Prostaglandins, in inflammation

There are two isoforms of COX in animals COX-1 (figure a), which carries out normal, physiological production of prostaglandins, and COX-2 (figure b), which is induced by cytokines, mitogens, and endotoxins in inflammatory cells and is responsible for the production of prostaglandins in inflammation. 

The recognition of the role of prostaglandins in inflammation and platelet function led to the rapid use of the production or inhibition of various prostaglandins as markers for inflammatory and thrombotic diseases. 

Inhibition of the cyclooxygenase of PGH synthase by aspirin reduces inflammation, implicating prostaglandins in inflammation. 

Hata AN, Breyer RM (2004) Pharmacology and signaling of prostaglandin receptors Multiple roles in inflammation and immune modulation. Pharmacol Ther 103 147-166... 

Alcantara C, Stenson WF, Steiner TS, Guerrant RL Role of inducible cyclooxygenase and prostaglandins in Clostridium difficile toxin A-induced secretion and inflammation in an animal model. J Infect Dis 2001 184 648-652. 

The effects of LCPUFAs in inflammation have been reviewed by Calder (2006). Briefly, if is h) ofhesized fhaf fhe effecfs of LCPUFA n-3 fatty acids on immune function are mediated by their ability to compete with the metabolism of fhe n-6 fatty AA. AA can be metabolized into the pro-inflammatory prostaglandin-E2 (PGE2) or leukotriene-B4 (LTB4). 

V.c.1.1. Cyclo-oxygenase inhibition. Inhibition of cyclo-oxygenase reduces the level of circulating prostaglandins and neurogenic inflammation. This is the mechanism of action of nonsteroidal antiinflammatory drugs (NSAID) and aspirin. The mode of action of paracetamol is less clear (inhibition of prostaglandins in the nociceptors of the posterior horn of the spinal cord and action on the supraspinal structures implicated in nociception). 

The cell damage associated with inflammation acts on cell membranes to cause leukocytes to release lysosomal enzymes arachidonic acid is then liberated from precursor compounds, and various eicosanoids are synthesized. As discussed in Chapter 18, the cyclooxygenase (COX) pathway of arachidonate metabolism produces prostaglandins, which have a variety of effects on blood vessels, on nerve endings, and on cells involved in inflammation. The lipoxygenase pathway of arachidonate metabolism yields leukotrienes, which have a powerful chemotactic effect on eosinophils, neutrophils, and macrophages and promote bronchoconstriction and alterations in vascular permeability. 

Prostaglandins have been implicated both in the induction of inflammation and in its relief. In inflammation small blood vessels become dilated, and fluid and proteins leak into the interstitial spaces to produce the characteristic swelling (edema). Many polymorphonuclear leukocytes attracted by chemotactic factors that include LTB4309 (Chapter 19) migrate into the inflamed area, engulfing dead tissue and bacteria. In this process lysosomes of the leukocytes release phospholipase A, which hydrolyzes phospholipids and initiates the arachidonate cascade. The leukotrienes that are formed promote the inflammatory response. However, cAMP can suppress inflammation, and PGE2 has a similar effect. Indeed, E prostaglandins, when inhaled in small amounts, relieve asthma. 

Besides 12-LOX in platelets, the 5-LOX isoforms are constitutive in neutrophils. Evidences indicate that LOXs are involved in inflammation diseases and in atherosclerosis. 5-LOX is the enzyme that catalyzes the formation of leukotrienes with potential role for leukocytes and platelets interaction and inflammation. After platelet and leukocyte stimulation, products of both COX-1 and 5-LOX pathways increase. COX-1 activity derivatives increase the vascular permeability mediated by prostaglandins and produce platelet aggregation mediated by TXA2. The product of the lipoxygenase pathway, 5-oxo-6,8,1 1,14-eicosatetraenoic acid (5-Oxo-ETE), induces leukocyte chemotaxis and inflammation. 5-Oxo-ETE is formed by the oxidation of 5S-hydroxy-ETE (5-HETE) by 5-hydroxyeicosanoid dehydrogenase (5-HEDH), a microsomal enzyme found in leukocytes and platelets (42). 

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