EICOSANOIDS AND RELATED COMPOUNDS – AN INTRODUCTION Structures and Key Enzymes

The term eicosanoid is used to embrace biologically active lipid mediators (C20 fatty acids and their metabolites), including prostaglandins, thromboxanes, leukotrienes and other oxygenated derivatives, which are produced primarily by three classes of enzymes, cyclooxygenases (COX-1 and COX-2), lipoxygenases (LOX) and cytochrome P450 epoxygenase. The key precursor fatty acids are 8c,11c,14c-eicosatrienoic (dihomo-γ-linolenic or 20:3(n-6)), 5c,8c,11c,14ceicosatetraenoic (arachidonic or 20:4(n-6)) and 5c,8c,11c,14c,17c-eicosapentaenoic (20:5(n-3) or EPA) acids (see our web page on ‘polyunsaturated fatty acids’). However, it is now impossible to discuss these compounds and their biological activities properly without also considering related products produced by non-enzymic means (isoprostanes), and the docosanoids (resolvins) derived from 4c,7c,10c,13c,16c,19c-docosahexaenoic acid (22:6(n-3) or DHA). Nor can analogous plant products, such as the jasmonates and other oxylipins derived from 9c,12c,15coctadecatrienoic (α-linolenic or 18:3(n-3)) acid, be ignored. It is noteworthy that the precursor fatty acids belong to both the omega-6 and omega-3 families.