Epi-lipoxin


Epi-lipoxins are trihydroxy metabolites of arachidonic acid. They are 15R-epimers of their lipoxin counterparts; that is, the epi-lipoxins, 15-epi-lipoxin A4 and 15-epi-lipoxin B4, differ from their respective lipoxin A4 and lipoxin B4 epimers in that their 15-hydroxy residue has R rather than S chirality. Formulae for these lipoxins are:

The two-epi-Lx's as well as the two lx's are nonclassic eicosanoids that, like other members of the specialized pro-resolving mediators class of autocoids, form during and act to resolve inflammatory responses. Synthesis of the lipoxins typically involves a lipoxygenase enzyme which acts to add a 15S-hydroxyl residue to the lipoxin precursor, arachidonic acid, whereas synthesis of the epi-lipoxins involves aspirin-pretreated cyclooxygenase 2 or a cytochrome P450 enzyme which adds a 15R-hydroxyl residue to arachidonic acid. In acknowledgement of the role played by aspirin-treated cyclooxygenase 2 in forming these products, the epi-lipoxins are sometimes termed ATL which stands for Aspirin-Triggered Lipoxins.
The counter-regulatory role of the epi-lipoxins in serving as stop signals for diverse inflammation responses is detailed at the lipoxin site.