Cell-derived microparticles generated in patients during cardiopulmonary bypass are highly procoagulant

Hemocompatibility of Inorganic Physical Vapor Deposition (PVD) Coatings on Thermoplastic Polyurethane Polymers

Biocompatibility improvements for blood contacting materials are of increasing interest for implanted devices and interventional tools. The current study focuses on inorganic (titanium, titanium nitride, titanium oxide) as well as diamond-like carbon (DLC) coating materials on polymer surfaces (thermoplastic polyurethane), deposited by magnetron sputtering und pulsed laser deposition at room temperature. DLC was used pure (a-C:H) as well as doped with silicon, titanium, and nitrogen + titanium (a-C:H:Si, a-C:H:Ti, a-C:H:N:Ti). In-vitro testing of the hemocompatibility requires mandatory dynamic test conditions to simulate in-vivo conditions, e.g., realized by a cone-and-plate analyzer. In such tests, titanium- and nitrogen-doped DLC and titanium nitride were found to be optimally anti-thrombotic and better than state-of-the-art polyurethane polymers. This is mainly due to the low tendency to platelet microparticle formation, a high content of remaining platelets in the whole blood after testing and low concentration of platelet activation and aggregation markers. Comparing this result to shear-flow induced cell motility tests with e.g., Dictostelium discoideum cell model organism reveals similar tendencies for the investigated materials.

Climacteric lowers plasma levels of platelet-derived microparticles: a pilot study in pre- versus postmenopausal women

BACKGROUND

Climacteric increases the risk of thrombotic events by alteration of plasmatic coagulation. Up to now, less is known about changes in platelet- (PMP) and endothelial cell-derived microparticles (EMP).

METHODS

In this prospective study, plasma levels of microparticles (MP) were compared in 21 premenopausal and 19 postmenopausal women.

RESULTS

No altered numbers of total MP or EMP were measured within the study groups. However, the plasma values of CD61-exposing MP from platelets/megakaryocytes were higher in premenopausal women (5,364 × 10(6)/l, range 4,384-17,167) as compared to postmenopausal women (3,808 × 10(6)/l, range 2,009-8,850; p = 0.020). This differentiation was also significant for the subgroup of premenopausal women without hormonal contraceptives (5,364 × 10(6)/l, range 4,223-15,916; p = 0.047; n = 15). Furthermore, in premenopausal women, higher plasma levels of PMP exposing CD62P were also present as compared to postmenopausal women (288 × 10(6)/l, range 139-462, vs. 121 × 10(6)/l, range 74-284; p = 0.024). This difference was also true for CD63+ PMP levels (281 × 10(6)/l, range 182-551, vs. 137 × 10(6)/l, range 64-432; p = 0.015).

CONCLUSION

Climacteric lowers the level of PMP but has no impact on the number of EMP in women. These data suggest that PMP and EMP do not play a significant role in enhancing the risk of thrombotic events in healthy, postmenopausal women.

Chronic renal failure is accompanied by endothelial activation and a large increase in microparticle numbers with reduced procoagulant capacity

BACKGROUND

In patients with chronic renal failure (CRF), cardiovascular disease is the leading cause of increased morbidity and mortality. We hypothesized a role for endothelial activation and microparticle (MP) numbers and procoagulant activity in the pre-thrombotic state of these patients.

METHODS

We analysed blood samples of 27 patients with CRF [8 chronic kidney disease Stage 4 (CKD4), 9 peritoneal dialysis (PD) and 10 haemodialysis (HD), samples taken before and after HD] and 10 controls. Degree and nature of endothelial activation were assessed by measuring mature von Willebrand factor (vWF) and vWF propeptide levels. Cellular MPs were characterized by flow cytometry and MP-specific thrombin generation (TG) measurements.

RESULTS

CRF was accompanied by chronic (CKD4 and PD) or acute (HD) endothelial activation. Patients with CRF had substantially higher MP numbers than controls (median 9400 versus 4350×10(6)/L, P=0.001), without significant differences between the treatment subgroups or between pre- and post-HD. The vast majority of MPs were platelet derived. Of the minor populations, endothelial MPs and tissue factor-bearing MPs were more abundant in CRF. MPs were procoagulant, but the increase in numbers was not reflected in a proportional increase in MP-specific TG.

CONCLUSION

Renal failure is accompanied by endothelial activation of a different nature in CKD4 and PD patients compared to HD patients, and results in all subgroups in an increase of mainly platelet-derived MPs that appear to be less procoagulant than in other disease states, possibly because of the uraemic functional defect of their cellular source.

Transglutaminase 2 is secreted from smooth muscle cells by transamidation-dependent microparticle formation

Transglutaminase 2 (TG2) is a pleiotropic enzyme involved in both intra- and extracellular processes. In the extracellular matrix, TG2 stabilizes the matrix by both covalent cross-linking and disulfide isomerase activity. These functions become especially apparent during matrix remodeling as seen in wound healing, tumor development and vascular remodeling. However, TG2 lacks the signal sequence for a classical secretory mechanism, and the cellular mechanism of TG2 secretion is currently unknown. We developed a green fluorescent TG2 fusion protein to study the hypothesis that TG2 is secreted via microparticles. Characterization of TG2/eGFP, using HEK/293T cells with a low endogenous TG2 expression, showed that cross-linking activity and fibronectin binding were unaffected. Transfection of TG2/eGFP into smooth muscle cells resulted in the formation of microparticles (MPs) enriched in TG2, as detected both by immunofluorescent microscopy and flow cytometry. The fraction of TG2-positive MPs was significantly lower for cross-linking-deficient mutants of TG2, implicating a functional role for TG2 in the formation of MPs. In conclusion, the current data suggest that TG2 is secreted from the cell via microparticles through a process regulated by TG2 cross-linking.

