Heparin-Functionalized Adsorbents Eliminate Central Effectors of Immunothrombosis, including Platelet Factor 4, High-Mobility Group Box 1 Protein and Histones

Effect of a biomimetic pathogen adsorbing device on inflammatory biomarkers in COVID-19 patients

INTRODUCTION

The Seraph 100 Microbind Affinity blood filter eliminate bacteria, viruses, fungi and toxins from blood stream.

METHODS

This is a prospective multicenter observational biomarker trial in PCR-positive SARS-CoV-2 patients with acute respiratory failure. Biomarkers were sequentially tested at three time points.

RESULTS

Forty-two patients with SARS-CoV-2 detected by PCR with acute respiratory failure were included. When receiving hemoperfusion treatment, 27 (64%) patients were on mechanical ventilation, 41 (98%) patients were treated in the ICU. The 3-month survival was 52%. After one hemoperfusion treatment cycle, D-dimer (p = 0.014), hemoglobin (p = 0.003) and LDH (p = 0.001) concentrations were significantly reduced 4 days after treatment. From the multiplex assay IL-1b, CXCL8/ IL-8, IL-10, IL-13, IL-15, CCL11/Eotaxin, G-CSF, and CXCL10/IP-10 were significantly reduced 1 h after treatment, however not 4 days later.

CONCLUSION

Hemoperfusion with Seraph 100 Microbind Affinity Filter in patients with severe COVID-19 can transiently reduce several inflammatory biomarkers in the blood.

Selective Clearance of Circulating Histones Based on Dodecapeptide-Grafted Copolymer Material for Sepsis Blood Purification

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Research indicates that circulating histones, as pathogenic factors, may represent a therapeutic target for sepsis. However, effectively clearing circulating histones poses a challenge due to their structural similarity to normal blood proteins, their low abundance in the bloodstream, and serious interference from other blood biomacromolecules. Here we design a dodecapeptide-based functional polymer that can selectively adsorb circulating histones from the blood. The peptide, named P1 (HNHHQLALVESY), was discovered through phage display screening and demonstrated a strong affinity for circulating histones while exhibiting negligible affinities for common proteins in the blood, such as human serum albumin (HSA), immunoglobulin G (IgG), and transferrin (TRF). Furthermore, the P1 peptide was incorporated into a functional polymer design, poly(PEGMA-co-P1), which was immobilized onto a silica gel surface through reversible addition-fragmentation chain transfer polymerization. The resulting material was characterized using solid nuclear magnetic resonance, thermogravimetric analysis, and X-ray photoelectron spectroscopy. This material demonstrated the ability to selectively and efficiently capture circulating histones from both model solutions and whole blood samples while also exhibiting satisfactory blood compatibility, good antifouling properties, and resistance to interference. Satisfactory binding affinity and efficient capture capacity toward histone were also observed for the other screened peptide P2 (QMSMDLFGSNFV)-grafted polymer, validating phage display as a reliable ligand screening strategy. These findings present an approach for the specific clearance of circulating histones and hold promise for future clinical applications in blood purification toward sepsis.

Platelet HMGB1 steers intravascular immunity and thrombosis

Platelets navigate the fine balance between homeostasis and injury. They regulate vascular homeostasis and drive repair after injury amidst leukocyte extravasation. Crucially, platelets initiate extracellular traps generation and promote immunothrombosis. In chronic human diseases, platelet action often extends beyond its normative role, sparking sustained reciprocal activation of leukocytes and mural cells, culminating in adverse vascular remodeling. Studies in the last decade have spotlighted a novel key player in platelet activation, the high mobility group box 1 (HMGB1) protein. Despite its initial characterization as a chromatin molecule, anucleated platelets express abundant HMGB1, which has emerged as a linchpin in thromboinflammatory risks and microvascular remodeling. We propose that a comprehensive assessment of platelet HMGB1, spanning quantification of content, membrane localization, and accumulation of HMGB1-expressing vesicles in biological fluids should be integral to dissecting and quantifying platelet activation. This review provides evidence supporting this claim and underscores the significance of platelet HMGB1 as a biomarker in conditions associated with heightened thrombotic risks and systemic microvascular involvement, spanning cardiovascular, autoimmune, and infectious diseases.

