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, Tryp anosoma cruzi and Leishmania donovani. The acetone fraction of the stem bar k of this plant prepared by soxhlet extraction was inactive against the int racellular amastigotes of L. donovani and T. cruzi in murine peritoneal mac rophages but showed significant activity against extracellular T. b. rhodes iense blood stream form trypomastigotes and trophozoites of P. falciparum w ith IC50 values of 2.19 and 8.17 mug/mL, respectively. Phytochemical examin ation of the bioactive fraction resulted in the isolation of two tannins an d two oleanane-type pentacyclic triterpene glycosides. One of the tannins w as identified as the ellagitannin, punicalagin, whilst the structure of the other (CM-A) has not yet been fully elucidated. The saponins that were cha racterized as arjunglucoside (also called 4-epi-sericoside) and sericoside displayed no activity against any of the four species of protozoa tested. O n the other hand, punicalagin and CM-A had IC50 values of 1.75 and 1.50 muM , respectively, against T. b. rhodesiense and were relatively less toxic to KB cells (eytotoxic/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 abov e. It appears that our findings are the first report of hydrolysable tannin s exhibiting antitrypanosomal and antiplasmodial activities. Copyright (C) 2001 John Wiley & Sons, Ltd.