- Linoleic acid
-
Not to be confused with linolenic acid.
Linoleic acid 
cis, cis-9,12-Octadecadienoic acid[1]Other namesC18:2 (Lipid numbers)Identifiers CAS number 60-33-3 
ChemSpider 4444105 UNII 9KJL21T0QJ KEGG C01595 ChEBI CHEBI:17351 
ChEMBL CHEMBL267476 Jmol-3D images Image 1 - CCCCC/C=C\C/C=C\CCCCCCCC(=O)O
- InChI=1S/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9-
Key: OYHQOLUKZRVURQ-HZJYTTRNSA-N
InChI=1/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9-
Key: OYHQOLUKZRVURQ-HZJYTTRNBX
Properties Molecular formula C18H32O2 Molar mass 280.45 g mol−1 Appearance Colorless oil Density 0.9 g/cm3[2] Melting point Boiling point Solubility in water 0.139 mg/L[3] Vapor pressure 16 Torr at 229 °C[citation needed] Hazards Flash point 112 °C (234 °F)[3] 
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)Infobox references Linoleic acid (LA) is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2(n-6). Chemically, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; the first double bond is located at the sixth carbon from the methyl end.[4]
Linoleic acid belongs to one of the two families of essential fatty acids that humans and animals must ingest for good health, because the body requires them for various biological processes, but cannot synthesize them from other food components.[5]
The word "linoleic" comes from the Greek word linon (flax). Oleic means "of, relating to, or derived from oil or olive" or "of or relating to oleic acid" because saturating the n-6 double bond produces oleic acid.
Contents
In physiology
LA is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins. It is found in the lipids of cell membranes. It is abundant in many vegetable oils, comprising over half (by weight) of poppy seed, safflower, sunflower, and corn oils.[6]
Linoleic acid is an essential fatty acid that must be consumed for proper health. A lack of LA and other n-6 fatty acids in the diet causes dry hair, hair loss,[7] and poor wound healing.[8] However, achieving a deficiency in linoleic acid is nearly impossible consuming any normal diet and is thus not considered to be of clinical concern.
Along with oleic acid, linoleic acid is released by cockroaches upon death to deter other roaches from entering the area. This is similar to the mechanism found in ants and bees, in which oleic acid is released upon death.[9]
Metabolism and eicosanoids
The first step in the metabolism of LA is performed by Δ6desaturase, which converts LA into gamma-linolenic acid (GLA).
There is evidence suggesting that infants lack Δ6desaturase of their own, and must acquire it through breast milk. Studies show that breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA.[10]
GLA is converted to Dihomo-gamma-linolenic acid (DGLA), which in turn is converted to arachidonic acid (AA). One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids, a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to be inflammatory.[11] For example, both AA-derived thrombaxane and leukotrieneB4 are proaggretory and vasoconstrictive eicosanoids. The oxidized metabolic products of linolenic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1, the capsaicin receptor, and through this might play a major role in hyperalgesia and allodynia.[12]
An increased intake of certain [13] n–3 fatty acids with a decrease in n-6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.[14]
One study monitoring two groups of survivors of myocardial infarction concluded “the concentration of alpha-linolenic acid was increased by 68%, in the experimental group, and that of linoleic acid reduced by 7%...the survivors of a first myocardial infarction, assigned to a Mediterranean alpha-linolenic acid rich diet, had a markedly reduced rate of recurrence, other cardiac events and overall mortality.” [15]
Industrial uses
Linoleic acid is used in making quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the easy reaction of the linoleic acid with oxygen in air, which leads to crosslinking and formation of a stable film.
Reduction of linoleic acid yields linoleyl alcohol.
Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, and moisture retentive properties when applied topically on the skin.[16][17][18]
Appendix: Dietary sources
Name % LA† ref. Safflower oil 78% Grape seed oil 73% Poppyseed oil 70% Sunflower oil 68% Hemp oil 60% Corn oil 59% Wheat germ oil 55% Cottonseed oil 54% Soybean oil 51% Walnut oil 51% Sesame oil 45% Rice bran oil 39% Pistachio oil 32.7% Peanut oil 32% [19] Canola oil 21% Chicken fat 18-23% [20] Egg yolk 16% Linseed oil 15% Lard 10% Olive oil 10% Palm oil 10% Cocoa butter 3% Macadamia oil 2% Butter 2% Coconut oil 2% †average val See also
- Conjugated linoleic acid
- Essential fatty acids
- Essential fatty acid interactions
- Eicosanoids
- Essential nutrients
- Linolein
References
- ^ Beare-Rogers (2001). "IUPAC Lexicon of Lipid Nutrition" (PDF). http://www.iupac.org/publications/pac/2001/pdf/7304x0685.pdf. Retrieved 2006-02-22.
- ^ a b c The Merck Index, 11th Edition, 5382
- ^ a b c d Record of CAS RN 60-33-3 in the GESTIS Substance Database from the IFA
- ^ David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_245.pub2
- ^ Burr, G.O., Burr, M.M. and Miller, E. (1930). "On the nature and role of the fatty acids essential in nutrition". J. Biol. Chem. 86 (587): 1–9. http://www.jbc.org/cgi/reprint/97/1/1.pdf.
