Peptide-mediated inactivation of recombinant and platelet plasminogen activator inhibitor-1 in vitro

Identification and validation of SERPINE1 as a prognostic and immunological biomarker in pan-cancer and in ccRCC

Background: SERPINE1, a serine protease inhibitor involved in the regulation of the plasminogen activation system, was recently identified as a cancer-related gene. However, its clinical significance and potential mechanisms in pan-cancer remain obscure. Methods: In pan-cancer multi-omics data from public datasets, including The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx), and online web tools were used to analyze the expression of SERPINE1 in different cancers and its correlation with prognosis, genetic alteration, DNA promoter methylation, biological processes, immunoregulator expression levels, immune cell infiltration into tumor, tumor mutation burden (TMB), microsatellite instability (MSI), immunotherapy response and drug sensitivity. Further, two single-cell databases, Tumor Immune Single-cell Hub 2 (TISCH2) and CancerSEA, were used to explore the expression and potential roles of SERPINE1 at a single-cell level. The aberrant expression of SERPINE1 was further verified in clear cell renal cell carcinoma (ccRCC) through qRT-PCR of clinical patient samples, validation in independent cohorts using The Gene Expression Omnibus (GEO) database, and proteomic validation using the Clinical Proteomic Tumor Analysis Consortium (CPTAC) database. Results: The expression of SERPINE1 was dysregulated in cancers and enriched in endothelial cells and fibroblasts. Copy number amplification and low DNA promoter methylation could be partly responsible for high SERPINE1 expression. High SERPINE1 expression was associated with poor prognosis in 21 cancers. The results of gene set enrichment analysis (GSEA) indicated SERPINE1 involvement in the immune response and tumor malignancy. SERPINE1 expression was also associated with the expression of several immunoregulators and immune cell infiltration and could play an immunosuppression role. Besides, SERPINE1 was found to be related with TMB, MSI, immunotherapy response and sensitivity to several drugs in cancers. Finally, the high expression of SERPINE1 in ccRCC was verified using qRT-PCR performed on patient samples, six independent GEO cohorts, and proteomic data from the CPTAC database. Conclusion: The findings of the present study revealed that SERPINE1 exhibits aberrant expression in various types of cancers and is associated with cancer immunity and tumor malignancy, providing novel insights for individualized cancer treatment.

Development potential of extracellular matrix hydrogels as hemostatic materials

The entry of subcutaneous extracellular matrix proteins into the circulation is a key step in hemostasis initiation after vascular injury. However, in cases of severe trauma, extracellular matrix proteins are unable to cover the wound, making it difficult to effectively initiate hemostasis and resulting in a series of bleeding events. Acellular-treated extracellular matrix (ECM) hydrogels are widely used in regenerative medicine and can effectively promote tissue repair due to their high mimic nature and excellent biocompatibility. ECM hydrogels contain high concentrations of extracellular matrix proteins, including collagen, fibronectin, and laminin, which can simulate subcutaneous extracellular matrix components and participate in the hemostatic process. Therefore, it has unique advantages as a hemostatic material. This paper first reviewed the preparation, composition and structure of extracellular hydrogels, as well as their mechanical properties and safety, and then analyzed the hemostatic mechanism of the hydrogels to provide a reference for the application and research, and development of ECM hydrogels in the field of hemostasis.

Targeting PAI-1 in Cardiovascular Disease: Structural Insights Into PAI-1 Functionality and Inhibition

Plasminogen activator inhibitor-1 (PAI-1), a member of the serine protease inhibitor (serpin) superfamily with antiprotease activity, is the main physiological inhibitor of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators (PAs). Apart from being crucially involved in fibrinolysis and wound healing, PAI-1 plays a pivotal role in various acute and chronic pathophysiological processes, including cardiovascular disease, tissue fibrosis, cancer, and age-related diseases. In the prospect of treating the broad range of PAI-1-related pathologies, many efforts have been devoted to developing PAI-1 inhibitors. The use of these inhibitors, including low molecular weight molecules, peptides, antibodies, and antibody fragments, in various animal disease models has provided ample evidence of their beneficial effect in vivo and moved forward some of these inhibitors in clinical trials. However, none of these inhibitors is currently approved for therapeutic use in humans, mainly due to selectivity and toxicity issues. Furthermore, the conformational plasticity of PAI-1, which is unique among serpins, poses a real challenge in the identification and development of PAI-1 inhibitors. This review will provide an overview of the structural insights into PAI-1 functionality and modulation thereof and will highlight diverse approaches to inhibit PAI-1 activity.

Peptides based on the reactive center loop of Manduca sexta serpin-3 block its protease inhibitory function

One innate immune response in insects is the proteolytic activation of hemolymph prophenoloxidase (proPO), regulated by protease inhibitors called serpins. In the inhibition reaction of serpins, a protease cleaves a peptide bond in a solvent-exposed reactive center loop (RCL) of the serpin, and the serpin undergoes a conformational change, incorporating the amino-terminal segment of the RCL into serpin β-sheet A as a new strand. This results in an irreversible inhibitory complex of the serpin with the protease. We synthesized four peptides with sequences from the hinge region in the RCL of Manduca sexta serpin-3 and found they were able to block serpin-3 inhibitory activity, resulting in suppression of inhibitory protease-serpin complex formation. An RCL-derived peptide with the sequence Ser-Val-Ala-Phe-Ser (SVAFS) displayed robust blocking activity against serpin-3. Addition of acetyl-SVAFS-amide to hemolymph led to unregulated proPO activation. Serpin-3 associated with Ac-SVAFS-COO⁻ had an altered circular dichroism spectrum and enhanced thermal resistance to change in secondary structure, indicating that these two molecules formed a binary complex, most likely by insertion of the peptide into β-sheet A. The interference of RCL-derived peptides with serpin activity may lead to new possibilities of “silencing” arthropod serpins with unknown functions for investigation of their physiological roles.

Identification of novel plasminogen activator inhibitor-1 inhibitors with improved oral bioavailability: Structure optimization of N-acylanthranilic acid derivatives

Novel plasminogen activator inhibitor-1 (PAI-1) inhibitors with highly improved oral bioavailability were discovered by structure-activity relationship studies on N-acyl-5-chloroanthranilic acid derivatives. Because lipophilic N-acyl groups seemed to be important for the anthranilic acid derivatives to strongly inhibit PAI-1, synthesis of compounds in which 5-chloroanthranilic acid was bound to a variety of highly lipophilic moieties with appropriate linkers was investigated. As the result it appeared that some of the derivatives possessing aryl- or heteroaryl-substituted phenyl groups in the acyl chain had potent in vitro PAI-1 inhibitory activity. Oral absorbability of typical compounds was also evaluated in rats, and compounds 40, 55, 60 and 76 which have diverse chemical structure with each other were selected for further pharmacological evaluation.

