The phytochemical investigation on the surface exudate of Microglossa pyrifolia: Case study as anti-plasmodial, anti-oxidant, antileishmanial and anti-microbial

Abstract

Malaria is a global disease prevalent in the tropics caused by Plasmodium species. It affects 300-500 million people and kills 1.5-2.7 million people annually. To date, a large number of herbal remedies are used to treat malaria and manage related fever; nevertheless, in most of these cases of plant therapies, efficacies have not been proven nor have their active components been identified. Most malaria episodes are accompanied by clinical complications attributable to radical oxygen species. In an effort to address the problem of malaria and the associated complications, phytochemical analysis of Microglassa pyrifolia (Asteraceae), used to treat malaria ethnomedically, was investigated for compounds with anti-plasmodial, antimicrobial, antileishmanial and anti-oxidant activities. In the preliminary investigation, the crude extracts of aerial parts of the plant [dichloromethane: methanol (1:1) extract] had an anti-plasmodial activity against D6 and W2 strains of Plasmodium falciparum of IC50 value of 8.0 and 13.0 µg/ml respectively. In this study crude leaf surface extract was obtained by dipping a handful of fresh leaves into ethyl acetate for a short period of 15 seconds to avoid the extraction of internal tissue components. Separation of compounds was carried out using chromatographic methods and their identification done by spectroscopic methods. A total of seven compounds were isolated, namely; 5,7,4’-trihydroxy-3,8,3’-trimethoxyflavone (81) 5,7,4’-trihydroxy-3,8,3’,5’- tetramethoxyflavone (82), 5,3’4’-trihydroxy-7-methoxyflavanone (83), 5,7,3’-trihydroxy- 3,8,2’,5’-tetramethoxyflavone (84), 5,3’4’-trihydroxy-3,7,8-trimethoxyflavone (85), 8- acetoxyisochiliolide lactone (86) and 7,8-epoxyisocholiolide lactone (87) out of which compounds 82, 84 and 86 were new. The in vitro anti-plasmodial tests were done by a colorimetric assay that determined the parasitic lactate dehydrogenase (pLDH) activity in 96- well microplate. Anti-oxidant activity was performed by UV-VIS spectrometry method based on the stable radical compound DPPH. The compounds showed no anti-plasmodial, anti-bacterial, anti-fungal and anti-leishmanial activities except 5,3,4’-trihydroxy-7-methoxyflavone (83) which exhibited mild anti-leishmanial activity (IC50 13.13 µg/ml). Anti-oxidant activities were exhibited, with IC50 of 6.02 ±.0.2 for 5,7,4’-trihydroxy-3,8,3’-trimethoxyflavone (81), 6.45 ± 0.3 for 5,7,4’-trihydroxy-3,8,3’5’-tetramethoxyflavone (82), 8.5 ± 0.3 for 5,3’4’-trihydroxy-7- methoxyflavonone (83), 8.79 ± 0.3 for 5,7,3’-trihydroxy-8,4’5’-trimethoxyflavone (84) and 6.02 ± 0.2 for 5,3’,4’-trihydroxy-3,7,8-trimethoxyflavone (85)