Degree Of Platelet Activation Research Articles

Mean platelet volume: An important predictor of coronary collateral development

Collaterals, which develop in response to ischemic stimuli derived from coronary artery disease (CAD), contribute to reduction of infarct size, left ventricular dysfunction, and mortality. However, there is considerable variation among patients with coronary heart disease regarding the extent of coronary collateral development (CCD). In this study, we aimed to investigate the association of the degree of platelet activation via mean platelet volume (MPV) with coronary collateral circulation. Therefore, 210 patients who underwent coronary angiography and had coronary stenosis ≥50 % in at least one coronary artery were included in the study. Clinical information and analyses of blood samples were obtained from a review of the patients’ chart. Blood samples for MPV were analyzed by K3 EDTA and collateral vessels were graded according to the Rentrop classification. In the study group, 150 of the 210 patients were found to have inadequate CCD. Although there was no difference between the two groups with regard to platelet count, MPV levels were significantly higher in the patients who had inadequate CCD (11.3 ± 1.0 fl vs. 9.5 ± 1.5 fl, p < 0.001). Furthermore, the Gensini score was significantly lower in patients who had inadequate CCD (45 ± 46 vs. 91 ± 35, p < 0.001). MPV, Gensini score, age, female gender, total cholesterol, red cell distribution width, triglyceride, and fasting glucose levels were found to have univariate association with poor CCD. In multivariate logistic regression model, MPV (OR = 2.45, p < 0.001) and Gensini score (OR = 0.98, p < 0.001) were found to be the independent predictors of impaired CCD. In receiver operator characteristic curve analysis, optimal cut-off value of MPV to predict inadequate CCD was found as >9.6 fl, with 96% sensitivity and 84.7% positive predictive value. In conclusion, we can say that MPV is an important, simple, effortless, and cost effective tool and can be useful in predicting the CCD in patients with significant CAD.

Reactive oxygen and nitrogen species modulate the ex-vivo effects of LPS on platelet adhesion to fibrinogen

AimsExcessive production of nitric oxide (NO) and reactive oxygen species (ROS) in sepsis modulates different cell functions. Since the sepsis severity is associated with the degree of platelet activation, we decided to investigate the role of systemic generation of NO and ROS in modulating the platelet adhesion of lipopolysaccharide (LPS)-treated rats. Main methodsPlatelet adhesion was evaluated using fibrinogen-coated 96-well microtiter plates. Cyclic GMP levels were measured using enzyme immunoassay kit. Key findingsTreatment of rats with LPS significantly increased spontaneous platelet adhesion, but reduced the thrombin-activated platelet adhesion when compared with control rats. Chronic treatment of rats with the NO synthase inhibitor L-NAME (20mg/rat/day, 7days) prior to LPS injection normalized the increased adhesion in non-activated platelets, but failed to affect the adhesion in thrombin-activated platelets. The cGMP levels were modified neither in non-activated nor in thrombin-activated platelets of LPS-treated rats when compared with control rats. The incubation of non-activated platelets with the O2− scavenger PEG-SOD reversed the stimulatory effect of LPS on spontaneous adhesion, but had no effect in stimulated-platelet adhesion of non-treated or LPS-treated groups. Moreover, pretreatment of rats with the antioxidant N-acetylcysteine (NAC; 150mg/kg) prevented the increase of non-activated platelet adhesion, and significantly reduced the inhibitory effect of LPS on thrombin-stimulated adhesion. SignificanceOur findings suggest that in LPS-treated rats, NO plays an important modulatory role only in non-stimulated platelet adhesion through cGMP-independent mechanisms, while ROS, directly or by affecting the redox state of the animals, modulates both non-activated and thrombin-activated platelet adhesion.

