Linoleic acid (LA) is an organic compound with the formula COOH(CH₂)₇CH=CHCH₂CH=CH(CH₂)₄CH₃. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid. Linoleic acid is a polyunsaturated omega-6 fatty acid. It is a colorless liquid that is virtually insoluble in water but soluble in many organic solvents. It typically occurs in nature as a triglyceride (ester of glycerin) rather than as a free fatty acid. It is one of two essential fatty acids for humans, who must obtain it through their diet, and the most essential, because the body uses it as a base to make the others. The word "linoleic" derives from the Latin ''linum'' "flax" + ''oleum'' "oil", reflecting the fact that it was first isolated from

linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...

History

In 1844,

F. Sacc F is the sixth letter of the Latin alphabet. F may also refer to: Science and technology Mathematics * F or f, the number 15 in hexadecimal and higher positional systems * ''p'F'q'', the hypergeometric function * F-distribution, a cont ...

, working at the laboratory of

Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at t ...

, isolated linoleic acid from linseed oil. In 1886,

K. Peters K is the eleventh letter of the Latin alphabet. K may also refer to: General uses * K (programming language), an array processing language developed by Arthur Whitney and commercialized by Kx Systems * K (cider), a British draft cider manufact ...

determined the existence of two double bonds.(1886), ''Monatsch''., volume 7, pages 522- Its essential role in human diet was discovered by G. O. Burr and others in 1930. Its chemical structure was determined by

T.P. Hilditch Thomas Percy Hilditch (22 April 1886 – 9 August 1965) was an English chemist who researched organic synthesis, lipid chemistry, and catalytic production techniques. He served as a professor of industrial chemistry at the University of Liverpool. ...

and others in 1939, and it was synthesized by R. A. Raphael and F. Sondheimer in 1950.

In physiology

The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid.

Metabolism and eicosanoids

Linoleic acid (LA: C₁₈ H₃₂ O₂; 18: 2, ω-6) is a precursor to

arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''arachi ...

(AA: C₂₀H₃₂O₂; 20: 4, ω-6) with elongation and saturation. AA is the precursor to some

prostaglandin The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derive ...

s, leukotrienes (LTA, LTB, LTC), thromboxane (TXA) and the N-acylethanolamine (NAE)

arachidonoylethanolamine Anandamide (ANA), also known as ''N''-arachidonoylethanolamine (AEA), is a fatty acid neurotransmitter. Anandamide was the first endocannabinoid to be discovered: it participates in the body's endocannabinoid system by binding to cannabinoid rece ...

(AEA: C₂₂ H₃₇ NO₂; 20:4, ω-6), and other endocannabinoids and eicosanoids. The metabolism of LA to AA begins with the conversion of LA into gamma-linolenic acid (GLA), effected by Δ⁶desaturase.Evidence suggests that infants must acquire Δ⁶desaturase breast milk. Breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA. GLA is converted to

dihomo-γ-linolenic acid Dihomo-γ-linolenic acid (DGLA) is a 20-carbon ω−6 fatty acid. (also called, cis,cis,cis-8,11,14-Eicosatrienoic acid) In physiological literature, it is given the name 20:3 (ω−6). DGLA is a carboxylic acid with a 20-carbon chain and thre ...

(DGLA), the immediate precursor to AA. LA is also converted by various lipoxygenases, cyclooxygenases,

cytochrome P450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...

enzymes (the CYP monooxygenases), and non-enzymatic autoxidation mechanisms to mono- hydroxyl products viz., 13-Hydroxyoctadecadienoic acid, and

9-Hydroxyoctadecadienoic acid 9-Hydroxyoctadecadienoic acid (or 9-HODE) has been used in the literature to designate either or both of two stereoisomer metabolites of the essential fatty acid, linoleic acid: 9(''S'')-hydroxy-10(''E''),12(''Z'')-octadecadienoic acid (9(''S'')- ...

; these two hydroxy metabolites are enzymatically oxidized to their keto metabolites, 13-oxo-octadecadienoic acid and 9-oxo-octadecdienoic acid. Certain cytochrome P450 enzymes, the CYP epoxygenases, catalyze oxidation of LA to epoxide products viz., its 12,13-epoxide,

Vernolic acid Vernolic acid (leukotoxin) is a long chain fatty acid that is monounsaturated and contains an epoxide. It is the R,R-''cis'' epoxide derived from the C12–C13 alkene of linoleic acid. Vernolic acid was first definitively characterized in 1954. I ...

