Basic mechanisms and pathogenesis of venous thrombosis

Portal vein thrombosis

Portal vein thrombosis (PVT) is a rare event in the general medical setting that commonly complicates cirrhosis with portal hypertension, and can also occur with liver tumors. The diagnosis is often incidental when a thrombus is found in the portal vein on imaging tests. However, PVT may also present with clinical symptoms and can progress to life-threatening complications of ischemic hepatitis, liver failure, and/or small intestinal infarction. This article reviews the pathophysiology of this disorder, with a major focus on PVT in patients with cirrhosis, and presents detailed guidelines on optimal diagnostic and therapeutic strategies.

Sudden Death by Pulmonary Thromboembolism due to a Large Uterine Leiomyoma with a Parasitic Vein to the Mesentery

The pathophysiology of venous thrombosis is classically attributed to alterations in one or more components of Virchow's triad: hypercoagulability, stasis, and damage to the vascular endothelium. Deep vein thrombosis (DVT) may lead to pulmonary thromboembolism (PE), and the latter is culpable for many deaths annually in the United States; however, DVT as a complication of uterine leiomyoma has rarely been reported. We report a case of a 57-year-old woman whose death was due to a large pedunculated subserosal leiomyoma externally compressing the pelvic veins resulting in stasis and venous thrombosis leading to fatal PE. The association of large pelvic masses with venous thrombosis has clinical implications, since prophylactic surgery could be life-saving.

Spatial aspects of blood coagulation: two decades of research on the self-sustained traveling wave of thrombin

In a number of experimental studies, it has been demonstrated that the forefront of blood coagulation can propagate in the manner of a signal relay. These data strongly support the concept that the formation of a blood clot is governed by a self-sustained traveling wave of thrombin. The present review critically appraises the experimental data obtained in recent decades concerning the self-sustained spatial propagation of thrombin. Open questions regarding the experimental detection of the self-sustained propagation of thrombin are discussed.

Update on the lower extremity venous ultrasonography examination

Lower extremity venous ultrasonography is an accurate method to diagnose acute deep venous thrombosis (DVT). Recurrent DVT is often difficult diagnosis. The decision to order ultrasonography can be based on pretest risk assessment. If the ultrasonography study is negative, the report may recommend follow-up for patients whose clinical condition changes or for patients with specific risks. Lower extremity venous ultrasonography is the gold standard for diagnosis of DVT. It is accurate and objective, and because the clinical assessment of patients is limited and its potential complication, pulmonary embolism, is significant, the impact of a positive and negative test is high.

A case of heart failure due to alcoholic cardiomyopathy combined with acute pulmonary embolism

It has not been reported that cases of alcoholic cardiomyopathy (ACM) combined with acute pulmonary embolism (PE). We hereby present a case of a 48-year-old male with ACM with significant enlargement of the heart and heart failure is described. Then, the patient was seized with acute PE which was confirmed by specific examination and his symptoms.

Clear cell carcinoma of the ovary associated with increased risk of venous thrombosis

Clear cell carcinoma of the ovary (CCCO) is an uncommon, clinically aggressive neoplasm that has a propensity for the development of venous thrombosis and embolization, especially when compared to other subtypes of ovarian malignancies. We present a fatal case of a 59-year-old woman with a clinical course complicated by venous thrombosis and pulmonary thromboembolism that was attributed to CCCO discovered initially at autopsy.

Enhanced pre-operative thrombolytic status is associated with the incidence of deep venous thrombosis in patients undergoing total knee arthroplasty

Background

Deep venous thrombosis (DVT), which is often associated with pulmonary embolism (PE), is a serious complication after total knee arthroplasty (TKA). In the present study, we examined the overall thrombotic and thrombolytic status using Global Thrombosis Test (GTT) in non-anticoagulated blood of patients undergoing TKA to develop the predictable marker for the incidence of DVT.

Methods

DVT was diagnosed using doppler ultrasonography a day after the surgery in 31 patients with osteoarthritis (n = 24), rheumatoid arthritis (n = 6) and ankylosing spondylitis (n = 1) by the well-trained operator. We measured overall thrombotic and thrombolytic status using GTT and other biomarkers, which is associated with blood coagulation and fibrinolysis, before and immediately after the surgery.

Results

Newly-generated DVT during the operation was detected in 11 of 31 patients (35.4%) 1 day after TKA. There were no differences in markers of coagulation (PT and APTT), platelet activity (platelet aggregation-induced by ADP and collagen) and fibrinolysis (FDP and D-dimer) between non-DVT and DVT group both before and after the surgery. Both Pre- and Post-operative GTT-occlusion times (OT), an index of platelet reactivity, were tended to be shorter, but not significant, in DVT group compared with non-DVT group. Pre-operative GTT-lysis time (LT), an index of thrombolytic activity, was significantly shorter in DVT group compared with non-DVT group, while there were no differences in post-operative value of this index between DVT group and non-DVT group, suggesting overall thrombolytic activity was enhanced in DVT group before surgery.

Conclusions

Our data suggest that enhancement of pre-operative thrombolytic activity assessed by GTT may be a predictable marker for the incidence of DVT after TKA.

No effect of isolated long-term supine immobilization or profound prolonged hypoxia on blood coagulation

BACKGROUND

Long-distance air travel is associated with an increased risk of venous thrombosis. The most obvious factor that can explain air travel-related thrombosis is prolonged seated immobilization. In addition, hypobaric hypoxia has been shown to affect coagulation, and the lowered atmospheric pressures present in the cabin during the flight may therefore play an etiologic role. Because immobilization and hypoxic conditions are usually present simultaneously in airplanes or hypobaric chambers, their separate effects on the coagulation system or on thrombosis risk have not been studied extensively.

OBJECTIVES

To investigate the separate effects of long-term immobilization and profound prolonged hypoxia on blood coagulation.

PATIENTS AND METHODS

We performed two studies in collaboration with European Space Agency/European Space Research and Technology Centre. In the first study, 24 healthy, non-smoking, adult women underwent 60 days of -6° head-down bed rest. In the second study, we took blood samples from 25 healthy men who participated during their stay in the Concordia station in Antarctica, where, due to the atmospheric conditions, continuous severe hypobaric hypoxia is present. In both studies, we measured markers of blood coagulation at baseline and at several time points during the exposures.

