Erythrocyte-Derived Microparticles Activate Pulmonary Endothelial Cells in a Murine Model of Transfusion

Whole blood storage duration alters fibrinogen levels and thrombin formation

INTRODUCTION

Whole blood resuscitation for hemorrhagic shock in trauma represents an opportunity to correct coagulopathy in trauma while also supplying red blood cells. The production of microvesicles in stored whole blood and their effect on its hemostatic parameters have not been described in previous literature. We hypothesized that microvesicles in aged stored whole blood are procoagulant and increase thrombin production via phosphatidylserine.

METHODS

Whole blood was obtained from male C57BL/6 male mice and stored in anticoagulant solution for up to 10 days. At intervals, stored whole blood underwent examination with rotational thromboelastography, and platelet-poor plasma was prepared for analysis of thrombin generation. Microvesicles were prepared from 10-day-old whole blood aliquots and added to fresh whole blood or platelet-poor plasma to assess changes in coagulation and thrombin generation. Microvesicles were treated with recombinant mouse lactadherin prior to addition to plasma to inhibit phosphatidylserine's role in thrombin generation.

RESULTS

Aged murine whole blood had decreased fibrin clot formation compared with fresh samples with decreased plasma fibrinogen levels. Thrombin generation in plasma from aged blood increased over time of storage. The addition of microvesicles to fresh plasma resulted in increased thrombin generation compared with controls. When phosphatidylserine on microvesicles was blocked with lactadherin, there was no difference in the endogenous thrombin potential, but the generation of thrombin was blunted with lower peak thrombin levels.

CONCLUSION

Cold storage of murine whole blood results in decreased fibrinogen levels and fibrin clot formation. Aged whole blood demonstrates increased thrombin generation, and this is due in part to microvesicle production in stored whole blood. One mechanism by which microvesicles are procoagulant is by phosphatidylserine expression on their membranes.

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.

Adverse effects of microparticles on transfusion of stored red blood cell concentrates

BACKGROUND

Systemic and pulmonary coagulopathy and inflammation are important characteristics of transfusion-related acute lung injury (TRALI). Whether microparticles that accumulate in transfused red blood cell concentrates (RBCs) have proinflammatory and procoagulant potential and contribute to adverse reactions of RBC transfusions is unclear.

AIM

To investigate the ability of microparticles in stored RBCs to promote thrombin generation and induce human pulmonary microvascular endothelial cell (HMVEC) activation and damage.

METHODS

The number and size of microparticles were determined by flow cytometric and nanoparticle tracking analyses, respectively. Thrombin generation and the intrinsic coagulation pathway were assayed by a calibrated automated thrombogram and by measuring activated partial thromboplastin time (aPTT), respectively. The expression of ICAM-1 and the release of cytokines by endothelial cells were detected by flow cytometric analyses. HMVEC damage was assessed by incubating lipopolysaccharide-activated endothelial cells with MP-primed polymorphonuclear neutrophils (PMNs).

RESULTS

The size of the microparticles in the RBC supernatant was approximately 100-300 nm. Microparticles promoted thrombin generation in a dose-dependent manner and the aPTT was shortened. Depleting microparticles from the supernatant of RBCs stored for 35 days by either filtration or centrifugation significantly decreased the promotion of thrombin generation. The expression of ICAM-1 on HMVECs was increased significantly by incubation with isolated microparticles. Furthermore, microparticles induced the release of interleukin-6 (IL-6) and interleukin-8 (IL-8) from HMVECs. Microparticles induced lipopolysaccharide-activated HMVEC damage by priming PMNs, but this effect was prevented by inhibiting the PMNs respiratory burst with apocynin.

CONCLUSION

Microparticles in stored RBCs promote thrombin generation, HMVEC activation and damage which may be involved in TRALI development.

