Evaluation of the antitrypanosomal activities of nine selected Nigerian medicinal plants in mice
The study investigated nine selected Nigerian medicinal plants for antitrypanosomal activity with a view to providing information on the potential role of any of the nine plants as an antitrypanosomal and/or anti-inflammatory agent. The ethanolic crude extract and ethylacetate fraction of the stem bark of Terminalia ivorensis A. Chev, and with other plant extracts; Harugana madagascariensis(stem bark), Landolphia dulcis (leaves), Curcuma longa (rhizome), Ocimum gratissimum (stem), Khaya senegalensis (stem bark), Alcornea cordifolia (leaves), Achyranthes aspera (leaves), and Aloe schweinfurthii (leaves) were tested for their antitrypanosomal activity using Trypanosoma brucei brucei infected mice. A dose probing acute toxicity test was carried out on L. dulcis and T. ivorensis, while the LD50 data in literature were used for the other plants. The antitrypanosomal effects of the extracts were evaluated by monitoring changes in parasitemia level and mortality of infected mice. The anti-inflammatory property of the most promising plant extract was assessed using acute oedema of the mice paw model as a probable mechanism of antitrypanosomal action. The data were subjected to statistical analysis by employing the paired t-test. Acute toxicity experiments established an oral LD50 for T. ivorensis and L. dulcis respectively as (> 5000 mg/kg and >1600 <5000 mg/kg) while the interperitoneal LD50 of T. ivorensis is 100 mg/kg. T. ivorensis, H. madagascariensis, C. longa, O. gratissimum, K. senegalensis, A. cordifolia, A. aspera, and A. schweinfurthii had weak antitrypanosomal effect against T. brucei brucei when compared with the positive control group (Diminal®), but shows some significance (P < 0.05) as compared with the negative control group. However, L. dulcis crude extract demonstrated a significant effect (P < 0.01) by parasite clearance on day 5 of treatment but there was a relapse thereafter from day 7. The activities of the 3 fractions of L. dulcis also showed a disappearance of the parasites from the bloodstream of the animals from day 3 of treatment and thereafter, a relapse with a lesser parasite count for the n-Hexane fraction with a value of (9.53 ± 0.56) when compared with the aqueous and ethyl acetate fractions with values of (25.53 ± 1.53) and (22.13 ± 1.93) respectively on day 9. Administration of n-hexane fraction of L. dulcis (1000 mg/kg) inhibited oedema induced by subplantar injection of egg albumin in systemic acute anti-inflammatory test by 107 %. The study concluded that L. dulcis has a potential as an anti-trypanosomal and anti- inflammatory agent because it increased the survival time of infected mice due to reduction in parasitemia caused by T. brucei brucei.