Generation of annexin V-positive platelets and shedding of microparticles with stimulus-dependent procoagulant activity during storage of platelets at 4 degrees C

Cofilin-1-induced actin reorganization in stored platelets

BACKGROUND

During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in stored platelets, is a major mediator these changes. Cofilin-1 is an effector of actin reorganization. We examined the effect of cofilin-1 deficiency on cytoskeleton and phosphatidylserine exposure during storage and following activation of apoptosis.

METHODS AND RESULTS

We assessed actin filaments by Alexa-647-phalloidin and phosphatidylserine exposure by fluorescein isothiocyanate-lactadherin by fluorescence microscopy. In fresh platelets, actin filaments are distributed in the subcortical region, and they do not express phosphatidylserine in the outer surface. In stored platelets, there is retraction of actin filaments from the subcortical region with increased phosphatidylserine expression. These changes are seen in 20% of platelets of 6 days old and increases further with storage. Treatment with ABT-737, which activates the mitochondrial apoptosis, induces similar cytoskeletal changes in actin filaments with increased phosphatidylserine. Cofilin-1 is activated in stored platelets as well as in ABT-737 treated platelets by dephosphorylation. In cofilin-1 deficient murine platelets actin filaments are abnormal and ABT-737 induces less phosphatidylserine. Despite these changes in vitro, platelet survival of cofilin-1 deficient platelets in mice was not significantly different from their wild-type controls.

CONCLUSION

These results show that cofilin-1 plays a role in apoptosis-induced actin rearrangement and phosphatidylserine exposure during storage. Despite the defects in platelet cytoskeleton and phosphatidylserine exposure in cofilin-1-deficient platelets, the in vivo life span of platelets is similar to littermate controls, indicating multiple redundant pathways for the clearance of platelets in vivo.

Therapeutic Effects of Hyaluronic Acid in Bacterial Pneumonia in Ex Vivo Perfused Human Lungs

Rationale: Recent studies have demonstrated that extracellular vesicles (EVs) released during acute lung injury (ALI) were inflammatory.Objectives: The current study was undertaken to test the role of EVs induced and released from severe Escherichia coli pneumonia (E. coli EVs) in the pathogenesis of ALI and to determine whether high-molecular-weight (HMW) hyaluronic acid (HA) administration would suppress lung injury from E. coli EVs or bacterial pneumonia.Methods:E. coli EVs were collected from the perfusate of an ex vivo perfused human lung injured with intrabronchial E. coli bacteria for 6 hours by ultracentrifugation and then given intrabronchially or intravenously to naive human lungs. One hour later, HMW HA was instilled into the perfusate (n = 5-6). In separate experiments, HMW HA was given after E. coli bacterial pneumonia (n = 6-10). In vitro experiments were conducted to evaluate binding of EVs to HMW HA and uptake of EVs by human monocytes.Measurements and Main Results: Administration of HMW HA ameliorated the impairment of alveolar fluid clearance, protein permeability, and acute inflammation from E. coli EVs or pneumonia and reduced total bacteria counts after E. coli pneumonia. HMW HA bound to E. coli EVs, inhibiting the uptake of EVs by human monocytes, an effect associated with reduced TNFα (tumor necrosis factor α) secretion. Surprisingly, HMW HA increased E. coli bacteria phagocytosis by monocytes.Conclusions: EVs induced and released during severe bacterial pneumonia were inflammatory and induced ALI, and HMW HA administration was effective in inhibiting the uptake of EVs by target cells and decreasing lung injury from E. coli EVs or bacterial pneumonia.

