Vascular-bed--specific hemostasis and hypercoagulable states

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.

Inhibition of Factor Xa : a potential target for the development of new anticoagulants

Anticoagulant therapy plays an important role in the prevention and treatment of pathologic arterial and venous thrombosis. There is increasing enthusiasm in the inhibition of Factor Xa as a target to achieve therapeutic anticoagulation because of its central and 'upstream' position in the coagulation process. The indirect, selective, parenteral Factor Xa inhibitor fondaparinux sodium (synthetic pentasaccharide) has been studied extensively in the prevention and treatment of venous thromboembolism. In an overview of four studies in patients undergoing major orthopedic surgery, fondaparinux sodium was associated with a 55% reduction in recurrent thromboembolism, albeit with a modest increase in bleeding. Preliminary results from phase II studies of fondaparinux sodium in patients with ST-elevation and non-ST-elevation acute coronary syndromes have been promising and have led to the initiation of two large phase III trials, which are currently underway. Idraparinux sodium, a long-acting synthetic pentasaccharide, is currently being investigated as a once-weekly alternative to other long-term anticoagulants. DX-9065a and razaxaban are two of many direct selective Factor Xa inhibitors currently in development. DX-9065a has been studied in phase II trials in patients undergoing percutaneous coronary intervention and in those with non-ST-elevation acute coronary syndromes. Razaxaban has been studied in a phase II trial in patients who have undergone orthopedic surgery. Data from these trials, although preliminary and based on small numbers of patients, suggest that direct selective Factor Xa inhibition may provide effective anticoagulation, perhaps without excessive bleeding. Inhibition of Factor Xa is a promising target for the prevention and treatment of thrombosis in both the venous and arterial circulation. Ongoing investigation with numerous oral and parenteral inhibitors of Factor Xa will establish the potential of Factor Xa as a target for therapeutic anticoagulation.

Tissue factor-dependent coagulation is preferentially up-regulated within arterial branching areas in a baboon model of Escherichia coli sepsis

Endothelium plays a critical role in the pathobiology of sepsis by integrating systemic host responses and local rheological stimuli. We studied the differential expression and activation of tissue factor (TF)-dependent coagulation on linear versus branched arterial segments in a baboon sepsis model. Animals were injected intravenously with lethal doses of Escherichia coli or saline and sacrificed after 2 to 8 hours. Whole-mount arterial segments were stained for TF, TF-pathway inhibitor (TFPI), factor VII (FVII), and markers for endothelial cells (ECs), leukocytes, and platelets, followed by confocal microscopy and image analysis. In septic animals, TF localized preferentially at branches, EC surface, leukocytes, and platelet aggregates and accumulated in large amounts in the subendothelial space. FVII strongly co-localized with TF on ECs and leukocytes but less so with subendothelial TF. TFPI co-localized with TF and FVII on endothelium and leukocytes but not in the subendothelial space. Focal TF increases correlated with fibrin deposition and increased endothelial permeability to plasma proteins. Biochemical analysis confirmed that aortas of septic baboons expressed more TF mRNA and protein than controls. Branched segments contained higher TF protein levels and coagulant activity than equivalent linear areas. These data suggest that site-dependent endothelial heterogeneity and rheological factors contribute to focal procoagulant responses to E. coli.

[Acute coronary syndrome in the prehospital phase]

Cardiovascular diseases are the number one cause of death in Germany. In 2002 about 70,000 people died of acute myocardial infarction (AMI) and of these 37% died before arrival at hospital which underlines the relevance of adequate prehospital care. The generic term acute coronary syndrome (ACS) was introduced because a single pathomechanism accounts for the different forms and comprises unstable angina pectoris (iAP), non-ST-elevation myocardial infarction (NSTEMI), ST-elevation myocardial infarction (STEMI) and sudden cardiac death (SCD). Characteristic features are retrosternal pain, vegetative symptoms and radiation of pain into the adjoining regions. Further differentiation can only be achieved by the 12-lead ECG, as cardiac-specific enzymes do not play a role in prehospital decisions. Prehospital delays should be avoided, history and physical examination should be brief but focused, vital parameters should be assessed and monitored. Basic treatment for ACS should comprise inhalative oxygen, nitrates, morphine, aspirin and beta-blockers. If STEMI is diagnosed, patients with symptoms <12 h should undergo fibrinolytic therapy unless there is primary percutaneous coronary intervention (PCI) available within 90 min or if contraindicated. Heparin should be given to patients with STEMI depending on the choice of fibrinolytic agent, it otherwise results in a higher risk of bleeding, but in patients with iAP or NSTEMI it reduces mortality. All patients must be accompanied by the emergency physician during transportation and should be brought to a hospital with primary PCI, especially those with complicated ACS. Treatment of complications depends largely on the type, persistence and severity.

Tissue-specific hemostasis in mice

Blood coagulation is essential to maintain hemostasis in organisms with a vascular network. Formation of a fibrin-rich clot at a site of vessel injury is a highly complex process that is orchestrated by the coagulation protease cascade. This cascade is regulated by 3 major anticoagulant pathways. Removal of a clot is mediated by the fibrinolytic system. Defects in the regulation of clot formation lead to either hemorrhage or thrombosis. Tissue factor, the primary cellular initiator of blood coagulation, is a transmembrane receptor that is expressed in a tissue-specific manner. The 3 major anticoagulants are tissue factor pathway inhibitor, antithrombin, and protein C, the latter requiring a transmembrane receptor called thrombomodulin for its activation. Tissue factor pathway inhibitor and thrombomodulin are expressed by endothelial cells in a tissue-specific manner, whereas antithrombin and protein C circulate in the plasma. Fibrinolysis requires the activation of plasminogen to plasmin, which is mediated by tissue-type plasminogen activator and urokinase-type plasminogen activator. Interestingly, tissue-type plasminogen activator is expressed by a subset of endothelial cells of discrete size and location. These observations, together with the phenotypes of mice that have defects in the procoagulant, anticoagulant, and fibrinolytic pathways, indicate that hemostasis is regulated in a tissue-specific manner.

Sepsis and coagulation

The host response to infection is a highly complex yet well-orchestrated process that involves an elaborate array of soluble mediators and cells. Normally, the host response prevails in containing and eliminating the pathogenic threat. When excessive or sustained, however, the host response may "turn on its bearer" and lead to organ dysfunction. Severe sepsis is invariably associated with activation of primary and secondary hemostasis. This article describes sepsis-associated changes in coagulation, discusses the putative role for these changes in pathogenesis of the sepsis syndrome, and outlines current diagnostic and therapeutic strategies.