Blood Utilization in Neonates and Infants Undergoing Cardiac Surgery Requiring Cardiopulmonary Bypass

Neonates and infants undergoing cardiac surgery with cardiopulmonary bypass are exposed to multiple blood products from different donors. The volume of the bypass circuit is often as large as the patient’s total blood volume and asanguineous bypass primes are unusual. As a result, blood products are required for the cardiopulmonary bypass prime and are often used to treat the postbypass dilutional coagulopathy. We review clot formation and strength, cardiopulmonary bypass prime considerations, assessment of postbypass coagulopathy, component therapy use, ultrafiltration techniques, and use of antifibrinolytic medications. A combined approach including techniques to minimize the prime volume, utilization of ultrafiltration, administration of antifibrinolytics during surgery, and the proper treatment of the dilutional coagulopathy can limit the transfusion requirements.

Role of tissue factor in venous thrombosis

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality worldwide. However, the mechanisms by which clots are formed in the deep veins have not been determined. Tissue factor (TF) is the primary initiator of the coagulation cascade and is essential for hemostasis. Under pathological conditions, TF is released into the circulation on small-membrane vesicles termed microparticles (MPs). Recent studies suggest that elevated levels of MP TF may trigger thrombosis. This review provides an overview of the role of TF in VTE.

Extracellular heat shock proteins, cellular export vesicles, and the Stress Observation System: a form of communication during injury, infection, and cell damage. It is never known how far a controversial finding will go! Dedicated to Ferruccio Ritossa

Heat shock proteins (hsp) have been found to play a fundamental role in the recovery from multiple stress conditions and to offer protection from subsequent insults. The function of hsp during stress goes beyond their intracellular localization and chaperone role as they have been detected outside cells activating signaling pathways. Extracellular hsp are likely to act as indicators of the stress conditions, priming other cells, particularly of the immune system, to avoid the propagation of the insult. Some extracellular hsp, for instance Hsp70, are associated with export vesicles, displaying a robust activation of macrophages. We have coined the term Stress Observation System (SOS) for the mechanism for sensing extracellular hsp, which we propose is a form of cellular communication during stress conditions. An enigmatic and still poorly understood process is the mechanism for the release of hsp, which do not contain any consensus secretory signal. The export of hsp appears to be a very complex phenomenon encompassing different alternative pathways. Moreover, extracellular hsp may not come in a single flavor, but rather in a variety of physical conditions. This review addresses some of our current knowledge about the release and function of extracellular hsp, in particular those associated with vesicles.

Cell-derived vesicles exposing coagulant tissue factor in saliva

On vascular damage, coagulation is initiated by extravascular tissue factor (TF). Intravascular TF, which is present on circulating cell-derived vesicles, is noncoagulant under physiologic conditions but prothrombotic under pathologic conditions. Human saliva triggers coagulation, but the mechanism and physiologic relevance are unknown. Because saliva is known to contain TF, we hypothesized that this TF may also be associated with cell-derived vesicles to facilitate coagulation when saliva directly contacts blood. The saliva-induced shortening of the clotting time of autologous plasma and whole blood from healthy subjects (n = 10) proved TF-dependent. This TF was associated with various types of cell-derived vesicles, including microparticles and exosomes. The physiologic function was shown by adding saliva to human pericardial wound blood collected from patients undergoing cardiac surgery. Addition of saliva shortened the clotting time from 300 ± 96 to 186 ± 24 seconds (P = .03). Our results show that saliva triggers coagulation, thereby reducing blood loss and the risk of pathogens entering the blood. We postulate that our reflex to lick a wound may be a mechanism to enable TF-exposing vesicles, present in saliva, to aid in the coagulation process and thus protect the organism from entering pathogens. This unique compartmentalization may be highly conserved because also animals lick their wounds.

Surveillance of megakaryocytic function by measurement of CD61-exposing microparticles in allogeneic hematopoietic stem cell recipients

Increasing evidence suggests that circulating microparticles (MP) exposing CD61 originate predominantly from megakaryocytes. Dramatic changes in megakaryocytic homeostasis are regularly observed following allogeneic hematopoietic stem cell transplantation (HSCT) and associated with transplantation-associated complications. We studied MP plasma levels prospectively in healthy subjects (n = 10) and allogeneic HSCT recipients (n = 19) twice weekly from the start of conditioning therapy up to day 30. A total of 224 measurement points were evaluated. MP were isolated, double-stained with annexin V and anti-CD61, and analyzed by flow cytometry. In uncomplicated HSCT, we found a correlation between platelet and CD61-exposing MP count, which resulted in a constant ratio of MP per platelet. The ratio was increased in patients with active hematological malignancies before transplantation and normalized during conditioning therapy. After take, the MP ratio increased, whereas infections and microangiopathic hemolytic anemia did not affect the ratio. In patients with GvHD, a decreased MP ratio was observed depending on the grade of GvHD, possibly indicating megakaryocytic damage. The MP ratio was able to discriminate between toxic, septic, and GvHD-induced hyperbilirubinemia. We first describe CD61+ MP levels during allogeneic HSCT and postulate that the MP ratio might be a useful biomarker for the surveillance of megakaryocytes during HSCT.