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) in label-free characterization of erythrocyte membranes and extracellular vesicles at the nano-scale and molecular level

The manuscript presents the potential of surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) for label-free characterization of extracellular microvesicles (EVs) and their isolated membranes derived from red blood cells (RBCs) at the nanoscale and at the single-molecule level, providing detection of a few individual amino acids, protein and lipid membrane compartments. The study shows future directions for research, such as investigating the use of the mentioned techniques for the detection and diagnosis of diseases. We demonstrate that SERS and TERS are powerful techniques for identifying the biochemical composition of EVs and their membranes, allowing the detection of small molecules, lipids, and proteins. Furthermore, extracellular vesicles released from red blood cells (REVs) can be broadly classified into exosomes, microvesicles, and apoptotic bodies, based on their size and biogenesis pathways. Our study specifically focuses on microvesicles that range from 100 to 1000 nanometres in diameter, as presented in AFM images. Using SERS and TERS spectra obtained for REVs and their membranes, we were able to characterize the chemical and structural properties of microvesicle membranes with high sensitivity and specificity. This information may help better distinguish and categorize different types of EVs, leading to a better understanding of their functions and potential biomedical applications.

Extracellular vesicles: effectors of transfusion-related acute lung injury

Respiratory transfusion reactions represent some of the most severe adverse reactions related to receiving blood products. Of those, transfusion-related acute lung injury (TRALI) is associated with elevated morbidity and mortality. TRALI is characterized by severe lung injury associated with inflammation, pulmonary neutrophil infiltration, lung barrier leak, and increased interstitial and airspace edema that cause respiratory failure. Presently, there are few means of detecting TRALI beyond clinical definitions based on physical examination and vital signs or preventing/treating TRALI beyond supportive care with oxygen and positive pressure ventilation. Mechanistically, TRALI is thought to be mediated by the culmination of two successive proinflammatory hits, which typically comprise a recipient factor (1st hit-e.g., systemic inflammatory conditions) and a donor factor (2nd hit-e.g., blood products containing pathogenic antibodies or bioactive lipids). An emerging concept in TRALI research is the contribution of extracellular vesicles (EVs) in mediating the first and/or second hit in TRALI. EVs are small, subcellular, membrane-bound vesicles that circulate in donor and recipient blood. Injurious EVs may be released by immune or vascular cells during inflammation, by infectious bacteria, or in blood products during storage, and can target the lung upon systemic dissemination. This review assesses emerging concepts such as how EVs: 1) mediate TRALI, 2) represent targets for therapeutic intervention to prevent or treat TRALI, and 3) serve as biochemical biomarkers facilitating TRALI diagnosis and detection in at-risk patients.

Different-sized extracellular vesicles derived from stored red blood cells package diverse cargoes and cause distinct cellular effects

BACKGROUND

The formation of extracellular vesicles (EVs) occurs during cold storage of RBCs. Transfusion of EVs may contribute to adverse responses in recipients receiving RBCs. However, EVs are poorly characterized with limited data on whether distinct vesicles are formed, their composition, and potential biological effects.

STUDY DESIGN AND METHODS

Stored RBC-derived EVs were purified using protocols that separate larger microvesicle-like EVs (LEVs) from smaller exosome-like vesicles (SEVs). Vesicles were analyzed by electron microscopy, content of hemoglobin, heme, and proteins (by mass spectrometry), and the potential to mediate lipid peroxidation and endothelial cell permeability in vitro.

RESULTS

SEVs were characterized by having an electron-dense double membrane whereas LEVs had more uniform electron density across the particles. No differences in hemoglobin nor heme levels per particle were observed, however, due to smaller volumes, SEVs had higher concentrations of oxyHb and heme. Both particles contained antioxidant proteins peroxiredoxin-2 and copper/zinc superoxide dismutase, these were present in higher molecular weight fractions in SEVs suggesting either oxidized proteins are preferentially packaged into smaller vesicles and/or that the environment associated with SEVs is more pro-oxidative. Furthermore, total glutathione (GSH + GSSG) levels were lower in SEVs. Both EVs mediated oxidation of liposomes that were prevented by hemopexin, identifying heme as the pro-oxidant effector. Addition of SEVs, but not LEVs, induced endothelial permeability in a process also prevented by hemopexin.

