COX1

COX-1, or cyclooxygenase-1, is an enzyme encoded by the PTGS1 gene in humans. It is one of the two cyclooxygenase (COX) isoforms, with COX-2 being the other. COX-1 catalyzes the first step in the conversion of arachidonic acid to prostaglandin H2, the precursor to various prostanoids. The enzyme functions as a membrane-associated homodimer and carries both cyclooxygenase and peroxidase activities within a single polypeptide.

COX-1 is expressed broadly in many tissues, with relatively high levels in platelets, the gastrointestinal tract, and kidneys. Its activity provides baseline, constitutive prostanoid production that supports several physiological processes, including gastric mucosal protection, renal perfusion, and platelet aggregation through thromboxane A2.

In physiological terms, COX-1–derived prostaglandins and thromboxanes help maintain mucosal integrity, regulate renal blood flow, and enable normal hemostasis. COX-2, by contrast, is inducible and upregulated during inflammation and certain disease states.

Pharmacologically, nonsteroidal anti-inflammatory drugs (NSAIDs) typically inhibit both COX-1 and COX-2, reducing prostanoid synthesis. Aspirin irreversibly inhibits COX-1 in platelets, producing a lasting antiplatelet effect. Inhibition of COX-1 can contribute to adverse effects such as gastritis and peptic ulcers. Selective COX-2 inhibitors were developed to lessen gastrointestinal toxicity, but concerns about cardiovascular risk have limited their use due to imbalances in prostacyclin and thromboxane signaling.