Circulating Histone Concentrations Differentially Affect the Predominance of Left or Right Ventricular Dysfunction in Critical Illness. Crit Care Med. 2016;44:e278-e288. [PMID: 26588828 DOI: 10.1097/ccm.0000000000001413]

Emerging therapeutic strategies targeting extracellular histones for critical and inflammatory diseases: an updated narrative review

Extracellular histones are crucial damage-associated molecular patterns involved in the development and progression of multiple critical and inflammatory diseases, such as sepsis, pancreatitis, trauma, acute liver failure, acute respiratory distress syndrome, vasculitis and arthritis. During the past decade, the physiopathologic mechanisms of histone-mediated hyperinflammation, endothelial dysfunction, coagulation activation, neuroimmune injury and organ dysfunction in diseases have been systematically elucidated. Emerging preclinical evidence further shows that anti-histone strategies with either their neutralizers (heparin, heparinoids, nature plasma proteins, small anion molecules and nanomedicines, etc.) or extracorporeal blood purification techniques can significantly alleviate histone-induced deleterious effects, and thus improve the outcomes of histone-related critical and inflammatory animal models. However, a systemic evaluation of the efficacy and safety of these histone-targeting therapeutic strategies is currently lacking. In this review, we first update our latest understanding of the underlying molecular mechanisms of histone-induced hyperinflammation, endothelial dysfunction, coagulopathy, and organ dysfunction. Then, we summarize the latest advances in histone-targeting therapy strategies with heparin, anti-histone antibodies, histone-binding proteins or molecules, and histone-affinity hemoadsorption in pre-clinical studies. Finally, challenges and future perspectives for improving the clinical translation of histone-targeting therapeutic strategies are also discussed to promote better management of patients with histone-related diseases.

Fibrinogen binding to histones in circulation protects against adverse cellular and clinical outcomes

BACKGROUND

Circulating histones are released by extensive tissue injury or cell death and play important pathogenic roles in critical illnesses. Their interaction with circulating plasma components and the potential roles in the clinical setting are not fully understood.

OBJECTIVES

We aimed to characterize the interaction of histones with fibrinogen and explore its roles in vitro, in vivo, and in patient samples.

METHODS

Histone-fibrinogen binding was assessed by electrophoresis and enzyme-linked immunosorbent assay-based affinity assay. Functional significance was explored using washed platelets and endothelial cells in vitro and histone-infusion mouse models in vivo. To determine clinical translatability, a retrospective single-center cohort study was conducted on patients requiring intensive care admission (n = 199) and validated in a cohort of hospitalized patients with COVID-19 (n = 69).

RESULTS

Fibrinogen binds histones through its D-domain with high affinity (calf thymus histones, KD = 18.0 ± 5.6 nM; histone 3, KD = 2.7 ± 0.8 nM; and histone 4, KD = 2.0 ± 0.7 nM) and significantly reduces histone-induced endothelial damage and platelet aggregation in vitro and in vivo in a histone-infusion mouse model. Physiologic concentrations of fibrinogen can neutralize low levels of circulating histones and increase the cytotoxicity threshold of histones to 50 μg/mL. In a cohort of patients requiring intensive care, a histone:fibrinogen ratio of ≥6 on admission was associated with moderate-severe thrombocytopenia and independently predicted mortality. This finding was validated in a cohort of hospitalized patients with COVID-19.

CONCLUSION

Fibrinogen buffers the cytotoxic properties of circulating histones. Detection and monitoring of circulating histones and histone:fibrinogen ratios will help identify critically ill patients at highest risk of adverse outcomes who might benefit from antihistone therapy.

Types of Septic Cardiomyopathy: Prognosis and Influencing Factors - A Clinical Study

Objective

To explore the prognostic outcomes associated with different types of septic cardiomyopathy and analyze the factors that exert an influence on these outcomes.

Methods

The data collected within 24 hours of ICU admission included cardiac troponin I (cTnI), N-terminal pro-Brain Natriuretic Peptide (NT-proBNP); SOFA (sequential organ failure assessment) scores, and the proportion of vasopressor use. Based on echocardiographic outcomes, septic cardiomyopathy was categorized into left ventricular (LV) systolic dysfunction, LV diastolic dysfunction, and right ventricular (RV) systolic dysfunction. Differences between the mortality and survival groups, as well as between each cardiomyopathy subgroup and the non-cardiomyopathy group were compared, to explore the influencing factors of cardiomyopathy.

Results

A cohort of 184 patients were included in this study, with LV diastolic dysfunction having the highest incidence rate (43.5%). The mortality group had significantly higher SOFA scores, vasopressor use, and cTnI levels compared to the survival group; the survival group had better LV diastolic function than the mortality group (p < 0.05 for all). In contrast to the non-cardiomyopathy group, each subgroup within the cardiomyopathy category exhibited elevated levels of cTnI. The subgroup with left ventricular diastolic dysfunction demonstrated a higher prevalence of advanced age, hypertension, diabetes mellitus, coronary artery disease, and an increased mortality rate; the RV systolic dysfunction subgroup had higher SOFA scores and NT-proBNP levels, and a higher mortality rate (P < 0.05 for all); the LV systolic dysfunction subgroup had a similar mortality rate (P > 0.05).

Conclusion

Patients with advanced age, hypertension, diabetes mellitus, or coronary artery disease are more prone to develop LV diastolic dysfunction type of cardiomyopathy; cardiomyopathy subgroups had higher levels of cTnI. The RV systolic dysfunction cardiomyopathy subgroup had higher SOFA scores and NT-proBNP levels. The occurrence of RV systolic dysfunction in patients with sepsis significantly increased the mortality rate.