An antibody that prevents serpin polymerisation acts by inducing a novel allosteric behaviour

Serpins are important regulators of proteolytic pathways with an antiprotease activity that involves a conformational transition from a metastable to a hyperstable state. Certain mutations permit the transition to occur in the absence of a protease; when associated with an intermolecular interaction, this yields linear polymers of hyperstable serpin molecules, which accumulate at the site of synthesis. This is the basis of many pathologies termed the serpinopathies. We have previously identified a monoclonal antibody (mAb4B12) that, in single-chain form, blocks α1-antitrypsin (α1-AT) polymerisation in cells. Here, we describe the structural basis for this activity. The mAb4B12 epitope was found to encompass residues Glu32, Glu39 and His43 on helix A and Leu306 on helix I. This is not a region typically associated with the serpin mechanism of conformational change, and correspondingly the epitope was present in all tested structural forms of the protein. Antibody binding rendered β-sheet A - on the opposite face of the molecule - more liable to adopt an 'open' state, mediated by changes distal to the breach region and proximal to helix F. The allosteric propagation of induced changes through the molecule was evidenced by an increased rate of peptide incorporation and destabilisation of a preformed serpin-enzyme complex following mAb4B12 binding. These data suggest that prematurely shifting the β-sheet A equilibrium towards the 'open' state out of sequence with other changes suppresses polymer formation. This work identifies a region potentially exploitable for a rational design of ligands that is able to dynamically influence α1-AT polymerisation.

The 4G/4G Genotype of PAI-1 Polymorphism Is Associated with Higher Plasma PAI-1 Concentrations and Mortality in Patients with Severe Sepsis

Objective

Two studies have reported that patients with the 4G/4G genotype of the plasminogen activator inhibitor-1 (PAI-1) genetic polymorphism had higher plasma PAI-1 concentrations and higher risk of death than those with the 4G/5G or 5G/5G genotypes; one study involved 175 children with meningococcal disease, and the other included 88 adult patients with septic shock. Thus, the objective of this study was to determine whether there is an association between carriage of the 4G/4G genotype, plasma PAI-1 concentrations and mortality in a large series of adult septic patients.

Methods

An observational, prospective, multicenter study was carried out in six Spanish Intensive Care Units including severe septic patients. We determined the PAI-1 4G/5G polymorphism and plasma PAI-1 concentrations in all patients. The end-points of the study were 30-day and 6-month mortality.

Results

We included a total of 260 patients, 82 (31.5%) with 4G/4G, 126 (48.5%) with 4G/5G and 52 (20.0%) with 5G/5G genotype. Multivariate logistic regression analysis showed that the 4G/4G genotype was associated with higher mortality at 30 days (Odds Ratio = 1.95; 95% CI = 1.063–3.561; p = 0.03) and at 6 months (Odds Ratio = 2.19; 95% CI = 1.221–3.934; p = 0.01), and that higher plasma PAI-1 concentrations were associated with higher mortality at 30 days (Odds Ratio = 1.01; 95% CI = 1.002–1.022; p = 0.02) at 6 months (Odds Ratio = 1.01; 95% CI = 1.003–1.023; p = 0.01). Multivariate linear regression analysis showed that increased plasma PAI-1 concentrations were associated with the PAI-1 4G/4G genotype (regression coefficient = 4.82; 95% CI = 3.227 to 6.406; p<0.001).

Conclusions

The major findings of our study, to our knowledge the largest series reporting data about 4G/5G polymorphism of the PAI-1 gene, plasma PAI-1 concentrations and mortality in septic patients, were that septic patients with the 4G/4G genotype had higher plasma PAI-1 concentrations and higher risk of death than those with 4G/5G or 5G/5G genotypes.

Small molecules inhibitors of plasminogen activator inhibitor-1 - an overview

PAI-1, a glycoprotein from the serpin family and the main inhibitor of tPA and uPA, plays an essential role in the regulation of intra and extravascular fibrinolysis by inhibiting the formation of plasmin from plasminogen. PAI-1 is also involved in pathological processes such as thromboembolic diseases, atherosclerosis, fibrosis and cancer. The inhibition of PAI-1 activity by small organic molecules has been observed in vitro and with some in vivo models. Based on these findings, PAI-1 appears as a potential therapeutic target for several pathological conditions. Over the past decades, many efforts have therefore been devoted to developing PAI-1 inhibitors. This article provides an overview of the publishing activity on small organic molecules used as PAI-1 inhibitors. The chemical synthesis of the most potent inhibitors as well as their biological and biochemical evaluations is also presented.

Mixture-based combinatorial libraries from small individual peptide libraries: a case study on α1-antitrypsin deficiency

The design, synthesis and screening of diversity-oriented peptide libraries using a "libraries from libraries" strategy for the development of inhibitors of α1-antitrypsin deficiency are described. The major buttress of the biochemical approach presented here is the use of well-established solid-phase split-and-mix method for the generation of mixture-based libraries. The combinatorial technique iterative deconvolution was employed for library screening. While molecular diversity is the general consideration of combinatorial libraries, exquisite design through systematic screening of small individual libraries is a prerequisite for effective library screening and can avoid potential problems in some cases. This review will also illustrate how large peptide libraries were designed, as well as how a conformation-sensitive assay was developed based on the mechanism of the conformational disease. Finally, the combinatorially selected peptide inhibitor capable of blocking abnormal protein aggregation will be characterized by biophysical, cellular and computational methods.

Sustained high plasma plasminogen activator inhibitor-1 levels are associated with severity and mortality in septic patients

BACKGROUND

Higher plasma plasminogen activator inhibitor-1 (PAI-1) levels have been reported in septic patients. However, some questions remain unanswered, such as whether there is an association between plasma PAI-1 levels and sepsis severity and mortality, and inflammation state during the first week.

METHODS

Multicenter, observational and prospective study carried out in six Spanish Intensive Care Units of 260 patients with severe sepsis. Circulating levels of PAI-1 and tumour necrosis factor (TNF)-α were measured at day 1, 4 and 8. End-point was 30-day mortality.

RESULTS

Nonsurviving septic patients (n=89) presented higher PAI-1 levels than surviving (n=171) at day 1 (58.4 (33.3-83.8) vs 36.5 (21.1-62.5) ng/mL; p<0.001), 4 (34.0 (14.7-53.3) vs 16.2 (10.2-27.4) ng/mL; p<0.001) and 8 (30.6 (16.2-47.8) vs 18.9 (10.4-29.5) ng/mL; p=0.004). We found a positive correlation of PAI-1 levels with SOFA, lactic acid, aPTT, INR and TNF-α, and negative with platelet count at day 1, 4 and 8. Logistic regression analyses showed that PAI-1 levels at day 1 (p<0.001), 4 (p<0.001) and 8 (p=0.001) were associated with 30-day mortality. On ROC curve analysis to predict 30- day survival, the area under the curve of PAI-1 levels at day 1, 4 and 8 were 0.65 (95% CI=0.58-0.72; p<0.001), 0.69 (95% CI=0.60-0.78; p<0.001) and 0.65 (95% CI=0.54-0.75; p=0.005) respectively.

