Abstract:
Recent interest in the immunomodulatory effects of honey and the components responsible for this activity has led to numerous investigations. The bioactive properties of honey to heal wounds and promote the growth of new tissues have been rediscovered. Some of this activity could be explained by the presence of arabinogalactan proteins (AGPs), an immunomodulatory component in honey. The main objective of this study has been to determine the profile of and quantify the AGPs that often present as type II arabinogalactans (AG-II), which may play an important role in wound healing through stimulation of the immune system. A precise structural elucidation of AGPs from different types of New Zealand honey is critical in order to explain their structure and immunomodulatory activity. As part of this present investigation, five New Zealand honey samples (derived predominantly from kanuka, manuka, and clover) were purified to obtain pure AGPs from precipitation with β-glucosyl Yariv reagent. The purified AGPs were further subjected to structural and immunostimulatory activity investigation. However, the isolation and purification process has indicated that only honey used in skincare, derived predominantly from kanuka, was rich in AGPs. The AGPs’ concentration variation was analysed with both crude and ultrafiltered honeys through gel electrophoresis assay with β-glucosyl Yariv reactivity. The sub investigation exhibited similar concentration levels of AGPs that correlated with the yield from pure AGPs. It was concluded that the purification process is not a factor for poor yields of AGPs. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy was employed for the first time to investigate the AGPs’ structural composition; however, further process improvement is needed to obtain significant spectra. Liquid NMR spectroscopy has indicated that the AGPs from honey skin (Kanuka # 4), honey which is used for skin care, show similar structural composition to the AGPs that have previously been reported in kanuka (Steinhorn, Sims, Carnachan, Carr, & Schlothauer, 2011). ELISA assay was carried out on purified AGPs and crude honeys to evaluate their ability to stimulate the release of tumour necrosis factor-α (TNF-α). An immunomodulatory effect was demonstrated by honey skin (Kanuka # 4) AGPs only. The immunostimulatory expression shown by all the crude honeys may be due to their particular or synergistic action with immunostimulatory components in honey. In summary, this research has shown that AGPs are mostly present in honey that is derived predominantly from kanuka. Further studies could be done to characterise AGPs from different international honeys and isolate AGPs using alternative purification methods.