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The Role of Cyclooxygenase-2 (COX-2) in Inflammatory Bone Resorption

2007; Elsevier BV; Volume: 33; Issue: 4 Linguagem: Inglês

10.1016/j.joen.2006.12.001

1878-3554

David Coon, Ajay Gulati, Cameron S. Cowan, Jianing He,

Inflammatory mediators and NSAID effects

Prostaglandin E2 (PGE(2)) is an important inflammatory mediator that plays an essential role in the development and progression of periradicular diseases. Cyclooxygenase-2 (COX-2) is the inducible enzyme responsible for increased PGE(2) levels during inflammation and other pathologic processes. The purpose of this study was to determine the role of COX-2-mediated PGE(2) synthesis in osteoclast formation in response to endodontic pathogens and materials. Primary osteoblast cultures and osteoclast cultures were prepared from COX-2 knockout (K/O) and wild-type (WT) littermates. These cultured cells were exposed to lipopolysaccharide (LPS) or root canal obturation materials including gutta-percha (GP), Resilon (RS), mineral trioxide aggregates (MTAs), and AH Plus (AH+). Osteoclast formation was evaluated using tartrate-resistant acid phosphatase (TRAP) staining. The expression of receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) was determined by real-time polymerase chain reaction (PCR) analysis. It was found that in both WT and K/O cultures, treatment with LPS led to a marked increase in osteoclast formation. The number of osteoclasts formed was significantly lower in K/O cultures compared to WT cultures. Exposure to endodontic materials did not lead to any significant osteoclast formation. LPS and endodontic materials caused a decrease in both RANKL and OPG expression in WT cells. In K/O cells, the baseline levels of RANKL and OPG expression were dramatically decreased compared to the WT cells. In conclusion, COX-2-mediated PGE(2) expression is required for LPS-induced inflammatory bone resorption and maintaining the baseline level of RANKL and OPG expression. LPS-induced osteoclast formation may be independent of the RANKL pathway.