Platelets and Thrombosis in Myeloproliferative Diseases

Acute Myocardial Infarction Followed by Cerebral Hemorrhagic Infarction in Polycythemia Vera: Case Report and Literature Review

A 60-year-old man presented to our emergency room with severe chest pain. Based on the electrocardiogram and elevated serum troponin T levels, acute coronary syndrome was suspected. Coronary angiography revealed total occlusion of the middle of the left anterior descending coronary artery. However, blood cell count abnormalities were not of concern. Twelve days later, the patient developed hemorrhagic infarction in the right parieto-occipital lobe. Acute coronary syndrome and cerebral hemorrhagic infarction were primarily caused by thrombus formation due to polycythemia vera (PV), based on the presence of increased blood consistency on admission. PV was diagnosed after bone marrow biopsy and genetic testing. The patient was treated with descending cell and antiplatelet therapy. Our case highlights the importance of the urgent identification of PV. When acute myocardial infarction occurs in patients with no significant risk factors for cardiovascular disease, blood routine abnormalities should be paid close attention to. If PV was diagnosed as early as possible, thrombotic and hemorrhagic complications could be prevented in the early stages.

Inflammatory cell-associated tumors. Not only macrophages (TAMs), fibroblasts (TAFs) and neutrophils (TANs) can infiltrate the tumor microenvironment. The unique role of tumor associated platelets (TAPs)

It is well known that various inflammatory cells infiltrate cancer cells. Next to TAMs (tumor-associated macrophages), TAFs (tumor-associated fibroblasts) and TANs (tumor-associated neutrophils) also platelets form the tumor microenvironment. Taking into account the role of platelets in the development of cancer, we have decided to introduce a new term: tumor associated platelets-TAPs. To the best of our knowledge, thus far this terminology has not been employed by anyone. Platelets are the first to appear at the site of the inflammatory process that accompanies cancer development. Within the first few hours from the start of the colonization of cancer cells platelet-tumor aggregates are responsible for neutrophils recruitment, and further release a number of factors associated with tumor growth, metastasis and neoangiogenesis. On the other hand, it also has been indicated that factors delivered from platelets can induce a cytotoxic effect on the proliferating neoplastic cells, and even enhance apoptosis. Undoubtedly, TAPs' role seems to be more complex when compared to tumor associated neutrophils and macrophages, which do not allow for their division into TAP P1 and TAP P2, as in the case of TANs and TAMs. In this review we discuss the role of TAPs as an important element of tumor invasiveness and as a potentially new therapeutic target to prevent cancer development. Nevertheless, better exploring the interactions between platelets and tumor cells could help in the formulation of new therapeutic goals that support or improve the effectiveness of cancer treatment.

Evaluation of platelet function in essential thrombocythemia under different analytical conditions

Background. Studies of platelet aggregation (PA) in essential thrombocythemia (ET) reported contrasting results, likely due to differences in analytical conditions.Objective. We investigated platelet aggregation using different techniques and analytical conditions.Patients and Methods. PA was studied by light-transmission aggregometry (LTA) in platelet-rich plasma (PRP) and impedance aggregometry in PRP and whole blood (WB). ADP, collagen, thrombin receptor activating peptide (TRAP-14) and adrenaline were used as agonists. Since ET patients (n = 41) were on treatment with aspirin (100 mg/d), healthy controls (n = 29) were given aspirin (100 mg/d) for 5 days before testing: therefore, thromboxane A₂-independent PA was tested in all subjects. Blood samples were collected in citrate (C) [low Ca²⁺] or lepirudin (L) [physiological Ca²⁺]; platelet count was adjusted to 250 x 10⁹/L in a set of C-PRP (adjusted C-PRP) and left unmodified in the other samples.Results. Results of PA in 17 ET patients who were poor responders to aspirin (high serum thromboxane B2 levels) were not included in the analysis. With LTA, PA in ET was lower than in controls in adjusted C-PRP and normal in native C-PRP and L-PRP. With impedance aggregometry, PA in L-PRP and L-WB tended to be higher in ET than in controls. Platelet serotonin and ADP contents were reduced in ET. The percentages of circulating platelets expressing P-selectin and platelet-leukocyte hetero-aggregates were higher in ET.Conclusions. Analytical conditions dramatically affect in vitro PA of ET patients, which appears defective under the least physiological conditions and normal/supranormal under conditions that are closer to the physiological.

