Platelet function in acute myocardial infarction treated with direct angioplasty

Circulating platelet-derived microparticles with procoagulant activity may be a potential cause of thrombosis in uremic patients

BACKGROUND

Clinical experience indicates that bleeding and thrombotic tendencies co-exist in uremic patients. Numerous studies have shown that platelet functional defects contribute to the bleeding tendency in uremic patients. In contrast, there are no solid studies clarifying the pathogenesis of the prothrombotic state in uremic patients. Platelet-derived microparticles (PMPs), which are small vesicles with procoagulant activity released from activated platelets, are thought to be involved in clinical thrombogenesis. This study addressed the question of why uremic patients are thrombophilic even though they have a bleeding tendency, focusing on the clinical significance of PMPs.

METHODS

The subjects were pre-dialyzed patients, patients under hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) therapy, and age-matched healthy controls. Analyses of PMPs were performed using a flow cytometer. Annexin V was used to probe procoagulant activity of PMPs. The impacts of the HD procedure, arteriovenous (AV) fistula, and recombinant human erythropoietin (rHuEPO) treatment on the release of PMPs were additionally assessed.

RESULTS

Major results are: (1) PMP counts were significantly greater in each uremic group than in controls. The PMP counts were not different among three types of uremic groups; (2) PMP counts were significantly higher in uremic patients with thrombotic events than in those without thrombotic events; and (3) the HD procedure and existence of AV fistula did not affect PMP counts, but rHuEPO treatment possibly enhanced the PMP release in these patients.

CONCLUSIONS

Elevated PMP counts may trigger thrombosis in uremic patients. The primary cause of PMP elevation in uremia was not clarified in this study.

Effect of additional temporary glycoprotein IIb/IIIa receptor inhibition on troponin release in elective percutaneous coronary interventions after pretreatment with aspirin and clopidogrel (TOPSTAR trial)

OBJECTIVES

The Troponin in Planned PTCA/Stent Implantation With or Without Administration of the Glycoprotein IIb/IIIa Receptor Antagonist Tirofiban (TOPSTAR) trial investigated: 1) the amount of troponin T (TnT) release after nonacute, elective percutaneous coronary intervention (PCI) in patients pretreated with aspirin and clopidogrel; and 2) the effect of additional glycoprotein (GP) IIb/IIIa receptor inhibiton on postinterventional TnT release.

BACKGROUND

No data are available yet as to whether additional administration of a GP IIb/IIIa receptor antagonist might be beneficial in patients undergoing elective PCI already pretreated with aspirin and clopidogrel.

METHODS

After bolus application of the study medication (tirofiban [T] or placebo [P]), PCI was performed followed by an 18-h continuous infusion of T/P. Primary end point of the study was incidence and amount of TnT release after elective PCI after 24 h.

RESULTS

A total of 12 h after PCI troponin release was detected in 63% of the patients receiving P and in 40% of the patients receiving T (p < 0.05), after 24 h in 69% (P) and 48% (T) (p < 0.05) and after 48 h in 74% (P) versus 58% (T) (p < 0.08) of the patients. No differences were observed regarding major bleeding, intracranial bleeding or nonhemorrhagic strokes. After nine months a reduction of combined death/myocardial infarction/target vessel revascularization could be observed in the tirofiban group ([T] 2.3% vs. [P] 13.04%, p < 0.05).

CONCLUSIONS

Troponin T release occurs after successful intervention in 74% of the patients undergoing elective PCI after 48 h even after pretreatment with aspirin and clopidogrel. The GP IIb/IIIa receptor antagonist tirofiban is able to decrease the incidence of troponin release significantly in this patient population.

Association of platelet-derived microparticles with C-C chemokines on vascular complication in patients with acute myocardial infarction

The levels of platelet-derived microparticles (PDMPs), platelet activation markers (P-selectin, CD63, and PAC-1 on activated platelets), and C-C chemokines (monocyte chemotactic peptide [MCP]-1 and regulated on activation normally T-cell expressed and secreted [RANTES] were measured and compared in patients with acute myocardial infarction (AMI) or stable pectoris angina. These substances are thought to paricipate in the development of complications in patients with AMI. The percentage binding of anti-P-selectin, CD63, and PAC-1 antibody to platelets, and the levels of PDMPs (per 10(4) platelets) were higher in the patients with AMI than in those with stable pectoris angina (P-selectin, 23.1% +/- 2.1% vs. 10.3% +/- 1.2%, p < 0.001; CD63, 24.6% +/- 3.3% vs. 11.2% +/- 3.1%, p < 0.01; PAC-1, 14.1% +/- 1.7% vs. 9.3% +/- 2.1%, p < 0.05; PDMPs, 613 +/- 71 vs. 413 +/- 55, p < 0.01). There were no differences in platelet levels of GPIIb/IIIa and GPIb between groups. Levels of MCP-1 and RANTES were higher in the patients with AMI than in patients with stable pectoris angina (MCP-1, 430 +/- 35 vs. 265 +/- 23, p<0.01; RANTES, 175 +/- 32 vs. 88 +/- 29, p<0.001). The effects of percutaneous transluminal coronary angioplasty (PTCA) on the levels of these agents in patients with AMI were studied. Platelet activation markers were significantly decreased in patients with AMI after PTCA. RANTES level was also significantly decreased after treatment, but MCP-1 level was not changed. In addition, this tendency was clearer in STENT patients. These findings suggest that in patients with AMI PTCA, particularly STENT, may prevent the development of complications in which activated platelet and RANTES participate.

Glycoprotein IIb/IIIa antagonists in the setting of rescue percutaneous coronary intervention

It is clear that survival and better outcomes after acute myocardial infarction (AMI) are dependent on rapid, complete, and sustained reperfusion of the affected myocardium. Thrombolytic therapy is currently the most common reperfusion strategy in AMI, however, a significant proportion of patients fail to reach reperfusion with this form of therapy. There is evidence from randomized trials that rescue percutaneous coronary intervention (PCI) for failed thrombolysis may convey better outcomes to patients when compared to a conservative management. Nevertheless, it is not surprising that in this inherently thrombogenic milieu, rescue PCI has a lower success rate and a high incidence of rethrombosis, which have a profoundly negative impact on the outcome of patients. Platelets are thought to play a central role in the pathophysiology of failed thrombolysis and in the thrombotic complications following PCIs. Therefore, platelet glycoprotein (GP) IIb/IIIa antagonist may be of benefit in the setting of rescue PCI. Two retrospective subgroup analyses have suggested that these potent antiplatelet agents may improve the outcome of patients undergoing rescue PCI after failed full-dose thrombolytic therapy. An increase in major bleeding, however, has also been noted. Therefore, in light of the lack of evidence deriving from randomized, placebo-controlled trials, careful consideration of several aspects relevant to this setting is needed before GP IIb/IIIa antagonists are administered in rescue percutaneous coronary procedures.

Overproduction of platelet microparticles in cyanotic congenital heart disease with polycythemia

OBJECTIVES

We sought to clarify the role of platelets in the pathogenesis of abnormal coagulation in patients with cyanotic congenital heart disease (CCHD) with polycythemia; we evaluated the production of platelet microparticles (MPs), platelet degranulation and aggregation response, as well as the correlations of these variables with polycythemia.

BACKGROUND

A shortened life span and suppressed aggregability of platelets are well known in patients with CCHD. Although platelet MPs are overproduced and play an important role in the coagulation process in various hematologic and cardiovascular disorders, the production of MPs remains to be elucidated in CCHD. We studied 19 patients who had CCHD with polycythemia and 21 age-matched subjects with acyanotic congenital heart disease (ACHD). Flow cytometry, using monoclonal antibodies, showed the presence of MPs as particles positive for the surface antigen (glycoprotein IIb/IIIa) specific to platelets, and platelet alpha-degranulation was recognized as platelets positive for the surface antigen of P-selectin. Platelet aggregation was assessed as the response to adenosine diphosphate (ADP). Relationships between these indexes and hematocrit (Hct) values were also evaluated.

