Resolvin E1 selectively interacts with leukotriene B4 receptor BLT1 and ChemR23 to regulate inflammation

Resolvin E1 (RvE1) is a potent anti-inflammatory and proresolving mediator derived from omega-3 eicosapentaenoic acid generated during the resolution phase of inflammation. RvE1 possesses a unique structure and counterregulatory actions that stop human polymorphonuclear leukocyte (PMN) transendothelial migration and PMN infiltration in several murine inflammatory models. To examine the mechanism(s) underlying anti-inflammatory actions on PMNs, we prepared [H-3]RvE1 and characterized its interactions with human PMN. Results with membrane fractions of human PMN demonstrated specific binding with a K-d of 48.3 nM. [H-3]RvE1 specific binding to human PMN was displaced by leukotriene B-4 (LTB4) and LTB4 receptor 1 (BLT1) antagonist U-75302, but not by chemerin peptide, a ligand specific for another RvE1 receptor ChemR23. Recombinant human BLT1 gave specific binding with [H-3]RvE1 with a K-d of 45 nM. RvE1 selectively inhibited adenylate cyclase with BLT1, but not with BLT2. In human PBMC, RvEl partially induced calcium mobilization, and blocked subsequent stimulation by LTB4. RvEl also attenuated LTB4 induced NF-kappa B activation in BLT1-transfected cells. In vivo anti-inflammatory actions of RvEl were sharply reduced in BLT1 knockout mice when given at low doses (100 ng i.v.) in peritonitis. In contrast, RvEl at higher doses (1.0 mu g i.v.) significantly reduced PMN infiltration in a BLT1-independent manner. These results indicate that RvEl binds to BLT1 as a partial agonist, potentially serving as a local damper of BLT1 signals on leukocytes along with other receptors (e.g., ChemR23-mediated counterregulatory actions) to mediate the resolution of inflammation.