Microparticles and acute lung injury

The pathophysiology of acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), is characterized by increased vascular and epithelial permeability, hypercoagulation and hypofibrinolysis, inflammation, and immune modulation. These detrimental changes are orchestrated by cross talk between a complex network of cells, mediators, and signaling pathways. A rapidly growing number of studies have reported the appearance of distinct populations of microparticles (MPs) in both the vascular and alveolar compartments in animal models of ALI/ARDS or respective patient populations, where they may serve as diagnostic and prognostic biomarkers. MPs are small cytosolic vesicles with an intact lipid bilayer that can be released by a variety of vascular, parenchymal, or blood cells and that contain membrane and cytosolic proteins, organelles, lipids, and RNA supplied from and characteristic for their respective parental cells. Owing to this endowment, MPs can effectively interact with other cell types via fusion, receptor-mediated interaction, uptake, or mediator release, thereby acting as intrinsic stimulators, modulators, or even attenuators in a variety of disease processes. This review summarizes current knowledge on the formation and potential functional role of different MPs in inflammatory diseases with a specific focus on ALI/ARDS. ALI has been associated with the formation of MPs from such diverse cellular origins as platelets, neutrophils, monocytes, lymphocytes, red blood cells, and endothelial and epithelial cells. Because of their considerable heterogeneity in terms of origin and functional properties, MPs may contribute via both harmful and beneficial effects to the characteristic pathological features of ALI/ARDS. A better understanding of the formation, function, and relevance of MPs may give rise to new promising therapeutic strategies to modulate coagulation, inflammation, endothelial function, and permeability either through removal or inhibition of "detrimental" MPs or through administration or stimulation of "favorable" MPs.

Role of zebrafish thrombocyte and non-thrombocyte microparticles in hemostasis

Hemostasis is a defense mechanism that protects an organism from bleeding in the event of injury. We have previously demonstrated the utility of the zebrafish as a model to study human hemostasis. However, there are no studies on the role of microparticles in hemostasis in early vertebrates. Studying microparticles in zebrafish may provide insight into the evolution of microparticle function in hemostasis and may lead to direct observation of these microparticles in zebrafish larvae due to transparency of the vessels. In this investigation we demonstrate the presence of cellular microparticles in fish blood by both immunostaining as well as by using zebrafish whose thrombocytes are labeled with green fluorescent protein. Further investigation showed that microparticles were also labeled by fluorescein isothiocyanate annexin V, suggesting that these particles are derived via apoptosis. A portion of the fluorescein isothiocyanate annexin V labeled microparticles was also labeled by DiI-C18. Labeling by DiI-C18 suggests that some microparticles are derived from young thrombocytes. Additionally, GpIIb antibody labels almost all thrombocyte-derived microparticles and a greater percentage of microparticles are labeled by GpIIb antibody than by DiI-C18. This suggests that thrombocyte microparticles are derived from both young and mature thrombocytes. Furthermore, the increase of microparticles by adding excessive microparticles into blood in vitro and through intravenous injections led to an increased hemostatic response. In addition, treatment with tumor necrosis factor alpha resulted in an increased number of thrombocyte microparticles and enhanced hemostasis; in contrast, treatment with zVAD-FMK, a caspase inhibitor, resulted in a decrease in thrombocyte microparticles and decreased hemostasis. We also found that thrombocyte microparticles agglutinate, along with other cells and cellular microparticles, in the presence of an excess of either ristocetin or ultra-large von Willebrand factor. Also, stimulation of von Willebrand factor release in vivo resulted in clusters of thrombocyte microparticles in the veins. Moreover, thrombocyte microparticles were the first to appear at the site of arterial injury. We found that thrombocyte microparticles are functionally equivalent to platelet microparticles. The microparticles initiate arterial thrombus formation in a von Willebrand factor-dependent manner and further enhance thrombus formation by forming clusters of microparticles in venous thrombosis. This finding may have applications for understanding the role of platelet microparticles in humans and may have diagnostic applications.

Circulating microparticles: new insights into the biochemical basis of microparticle release and activity

Circulating microparticles released from various cell types are present in healthy individuals and the number and composition of their membrane vary in different disorders. Long considered to be cellular debris, microparticles have been recently identified as regulatory vectors of intercellular cross-talk. Indeed, circulating microparticles represent a heterogeneous mixture of spheroids of diverse surface membrane glycoproteins and lipids, with diverse cytoplasm components, the pattern of which depends on the type of stimulation and pathophysiology of parental cells. Despite extensive research into the procoagulant and proinflammatory properties of microparticles, there are few data that can provide information on the mechanism(s) of their formation and biological effects. Although several mechanisms of microparticle release have been suggested, the precise order of the events associated with key features of microparticle formation, transmembrane phosphatidylserine redistribution and cytoskeleton disruption remain to be clarified. In this review, we provide an overview of the molecular mechanisms involved in microparticle formation, as well as the diverse physiological and pathological roles they are able to undertake. Understanding the mechanism(s) governing microparticle release processes may be critical to understanding their precise role in various pathophysiological processes and thus indicate new potential routes to therapy.