Modification of the VerifyNow® P2Y12 test BASE channel to accommodate high levels of P2Y12 antagonism

The VerifyNow® P2Y12 (VN-P2Y12) test reports thienopyridine-mediated platelet inhibition relative to a “BASE” channel, potentially eliminating the need for predrug patient assessment, by activating platelets through a P2Y12-independent pathway. The original formulation of the BASE channel used a protease activated receptor-1 (PAR-1) peptide as agonist. However, more potent P2Y12 antagonism required more complete activation of platelet thrombin receptors for the BASE measurement in order to negate any contribution of the P2Y12 receptor. Accordingly, the current BASE channel formulation consists of both PAR-1 and protease activated receptor-4 (PAR-4) activating peptides to facilitate a higher degree of platelet activation. The aim of this study was to compare the performance of PAR-1 versus PAR-1/PAR-4 activating peptides as the BASE channel formulation using prasugrel's active metabolite, R-138727, in vitro to achieve high-grade P2Y12 inhibition. Blood samples from 20 healthy donors were spiked in vitro with R-138727 at concentrations that include plasma levels achieved following prasugrel administration and were incubated for 30 minutes at 37°C. All samples were run in triplicate using both the PAR-1 and the PAR-1/PAR-4 BASE formulation in the VN-P2Y12 test device. The data confirmed the sensitivity of the original BASE formulation to high-grade P2Y12 inhibition as reflected in the concentration-dependent decrease in values. Incorporation of PAR-4 activating peptide eliminated the effect of P2Y12 blockade at all concentrations of R-138727. Thus, the use of PAR-1/PAR-4 in the BASE channel of the VN-P2Y12 cartridge addresses the impact of high grade P2Y12 blockade and may allow more accurate reporting of “% inhibition” in patients treated with more effective P2Y12 antagonists.

Heparinized polyvinyl alcohol to specifically adsorb low-density lipoprotein from plasma

Introduction A medical adsorbent for blood purification was developed to specifically adsorb low-density lipoprotein (LDL) from hypercholesterolemia patient’s plasma by covalently immobilizing heparin onto the surface of polyvinyl alcohol (PVA) with the couplant toluence-2,4-diisocyanate (TDI). Methods We used IR to demonstrate the success of covalently immobilizing heparin onto the surface, and investigated its adsorption of LDL, and primarily evaluated its hemo-compatibility using tests for platelet adhesion, the degree of platelet activation and a hemolysis test. Results (1) Heparin was successfully covalently immobilized onto the surface, the maximum amount of heparin immobilized on the surface of 1 g PVA–1799 granules was about 5 μg; (2) one optimal condition for adsorption of LDL from hyperlipidemia plasma was a pH within the range of 7.2∼9.5, accordingly the adsorptive ratio (adsorbent/g: plasma/L = 1:2) for LDL was about 70%; (3) it exhibited good hemo-compatibility. Conclusion The adsorbent results in satisfactory adsorption of LDL with good hemo-compatibility; it could potentially be used as a blood purification material, and immobilization of heparin onto medical materials may be a way to develop an LDL-specific adsorbent for blood purification.

Predictive Value of Platelet Activation for the Rate of Cognitive Decline in Alzheimer's Disease Patients

Vascular risk factors contribute to the progression of dementia in Alzheimer's disease (AD) and influence platelet activation. However, the degree of platelet activation as a possible underlying mechanism of this progression has not been studied till now. Significantly higher baseline expression of both platelet activation biomarkers, activated glycoprotein IIb-IIIa complex and P-selectin, was observed in patients with AD with fast cognitive decline compared with AD patients with slow cognitive decline during a 1-year follow-up period. These results suggest that platelet activation could be a putative prognostic biomarker for the rate of cognitive decline and a potential new treatment target in AD patients.

Patterns of activation and deposition of platelets exposed to the polymeric surface of the paclitaxel eluting stent

