[Molecular dynamics simulation of force-regulated interaction between glycoprotein Ib and filamin]

In resting platelets, the 17 th domain of filamin a (FLNa17) constitutively binds to the platelet membrane glycoprotein Ibα (GPIbα) at its cytoplasmic tail (GPIbα-CT) and inhibits the downstream signal activation, while the binding of ligand and blood shear force can activate platelets. To imitate the pull force transmitted from the extracellular ligand of GPIbα and the lateral tension from platelet cytoskeleton deformation, two pulling modes were applied on the GPIbα-CT/FLNa17 complex, and the molecular dynamics simulation method was used to explore the mechanical regulation on the affinity and mechanical stability of the complex. In this study, at first, nine pairs of key hydrogen bonds on the interface between GPIbα-CT and FLNa17 were identified, which was the basis for maintaining the complex structural stability. Secondly, it was found that these hydrogen bonding networks would be broken down and lead to the dissociation of FLNa17 from GPIbα-CT only under the axial pull force; but, under the lateral tension, the secondary structures at both terminals of FLNa17 would unfold to protect the interface of the GPIbα-CT/FLNa17 complex from mechanical damage. In the range of 0~40 pN, the increase of pull force promoted outward-rotation of the nitrogen atom of the 563 rd phenylalanine (PHE 563-N) at GPIbα-CT and the dissociation of the complex. This study for the first time revealed that the extracellular ligand-transmitted axial force could more effectively relieve the inhibition of FLNa17 on the downstream signal of GPIbα than pure mechanical tension at the atomic level, and would be useful for further understanding the platelet intracellular force-regulated signal pathway.

Biomarkers involved in evaluation of platelets function in South-Eastern Romanian patients with hematological malignancies subtypes

ABSTRACT

At present, various researches presented how subtypes of hematological malignancies are related to stages of the immune response, because the activated immune system represents a promising form in cancer treatment. This study explores the relationship between the adaptive immune system (T cells), and the coagulation system (platelets, platelet membrane glycoproteins, platelets derivate microparticles) which seems to play an important role in host immune defense of patients with acute myeloblastic leukemia (AML) or B cell lymphoma (BCL), 2 of the most common hematological malignancies subtypes.Blood samples (n = 114) obtained from patients with AML or BCL were analyzed for platelet membrane glycoproteins (CD42b, CD61), glycoprotein found on the surface of the T helper cells (CD4+), protein complex-specific antigen for T cells (CD3+), platelet-derived microparticles (CD61 PMP) biomarkers by flow cytometry, and hematological parameters were quantified by usual methods.In patients with AML, the means of the percentage of the expressions of the molecules on platelet surfaces (CD61 and CD42b, P < .01; paired T test) were lower as compared to both control subgroups. The expression of cytoplasmic granules content (CD61 PMP) had a significantly higher value in patients with AML reported to controlling subgroups (P < .01; paired T test), which is suggesting an intravascular activation of platelets.The platelet activation status was presented in patients with low stage BCL because CD61 and CD42b expressions were significantly higher than control subgroups, but the expression of CD 61 PMP had a significantly decreased value reported to control subgroups (all P < .01; paired T test). T helper/inducer lineage CD4+ and T lymphoid lineage CD3+ expressions presented significant differences between patients with AML or low stage BCL reported to control subgroups (all P < .01; paired T test).Platelet-lymphocyte interactions are involved in malignant disorders, and CD61, CD42b present on platelet membranes, as functionally active surface receptors mediate the adhesion of active platelets to lymphocytes, endothelial cells, and cancer cells.

The sensitivity and specificity of platelet autoantibody testing in immune thrombocytopenia: a systematic review and meta-analysis of a diagnostic test

Essentials The diagnosis of ITP is based on a platelet count < 100 × 109  L-1 and exclusion of other causes. There are no standard tests or biomarkers to diagnose ITP. The sensitivity of platelet autoantibody testing is low (53%). The specificity is high (> 90%). A positive autoantibody test can be useful to rule in ITP but a negative does not rule out ITP. SUMMARY: Background Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. The sensitivity and specificity of platelet autoantibody tests is variable and their utility is uncertain. Objective The purpose of this study was to perform a systematic review and meta-analysis of platelet autoantibody tests in the diagnosis of ITP. Methods Ovid Medline, PubMed, and Web of Science were searched from inception until 31 May 2018. Two reviewers independently assessed studies for eligibility and extracted data. Studies that reported testing results for antiplatelet autoantibodies on platelets (direct tests) or in plasma/serum (indirect tests) for 20 or more ITP patients were included. Results Pooled estimates for sensitivity and specificity were calculated using a random effects model. Pooled estimates for the sensitivity and specificity of direct anti-platelet autoantibody testing for either anti-glycoprotein IIbIIIa or anti-glycoprotein IbIX were 53% (95% confidence interval [CI], 44-61%) and 93% (95% CI, 81-99%), respectively. For indirect testing, the pooled estimates for the sensitivity and specificity were 18% (95% CI, 12-24%) and 96% (95% CI, 87-100%), respectively. Conclusions Autoantibody testing in ITP patients has a high specificity but low sensitivity. A positive autoantibody test can be useful for ruling in ITP, but a negative test does not rule out ITP.

Use of CD42b immunohistochemical stain for the detection of Histoplasma

In pathologic specimen, Histoplasma capsulatum can frequently be identified by morphology and special stains such as GMS and PAS. Incidentally, we noted unusual staining of the platelet associated marker CD42b/GP1b expressed on the surface of fungal organisms. Evaluation of additional cases demonstrated that a majority of histoplasmosis cases (15/18 cases; 83%) showed positive staining with CD42b/GP1b, comparable to GMS stain results. Other platelet associated markers such as Factor VIII and CD61 showed no or rare expression (1/18 cases with Factor VIII). Studies have shown that 14-3-3 proteins bind directly to cytoplasmic domain of CD42b/GP1b. Significant homology is seen between fungal and human 14-3-3 proteins which may represent a molecular basis for our observation. Our study demonstrated that CD42b/GP1b staining by immunohistochemistry can aid in detection of Histoplasma organisms. Further studies with organisms with similar morphologic features such as Blastomyces and Leishmania may demonstrate a diagnostic utility in speciating organisms.

A standardized exercise intervention differentially affects premenopausal and postmenopausal African-American women

OBJECTIVE

African-American women represent an understudied population in menopause research yet face greater postmenopausal challenges associated with mortality than their white peers. We investigated the effects of a mild-intensity aerobic exercise training program on markers of mortality risk in both premenopausal and postmenopausal African-American women.

METHODS

Sixteen premenopausal women and 19 postmenopausal women underwent 6 months of mild-intensity aerobic exercise training. Measurements included markers of blood lipid and glucose profile, inflammation, kidney function, vascular health, and aerobic fitness before and after the exercise intervention.

RESULTS

Before the exercise intervention, the premenopausal and postmenopausal groups only differed in age, low-density lipoprotein, and total cholesterol levels, with the latter two being higher in the postmenopausal group. Both triglycerides and markers of early-stage endothelial dysfunction (CD62E endothelial microparticles) improved in both groups with aerobic exercise training. Aerobic fitness, glomerular filtration rate, body mass index, plasma glucose levels, and markers of late-stage endothelial dysfunction (CD31/CD42b endothelial microparticles) only improved in the premenopausal group.

CONCLUSIONS

Mild-intensity aerobic exercise training succeeds in improving some markers of cardiovascular disease and mortality in postmenopausal women. Higher levels of exercise intensity or perhaps additional interventions may need to be considered to further decrease mortality risk in this population.

Activated platelets in patients suffering from inflammatory bowel disease

BACKGROUND

There is an increased risk of thromboembolic complications in inflammatory bowel disease. Activated platelets play a crucial role in the pathogenesis of this disease.

AIM

To evaluate platelet activation in inflammatory bowel disease.

MATERIAL AND METHOD

This study comprised 20 healthy control subjects and a total of 20 patients. Out of them, 4 patients and 16 patients had suffered from Crohn's disease and ulcerative colitis, respectively. Nine patients were in active phase and 11 were in inactive phase of the disease. To evaluate platelet activation, we used the monoclonal antibodies of mouse anti-human CD42a-Fluorescein isothiocyanate (FITC), CD42b-FITC and mouse anti-human CD62P-phycoerythrin. We assessed the activation of platelets in peripheral blood using flow cytometric analysis.

RESULT

The platelet activation was found to be statistically significantly higher in the active-phase patient group when compared with the control subjects group. On the other hand, it was insignificant in the inactive patient group.