A Study of Haemostatic Parameters in Patients of Chronic Myeloid Leukaemia

INTRODUCTION

Chronic Myeloid Leukaemia (CML) is characterized by derangement of various components of the haemostatic system resulting in thrombo-haemorrhagic complications. Although less common than other myeloproliferative neoplasms, derangement of various components of the haemostatic system is observed in CML. Haemostatic abnormalities have been described in relation to hyperleucostasis and drugs used to treat CML. However, the correlation between haemostatic derangements and phase of CML is unclear in the literature.

AIM

The purpose of this cross-sectional study was to assay various haemostatic parameters in patients of CML receiving Imatinib and to determine any correlation between them and phases of disease as well as the status of remission.

MATERIALS AND METHODS

The study included 30 patients with CML (17 males, 13 females, mean age of 35.53 ± 8.92 years) receiving imatinib mesylate. Haemostatic parameters including platelet counts, Prothrombin Time (PT), activated Partial Thromboplastin Time (APTT), fibrinogen, D-dimers and Factor VIII levels were assayed for all patients using standard methods. Bcr-abl gene product (quantitative) was determined on the peripheral blood by reverse transcriptase polymerase chain reaction (RT-PCR). Patients were grouped into phases of disease (chronic, accelerated and blast) and their response to imatinib was determined in the form of remission (clinical, haematological and molecular). Correlations were drawn between them using spearman's coefficient.

RESULTS

A significant positive correlation was found between PT (p=0.002), fibrinogen (p=0.011), D-dimers (p=0.050), Factor VIII levels (p=0.006) with the phase of CML and a significant negative correlation was observed between PT (p=0.003, 0.006), fibrinogen (p=0.010, 0.005), D-dimers (p=0.035, 0.017), Factor VIII levels (p=0.005, 0.001) and clinical and haematological remission respectively. No significant correlation of platelet counts and APTT was seen with the phase of CML or remission status.

CONCLUSION

Haemostatic system is significantly disturbed in CML and correlate positively with the progression of the disease. Imatinib treatment leads to improvement in some of these parameters.

Increased mean platelet volume and immature platelet fraction as potential predictors of thrombotic complications in BCR/ABL-negative myeloproliferative neoplasms

BCR/ABL-negative myeloproliferative neoplasms (MPNs) are considered to be acquired thrombophilic conditions. Persistently enhanced platelet activation has been described in polycythaemia vera and essential thrombocythaemia (ET), and shown to contribute to a higher risk of arterial and venous thrombotic complications. Recent studies have shown that mean platelet volume (MPV) and immature platelet fraction (IPF) can serve as useful markers of platelet activation and increased risk of thrombosis. The aim of the present study was to investigate the relationship between these parameters and thrombotic events in BCR/ABL-negative MPN. MPV values in patients with BCR/ABL-negative MPN were significantly higher than MPV values of healthy individuals (P < 0.001). No significant difference in MPV or IPF was observed between groups of patients with and without thrombotic complications (P = 0.441; P = 0.110); the difference in IPF values was close to the significance level for patients with ET (P = 0.073). Higher values of IPF were more frequently detected in patients with JAK2 V617F positivity (P = 0.030). These patients had higher MPV more frequently than others, and this difference was close to the significance level (P = 0.056). Further studies should validate the use of platelet parameters to identify patients at high risk.

Thrombotic disease in the myeloproliferative neoplasms

Thrombosis is a leading cause of morbidity and mortality in patients with Philadelphia chromosome–negative myeloproliferative neoplasms (MPNs), particularly polycythemia vera and essential thrombocythemia. Mechanisms involved in the pathogenesis of the acquired thrombophilic state associated with these diseases include abnormalities of MPN clone–derived blood cells, which display prothrombotic features, and abnormalities of normal vascular cells, which become procoagulant in response to inflammatory stimuli. Ultimately, the release into the blood of elevated levels of procoagulant microparticles by platelets and vascular cells and the increase in the global thrombin generation due to an acquired activated protein C resistance result in a highly prothrombotic scenario in patients with polycythemia vera and essential thrombocythemia. The acquired point mutation in the pseudokinase domain of JAK2 (JAK2V617F) in these disorders is variably associated with thrombosis and, more consistently, with elevations in WBC counts and alterations in biomarkers of blood-clotting abnormalities. The predictive value of these biomarkers for thrombosis remains to be established to identify subsets of patients at elevated risk who may benefit from prophylaxis with antithrombotic drugs.

