Expressions of cyclooxygenase 1 and 2 in endotoxin-induced otitis media with effusion in the rat

Objective: Recently, a selective COX-2 inhibitor was developed and used for reducing the levels of inflammation-inducing prostaglandin (PG) whilst not inhibiting the release of protective PG by COX-1. COX-1 may be the critical isoform required for the production of PG with a homeostatic function, whereas COX-2 may be the main contributor to PG production in inflammation. The purpose of this study was to investigate COX-1 and 2 expressions in experimental endotoxin-induced OME in rats and to quantify their temporal expressions. Methods: In a rat model, lipopolysaccharides (LPS) were inoculated into the middle ear cavity. Middle ear mucosa and temporal bone were samples at 0, 1, 3, 6, and 12 h, and on days 1, 3 and 7 after instilling either LPS or sterile PBS. RT-PCR, Western blotting and immunohistochemical staining were performed to determine the expressions of COX-1 and COX-2. Results: COX-1 mRNA and protein were detected in normal middle ear mucosa but their levels did not change after endotoxin instillation. However, COX-2 was not identified in normal middle ear mucosa, but COX-2 mRNA was maximally increased at 6 h after endotoxin instillation and COX-2 protein was maximally increased at 12 h. COX-2 expression, by immunohistochemical staining, was identified only at 12 h after endotoxin injection. Conclusions: In this study, the basal expressions of COX-1 and COX-2 mRNA and protein in middle ear mucosa, as well as their regulations by endotoxin were investigated. COX-1 was not induced in middle ear mucosa by endotoxin whereas COX-2 was induced within 12 h of stimulation. Our findings indicate that COX-2 inhibitor administration for the relief of inflammation should be considered within 12 h of the initiation of an inflammatory process. These findings may provide an understanding of the mechanisms regulating PG formation in infection of the middle ear cavity.