Elevated levels of thrombin-generating microparticles in stored red blood cells

Microvesicles from stored red blood cells induce P-selectin and von Willebrand factor release from endothelial cells via a protein kinase C-dependent mechanism

INTRODUCTION

The use of packed red blood cells (pRBCs) for resuscitation is limited by the red blood cell storage lesion, a series of biochemical and physiological changes that occur during the storage and aging of blood. Microvesicles (MVs) shed from pRBCs during this process are one component of the red blood cell storage lesion and lead to acute lung injury and pulmonary vascular microthrombi. We hypothesized that MVs from stored pRBCs lead to the release of P-selectin and von Willebrand factor (vWF) from endothelial cells and that this mechanism is mediated via activation of protein kinase C (PKC) or protein kinase A (PKA).

METHODS

Leukoreduced, platelet-poor murine pRBCs were isolated from C57BL/6 8-12 week-old male mice via cardiac puncture, prepared via centrifugation using a Ficoll gradient, and stored for up to 14 days, the equivalent of 42 days of storage in humans. MVs were isolated from the stored pRBC units via sequential high-speed centrifugation. Murine lung endothelial cells (MLECs) were cultured and grown to confluence, then treated with MVs and either calphostin C, a PKC inhibitor (10 μg/mL), or PKI 14-22 amide, a PKA inhibitor (10 μM). The supernatant was collected after 1 h. P-selectin and vWF A2 concentrations were quantified via ELISA. Immunofluorescent staining for vWF was performed on MLECs. Statistical analysis was performed via unpaired t-test or ANOVA as indicated and reported as mean ± SD. Concentration is reported as pg/mL.

RESULTS

MLECs treated with MVs isolated from stored pRBCs demonstrated increased release of P-selectin and vWF A2 in a dose-dependent fashion. MLECs treated with MVs prepared from stored as compared to fresh pRBCs demonstrated increased release of P-selectin (3751 ± 726 vs 359 ± 64 pg/mL, p < 0.0001) and vWF A2 (3141 ± 355 vs 977 ± 75 pg/mL, p < 0.0001) with increasing duration of storage. The treatment of MVs with calphostin C decreased the amount of P-selectin (1471 ± 444 vs 3751 ± 726 pg/mL, p < 0.0001) and VWF A2 (2401 ± 289 vs 3141 ± 355 pg/mL, p = 0.0017) released into the supernatant by MLECs compared to MVs alone. The treatment of MVs with PKI 14-22 increased the amount of P-selectin released compared to MVs alone (1999 ± 67 vs 1601 ± 135 pg/mL, p = 0.0018).

CONCLUSIONS

MVs from stored pRBCs stimulate the release of P-selectin and VWF A2 from endothelial cells. The effect of MVs increases with both dose of MVs and age of stored pRBCs from which they are formed. This mechanism is dependent on activation of PKC and inhibition of this enzyme represents a potentially significant strategy to modulate the inflammatory response to resuscitation with stored pRBCs.

Impact of production methods and storage conditions on extracellular vesicles in packed red blood cells and platelet concentrates

The use of blood and blood products can be life-saving, but there are also certain risks associated with their administration and use. Packed red blood cells (pRBCs) and platelet concentrates are the most commonly used blood products in transfusion medicine to treat anemia or acute and chronic bleeding disorders, respectively. During the production and storage of blood products, red blood cells and platelets release extracellular vesicles (EVs) as a result of the storage lesion, which may affect product quality. EVs are subcellular structures enclosed by a lipid bilayer and originate from the endosomal system or from the plasma membrane. They play a pivotal role in intercellular communication and are emerging as important regulators of inflammation and coagulation. Their cargo and their functional characteristics depend on the cell type from which they originate, as well as on their microenvironment, influencing their capacity to promote coagulation and inflammatory responses. Hence, the potential involvement of EVs in transfusion-related adverse events is increasingly recognized and studied. Here, we review the knowledge regarding the effect of production and storage conditions of pRBCs and platelet concentrates on the release of EVs. In this context, the mode of processing and anticoagulation, the influence of additive solutions and leukoreduction, as well as the storage duration will be addressed, and we discuss potential implications of EVs for the clinical outcome of transfusion.

P. falciparum Invasion and Erythrocyte Aging

Plasmodium parasites need to find red blood cells (RBCs) that, on the one hand, expose receptors for the pathogen ligands and, on the other hand, maintain the right geometry to facilitate merozoite attachment and entry into the red blood cell. Both characteristics change with the maturation of erythrocytes. Some Plasmodia prefer younger vs. older erythrocytes. How does the life evolution of the RBC affect the invasion of the parasite? What happens when the RBC ages? In this review, we present what is known up until now.

Vesiculation in irradiated and cation-leaky-stored red blood cells

BACKGROUND

Extracellular vesicles (EVs) are released by red blood cells (RBCs) throughout their life-span and also during hypothermic storage when they accumulate in the blood bag. We queried whether stored RBCs with increased cation permeability, either from donors with familial pseudohyperkalaemia (FP) or caused by irradiation, vesiculate more readily.

STUDY DESIGN AND METHODS

Recent technical advances have revealed at least two sub-populations of MVs in RBC storage units: macrovesicles (2-6 μm) and microvesicles (1-2 μm). Using nanoparticle tracking analysis, imaging flow cytometry, and protein quantification methods, we measured and characterized vesicles released by RBCs from control and FP individuals at three different storage time-points (day 4, day 17, and day 29). The RBCs had either been stored untreated or irradiated on either day 1 or day 14 of storage.

RESULTS

We found no difference in the number or size of vesicles released between cation-leaky FP RBCs and non-FP controls. Similarly, irradiated and non-irradiated RBCs showed very similar patterns of vesicle release to during cold-storage. The only significant difference in vesicle release was the increase in accumulated vesicles with length of storage time which has been reported previously.

DISCUSSION

EVs in stored blood are potential contributors to adverse transfusion reactions. The number of vesicles released during 35-day hypothermic storage varies between donors and increases with storage duration. However, increased cation permeability and irradiation do not appear to affect vesicle formation during RBC cold-storage.

Transfusion policy in pediatric extracorporeal membrane oxygenation patients: Less could be more

OBJECTIVE

To evaluate a restrictive transfusion policy of red blood cells (RBC) and platelets in pediatric patients submitted to extracorporeal membrane oxygenation (ECMO).

METHODS

Retrospective descriptive study of pediatric patients supported with ECMO, from January 2010 to December 2019. Hemoglobin, platelet, lactate and mixed venous oxygen saturation (SvO2) values of each patient while on ECMO, were collected. Transfusion efficiency and tissue oxygenation were statistically evaluated comparing pre-transfusion hemoglobin, lactate and SvO2 with post-transfusion values. Ranges of hemoglobin and platelets were established, and the number of transfusions registered. The bleeding complications and outcome were documented.

RESULTS

Of a total of 1016 hemoglobin values, the mean value before transfusion was 8.6 g/dl. Hemoglobin and SvO2 increased significantly post-transfusion. Red blood cell transfusion varied with hemoglobin values: when hemoglobin value was less than 7 g/dl, 89% (41/46) were transfused but just 23% (181/794) when greater or equal to 7 g/dl. In the presence of active bleeding, the frequency of RBC transfusion increased from 32% to 62%, with hemoglobin between 7 g/dl and 8 g/dl.The mean value for platelet transfusion was 32 x 109/L. Thirty-eight (43%) platelet values between 20 x 109/L and 30x109/L, and 31 (40%) between 30 x 109/L and 40 x 109/L led to platelet transfusion; between 40 x 109/L and 50 x 109/L, only 7 (9%) prompted platelet transfusion.Comparing the 2010-2015 to 2016-2019 periods there was a decrease in RBC and platelet transfusion threshold with similar survival (p = .528). Survival to discharge was 68%.

CONCLUSIONS

Using a restrictive RBC and platelet transfusion policy was safe and allowed a good outcome in this case series. The presence of active bleeding was an important decision factor when hemoglobin was above 7 g/dl and platelets were above 30 x 109/L.