In vitro procoagulant activity induced in endothelial cells by chemotherapy and antiangiogenic drug combinations: modulation by lower-dose chemotherapy

One of the emerging problems concerning the use of antiangiogenic drugs, when used in combination with certain chemotherapy regimens, is enhanced rates and severity of adverse clotting events. For as yet unknown reasons, certain drugs and particular combinations can induce an elevated incidence of thromboembolic events in treated cancer patients [e.g., SU5416, a vascular endothelial cell growth factor receptor-2 (VEGFR-2) antagonist, when combined with gemcitabine and cisplatin (CDDP)]. Such results highlight the need to develop assays capturing the essence of enhanced clot formation under such combination treatment and which may have predictive potential as well. Here, we report the possibility of such an assay (i.e., the ratio of tissue factor over tissue factor pathway inhibitor expression or activity in cultured human endothelial cells calculated as a coagulation index). A marked increase in coagulation index was observed after exposure to SU5416 and the CDDP/gemcitabine chemotherapy combination in contrast to either of these treatments used alone. Substitution of SU5416 with any one of ZD6474, SU6668, IMC-1121, a monoclonal antibody to VEGFR-2, or an antibody to VEGF (bevacizumab) did not cause a marked increase in the coagulation index, nor did the combination of SU5416 with 5-fluorouracil and leucovorin. Finally, we noted that reducing the concentrations of gemcitabine and CDDP (i.e., use of "metronomic dosing" in vitro) significantly attenuated the coagulation index increase induced by these drugs, suggesting that use of low-dose chemotherapy regimens might be an approach to consider for reducing the incidence of adverse clotting events associated with chemotherapy alone or in conjunction with antiangiogenic drug combination therapies.

PAI-1 and atherothrombosis

Plasminogen activator inhibitor-1 (PAI-1) is the major physiologic inhibitor of tissue-type plasminogen activator in plasma, and is elevated in a variety of clinical situations that are associated with increased risk of ischemic cardiovascular events. Recent insights into the biology of PAI-1 suggest that it is more than just an innocent bystander in the pathogenesis of ischemic heart disease. Elevated PAI-1 levels appear to increase the risk of atherothrombotic events and may also promote the progression of vascular disease. The development and testing of specific PAI-1 antagonists will enable basic and clinical investigators the opportunity to test the hypothesis that vascular PAI-1 excess promotes the development of intravascular thrombosis and atherosclerosis.

Patterns of inflammation associated with peripheral arterial disease: the InCHIANTI study

OBJECTIVE

To determine whether peripheral arterial disease is associated with high circulating levels of pro-inflammatory cytokines, independent of confounders.

METHODS

Participants were 955 men and women aged 60 years and older representative of the population in 2 Italian communities (107 with peripheral arterial disease). Measurements included the ankle brachial index, comorbidities, total cholesterol and high-density lipoprotein cholesterol (HDL-C) levels, and these inflammatory factors: albumin, alpha-2 macroglobulin, C-reactive protein, fibrinogen, interleukin (IL)-1beta, IL-1 receptor antagonist, IL-6, IL-6 receptor, IL-10, IL-18, tumor necrosis factor alpha, and transforming growth factor beta.

RESULTS

Adjusting for age, sex, body mass index, smoking, comorbidities, HDL-C, and total cholesterol, participants with peripheral arterial disease had higher levels of IL-1 receptor antagonist (147.97 vs 131.24 pg/mL, P = .002), IL-6 (1.65 vs 1.37 pg/mL, P = .026), fibrinogen (362.49 vs 345.50 mg/dL, P = .039), and C-reactive protein (3.18 vs 2.56 mg/dL, P = .043) compared with those without peripheral arterial disease. These associations were attenuated after additional adjustment for physical activity.

CONCLUSION

In a community population, peripheral arterial disease is associated with increased circulating levels of IL-6, IL-1 receptor antagonist, fibrinogen, and C-reactive protein compared to persons without peripheral arterial disease. Further study is needed to determine whether reducing levels of certain inflammatory factors lowers the incidence and progression of peripheral arterial disease.

Spatial and temporal dynamics of the endothelium

The endothelium is a highly metabolically active organ that is involved in many physiological processes, including the control of vasomotor tone, barrier function, leukocyte adhesion and trafficking, inflammation, and hemostasis. Endothelial cell phenotypes are differentially regulated in space and time. Endothelial cell heterogeneity has important implications for developing strategies in basic research, diagnostics and therapeutics. The goals of this review are to: (i) consider mechanisms of endothelial cell heterogeneity; (ii) discuss the bench-to-bedside gap in endothelial biomedicine; (iii) revisit definitions for endothelial cell activation and dysfunction; and (iv) propose new goals in diagnosis and therapy. Finally, these themes will be applied to an understanding of vascular bed-specific hemostasis.

Hypercoagulable states and stroke: a selective review

Blood disorders have been implicated in approximately 5% to 10% of ischemic stroke, with an increased frequency in younger patients. Most disorders are associated with an increased thrombotic tendency and, therefore, an increased risk of ischemic stroke. Less commonly, a bleeding diathesis may predispose a patient to intracranial hemorrhage. While many conditions predisposing to thrombosis have been associated with stroke, there are relatively few prospective, epidemiological studies addressing hypercoagulable states and arterial stroke compared with the number of studies on the genetic thrombophilias, which are predominantly associated with venous thrombosis. When ordering tests of coagulation in stroke patients, one should keep in mind whether the results will influence therapy and/or patient outcome. It is generally not advocated to screen all stroke patients for a "hypercoagulable workup". Typically, patients to be screened for coagulation defects will have a prior history of one or more unexplained thromboembolic events. The yield for diagnosing a hypercoagulable state is typically greatest for young stroke patients or those with a family history of thrombosis and who have no other explanations for their stroke (cryptogenic stroke). The yield in typically low in unselected ischemic stroke patients and older patients. Treatment of a first stroke with a documented hypercoagulable state is typically long-term or indefinite duration warfarin, although there is a paucity of clinical trial data supporting this clinical approach.

Obesity enhances the induction of plasminogen activator inhibitor-1 by restraint stress: a possible mechanism of stress-induced renal fibrin deposition in obese mice

BACKGROUND AND OBJECTIVES

Cardiovascular/thrombotic diseases are frequently induced by a variety of stressors. Obese patients are susceptible to thrombotic diseases associated with stress, but the underlying mechanism is still unknown. We have begun to investigate the expression of a primary inhibitor of fibrinolysis, plasminogen activator inhibitor-1 (PAI-1), in association with tissue thrombosis, using restraint-stressed obese mice.

METHODS AND RESULTS

We analyzed the expression of PAI-1 after restraint (immobilization) stress in genetically obese mice in comparison with their lean counterparts. Dramatic increases in PAI-1 antigen in plasma and in tissue extracts were observed in the obese mice exposed to restraint stress. The induction of PAI-1 mRNA by stress in the tissues was also pronounced in the stressed obese mice as compared with the lean mice, especially in the hearts and adipose tissues. In situ hybridization analysis revealed that strong signals for PAI-1 mRNA were localized in the adipocytes, cardiovascular endothelial cells, and renal glomerular cells of the stressed obese mice. Histological examination revealed that renal glomerular fibrin deposition was detected only in the obese mice after 2 h of restraint stress.

