Vascular-bed--specific hemostasis and hypercoagulable states

Mucosal tolerization to E-selectin protects against memory dysfunction and white matter damage in a vascular cognitive impairment model

Vascular cognitive impairment (VCI) is the second most prevalent type of dementia in the world. The white matter damage that characterizes the common subcortical ischemic form of VCI can be modeled by ligating both common carotid arteries in the Wistar rat to induce protracted cerebral hypoperfusion. In this model, we find that repetitive intranasal administration of recombinant E-selectin to induce mucosal tolerance and to target immunomodulation to activating blood vessels potently suppresses both white matter (and possibly gray matter) damage and markers of vessel activation (tumor necrosis factor and E-selectin); it also preserves behavioral function in T-maze spontaneous alternation, T-maze spatial discrimination memory retention, and object recognition tests. Immunomodulation may be an effective novel strategy to prevent progression of VCI.

Pro-healing drug-eluting stents: a role for antioxidants?

Current strategies to lower the incidence of ISR (in-stent restenosis) following PCI (percutaneous coronary intervention) are aimed at modifying arterial healing after stent injury. This can impair endothelial recovery and render the vessel prone to acute thrombosis. As early restoration of endothelial integrity inhibits neointimal growth and thrombosis, alternative approaches which encourage this process may provide a more effective long-term result after PCI. Oxidative stress is enhanced after PCI and participates in the regulation of endothelial regeneration and neointimal growth. Moreover, evidence suggests antioxidants improve re-endothelialization and inhibit ISR. By promoting, rather than blocking, the healing process, antioxidant and other therapies may offer an alternative or additional approach over the antiproliferative approaches common to many current devices.

Levels of protein C activity and clinical factors in early phase of pediatric septic shock may be associated with the risk of death

Severe sepsis and septic shock are major causes of morbidity and mortality among children in pediatric intensive care units (PICUs) worldwide. Activated protein C (PC) is a critical endogenous regulator of coagulation and inflammation in patients with sepsis. However, the role of PC in pediatric sepsis is still obscure. We prospectively recruited infants and children aged between 1 month and 15 years old who were admitted to PICU with a clinical diagnosis of systemic inflammatory response syndrome, sepsis, or septic shock. Clinical data were recorded and blood samples kept for further analysis. We then measured the levels of PC activity. Of the approximately 1,100 pediatric patients admitted to PICU from January 1, 2004 to December 31, 2005, 75 were diagnosed with septic shock (6.8%), and 67 samples were available for analysis. Out of these, 41 (61%) were survivors, and 26 (39%) were nonsurvivors. The average plasma PC activity (%) was at 37.8 +/- 4.4. Plasma PC activity (%) was significantly lower in the nonsurvivors compared with the survivors at 23.6 +/- 4.3 and 46.8 +/- 6.3 (P = 0.002), respectively. D-Dimer levels were not significantly different between the survivors (1,461 +/- 266 ng/mL) and the nonsurvivors (1,989 +/- 489 ng/mL) (P = 0.68). Also, there was no correlation between plasma PC activity and D-dimer levels (r = -0.07; P = 0.6). Importantly, the odds of dying were significantly higher in patients whose level of PC activity was less than 25% (odds ratio = 5.6; P = 0.02). Pediatric patients with septic shock demonstrate very low levels of PC activity, and this may be associated with an increased risk of death.

Prophylactic thrombolysis by thrombin-activated latent prourokinase targeted to PECAM-1 in the pulmonary vasculature

A recombinant prodrug, single-chain urokinase-type plasminogen activator (scuPA) fused to an anti-PECAM-1 antibody single-chain variable fragment (anti-PECAM scFv/scuPA) targets endothelium and augments thrombolysis in the pulmonary vasculature.(1) To avoid premature activation and inactivation and to limit systemic toxicity, we replaced the native plasmin activation site in scFv/low-molecular-weight (lmw)-scuPA with a thrombin activation site, generating anti-PECAM scFv/uPA-T that (1) is latent and activated by thrombin instead of plasmin; (2) binds to PECAM-1; (3) does not consume plasma fibrinogen; (4) accumulates in mouse lungs after intravenous injection; and (5) resists PA inhibitor PAI-1 until activated by thrombin. In mouse models of pulmonary thrombosis caused by thromboplastin and ischemia-reperfusion (I/R), scFv/uPA-T provided more potent thromboprophylaxis and greater lung protection than plasmin-sensitive scFv/uPA. Endothelium-targeted thromboprophylaxis triggered by a prothrombotic enzyme illustrates a novel approach to time- and site-specific regulation of proteolytic reactions that can be modulated for therapeutic benefit.

Air pollution and atherothrombosis

Observational studies have consistently demonstrated an association between exposure to air pollution and increased cardiovascular morbidity and mortality. This association is strongest for particulate matter (PM), of which combustion-derived particulate is an important component. Studies assessing the effects of PM exposure in vitro and in vivo have provided insight into the biological mechanisms underlying these observations. In this review we discuss the potential for inhaled particles to impact on the development and progression of atherosclerosis. Oxidative stress and inflammation are central to both the toxicology of PM and the pathogenesis of atherosclerosis. It is possible that nanoparticulates or soluble components of PM may translocate into the bloodstream, resulting in direct effects on atherosclerotic plaque stability, the vascular endothelium, platelet function, and thrombosis. We summarize the latest experimental research and relate this to current understanding of the role of inflammation and vascular dysfunction in the pathogenesis of atherothrombosis. Ongoing research in this area will continue to provide insight into the adverse vascular effects of PM, with the possibility of therapeutic interventions to reduce the impact of environmental air pollution on cardiovascular disease a realistic goal.

Intrinsic pathway of coagulation and arterial thrombosis

Formation of a fibrin clot is mediated by a group of tightly regulated plasma proteases and cofactors. While this system is essential for minimizing blood loss from an injured blood vessel (hemostasis), it also contributes to pathologic fibrin formation and platelet activation that may occlude vessels (thrombosis). Many antithrombotic drugs target key elements of the plasma coagulation mechanism such as thrombin and factor Xa, based on the premise that plasma elements contributing to thrombosis are primarily those involved in hemostasis. Recent studies with genetically altered mice raise questions about this paradigm. Deficiencies of the intrinsic pathway proteases factor XII and factor XI are not associated with abnormal hemostasis in mice, but impair formation of occlusive thrombi in arterial injury models, indicating that pathways not essential for hemostasis participate in arterial thrombosis. If factor XII or factor XI make similar contributions to thrombosis in humans, these proteases could be ideal targets for drugs to treat or prevent thromboembolic disease with minimal risk of therapy-associated bleeding.