RESULTS

Production of MPs correlated positively with Hct and markedly increased at Hct values above 60% in patients with CCHD. Surface P-selectin and the mean platelet volume in patients with CCHD were comparable with those in patients with ACHD. The platelet aggregation response to ADP significantly and negatively correlated with Hct. In two subjects who showed hemoptysis and underwent phlebotomy, MPs were reduced 6 h after the procedure.

CONCLUSIONS

Platelet MPs are overproduced in patients who have CCHD with polycythemia, probably due to a high shear stress derived from blood hyperviscosity. Circulating incompetent platelets, which have already been activated, as well as MPs, might play an important role in the coagulation abnormalities identified in such patients.

Myocardial salvage after coronary stenting plus abciximab versus fibrinolysis plus abciximab in patients with acute myocardial infarction: a randomised trial

BACKGROUND

Patients with acute myocardial infarction might benefit from the addition of glycoprotein IIb/IIIa inhibitors to fibrinolytic or mechanical reperfusion strategies. We compared two strategies, stenting and fibrinolysis, both combined with abciximab, in terms of their ability to salvage myocardium in patients with acute myocardial infarction.

METHODS

We enrolled 162 patients with acute myocardial infarction within 12 h of onset of symptoms, assigning 81 stenting plus abciximab and 81 alteplase plus abciximab. Technetium-99m sestamibi scintigraphy was done at admission and after a median of 11 days to calculate initial perfusion defect, final infarct size, and degree of myocardial salvage. The primary endpoint was the salvage index (the ratio of the degree of myocardial salvage to the initial perfusion defect). Major adverse clinical events within 6 months from randomisation were also compared between the two treatments.

FINDINGS

Paired scintigraphic measurements were available for 70 patients in the stent group and 71 in the alteplase group. Stenting was associated with greater myocardial salvage than alteplase (median 13.6% [IQR 5.9-23.9] vs 8.0% [2.5-16.0] of the left ventricle; p=0.007). Salvage index was greater in the stent group than in the alteplase group (median 0.60 [0.37-0.82] vs 0.41 [0.13-0.58]; p=0.001). The 6-month mortality rate was 5% (four deaths) in the stent group and 9% (seven deaths) in the alteplase group (relative risk 0.56 [95% CI 0.17-1.88]; p=0.35).

INTERPRETATION

In patients with acute myocardial infarction, a reperfusion strategy based on stenting with abciximab produced more myocardial salvage than the combination of fibrinolysis plus abciximab. Larger studies are needed to assess whether these effects translate into clinical benefit.

Close relationship between the platelet activation marker CD62 and the granular release of platelet-derived growth factor

The expression of CD62 on the surface of platelets is considered to be an indicator of platelet degranulation and secretion. We characterized the relationship between CD62 expression and platelet-derived growth factor (PDGF)(AB) and PDGF(BB) secretion in response to thrombin-receptor activating peptide (TRAP). The principal findings were 1) expression of CD62 as a constituent of platelet alpha-granule membrane and secretion of PDGF, an important ingredient of alpha-granules, can be stimulated by TRAP-induced activation in a dose-dependent fashion; 2) the activation marker and secretion product are closely correlated with each other; and 3) changes in the CD62 expression induced by a drug, namely clopidogrel, or by a disease, namely diabetes, are paralleled by changes in PDGF secretion. Although CD62 is perceived as an activation marker of platelets indicating enhanced aggregability and secretion of alpha-granular content, the proof that the CD62 status and its modifications reflect directly the actual secretion of the most important platelet mitogen, PDGF, has so far not been given. This ex vivo-in vitro study shows that at least for the activation pathway provided by the PAR-1 receptor for which TRAP is the selective agonist, CD62 expression on platelets could be a surrogate for their secretory activity.

Function and clinical significance of platelet-derived microparticles

Microparticles released from platelets (PMPs) may play a role in the normal hemostatic response to vascular injury because they demonstrate prothrombinase activity. PMPs were first observed as released vesicles from platelets following adhesion to vessel walls, and flow cytometry is now the most widely used method for studying PMPs. PMPs are thought to play a role in clinical disease because they express phospholipids that function as procoagulants. High shear stress can initiate both platelet aggregation and shedding of procoagulant-containing PMP, suggesting that PMP generation by high shear stress occurs in small diseased arteries and arterioles under various clinical conditions. In addition, the possibility that PMPs evoke cellular responses in their immediate microenvironments has recently been suggested. Despite many interesting findings, the significance of PMPs in various clinical conditions remains controversial. For example, it is not known whether PMPs found in peripheral blood vessels cause thrombosis, or if they are the results of thrombosis. There has been some question about whether the PMPs found in thromboses are consumed locally, meaning that PMPs circulating in the peripheral blood are not functionally important. Currently, the number of clinical disorders associated with elevated PMPs is increasing.

[Variable response to the biological inhibition of platelets by abciximab in patients subjected to percutaneous coronary angioplasty]

INTRODUCTION AND OBJECTIVES

Abciximab has been shown to reduce the risk of thrombotic complications during coronary angioplasty, however there are still many aspects to be resolved. The aim of this study was to investigate the various biological effects of abciximab on platelets during coronary angioplasty.

METHODS

The degree of platelet inhibition (with 5 and 20 mol/l concentrations of ADP), occlusion time (measurement of platelet haemostatic capacity, PFA-100), and the platelet activation markers were determined in 15 patients who underwent basal coronary angioplasty and abciximab treatment. Determinations were obtained before, 15 minutes after procedure initiation, at procedure termination, and 24 hours after procedure termination.

RESULTS

More than 80% platelet aggregation inhibition was observed in 13 patients during the procedure, but after 24 hours (p < 0.05) was only detected in two. The occlusion time during the procedure was > 300 sec. in 13 patients, 6 of whom evolved to normal values after 24 hours (p < 0.05). A high correlation (p = 0.02) was found between these two parameters during the intervention, but not after 24 hours. No platelet inhibition or occlusion time changes were observed in 2 patients during the study. The expression of p-selectin increased significantly during the procedure (p < 0.05).

CONCLUSIONS

The variability of platelet function inhibition and existence of circulating activation during coronary angioplasty following the administration of abciximab support the use of early analytical controls with the objective of modifying guidelines for use in order to optimize its effect or to combine it with other antithrombotic agents.

High-shear-stress-induced activation of platelets and microparticles enhances expression of cell adhesion molecules in THP-1 and endothelial cells

Interaction between leukocyte and endothelial cells (ECs) is essential for vascular homeostasis and competent immune-inflammatory responses in vivo. Platelet-derived microparticles (PMPs) are generated by high shear stress and may appear in diseased small arteries and arterioles in various clinical settings. In this study, we used flow cytometry and confocal laser scanning microscopy to investigate the effects of high-shear-induced platelet and microparticle activation in adhesion molecules of THP-1 and ECs. We also measured the production of some cytokines and studied cytokine mRNA from THP-1 and ECs after PMP stimulation. PMP stimulation of THP-1 cells increased CD11b, CD32, and CD33 but not CD29, CD31, and CD36. PMP stimulation of ECs increased CD54 and CD63 but not CD9, CD29, and CD31. PMPs induced interleukin-8 (IL-8), interleukin-1 beta (IL-1 beta), and tumor necrosis factor alpha (TNF alpha) production by THP-1. PMPs also induced IL-8, IL-1 beta, and interleukin-6 (IL-6) production by ECs. Production was time-dependent. With RT-PCR, some cytokine mRNAs were detected in THP-1 and ECs after PMP stimulation. In relation to adhesiveness after PMP stimulation, we could clearly observe a shift in distribution not only of CD11b in THP-1 cells but also of CD54 in ECs. In addition, anti-P-selectin glycoprotein ligand-1 antibody reduced the expression of CD11b, CD32, and CD33 in THP-1 after PMP stimulation. These results suggest that high-shear-induced microparticles may contribute to the development of atherosclerosis and participate in vascular damage in inflammatory disorders.