Plasma Kallikrein as a Forgotten Clotting Factor

For decades, it was considered that plasma kallikrein's (PKa) sole function within the coagulation cascade is the activation of factor (F)XII. Until recently, the two key known activators of FIX within the coagulation cascade were activated FXI(a) and the tissue factor-FVII(a) complex. Simultaneously, and using independent experimental approaches, three groups identified a new branch of the coagulation cascade, whereby PKa can directly activate FIX. These key studies identified that (1) FIX or FIXa can bind with high affinity to either prekallikrein (PK) or PKa; (2) in human plasma, PKa can dose dependently trigger thrombin generation and clot formation independent of FXI; (3) in FXI knockout murine models treated with intrinsic pathway agonists, PKa activity results in increased formation of FIXa:AT complexes, indicating direct activation of FIX by PKa in vivo. These findings suggest that there is both a canonical (FXIa-dependent) and non-canonical (PKa-dependent) pathway of FIX activation. These three recent studies are described within this review, alongside historical data that hinted at the existence of this novel role of PKa as a coagulation clotting factor. The implications of direct PKa cleavage of FIX remain to be determined physiologically, pathophysiologically, and in the context of next-generation anticoagulants in development.

Hepatitis E in a Portuguese cohort of human immunodeficiency virus positive patients: High seroprevalence but no chronic infections

Introduction

Hepatitis E virus (HEV) infection causes zoonotic hepatitis in Europe, with a higher risk of complications in immunocompromised hosts. HEV natural history in human immunodeficiency virus (HIV) positive patients is not fully understood, and its prevalence is unknown.

Objectives

To study the seroprevalence of HEV and prevalence of chronic HEV in HIV‐positive patients from Porto, Portugal.

Methods

We randomly selected patients from the cohort of HIV‐positive patients followed in our hospital. We performed an enzyme‐linked immunosorbent assay to search for immunoglobulin G for HEV. When the absorbance/cut‐off was inferior to 3.5, the test was repeated, and a confirmatory test executed in that sample. For reactive tests and for immunosuppressed patients (CD4 count < 200/mm³) with nonreactive test, a polymerase chain reaction (PCR) test was also performed.

Results

We included 299 patients. The mean age was 48 and 75.3% were men. Regarding HIV infection, the median follow‐up time was 10 years, the acquisition was mainly heterosexual contact, and 94% were on antiretroviral therapy. Seventy‐six patients (25.4%) had reactive immunoglobulin G (IgG) hepatitis E serology. Patients with a reactive test were older (statistically significant difference). Otherwise, there was no difference between groups concerning birthplace, rural residence, chronic viral hepatitis coinfection, or cirrhosis. Nadir and actual T_CD4+ lymphocyte counts did not differ significantly from patients with HEV reactive and nonreactive serology. Gamma‐glutamyl‐transferase (GGT) was higher in patients with reactive IgG HEV. All serum HEV PCR tests were negative.

Conclusions

Seroprevalence of HEV was 25.4% in HIV‐positive patients. Older age and higher GGT correlated to HEV reactive IgG test. No cases of current hepatitis E were found.

Ozonation of Whole Blood Results in an Increased Release of Microparticles from Blood Cells

Autohemotherapy with ozonated blood is used in the treatment of a broad spectrum of clinical disorders. Ozone demonstrates strong oxidizing properties and causes damage to cell membranes. The impact of whole-blood ozonation on the release of microparticles from blood and endothelial cells and the concentration of selected markers in the hemostatic system (APTT, PT, D-dimer, fibrinogen) were investigated. Venous blood, obtained from 19 healthy men, was split into four equal parts and treated with air, 15 µg/mL ozone, or 30 µg/mL ozone, or left untreated. The number and types of microparticles released were determined using flow cytometry on the basis of surface antigen expression: erythrocyte-derived microparticles (CD235⁺), platelet-derived microparticles (CD42⁺), leukocyte-derived microparticles (CD45⁺), and endothelial-derived microparticles (CD144⁺). The study is the first to demonstrate that ozone induces a statistically significant increase in the number of microparticles derived from blood and endothelial cells. Although statistically significant, the changes in some coagulation factors were somewhat mild and did not exceed normal values.

Storage conditions determine the characteristics of red blood cell derived extracellular vesicles

Extracellular vesicles (EVs) are released during the storage of red blood cell (RBC) concentrates and might play adverse or beneficial roles throughout the utilization of blood products (transfusion). Knowledge of EV release associated factors and mechanism amends blood product management. In the present work the impact of storage time and medium (blood preserving additive vs isotonic phosphate buffer) on the composition, size, and concentration of EVs was studied using attenuated total reflection infrared (ATR-IR) spectroscopy, microfluidic resistive pulse sensing (MRPS) and freeze-fraction combined transmission electron micrography (FF-TEM). The spectroscopic protein-to-lipid ratio based on amide and the C-H stretching band intensity ratio indicated the formation of various vesicle subpopulations depending on storage conditions. After short storage, nanoparticles with high relative protein content were detected. Spectral analysis also suggested differences in lipid and protein composition, too. The fingerprint region (from 1300 to 1000 cm^-1) of the IR spectra furnishes additional information about the biomolecular composition of RBC-derived EVs (REVs) such as adenosine triphosphate (ATP), lactose, glucose, and oxidized hemoglobin. The difference between the vesicle subpopulations reveals the complexity of the REV formation mechanism. IR spectroscopy, as a quick, cost-effective, and label-free technique provides valuable novel biochemical insight and might be used complementary to traditional omics approaches on EVs.

Platelet, Red Cell, and Endothelial Activation and Injury During Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) can be lifesaving but suffers from high rates of bleeding and repeated transfusions. Current monitoring of blood cell damage during ECMO is limited to platelet counts, hematocrit, and plasma hemoglobin levels. Extracelluar vesicles (EV) are small cell fragments released when cells are activated/injured. The objective was to evaluate flow cytometric measurements of EV during ECMO as an indication of platelet, red cell, and endothelial activation/injury. Samples were collected from 55 patients (1 day to 19 years) during 58 ECMO runs. ECMO activated or injured blood cells, but the extent was highly variable and patient dependent. On average platelet activation was increased sevenfold during ECMO with up to 60-fold increased activation during the first 24 hours in some patients. EV associated with platelet and red-cell injury were increased eightfold on average but up to 200-fold in patients with disseminated intravascular coagulation, severe hemolysis, or massive transfusion. Approximately 9% of ECMO patients showed a red-cell and endothelial activation pattern that was associated with poor prognosis. Extracellular vesicles with autofluorescence similar to bilirubin appeared to come from monocytes processing hemoglobin. ECMO is associated with a highly variable, sustained increase in platelet, red-cell, and endothelial activation and injury that is a combination of circuit and transfusion related events, the patients underlying condition and possibly genetic influences on blood cell activation and injury. Extracellular vesicle measurements may improve our understanding of cellular activation and injury during ECMO as we work to improve the biocompatibility of these systems.

Bedside Allogeneic Erythrocyte Washing with a Cell Saver to Remove Cytokines, Chemokines, and Cell-derived Microvesicles

BACKGROUND

Removal of cytokines, chemokines, and microvesicles from the supernatant of allogeneic erythrocytes may help mitigate adverse transfusion reactions. Blood bank-based washing procedures present logistical difficulties; therefore, we tested the hypothesis that on-demand bedside washing of allogeneic erythrocyte units is capable of removing soluble factors and is feasible in a clinical setting.

METHODS

There were in vitro and prospective, observation cohort components to this a priori planned substudy evaluating bedside allogeneic erythrocyte washing, with a cell saver, during cardiac surgery. Laboratory data were collected from the first 75 washed units given to a subset of patients nested in the intervention arm of a parent clinical trial. Paired pre- and postwash samples from the blood unit bags were centrifuged. The supernatant was aspirated and frozen at -70°C, then batch-tested for cell-derived microvesicles, soluble CD40 ligand, chemokine ligand 5, and neutral lipids (all previously associated with transfusion reactions) and cell-free hemoglobin (possibly increased by washing). From the entire cohort randomized to the intervention arm of the trial, bedside washing was defined as feasible if at least 75% of prescribed units were washed per protocol.

RESULTS

Paired data were available for 74 units. Washing reduced soluble CD40 ligand (median [interquartile range]; from 143 [1 to 338] ng/ml to zero), chemokine ligand 5 (from 1,314 [715 to 2,551] to 305 [179 to 488] ng/ml), and microvesicle numbers (from 6.90 [4.10 to 20.0] to 0.83 [0.33 to 2.80] × 106), while cell-free hemoglobin concentration increased from 72.6 (53.6 to 171.6) mg/dl to 210.5 (126.6 to 479.6) mg/dl (P < 0.0001 for each). There was no effect on neutral lipids. Bedside washing was determined as feasible for 80 of 81 patients (99%); overall, 293 of 314 (93%) units were washed per protocol.