Trauma-induced innate immune activation and disseminated intravascular coagulation

Dysregulated innate immunity participates in the pathomechanisms of disseminated intravascular coagulation (DIC) in trauma-induced coagulopathy. Accidental and regulated cell deaths and neutrophil extracellular traps release damage-associated molecular patterns (DAMPs), such as histones, nuclear and mitochondrial DNA, and high-mobility group box 1, into circulation immediately after trauma. DAMP-induced inflammation activation releases tissue factor-bearing procoagulant extracellular vesicles through gasdermin D-mediated pore formation and plasma membrane rupture by regulated cell death. DAMPs also evoke systemic inflammation, platelet, coagulation activation, and impaired fibrinolysis associated with endothelial injury, leading to the dysfunction of anticoagulation systems, which are the main pathophysiological mechanisms of DIC. All these processes induce systemic thrombin generation in vivo, not restricted to the injury sites immediately after trauma. Thrombin generation at the site of injury stops bleeding and maintains homeostasis. However, DIC associated with endothelial injury generates massive thrombin, enhancing protease-activated, receptor-mediated bidirectional interplays between inflammation and coagulation, aggravating the diverse actions of thrombin and disturbing homeostasis. Insufficiently regulated thrombin causes disseminated microvascular thrombosis, resulting in tissue hypoxia due to reduced oxygen delivery, and mitochondrial dysfunction due to DAMPs causes tissue dysoxia. In addition, DAMP-induced calcium influx and overload, as well as neutrophil activation, play a role in endothelial cell injury. Tissue hypoxia and cytotoxicity result in multiple organ dysfunction in DIC after trauma. Controls against dysregulated innate immunity evoking systemic inflammation, thrombin generation, and cytotoxicity are key issues in improving the prognosis of DIC in trauma-induced coagulopathy.

Cardiovascular Subphenotypes in ARDS: Diagnostic and Therapeutic Implications and Overlap with Other ARDS Subphenotypes

Acute respiratory distress syndrome (ARDS) is a highly heterogeneous clinical condition. Shock is a poor prognostic sign in ARDS, and heterogeneity in its pathophysiology may be a barrier to its effective treatment. Although right ventricular dysfunction is commonly implicated, there is no consensus definition for its diagnosis, and left ventricular function is neglected. There is a need to identify the homogenous subgroups within ARDS, that have a similar pathobiology, which can then be treated with targeted therapies. Haemodynamic clustering analyses in patients with ARDS have identified two subphenotypes of increasingly severe right ventricular injury, and a further subphenotype of hyperdynamic left ventricular function. In this review, we discuss how phenotyping the cardiovascular system in ARDS may align with haemodynamic pathophysiology, can aid in optimally defining right ventricular dysfunction and can identify tailored therapeutic targets for shock in ARDS. Additionally, clustering analyses of inflammatory, clinical and radiographic data describe other subphenotypes in ARDS. We detail the potential overlap between these and the cardiovascular phenotypes.

Extracellular Histone-Induced Protein Kinase C Alpha Activation and Troponin Phosphorylation Is a Potential Mechanism of Cardiac Contractility Depression in Sepsis

Reduction in cardiac contractility is common in severe sepsis. However, the pathological mechanism is still not fully understood. Recently it has been found that circulating histones released after extensive immune cell death play important roles in multiple organ injury and disfunction, particularly in cardiomyocyte injury and contractility reduction. How extracellular histones cause cardiac contractility depression is still not fully clear. In this work, using cultured cardiomyocytes and a histone infusion mouse model, we demonstrate that clinically relevant histone concentrations cause significant increases in intracellular calcium concentrations with subsequent activation and enriched localization of calcium-dependent protein kinase C (PKC) α and βII into the myofilament fraction of cardiomyocytes in vitro and in vivo. Furthermore, histones induced dose-dependent phosphorylation of cardiac troponin I (cTnI) at the PKC-regulated phosphorylation residues (S43 and T144) in cultured cardiomyocytes, which was also confirmed in murine cardiomyocytes following intravenous histone injection. Specific inhibitors against PKCα and PKCβII revealed that histone-induced cTnI phosphorylation was mainly mediated by PKCα activation, but not PKCβII. Blocking PKCα also significantly abrogated histone-induced deterioration in peak shortening, duration and the velocity of shortening, and re-lengthening of cardiomyocyte contractility. These in vitro and in vivo findings collectively indicate a potential mechanism of histone-induced cardiomyocyte dysfunction driven by PKCα activation with subsequent enhanced phosphorylation of cTnI. These findings also indicate a potential mechanism of clinical cardiac dysfunction in sepsis and other critical illnesses with high levels of circulating histones, which holds the potential translational benefit to these patients by targeting circulating histones and downstream pathways.

