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Phyto-chemical and pharmacological study of plants used in traditional medicine in Cameroon

Final Activity Report Summary - PHYTOPHARM (Phytochemical and Pharmacological Study of Plants Used in Traditional Medicine in Cameroon)

Protozoal diseases represent a major cause of mortality and morbidity throughout the world according to the World Health Organisation (WHO). Malaria infects each year over 350 to 500 million people and claims one million lives, primarily children under five years of age. The chemotherapy of all these tropical malaria and other parasitic diseases is undermined by the fact that currently used drugs are relatively toxic or, to a certain extent, ineffective by the spreading of resistance. Therefore, there is an urgent need to discover new therapeutic agents and traditional medicine knowledge could be useful to open new ways in this field.

For many decades, traditional healers have used medicinal plants to prevent or cure some diseases without knowing the active principles. In Cameroon, traditional pharmacopoeia plays an essential role in health care due to elevated costs of synthetic agents and, sometimes, their undesirable side effects. Since the devaluation of the Colloquially franc (CFA) in 1994, the number of phytomedicine treatment centres has increased. Local preparations of antimalarials and antimicrobials involve maceration, infusion or decoction administrated in a drink, a bath or fumigation of different parts with water and alcohol. Nevertheless, very few pharmacological or phytochemical studies have focussed on these plants which are potential sources of new drugs. It is hence of primary importance to reflect on issues of toxicity, viability and efficiency of such remedies, dosage, as well as on the role of different additives, which vary from one region of the country to another.

Considering the Cameroon biodiversity, we undertook ethnopharmacological investigation via interviews with local traditional healers in the south region of Cameroon on medicinal plants used against parasitic and microbial diseases. A literature survey and chemotaxonomical criteria permitted afterwards to select plants of the species psorospermum densipunctum, psorospermum adamaouense, salacia camerunensis, pentadesma butyracea, beilschmiedia obscura, quassia sanguinea and canthium subcordatum. Preliminary screening with respect to malaria helped to select the most active plants for phytochemical investigation. Psorospermum densipunctum, psorospermum adamaouense, salacia camerunensis, quassia sanguinea and pentadesma butyracea showed particularly strong activities in vitro with IC50 below 5 mg/ml.

Phytochemical investigation of pentadesma butyracea, a plant of the clusiaceae family, led to the isolation of 12 compounds, of which one was a new xanthone named pentadexanthone (1) and the other eleven were known compounds. All isolated compounds were tested for their antiplasmodial activity in vitro against the W2 strain of plasmodium falciparum and all xanthones were found to exhibit good antiplasmodial activity in vitro with IC50 values below 3 µM.

Following our investigation, the methanolic extract of salacia camerunensis, which demonstrated good antiplasmodial activity in vitro during preliminary antiplasmodial screening (IC50 value of 2.28 µg/ml) against plasmodium falciparum chloroquine resistant W2 strain, was studied. Twelve compounds with various skeletons were isolated. Seven of these compounds were fully characterised and five of them, essentially oxygenated sesquiterpenoids and salaterpenoid A-E (13, 14, 15, 17, and 18) were new compounds. The structure elucidation of other compounds was under process by the time of the project completion. All these compounds were tested in vitro for their antiplasmodial activity against plasmodium falciparum chloroquine resistant W2 strain. All new compounds exhibited good potency with IC50 values below 1.6 µg/mL.

In our continuing search for bioactive constituents from Cameroonian medicinal plants we also examined the stem bark of beilschmiedia obscura which showed good antibacterial activity against bacillus subtilis with MIC of 167 µM and moderate antiplasmodial activity in vitro against plasmodium falciparum chloroquine resistant W2 strain with IC50 of 12 µg/ml during preliminary screening. The methanolic extract was selectively extracted with dichloromethane. The dichloromethane soluble part was fractionated and purified using column chromatography and yielded a new compound obscurine (20), along with the known compounds 3-ß-acetylsitosterol (21), ß-sitosterol (22), 2,3-dihydroxypropylhexacosanoate (23), 1-(26-ferulyloxyhexacosanoyl)-glycerol (24), 1-(26-hydroxyhexacosanoyl)-glycerol (25) and ß-sitosterol-3-O-D-glucopyranose (26). These compounds were tested for their antiplasmodial activity in vitro by the time of the project completion.

Following our study, the methanolic extract of canthium subcordatum which was active against plasmodium falciparum and bacteria in vitro during preliminary screening was investigated. Eight compounds were isolated and characterised as ursolic acid (27), stigmasterol (28), quinovic acid (29), 3-O-ß-D-glucopyranosyl quinovic acid (30), methyl 7-formyl-1,6-dihydrocyclopenta[c]pyran-4-carboxylate (31), 28-O-ß-(6´-deoxy)-D-glucopyranosylquinovic acid (32), 28-O-ß-D-glucopyranoside quinovic acid (33) and the cylclic ester 34. These compounds were tested in vitro for their antimicrobial activity against four strains of microbes, namely Escherichia coli, streptococcus feacalis, staphylococcus aureus and klebsiella pneumonia. They showed weak antibacterial activities compared to reference drugs ampicillin and gentamicin. These compounds were furthermore tested for their antiplasmodial activity in vitro by the time of the project completion.

The interesting results that were obtained valorised the biodiversity of Cameroon and highlighted the antiplasmodial potency of the studied plants. These results contributed to the validation of the use of these plants in Cameroon traditional medicine and indicated that they might be investigated in search for lead compounds for the development of new drugs against malaria. In the continuation of this study, we planned to evaluate the toxicity of these extracts, fractions and isolated compounds, synthesise derivatives of the active compounds in order to study the relation between structure and activity and prepare enriched active fractions that could be used for the formulation for new antimalaria agents to make them efficient and affordable.