'University of Pretoria - Department of Philosophy'
Abstract
Despite the significant advances achieved in lessening the burden of malaria
and other tropical diseases in recent years, protozoal infections remain a major
cause of mortality in many developing countries, with malaria accounting for a large
proportion of the recorded mortality. The main aim of this study was to bioprospect
indigenous plant species for novel antiplasmodial plant products by means of NMRbased
metabolomics.
In this study, an ethnobotanical criterion was followed in collecting twenty
indigenous plant species used to treat malaria or its symptoms by Vha-Venda people
living in Mutale Municipality of Limpopo Province, South Africa. Plant samples were
extracted in dichloromethane:50% methanol (1:1), separated into polar and nonpolar
fractions, and tested on Trypanosoma brucei rhodesiense, T. cruzi, Leishmania
donovani and Plasmodium falciparum. Plant extracts were correspondingly
subjected to an antiproliferative bioassay against mammalian skeletal myoblast cells.
The current study is the first scientific account on the significant
antileishmanial efficacy (IC50 ? 5 ?g/ml) of Bridelia mollis (Phyllanthaceae),
Vangueria infausta subsp. infausta (Rubiaceae), Syzygium cordatum (Myrtaceae)
and Xylopia parviflora (Annonaceae), as well as high antitrypanosomal activity (IC50
= 3.45 ?g/ml) of Albizia versicolor (Fabaceae). Ten plant extracts exhibited
significant in vitro antiplasmodial activity (IC50 ? 5 ?g/ml), with Tabernaemontana
elegans (IC50 = 0.331 ?g/m and IC50 = 0.834 ?g/m) and V. infausta subsp. infausta
(IC50 = 1.84 ?g/ml) being the best samples. This is the first scientific report to
document significant antiplasmodial activity of extracts from T. elegans. The findings
of this study substantiate the rationale for adopting an ethnopharmacological
approach when bioprospecting medicinal plants for antiplasmodial compounds. Dichloromethane extracts were subjected to 1H NMR-based metabolomic
analysis, where each crude extract was reconstituted in CDCl3, analysed on a Varian
600 MHz spectrometer and the acquired
1H NMR spectra were then analysed
collectively using multivariate data analysis (MDA). Principal Component Analysis
(PCA) could not separate the analysed profiles according to the detected
antiplasmodial bioactivity. Application of supervised Orthogonal Projections to Latent
Structures Discriminant Analysis (OPLS-DA) on the 1H NMR profiles resulted in a
discrimination pattern that could be correlated to the observed antimalarial
bioactivity. A contribution plot generated from the OPLS-DA scoring plot illustrated
the classes of compounds responsible for the observed grouping.
Further phytochemical analyses were conducted on lipophilic extracts of T.
elegans and V. infausta subsp. infausta. These best candidates were fractionated,
purified and identified based on conventional chromatographic and spectroscopic
techniques. Two known indole alkaloids isolated from T. elegans, were identified as
dregamine and tabernaemontanine. The antiplasmodial activity of these acyl indole
alkaloids has previously been established and ranges from moderate to good. Three
compounds were isolated from V. infausta subsp. infausta of which two were
identified as friedelin (IC50 = 3.01 ?g/ml) and morindolide (IC50 = 18.5 ?g/ml). While
these compounds have been previously identified, this is the first account of their
occurrence in the genus Vangueria and their antiplasmodial activity. An unidentified
compound with significant antiplasmodial activity (IC50 = 0.143 ?g/ml) was also
isolated. The study demonstrated the potential of discovering novel antiplasmodial
scaffolds from medicinal plants.Thesis (PhD)--University of Pretoria, 2016.Plant SciencePhDUnrestricte