CONCLUSION

These data show that distinct EVs are formed during cold storage of RBCs with smaller particles being more likely to mediate pro-oxidant and inflammatory effects associated with heme.

Storage with ethanol attenuates the red blood cell storage lesion

BACKGROUND

Current management of hemorrhagic shock relies on control of surgical bleeding along with resuscitation with packed red blood cells and plasma in a 1-to-1 ratio. Transfusion, however, is not without consequence as red blood cells develop a series of biochemical and physical changes during storage termed "the red blood cell storage lesion." Previous data has suggested that ethanol may stabilize the red blood cell membrane, resulting in improved deformability. We hypothesized that storage of packed red blood cells with ethanol would alter the red blood cell storage lesion.

METHODS

Mice underwent donation and storage of red blood cells with standard storage conditions in AS-3 alone or ethanol at concentrations of 0.07%, 0.14%, and 0.28%. The red blood cell storage lesion parameters of microvesicles, Band-3, free hemoglobin, annexin V, and erythrocyte osmotic fragility were measured and compared. In additional experiments, the mice underwent hemorrhage and resuscitation with stored packed red blood cells to further evaluate the in vivo inflammatory impact.

RESULTS

Red blood cells stored with ethanol demonstrated decreased microvesicle accumulation and Band-3 levels. There were no differences in phosphatidylserine or cell-free hemoglobin levels. After hemorrhage and resuscitation with packed red blood cells stored with 0.07% ethanol, mice demonstrated decreased serum levels of interleukin-6, macrophage inflammatory protein-1α, keratinocyte chemokine, and tumor necrosis factor α compared to those mice receiving packed red blood cells stored with additive solution-3.

CONCLUSION

Storage of murine red blood cells with low-dose ethanol results in decreased red blood cell storage lesion severity. Resuscitation with packed red blood cells stored with 0.07% ethanol also resulted in a decreased systemic inflammatory response in a murine model of hemorrhage.

Improving packed red blood cell storage with a high-viscosity buffered storage solution

BACKGROUND

Massive transfusion with older packed red blood cells is associated with increased morbidity and mortality. As packed red blood cells age, they undergo biochemical and structural changes known as the storage lesion. We developed a novel solution to increase viscosity in stored packed red blood cells. We hypothesized that packed red blood cell storage in this solution would blunt storage lesion formation and mitigate the inflammatory response after resuscitation.

METHODS

Blood was obtained from 8- to 10-week-old C57BL/6 male donor mice or human volunteers and stored as packed red blood cell units for 14 days for mice or 42 days for humans in either standard AS-3 storage solution or EAS-1587, the novel packed red blood cell storage solution. Packed red blood cells were analyzed for microvesicles, cell-free hemoglobin, phosphatidylserine, band-3 protein, glucose utilization, and osmotic fragility. Additional mice underwent hemorrhage and resuscitation with packed red blood cells stored in either AS-3 or EAS-1587. Serum was analyzed for inflammatory markers.

RESULTS

Murine packed red blood cells stored in EAS-1587 demonstrated reductions in microvesicle and cell-free hemoglobin accumulation as well as preserved band-3 expression, increase glucose utilization, reductions in phosphatidylserine expression, and susceptibility to osmotic stress. Serum from mice resuscitated with packed red blood cells stored in EAS-1587 demonstrated reduced proinflammatory cytokines. Human packed red blood cells demonstrated a reduction in microvesicle and cell-free hemoglobin as well as an increase in glucose utilization.

CONCLUSION

Storage of packed red blood cells in a novel storage solution mitigated many aspects of the red blood cell storage lesion as well as the inflammatory response to resuscitation after hemorrhage. This modified storage solution may lead to improvement of packed red blood cell storage and reduce harm after massive transfusion.

