Patients with venous stasis ulceration have increased monocyte-platelet aggregation

Screening and diagnosis of inherited platelet disorders

Inherited platelet disorders are important conditions that often manifest with bleeding. These disorders have heterogeneous underlying pathologies. Some are syndromic disorders with non-blood phenotypic features, and others are associated with an increased predisposition to developing myelodysplasia and leukemia. Platelet disorders can present with thrombocytopenia, defects in platelet function, or both. As the underlying pathogenesis of inherited thrombocytopenias and platelet function disorders are quite diverse, their evaluation requires a thorough clinical assessment and specialized diagnostic tests, that often challenge diagnostic laboratories. At present, many of the commonly encountered, non-syndromic platelet disorders do not have a defined molecular cause. Nonetheless, significant progress has been made over the past few decades to improve the diagnostic evaluation of inherited platelet disorders, from the assessment of the bleeding history to improved standardization of light transmission aggregometry, which remains a "gold standard" test of platelet function. Some platelet disorder test findings are highly predictive of a bleeding disorder and some show association to symptoms of prolonged bleeding, surgical bleeding, and wound healing problems. Multiple assays can be required to diagnose common and rare platelet disorders, each requiring control of preanalytical, analytical, and post-analytical variables. The laboratory investigations of platelet disorders include evaluations of platelet counts, size, and morphology by light microscopy; assessments for aggregation defects; tests for dense granule deficiency; analyses of granule constituents and their release; platelet protein analysis by immunofluorescent staining or flow cytometry; tests of platelet procoagulant function; evaluations of platelet ultrastructure; high-throughput sequencing and other molecular diagnostic tests. The focus of this article is to review current methods for the diagnostic assessment of platelet function, with a focus on contemporary, best diagnostic laboratory practices, and relationships between clinical and laboratory findings.

Immunological aspects of chronic venous disease pathogenesis

Chronic venous disease (CVD) is a very common health problem concerning up to 1/3 of the society. Although venous hypertension and valvular incompetence have been long known to be crucial for development of the illness, its exact aetiology remains unclear. Recent findings indicate that inflammatory processes may be crucial for development of incompetent valves and vein wall remodelling. One of the most interesting theories describes “leucocyte trapping” as the mechanism responsible for elevated vein wall permeability and oxidative stress in the veins. At the same time, the cytokine profile of the blood in incompetent veins has not been thoroughly examined. Popular anti-inflammatory drugs relieve some symptoms but do not have much proved effects in prevention and treatment.

We intend to summarize the existing knowledge of the immunological aspects of CVD in order to emphasize its importance for understanding the aetiology of this illness. We also wish to indicate some aspects that remain to be studied in more detail.

Platelet flow cytometry

Flow cytometry is a powerful and versatile tool which can be used to provide substantial phenotypic data on platelets by yielding quantitative information of their physical and antigenic properties. This includes surface expression of functional receptors, bound ligands, expression of granule components, interaction of platelets with other platelets via aggregation, or interaction with other blood components, such as leukocytes or the plasma coagulation system. Quantitative assessment of these parameters may facilitate the diagnosis of inherited or acquired platelet disorders, assist in the diagnosis of diseases associated with platelet activation, or assist in the monitoring of safety and efficacy of antiplatelet therapy.

Does inflammation have a role in the pathogenesis of venous ulcers? A critical review of the evidence

Chronic venous disease, a disorder involving venous return from the legs, is a growing epidemic in the developed world. Numerous studies have been conducted in the past two decades in an attempt to elucidate its underlying pathophysiology. Many theories have been proposed to address the profound inflammatory dysregulation, with the majority focusing on fibrin trap, inflammatory trap, cytokines, growth factors, and matrix metalloproteinases. Although many of these theories have obtained great momentum, much of the data are contradictory. Moreover, many treatments built on these theories have claimed overwhelming success despite insufficient evidence. At the same time, there are few reviews that critically analyze and evaluate these data. Therefore, in this paper, we will provide summaries of the background data and evolution of these theories and examine their supporting evidence.

Monocyte-platelet aggregates and platelet micro-particles in patients with post-hepatitic liver cirrhosis

INTRODUCTION

Monocytes are the cells that play a crucial role in the pathogenesis of liver damage and liver cirrhosis (LC), and as platelets, by connecting hemostasis and inflammatory processes, participate in pathogenesis of chronic liver diseases, we aimed to investigate the presence of monocyte-platelet aggregates and platelet micro-particles (PMPs) and their role in LC.

