Characterization of Microvesicles in Septic Shock Using High-Sensitivity Flow Cytometry

Associations of tissue factor and tissue factor pathway inhibitor with organ dysfunctions in septic shock

Coagulopathy, microvascular alterations and concomitant organ dysfunctions are hallmarks of sepsis. Attempts to attenuate coagulation activation with an inhibitor of tissue factor (TF), i.e. tissue factor pathway inhibitor (TFPI), revealed no survival benefit in a heterogenous group of sepsis patients, but a potential survival benefit in patients with an international normalized ratio (INR) < 1.2. Since an increased TF/TFPI ratio determines the procoagulant activity specifically on microvascular endothelial cells in vitro, we investigated whether TF/TFPI ratio in blood is associated with INR alterations, organ dysfunctions, disseminated intravascular coagulation (DIC) and outcome in septic shock. Twenty-nine healthy controls (HC) and 89 patients with septic shock admitted to a tertiary ICU were analyzed. TF and TFPI in blood was analyzed and related to organ dysfunctions, DIC and mortality. Patients with septic shock had 1.6-fold higher levels of TF and 2.9-fold higher levels of TFPI than HC. TF/TFPI ratio was lower in septic shock compared to HC (0.003 (0.002-0.005) vs. 0.006 (0.005-0.008), p < 0.001). Non-survivors had higher TFPI levels compared to survivors (43038 (29354-54023) vs. 28041 (21675-46582) pg/ml, p = 0.011). High TFPI levels were associated with acute kidney injury, liver dysfunction, DIC and disease severity. There was a positive association between TF/TFPI ratio and troponin T (b = 0.531 (0.309-0.754), p < 0.001). A high TF/TFPI ratio is exclusively associated with myocardial injury but not with other organ dysfunctions. Systemic TFPI levels seem to reflect disease severity. These findings point towards a pathophysiologic role of TF/TFPI in sepsis-induced myocardial injury.

Exosomal mediators in sepsis and inflammatory organ injury: unraveling the role of exosomes in intercellular crosstalk and organ dysfunction

Sepsis, a severe systemic inflammatory response to infection, remains a leading cause of morbidity and mortality worldwide. Exosomes, as mediators of intercellular communication, play a pivotal role in the pathogenesis of sepsis through modulating immune responses, metabolic reprogramming, coagulopathy, and organ dysfunction. This review highlights the emerging significance of exosomes in these processes. Initially, it provides an in-depth insight into exosome biogenesis and characterization, laying the groundwork for understanding their diverse and intricate functions. Subsequently, it explores the regulatory roles of exosomes in various immune cells such as neutrophils, macrophages, dendritic cells, T cells, and B cells. This analysis elucidates how exosomes are pivotal in modulating immune responses, thus contributing to the complexity of sepsis pathophysiology. Additionally, this review delves into the role of exosomes in the regulation of metabolism and subsequent organ dysfunction in sepsis. It also establishes a connection between exosomes and the coagulation cascade, which affects endothelial integrity and promotes thrombogenesis in sepsis. Moreover, the review discusses the dual role of exosomes in the progression and resolution of sepsis, exploring their complex involvement in inflammation and healing processes. Furthermore, it underscores their potential as biomarkers and therapeutic targets. Understanding these mechanisms presents new opportunities for novel interventions to mitigate the severe outcomes of sepsis, emphasizing the therapeutic promise of exosome research in critical care settings.

Communication from the Scientific Standardization Committees of the International Society on Thrombosis and Haemostasis on vascular endothelium-related biomarkers in disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is not a disease criterion but a pathomechanistic process that accompanies various underlying diseases. According to the International Society on Thrombosis and Haemostasis definition, endothelial injury is an essential component in addition to systemic coagulation activation. Despite this definition, current diagnostic criteria for DIC do not include biomarkers for vascular endothelial injury. Endothelial cells are critical for hemostatic regulation because they produce various antithrombotic substances and express anticoagulant factors at the same time as facilitating coagulation, inflammatory reactions, platelet aggregation, and fibrinolysis with acute injury. Endothelial cells also exhibit various receptors, adhesion molecules, and the critical role of glycocalyx that regulates cellular interactions in thromboinflammation. For clinicians, biomarkers suitable for assessing endothelial injury are not readily available. Although we still do not have ideal biomarkers, antithrombin activity and von Willebrand factor can be candidates for the endothelium-related markers because those reflect the severity and are available in most clinical settings. Further, the dysfunction of endothelial cell in DIC arising from various underlying diseases is likely highly variable. For example, the involvement of endothelial dysfunction is significant in sepsis-induced coagulopathy, while moderate in trauma-induced coagulopathy, and variable in hematologic malignancy-associated coagulopathy. Because of the complexity of disease status associated with DIC, further research searching clinically available endothelium-related biomarkers is expected to establish individualized diagnostic criteria and potential therapeutic approaches.

THE ROLES OF EXTRACELLULAR VESICLES IN SEPSIS AND SYSTEMIC INFLAMMATORY RESPONSE SYNDROME

ABSTRACT

Sepsis is a life-threatening organ dysfunction, caused by dysregulation of the host response to infection. To understand the underlying mechanisms of sepsis, the vast spectrum of extracellular vesicles (EVs) is gaining importance in this research field. A connection between EVs and sepsis was shown in 1998 in an endotoxemia pig model. Since then, the number of studies describing EVs as markers and mediators of sepsis increased steadily. Extracellular vesicles in sepsis could be friends and foes at the same time depending on their origin and cargo. On the one hand, transfer of EVs or outer membrane vesicles can induce sepsis or systemic inflammatory response syndrome with comparable efficiency as well-established methods, such as cecal ligation puncture or lipopolysaccharide injection. On the other hand, EVs could provide certain therapeutic effects, mediated via reduction of reactive oxygen species, inflammatory cytokines and chemokines, influence on macrophage polarization and apoptosis, as well as increase of anti-inflammatory cytokines. Moreover, EVs could be helpful in the diagnosis of sepsis. Extracellular vesicles of different cellular origin, such as leucocytes, macrophages, platelets, and granulocytes, have been suggested as potential sepsis biomarkers. They ensure the diagnosis of sepsis earlier than classical clinical inflammation markers, such as C-reactive protein, leucocytes, or IL-6. This review summarizes the three roles of EVs in sepsis-mediator/inducer, biomarker, and therapeutic tool.

