Circulating nucleosomes and severity of illness in children suffering from meningococcal sepsis treated with protein C:

Circulating Nucleosomes as a Novel Biomarker for Sepsis: A Scoping Review

Circulating nucleosome levels are commonly elevated in physiological and pathological conditions. Their potential as biomarkers for diagnosing and prognosticating sepsis remains uncertain due, in part, to technical limitations in existing detection methods. This scoping review explores the possible role of nucleosome concentrations in the diagnosis, prognosis, and therapeutic management of sepsis. A comprehensive literature search of the Cochrane and Medline libraries from 1996 to 1 February 2024 identified 110 potentially eligible studies, of which 19 met the inclusion criteria, encompassing a total of 39 SIRS patients, 893 sepsis patients, 280 septic shock patients, 117 other ICU control patients, and 345 healthy volunteers. The enzyme-linked immunosorbent assay [ELISA] was the primary method of nucleosome measurement. Studies consistently reported significant correlations between nucleosome levels and other NET biomarkers. Nucleosome levels were higher in patients with sepsis than in healthy volunteers and associated with disease severity, as indicated by SOFA and APACHE II scores. Non-survivors had higher nucleosome levels than survivors. Circulating nucleosome levels, therefore, show promise as early markers of NETosis in sepsis, with moderate diagnostic accuracy and strong correlations with disease severity and prognosis. However, the available evidence is drawn mainly from single-center, observational studies with small sample sizes and varied detection methods, warranting further investigation.

A Fully Integrated Microfluidic Device with Immobilized Dyes for Simultaneous Detection of Cell-Free DNA and Histones from Plasma Using Dehydrated Agarose Gates

Sepsis, a life-threatening condition resulting from a failing host response to infection, causes millions of deaths annually, necessitating rapid and simple prognostic assessments. A variety of genomic and proteomic biomarkers have been developed for sepsis. For example, it has been shown that the level of plasma cell-free DNA (cfDNA) and circulating histones increases considerably during sepsis, and they are linked with sepsis severity and mortality. Developing a diagnostic tool that is capable of assessing such diverse biomarkers is challenging as the detection methodology is quite different for each. Here, a fully integrated microfluidic device capable of detecting a genomic biomarker (cfDNA) and a proteomic biomarker (total circulating histones) using a common detection platform has been demonstrated. The microfluidic device utilizes dehydrated agarose gates loaded with pH-specific agarose to electrophoretically trap cfDNA and histones at their respective isoelectric points. It also incorporates fluorescent dyes within the device, eliminating the need for off-chip sample preparation and allowing the direct testing of plasma samples without the need for labeling DNA and histones with fluorescent dyes beforehand. Xurography, which is a low-cost and rapid method for fabrication of microfluidics, is used in all the fabrication steps. Experimental results demonstrate the effective accumulation and separation of cfDNA and histones in the agarose gates in a total processing time of 20 min, employing 10 and 30 Volts for cfDNA and histone accumulation and detection, respectively. The device can potentially be used to distinguish between the survivors and non-survivors of sepsis. The integration of the detection of both biomarkers into a single device and dye immobilization enhances its clinical utility for rapid point-of-care assessment of sepsis prognosis.

Association of pronounced elevation of NET formation and nucleosome biomarkers with mortality in patients with septic shock

BACKGROUND

Understanding the mechanisms underlying immune dysregulation in sepsis is a major challenge in developing more individualized therapy, as early and persistent inflammation, as well as immunosuppression, play a significant role in pathophysiology. As part of the antimicrobial response, neutrophils can release extracellular traps (NETs) which neutralize and kill microorganisms. However, excessive NETs formation may also contribute to pathogenesis, tissue damage and organ dysfunction. Recently, a novel automated assay has been proposed for the routine measurement of nucleosomes H3.1 (fundamental units of chromatin) that are released during NETs formation. The aim of the present study was to measure nucleosome levels in 151 septic shock patients (according to sepsis-3 definition) and to determine association with mortality.

RESULTS

The nucleosome H3.1 levels (as determined by a chemiluminescence immunoassay performed on an automated immunoanalyzer system) were markedly and significantly elevated at all-time points in septic shock patients compared to the control group. Immunological parameters indicated tremendous early inflammation (IL-6 = 1335 pg/mL at day 1-2) along with marked immunosuppression (e.g., mHLA-DR = 3853 AB/C and CD4 = 338 cell /µL at day 3-4). We found significantly positive correlation between nucleosome levels and organ failure and severity scores, IL-6 concentrations and neutrophil count. Significantly higher values (day 1-2 and 3-4) were measured in non-survivor patients (28-day mortality). This association was still significant after multivariate analysis and was more pronounced with highest concentration. Early (day 1-2) increased nucleosome levels were also independently associated with 5-day mortality. At day 6-8, persistent elevated nucleosome levels were negatively correlated to mHLA-DR values.

CONCLUSIONS

This study reports a significant elevation of nucleosome in patients during a one-week follow-up. The nucleosome levels showed correlation with neutrophil count, IL-6 and were found to be independently associated with mortality assessed at day 5 or 28. Therefore, nucleosome concentration seems to be a promising biomarker for detecting hyper-inflammatory phenotype upon a patient's admission. Additional investigations are required to evaluate the potential association between sustained elevation of nucleosome and sepsis-induced immunosuppression.

Clusterin Neutralizes the Inflammatory and Cytotoxic Properties of Extracellular Histones in Sepsis

Rationale: Extracellular histones, released into the surrounding environment during extensive cell death, promote inflammation and cell death, and these deleterious roles have been well documented in sepsis. Clusterin (CLU) is a ubiquitous extracellular protein that chaperones misfolded proteins and promotes their removal. Objectives: We investigated whether CLU could protect against the deleterious properties of histones. Methods: We assessed CLU and histone expression in patients with sepsis and evaluated the protective role of CLU against histones in in vitro assays and in vivo models of experimental sepsis. Measurements and Main Results: We show that CLU binds to circulating histones and reduces their inflammatory, thrombotic, and cytotoxic properties. We observed that plasma CLU levels decreased in patients with sepsis and that the decrease was greater and more durable in nonsurvivors than in survivors. Accordingly, CLU deficiency was associated with increased mortality in mouse models of sepsis and endotoxemia. Finally, CLU supplementation improved mouse survival in a sepsis model. Conclusions: This study identifies CLU as a central endogenous histone-neutralizing molecule and suggests that, in pathologies with extensive cell death, CLU supplementation may improve disease tolerance and host survival.

Circulating Histones and Severity of Illness in Children with Sepsis: A Prospective Observational Study

OBJECTIVES

To measure circulating histone H3 levels in children with severe sepsis and explore its relationship with severity of illness and organ failures.

METHODS

Children aged 3 mo to 12 y with severe sepsis admitted to pediatric intensive care unit (PICU) were prospectively studied. Healthy controls were enrolled from the outpatient department for comparison. Levels of H3 histones were measured on day 1 and day 3.

RESULTS

Thirty-seven patients and 14 controls with median (IQR) age 5 (0.67, 8) and 5 (3, 7) y, respectively were enrolled. Common diagnoses included severe pneumonia (n = 9), staphylococcal sepsis (n = 6), and seasonal tropical infections (n = 4). Two-third (n = 26, 70%) had septic shock. One third (35%) had an unfavorable outcome; 11 died and 2 discontinued care. Median (IQR) H3 levels were not statistically different among patients with sepsis and controls [0.84 (0.62, 1.13) vs. 0.72 (0.52, 0.87) ng/mL; p = 0.10]. There was no significant change in H3 between day 1 and day 3 [0.84 (0.62, 1.13) vs 0.74 (0.5, 0.98) ng/mL; p = 0.22]. Children with thrombocytopenia (n = 27) showed a trend towards higher H3 compared to those without thrombocytopenia (n = 10) [0.9 vs. 0.67 ng/mL; p = 0.06]. However, H3 levels were not elevated in patients with cardiovascular dysfunction, those needing renal-replacement therapy, or unfavorable outcomes.