Extracellular histones cause intestinal epithelium injury and disrupt its barrier function in vitro and in vivo

Extracellular histones are cytotoxic to various cells and have been extensively proven a vital mediator of multiple organ injuries. However, the effect of extracellular histones on the intestine remains largely unknown. This study aimed to clarify the effect of extracellular histones on the intestine. IEC-6, a cell line of rat small intestinal epithelial crypt, and C57BL/6 or ICR mice were treated with histones. The IEC-6 cells treated with histones from 20 μg/mL to 200 μg/mL for 0-24 h displayed a decline of cell viability and an increase of cell death in a concentration- and time-dependent manner. Moreover, histones (100 μg/mL) induced IEC-6 apoptosis through activating caspase 3 and necroptosis through up-regulation of receptor-interacting serine/threonine protein kinase 1 and 3 (RIPK1 and RIPK3), phosphorylated mixed-lineage kinase domain-like protein (p-MLKL) along with the decrease of caspase-8. Histones treatment disturbed zonular occludens 1 (ZO-1) expression and increased permeability of IEC-6 cell monolayer. In vivo, histones 50 mg/kg injection caused mice intestinal edema, loss apex of villus, epithelial lifting down the sides of the villi, and increased neutrophil infiltration. Elevation of serum intestinal fatty acid binding protein (I-FABP), D-lactate, or Diamine oxidase (DAO) and loss of tight junction protein, ZO-1, at 3 h and 6 h after histones injection strongly indicated severe intestinal epithelium injury, which led to increased permeability of the intestine. In conclusion, extracellular histones cause intestinal epithelial damage via direct cytotoxicity. Consequently, intestinal epithelial tight junction and barrier integrity are disrupted, which may play pivotal roles in diverse diseases.

Unfractionated Heparin Attenuated Histone-Induced Pulmonary Syndecan-1 Degradation in Mice: a Preliminary Study on the Roles of Heparinase Pathway

Endothelial glycocalyx degradation is thought to facilitate the development of sepsis. Histone is a significant mediator in sepsis. Unfractionated heparin (UFH) possessed beneficial effects on sepsis. Thereby, this study aims to figure out whether histone can disrupt glycocalyx and to investigate the protective effect and mechanism of UFH. Male mice (C57BL/6, 8-10 weeks old, weighing 20-25 g) were randomly divided into five groups including control group, histone group, histone + UFH group, histone + heparinase (HPA) inhibitor group, and histone + UFH + HPA inhibitor group. The mice were treated with histone (50 mg/kg) via tail vein immediately after HPA (20 mg/kg) injection. UFH (400 U/kg) was injected 1h after histone administration. The other groups were injected with equal volume of sterile saline accordingly. UFH alleviated histone-induced lung injury and pulmonary edema. UFH inhibited histone-induced lung coagulation activation and inflammatory response. UFH treatment markedly inhibited pulmonary glycocalyx degradation by reducing the histone-induced decrease in the levels of lung syndecan-1 mRNA and protein. UFH downregulated histone-induced expression of HPA mRNA and protein, and thus alleviated glycocalyx degradation. UFH protects against histone-induced pulmonary glycocalyx injury partly by heparinase pathway.

Parasite histones are toxic to brain endothelium and link blood barrier breakdown and thrombosis in cerebral malaria

Microvascular thrombosis and blood-brain barrier (BBB) breakdown are key components of cerebral malaria (CM) pathogenesis in African children and are implicated in fatal brain swelling. How Plasmodium falciparum infection causes this endothelial disruption and why this occurs, particularly in the brain, is not fully understood. In this study, we have demonstrated that circulating extracellular histones, equally of host and parasite origin, are significantly elevated in CM patients. Higher histone levels are associated with brain swelling on magnetic resonance imaging. On postmortem brain sections of CM patients, we found that histones are colocalized with P falciparum-infected erythrocytes sequestered inside small blood vessels, suggesting that histones might be expelled locally during parasite schizont rupture. Histone staining on the luminal vascular surface colocalized with thrombosis and leakage, indicating a possible link between endothelial surface accumulation of histones and coagulation activation and BBB breakdown. Supporting this, patient sera or purified P falciparum histones caused disruption of barrier function and were toxic to cultured human brain endothelial cells, which were abrogated with antihistone antibody and nonanticoagulant heparin. Overall, our data support a role for histones of parasite and host origin in thrombosis, BBB breakdown, and brain swelling in CM, processes implicated in the causal pathway to death. Neutralizing histones with agents such as nonanticoagulant heparin warrant exploration to prevent brain swelling in the development or progression of CM and thereby to improve outcomes.

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.

Plasma Nucleosomes Are Associated With Mortality in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Circulating nucleosomes and their component histones have been implicated as pathogenic in sepsis and acute respiratory distress syndrome in adults. However, their role in pediatric acute respiratory distress syndrome is unknown.

DESIGN

We performed a prospective cohort study in children with acute respiratory distress syndrome, with plasma collection within 24 hours of acute respiratory distress syndrome onset. We associated nucleosome levels with severity of acute respiratory distress syndrome and with nonpulmonary organ failures and tested for association of nucleosomes with PICU mortality and ventilator-free days at 28 days in univariate and multivariable analyses. We also performed proteomics of DNA-bound plasma proteins in a matched case-control study of septic children with and without acute respiratory distress syndrome in order to identify specific histone proteins elevated in acute respiratory distress syndrome.

SETTING

Large academic tertiary-care PICU.

PATIENTS

Intubated children meeting Berlin criteria for acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We enrolled 333 children with acute respiratory distress syndrome, with 69 nonsurvivors (21%). Plasma nucleosomes were correlated with acute respiratory distress syndrome severity and with the number of nonpulmonary organ failures at acute respiratory distress syndrome onset. Nucleosomes were higher (p < 0.001) in nonsurvivors (0.40 [interquartile range, 0.20-0.71] arbitrary units) relative to survivors (0.10 [interquartile range, 0.04-0.25] arbitrary units). Nucleosomes were associated with PICU mortality in multivariable analysis (adjusted odds ratio 1.84 per 1 sd increase; 95% CI, 1.38-2.45; p < 0.001). Nucleosomes were also associated with a lower probability of being extubated alive by day 28 after multivariable adjustment (adjusted subdistribution hazard ratio, 0.74; 95% CI, 0.63-0.88; p = 0.001). Proteomic analysis demonstrated higher levels of the core nucleosome histones H2A, H2B, H3, and H4 in septic children with acute respiratory distress syndrome, relative to septic children without acute respiratory distress syndrome.

