Gamma-Linolenic acid

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The correct title of this article is gamma-Linolenic acid. The initial letter is shown capitalized due to technical restrictions.

gamma-Linolenic acid (GLA) is an omega-6 essential fatty acid found primarily in vegetable oils. It is sold as a dietary supplement for treating problems with inflammation and auto-immune diseases. Such use is controversial.

1 Chemistry
2 Dietary Sources
3 A Source of Eicosanoids
4 Health and Medicine
5 History
6 References
7 See also

[edit] Chemistry

gamma-linolenic acid

The chemical structure of GLA showing physiological numbering (red) and chemical numbering (blue) conventions.
Chemical name	all-cis-6,9,12-octadecatrienoic acid
Chemical formula	C₁₈H₃₀O₂
Molecular mass	278.43 g/mol
CID	?
PubChem	5280933
SMILES	CCCCC\C=C/C\C=C/C\C=C/CCCCC(=O)O
Disclaimer and references

In physiological literature, GLA is designated as 18:3(ω-6). Chemically, GLA is a carboxylic acid with an 18-carbon chain and three cis double bonds; the first double bond is located at the sixth carbon from the omega end. It is also sometimes called gamolenic acid. It is an isomer of alpha-linolenic acid, which is the omega-3 fatty acid found in flax seed. Although there are alpha- and gamma- forms of linolenic acid, there is no beta form. One was once identified but it turned out to be an artifact of the original analytical process, (Gunstone).

[edit] Dietary Sources

GLA is obtained from vegetable oils, such as evening primrose (oenothera biennis) oil, blackcurrant seed oil, borage oil and hemp seed oil, and from spirulina, a cyanobacteria. Each contains varying amounts of the fatty acid, with borage oil usually being the most heavily concentrated form. All are widely available in pharmacies, health food stores, or online shops.

The human body produces GLA from linoleic acid (LA). This reaction is catalized by Δ⁶-desaturase (D6D), an enzyme which allows the creation of a double bond on the 6th 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 people grow older and their bodies become unable to produce it in sufficient quantities, or due to specific dietary deficiencies.^{[citation needed]}

[edit] A Source of Eicosanoids

GLA is an Omega-6 essential fatty acid. From GLA, the body forms dihomo-gamma-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.

Unlike AA and EPA, DGLA cannot yield leukotrienes. However it can inhibit the formation of pro-inflammatory leukotrienes from AA, (Belch and Hill, 2000).

Although GLA is an ω-6 fatty acid (which are generally pro-inflammatory) it has anti-inflammatory properties; see discussion at Essential fatty acid interactions - The paradox of dietary GLA.

[edit] Health and Medicine

The seed oil of Oenothera biennis (evening primrose) is a source of GLA

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. Conflicting data is found for GLA in the treatment of eczema; but the UK's Medicines Control Agency has withdrawn GLA's product licence for atopic eczema (Smith, 2003). 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 (Fan and Chapkin, 1998).

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 (NIH Medline Plus).

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.^{[citation needed]}

[edit] History

In the Middle Ages, a folk remedy would be to take borage for any problems from rheumatism to heart disease.

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; (e.g. Horrobin, 2000). He also founded Scotia Pharmaceuticals, which sold this oil as a pharmaceutical, which led to controversy even after his death (Williams 2003).

[edit] References

Belch, Jill JF and Hill, Alexander (January 2000). Evening primrose oil and borage oil in rheumatologic conditions. Retrieved on February 12, 2006. PubMed cite.
- "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."