DNA-histone Complexes Research Articles

MiR-155 regulates neutrophil extracellular trap formation and lung injury in abdominal sepsis.

Neutrophil extracellular traps (NETs)-mediated tissue damage is a hallmark in abdominal sepsis. Under certain conditions, microRNAs (miRs) can regulate protein expression and cellular functions. The aim of this study was to investigate the role of miR-155 in sepsis-induced NET formation, lung inflammation, and tissue damage. Abdominal sepsis was induced in wild-type (WT) C57BL/6 and miR-155 gene-deficient mice by cecal ligation and puncture (CLP). The amount of DNA-histone complex formation as well as myeloperoxidase (MPO) and citrullinated histone 3 in neutrophils isolated from bone marrow were examined by ELISA and flow cytometry. NETs were detected by electron microscopy in the septic lung. Levels of PAD4 and citrullinated histone 3 were determined by Western blot in the blood neutrophils. Lung levels of MPO, CXC chemokines, and plasma levels of DNA-histone complexes and CXC chemokines were quantified. In vitro studies revealed that neutrophils from miR-155 gene-deficient mice had less NETs forming ability than WT neutrophils. In the miR-155 gene-deficient mice, CLP yielded much less NETs in the lung tissue compared with WT control. CLP-induced PAD4 levels, histone 3 citrullination, edema, MPO activity, and neutrophil recruitment in the lung were markedly reduced in the mice lacking miR-155. Furthermore, tissue and plasma levels of CXCL1 and CXCL2 were significantly lower in the miR-155 gene-deficient mice compared with WT after induction of abdominal sepsis. Taken together, our findings suggest that miR-155 regulates pulmonary formation of NETs in abdominal sepsis via PAD4 up-regulation and histone 3 citrullination. Thus, targeting miR-155 could be a useful target to reduce pulmonary damage in abdominal sepsis.

Mechanistic Studies of DNase I Activity: Impact of Heparin Variants and PAD4.

Excessive production of neutrophil extracellular traps (NETs) in sepsis contributes to vascular occlusion by acting as a scaffold and stimulus for thrombus formation. Removal of extracellular DNA, the major structural component of NETs, by DNase I may reduce host injury. (1) To determine how heparin variants (unfractionated heparin, enoxaparin, Vasoflux, and fondaparinux) affect DNase I activity, (2) to measure temporal changes in circulating DNA and DNase I in septic patients. DNA–histone complexes were treated with DNase I ± heparin variants and visualized via agarose gels. We compared the ability of DNase I ± heparin variants to digest NETs released by phorbol 12-myristate 13-acetate-stimulated neutrophils versus DNA–histone complexes released by necrotic HEK293 cells. Plasma DNA and DNase I levels were measured longitudinally in 76 septic patients. Heparin enhances DNase I-mediated digestion of DNA–histone complexes in a size-dependent manner that does not require the antithrombin-binding region. In contrast, DNase I alone was able to degrade the DNA–histone component of NETs presumably due to peptidylarginine deiminase 4 (PAD4)-mediated histone citrullination that weakens DNA–histone interactions. In purified systems, PAD4 treatment of DNA–histone complexes enhanced the ability of DNase I to degrade histone-bound DNA. In septic patients, endogenous DNase I levels remained persistently low over 28 days, and there were no significant correlations between DNA and DNase I levels. Heparin enhances DNA-mediated digestion of DNA–histone complexes in a size-dependent manner that is independent of its anticoagulant properties. Citrullination of histones by PAD4 renders DNA–histone complexes susceptible to DNase I digestion. Endogenous DNase I levels are persistently decreased in septic patients, which supports the potential utility of DNase I as a therapy for sepsis.

Histone-DNA Complexes and Coagulation after Intracerebral and Subarachnoid Hemorrhage.

Intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) have limited treatment options and a high mortality. We have previously shown that both conditions are associated with early hypercoagulation. 1 2 Histones have been demonstrated to promote thrombin generation. 3 In sepsis and trauma patients, studies have revealed an association between histone-DNA complexes and free histone levels and mortality or morbidity. 4 5 6 Theoretically, the effects on coagulation of histones can be investigated in vitro by attempting to block histones with specific antibodies. The aim of this study was to quantify histone-DNA complex levels in patients with ICH or SAH at the time of admission to hospital compared with 24 hours after symptom onset and to investigate the possible in vitro effect of anti-histone antibodies on thrombin generation.

