Antimalarial activity of hypoxis colchicifolia, bak, mimusops caffra, E. Mey. ex A.DC and mimusops obtusifolia, lam from South Africa
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Date
2014
Journal Title
Journal ISSN
Volume Title
Publisher
University of Zululand
Abstract
Malaria is one of the major health problems of today, more so since the parasite has
become resistant to the currently used drugs. There is a need for research into new
drugs from medicinal plant species which are used by local traditional healers for the
treatment of malaria. Mimusops caffra, E.Mey. ex A.DC, Mimusops obtusifolia, Lam
(both members of Sapotaceae family) and Hypoxis colchicifolia, Bak are used by
traditional healers in Zululand to manage malaria.
In this study, the plants were separately extracted exhaustively with methanol, ethyl
acetate, hexane and dichloromethane (DCM). The crude extracts were screened for
antioxidant, antipyretic, and antimalarial activity.
The antioxidant activity of the methanol extracts was determined by measuring the
decrease in the colour of an oxidative system in the presence and absence of the
extract. The various antioxidant activities tested include free radical scavenging, Fe2+
chelating, reducing power, and total antioxidant capacity. Yeast induced pyrexia was
used to evaluate the antipyretic activity of the plant extracts. In vitro antimalarial
activity of the extracts was investigated against the chloroquine sensitive (CQS)
strain of Plasmodium falciparum (D10) and the in vivo antiplasmodial activity was
done against Plasmodium berghei. The most active in vitro antiplasmodial crude
extracts were subjected to isolation, purification and characterization of the active
components using column chromatographic techniques. The triterpenes isolated
were confirmed using Nuclear Magnetic Resonance (NMR) techniques with the
application of 2D-NMR (1H-1H, 13C, DEPT, COSY, HMQC, HMBC and NOESY) and
infrared (IR). The preliminary phytochemical analysis of plants’ extracts revealed the presence
mainly of saponins, tannins, alkaloids and flavonoids. Methanol extracts of the plants
exhibited strong scavenging of 2,2-Diphenyl-1-picryl-hydrazyl (DPPH) and 3-
ethylbenzothiazoline-6-sulfonate (ABTS) radicals, but showed poor (< 50%) radical
scavenging of nitric oxide, superoxide and hydroxyl radicals. The DCM extract of the leaves of M. caffra and the ethyl acetate extract of the bark
of M. obtusifolia exhibited antimalarial activity against the chloroquine sensitive
(CQS) strain of Plasmodium falciparum (D10). The leaf extracts of M. caffra
exhibited higher activity (IC50=2.14 μg/ml) compared to the extracts of M. obtusifolia
(IC50=32.5 μg/ml). The pentacyclic tritepenoid (PTCs) ursolic acid isolated from the
leaves of M. caffra was most active (IC50 = 6.8 μg/mL) in comparison to taraxerol and
Sawamilletin isolated from the stem bark of M. obtusifolia with IC50 of > 100.
Chemical modification of the ursolic acid to 3β-acetylursolic acid greatly enhanced
(72%) its anti-plasmodial activity. The 3β-acetylursolic acid reduced parasitaemia
against Plasmodium berghei by 94.01% in in vivo studies in mice.
An attempt to elucidate the possible mechanism of action for the active compound
was carried out.
3β-acetylursolic acid prevented the aggregation of MDH in vitro but did not prevent
the expression of PfHsp 70 in E.coli XL1 blue cells. However, it showed PfHsp 70
ATPase activity with the specific activity of 65 (amount of phosphate released 73.83
nmolPi/min/mg). The cytotoxicity of 3β-acetylursolic acid (IC50) to two human cell
lines (HEK293 and HepG2) was 366.00 μg/ml and 566.09 μg/mL, respectively. The results validate the use of these plants in folk medicine.
Description
Dissertation submitted to the Department of Biochemistry and Microbiology, in the Faculty
of Science and Agriculture, in fulfillment of the requirements for Doctoral (PhD) degree in Biochemistry at the University of Zululand, South Africa, 2014.
Keywords
Malaria -- treatment of, Malaria -- traditional healers