Aspirin-triggered 15-Epi-Lipoxin A₄ (LXA₄) and LXA₄ Stable Analogues Are Potent Inhibitors of Acute Inflammation: Evidence for Anti-inflammatory Receptors

Lipoxins are bioactive eicosanoids that are immunomodulators. In human myeloid cells, lipoxin (LX) A₄ actions are mediated by interaction with a G protein–coupled receptor. To explore functions of LXA₄ and aspirin-triggered 5(S),6(R),15(R)-trihydroxy-7,9,13-trans-11-cis–eicosatetraenoic acid (15-epi-LXA₄) in vivo, we cloned and characterized a mouse LXA₄ receptor (LXA₄R). When expressed in Chinese hamster ovary cells, the mouse LXA₄R showed specific binding to [³H]LXA₄ (K_d ≈ 1.5 nM), and with LXA₄ activated GTP hydrolysis. Mouse LXA₄R mRNA was most abundant in neutrophils. In addition to LXA₄ and 15-epi-LXA₄, bioactive LX stable analogues competed with both [³H]LXA₄ and [³H]leukotriene D₄ (LTD₄)– specific binding in vitro to neutrophils and endothelial cells, respectively. Topical application of LXA₄ analogues and novel aspirin-triggered 15-epi-LXA₄ stable analogues to mouse ears markedly inhibited neutrophil infiltration in vivo as assessed by both light microscopy and reduced myeloperoxidase activity in skin biopsies. The 15(R)-16-phenoxy-17,18, 19,20-tetranorLXA₄ methyl ester (15-epi-16-phenoxy-LXA₄), an analogue of aspirin triggered 15-epi-LXA₄, and 15(S)-16-phenoxy-17,18,19,20-tetranor-LXA₄ methyl ester (16-phenoxy-LXA₄) were each as potent as equimolar applications of the anti-inflammatory, dexamethasone. Thus, we identified murine LXA₄R, which is highly expressed on murine neutrophils, and showed that both LXA₄ and 15-epi-LXA₄ stable analogues inhibit neutrophil infiltration in the mouse ear model of inflammation. These findings provide direct in vivo evidence for an anti-inflammatory action for both aspirin-triggered LXA₄ and LXA₄ stable analogues and their site of action in vivo.