Tissue factor-bearing microparticles and thrombus formation

Blood microparticles are vesicular structures with a diameter of 100 to 1000 nm that are present in the blood of normal subjects and in patients with various diseases. These microparticles are derived from cells that circulate in the blood and cells associated with the blood vessel wall. Microparticle membranes retain the protein receptors of their parent cells and may retain RNAs and other cytosolic content. On the basis of surface protein expression, microparticles are known to be derived from platelets, granulocytes, monocytes, endothelial cells, smooth muscle cells, and tumor cells. Only a subpopulation of these microparticles expresses tissue factor.

Clearance of platelet microparticles in vivo

At present, little is known about the clearance of platelet-derived microparticles (PMP) in human blood, as due to ethical considerations infusion experiments with labeled microparticles are delicate. Therefore, we investigated the kinetics of PMP, which are abundantly present in apheresis platelet concentrates (PC), following platelet transfusion in severe thrombocytopenic patients (n=11). PMP were double-stained with annexin V and cell-specific antibodies (anti-CD61, anti-CD63 or anti-CD62P, respectively) and detected by flow cytometry before and after transfusion of a single PC at fixed time intervals. Upon transfusion, the plasma levels of MP binding annexin V (2.5-fold), PMP (CD61+; 2.9-fold), and PMP from activated platelets (CD63+; 1.9-fold) or P-selectin (2.5-fold) increased immediately. The plasma levels of MP decreased with a half life of 5.8 hours (annexin V; 95% CI: 1.8?18.3) and 5.3 hours (CD61; 95% CI: 2.0?14.2). This is the first report in which the half life time of transfused PMP has been investigated in humans.

Activated platelets and atherosclerosis

Several studies suggest an important role for platelets in atherogenesis, not only as mediators of thrombus formation, but also as inducers of inflammation. Several lines of evidence indicate that platelets are potent inflammatory cells that induce inflammatory responses in adjacent cells such as leukocytes and endothelial cells. Platelets may also themselves respond to inflammatory mediators produced by these neighboring cells. These platelet-mediated inflammatory pathways contribute to atherogenesis in both the early and late stage of the process. The bidirectional interaction between platelets and other cells may also be involved in the nonresolving inflammation characterizing atherosclerosis. In patients with atherosclerotic disorders, platelet-mediated inflammation appears to be operating in spite of the wide use of platelet-inhibiting drugs. This underscores the need for new therapeutic tools that more specifically target the pathways in platelet-mediated inflammation.

Ectosomes as immunomodulators

Considerable progress has been made in recognizing microvesicles as important mediators of intercellular communication rather than irrelevant cell debris. Microvesicles released by budding directly from the cell membrane surface (i.e., ectocytosis) either spontaneously or in response to various stimuli are called shed vesicles or ectosomes. Ectosomes are rightside-out vesicles with cytosolic content, and they expose phosphatidylserine in the outer leaflet of their membrane. Depending on their cellular origin, ectosomes have been associated with a broad spectrum of biological activities. In the light of recent findings, we now know that ectosomes derived from polymorphonuclear leukocytes, erythrocytes, platelets, and tumor cells have profound effects on the innate immune system, as well as on the induction of the adaptive immunity, globally reprogramming cells such as macrophages or dendritic cells toward an immunosuppressive and possibly tolerogenic phenotype. Although the effects observed in the circulation are mainly procoagulant and pro-inflammatory, ectosomes might be anti-inflammatory/immunosuppressive in local inflammation.

Optical and non-optical methods for detection and characterization of microparticles and exosomes

Microparticles and exosomes are cell-derived microvesicles present in body fluids that play a role in coagulation, inflammation, cellular homeostasis and survival, intercellular communication, and transport. Despite increasing scientific and clinical interest, no standard procedures are available for the isolation, detection and characterization of microparticles and exosomes, because their size is below the reach of conventional detection methods. Our objective is to give an overview of currently available and potentially applicable methods for optical and non-optical determination of the size, concentration, morphology, biochemical composition and cellular origin of microparticles and exosomes. The working principle of all methods is briefly discussed, as well as their applications and limitations based on the underlying physical parameters of the technique. For most methods, the expected size distribution for a given microvesicle population is determined. The explanations of the physical background and the outcomes of our calculations provide insights into the capabilities of each method and make a comparison possible between the discussed methods. In conclusion, several (combinations of) methods can detect clinically relevant properties of microparticles and exosomes. These methods should be further explored and validated by comparing measurement results so that accurate, reliable and fast solutions come within reach.

Complement activation on the surface of cell-derived microparticles during cardiac surgery with cardiopulmonary bypass - is retransfusion of pericardial blood harmful?

OBJECTIVES

To investigate whether cell-derived microparticles play a role in complement activation in pericardial blood of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) and whether microparticles in pericardial blood contribute to systemic complement activation upon retransfusion.

