title: Red blood cells serve as intravascular carriers of myeloperoxidase.
abstract: Myeloperoxidase (MPO) is a heme enzyme abundantly expressed in polymorphonuclear neutrophils. MPO is enzymatically capable of catalyzing the generation of reactive oxygen species (ROS) and the consumption of nitric oxide (NO). Thus MPO has both potent microbicidal and, upon binding to the vessel wall, pro-inflammatory properties. Interestingly, MPO - a highly cationic protein - has been shown to bind to both endothelial cells and leukocyte membranes. Given the anionic surface charge of red blood cells, we investigated binding of MPO to erythrocytes. Red blood cells (RBCs) derived from patients with elevated MPO plasma levels showed significantly higher amounts of MPO by flow cytometry and ELISA than healthy controls. Heparin-induced MPO-release from patient-derived RBCs was significantly increased compared to controls. Ex vivo experiments revealed dose and time dependency for MPO-RBC binding, and immunofluorescence staining as well as confocal microscopy localized MPO-RBC interaction to the erythrocyte plasma membrane. NO-consumption by RBC-membrane fragments (erythrocyte "ghosts") increased with incrementally greater concentrations of MPO during incubation, indicating preserved catalytic MPO activity. In vivo infusion of MPO-loaded RBCs into C57BL/6J mice increased local MPO tissue concentrations in liver, spleen, lung, and heart tissue as well as within the cardiac vasculature. Further, NO-dependent relaxation of aortic rings was altered by RBC bound-MPO and systemic vascular resistance significantly increased after infusion of MPO-loaded RBCs into mice. In summary, we find that MPO binds to RBC membranes in vitro and in vivo, is transported by RBCs to remote sites in mice, and affects endothelial function as well as systemic vascular resistance. RBCs may avidly bind circulating MPO, and act as carriers of this leukocyte-derived enzyme.
authors: Stanford University, Division of Cardiovascular Medicine, Stanford, CA, USA; Stanford Cardiovascular Institute, Stanford, CA, USA. Electronic address: matti.adam@stanford.edu.
authors: Matti
authors: M
authors: Adam
authors: Academy of Sciences of the Czech Republic, Institute of Biophysics, Brno, Czech Republic.
authors: Silvie
authors: S
authors: Gajdova
authors: Academy of Sciences of the Czech Republic, Institute of Biophysics, Brno, Czech Republic.
authors: Hana
authors: H
authors: Kolarova
authors: Academy of Sciences of the Czech Republic, Institute of Biophysics, Brno, Czech Republic; International Clinical Research Center-CBCE, St. Anne's University Hospital Brno, Brno, Czech Republic.
authors: Lukas
authors: L
authors: Kubala
authors: University of Hamburg, Heart Center, Department of Cardiovascular Medicine, Hamburg, Germany.
authors: Denise
authors: D
authors: Lau
authors: University of Hamburg, Heart Center, Department of Cardiovascular Medicine, Hamburg, Germany.
authors: Anne
authors: A
authors: Geisler
authors: Heart Center, Department of Cardiology and Cologne Cardiovascular Research Center, University of Cologne, Cologne, Germany.
authors: Thorben
authors: T
authors: Ravekes
authors: Heart Center, Department of Cardiology and Cologne Cardiovascular Research Center, University of Cologne, Cologne, Germany.
authors: Volker
authors: V
authors: Rudolph
authors: Stanford University, Division of Cardiovascular Medicine, Stanford, CA, USA; Stanford Cardiovascular Institute, Stanford, CA, USA.
authors: Philip S
authors: PS
authors: Tsao
authors: University of Hamburg, Heart Center, Department of Cardiovascular Medicine, Hamburg, Germany.
authors: Stefan
authors: S
authors: Blankenberg
authors: Heart Center, Department of Cardiology and Cologne Cardiovascular Research Center, University of Cologne, Cologne, Germany.
authors: Stephan
authors: S
authors: Baldus
authors: Heart Center, Department of Cardiology and Cologne Cardiovascular Research Center, University of Cologne, Cologne, Germany.
authors: Anna
authors: A
authors: Klinke
mesh_terms: D054058:Acute Coronary Syndrome / Q000097:blood* / Q000473:pathology; D000818:Animals; D001011:Aorta / Q000187:drug effects; D001692:Biological Transport; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000187:drug effects; D004912:Erythrocytes / Q000378:metabolism* / Q000473:pathology; D006321:Heart / Q000187:drug effects; D006333:Heart Failure / Q000097:blood* / Q000473:pathology; D006493:Heparin / Q000737:chemistry; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology; D009924:Organ Culture Techniques; D009195:Peroxidase / Q000097:blood* / Q000494:pharmacology; D011485:Protein Binding; D046509:Tissue Culture Techniques; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D009569:Nitric Oxide; D006493:Heparin; D009195:Peroxidase
keywords: Cell membranes; Erythrocyte; Myeloperoxidase; Systemic vascular resistance; Vascular endothelium-dependent relaxation