Γ-Linolenic acid

Not to be confused with linoleic acid.
This article is about Gamma-Linolenic acid. For other uses, see Linolenic acid.
γ-Linolenic acid
Identifiers
CAS number 506-26-3 YesY
PubChem 5280933
ChemSpider 4444436 YesY
UNII 78YC2MAX4O YesY
ChEBI CHEBI:28661 YesY
ATC code AX02
Jmol-3D images Image 1
Properties
Molecular formula C18H30O2
Molar mass 278.43 g mol−1
Appearance Colorless oil
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

γ-Linolenic acid (gamma-linolenic acid or GLA, INN and USAN gamolenic acid) is a fatty acid found primarily in vegetable oils. It is sold as a dietary supplement for a variety of human health problems, although there is little or no evidence of its effectiveness.

Chemistry

GLA is categorized as an n−6 (also called ω−6 or omega-6) fatty acid, meaning that the first double bond on the methyl end (designated with n or ω) is the sixth bond. In physiological literature, GLA is designated as 18:3 (n−6). GLA is a carboxylic acid with an 18-carbon chain and three cis double bonds. It is an isomer of α-linolenic acid, which is a polyunsaturated n−3 (omega-3) fatty acid, found in rapeseed canola oil, soy beans, walnuts, flax seed (linseed oil), perilla, chia, and hemp seed.

History

GLA was first isolated from the seed oil of evening primrose. This herbal plant was grown by Native Americans to treat swelling in the body. In the 17th century, it was introduced to Europe and became a popular folk remedy, earning the name king'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]

Dietary sources

GLA is obtained from vegetable oils such as GLA safflower oil (Carthamus tinctorius), evening primrose (Oenothera biennis) oil, blackcurrant seed oil, borage oil, and hemp seed oil. GLA is also found in edible hemp seeds, oats, barley,[3][full citation needed] and spirulina. Each contains varying amounts of the fatty acid, with GLA safflower oil at 40% GLA being a novel concentrated form. This is a new genetically modified oil and has been available in commercial quantities since 2011. It should be noted that conventional safflower oils have zero GLA. Borage oil ranges from 15% to 20% and evening primrose oil ranges from 8% to 10% GLA.[4][5]

The human body produces GLA from linoleic 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 as cooking oils and meats. 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.[6][dubious ]

Source of eicosanoids

From GLA, the body forms dihomo-γ-linolenic acid (DGLA). This is one of the body's three sources of eicosanoids (along with AA and EPA.) DGLA is the precursor of the prostaglandin PGH1, which in turn forms PGE1 and the thromboxane TXA1. Both PGE11 and TXA1 are anti-inflammatory; thromboxane TXA1, unlike its series-2 variant, induces vasodilation, and inhibits platelet[7] consequently, TXA1 modulates (reduces) the pro-inflammatory properties of the thromboxane TXA2. PGE1 has a role in regulation of immune system function and is used as the medicine alprostadil.

Unlike AA and EPA, DGLA cannot yield leukotrienes. However it can inhibit the formation of pro-inflammatory leukotrienes from AA.[8]

Although GLA is an n−6 fatty acid, a type of acid that is, in general, pro-inflammatory, it has anti-inflammatory properties. (See discussion at Essential fatty acid interactions: The paradox of dietary GLA.)

Health and medicine

GLA has been promoted as medication for a variety of ailments including breast pain and eczema, most notoriously by David Horrobin (1939 – 2003), whose marketing of evening primrose oil was described by the British Medical Journal as ethically dubious – the substance was likely to be remembered as "a remedy for which there is no disease".[9] In 2002, the UK's Medicines and Healthcare products Regulatory Agency withdrew marketing authorisations for evening primrose oil as an eczma remedy.[10] The British Medical Journal commented that it had taken 20 years to demonstrate that the substance was of no use in atopic dermatitis, and called for more transparency in the research on which drug licensing decisions were taken.[11]

GLA is also sometimes promoted as an anti-cancer agent. According to the American Cancer Society there is very little evidence for its effectiveness, and "neither GLA nor other GLA-rich supplements (such as evening primrose oil) have been convincingly shown to be useful in preventing or treating any other health conditions."[12]

Notes and references

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