METHODS

Pericardial blood of 13 patients was retransfused in 9 and discarded in 4 cases. Microparticles were isolated from systemic blood collected before anesthesia (T1) and at the end of CPB (T2), and from pericardial blood. The microparticles were analyzed by flow cytometry for bound complement components C1q, C4 and C3, and bound complement activator molecules C-reactive protein (CRP), serum amyloid P-component (SAP), immunoglobulin (Ig)M and IgG. Fluid-phase complement activation products (C4b/c, C3b/c) and activator molecules were determined by ELISA.

RESULTS

Compared with systemic T1 blood, pericardial blood contained increased C4b/c and C3b/c, and increased levels of microparticles with bound complement components. In systemic T1 samples, microparticle-bound CRP, whereas in pericardial blood, microparticle-bound SAP and IgM were associated with complement activation. At the end of CPB, increased C3b/c (but not C4b/c) was present in systemic T2 blood compared with T1, while concentrations of microparticles binding complement components and of those binding complement activator molecules were similar. Concentrations of fluid-phase complement activation products and microparticles were similar in patients whether or not retransfused with pericardial blood.

CONCLUSIONS

In pericardial blood of patients undergoing cardiac surgery with CPB, microparticles contribute to activation of the complement system via bound SAP and IgM. Retransfusion of pericardial blood, however, does not contribute to systemic complement activation.

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.

Proteomic and functional characterisation of platelet microparticle size classes

Activated platelets release large lipid-protein complexes termed microparticles. These platelet microparticles (PMP) are composed of vesicular fragments of the plasma membrane and alpha-granules. PMP facilitate coagulation, promote platelet and leukocyte adhesion to the subendothelial matrix, support angiogenesis and stimulate vascular smooth muscle proliferation.

OBJECTIVES

PMP were separated into 4 size classes to facilitate identification of active protein and lipid components. PMP were obtained from activated human platelets and separated into 4 size classes by gel filtration chromatography. Proteins were identified using 2-dimensional, liquid chromatography tandem mass spectrometry. Functional effects on platelets were determined using the PFA-100 and on endothelial cells by measuring transendothelial cell electrical resistance. PMP size classes differed significantly in their contents of plasma membrane receptors and adhesion molecules, chemokines, growth factors and protease inhibitors. The two smallest size classes (3 and 4) inhibited collagen/adenosine-diphosphate-mediated platelet thrombus formation, while fractions 2 and 4 stimulated barrier formation by endothelial cells. Heat denaturation blocked the effect of fraction 4 on endothelial cell function, but not fraction 2 implying that the active component in fraction 4 is a protein and in fraction 2 is a heat-stable protein or lipid but not sphingosine-1-phosphate. Proteomic and functional analysis of PMP size fractions has shown that PMP can be separated into different size classes that differ in protein components, protein/lipid ratio, and functional effects on platelets and endothelial cells. This analysis will facilitate identification of active components in the PMP and clarify their involvement in diseases such as atherosclerosis and cancer.

Managing fibrinolysis without aprotinin

Cardiopulmonary bypass increases perioperative bleeding and produces a consumptive coagulopathy, which is defined as the simultaneous production of thrombin and fibrinolysis. Thrombin formation and fibrinolysis primarily occur in the surgical wound and peak at the time heparin is reversed by protamine. Neither aprotinin nor lysine analogs successfully control bleeding in many complex procedures, reoperations, aortic resections, or in implantations of mechanical circulatory devices. This analysis reviews the mechanisms involved and current treatment protocols, with the conclusion that changes in treatment protocols rather than use of a specific anti-fibrinolytic drug may provide better control of bleeding in these patients.

Increased vitreous shedding of microparticles in proliferative diabetic retinopathy stimulates endothelial proliferation

OBJECTIVE

Diabetic retinopathy is associated with progressive retinal capillary activation and proliferation, leading to vision impairment and blindness. Microparticles are submicron membrane vesicles with biological activities, released following cell activation or apoptosis. We tested the hypothesis that proangiogenic microparticles accumulate in vitreous fluid in diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Levels and cellular origin of vitreous and plasma microparticles from control (n = 26) and diabetic (n = 104) patients were analyzed by flow cytometry, and their proangiogenic activity was assessed by in vitro thymidine incorporation and neovessel formation in subcutaneous Matrigel plugs in mice.

RESULTS

Microparticles of endothelial, platelet, photoreceptor, and microglial origin were identified in vitreous samples. Levels of photoreceptor and microglial microparticles were undetectable in plasmas but were comparable in diabetic and control vitreous samples. Vitreous platelet and endothelial microparticles levels were increased in diabetic patients and decreased following panretinal laser photocoagulation or intravitreal antivascular endothelial growth factor injection in proliferative diabetic retinopathy (PDR). The ratio of vitreous to plasma microparticle levels was calculated to estimate local formation versus potential plasma leakage. In PDR, the endothelial microparticles ratio--but not that for platelet--was greater than 1.0, indicating local formation of endothelial microparticles from retinal vessels and permeation of platelet microparticles from plasma. Isolated vitreous microparticles stimulated by 1.6-fold endothelial proliferation and increased new vessel formation in mice.

CONCLUSIONS

The present study demonstrates that vitreous fluid contains shed membrane microparticles of endothelial, platelet, and retinal origin. Vitreous microparticles levels are increased in patients with diabetic retinopathy, where they could contribute to disease progression.

