Eicosanoids — Prostaglandins, Thromboxanes and Leukotrienes

Introduction

• Eicosanoids — (Greek eikosi = twenty) are oxygenation products of 20-carbon polyunsaturated fatty acids — the most universally distributed autacoids (local hormones formed locally, acting locally, with brief action and local destruction); virtually every cell can synthesise one or more.
• The umbrella covers prostaglandins (PGs), prostacyclin (PGI₂), thromboxanes (TX), leukotrienes (LTs), lipoxins, HETEs/EETs (CYP products), isoprostanes and ω-3-derived resolvins/protectins/maresins.
• Prostanoids — = the cyclooxygenase products only (PGs + TXs + prostacyclin; share a cyclopentane ring). Leukotrienes = straight-chain lipoxygenase products (leuko = leukocytes + triene = 3 conjugated double bonds).
• Major mammalian precursor = arachidonic acid (AA, eicosatetraenoic acid) → series-2 prostanoids; subscript = number of side-chain double bonds, letter (A–I) = ring structure.
• Clinical relevance: govern vascular tone, haemostasis, parturition, GI mucosal integrity, renal function, inflammation, fever and pain — and NSAIDs/aspirin owe their action to blocking PG synthesis (Vane, 1971; Nobel Prize 1982).