Plasminogen activator inhibitor-1 inhibitors: a patent review (2006-present)

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.

Circadian rhythm of plasminogen activator inhibitor-1 and cardiovascular complications in type 2 diabetes

Cardiovascular complications are a common death cause in type 2 diabetes patients, as they are often combined. Plasminogen-activator Inhibitor 1 (PAI-1) participates in the development and progression of cardiovascular complications in diabetes. Insulin resistance increases PAI-1 production, and high PAI-1 levels lead to an environment conducive to thrombosis and earlier and more severe vascular disease. Current evidence also suggests that PAI-1 has a rhythmic profile of circadian fluctuations and acrophase in the morning within a single day, which might explain the high morning incidence of cardiovascular events. Thus, PAI-1 is a possible drug target. Although several PAI-1 inhibitors have been developed, none have yet been allowed for clinical use. Research on rhythm has also led to the concept of "chronotherapy", a rhythm-based drug regimen expected to improve the treatment of cardiovascular complications in diabetic patients. Herein, we searched several databases and reviewed relevant articles to describe the circadian rhythm characteristics and endogenous molecular mechanisms of PAI-1, its relationship with insulin resistance, the causes of cardiovascular complications caused by PAI-1, and the current development of PAI-1 inhibitors. We also summarized the possibility of using the circadian rhythm of PAI-1 to treat cardiovascular complications in diabetic patients.

Correlation of Vitamin D3, PAI-1, and HCG Hormone in Pre- and Post-Menopausal in Babylon Province

Background

Menopause is a unique event in women's life it usually occurs naturally, most often after age 50 when woman has not menstruated in 12 consecutive months. This study was planned to assess the relationship between Vitamin D3 level, PAI-1 and HCG in Babylon women at age <50 years as pre-menopausal and> 50 years as post-menopausal.

Methods

The sample were selected from a group of pre- and post-menopausal women, 30 and 50 respectively. All the tests were evaluated to measure Vitamin D3 level, PAI-1 and HCG level. The sample was collected between July 2019 and January 2020 at Merjan medical city GIT and Liver Center, Babylon province, Iraq.

Results

The result of current study revealed that there are significant differences in vitamin D3 level in various age categories within postmenopausal women (p= 0.02) also there is no significant differences in PAI-1 and HCG with in these two groups, p= 0.08 and 0.07, respectively. Also, there is significant negative correlation between vitamin D3 and PAI-1 in postmenopausal women (p. value is 0.01).

Conclusion

Indeed, postmenopausal women regarded as elderly, but they have sufficient vitamin D3 and normal PAI-I levels as markers for normal non fibrosis status.

Fabrication of Angiogenic Sprouting Coculture of Cell Clusteroids Using an Aqueous Two-Phase Pickering Emulsion System

Tumor cell spheroids and 3D cell culture have generated a lot of interest in the past decade due to their relative ease of production and biomedical research applications. To date, the frontier in tumor 3D models has been pushed to the level of personalized cancer treatment and customized tissue engineering applications. However, without vascularization, the central parts of these artificial constructs cannot survive without an adequate oxygen and nutrient supply. The formation of a necrotic core into in vitro 3D cell models still serves as the major obstacle in their wider practical application. Here, we propose a rapid formation protocol based on using a water-in-water (w/w) Pickering emulsion template to generate phenotypically endothelial/hepatic (ECV304/Hep-G2) coculture cell clusteroids with angiogenic capability. The w/w Pickering emulsion template was based on a dextran/poly(ethylene oxide) aqueous two-phase system stabilized by whey protein particles. The initial cell proportion in the coculture clusteroids can easily be manipulated for optimal performance. The cocultured pattern of the endothelial/hepatic cells could significantly promote the production of angiogenesis-related proteins. Our study confirmed that cocultured clusteroids can stimulate cell sprouting without the addition of vascular endothelial growth factor (VEGF) or other angiogenesis inducers at a 1:2 ratio of Hep-G2/ECV304. Angiogenesis gene production in the coculture clusteroids was enhanced with VEGF, urea, and insulin-like growth factor-binding protein along with angiogenesis-related marker CD34 levels, also indicating angiogenesis progress. Our aqueous two-phase Pickering emulsion templates provided a convenient approach to vascularize a target cell type in 3D cell coculture without additional stimulating factors, which could potentially apply to either cell lines or biopsy tissues, expanding the clusteroids downstream applications.

