ABSTRACT
Malaria is a life threatening disease that affects approximately 1.2 billion people worldwide. The emergence of drug resistance parasite to currently available drugs and the spread of insecticide resistance mosquito vector have resulted in drawback to malaria control programs. Hence the need to develop novel antiplasmodial agent that will be cheaper and effective against the Plasmodium parasite. This study was aimed at evaluating the antiplasmodial property and cytotoxicity of methanol extracts of Tetrorchidium didymostemon leaves and stem bark. The study entailed preliminary evaluation of the phytochemicals and in vitro antioxidant activity of the plant extracts. The in vitro antiplasmodial property of the plant extracts (using the candle jar method) in chloroquine sensitive strain of P. falciparum (3D7 strain) and cytotoxicity (using Vero cell line) were assessed. In vivo antiplasmodial property of the extracts was evaluated on Plasmodium berghei ANKA infected Swiss mice. Fractionation of the most active extract; in vitro antiplasmodial activity and cytotoxicity of the subsequent fractions were also carried out. The most active fraction was analyzed using gas chromatography with flame ionization detector (GC-FID). Preliminary investigation revealed the presence of flavonoids, phenolics, cardiac glycosides, tannins, saponins, terpenoids, sterols, quinones, coumarins, and alkaloids in both extracts. The leaves extract had significantly higher (p < 0.05) DPPH radicals scavenging ability (IC50 = 41.29 µg/mL) when compared to the stem bark extract (87.03 µg/mL). Also, the leaves extract had a higher in vitro antiplasmodial activity (IC50 = 25 ± 0.81 µg/mL) in comparison to the stem bark extract (IC50 = 50 ± 1.09 µg/mL). Both extracts were found to be non-cytotoxic against Vero cells (IC50 values > 30 µg/mL). However, the leaves extract had higher selectivity index than the stem bark extract. The LD50 values of both extracts were above 5000 mg/kg body weight. The leaves extract, at 500 mg/kg body weight, showed higher curative potential (67.92%) and mean survival time (MST) (20.4 days) than the stem bark counterpart (48.37% and 18.6 days, respectively). Similarly, the leaves extract at 500 mg/kg b. wt. also showed a higher suppressive potential of parasite growth (73.11%) in contrast to the stem bark extract (49.67%). Biochemically, T. didymostemon leaves extract was able to ameliorate changes in some hematological indices, liver function enzymes, oxidative stress indices and histopathological changes in the liver, spleen and brain induced by malaria infection. Furthermore, the leaves extract had a higher immunomodulatory effect on TNF-α and IFN-γ than the stem bark extract. Fractionation of the xxvi leaves extract revealed higher antioxidant property and phytochemicals in the dichloromethane fraction when compared to the n-hexane, ethylacetate and hydromethanol fractions. However, nhexane fraction had a significantly higher (p < 0.05) in vitro antiplasmodial property (IC50 = 3.92 ± 0.06 µg/mL) and selectivity index relative to the other fractions. GC-FID analysis of the nhexane fraction revealed high amount of flavonoid (kaempferol) and terpenes (pinene and βcaryophyllene) which have been reported to have antiplasmodial property. This study provides preliminary evidence for the ethnomedicinal claim on the efficacy of T. didymostemon extracts in the treatment of malaria infection.
