IN VITRO ANTIPLASMODIAL PROPERTY AND CYTOTOXICITY

ABSTRACT

Malaria is one of the most important parasitic diseases and a worldwide threat. It remains a major problem in Africa and is responsible for the annual death of over one million children below the age of five years. Plasmodium falciparum is the most widespread etiological agent for human malaria and has become increasingly resistant to standard antimalarial drugs. This has necessitated the continuous search for new drugs, particularly with novel modes of action in the management of the disease. The medicinal plants have invariably been a rich source for new drugs and some antimalarial drugs in use today (quinine and artemisinin) were either obtained from plants or developed using their chemical structures as templates. The aim of this study was to evaluate the antiplasmodial and cytotoxic properties of methanol extract of Tetrorchidium didymostemon leaf and stem bark. The bioactive principles present in T. didymostemon leaves and stem bark were extracted using methanol as solvent. Phytochemical screening of the phytochemicals present in the extracts was carried out using standard procedures. Plasmodium falciparum was cultivated and maintained in fresh O+ human erythrocytes at 3% haematocrit in complete medium (RPMI 1640 with Albumax II). The ring stage synchronized P. falciparum strain (chloroquine sensitive) and 1% parasitemia, (5% hematocrit) were incubated in a 96-well microplate for 48 h with different concentrations of the leaves and stem bark extracts ranging from (1.56 to 100 μg/mL). RPMI and 0.4% DMSO were used as negative controls while chloroquine (1μM) served as the positive control. The extracts were respectively tested for their cytotoxicity effect in 96 microplate format against normal Vero cells. The percentage viability of the cells was evaluated using Trypan blue dye exclusion method. The cytotoxicity of Tetrorchidium didymostemon on Vero cell was evaluated by the MTT assay. Cisplastin which is a standard cytotoxic drug was used as positive control. Preliminary phytochemical screening test on the extracts showed that they both contain flavonoids, phenolics, cardiac glycosides, tannins, saponins, terpenoids, sterols, quinones, coumarins, and alkaloids while phlobatannins was detected in the leaves extract only. Of the 2 plant extracts tested, the leaf extract of Tetrorchidium didymostemon showed significantly (p < 0.05) higher antiplasmodial activity (IC50 of 25 μg/mL) when compared with the stem bark 14 extract (50 μg/mL). The MTT assay revealed that the CC50 values for the leaf and stem extracts of Tetrorchidium didymostemon on normal Vero cells were 1747.26 ± 12.45 μg/mL and 1365.30 ± 18.87 μg/mL, respectively in contrast to the reference cytotoxic drug, ciplastin (26.62 ± 0.25 μg/mL). The selectivity indices of the leaf and stem bark extracts were 12.29 and 20.18, respectively. The results from this study revealed that the leaves extract of T. didymostemon was most active against the Plasmodium falciparum 3D7 (Pf3D7) strain than the stem bark extract. Evidence for the ethnomedicinal claim on the safety and efficacy of Tetrorchidium didymostemon in the treatment of malaria infection is therefore provided.