A call for using natural compounds in the development of new antimalarial treatments – an introduction

Natural compounds, mostly from plants, have been the mainstay of traditional medicine for thousands of years. They have also been the source of lead compounds for modern medicine, but the extent of mining of natural compounds for such leads decreased during the second half of the 20th century. The advantage of natural compounds for the development of drugs derives from their innate affinity for biological receptors. Natural compounds have provided the best anti-malarials known to date. Recent surveys have identified many extracts of various organisms (mostly plants) as having antiplasmodial activity. Huge libraries of fractionated natural compounds have been screened with impressive hit rates. Importantly, many cases are known where the crude biological extract is more efficient pharmacologically than the most active purified compound from this extract. This could be due to synergism with other compounds present in the extract, that as such have no pharmacological activity. Indeed, such compounds are best screened by cell-based assay where all potential targets in the cell are probed and possible synergies identified. Traditional medicine uses crude extracts. These have often been shown to provide many concoctions that deal better with the overall disease condition than with the causative agent itself. Traditional medicines are used by ~80 % of Africans as a first response to ailment. Many of the traditional medicines have demonstrable anti-plasmodial activities. It is suggested that rigorous evaluation of traditional medicines involving controlled clinical trials in parallel with agronomical development for more reproducible levels of active compounds could improve the availability of drugs at an acceptable cost and a source of income in malaria endemic countries

<it>In vitro</it> antiplasmodial, antileishmanial and antitrypanosomal activities of selected medicinal plants used in the traditional Arabian Peninsular region

<p>Abstract</p> <p>Background</p> <p>Worldwide particularly in developing countries, a large proportion of the population is at risk for tropical parasitic diseases. Several medicinal plants are still used traditionally against protozoal infections in Yemen and Saudi Arabia. Thus the present study investigated the <it>in vitro</it> antiprotozoal activity of twenty-five plants collected from the Arabian Peninsula.</p> <p>Methods</p> <p>Plant materials were extracted with methanol and screened <it>in vitro</it> against erythrocytic schizonts of <it>Plasmodium falciparum</it>, intracellular amastigotes of <it>Leishmania infantum</it> and <it>Trypanosoma cruzi</it> and free trypomastigotes of <it>T. brucei</it>. Cytotoxic activity was determined against MRC-5 cells to assess selectivity. The criterion for activity was an IC₅₀ < 10 μg/ml (<5 μg/ml for <it>T. brucei</it>) and selectivity index of >4.</p> <p>Results</p> <p>Antiplasmodial activity was found in the extracts of <it>Chrozophora oblongifolia</it>, <it>Ficus ingens</it>, <it>Lavandula dentata</it> and <it>Plectranthus barbatus</it>. Amastigotes of <it>T. cruzi</it> were affected by <it>Grewia erythraea</it>, <it>L. dentata</it>, <it>Tagetes minuta</it> and <it>Vernonia leopoldii</it>. Activity against <it>T. brucei</it> was obtained in <it>G. erythraea</it>, <it>L. dentata</it>, <it>P. barbatus</it> and <it>T. minuta</it>. No relevant activity was found against <it>L. infantum</it>. High levels of cytotoxicity (MRC-5 IC₅₀ < 10 μg/ml) and hence non-specific activities were noted in <it>Cupressus sempervirens</it>, <it>Kanahia laniflora</it> and <it>Kniphofia sumarae</it>.</p> <p>Conclusion</p> <p>The results endorse that medicinal plants can be promising sources of natural products with antiprotozoal activity potential. The results support to some extent the traditional uses of some plants for the treatment of parasitic protozoal diseases.</p