Platelet Activation In Patients Research Articles

The Effects of Nasal Continuous Positive Airway Pressure on Platelet Activation in Obstructive Sleep Apnea Syndrome

A case-controlled study to assess the effects of nasal continuous positive airway pressure (CPAP) on platelet activation in patients with obstructive sleep apnea (OSAS) syndrome. We recruited 65 patients with suspected OSAS for this study. Blood samples were taken with the patient in the supine position in the morning immediately after polysomnography, and 1 night and 3 months after the start of nasal CPAP therapy to measure an index of platelet activation (IPA+), which reflected both the quantity and quality of platelet activation. Significant OSAS was defined as an apnea-hypopnea index (AHI) of > or = 10 events per hour. There were 42 patients with significant OSAS and 23 control subjects with AHI < 10 events per hour. The mean (+/- SD) age for the OSAS patients was 48 +/- 9 years, the mean body mass index was 30.7 +/- 4.8, the mean AHI was 47 +/- 25 events per hour, the mean arousal index (AI) was 37 +/- 23 events per hour, and the mean minimum arterial oxygen saturation was 74 +/- 11%. Following multiple linear regression analyses of the clinical and polysomnography parameters, AI was the independent factor that correlated best with the baseline IPA+ (beta-coefficient, 0.386; p = 0.006). Following nasal CPAP treatment with a mean objective CPAP compliance of 3.9 +/- 1.9 h per night, there was a significant decrease in IPA+ from 15.1 +/- 12.2 U (at baseline) to 12.2 +/- 5.2 U (p < 0.001) and 9.8 +/- 4.3 U (p = 0.005), respectively, after 1 night and 3 months, whereas no significant change was noted among the control subjects. Using univariate analysis of variance to compare the changes in IPA+ between the two groups at 3 months with adjustment for the baseline value, nasal CPAP reduced IPA+ by 5.63 (SE, 1.85), whereas IPA+ increased in control subjects by 1.33 (SE, 1.27) [least-squared mean difference between groups, 3.34; 95% confidence interval, 0.42 to 6.26; p = 0.026]. OSAS, through repeated episodes of arousals, may lead to platelet activation, which can be reduced by nasal CPAP therapy.

Markers of endothelial and in vivo platelet activation in patients with essential thrombocythemia and polycythemia vera.

We investigated endothelial and in vivo platelet activation in a cohort of 52 patients with essential thrombocythemia (ET) and polycythemia vera (PV) before and after cytoreductive treatment, 22 healthy controls, and 17 patients with acute cerebrovascular ischemia (ACVI) and normal platelet counts. We measured platelet expression of CD62P and CD63 antigens and levels of soluble vascular cell adhesion molecule 1 (sVCAM-1). We found increased in vivo platelet activation in all patients with ET and PV, both before and after cytoreductive treatment, compared with controls. In patients with arterial thrombosis, platelet expression of CD62P, and in patients with erythromelalgia, expression of both markers was higher compared with expression in patients without thrombotic complications. In patients with ET and PV before and after treatment, sVCAM-1 expression was increased compared with expression in controls but also compared with expression in patients with ACVI and normal platelet counts. In patients with arterial thrombosis and erythromelalgia, in vivo platelet activation correlated with the level of sVCAM-1. Our findings indicated that in vivo platelet activation reflects intrinsic platelet defects in patients with ET and PV, persists after cytoreductive treatment, and results in endothelial damage, probably through release of angiogenic factors and/or activation of white blood cells.

Assessment of platelet activation in myeloproliferative disorders with complementary techniques.

Bleeding and thrombosis in myeloproliferative disorders (MPD) are common events, sometimes both are present in the same patient during the course of the disease. Platelet activation in patients with MPD is often suggested. The present study analyses the presence of circulating activated platelets, using simultaneously flow cytometry and aggregometric studies in MPD. We studied 28 patients: 13 with polycythaemia vera, seven with essential thrombocythaemia, and eight chronic myeloid leukaemia. We performed functional tests, aggregation and adenosine triphosphate (ATP) release and flow cytometric assays (mepacrine staining and platelet activation markers CD62, CD63 and fibrinogen binding (B-FG)). Twenty-one MPD samples (75%) had reduced aggregation and ATP release. Acquired delta-SPD was detected in 11 of 28 MPD patients (39%), and we found no association between reduced mepacrine labelling and abnormal ATP release. High levels of activation markers were obtained: CD62 in 19 of 28 patients (68%), CD63 in 13 of 28 patients (46%) and B-FG in 19 of 28 patients (68%). The most prevalent abnormality was a reduced aggregation and ATP release. The lack of association between ATP release and mepacrine labelling suggests that other mechanisms, besides the deficit of intraplatelet ATP/adenosine diphosphate, might occur. High levels of activation markers were also observed. We conclude that both tests are complementary and necessary to understand the functional status of platelets in MPD.