PATIENTS AND METHODS

The study included 60 patients with post-hepatitic LC and 20 healthy controls. Activated monocytes (CD11b, HLA-DR, CD14, CD16), monocyte-platelet aggregates (CD41/CD14), activated platelets (CD41/CD62) and PMPs were analyzed by flow cytometry. Their relations to the clinical and laboratory data were assessed in the studied group.

RESULTS

Patients with LC had higher levels of activated platelets, activated monocytes and monocyte-platelet aggregations as compared to healthy controls. PMPs percentage showed no significant differences between patients and controls but significantly increased in both patients with no bleeding and patients with splenomegaly compared to patients without. All studied markers showed no significant differences between patients with thrombocytopenia and those with normal platelet counts and also between patients with different disease stages. Positive correlations between monocyte-platelet aggregates and both activated platelets and monocytes were demonstrated. There were significant negative correlations between PMPs and both age and prothrombin time among patients.

CONCLUSIONS

The stage of post-hepatitic LC is not the only factor that affects the level of activated platelets, activated monocytes and monocyte-platelet aggregates. PMPs have no influence on thrombocytopenia but may have the potential to influence the progression of clotting activity in LC.

Platelet Monocyte Aggregates and Monocyte Chemoattractant Protein-1 are not Inhibited by Aspirin in Critical Limb Ischaemia

OBJECTIVES

Platelet monocyte aggregates (PMA) and monocyte chemoattractant protein-1 (MCP-1) play a significant role in atherosclerotic disease but the effect of aspirin and their role in peripheral arterial disease (PAD) requires further investigation. We have compared p-selectin, PMA and MCP-1 in patients with PAD treated with aspirin (75 mgs daily), with age matched controls not treated with aspirin.

MATERIALS AND METHODS

Using flow cytometry and ELISA, P-selectin, PMA and MCP-1 were compared in 3 populations; healthy controls (n=12), intermittent claudication (n=19) and critical limb ischaemia (CLI), (n=10).

RESULTS

P-selectin was significantly higher in CLI patients (3.48% positive) compared to the claudicants (1. 36% positive) and the controls (1.76% positive). PMA levels were significantly higher for CLI population (44.5% positive) compared to the claudicants (20.48% positive) and the controls (28.33% positive). MCP-1 levels expression was significantly higher for the CLI patients (175.4 pg/mL) compared to the claudicants (76.1 pg/mL) and the controls (117.0 pg/mL).

CONCLUSION

Despite aspirin treatment CLI patients have higher platelet activation and MCP-1 expression than controls and claudicants. With increasing severity of disease aspirin is unable to suppress markers of platelet activation and pro-atherosclerotic chemokine expression which may represent another form of aspirin resistance.

Venous ulcers

Veneous ulcers are extremely common, accounting for a large proportin of all lower extremity ulcers. Due to their chronicity and relatively high prevalence, their impact on the cost of healthcare and the lives of the patients affected is quite significant. There has been progress in understanding the pathophysiology, clinical features, and diagnosis of these ulcers, but the basic principles of care have remained consistent for almost a half century. To allow for optimal healing, it is important to maintain a clean moist wound bed, treat any clinically significant infection, and decrease surrounding edema.

Effects of platelet binding on whole blood flow cytometry assays of monocyte and neutrophil procoagulant activity

BACKGROUND

Monocytes and neutrophils form heterotypic aggregates with platelets initially via engagement of platelet surface P-selectin with leukocyte surface P-selectin glycoprotein ligand-1 (PSGL-1). The resultant intracellular signaling causes the leukocyte surface expression of tissue factor and activation of leukocyte surface Mac-1 (integrin alphaMbeta2, CD11b/CD18). The activation-dependent conformational change in monocyte surface Mac-1 results in the binding of coagulation factor Xa (FXa) and/or fibrinogen to Mac-1. The aim of this study was to develop whole blood flow cytometry assays of these procoagulant activities and to investigate the effects of platelet binding to monocytes and neutrophils.

