Adhesion between neutrophils and platelets: a modulator of thrombotic and inflammatory events?

The differential formation and composition of leukocyte-platelet aggregates induced by various cellular stimulants

BACKGROUND

Leukocyte-platelet aggregates comprise a pathogenic link between hemostasis and immunity, but the prerequisites and mechanisms of their formation remain not understood.

AIMS

To quantify the formation, composition, and morphology of leukocyte-platelet aggregates in vitro under the influence of various cellular activators.

METHODS

Phorbol-12-myristate-13-acetate (PMA), lipopolysaccharide (LPS), thrombin receptor-activating peptide (TRAP-6), and adenosine diphosphate (ADP) were used as cellular activators. Flow cytometry was utilized to identify and quantify aggregates in whole human blood and platelet-rich plasma. Cell types and cellular aggregates were identified using fluorescently labeled antibodies against the appropriate cellular markers, and cell activation was assessed by the expression of appropriate surface markers. For confocal fluorescent microscopy, cell membranes and nuclei were labeled. Neutrophil-platelet aggregates were studied using scanning electron microscopy.

RESULTS

In the presence of PMA, ADP or TRAP-6, about 17-38 % of neutrophils and 61-77 % of monocytes formed aggregates with platelets in whole blood, whereas LPS did not induce platelet aggregation with either neutrophils or monocytes due the inability to activate platelets. Similar results were obtained when isolated neutrophils were added to platelet-rich plasma. All the cell types involved in the heterotypic aggregation expressed molecular markers of activation. Fluorescent and electron microscopy of the aggregates showed that the predominant platelet/leukocyte ratios were 1:1 and 2:1.

CONCLUSIONS

Formation of leukocyte-platelet aggregates depends on the nature of the cellular activator and the spectrum of its cell-activating ability. An indispensable condition for formation of leukocyte-platelet aggregates is activation of all cell types including platelets, which is the restrictive step.

Activation of canine neutrophils by platelet-activating factor

Neutrophils are essential for innate immunity as the first line of defence. Neutrophils act as phagocytic white blood cells to kill bacteria and other microorganisms. A strong respiratory burst of neutrophils, dependent on reactive oxygen species, is produced during phagocytosis. Platelet-activating factor (PAF) is a signalling molecule with several prominent roles in tissue injury, inflammation, and platelet aggregation. However, the detailed mechanisms and intracellular signalling pathways involved in PAF-mediated neutrophil activation remain unclear. Here, we investigated the effect of PAF on changes in calcium concentration ([Ca²⁺]_i) and oxygen radical (O₂^-) generation in activating canine neutrophils. We further evaluated these effects of PAF with inhibition of G protein-coupled receptors using the specific inhibitor suramin. Blood samples were collected from a total of five dogs and neutrophils were isolated. PAF stimulation of canine neutrophils caused an increase in [Ca²⁺]_i as well as the generation of O₂^-, and the PAF receptor was sensitive to suramin. The results suggested that PAF stimulation of canine neutrophils may cause Ca²⁺ influx from the endoplasmic reticulum into the cytoplasm (as the first wave) and then trigger store-operated Ca²⁺ entry (as the second wave), which is an important intracellular signal transduction pathway for neutrophil activation. Furthermore, O₂^- generation by PAF stimulation may depend on the intracellular signalling pathway, with increasing inositol trisphosphate levels and [Ca²⁺]_i via G protein-coupled receptors. The finding that PAF-activating platelet aggregation is involved in canine neutrophil activation suggests a close relationship between haemostasis and neutrophil activation in dogs, offering new insight into the response to infection.

State-of-the-Art Review: Usefulness of Laboratory Techniques for Evaluating Antithrombotic Efficacy of New Therapeutic Strategies

New drugs and new therapeutic strategies are being introduced for the prevention and the management of cardiovascular and thromboembolic disorders. Extensive clinical studies and large-scale epidemiological investigations are conducted to demonstrate the efficacy of these therapeutic approaches. Laboratory assays are invaluable tools for this exploration. We discuss how the new understanding concerning the regulation of the coagulolytic equilibrium offers novel investigation tools. Parameters reflecting the activities of new drugs targeted to their impact site and presenting few side effects are available. In addition to global clotting methods and chromogenic substrate-based assays, introduction of immunoassays has allowed measurement of most of the molecular markers of hemostatic activation. We recommend use of a panel of markers exploring the endothelial damage, the blood cell involvement, the early coagulant pathways' activation (XIIa and VIIa), the thrombin-formation pathways, the fibrin formation, and the evaluation of the global fibrinolytic capacity. When related to the clinical end points, all these laboratory assays offer useful and reliable monitoring of new drugs. They contribute to the establishment of new therapeutic strategies. Key Words: Hemostasis—Activation—Antithrombotic—Therapy— Laboratory monitoring.

Endothelial progenitor cells inhibit platelet function in a P-selectin-dependent manner

Background

The role of endothelial progenitor cells (EPCs) in vascular repair is related to their recruitment at the sites of injury and their interaction with different components of the circulatory system. We have previously shown that EPCs bind and inhibit platelet function and impair thrombus formation via prostacyclin secretion, but the role of EPC binding to platelet P-selectin in this process has not been fully characterized. In the present study, we assessed the impact of EPCs on thrombus formation and we addressed the implication of P-selectin in this process.

Methods

EPCs were generated from human peripheral blood mononuclear cells cultured on fibronectin in conditioned media. The impact of EPCs on platelet aggregation and thrombus formation was investigated in P-selectin deficient (P-sel^−/−) mice and their wild-type (WT) counterparts.

