The p38 MAP kinase inhibitor, SB 242235, was evaluated for its effects on the metabolism of bovine and human cartilage and primary chondrocyte cultures. SB 242235 had no effect on proteoglycan synthesis (PG) in bovine articular cartilage explants (BAC), as measured by [(35)S]-sulfate incorporation into glycosaminoglycans (GAGs). In addition, the compound had no effect on IL-1 alpha-induced GAG release from these cultures. However, there was a potent, dose-dependent inhibition of nitric oxide (NO) release from IL-1 alpha-stimulated BAC with an IC(50)of approximately 0.6 microM, with similar effects observed in primary chondrocytes. The effect on BAC was time dependent, and mechanistically did not appear to be the result of inhibition of protein kinase C (PKC), protein kinase A (PKA) or MEK-1. The effect on NO release in bovine chondrocytes was at the level of inducible nitric oxide synthase (iNOS) gene expression, which was inhibited at similar concentrations as nitrite production. In primary human chondrocytes, IL-1 beta induction of p38 MAP kinase was inhibited by SB 242235 with an IC(50)of approximately 1 microM. Surprisingly, however, treatment of IL-beta-stimulated human cartilage or chondrocytes with SB 242235 did not inhibit either NO production or the induction of iNOS. On the other hand, the natural product hymenialdisine (HYM), a protein tyrosine kinase (PTK) inhibitor, inhibited NO production and iNOS in both species. In contrast to the differential control of iNOS, PGE(2)was inhibited by SB 242235 in both IL-1-stimulated bovine and human chondrocyte cultures. These studies indicate that there are species differences in the control of iNOS by p38 inhibitors and also that different pathways may control IL-1-induced proteoglycan breakdown and NO production.