Expired But Not Yet Dead: Examining the Red Blood Cell Storage Lesion in Extended-Storage Whole Blood

ABSTRACT

Whole blood is a powerful resuscitation strategy for trauma patients but has a shorter shelf life than other blood products. The red blood cell storage lesion in whole blood has not previously been investigated beyond the standard storage period. In the present study, we hypothesized that erythrocytes in stored whole blood exhibit similar aspects of the red blood cell storage lesion and that transfusion of extended storage whole blood would not result in a more severe inflammatory response after hemorrhage in a murine model. To test this hypothesis, we stored low-titer, O-positive, whole blood units, and packed red blood cells (pRBCs) for up to 42 days, then determined aspects of the red blood cell storage lesion. Compared with standard storage pRBCs, whole blood demonstrated decreased microvesicle and free hemoglobin at 21 days of storage and no differences in osmotic fragility. At 42 days of storage, rotational thromboelastometry demonstrated that clotting time was decreased, alpha angle was increased, and clot formation time and maximum clot firmness similar in whole blood as compared with pRBCs with the addition of fresh frozen plasma. In a murine model, extended storage whole blood demonstrated decreased microvesicle formation, phosphatidylserine, and cell-free hemoglobin. After hemorrhage and resuscitation, TNF-a, IL-6, and IL-10 were decreased in mice resuscitated with whole blood. Red blood cell survival was similar at 24 h after transfusion. Taken together, these data suggest that red blood cells within whole blood stored for an extended period of time demonstrate similar or reduced accumulation of the red blood cell storage lesion as compared with pRBCs. Further examination of extended-storage whole blood is warranted.

Unexpected Role of Nonimmune Cells: Amateur Phagocytes

Effective and efficient efferocytosis of dead cells and associated cellular debris are critical to tissue homeostasis and healing of injured tissues. This important task was previously thought to be restricted to professional phagocytes (PPs). However, accumulating evidence has revealed another type of phagocyte, the amateur phagocyte (AP), which can also participate in efferocytosis. APs are non-myeloid progenitor/nonimmune cells that include differentiated cells (e.g., epithelial cells, fibroblasts, and endothelial cells [ECs]) and stem cells (e.g., neuronal progenitor cells and mesenchymal cells) and can be found throughout the human body. Studies have shown that APs have two prominent roles: identifying and removing dead cells presumably before PPs reach the site of injury and assisting PPs in the removal of cell corpses and the resolution of inflamed tissue. With respect to the engulfment and degradation of dead cells, APs are slower and less efficient than PPs. However, APs are fundamental to preventing the spread of inflammation over a large area. In this review, we present the diversity and characteristics of healthy and non-neoplastic APs in mammals. We also propose a hypothetical mechanism of the efferocytosis of immunoglobulin G (IgG)-opsonized myelin debris by ECs (APs). Furthermore, the ingestion and clearance of dead cells can induce proinflammatory or anti-inflammatory cytokine production, endothelial activation, and cellular fate transition, which contribute to the progression of disease. An understanding of the role of APs is necessary to develop effective intervention strategies, including potential molecular targets for clinical diagnosis and drug development, for inflammation-related diseases.

Save it-don't waste it! Maximizing utilization of erythrocytes from previously stored whole blood

BACKGROUND

Recent military and civilian experience suggests that fresh whole blood may be the preferred for treatment of hemorrhagic shock, but its use is limited by its 21-day shelf life. The red blood cell storage lesion and coagulation status of packed red blood cells (pRBCs) salvaged from expired whole blood are unknown. We hypothesized that pRBCs can be salvaged from previously stored whole blood.

METHODS

Cold stored, low-titer, O-positive, nonleukoreduced, whole blood units were obtained at 21 days of storage. Erythrocytes were separated by centrifugation, resuspended in AS-3, and stored for 21 additional days as salvaged pRBCs. The red blood cell storage lesion parameters of microvesicles, Band-3, free hemoglobin, annexin V, and erythrocyte osmotic fragility were measured and compared with pRBCs prepared at the time of donation and stored in AS-3 for 42 days (standard pRBCs). In additional experiments, murine pRBCs were prepared from expired whole blood units and compared with those stored under standard conditions. Mice underwent hemorrhage and resuscitation with standard and salvaged pRBC units, and serum cytokines and free hemoglobin were determined.

