Inhibitory function of Shikonin on MRGPRX2-mediated pseudo-allergic reactions induced by the secretagogue

Background: Mast cells (MCs) are crucial effectors in allergic disorders by secreting inflammatory mediators. The Mas-related G-protein-coupled receptor X2 (Mrgprx2) was shown to have a key role in IgE-independent allergic reactions. Therefore, potential drug candidates that directly target Mrgprx2 could be used to treat pseudo-allergic diseases. Shikonin, an active ingredient derived from Lithospermum erythrorhizon Sieb. et Zucc has been used for its anti-inflammatory properties since ancient China. Purpose: To investigate the inhibitory effects of Shikonin on IgE-independent allergy both in vitro and in vivo, as well as the mechanism underlying its effects. Methods/study designs: The anti-anaphylactoid activity of Shikonin was evaluated in PCA and systemic anaphylaxis models, Calcium imaging was used to assess intracellular Ca2+ mobilization. The release of cytokines and chemokines was measured using enzyme immunoassay kits. Western blot analysis was conducted to investigate the molecules of PLC gamma-PKC-IP3 signaling pathway. The analytical method of surface plasmon resonance was employed to study the interaction between Shikonin and potential target protein Mrgprx2. Results: Shikonin can suppress compound 48/80 (C48/80)-induced PCA, active systemic anaphylaxis, and MCs degranulation in mice in a dose-dependent manner. In addition, Shikonin reduced C48/80-induced calcium flux and suppressed LAD2 cell degranulation via PLC gamma-PKC-IP3 signaling pathway. Moreover, Shikonin was found to inhibit C48/80-induced Mrgprx2 expression in HEK cells, displaying specific interactions with the Mrgprx2 protein. Conclusion: Shikonin could be a potential antagonist of Mrgprx2, thereby inhibiting pseudo-allergic reactions through Ca2+ mobilization.