Articular chondrocytes synthesize nitric oxide in response to cytokines and lipopolysaccharide.

Although IL-1 is an important modulator of chondrocyte metabolism, the postreceptor events triggered by IL-1 remain obscure. The present study shows that IL-1 induces the biosynthesis of nitric oxide (.N = O) by articular chondrocytes. Synthesis of .N = O is also induced by LPS. Other inflammatory mediators such as IFN-gamma, fibroblast growth factor, and TNF-alpha fail to provoke the production of .N = O, but they increase the potency of IL-1. A combination of IL-1, LPS, and TNF-alpha was shown to induce maximal production of 355 +/- 51 nmol/10(6) cells/72 h of nitrite (NO2-), which was measured as a stable end-product of .N = O generation. The biosynthesis of .N = O requires an induction period of approximately 6 h and continues for at least 72 h. Inhibition of .N = O production with the competitive inhibitor NG-monomethyl-L-arginine (NMA) leads to a suppression of gelatinase and PGE2 synthesis by chondrocytes activated with IL-1 alone. In contrast, NMA enhances the synthesis of both gelatinase and PGE2 after activation with a combination of IL-1, LPS, and TNF-alpha. An increase of PGE2 synthesis from 42.0 +/- 21.0 to 174.0 +/- 33.5 ng/10(6) cells/72 h resulted from the addition of NMA when these stimulatory agents were combined. Exposure of IL-1 and fibroblast growth factor-stimulated chondrocytes to authentic, exogenous .N = O led to an increase of PGE2 synthesis from 5.6 +/- 1.7 of untreated cells to 15.8 +/- 6.8 ng/10(6) of .N = O treated cells within the 1st h. This was followed by a suppression of PGE2 synthesis within the next 2 h.