CONCLUSIONS

Obesity enhances the stress-mediated PAI-1 induction in the blood and tissues. This phenomenon may be associated with the increased risk of stress-induced renal fibrin deposition in obese subjects.

Disseminated Intravascular Coagulation: What's New?

Disseminated intravascular coagulation (DIC) is a syndrome characterized by a systemic activation of coagulation leading to the intravascular deposition of fibrin in the (micro) vasculature and the simultaneous consumption of coagulation factors and platelets. The occurrence of microvascular thrombosis as a consequence of DIC is underscored by pathological, experimental and clinical findings, demonstrating a link between DIC and organ dysfunction. Pathogenetic pathways that play a role in the development of DIC include tissue factor-dependent activation of coagulation, defective physiological anticoagulant pathways (such as the antithrombin system and the protein C system), and impaired fibrinolysis, caused by elevated levels of plasminogen activator inhibitor type 1. Novel therapeutic strategies are based on current insights into the pathogenesis of DIC, and include anticoagulant strategies (eg, directed at tissue factor) and strategies to restore physiological anticoagulant pathways (such as activated protein C concentrate).

Effect of plasma exchange on cytokines measured by multianalyte bead array in thrombotic thrombocytopenic purpura

The serum cytokine profile in thrombotic thrombocytopenic purpura (TTP) has not been extensively characterized. In this pilot study, a novel technique was utilized to evaluate multiple cytokines in patients with idiopathic TTP during a course of plasma exchange (PE). Single serum samples were obtained from five TTP patients before and after each PE. Random sera were obtained from nine healthy volunteers who served as controls. The samples were evaluated for 13 cytokines (IL-1B, IL-2 , IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IFN-gamma, GM-CSF, and TNF-alpha) using the Luminex bead array (LINCOplex) multianalyte detection system that permits simultaneous detection of multiple cytokines from a single sample. Each patient received 4-6 PEs (Cobe Spectra) with 3.0-4.0 L of fresh frozen plasma as replacement fluid. Four of 5 patients received corticosteroids prior to and during PE. The control group did not receive steroids. Baseline values for IL-8 (182.9 vs. 6.5 pg/mL, P < 0.05) and TNF-alpha (11.4 vs. 0.9 pg/mL, P < 0.001) were significantly higher in TTP patients compared with controls. Other tested cytokines were not significantly different between the two groups. Comparison of cytokine values pre- and post-PE indicate a substantial decrease after each PE. However, cytokines rebounded to abnormal levels by the following day. There was no correlation between cytokines and serum LDH or platelet count. These findings suggest that certain cytokines, particularly IL-8 and TNF-alpha, are altered in TTP, and this may indicate a direct role in TTP pathogenesis, reflect ongoing tissue injury, or perhaps indicate an inadequate attempt to limit tissue injury.

Homozygosity for Factor V Leiden Leads to Enhanced Thrombosis and Atherosclerosis in Mice

Background— Activated protein C resistance due to factor V Leiden (FVL) is a common genetic risk factor for venous thrombosis in humans. Although the impact of FVL on the development of venous thrombosis is well established, its effect on arterial thrombosis and atherosclerosis is controversial.

Methods and Results— To determine the effect of the FVL mutation on arterial thrombosis in the mouse, wild-type ( Fv +/+ ), heterozygous FVL ( Fv Q /+ ), and homozygous FVL ( Fv Q/Q ) mice underwent photochemical carotid arterial injury to induce occlusive thrombosis. Fv Q/Q mice formed occlusive thromboses 27±3 minutes (n=7) after the onset of injury, which was significantly shorter than that observed for Fv +/+ mice (56±7 minutes, n=9, P <0.01), whereas Fv Q /+ mice (41±7 minutes, n=5) were intermediate ( P =0.5, compared with Fv +/+ ). To determine the source of FVL relevant to the enhanced vascular thrombosis, bone marrow transplantation experiments were performed between Fv +/+ and Fv Q/Q mice. Fv Q/Q mice transplanted with Fv +/+ bone marrow formed occlusive thromboses at 35±5 minutes (n=7, P <0.05 compared with Fv +/+ mice), whereas Fv +/+ mice transplanted with Fv Q/Q bone marrow occluded at 59±7 minutes (n=6, P <0.001 compared with Fv Q/Q mice). To assess the effect of the FVL mutation on the development of atherosclerosis, Fv Q/Q mice were crossed with the atherosclerosis-prone apolipoprotein E (ApoE)–deficient strain ( ApoE −/− ) to generate Fv Q/Q ,ApoE −/− mice. By 52 weeks of age, Fv Q/Q ,ApoE −/− mice (n=8) had developed more aortic atherosclerosis (40±6% lesion area) compared with Fv +/+ ,ApoE −/− mice (15±3% lesion area; n=12, P <0.02).

Conclusions— In conclusion, homozygosity for the FVL mutation in mice leads to enhanced arterial thrombosis and atherosclerosis. The source of the FVL leading to accelerated thrombosis appears to be circulating, non–platelet-derived plasma FVL.

Risk factors for thrombophilia in extrahepatic portal vein obstruction

Scant information exists on the role of thrombophilia in extrahepatic portal vein obstruction (EHPVO). We studied 65 patients with EHPVO, 500 with deep vein thrombosis (DVT) of the lower limbs, and 700 healthy controls referred for thrombophilia screening, including the search for gain-of-function mutations in genes encoding coagulation factor V (factor V Leiden) and prothrombin (prothrombin G20210A); antithrombin, protein C, and protein S deficiency; and hyperhomocysteinemia. At least one abnormality in the thrombophilia screening was found in 40% of patients with either EHPVO or lower limb DVT and in 13% of controls, for odds ratios of 4.0 (95% CI, 2.3-7.0) and 4.4 (95% CI, 3.3-5.9), respectively. Statistically significant associations with EHPVO were observed for the prothrombin G20210A mutation (odds ratio, 8.1; 95% CI, 3.8-17.5) and the deficiencies of antithrombin, protein C, or protein S taken together (odds ratio, 4.5; 95% CI, 1.1-18.0). The odds ratio for the prothrombin G20210A was approximately twice that for lower limb DVT. Patients with factor V Leiden had an odds ratio for EHPVO of 0.8 (95% CI, 0.1-6.4) and for lower limb DVT of 7.5 (95% CI, 4.4-13.0). The odds ratio for EHPVO in patients with hyperhomocysteinemia was 2.0 (95% CI, 0.9-4.9). At variance with lower limb DVT, oral contraceptive use was not associated with an increased risk of EHPVO. Myeloproliferative disorders were diagnosed in 35% of patients with EHPVO. In conclusion, the risk for EHPVO is increased in the presence of thrombophilia resulting from the prothrombin G20210A mutation and from the deficiencies of the naturally occurring anticoagulant proteins, but not from factor V Leiden.