CONCLUSIONS

The most interesting findings of our study, to our knowledge the largest series reporting PAI-1 levels during follow-up in septic patients, were that plasma PAI-1 levels during the first week were associated with inflammation, severity and mortality.

New antithrombotic drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article focuses on new antithrombotic drugs that are in or are entering phase 3 clinical testing. Development of these new agents was prompted by the limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this article (1) outlines the rationale for development of new antithrombotic agents; (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs; and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Review: Therapeutic potential of plasminogen activator inhibitor-1 inhibitors

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of fibrinolysis and regulates cell migration and fibrosis. Preclinical studies using genetically altered mice and biological or small molecule inhibitors have elucidated a role for PAI-1 in the pathogenesis of thrombosis, vascular remodeling, renal injury, and initiation of diabetes. Inhibition of PAI-1 is a potential therapeutic strategy in these diseases.

Development and characterization of a rat model of nonpenetrating liver trauma

The aim of this study was to develop and characterize a rodent model of liver trauma suitable for preclinical evaluation of new treatments and diagnostic technologies. Liver trauma was created by dropping a steel cylinder through a plastic tube onto the abdomen of supine, anesthetized rats. Internal hemorrhage in the absence of liver trauma was simulated by instilling fresh blood into the peritoneum. Platelet counts were elevated significantly after liver trauma but not simulated hemorrhage. Liver trauma and simulated internal hemorrhage both increased blood levels of the factor growth-regulated oncogene-Kupffer cell. Transcription of plasminogen activator inhibitor 1, heat shock protein 70, and suppressor of cytokine syntheses 3 was increased 77-, 22-, and 27-fold, respectively, 2 h after liver trauma but was unaltered by simulated internal hemorrhage. Levels returned to pretrauma levels by 24 h after trauma. Transcript levels for hypoxia-inducible transcription factor 1alpha were increased 2.8-fold at 24 h but not 2 h after trauma and were not affected by simulated hemorrhage. Production of heat shock protein 70 and inducible nitric oxide synthase in liver was limited to a penumbra surrounding areas of necrosis associated with trauma. The rat model described produces lesions similar to those that occur in humans after blunt trauma.

Plasminogen Activator Inhibitor I 4G/5G Polymorphism in Neonatal Respiratory Distress Syndrome

Fibrin monomers inhibit surfactant function. 4G/5G insertion/deletion polymorphism plays an important role in the regulation of plasminogen activator inhibitor 1 (PAI-1) gene expression. To examine the genotype distribution of PAI-1 polymorphism in 60 infants with respiratory distress syndrome (RDS) and 53 controls, an allele-specific polymerase chain reaction (PCR) was used. The proportion of 4G/4G, 4G/5G, and 5G/5G genotypes did not differ statistically between the RDS and control groups (P > .05). Having PAI-1 4G/4G genotype polymorphism appears to increase the risk of RDS (odds ratio [OR] =1.5; 95% confidence interval [CI], 0.5-4.3), although it was not statistically significant. No relation was found between the PAI-1 4G/5G polymorphisms and RDS, but there was an increased risk associated with the 4G variant of the PAI-1 gene. We believe that our findings of increased 4G allele of the PAI-1 gene in infants with RDS would also help to clarify the pathogenesis of RDS.

New antithrombotic drugs: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter focuses on new antithrombotic drugs that are in phase II or III clinical testing. Development of these new agents was prompted by limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this chapter (1) outlines the rationale for development of new antithrombotic agents, (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs, and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

A peptide accelerating the conversion of plasminogen activator inhibitor-1 to an inactive latent state

The serpin plasminogen activator inhibitor-1 (PAI-1) is a specific inhibitor of plasminogen activators and a potential therapeutic target in cancer and cardiovascular diseases. Accordingly, formation of a basis for development of specific PAI-1-inactivating agents is of great interest. One possible inactivation mode for PAI-1 is conversion to the inactive, so-called latent state. We have now screened a phage-displayed peptide library with PAI-1 as bait and isolated a 31-residue cysteine-rich peptide that will be referred to as paionin-4. A recombinant protein consisting of paionin-4 fused to domains 1 and 2 of the phage coat protein g3p caused a 2- to 3-fold increase in the rate of spontaneous inactivation of PAI-1. Paionin-4-D1D2 bound PAI-1 with a K(D) in the high nanomolar range. Using several biochemical and biophysical methods, we demonstrate that paionin-4-D1D2-stimulated inactivation consists of an acceleration of conversion to the latent state. As demonstrated by site-directed mutagenesis and competition with other PAI-1 ligands, the binding site for paionin-4 was localized in the loop between alpha-helix D and beta-strand 2A. We also demonstrate that a latency-inducing monoclonal antibody has an overlapping, but not identical binding site, and accelerates latency transition by another mechanism. Our results show that paionin-4 inactivates PAI-1 by a mechanism clearly different from other peptides, small organochemical compounds, or antibodies, whether they cause inactivation by stimulating latency transition or by other mechanisms, and that the loop between alpha-helix D and beta-strand 2A can be a target for PAI-1 inactivation by different types of compounds.

Inhibition of Plasminogen Activator Inhibitor-1

Objective— Serine protease inhibitors (serpin) play a central role in various pathological processes including coagulation, fibrinolysis, malignancy, and inflammation. Inhibition of serpins may prove therapeutic. As yet, however, only very few small molecule serpin inhibitors have been reported. For the first time, we apply a new approach of virtual screening to discover novel, orally active, small molecule serpin inhibitors and report their effectiveness.

Methods and Results— We focused on a clinically important serpin, plasminogen activator inhibitor-1 (PAI-1), whose crystal structure has been described. We identify novel, orally active molecules able to enter into the strand 4 position (s4A) of the A β-sheet of PAI-I as a mock compound. In vitro they specifically inhibit the PAI-1 activity and enhance fibrinolysis activity. In vivo the most effective molecule (TM5007) inhibits coagulation in 2 models: a rat arteriovenous (AV) shunt model and a mouse model of ferric chloride–induced testicular artery thrombosis. It also prevents the fibrotic process initiated by bleomycin in mouse lung.

Conclusions— The present study demonstrates beneficial in vitro and in vivo effects of novel PAI-1 inhibitors. Our methodology proves to be a useful tool to obtain effective inhibitors of serpin activity.

Design and screening of antisense oligodeoxynucleotides against PAI-1 mRNA in endothelial cells in vitro

AIM

To design and screen antisense oligodeoxynucleotides (ASODNs), which inhibit type-1 plasminogen activator inhibitor (PAI-1) expression in human umbilical vein endothelial cells (HUVEC) in vitro.

METHODS

Twenty seven ASODNs against different sites of PAI-1 mRNA were designed and transfected to HUVEC by lipofectin in vitro. The effects of ASODNs on PAI-1 antigen, PAI-1 activity and PAI-1 mRNA expression were detected by ELISA, amidolytical assay and RT-PCR, respectively.