Increased blood coagulation and platelet activation in patients with infective endocarditis and embolic events.

Inflammation-induced procoagulant changes and alterations in platelet activity appear to play an important role in thromboembolic complications of infective endocarditis (IE). The aim of this study was to investigate systemic coagulation activity, fibrinolytic capacity, and platelet activation in patients with IE with and without embolic events by measuring the plasma levels of prothrombin fragment 1+2 (PF1+2), thrombin-antithrombin III complex (TAT), plasminogen activator inhibitor-1 (PAI-1), beta-thromboglobulin (beta-TG), and platelet factor 4 (PF4), respectively. The study included 76 consecutive patients (female = 55, male = 21, mean age 26 years, range 8-64 years) with definite IE according to the Duke criteria; of these, 13 (17.1%) had embolic events. Plasma concentrations of PF1+2 (3.2 +/- 1.3 vs. 1.7 +/- 0.7 and 1.4 +/- 0.7 nmol/l, p < 0.001, respectively) and TAT (7.3 +/- 1.5 vs. 2.9 +/- 1.2 and 2.2 +/- 1.1 ng/ml, p < 0.001, respectively) were elevated in patients with embolic events compared with patients without embolic events and control subjects. Similarly, patients with embolic events had increased plasma levels of beta-TG (63.3 +/- 10.9 vs. 33.1 +/- 11.6 and 19.1 +/- 10.6 ng/ml, p < 0.001, respectively) and PF4 (106.0 +/- 28.7 vs. 50.3 +/- 16.7 and 43.0 +/- 15.8 ng/ml, p < 0.001, respectively) compared with those without embolic events and the control group. Embolic patients also had higher PAI-1 levels than nonembolic patients and healthy subjects (14.4 +/- 6.4 vs. 8.6 +/- 5.9 and 5.4 +/- 4.3 ng/ml, p = 0.002, respectively). Patients with IE and with subsequent thromboembolism have increased systemic coagulation activation, enhanced platelet activity/damage, and impaired fibrinolysis. The resulting imbalance produces a sustained hypercoagulable state, which contributes to the increased risk of thromboembolic events in this particular group.

1027-183 Functional interplay between endothelial dysfunction and platelet activation in patients with stable coronary heart disease

1027-183 Functional interplay between endothelial dysfunction and platelet activation in patients with stable coronary heart disease

Helicobacter pylori seropositivity is associated with enhanced platelet activation in patients with intermittent claudication

Objective Patients with intermittent claudication have a significantly increased risk of mortality from cardiovascular and cerebrovascular causes. Helicobacter pylori infection and abnormal platelet function have been shown to be associated with atherosclerosis as well as with acute ischemic events. The aim of this study was to assess for the first time the relation between H pylori serology status, platelet activation, and endothelial injury in patients with intermittent claudication. Design of study : A prospective observational study of 125 patients with intermittent claudication suitable for angioplasty was conducted at the Vascular Unit of the Aberdeen Royal Infirmary. Main outcome measures Main outcome measures were (1) H pylori serology using ELISA kit for immunoglobulin G antibody to H pylori and (2) whole blood flow cytometric analysis of resting platelet P-selectin expression and fibrinogen binding as measures of platelet activation. Results are presented as platelet percentage. von Wildebrand factor levels were measured using ELISA as a marker of endothelial injury. Carstair deprivation scores were calculated for all patients. Results H pylori serology was positive in 62 patients (49.6%), negative in 56 (44.8%) and equivocal in 7 (5.6%). Median P-selectin expression was significantly increased in H pylori–positive patients compared with seronegative patients (0.815 vs 0.65; P = .039). Median platelet fibrinogen binding was higher in seropositive patients, but this failed to reach statistical significance (2.135 vs 1.85%; P = .11). There was no difference in von Wildebrand factor levels between the two groups ( P = .51). There was no difference in socioeconomic status between the two groups. Conclusion Patients with intermittent claudication who are H pylori positive show enhanced platelet activation that does not appear to be mediated by means of endothelial cell injury.

