Saikosaponin A inhibits compound 48/80-induced pseudo-allergy via the Mrgprx2 pathway in vitro and in vivo.

Pseudo-allergic reactions-adverse, non-immunologic, anaphylaxis-like sudden onset reactions mediated through an IgE-independent pathway-are activated by various basic compounds and occur at least as frequently as IgE-mediated reactions to drugs. A large family of G protein coupled receptors (Mas-related genes; Mrgprs) is closely related to pseudo-allergies. However, few therapies can directly target pseudo-allergies and related Mrgprs. Saikosaponin A (SSA) is effective in the treatment of passive cutaneous anaphylaxis (PCA), adjuvant arthritis, and delayed hypersensitiveness. In this study, we investigated the anti-pseudo-allergy effect of SSA and its underlying mechanism. We examined the effect of SSA on both IgE-independent and IgE-dependent responses using PCA and active systemic anaphylaxis models, as well as in vitro-cultured mast cells. We also evaluated whether the anti-allergy effect is related to Mrgprs by using in vitro Mrgprx2-expressing HEK293 cells. SSA dose dependently suppressed compound 48/80 (C48/80)-induced PCA and mast cell degranulation in mice. When SSA and C48/80 were administered together through the vein, C48/80-induced systemic anaphylaxis did not occur, and C48/80-induced shock ratio decreased dose-dependently upon SSA treatment. However, SSA did not affect IgE-dependent allergy. When administered topically 24 h before antigen challenge, Evans blue leakage and paw swelling were induced in the SSA-treated group and the vehicle group. Our in vitro studies revealed that SSA reduced C48/80-induced calcium flux and suppressed degranulation in LAD2 cells. SSA could also dose-dependently inhibit C48/80-induced Mrgprx2-expressing HEK293 cell activation. As a conclusion, SSA could inhibits IgE-independent allergy, but not IgE-dependent allergy, and this effect involves the Mrgprx2 pathway. This study provided a new sight on pseudo-allergy and its therapy.