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The actions of the ω-3 (omega-3) and ω-6 (omega-6) essential fatty acids (EFAs) are best characterized by their interactions; they cannot be understood separately. Arachidonic acid (AA) is a 20-carbon ω-6 conditionally essential fatty acid. It sits at the head of the "arachidonic acid cascade" – more than 20 different signalling paths that control a wide array of bodily functions, but especially those functions involving inflammation, cell growth and the central nervous system. Most AA in the human body derives from dietary linoleic acid (another essential fatty acid, 18:2 ω-6), which is derived from nuts, seeds, vegetable oils and animal fats. In the inflammatory response, two other groups of dietary essential fatty acids form cascades that parallel and compete with the arachidonic acid cascade. EPA (20:5 ω-3) provides the most important competing cascade. It is ingested from oily fish, and algae oil or derived from dietary alpha-linolenic acid found in, for instance, walnuts, hemp oil and flax oil. DGLA (20:3 ω-6) provides a third, less prominent cascade. It derives from dietary GLA (18:3 ω-6) found in, e.g. borage oil. These two parallel cascades soften the inflammatory promoting effects of certain eicosanoids made from AA. Low dietary intake of these less inflammatory promoting essential fatty acids, especially the ω-3s, is correlated with a variety of inflammation-related diseases. Today, the usual diet in industrial countries contains much less ω-3 fatty acids than the diet of a century ago and a much greater amount of pollution that evokes the inflammatory response. The diet from a century ago had much less ω-3 than the diet of early hunter-gatherers and much less pollution. We can also look at the ratio of ω-3 to ω-6 in comparisons of their diets. These changes have been accompanied by increased rates of many diseases – the so-called diseases of civilization – that involve inflammatory processes. There is now very strong evidence that several of these diseases are ameliorated by increasing dietary ω-3, and good evidence for many others. There is also more preliminary evidence showing that dietary ω-3 can ease symptoms in several psychiatric disorders. Nonetheless, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes. ==Eicosanoid series nomenclature== Eicosanoids are signalling molecules derived from the essential fatty acids (EFA); they are a major pathway by which the EFAs act in the body. There are four classes of eicosanoid and two or three series within each class. Before discussing eicosanoid action, we will explain the series nomenclature. The plasma membranes of cells contain phospholipids, which are composed of a hydrophilic phosphate head and two hydrophobic fatty acid tails. Some of these fatty acids are 20-carbon polyunsaturated essential fatty acids – AA, EPA or DGLA. In response to a variety of inflammatory signals, these EFAs are cleaved out of the phospholipid and released as free fatty acids. Next, the EFA is oxygenated (by either of two pathways), then further modified, yielding the eicosanoids.〔(【引用サイトリンク】 url=http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_p_36zPzhtm#1085994 )〕 Cyclooxygenase (COX) oxidation removes two C=C double bonds, leading to the TX, PG and PGI series. Lipoxygenase oxidation removes no C=C double bonds, and leads to the LK.〔(【引用サイトリンク】 title= Polyenoic fatty acids )〕 After oxidation, the eicosanoids are further modified, making a ''series''. Members of a series are differentiated by an ''ABC...'' letter, and are numbered by the number of double bonds, which does not change within a series. For example, cyclooxygenase action upon AA (with 4 double bonds) leads to the series-2 thromboxanes (TXA2, TXB2... ) each with two double bonds. Cyclooxygenase action on EPA (with 5 double bonds) leads to the series-3 thromboxanes (TXA3, TXB3... ) each with three double bonds. There are exceptions to this pattern, some of which indicate stereochemistry (PGF2α). Table (1) shows these sequences for AA (20:4 ω-6). The sequences for EPA (20:5 ω-3) and DGLA (20:3 ω-6) are analogous. All the prostenoids are substituted prostanoic acids. Cyberlipid Center's Prostenoid page〔(【引用サイトリンク】 title=Prostanoids )〕 illustrates the parent compound and the rings associated with each series–letter. The IUPAC and the IUBMB use the equivalent term Icosanoid.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Essential fatty acid interactions」の詳細全文を読む スポンサード リンク
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