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|Molar mass||278.43 g mol−1|
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 treating problems with inflammation and auto-immune diseases, although its efficacy is disputed.
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.
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.
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.
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,[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.
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.
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. PGE1 has a role in regulation of immune system function and is used as the medicine alprostadil. TXA1 modulates the pro-inflammatory properties of the thromboxane TXA2.
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 is sometimes prescribed in the belief that it has anti-inflammatory properties lacking some of the common side-effects of other anti-inflammatory drugs. Herbal medicine advocates recommend GLA for autoimmune disorders, arthritis, eczema, and PMS, with noticeable results not expected for months. Research is ongoing, investigating GLA as a potential anticancer agent. GLA is unique among the omega-6 polyunsaturated fatty acids (linoleic acid, GLA and arachidonic acid) in its potential to suppress tumor growth and metastasis.
GLA can also form a lithium salt, increasing its solubility in water. The resulting compound is Li-GLA, also called lithium gammalinolenate. Li-GLA is currently in phase II clinical trials to determine whether it is useful in the treatment of HIV infections, since it has the ability to destroy HIV-infected T cells in vitro. It has a number of side-effects, including a reduction in hemoglobin, hematuria, gastrointestinal disturbance, fatigue, and headache.
Atopic eczema 
Conflicting data are found for GLA in the treatment of eczema. The UK's Medicines and Healthcare products Regulatory Agency has withdrawn GLA's product licence for atopic eczema. Still, the US National Institute of Health's MedlinePlus states that there is 'B' grade evidence ('good scientific evidence') for the efficacy of evening primrose oil in the treatment of eczema and skin irritation. But it cautions that large well-designed studies are still needed.
A controlled study of borage oil for eczema found no benefit to GLA; it underperformed placebo.
The medical use of GLA has been controversial. David Horrobin published much research on the use of GLA (as evening primrose oil) as a dietary supplement for treating atopic eczema. He also founded Scotia Pharmaceuticals, which sold this oil as a pharmaceutical, which led to controversy even after his death.
Notes and references 
- Yung-Sheng Huang, Vincent A. Ziboh (2001). Gamma-Linolenic Acid: Recent Advances in Biotechnology and Clinical Applications. AOCS Press. p. 259. ISBN 1-893997-17-0. Retrieved 2007-12-07.
- Eckey, EW (1954). Vegetable Fats and Oils (volume 123 of American Chemical Society monograph series). Reinhold. p. 542.
- Qureshi AA et al. (1984). Fed. Proc. 43: 2626.
- Flider, Frank J (May 2005). "GLA: Uses and New Sources". INFORM 16 (5): 279–282.
- Nykiforuk, C.; Shewmaker, C. (19). "High level accumulation of gamma linolenic acid in transgenic safflower (Carthamus tinctorius) seeds". Transgenic Research 21 (2): 367–81. doi:10.1007/s11248-011-9543-5. PMID 21853296.
- Horrobin DF (1993). "Fatty acid metabolism in health and disease: the role of delta-6-desaturase" (pdf). Am. J. Clin. Nutr. 57 (5 Suppl): 732S–736S; discussion 736S–737S. PMID 8386433.
- Belch JJ, Hill A (2000). "Evening primrose oil and borage oil in rheumatologic conditions". Am. J. Clin. Nutr. 71 (1 Suppl): 352S–6S. PMID 10617996. Retrieved 2007-12-07. "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."
- "Plant oil 'acts like cancer drug'". BBC News. 2005-11-02. Retrieved 2010-01-04. (describing work by Dr Javier Menendez and colleagues at Northwestern University and published in Journal of the National Cancer Institute).
- Fan, Yang-Yi and Robert S. Chapkin (9 September 1998). "Importance of Dietary γ-Linolenic Acid in Human Health and Nutrition". Journal of Nutrition 128 (9): 1411–4. PMID 9732298. Retrieved 2007-01-05.
- CTN#083,LiGLA[dead link]
- Smith, Richard (13 December 2003). "The drugs don't work". British Medical Journal 327 (7428): 0–h. doi:10.1136/bmj.327.7428.0-h. Retrieved 2007-01-05.
- NIH Medline Plus. "MedlinePlus Herbs and Supplements: Evening primrose oil". Retrieved January 19, 2007.
- Takwale A, Tan E, Agarwal S et al. (2003). "Efficacy and tolerability of borage oil in adults and children with atopic eczema: randomised, double blind, placebo controlled, parallel group trial". BMJ 327 (7428): 1385. doi:10.1136/bmj.327.7428.1385. PMC 292992. PMID 14670885.
- Callaway, J.; Schwab, U.; Harvima, I.; Halonen, P.; Mykkänen, O.; Hyvönen, P.; Järvinen, T. (2005). "Efficacy of dietary hempseed oil in patients with atopic dermatitis". Journal of Dermatological Treatment 16 (2): 87–94. doi:10.1080/09546630510035832. PMID 16019622.
- Horrobin, David (January 1, 2000). "Essential fatty acid metabolism and its modification in atopic eczema". American Journal of Clinical Nutrition 71 (1): 367S–72S. PMID 10617999. Retrieved 2007-01-05.
- Williams, Hywel C (13 Dec 2003). "Editorial: Evening primrose oil for atopic dermatitis—Time to say goodnight". BMJ 327 (7428): 1358–9. doi:10.1136/bmj.327.7428.1358. PMC 292973. PMID 14670851. Retrieved 2007-01-19. British Medical Journal summary editorial on evening primrose oil in the treatment of eczema