Histone-Complexed DNA Fragments Levels are Associated with Coagulopathy, Endothelial Cell Damage, and Increased Mortality after Severe Pediatric Trauma

ENDOTHELIAL-SPECIFIC KNOCKOUT OF THE SCRAMBLASE TMEM16F IMPAIRS IN VIVO CLOT FORMATION

ABSTRACT

Objective: Loss of function of the phospholipid scramblase (PLS) TMEM16F results in Scott syndrome, a hereditary bleeding disorder generally attributed to intrinsic platelet dysfunction. The role of TMEM16F in endothelial cells, however, is not well understood. We sought to test the hypothesis that endothelial TMEM16F contributes to hemostasis by measuring bleeding time and venous clotting in endothelial-specific knockout (ECKO) mice. Materials and Methods: We initially evaluated the extent to which TMEM16F contributes to endothelial calcium events produced by trauma factors in vitro using a pharmacological approach. Cultured endothelial cells were exposed to histones in the presence or absence of the PLS inhibitor, niclosamide, for live-cell calcium imaging and flow cytometry with annexin V staining. We then applied a genetic approach to specifically ablate TMEM16F in vascular endothelial cells in vivo using a murine tamoxifen-inducible cre-lox system under control of a Cdh5 promoter. Hemostasis was evaluated by measuring tail bleeding time after a distal 5-mm tail resection. Venous thrombus formation was evaluated by creating a surgical stenosis of the inferior vena cava (IVC) and harvesting the resultant clot 24 h after procedure for measurement. Blood samples were obtained via IVC cannulation to assay plasma-based coagulation. Mesenteric arteries were isolated and cannulated for assessment of endothelial-dependent vasodilation by pressure myography. Results: Pretreatment with the PLS inhibitor niclosamide prevented pathological calcium signals and mitigated phosphatidylserine translocation in cultured endothelial cells exposed to extracellular histones. TMEM16F ECKO mice exhibited prolonged bleeding compared to controls (time, 205.6 ± 234.5 vs. 38.1 ± 29.11 s; P < 0.05). The ECKO mice also generated significantly smaller IVC thrombi (length, 0.9 ± 1.4 vs. 4.7 ± 3.3 mm; P < 0.05). TMEM16F ablation did not impact prothrombin time or endothelial-dependent vasodilatory function. Conclusions: Endothelial TMEM16F function is essential for normal hemostasis. ECKO of TMEM16F is sufficient to produce a coagulopathic phenotype, as shown by the prolonged bleeding time after tail transection and decreased thrombus generation in response to IVC stenosis. Because endothelial calcium events are pathologically amplified in response to trauma factors, these results suggest that TMEM16F may play a role in trauma-induced coagulopathy.

Patterns of trauma-induced coagulopathy in injured children: A principal component analysis investigating endothelial, coagulation, and platelet biomarkers

BACKGROUND

Trauma-induced coagulopathy is common and associated with poor outcomes in injured children. Our aim was to identify patterns of coagulopathy after injury using endothelial, platelet, and coagulation biomarkers, and associate these phenotypes with relevant patient factors and clinical outcomes in a pediatric trauma cohort.

METHODS

Principal component (PC) analysis was performed on data from injured children between 2018 and 2022. Laboratories included endothelial markers (syndecan-1, thrombomodulin, tissue factor, and vascular endothelial growth factor), international normalized ratio, platelet count, rapid thromboelastography maximum amplitude, and base deficit. Variables were reduced to PCs; PC scores were generated for each subject and used in logistic regression with outcomes including mortality, blood transfusion, shock (pediatric-adjusted shock index), and patient characteristics including age, sex, injury mechanism, and traumatic brain injury.

RESULTS

In total, 59 children had complete data for analysis. Median (interquartile range) age was 10 (4-14) years, 31% female, 21% penetrating mechanism, and median (interquartile range) injury severity score of 16 (9-21). Principal component analysis identified two significant PCs accounting for 67% of overall variance. PC1 included syndecan-1, thrombomodulin, vascular endothelial growth factor, international normalized ratio, and base deficit; PC1 scores were associated with mortality, blood transfusion, and shock (all p < 0.001). PC2 included tissue factor, platelet count, and rapid thromboelastography maximum amplitude; PC2 scores were associated with age (ρ = -0.42, p = 0.001) but no studied clinical outcome. Neither PC was significantly associated with sex, injury mechanism, or traumatic brain injury.

CONCLUSION

Principal component analysis detected two distinct biomarker patterns in injured children involving the domains of the endothelium, coagulation, and platelets. The first phenotype was associated with poor clinical outcomes, while the second was associated with age. This supports the concept that pediatric trauma-induced coagulopathy elicits a heterogeneous response, and suggests that there may be a prognostic value to these phenotypes that warrants further investigation.

LEVEL OF EVIDENCE

Prognostic and Epidemiological; Level IV.

Sepsis-Induced Endothelial Dysfunction: Permeability and Regulated Cell Death

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Endothelial cells (ECs) are an important cell type typically affected in sepsis, resulting in compromised barrier function and various forms of regulated cell death (RCD). However, the precise mechanisms underlying sepsis-induced EC damage remain unclear. This review summarizes the recent research progress on factors and mechanisms that may affect the permeability and RCD of ECs under septic conditions, including glycocalyx, damage-associated molecular patterns, and various forms of RCD in ECs, such as apoptosis, pyroptosis, ferroptosis, and autophagy. This review offers important insights into the underlying mechanisms of endothelial dysfunction in sepsis, aiming to contribute to developing small-molecule targeted clinical therapies.