CONCLUSIONS

Bedside erythrocyte washing was clinically feasible and greatly reduced concentrations of soluble factors thought to be associated with transfusion-related adverse reactions, increasing concentrations of cell-free hemoglobin while maintaining acceptable (less than 0.8%) hemolysis.

EDITOR’S PERSPECTIVE

Effects of storage and leukocyte reduction on the concentration and procoagulant activity of extracellular vesicles in canine packed red cells

OBJECTIVES

To characterize the size and procoagulant activity of extracellular vesicles (EV) that accumulate in canine packed red blood cells (pRBCs) over time and the effect of leukocyte reduction on these characteristics.

DESIGN

Prospective cohort study.

SETTING

Private small animal specialty referral hospital and university research laboratories.

ANIMALS

Ten healthy blood donor dogs.

INTERVENTIONS

Five pRBCs units were obtained according to standard protocols, and 5 were leukocyte-reduced prior to processing. Platelet-free supernatant from the pRBC units was collected on days 0, 10, 20, 32, and 42.

MEASUREMENTS AND MAIN RESULTS

Nanoparticle tracking analysis was performed to determine the size and concentration of EVs. Thrombin generation associated with phosphatidylserine-positive EVs was determined using a capture assay. Factor Xa generation associated with phosphatidylserine-positive EVs and tissue factor-positive EVs was measured in a subset of EVs isolated by centrifugation of the supernatant at 20,000 × g. R package nparLD and the Mann-Whitney U-test were used to determine the effect of duration of storage and the effect of leukocyte reduction, respectively. Small (mean < 125 nm) procoagulant EVs accumulated over time, with significant increases occurring on or after day 20 in both non-leukocyte reduced and leukocyte-reduced units. The procoagulant activity of the EVs was due to phosphatidylserine, not tissue factor. Increases in EV concentration and procoagulant activity occurred earlier in non-leukocyte reduced units. Extracellular vesicle accumulation and procoagulant activity were not decreased at any individual time point by leukocyte reduction.

CONCLUSIONS

Further studies characterizing and determining the clinical relevance of small procoagulant EVs in pRBCs are warranted.

Exploring the utility of a novel point-of-care whole blood thrombin generation assay following trauma: A pilot study

INTRODUCTION

Plasma thrombin generation kinetics as measured by the calibrated automated thrombogram (CAT) assay is a predictor of symptomatic venous thromboembolism after trauma. We hypothesized that data from a new prototype assay for measurement of thrombin generation kinetics in fresh whole blood (near patient testing of thrombin generation), will correlate with the standard CAT assay in the same patients, making it a potential tool in the future care of trauma patients.

METHODS

Patients were enrolled from June 2018 to February 2020. Within 12 hours of injury, blood samples were collected simultaneously for both assays. Variables compared and correlated between assays were lag time, peak height, time to peak, and endogenous thrombin potential. Data are presented as median with interquartile range (IQR). Spearman and Pearson correlations were estimated and tested between both assays; a P value of <0.05 was considered to be significant.

RESULTS

A total of 64 trauma patients had samples analyzed: injury severity score = 17 (IQR), 10-26], hospital length of stay = 7.5 (IQR), 2-18) days, age = 52 (IQR, 35-63) years, 71.9% male, and 42.2% of patients received a transfusion within 24 hours of injury. Thrombin generation parameters between plasma and whole blood were compared and found that all parameters of the two assays correlate in trauma patients.

CONCLUSION

In this pilot study, we have found that a novel point-of-care whole blood thrombin generation assay yields results with modest but statistically significant correlations to those of a standard plasma thrombin generation assay. This finding supports studying this device in a larger, adequately powered study.

Red Blood Cell Contribution to Hemostasis

Red Blood Cells (RBCs) have been increasingly recognized to play important roles in hemostasis and the mechanisms by which they do so continue to be elucidated. First and foremost, RBC biomechanics are the principal determinant of viscosity and flow dynamics of blood, which strongly influence all features of hemostasis. Of note, morphologic pathology, such as that found in sickle cell disease, leads to increased risk of thrombotic disease. RBC surface interactions govern signaling between platelets and RBCs and also aid in the conversion of prothrombin to thrombin. Additionally, RBCs generate microparticles which have been shown to reduce clotting time. Finally, blood clot structure and maturation are dependent on the inclusion of RBCs in forming thrombi. Here, we review the above mechanisms of RBC contribution to hemostasis.

Red blood cell supernatant increases activation and agonist-induced reactivity of blood platelets

INTRODUCTION

Transfusion of "older" packed red blood cells (PRBCs) in patients with cardiovascular disorders (CVD) may be associated with an increased risk of pro-thrombotic events, but the underlying mechanisms are poorly understood. We hypothesized that the PRBC supernatant can activate blood platelets due to hemolysis-induced oxidative stress.

METHODS

Effects of the PRBC supernatants, and their filtrates (containing the soluble substances of molecular weight <10 kDa) prepared at day 1 and 42 of storage, from non-leukoreduced (D1 NLR, D42 NLR) and leukoreduced (D1 LR, D42 LR) PRBCs on PLT activation/reactivity and collagen-induced aggregation were measured by flow cytometry and turbidimetry, respectively.

RESULTS

Supernatants display a stimulating effect on PLTs, which was manifested by a release of PLT-derived microparticles, generation of PLT aggregates, increased P-selectin expression on the membrane surface, and activation of integrin αIIbβ3. Moreover, supernatants interacted in a way that may be additive or synergistic with collagen or with ADP. The pre-storage LR did not affect the levels of PLT activation markers. The enhanced PLT activation was presumably mediated by free hemoglobin and/or the products of its breakdown, accumulating in the PRBC milieu, and their ability to trigger the ROS generation. Additionally, collagen-induced PLT aggregation was increased by low molecular weight substances possibly derived from the residual leukocytes and PLTs present in PRBCs.

CONCLUSION

Transfusion of aged PRBCs may result in the hyper-activity of PLTs, which, at least in part, could be a cause of transfusion-related thrombotic complications reported in CVD patients.

Assessment of extracellular vesicles using IFC for application in transfusion medicine

Extracellular vesicles (EVs) have been shown to be involved in various physiological and pathophysiological processes. With respect to Transfusion Medicine, the accumulation of EVs in blood products during hypothermic storage is an indicator of the storage lesion and reportedly correlates with adverse effects after transfusion, including but not limited to immunomodulation, activation of coagulation, endothelial activation, and others. To optimally reduce such an impact on blood product quality degradation and improve post-transfusion outcomes, better methods for detection, enumeration, characterisation by size and phenotype, and functional involvement of EVs in different pathophysiological and physiological processes are required. Currently, Imaging Flow Cytometry (IFC) technology provides the most comprehensive assessment of EV subsets in different body fluids. The unique ability of IFC to detect EVs of 20 nm size by registration of a single pixel of fluorescence signal makes this approach highly promising for comprehensive studies of EVs. In this review, we will focus on the recent breakthrough and advantages of using the ImageStream^X MKII IFC platform for the detection and characterisation of EVs and its future prospects for routine application of IFC in Transfusion Medicine.

Extracellular Vesicles Derived From Platelets, Red Blood Cells, and Monocyte-Like Cells Differ Regarding Their Ability to Induce Factor XII-Dependent Thrombin Generation

As transmitters of biological information, extracellular vesicles (EVs) are crucial for the maintenance of physiological homeostasis, but also contribute to pathological conditions, such as thrombotic disorders. The ability of EVs to support thrombin generation has been linked to their exposure of phosphatidylserine, an anionic phospholipid that is normally restricted to the inner leaflet of the plasma membrane but exposed on the outer leaflet during EV biogenesis. Here, we investigated whether EVs of different cellular origin and from different settings, namely platelets and red blood cells from blood bank units and a monocyte-like cell line (THP-1), differ regarding their potential to support factor XII-dependent thrombin generation. EVs were isolated from blood products or THP-1 cell culture supernatants using differential centrifugation and characterized by a combination of flow cytometry, nanoparticle tracking analysis, and Western blotting. Soluble factors co-enriched during the isolation of EVs were depleted from blood-cell derived EV fractions using size exclusion chromatography, while proteins bound to the surface of EVs were degraded by mild protease treatment. We found that platelet-derived and red blood cell-derived EVs supported factor XII-dependent thrombin generation to comparable extents, while monocytic EVs failed to support thrombin generation when added to EV-depleted human plasma. We excluded a major contribution of co-enriched soluble proteins or of proteins bound to the EV surface to the thrombogenicity of blood cell-derived EVs. Our data suggest that the enhanced potential of blood cell-derived EVs to support thrombin generation is rather due to enhanced exposure of phosphatidylserine on the surface of blood cell-derived EVs. Extending these investigations to EVs from other cell types, such as mesenchymal stromal cells, will be crucial for their future therapeutic applications.