The association between EAE development in mice and the production of autoantibodies and abzymes after immunization of mice with different antigens.

We have previously shown that immunization of C57BL/6 mice, prone to spontaneous development of experimental autoimmune encephalomyelitis (EAE), with three antigens (MOG35‐55, DNA‐histone complex or DNA‐methylated BSA complex), alters the differentiation profiles of bone marrow haematopoietic stem cells (HSCs). These are associated with the production of autoantibodies (auto‐Abs) against these antigens and the formation of abzymes hydrolysing DNA, MOG, myelin basic protein (MBP) and histones. Immunization of mice with antigens accelerates the development of EAE. This work is the first to analyse the ratio of auto‐Abs without and with catalytic activities at different stages of EAE development (onset, acute and remission phases) after immunization of mice with the three specific antigens. Prior to immunization and during spontaneous in‐time development of EAE, the concentration of auto‐Abs against MBP, MOG, histones and DNA and activities of IgG antibodies in the hydrolysis of substrates increased in parallel; correlation coefficients = +0.69‐0.94. After immunization with MOG, DNA‐histone complex or DNA‐met‐BSA complex, both positive (from +0.13 to +0.98) and negative correlations (from −0.09 to −0.69) were found between these values. Our study is the first showing that depending on the antigen, the relative amount of harmful auto‐Abs without and abzymes with low or high catalytic activities may be produced only at onset and in acute or remission phases of EAE. The antigen governs the EAE development rate, whereby the ratio of auto‐Abs without catalytic activity and with enzymatic activities of harmful abzymes hydrolysing MBP, MOG, histones and DNA varies strongly between different disease phases.

Complement Component 3 Is Required for Tissue Damage, Neutrophil Infiltration, and Ensuring NET Formation in Acute Pancreatitis

Background: Neutrophil extracellular traps (NETs) are known to play an important role in the pathophysiology of acute pancreatitis (AP). Activation of the complement cascade has been shown to occur in AP. The aim of this study was to examine whether complement component 3 is involved in the generation of NETs in AP. Methods: AP was induced in wild-type and C3-deficient mice by retrograde infusion of taurocholate into the pancreatic duct. Blood, lung, and pancreas tissue were collected and MPO activity was determined in lung and pancreas tissue. Histological examination of the inflamed pancreas was performed. Plasma levels of CXCL2, MMP-9, IL-6, and DNA-histone complexes as well as pancreatic levels of CXCL1 and CXCL2 were determined by use of enzyme-linked immunosorbent assay. NETs were detected in the pancreas by electron microscopy. The amount of MPO and citrullinated histone 3 in neutrophils isolated from bone marrow was examined using flow cytometry. Results: In C3-deficient mice, challenge with taurocholate yielded much fewer NETs in the pancreatic tissue compared with wild-type controls. Taurocholate-induced blood levels of amylase, tissue injury, and neutrophil recruitment in the pancreas were markedly reduced in the mice lacking C3. Furthermore, MPO levels in the lung, and plasma levels of IL-6, MMP-9, and CXCL2 were significantly lower in the C3-deficient mice compared to wild-type mice after the induction of AP. In vitro studies revealed that neutrophils from C3-deficient mice had normal NET-forming ability and recombinant C3a was not capable of directly inducing NETs formation in the wild-type neutrophils. Conclusion: C3 plays an important role in the pathophysiology of AP as it is necessary for the recruitment of neutrophils into the pancreas and ensuring NETs formation. Targeting C3 could hence be a potential strategy to ameliorate local damage as well as remote organ dysfunction in AP.

Application of Polymer Microspheres for Developing Approaches to Estimating the Number of Neutrophilic Extractive Traps

Abstract—Neutrophil extracellular traps (NET) play an important role in a body’s antimicrobial defense. However, excessive formation leads to various pathological processes in the body. Therefore, a quantitative assessment of the NET content in human whole blood is very important in clinical practice. An approach is proposed allowing the use of polymer microspheres (PMS), the surfaces of which are modified with heparin as sorbents for isolation from whole blood and quantitative determination of NET. To solve this problem, polystyrene microspheres with an average diameter of 140 μm were synthesized, which contain amino groups; covalent immobilization of heparin on their surface was carried out, and a close to linear relationship between the amount of NET and DNA-histone complexes binding to the surface of the synthesized PMS was demonstrated. The data indicate that the approach may be promising both in basic research and clinical practice.

Mechanical and structural properties of archaeal hypernucleosomes.