Recombinant thrombomodulin and recombinant antithrombin attenuate pulmonary endothelial glycocalyx degradation and neutrophil extracellular trap formation in ventilator-induced lung injury in the context of endotoxemia

BACKGROUND

Vascular endothelial damage is involved in the development and exacerbation of ventilator-induced lung injury (VILI). Pulmonary endothelial glycocalyx and neutrophil extracellular traps (NETs) are endothelial protective and damaging factors, respectively; however, their dynamics in VILI and the effects of recombinant thrombomodulin and antithrombin on these dynamics remain unclear. We hypothesized that glycocalyx degradation and NETs are induced by VILI and suppressed by recombinant thrombomodulin, recombinant antithrombin, or their combination.

METHODS

VILI was induced in male C57BL/6J mice by intraperitoneal lipopolysaccharide injection (20 mg/kg) and high tidal volume ventilation (20 mL/kg). In the intervention groups, recombinant thrombomodulin, recombinant antithrombin, or their combination was administered at the start of mechanical ventilation. Glycocalyx degradation was quantified by measuring serum syndecan-1, fluorescence-labeled lectin intensity, and glycocalyx-occupied area in the pulmonary vascular lumen. Double-stranded DNA in the bronchoalveolar fluid and fluorescent areas of citrullinated histone H3 and myeloperoxidase were quantified as NET formation.

RESULTS

Serum syndecan-1 increased, and lectin fluorescence intensity decreased in VILI. Electron microscopy revealed decreases in glycocalyx-occupied areas within pulmonary microvessels in VILI. Double-stranded DNA levels in the bronchoalveolar lavage fluid and the fluorescent area of citrullinated histone H3 and myeloperoxidase in lung tissues increased in VILI. Recombinant thrombomodulin, recombinant antithrombin, and their combination reduced glycocalyx injury and NET marker levels. There was little difference in glycocalyx injury and NET makers between the intervention groups.

CONCLUSION

VILI induced glycocalyx degradation and NET formation. Recombinant thrombomodulin and recombinant antithrombin attenuated glycocalyx degradation and NETs in our VILI model. The effect of their combination did not differ from that of either drug alone. Recombinant thrombomodulin and antithrombin have the potential to be therapeutic agents for biotrauma in VILI.

Self-DNA driven inflammation in COVID-19 and after mRNA-based vaccination: lessons for non-COVID-19 pathologies

The coronavirus disease 2019 (COVID-19) pandemic triggered an unprecedented concentration of economic and research efforts to generate knowledge at unequalled speed on deregulated interferon type I signalling and nuclear factor kappa light chain enhancer in B-cells (NF-κB)-driven interleukin (IL)-1β, IL-6, IL-18 secretion causing cytokine storms. The translation of the knowledge on how the resulting systemic inflammation can lead to life-threatening complications into novel treatments and vaccine technologies is underway. Nevertheless, previously existing knowledge on the role of cytoplasmatic or circulating self-DNA as a pro-inflammatory damage-associated molecular pattern (DAMP) was largely ignored. Pathologies reported 'de novo' for patients infected with Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 to be outcomes of self-DNA-driven inflammation in fact had been linked earlier to self-DNA in different contexts, e.g., the infection with Human Immunodeficiency Virus (HIV)-1, sterile inflammation, and autoimmune diseases. I highlight particularly how synergies with other DAMPs can render immunogenic properties to normally non-immunogenic extracellular self-DNA, and I discuss the shared features of the gp41 unit of the HIV-1 envelope protein and the SARS-CoV 2 Spike protein that enable HIV-1 and SARS-CoV-2 to interact with cell or nuclear membranes, trigger syncytia formation, inflict damage to their host's DNA, and trigger inflammation - likely for their own benefit. These similarities motivate speculations that similar mechanisms to those driven by gp41 can explain how inflammatory self-DNA contributes to some of most frequent adverse events after vaccination with the BNT162b2 mRNA (Pfizer/BioNTech) or the mRNA-1273 (Moderna) vaccine, i.e., myocarditis, herpes zoster, rheumatoid arthritis, autoimmune nephritis or hepatitis, new-onset systemic lupus erythematosus, and flare-ups of psoriasis or lupus. The hope is to motivate a wider application of the lessons learned from the experiences with COVID-19 and the new mRNA vaccines to combat future non-COVID-19 diseases.

Mechanism matters: mortality and endothelial cell damage marker differences between blunt and penetrating traumatic injuries across three prehospital clinical trials

Injury mechanism is an important consideration when conducting clinical trials in trauma. Mechanisms of injury may be associated with differences in mortality risk and immune response to injury, impacting the potential success of the trial. We sought to characterize clinical and endothelial cell damage marker differences across blunt and penetrating injured patients enrolled in three large, prehospital randomized trials which focused on hemorrhagic shock. In this secondary analysis, patients with systolic blood pressure < 70 or systolic blood pressure < 90 and heart rate > 108 were included. In addition, patients with both blunt and penetrating injuries were excluded. The primary outcome was 30-day mortality. Mortality was characterized using Kaplan-Meier and Cox proportional-hazards models. Generalized linear models were used to compare biomarkers. Chi squared tests and Wilcoxon rank-sum were used to compare secondary outcomes. We characterized data of 696 enrolled patients that met all secondary analysis inclusion criteria. Blunt injured patients had significantly greater 24-h (18.6% vs. 10.7%, log rank p = 0.048) and 30-day mortality rates (29.7% vs. 14.0%, log rank p = 0.001) relative to penetrating injured patients with a different time course. After adjusting for confounders, blunt mechanism of injury was independently predictive of mortality at 30-days (HR 1.84, 95% CI 1.06-3.20, p = 0.029), but not 24-h (HR 1.65, 95% CI 0.86-3.18, p = 0.133). Elevated admission levels of endothelial cell damage markers, VEGF, syndecan-1, TM, S100A10, suPAR and HcDNA were associated with blunt mechanism of injury. Although there was no difference in multiple organ failure (MOF) rates across injury mechanism (48.4% vs. 42.98%, p = 0.275), blunt injured patients had higher Denver MOF score (p < 0.01). The significant increase in 30-day mortality and endothelial cell damage markers in blunt injury relative to penetrating injured patients highlights the importance of considering mechanism of injury within the inclusion and exclusion criteria of future clinical trials.

