Irsogladine maleate abolishes the increase in interleukin-8 levels caused by outer membrane protein 29 from Aggregatibacter (Actinobacillus) actinomycetemcomitans through the ERK pathway in human gingival epithelial cells

Background and Objective: Irsogladine maleate (IM) suppresses the increase in interleukin (IL)‐8 production induced by outer membrane protein (OMP) 29 from Aggregatibacter (Actinobacillus) actinomycetemcomitans in cultures of human gingival epithelial cells (HGEC). However, how IM suppresses the OMP29‐induced increase in IL‐8 expression remains unknown. In this study, we focused on intracellular signaling pathways to elucidate the mechanism behind the suppression. Material and Methods: HGEC, which had been pretreated with inhibitors of intracellular signaling molecules, were exposed to OMP29 (1 μg/mL) with or without IM (1 μm). IL‐8 expression at the mRNA and protein levels was examined by real‐time polymerase chain reaction and enzyme‐linked immunosorbent assay, respectively. Extracellular signal‐regulated kinase (ERK) activity was measured with a p44/42 mitogen‐activated protein kinase assay kit. Results: An ERK inhibitor, PD98059, as well as IM, obviated the OMP29‐induced increase in IL‐8 levels in HGEC. A Jun kinase inhibitor, SP600125, and a nuclear factor κB inhibitor, PDTC, did not influence the OMP29‐induced increase in IL‐8 mRNA expression. The OMP29 stimulated phosphorylation of ERK in HGEC. Irsogladine maleate inhibited the phosphorylation. Conclusion: The suppression of the phosphorylation of ERK by IM in HGEC culminates in inhibition of the OMP29‐induced increase in IL‐8.