Fibroblast Cyclo‐Oxygenase‐2 Associated With the Kidney Restrains Methylarginines and Thrombosis: Relevance to Cardiovascular Side Effects of Non‐Steroidal Anti‐Inflammatory Drugs

Use of non-steroidal anti-inflammatory drugs (NSAIDs), which work by inhibiting cyclo-oxygenase-2, is associated with an increased risk of thrombotic cardiovascular events. There is increasing evidence for a role of renal cyclo-oxygenase-2 in NSAID-induced cardiovascular side effects, including through dysregulation of methylarginines, endogenous inhibitors of nitric oxide synthase. However, delineating the significance of renal pathways has been hampered by a lack of suitable models. Here we have generated mouse models of cyclo-oxygenase-2 deficiency from relevant cell types to test directly their contributions. Deletion of cyclo-oxygenase-2 from fibroblasts reduced total renal expression without altering expression elsewhere. Fibroblast cyclo-oxygenase-2 knockout increased thrombosis after arterial injury, which was associated with the accumulation of plasma methylarginines and consequent systemic endothelial nitric oxide dysfunction. The pro-thrombotic phenotype in these animals was reversed by L-arginine, which competes against the inhibitory effect of methylarginines, in line with a mechanistic contribution. By comparison, pro-thrombotic phenotypes in endothelial cyclo-oxygenase-2 knockout mice, which occur via a vascular mechanism, were not associated with changes in methylarginines and were insensitive to L-arginine. Taken together, these studies provide direct evidence for a role of fibroblast and renal cyclo-oxygenase-2 in anti-thrombotic protection and demonstrate that to understand, predict, treat, and/or prevent NSAID-induced cardiovascular side effects, we must consider these pathways.