The Polyanionic Drug Suramin Neutralizes Histones and Prevents Endotheliopathy

Drugs are needed to protect against the neutrophil-derived histones responsible for endothelial injury in acute inflammatory conditions such as trauma and sepsis. Heparin and other polyanions can neutralize histones but challenges with dosing or side effects such as bleeding limit clinical application. In this study, we demonstrate that suramin, a widely available polyanionic drug, completely neutralizes the toxic effects of individual histones, but not citrullinated histones from neutrophil extracellular traps. The sulfate groups on suramin form stable electrostatic interactions with hydrogen bonds in the histone octamer with a dissociation constant of 250 nM. In cultured endothelial cells (Ea.Hy926), histone-induced thrombin generation was significantly decreased by suramin. In isolated murine blood vessels, suramin abolished aberrant endothelial cell calcium signals and rescued impaired endothelial-dependent vasodilation caused by histones. Suramin significantly decreased pulmonary endothelial cell ICAM-1 expression and neutrophil recruitment caused by infusion of sublethal doses of histones in vivo. Suramin also prevented histone-induced lung endothelial cell cytotoxicity in vitro and lung edema, intra-alveolar hemorrhage, and mortality in mice receiving a lethal dose of histones. Protection of vascular endothelial function from histone-induced damage is a novel mechanism of action for suramin with therapeutic implications for conditions characterized by elevated histone levels.

Extracellular histones as damage-associated molecular patterns in neuroinflammatory responses

The four core histones H2A, H2B, H3, H4, and the linker histone H1 primarily bind DNA and regulate gene expression within the nucleus. Evidence collected mainly from the peripheral tissues illustrates that histones can be released into the extracellular space by activated or damaged cells. In this article, we first summarize the innate immune-modulatory properties of extracellular histones and histone-containing complexes, such as nucleosomes, and neutrophil extracellular traps (NETs), described in peripheral tissues. There, histones act as damage-associated molecular patterns (DAMPs), which are a class of endogenous molecules that trigger immune responses by interacting directly with the cellular membranes and activating pattern recognition receptors (PRRs), such as toll-like receptors (TLR) 2, 4, 9 and the receptor for advanced glycation end-products (RAGE). We then focus on the available evidence implicating extracellular histones as DAMPs of the central nervous system (CNS). It is becoming evident that histones are present in the brain parenchyma after crossing the blood-brain barrier (BBB) or being released by several types of brain cells, including neurons, microglia, and astrocytes. However, studies on the DAMP-like effects of histones on CNS cells are limited. For example, TLR4 is the only known molecular target of CNS extracellular histones and their interactions with other PRRs expressed by brain cells have not been observed. Nevertheless, extracellular histones are implicated in the pathogenesis of a variety of neurological disorders characterized by sterile neuroinflammation; therefore, detailed studies on the role these proteins and their complexes play in these pathologies could identify novel therapeutic targets.

Extracellular histone proteins activate P2XR7 channel current

Extracellular histone proteins are elevated in circulation after injury or activation of the innate immune response. In resistance-size arteries, extracellular histone proteins increased endothelial cell (EC) Ca2+ influx and propidium iodide (PI) labeling, but paradoxically decreased vasodilation. These observations could be explained by the activation of an EC resident non-selective cation channel. We tested the hypothesis that the ionotropic purinergic receptor 7 (P2XR7), a non-selective cation channel associated with cationic dye uptake, is activated by histone proteins. We expressed mouse P2XR7 (C57BL/6J variant 451L) in heterologous cells and measured inward cation current using two-electrode voltage clamp (TEVC). Cells expressing mouse P2XR7 had robust ATP- and histone-evoked inward cation currents. ATP- and histone-evoked currents reversed approximately at the same potential. Current decay with agonist removal was slower for histone-evoked than ATP- or BzATP-evoked currents. As with ATP-evoked P2XR7 currents, histone-evoked currents were inhibited by non-selective P2XR7 antagonists (Suramin, PPADS, and TNP-ATP). Selective P2XR7 antagonists, AZ10606120, A438079, GW791343, and AZ11645373, inhibited ATP-evoked P2XR7 currents but did not inhibit histone-evoked P2XR7 currents. As previously reported with ATP-evoked currents, histone-evoked P2XR7 currents were also increased in conditions of low extracellular Ca2+. These data demonstrate that P2XR7 is necessary and sufficient for histone-evoked inward cation currents in a heterologous expression system. These results provide insight into a new allosteric mechanism of P2XR7 activation by histone proteins.

