Clinical CVVH model removes endothelium-derived microparticles from circulation

Mesenchymal stem cells-derived extracellular vesicles in acute respiratory distress syndrome: a review of current literature and potential future treatment options

Acute respiratory distress syndrome (ARDS) is a life-threatening inflammatory lung condition associated with significant morbidity and mortality. Unfortunately, the current treatment for this disease is mainly supportive. Mesenchymal stem cells (MSCs) due to their immunomodulatory properties are increasingly being studied for the treatment of ARDS and have shown promise in multiple animal studies. The therapeutic effects of MSCs are exerted in part in a paracrine manner by releasing extracellular vesicles (EVs), rather than local engraftment. MSC-derived EVs are emerging as potential alternatives to MSC therapy in ARDS. In this review, we will introduce EVs and briefly discuss current data on EVs and MSCs in ARDS. We will discuss current literature on the role of MSC-derived EVs in pathogenesis and treatment of ARDS and their potential as a treatment strategy in the future.

Effect of hemodialysis on extracellular vesicles and circulating submicron particles

BACKGROUND

Although hemodialysis is a highly effective treatment for diffusive clearance of low molecular weight uremic toxins, its effect on circulating extracellular vesicles and submicron particles is less clear. The purpose of this study was to examine the impact of hemodialysis on circulating levels of submicron particles.

METHODS

Plasma samples from patients were collected immediately before and after the mid-week hemodialysis session. Total submicron particles were assessed by nanoparticle tracking analysis and levels of endothelial (CD144+), platelet (CD41+), leukocyte (CD45+), and total (Annexin V+) membrane microparticles (MPs) were assessed by flow cytometry.

RESULTS

Total submicron particle number was significantly lower post-dialysis with reductions in particles < 40 nm, 40-100 nm, and 100-1000 nm in size. Circulating annexin V+ MPs, platelet MPs, leukocyte MPs, and endothelial MPs were all reduced following dialysis. Assessment of protein markers suggested that extracellular vesicles were not present in the dialysate, but rather adsorbed to the dialysis membrane.

CONCLUSIONS

In summary, hemodialysis is associated with reductions in circulating submicron particles including membrane MPs. Accordingly, there may be significant interdialytic variation in circulating submicron particles. Investigators interested in measuring extracellular vesicles in patients undergoing hemodialysis should therefore carefully consider the timing of biosampling.

Extracellular vesicles: biomarkers and regulators of vascular function during extracorporeal circulation

Extracellular vesicles (EVs) are generated at increased rates from parenchymal and circulating blood cells during exposure of the circulation to abnormal flow conditions and foreign materials associated with extracorporeal circuits (ExCors). This review describes types of EVs produced in different ExCors and extracorporeal life support (ECLS) systems including cardiopulmonary bypass circuits, extracorporeal membrane oxygenation (ECMO), extracorporeal carbon dioxide removal (ECCO₂R), apheresis, dialysis and ventricular assist devices. Roles of EVs not only as biomarkers of adverse events during ExCor/ECLS use, but also as mediators of vascular dysfunction are explored. Manipulation of the number or subtypes of circulating EVs may prove a means of improving vascular function for individuals requiring ExCor/ECLS support. Strategies for therapeutic manipulation of EVs during ExCor/ECLS use are discussed such as accelerating their clearance, preventing their genesis or pharmacologic options to reduce or select which and how many EVs circulate. Strategies to reduce or select for specific types of EVs may prove beneficial in preventing or treating other EV-related diseases such as cancer.

Lung Repair and Regeneration in ARDS: Role of PECAM1 and Wnt Signaling

ARDS is an acute inflammatory pulmonary process triggered by severe pulmonary and systemic insults to the alveolar-capillary membrane. This causes increased vascular permeability and the development of interstitial and alveolar protein-rich edema, leading to acute hypoxemic respiratory failure. Supportive treatment includes the use of lung-protective ventilatory strategies that decrease the work of breathing, can improve oxygenation, and minimize ventilator-induced lung injury. Despite substantial advances in supportive measures, there are no specific pharmacologic treatments for ARDS, and the overall hospital mortality rate remains about 40% in most series. The pathophysiology of ARDS involves interactions among multiple mechanisms, including immune cell infiltration, cytokine storm, alveolar-capillary barrier disruption, cell apoptosis, and the development of fibrosis. Here we review some new developments in the molecular basis of lung injury, with a focus on possible novel pharmacologic interventions aimed at improving the outcomes of patients with ARDS. Our focus is on platelet-endothelial cell adhesion molecule-1, which contributes to the maintenance and restoration of vascular integrity following barrier disruption. We also highlight the wingless-related integration site signaling pathway, which appears to be a central mechanism for lung healing as well as for fibrotic development.