Extracellular vesicles participate in the pathogenesis of sepsis

Sepsis is one of the leading causes of mortality worldwide and is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The early diagnosis and effective treatment of sepsis still face challenges due to its rapid progression, dynamic changes, and strong heterogeneity among different individuals. To develop novel strategies to control sepsis, a better understanding of the complex mechanisms of sepsis is vital. Extracellular vesicles (EVs) are membrane vesicles released from cells through different mechanisms. In the disease state, the number of EVs produced by activated or apoptotic cells and the cargoes they carry were altered. They regulated the function of local or distant host cells in autocrine or paracrine ways. Current studies have found that EVs are involved in the occurrence and development of sepsis through multiple pathways. In this review, we focus on changes in the cargoes of EVs in sepsis, the regulatory roles of EVs derived from host cells and bacteria, and how EVs are involved in multiple pathological processes and organ dysfunction in sepsis. Overall, EVs have great application prospects in sepsis, such as early diagnosis of sepsis, dynamic monitoring of disease, precise therapeutic targets, and prevention of sepsis as a vaccine platform.

Pathophysiology of Coagulation and Emerging Roles for Extracellular Vesicles in Coagulation Cascades and Disorders

The notion of blood coagulation dates back to the ancient Greek civilization. However, the emergence of innovative scientific discoveries that started in the seventeenth century formulated the fundamentals of blood coagulation. Our understanding of key coagulation processes continues to evolve, as novel homeostatic and pathophysiological aspects of hemostasis are revealed. Hemostasis is a dynamic physiological process, which stops bleeding at the site of injury while maintaining normal blood flow within the body. Intrinsic and extrinsic coagulation pathways culminate in the homeostatic cessation of blood loss, through the sequential activation of the coagulation factors. Recently, the cell-based theory, which combines these two pathways, along with newly discovered mechanisms, emerged to holistically describe intricate in vivo coagulation mechanisms. The complexity of these mechanisms becomes evident in coagulation diseases such as hemophilia, Von Willebrand disease, thrombophilia, and vitamin K deficiency, in which excessive bleeding, thrombosis, or unnecessary clotting, drive the development and progression of diseases. Accumulating evidence implicates cell-derived and platelet-derived extracellular vesicles (EVs), which comprise microvesicles (MVs), exosomes, and apoptotic bodies, in the modulation of the coagulation cascade in hemostasis and thrombosis. As these EVs are associated with intercellular communication, molecular recycling, and metastatic niche creation, emerging evidence explores EVs as valuable diagnostic and therapeutic approaches in thrombotic and prothrombotic diseases.

The Role of Platelet-Derived Extracellular Vesicles in Immune-Mediated Thrombosis

Platelet-derived extracellular vesicles (PEVs) play important roles in hemostasis and thrombosis. There are three major types of PEVs described based on their size and characteristics, but newer types may continue to emerge owing to the ongoing improvement in the methodologies and terms used to define various types of EVs. As the literature on EVs is growing, there are continuing attempts to standardize protocols for EV isolation and reach consensus in the field. This review provides information on mechanisms of PEV production, characteristics, cellular interaction, and their pathological role, especially in autoimmune and infectious diseases. We also highlight the mechanisms through which PEVs can activate parent cells in a feedback loop.

Blood Cell-Derived Microvesicles in Hematological Diseases and beyond

Microvesicles or ectosomes represent a major type of extracellular vesicles that are formed by outward budding of the plasma membrane. Typically, they are bigger than exosomes but smaller than apoptotic vesicles, although they may overlap with both in size and content. Their release by cells is a means to dispose redundant, damaged, or dangerous material; to repair membrane lesions; and, primarily, to mediate intercellular communication. By participating in these vital activities, microvesicles may impact a wide array of cell processes and, consequently, changes in their concentration or components have been associated with several pathologies. Of note, microvesicles released by leukocytes, red blood cells, and platelets, which constitute the vast majority of plasma microvesicles, change under a plethora of diseases affecting not only the hematological, but also the nervous, cardiovascular, and urinary systems, among others. In fact, there is evidence that microvesicles released by blood cells are significant contributors towards pathophysiological states, having inflammatory and/or coagulation and/or immunomodulatory arms, by either promoting or inhibiting the relative disease phenotypes. Consequently, even though microvesicles are typically considered to have adverse links with disease prognosis, progression, or outcomes, not infrequently, they exert protective roles in the affected cells. Based on these functional relations, microvesicles might represent promising disease biomarkers with diagnostic, monitoring, and therapeutic applications, equally to the more thoroughly studied exosomes. In the current review, we provide a summary of the features of microvesicles released by blood cells and their potential implication in hematological and non-hematological diseases.

Role of extracellular vesicles in severe pneumonia and sepsis

INTRODUCTION

Extracellular vesicles (EV) released constitutively or following external stimuli from structural and immune cells are now recognized as important mediators of cell-to-cell communication. They are involved in the pathogenesis of pneumonia and sepsis, leading causes of acute respiratory distress syndrome (ARDS) where mortality rates remain up to 40%. Multiple investigators have demonstrated that one of the underlying mechanisms of the effects of EVs is through the transfer of EV content to host cells, resulting in apoptosis, inflammation, and permeability in target organs.