Results

EPCs significantly and dose-dependently impaired collagen-induced whole blood platelet aggregation in WT mice, whereas no effects were observed in P-sel^−/− mice. Moreover, in a ferric chloride-induced arterial thrombosis model, infusion of EPCs significantly reduced thrombus formation in WT, but not in P-sel^−/− mice. Furthermore, the relative mass of thrombi generated in EPC-treated P-sel^−/− mice were significantly larger than those in EPC-treated WT mice, and the number of EPCs recruited within the thrombi and along the arterial wall was reduced in P-sel^−/− mice as compared to WT mice.

Conclusion

This study shows that EPCs impair platelet aggregation and reduce thrombus formation via a cellular mechanism involving binding to platelet P-selectin. These findings add new insights into the role of EPC-platelet interactions in the regulation of thrombotic events during vascular repair.

Can the antiplatelet effects of cangrelor be reliably studied in mice under in vivo and in vitro conditions using flow cytometry?

BACKGROUND

The effects of blood platelet inhibitors are often not quite equivalent under in vivo and in vitro conditions. Amongst various models of human pathology using laboratory animals, mice offer several benefits that make them convenient tools for studying the putative therapeutic value of various compounds. However, despite its advantages, the mouse model has methodological limitations concerning the small amount of blood available and technical difficulties with its collection. Among the variety of available methods used to study blood platelet activation and/or reactivity, flow cytometry seems an attractive technique that largely minimizes the constraints of using small rodents and enables outcomes of laboratory research to be transferred successfully to clinical practice. In this study we aimed at a critical evaluation of the optimal discriminative flow cytometric protocol, useful for reliable studies of the effect of cangrelor, a P2Y12 receptor antagonist, on mouse platelets under in vitro and in vivo conditions.

METHODS

Blood samples were drawn from two-month-old female BALB/c mice. Protocols differing in methods of anesthesia, blood withdrawal, anticoagulation, gating antibodies, blood preparation and fixation were tested to optimize the one best suited to discrimination between resting and activated platelets. The antiplatelet capabilities of cangrelor were tested in vitro (140 μM in whole blood) and in vivo (7.8 mg/kg b.w. administered once, directly into the bloodstream through the vena cava of the anesthetized animal, 15 min prior to blood withdrawal). Expressions of P-selectin, activated α(IIb)β3 complex and GPIba were monitored using two-color flow cytometry.

RESULTS

"Washed blood" anticoagulated with low molecular weight heparin demonstrated the best discrimination between circulating (resting) platelets and upon their in vitro response to thrombin, collagen or ADP in freshly-stained unfixed cell suspensions. Cangrelor inhibited the expression of the active form of the integrin a(IIb)β3 to approximately the same extent under in vitro and in vivo conditions (84.5 ± 7.7% vs. 75.4 ± 19.5% for the in vitro and in vivo approaches, respectively, n.s.).

CONCLUSIONS

The agreement between the in vivo and in vitro approaches with respect to cangrelor-inhibited hallmarks of blood platelet activation and reactivity supports our proposal that flow cytometry is useful and reliable for determining the effects of antiplatelet agents on the activation of circulating platelets in the mouse model, as well as the in vitro response of platelets to agonists.

Platelet-neutrophil aggregate formation in blood samples from dogs with systemic inflammatory disorders

OBJECTIVE

To evaluate platelet-neutrophil aggregate (PNA) formation and neutrophil shape as indicators of neutrophil activation in dogs with systemic inflammatory diseases and after blood sample incubation with various platelet and neutrophil agonists.

ANIMALS

20 dogs with systemic inflammatory response syndrome (SIRS) and 10 healthy Beagles.

PROCEDURES

Neutrophils were isolated from blood samples directly after blood sample collection and after incubation of blood samples with phorbol myristate acetate, collagen, adenosine diphosphate, epinephrine, or various concentrations of lipopolysaccharide or arachidonic acid. CD61+ neutrophils as an indicator of PNA formation were evaluated, and neutrophil size and granularity were assessed via flow cytometry.

RESULTS

Dogs with SIRS had more PNA formation, larger neutrophil size, and less granularity relative to control dogs, but no differences were evident when these dogs were grouped by whether they had sepsis (n = 6) or disseminated intravascular coagulation (12). A significant increase in PNA formation occurred after neutrophil incubation with all agonists, and incubation with phorbol myristate acetate elicited the strongest response. Neutrophils increased in size and decreased in granularity after incubation with all agonists except epinephrine. Incubation with lipopolysaccharide or arachidonic acid resulted in a dose-dependent effect on PNA formation and neutrophil shape.

CONCLUSIONS AND CLINICAL RELEVANCE

SIRS appeared to increase the degree of PNA formation and neutrophil shape change. Similar changes after neutrophil incubation with platelet agonists suggested that platelet activation has a role in PNA formation. Additional studies are necessary to determine the clinical importance and diagnostic value of PNA formation in dogs with SIRS and sepsis.

Targeting P-selectin in acute pancreatitis

IMPORTANCE OF THE FIELD

Acute pancreatitis (AP) is a multifactorial disorder not fully understood yet. In particular, the pathogenetic pathways promoting a severe life-threatening course of AP are the subject of ongoing investigations. P-selectin has been shown to play a central role in the complex pathophysiology in AP as well as various other inflammatory conditions.

AREAS COVERED IN THIS REVIEW

P-selectin function in AP is reviewed with focus on its dual function as a mediator of leukocyte recruitment and cell adhesion, which implies the unique effect of linking both inflammation and coagulation, especially in the progression from mild to severe necrotizing AP. Potential therapeutic aspects are discussed with regard to the clinical situation.

WHAT THE READER WILL GAIN

A better understanding of the pathogenic role of P-selectin in AP and of the rationale for a therapeutic blockade.