CONCLUSION

The present data provides early evidence that in children hospitalized with severe sepsis, histone H3 is not elevated as compared to healthy controls. H3 levels during initial days of sepsis requiring PICU admission were not different with regards to severity of illness, organ dysfunction, and clinical outcome. There was a trend towards elevated H3 in children with thrombocytopenia, which needs further evaluation.

Cell-free DNA levels are increased in acute graft-versus-host disease

BACKGROUND

Cell-free DNA (cfDNA) and nucleosomes, consisting of cfDNA and histones, are markers of cell activation and damage. In systemic inflammation these markers predict severity and fatality. However, the role of cfDNA in acute Graft-versus-Host Disease (aGvHD), a major complication of allogeneic hematopoietic stem cell transplantation (HSCT), is unknown.

OBJECTIVE

The aim of this study is to investigate the role of cfDNA as a marker of aGvHD.

METHODS

We followed nucleosome levels in 37 allogeneic HSCT patients and an established xenotransplantation mouse model. We determined the origin of cfDNA with a species-specific polymerase chain reaction.

RESULTS

In the plasma of aGvHD patients, nucleosome levels significantly increased around the time of aGvHD diagnosis compared to pretransplant, concurrently with a significant increase of known aGvHD markers ST2 and REG3α. In mice, we confirmed that nucleosomes were elevated during clinically detectable aGvHD. We found cfDNA to be mainly of human origin and to a lesser extent of mouse origin, indicating that cfDNA is released by (proliferating) human xeno-reactive PBMC and damaged mouse cells.

CONCLUSION

We show increased cfDNA both in an aGvHD mouse model and in aGvHD patients. We also demonstrate that donor hematopoietic cells and to a lesser degree (damaged) host cells are the cellular source of cfDNA in aGvHD. We propose that nucleosomes and cfDNA might be an additive marker for aGvHD.

Comparative Analysis of Chromatin-Delivered Biomarkers in the Monitoring of Sepsis and Septic Shock: A Pilot Study

Sepsis management remains one of the most important challenges in modern clinical practice. Rapid progression from sepsis to septic shock is practically unpredictable, hence the critical need for sepsis biomarkers that can help clinicians in the management of patients to reduce the probability of a fatal outcome. Circulating nucleoproteins released during the inflammatory response to infection, including neutrophil extracellular traps, nucleosomes, and histones, and nuclear proteins like HMGB1, have been proposed as markers of disease progression since they are related to inflammation, oxidative stress, endothelial damage, and impairment of the coagulation response, among other pathological features. The aim of this work was to evaluate the actual potential for decision making/outcome prediction of the most commonly proposed chromatin-related biomarkers (i.e., nucleosomes, citrullinated H3, and HMGB1). To do this, we compared different ELISA measuring methods for quantifying plasma nucleoproteins in a cohort of critically ill patients diagnosed with sepsis or septic shock compared to nonseptic patients admitted to the intensive care unit (ICU), as well as to healthy subjects. Our results show that all studied biomarkers can be used to monitor sepsis progression, although they vary in their effectiveness to separate sepsis and septic shock patients. Our data suggest that HMGB1/citrullinated H3 determination in plasma is potentially the most promising clinical tool for the monitoring and stratification of septic patients.

Traumatic Brain Injury Impairs Systemic Vascular Function Through Disruption of Inward-Rectifier Potassium Channels

Trauma can lead to widespread vascular dysfunction, but the underlying mechanisms remain largely unknown. Inward-rectifier potassium channels (Kir2.1) play a critical role in the dynamic regulation of regional perfusion and blood flow. Kir2.1 channel activity requires phosphatidylinositol 4,5-bisphosphate (PIP₂), a membrane phospholipid that is degraded by phospholipase A₂ (PLA₂) in conditions of oxidative stress or inflammation. We hypothesized that PLA₂-induced depletion of PIP₂ after trauma impairs Kir2.1 channel function. A fluid percussion injury model of traumatic brain injury (TBI) in rats was used to study mesenteric resistance arteries 24 hours after injury. The functional responses of intact arteries were assessed using pressure myography. We analyzed circulating PLA₂, hydrogen peroxide (H₂O₂), and metabolites to identify alterations in signaling pathways associated with PIP₂ in TBI. Electrophysiology analysis of freshly-isolated endothelial and smooth muscle cells revealed a significant reduction of Ba²⁺-sensitive Kir2.1 currents after TBI. Additionally, dilations to elevated extracellular potassium and BaCl₂- or ML 133-induced constrictions in pressurized arteries were significantly decreased following TBI, consistent with an impairment of Kir2.1 channel function. The addition of a PIP₂ analog to the patch pipette successfully rescued endothelial Kir2.1 currents after TBI. Both H₂O₂ and PLA₂ activity were increased after injury. Metabolomics analysis demonstrated altered lipid metabolism signaling pathways, including increased arachidonic acid, and fatty acid mobilization after TBI. Our findings support a model in which increased H₂O₂-induced PLA₂ activity after trauma hydrolyzes endothelial PIP₂, resulting in impaired Kir2.1 channel function.

Epigenetic biomarkers for human sepsis and septic shock: insights from immunosuppression

Sepsis is a life-threatening condition that occurs when the body responds to an infection damaging its own tissues. Sepsis survivors sometimes suffer from immunosuppression increasing the risk of death. To our best knowledge, there is no 'gold standard' for defining immunosuppression except for a composite clinical end point. As the immune system is exposed to epigenetic changes during and after sepsis, research that focuses on identifying new biomarkers to detect septic patients with immunoparalysis could offer new epigenetic-based strategies to predict short- and long-term pathological events related to this life-threatening state. This review describes the most relevant epigenetic mechanisms underlying alterations in the innate and adaptive immune responses described in sepsis and septic shock, and their consequences for immunosuppression states, providing several candidates to become epigenetic biomarkers that could improve sepsis management and help predict immunosuppression in postseptic patients.

Systemic inflammation induces release of cell-free DNA from hematopoietic and parenchymal cells in mice and humans

During a systemic inflammatory response, cell-free DNA is first released by hematopoietic cells and thereafter by nonhematopoietic cells.

Neutrophil extracellular traps (NETs) exacerbate severity of infant sepsis

Background

Neutrophil extracellular traps (NETs) are innate defense mechanisms that are also implicated in the pathogenesis of organ dysfunction. However, the role of NETs in pediatric sepsis is unknown.

Methods

Infant (2 weeks old) and adult (6 weeks old) mice were submitted to sepsis by intraperitoneal (i.p.) injection of bacteria suspension or lipopolysaccharide (LPS). Neutrophil infiltration, bacteremia, organ injury, and concentrations of cytokine, NETs, and DNase in the plasma were measured. Production of reactive oxygen and nitrogen species and release of NETs by neutrophils were also evaluated. To investigate the functional role of NETs, mice undergoing sepsis were treated with antibiotic plus rhDNase and the survival, organ injury, and levels of inflammatory markers and NETs were determined. Blood samples from pediatric and adult sepsis patients were collected and the concentrations of NETs measured.

