In vitro antitrypanosomal activity of African plants used in traditional medicine in Uganda to treat sleeping sickness.

In Uganda, as in many other African countries, herbal treatment of various diseases is still common. In the present study, 9 plant species collected from Tanzania and Uganda and used by traditional healers in southern-eastern Uganda for the treatment of human African trypanosomiasis (sleeping sickness) were extracted and screened for their in vitro activity against Trypanosoma brucei rhodesiense, one of the two causative agents of sleeping sickness. Eight lipophilic extracts of 5 plants revealed very promising antitrypanosomal activity with IC50 values below 1 microgram/ml; among them were extracts prepared from Albizia gummifera (2), Ehretia amoena (1), Entada abyssinica (2), Securinega virosa (1) and Vernonia subuligera (2). Activity with IC50 values between 1 and 10 micrograms/ml was determined for 15 further extracts. Cytotoxicity of active extracts, tested on a human fibroblast cell line (WI-38), was found to be high, and therefore selectivity indices resulted in less favourable ranges than those for the few commercially available drugs. Nevertheless, the results confirm the potential of ethnobotanically selected plants as remedies against sleeping sickness and call for phytochemical studies.