Lipoxin and resolvin biosynthesis is dependent on 5‐lipoxygenase activating protein

Resolution of acute inflammation is an active process coordinated by proresolving lipid mediators (SPMs) such as lipoxins (LXs) and resolvins (Rvs), which are formed by the concerted action of 2 lipoxygenases (LOs). Because the exact molecular mechanisms of SPM biosynthesis are not completely understood, we aimed to investigate LX and D‐type Rv formation in human leukocytes and HEK293T cells overexpressing leukotriene (LT) pathway enzymes. Activity assays in precursor (15‐hydroxyeicosatetraenoic acids, 17‐HDoHE)‐treated granulocytes [polymorphonuclear leukocytes (PMNLs)] showed a strict dependence of LXA 4 /RvD 1 biosynthesis on cell integrity, and incubation with recombinant human 5‐LO did not lead to LX or Rv formation. Pharmacologic inhibition of 5‐LO activating protein (FLAP) by MK‐886 inhibited LXA 4 /RvD 1 biosynthesis in precursor‐treated PMNLs (drug concentration causing 50% inhibition ∼0.3/0.2 μM), as did knockdown of the enzyme in MM6 cells, and precursor‐treated HEK293T overexpressing 5‐LO produced high amounts of LXA 4 only in the presence of FLAP. In addition, inhibition of cytosolic phospholipase A 2α (cPLA 2α ) interfered with LXA 4 /RvD 1 formation from exogenous precursors in PMNLs. Furthermore, inhibition of the LT synthases LTA 4 hydrolase and LTC 4 synthase in PMNL/platelet coincubations augmented LXA 4 levels. These findings show that several enzymes known to be involved in the biosynthesis of proinflammatory LTs, such as FLAP and cPLA 2α , also contribute to LX and Rv formation.—Lehmann, C., Homann, J., Ball, A.‐K., Blöcher, R., Kleinschmidt, T. K., Basavarajappa, D., Angioni, C., Ferreirós, N., Häfner, A.‐K., Rådmark, O., Proschak, E., Haeggström, J. Z., Geisslinger, G., Parnham, M. J., Steinhilber, D., Kahnt, A. S. Lipoxin and resolvin biosynthesis is dependent on 5‐lipoxygenase activating protein. FASEB J. 29, 5029–5043 (2015). www.fasebj.org