Proteomics of microparticles after deep venous thrombosis

BACKGROUND

Microparticles (MP) are submicron size membrane vesicles released from activated cells that are associated with thrombosis and inflammation. MP present diverse biological expressions that may be linked to a unique subset of proteins derived from their origin cells.

METHODS

To identify these proteins, plasma samples were taken from 9 patients with deep venous thrombosis (DVT) documented by duplex ultrasound, 9 with leg pain but negative for DVT by duplex, and 6 healthy controls without a history of thrombosis, for fold variation. MP were extracted from platelet-poor plasma, digested separately with trypsin and tagged using iTRAQ reagents. The digests were subjected to 2-D LC separation followed by MALDI tandem mass spectrometry. Peak lists were generated and searched against all human sequences. For protein identification, a minimum of two peptides at 95% confidence was required. Later, iTRAQ ratios were generated comparing relative protein levels of DVT patients to baseline. The proteomic analysis was performed twice for each blood sample. Proteins were considered elevated or depressed if the iTRAQ ratio (R) deviated by 20% change from normal and a p-value less than 0.05.

RESULTS

Two proteins (Galectin-3 Binding Protein, [Gal3BP], R=1.76 and Alpha-2 macroglobulin [A2M] R=1.57) were differentially expressed on DVT patients. Nine proteins were depleted including fibrinogen beta and gamma chain precursors (R=0.65).

CONCLUSIONS

These proteins influence thrombosis through inflammation, cell shedding, inhibition of fibrinolysis and hemostatic plug formation. Further studies are needed to confirm the mechanistic role of these proteins in the pathogenesis of venous thrombosis in humans.

Detection of endogenous tissue factor levels in plasma using the calibrated automated thrombogram assay

BACKGROUND

The calibrated automated thrombogram (CAT) assay measures thrombin generation in plasma.

OBJECTIVE

Use the CAT assay to detect endogenous tissue factor (TF) in recalcified platelet-rich plasma (PRP) and platelet-free plasma (PFP).

METHODS

Blood from healthy volunteers was collected into citrate and incubated at 37 degrees C with or without lipopolysaccharide (LPS) for 5 hours. PRP and PFP were prepared and clotting was initiated by recalcification. Thrombin generation was measured using the CAT assay.

RESULTS

The lag time (LT) was significantly shortened in PRP prepared from LPS-treated blood compared with untreated blood (10+/-3 min versus 20+/-6 min), and this change was reversed by the addition of inactivated human factor VIIa. LPS stimulation did not change the peak thrombin. Similar results were observed in PFP (21+/-4 min versus 35+/-5 min). LPS stimulation also significantly reduced the LT of PRP and PFP derived from blood containing citrate and a factor XIIa inhibitor. Finally, a low concentration of exogenous TF shortened the LT of PFP prepared from unstimulated, citrated blood without affecting the peak thrombin.

CONCLUSION

Changes in LT in the CAT assay can be used to monitor levels of endogenous TF in citrated plasma.

Do galectins play a role in venous thrombosis? a review

Galectins are a family of carbohydrate-binding proteins that have a high affinity to galactosides on cell surfaces and extra cellular glycoproteins. They are involved in a variety of biological functions, including modulation of cell apoptosis, cell activation and inflammation. Our laboratory has recently identified galectin-3 binding protein (Gal-3BP) as being up-regulated in a microparticle proteomics analysis for deep venous thrombosis (DVT) patients compared to negative controls. P-selectin, another glycoprotein involved in thrombus propagation, has proven a promising target for DVT management and has been widely studied by our group. Galectins are involved in P-selectin expression and can potentially be implicated in the venous thrombogenesis process. The function of galectins, their role in inflammation and thrombosis as well as their potential implications as a new pharmacological target for DVT management are reviewed in this manuscript.

Circulating erythrocyte-derived microparticles are associated with coagulation activation in sickle cell disease

BACKGROUND

Sickle cell disease is characterized by a hypercoagulable state as a result of multiple factors, including chronic hemolysis and circulating cell-derived microparticles. There is still no consensus on the cellular origin of such microparticles and the exact mechanism by which they may enhance coagulation activation in sickle cell disease.

DESIGN AND METHODS

In the present study, we analyzed the origin of circulating microparticles and their procoagulant phenotype during painful crises and steady state in 25 consecutive patients with sickle cell disease.

RESULTS

The majority of microparticles originated from platelets (GPIIIa,CD61) and erythrocytes (glycophorin A,CD235), and their numbers did not differ significantly between crisis and steady state. Erythrocyte-derived microparticles strongly correlated with plasma levels of markers of hemolysis, i.e. hemoglobin (r=-0.58, p<0.001) and lactate dehydrogenase (r=0.59, p<0.001), von Willebrand factor as a marker of platelet/endothelial activation (r=0.44, p<0.001), and D-dimer and prothrombin fragment F1+2 (r=0.52, p<0.001 and r=0.59, p<0.001, respectively) as markers of fibrinolysis and coagulation activation. Thrombin generation depended on the total number of microparticles (r=0.63, p<0.001). Anti-human factor XI inhibited thrombin generation by about 50% (p<0.001), whereas anti-human factor VII was ineffective (p>0.05). The extent of factor XI inhibition was associated with erythrocyte-derived microparticles (r=0.50, p=0.023).

