Cyclooxygenase-2-Dependent Prostaglandin Production by Peripheral Blood Monocytes Stimulated With Lipopolysaccharides Isolated From Periodontopathogenic Bacteria

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Abstract
Prostaglandin E2 (PGE2) plays important roles in the pathogenesis of periodontal disease. Recent studies have revealed the existence of 2 isozymes of cyclooxygenase (COX), called COX-1 and COX-2. The purpose of the present study was to investigate the contribution of COX-1 and COX-2 to PGE2 production by human peripheral blood monocytes that are stimulated with lipopolysaccharides (LPS) from periodontopathogenic bacteria. LPS were isolated from Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) and Porphyromonas gingivalis (P. gingivalis) by the phenol-water method. Peripheral blood monocytes were stimulated with LPS for the indicated periods, and the levels of PGE2 or interleukin (IL)-1 beta in the culture media were measured by enzyme-linked immunosorbent assay. Expression of COX-1 and -2 proteins was studied by immunocytochemical staining, and COX-2 mRNA expression was examined by Northern blot analysis. Peripheral blood monocytes stimulated with A. actinomycetemcomitans- or P. gingivalis-LPS produced PGE2 in a time- and dose-dependent manner. Indomethacin, a non-selective COX-1/COX-2 inhibitor, and NS-398, a specific COX-2 inhibitor, completely inhibited PGE2 production. Immunocytochemical staining of COX-1 and COX-2 proteins showed that expression of COX-2 protein was increased in monocytes that were stimulated with A. actinomycetemcomitans- or P. gingivalis-LPS, compared with that in unstimulated monocytes, whereas expression of COX-1 protein was not altered. Northern blot analysis showed that monocytes stimulated with A. actinomycetemcomitans- or P. gingivalis-LPS expressed COX-2 mRNA, while COX-2 mRNA was not detectable in unstimulated cells. Treatment of A. actinomycetemcomitans-LPS-stimulated monocytes with NS-398 induced a significant increase of IL-1 beta production to the same extent as treatment with indomethacin. These results suggest that COX-2 is induced in monocytes stimulated with LPS derived from A. actinomycetemcomitans and P. gingivalis and that the COX-2 is primarily responsible for PGE2 production. COX-2 may be pivotal in PGE2 production in periodontal lesions and may be involved in inflammatory responses.