Interleukin-1, Tumor Necrosis Factor α, and Interleukin-17 Synergistically Up-Regulate Nitric Oxide and Prostaglandin E₂ Production in Explants of Human Osteoarthritic Knee Menisci

Objective. In osteoarthritis (OA), a combination of biochemical and biomechanical factors may damage both menisci and articular cartilage. Nitric oxide (NO) and prostaglandin E₂ (PGE₂) have been implicated as mediators of inflammation in OA. The goals of this study were to determine if menisci from patients with OA produce NO and PGE₂, and if the proinflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor a (TNFα), and IL-17 augment NO and PGE₂ production by these tissues. Methods. Menisci were obtained from 17 patients (age 47-75 years) undergoing total knee replacement for OA. Tissue explants were cultured alone or with IL-1β, IL-17, or TNFα, and the release of NO and PGE₂ from the tissue as well as the presence of type 2 nitric oxide synthase (NOS2) and cyclooxygenase 2 (COX-2) antigens were measured. Results. All menisci constitutively produced NO, and significant increases in NO production were observed in the presence of IL-1β, TNFα, or IL-17 (P < 0.05). The combination of IL-17 and TNFα significantly increased NO production compared with either cytokine alone. Basal and cytokine-stimulated NO synthesis was inhibited by the NOS inhibitors N^G-monomethyl-L-arginine or N-3-aminoethylbenzylacetamidine (1400W). IL-1β significantly increased PGE₂ production. The combination of IL-1β and TNFα had an additive effect on PGE₂ production, while addition of IL-17 to TNFα or IL-1β synergistically enhanced PGE₂ production. Inhibition of NO production by 1400W significantly increased IL-1β-stimulated PGE₂ production, and inhibition of PGE₂ production by the COX-2 inhibitor N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide significantly increased IL-17-stimulated NO production. Conclusion. Menisci from humans with OA spontaneously produced NO and PGE₂ in a manner that was synergistically or additively augmented by cytokines. NO and PGE₂ exhibited reciprocal regulatory effects on one another, suggesting that pharmaceutical agents designed to inhibit NOS2 or COX-2 production may in fact be influencing both pathways.