Sustained postoperative plasma elevations of plasminogen activator inhibitor-1 following minimally invasive colorectal cancer resection

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor that inhibits urokinase-type plasminogen activator and tissue-type plasminogen activator. PAI-1 participates in angiogenesis, wound healing and tumor invasion, and additionally regulates endothelial cell proliferation, angiogenesis and tumor growth. The purpose of the present study was to measure plasma PAI-1 levels perioperatively in patients with colorectal cancer (CRC) undergoing minimally invasive colorectal resection (MICR). Patients with CRC who underwent elective MICR were eligible for the study. All patients were enrolled in an approved data/plasma bank. Patients with preoperative, postoperative day (POD) 1, POD 3, and at least one POD 7-34 plasma sample collection were studied. Plasma PAI-1 levels were determined in duplicate using ELISA, and the medians and 95% confidence intervals (CIs) were determined. The correlations between postoperative plasma PAI-1 levels and length of surgery were evaluated. PAI-1 levels were compared between patients who underwent laparoscopic-assisted vs. hand-assisted surgery. The preoperative PAI-1 levels of stage I, II, III and IV pathological stage subgroups were also compared. A total of 91 patients undergoing MICR for CRC were studied. The mean incision length was 8.0±3.9 cm, and the length of stay was 6.8±4.3 days. Compared with the median preoperative levels (17.30; 95% CI: 15.63-19.78 ng/ml), significantly elevated median levels were observed on POD 1 (28.86; 95% CI: 25.46-31.22 ng/ml; P<0.001), POD 3 (18.87; 95% CI: 17.05-21.78 ng/ml; P=0.0037), POD 7-13 (26.97; 95% CI: 22.81-28.74 ng/ml; P<0.001), POD 14-20 (25.92; 95% CI: 17.85-35.89 ng/ml; P=0.001) and POD 21-27 (22.63; 95% CI: 20.03-30.09 ng/ml; P<0.001). The PAI-1 levels in the hand-assisted group were higher compared with those in the laparoscopic-assisted group for 4 weeks after surgery; however, a significant difference was found only on POD 1. Therefore, plasma PIA-1 levels were found to be significantly elevated for 4 weeks after MICR, and the surgery-related acute inflammatory response may account for the early postoperative PIA-1 increase. Furthermore, PAI-1-associated VEGF-induced angiogenesis in the healing wounds may account for the late postoperative elevations, and increased PAI-1 levels may promote angiogenesis in residual tumor deposits.

Fibrin(ogen) as a Therapeutic Target: Opportunities and Challenges

Fibrinogen is one of the key molecular players in haemostasis. Thrombin-mediated release of fibrinopeptides from fibrinogen converts this soluble protein into a network of fibrin fibres that form a building block for blood clots. Thrombin-activated factor XIII further crosslinks the fibrin fibres and incorporates antifibrinolytic proteins into the network, thus stabilising the clot. The conversion of fibrinogen to fibrin also exposes binding sites for fibrinolytic proteins to limit clot formation and avoid unwanted extension of the fibrin fibres. Altered clot structure and/or incorporation of antifibrinolytic proteins into fibrin networks disturbs the delicate equilibrium between clot formation and lysis, resulting in either unstable clots (predisposing to bleeding events) or persistent clots that are resistant to lysis (increasing risk of thrombosis). In this review, we discuss the factors responsible for alterations in fibrin(ogen) that can modulate clot stability, in turn predisposing to abnormal haemostasis. We also explore the mechanistic pathways that may allow the use of fibrinogen as a potential therapeutic target to treat vascular thrombosis or bleeding disorders. Better understanding of fibrinogen function will help to devise future effective and safe therapies to modulate thrombosis and bleeding risk, while maintaining the fine balance between clot formation and lysis.

