Decreased Platelet Reactivity Research Articles

Decreased platelet reactivity identified by whole blood flow cytometry in Fanconi anaemia patients

Fanconi anaemia (FA) is a rare inherited chromosome instability disorder characterized by congenital anomalies and a high risk for bone marrow failure and cancer. Bleeding is a frequent complication in FA, leading to substantial morbidity and mortality. Thrombocytopenia is a major factor leading to this complication, but the bleeding tendency of FA patients often exceeds what one might expect based on their platelet counts. We therefore investigated if alterations of platelet function contribute to the bleeding tendency of FA patients. We assessed platelet function in 11 FA patients and 23 controls with whole blood flow cytometry. We analyzed the expression of platelet membrane glycoprotein receptors, reactivity of platelets to physiologic agonists and the proportion of young platelets. In FA patients platelet reactivity was decreased: Expression of P-selectin and binding of PAC-1 after stimulation with thrombin receptor activating peptide (TRAP) and adenosine diphosphate (ADP) were 15-70% lower than in controls. We found no or only minor differences of platelet glycoprotein receptor expression between groups. While the proportion of reticulated platelets was not different, the absolute number of reticulated platelets was markedly lower in FA patients. Our data show that FA is associated with reduced platelet reactivity, which may contribute to the high bleeding tendency in FA patients. Whole blood flow cytometry is a suitable method for analysis of platelet function in FA patients.

Flavanol-Rich Extract Decreases Platelet Reactivity in Male Smokers

Flavanol-Rich Extract Decreases Platelet Reactivity in Male Smokers

Periprocedural Cardiac Enzyme Elevation Predicts Adverse Outcomes

Extensive clinical investigation throughout the 1990s validated periprocedural myonecrosis as a powerful predictor of adverse outcomes, so it is surprising that this remains a contentious point. Originally derided as “enzyme leaks” or “myocardial infarctlets,” periprocedural myocardial infarction (MI) has now been definitively linked in large data sets to long-term adverse outcomes, most notably mortality. It is not, however, always directly contributory or causative. For example, a large creatine kinase (CK) elevation caused by closure of a major side branch resulting in chest pain and development of new Q waves is obviously undesirable and causally related to the interventional procedure. Alternatively, even small, asymptomatic CK elevations have been clearly associated with worse long-term outcome, and although this may in part be causally related to the procedure, it is more likely that the relationship is caused by the underlying predisposing factors that led to the periprocedural MI, such as arterial inflammation predilecting to the occurrence of embolization or to a large degree of atheroma burden leading to more myonecrosis. Under these circumstances, it is likely that the heightened inflammatory state and the diffuse disease that is present are the real causative factors for worse long-term outcomes. Recently, aspirin resistance has been demonstrated to predict periprocedural myonecrosis. Thus, both through direct causation and also as an epiphenomenon, embolization and attendant periprocedural myonecrosis are associated with short, intermediate, and long-term adverse outcomes (Table 1). This review details this evolution in thought. View this table: TABLE 1. Mechanisms Behind Periprocedural Myonecrosis Periprocedural myonecrosis is a frequent occurrence in percutaneous coronary intervention (PCI). CK or CK myocardial band (CK-MB) elevation occurs in ≈25% of patients undergoing PCI. With the advent of sensitive troponin measurements, it is clear that at least 50% of patients undergoing PCI have postprocedural troponin elevation, reflecting the frequency with which embolization occurs. However, troponin offers …

Decreased prothrombotic effects of pegylated recombinant human megakaryocyte growth and development factor in thrombocytopenic state in a rat thrombosis model

Previous in vitro studies demonstrated that thrombopoietin (TPO) acts on platelets to activate a variety of intracellular signaling pathways and to enhance platelet sensitivity to multiple agonists. Little is known, however, about whether TPO exerts prothrombotic effects in vivo. The aim of this study was to examine the effects of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a pegylated N-terminal domain of human TPO, in a rat model of venous thrombosis. A microthrombus was photochemically induced on the vessel wall of a mesenteric venule, but the vessel was not occluded by it. A single intravenous injection of PEG-rHuMGDF (3 microg kg(-1)) after the thrombus generation into normal rats enhanced the thrombus size, resulting in transient thrombotic occlusion in the majority of rats. Stimulatory effects on thrombus growth were also observed following administration of glycosylated recombinant human full-length TPO (6 microg kg(-1)). In rats rendered thrombocytopenic by total body irradiation, however, PEG-rHuMGDF, even at 300 microg kg(-1), did not induce a significant increase in thrombus size or thrombotic occlusion. Platelets from thrombocytopenic rats had decreased surface levels of c-Mpl and decreased sensitivity to PEG-rHuMGDF in an in vitro aggregation response. Thus, decreased prothrombotic effects of PEG-rHuMGDF in thrombocytopenic rats might be the result not only of low platelet counts but also of decreased platelet reactivity to PEG-rHuMGDF. These results indicate that PEG-rHuMGDF has little effect on venous thrombus formation in thrombocytopenic states associated with high endogenous TPO levels.

