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

Abstract

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 β-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.