The interaction of platelets with the polymeric surface of drug eluting stents has not been fully described in the literature. Our aim was to analyze the patterns of activation and deposition of platelets exposed to two different stent platforms; (a) the polymeric surface of the paclitaxel eluting stent (Taxus((R)) stent, PES,) and (b) the metallic surface of a stent with identical structural design (Express((R)) stent, BMS). Platelet activation was tested by deploying stents in an in vitro flow chamber model. Anticoagulated blood of 25 healthy volunteers was circulated (flow rate 10 ml/min for 60 min) into the flow chamber system. P-selectin expression, glycoprotein IIb/IIIa activation (PAC-1 binding) and platelet-monocyte complexes (PMC) formation were evaluated at 0, 10, 30 and 60 min. Surface platelet deposition was assessed by surface electron microscopy in stents implanted in the in vitro system for 60 min and in stents implanted in normal porcine coronary arteries for 24 h. Platelet activation evaluation showed a higher P-Selectin expression (92.9% of baseline in PES versus 68.3 % in BMS, P = 0.01) and higher PMC formation (125.7 % of baseline in PES versus 75.6% in BMS, P < 0.01) in the PES compared to the BMS control group. PAC-1 binding levels did not differ among groups. In the in vitro study, SEM analysis of the stent surface showed no statistical differences on platelet deposition between the groups. In addition, presence of proteinaceous material was more frequently seen on the BMS group (moderate to complete coverage = 80% in BMS versus 26% in PES, P < 0.01). In the in vivo study, complete platelet coverage was similar between groups (PES = 7% versus BMS = 8%, P = NS). However, there was an overall trend towards less platelet deposition on the BMS surface (mild and moderate coverage = 83%, 9% in BMS versus 49%, 44% in PES, P < 0.001 for both) but thrombus formation was not observed in either group. The polymeric surface of the PES appears to induce a higher degree of platelet activation and deposition compared to the BMS surface. The biological implications of these findings on the patterns of vascular healing need to be further studied in vivo. Condensed Abstract The interaction of human platelets with the surface of drug eluting stents has not been fully characterized. Patterns of platelet activation and adhesion were evaluated in vitro and in vivo after exposing platelets to the surface of the paclitaxel-eluting stent and identical bare metal stent. The degree of PMC formation and P-selectin expression was increased in PES compared to BMS. In the in vivo study, complete platelet coverage was similar between groups. There was an overall trend towards less platelet deposition on the BMS surface, however, thrombus formation was not observed on either surface. The polymeric surface of the PES appears to induce a higher degree of platelet activation and deposition compared to the BMS surface.

Expression of stromal-cell-derived factor-1 on circulating platelets is increased in patients with acute coronary syndrome and correlates with the number of CD34+ progenitor cells

Previous experimental studies have suggested that platelet stromal-cell-derived factor-1 (SDF-1) regulates mobilization and recruitment of haematopoietic progenitor cells supporting revascularization in mice. However, there are no clinical data available regarding platelet-bound SDF-1 in patients with acute coronary syndrome (ACS). The objective of this study was to evaluate the platelet-surface expression of SDF-1 in patients with ACS. Patients with ACS (n = 418) showed a significantly enhanced SDF-1 expression on admission compared with those with stable angina pectoris (SAP, n = 486) [SAP (mean fluorescence intensity (MFI) +/- SD): 13.48 +/- 5.27; ACS: 18.45 +/- 12.85; P < 0.001) independent of cardiovascular risk factors and medication. Enhanced platelet-bound SDF-1 expression was found in patients with reduced left ventricular ejection fraction (LVEF <55%) in comparison to patients with normal LVEF (P = 0.005). Platelet-bound SDF-1 expression positively correlated with the degree of platelet activation [CD62P: r = 0.325; glycoprotein VI (GPVI): r = 0.277; PAC-1: r = 0.501; P < 0.001 for all] and showed a significant, but slight association with plasma levels of SDF-1 (r = 0.084; P = 0.045). In a subgroup of patients with coronary artery disease, platelet-bound SDF-1, but not other platelet activation markers, significantly correlated with the number of circulating CD34(+) progenitor cells (r = 0.252; P = 0.002) or CD34(+)/CD133(+) endothelial progenitor cells (r = 0.352; P = 0.008). Platelet-bound SDF-1 may play an important role in peripheral homing of circulating progenitor cells thus in tissue regeneration.

Complexes leucoplaquettaires en tant que marqueur d’activation dans les concentrés plaquettaires standards

Objectives Several in vitro laboratory tests to assess the quality control of platelet concentrates (PC) are available. Some of them have a good correlation with the platelet recovery index. To assess the quality control of standard PC prepared in our blood bank, we measured the blood gas and the degree of platelet activation. Materials and methods SPC were prepared by the PRP method. Fifty-five SPC (45 SPC at day one of storage and 20 SPC at day five of storage) were analysed. Blood gas (pH, PO 2, PCO 2 and bicarbonate concentration) in the SPC were measured by blood gas automate. Platelet activation profile were determined by measuring the percentage of platelet expressing the CD62p (% CD62) and the percentage of platelet-leukocyte aggregate (% PLA). Results The pH values of all studied SPC were comprised between 7.0 and 7.6. SPC at day 1 of storage have a significantly higher pH than those at day 5 of storage (7.5 ± 0.05 versus 7.3 ± 0.14; p < 0.001). The % CD62p were higher in SPC at day five compared to the SCP at day one without reaching a statistical significance (28.4 ± 15% versus 24.3 ± 9.7%, p = 0.052). The percentage of PLA were higher in SPC at day one compared to SCP at day five although this difference is not statistically significant (22.2 ± 7.5% versus 17.9 ± 8.0%; p = 0.23). Conclusion Preparation and storage procedure adopted in our centre did not significantly affect the quality SPC. Our study is the first to assess the PLA in PC. Studies assessing the PLA are warranted to appreciate the clinical impact of this parameter.

