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African trypanosomiasis is a disease caused by the parasitic protozoa of the Trypanosoma genus. Despite several efforts at chemotherapeutic interventions, the disease poses serious health and economic concerns to humans and livestock of many sub-Saharan African countries. Zanthoxylum zanthoxyloides (Lam.) Zepern. & Timler (Z. zanthoxyloides LZT) is a plant species of important phytochemical and pharmacological relevance in the subtropical zones of the African continent. However, the mechanisms of its antitrypanosomal effects in African trypanosomes remain to be elucidated. The aim of the study was to determine the in vitro effects and mechanisms of action of Z. zanthoxyloides LZT (root) fractions against Trypanosoma brucei. T. brucei (GUTat 3.1 strain), L. donovani (D10 strain), P. falciparum (3D 7 strain), Jurkat cells, and Chang liver cells were cultivated in vitro to the log phase in their respective media at 37°C. Crude extracts and fractions were prepared from air-dried pulverized plant material of Z. zanthoxyloides LZT (root) using the modified Kupchan method of solvent partitioning. Half-maximal inhibitory concentrations (IC50) were determined through the alamar blue cell viability assay. Effects of fractions on cell death and cell cycle of T. brucei were determined using flow cytometry. Fluorescence microscopy was used to investigate the effects of fractions on the morphology and distribution of T. brucei. Antitrypanosomal compounds of fractions were characterized using high-performance liquid chromatography (HPLC) and attenuated total reflectance infrared (ATR-IR) spectroscopy. Methanol, butanol, and dichloromethane fractions were selectively active against T. brucei with respective IC50 values of 3.89, 4.02, and 5.70 μg/ml. Moreover, methanol, butanol, and dichloromethane fractions significantly induced apoptosis-like cell death with remarkable alteration in the cell cycle of T. brucei. Furthermore, dichloromethane and methanol fractions altered the morphology, induced aggregation, and altered the ratio of nuclei to kinetoplasts in the parasite. The HPLC chromatograms and ATR-IR spectra of the active fractions suggested the presence of aromatic hydrocarbons with hydroxyl, carbonyl, amine, or amide functional groups. The results suggest that Z. zanthoxyloides LZT have potential chemotherapeutic effects on African trypanosomes with implications for novel therapeutic interventions in African trypanosomiasis.

In the absence of vaccines, there is a need for alternative sources of effective chemotherapy for African trypanosomiasis (AT). The increasing rate of resistance and toxicity of commercially available antitrypanosomal drugs also necessitates an investigation into the mode of action of new antitrypanosomals for AT. In this study, furoquinoline 4, 7, 8-trimethoxyfuro (2, 3-b) quinoline (compound 1) and oxylipin 9-oxo-10, 12-octadecadienoic acid (compound 2) were isolated from the plant species Zanthoxylum zanthoxyloides (Lam) Zepern and Timler (root), and their in vitro efficacy and mechanisms of action investigated in Trypanosoma brucei (T. brucei), the species responsible for AT. Both compounds resulted in a selectively significant growth inhibition of T. brucei (compound 1, half-maximal effective concentration EC50 = 1.7 μM, selectivity indices SI = 74.9; compound 2, EC50 = 1.2 μM, SI = 107.3). With regards to effect on the cell cycle phases of T. brucei, only compound 1 significantly arrested the second growth-mitotic (G2-M) phase progression even though G2-M and DNA replication (S) phase arrest resulted in the overall reduction of T. brucei cells in G0-G1 for both compounds. Moreover, both compounds resulted in the aggregation and distortion of the elongated slender morphology of T. brucei. Analysis of antioxidant potential revealed that at their minimum and maximum concentrations, the compounds exhibited significant oxidative activities in T. brucei (compound 1, 22.7 μM Trolox equivalent (TE), 221.2 μM TE; compound 2, 15.0 μM TE, 297.7 μM TE). Analysis of growth kinetics also showed that compound 1 exhibited a relatively consistent growth inhibition of T. brucei at different concentrations as compared to compound 2. The results suggest that compounds 1 and 2 are promising antitrypanosomals with the potential for further development into novel AT chemotherapy.

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