: "Eicosanoid" is the collective term for oxygenated derivatives of three different 20-carbon
essential fatty acids—
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—
prostaglandins (
PG)
prostacyclins (
PGI), and
thromboxanes (
TX). However, several other classes can technically be termed eicosanoid, including the
eoxins,
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
EFAs (chiefly AA) from either
cyclooxygenase (COX) or
5-lipoxygenase. Broadly, the nonclassic eicosanoids are the products of 20-carbon EFAs and • Other oxygenation enzymes, (
eoxins,
hepoxilins,
resolvins,
lipoxins,
epi-lipoxins,
epoxyeicosatrienoic acids (EETs)); • Uncatalyzed oxygenation reactions, (
isofurans,
isoprostanes,
phytoprostanes); • Addition reactions other than oxygenation (
endocannabinoids). Also included are • Side products from the classic eicosanoid biosynthesis, (
levuglandins,
Oxoeicosanoids); • Reactions between other fatty acids and these pathways (the COX products of
pinolenic and
mead acid). ==See also==