FIGURE 1.

Eicosanoid biosynthesis pathways in animals. Arachidonic acid-derived eicosanoids are biosynthesized through cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) pathways. Cyclooxygenases, including COX-1 and COX-2, produce prostaglandin H₂ (PGH₂) that is further converted by prostaglandin synthases (PGES, PGFS, PGDS), prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) to prostaglandins, prostacyclin, and thromboxane respectively. Lipoxygenases, including Alox5, Alox15, Alox12, and Alox8 synthesize hydroperoxyeicosatetraenoic acids (HPETEs) that are further converted to various hydroxylated and epoxidized eicosanoids. Cytochrome P450 (CYP 450) enzymes catalyze formation of various epoxyeicosatrienoic acids (EETs), which are short-lived and rapidly converted to dihydroxyeicosatrienoic acid (DHETs). HETEs, hydroxyeicosatetraenoic acids; PGH₂, prostaglandin H₂; PGE₂, prostaglandin E₂; PGF_2α, prostaglandin F_2α; PGD₂, prostaglandin D₂; PGI₂, prostacyclin; TXA₂, thromboxane A₂; PGES, PGE synthase; PGFS, PGF synthase; PGDS, PGD synthase; PGIS, PGI synthase; TXA, TXA synthase