Results

Infant C57BL/6 mice subjected to sepsis or LPS-induced endotoxemia produced significantly higher levels of NETs than the adult mice. Moreover, compared to that of the adult mice, this outcome was accompanied by increased organ injury and production of inflammatory cytokines. The increased NETs were associated with elevated expression of Padi4 and histone H3 citrullination in the neutrophils. Furthermore, treatment of infant septic mice with rhDNase or a PAD-4 inhibitor markedly attenuated sepsis. Importantly, pediatric septic patients had high levels of NETs, and the severity of pediatric sepsis was positively correlated with the level of NETs.

Conclusion

This study reveals a hitherto unrecognized mechanism of pediatric sepsis susceptibility and suggests that NETs represents a potential target to improve clinical outcomes of sepsis.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2407-8) contains supplementary material, which is available to authorized users.

Bacillus anthracis Edema Toxin Inhibits Efferocytosis in Human Macrophages and Alters Efferocytic Receptor Signaling

The Bacillus anthracis Edema Toxin (ET), composed of a Protective Antigen (PA) and the Edema Factor (EF), is a cellular adenylate cyclase that alters host responses by elevating cyclic adenosine monophosphate (cAMP) to supraphysiologic levels. However, the role of ET in systemic anthrax is unclear. Efferocytosis is a cAMP-sensitive, anti-inflammatory process of apoptotic cell engulfment, the inhibition of which may promote sepsis in systemic anthrax. Here, we tested the hypothesis that ET inhibits efferocytosis by primary human macrophages and evaluated the mechanisms of altered efferocytic signaling. ET, but not PA or EF alone, inhibited the efferocytosis of early apoptotic neutrophils (PMN) by primary human M2 macrophages (polarized with IL-4, IL-10, and/or dexamethasone) at concentrations relevant to those encountered in systemic infection. ET inhibited Protein S- and MFGE8-dependent efferocytosis initiated by signaling through MerTK and αVβ5 receptors, respectively. ET inhibited Rac1 activation as well as the phosphorylation of Rac1 and key activating sites of calcium calmodulin-dependent kinases CamK1α, CamK4, and vasodilator-stimulated phosphoprotein, that were induced by the exposure of M2(Dex) macrophages to Protein S-opsonized apoptotic PMN. These results show that ET impairs macrophage efferocytosis and alters efferocytic receptor signaling.

Evaluating the discriminating capacity of cell death (apoptotic) biomarkers in sepsis

Background

Sepsis biomarker panels that provide diagnostic and prognostic discrimination in sepsis patients would be transformative to patient care. We assessed the mortality prediction and diagnostic discriminatory accuracy of two biomarkers reflective of cell death (apoptosis), circulating cell-free DNA (cfDNA), and nucleosomes.

Methods

The cfDNA and nucleosome levels were assayed in plasma samples acquired in patients admitted from four emergency departments with suspected sepsis. Subjects with non-infectious systemic inflammatory response syndrome (SIRS) served as controls. Samples were acquired at enrollment (T0) and 24 h later (T24). We assessed diagnostic (differentiating SIRS from sepsis) and prognostic (28-day mortality) predictive power. Models incorporating procalcitonin (diagnostic prediction) and APACHE II scores (mortality prediction) were generated.

Results

Two hundred three subjects were included (107 provided procalcitonin measurements). Four subjects exhibited uncomplicated sepsis, 127 severe sepsis, 35 septic shock, and 24 had non-infectious SIRS. There were 190-survivors and 13 non-survivors. Mortality prediction models using cfDNA, nucleosomes, or APACHEII yielded AUC values of 0.61, 0.75, and 0.81, respectively. A model combining nucleosomes with the APACHE II score improved the AUC to 0.84. Diagnostic models distinguishing sepsis from SIRS using procalcitonin, cfDNA(T0), or nucleosomes(T0) yielded AUC values of 0.64, 0.65, and 0.63, respectively. The three parameter model yielded an AUC of 0.74.

Conclusions

To our knowledge, this is the first head-to-head comparison of cfDNA and nucleosomes in diagnosing sepsis and predicting sepsis-related mortality. Both cfDNA and nucleosome concentrations demonstrated a modest ability to distinguish sepsis survivors and non-survivors and provided additive diagnostic predictive accuracy in differentiating sepsis from non-infectious SIRS when integrated into a diagnostic prediction model including PCT and APACHE II. A sepsis biomarker strategy incorporating measures of the apoptotic pathway may serve as an important component of a sepsis diagnostic and mortality prediction tool.

Clinical spectrum and short-term outcome of adult patients with purpura fulminans: a French multicenter retrospective cohort study

PURPOSE

Data on purpura fulminans (PF) in adult patients are scarce and mainly limited to meningococcal infections. Our aim has been to report the clinical features and outcomes of adult patients admitted in the intensive care unit (ICU) for an infectious PF, as well as the predictive factors for limb amputation and mortality.

METHODS

A 17-year national multicenter retrospective cohort study in 55 ICUs in France from 2000 to 2016, including adult patients admitted for an infectious PF defined by a sudden and extensive purpura, together with the need for vasopressor support. Primary outcome variables included hospital mortality and amputation during the follow-up period (time between ICU admission and amputation, death or end of follow-up).

RESULTS

Among the 306 included patients, 126 (41.2%; 95% CI 35.6-46.9) died and 180 (58.8%; 95% CI 53.3-64.3) survived during the follow-up period [13 (3-24) days], including 51/180 patients (28.3%, 95% CI 21.9-35.5) who eventually required limb amputations, with a median number of 3 (1-4) limbs amputated. The two predominantly identified microorganisms were Neisseria meningitidis (63.7%) and Streptococcus pneumoniae (21.9%). By multivariable Cox model, SAPS II [hazard-ratio (HR) = 1.03 (1.02-1.04); p < 0.001], lower leucocytes [HR 0.83 (0.69-0.99); p = 0.034] and platelet counts [HR 0.77 (0.60-0.91); p = 0.007], and arterial blood lactate levels [HR 2.71 (1.68-4.38); p < 0.001] were independently associated with hospital death, while a neck stiffness [HR 0.51 (0.28-0.92); p = 0.026] was a protective factor. Infection with Streptococcus pneumoniae [sub-hazard ratio 1.89 (1.06-3.38); p = 0.032], together with arterial lactate levels and ICU admission temperature, was independently associated with amputation by a competing risks analysis.

CONCLUSION

Purpura fulminans carries a high mortality and morbidity. Pneumococcal PF leads to a higher risk of amputation.

TRIALS REGISTRATION

NCT03216577.

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

Histones are positively charged nuclear proteins that facilitate packaging of DNA into nucleosomes common to all eukaryotic cells. Upon cell injury or cell signalling processes, histones are released passively through cell necrosis or actively from immune cells as part of extracellular traps. Extracellular histones function as microbicidal proteins and are pro‐thrombotic, limiting spread of infection or isolating areas of injury to allow for immune cell infiltration, clearance of infection and initiation of tissue regeneration and repair. Histone toxicity, however, is not specific to microbes and contributes to tissue and end‐organ injury, which in cases of systemic inflammation may lead to organ failure and death. This review details the processes of histones release in acute inflammation, the mechanisms of histone‐related tissue toxicity and current and future strategies for therapy targeting histones in acute inflammatory diseases.

Neutrophil Extracellular Traps in Children With Meningococcal Sepsis

OBJECTIVES

Children with meningococcal sepsis are highly at risk for fulminant disease, multiple organ failure, and death. Recently, neutrophil extracellular traps levels have been indicated as a marker for severity in different kinds of sepsis. Our aim was to study the role of neutrophil extracellular traposis in meninogococcal sepsis in children.

