Abstract
Extracts from twelve samples of propolis collected from different regions of Libya were tested for their activity against Trypanosoma brucei, Leishmania donovani, Plasmodium falciparum, Crithidia fasciculata and Mycobacterium marinum and the cytotoxicity of the extracts was tested against mammalian cells. All the extracts were active to some degree against all of the protozoa and the mycobacterium, exhibiting a range of EC50 values between 1.65 and 53.6 μg/ml. The toxicity against mammalian cell lines was only moderate; the most active extract against the protozoan species, P2, displayed an IC50 value of 53.2 μg/ml. The extracts were profiled by using liquid chromatography coupled to high resolution mass spectrometry. The data sets were extracted using m/z Mine and the accurate masses of the features extracted were searched against the Dictionary of Natural Products (DNP). A principal component analysis (PCA) model was constructed which, in combination with hierarchical cluster analysis (HCA), divided the samples into five groups. The outlying groups had different sets of dominant compounds in the extracts, which could be characterised by their elemental composition. Orthogonal partial least squares (OPLS) analysis was used to link the activity of each extract against the different micro-organisms to particular components in the extracts.
Highlights
Bees collect propolis from plants and use it to coat the inside surfaces of the hive in order to maintain a sterile environment
In a recent publication it was found that Crithidia mellificae and Nosema ceranae infections are associated with winter mortality in European bees [5]
Crithidia, which are classified as lower Trypanosomatidae, which are very prevalent in the infection of invertebrates, are closely related to the human pathogens of the genera Leishmania and Trypanosoma [8]
Summary
Bees collect propolis from plants and use it to coat the inside surfaces of the hive in order to maintain a sterile environment. It would seem logical that selection pressure would drive bees to collect phytochemicals that are effective against protozoa and other micro-organisms that could infect the hive [6, 7]. Since propolis is collected by bees for the specific purpose of providing phytochemical protection against pathogens, there is a strong likelihood of finding highly active antimicrobials in it which might be effective in treating humans [9]. The current work follows from our earlier work on a sample of propolis collected from the East of Libya, from which four known compounds with activity against T. brucei and L. donovani were isolated [12]. The aim of the study was to continue our chemical mapping of the composition of African propolis and carry out anti-parasitic screens in search of high activity samples which might be useful in treating human parasitic infections
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