CONCLUSION

The results of our study might suggest that the elevation of CD62P expression in patients with inflammatory bowel disease could be used as a criterion of disease activation. Furthermore, agents with properties to diminish the platelet activation could prevent the development of thromboembolic complications in a patient with inflammatory bowel disease (Fig. 1, Ref. 15).

Disturbed blood flow acutely induces activation and apoptosis of the human vascular endothelium

There is strong and consistent evidence from in vitro studies that disturbed blood flow produces a proatherogenic vascular endothelial phenotype. However, data from human studies are lacking. To address this, a 220 mm Hg occlusion cuff was placed on the distal forearm of 10 young, healthy men to induce a localized region of disturbed blood flow in the proximal vasculature for 20 minutes. We hypothesized that disturbed blood flow would induce endothelial activation and apoptosis as indicated by increases in local concentrations of CD62E(+) and CD31(+)/CD42b(-) endothelial microparticles, respectively. Distal cuff occlusion induced reductions in mean blood flow, mean shear, and antegrade shear, and increases in retrograde flow, retrograde shear, and oscillatory shear stress, confirming that our protocol produced a disturbed blood flow stimulus in the experimental arm. Relative to baseline (0 minutes), CD62E(+) endothelial microparticles increased by ≈3-fold at 10 minutes and ≈4-fold at 20 minutes in the experimental arm (P<0.05). CD31(+)/CD42b(-) endothelial microparticles were elevated by ≈9-fold at the 20 minutes time point (P<0.05). There were no changes in the concentrations of either endothelial microparticle population throughout the experiment in the contralateral arm, exposed to normal resting blood flow (no cuffs). These findings indicate that disturbed blood flow acutely induces endothelial activation and apoptosis in humans, as reflected by release of microparticles from activated (CD62E(+)) and apoptotic (CD31(+)/CD42b(-)) endothelial cells. These data provide the first in vivo experimental evidence of disturbed blood flow-induced endothelial injury in humans.

Platelet receptors

Well-understood functions for "traditional" platelet receptors are described, but "newer" receptors are equally discussed. Receptors are described biochemically (structure, ligand(s), protein partners, and function) and whenever possible, their clinical importance (mutations, polymorphisms, syndrome) are highlighted.

A single dose of aprotinin prevents platelet hyporeactivity after coronary artery bypass graft surgery

INTRODUCTION

Bleeding after coronary artery bypass graft (CABG) surgery is associated with a significant increase in mortality. Even though aprotinin significantly reduces bleeding in patients undergoing cardiac surgery, its use has been recently substantially limited because of serious cardiovascular complications. The exact mechanism of its action, particularly its effect on platelet function, remains unclear.

OBJECTIVES

The aim of the study was to assess the effect of aprotinin on platelet function in patients undergoing CABG.

PATIENTS AND METHODS

In a randomized placebo-controlled double-blind study, we investigated the effect of a single dose of aprotinin on platelet function in 24 patients who underwent CABG between 2005 and 2006. Before surgery and in the postoperative period, we measured platelet activation markers (P-selectin and activated form of glycoprotein IIb/IIIa) at baseline and following in vitro platelet activation with adenosine diphosphate (ADP) or protease-activated receptor 1 (PAR-1) agonist--thrombin receptor activator for peptide 6 (TRAP-6). Perioperative bleeding and urinary metabolites of thromboxane A2 were also determined.

RESULTS

Aprotinin reduced perioperative bleeding by 26% (P <0.01) and prevented a decrease in platelet sensitivity to ADP immediately after CABG. In vitro platelet reactivity to TRAP-6 remained unchanged. Aprotinin did not affect blood platelet count or urinary thromboxane A2 metabolite excretion after CABG.

CONCLUSIONS

Our results indicate that aprotinin may reduce perioperative bleeding by its interference with ADP pathway of platelet activation, thereby preventing postoperative hyporeactivity of platelets to ADP. Platelet reactivity to PAR-1 receptor agonist was not affected by aprotinin.

P-selectin, tissue factor and CD40 ligand expression on platelet-leucocyte conjugates in the presence of a GPIIb/IIIa antagonist

This study was to investigate the appearance of P-selectin, tissue factor (TF) and CD40 ligand (CD40L) on platelet-leucocyte conjugates in the absence and presence of a GPIIb/IIIa antagonist, MK-852, and the effect of adding EDTA to pre-formed conjugates. The purpose was to find out whether these antigens are displaced from the conjugates along with the platelets, thus providing information on their location. Hirudinized blood was stirred with collagen ((2 microg/mL) in the absence and presence of MK-852 (10 micromol/mL)). P-selectin, TF and CD40L were measured on platelet-leucocyte conjugates (CD42a positive monocytes and neutrophils) and on single platelets by flow cytometry. Measurements were also made after subsequent addition of EDTA (4 mmol/L). Platelet-leucocyte conjugate formation was markedly enhanced in the presence of MK-852. P-selectin, TF and CD40L expression on the conjugates was also enhanced. Monocytes bound more platelets and expressed more P-selectin, TF and CD40L than neutrophils. EDTA displaced the majority of platelets from the conjugates and also the P-selectin, TF and CD40L, whereas it did not displaced P-selectin or CD40 ligand from the platelets themselves. It is concluded that a GPIIb/IIIa antagonist promotes formation of platelet-leucocyte conjugates, which display P-selectin, TF and CD40L that appears to be associated with the adherent platelets. Platelet-monocyte conjugates are prime candidates for arterial inflammation and thrombosis. Pro-inflammatory and pro-thrombotic effects of CD40L and tissue factor may be an explanation of the negative clinical effects using GPIIb/IIIa antagonists.

Leukocytapheresis (LCAP) decreases the level of platelet-derived microparticles (MPs) and increases the level of granulocytes-derived MPs: a possible connection with the effect of LCAP on rheumatoid arthritis

Microparticles (MPs) are believed to play an important role in inflammatory diseases such as rheumatoid arthritis (RA). Leukocytapheresis (LCAP) is one of the options available for the treatment of RA. We analyzed the levels of MPs in RA, by flow cytometry, especially in relation to the effect of LCAP. Twenty female patients with RA were recruited into this study. Six of the 20 patients with RA further received LCAP. Plasma levels of platelet-derived MPs were high in patients with RA and are correlated with disease activity. LCAP significantly improved RA in all six patients. The numbers of platelet-derived MPs significantly decreased after the first session of LCAP, which was probably due to direct removal by LCAP. Mean numbers of platelet-derived MPs after four sessions of LCAP markedly decreased. The numbers of granulocyte-derived MPs, which are suggested to have an anti-inflammatory effect, were markedly increased after the first session of LCAP. These data suggest that removal of platelet-derived MPs and increase of granulocyte-derived MPs are novel mechanisms of LCAP as effective treatment in RA.

[Cryopreservation strengthens procoagulative activities of platelets]

The aim of this study was to explore the potential relationship between the enhancement of instant hemostatic function in vivo of cryopreserved platelets and its procoagulative related molecule activities. The ability of platelet binding factor V density of GPIb-IX-V (CD42a) at platelet member surface were detected by flow cytometry, the clotting time induced by activated platelets were evaluated by coagulometer and platelet count, MPV and PDW were measured by hemocytometer before and after fresh platelets were cryopreserved. The results showed that the clotting time induced by activated cryopreserved platelets decreased by 43.9%, even quicker than that induced by fresh platelets; the fluorescence intensity of cryopreserved platelet binding factor V increased by 117%, more than that of fresh platelets binding factor V; the GPIb-IX-V (CD42a) density at cryopreserved platelet membrane surface increased by 32%, higher than that at fresh platelet surface. It is concluded that the enhancement of instant hemostatic function in vivo of cryopreserved platelet may be related to higher expression of procoagulative molecules or to their enhanced activity and rapid hemostatic effect.

[Relationship between alterations of circulating cell-derived microparticles and glucocorticosteroid application]

OBJECTIVE

To explore the relationship between the alterations of circulating cell-derived microparticles (MPs) and large-dose glucocorticosteroid application.

METHODS

Peripheral blood samples were collected from 33 patients with history of large-dose glucocorticosteroid application (glucocorticosteroid group) and 24 age-, sex-, and race-matched healthy controls (healthy control group). Platelet-poor plasma was obtained by centrifugation. Plasma microparticles were labeled with monoclonal antibodies of PE-conjugated mouse anti-human CD31, CD54, and FITC-conjugated mouse anti-human CD42b, CD45, CD51/61, CD105, and PE-Cy5-conjugated mouse anti-human CD62E. Cell-derived microparticles were measured by three-color flow cytometry.