[Cell-derived microparticules: key players at the crossroad between inflammation and thrombosis]

Cell-derived microparticles are complex vesicular structures that can be shedded by activated or apoptotic endothelial cells. Cell-derived microparticles are composed of a phospholipid bilayer that exposes transmembrane proteins and receptors and encloses cytosolic components such as enzymes, transcription factors and mRNA derived from their parent cells. Thus, they behave as biological conveyors playing a key role in the tuning of vascular homeostasis. This review will address the potential of microparticles as efficient vectors of biological activities in pathologies. Based on the model of endothelial vesiculation, the first part of this review will develop the contribution of endothelial microparticles to coagulation inflammation and angiogenesis and their role in vascular disorders. The second part will be focused on the multifaceted impact of cell-derived microparticles present in blood products and its relevance to transfusion medicine.

Elevated cell-specific microparticles are a biological marker for cerebral dysfunctions in human severe malaria

Cerebral malaria (CM) and severe anemia (SA) are the most severe complications of Plasmodium falciparum infections. Although increased release of endothelial microparticles (MP) correlates with malaria severity, the full extent of vascular cell vesiculation remains unknown. Here, we characterize the pattern of cell-specific MP in patients with severe malaria. We tested the hypothesis that systemic vascular activation contributes to CM by examining origins and levels of plasma MP in relation to clinical syndromes, disease severity and outcome. Patients recruited in Douala, Cameroon, were assigned to clinical groups following WHO criteria. MP quantitation and phenotyping were carried out using cell-specific markers by flow cytometry using antibodies recognizing cell-specific surface markers. Platelet, erythrocytic, endothelial and leukocytic MP levels were elevated in patients with cerebral dysfunctions and returned to normal by discharge. In CM patients, platelet MP were the most abundant and their levels significantly correlated with coma depth and thrombocytopenia. This study shows for the first time a widespread enhancement of vesiculation in the vascular compartment appears to be a feature of CM but not of SA. Our data underpin the role of MP as a biomarker of neurological involvement in severe malaria. Therefore, intervention to block MP production in severe malaria may provide a new therapeutic pathway.

Quiescent platelets stimulate angiogenesis and diabetic wound repair

INTRODUCTION

Platelets partake in hemostasis, wound healing, and tumor growth. Although platelet-rich-plasma (PRP) has been used in surgery for several years, its mechanism of action and application methods are still poorly characterized.

MATERIALS AND METHODS

A single unit of human platelets obtained by plateletpheresis was diluted in plasma and divided into three equal volumes. One volume was stored at room temperature as fresh platelets (RT), another volume was frozen by storage at -80 degrees C (FZ), and the third volume was frozen at -80 degrees C with 6% DMSO (FZ6). Plasma (PL) was used as control. Using flow cytometry, platelets were tested for platelet glycoprotein GPIb and annexin V binding, as survival and activation markers, respectively. Hemostatic function was assessed by thromboelastometry. In vivo, platelets were topically applied on 1 cm,(2) full-thickness wounds on db/db mice (n = 10/group) and healing was staged microscopically and macroscopically.

RESULTS

All platelet preparations showed hemostatic ability. RT platelets were GPIb positive (nonactivated-quiescent platelets) and stimulated angiogenesis by threefold, and cell proliferation by fourfold in vivo. FZ platelets were positive for annexin V, indicating activated platelets and, in vivo, increased only wound granulation. FZ6 platelets contained 30% nonactivated-quiescent and 50% activated platelets and stimulated granulation, angiogenesis, cell proliferation, and promoted re-epithelialization in vivo.

CONCLUSIONS

Platelets showed distinct mechanisms to induce hemostasis and wound healing. Quiescent platelets are required to induce angiogenesis in vivo. Platelets stored at room temperature and frozen with 6% DMSO and stored at -80 degrees C achieved optimal wound healing in diabetic mice.

Past and Future Approaches to Assess the Quality of Platelets for Transfusion

No automated test exists to routinely measure platelet quality. Currently, the short, 5-day shelf life of platelet concentrates is largely dictated by the risk associated with bacterial contamination and not by platelet quality. With the implementation of bacterial testing and pathogen inactivation, platelet quality will become the major determinant for the shelf life of platelet concentrates. However, extended use of platelet concentrates stored beyond 5 days will require quality testing. In addition, high platelet quality would be expected to result in improved clinical efficacy, determined by count increment, improved hemostasis, and lower risk for adverse reactions in recipients. No in vitro quality test has yet demonstrated a good correlation with clinical efficacy or improved hemostasis. This review focuses on those tests of platelet quality that are based on platelet morphology. These include visual inspection of swirling, microscopic morphology score, measurement of light transmission through platelet concentrates, and platelet light scattering techniques. Recently, a new test for platelet quality has been introduced that uses dynamic light scattering. The advantages and remaining challenges for dynamic light scattering before it can become a routine platelet quality test are discussed.

