Isolation of tannins from Agrimonia eupatoria, Lythrum salicaria and Geum urbanum and their influence on the release of elastase from stimulated human neutrophils – structure-activity studies

Tannin rich plant materials are traditionally used as antiinflammatory and astringent agents. However, there are limited studies on chemical composition of those plant materials, as well as on bioactivity of their constituents. The aim of the study was to isolate the dominating tannin compounds from Lythri herba, Gei urbani radix and Agrimoniae eupatoriae herba and to investigate their influence on the release of elastase from stimulated human neutrophils. The structure-bioactivity relationship was also investigated. The isolation was carried out using column chromatography with Diaion HP-20 and Toyopearl HW40F eluted with MeOH-H₂O and acetone-H₂O solvent system. The assignment of chemical structures of isolated compounds was performed using 1D and 2D NMR experiments and by MS. If possible the comparisons to the literature were made. The elucidation led to the identification of salicarinin A, B and C, vescalagin and castalagin from Lythri herba, agrimoniin from A. eupatoriae herba and pedunculagin, sthenophylanin A, stachyurin and gemin A and G from G. urbani radix. All compounds were investigated as elastase release inhibitors in human neutrophils' model. Compounds were tested at concentrations of 1,5 and 20 mM. It revealed that only non-cyclic dimeric ellagitannins such as gemins A and G, agrimoniin and salicarinins A, B and C inhibit the release of elastase from neutrophils by 20 – 50% compared to control. Non-cyclic dimeric ellagitannins displayed similar properties in used model as possitive control – quercetin. The current study has shown that investigated plant materials are a rich source of tannins. The inhibitory activity towards the elastase release of dimeric ellagitannins should be considered as important contribution of those compounds to the antiinflammatory activity of plant materials from which they were isolated.

Acknowledgements: Project was financially supported by Polish National Science Center research grant PRELUDIUM UMO-2012/07/N/NZ7/01136.

Keywords: tannins, elastase, neutrophils, inflammation