Two different mechanisms in patients with venous thrombosis and defective fibrinolysis: low concentration of plasminogen activator or increased concentration of plasminogen activator inhibitor

Regulation of macrophage fibrinolysis during venous thrombus resolution

BACKGROUND

Venous thromboembolism (VTE), which includes pulmonary embolism (PE) and deep vein thrombosis (DVT), is a serious cardiovascular disease with significant mortality and morbidity. Clinically, patients with faster resolution of a venous thrombi have improved prognosis. Urokinase-plasminogen activator (uPA), produced by macrophages, is a key mediator of fibrinolysis required for resolving venous thrombi and restoring vascular integrity. The major macrophage protein, plasminogen activator inhibitor type-2 (PAI-2), was originally identified as an inhibitor of uPA and is implicated in the modulation of pathways affecting fibrinolytic uPA activity, however its direct role in blocking uPA-mediated clot lysis is not known.

OBJECTIVE

To determine the contribution of macrophage PAI-2 in inhibiting uPA-mediated fibrinolysis during resolution of DVT.

METHODS

Using a murine model of venous thrombosis and resolution, we determined histological changes and molecular features of fibrin degradation in venous thrombi from WT mice and mice genetically deficient in PAI-2 and PAI-1, and determined the fibrinolytic activities of macrophages from these genotypes ex vivo.

RESULTS

Acceleration of venous thrombus resolution by PAI-2-/- mice increases fibrin degradation in venous thrombi showing a pattern similar to genetic deficiency of PAI-1, the major attenuator of fibrinolysis. PAI-2 deficiency was not associated with increased macrophage infiltration into thrombi or changes in macrophage PAI-1 expression. uPA-initiated fibrinolysis by macrophages in vitro could be accelerated by PAI-1 deficiency, but not PAI-2 deficiency.

CONCLUSION

PAI-2 has an alternate anti-fibrinolytic activity that is macrophage uPA independent, where PAI-1 is the dominant uPA inhibitor during DVT resolution.

Targeting Fibrinolytic Inhibition for Venous Thromboembolism Treatment: Overview of an Emerging Therapeutic Approach

Venous thrombosis and pulmonary embolism (venous thromboembolism) are important causes of morbidity and mortality worldwide. In patients with venous thromboembolism, thrombi obstruct blood vessels and resist physiological dissolution (fibrinolysis), which can be life threatening and cause chronic complications. Plasminogen activator therapy, which was developed >50 years ago, is effective in dissolving thrombi but has unacceptable bleeding risks. Safe dissolution of thrombi in patients with venous thromboembolism has been elusive despite multiple innovations in plasminogen activator design and catheter-based therapy. Evidence now suggests that fibrinolysis is rigidly controlled by endogenous fibrinolysis inhibitors, including α2-antiplasmin, plasminogen activator inhibitor-1, and thrombin-activable fibrinolysis inhibitor. Elevated levels of these fibrinolysis inhibitors are associated with an increased risk of venous thromboembolism in humans. New therapeutic paradigms suggest that accelerated and effective fibrinolysis may be achieved safely by therapeutically targeting these fibrinolytic inhibitors in venous thromboembolism. In this article, we discuss the role of fibrinolytic components in venous thromboembolism and the current status of research and development targeting fibrinolysis inhibitors.

Chemical Adjustment of Fibrinolysis

Fibrinolysis is the process of the fibrin-platelet clot dissolution initiated after bleeding has been stopped. It is regulated by a cascade of proteolytic enzymes with plasmin at its core. In pathological cases, the balance of normal clot formation and dissolution is replaced by a too rapid lysis, leading to bleeding, or an insufficient one, leading to an increased thrombotic risk. The only approved therapy for emergency thrombus lysis in ischemic stroke is recombinant tissue plasminogen activator, though streptokinase or urokinase-type plasminogen activators could be used for other conditions. Low molecular weight compounds are of great interest for long-term correction of fibrinolysis dysfunctions. Their areas of application might go beyond the hematology field because the regulation of fibrinolysis could be important in many conditions, such as fibrosis. They enhance or weaken fibrinolysis without significant effects on other components of hemostasis. Here we will describe and discuss the main classes of these substances and their mechanisms of action. We will also explore avenues of research for the development of new drugs, with a focus on the use of computational models in this field.

Fibrinolysis Shutdown and Hypofibrinolysis Are Not Synonymous Terms: The Clinical Significance of Differentiating Low Fibrinolytic States

Low fibrinolytic activity has been associated with pathologic thrombosis and multiple-organ failure. Low fibrinolytic activity has two commonly associated terms, hypofibrinolysis and fibrinolysis shutdown. Hypofibrinolysis is a chronic state of lack of ability to generate an appropriate fibrinolytic response when anticipated. Fibrinolysis shutdown is the shutdown of fibrinolysis after systemic activation of the fibrinolytic system. There has been interchanging of these terms to describe critically ill patients in multiple settings. This is problematic in understanding the pathophysiology of disease processes related to these conditions. There is also a lack of research on the cellular mediators of these processes. The purpose of this article is to review the on and off mechanisms of fibrinolysis in the context of low fibrinolytic states to define the importance in differentiating hypofibrinolysis from fibrinolysis shutdown. In many clinical scenarios, the etiology of a low fibrinolytic state cannot be determined due to ambiguity if a preceding fibrinolytic activation event occurred. In this scenario, the term "low fibrinolytic activity" or "fibrinolysis resistance" is a more appropriate descriptor, rather than using assumptive of hypofibrinolysis and fibrinolysis shutdown, particularly in the acute setting of infection, injury, and surgery.

Pathophysiological Aspects of Aging in Venous Thromboembolism: An Update

The aim of this review is to highlight all the factors that associate venous thromboembolism (VTE) with aging. Elderly people are characterized by a higher incidence of thrombosis taking into account the co-existing comorbidities, complications and fatality that arise. Based on the Virchow triad, pathophysiological aspects of venous stasis, endothelium injury and hypercoagulability in elderly people (≥65 years) are described in detail. More precisely, venous wall structure, nitric oxide (NO) and endothelin-1 expression are impaired in this age group. Furthermore, an increase in high-molecular-weight kininogen (HMWK), prekallikrein, factors V, VII, VIII, IX and XI, clot lysis time (CLT) and von Willebrand factor (vWF) is observed. Age-dependent platelet dysfunction and changes in anticoagulant factors are also illustrated. A “low-grade inflammation stage” is delineated as a possible risk factor for thrombosis in the elderly. Consequently, clinical implications for frail elderly people related to diagnosis, treatment, bleeding danger and VTE recurrence emerge. We conclude that aging is an acquired thrombotic factor closely related to pathophysiological changes.

Fibrinolysis and Inflammation in Venous Thrombus Resolution

Clinical observations and accumulating laboratory evidence support a complex interplay between coagulation, inflammation, innate immunity and fibrinolysis in venous thromboembolism (VTE). VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), and the subsequent complications of post-thrombotic syndrome (PTS), are significant causes of morbidity and mortality in patients. Clinical risk factors for VTE include cancer, major trauma, surgery, sepsis, inflammatory bowel disease, paralysis, prolonged periods of immobility, and aging. Abnormalities in venous blood flow or stasis initiates the activation of endothelial cells, and in concert with platelets, neutrophils and monocytes, propagates VTE in an intact vein. In addition, inflammatory cells play crucial roles in thrombus recanalization and restoration of blood flow via fibrinolysis and vascular remodeling. Faster resolution of the thrombus is key for improved disease prognosis. While in the clinical setting, anticoagulation therapy is successful in preventing propagation of venous thrombi, current therapies are not designed to inhibit inflammation, which can lead to the development of PTS. Animal models of DVT have provided many insights into the molecular and cellular mechanisms involved in the formation, propagation, and resolution of venous thrombi as well as the roles of key components of the fibrinolytic system in these processes. Here, we review the recent advances in our understanding of fibrinolysis and inflammation in the resolution of VTE.

