Anti-inflammatory and antibacterial profiles of selected compounds found in South African propolis

Introduction Propolis is a complex resinous substance manufactured by honeybees. It consists of exudates collected from the parts of various plant species, substances secreted from bee metabolism, and materials which are introduced during propolis elaboration. In general, it is composed of 50% resin and vegetable balsam, 30% wax, 10% essential and aromatic oils, 5% pollen and 5% various other organic substances including debris. Exudates collected from leaves and leaf buds, mucilages, gums, resins and latices contribute the most to the constituents of propolis. Of these, the largest group of compounds is the flavonoid pigments, such as luteolin, eriodictyol, galangin and quercetin. Flavonoids are ubiquitous in the plant kingdom, occurring naturally in foods and at concentrations of <0.1–0.7% in propolis. Other non-flavonoid constituents include caffeic acids and their esters (2–20%), such as caffeic acid phenethyl ester (CAPE). Since the chemical composition of propolis is largely dependent on plant exudates, the geographical region in which particular plants are present and the season during which they are harvested play an important role. This chemical diversity becomes more apparent as it has been reported that between ten and two hundred different compounds, at varying concentrations, were detected in propolis from different collection sites. In addition, it has been shown that the species of bee influences the composition of propolis. Thus the chemical standardisation of propolis has been difficult to achieve. Bees use propolis to scaffold the hive and embalm killed invader organisms. Propolis has been recognised by man for its medicinal properties since ancient times. Claims to promote propolis as a ‘global remedy’ are supported by its numerous medicinal uses that include, amongst others, antibacterial and anti-inflammatory properties. The list of preparations and uses is nearly endless. For example, propolis is used in toothpaste to prevent gingivitis and in cosmetic products to promote tissue regeneration. Considering the striking variability in the chemical composition of propolis and its claimed therapeutic uses, it is unknown whether observed activity is dependent on the concentrations of specific constituents or on potentiation between these. The goal of this study was to investigate the pharmacological properties of some components commonly found in propolis, taking into consideration that in South African propolis, flavonoids are the main constituents. Specifically, the ability of each of the flavonoids luteolin, quercetin and galangin to reduce croton oil-induced swelling in a mouse model was investigated. In addition, the susceptibility of the important invasive pathogen Staphylococcus aureus to each of the flavonoids luteolin, eriodictyol and quercetin was tested. Since these flavonoids exhibited little antibacterial activity alone, it was sought to identify potential potentiation of activity in combination with CAPE. Whereas antibacterial activity was less pronounced and variable when flavonoids were combined with CAPE, the topical anti-inflammatory activity of all the flavonoids was significant on their own.