Linoleic acid (LA) is an unsaturated omega-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it is called 18:2(n-6). Chemically, linoleic acid is a carboxylic acid with an 18-carbon chain and two ''cis'' double bonds; the first double bond is located at the sixth carbon from the omega end.
Linoleic acid (LA) is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins. It is found in the lipids of cell membranes. It is abundant in many vegetable oils, comprising over half (by weight) of poppy seed, safflower, sunflower, and corn oils.
Linoleic acid is a member of the group of essential fatty acids called omega-6 fatty acids which are essential dietary requirements for all mammals. The other group of essential fatty acids is the omega-3 fatty acids, for example Alpha-linolenic acid. Omega-6 deficiency symptoms include dry hair, hair loss, and poor wound healing.
Metabolism and eicosanoids
The first step in the metabolism of Linoleic Acid (LA) is performed by Δ-6-desaturase, which converts LA into gamma-Linolenic acid (GLA).
There is evidence suggesting that infants lack Δ-6-desaturase of their own, and must acquire it through breast milk. Studies show that breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA.
GLA is converted to Dihomo-gamma-linolenic acid (DGLA), which in turn is converted to Arachidonic acid (AA). One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids, a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids are only produced from AA and tend to be pro-inflammatory. For example, both Thrombaxane and LeukotrieneB4 are proaggretory and vasoconstrictive eicosanoids. Another important clinical effect is that the oxidized metabolic products of linolenic acid such as 9--hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid have also been shown to activate TRPV1, the capsaicin receptor and through this might play a major role in hyperalgesia and allodynia.
An increased intake of Omega 3 fatty acids with a decrease in Omega 6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.
One study monitoring two groups of survivors of myocardial infarction concluded that “the concentration of alpha-linolenic acid was increased by 68%, in the experimental group, and that of linoleic acid reduced by 7%...the survivors of a first myocardial infarction, assigned to a Mediterranean alpha-linolenic acid rich diet, had a markedly reduced rate of recurrence, other cardiac events and overall mortality.”
Possible roles in disease
A study in mice has shown that dietary intake of Conjugated Linoleic Acid (CLA) can help prevent cancer in mice. The study looked at a specific isomer of LA and studied its effect on cancer induced by dimethylbenz(a)anthracene. The study suggested a significant effect of CLA intake on the reduction of carcinogenesis.
Since children with cystic fibrosis suffer from Essential Fatty Acid Deficiency due to malabsorption, it was hypothesized that high doses of LA might aid in their growth. The study looked at two groups of infants with cystic fibrosis on diets with two different levels of LA. It was shown that supplementary LA, indeed, has a positive effect on the growth of infants with cystic fibrosis, especially between 6 and 9 months of age.
Dermatitis is one of the first signs of an Essential Fatty Acid deficiency in both humans and animals. Until 1955, one of the most widely applied treatments for atopic eczema was a high dose of GLA.
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