Fibrinolysis in Acute and Chronic Cardiovascular Disease

The formation of an obstructive thrombus within an artery remains a major cause of mortality and morbidity worldwide. Despite effective inhibition of platelet function by modern antiplatelet therapies, these agents fail to fully eliminate atherothrombotic risk. This may well be related to extensive vascular disease, beyond the protective abilities of the treatment agents used. However, recent evidence suggests that residual vascular risk in those treated with modern antiplatelet therapies is related, at least in part, to impaired fibrin clot lysis. In this review, we attempt to shed more light on the role of hypofibrinolysis in predisposition to arterial vascular events. We provide a brief overview of the coagulation system followed by addressing the role of impaired fibrin clot lysis in acute and chronic vascular conditions, including coronary artery, cerebrovascular, and peripheral vascular disease. We also discuss the role of combined anticoagulant and antiplatelet therapies to reduce the risk of arterial thrombotic events, addressing both efficacy and safety of such an approach. We conclude that impaired fibrin clot lysis appears to contribute to residual thrombosis risk in individuals with arterial disease on antiplatelet therapy, and targeting proteins in the fibrinolytic system represents a viable strategy to improve outcome in this population. Future work is required to refine the antithrombotic approach by modulating pathological abnormalities in the fibrinolytic system and tailoring therapy according to the need of each individual.

PAI-1 in Diabetes: Pathophysiology and Role as a Therapeutic Target

Hypofibrinolysis is a key abnormality in diabetes and contributes to the adverse vascular outcome in this population. Plasminogen activator inhibitor (PAI)-1 is an important regulator of the fibrinolytic process and levels of this antifibrinolytic protein are elevated in diabetes and insulin resistant states. This review describes both the physiological and pathological role of PAI-1 in health and disease, focusing on the mechanism of action as well as protein abnormalities in vascular disease with special focus on diabetes. Attempts at inhibiting protein function, using different techniques, are also discussed including direct and indirect interference with production as well as inhibition of protein function. Developing PAI-1 inhibitors represents an alternative approach to managing hypofibrinolysis by targeting the pathological abnormality rather than current practice that relies on profound inhibition of the cellular and/or acellular arms of coagulation, and which can be associated with increased bleeding events. The review offers up-to-date knowledge on the mechanisms of action of PAI-1 together with the role of altering protein function to improve hypofirbinolysis. Developing PAI-1 inhibitors may form for the basis of future new class of antithrombotic agents that reduce vascular complications in diabetes.

A Narrative Review on Plasminogen Activator Inhibitor-1 and Its (Patho)Physiological Role: To Target or Not to Target?

Plasminogen activator inhibitor-1 (PAI-1) is the main physiological inhibitor of plasminogen activators (PAs) and is therefore an important inhibitor of the plasminogen/plasmin system. Being the fast-acting inhibitor of tissue-type PA (tPA), PAI-1 primarily attenuates fibrinolysis. Through inhibition of urokinase-type PA (uPA) and interaction with biological ligands such as vitronectin and cell-surface receptors, the function of PAI-1 extends to pericellular proteolysis, tissue remodeling and other processes including cell migration. This review aims at providing a general overview of the properties of PAI-1 and the role it plays in many biological processes and touches upon the possible use of PAI-1 inhibitors as therapeutics.

Structural Insight into the Two-Step Mechanism of PAI-1 Inhibition by Small Molecule TM5484

Plasminogen activator inhibitor-1 (PAI-1), a key regulator of the fibrinolytic system, is the main physiological inhibitor of plasminogen activators. By interacting with matrix components, including vitronectin (Vn), PAI-1 plays a regulatory role in tissue remodeling, cell migration, and intracellular signaling. Emerging evidence points to a role for PAI-1 in various pathological conditions, including cardiovascular diseases, cancer, and fibrosis. Targeting PAI-1 is therefore a promising therapeutic strategy in PAI-1-related pathologies. A class of small molecule inhibitors including TM5441 and TM5484, designed to bind the cleft in the central β-sheet A of PAI-1, showed to be potent PAI-1 inhibitors in vivo. However, their binding site has not yet been confirmed. Here, we report two X-ray crystallographic structures of PAI-1 in complex with TM5484. The structures revealed a binding site at the flexible joint region, which is distinct from the presumed binding site. Based on the structural analysis and biochemical data we propose a mechanism for the observed dose-dependent two-step mechanism of PAI-1 inhibition. By binding to the flexible joint region in PAI-1, TM5484 might restrict the structural flexibility of this region, thereby inducing a substrate form of PAI-1 followed by a conversion to an inert form.