Inflammation, endothelial dysfunction, and platelet activation in patients with chronic kidney disease: the chronic renal impairment in Birmingham (CRIB) study

Background: Studies in the general population suggest that low-grade inflammation, endothelial dysfunction, and platelet activation are associated with an increased risk of cardiovascular events. Methods: Markers of inflammation, endothelial dysfunction, and platelet activation were measured in 334 patients with chronic kidney disease (serum creatinine >1.47 mg/dL [>130 μmol/L] at screening) and compared with 2 age- and sex-matched control groups, 1 comprising 92 patients with coronary artery disease and the other comprising 96 apparently healthy individuals with no history of cardiovascular or kidney disease. Results: There was evidence of low-grade inflammation in the chronic renal impairment group compared with healthy controls, with higher concentrations of C-reactive protein (3.70 versus 2.18 mg/L, P < 0.01) and fibrinogen (3.48 versus 2.67 g/L, P < 0.001) and lower serum albumin concentration (41.8 versus 44.0 g/dL [418 versus 440 g/L], P < 0.001). More severe renal impairment was associated with a trend towards higher fibrinogen and lower albumin concentrations (both P < 0.001), although there was no association with higher C-reactive protein level. As compared to healthy controls, plasma von Willebrand factor (142 versus 108 IU/dL, P < 0.001) and soluble P-selectin concentrations (57.0 versus 43.3 ng/mL, P < 0.001) were also higher in the chronic renal impairment group. More severe renal impairment was associated with a trend towards higher levels of von Willebrand factor (P < 0.001) and of soluble P selectin (P < 0.05). Conclusion: This cross-sectional analysis demonstrates that chronic kidney disease is associated with low-grade inflammation, endothelial dysfunction, and platelet activation, even among patients with moderate renal impairment.

Platelets in patients with acute ischemic stroke are exhausted and refractory to thrombin, due to cleavage of the seven-transmembrane thrombin receptor (PAR-1)

Platelet activation is involved in the pathogenesis of cerebrovascular ischemia, but the major agonist involved has yet to be identified. To investigate the role of thrombin in platelet activation in patients with acute ischemic stroke, and while thrombin is the most likely candidate for activation of the thrombin receptor PAR-1 in vivo, we assessed its cleavage and internalization using the antibodies SPAN12, binding to uncleaved PAR-1, and WEDE15, recognizing cleaved and uncleaved, but not internalized PAR-1. In contrast to healthy age-matched controls, platelets from stroke patients exhibited significant cleavage and internalization of PAR-1 (P<0.001) and failed to respond to thrombin in vitro. Enhanced surface expression of CD62P, CD63, TSP-1 and less mepacrine uptake showed platelet degranulation during stroke. Platelets from patients with acute cerebral ischemia are exhausted and desensitized to thrombin through cleavage of PAR-1, indicating that high concentrations of thrombin occur with acute cerebrovascular ischemic events in vivo.

Lack of uniform platelet activation in patients after ischemic stroke and choice of antiplatelet therapy

Introduction: Platelets play an important role in the natural history of ischemic stroke, and are known to be activated in the acute phase. Although aspirin reduces risks of myocardial infarction, stroke and cardiovascular death, the extent of platelet action and the effect of aspirin on platelet function in patients recovering from stroke remain unclear. Methods: We studied 120 individuals divided into three equal groups: aspirin-free patients after ischemic stroke, post-stroke patients receiving aspirin (81–650 mg/daily), and aspirin-free subjects with multiple risk factors for vascular disease. Conventional platelet aggregation induced by 5 μM ADP and 5 μM epinephrine, cartridge-based analyzers (Ultegra®, and PFA-100™) readings, and expression of CD31, CD41a, CD42b, GPIIb/IIIa activity, CD51/CD61, CD62p, CD63, CD107a, CD154, CD165, formation of platelet–monocyte aggregates, intact (SPAN12), and cleaved (WEDE15) PAR-1 thrombin receptors by flow cytometry were analyzed. Results: There were no differences between aspirin-free post-stroke patients and aspirin-free controls. Although aggregation was slightly higher, 12 out of the 14 receptor analyses, were surprisingly lower in the post-stroke cohort. Aspirin-treated patients exhibited highly significant inhibition of epinephrine-induced aggregation ( p=0.0001), prolongation of the closure time ( p=0.03), and reduction of the aspirin reactive units ( p=0.02) measured by the Ultegra® device. In addition, surface platelet expression of thrombospondin ( p=0.001), GPIIb/IIIa activity ( p=0.04), P-selectin ( p=0.03), CD40-ligand ( p=0.04), CD165 ( p=0.02), the formation of the platelet–monocyte aggregates ( p=0.01), and intact epitope of PAR-1 thrombin receptor ( p=0.03) were significantly lower in the aspirin-treated group. Conclusions: Platelets are not activated in aspirin-free patients after ischemic stroke. Platelet function is significantly inhibited in those treated with aspirin when compared with healthy subjects with risk factors for vascular disease. Bleeding complications and hemorrhagic transformations after aggressive antiplatelet regimens could be related to the decreased or normal baseline platelet characteristics in such patients. Further analysis of platelet heterogeneity and its clinical significance remains to be determined in randomized trials.

