thromboxanes

Thromboxanes are a family of eicosanoids derived from arachidonic acid through the cyclooxygenase (COX) pathway. The principal member is thromboxane A2 (TXA2), with thromboxane B2 (TXB2) as its stable, inactive metabolite used as a biomarker. Thromboxanes are produced primarily by activated platelets, and their activity is balanced by endothelial production of prostacyclin, which inhibits platelet aggregation.

Synthesis and metabolism: liberation of arachidonic acid from membrane phospholipids allows COX to convert it to prostaglandin H2 (PGH2). Thromboxane synthase then converts PGH2 to TXA2. TXA2 is short-lived, rapidly hydrolyzing to TXB2 in blood and tissues; TXB2 levels are commonly measured to assess TXA2 production.

Biological actions: TXA2 acts on TP receptors to promote vasoconstriction and platelet aggregation, supporting hemostasis but contributing to thrombosis when overproduced. It functions in autocrine and paracrine signaling within platelets and vascular smooth muscle, and its effects are counterbalanced by prostacyclin (PGI2) produced by the endothelium.

Clinical relevance: antiplatelet therapies, such as aspirin, inhibit COX-1 in platelets and reduce TXA2 synthesis, lowering thrombotic risk. Dysregulation of TXA2 signaling is implicated in cardiovascular disease and stroke. TXB2 is often used in research as a surrogate marker of TXA2 production.