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| Names | |||
|---|---|---|---|
| Preferred IUPAC name (6Z,9Z,12Z)-Octadeca-6,9,12-trienoic acid | |||
| Other names Gamma-linolenic acid, gamolenic acid, GLA | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.107.263 | ||
| UNII | |||
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| Properties | |||
| C18H30O2 | |||
| Molar mass | 278.436 g·mol−1 | ||
| Appearance | Colorless oil | ||
| Pharmacology | |||
| D11AX02 (WHO) | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
γ-Linolenic acid orGLA (INN:gamolenic acid) is ann−6, or omega-6, fatty acid found primarily in seed oils. When acting on GLA,arachidonate 5-lipoxygenase produces noleukotrienes and the conversion by the enzyme ofarachidonic acid to leukotrienes is inhibited.
GLA is categorized as ann−6 (also called ω−6 or omega-6) fatty acid, meaning that the first double bond on the methyl end (designated withn or ω) is the sixth bond. In physiological literature, GLA is designated as 18:3 (n−6). GLA is acarboxylic acid with an 18-carbon chain and threecisdouble bonds. It is aregioisomer ofα-linolenic acid, which is a polyunsaturatedn−3 (omega-3) fatty acid, found inrapeseedcanola oil,soybeans,walnuts,flax seed (linseed oil),perilla,chia, andhemp seed.
GLA was first isolated from the seed oil ofevening primrose. This herbal plant was grown byNative Americans to treat swelling in the body.In the 17th century, it was introduced to Europe and became a popular folk remedy, earning the nameking's cure-all.In 1919, Heiduschka and Lüft extracted the oil from evening primrose seeds and described an unusual linolenic acid, which they name γ-.Later, the exact chemical structure was characterized by Riley.[1]
Although there are α- and γ- forms of linolenic acid, there is no β- form. One was once identified, but it turned out to be an artifact of the original analytical process.[2]
GLA is obtained from vegetable oils such as evening primrose (Oenothera biennis) oil (EPO),blackcurrant seed oil,borage seed oil, andhemp seed oil. GLA is also found in varying amounts in ediblehemp seeds, oats, barley,[3] andspirulina.[4] Normalsafflower (Carthamus tinctorius) oil does not contain GLA, but a genetically modified GLA safflower oil available in commercial quantities since 2011 contains 40% GLA.[5] Borage oil contains 20% GLA, evening primrose oil ranges from 8% to 10% GLA, and black-currant oil contains 15–20%.[6]
The human body produces GLA fromlinoleic acid (LA). This reaction is catalyzed by Δ6-desaturase (D6D), an enzyme that allows the creation of a double bond on the sixth carbon counting from the carboxyl terminus. LA is consumed sufficiently in most diets, from such abundant sources ascooking oils andmeats. However, a lack of GLA can occur when there is a reduction of the efficiency of the D6D conversion (for instance, as people grow older or when there are specific dietary deficiencies) or in disease states wherein there is excessive consumption of GLA metabolites.[7]
From GLA, the body formsdihomo-γ-linolenic acid (DGLA). This is one of the body's three sources ofeicosanoids (along withAA andEPA.) DGLA is the precursor of theprostaglandin PGH1, which in turn forms PGE1 and thethromboxane TXA1. Both PGE11 and TXA1 are anti-inflammatory;thromboxane TXA1, unlike its series-2 variant, induces vasodilation, and inhibits platelet[8] consequently, TXA1 modulates (reduces) the pro-inflammatory properties of the thromboxane TXA2. PGE1 has a role in regulation ofimmune system function and is used as the medicinealprostadil.
Unlike AA and EPA, DGLA cannot yieldleukotrienes. However, it can inhibit the formation of pro-inflammatory leukotrienes from AA.[9]
Although GLA is ann−6 fatty acid, a type of acid that is, in general, pro-inflammatory[citation needed], it has anti-inflammatory properties.(See discussion atEssential fatty acid interactions: The paradox of dietary GLA.)
In 2002, the UKMedicines and Healthcare products Regulatory Agency withdrew marketing authorisations for evening primrose oil as aneczema remedy.[10]
DGLA itself cannot be converted to LTs but can form a 15-hydroxyl derivative that blocks the transformation of arachidonic acid to LTs. Increasing DGLA intake may allow DGLA to act as a competitive inhibitor of 2-series PGs and 4-series LTs and, thus, suppress inflammation.