CONCLUSIONS

We conclude that the procoagulant state in sickle cell disease is partially explained by the factor XI-dependent procoagulant properties of circulating erythrocyte-derived microparticles.

Microparticle surface protein are associated with experimental venous thrombosis: a preliminary study

Microparticles are small membrane vesicles released from activated cells and are associated with thrombosis and inflammation. Microparticle contain a unique subset of surface protein derived form the parent cell and may be responsible for their diverse biological functions. To identify these proteins, juvenile baboons (Papio anubis, n = 4) underwent iliac vein thrombosis with 6-hour balloon occlusion. Plasma samples were taken at baselines and at 2 days postthrombosis for microparticle analysis. Microparticles were extracted from platelet-poor plasma, digest separately with trypsin and tagged using isobaric tagging for relative and absolute quantitation reagents. The digests were subjected to 2-dimensional liquid chromatographic separation followed by matrix-assisted laser desorption/ionization tandem mass spectrometry. Peak lists were generated and searched against all primate sequences. For protein identity, a minimum of 2 peptides at 95% confidence interval was required. Later, isobaric tagging for relative and absolute quantitation ratios were generated comparing relative protein level of day 2 to baseline. The proteomic analysis was performed twice for each blood sample, totaling 8 experiments. Proteins were considered elevated of depressed if the isobaris tagging for relative and absolute quantitation ratio deviated by 20% changes from normal and a P value less than .05. Significantly, 7 proteins were differentially expressed on day 2 compared to baseline, and appeared in at least 3 animals and regulated in at least 4 experiment. Among these 7 proteins, upregulated proteins include various forms of fibrinogen and alpha-1-antichymotrypsin and downregulated proteins include immunoglobulins. These proteins influence thrombosis and inflammation through hemostatic plug formation (fibrinogen), inhibiting neutrophil adhesion (alpha-1-antichymoptrypsin), and immunoregulation (immunoglobulins). Further studies are needed to confirm the mechanistic role of these proteins in the pathogenesis of venous thrombosis.

Role of tissue factor in cancer

Tissue factor (TF) is a transmembrane glycoprotein that localizes the coagulation serine protease factor VII/VIIa (FVII/VIIa) to the cell surface. The primary function of TF is to activate the clotting cascade. The TF:FVIIa complex also activates cells by cleavage of a G-protein coupled receptor called protease-activated receptor 2 (PAR2). TF is expressed by tumor cells and contributes to a variety of pathologic processes, such as thrombosis, metastasis, tumor growth, and tumor angiogenesis. For instance, tumor cells release TF-positive procoagulant microparticles into the circulation and these may trigger venous thromboembolism in patients with cancer. TF on circulating tumor cells also leads to the coating of the cells with fibrin that traps them within the microvasculature and facilitates hematogenous metastasis. In addition, TF:FVIIa-dependent activation of PAR2 on tumor cells increases tumor growth via an undefined mechanism. One possibility is that PAR2-dependent signaling increases the expression of proangiogenic proteins. Other studies have reported that endothelial cells in the tumor vasculature express TF and this may enhance angiogenesis. These results suggest that inhibition of TF should reduce several pathologic pathways that increase tumor growth and metastasis. This would represent a novel approach to anticancer therapy. Initial studies using inhibitors of the TF:FVIIa complex in mouse tumor models have produced encouraging results. Nevertheless, additional studies are needed to determine if this strategy can be successfully translated to the treatment of cancer patients.

Intradialytic and postdialytic platelet activation, increased platelet phosphatidylserine exposure and ultrastructural changes in platelets in children with chronic uremia

The present research evaluated the intradialytic and postdialytic changes in platelet factor-4 and beta-thromboglobulin plasma levels by enzyme-linked immunoadsorbent assay method and platelet aggregation by ADP as well as flow cytometric percentage of annexin-V-positive platelets as a measure of phosphatidylserine externalization and ultrastructural examination of platelets in 37 uremic patients on regular hemodialysis and 25 age-matched and sex-matched controls. Platelet factor-4 plasma levels increased, remain consistently high during hemodialysis session (20.24 +/- 3.05 IU/ml after 30 min, P < 0.001 and 23.67 +/- 3.68 IU/ml after 240 min, P < 0.001) and returned to control values (6.10 +/- 1.54 IU/ml) only after 24 h following the end of the session. beta-Thromboglobulin showed a trend similar to that of platelet factor-4. Platelet aggregation by ADP showed reduced function in comparison with controls (69.32 +/- 12.37 versus 91.95 +/- 1.59%, P < 0.001). Flow cytometric percentage of annexin-V-positive platelet was significantly elevated (P < 0.001) in uremic patients when compared with normal controls. Ultrastructural studies of platelets 30 min after starting of dialysis showed degranulation of its granules and at 240 min showed complete degranulation, whereas in the postdialytic phase (12 h after the end of dialysis) refilled alpha-granules started to appear. Positive correlations were found between platelet concentration and platelet factor-4 and beta-thromboglobulin plasma levels during and after dialysis (P < 0.001) and with annexin-V-positive platelets percentage (P < 0.001). In conclusion, activated platelets were found in chronic hemodialysis patients, a finding that may explain why uremic patients often suffer from thrombotic accidents. The platelet activation is associated with exposure of phosphatidylserine on the platelet exterior. Platelet factor-4 and beta-thromboglobulin are released from platelets as a result of a defect in their granules membrane as shown by the electron microscopy, mainly as a consequence of the blood-membrane contact during dialysis, and they return only slowly to control values.