Coronary stenting and platelet glycoprotein IIb/IIIa receptor blockade in acute myocardial infarction

BACKGROUND

Myocardial reperfusion in patients with acute myocardial infarction may be successfully achieved with primary angioplasty. However, angioplasty, as a primary reperfusion strategy, has limitations such as early recurrent ischemia and late restenosis and reocclusion. To improve the short- and long-term results of primary angioplasty, the use of adjunct strategies has been proposed.

METHODS

We reviewed published studies on the effectiveness of primary angioplasty, stenting, and platelet glycoprotein IIb/IIIa receptor blockade and identified the advantages and disadvantages of these interventions in patients with acute myocardial infarction.

RESULTS

Recent findings suggest that patients may benefit from stenting of the infarct artery and from the use of more potent antiplatelet agents such as platelet glycoprotein IIb/IIIa receptor inhibitors. In randomized trials that compared primary angioplasty versus primary stenting, stent implantation was associated with a lower rate of death, reinfarction, and especially target vessel revascularization. Platelet glycoprotein IIb/IIIa receptor inhibitors prevented acute ischemic complications after primary angioplasty and primary stenting. In addition to maintaining large vessel patency, these drugs may protect the microvasculature after primary stenting, allowing better functional recovery of the risk area.

CONCLUSIONS

Coronary artery stenting in acute myocardial infarction reduces the rate of restenosis and the incidence of problems related to recurrent ischemia. Platelet glycoprotein IIb/IIIa receptor inhibitors may come to play a key role in association with mechanical reperfusion. However, the cost-effectiveness and long-term clinical outcome of this combined pharmacologic/mechanical intervention require further study before this strategy can be recommended for routine use.

Coagulation, fibrinolysis and platelet P-selectin expression in peripheral vascular disease

OBJECTIVES

to examine coagulation, fibrinolysis, and platelet activity in patients with peripheral vascular disease (PVD).

DESIGN

fifty consecutive PVD patients and 50 healthy volunteers. (Prospective comparative study.)

MATERIALS AND METHODS

P-selectin expression in non-fixed, whole blood was measured flow cytometrically on non-stimulated and ADP- and TRAP-6-stimulated samples. Plasma fibrinogen, von Willebrand factor (vWF), tissue plasminogen activator (tPA), and plasminogen activator inhibitor-1 were determined using standard techniques. Disease severity was stratified on the basis of the ankle-brachial pressure index (ABPI) and the angiographic data were assessed using the Bollinger score.

RESULTS

coagulation and fibrinolysis parameters as well as the P-selectin expression on both stimulated and non-stimulated platelets were significantly increased in patients vs controls (all p<0.01). The respective sensitivity and specificity were as follows: P-selectin expression (81%, 94%), vWF (72%, 86%), fibrinogen (64%, 98%), PAI-1 (44%, 90%), tPA (15%, 100%). P-selectin expression on TRAP-6-stimulated MP correlated with disease severity (r=0.40, p<0.01).

CONCLUSIONS

these findings support the concept of ongoing thrombogenesis in the subclinical progression of PVD and demonstrate the high diagnostic sensitivity of flow cytometric analysis of platelet activation.

P-Selectin expression, platelet aggregates, and platelet-derived microparticle formation are increased in peripheral arterial disease

Platelet volume has been reported to be increased in vascular disease. Therefore, we studied the relationship of mean platelet volume and platelet count as well as flow cytometrically measured platelet size and platelet function in 50 patients with peripheral arterial disease and 50 healthy volunteers. Platelet activation was measured by P-selectin expression analysis on resting and on stimulated platelets, and the determination of platelet aggregates and platelet-derived microparticles using flow cytometry. P-Selectin expression on platelets was significantly elevated in patients suffering from peripheral arterial disease (all P<0.0001). Platelet aggregates (P<0.0001) and platelet-derived microparticles (P<0.0001) were significantly higher in the patient group compared with controls, whereas mean platelet volume and platelet count showed no significant differences. Platelet count was inversely related to mean platelet volume in patients and controls (r = -0.43, P<0.001). The present study supports the hypothesis of platelet hyperreactivity and circulating activated platelets in peripheral arterial disease. Mean platelet volume, and platelet count cannot be used as predictive markers for platelet activation in peripheral arterial disease patients.

Importance of microembolization and inflammation in atherosclerotic heart disease

Considerable evidence now exists that inflammation is a central component of events that initiate and propagate an acute coronary syndrome. This process evokes the potential for embolization, which occurs more often than previously suspected, and imparts poor cardiovascular prognosis. Recent development of techniques to detect inflammation and embolization represents an important advance. In addition, therapies that diminish occurrence of these phenomena such as aspirin, statins, angiotensin converting enzyme (ACE) inhibitors, and IIb/IIIa receptor antagonists have been shown to improve outlook.

Antiplatelet effects of clopidogrel compared with aspirin after myocardial infarction: enhanced inhibitory effects of combination therapy

OBJECTIVES

We sought to compare the inhibitory effects of the combination of two doses of aspirin plus clopidogrel with either drug alone on platelet aggregation and activation.

BACKGROUND

Enhanced platelet inhibitory effects of clopidogrel by aspirin on platelet aggregation and activation are suggested by experimental studies but have not been shown in humans.

METHODS

The effects of clopidogrel 75 mg or aspirin 100 (300) mg on platelet aggregation and activation by flow cytometry after stimulation with various agonists were determined in 30 patients with a past history of myocardial infarction.

RESULTS

Clopidogrel alone or in combination with aspirin markedly inhibited adenosine diphosphate (ADP)-mediated platelet aggregation compared with monotherapy with aspirin (24.6 +/- 3.3% or 26.6 +/- 2.7% vs. 44.7 +/- 2.9%; p < 0.001). Combined treatment significantly inhibited collagen-induced aggregation compared with aspirin and clopidogrel (16.4 +/- 2.4%, 36.5 +/- 4.2% and 59.3 +/- 5.1%, respectively;, p < 0.001) and resulted in considerable inhibition of aggregation induced by thrombin receptor agonist peptide (TRAP, p < 0.03). Clopidogrel with or without aspirin significantly suppressed expression of platelet activation markers CD 62p, CD 63 and PAC-1 after stimulation with ADP or thrombin (p < 0.001). In addition, the combined treatment was more effective than either agent alone after activation with low dose thrombin (p < 0.05). Both doses of aspirin equally potentiated the platelet inhibitory effects of clopidogrel. CONCLUSIONS In this prospective clinical ex vivo platelet study, clopidogrel was more effective than aspirin in inhibiting ADP-mediated platelet aggregation and activation. Clopidogrel in combination with aspirin showed synergistic inhibitory effects after stimulation with collagen and thrombin compared with monotherapies. Thus, this dual antiplatelet treatment strategy deserves further evaluation in clinical trials for secondary prevention of acute myocardial infarction or unstable angina.

