Novel Therapeutic Targets for Human African Trypanosomiasis

Digalloyl Glycoside: A Potential Inhibitor of Trypanosomal PFK from Euphorbia abyssinica J.F. Gmel

Human African trypanosomiasis is an endemic infectious disease caused by Trypanosoma brucei via the bite of tsetse-fly. Most of the drugs used for the treatment, e.g., Suramin, have shown several problems, including the high level of toxicity. Accordingly, the discovery of anti-trypanosomal drugs from natural sources has become an urgent requirement. In our previous study on the anti-trypanosomal potential of Euphorbia species, Euphorbia abyssinica displayed significant anti-trypanosomal activity. Therefore, a phytochemical investigation of the methanolic extract of E. abyssinica was carried out. Twelve compounds, including two triterpenes (1, 2); one sterol-glucoside (4); three ellagic acid derivatives (3, 9, 11); three gallic acid derivatives (5, 6, 10); and three flavonoids (7, 8, 12), were isolated. The structures of isolated compounds were determined through different spectroscopic techniques. Compound (10) was obtained for the first time from genus Euphorbia while all other compounds except compound (4), were firstly reported in E. abyssinica. Consequently, an in silico study was used to estimate the anti-trypanosomal activity of the isolated compounds. Several compounds displayed interesting activity where 1,6-di-O-galloyl-d-glucose (10) appeared as the most potent inhibitor of trypanosomal phosphofructokinase (PFK). Moreover, molecular dynamics (MD) simulations and ADMET calculations were performed for 1,6-di-O-galloyl-d-glucose. In conclusion, 1,6-di-O-galloyl-d-glucose revealed high binding free energy as well as desirable molecular dynamics and pharmacokinetic properties; therefore, it could be suggested for further in vitro and in vivo studies for trypanosomiasis.

Antiprotozoal activities of Triterpenic Acids and Ester Derivatives Isolated from the Leaves of Vitellaria paradoxa

Leaves of Vitellaria paradoxa, also called "Shea butter tree", are used in traditional medicine to treat various symptoms including malaria fever, dysentery, or skin infections. Composition of the dichloromethane extract of V. paradoxa leaves possessing antiparasitic activities was investigated. Five pentacyclic triterpenic acids together with 6 ester derivatives were isolated and identified by standards comparison, MS and ¹H-NMR analysis. Corosolic, maslinic, and tormentic coumaroyl esters and their corresponding triterpenic acids were isolated from this plant for the first time. The antiparasitic activities of the 11 isolated compounds were evaluated in vitro on Plasmodium falciparum, Trypanosoma brucei brucei, and Leishmania mexicana mexicana and their selectivity determined by cytotoxicity evaluation on WI38 cells. None of the isolated compounds showed good antiplasmodial activity. The antitrypanosomal activity of individual compounds was in general higher than their antileishmanial one. One isolated triterpenic ester mixture in equilibrium, 3-O-p-E/Z-coumaroyltormentic acids, showed an attractive promising antitrypanosomal activity (IC₅₀ = 0.7 µM) with low cytotoxicity (IC₅₀= 44.5 µM) compared to the corresponding acid. Acute toxicity test on this ester did not show any toxicity at the maximal cumulative dose of 100 mg/kg intraperitoneally on mice. In vivo efficacy evaluation of this compound, at 50 mg/kg by intraperitoneal route on a T. b. brucei-infected mice model, showed a significant parasitemia reduction on day 4 post-infection together with 33.3% survival improvement. Further bioavailability and PK studies are needed along with mode of action investigations to further assess the potential of this molecule.