SB-203580 INHIBITS P38 MITOGEN-ACTIVATED PROTEIN-KINASE, NITRIC-OXIDEPRODUCTION, AND INDUCIBLE NITRIC-OXIDE SYNTHASE IN BOVINE CARTILAGE-DERIVED CHONDROCYTES

Nitric oxide (NO) is implicated in a number of inflammatory processes and is an important mediator in animal models of rheumatoid arthritis and in in vitro models of cartilage degradation. The pyridinyl imidazo le SE 203580 inhibits p38 mitogen-activated protein (MAP) kinase in vi tro, blocks proinflammatory cytokine production in vitro and in vivo, and is effective in animal models of arthritis. The purpose of this st udy was to determine whether SE 203580 could inhibit p38 MAP kinase ac tivity, NO production, and inducible NO synthase (iNOS) in IL-1 stimul ated bovine articular cartilage/chondrocyte cultures. The results indi cated that SE 203580 inhibited both IL-I stimulated p38 MAP kinase act ivity in isolated chondrocytes and NO production in bovine chondrocyte s and cartilage explants with an IC50 value of approximately 1 mu M. T o inhibit NO production, SE 203580 had to be present in cartilage expl ant cultures during the first 8 h of IL-1 stimulation, and activity wa s lost when it was added 24 h following IL-1, SE 203580 did not inhibi t iNOS activity, as measured by the conversion of arginine to citrulli ne, when added directly to cultures where the enzyme had already been induced, but had to be present during the induction period. Using a 37 2-bp probe for bovine iNOS we demonstrated inhibition of IL-1-induced mRNA by SB 203580 at both 4 and 24 h following IL-1 treatment. The iNO S mRNA levels were consistent with NO levels in 24-h cell culture supe rnatants of the IL-l-stimulated bovine chondrocytes used to obtain the RNA.