Release of platelet activation markers during coronary angioplasty

BACKGROUND

Authors of several studies have reported that activation of platelets occurs during coronary angioplasty, but consistent results have not been obtained. Levels of serotonin in coronary circulation have been found to be elevated during percutaneous transluminal coronary angioplasty but greater than normal concentrations of beta-thromboglobulin and platelet factor 4 have not been detected.

OBJECTIVE

To perform a serial analysis of platelet-activation markers with simultaneous measurements of levels of serotonin, beta-thromboglobulin and platelet factor 4 in blood samples from the coronary artery and coronary sinus of patients undergoing coronary angioplasty.

METHODS

Twenty patients undergoing elective coronary angioplasty were studied. Measurements of levels of beta-thromboglobulin, platelet factor 4, and serotonin in samples from the ostium of the coronary artery and the coronary sinus were performed immediately before angioplasty and after the first balloon deflation.

RESULTS

Concentrations of beta-thromboglobulin and platelet factor 4 in coronary artery and coronary sinus were elevated in all patients before dilatation, whereas concentrations of serotonin were elevated in 85% of the patients. Concentrations of all markers in coronary sinus decreased after the first inflation. The coronary-sinus: coronary-artery concentration ratios before dilatation for beta-thromboglobulin, platelet factor 4, and serotonin were > 1 for the majority of patients, particularly for those with complex culprit lesions, indicating that coronary activation of platelets was occurring. Ratios remained unchanged or decreased after the first inflation, depending on initial values.

CONCLUSIONS

Both systemic and coronary activation occur in patients subjected to percutaneous transluminal coronary angioplasty before the onset of intervention. After balloon deflation the greater than normal baseline coronary-sinus:coronary-artery concentration ratios of all markers (beta-thromboglobulin, platelet factor 4 and serotonin) tend to decline or remain unchanged, depending on the level of activation.

Platelet-derived microparticles stimulate coronary artery smooth muscle cell mitogenesis by a PDGF-independent mechanism

This study investigates the role of platelet-derived microparticles for vascular smooth muscle cell (SMC) proliferation. Microparticles concentration dependently stimulated p42/p44 MAP kinase phosphorylation, c-fos induction, DNA synthesis, and proliferation of cultured bovine coronary artery SMC. The maximum mitogenic effects of microparticles were significantly higher than those of platelet-derived growth factor (PDGF)-BB. Microparticle-induced SMC mitogenesis was heat sensitive, whereas the effects of PDGF were not. In addition, neutralizing anti-PDGF antibodies prevented PDGF-induced DNA synthesis but did not inhibit the effects of microparticles. In contrast to PDGF, which potently stimulated SMC migration, microparticles had only minor migratory activity. These results demonstrate a novel mechanism of SMC mitogenesis by platelet-derived microparticles that is probably independent of PDGF.

The pre-procedural platelet state predicts clinical recurrence after coronary angioplasty

Percutaneous transluminal coronary angioplasty is an established therapy for coronary artery disease, but restenosis still occurs at a rate of 25%-40%. The aim of this study was to investigate the acute effect of percutaneous transluminal coronary angioplasty on platelet function and the relationship between platelet function and clinical recurrence. Spontaneous platelet aggregation was assessed before and after successful coronary angioplasty in 155 patients (120 men, 35 women). Patients were followed for a mean time of 20 months; follow-up angiography was performed only in patients with clinical recurrence. In 122 of 155 patients (79%) a significant increase in spontaneous platelet aggregation was observed immediately after coronary angioplasty. Baseline spontaneous platelet aggregation in platelet-rich plasma was significantly lower in patients with clinical recurrence than in those without (P<0.05). Kaplan-Meier event-free survival estimate showed a significant difference in clinical recurrence between patients with spontaneous platelet aggregation in platelet-rich plasma below and above the first quintile (P<0.05) with a relative risk of 2.5. In conclusion. these results indicate that percutaneous transluminal coronary angioplasty enhances spontaneous platelet aggregation and that the platelet state before coronary angioplasty affects the risk of clinical recurrence after the procedure.

Platelet-derived microparticles in patients with arteriosclerosis obliterans: enhancement of high shear-induced microparticle generation by cytokines

We evaluated the plasma concentrations of cytokines and platelet-derived microparticles in patients with arteriosclerosis obliterans and studied the effect of cytokines on platelet-derived microparticle generation under high shear stress. Interleukin-6 levels peaked at 48 hours after vascular surgery, while thrombopoietin started to increase at 24 to 48 hours postoperatively and peaked on the seventh day. Platelet activation markers were increased in the arteriosclerosis obliterans patients preoperatively. Levels of P-selectin and CD63 both increased further, peaking at 6 to 24 hours postoperatively. Platelet-derived microparticle levels were also increased preoperatively. At 6 hours postoperatively, the plasma level of platelet-derived microparticles was significantly increased. Plasma platelet-derived microparticle level was lower at 12 hours but only returned to the preoperative value at 7 days after grafting. There was a difference in the platelet-derived microparticle level at 7 days between patients with or without antiplatelet therapy (cilostazol). The effect of cytokines on platelet activation under high shear stress was also studied. Interleukin-6 and thrombopoietin enhanced both P-selectin expression and platelet-derived microparticle generation under high shear stress. These results suggest that platelet-derived microparticles are released by platelet activation after vascular grafting when certain cytokines increase under high shear stress and that antiplatelet therapy may reduce platelet-derived microparticle levels postoperatively.

Antiplatelet use in interventional cardiology

Thrombosis within the target vessel is one of the most feared complications associated with coronary intervention, as it is often associated with severe adverse clinical sequelae. This thrombosis is mediated via the activation and aggregation of platelets and therefore considerable effort has been directed at ways of inhibiting platelet function. It is now mandatory to consider the use of two and often three different antiplatelet agents, particularly when intracoronary stents are inserted. Using these regimes, many of the adverse clinical outcomes associated with platelet activation can be reduced.

Elevation of vascular endothelial growth factor-A serum levels following acute myocardial infarction. Evidence for its origin and functional significance

Following the onset of acute myocardial infarction (AMI), a number of serum parameters show well-defined changes reflecting myocardial injury. During the consecutive repair phase, compensatory processes are initiated including the formation of a collateral circulation on the basis of angiogenesis and arteriogenesis. An important angiogenic factor is vascular endothelial growth factor-A (VEGF-A), shown to be upregulated in the ischemic myocardium. It is unclear, however, whether acute myocardial ischemia leads to a detectable elevation of VEGF-A serum concentrations. With the use of an immunoradiometric assay, we measured the levels of VEGF-A in the serum of patients after AMI at defined time intervals, of patients with unstable angina pectoris (UAP) and of healthy individuals. In addition, in a small group of patients with subacute myocardial infarction VEGF-A concentrations were measured in coronary sinus blood. The data are given as median followed by the 25th and 75th percentiles. In the group with AMI serum VEGF-A measured 105 [78; 176] pg/ml on day 1 and 114 pg/ml [72; 163] pg/ml on day 3 after onset of AMI. Serum levels of VEGF-A significantly increased on day 7 after AMI to 189 [119; 373] pg/ml (P=0.0103) and on day 10 to 255 [162; 371] pg/ml (P=0.0007). The VEGF-A serum level in healthy controls and in patients with UAP measured 98 [75; 137] pg/ml and 116 [57; 140] pg/ml, respectively. Serum at day 10 after AMI contained VEGF-A at a biologically relevant concentration capable of stimulating proliferation of endothelial cells. Surprisingly, VEGF-A serum levels were similar in samples taken from the coronary sinus with 61 [43; 83] pg/ml. Therefore the main source for VEGF-A in the blood stream is not the infarcted myocardium. However, the number of platelets, a rich source of VEGF-A, is significantly increased after myocardial infarction, i.e. 284 [252; 363] x 10(9)/litre v 220 [177; 250] x 10(9)/litre. In conclusion, the time course of VEGF-A elevation following AMI strongly suggests that VEGF-A plays a role as an endogenous activator of coronary collateral formation in the human heart. The most likely source of the elevated VEGF-A are platelets, rather than the infarcted myocardium.