miRSystem: an integrated system for characterizing enriched functions and pathways of microRNA targets

Background

Many prediction tools for microRNA (miRNA) targets have been developed, but inconsistent predictions were observed across multiple algorithms, which can make further analysis difficult. Moreover, the nomenclature of human miRNAs changes rapidly. To address these issues, we developed a web-based system, miRSystem, for converting queried miRNAs to the latest annotation and predicting the function of miRNA by integrating miRNA target gene prediction and function/pathway analyses.

Results

First, queried miRNA IDs were converted to the latest annotated version to prevent potential conflicts resulting from multiple aliases. Next, by combining seven algorithms and two validated databases, potential gene targets of miRNAs and their functions were predicted based on the consistency across independent algorithms and observed/expected ratios. Lastly, five pathway databases were included to characterize the enriched pathways of target genes through bootstrap approaches. Based on the enriched pathways of target genes, the functions of queried miRNAs could be predicted.

Conclusions

MiRSystem is a user-friendly tool for predicting the target genes and their associated pathways for many miRNAs simultaneously. The web server and the documentation are freely available at http://mirsystem.cgm.ntu.edu.tw/.

Myeloproliferative disorders in pregnancy

This article reviews pregnancy outcome in women diagnosed with a myeloproliferative neoplasm (MPN), and discusses possible risk markers and the pathogenesis of poor pregnancy outcome. An outline of the key factors regarding the diagnosis and management of MPN in women of reproductive potential is followed by a description of the authors' management strategy for standard and high-risk pregnancy in MPN patients.

Platelet-induced thrombin generation by the calibrated automated thrombogram assay is increased in patients with essential thrombocythemia and polycythemia vera

The platelet contribution to the thrombophilic state of patients with myeloproliferative neoplasms (MPNs), i.e., essential thrombocythemia (ET) and polycythemia vera (PV), remains uncertain. In this study we aimed to characterize the thrombin generation (TG) potential expressed by platelets from these subjects, compare it to normal platelets, and identify what factors might be responsible for platelet TG. In a group of 140 MPN patients (80 ET and 60 PV) and 72 healthy subjects, we measured the global procoagulant potential of platelet-rich plasma (PRP) utilizing the TG assay by the calibrated automated thrombogram (CAT). To characterize the procoagulant contribution of platelets in PRP, the TG of both isolated platelets and platelet-poor plasma was measured, and the platelet surface expression of TF was determined. Finally, the activation status of platelets was assessed by the levels of P-selectin expressed on platelet surface. MPN patients had significantly increased PRP and isolated platelet TG potential compared to controls. This was associated to the occurrence of platelet activation. Patients carriers of the JAK2V617F mutation showed the highest values of TG and platelet surface TF and P-selectin. Platelet TG potential was significantly lower in hydroxyurea(HU) compared to non-HU-treated patients and was lowest in HU-treated JAK2V617F carriers. In subjects not receiving HU, platelet TG significantly increased by JAK2V617F allele burden increment (P < 0.05).This study demonstrates a platelet-dependent form of hypercoagulability in MPN patients, particularly in those carriers of the JAK2V617F mutation. The cytoreductive therapy with HU significantly affects this prothrombotic phenotype.

Progressive postinjury thrombocytosis is associated with thromboembolic complications

BACKGROUND

Our previous investigation demonstrated that despite routine chemoprophylaxis, thrombelastography, which is a comprehensive test measuring the viscoelastic properties of blood, identified a hypercoagulable state in a cohort of critically ill surgical patients that was associated with thromboemobolic events. Furthermore, because thrombelastography allows for the comprehensive assessment of coagulation status, this work suggested that platelet hyperactivity is a component of the hypercoagulable state. We hypothesized that progressive postinjury thrombocytosis contributes to a hypercoagulable state that is associated with thrombelastography.