Role of glycoprotein Ibalpha in phagocytosis of platelets by macrophages

BACKGROUND

Platelet (PLT) storage at 0 to 4 degrees C suppresses bacterial multiplication, but induces clusters of glycoprotein (GP) Ibalpha that trigger their phagocytosis by macrophages and reduce their survival after transfusion. A method was sought that detects cold-induced changes in GPIbalpha involved in phagocytosis.

STUDY DESIGN AND METHODS

Human PLTs were isolated and stored for up to 48 hours at 0 degrees C. Binding of a phycoerythrin (PE)-labeled antibody directed against amino acids (AA) 1-35 on GPIbalpha (AN51-PE) was compared with phagocytosis of PLTs by matured monocytic THP-1 cells, analyzed by fluorescence-activated cell sorting.

RESULTS

Freshly isolated PLTs were detected as a single population of AN51-PE-positive particles and showed less than 5 percent phagocytosis. Cold storage led to a decrease in AN51-PE binding and an increase in phagocytosis. N-Acetylglucosamine, known to interfere with macrophage recognition of GPIbalpha clusters, restored normal AN51-PE binding to cold-stored PLTs and suppressed phagocytosis.

CONCLUSIONS

It is concluded that binding of an antibody against AA 1-35 on GPIbalpha reflects changes in GPIbalpha that make PLTs targets for phagocytosis by macrophages.

Freezing human platelets with 6 percent dimethyl sulfoxide with removal of the supernatant solution before freezing and storage at -80 degrees C without postthaw processing

BACKGROUND

Platelets (PLTs) can be frozen with 6 percent dimethyl sulfoxide (DMSO) at -80 degrees C for up to 2 years. This method has been modified by concentrating the PLTs and removing the supernatant before freezing.

STUDY DESIGN AND METHODS

High-yield leukoreduced PLTs stored at 22 degrees C for up to 5 days were divided into three equal volumes: one was frozen with 6 percent DMSO at -80 degrees C, thawed, washed, and resuspended in plasma (old method with DMSO); the second was treated with 6 percent DMSO, concentrated to remove the supernatant DMSO, frozen at -80 degrees C, thawed, and diluted with 0.9 percent NaCl (new method with DMSO); and the third was treated with 0.9 percent NaCl without DMSO, concentrated to remove the supernatant solution, frozen at -80 degrees C, thawed, and diluted with 0.9 percent NaCl (new method without DMSO).

RESULTS

Freeze-thaw-wash recovery of PLTs frozen by the old method with DMSO was 74 +/- 2 percent with 5 percent PLT microparticles. Freeze-thaw recovery was 94 +/- 2 percent with 7 percent PLT microparticles (new method with DMSO) and 69 +/- 9 percent with 15 percent PLT microparticles (new method without DMSO). Total DMSO in washed PLTs was 400 and 600 mg in PLTs concentrated before freezing. In vivo recovery of PLTs frozen by the new method with DMSO and transfused into normal volunteers was 30 percent and the life span was 7 days.

CONCLUSION

Concentrating PLTs before freezing simplified the procedure by eliminating postthaw washing. PLTs frozen by this method had more PLTs with reduced GPIb and increased annexin V binding than those frozen by the old method.

Effects of a new pathogen-reduction technology (Mirasol PRT) on functional aspects of platelet concentrates

BACKGROUND

Several strategies are being developed to reduce the risk of pathogen transmission associated with platelet (PLT) transfusion.

STUDY DESIGN AND METHODS

The impact of a new technology for pathogen reduction based on riboflavin plus illumination (Mirasol PRT, Navigant Biotechnologies, Inc.) at 6.2 and 12.3 J per mL on functional and biochemical characteristics of PLTs was evaluated. PLT concentrates (PCs) obtained by apheresis were treated with Mirasol PRT and stored at 22 degrees C. Modifications in major PLT glycoproteins (GPIbalpha, GPIV, and GPIIb-IIIa), adhesive ligands (von Willebrand factor [VWF], fibrinogen [Fg], and fibronectin), activation antigens (P-selectin and LIMP), and apoptotic markers (annexin V binding and factor [F]Va) were analyzed by flow cytometry. Adhesive and cohesive PLT functions were evaluated with well-established perfusion models. Studies were performed on the preparation day (Day 0) and during PCs storage (Days 3 and 5).