Red blood cell microvesicles activate the contact system, leading to factor IX activation via 2 independent pathways

Storage lesion-induced, red cell-derived microvesicles (RBC-MVs) propagate coagulation by supporting the assembly of the prothrombinase complex. It has also been reported that RBC-MVs initiate coagulation via the intrinsic pathway. To elucidate the mechanism(s) of RBC-MV-induced coagulation activation, the ability of storage lesion-induced RBC-MVs to activate each zymogen of the intrinsic pathway was assessed in a buffer system. Simultaneously, the thrombin generation (TG) assay was used to assess their ability to initiate coagulation in plasma. RBC-MVs directly activated factor XII (FXII) or prekallikrein, but not FXI or FIX. RBC-MVs initiated TG in normal pooled plasma and in FXII- or FXI-deficient plasma, but not in FIX-deficient plasma, suggesting an alternate pathway that bypasses both FXII and FXI. Interestingly, RBC-MVs generated FIXa in a prekallikrein-dependent manner. Similarly, purified kallikrein activated FIX in buffer and initiated TG in normal pooled plasma, as well as FXII- or FXI-deficient plasma, but not FIX-deficient plasma. Dual inhibition of FXIIa by corn trypsin inhibitor and kallikrein by soybean trypsin inhibitor was necessary for abolishing RBC-MV-induced TG in normal pooled plasma, whereas kallikrein inhibition alone was sufficient to abolish TG in FXII- or FXI-deficient plasma. Heating RBC-MVs at 60°C for 15 minutes or pretreatment with trypsin abolished TG, suggesting the presence of MV-associated proteins that are essential for contact activation. In summary, RBC-MVs activate both FXII and prekallikrein, leading to FIX activation by 2 independent pathways: the classic FXIIa-FXI-FIX pathway and direct kallikrein activation of FIX. These data suggest novel mechanisms by which RBC transfusion mediates inflammatory and/or thrombotic outcomes.

Characterization and function of medium and large extracellular vesicles from plasma and urine by surface antigens and Annexin V

Background

Extracellular vesicles (EVs) are released by most cell types and are involved in multiple basic biological processes. Medium/large EVs (m/lEVs), which are of a different size from exosomes, play an important role in the coagulation in blood, and are secreted from cancer cells, etc., suggesting functions related to malignant transformation. The m/lEVs levels in blood or urine may help unravel pathophysiological findings in many diseases. However, it remains unclear how many naturally-occurring m/lEV subtypes exist as well as how their characteristics and functions differ from one another.

Methods

We used the blood and urinal sample from each 10 healthy donors for analysis. Using a flow cytometer, we focus on characterization of EVs with large sizes (>200 nm) that are different from exosomes. We also searched for a membrane protein for characterization with a flow cytometer using shotgun proteomics. We then identified m/lEVs pelleted from plasma and urine samples by differential centrifugation and characterized by flow cytometry.

Results

Using proteomic profiling, we identified several proteins involved in m/lEV biogenesis including adhesion molecules, peptidases and exocytosis regulatory proteins. In healthy human plasma, we could distinguish m/lEVs derived from platelets, erythrocytes, monocytes/macrophages, T and B cells, and vascular endothelial cells with more than two positive surface antigens. The ratio of phosphatidylserine appearing on the membrane surface differed depending on the cell-derived m/lEVs. In urine, 50% of m/lEVs were Annexin V negative but contained various membrane peptidases derived from renal tubular villi. Urinary m/lEVs, but not plasma m/lEVs, showed peptidase activity. The knowledge of the new characteristics is considered to be useful as a diagnostic material and the newly developed method suggests the possibility of clinical application.

Contrasting effects of stored allogeneic red blood cells and their supernatants on permeability and inflammatory responses in human pulmonary endothelial cells

Transfusion of red blood cells (RBCs) is a common life-saving clinical practice in severely anemic or hemorrhagic patients; however, it may result in serious pathological complications such as transfusion-related acute lung injury. The factors mediating the deleterious effects of RBC transfusion remain unclear. In this study, we tested the effects of washed long-term (RBC-O; >28 days) versus short-term (RBC-F; <14 days) stored RBCs and their supernatants on lung endothelial (EC) permeability under control and inflammatory conditions. RBCs enhanced basal EC barrier function as evidenced by an increase in transendothelial electrical resistance and decrease in permeability for macromolecules. RBCs also attenuated EC hyperpermeability and suppressed secretion of EC adhesion molecule ICAM-1 and proinflammatory cytokine IL-8 in response to LPS or TNF-α. In both settings, RBC-F had slightly higher barrier protective effects as compared with RBC-O. In contrast, supernatants from both RBC-F and RBC-O disrupted the EC barrier. The early phase of EC permeability response caused by RBC supernatants was partially suppressed by antioxidant N-acetyl cysteine and inhibitor of Src kinase family PP2, while addition of heme blocker and inhibition of NOD-like receptor family pyrin domain containing protein 3 (NLRP3), stress MAP kinases, receptor for advanced glycation end-products (RAGE), or Toll-like receptor-4 (TLR4) signaling were without effect. Morphological analysis revealed that RBC supernatants increased LPS- and TNF-α-induced breakdown of intercellular junctions and formation of paracellular gaps. RBC supernatants augmented LPS- and TNF-α-induced EC inflammation reflected by increased production of IL-6, IL-8, and soluble ICAM-1. These findings demonstrate the deleterious effects of RBC supernatants on EC function, which may have a major impact in pathological consequences associated with RBC transfusion.

Pulmonary embolism associated with transfusion after severe post-partum haemorrhage: is less more?

BACKGROUND

Transfusion of red blood cells is associated with superficial vein thrombosis (SVT) and venous thromboembolism (deep vein thrombosis and/or pulmonary embolism, VTE). The present study investigated the prevalence of SVT and VTE in women transfused in the peri-partum period.

MATERIALS AND METHODS

We carried out an observational study in a tertiary level obstetrics department in the Apulia Region of Southern Italy to investigate VTE in women transfused during or after labour. The study included all women who delivered between January 1st and November 30th, 2018. A thrombotic event was defined as an admission with an ICD-9 code of SVT and VTE as a primary or secondary diagnosis. Maternal "near-miss" rate, as defined by the World Health Organization, was calculated and outcome of transfused women was recorded.

RESULTS

From January 1st to November 30th, a total of 1,028 women delivered, 39% of them by caesarean section (CS). One-hundred and thirty-two women (12.8%) had been classified with one or more complication codes. Most complications occurred in women who underwent CS with an odds ratio (OR) of 7.0 (95% CI: 4.0-12.5; p=0.000). Twelve women (1.2%) were transfused in the peri-partum period, 7 of them had delivered by CS. The only thrombotic events recorded in the entire cohort of 1,028 patients were isolated pulmonary embolisms observed in 2 out of 12 transfused women. Overall, patients had received a mean of 7.5 units of packed red blood cells (1 patient also received 7 plasma units, while 1 patient also received 1 platelet unit). Consequently, the near-miss rate was 2.0/1,000 deliveries, which is not significantly different from that expected in Italy and in high-income countries.

CONCLUSIONS

Pulmonary embolism is a life-threatening complication, which can be associated with transfusion in the peri-partum period.

