Differential roles of nitric oxide and oxygen radicals in chondrocytes affected by osteoarthritis and rheumatoid arthritis

Osteoarthritis and rheumatoid arthritis are characterized by focal loss of cartilage due to an upregulation of catabolic pathways, induced mainly by pro-inflammatory cytokines, such as interleukin-1 (IL-1) and tumour necrosis factor alpha (TNF alpha). Since reactive oxygen species are also involved in this extracellular-matrix-degrading activity, we aimed to compare the chondrocyte oxidative status responsible for cartilage damage occurring in primarily degenerative (osteoarthritis) and inflammatory (rheumatoid arthritis) joint diseases. Human articular chondrocytes were isolated from patients with osteoarthritis or rheumatoid arthritis, or from multi-organ donors, and stimulated with IL-1 beta and/or TNF alpha. We evaluated the oxidative stress related to reactive nitrogen and oxygen intermediates, measuring NO2- as a stable end-product of nitric oxide generation and superoxide dismutase as an antioxidant enzyme induced by radical oxygen species. We found that cells from patients with osteoarthritis produced higher levels of NO2- than those from patients with rheumatoid arthritis. In addition, IL-1 beta was more potent than TNF alpha in inducing nitric oxide in both arthritides, and TNFa alone was almost ineffective in cells from rheumatoid arthritis patients. We also observed that the intracellular content of copper/zinc superoxide dismutase (Cu/ZnSOD) was always lower in rheumatoid arthritis chondrocytes than in those from multi-organ donors, whereas no differences were found in intracellular manganese SOD (MnSOD) or in supernatant Cu/ZnSOD and MnSOD levels. Moreover, intracellular MnSOD was up-regulated by cytokines in osteoarthritis chondrocytes, In conclusion, our results suggest that nitric oxide may play a major role in altering chondrocyte functions in osteoarthritis, whereas the harmful effects of radical oxygen species are more evident in chondrocytes from patients with rheumatoid arthritis, due to an oxidant/antioxidant imbalance.