Induction of stromelysin gene expression by tumor necrosis factor alpha isinhibited by dexamethasone, salicylate, and N-acetylcysteine in synovial fibroblasts

Proinflammatory cytokines, altered connective tissue metabolism, and overex pression of matrix metalloproteinases (MMPs) such as stromelysin compared t o tissue inhibitors of metalloproteinases (TIMPs) result in synovial inflam mation and erosion of arthritic cartilage. Tumor necrosis factor alpha (TNF -alpha) is a major synovial inflammatory mediator responsible for inhibitin g extracellular matrix (ECM) synthesis and stimulating degradation of carti lage ECM by activated MMPs in arthritic joints. To suppress these effects a nd to gain insight into the mechanism of TNF-alpha action, we identified th e inhibitors of TNF-alpha stimulation of stromelysin gene expression. In bo vine synovial fibroblasts, TNF-alpha did not affect a recently identified i nhibitor, TIMP-3, but induced stromelysin mRNA expression in a dose- and ti me-dependent fashion (3- to 5-fold) which required de novo protein synthesi s. Stimulation by TNF-alpha was potently inhibited (99-100%) by the synthet ic glucocorticoid, dexamethasone. Sodium salicylate dose-dependently inhibi ted (100%) the TNF-alpha action. Indomethacin and ibuprofen were partially inhibitory. Free radical scavenger antioxidant, N-acetylcysteine (but not o ther antioxidants) also suppressed the TNF-alpha induction (36-100%) of str omelysin suggesting involvement of reactive oxygen species in the induction process. TNF-alpha induction of stromelysin gene expression can therefore be inhibited at the gene expression level by several pharmacological agents which are likely to function via arachidonic acid metabolites, free radica l scavenging or interference with the activator protein 1, polyoma virus en hancer A-binding protein 3, and nuclear factor kappa B classes of transcrip tion factors. Our results may help to elucidate the mechanism of TNF-alpha action and explain the beneficial role of these agents in the treatment of inflammatory diseases.