Epi-lipoxin
Epi-lipoxins are trihydroxy (i.e. containing 3 hydroxyl residues) metabolites of arachidonic acid. They are 15R-epimers 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: 5S,6R,15S-trihydroxy-7E,9E,11Z,13E-eicosatetraenoic acid
- LxB4: 5S,14R,15S-trihydroxy-6E,8Z,10E,12E-eicosatetraenoic acid
- 15-epi-LxA4: 5S,6R,15R-trihydroxy-7E,9E,11Z,13E-eicosatetraenoic acid
- 15-epi-LxB4: 5S,14R,15R-trihydroxy-6E,8Z,10E,12E-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 autocoids, form during and act to resolve inflammatory responses.{{cite journal |author=Serhan CN |title=Lipoxins and aspirin-triggered 15-epi-lipoxins are endogenous components of antiinflammation: emergence of the counterregulatory side |journal=Arch. Immunol. Ther. Exp. (Warsz.) |volume=49 |issue=3 |pages=177–88 |year=2001 |pmid=11478391 }}{{cite journal | vauthors = Chandrasekharan JA, Sharma-Walia N | title = Lipoxins: nature's way to resolve inflammation | journal = Journal of Inflammation Research | volume = 8 | pages = 181–92 | year = 2015 | pmid = 26457057 | pmc = 4598198 | doi = 10.2147/JIR.S90380 | doi-access = free }}{{cite journal | vauthors = Romano M, Cianci E, Simiele F, Recchiuti A | title = Lipoxins and aspirin-triggered lipoxins in resolution of inflammation | journal = European Journal of Pharmacology | volume = 760 | pages = 49–63 | year = 2015 | pmid = 25895638 | doi = 10.1016/j.ejphar.2015.03.083 }} 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.{{cite journal |author=Clària J, Serhan CN |title=Aspirin triggers previously undescribed bioactive eicosanoids by human endothelial cell-leukocyte interactions |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=92 |issue=21 |pages=9475–9 |year=1995 |pmid=7568157 |doi=10.1073/pnas.92.21.9475 |pmc=40824 |bibcode=1995PNAS...92.9475C |doi-access=free }} 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.