Antiplasmodial potential of medicinal plant extracts from Malaiyur and Javadhu hills of South India

Abstract

The emergence and spread of Plasmodium falciparum with resistance to chloroquine (CQ), the safest and cheapest anti-malarial drug, coupled with the increasing cost of alternative drugs especially in developing countries have necessitated the urgent need to tap the potential of plants for novel anti-malarials. The present study investigates the anti-malarial activity of the methanolic extracts of 13 medicinal plants from the Malaiyur and Javadhu hills of South India against blood stage CQ-sensitive (3D7) and CQ-resistant (INDO) strains of P. falciparum in culture using the fluorescence-based SYBR Green I assay. Sorbitol-synchronized parasites were incubated under normal culture conditions at 2% hematocrit and 1% parasitemia in the absence or presence of increasing concentrations of plant extracts. CQ and artemisinin were used as positive controls, while 0.4% DMSO was used as the negative control. The cytotoxic effects of extracts on host cells were assessed by functional assay using HeLa cells cultured in RPMI containing 10% fetal bovine serum, 0.21% sodium bicarbonate and 50 μg/mL gentamycin (complete medium). Plant extracts (bark methanol extracts of Annona squamosa (IC(50), 30 μg/mL), leaf extracts of Ocimum gratissimum (IC(50), 32 μg/mL), Ocimum tenuiflorum (IC(50), 31 μg/mL), Solanum torvum (IC(50), 31 μg/mL) and Justicia procumbens (IC(50), 63 μg/mL), showed moderate activity. The leaf extracts of Aristolochia indica (IC(50), 10 μg/mL), Cassia auriculata (IC(50), 14 μg/mL), Chrysanthemum indicum (IC(50), 20 μg/mL) and Dolichos biflorus (IC(50), 20 μg/mL) showed promising activity and low activity was observed in the flower methanol extracts of A. indica , leaf methanol extract of Catharanthus roseus, and Gymnema sylvestre (IC(50), >100 μg/mL). These four extracts exhibited promising IC(50) (μg/mL) of 17, 24, 19 and 24 respectively also against the CQ resistant INDO strain of P. falciparum. The high TC(50) in mammalian cell cytotoxicity assay and the low IC(50) in anti-malarial P. falciparum assay indicates selectivity and good resistance indices in the range of 0.9-1.7 for leaf extracts of A. indica, C. auriculata, C. indicum and D. biflorus suggests that these may serve as anti-malarial agents even in their crude form. These results indicate a possible explanation of the traditional use of some of these medicinal plants against malaria or malaria-like conditions.