In vitro antiprotozoal activity of extract and compounds from the stem bark of Combretum molle.

The antiprotozoal activity of the Ethiopian medicinal plant Combretum molle (R. Br. ex G. Don.) Engl & Diels (Combretaceae) was evaluated by in vitro testing against Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The acetone fraction of the stem bark of this plant prepared by soxhlet extraction was inactive against the intracellular amastigotes of L. donovani and T. cruzi in murine peritoneal macrophages but showed significant activity against extracellular T. b. rhodesiense blood stream form trypomastigotes and trophozoites of P. falciparum with IC(50) values of 2.19 and 8.17 microg/mL, respectively. Phytochemical examination of the bioactive fraction resulted in the isolation of two tannins and two oleanane-type pentacyclic triterpene glycosides. One of the tannins was identified as the ellagitannin, punicalagin, whilst the structure of the other (CM-A) has not yet been fully elucidated. The saponins that were characterized as arjunglucoside (also called 4-epi-sericoside) and sericoside displayed no activity against any of the four species of protozoa tested. On the other hand, punicalagin and CM-A had IC(50) values of 1.75 and 1.50 microM, respectively, against T. b. rhodesiense and were relatively less toxic to KB cells (cytotoxic/antiprotozoal ratios of 70 and 48, respectively). The tannins also showed intermediate activity against P. falciparum, although their selectivity against these parasites was less favourable than the above. It appears that our findings are the first report of hydrolysable tannins exhibiting antitrypanosomal and antiplasmodial activities.