Many archaea express histones, which organize the genome and play a key role in gene regulation. The structure and function of archaeal histone–DNA complexes remain however largely unclear. Recent studies show formation of hypernucleosomes consisting of DNA wrapped around an ‘endless’ histone-protein core. However, if and how such a hypernucleosome structure assembles on a long DNA substrate and which interactions provide for its stability, remains unclear. Here, we describe micromanipulation studies of complexes of the histones HMfA and HMfB with DNA. Our experiments show hypernucleosome assembly which results from cooperative binding of histones to DNA, facilitated by weak stacking interactions between neighboring histone dimers. Furthermore, rotational force spectroscopy demonstrates that the HMfB–DNA complex has a left-handed chirality, but that torque can drive it in a right-handed conformation. The structure of the hypernucleosome thus depends on stacking interactions, torque, and force. In vivo, such modulation of the archaeal hypernucleosome structure may play an important role in transcription regulation in response to environmental changes.

Histone variants in archaea and the evolution of combinatorial chromatin complexity

Nucleosomes in eukaryotes act as platforms for the dynamic integration of epigenetic information. Posttranslational modifications are reversibly added or removed and core histones exchanged for paralogous variants, in concert with changing demands on transcription and genome accessibility. Histones are also common in archaea. Their role in genome regulation, however, and the capacity of individual paralogs to assemble into histone-DNA complexes with distinct properties remain poorly understood. Here, we combine structural modeling with phylogenetic analysis to shed light on archaeal histone paralogs, their evolutionary history, and capacity to generate combinatorial chromatin states through hetero-oligomeric assembly. Focusing on the human commensal Methanosphaera stadtmanae as a model archaeal system, we show that the heteromeric complexes that can be assembled from its seven histone paralogs vary substantially in DNA binding affinity and tetramer stability. Using molecular dynamics simulations, we go on to identify unique paralogs in M. stadtmanae and Methanobrevibacter smithii that are characterized by unstable interfaces between dimers. We propose that these paralogs act as capstones that prevent stable tetramer formation and extension into longer oligomers characteristic of model archaeal histones. Importantly, we provide evidence from phylogeny and genome architecture that these capstones, as well as other paralogs in the Methanobacteriales, have been maintained for hundreds of millions of years following ancient duplication events. Taken together, our findings indicate that at least some archaeal histone paralogs have evolved to play distinct and conserved functional roles, reminiscent of eukaryotic histone variants. We conclude that combinatorially complex histone-based chromatin is not restricted to eukaryotes and likely predates their emergence.

Extracellular cold-inducible RNA-binding protein regulates neutrophil extracellular trap formation and tissue damage in acute pancreatitis

AbstractNeutrophil extracellular traps (NETs) play a key role in the development of acute pancreatitis (AP). In the present study, we studied the role of extracellular cold-inducible RNA-binding protein (eCIRP), a novel damage-associated-molecular-pattern molecule, in severe AP. C57BL/6 mice underwent retrograde infusion of taurocholate into the pancreatic duct. C23, an eCIRP inhibitor, was given 1 h prior to induction of AP. Pancreatic, lung, and blood samples were collected and levels of citrullinated histone 3, DNA-histone complexes, eCIRP, myeloperoxidase (MPO), amylase, cytokines, matrix metalloproteinase-9 (MMP-9), and CXC chemokines were quantified after 24 h. NETs were detected by electron microscopy in the pancreas and bone marrow-derived neutrophils. Amylase secretion was analyzed in isolated acinar cells. Plasma was obtained from healthy individuals and patients with mild and moderate severe or severe AP. Taurocholate infusion induced NET formation, inflammation, and tissue injury in the pancreas. Pretreatment with C23 decreased taurocholate-induced pancreatic and plasma levels of eCIRP and tissue damage in the pancreas. Blocking eCIRP reduced levels of citrullinated histone 3 and NET formation in the pancreas as well as DNA-histone complexes in the plasma. In addition, administration of C23 attenuated MPO levels in the pancreas and lung of mice exposed to taurocholate. Inhibition of eCIRP reduced pancreatic levels of CXC chemokines and plasma levels of IL-6, HMGB-1, and MMP-9 in mice with severe AP. Moreover, eCIRP was found to be bound to NETs. Coincubation with C23 reduced NET-induced amylase secretion in isolated acinar cells. Patients with severe AP had elevated plasma levels of eCIRP compared with controls. Our novel findings suggest that eCIRP is a potent regulator of NET formation in the inflamed pancreas. Moreover, these results show that targeting eCIRP with C23 inhibits inflammation and tissue damage in AP. Thus, eCIRP could serve as an effective target to attenuate pancreatic damage in patients with AP.The authors investigated the role of extracellular cold-inducible RNA-binding protein (eCIRP) in acute pancreatitis (AP) and found that eCIRP acts as a potent regulator of neutrophil extracellular traps (NETs) formation in AP. They observed that eCIRP itself is one of the NETs associated proteins. Furthermore, they demonstrate that C23 (a potent eCIRP inhibitor) reduces NETs formation and inflammation in AP.