RESULTS

The mean ranks of CD31+ MPs, CD45+ MPs, CD51/61 MPs, CD31+ CD42b+ MPs, and CD31+ CD45+ MPs of the glucocorticosteroid group were: 24.1, 25.5, 25.6, 21.6, and 24.8 respectively, all significantly lower than those of the control group (35.7, 33.8, 33.7, 39.3, and 34.8 respectively, P = 0.009, 0.019, 0.045, 0.000, and 0.009).

CONCLUSION

High-dose glucocorticosteroid application remarkably reduces plasma MPs that may be responsible for microcirculation disturbance.

Increased circulating CD31+/CD42- microparticles are associated with impaired systemic artery elasticity in healthy subjects

BACKGROUND

Impaired artery elasticity has been found in various pathological conditions related to endothelial dysfunction. Recently, CD31+/CD42- microparticles (MPs) emerged as a marker of endothelial injury. Whether CD31+/CD42- MPs, generated under physiological conditions, are correlated with artery properties has not been reported.

METHODS

We evaluated brachia-ankle pulse-wave velocity (baPWV) (n = 76) and C1 large-artery and C2 small-artery elasticity indices (n = 56), using noninvasive devices for pulse-wave analysis in a group of healthy persons. The number of circulating CD31+/CD427- MPs (n = 76) was measured by flow cytometric analysis.

RESULTS

Circulating CD31+/CD42- MPs were positively correlated with values of baPWV (r = 0.371, P = .008) and with C1 large-artery and C2 small-artery elasticity indices (r = -0.294, P = .037; and r = -0.310, P = .027, respectively). Multivariate analysis identified CD31+/CD42- MPs as potent contributors to the development of impaired systemic artery elasticity.

CONCLUSIONS

The level of circulating CD31+/CD42- MPs, an important biomarker of dysfunctional endothelium and vascular injury, is closely associated with impaired systemic artery elasticity in healthy subjects. The present study suggests that CD31+/CD42- MPs may be a novel surrogate marker for the clinical evaluation of vascular damage.

[Platelet and endothelial cell-derived microparticles in steroid-induced osteonecrosis of the femoral head of rabbit model]

OBJECTIVE

To explore the relationship between the alterations of platelet-derived microparticles (PMPs) and endothelial cell-derived microparticles (EMPs) and steroid-induced osteonecrosis of the femoral head.

METHODS

Forty-four adult Japanese white rabbits were randomly divided into 2 groups: experimental group (n = 44), injected intramuscularly once with 20 mg/kg of methylprednisolone acetate, and control group (n = 28) injected with normal saline of the same dose. Blood samples were collected from the auricular vein while the animals were in a fasting state in early morning prior to experiment (week 0), and 2, 4, and 8 weeks after the injection. The levels of prothrombin time (PT), activated partial prothrombin time (APTT), and anti-thrombokinase-III (AT-III) were examined. Plasma was ultra-centrifuged and the circulating platelet and EMPs were isolated to undergo flow cytometry to detect the amounts of CD31, CD42a, CD54, and CD62E. 1, 2, 4, and 8 week after the injection 6 rabbits from the experimental group and 4 rabbits from the control group were sacrificed respectively and their femoral heads were taken out to undergo histopathologic examination with HE staining and microthrombus and elastic fiber staining.

RESULTS

The PT, APTT, and AT-III levels increased significantly 1 to 8 weeks after the injection. The numbers of EMPs and PMPs were also increased markedly after steroid administration. Histopathologic examination demonstrated an accumulation of bone marrow cell debris, presence bone empty lacunae in the trabeculae 1 week after the steroid injection. 2, 4, and 8 weeks after the steroid injection the bone necrosis was remarkable, fatty degeneration of bone marrow cells occurred, the diameter of fat cells increased, and the area ratio of fatty cells became higher. MSB staining was positive.

CONCLUSION

High dose glucocorticosteroid increases the levels of PMPs and EMPs that may be related to hypercoagulability and thrombosis in microcirculation and play an important role in steroid-induced osteonecrosis. MP can be considered a true target in the pharmacological control of steroid-induced osteonecrosis.

Trp207Gly in platelet glycoprotein Ibalpha is a novel mutation that disrupts the connection between the leucine-rich repeat domain and the disulfide loop structure and causes Bernard-Soulier syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is a severe inherited bleeding disorder that is caused by a defect in glycoprotein (GP)Ib-IX-V complex, the platelet membrane receptor for von Willebrand factor.

PATIENTS

The diagnosis of BSS was made in two members of a Bukharian Jewish family who had life-long thrombocytopenia associated with mucocutaneous bleeding manifestations.

METHODS AND RESULTS

Flow cytometry and Western blot analyses showed only trace amounts of GPIb and GPIX on the patients' platelets. Sequence analysis of the GPIbalpha gene revealed a homozygous T > G transversion at nucleotide 709 predicting Trp207Gly substitution in the mature protein. Introduction of the mutation into a mammalian expression construct abolished the surface expression of GPIbalpha in transfected baby hamster kidney cells. The crystal structure of the N-terminus of GPIbalpha (PDB: 1SQ0) indicates that Trp207 is completely buried and located in a disulfide loop structure that interacts with the leucine-rich repeat (LRR) domain.

CONCLUSION

A novel mutation, Trp207Gly, causes BSS and predicts disruption of the interaction between a disulfide loop and the LRR domain that is essential for the integrity of GPIbalpha structure.

Platelet microparticles are heterogeneous and highly dependent on the activation mechanism: Studies using a new digital flow cytometer

BACKGROUND

Platelet-derived microparticles (MPs) are believed to play an important role in coagulation and inflammatory disorders. Unfortunately, MP size renders them difficult to study and analyze by conventional flow cytometry.

METHODS

We analyzed and characterized platelet-derived MPs, using antibodies against the major surface glycoproteins (GP), the platelet activation antigen P-selectin (CD62P), and a marker of procoagulant activity (phosphatidylserine exposure). MPs were generated by exposure of platelets to thrombin receptor activating peptide (TRAP) or ionophore. Both agonists induced significant microvesiculation of platelets, and the resulting MPs were analyzed by a new digital flow cytometer: Becton-Dickinson FACSAria.

RESULTS

Membrane GPs were equally well represented in MPs generated by either reagent. In contrast, P-selectin was more intensely expressed in TRAP-MPs, while phosphatidylserine (PS) expression was markedly increased in ionophore-MPs. Two distinct populations of TRAP-MPs (one PS-positive and another PS-negative) were apparent. The latter characteristic facilitated sorting of MPs according to their PS exposure.

CONCLUSIONS

The data presented herein show a significant improvement in the methodology applied until now to the characterization of MPs. The ability to characterize and sort MP subpopulations may help to resolve their contributions to normal and pathological functions.

[Role of adenosine diphosphate in the course of thrombin signal transmission]

OBJECTIVE

To study the effects adenosine diphosphate (ADP) on platelet aggregation and expression of glycoprotein (GP) on the surface of platelet membrane after activation of thrombin receptors, so as to investigate its role in thrombin signal transmission.

METHODS

Peripheral blood samples were collected from from 10 healthy volunteers. Platelets were extracted. The thrombin receptor activating peptides (TRAP), protease-activated receptor 1 activated peptide (PAR1-AP, SFLLRN, 25 micromol/L) and PAR4-AP (AYPGKF, 250 micromol/L) were added into the suspension of platelets respectively to induce platelet aggregation. In apyrase inhibition test apyrase II was added into the suspension of platelets for 2 hours and then PAR1-AP or PAR4-AP was added respectively to observe the the expression of GPIb and P-selectin with flow cytometry.

RESULTS

Either PAR1 and PAR4 induced platelet aggregation. After apyrase II stimulation the PAR4-AP induced platelet aggregation was not influenced and PAR1-AP induced platelet aggregation was partially inhibited with a reversible aggregation curve. Stimulated by PAR1-AP and PAR4-AP the GPIb decreased firstly and then gradually returned to normal. Apyrase VII have not significant influence on the GPIb expression, but accelerated the return of GPIb to the platelet surface after PAR1 stimulation so that the lowest point was accelerated to 2 min, compared to that of the control group (5 min) and there were significantly differences 10 and 30 min later between these 2 groups (all P < 0.05). The P-selectin expression was remarkably increased 2 min after the PAR1-AP and PAR4-AP induction and peaked 2 min later. Apyrase VII did not significantly influence the P-selectin expression in these 2 activation ways.

CONCLUSION

ADP plays an important role in the thrombin signal transmission, especially in the PAR1 pathway.