Heparin-induced thrombocytopenia: A stoichiometry-based model to explain the differing immunogenicities of unfractionated heparin, low-molecular-weight heparin, and fondaparinux in different clinical settings

IntroductionHeparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies that recognize platelet factor 4 (PF4)/heparin complexes. The frequency of HIT is highly variable in different clinical settings, and is more frequent with unfractionated heparin (UFH) than with low-molecular-weight heparin (LMWH), despite the in vitro observation that HIT antibodies activate platelets similarly well with LMWH as with UFH. An important difference between UFH, LMWH, and fondaparinux is their widely differing plasma concentrations. We aimed to provide a model that included anticoagulant concentrations and PF4 availability as risk factors influencing the anti-PF4/heparin immune response. Materials and methodsBy photon correlation spectroscopy we determined the concentrations at which UFH, LMWH, and fondaparinux form complexes optimally with PF4. Plasma concentrations of UFH and LMWH were calculated based on ex vivo pharmacokinetic data, with information on fondaparinux and PF4 concentrations taken from the literature. Results and conclusionsThe main features of our model are: optimal complex formation occurs at prophylactic-dose UFH and high PF4 levels, whereas therapeutic-dose LMWH concentrations are too high for optimal complex formation; in contrast, concentrations of fondaparinux are usually below the optimal stoichiometric range. Thus, immunization should occur more often in situations with major rather than minor platelet activation, and—for a given degree of platelet activation (PF4 availability)—as: prophylactic-dose UFH>therapeutic-dose UFH>prophylactic-dose LMWH, fondaparinux>therapeutic-dose LMWH. Our model provides a framework for explaining empirical observations that LMWH induces less anti-PF4/heparin antibodies than does UFH, and that anti-PF4/heparin antibodies are more often found in patients undergoing major surgery than in medical patients.

Genetic Variants in P-Selectin and C-Reactive Protein Influence Susceptibility to Cognitive Decline After Cardiac Surgery

We hypothesized that candidate gene polymorphisms in biologic pathways regulating inflammation, cell matrix adhesion/interaction, coagulation-thrombosis, lipid metabolism, and vascular reactivity are associated with postoperative cognitive deficit (POCD). Cognitive decline is a common complication of coronary artery bypass graft (CABG) surgery and is associated with a reduced quality of life. In a prospective cohort study of 513 patients (86% European American) undergoing CABG surgery with cardiopulmonary bypass, a panel of 37 single-nucleotide polymorphisms (SNPs) was genotyped by mass spectrometry. Association between these SNPs and cognitive deficit at 6 weeks after surgery was tested using multiple logistic regression accounting for age, level of education, baseline cognition, and population structure. Permutation analysis was used to account for multiple testing. We found that minor alleles of the CRP 1059G/C SNP (odds ratio [OR] 0.37, 95% confidence interval [CI] 0.16 to 0.78; p = 0.013) and the SELP 1087G/A SNP (OR 0.51, 95% CI 0.30 to 0.85; p = 0.011) were associated with a reduction in cognitive deficit in European Americans (n = 443). The absolute risk reduction in the observed incidence of POCD was 20.6% for carriers of the CRP 1059C allele and 15.2% for carriers of the SELP 1087A allele. Perioperative serum C-reactive protein (CRP) and degree of platelet activation were also significantly lower in patients with a copy of the minor alleles, providing biologic support for the observed allelic association. The results suggest a contribution of P-selectin and CRP genes in modulating susceptibility to cognitive decline after cardiac surgery, with potential implications for identifying populations at risk who might benefit from targeted perioperative antiinflammatory strategies.

Platelet Activation Is Linked to the Severity of Pulmonary Hypertension in Sickle Cell Disease and Normalizes on Sildenafil Therapy.

