The importance of including toxicity assays when screening plant extracts for antimalarial activity

Abstract

Identifying plant extracts as sources of antimalarial compounds needs to be addressed as numerous studies screen extracts without the means of eliminating extracts that are merely cytotoxic. Fifty-nine organic solvent extracts from South African plants were screened for antiplasmodial activity using the [3H]-hypoxanthine incorporation assay against the chloroquine-resistant Plasmodium falciparum. Variable antiplasmodial activity and toxicity was observed. Extracts form Combretum erythrophyllum and Crinum bulbispermum, had IC50 values ≤ 1 μg/ml with the ethyl acetate extracts of C. bulbispermum roots and bulbs having values comparable to chloroquine (0.04 µg/ml). Nine extracts had toxicity indexes ≥ 100. Lycorine, isolated from C. bulbispermum was as active as chloroquine (IC50 of 0.03 µg/ml) and had a favourable security index.