Taurine chloramine (Tau-Cl) was recently demonstrated to inhibit production of nitric oxide and tumor necrosis factor-alpha (TNF-alpha) by activated macrophages. Since increased production of prostaglandin E2 (PGE2), a reaction catalyzed by induction of cyclooxygenase-2 (COX-2), is also associated with the inflammatory response, we determined the effects of Tau-Cl on PGE2 production and on expression of COX-2 protein and COX-2 mRNA in activated RAW 264.7 cells, a murine macrophage-like cell line. Tau-Cl inhibited production of PGE2 in a concentration dependent manner with an IC50 of 0.4 mM. The decrease in PGE2 production was largely accounted for by decreased expression of COX-2 protein. Although the kinetics of COX-2 mRNA expression was altered in Tau-Cl treated cells, mRNA expression appeared to be quantitatively unimpaired. These results suggest that Tau-Cl affects the post-transcriptional regulation of COX-2 expression and support the idea that Tau-Cl may function as an inhibitory modulator of the inflammatory response.
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Objective: To investigate the effects of taurine chloramine (Tau-Cl), a chlorinated derivative of the amino acid taurine, on the expression of cyclooxygenase (COX) isoenzymes and prostaglandin E(2) (PGE(2)) synthesis in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS).
Methods: FLS, isolated from the synovial tissue of RA patients, were treated in vitro with either interleukin-1beta (IL-1beta; 1 ng/ml) alone or together with 200-500 microM Tau-Cl. The expression of COX isoenzymes was evaluated at both the protein (Western blotting) and the messenger RNA (mRNA) (reverse transcriptase-polymerase chain reaction) levels. The concentration of PGE(2) was measured by competitive acetylcholinesterase enzyme immunoassay.
Results: Resting FLS expressed mRNA encoding both COX-1 and COX-2, but only COX-1 was present at the protein level. These cells produced negligible amounts of PGE(2). Upon stimulation with IL-1beta, elevation of COX-2, but not COX-1, mRNA and protein preceded the enhancement of PGE(2) synthesis. In the presence of 300-400 microM Tau-Cl, significant inhibition of IL-1beta-triggered COX-2 mRNA and protein, and a related decrease in PGE(2) production, was observed. In contrast, no significant changes in COX-1 mRNA and protein levels were noted.
Conclusion: Tau-Cl inhibits IL-1beta-triggered elevation of COX-2 and generation of PGE(2) by RA FLS. These results expand the spectrum of known antiinflammatory activities of this compound.