METHODS

One thousand four hundred and forty severely injured patients surviving >48 h were entered into a database prospectively over 12 years. The variables that were evaluated in associated with thrombocytosis (platelet count >450,000) included age, Injury Severity Score, packed red blood cell transfusions in 12 h, and thromboemobolic complications (TE) (deep venous thrombosis, pulmonary embolus, mesenteric thrombosis, stroke, and arterial thrombosis). The time frame for the development of thrombocytosis was assessed at greater or less than 7 days postinjury. Logistic regression was used to identify the independent variables predictive of thrombocytosis and to adjust the association of thrombocytosis with TE for other risk factors. C-statistic was used to assess the discriminative power of thrombocytosis for prediction of TE.

RESULTS

The mean age was 37.4 ± 0.4 years. The Injury Severity Score was 29.3 ± 0.3, and mean red blood cell transfusions in 12 h was 4.4 ± 0.2 units. Injury via blunt force occurred in 76% of patients, and 72% of patients were male. Thrombocytosis was identified in 447 (31%) patients and was noted almost exclusively >7 days postinjury (98%). TE developed in 35 (8%) of the 447 patients with thrombocytosis, compared with 45 (4.5%) of the remaining 993 patients who did not develop thrombocytosis. Persistent thrombocytosis >7 days was associated with TE (P > .0001). Logistic regression analysis indicated that when adjusted for intensive care unit duration of stay, transfusions, age, and Injury Severity Score, patients with sustained thrombocytosis more than 3 days were noted to have a 1.4 × increased risk of TE (odds ratio, 1.12; 95% confidence interval, 1.04-1.2; P = .002; C-statistic = 0.82).

CONCLUSION

Persistent thrombocytosis in critically injured patients receiving routine chemoprophylaxis is associated with thrombotic complications. Subsequent investigation is warranted to differentiate enzymatic from platelet hypercoagulability to ascertain the role of antiplatelet therapy for prevention of TE.

Aortic thrombus in a patient with myeloproliferative thrombocytosis, successfully treated by pharmaceutical therapy: a case report

Introduction

Thrombosis in myeloproliferative thrombocytosis occurs usually in the microvessels and medium-sized arteries and veins and only rarely in the aorta. Aortic thrombosis is usually treated with thrombectomy. Reported here is a rare case that was treated pharmacologically.

Case presentation

A 60-year-old Japanese woman presented with numbness of both lower extremities. Her platelet count was 1787 × 10³/μl. Through bone marrow examination, we diagnosed her condition as myelodysplastic and/or myeloproliferative disorder-unclassifiable. Abdominal ultrasonography and computed tomographic scan revealed aortic thrombosis. Her platelet count was controlled with hydroxyurea and ranimustine. Aspirin and ticlopidine improved the numbness in both lower limbs on the second day. Aortic thrombosis was not observed in a computed tomographic scan on the seventh day.

Conclusion

For aortic thrombosis, surgical management is usually adopted, but pharmacological management is also an option because of its immediate curative effects.

Src tyrosine kinase preactivation is associated with platelet hypersensitivity in essential thrombocythemia and polycythemia vera

Polycythemia vera (PV) and essential thrombocythemia (ET) are chronic myeloproliferative disorders characterized by an increased incidence of thrombo-hemorrhagic complications. The acquired somatic Janus kinase 2 (JAK2) V617F mutation is present in the majority of PV and ET patients. Because aberrant protein Tyr-phosphorylation has been associated with hematopoietic malignancies, the activity of the tyrosine kinases Src and JAK2 was analyzed in resting and thrombin-stimulated platelets from 13 PV and 42 ET patients. JAK2 was found inactive in healthy and pathological resting cells regardless of the V617F mutation. In addition, Src was inactive in all resting platelets, but in the pathological specimens it was present in a preactivated conformation as a consequence of anomalous dephosphorylation of its inhibitory phospho-Tyr527 residue, likely mediated by Src homology-2 domain-containing protein Tyr-phosphatase-2 (SHP-2), whose constitutive activity correlated with its recruitment to Src. Low thrombin concentration triggered a more rapid Src-signaling activation, higher [Ca2+]c increase, and aggregation in pathological platelets compared with controls. Thrombin-induced Src activation preceded JAK2 activation, which occurred simultaneously in normal and pathological platelets. Our results indicate that a constitutive Src kinase preactivation is implicated in platelet hypersensitivity and likely involved, at least partially, in the functional abnormalities of PV and ET platelets.