RESULTS

Levels of glycoproteins remained stable during storage in PCs treated with 6.2 J per mL pathogen reduction technology (PRT) and similar to those observed in nontreated PCs. When 12.3 J per mL PRT was applied, however, levels of GPIbalpha moderately decreased on Days 3 and 5. VWF, Fg, and FVa were not modified in their expression levels, either by treatment or by storage period. Fibronectin appeared more elevated in all PRT samples. A progressive increase in P-selectin and LIMP expression and in annexin V binding was observed during storage of PRT-treated PCs. Functional studies indicated that 6.2 J per mL Mirasol PRT-treated PLTs preserved adhesive and cohesive functions to levels compatible with those observed in the respective control PCs.

CONCLUSION

PLT function was well preserved in PCs treated with 6.2 J per mL Mirasol PRT and stored for 5 days.

Stored platelets contain residual amounts of tissue factor: evidence from studies on platelet concentrates stored for prolonged periods

BACKGROUND

The advent of new strategies for pathogen reduction has raised the question of whether platelet (PLT) concentrates (PCs) exposed to longer periods of storage retain adequate hemostatic function.

STUDY DESIGN AND METHODS

The effects of prolonged storage on adhesive and procoagulant functions of PLTs in PCs have been analyzed. The ability of PLTs to interact with surfaces was assessed by en face electron microscopy. Exposure of anionic phospholipids or tissue factor (TF) antigen on PLTs was assessed by flow cytometry and by immunocytochemical methods at the ultrastructural level. Studies were performed in six different PCs followed 0, 3, 5, 7, and 11 days of storage.

RESULTS

A progressive impairment of PLT-adhesive functions was observed after 5 days of storage. A progressive increase in expression of anionic phospholipids and development of procoagulant activity (PCA) measured by a modified prothrombin time (mPT) was observed along the storage. Incubation of PLTs with a specific anti-TF resulted in prolongation of the mPT by approximately 10 to 15 percent. Flow cytometry revealed minimal TF expression at later storage times. Immunocytochemical studies showed minimal TF labeling when studies were performed on PLT whole mounts. Labeling was markedly improved when PLTs were previously exposed to sonication.

CONCLUSION

Prolonged storage of PCs was associated with decreased PLT-adhesive capacities and enhanced PCA. Current preparation procedures and storage media have important limitations for preserving PCs for longer than 1 week. PLTs in PCs retain residual amounts of TF as assessed by immunocytochemical and functional assays. The origin and hemostatic significance of this TF should be investigated further.

The mitochondrial membrane potential in human platelets: a sensitive parameter for platelet quality

BACKGROUND

Deterioration of platelet (PLT) quality during storage is accompanied by an increase in lactate production, indicating a decrease in mitochondrial function. In this study, the optimal conditions under which the fluorescent dye JC-1 can be used to detect changes in mitochondrial function in PLTs were established.

STUDY DESIGN AND METHODS

PLTs were incubated at 37 degrees C in synthetic medium under various conditions of JC-1 loading. In the presence of a high membrane potential, this dye accumulates in the mitochondria with a concomitant increase in red fluorescence. After JC-1 loading, the ratio of red (FL2) to green (FL1) fluorescence was determined by flow cytometry.

RESULTS

The FL2-to-FL1 ratio of PLTs (3 x 10(7)/mL, loaded with 0.5 micromol/L JC-1) amounted to about 5 in 1-day-old PLTs. At higher dye concentrations, the FL2-to-FL1 ratio was significantly lower, suggesting uncoupling by the dye itself. Plasma concentrations above 3 percent significantly affected the JC-1 signal. The FL2-to-FL1 ratio showed a dose-dependent decrease to an uncoupler of oxidative phosphorylation or to inhibition of the respiratory chain. JC-1-loaded PLTs showed a clear decrease in FL2-to-FL1 ratio after prolonged storage or upon ultraviolet (UV) illumination. Only after UV treatment did changes in JC-1 signal correlate with changes in CD62P expression.