TAKE HOME MESSAGE

P-selectin is a glycoprotein that mediates the adhesion of activated platelets and leukocytes to the vessel wall in various inflammatory conditions. Both pathophysiological steps are closely linked and play a key role in the course of severe AP. A treatment approach by inhibition of P-selectin could be of distinct interest as a therapeutic option in severe AP.

Recombinant P-selectin glycoprotein-ligand-1 delays thrombin-induced platelet aggregation: a new role for P-selectin in early aggregation

1. P-selectin is involved, with P-selectin glycoprotein (GP)-ligand-1 (PSGL-1), in platelet/leukocyte interactions during thrombo-inflammatory reactions; it also stabilizes platelet aggregates. Its antagonism accelerates thrombolysis and enhances the anti-aggregatory effects of GPIIb-IIIa inhibitors. This study was designed to investigate the mechanisms of P-selectin-mediated platelet aggregation. 2. In freshly isolated human platelets, P-selectin translocation after thrombin stimulation increased rapidly to 48, 72, and 86% positive platelets after 60, 120, and 300 s, respectively. Platelet aggregation at 60 s post-stimulation averaged 46.7 +/- 1.9% and its extent followed closely the kinetics of P-selectin translocation. 3. Pre-treatment of platelets with P-selectin antagonists, a recombinant PSGL-1 (rPSGL-Ig) or a blocking monoclonal antibody, significantly delayed platelet aggregation in a dose-dependent manner. At 100 microg ml(-1) of rPSGL-Ig, platelet aggregation was completely inhibited up to 60 s post-stimulation and increased thereafter to reach maximal aggregation at 5 min. The second phase of platelet aggregation, in the presence of rPSGL-Ig, was completely prevented by the addition of a GPIIb-IIIa antagonist (Reopro) at 60 s, whereas its addition in the absence of rPSGL-Ig was without any significant effect. 4. Combination of rPSGL-Ig with Reopro or with an inhibitor of Pi3K (LY294002), which reduces GPIIb-IIIa activation, showed to be more effective in inhibiting platelet aggregation, in comparison to the effects observed individually. 5. rPSGL-Ig blocks P-selectin, whereas Reopro and LY294002 block GPIIb-IIIa and its activation, respectively, without a major effect on the percentage of platelets expressing P-selectin. 6. In summary, platelet P-selectin participates with GPIIb-IIIa in the initiation of platelet aggregation. Its inhibition, with rPSGL-Ig, delays the aggregation process and increases the anti-aggregatory potency of Reopro. Thus, combination of P-selectin and GPIIb-IIIa antagonism may constitute a promising therapeutic option in the management of thrombotic disorders.

Platelet-leukocyte interactions in hemodialysis patients: culprit or bystander?

The formation of circulating platelet-leukocyte complexes has been observed in a variety of conditions and may be pathophysiologically significant. Platelet-leukocyte interactions in fact facilitate metabolic cooperation and mutual activation, which may be of relevance in many biological processes including inflammation, atherogenesis and hemostasis. During hemodialysis procedure, the series of reactions that can occur upon blood contact with the foreign membrane surface may involve a variety of changes affecting almost every cellular and plasmatic component of the blood. This article reviews the evidence for abnormal interactions between circulating platelets and leukocytes in uremic patients undergoing maintenance hemodialysis and the pathophysiologic implications which may stem from such interactions.

Functional role of NADPH oxidase in activation of platelets

Involvement of phagocyte NADPH oxidase in host defense response is well established. In contrast, little is known about the functional role of NADPH oxidase in platelets. In this study, we analyzed involvement of platelet NADPH oxidase in aggregation of human platelets and in amplification of production of reactive oxygen species (ROS) by activated human neutrophils. Apocynin, a known NADPH oxidase inhibitor, as well as superoxide dismutase mimetic Mn(III)tetrakis(1-methyl-1-pyridyl)porphyrin, inhibited ROS generation by collagen-activated platelets, collagen-induced aggregation of platelets, as well as collagen-induced release of thromboxane B2. These data suggest the key role of intracellular ROS derived from NADPH oxidase in the control of thromboxane A2 (TXA2) production in platelets stimulated by collagen. Apocynin also inhibited thrombin-induced ROS production and thrombin-induced platelet aggregation. Activation of neutrophils with latex resulted in an outburst of ROS that was inhibited by apocynin. ROS production by latex-stimulated platelets was modest and also inhibited by apocynin. However, when a mixture of platelets and neutrophils was stimulated with latex, ROS production was three to six times higher in comparison with activation of neutrophils alone. Platelet-dependent augmentation of neutrophil ROS production was abrogated by TXA2 synthase inhibitor (furegrelate, 1 microM) or by aspirin (300 microM). In summary, NADPH oxidase in platelets seems to play a major role as an intracellular signaling mechanism in the activation of platelets. However, in host defense response involving neutrophils and platelets, platelets enhance ROS production by neutrophils and possibly their cytotoxic potential via the release of TXA2, which in turn in platelets is not affected by the extracellular release of free radicals.

Platelet-leukocyte interaction and platelet activation in migraine: a link to ischemic stroke?

OBJECTIVES

Migraine has been identified as an independent risk factor for ischemic stroke. Both neurogenic inflammation and platelet activation have been linked to the pathophysiology of migraine. Increased platelet activation results in up-regulation of specific binding to leukocytes which promotes pro-inflammatory leukocyte secretion and their tethering to endothelium, a mechanism that has been demonstrated in stroke and which could provide a link to migraine. We aimed to determine whether platelet-leukocyte aggregation is increased in migraine patients outside an acute attack.