Integrative identification of human serpin PAI-1 inhibitors from Dracaena dragon blood and molecular implications for inhibitor-induced PAI-1 allosterism

Human plasminogen activator inhibitor-1 (PAI-1) is an important component of the coagulation system and has been recognized as a potential therapeutic target of diverse cardiovascular disorders. Previously, it was found that the extracts from the Chinese medicine Dracaena dragon blood have potent inhibitory activity against PAI-1, but it is unclear which constituents directly participate in the inhibition and how do they regulate PAI-1 at molecular level. Here, we describe an integrated strategy to identify the dragon blood's chemical constituents that can directly target PAI-1. With the strategy, five compounds 1-5 are hit as promising PAI-1 inhibitor candidates, from which three are measured to have high or moderate activity against PAI-1. In particular, the compound 3 is determined to exhibit the highest potency; this value is roughly comparable with the widely used PAI-1 inhibitor Tiplaxtinin. We further examine the molecular effect of compound 3 on PAI-1 conformation at structural level. It is supposed that small-molecule inhibitor regulates the reactive center loop (RCL) of PAI-1 through an allosterism, that is, binding of compound 3 to PAI-1 can allosterically stabilize RCL in latent form, thus promoting PAI-1 conformational conversion from metastable active form to the inactive latent form. Long-term atomistic simulations also demonstrate that removal of compound 3 can destabilize the structured β-stranded conformation of RCL in latent form, although the current simulations are still not sufficient to characterize the full conversion dynamics trajectory.

Serpins in Hemostasis as Therapeutic Targets for Bleeding or Thrombotic Disorders

Bleeding and thrombotic disorders result from imbalances in coagulation or fibrinolysis, respectively. Inhibitors from the serine protease inhibitor (serpin) family have a key role in regulating these physiological events, and thus stand out as potential therapeutic targets for modulating fibrin clot formation or dismantling. Here, we review the diversity of serpin-targeting strategies in the area of hemostasis, and detail the suggested use of modified serpins and serpin inhibitors (ranging from small-molecule drugs to antibodies) to treat or prevent bleeding or thrombosis.

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.

Association of Plasminogen Activator Inhibitor 1 (PAI-1) 4G/5G Polymorphism and Susceptibility to SLE in Egyptian Children and Adolescents: A Multicenter Study

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) is a key molecule residing at the nexus between thrombosis and inflammatory processes. Recently, PAI-1 and its gene expression have emerged as a potential candidate for autoimmune disorders such as SLE.

OBJECTIVE

To investigate whether the PAI-1 4G/5G polymorphism at position -675 could be a genetic marker for susceptibility to childhood-onset SLE and development of lupus nephritis among Egyptian children and adolescents.

METHODS

Three hundred fifty patients diagnosed with childhood-onset SLE and 350 well-matched healthy controls were included in this multi-center study. All subjects were genotyped for the PAI-1 promoter 4G/5G polymorphism at position -675 using PCR- restriction fragment length polymorphism (RFLP). Serum PAI-1 levels were measured by ELISA.

RESULTS

The PAI-1 (- 675) 4G/4G genotype was more represented in c-SLE patients, as compared to the control group (38% vs 23%; OR =2.7; [95% CI: 1.47-2.9]; P < 0.001). Patients carrying the PAI-1 4G/4G genotype or 4G allele were more likely to develop lupus nephritis (OR: 3.38; [95% CI: 1.9-5.9]; P <0.001, for the 4G/4G genotype and OR: 2.6; [95% CI: 1.85-3.67]; for the 4G allele; P < 0.01). The PAI-1 4G/4G genotype was associated with higher PAI-1 serum concentrations (mean; 86.6±22.7 ng/mL) as compared to those with a 4G/5G genotype (mean; 48.3±16.5 ng/mL) and the lowest for the 5G/5G genotype (mean; 34.7±11.4 ng/mL); P = 0.004.