Ischemic and thrombotic effects of dilute diesel-exhaust inhalation in men with coronary heart disease

BACKGROUND

Exposure to air pollution from traffic is associated with adverse cardiovascular events. The mechanisms for this association are unknown. We conducted a controlled exposure to dilute diesel exhaust in patients with stable coronary heart disease to determine the direct effect of air pollution on myocardial, vascular, and fibrinolytic function.

METHODS

In a double-blind, randomized, crossover study, 20 men with prior myocardial infarction were exposed, in two separate sessions, to dilute diesel exhaust (300 mug per cubic meter) or filtered air for 1 hour during periods of rest and moderate exercise in a controlled-exposure facility. During the exposure, myocardial ischemia was quantified by ST-segment analysis using continuous 12-lead electrocardiography. Six hours after exposure, vasomotor and fibrinolytic function were assessed by means of intraarterial agonist infusions.

RESULTS

During both exposure sessions, the heart rate increased with exercise (P<0.001); the increase was similar during exposure to diesel exhaust and exposure to filtered air (P=0.67). Exercise-induced ST-segment depression was present in all patients, but there was a greater increase in the ischemic burden during exposure to diesel exhaust (-22+/-4 vs. -8+/-6 millivolt seconds, P<0.001). Exposure to diesel exhaust did not aggravate preexisting vasomotor dysfunction, but it did reduce the acute release of endothelial tissue plasminogen activator (P=0.009; 35% decrease in the area under the curve).

CONCLUSIONS

Brief exposure to dilute diesel exhaust promotes myocardial ischemia and inhibits endogenous fibrinolytic capacity in men with stable coronary heart disease. Our findings point to ischemic and thrombotic mechanisms that may explain in part the observation that exposure to combustion-derived air pollution is associated with adverse cardiovascular events. (ClinicalTrials.gov number, NCT00437138 [ClinicalTrials.gov].).

Coagulopathy: its pathophysiology and treatment in the injured patient

Hemorrhage continues to be one of the leading causes of death following trauma. Trauma patients are susceptible to the early development of coagulopathy and the most severely injured patients are coagulopathic on hospital admission. Hypothermia, acidosis, and dilution from standard resuscitation can worsen the presenting coagulopathy and perpetuate bleeding. Early identification of coagulopathy is dependent on clinical awareness and point of care laboratory values. Routinely used laboratory coagulation parameters fail to adequately describe this state. Thrombelastography is a test that can be done at the bedside and uses whole blood to provide a functional evaluation of coagulation. Rapid diagnosis of coagulopathy, followed by prevention or correction of hypothermia and acidosis should be a priority during the initial evaluation and resuscitation. Judicious use of resuscitation fluids and early replacement of coagulation factors will help prevent iatrogenic hemodilution. This review covers the pathophysiology as well as the clinical and laboratory diagnosis of coagulopathy. Prevention and treatment strategies are discussed, including early transfusion of coagulation factors during massive transfusion and the use of recombinant factor VIIa. Damage control resuscitation is briefly discussed, and it involves the combination of hypotensive resuscitation and hemostatic resuscitation. Finally, a description of the use of fresh whole blood in the military setting is included. Its use has been proven to be safe and beneficial in this setting and warrants further investigation as an adjunct to the management of civilian trauma patients.

Vascular bed-specific thrombosis

Hemostasis represents a finely tuned balance between procoagulant and anticoagulant forces. An imbalance of these forces may lead to clinically significant disease, including arterial, venous and/or microvascular thrombosis. The vast majority of hypercoagulable states are associated with local thrombus formation. The goal of this review is to discuss the mechanisms underlying site-specific thrombosis.

Murine models of vascular thrombosis (Eitzman series)

Thrombotic complications of vascular disease are the leading cause of morbidity and mortality in most industrialized countries. Despite this, safe and effective drugs targeting these complications are limited, especially in the chronic setting. This is because of the complexity of thrombosis in both arteries and veins, which is becoming increasingly evident as numerous factors are now known to affect the fate of a forming thrombus. To fully characterize thrombus formation in these settings, in vivo models are necessary to study the various components and intricate interactions that are involved. Genetic manipulations in mice are greatly facilitating the dissection of relevant pro- and antithrombotic influences. Standardized models for the study of thrombosis in mice as well as evolving techniques that allow imaging of molecular events during thrombus formation are now available. This review will highlight some of the recent developments in the field of thrombosis using mouse models and how these studies are expanding our knowledge of thrombotic disease.

Endothelial fibrinolytic capacity predicts future adverse cardiovascular events in patients with coronary heart disease

OBJECTIVE

The endothelium-derived fibrinolytic factor tissue plasminogen activator (t-PA) is a major determinant of vessel patency after coronary plaque rupture and thrombosis. We assessed whether endothelial fibrinolytic capacity predicts atherothrombotic events in patients with coronary heart disease.

METHODS AND RESULTS

Plasma t-PA and plasminogen activator inhibitor (PAI)-1 concentrations were measured during intrabrachial substance P infusion in 98 patients with angiographically proven stable coronary heart disease. Forearm blood flow was measured during infusion of substance P and sodium nitroprusside. Cardiovascular events (cardiovascular death, myocardial infarction [MI], ischemic stroke [CVA], and emergency hospitalization for unstable angina) were determined during 42 months of follow-up. Patients experiencing a cardiovascular event (n=19) had similar baseline characteristics to those free of events. Substance P caused a dose-dependent increase in plasma t-PA concentrations (P<0.001). However, net t-PA release was 72% lower in the patients who experienced death, MI, or CVA, and 48% lower in those who suffered death, MI, CVA or hospitalization for unstable angina (P<0.05). Major adverse cardiovascular events were most frequent in those with the lowest fibrinolytic capacity (P=0.03 for trend); patients with the lowest quartile of t-PA release had the highest rate of adverse events (P=0.01).

CONCLUSION

Endothelial fibrinolytic capacity, as measured by stimulated t-PA release, predicts the future risk of adverse cardiovascular events in patients with coronary heart disease. We suggest that endothelial fibrinolytic capacity is a powerful novel determinant of cardiovascular risk.