CONCLUSION

The FL2-to-F1 ratio of PLTs loaded with JC-1 is a reliable and sensitive indicator of the mitochondrial membrane potential, provided that the proper experimental conditions have been applied.

Platelet characteristic antigens of CD34+ cells in cryopreserved cord blood: a study of platelet-derived microparticles in transplant processing

BACKGROUND AND OBJECTIVES

In previous studies, we found that platelet microparticles (PMPs) bind to cord blood (CB) CD34+ cells and transfer adhesion molecules to them, which enhances their engraftment. Before applying this phenomenon in actual transplants, we investigated the effect of PMPs on cryopreserved CD34+ cells in CB.

MATERIALS AND METHODS

We cryopreserved 18 CB units, then evaluated the binding of PMPs to CD34+ cells after thawing, by varying the expression of platelet characteristic antigens (CD41a, CD61, CD62P and CXCR4) on these cells. Adherence of the CD34+ cells, coated with freeze/thaw-induced PMPs, to endothelium and fibronectin was also studied, as were the effects of thrombin-induced PMPs from both fresh and preserved CB platelets.

RESULTS

PMPs induced by freezing and thawing adhered less well to CD34+ cells than did those from fresh CB, and cells coated with these PMPs had poor adherence. However, thrombin-induced PMPs from both fresh and preserved CB platelets bound equally well to cryopreserved CD34+ cells and improved their adhesion properties.

CONCLUSIONS

PMPs could be a useful tool for enhancing engraftment after CB transplantation.

Effects of platelet inhibitors on propyl gallate-induced platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activation

Propyl gallate (PG) is a platelet agonist characterized by inducing platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activity. The mechanisms of platelet activation following PG stimulation were examined by pre-incubating platelets with well-defined platelet inhibitors using platelet aggregation, protein tyrosine phosphorylation, activated plasma clotting time, and annexin V binding by flow cytometry. PG-induced platelet aggregation and tyrosine phosphorylation of multiple proteins were substantially abolished by aspirin, apyrase, and abciximab (c7E3), suggesting that PG is associated with activation of platelet cyclooxygenase 1, adenosine phosphate receptors, and glycoprotein IIb/IIIa, respectively. The phosphorylation of the cytoskeletal enzyme pp60(c-src) increased following PG stimulation, but was blunted by pre-incubation of platelets with aspirin, apyrase, and c7E3, suggesting that tyrosine kinase is important for the signal transduction of platelet aggregation. Propyl gallate also activates platelet factor 3 by decreasing the platelet coagulation time and increasing platelet annexin V binding. Platelet incubation with aspirin, apyrase, and c7E3 did not alter PG-induced platelet coagulation and annexin V binding. The results suggest that platelet factor 3 activation and membrane phosphotidylserine expression were not involved with activation of platelet cyclooxygenase, adenosine phosphate receptors, and glycoprotein IIb/IIIa. PG is unique in its ability to stimulate platelet aggregation and coagulation simultaneously, and platelet inhibitors in this study affect only platelet aggregation but not platelet coagulation.

Advanced Hemostatic Dressing Development Program: Animal Model Selection Criteria and Results of a Study of Nine Hemostatic Dressings in a Model of Severe Large Venous Hemorrhage and Hepatic Injury in Swine

BACKGROUND

An advanced hemostatic dressing is needed to augment current methods for the control of life-threatening hemorrhage. A systematic approach to the study of dressings is described. We studied the effects of nine hemostatic dressings on blood loss using a model of severe venous hemorrhage and hepatic injury in swine.

METHODS

Swine were treated using one of nine hemostatic dressings. Dressings used the following primary active ingredients: microfibrillar collagen, oxidized cellulose, thrombin, fibrinogen, propyl gallate, aluminum sulfate, and fully acetylated poly-N-acetyl glucosamine. Standardized liver injuries were induced, dressings were applied, and resuscitation was initiated. Blood loss, hemostasis, and 60-minute survival were quantified.

RESULTS

The American Red Cross hemostatic dressing (fibrinogen and thrombin) reduced (p < 0.01) posttreatment blood loss (366 mL; 95% confidence interval, 175-762 mL) and increased (p < 0.05) the percentage of animals in which hemostasis was attained (73%), compared with gauze controls (2,973 mL; 95% confidence interval, 1,414-6,102 mL and 0%, respectively). No other dressing was effective. The number of vessels lacerated was positively related to pretreatment blood loss and negatively related to hemostasis.