Plasma glycoprotein V levels in the general population: normal distribution, associated parameters and implications for clinical studies

Soluble glycoprotein V (sGPV) is a new plasma marker of thrombosis released from the platelet surface by thrombin. sGPV levels are increased in patients with atherothrombotic diseases, but the determinants of sGPV levels are unknown in the general population. Identification of these potential confounding factors is needed for correct design and analysis of clinical studies on cardiovascular diseases. The aim of this study was to determine the normal range of plasma values and the factors controlling sGPV levels in a population of normal individuals. Three hundred blood donors were recruited at the Etablissement Français du Sang-Alsace for the measurement of plasma levels of sGPV, platelet factor 4 (PF4), thrombin-antithrombin complexes (TAT) and D-dimers. The plasma level of sGPV was (median [interquartile range]) 27.5 [23.5-34.4] microg/l and displayed a Gaussian distribution. sGPV had a lower interindividual coefficient of variation (33%) than PF4 (176%), TAT (87%) or D-dimers (82%). sGPV levels were independent of age and sex but sensitive to red cell (r = 0.412; p < 0.0001) and platelet counts (r = 0.267; p = 0.001), total cholesterol (r = -0.313; p < 0.0001), food intake (r = 0.184; p = 0.0014) and smoking (r = -0.154; p = 0.039). Contrary to PF4 and TAT, sGPV did not differ between venous and arterial blood samples of 12 healthy individuals. Red cell and platelet counts, total cholesterol, current smoking and recent food intake are important determinants of sGPV levels and must be taken into account in clinical studies using sGPV as a thrombosis marker. Normal distribution of sGPV levels in the general population supports its use in clinical applications.

Prolonged thrombocytopenia after allogeneic hematopoietic stem cell transplantation: associations with impaired platelet production and increased platelet turnover

To evaluate the mechanisms underlying prolonged thrombocytopenia after allogeneic hematopoietic stem cell transplantation (SCT), an index for plasma glycocalicin normalized for the individual platelet count (GCI), plasma thrombopoietin (TPO), and circulating B cells producing anti-GPIIb-IIIa antibodies were measured in 50 SCT recipients with or without prolonged thrombocytopenia, 42 patients with idiopathic thrombocytopenic purpura, nine patients with aplastic anemia, and 22 healthy individuals. All three indices were significantly higher in the SCT recipients with thrombocytopenia than in those without (P < 0.01 for all comparisons), and were significantly correlated with the platelet count in SCT recipients. Stepwise multiple regression analysis of the samples from the SCT recipients revealed that GCI and TPO independently pointed to specific mechanisms of thrombocytopenia. The GCI and TPO status in SCT recipients with thrombocytopenia had a pattern similar to that seen in aplastic anemia, suggesting a major role for impaired thrombopoiesis. An antiplatelet antibody response was frequently detected in SCT recipients, but the development of thrombocytopenia is likely to depend on additional factors, such as reticuloendothelial function. In summary, post transplant prolonged thrombocytopenia is associated with complex mechanisms, including impaired thrombopoiesis and increased platelet turnover.

The impact of genetic variation in the region of the GPIIIa gene, on Pl expression bias and GPIIb/IIIa receptor density in platelets

Some studies have suggested that genetic variability in the glycoprotein (GP) IIIa gene modulates expression of platelet GPIIb/IIIa (alpha(2b)beta(3)). We sought to determine as to whether combinations of genetic variants within the GPIIIa gene (haplotypes) influenced the expression of GPIIIa RNA and protein levels in human platelets. Three promoter polymorphisms, Pl(A1/A2) genotype and platelet receptor densities were determined in 207 acute coronary syndrome (ACS) patients. Allele-specific quantitative reverse transcription-polymerase chain reaction of platelet RNA from Pl(A1/A2) heterozygotes identified a greater expression of Pl(A2) bearing transcripts among heterozygotes. Among the patients studied, the ratio of Pl(A1)/Pl(A2) RNA expression was significantly influenced by promoter haplotype (P < 0.01). However, this effect reflected carriership of rare not common haplotypes (P = 0.2). There was a threefold variation between subjects in the number of GPIIb/IIIa receptors expressed per platelet, although no association between receptor density and the Pl(A2) (P = 0.93) or promoter polymorphisms was demonstrated (-468A, P = 0.52; -425C, P = 0.59; -400A, P = 0.52). Among common haplotypes, Pl(A1)/Pl(A2) RNA expression was negatively correlated with adjusted GPIIb/IIIa receptor density (P = 0.04). The overall trend towards higher expression of Pl(A2) bearing message in Pl(A1/A2) heterozygotes, and the existence of rare haplotypes with more pronounced changes indicate the existence of cis-acting genetic factors that remain to be identified.

Increased soluble glycoprotein V concentration during the acute onset of unstable angina pectoris in association with chronic cigarette smoking

Platelet hyperactivity is important in the pathobiology of acute coronary syndromes. Glycoprotein V (GPV) is an integral membrane protein of platelets in the function of the GPIb-V-IX receptor for vWf/shear-dependent platelet adhesion in arteries. Soluble GPV is a novel marker of platelet activation. The aim of this study is to assess circulating soluble GPV levels in unstable angina pectoris (UA). Twenty-one patients (15 men, six women, aged 52+/-7 years) with UA pectoris were studied. The inclusion criteria were angina at rest lasting >20 min during the preceding 6 h, with transient ST segment depression and/or T wave inversion and no evidence of myocardial infarction detected with the use of cardiac troponin-T. Coronary artery stenosis was angiographically confirmed in all patients. Twenty age- and sex-matched healthy adults (14 men, six women, aged 48+/-7 years) served as controls. There were no significant differences among the studied groups with respect to age, sex, obesity, smoking, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglyceride and platelet counts. Plasma-soluble GPV concentrations were higher in the UA patient group (126+/-46 ng/ml) than those in the healthy controls (82+/-15 ng/ml) (P=0.001). There was a significant correlation only between plasma-soluble GPV levels and smoking (r=0.526, P=0.0001). Smoker UA patients had higher levels of soluble GPV than the non-smoker patients (139+/-40 vs. 113+/-50 ng/ml, respectively, P=0.02). However, soluble GPV levels were similar in smoker and non-smoker healthy controls (P=0.2). It is concluded that soluble GPV concentrations are significantly increased during the acute clinical course of unstable angina pectoris, indicating that soluble GPV may be useful marker of platelet activation in those patients. The level of the molecule is significantly affected from smoking in those patients.

Effects of platelet binding on whole blood flow cytometry assays of monocyte and neutrophil procoagulant activity

BACKGROUND

Monocytes and neutrophils form heterotypic aggregates with platelets initially via engagement of platelet surface P-selectin with leukocyte surface P-selectin glycoprotein ligand-1 (PSGL-1). The resultant intracellular signaling causes the leukocyte surface expression of tissue factor and activation of leukocyte surface Mac-1 (integrin alphaMbeta2, CD11b/CD18). The activation-dependent conformational change in monocyte surface Mac-1 results in the binding of coagulation factor Xa (FXa) and/or fibrinogen to Mac-1. The aim of this study was to develop whole blood flow cytometry assays of these procoagulant activities and to investigate the effects of platelet binding to monocytes and neutrophils.

METHODS

Citrate or D-Phe-Pro-Arg-chloromethylketone (PPACK) anticoagulated whole blood was incubated with monoclonal antibodies against CD14 (PECy5), CD42a (PE), FITC-conjugated test antibody and an agonist, and then fixed with FACS lyse. Appropriate isotype negative controls were prepared in parallel. A BD FACSCalibur was used to analyze monocytes and neutrophils, which were identified based on CD14 fluorescence, forward and 90 degrees light scatter. These populations were further gated into CD42a-positive (platelet-bound) and CD42a-negative (platelet-free). Geometric mean fluorescence and per cent positive data were collected for each subpopulation to measure the binding of test antibodies directed at CD42a, tissue factor, coagulation FXa, bound fibrinogen, activated Mac-1, and CD11b. Compensation controls were prepared on six normal donors prior to the study and these settings were used throughout the 10 donor study. Negative controls verified the lack of cross talk, particularly in the quantified FITC and PE parameters.

RESULTS

The physiologic agonists collagen and ADP increased monocyte-platelet and neutrophil-platelet aggregates and increased leukocyte surface Mac-1/CD11b and surface-bound tissue factor, FXa and fibrinogen. Whereas the increases in Mac-1/CD11b were mainly independent of leukocyte-platelet binding, the increases in surface-bound tissue factor, FXa and fibrinogen were mainly dependent on leukocyte-platelet binding.

