An exploration of the ability of tepoxalin to ameliorate the degradation of articular cartilage in a canine in vitro model

BACKGROUND: To study the ability of tepoxalin, a dual inhibitor of cyclooxygenase (COX) and lipoxygenase (LOX) and its active metabolite to reduce the catabolic response of cartilage to cytokine stimulation in an in vitro model of canine osteoarthritis (OA). Grossly normal cartilage was collected post-mortem from seven dogs that had no evidence of joint disease. Cartilage explants were cultured in media containing the recombinant canine interleukin-1β (IL-1β) at 100 ng/ml and recombinant human oncostatin-M (OSM) at 50 ng/ml. The effects of tepoxalin and its metabolite were studied at three concentrations (1 × 10(-5), 1 × 10(-6 )and 1 × 10(-7 )M). Total glycosaminoglycan (GAG) and collagen (hydroxyproline) release from cartilage explants were used as outcome measures of proteoglycan and collagen depletion respectively. PGE(2 )and LTB(4 )assays were performed to study the effects of the drug on COX and LOX activity. RESULTS: Treatment with IL-1β and OSM significantly upregulated both collagen (p = 0.004) and proteoglycan (p = 0.001) release from the explants. Tepoxalin at 10(-5 )M and 10(-6 )M caused a decrease in collagen release from the explants (p = 0.047 and p = 0.075). Drug treatment showed no effect on GAG release. PGE(2 )concentration in culture media at day 7 was significantly increased by IL-1β and OSM and treatment with both tepoxalin and its metabolite showed a trend towards dose-dependent reduction of PGE(2 )production. LTB(4 )concentrations were too low to be quantified. Cytotoxicity assays suggested that neither tepoxalin nor its metabolite had a toxic effect on the cartilage chondrocytes at the concentrations and used in this study. CONCLUSION: This study provides evidence that tepoxalin exerts inhibition of COX and can reduce in vitro collagen loss from canine cartilage explants at a concentration of 10(-5 )M. We can conclude that, in this model, tepoxalin can partially inhibit the development of cartilage degeneration when it is available locally to the tissue.