In vitro antiplasmodial activity and cytotoxicity of extracts and chromatographic fractions of twigs from Pappea capensis EckI & Zeyh. (Sapindaceae).

ETHNOPHARMACOLOGICAL RELEVANCE: The Vha-Venda people of South Africa use Pappea capensis EckI & Zeyh. (Sapindaceae) twigs to treat malaria and its related symptoms. AIM OF STUDY: The main aim of this study was to evaluate the antiplasmodial and cytotoxic activity of P. capensis extracts and chromatographic fractions. Spectroscopy analysis was conducted using 1H NMR and GC-MS to tentatively identify the major classes of compounds and phytoconstituents that can be attributed to the observed antiplasmodial bioactivity. MATERIALS AND METHODS: Pappea capensis twigs were dried and then ground to fine powder. A solvent mixture of dichloromethane: methanol: water (1:0.5:0.5, v/v) was used to extract. The polar extract was separated from the non-polar. The organic extract was dried to yield a DCM (I = 60 g) extract. The methanol in the aqueous extract was evaporated using a rotary vapour and the remaining water freeze dried to yield a water extract (II = 287 g). Extract I was further partitioned using a solvent mixture of DCM: MeOH (1:1, v/v), separated and concentrated under vacuum to yield dichloromethane (III = 40 g) and methanol (IV = 15 g) extracts. A water-based decoction (V = 10 g) was also prepared to establish the clinical relevance of the preparation administered by Vha-Venda people in South Africa. Extracts II, III and IV were further subjected to silica column chromatography, eluting with a series of different solvents with increasing polarity to yield a total of 25 fractions (A - Y). In vitro antiplasmodial tests on Plasmodium falciparum (NF54) and cytotoxicity screens on mammalian L-6 rat skeletal myoblast cells were performed on all extracts and fractions. Selectivity indices (SI) were also computed for all tested extracts and fractions which were further subjected to 1H NMR spectroscopy and GC-MS analysis for the identification of the major classes of compounds present in the extracts. RESULTS: From the assayed extracts, only extract I (IC50 = 2.93 µg/ml; SI = 14), III (IC50 = 2.59 µg/ml; SI = 21) and IV (IC50 = 3.56 µg/ml; SI = 13) demonstrated the best antiplasmodial activity and selectivity. Of all assayed fractions, only N (0.6 µg/ml; SI = 91), D (0.85 µg/ml; SI = 37) and E (0.91 µg/ml; SI = 30) depicted the best antiplasmodial activity and selectivity. The 1H NMR analysis of the extracts and fractions identified the prominent class of constituents to be aliphatic based which was tentatively identified as terpenoids. When further GC-MS analysis was conducted, the presence of lupin-3-one, lupeol acetate, α-amyrin, and ß-amyrin phytoconstituents were tentatively confirmed. These constituents are triterpenoids with established antiplasmodial activity which can be tentatively attributed to the bioactivity observed in P. capensis twigs. CONCLUSION: The study validates the ethnomedicinal use of P. capensis for malaria treatment. It demonstrated the potential of discovering novel antiplasmodial constituents that could serve as drug hits through dereplication approaches where known compounds with established antimalarial activity can be bypassed to focus on the unknown.

1H NMR-based metabolomics of antimalarial plant species traditionally used by Vha-Venda people in Limpopo Province, South Africa and isolation of antiplasmodial compounds.

ETHNOPHARMACOLOGICAL RELEVANCE: The Vha-Venda people living in rural areas of Limpopo Province of South Africa regularly use traditional plant-based medicines to treat malaria. In our earlier publication, twenty indigenous plant species used to treat malaria or its symptoms by Vha-Venda people were evaluated for antiplasmodial activity. The main objective of the current study was to assess the robustness of NMR-based metabolomics in discriminating classes of secondary compounds that are responsible for the observed antimalarial activity and the isolation of antiplasmodial compounds. MATERIALS AND METHODS: Twenty dichloromethane extracts were reconstituted in CDCl3, subjected to 1H NMR-based metabolomic analysis on a Varian 600 MHz spectrometer and the acquired 1H NMR spectra were then evaluated collectively using multivariate data analysis (MDA). Principal Component Analysis (PCA) and Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA) were used to 'globally' discern antiplasmodial profiles. A contribution plot was then generated from the OPLS-DA scoring plot in an attempt to determine the classes of compounds that are responsible for the observed grouping. Further phytochemical analyses were conducted on the lipophilic extracts of Tabernaemontana elegans and Vangueria infausta subsp. infausta. These best candidates were fractionated, purified and their isolated compounds identified based on conventional chromatographic and spectroscopic techniques. RESULTS: The PCA did not separate the acquired profiles according to the detected antiplasmodial bioactivity. Application of a supervised 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. Prominent peaks were observed in the aromatic, sugar-based/N-containing and aliphatic spectral regions of the contribution plot. Two known indole alkaloids were isolated from T. elegans, and identified as tabernaemontanine (IC50 = 12.0 ±â€¯0.8 µM) and dregamine (IC50 = 62.0 ±â€¯2.4 µM). Friedelin (IC50 = 7.20 ±â€¯0.5 µM) and morindolide (IC50 = 107.1 ±â€¯0.6 µM) were isolated from V. infausta subsp. infausta. This is the first report of the rare iridoid lactone, morindolide's antimalarial activity. While these two compounds have been previously identified, this is the first account of their occurrence in the genus Vangueria. CONCLUSION: The study illustrated the potential of NMR-based metabolomics in discriminating classes of compounds that may be attributed to antiplasmodial activity. Additionally, the study demonstrated the potential of discovering novel antiplasmodial scaffolds from medicinal plants and the rationale for the bioprospecting antimalarial plant species used by Vha-Venda people.

In vitro antiplasmodial screening of ethnopharmacologically selected South African plant species used for the treatment of malaria.

ETHNOPHARMACOLOGICAL RELEVANCE: Plant species used by Venda people of South Africa in the treatment of malaria and associated symptoms were evaluated for their antiplasmodial efficacy as well as cytotoxic properties and some showed significant activity. MATERIALS AND METHODS: In vitro antiplasmodial activity and cytotoxic properties were evaluated on 20 indigenous plant species. Ground plant material was extracted in dichloromethane: 50% methanol (1:1). Antiplasmodial activity was evaluated against the chloroquine-sensitive strain of Plasmodium falciparum (NF54). The cytotoxicity of the plant extracts were assessed against mammalian L-6 rat skeletal myoblast cells and the selectivity index (SI) calculated. RESULTS: Of the 43 plant extracts evaluated, 10 exhibited pronounced antiplasmodial activity (IC50 ≤ 5 µg/ml) with good therapeutic indices (SI ≥ 10). Lipophilic plant extracts were relatively more potent than polar extracts. Tabernaemontana elegans Stapf. (Apocynaceae) and Vangueria infausta Burch. subsp. infausta (Rubiaceae) extracts displayed significant antiplasmodial activity (IC50 < 2 µg/ml). CONCLUSION: Findings of this study partly support the ethnomedical use of the investigated plant species by Venda people as antimalarial remedies. The study also highlights some of the knowledge gaps that require further phytochemical studies on the specified plant species.