RESULTS

Transforming growth factor beta1 (TGF-beta1)-treated HUVEC increased the expression of PAI-1 compared with the normal HUVEC. Five among twenty seven designed ASODNs were effective in inhibiting the increase in PAI-1 antigen and PAI-1 activity in a dose-dependent manner after 48-h transfection. In particular, ASODN 14 (AO14) exhibited the best inhibitory effect. The control sequences of AO14, including sense, scramble, and mismatch sequences, did not significantly inhibit PAI-1 activity. It was revealed that the inhibitory efficacy of AO14 was in a sequence-specific manner. RT-PCR showed that ASODN 1, 7, 8, 14, and 15 decreased PAI-1 mRNA expression induced by TGF-beta1 and AO14 showed the best inhibitory effect.

CONCLUSION

ASODN 1, 7, 8, 14, and 15, among twenty seven designed ASODNs against PAI-1 mRNA, significantly decreased PAI-1 antigen and PAI-1 activity induced by TGF-beta1 in a dose-dependent manner in HUVEC in vitro. AO14 showed the best inhibitory effect on PAI-1 expression in a sequence-specific manner. The results of RT-PCR indicated that inhibitory effects of ASODNs on PAI-1 biosynthesis occurred at the mRNA level. Four among five effective target sites of ASODNs located at the translation initiation site or within the translation area of PAI-1 mRNA, suggesting that these sites may be promising sites for the design of effective ASODNs.

Enhanced spontaneous thrombolysis: A new therapeutic challenge

Spontaneous thrombolysis is an endogenous protective mechanism against lasting arterial thrombotic occlusion, which is implicated in the pathogenesis of myocardial infarction and acute coronary events. Novel therapies for coronary heart disease (CHD) targeting atherosclerosis and thrombosis, together with cardiovascular prevention programs targeting risk-factors and lifestyle provide evidence that CHD is preventable. Although reduced fibrinolytic activity is a recognized risk-factor for ischemic cardiovascular events, it has so far been neglected. Our knowledge of the fibrinolytic effect of drugs commonly used for CHD such as antiplatelet agents (aspirin, ticlopidine, clopidogrel), anti-diabetic biguanides (phenformin, metformin) or anti-hypertensive drugs is scanty and conflicting. This is mainly due to the lack of a global test of spontaneous thrombolysis, as opposed to fibrinolysis of plasma or whole blood, i.e. the assessment of various activators and inhibitors of the fibrinolytic system. A recently described technique allows the measurement of spontaneous thrombolysis, that is, lysis of an autologous platelet-rich thrombus in the absence of added plasminogen activators. Early results suggest that this test may have significant clinical potential both in identifying those at risk of fatal cardiac events and in finding new therapeutic avenues or lifestyles to improve spontaneous thrombolytic activity.

Synthesis and SAR of 2-carboxylic acid indoles as inhibitors of plasminogen activator inhibitor-1

We synthesized and evaluated a novel series of 2-carboxylic acid indole-based inhibitors of plasminogen activator inhibitor-1 (PAI-1). Systematic modification of the N-1 position and the 5-position of the indole scaffold resulted in the identification of several compounds that showed good potency against PAI-1 in the spectrophotometric assay. This potency did not always translate to the antibody assay. Solubility and serum protein binding studies on selected analogs revealed that protein binding might be a factor in the poor correlation between the two assays.

Antithrombotic agents in the treatment of severe sepsis

Sepsis, a systemic inflammatory syndrome, is a response to infection and when associated with multiple organ dysfunction is termed severe sepsis. It remains a leading cause of mortality in the critically ill. The response to the invading microorganisms may be considered as a balance between a pro-inflammatory and an anti-inflammatory reaction. While an inadequate pro-inflammatory reaction and a strong anti-inflammatory response could lead to overwhelming infection and the death of the patient, a strong and uncontrolled pro-inflammatory response, manifested by the release of pro-inflammatory mediators may lead to microvascular thrombosis and multiple organ failure. Endotoxin triggers sepsis via the release of various mediators such as tumour necrosis factor-alpha and interleukin-1 (IL-1). These cytokines activate the complement and coagulation systems, release adhesion molecules, prostaglandins, leukotrienes, reactive oxygen species and nitric oxide. Other mediators involved in the sepsis syndrome include IL-1, -6 and -8; arachidonic acid metabolites; platelet activating factor; histamine; bradykinin; angiotensin; complement components and vasoactive intestinal peptide. These pro-inflammatory responses are counteracted by IL-10. Most of the trials targeting the different mediators of the pro-inflammatory response have failed due to a lack of correct definition of sepsis. Understanding the exact pathophysiology of the disease will enable more advanced treatment options. Targeting the coagulation system with various anticoagulant agents including, activated protein C, and tissue factor pathway inhibitor (TFPI) is a rational approach. Many clinical trials have been conducted to evaluate these agents in severe sepsis. While trials on antithrombin and TFPI were not so successful, the double-blind, placebo-controlled, Phase III trial of recombinant human activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) was successful, creating a significant decrease in mortality when compared to the placebo group. A better understanding of the pathophysiologic mechanism of severe sepsis will provide better treatment options, and combination antithrombotic treatment may provide a multipronged approach for the treatment of severe sepsis.

Emerging anticoagulant and thrombolytic drugs

Since its discovery, heparin has been used intensely as an anticoagulant for several medical and surgical indications. However, efforts are in progress to replace heparin because of its serious complications, such as intraoperative and postoperative bleeding, osteoporosis, alopecia, heparin resistance, heparin rebound, heparin-induced thrombocytopenia (HIT) and thrombosis syndrome (HITTS), and other disadvantages. Significant developments in the field of new anticoagulants have resulted in the evaluation and introduction of low molecular weight heparins (LMWHs) and heparinoids, hirudin, ancrod, synthetic peptides and peptidomimetics. However, despite significant progress in the development of these new anticoagulants, a better or an ideal anticoagulant for cardiovascular patients is not yet available and heparin still continues to amaze both basic scientists and the clinicians. To minimise the adverse effects of heparin, newer approaches to optimise its use in combination with the new anticoagulants may provide better clinical outcome. In our experience, the off-label use of argatroban at a dose of 300 microg/kg iv. bolus followed by 10 microg/kg/minute infusion in combination with aggrastat (a glycoprotein [GP] IIb/IIIa inhibitor) at a dose of 10 microg/kg iv. bolus followed by an infusion of 0.15 microg/kg/minute in patients with HIT undergoing percutaneous coronary interventions resulted in elevation of celite activated clotting time (ACT) to 300 seconds followed by a gradual decline and the ACT remained above 200 seconds even after 200 min of drug administration. A bewildering array of newer anticoagulants now exist, such as LMWHs and heparinoids, indirect or direct thrombin inhibitors, oral thrombin inhibitors, such as melagatran (AstraZeneca) and HC-977 (Mitsubishi Pharmaceuticals), Factor IXa inhibitors, indirect or direct Factor Xa inhibitors, Factor VIIa/tissue factor (TF) pathway inhibitor, newer antiplatelet agents, such as GPIIb/IIIa inhibitors, fibrin specific thrombolytic agent, such as tenecteplase and modulation of the endogenous fibrinolytic activity by thrombin activatable fibrinolytic inhibitor (TAFI), Factor XIIIa inhibitors and PAI-1 inhibitors. The quest for newer anticoagulant, antiplatelet and fibrinolytic agents will continue until ideal agents are found.

