Linoleic acid

Not to be confused with linolenic acid or lipoic acid.

Linoleic acid

Names
IUPAC name (9Z,12Z)-9,12-Octadecadienoic acid
Other names C18:2 (Lipid numbers)
Identifiers
CAS Number	60-33-3 Y
ChEBI	CHEBI:17351 Y
ChEMBL	ChEMBL267476 Y
ChemSpider	4444105 Y
IUPHAR/BPS	1052
Jmol 3D model	Interactive image
KEGG	C01595 Y
UNII	9KJL21T0QJ Y
InChI 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- Y Key: OYHQOLUKZRVURQ-HZJYTTRNSA-N Y 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
SMILES CCCCC/C=C\C/C=C\CCCCCCCC(=O)O
Properties
Chemical formula	C18H32O2
Molar mass	280.45 g·mol−1
Appearance	Colorless oil
Density	0.9 g/cm3
Melting point	−5 °C (23 °F) −12 °C (10 °F)
Boiling point	230 °C (446 °F) at 21 mbar 230 °C (446 °F) at 16 mmHg
Solubility in water	0.139 mg/L
Vapor pressure	16 Torr at 229 °C
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

Linoleic acid (LA) is a polyunsaturated omega-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2 cis,cis-9,12. From the chemistry perspective, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; with the first double bond located at the sixth carbon from the methyl end.

Linoleic acid belongs to one of the two families of essential fatty acids, which means that the human body cannot synthesize it from other food components.

The word "linoleic" derived from the Greek word linon (flax). Oleic means "of, relating to, or derived from oil of olive" or "of or relating to oleic acid" because saturating the omega-6 double bond produces oleic acid.

In physiology

LA is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins, leukotrienes (LTA, LTB, LTC), and thromboxane (TXA). It is found in the lipids of cell membranes. It is abundant in many nuts, fatty seeds (flax seeds, hemp seeds, poppy seeds, sesame seeds, etc.) and their derived vegetable oils; comprising over half (by weight) of poppy seed, safflower, sunflower, corn, and soybean oils.

Linoleic acid is an essential fatty acid that must be consumed for proper health. A diet only deficient in linoleate (the salt form of the acid) causes mild skin scaling, hair loss, and poor wound healing in rats.

Along with oleic acid, linoleic acid is released by cockroaches upon death which has the effect of preventing other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death.

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.

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 during the inflammatory response and during physical activity; eicosanoids are a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to promote (not cause) inflammation and promote growth during and after physical activity in healthy humans. For example, both AA-derived thrombaxane and leukotriene_B4 are proaggregatory and vasoconstrictive eicosanoids during inflammation. The oxidized metabolic products of linoleic 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.

An increased intake of certain omega–3 fatty acids with a decrease in omega-6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.

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.”

Uses

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 is a surfactant 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, and moisture retentive properties when applied topically on the skin.

Use in research

Linoleic acid lipid radicals can be used to show the antioxidant effect of natural phenols. Experiments on linoleic acid subjected to 2,2′-azobis (2-amidinopropane) dihydrochloride induced oxidation of linoleic acid; hence producing lipid radicals and then the use of different combinations of phenolics show that binary mixtures can lead to either a synergetic antioxidant effect or to an antagonistic effect towards the lipid radicals. Research like this is useful in discovering which phenols prevent the autoxidation of lipids in vegetable oils.

Linoleic acid may be linked to obesity by promoting overeating and damaging the arcuate nucleus in the brain's hypothalamus.

Dietary sources

Note: Unless cited, none of these percentages have been verified by scientific research.

Name	% LA†	ref.
Salicornia oil	75%
Safflower oil	74.62%
Evening Primrose oil	73%
Poppyseed oil	70%
Grape seed oil	69.6%
Sunflower oil	65.7%
Barbary Fig Seed Oil	65%
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%
Argan oil	37%
Pistachio oil	32.7%
Peanut oil	32%
Almonds	24%
Canola oil	21%
Chicken fat	18-23%
Egg yolk	16%
Linseed oil	15%
Lard	10%
Olive oil	10% (3.5 - 21%)
Palm oil	10%
Cocoa butter	3%
Macadamia oil	2%
Butter	2%
Coconut oil	2%
	†average val

See also

• Conjugated linoleic acid
• Omega-6 fatty acid: Negative health effects
• Essential fatty acids
• Essential fatty acid interactions
• Eicosanoids
• Essential nutrients
• Linolein

External links

• Linoleic acid MS Spectrum
• Fatty Acids: Methylene-Interrupted Double Bonds, AOCS Lipid Library