Caffeic acid phenethyl ester inhibits pseudo-allergic reactions via inhibition of MRGPRX2/MrgprB2-dependent mast cell degranulation.

Mast cells play essential role in allergic reactions through the process called mast cell degranulation. Recent studies have found that a basic secretagogue compound 48/80 (C48/80) induces non-IgE-mediated mast cell degranulation via activation of human Mas-related G protein-coupled receptor X2 (MRGPRX2) and mouse MrgprB2. Although previous studies have revealed that caffeic acid (CA) and its derivatives possess anti-allergic effects via IgE-dependent manner, it is largely elusive whether these compounds have impact on MRGPRX2/MrgprB2 to exert inhibitory effects. Therefore, the present study investigated whether CA as well as its derivatives - rosmarinic acid (RA) and caffeic acid phenethyl ester (CAPE) - has the ability to inhibit the activity of MRGPRX2/MrgprB2 to evoke pseudo-allergic effects. As a result, it was found that CAPE inhibits C48/80-induced activation of MRGPRX2/MrgprB2, but neither CA nor RA showed discernible inhibition. Furthermore, the β-hexosaminidase release assay showed that CAPE inhibits mouse peritoneal mast cell degranulation in both IgE-dependent and MrgprB2-dependent manners. Additionally, mouse paw edema induced by C48/80 was dramatically suppressed by co-treatment of CAPE, suggesting that CAPE possesses a protective effect on C48/80-evoked pseudo-allergic reactions. The pretreatment of CAPE also significantly decreased scratching bouts of mice evoked by C48/80, demonstrating that CAPE also has an anti-pruritic effect. Therefore, these data implicate that CAPE can suppress pseudo-allergic reactions evoked by C48/80 via MrgprB2-dependent manner. Finally, molecular docking analysis showed that CAPE is predicted to bind to human MRGPRX2 in the region where C48/80 also binds, implying that CAPE can be a competitive inhibitor of MRGPRX2. In conclusion, it is found that CAPE has the ability to inhibit MRGPRX2/MrgprB2, leading to the prevention of mast cell degranulation and further to the alleviation of mast cell reactions. These results indicate that CAPE as a CA derivative could be developed as a new protective agent that exerts dual inhibition of mast cell degranulation mediated by IgE and MRGPRX2/MrgprB2.