New anticoagulant drugs: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This article about new anticoagulant drugs is part of the seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The limitations of existing oral and parenteral anticoagulant agents have prompted a search for novel agents. Focusing on new anticoagulant drugs for the prevention and treatment of arterial and venous thrombosis, this article (1) reviews arterial and venous thrombogenesis, (2) discusses the regulation of coagulation, (3) describes the pathways for testing new anticoagulant agents, (4) describes new anticoagulant strategies focusing primarily on agents in phase II or III clinical testing, and (5) provides clinical perspective as to which of these new strategies is most likely to succeed.

Design and synthesis of oxadiazolidinediones as inhibitors of plasminogen activator inhibitor-1

A novel series of PAI-1 inhibitors containing an oxadiazolidinedione moiety were identified by high through-put screening. Optimization of substituents by parallel synthesis and the iterative design toward understanding structure-activity relationship to improve potency are described.

Site-directed targeting of plasminogen activator inhibitor-1 as an example for a novel approach in rational drug design

As plasminogen activator inhibitor-1 (PAI-1), the physiological inhibitor of tissue-type plasminogen activator, is considered to be an important risk factor in several (patho)physiological conditions, many research activities focus on attempts to inhibit this serpin. The approach illustrated in the current study focuses on elucidating important interaction sites allowing the inhibition of PAI-1. Since monoclonal antibodies are in most cases not ideal for therapeutic use, the question of whether smaller molecules exert comparable effects is a hot issue. To answer this question, Cys residues were introduced in PAI-1 at positions previously identified as determining the epitope of a PAI-1-inhibiting antibody, MA-8H9D4, resulting in PAI-1-R300C, PAI-1-Q303C, and PAI-1-D305C. Subsequently, low molecular mass sulfhydryl-specific reagents (i.e. BODIPY 530/550 IA (molecular mass 626 Da) and BODIPY FL C(1)-IA (molecular mass 417 Da)) were allowed to react covalently with the cysteine. The functional distribution (inhibitory versus substrate) toward tissue-type plasminogen activator was determined for the labeled and the unlabeled samples. Labeling at position 300 leads to a 1.7- and 2.2-fold increase in SI value for BODIPY 530/550 IA and BODIPY FL C(1)-IA, respectively. Labeling at position 303 results in a 3.3- and 1.9-fold increase of the SI value for the large and the small label, respectively. At position 305, the SI values are 3.1-fold increased for both labels. The effect (on SI and on serpin activity) of the manipulations at these positions is in good agreement with the effect exerted by MA-8H9D4. In conclusion, our study provides proof of concept for the proposed approach in evaluating whether targeting a functional epitope with a small synthetic compound may be a feasible strategy in rational drug design.

WAY-140312 reduces plasma PAI-1 while maintaining normal platelet aggregation

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of tissue plasminogen activator (tPA) and is elevated in diseases of vascular remodeling. In this study, we describe an inhibitor of active PAI-1, WAY-140312. Using fluorescence spectroscopy, it was determined that WAY-140312 bound PAI-1 at a single binding site with a dissociation constant of 5 microM. In a biochemical assay determining direct tPA activity, human recombinant PAI-1 completely inhibited tPA, but this inhibition was blocked by WAY-140312 at an IC(50) of 15.6 microM. In vivo, a 10 mg/kg oral dose of WAY-140312 to rats produced a significant plasma reduction of active PAI-1. Bleeding time, thrombin clotting time, and ex vivo platelet aggregation induced by ADP (20 microM) or collagen (2.5 microg/ml) were not affected by administration of WAY-140312. These results are the first to demonstrate that an orally active PAI-1 inhibitor can reduce plasma PAI-1 activity while maintaining normal platelet aggregation and coagulation.

Inhibition of plasminogen activator inhibitor-1: antibody fragments and their unique sequences as a tool for the development of profibrinolytic drugs

Physiological inhibition of plasminogen activator inhibitor-1 (PAI-1) might improve the prevention and treatment of various cardiovascular diseases. To date, a variety of monoclonal antibodies that neutralize PAI-1 have been generated. The current study presents the cloning, expression and characterization of four single-chain variable fragments (i.e. scFv-33B8, scFv-33H1F7, scFv-35A5 and scFv-55F4C12) from the corresponding PAI-1 neutralizing monoclonal antibodies. Surprisingly, affinity constants of scFv-33B8, scFv-33H1F7 and scFv-55F4C12 for PAI-1 (KA = 1.4 +/- 0.2 x 1010 m-1, 3.7 +/- 0.1 x 109 m-1, 1.0 +/- 0.2 x 109 m-1, respectively) were only 2- to 4-fold lower compared to those of the respective monoclonal antibodies (MAs). In contrast, scFv-35A5 exhibited a 6250-fold decrease in affinity (KA = 3.2 +/- 0.8 x 106 m-1 vs. 2.0 +/- 0.8 x 1010 m-1 observed for MA-35A5) with a concomitant absence of functional effects on PAI-1 activity. Evaluation of the dose-response curves of the PAI-1 neutralizing effect of the other scFvs revealed a shift towards slightly higher concentrations (in line with the small decrease in affinity) eventually resulting in a similar maximum effect as the corresponding MAs (i.e. 92 +/- 2%, 34 +/- 3% and 66 +/- 5% PAI-1 inhibition for scFv-33B8, scFv-33H1F7 and scFv-55F4C12, respectively). In conclusion, the sequence information of the scFvs allows to humanize MAs with PAI-1 inhibiting properties whereas the scFv constructs serve as an excellent starting point for structure based drug design, both aiming at the reduction of cardiovascular diseases.

Synthesis and biological evaluation of piperazine-based derivatives as inhibitors of plasminogen activator inhibitor-1 (PAI-1)

Compound 2 was identified by high throughput screening as a novel PAI-1 inhibitor. Systematic optimization of the A, B, and C segments of 2 resulted in the identification of a more potent compound 39 with good oral bioavailability. The synthesis and SAR data are presented in this report.