DESIGN

We measured myeloperoxidase-DNA, a marker for neutrophil extracellular traps, in serum of meningococcal sepsis patients upon admission to PICU, at 24 hours, and at 1 month and studied the association with clinical outcome. Subsequently, we tested whether Neisseria meningitidis, isolated from children with meningococcal sepsis, were able to induce neutrophil extracellular traposis, using confocal microscopy live imaging.

SETTING

We used enzyme-linked immunosorbent assays to measure myeloperoxidase-DNA in patient serum. We also included inflammatory markers that were previously measured in this group.

PATIENTS

We included exclusively children with meningococcal sepsis.

INTERVENTIONS

From each patient, serum was collected for analysis.

MEASUREMENTS AND MAIN RESULTS

Myeloperoxidase-DNA levels at admission (n = 35; median, 0.21 AU/mL; interquartile range, 0.12-0.27) and at 24 hours (n = 39; median, 0.14 AU/mL; interquartile range, 0.09-0.25) were significantly higher than the myeloperoxidase-DNA levels after 1 month (controls: n = 36; median, 0.07 AU/mL; interquartile range, 0.05-0.09; p < 0.001). We did not observe a correlation between myeloperoxidase-DNA levels and mortality, cell-free DNA, or other inflammatory markers. In addition, N. meningitidis are fast and strong inducers of neutrophil extracellular traposis.

CONCLUSIONS

Children admitted to PICU for meningococcal sepsis have higher neutrophil extracellular traps levels at admission and after 24 hours than controls. Neutrophil extracellular traps levels were not associated with outcome, cell-free DNA, or other inflammatory markers. These neutrophil extracellular traps may be induced by N. meningitidis, since these are strong neutrophil extracellular traposis inducers.

Markers of neutrophil extracellular traps predict adverse outcome in community-acquired pneumonia: secondary analysis of a randomised controlled trial

Neutrophil extracellular traps (NETs) are a hallmark of the immune response in inflammatory diseases. However, the role of NETs in community-acquired pneumonia (CAP) is unknown. This study aims to characterise the impact of NETs on clinical outcomes in pneumonia.This is a secondary analysis of a randomised controlled, multicentre trial. Patients with CAP were randomly assigned to either 50 mg prednisone or placebo for 7 days. The primary end-point was time to clinical stability; main secondary end-points were length of hospital stay and mortality.In total, 310 patients were included in the analysis. Levels of cell-free nucleosomes as surrogate markers of NETosis were significantly increased at admission and declined over 7 days. NETs were significantly associated with reduced hazards of clinical stability and hospital discharge in multivariate adjusted analyses. Moreover, NETs were associated with a 3.8-fold increased adjusted odds ratio of 30-day mortality. Prednisone treatment modified circulatory NET levels and was associated with beneficial outcome.CAP is accompanied by pronounced NET formation. Patients with elevated serum NET markers were at higher risk for clinical instability, prolonged length of hospital stay and 30-day all-cause mortality. NETs represent a novel marker for outcome and a possible target for adjunct treatments of pneumonia.

Neutrophil Extracellular Traps in Plasma from Dogs with Immune-mediated Hemolytic Anemia

Background

Neutrophil extracellular traps (NETs) are part of the innate immune response and are essential in local pathogen control, but are associated with pathological inflammation, organ damage, autoimmunity, and thrombosis. Immune‐mediated hemolytic anemia (IMHA) is a pro‐inflammatory, prothrombotic disease associated with high mortality.

Hypothesis/Objectives

Neutrophil extracellular traps (NETs) are a feature of the inflammatory process in dogs with IMHA. The objective of the study was to evaluate plasma from dogs with IMHA for the presence of 2 indirect markers and 1 direct marker of NETs.

Animals

Healthy client‐owned dogs (56) and hospitalized dogs with IMHA (n = 35).

Methods

Prospective study. Plasma samples for all dogs were evaluated for cell‐free DNA using a fluorescence assay, histone‐DNA (hisDNA) complex using an ELISA, and citrullinated histone H3 (specific for NETosis) using Western blot. Reference intervals were generated using plasma from healthy dogs.

Results

In dogs with IMHA, cell‐free DNA concentration was above the reference interval in 17% of samples with a median (range) of 1.0 μg/mL (0.1–17.3), and hisDNA concentration was above the reference interval in 94% of samples with a median (range) of 30.7 × pooled normal plasma (PNP; 0.6–372.1). Western blot for citrullinated histone H3 identified detectable bands in 84% samples from dogs with IMHA.

Conclusions and Clinical Importance

The assay for cell‐free DNA detected evidence of NETs in fewer dogs than did the other approaches. Excessive NETs appears to be a feature of IMHA in dogs and contributions to the prothrombotic state deserve further study.

Cell Death Biomarkers and Obstructive Sleep Apnea: Implications in the Acute Coronary Syndrome

Study Objectives

Nucleosomes and cell-free double-stranded DNA (dsDNA) have been suggested as promising biomarkers in cell death-related diseases, such as acute coronary syndrome (ACS). Currently, the impact of obstructive sleep apnea (OSA) in patients with ACS is unclear. Our aim was to evaluate the relationship between OSA, dsDNA, and nucleosomes and to assess their potential implication in the development of ACS.

Methods

Up to 549 patients were included in the study and divided into four groups (145 ACS; 290 ACS + OSA; 62 OSA; 52 controls). All patients underwent a sleep study, and serum concentrations of dsDNA and nucleosomes were measured.

Results

Nucleosome and dsDNA levels were higher in patients with OSA than in controls (nucleosomes: 1.47 ± 0.88 arbitary units [AU] vs. 1.00 ± 0.33 AU; p < .001, dsDNA: 315.6 ± 78.0 ng/mL vs. 282.6 ± 55.4 ng/mL; p = .007). In addition, both biomarker levels were higher in patients with ACS than in non-ACS, independently of the presence of OSA.

Conclusions

Both nucleosomes and dsDNA are increased in patients with OSA and might be related with the high cardiovascular risk seen in these patients. The extensive cell lysis during a myocardial infarction seems to be the major contributor to the high biomarker levels, and OSA does not seem to be implicated in such elevation when this acute event occurs.

Clinical trial registration

NCT01335087 (clinicaltrials.gov).

An Investigation of Extracellular Histones in Pig-To-Baboon Organ Xenotransplantation

BACKGROUND

Serum (extracellular) histone levels are increased in inflammatory states and in the presence of coagulation dysfunction, for example, trauma, chemical/ischemic injury, infection. There is increasing evidence of a systemic inflammatory response associated with the presence of a pig xenograft in a nonhuman primate. We evaluated extracellular histone levels in baboons with various pig xenografts.

METHODS

We measured serum histones in baboons with pig heterotopic heart (n = 8), life-supporting kidney (n = 5), orthotopic liver (n = 4), and artery patch (n = 9) grafts by enzyme-linked immunosorbent assay. C-reactive protein (CRP), free triiodothyronine (fT3), serum amyloid A (SAA), and platelet counts were also measured, all of which may provide an indication of an inflammatory state. We investigated the effect of histones on platelet aggregation and on cytotoxicity of pig cells in vitro.

RESULTS

Serum histones increased when baboons developed consumptive coagulopathy (eg, thrombocytopenia) or infection. CRP levels tended to be higher and fT3 levels lower when consumptive coagulopathy developed. Measurement of SAA correlated fairly well with CRP and indicated the state of inflammation. Treatment of the recipient with tocilizumab reduced the level of serum histones, CRP, and SAA, and increased the level of fT3 and platelet counts. In vitro, histone-induced platelet aggregation and endothelial cell apoptosis were both significantly reduced by the NF-κB pathway inhibitor, parthenolide.

