Tetracycline up-regulates COX-2 expression and prostaglandin E-2 production independent of its effect on nitric oxide

Tetracyclines (doxycycline and minocycline) augmented (one- to twofold) the PGE(2) production in human osteoarthritis-affected cartilage (in the prese nce or absence of cytokines and endotoxin) in ex vivo conditions. Similarly , bovine chondrocytes stimulated with LPS showed (one- to fivefold) an incr ease in PGE(2) accumulation in the presence of doxycycline, This effect was observed at drug concentrations that did not affect nitric oxide (Nd) prod uction. In murine macrophages (RAW 264.7) stimulated with LPS, tetracycline s inhibited NO release and increased PGE(2) production. Tetracycline(s) and L-N-monomethylarginine (L-NMMA) (NO synthase inhibitor) showed an additive effect on inhibition of NO and PGE(2) accumulation, thereby uncoupling the effects of tetracyclines on NO and PGE(2) production. The enhancement of P GE(2) production in RAW 264.7 cells by tetracyclines was accompanied by the accumulation of both cyclooxygenase (COX)-2 mRNA and cytosolic COX-2 prote in. In contrast to tetracyclines, L-NMMA at low concentrations (less than o r equal to 100 mu M) inhibited the spontaneous release of NO in osteoarthri tis-affccted explants and LPS-stimulated macrophages but had no significant effect on the PGE(2) production. At higher concentrations, L-NMMA (500 mu M) inhibited NO release but augmented PGE(2) production, This study indicat es a novel mechanism of action of tetracyclines to augment the expression o f COX-2 and PGE(2) production, an effect that is independent of endogenous concentration of NO.