Abstract:
Plasmodium parasite resistance to Artemisinin Combination Therapy (ACT) in Thailand-Cambodia border, lately in Kigali Rwanda and Uganda, calls for development of new, affordable, safe and effective anti-malarial drugs. Studies done previously on soybean have established that it possesses anti-microbial, anti-inflammatory, anti-cancerous and anti-oxidant properties. The aim of this study was to conduct an in vitro evaluation of the anti-plasmodial activity of Soybean extracts using Plasmodium falciparum cultures, followed by in vivo evaluation of anti-malarial activity and safety of the extracts in Plasmodium berghei strain ANKA infected mice. Aqueous, methanol and peptide extracts of soy bean seeds were prepared. In vitro evaluation of the extracts for anti-plasmodial 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 obtained from KEMRI, Nairobi. Following the in vitro assessment, extracts showing the best activity (peptide and methanol) were selected for in vivo assay with mice infected with P. berghei ANKA strain. Plasmodium berghei ANKA is a surrogate for malaria. 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. 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. The dosages were selected based on existing literature of animal studies, that at 1000mg/kg, the extract is considered lethal and as such, 800mg/kg was ideal. The study followed a dose dependent model. 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 as a standard procedure. From the in vitro assay, 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. On in vivo assay, methanol and peptide extracts exhibited high parasite suppressive activity of 72.9% and 71.9%, respectively using the 800 mg/kg dose. In prophylactic test, the peptide extracts group suppression of parasitemia was 64.66%, 57.12% and 43.14% for doses of 800, 400 and 200 mg/kg. Notably, there was significant decrease (p<0.001) in suppression with lower doses. The extract showed no mortality in mice up to a dose of 5000mg/kg within initial 24h and subsequent 14 days. This is an indication that the plant is safer to use with the recorded antimalarial activity. However, more research needs to be done on this plant to possibly establish lead compounds.
