Isolation and characterization of novel antiplasmodial compounds from Siphonochilus aethiopicus

The rhizomes of Siphonochilus aethiopicus are traditionally used to treat colds, coughs, malaria and other ailments [1]. The aim of this study was to investigate S. aethiopicus for its antimalarial properties and to isolate and characterize novel antiplasmodial compounds. Dried ground roots of S. aethiopicus were initially donated by Nigel Gericke (SANBI, South Africa). Plant material was extracted with ethyl acetate and subjected to bioassay-guided fractionation. Nuclear magnetic resonance and mass spectrometry was used to determine the chemical structure of compounds. In vitro antiplasmodial activity was determined against Plasmodium falciparum using a modification of the parasite lactate dehydrogenase assay by Makler et al. [2]. In vivo antiplasmodial activity was evaluated against the chloroquine (CQ) resistant P.yeolli NS strain using the Peters 4-day suppressive test [3]. The in vitro cytotoxicity screens were performed against the Chinese hamster ovarian cell-line using the MTT-assay [4]. The crude extract was active in vitro against the CQ sensitive D10 and CQ resistant K1 strains of P. falciparum with IC₅₀ values of 2.9µg/ml and 1.4µg/ml, respectively. Three structurally-related furanoterpenoids were isolated. The most active compound had an IC₅₀ value of 3.4µg/ml against the CQ sensitive strain and 1.5µg/ml against the CQ resistant strain of P. falciparum. No cytotoxicity was observed with the crude extract and the compounds. The crude extract and compounds isolated were more active against the CQ resistant strain of P.falciparum compared to the CQ sensitive strain. Preliminary in vivo results with the plant extract showed a reduction in parasitaemia on day 4.

Acknowledgements: We would like to thank the Medical Research Council (South Africa) and the National Research Foundation (South Africa) for financial support. The technical support of Mr and Mrs Salie is greatly appreciated.

References: 1. Hutchings, A. (1996) Zulu medicinal plants. University of Natal Press. South Africa. 2. Makler, M.T. et al. (1993) Am J Trop Med Hyg 48: 739–741. 3. Peters, W., Robinson, B.L. (1993) Ann Trop Med Parasitol 87: 111–123. 4. Mossman, T. (1983)J Immunol Meth 65: 55–63.