Honey, polen, and propolis extracts show potent inhibitory activity against the zinc metalloenzyme carbonic anhydrase

Three different honey extracts from the endemic plant in the Black Sea region Rhododendron ponticum, were investigated for their inhibitory effects against the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), more precisely the human (h) isoforms hCA I and hCA II. Hexane, methanol, ethanol, and water solid-phase extractions (SPEs) showed inhibitory activity towards the two CA isozymes which were related to the total phenolic content. The highest inhibitory effects (0.036--0.039 mg/mL) were those of propolis methanolic extract. Among the three different samples investigated here, the aqueous extracts showed lower inhibitory effects compred to the organic solvent SPE extracts (in the range of 1.150-- 5.144 mg/mL). The studied honey extracts constitute an interesting source of phenolic derivatives that might serve to identify lead compounds, targeting the physiologically relevant enzymes CA I and CA II.