CEMIP (KIAA1199) induces a fibrosis-like process in osteoarthritic chondrocytes

CEMIP (for "Cell migration-inducing protein" also called KIAA1199 and Hybid for "Hyaluronan-binding protein") expression is increased in cancers and described as a regulator of cell survival, growth and invasion. In rheumatoid arthritis, CEMIP is referred to as an angiogenic marker and participates in hyaluronic acid degradation. In this study, CEMIP expression is investigated in healthy and osteoarthritis (OA) cartilage from human and mouse. Its role in OA physiopathology is deciphered, specifically in chondrocytes proliferation and dedifferentiation and in the extracellular matrix remodeling. To this end, CEMIP, αSMA and types I and III collagen expressions were assessed in human OA and non-OA cartilage. CEMIP expression was also investigated in a mouse OA model. CEMIP expression was studied in vitro using a chondrocyte dedifferentiation model. High-throughput RNA sequencing was performed on chondrocytes after CEMIP silencing. Results showed that CEMIP was overexpressed in human and murine OA cartilage and along chondrocytes dedifferentiation. Most of genes deregulated in CEMIP-depleted cells were involved in cartilage turnover (e.g., collagens), mesenchymal transition and fibrosis. CEMIP regulated β-catenin protein level. Moreover, CEMIP was essential for chondrocytes proliferation and promoted αSMA expression, a fibrosis marker, and TGFβ signaling towards the p-Smad2/3 (Alk5/PAI-1) pathway. Interestingly, CEMIP was induced by the pSmad1/5 (Alk1) pathway. αSMA and type III collagen expressions were overexpressed in human OA cartilage and along chondrocytes dedifferentiation. Finally, CEMIP was co-expressed in situ with αSMA in all OA cartilage layers. In conclusion, CEMIP was sharply overexpressed in human and mouse OA cartilage and along chondrocytes dedifferentiation. CEMIP-regulated transdifferentiation of chondrocytes into "chondro-myo-fibroblasts" expressing α-SMA and type III collagen, two fibrosis markers. Moreover, these "chondro-myo-fibroblasts" were found in OA cartilage but not in healthy cartilage.

Serpins in Venous Thrombosis and Venous Thrombus Resolution

Several serpins function as potent inhibitors of thrombolytic serine proteases. Venous thrombosis is a common and debilitating condition whose incidence is on the rise. Studies using genetically modified mice and inhibitors have shown that the plasminogen activator inhibitors (PAI), PAI-1 and PAI-2, are primary regulators of plasminogen activation and contribute to regulating the resolution of experimental venous thrombi, via inflammatory mechanisms, vascular remodeling, and inhibition of fibrinolysis. Therapies to accelerate venous thrombus resolution would be beneficial, since delayed or incomplete clot resolution frequently leads to postthrombotic syndrome, a long-term complication associated with debilitating limb swelling, pain, and recurrent skin ulceration. Here we describe a useful and reproducible mouse model for the study of venous thrombus resolution involving ligation of the inferior vena cava and elucidation of the molecular and cellular determinants of venous thrombus formation and resolution.

Causal Effect of Plasminogen Activator Inhibitor Type 1 on Coronary Heart Disease

Background

Plasminogen activator inhibitor type 1 (PAI‐1) plays an essential role in the fibrinolysis system and thrombosis. Population studies have reported that blood PAI‐1 levels are associated with increased risk of coronary heart disease (CHD). However, it is unclear whether the association reflects a causal influence of PAI‐1 on CHD risk.

Methods and Results

To evaluate the association between PAI‐1 and CHD, we applied a 3‐step strategy. First, we investigated the observational association between PAI‐1 and CHD incidence using a systematic review based on a literature search for PAI‐1 and CHD studies. Second, we explored the causal association between PAI‐1 and CHD using a Mendelian randomization approach using summary statistics from large genome‐wide association studies. Finally, we explored the causal effect of PAI‐1 on cardiovascular risk factors including metabolic and subclinical atherosclerosis measures. In the systematic meta‐analysis, the highest quantile of blood PAI‐1 level was associated with higher CHD risk comparing with the lowest quantile (odds ratio=2.17; 95% CI: 1.53, 3.07) in an age‐ and sex‐adjusted model. The effect size was reduced in studies using a multivariable‐adjusted model (odds ratio=1.46; 95% CI: 1.13, 1.88). The Mendelian randomization analyses suggested a causal effect of increased PAI‐1 level on CHD risk (odds ratio=1.22 per unit increase of log‐transformed PAI‐1; 95% CI: 1.01, 1.47). In addition, we also detected a causal effect of PAI‐1 on elevating blood glucose and high‐density lipoprotein cholesterol.

Conclusions

Our study indicates a causal effect of elevated PAI‐1 level on CHD risk, which may be mediated by glucose dysfunction.

Hypercoagulable States

The hypercoagulable states consist of a group of prothrombotic clinical disorders associated with an increased risk for thromboembolic events. The abnormalities lead to inappropriate thrombus formation. After a review of the coagulation process, inherited disorders (including antithrombin-III deficiency, protein CS system deficiencies, disorders of plasmin generation, dysfibrinogenemias, and homocysteinuria) and acquired disorders (including responses to surgery, cancer, drugs, and the antiphospholipid syndrome) are described. Screening and management methods are discussed. Copyright © 1997 by W. B. Saunders Company.

Significance of the PAP Complex in Thermal Injury

Plasmin-antiplasmin complex (PAP) has been reported previously as elevated in sepsis syndrome and infection. To assess the value of PAP complex and the thrombin-antithrombin (TAT)/PAP ratio in thermal injury, sixty patients were studied within the first 36 h, at 5-7 days following injury, and at time of infection. The patient population was categorized by percent burn (2° + 3°): <20%, n = 22; 20-40%, n = 18; >40%, n = 20. PAP increased significantly between days 1 and 5 in the <20% and 20-40% burn groups ( p < 0.01) and in the >40% group ( p < 0.002). The TAT/PAP ratio was elevated on day 1 in the 20-40% group ( p < 0.04) and the >40% group ( p < 0.001), and decreased to near normal limits on day 5 in both groups. These data revealed a proportionately greater incidence of coagulation activation than fibrinolysis on day 1. Of 16 episodes of sepsis syndrome or severe infection, PAP was elevated, average 14.6 nM (normal < 8 n M), in 10 (63%) patients. PAP was significantly elevated on day 5 during the clinically stabilized phase regardless of percent burn ( p = 0.01). In individuals who had a burn wound surface area of >40%, the PAP values were significantly higher for those who did not survive ( p < 0.03). PAP did not appear to correlate with the type of burn or with inhalation. Although PAP complex levels were elevated in thermal injury patients with sepsis syndrome or severe infection, they were not a specific predictor of infection. In conclusion, PAP complex and the TAT/PAP ratio provided useful information as to the fibrinolytic status of thermally injured patients with correlation to survival, but without correlation to sepsis and infection.

Recurrence and Late Sequelae after First-Time Deep Vein Thrombosis: Relationship to Initial Signs

Objective:

To investigate the relation between initial symptoms and long-term sequelae in first-time deep venous thrombosis (DVT).

Design:

Follow-up study of patients 6 years after an episode of suspected symptomatic DVT.

Setting:

Vascular laboratory, University Hospital of Lund.

Patients:

66 patients, 19 with femoral DVT, 20 with calf DVT and 27 with normal phlebograms at initial investigation.