Delivery of Anti-Platelet-Endothelial Cell Adhesion Molecule Single-Chain Variable Fragment-Urokinase Fusion Protein to the Cerebral Vasculature Lyses Arterial Clots and Attenuates Postischemic Brain Edema

Efficacy and safety of current means to prevent cerebrovascular thrombosis in patients at high risk of stroke are suboptimal. In theory, anchoring fibrinolytic plasminogen activators to the luminal surface of the cerebral endothelium might arrest formation of occlusive clots in this setting. We tested this approach using the recombinant construct antiplatelet-endothelial cell adhesion molecule (PECAM) single-chain variable fragment (scFv)-urokinase-type plasminogen activator (uPA), fusing low-molecular-weight single-chain urokinase-type plasminogen activator with a scFv of an antibody directed to the stably expressed endothelial surface determinant PECAM-1, implicated in inflammation and thrombosis. Studies in mice showed that scFv-uPA, but not unconjugated uPA 1) accumulates in the brain after intravascular injection, 2) lyses clots lodged in the cerebral arterial vasculature without hemorrhagic complications, 3) provides rapid and stable cerebral reperfusion, and 4) alleviates post-thrombotic brain edema. Effective and safe thromboprophylaxis in the cerebral arterial circulation by anti-PECAM scFv-uPA represents a prototype of a new paradigm to prevent recurrent cerebrovascular thrombosis.

Retrospective analysis of coagulation factor II receptor (F2R) sequence variation and coronary heart disease in hypertensive patients

OBJECTIVES

The purpose of this study was to evaluate the role of genetic variants within the coagulation factor II receptor (F2R) in the occurrence of coronary heart disease (CHD).

METHODS AND RESULTS

Four SNPs (-1738 G/A, 2860 G/A, 2930 T/C, and 9113 C/A) and an ins/del polymorphism -506-/GGCCGCGGGAAGC (D/I), replicating a consensus sequence for Ets-1 transcription factor, and their related haplotypes were tested for association to CHD in 1600 hypertensive patients divided in 2 groups according to presence (cases, n=559) and absence (controls, n=1041) of CHD. Allele I at -506 locus was associated with increased risk of CHD under additive, dominant, and recessive models of inheritance (all P<0.01). Three haplotypes carrying I allele were consistently associated with an increased risk of CHD (all P<0.05). Patients homozygous for the C allele at the 2930 locus also showed an increased risk of CHD (P<0.05). To test the functionality of -506 locus, nuclear extracts were incubated with -506D and -506I sequences by EMSA and F2R promoter activity (F2R-A) were assessed in HUVECs transfected with vectors carrying -506D and -506I sequences and exposed to hypoxia. Presence of the -506I sequence was associated with a 26% reduction of affinity binding to nuclear proteins and to blunted F2R-A in response to hypoxia as compared with the -506D sequence (all P<0.05).

CONCLUSIONS

F2R genetic variants may influence the natural history of CHD in patients at high risk of cardiovascular events.

Long-term effects of hemostatic variables on fatal coronary heart disease: 30-year results from the first prospective Northwick Park Heart Study (NPHS-I)

BACKGROUND

The long-term associations of established risk factors for coronary heart disease (CHD), for example cholesterol, are well known, but not for the less familiar hemostatic variables.

OBJECTIVES

To establish whether associations between hemostatic variables and CHD first identified nearly three decades ago have persisted long-term.

METHODS

The first Northwick Park Heart Study (NPHS-I) recruited 2167 white men and 941 white women, average age at entry 48 years, on whom measures of factor (F) VII activity (VIIc) and plasma fibrinogen were carried out, both at entry and at follow-up approximately 6 years later.

RESULTS

During a median follow-up of 29 years, 231 male and 36 female CHD deaths were recorded from notifications by the Office for National Statistics. VIIc at recruitment was significantly related to CHD mortality, corrected rate ratio, RR, per 1 SD increase 1.56 (95% CI 1.29, 1.88) in men and RR 1.78 (95% CI 1.17, 2.72) in women. Recruitment fibrinogen was also strongly related to CHD mortality in men, RR 1.63 (95% CI 1.33, 1.99) but not in women, RR 0.75 (95% CI 0.40, 1.43). The associations persisted after controlling for confounders and were confirmed using 6-year follow-up measurements and in analyses omitting deaths within 10 years of recruitment.

CONCLUSIONS

The hemostatic system contributes to CHD mortality, and its effect is stable over time. For VIIc, the effect was similar in men and women, while for fibrinogen it appeared to be present only in men.

Mechanism of inactivation of plasminogen activator inhibitor-1 by a small molecule inhibitor

The inactivation of plasminogen activator inhibitor-1 (PAI-1) by the small molecule PAI-1 inhibitor PAI-039 (tiplaxtinin) has been investigated using enzymatic analysis, direct binding studies, site-directed mutagenesis, and molecular modeling studies. Previously PAI-039 has been shown to exhibit in vivo activity in various animal models, but the mechanism of inhibition is unknown. PAI-039 bound specifically to the active conformation of PAI-1 and exhibited reversible inactivation of PAI-1 in vitro. SDS-PAGE indicated that PAI-039 inactivated PAI-1 predominantly through induction of PAI-1 substrate behavior. Preincubation of PAI-1 with vitronectin, but not bovine serum albumin, blocked PAI-039 activity while analysis of the reciprocal experiment demonstrated that preincubation of PAI-1 with PAI-039 blocked the binding of PAI-1 to vitronectin. Together, these data suggest that the site of interaction of the drug on PAI-1 is inaccessible when PAI-1 is bound to vitronectin and may overlap with the PAI-1 vitronectin binding domain. This was confirmed by site-directed mutagenesis and molecular modeling studies, which suggest that the binding epitope for PAI-039 is localized adjacent to the previously identified interaction site for vitronectin. Thus, these studies provide a detailed characterization of the mechanism of inhibition of PAI-1 by PAI-039 against free, but not vitronectin-bound PAI-1, suggesting for the first time a novel pool of PAI-1 exists that is vulnerable to inhibition by inactivators that bind at the vitronectin binding site.

Phenotypic Heterogeneity of the Endothelium

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the first of a 2-part review focused on phenotypic heterogeneity of blood vessel endothelium. This review provides an historical perspective of our understanding of endothelial heterogeneity, discusses the scope of phenotypic diversity across the vascular tree, and addresses proximate and evolutionary mechanisms of endothelial cell heterogeneity. The overall goal is to underscore the importance of phenotypic heterogeneity as a core property of the endothelium.