Patients with paroxysmal atrial fibrillation but not paroxysmal supraventricular tachycardia display evidence of platelet activation during arrhythmia

It is well known that chronic atrial fibrillation (CAF) and paroxysmal atrial fibrillation (PAF) are associated with a hypercoagulable state. However, pathological hemostatic changes during the paroxysmal supraventricular tachycardia (PSVT) have not yet been elucidated. To determine platelet activity in patients with PSVT, PAF and CAF, we examined the levels of β-thromboglobulin (BTG) and platelet factor 4 (PF4) during tachyarrhythmia attacks. We measured the levels of BTG and PF4, as an index of platelet activation in 15 patients with PAF (9 men, mean age 45 ± 11), and 14 patients with PSVT (8 men, mean age 40 ± 10). Levels were compared to 22 age and sex-matched healthy controls in sinus rhythm and with 25 patients with CAF (16 men, mean age 51 ± 12). Blood samples were taken during arrhythmia and 24 hours after conversion to sinus rhythm. Patients taking medications or have clinical conditions that may affect the BTG and PF4 levels were excluded.In patients with PAF, BTG and PF4 levels were significantly higher than in controls ( p<0.009, and p = 0.002, respectively), and in patients with PSVT ( p<0.04, and p = 0.009, respectively), however, BTG and PF4 levels were significantly lower than CAF patients ( p = 0.002, and p = 0.02, respectively). Moreover, BTG and PF4 levels were significantly decreased 24 hours after conversion to sinus rhythm ( p<0.0001, and p = 0.004, respectively). Although BTG and PF4 levels in patients with PSVT were significantly lower than in patients with PAF ( p = 0.04, and p = 0.009, respectively) and CAF ( p = 0.0001, and p = 0.0001, respectively), BTG and PF4 levels were similar to controls and did not change significantly after recovery to sinus rhythm ( p = NS for all).These results indicate that there was no platelet activation in patients with PSVT during tachyarrhythmia but significantly increased platelet activity in PAF and CAF patients. There was a significant decrement of the platelet activity to a level of control subjects twenty-four hours after cardioversion of PAF.

Platelet activity in patients with hyper- and hypoparathyroidism

Platelet aggregatory activity was studied in a patient with hyperparathyroidism before and after parathyroid adenomectomy and in 3 patients with hypoparathyroidism. In these patients, changes in the aggregation activity of platelet were evaluated after their incubation with parathyroid hormone. The patient with hyperparathyroidism was found to have activated platelets, their high readiness for an aggregation response, increased and a highly effective aggregatory activity and insignificantly decreased stability of formed platelet aggregates. After parathyroid adenomectomy there was a partial recovery ofplatelet functional activity. The patients with hypoparathyroidism had a lower platelet functional activity as compared with the controls. Preincubation of platelet-rich plasma from the patients with hypoparathyroidism with parathyroid hormone caused a varying recovery of platelet functional activity.