Main outcome measures:

Symptoms and signs of chronic venous insufficiency (CVI), foot volumetry and measurement of plasminogen activator inhibitor 1 (PAI-1) activity. Initial clinical signs and results at phlebography were compared with findings at follow-up.

Results:

Of patients with DVT, 11 (28%) had been treated for a recurrent DVT during follow-up. No relation was found between initial signs of DVT and late signs of CVI. Patients with DVT had significantly more signs of CVI but symptoms did not differ between the groups. Mean levels of PAI-1 activity were similar in the three groups, and patients with recurrent DVT did not differ. Refilling flow was related to the clinical CVI-score, and expelled volume was inversely related to the extension of DVT at phlebography.

Conclusion:

The recurrence rate is high in first-time DVT, but symptoms are mostly mild as long as after 6 years. There is a poor correlation between symptoms of CVI and objective findings. The late development of CVI cannot be predicted from the clinical signs in the acute phase. Levels of PAI-1 do not correlate with the degree of CVI.

Is Abnormal Coagulation or Defective Fibrinolysis of Aetiological Importance in the Development of Deep Venous Thrombosis?

The present investigation was performed to study the aetiological importance of abnormal coagulation or defective fibrinolysis in the development of deep venous thrombosis (DVT). Sixty-nine patients with acute iliofemoral venous thrombosis were subjected to evaluation of coagulation and fibrinolytic parameters. Defective fibrinolysis, usually with an increased activity of the rapid tissue plasminogen inhibitor, was detected in 31 patients (45%), and increased factor VIII with normal fibrinogen was recorded in 10 patients (14%). Two patients had a hereditary deficiency of plasminogen and protein C, respectively, and a lupus anticoagulant was demonstrated in another patient. Antithrombin III deficiency was not detected in any patient. Abnormal findings were most frequently recorded in patients with ‘idiopathic’ DVT. Although the exact relationship between the development of DVT and the recorded abnormalities could not be determined in all instances, it is obvious that defective vessel wall fibrinolysis and increased factor VIII are frequently recorded in patients with extensive DVT of the lower limb. Pathological alternations of antithrombin III, plasminogen and protein C seem to be less common.

Comparison of the effects of Korean mindfulness-based stress reduction, walking, and patient education in diabetes mellitus

The purpose of this study was to compare the effects of Korean mindfulness-based stress reduction (K-MBSR), walking, and patient education regarding diabetes mellitus (DM) on stress response, glycemic control, and vascular inflammation in patients with diabetes mellitus. A cluster randomized trial including 56 adults with diabetes mellitus (K-MBSR group = 21, walking group = 18, patient education group = 17) was conducted between 13 July and 14 September 2012. The questionnaire included the Diabetes Distress Scale and Perceived Stress Response Inventory. Fasting blood samples were used to measure levels of cortisol, blood glucose, plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA). There were no statistically significant differences between the effects of K-MBSR, walking, and patient education on stress, glycemic control, or vascular inflammation. However, in the K-MBSR and walking groups, significant reductions in the levels of serum cortisol and PAI-1 were observed. A significant reduction in psychological responses to stress was observed in the walking and patient education groups. Longitudinal studies could provide better insight into the impact of K-MBSR, walking, and patient education on health outcomes in adults with diabetes mellitus.

Enhanced venous thrombus resolution in plasminogen activator inhibitor type-2 deficient mice

BACKGROUND

The resolution of deep vein thrombosis requires an inflammatory response and mobilization of proteases, such as urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs), to degrade the thrombus and remodel the injured vein wall. Plasminogen activator inhibitor type 2 (PAI-2) is a serine protease inhibitor (serpin) with unique immunosuppressive and cell survival properties that was originally identified as an inhibitor of uPA.

OBJECTIVE

To investigate the role of PAI-2 in venous thrombus formation and resolution.

METHODS

Venous thrombus resolution was compared in wild-type C57BL/6, PAI-2(-/-) , and PAI-1(-/-) mice using the stasis model of deep vein thrombosis. Formed thrombi were harvested, thrombus weights were recorded, and tissue was analyzed for uPA and MMP activities, PAI-1 expression, and the nature of inflammatory cell infiltration.

RESULTS

We found that the absence of PAI-2 enhanced venous thrombus resolution, while thrombus formation was unaffected. Enhanced venous thrombus resolution in PAI-2(-/-) mice was associated with increased uPA activity and reduced levels of PAI-1, with no significant effect on MMP-2 and -9 activities. PAI-1 deficiency resulted in an increase in thrombus resolution similar to PAI-2 deficiency, but additionally reduced venous thrombus formation and altered MMP activity. PAI-2-deficient thrombi had increased levels of the neutrophil chemoattractant CXCL2, which was associated with early enhanced neutrophil recruitment.

CONCLUSIONS

These data identify PAI-2 as a novel regulator of venous thrombus resolution, which modulates several pathways involving both inflammatory and uPA activity mechanisms, distinct from PAI-1. Further examination of these pathways may lead to potential therapeutic prospects in accelerating thrombus resolution.

Use of mouse models to study plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and therefore plays an important role in the plasminogen/plasmin system. PAI-1 is involved in a variety of cardiovascular diseases (mainly through inhibition of t-PA) as well as in cell migration and tumor development (mainly through inhibition of u-PA and interaction with vitronectin). PAI-1 is a unique member of the serpin superfamily, exhibiting particular unique conformational and functional properties. Since its involvement in various biological and pathophysiological processes PAI-1 has been the subject of many in vivo studies in mouse models. We briefly discuss structural and physiological differences between human and mouse PAI-1 that should be taken into account prior to extrapolation of data obtained in mouse models to the human situation. The current review provides an overview of the various models, with a focus on cardiovascular disease and cancer, using wild-type mice or genetically modified mice, either deficient in PAI-1 or overexpressing different variants of PAI-1.

Effect of preoperative biliary drainage on coagulation and fibrinolysis in severe obstructive cholestasis

GOALS

To evaluate the function of coagulation and fibrinolysis in cholestatic patients before and after preoperative biliary drainage (PBD).

BACKGROUND

Cholestasis owing to an obstructive biliary malignancy is associated with postoperative complications related to a proinflammatory state, an impaired hepatic synthesis function, and a potential derangement of hemostasis. Hence, PBD is advocated for cholestatic patients undergoing major surgery.

STUDY

Plasma coagulation and fibrinolytic parameters were assessed in 24 cholestatic patients and 10 controls. In 9 cholestatic patients, the parameters were reassessed at least 4 weeks after PBD.

RESULTS

Compared with controls, cholestatic patients showed lower concentrations (P<0.001) of plasma vitamin K-dependent factors II and VII, whereas prothrombin time, activated partial thromboplastin time, and factor V were unaltered. Thrombin generation was increased in cholestatic patients, as reflected by higher plasma concentrations of thrombin-antithrombin complexes and D-dimers. Fibrinolysis was significantly impaired as evidenced by low plasminogen activator activity (PAA) owing to an increase in plasminogen activator inhibitor -1). Elevated markers for thrombin generation thrombin-antithrombin decreased after PBD from 10.7±1.2 to 5.7±0.7 ng/mL (P<0.05). Additionally, impairment of fibrinolysis in cholestatic patients resolved after PBD (plasminogen activator inhibitor-1 levels decreased from 19±1 to 10±1 IU/mL and plasminogen activator activity increased from 82±3 to 110±4%, respectively). D-dimers remained unaltered after PBD, likely because of normalization of coagulation and fibrinolytic activity.

CONCLUSIONS

Obstructive cholestasis is associated with a procoagulant state, despite an impaired vitamin K-dependent coagulation factor synthesis. Virtually all alterations in coagulation and fibrinolysis were reversed by biliary drainage.

