Evaluation Of Indigenous Namibian Mushrooms And Plants For Antimalarial Properties

ABSTRACT

Malaria is a parasitic disease caused by Plasmodium species and transmitted by Anopheles mosquitoes. The disease is currently ranked high among the most problematic infectious diseases around the world. Despite the significant progress that has been made toward reducing the global burden of malaria, it remains one of the most significant public health threats in sub-Saharan Africa and many other parts of the developing world. Current malaria control measures have adverse environmental and human effects. The synthetic repellents used for controlling vectors are causing irreversible damage to the ecosystem since the chemicals are non-degradable in nature. The current antimalarial drugs are also facing the specter of parasite resistance, hence the need to discover novel drugs from natural products. The overall objective of the study was to perform bioassay-guided fractionation and determine the antiplasmodial activities, phytochemical profiles, active compounds and cytotoxicities of mushroom and plant extracts. The study involved an ethnobotanical survey of putative antimalarial mushrooms and plants. Preparation of mushroom and plant organic extracts; evaluation of antiplasmodial activity of the extracts using the parasite lactate dehydrogenase (pLDH) assay; verification of phytochemical profiles (saponins, terpenoids, anthraquinones, coumarins, alkaloids, and flavonoids) using standard procedures; elucidation of active antiplasmodial compounds using Gas chromatography-Mass Spectrometry (GC-MS), Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance spectroscopy (NMR) and determination of cytotoxicity using the (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) (MTT) method. Four mushroom and thirteen plant species used in this study were collected from north-central Namibian regions namely Kavango East, Kavango West, Ohangwena, and Oshikoto. Of these, only two plants were active against 3D7 strains of the malaria parasite, Plasmodium falciparum. None of the evaluated mushrooms showed activity. The phytochemical screening of the plants revealed presence of anthraquinones, saponins, terpenoids, coumarins, alkaloids, and flavonoids. Two antiplasmodial compounds namely Npk1 F70 (IC50 = 2.63 ± 0.48 μg/mL) and NPk1 F78 (IC50 2.64 ± 0.32 μg/mL) were isolated from Npk1 (Pechuel-loeschea leubnitiziae) dichloromethane (DCM) extracts. The compounds were screened for cytotoxicity on the Chinese hamster ovary (CHO) cell line using the MTT assay and were found to be toxic to the mammalian cells. GraphPad Prism was used to calculate the compounds’ IC50 values of 2.7 μg/mL and 2.22 μg/mL for NPk1 F78, and Npk1 F70, respectively. The molecular weight of the two anti-3D7 compounds was determined by GC-MS to be 246 g/mol. When FTIR and NMR were performed, the structure of the active compound was identified as xerantholide. This is the first study to elucidate an active antiplasmodial compound from this indigenous Namibian plant P. leubnitiziae which is used by local people to manage malaria. This study, to the best of my knowledge is the first to report the antimalarial activity of xerantholide, a known guaianolide extracted from aerial parts of P. leubnitiziae. It is recommended that pharmacomodulation study be carried out on the compound identified in this study in order to decrease the compound’s toxicity, while maintaining or improving its activity. Further studies also need to be done on xerantholide to determine the diastereomers (stereoisomers that are not mirror images of one another). Modification on xerantholide chemical structure also needs to be carried out so that the toxic compounds can be used for possible anti-cancer therapy..