Propolis as anti-inflammatory and anti-allergic compounds: which role for flavonoids?

A recent article by Nakamura R. and colleagues has reported the effects of propolis from different geographical areas on mast cell degranulation [1]. As well as flavonoids, propolis is well known among general population for its anti-allergic properties [2,3]. Actually, propolis has plenty of biological and pharmacological properties and its mechanisms of action have been widely investigated in the last years, using different experimental models in vitro and in vivo. While several researchers are interested in the investigation of isolated compounds responsible for propolis action, there is lack of clinical research on the effects of this substance; so, clinical investigation is needed to evaluate propolis potential in patients or healthy individuals, in order to understand under which conditions propolis may promote health and prevent allergy or inflammatory ailments. Some criticismabout propolis benefits has also been raised [4,5], anyway propolis appears to represent nowadays one possible investment for research in drug therapy of allergy [3]. Biological activity of propolis may depend on the geographical area from which the propolis is produced, as this should affect the composition in polyphenolic compounds with healthy and/or preventive potential. In Chinese propolis the following flavonoids were identified in ethanol extracts by normal-phase chromatography: chrysin, galandin, kaempferol, 3-O-methyl-kaempferol but however their amounts in the fractionswere very low [1].Whilewater (WEP) and ethanol (EEP) extracts from propolis coming from Brazil had a higher content in flavonoids than propolis from China, the latter proved to possess the strongest inhibition of antigen-induced mast cell degranulation and the lowest harmful effects on RBL-2H3 mast cell lines [1]. This evidence should suggest that anti-allergic and/or anti-inflammatory activity of propolis, rather than on single molecules, might depend on a complex interaction between different natural phenolic compounds. Phenolic acids, such as caffeic acid, andflavonoids belong to the same polyphenolic derivatives from phenylalanine and shikimic acid biochemical pathway: their kinship gives them the potential to behave as competitors or as synergistic substances, depending on doses, composition in extracts, cell type and molecular asset. Chrysin and kaempferol were identified as the major anti-allergic components in EEP. Chrysin is commonlypresent in propolis [2]; itwas associated, as a main dietary component with quercetin, to the UVinduced suppression of the contact hypersensitivity (CHS) response to picryl chloride (PCl) in SKH-1 mice [6], and, as with apigenin, to the down-regulation of IgE high affinity receptor (FcεRI) in basophil line KU812, due to ERK1/2 kinase inhibition [7]. Kaempferol effects on basophil and mast cells have been extensively reviewed [2] and one suggestion for its inhibitory effect exerted on RBL-2H3 comes from the involvement of heme oxygenase-1 [1]. The presence of caffeic acid phenetyl ester (CAPE) in Chinese propolis as a current inhibitor ofmast cell degranulation, is another hallmark of phenolic compounds as antiallergic substances. Caffeic acid is commonly present in propolis