METHODS

Citrate or D-Phe-Pro-Arg-chloromethylketone (PPACK) anticoagulated whole blood was incubated with monoclonal antibodies against CD14 (PECy5), CD42a (PE), FITC-conjugated test antibody and an agonist, and then fixed with FACS lyse. Appropriate isotype negative controls were prepared in parallel. A BD FACSCalibur was used to analyze monocytes and neutrophils, which were identified based on CD14 fluorescence, forward and 90 degrees light scatter. These populations were further gated into CD42a-positive (platelet-bound) and CD42a-negative (platelet-free). Geometric mean fluorescence and per cent positive data were collected for each subpopulation to measure the binding of test antibodies directed at CD42a, tissue factor, coagulation FXa, bound fibrinogen, activated Mac-1, and CD11b. Compensation controls were prepared on six normal donors prior to the study and these settings were used throughout the 10 donor study. Negative controls verified the lack of cross talk, particularly in the quantified FITC and PE parameters.

RESULTS

The physiologic agonists collagen and ADP increased monocyte-platelet and neutrophil-platelet aggregates and increased leukocyte surface Mac-1/CD11b and surface-bound tissue factor, FXa and fibrinogen. Whereas the increases in Mac-1/CD11b were mainly independent of leukocyte-platelet binding, the increases in surface-bound tissue factor, FXa and fibrinogen were mainly dependent on leukocyte-platelet binding.

CONCLUSIONS

(i) We have developed novel whole blood flow cytometry assays to measure bound tissue factor, coagulation FXa, fibrinogen, activated Mac-1 and CD11b on the surface of monocytes and neutrophils, allowing independent analysis of monocytes and neutrophils with and without surface-adherent platelets. (ii) The monocyte and neutrophil surface binding of tissue factor, FXa and fibrinogen is mainly dependent on platelet adherence to monocytes and neutrophils, whereas the monocyte and neutrophil surface expression of CD11b and activated Mac-1 is mainly independent of platelet adherence to monocytes and neutrophils.

Venous ulcer: epidemiology, physiopathology, diagnosis and treatment

This review discusses the epidemiology, pathogenesis, diagnosis and current therapeutic options for venous ulcer. Venous ulcer is a severe clinical manifestation of chronic venous insufficiency (CVI). It is responsible for about 70% of chronic ulcers of the lower limbs. The high prevalence of venous ulcer has a significant socioeconomic impact in terms of medical care, days off work and reduced quality of life. Long-term therapeutics are needed to heal venous ulcers and recurrence is quite common, ranging from 54 to 78%. Thrombophlebitis and trauma with long-term immobilization predisposing to deep venous thrombosis are important risk factors for CVI and venous ulcer. The most recent theories about pathogenesis of venous ulcer have associated it with microcirculatory abnormalities and generation of an inflammatory response. Management of venous leg ulcers is based on understanding the pathogenesis. In recent years novel therapeutic approaches for venous ulcers have offered valuable tools for the management of patients with this disorder.

Leukocyte-platelet interaction in patients with essential thrombocythemia and polycythemia vera

OBJECTIVE

Circulating polymorphonuclear leukocyte (PMN) activation occurs in patients with essential thrombocythemia (ET) and polycythemia vera (PV). We want to define whether this phenomenon plays a role in the formation of circulating PMN-platelet aggregates in these conditions.

METHODS

In 80 patients (46 ET and 34 PV) and 50 control subjects, we conducted a flow cytometric analysis to evaluate the levels of PMN-platelet aggregates (defined as the percentage of CD11b-positive PMN coexpressing a platelet-specific marker, i.e., CD42b or CD62P) and the levels of activated PMN and activated platelets. In addition, the in vitro PMN-platelet aggregate formation in response to N-formyl-methionyl-leucyl-phenylalanine (f-MLP)-induced activation of PMN was studied.

RESULTS

Significantly high PMN-platelet aggregates in ET and PV patients were found and were associated with increased PMN surface CD11b and surface platelet CD62P expression. In vitro f-MLP stimulation upregulated PMN-CD11b expression and simultaneously increased CD11b/CD42b and CD11b/CD62P aggregates, without affecting platelet surface antigens. In ET patients receiving aspirin, the increments in f-MLP-induced PMN-CD11b and in PMN-platelet aggregates were significantly lower versus ET subjects not treated with aspirin.

CONCLUSION

Our data show that in ET and PV patients PMN activation plays an important role in increasing circulating PMN-platelet aggregates and suggest that aspirin treatment may decrease their formation.