Smad6s regulates plasminogen activator inhibitor-1 through a protein kinase C-beta-dependent up-regulation of transforming growth factor-beta

Plasminogen activator inhibitor-1 (PAI-1) is a serpin class protease inhibitor that plays a central role in the regulation of vascular function and tissue remodeling by modulating thrombosis, inflammation, and the extracellular matrix. A central mediator controlling PAI-1 is transforming growth factor-beta (TGF-beta), which induces its expression and promotes fibrosis. We have found that a unique member of the Smad family of signal transduction molecules, Smad6s, modulates the expression of PAI-1. Overexpression of Smad6s in endothelial cells increases promoter activity and PAI-1 secretion, and an antisense to Smad6s suppresses the induction of PAI-1 by TGF-beta. The effect of Smad6s on the PAI-1 promoter appeared to be the result of increase binding of the forkhead winged helix factor FoxD1 to a TGF-beta-responsive element. Furthermore, the effect of Smad6s on PAI-1 up-regulation and on FoxD1 binding was found to result from up-regulation of TGF-beta and could be inhibited by the blocking TGF-beta signaling with Smad7. The ability of Smad6s to regulate the TGF-beta promoter and subsequent PAI-1 induction was suppressed by a selective protein kinase C-beta (PKC-beta) inhibitor. Consistent with the in vitro data, we found that increased Smad6s in diseased vessels correlated with increased TGF-beta and PAI-1 levels. Overall, our results demonstrate that the level of Smad6s can alter the level of TGF-beta and the subsequent induction of PAI-1 via a FoxD1 transcription site. Furthermore, our data suggest that this process, which is up-regulated in diseased vessels, can be modulated by the inhibition of PKC-beta.

Drotrecogin alfa: a role in emergency department treatment of severe sepsis?

Human protein C is a serine protease that circulates in the blood as an inactive zymogen. It is converted to its active form by interaction with thrombomodulin on the endothelial wall. Activated protein C has a significant role in maintaining haemostasis, and is a major mechanism of controlling microvascular thrombosis. Recent reports describe the use of drotrecogin alfa (recombinant activated protein C) in severe sepsis, a condition relevant to emergency medicine. This review describes the physiology of the protein C pathway and its importance in sepsis. It will also focus on the use of drotrecogin alfa in sepsis, and its use in the ED.

A balance between tissue factor and tissue factor pathway inhibitor is required for embryonic development and hemostasis in adult mice

Inactivation of the murine tissue factor (TF) gene or tissue factor pathway inhibitor 1 (TFPI) gene results in embryonic lethality, indicating that both are required for embryonic development. We have shown that expression of low levels of TF from a transgene (hTF) rescues TF-null embryos. However, low-TF mice (mTF(-/-)/hTF+) have hemostatic defects in the uterus, placenta, heart, and lung. In this study, we hypothesized that the death of TFPI-/- embryos was due to unregulated TF/FVIIa activity and that the hemostatic defects in low-TF mice were due to insufficient TF expression. Therefore, we attempted to rescue TFPI-/- embryos by reducing TF expression, and to restore hemostasis in low-TF mice by abolishing TFPI expression. Intercrossing TFPI(+/-)/mTF(+/-)/hTF+/- mice generated close to the expected number of TFPI(-/-)/low-TF mice at weaning age from 128 offspring, indicating rescue of TFPI-/- embryos from embryonic lethality. Conversely, a decrease in TFPI levels dose-dependently prolonged the survival of low-TF mice and rescued the hemorrhagic defects in the lung and placenta but not in the heart or uterus. These results indicate that the correct balance between TF and TFPI in different organs is required to maintain hemostasis during embryonic development and in adult mice.

Drotrecogin alfa (activated) for the treatment of severe sepsis and septic shock

Coagulopathy and systemic inflammation are almost universal in patients with severe sepsis. Interaction between the two results in an intense inflammatory response and microthrombi formation in the vessels of multiple organs, resulting in organ dysfunction or severe sepsis. Recombinant human activated protein C, also known as drotrecogin alfa (activated), possesses anti-inflammatory, antithrombotic, and profibrinolytic properties. Treatment with drotrecogin alfa (activated) significantly reduces morbidity and mortality in patients with severe sepsis. An increased risk of bleeding during the infusion was the only side effect experienced. Recent data demonstrate that early administration of drotrecogin alfa (activated) is associated with lower mortality rates. Despite concern over its relatively high cost, analysis has demonstrated that recombinant human activated protein C is as cost-effective as other commonly used treatments in the intensive care unit.

Effects of drotrecogin alfa (activated) in human endotoxemia

In a phase III clinical trial, drotrecogin alfa (activated) was shown to improve survival and promote faster improvement of cardiovascular and respiratory dysfunction in patients with severe sepsis. To further examine mechanisms involved in the action of this drug, a healthy human endotoxin model was used. Healthy volunteers (eight per group) received drotrecogin alfa (activated) or placebo intravenously for 8 h in a randomized, double-blind, controlled manner. After 2 h of study drug infusion, endotoxin (2 ng/kg) was infused and measurement of physiologic responses and biomarkers continued for 24 h. Consistent with results from severe sepsis clinical trials, drotrecogin alfa (activated) improved mean arterial pressure during the period of infusion after endotoxin exposure. In contrast to severe sepsis clinical trials using drotrecogin alfa (activated) but similar to another human endotoxin study, no significant antithrombotic, profibrinolytic, or anti-inflammatory effects were observed. These results suggest a novel role for drotrecogin alfa (activated) in the human endotoxin model.

Extracorporeal therapies in non-renal disease: treatment of sepsis and the peak concentration hypothesis

In the setting of intensive care, patients with acute renal failure often present a clinical picture of the systemic inflammatory response syndrome (SIRS). SIRS can be caused by bacterial stimuli or by non-microbiological stimuli that induce a significant inflammatory response. When this response is exaggerated, the patient experiences multiple organ system failure and a condition of sepsis also defined as a systemic malignant inflammation. This is mostly characterized by an invasion of cytokines and other pro-inflammatory mediators into the systemic circulation where major biological effects take place, including vasopermeabilization, hypotension and shock. At the same time, the monocyte of the septic patient seems to be hyporesponsive to inflammatory stimuli to a certain extent. In this condition, the patient faces a situation of hyperinflammation but at the same time of immunodepression expressing a clinical entity defined as counter anti-inflammatory response syndrome. The general picture of the clinical disorder is therefore better characterized by an immunodysregulation than by a simple pro- or anti-inflammatory disorder. Due to the short half-life of cytokines and other mediators spilled over into the circulation, it is extremely difficult to approach the problem at the right moment with the right pharmacological agent. For these reasons, the peak concentration hypothesis suggests that continuous renal replacement therapies, due to their continuity and unspecific capacity of removal, might be beneficial in cutting the peaks of the concentrations of both pro- and anti-inflammatory mediators, restoring a situation of immunohomeostasis. Thus the patient may benefit from a lesser degree of immunodysregulation and he/she may restore a close-to-normal capacity of response to exogenous stimuli.

