ABSTRACT
Nauclea latifolia Sm., Azadirachta indica A. Juss., Morinda lucida Benth., Spondias mombin Linn., Alstonia boonei De Wild and Gongronema latifolium possess ethno-pharmacological properties. The present study was aimed at isolation and characterization of phytochemicals from these plants and determination of their antimalarial, leishmanicidal and other biological activities.
Crude plants were macerated in hydro-alcohol solvents and extracts/fractions screened for antimalarial activity against Plasmodium berghei NK65 in mice using the four-day chemosuppressive, prophylactic and mean survival time (MST) tests. Isolation of phytoconstituents by chromatography was done on the most active fraction from each of the two most active extracts. Characterization of isolates was by spectroscopic techniques and literature search. Effects of the isolates/fractions/crude extracts on malaria, leishmaniasis, antioxidants, glucose, haematology, liver architecture, inflammation, and cytotoxicity were determined. Molecular docking of isolates on Plasmodium falciparum dihydrofolate reductase (pfDHFR) and mitogen-activated protein kinase 3 (MAPK3) enzymes was also performed.
Crude extracts reduced parasitaemia and prolonged MST relative to the infected untreated group. Stem bark extracts of Spondias mombin (SMSB) and Alstonia boonei (ABSB) were the most active. Partitioning of SMSB crude extract yielded hexane, hexane:ethylacetate - HEF, ethylacetate - EAF, ethylacetate:methanol- EMF and methanol residue- MR fractions; while ABSB gave petroleum ether- PE, dichloromethane- DCM, basified-dichloromethane-BDCM, acidified-dichloromethane-ADCM and aqueous residue-AR fractions. At a dose of 800 mg/kg bw, fractions had varying antimalarial activity with some almost doubling MST relative to the infected untreated group. The highest activity was in groups administered EAF and BDCM (chemosuppressions: 78.32% and 70.91%; MST: 17.80 and 16.50 days respectively). Gallic acid, (+)-catechin, catechin-5-O-gallate, 1-O-gallylglycerol, (+)-epicatechin, β-sistosterol-D-glucose and β-sistosterol were isolated from EAF; while, echitamine chloride was from BDCM. Only gallic acid, (+)-catechin, (+)-epicatechin and echitamine chloride were further studied. (+)-catechin, echitamine chloride and a 1:1 combination of both had significant (p < 0.05) antimalarial activity on the 9th day of peak parasitaemia with significant (p < 0.05) MST. Gallic
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acid, (+)-catechin and (+)-catechin:echitamine chloride significantly (p < 0.05) increased SOD, CAT, GPx, GST and GSH values, while GR, lipid peroxidation and nitric oxide were reduced significantly (p > 0.05) in a dose-dependent manner. Others (except (+)-epicatechin) significantly (p < 0.05) halted glucose depletion and modulated haematological parameters. The liver architecture was significantly restored in groups administered gallic acid, (+)-catechin, echitamine chloride and (+)-catechin:echitamine chloride. (+)-catechin demonstrated the significant (p < 0.05) leishmanicidal effect (IC50 = 16.6 ± 0.45 μg/ml). Gallic acid, (+)-catechin and DCM exhibited potent anti-inflammatory activity (IC50 = 7.9 ± 2.70, 14.5 ± 1.10 and 8.1 ± 1.0 μg/ml). Only EAF (IC50 = 27.0 ± 0.9 μg/ml) and HEF (IC50 = 19.5 ± 1.5 μg/ml) were cytotoxic against HeLa and 3T3 cancer cell lines, respectively. The isolates docked favourably with amino acids in the active sites of Plasmodium falciparum dihydrofolate reductase (pfDHFR) and mitogen-activated protein kinase 3 (MAPK3) enzymes. The present study reveals that polyphenols and imino alkaloid from SMSB and ABSB, respectively, had antimalari