CONCLUSIONS

(i) We have developed novel whole blood flow cytometry assays to measure bound tissue factor, coagulation FXa, fibrinogen, activated Mac-1 and CD11b on the surface of monocytes and neutrophils, allowing independent analysis of monocytes and neutrophils with and without surface-adherent platelets. (ii) The monocyte and neutrophil surface binding of tissue factor, FXa and fibrinogen is mainly dependent on platelet adherence to monocytes and neutrophils, whereas the monocyte and neutrophil surface expression of CD11b and activated Mac-1 is mainly independent of platelet adherence to monocytes and neutrophils.

Quantitation of microparticles released from coated-platelets

Dual agonist stimulation of platelets with thrombin and convulxin results in generation of coated-platelets, a sub-population of cells known formerly as COAT-platelets (collagen and thrombin). Coated-platelets retain several procoagulant proteins on their surface and express phosphatidylserine (PS). In this report, we utilize a new methodology to demonstrate that coated-platelets also release microparticles. Platelets were prelabeled with 2.5 microm Bodipy-maleimide and then stimulated with convulxin plus thrombin. Microparticles, 0.3-0.5 microm in diameter, were observed by fluorescence confocal microscopy. Confocal microscopy was also used to demonstrate that microparticles were positive for glycoprotein IIb/IIIa, glycoprotein Ib, CD9, and PS, but negative for fibrinogen and thrombospondin. Furthermore, microparticles released from Bodipy-labeled platelets were observed by flow cytometry, and activation with convulxin plus thrombin produced 15 +/- 5 microparticles per coated-platelet. In contrast, platelets stimulated with thrombin or convulxin alone produced few microparticles. Phenylarsine oxide and diamide, both of which potentiate the mitochondrial permeability transition pore and coated-platelet production, significantly increased the number of microparticles released per coated-platelet.

Turkish population data on the factor XIII Val34Leu,glycoprotein (GP)Ibalpha Kozak and P-selectin glycoprotein ligand 1 (PSGL-1) loci

We determined the allele and genotype frequencies of three PCR-based gene polymorphisms factor XIII (FXIII) Val34Leu, glycoprotein (GP) Ibalpha Kozak and P-selectin glycoprotein ligand 1 (PSGL-1) in the Turkish population (n = 126 for FXIII Val34Leu, n = 110 for GPIbalpha Kozak and n = 203 for PSGL-1). To detect these polymorphisms, DNA was extracted from venous blood. Genomic DNA samples were replicated and analysed by a polymerase chain reaction (PCR) method. PCR products were digested by restriction endonuclease enzymes for FXIII Val34Leu and GPIbalpha Kozak. PSGL-1 was analysed by variable number of tandem repeats (VNTR). Allele frequencies of V (Val) and L (Leu) were found to be 0.805 and 0.195 respectively for the FXIII Val34Leu polymorphism. No significant difference was observed between French and Turkish populations for FXIII Val34Leu. Allele frequencies of T and C were calculated to be 0.873 and 0.127 for the GPIbalpha Kozak polymorphism and no significant difference was found between Turkish and French populations. In contrast, the difference between Turkish and Japanese populations was statistically significant (p<0.0001). In the PSGL-1 group, allele frequencies of A, B and C were calculated as 0.818, 0.160, 0.022 respectively. For the PSGL-1, although the difference between Turkish and French populations was not significant, the difference between the Turkish and Japanese was extremely significant (p<0.0001). In conclusion, a Turkish population database has been established for three gene polymorphisms.

[Activation of platelet-neutrophil mediated by platelet-activating factor]

To investigate the pathophysiological mechanisms for platelet-neutrophils cross talk mediated by platelet-activating factor (PAF) and to lay a foundation for clinical application, ginkgolides B (GB), a PAF receptor antagonist, was added in the whole blood to block the effects of PAF on activation of platelet-neutrophil; PAF and ADP were respectively added in the whole blood to monitor the expression of CD62P on platelet by flow cytometry; PAF and ADP were added in the whole blood to monitor the expression of CD11b on neutrophil by flow cytometry; PAF and ADP were added in the whole blood to monitor the platelet-leucocyte aggregates (PLA) which were PLA in the total leucocyte population (PLA/L) and the mean fluorescence intensity (MFI) of CD42b. Outcomes were analyzed by t-test, and the differences were statistically significant (P < 0.05). The results showed that the expression of CD62P on platelats, the expression of CD11b on neutrophils and PLA formation were all increased by PAF and ADP; the PAF receptor antagonists (GB) could obviously inhibit the expression of CD62P, CD11b and PLA formation induced by PAF, but could not completely inhibit the activation of platelet and neutrophil, and the platelet-neutrophil cross talk; GB could inhibit the expression of CD62P and CD11b induced by ADP, but could not conpletely inhibit the activation of platelet and neutrophli; GB could not obviously inhibit the platelet-leucocyte aggregates mediated by ADP. It is concluded that the multiligand-receptor systems involved in PLA formation and platelet-netrophils cross talk seem to be regulated by complex mechanisms; the PAF receptor antagonists (GB) obviously inhibit the effect of PAF, and may be widely utilized in the therapy of thrombosis and inflammation.

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.

Combined administration of nitric oxide gas and iloprost during cardiopulmonary bypass reduces platelet dysfunction: a pilot clinical study

BACKGROUND

Thrombocytopenia and platelet dysfunction are major mechanisms of cardiopulmonary bypass-induced postoperative hemorrhage. This study evaluated the effects of low amounts of nitric oxide, iloprost (prostacyclin analog), and their combination administered directly into the oxygenator on platelet function, platelet-leukocyte interactions, and postoperative blood loss in patients undergoing coronary artery bypass grafting.

METHODS

Blood samples from 41 patients randomized to the control, nitric oxide (20 ppm), iloprost (2 ng x kg -1 x min -1 ), or nitric oxide plus iloprost groups were collected during cardiopulmonary bypass. Platelets and leukocytes were enumerated. Platelet membrane glycoprotein Ib and glycoprotein IIb/IIIa, P-selectin, platelet-derived microparticles, leukocyte CD11b/CD18 (Mac-1), and platelet-leukocyte aggregate were quantified by means of flow cytometry. Collagen and thrombin receptor-activating peptide-induced platelet aggregation in whole blood was analyzed by means of aggregometry.

RESULTS

Both nitric oxide or iloprost attenuated cardiopulmonary bypass-induced thrombocytopenia, reduction of glycoprotein Ib and glycoprotein IIb levels, translocation of P-selectin, microparticle formation, Mac-1 upregulation, and suppression of collagen-induced aggregation. Nitric oxide plus iloprost was significantly more effective in preventing thrombocytopenia, microparticle formation, and P-selectin translocation. Moreover, this treatment preserved thrombin receptor-activating peptide-induced aggregation, which was not rescued by single treatments. Both nitric oxide and nitric oxide plus iloprost attenuated postoperative blood loss.

CONCLUSIONS

Nitric oxide plus iloprost reduced the deleterious effects of cardiopulmonary bypass, such as thrombocytopenia, platelet activation, platelet-leukocyte aggregate formation, and suppression of platelet aggregative responses. The reduced postoperative bleeding observed with this treatment suggests that this is a new and clinically feasible therapeutic option for patients subjected to cardiopulmonary bypass.

Increased peripheral platelet destruction and caspase-3–independent programmed cell death of bone marrow megakaryocytes in myelodysplastic patients

To investigate underlying mechanisms of thrombocytopenia in myelodysplastic syndrome (MDS), radiolabeled platelet studies were performed in 30 MDS patients with platelet counts less than 100 × 109/L. Furthermore, plasma thrombopoietin and glycocalicin index (a parameter of platelet or megakaryocyte destruction) were determined. Mean platelet life (MPL), corrected for the degree of thrombocytopenia, was reduced in 15 of 30 patients (4.3 ± 0.9 days [mean ± SD] vs 6.0 ± 1.3, P = .0003). Platelet production rate (PPR) was reduced in 25 of 30 patients (68 ± 34 × 109/d vs 220 ± 65, P &lt; .0001). Thrombopoietin levels were not significantly correlated with the PPR. However, the glycocalicin index was significantly higher compared with controls (15 ± 16 vs 0.7 ± 0.2, P = .001) and significantly correlated with the PPR (P = .02, r = -0.5), but not with the MPL (P = 1.8). Ultrastructural studies demonstrated necrosis-like programmed cell death (PCD) in mature and immature megakaryocytes (n = 9). Immunohistochemistry of the bone marrow biopsies demonstrated no positive staining of MDS megakaryocytes for activated caspase-3 (n = 24) or cathepsin D (n = 21), while activated caspase-8 was demonstrated in a subgroup of patients (5/21) in less than 10% of megakaryocytes. These results indicate that the main cause of thrombocytopenia in MDS is caspase-3–independent necrosis-like PCD resulting in a decreased PPR in conjunction with an increased glycocalicin index.