RESULTS AND CONCLUSIONS

We observed no increase in coagulation markers during immobilization or in the hypobaric environment, compared with baseline measurements. Our results indicate that neither immobilization nor hypoxia per se affects blood coagulation. These results implicate that a combination of risk factors is necessary to induce the coagulation system during air travel.

Roles of the Oxidative Stress and ADMA in the Development of Deep Venous Thrombosis

Venous thromboembolism has multifactorial origin and occurs in the context of complex interactions between environmental and genetic predisposing factors. Oxidative stress plays an important role in the physiopathology of venous thrombosis. Current study examined the role of oxidative stress and asymmetric dimethylarginine in the development of DVT with the parameters such as serum malondialdehyde (MDA), glutathione peroxidase (GSH-Px), catalase, ADMA, homocysteine, folic acid, vitamin B₆, and vitamin B₁₂ levels. Serum MDA levels were found significantly (P < 0.005) high in patients with DVT compared with control group. Additionally, serum B₆ levels were found significantly (P < 0.009) low in patients with DVT compared with healthy volunteers. There were no significant differences between the groups in terms of the other parameters (P > 0.05). This study showed that patients with DVT have increased oxidative stress compared with the healthy volunteers whereas there was no significant difference between the groups in terms of serum ADMA levels. Thus serum ADMA levels seemed to be not related with development of DVT.

Systemic lupus erythematosus increases the risks of deep vein thrombosis and pulmonary embolism: a nationwide cohort study

BACKGROUND

Studies on the risks of deep vein thrombosis (DVT) and pulmonary embolism (PE) in patients with systemic lupus erythematosus (SLE) are limited. We evaluated the effects of SLE on the risks of developing DVT and PE in a nationwide, population-based cohort study in Taiwan.

METHODS

We randomly selected patients without SLE from the National Health Insurance database (N = 23.74 million), and frequency-matched four of them, on the basis of age, sex, and index year, to each SLE patient in the catastrophic illness registry of the NHI who was diagnosed with SLE between 1998 and 2008. Using a follow-up period ending in 2010, we analyzed the risks of DVT and PE with a Cox proportional-hazards regression analysis.

RESULTS

The 13 084 SLE patients (87.9% women; mean age of 35.6 years) and 52 336 controls were followed for 90 237 and 379 185 person-years, respectively. After adjustment for age, sex, and comorbidities, the SLE patients' risks of developing DVT and PE were 12.8-fold and 19.7-fold higher, respectively, than those of the comparison cohort. The risks of DVT and PE increased in both study groups when the data were stratified on the basis of sex, age, and comorbidities. The SLE patients aged ≤ 35 years had the highest risks of developing DVT and PE. The multiplicative increased risks of DVT and PE were also significant in SLE patients with any comorbidity.

CONCLUSION

The risks of DVT and PE are significantly higher in SLE patients than in the general population.

Impact of anticoagulation on the effectiveness of loop diuretics in heart failure with cardiorenal syndrome and venous thromboembolism

The limitations of diuretics in the treatment of acute decompensated heart failure (ADCHF) are progressive worsening of renal function and resistance to up-titrated doses. The occurrence of resistance to loop diuretics in patients with ADCHF is associated with worsening prognosis and increased mortality. In this study, we report two patients with ADCHF and resistance to loop diuretics suspected for venous thromboembolism, suggesting that heparin administered to ADCHF patients treated for venous thromboembolism with cardiorenal syndrome decreases right-ventricular overload and improves renal function. To our knowledge, these are the first reported cases describing restored responsiveness to loop diuretics in ADCHF patients after additional heparin administration.

Time-dependent hardening of blood clots quantitatively measured in vivo with shear-wave ultrasound imaging in a rabbit model of venous thrombosis

OBJECTIVE

Provide in vivo blood clot hardening evolution with ultrasound using supersonic imaging of shear waves.

METHODS

We conducted a prospective study in flow stasis-induced venous thrombosis within jugular veins of white female New Zealand rabbits. Blood clot elasticity was noninvasively measured in vivo using the Young's modulus (in kilopascals), on a 2-hour and a 2-week periods after thrombus induction. Monitoring was followed by a necropsy and ex vivo mechanical characterization to validate the existence and elasticity of explanted thrombi.

RESULTS

Stagnant blood in the region of interest underwent clotting and progressive hardening with thrombus aging. The mean Young's moduli varied from 1.0 ± 0.6 kPa (at 10 min) to 5.3 ± 1.6 kPa (at 2 hours), then to 25.0 ± 6.8 kPa (at 14 days) post-surgery. Mean ex vivo moduli of 6.2 ± 0.7 kPa at 2 hours and 29.0 ± 2.4 kPa at 2 weeks agreed with in vivo measures.

CONCLUSIONS

Supersonic imaging of shear waves provides consistent quantitative non-invasive elasticity measurements not available with standard compression ultrasound imaging for diagnosing and following venous thromboembolism. This information translatable to humans could aid in determining whether continued anticoagulant treatment is necessary, especially in the setting of unprovoked venous thromboembolism.

The impact of smoking on neurosurgical outcomes

Cigarette smoking is a common health risk behavior among the general adult population, and is the leading preventable cause of morbidity and mortality in the US. The surgical literature shows that active tobacco smoking is a major risk factor for perioperative morbidity and complications, and that preoperative smoking cessation is an effective measure to lower these risks associated with active smoking. However, few studies have examined the effects of smoking and perioperative complications following neurosurgical procedures. The goal of this review was to highlight the scientific data that do exist regarding the impact of smoking on neurosurgical outcomes, to promote awareness of the need for further work in the specific neurosurgical context, and to suggest ways that neurosurgeons can promote smoking cessation in their patients and lead efforts nationally to emphasize the importance of preoperative smoking cessation. This review indicates that there is limited but good evidence that smoking is associated with higher rates of perioperative complications following neurosurgical intervention. Specific research is needed to understand the effects of smoking and perioperative complications. Neurosurgeons should encourage preoperative smoking cessation as part of their clinical practice to mitigate perioperative morbidity associated with active smoking.

