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Encyclopedia > Eicosanoid

In biochemistry, eicosanoids are a class of oxygenated hydrophobic molecules that largely function as autocrine and paracrine mediators. Eicosanoids derive from 20-carbon polyunsaturated essential fatty acids, most commonly arachidonic acid (AA) in humans. The IUPAC and the IUBMB use the equivalent term Icosanoid.[1] Biochemistry is the study of the chemical processes and transformations in living organisms. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Autocrine signalling is a form of signalling in which the target cell is the secretory cell itself. ... Paracrine signalling is a form of signalling in which the target cell is close to the signal releasing cell, and the signal chemical is broken down too quickly to be carried to other parts of the body. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Essential fatty acids, or EFAs, are fatty acids that are required in the human diet. ... Arachidonic acid is a polyunsaturated fatty acid with twenty carbons and four cis double bonds, the first at the omega-6 position (20:4n-6). ... IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ... Italic text ...

Contents

Nomenclature

The prefix eicosa- or icosa- (from the Greek for twenty; see icosahedron) denotes the number of carbon atoms in arachidonic acid. The term "eicosanoids" is used as a collective name for molecules derived from 20-carbon fatty acids[2]. Current usage limits this to the leukotrienes, prostanoids and thromboxanes, but several other classes are technically eicosanoid, including the hepoxilins, resolvins, isofurans, isoprostanes, lipoxins, epoxyeicosatrienoic acids (EETs), neuroprotectin D and some endocannabinoids. An icosahedron [ˌaıkəsəhiːdrən] noun (plural: -drons, -dra [-drə]) is a polyhedron having 20 faces, but usually a regular icosahedron is meant, which has faces which are equilateral triangles. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Leukotrienes are autocrine and paracrine eicosanoid lipid mediators derived from arachidonic acid by 5-lipoxygenase. ... Prostanoid is the term used to describe three classes of eicosanoids: the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction) and the prostacyclins (active in the resolution phase of inflamation. ... Thromboxane is a member of the family of lipids known as eicosanoids. ... Resolvins are compounds that are made by the human body from eicosapentaenoic acid (EPA). ... ... Chemical structure of 14,15-epoxyeicosatrienoic acid. ... Cannabinoids are a group of chemicals which activate the bodys cannabinoid receptors. ...


The numbering of eicosanoids is used to denote the number of double bonds. The AA-derived prostanoids have two, while the leukotrienes have four. This article does not cite its references or sources. ...

See more detail at Essential Fatty Acid Interactions - Nomenclature

The actions of the ω-3 and ω-6 essential fatty acids (EFAs) are best characterized by their interactions; they cannot be understood separately. ...

Synthesis

The first step of eicosanoid biosynthesis is the release from phospholipids (by phospholipase A2) or diacylglycerol (by phospholipase C) of a 20-carbon essential fatty acid (EFA) containing three, four, or five double bonds, (the ω-6 DGLA, ω-6 AA or ω-3 EPA, respectively). Most human eicosanoids derive from AA. This EFA has two possible eicosanoid fates: Image File history File links Eicosanoid synthesis. ... Two schematic representations of a phospholipid. ... A phospholipase is an enzyme that converts phospholipids into fatty acids and other lipophilic substances. ... Diacylglycerol (DAG) is a second messenger molecule made by phospholipase C (a membrane-bound enzyme), together with inositol triphosphate. ... Essential fatty acids, or EFAs, are fatty acids that are required in the human diet. ... Dihomo-gamma-linolenic acid (DGLA) is 20-carbon ω-3 fatty acid. ... Eicosapentaenoic acid (more commonly known as EPA; C20H30O2, all-cis-fatty acid 20:5 omega-3) is a polyunsaturated fatty acid that acts as a precursor for prostaglandin-3, which inhibits platelet aggregation) and thromboxane-3 groups. ...

Lipoxygenases are iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids in reaction: fatty acid + O2 = fatty acid hydroperoxide Lipoxygenases are found in plants and in animals. ... Leukotrienes are autocrine and paracrine eicosanoid lipid mediators derived from arachidonic acid by 5-lipoxygenase. ... Lipoxygenases are iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids in reaction: fatty acid + O2 = fatty acid hydroperoxide Lipoxygenases are found in plants and in animals. ... Cyclooxygenase (COX) is an enzyme (EC 1. ... Chemical structure of prostaglandin E1 (PGE1). ... Prostacyclin is a member of the family of lipid molecules known as eicosanoids. ... Thromboxane is a member of the family of lipids known as eicosanoids. ...

Leukotrienes

5-lipoxygenase uses the nuclear-membrane protein cofactor 5-lipoxygenase-activating protein (FLAP) to sequentially convert arachidonic acid, first into 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and then 5-HPETE into leukotriene A4 (LTA4). LTA4 may be converted into LTB4 by the enzyme leukotriene A4 epoxide hydrolase. Eosinophils, mast cells, and alveolar macrophages use the enzyme leukotriene C4 synthase to conjugate glutathione with LTA4 to make leukotriene C4 (LTC4). LTC4 is transported out of the cell, where a glutamic acid moiety is removed from it to make leukotriene D4 (LTD4). LTD4 is cleaved by dipeptidases to make leukotriene E4 (LTE4). A cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction. ... Eosinophils are white blood cells that are responsible for combating infection by parasites in the body. ... Mast cells A mast cell (or mastocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, makros = long, phagein = eat) are white blood cells, more specifically phagocytes, acting in the nonspecific defense as well as the specific defense system of vertebrate animals. ... Skeletal formula of glutathione 3D model of glutathione Glutathione (GSH), whose IUPAC name is 2-amino-5-{[2-[(carboxymethyl)amino]- 1-(mercaptomethyl)-2-oxoethyl]amino}-5-oxopentanoic acid, is γ-glutamylcysteinylglycine, a tripeptide. ... Glutamic acid (Glu), also referred to as glutamate (the anion), is one of the 20 proteinogenic amino acids. ... Look up moiety in Wiktionary, the free dictionary. ...