Increased glycocalicin index and normal thrombopoietin levels in patients with idiopathic thrombocytopenic purpura with a decreased rate of platelet production

Platelet kinetic studies in idiopathic thrombocytopenic purpura (ITP) have shown that in a subgroup of patients a shortened mean platelet life (MPL) is associated with a decreased platelet production rate (PPR). Other methods of studying certain aspects of thrombocytopoiesis are the plasma concentrations of thrombopoietin and glycocalicin.

Survival of baboon biotin-X-N-hydroxysuccinimide and 111In-oxine-labelled autologous fresh and lyophilized reconstituted platelets

BACKGROUND AND OBJECTIVES

In accordance with Food and Drug Administration (FDA) regulations, platelets can be stored in the liquid state at 22 degrees C for only 5 days. Platelets frozen with 6% dimethylsulphoxide (DMSO) can be stored at -80 degrees C for 2 years, and platelets frozen with 5% DMSO can be stored at -150 degrees C for 3 years. Studies are being conducted to determine the effects of lyophilization of platelets. In the present study, we assessed the survival of autologous lyophilized-reconstituted platelets in the baboon.

MATERIALS AND METHODS

We studied fresh baboon platelets and baboon platelets that had been treated with paraformaldehyde, frozen, lyophilized, thawed and reconstituted. Aliquots of these platelets were labelled with (111)In-oxine or biotin-X-N-hydroxysuccinimide (biotin-X-NHS) before autotransfusion, and measurements were made of the in vivo recovery and lifespan. We also evaluated the response of fresh and lyophilized platelets to in vitro agonists by measuring the level of platelet surface markers and heterotypic aggregates in the peripheral blood following the autotransfusions.

RESULTS

The (111)In-oxine- or biotin-X-NHS-labelled lyophilized, reconstituted platelets exhibited survival times of less than 15 min. These platelets did not respond to stimulation with agonists to decrease platelet GPIb and increase platelet P-selectin and platelet GPIIb-IIIa levels 1 min post-transfusion and they accumulated more procoagulant factor V than did the fresh platelets.

CONCLUSIONS

Lyophilized reconstituted baboon platelets labelled with (111)In-oxine or biotin-X-NHS before autotransfusion exhibited an in vivo circulation time of less than 15 min. Further study of the lyophilized, reconstituted platelets is required to evaluate their haemostatic function.

Platelet count, previous infection and FCGR2B genotype predict development of chronic disease in newly diagnosed idiopathic thrombocytopenia in childhood: results of a prospective study

About 25-30% of children with acute idiopathic thrombocytopenia (ITP) develop chronic disease. It is not well known which patient characteristics influence the course of the ITP. A prospective study in 60 children with newly diagnosed ITP was performed. The aim of the study was to identify patient characteristics at the onset of thrombocytopenia that predicts the progression to chronic ITP. Clinical data and blood samples were collected at several time points during the first 6 months of the disease. Variables predicting chronic disease, as calculated in a multivariate logistic regression analysis, were a platelet count >10 x 10(9)/l at the onset [odds ratio (OR) 1.1, 95% confidence interval (CI) 1.01-1.14], the absence of infection shortly before the onset of the disease (OR 4.8, CI 1.16-19.57) and FGR2B-232I/T genotype (OR 7.9, CI 0.96-65.27). The latter may point at an immune-modulating role of Fc gamma RIIb in ITP. Although only three patients had serious bleeds, 35 patients received immune-modulating treatment for low platelet counts only. Seventeen patients were treated with intravenous immunoglobulin (IVIG) and 18 patients received corticosteroids. Patient variables did not differ between these treatment groups. However, patients receiving IVIG had significantly lower risk for chronic disease.

Cyclosporin A does not affect platelets in children with idiopathic nephrotic syndrome

The immunosuppressive agents administered to maintain the remission of idiopathic nephrotic syndrome (INS) may have a deleterious effect on several cell types. The aim of this study was to analyze platelet activation and reactivity in children with INS treated with cyclosporin A (CyA). The study groups comprised 16 children with remission of INS induced by CyA and 16 children with glucocorticosteroid-induced remission 8 weeks from the onset of INS relapse. Fifteen healthy children served as controls. Surface expression of CD61, CD62P, and CD42b on resting and thrombin-stimulated platelets was analyzed with flow cytometry. No differences between groups were found in CD61, CD62P, and CD42b surface expression, but markers of the coagulation cascade and fibrinolysis or endothelial injury (F1+2 prothrombin fragments, tissue plasminogen activator inhibitor 1) were elevated in patients treated with CyA compared with children on steroids and healthy controls. No correlations between markers of platelet function and CyA concentration were found. We postulate that CyA administration in nephrotic patients causes an activation of thrombinogenesis but does not influence platelet activation and reactivity in INS.

Platelet-derived microvesicles transfer tissue factor to monocytes but not to neutrophils

Activated platelets are known to adhere to both blood monocytes and neutrophils, and this adhesion is mainly mediated by the surface exposure of the platelet granule protein CD62P. Platelets as well as platelet-derived microvesicles (PMV) have also been shown to contain and to transfer tissue factor (TF), the most important initiator of intravascular thrombin and fibrin formation, to monocytes. However, the role of neutrophils for gathering platelet-derived TF is controversial. Here we studied the interaction of PMV with monocytes and neutrophils using a whole blood system. Platelet-rich plasma (PRP) obtained from citrated human blood was incubated with collagen (5 microg/ml, 15 min) and the platelets were removed by centrifugation (5 min at 5000 x g). After incubating the PMV-containing plasma for further 30 min with a sediment of red and white bloods cells that had been obtained after PRP preparation, monocytes and neutrophils were analysed by flow cytometry for the surface exposure of the platelet-specific antigen CD42a and TF. Compared to a control with non-activated PRP, there was a significant increase in the number of both CD42a-positive monocytes and neutrophils. In contrast, there was no change in the number of TF-positive neutrophils, but a more than 2-fold increase in the number of TF-positive monocytes. The changes in CD42a on monocytes and neutrophils as well as the changes in TF on monocytes could be significantly reduced by an anti-CD62P antibody or by removal of PMV from the plasma samples. The data indicate that the transfer of TF to monocytes is not simply an CD62P-mediated adhesion of platelets or PMV to monocytes, but may involve other not yet identified mechanisms.

Human marrow megakaryocyte differentiation: multiparameter correlative analysis identifies von Willebrand factor as a sensitive and distinctive marker for early (2N and 4N) megakaryocytes

Human megakaryocyte differentiation and maturation were studied in fresh marrow aspirates by using multiparameter flow cytometric correlative analysis. The expression of glycoprotein (GP)IIb/IIIa, GPIIIa, GPIb, and CD36 correlated directly with cell size and ploidy (r &gt; 0.97); however, GPIb acquisition was relatively slow. von Willebrand factor (VWF) is robustly expressed by early (2N and 4N) megakaryocytes, enabling their complete resolution from the other marrow cells at a level superior to that achieved with GPIIb/IIIa. Expression of myeloid CD45 and immunoglobulin G (IgG)-FcγRII receptor (CDw32) increased with megakaryocyte maturation and contrasted with the declining expression of HLA-DR (negative in platelets). Interleukin-6 receptor expression in megakaryocytes was higher than in other marrow cells. By using the time-of-flight technique, the diameter of the megakaryocyte population was 37 ± 4 μm (mean ± 1 SD) compared with 14 ± 2 μm for the total marrow cells, ranging from 21 ± 4 μm for 2N cells to 56 ± 8 μm for 64N cells. Cell size directly correlated with cell DNA (r = 0.98). Receptor density of GPIIb/IIIa and GPIb decreased with the transition from 2N to 4N cells, then reached maximum at 32N cells. In conclusion, the present methods are useful for studying in vivo human megakaryocytopoiesis in normal and altered states. The expression of VWF is a sensitive and distinctive marker for the identification of young marrow megakaryocytes. (Blood. 2004; 104:2722-2727)

Increased platelet CD63 and P-selectin expression persist in atherosclerotic ischemic stroke

Platelet activation is an important process in the pathogenesis of atherothrombosis. However, the serial changes of platelet activation in atherosclerotic ischemic stroke have not been determined. In this study, we measured serially platelet expression of CD63 and P-selectin and platelet aggregability to ADP and collagen. Measurements were made 24 and 72 h and 7 and 90 days after the ischemic event in 29 patients with atherosclerotic ischemic stroke. Platelet aggregability was significantly decreased after 72 h compared to that at 24 h of stroke onset. However, platelet CD63 and P-selectin expression remained high even 90 days after the events. These findings suggest that platelet hyperactivation in atherosclerotic ischemic stroke may be sustained for a considerable period.

