title: Impact of plasma histones in human sepsis and their contribution to cellular injury and inflammation.
abstract: BACKGROUND
  Circulating histones have been identified as mediators of damage in animal models of sepsis and in patients with trauma-associated lung injury. Despite existing controversies on actual histone concentrations, clinical implications and mechanism of action in various disease conditions, histone levels in human sepsis, association with disease progression and mediated effects on endothelial and immune cells remain unreported. This study aimed to determine histone levels and its clinical implication in septic patients and to elucidate histone-mediated effects ex-vivo.
  
  
  METHODS
  Histone levels, endogenous activated protein C (APC) levels and clinical data from two independent cohorts of septic patients were obtained. Histone levels were compared with various control groups including healthy individuals, intensive care unit (ICU) patients without sepsis, ICU patients with multiple organ failure and patients with minor or multiple trauma, all without infection. Endothelial and monocytic cells were stimulated with histones. Cellular integrity and sepsis prototypical cytokines were evaluated. The mechanism of action of histones via Toll-like receptor 4 (TLR4) was evaluated using a function blocking antibody. Histone degradation in plasma was studied by immunoblotting.
  
  
  RESULTS
  Histone H4 levels were significantly elevated in patients with sepsis (cohort I; n = 15 and cohort II; n = 19) versus ICU controls (n = 12), patients with multiple organ failure (n = 12) or minor trauma (n = 7), associated with need for renal replacement therapy and decrease in platelet count during disease progression, and remarkably were significantly associated with increased mortality rates in septic patients (ICU-, 28 day- and 90 day mortality rates). There was an inverse correlation between plasma histones and endogenous APC levels. Histone stimulation induced the release of sepsis prototypic cytokines and decreased cell integrity indicated by a significant increase of lactate dehydrogenase (LDH) and propidium iodide (PI) staining. Blocking of TLR4 decreased cellular cytotoxicity on endothelial cells. The calculated half-life of histones in spiked plasma was 4.6 minutes.
  
  
  CONCLUSIONS
  Histone levels in septic patients are significantly increased and might mediate disease aggravation by cellular injury and inflammation via TLR4 signaling, which potentially results in multiple organ failure and fatal outcome.
authors.forename: Michael Liembo
authors.initials: ML
authors.lastname: Ekaney
authors.forename: Gordon Philipp
authors.initials: GP
authors.lastname: Otto
authors.forename: Maik
authors.initials: M
authors.lastname: Sossdorf
authors.forename: Christoph
authors.initials: C
authors.lastname: Sponholz
authors.forename: Michael
authors.initials: M
authors.lastname: Boehringer
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Loesche
authors.forename: Daniel
authors.initials: D
authors.lastname: Rittirsch
authors.forename: Arne
authors.initials: A
authors.lastname: Wilharm
authors.forename: Oliver
authors.initials: O
authors.lastname: Kurzai
authors.forename: Michael
authors.initials: M
authors.lastname: Bauer
authors.forename: Ralf Alexander
authors.initials: RA
authors.lastname: Claus
mesh_terms: D000368:Aged; D016207:Cytokines / Q000097:blood; D018450:Disease Progression; D005260:Female; D006657:Histones / Q000097:blood*; D006801:Humans; D007362:Intensive Care Units; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008297:Male; D008875:Middle Aged; D009102:Multiple Organ Failure / Q000276:immunology; D009104:Multiple Trauma / Q000276:immunology; D011446:Prospective Studies; D011486:Protein C / Q000378:metabolism; D018805:Sepsis / Q000276:immunology* / Q000401:mortality; D051197:Toll-Like Receptor 4 / Q000276:immunology
chemical_list: D016207:Cytokines; D006657:Histones; D011486:Protein C; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D007770:L-Lactate Dehydrogenase