Soluble adhesion molecules in healthy subjects: a dose-response study using n-3 fatty acids

Long-chain n-3 polyunsaturated fatty acids (PUFA) may protect against atherosclerotic disease, and serum levels of soluble cellular adhesion molecules (sCAMs) possibly reflect the inflammatory process underlying atherosclerosis. We studied the effect of n-3 PUFA dietary supplementation on the serum levels of sP-selectin, soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular adhesion molecule-1 (sVCAM-1), and the correlation between sCAMs and the fatty acid composition of granulocyte membranes. Sixty healthy volunteers were randomly assigned to receive a daily supplement of n-3 PUFA 6.6 g, n-3 PUFA 2.0 g, or olive oil for 12 weeks in a double blind design. A significant negative correlation was found between serum sICAM-1 levels and the DHA content of granulocyte membranes at entry. After supplementation with 6.6 g of n-3 PUFA, there was a significant decrease only in sP-selectin, which a gender subanalysis showed to be more marked in men. Among the women, there was a significant decrease in sICAM-1 in the PUFA 2.0 g group and a significant increase in sVCAM-1 in the PUFA 6.6 g group. The results indicate that high-dose supplementation with n-3 PUFA decreases sP-selectin levels in healthy subjects, thus suggesting a decrease in platelet reactivity or endothelial activation. However, the effect of n-3 PUFA on sCAMs is complex and may depend on gender and n-3 PUFA dose.

Biphasic effects of hemodialysis on platelet reactivity in patients with end-stage renal disease: A potential contributor to cardiovascular risk

Background: Cardiovascular disease is rampant in patients with end-stage renal disease (ESRD), and increased platelet reactivity may contribute. This study is designed to determine effects of hemodialysis in patients with ESRD on platelet reactivity per se. Methods: Platelet reactivity was determined by flow cytometry in 36 patients with ESRD undergoing hemodialysis. Blood was obtained from arterial and venous ends of the hemodialysis circuit at the beginning and end of the dialysis session. Platelet reactivity was defined with respect to capacity to bind fibrinogen (activation of glycoprotein IIb-IIIa) and expression of P-selectin in response to adenosine diphosphate (ADP; 0, 0.2, and 1.0 μmol/L). Comparison studies were performed with 55 patients with coronary artery disease (CAD) and 38 healthy subjects. Results: Platelet reactivity was increased by exposure to the dialysis circuit (capacity to bind fibrinogen: arterial, 28% ± 13%; venous, 47% ± 20%; P < 0.001). Despite this effect, surface expression of P-selectin in response to 1 μmol/L of ADP was lower at the end of the dialysis session (arterial blood at its onset, 40% ± 16%; arterial blood at its conclusion, 24% ± 15%; P < 0.05). Confocal microscopy showed increased nonspecific association of fibrinogen with platelets after dialysis, suggesting that increased aggregation after dialysis may be secondary to effects of dialysis on fibrinogen binding, rather than on platelet reactivity. Platelet reactivity was increased similarly in patients with ESRD and those with CAD compared with healthy subjects. Conclusion: Although interaction between platelets and the dialysis circuit increases platelet reactivity, continued dialysis decreases platelet reactivity. © 2002 by the National Kidney Foundation, Inc.

A new model for evaluation of thrombosis and ischaemia/reperfusion injury

The purpose of the present study was to describe infarct size and platelet accumulation when reperfusion injury was combined with a thrombogenic lesion in the coronary artery. The left anterior descending artery was damaged in 11 pigs and subsequently occluded proximal to the lesion for 50 min, followed by 4 h of reperfusion. The infarct size/area at risk was 40 (35 63)%. Infarct size correlated with troponin-T-3 h (p=0.85, p<0.002), but not with creatine kinase-3 h. Platelet aggregation decreased by 34% (p<0.01) at 15 min of reperfusion, but returned to baseline. Platelet accumulation in the left ventricle was significantly higher in the area at risk (194 (157-206)%) compared to the right ventricle (137 (120-142)%); p<0.05). A decreased platelet reactivity and increased accumulation of platelets in the area at risk indicates that activated platelets become entrapped in the myocardium. Troponin-T was a better marker of myocardial damage than creatine kinase in this in vivo model with pigs.

Decreased intraplatelet Ca2+ release and ATP secretion in pediatric nephrotic syndrome.