Neutrophil, neutrophil extracellular traps and endothelial cell dysfunction in sepsis

Sepsis is a persistent systemic inflammatory condition involving multiple organ failures resulting from a dysregulated immune response to infection, and one of the hallmarks of sepsis is endothelial dysfunction. During its progression, neutrophils are the first line of innate immune defence against infection. Aside from traditional mechanisms, such as phagocytosis or the release of inflammatory cytokines, reactive oxygen species and other antibacterial substances, activated neutrophils also release web-like structures composed of tangled decondensed DNA, histone, myeloperoxidase and other granules called neutrophil extracellular traps (NETs), which can efficiently ensnare bacteria in the circulation. In contrast, excessive neutrophil activation and NET release may induce endothelial cells to shift toward a pro-inflammatory and pro-coagulant phenotype. Furthermore, neutrophils and NETs can degrade glycocalyx on the endothelial cell surface and increase endothelium permeability. Consequently, the endothelial barrier collapses, contributing to impaired microcirculatory blood flow, tissue hypoperfusion and life-threatening organ failure in the late phase of sepsis.

Pediatric traumatic hemorrhagic shock consensus conference research priorities

BACKGROUND

Traumatic injury is the leading cause of death in children and adolescents. Hemorrhagic shock remains a common and preventable cause of death in the pediatric trauma patients. A paucity of high-quality evidence is available to guide specific aspects of hemorrhage control in this population. We sought to identify high-priority research topics for the care of pediatric trauma patients in hemorrhagic shock.

METHODS

A panel of 16 consensus multidisciplinary committee members from the Pediatric Traumatic Hemorrhagic Shock Consensus Conference developed research priorities for addressing knowledge gaps in the care of injured children and adolescents in hemorrhagic shock. These ideas were informed by a systematic review of topics in this area and a discussion of these areas in the consensus conference. Research priorities were synthesized along themes and prioritized by anonymous voting.

RESULTS

Eleven research priorities that warrant additional investigation were identified by the consensus committee. Areas of proposed study included well-designed clinical trials and evaluations, including increasing the speed and accuracy of identifying and treating hemorrhagic shock, defining the role of whole blood and tranexamic acid use, and assessment of the utility and appropriate use of viscoelastic techniques during early resuscitation. The committee recommended the need to standardize essential definitions, data elements, and data collection to facilitate research in this area.

CONCLUSION

Research gaps remain in many areas related to the care of hemorrhagic shock after pediatric injury. Addressing these gaps is needed to develop improved evidence-based recommendations for the care of pediatric trauma patients in hemorrhagic shock.

Pediatric traumatic hemorrhagic shock consensus conference recommendations

ABSTRACT

Hemorrhagic shock in pediatric trauma patients remains a challenging yet preventable cause of death. There is little high-quality evidence available to guide specific aspects of hemorrhage control and specific resuscitation practices in this population. We sought to generate clinical recommendations, expert consensus, and good practice statements to aid providers in care for these difficult patients.The Pediatric Traumatic Hemorrhagic Shock Consensus Conference process included systematic reviews related to six subtopics and one consensus meeting. A panel of 16 consensus multidisciplinary committee members evaluated the literature related to 6 specific topics: (1) blood products and fluid resuscitation for hemostatic resuscitation, (2) utilization of prehospital blood products, (3) use of hemostatic adjuncts, (4) tourniquet use, (5) prehospital airway and blood pressure management, and (6) conventional coagulation tests or thromboelastography-guided resuscitation. A total of 21 recommendations are detailed in this article: 2 clinical recommendations, 14 expert consensus statements, and 5 good practice statements. The statement, the panel's voting outcome, and the rationale for each statement intend to give pediatric trauma providers the latest evidence and guidance to care for pediatric trauma patients experiencing hemorrhagic shock. With a broad multidisciplinary representation, the Pediatric Traumatic Hemorrhagic Shock Consensus Conference systematically evaluated the literature and developed clinical recommendations, expert consensus, and good practice statements concerning topics in traumatically injured pediatric patients with hemorrhagic shock.

Mechanisms of pulmonary endothelial permeability and inflammation caused by extracellular histone subunits H3 and H4

Extracellular DNA-binding proteins such as histones are danger-associated molecular pattern released by the injured tissues in trauma and sepsis settings, which trigger host immune response and vascular dysfunction. Molecular events leading to histone-induced endothelial cell (EC) dysfunction remain poorly understood. This study performed comparative analysis of H1, H2A, H2B, H3, and H4 histone subunits effects on human pulmonary EC permeability and inflammatory response. Analysis of transendothelial electrical resistance and EC monolayer permeability for macromolecues revealed that H3 and H4, but not H1, H2A, or H2B caused dose-dependent EC permeability accompanied by disassembly of adherens junctions. At higher doses, H3 and H4 activated nuclear factor kappa B inflammatory cascade leading to upregulation EC adhesion molecules ICAM1, VCAM1, E-selectin, and release of inflammatory cytokines. Inhibitory receptor analysis showed that toll-like receptor (TLR) 4 but not TLR1/2 or receptor for advanced glycation end inhibition significantly attenuated deleterious effects of H3 and H4 histones. Inhibitor of Rho-kinase was without effect, while inhibition of Src kinase caused partial preservation of cell-cell junctions, H3/H4-induced permeability and inflammation. Deleterious effects of H3/H4 were blocked by heparin. Activation of Epac-Rap1 signaling restored EC barrier properties after histone challenge. Intravenous injection of histones in mice caused elevation of inflammatory markers and increased vascular leak. Post-treatment with pharmacological Epac/Rap1 activator suppressed injurious effects of histones in vitro and in vivo. These results identify H3 and H4 as key histone subunits exhibiting deleterious effects on pulmonary vascular endothelium via TLR4-dependent mechanism. In conclusion, elevation of circulating histones may represent a serious risk of exacerbated acute lung injury (ALI) and multiple organ injury during severe trauma and infection.