Overview and assessment of risk factors for pulmonary embolism

Pulmonary embolism is one of the most common undiagnosed conditions affecting hospitalized patients. There are a plethora of risk factors for venous thromboembolism and pulmonary emboli. These factors are grouped under the broad triad of hypercoagulability, stasis and injury to provide a framework for understanding. Important risk factors include inherited thrombophilia, age, malignancy and estrogens. These risk factors are reviewed in detail and several risk assessment models are reviewed. These risk assessment models help identify those at risk for disease and therefore candidates for thromboprophylaxis. Diagnosis can be difficult and is aided by clinical decision rules that incorporate clinical scores that define the likelihood of pulmonary embolism. These are important considerations, not only for diagnostic purposes, but also to minimize excessive use of imaging, which increases exposure to and risks associated with radiation. A healthy index of suspicion is often the key to diagnosis.

Fibrin networks regulate protein transport during thrombus development

Thromboembolic disease is a leading cause of morbidity and mortality worldwide. In the last several years there have been a number of studies attempting to identify mechanisms that stop thrombus growth. This paper identifies a novel mechanism related to formation of a fibrin cap. In particular, protein transport through a fibrin network, an important component of a thrombus, was studied by integrating experiments with model simulations. The network permeability and the protein diffusivity were shown to be important factors determining the transport of proteins through the fibrin network. Our previous in vivo studies in mice have shown that stabilized non-occluding thrombi are covered by a fibrin network (‘fibrin cap’). Model simulations, calibrated using experiments in microfluidic devices and accounting for the permeable structure of the fibrin cap, demonstrated that thrombin generated inside the thrombus was washed downstream through the fibrin network, thus limiting exposure of platelets on the thrombus surface to thrombin. Moreover, by restricting the approach of resting platelets in the flowing blood to the thrombus core, the fibrin cap impaired platelets from reaching regions of high thrombin concentration necessary for platelet activation and limited thrombus growth. The formation of a fibrin cap prevents small thrombi that frequently develop in the absence of major injury in the 60000 km of vessels in the body from developing into life threatening events.

To restrict the loss of blood following rupture of blood vessels, the human body rapidly forms a clot consisting mainly of platelets and fibrin. However, to prevent formation of a pathological clot within vessels (thrombus) as a result of vessel damage or dysfunction, the response must be regulated, and clot formation must be limited. Our previous studies demonstrated that as a laser-induced thrombus stabilized in mice, the ratio of fibrin to platelets at the thrombus surface increased significantly. Stabilized non-occluding thrombi were observed to be covered by a fibrin network (‘fibrin cap’). In the present work the role of the fibrin network in protein transport is examined by integrating experiments in microfluidic devices with the hemodynamic thrombus model. The study reveals permeability of the fibrin network and protein diffusivity to be important factors determining the transport of blood proteins inside the thrombus. It is shown that the fibrin network does not dramatically limit the diffusion of thrombin but impairs flowing platelets in blood from reaching regions of high thrombin concentration thus, reducing the probability they are activated and stably integrated into the thrombus. This novel, counter-intuitive mechanism suggests that a fibrin network formed at early stages of thrombus initiation can prevent normally asymptomatic thrombi from developing into pathological clots.

Cytokines associated with increased erythropoiesis in Sprague-Dawley rats administered a novel hyperglycosylated analog of recombinant human erythropoietin

We previously reported an increased incidence of thrombotic toxicities in Sprague-Dawley rats administered the highest dose level of a hyperglycosylated analog of recombinant human erythropoietin (AMG 114) for 1 month as not solely dependent on high hematocrit (HCT). Thereafter, we identified increased erythropoiesis as a prothrombotic risk factor increased in the AMG 114 high-dose group with thrombotic toxicities, compared to a low-dose group with no toxicities but similar HCT. Here, we identified pleiotropic cytokines as prothrombotic factors associated with AMG 114 dose level. Before a high HCT was achieved, rats in the AMG 114 high, but not the low-dose group, had imbalanced hemostasis (increased von Willebrand factor and prothrombin time, decreased antithrombin III) coexistent with cytokines implicated in thrombosis: monocyte chemotactic protein 1 (MCP-1), MCP-3, tissue inhibitor of metalloproteinases 1, macrophage inhibitory protein-2, oncostatin M, T-cell-specific protein, stem cell factor, vascular endothelial growth factor, and interleukin-11. While no unique pathway to erythropoiesis stimulating agent-related thrombosis was identified, cytokines associated with increased erythropoiesis contributed to a prothrombotic intravascular environment in the AMG 114 high-dose group, but not in lower dose groups with a similar high HCT.

Mechanical stability and fibrinolytic resistance of clots containing fibrin, DNA, and histones

Neutrophil extracellular traps are networks of DNA and associated proteins produced by nucleosome release from activated neutrophils in response to infection stimuli and have recently been identified as key mediators between innate immunity, inflammation, and hemostasis. The interaction of DNA and histones with a number of hemostatic factors has been shown to promote clotting and is associated with increased thrombosis, but little is known about the effects of DNA and histones on the regulation of fibrin stability and fibrinolysis. Here we demonstrate that the addition of histone-DNA complexes to fibrin results in thicker fibers (increase in median diameter from 84 to 123 nm according to scanning electron microscopy data) accompanied by improved stability and rigidity (the critical shear stress causing loss of fibrin viscosity increases from 150 to 376 Pa whereas the storage modulus of the gel increases from 62 to 82 pascals according to oscillation rheometric data). The effects of DNA and histones alone are subtle and suggest that histones affect clot structure whereas DNA changes the way clots are lysed. The combination of histones + DNA significantly prolongs clot lysis. Isothermal titration and confocal microscopy studies suggest that histones and DNA bind large fibrin degradation products with 191 and 136 nm dissociation constants, respectively, interactions that inhibit clot lysis. Heparin, which is known to interfere with the formation of neutrophil extracellular traps, appears to prolong lysis time at a concentration favoring ternary histone-DNA-heparin complex formation, and DNase effectively promotes clot lysis in combination with tissue plasminogen activator.