Pulmonary hypertension (PHT) is a severe complication of sickle cell disease (SCD) characterized by abnormal vascular tone, vascular proliferation and thrombosis, associated with chronic hemolysis, and nitric oxide (NO) consumption by cell-free hemoglobin. Since platelets are central to the development of large-vessel thrombosis, and increased platelet activation has been described independently in patients with primary PHT and in patients with SCD, we sought to define the degree of platelet activation in SCD patients with secondary PHT. We hypothesized that the degree of platelet activation may be linked to the severity of PHT, hemolytic rate and NO bioavailability; conversely, platelet activation may decrease with therapy directed to PHT by increasing NO-dependent signaling. We obtained blood samples from SCD patients with PHT (n=16) and without PHT (n=17) during steady state (not in pain crisis). PHT was defined by a tricuspid regurgitant jet (TRjet) velocity >= 2.5 m/sec by Doppler echocardiography. Platelet activation was measured by the flow cytometry detection of activated fibrinogen receptors (activated GPIIb/IIIa) and surface expression of P-Selectin. The mean percentage of platelets with activated GPIIb/IIIa was 10.3 ± 1.8%( mean ± SEM) for non-PHT SCD patients vs. 27.2 ± 4.7% for PHT SCD patients (p = 0.001). The percentage of platelets positive for P-Selectin was 2.0 ± 0.8% for non-PHT SCD patients vs. 5.1 ± 2.5% for PHT SCD patients (p = 0.02). The percentage of activated platelets strongly correlated with TR jet velocities (r = 0.63 and p = 0.0006). (Figure 1) In addition, the percentage of activated platelet correlated to surrogate markers of hemolysis LDH and reticulocyte count. This link may not prove causation but it suggests a common pathophysiology. Nitric oxide plays a central role in vascular homeostasis by regulating vascular tone and platelet activation through the generation of cyclic guanosine 5′-monophosphate (cGMP). It is possible that decreased NO bioavailability is responsible for both pulmonary vasculopathy and platelet activation. Our pilot studies indicate sildenafil, which enhances NO responsiveness by promoting the accumulation of its downstream mediator cGMP, may be useful in treating PHT.To verify the effect of this therapy on the degree of platelet activation, we studied a group of 12 SCD patients receiving sildenafil. Platelet activation was determined from blood samples obtained before and after (120–150 minutes) a single dose of 100 mg. of sildenafil. The mean percentage of activated platelets was higher before than after sildenafil; for activated GPIIb/IIIa 31.2 ± 4.7% vs. 17.1 ±3.9% (p = 0.001); for P-Selectin 6.3 ± 1.6% vs. 3.2 ±0.6% (p = 0.11).Our findings show for the first time the association of platelet activation and pulmonary hypertension in SCD. Furthermore, by demonstrating that platelet activation of SCD patients with PHT is decreased by sildenafil, a drug that potentiates the effects of NO, this work suggests a common pathophysiology. Additional research is needed to define whether platelet activation plays a role in the thrombo-vascular events that characterize PHT.

Relation of Platelet Activation to Coronary Angiographic Severity and Collateralization

We investigated whether platelet activation can be correlated with angiographic severity and the degree of collateralization in coronary artery disease (CAD), as well as endothelial damage/dysfunction. No studies have attempted to correlate platelet activation status, as measured by soluble plasma markers (soluble CD40 ligand, soluble P-selectin, soluble glycoprotein V), with the appearance of diseased coronary arteries. We found evidence of increased platelet activation in CAD, but a lack of correlation between the degree of platelet activation and the angiographic disease severity, which may reflect the presence of disease elsewhere or the presence of coronary atheroma not detected by angiography.

Platelet activation can occur by shear stress alone in the PFA-100 platelet analyser

The PFA-100 platelet function analyser simulates high-shear platelet function; however, the relative importance of the high shear rates alone has not been examined in this system. Normal blood was analysed by the PFA-100 using modified cartridges that contained a blank membrane lacking the usual platelet agonists (collagen/epinephrine or collagen/ADP) thus isolating the effects of shear stress alone. We found evidence of platelet activation with significant increases in platelet–leucocyte aggregates. There was no significant change in surface CD62P nor PAC-1 expression. A degree of platelet activation occurs in the PFA-100 due to shear stress alone.