Proteomics of Coagulopathy Following Injury Reveals Limitations of Using Laboratory Assessment to Define Trauma-Induced Coagulopathy to Predict Massive Transfusion

Objective

Trauma-induced coagulopathy (TIC) is provoked by multiple mechanisms and is perceived to be one driver of massive transfusions (MT). Single laboratory values using prothrombin time (INR) or thrombelastography (TEG) are used to clinically define this complex process. We used a proteomics approach to test whether current definitions of TIC (INR, TEG, or clinical judgement) are sufficient to capture the majority of protein changes associated with MT.

Methods

Eight level-I trauma centers contributed blood samples from patients available early after injury. TIC was defined as INR >1.5 (INR-TIC), TEG maximum amplitude <50mm (TEG-TIC), or clinical judgement (Clin-TIC) by the trauma surgeon. MT was defined as > 10 units of red blood cells in 24 hours or > 4 units RBC/hour during the first 4 hr. SomaLogic proteomic analysis of 1,305 proteins was performed. Pathways associated with proteins dysregulated in patients with each TIC definition and MT were identified.

Results

Patients (n=211) had a mean injury severity score of 24, with a MT and mortality rate of 22% and 12%, respectively. We identified 578 SOMAscan analytes dysregulated among MT patients, of which INR-TIC, TEG-TIC, and Clin-TIC patients showed dysregulation only in 25%, 3%, and 4% of these, respectively. TIC definitions jointly failed to show changes in 73% of the protein levels associated with MT, and failed to identify 26% of patients that received a massive transfusion. INR-TIC and TEG-TIC patients showed dysregulation of proteins significantly associated with complement activity. Proteins dysregulated in Clin-TIC or massive transfusion patients were not significantly associated with any pathway.

Conclusion

These data indicate there are unexplored opportunities to identify patients at risk for massive bleeding. Only a small subset of proteins that are dysregulated in patients receiving MT are statistically significantly dysregulated among patients whose TIC is defined based solely on laboratory measurements or clinical assessment.

The endothelial glycocalyx in critical illness: A pediatric perspective

The vascular endothelium is the interface between circulating blood and end organs and thus has a critical role in preserving organ function. The endothelium is lined by a glycan-rich glycocalyx that uniquely contributes to endothelial function through its regulation of leukocyte and platelet interactions with the vessel wall, vascular permeability, coagulation, and vasoreactivity. Degradation of the endothelial glycocalyx can thus promote vascular dysfunction, inflammation propagation, and organ injury. The endothelial glycocalyx and its role in vascular pathophysiology has gained increasing attention over the last decade. While studies characterizing vascular glycocalyx injury and its downstream consequences in a host of adult human diseases and in animal models has burgeoned, studies evaluating glycocalyx damage in pediatric diseases are relatively few. As children have unique physiology that differs from adults, significant knowledge gaps remain in our understanding of the causes and effects of endothelial glycocalyx disintegrity in pediatric critical illness. In this narrative literature overview, we offer a unique perspective on the role of the endothelial glycocalyx in pediatric critical illness, drawing from adult and preclinical data in addition to pediatric clinical experience to elucidate how marked derangement of the endothelial surface layer may contribute to aberrant vascular biology in children. By calling attention to this nascent field, we hope to increase research efforts to address important knowledge gaps in pediatric vascular biology that may inform the development of novel therapeutic strategies.

The Endothelial Glycocalyx: Physiology and Pathology in Neonates, Infants and Children

The endothelial glycocalyx (EG) as part of the endothelial surface layer (ESL) is an important regulator of vascular function and homeostasis, including permeability, vascular tone, leukocyte recruitment and coagulation. Located at the interface between the endothelium and the blood stream, this highly fragile structure is prone to many disruptive factors such as inflammation and oxidative stress. Shedding of the EG has been described in various acute and chronic diseases characterized by endothelial dysfunction and angiopathy, such as sepsis, trauma, diabetes and cardiovascular disease. Circulating EG components including syndecan-1, hyaluronan and heparan sulfate are being evaluated in animal and clinical studies as diagnostic and prognostic markers in several pathologies, and advances in microscopic techniques have enabled in vivo assessment of the EG. While research regarding the EG in adult physiology and pathology has greatly advanced throughout the last decades, our knowledge of the development of the glycocalyx and its involvement in pathological conditions in the pediatric population is limited. Current evidence suggests that the EG is present early during fetal development and plays a critical role in vessel formation and maturation. Like in adults, EG shedding has been demonstrated in acute inflammatory conditions in infants and children and chronic diseases with childhood-onset. However, the underlying mechanisms and their contribution to disease manifestation and progression still need to be established. In the future, the glycocalyx might serve as a marker to identify pediatric patients at risk for vascular sequelae and as a potential target for early interventions.

