Lipopolysaccharide of Aggregatibacter actinomycetemcomitans up-regulates inflammatory cytokines, prostaglandin E2 synthesis and osteoclast formation in interleukin-1 receptor antagonist-deficient mice

Background and Objective The interleukin (IL)‐1 receptor antagonist (Ra) binds to IL‐1 receptors and inhibits IL‐1 activity. However, it is unclear whether the IL‐1Ra plays a protective role in periodontal disease. The purpose of this study was to compare IL‐1Ra knockout (KO) and wild‐type (WT) mice in regard to proinflammatory cytokine production, osteoclast formation and bone resorption in response to periodontal bacterial lipopolysaccharide (LPS). Material and Methods Peritoneal macrophages (Mφs) were obtained from 13‐wk‐old IL‐1Ra KO and WT mice. Peritoneal Mφs were cultured with or without 10 μg/mL of Aggregatibacter actinomycetemcomitans LPS for 24 h. The levels of IL‐1alpha (IL‐1α), IL‐1beta (IL‐1β), tumor necrosis factor‐α (TNF‐α) and IL‐6 were measured in periotoneal Mφs supernatant fluid (PM‐SF) using an ELISA. Bone marrow cells were obtained from the mice and stimulated with PM‐SF for 9 d, then stained with TRAP. The frequency of TRAP‐positive multinucleated giant cell formation was calculated based on a fusion index. PM‐SF‐stimulated calvarial bone resorption was analyzed using micro‐computed tomography, and calvarial histological analysis was performed using hematoxylin and eosin and TRAP staining. The expression of cyclooxygenase‐2 (Cox2), prostanoid receptor EP4 (Ep4) and Rank mRNAs in bone marrow cells were measured using real‐time quantitative PCR, while prostaglandin E2 (PGE2) production was determined by ELISA. Results The levels of IL‐1α, IL‐1β, TNF‐α and IL‐6 in IL‐1Ra KO mice PM‐SF stimulated with A. actinomycetemcomitans LPS were significantly increased by approximately 4‐ (p