (peptide and methanol) were selected for in vivo assay with mice infected with P. berghei ANKA strain. The two extracts were tested for their therapeutic potential (curative test). The peptide extract was further assessed to determine whether it could prevent the establishment of a P. berghei infection (prophylactic test). For the curative tests, methanol and peptide extracts were separately administered orally to three groups of five P. berghei-infected Swiss albino mice for four days, at three dosage levels: 800, 400, and 200 mg/kg/day. In the prophylactic test, the similar dosage regimen was applied at baseline to 3 groups of uninfected mice using the peptide extract which was administered orally for 4 days. Results. Peptide and methanol extracts showed good activity with IC50 of 19.97 ± 2.57 μg/ml and 10.14 ± 9.04 μg/ml, respectively, against the D6 strain. The IC50 values for the peptide and methanol extracts were 28.61 ± 1.32 μg/ml and 14.87 ± 3.43 μg/ml, respectively, against the W2 strain. Methanol and peptide extracts exhibited high parasite-suppressive (therapeutic) activity of 72.9% and 71.9%, respectively, using the 800 mg/kg dose. In the prophylactic test, the peptide extract exhibited suppressive activity of 64.7% upon use of 800 mg/kg. Notably, there was a significant decrease (P<0.001) in suppression with lower doses. Conclusion. The results show the presence of antimalarial properties in soybean extracts with higher curative activity when compared to the prophylactic activity. However, more research needs to be conducted on this plant to possibly establish lead compounds.