Thrombosis as an intravascular effector of innate immunity

Thrombosis is the most frequent cause of mortality worldwide and is closely linked to haemostasis, which is the biological mechanism that stops bleeding after the injury of blood vessels. Indeed, both processes share the core pathways of blood coagulation and platelet activation. Here, we summarize recent work suggesting that thrombosis under certain circumstances has a major physiological role in immune defence, and we introduce the term immunothrombosis to describe this process. Immunothrombosis designates an innate immune response induced by the formation of thrombi inside blood vessels, in particular in microvessels. Immunothrombosis is supported by immune cells and by specific thrombosis-related molecules and generates an intravascular scaffold that facilitates the recognition, containment and destruction of pathogens, thereby protecting host integrity without inducing major collateral damage to the host. However, if uncontrolled, immunothrombosis is a major biological process fostering the pathologies associated with thrombosis.

Diseases associated with thrombosis

Coagulation abnormalities are commonly encountered in critical illness. Traditionally, clinically relevant coagulation disorders have consisted mostly of bleeding associated with advanced stages of disseminated intravascular coagulation or toxin ingestion. However, advances in critical care have highlighted hypercoagulability as a clinically relevant state that must be recognized and treated to optimize the chances of a positive outcome. Retrospective studies of dogs with confirmed thrombosis in varying locations have identified populations most likely to experience hypercoagulable states. Diseases most frequently complicated by thrombosis include immune-mediated disease, neoplasia, systemic inflammation and sepsis, cardiac disease, protein-losing states, and infectious diseases. In this report, the existing retrospective studies will be discussed along with a review of specific disease processes that predispose to a hypercoagulable state. Studies targeting those populations most at risk for thrombotic complications are necessary for better understanding the need for prophylactic anticoagulant therapy.

Circulating and vein wall P-selectin promote venous thrombogenesis during aging in a rodent model

INTRODUCTION

The objective of this study was to identify the direct relationship between aging and selectin activation during acute venous thrombosis in mice of varying ages. We hypothesized that older animals would have increased venous thrombus formation as a result of age associated-increases of pro-inflammatory molecules within the vein wall when compared to younger animals.

MATERIALS AND METHODS

Deep venous thrombosis (DVT) was induced in 4 and 18month old C57BL/6 mice using the electrolytic inferior vena cava model (EIM) of DVT. Blood and tissue samples were collected at baseline (TC), 6hours, and 2days post-thrombosis induction.

RESULTS

Older mice had significantly larger thrombi versus younger mice at 6H (18.4±6.21 vs. 13.0±4.29×10(-3) grams, p=0.0033) and 2D (18.4±4.27 vs. 13.0±5.01×10(-3) grams, p=0.0005), higher soluble P-selectin levels at 6H (13±2.5 vs. 8.4±2.7ng/mg p=0.0010) and 2D (12.7±5.0 vs. 5.9±1.3ng/mg p=0.0020), and higher vein wall P-selectin levels at 6H (1.94×10(5)±3.56×10(4) vs. 4.81±2.29×10(4) pg/mg p=0.0001) and 2D (1.38×10(5)±5.65×10(4) vs. 3.73±1.66×10(4) pg/mg p=0.0177). Older animals also had significantly higher platelet numbers at 6H (841±203.8 vs. 564±164.8K/μL p=0.0001), and 2D (1002±342.9 vs. 690±186.1K/μL p=0.0003), with corresponding increases in mean platelet volume versus younger mice post thrombosis (p≤0.01).

CONCLUSIONS

Older animals had significantly larger venous thrombi versus younger animals post-thombosis, as a result of high levels of P-selectin both in the circulation and locally at the level of the vein wall. Expression of local and soluble P-selectin increased with age, resulting in a pro-thrombotic environment not represented in younger mice.

AF and Venous Thromboembolism - Pathophysiology, Risk Assessment and CHADS-VASc score

Atrial fibrillation (AF) and venous thromboembolism (VTE) are the two most common medical conditions managed with anti-coagulation therapy. Not all the patients with decreased mobility or AF have a similar risk for thromboembolism. The risk factors for venous thromboembolism and thromboembolism associated with AF are described in various studies. Considering that the two conditions have similar pathophysiologic basis of clot formation, one could imply that the risk factors for the occurrence of thrombosis could be similar. The present review focuses on the similarities and differences in the clinical risk factors of VTE and AF related thromboembolism. We will also be discussing the role of CHADS₂-VASc scoring system in the risk assessment of VTE.

Autoimmune diseases and venous thromboembolism: a review of the literature

Venous thromboembolism (VTE) is major health problem and is sometimes complicated by lethal pulmonary embolism (PE). Disturbances of the coagulation and anticoagulation systems are important risk factors for VTE. Comparative studies suggest that coagulation and innate immunity have a shared evolutionary origin. It is therefore unsurprising that the immune and coagulation systems are linked, with many molecular components being important for both systems. Systemic inflammation modulates thrombotic responses by suppressing fibrinolysis, upregulating procoagulant, and downregulating anticoagulants, and autoimmune disorders such as systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), and Behçet's syndrome have been linked to an increased risk of VTE. Recent reports have further shown that a majority of autoimmune and immune-mediated disorders are linked to an increased risk of venous thrombosis, PE, or VTE. For instance, a Swedish nationwide study found that the risk of PE was increased in the first year after hospitalization for 33 different autoimmune disorders. Especially high risks were noted for several autoimmune diseases such as immune thrombocytopenic purpura, polyarteritis nodosa, polymyositis/dermatomyositis, ulcerative colitis, and SLE. Another study from England, also based on hospitalization data, found that immune-mediated disorders were associated with an increased risk of VTE compared with other medical causes of hospitalization. Multiple mechanisms may operate and disease-specific factors, such as cardiolipin antibodies, have been identified. However, inflammation by itself appears to change the hemostatic balance in a thrombogenic direction. Recent epidemiological studies, together with previous experimental and clinical studies, indicate that autoimmune disorders should not only be viewed as inflammatory disorders, but also hypercoagulable disorders. Research to identify thrombotic risk factors, elucidate the mechanisms involved, and investigate prophylactic regiments is needed. The present review describes the epidemiological, clinical, and experimental evidence for the connection between VTE and autoimmune and immune-mediated disorders.

