In vitro antiplasmodial activity of some plants used in Kisii, Kenya against malaria and their chloroquine potentiation effects

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Abstract

Fifty-five organic and aqueous extracts of 11 plants used in malaria therapy in Kisii District, Kenya were tested in vitro against chloroquine (CQ)-sensitive and resistant strains of Plasmodium falciparum. Of the plants tested, 73% were active (IC50<100 μg/ml). Three plants, Vernonia lasiopus, Rhamnus prinoides and Ficus sur afforded extracts with IC50 values ranging less than 30 μg/ml against both CQ-sensitive and resistant strains. Combination of some extracts with CQ against the multi-drug resistant P. falciparum isolate V1/S revealed some synergistic effect. The plant extracts with low IC50 values may be used as sources for novel antimalarial compounds to be used alone or in combination with CQ.

Introduction

Plasmodium falciparum, the most widespread etiological agent for human malaria is becoming increasingly resistant to standard antimalarial drugs which necessitates a continuous effort to search for new antimalarial drugs. Plants have invariably been a rich source for new drugs and some antimalarial drugs in use today (quinine and artemisinine) were either obtained from plants or developed using their chemical structures as templates (Gessler et al., 1994). Scientific evaluation of medicinal plants used in the preparation of traditional medicine has in the past provided modern medicine with effective drugs for the treatment of parasitic diseases (Iwu et al., 1994).

Over the past years, the scientific progress in malaria chemotherapy has been more on the effects of already existing drugs than the development of new ones. The search for new antimalarial drugs has regained importance due to resurgence of drug resistant parasites in many countries. Malaria chemotherapy and prophylaxis are now targeting drug combinations with the hope of achieving drug potentiation to circumvent or delay resistance (Zucker and Campbell, 1993, WHO, 2000). In South East Asia, the use of firstline drugs with artemisinine derivates such as artesunate have shown to increase efficacy, protect drugs against resistance development, reduce transmission of malaria and increase the lifespan of antimalarial compounds (TDR, 2000). In Kenya, chloroquine (CQ) has been discontinued as the firstline treatment for malaria due to overwhelming presence of resistant P. falciparum strains. Reports of resistance to sulfadoxine-pyrimethamine, which is currently used as the firstline drug, are on the increase (WHO, 1998, WHO, 2000, USN, 2001).

Section snippets

Plant materials

The plant samples were collected between March and September 1999 from Kisii District, Nyanza Province, Kenya based on ethnomedical use through interviews with local communities (Table 1). These were identified and voucher specimens deposited at the Herbarium, Botany Department, University of Nairobi, Nairobi. The plant parts were air-dried under shade and ground using a laboratory mill (root bark and stem bark) and a kitchen blender (leaves).

Extraction

For each plant part, 25 g of the chaff was boiled

Results and discussion

In the preliminary studies, all the 55 extracts from the 11 plants were screened against K39. At least one extract from 73% of all the plants screened against K39, a CQ-sensitive P. falciparum isolate, showed activity of IC50 values below 100 μg/ml (Table 2). The extracts that were with IC50<20 μg/ml were further assayed against NF 54, ENT 30 and V1/S (Table 3).

For K39, the two plants from Rhamnaceae (R. prinoides and R. staddo) showed mild antiplasmodial activity with methanol extracts being

Conclusion

The fact that 73% of the plants screened in vitro had some level of antiplasmodial activity would justify their ethnopharmacological uses as traditional antimalarials. After detailed in vivo antimalarial evaluation and thorough toxicological studies, some of these plants may be recommended as antimalarials in known dosages especially in rural communities where the conventional drugs are unaffordable or unavailable and the health facilities inaccessible. Similarly, some of these plants like V.

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