CONCLUSIONS

Plasma nucleosomes are associated with acute respiratory distress syndrome severity, nonpulmonary organ failures, and worse outcomes in pediatric acute respiratory distress syndrome.

Extracellular histones stimulate collagen expression in vitro and promote liver fibrogenesis in a mouse model via the TLR4-MyD88 signaling pathway

BACKGROUND

Liver fibrosis progressing to liver cirrhosis and hepatic carcinoma is very common and causes more than one million deaths annually. Fibrosis develops from recurrent liver injury but the molecular mechanisms are not fully understood. Recently, the TLR4-MyD88 signaling pathway has been reported to contribute to fibrosis. Extracellular histones are ligands of TLR4 but their roles in liver fibrosis have not been investigated.

AIM

To investigate the roles and potential mechanisms of extracellular histones in liver fibrosis.

METHODS

In vitro, LX2 human hepatic stellate cells (HSCs) were treated with histones in the presence or absence of non-anticoagulant heparin (NAHP) for neutralizing histones or TLR4-blocking antibody. The resultant cellular expression of collagen I was detected using western blotting and immunofluorescent staining. In vivo, the CCl4-induced liver fibrosis model was generated in male 6-week-old ICR mice and in TLR4 or MyD88 knockout and parental mice. Circulating histones were detected and the effect of NAHP was evaluated.

RESULTS

Extracellular histones strongly stimulated LX2 cells to produce collagen I. Histone-enhanced collagen expression was significantly reduced by NAHP and TLR4-blocking antibody. In CCl4-treated wild type mice, circulating histones were dramatically increased and maintained high levels during the duration of fibrosis-induction. Injection of NAHP not only reduced alanine aminotransferase and liver injury scores, but also significantly reduced fibrogenesis. Since the TLR4-blocking antibody reduced histone-enhanced collagen I production in HSC, the CCl4 model with TLR4 and MyD88 knockout mice was used to demonstrate the roles of the TLR4-MyD88 signaling pathway in CCl4-induced liver fibrosis. The levels of liver fibrosis were indeed significantly reduced in knockout mice compared to wild type parental mice.

CONCLUSION

Extracellular histones potentially enhance fibrogenesis via the TLR4-MyD88 signaling pathway and NAHP has therapeutic potential by detoxifying extracellular histones.

Site-specific opening of the blood-brain barrier by extracellular histones

BACKGROUND

Increased extracellular histones in the bloodstream are known as a biomarker for vascular dysfunction associated with severe trauma or sepsis. There is limited information regarding the pathogenic role of circulating histones in neuroinflammation and cerebrovascular endothelial injury. Particularly, it remains unclear whether histones affect the blood-brain barrier (BBB) permeability function.

METHODS

The direct effects of unfractionated histones on endothelial barrier properties were first assessed in brain microvascular endothelial cell monolayers by measuring transendothelial electrical resistance and solute flux. This was followed by in vivo mouse experiments, where BBB function was assessed by quantifying brain tissue accumulation of intravenously injected tracers of different molecular sizes, and comparison was made in mice receiving a sublethal dose of histones versus sterile saline. In parallel, the endothelial barrier ultrastructure was examined in histone- and saline-injected animals under transmission electron microscopy, corresponding to the expression of tight junction and adherens junction proteins.

RESULTS

Histones increased paracellular permeability to sodium fluorescein and reduced barrier resistance at 100 μg/mL; these responses were accompanied by discontinuous staining of the tight junction proteins claudin-5 and zona ocludens-1. Interestingly, the effects of histones did not seem to result from cytotoxicity, as evidenced by negative propidium iodide staining. In vivo, histones increased the paracellular permeability of the BBB to small tracers of < 1-kDa, whereas tracers larger than 3-kDa remained impermeable across brain microvessels. Further analysis of different brain regions showed that histone-induced tracer leakage and loss of tight junction protein expression mainly occurred in the hippocampus, but not in the cerebral cortex. Consistently, opening of tight junctions was found in hippocampal capillaries from histone-injected animals. Protein expression levels of GFAP and iBA1 remained unchanged in histone-injected mice indicating that histones did not affect reactive gliosis. Moreover, cell membrane surface charge alterations are involved in histone-induced barrier dysfunction and tight junction disruption.

CONCLUSIONS

Extracellular histones cause a reversible, region-specific increase in BBB permeability to small molecules by disrupting tight junctions in the hippocampus. We suggest that circulating histones may contribute to cerebrovascular injury or brain dysfunction by altering BBB structure and function.

