Eoxins
Eoxins are a family of proinflammatory eicosanoids (signaling compounds that regulate inflammatory and immune responses) that are produced in human eosinophils (a class of white blood cells) and mast cells through the metabolism of arachidonic acid, an omega-6 (ω-6) fatty acid, by the arachidonate 15-lipoxygenase-1 enzyme. The eoxins represent 14,15-leukotriene analogs and are synthesized in a similar manner to the standard leukotrienes. Eoxins contribute to inflammation in airway allergies and certain types of cancers, particularly Hodgkin's lymphoma (a cancer originating from white blood cells), prostate cancer, and colon carcinoma.
The eoxins are 14,15-analogs of LTA4, LTC4, LTD4, and LTE4. Because the leukotrienes and 14,15-leukotrienes have very similar names, the 14,15-leukotrienes were renamed "eoxins" to avoid the confusion that might arise from referring to both group as "leukotrienes". The eoxins derive their name from eosinophils, the cell type where they were originally discovered in abundance.
As indicated in the following Biochemstry section, there are 4 types of chemically distinct eoxins that are made serially from 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid:
A 15-lipoxygenase (i.e. ALOX15 or ALOX15B) metabolizes arachidonic acid to 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15(S)-HpETE (see 15-Hydroxyicosatetraenoic acid); 15(S)-HpETE is then converted to its 14,15-trans-epoxide, 14,15-trans-epoxide oxido-5Z,8Z,10E,13E-eicosatetraenoic acid (i.e., Eoxin A4 or EXA4) by ALOX15 and thereafter to 14(R)-glutothionyl-15(S)hydroxy-5Z,8Z,10E,13E-eicosatetraenoic acid (i.e. Eoxin C4 or EXC4) by conjugation to glutathione through the action of leukotriene C4 synthase. EXC4 contains glutathione (i.e. γ-L-glutamyl-L-cysteinylglycine) bound in the R configuration to carbon 14. EXC4 is further metabolized by removal of the γ-L-glutamyl residue to form EXD4 which is in turn further metabolized by removal of the glycine residue to form EXE4. These metabolic transformations are similar to and therefore presumed to be mediated by the same enzymes that metabolizes arachidonic acid to LTA4, LTC4, LTD4, and LTE4.
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