Eicosanoids

Eicosanoids are signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, like arachidonic acid, 20 carbon units in length. They are a sub-category of oxylipins, i.e. oxidized fatty acids of diverse carbon units in length but are further distinguished from other oxylipins by their overwhelming importance as cell signaling molecules. Eicosanoids function in diverse physiological and pathological systems including those: mounting or inhibiting inflammation, allergy, fever and other immune responses; influencing the abortion of pregnancy and normal childbirth; contributing to the perception of pain; regulating cell growth; controlling blood pressure; and modulating the regional flow of blood to tissues. In performing these tasks, eicosanoids most often act as agents to impact their cells of origin or as paracrine signaling agents to impact cells near to their cells of origin. However, they can also act as endocrine agents to control the function of distant cells.

There are multiple subfamilies of eicosanoids, including most prominently the prostaglandins, thromboxanes, leukotrienes, lipoxins, resolvins, and eoxins but also others as noted in the following Nomenclature section. For each subfamily, there is the potential to have at least 5 separate series of metabolites, two series derived from ω-6 PUFAs (arachidonic and dihomo-gamma-linolenic acids), one series derived from the ω-3 PUFA (eicosapentaenoic acid), and one series derived from the ω-9 PUFA (mead acid). This subfamily distinction is important. Mammals, including humans, are unable to convert ω-6 into ω-3 PUFA. In consequence, tissue levels of the ω-6 and ω-3 PUFAs and their corresponding eicosanoid metabolites link directly to the amount of dietary ω-6 versus ω-3 PUFAs consumed. Since certain of the ω-6 and ω-3 PUFA series of metabolites have almost diametrically opposing physiological and pathological activities, it has often been suggested that the deleterious consequences associated with the consumption of ω-6 PUFA-rich diets reflects excessive production and activities of ω-6 PUFA-derived eicosanoids while the beneficial effects associated with the consumption of ω-3 PUFA-rich diets reflect the excessive production and activities of ω-3 PUFA-derived eicosanoids. In this view, the opposing effects of ω-6 PUFA-derived and ω-3 PUFA-derived eicosanoids on key target cells underlie the detrimental and beneficial effects of ω-6 and ω-3 PUFA-rich diets on inflammation and allergy reactions, atherosclerosis, hypertension, cancer growth, and a host of other processes.

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