Endothelial cell activation by antiphospholipid antibodies

Antiphospholipid antibodies are mainly directed against beta 2 glycoprotein I, a phospholipid-binding protein expressed on endothelial cell membranes of different anatomical localizations and recognized by the specific autoantibodies. Antibody binding induces an endothelial activation both in in vitro and in vivo experimental models that might contribute to the prothrombotic state. Endothelial beta 2 glycoprotein I adhesion is mediated by the electrostatic interaction between its cationic phospholipid binding site and anionic structures on the cell membrane; however, binding to annexin II--the endothelial cell receptor for tissue plasminogen activator--plays also a role. Anti-beta-2 glycoprotein I antibodies up-regulate mRNA expression of pro-inflammatory mediators through NF-kappaB translocation and the signaling cascade triggered by Toll-like receptors. Because of the molecular mimicry between beta 2 glycoprotein I and viral/bacterial structures-the natural ligands for Toll-like receptors (TLR)-antibodies might cross-link the molecule associated to the receptors eventually triggering their signaling.

Risk Factors and Recurrence Rate of Primary Deep Vein Thrombosis of the Upper Extremities

BACKGROUND

One third of cases of upper-extremity deep vein thrombosis (DVT) are primary, ie, they occur in the absence of central venous catheters or cancer. Risk factors for primary upper-extremity DVT are not well established, and the recurrence rate is unknown.

METHODS AND RESULTS

We studied 115 primary upper-extremity DVT patients and 797 healthy controls for the presence of thrombophilia due to factor V Leiden, prothrombin G20210A, antithrombin, protein C, protein S deficiency, and hyperhomocysteinemia. Transient risk factors for venous thromboembolism were recorded. Recurrent upper-extremity DVT was evaluated prospectively over a median of 5.1 years of follow-up. The adjusted odds ratio for upper-extremity DVT was 6.2 (95% CI 2.5 to 15.7) for factor V Leiden, 5.0 (95% CI 2.0 to 12.2) for prothrombin G20210A, and 4.9 (95% CI 1.1 to 22.0) for the anticoagulant protein deficiencies. Hyperhomocysteinemia and oral contraceptives were not associated with upper-extremity DVT. However, in women with factor V Leiden or prothrombin G20210A who were taking oral contraceptives, the odds ratio for upper-extremity DVT was increased up to 13.6 (95% CI 2.7 to 67.3). The recurrence rate was 4.4% patient-years in patients with thrombophilia and 1.6% patient-years in those without thrombophilia. The hazard ratio for recurrent upper-extremity DVT in patients with thrombophilia compared with those without was 2.7 (95% CI 0.7 to 9.8).

CONCLUSIONS

Inherited thrombophilia is associated with an increased risk of upper-extremity DVT. Oral contraceptives increase the risk only when combined with inherited thrombophilia. The recurrence rate of primary upper-extremity DVT is low but tends to be higher in patients with thrombophilia than in those without.

Gene therapy in tissue-engineered blood vessels

Cardiovascular disease is the leading cause of morbidity and mortality in Western society. More than 1 million arterial bypass procedures are performed annually in the United States, where either autologous veins or synthetic grafts are used to replace arteries in the coronary or peripheral circulation. Tissue engineering of blood vessels from autologous cells has the potential to produce biological grafts for use in bypass surgery. Ex vivo development of vascular grafts also provides an ideal target of site-specific gene therapy to optimize the physiology of the developing conduit, and for the possible delivery of other therapeutic genes to a vascular bed of interest. In this article, we demonstrate that by using a novel retroviral gene delivery system, a target gene of interest can be specifically delivered to the endothelial cells of a developing engineered vessel. Further, we demonstrate that this technique results in stable incorporation of the delivered gene into the target endothelial cells for more than 30 days. These data demonstrate the utility of the retroviral gene delivery approach for optimizing the biologic phenotype of engineered vessels. This also provides the framework for testing an array of genes that may improve the function of engineered blood vessels after surgical implantation.

The contribution of inherited and acquired thrombophilic defects, alone or combined with antiphospholipid antibodies, to venous and arterial thromboembolism in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with an increased risk of venous (VTE) and arterial thromboembolism (ATE). Lupus anticoagulant (LA) and anticardiolipin antibodies (ACAs) are established risk factors. We assessed the contribution of deficiencies of antithrombin, protein C, total protein S, factor V Leiden, the prothrombin G20210A mutation and APC resistance, either alone or in various combinations with LA and/or ACAs, to the thrombotic risk in a cohort of 144 consecutive patients with SLE. Median follow-up was 12.7 years. VTE had occurred in 10% and ATE in 11% of patients. LA,ACAs, factor V Leiden, and the prothrombin mutation were identified as risk factors for VTE. Annual incidences of VTE were 2.01 (0.74-4.37) in patients with one of these disorders and 3.05 (0.63-8.93) in patients with 2 disorders. The risk of VTE was 20- and 30-fold higher, respectively, compared with the normal population. In contrast with LA and ACAs, thrombophilic disorders did not influence the risk of ATE. In conclusion, factor V Leiden and the prothrombin mutation contribute to the risk of VTE in patients with SLE, and potentiate this risk when one of these thrombophilic defects are combined with LA and/or ACAs.

Tissue plasminogen activator -7351C/T enhancer polymorphism is a risk factor for lacunar stroke

BACKGROUND AND PURPOSE

Occlusive thrombosis is an important component of small- and large-vessel ischemic stroke. Endogenous tissue plasminogen activator (TPA) is the primary mediator of intravascular fibrinolysis and is predominantly expressed by the endothelium of small vessels. The acute release of TPA is influenced by the TPA -7351C/T polymorphism and therefore may play an important role in the pathogenesis of lacunar stroke. In this study, we investigated the risk of lacunar and nonlacunar ischemic stroke associated with the TPA -7351C/T polymorphism.

METHODS

We conducted a case-control study of 182 cases of ischemic stroke and 301 community controls. Participants were evaluated for known cerebrovascular risk factors, and the TPA -7351C/T genotype was established by a polymerase chain reaction (PCR) method. Logistic regression was used to determine the risk of lacunar and nonlacunar ischemic stroke associated with the TPA -7351C/T polymorphism.

RESULTS

The prevalence of the TPA -7351 CC, CT, and TT genotypes were 46%, 45%, and 9% for controls and 41%, 46%, and 13% for stroke patients, respectively. After adjustment for known cerebrovascular risk factors, the TT genotype was significantly associated with ischemic stroke (OR: 1.9; 95% CI: 1.01 to 3.6). Stratification for stroke subtype showed a significant association between the TT genotype and lacunar stroke but not nonlacunar stroke (OR: 2.7; 95% CI: 1.1 to 6.7).

