Anti-malarial Activity and Pharmacokinetic Profiles of Methanol Extract of strophanthus hispidus Leaves

Abstract

Strophantus hispidus is a plant known to be used locally in the treatment of several diseases including malaria. Currently, there is sperse scientific reports found on the anti-malarial activity and bioactive compounds of the plant leaves. Thus the aim of the study was to investigate the anti-malarial properties of the methanol extract of Strophanthus hispidus (MESH) leaves and the possible elucidation of the bioactive compound(s). The percentage yield of the methanol extract of Strophanthus hispidus leaves obtained was 12.53%. The phytochemical compositions of the plant extract showed the presence of bioactive organic compounds such as alkaloids, flavonoids, terpenoids, steroids, phenols, saponins, tannins, soluble carbohydrates, reducing sugars and glycosides. The LD50 of the extract in mice was found to be above 5000 mg/kg b.w. Antimalarial activity of the crude extract of Strophanthus hispidus leaves showed that the extract was effective at various doses of 200, 400 and 800 mg/kg b.w. and showed a dose-dependent significant (p < 0.05) reduction in the parasitemia count of all the treatment groups when compared to the positive (untreated) control group. The P.berghei infected mice treated with various doses of the extract showed a significantly (p < 0.05) higher packed cell volume, red blood cell count and haemoglobin concentration compared to the positive control group. Conversely the packed cell volume, red blood cell count and haemoglobin concentration of the treatment groups showed significant (p < 0.05) decrease when compared to the negative control group. The mice treated with various doses of the extract showed significant (p < 0.05) reduction in the activities of liver marker enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) compared to the positive control group. Partitioning of the extract with different solvents gave the following percentage yields: n-Hexane (22%), dichloromethane (20%) and ethyl acetate (35.38%). Treatment with various doses (400 and 800 mg/kg b.w) of the fractions showed a dose dependent significant (p < 0.05) reduction in the parasitemia count of all the groups when compared to the untreated group. The P. berghei-infected mice treated with various doses of the fractions showed significantly (p < 0.05) higher packed cell volume, red blood cell count and haemoglobin concentration compared to the positive control group. The mice treated with various doses of the fractions showed significant (p < 0.05) reduction in the activities of liver marker enzymes (ALT, AST and ALP) compared to the positive control group. The animals treated with the n-Hexane fraction showed a non-significant difference (p > 0.05) in the AST and ALP activities when compared to the Negative control. Activities of some antioxidant enzymes such as superoxide dismutase (SOD) and catalase activity were found to be significantly (p < 0.05) higher in the groups treated with the fractions when compared to the positive control. There was a significant (p < 0.05) reduction in the formation of hemozoin in the groups treated with the non-polar fractions when compared to the positive control group. However comparatively the non-polar fractions were more effective than the polar fraction with n-Hexane fraction being the most active fraction. The calculated LC50 of the S. hispidus n-hexane fraction was found to be 245.5 µg/ml using Brine shrimp lethality Assay. Ninety-five fractions were obtained from column chromatography and combined based on their TLC profiles to give 9 fractions. The 9 fractions showed various levels of potency by inhibiting β-hematin synthesis. However, fractions 7-9 were the most potent fractions with percentage inhibition of 93%. Beta-setosterol-d-glucoside a steroid was identified as the active compound using 1H NMR, 13C NMR and IR spectra. ADME based on the Lipinski’s rule of 5 analysis revealed molecular weight (MW) of 576.86, hydrogen bond acceptor (HBA) of 6.0, hydrogen bond donor (HBD) of 4.0 and logP o/w 5.51. Beta-setosterol-d-glucose as the most active compound could take a lead in the discovery of new anti-malarial agent or used in combination therapy with artemisinin (ACT).