Abstract
Brazilian green propolis is a popular health supplement because of its various biological properties. The ethanol extract of Brazilian green propolis (EEBP) is characteristic for its herb-like smell and unique pungent taste. However, the ingredients responsible for its pungency have not yet been identified. This study provides the first evidence that artepillin C is the main pungent ingredient in EEBP and that it potently activates human transient receptor potential ankyrin 1 (TRPA1) channels. EEBP was fractionated using column chromatography with a step gradient elution of an ethanol-water solution, and the fractions having the pungent taste were determined by sensory tests. HPLC analysis revealed that the pungent fraction was composed primarily of artepillin C, a prenylated derivative of cinnamic acid. Artepillin C was also identified as the pungent compound of EEBP by organoleptic examiners. Furthermore, the effects of artepillin C and other cinnamic acids found in EEBP on TRPA1 channels were examined by calcium imaging and plate reader-based assays in human TRPA1-expressing cells to investigate the molecular mechanisms underlying their pungent tastes. Artepillin C and baccharin activated the TRPA1 channel strongly, whereas drupanin caused a slight activation and p-coumaric acid showed no activation. Because the EC50 values of artepillin C, baccharin, and allyl isothiocyanate were 1.8 µM, 15.5 µM, and 6.2 µM, respectively, artepillin C was more potent than the typical TRPA1 agonist allyl isothiocyanate. These findings strongly indicate that artepillin C is the main pungent ingredient in EEBP and stimulates a pungent taste by activating TRPA1 channels.
Highlights
Propolis is a plant mastic produced by honeybees from resinous substances collected from tree buds and sap
The present study demonstrated that artepillin C primarily contributed to the pungent taste of ethanol extract of Brazilian green propolis (EEBP) (Fig. 2)
We found that artepillin C strongly stimulates hTRPA1 channels, which are activated by pungent foods, such as wasabi, a typical pungent food in Japan [19]
Summary
Propolis is a plant mastic produced by honeybees from resinous substances collected from tree buds and sap. Bees bring the resin to the hive and mix it with their own secretions, such as bee wax and saliva. Propolis contains numerous chemical ingredients, including cinnamic acid derivatives (e.g., p-coumaric acid, drupanin, artepillin C, and baccharin (Fig. 1)), benzoic acids, substituted phenolic acids, flavonoids, and amino acids [11,12,13], and the chemical composition of propolis depends on various factors, such as the geographical origin, types of plant sources [5,13], and season of the year. Baccharis dracunculifolia DC (Asteraceae) [14,15,16], a plant native to Brazil, is the most important botanical source of southeastern Brazilian propolis, which is known as green propolis because of its deep green color
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