title: Neutrophil-derived microparticles induce myeloperoxidase-mediated damage of vascular endothelial cells.
abstract: BACKGROUND
  Upon activation neutrophil releases microparticles - small plasma membrane vesicles that contain cell surface proteins and cytoplasmic matter, with biological activities. In this study we investigated the potential role of myeloperoxidase in the endothelial cell injury caused by neutrophil-derived microparticles.
  
  
  RESULTS
  Microparticles were produced by activating human neutrophils with a calcium ionophore and characterized by flow cytometry and transmission and scanning electron microscopy. Myeloperoxidase activity was measured by luminol-dependent chemiluminescence. Neutrophil microparticles-induced injuries and morphological alterations in human umbilical vein endothelial cells (HUVECs) were evaluated by microscopy and flow cytometry. Neutrophil microparticles were characterized as structures bounded by lipid bilayers and were less than 1 μm in diameter. The microparticles also expressed CD66b, CD62L and myeloperoxidase, which are all commonly expressed on the surface of neutrophils, as well as exposition of phosphatidylserine. The activity of the myeloperoxidase present on the microparticles was confirmed by hypochlorous acid detection. This compound is only catalyzed by myeloperoxidase in the presence of hydrogen peroxide and chloride ion. The addition of sodium azide or taurine inhibited and reduced enzymatic activity, respectively. Exposure of HUVEC to neutrophil microparticles induced a loss of cell membrane integrity and morphological changes. The addition of sodium azide or myeloperoxidase-specific inhibitor-I consistently reduced the injury to the endothelial cells. Taurine addition reduced HUVEC morphological changes.
  
  
  CONCLUSIONS
  We have demonstrated the presence of active myeloperoxidase in neutrophil microparticles and that the microparticle-associated myeloperoxidase cause injury to endothelial cells. Hence, the microparticle-associated myeloperoxidase-hydrogen peroxide-chloride system may contribute to widespread endothelial cell damage in conditions of neutrophil activation as observed in vasculitis and sepsis.
authors.forename: Thassila Nogueira
authors.initials: TN
authors.lastname: Pitanga
authors.forename: Luciana
authors.initials: L
authors.lastname: de Aragão França
authors.forename: Viviane Costa Junqueira
authors.initials: VC
authors.lastname: Rocha
authors.forename: Thayna
authors.initials: T
authors.lastname: Meirelles
authors.forename: Valéria Matos
authors.initials: VM
authors.lastname: Borges
authors.forename: Marilda Souza
authors.initials: MS
authors.lastname: Gonçalves
authors.forename: Lain Carlos
authors.initials: LC
authors.lastname: Pontes-de-Carvalho
authors.forename: Alberto Augusto
authors.initials: AA
authors.lastname: Noronha-Dutra
authors.affiliation: Fundação Oswaldo Cruz-BA, Gonçalo Moniz Research Center, Salvador, BA, Brazil. wluis@bahia.fiocruz.br.
authors.forename: Washington Luis Conrado
authors.initials: WL
authors.lastname: dos-Santos
mesh_terms: D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D055252:Cell-Derived Microparticles / Q000201:enzymology* / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism*; D018384:Oxidative Stress; D009195:Peroxidase / Q000378:metabolism*
chemical_list: D006861:Hydrogen Peroxide; D009195:Peroxidase; D002118:Calcium