Bioassay-guided isolation of active principles from Nigerian medicinal plants identifies new trypanocides with low toxicity and no cross-resistance to diamidines and arsenicals.
BACKGROUND
Leaves from the plant species studied herein are traditionally used in northern Nigeria against various protozoan infections. However, none of these herbal preparations have been standardized, nor have their toxicity to mammalian cells been investigated. In search of improved and non-toxic active antiprotozoal principles that are not cross-resistant with current anti-parasitics, we here report the results of the in vitro screening of extracts from seven selected medicinal plant species (Centrosema pubescens, Moringa oleifera, Tridax procumbens, Polyalthia longifolia, Newbouldia laevis, Eucalyptus maculate, Jathropha tanjorensis), used traditionally to treat kinetoplastid infections in Nigeria, and the isolation of their bioactive principles.


OBJECTIVE
To investigate the efficacies of medicinal plant extracts, and of compounds isolated therefrom, against kinetoplastid parasites, assess cross-resistance to existing chemotherapy, and assay their toxicity against mammalian cells in vitro.


METHODS
Plants were extracted with hexane, ethyl acetate and methanol. Active principles were isolated by bioassay-led fractionation, testing for trypanocidal activity, and identified using NMR and mass spectrometry. EC50values for their activity against wild-type and multi-drug resistant Trypanosoma brucei were obtained using the viability indicator dye resazurin.


RESULTS
Seven medicinal plants were evaluated for activity against selected kinetoplastid parasites. The result shows that crude extracts and isolated active compounds from Polyalthia longifolia and Eucalyptus maculata, in particular, display promising activity against drug-sensitive and multi-drug resistant Trypanosoma brucei. The EC50value of a clerodane (16α-hydroxy-cleroda-3,13(14)-Z-dien-15,16-olide) isolated from Polyalthia longifolia was as low as 0.38µg/mL, while a triterpenoid (3β,13β-dihydroxy-urs-11-en-28-oic acid) isolated from Eucalyptus maculata displayed an EC50of 1.58µg/mL. None of the isolated compounds displayed toxicity towards Human Embryonic Kidney cells at concentrations up to 400µg/mL. In addition, the isolated compounds were active against Leishmania mexicana, as well as against T. congolense.


CONCLUSIONS
We have isolated a clerodane compound from Polyalthia longifolia that shows low toxicity, no cross-resistance with current treatments, and promising activity against both human-infective and veterinary Trypanosoma species.
Institute of Infection, Immunity and Inflammation, University of Glasgow, United Kingdom; Department of Biochemistry, Faculty of Natural Sciences, Kogi State University, Nigeria.
Godwin Unekwuojo
GU
Ebiloma
Department of Chemistry, College of Science, University of Agriculture, Makurdi, Nigeria; Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom.
John Ogbaji
JO
Igoli
Institute of Infection, Immunity and Inflammation, University of Glasgow, United Kingdom.
Evangelos
E
Katsoulis
Institute of Infection, Immunity and Inflammation, University of Glasgow, United Kingdom.
Anne-Marie
AM
Donachie
Department of Biochemistry, College of Health sciences, University of Nigeria, Nigeria.
Anthonius
A
Eze
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom.
Alexander Ian
AI
Gray
Institute of Infection, Immunity and Inflammation, University of Glasgow, United Kingdom. Electronic address: Harry.De-Koning@glasgow.ac.uk.
Harry P
HP
de Koning
D000578:Amidines / Q000494:pharmacology*; D001152:Arsenicals / Q000494:pharmacology*; D001681:Biological Assay / Q000379:methods*; D002460:Cell Line; D045785:Diterpenes, Clerodane / Q000494:pharmacology / Q000633:toxicity; D004351:Drug Resistance; D057809:HEK293 Cells; D006801:Humans; D007894:Leishmania mexicana / Q000187:drug effects; D016488:Medicine, African Traditional; D009549:Nigeria; D018515:Plant Leaves / Q000737:chemistry; D014344:Trypanocidal Agents / Q000494:pharmacology* / Q000633:toxicity*; D014346:Trypanosoma brucei brucei / Q000187:drug effects; D014348:Trypanosoma congolense / Q000187:drug effects
D000578:Amidines; D001152:Arsenicals; D045785:Diterpenes, Clerodane; D014344:Trypanocidal Agents
Antiparasite chemotherapy; Ethnopharmacology; Extracts; Leishmania mexicana; Purified compounds; Trypanosoma brucei