Sustained elevated amounts of circulating procoagulant membrane microparticles and soluble GPV after acute myocardial infarction in diabetes mellitus

During myocardial infarction (MI), platelet activation and endothelial apoptosis are responsible for the release of procoagulant membrane-derived microparticles (MP) in the blood flow. MP prothrombotic and proinflammatory properties may be crucial for coronary prognosis. Elevated amounts of circulating procoagulant MP were described in diabetes mellitus (DM), and could be of particular significance in a MI context. We evaluated the prothrombotic status of DM and non-DM (NDM) patients at days 1 and 6 after MI, by measurement of circulating procoagulant MP and soluble GPV (sGPV), the platelet glycoprotein V major fragment released upon thrombin cleavage. Variations were compared to values measured in healthy volunteers (HV). Procoagulant MP were captured onto insolubilized annexin V and quantified by prothrombinase assay. Their cellular origin was assessed. With respect to HV, the levels of procoagulant MP detected at D1 and D6 were elevated in DM and NDM, MP being significantly higher in DM vs. NDM. The high amounts of platelet-derived MP and the correlation between procoagulant MP and sGPV, testify to the central role of thrombin-activated platelets during MI in both DM and NDM subsets. The release of platelet and endothelial cell-derived MP persisted at D6 and was more important in DM, the associated prothrombotic risk being also reflected by higher levels of sGPV. The endothelial damage revealed by endothelial-derived MP was twice that observed in NDM patients. In DM patients presenting cardio-vascular events at 6 month follow-up, MP levels were significantly higher at D1 after MI than in those without complication (24.9 +/- 4.8 vs. 12.3 +/- 2.7 nM PhtdSer, p = 0.02), suggesting a prognostic potential for MP.

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.

Inhibition of Platelet Adherence to Mononuclear Cells by α-Tocopherol

BACKGROUND

Platelet-leukocyte interaction is an early important event for thrombogenesis, and this process is mainly mediated by P-selectin on platelets. Although alpha-tocopherol has been shown to inhibit thrombotic disorders, the effect of alpha-tocopherol on platelet P-selectin expression and platelet-leukocyte interaction is little known.

METHODS AND RESULTS

We examined whether alpha-tocopherol inhibited human platelet P-selectin expression and platelet-leukocyte interaction. Alpha-tocopherol (50 to 500 microg/mL) inhibited thrombin-induced or phorbol 12-myristate 13-acetate (PMA)-induced P-selectin expression on platelets. alpha-Tocopherol suppressed platelet-mononuclear cell (MNC) interaction, platelet aggregation, and platelet protein kinase C (PKC) activity stimulated with either PMA (100 nmol/L) or thrombin. Inhibitory actions of alpha-tocopherol against the platelet functions were mimicked by staurosporine, a selective PKC inhibitor. After oral supplementation of alpha-tocopherol (300 mg/d for 3 weeks) in healthy subjects, thrombin-mediated or PMA-mediated P-selectin expression, platelet-MNC interaction, and platelet aggregation ex vivo were suppressed.

CONCLUSIONS

alpha-Tocopherol inhibited P-selectin expression on human platelets and thereby attenuated platelet-MNC interactions, which were mediated at least in part by the inhibition of intraplatelet PKC activity. These actions of alpha-tocopherol on platelet functions provide new insights into the antithromboatherogenic properties of alpha-tocopherol.

Circulating procoagulant microparticles and soluble GPV in myocardial infarction treated by primary percutaneous transluminal coronary angioplasty. A possible role for GPIIb-IIIa antagonists

Circulating procoagulant microparticles (MP) were measured as markers of vascular damage and prothrombotic risk in patients undergoing ST-segment myocardial infarction (STEMI) treated by primary percutaneous transluminal coronary angioplasty (PTCA) and additional GPIIb-IIIa antagonists. Cells possibly more responsive to GPIIb-IIIa (alpha(IIb)beta(3)) antagonists were evidenced through MP phenotypes by comparison with healthy volunteers (HV) and STEMI patients treated by PTCA without GPIIb-IIIa antagonist (CP). In 50 STEMI patients, blood samples were collected at day 1 and day 6. Circulating procoagulant MP were captured on annexin V and quantified by prothrombinase assay as nanomolar phosphatidylserine equivalents (nm PhtdSer). Platelet activation by thrombin was confirmed through independent measurement of soluble GPV (sGPV). With respect to HV, procoagulant MP levels were high in patients with STEMI or unstable angina, platelet-derived MP and elevated sGPV testifying to significant platelet activation. A substantial release of endothelial-derived MP was evidenced simultaneously. In abciximab-treated patients, procoagulant MP, mainly of platelet origin, decreased precociously at day 1 (4.2 +/- 0.6 vs. CP 15.5 +/- 2.1 nm PhtdSer; P = 0.001) together with sGPV (36 +/- 3 vs. CP 58 +/- 8 ng mL(-1); P = 0.02). Leukocyte-derived MP decreased at day 6 (0.12 +/- 0.04 vs. CP 0.56 +/- 0.12 nm PhtdSer; P = 0.01) suggesting a possible effect on underlying inflammatory status. In patients presenting cardiovascular events at 6-month follow-up, procoagulant MP levels at day 1 could be indicative of a worsened outcome. MP could constitute a relevant parameter for the follow-up of STEMI patients treated by GPIIb-IIIa antagonists.

In Vitro Effects of Poly-N-Acetyl Glucosamine on the Activation of Platelets in Platelet-Rich Plasma with and without Red Blood Cells

BACKGROUND

This study was performed to assess the effect of poly-N-acetyl glucosamine fiber slurry on plasma clotting proteins, platelets, and red blood cells in the clotting of the blood.

METHODS

Citrate phosphate dextrose whole blood was stored at 22degreesC for 48 hours to prepare platelet-poor plasma, platelet-rich plasma (PRP), and PRP plus red blood cells with hematocrit values of 20%, 35%, and 45% with and without an equal volume of poly-N-acetyl glucosamine fibers (1 mg/mL 0.9% NaCl).

RESULTS

Thromboelastogram data show that poly-N-acetyl glucosamine fibers (p-GlcNAc) significantly reduced the R time in platelet-poor plasma, PRP, and PRP supplemented with red blood cells. Poly-N-acetyl glucosamine fibers increased, but not significantly, Annexin V and factor X binding to platelets, platelet microparticles, and red blood cell Annexin V binding. Poly-N-acetyl glucosamine fibers increased the production of thromboxane B2 by PRP.

CONCLUSION

Poly-N-acetyl glucosamine slurry activates platelets.

Identification of the Amino Acid Residues of the Platelet Glycoprotein Ib (GPIb) Essential for the von Willebrand Factor Binding by Clustered Charged-to-Alanine Scanning Mutagenesis

At the site of vascular injury, von Willebrand factor (VWF) mediates platelet adhesion to subendothelial connective tissue through binding to the N-terminal domain of the alpha chain of platelet glycoprotein Ib (GPIbalpha). To elucidate the molecular mechanisms of the binding, we have employed charged-to-alanine scanning mutagenesis of the soluble fragment containing the N-terminal 287 amino acids of GPIbalpha. Sixty-two charged amino acids were changed singly or in small clusters, and 38 mutant constructs were expressed in the supernatant of 293T cells. Each mutant was assayed for binding to several monoclonal antibodies for human GPIbalpha and for ristocetin-induced and botrocetin-induced binding of 125I-labeled human VWF. Mutations at Glu128, Glu172, and Asp175 specifically decreased both ristocetin- and botrocetin-induced VWF binding, suggesting that these sites are important for VWF binding of platelet GPIb. Monoclonal antibody 6D1 inhibited ristocetin- and botrocetin-induced VWF binding, and a mutation at Glu125 specifically reduced the binding to 6D1. In contrast, antibody HPL7 had no effect for VWF binding, and mutant E121A reduced the HPL7 binding. Mutations at His12 and Glu14 decreased the ristocetin-induced VWF binding with normal botrocetin-induced binding. Crystallographic modeling of the VWF-GPIbalpha complex indicated that Glu128 and Asp175 form VWF binding sites; the binding of 6D1 to Glu125 interrupts the VWF binding of Glu128, but HPL7 binding to Glu121 has no effect on VWF binding. Moreover, His12 and Glu14 contact with Glu613 and Arg571 of VWF A1 domain, whose mutations had shown similar phenotype. These findings indicated the novel binding sites required for VWF binding of human GPIbalpha.

