ABSTRACT
Infectious diseases remain a major public health problem. Enantia chlorantha (EC) and Asteriscus hierochunticus (AH) are both used in traditional medicine to treat various diseases. This study was designed to determine the phytochemical properties and biological activity of both plant extracts/fractions and isolated compounds against leishmaniasis, trypanosomiasis, malaria, pathogenic fungi and bacteria, and SARS-CoV-2 virus proteins.
Phytochemical and in vitro antiprotozoal studies were done according to standard methods. The powdered stem bark of EC (1.6 kg) and whole plant of AH (500 g) were extracted with methanol and concentrated in vacuo at 40ºC to give 170 g and 35 g of crude extracts, respectively. Fractionation of the extracts led to the isolation of 10 compounds, 1-4 (EC), 5-7, 8a, 8b, and 9 (AH). All compounds were identified by a combination of HRESIMS, 1D, and 2D NMR, other spectroscopic methods, and by comparison with literature. Extracts, fractions, and compounds were screened for activity against L. donovani (promastigotes, axenic amastigotes, and intracellular amastigotes), T. brucei trypomastigotes; Plasmodium falciparum (D6 and W2 strains), and pathogenic microbes. IC50 values were calculated from the dose-response curve, and selectivity indices (SI) were determined. Compounds 5 - 7 were docked against four different SARS-CoV-2 virus proteins; leishmania and plasmodium tubulin. In vivo antimalarial activity of EC crude extract combined with chloroquine and artesunate was investigated against P. berghei (NK-65) infected mice. Statistical significance was calculated by one-way Analysis of Variance, and results expressed as mean ± SD.
Phytochemical screening revealed important secondary metabolites (Alkaloids, saponins, phenols, and terpenoids). Neither deaths nor signs of toxicity at an oral dose of 5000 mg/kg bw were observed. At 400 mg/kg p.o/bw, EC crude extract (TE) and TE plus chloroquine (CQ) fractions showed 71.10% and 73.34 – 75.67% curative effects in the P. berghei (NK-65) infected mice. In the in vitro assay, TE and other fractions exhibited significant antimalarial activity with IC50 ranging from ˂ 0.37 - 14.57 μg/mL against both strains of PF, antileishmanial IC50 < 0.80 - > 20 μg/mL, trypanocidal IC50 1.7-> 20 μg/mL, and antimicrobial IC50 57.569 - > 200 μg/mL. Compounds 1-4 were active against P. falciparum with IC50 values from 0.615- >4.760 μg/mL. Fractions of AH showed significant leishmanicidal activity with IC50 ranging from 6.71 - >20 μg/mL; T. brucei IC50 4.130 – 17.120 μg/mL. Compounds 5-9 were active against P. falciparum IC50 from 3.134 - 4.760 µg/mL. Compound 6 was active against E. coli, IC50 10.970 µg/mL. The in silico docking studies revealed that compound 5 possess good binding affinities with COVID-19 main protease (ΔG = -21.65 kcal/mol), nucleocapsid phosphoprotein (ΔG = -7.64 kcal/mol), membrane glycoprotein (ΔG = -5.28 kcal/mol), and NSP10 (ΔG = -20.05 kcal/mol), compared to the co-crystallized ligands. This study has shown that compounds from EC and AH are potential sources of anti-infective agents. The crude extract (TE) of EC potentiates the antiplasmodial activity of chloroquine in vivo. The in silico studies revealed that the antileishmanial and antimalarial activities of compounds 6 and 7 might be due to their affinity for the colchicine binding sites of the parasite tubulin. Compound 5 could be a potent inhibitor of the SARS-CoV-2 virus.