METHODS

Seventy two patients with migraine according to IHS criteria were compared to a control group (n = 72). Whole blood flow cytometry was used to quantify the activation dependent P selectin on the platelet, and to assess the fraction of platelets bound to the different leukocyte subsets.

RESULTS

Migraine patients showed significantly more platelet-leukocyte aggregates compared to the control subjects (p = 0.003). This effect was driven by an increased polymorphonuclear cell-platelet aggregation (p = 0.003) whereas platelet aggregation with monocytes and lymphocytes was not. Platelet activation was also increased (p = 0.001).

CONCLUSIONS

In migraine pro-inflammatory platelet adhesion to leukocytes occurs during the headache free interval similar to that seen in acute coronary and cerebrovascular syndromes. This may suggest a link between migraine and stroke on a cellular level.

Obligatory role of lipid mediators in platelet-neutrophil adhesion

Platelet-neutrophil interactions play an important role in thrombotic and inflammatory responses. Although it is well known that adhesion of platelets to neutrophils requires interactions of adhesion molecules on platelets such as P-selectin, or GPIIb/IIIa with their counterparts on neutrophils, little is known on the role of lipid mediators in this response. Here we studied involvement of thromboxane (TX) A2, platelet activating factor (PAF) and cysteinyl leukotrienes (cysLTs) in the mechanisms of platelet-neutrophil adhesion that was induced by thrombin (10-100 mU/ml), fMLP (0.01-1 microM) or LPS (0.001-100 microg/ml). All three stimulators in a concentration- and time-dependent manner induced platelet-neutrophil adhesion as quantified by the method of Jungi et al. [Blood 67(3) (1986) 629]. Platelet-neutrophil adhesion induced by each of the three activators was inhibited by blocking antibodies towards P-selectin, GPIIb/IIIa or CD18, but it was not affected by anti-E selectin antibody. Moreover, platelet-neutrophil adhesion induced by thrombin, fMPL or LPS was inhibited by the inhibitor of cyclooxygenase (aspirin), by TXA2 synthase inhibitor (camonagrel), by PAF receptor antagonist (WEB 2170), by the inhibitor of FLAP (MK 886) and by cysLTs receptors antagonist (MK 571). On the other hand, the selective inhibitor of COX-2 (rofecoxib) as well as the inhibitor of cytochrome P450-dependent monoxygenase (17-ODYA) were ineffective. In summary, adhesion of platelets to neutrophils is regulated not only by specific interaction between adhesion molecules on platelets and neutrophils, but also by lipid mediators such as TXA2, PAF and cysLTs released upon activation of platelets or/and neutrophils.

Relation of interleukin-6, C-reactive protein, and the prothrombotic state to transesophageal echocardiographic findings in atrial fibrillation

Atrial fibrillation (AF) is a major cause of morbidity and mortality from stroke due to thromboembolism from the fibrillating left atrium, including its appendage. We hypothesized that indexes of inflammation (as indicated by C-reactive protein and interleukin-6) and indexes of the prothrombotic state in AF that represent platelet activation (soluble P-selectin levels), endothelial damage or dysfunction (von Willebrand factor), coagulation (tissue factor and fibrinogen), and hemorrheology (plasma viscosity and hematocrit) would be related to the presence of thromboembolic predictors on transesophageal echocardiography in patients with long-term AF. To test this hypothesis, we recruited 37 patients with long-term AF who were receiving warfarin therapy with an international normalized ratio of > or =2.0 for > or =3 weeks before transesophageal echocardiography. Twenty-two patients had dense spontaneous echo contrast (SEC) visible in the left atrium or left atrial appendage, 10 had complex atheromatous plaque in the descending aorta, 11 had peak left atrial appendage velocities < or =0.2 m/s, and 3 had thrombus visible in the left atrial appendage. Twenty-eight patients had > or =1 transesophageal echocardiographic (TEE) risk factor for thromboembolism. Plasma levels of C-reactive protein (p = 0.03) and soluble P-selectin (p = 0.04) and hematocrit (p = 0.004) were higher among patients with AF with dense SEC than among those without. No significant associations were found for other TEE risk factors. Hematocrit was the only variable significantly associated with the presence of > or =1 TEE risk factor among patients with AF (p = 0.007) and the only independent associate of dense SEC after multivariate analysis (relative risk 1.4, 95% confidence interval 1.1 to 1.6) per 1% increase in hematocrit (p = 0.003, r(2) = 0.22). Although hematocrit was the only independent associate of dense SEC and > or =1 TEE risk factor, significant associations between dense SEC and the 2 indexes, C-reactive protein and soluble P-selectin, may indicate that mechanisms other than stasis are present with dense SEC. These observations support an "inflammatory hypothesis" in the pathogenesis of SEC that may have implications for thrombogenesis in AF.

Platelets in inflammatory bowel disease: clinical, pathogenic, and therapeutic implications

Both Crohn's disease (CD) and ulcerative colitis (UC) are associated with abnormalities of platelet number and function. In the peripheral circulation the state of platelet activation is typically increased, and inflammatory bowel disease (IBD)-involved mucosa frequently contains platelet aggregates within mucosal microthrombi. The relevance of platelet dysfunction to IBD pathogenesis is still unclear, but there is solid evidence demonstrating that platelets, in addition to their traditional role in hemostasis, can also function as potent proinflammatory cells. Upon activation, platelets secrete a large number of biologically active molecules able to induce or amplify an inflammatory process through many of the same cellular and molecular pathways conventionally utilized by immune cells mediating IBD. The aim of this article is to review data on the existence of platelet dysfunction in IBD, substantiate platelets' inflammatory potential, discuss the implications of abnormal platelet activity for chronic intestinal inflammation, and consider the potential benefits of platelet modulation for treatment of IBD.