Thrombin receptor activating peptide (SFLLRN) potentiates shear-induced platelet microvesiculation

Shear-induced activation of platelets plays a major role in vascular thrombosis. Shear stress tends to increase both platelet aggregation and procoagulant activity. One mechanism for increased procoagulant activity is promotion of the transbilayer movement of anionic phospholipids from the inner to the outer leaflet of the platelet membrane bilayer. This is accompanied by vesiculation of the platelet membrane, resulting in the formation of procoagulant membrane particles called microvesicles. In this study we have examined the effect of various platelet agonists on shear-induced platelet microvesiculation and the development of platelet procoagulant activity. Normal citrated whole blood was subjected to laminar shear rate up to 12,500 sec(-1) (shear stress approximately 375 dyne/cm2) in a cone-and-plate viscometer, and the formation of platelet microvesicles was measured by flow cytometry under different conditions. Elevated levels of shear stress induced significant microvesiculation. We investigated the effects of adenosine diphosphate, epinephrine, thromboxane A2 analog, collagen, and thrombin receptor activation peptide (SFLLRN) on shear-induced platelet microvesiculation. The thrombin peptide significantly increased shear-induced microvesicle formation. In contrast, under similar conditions, the other agonists had no significant effect on shear-induced microvesiculation. These studies suggest that thrombin formed in the vicinity of primary hemostatic plugs in areas of elevated shear stress may have a major role in the propagation of thrombi by potentiating shear-induced platelet microvesiculation.

Platelets induce alterations of chemotactic and adhesive properties of endothelial cells mediated through an interleukin-1-dependent mechanism. Implications for atherogenesis

Platelets and alterations of chemotactic and adhesive properties of endothelium play an important role in the pathophysiology of atherosclerosis. We investigated the effect of platelets on secretion of monocyte chemotactic protein-1 (MCP-1) and on surface expression of intercellular adhesion molecule-1 (ICAM-1) of cultured endothelium. Pretreatment of cultured monolayers of endothelial cells with alpha-thrombin-activated platelets significantly enhanced secretion of MCP-1 and ICAM-1 surface expression (P<0.01) that could be inhibited by interleukin-1 (IL-1) antagonists by approximately 40%. Activation of transcription factor nuclear factor-kappaB (NF-kappaB) which regulates transcription of early inflammatory response genes such as MCP-1, was significantly increased in endothelial cells treated with activated platelets via an IL-1 mediated mechanism as determined by electrophoretic mobility shift assay (EMSA) and kappaB-dependent transcriptional activity. In trans-well experiments, alpha-thrombin-activated platelets enhanced IL-1-dependent surface expression of vitronectin receptor (alpha(v)beta(3)) on the luminal aspect of endothelial monolayers and promoted alpha(v)beta(3)-mediated platelet/endothelium adhesion that could be inhibited by the antiadhesive peptides GRGDSP and c(RGDfV). We conclude that activated platelets induce significant changes in chemotactic (secretion of MCP-1) and adhesive (surface expression of ICAM-1 and alpha(v)beta(3)) properties of cultured endothelium. These findings imply a potential pathophysiological mechanism of platelets in an early stage of atherogenesis.

Increased platelet surface expression of P-selectin and thrombospondin as markers of platelet activation in essential thrombocythaemia

Essential thrombocythaemia (ET) is a clonal myeloproliferative disorder associated with an increased risk of both thromboembolic and bleeding complications. Platelet activation plays a crucial role in the pathogenesis of prethrombotic conditions. The platelet surface expression of p-selectin (CD62p) and thrombospondin (TSP) has been shown to correlate with platelet activation. In the present study, we used a flow cytometric assay to study whether the fraction of platelets expressing CD62p and TSP is increased in newly diagnosed ET. Thirty-four patients with newly diagnosed ET and 25 healthy control subjects were investigated. The proportion of platelets expressing the activation-dependent antigens CD62p and TSP was higher in patients with ET (CD62p: 14.7+/-15.0%; TSP: 12.4+/-9.9%) as compared with healthy control subjects (CD62p: 3.0+/-4.0%; TSP: 3.2+/-3.2%; p< 0.001). In ET, there was a linear correlation between platelet surface expression of CD62p and TSP (p<0.0001, r=0.83). At diagnosis of ET, 20 patients were symptomatic and 14 asymptomatic. Compared with asymptomatic ET patients there was no difference in the expression of CD62p (18.3+/-16.2% vs. 14.5+/-13.4%) and TSP (14.4+/-9.8% vs. 12.8+/-9.5%) in symptomatic ET patients. In conclusion, increased expression of platelet neoantigens is present at the diagnosis of ET. Both activation-dependent epitopes CD62p and TSP are increasingly expressed on the platelet surface in newly diagnosed ET patients.

Primary stenting in acute myocardial infarction: influence of diabetes mellitus in angiographic results and clinical outcome

BACKGROUND

The outcome of patients with diabetes after myocardial infarction (MI) has traditionally been worse than in their nondiabetic counterparts before and during the thrombolytic therapy era. Whether the fate of patients with diabetes might improve with mechanical intervention, particularly with primary stenting, has not previously been studied.

METHODS

We compared the angiographic and clinical outcome of 76 nondiabetic patients (aged 61 +/- 14 years; 66% male) and 28 patients with diabetes (aged 65 +/- 12 years; 64% male) consecutively treated with primary stenting for acute MI. Coronary Thrombolysis In Myocardial Infarction grade 3 flow was restored in 96% of diabetic and 97% of nondiabetic patients.

RESULTS

Angiographic results after stent deployment were similar in the 2 groups. At 1-month follow-up, all patients in both groups were alive. Patients with diabetes had a much higher incidence of stent thrombosis (18% vs 1%; P =.003), which accounted for the majority of the major cardiac events at 1 month (21% vs 4%; P =.009). At a mean follow-up of 315 +/- 13 days, 99% of nondiabetic and 89% of patients with diabetes were alive (P =.04). Overall freedom from a major cardiac event (death, MI, target vessel revascularization) at 315 +/- 13 day follow-up was 88% for nondiabetics and 54% for patients with diabetes (P =.0003). By multivariate analysis, diabetes mellitus was the most important predictor for development of 1-month (RR 9.89; 95% confidence interval, 1.6-30) and late major cardiovascular events (RR 8.39; 95% confidence interval, 2.93-24).

CONCLUSIONS

Primary stenting in acute MI is highly effective in restoring immediate TIMI 3 coronary flow in nondiabetic patients and patients with diabetes. This procedure may improve benefit in terms of mortality rate to both groups, particularly in patients with diabetes, compared with previous reports with thrombolytic therapy. Nevertheless, stent thrombosis and major cardiovascular events at 1 month and late follow-up are more frequent in patients with diabetes.

