Hemolysis or extensive cell damage can lead to high concentrations of free heme, causing oxidative stress and inflammation. Considering that heme induces neutrophil chemotaxis, we hypothesize that heme activates a G protein-coupled receptor. Here we show that similar to heme, several heme analogs were able to induce neutrophil migration in vitro and in vivo. Mesoporphyrins, molecules lacking the vinyl groups in their rings, were not chemotactic for neutrophils and selectively inhibited

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... ced migration. Moreover, migration of neutrophils induced by heme was abolished by pretreatment with pertussis toxin, an inhibitor of G␣ inhibitory protein, and with inhibitors of phosphoinositide 3-kinase, phospholipase C␤, mitogen-activated protein kinases, or Rho kinase. The induction of reactive oxygen species by heme was dependent of G␣ inhibitory protein and phosphoinositide 3-kinase and partially dependent of phospholipase C␤, protein kinase C, mitogen-activated protein kinases, and Rho kinase. Together, our results indicate that heme activates neutrophils through signaling pathways that are characteristic of chemoattractant molecules and suggest that mesoporphyrins might prove valuable in the treatment of the inflammatory consequences of hemorrhagic and hemolytic disorders.