Effects of TNFα-antagonists on nitric oxide production in human cartilage

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Objective Nitric oxide (NO) produced by cartilage and synovial membrane is implicated in the pathogenesis of osteoarthritis (OA) and rheumatoid arthritis (RA). In inflamed joints NO is synthesized in response to proinflammatory cytokines and it is involved in the joint destruction. The aim of the present study was to investigate the effects of TNFα-antagonists infliximab and etanercept on NO production in human cartilage.DesignCartilage specimen obtained from OA patients undergoing knee replacement surgery were studied for iNOS expression and NO production in organ culture to allow intact chondrocyte–matrix interactions. TNFα and soluble TNFα receptor release was measured by ELISA.Results Osteoarthritic cartilage produced NO spontaneously and its production was enhanced by proinflammatory cytokines TNFα (tumor necrosis factor α), IL-1β (interleukin-1β), IL-17 (interleukin-17) and by bacterial lipopolysaccharide (LPS). TNFα-antagonists infliximab and etanercept inhibited TNFα-induced NO production in a dose dependent manner but they had no effect on IL-1β-, IL-17- and LPS-stimulated NO synthesis. TNFα and soluble TNFα receptors (sTNFRI and sTNFRII) were produced by human osteoarthritic cartilage. A neutralizing antibody against soluble TNFRI enhanced spontaneous NO production whereas an antibody against soluble TNFRII had no effect.Conclusions TNFα-antagonists infliximab and etanercept suppressed TNFα-induced NO production. This effect was not seen on IL-1-, IL-17- or LPS-induced NO production suggesting that TNFα is not an autacoid mediator in these processes. The studies with neutralizing antibodies against soluble TNFRI suggest that endogenous cartilage-derived TNFα-antagonists modulate NO production in osteoarthritic cartilage.