Assembly of alternative prothrombinase by extracellular histones initiate and disseminate intravascular coagulation

Thrombin generation is pivotal to both physiological blood clot formation and pathological development of disseminated intravascular coagulation (DIC). In critical illness, extensive cell damage can release histones into the circulation, which can increase thrombin generation and cause DIC, but the molecular mechanism is not clear. Typically, thrombin is generated by the prothrombinase complex, comprising activated factor X (FXa), activated co-factor V (FVa) and phospholipids to cleave prothrombin in the presence of calcium. In this study, we found that in the presence of extracellular histones, an alternative prothrombinase could form without FVa and phospholipids. Histones directly bind to prothrombin fragments F1 and F2 specifically, to facilitate FXa cleavage of prothrombin to release active thrombin, unlike FVa which requires phospholipid surfaces to anchor the classical prothrombinase complex. In vivo, histone infusion into mice induced DIC, which was significantly abrogated when prothrombin fragments F1+F2 were infused prior to histones, to act as decoy. In a cohort of intensive care unit (ICU) patients with sepsis (n=144), circulating histone levels were significantly elevated in patients with DIC. These data suggest that histone-induced alternative prothrombinase without phospholipid anchorage may disseminate intravascular coagulation, and reveal a new molecular mechanism of thrombin generation and DIC development. In addition, histones significantly reduced the requirement for FXa in the coagulation cascade to enable clot formation in Factor VIII and IX-deficient plasma, as well as in Factor VIII-deficient mice. In conclusion, this study highlights a novel mechanism in coagulation with therapeutic potential in both targeting systemic coagulation activation as well as in correcting coagulation factor deficiency.

Unfractionated heparin inhibits histone-mediated coagulation activation and thrombosis in mice

INTRODUCTION

Histones play pivotal roles in the pathophysiology of sepsis. Different studies have reported that unfractionated heparin (UFH) can improve histone-mediated organ dysfunction. However, in such studies, UFH was usually pretreated or injected with histones concurrently, which was obviously inconsistent with clinical practice. Therefore, this study aimed to figure out whether UFH can inhibit histone-induced coagulation activation and thrombosis when histones have caused coagulation disorder already.

METHODS

Male C57/BL6 mice of average weight ~22 g were randomly divided into three groups. The histone group was injected with histones 50 mg/kg through the tail vein. The histone + UFH group was injected with UFH (400 U/kg) through the tail vein 1 h or 6 h after the induction of histones. The control group was injected with equal volume of sterile saline. The lungs were harvested 3 h after UFH administration. In survival studies, mice were treated with UFH (800 U/kg, n = 10) or sterile saline (n = 10) intravenously after histones (75 mg/kg) injection and observed for 7 days.

RESULTS

1) UFH improved survival rate in mice injected with lethal doses of histones; 2) UFH alleviated histone-induced lung injury and pulmonary edema; 3) UFH improved histone-induced endothelial cell injury; 4) UFH improved histone-mediated high expression of TF, PAI-1, fibrinogen and low expression of TM.

CONCLUSION

UFH can effectively attenuate histone-induced lung injury, coagulation activation and thrombosis.

Circulating Histones Are Major Mediators of Multiple Organ Dysfunction Syndrome in Acute Critical Illnesses

OBJECTIVES

Multiple organ dysfunction syndrome is characterized by simultaneous multiple organ failure, which is the leading cause of death in acute critically ill patients. However, what mediates multiple organ dysfunction syndrome is not fully understood. The discovery of toxic effects by extracellular histones on different individual organs strongly suggests their involvement in multiple organ dysfunction syndrome. In this study, we investigate whether circulating histones are major mediators of multiple organ dysfunction syndrome in acute critical illnesses.

DESIGN

Combination of retrospective clinical studies and animal models with intervention.

SETTING

ICU in a tertiary hospital and research laboratories.

PATIENTS

Four hundred and twenty ICU patients, including sepsis (140), severe trauma (63), severe pancreatitis (89), and other admission diagnoses (128).

LABORATORY INVESTIGATION

Cells from major organs are treated with calf thymus histones or histone-containing sera. Animal models for sepsis, trauma, and acute pancreatitis are treated with antihistone reagents.

INTERVENTION

Antihistone reagents in in vitro, ex vivo, and animal models.

MEASUREMENT AND MAIN RESULTS

Retrospective analysis of a prospectively recruited ICU cohort demonstrated a strong correlation between circulating histones and organ injury markers and Sequential Organ Failure Assessment scores. Ex vivo experiments showed that patient sera containing high histone levels were toxic to cultured cells from different origins, suggesting their universal toxicity to multiple organs. Animal models of sepsis, trauma, and pancreatitis further demonstrated a temporal correlation between histone levels and disease severity and multiple organ injury. Importantly, antihistone reagents, that is, antihistone single-chain variable fragment and nonanticoagulant heparin, could dramatically reduce multiple organ injury, particularly of the heart and lungs, and improve survival in mouse models.

CONCLUSIONS

High levels of circulating histones are major mediators of multiple organ dysfunction syndrome. Our results indicate that monitoring upon ICU admission could inform on disease severity and developing antihistone therapy holds great potential of reducing multiple organ dysfunction syndrome and improving survival of critically ill patients.

Mechanisms for Reducing Neuropathic Pain

Injury typically results in the development of neuropathic pain, but the pain normally decreases and disappears in paralleled with wound healing. The pain results from cells resident at, and recruited to, the injury site releasing pro-inflammatory cytokines and other mediators leading to the development of pro-inflammatory environment and causing nociceptive neurons to develop chronic ectopic electrical activity, which underlies neuropathic pain. The pain decreases as some of the cells that induce pro-inflammation, changing their phenotype leading to the blocking the release of pro-inflammatory mediators while releasing anti-inflammatory mediators, and blocking nociceptive neuron chronic spontaneous electrical activity. Often, despite apparent wound healing, the neuropathic pain becomes chronic. This raises the question of how chronic pain can be eliminated. While many of the cells and mediators contributing to the development and maintenance of neuropathic pain are known, a better understanding is required of how the injury site environment can be controlled to permanently eliminate the pro-inflammatory environment and silence the chronically electrically active nociceptive neurons. This paper examines how methods that can promote the transition of the pro-inflammatory injury site to an anti-inflammatory state, by changing the composition of local cell types, modifying the activity of pro- and anti-inflammatory receptors, inducing the release of anti-inflammatory mediators, and silencing the chronically electrically active nociceptive neurons. It also examines the hypothesis that factors released from platelet-rich plasma applied to chronic pain sites can permanently eliminate chronic inflammation and its associated chronic pain.

