Microparticles during sepsis: target, canary or cure?

Surface Mineralization of Engineered Bacterial Outer Membrane Vesicles to Enhance Tumor Photothermal/Immunotherapy

Gram-negative bacteria can naturally produce nanosized spherical outer membrane vesicles (OMVs) with a lipid bilayer membrane, possessing immunostimulatory capabilities to be potentially applied in tumor therapy. However, the systemic toxicity induced by pathogen-associated molecular patterns (PAMPs) of OMVs is the main obstacle for their clinical translation. Herein, melanin-loaded OMVs were produced with a genetic engineering strategy and further coated with calcium phosphate (CaP) to reduce their toxicity to enhance tumor treatment effects. Wild-type bacterium Escherichia coli Nissle 1917 (EcN) was genetically engineered to highly express tyrosinase to catalyze the intracellular synthesis of melanin, giving melanin-loaded OMVs (OMVMel). To reduce the systemic toxicity in tumor therapy, OMVMel was coated with CaP by surface mineralization to obtain OMVMel@CaP. In comparison with OMVMel, OMVMel@CaP showed lower systemic inflammatory responses in healthy mice and less damage to the liver, spleen, lung, and kidney, so the administration dose could be increased to enhance the antitumor effect. In the acidic tumor microenvironment, the CaP shell disintegrated to release OMVMel to trigger antitumor immune responses. Under costimulation of OMVMel acting as immunoadjuvants and the damage-associated molecular patterns (DAMPs) released by the photothermal effect, the efficiency of tumor photothermal/immunotherapy was largely boosted through promoting the infiltration of matured DCs, M1 macrophages, and activated CD8+ T cells, decreasing the ratio of MDSCs in tumors.

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.

Blood Bacteria-Free DNA in Septic Mice Enhances LPS-Induced Inflammation in Mice through Macrophage Response

Although bacteria-free DNA in blood during systemic infection is mainly derived from bacterial death, translocation of the DNA from the gut into the blood circulation (gut translocation) is also possible. Hence, several mouse models with experiments on macrophages were conducted to explore the sources, influences, and impacts of bacteria-free DNA in sepsis. First, bacteria-free DNA and bacteriome in blood were demonstrated in cecal ligation and puncture (CLP) sepsis mice. Second, administration of bacterial lysate (a source of bacterial DNA) in dextran sulfate solution (DSS)-induced mucositis mice elevated blood bacteria-free DNA without bacteremia supported gut translocation of free DNA. The absence of blood bacteria-free DNA in DSS mice without bacterial lysate implies an impact of the abundance of bacterial DNA in intestinal contents on the translocation of free DNA. Third, higher serum cytokines in mice after injection of combined bacterial DNA with lipopolysaccharide (LPS), when compared to LPS injection alone, supported an influence of blood bacteria-free DNA on systemic inflammation. The synergistic effects of free DNA and LPS on macrophage pro-inflammatory responses, as indicated by supernatant cytokines (TNF-α, IL-6, and IL-10), pro-inflammatory genes (NFκB, iNOS, and IL-1β), and profound energy alteration (enhanced glycolysis with reduced mitochondrial functions), which was neutralized by TLR-9 inhibition (chloroquine), were demonstrated. In conclusion, the presence of bacteria-free DNA in sepsis mice is partly due to gut translocation of bacteria-free DNA into the systemic circulation, which would enhance sepsis severity. Inhibition of the responses against bacterial DNA by TLR-9 inhibition could attenuate LPS-DNA synergy in macrophages and might help improve sepsis hyper-inflammation in some situations.

Non-coding RNAs and Exosomes: Their Role in the Pathogenesis of Sepsis

Sepsis is characterized as an uncontrolled host response to infection, and it represents a serious health challenge, causing excess mortality and morbidity worldwide. The discovery of sepsis-related epigenetic and molecular mechanisms could result in improved diagnostic and therapeutic approaches, leading to a reduced overall risk for affected patients. Accumulating data show that microRNAs, non-coding RNAs, and exosomes could all be considered as novel diagnostic markers for sepsis patients. These biomarkers have been demonstrated to be involved in regulation of sepsis pathophysiology. However, epigenetic modifications have not yet been widely reported in actual clinical settings, and further investigation is required to determine their importance in intensive care patients. Further studies should be carried out to explore tissue-specific or organ-specific epigenetic RNA-based biomarkers and their therapeutic potential in sepsis patients.

Cell-derived microvesicles in infective endocarditis: Role in diagnosis and potential for risk stratification at hospital admission

OBJECTIVES

To characterize the plasmatic profile of cell-derived microvesicles (MVs) at diagnosis and during the treatment of patients with infective endocarditis (IE).

METHODS

Blood samples from 57 patients with IE were obtained on 3 consecutive moments: upon admission (T0), at 2 weeks (T1), and at the end of treatment (T2), and were compared with 22 patients with other bacterial infections. MPs were measured by flow cytometry and labeled for specific cell markers of CD45 (leukocytes), CD66b (neutrophils), CD14 (monocytes), CD41a (platelets), CD51 (endothelial cells), CD3 (T lymphocyte) and CD235a (erythrocytes).