The role of soluble cell adhesion molecules in patients with suspected deep vein thrombosis

Activation of the endothelium, platelets and leukocytes has been shown to play an important role in the aetiology of deep venous thrombosis (DVT) in in-vitro experiments, resulting in the release of soluble cell adhesion molecules (sCAMs). We therefore assessed the value of soluble intracellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble E-selectin and soluble P-selectin for the diagnostic process in 69 consecutive patients with suspected DVT. Final diagnosis was based on the results of Duplex sonography or ascending venography. Thirty-seven patients (53.6%) finally suffered from DVT. Mean levels of sVCAM-1 were 589 +/- 530 ng/ml for controls and 587 +/- 328 ng/ml for patients. Corresponding levels concerning sICAM-1 were 316 +/- 161 and 342 +/- 186 ng/ml, those concerning soluble E-selectin were 54 +/- 38 and 42 +/- 18 ng/ml, and those concerning soluble P-selectin were 94 +/- 37 and 99 +/- 36 ng/ml (all P > 0.05). There was no significant correlation of the thrombus extension (all P > 0.05) or the duration of symptoms with sCAMs (all P > 0.05). In conclusion, we detected no significant differences concerning the concentration of four major sCAMs between patients with DVT and controls, so their assessment does not add any useful information for the diagnostic process of DVT.

Peroxynitrite in myocardial ischemia-reperfusion injury

Peroxynitrite is a highly reactive oxidant which is produced during reperfusion of the ischemic heart. The role that this molecule plays in reperfusion injury has been controversial. Many investigations have demonstrated toxic effects of peroxynitrite, whereas others have found it to be protective during reperfusion. This review surveys evidence supporting both sides and proposes that peroxynitrite is a dichotomous molecule with beneficial and detrimental effects on the reperfused heart. Its toxic effects are mediated by modification and activation of a variety of targets (including poly (ADP) ribose synthetase and matrix metalloproteinases) while its beneficial effects are primarily mediated through its reaction with thiols, resulting in the formation of NO donor compounds (S-nitrosothiols).

Mechanisms of platelet-neutrophil interactions and effects on cell filtration in septic shock

ABSTRACT-We examined the mechanisms and the adhesive molecules mediating platelet-neutrophil adhesion in patients with septic shock. Neutrophils, platelets, and platelet poor plasma (NPPP) were isolated from 12 normal volunteers. Platelets and neutrophils were stimulated with platelet poor plasma (SPPP) removed from 12 patients in septic shock. Cell adhesion was assessed by filtration through 5-microm pore filters and by flow cytometry. Blocking monoclonal antibodies were used against the platelet and neutrophil surface receptors glycoprotein complex IIb/IIla, P-selectin, ICAM-2, CD11a, CD11b, and CD18. The filtration pressure (Pi) of cells suspended in SPPP was significantly greater than that of cells suspended in NPPP (24 +/- 1.0 mmHg vs. 14 +/- 1.0 mmHg; P< 0.05). The difference between the Pi of cells suspended in SPPP or NPPP (deltaPi SPPP-NPPP) in the presence of monoclonal antibodies anti-CD41, anti-CD62P, abciximab, anti-CD11a, anti-CD11b, and anti-CD18 was significantly less than the APi SPPP-NPPP of cell suspensions without the addition of these monoclonal antibodies (P < 0.01). The greatest reduction in Pi occurred when platelet receptor P-selectin was blocked simultaneously with the CD11b receptor on the neutrophil as compared to all other single blocking monoclonal antibodies or combinations of monoclonal antibodies. The mean fluorescence of activated platelet CD63-PE binding to neutrophils suspended in SPPP was significantly greater than that of cells suspended in NPPP (780 +/- 130 Ifu vs. 295 +/- 35 Ifu; P < 0.05). The greatest attenuation in mean fluorescence occurred by blocking the P-selectin receptor on the platelet simultaneously with CD11b receptor on the neutrophil. We conclude that platelet-neutrophil aggregation is increased in septic shock. This aggregation is mediated by the interaction of multiple platelet and neutrophil surface receptors. The platelet receptor P-selectin and the neutrophil receptor CD11b/CD18 appear to play the most important role in these interactions.

Circulating monocyte-platelet aggregates are an early marker of acute myocardial infarction

OBJECTIVES

We investigated whether elevated levels of circulating monocyte-platelet aggregates (MPA) can be used to identify patients with acute myocardial infarction (AMI).

BACKGROUND

Commonly used blood markers of AMI reflect myocardial cell death, but do not reflect the earlier pathophysiologic processes of plaque rupture, platelet activation and resultant thrombus formation. Circulating MPA form after platelet activation.

METHODS

In a single center between October 1998 and November 1999, we measured circulating MPA in a blinded fashion by whole blood flow cytometry in 211 consecutive patients who presented to the emergency department (ED) with chest pain and were admitted to rule out AMI. Acute myocardial infarction was diagnosed by a CK-MB fraction greater than three times control.

RESULTS

Patients with AMI (n = 61), as compared with those without AMI (n = 150), had significantly higher numbers of circulating MPA (11.6 +/- 11.4 vs. 6.4 +/- 3.6, mean +/- SD, p < 0.0001). After controlling for age, the adjusted odds of developing AMI for patients in the 2nd, 3rd and 4th quartiles of MPA, in comparison with patients in the lowest quartile (odds ratio = 1.0), were 2.1 (95% confidence interval [CI]: 0.7, 6.8), 4.4 (95% CI: 1.5, 13.1) and 10.8 (95% CI: 3.6, 32.0), respectively. The number of circulating MPA in patients with AMI presenting within 4 h of symptom onset (14.4) was significantly greater than those presenting after 4 h (9.4) and after 8 h (7.0), (p < 0.001). Of the 61 patients with AMI, 35 (57%) had a normal creatine kinase isoenzyme ratio at the time of presentation to the ED, but had high levels of circulating MPA (13.3).