RESULTS

There were no significant differences in microvesicle formation or cell-free hemoglobin concentration between salvaged and standard pRBCs. There was decreased Band-3 and increased phosphatidylserine in the salvaged units as well as greater osmotic fragility. Salvaged pRBCs maintained consistent clot firmness. After hemorrhage and resuscitation in a murine model, salvaged pRBCs did not demonstrate increased serum cytokine levels.

CONCLUSION

Salvaged pRBCs from previously stored whole blood accumulate the red blood cell storage lesion in a similar fashion to standard pRBCs and maintain consistent coagulability when reconstituted with plasma. Salvaged pRBCs are not associated with an increased inflammatory response when used for resuscitation in a murine model. Salvaged pRBCs may be a viable product for utilization in the treatment of traumatic hemorrhagic shock.

Extracellular Vesicles Derived from Intermittent Hypoxia-Treated Red Blood Cells Impair Endothelial Function Through Regulating eNOS Phosphorylation and ET-1 Expression

PURPOSE

Intermittent hypoxia (IH), a main characteristic of obstructive sleep apnea (OSA) syndrome, has been known as a dominant cause of OSA-related endothelial dysfunction and hypertension. However, the underlying mechanism still remains unclear. Extracellular vesicles (EVs), small vesicles secreted by various cells, can be absorbed by endothelial cells and then influence vascular function. The aim of this research is to clarify whether and how EVs shedding from red blood cells (RBCs) are involved in IH-induced endothelial dysfunction.

METHODS

EVs were extracted by ultracentrifugation. After the identification of property and purity, EVs from IH-exposed RBCs (IH REVs) and normoxia-exposed RBCs (NOR REVs) or from OSA and non-OSA patient RBCs were utilized to treat C57BL/6 mouse aortas or human umbilical vein endothelial cells (HUVECs) for mechanistic exploration.

RESULTS

Functional results demonstrated that REVs from OSA patients dramatically impaired endothelium-dependent relaxations (EDRs). Similarly, in vivo and ex vivo studies showed that IH REVs caused significant endothelial dysfunction compared to control group. Further results presented that IH REVs blocked endothelial nitric oxide synthase (eNOS) phosphorylation through inhibiting PI3K/Akt pathway and enhanced endothelin-1 (ET-1) expression through activating Erk1/2 pathway in endothelial cells. Meanwhile, endothelial dysfunction caused by IH REVs was reversed by Akt activator SC79 as well as Erk kinase inhibitor PD98059, suggesting that PI3K/Akt/eNOS and Erk1/2/ET-1 pathways were implicated in IH REV-induced impaired EDRs.

CONCLUSIONS

This study reveals a novel role of REVs in endothelial dysfunction under IH and dissects the relevant mechanism involved in this process, which will help to establish a comprehensive understanding of OSA or IH-related endothelial dysfunction from a new scope.

Complement C5a Induces Pro-inflammatory Microvesicle Shedding in Severely Injured Patients

Initially underestimated as platelet dust, extracellular vesicles are continuously gaining interest in the field of inflammation. Various studies addressing inflammatory diseases have shown that microvesicles (MVs) originating from different cell types are systemic transport vehicles carrying distinct cargoes to modulate immune responses. In this study, we focused on the clinical setting of multiple trauma, which is characterized by activation and dysfunction of both, the fluid-phase and the cellular component of innate immunity. Given the sensitivity of neutrophils for the complement anaphylatoxin C5a, we hypothesized that increased C5a production induces alterations in MV shedding of neutrophils resulting in neutrophil dysfunction that fuels posttraumatic inflammation. In a mono-centered prospective clinical study with polytraumatized patients, we found significantly increased granulocyte-derived MVs containing the C5a receptor (C5aR1, CD88) on their surface. This finding was accompanied by a concomitant loss of C5aR1 on granulocytes indicative of an impaired cellular chemotactic and pro-inflammatory neutrophil functions. Furthermore, in vitro exposure of human neutrophils (from healthy volunteers) to C5a significantly increased MV shedding and C5aR1 loss on neutrophils, which could be blocked using the C5aR1 antagonist PMX53. Mechanistic analyses revealed that the interaction between C5aR1 signaling and the small GTPase Arf6 acts as a molecular switch for MV shedding. When neutrophil derived, C5a-induced MV were exposed to a complex ex vivo whole blood model significant pro-inflammatory properties (NADPH activity, ROS and MPO generation) of the MVs became evident. C5a-induced MVs activated resting neutrophils and significantly induced IL-6 secretion. These data suggest a novel role of the C5a-C5aR1 axis: C5a-induced MV shedding from neutrophils results in decreased C5aR1 surface expression on the one hand, on the other hand it leads to profound inflammatory signals which likely are both key drivers of the neutrophil dysfunction which is regularly observed in patients suffering from multiple traumatic injuries.