Elevated Plasma Histone H4 Levels Are an Important Risk Factor in the Development of Septic Cardiomyopathy

Background:

Myocardial impairment is a major complication and an important prognostic predictor of sepsis. Therefore, early and accurate diagnosis as well as timely management of septic cardiomyopathy is critical to achieve favorable outcomes.

Aims:

To investigate the risk factors of septic cardiomyopathy.

Study Design:

Cross-sectional study.

Methods:

This study performed between May 2016 and June 2018 recruited 93 septic patients from the intensive care unit. All patients received standardized treatments. Septic patients were divided into two groups: non cardiomyopathy (n=45) and septic cardiomyopathy group (n=48). Blood samples were collected and transthoracic echocardiography was performed within 24 hours of intensive care unit admission. Septic patients with one ultrasound abnormality but no history of heart disease were diagnosed as having septic cardiomyopathy. Plasma histones, cardiac troponin I, and N-terminal pro-brain natriuretic peptide were measured using ELISA. Sequential Organ Failure Assessment scores, vasopressor use, and the outcomes of intensive care unit stay were analyzed. Spearman rank analysis was used to determine the correlation between plasma histone H4 and other parameters. Binary logistic regression and receiver operating characteristic curve analysis were used to determine the risk factors for septic cardiomyopathy.

Results:

Compared with the non-cardiomyopathy group, the septic cardiomyopathy group had significantly higher plasma H4 and cardiac troponin I levels, a higher Sequential Organ Failure Assessment score, more frequent vasopressor use, and a higher mortality rate (p<0.05). Plasma histone H4 levels positively correlated with cardiac troponin I (r=0.577, p<0.001), N-terminal pro-brain natriuretic peptide (r=0.349, p=0.001), and Sequential Organ Failure Assessment scores (r=0.469, p<0.001). Binary logistic regression and receiver operating characteristic curve analyses revealed that elevated plasma histone H4 levels and vasopressor use were important risk factors for septic cardiomyopathy (p<0.05).

Conclusion:

Elevated plasma histone H4 levels could be used to predict septic cardiomyopathy in patients with sepsis.

The Role of ALDH2 in Sepsis and the To-Be-Discovered Mechanisms

Sepsis, defined as life-threatening tissue damage and organ dysfunction caused by a dysregulated host response to infection, is a critical disease which imposes global health burden. Sepsis-induced organ dysfunction, including circulatory and cardiac dysfunction, hepatic dysfunction, renal dysfunction, etc., contributes to high mortality and long-term disability of sepsis patients. Altered inflammatory response, ROS and reactive aldehyde stress, mitochondrial dysfunction, and programmed cell death pathways (necrosis, apoptosis, and autophagy) have been demonstrated to play crucial roles in septic organ dysfunction. Unfortunately, except for infection control and supportive therapies, no specific therapy exists for sepsis. New specific therapeutic targets are highly warranted. Emerging studies suggested a role of potential therapeutic target of ALDH2, a tetrameric enzyme located in mitochondria to detoxify aldehydes, in septic organ dysfunction. In this article, we will review the presentations and pathophysiology of septic organ dysfunction, as well as summarize and discuss the recent insights regarding ALDH2 in sepsis.

Response and outcome from fluid resuscitation in acute pancreatitis: a prospective cohort study

BACKGROUND

Intravenous (IV) fluid resuscitation remains the cornerstone for early management of acute pancreatitis (AP), but many questions remain unanswered, including how to determine whether patients will benefit from additional fluids. The aim was to investigate the utility of serum biomarkers of responsiveness IV fluid resuscitation in patients with AP and systemic inflammatory response syndrome (SIRS).

METHODS

Eligible adult patients had abdominal pain for <36 h and ≥2 SIRS criteria. Mean arterial pressure (>65 mmHg) and urine output (>0.5 ml/kg/h) were used to assess responsiveness at 2 and 6-8 h after initiation of IV fluids. Comparison was made between responsive and refractory patients at time points for fluid volume, biomarkers and outcomes.

RESULTS

At 2 h 19 patients responded to fluids (Group 1) while 4 were refractory (Group 2); at 6-8 h 14 responded (Group 3) and 9 were refractory (Group 4). No demographic differences between patient groups, but Group 4 had worse prognostic features than Group 3. Refractory patients received significantly more fluid (Group 4 mean 7082 ml vs. Group 3 5022 mL, P < 0.001) in first 24 h and had worse outcome. No significant differences in biomarkers between the groups.

CONCLUSIONS

The serum biomarkers did not discriminate between fluid responsive and refractory patients. Refractory patients at 6-8 h had more severe disease on admission, did not benefit from additional fluids and had a worse outcome. New approaches to guide fluid resuscitation in patients with AP are required.

