Celecoxib, a COX-2 specific inhibitor, has recently been used for the treatment of rheumatoid arthritis. However, the molecular and cellular mechanisms of celecoxib against RA inflammation remain to be defined. To elucidate the action mechanism of celecoxib on inflammatory cells, we investigated the effect of celecoxib on the production of two important mediators of inflammation, nitric oxide and PGE2.

RAW 264.7 cells stimulated with LPS were preincubated with various concentrations of celecoxib (from 10^-8 to 10^-5 M) and 10µM hydrocortisone, respectively. The production of NO and PGE2, the end products of iNOS and COX-2 genes, were estimated in culture supernatants by Greiss method and EIA, respectively. The expression of iNOS gene, COX-2 gene, NF-κB, and I-κB were determined by RT-PCR and western blot analysis.

Celecoxib and hydrocortisone inhibited the production of NO and PGE2 in dose dependent manner, when RAW 264.7 cells were stimulated with LPS. The expression of iNOS was also down-regulated by celecoxib and hydrocortisone. Interestingly, COX-2 gene differentially expressed according to the dose of celecoxib, a decrease with lower dose (10^-8 M) but an increase with higher dose (10^-5 M). NF-κB binding activity was decreased by lower dose of celecoxib, whereas was not affected by higher dose of it. The expression of I-κB was suppressed by higher dose of celecoxib.

The celecoxib strongly suppressed the production of NO and PGE2 in LPS-stimulated RAW264.7 cells. The decrease of NO seems to be linked to the inhibition of iNOS by celecoxib. The lower and higher dose of celecoxib differentially regulated the COX-2 expression and NF-κB activity.