Nitric oxide downregulates interleukin 1β (IL-1β) stimulated IL-6, IL-8, and prostaglandin E2 production by human chondrocytes

Objective. To investigate the effects of endogenously produced nitric oxide (NO) on interleukin 6 (IL-6), IL-8, prostaglandin E-2 (PGE(2)), and proteoglycan production by human chondrocytes. Methods. Human articular chondrocytes were isolated from their extracellular matrix by triple successive enzymatic digestion of the cartilage and cultured 48 h in a well defined culture medium. IL-6 and IL-8 were directly assayed into culture media by specific enzyme amplified sensitivity immunoassays. Proteoglycans and PGE(2) were quantified by specific radioimmunoassays. Cell culture media were assayed for NO2 using a spectrophotometric assay based upon the Griess reaction. Results. Unstimulated chondrocytes produced low levels of NO, IL-6, IL-8, and PGE(2). Production was significantly stimulated by IL-1 beta and lipopolysaccharide (LPS). As well, proteoglycan synthesis was profoundly inhibited by IL-1 beta and LPS. Inhibition of NO synthesis with the competitive inhibitor N-G-monomethyl-L-arginine (L-NMMA) led to enhancement of IL-6, IL-8, and PGE(2) production stimulated by either IL-1 beta alone or in combination with LPS, whereas the inhibition of proteoglycan production by IL-1 beta was not modified by L-NMMA. Conclusion. LPS and IL-1 beta stimulated IL-6, IL-8, and PGE(2) production are downregulated by endogenously produced NO, which could limit the inflammatory reaction occurring in arthritis.