Antiproliferative Agents Alter Vascular Plasminogen Activator Inhibitor-1 Expression

OBJECTIVE

Drug eluting stents (DES) reduce the incidence of restenosis after coronary angioplasty. Enthusiasm has been tempered by a possible increased risk of in-stent thrombosis. We examined the effects of paclitaxel and rapamycin on the endothelial transcriptome to identify alterations in gene expression associated with thrombosis.

METHODS AND RESULTS

Gene expression profiling was performed on human coronary artery endothelial cells treated with rapamycin or paclitaxel. Plasminogen activator inhibitor-1 (PAI-1) was the most consistently induced transcript in rapamycin-treated human coronary artery endothelial cells. RT-PCR and ELISA were performed to confirm positive findings. Transgenic mice engineered to express enhanced green fluorescent protein under control of the human PAI-1 promoter were also treated. Rapamycin and paclitaxel treated endothelial cells produced dose-dependent increases in PAI-1. There was a variable effect on endothelial tissue-type plasminogen activator (t-PA) expression. Enhanced expression of PAI-1 and enhanced green fluorescent protein were detected in coronary arteries, the aorta, and kidney of the mice.

CONCLUSIONS

Antiproliferative agents stimulate the expression of prothrombotic genes. PAI-1 expression may also play a role in the prevention of restenosis through an antimigratory mechanism. The effects of antiproliferatives on vascular gene expression deserve further scrutiny in view of the increasing utilization of drug-eluting stents.

In-hospital onset ischemic stroke may be associated with atrial fibrillation and right-to-left shunt

BACKGROUND AND PURPOSE

Ischemic stroke during hospitalization can occasionally be found, but the mechanisms and causes underlying stroke have not been investigated in detail. The present study aimed to identify differences in stroke etiology between in-hospital and out-of-hospital onset.

METHODS

Subjects comprised 357 consecutive patients (221 men, 136 women) with ischemic stroke prospectively enrolled within 24 h of onset. Contrast saline transcranial Doppler ultrasonography (c-TCD) or transesophageal echocardiography (TEE) was performed in all participants to identify right-to-left shunts (RLS). Patients were divided into 2 groups: in-hospital onset (IHO group, n=49); and out-of-hospital onset (OHO group, n=308). Clinical characteristics were compared between groups.

RESULTS

Mean age was 71.5+/-12.3 years. Mean National Institute of Health stroke scale score was 6.9+/-7.2. RLS, atrial fibrillation (AF) and malignancy were more frequent in the IHO group than in the OHO group (39% vs. 20%, p=0.006; 45% vs. 16%, p<0.001; 18% vs. 4%, p<0.001, respectively). AF and/or RLS was more frequent in the IHO group (61%) than in the OHO group (30%, p<0.001).

CONCLUSION

Ischemic stroke with in-hospital onset may be associated with AF and RLS.

Fibrin D-dimer: a marker of psychosocial distress and its implications for research in stress-related coronary artery disease

Psychosocial factors might mediate their adverse impact on coronary arteries by eliciting a hypercoagulable state via changes in sympathetic nervous system activity. A recent meta-analysis of prospective studies reported an association of the hypercoagulability marker D-dimer with an increased risk for coronary events. This review provides evidence that an elevated plasma D-dimer level is a suitable marker for acute and chronic psychosocial distress. Prospective studies need to show whether stress-related changes in D-dimer may help explain the increased coronary risk with psychosocial distress.

A case of deep venous thrombosis associated with pegylated interferon alpha2b plus ribavirin treatment of chronic hepatitis C

We present a case of deep venous thrombosis (DVT) during pegylated interferon (peg-IFN)-alpha2b plus ribavirin treatment of chronic hepatitis C (CHC). A 67-year-old man, who had been under treatment for hypertension and diabetes mellitus, was admitted to our hospital for peg-IFN-alpha2b plus ribavirin treatment for CHC. His serum hepatitis C virus (HCV) RNA level became undetectable 1 week after the initiation of peg-IFN-alpha2b plus ribavirin treatment. He suffered from severe pain, flare, and edema in both of his lower legs 6 weeks after the initiation of peg-IFN-alpha2b plus ribavirin treatment. He was diagnosed as having DVT because of the presence of a thrombus in the right soleus vein by ultrasonography. Peg-IFN-alpha2b plus ribavirin treatment was discontinued because a causal relationship between DVT and peg-IFN-alpha2b plus ribavirin treatment was suspected. DVT was not observed and the symptoms in both of his legs were improved after the administration of warfarin potassium. Subsequently, DVT has not recurred, and he has remained HCV-RNA negative.

Management of sepsis during the early "golden hours"

Severe sepsis and septic shock are common causes of morbidity and mortality. Interventions directed at specific endpoints, when initiated early in the "golden hours" of patient arrival at the hospital, seem to be promising. Early hemodynamic optimization, administration of appropriate antimicrobial therapy, and effective source control of infection are the cornerstones of successful management. In patients with vasopressor-dependent septic shock, provision of physiologic doses of replacement steroids may result in improved survival. Administration of drotrecogin alfa (activated), (activated protein C) has been shown to improve survival in patients with severe sepsis and septic shock who have a high risk of mortality. In this article we review the multi-modality approach to early diagnosis and intervention in the therapy of patients with severe sepsis and septic shock.

Statins blunt thrombin-induced down-regulation of endothelial nitric oxide synthase expression in human endothelial cells

Thrombin plays a pivotal role in the pathophysiology of acute coronary syndromes by mediating thrombus formation and endothelium-dependent vasomotor dysfunction. In human endothelial cells, prolonged incubation with thrombin down-regulates endothelial nitric oxide synthase (eNOS) expression via activation of Rho. Statins are effective in patients with acute coronary syndromes. These beneficial effects are attributed to their pleiotropic effects and also to an improved lipid profile. We hypothesized that statins may prevent the down-regulation of eNOS induced by thrombin in human endothelial cells. Human umbilical vein endothelial cells were used. Expression and activity of eNOS protein were evaluated by Western blotting and L-citrulline assay, respectively. Rho A membrane translocation was evaluated by Wesern blotting after fractionation. Stimulation of human umbilical vein endothelial cells with thrombin (4 U/mL, 24 h) significantly decreased eNOS expression. The addition of simvastatin significantly prevented thrombin-induced down-regulation of eNOS expression in a concentration-dependent manner (100 nmol/L to 10 micromol/L). Cerivastatin (10 micromol/L) also reversed the down-regulation of eNOS by thrombin. Both simvastatin and cerivastatin-blocked thrombin-induced decrease in NOS activity. Stimulation with thrombin (4 U/mL, 10 min) significantly increased the membrane translocation of Rho A. Simvastatin (10 micromol/L) and cerivastatin (10 micromol/L) significantly decreased thrombin-induced membrane translocation of Rho A. Therefore, statins blunt thrombin-induced down-regulation of eNOS expression in human endothelial cells. This finding provides a novel mechanism of the pleiotropic effects of statins, which may be beneficial for patients with acute coronary syndromes.