CONCLUSIONS

The TPA -7351C/T polymorphism is an independent risk factor for lacunar stroke. The findings suggest that impaired fibrinolysis may play a role in the pathogenesis of lacunar stroke.

Natural anticoagulant inhibitors: activated Protein C

Protein C is a vitamin-K-dependent zymogen, whose congenital deficiency state leads to increased risk for venous thrombosis. Activated Protein C (aPC) exerts its anticoagulant function by inhibiting the cofactors in the clotting cascade, Factors Va and VIIIa. In addition, aPC displays anti-inflammatory, anti-apoptotic and profibrinolytic activities. A recombinant form of human aPC (rhAPC) is the first drug reported to improve survival in patients with severe sepsis. The major toxicity associated with treatment is bleeding. Appropriate use of rhAPC depends on an understanding of its mechanisms of action and risk:benefit profile. The goals of this review are: to describe the Protein C pathway; to discuss the definitions, epidemiology and pathophysiology of severe sepsis; to provide a conceptual framework for understanding the role of rhAPC in this syndrome; and to address frequently asked questions about the day-to-day use of this agent.

Genetic and acquired thrombotic factors in chronic hepatitis C

OBJECTIVES

During the progression of chronic liver disease towards cirrhosis, morphological studies have shown a close association between parenchymal remodeling and obliterative lesions of intrahepatic small portal and hepatic veins. These lesions are highly suggestive of intrahepatic thrombotic events, which may have a key role in the pathogenesis of hepatic fibrosis. The aim of the study was to investigate thrombotic risk factors in chronic hepatitis C patients with different extent of liver fibrosis.

METHODS

The following thrombotic factors were evaluated in 68 hepatitis C patients with prothrombin activity >/= 80% (34 consecutive patients with extensive fibrosis and/or cirrhosis compared with 34 consecutive patients without extensive fibrosis and/or cirrhosis): factor V Leiden, G20210A prothrombin mutation, antithrombin, protein C and S deficiencies, hyperhomocysteinemia, elevated factor VIII level, and lupus anticoagulant.

RESULTS

Three thrombotic risk factors were significantly more frequent in patients with extensive fibrosis and/or cirrhosis than in those without extensive fibrosis: protein C deficiency present in 14 patients (41%) as compared with three patients (9%), p= 0.004; elevated factor VIII level present in 19 patients (56%) as compared with six patients (18%), p= 0.002; and hyperhomocysteinemia present in 10 patients (29%) as compared with two patients (6%), p= 0.023. The association of two or three prothrombotic factors was present in 19 patients (56%) with extensive fibrosis and/or cirrhosis as compared with one patient (3%) without extensive fibrosis and/or cirrhosis, p < 0.001.

CONCLUSION

Multiple thrombotic risk factors coexist frequently in patients with extensive fibrosis and early stage of cirrhosis. Their association with local inflammation could favor thrombotic events in the liver micro-circulatory bed.

Annexin II regulates fibrin homeostasis and neoangiogenesis in vivo

A central tenet of fibrinolysis is that tissue plasminogen activator-dependent (t-PA- dependent) conversion of plasminogen to active plasmin requires the presence of the cofactor/substrate fibrin. However, previous in vitro studies have suggested that the endothelial cell surface protein annexin II can stimulate t-PA-mediated plasminogen activation in the complete absence of fibrin. Here, homozygous annexin II-null mice displayed deposition of fibrin in the microvasculature and incomplete clearance of injury-induced arterial thrombi. While these animals demonstrated normal lysis of a fibrin-containing plasma clot, t-PA-dependent plasmin generation at the endothelial cell surface was markedly deficient. Directed migration of annexin II-null endothelial cells through fibrin and collagen lattices in vitro was also reduced, and an annexin II peptide mimicking sequences necessary for t-PA binding blocked endothelial cell invasion of Matrigel implants in wild-type mice. In addition, annexin II-deficient mice displayed markedly diminished neovascularization of fibroblast growth factor-stimulated cornea and of oxygen-primed neonatal retina. Capillary sprouting from annexin II-deficient aortic ring explants was markedly reduced in association with severe impairment of activation of metalloproteinase-9 and -13. These data establish annexin II as a regulator of cell surface plasmin generation and reveal that impaired endothelial cell fibrinolytic activity constitutes a barrier to effective neoangiogenesis.

Annexin II regulates fibrin homeostasis and neoangiogenesis in vivo

A central tenet of fibrinolysis is that tissue plasminogen activator-dependent (t-PA- dependent) conversion of plasminogen to active plasmin requires the presence of the cofactor/substrate fibrin. However, previous in vitro studies have suggested that the endothelial cell surface protein annexin II can stimulate t-PA-mediated plasminogen activation in the complete absence of fibrin. Here, homozygous annexin II-null mice displayed deposition of fibrin in the microvasculature and incomplete clearance of injury-induced arterial thrombi. While these animals demonstrated normal lysis of a fibrin-containing plasma clot, t-PA-dependent plasmin generation at the endothelial cell surface was markedly deficient. Directed migration of annexin II-null endothelial cells through fibrin and collagen lattices in vitro was also reduced, and an annexin II peptide mimicking sequences necessary for t-PA binding blocked endothelial cell invasion of Matrigel implants in wild-type mice. In addition, annexin II-deficient mice displayed markedly diminished neovascularization of fibroblast growth factor-stimulated cornea and of oxygen-primed neonatal retina. Capillary sprouting from annexin II-deficient aortic ring explants was markedly reduced in association with severe impairment of activation of metalloproteinase-9 and -13. These data establish annexin II as a regulator of cell surface plasmin generation and reveal that impaired endothelial cell fibrinolytic activity constitutes a barrier to effective neoangiogenesis.

New approaches to the treatment of sepsis

The clinical spectrum of sepsis, severe sepsis, and septic shock is responsible for a growing number of deaths and excessive health care expenditures. Until recently, despite multiple clinical trials, no intervention provided a beneficial outcome in septic patients. Within the last 2 years, studies that involved drotrecogin alfa (activated), corticosteroid therapy, and early goal-directed therapy showed efficacy in those with severe sepsis and septic shock. These results have provided optimism for reducing sepsis-related mortality.

Acute myocardial infarction caused by embolism of thrombus in the right coronary sinus of valsalva: a case report and review of the literature

A 56-year-old man presented with sustained chest pain. Coronary angiography revealed total occlusion of the distal right coronary artery and left anterior descending branch. Left ventriculography depicted a mobile mass in the right sinus of Valsalva originating from the ostium of the right coronary artery. Transesophageal echocardiography (TEE) showed a mobile mass in the sinus of Valsalva and another mobile mass in the aortic arch. The mass at the right sinus of Valsalva was surgically resected, and histologic examination revealed an organized thrombus. Coagulation study showed protein S deficiency. This is the first case of acute myocardial infarction as a result of multiple coronary embolism caused by thrombosis in the right sinus of Valsalva with a second aortic arch thrombosis, contributed by protein S deficiency.