Modeling of human factor Va inactivation by activated protein C

BACKGROUND

Because understanding of the inventory, connectivity and dynamics of the components characterizing the process of coagulation is relatively mature, it has become an attractive target for physiochemical modeling. Such models can potentially improve the design of therapeutics. The prothrombinase complex (composed of the protease factor (F)Xa and its cofactor FVa) plays a central role in this network as the main producer of thrombin, which catalyses both the activation of platelets and the conversion of fibrinogen to fibrin, the main substances of a clot. A key negative feedback loop that prevents clot propagation beyond the site of injury is the thrombin-dependent generation of activated protein C (APC), an enzyme that inactivates FVa, thus neutralizing the prothrombinase complex. APC inactivation of FVa is complex, involving the production of partially active intermediates and "protection" of FVa from APC by both FXa and prothrombin. An empirically validated mathematical model of this process would be useful in advancing the predictive capacity of comprehensive models of coagulation.

RESULTS

A model of human APC inactivation of prothrombinase was constructed in a stepwise fashion by analyzing time courses of FVa inactivation in empirical reaction systems with increasing number of interacting components and generating corresponding model constructs of each reaction system. Reaction mechanisms, rate constants and equilibrium constants informing these model constructs were initially derived from various research groups reporting on APC inactivation of FVa in isolation, or in the presence of FXa or prothrombin. Model predictions were assessed against empirical data measuring the appearance and disappearance of multiple FVa degradation intermediates as well as prothrombinase activity changes, with plasma proteins derived from multiple preparations. Our work integrates previously published findings and through the cooperative analysis of in vitro experiments and mathematical constructs we are able to produce a final validated model that includes 24 chemical reactions and interactions with 14 unique rate constants which describe the flux in concentrations of 24 species.

CONCLUSION

This study highlights the complexity of the inactivation process and provides a module of equations describing the Protein C pathway that can be integrated into existing comprehensive mathematical models describing tissue factor initiated coagulation.

Formation of the venous thrombus after venous occlusion in the experimental mouse model of metabolic syndrome

INTRODUCTION

The metabolic syndrome is considered to be a risk factor for the venous thromboembolism (VTE) as well as arterial thrombosis. Although obesity, hyperglycemia and dyslipidemia are considered to be important triggering factors, it is difficult to evaluate the relationship between VTE and the metabolic syndrome in a clinical study. Furthermore the mechanism of venous thrombosis initiation still remains elusive.

MATERIALS AND METHODS

20 min clamp of superior mesenteric vein was applied to 7 w, 16 w-old KK-A(y) mouse and 16 w-old B6J mouse (n = 6 in each group), after de-clamp, the view of the mesenteric vein and intestinal submucosal venule were observed by the intravital microscopy.

RESULTS

Massive thrombi formed in the mesenteric vein in 16 w-old KK-A(y) mice, moderate thrombi formation was observed in 7 w-old KK-A(y) mice, while very few thrombi were observed in B6 J mice. The first event in submucosal venule after de-clamp was the adhesion of leukocytes to the endothelium. Subsequently, leukocytes assembled and platelets covered the leukocyte cluster. These leukocyte-platelet aggregates move from the venule to the vein and finally formed a venous thrombus.

CONCLUSION

Metabolic syndrome is a risk factor for venous thrombosis. Intravital microscopic examination revealed leukocyte and platelet recruitment to the venule in the early stages of venous thrombosis formation.

Monocytes, neutrophils, and platelets cooperate to initiate and propagate venous thrombosis in mice in vivo

Deep vein thrombosis (DVT) is a major cause of cardiovascular death. The sequence of events that promote DVT remains obscure, largely as a result of the lack of an appropriate rodent model. We describe a novel mouse model of DVT which reproduces a frequent trigger and resembles the time course, histological features, and clinical presentation of DVT in humans. We demonstrate by intravital two-photon and epifluorescence microscopy that blood monocytes and neutrophils crawling along and adhering to the venous endothelium provide the initiating stimulus for DVT development. Using conditional mutants and bone marrow chimeras, we show that intravascular activation of the extrinsic pathway of coagulation via tissue factor (TF) derived from myeloid leukocytes causes the extensive intraluminal fibrin formation characteristic of DVT. We demonstrate that thrombus-resident neutrophils are indispensable for subsequent DVT propagation by binding factor XII (FXII) and by supporting its activation through the release of neutrophil extracellular traps (NETs). Correspondingly, neutropenia, genetic ablation of FXII, or disintegration of NETs each confers protection against DVT amplification. Platelets associate with innate immune cells via glycoprotein Ibα and contribute to DVT progression by promoting leukocyte recruitment and stimulating neutrophil-dependent coagulation. Hence, we identified a cross talk between monocytes, neutrophils, and platelets responsible for the initiation and amplification of DVT and for inducing its unique clinical features.

Early adulthood television viewing and cardiometabolic risk profiles in early middle age: results from a population, prospective cohort study

AIMS/HYPOTHESIS

Little research has been done on the long-term longitudinal associations between markers of sedentary behaviour and health risks. We hypothesised that television (TV) viewing in early to mid-adulthood predicts an adverse cardiometabolic risk factor profile in middle age independently of participation in physical activity.

METHODS

We used prospective data from 5,972 (2,947 men) participants of the 1958 British Birth Cohort study. TV viewing and exercise frequency were obtained at age 23 years. Daily TV viewing and weekly moderate to vigorous physical activity were assessed at age 44 years, as well as HbA(1c), triacylglycerol, total and HDL-cholesterol, systolic and diastolic blood pressure, and waist circumference. We used generalised linear models and multiple linear regression to examine the associations between TV viewing at age 23 years and the cardiometabolic risk markers (including a clustered cardiometabolic risk score) at 44 years, while adjusting for sex, exercise participation and TV viewing at age 44 years, and other potential confounders.