Predictors of stent thrombosis after primary stenting for acute myocardial infarction

The aim of the study was to determine if a hypercoagulable state that may persist for several months after an acute myocardial infarction may contribute to an increased incidence of stent thrombosis. Primary stenting was performed in 104 consecutive patients with acute myocardial infarction using 147 coronary stents. Twenty-eight patients (27%) were diabetic and 55 patients (53%) were smokers. A single stent was placed in 63%, two stents in 33%, and more than two stents in 4% of the patients. Procedural success was obtained in 97% of the patients. All stents were deployed using high-pressure balloon inflation. The reference vessel diameter and minimal lumen diameter after stent deployment were 3.30 +/- 0.42 and 3.23 +/- 0.42 mm, respectively. Six patients (5.7%) developed stent thrombosis within 1 month after the procedure complicated by reinfarction in five of the six patients. At 1-month follow-up, all patients remained alive. On multivariate analysis, independent predictors of stent thrombosis were diabetes mellitus (relative risk [RR] 5.2; 95% confidence interval [CI] 1.8, 25.1), tobacco use (RR 4.5; 95% CI 1.3, 24.5), number of stents: 1 vs. > 1 (RR 3.7; 95% CI 1.1, 15.9), minimal lumen diameter poststent placement (RR 0.03; 95% CI 0.0002, 0.74), and duration of chest pain before intervention (RR 1.1; 95% CI 1.01, 1.25). Stent thrombosis had not been associated with diabetes mellitus and tobacco use previously but is in agreement with the enhanced platelet aggregability, coagulation factor abnormalities, and impaired fibrinolysis characteristic of these patients.

In vitro generation of endothelial microparticles and possible prothrombotic activity in patients with lupus anticoagulant

Microparticles (MPs) resulting from vesiculation of platelets and other blood cells have been extensively documented in vitro and have been found in increased numbers in several vascular diseases, but little is known about MPs of endothelial origin. The aim of this study was to analyze morphological, immunological, and functional characteristics of MPs derived from human umbilical vein endothelial cells (HUVECs) stimulated by TNF, and to investigate whether these MPs are detectable in healthy individuals and in patients with a prothrombotic coagulation abnormality. Electron microscopy evidenced bleb formation on the membrane of TNF-stimulated HUVECs, leading to increased numbers of MPs released in the supernatant. These endothelial microparticles (EMPs) expressed the same antigenic determinants as the corresponding cell surface, both in resting and activated conditions. MPs derived from TNF-stimulated cells induced coagulation in vitro, via a tissue factor/factor VII-dependent pathway. The expression of E-selectin, ICAM-1, alphavbeta3, and PECAM-1 suggests that MPs have an adhesion potential in addition to their procoagulant activity. In patients, labeling with alphavbeta3 was selected to discriminate EMPs from those of other origins. We provide evidence that endothelial-derived MPs are detectable in normal human blood and are increased in patients with a coagulation abnormality characterized by the presence of lupus anticoagulant. Thus, MPs can be induced by TNF in vitro, and may participate in vivo in the dissemination of proadhesive and procoagulant activities in thrombotic disorders.

Pharmacokinetics and pharmacodynamics of sibrafiban, an orally administered IIb/IIIa antagonist, in patients with acute coronary syndrome

Sibrafiban is a double prodrug that is converted to the inactive single prodrug and to the active IIb/IIIa antagonist following oral administration. Pharmacokinetics (PK) and pharmacodynamics (PD) of oral sibrafiban and its metabolites were evaluated in patients postacute coronary syndrome receiving once- or twice-daily sibrafiban for up to 28 days at several dose levels. Mean peak concentrations of sibrafiban were < 5 ng/mL. Peak single prodrug concentrations occurred 1.7 +/- 1.0 (mean +/- SD) hours after sibrafiban dosing. Total apparent plasma clearance of the single prodrug was 40 +/- 15 L/h, and the elimination half-life was 2.3 +/- 0.8 hours. Mean values of the steady-state pharmacokinetics for total concentrations of the active drug over all doses were: time to peak plasma concentration, 5.0 +/- 1.7 hours; apparent clearance, 13.9 +/- 3.9 L/h; and half-life, 11.0 +/- 2.8 hours. Once-daily dosing resulted in high peak-trough excursions in active drug concentrations: trough concentrations were 21% +/- 6% of peak. Twice-daily dosing resulted in an AUC for the active drug on Day 28 that was 168% +/- 36% of that on Day 1, and steady-state trough concentrations were 54% +/- 10% of peak with sustained inhibition of platelet aggregation. Dose-adjusted steady-state active drug concentrations increased with increasing age and with decreasing renal function and body weight.

Influence of valproate monotherapy on platelet activation and hematologic values

PURPOSE

Valproate (VPA) has been linked to coagulation disturbances, with both impaired and exaggerated clotting, which has been attributed to an effect of VPA on platelets or hemostatic proteins. Additional thrombocytic function testing may help to identify patients at risk of increased bleeding caused by platelet dysfunction.

METHODS

We evaluated the influence of VPA on hematologic routine values and platelet activation by using immunostaining and flow cytometry in 30 patients receiving long-term VPA therapy and in 30 controls.

RESULTS

The fraction of activated platelets was similar in both groups; however, the general extent of platelet activation was significantly lower in the patient group, with considerable interindividual variability. In addition, patients had a significantly lower platelet count, prolonged thrombin time, and higher mean corpuscular hemoglobin.

CONCLUSIONS

Our data confirm the previously reported hematologic changes caused by VPA and additionally suggest that VPA impairs procoagulatory thrombocytic function, which is reflected by reduced platelet activation and increased thrombin time. Possible mechanisms of VPA-platelet interaction are discussed.

Chimeric 7E3 Fab (ReoPro) decreases detectable CD11b on neutrophils from patients undergoing coronary angioplasty

OBJECTIVES

The purpose of this study was to monitor the effects of chimeric 7E3 Fab (ReoPro) on leukocyte and platelet activation and interaction during coronary angioplasty.

BACKGROUND

Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere via P-selectin to monocytes and neutrophils. These cell interactions may affect the outcome of coronary angioplasty.

METHODS

During coronary angioplasty, venous blood was obtained for flow cytometric detection of leukocyte CD11b; platelet CD41a, CD61a and CD62P; the percentage of leukocytes with adherent platelets and the intensity of bound platelet fluorescence.

RESULTS

Leukocyte CD11b expression increased after angioplasty in control patients (neutrophils 171+/-25 to 255+/-31 mean fluorescence intensity [MFI, mean+/-SEM], n=25, p < 0.0001; monocytes 200+/-40 to 248+/-36 MFI, n=17, p < 0.05) and decreased in the patients selected to receive chimeric 7E3 Fab (neutrophils 146+/-30 to 82+/-22 MFI, n=25, p < 0.0001; monocytes 256+/- 53 to 160+/-38 MFI, n= 17, p < 0.05). Neutrophil CD11b decreased after in vitro incubation of whole blood with chimeric 7E3 Fab (n=5, p=0.01), but fMLP-induced increases in CD11b were not prevented. The CD11b expression was unchanged and increased with fMLP stimulation after in vitro incubation of isolated neutrophils with chimeric 7E3 Fab. Direct-labeled chimeric 7E3 Fab was not detected bound to neutrophils in whole blood or isolated cells using flow cytometric techniques. Adhesion of isolated neutrophils to protein-coated glass was not prevented by in vitro incubation with chimeric 7E3 Fab. Platelet activation increased after angioplasty in control patients (CD62P 8.9+/-0.8 to 12.3+/-1.2 MFI, n=25, p < 0.05; CD41a 382+/-25 to 454+/-26 MFI, n=25, p < 0.05, CD61a 436+/-52 to 529+/-58 MFI, n=11, p < 0.05); it did not increase in the patients selected to receive chimeric 7E3 Fab (CD62P 13.2+/-1.0 to 9.0+/-0.9 MFI, n=25, p < 0.05; CD61a 398+/-32 to 410+/-38 MFI, n=7, p=NS). Leukocytes with adherent platelets tended to increase in the control group of patients and decrease after the procedure in patients selected to receive chimeric 7E3 Fab; individual and procedure-related variability were marked.