Pharmacodynamics (PD) of clopidogrel in patients with acute coronary syndromes undergoing percutaneous interventions (PCI)

Background/Aims Little is known about the PD of clopidogrel in patients suffering from acute coronary syndromes (ACS) undergoing PCI. We hypothesized that the high degree of platelet activation in ACS patients may impede the PD effects of clopidogrel early after onset of ACS. Methods ACS patients (n=200), who presented to the University Hospital, were included into a prospective trial. Patients received a loading dose of clopidogrel (300 mg) followed by 75mg/d clopidogrel up to 12 months. Platelet function was assessed by the collagen adenosine diphosphate closure time (CAPD-CT) with the FDA approved platelet function analyzer (PFA-100). The single nucleotide polymorphism (SNP) i-744 of the purinergic receptor P2Y12 was determined by Taqman technology. Results Baseline CAPD-CT averaged 99s (CI: 90-110), and a 10% increase in CADP-CT was observed only after a time-lag of 7 days (p=0.03). Maximum effectiveness was observed only after period of 3 months on therapy[CADP-CT: 154s (138–169); p<0.0001]. The diagnosis of myocardial infarction and high plasma levels of von Willebrand Factor levels predicted decreased responsiveness to clopidogrel therapy, whereas the assessed P2Y12R SNP had no impact. Conclusions Our pharmacodynamic data indicate that ACS patients could profit from higher clopidogrel dosages particularly in the early weeks after PCI, and dose finding studies appear recommendable. Clinical Pharmacology & Therapeutics (2005) 77, P53–P53; doi: 10.1016/j.clpt.2004.12.094

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 PlA2 polymorphism and platelet activation are associated with increased troponin I release after cardiopulmonary bypass.

The PlA2 polymorphism of platelet glycoprotein IIIa has been identified as a prothrombotic risk factor in a number of cardiovascular settings. The aim of this study was to determine whether the PlA2 polymorphism of platelet glycoprotein IIIa and degree of platelet activation were associated with more severe myocardial injury as indicated by troponin I release following cardiopulmonary bypass. The PlA2 genotype was determined in 66 patients undergoing elective coronary artery bypass grafting requiring cardiopulmonary bypass. Troponin I concentrations and the percentage of circulating, activated (CD62P+) platelets were measured at predetermined intervals perioperatively. Forty-six patients were Pl(A1,A1), and 20 were Pl(A1,A2) or Pl(A2,A2). Patients with at least one PlA2 allele had significantly greater postoperative troponin I concentrations than PlA1 homozygotes (P = 0.006, analysis of variance). Peak troponin I concentrations also correlated significantly with the increase in circulating, activated platelets (P = 0.02, Spearman rank correlation). The PlA2 allele of platelet glycoprotein IIIa is associated with higher troponin I concentrations following cardiopulmonary bypass surgery, suggesting that this platelet polymorphism contributes to perioperative myocardial injury.

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

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 <0.40 and NYHA Class II to IV symptoms who presented to the Duke Heart Failure Clinic and 14 healthy control subjects formed the study groups. Baseline characteristics and blood analyzed for thromboxane (Tx) B2, 6-keto PGF1α, 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 B2 (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.)

Fibrinogen adsorption and platelet interactions on polymer membranes

The hemocompatibility of four different wettable polymer membranes, namely Cuprophan (CE), polyether-polycarbonate (PC-PE), polysulfone (PSU), and polyetherimide (PEI), was investigated with respect to flbrinogen (Fng) adsorption and platelet adhesion/activation. In order to estimate the polar and dispersion components of the surface free energy, contact angles using water/vapor and water/n-hexadecane systems were measured. Adsorption of flbrinogen was studied using fluorescence-labeled protein. The adsorption isotherms showed that the amount and the affinity of adsorbed Fng increased with decreasing surface wettability of the membranes, which correlates with the dispersion and polar components of the surface free energy. The conformational changes of adsorbed Fng were detected by measuring the difference between monoclonal antibody binding to the conformation-sensitive epitope in the D-domain and the binding of polyclonal anti-Fng antibody. The anticipated conformational/orientational changes were greater for PEI and PSU membranes (the least wettable membranes) and negligible for the more wettable PC-PE and CE membranes. In addition, a possible relationship with the degree of platelet activation was found, showing negligible platelet adhesion on PC-PE and CE, but high platelet adhesion on PEI and PSU. Furthermore, platelets were spread to a large extent on PEI, while the formation of aggregates was observed on PSU. This may correspond to the anticipated differences in the conformational state of Fng on both membranes.