CONCLUSION

The PAI-1 4G/5G polymorphism may confer susceptibility to childhood-onset SLE and development of lupus nephritis among Egyptian children and adolescents. Moreover, the PAI-1 4G/4G genotype and 4G allele were associated with higher PAI-1 serum levels and higher disease activity scores.

Structural Insights into the Mechanism of a Nanobody That Stabilizes PAI-1 and Modulates Its Activity

Plasminogen activator inhibitor-1 (PAI-1) is the main physiological inhibitor of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators (PAs). Apart from being critically involved in fibrinolysis and wound healing, emerging evidence indicates that PAI-1 plays an important role in many diseases, including cardiovascular disease, tissue fibrosis, and cancer. Targeting PAI-1 is therefore a promising therapeutic strategy in PAI-1 related pathologies. Despite ongoing efforts no PAI-1 inhibitors were approved to date for therapeutic use in humans. A better understanding of the molecular mechanisms of PAI-1 inhibition is therefore necessary to guide the rational design of PAI-1 modulators. Here, we present a 1.9 Å crystal structure of PAI-1 in complex with an inhibitory nanobody VHH-s-a93 (Nb93). Structural analysis in combination with biochemical characterization reveals that Nb93 directly interferes with PAI-1/PA complex formation and stabilizes the active conformation of the PAI-1 molecule.

Molecular mechanism of two nanobodies that inhibit PAI-1 activity reveals a modulation at distinct stages of the PAI-1/plasminogen activator interaction

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1), a key inhibitor of plasminogen activators (PAs) tissue-type PA (tPA) and urokinase-type PA (uPA) plays a crucial role in many (patho)physiological processes (e.g., cardiovascular disease, tissue fibrosis) as well as in many age-related pathologies. Therefore, much effort has been put into the development of small molecule or antibody-based PAI-1 inhibitors.

OBJECTIVE

To elucidate the molecular mechanism of nanobody-induced PAI-1 inhibition.

METHODS AND RESULTS

Here we present the first crystal structures of PAI-1 in complex with two neutralizing nanobodies (Nbs). These structures, together with biochemical and biophysical characterization, reveal that Nb VHH-2g-42 (Nb42) interferes with the initial PAI-1/PA complex formation, whereas VHH-2w-64 (Nb64) redirects the PAI-1/PA interaction to PAI-1 deactivation and regeneration of active PA. Furthermore, whereas vitronectin does not have an impact on the inhibitory effect of Nb42, it strongly potentiates the inhibitory effect of Nb64, which may contribute to a strong inhibitory potential of Nb64 in vivo.

CONCLUSIONS

These findings illuminate the molecular mechanisms of PAI-1 inhibition. Nb42 and Nb64 can be used as starting points to engineer further improved antibody-based PAI-1 inhibitors or guide the rational design of small molecule inhibitors to treat a wide range of PAI-1-related pathophysiological conditions.

The -675 4G/5G PAI-1 polymorphism confers genetic susceptibility to systemic lupus erythematosus, its clinical manifestations, and comorbidities in Mexican-Mestizo population

Systemic lupus erythematosus (SLE) involves a broad range of factors that contribute to the development of the disease and its comorbidities. Genetic predisposition influences the development of SLE, and the -675 4G/5G PAI-1 polymorphism has been associated with several pathologies with a chronic inflammatory component. Our objective was to investigate the genetic association between the -675 4G/5G PAI-1 polymorphism with SLE, its clinical manifestations, and comorbidities in a Mexican-Mestizo population. The -675 PAI-1 polymorphism was determined by PCR-RFLP in 716 subjects: 293 SLE patients and 423 control subjects. Significant associations for SLE genetic susceptibility were found in carriers of 4G/5G (OR = 2.63; CI 1.81-3.87; p < .001) and 4G/4G (OR = 2.70; CI 1.62-4.51; p < .001) genotype in comparison with the 5G/5G genotype; 4G allele carriers also presented genetic risk for SLE (OR = 1.63; CI 1.31-2.03; p < .001) compared to the 5G allele. Following a dominant genetic model, a similar association was found with the 4G allele to SLE (OR = 2.66; CI1.84-3.84; p < .001). The 4G/5G genotype was associated with shorter disease duration (p = .039), as well as lower levels of haemoglobin (p = .001) and haematocrit (p = .009); the need for prednisone treatment (p = .001), higher BMI (p = .03), presence of type 2 DM (p = .015), clinical activity (Mex-SLEDAI = 57%; p = .047), Chronicity (SLICC-ACR = 0; p = .015) and CRP levels (p = .015) were associated with 5G/5G genotypes. In conclusion, the -675 4G/5G and 4G/4G PAI-1genotypes were found as genetic risk markers of susceptibility for SLE in the Mexican-Mestizo population, and each genotype could influence the clinical manifestations and comorbidities differently in SLE.