CONCLUSION

The hemorrhage model allowed differentiation among topical hemostatic agents for severe hemorrhage. The American Red Cross hemostatic dressing was effective and warrants further development.

Comparison of 10 different hemostatic dressings in an aortic injury

BACKGROUND

Uncontrolled hemorrhage is the leading preventable cause of death on the battlefield. Similarly, hemorrhage accounts for 80% of all deaths within the first 48 hours of injury in civilian trauma patients. New methods of hemostasis are required to reduce hemorrhagic mortality. The purpose of this study was to compare nine hemostatic dressings for their efficacy in controlling bleeding from an otherwise fatal aortic injury in a pig model. Each hemostatic dressing was compared with the current standard U.S. Army field gauze dressing for a 1-hour period.

METHODS

Fifty-nine anesthetized pigs were instrumented with catheters and splenectomized. Nine test dressings (n = 5 per group) and two control groups (gauze, n = 9; suture, n = 5) were applied to a 4.4-mm aortotomy through the spraying jet of blood, and direct pressure was held for 4 minutes and then released. Survival, blood loss, and other variables were measured over a 1-hour period.

RESULTS

All animals with fibrin dressing and those receiving suture repair (five of five in both groups) survived the 1-hour observation period with minimal bleeding in the postocclusion period (< 37 mL). Those in the other dressing groups exsanguinated within 10 minutes, except for two animals in the gauze group surviving 1 hour.

CONCLUSION

With one 4-minute application, a single fibrin dressing stopped bleeding from an aortotomy, which was equivalent to sutured repair. No other test group exhibited any evidence of significant hemostatic efficacy.

Addition of a propyl gallate-based procoagulant to a fibrin bandage improves hemostatic performance in a swine arterial bleeding model

Fibrin bandages manufactured by Nycomed Austria (TC-S) were modified by the addition of Hemostyptin (HS), a proprietary platelet-activating reagent containing propyl gallate. HS was added as an additional layer to TC-S fibrin bandages and the bandages were tested for hemostatic efficacy in a swine femoral artery bleeding model. Injuries were treated with a TC-S+HS bandage preparation using HS lyophilized onto a bandage surface that was then attached to the fibrin dressing. This preparation qualitatively and quantitatively exhibited more robust blood clotting at the surgical site than the control bandages. TC-S+HS bandages were more effective than control bandages with a difference in blood loss of 251.8+/-66.5 g for TC-S bandage alone, n=12 vs. 121+/-40.7 g, n=13 for the TC-S+HS bandage, P=0.05. Bleeding times were shortened for animals treated with the HS fortified bandages and residual platelets counts in these animals were higher.

Thrombin-induced platelet microparticles improved the aggregability of cryopreserved platelets

Platelets were activated with freezing/thawing and thrombin stimulation, and platelet microparticles generated following platelet activation were isolated with ultracentrifugation. The effects of platelet microparticles on platelet activation were studied with annexin V assay, protein tyrosine phosphorylation, and platelet aggregation. Freezing-induced platelet microparticles decreased but thrombin-induced platelet microparticles increased platelet annexin V binding and aggregation. Freshly washed platelets were cryopreserved using epinephrine and dimethyl sulfoxide (Me(2)SO) as combined cryoprotectants, and stimulated with thrombin-induced platelet microparticles. Following incubation of thrombin-induced platelet microparticles, the reaction time of platelets to agonists decreased but the percentages of aggregation increased, such as washed platelets from 44% +/- 30 to 92% +/- 7, p < 0.001, and cryopreserved platelets from 66% +/- 10 to 77% +/- 7, p < 0.02. By increasing platelet aggregability, platelet microparticles recovered after thrombin stimulation improved platelet function for transfusion. A 53-kDa platelet microparticle protein showed little phosphorylation if it was released from resting platelets or platelets stimulated with ADP, epinephrine, propyl gallate or dephosphorylation if it was derived from ionophore A 23187-stimulated platelets. However, the same protein released from frozen platelets showed significant tyrosine phosphorylation. Since a microparticle protein with 53 kDa was compatible with protein tyrosine phosphatase-1B (PTP-1B), its phosphorylation suggests the inhibition of enzyme activity. The microparticle proteins derived from thrombin-stimulated platelets were significantly phosphorylated at 64 kDa and pp60c-src, suggesting that the activation of tyrosine kinases represents a possible mechanism of thrombin-induced platelet microparticles to improve platelet aggregation.

