Larvicical and anti-plasmodial constituents of Carapa Procera Dc. (Meliaceae) and Hyptis Suaveolens L. Poit (Lamiaceae)

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Missah, Beatrice
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Malaria is a serious health problem worldwide due to the emergence of parasite resistance to well established antimalarial drugs. This has heightened the need for the development of new antimalarial drugs as well as other control methods. Plant based antimalarial drugs continue to be used in many tropical areas for the treatment and control of malaria and hence the need for scientific investigation into their usefulness as alternatives to conventional treatment. The work presented in this thesis involves the scientific investigation of the traditional uses of Carapa procera and Hyptis suaveolens as insecticidal agents. Carapa procera was also investigated for its antiplasmodial activity. The petroleum ether, ethyl acetate and 70% ethanol extracts of stem bark of Carapa procera and aerial parts of Hyptis suaveolens were investigated for their larvicidal and antiplasmodial activities. The larvicidal activities of the plant extracts and isolates were investigated using the method described by WHO against third instar Anopheles gambie larvae. The larvae were exposed to various concentrations of the extracts and the percentage mortality was recorded after 24 hours. Temephos, a synthetic insecticide was used as the standard drug. All extracts exhibited dose dependent increase in larvicidal activity with the Petroleum ether extracts of both Hyptis suaveolens and Carapa procera having the highest activity (EC 50 34.96 mg/ml and 16.91 mg/ml respectively) followed by ethyl acetate and ethanol extracts. For the antiplasmodial assay, the Lactate dehydrogenase method was used against chloroquine resistance strains of Plasmodium falciparum. The ethyl acetate extract of Carapa procera showed the highest activity (EC 50 18.60 µg/ml) followed by v petroleum ether (EC 50 24.71 µg/ml ) and ethanol extracts (EC50 95.46 µg/ml) as compared to artesunate the standard drug with EC50 of 4.90 µg/ml. Carapolides A and B, evodulone and proceranolide were isolated from the bioactive petroleum ether extract of Carapa procera stem bark. They exhibited various degrees of larvicidal activities against the third instar Anopheles gambie larvae with EC50 values of 15.01mg/ml, 53.74mg/ml, 198.9mg/ml and 273.6mg/ml for Carapolide A, proceranolide, evodulone and carapolide B respectively. They also exhibited dose dependant antiplasmodial activities with EC 50 values of 23.96 µg/ml, 26.66 µg/ml, 30.52 µg/ml and 32.68 µg/ml for carapolide A, evodulone, carapolide B and proceranolide respectively. Carapolide A and B are being reported for the first time in the stem bark of Carapa procera.
A thesis submitted in partial fulfilment of the requirements for the degree of Mphil Pharmacognosy in the Department of Pharmacognosy, 2014