Eicosanoid naming

The EFA are the precursors of the eicosanoids, namely prostaglandins, leukotrienes, thromboxanes, hydroxy fatty acids, and lipoxins. These important extracellular mediators at low concentrations have critical roles in skin homeostasis. At high concentrations they are involved... 

Eicosanoids, so named because they are all derived from 20-carbon fatty acids, are ubiquitous breakdown products of phospholipids. In response to appropriate stimuli, cells activate the breakdown of selected phospholipids (Figure 25.27). Phospholipase Ag (Chapter 8) selectively cleaves fatty acids from the C-2 position of phospholipids. Often these are unsaturated fatty acids, among which is arachidonic acid. Arachidonic acid may also be released from phospholipids by the combined actions of phospholipase C (which yields diacyl-glycerols) and diacylglycerol lipase (which releases fatty acids). 

Fatty acid derivatives include a large and diverse group of compounds named eicosanoids, which includes thromboxanes, prostaglandins and leukotrienes, all of which are biochemically derived from arachidonic acid (a long-chain polyunsaturated fatty acid). 

Eicosanoids include prostaglandins, leukotrienes, prostacyclins and thromboxanes. They are given their collective name since they contain 20 carbon atoms (Figure 11.16). 

The final product of this chain of events—arachidonic acid—is one of the eicosanoids, so called because eicosa is Greek for twenty, and the systematic names for these compounds contain eicosanoic acid in some form. The leukotrienes resemble arachidonic acid most closely, the prostaglandins have a closed chain forming a five-membered ring, and the thromboxanes resemble the prostaglandins but have a broken chain. A)] are C20 compounds with the sites of the alkenes (C5, C8, Cl 1, and Cl 4) marked by functionality or some other structural feature. 

Eicosanoids are named by their ring system, substitution pattern and number of double bonds. 

Eicosanoids, also referred to as icosanoids, are so named because of the 20-carbon constituency that identifies this class of oxygenated lipid molecules. A primary synthetic pathway for these molecules involves the phospholipase-mediated cleavage of a membrane phospholipid to produce arachidonic acid [(all-Z)-ik osa-5,8,ll,14-tetraenoic acid]. From this biologically essential intermediate fatty acid, two major subclasses of eicosanoids can be produced 1) leukotrienes, via the action of lipooxygenases, and 2) prostanoids, via the action of cyclooxygenases (COX-1 and COX-2). Examples of chemical structures for a leukotriene (Fig. la) and three types of prostanoids (Fig. Ib-d) underscore their shared arachidonate origin. 

Figure 1 Chemical structures of representative eicosanoid molecules (a) leukotriene, (b) prostaglandin, (c) prostacyclin, and (d) thromboxane. Common names, chemical formulas, and molecular weights (g/mol) are shown.

Eicosanoids (prostaglandins, thromboxanes, leuko-trienes, lipoxins) is the name given to a group of 20-carbon unsaturated fatty acids derived principally from arachidorric acid in cell walls. They are shortlived, extremely potent and formed in almost every tissue in the body. Eicosanoids are involved in most types of inflammation and it is on manipulation of their biosynthesis that most present anti-inflammatory therapy is based. Their biosynthetic paths appear in Figure 15.1 and are amplified by the following account. 

LEUKOTRIENE RECEPTOR AGONISTS act at receptors recognizing leukotrienes and analogues. The lipoxygenase system forms the leukotrienes, which are members of the eicosanoid family of phospholipid mediators. Their name derives from the fact that leukotrienes are found in leucocytes and contain a triene system of double bonds. The other members of the eicosanoid family are the prostanoids (thromboxanes and the prostaglandins), and these are formed by the cyclooxygenase system see cyclooxygenase INHIBITORS. All the eicosanoids are derived mainly from arachidonic acid. These mediators are synthesized on demand, and in some cases their half-lives are short. The... 

The answer is b. (Murray, pp 505-626. Scriver, pp 5029-5250. Sack, pp 121-138. Wilson, pp 287-320.) The essential fatty acid linoleic acid, with 18 carbons and two double bonds at carbons 9 and 18 (C-18 2-A ) is desaturated to form a-linolenic acid (C-18 3-A ), which is sequentially elongated and desaturated to form eicosatrienoic acid (C-20 3-2 8,11,1+) arachidonic acid (C-20 4-A " ), respectively. Many of the eicosanoids (20-carbon compounds)—prostaglandins, thromboxanes, and leukotrienes—are derived from arachidonic acid. The scientific name of arachidonic acid is eicosatetraenoic acid. Arachidonic acid can only be synthesized from essential fatty acids obtained from the diet. Palmitic acid (C-16 0) and oleic acid (C-18 l-A" ) can be synthesized by the tissues. 

The leukotrienes, a new class of acyclic eicosanoids, are normally named using either a systematic or an abbreviated nomenclature. A note is in order on this latter system, which was introduced by Samuelsson. ... 

Some of the unsaturated fatty acids containing more than one double bond cannot be synthesized by the body For many years it has been known that linolenic acid and linoleic acid, called the essential fatty acids, are necessary for specific biochemical functions and must be supplied in the diet (see Table 18.1). The fimction of linoleic acid became clear in the 1960s when it was discovered that linoleic acid is required for the bios)mthesis of arachidonic acid, the precursor of a class of hormonelike molecules known as eicosanoids. The name is derived from the Greek word eikos, meaning "twenty," because they are all derivatives of twenty-carbon fatty acids. The eicosanoids include three groups of structurally related compounds the prostaglandins, the leukotrienes, and the thromboxanes. 

Eicosanoids are a class of lipids that include the prostaglandins, thromboxanes, and leukotrienes. Eicosanoids derive their name from their common origin, that is, from C20 polyunsaturated fatty acids, the eicosaenoic acids, particularly arachidonic acid (all-cw-5,8,ll,14-eicosatetraenoic acid). Related trienoic and pentaenoic acids are minor precursors to some of these compounds. 

Leukotrienes are eicosanoids that were originally isolated from leukocytes and contain three double bonds, which explains how they were named. As shown in Figure 19.32, leukotrienes are formed by a pathway independent of that of forming the prostaglandins and thromboxanes. 

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