Impact of plasma histones in human sepsis and their contribution to cellular injury and inflammation

Abstract

IntroductionCirculating 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.MethodsHistone 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.ResultsHistone 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.ConclusionsHistone 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.

Biology, role and therapeutic potential of circulating histones in acute inflammatory disorders

“…A number of innate and synthetic substances have demonstrated the ability to inhibit histone‐related toxicity based on surface charge alone, including plasma proteins (albumin,123 CRP14), polypeptides (polyglutamic acid126) and polysaccharides (heparin/heparanoids,111, 146 polysialic acid,147 bacterial O‐antigen148). Elevated histone‐degrading activated protein C (APC) levels are associated with better outcomes in sepsis115, 149 and trauma patients137; APC therapy is being evaluated for treatment of sepsis150 and pancreatitis 151. The effects of histones and NETs on the coagulation cascade can be overcome by therapy with thrombomodulin121 or tissue plasminogen activator (tPA),143 but the clot‐stabilizing effects of DNA in NETs must be overcome, which is well illustrated by the finding that DNAse therapy in addition to tPA is more effective than either therapy alone 152…”

Necroinflammation in Kidney Disease

“…65,73,74 These mechanisms of remote disease exacerbation apply to any source of sepsis or trauma. 75,76 Massive local DAMP or histone release can cause remote microvascular injuries and clotting (e.g., in the lung), which serves as a pathophysiologic explanation to acute respiratory distress syndrome in such settings. 76 Acute Tubular Necrosis Ex vivo microscopy (high-resolution microscopy of freshly isolated primary kidney tubules) revealed how single-cell necrosis can spread on neighboring cells so that the entire tubule segment undergoes a synchronized cell death.…”

DNA and factor VII–activating protease protect against the cytotoxicity of histones

“…Indeed, increased levels of circulating histones and nucleosomes have been found in patients with a range of inflammatory conditions, including sepsis, [1][2][3] traumatic injury and surgery, [3][4][5][6] cerebral stroke, 7 systemic lupus erythematosus, 8 and cancer. 9,10 In 2009, Xu et al 11 demonstrated that histones released by macrophages upon inflammatory challenge were cytotoxic to endothelial cells in vitro.…”