Washing packed red blood cells decreases red blood cell storage lesion formation

BACKGROUND

Transfusion of blood products is the ideal resuscitative strategy after hemorrhage. Unfortunately, older packed red blood cells have been associated with increased morbidity and mortality after massive transfusion. These packed red blood cells accumulate biochemical and structural changes known as the red blood cell storage lesions. The effect of washing on the formation of red blood cell storage lesions is unknown. We hypothesized that washing packed red blood cells during storage would decrease the development of the red blood cell storage lesions.

METHODS

Blood from 8- to 10-week-old male mice donors was stored as packed red blood cells for 14 days. A subset of packed red blood cells were washed with phosphate-buffered saline on storage day 7 and resuspended in AS-1 solution for an additional 7 days as washed packed red blood cells. Subsequently, the packed red blood cells were analyzed for microvesicle release, band-3 erythrocyte membrane integrity protein (Band-3), expression of phosphatidylserine, cell viability (calcein), accumulation of cell-free hemoglobin, and osmotic fragility.

RESULTS

In the washed packed red blood cells group, there was less microvesicle accumulation, greater Band-3 expression, less phosphatidylserine expression, a decrease in cell-free hemoglobin accumulation, and a decrease in osmotic fragility, but no differences in red blood cells viability.

CONCLUSION

Washing packed red blood cells during storage decreases the accumulation of red blood cell storage lesions. This strategy may lessen the sequelae associated with transfusion of older packed red blood cells.

Innate coagulability changes with age in stored packed red blood cells

BACKGROUND

Packed red blood cell (pRBC) units administered during resuscitation from hemorrhagic shock are of varied storage ages. We have previously shown that RBC-derived microparticles' impact on thrombogenesis. However, the impact of storage age on pRBC coagulability is unknown. Therefore, we sought to investigate the effect of storage age on innate coagulability and aggregability of stored pRBCs.

METHODS

pRBCs prepared from male C57BL/6J mice were stored in Additive Solution-3 according to our standardized murine blood banking protocols for 14 days. Rotational thromboelastometry (ROTEM) was used to assess the innate coagulation status of fresh and 14-day old pRBCs. Viscoelastic coagulation parameters of clotting time (CT), clot formation time (CFT), alpha angle, and maximum clot firmness (MCF) were analyzed to determine coagulability. Plasma was added to the fresh pRBCs and 15-day old pRBCs to determine if the storage-associated coagulopathy was reversible with plasma. Statistical analyses were conducted with a Student's t-test.

RESULTS

Fifteen-day old pRBCs demonstrated a significant reduction in MCF (10.3 vs. 24.4 mm, P-value <0.001) and alpha angle (6.0 vs. 27.2 degrees, P-value <0.001) as well as significant prolongation of CFT and CT (1126.5 vs. 571.4 s, P-value <0.001) compared to fresh pRBCs. FFP addition to 15-day old and fresh pRBCs, demonstrated a significant reduction in MCF and persistent prolongation of CFT. This suggests that pRBCs lost coagulability as they aged and this deficit was not completely corrected by plasma administration.

CONCLUSIONS

Storage duration may be an important factor in coagulation potential of pRBCs. Transfusion with older pRBCs may contribute to coagulopathy in massively transfused patients.