CONCLUSIONS

These noninvasive assays may be useful for monitoring the health status of nonhuman primate recipients of pig organ grafts and may help in management after xenotransplantation. Tocilizumab and NF-κB inhibitors might prove valuable in reducing the inflammatory response to a pig xenograft.

A new mass spectrometry-based method for the quantification of histones in plasma from septic shock patients

The aim of this study was to develop a novel method to detect circulating histones H3 and H2B in plasma based on multiple reaction monitoring targeted mass spectrometry and a multiple reaction monitoring approach (MRM-MS) for its clinical application in critical bacteriaemic septic shock patients. Plasma samples from 17 septic shock patients with confirmed bacteraemia and 10 healthy controls were analysed by an MRM-MS method, which specifically detects presence of histones H3 and H2B. By an internal standard, it was possible to quantify the concentration of circulating histones in plasma, which were significantly higher in patients, and thus confirmed their potential as biomarkers for diagnosing septic shock. After comparing surviving patients and non-survivors, a correlation was found between higher levels of circulating histones and unfavourable outcome. Indeed, histone H3 proved a more efficient and sensitive biomarker for septic shock prognosis. In conclusion, these findings suggest the accuracy of the MRM-MS technique and stable isotope labelled peptides to detect and quantify circulating plasma histones H2B and H3. This method may be used for early septic shock diagnoses and for the prognosis of fatal outcomes.

Evaluation of the effect of recombinant thrombomodulin on a lipopolysaccharide-induced murine sepsis model

To evaluate the effect of recombinant human thrombomodulin (rTM) on sepsis, the levels of nucleosome as well as high-mobility group box 1 (HMGB1) and cytokines in sera and peritoneal fluids were measured in a mouse model of lipopolysaccharide (LPS)-induced sepsis after administration of rTM. C57BL/6 mice were intraperitoneally injected with LPS (15 mg/kg; Escherichia coli O111:B4) with or without the intravenous administration of rTM (3 mg/kg; 30 min prior to or 2 h after LPS injection). The survival rates were evaluated and levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, HMGB1 and nucleosome in sera and peritoneal fluids were analyzed by ELISA. Administration of rTM prior to or after LPS improved the survival rate of septic mice. In addition, rTM administered prior to or after LPS suppressed the level of pro-inflammatory cytokine TNF-α in sera at 1-3 h after LPS injection, whereas only the administration of rTM after LPS suppressed the levels of HMGB1 and nucleosome (late-phase mediators of sepsis) (9-12 h) in sera after the LPS injection. Furthermore, administration of rTM prior to or after LPS suppressed the level of TNF-α in the peritoneal fluids at 1-3 h after LPS injection, whereas only the administration of rTM after LPS suppressed the levels of IL-6 and MCP-1 in the peritoneal fluids at 6-9 h after LPS injection. These observations indicated that administration of rTM significantly improves the survival rate and suppresses the increased levels of TNF-α, IL-6, MCP-1, HMGB1 and nucleosome in the LPS-induced septic shock model. Thus, rTM may exert a protective action on sepsis and reduce mortality, possibly by reducing not only the levels of cytokines and chemokine but also the levels of late-phase mediators of sepsis.

Extracellular histones, cell-free DNA, or nucleosomes: differences in immunostimulation

In inflammation, extensive cell death may occur, which results in the release of chromatin components into the extracellular environment. Individually, the purified chromatin components double stranded (ds)DNA and histones have been demonstrated, both in vitro and in vivo, to display various immunostimulatory effects, for example, histones induce cytotoxicity and proinflammatory signaling through toll-like receptor (TLR)2 and 4, while DNA induces signaling through TLR9 and intracellular nucleic acid sensing mechanisms. However, DNA and histones are organized in nucleosomes in the nucleus, and evidence suggests that nucleosomes are released as such in inflammation. The cytotoxicity and proinflammatory signaling induced by nucleosomes have not been studied as extensively as the separate effects brought about by histones and dsDNA, and there appear to be some marked differences. Remarkably, little distinction between the different forms in which histones circulate has been made throughout literature. This is partly due to the limitations of existing techniques to differentiate between histones in their free or DNA-bound form. Here we review the current understanding of immunostimulation induced by extracellular histones, dsDNA and nucleosomes, and discuss the importance of techniques that in their detection differentiate between these different chromatin components.

Toll-like receptor 9 enhances bacterial clearance and limits lung consolidation in murine pneumonia caused by methicillin resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in pneumonia, associated with severe lung damage. Tissue injury causes release of Damage Associated Molecular Patterns (DAMPs), which may perpetuate inflammation. DNA has been implicated as a DAMP that activates inflammation through Toll-like receptor (TLR)9. The aim of this study was to evaluate the role of TLR9 in MRSA pneumonia. Wild-type (Wt) and TLR9 knockout (tlr9^-/-) mice were infected intranasally with MRSA USA300 (BK 11540) (5^E7CFU) and euthanized at 6,24,48 or 72 hours for analyses. MRSA pneumonia was associated with profound release of cell-free host DNA in the airways, as reflected by increases in nucleosome and DNA levels in bronchoalveolar lavage fluid (BALF), accompanied by transient detection of pathogen DNA in MRSA-free BALF supernatants. In BALF, as compared to Wt -mice tlr9^-/- mice showed reduced TNFα and IL-6 levels at 6 hours and reduced bacterial clearance at 6 and 24 hours post infection. Furthermore, tlr9^-/- mice exhibited a greater influx of neutrophils in BALF and increased lung consolidation at 24 and 48 hours. This study demonstrates the release of host- and pathogen-derived TLR9 ligands (DNA) into the alveolar space after infection with MRSA via the airways and suggests that TLR9 has pro-inflammatory effects during MRSA pneumonia associated with enhanced bacterial clearance and limitation of lung consolidation.

Circulating nucleosomes are associated with mortality in pediatric acute respiratory distress syndrome

Mechanisms underlying pediatric acute respiratory distress syndrome (PARDS) are poorly understood. The recent implication of circulating nucleosomes as pathogenic in sepsis and trauma-associated ARDS in adults led us to investigate the significance of nucleosomes in PARDS. We conducted a prospective, observational study on children with PARDS at the Children's Hospital of Philadelphia between July 2014 and September 2015. Plasma was collected within 48 h of PARDS onset and nucleosomes quantified by enzyme-linked immunosorbent assay. Samples from 76 children with PARDS (11 deaths, 14%) were collected early [median 15 (IQR 7, 21) h] after PARDS onset. Nucleosome levels were higher in nonsurvivors [0.59 AU (IQR 0.46, 0.84)] relative to survivors [0.21 AU (IQR 0.08, 0.33), rank sum P < 0.001]. Nucleosome levels were not associated with either Berlin (P = 0.845) or PALICC (P = 0.886) oxygenation categories, nor with etiology of PARDS (P = 0.527). Nucleosomes were correlated with increasing numbers of nonpulmonary organ failures (P = 0.009 for trend), and were higher in patients whose PaO2 /FiO2 worsened (P = 0.012) over the first 72 h of PARDS. In regression analysis, nucleosome levels were independently associated with mortality after adjusting for either age, severity of illness score, number of nonpulmonary organ failures, vasopressor score, or PaO2 /FiO2 (all P < 0.05). In conclusion, plasma nucleosome levels in early PARDS were associated with increased mortality, correlated with number of nonpulmonary organ failures, and preceded worsening oxygenation. The potential utility of this biomarker for prognostication, risk stratification, and mechanistic insight should be investigated further.

