Effects of glucocorticoids on chondrocytes and cartilage
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OBJECTIVE: Osteoarthritis (OA) is a leading cause of disability worldwide. This disease is characterized by the inflammation and degradation of the cartilage and surrounding tissue in a joint. The disease manifests as either a result of years of wear and tear or after a joint injury. Post-traumatic osteoarthritis, as this latter case is named, is frequently studied since the exact trigger of the disease is known. In addition to several changes within the joint space, a significant alteration is the degradation of cartilage caused primarily by the release of inflammatory cytokines including interleukin-1 and 6 and tumor necrosis factor α. One current pharmacological treatment for the pain caused by OA is an intra-articular injection of glucocorticoids such as dexamethasone. As this is a common treatment, the goal of this research was to determine if, at the cellular level, this treatment impacts cell viability in the presence of pro-inflammatory cytokines. Another goal was to investigate how such treatment affects the progression of cartilage degradation caused by cytokines. OA results in the loss of the key extracellular matrix molecule, aggrecan, which contains negatively charged glycosaminoglycan (GAG) chains. Measurement of the amount of GAGs lost is an early indicator of cartilage degradation. In addition, biosynthesis of GAG chains can be measured to estimate the overall metabolic health of the cells. We hypothesized that dexamethasone blunts the harmful effects of proinflammatory cytokines and improves GAG biosynthesis and chondrocyte viability. METHODS: Cylindrical cartilage explants were collected from bovine knee joints and trimmed to a uniform 3 millimeters in diameter and 1 millimeter thick. Each treatment group consisted of n=6 explants from the same knee joint. In one set of experiments, these explants were subjected to two different doses of interleukin-1α (1 ng/mL and 10 ng/mL) with and without dexamethasone at 100 nM. In another set of experiments, explants were subjected to both interleukin-1α and tumor necrosis factor-α (1 ng/mL and 25 ng/mL respectively). The explants were cultured in medium for 6 days and were digested for outcome measurements on the final day. On day 4, 35S-sulfate was added to the explant medium for later measurement of radiolabel incorporation as a measure of GAG biosynthesis. Cell viability was measured on day 5 using red/green fluorescent viability dyes fluorescein diacetate (FDA) which stains live cells green and propidium iodide (PI) which stains dead cells red. RESULTS: Compared with untreated controls, explants subjected to the pro-inflammatory cytokines interleukin-1α and tumor necrosis factor-α exhibited greater glycosaminoglycan loss and a decrease in GAG biosynthesis. These treatments also decreased cell viability. Addition of dexamethasone improved cell viability compared to treatment with the cytokines. In addition, dexamethasone prevented glycosaminoglycan loss and increased GAG biosynthesis in the presence of interleukin-1α. However, dexamethasone did not prevent tumor necrosis factor-α mediated loss of GAGs. CONCLUSION: These studies demonstrated that dexamethasone inhibited specific aspects of cartilage degradation associated with inflammation in early OA. This therapeutic counteracts the degradative changes initiated by inflammatory cytokines such as interleukin-1α without compromising cell viability. Future studies are needed to identify the mechanisms of dexamethasone action and the ideal concentration to use if it is to be used as a treatment for OA following acute joint injury.