AREAS COVERED

The current review focuses on preclinical research examining the role of EVs released into the plasma and injured alveolus during pneumonia and sepsis.

EXPERT OPINION

Inflammation is associated with elevated levels of circulating EVs that are released by activated structural and immune cells and can have significant proinflammatory, procoagulant, and pro-permeability effects in critically ill patients with pneumonia and/or sepsis. However, clinical translation of the use of EVs as biomarkers or potential therapeutic targets may be limited by current methodologies used to identify and quantify EVs accurately (whether from host cells or infecting organisms) and lack of understanding of the role of EVs in the reparative phase during recovery from pneumonia and/or sepsis.

A new strategy to count and sort neutrophil-derived extracellular vesicles: Validation in infectious disorders

Newly recognized polymorphonuclear neutrophil (PMNs) functions include the ability to release subcellular mediators such as neutrophil-derived extracellular vesicles (NDEVs) involved in immune and thrombo-inflammatory responses. Elevation of their plasmatic level has been reported in a variety of infectious and cardiovascular disorders, but the clinical use of this potential biomarker is hampered by methodological issues. Although flow cytometry (FCM) is currently used to detect NDEVs in the plasma of patients, an extensive characterization of NDEVs has never been done. Moreover, their detection remains challenging because of their small size and low antigen density. Therefore, the objective of the present study was first to establish a surface antigenic signature of NDEVs detectable by FCM and therefore to improve their detection in biological fluids by developing a strategy allowing to overcome their low fluorescent signal and reduce the background noise. By testing a large panel of 54 antibody specificities already reported to be positive on PMNs, we identified a profile of 15 membrane protein markers, including 4 (CD157, CD24, CD65 and CD66c) never described on NDEVs. Among them, CD15, CD66b and CD66c were identified as the most sensitive and specific markers to detect NDEVs by FCM. Using this antigenic signature, we developed a new strategy combining the three best antibodies in a cocktail and reducing the background noise by size exclusion chromatography (SEC). This strategy allowed a significant improvement in NDEVs enumeration in plasma from sepsis patients and made it feasible to efficiently sort NDEVs from COVID-19 patients. Altogether, this work opens the door to a more valuable measurement of NDEVs as a potential biomarker in clinical practice. A similar strategy could also be applied to improve detection by FCM of other rare subpopulations of EVs generated by tissues with limited access, such as vascular endothelium, cancer cells or placenta.

Detection of Sepsis in Platelets Using MicroRNAs and Membrane Antigens

The present study proposes to legitimize in sepsis a characteristic found in platelets that suffer storage lesions in blood banks, which is the increased expression of miRNA miR-320a in relation to miR-127. Under physiologically normal conditions, an inverse relationship is observed. The aim of this study was to verify whether the analysis of miR-320a and miR-127 expression in platelets could detect a decrease in their viability and function due to the presence of pathogens in the blood of patients hospitalized in the Intensive Care Unit. We also investigated the expression of membrane antigens sensitive to platelet activation. Of the 200 patients analyzed, only those who developed sepsis (140) were found to have a higher relative quantity of miR-320a than that of miR-127. This characteristic and the increased expression of membrane antigens P2Y12, CD62P, CD41, and CD61 showed a significant association (p < 0.01) with all types of sepsis evaluated in this study. Additionally, 40% of patients hospitalized for sepsis had negative results for the first cultures. We conclude that analysis of miR-127 and miR-320a expression combined with membrane antigens evaluation, in association with the available clinical and diagnostic parameters, are important tools to detect the onset of sepsis.

The Concentration of Large Extracellular Vesicles Differentiates Early Septic Shock From Infection

Septic shock represents a subset of sepsis with severe physiological aberrations and a higher mortality rate than sepsis alone. Currently, the laboratory tools which can be used to identify the state of septic shock are limited. In pre-clinical studies, extracellular vesicles (EVs), especially large EVs (lEVs), have been demonstrated a role as functional inflammatory mediators of sepsis. However, its longitudinal trend during the disease course has not been explored. In this study, the quantities and subtypes of plasma-derived lEVs were longitudinally compared between patients with septic shock (n = 21) and non-sepsis infection (n = 9), who presented within 48 h of their symptom onset. Blood specimens were collected for seven consecutive days after hospital admission. lEVs quantification and subtyping were performed using an imaging flow cytometer. The experiments revealed a higher lEVs concentration in septic shock patients than infected patients at the onset of the disease. In septic shock patients, lEVs concentration decreased over time as opposed to infected patients whose lEVs concentration is relatively static throughout the study period. The major contributors of lEVs in both septic shock and infected patients were of non-leukocyte origins; platelets, erythrocytes, and endothelial cells released approximately 40, 25, and 15% of lEVs, respectively. Among lEVs of leukocyte origins, neutrophils produced the highest number of EVs. Nevertheless, the proportion of each subtype of lEVs among the given amount of lEVs produced was similar between septic shock and infected patients. These findings raise the possibility of employing lEVs enumeration as a septic shock identifying tool, although larger studies with a more diverse group of participants are warranted to extrapolate the findings to a general population.

Extracellular Vesicles: A Double-Edged Sword in Sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to an infection. Several studies on mouse and patient sepsis samples have revealed that the level of extracellular vesicles (EVs) in the blood is altered compared to healthy controls, but the different functions of EVs during sepsis pathology are not yet completely understood. Sepsis EVs are described as modulators of inflammation, lymphocyte apoptosis, coagulation and organ dysfunction. Furthermore, EVs can influence clinical outcome and it is suggested that EVs can predict survival. Both detrimental and beneficial roles for EVs have been described in sepsis, depending on the EV cellular source and the disease phase during which the EVs are studied. In this review, we summarize the current knowledge of EV sources and functions during sepsis pathology based on in vitro and mouse models, as well as patient samples.