Circulating Histones Are Major Mediators of Cardiac Injury in Patients With Sepsis

OBJECTIVE

To investigate the impact of circulating histones on cardiac injury and dysfunction in a murine model and patients with sepsis.

DESIGN

Prospective, observational clinical study with in vivo and ex vivo translational laboratory investigations.

SETTING

General ICU and university research laboratory.

SUBJECTS

Sixty-five septic patients and 27 healthy volunteers. Twelve-week-old male C57BL/6N mice.

INTERVENTIONS

Serial blood samples from 65 patients with sepsis were analyzed, and left ventricular function was assessed by echocardiography. Patients' sera were incubated with cultured cardiomyocytes in the presence or absence of antihistone antibody, and cellular viability was assessed. Murine sepsis was initiated by intraperitoneal Escherichia coli injection (10(8) colony-forming unit/mouse) in 12-week-old male C57BL/6N mice, and the effect of antihistone antibody (10 mg/kg) was studied. Murine blood samples were collected serially, and left ventricular function was assessed by intraventricular catheters and electrocardiography.

MEASUREMENTS AND MAIN RESULTS

Circulating histones and cardiac troponins in human and murine plasma were quantified. In 65 patients with sepsis, circulating histones were significantly elevated compared with healthy controls (n = 27) and linearly correlated with cardiac troponin T levels (rs = 0.650; p < 0.001), noradrenaline doses required to achieve hemodynamic stability (rs = 0.608; p < 0.001), Sequential Organ Failure Assessment scores (p = 0.028), and mortality (p = 0.008). In a subset of 36 septic patients without prior cardiac disease, high histone levels were significantly associated with new-onset left ventricular dysfunction (p = 0.001) and arrhythmias (p = 0.01). Left ventricular dysfunction only predicted adverse outcomes when combined with elevated histones or cardiac troponin levels. Furthermore, patients' sera directly induced histone-specific cardiomyocyte death ex vivo, which was abrogated by antihistone antibodies. In vivo studies on septic mice confirmed the cause-effect relationship between circulating histones and the development of cardiac injury, arrhythmias, and left ventricular dysfunction.

CONCLUSION

Circulating histones are novel and important mediators of septic cardiomyopathy, which can potentially be utilized for prognostic and therapeutic purposes.

Increased Nucleosomes and Neutrophil Activation Link to Disease Progression in Patients with Scrub Typhus but Not Murine Typhus in Laos

Cell-mediated immunity is essential in protection against rickettsial illnesses, but the role of neutrophils in these intracellular vasculotropic infections remains unclear. This study analyzed the plasma levels of nucleosomes, FSAP-activation (nucleosome-releasing factor), and neutrophil activation, as evidenced by neutrophil-elastase (ELA) complexes, in sympatric Lao patients with scrub typhus and murine typhus. In acute scrub typhus elevated nucleosome levels correlated with lower GCS scores, raised respiratory rate, jaundice and impaired liver function, whereas neutrophil activation correlated with fibrinolysis and high IL-8 plasma levels, a recently identified predictor of severe disease and mortality. Nucleosome and ELA complex levels were associated with a 4.8-fold and 4-fold increased risk of developing severe scrub typhus, beyond cut off values of 1,040 U/ml for nucleosomes and 275 U/ml for ELA complexes respectively. In murine typhus, nucleosome levels associated with pro-inflammatory cytokines and the duration of illness, while ELA complexes correlated strongly with inflammation markers, jaundice and increased respiratory rates. This study found strong correlations between circulating nucleosomes and neutrophil activation in patients with scrub typhus, but not murine typhus, providing indirect evidence that nucleosomes could originate from neutrophil extracellular trap (NET) degradation. High circulating plasma nucleosomes and ELA complexes represent independent risk factors for developing severe complications in scrub typhus. As nucleosomes and histones exposed on NETs are highly cytotoxic to endothelial cells and are strongly pro-coagulant, neutrophil-derived nucleosomes could contribute to vascular damage, the pro-coagulant state and exacerbation of disease in scrub typhus, thus indicating a detrimental role of neutrophil activation. The data suggest that increased neutrophil activation relates to disease progression and severe complications, and increased plasma levels of nucleosomes and ELA complexes represent independent risk factors for developing severe scrub typhus.

Tropical rickettsial illnesses, especially scrub typhus and murine typhus, are increasingly recognized as a leading cause of treatable undifferentiated febrile illness in Asia, but remain severely neglected and under appreciated diseases in many areas. In this study we investigated the relationship of markers of neutrophil activation and cell death with disease severity in patients with acute scrub typhus and murine typhus in Laos. These easily measurable circulating markers were associated with a 4 to 5-fold increased risk of developing severe clinical disease manifestations in scrub typhus and represent independent predictors of severe disease, and possibly death. We also found strong correlations between circulating markers of cell death and neutrophil activation in patients with scrub typhus, but not murine typhus, providing indirect evidence that neutrophil extracellular traps could contribute to the vascular damage and pro-coagulant state leading to exacerbation of disease in scrub typhus, thus indicating a detrimental role of neutrophil activation. The data suggest that increased neutrophil activation relates to disease progression and severe complications, and increased plasma levels of nucleosomes and ELA complexes represent independent risk factors for developing severe scrub typhus.

Extracellular histone H3 levels are inversely correlated with antithrombin levels and platelet counts and are associated with mortality in sepsis patients

OBJECTIVE

Sepsis is a leading cause of death worldwide. Extracellular histones are cytotoxic compounds mediating death in murine sepsis and circulating nucleosome levels predict mortality in human inflammation and sepsis. Whether or not circulating extracellular histone H3 correlates with other plasma parameters and/or ICU scoring systems has not been completely established, nor if levels of circulating extracellular histones can be used as predictive markers for clinical outcome in sepsis.

METHODS

We measured plasma histone H3 (H3) levels in the plasma of 43 sepsis patients who were admitted to the Intensive Care Unit and determined their correlation with disease severity, organ failure, mortality and coagulation- and tissue homeostasis parameters including LDH levels, thrombin potential (ETP), prothrombin levels, antithrombin levels and platelet counts.

RESULTS

Median H3 levels of sepsis patients at the ICU were significantly increased in non-survivors as compared to survivors with levels found being 3.15μg/ml versus 0.57μg/ml respectively, P=0.04. H3 levels are positively correlated with lactate dehydrogenase (LDH) activity (Spearman's rho=0.49, P<0.001), and negatively correlated with antithrombin levels (rho=-0.34, P=0.027) and platelet counts (rho=-0.33, P=0.031).

CONCLUSIONS

We conclude that circulating H3 levels correlate with mortality in sepsis patients and inversely correlate with antithrombin levels and platelet counts.

Myeloid-related protein-14 deficiency promotes inflammation in staphylococcal pneumonia

Staphylococcus aureus has evolved as an important cause of pneumonia in both hospital and community settings. Staphylococcal lung infection can lead to overwhelming pulmonary inflammation. During infection, neutrophils release complexes of myeloid-related protein (MRP)8 and MRP14 (MRP8/14). MRP8/14 has been shown to exert pro-inflammatory and chemotactic activity, and to assist in the killing of S. aureus. In the current study we sought to determine the role of MRP8/14 in the host response during S. aureus pneumonia.Pneumonia was induced in wildtype and MRP14-deficient mice (mice unable to form MRP8/14) by intranasal inoculation of 1×10(7) CFU of S. aureus USA300. Mice were sacrificed at 6, 24, 48 or 72 h after infection for analyses.S. aureus pneumonia was associated with a strong rise in MRP8/14 in bronchoalveolar lavage fluid and lung tissue. Surprisingly, MRP14 deficiency had a limited effect on bacterial clearance and was associated with increased cytokine levels in bronchoalveolar lavage fluid and aggravated lung histopathology. MRP14 deficiency in addition was associated with a diminished transmigration of neutrophils into bronchoalveolar lavage fluid at late time-points after infection together with reduced release of nucleosomes.MRP8/14 serves in an unexpected protective role for the lung in staphylococcal pneumonia.