Levels of microparticle tissue factor activity correlate with coagulation activation in endotoxemic mice

BACKGROUND

Tissue factor (TF) is present in blood in various forms, including small membrane vesicles called microparticles (MPs). Elevated levels of these MPs appear to play a role in the pathogenesis of thrombosis in a variety of diseases, including sepsis.

OBJECTIVE

Measure levels of MP TF activity and activation of coagulation in control and endotoxemic mice.

MATERIALS AND METHODS

MPs were prepared from plasma by centrifugation. The procoagulant activity (PCA) of MPs was measured using a two-stage chromogenic assay. We also measured levels of thrombin-antithrombin and the number of MPs.

RESULTS

Lipopolysaccharide (LPS) increased MP PCA in wild-type mice; this PCA was significantly reduced by an anti-mouse TF antibody (1H1) but not with an anti-human TF antibody (HTF-1). Conversely, in mice expressing only human TF, MP PCA was inhibited by HTF-1 but not 1H1. MPs from wild-type mice had 6-fold higher levels of PCA using mouse factor (F)VIIa compared with human FVIIa, which is consistent with reported species-specific differences in FVIIa. Mice expressing low levels of human TF had significantly lower levels of MP TF activity and TAT than mice expressing high levels of human TF; however, there were similar levels of phosphatidylserine (PS)-positive MPs. Importantly, levels of MP TF activity in wild-type mice correlated with levels of TAT but not with PS-positive MPs in endotoxemic mice.

CONCLUSION

These results suggest that the levels of TF-positive MPs can be used as a biomarker for evaluating the risk of disseminated intravascular coagulation in endotoxemia.

Plasma markers of coagulation and endothelial activation in Fabry disease: impact of renal impairment

BACKGROUND

In Fabry disease, storage of globotriaosylceramide (Gb3) in arterial walls is one of the main pathogenetic factors that are thought to underlie the clinical manifestations of the disease. Abnormalities of the vessel wall, haemodynamics and pro- and anticoagulant factors may play a role, though the exact pathophysiology is incompletely understood. In this study, we try to clarify inconsistencies regarding coagulation activation, fibrinolysis, platelet activation and endothelial activation in 36 patients with Fabry disease.

METHODS

Cell-derived microparticles, markers for coagulation activation (F(1+2), TAT, sTF, sEPCR), fibrinolysis (D-dimer, tPA, alpha(2)-AP), platelet activation (beta-TG, PF4), endothelial activation (vWF) and acute phase response (IL-6, CRP) were studied in relation to renal function and severity of the disease and compared to data from 36 age- and sex-matched healthy controls (17 males).

RESULTS

Markers for endothelial activation and fibrinolysis were normal. Male patients had elevated levels of sTF and beta-TG, with an association between sTF and renal function and severity of the disease. In female patients, levels of TAT, beta-TG, PF4, CD63-positive platelet-derived microparticles and IL-6 were somewhat increased, with no correlation with renal function or disease severity.

CONCLUSIONS

Only minimal abnormalities in markers for platelet, endothelial activation and coagulation activation and fibrinolysis could be established in a large cohort of Fabry disease patients. The existing laboratory abnormalities are more likely related to renal insufficiency rather than to Fabry disease itself.

Elevated procoagulant microparticles expressing endothelial and platelet markers in essential thrombocythemia

BACKGROUND

Most cell types, including blood--and vascular cells, produce microparticles upon activation. Since cellular microparticles are known to be elevated in thromboembolic diseases, we hypothesized a role for microparticles in the pathogenesis of thrombosis in essential thrombocythemia.

DESIGN AND METHODS

In plasma samples from 21 patients with essential thrombocythemia and ten healthy subjects, the levels and the cellular origin of microparticles were determined by flowcytometric analysis, while the microparticle-associated procoagulant activity was measured using a thrombin generation assay.

RESULTS

Patients with essential thrombocythemia had significantly higher numbers of circulating annexin V-positive microparticles than controls (median 4500 vs. 2500x10(6) events/L; p=0.039), including significantly higher numbers of microparticles positive for the platelet marker CD61 (p=0.043), the endothelial markers CD62E (p=0.009) and CD144 (p=0.021), and for tissue factor (p=0.036). CD62E was co-expressed with the platelet marker CD41 on microparticles, suggesting a bilineage origin of such microparticles, which were observed only in patients with risk factors for thrombosis. Patients with essential thrombocythemia had higher plasma levels of mature von Willebrand factor (p=0.045) but similar propeptide levels compared to controls. In thrombin generation analyses, microparticle-rich plasma from patients with essential thrombocythemia had a shorter lag time (p=0.001) and higher peak height (p=0.038) than plasma from controls. Peak height correlated significantly with the total number of microparticles (R=0.634, p<0.001).

CONCLUSIONS

Patients with essential thrombocythemia had higher number of circulating microparticles with platelet and endothelial markers, suggesting ongoing platelet and endothelial activation. This was confirmed by an increased level of mature von Willebrand factor, an abnormal mature von Willebrand factor/propeptide ratio, and a hypercoagulable state reflected in thrombin generation. These findings suggest a role for microparticles in thrombosis in essential thrombocythemia.