Hypercoagulability in renal transplant recipients. Identifying patients at risk of renal allograft thrombosis and evaluating strategies for prevention

Renal transplantation improves survival and quality of life for patients with end-stage renal disease (ESRD). Improvements in immunosuppressive therapy have reduced early allograft loss due to acute rejection to very low levels. Early allograft loss, due to acute thrombotic complications, remains a constant and proportionally increasing complication of renal transplantation. Identifying risk factor(s) for thrombosis amenable to preventive strategies has been elusive. Epidemiological studies have attempted to define risk in terms of modifiable (drugs, dialysis modality, surgical procedure) and non-modifiable (age, diabetes mellitus, vascular anomalies) factors, or identify changes in coagulation or fibrinolysis promoting a more thrombotic state. Most recently the evolution of thrombophilia research has established the potential for inherited hypercoagulability to predispose to acute allograft thrombosis. Inheritance of the factor V Leiden (FVL), prothrombin G20210A mutation, or the presence of antiphospholipid antibodies (APA) may increase the risk of renal allograft thrombosis approximately 3-fold in selected patients. Patients with ESRD due to systemic lupus erythematosus (SLE) appear at particularly high risk of thrombosis, especially if they have either APA or detectable beta(2)-glycoprotein-1. Data for other hypercoagulable states such as hyperhomocystinemia or the C677T polymorphism of the methylenetetrahydrofolate reductase gene are deficient. Patients with APA, FVL, or prothrombin G20210A mutation also appear to have greater graft loss due to vascular rejection, possibly reflecting immunological injury upon the vascular wall exacerbated or induced by the prothrombotic state. While substantial in vitro data suggest cyclosporine is prothrombotic, an independent clinical association with allograft thrombosis is unproven. Interventions to reduce thrombotic risk including heparin, warfarin, and aspirin have been evaluated in both selected high-risk groups (heparin and warfarin) and unselected populations (heparin and aspirin). In unselected patients at low clinical risk, aspirin (75-150 mg/day) with or without a short period of unfractionated heparin (5000U twice a day for 5 days) appears to reduce the risk of renal allograft thrombosis significantly with a low risk of bleeding, especially when compared with low molecular weight heparins which risk accumulation in renal failure. In high-risk groups (identified thrombophilic risk factor, previous thrombosis, or SLE) longer period of heparin, with or without aspirin and maintenance with warfarin, should be considered. Re-transplantation following graft loss due to vascular thrombosis can be undertaken with a low risk of recurrence. Further prospective studies evaluating both putative risk factors and intervention strategies are required to determine whether routine clinical screening for thrombophilic factors is justified.

The blood coagulation system as a molecular machine

The human blood coagulation system comprises a series of linked glycoproteins that upon activation induce the generation of downstream enzymes ultimately forming fibrin. This process is primarily important to arrest bleeding (hemostasis). Hemostasis is a typical example of a molecular machine, where the assembly of substrates, enzymes, protein cofactors and calcium ions on a phospholipid surface markedly accelerates the rate of coagulation. Excess, pathological, coagulation activity occurs in "thrombosis", the formation of an intravascular clot, which in the most dramatic form precipitates in the microvasculature as disseminated intravascular coagulation. Thrombosis occurs according to a biochemical machine model in the case of atherothrombosis on a ruptured atherosclerotic plaque, but may develop at a slower rate in venous thrombosis, illustrating that the coagulation machinery can act at different velocities. The separate coagulation enzymes are also important in other biological processes, including inflammation for which the rapid conversion of one coagulation factor by the other is not a prerequisite. The latter role of coagulation enzymes may be related to the old and probably maintained function of the coagulation machine in innate immunity.

Markers of Coagulation and Angiogenesis in Cancer-Associated Venous Thromboembolism

Purpose: We sought to determine whether venous thromboembolism in cancer patients is associated with aberrant plasma levels of hemostatic and angiogenic factors.

Patients and Methods: Peripheral blood was collected before anticoagulant therapy from cancer patients with acute deep venous thrombosis (DVT; DVT + cancer group, n = 32), those without DVT (cancer control group, n = 36), and patients with acute DVT but no cancer (DVT control group, n = 58). Plasma assays of activation and inhibition of coagulation and fibrinolysis, as well as angiogenesis activation, were then performed.

Results: Median levels of thrombin-antithrombin complex, prothrombin fragments 1 + 2, and von Willebrand factor antigen were significantly greater in the DVT + cancer group than in the cancer control and DVT control groups (17.8 ng/mL v 4.6 ng/mL and 9.8 ng/mL, P = .0001 and P = .003, respectively; 3.65 nmol/L v 1.60 nmol/L and 2.71 nmol/L, P < .0001 and P = .011, respectively; and 4.04 U/mL v 2.26 U/mL and 2.06 U/mL, P < .0001, respectively). Median levels of tissue-type plasminogen activator were also significantly higher, while protein C activity was lower in the DVT + cancer group than in the DVT control group (14.6 ng/mL v 9.50 ng/mL, respectively, P = .0005; 0.89 U/mL v 1.11 U/mL, respectively, P = .0008).

Conclusion: These data not only support prior observations of coagulation activation in patients with malignancy, but also provide new evidence for enhanced coagulation activation in the setting of acute venous thromboembolism in cancer. Future prospective studies are warranted to determine whether these and other potential markers of hypercoagulability may help to identify cancer patients at highest risk for venous thromboembolism.

Genetic determinants of arterial thrombosis

Arterial thrombosis is a complex disorder that involves multiple genetic and environmental factors interacting to produce the characteristic phenotype. In the past decades, investigators have focused on the molecular genetics of arterial vascular disorders and have identified numerous polymorphisms and mutations in genes related to the hemostatic system and to enzymes involved in the synthesis and bioavailability of nitric oxide (NO); however, the relation between most polymorphisms and the risk of coronary artery disease, ischemic stroke, and peripheral vascular disease remains highly controversial. In this review, we describe the most common genetic variations involved in the pathogenesis of arterial thrombosis, their functional implications, and their association with disease risk. Specifically, we consider polymorphisms in coagulation factors (fibrinogen, prothrombin, FV Leiden, FVII, and FXIII); fibrinolytic factors (tissue-type plasminogen activator, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor); platelet surface receptors; methylenetetrahydrofolate reductase; endothelial NO synthase; and the antioxidant enzymes paraoxonase and plasma glutathione peroxidase. Overall, there seems to be a modest contribution of individual genetic variants in the hemostatic and antioxidant systems to the risk of arterial thrombosis. Thus, future research ought to focus on identifying novel genetic determinants and on the interaction of these genetic risk factors with each other and the environment to understand better the pathobiology and susceptibility to arterial thrombotic disease.

