Maresins are produced by macrophages from
docosahexaenoic acid (DHA) and exert potent proresolving and tissue homeostatic actions.
Maresin 1 (MaR1; 7R,14S-dihydroxy-docosa-4Z,8E,10E,12Z,16Z,19Z-hexaenoic
acid) is the first identified maresin. Here, we investigate formation, stereochemistry, and precursor role of 13,14-epoxy-docosahexaenoic
acid, an intermediate in MaR1 biosynthesis. The 14-lipoxygenation of DHA by human macrophage
12-lipoxygenase (hm12-LOX) gave 14-hydro(peroxy)-docosahexaenoic
acid (14-HpDHA), as well as several dihydroxy-
docosahexaenoic acids, implicating an
epoxide intermediate formation by this
enzyme. Using a stereo-controlled synthesis, enantiomerically pure 13S,14S-epoxy-docosa-4Z,7Z,9E,11E,16Z,19Z-hexaenoic
acid (13S,14S-epoxy-DHA) was prepared, and its stereochemistry was confirmed by NMR spectroscopy. When this 13S,14S-epoxide was incubated with human macrophages, it was converted to MaR1. The synthetic 13S,14S-epoxide inhibited
leukotriene B4 (
LTB4) formation by human
leukotriene A4 hydrolase (LTA4H) ∼40% (P<0.05) to a similar extent as
LTA4 (∼50%, P<0.05) but was not converted to MaR1 by this
enzyme. 13S,14S-epoxy-DHA also reduced (∼60%; P<0.05)
arachidonic acid conversion by hm12-LOX and promoted conversion of M1 macrophages to M2 phenotype, which produced more MaR1 from the
epoxide than M1. Together, these findings establish the biosynthesis of the 13S,14S-epoxide, its absolute stereochemistry, its precursor role in MaR1 biosynthesis, and its own intrinsic bioactivity. Given its actions and role in MaR1 biosynthesis, this
epoxide is now termed 13,14-epoxy-maresin (13,14-eMaR) and exhibits new mechanisms in resolution of
inflammation in its ability to inhibit proinflammatory mediator production by
LTA4 hydrolase and to block arachidonate conversion by human 12-LOX rather than merely terminating phagocyte involvement.