Extracellular vesicles in renal inflammatory and infectious diseases

Extracellular vesicles can mediate cell-to-cell communication, or relieve the parent cell of harmful substances, in order to maintain cellular integrity. The content of extracellular vesicles includes miRNAs, mRNAs, growth factors, complement factors, cytokines, chemokines and receptors. These may contribute to inflammatory and infectious diseases by the exposure or transfer of potent effectors that induce vascular inflammation by leukocyte recruitment and thrombosis. Furthermore, vesicles release cytokines and induce their release from cells. Extracellular vesicles possess immune modulatory and anti-microbial properties, and induce receptor signaling in the recipient cell, not least by the transfer of pro-inflammatory receptors. Additionally, the vesicles may carry virulence factors systemically. Extracellular vesicles in blood and urine can contribute to the development of kidney diseases or exhibit protective effects. In this review we will describe the role of EVs in inflammation, thrombosis, immune modulation, angiogenesis, oxidative stress, renal tubular regeneration and infection. Furthermore, we will delineate their contribution to renal ischemia/reperfusion, vasculitis, glomerulonephritis, lupus nephritis, thrombotic microangiopathies, IgA nephropathy, acute kidney injury, urinary tract infections and renal transplantation. Due to their content of miRNAs and growth factors, or when loaded with nephroprotective modulators, extracellular vesicles have the potential to be used as therapeutics for renal regeneration.

Therapeutic Potential of Extracellular Vesicles for Sepsis Treatment

Sepsis is a deadly condition lacking a specific treatment despite decades of research. This has prompted the exploration of new approaches, with extracellular vesicles (EVs) emerging as a focal area. EVs are nanosized, cell-derived particles that transport bioactive components (i.e., proteins, DNA, and RNA) between cells, enabling both normal physiological functions and disease progression depending on context. In particular, EVs have been identified as critical mediators of sepsis pathophysiology. However, EVs are also thought to constitute the biologically active component of cell-based therapies and have demonstrated anti-inflammatory, anti-apoptotic, and immunomodulatory effects in sepsis models. The dual nature of EVs in sepsis is explored here, discussing their endogenous roles and highlighting their therapeutic properties and potential. Related to the latter component, prior studies involving EVs from mesenchymal stem/stromal cells (MSCs) and other sources are discussed and emerging producer cells that could play important roles in future EV-based sepsis therapies are identified. Further, how methodologies could impact therapeutic development toward sepsis treatment to enhance and control EV potency is described.

Extracellular vesicles as regulators of kidney function and disease

Extracellular vesicles (EVs) are small, lipid bilayer-delimited particles of cellular origin that recently gained increasing attention for their potential use as diagnostic biomarkers, and beyond that for their role in intercellular communication and as regulators of homeostatic and disease processes. In acute kidney injury (AKI) and chronic kidney disease (CKD), the potential use of EVs as diagnostic and prognostic markers has been evaluated in a series of clinical studies and contributions to pathophysiologic pathways have been investigated in experimental models. While EV concentrations in biofluids could not distinguish renal patients from healthy subjects or determine disease progression, specific EV subpopulations have been identified that may provide useful diagnostic and prognostic tools in AKI. Specific EV subpopulations are also associated with clinical complications in sepsis-induced AKI and in CKD. Beyond their role as biomarkers, pathophysiologic involvement of EVs has been shown in hemolytic uremic syndrome- and sepsis-induced AKI as well as in cardiovascular complications of CKD. On the other hand, some endogenously formed or therapeutically applied EVs demonstrate protective effects pointing toward their usefulness as emerging treatment strategy in kidney disease.

Circulating Neutrophil-Derived Microparticles Associated with the Prognosis of Patients with Sepsis

Introduction

Because of its high morbidity and mortality, sepsis remains the leading cause of death in the ICU. Microparticles (MP) have been largely studied as potential diagnostic or prognostic markers in various diseases including sepsis.

Objective

The biological and clinical relevance of neutrophil-derived microparticles (NDMPs) within the MP population remains unclear. The objective of this study was to elucidate the relationship between plasma NDMPs and the prognosis of patients with sepsis and/or septic shock.

Methods

The study was designed as an observational, noninterventional clinical study. The cohort for this study included 40 sepsis and 40 septic shock patients together with 10 healthy controls admitted to the Intensive Care Unit (ICU) and the Health Surveillance Center in the Affiliated Hospital of Guangdong Medical University, Zhanjiang, Guangdong, China, from January to November 2018, respectively. The degree of critical disease for sepsis and septic shock was evaluated, with data analyses conducted from 2018 to 2019.

Results

On days 1, 3 and 5 post-admission a series of data including plasma NDMP levels, patient demographics, TNF-α levels, IL-6 levels, sTREM-1 levels, and the sepsis severity score measurements were collected. A survival curve was plotted against levels of plasma NDMPs. Levels of NDMPs were observed to be higher in the septic shock patients than in the sepsis patients on days 1, 3, and 5 post-ICU admission (p < 0.05). NDMP levels were significantly increased in sepsis and septic shock patients with a parallel increase in pro-inflammatory mediators and sepsis severity score (p < 0.05) as well as mortality.

Conclusion

Our data suggest that NDMPs may be a biomarker of sepsis severity and mortality although its implications on sepsis prognosis warrant further study.