Cause-effect relation between hyperfibrinogenemia and vascular disease

Elevated plasma levels of fibrinogen are associated with the presence of cardiovascular disease, but it is controversial whether elevated fibrinogen causally imparts an increased risk, and as such is a true modifier of cardiovascular disease, or is merely associated with disease. By investigating a transgenic mouse model of hyperfibrinogenemia, we show that elevated plasma fibrinogen concentration (1) elicits augmented fibrin deposition in specific organs, (2) interacts with an independent modifier of hemostatic activity to regulate fibrin turnover/deposition, (3) exacerbates neointimal hyperplasia in an experimental model of stasis-induced vascular remodeling, yet (4) may suppress thrombin generation in response to a procoagulant challenge. These findings provide direct experimental evidence that hyperfibrinogenemia is more than a by-product of cardiovascular disease and may function independently or interactively to modulate the severity and/or progression of vascular disease.

Risk of ischemic stroke associated with functional thrombin-activatable fibrinolysis inhibitor plasma levels

BACKGROUND AND PURPOSE

Recently, a novel procarboxypeptidase B-like proenzyme, called thrombin-activatable fibrinolysis inhibitor (TAFI), has been described. It plays an important role in the delicate balance between coagulation and fibrinolysis. TAFI leads to potent inhibition of tissue plasminogen activator-induced fibrinolysis. The relevance of TAFI in thromboembolic disease is unclear. We have investigated the risk of ischemic stroke (IS) in relation to plasma levels of functional TAFI.

METHODS

In a case-control study, we enrolled 264 individuals; 114 had IS, and 150 were recruited as controls who were age and sex matched and had no history of arterial disease. The individuals supplied information on their personal and family histories of cardiovascular diseases and conventional cardiovascular risk factors. Functional TAFI assays were performed by use of a method based on the activation of TAFI with thrombin-thrombomodulin and the measure of the TAFI activity generated. Other hemostatic parameters assayed were factor VIIIc, anti-phospholipid antibodies,fibrinogen, factor V Leiden, and the prothrombin gene G20210A mutations (PT20210A).

RESULTS

Functional TAFI levels were significantly higher in patients with IS (113.7+/-25%; range, 57% to 209%) than in controls (102.6+/-19%). The odds ratio for IS in patients with functional TAFI levels >120% was 5.7 (95% confidence interval, 2.3 to 14.1).

CONCLUSIONS

We found that functional TAFI levels in plasma (>120%) increased the risk of IS approximately 6-fold. Further studies should elucidate the physiological role of TAFI in arterial disease and possibly provide clues to therapeutic approaches.

Endothelium as a target for antiphospholipid antibodies

Several, and not necessarily alternative, pathogenic mechanisms have been suggested to sustain the thrombophilic diathesis of the anti-phospholipid syndrome. Among them, interference of anti-phospholipid antibodies with cell acting in the coagulation cascade likely plays a major role. Anti-phospholipid antibodies have been shown to react with endothelial cells mainly by reacting with beta 2 glycoprotein I expressed on the cell membrane surface. Beta 2 glycoprotein I can adhere to endothelial cell surface through the Annexin II receptor and through negatively charged structures (heparin-like molecules) that are bound by the phospholipid-binding site of the molecule. The autoantibody binding involves a yet unknown receptor that activates a signalling pathway able to translocate NFkappaB from the cytoplasm to the nucleus and to activate genes for adhesion molecule, pro-inflammatory cytokine and Tissue Factor up-regulation. The ultimate effect is the induction of a pro-inflammatory and a pro-coagulant endothelial phenotype that has been reproduced both in vitro and in vivo experimental models. Additional effects of anti-phospholipid-mediated endothelial cell activation are the interference with the protein C/S system, with the Annexin V binding, the up-regulation of endothelin I synthesis and the induction of apoptosis. Altogether these effects cooperate in switching endothelium from an anti-coagulant to a pro-coagulant surface.

Interpreting the mechanisms of continuous renal replacement therapy in sepsis: the peak concentration hypothesis

Severe sepsis and septic shock are the primary causes of multiple organ dysfunction syndrome (MODS), which is the most frequent cause of death in intensive care unit patients. Many water-soluble mediators with pro- and anti-inflammatory action such as TNF, IL-6, IL-8, and IL-10 play a strategic role in septic syndrome. In intensive care medicine, blocking any one mediator has not led to a measurable outcome improvement in patients with sepsis. CRRT is a continuously acting therapy, which removes in a nonselective way pro- and anti-inflammatory mediators; "the peak concentration hypothesis" is the concept of cutting peaks of soluble mediators through continuous hemofiltration. Furthermore, there is evidence of increased efficacy of high-volume hemofiltration compared to conventional CVVH, and other blood purification techniques that utilize large-pore membranes or sorbent plasmafiltration are conceptually interesting.

Surgical treatment of Budd-Chiari syndrome

Shunting and transplantation are satisfactory methods of treating Budd-Chiari syndrome (BCS). Selection of treatment is based on the degree of hepatic injury (clinical settings), liver biopsy results, potential for parenchymal recovery, and pressure measurements. Shunting is recommended in cases of preserved hepatic function and architecture. In the presence of fulminant forms of BCS, in cases of established cirrhosis or frank fibrosis, or for patients with defined hepatic metabolic defects (e.g., protein C or protein S deficiency), liver transplantation is the treatment of choice. Nonsurgical alternatives, although encouraging, have limited long-term outcome results at the present time. In most cases of BCS, a thrombophilic disorder can be identified. However, it is important to note that postoperative vascular thrombosis has been identified in patients with BCS who do not have a definable hypercoagulable predisposition. It therefore is our practice to recommend early (<24 hours postoperatively) initiation of intravenous heparin therapy in all patients with BCS, who then undergo life-long anticoagulation with coumadin.

Is screening for factor V Leiden and prothrombin G20210A mutations in renal transplantation worthwhile? Results of a large single-center U.K. study

This single center study is the largest series of renal transplant recipients and donors screened for the commonest prothrombotic genotypes. A total of 562 transplant recipients and 457 kidney donors were genotyped for the factor V Leiden and prothrombin G20210A mutations. The prevalence of heterozygous factor V Leiden was 3.4% and 2.6% and prothrombin G20210A was 2.0% and 1.1% in recipients and donors, respectively, similar frequencies to that of the general U.K. population. The 30-day and 1-year graft survival rates in recipients with thrombophilic mutations were 93% and 93%, compared with 88% and 82% in patients without these mutations (log-rank P=0.34). Thrombophilia in recipients (odds ratio 0.55; confidence interval 0.06-2.29; P=0.56) or in donors (odds ratio 1.53; confidence interval 0.27-5.74; P=0.46) did not correlate with graft loss at 30 days after transplantation. In contrast to recent reports, this study did not demonstrate an association between thrombophilia and renal allograft loss, and routine screening is not recommended.