Immunomodulation strategies for preventing vascular disease of the brain and heart: workshop summary

This workshop examined the opportunities for translational research directed at immune and inflammatory mechanisms. This summary presents the background data in 3 general areas: (1) inflammation and hemostasis in cerebrovascular and cardiovascular disease, (2) immune interactions in the central nervous system and heart, and (3) translation of immune modulation in the brain and heart, all of which supported a consensus derivation of the opportunities for future research in these areas. The summary concludes with 11 recommendations.

Genetic background determines response to hemostasis and thrombosis

Background

Thrombosis is the fatal and disabling consequence of cardiovascular diseases, the leading cause of mortality and morbidity in Western countries. Two inbred mouse strains, C57BL/6J and A/J, have marked differences in susceptibility to obesity, atherosclerosis, and vessel remodeling. However, it is unclear how these diverse genetic backgrounds influence pathways known to regulate thrombosis and hemostasis. The objective of this study was to evaluate thrombosis and hemostasis in these two inbred strains and determine the phenotypic response of A/J chromosomes in the C57BL/6J background.

Methods

A/J and C57Bl/6J mice were evaluated for differences in thrombosis and hemostasis. A thrombus was induced in the carotid artery by application of the exposed carotid to ferric chloride and blood flow measured until the vessel occluded. Bleeding and rebleeding times, as surrogate markers for thrombosis and hemostasis, were determined after clipping the tail and placing in warm saline. Twenty-one chromosome substitution strains, A/J chromosomes in a C57BL/6J background, were screened for response to the tail bleeding assay.

Results

Thrombus occlusion time was markedly decreased in the A/J mice compared to C57BL/6J mice. Tail bleeding time was similar in the two strains, but rebleeding time was markedly increased in the A/J mice compared to C57BL/6J mice. Coagulation times and tail morphology were similar, but tail collagen content was higher in A/J than C57BL/6J mice. Three chromosome substitution strains, B6-Chr5^A/J, B6-Chr11^A/J, and B6-Chr17^A/J, were identified with increased rebleeding time, a phenotype similar to A/J mice. Mice heterosomic for chromosomes 5 or 17 had rebleeding times similar to C57BL/6J mice, but when these two chromosome substitution strains, B6-Chr5^A/J and B6-Chr17^A/J, were crossed, the A/J phenotype was restored in these doubly heterosomic progeny.

Conclusion

These results indicate that susceptibility to arterial thrombosis and haemostasis is remarkably different in C57BL/and A/J mice. Three A/J chromosome substitution strains were identified that expressed a phenotype similar to A/J for rebleeding, the C57Bl/6J background could modify the A/J phenotype, and the combination of two A/J QTL could restore the phenotype. The diverse genetic backgrounds and differences in response to vascular injury induced thrombosis and the tail bleeding assay, suggest the potential for identifying novel genetic determinants of thrombotic risk.

Tissue plasminogen activator genetic polymorphisms do not influence tissue plasminogen activator release in patients with coronary heart disease

OBJECTIVES

To determine if polymorphisms of the tissue plasminogen activator (t-PA) gene influence acute endogenous t-PA release in patients with coronary heart disease (CHD).

METHODS

Forearm blood flow and plasma t-PA concentrations were measured in response to intra-brachial infusion of substance P and sodium nitroprusside in 96 patients with stable CHD. Genotyping was performed using a Taqman polymerase chain reaction assay specifically designed to detect the polymorphisms of interest: (i) Alu-repeat insertion/deletion sequence; (ii) C-->T substitution in an upstream enhancer region (-7351 C/T); (iii) T-->C in exon 6 (20 099 T/C); and (iv) T-->A (27 445 T/A) in intron 10.

RESULTS

Substance P and sodium nitroprusside caused dose-dependent increases in forearm blood flow in all patients (P < 0.001 for all) that were independent of the four genetic polymorphisms. Similarly, there were no differences in basal plasma t-PA antigen concentrations or net t-PA release between genotypes. Compared to non-smokers, smokers exhibited impaired substance P-induced vasodilatation (P < 0.001) and t-PA release (P = 0.05).

CONCLUSIONS

Despite confirming our previous findings in cigarette smokers, we have found no effect of polymorphisms of the t-PA gene on two complementary aspects of endothelial function. We conclude that genetic variation of the t-PA locus is unlikely to have a major influence on acute t-PA release in subjects with established CHD.

Primary antiphospholipid syndrome associated with small aorta syndrome: a case report

It has been widely accepted that the antiphospholipid syndrome (APS) is an autoimmune hypercoagulability syndrome in which a variety of venous and arterial thrombotic events may occur. Peripheral obliterating arterial disease characterized by aortoiliac steno-occlusion occurring in young women, is reported in the literature under the name of Small Aorta Syndrome (SAS). Although it remains unclear whether SAS represents a separate entity, the small size of the distal aorta increases the risk for aortoiliac occlusive disease. A 41-year old white woman was admitted with acute digital ischemia of the left foot. She had positive lupus anticoagulant and IgG anti-cardiolipin antibodies (61 UI/mL), but antinuclear antibodies and anti-ds-DNA antibodies were negative. She previously had two deep venous thromboses of the legs and, despite the oral anticoagulant therapy, pulmonary embolism occurred. Shortly thereafter, abdominal angio-magnetic resonance imaging suggested that the infra-renal aorta was narrowed more than 50%, without thrombotic occlusion of the terminal aorta and common iliac arteries. These findings were compatible with the features of SAS. There were no atherosclerotic changes in the artery wall and no other prediposing risk factors such as smoking, oral contraceptive or hyperlipidemia. After adequate anticoagulation and intravenous prostacyclin treatment the patient's symptoms and the ischemic lesions improved markedly. To our knowledge this is the first report of the association of SAS and primary APS. The occurrence of SAS in patients with APS may dramatically increase the risk of trombothic events.