Removal of Circulating Neutrophil Extracellular Trap Components With an Immobilized Polymyxin B Filter: A Preliminary Study

Components of neutrophil extracellular traps (NETs) are released into the circulation by neutrophils and contribute to microcirculatory disturbance in sepsis. Removing NET components (DNA, histones, and proteases) from the circulation could be a new strategy for counteracting NET-dependent tissue damage. We evaluated the effect of hemoperfusion with a polymyxin B (PMX) cartridge, which was originally developed for treating gram-negative infection, on circulating NET components in patients with septic shock, as well as the effect on phorbol myristate acetate (PMA)-stimulated neutrophils obtained from healthy volunteers. Ex vivo closed loop hemoperfusion was performed through PMX filters in a laboratory circuit. Whole blood from healthy volunteers (incubated with or without PMA) or from septic shock patients was perfused through the circuit. For in vivo experiment blood samples were collected before and immediately after hemoperfusion with PMX to measure the plasma levels of cell-free NETs. The level of cell-free NETs was assessed by measuring myeloperoxidase-associated DNA (MPO-DNA), neutrophil elastase-associated DNA (NE-DNA), and cell-free DNA (cf-DNA). Plasma levels of MPO-DNA, NE-DNA, and cf-DNA were significantly increased after 2 h of PMA stimulation. When the circuit was perfused with blood from septic shock patients or PMA-stimulated neutrophils from healthy volunteers, circulating levels of MPO-DNA, NE-DNA, and cf-DNA were significantly reduced after 1 and 2 h of perfusion with a PMX filter compared with perfusion without a PMX filter. In 10 patients with sepsis, direct hemoperfusion through filters with immobilized PMX significantly reduced plasma levels of MPO-DNA and NE-DNA. These ex vivo and in vivo findings demonstrated that hemoperfusion with PMX removes circulating NET components. Selective removal of circulating NET components from the blood could be effective for prevention/treatment of NET-related inappropriate inflammation and thrombogenesis in patients with sepsis.

Human glycocalyx shedding: Systematic review and critical appraisal

BACKGROUND

The number of studies measuring breakdown products of the glycocalyx in plasma has increased rapidly during the past decade. The purpose of the present systematic review was to assess the current knowledge concerning the association between plasma concentrations of glycocalyx components and structural assessment of the endothelium.

METHODS

We performed a literature review of Pubmed to determine which glycocalyx components change in a wide variety of human diseases and conditions. We also searched for evidence of a relationship between plasma concentrations and the thickness of the endothelial glycocalyx layer as obtained by imaging methods.

RESULTS

Out of 3,454 publications, we identified 228 that met our inclusion criteria. The vast majority demonstrate an increase in plasma glycocalyx products. Sepsis and trauma are most frequently studied, and comprise approximately 40 publications. They usually report 3-4-foldt increased levels of glycocalyx degradation products, most commonly of syndecan-1. Surgery shows a variable picture. Cardiac surgery and transplantations are most likely to involve elevations of glycocalyx degradation products. Structural assessment using imaging methods show thinning of the endothelial glycocalyx layer in cardiovascular conditions and during major surgery, but thinning does not always correlate with the plasma concentrations of glycocalyx products. The few structural assessments performed do not currently support that capillary permeability is increased when the plasma levels of glycocalyx fragments in plasma are increased.

CONCLUSIONS

Shedding of glycocalyx components is a ubiquitous process that occurs during both acute and chronic inflammation with no sensitivity or specificity for a specific disease or condition.

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.

Dynamics of Platelet Counts in Major Trauma: The Impact of Haemostatic Resuscitation and Effects of Platelet Transfusion-A Sub-Study of the Randomized Controlled RETIC Trial

Although platelets play a central role in haemostasis, the dynamics of platelet counts during haemostatic resuscitation, the response to platelet transfusion, and effects on clinical outcome are poorly described for trauma patients. As a sub-study of the already published randomized controlled RETIC Study "Reversal of Trauma-induced Coagulopathy using First-line Coagulation Factor Concentrates or Fresh-Frozen Plasma" trial, we here analysed whether the type of first-line haemostatic resuscitation influences the frequency of platelet transfusion and determined the effects of platelet transfusion in coagulopathic patients with major trauma. Patients randomly received first-line plasma (FFP) or coagulation factor concentrates (CFC), mainly fibrinogen concentrate. In both groups, platelets were transfused to maintain platelet counts between 50 and 100 × 10⁹ /L. Transfusion rates were significantly higher in the FFP (n = 44) vs. CFC (n = 50) group (FFP 47.7% vs. CFC 26%); p = 0.0335. Logistic regression analysis adjusted for the stratification variables injury severity score (ISS) and brain injury confirmed that first-line FFP therapy increases the odds for platelet transfusion (odds ratio (OR) 5.79 (1.89 to 20.62), p = 0.0036) and this effect was larger than a 16-point increase in ISS (OR 4.33 (2.17 to 9.74), p =0.0001). In conclusion, early fibrinogen supplementation exerted a platelet-saving effect while platelet transfusions did not substantially improve platelet count and might contribute to poor clinical outcome.

Prehospital plasma is associated with distinct biomarker expression following injury

BACKGROUNDPrehospital plasma improves survival in severely injured patients transported by air ambulance. We hypothesized that prehospital plasma would be associated with a reduction in immune imbalance and endothelial damage.METHODSWe sampled blood from 405 trauma patients enrolled in the Prehospital Air Medical Plasma (PAMPer) trial upon hospital admission (0 hours) and 24 hours post admission across 6 U.S. sites. We assayed samples for 21 inflammatory mediators and 7 markers associated with endothelial function and damage. We performed hierarchical clustering analysis (HCA) of these biomarkers of the immune response and endothelial injury. Regression analysis was used to control for differences across study and to assess any association with prehospital plasma resuscitation.RESULTSHCA distinguished two patient clusters with different injury patterns and outcomes. Patients in cluster A had greater injury severity and incidence of blunt trauma, traumatic brain injury, and mortality. Cluster A patients that received prehospital plasma showed improved 30-day survival. Prehospital plasma did not improve survival in cluster B patients. In an adjusted analysis of the most seriously injured patients, prehospital plasma was associated with an increase in adiponectin, IL-1β, IL-17A, IL-23, and IL-17E upon admission, and a reduction in syndecan-1, TM, VEGF, IL-6, IP-10, MCP-1, and TNF-α, and an increase in IL-33, IL-21, IL-23, and IL-17E 24 hours later.CONCLUSIONPrehospital plasma may ameliorate immune dysfunction and the endotheliopathy of trauma. These effects of plasma may contribute to improved survival in injured patients.TRIAL REGISTRATIONNCT01818427.FUNDINGDepartment of Defense; National Institutes of Health, U.S. Army.