Platelets play an important role in the natural history of idiopathic nephrotic syndrome (NS). Although thromboembolic events are rare, the activation of circulating platelets is generally considered an important factor in the prethrombotic state in children with NS. Platelet-activating factor (PAF), a potent endogenous phospholipid mediator of inflammation, stimulates intracellular free calcium (Ca2+) mobilization, aggregation, and release reactions in platelets obtained from normal donors. Platelet-related effects of PAF in children with NS are unknown. We studied PAF-induced intracellular Ca2+ mobilization in washed platelets and ATP secretion in platelet-rich plasma in 34 children with idiopathic NS and in 7 healthy children. There was a significant decrease in ATP secretion: 0.021+/-0.011 microg/10(7) cells with 20 nM PAF and 0.089+/-0.017 microg/10(7) platelets with 200 nM PAF versus control values (0.195+/-0.004 microg/10(7) and 0.813+/-0.09 microg/10(7), respectively). Moreover, PAF-evoked increase in intracellular free Ca2+ concentration was twofold lower in NS patients than in control subjects (230.1+/-22.4 nM versus 455.6+/-15.3 nM). Also, thrombin-induced intracellular free Ca2+ mobilization was diminished in children with NS compared with the control group. Thus, contrary to expectations, a decrease of platelet reactivity in response to PAF in vitro was observed in children with idiopathic NS. We suggest that this decreased platelet reactivity may reflect a period refractory to PAF and may be considered as platelet desensitization to PAF released in vivo in children with NS.

Omega-3 and omega-6 fatty acids in the insulin resistance syndrome. Lipid and lipoprotein metabolism and atherosclerosis.

Dietary fatty acids appear to be of significant importance for several of the most-common diseases in modern societies. To obtain more knowledge about the health consequences of dietary fatty acids, we depend upon a better understanding of the mechanisms of action of these fatty acids in vivo. With regard to the IRS, omega-3 PUFA may exert beneficial effects upon many of the associated pathophysiological metabolic changes. Omega-3 PUFA reduce fasting and postprandial TG, may improve insulin sensitivity (as shown in animal experiments), decrease platelet and leukocyte reactivity, alter immunological functions, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, both types of PUFA (omega-3 and omega-6) have been shown to inhibit cardiac arrhythmias in animals. The role of omega-3 PUFA in blood clotting and fibrinolysis still remains controversial, whereas omega-6 fatty acids may lead to increased oxidation of lipoproteins. Regardless of the effects on LDL oxidizability, both types of PUFA have shown beneficial effects on the development of atherosclerosis. As yet, little is known about the effect of specific omega-6 fatty acids with respect to the IRS. Potential adverse effects of dietary PUFA must not be neglected, but should be viewed in light of the beneficial effects of these agents.

Omega-3 fatty acids. Current status in cardiovascular medicine.

Omega-3 polyunsaturated fatty acids (PUFA) reduce fasting and postprandial triglycerides, decrease platelet and leucocyte reactivity, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, these compounds have been shown to inhibit ventricular tachyarrhythmias in animals. Omega-3 PUFA may impair fibrinolysis and could lead to increased oxidation of lipoproteins. Potential adverse effects must not be neglected, but should be viewed in light of the beneficial effects of these agents. Clinical studies investigating the effects of dietary omega-3 PUFA in the prevention and treatment of cardiovascular disease (CVD) are beginning to emerge. The results have offered some promise, but further studies are needed to define the role of these agents in CVD. Long term trials and studies using omega-3 PUFA as adjuvants to conventional therapy in patients with coronary artery disease, hyperlipidaemia and hypertension may be of particular interest.

Modification of platelet function by isosorbide dinitrate in patients with coronary artery disease

The effect of a four weeks oral treatment with 100mg isosorbide dinitrate (ISDN) daily on platelet function was evaluated in 40 patients (aged 40–65 years) with proven coronary artery diseae. Isosorbide dinitrate decreased platelet reactivity to ADP (p < 0.001), increased platelet sensitivity to PGI2 (p < 0.01) while the production of TXB2 from exogenous arachidonic acid substrate and from endogenous substrate were both significantly reduced. Circulating platelet aggregates as measured by the Wu-test were markedly reduced (p < 0.001) but there was little change in the plasma concentration of the platelet proteins β-thromboglobulin and platelet factor 4. Overall, platelet activation correlated with smoking, hypertension and a family history of coronary artery disease. The reduced platelet activation seen during treatment with isosorbide dinitrate may contribute to the therapeutic benefit seen with this drug in patients with coronary artery disease.

Rapid Aequorin Loading into Platelets in the Presence of DMSO - Characteristics of the Responses (Changes in Light Transmission and in Calcium) to Various Agonists

We have looked at different parameters which could modify platelet behaviour during and after aequorin loading in the presence of DMSO. There is a decreased platelet reactivity in response to ADP, PAF and A-23,187 which appears to be mainly due to the exposure to EGTA during washing and loading and the 1 ml volume of the test suspension. All the studied agonists (including PMA) which elicit aggregation are able to induce an intracellular Ca2+ change detected with the aequorin probe. By contrast, epinephrine alone induces neither aggregation nor Ca2+ rise, but potentiates the responses to ADP. Different consecutive phases in Ca2+ changes after stimulation with ADP, PMA and A-23,187 can be evidenced. In the presence of external Ca2+, the second component of the Ca2+ change evoked with ADP is dependent on aggregation and the subsequent TXA2 synthesis. When the external medium is Ca2+ depleted, the two Ca2+ peaks induced by ADP disappear whereas a Ca2+ rise persists (endogenous mobilization) with the other agonists, being independent of TXA2 and ADP release. Ca2+ mobilization parallels activation with A-23,187 but not with low concentrations of thrombin.