Flow cytometric analysis of platelet activation in hypertensive patients. Effect of doxazosin

The percentage of spontaneously activated platelets and the platelet response to several agonists were studied in 26 hypertensive patients. The percentage of platelets expressing glycoprotein (GP) IIb/IIIa in its active conformation (GPIIb/IIIa*), P-selectin and phosphatidylserine (PS) was measured by flow cytometry at baseline and 1 and 2 months after treatment with doxazosin (4 mg/day). The response to ADP and Ca 2+ ionophore was also evaluated. The results were compared with those of a control group of 71 normotensive volunteers. Spontaneous platelet activation was higher in patients than in controls (P-selectin-positive results in 4.4±2.0% patients vs. 2.7±1.7 controls, p<0.05; phosphatidylserine-positive results in 0.7±0.4% vs. 0.5±0.3%, respectively, p<0.05), and higher in response to ionophore action (phosphatidylserine-positive results 51.8±11.1% vs. 43.4±11.7%, p<0.01). Platelet activation in patients decreased after 2 months of doxazosin administration compared to baseline (P-selectin-positive results 2.7±1.4% vs. 4.4±2.0%, p<0.05; phosphatidylserine-positive results 0.3±0.2% vs. 0.7±0.4%, p<0.05). No significant differences were noted in GPIIb/IIIa*. The clinical significance of normalization of platelet activity by doxazosin remains to be established.

Platelet activation in patients with congestive heart failure: Do we have enough evidence to consider clopidogrel?

Our understanding of the pathogenesis of congestive heart failure (CHF) has improved remarkably in recent years. However, despite better knowledge and novel pharmaceutical strategies, this disease is still one of the most brutal killers in the Western world. The pathophysiology of CHF is complex, and much of our comprehension revolves strictly around the neurohormonal and mechanical mechanisms involved. It has been suggested that CHF is associated with altered hemostasis, but whether a prothrombotic state contributes to the pathogenesis and progression of the disease is still not well known. The purpose of this review article is to discuss our current knowledge of platelet activation in patients with CHF and the potential role of antiplatelet agents in preventing these hemostatic abnormalities. Clopidogrel is an established medication that reduces the incidence of stroke, myocardial ischemia, or vascular death. It is currently the drug of choice in the prophylaxis of subacute stent thrombosis and postischemic stroke treatment. Promising results of the most resent trials (Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events [CAPRIE] and Clopidogrel in Unstable angina to prevent Recurrent Events [CURE]) may expand future indications of this ADP receptor antagonist for prevention of thrombotic complications in the CHF population. Currently conducted clinical trials (Warfarin and Antiplatelet Therapy in Chronic Heart Failure [WATCH] and Plavix Use for Treatment of Congestive Heart Failure [PLUTO-CHF] should clarify the role of clopidogrel in these patients. (Am Heart J 2003;145:397-403.)

P2868 Effect of dual antiplatelet therapy on platelet activation in patients with acute coronary syndromes in the presence of elevated C-reactive protein

P2868 Effect of dual antiplatelet therapy on platelet activation in patients with acute coronary syndromes in the presence of elevated C-reactive protein

Acute, short-term hyperglycemia enhances shear stress-induced platelet activation in patients with type II diabetes mellitus

ObjectivesThe aim of our study was to assess whether acute, short-term hyperglycemia affects platelet reactivity in patients with Type II diabetes mellitus (T2DM). BackgroundHyperglycemic spikes are thought to precipitate ischemic events in T2DM. Previous studies have shown in vivo platelet activation in diabetes; however, no studies have assessed whether acute in vivo hyperglycemia induces further activation of platelets. MethodsIn a cross-over, randomized, double-blind study, 12 patients with T2DM underwent 4 h of either acute hyperglycemia (13.9 mmol/l, 250 mg/dl) or euglycemia (5.5 mmol/l, 100 mg/dl). Shear stress-induced platelet activation, P-selectin and lysosomal integral membrane protein (LIMP) expression on platelets in the bleeding-time blood, urinary 11-dehydro-thromboxane B2(TxB2) excretion, von Willebrand factor:antigen (vWF:Ag), and von Willebrand factor:activity (vWF:activity) were measured before and after hyperglycemia or euglycemia. ResultsShear stress-induced platelet activation, P-selectin and LIMP expression on platelets in the bleeding-time blood, and urinary 11-dehydro-TxB2excretion increased significantly after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping. Plasma vWF:Ag and vWF:activity increased strikingly in parallel fashion after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping. ConclusionsOur data demonstrate that acute, short-term hyperglycemia induces an increased activation of platelets exposed to high shear stress conditions in vitro (filtration method) or in vivo (bleeding time). In vivo platelet activation is reflected by an increased urinary excretion of 11-dehydro-TxB2. The increased levels of vWF in the circulation correlate with the increase in platelet activation markers and may indicate some degree of causation. Acute, short-term hyperglycemia in T2DM may precipitate vascular occlusions by facilitating platelet activation.

