Abstract
BackgroundThe anti-malarials quinine and artemisinin were isolated from traditionally used plants (Cinchona spp. and Artemisia annua, respectively). The synthetic quinoline anti-malarials (e.g. chloroquine) and semi-synthetic artemisinin derivatives (e.g. artesunate) were developed based on these natural products. Malaria is endemic to the Amazon region where Plasmodium falciparum and Plasmodium vivax drug-resistance is of concern. There is an urgent need for new anti-malarials. Traditionally used Amazonian plants may provide new treatments for drug-resistant P. vivax and P. falciparum. Herein, the in vitro and in vivo antiplasmodial activity and cytotoxicity of medicinal plant extracts were investigated.MethodsSixty-nine extracts from 11 plant species were prepared and screened for in vitro activity against P. falciparum K1 strain and for cytotoxicity against human fibroblasts and two melanoma cell lines. Median inhibitory concentrations (IC50) were established against chloroquine-resistant P. falciparum W2 clone using monoclonal anti-HRPII (histidine-rich protein II) antibodies in an enzyme-linked immunosorbent assay. Extracts were evaluated for toxicity against murine macrophages (IC50) and selectivity indices (SI) were determined. Three extracts were also evaluated orally in Plasmodium berghei-infected mice.ResultsHigh in vitro antiplasmodial activity (IC50 = 6.4–9.9 µg/mL) was observed for Andropogon leucostachyus aerial part methanol extracts, Croton cajucara red variety leaf chloroform extracts, Miconia nervosa leaf methanol extracts, and Xylopia amazonica leaf chloroform and branch ethanol extracts. Paullinia cupana branch chloroform extracts and Croton cajucara red variety leaf ethanol extracts were toxic to fibroblasts and or melanoma cells. Xylopia amazonica branch ethanol extracts and Zanthoxylum djalma-batistae branch chloroform extracts were toxic to macrophages (IC50 = 6.9 and 24.7 µg/mL, respectively). Andropogon leucostachyus extracts were the most selective (SI >28.2) and the most active in vivo (at doses of 250 mg/kg, 71 % suppression of P. berghei parasitaemia versus untreated controls).ConclusionsEthnobotanical or ethnopharmacological reports describe the anti-malarial use of these plants or the antiplasmodial activity of congeneric species. No antiplasmodial activity has been demonstrated previously for the extracts of these plants. Seven plants exhibit in vivo and or in vitro anti-malarial potential. Future work should aim to discover the anti-malarial substances present.
Highlights
The anti-malarials quinine and artemisinin were isolated from traditionally used plants (Cinchona spp. and Artemisia annua, respectively)
All extracts prepared from Anacardium occidentale, Derris floribunda, Parkia nitida and Stigmaphyllon sinuatum were inactive in vitro against P. falciparum as were Croton cajucara red variety bark and Paullina cupana leaf extracts
The identification of antiplasmodial and cytotoxic, traditionally used species can be useful as an initial step in pharmacological evaluations that can lead to more rational use
Summary
The anti-malarials quinine and artemisinin were isolated from traditionally used plants (Cinchona spp. and Artemisia annua, respectively). In the Amazon region, the occurrence of malaria is related to demographic, ecological, socio-economic, and cultural changes, especially in the first half of the twentieth century In this period, relatively few plants from this region were used to treat this disease [1, 2]. The co-existence of traditional populations with this disease caused a search for new therapeutic resources in the Amazonian environment, especially among plants, to treat the symptoms of malaria. Nowadays, this traditional knowledge, available through ethnopharmacological studies, is the most often used means to target plants for the discovery of new bioactive substances. The chemosystematic approach for the selection of anti-malarial plants for study is valid especially where ethnopharmacological studies have shown a plant family, or a particular genus, to contain anti-malarial extracts and chemical constituents
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