Our study provides evidence for an antimalarial potential of caffeic acid derivatives which are common in several medicinal plants traditionally used against malaria. It also demonstrates the possibility to use such derivatives in the treatment of malaria.
One hundred and ninety plants, of which 51 are used to treat malaria in traditional medicine, were collected in five different ecosystems of Madagascar for a screening programme devoted to the search of naturally-occurring antimalarial compounds. Thirty-nine plants, of which 12 are used as herbal antimalarials, were found to display in vitro activity against Plasmodium falciparum with a median inhibitory concentration (IC50) lower than 5 microg/ml while 9 had an IC50 ranging from 5 to 7.5 microg/ml. Seventeen of them exhibited cytotoxic effects on murine P388 leukemia cells with an IC50 < 10 microg/ml. The biological activities were mostly located in the ethyl acetate fractions. Bioassay-directed fractionation is underway to isolate the active constituents.
Vernonia amygdalina Del. is a conventional herbal drug in Congolese traditional medicine and is widely used for the treatment of malaria.The aim of this work is to evaluate its efficacy and safety and the potential antimalarial activity of another species originating from Madagascar. Standard bioassay models based on in vitro and in vivo systems that enable bioactivity screening of traditionally used medicinal plants were used. In particular, hydro-alcoholic extracts of two Vernonia species growing in two different geographical regions(Congo DR and Madagascar) were evaluated for the inhibitory effects on two malaria parasites strains and cytotoxicity towards leukaemia P-388 cell lines. Results indicate that, V. amygdalina possess a very good in vitro and in vivo activities and a good therapeutic index than V. cinerea subsp vialis endemic to Madagascar, thus validate scientifically the efficacy and safety of Vernonia amygdalina in the traditional treatment of malaria in Congo DR. Using chemotaxonomic approach, we also detected moderate antiplasmodial activities in V. cinerea subsp vialis a plant species not previously reported as antimalarial in the traditional medicine knowlegde of Madagascar. It would be concluded that despite the long spatial isolation of Madagascar and allopatric speciation, Vernonia ecotype as V. cinerea subsp vialis has preserved the antiplasmodial properties. This approach gives the possibility to select plant species of the same genus from different geographical regions in order to increase the chance of discovering new biologically active plants.
Crude alkaloids of Strychnos myrtoides Gilg & Busse, empirically used as an adjuvant to chloroquine (CQ) in Malagasy herbal remedies, were practically devoid of intrinsic in vitro and in vivo antimalarial activity. However, when combined with CQ at a dose level much lower than their IC50 value, they markedly enhanced in vitro the effectiveness of the synthetic drug against a CQ-resistant strain of Plasmodium falciparum. They also enhanced in vivo CQ activity against a resistant strain of Plasmodium yoelii. By counter-current distribution (CCD) separation of the crude alkaloid extract, the two major alkaloids strychnobrasiline (1) and malagashanine (2), together with four minor alkaloids, were isolated. Strychnobrasiline and malagashanine were devoid of both intrinsic antimalarial activity and cytotoxicity effect, but exhibited significant CQ-potentiating actions. These findings could account for the above-mentioned empirical use of S. myrtoides. The present state of research on antimalarial drug from Strychnos genus is also discussed.
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