Magnetic Accumulation of SPIONs under Arterial Flow Conditions: Effect of Serum and Red Blood Cells

Magnetic drug targeting utilizes an external magnetic field to target superparamagnetic iron oxide nanoparticles (SPIONs) and their cargo to the diseased vasculature regions. In the arteries, the flow conditions affect the behavior of magnetic particles and the efficacy of their accumulation. In order to estimate the magnetic capture of SPIONs in more physiological-like settings, we previously established an ex vivo model based on human umbilical cord arteries. The artery model was employed in our present studies in order to analyze the effects of the blood components on the efficacy of magnetic targeting, utilizing 2 types of SPIONs with different physicochemical characteristics. In the presence of freshly isolated human plasma or whole blood, a strong increase in iron content measured by AES was observed for both particle types along the artery wall, in parallel with clotting activation due to endogenous thrombin generation in plasma. Subsequent studies therefore utilized SPION suspensions in serum and washed red blood cells (RBCs) at hematocrit 50%. Interestingly, in contrast to cell culture medium suspensions, magnetic accumulation of circulating SPION-3 under the external magnet was achieved in the presence of RBCs. Taken together, our data shows that the presence of blood components affects, but does not prevent, the magnetic accumulation of circulating SPIONs.

Selected CD molecules and the phagocytosis of microvesicles released from erythrocytes ex vivo

BACKGROUND AND OBJECTIVES

The accumulation of microvesicles in erythrocyte concentrates during storage or irradiation may be responsible for clinical symptoms such as inflammation, coagulation and immunization. Our aim was to determine whether any of the cluster of differentiation (CD) molecules responsible for important functions are present on microvesicles, and if their expression level is dependent on the storage period of erythrocyte concentrates.

MATERIAL AND METHODS

Erythrocyte microvesicles were isolated from 'fresh' (2^nd day) and 'old' (42^nd day) stored erythrocyte concentrates. Qualitative cytometric analysis of 0·5 µm, erythrocyte-derived, PS-exposing vesicles was performed using the annexin V-FITC, anti-CD235a-PE antibody and calibrated beads. The microvesicles were also visualized under a confocal microscope. The expression of the molecules CD235a, CD44, CD47, CD55, CD59 and of phosphatidylserine (PS) was compared using flow cytometry. Measurements of microvesicle phagocytosis by human monocytes were carried out using a flow cytometer and a confocal microscope.

RESULTS

The analysis of the microvesicles with calibration beads allowed us to identify these structures with a diameter of about 0·5 µm in the 'fresh' and 'old' samples. At day 2, the microvesicles had elevated expression levels of CD47, reduced expression levels of PS, CD55 and CD59. The phagocytosis index was higher for the microvesicles isolated from the 42-day-old erythrocyte concentrates.

CONCLUSION

This research may bring us closer to understanding the factors responsible for erythrocyte ageing and to evaluate the quality of stored red blood concentrates intended for transfusion.

Extracellular vesicle concentration and procoagulant activity of canine haemoperitoneum fluid and packed red blood cells

OBJECTIVES

To compare the concentration of phosphatidylserine-positive extracellular vesicles and phosphatidylserine-derived procoagulant activity of canine haemoperitoneum fluids and packed red blood cell units.

MATERIALS AND METHODS

Ten dogs with haemoperitoneum (neoplasia = 7; trauma = 1; other = 2) were recruited, and five non-leukoreduced packed red blood cell units purchased. Supernatants were collected from haemoperitoneum samples and packed red blood cell units using a consistent centrifugation protocol. Phosphatidylserine-positive extracellular vesicle concentrations were measured by flow cytometry and phosphatidylserine-mediated procoagulant activity by a commercial thrombin generation assay.

RESULTS

Phosphatidylserine-mediated procoagulant activity was significantly higher for supernatants collected from packed red blood cell units (median 54 nM, range 53 to 60 nM) than haemoperitoneum samples (median 43 nM; range 7 to 51 nM; P = 0.0007). By flow cytometry, the concentration of phosphatidylserine-positive extracellular vesicles was not significantly different between packed red blood cell (median: 415/μL, range 173 to 1331/μL) and haemoperitoneum samples (median: 314/μL, range 132 to 3880/μL; P = 0.77).

CLINICAL SIGNIFICANCE

This study does not suggest that shed abdominal blood contains more extracellular vesicles with phosphatidylserine-mediated procoagulant activity than donor packed red blood cell units. Clinical studies to compare the effects of autologous transfusion of shed abdominal blood and packed red blood cell units on coagulation status and clinical outcome are required.

Effects of blood storage age on immune, coagulation, and nitric oxide parameters in transfused patients undergoing cardiac surgery

BACKGROUND

Retrospective studies suggested that storage age of RBCs is associated with inflammation and thromboembolism. The Red Cell Storage Duration Study (RECESS) trial randomized subjects undergoing complex cardiac surgery to receive RBCs stored for shorter versus longer periods, and no difference was seen in the primary outcome of change in multiple organ dysfunction score.

STUDY DESIGN AND METHODS

In the current study, 90 subjects from the RECESS trial were studied intensively using a range of hemostasis, immunologic, and nitric oxide parameters. Samples were collected before transfusion and on Days 2, 6, 28, and 180 after transfusion.

RESULTS

Of 71 parameters tested, only 4 showed a significant difference after transfusion between study arms: CD8+ T-cell interferon-γ secretion and the concentration of extracellular vesicles bearing the B-cell marker CD19 were higher, and plasma endothelial growth factor levels were lower in recipients of fresh versus aged RBCs. Plasma interleukin-6 was higher at Day 2 and lower at Days 6 and 28 in recipients of fresh versus aged RBCs. Multiple parameters showed significant modulation after surgery and transfusion. Most analytes that changed after surgery did not differ based on transfusion status. Several extracellular vesicle markers, including two associated with platelets (CD41a and CD62P), decreased in transfused patients more than in those who underwent surgery without transfusion.

CONCLUSIONS

Transfusion of fresh versus aged RBCs does not result in substantial changes in hemostasis, immune, or nitric oxide parameters. It is possible that transfusion modulates the level of platelet-derived extracellular vesicles, which will require study of patients randomly assigned to receipt of transfusion to define.

Microparticles formed during storage of red blood cell units support thrombin generation

BACKGROUND

Intact red blood cells (RBCs) appear to support thrombin generation in in vitro models of blood coagulation. During storage of RBC units, biochemical, structural, and physiological changes occur including alterations to RBC membranes and release of microparticles, which are collectively known as storage lesion. The clinical consequences of microparticle formation in RBC units are unclear. This study was performed to assess thrombin generation via the prothrombinase complex by washed RBCs and RBC-derived microparticles as a function of RBC unit age.

METHODS

Well-characterized kinetic and flow cytometric assays were used to quantify and characterize microparticles isolated from leukocyte-reduced RBC units during storage for 42 days under standard blood banking conditions.

RESULTS

Stored RBCs exhibited known features of storage lesion including decreasing pH, cell lysis, and release of microparticles demonstrated by scanning electron microscopy. The rate of thrombin formation by RBC units linearly increased during storage, with the microparticle fraction accounting for approximately 70% of the prothrombinase activity after 35 days. High-resolution flow cytometric analyses of microparticle isolates identified phosphatidylserine-positive RBC-derived microparticles; however, their numbers over time did not correlate with thrombin formation in that fraction.

CONCLUSION

Red blood cell-derived microparticles capable of supporting prothrombinase function accumulate during storage, suggesting an increased potential of transfused units as they age to interact in unplanned ways with ongoing hemostatic processes in injured individuals, especially given the standard blood bank practice of using the oldest units available.

Red blood cells: the forgotten player in hemostasis and thrombosis

New evidence has stirred up a long-standing but undeservedly forgotten interest in the role of erythrocytes, or red blood cells (RBCs), in blood clotting and its disorders. This review summarizes the most recent research that describes the involvement of RBCs in hemostasis and thrombosis. There are both quantitative and qualitative changes in RBCs that affect bleeding and thrombosis, as well as interactions of RBCs with cellular and molecular components of the hemostatic system. The changes in RBCs that affect hemostasis and thrombosis include RBC counts or hematocrit (modulating blood rheology through viscosity) and qualitative changes, such as deformability, aggregation, expression of adhesive proteins and phosphatidylserine, release of extracellular microvesicles, and hemolysis. The pathogenic mechanisms implicated in thrombotic and hemorrhagic risk include variable adherence of RBCs to the vessel wall, which depends on the functional state of RBCs and/or endothelium, modulation of platelet reactivity and platelet margination, alterations of fibrin structure and reduced susceptibility to fibrinolysis, modulation of nitric oxide availability, and the levels of von Willebrand factor and factor VIII in blood related to the ABO blood group system. RBCs are involved in platelet-driven contraction of clots and thrombi that results in formation of a tightly packed array of polyhedral erythrocytes, or polyhedrocytes, which comprises a nearly impermeable barrier that is important for hemostasis and wound healing. The revisited notion of the importance of RBCs is largely based on clinical and experimental associations between RBCs and thrombosis or bleeding, implying that RBCs are a prospective therapeutic target in hemostatic and thrombotic disorders.

