Polyphenolic composition and biological activities of Bulgarian propolis samples with potential pharmaceutical applications

Propolis (bee glue) is a complex biological substance produced by honeybee (Apis mellifera L.) and used as a natural remedy due to its therapeutic properties. The present research aimed to investigate the phenolic content, antioxidant, acetylcholinesterase inhibitory, antihemolytic, and ex vivo anti-inflammatory activities of DMSO extracts of six propolis samples (P1-P6) from three regions of Bulgaria. The DMSO extracts exhibited TPC values from 189.30 to 290.80 mg GAE.g-1, TFC values from 64.41 to 151.60 mg QE.g-1 and significant antioxidant activity (863.73 - 1799.22 mM TE.g-1 by the DPPH assay, and 796.86 - 1168.02 mM TE.g-1 by the FRAP assay). The values of AChE inhibitory activity at concentration of 1 mg.ml-1 ranged between 40.12 and 46.44% (IC50 = 1.07 - 1.39 mg.ml-1). All extracts demonstrated high antihemolytic activity, which at concentration of 0.5 mg.ml-1 showed erythrocyte protection of 76.28 - 89.32% (IC50 = 0.06 - 0.14 mg.ml-1). The results of the immunohistochemical analysis showed that extracts P1, P2, P3, P4 and P6 suppressed the expression of IL-1β and NOS3 in varying degree. The samples P1 and P2 completely suppressed NOS3 expression and strongly reduced the intensity of IL-1β expression; consequently, they had the highest ex vivo anti-inflammatory activity. Based on the results, we can conclude that the investigated propolis samples possessed promising antioxidant and anti-inflammatory potential. Therefore, they can find application as prospective therapeutic agents.