CONCLUSIONS

Despite standard aspirin and heparin therapy, leukocyte and platelet activation with platelet adherence to leukocytes occurs after coronary angioplasty. Although chimeric 7E3 Fab does not bind to leukocytes directly, it influences CD11b expression in whole blood. Modulation of platelet and leukocyte activation and interaction by chimeric 7E3 Fab may contribute to an improved outcome after coronary angioplasty.

Plasma soluble P-selectin in acute myocardial infarction: effects of coronary recanalization therapy

P-selectin is translocated from platelets and endothelial cells to initiate the first step in a sequence of events leading to the adherence of leukocytes, possibly inducing reperfusion injury and the no-reflow phenomenon in acute myocardial infarction (AMI). This study was undertaken to investigate plasma P-selectin in AMI patients undergoing coronary recanalization therapy. A total of 40 patients were studied: 20 patients with AMI who underwent coronary recanalization by direct percutaneous transluminal coronary angioplasty (PTCA), 10 patients with AMI who underwent thrombolytic therapy by tissue-type plasminogen activator (TPA), and 10 patients with stable angina pectoris who underwent elective PTCA. Blood samples were obtained from systemic arteries before and immediately after PTCA or thrombolytic therapy. Plasma-soluble P-selectin was measured by enzyme immunoassay. Plasma P-selectin was significantly higher in AMI than in stable angina pectoris (176.6 +/- 12.9 ng/mL vs 91.4 +/- 9.5 ng/mL, p<0.001). Plasma P-selectin did not change significantly as a result of elective PTCA in patients with stable angina (from 91.4 +/- 9.5 ng/mL to 87.9 +/- 7.9 ng/mL). Plasma P-selectin was decreased by direct PTCA in all of the 20 patients with AMI (from 176.2 +/- 17.7 ng/mL to 141.7 +/- 12.6 ng/mL; p<0.001, paired t-test), whereas it was increased by thrombolysis using TPA in nine of the 10 AMI patients (from 177.4 +/- 17.2 ng/mL to 248.8 +/- 17.3 ng/mL, p<0.005). Increased P-selectin activity in AMI appeared to be attenuated by direct PTCA, but augmented by thrombolysis, possibly due to direct stimulatory effects of TPA on P-selectin expression. This may lead to less favorable results in salvaging the ischemic myocardium by thrombolytic than mechanical coronary recanalization therapy in AMI.

Glycoprotein IIb/IIIa inhibitors in acute coronary syndromes: pathophysiologic foundation and clinical findings

The pathophysiologic basis for potent platelet inhibition in the acute coronary syndromes has been established. In the setting of PTCA for unstable angina and non-Q-wave myocardial infarction, there are clear data for a benefit of GP IIb/IIIa inhibition, whereas for primary PTCA in evolving myocardial infarction, preliminary data are very encouraging and a large-scale clinical trial is nearly completed. Glycoprotein IIb/IIIa inhibition as an adjunct to medical therapy for unstable angina is also the subject of encouraging preliminary data, and 3 large-scale clinical trials have just been completed. Preliminary data have also been accrued for GP IIb/IIIa inhibition as conjunctive therapy with thrombolytic agents, and large clinical trials are now commencing.

Determinants of rebound thrombin activity after cessation of heparin in patients undergoing coronary interventions

This study was designed to characterize hemostatic activation (using fibrinopeptide A (FPA), a marker of thrombin activity, and beta-thromboglobulin (BTG), a marker of platelet activation) sequentially in the coronary and peripheral circulation in patients during percutaneous coronary intervention (PCI) and several hours after PCI and discontinuation of heparin therapy. Heparin administered during PCI is known to nonuniformly suppress thrombin activity in the coronary. Persistent elevations of FPA in coronary sinus (CS) blood during PCI have been associated with subsequent ischemic events. As a related consideration, rebound thrombin activity has been demonstrated in peripheral blood samples several hours after cessation of heparin therapy in patients with acute coronary syndromes. Accordingly, we hypothesized that increased thrombin activity occurs in the coronary circulation after PCI and is induced by cessation of intravenous heparin to facilitate vascular sheath removal. Such a rebound prothrombotic effect, may contribute to suboptimal outcomes after PCI. In 21 patients undergoing PCI, heparin-bonded catheters were employed to obtain sequential CS and femoral vein (FV) blood samples for measurement in the coronary and peripheral circulation of plasma FPA, a marker of thrombin activity in vivo, and BTG released by platelets during degranulation. Following heparin administration samples were obtained immediately prior to (base) and during (start and end) PCI. Late samples were obtained several hours after PCI (284 +/- 46 min, mean +/- SD) following the cessation of heparin and prior to planned vascular sheath removal. Mean FPA concentration in CS blood was low at baseline (3.82 +/- 2.09 ng/ml) and did not increase during PCI. Mean FPA concentration in CS blood increased significantly several hours after cessation of heparin (3.42 +/- 2.36 vs. 7.82 +/- 9.98, end vs. late, P < 0.001). In contrast, mean FPA concentration in FV blood was highest at baseline following vascular sheath insertion, decreased during PCI (69%, P < 0.05, base vs. end), and trended upward after PCI and cessation of heparin. Mean FPA values were higher at all times in FV compared with CS blood samples and were not concordant after PCI. Elevation of coronary circulation FPA after PCI was maximal in patients with myocardial infarction within 7 days (13.7 +/- 12.4 vs. 5.6 +/- 7.9 ng/ml, P = 0.08), but was not influenced by heparin treatment prior to PCI, a history of unstable angina, or coronary stent placement during PCI (9 of 21 patients). BTG values showed less variation than did FPA values, and cessation of heparin after PCI was not associated with an increase in BTG in CS or FV blood samples. An increase in thrombin activity occurs in the coronary circulation after PCI following discontinuation of heparin. The extent of increased thrombin activity was greatest in patients with recent myocardial infarction and was not exacerbated by coronary stent placement during PCI. This phenomenon may contribute to the important minority of ischemic complications early after PCI.

Therapeutic Concentrations of Heparin Augment Platelet Activation at the Time of Coronary Angiography

Background: Besides its anticoagulant effects, heparin is known to alter platelet (PLT) function. We examined the effects of unfractionated heparin on PLT function in patients with stable coronary artery disease (CAD). Methods and Results: PLT function was evaluated by whole-blood flow cytometry to detect PLT CD62 expression and by impedance aggregometry to assess the platelet aggregation (PA) before and after bolus intravenous administration of low-dose heparin (2713 +/- 1231 U) in 16 patients undergoing coronary angiography (group 1) and high-dose heparin (7937 +/- 2414 U) in 16 patients undergoing coronary angioplasty (group 2). Activated clotting time (ACT) and plasma antifactor-Xa heparin levels also were measured. Heparin increased PLT CD62 expression, which was significantly more pronounced in group 1 patients with plasma heparin levels less than 0.7 U/mL and ACT of 222 +/- 52 seconds compared with group 2 patients with heparin levels greater than 0.7 U/mL and ACT of 365 +/- 86 seconds (8 +/- 9 v -1 +/- 4% change in resulting PLTs, P =.01, and 11 +/- 12 v 1 +/- 6% increase in adenosine diphosphate (ADP) [5 µM]-stimulated PLTs, P =.02). Heparin produced a slight increase in PA in group 1 patients (1.4 +/- 5.3 ohms) as compared with the group 2 patients, where it significantly suppressed PA (-3.0 +/- 5.3 ohms, P.05 v group 1). A strong and statistically significant negative correlation between change in platelet CD62 expression and heparin concentration was observed in group 1 patients (r = -.5, P =.05, -ADP; r = -.65, P =.006, +ADP), whereas this relationship was weak and did not reach statistical significance in group 2 patients (r = -0.4, P =.2, -ADP; r =.11, P = 0.9; +ADP). Conclusion: Bolus administration of intravenous heparin augmented PLT activation in patients at clinically relevant anticoagulant concentrations (<0.7 U/mL). These findings may have implications for optimal dosing strategy for heparin as an antithrombotic agent in clinical situations characterized by platelet-dependent thrombotic events.