Screening of red blood cells for extracellular vesicle content as a product quality indicator

BACKGROUND

The controversy around the quality and clinical impact of stored and differentially manufactured red cell concentrates (RCCs) from different donor groups is ongoing. Current studies are limited by the lack of quality measures suitable for routine screening of RCCs. As extracellular vesicles (EVs) are markers of cellular activation or degradation, this study investigated the utility of EV screening to characterize the effects of RBCs production methods and storage.

STUDY DESIGN AND METHODS

RCCs were prepared by whole blood filtration or red blood cell (RBC) filtration methods, centrifuged to prepare a supernatant, and tested for EV content (dynamic light scattering or tunable resistive pulse-sensing techniques), hemolysis, ATP, and RBC deformability on Days 7, 21, and 42 of storage. To simulate nondestructive quality control (QC) testing, 1 RBC unit was tested in parallel with six 10-mL aliquots that were stored in small-volume containers.

RESULTS

EV content showed a linear increase with storage time (p < 0.001) and correlated with supernatant hemoglobin and inversely with ATP or RBC deformability. The method of component manufacturing influenced the characteristics of the EVs during storage. A strong correlation between both EV testing methods' measure of total EV was observed. EV content in the six aliquots were consistent at each time point but statistically higher than in the original RCCs on and after 21 days of storage.

CONCLUSIONS

EV content correlates with measures of hemolysis and other RBC quality indicators and could be implemented as a routine screening tool for nondestructive QC testing of RCCs.

Effects of donor age, donor sex, blood-component processing, and storage on cell-derived microparticle concentrations in routine blood-component preparation

BACKGROUND

A number of factors cause increases in the number of cell-derived microparticles (MPs) in blood components. However, the overall effects of these factors on the concentration of MPs during routine blood-component preparation have not fully been elucidated.

AIM

To evaluate the effects of donor age, donor sex, blood-component preparation, and storage on MP concentrations.

METHODS

Flow cytometry was used to quantitate the number of whole blood-derived MPs.

RESULTS

The total MP concentration was similar in male and female donors (26,044 ± 1254 particles/μL vs. 27,696 ± 1584 particles/μL). The total MP concentration did not differ significantly among the different age groups: 18-30 years (28,730 ± 1600 particles/μL), 31-40 years (24,972 ± 5947 particles/μL), and 41-58 years (25,195 ± 1727 particles/μL). However, the total number of MPs in fresh plasma (152,110 ± 46,716 particles/μL) was significantly higher (p <  0.05) than that in unprocessed whole blood (26,752 ± 985 particles/μL), fresh packed red blood cells (PRBCs) (28,574 ± 1028 particles/μL), and platelet concentrate (PC) (33,072 ± 1858 particles/μL). Furthermore, the total numbers of MPs in stored PRBCs and fresh-frozen plasma (FFP) were significantly higher (p <  0.05) than those in fresh PRBCs and fresh plasma, respectively.

CONCLUSIONS

The study suggests that donor factors, blood-component processing and storage contribute to the MP concentration in routine blood-product preparation. The findings can improve quality control and management of blood-product manufacturing in routine transfusion laboratories.

RBC Transfusion Practice in Pediatric Extracorporeal Membrane Oxygenation Support

OBJECTIVES

To determine RBC transfusion practice and relationships between RBC transfusion volume and mortality in infants and children treated with extracorporeal membrane oxygenation.

DESIGN

Secondary analysis of a multicenter prospective observational study.

SETTING

Eight pediatric institutions within the Eunice Kennedy Shriver National Institute of Child Health and Human Development's Collaborative Pediatric Critical Care Research Network.

PATIENTS

Patients age less than 19 years old treated with extracorporeal membrane oxygenation at a participating center.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Clinical data and target hemoglobin or hematocrit values (if set) were recorded daily by trained bedside extracorporeal membrane oxygenation specialists and research coordinators. Laboratory values, including hemoglobin and hematocrit, were recorded daily using the value obtained closest to 8:00 AM. RBC transfusion was recorded as total daily volume in mL/kg. Multivariable logistic regression was used to determine the relationship between RBC transfusion volume and hospital mortality, accounting for potential confounders. Average goal hematocrits varied across the cohort with a range of 27.5-41.3%. Overall, actual average daily hematocrit was 36.8%, and average RBC transfusion volume was 29.4 mL/kg/d (17.4-49.7 mL/kg/d) on extracorporeal membrane oxygenation. On multivariable analysis, each additional 10 mL/kg/d of RBC transfusion volume was independently associated with a 9% increase in odds of hospital mortality (adjusted odds ratio, 1.09 [1.02-1.16]; p = 0.009).

CONCLUSIONS

In this multicenter cohort of pediatric extracorporeal membrane oxygenation patients, daily hematocrit levels were maintained at normal or near-normal values and RBC transfusion burden was high. RBC transfusion volume was independently associated with odds of mortality. Future clinical studies to identify optimum RBC transfusion thresholds for pediatric extracorporeal membrane oxygenation are urgently needed.

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.

Transfusion of autologous extracellular vesicles from stored red blood cells does not affect coagulation in a model of human endotoxemia

BACKGROUND

Red blood cell (RBC) transfusion has been related to thromboembolic events. Microvesicles in the RBC product may support coagulation because they have procoagulant effects in vitro. We investigated whether transfusion of RBCs containing extracellular vesicles promotes coagulation in human recipients. As transfusion is mostly administered to ill patients, we used a model of endotoxemia.

STUDY DESIGN AND METHODS

Eighteen healthy volunteers were randomized to receive either saline or fresh (2 days stored) or stored autologous (35 days stored) RBC transfusion (Dutch Trial Register: NTR4455). Two hours after infusion of lipopolysaccharide (LPS, from Escherichia coli, 2 ng/kg body weight), subjects received either saline or fresh or stored RBCs. Blood was sampled every 2 hours up to 8 hours after LPS infusion. Vesicles were measured with a flow cytometer (A50-Micro, Apogee Flow Systems).

RESULTS

LPS resulted in increased thrombin generation compared to baseline. During storage, the total number of extracellular vesicles increased from 1.4 × 10⁸ /mL (interquartile range [IQR], 8.3 × 10⁷ -1.9 × 10⁸ /mL) in the fresh product to 1.7 × 10¹⁰ /mL (IQR, 7.9 × 10⁹ -2.3 × 10¹⁰ /mL; p < 0.01) in the stored product (p < 0.001). Vesicles appeared to be mostly RBC derived.

CONCLUSION

After transfusion, extracellular vesicles from stored RBC products, but not from fresh products, could be detected in the circulation of healthy volunteers. However, infusion of stored RBC extracellular vesicles did not augment thrombin generation compared to endotoxemic controls. Also, levels of d-dimer and thrombin-antithrombin complex were unaffected. In conclusion, transfusion of autologous RBCs containing high levels of extracellular vesicles does not enhance coagulation in human volunteers with endotoxemia.

Red blood cells ageing markers: a multi-parametric analysis

BACKGROUND

Red blood cells collected in citrate-phosphate-dextrose can be stored for up to 42 days at 4 °C in saline-adenine-glucose-mannitol additive solution. During this controlled, but nevertheless artificial, ex vivo ageing, red blood cells accumulate lesions that can be reversible or irreversible upon transfusion. The aim of the present study is to follow several parameters reflecting cell metabolism, antioxidant defences, morphology and membrane dynamics during storage.

MATERIALS AND METHODS

Five erythrocyte concentrates were followed weekly during 71 days. Extracellular glucose and lactate concentrations, total antioxidant power, as well as reduced and oxidised intracellular glutathione levels were quantified. Microvesiculation, percentage of haemolysis and haematologic parameters were also evaluated. Finally, morphological changes and membrane fluctuations were recorded using label-free digital holographic microscopy.

