It is becoming increasingly clear that one of the major biological activities of propolis is antiprotozoal activity. This study aimed to investigate the chemical profile of different propolis samples and examine their in vitro activity of against the protozoal parasites: Crithidia fasciculata, Trypansoma congolense, drug resistant Trypansoma congolense (6C3), Trypanosoma b. brucei and pentamidine resistant Trypanosoma brucei (B48), which cause disease in humans and other animals as well as insects. In addition, the samples were assayed for their toxicity against human U937 cells and murine RAW 246.7 cells in vitro. Chemical profiling was conducted by using negative ion spray ESI (LC-MS) with principal components analysis (PCA) of the data obtained and indicated that there was a wide variation in the composition of the propolis samples. The active principles were targeted for isolation by bioassay-led fractionation, using medium pressure chromatographic (MPLC) and/or other chromatographic methods, including column chromatography CC, Thin Layer Chromatography (TLC) and Size Exclusion Chromatography (SEC) and Solid-phase extraction (SPE). Twenty pure compounds were isolated, and their structures were elucidated by spectroscopic methods. Twelve triterpenoid compounds were identified from Papua New Guinea propolis as: mangiferonic acid (1), isomangiferolic acid (2), 27- hydroxyisomangiferolic acid (3), cycloartenol (4), ambonic acid (5), ambolic acid (6), 24- methylenecycloartenol (7), cycloeucalenol (8), 20-hydroxybetulin (9), botulin (10), betulinic acid (11) and madecassic acid (12). Three flavanones were isolated from Tanzanian and Zambian propolis, two of them were found to be novel compounds. They were characterized based on their spectral and physical data and identified as 6-(1,1-dimethylallyl) pinocembrin (13) and 5-hydroxy-4",4"-dimethyl-5"-methyl-5"-H-dihydrofuranol [2",3",6,7] flavanone (15). While the other compound was a known compound 6-(1,1-dimethylallyl) eriodictyol (14). Fractionation of a Nigerian propolis sample yielded of five known flavanones, isoflavan and the isoflavonoids 7-O-methylvestitol (16), neovestitol (17), vestitol (18), medicarpin (19) and 7-hydroxyflavanone (20). The samples had high levels of activity against T. congolense and T. b..brucei and moderate activity against Crithidia fasciculata. The crude sample extracts displayed a high selectivity index against kinetoplastid parasites compared to mammalian cells. The Tanzanian, Zambian and Nigerian propolis extracts were found to be more active than their purified compounds in these assays. A growth curve of T. brucei at concentrations ≥ EC50 of the most active purified compounds in these assays was conducted and found that 20-hydroxybetuline was trypanostatic with an IC50 of 2.04 μg/ml against T. b. brucei. Overall, the propolis extracts showed lower toxicity than the purified compounds to both U937 and RAW 26.7 cells.
|Date of Award||26 May 2021|
- University Of Strathclyde
|Supervisor||David Watson (Supervisor) & Ruangelie Edrada-Ebel (Supervisor)|