Abstract 16640: Neutrophil Expansion is Essential for Adverse Left Ventricular Remodeling and Dysfunction in Chronic Ischemic Heart Failure

Chronic inflammation contributes significantly to disease progression in heart failure (HF), and is characterized by expansion of activated macrophages, dendritic cells, and T cells in the failing heart. Neutrophils play a well-known role as the initial drivers of inflammatory response to myocardial infarction (MI), thereby providing the platform for the subsequent recruitment of macrophages and T cells. However, whether and how neutrophils contribute to inflammation and adverse LV remodeling in chronic HF are unknown. We tested the hypothesis that activated neutrophils are required for tissue remodeling and disease progression in HF. Male C57Bl/6 mice were studied 4 and 8 weeks after left coronary artery ligation during established ischemic HF (sham-operated controls). As assessed by flow cytometry, CD11b + Ly6G + neutrophils were expanded in the peripheral blood (4 w post-MI), and in the bone marrow, spleen, and heart at 8 w post-MI. Immunostaining revealed that in the failing heart, neutrophils were primarily localized to the MI border zone, but also augmented in remote zone myocardium. CXCL1 and CXCL5 chemokine expression was increased in the failing heart, consistent with chemotactic signals for myocardial neutrophil recruitment. Isolated naïve neutrophils also exhibited increased chemotaxis in response to plasma from HF mice (versus plasma from naïve mice), as assessed by time-lapse video microscopy. Moreover, blood neutrophils isolated from HF mice exhibited significantly increased neutrophil extracellular trap (NET) production as compared to control neutrophils, whereas plasma NETs (histone-DNA complexes) were increased in HF mice. Finally, the in vivo role of neutrophils in chronic HF (8 w post-MI) was determined via depletion studies using genetic (Ly6G-diptheria toxin receptor mice) and antibody (1A8) based approaches. In both models, 2 and 4 w of neutrophil depletion, respectively, significantly improved LV systolic function and reduced end systolic volume. 1A8 treated HF mice also exhibited reduced remote zone fibrosis. We conclude: neutrophil expansion and activation are important components of the chronic inflammatory response in HF, and play an obligatory role in the progression of LV remodeling in ischemic cardiomyopathy.

HIV-Infected Patients: Cross Site-Specific Hydrolysis of H2a and H2b Histones and Myelin Basic Protein with Antibodies against These Three Proteins.

Anti-DNA antibodies are usually produced against histone-DNA complexes appearing during cell apoptosis, while histones are known as damage-associated molecules. A myelin sheath of axons contains myelin basic protein (MBP) playing an important role in the pathogenesis of autoimmune diseases. Antibodies with enzymatic activities (abzymes) are distinctive features of some autoimmune and viral diseases. Abzymes against different proteins can usually only hydrolyze these specific proteins. Using sequential chromatographies of homogeneous IgG preparations from sera of HIV-infected patients on columns with immobilized MBP, H2a, and H2b histones, the anti-MBP, anti-H2a, and anti-H2b antibodies were obtained. It was first shown that IgGs against H2a and H2b effectively hydrolyze these histones and MBP, while anti-MBP split MBP, H2a, and H2b, but no other control proteins. Using the MALDI mass spectrometry, the cleavage sites of H2a, H2b, and MBP by abzymes against these three proteins were found. Among 14 sites of hydrolysis of H2a by IgGs against H2a and 10 sites by anti-MBP IgGs, only one site of hydrolysis was the same for these abzymes. Eleven cleavage sites of H2b with IgGs against H2b and 10 sites of its hydrolysis with antibodies against MBP were different. Anti-H2a, anti-H2b, and anti-MBP abzymes are unpredictable examples of IgGs possessing not only cross-complexation but also catalytic cross-reactivity, which may be a common phenomenon for such abzymes in patients with different autoimmune diseases. The existence of cross-reactivity of abzymes against H2a and H2b histones and MBP represent a great danger to humans since, in contrast with MBP, histones due to cell apoptosis constantly occur in human blood. Anti-H2a, anti-H2b, and anti-MBP can attack and hydrolyze myelin basic protein of the myelin sheath of axons and plays a negative role in the pathogenesis of several pathologies.