CONCLUSIONS

Circulating MPA are an early marker of AMI.

Recombinant soluble p-selectin glycoprotein ligand-1-Ig reduces restenosis through inhibition of platelet-neutrophil adhesion after double angioplasty in swine

BACKGROUND

P-selectin mediates leukocyte recruitment to activated platelets and endothelium through its high-affinity receptor P-selectin glycoprotein ligand-1 (PSGL-1). Platelet and leukocyte activation and binding have been reported after coronary angioplasty and were correlated with restenosis. We investigated the effect of a recombinant soluble PSGL-1 (rPSGL-Ig) on the adhesion of platelets and neutrophils and the development of restenosis after double arterial injury.

METHODS AND RESULTS

Four weeks after angioplasty of both carotid arteries in pigs, a second angioplasty was performed at the same sites, 15 minutes after a single administration of vehicle or rPSGL-1 (1 mg/kg IV). Animals were euthanized 1 hour, 4 hours, 1 week, or 4 weeks later. Adhesion of autologous (51)Cr-platelets and (111)In-neutrophils was quantified and histological/morphometric analyses were performed. Although rPSGL-Ig did not affect adherence of these cells 1 hour after injury, it significantly reduced the adhesion of platelets (50% at 4 hours and 85% at 1 week) and neutrophils (50% at 4 hours and 78% at 1 week) to deeply injured arteries. At 4 weeks, the residual lumen was 63% larger in rPSGL-Ig-treated arteries as compared with control arteries (6.1+/-0.6 versus 3.8+/-0.1 mm(2); P:<0.002). The neointimal area was slightly reduced (0.5 in rPSGL-Ig versus 0.7 mm(2) in control). The ratio of the external elastic lamina of injured to uninjured reference segments was >1 in treated arteries and <1 in control arteries.

CONCLUSIONS

P-selectin antagonism with rPSGL-Ig inhibits early platelet/leukocyte adhesion on injured arteries and reduces restenosis through a positive impact on vascular remodeling. Hence, rPSGL-Ig may have potential in the prevention of restenosis.

Neutrophil-platelet interactions and their relevance to bovine respiratory disease

Respiratory disease is a serious and significant health problem for the bovine industry. Classically, the clinical and research focus has been on the putative causative agents and conditions, and their interactions with host inflammatory cells, particularly alveolar macrophages and blood neutrophils. There is, currently, growing acceptance of the concept that blood platelets play a primary role in the inflammatory process. This review explores the implications of such pro-inflammatory activity, especially in the context of neutrophil-platelet interactions, and the species specificity of cellular responses. The relevance of these issues for the treatment and prevention of bovine respiratory disease is also discussed.

Increased plasma fibrinogen level and future risk of coronary artery disease after repair of abdominal aortic aneurysm

BACKGROUND

Cardiovascular disease such as coronary artery disease is a major cause of late death after repair of abdominal aortic aneurysm (AAA). But risk factors are not well known. So, we investigated the incidence of cardiovascular events after surgery and examined the prognostic factors.

STUDY DESIGN

We retrospectively reviewed 270 patients who underwent elective surgery for AAA from 1985 to 1995. Kaplan-Meier survival analysis was used to estimate survival rates and the probability of coronary, cerebrovascular, and cardiovascular events. The risk factors for each endpoint were investigated using multivariate analysis.

RESULTS

The overall survival rate was 87.3% at 3 years, 76.4% at 5 years, and 52.3% at 10 years. Current cigarette use, renal insufficiency, advanced age (> or = 70 years old), and higher plasma fibrinogen level (> or = 300 mg/dL) were significant factors influencing survival. The probability of a coronary event was 4.9% at 3 years, 7.1% at 5 years, and 20.7% at 10 years. Plasma fibrinogen level and cerebrovascular disease were significant prognostic factors for coronary events. The probability of a cerebrovascular event was 5.3% at 3 years, 7.6% at 5 years, and 18.0% at 10 years. No significant prognostic factors for cerebrovascular events existed. The probability of a cardiovascular event was 10.3% at 3 years, 14.9% at 5 years, and 33.6% at 10 years. Plasma fibrinogen level was a significant risk factor for cardiovascular events. But the presence of coronary artery disease did not affect survival or the incidence of coronary, cerebrovascular, or cardiovascular events.

CONCLUSIONS

Plasma fibrinogen level is an independent risk factor of future coronary events after surgery for AAA, and the increased risk of coronary artery events contributes to the impaired survival. Patients with higher plasma fibrinogen level need careful surveillance for cardiovascular disease after surgery.

Effect of laser welding with human serum albumin on the expression of P-selectin on platelets

BACKGROUND AND OBJECTIVE

Artery repair by means of laser energy induces activation of platelets with a risk of thrombosis and local inflammatory reactions. The aim of this study was to investigate the effect of human serum albumin, the most common solder in laser surgery, on platelet activation.

STUDY DESIGN/MATERIALS AND METHODS

Platelet activation was evaluated in canine blood by using two-color flow cytometry with a phycoerythrin-labeled antibody to a common platelet marker, glycoprotein IIb/IIIa and fluorescein isothiocyanate-labeled antibody to a platelet activation molecule, P-selectin. Human serum albumin was applied in vitro and in vivo, as a solder during laser reconstruction of canine arteries.