Association of congenital cardiovascular malformations with 33 single nucleotide polymorphisms of selected cardiovascular disease-related genes

INTRODUCTION

Clark (1996) proposed that abnormal blood flow is related to some congenital cardiovascular malformations (CCVMs), particularly CCVM with obstruction to blood flow. Our hypothesis is that CCVMs may relate to genes that affect blood coagulation or flow. We studied whether polymorphisms of such genes are related to CCVMs; previous association of these SNPs to conotruncal CCVMs is described.

METHODS

We assessed risk of pulmonary stenosis (PS, N = 120), atrial septal defect (ASD, N = 108), aortic stenosis (AS, N = 36), and coarctation of the aorta (CoAo, N = 64), associated with 33 candidate genes, selected for their relationship to blood flow affected by homocysteine metabolism, coagulation, cell-cell interaction, inflammation, or blood pressure regulation.

RESULTS

Effects were specific to cardiac phenotype and race. CoAo was associated with MTHFR (-667) C>T (odds ratio [OR] for TT 3.5, 95% confidence limits [CI] 1.4-8.6). AS was associated with a polymorphism of SERPINE1, G5>G4, OR = 5.6 for the homozygote with 95% CI 1.4-22.9. Unique polymorphisms were associated with increased risk of ASD and PS: NPPA 664G>A with ASD (OR of 2.4, 95%CI 1.3-4.4) and NOS3 (-690) C>T with PS (OR 6.1; 95% CI 1.6-22.6 in the African American population only). For ASD, the NPPA (-664) G>A SNP there was increased risk from the variant genotype only in maternal smokers (OR 2.6; 95% CI 1.0-7.2).

CONCLUSIONS

Genes affecting vascular function and coagulation appear to be promising candidates for the etiology of cardiac malformations and warrant further study.

Impaired fibrinolysis as a risk factor for Budd-Chiari syndrome

In Budd-Chiari syndrome (BCS), thrombosis develops in the hepatic veins or inferior vena cava. To study the relationship between hypofibrinolysis and BCS, we measured plasma levels of fibrinolysis proteins in 101 BCS patients and 101 healthy controls and performed a plasma-based clot lysis assay. In BCS patients, plasminogen activator inhibitor 1 (PAI-1) levels were significantly higher than in controls (median, 6.3 vs 1.4 IU/mL, P < .001). Thrombin-activatable fibrinolysis inhibitor and plasmin inhibitor levels were lower than in controls (13.8 vs 16.9 μg/mL and 0.91 vs 1.02 U/L, both P < .001). Median plasma clot lysis time (CLT) was 73.9 minutes in cases and 73.0 minutes in controls (P = .329). A subgroup of cases displayed clearly elevated CLTs. A CLT above the 90th or 95th percentile of controls was associated with an increased risk of BCS, with odds ratios of 2.4 (95% confidence interval, 1.1-5.5) and 3.4 (95% confidence interval, 1.2-9.7), respectively. In controls, only PAI-1 activity was significantly associated with CLT. Analysis of single nucleotide polymorphisms of fibrinolysis proteins revealed no significant differences between cases and controls. This case-control study provides the first evidence that an impaired fibrinolytic potential, at least partially caused by elevated PAI-1 levels, is related to the presence of BCS.

Increased fibrinolytic potential after diet intervention in healthy coronary high-risk individuals

Twenty healthy individuals (15 men and 5 women) with initial fasting serum triglycerides greater than or equal to 1.80 mmol/l and euglobulin clot lysis time after venous occlusion greater than or equal to 60 min (upper normal limit 45 min) were tested for fibrinolytic response to venous occlusion and intravenous injection of desmopressin (DDAVP), serum lipids, serum glucose and relative body weight before and after a minimum of 3 to a maximum of 12 months' diet intervention. In order to be defined as a good diet responder, at least 20% reduction of the initial serum triglyceride concentration was required. At the end of the study, half of the participants (7 men and 3 women) met the criteria of good diet responders. All of these showed an improved fibrinolytic response to DDAVP injection, and 7 out of 10 had a normalized fibrinolytic response to venous occlusion. We conclude that, through dietary measures with substantial reduction of hypertriglyceridaemia, it is possible to improve and even normalize the fibrinolytic potential.

Design, synthesis, and evaluation of orally active inhibitors of plasminogen activator inhibitor-1 (PAI-1) production

A novel series of butadiene-imide 1 (T-686) derivatives having an inhibitory activity against PAI-1 production was synthesized and evaluated their biological activities and DMPK profiles, in which 15k (T-2639) was selected as the best compound based on its strong antithrombotic activity and good bioavailability.

The role of plasminogen activator inhibitor-1 polymorphism, factor-V-Leiden, and prothrombin-20210 mutations in pulmonary thromboembolism

Polymorphism in plasminogen activator inhibitor-1 gene is suggested to be associated with an increased risk of venous thromboembolism. The aim of this study was to investigate the association of plasminogen activator inhibitor-1 gene polymorphism and its coexistence with factor-V-Leiden and prothrombin-20210 mutations in pulmonary thromboembolism. The authors investigated plasminogen activator inhibitor-1 4G/5G polymorphism, factor-V-Leiden, and prothrombin-20210 mutations in 143 pulmonary thromboembolism patients and 181 controls. Plasminogen activator inhibitor-1 4G/4G, 4G/5G, and 5G/5G gene polymorphisms and prothrombin-20210 mutations were not different between cases and controls. Factor-V-Leiden mutation was present in 21.0% and 7.7% of the cases and controls, respectively, P = .001. Neither different plasminogen activator inhibitor-1 genotypes and 4G allele nor coexistence of the allele with factor-V-Leiden or prothrombin-20210 was associated with the risk of recurrence. As a result, plasminogen activator inhibitor-1 gene polymorphism or its concomitant presence with mentioned mutations was not found to be associated with increased risk for pulmonary thromboembolism or recurrent disease in this study.

Fibrinolytic markers and vasodilatory capacity following acute exercise among men of differing training status

We evaluated the effect of differing physical activity patterns on fibrinolysis and vasodilatory capacity using a cross-sectional design with 16 endurance-trained (ET) (mean+/-SE) (28+/-6 years), 14 resistance-trained (RT) (28+/-7 years), and 10 untrained (UT) (26+/-7 years) men. t-PA and PAI-1 activity and t-PA antigen were measured before and after a maximal treadmill test (VO2peak). Vasodilatory capacity was assessed using strain-gauge plethysmography on the forearm following reactive hyperemia (RH) before and after the treadmill test. The ET group had a smaller body mass index (BMI) (22.8+/-0.5 ET, 26.4+/-0.4 RT, 25.1+/-0.8 UT kg m(-2)) (P<0.05) and a greater VO2peak (57+/-1 ET, 42+/-2 RT, 45+/-2 UT mL min(-1) kg(-1)) (P<0.05). Peak vasodilatory capacity (29.7+/-2 ET, 32.0+/-2 RT, 27.4+/-2 UT mL min(-1) 100 mL of tissue) was similar between groups before and after exercise. Area under the curve for forearm blood flow was greater following acute exercise (212 vs. 122, P<0.05), again with no differences between groups. t-PA activity and antigen increased following maximal exercise in all groups (P<0.0001), with no group differences. PAI-1 activity decreased the least in RT after exercise (70% decrease vs. 86% ET and 82% UT; P<0.05). The change in t-PA activity with exercise was not related to exercise-induced change in overall vasodilatory capacity. These findings demonstrate that in healthy young men different physical activity patterns do not appear to impact the exercise-induced changes in fibrinolysis or vasodilatory capacity.

