Abstract
Onopordopicrin (OPP), found in burdock leaves and stems, exerts antiallergic properties whose mechanism remains elusive. We aimed to elucidate its mechanism using rat basophilic leukemia cells in vitro. Purified OPP demonstrated concentration‐dependent inhibition of degranulation after allergen or PMA/A23187 stimulation. OPP effectively suppressed TNF‐α and PGD2 releases. However, OPP did not suppress the increase in intracellular Ca2+ concentration after allergen stimulation. The α, β‐unsaturated carbonyl structure of OPP suggests potential electrophilic reactivity with polyfunctional thiol‐trapping agents, such as cysteine residues. Indeed, the degranulation‐inhibiting effect of OPP disappeared with the addition of cysteamine, which possesses a thiol group. I kappa B kinase β (IKKβ), which regulates degranulation in an NF‐κB‐independent manner, possesses a cysteine residue between the activation loop. Moreover, IKKβ plays an important role in TNF‐α and PGD2 production. OPP was found to reduce IKKβ activity in a concentration‐dependent manner. Together, our findings suggest that OPP exerts its antiallergic action via binding to cysteine residues in signal proteins such as IKKβ, thereby inhibiting their activation.