Effect of antiinflammatory drugs on COX-1 and COX-2 activity in human articular chondrocytes

Objective, To study the effect of steroidal and nonsteroidal antiinflammatory drugs (NSAID) on cyclooxygenase (COX-1 and COX-2) activity in human articular chondrocytes. Methods. Chondrocytes were isolated from articular cartilage of donors with no articular disease. Unstimulated and interleukin 1 (IL-1) stimulated chondrocytes were used as models to study the effects of drugs on COX-1 and COX-2. Cells were incubated with vehicle or drugs; supernatants were removed and the level of prostaglandin E-2 (PGE(2)) in each sample was determined by enzyme immunoassay. IC50 were calculated from the reduction in PGE(2) content by different concentrations of the test substance by linear regression analysis. Results, COX-1 mRNA was detected in unstimulated cells, but stimulation with IL-1 for up 12 h did not modify the levels of COX-1 mRNA. In contrast, COX-2 mRNA was not detectable in unstimulated cells, but it was induced by IL-1. Dexamethasone inhibited COX-2 mRNA expression induced by IL-1, COX-2, protein levels correlated with mRNA expression. Dexamethasone was the strongest drug inhibitor of COX-2 (IC50 = 0.0073 mu M). However, it did not inhibit COX-1 activity. Among all NSAID tested, meloxicam and aspirin were the least potent inhibitors of COX-1 (IC50 = 36.6 mu M and 3.57 mu M, respectively). Indomethacin and diclofenac were the most patent inhibitors of COX-1 (IC50 = 0.063 mu M and 0.611 mu M, respectively) and COX-2 isoforms (IC50 = 0.48 mu M and IC50 = 0.63 mu M, respectively). Meloxicam was a more potent inhibitor of COX-2 (IC50 = 4.7 mu M) than aspirin (IC50 = 29.3 mu M) and similar to piroxicam (IC50 = 4.4 mu M). Among all drugs tested dexamethasone showed the greatest selectivity for COX-2 and meloxicam was the NSAID with the best COX-2/COX-1 ratio (r = 0.12). Aspirin and piroxicam were about 8 times more active against COX-1 than COX-2, indomethacin was 7 times more active, and diclofenac was an equipotent inhibitor of COX-1 and COX-2. Conclusion. We found that COX-1 and COX-2 isoforms are expressed in human chondrocytes at rest and in IL-1 stimulated cells, respectively. Antiinflammatory drugs have different capacities to inhibit COX enzyme in human articular chondrocytes.