In vitro inhibition of Plasmodium falciparum early and late stage gametocyte viability by extracts from eight traditionally used South African plant species

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts of plant species, used traditionally to treat malaria, have been extensively investigated for their activity against Plasmodium intraerythrocytic asexual parasites in search of new antimalarial drugs. However, less effort has been directed towards examining their efficacy in blocking transmission. Here, we report the results of the in vitro screening of extracts from eight selected plant species used traditionally to treat malaria in South Africa for activity against Plasmodium falciparum NF54 early and late stage gametocytes. The species used were Khaya anthotheca, Trichilia emetica, Turraea floribunda, Leonotis leonurus, Leonotis leonurus ex Hort, Olea europaea subsp. Africana, Catha edulis and Artemisia afra.

AIM OF THE STUDY

To investigate the activities of extracts from plant species traditionally used for malaria treatment against P. falciparum gametocytes.

MATERIAL AND METHODS

Air-dried and ground plant leaves were extracted using acetone. Primary two point in vitro phenotypic screens against both early and late stage gametocytes were done at 10 and 20µg/ml followed by full IC50 determination of the most active extracts. Inhibition of gametocyte viability in vitro was assessed using the parasite lactate dehydrogenase (pLDH) assay.

RESULTS

Of the eight crude acetone extracts from plant species screened in vitro, four had good activity with over 50-70% inhibition of early and late stage gametocytes' viability at 10 and 20µg/ml, respectively. Artemisia afra (Asteraceae), Trichilia emetica (Meliaceae) and Turraea floribunda (Meliaceae) were additionally highly active against both gametocyte stages with IC50 values of less than 10µg/ml while Leonotis leonurus ex Hort (Lamiaceae) was moderately active (IC50<20µg/ml). The activity of these three highly active plant species was significantly more pronounced on late stage gametocytes compared to early stages.

CONCLUSION

This study shows the potential transmission blocking activity of extracts from selected South African medicinal plants and substantiates their traditional use in malaria control that broadly encompasses prevention, treatment and transmission blocking. Further studies are needed to isolate and identify the active principles from the crude extracts of A. afra, T. emetica and T. floribunda, as well as to examine their efficacy towards blocking parasite transmission to mosquitoes.

Theory development in perspective: the role of conceptual frameworks and models in theory development

An analysis of most scientific theories reveals the presence of a variety of components which function as constitutive elements of theories. Wider cultural paradigms often influence the construction and content of theories in a decisive way. Analogies between incongruent domains provide significant points of departure for the development of models which are often metaphoric in nature. Different metaphors provide alternative conceptual frameworks in terms of which it is possible to describe and explain nursing phenomena. Scientific theories that are developed on the basis of such metaphorical models are limited in their explanatory capacity. When the intrinsic limitations of such scientific models are not recognized, they often lead to distorted, one-sided and reductionistic explanations of phenomena. Metaphysical assumptions concerning the nature of human beings, illness, health, etc., are also of decisive significance in this process, e.g. mechanistic models based on a naturalistic view of man lead theorizing astray. These theses are illustrated with reference to behavioral systems theory as developed by Dorothy Rogers.