Neutrophils release extracellular DNA traps during storage of red blood cell units

Intermittent scavenging of storage lesion from stored red blood cells by electrospun nanofibrous sheets enhances their quality and shelf-life

Transfusion of healthy red blood cells (RBCs) is a lifesaving process. However, upon storing RBCs, a wide range of damage-associate molecular patterns (DAMPs), such as cell-free DNA, nucleosomes, free-hemoglobin, and poly-unsaturated-fatty-acids are generated. DAMPs can further damage RBCs; thus, the quality of stored RBCs declines during the storage and limits their shelf-life. Since these DAMPs consist of either positive or negative charged species, we developed taurine and acridine containing electrospun-nanofibrous-sheets (Tau-AcrNFS), featuring anionic, cationic charges and an DNA intercalating group on their surfaces. We show that Tau-AcrNFS are efficient in scavenging DAMPs from stored human and mice RBCs ex vivo. We find that intermittent scavenging of DAMPs by Tau-AcrNFS during the storage reduces the loss of RBC membrane integrity and reduces discocytes-to-spheroechinocytes transformation in stored-old-RBCs. We perform RBC-transfusion studies in mice to reveal that intermittent removal of DAMPs enhances the quality of stored-old-RBCs equivalent to freshly collected RBCs, and increases their shelf-life by ~22%. Such prophylactic technology may lead to the development of novel blood bags or medical device, and may therefore impact healthcare by reducing transfusion-related adverse effects.

Plasma Exchange Therapy Using Solvent Detergent-Treated Plasma: An Observational Pilot Study on Complement, Neutrophil and Endothelial Cell Activation in a Case Series of Patients Suffering from Atypical Hemolytic Uremic Syndrome

Introduction

Plasma exchange therapy (PEX) was standard treatment for thrombotic microangiopathy before eculizumab was available and is still widely applied. However, most PEX patients still ultimately progress to end-stage renal disease (ESRD). It has been suggested that infusion of plasma that contains active complement may induce additional complement activation with subsequent activation of neutrophils and endothelial cells, leading to exacerbation of organ damage and deterioration of renal function.

Objective

This observational pilot study examines the effect of hemodialysis, eculizumab and PEX before and after treatment in plasma of aHUS patients on complement-, neutrophil and endothelial cell activation.

Methods

Eleven patients were included in this pilot study. Six patients were treated with hemodialysis, 2 patients received regular infusions of eculizumab, and 3 patients were on a regular schedule for PEX. Patients were followed during 3 consecutive treatments. Blood samples were taken before and after patients received their treatment.

Results

Complement activation products increased in plasma of patients after PEX, as opposed to patients treated with hemodialysis or eculizumab. Increased levels of complement activation products were detected in omniplasma used for PEX. Additionally, activation of neutrophils and endothelial cells was observed in patients after hemodialysis and PEX, but not in patients receiving eculizumab treatment.

Conclusion

In this pilot study we observed that PEX induced complement and neutrophil activation, and that omniplasma contains significant amounts of complement activation products. Additionally, we demonstrate that hemodialysis induces activation of neutrophils and endothelial cells. Complement activation with subsequent neutrophil activation may contribute to the deterioration of organ function and may result in ESRD. Further randomized controlled studies are warranted to investigate the effect of PEX on complement- and neutrophil activation in patients with thrombotic microangiopathy.

Microfluidic capture of chromatin fibres measures neutrophil extracellular traps (NETs) released in a drop of human blood

Neutrophils are the largest population of white blood cells in the circulation, and their primary function is to protect the body from microbes. They can release the chromatin in their nucleus, forming characteristic web structures and trap microbes, contributing to antimicrobial defenses. The chromatin webs are known as neutrophil extracellular traps (NETs). Importantly, neutrophils can also release NETs in pathological conditions related to rheumatic diseases, atherosclerosis, cancer, and sepsis. Thus, determining the concentration of NETs in the blood is increasingly important for monitoring patients, evaluating treatment efficacy, and understanding the pathology of various diseases. However, traditional methods for measuring NETs require separating cells and plasma from blood, are prone to sample preparation artifacts, and cannot distinguish between intact and degraded NETs. Here, we design a microfluidic analytical tool that captures NETs mechanically from a drop of blood and measures the amount of intact NETs unbiased by the presence of degraded NETs in the sample.