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

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

Extracellular Histones Inhibit Complement Activation through Interacting with Complement Component 4

Complement activation leads to membrane attack complex formation, which can lyse not only pathogens but also host cells. Histones can be released from the lysed or damaged cells and serve as a major type of damage-associated molecular pattern, but their effects on the complement system are not clear. In this study, we pulled down two major proteins from human serum using histone-conjugated beads: one was C-reactive protein and the other was C4, as identified by mass spectrometry. In surface plasmon resonance analysis, histone H3 and H4 showed stronger binding to C4 than other histones, with K_D around 1 nM. The interaction did not affect C4 cleavage to C4a and C4b. Because histones bind to C4b, a component of C3 and C5 convertases, their activities were significantly inhibited in the presence of histones. Although it is not clear whether the inhibition was achieved through blocking C3 and C5 convertase assembly or just through reducing their activity, the outcome was that both classical and mannose-binding lectin pathways were dramatically inhibited. Using a high concentration of C4 protein, histone-suppressed complement activity could not be fully restored, indicating C4 is not the only target of histones in those pathways. In contrast, the alternative pathway was almost spared, but the overall complement activity activated by zymosan was inhibited by histones. Therefore, we believe that histones inhibiting complement activation is a natural feedback mechanism to prevent the excessive injury of host cells.

Recent advances in pathophysiology of disseminated intravascular coagulation: the role of circulating histones and neutrophil extracellular traps

Disseminated intravascular coagulation (DIC) is an acquired condition that develops as a complication of systemic and sustained cell injury in conditions such as sepsis and trauma. It represents major dysregulation and increased thrombin generation in vivo. A poor understanding and recognition of the complex interactions in the coagulation, fibrinolytic, inflammatory, and innate immune pathways have resulted in continued poor management and high mortality rates in DIC. This review focuses attention on significant recent advances in our understanding of DIC pathophysiology. In particular, circulating histones and neutrophil extracellular traps fulfil established criteria in DIC pathogenesis. Both are damaging to the vasculature and highly relevant to the cross talk between coagulation and inflammation processes, which can culminate in adverse clinical outcomes. These molecules have a strong potential to be novel biomarkers and therapeutic targets in DIC, which is still considered synonymous with 'death is coming'.

Extracellular histones are clinically relevant mediators in the pathogenesis of acute respiratory distress syndrome

Background

Extracellular histones were recently identified as an inflammatory mediator involved in the pathogenesis of various organ injuries. This study aimed to examine extracellular histone levels and their clinical implications in acute respiratory distress syndrome (ARDS) patients and to explore histone-mediated effects through ex-vivo investigations.

Methods

Extracellular histones, cytokine profiles and clinical data from 96 ARDS patients and 30 healthy volunteers were obtained. Human bronchial epithelial cells (BEAS-2B), human pulmonary artery endothelial cells (HPAEC), and human monocytic U937 cells were exposed to bronchoalveolar lavage fluid (BALF) collected from ARDS patients, and cellular damage and cytokine production were assessed. Furthermore, the effect of histone-targeted interventions by heparin or anti-histone antibody was evaluated.

Results

Plasma and BALF extracellular histone levels were much higher in ARDS patients than in healthy controls. There was a significant association between extracellular histones and ARDS severity and mortality. In addition, extracellular histones correlated with an evident systemic inflammation detected in ARDS patients. Ex-vivo analysis further showed that ARDS patient’s BALF remarkably induced epithelial and endothelial cell damage and stimulated cytokine production in the supernatant of U937 cells. The adverse effects on these cells could be abrogated by heparin or anti-histone antibody.

Conclusions

Extracellular histones in ARDS patients are excessively increased and may contribute to disease aggravation by inducing cellular damage and promoting systemic inflammation. Targeting extracellular histones may provide a promising approach for treating ARDS.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0651-5) contains supplementary material, which is available to authorized users.

Accuracy of circulating histones in predicting persistent organ failure and mortality in patients with acute pancreatitis

BACKGROUND

Early prediction of acute pancreatitis severity remains a challenge. Circulating levels of histones are raised early in mouse models and correlate with disease severity. It was hypothesized that circulating histones predict persistent organ failure in patients with acute pancreatitis.

METHODS

Consecutive patients with acute pancreatitis fulfilling inclusion criteria admitted to Royal Liverpool University Hospital were enrolled prospectively between June 2010 and March 2014. Blood samples were obtained within 48 h of abdominal pain onset and relevant clinical data during the hospital stay were collected. Healthy volunteers were enrolled as controls. The primary endpoint was occurrence of persistent organ failure. The predictive values of circulating histones, clinical scores and other biomarkers were determined.

RESULTS

Among 236 patients with acute pancreatitis, there were 156 (66·1 per cent), 57 (24·2 per cent) and 23 (9·7 per cent) with mild, moderate and severe disease respectively, according to the revised Atlanta classification. Forty-seven healthy volunteers were included. The area under the receiver operating characteristic (ROC) curve (AUC) for circulating histones in predicting persistent organ failure and mortality was 0·92 (95 per cent c.i. 0·85 to 0·99) and 0·96 (0·92 to 1·00) respectively; histones were at least as accurate as clinical scores or biochemical markers. For infected pancreatic necrosis and/or sepsis, the AUC was 0·78 (0·62 to 0·94). Histones did not predict or correlate with local pancreatic complications, but correlated negatively with leucocyte cell viability (r = -0·511, P = 0·001).

CONCLUSION

Quantitative assessment of circulating histones in plasma within 48 h of abdominal pain onset can predict persistent organ failure and mortality in patients with acute pancreatitis. Early death of immune cells may contribute to raised circulating histone levels in acute pancreatitis.