RESULTS

MVs from platelets (pltMVs), leukocytes (leukMVs), neutrophils (neutMVs), monocytes (monoMVs) and lymphocytes (lymphMVs) were significantly more elevated in the patients with IE, compared to the patients with other bacterial infections, despite comparable age, sex, blood counts and C-reactive protein levels. MVs values revealed a relatively stable pattern over time in IE, except for a significant increase in leukMVs and neutMVs in T1. LeukMVs (p = 0.011), neutMVs (p = 0.010), monoMVs (p = 0.016) and lymphMVs (p = 0.020), measured at admission, were significantly higher in IE patients that died during hospitalization in comparison with those that survived. In a multivariable analyses, the levels of neutMVs remained as an independent factor associated with mortality (odds ratio 2.203; 95% confidence interval 1.217 - 3.988; p = 0.009), adjustment for heart failure during the treatment.

CONCLUSIONS

Plasma levels of pltMVs, leukMVs, neutMVs, monoMVs and lymphMVs were significantly more elevated in patients with IE than in patients with other bacterial infections at hospital admission. Furthermore, neutMVs at admission have been identified as an independent predictor of mortality in patients with IE. Thus, cell derived MPs may become an important tool in the differential diagnosis and mortality risk assessment early in the course of IE suspected cases.

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.

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.

Recent advances in the pathogenetic mechanisms of sepsis-associated acute kidney injury

Sepsis is a serious medical condition that can lead to multi-organ failure and shock, and it is associated with increased mortality. Acute kidney injury (AKI) is a frequent complication of sepsis in critically ill patients, and often requires renal replacement therapy. The pathophysiology of AKI in sepsis has not yet been fully defined. In the past, classic theories were mainly focused on systemic hemodynamic derangements, underscoring the key role of whole kidney hypoperfusion due to reduced renal blood flow. However, a growing body of experimental and clinical evidence now shows that, at least in the early phase of sepsis-associated AKI, renal blood flow is normal, or even increased. This could suggest a dissociation between renal blood flow and kidney function. In addition, the scant data available from kidney biopsies in human studies do not support diffuse acute tubular necrosis as the predominant lesion. Instead, increasing importance is now attributed to kidney damage resulting from a complex interaction between immunologic mechanisms, inflammatory cascade activation, and deranged coagulation pathways, leading to microvascular dysfunction, endothelial damage, leukocyte/platelet activation with the formation of micro-thrombi, epithelial tubular cell injury and dysfunction. Moreover, the same processes, through maladaptive responses leading to fibrosis acting from the very beginning, may set the stage for progression to chronic kidney disease in survivors from sepsis-associated AKI episodes. The aim of this narrative review is to summarize and discuss the latest evidence on the pathophysiological mechanisms involved in septic AKI, based on the most recent data from the literature.

Circulating microparticles as a predictor of vascular properties in patients on mechanical circulatory support; hype or hope?

Microparticles are small circulating vesicles originating from circulatory system and vascular wall cells released during their activation or damage. They possess different roles in regulation of endothelial function, inflammation, thrombosis, angiogenesis, and in general, cellular stress. Microparticles are the subject of intensive research in pulmonary hypertension, atherosclerotic disease, and heart failure. Another recently emerging role is the evaluation of the status of vasculature in end-stage heart failure patients treated with implantable ventricular assist devices. In patients implanted as destination therapy, assessment of the long-term effect of currently used continuous-flow left ventricular assist devices (LVADs) on vasculature might be of critical importance. However, unique continuous flow pattern generated by LVADs makes it difficult to assess reliably the vascular function with most currently used methods, based mainly on ultrasound detection of changes of arterial dilatation during pulsatile flow. In this respect, the measurement of circulating microparticles as a marker of vascular status may help to elucidate both short- and long-term effects of LVADs on the vascular system. Because data regarding this topic are very limited, this review is focused on the advantages and caveats of the circulating microparticles as markers of vascular function in patients on continuous-flow LVADs.

Microparticles: markers and mediators of sepsis-induced microvascular dysfunction, immunosuppression, and AKI

Sepsis is a severe and complex syndrome that lacks effective prevention or therapeutics. The effects of sepsis on the microvasculature have become an attractive area for possible new targets and therapeutics. Microparticles (MPs) are cell membrane-derived particles that can promote coagulation, inflammation, and angiogenesis, and they can participate in cell-to-cell communication. MPs retain cell membrane and cytoplasmic constituents of their parental cells, including two procoagulants: phosphatidylserine and tissue factor. We highlight the role of microparticles released by endothelial and circulating cells after sepsis-induced microvascular injury, and we discuss possible mechanisms by which microparticles can contribute to endothelial dysfunction, immunosuppression, and multiorgan dysfunction--including sepsis-AKI. Once viewed as cellular byproducts, microparticles are emerging as a new class of markers and mediators in the pathogenesis of sepsis.