Linkage of alterations in systemic iron homeostasis to patients' outcome in sepsis: a prospective study

Background

Sepsis, a dysregulated host response following infection, is associated with massive immune activation and high mortality rates. There is still a need to define further risk factors and laboratory parameters predicting the clinical course. Iron metabolism is regulated by both, the body’s iron status and the immune response. Iron itself is required for erythropoiesis but also for many cellular and metabolic functions. Moreover, iron availability is a critical determinant in infections because it is an essential nutrient for most microbes but also impacts on immune function and intravascular oxidative stress. Herein, we used a prospective study design to investigate the putative impact of serum iron parameters on the outcome of sepsis.

Methods

Serum markers of iron metabolism were measured in a prospective cohort of 61 patients (37 males, 24 females) with sepsis defined by Sepsis-3 criteria in a medical intensive care unit (ICU) and compared between survivors and non-survivors. Regulation of iron parameters in patients stratified by focus of infection and co-medication as well as association of the markers with sepsis severity scores and survival were investigated with linear and logistic regression corrected for sex and age effects.

Results

Positive correlations of increased serum iron and ferritin concentrations upon ICU admission with the severity of organ failure (SOFA score) and with mortality were observed. Moreover, high TF-Sat, elevated ferritin and serum iron levels and low transferrin concentrations were associated with reduced survival. A logistic regression model consisting of SOFA and transferrin saturation (SOFA–TF-Sat) had the best predictive power for survival in septic ICU patients. Of note, administration of blood transfusions prior to ICU admission resulted in increased TF-Sat and reduced survival of septic patients.

Conclusions

Our study could show an important impact of serum iron parameters on the outcome of sepsis. Furthermore, we identified transferrin saturation as a stand-alone predictor of sepsis survival and as a parameter of iron metabolism which may in a combined model improve the prediction power of the SOFA score.

Trial registration

The study was carried out in accordance with the recommendations of the Declaration of Helsinki on biomedical research. The study was approved by the institutional ethics review board of the Medical University Innsbruck (study AN2013-0006).

Antimicrobial peptide LL-37 ameliorates a murine sepsis model via the induction of microvesicle release from neutrophils

Sepsis is a life-threatening disease caused by systemic dys-regulated inflammatory response to infection. We previously revealed that LL-37, a human cathelicidin antimicrobial peptide, improves the survival of cecal ligation and puncture septic mice. Ectosomes, microvesicles released from neutrophils, are reported to be elevated in sepsis survivors; however, the functions of ectosomes in sepsis remain largely unknown. Therefore, we herein elucidated the protective action of LL-37 on sepsis, by focusing on LL-37-induced ectosome release in a cecal ligation and puncture model. The results demonstrated the enhancement of ectosome levels by LL-37 administration, accompanied by a reduction of bacterial load. Importantly, ectosomes isolated from LL-37-injected cecal ligation and puncture mice contained higher amounts of antimicrobial proteins/peptides and exhibited higher antibacterial activity, compared with those from PBS-injected cecal ligation and puncture mice, suggesting that LL-37 induces the release of ectosomes with antibacterial potential in vivo. Actually, LL-37 stimulated mouse bone-marrow neutrophils to release ectosomes ex vivo, and the LL-37-induced ectosomes possessed antibacterial potential. Furthermore, administration of LL-37-induced ectosomes reduced the bacterial load and improved the survival of cecal ligation and puncture mice. Together these observations suggest LL-37 induces the release of antimicrobial ectosomes in cecal ligation and puncture mice, thereby reducing the bacterial load and protecting mice from lethal septic conditions.

Integrin and PD-1 Ligand Expression on Circulating Extracellular Vesicles in Systemic Inflammatory Response Syndrome and Sepsis

Extracellular vesicles (EVs) in the plasma mediate important intercellular communications in the pathogenesis of cancer and inflammatory diseases. EVs express integrins that regulate target specificities and programmed cell death ligand 1 and 2 (PD-L1 and 2) that suppress lymphocyte activation. However, the roles of these molecules on EVs in systemic inflammatory response syndrome (SIRS) and sepsis remain little understood. This study aimed to investigate how the EV expression of integrins and PD-1 ligands might differ in SIRS and sepsis, compared with healthy controls, and to correlate their expression with the clinical parameters reflecting pathogenesis. Twenty-seven SIRS patients without sepsis, 27 sepsis patients, and 18 healthy volunteers were included. EVs were isolated from plasma samples. The expression of three major integrins (β1, β2, β3 integrins) and PD-L1 and 2 were measured. The EV expression of β2 integrin and PD-L2 was significantly increased in sepsis patients compared with healthy controls. EV expression of PD-L1 was not elevated in sepsis and SIRS; however, circulating soluble PD-L1 levels were significantly higher in sepsis. Furthermore, EV expression of β2 integrin in sepsis patients correlated with hypotension and reduced kidney function. In addition, soluble PD-L1 levels correlated with sepsis severity, impaired kidney function, and impaired central nervous system function. These results suggest the potential involvements of the EV β2 integrin, as well as EV PD-L2 and soluble PD-L1, in the septic pathogenesis that occurs with the systemic immune activation leading to multiple organ dysfunctions.

Impact of extracellular vesicles on innate immunity

PURPOSE OF REVIEW

Extracellular vesicles released by prokaryote or eukaryote cells are emerging as mechanisms of cell-to-cell communication, by either physically interacting with the surface of target cells or transferring proteins/peptides, lipids, carbohydrates, and nuclei acids to acceptor cells. Accumulating evidence indicates that extracellular vesicles, among other functions, regulate innate and adaptive immune responses. We revisit here the effects that extracellular vesicles of various origins have on innate immunity.

