Gamma-Linolenic acid

Overview
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. The efficacy of such use is disputed.

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).

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 cyanobacterium. 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.

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.

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. Conflicting data are found for GLA in the treatment of eczema; but the UK's Medicines and Healthcare products Regulatory 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.

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).