The presence of tumour-infiltrating neutrophils is an independent adverse prognostic feature in clear cell renal cell carcinoma

Tumour-promoting inflammation is an emerging hallmark of cancer that is increasingly recognised as a therapeutic target. As a constituent measure of inflammation, tumour-infiltrating neutrophils (TINs) have been associated with inferior prognosis in several cancers. We analysed clinically annotated cohorts of clear cell renal cell carcinoma (ccRCC) to assess the presence of neutrophils within the tumour microenvironment as a function of outcome. We centrally reviewed ccRCC surgical resection and fine-needle aspiration (FNA) specimens, including primary and metastatic sites, from three centres. TINs were scored based on the presence of neutrophils in resection and FNA specimens by two pathologists. TIN count was correlated with tumour characteristics including stage, WHO/ISUP grade, and immunohistochemistry (IHC). In parallel, we performed CIBERSORT analysis of the tumour microenvironment in a cohort of 516 ccRCCs from The Cancer Genome Atlas (TCGA). We included 102 ccRCC cases comprising 65 resection specimens (37 primary and 28 metastatic resection specimens) and 37 FNAs from primary lesions. High TINs were significantly associated with worse overall survival (p = 0.009) independent of tumour grade and stage. In ccRCCs sampled via FNA, all cases with high TINs had distant metastasis, whereas they were seen in only 19% of cases with low TINs (p = 0.0003). IHC analysis showed loss of E-cadherin in viable tumour cells in areas with high TINs, and neutrophil activation was associated with elastase and citrullinated histone H3 expression (cit-H3). In the TCGA cohort, neutrophilic markers were also associated with worse survival (p < 0.0001). TINs are an independent predictor of worse prognosis in ccRCC, which have the potential to be assessed at the time of first biopsy or FNA. Neutrophils act directly on tumour tissue by releasing elastase, a factor that contributes to the breakdown of cell-cell adhesion and to facilitate tumour dissemination.

A focus on the roles of histones in health and diseases

Over time, the knowledge on the role of histones has significantly changed. Initially, histones were only known as DNA packaging proteins but later, it was discovered that they act extracellularly as powerful antimicrobial agents and also as potentially self-detrimental agents. Indeed, histones were found to be the most abundant proteins within neutrophil extracellular traps what ultimately highlighted their microbicidal function. In addition, extracellular histones proved to be involved in triggering exacerbated inflammatory and coagulation responses, depending on the cell type affected. Consequently, several investigations were conducted towards studying the potential of histones and their derivatives as either biomarkers or therapeutic target candidates in different diseases in which inflammation and thrombosis have a key pathophysiological role, such as sepsis, thrombosis and different types of cancer. The main objective of this review is to summarize and discuss the current state of the art with regard to both beneficial and harmful roles of histones and also their possible use as biomarkers and therapeutic targets.

Plasma or Serum: Which Is Preferable for Mutation Detection in Liquid Biopsy?

BACKGROUND

Blood-based analysis of circulating tumor DNA (ctDNA) is a promising tool for cancer screening, monitoring relapse/recurrence and evaluating response to treatment. Although plasma is widely used to obtain ctDNA, biorepositories worldwide possess a huge number of serum samples and comparative studies on the use of serum vs plasma as ctDNA sources are essential.

METHODS

We analyzed cell-free DNA (cfDNA) from matched EDTA-plasma and serum samples from healthy donors and patients with colorectal or lung cancer, and used targeted next-generation sequencing to evaluate mutation detection efficiency and reproducibility. Matched samples from healthy individuals were spiked with reference oligonucleotides and sequenced using the Ion-S5 Oncomine-Pan-Cancer panel. Detection efficiency in matched samples from patients with cancer was evaluated using 2 distinct gene panels and compared to mutations found in tissue-biopsy samples at diagnosis.

RESULTS

Mean total cfDNA was 55% higher in serum samples and the presence of longer DNA fragments was significantly increased in serum compared with plasma samples (P = 0.0001 to 0.015). Spiked mutated nucleotides were detected in both samples, but allele frequencies (AF) were approximately half in serum compared with plasma, suggesting ctDNA from serum was more diluted by DNA of noncancerous origins. Matched samples from patients with cancer revealed that up to 44.8% of mutations with low AF were missed in serum samples and concordance rates with somatic mutations found in tissue biopsy at diagnosis was better in plasma samples.

CONCLUSION

The use of serum in retrospective studies should consider the limitations for detecting low AF mutations. Plasma is clearly preferable for prospective clinical applications of liquid biopsy.