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.

[Extracorporeal removal of pathogens using a biomimetic adsorber-A new treatment strategy for the intensive care unit : Seraph® 100 Microbind® Affinity Blood Filter and its fields of application]

BACKGROUND

In 2019 the World Health Organization (WHO) listed antimicrobial resistance among the top 10 threats to global health. The Seraph® 100 Microbind® Affinity blood filter (Seraph® 100) has been in use since 2019 to eliminate pathogens from the bloodstream in addition to anti-infective pharmacotherapy. It is the first device used to rapidly and efficiently reduce the number of circulating bacteria and viruses.

OBJECTIVE

After a background on the concept of extracorporeal pathogen removal in general, this review summarizes the preclinical and clinical data on the Seraph® 100 Affinity Blood Filter. The clinical effect of this treatment and potential therapeutic options are described.

METHODS

Structured PubMed review including references published up to February 2024.

RESULTS

Case reports, uncontrolled observational studies and data from registries show widespread clinical use of the Seraph® 100 ranging from difficult to treat bacterial (super) infections to viral infections. The treatment can be done as stand-alone hemoperfusion or in combination with all forms of kidney replacement therapy as well as in extracorporeal membrane oxygenation.

CONCLUSION

The use of the Seraph® 100 varies in terms of duration, concomitant therapy and clinical settings. Due to the absence of prospective controlled trials the clinical effect cannot be properly evaluated.

Targeting extranuclear histones to alleviate acute and chronic inflammation

Extracellular histones instigate an inflammatory triad - centered on cytotoxicity, immune cell stimulation, and coagulation - ultimately shaping the dynamics and outcome of various inflammatory pathologies. Given the virtual absence of beneficial functions of histones in the extracellular space, in recent years a number of interference strategies have emerged. In this review we summarize pathogenic functions of extracellular histones and highlight current developments of therapeutic interference. Finally, we elaborate on the current status of preclinical attempts to interfere with extracellular histones in the context of a focus on sepsis and cardiovascular diseases, both of which are leading causes of mortality worldwide.

Targeting Neutrophil Extracellular Trap Formation: Exploring Promising Pharmacological Strategies for the Treatment of Preeclampsia

Neutrophils, which constitute the most abundant leukocytes in human blood, emerge as crucial players in the induction of endothelial cell death and the modulation of endothelial cell responses under both physiological and pathological conditions. The hallmark of preeclampsia is endothelial dysfunction induced by systemic inflammation, in which neutrophils, particularly through the formation of neutrophil extracellular traps (NETs), play a pivotal role in the development and perpetuation of endothelial dysfunction and the hypertensive state. Considering the potential of numerous pharmaceutical agents to attenuate NET formation (NETosis) in preeclampsia, a comprehensive assessment of the extensively studied candidates becomes imperative. This review aims to identify mechanisms associated with the induction and negative regulation of NETs in the context of preeclampsia. We discuss potential drugs to modulate NETosis, such as NF-κβ inhibitors, vitamin D, and aspirin, and their association with mutagenicity and genotoxicity. Strong evidence supports the notion that molecules involved in the activation of NETs could serve as promising targets for the treatment of preeclampsia.

The fluorochrome-to-protein ratio is crucial for the flow cytometric detection of tissue factor on extracellular vesicles

Extracellular vesicles (EVs) have crucial roles in hemostasis and coagulation. They sustain coagulation by exposing phosphatidylserine and initiate clotting by surface expression of tissue factor (TF) under inflammatory conditions. As their relevance as biomarkers of coagulopathy is increasingly recognized, there is a need for the sensitive and reliable detection of TF+ EVs, but their flow cytometric analysis is challenging and has yielded controversial findings for TF expression on EVs in the vascular system. We investigated the effect of different fluorochrome-to-protein (F/P) ratios of anti-TF-fluorochrome conjugates on the flow cytometric detection of TF+ EVs from activated monocytes, mesenchymal stem cells (MSCs), and in COVID-19 plasma. Using a FITC-labeled anti-TF antibody (clone VD8), we show that the percentage of TF+ EVs declined with decreasing F/P ratios. TF was detected on 7.6%, 5.4%, and 1.1% of all EVs derived from activated monocytes at F/P ratios of 7.7:1, 6.6:1, and 5.2:1. A similar decline was observed for EVs from MSCs and for EVs in plasma, whereas the detection of TF on cells remained unaffected by different F/P ratios. We provide clear evidence that next to the antibody clone, the F/P ratio affects the flow cytometric detection of TF+ EVs and should be carefully controlled.