Low level of tissue plasminogen activator activity in non-diabetic patients with a first myocardial infarction

OBJECTIVE

To explore the role of tissue plasminogen activator (tPA) activity and plasminogen activator inhibitor type 1 (PAI-1) in survivors of a first myocardial infarction (MI). Insulin and proinsulin were analysed as potential risk factors.

DESIGN

Case-control study in northern Sweden.

SUBJECTS

A total of 115 patients under 65 years of age with a first MI were enrolled and recalled for further examination 3 months later. Twenty-seven patients were excluded, 17 with known diabetes and 10 who did not come to the follow-up, giving a final number of 88 patients, 73 men and 15 women. Patients were age- and sex-matched with control subjects drawn from the local cohort in the MONICA population survey 1994.

MAIN OUTCOME MEASURES

We compared MI patients and controls using univariate and multiple regression analyses including odds ratios (OR).

RESULTS

PAI-1 activity, fibrinogen, postload insulin and -proinsulin were significantly higher and tPA activity significantly lower in MI patients in the univariate analysis. In a multiple regression analysis, including also age, sex and cardiovascular risk factors, these parameters were divided in quartiles. The lowest quartile of tPA activity was significantly associated with MI (OR = 19.1; CI 3.0-123) together with the highest quartiles of fibrinogen (OR = 25; CI 5.2-120) but other variables were not.

CONCLUSION

Low tPA activity, i.e. low fibrinolytic activity, characterized nondiabetic subjects after a first MI which is not explained by concomitant disturbances in metabolic and anthropometric variables.

Relationship of physical fitness, hormone replacement therapy, and hemostatic risk factors in postmenopausal women

This cross-sectional study evaluated the relationship of physical fitness, hormone replacement therapy (HRT), and hemostatic profiles at rest and after an acute bout of maximal exercise in 48 healthy postmenopausal women. Subjects were categorized by fitness and HRT user status into four groups: unfit nonusers, fit nonusers, unfit users, and fit users. Fibrinolytic variables tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) activity, and antigen and prothrombin fragment 1 + 2, a molecular marker of in vivo thrombin generation, were measured before and after maximal exercise. Fibrinogen was also measured at rest. Higher tPA and lower PAI-1 activities ( P < 0.05) were seen in HRT users and fit groups. tPA and PAI-1 antigens were lower in HRT and fit groups ( P < 0.05) but not after correction for body mass index. Prothrombin fragment 1 + 2 was lower in the fit groups regardless of HRT status ( P < 0.05). Fibrinogen was similar in all groups. Favorable hemostatic profiles were observed in physically fit compared with unfit women, especially in HRT nonusers. Thus fitness is more strongly related to these hemostatic risk factors compared with HRT since HRT did not affect these hemostatic variables in fit postmenopausal women.

Impaired fibrinolytic activity is present in children with dyslipidemias

Dyslipidemias are major risk factors for atherosclerosis and cardiovascular disease. Abnormalities of fibrinolytic and coagulation components are considered useful predictors of cardiovascular morbidity and mortality in adults. This study examined whether fibrinolytic and coagulation components are abnormal in children with dyslipidemia. Thirty-six children with asymptomatic dyslipidemia, and 26 control subjects underwent venous occlusion stress testing with collection of preocclusion and postocclusion blood samples. All samples were assayed for tissue plasminogen activator, plasminogen, plasminogen activator inhibitor-1, alpha(2)-antiplasmin, alpha(2)-macroglobulin, D-dimer, fibrinogen, and von Willebrand factor. Children with dyslipidemia had significantly decreased levels of tissue plasminogen activator in both preocclusion and postocclusion samples compared with control subjects, reflecting decreased fibrinolytic activity. Children with dyslipidemia also had significantly increased levels of plasminogen, alpha(2)-macroglobulin, and fibrinogen in preocclusion and postocclusion samples compared with control subjects. In conclusion, decreased fibrinolytic activity is present in asymptomatic children with dyslipidemias, potentially reflecting endothelial dysfunction and increased risk of cardiovascular disease in early adult life. Further studies are required to determine the usefulness of this marker in predicting disease progression or response to therapy.

The Reactive-center Loop of Active PAI-1 is Folded Close to the Protein Core and can be Partially Inserted

Plasminogen activator inhibitor 1 (PAI-1) is the main inhibitor of plasminogen activators and plays an important role in many pathophysiological processes. Like other members of the serpin family, PAI-1 has a reactive center consisting of a mobile loop (RCL) with P1 and P1' residues acting as a "bait" for cognate protease. In contrast to the other serpins, PAI-1 loses activity by spontaneous conversion to an inactive latent form. This involves full insertion of the RCL into beta-sheet A. To search for molecular determinants that could be responsible for conversion of PAI-1 to the latent form, we studied the conformation of the RCL in active PAI-1 in solution. Intramolecular distance measurements by donor-donor energy migration and probe quenching methods reveal that the RCL is located much closer to the core of PAI-1 than has been suggested by the recently resolved X-ray structures of stable PAI-1 mutants. Disulfide bonds can be formed in double-cysteine mutants with substitutions at positions P11 or P13 of the RCL and neighboring residues in beta-sheet A. This suggests that the RCL may be preinserted up to residue P13 in active PAI-1, and possibly even to residue P11. We propose that the close proximity of the RCL to the protein core, and the ability of the loop to preinsert into beta-sheet A is a possible reason for PAI-1 being able to convert spontaneously to its latent form.

Fibrinolytic activity in multiple myeloma

The incidence of thromboembolic events is high as a result of disease, disease-related complications, and therapy in multiple myeloma (MM). In patients with hematologic tumors, impaired fibrinolysis may be present and may contribute to the development of thrombotic complications. Therefore, we designed a study to investigate fibrinolytic activity in MM. We compared plasma levels of interleukin (IL)-6, C-reactive protein (CRP), IL-1beta, IL-11, tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor-1 (PAI-1) activity, and global fibrinolytic capacity (GFC) in patients with MM (n = 66) and in control subjects (n = 18). The prevalence of venous thromboembolism was 4.5%, with a median follow-up period of 7 months in our myeloma group. Results are given as mean (median, range). Plasma levels of IL-6 (8.27 +/- 0.74 [9.65, 0.90-13.32] pg/mL versus 2.64 +/- 0.66 [1.80, 0.10-11.86] pg/mL, P < 0.001), CRP (45.57 +/- 9.92 [21.00, 1.34-330.00] mg/L versus 1.96 +/- 0.50 [1.05, 0.19-8.03] mg/L, P < 0.001), PAI-1 (7.40 +/- 0.67 [5.57, 2.40-31.80] IU/mL versus 4.73 +/- 0.65 [3.60, 2.32-11.00] IU/mL, P < 0.01), GFC score (1.90 +/- 0.02 [2, 1-3] versus 2.50 +/- 0.14 [3, 1-3], P < 0.001) were increased compared with controls. In patients with MM, the level of IL-6 was positively correlated with CRP (r = 0.66, P < 0.001), IL-1beta (r = 0.29, P < 0.05), and PAI-1 (r = 0.35, P < 0.01) and negatively correlated with GFC (r = -0.37, P < 0.01). CRP level was positively correlated with plasma PAI-1 level (r = 0.40, P < 0.01) and negatively correlated with GFC (r = -0.44, P < 0.001). A significant negative correlation between PAI-1 level and GFC (r = -0.75, P < 0.001) was also detected. IL-1beta levels were negatively correlated with tPA level (r = -0.26, P < 0.05). These results suggest that patients with myeloma have a decreased fibrinolytic activity mainly because of increased PAI-1 activity. In MM, increased PAI-1 activity seems to be related with elevated IL-6 level. MM should be considered as a hypercoagulable state as a result of both increased procoagulant activity and decreased fibrinolytic activity. Achieving a plateau by means of conventional chemotherapies does not improve the decreased fibrinolytic activity.

