Mediators of Disseminated Intravascular Coagulation: Molecular Mechanisms

Disseminated intravascular coagulation (DIC) is characterized by a spectrum of haemorrhage and microvascular thrombosis complicating many conditions including sepsis and trauma. In recent years, there is growing evidence that damage associated molecular patterns (DAMPs) play a crucial role in the pathogenesis of DIC. Upon cell death and/or cell activation, extracellular DNA as well as DNA binding proteins (e.g. histones and high mobility group box 1 protein) are released into the circulation. These molecules can influence hemostasis by promoting coagulation via the contact pathway, inducing platelet aggregation, activating endothelial cells, and inhibiting fibrinolysis. Extracellular HMGB1 also activates neutrophils to induce the release of neutrophil extracellular traps, which may further contribute to tissue injury and organ dysfunction. Cell-free DNA (cfDNA) from nuclear, mitochondrial, and bacterial sources has varying pro-inflammatory effects, although all three have similar procoagulant and platelet-stimulating potential. Elevated levels of cfDNA and histones are predictive of poor outcome in sepsis and trauma, with neutrophils being the major source of DNA released from whole blood in vitro. In septic patients, endogenous cfDNA correlates positively with thrombin generation potential, and addition of recombinant DNase attenuates thrombin generation. In a cecal ligation and puncture (CLP) model of sepsis, plasma cfDNA levels rise within a few hours and are accompanied by elevations in IL-6 and thrombin-antithrombin complexes. Delayed (ie. 6 hours post-CLP surgery) but not early administration of recombinant DNase decreases bacterial load in the lungs, blood, and peritoneal cavity, and attenuates organ damage. Thus, the timing of DNase administration may be a crucial element in future investigations of the therapeutic potential of DNase in sepsis. With respect to potential therapeutic inhibitors of histones, activated protein C (APC) cleaves histones H2A, H3, and H4. Co-injection of APC with histones rescues mice from death. C-reactive protein (CRP) is an acute phase protein that reduces histone-induced endothelial cell damage and platelet aggregation. Administration of histones and CRP to mice reduces endothelial damage, alleviates thrombocytopenia, and attenuates coagulation activation. Heparin can also bind histones and prevent histone-mediated cytotoxicity of endothelial cells. In vivo, non-anticoagulant heparin reduces mortality from sterile inflammation and from sepsis in mouse models. Translational studies of septic patients have shown that the prognostic utility of clinical scores can be enhanced by combining it with cfDNA and protein C levels, suggesting that inclusion of cfDNA and protein C in risk stratification tools may be valuable for monitoring response to treatment, enhancing confidence in clinical decision making, or for inclusion in trials of new anti-sepsis therapies. In summary, cfDNA and DNA-binding proteins are critically involved in the pathogenesis of DIC. Strategies that inhibit or neutralize the harmful effects of cfDNA and histones may have great therapeutic potential.