The Emerging Role of Neutrophil Extracellular Traps (NETs) in Tumor Progression and Metastasis.

Neutrophil Extracellular Traps (NETs) are net-like structures composed of DNA-histone complexes and proteins released by activated neutrophils. In addition to their key role in the neutrophil innate immune response, NETs are also involved in autoimmune diseases, like systemic lupus erythematosus, rheumatoid arthritis, psoriasis, and in other non-infectious pathological processes, as coagulation disorders, thrombosis, diabetes, atherosclerosis, vasculitis, and cancer. Recently, a large body of evidence indicates that NETs are involved in cancer progression and metastatic dissemination, both in animal models and cancer patients. Interestingly, a close correlation between cancer cell recruitment of neutrophils in the tumor microenvironment (Tumor Associated Neutrophils. TANs) and NET formation has been also observed either in primary tumors and metastatic sites. Moreover, NETs can also catch circulating cancer cells and promote metastasis. Furthermore, it has been reported that wake dormant cancer cells, causing tumor relapse and metastasis. This review will primarily focus on the pro-tumorigenic activity of NETs in tumors highlighting their ability to serve as a potential target for cancer therapy.

Assays for Validating Histone Acetyltransferase Inhibitors.

Lysine acetyltransferases (KATs) catalyze acetylation of lysine residues on histones and other proteins to regulate chromatin dynamics and gene expression. KATs, such as CBP/p300, are under intense investigation as therapeutic targets due to their critical role in tumorigenesis of diverse cancers. The development of novel small molecule inhibitors targeting the histone acetyltransferase (HAT) function of KATs is challenging and requires robust assays that can validate the specificity and potency of potential inhibitors. This article outlines a pipeline of three methods that provide rigorous in vitro validation for novel HAT inhibitors (HATi). These methods include a test tube HAT assay, Chromatin Hyperacetylation Inhibition (ChHAI) assay, and Chromatin Immunoprecipitation-quantitative PCR (ChIP-qPCR). In the HAT assay, recombinant HATs are incubated with histones in a test tube reaction, allowing for acetylation of specific lysine residues on the histone tails. This reaction can be blocked by a HATi and the relative levels of site-specific histone acetylation can be measured via immunoblotting. Inhibitors identified in the HAT assay need to be confirmed in the cellular environment. The ChHAI assay uses immunoblotting to screen for novel HATi that attenuate the robust hyperacetylation of histones induced by a histone deacetylase inhibitor (HDACi). The addition of an HDACi is helpful because basal levels of histone acetylation can be difficult to detect via immunoblotting. The HAT and ChHAI assays measure global changes in histone acetylation, but do not provide information regarding acetylation at specific genomic regions. Therefore, ChIP-qPCR is used to investigate the effects of HATi on histone acetylation levels at gene regulatory elements. This is accomplished through selective immunoprecipitation of histone-DNA complexes and analysis of the purified DNA through qPCR. Together, these three assays allow for the careful validation of the specificity, potency, and mechanism of action of novel HATi.

Inhomogeneous Forces in Semiflexible Biopolymers

Major developments in single-molecule experiments over the past few decades have permitted the manipulation of biomolecules and the study of their responses to force fields in unprecedented detail. These methods have led to the greater understanding of a wide range of biologically relevant processes, including the dynamics of cytoskeletal filaments, the stability of DNA double helix, or the formation of histone-DNA complexes. The wormlike chain model has been successfully applied to predict force-extension relations of semiflexible biopolymers. Despite these successes, the effects of inhomogeneous forces (for example effects of charge heterogeneity in a polyelectrolyte) are not well understood. In this work, we develop a new analytical model to understand the statistics of an inextensible polyelectrolyte chain under inhomogeneous tension. We show that an existing mean-field formalism that does not account for the inhomogeneity in the tension results in local over-stretching of the chain. We improve upon this approach by subdividing the chain into smaller segments over which the homogeneity assumption is only approximately valid. This technique can analytically impose inextensibility of the chain and help us study the statistical properties of the chain. We can also extend the theory to predict the protein-binding statistics in experiments that probe protein-DNA interactions under an external field, applicable to DNA wrapping around histone octamers. This proposed method may prove valuable to other biologically relevant problems involving inhomogeneities in actin bundles, semiflexible chains under shear flow or in the design of biomimetic materials.

