Isolation of Natural Product Hits from Peperomia species with Synergistic Activity against Resistant Plasmodium falciparum Strains

Abstract

Aims: This study investigated the antiplasmodial activity of crude extracts, fractions and pure isolates of P. vulcanica and P. fernandopoioana (Piperaceae). Toxicity and interaction between the most active natural products were also assessed. Study Design: Bioassay-guided approach was used to identify and further investigate the most active components against chloroquine-sensitive and resistant P. falciparum strains.  Place and Duration of Study: Departments of Biochemistry and Molecular Biology, Chemistry and Biotechnology Unit, Faculty of Science, University of Buea, Cameroon for one year. Methodology: Test substances were prepared from the two plants and screened on four strains of P. falciparum (chloroquine-sensitive 3D7, multidrug resistant W2mef and Dd2, and a field isolate SHF4). Activity was determined by fluorescence microscopy and the parasite lactate dehydrogenase assay. The most active pure compounds were tested in combination and also tested in BALB/c mice for acute toxicity. Results: The crude extracts showed moderate activity (IC50 from 7.05 – 22.59 µg/mL). Eight of 16 compounds isolated from the hexane and methylene chloride extracts of P. vulcanica showed high activity (IC50 from 0.89 - 3.23 µg/mL against W2mef). Four of the most active compounds tested in two different combinations showed synergism and two of them showed no signs of acute toxicity. Four fully characterized isolates: 5-Demethyltangeretin (1), Stigmasterol (2), Matairesinol dimethyl ether (3) and Peperovulcanone A (4) showed high to moderate activity (IC50s ranging from 1.14 – 22.29 µg/mL). Conclusion: These findings support the use of P. vulcanica in traditional medicine for the treatment of malaria and the plant material should be further evaluated towards development into a phytomedicine. Further exploration of the hits in combination with standard antimalarials may yield new efficacious antimalarial treatments.