A study of the toxicological properties of propolis samples from Europe and Saudi Arabia and of their biological activity against protozoa

Abstract

Propolis is a natural product collected by bees from plants to seal their hives for defense against external contamination, and a range of microorganisms and parasites including the protozoal species Crithidia. Propolis has been used as a folk medicine due to its therapeutic properties; thus, it is more likely that active components would be found in propolis rather than from random screening of plants. Ethanolic extracts of four samples from the UK (S224, S225, D6, D7), one from Poland(P) and two from Saudi Arabia (SB, T2) were profiled by high-resolution LC-MS and tested against a wide range of microorganisms including T. brucei, L. mexicana, C. fasiculata, S. aureus. Additionally, cell-based assays for cytotoxicity activities were evaluated. Several compounds were isolated, which are related to the three groups: flavonoids, phenylpropanoids and triterpenes. In total fifteen isolated compounds were obtained as follows: twelve from the UK samples most of which were flavonoids including 3-Acetoxypinobanksin (1), 7-Methoxychrysin (2), Kaempferol (3), Pinocembrin (4), 4’-Methoxykaempferol (5), Galangin (6), Chrysin (7), Apigenin (8), Pinostrobin (9), Cinnamic acid (10), Coumaric acid cinnamyl ester (11a) and Coumaric acid benzyl ester (11b). Two compounds were isolated from Polish propolis namely 4’,7-Dimethoxykaempferol (12) and Naringenin 4',7-dimethyl ether (13), and three compounds from a Saudi propolis sample: Hesperetin-7-methyl ether (14a), Sakuranetin (14b) and Lupeol (15). Both the crude extracts and isolated compounds displayed variable activity against the range of microorganisms which were tested against including S. aureus, T. brucei, C. fasiculata, T. congolense and L. mexicana.