RECENT FINDINGS

Extracellular vesicles comprise a heterogeneous group of vesicles with different biogenesis, composition and biological properties, which include exosomes, microvesicles, apoptotic cell-derived extracellular vesicles, and other extracellular vesicles still not well characterized. Extracellular vesicles released by pathogens, leukocytes, nonhematopoietic cells, tumor cells, and likely allografts, can either stimulate or suppress innate immunity via multiple mechanisms. These include transfer to target leukocytes of pro-inflammatory or anti-inflammatory mediators, membrane receptors, enzymes, mRNAs, and noncoding RNAs; and interaction of extracellular vesicles with the complement and coagulation systems. As a result, extracellular vesicles affect differentiation, polarization, activation, tissue recruitment, cytokine and chemokine production, cytolytic and phagocytic function, and antigen transfer ability, of different types of innate immune cells.

SUMMARY

The field of intercellular communication via extracellular vesicles is a rapid evolving area and the effects of pathogen-derived and host-derived extracellular vesicles on innate immunity in particular, have received increasing attention during the past decade. Future studies will be necessary to assess the full potential of the crosstalk between extracellular vesicles and the innate immune system and its use for therapeutic applications to treat chronic inflammation-based diseases and cancer growth and dissemination, among the growing list of disorders in which the innate immune system plays a critical role.

Microvesicles as new therapeutic targets for the treatment of the acute respiratory distress syndrome (ARDS)

Introduction: Acute respiratory distress syndrome (ARDS) is a heterogeneous and multifactorial disease; it is a common and devastating condition that has a high mortality. Treatment is limited to supportive measures hence novel pharmacological approaches are necessary. We propose a new direction in ARDS research; this means moving away from thinking about individual inflammatory mediators and instead investigating how packaged information is transmitted between cells. Microvesicles (MVs) represent a novel vehicle for inter-cellular communication with an emerging role in ARDS pathophysiology.Areas covered: This review examines current approaches to ARDS and emerging MV research. We describe advances in our understanding of microvesicles and focus on their pro-inflammatory roles in airway and endothelial signaling. We also offer reasons for why MVs are attractive therapeutic targets.Expert opinion: MVs have a key role in ARDS pathophysiology. Preclinical studies must move away from simple models toward more realistic scenarios while clinical studies must embrace patient heterogeneity. Microvesicles have the potential to aid identification of patients who may benefit from particular treatments and act as biomarkers of cellular status and disease progression. Understanding microvesicle cargoes and their cellular interactions will undoubtedly uncover new targets for ARDS.

Surface Proteome of Plasma Extracellular Vesicles as Biomarkers for Pneumonia and Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Background

Community-acquired pneumonia (CAP) and acute exacerbation of chronic obstructive pulmonary disease (AECOPD) represent a major burden of disease and death and their differential diagnosis is critical. A potential source of relevant accessible biomarkers are blood-borne small extracellular vesicles (sEVs).

Methods

We performed an extracellular vesicle array to find proteins on plasma sEVs that are differentially expressed and possibly allow the differential diagnosis between CAP and AECOPD. Plasma samples were analyzed from 21 healthy controls, 24 patients with CAP, and 10 with AECOPD . The array contained 40 antibodies to capture sEVs, which were then visualized with a cocktail of biotin-conjugated CD9, CD63, and CD81 antibodies.

Results

We detected significant differences in the protein decoration of sEVs between healthy controls and patients with CAP or AECOPD. We found CD45 and CD28 to be the best discrimination markers between CAP and AECOPD in receiver operating characteristic analyses, with an area under the curve >0.92. Additional ensemble feature selection revealed the possibility to distinguish between CAP and AECOPD even if the patient with CAP had COPD, with a panel of CD45, CD28, CTLA4 (cytotoxic T-lymphocyte-associated protein 4), tumor necrosis factor–R-II, and CD16.

Conclusion

The discrimination of sEV-associated proteins is a minimally invasive method with potential to discriminate between CAP and AECOPD.

Platelets and Platelet-Derived Extracellular Vesicles in Liver Physiology and Disease

Beyond their role in hemostasis, platelets are proposed as key mediators of several physiological and pathophysiological processes of the liver, such as liver regeneration, toxic or viral acute liver injury, liver fibrosis, and carcinogenesis. The effects of platelets on the liver involve interactions with sinusoidal endothelial cells and the release of platelet‐contained molecules following platelet activation. Platelets are the major source of circulating extracellular vesicles, which are suggested to play key roles in platelet interactions with endothelial cells in several clinical disorders. In the present review, we discuss the implications of platelet‐derived extracellular vesicles in physiological and pathophysiological processes of the liver.

Targeting Complement Pathways in Polytrauma- and Sepsis-Induced Multiple-Organ Dysfunction

Exposure to traumatic or infectious insults results in a rapid activation of the complement cascade as major fluid defense system of innate immunity. The complement system acts as a master alarm system during the molecular danger response after trauma and significantly contributes to the clearance of DAMPs and PAMPs. However, depending on the origin and extent of the damaged macro- and micro -milieu, the complement system can also be either excessively activated or inhibited. In both cases, this can lead to a maladaptive immune response and subsequent multiple cellular and organ dysfunction. The arsenal of complement-specific drugs offers promising strategies for various critical conditions after trauma, hemorrhagic shock, sepsis, and multiple organ failure. The imbalanced immune response needs to be detected in a rational and real-time manner before the translational therapeutic potential of these drugs can be fully utilized. Overall, the temporal-spatial complement response after tissue trauma and during sepsis remains somewhat enigmatic and demands a clinical triad: reliable tissue damage assessment, complement activation monitoring, and potent complement targeting to highly specific rebalance the fluid phase innate immune response.

Role of extracellular vesicles in the development of sepsis-induced coagulopathy

Background

The advances of research on extracellular vesicles (EVs) are of particular interest to the clinicians as well as the researchers who are studying coagulation disorder in sepsis. Here, we intend to update the latest knowledge and currently unsolved problems that should be addressed.

