Evaluation of the in vitro trypanocidal activity of Vernonia amygdalina leaf extracts and isolated compounds

Human African trypanosomiasis (HAT), also known as African sleeping sickness, is a neglected disease caused by two subspecies of the protozoan parasite Trypanosoma brucei, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. The parasites are introduced into the mammalian host by the bite of an infected tsetse fly and HAT progresses in two stages: the hemo-lymphatic or early stage and the meningoencephalitic or late stage on which the parasites enter the central nervous system (CNS) (1). HAT threatens primarily rural populations and is fatal unless treated. To date, there are five drugs approved, although none of them are satisfactory, due to treatment failures and toxicity, and the parenteral administration that is inappropriate in settings with poor medical infrastructure. Therefore, there is an urgent need to improve HAT treatment by enhancing the oral administration and the discovery and development of cost-effective new drugs. Drug discovery efforts are nowadays directed towards natural products and medicinal plants represent a validated source for discovery of new lead compounds and standardized herbal medicines against trypanosomiasis (2). Vernonia amygdalina def., generally called “bitter leaf”, is a small shrub that can grow as tall as 5 m in height, and is member of the Asteraceae (or Compositae) family. The species is indigenous to tropical Africa and is found wild or cultivated all over sub-Saharan Africa. Due to its abundant availability in sub-Saharan countries, V. amygdalina has become commonly used in the traditional medicine by local ethnic groups. The leaves of V. amygdalina are used in phyto-medicine to treat fever, hiccups, kidney disease and stomach discomfort, as well as anthelmintic and for treatment and prevention of malaria (3). On the basis of the above-illustrated therapeutic properties, the V. amygdalina leaf extracts and isolated compounds have been selected as valid candidates for investigation as potential inhibitors of Trypanosoma brucei. The results of this study will be discussed. (1) Jacobs, R. T.; Nare, B.; Phillips, M. A. State of the Art in African Trypanosome Drug Discovery. Curr. Top. Med. Chem. 2011, 11, 1255−1274. (2) Scotti, L.; Mendonça, F.J.; da Silva, M.S.; Scotti, M.T. Enzymatic Targets in Trypanosoma brucei. Curr. Protein Pept. Sci. 2016, 17, 243-259. (3) Abay, S.M; Lucantoni, L.; Dahiya, N.; Esposito, F.; Lupidi, G.; Taglialatela-Scafati, O.; Bramucci, M.; Quassinti, L.; Habluetzel, A. Plasmodium transmission blocking activities of Vernonia amygdalina extracts and isolated compounds. Malar J. 2015, 14, 288-306.