Decrease in the Risk of Posttransplant Hepatocellular Carcinoma Recurrence After the Conversion to Prestorage Leukoreduction for Transfused Red Blood Cells

BACKGROUND

Prestorage leukoreduction has the advantage over poststorage leukoreduction in reducing leukocyte-derived molecules in red blood cells (RBC) unit, which induce immunomodulation. Our institution newly introduced prestorage leukoreduction, instead of conventional poststorage leukoreduction, for liver transplant recipients since March 2012. In this study, we aimed to evaluate the risk of posttransplant hepatocellular carcinoma (HCC) recurrence after the conversion of poststorage leukoreduction into prestorage leukoreduction for transfused allogeneic RBCs.

METHODS

Among 220 patients who underwent living-donor liver transplantation for HCC, 83 of 113 who received only poststorage-leukoreduced RBCs were matched with 83 of 107 who received only prestorage-leukoreduced RBCs using 1:1 propensity score matching based on factors like tumor biology. The primary outcome was overall HCC recurrence. Survival analysis was performed with death as a competing risk event.

RESULTS

In the matched cohort, recurrence probability at 1, 2, and 5 years posttransplant was 9.6%, 15.6%, and 18.1% in prestorage group and 15.6%, 21.6%, and 33.7% in poststorage group (hazard ratio [HR], 0.52; 0.28-0.97; P = 0.040). Multivariable analysis confirmed a significance of prestorage leukoreduction (HR, 0.29; 0.15-0.59; P < 0.001). Overall death risk was also lower with prestorage leukoreduction (HR, 0.51; 0.26-0.99; P = 0.049). In subgroup analysis for the unmatched cohort, recurrence risk was significantly lower in prestorage group within the patients who underwent surgery 2 years (HR, 0.24; 0.10-0.61; P = 0.002), 1 year (HR, 0.16; 0.03-0.92; P = 0.040), and 6 months (HR, 0.13; 0.02-0.85; P = 0.034), respectively, before and after the conversion to prestorage leukoreduction.

CONCLUSIONS

Our findings suggest a potential benefit of prestorage leukoreduction in reducing the risk of HCC recurrence in liver transplant recipients who received allogeneic RBCs during the perioperative period.

Neutrophil extracellular traps in stored canine red blood cell units

Background

Neutrophil extracellular traps (NETs), webs of DNA and citrullinated histones extruded from activated neutrophils cause transfusion‐related acute lung injury. Supernatants of stored red blood cell (RBC) units might promote NETosis in neutrophils from the units or from transfusion recipients.

Hypotheses

(1) NETs form during storage of canine RBC, (2) leukoreduction (LR) before storage of RBC reduces NETosis, and (3) supernatant from stored, nonleukoreduced (NLR) RBC units induces NETosis in healthy canine neutrophils modeling transfusion recipients.

Animals

Six healthy purpose‐bred research dogs were utilized for blood donation.

Methods

Prospective controlled study. RBC units were collected from each dog, aseptically divided into 2 equal subunits, 1 of which was leukoreduced, and stored for 42 days. Stored units were sampled biweekly for quantification of NET markers citrullinated histone H3 (Western blot) and cell‐free DNA (cfDNA) (DNA dye binding). Unit supernatants were applied ex vivo to canine neutrophils and extracellular DNA release representing NETosis was assessed.

Results

Markers of NETs increased during RBC storage (cfDNA P < .0001 and citrullinated H3 P = .0002) and were higher in NLR than LR units (day 42 LR cfDNA 0.34 ± 0.82 ng/mL vs day 42 NLR 1361.07 ± 741.00 ng/mL, P < .0001; day 42 LR citrullinated H3 0.19 ± 0.13 AU vs NLR 0.57 ± 0.34 AU, P = .007). Isolated neutrophils did not form NETs when exposed to stored canine RBC supernatant.

Conclusions and Clinical Importance

NETosis occurs in stored canine NLR RBC units, and is attenuated by LR before storage. NETs might be mediators of transfusion reactions.

Prospective Cohort Study to Assess the Effect of Storage Duration, Leuko-Filtration, and Gamma Irradiation on Cell-Free DNA in Red Cell Components

Introduction

Damage to a cell and the loss of integrity of its cell membrane leads to the release of endogenous immunogenic molecules, which together are classified as "damage-associated molecular patterns" (DAMPs). Cell-free DNA (cf-DNA) released from nucleosomes may serve as a proco-agulant cofactor and may be an important mediator of immunomodulatory and proinflammatory effects associated with blood transfusion.

Objectives

To assess the levels of cf-DNA in supernatants of stored red cell components and the effect of leukoreduction and gamma irradiation on the release of cf-DNA during storage.