Cloning and paratope analysis of an antibody fragment, a rational approach for the design of a PAI-1 inhibitor

This study reports the cloning, characterization and paratope analysis of the plasminogen activator inhibitor-1 (PAI-1) neutralizing single-chain variable fragment 56A7C10 (scFv-56A7C10). ScFv-56A7C10-wt exhibits a similar affinity (KA = 1.01 +/- 0.3 x 109 m-1) and PAI-1 inhibitory capacity (90 +/- 6% PAI-1 inhibition at a 16-fold molar excess and IC50 = 44 +/- 14 ng mL-1) as MA-56A7C10 (KA = 1.43 +/- 0.4 x 109 m-1, 90 +/- 2% PAI-1 inhibition at a 16-fold molar excess and IC50 = 122 +/- 26 ng mL-1). Subsequently, alanine scanning of the six complementarity determining regions (CDRs) was performed and the scFv-56A7C10-mutants (n = 26) were analyzed for their PAI-1 binding and PAI-1 inhibitory properties. Mutation of the residues Y32 and V33 in the CDR1 of the heavy chain (HCDR1) and the residues R98, H99, W100 or F100a (HCDR3) resulted in reduced PAI-1 inhibitory capacities (IC50 >/= 418 ng mL-1), confirmed by reduced affinities (14-, 17-, 7-, 9- and 16-fold reduced, respectively, vs. scFv-56A7C10-wt). In the light chain, mutation of the residues W50 (LCDR2), H91, Y92, D93, or W96 (LCDR3) resulted in reduced PAI-1 inhibitory properties (IC50 >/= 160 ng mL-1) and decreased affinities (i.e. 4-, 9-, 3-, 3- and 2-fold reduced affinity, respectively, vs. scFv-56A7C10-wt). Furthermore, an overlapping peptide scan confirmed the importance of the HCDR3 region. These data, combined with a three-dimensional model of scFv-56A7C10, reveal the molecular and structural properties of the paratope and contribute to the rational design of PAI-1 neutralizing compounds.

Synthesis and biological evaluation of menthol-based derivatives as inhibitors of plasminogen activator inhibitor-1 (PAI-1)

Compound 1 was identified by high throughput screening as a novel PAI-1 inhibitor. Optimization of the B and C-segments of 1 resulted in a series of structurally simplified compounds with improved potency. The synthesis and SAR data of these compounds are presented here.

New fibrinolytic agents: benzothiophene derivatives as inhibitors of the t-PA-PAI-1 complex formation

The synthesis and activity of novel benzothiophene derivatives are described. In the t-Pa-induced fibrin clot lysis assay, several compounds inhibit the formation of the tPa-PAI-1 complex with submicromolar IC(50). This class of compounds potentially represents a new generation of antithrombotic-fibrinolytic agents.

Elucidation of a novel epitope of a substrate-inducing monoclonal antibody against the serpin PAI-1

Plasminogen activator inhibitor-1 (PAI-1) is the most important physiological inhibitor of plasminogen activators. Inhibition of PAI-1 constitutes a putative strategy for the prevention of cardiovascular disease. The monoclonal antibody MA-8H9D4 inhibits PAI-1 activity by inducing a substrate behavior in PAI-1. To identify the epitope, a rational approach was used to design various PAI-1 alanine mutants (n = 16) for evaluation of their affinity. PAI-1-R300A, PAI-1-Q303A and PAI-1-D305A had affinities for MA-8H9D4 of < 10(5) M(-1), 2.0 x 10(8) M(-1) and 2.5 x 10(8) M(-1), respectively, whereas the affinity of wtPAI-1 is 3.3 x 10(9) M(-1). The epitope on the axis of arginine 300, glutamine 303 and aspartic acid 305, located on the loop between alpha-helix I and beta-strand 5A, demonstrates that MA-8H9D4 interferes with the final locking step in the serpin/proteinase interaction, thereby explaining its substrate inducing properties. The location of the epitope as well as the proposed mechanism of action is clearly different from that of other substrate inducing monoclonal antibodies against PAI-1. Elucidation of this novel epitope and the previously unidentified molecular mechanism opens new perspectives for the rational development of PAI-1-neutralizing compounds, as well as for the further exploration of synergistic effects between different PAI-1-inhibiting compounds.

A novel antithrombotic role for high molecular weight kininogen as inhibitor of plasminogen activator inhibitor-1 function

The adhesive glycoprotein vitronectin (VN) forms a function-stabilizing complex with plasminogen activator inhibitor-1 (PAI-1), the major fibrinolysis inhibitor in both plasma and vessel wall connective tissue. VN also interacts with two-chain high molecular weight kininogen (HKa), particularly its His-Gly-Lys-rich domain 5, and both HKa and PAI-1 are antiadhesive factors that have been shown to compete for binding to VN. In this study the influence of HKa and domain 5 on the antifibrinolytic function of PAI-1 was investigated. In a purified system, HKa and particularly domain 5 inhibited the binding of PAI-1 to VN and promoted PAI-1 displacement from both isolated VN as well as subendothelial extracellular matrix-associated VN. The sequence Gly(486)-Lys(502) of HKa domain 5 was identified as responsible for this inhibition. Although having no direct effect on PAI-1 activity itself, HKa domain 5 or the peptide Gly(486)-Lys(502) markedly destabilized the VN.PAI-1 complex interaction, resulting in a significant reduction of PAI-1 inhibitory function on plasminogen activators, resembling the effect of VN antibodies that prevent stabilization of PAI-1. Furthermore, high affinity fibrin binding of PAI-1 in the presence of VN as well as the VN-dependent fibrin clot stabilization by the inhibitor were abrogated in the presence of the kininogen forms mentioned. Taken together, our data indicate that the peptide Gly(486)-Lys(502) derived from domain 5 of HKa serves to interfere with PAI-1 function. Based on these observations potential low molecular weight PAI-1 inhibitors could be designed for the use in therapeutic interventions against thromboembolic complications.

Novel inhibitors of plasminogen activator inhibitor-1: development of new templates from diketopiperazines

Several isoquinoline-based templates were identified from the studies of the conformational effects of the diketopiperazine structures for PAI-1 inhibition. Moderate to good activity was retained with the elimination of unattractive characteristics in the diketopiperazine template.

The molecular basis for anti-proteolytic and non-proteolytic functions of plasminogen activator inhibitor type-1: roles of the reactive centre loop, the shutter region, the flexible joint region and the small serpin fragment

The serine proteinase inhibitor plasminogen activator inhibitor type-1 (PAI-1) is the primary physiological inhibitor of the tissue-type and the urokinase-type plasminogen activator (tPA and uPA, respectively) and as such an important regulator of proteolytic events taking place in the circulation and in the extracellular matrix. Moreover, a few non-proteolytic functions have been ascribed to PAI-1, mediated by its interaction with vitronectin or the interaction between the uPA-PAI-1 complex bound to the uPA receptor and members of the low density lipoprotein receptor family. PAI-1 belongs to the serpin family, characterised by an unusual conformational flexibility, which governs its molecular interactions. In this review we describe the anti-proteolytic and non-proteolytic functions of PAI-1 from both a biological and a biochemical point of view. We will relate the various biological roles of PAI-1 to its biochemistry in general and to the different conformations of PAI-1 in particular. We put emphasis on the intramolecular rearrangements of PAI-1 that are required for its antiproteolytic as well as its non-proteolytic functions.

