Association of myocardial infarctions with COX-2 inhibition may be related to immunomodulation towards a Th1 response resulting in atheromatous plaque instability: an evidence-based interpretation

Cyclooxygenase (COX) inhibitors remain a major class of drugs in rheumatology and their widespread use is expected to continue. The view that a prothrombotic effect explains the increase in myocardial infarction (MI) associated with both COX-2 selective and traditional NSAIDs (tNSAIDs) has been increasingly questioned. We review the evidence that prostanoids direct the immune response away from a Th1 response and that consequently inhibition of prostaglandin synthesis results in augmentation of the Th1 response by limiting prostanoid synthesis. Although the role of prostanoids as mediators of inflammation in the periphery is well understood, the systemic immunomodulatory role of prostanoids shifting the immune response away from a Th1 type is less appreciated. Atherosclerosis is an inflammatory arterial disease driven by a Th1 type immune response. Moreover, the vulnerable phenotype of atheroma is associated with the cellular Th1 immune response in contrast to the stable plaque phenotype associated with a Th2 type response. We propose a class effect of COX-2 selective and tNSAIDs, which results in augmentation of Th1-mediated atherogenesis/ production of pro-atherogenic cytokines associated with detrimental plaque remodeling, instability, rupture and embolization resulting in MI. Understanding of the Th1 mediated immunity, which underlies the cardiovascular, and the non-Th1, which underlies gastrointestinal adverse effects associated with the use of COX inhibitors, should lead to better risk assessment and the development of anti-inflammatory treatments with improved safety. Our explanation also emphasizes the pharmacological effects and consequences of immunomodulation in the inflammation associated with atherosclerosis and other Th1- as well as non-Th1-driven diseases.