Methods

This is a prospective cohort study on 99 stored red cell components, randomly divided into three groups - buffy coat (BC)-depleted, leuko-filtered (LP), and irradiated (IR) packed red blood cells. Red cell supernatants were drawn over a period of 21 days at three different time points (day 0, 7, and 21) from the study units. cf-DNA extraction was done and quantified by a bench top fluorometer. Change in cf-DNA content, rate of change (μg/day), and percent change were estimated and compared across different groups.

Results

cf-DNA content increased (p = 0.000) with storage duration in the BC (median = 238.66 μg, interquartile range [IQR] = 168.42 on day 21 vs. median = 9.44 μg, IQR = 5.23 on day 0) and IR groups (p = 0.000) (median = 245.55 μg, IQR = 253.88 on day 21 vs. median = 7.07 μg, IQR = 13.58 on day 0), while there was a decreasing trend (p = 0.032) in the LP group (median = 4.55 μg, IQR = 10.73 on day 21 vs. median = 8.66 μg, IQR = 6.56 on day 0). The median rate of change in cf-DNA content (11.13 μg/day) and percent change in cf-DNA content (median = 4,106.16%) was highest in the IR group.

Conclusions

Stored red cell components contain significant amount of cf-DNA. Release of cf-DNA is further aggravated by irradiation while leukoreduction leads to a decrease in cf-DNA content.

Damage-associated molecular patterns in intensive care unit patients with acute liver injuries: A prospective cohort study

Acute liver injury (ALI) is frequently detected in an intensive care unit (ICU) and reportedly affects prognosis. Experimental animal studies suggested that increased extracellular histone and high morbidity group box-1 (HMGB1) levels might contribute to ALI development. Whether these damage-associated molecular patterns (DAMPs) play a crucial role in ALI remains unclear in the human clinical setting.We consecutively enrolled the patients admitted to our ICU. The patients with ALI were included in the analysis together with those without ALI by using frequency matching. Extracellular histone, HMGB1, soluble thrombomodulin (sTM), and interleukin-6 (IL-6) levels were measured in plasma collected at ICU admission. ALI was defined as an acute elevation in serum aminotransferase levels to >200 IU/L.A total of 805 patients were enrolled. Twenty ALI and forty non-ALI patients were analyzed. Plasma histone levels were significantly higher in the ALI group than in the non-ALI group, whereas HMGB1 levels were significantly lower in the ALI group. Furthermore, sTM was significantly increased in the ALI patients, whereas IL-6 levels were comparable between the groups. Multivariate logistic regression analysis demonstrated that histones were independently associated with ALI. There was no significant impact of ALI on in-hospital mortality.Extracellular histones showed an independent association with ALI. Histone elevation might be one of the possible pathogenic mechanisms in the development of ALI of ICU patients.

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.

Cell-Free DNA and DNase Activity in Dogs with Immune-Mediated Hemolytic Anemia

Background

Immune‐mediated hemolytic anemia (IMHA) in dogs has a high risk of thrombosis and is associated with marked neutrophilia and necrosis. Cell death and release of neutrophil extracellular traps contribute to increased serum concentrations of cell‐free DNA, and in human autoimmune disease reduced DNase activity further increases cell‐free DNA. Free DNA in blood has prothrombotic properties and could contribute to hypercoagulability in IMHA.

Hypothesis

Cell‐free DNA is elevated and DNase activity reduced in dogs with IMHA compared to healthy dogs.

Animals

Dogs presenting to two referral hospitals with IMHA (n = 28) and healthy controls (n = 20).

Methods

Prospective observational study. Blood was collected and death and thrombotic events occurring in the first 14 days after hospitalization recorded. DNA was extracted from plasma with a commercial kit and quantified by PicoGreen fluorescence. DNase activity of serum was measured by radial diffusion assay.

Results

Cell‐free DNA was significantly higher in cases (median: 45 ng/mL, range: 10–2334 ng/mL) than controls (26 ng/mL, range 1–151 ng/mL, P = 0.0084). DNase activity was not different between cases and controls (P = 0.36). Four cases died and there were five suspected or confirmed thrombotic events. Cell‐free DNA concentration was associated with death (odds ratio for upper quartile versus lower 3 quartiles: 15; 95% confidence interval 1.62–201; P = 0.03) but not thrombosis (P = 0.57).

Conclusions and Clinical Importance

Cell‐free DNA is elevated in dogs with IMHA and likely reflects increased release rather than impaired degradation of DNA. Cell‐free DNA concentration is potentially associated with death and might be a prognostic indicator, but this requires confirmation in a larger population.