Current Pathological and Laboratory Considerations in the Diagnosis of Disseminated Intravascular Coagulation

Systemically sustained thrombin generation in vivo is the hallmark of disseminated intravascular coagulation (DIC). Typically, this is in response to a progressing disease state that is associated with significant cellular injury. The etiology could be infectious or noninfectious, with the main pathophysiological mechanisms involving cross-activation among coagulation, innate immunity, and inflammatory responses. This leads to consumption of both pro- and anticoagulant factors as well as endothelial dysfunction and disrupted homeostasis at the blood vessel wall interface. In addition to the release of tissue plasminogen activator (tPA) and soluble thrombomodulin (sTM) following cellular activation and damage, respectively, there is the release of damage-associated molecular patterns (DAMPs) such as extracellular histones and cell-free DNA. Extracellular histones are increasingly recognized as significantly pathogenic in critical illnesses through direct cell toxicity, the promotion of thrombin generation, and the induction of neutrophil extracellular trap (NET) formation. Clinically, high circulating levels of histones and histone–DNA complexes are associated with multiorgan failure, DIC, and adverse patient outcomes. Their measurements as well as that of other DAMPs and molecular markers of thrombin generation are not yet applicable in the routine diagnostic laboratory. To provide a practical diagnostic tool for acute DIC, a composite scoring system using rapidly available coagulation tests is recommended by the International Society on Thrombosis and Haemostasis. Its usefulness and limitations are discussed alongside the advances and unanswered questions in DIC pathogenesis.

Epidemiology, virulence factors and management of the pneumococcus

Pneumococcal infections continue to cause significant morbidity and mortality in patients throughout the world. This microorganism remains the most common bacterial cause of community-acquired pneumonia and is associated with a considerable burden of disease and health-care costs in both developed and developing countries. Emerging antibiotic resistance has been a concern because of its potential negative impact on the outcome of patients who receive standard antibiotic therapy. However, there have been substantial changes in the epidemiology of this pathogen in recent years, not least of which has been due to the use of pneumococcal conjugate vaccines in children, with subsequent herd protection in unvaccinated adults and children. Furthermore, much recent research has led to a better understanding of the virulence factors of this pathogen and their role in the pathogenesis of severe pneumococcal disease, including the cardiac complications, as well as the potential role of adjunctive therapy in the management of severely ill cases. This review will describe recent advances in our understanding of the epidemiology, virulence factors, and management of pneumococcal community-acquired pneumonia.

Disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is an acquired syndrome characterized by widespread intravascular activation of coagulation that can be caused by infectious insults (such as sepsis) and non-infectious insults (such as trauma). The main pathophysiological mechanisms of DIC are inflammatory cytokine-initiated activation of tissue factor-dependent coagulation, insufficient control of anticoagulant pathways and plasminogen activator inhibitor 1-mediated suppression of fibrinolysis. Together, these changes give rise to endothelial dysfunction and microvascular thrombosis, which can cause organ dysfunction and seriously affect patient prognosis. Recent observations have pointed to an important role for extracellular DNA and DNA-binding proteins, such as histones, in the pathogenesis of DIC. The International Society on Thrombosis and Haemostasis (ISTH) established a DIC diagnostic scoring system consisting of global haemostatic test parameters. This scoring system has now been well validated in diverse clinical settings. The theoretical cornerstone of DIC management is the specific and vigorous treatment of the underlying conditions, and DIC should be simultaneously managed to improve patient outcomes. The ISTH guidance for the treatment of DIC recommends treatment strategies that are based on current evidence. In this Primer, we provide an updated overview of the pathophysiology, diagnosis and management of DIC and discuss the future directions of basic and clinical research in this field.

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

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

The role of extracellular histones in haematological disorders

Over the past decades, chromosomal alterations have been extensively investigated for their pathophysiological relevance in haematological malignancies. In particular, epigenetic modifications of intra-nuclear histones are now known as key regulators of healthy cell cycles that have also evolved into novel therapeutic targets for certain blood cancers. Thus, for most haematologists, histones are DNA-chained proteins that are buried deep within chromatin. However, the plot has deepened with recent revelations on the function of histones when unchained and released extracellularly upon cell death or from activated neutrophils as part of neutrophil extracellular traps (NETs). Extracellular histones and NETs are increasingly recognized for profound cytotoxicity and pro-coagulant effects. This article highlights the importance of recognizing this new paradigm of extracellular histones as a key player in host defence through its damage-associated molecular patterns, which could translate into novel diagnostic and therapeutic biomarkers in various haematological and critical disorders.

Sepsis: in search of cure

INTRODUCTION

Sepsis is a complex inflammatory disorder believed to originate from an infection by any types of microbes and/or their products. It is the leading cause of death in intensive care units (ICUs) throughout the globe. The mortality rates depend both on the severity of infection and the host's response to infection.

METHODS

Literature survey on pathobiology of sepsis in general and failure of more than hundred clinical trials conducted so far in search of a possible cure for sepsis resulted in the preparation of this manuscript.

FINDINGS

Sepsis lacks a suitable animal model that mimics human sepsis. However, based on the results obtained in animal models of sepsis, clinical trials conducted so far have been disappointing. Although involvement of multiple mediators and pathways in sepsis has been recognized, only few components are being targeted and this could be the major reason behind the failure of clinical trials.

CONCLUSION

Inability to recognize a single critical mediator of sepsis may be the underlying cause for the poor therapeutic intervention of sepsis. Therefore, sepsis is still considered as a disease-in search of cure.