To characterize the effects of nimesulide (NIM) on basal and induced cyclo-oxygenase-2 (COX-2) gene expression in human synovial fibroblasts (HSF) and to define the intracellular mechanisms that mediate the changes in COX-2 expression and synthesis in response to the drug.
HSF were incubated with NIM and NS-398 (0, 0.03, 0.3, 3 microg/ml) in the absence or presence of the COX-2 inducers interleukin-1beta (IL-1beta) or endotoxin (LPS). Treated cells were analysed for COX-2 mRNA and protein by Northern and Western blotting analysis, respectively. Putative transcriptional, post-transcriptional, and signaling effects of NIM on basal and induced-COX-2 expression were investigated by human COX-2 promoter studies, calcium studies, reactive oxygen species (ROS) evaluations, electrophoretic mobility shift analysis (EMSA) and half-life studies of COX-2 mRNA.
NIM inhibited IL-1beta-induced COX-2 expression and protein at sub and therapeutic concentrations (0.03-0.3 microg/ml) while the non-specific NSAID, naproxen, did not. Both drugs suppressed PGE2 release by about 95%. NIM had no effect on (1) IL-1beta-induced increases in NF-kappaB or c/EBP signaling, or (2) human COX-2 promoter activity. Stability of induced COX-2 mRNA was unaffected by NIM treatments. Pre-treatment of cells with O(2)radical scavengers (e.g. PDTC) or with Ca(++)channel blockers (e.g. verapamil) had a modest effect on IL-1beta-induced COX-2 expression. NIM blocked ionomycin+thapsigargin and H(2)O(2)-induced increases in COX-2 protein synthesis.
NIM inhibits cytokine-induced COX-2 expression and protein at sub and therapeutic concentrations. At least part of this activity may be the result of NIM inhibition of calcium and/or free radical generation induced by cytokines.