Exploring donor and product factors and their impact on red cell post-transfusion outcomes

The impact of donor characteristics, red cell age, and red cell processing methods on recipient outcomes is an emerging area of research. Knowledge generated from exploring this transfusion continuum has the potential to change the way donors are selected and how donations are processed and stored with important clinical and operational impact. Recently, donor characteristics including age, gender, donation frequency, genetics, and ethnicity have been shown to affect product quality and possibly recipient outcomes. The structural, biochemical and immunological changes that occur with red cell storage appear to not cause harm to blood recipients after 14 randomized clinical trials. However, both in vitro and clinical data are now beginning to question the safety of blood stored for a shorter duration. Whole blood filtration, a method of blood processing, has been linked to inferior recipient outcomes when compared to red cell filtration. Collectively, this emerging body of literature suggests that pre-transfusion parameters impact product quality and recipient outcomes and that no 2 units of red cells are quite the same. This review will summarize both the pre-clinical and clinical studies evaluating these associations.

Valproic acid alters the content and function of the cell-free DNA released by hepatocellular carcinoma (HepG2) cells in vitro

BACKGROUND

It has long been believed that cell-free DNA (cfDNA) actively released into circulation can serve as intercellular messengers, and their involvement in processes such as the bystander effect strongly support this. However, this intercellular messaging function of cfDNA may have clinical implications that have not yet been considered.

METHODS

CfDNA was isolated from the growth medium of HepG2 cells treated with valproic acid (VPA). This cfDNA was then administered to untreated cells and cellular metabolic activity was measured.

RESULTS

VPA altered the characteristics of cfDNA released by treated HepG2 cells in vitro. When administered to untreated cells, the cfDNA from cells treated with VPA resulted in the dose-dependent induction of glycolytic activity within 36 min of administration, but little to no alterations in oxidative phosphorylation. The glycolytic activity lasted for 4-6 h, whereas changes in subsequent cfDNA release and characteristics were found to remain persistent after two 24 h treatments. Fragmented genomic DNA from VPA-treated cells did not induce the effects observed for cfDNA obtained VPA-treated cells.

CONCLUSIONS

It is possible for cfDNA to, under in vitro conditions, transfer pharmaceutically-induced effects to untreated recipient cells. Further investigation regarding this occurrence under in vivo conditions is, therefore, strongly encouraged.

GENERAL SIGNIFICANCE

The intercellular messaging functions of cfDNA present in donated biological fluids has potential clinical implications that require urgent attention. These implications may, however, also have potential as new forms of treatment that can circumvent pharmacological barriers.

Gestational Diabetes Mellitus Is Associated with Altered Neutrophil Activity

Gestational diabetes mellitus (GDM) is a unique form of glucose intolerance, in that it is transient and solely occurs in pregnancy. Pregnancies with GDM are at high risk of developing preeclampsia (PE), a leading cause of fetal and maternal morbidity or mortality. Since PE is associated with excessive activation of circulatory neutrophils and occurrence of neutrophil extracellular traps (NETs) in affected placentae, we examined these features in cases with GDM, as this could be a feature linking the two conditions. Our data indicate that neutrophil activity is indeed altered in GDM, exhibiting pronounced activation and spontaneous generation of NETs by isolated neutrophils in in vitro culture. In this manner, GDM may similarly affect neutrophil behavior and NET formation as witnessed in other forms of diabetes, with the addition of the physiological changes mediated by pregnancy. Since circulatory TNF-α levels are elevated in cases with GDM, a feature also observed in this study, we examined whether this pro-inflammatory cytokine contributed to neutrophil activation. By using infliximab, a clinically utilized TNF-α antagonist, we observed that the pro-NETotic effect of GDM sera was significantly reduced. We also detected pronounced neutrophil infiltrates in placentae from GDM cases. The occurrence of NETs in these tissues is suggested by the extracellular co-localization of citrullinated histones and myeloperoxidase. In addition, elevated neutrophil elastase (NE) mRNA and active enzymatic protein were also detected in such placentae. This latter finding could be important in the context of previous studies in cancer or diabetes model systems, which indicated that NE liberated from infiltrating neutrophils enters surrounding cells, altering cell signaling by the degradation of IRS1. These findings could potentiate the underlying inflammatory response process in GDM and possibly open an avenue for the therapeutic interventions in gestational hyperglycemia.

