Eicosanoids are hormone-like hydrophobic substances that function as neurotransmitters or immune modulators. They are formed as part of lipid metabolism. Starting materials are omega-6 and omega-3 fatty acids.
What are eicosanoids?
The hormone-like eicosanoids play a major role as neurotransmitters or immune modulators. In some cases, they elicit opposite reactions. Basically, they are mediators between the immune system and the nervous system. Eicosanoids are derived from omega-6 or omega-3 fatty acids. They contain 20 carbon atoms, from which their name is derived. In Greek, the word twenty means “eikosi”. All eicosanoids contain prostanoic acid as their basic skeleton. There are three series of eicosanoids. Series 1 is synthesized from dihomogammalinolenic acid (DGLA) and has an anti-inflammatory effect. Therefore, the active ingredients of this series are often called the good eicosanoids. Series 2 with the so-called bad eicosanoids is responsible for inflammatory reactions and pain conduction. It is produced from arachidonic acid (AA). Series 3 is derived from eicosapentaenoic acid (EPA). This series also has an anti-inflammatory effect and is the counterpart of series 2. The substance groups resulting from these series act via G-protein-coupled membrane receptors. The individual substance groups can be divided into prostaglandins, prostacyclin, thromboxanes and leukotrienes. Series 2 proves to be the most important series of eicosanoids, although it contains substances that promote inflammation. However, these are defensive reactions of the body, which are necessary in the acute situation.
Function, effect and tasks
Eicosanoids represent a variety of hormone-like agents that perform different functions for the organism. In general, they are substances that mediate between the immune system and the nervous system. In the case of infection, injury, trauma or exposure to foreign particles, some of the eicosanoids stimulate defense reactions that manifest themselves in inflammation and pain. Counterparts of these substances, which belong to the same substance class, simultaneously have an anti-inflammatory effect. Both functions are vital for the body. Dihomogammalinolenic acid (DGLA) is the starting substance for series 1. This compound is the precursor of series 1 anti-inflammatory eicosanoids, but at the same time it is also the precursor of arachidonic acid, which in turn acts as the precursor of series 2 eicosanoids. Arachidonic acid is always associated with the synthesis of pro-inflammatory eicosanoids. In reality, metabolites with sometimes very opposite functions are formed during arachidonic acid metabolism. Thus, again, there are proinflammatory and fever-increasing metabolites as well as anti-inflammatory and fever-reducing metabolites. Series-3 eicosanoids, on the other hand, are anti-inflammatory and act as true counterparts to series 2. Their parent compound is eicosapentaenoic acid and, unlike the other series, is an omega-3 fatty acid. Most eicosanoids are also so-called prostaglandins. They are almost congruent with the three series. So there are both pro-inflammatory and anti-inflammatory prostaglandins. By far the most important role is played by series 2 prostaglandins, which are responsible for pain, inflammation and blood clotting and are therefore a particular target of the pharmaceutical industry. Various drugs are being tested to limit their effect. Series 2 prostaglandins include prostacyclin and thromboxane. Prostacyclin is involved in inflammatory reactions. At the same time, however, it counteracts blood clotting. Thromboxane is the antagonist of prostacyclin with regard to blood coagulation. It activates platelet aggregation. The group of substances known as leukotrienes also belongs to the group of eicosanoids. The leukotrienes are not prostaglandins. But they are also derived from arachidonic acid. They are found in white blood cells and also promote inflammatory processes.
Formation, occurrence, properties, and optimal levels
Eicosanoids are derived from unsaturated fatty acids. The omega-6 and omega-3 fatty acids mainly play a role. For series 1 and 2 eicosanoids, gamma-linolenic acid serves as the starting material. It is an omega-6 fatty acid synthesized from essential linoleic acid or ingested through vegetable oils. Dihomogammalinolenic acid and arachidonic acid are formed from linoleic acid and finally gamma-linolenic acid.However, arachidonic acid is also supplied via the diet independently of biosynthesis. Linoleic acid, after all, is the starting material for both anti-inflammatory and pro-inflammatory eicosanoids. Gamma-linolenic acid is found in particular in borage oil, evening primrose oil and hemp oil. Its raw material (linoleic acid) is found in many vegetable oils such as sunflower oil, rapeseed oil or olive oil. The omega-3 fatty acid eicosapentaenoic acid is the starting material for the anti-inflammatory eicosanoids of series 3, which are also counterparts to series 2. Eicosapentaenoic acid is mainly found in fish oil. Especially salmon or herring are rich in eicosapentaenoic acid.
Diseases and disorders
All eicosanoids perform exceedingly important functions in the body. The inflammatory reactions caused by various prostaglandins are also vital for bodily defense reactions. However, these prostaglandins are also active in allergic reactions and autoimmune diseases. In this case, the immune reaction is directed against normally harmless foreign proteins or, in the case of autoimmune diseases, even against the body’s own proteins. Which processes lead to these misreactions has not yet been fully elucidated. However, the increased effect of series 2 eicosanoids can also lead to this. To prevent this, there must be a balanced ratio of omega-6 and omega-3 fatty acids in the diet. Today, omega-6 fatty acids are consumed in sufficient quantities in the diet. However, there is often a deficit of omega-3 fatty acids, as this can be taken in today mainly via fish oil. However, diseases such as diabetes mellitus, obesity, stress, liver disease, physical inactivity or vitamin and mineral deficiencies can also influence the metabolic processes in the body in such a way that an unbalanced ratio between omega-6 and omega-3 fatty acids develops. The result is increased inflammatory reactions and the increased incidence of allergies, asthmatic complaints and autoimmune diseases.
