Sulochrin inhibits eosinophil activation and chemotaxis

Objective: Because eosinophils likely play important roles in the pathophysiology of allergic diseases, specific inhibitors of eosinophils may be desirable to treat such diseases. To evaluate the capacity of a novel compound, sulochrin, as an inhibitor of eosinophilic inflammation, we examined the effects of this compound on various effector functions of eosinophils. Materials and methods: We examined the effects of sulochrin on degranulation of human eosinophils stimulated with platelet-activating factor (PAF) or Sepharose 4B beads coated with secretory IgA (sIgA) or IgG. The effects of sulochrin on other effector functions of human eosinophils, including superoxide anion (O₂^-) production, leukotriene (LT) C₄ release, and interleukin (IL)-8 production induced by sIgA-beads were also studied. Finally, using PAF and LTB₄ as chemoattractants, we evaluated the potency of sulochrin to inhibit eosinophil migration in vitro and in vivo. Results: Sulochrin inhibited EDN release by eosinophils stimulated with sIgA-beads, IgG-beads and PAF in a concentration-dependent manner; IC₅₀ values were 0.75 μM, 0.30 μM and 0.03 μM. Eosinophil O₂^- production, LTC₄ release, and IL-8 production were also inhibited by sulochrin. Furthermore, PAF-induced chemotaxis of human eosinophils and LTB₄-induced chemotaxis of guinea pig eosinophils were abolished by 1 μM of sulochrin. Finally, sulochrin potently inhibited LTB₄-induced infiltration of eosinophils into the skin of guinea-pig in vivo. Conclusions: These results suggest that sulochrin is a potent inhibitor of various effector functions of eosinophils. Sulochrin and its derivatives may be useful in the development of therapeutic approaches for patients with allergic diseases.