Cell-free DNA from human plasma and serum differs in content of telomeric sequences and its ability to promote immune response

Circulating cell-free DNA (cfDNA) may be involved in immune response regulation. We studied the variations in abundance of telomeric sequences in plasma and serum in young healthy volunteers and the ability of cfDNA contained in these samples to co-activate the TNF-α m RNA expression in monocytes. We performed qPCR to determine relative telomere length (T/S ratios) in plasma, serum and whole blood of 36 volunteers. Using paired samples of plasma and serum and DNase treatment, we analysed the contribution of cfDNA to the co-activation of TNF-α mRNA expression in THP1 monocytic cell line. We found significant differences between paired plasma and serum samples in relative T/S ratios (median 1.38 ± 1.1 vs. 0.86 ± 0.25, respectively) and in total amounts of cfDNA and in estimated total amounts of telomeres which were significantly higher in serum than in plasma. TNF-α mRNA expression in THP1 cells increased significantly after DNase treatment of all samples used for stimulation. The highest TNF-α mRNA expressions were observed after stimulation with DNase treated serum samples. Our results suggest that the different content of telomeric sequences in plasma and serum may contribute to the tuning of immune response. Further studies of this interesting phenomenon are needed.

Neutrophil extracellular trap formation and circulating nucleosomes in patients with chronic myeloproliferative neoplasms

The mechanisms underlying increased thrombotic risk in chronic myeloproliferative neoplasms (MPN) are incompletely understood. We assessed whether neutrophil extracellular traps (NETs), which promote thrombosis, contribute to the procoagulant state in essential thrombocythemia, polycythemia vera and myelofibrosis (MF) patients. Although MPN neutrophils showed increased basal reactive oxygen species (ROS), enhanced NETosis by unstimulated neutrophils was an infrequent finding, whereas PMA-triggered NETosis was impaired, particularly in MF, due to decreased PMA-triggered ROS production. Elevated circulating nucleosomes were a prominent finding and were higher in patients with advanced disease, which may have potential prognostic implication. Histone-MPO complexes, proposed as specific NET biomarker, were seldomly detected, suggesting NETs may not be the main source of nucleosomes in most patients, whereas their correlation with high LDH points to increased cell turn-over as a plausible origin. Lack of association of nucleosomes or NETs with thrombosis or activation markers does not support their use as predictors of thrombosis although prospective studies in a larger cohort may help define their potential contribution to MPN thrombosis. These results do not provide evidence for relevant in vivo NETosis in MPN patients under steady state conditions, although availability of standardized NET biomarkers may contribute to further research in this field.

Quantification of Cell-Free DNA in Red Blood Cell Units in Different Whole Blood Processing Methods

Background. Whole blood donations in Canada are processed by either the red cell filtration (RCF) or whole blood filtration (WBF) methods, where leukoreduction is potentially delayed in WBF. Fresh WBF red blood cells (RBCs) have been associated with increased in-hospital mortality after transfusion. Cell-free DNA (cfDNA) is released by neutrophils prior to leukoreduction, degraded during RBC storage, and is associated with adverse patient outcomes. We explored cfDNA levels in RBCs prepared by RCF and WBF and different storage durations. Methods. Equal numbers of fresh (stored ≤14 days) and older RBCs were sampled. cfDNA was quantified by spectrophotometry and PicoGreen. Separate regression models determined the association with processing method and storage duration and their interaction on cfDNA. Results. cfDNA in 120 RBC units (73 RCF, 47 WBF) were measured. Using PicoGreen, WBF units overall had higher cfDNA than RCF units (p = 0.0010); fresh WBF units had higher cfDNA than fresh RCF units (p = 0.0093). Using spectrophotometry, fresh RBC units overall had higher cfDNA than older units (p = 0.0031); fresh WBF RBCs had higher cfDNA than older RCF RBCs (p = 0.024). Conclusion. Higher cfDNA in fresh WBF was observed compared to older RCF blood. Further study is required for association with patient outcomes.

The Role of Physical Stabilization in Whole Blood Preservation

The rapid degradation of blood ex vivo imposes logistical limitations on the utilization of blood-borne cells in medical diagnostics and scientific investigations. A fundamental but overlooked aspect in the storage of this fluid tissue is blood settling, which induces physical stress and compaction, aggregates blood cells, and causes collateral damage due to leukocyte activation. Here we show that the polymer Ficoll 70 kDa stabilized blood samples and prevented blood settling over the course of 72 hours, primarily by inhibiting depletion-mediated red blood cell aggregation. Physical stabilization decreased echinocyte formation, improved leukocyte viability, and inhibited the release of neutrophil elastase—a marker of neutrophil extracellular trap formation. In addition, Ficoll-stabilized blood was compatible with common leukocyte enrichment techniques including red blood cell lysis and immunomagnetic purification. This study showed for the first time that blood settling can be prevented using polymers and has implications in diagnostics.