Megakaryocytes contain extranuclear histones and may be a source of platelet-associated histones during sepsis

Histones are typically located within the intracellular compartment, and more specifically, within the nucleus. When histones are located within the extracellular compartment, they change roles and become damage-associated molecular patterns (DAMPs), promoting inflammation and coagulation. Patients with sepsis have increased levels of extracellular histones, which have been shown to correlate with poor prognosis and the development of sepsis-related sequelae, such as end-organ damage. Until now, neutrophils were assumed to be the primary source of circulating histones during sepsis. In this paper, we show that megakaryocytes contain extranuclear histones and transfer histones to their platelet progeny. Upon examination of isolated platelets from patients with sepsis, we identified that patients with sepsis have increased amounts of platelet-associated histones (PAHs), which appear to be correlated with the type of infection. Taken together, these results suggest that megakaryocytes and platelets may be a source of circulating histones during sepsis and should be further explored.

Are Neutrophil-to-Lymphocyte and Platelet-to-Lymphocyte Ratios Associated with Mortality in Pediatric Trauma Patients? A Retrospective Study

BACKGROUND

There are very limited data on the prognostic capacity of the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) for the systemic inflammatory response in pediatric trauma (PT) patients. The purpose of this study was to evaluate the prognostic ability of NLR and PLR on mortality in pediatric trauma patients.

METHODS

This study looked at 358 PT patients who were admitted to the Cumhuriyet University Hospital's Emergency Department between January 2010 and June 2018. The NLR and PLR were calculated by dividing the blood neutrophil count and blood platelet count, respectively, by the lymphocyte count, at the time of admission. After performing a stepwise logistic regression analysis to determine the predictive factors on the mortality risk of post-traumatic systemic inflammatory response syndrome (SIRS), receiver operating characteristic (ROC) curve analysis was used to define the optimum cut-off values of the NLR and the PLR parameters for survival.

RESULTS

The NLR, and PLR values were significantly higher in survivors than in non-survivors (NLR, 6.2±5.7 versus 2.6±2.5, P<0.001; PLR, 145.3±85.0 versus 46.2±25.2, P<0.001 ). The NLR (odds ratio [OR], 3.21; P=0.048), PLR (OR, 0.90; P=0.032), blood glucose (OR, 1.02; P=0.024), and Injury Severity Score (ISS) (OR, 1.28; P=0.011) were independent predictors of the mortality risk in PT patients. The area under the curve in the ROC curve analysis was 0.764 with a cut-off of 2.77 (sensitivity 70%, specificity 77%) for the NLR; and 0.928 with a cut-off of 61.83 (sensitivity 90%, specificity 85%) for the PLR.

CONCLUSION

Acquiring the NLR and PLR at the time of admission could be a useful predictor for mortality in PT patients.

Extracellular histones induce calcium signals in the endothelium of resistance-sized mesenteric arteries and cause loss of endothelium-dependent dilation

Histone proteins are elevated in the circulation after traumatic injury owing to cellular lysis and release from neutrophils. Elevated circulating histones in trauma contribute to coagulopathy and mortality through a mechanism suspected to involve endothelial cell (EC) dysfunction. However, the functional consequences of histone exposure on intact blood vessels are unknown. Here, we sought to understand the effects of clinically relevant concentrations of histones on the endothelium in intact, resistance-sized, mesenteric arteries (MAs). EC Ca2+ was measured with high spatial and temporal resolution in MAs from mice selectively expressing the EC-specific, genetically encoded ratiometric Ca2+ indicator, Cx40-GCaMP-GR, and vessel diameter was measured by edge detection. Application of purified histone protein directly to the endothelium of en face mouse and human MA preparations produced large Ca2+ signals that spread within and between ECs. Surprisingly, luminal application of histones had no effect on the diameter of pressurized arteries. Instead, after prolonged exposure (30 min), it reduced dilations to endothelium-dependent vasodilators and ultimately caused death of ~25% of ECs, as evidenced by markedly elevated cytosolic Ca2+ levels (793 ± 75 nM) and uptake of propidium iodide. Removal of extracellular Ca2+ but not depletion of intracellular Ca2+ stores prevented histone-induced Ca2+ signals. Histone-induced signals were not suppressed by transient receptor potential vanilloid 4 (TRPV4) channel inhibition (100 nM GSK2193874) or genetic ablation of TRPV4 channels or Toll-like receptor receptors. These data demonstrate that histones are robust activators of noncanonical EC Ca2+ signaling, which cause vascular dysfunction through loss of endothelium-dependent dilation in resistance-sized MAs. NEW & NOTEWORTHY We describe the first use of the endothelial cell (EC)-specific, ratiometric, genetically encoded Ca2+ indicator, Cx40-GCaMP-GR, to study the effect of histone proteins on EC Ca2+ signaling. We found that histones induce an influx of Ca2+ in ECs that does not cause vasodilation but instead causes Ca2+ overload, EC death, and vascular dysfunction in the form of lost endothelium-dependent dilation.

