Background and objective: The selective COX-2 inhibitor celecoxib is widely used to treat pain and inflammation in rheumatoid arthritis, osteoarthritis, and ankylosing spondylitis. The drug has well-known important effects on immune cells but its direct and/or indirect influence on osteoblasts has not yet been explored in detail. This study aimed to investigate the dose-dependent effects of celecoxib on cell viability, energy metabolism and bone remodeling processes in cultured human osteoblastic cells.
Methods: Primary human osteoblasts and MG-63 cells were incubated with celecoxib (2, 10, 50microM). Cell viability and apoptosis were determined by trypan blue, 7AAD and Annexin-V staining. Effects on cellular oxygen consumption were measured amperometrically using a Clark electrode. mRNA expression of GLUT-1 and OPG was determined by RT-PCR; OPG protein secretion by ELISA and HIF-1alpha protein expression by immunoblotting.
Results: While celecoxib at a concentration of 2 and 10microM showed only marginal effects, a suprapharmacological concentration of 50microM influenced viability and energy metabolism, as well as OPG expression and secretion of osteoblastic cells. Cell viability was significantly reduced by celecoxib treatment. Celecoxib at 50microM stimulated oxygen consumption significantly. Corresponding experiments with the protonophore FCCP suggest that this effect is due to mitochondrial uncoupling. After 24h, GLUT-1 mRNA expression was significantly increased. HIF-1alpha protein was not expressed under any of our experimental conditions. We also showed that celecoxib at 50microM significantly inhibits OPG protein secretion leading to a compensative increase of mRNA expression.
Conclusion: Pronounced effects of celecoxib on cell viability (reduction), oxygen consumption (stimulation), GLUT-1 mRNA expression (stimulation) and OPG protein secretion (inhibition) in osteoblastic cells were observed only at 50microM-a concentration not reached by therapeutic doses giving plasma concentrations less than 10microM. On the contrary, celecoxib at 2 and 10microM showed only marginal effects, suggesting that celecoxib administration is probably safe with respect to bone metabolism in cases requiring potent treatment of pain and inflammation. However, higher intracellular concentrations, which might occur through accumulation, necessitate investigations with high concentrations.