Comparison of antioxidant and anti-inflammatory activity profiles of various chemically characterized Turkish propolis sub-types: Which propolis type is a promising source for pharmaceutical product development?

Abstract Propolis shows a great variation in its chemical content depending on the vegetation around the beehive. Determination of its botanical origin and the chemical characterization are the most important issues for the standardization and the quality evaluation for propolis samples that are intended to be used in the pharmaceutical industry. This study has focused on the identification of the botanical origin of 47 propolis samples collected from different locations in the Black Sea Region of Turkey. Firstly, palynological and chromatographic analyses were carried out. Then, the major distinguishing components were identified by high-performance thin-layer chromatography (HPTLC), or by nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS) after isolation of the components. Based on the results, the samples were categorized into three main groups as black poplar-type, Euroasian aspen-type, and non-phenolic-type. Key markers of black poplar-type were assigned as phenolic acids and flavonoids, whereas lasiocarpin B and C (phenolic glycerides) were determined as markers for Euroasian aspen-type propolis. The total phenolics and flavonoid contents (TPC and TFC) and antioxidant capacities of the samples were comparatively assessed by free radical-scavenging activity (DPPH) and metal-reducing activity (CUPRAC and FRAP) methods. Additionally, HPTLC-direct bioautography was applied to determine the contribution of components to antioxidant activity. Hierarchical clustering analysis revealed similarities in TFC, TPC values, and antioxidant activity related to the sample origins' geographic proximity. The anti-inflammatory activities of the black poplar sub-type and Euroasian aspen-type propolis samples were comparatively investigated on RAW 264.7 macrophage cells. The black poplar-type propolis extract dominated by caffeic acid, caffeic acid phenethyl ester, apigenin, quercetin, kaempferol, pinocembrin, and galangin exhibited the highest anti-inflammatory and antioxidant activities. Therefore, chemically characterized black poplar-type propolis may be suggested as a good candidate to develop pharmaceutical products.