Nucleic Acid Sensing in Mammals and Plants: Facts and Caveats

The accumulation of nucleic acids in aberrant compartments is a signal of danger: fragments of cytosolic or extracellular self-DNA indicate cellular dysfunctions or disruption, whereas cytosolic fragments of nonself-DNA or RNA indicate infections. Therefore, nucleic acids trigger immunity in mammals and plants. In mammals, endosomal Toll-like receptors (TLRs) sense single-stranded (ss) or double-stranded (ds) RNA or CpG-rich DNA, whereas various cytosolic receptors sense dsDNA. Although a self/nonself discrimination could favor targeted immune responses, no sequence-specific sensing of nucleic acids has been reported for mammals. Specific immune responses to extracellular self-DNA versus DNA from related species were recently reported for plants, but the underlying mechanism remains unknown. The subcellular localization of mammalian receptors can favor self/nonself discrimination based on the localization of DNA fragments. However, autoantibodies and diverse damage-associated molecular patterns (DAMPs) shuttle DNA through membranes, and most of the mammalian receptors share downstream signaling elements such as stimulator of interferon genes (STING) and the master transcription regulators, nuclear factor (NF)-κB, and interferon regulatory factor 3 (IRF3). The resulting type I interferon (IFN) response stimulates innate immunity against multiple threats-from infection to physical injury or endogenous DNA damage-all of which lead to the accumulation of eDNA or cytoplasmatic dsDNA. Therefore, no or only low selective pressures might have favored a strict self/nonself discrimination in nucleic acid sensing. We conclude that the discrimination between self- and nonself-DNA is likely to be less strict-and less important-than assumed originally.

Low Plasma ADAMTS13 Activity Is Associated with Coagulopathy, Endothelial Cell Damage and Mortality after Severe Paediatric Trauma

Decrease of plasma activity of ADAMTS13, a metalloenzyme that cleaves von Willebrand factor (VWF) and prevents adhesion and aggregation of platelets, has been reported early after onset of systemic inflammation resulting from infections and after severe trauma. Here, we determined whether trauma-induced systemic (sterile) inflammation would be associated with a reduction of plasma ADAMTS13 activity in paediatric patients and its association with disease severity and outcome. Paediatric patients (n = 106) with severe trauma at a level 1 paediatric trauma centre between 2014 and 2016 were prospectively enrolled. Blood samples were collected upon arrival and at 24 hours and analysed for plasma levels of ADAMTS13 activity, VWF antigen, collagen binding activity, human neutrophil peptides (HNP) 1-3, coagulation abnormalities, endothelial glycocalyx damage and clinical outcome. Plasma samples were also collected for similar measurements from 52 healthy paediatric controls who underwent elective minor surgery. The median age of patients was 9 years with 81% sustaining blunt trauma. The median injury severity score was 22 and the mortality rate was 11%. Plasma levels of ADAMTS13 activity were significantly lower and plasma levels of VWF antigen and HNP 1-3 proteins were significantly higher for paediatric trauma patients on admission and at 24 hours when compared with controls. Finally, the lowest plasma ADAMTS13 activity was found in patients who died from their injuries. We conclude that relative plasma deficiency of ADAMTS13 activity may be associated with more severe traumatic injury, significant endothelial glycocalyx damage, coagulation abnormalities and mortality after severe trauma in paediatric patients.

Endotheliopathy is associated with higher levels of cell-free DNA following major trauma: A prospective observational study

BACKGROUND

Cell free deoxyribonucleic acid (cfDNA) has been proposed as a biomarker of secondary complications following trauma. Raised thrombomodulin and syndecan-1 levels have been used to indicate endotheliopathy, and are associated with inflammation, coagulopathy, and mortality. The current study aimed to analyse the association between cfDNA and biomarkers of endotheliopathy in a cohort of trauma patients, and whether raised levels of cfDNA were associated with poorer clinical outcomes.

METHODS

Serum thrombomodulin and syndecan-1 were used as biomarkers of endotheliopathy and compared to plasma cfDNA in trauma patients from two prospective longitudinal observational studies. Cohort A (n = 105) had a predicted injury severity score (ISS) >8, and had blood sampled within 1h of injury and at 4-12h. Cohort B (n = 17) had evidence of haemorrhagic shock, and had blood sampled at a median time of 3.5h after injury. Relationships between biomarkers were tested using multivariable linear regression models that included the covariates of gender, age, ISS, Glasgow Coma Scale, lactate, systolic blood pressure, and heart rate. A model was fitted to investigate whether changes in cfDNA were associated with similar changes in endothelial biomarkers.

RESULTS

The mean age was 41 (SD 19), and the median ISS was 25 (IQR 12-34). There was a significant association between cfDNA levels and both syndecan-1 and thrombomodulin levels (both p<0.001). This was independent of all covariates except for ISS, which significantly correlated with cfDNA levels. 50 ng/ml change in syndecan-1 and 1 ng/ml change in thrombomodulin corresponded to 15% and 20% increases in cfDNA levels respectively (both p<0.001). Patients who died had significantly higher prehospital and in-hospital cfDNA levels (both p<0.05).

CONCLUSIONS

Raised cfDNA levels are associated with markers of endotheliopathy following trauma, and are associated with mortality. This relationship is present within the first hour of injury, and a change in one biomarker level is reflected by similar changes in the others. These findings are in keeping with the hypothesis that circulating DNA and endothelial injury share a common pathway following trauma.