Epi-lipoxin

 ( Eicosanoids ) 

Epi-lipoxins are trihydroxy (i.e. containing 3 hydroxyl residues) metabolites of arachidonic acid. They are Epimer of their lipoxin counterparts; that is, the epi-lipoxins, 15-epi-lipoxin A4 (15-epi-LxA4) and 15-epi-lipoxin B4 (15-epi-LXB4), differ from their respective lipoxin A4 (LxA4) and lipoxin B4 (LxB4) epimers in that their 15-hydroxy residue has R rather than S chirality. Formulae for these lipoxins (Lx) are:

• LxA4: 5 S,6 R,15 S-trihydroxy-7 E,9 E,11 Z,13 E-eicosatetraenoic acid
• LxB4: 5 S,14 R,15 S-trihydroxy-6 E,8 Z,10 E,12 E-eicosatetraenoic acid
• 15-epi-LxA4: 5 S,6 R,15 R-trihydroxy-7 E,9 E,11 Z,13 E-eicosatetraenoic acid
• 15-epi-LxB4: 5 S,14 R,15 R-trihydroxy-6 E,8 Z,10 E,12 E-eicosatetraenoic acid

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 , form during and act to resolve inflammatory responses. Synthesis of the lipoxins typically involves a lipoxygenase enzyme which acts to add a 15 S-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 15 R-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.

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See also

• Specialized pro-resolving mediators

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