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.

A Pediatric Case of Diffuse Alveolar Hemorrhage Secondary to Poststreptococcal Glomerulonephritis

This report summarizes a case of a 4-year-old girl with poststreptococcal glomerulonephritis and diffuse alveolar hemorrhage, an atypical presentation in this age group and type of vasculitic disease. We propose that her rapid improvement in clinical status was due to her treatment, continuous renal replacement therapy (CRRT). This mechanism would have impacted recovery by removing factors such as endothelial microparticles, superantigens, and immune complexes that have been postulated as the pulmonary-renal link. This may be an interesting avenue of exploration going forward given the lack of evidence in treating such conditions and emergence of CRRT.

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.

Altered Profile of Circulating Endothelial-Derived Microparticles in Ventilator-Induced Lung Injury

OBJECTIVES

Pulmonary endothelial cell injury is central to the pathophysiology of acute lung injury. Mechanical ventilation can cause endothelial disruption and injury, even in the absence of preexisting inflammation. Platelet-endothelial cell adhesion molecule-1 is a transmembrane protein connecting adjacent endothelial cells. We hypothesized that injurious mechanical ventilation will increase circulating lung endothelial-derived microparticles, defined as microparticles positive for platelet-endothelial cell adhesion molecule-1, which could serve as potential biomarkers and mediators of ventilator-induced lung injury.

DESIGN

Prospective randomized, controlled, animal investigation.

SETTING

A hospital preclinical animal laboratory.

SUBJECTS

Forty-eight Sprague-Dawley rats.

INTERVENTIONS

Animals were randomly allocated to one of the three following ventilatory protocols for 4 hours: spontaneous breathing (control group), mechanical ventilation with low tidal volume (6 mL/kg), and mechanical ventilation with high tidal volume (20 mL/kg). In both mechanical ventilation groups, positive end-expiratory pressure of 2 cm H2O was applied.

MEASUREMENTS AND MAIN RESULTS

We analyzed histologic lung damage, gas exchange, wet-to-dry lung weight ratio, serum cytokines levels, circulating endothelial-derived microparticles, platelet-endothelial cell adhesion molecule-1 lung protein content, and immunohistochemistry. When compared with low-tidal volume mechanical ventilation, high-tidal volume ventilation increased lung edema score and caused gas-exchange deterioration. These changes were associated with a marked increased of circulating endothelial-derived microparticles and a reduction of platelet-endothelial cell adhesion molecule-1 protein levels in the high-tidal volume lungs (p < 0.0001).

CONCLUSIONS

There is an endothelial-derived microparticle profile associated with disease-specific features of ventilator-induced lung injury. This profile could serve both as a biomarker of acute lung injury and, potentially, as a mediator of systemic propagation of pulmonary inflammatory response.

Lipoprotein-apheresis reduces circulating microparticles in individuals with familial hypercholesterolemia

Lipoprotein-apheresis (apheresis) removes LDL-cholesterol in patients with severe dyslipidemia. However, reduction is transient, indicating that the long-term cardiovascular benefits of apheresis may not solely be due to LDL removal. Microparticles (MPs) are submicron vesicles released from the plasma membrane of cells. MPs, particularly platelet-derived MPs, are increasingly being linked to the pathogenesis of many diseases. We aimed to characterize the effect of apheresis on MP size, concentration, cellular origin, and fatty acid concentration in individuals with familial hypercholesterolemia (FH). Plasma and MP samples were collected from 12 individuals with FH undergoing routine apheresis. Tunable resistive pulse sensing (np200) and nanoparticle tracking analysis measured a fall in MP concentration (33 and 15%, respectively; P < 0.05) pre- to post-apheresis. Flow cytometry showed MPs were predominantly annexin V positive and of platelet (CD41) origin both pre- (88.9%) and post-apheresis (88.4%). Fatty acid composition of MPs differed from that of plasma, though apheresis affected a similar profile of fatty acids in both compartments, as measured by GC-flame ionization detection. MP concentration was also shown to positively correlate with thrombin generation potential. In conclusion, we show apheresis nonselectively removes annexin V-positive platelet-derived MPs in individuals with FH. These MPs are potent inducers of coagulation and are elevated in CVD; this reduction in pathological MPs could relate to the long-term benefits of apheresis.