Role of platelet counts in the management of essential thrombocythemia: experience with anagrelide

An elevated platelet count is the hallmark of essential thrombocythemia (ET). Therapeutic control of platelet counts in ET has proven effective for minimizing the risk of bleeding complications. By contrast, the relationship between platelet count and thrombotic complications is less well defined. The beneficial effects of lowering the platelet count are greatest when levels are reduced close to or within the normal range, thus supporting the trend within the medical community to reduce platelet treatment targets to below 400-450 × 10(9)/l. Platelet counts have further utility in ET as a marker to indicate intolerance/resistance to hydroxyurea according to recently published guidelines. In the current era, where novel risk factors for ET complications are being discussed, this article takes a back-to-basics approach, considering what platelet counts reveal in practice as a risk factor for complications and a marker of treatment efficacy, with particular focus on data for the platelet-selective agent anagrelide.

Association of Hematological Parameters with Clustered Components of Metabolic Syndrome among Professional and Office Workers in Bangkok, Thailand

BACKGROUND: Accumulating evidence documents associations between alterations in hematological parameters, indicative of prothrombotic and proinflammatory states, and risk of metabolic syndrome (MetS). We investigated associations of hematological parameters with MetS and individual criteria of the syndrome among Thai professional and office workers. METHODS: Study subjects were 1,314 patients (531 men and 783 women) who participated in annual health examinations during the period of August through December 2001. MetS was defined using the modified ATP III criteria. Multivariable logistic regression procedures were used to estimate odds ratios (OR) and 95% confidence intervals (95%CI) of MetS risk according to quartiles of each hematological parameter with the lowest quartile specified as the referent group. RESULTS: WBC counts increased with increasing numbers of MetS components in both men and women. Among women, platelet counts, hemoglobin and hematocrit concentrations increased with increasing numbers of MetS components (p<0.05). No similar trends were observed for men. Of the hematological parameters studied, elevated platelet and WBC were statistically significantly associated with MetS among men (OR=1.86, 95% CI: 1.03-3.36; OR=2.26, 95% CI: 1.27-4.02), respectively. Among women, MetS risk increased across successive quartiles of hemoglobin (1.00, 2.63, 3.59 and 4.36; p for trend = 0.002), hematocrit (1.00, 2.35, 3.04 and 5.70; p-for trend <0.001), platelet (1.00, 2.37, 2.83 and 3.11; p-for trend = 0.014) and WBC counts (1.00, 2.97, 4.09 and 5.41; p-for trend < 0.001). CONCLUSIONS: Our data are consistent with an emerging literature demonstrating altered hematological status in patients at high risk of MetS.

JAK2 V617F mutation in patients with catastrophic intra-abdominal thromboses

Catastrophic intra-abdominal thrombosis can result from a variety of prothrombotic states, including polycythemia vera and essential thrombocythemia, both of which are frequently associated with an acquired mutation (V617F) in the JAK2 gene. To assess the prevalence and clinical implications of this mutation in the setting of intra-abdominal thrombosis, JAK2 V617F genotyping was performed in 42 patients who had catastrophic intra-abdominal thromboses resulting in visceral transplants. The prevalence of V617F was compared with that of other prothrombotic states for which molecular testing is routinely performed. V617F mutations were detected in 7 patients (17%), who were not distinguishable on the basis of their peripheral blood cell counts. The median posttransplantation survival of V617F+ patients was 17.5 months, compared with 116.4 months for the V617F- patients (ratio, 6.6; 95% confidence interval, 6.3-7.0). These results highlight the diagnostic usefulness of JAK2 V617F testing in this setting and underscore the clinical significance of a positive result.

V617F JAK-2 mutation in patients with essential thrombocythemia: relation to platelet, granulocyte, and plasma hemostatic and inflammatory molecules

OBJECTIVE

This article evaluates patients with essential thrombocythemia (ET) to determine whether the V617F mutation in the JAK2 gene affects platelet hemostatic and adhesive molecules, platelet-polymorphonuclear leukocyte (PMN) interactions, and PMN-activation characteristics, as well as plasma hypercoagulation markers.