Main body

Secreted membrane-enclosed vesicles including apoptotic bodies, exosomes, ectosomes, microvesicles, and microparticles are generically called EVs. Though the basic structure of these vesicles is the same, i.e., originating from the plasma membrane, their characteristics differ significantly depending on their surface structures and interior components. Numerous studies have shown elevated levels of circulating EVs that exhibit proinflammatory and procoagulant properties during sepsis. These EVs are known to play important roles in the development of coagulation disorder and organ dysfunction in sepsis. Coagulation disorder in sepsis is characterized by activated coagulation, disrupted anticoagulant systems, and imbalanced fibrinolytic systems. These processes collaborate with one another and contribute to the development of disseminated intravascular coagulation (DIC), with devastating consequences. As part of this pathogenesis, the membrane-exposed tissue factor, phosphatidylserine and bioactive substances contained within the vesicles, such as histones, nucleosomes, and high-mobility group box 1, contribute to the development of DIC. EVs not only upregulate the procoagulant systems by themselves, but they also disseminate prothrombotic activities by transferring their procoagulant properties to distant target cells. Though the basic concept behind the role of procoagulant properties, EVs in the development of sepsis-induced coagulopathy has started to be unveiled, knowledge of the actual status is far from satisfactory, mainly because of the lack of standardized assay procedures. Recent advances and current problems that remain to be resolved are introduced in this review.

Conclusion

The recent studies succeeded to elucidate the important roles of EVs in the progress of coagulation disorder in sepsis. However, further harmonization in terminology, methodology, and evaluation methods is required for future studies.

Endothelial Extracellular Vesicles in Pulmonary Function and Disease

The pulmonary vascular endothelium is involved in the pathogenesis of acute and chronic lung diseases. Endothelial cell (EC)-derived products such as extracellular vesicles (EVs) serve as EC messengers that mediate inflammatory as well as cytoprotective effects. EC-EVs are a broad term, which encompasses exosomes and microvesicles of endothelial origin. EVs are comprised of lipids, nucleic acids, and proteins that reflect not only the cellular origin but also the stimulus that triggered their biogenesis and secretion. This chapter presents an overview of the biology of EC-EVs and summarizes key findings regarding their characteristics, components, and functions. The role of EC-EVs is specifically delineated in pulmonary diseases characterized by endothelial dysfunction, including pulmonary hypertension, acute respiratory distress syndrome and associated conditions, chronic obstructive pulmonary disease, and obstructive sleep apnea.

Phosphatidylserine expressing platelet microparticle levels at hospital presentation are decreased in sepsis non-survivors and correlate with thrombocytopenia

BACKGROUND

Sepsis induced platelet activation releases platelet microparticles (PMPs). PMPs express phosphatidylserine (PS) and can serve as a scaffold for the prothrombinase complex, thereby promoting coagulation. Studies of PMPs in intensive care unit sepsis patients demonstrate mixed results, while the earliest changes and potential effects of clinical interventions remain understudied. We hypothesized PMPs would be associated with patient outcome and dysfunctional coagulation shortly after emergency department presentation with sepsis.

METHODS

Cohort study of patients from a single center enrolled in a previously published randomized control trial comparing two early resuscitation strategies. Adults presenting to the emergency department (ED) with suspected infection, ≥2 SIRS criteria, and either systolic blood pressure <90 mm Hg or lactate >4 mmol/L were eligible. Triple positive platelet microparticles (PMPs) expressing phosphatidylserine and integrin complexes alphaIIb (CD41) and beta3 (CD61) were quantitated using plasma from the time of enrollment. The primary outcome was in-hospital mortality. Secondary outcomes included platelet count, disseminated intravascular coagulation (DIC), and prothrombin time (PT).

RESULTS

193 patients were enrolled and 184 had samples available. In-hospital mortality was 21%. 10 (5%) patients developed DIC. Median platelet count was 197 (IQR 135, 280) and PT was 13.2 (IQR 11.9, 16.8). Median triple positive PMP counts were 932 per μL (IQR 381, 1872). PMPs were significantly lower in non-survivors (575 vs 1128, p = 0.02) and non-significantly lower in DIC (387 vs 942, p = 0.17). PMPs demonstrated a positive linear association with platelet count (p < 0.001, R2 = 0.21). After adjusting for platelet count, PMPs were no longer significant predictors of mortality (p = 0.28). We observed no association between PMPs and PT.

CONCLUSION

Similar to patients enrolled later in the intensive care unit, PS-expressing PMPs are lower in emergency department sepsis non-survivors. These changes primarily reflect the degree of thrombocytopenia, and an independent prognostic role was not observed. Future studies should control for platelet count in assessment of PMP prognosis in sepsis.

Extracellular Vesicles as Markers and Mediators in Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains a highly lethal condition in which current tools for early diagnosis and therapeutic decision-making are far from ideal. Extracellular vesicles (EVs), 30 nm to several micrometers in size, are released from cells upon activation and apoptosis and express membrane epitopes specific for their parental cells. Since their discovery two decades ago, their role as biomarkers and mediators in various diseases has been intensively studied. However, their potential importance in the sepsis syndrome has gained attention only recently. Sepsis and EVs are both complex fields in which standardization has long been overdue. In this review, several topics are discussed. First, we review current studies on EVs in septic patients with emphasis on their variable quality and clinical utility. Second, we discuss the diagnostic and therapeutic potential of EVs as well as their role as facilitators of cell communication via micro RNA and the relevance of micro-organism-derived EVs. Third, we give an overview over the potential beneficial but also detrimental roles of EVs in sepsis. Finally, we focus on the role of EVs in selected intensive care scenarios such as coagulopathy, mechanical ventilation and blood transfusion. Overall, the prospect for EV use in septic patients is bright, ranging from rapid and precise (point-of-care) diagnostics, prevention of harmful iatrogenic interventions, to using EVs as guides of individualized therapy. Before the above is achieved, however, the EV research field requires reliable standardization of the current methods and development of new analytical procedures that can close the existing technological gaps.