RESULTS

In the multivariable models, TV viewing frequency at age 23 years showed positive associations with C-reactive protein (generalised linear model change 12.6%, 95% CI 3.5, 22.8; p = 0.005), fibrinogen (change 1.8%, 95% CI 0.3, 3.3; p = 0.020), waist circumference (coefficient 1.17, 95% CI 0.32, 2.01; p = 0.004), systolic (coefficient 1.44, 95% CI 0.33, 2.54; p = 0.019) and diastolic (coefficient 0.75, 95% CI -0.01, 1.51; p = 0.053) blood pressure, and clustered cardiometabolic risk score (men only, coefficient 0.06, 95% CI 0.01, 0.11; p = 0.038). Adjustments for baseline (age 23 years) BMI attenuated these associations towards null.

CONCLUSIONS/INTERPRETATION

TV viewing habits in early adulthood are associated with adverse cardiometabolic profiles in early middle adulthood that are independent of TV viewing habits and physical activity in middle age, but not independent of BMI in early adulthood.

Lower extremity deep venous thrombosis with fatal pulmonary thromboembolism caused by benign pelvic space-occupying lesions--an overview

Venous stasis predisposes to thrombosis. One hundred and sixty cases of fatal pulmonary thromboembolism were reviewed to determine how many cases had deep venous thromboses associated with venous blood flow reduction caused by external pressure from benign pelvic masses. Three cases were identified, representing 2% of cases overall (3/160): a 44-year-old woman with a large uterine leiomyoma (1048 g); a 74-year-old man with prostatomegaly and bladder distension (containing 1 L of urine); and a 70-year-old man with prostatomegaly and bladder distension (containing 3 L of urine). Although a rare cause of fatal deep venous thrombosis and pulmonary thromboembolism, space-occupying pelvic lesions can lead to extrinsic pressure on adjacent veins reducing blood flow and causing stasis and thrombosis. Individuals with large pelvic masses may, therefore, be at increased risk of pulmonary thromboembolism from deep venous thrombosis, particularly in the presence of concurrent risk factors such as immobility, thrombophilias, malignancy, and significant cardiopulmonary disease.

Multiscale model of fibrin accumulation on the blood clot surface and platelet dynamics

A multiscale computational model of thrombus (blood clot) development is extended by incorporating a submodel describing formation of fibrin network through "fibrin elements" representing regions occupied by polymerized fibrin. Simulations demonstrate that fibrin accumulates on the surface of the thrombus and that fibrin network limits growth by reducing thrombin concentrations on the thrombus surface and decreasing adhesivity of resting platelets in blood near thrombus surface. These results suggest that fibrin accumulation may not only increase the structural integrity of the thrombus but also considerably contribute toward limiting its growth. Also, a fast Graphics Processing Unit implementation is described for a multiscale computational model of the platelet-blood flow interaction.

MR phase-contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

PURPOSE

To evaluate the feasibility of using un-gated, real-time MRI for venous blood velocity mapping in the calf, comparing an interleaved spiral k-space sequence (ISP) against a standard segmented gradient echo sequence (GRE).

MATERIALS AND METHODS

A flow phantom with a variable flow-rate was scanned using both GRE and ISP sequences for an in vitro comparison. Seven subjects were scanned prone, performing metronome guided breathing, using the (externally triggered) segmented GRE and real-time ISP sequences. The segmented GRE acquisition duration was 2.5 mins (22 guided respiratory cycles) and the ISP sequence ran continuously for 35 s, 4 full guided respiratory cycles. Mean velocity from each of the deep veins was measured and peak mean velocity, peak flow rate and cumulative volume flow over a respiratory cycle compared between sequences.

RESULTS

The two sequences compared well both in vitro and in vivo. The real-time ISP sequence showed short-term variations in mean velocity superimposed on the respiratory induced flow, which were averaged out using the segmented GRE sequence.

CONCLUSION

Real-time ISP provides comparable time-averaged flow results to the standard sequence with additional information on real-time flow variations and so could be used for further investigation into venous blood flow in the lower leg.

The link between vascular features and thrombosis

The mechanisms of vascular control of thrombotic events remain unclear. The vasculature possesses essential anticoagulant factors that regulate coagulation. Because the endothelium-to-blood ratios are much higher in the microcirculation, it is likely that stasis contributes to thrombotic risk, due in large part to failure to rapidly access the microcirculation and to gain access to this highly anticoagulant environment. Inflammation can potentiate thrombosis in part through downregulation of the vascular anticoagulants, a process that appears to be exacerbated in aging, a well-known risk factor for thrombosis. Surgery and trauma, two major risk factors for thrombosis, result in the release of a variety of cellular components that trigger coagulation through separate mechanisms.

Innate immunity and coagulation

Infection frequently elicits a coagulation response. Endotoxin triggers the formation of tissue factor initiating coagulation, down regulates anticoagulant mechanisms including the protein C pathway and heparin-like proteoglycans and up regulates plasminogen activator inhibitor. The overall physiological result of this is to promote coagulation through enhancing initiation, suppressing negative regulation and impairing fibrin removal. The response to infection also leads to tissue destruction. Nucleosomes and histones released from the injured cells trigger further inflammation, protection from the pathogen but further tissue injury leading to multi-organ failure. Such a complex response to infection presumably arises due to the role of coagulation in the control and clearance of the infectious agent.

Expression and shedding of endothelial protein C receptor in prostate cancer cells

Background

Increasing evidences show that beyond its role in coagulation, endothelial protein C receptor (EPCR) interferes with carcinogenesis. Pro-carcinogenic effects of EPCR were linked with a raised generation of activated protein C (aPC) and anti-apoptotic signalling. This study was carried out to analyze the expression, cell surface exposition, and shedding of EPCR in normal and malignant prostate cell lines.