PAR4, but not PAR1, signals human platelet aggregation via Ca2+ mobilization and synergistic P2Y12 receptor activation

Regulation of platelet activation plays a central role in hemostasis and pathophysiological processes such as coronary artery disease. Thrombin is the most potent activator of platelets. Human platelets express two thrombin receptors, PAR1 and PAR4, both of which signal platelet activation. Evidence is lacking on the mechanism by which PAR1 and PAR4 may differentially signal platelet aggregation. Here we show that at the relatively high concentration of agonist most likely found at the site of a local thrombus, dual inhibition of the P2Y12 receptor and calcium mobilization result in a complete inhibition of PAR4-induced aggregation, while having no effect on either thrombin or PAR1-mediated platelet aggregation. Both PAR1- and PAR4mediated aggregation are independent of calcium mobilization. Furthermore, we show that P2Y12 receptor activation is not required for protease-activated receptor-mediated aggregation at higher agonist concentrations and is only partially required for Rap1 as well as GPIIbIIIa activation. P2Y12 receptor inhibitors clinically in use such as clopidogrel are postulated to decrease platelet aggregation through partial inhibition of PAR1 signaling. Our data, however, indicate that at high local concentrations of thrombin, it is the signaling through PAR4 rather than PAR1 that may be regulated through purinergic feedback. Thus, our data identify an intra-platelet mechanism that may function as a future site for therapeutic intervention.

Effect of varying the ratio of n-6 to n-3 fatty acids by increasing the dietary intake of alpha-linolenic acid, eicosapentaenoic and docosahexaenoic acid, or both on fibrinogen and clotting factors VII and XII in persons aged 45-70 y: the OPTILIP study

BACKGROUND

Elevated fibrinogen, activated factor XII (FXIIa), and factor VII coagulant activity (FVIIc) are associated with higher risk of fatal ischemic heart disease. This study tested the hypothesis that lowering the dietary ratio of n-6 to n-3 polyunsaturated fatty acids (n-6:n-3) would modify these risk factors in older men and women.

OBJECTIVE

The objective of the study was to measure fasting hemostatic risk factors and postprandial changes in activated FVII (FVIIa) concentrations after a 6-mo alteration in dietary n-6:n-3.

DESIGN

In a randomized, parallel design in 258 subjects aged 45-70 y, we compared 4 diets providing 6% of energy as polyunsaturated fatty acids at an n-6:n-3 between 5:1 and 3:1 with a control diet that had an n-6:n-3 of 10:1. The diets were enriched in alpha-linolenic acid, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, or both.

RESULTS

Fasting and 3-h plasma triacylglycerol concentrations were 11.1% and 7.2% lower with the diet that had an n-6:n-3 of approximately 3:1 and that was enriched with EPA and DHA than with the other diets. Fasting fibrinogen, FXIIa, FVIIc, FVIIa, and FVII antigen and postprandial FVIIa were not influenced by the diets. Avoiding foods high in fat the day before measurement decreased FVIIc and FVIIa by 8% and 19.2%, respectively. A test meal containing 50 g fat resulted in a mean 47% (95% CI: 42%, 52%) increase in FVIIa 6 h later, but the response did not differ by n-6:n-3.

CONCLUSION

Decreasing the n-6:n-3 to approximately 3:1 by increasing the intake of EPA and DHA lowers fasting and postprandial plasma triacylglycerol concentrations in older persons but does not influence hemostatic risk factors.

A case report of a new pulmonary embolism occurring in a patient receiving continuous infusion of recombinant activated protein C

BACKGROUND

There are no guidelines governing the concomitant use of recombinant human activated protein C (rhAPC) and deep venous thrombosis/pulmonary embolism (DVT/PE) prophylaxis in critically ill patients. It is unknown if rhAPC provides any protection against DVT/PE in this population of patients.

METHODS

Case report.

RESULTS

This report describes the first case of a radiographically demonstrated pulmonary embolism occurring in a patient receiving continuous therapeutic infusion of rhAPC.

CONCLUSION

The administration of rhAPC alone may not be sufficient DVT/PE prophylaxis in high risk patients. The risks associated with concomitant anticoagulation and rhAPC therapy are unknown. Further research is necessary to determine the safest and most effective regimen for DVT/PE prophylaxis in patients receiving rhAPC.

TNF-alpha mediated suppression of tissue type plasminogen activator expression in vascular endothelial cells is NF-kappaB- and p38 MAPK-dependent

BACKGROUND

Several proatherothrombotic conditions are associated with enhanced levels of circulating proinflammatory cytokines, which are believed to impair endothelial fibrinolytic capacity.

OBJECTIVE

This study aims at investigating how tumor necrosis factor (TNF)-alpha regulates endothelial gene expression of the key fibrinolytic enzyme tissue-type plasminogen activator (t-PA).

METHODS

Cultured human umbilical vein endothelial cells were pretreated with selective inhibitors of the three major inflammatory signaling pathways activated by TNF-alpha; the nuclear factor kappa-B (NF-kappaB), the p38 mitogen-activated protein kinase (p38 MAPK), and the c-jun N-terminal kinase (JNK) pathways. Following TNF-alpha stimulation, effects on t-PA gene expression were evaluated with real-time reverse transcriptase polymerase chain reaction and interactions of nuclear proteins with potential gene regulatory elements were studied with electrophoretic mobility shift assays.

RESULTS

Approximately 50% suppression of t-PA gene expression was observed after prolonged stimulation with TNF-alpha (> or =24 h). The repression was shown to be preferentially dependent on NF-kappaB activation, but also on p38 MAPK signaling. Further, we provide evidence for a TNF-alpha induced binding of NF-kappaB to the recently described kappaB site in the t-PA gene and of cyclic adenosine monophosphate response element binding protein (CREB) to the t-PA CRE-like site.

CONCLUSIONS

We conclude that TNF-alpha impairs fibrinolytic capacity in vascular endothelial cells by a NF-kappaB and p38 MAPK-dependent suppression of t-PA. This mechanism sheds a light on how inflammation contributes to the pathogenesis of cardiovascular diseases.