RESULTS

The antioxidant power as well as the intracellular glutathione concentration first increased, reaching maximal values after one and two weeks, respectively. Irreversible morphological lesions appeared during week 5, where discocytes began to transform into transient echinocytes and finally spherocytes. At the same time, the microvesiculation and haemolysis started to rise exponentially. After six weeks (expiration date), intracellular glutathione was reduced by 25%, reflecting increasing oxidative stress. The membrane fluctuations showed decreased amplitudes during shape transition from discocytes to spherocytes.

DISCUSSION

Various types of lesions accumulated at different chemical and cellular levels during storage, which could impact their in vivo recovery after transfusion. A marked effect was observed after four weeks of storage, which corroborates recent clinical data. The prolonged follow-up period allowed the capture of deep storage lesions. Interestingly, and as previously described, the severity of the changes differed among donors.

Proceedings of the Food and Drug Administration's public workshop on new red blood cell product regulatory science 2016

The US Food and Drug Administration (FDA) held a workshop on red blood cell (RBC) product regulatory science on October 6 and 7, 2016, at the Natcher Conference Center on the National Institutes of Health (NIH) Campus in Bethesda, Maryland. The workshop was supported by the National Heart, Lung, and Blood Institute, NIH; the Department of Defense; the Office of the Assistant Secretary for Health, Department of Health and Human Services; and the Center for Biologics Evaluation and Research, FDA. The workshop reviewed the status and scientific basis of the current regulatory framework and the available scientific tools to expand it to evaluate innovative and future RBC transfusion products. A full record of the proceedings is available on the FDA website (http://www.fda.gov/BiologicsBloodVaccines/NewsEvents/WorkshopsMeetingsConferences/ucm507890.htm). The contents of the summary are the authors' opinions and do not represent agency policy.

Microcirculation and red cell transfusion in patients with sepsis

Early identification of sepsis followed by diagnostic blood cultures and prompt administration of appropriate intravenous antibiotics covering all likely pathogen remains the corner stone in the initial management of sepsis. Source control, obtained by harvesting microbiological cultures and removal or drainage of the infected foci, is mandatory. However, optimization of hemodynamically unstable patients including volume support supplemented with vasopressor, inotropic and transfusion of red blood cells (RBCs) in case of persistent hypoperfusion have the potential to reduce morbidity and mortality. Given the imbalance between the ability of the cardiovascular system to deliver enough oxygen to meet the oxygen demand, transfusion of RBCs should theoretically provide the ideal solution to the challenge. However, both changes in the septic patients' RBCs induced by endogenous factors as well as the storage lesion affecting transfused RBCs have negative effects on the microcirculation. RBC morphology, distribution of fatty acids on the membrane surface, RBC deformability needed for capillary circulation and the nitrogen oxide (NO) signaling systems are involved. Although these deteriorating effects develop during storage, transfusion of fresh RBCs has not proven to be beneficial, possibly due to limitations of the studies performed. Until better evidence exists, transfusion guidelines recommend a restrictive strategy of RBC transfusion i.e. transfuse when hemoglobin (Hb)<7g/dL in septic patients.

Acid Sphingomyelinase Inhibition in Stored Erythrocytes Reduces Transfusion-Associated Lung Inflammation

OBJECTIVE

We aimed to identify the role of the enzyme acid sphingomyelinase in the aging of stored units of packed red blood cells (pRBCs) and subsequent lung inflammation after transfusion.

SUMMARY BACKGROUND DATA

Large volume pRBC transfusions are associated with multiple adverse clinical sequelae, including lung inflammation. Microparticles are formed in stored pRBCs over time and have been shown to contribute to lung inflammation after transfusion.

METHODS

Human and murine pRBCs were stored with or without amitriptyline, a functional inhibitor of acid sphingomyelinase, or obtained from acid sphingomyelinase-deficient mice, and lung inflammation was studied in mice receiving transfusions of pRBCs and microparticles isolated from these units.

RESULTS

Acid sphingomyelinase activity in pRBCs was associated with the formation of ceramide and the release of microparticles. Treatment of pRBCs with amitriptyline inhibited acid sphingomyelinase activity, ceramide accumulation, and microparticle production during pRBC storage. Transfusion of aged pRBCs or microparticles isolated from aged blood into mice caused lung inflammation. This was attenuated after transfusion of pRBCs treated with amitriptyline or from acid sphingomyelinase-deficient mice.

CONCLUSIONS

Acid sphingomyelinase inhibition in stored pRBCs offers a novel mechanism for improving the quality of stored blood.

Red blood cell transfusion in surgical cancer patients: Targets, risks, mechanistic understanding and further therapeutic opportunities

Anemia is present in more than half of cancer patients and appears to be an independent prognostic factor of short- and long-term adverse outcomes. It increases in the advanced period of cancer and perioperatively, in patients with solid tumors who undergo surgery. As a result, allogeneic red blood cell (RBC) transfusion is an indispensable treatment in cancer. However, its safety remains controversial, based on several laboratory and clinical data reporting a linkage with increased risk for cancer recurrence, infection and cancer-related mortality. Immunological, inflammatory and thrombotic reactions mediated by the residual leukocytes and platelets, the stored RBCs per se, the biological response modifiers and the plasticizer of the unit may underlie infection and tumor-promoting effects. Although the causality between transfusion and infection has been established, the effects of transfusion on cancer recurrence remain confusing; this is mainly due to the extreme biological heterogeneity that characterizes RBC donations and cancer context. In fact, the functional interplay between donation-associated factors and recipient characteristics, including tumor biology per se, inflammation, infection, coagulation and immune activation state and competence may synergistically and individually define the clinical impact of each transfusion in any given cancer patient. Our understanding of how the potential risk is mediated is important to make RBC transfusion safer and to pave the way for novel, promising and highly personalized strategies for the treatment of anemia in surgical cancer patients.

Role of red blood cells in haemostasis and thrombosis

In contrast to an obsolete notion that erythrocytes, or red blood cells (RBCs), play a passive and minor role in hemostasis and thrombosis, over the past decades there has been increasing evidence that RBCs have biologically and clinically important functions in blood clotting and its disorders. This review summarizes the main mechanisms that underlie the involvement of RBCs in hemostasis and thrombosis in vivo, such as rheological effects on blood viscosity and platelet margination, aggregation and deformability of RBCs; direct adhesion and indirect biochemical interactions with endothelial cells and platelets, etc. The ability of stored and pathologically altered RBCs to generate thrombin through exposure of phosphatidylserine has been emphasized. The procoagulant and prothrombotic potential of RBC-derived microparticles transfused with stored RBCs or formed in various pathological conditions associated with hemolysis has been described along with prothrombotic effects of free hemoglobin and heme. Binding of fibrinogen or fibrin to RBCs may influence their effects on fibrin network structure, clot mechanical properties, and fibrinolytic resistance. Recent data on platelet-driven clot contraction show that RBCs compressed by platelets pulling on fibrin form a tightly packed array of polyhedral erythrocytes, or polyhedrocytes, which comprises a nearly impermeable barrier important for hemostasis and wound healing. RBCs may perform dual roles, both helping to stem bleeding but at the same time contributing to thrombosis in a variety of ways.

Microparticles from splenectomized β-thalassemia/HbE patients play roles on procoagulant activities with thrombotic potential

Thromboembolic events including cerebral thrombosis, deep vein thrombosis, and pulmonary embolism are major complications in β-thalassemia. Damaged red blood cells and chronic platelet activation in splenectomized β-thalassemia/HbE patients were associated with increased microparticles (MPs) releases into blood circulation. MPs are small membrane vesicles, which play important roles on coagulation. However, the role of MP in thalassemia is poorly understood. In this study, the effects of splenectomized-MPs on platelet activation and aggregation were investigated. The results showed that isolated MPs from fresh platelet-free plasma of patients and normal subjects directly induce platelet activation, platelet aggregation, and platelet-neutrophil aggregation in a dose-dependent manner. Interestingly, MPs obtained from splenectomized patients are more efficient in induction of platelet activation (P-selectin⁺) when compared to MPs from normal subjects (P < 0.05), tenfold lower than pathophysiological level, at 1:0.1 platelet MP ratio. Co-incubation of splenectomized-MPs with either normal-, non-splenectomized- or splenectomized-platelets at 1:10 platelet MP ratio increased platelet activation up to 5.1 ± 2.2, 5.6 ± 3.7, and 9.5 ± 3.0%, respectively, when normalized with individual baseline. These findings suggest that splenectomized patients were proned to be activated by MPs, and splenectomized-MPs could play an important role on chronic platelet activation and aggregation, leading to thrombus formation in β-thalassemia/HbE patients.

