NSAIDS inhibit in vitro MSC chondrogenesis but not osteogenesis: implications for mechanism of bone formation inhibition in man

The non‐steroidal anti‐inflammatory drugs (NSAIDs) are widely used for analgesia but may inhibit bone formation. We investigated whether the reported NSAID effect on bone is related to inhibition of bone marrow mesenchymal stem cell (MSC) proliferation and osteogenic and chondrogenic differentiation and evaluated both cyclooxygenase (COX)‐1 and COX‐2 specific drugs. The effects of seven COX‐1 and COX‐2 inhibitors on MSC proliferation and osteogenic and chondrogenic differentiation were tested using Vybrant, sodium 3′‐[1‐(phenylaminocarbonyl)‐ 3,4‐tetrazolium]‐bis (4‐methoxy‐6‐nitro) benzene sulfonic acid hydrate (XTT), functional and quantitative assays of MSC differentiation. The MSC expression of COX‐1 and COX‐2 and prostaglandin E2 (PGE‐2) levels were evaluated serially during lineage differentiation by quantitative PCR and ELISA. None of the NSAIDs at broad range of concentration (range 10−3 to 100 μg/ml) significantly affected MSC proliferation. Surprisingly, MSC osteogenic differentiation inhibition was not evident. However, NSAIDs affected chondrogenic potential with a reduction in sulphated glycosaminoglycans (sGAG) content by 45% and 55% with diclofenac and ketorolac, respectively (P < 0.05 compared to controls). Parecoxib and meloxicam, more COX‐2 specific reagents inhibited sGAG to a lesser degree, 22% and 27% respectively (P < 0.05 compared to controls). Cartilage pellet immunohistochemistry confirmed the above results. Pellet chondrogenesis was associated with increased COX‐1 expression levels but not COX‐2, and COX‐1 specific drugs suppressed MSC PGE‐2 more than COX‐2 specific inhibitors. These findings suggest that NSAIDs may inhibit bone formation via blockage of MSC chondrogenic differentiation which is an important intermediate phase in normal endochondral bone formation.