The coagulopathy of trauma versus disseminated intravascular coagulation

The coagulopathy of trauma is a syndrome of non-surgical bleeding from mucosal lesions, serosal surfaces, and wound and vascular access sites associated with serious injury, hypothermia, acidosis, hemodilution, and occasionally with classic disseminated intravascular coagulation (DIC). It can be largely explained by the effects of cold on platelet function, the effect of pH on coagulation factor activity, and the dilutional effects of resuscitation fluids and conventional blood products. DIC occurs acutely after trauma when brain, fat, amniotic fluid, or other strong thromboplastins enter the circulation. It occurs subacutely when endothelial inflammation or failure reduces clearing of activated coagulation factors allowing microthrombi to cause secondary injury. The coagulopathy of trauma should be anticipated in massive transfusion situations. Early treatment with plasma can delay its onset. The underlying mechanisms should be confirmed with laboratory testing.

Conjugated equine estrogens and peripheral arterial disease risk: the Women's Health Initiative

BACKGROUND

Estradiol reduced progression of ultrasonographic carotid disease in a randomized trial. No trials of unopposed estrogen for prevention of lower extremity arterial disease or aortic aneurysm have been conducted.

METHODS

The Estrogen Alone trial randomized 10739 postmenopausal women with prior hysterectomy, mean age 63.6 +/- 7.3 years, to conjugated equine estrogens (CEE 0.625 mg/d) or placebo and documented health outcomes over an average of 7.1 +/- 1.6 years.

RESULTS

A trend toward increased risk of peripheral arterial events with CEE was observed (hazard ratio [HR] 1.32, 95% CI 0.99-1.77). Carotid arterial events (HR 1.19, 95% CI 0.82-1.74), lower extremity arterial events (HR 1.41, 95% CI 0.86-2.32), and abdominal aortic aneurysm (HR 2.40, 95% CI 0.92-6.23) were more frequent, but not individually significant, in the CEE group. However, the composite of lower extremity arterial disease/abdominal aortic aneurysm was significantly more frequent among women assigned to CEE (HR 1.63, 95 % CI 1.05-2.51). In subgroup analyses, no clear pattern of risk with CEE was apparent by age or by time since menopause.

CONCLUSIONS

Unopposed CEE conferred no protection against peripheral arterial disease among generally healthy postmenopausal women; in fact, there was a suggestion of increased risk.

In situ assays demonstrate that interferon-gamma suppresses infection-stimulated hepatic fibrin deposition by promoting fibrinolysis

BACKGROUND

Inflammatory cytokines potently impact hemostatic pathways during infection, but the tissue-specific regulation of coagulation and fibrinolysis complicates studies of the underlying mechanisms.

METHODS AND RESULTS

Here, we describe assays that quantitatively measuring prothrombinase (PTase), protein C-ase (PCase) and plasminogen activator (PA) activities in situ, thereby facilitating studies of tissue-specific hemostasis. Using these assays, we investigate the mechanisms regulating hepatic fibrin deposition during murine toxoplasmosis and the means by which interferon-gamma (IFN-gamma) suppresses infection-stimulated fibrin deposition. We demonstrate that Toxoplasma infection upregulates hepatic PTase, PCase, and PA activity. Wild type and gene-targeted IFN-gamma-deficient mice exhibit similar levels of infection-stimulated PTase activity. By contrast, IFN-gamma-deficiency is associated with increased PCase activity and reduced PA activity during infection. Parallel analyses of hepatic gene expression reveal that IFN-gamma-deficiency is associated with increased expression of thrombomodulin (TM), a key component of the PCase, increased expression of thrombin-activatable fibrinolysis inhibitor (TAFI), a PC substrate, and reduced expression of urokinase PA (u-PA).

CONCLUSIONS

These findings suggest that IFN-gamma suppresses infection-stimulated hepatic fibrin deposition by suppressing TM-mediated activation of TAFI, thereby destabilizing fibrin deposits, and concomitantly increasing hepatic u-PA activity, thereby promoting fibrinolysis. We anticipate that further application of these in situ assays will improve our understanding of tissue-specific hemostasis, its regulation by cytokines, and its dysregulation during coagulopathy.

Incidence and risk factors for development of venous thromboembolism in Indian patients undergoing major orthopaedic surgery: results of a prospective study

INTRODUCTION

The incidence of venous thromboembolism (VTE) in Western populations undergoing major orthopaedic surgery without any thromboprophylaxis has been reported to range from 32% to 88%. There is however limited information on incidence of VTE in Indian patients and most of the Indian patients undergoing these surgeries do not receive any form of prophylaxis regardless of their risk profile.

METHODS

A prospective study was performed on 147 patients undergoing major orthopaedic surgery for total knee replacement (TKR), total hip replacement (THR), and proximal femur fracture fixation (PFF) without any prophylaxis. These patients were profiled for presence of the known risk factors responsible for development of VTE. A duplex ultrasound on both lower limbs was done 6 to 10 days after surgery. Twenty three patients underwent THR, 22 patients underwent TKR, and 102 underwent surgery for PFF. The patients were assessed clinically for any signs of deep venous thrombosis (DVT) and pulmonary embolism (PE). A helical CT scan was done in case of suspicion of PE and a duplex ultrasound was done in case of clinical suspicion of DVT irrespective of the stage of study.

RESULTS

The overall incidence of VTE was 6.12% and that of PE was 0.6%. The risk factors that were found to be significantly responsible for development of VTE (p < 0.05) were: immobility greater than 72 hours, malignancy, obesity, surgery lasting more than two hours.

CONCLUSION

The study reconfirms the belief that DVT has a lower incidence in Indian patients as compared with other ethnic groups.

Interleukin-1β enhances the angiotensin-induced expression of plasminogen activator inhibitor-1 through angiotensin receptor upregulation in human astrocytes

Plasminogen activator inhibitor-1 (PAI-1) regulates not only fibrinolysis but extracellular matrix remodeling, and angiotensin II is known to play an important role in controlling the expression of PAI-1 in astrocytes. We have studied the effect of interleukin-1beta (IL-1beta), one of major cytokines also active in the nervous system, on the angiotensin II-induced expression of PAI-1 in human astrocytes. Cultures of normal human astrocytes were stimulated with IL-1beta and angiotensin II, and the expression of mRNAs for angiotensin II type 1 receptor (AT1) and PAI-1 was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or real-time quantitative PCR. PAI-1 protein in astrocyte-conditioned medium was measured by enzyme-linked immunosorbent assay (ELISA). IL-1beta enhanced the expression of AT1 in astrocytes in time- and concentration-dependent manners. After 24-h stimulation, 10 ng/ml IL-1beta and 10 nM angiotensin II increased the levels of PAI-1 protein in astrocyte-conditioned medium by 1.9-fold and 1.8-fold of the basal value, respectively. There was no synergistic effect when the cells were stimulated simultaneously with IL-1beta and angiotensin II. When the cells were stimulated, with angiotensin II, 16 h after the stimulation with IL-1beta, the production of PAI-1 was enhanced by 1.4-fold as compared to the cells stimulated only with IL-1beta. CV-11794, an AT1 antagonist, inhibited the enhanced PAI-1 production in response to angiotensin II. We conclude that IL-1beta increases angiotensin II-induced PAI-1 secretion by astrocytes through the induction of AT1, and the enhanced secretion of PAI-1 may modulate functions of plasminogen activators in the nervous system.