Evaluation of platelets in heart failure: Is platelet activity related to etiology, functional class, or clinical outcomes?

Abstract Objectives We sought to determine whether platelet activity in patients with heart failure is related to an ischemic versus nonischemic etiologic condition, clinical disease severity, or adverse clinical outcomes. Background Platelet activity may affect outcome in patients with heart failure. A prospective evaluation of the relation of baseline platelet function to etiologic condition, New York Heart Association (NYHA) class, and clinical outcomes has not been previously reported. Methods Ninety-six consecutive outpatients with ambulatory heart failure with an ejection fraction 2 , 6-keto PGF 1α , platelet contractile force, adenosine diphosphate/collagen shear-induced closure time, whole blood aggregation and CD41, CD31, CD62p, and CD51/CD61 by flow cytometry were determined. Survival status and hospitalizations were determined in the heart failure patient cohort. Results The median age of patients was 65 years (22% female, 64% white). An ischemic etiologic condition was present in 61% of patients. The population had mild to moderate heart failure: NYHA class I (1%), II (41%), III (46%), and IV (12.5%) and severe ventricular dysfunction (median ejection fraction=0.20). There were 39 clinical events (7 deaths, 3 cardiac transplants, 29 other first hospitalizations) in 305 median days of observation. Platelet activity, indicated by whole blood aggregation with 5 μmol adenosine diphosphate ( P =.04) and Tx B 2 ( P =.01), was higher in patients with heart failure. Whole blood aggregation was greater than the 90th percentile in 22% of patients with heart failure versus 7% of control subjects. Platelet function did not differ for any of the markers between the ischemic and nonischemic groups and was not affected by antecedent aspirin. There was no relation of NYHA class or the occurrence of events to platelet activity. Conclusion Platelet activity is heightened in 22% of outpatients with stable heart failure symptoms and is not affected by antecedent aspirin therapy. The degree of platelet activation is similar in ischemic and nonischemic patients with heart failure and is not related to clinical disease severity. Current methods to assess platelet activation do not appear to predict outcome. (Am Heart J 2002;143:1068-75.)

Platelet activation in patients with diabetic retinopathy.

To clarify the diabetic complications mediated by increased platelet activity, we undertook a study of the mean platelet component (MPC), as determined by an automated hematologic analyzer (ADVIA 120, Bayer). Prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen were also measured to investigate blood viscosity abnormalities. MPC was determined in 100 healthy controls and in 100 diabetic patients, the latter of which were subdivided into no diabetic retinopathy (DR) (n = 25), nonproliferative DR (n = 30), and proliferative DR (n = 45) groups. The mean MPC level was 26.9 g/dl in the control group and 22.5 g/dl in the diabetic patients (p < 0.05). PT and aPTT were similar for the diabetic patients and the controls; however, their corresponding fibrinogen levels were significantly different between the two groups(3.26 +/- 1.14 g/L vs. 4.21 +/- 2.35 g/L, p < 0.05). Our results suggest that platelet hyperfunction in diabetic patients may be implicated in the pathogenesis of diabetic retinopathy.

A whole blood flow cytometric determination of platelet activation by unfractionated and low molecular weight heparin in vitro

The influence of unfractionated (Heparin–Natrium) and low-molecular heparin (Fragmin®) on platelet activation in whole blood was investigated by FACS analysis in vitro using antibodies against glycoprotein (gp) IIb/IIIa (CD 41), GMP 140 (CD 62P), gp 53 (CD 63) and fibrinogen. Samples were also labeled with anti-gp Ib (CD 42b). Neither unfractionated heparin (UFH) nor low molecular weight heparin (LMWH) led to significant (i.e., p<0.05) changes in fluorescence intensities of platelets labeled with anti-gp IIb/IIIa or anti-gp 53. Significant platelet activation due to unfractionated heparin could be observed by labeling with anti-GMP 140 (UFH: p=0.009; LMWH: p=0.16). The proportion of platelets with surface-bound fibrinogen was significantly increased (UFH: p=0.00006; LMWH: p=0.008). After incubation with heparins, activation ability of platelets by adenosine diphosphate (ADP) was significantly increased. The potentiating action of unfractionated heparin was larger. Therefore, flow cytometric results of platelet activation in patients receiving heparin should be interpreted carefully.