Neutrophil extracellular traps: a walk on the wild side of exercise immunology

Intense exercise evokes a rapid and transient increase in circulating cell-free DNA (cf-DNA), a phenomenon that is commonly observed in a variety of acute and chronic inflammatory conditions. While the potential value of cf-DNA for the prediction of disease outcome and therapeutic response is well documented, the release mechanisms and biological relevance of cf-DNA have long remained enigmatic. The discovery of neutrophil extracellular traps (NETs) provided a novel mechanistic explanation for increased cf-DNA levels. Now there is increasing evidence that NETs may contribute to cf-DNA in diverse infectious, non-infectious and autoinflammatory conditions, as well as in response to acute exercise. NETs have now been firmly established as a fundamental immune mechanism used by neutrophils to respond to infection and tissue injury. On the other side, aberrant formation of NETs appears to be a driving force in the pathogenesis of autoimmunity and cardiovascular disease. Thus, the emergence of NETs in the 'exercising vasculature' raises important questions considering beneficial effects, as well as occasional adverse effects, of exercise on immune homeostasis. This review gives an overview of the current state of research into the mechanisms of how NETs are released, contribute to host defence and participate in inflammatory disorders. We discuss the impact of exercise-induced NETs, considering a potentially beneficial role in the prevention of lifestyle-related diseases, as well as putative detrimental effects that may arise in elite sports. Finally, we propose that exercise-induced cf-DNA responses could be exploited for diagnostic/prognostic purposes to identify individuals who are at increased risk of cardiovascular events or autoimmunity.

Nouvelle cuisine: platelets served with inflammation

Platelets are small cellular fragments with the primary physiological role of maintaining hemostasis. In addition to this well-described classical function, it is becoming increasingly clear that platelets have an intimate connection with infection and inflammation. This stems from several platelet characteristics, including their ability to bind infectious agents and secrete many immunomodulatory cytokines and chemokines, as well as their expression of receptors for various immune effector and regulatory functions, such as TLRs, which allow them to sense pathogen-associated molecular patterns. Furthermore, platelets contain RNA that can be nascently translated under different environmental stresses, and they are able to release membrane microparticles that can transport inflammatory cargo to inflammatory cells. Interestingly, acute infections can also result in platelet breakdown and thrombocytopenia. This report highlights these relatively new aspects of platelets and, thus, their nonhemostatic nature in an inflammatory setting.

Circulating histones in inflammation and cancer

Histones are highly-conserved and positively-charged proteins expressed in various types of eukaryotic cells and some archaea. Inside nuclei, histones are fundamental components of nucleosomes, which are the structural units of chromatin. Histones and their post-translational modifications play vital roles in chromatin construction and gene transcription. Besides intranuclear functions, histones act as damage-associated molecular pattern molecules (DAMP) when released into the extracellular space. The circulating histones lead to systemic inflammatory and toxic responses through activating Toll-like receptors (TLR) (e.g., TLR2, TLR4 and TLR9) and inflammasome pathways. Anti-histone treatment (e.g., neutralizing antibodies, activated protein C, recombinant thrombomodulin, heparin and albumin) protects mice against sterile and non-sterile inflammation. In addition, elevated serum histone and nucleosome levels have been implicated in multiple pathophysiological processes and progression of diseases including inflammatory diseases and cancer. This review will focus on the role of circulating histones in inflammation and cancer.

Release and activity of histone in diseases

Histones and their post-translational modifications have key roles in chromatin remodeling and gene transcription. Besides intranuclear functions, histones act as damage-associated molecular pattern molecules when they are released into the extracellular space. Administration of exogenous histones to animals leads to systemic inflammatory and toxic responses through activating Toll-like receptors and inflammasome pathways. Anti-histone treatment (e.g., neutralizing antibodies, activated protein C, recombinant thrombomodulin, and heparin) protect mice against lethal endotoxemia, sepsis, ischemia/reperfusion injury, trauma, pancreatitis, peritonitis, stroke, coagulation, and thrombosis. In addition, elevated serum histone and nucleosome levels have been implicated in multiple pathophysiological processes and progression of diseases including autoimmune diseases, inflammatory diseases, and cancer. Therefore, extracellular histones could serve as biomarkers and novel therapeutic targets in human diseases.

Enhanced neutrophil extracellular trap generation in rheumatoid arthritis: analysis of underlying signal transduction pathways and potential diagnostic utility

INTRODUCTION

Neutrophil extracellular traps (NETs) have recently been implicated in a number of autoimmune conditions, including rheumatoid arthritis (RA). We examined the underlying signaling pathways triggering enhanced NETosis in RA and ascertained whether the products of NETosis had diagnostic implications or usefulness.

