Abstract:
Introduction. Honey has had a significant involvement in human societies from the earliest historical periods both for nutritional and medicinal purposes. Honey is used currently in the treatment of surface wounds and burns largely because of its antibacterial properties. Medicinal uses of honey could also be influenced by its immuno-modulatory effects, either through the production of inflammatory mediators or conversely by exerting an antiinflammatory effect. Aims. This research sought to define the immuno-modulatory effects of various New Zealand honeys, to determine the components(s) of honey responsible for inhibition of reactive oxygen production by activated neutrophils and identify the mechanism of this inhibition. Methods. RAW264.7 cells and PMA-stimulated human neutrophils were used as in vitro cell models to investigate the immuno-modulatory effects of honey. The production of inflammatory mediators was measured either directly in the presence of honey or after previous stimulation of cells with the Toll-like receptor 4 agonist lipopolysaccharide (LPS) followed by addition of honey. Superoxide (O2 -) production and NADPH oxidase activity was measured in the presence of honey and various derivatives following treatment of freshly isolated human neutrophils with the phorbol ester phorbol 12-myristate 13-acetate (PMA). Fractionation of honey by ultrafiltration, solid phase extraction (SPE) and high-performance liquid chromatography (HPLC) was used to identify fractions and components in honey that exhibit pro-and anti-inflammatory effects. Results and Conclusions. Honey exhibited an anti-proliferative effect on RAW264.7 cells, due to its high osmotic pressure caused by the high concentration of mono- and disaccharides in honey. These cells secrete pro-inflammatory mediators including nitric oxide (NO), tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) when exposed to the high molecular weight fraction of certain honeys. In contrast, honey was shown to inhibit the production of superoxide by NADPH oxidase and reduce the membrane translocation of Rac2 in PMAstimulated neutrophils. Honey components with a molecular weight less than 10 kDa (LMW fraction) but excluding hydrophobic phenolic compounds and mono- and disaccharides present in honey were found to be responsible for the inhibition of NADPH oxidase. HPLC analysis of the LMW fraction revealed similarity in elution profiles of New Zealand honeys. Therefore, this thesis presents new evidence that New Zealand honeys can selectively modulate innate immunity through the actions of different components present within honey.