Markers of platelet activation and platelet–leukocyte interaction in patients with myeloproliferative syndromes

Introduction: Changes in platelet count and function contribute to thrombo-hemorrhagic episodes in chronic myeloproliferative syndromes (MPS). We used flow cytometry to study platelet–leukocyte conjugates and markers of platelet activation in patients with MPS. Methods: Whole blood from patients with chronic myelogenous leukemia (CML), polycythemia vera (PV), chronic myelofibrosis (MF), and essential thrombocythemia (ET) and from healthy volunteers was prepared for flow cytometry. Platelet microparticles and platelet microaggregates were identified with anti-CD42b and forward scatter, activated platelets with anti-CD62p. Anti-CD42b, anti-CD14, and anti-CD45 were used to study platelet–leukocyte conjugates. Results: The percentage of CD62p-positive platelets was elevated in all myeloproliferate syndrome subtypes. The median percentage of platelet microparticles was 5.2% in controls and significantly higher in PV (12.0%), MF (11.0%), and ET (11.0%, all p<0.05). There was an increased percentage of platelet–neutrophil conjugates in patients with PV (8.3%) and ET (10.4%) compared to normal controls (6.8%, all p<0.05). Platelet–monocyte conjugates were 8.0% in controls and elevated in PV (15.4%) and ET (15.0%, all p<0.05). Patients with a history of venous or arterial thrombotic events had slightly less platelet–leukocyte conjugates and slightly more microparticles than patients without thrombosis; however, this difference was not statistically significant. Conclusions: These findings suggest that platelet–leukocyte conjugate formation occurs in myeloproliferative syndromes and indicates platelet activation. Also, platelet microparticles are elevated and might provide a catalytic surface for thrombin generation. This could explain the clinical observation that patients with myeloproliferative syndromes have an increased risk to experience arterial or venous thrombotic events.

A study of platelet activation in paroxysmal, persistent and permanent atrial fibrillation.

We hypothesized that the 'residual' thromboembolic risk in therapeutically anticoagulated patients undergoing cardioversion could potentially be related to abnormal haemorheology and platelet activation. To test this hypothesis, we firstly investigated the role of haemorheology and platelet activation in patients with paroxysmal and persistent atrial fibrillation (AF), who were compared with healthy controls and patients with permanent AF. Second, we compared these indices in patients with persistent AF, before and after successful cardioversion. We measured indices of haemorheology (haematocrit, plasma viscosity, and fibrinogen), fibrin D-dimer (an index of thrombogenesis and fibrin turnover) and platelet activation (as assessed by platelet aggregation and plasma levels of beta-thromboglobulin, and soluble P-selectin) in 29 patients with paroxysmal AF, 87 patients with permanent AF and 29 healthy controls in sinus rhythm. The effects of cardioversion were studied in 20 patients with persistent AF, who maintained sinus rhythm at 2 months follow-up. Plasma levels of beta-thromboglobulin (P = 0.03) and fibrin D-dimer (P = 0.001) were higher in patients with AF, when compared with controls; the highest levels were seen in those with permanent AF (Tukey's test, < 0.05). Plasma viscosity was significantly higher in the patients with paroxysmal AF compared with healthy controls (P = 0.02). Plasma soluble P-selectin levels and platelet aggregation responses to all four platelet agonists (adenosine diphosphate, collagen, epinephrine and thrombin) in patients with paroxysmal AF and permanent AF were similar to controls. Plasma fibrinogen, viscosity and other markers of platelet activation (including platelet aggregation) were not significantly different in patients with paroxysmal AF, during episodes of AF and sinus rhythm (P = not significant), although mean haematocrit was significantly higher during the episodes of AF compared with episodes of sinus rhythm (P = 0.03). Among the patients with persistent AF who remained in sinus rhythm at 2 months following successful cardioversion, there was a significant decrease in the plasma levels of soluble P-selectin at 2 weeks and 2 months, when compared with baseline (pre-cardioversion) levels (P < 0.001). Haemorheology and platelet aggregation response to agonists did not change significantly, except for a transient increase in platelet aggregation response to collagen at 2 weeks (P = 0.045). In conclusion. abnormal haemostatic and platelet activation in patients with permanent AF are not consistently observed in patients with paroxysmal and persistent AF. Abnormal haemorheology appears to play an important role in patients with paroxysmal AF, especially during the paroxysms of AF. Cardioversion of persistent AF to sinus rhythm appears to decrease the platelet activation, but whether this translates into a beneficial reduction in thromboembolic risk requires further study.