Diabetes-independent increase of factor VII-activating protease activation in patients with Gram-negative sepsis (melioidosis)

BACKGROUND

The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. Nucleosomes are markers of cell death, and extracellular cell-free DNA has been suggested to play an important role in inflammation and has been demonstrated to correlate with severity and outcome in sepsis patients.

OBJECTIVE

To investigate FSAP activation in patients suffering from Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia. As diabetes mellitus (DM) is the most important risk factor for both melioidosis and sepsis, we were also able to examine the role of DM in FSAP activation in this cohort of patients.

METHODS

In a prospective observational study, complexes of FSAP with α2 -antiplasmin (AP) were assayed in 44 patients with melioidosis, 34 of whom were classified as diabetic. Eighty-two healthy subjects served as controls (52 with DM and 30 without).

RESULTS

FSAP-AP complex levels were markedly elevated in patients as compared with controls. The FSAP level increased by 16.82 AU mL(-1) in patients with melioidosis after adjustment for the effect of DM in the regression model. As expected, FSAP activation was correlated with nucleosome release (slope = 0.74). No difference in FSAP activation on admission was seen between survivors and non-survivors, but the extent of FSAP activation correlated with stage of the disease; repeated testing during convalescence showed a return towards normal values (day 0 vs. day 28, 4.16 AU mL(-1) , 95% confidence interval [CI] 1.42-12.22).

CONCLUSION

Patients with Gram-negative sepsis caused by B. pseudomallei have abundant FSAP activation, which significantly correlates with stage of disease. The presence of DM, however, does not influence the extent of FSAP activation.

Impact of calcium signaling during infection of Neisseria meningitidis to human brain microvascular endothelial cells

The pili and outer membrane proteins of Neisseria meningitidis (meningococci) facilitate bacterial adhesion and invasion into host cells. In this context expression of meningococcal PilC1 protein has been reported to play a crucial role. Intracellular calcium mobilization has been implicated as an important signaling event during internalization of several bacterial pathogens. Here we employed time lapse calcium-imaging and demonstrated that PilC1 of meningococci triggered a significant increase in cytoplasmic calcium in human brain microvascular endothelial cells, whereas PilC1-deficient meningococci could not initiate this signaling process. The increase in cytosolic calcium in response to PilC1-expressing meningococci was due to efflux of calcium from host intracellular stores as demonstrated by using 2-APB, which inhibits the release of calcium from the endoplasmic reticulum. Moreover, pre-treatment of host cells with U73122 (phospholipase C inhibitor) abolished the cytosolic calcium increase caused by PilC1-expressing meningococci demonstrating that active phospholipase C (PLC) is required to induce calcium transients in host cells. Furthermore, the role of cytosolic calcium on meningococcal adherence and internalization was documented by gentamicin protection assay and double immunofluorescence (DIF) staining. Results indicated that chelation of intracellular calcium by using BAPTA-AM significantly impaired PilC1-mediated meningococcal adherence to and invasion into host endothelial cells. However, buffering of extracellular calcium by BAPTA or EGTA demonstrated no significant effect on meningococcal adherence to and invasion into host cells. Taken together, these results indicate that meningococci induce calcium release from intracellular stores of host endothelial cells via PilC1 and cytoplasmic calcium concentrations play a critical role during PilC1 mediated meningococcal adherence to and subsequent invasion into host endothelial cells.

Neutrophil extracellular traps in the host defense against sepsis induced by Burkholderia pseudomallei (melioidosis)

Background

Neutrophil extracellular traps (NETs) are a central player in the host response to bacteria: neutrophils release extracellular DNA (nucleosomes) and neutrophil elastase to entrap and kill bacteria. We studied the role of NETs in Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia.

Methods

In a prospective observational study, circulating nucleosomes and neutrophil elastase were assayed in 44 patients with Gram-negative sepsis caused by B. pseudomallei (melioidosis) and 82 controls. Functional assays included human neutrophil stimulation and killing assays and a murine model of B. pseudomallei infection in which NET function was compromised using DNase. Specified pathogen-free 8- to 12-week-old C57BL/6 mice were sacrificed post-infection to assess bacterial loads, inflammation, and pathology.

Results

Nucleosome and neutrophil elastase levels were markedly elevated in patients compared to controls. NETs killed B. pseudomallei effectively, and neutrophils stimulated with B. pseudomallei showed increased elastase and DNA release in a time- and dose-dependent matter. In mice, NET disruption with intravenous DNase administration resulted in decreased nucleosome levels. Although DNase treatment of mice resulted in diminished liver inflammation, no differences were observed in bacterial dissemination or systemic inflammation.

Conclusion

B. pseudomallei is a potent inducer of NETosis which was reflected by greatly increased levels of NET-related components in melioidosis patients. Although NETs exhibited antibacterial activity against B. pseudomallei, NET formation did not protect against bacterial dissemination and inflammation during B. pseudomallei-induced sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-014-0021-2) contains supplementary material, which is available to authorized users.

Extracellular histones in tissue injury and inflammation

Neutrophil NETosis is an important element of host defense as it catapults chromatin out of the cell to trap bacteria, which then are killed, e.g., by the chromatin's histone component. Also, during sterile inflammation TNF-alpha and other mediators trigger NETosis, which elicits cytotoxic effects on host cells. The same mechanism should apply to other forms of regulated necrosis including pyroptosis, necroptosis, ferroptosis, and cyclophilin D-mediated regulated necrosis. Beyond these toxic effects, extracellular histones also trigger thrombus formation and innate immunity by activating Toll-like receptors and the NLRP3 inflammasome. Thereby, extracellular histones contribute to the microvascular complications of sepsis, major trauma, small vessel vasculitis as well as acute liver, kidney, brain, and lung injury. Finally, histones prevent the degradation of extracellular DNA, which promotes autoimmunization, anti-nuclear antibody formation, and autoimmunity in susceptible individuals. Here, we review the current evidence on the pathogenic role of extracellular histones in disease and discuss how to target extracellular histones to improve disease outcomes.

Neutrophil extracellular traps, damage-associated molecular patterns, and cell death during sepsis

In addition to pathogen-associated molecular patterns from invasive microorganisms, alarmins, which are major components of host defense mechanisms, are involved in the pathophysiology of sepsis. In fact, the magnitude of the insult is defined according to the damage-associated molecular pattern (DAMP), which is composed of alarmins as well as pathogen-associated molecular patterns, such as those involving nucleosomes, histones, and DNA. Regarding the antimicrobial mechanism of neutrophils, an alternative non-phagocytic mechanism was first recognized as "NETosis" in 2004. In this mechanism, microorganisms are trapped and eliminated by neutrophil extracellular traps (NETs). These NETs are composed of histones and DNA that have been expelled from the nucleus as well as antimicrobial proteases, including elastase and myeloperoxidase. NETosis, a cell death pathway reported to be distinct from apoptosis, is an active area of research. As NETs are composed of deleterious substances, they are extremely harmful to the host cells once they are released into the circulating blood. Therefore, the meanings and putative roles of these components in sepsis have attracted much attention.