Dextran 40 reduces in vitro platelet aggregation in peripheral arterial disease

Dextran 40 has been used to prevent post-operative thrombosis. However, its antithrombotic and antiplatelet effects in peripheral arterial disease (PAD) are poorly understood. We studied the in vitro effects of Dextran 40 on platelet function in control subjects and PAD patients using whole blood methods. Platelet function was assessed in 20 control subjects and 20 PAD patients. Spontaneous platelet aggregation (SPA) and agonist-induced platelet aggregation in response to increasing concentrations of Dextran 40 in vitro were measured by whole blood aggregometry. Flow cytometric measurements of platelet P-selectin, GpIIb/IIIa, GpIb and PAC-1 binding were also performed. There was no difference in SPA or ADP-induced aggregation in control patients with Dextran 40 in vitro. However, Dextran 40 inhibited collagen-induced aggregation in control patients (P < 0.05, Friedman test). In PAD patients, SPA and ADP (1 microM)-induced aggregation were significantly reduced by Dextran 40 in vitro (P < 0.001, Friedman test). In PAD patients, collagen-induced platelet aggregation (1 and 5 microg/ml) was significantly reduced by Dextran 40 in vitro (P < 0.01, Friedman test). GpIIb/IIIa, PAC-1 and P-selectin expression were significantly reduced in whole blood samples from PAD patients following incubation with Dextran 40 (P < 0.05, Wilcoxon rank test) but not in samples from control patients. Dextran 40 reduces spontaneous and agonist-induced platelet aggregation as well as the surface expression of markers of platelet activation in PAD patients. This antiplatelet effect may be of benefit to patients undergoing vascular surgical procedures where thrombosis is a significant risk.

Activated platelets enhance microparticle formation and platelet-leukocyte interaction in severe trauma and sepsis

BACKGROUND

Activated platelets have been recently reported to produce platelet microparticles and to enhance platelet-leukocyte interaction. The precise role of platelets in systemic inflammatory response syndrome (SIRS) has not been clarified. The objective of this study was to evaluate microparticle formation and platelet-leukocyte interaction in severe trauma and sepsis.

METHODS

Twenty-six patients with severe SIRS (SIRS criteria and serum C-reactive protein > 10 mg/dL) and 12 healthy volunteers were studied. The severe SIRS was caused by trauma in 12 patients and sepsis in 14. Microparticle formation, P-selectin expression on platelets, platelet-monocyte binding, and platelet-polymorphonuclear leukocyte (PMNL) binding were measured by flow cytometry in the presence or absence of ionomycin, N-formyl-methionyl-leucyl-phenylalanine, or anti-CD62p monoclonal antibody. Soluble P-selectin, thrombomodulin, neopterin, and PMNL elastase in blood were also measured.

RESULTS

Microparticle formation, P-selectin expression on platelets, platelet-monocyte binding with or without ionomycin, and platelet-PMNL binding with ionomycin significantly increased in patients with severe SIRS in comparison with values in normal volunteers. The increased platelet-leukocyte binding in severe SIRS patients was markedly inhibited by P-selectin blockade and was not enhanced by N-formyl-methionyl-leucyl-phenylalanine. Soluble P-selectin, thrombomodulin, neopterin, and PMNL elastase in blood also increased in these patients.

CONCLUSION

Activated platelets enhance microparticle formation and platelet-leukocyte interaction in severe trauma and sepsis. Enhanced platelet-leukocyte interaction is dependent on P-selectin expression and may be involved in the systemic inflammatory response after severe inflammatory insult.

Increased circulating platelet-leukocyte aggregates in myeloproliferative disorders is correlated to previous thrombosis, platelet activation and platelet count

Platelet-leukocyte adhesion may occur as a consequence of platelet activation and possibly plays a key role in the deposition of activated platelets and fibrin in the thrombotic plug. The aim of the present study was to assess by whole blood flow cytometry the presence of circulating platelet-leukocyte aggregates (PLA) and the platelet-leukocyte response to platelet agonist stimulation (ADP and TRAP) in 50 patients with chronic myeloproliferative disorders (MPD) and 30 controls. PLA were identified as platelet-granulocyte/monocyte aggregates (PGMA), platelet-monocyte aggregates (PMA) and defined as the percentage of leukocytes coexpressing the platelet-specific marker glycoprotein Ib. Compared to controls the mean percentage of PGMA and PMA was increased in unstimulated whole blood from patients with MPD (7.98 vs. 1.76%; p<0.001 and 12.34 vs. 3.2%; p<0.001, respectively). The percentage of PGMA was correlated to the platelet count (r=0.46; p<0.001), percentage of P-selectin (r=0.69; p<0.001) and thrombospondin (r=0.58; p<0.001) positive platelets and platelet expression of GPIV (r=0.33; p=0.02). The mean percentage of PGMA and PMA was significantly increased in ADP-stimulated whole blood of patients (57.14 vs. 47.92%; p=0.009 and 54.91 vs. 45.89%; p<0.001, respectively). Compared to patients without a history of thrombosis, patients having experienced microvascular disturbances or a thrombotic event had a higher mean percentage of PGMA and PMA in non-stimulated whole blood (10.07 vs. 6.34%; p=0.025 and 14.81 vs. 10.48%; p=0.021, respectively) and a higher percentage of PGMA in ADP stimulated whole blood (64.32 vs. 51.50%; p<0.01). These data document an increased frequency of PLA in non-stimulated whole blood in MPD associated with a previous history of thrombosis or microvascular disturbances.