Cardiopulmonary bypass and mitral valve replacement during pregnancy

Gravid patient cardiopulmonary bypass remains a high-risk procedure with regard to fetal preservation. Maternal mortality is similar to that of the nonpregnant female at 1.5-5%. However, fetal mortality remains high at 16-33%, with an average of 19% over the past 25 years, with no correlation to gestational age. Teratogenesis is a major consideration in the first trimester. Variations in the timing of surgical intervention, gestational age, maternal health status, type of procedure, pre- or postorganogenesis, perfusion protocol, and pharmaceutical therapy are all factors that can influence fetomaternal outcome. In this report, we present a literature review along with our experience of a 26-year-old female who developed complications with her pregnancy at approximately 17 weeks gestation, with adverse neurological sequelae. The patient was 152 cm in height and weighed 48 kg, with a calculated body surface area of 1.40 M2. She had no prior history of cardiac disease and, upon admission to our institution, presented with a declining health status in pulmonary edema and was treated medically, with an ultimate requirement for mitral valve replacement. The total cardiopulmonary bypass time was 99 min with an aortic crossclamp time of 83 min. The literature, as expected, is limited to case reports and reviews since a controlled clinical trial during pregnancy is nonexistent, using extracorporeal circulation. This greatly challenges the medical staff in managing such difficult cases, with an incidence of heart disease during pregnancy of 1.2-3.7%.

A case of reversible posterior leukoencephalopathy syndrome caused by transient hypercoagulable state induced by infection

We report a normotensive case of reversible posterior leukoencephalopathy syndrome caused by transient hypercoagulable state. Hypertension is the main risk factor for reversible posterior leukoencephalopathy syndrome, which is believed to occur as a result of high blood pressure-related dysfunction of cerebrovascular endothelial cells, because it commonly appears in hypertensive emergency. However, in this completely normotensive case, the typical clinical findings of reversible posterior leukoencephalopathy syndrome were triggered by transient hypercoagulable state without any blood pressure variation. The case was successfully treated with anticoagulation therapy using heparin. Thus, this case indicates that reversible posterior leukoencephalopathy syndrome is induced by cerebrovascular endothelial dysfunction, which is induced not only by high blood pressure but also hemostatic dysfunction.

Endothelial cell heterogeneity and atherosclerosis

Vascular diseases are the most common causes of morbidity and mortality in the Western world. These conditions, whether they involve small and/or large vessels, invariably manifest as localized lesions within the vascular tree. For example, atherosclerosis preferentially affects arteries at branch points, the outer wall of bifurcations, and the inner walls of curvatures. An important question is how systemic alterations in blood-borne factors (eg, those associated with cardiac risk factors) result in focal vasculopathy. A clue to the answer lies in the complex spatial and temporal dynamics of the endothelium. The goal of this review is to highlight concepts of endothelial cell heterogeneity and to apply these principles to an understanding of the pathogenesis, diagnosis, and treatment of atherosclerosis.

Atherothrombosis and high-risk plaque: part I: evolving concepts

Atherothrombosis is a complex disease in which cholesterol deposition, inflammation, and thrombus formation play a major role. Rupture of high-risk, vulnerable plaques is responsible for coronary thrombosis, the main cause of unstable angina, acute myocardial infarction, and sudden cardiac death. In addition to rupture, plaque erosion may also lead to occlusive thrombosis and acute coronary events. Atherothrombosis can be evaluated according to histologic criteria, most commonly categorized by the American Heart Association (AHA) classification. However, this classification does not include the thin cap fibroatheroma, the most common form of high-risk, vulnerable plaque. Furthermore, the AHA classification does not include plaque erosion. As a result, new classifications have emerged and are reviewed in this article. The disease is asymptomatic during a long period and dramatically changes its course when complicated by thrombosis. This is summarized in five phases, from early lesions to plaque rupture, followed by plaque healing and fibrocalcification. For the early phases, the role of endothelial dysfunction, cholesterol transport, high-density lipoprotein, and proteoglycans are discussed. Furthermore, the innate and adaptive immune response to autoantigens, the Toll-like receptors, and the mechanisms of calcification are carefully analyzed. For the advanced phases, the role of eccentric remodeling, vasa vasorum neovascularization, and mechanisms of plaque rupture are systematically evaluated. In the final thrombosis section, focal and circulating tissue factor associated with apoptotic macrophages and circulatory monocytes is examined, closing the link between inflammation, plaque rupture, and blood thrombogenicity.

Antiplatelets in Stroke Prevention: The MATCH Trial

Antiplatelet drugs have an established efficacy in the secondary prevention of ischemic stroke. The recent results of the CAPRIE, CURE, and CREDO studies formed the rationale for the MATCH, designed to test whether the association of clopidogrel and aspirin was better than clopidogrel alone for the prevention of vascular events among high-risk ischemic cerebrovascular patients. Although the benefits were outweighed for a higher bleeding risk in the combination group, this study will provide important insight for upcoming trials in other to determine what populations might mostly benefit from these drugs for the secondary prevention of stroke in the future.

Stimulated Tissue Plasminogen Activator Release as a Marker of Endothelial Function in Humans

The initiation, modulation, and resolution of thrombus associated with eroded or unstable coronary plaques are critically dependent on the efficacy of endogenous fibrinolysis. This is dependent on the cellular function of the surrounding endothelium and vascular wall. In particular, the acute release of tissue plasminogen activator from the endothelium makes an important contribution to the defense against intravascular thrombosis. Here, we describe the rationale and methodology for, and clinical relevance of, assessing acute endothelial tissue plasminogen activator release in humans. The investigation of endothelial fibrinolytic function has the potential to provide major new insights into the pathophysiology of cardiovascular disease, and to shape future therapeutic interventions.