Synthesis and in vitro evaluation of a series of diketopiperazine inhibitors of plasminogen activator inhibitor-1

We have synthesized and evaluated a series of diketopiperazine-based inhibitors of PAI-1. These studies resulted in the identification of 34 which inhibited PAI-1 in vitro with an IC(50)=0.2 microM. The synthesis and SAR of these compounds are described.

New anticoagulant drugs

Arterial and venous thrombosis are major causes of morbidity and mortality. Arterial thrombosis is the most common cause of myocardial infarction, stroke, and limb gangrene. Venous thrombosis leads to potentially fatal pulmonary embolism and to post-phlebitic syndrome. Because arterial thrombi consist of platelet aggregates held together by small amounts of fibrin, strategies to inhibit arterial thrombogenesis focus mainly on blocking platelet function, but often include anticoagulants to prevent fibrin deposition. Anticoagulants are used for the prevention and treatment of venous thrombosis because venous thrombi consist mainly of fibrin and red blood cells. This paper (1) reviews arterial and venous thrombogenesis, (2) outlines new anticoagulant strategies, and (3) provides clinical perspectives on these new strategies.

A regulatory hydrophobic area in the flexible joint region of plasminogen activator inhibitor-1, defined with fluorescent activity-neutralizing ligands. Ligand-induced serpin polymerization

We have characterized the neutralization of the inhibitory activity of the serpin plasminogen activator inhibitor-1 (PAI-1) by a number of structurally distinct organochemicals, including compounds with environment-sensitive spectroscopic properties. In contrast to latent and reactive center-cleaved PAI-1 and PAI-1 in complex with urokinase-type plasminogen activator (uPA), active PAI-1 strongly increased the fluorescence of the PAI-1-neutralizing compounds 1-anilinonaphthalene-8-sulfonic acid and 4,4'-dianilino-1,1'-bisnaphthyl-5,5'-disulfonic acid. The fluorescence increase could be competed by all tested nonfluorescent neutralizers, indicating that all neutralizers bind to a common hydrophobic area preferentially accessible in active PAI-1. Activity neutralization proceeded through two consecutive steps as follows: first step is conversion to forms displaying substrate behavior toward uPA, and second step is to forms inert to uPA. With some neutralizers, the second step was associated with PAI-1 polymerization. Vitronectin reduced the susceptibility to the neutralizers. Changes in sensitivity to activity neutralization by point mutations were compatible with the various neutralizers having overlapping, but not identical, binding sites in the region around alpha-helices D and E and beta-strand 1A, known to act as a flexible joint when beta-sheet A opens and the reactive center loop inserts as beta-strand 4A during reaction with target proteinases. The defined binding area may be a target for development of compounds for neutralizing PAI-1 in cancer and cardiovascular diseases.

Linkage between the hormone binding site and the reactive center loop of thyroxine binding globulin

Thyroxine binding globulin (TBG) is the major carrier of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in plasma. TBG is member of the serpin family of proteins although it has no proteinase inhibitory activity. In this study we show that TBG has properties typical of a metastable serpin and provide evidence that occupancy of the hormone binding site alters the conformation of the reactive center loop. After reactive center loop cleavage by endoproteinase Asp-N or neutrophil elastase the protein became more stable to guanidine hydrochloride denaturation compared to the native protein, as a result of loop insertion. In addition, incubation of the native protein with a reactive center loop peptide, caused a change in mobility on a native gel. This is consistent with the idea that thyroxine binding globulin is able to form a binary complex with the peptide as a result of beta-sheet A expansion. To assess the effect of cleavage and loop insertion on the hormone binding site we used the specific binding of a fluorophore, 1,8-anilinonaphthalene sulfonic acid (ANS). Loop insertion itself had no effect on ANS affinity, but cleavage with elastase at the P4'-P5' bond caused a reduction in affinity, presumably because this cleavage site is located within the hormone binding site. These data support the concept that cleavage of TBG by proteinases released in inflammation is a mechanism to deliver thyroid hormones to target tissues. A linkage between the occupancy state of the hormone binding site and the conformation of the reactive center loop was indicated by the observation that binding of T3 to native TBG reduced proteolytic susceptibility by both endoproteinase Asp-N and elastase.

Plasminogen activator inhibitor type 1 is a potential target in renal fibrogenesis

Plasminogen activator inhibitor type 1 is a potential target in renal fibrogenesis. The progression of renal lesions to fibrosis involves several mechanisms, among which the inhibition of extracellular matrix (ECM) degradation appears to play an important role. Two interrelated proteolytic systems are involved in matrix degradation: the plasminogen activation system and the matrix metalloproteinase system. The plasminogen activator inhibitor type 1 (PAI-1), as the main inhibitor of plasminogen activation, regulates fibrinolysis and the plasmin-mediated matrix metalloproteinase activation. PAI-1 is also a component of the ECM, where it binds to vitronectin. PAI-1 is not expressed in the normal human kidney but is strongly induced in various forms of kidney diseases, leading to renal fibrosis and terminal renal failure. Thrombin, angiotensin II, and transforming growth factor-beta are potent in vitro and in vivo agonists in increasing PAI-1 synthesis. Several experimental and clinical studies support a role for PAI-1 in the renal fibrogenic process occurring in chronic glomerulonephritis, diabetic nephropathy, focal segmental glomerulosclerosis, and other fibrotic renal diseases. Experimental models of renal diseases in PAI-1-deficient animals are in progress, and preliminary results indicate a role for PAI-1 in renal fibrogenesis. Inhibition of PAI-1 activity or of PAI-1 synthesis by specific antibodies, peptidic antagonists, antisense oligonucleotides, or decoy oligonucleotides has been obtained in vitro, but needs to be evaluated in vivo for the prevention or the treatment of renal fibrosis.

Production of plasminogen activator inhibitor-1 by human mast cells and its possible role in asthma

The plasminogen activator inhibitor type 1 (PAI-1) has an essential role in tissue remodeling. The PAI-1 gene was induced by a combination of phorbol ester and calcium ionophore at the highest level among the inducible human mast cell genes that we have analyzed on a DNA microarray. PAI-1 was secreted by both a human mast cell line (HMC)-1 and primary cultured human mast cells upon stimulation, whereas PAI-1 was undetectable in either group of unstimulated cells. The secretion of PAI-1 was due to de novo synthesis of PAI-1 rather than secretion of preformed PAI-1. The functional significance of PAI-1 secretion was demonstrated by complete inhibition of tissue-type plasminogen activator activity with supernatants of stimulated HMC-1 cells. Furthermore, we were able to regulate PAI-1 gene expression in HMC-1 cells by known therapeutic agents. High-dose (1 microM) dexamethasone induced PAI-1 mRNA expression. Cyclosporin down-regulated the expression of the PAI-1 gene. Cycloheximide abrogated PAI-1 mRNA expression, suggesting that transcription of the PAI-1 gene requires de novo synthesis of early gene products, including transcription factors. Finally, we demonstrated PAI-1 in lung mast cells from a patient with asthmatic attack by double-immunofluorescence study. This is the first report demonstrating that activated human mast cells release a striking amount of functionally active PAI-1. These results suggest that PAI-1 could play an important role in airway remodeling of asthma, and inhibition of PAI-1 activity could represent a novel therapeutic approach in the management of airway remodeling.