Discovery and characterisation of an antibody that selectively modulates the inhibitory activity of plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor (serpin) that regulates fibrinolysis, cell adhesion and cell motility via its interactions with plasminogen activators and vitronectin. PAI-1 has been shown to play a role in a number of diverse pathologies including cardiovascular diseases, obesity and cancer and is therefore an attractive therapeutic target. However the multiple patho-physiological roles of PAI-1, and understanding the relative contributions of these in any one disease setting, make the development of therapeutically relevant molecules challenging. Here we describe the identification and characterisation of fully human antibody MEDI-579, which binds with high affinity and specificity to the active form of human PAI-1. MEDI-579 specifically inhibits serine protease interactions with PAI-1 while conserving vitronectin binding. Crystallographic analysis reveals that this specificity is achieved through direct binding of MEDI-579 Fab to the reactive centre loop (RCL) of PAI-1 and at the same exosite used by both tissue and urokinase plasminogen activators (tPA and uPA). We propose that MEDI-579 acts by directly competing with proteases for RCL binding and as such is able to modulate the interaction of PAI-1 with tPA and uPA in a way not previously described for a human PAI-1 inhibitor.

(-)-Epigallocatechin gallate derivatives reduce the expression of both urokinase plasminogen activator and plasminogen activator inhibitor-1 to inhibit migration, adhesion, and invasion of MDA-MB-231 cells

Urokinase plasminogen activator (uPA) and its inhibitor plasminogen activator inhibitor-1 (PAI-1) are established independent biomarkers for high metastasis risk in breast cancer. In this study, we investigated the regulatory activity of (-)-epigallocatechin-3-gallate (EGCG) and its derivatives on uPA and PAI-1 expression and thereby their anti-metastatic potential. EGCG showed only marginal effects on the uPA system and on the metastatic behavior of breast cancer cells (MDA-MB-231). However, the EGCG derivative 3e with a methyl-substituted carbonate substituent at the 4″-position showed potent inhibition of PAI-1 (62%) and uPA (50%) expression. The Ras-extracellular-signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), and phosphatidylinositol-3-kinase (PI3K)/Akt/NF-κB pathways, which regulate uPA and PAI-1 expression, were also affected by 3e (25%, 45%, and 25% reduction, respectively). In line with these findings, substantial reduction in metastatic behavior of MDA-MB-231 cells, such as adhesion (40%), invasion (56%), and migration (40%), was observed in the presence of 3e. It is also noteworthy that, in MDA-MB-231 cells, 3e did not exert any beneficial effect on the expression of matric metalloprotein (MMP) 2 and 9, which indicates that the anti-metastatic activity of 3e in MDA-MB-231 cells is not related to its regulation of the expression of MMPs. Taken together, we have shown that the EGCG derivative 3e could suppress the metastatic behavior of MDA-MB-231 cells through regulation of uPA and PAI-1.

uPA/uPAR and SERPINE1 in head and neck cancer: role in tumor resistance, metastasis, prognosis and therapy

There is strong evidence supporting the role of the plasminogen activator system in head and neck squamous cell carcinoma (HNSCC), particularly of its uPA (urokinase plasminogen activator) / uPAR (urokinase plasminogen activator receptor) and SERPINE1 components. Overexpression of uPA/uPAR and SERPINE1 enhances tumor cell migration and invasion and plays a key role in metastasis development, conferring poor prognosis. The apparent paradox of uPA/uPAR and its inhibitor SERPINE1 producing similar effects is solved by the identification of SERPINE1 activated signaling pathways independent of uPA inhibition. Both uPA/uPAR and SERPINE1 are directly linked to the induction of epithelial-to-mesenchymal transition, the acquisition of stem cell properties and resistance to antitumor agents. The aim of this review is to provide insight on the deregulation of these proteins in all these processes.