Evaluation of neutrophil extracellular traps as the circulating marker for patients with acute coronary syndrome and acute ischemic stroke.

IntroductionNeutrophil extracellular traps (NETs) are known to be induced by various factors. In this study, we tried to identify circulating levels of NETs in patients with acute coronary syndrome (ACS) and acute ischemic stroke (AIS) and to confirm its suitability as a new circulating marker in their detection.MethodsWe prospectively enrolled 95 patients with a diagnosis of ACS (N = 37) or AIS (N = 58) in Dong‐A University Hospital, Busan, Korea. The control group was selected from healthy adults (N = 25) who visited the hospital for health screening. Circulating levels of NETs were evaluated by measuring plasma concentrations of double‐stranded DNA (dsDNA) and DNA‐histone complex.ResultsThe concentrations of dsDNA were statistically higher in patients with ACS or AIS than those in the control group (both P < .001). In the univariable and multivariable analyses, statistically significant risk factors were troponin I (TnI) level and dsDNA concentration in the ACS group (P = .046 and P = .015, respectively) and only dsDNA concentration in the AIS group (P = .002). In the receiver operating characteristic curve analyses, the area under the curve values for TnI level and dsDNA concentration in the ACS group were 0.878 and 0.968, respectively, and the value for dsDNA concentration in the AIS group was 0.859.ConclusionsIn this study, it was confirmed that the circulating level of NETs was increased in patients with ACS and AIS at initial presentation. Findings in this study show that NETs could be used as a new circulating marker for the initial diagnosis of ACS or AIS.

Does cell-free DNA promote coagulation and inhibit fibrinolysis in patients with unprovoked venous thromboembolism?

IntroductionCell-free DNA (CFDNA) is the major structural component of neutrophil extracellular traps (NETs). CFDNA contributes to the prothrombotic potential of NETs by promoting thrombin generation and inhibiting fibrinolysis. Patients with venous thromboembolism (VTE) have elevated circulating nucleosomes (i.e. DNA-histone complexes). In this study, we investigated if CFDNA contributes to a procoagulant and an antifibrinolytic state in patients with unprovoked VTE. Materials and methodsPlasma samples from patients with a first episode of unprovoked VTE were obtained from the D-Dimer Optimal Duration Study (DODS). We measured CFDNA plasma levels in 263 patients while on warfarin and 1-month after stopping. Thrombin generation assays and clot lysis assays were measured in patients after stopping warfarin. Comparisons were made with healthy controls. ResultsCFDNA levels in VTE patients who stopped warfarin (5.53 μg/mL; 95%CI: 5.34–5.72) were higher than during warfarin therapy (3.11 μg/mL; 95%CI: 2.98–3.25; p < .001), and higher than in healthy controls (2.77 μg/mL; 95%CI: 2.42–3.11; p < .001). VTE patients had a procoagulant state as evidenced by a shorter lag time (30.8 min; 95%CI: 29.2–32.4) compared to controls (48.2 min; 95%CI :41.0–55.5; p < .001) and a greater endogenous thrombin potential (2656 nM∗min; 95%CI: 2479–2836) compared to healthy controls (1198 nM ∗ min; 95%CI: 793–1603). There was a higher proportion of clots generated from patient plasma that were resistant to lysis (43.7%) compared to healthy controls (46.3%; p < .05). CFDNA levels were not associated with enhanced thrombin generation or impaired fibrinolysis in VTE patients. ConclusionCFDNA levels are elevated in patients with unprovoked VTE but do not correlate with the procoagulant or anti-fibrinolytic properties of patient plasma. This study suggests that additional factors in addition to CFDNA may contribute to the pathogenesis of VTE.

Detection, Visualization, and Quantification of Neutrophil Extracellular Traps (NETs) and NET Markers.

