Nonclassic eicosanoid

Nonclassic eicosanoids are biologically active signaling molecules made by oxygenation of twenty-carbon fatty acids, other than the classic eicosanoids.

Terminology


"Eicosanoid" is the collective term for oxygenated derivatives of three different 20-carbon essential fatty acids&mdash;Eicosapentaenoic acid (EPA), Arachidonic acid (AA) and Dihomo-gamma-linolenic acid (DGLA).

Current usage limits the term to the leukotrienes (LT) and three types of prostanoids&mdash;prostaglandins (PG) prostacyclins (PGI), and  thromboxanes (TX). However, several other classes can technically be termed eicosanoid, including the hepoxilins, resolvins, isofurans, isoprostanes, lipoxins, epi-lipoxins, epoxyeicosatrienoic acids (EETs) and endocannabinoids. LTs and prostanoids are sometimes termed 'classic eicosanoids' in contrast to the 'novel', 'nonclassic' or 'eicosanoid-like' eicosanoids.

The classic eicosanoids are autocrine and paracrine mediators, active at micromolar concentrations (or lower), produced with high stereospecificity. They are produced from EPAs (chiefly AA) from either cyclooxygenase (COX) or 5-lipoxygenase.

Broadly, the nonclassic eicosanoids are the products of 20-carbon EFAs and Also included are
 * Other oxygenation enzymes, (hepoxilins, resolvins, lipoxins, epi-lipoxins, epoxyeicosatrienoic acids (EETs));
 * Uncatalyzed oxygenation reactions, (isofurans, isoprostanes, phytoprostanes);
 * Addition reactions other than oxygenation (endocannabinoids).
 * Side products from the classic eicosanoid biosynthesis, (levuglandins, Oxo-eicosanoidss);
 * Reactions between other 20-carbon fatty acids and these pathways (the COX products of pinolenic and mead acid).