Tryptophan properties in fluorescence and functional stability of plasminogen activator inhibitor 1

Plasminogen activator inhibitor 1 harbors four tryptophan residues at positions 86, 139, 175, and 262. To investigate the contribution of each tryptophan residue to the total fluorescence and to reveal the mutual interactions of the tryptophan residues and interactions with the other amino acids, 15 mutants in which tryptophan residues have been replaced by phenylalanines were constructed, purified, and characterized. Conformational distribution analysis revealed that the tryptophan mutants have a similar conformational distribution pattern as wild-type plasminogen activator inhibitor 1. Mutants in which tryptophan residue 175 was replaced by a phenylalanine displayed an increased functional half-life of the active conformation, whereas the functional half-life of mutants in which tryptophan residue 262 was replaced by a phenylalanine was substantially decreased. Comparative analysis of the fluorescence lifetimes, the extinction coefficients, and the quantum yields of the individual tryptophan residues demonstrates that tryptophan residue 262 gives the highest contribution to the total fluorescence. The other tryptophan residues have a very low quantum yield. In the wild-type protein, the fluorescence of all tryptophan residues is partially quenched as compared to the mutants that contain single tryptophan residues, due to conformational effects. The fluorescence of tryptophan residue 262 is very likely also partially quenched by energy transfer to tryptophan residue 175.

Lipopolysaccharide attenuates thrombolysis in batroxobin-induced lung vasculature fibrin deposition but not in ferrous chloride-induced carotid artery thrombus in rats: role of endogenous PAI-1

In this study, we investigated if elevation of endogenous plasminogen activator inhibitor type 1 (PAI-1) by lipopolysaccharide (LPS) can retard thrombolysis in both a rat model of lung vasculature fibrin deposition and a platelet-rich thrombus model induced by endothelial injury. By 3 h following an intravenous bolus injection of 0.5 mg/kg LPS, the plasma PAI-1 level had increased to approximately 8 ng/ml. 125I-labeled fibrinogen was injected intravenously followed by an injection of batroxobin. Batroxobin converts fibrinogen into insoluble fibrin, which was then deposited in the lungs within 5 min, followed by spontaneous fibrinolysis that completely cleared fibrin deposition in the lungs by 30 min. In rats pre-treated with LPS, spontaneous fibrinolysis was significantly retarded. In the endothelial injury model, topical application of FeCl2 on the carotid artery induced an occlusive platelet-rich thrombus, which was not sensitive to endogenous thrombolysis. Exogenous tissue-type plasminogen activator (tPA) was required to recanalize the occlusive thrombus in a dose-dependent manner. Pre-treatment with LPS did not alter the dose-response curve of exogenous tPA-induced thrombolysis. These data indicate that batroxobin-induced lung vasculature fibrin deposition in rats, unlike the FeCl2 model, is sensitive to the impact of endogenous PAI-1 on fibrinolysis.

Plasminogen and tissue-type plasminogen activator deficiency as risk factors for thromboembolic disease

OBJECTIVE

To review the published evidence for an association between a deficiency of plasminogen or tissue-type plasminogen activator (tPA) and the risk of thrombosis.

DATA SOURCES

Review of the medical literature, with an emphasis on the last 10 years.

DATA EXTRACTION AND SYNTHESIS

After an initial assessment of the literature, including review of clinical study design and laboratory methods, a draft manuscript summarizing the findings was prepared and circulated to participants in the College of American Pathologists Conference on Diagnostic Issues in Thrombophilia. The key findings and each recommendation were presented for discussion at the conference. Recommendations were accepted if a consensus of the 27 experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form.

CONCLUSIONS

The consensus of the conference was that routine laboratory assessment of plasminogen and tPA concentration in patients with thrombophilia is not warranted at this time. Analysis of plasminogen and tPA gene alterations in patients with thrombophilia is also not warranted at this time. Determination of plasminogen concentration should be performed in patients suspected of having ligneous conjunctivitis.

Plasminogen activator inhibitor-1 levels and polymorphisms

OBJECTIVE

To review the published evidence of a relationship between levels of plasminogen activator inhibitor-1 (PAI-1) or the 4G/5G polymorphism of the PAI-1 gene and the occurrence of venous thromboembolic disease.

METHODS

Review of the medical literature using computerized databases and a review of secondary sources identified through bibliographies.

DATA SYNTHESIS

Plasminogen activator inhibitor-1 is an important inhibitor of the fibrinolytic system, so it is biologically plausible that elevated levels could suppress fibrinolysis and result in an increased risk of thrombosis. Several small studies reported associations between PAI-1 levels and venous thromboembolism, some of which appear to be familial. Problems with these studies include variations in PAI-1 plasma levels due to circadian changes and the acute phase response, as well as alterations due to common comorbid disease states. More recent investigations have focused on genetic polymorphisms, particularly the 4G/5G insertion/deletion in the promoter region, affecting transcription rates. The relation of 4G/5G to venous thrombosis has been investigated primarily in case-control studies, which have produced inconsistent findings. Most studies, however, have reported higher PAI-1 plasma levels in individuals with 4G/4G.

CONCLUSIONS

The evidence regarding the relationship between an elevated PAI-1 plasma level or PAI-1 genetic polymorphism and the risk of venous thromboembolism is conflicting. There is insufficient information to recommend use of PAI-1 levels or genotype in evaluating thrombophilia.

Insulin resistance and polycystic ovary syndrome

Insulin resistance plays a central role in the pathogenesis of the reproductive as well as metabolic aberrations that characterize the syndrome. Many women with polycystic ovary syndrome (PCOS) manifest a phenotype that overlaps substantially with the so-called "metabolic syndrome" or "syndrome X." These manifestations include obesity, glucose intolerance, hypertension, macrovascular disease, and dyslipidemia. The etiology and manifestations of insulin resistance in PCOS are reviewed in this article.

Platelet hyperaggregability persists even after the improvement of increased blood coagulation and impaired fibrinolysis with the stabilization of symptoms in patients with unstable angina

BACKGROUND

Platelet aggregation, blood coagulation, and fibrinolysis play a pivotal role in the pathogenesis of unstable angina.

METHODS

Platelet aggregability was examined on admission and after 2 weeks of treatment in 22 patients with unstable angina, in particular with regard to small-sized platelet aggregates, plasma tissue factor (TF) antigen levels as a marker of blood coagulation, and plasma plasminogen activator inhibitor (PAI) activity levels as an indicator of fibrinolysis. We also examined the same parameters in 19 patients with stable exertional angina and 17 patients with chest pain syndrome.

RESULTS

The number of small-sized platelet aggregates increased more significantly in the unstable angina group than in the stable exertional angina and chest pain syndrome groups. In the unstable angina group, the number of small-sized platelet aggregates decreased significantly after 2 weeks of treatment, but was still higher than that in the stable exertional angina and chest pain syndrome groups. Plasma TF antigen and PAI activity were higher in the unstable angina group than in the stable exertional angina and chest pain syndrome groups. TF and PAI activity decreased to normal ranges after 2 weeks of treatment in the unstable angina group. There were significant positive correlations among the three parameters on admission.

CONCLUSIONS

It was demonstrated that small-sized platelet aggregates, plasma TF antigen and PAI activity levels increased concomitantly in the unstable angina group. While the blood coagulation and fibrinolytic parameters decreased after stabilization of the clinical symptoms, platelet hyperaggregability still persisted. These results suggest that continuous antiplatelet therapy is essential for the treatment of unstable angina.