, and its 9,10-epoxide, Coronaric acid. These linoleic acid products are implicated in human physiology and pathology. Hydroperoxides derived from the metabolism of anandamide (AEA: C₂₂H₃₇ NO₂; 20:4,n-6), or its linoleoyl analogues, is by a lipoxygenase action found to be competitive inhibitors of brain and immune cell

FAAH Fatty acid amide hydrolase or FAAH (, oleamide hydrolase, anandamide amidohydrolase) is a member of the serine hydrolase family of enzymes. It was first shown to break down anandamide in 1993. In humans, it is encoded by the gene ''FAAH''.; Fun ...

, the enzyme that breaks down AEA and other endocannabinoids, and the compound linoleoyl-ethanol-amide (C₂₀H₃₇NO₂; 18:2,n-6), an N-acylethanolamine, - the

ethanolamide Ethanolamides are chemical compounds which are amides formed from carboxylic acids and ethanolamine. Some ethanolamides are naturally occurring, such as anandamide, palmitoylethanolamide and prostamides, which play physiological roles as lipid neur ...

of linoleic acid (LA: C₁₈ H₃₂ O₂; 18: 2, n-6) and its metabolized incorporated

ethanolamine Ethanolamine (2-aminoethanol, monoethanolamine, ETA, or MEA) is an organic chemical compound with the formula or . The molecule is bifunctional, containing both a primary amine and a primary alcohol. Ethanolamine is a colorless, viscous liquid wit ...

(MEA: C₂H₇NO), is the first natural inhibitor of FAAH, discovered.

Uses and reactions

Linoleic acid is a component of quick- drying oils, which are useful in oil paints and

varnish Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in various ...

es. These applications exploit the lability of the doubly

allylic In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...

C-H groups (-CH=CH-C''H''₂-CH=CH-) toward oxygen in air ( autoxidation). Addition of oxygen leads to

crosslinking Cross-linking may refer to *Cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers ca ...

and formation of a stable film. Reduction of the carboxylic acid group of linoleic acid yields

linoleyl alcohol Linoleyl alcohol is a fatty alcohol. A colorless oil, it is produced by the organic redox reaction, reduction of the carboxylic acid group in linoleic acid. References Fatty alcohols Polyunsaturated compounds Alkenols {{alcohol ...

. Linoleic acid is a

surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...

with a critical micelle concentration of 1.5 x 10⁻⁴ M @ pH 7.5. 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, skin-lightening and moisture retentive properties when applied topically on the skin. Linoleic acid is also used in some bar of soap products.

Dietary sources

It is abundant in safflower, and

corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...

oil, and comprises over half their composition by weight. It is present in medium quantities in soybean oils,

sesame Sesame ( or ; ''Sesamum indicum'') is a flowering plant in the genus ''Sesamum'', also called benne. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalized in tropical regions around the world and is cu ...

, and

almonds The almond (''Prunus amygdalus'', Synonym (taxonomy)#Botany, syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of th ...

Other occurrences

Cockroaches release oleic and linoleic acid upon death, which discourages other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death.

Health effects

Consumption of linoleic acid has been associated with lowering the risk of

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...

and premature death.

References

F. Sacc (1844) "Ueber das Leinöl, seine physicalischen und chemischen Eigenscharften und seine Oxydationsproducte". ''Liebig Annalen'', volume 51, pages 213-230. F. Sacc (1845):
Expériences sur les propriétés physiques et chimiques de l'huile de Lin
. ''SChweizer. Gesell. N. Dekschr.'', volume 7 (1930: ''J Biol Chem'', volume 86, pages 587- R. A. Raphael and Franz Sondheimer (1950): "The synthesis of long-chain aliphatic acids from acetylenic compounds. Part III. The synthesis of linoleic acid". ''Journal of the Chemical Society'' (''Resumed''), article 432,

External links

Linoleic acid MS Spectrum
AOCS Lipid Library {{DEFAULTSORT:Linoleic Acid 5α-Reductase inhibitors Alkenoic acids Aromatase inhibitors Essential fatty acids Essential nutrients Fatty acids