Evaluation of platelet function by flow cytometry

Platelet function in whole blood can be comprehensively evaluated by flow cytometry. Flow cytometry can be used to measure platelet reactivity, circulating activated platelets, platelet-platelet aggregates, leukocyte-platelet aggregates, procoagulant platelet-derived microparticles, and calcium flux. Clinical applications of whole blood flow cytometric assays of platelet function in disease states (e.g., acute coronary syndromes, angioplasty, and stroke) may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte-platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of GPIIb-IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis.

Chronic venous insufficiency is associated with increased platelet and monocyte activation and aggregation

PURPOSE

This study assessed whether the increased numbers of platelet-monocyte aggregates observed in patients with venous stasis ulceration (VSU) represent a response to dermal ulceration or if it is a condition associated with underlying chronic venous insufficiency (CVI). We also analyzed the expression of CD11b in patients with CVI to determine whether leukocyte activation, known to occur in VSU, is a precursor of or a response to ulceration.

METHODS

Patients with varying classes of CVI (n = 24) and healthy control subjects (n = 15), whose status was documented by means of duplex scanning, stood upright and stationary for 10 minutes. Two aliquots of blood, drawn from a distal leg vein and an antecubital fossa vein, were incubated with either buffer or one of three platelet agonists. After fixation, these samples were further incubated with fluorescent-labeled monoclonal antibodies (f-MoAb) specific for CD14 (monocytes) and CD61 (platelets). The activated leukocyte assay was performed by incubating another aliquot of the blood samples with f-MoAb specific for CD11b and CD14. All samples were evaluated by means of flow cytometry.

RESULTS

We observed significantly more platelet-monocyte aggregates throughout the circulation in patients with CVI than in control subjects (29% vs. 8%; P <.0002). Furthermore, patients with CVI formed significantly more of these aggregates in response to all platelet agonists than did control subjects. There were no significant differences between baseline numbers of aggregates or response to agonists in patients who had CVI with (n = 10) or without (n = 14) ulceration. Patients with CVI had more circulating platelet-neutrophil aggregates than control subjects (7.2% vs. 3.6%; P =.05). The addition of platelet agonists to the blood of patients with CVI resulted in more platelet-neutrophil aggregates than in control subjects. Monocyte CD11b expression was higher in patients with CVI than in control subjects (7.5 vs. 3.7; P <.01), with no differences noted in CD11b expression between patients with or without ulceration. Neutrophil CD11b expression was low and similar in control subjects and patients with CVI.

CONCLUSION

All classes of CVI are associated with significantly increased percentages of platelet-monocyte aggregates and increased percentages of platelet-neutrophil aggregates throughout the circulation. The presence of more of these aggregates and the increased propensity to form aggregates in the presence of platelet agonists in all classes of CVI suggests an underlying state of platelet activation and increased reactivity that is independent of the presence of ulceration. The increased expression of monocyte CD11b throughout the circulation in all classes of CVI suggests that although systemic monocyte activation occurs in CVI, its presence is independent of VSU as well.

Laboratory markers of platelet activation and their clinical significance

Whole blood flow cytometry is a powerful new laboratory technique for assessment of platelet activation and function. Flow cytometry can be used to measure platelet hyperreactivity, circulating activated platelets, leukocyte-platelet aggregates, and procoagulant platelet-derived microparticles in a number of clinical settings, including acute coronary syndromes, angioplasty, cardiopulmonary bypass, acute cerebrovascular ischemia, peripheral vascular disease, diabetes mellitus, preeclampsia, and Alzheimer's disease. Clinical applications of whole blood flow cytometric assays of platelet function in these diseases may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte-platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of glycoprotein IIb-IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis.