The physiological effects of gamma-linolenic acid are based on its function as a precursor of eicosanoids and on its property as a component of cell membranes.
Precursors of eicosanoids – immunomodulation
Gamma-linolenic acid is the initial substrate for dihomo-gamma-linolenic acid. From the latter, under the influence of the enzyme cyclooxygenase, the prostaglandins of series 1 – PGE1, PGD1, PGI1, and TXA1 are formed. Along with prostacyclins, thromboxanes and leukotrienes, prostaglandins belong to the group of eicosanoids. These are hormone-like substances that can only be formed from polyunsaturated fatty acids with a chain length of 20 C atoms. Accordingly, eicosanoids are oxygenated derivatives of the following fatty acids.
- Dihomo-gamma-linolenic acid – C20:4 omega-6
- Arachidonic acid – C20:4 Omega-6
- Eicosapentaenoic acid (EPA) – C20:5 omega-3
Eicosanoids have multiple hormone-like functions and are involved in the following physiological processes:
- Regulation of vascular tone – blood pressure
- Blood clotting
- Regulation of platelets – platelet aggregation, process of atherogenesis.
- Regulation of lipoprotein metabolism.
- Allergic and inflammatory processes.
- Influence on heart rate and pain sensation.
- Influence on uterine smooth muscle and musculature.
Depending on the parent compound, eicosanoids exhibit different or opposite mechanisms of action. While series 1 prostaglandins, which originate from dihomo-gamma-linolenic acid, have essentially anti-inflammatory (anti-inflammatory) effects, series 2 prostaglandins, which has arachidonic acid as a precursor, promote inflammatory processes, such as pain, swelling, increased blood flow and fever. The following is a review of the functions of series 1 prostaglandins:
- Cardiovascular system – vascular dilatation (vasodilatation).
- Respiratory tract – relaxation
- Stomach – reduction of acid secretion
- Inflammatory processes – regulation of the secretion of inflammatory substances; inhibits the release of lysomal enzymes that cause tissue damage GLA is used for its anti-inflammatory properties in rheumatoid diseases.
- Regulation of hormone production and nerve conduction – relevant to the prevention of premenstrual syndrome (PMS) – GLA can relieve some symptoms associated with PMS, such as headaches, cyclic breast discomfort, depression, irritability, and bloating; GLA can also be used in the form of borage or evening primrose oil in the presence of diabetic polyneuropathy
- Skin – immunoregulatory effects, controlled sebum secretion – GLA is used in particular for the prevention of eczema and therapy of atopic eczema (neurodermatitis) and psoriasis.
Finally, gamma-linolenic acid is of great importance for important metabolic processes due to the synthesis of series 1 prostaglandins. A conversion of GLA – via dihomo-gamma-linolenic acid – into arachidonic acid, occurs in humans only to a small extent, so that the arachidonic acid as a precursor of pro-inflammatory metabolites – series 2 prostaglandins, such as TXA2, PGE2 and PGI2, as well as series 4 leukotrienes – plays only a minor role. In particular, arachidonic acid is held responsible as one of the triggering factors in inflammatory processes and the development of pain signals in joint diseases, such as activated osteoarthritis and other forms of arthritis. Important note!To form higher unsaturated polyene fatty acids and eicosanoids, omega-3 and omega-6 fatty acids compete for the same enzymes. They require both delta-6 desaturase to convert linoleic acid and alpha-linolenic acid, respectively, and cyclooxygenases and lipoxygenases to form prostaglandins, thromboxanes and leukotrienes. For this reason, both types of fatty acids must be supplied in a different ratio.The intake of omega-6 fatty acids must be higher because the affinity of this type of fatty acid for desaturases – insert double bonds – and elongases – extend the carbon chain – is lower than for omega-3 fatty acids. According to current knowledge, the optimal ratio of linoleic acid (omega-6 fatty acid) to alpha-linolenic acid (omega-3 fatty acid) is 5:1. Finally, the respective supply of omega-3 and -6 fatty acids determines the amount of eicosanoids synthesized. Thus, it is possible to influence a variety of functional processes controlled by eicosanoids dietarily-that is, through dietary intake-by changing the supply of fatty acids.
Components of cell membranes-structural function
A large proportion of essential fatty acids are incorporated into the phospholipids of cell membranes and the membranes of cell organelles, such as mitochondria and lysosomes. There, gamma-linolenic acid has a beneficial effect on fluidity (flowability) and cellular functions that depend on it. Phospholipids are found in all body cells, especially those of the nervous system. The brain contains the largest amount of structural fat, relatively speaking.Finally, gamma-linolenic acid is essential for the brain, especially for nerve conduction. GLA also plays a crucial role in fetal brain development. In response to specific stimuli, omega-3 and -6 fatty acids are released from membrane lipids and made available for the biosynthesis of eicosanoids.
Influence on atopic eczema (neurodermatitis)
Neurodermatitis patients are deficient in the enzyme delta-6-desaturase, which reduces their gamma-linolenic acid concentration by about 50%. Finally, a deficit of gamma-linolenic acid leads to a deficiency of prostaglandin E1. The insufficient concentration of this eicosanoid is probably partly responsible for a disturbed maturation of the cellular immune system already in early infancy and may be associated, among other things, with a lifelong functional weakness of the T-suppressor lymphocytes. Finally, an intake of oils rich in gamma-linolenic acid may alleviate the symptoms of patients with atopic dermatitis. Graphic – Omega-6 fatty acids metabolic pathway.