RESULTS

In vitro, albumin significantly (P < 0.01) reduces the expression of P-selectin on platelets. This is most likely related to the blockage of P-selectin by albumin, which binds to the platelet surface, as confirmed by flow cytometry with fluorescein isothiocyanate-labeled albumin. In vivo, application of albumin solder tended to result in a lower percentage of P-selectin-expressing platelets in laser-repaired arteries compared to suture-repaired arteries.

CONCLUSION

Albumin decreases the percentage of P-selectin-expressing platelets in vitro. Further research may allow the platelet activation inhibiting properties of albumin to be further optimized in vivo.

Inhibition of platelet-neutrophil interactions by Fucoidan reduces adhesion and vasoconstriction after acute arterial injury by angioplasty in pigs

The selectin family of cell-adhesion molecules contributes to the interactions of leukocytes and platelets at the site of vascular injury. Such interactions enhance inflammatory reactions and thrombus formation during the arterial response to injury. In this study, we investigated the effects of a selectin inhibitor (Fucoidan) on platelet and neutrophil interactions after arterial injury produced by angioplasty in pigs. [51Cr]-platelet deposition and [111In]-neutrophil adhesion were quantified on intact, mildly, and deeply injured carotid arterial segments, produced by balloon dilation in control (saline, n = 7) and Fucoidan-treated (i.v.; 1 mg/kg, n = 6; 5 mg/kg, n = 5) pigs. In the control group, platelet deposition (x10(6)/cm2) was influenced by the severity of injury and increased significantly (p < 0.05) from 0.06+/-0.06 on intact endothelium to 3.8+/-0.6 and 33.6+/-4.9 on mildly and deeply injured segments, respectively. Fucoidan, 1 mg/kg, had no significant effect, although doses of 5 mg/kg reduced platelet deposition by 73% on deeply injured segments. The level of neutrophil adhesion (x10(3)/cm2) was also influenced by the severity of injury: it increased in the control group from 8.8+/-2.5 on intact endothelium to 226.6+/-45.5 and 397.4+/-61.3 on mildly and deeply injured arterial segments, respectively (p < 0.05). Again, 1 mg/kg Fucoidan had no effect, although doses of 5 mg/kg reduced neutrophil adhesion by 92% and by 84% on mildly and deeply injured segments, respectively. The effects of Fucoidan were associated with a 51% decrease in the vasoconstrictive response at the site of arterial injury. However, Fucoidan had no significant effect on either platelet aggregation or activated clotting time (ACT). In the in vitro perfusion experiments, Fucoidan inhibited both isolated platelet, and neutrophil, adhesion to damaged arterial surfaces. This inhibition was more pronounced in experiments using mixed cell preparations, indicating that Fucoidan interferes with platelet and neutrophil interactions. These results highlight the importance of selectins in the acute physiopathologic reactions related to platelet-neutrophil interactions after arterial injury.

A model of in vivo human venous thrombosis that confirms changes in the release of specific soluble cell adhesion molecules in experimental venous thrombogenesis

PURPOSE

The mechanisms of venous thrombogenesis have been studied by using animal models and cells in culture. The results from these systems may not, however, be relevant to the human condition. The aim of this study was to develop a method by which thrombus could be safely produced in a human vein in vivo. The model that was developed was used as a means of studying the changes in soluble adhesion molecule expression in human venous thrombogenesis.

METHODS

An autologous thrombin extract was used to generate experimental thrombi in the disconnected portion of the long saphenous veins of 30 patients who were undergoing routine bilateral varicose vein surgery. The contralateral vein was perfused with thrombin extract diluent buffer to act as the control. The concentration of soluble P-, E- and L-selectin, intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule-1 were measured by means of specific enzyme-linked immunosorbent assays in samples of blood taken from veins in which thrombus had formed and in contralateral control veins.

RESULTS

Thrombosis invariably formed when at least 100 IU of thrombin activity was administered. Thrombus formation was independent of the time that the thrombin extract was allowed to remain within the emptied vessel. Thrombosis never developed in control vessels that were similarly treated with the buffer used to dilute the thrombin extract. Experimental thrombi were composed mainly of red cells, with layers of fibrin next to platelet and leukocyte packages. These findings are similar to those observed in samples of established human venous thrombi. There were small but significantly higher levels of the adhesion molecules, soluble P-selectin, and vascular cell adhesion molecule-1 in blood taken from veins in which experimental thrombi had formed, compared with controls (P =.015 and.007, respectively; Wilcoxon signed rank test). Serum levels of soluble L-selectin, E-selectin, and ICAM-1 were not affected by thrombosis.

CONCLUSION

This model is safe and reproducible. It produces thrombi with a morphology similar to that described for established human deep venous thrombi. The model may be appropriate for the study of the early changes that occur during human venous thrombogenesis and may also be of value in testing the efficacy of novel antithrombotic agents.

Potential interactions between iloprost and SIN-1 on platelet aggregation and myocardial infarct size in vivo

Nitric oxide and prostacyclin are endothelial-derived vasodilators which inhibit platelet aggregation in a synergistic manner. Experiments were designed to examine whether 3-morpholino-sydnonimine (SIN-1) and iloprost have synergistic cardioprotective actions and whether their effects on infarct size are related to inhibition of platelet aggregation. Anaesthetized rabbits (n = 9-10 per group) were subject to 40 min myocardial ischaemia followed by 3 h reperfusion. Infarct size (percentage of area at risk) was not altered significantly by 3 microg kg(-1) min(-1) SIN-1 (29.7 +/- 1.9%), but was reduced by 0.03 microg kg(-1) min(-1) iloprost (24.6 +/- 1.6%) and to a greater extent by the combination of SIN-1 and iloprost (18.8 +/- 1.7%), compared to controls (33.6 +/- 4.7%). In control rabbits, there were reductions in the ex vivo aggregation of platelets in response to ADP or collagen after ischaemia and reperfusion. SIN-1 and iloprost caused some alterations in platelet responses, but combined administration of both drugs did not produce greater effects. Although the reduction in myocardial infarct size was greatest with both drugs, this did not appear to be a synergistic interaction and was not dependent on the effects of the drugs on haemodynamics or platelet aggregation.

