Inducible cyclooxygenase and nitric oxide synthase

Prostacyclin and nitric oxide-related gene transfer in preventing arterial thrombosis and restenosis

Prostacyclin (PGI2) and nitric oxide (NO) are potent vascular mediators, playing key roles in protecting arterial wall from injury-induced lesions. The key enzyme that catalyzes PGI2 biosynthesis is cyclooxygenase (COX). COX-1 undergoes auto-inactivation, which severely limits PGI2 synthesis. Overexpression of COX-1 in cultured endothelial cells by COX-1 gene transfer was accompanied by a higher capacity for and sustained synthesis of PGI2. Adenovirus-mediated COX-1 gene transfer to angioplasty damaged carotid arteries in pigs augmented PGI2 synthesis and prevents thrombus formation. Transfer of endothelial NO synthase (eNOS) into angioplasty injured, carotid arteries was reported to suppress intimal hyperplasia in rats. Transfer of PGI2 and NO synthetic enzymes restores the vasoprotective properties and represents an exciting new strategy for treating arterial thrombotic disorders.

Role of endothelium in thrombosis and hemostasis

Vascular endothelium is strategically located at the interface between tissue and blood. It is pivotal for protecting against vascular injury and maintaining blood fluidity. Normal endothelium releases prostacyclin and nitric oxide, potent inhibitors of platelet and monocyte activation and vasodilators. Their syntheses are governed by isoforms of enzymes. Normal endothelial surface expresses ecto-adenosine diphosphatase, which degrades adenosine diphosphate and inhibits platelet aggregation; thrombomodulin, which serves as a binding site for thrombin to activate protein C; and heparin-like molecules, which serve as a cofactor for antithrombin III. Normal endothelium secretes tissue plasminogen activator, which activates the fibrinolysis system. Endothelium produces and secretes von Willebrand factor, which mediates platelet adhesion and shear-stress-induced aggregation. Injury to endothelium is accompanied by loss of protective molecules and expression of adhesive molecules, procoagulant activities, and mitogenic factors, leading to development of thrombosis, smooth muscle cell migration, and proliferation and atherosclerosis.