No association between the 4g/5G polymorphism of the plasminogen activator inhibitor-1 gene promoter and autistic disorder

Plasmin, a serine protease, is involved in many physiologically relevant processes, including haemostasis, cellular recruitment during immune response, tumour growth, and also neuronal migration and synaptic remodelling. Both tissue-type and urokinase-type plasminogen activators can be efficiently inhibited by plasminogen activator inhibitor-1 (PAI-1), a protease inhibitor of the serpin family. The human PAI-1 gene is located on chromosome 7q, within or close to a region that has been linked to autism in several linkage studies. Autism seems to be characterized by altered neuronal cytoarchitecture, synaptogenesis and possibly also cellular immune responses. We began addressing the potential involvement of the PAI-1 gene in autistic disorder with this linkage/association study, assessing transmission patterns of the 4G/5G polymorphism in the PAI-1 gene promoter that was previously shown to significantly affect PAI-1 plasma levels. No linkage/association was found in 167 trios with autistic probands, recruited in Italy and in the USA. We thus found no evidence that this polymorphism, or putative functionally relevant gene variants in linkage disequilibrium with it, confer vulnerability to autistic disorder.

Extending the capabilities of targeted molecular dynamics: simulation of a large conformational transition in plasminogen activator inhibitor 1

Plasminogen activator inhibitor type 1 (PAI-1) is an inhibitor of plasminogen activators such as tissue-type plasminogen activator or urokinase-type plasminogen activator. For this molecule, different conformations are known. The inhibiting form that interacts with the proteinases is called the active form. The noninhibitory, noncleavable form is called the latent form. X-ray and modeling studies have revealed a large change in position of the reactive center loop (RCL), responsible for the interaction with the proteinases, that is inserted into a beta-sheet (s4A) in the latent form. The mechanism underlying this spontaneous conformational change (half-life = 2 h at 37 degrees C) is not known in detail. This investigation attempts to predict a transition path from the active to the latent structure at the atomic level, by using simulation techniques. Together with targeted molecular dynamics (TMD), a plausible assumption on a rigid body movement of the RCL was applied to define an initial guess for an intermediate. Different pathways were simulated, from the active to the intermediate, from the intermediate to the latent structure and vice versa under different conditions. Equilibrium simulations at different steps of the path also were performed. The results show that a continuous pathway from the active to the latent structure can be modeled. This study also shows that this approach may be applied in general to model large conformational changes in any kind of protein for which the initial and final three-dimensional structure is known.

Quantitative analysis of specific mRNA species in minute cell samples by RT-PCR and flow cytometry

A method for the quantitative determination of specific mRNAs in small numbers of cells, freshly isolated from tissues or early cell cultures, was developed by combining quantitative reverse transcription-polymerase chain reaction (RT-PCR) and quantitative flow cytometry. Freshly isolated umbilical vein endothelial cells were sorted by flow cytometry and then lysed. The number of cells in the lysate was determined by counting of nuclei after propidium iodide staining using flow cytometry. The number of plasminogen activator inhibitor-1 (PAI-1) mRNA copies per cell was determined by quantitative RT-PCR using point-mutated PAI-1 cRNA as an internal standard. The cells were shown to contain 400-900 copies of PAI-1 mRNA molecules per cell which confirms that endothelial cells in vivo express PAI-1. PAI-1 mRNA expression was also analyzed in small numbers of endothelial cells in primary culture in basal conditions and after incubation with different interleukins. The method allowed reliable and reproducible estimation of the number of mRNA copies per cell from original cell samples containing less than 1000 cells. This method can be used for the quantitative determination of various mRNA species in specified cell populations from small tissue samples or cultured cells.

Anticoagulant proteins in childhood venous and arterial thrombosis: a review

Thrombotic disease is less frequent in children than in adults, but may result in severe morbidity and mortality. The coagulation system is balanced to provide rapid activation to stop bleeding and appropriate inhibition to prevent unwanted clot extension. It is regulated by fibrinolysis and by three major anticoagulant pathways: the protein C, antithrombin, and tissue factor pathway inhibitor systems. Acquired or inherited abnormalities of coagulation proteins or hemostatic regulatory mechanisms, particularly when combined with dehydration or the presence of indwelling catheters, may pose a high risk for thrombosis. Thrombosis in a child warrants investigation of potential underlying prothrombotic conditions. These include acquired antiphospholipid antibodies or the lupus anticoagulant as well as abnormalities of the inherited anticoagulant factors including protein C, protein S, antithrombin, and Factor V Leiden. Other abnormalities may result in heightened levels of otherwise normal coagulation proteins such as hyperprothrombinemia due to the prothrombin 20210 mutation. A large survey of children with thrombosis indicated that Factor V Leiden, protein C deficiency, and increased lipoprotein(a) were found most commonly. The most severe predisposition occurs with homozygous protein S or protein C deficiency with resultant purpura fulminans in the newborn. The risk of thrombosis in children with heterozygous deficiencies of anticoagulant proteins is not well defined, although it is clear that combined heterozygotes or a combination of an inherited and an acquired defect heightens the risk for thrombosis. Treatment of thrombosis primarily involves a rapidly acting anticoagulant such as heparin or low-molecular-weight heparin to prevent extension, and long-term anticoagulation with warfarin may be instituted to prevent recurrence. Fibrinolytic therapy is infrequently used because of the risk of serious bleeding complications and is reserved for selected cases of arterial thrombosis to initiate rapid reperfusion of ischemic tissue or used in those patients with a large venous thrombosis and pulmonary emboli causing hemodynamic compromise.

The effects of hormone replacement therapy on thrombin generation, fibrinolysis inhibition, and resistance to activated protein C: prospective cohort study and review of literature

Recent studies have found that hormone replacement therapy (HRT) is associated with a two- to fourfold increased risk of venous thromboembolism, but the thrombogenic mechanism of HRT remains unclear. To investigate whether HRT use induces a procoagulant state, we undertook a prospective cohort study in postmenopausal women to investigate the effects of 3 months of treatment with oral HRT (conjugated equine estrogen 0.625 mg daily and medroxyprogesterone 2.5 mg daily) on markers of thrombin generation (prothrombin fragment 1+2, thrombin-antithrombin complexes), fibrinolytic potential (plasminogen activator inhibitor-1 (PAI-1) activity), and activated protein C (APC) resistance. In addition, we reviewed the literature for studies investigating the effects of HRT on markers of thrombin generation and fibrinolytic potential. In 12 patients who received HRT for a mean of 3.8 months, there was no significant effect of HRT on levels of F1+2, thrombin-antithrombin complexes, or the APC ratio. HRT use had the greatest effect on PAI-1 activity (mean difference = -3.75 UI/mL; 95% confidence interval: - 8.9, 1.1) compared to other coagulation parameters, but this did not attain statistical significance (p = 0.12). In the literature review, the effects of HRT on markers of thrombin generation were inconsistent across studies. There was a consistent pattern of increased fibrinolytic potential with HRT use associated with one marker (PAI-1), but not with another marker (tissue plasminogen activator antigen). We conclude that there is a lack of consistent evidence that the increased risk of venous thromboembolism associated with HRT use is due to a procoagulant state related to increased thrombin generation, decreased fibrinolytic potential, or acquired APC resistance.

Human genetic diseases of proteolysis

Although in the past protein stability commonly has been considered an inherent property of a given protein, the truth is far more complex. Elaborate enzymatic systems exist in multiple intracellular compartments to hydrolyze proteins. These systems are capable of providing a sensitive mechanism to regulate protein expression, a mechanism that is complementary to the transcriptional and translational control mechanisms that influence protein synthesis. The power of regulated proteolysis has been well-demonstrated in the abrupt degradation of cyclins that underlies eukaryotic cell cycle progression. Coincidental with the recent rapid gains in understanding proteolysis at a biochemical level, several human diseases have been found to result from disordered proteolysis. This article reviews several examples of human disease resulting from mutations of genes encoding serine proteases, cysteine proteases, and their inhibitors. Examples are also presented of human diseases resulting from disorders in the highly intricate ubiquitin-proteasome pathway of protein degradation. It is certain that many more human diseases will be associated in the future with disorders of proteolysis.