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.

Microparticles from aged packed red blood cell units stimulate pulmonary microthrombus formation via P-selectin

INTRODUCTION

During storage, packed red blood cells undergo a series of physical, metabolic, and chemical changes collectively known as the red blood cell storage lesion. One key component of the red blood cell storage lesion is the accumulation of microparticles, which are submicron vesicles shed from erythrocytes as part of the aging process. Previous studies from our laboratory indicate that transfusion of these microparticles leads to lung injury, but the mechanism underlying this process is unknown. In the present study, we hypothesized that microparticles from aged packed red blood cell units induce pulmonary thrombosis.

MATERIALS AND METHODS

Leukoreduced, platelet-depleted, murine packed red blood cells (pRBCS) were prepared then stored for up to 14 days. Microparticles were isolated from stored units via high-speed centrifugation. Mice were transfused with microparticles. The presence of pulmonary microthrombi was determined with light microscopy, Martius Scarlet Blue, and thrombocyte stains. In additional studies microparticles were labelled with CFSE prior to injection. Murine lung endothelial cells were cultured and P-selectin concentrations determined by ELISA. In subsequent studies, P-selectin was inhibited by PSI-697 injection prior to transfusion.

RESULTS

We observed an increase in microthrombi formation in lung vasculature in mice receiving microparticles from stored packed red blood cell units as compared with controls. These microthrombi contained platelets, fibrin, and microparticles. Treatment of cultured lung endothelial cells with microparticles led to increased P-selectin in the media. Treatment of mice with a P-selectin inhibitor prior to microparticle infusion decreased microthrombi formation.

CONCLUSIONS

These data suggest that microparticles isolated from aged packed red blood cell units promote the development of pulmonary microthrombi in a murine model of transfusion. This pro-thrombotic event appears to be mediated by P-selectin.

Early Identification of Acute Lung Injury in a Porcine Model of Hemorrhagic Shock

BACKGROUND

Acute lung injury (ALI) is a frequent complication after severe trauma. Lung-protective ventilation strategies and damage control resuscitation have been proposed for the prevention of ALI; however, there are no clinical or laboratory parameters to predict who is at risk of developing ALI after trauma. In the present study, we explored pulmonary inflammatory markers as a potential predictor of ALI using a porcine model of hemorrhagic shock.

MATERIALS AND METHODS

Female swine were randomized to mechanical ventilation with low tidal volume (V_T) (6 mL/kg) or high V_T (12 mL/kg). After equilibration, animals underwent pressure-controlled hemorrhage (mean arterial pressure [MAP] 35 ± 5 mmHg) for 1 h, followed by resuscitation with fresh whole blood or Hextend. They were maintained at MAP of 50 ± 5 mmHg for 3 h in the postresuscitation phase. Bronchoalveolar lavage fluids were collected hourly and analyzed for inflammatory markers. Lung samples were taken, and porcine neutrophil antibody staining was used to evaluate the presence of neutrophils. ELISA evaluated serum porcine surfactant protein D levels. Sham animals were used as negative controls.

RESULTS

Pigs that underwent hemorrhagic shock had higher heart rates, lower cardiac output, lower MAPs, and worse acidosis compared with sham at the early time points (P < 0.05 each). There were no significant differences in central venous pressure or pulmonary capillary wedge pressure between groups. Pulmonary neutrophil infiltration, as defined by neutrophil antibody staining on lung samples, was greater in the shock groups regardless of resuscitation fluid (P < 0.05 each). Bronchoalveolar lavage fluid neutrophil levels were not different between groups. There were no differences in levels of porcine surfactant protein D between groups at any time points, and the levels did not change over time in each respective group.

CONCLUSIONS

Our study demonstrates the reproducibility of a porcine model of hemorrhagic shock that is consistent with physiologic changes in humans in hemorrhagic shock. Pulmonary neutrophil infiltration may serve as an early marker for ALI; however, the practicality of this finding has yet to be determined.

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.