Neutrophil extracellular traps (NETs) have been identified as a key player in the pathogenesis of infection and inflammation in human and animals. On the one hand, NETs have been characterized as fundamental to the innate immune defense against different pathogens since they are able to entrap and immobilize invading pathogens. On the other hand, NETs have been shown to contribute to several diseases, based on their detrimental consequences. This chapter describes methods to detect NETs and NET markers in blood-derived isolated neutrophils of human, pigs, and horses in vitro, as well as NETs and NET marker detection in body fluids from in vivo studies. To avoid nonspecific background in NET-formation, a well-established isolation method for the neutrophils from fresh blood is needed. After stimulation of neutrophils to release NETs, NETs are stained with different antibodies to confirm the presence of extracellular DNA extrusion consisting of histone-DNA complexes, as well as granule components (e.g., myeloperoxidase or elastase). Furthermore, specific methods to quantify NETs and NET markers in the cerebrospinal fluid (CSF) and bronchoalveolar lavage fluid (BALF) are described in detail. In addition to immunofluorescence microscopy, quantification of NET markers from in vivo experiments in various body fluids is described (e.g., nuclease activity, free extracellular DNA, or cationic host defense peptides, such as the porcine PR-39 in BALF and CSF).

Plasma Levels of Histone-DNA Complex and Cell-Free DNA Predict Mortality in Patients with Immune Thrombotic Thrombocytopenic Purpura

Background: Deficiency of plasma ADAMTS13 activity resulting from acquired autoantibody against ADAMTS13 is the primary cause of immune thrombotic thrombocytopenic purpura (iTTP). Therapeutic plasma exchange plus corticosteroids and immunosuppression is the standard of care for patients with iTTP. However, mortality rate remains high and clinical factors or laboratory biomarkers that predict mortality are not fully established. Previous studies have demonstrated that plasma levels of histone-DNA complexes and cell-free DNA are dramatically elevated in patients with acute disease but reduced during remission. We hypothesize that elevated histone-DNA complexes or cell-free DNA may have a predictive role for mortality in patients with acute iTTP. Methods: 102 unique patients with a confirmed diagnosis of iTTP who underwent therapeutic plasma exchange (TPE) at UAB-Medical Center from April 2006 to December 2018 were enrolled into the study. Demographic information and laboratory parameters were collected on admission and during the follow-up. Plasma levels of histone-DNA complexes and cell-free DNA were determined by an enzyme-linked immunosorbent assay and PicoGreen dsDNA assay, respectively. Mann-Whitney, Fisher's exact, t test, log-rank test, and Cox proportional hazard regression analysis were performed to determine the significance of each marker in predicting death. Results: In this cohort, age was 44.7 ± 1.3 (mean ± SD) years old, 56.9% were female, 82.4% were African Americans, 61.8% had an initial episode, the median (IQR) body mass index (BMI) was 33.6 (29.3-41.5). 52.9% of patients had hypertension, 21.6% diabetes, 18.6% systemic lupus erythematous and 8.7% HIV. The overall mortality rate was 10.8% (11/102). Plasma levels, median (IQR), of histone-DNA complexes and cell-free DNA on admission were 56.3 (35.8-136.4) AU/mL and 952.2 (799.7-1431.4) ng/mL, respectively. Mann-Whitney test revealed that high plasma levels of histone-DNA complex (≥134.9 U/mL) (p=0.007) and cell-free DNA (≥952.2 ng/mL) (p=0.009) were associated with the increased risks of myocardial injury (e.g. elevated troponin). Cox proportional hazard regression analysis demonstrated that the increased levels of histone-DNA complexes and cell-free DNA were also predictive for the increased mortality rates in patients with iTTP with hazard ratios (HRs) of 4.1 (95% CI, 1.2-13.4) (p=0.02) and 8.5 (95% CI, 2.2-33.3 (p=0.002), respectively. Kaplan-Meier survival analysis revealed significant differences in the disease-free survival rates of patients with high levels (≥75 percentile) vs. low levels (&lt;75 percentile) of plasma histone-DNA complexes and cell-free DNA, respectively (see Fig. 1). Conclusion: Our results demonstrate that the elevated plasma levels of histone-DNA complexes and cell-free DNA predict the worse outcome (e.g. the increased mortality rates) in patients with iTTP. *SD, standard deviation; IQR, interquartile range; 95% CI, 95% confidential interval. Disclosures Zheng: Ablynx/Sanofi: Consultancy, Speakers Bureau; Alexion: Speakers Bureau; Shire/Takeda: Research Funding; Clotsolution: Other: Co-Founder.