Insights into red blood cell storage lesion: Toward a new appreciation

Red blood cell storage lesion (RSL) is a multifaceted biological phenomenon. It refers to deterioration in RBC quality that is characterized by lethal and sub-lethal, reversible and irreversible defects. RSL is influenced by prestorage variables and it might be associated with variable clinical outcomes. Optimal biopreservation conditions are expected to offer maximum levels of RBC survival and acceptable functionality and bioreactivity in-bag and in vivo; consequently, full appraisal of RSL requires understanding of how RSL changes interact with each other and with the recipient. Recent technological innovation in MS-based omics, imaging, cytometry, small particle and systems biology has offered better understanding of RSL contributing factors and effects. A number of elegant in vivo and in vitro studies have paved the way for the identification of quality control biomarkers useful to predict RSL profile and posttransfusion performance. Moreover, screening tools for the early detection of good or poor "storers" and donors have been developed. In the light of new perspectives, storage time is not the touchstone to rule on the quality of a packed RBC unit. At least by a biochemical standpoint, the metabolic aging pattern during storage may not correspond to the currently fresh/old distinction of stored RBCs. Finally, although each unit of RBCs is probably unique, a metabolic signature of RSL across storage variables might exist. Moving forward from traditional hematologic measures to integrated information on structure, composition, biochemistry and interactions collected in bag and in vivo will allow identification of points for intervention in a transfusion meaningful context.

Reduction of biological response modifiers in the supernatant of washed paediatric red blood cells

BACKGROUND

Washing of red blood cells (RBC) can reduce unwanted biological response modifiers (BRMs) that can mediate transfusion complications in infants. The aim of this study was to examine the in vitro quality and the changes in BRMs following washing in paediatric RBC units.

MATERIALS AND METHODS

A pool and split design was used to prepare RBC (either 1 or 4 days old; n = 26 pairs). One unit was washed with 0·9% saline by centrifugation and then resuspended in SAG-M, while the other remained unwashed. Each RBC unit was divided to produce four units of paediatric-sized components. Samples were taken after 3 h and subsequently on days 1, 2, 7 and 14 post-wash.

RESULTS

Washing of RBC resulted in some red cell loss, with a minor increase in haemolysis. Washing effectively reduced supernatant potassium and IgA, as well as cytokines and complement proteins. RBC microparticles were significantly reduced in RBC washed at 1, but not 4 days post-collection. Incubation with supernatant from unwashed but not washed RBC led to endothelial cell activation, with increased cell surface expression of CD62E (E-selectin) and CD106 (VCAM).

CONCLUSION

Although washing affected some aspects of the in vitro quality of RBC, it effectively reduced the concentration and activity of BRMs in the supernatant of RBC. Such a reduction may be clinically beneficial in selected patient groups.

Procoagulant activity in stored units of red blood cells

The procoagulant activity (PA) of stored units of red blood cells (RBC) increases over time, which is related to the expression/exposure of tissue factor (TF). However, there is a discrepancy between the TF measured and changes in PA observed, suggesting that other blood components contribute to this activity. Our goal was to evaluate changes in PA of stored RBCs and to determine possible contributors to it. RBC units from 4 healthy donors were prepared and stored at 4 °C. On selected days, RBC aliquots were reconstituted with autologous plasma and tested in the thromboelastography assay. Corresponding supernatants were tested in a clotting assay. For all donors, the clotting time (CT) of reconstituted RBC units decreased from ∼3000-4000s on day 1 to ∼1000-1600s on day 30, with the most dramatic changes occurring between days 1 and 5. Anti-TF antibody slightly prolonged the CT. The concentration of TF did not change significantly over time and was within the range of 0.3-2.3 pM. Bovine lactadherin (LTD) prolonged the CT of the RBC (by 2.4-3.4-fold in days 3-5 and by 1.3-1.8-fold at day 30). Anti-TF antibody together with LTD had a cumulative effect on the CT prolongation. CT of supernatants responded to both anti-TF and anti-FXIa antibodies. Three contributors to the PA of stored RBC were identified, i.e. FXIa in solution and phosphatidylserine and TF exposed on blood cells and microparticles. Failure of LTD and antibodies to completely eliminate PA suggests that other components of blood could contribute to it.

Procoagulant microparticles promote coagulation in a factor XI-dependent manner in human endotoxemia

Essentials The procoagulant effects of microparticles (MPs) on coagulation in endotoxemia are not known. MPs from endotoxemia volunteers were evaluated for procoagulant activity in a plasma milieu. MPs from endotoxemia volunteers shortened clotting times and enhanced thrombin generation. MP procoagulant effects were mediated in a factor XI-dependent manner.

SUMMARY

Background Human endotoxemia is characterized by acute inflammation and activation of coagulation, as well as increased numbers of circulating microparticles (MPs). Whether these MPs directly promote coagulation and through which pathway their actions are mediated, however, has not been fully explored. Objectives In this study, we aimed to further characterize endotoxin-induced MPs and their procoagulant properties using several approaches. Methods Enumeration and characterization of MPs were performed using a new-generation flow cytometer. Relative contributions of the extrinsic and intrinsic pathways in MP-mediated procoagulant activity were assessed using plasmas deficient in factor (F) VII or FXI or with blocking antibodies to tissue factor (TF) or FXIa. Results Total MPs and platelet MPs were significantly elevated in plasma at 6 h after infusion of endotoxin in healthy human subjects. MPs isolated from plasma following endotoxin infusion also demonstrated increased TF activity in a reconstituted buffer system. When added to recalcified platelet-poor plasma, these MPs also promoted coagulation, as judged by a decreased clotting time with shortening of the lag time and time to peak thrombin using calibrated automated thrombography (CAT). However, the use of FVII-deficient plasma or blocking antibody to TF did not inhibit these procoagulant effects. In contrast, plasma clotting time was prolonged in FXI-deficient plasma and a blocking antibody to FXIa inhibited all MP-mediated parameters in the CAT assay. Conclusions The initiation of coagulation by cellular TF in endotoxemia is in contrast to (and presumably complemented by) the intrinsic pathway-mediated procoagulant effects of circulating MPs.

Effects of Aged Stored Autologous Red Blood Cells on Human Endothelial Function

RATIONALE

A major abnormality that characterizes the red cell "storage lesion" is increased hemolysis and reduced red cell lifespan after infusion. Low levels of intravascular hemolysis after transfusion of aged stored red cells disrupt nitric oxide (NO) bioavailabity, via accelerated NO scavenging reaction with cell-free plasma hemoglobin. The degree of intravascular hemolysis post-transfusion and effects on endothelial-dependent vasodilation responses to acetylcholine have not been fully characterized in humans.

OBJECTIVES

To evaluate the effects of blood aged to the limits of Food and Drug Administration-approved storage time on the human microcirculation and endothelial function.

METHODS

Eighteen healthy individuals donated 1 U of leukopheresed red cells, divided and autologously transfused into the forearm brachial artery 5 and 42 days after blood donation. Blood samples were obtained from stored blood bag supernatants and the antecubital vein of the infusion arm. Forearm blood flow measurements were performed using strain-gauge plethysmography during transfusion, followed by testing of endothelium-dependent blood flow with increasing doses of intraarterial acetylcholine.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that aged stored blood has higher levels of arginase-1 and cell-free plasma hemoglobin. Compared with 5-day blood, the transfusion of 42-day packed red cells decreases acetylcholine-dependent forearm blood flows. Intravascular venous levels of arginase-1 and cell-free plasma hemoglobin increase immediately after red cell transfusion, with more significant increases observed after infusion of 42-day-old blood.

CONCLUSIONS

We demonstrate that the transfusion of blood at the limits of Food and Drug Administration-approved storage has a significant effect on the forearm circulation and impairs endothelial function. Clinical trial registered with www.clinicaltrials.gov (NCT 01137656).