LTC4, LTD4 and LTE4 all contain cysteine and are collectively known as the cysteinyl leukotrienes. Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins, though only in small quantities. ...


Prostanoids

All prostanoids originate from prostaglandin H (PGH, as PGH1, PGH2, or PGH3), which is converted by different enzymes into the various compounds. The enzyme PGH2-synthase is in fact a combination of a peroxidase and a cyclooxygenase (Cox-1 or Cox-2). The Cox enzymes are the molecular target of the NSAIDs, such as aspirin (see below). Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Glutathione Peroxidase 1 A peroxidase (eg. ... Cyclooxygenase (COX) is an enzyme (EC 1. ... Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. ... Aspirin or acetylsalicylic acid (acetosal) is a drug in the family of salicylates, often used as an analgesic (against minor pains and aches), antipyretic (against fever), and anti-inflammatory. ...


PGH is converted:

  • By PGE synthetase into PGE (which in turn is converted into PGF)
  • By PGD synthetase into PGD
  • By Prostacyclin synthase into prostacyclin (PGI2)
  • By Thromboxane synthase into thromboxanes

Prostacyclin is a member of the family of lipid molecules known as eicosanoids. ... Thromboxane is a member of the family of lipids known as eicosanoids. ...

Receptors

There are specific receptors for all eicosanoids (see also specific articles):

  • Leukotrienes:
    • CysLT1 (Cysteinyl leukotriene receptor type 1)
    • CysLT2 (Cysteinyl leukotriene receptor type 2)
    • BLT1 (Leukotriene B4 receptor)
  • Prostanoids:
    • PGD2: DP-(PGD2)
    • PGE2:
      • EP1-(PGE2)
      • EP2-(PGE2)
      • EP3-(PGE2)
      • EP4-(PGE2)
    • PGF: FP-(PGF)
    • PGI2 (prostacyclin): IP-(PGI2)
    • TXA2 (thromboxane): TP-(TXA2)

Function and pharmacology

Eicosanoids have a short lifetime, ranging from seconds to minutes.


Leukotrienes

Leukotrienes play an important role in inflammation, especially as part of the Slow Reacting Substance of Anaphylaxis, and blocking leukotriene receptors can play a role in the management of inflammatory diseases such as asthma (montelukast, zafirlukast), psoriasis, and rheumatoid arthritis. Inflammation is the first response of the immune system to infection or irritation and may be referred to as the innate cascade. ... Montelukast is an oral leukotriene receptor antagonist (LTRA) for the maintenance treatment of asthma and to relieve symptoms of seasonal allergies. ... Zafirlukast is an oral leukotriene receptor antagonist (LTRA) for the maintenance treatment of asthma. ...


Prostanoids

Main articles: Prostaglandin, Prostacyclin and Thromboxane.

Prostanoids mediate local symptoms of inflammation: vasoconstriction or vasodilation, coagulation, pain and fever. Inhibition of cyclooxygenase, specifically the inducible COX II isoform, is the hallmark of NSAIDs (non-steroidal anti-inflammatory drugs), such as aspirin. COX II is responsible for pain and inflammation, while COX I is responsible for platelet clotting actions. Chemical structure of prostaglandin E1 (PGE1). ... Prostacyclin is a member of the family of lipid molecules known as eicosanoids. ... Thromboxane is a member of the family of lipids known as eicosanoids. ... Inflammation is the first response of the immune system to infection or irritation and may be referred to as the innate cascade. ... The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... The coagulation of blood is a complex process during which blood forms solid clots. ... Look up Pain in Wiktionary, the free dictionary. ... An analogue medical thermometer showing the temperature of 38. ... Cyclooxygenase (COX) is an enzyme (EC 1. ... Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. ... Aspirin or acetylsalicylic acid (acetosal) is a drug in the family of salicylates, often used as an analgesic (against minor pains and aches), antipyretic (against fever), and anti-inflammatory. ...


See Also

The actions of the ω-3 and ω-6 essential fatty acids (EFAs) are best characterized by their interactions; they cannot be understood separately. ... Cannabinoids are a group of chemicals which activate the bodys cannabinoid receptors. ...

References

  1.  Beare-Rogers (2001). IUPAC Lexicon of Lipid Nutrition. Retrieved on June 1, 2006. (in .pdf format)
  2.   Cyberlipid Center. Prostanoids. Retrieved on June 1, 2006.
  3. Dr M.W. King's biochemistry page

  Results from FactBites:
 
Eicosanoid - Wikipedia, the free encyclopedia (491 words)
In biochemistry, eicosanoids are a class of oxygenated hydrophobic molecules that largely function as autocrine and paracrine mediators.
Eicosanoids derive from 20-carbon polyunsaturated essential fatty acids, most commonly arachidonic acid (AA) in humans.
The numbering of eicosanoids is used to denote the number of double bonds.
The Eicosanoid Power (822 words)
Eicosanoids are composed of about a dozencompounds whose importance has been discovered only in the last 10 to 15 years.
Eicosanoids are mainly formed in the body by arachidonic acid (AA), an omega-6 fatty acid found in vegetable oils.
Eicosanoids are divided into two families: the prostaglandins (PGs), which are made by an enzyme called cyclooxygenase; and the leukotrienes, which are made by an enzyme called lipooxygenase (Fig.
  More results at FactBites »

 
 

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