ANTI-MALARIAL ACTIVITIES AND TOXICITY LEVELS OF EXTRACTS OF FOUR SELECTED MEDICINAL PLANTS USED IN PARTS OF KENYA

Abstract

Malaria is a life threatening vector borne disease and with a long history in Africa South of Sahara. Conventional drugs have been used to manage malaria only during the last 5 decades. The spectacular results of western medicine and medical teaching based upon it led to devaluation of the use of herbal medicine in malaria treatment and associated science-driven research and developement on this medicine. On the other hand, resistance development to most of the existing malaria drugs, and recently to the first line Artemisinine based drug in Cambodia, and the increasing burden of the disease in Africa, demand a fresh look at the potential of traditional medicines. Significantly, crude preparations from different communities in malaria endemic areas have been in use in Kenya. The main aim of this study was to determine the efficacy and safety of plant extracts from four selected medicinal plants used in Kenya for treatment of malaria. To achieve this, crude extracts from four medicinal plants with traditional reputation were extracted using methanol and water solvents. Their yields were determined and then, they were screened for their in vitro antiplasmodial activity using a radioisotopic uptake of hypoxanthine against chloroquine sensitive D6 strain and the Chloroquine resistant W2 strain of Plasmodium falciparum. They were also screened for their antimalarial activity in vivo in a 4 day suppressive test against Plasmodium berghei ANKA. Animal acute toxicity and cell cytotoxicity using VERO E 99 cells was also carried out for all the extracts. It was found out that all the crude water extracts were significantly (P=0.023) more than the crude methanol extracts and were all active against chloroquine sensitive D6 strain of Plasmodium falciparum. Aerial parts of Fuerstia africana, methanol extract had the highest activity (IC50 , 1.841± 0.82 μg/ml) followed by stem bark of Ximenia americana, methanol extract ( IC50, 2.108 μg/ml) and the roots of Sericocomopsis hilderbrandtii (IC50, 2.12 μg/ml) against D6 strain of Plasmodium falciparum. All water extracts also had high antiplasmodial activities against D6 strain. Methanol extracts of Sericocomopsis hilderbrandtii aerial parts, roots, Pentas lanceolata aerial part and Ximenia americana stem bark had moderate antiplasmodial activity against W2 strain of Plasmodium falciparum. Water extracts of Pentas lanceolata aerial part and Fuerstia africana also had moderate activities against chloroquine resistant W2 strain of Plasmodium falciparum. The roots and aerial parts of Sericocomopsis hilderbrandtii and stem bark of Ximenia americana had low antiplasmodial activities against W2 strain of Plasmodium falciparum. Of the ten extracts that were tested in vivo seven showed good anti-malarial activity with Chemosuppresion ranging from 30.29% to 64.92% while three demonstrated low activity. There was significant difference (P=0.012) in the parasite density between the mice treated with the active plant extracts and the untreated controls. Whereas most of the plant extracts were not cytotoxic at 100μg/ml, Fuerstia africana was moderately toxic with CC50 at 63.45μg/ml. All the extracts tested for acute toxicity were safe with LD50 > 5000mg/Kg. The confirmed activity activity of most of these plants extracts and their lack of toxicity in mice and in VERO E 99 cells may partially validate their use as antimalarials by some Kenyan communities. It was therefore recommended that some of these extracts should be further evaluated for large scale production, formulation and use.