PATIENTS AND METHODS

Thirty-seven ET patients with V617F JAK2 mutation and 38 wild-type, and 50 healthy controls were studied.

RESULTS

Platelets from overall ET patients, compared to controls, expressed significantly higher membrane tissue factor (TF) and P-selectin (p < 0.01) and lower CD41 and CD42b (p < 0.01). TF appeared significantly higher in the V617F JAK2 carriers compared to wild-type, and total platelet TF antigen levels confirmed the same result. The presence of circulating platelet/PMN aggregates was significantly greater in the JAK2-mutation carriers than in the wild-type and controls (p < 0.05). PMN surface activation and inflammatory markers (i.e., CD14, TF, CD11b, and leukocyte alkaline phosphatase [LAP]) were all significantly higher in ET versus control subjects, with CD14 and LAP being the highest in the JAK2 mutation carriers. Finally, a significant increase in plasma hypercoagulation markers was found in ET patients, and the only difference for the V617F JAK2 carriers was higher plasma thrombomodulin levels (p < 0.01). Differences in white blood cell and PMN count, platelet TF, PMN CD14, and LAP, and plasma thrombomodulin remained significant after multivariate analysis.

CONCLUSIONS

These results show that a correlation exists between the presence of V617F JAK2 mutation and selected hemostatic activation variables.

Thrombocytosis and thrombosis

The aim of this review is to discuss current diagnostic approaches to, and classification of, patients presenting with thrombocytosis, in light of novel information derived from the discovery of specific molecular abnormalities in chronic myeloproliferative disorders (CMPD), which represent the most common cause of primary thrombocytosis. The JAK2V617F and the MPLW515L/K mutations have been found in patients with essential thrombocythemia, polycythemia vera, and primary myelofibrosis, and less frequently in other myeloproliferative disorders complicated by thrombocytosis. However, neither mutation is disease specific nor is it universally present in patients with elevated platelet counts due to a CMPD; therefore, distinguishing between reactive and primary forms of thrombocytosis, as well as among the different clinical entities that constitute the CMPD, still requires a multifaceted diagnostic approach that includes as a key step the accurate evaluation of bone marrow histology. The role of elevated platelet counts in thrombosis, which represent the predominant complication of CMPD,significantly affecting prognosis and quality of life as well as, paradoxically, in the pathogenesis of the hemorrhagic manifestations, will be discussed. Established and novel potential risk factors for thrombosis, including the clinical relevance of the JAK2V617F mutation, and current management strategies for thrombocytosis are also briefly discussed.

JAK2 V617F in myeloid disorders: molecular diagnostic techniques and their clinical utility: a paper from the 2005 William Beaumont Hospital Symposium on Molecular Pathology

In early 2005, several groups of investigators studying myeloid malignancies described a novel somatic point mutation (V617F) in the conserved autoinhibitory pseudokinase domain of the Janus kinase 2 (JAK2) protein, which plays an important role in normal hematopoietic growth factor signaling. The V617F mutation is present in blood and marrow from a large proportion of patients with classic BCR/ABL-negative chronic myeloproliferative disorders and of a few patients with other clonal hematological diseases such as myelodysplastic syndrome, atypical myeloproliferative disorders, and acute myeloid leukemia. The JAK2 V617F mutation causes constitutive activation of the kinase, with deregulated intracellular signaling that mimics continuous hematopoietic growth factor stimulation. Within 7 months of the first electronic publication describing this new mutation, clinical molecular diagnostic laboratories in the United States and Europe began offering JAK2 mutation testing on a fee-for-service basis. Here, I review the various techniques used by research groups and clinical laboratories to detect the genetic mutation underlying JAK2 V617F, including fluorescent dye chemistry sequencing, allele-specific polymerase chain reaction (PCR), real-time PCR, DNA-melting curve analysis, pyrosequencing, and others. I also discuss diagnostic sensitivity, performance, and other practical concerns relevant to the clinical laboratorian in addition to the potential diagnostic utility of JAK2 mutation tests.