P12. Abstract Title: The Effects of Glycosaminoglycans on DNasel-Mediated Degradation of Neutrophil Extracellular Traps and DNA-Histone Complexes

<h3>Background</h3> Neutrophil extracellular traps (NETs), released from activated neutrophils, have been implicated in contributing to micro- and macro-vascular thrombosis. The major structural component of NETs is nucleosomes, which consists of DNA wrapped around a core histone octamer containing two copies each of histone H2A, H2B, H3, and H4. The release of NETs occurs via a unique cell death pathway (termed NETosis), which requires the decondensation of chromatin by PAD4. PAD4 is a nuclear enzyme that converts specific arginine residues to citrulline on histones, thereby reducing the positive charge of histones. DNA activates the intrinsic pathway of coagulation and impairs fibrinolysis, whereas histones activate platelets and are cytotoxic to vascular endothelial cells. In purified systems, DNA-histone complexes are resistant to digestion by DNaseI. The addition of unfractionated heparin (UFH) displaces the DNA-histone complex, thereby rendering DNA susceptible to digestion by DNaseI. <h3>Objectives</h3> The objective of this study is to examine the effects of various glycosaminoglycans (GAGs), including UFH (15kDa), Enoxaparin (4.5kDa), and Fondaparinux (1.7kDa) on DNaseI-mediated digestion of DNA-protein complexes as well as NETs released by activated neutrophils. <h3>Methods</h3> Genomic DNA was isolated from human leukocytes and incubated with a mixture of bovine histones. The DNA protein complexes were treated with recombinant human DNaseI (Pulmozyme) in the absence or presence of GAGs and visualized using agarose gel electrophoresis. To produce NETs, neutrophils from healthy volunteers were added to glass coverslips and stimulated with PMA for 4 hours. The NETs were then treated with DNaseI in the absence or presence of GAGs and visualized using fluorescence microscopy. The binding affinities between the different GAGs and histones were determined by Bio-layer Interferometry (BLItz instrument). <h3>Results</h3> DNaseI alone was unable to degrade DNA-histone complexes. The addition of UFH or Enoxaparin rendered the complexes susceptible to complete digestion by DNaseI, whereas Fondaparinux did not. Next, we measured the binding affinities between the GAGs and individual histones. We found that UFH and Enoxaparin bind histones H2A, H2B, H3, and H4 with high affinities (KD values ranging from 1 pM to 6.2 nM), which supports the model that these GAGs can displace histones from DNA-histone complexes. With respect to NETs released by activated neutrophils, DNaseI alone was able to completely digest the DNA component of NETs even in the absence of GAGs. <h3>Conclusions</h3> Our studies suggest that GAGs displace DNA-histone complexes, thereby rendering DNA susceptible to degradation by DNaseI. The inability of Fondaparinux to displace the DNA-histone complexes suggests that the GAG cofactor activity is size-dependent. In contrast, DNaseI is able to degrade DNA within NETs without a requirement for GAGs. The ability of DNaseI to degrade DNA within NETs may be due to histone citrullination that occurs during NETosis, a process that weakens DNA-histone interactions.

Activation of Factor XII and Kallikrein-Kinin System Combined with Neutrophil Extracellular Trap Formation in Diabetic Retinopathy.

In diabetic retinopathy (DR), neutrophil extracellular traps (NET) and kallikrein-kinin system are considered as contributing factors. However, the detail activation mechanisms has not been fully understood. Since the NET could provide negative-charged surface for factor XII activation and the activated factor XII (XIIa) can initiate kallikrein-kinin system, this study investigated whether patients with DR show activation of NET, factor XII and kallikrein-kinin system. The markers related to NET (DNA-histone complex) and kallikrein-kinin system (high-molecular-weight kininogen, prekallikrein, bradykinin) and factor XIIa were measured in 253 patients with diabetes. To access ex vivo effect of glucose, DNA-histone complex and factor XIIa were measured in whole blood stimulated by glucose. The circulating level of DNA-histone complex and factor XIIa were significantly higher in patients with DR than those without DR. In logistic regression analysis, DNA-histone complex, factor XIIa, and high-molecular-weight kininogen were the risk factors of DR. In recursive partitioning analysis, among patients with diabetes duration less than 10 years, patients with high level of DNA-histone complex (>426 AU) showed high risk of DR. In ex vivo experiment, glucose significantly elevated both DNA-histone complex and factor XIIa. Our findings suggest that activation of factor XII and kallikrein-kinin system combined with NET formation actively occur in patients with DR and circulating levels of DNA-histone complex, factor XIIa and HMWK can be potential biomarkers to estimate the risk of DR. Strategies against factor XII activation may be beneficial to inhibit DR.