Platelet aggregation through prothrombinase activation induced by non-aggregant doses of platelet agonists

Activation of the prothrombinase complex, which catalyzes the formation of thrombin from prothrombin, is crucial for the (patho)physiological processes of hemostasis and thrombosis. We here report that washed platelets supplemented with prothrombin can be irreversibly aggregated with otherwise non-aggregant doses of adenosine diphosphate (10 micromol/l), thrombin (0.06 U/ml), or collagen (1 microg/ml). Prothrombinase-catalyzed prothrombin to thrombin conversion most probably supports this aggregation response, since inhibitors of thrombin (hirudin or heparin) and an inhibitor of activated factor X (DX-9065a) impair the response. A certain degree of agonist-induced platelet activation seems to be required for this prothrombin-supported aggregation response, since prothrombin alone does not induce aggregation, and blockade of glycoprotein Ia/IIa with a specific antibody inhibits the platelet aggregation response to collagen and prothrombin. These results may suggest that activation of the prothrombinase complex could be a common step of the platelet response to distinct agonists, which may be achieved at low levels of platelet stimulation.

Application of cationic propyl gallate as inducer of thrombocyte aggregation for evaluation of effectiveness of antiaggregation therapy

INTRODUCTION AND AIM OF THE STUDY

Acetylsalicylic acid (ASA) is one of basic preparations used in the therapy of cardiovascular diseases. Application of ASA leads to irreversible reduction of platelet aggregation. The aim of the present study was to verify monitoring of effectiveness of ASA therapy using the measurement of platelet aggregability in vitro after induction by cationic propyl gallate (CPG), which is considered to be a highly potent inducer of aggregation.

METHODS

We examined a group of 27 healthy volunteers, divided into two subgroups (n = 19, n = 8). The first subgroup was examined for thrombocyte aggregation before and 24 hours after administration of 400 mg of ASA after induction by ADP, collagen, adrenalin and CPG. The second subgroup was examined for thrombocyte aggregation before and after a three-day administration of ASA in a dose of 100 mg/day.

RESULTS AND CONCLUSION

In the group of 27 healthy volunteers we determined normal values of aggregability for individual inducers. Low stability of the used methods was proved (weak or insignificant correlation of results of the same method before and after administration of ASA). The most advantageous parameter for monitoring of effectiveness of 400 and 100 mg of ASA was CPG slope (paired t test, p < 0.00000002, resp. p < 0.001). The parameter of CPG slope we determined in both subgroups the cut-off value (< 53s), by means of which it is possible to discriminate probands according to ASA therapy (in contrast to other routinely used inducers). The obtained results indicate that measurement of thrombocyte aggregation after CPG induction reveals a significantly lower percentage of ASA non-responders ASA than after other inducers. Measurement of thrombocyte aggregation after CPG induction is predicted to be highly promising for monitoring the effectiveness of anti-aggregation therapy.

Platelet cryopreservation using a combination of epinephrine and dimethyl sulfoxide as cryoprotectants

Current methods of platelet storage are unsatisfactory because of the short shelf life of platelets and the rapid loss of platelet viability. We have developed a cryopreservation method that results in less damage from freezing and higher recovered function of platelets. Platelets were cryopreserved using a combination of epinephrine (EPN) and dimethyl sulfoxide (Me(2)SO) as cryoprotectants. The response of platelets to agonists was studied by flow cytometry and aggregation tests. Cryopreserving platelets with Me(2)SO decreased platelet annexin V binding due to freezing. The combination of EPN with Me(2)SO enhanced Me(2)SO cryoprotection and decreased platelet microparticle generation, suggesting that cryopreserving platelets using this combination is associated with increased platelet integrity. Platelet cryopreservation with an Me(2)SO/EPN combination also increased platelet aggregability, which was demonstrated by decreasing the lag phase and increasing the aggregation density to 66.39% +/- 6.6 that of fresh platelet-rich plasmas. We conclude that adding EPN as a combined cryoprotectant improves the quality of Me(2)SO-frozen platelets. As a method of aggregation of cryopreserved platelets, this method is comparable to that of normal fresh platelets and may improve the conditions for platelet transfusion.