Protein kinase A enhances lipopolysaccharide-induced IL-6, IL-8, and PGE2 production by human gingival fibroblasts

Recently, we reported that the protein kinase A (PKA) inhibitor H-89 suppresses lipopolysaccharide (LPS)-induced IL-8 production by human gingival fibroblasts (HGFs). In the present study, the relevance of the PKA activity and two PKA-activating drugs, aminophylline and adrenaline, to LPS-induced inflammatory cytokines (IL-6 and IL-8) and PGE2 by HGFs were examined.HGFs were treated with LPS from Porphyromonas gingivalis and H-89, the cAMP analog dibutyryl cyclic AMP (dbcAMP), aminophylline, or adrenaline. After 24 h, IL-6, IL-8, and PGE2 levels were evaluated by ELISA.H-89 did not affect LPS-induced IL-6 production, but suppressed IL-8 and PGE2 production. In contrast, dbcAMP significantly increased LPS-induced IL-6, IL-8, and PGE2 production. Up to 10 μg/ml of aminophylline did not affect LPS-induced IL-6, IL-8, or PGE2 production, but they were significantly increased at 100 μg/ml. Similarly, 0.01 μg/ml of adrenaline did not affect LPS-induced IL-6, IL-8, or PGE2 production, but they were significantly increased at concentrations of 0.1 and 1 μg/ml. In the absence of LPS, H-89, dbcAMP, aminophylline, and adrenaline had no relevance to IL-6, IL-8, or PGE2 production.These results suggest that the PKA pathway, and also PKA-activating drugs, enhance LPS-induced IL-6, IL-8, and PGE2 production by HGFs. However, aminophylline may not have an effect on the production of these molecules at concentrations used in clinical settings (8 to 20 μg/ml in serum). These results suggest that aminophylline does not affect inflammatory responses in periodontal disease.Periodontal disease is accompanied by inflammation of the gingiva and destruction of periodontal tissues, leading to alveolar bone loss in severe clinical cases. Interleukin (IL)-6, IL-8, and prostaglandin E2 (PGE2) are known to play important roles in inflammatory responses and tissue degradation. IL-6 has the ability to induce osteoclastogenesis [1,2]. IL-8 acts as a chemoattractant for neutrophils [3] that produce