Results

EPCR expression is up-regulated both at the mRNA and protein levels in invasive prostate DU-145 and PC-3 cells in comparison to normal prostate epithelial cells (PrEC) and less-invasive LNCaP cells. Release of soluble EPCR (sEPCR) is induced by 12-myristate 13-acetate, ionomycin, H₂O₂, and disruptor of lipid rafts in PrEC, DU-145, and PC-3 cells. Furthermore, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), but not interleukin-6 or interferon-γ increase sEPCR release. In LNCaP cells, neither pharmacological agents nor IL-1β or TNF-α result in a significant increase of sEPCR release. The effects of IL-1β and TNF-α on EPCR shedding in DU-145 cells are mediated by MEK/ERK 1/2, JNK, and p38 MAPK signalling cascades. In PC-3 cells, however, the MEK/ERK 1/2 pathway is down-regulated and incubation with cytokines did not elevate the phosphorylated ERK-1/2 fraction as in the case of DU-145 cells. Treatment with 4-aminophenylmercuric acetate (APMA), an activator of metalloproteases, causes a disproportionately large increase of sEPCR release in DU-145 and PC-3 cells, compared to PrEC and LNCaP cells. Finally, an increased release of sEPCR mediated by APMA treatment is shown to be connected with reduced generation of activated protein C indicating the functionality of EPCR in these cells.

Conclusions

The study demonstrates a number of substantial differences in expression and shedding of EPCR in prostate cancer cell lines in comparison with normal cells that may be relevant for understanding the role of this receptor in carcinogenesis.

Haemostatic system in inflammatory bowel diseases: New players in gut inflammation

Inflammation and coagulation constantly influence each other and are constantly in balance. Emerging evidence supports this statement in acute inflammatory diseases, such as sepsis, but it also seems to be very important in chronic inflammatory settings, such as inflammatory bowel disease (IBD). Patients with Crohn’s disease and ulcerative colitis have an increased risk of thromboembolic events, and several abnormalities concerning coagulation components occur in the endothelial cells of intestinal vessels, where most severe inflammatory abnormalities occur. The aims of this review are to update and classify the type of coagulation system abnormalities in IBD, and analyze the strict and delicate balance between coagulation and inflammation at the mucosal level. Recent studies on possible therapeutic applications arising from investigations on coagulation abnormalities associated with IBD pathogenesis will also be briefly presented and critically reviewed.

Overexpression of the cell cycle inhibitor p16INK4a promotes a prothrombotic phenotype following vascular injury in mice

OBJECTIVE

Age-associated cellular senescence is thought to promote vascular dysfunction. p16(INK4a) is a cell cycle inhibitor that promotes senescence and is upregulated during normal aging. In this study, we examine the contribution of p16(INK4a) overexpression to venous thrombosis.

METHODS AND RESULTS

Mice overexpressing p16(INK4a) were studied with 4 different vascular injury models: (1) ferric chloride (FeCl(3)) and (2) Rose Bengal to induce saphenous vein thrombus formation; (3) FeCl(3) and vascular ligation to examine thrombus resolution; and (4) lipopolysaccharide administration to initiate inflammation-induced vascular dysfunction. p16(INK4a) transgenic mice had accelerated occlusion times (13.1 ± 0.4 minutes) compared with normal controls (19.7 ± 1.1 minutes) in the FeCl(3) model and 12.7 ± 2.0 and 18.6 ± 1.9 minutes, respectively in the Rose Bengal model. Moreover, overexpression of p16(INK4a) delayed thrombus resolution compared with normal controls. In response to lipopolysaccharide treatment, the p16(INK4a) transgenic mice showed enhanced thrombin generation in plasma-based calibrated automated thrombography assays. Finally, bone marrow transplantation studies suggested increased p16(INK4a) expression in hematopoietic cells contributes to thrombosis, demonstrating a role for p16(INK4a) expression in venous thrombosis.

CONCLUSIONS

Venous thrombosis is augmented by overexpression of the cellular senescence protein p16(INK4a).

Iliac vein stenting in postmenopausal leg swelling

BACKGROUND

Leg swelling in menopausal women is well known. Prevailing concept in primary care is that it is polycentric and a treatable cause may not be found. Patients are placed on empiric diuretics often without benefit. Our clinical experience indicates that iliac venous vein obstruction is the core cause; a variety of secondary factors common in postmenopausal women precipitate symptoms.

PATIENTS AND METHODS

A total of 163 limbs in 150 postmenopausal women (≥ 55 years of age) with leg swelling unresponsive to conservative therapy underwent intravascular ultrasound-guided iliac vein stenting over an 11-year period. Preoperative investigations included duplex, airplethysmography, venous pressure tests, contrast studies, and lymphangiography. The postmenopausal group constituted 9% of all limbs (n = 1760) stented for chronic venous disease (CVD) during the same period and 18% of those stented for swelling (n = 922). Median age was 67 (range, 55-92) and left-to-right ratio 2:1.

RESULTS

Iliac vein obstruction was "primary" (nonthrombotic) in 65% and postthrombotic in 35% of limbs; 35% of limbs had obstruction only and 65% combined obstruction/reflux. Lymphatic dysfunction was present in 21% of the limbs. Mean intravascular ultrasound area stenosis was 68% ± 22 SD. Mean follow-up was 22 months (± 26 SD) (range, 1-113 months). Secondary stent patency (6 years) was 100% in primary and 91% in postthrombotic limbs; overall 98%. Swelling improved significantly (P < .0001) from preoperative grade 2.5 (± 0.8 SD) to postoperative grade 1.2 (1.2 SD). Associated pain also improved significantly (P < .0001) from preoperative visual analog scale 3.5 (± 3 SD) to postoperative 0.9 (2.1 ± SD). Quality-of-life (CIVQ) scores improved significantly in every category and overall (P < .0001).