Plasminogen activator inhibitor-1 and vitronectin promote vascular thrombosis in mice

Occlusive thrombosis depends on the net balance between platelets, coagulation, and fibrinolytic factors. Epidemiologic information suggests that plasminogen activator inhibitor-1 (PAI-1), a central regulator of the fibrinolytic system, plays an important role in determining the overall risk for clinically significant vascular thrombosis. Vitronectin (VN), an abundant plasma and matrix glycoprotein, binds PAI-1 and stabilizes its active conformation. This study assessed the role of PAI-1 and VN expression in the formation of occlusive vascular thrombosis following arterial or venous injury. The common carotid arteries of 17 wild-type (WT) mice and 8 mice deficient in PAI-1 were injured photochemically while blood flow was continuously monitored. WT mice developed occlusive thrombi at 52.0 ± 3.8 minutes (mean ± SEM) following injury; mice deficient in PAI-1 developed occlusive thrombosis at 127 ± 15 minutes (P &lt; .0001). Mice deficient in VN (n = 12) developed vascular occlusion 77 ± 11 minutes after injury, intermediate between the values observed for WT mice (P &lt; .03) and mice deficient in PAI-1 (P &lt; .01). PAI-1 and VN also affected the time to occlusion after injury to the jugular vein. Three WT mice developed occlusive venous thrombosis an average of 39.7 ± 1 minutes following the onset of injury, whereas the jugular veins of 4 mice deficient in PAI-1 and 4 deficient in VN occluded 56.7 ± 5 and 58.7 ± 2 minutes, respectively, following injury (P &lt; .04 andP &lt; .01 compared to WT mice). These results suggest that endogenous fibrinolysis and its regulation by PAI-1 and VN have important roles in the development of occlusive vascular thrombosis after vascular injury.

Advances in Therapy and the Management of Antithrombotic Drugs for Venous Thromboembolism

This review focuses on antithrombotic therapy for venous thromboembolism and covers a diverse range of topics including a discussion of emerging anticoagulant drugs, a renewed focus on thrombolytic agents for selected patients, and an analysis of the factors leading to adverse events in patients on warfarin, and how to optimize therapy. In Section I Dr. Weitz discusses new anticoagulant drugs focusing on those that are in the advanced stages of development. These will include drugs that (a) target factor VIIa/tissue factor, including tissue factor pathway inhibitor and NAPc2; (b) block factor Xa, including the synthetic pentasaccharide and DX9065a; (c) inhibit factors Va and VIIIa, i.e., activated protein C; and (d) block thrombin, including hirudin, argatroban, bivalirudin and H376/95. Oral formulations of heparin will also be reviewed.

In Section II, Dr. Comerota will discuss the use of thrombolysis for selected patients with venous thromboembolism. Fibrinolytic therapy, which has suffered from a high risk/benefit ratio for routine deep venous thrombosis, may have an important role to play in patients with iliofemoral venous thrombosis. Dr. Comerota presents his own results with catheter-directed thrombolytic therapy and the results from a large national registry showing long-term outcomes and the impact on quality of life.

In Section III, Dr. Ansell presents a critical analysis of the factors responsible for adverse events with oral anticoagulants and the optimum means of improving outcomes. The poor status of present day anticoagulant management is reviewed and the importance of achieving a high rate of “time in therapeutic range,” is emphasized. Models of care to optimize outcomes are described, with an emphasis on models that utilize patient self-testing and patient self-management of oral anticoagulation which are considered to be the ultimate in anticoagulation care. The treatment of venous and arterial thromboembolism is undergoing rapid change with respect to the development of new antithrombotic agents, an expanding list of new indications, and new methods of drug delivery and management. In spite of these changes, many of the traditional therapeutics are still with us and continue to play a vital role in the treatment of thromboembolic disease. The following discussion touches on a wide range of therapeutic interventions, from old to new, exploring the status of anticoagulant drug development, describing a new intervention for iliofemoral venous thrombosis, and analyzing the critical factors for safe and effective therapy with oral anticoagulants.

Advances in Therapy and the Management of Antithrombotic Drugs for Venous Thromboembolism

This review focuses on antithrombotic therapy for venous thromboembolism and covers a diverse range of topics including a discussion of emerging anticoagulant drugs, a renewed focus on thrombolytic agents for selected patients, and an analysis of the factors leading to adverse events in patients on warfarin, and how to optimize therapy. In Section I Dr. Weitz discusses new anticoagulant drugs focusing on those that are in the advanced stages of development. These will include drugs that (a) target factor VIIa/tissue factor, including tissue factor pathway inhibitor and NAPc2; (b) block factor Xa, including the synthetic pentasaccharide and DX9065a; (c) inhibit factors Va and VIIIa, i.e., activated protein C; and (d) block thrombin, including hirudin, argatroban, bivalirudin and H376/95. Oral formulations of heparin will also be reviewed.

In Section II, Dr. Comerota will discuss the use of thrombolysis for selected patients with venous thromboembolism. Fibrinolytic therapy, which has suffered from a high risk/benefit ratio for routine deep venous thrombosis, may have an important role to play in patients with iliofemoral venous thrombosis. Dr. Comerota presents his own results with catheter-directed thrombolytic therapy and the results from a large national registry showing long-term outcomes and the impact on quality of life.

In Section III, Dr. Ansell presents a critical analysis of the factors responsible for adverse events with oral anticoagulants and the optimum means of improving outcomes. The poor status of present day anticoagulant management is reviewed and the importance of achieving a high rate of “time in therapeutic range,” is emphasized. Models of care to optimize outcomes are described, with an emphasis on models that utilize patient self-testing and patient self-management of oral anticoagulation which are considered to be the ultimate in anticoagulation care. The treatment of venous and arterial thromboembolism is undergoing rapid change with respect to the development of new antithrombotic agents, an expanding list of new indications, and new methods of drug delivery and management. In spite of these changes, many of the traditional therapeutics are still with us and continue to play a vital role in the treatment of thromboembolic disease. The following discussion touches on a wide range of therapeutic interventions, from old to new, exploring the status of anticoagulant drug development, describing a new intervention for iliofemoral venous thrombosis, and analyzing the critical factors for safe and effective therapy with oral anticoagulants.

Plasminogen Activator Inhibitor 1: Molecular Aspects and Clinical Importance

Plasminogen activator inhibitor-1 (PAI-1) is the major physiologic inhibitor of plasminogen activation in plasma and in the blood vessel wall. PAI-1 exhibits distinctive structural and functional properties that have been extensively studied over the past decade. Aside from the physiological role of PAI-1, there is accumulating evidence that increased production of PAI-1 may contribute to the development of ischemic cardiovascular disease. Efforts are now underway to develop and test specific inhibitors of PAI-1.