Influence of early fibrinolysis inhibition on thrombus formation following microvascular trauma

The effect of the fibrinolysis inhibitor tranexamic acid on early thrombus formation following microvascular trauma was investigated in the central arteries of ears in 86 rabbits (in all 172 vessels), divided into four separate blind randomised studies. In the first part a common end-to-end anastomosis was done and in the last three studies a severe trauma-arteriotomy/intimectomy was performed. Parameters studied were vessel bleeding times, patency rates, weights of intraluminal thrombotic material, haematocrit and plasma fibrinolytic activity. In the first study consisting of 14 control animals and 18 animals treated with 14 mg/kg bw of tranexamic acid, end-to-end anastomosis was performed on the central artery of one ear and on the central vein of the other ear. In the second, third, and fourth studies consisting of 18, 20, and 16 control vessels and the same number of corresponding vessels in treated animals a 7-mm longitudinal arteriotomy followed by a deep 5-mm-long intimectomy was performed. The second and third treated groups were given 14 mg/kg bw of tranexamic acid 5 min and 1 h, respectively, before reflow and the fourth group 28 mg/kg bw 5 min before reflow. The difference between the second and third studies was the addition, to mimic clinical situations, of 8.5 ml saline/kg bw 2 h before reflow in the third study. In conclusion, treatment with a single clinical dose, 14 mg/kg of tranexamic acid, did not influence vessel bleeding times or thrombus formation in the anastomotic or severe trauma models and seems safe to use. Not even a double clinical dose, 28 mg/kg, influenced thrombus formation in a statistically significant way.

Thrombin activatable fibrinolysis inhibitor and the risk for deep vein thrombosis

Thrombin activatable fibrinolysis inhibitor (TAFI, or procarboxypeptidase B) is the precursor of a recently described carboxypeptidase that potently attenuates fibrinolysis. Therefore, we hypothesized that elevated plasma TAFI levels induce a hypofibrinolytic state associated with an increased risk for venous thrombosis. To evaluate this hypothesis, we developed an electroimmunoassay for TAFI antigen and used this assay to measure TAFI levels in the Leiden Thrombophilia Study, a case–control study of venous thrombosis in 474 patients with a first deep vein thrombosis and 474 age- and sex-matched control subjects. In 474 healthy control subjects, an increase of TAFI with age was observed in women but not in men. Oral contraceptive use also increased the TAFI concentration. TAFI levels above the 90th percentile of the controls (&gt; 122 U/dL) increased the risk for thrombosis nearly 2-fold compared with TAFI levels below the 90th percentile (odds ratio, 1.7; 95% confidence interval, 1.1-2.5). Adjustment for various possible confounders did not materially affect this estimate. These results indicate that elevated TAFI levels form a mild risk factor for venous thrombosis. Such levels were found in 9% of healthy controls and in 14% of patients with a first deep vein thrombosis. Elevated TAFI levels did not enhance the thrombotic risk associated with factor V Leiden but may interact with high factor VIII levels.

Induction of the Plasminogen Activator Inhibitor-1 Gene Expression by Mild Hypoxia Via a Hypoxia Response Element Binding the Hypoxia-Inducible Factor-1 in Rat Hepatocytes

Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of both tissue-type and urokinase-type plasminogen activators. The balance between plasminogen activators and PAI-1 plays an important role in several physiological and pathophysiological processes such as atherosclerosis or thrombosis. Because these conditions are associated with hypoxia, it was the aim of the present study to investigate the influence of low O2tension on the expression of PAI-1 mRNA and protein using primary cultured rat hepatocytes as a model system. We found that PAI-1 mRNA and protein were induced by mild hypoxia (8% O2). The hypoxia-dependent PAI-1 mRNA induction was transcriptionally regulated because it was inhibited by actinomycin D (ActD). Luciferase (LUC) reporter gene constructs driven by about 800 bp of the 5′-flanking region of the rat PAI-1 gene were transiently transfected into primary rat hepatocytes; mild hypoxia caused a 3-fold induction, which was mediated by the PAI-1 promoter region -175/-158 containing 2 putative hypoxia response elements (HRE) binding the hypoxia-inducible factor (HIF-1). Mutation of the HRE-1 (-175/-168) or HRE-2 (-165/-158) also abolished the induction by mild hypoxia. Cotransfection of a HIF-1 vector and the PAI-1–LUC constructs, as well as gel shift assays, showed that the HRE-2 of the PAI-1 promoter was most critical for induction by hypoxia and HIF-1 binding. Thus, PAI-1 induction by mild hypoxia via a HIF-1 binding HRE in the rat PAI-1 promoter appears to be the mechanism causing the increase in PAI-1 in many clinical conditions associated with O2deficiency.

Induction of the Plasminogen Activator Inhibitor-1 Gene Expression by Mild Hypoxia Via a Hypoxia Response Element Binding the Hypoxia-Inducible Factor-1 in Rat Hepatocytes

Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of both tissue-type and urokinase-type plasminogen activators. The balance between plasminogen activators and PAI-1 plays an important role in several physiological and pathophysiological processes such as atherosclerosis or thrombosis. Because these conditions are associated with hypoxia, it was the aim of the present study to investigate the influence of low O2tension on the expression of PAI-1 mRNA and protein using primary cultured rat hepatocytes as a model system. We found that PAI-1 mRNA and protein were induced by mild hypoxia (8% O2). The hypoxia-dependent PAI-1 mRNA induction was transcriptionally regulated because it was inhibited by actinomycin D (ActD). Luciferase (LUC) reporter gene constructs driven by about 800 bp of the 5′-flanking region of the rat PAI-1 gene were transiently transfected into primary rat hepatocytes; mild hypoxia caused a 3-fold induction, which was mediated by the PAI-1 promoter region -175/-158 containing 2 putative hypoxia response elements (HRE) binding the hypoxia-inducible factor (HIF-1). Mutation of the HRE-1 (-175/-168) or HRE-2 (-165/-158) also abolished the induction by mild hypoxia. Cotransfection of a HIF-1 vector and the PAI-1–LUC constructs, as well as gel shift assays, showed that the HRE-2 of the PAI-1 promoter was most critical for induction by hypoxia and HIF-1 binding. Thus, PAI-1 induction by mild hypoxia via a HIF-1 binding HRE in the rat PAI-1 promoter appears to be the mechanism causing the increase in PAI-1 in many clinical conditions associated with O2deficiency.

Fibrinolysis and thrombosis

The fibrinolytic system generates plasmin, which dissolves fibrin in haemostatic plugs and in thrombi. It is often regarded simply as a secondary phenomenon responsive to the generation of thrombi but it is, rather, in dynamic balance with fibrin formation, such that abnormalities in either can lead to thrombosis. This chapter summarizes the fibrinolytic system and its regulation. It considers the components of the system in blood, both in plasma and in circulating cells, with emphasis on protease-inhibitor balance. It goes on to discuss local fibrinolytic potential in thrombi, both venous and arterial, and in the diseased vessel wall, presenting evidence that increased local inhibition of fibrinolysis by PAI-1, PAI-2 and alpha2-antiplasmin is intimately involved in thrombus stability and in the generation of fibrin-rich vessel wall lesions. Finally, it reviews the evidence that defective plasma fibrinolysis has a causal role in venous and arterial thrombosis.