Endothelial microparticles released in thrombotic thrombocytopenic purpura express von Willebrand factor and markers of endothelial activation

It has been suggested that endothelial apoptosis is a primary lesion in the pathogenesis of thrombotic thrombocytopenic purpura (TTP). We tested this hypothesis by examining the phenotypic signatures of endothelial microparticles (EMP) in TTP patients. In addition, the effect of TTP plasma on microvascular endothelial cells (MVEC) in culture was further delineated. EMP released by endothelial cells (EC) express markers of the parent EC; EMP released in activation carry predominantly CD54 and CD62E, while those in apoptosis CD31 and CD105. We investigated EMP release in vitro and in TTP patients. Following incubation of MVEC with TTP plasma, EMP and EC were analysed by flow cytometry for the expression of CD31, CD51, CD54, CD62E, CD105, CD106 and von Willebrand factor (VWF) antigen. EMP were also analysed in 12 TTP patients. In both EC and EMP, CD62E and CD54 expression were increased 3- to 10-fold and 8- to 10-fold respectively. However, CD31 and CD105 were reduced 40-60% in EC but increased twofold in EMP. VWF expression was found in 55 +/- 15% of CD62E+ EMP. Markers of apoptosis were negative. In TTP patients, CD62E+ and CD31+/CD42b- EMP were markedly elevated, and preceded and correlated well with a rise in platelet counts and a fall in lactate dehydrogenase. CD62E+ EMP (60 +/- 20%) co-expressed VWF and CD62E. The ratio of CD31+/42b- to CD62E+ EMP exhibited a pattern consistent with activation. In conclusion, our studies indicate endothelial activation in TTP. EMP that co-express VWF and CD62E could play a role in the pathogenesis of TTP.

Cell-to-cell variability in the differentiation program of human megakaryocytes

Differentiation of CD34(+) stem/progenitor cells into megakaryocytes is thought to be a uniform, unidirectional process, in which cells transform step by step from less differentiated precursor stages to more differentiated megakaryocytes. Here we propose the concept and present evidence based on single-cell analysis that differentiation occurs along multiple, partially asynchronous routes. In all CD34(+) cells cultured with thrombopoietin, surface appearance of glycoprotein IIIa (GPIIIa) preceded that of GPIb, indicating that the expression of these glycoproteins occurs in a timely ordered manner. Cellular F-actin content increased in parallel with GPIb expression. Only cells that expressed GPIb were polyploid, pointing to co-regulation of GPIb expression, actin cytoskeleton formation and polyploidization during megakaryocytopoiesis. On the other hand, most progenitor cells responded to thrombin but not to thromboxane A(2) analogue by rises in cytosolic [Ca(2+)](i). The appearance of thromboxane-induced responses during megakaryocytopoiesis was not strictly linked to glycoprotein expression, because cells showed responsiveness either before or after GPIb expression. The same non-strictly sequential pattern was observed for disappearance of the Ca(2+) response by prostacyclin mimetic; in some megakaryocytes it occurred before and in others after GPIb expression. Thus, megakaryocytic differentiation follows along independent routes that are either strictly sequential (GPIIIa and GPIb expression) or proceed at different velocities (Ca(2+) signal regulation).

Elevated FXIIIA and serine proteases upon filtration of platelet concentrate on negatively charged filters: comparison with other established haemostatic markers of platelet activation and storage lesion

Tests for the assessment of the platelet storage lesion are still evolving. To be of clinical value, they should reflect one of the physiological functions of platelets and should be simple, practical and fit in to the transfusion laboratory setting. In this respect, FXIIIA, Annexin V, vWF and glycocalicin (GC), measured by the established ELISA technology, are of particular relevance, as their roles in the maintenance of haemostatic balance are fully established and they can be released or cleaved upon platelet activation/injury/microvesiculation. The usefulness of these haemostatic markers for in process validation/process qualification, in particular subsequent to harsh procedures and when blood components come in contact with various artificial surfaces, is established and compared with a practical test for routine quality monitoring of platelet functional activity and aggregation states test.

A possible receptor for beta 2 glycoprotein I on the membrane of hepatoma cell line smmc7721

OBJECTIVES

To study the interaction of beta-2-glycoprotein I (beta 2GPI) with the membrane of hepatocytes and determine whether beta 2GPI participates in HBV infection.

METHODS

Ligand blotting, fluorescence microscopy, and fluorescence activated cell sorter (FACS) analysis were used to detect the specific interaction of beta 2GPI with the hepatoma cell line smmc7721, the gastric carcinoma cell line SGC7901, and the lymphoma cell line HL-60.

RESULTS

A specific 40 kDa beta 2GPI band was observed by ligand blotting in the case of smmc7721 cells. No such band was observed in SGC7901 or HL-60 cells. Fluorescence microscopy also revealed specific binding of FITC-beta 2GPI to smmc7721 cells, but neither to SGC7901 nor HL-60 cells. FACS analysis demonstrated that the binding rate of FITC-beta 2GPI to smmc7721 cells was significantly higher than these in SGC7901 and HL-60 cells (P < 0.01). The binding rate to smmc7721 cells did not increase with increasing amounts of FITC-beta 2GPI.

CONCLUSIONS

There is a specific beta 2GPI-binding protein on the membrane of hepatoma cells in cell line smmc7721 which as the beta 2GPI receptor may participate in HBV infection of hepatocytes.

Paraformaldehyde fixation induces a systematic activation of platelets

In whole blood flow cytometric platelet assays sample fixation using paraformaldehyde (PFA) is considered very advantageous to prevent spontaneous activation of platelets in vitro. However, fixation is an important variable in activation assays and its influence on platelets is poorly understood. Using a direct immunofluorescence labelling technique and whole blood flow cytometry, the effect of PFA fixation was investigated for 4 different epitopes on platelet surface each of which mirrors a different aspect of platelet activation, namely P-selectin (CD62P), GP IIbIIa complex (CD41), the fibrinogen binding site of the activated GP IIaIIIb complex (PAC-1) and GP Ib-V-IX complex (CD42b). Platelets fixed with PFA (0.5%) before antibody labelling showed significant (P<0.01) increases in mean fluorescence intensity (MFI) of CD62P (1.10 +/- 0.14 vs. 0.94 +/- 0.12 arbitrary units of fluorescence), CD41 (27.3 +/- 6.3 vs. 15.6 +/- 2.1) and PAC-1 (6.21 +/- 1.25 vs. 0.55 +/- 0.12) when compared to unfixed samples. At the same time, MFI of CD42b was reduced from 28.2 +/- 1.6 to 22.6 +/- 2.3 (P<0.01). When fixation was initiated after antibody labelling, we observed less prominent increases in MFI of CD41 (P<0.05) and PAC-1 (P<0.05) while there was no significant difference for CD62P and rather a moderate rise in CD42b than a decrease (P<0.05). Because these alterations cannot be explained by unspecific effects only, it must be concluded that PFA induces a systematic stimulation of platelets. The lowest in vitro platelet activation was found when antibody labelling was started immediately after blood sampling and when samples were analysed within 10 minutes after being stored without fixation of 4 degrees C in the dark.

Course of indicators of thrombin activity in the early phase of acute myocardial infarction: effect of fibrinolytic therapy and acute percutaneous coronary angioplasty

We evaluated assay systems for detection of in vivo thrombin activity in patients with acute myocardial infarction. The study included 31 consecutive patients with acute myocardial infarction treated either with fibrinolytic therapy (FLT), or acute PTCA. Blood samples were drawn at admission, after 30 min, 1 h, 3 h, 6 h, 12 h, 24, and 48 h. Assays related to the enzymatic action of thrombin included fibrinopeptide A ELISA, a novel latex-enhanced photometric immunoassay for soluble fibrin complexes, fibrin monomer antigen, D-dimer antigen, and soluble platelet glycoprotein V, which is released from the platelet surface by thrombin cleavage. The soluble fibrin assay displayed a high degree of correlation with fibrinopeptide A, and no correlation with D-dimer antigen, indicating that this parameter allows monitoring of in vivo thrombin activity in patients with acute myocardial infarction. Fibrin monomer antigen, and D-dimer antigen, were influenced by FLT, indicating cross-reactivity with proteolytic fragments of fibrin. No significant changes in soluble glycoprotein V were observed. The results show that the novel soluble fibrin assay appears to be a promising method for measurement of in vivo fibrin formation in patients with acute myocardial infarction, irrespective of the primary treatment decision for FLT or acute PTCA.