Cardiovascular Consequences of Prostanoid i Receptor Deletion in Microsomal Prostaglandin e Synthase-1-Deficient Hyperlipidemic Mice

Background: Inhibitors of cyclooxygenase-2 alleviate pain and reduce fever and inflammation by suppressing the biosynthesis of prostacyclin (PGI₂) and prostaglandin E₂. However, suppression of these prostaglandins, particularly PGI₂, by cyclooxygenase-2 inhibition or deletion of its I prostanoid receptor also predisposes to accelerated atherogenesis and thrombosis in mice. By contrast, deletion of microsomal prostaglandin E synthase 1 (mPGES-1) confers analgesia, attenuates atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E₂, but increasing biosynthesis of PGI₂. Methods: To address the cardioprotective contribution of PGI₂, we generated mice lacking the I prostanoid receptor together with mPges-1 on a hyperlipidemic background (low-density lipoprotein receptor knockouts). Results: mPges-1 depletion modestly increased thrombogenesis, but this response was markedly further augmented by coincident deletion of the I prostanoid receptor (n=10-18). By contrast, deletion of the I prostanoid receptor had no effect on the attenuation of atherogenesis by mPGES-1 deletion in the low-density lipoprotein receptor knockout mice (n=17-21). Conclusions: Although suppression of prostaglandin E₂ accounts for the protective effect of mPGES-1 deletion in atherosclerosis, augmentation of PGI₂ is the dominant contributor to its favorable thrombogenic profile. The divergent effects on these prostaglandins suggest that inhibitors of mPGES-1 may be less likely to cause cardiovascular adverse effects than nonsteroidal anti-inflammatory drugs specific for inhibition of cyclooxygenase-2.