HIT dynamics are Fab

Immune heparin-induced thrombocytopaenia (HIT) affects up to 3% of patients that receive heparin therapy and can lead to serious complications. Given the extensive use of heparin as an anticoagulant and its potential use in other clinical settings, such as inflammation, a better understanding of this adverse drug reaction is essential. In individuals with HIT, IgG antibodies are usually present in the plasma, which, in the presence of heparin, leads to the aggregation of platelets and possible vascular occlusion. Previous understanding of the pathophysiology of this prothrombotic condition has relied upon a model in which circulating IgG antibodies, bound to a complex of heparin and platelet factor 4 (PF4), bind to FcRII receptors on the platelet surface, leading to activation and aggregation. However, the mechanism by which antibody–platelet binding is effected is a matter of some controversy with regard to whether it is the Fc portion or the Fab region of HIT IgG that binds to the platelets. Therefore, the question is whether circulating IgG ligates heparin–PF4 in the plasma and the resultant immune complex binds to platelets or, as would be the case in the latter scenario, HIT IgG binds to heparin–PF4 complexes that are already present on the platelet surface.Newman and Chong1xHeparin-induced thrombocytopenia: new evidence for the dynamic binding of purified anti-PF4-heparin antibodies to platelets and the resultant platelet activation. Newman, P.M. and Chong, B.H. Blood. 2000; 96: 182–187PubMedSee all References1 investigated antibody–platelet binding under conditions that resemble those found in vivo far more closely than in previous studies: specifically, platelets were examined in plasma under shear force. Moreover, affinity-purified anti-PF4-heparin IgG from HIT plasma was used, as opposed to total IgG or the plasma itself, as seen in earlier investigations. The investigators found that the Fab region of HIT IgG binds to PF4–heparin on the platelet surface before the Fc region is able to bind and further activate the platelet and other platelets in the area. Upon activation in this manner, platelets release further PF4, which forms auxiliary complexes with heparin on the platelet surface and, hence, more IgG binding and thrombocyte activation occurs. Blockade of the FcRII receptor is sufficient to prevent direct activation of platelets by the antibody, yet it is clear from the results of the study that binding of HIT IgG to platelets is not dependent upon the availability of this receptor. Some degree of platelet activation, resulting in release and expression of PF4, is required for the initial binding of HIT IgG, via the Fab domain, an event that precedes further platelet activation through binding of the Fc portion of this antibody to FcRII receptors on the same, or on adjacent platelets.The authors have provided further insight into the mechanisms by which platelet activation and aggregation is induced in this serious adverse drug reaction and, in particular, indicate the likely dynamics of HIT antibody-platelet interactions, as they occur in vivo.

Autologous stem cell transplantation as post-remission therapy in adult acute myelogenous leukemia: does platelet contamination of peripheral blood mobilized stem cell grafts influence the risk of leukemia relapse?

Conventional chemotherapy of acute myelogenous leukemia (AML) results in an overall long-term disease-free survival of less than 50%, but for selected subsets of younger patients the prognosis can be improved by allogeneic stem cell transplantation. The use of autologous stem cell transplantation is now investigated as an alternative to allotransplantation due to its lower risk of serious complications. However, autotransplantation is associated with a relatively high risk of post-transplant AML relapse that can be derived from contaminating leukemia cells in the autograft. Peripheral blood mobilized stem cell (PBSC) grafts usually contain a higher number of platelets. The degree of platelet contamination is determined by the peripheral blood platelet count at the time of harvesting, and the platelets become activated and release soluble mediators during the ex vivo handling of PBSC grafts. Many of these platelet-derived mediators can bind to specific receptors expressed by AML blasts, and the platelet contamination may then alter AML blast survival and thereby influence the risk of post-transplant leukemia relapse. Therefore, we conclude that the platelet contamination of autologous stem cell grafts is possibly of clinical importance, but the effect of this nonstandardized parameter is difficult to predict in individual patients because the number of graft-contaminating platelets, the degree of platelet activation, and the effects of platelet-derived mediators on AML blasts differ between patients.