P-selectin antibody reduces hemorrhage and infarct volume resulting from MCA occlusion in the rat

We investigated the effect of an anti-P-selectin antibody (RMP-1) on ischemic cell damage and hemorrhage after transient middle cerebral artery occlusion (MCAo) in the rat. Animals were divided into four groups: (1) antibody (Ab) 1 group (n = 14) RMP-1 (2 mg/kg) was administered to rats 1 h prior to induction of 2 h of MCA occlusion; (2) control-vehicle group Ab2 (n = 12) rats were subjected to the same experimental protocol, except that an isotype-matched control antibody was administered; (3) Abl group (n = 10) rats were subjected to 2 h of MCA occlusion and RMP-1 (2 mg/kg) was administered upon reperfusion; (4) control-vehicle group Ab2 (n = 10) rats were subjected to the same experimental protocol, except that an isotype-matched control antibody was administered. Animals were sacrificed 48 h after onset of the MCAo for histological evaluation of infarction and hemorrhage, and to quantify number of neutrophils. The lesion volume was significantly smaller only in pretreated rats (RMP-1 group, 18.7+/-3.1%) compared to the vehicle-treated (31.6+/-2.6%) group (P<0.01). Total area of hemorrhage (5.94 x 10(3)+/-2.86 x 10(3) microm2) in the pre MCAo RMP-1 treated group animals was significantly reduced (P<0.02) compared to the vehicle group (6.1 x 10(4)+/-3.42 x 10(4) microm2), respectively. Our data demonstrate that administration of the anti-P-selectin antibody before transient focal cerebral ischemia in rat brain reduces ischemic cell damage and petechial hemorrhage.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

Investigation of platelet-neutrophil interactions in whole blood by flow cytometry

Evidence is increasing that platelets can initiate and propagate inflammatory processes by interacting with leucocytes and the vascular endothelium. Platelets have been shown to bind to neutrophils, existing as platelet/neutrophil complexes (PNC) within the circulation. We describe a simple flow cytometric method for assessing and investigating platelet interactions with neutrophils in small volumes of whole blood. Twenty-five percent (sd 6%) of circulating neutrophils from healthy adults were associated with platelets. Formation of these platelet-neutrophil complexes was CD62P (P-selectin) and divalent cation dependent. Platelet activation (with ADP or thrombin) caused a rapid and sustained rise in %PNC which differed from the pattern of free platelet activation as assessed by CD62P expression. F-met-leu-phe induced neutrophil activation but did not increase the percentage PNC. Platelet activation also caused increased neutrophil CD11b/CD18 expression which was most marked on neutrophils complexed with platelets. This straightforward technique is simple, reproducible, and allows assessment of platelet-neutrophil interactions and activation of neutrophils. It may also provide a method for estimating platelet activation in whole blood.

Immunomodulation, autoimmunity and haemostatic dysfunctions

Many links exist between the two major host defence mechanisms, haemostasis and immunity. Blood cells and endothelium are involved in these systems and their dysfunctions. The dual function of these cells is discussed. Once activated, cell-cell interactions enhance the biological response and contribute to development of pathology. Furthermore, autoimmunity presents a special clinical relevance, and could be involved in many haemostatic disorders. A hypothesis is presented on how some auto-antibodies are generated and can trigger pathology, by targeting the immune response onto blood or endothelial cells, or to body's organs.

Anti-P-selectin antibody decreases inflammation and thrombus formation in venous thrombosis

PURPOSE

Venous thrombosis and inflammation are interrelated. P-selectin contributes to activation of leukocyte-mediated inflammation. Therefore, we hypothesized that the neutralization of P-selectin would decrease vein wall inflammation and thrombosis.

METHODS

Twelve baboons underwent infrarenal inferior vena caval balloon occlusion to induce thrombosis. Two groups of four baboons received neutralizing intravenous anti-P-selectin antibody (PSab) GA6 or CY1748 before occlusion and at days 2 and 4. Four baboons received saline control injections. One baboon per group was killed at days 2, 6, and 13, and at 2 months. Analysis included phlebography, ultrasound, gadolinium (Gd)-enhanced magnetic resonance venography (reflecting vein wall inflammation), and histologic, morphometric, and protein evaluation of the vein wall. Thrombus presence or absence was assessed.

RESULTS

By day 2 in PSab baboons, vein wall Gd enhancement was decreased in the mid-inferior vena cava and the right iliac vein (p < 0.05; GA6 vs control baboons), normalizing by 2 months. The mid-inferior vena cava revealed fewer neutrophils and total leukocytes in PSab baboons; however, for GA6 in the right iliac vein these decreases were not present despite the absence of Gd enhancement; they were decreased with CY1748. PSab baboons demonstrated significantly less thrombus than control baboons (p < 0.01, GA6 and CY1748 vs control baboons).

CONCLUSIONS

Anti-P-selectin antibody decreases vein wall inflammation and thrombus formation. Inhibition of P-selectin may be useful in venous thrombosis prophylaxis.

Effect of elevated leukocyte count on in-hospital mortality following acute myocardial infarction

The peripheral white blood cell count on presentation with acute myocardial infarction directly correlates with short-term in-hospital mortality. This association is independent of other prognostic factors, including extent and size of the acute myocardial infarction.