Regulation of cardiomyocyte full-length tissue factor expression and microparticle release under inflammatory conditions in vitro

SUMMARY BACKGROUND

Myocardial inflammation is associated with an increase in circulating microparticles (MPs) and procoagulability.

OBJECTIVES

We determined whether acute inflammation was associated with altered full-length tissue factor (flTF) expression and increased procoagulability in cardiomyocytic cells.

METHODS

This study examined the transcriptional regulation of flTF expression in murine cardiomyocytic (HL-1) cells. Also, the generation of MPs by HL-1 cells and their ability to diffuse through an artificial endothelium was evaluated.

RESULTS

Constitutive and tumor necrosis factor-alpha (TNF-alpha)-induced flTF expression of HL-1 was reduced when c-Jun N-terminal kinase (JNK) was inhibited. Tissue factor (TF)-positive procoagulant MPs were released from HL-1 cells in response to TNF-alpha. JNK inhibition potentiated the release of MPs from HL-1 cells without affecting MP-associated TF activity. MP generation was dependent on RhoA activation and associated with a reorganization of the actin cytoskeleton. Increased diffusion of HL-1-derived MPs through an endothelial monolayer was found after TNF-alpha treatment. The increased diffusion was dependent not only on TNF-alpha but also on HL-1-released mediators.

CONCLUSIONS

Full-length TF expression in HL-1 cells was regulated through JNK. The TNF-alpha-induced increase in procoagulability was mediated through RhoA-dependent release of flTF-bearing MPs. These MPs were able to diffuse through an endothelial barrier adjacent to HL-1 cells and increased the procoagulability of the extracellular endothelial space. Cardiomyocytes seem to be a likely source of flTF-bearing procoagulant MPs.

Role of microparticles in atherothrombosis

Cell activation or apoptosis leads to plasma membrane blebbing and microparticle (MP) release in the extracellular space. MPs are submicron membrane vesicles which express a panel of phospholipids and proteins specific of the cells they are derived from. Exposure of negatively charged phospholipids and tissue factor confers a procoagulant potential to MPs. MPs accumulate in the lipid core of the atherosclertotic plaque and is a major determinant of its thrombogenecity. Elevation of plasma MPs levels, particularly those of endothelial origin, reflects cellular injury and is considered now as a surrogate marker of vascular dysfunction. Thus, MPs can be seen as triggers of a vicious circle for they promote prothrombogenic and pro-inflammatory responses as well as cellular dysfunction within the vascular compartment. A better knowledge of MP composition and biological effects as well as the mechanisms leading to their clearance will probably open new therapeutic approaches in the treatment of atherothrombosis.

The role of cell death in the pathogenesis of autoimmune disease: HMGB1 and microparticles as intercellular mediators of inflammation

Cell death is critical to normal homeostasis, although this process, when increased aberrantly, can lead to the production of pro-inflammatory mediators promoting autoimmunity. Two novel intercellular mediators of inflammation generated during cell death are high mobility group box 1 (HMGB1) protein and microparticles (MPs). HMGB1 is a nuclear protein that functions in transcription when inside the nucleus but takes on pro-inflammatory properties when released during cell death. Microparticles are small, membrane-bound structures that extrude from cells when they die and contain cell surface proteins and nuclear material from their parent cells. MPs circulate widely throughout the vasculature and mediate long-distance communication between cells. Both MPs and HMGB1 have been implicated in the pathogenesis of a broad spectrum of inflammatory diseases, including the prototypic autoimmune conditions systemic lupus erythematosus and rheumatoid arthritis. Given their range of activity and association with active disease, both structures may prove to be targets for effective therapy in these and other disorders.

Essential role of platelet activation via protease activated receptor 4 in tissue factor-initiated inflammation

Introduction

Tissue factor (TF) activation of the coagulation proteases enhances inflammation in animal models of arthritis and endotoxemia, but the mechanism of this effect is not yet fully understood – in particular, whether this is primarily due to fibrin formation or through activation of protease activated receptors (PARs).

Methods

We induced extravascular inflammation by injection of recombinant soluble murine TF (sTF_1–219) in the hind paw. The effects of thrombin inhibition, fibrinogen and platelet depletion were evaluated, as well as the effects of PAR deficiency using knockout mice deficient for each of the PARs.

Results

Injection of soluble TF provoked a rapid onset of paw swelling. Inflammation was confirmed histologically and by increased serum IL-6 levels. Inflammation was significantly reduced by depletion of fibrinogen (P < 0.05) or platelets (P = 0.015), and by treatment with hirudin (P = 0.04) or an inhibitor of activated factor VII (P < 0.001) compared with controls. PAR-4-deficient mice exhibited significantly reduced paw swelling (P = 0.003). In contrast, a deficiency in either PAR-1, PAR-2 or PAR-3 did not affect the inflammatory response to soluble TF injection.

Conclusion

Our results show that soluble TF induces acute inflammation through a thrombin-dependent pathway and both fibrin deposition and platelet activation are essential steps in this process. The activation of PAR-4 on platelets is crucial and the other PARs do not play a major role in soluble TF-induced inflammation.