Combination of antithrombin and recombinant thrombomodulin attenuates leukocyte-endothelial interaction and suppresses the increase of intrinsic damage-associated molecular patterns in endotoxemic rats

INTRODUCTION

Both antithrombin (AT) and thrombomodulin are key players in physiological anticoagulant systems. Because the levels of both factors are known to decrease significantly during severe sepsis, we hypothesized that a combination therapy would be effective.

METHODS

A sepsis model was established using the intravenous infusion of lipopolysaccharide (LPS). A dose of 125 IU/kg of AT, 0.25 mg/kg of recombinant thrombomodulin, or a combination of both agents was injected immediately after LPS infusion (n = 7, each). Intravital observation of the mesenteric microcirculation was performed, and leukocyte adhesion and blood flow were calculated at 3 h after LPS infusion. Immediately after the observation, blood samples were obtained and coagulation markers, organ damage markers, the circulating levels of nucleosome and high-mobility group box 1 were measured.

RESULTS

Microscopic findings revealed the suppression of leukocyte adhesion and thrombus formation in the combination group. The number of adhesive leukocytes on the endothelium was significantly suppressed (P < 0.01), and the blood flow in venules was better maintained in the combination group compared with the placebo control (P < 0.01). The blood samples showed the suppressed activation in coagulation, no significant changes were observed in the organ damage markers in the treatment groups. The circulating levels of nucleosome and high-mobility group box 1 were both decreased significantly in the combination group compared with the placebo control (P < 0.01).

CONCLUSIONS

The coadministration of AT and recombinant thrombomodulin is effective for the suppression of leukocyte activation and cell death during sepsis.

Nucleosomes and neutrophil activation in sickle cell disease painful crisis

Activated polymorphonuclear neutrophils play an important role in the pathogenesis of vaso-occlusive painful sickle cell crisis. Upon activation, polymorphonuclear neutrophils can form neutrophil extracellular traps. Neutrophil extracellular traps consist of a meshwork of extracellular DNA, nucleosomes, histones and neutrophil proteases. Neutrophil extracellular traps have been demonstrated to be toxic to endothelial and parenchymal cells. This prospective cohort study was conducted to determine neutrophil extracellular trap formation in sickle cell patients during steady state and painful crisis. As a measure of neutrophil extracellular traps, plasma nucleosomes levels were determined and polymorphonuclear neutrophil activation was assessed measuring plasma levels of elastase-α1-antitrypsin complexes in 74 patients in steady state, 70 patients during painful crisis, and 24 race-matched controls using Enzyme Linked Immunosorbent Assay. Nucleosome levels in steady state sickle cell patients were significantly higher than levels in controls. During painful crisis levels of both nucleosomes and elastase-α1-antitrypsin complexes increased significantly. Levels of nucleosomes correlated significantly to elastase-α1-antitrypsin complex levels during painful crisis, (Sr = 0.654, P<0.001). This was seen in both HbSS/HbSβ(0)-thalassemia (Sr=0.55, P<0.001) and HbSC/HbSβ(+-)thalassemia patients (Sr=0.90, P<0.001) during painful crisis. Levels of nucleosomes showed a correlation with length of hospital stay and were highest in patients with acute chest syndrome. These data support the concept that neutrophil extracellular trap formation and neutrophil activation may play a role in the pathogenesis of painful sickle cell crisis and acute chest syndrome.

Histone induced platelet aggregation is inhibited by normal albumin

INTRODUCTION

Histones are small, nuclear proteins that serve to package DNA. Recent reports suggest that extracellular histones, including histone H4, may contribute to the pathogenesis of sepsis; they promote platelet aggregation and thrombosis when released into the circulation during inflammation or cell death. The mechanisms by which the body minimizes the deleterious effects of circulating histones are unclear. Because histones can bind to plasma proteins, including albumin, we hypothesized that normal albumin can prevent histones from activating platelets.

MATERIALS AND METHODS

Platelets and platelet-free plasma were obtained from healthy, adult subjects. The dose-dependent effects of histone H4 on platelet aggregation were studied by optical aggregometry. The effects of native and albumin-depleted plasma (prepared by affinity chromatography) on histone-induced platelet aggregation were also assessed. The effects of normal and surface-neutralized albumin (through modification of carboxyl groups) on histone-induced platelet activation and aggregation were evaluated using flow cytometry and aggregometry.

RESULTS

Histone H4 induced platelet aggregation in a dose-dependent manner. This histone-induced platelet aggregation was inhibited by both plasma and human serum albumin in a dose-dependent fashion. Furthermore, depletion of albumin from plasma reduced its ability to inhibit aggregation. Finally, surface neutralization of albumin decreased its ability to inhibit histone-induced activation and aggregation.

DISCUSSION

These data suggest that normal albumin serves a role in preventing histone-induced platelet aggregation in a charge-dependent manner.

Extracellular nucleic acids as novel alarm signals in the vascular system. Mediators of defence and disease

Upon vascular injury or tissue damage, the exposed intracellular material such as nucleic acids, histones and other macromolecules may come into contact with vessel wall cells and circulating blood cells and may thus, have an enduring influence on wound healing and body defence processes. This short review summarizes recent work related to extracellular DNA and RNA and their role as prominent alarm signals and inducers of different defence reactions related to innate immunity and thrombus formation. Of particular importance are DNA-histone complexes (nucleosome material) that, having been expelled during stimulation of the neutrophils, not only trap and eliminate bacteria but also promote thrombus formation in the arterial and venous system. Consequently therefore, the administration of DNase exhibits strong antithrombotic functions. Similarly, extracellular RNA provokes activation of the contact phase system of blood coagulation and, by interacting with specific proteins and cytokines, it promotes vascular permeability and oedema formation. The development of RNA-mediated thrombosis, vasogenic oedema or proinflammatory responses are counteracted by the administration of RNase1 in several pathogenetic animal models. Thus, extracellular nucleic acids appear not only to function as host alarm signals that serve to amplify the defence response, but they also provide important links to thrombus formation as part of the innate immune system.

Circulating Nucleosomes and Neutrophil Activation as Risk Factors for Deep Vein Thrombosis

Objective—

The formation of neutrophil extracellular traps and the exposure of nucleosomes on these neutrophil extracellular traps contribute to coagulation activation and the propagation of deep vein thrombosis (DVT) in animal models. However, no data are available on the role of neutrophil extracellular traps or nucleosomes in patients with thrombosis.

Methods and Results—

We conducted a case–control study, in which levels of circulating nucleosomes and neutrophil elastase–α1-antitrypsin complexes were assessed in plasma from 150 patients with objectified symptomatic DVT (cases) and compared with 195 patients with a clinical suspicion of DVT but in whom DVT was excluded (controls). We explored the association between both nucleosomes and elastase–α1-antitrypsin complexes, and the presence of DVT by calculating the odds ratio with corresponding 95% CIs. Elevated levels of both circulating nucleosomes and elastase–α1-antitrypsin complexes were associated with a 3-fold risk of DVT, and the associations remained similar after adjustment for potential confounders (malignancy, smoking, recent immobilization, recent hospitalization). The risk increased with higher nucleosome and elastase–α1-antitrypsin complex levels, suggesting a dose-dependent relationship among circulating nucleosomes, activated neutrophils, and DVT.

Conclusion—

Our study suggests an association among circulating nucleosomes, activated neutrophils, and presence of DVT in humans, which might have implications for treatment and prevention.