Nitric oxide production in cells derived from the human joint.

We have investigated the ability of cells derived from the human joint to generate nitric oxide (NO). Synovial fibroblasts, articular chondrocytes and osteoblasts were cultured from tissues of patients undergoing hip replacement surgery, and synovial fluid leucocytes were obtained from patients undergoing joint aspiration. There was little spontaneous generation of NO by any of the cells after culture, but synovial fibroblasts, articular chondrocytes and osteoblasts all produced large quantities of NO in response to a cytokine mix of interleukin (IL)-1 beta + tumour necrosis factor alpha (TNF alpha) + interferon (IFN gamma). Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed the presence of mRNA transcripts for the inducible isoform of NO synthase in cytokine-stimulated but not in unstimulated cells. In contrast, leucocytes from synovial fluid did not produce NO either spontaneously or after cytokine stimulation, and mRNA for inducible NO synthase (iNOS) was not detected in these cells even by nested PCR. There were significant differences in the regulation of NO production between chondrocytes and other cells. Only chondrocytes generated NO in response to IL-1 beta or TNF alpha alone, whereas synovial fibroblasts and osteoblasts required the presence of at least two cytokines to generate NO. Dexamethasone (10(-6)M) had a small but significant inhibitory effect on NO production by chondrocytes, synovial fibroblasts and osteoblasts. Our results indicate that several cells within the human joint have the potential to generate NO in the presence of an appropriate pro-inflammatory cytokine stimulus, while leucocytes in synovial fluid are not a significant source of NO. The data support suggestions that NO is produced within the inflamed joint in diseases such as rheumatoid arthritis.