Extracellular Vesicles: Packages Sent With Complement

Cells communicate with other cells in their microenvironment by transferring lipids, peptides, RNA, and sugars in extracellular vesicles (EVs), thereby also influencing recipient cell functions. Several studies indicate that these vesicles are involved in a variety of critical cellular processes including immune, metabolic, and coagulatory responses and are thereby associated with several inflammatory diseases. Furthermore, EVs also possess anti-inflammatory properties and contribute to immune regulation, thus encouraging an emerging interest in investigating and clarifying mechanistic links between EVs and innate immunity. Current studies indicate complex interactions of the complement system with EVs, with a dramatic influence on local and systemic inflammation. During inflammatory conditions with highly activated complement, including after severe tissue trauma and during sepsis, elevated numbers of EVs were found in the circulation of patients. There is increasing evidence that these shed vesicles contain key complement factors as well as complement regulators on their surface, affecting inflammation and the course of disease. Taken together, interaction of EVs regulates complement activity and contributes to the pro- and anti-inflammatory immune balance. However, the molecular mechanisms behind this interaction remain elusive and require further investigation. The aim of this review is to summarize the limited current knowledge on the crosstalk between complement and EVs. A further aspect is the clinical relevance of EVs with an emphasis on their capacity as potential therapeutic vehicles in the field of translational medicine.

HMGB1/IL-1β complexes in plasma microvesicles modulate immune responses to burn injury

Modulating immune responses to sepsis and trauma remain one of the most difficult challenges in modern medicine. Large burn injuries (LBI) are a severe form of trauma associated with sepsis, immune impairment, and mortality. Immune dysfunction after LBI is complex, involving both enhanced and impaired immune activation. The release of Damage-Associated Molecular Patterns (DAMPs), such as HMGB1, and cytokines (e.g. IL-1β) creates an environment of immune dysfunction often leading to end organ failure and death. Both HMGB1 and IL-1β have been found to play critical roles in sepsis and post-burn immune dysfunction. HMGB1 and IL-1β have been shown previously to form potent complexes in vitro. We recently identified the presence of HMGB1/IL-1β heterocomplexes in human tissue. We now find HMGB1/IL-1β complexes in human and mouse plasma, and identify a synergistic role of HMGB1/IL-1β complexes in post-burn immune dysfunction. In both humans and mice, we found that HMGB1 was enriched in plasma microvesicles (MVs) after LBI. HMGB1 was found form complexes with IL-1β. Using flow cytometry of mouse plasma MVs, we identified an increase in an HMGB1+/IL-1β+ MVs. Using co-IP, HMGB1 was found to bind the pro-form of IL-1β in mouse and human plasma. Pro-IL-1β, which is traditionally considered inactive, became active when complexed with HMGB1. Human THP-1 monocytes treated with HMGB1-pro-IL-1β complexes showed increased transcription of LBI associated cytokines IL-6 and IFNβ along with suppression of iNOS, mimicking findings associated with LBI. These findings identify that HMGB1/IL-1β complexes released after burn injuries can modulate immune responses, and microvesicles are identified as a novel reservoir for these immune mediators. These complexes might serve as novel immune targets for the treatment of systemic immune responses due to LBI or other causes of sepsis.

Hemofiltration induces generation of leukocyte-derived CD31+/CD41- microvesicles in sepsis

BACKGROUND

Microvesicles (MV) are extracellular vesicles known to be associated with cellular activation and inflammation. Hemofiltration is an effective blood purification technique for patients with renal failure and possibly also eliminates inflammatory mediators in the setting of sepsis. On the other hand, proinflammatory stimuli are induced by blood contacting the artificial membrane during extracorporeal blood purification. In chronic dialysis patients a systemic increase in MV has been described. The aim of the study was to investigate whether hemofilter passage of blood in continuous veno-venous hemofiltration (CVVH) alters MV composition and levels in critically ill patients with sepsis.

METHODS

Pre- and postfilter bloods as well as ultrafiltrate samples from intensive care unit patients with severe sepsis were obtained during CVVH with regional citrate anticoagulation. MV subtypes in blood were analyzed by high-sensitivity flow cytometry. Additionally, tissue factor (TF) levels and MV-associated TF activities as well as MV activities were quantified. All parameters were corrected for hemoconcentration applied during CVVH.

RESULTS

Twelve patients were analyzed. A significant increase in presumably mostly leukocyte-derived CD31+/CD41- MV (1.32 (1.09-1.93)-fold [median (25th-75th quartiles)], p = 0.021) was observed post- to prefilter, whereas platelet-derived MV as well as AnnexinV-binding MV were unaltered. Increments of AnnexinV+, CD42b+ and CD31+/CD41- MV post- to prefilter correlated with filtration fraction (FF) (all p < 0.05). Significant reductions in MV activity [0.72 (0.62-0.84)-fold, p = 0.002] and TF level [0.95 (0.87-0.99)-fold, p = 0.0093] were detected postfilter compared to prefilter. No MV activity was measurable in ultrafiltrate samples.

CONCLUSIONS

Despite clearing a fraction of small PS-exposing MV CVVH does not eliminate larger MV. Concurrently, CVVH induces the release of CD31+/CD4- MV that indicate leukocyte activation during hemofilter passage in septic patients. Increments of several MV subtypes within the hemofilter correlate with FF, which supports common recommendations to keep FF low. A fraction of TF is being cleared by CVVH via ultrafiltration.