A crucial role of neutrophil extracellular traps in pulmonary infectious diseases

Neutrophil extracellular traps (NETs), extrusions of intracellular DNA with attached granular material that exert an antibacterial effect through entangling, isolating, and immobilizing microorganisms, have been extensively studied in recent decades. The primary role of NETs is to entrap and facilitate the killing of bacteria, fungi, viruses, and parasites, preventing bacterial and fungal dissemination. NET formation has been described in many pulmonary diseases, including both infectious and non-infectious. NETs are considered a double-edged sword. As innate immune cells, neutrophils release NETs to kill pathogens and remove cellular debris. However, the deleterious effects of excessive NET release in lung disease are particularly important because NETs and by-products of NETosis can directly induce epithelial and endothelial cell death while simultaneously inducing inflammatory cytokine secretion and immune-mediated thrombosis. Thus, NET formation must be tightly regulated to preserve the anti-microbial capability of NETs while minimizing damage to the host. In this review, we summarized the recent updates on the mechanism of NETs formation and pathophysiology associated with excessive NETs, aiming to provide insights for research and treatment of pulmonary infectious diseases.

Expression of Tissue Factor and Platelet/Leukocyte Markers on Extracellular Vesicles Reflect Platelet-Leukocyte Interaction in Severe COVID-19

Severe COVID-19 is frequently associated with thromboembolic complications. Increased platelet activation and platelet-leukocyte aggregate formation can amplify thrombotic responses by inducing tissue factor (TF) expression on leukocytes. Here, we characterized TF-positive extracellular vesicles (EVs) and their cellular origin in 12 patients suffering from severe COVID-19 (time course, 134 samples overall) and 25 healthy controls. EVs exposing phosphatidylserine (PS) were characterized by flow cytometry. Their cellular origin was determined by staining with anti-CD41, anti-CD45, anti-CD235a, and anti-CD105 as platelet, leukocyte, red blood cell, and endothelial markers. We further investigated the association of EVs with TF, platelet factor 4 (PF4), C-reactive protein (CRP), and high mobility group box-1 protein (HMGB-1). COVID-19 patients showed higher levels of PS-exposing EVs compared to controls. The majority of these EVs originated from platelets. A higher amount of EVs in patient samples was associated with CRP, HMGB-1, PF4, and TF as compared to EVs from healthy donors. In COVID-19 samples, 16.5% of all CD41+ EVs displayed the leukocyte marker CD45, and 55.5% of all EV aggregates (CD41+CD45+) co-expressed TF, which reflects the interaction of platelets and leukocytes in COVID-19 on an EV level.

Targeting circulating high mobility group box-1 and histones by extracorporeal blood purification as an immunomodulation strategy against critical illnesses

Both high mobility group box-1 (HMGB1) and histones are major damage-associated molecular patterns (DAPMs) that mediate lethal systemic inflammation, activation of the complement and coagulation system, endothelial injury and multiple organ dysfunction syndrome in critical illnesses. Although accumulating evidence collectively shows that targeting HMGB1 or histones by their specific antibodies or inhibitors could significantly mitigate aberrant immune responses in multiple critically ill animal models, routine clinical use of such agents is still not recommended by any guideline. In contrast, extracorporeal blood purification, which has been widely used to replace dysfunctional organs and remove exogenous or endogenous toxins in intensive care units, may also exert an immunomodulatory effect by eliminating inflammatory mediators such as cytokines, endotoxin, HMGB1 and histones in patients with critical illnesses. In this review, we summarize the multiple immunopathological roles of HMGB1 and histones in mediating inflammation, immune thrombosis and organ dysfunction and discuss the rationale for the removal of these DAMPs using various hemofilters. The latest preclinical and clinical evidence for the use of extracorporeal blood purification to improve the clinical outcome of critically ill patients by targeting circulating HMGB1 and histones is also gathered.