Endocytosis of Red Blood Cell Microparticles by Pulmonary Endothelial Cells is Mediated By Rab5

Microparticles are submicron vesicles shed from aging erythrocytes as a characteristic feature of the red blood cell (RBC) storage lesion. Exposure of pulmonary endothelial cells to RBC-derived microparticles promotes an inflammatory response, but the mechanisms underlying microparticle-induced endothelial cell activation are poorly understood. In the present study, cultured murine lung endothelial cells (MLECs) were treated with microparticles isolated from aged murine packed RBCs or vehicle. Microparticle-treated cells demonstrated increased expression of the adhesion molecules ICAM and E-selectin, as well as the cytokine, IL-6. To identify mechanisms that mediate these effects of microparticles on MLECs, cells were treated with microparticles covalently bound to carboxyfluorescein succinimidyl ester (CFSE) and cellular uptake of microparticles was quantified via flow cytometry. Compared with controls, there was a greater proportion of CFSE-positive MLECs from 15 min up to 24 h, suggesting endocytosis of the microparticles by endothelial cells. Colocalization of microparticles with lysosomes was observed via immunofluorescence, indicating endocytosis and endolysosomal trafficking. This process was inhibited by endocytosis inhibitors. SiRNA knockdown of Rab5 signaling protein in endothelial cells resulted in impaired microparticle uptake as compared with nonsense siRNA-treated cells, as well as an attenuation of the inflammatory response to microparticle treatment. Taken together, these data suggest that endocytosis of RBC-derived microparticles by lung endothelial cells results in endothelial cell activation. This response seems to be mediated, in part, by the Rab5 signaling protein.

Endothelial Extracellular Vesicles in Pulmonary Function and Disease

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

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.

Microparticles from stored red blood cells promote a hypercoagulable state in a murine model of transfusion

BACKGROUND

Red blood cell-derived microparticles are biologically active, submicron vesicles shed by erythrocytes during storage. Recent clinical studies have linked the duration of red blood cell storage with thromboembolic events in critically ill transfusion recipients. In the present study, we hypothesized that microparticles from aged packed red blood cell units promote a hypercoagulable state in a murine model of transfusion.

METHODS

Microparticles were isolated from aged, murine packed red blood cell units via serial centrifugation. Healthy male C57BL/6 mice were transfused with microparticles or an equivalent volume of vehicle, and whole blood was harvested for analysis via rotational thromboelastometry. Serum was harvested from a separate set of mice after microparticles or saline injection, and analyzed for fibrinogen levels. Red blood cell-derived microparticles were analyzed for their ability to convert prothrombin to thrombin. Finally, mice were transfused with either red blood cell microparticles or saline vehicle, and a tail bleeding time assay was performed after an equilibration period of 2, 6, 12, or 24 hours.

RESULTS

Mice injected with red blood cell-derived microparticles demonstrated an accelerated clot formation time (109.3 ± 26.9 vs 141.6 ± 28.2 sec) and increased α angle (68.8 ± 5.0 degrees vs 62.8 ± 4.7 degrees) compared with control (each P < .05). Clotting time and maximum clot firmness were not significantly different between the 2 groups. Red blood cell-derived microparticles exhibited a hundredfold greater conversion of prothrombin substrate to its active thrombin form (66.60 ± 0.03 vs 0.70 ± 0.01 peak OD; P<.0001). Additionally, serum fibrinogen levels were lower in microparticles-injected mice compared with saline vehicle, suggesting thrombin-mediated conversion to insoluble fibrin (14.0 vs 16.5 µg/mL, P<.05). In the tail bleeding time model, there was a more rapid cessation of bleeding at 2 hours posttransfusion (90.6 vs 123.7 sec) and 6 hours posttransfusion (87.1 vs 141.4 sec) in microparticles-injected mice as compared with saline vehicle (each P<.05). There was no difference in tail bleeding time at 12 or 24 hours.

CONCLUSION

Red blood cell-derived microparticles induce a transient hypercoagulable state through accelerated activation of clotting factors.