- ^ U.S. Department of Agriculture, Agricultural Research Service. 2007. USDA National Nutrient Database for Standard Reference, Release 20. Nutrient Data Laboratory Home Page
- ^ Cunnane S, Anderson M (1 April 1997). "Pure linoleate deficiency in the rat: influence on growth, accumulation of n-6 polyunsaturates, and (1-14C) linoleate oxidation". J Lipid Res 38 (4): 805–12. PMID 9144095. http://www.jlr.org/cgi/reprint/38/4/805. Retrieved 2007-01-15.
- ^ Ruthig DJ & Meckling-Gill KA. (1 October 1999). "Both (n-3) and (n-6) fatty acids stimulate wound healing in the rat intestinal epithelial cell line, IEC-6". Journal of Nutrition 129 (10): 1791–8. PMID 10498749. http://jn.nutrition.org/cgi/content/full/129/10/1791. Retrieved 2007-01-15.
- ^ BBC - Earth News - Ancient 'smell of death' revealed
- ^ David F. Horrobin (1993). "Fatty acid metabolism in health and disease: the role of Δ-6-desaturase". American Journal of Clinical Nutrition 57: 732S–7S.
- ^ Piomelli, Daniele (2000). "Arachidonic Acid". Neuropsychopharmacology: The Fifth Generation of Progress. http://www.acnp.org/g4/GN401000059/Default.htm. Retrieved on 4/16/09.
- ^ Patwardhan, AM; Scotland, PE; Akopian, AN; Hargreaves, KM (2009). "Activation of TRPV1 in the spinal cord by oxidized linoleic acid metabolites contributes to inflammatory hyperalgesia". Proceedings of the National Academy of Sciences of the United States of America 106 (44): 18820–4. doi:10.1073/pnas.0905415106. PMC 2764734. PMID 19843694. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2764734.
- ^ Kinsella, JE; Lokesh, B; Stone, RA (1990). "Dietary n-3 polyunsaturated fatty acids and amelioration of cardiovascular disease: possible mechanisms". The American journal of clinical nutrition 52 (1): 1–28. PMID 2193500.
- ^ Kinsella John E., Lokesh Belur, Stone Richard A. (1990). "Dietary n-3 polyunsatruated fatty acids and amelioration of cardiovascular disease: possible mechanisms". American Journal of Clinical Nutrition 52 (1): 1–28. PMID 2193500.
- ^ Michel, Renaud Serge (1994). "Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease". Lancet 343: 8911.
- ^ "Plant oils: Topical application and anti-inflammatory effects (croton oil test)". Dermatol. Monatsschr 179: 173. 1993.
- ^ Letawe,; Letawe C, Boone M, Pierard GE (March 1998). "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones". Clinical & Experimental Dermatology 23 (2): 56–58. doi:10.1046/j.1365-2230.1998.00315.x. PMID 9692305.
- ^ Darmstadt, G L; Darmstadt GL, Mao-Qiang M, Chi E, Saha SK, Ziboh VA, Black RE, Santosham M, Elias PM (2002). "Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries". Acta Paediatrica 91 (5): 546–554. doi:10.1080/080352502753711678. PMID 12113324.
- ^ Oil, peanut, salad or cooking: search for peanut oil on http://www.nal.usda.gov/fnic/foodcomp/search/
- ^ M. K. Nutter, E. E. Lockhart and R. S. Harris (1943). "The chemical composition of depot fats in chickens and turkeys". Journal of the American Oil Chemists' Society 20 (11): 231–234. http://www.springerlink.com/content/0837289583682243/.
External links
Lipids: fatty acids Saturated VFA: Acetic (C2) · Propionic (C3) · Butyric (C4) · Valeric (C5) · Caproic (C6) · Enanthic (C7) · Caprylic (C8) · Pelargonic (C9) · Capric (C10) · Undecylic (C11) · Lauric (C12) · Tridecylic (C13) · Myristic (C14) · Pentadecanoic (C15) · Palmitic (C16) · Margaric (C17) · Stearic (C18) · Nonadecylic (C19) · Arachidic (C20) · Heneicosylic (C21) · Behenic (C22) · Tricosylic (C23) · Lignoceric (C24) · Pentacosylic (C25) · Cerotic (C26) · Heptacosylic (C27) · Montanic (C28) · Nonacosylic (C29) · Melissic (C30) · Hentriacontylic (C31) · Lacceroic (C32) · Psyllic (C33) · Geddic (C34) · Ceroplastic (C35) · Hexatriacontylic (C36)n−3 Unsaturated n−6 Unsaturated n−9 Unsaturated biochemical families: prot · nucl · carb (glpr, alco, glys) · lipd (fata/i, phld, strd, gllp, eico) · amac/i · ncbs/i · ttpy/iCategories:- Carboxylic acids
- Essential fatty acids
- Essential nutrients
- Fatty acids
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