METHODS

Neutrophils were isolated from RA patients with active disease and from controls. Spontaneous NET formation from RA and control neutrophils was assessed in vitro with microscopy and enzyme-linked immunosorbent assay (ELISA) for NETosis-derived products. The analysis of the signal-transduction cascade included reactive oxygen species (ROS) production, myeloperoxidase (MPO), neutrophil elastase (NE), peptidyl arginine deiminase 4 (PAD4), and citrullinated histone 3 (citH3). NET formation was studied in response to serum and synovial fluid and immunoglobulin G (IgG) depleted and reconstituted serum. Serum was analyzed for NETosis-derived products, for which receiver operator characteristic (ROC) curves were calculated.

RESULTS

Neutrophils from RA cases exhibited increased spontaneous NET formation in vitro, associated with elevated ROS production, enhanced NE and MPO expression, nuclear translocation of PAD4, PAD4-mediated citrullination of H3, and altered nuclear morphology. NET formation in both anti-citrullinated peptide antibody (ACPA)-positive and -negative RA was abolished by IgG depletion, but restored only with ACPA-positive IgG. NETosis-derived products in RA serum demonstrated diagnostic potential, the ROC area under the curve for cell-free nucleosomes being >97%, with a sensitivity of 91% and a specificity of 92%. No significant difference was observed between ACPA-positive and -negative cases.

CONCLUSIONS

Signaling elements associated with the extrusion of NETs are significantly enhanced to promote NETosis in RA compared with healthy controls. NETosis depended on the presence of ACPA in ACPA-positive RA serum. The quantitation of NETosis-derived products, such as cell-free nucleosomes in serum, may be a useful complementary tool to discriminate between healthy controls and RA cases.

Neutrophils release extracellular DNA traps in response to exercise

Intense exercise evokes a rapid and transient increase in circulating cell-free DNA (cf-DNA), a phenomenon that is commonly observed in a variety of acute and chronic inflammatory conditions. In this study, we aimed to shed new light on the release and clearance mechanisms of cf-DNA in response to exercise. We hypothesized that activated neutrophils may primarily contribute to exercise-evoked cf-DNA levels by releasing neutrophil extracellular traps (NETs). Analysis of plasma and/or serum samples from male athletes at rest and in response to exhaustive treadmill exercise revealed an immediate and transient increase in cf-DNA that was concomitantly counterbalanced by an increase in serum DNase activity. Consistently, rapid release and clearance kinetics for cf-DNA could also be observed in response to intensive cycling exercise, with no significant differences between endurance-trained (V̇o2max >57 ml·min(-1)·kg(-1)) and healthy (V̇o2max <49 ml·min(-1)·kg(-1)) sedentary individuals. In postexercise blood smear samples, we detected seemingly intact neutrophils displaying morphological signs of NET release, as indicated by abnormal swollen nuclei and emanating DNA fibers. In support, we observed a striking correlation of postexercise cf-DNA concentrations with plasma levels of the granule-derived enzyme myeloperoxidase. Our study indicates that intense exercise induces liberation of NETs, which is sufficiently counterbalanced in healthy individuals by a concomitant rise in serum DNase activity. As aberrant release of NETs has been linked to diverse disease states, monitoring of cf-DNA/DNase levels or activities in response to standardized exercise testing could provide a valuable tool to identify people who are at increased risk for cardiac ischemia, thrombosis, autoimmunity, or chronic fatigue.

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.

Thrombosis: tangled up in NETs

The contributions by blood cells to pathological venous thrombosis were only recently appreciated. Both platelets and neutrophils are now recognized as crucial for thrombus initiation and progression. Here we review the most recent findings regarding the role of neutrophil extracellular traps (NETs) in thrombosis. We describe the biological process of NET formation (NETosis) and how the extracellular release of DNA and protein components of NETs, such as histones and serine proteases, contributes to coagulation and platelet aggregation. Animal models have unveiled conditions in which NETs form and their relation to thrombogenesis. Genetically engineered mice enable further elucidation of the pathways contributing to NETosis at the molecular level. Peptidylarginine deiminase 4, an enzyme that mediates chromatin decondensation, was identified to regulate both NETosis and pathological thrombosis. A growing body of evidence reveals that NETs also form in human thrombosis and that NET biomarkers in plasma reflect disease activity. The cell biology of NETosis is still being actively characterized and may provide novel insights for the design of specific inhibitory therapeutics. After a review of the relevant literature, we propose new ways to approach thrombolysis and suggest potential prophylactic and therapeutic agents for thrombosis.