CONCLUSIONS

Patients with postmenopausal leg swelling often have obstructive venous pathology even though suggestive venous history and other signs are often absent. Morbidity arises from painful swelling that affects mobility, quality of life, and ability of self-care at later stages of life. Outpatient percutaneous iliac vein stenting affords substantial symptom relief and improvement in quality-of-life measures. Recognition of the clinical complex as a distinct entity of venous origin may lead to greater awareness and effective treatment.

von Willebrand factor-mediated platelet adhesion is critical for deep vein thrombosis in mouse models

Deep vein thrombosis (DVT) and its complication, pulmonary embolism, are frequent causes of disability and mortality. Although blood flow disturbance is considered an important triggering factor, the mechanism of DVT initiation remains elusive. Here we show that 48-hour flow restriction in the inferior vena cava (IVC) results in the development of thrombi structurally similar to human deep vein thrombi. von Willebrand factor (VWF)-deficient mice were protected from thrombosis induced by complete (stasis) or partial (stenosis) flow restriction in the IVC. Mice with half normal VWF levels were also protected in the stenosis model. Besides promoting platelet adhesion, VWF carries Factor VIII. Repeated infusions of recombinant Factor VIII did not rescue thrombosis in VWF(-/-) mice, indicating that impaired coagulation was not the primary reason for the absence of DVT in VWF(-/-) mice. Infusion of GPG-290, a mutant glycoprotein Ibα-immunoglobulin chimera that specifically inhibits interaction of the VWF A1 domain with platelets, prevented thrombosis in wild-type mice. Intravital microscopy showed that platelet and leukocyte recruitment in the early stages of DVT was dramatically higher in wild-type than in VWF(-/-) IVC. Our results demonstrate a pathogenetic role for VWF-platelet interaction in flow disturbance-induced venous thrombosis.

Atherosclerosis and sex hormones: current concepts

CVD (cardiovascular disease) is the leading cause of death for women. Considerable progress has been made in both our understanding of the complexities governing menopausal hormone therapy and our understanding of the cellular and molecular mechanisms underlying hormone and hormone receptor function. Understanding the interplay of atherosclerosis and sex steroid hormones and their cognate receptors at the level of the vessel wall has important ramifications for clinical practice. In the present review, we discuss the epidemiology of CVD in men and women, the clinical impact of sex hormones on CVD, and summarize our current understanding of the pathogenesis of atherosclerosis with a focus on gender differences in CVD, its clinical presentation and course, and pathobiology. The critical animal and human data that pertain to the role of oestrogens, androgens and progestins on the vessel wall is also reviewed, with particular attention to the actions of sex hormones on each of the three key cell types involved in atherogenesis: the endothelium, smooth muscle cells and macrophages. Where relevant, the systemic (metabolic) effects of sex hormones that influence atherogenesis, such as those involving vascular reactivity, inflammation and lipoprotein metabolism, are discussed. In addition, four key current concepts in the field are explored: (i) total hormone exposure time and coronary heart disease risk; (ii) the importance of tissue specificity of sex steroid hormones, critical timing and the stage of atherosclerosis in hormone action; (iii) biomarkers for atherosclerosis with regard to hormone therapy; and (iv) the complex role of sex steroids in inflammation. Future studies in this field will contribute to guiding clinical treatment recommendations for women and help define research priorities.

Extracellular DNA traps promote thrombosis

Neutrophil extracellular traps (NETs) are part of the innate immune response to infections. NETs are a meshwork of DNA fibers comprising histones and antimicrobial proteins. Microbes are immobilized in NETs and encounter a locally high and lethal concentration of effector proteins. Recent studies show that NETs are formed inside the vasculature in infections and noninfectious diseases. Here we report that NETs provide a heretofore unrecognized scaffold and stimulus for thrombus formation. NETs perfused with blood caused platelet adhesion, activation, and aggregation. DNase or the anticoagulant heparin dismantled the NET scaffold and prevented thrombus formation. Stimulation of platelets with purified histones was sufficient for aggregation. NETs recruited red blood cells, promoted fibrin deposition, and induced a red thrombus, such as that found in veins. Markers of extracellular DNA traps were detected in a thrombus and plasma of baboons subjected to deep vein thrombosis, an example of inflammation-enhanced thrombosis. Our observations indicate that NETs are a previously unrecognized link between inflammation and thrombosis and may further explain the epidemiological association of infection with thrombosis.

Sepsis-associated disseminated intravascular coagulation and thromboembolic disease

Sepsis is almost invariably associated with haemostatic abnormalities ranging from subclinical activation of blood coagulation (hypercoagulability), which may contribute to localized venous thromboembolism, to acute disseminated intravascular coagulation (DIC), characterized by massive thrombin formation and widespread microvascular thrombosis, partly responsible of the multiple organ dysfunction syndrome (MODS), and subsequent consumption of platelets and coagulation proteins causing, in most severe cases, bleeding manifestations. There is general agreement that the key event underlying this life-threatening sepsis complication is the overwhelming inflammatory host response to the infectious agent leading to the overexpression of inflammatory mediators. Mechanistically, the latter, together with the micro-organism and its derivatives, causes DIC by 1) up-regulation of procoagulant molecules, primarily tissue factor (TF), which is produced mainly by stimulated monocytes-macrophages and by specific cells in target tissues; 2) impairment of physiological anticoagulant pathways (antithrombin, protein C pathway, tissue factor pathway inhibitor), which is orchestrated mainly by dysfunctional endothelial cells (ECs); and 3) suppression of fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) by ECs and likely also to thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor (TAFI). Notably, clotting enzymes non only lead to microvascular thrombosis but can also elicit cellular responses that amplify the inflammatory reactions. Inflammatory mediators can also cause, directly or indirectly, cell apoptosis or necrosis and recent evidence indicates that products released from dead cells, such as nuclear proteins (particularly extracellular histones), are able to propagate further inflammation, coagulation, cell death and MODS. These insights into the pathogenetic mechanisms of DIC and MODS may have important implications for the development of new therapeutic agents that could be potentially useful particularly for the management of severe sepsis.

Role of tissue factor in thrombosis in antiphospholipid antibody syndrome

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder defined by the presence of an antiphospholipid antibody (aPL) and the occurrence of at least one associated clinical condition that includes venous thrombosis, arterial thrombosis or pregnancy morbidity. The aPL detected in APS have long been thought to have a direct prothrombotic effect in vivo. However, the pathophysiology underlying their coagulopathic effect has not been defined. Emerging data suggest a role for the procoagulant protein tissue factor (TF). In this review we provide an overview of TF, describe mouse models used in the evaluation of the role of TF in thrombosis, as well as summarize recent work on TF and APS.