Assessment of platelet activation by coronary sinus blood sampling during balloon angioplasty and directional coronary atherectomy

Three markers of platelet activation (platelet-derived microparticles, fibrinogen binding and expression of P-selectin) were assessed by flow cytometry during diagnostic coronary angiography and therapeutic coronary interventions. In 24 patients undergoing diagnostic angiography, blood was collected to determine if our sampling techniques or coronary angiography caused platelet activation. Changes during diagnostic angiography were used to establish baseline values and interpret changes during coronary interventions. In 21 patients, blood samples were obtained at 5 time points during percutaneous transluminal coronary angioplasty (PTCA) (n = 17) or directional coronary atherectomy (DCA) (n = 4). During coronary interventions, mean values for the percentage of platelets expressing P-selectin or binding fibrinogen increased, but with considerable variation among patients. Individual responses for platelet activation markers in each patient were characterized using a twofold increase to indicate elevation related to the intervention. Patients were classified as having complicated or uncomplicated procedures based on the presence of acute closure, dissection, or thrombus observed by angiography. There were no differences in the percentage of elevated markers between patients with uncomplicated (12.5%) and complicated (19%) PTCA procedures. However, patients treated with DCA had more elevated markers (38%) than those treated with PTCA (15%) (p = 0.04). Our data suggest that the extent of platelet activation in individual patients cannot be predicted by common angiographic findings or complications. More markers of platelet activation were present after DCA and may reflect a greater degree of vascular trauma associated with this procedure.

Platelet activation In mice and human Helicobacter pylori infection

Extracts of Helicobacter pylori (HP) have been shown to induce leukocyte adhesion in mesenteric venules, but the effects of HP infection on gastric microvessels are unknown. Inflammatory cell interactions in the gastric microcirculation were studied by intravital videomicroscopy in mice inoculated with either saline or fresh isolates of HP. Platelet aggregates were detected and quantified in murine portal blood, while endothelial P-selectin expression was determined using the dual radiolabeled mAb technique. Platelet activation and aggregation were studied in HP-infected patients and controls by measuring the platelet-aggregate ratio and platelet P-selectin expression. HP infection induced a marked increase in the flux of rolling leukocytes and the appearance of platelet and leukocyte- platelet aggregates in murine gastric venules. The HP-induced rolling and platelet aggregate formation was abrogated by mAbs against L- or P-, but not E- selectin. Endothelial cell expression of P-selectin was not altered, but platelet P-selectin expression was enhanced in HP-infected mice. Circulating platelet aggregates and activated platelets were also detected in HP-infected patients. These findings indicate that platelet activation and aggregation contribute to the microvascular dysfunction and inflammatory cell recruitment associated with HP infections.

Platelet function and platelet-leukocyte adhesion in symptomatic coronary heart disease. Effects of intravenous magnesium

Spontaneous P-selectin surface expression on platelets and platelet-leukocyte adhesion was increased in patients with symptomatic coronary heart disease (n = 12) compared to normal controls (n = 10) (p < 0.05). ADP-induced P-selectin expression and platelet-leukocyte adhesion was also enhanced in the patient group (p < 0.05). Administration of intravenous Mg2+ significantly reduced both platelet surface expression of P-selectin and platelet-leukocyte adhesion ex vivo (p < 0.02). The effect of extracellular Mg2+ was evaluated in in vitro experiments. Both in whole blood and in isolated neutrophil suspension Mg2+ inhibited platelet adhesion to neutrophils dose dependently with half maximal effects at 4 mM. Moreover, Mg2+ inhibited adhesion of isolated platelet membranes to neutrophils. We conclude that platelet function is altered in symptomatic coronary heart disease and can be modulated by administration of intravenous Mg2+.

Changes in membrane glycoproteins of circulating platelets after coronary stent implantation

OBJECTIVES

To evaluate platelet function in patients with coronary stents.

DESIGN

A non-randomised control trial in 30 patients who had immediate implantation of Palmaz-Schatz coronary stents because of a suboptimal angioplasty result. All patients received a standardised anticoagulation regimen including intravenous heparin (activated partial thromboplastin time (APTT) 80 to 120 s), oral vitamin K antagonist (target international normalised ratio (INR) of 3.5), and 100 mg aspirin twice daily. Platelet surface expression of glycoprotein IIb-IIIa, activated fibrinogen receptor, and P-selectin as well as binding of von Willebrand factor and fibrinogen were determined by flow cytometry in peripheral venous blood samples collected before the intervention and then daily for 4 days after it. The results were compared with those in 30 patients undergoing elective coronary balloon angioplasty.

SETTING

University hospital.

RESULTS

After coronary stenting surface expression of the activated fibrinogen receptor significantly increased, peaking at day 2 (P < 0.001). Similar results were found for von Willebrand factor binding and P-selectin surface expression, with a maximum at day 2 to 4 after stenting (von Willebrand factor, P < 0.001; P-selectin, P < 0.001). The changes in platelet membrane glycoproteins coincided with a significant drop in peripheral platelet count after stent placement (P < 0.01). No significant change in fibrinogen receptor activity, von Willebrand factor binding, P-selectin surface expression, or platelet count was seen in the control group.

CONCLUSIONS

The present study shows that current anticoagulation treatment is inefficient in suppressing platelet activation in patients with coronary stents and, therefore, might not be the best treatment for reducing the incidence of subacute stent thrombosis.

Neutrophil and platelet activation at balloon-injured coronary artery plaque in patients undergoing angioplasty

OBJECTIVES

This study sought to investigate changes in the expression of activation-dependent adhesion receptors on neutrophils and platelets after exposure to the balloon-injured coronary artery plaque.

BACKGROUND

Activation of blood cells at the balloon-injured coronary artery plaque may contribute to abrupt vessel closure and late restenosis after percutaneous transluminal coronary angioplasty.

METHODS

In 30 patients undergoing elective coronary angioplasty, blood specimens were obtained through the balloon catheter proximal to the plaque before dilation and distal to the plaque after dilation. Simultaneous blood samples obtained through the guiding catheter served as control samples. Total surface expression of the inducible fibrinogen receptor (CD41) and surface expression of the activated fibrinogen receptor (LIBS1) on platelets as well as Mac-1 (CD11b) and L-selectin (CD62L) surface expression on neutrophils were assessed by flow cytometry.

RESULTS

After exposure to the dilated coronary artery plaque, surface expression of LIBS1 on platelets increased by 40.5 +/- 11.0 mean (+/-SE) fluorescence (p=0.001) and that of CD11b on neutrophils increased by 20.1 +/- 4.4 mean fluorescence (p=0.018). Concomitantly, anti-CD62L binding on neutrophils decreased by 6.6 +/- 2.4 mean fluorescence (p=0.022). In contrast, surface expression of the adhesion receptors did not change significantly between the coronary ostium and the prestenotic coronary segment.

CONCLUSIONS

The results of this study demonstrate neutrophil and platelet activation at the balloon-injured coronary artery plaque. This cellular activation may serve as a target for pharmacologic interventions to improve the outcome of coronary angioplasty.