Rationale for sequential extracorporeal therapy (SET) in sepsis

Sepsis and septic shock remain drivers for morbidity and mortality in critical illness. The clinical picture of patients presenting with these syndromes evolves rapidly and may be characterised by: (a) microbial host invasion, (b) establishment of an infection focus, (c) opsonisation of bacterial products (e.g. lipopolysaccharide), (d) recognition of pathogens resulting in an immune response, (e) cellular and humoral effects of circulating pathogen and pathogen products, (f) immunodysregulation and endocrine effects of cytokines, (g) endothelial and organ damage, and (h) organ crosstalk and multiple organ dysfunction. Each step may be a potential target for a specific therapeutic approach. At various stages, extracorporeal therapies may target circulating molecules for removal. In sequence, we could consider: (a) pathogen removal from the circulation with affinity binders and cartridges (specific), (b) circulating endotoxin removal by haemoperfusion with polymyxin B adsorbers (specific), (c) cytokine removal by haemoperfusion with sorbent cartridges or adsorbing membranes (non-specific), (d) extracorporeal organ support with different techniques for respiratory and cardiac support (CO₂ removal or extracorporeal membrane oxygenation), and renal support (haemofiltration, haemodialysis, or ultrafiltration). The sequence of events and the use of different techniques at different points for specific targets will likely require trials with endpoints other than mortality. Instead, the primary objectives should be to achieve the desired action by using extracorporeal therapy at a specific point.

What is the impact of circulating histones in COVID-19: a systematic review

The infectious respiratory condition COVID-19 manifests a clinical course ranging from mild/moderate up-to critical systemic dysfunction and death linked to thromboinflammation. During COVID-19 infection, neutrophil extracellular traps participating in cytokine storm and coagulation dysfunction have emerged as diagnostic/prognostic markers. The characterization of NET identified that mainly histones, have the potential to initiate and propagate inflammatory storm and thrombosis, leading to increased disease severity and decreased patient survival. Baseline assessment and serial monitoring of blood histone concentration may be conceivably useful in COVID-19. We performed a literature review to explore the association among increased circulating levels of histones, disease severity/mortality in COVID-19 patients, and comparison of histone values between COVID-19 and non-COVID-19 patients. We carried out an electronic search in Medline and Scopus, using the keywords "COVID-19" OR "SARS-CoV-2" AND "histone" OR "citrullinated histones" OR "hyperhistonemia", between 2019 and present time (i.e., June 07th, 2022), which allowed to select 17 studies, totaling 1,846 subjects. We found that substantially elevated histone values were consistently present in all COVID-19 patients who developed unfavorable clinical outcomes. These findings suggest that blood histone monitoring upon admission and throughout hospitalization may be useful for early identification of higher risk of unfavorable COVID-19 progression. Therapeutic decisions in patients with SARS-CoV-2 based on the use of histone cut-off values may be driven by drugs engaging histones, finally leading to the limitation of cytotoxic, inflammatory, and thrombotic effects of circulating histones in viral sepsis.

Activated Platelets and Platelet-Derived Extracellular Vesicles Mediate COVID-19-Associated Immunothrombosis

Activated platelets and platelet-derived extracellular vesicles (EVs) have emerged as central players in thromboembolic complications associated with severe coronavirus disease 2019 (COVID-19). Platelets bridge hemostatic, inflammatory, and immune responses by their ability to sense pathogens via various pattern recognition receptors, and they respond to infection through a diverse repertoire of mechanisms. Dysregulated platelet activation, however, can lead to immunothrombosis, a simultaneous overactivation of blood coagulation and the innate immune response. Mediators released by activated platelets in response to infection, such as antimicrobial peptides, high mobility group box 1 protein, platelet factor 4 (PF4), and PF4⁺ extracellular vesicles promote neutrophil activation, resulting in the release of neutrophil extracellular traps and histones. Many of the factors released during platelet and neutrophil activation are positively charged and interact with endogenous heparan sulfate or exogenously administered heparin via electrostatic interactions or via specific binding sites. Here, we review the current state of knowledge regarding the involvement of platelets and platelet-derived EVs in the pathogenesis of immunothrombosis, and we discuss the potential of extracorporeal therapies using adsorbents functionalized with heparin to deplete platelet-derived and neutrophil-derived mediators of immunothrombosis.