We also summarize their potential value as prognostic biomarkers or potential drug targets in HNSCC patients. Concomitant overexpression of uPA/uPAR and SERPINE1 is associated with a higher risk of metastasis and could be used to identify patients that would benefit from an adjuvant treatment. In the future, the specific inhibitors of uPA/uPAR and SERPINE1, which are still under development, could be used to design new therapeutic strategies in HNSCCs.

Plasminogen activator inhibitor-1 regulates the vascular expression of vitronectin

Essentials Vitronectin (VN) is produced by smooth muscle cells (SMCs) and promotes neointima formation. We studied the regulation of vascular VN expression by plasminogen activator inhibitor-1 (PAI-1). PAI-1 stimulates VN gene expression in SMCs by binding LDL receptor-related protein 1. Stimulation of VN gene expression may be a mechanism by which PAI-1 controls vascular remodeling.

SUMMARY

Background Increased expression of vitronectin (VN) by smooth muscle cells (SMCs) promotes neointima formation after vascular injury, and may contribute to chronic vascular diseases, such as atherosclerosis. However, the molecular regulation of vascular VN expression is poorly defined. Given the overlapping expression profiles and functions of VN and plasminogen activator inhibitor (PAI)-1, we hypothesized that PAI-1 regulates vascular VN expression. Objectives To determine whether PAI-1 regulates VN expression in SMCs and in vivo. Methods The effects of genetic alterations in PAI-1 expression, pharmacologic PAI-1 inhibition and recombinant PAI-1 on SMC VN expression were studied, and vascular VN expression in wild-type (WT) and PAI-1-deficient mice was assessed. Results VN expression was significantly lower in PAI-1-deficient SMCs and significantly increased in PAI-1-overexpressing SMCs. PAI-1 small interfering RNA and pharmacologic PAI-1 inhibition significantly decreased SMC VN expression. Recombinant PAI-1 stimulated VN expression by binding LDL receptor-related protein-1 (LRP1), but another LRP1 ligand, α2 -macroglobulin, did not. As compared with WT controls, carotid artery VN expression was significantly lower in PAI-1-deficient mice and significantly higher in PAI-1-transgenic mice. In a vein graft (VG) model of intimal hyperplasia, VN expression was significantly attenuated in PAI-1-deficient VGs as compared with WT controls. The plasma VN concentration was significantly decreased in PAI-1-deficient mice versus WT controls at 4 weeks, but not at 5 days or 8 weeks, after surgery. Conclusions PAI-1 stimulates SMC VN expression by binding LRP1, and controls vascular VN expression in vivo. Autocrine regulation of vascular VN expression by PAI-1 may play important roles in vascular homeostasis and pathologic vascular remodeling.

Plasminogen activator inhibitor-1 is an independent prognostic factor of ovarian cancer and IMD-4482, a novel plasminogen activator inhibitor-1 inhibitor, inhibits ovarian cancer peritoneal dissemination

In the present study, the therapeutic potential of targeting plasminogen activator inhibitor-1 (PAI-1) in ovarian cancer was tested. Tissues samples from 154 cases of ovarian carcinoma were immunostained with anti-PAI-1 antibody, and the prognostic value was analyzed. Among the samples, 67% (104/154) showed strong PAI-1 expression; this was significantly associated with poor prognosis (progression-free survival: 20 vs. 31 months, P = 0.0033). In particular, among patients with stage II-IV serous adenocarcinoma, PAI-1 expression was an independent prognostic factor. The effect of a novel PAI-1 inhibitor, IMD-4482, on ovarian cancer cell lines was assessed and its therapeutic potential was examined using a xenograft mouse model of ovarian cancer. IMD-4482 inhibited in vitro cell adhesion to vitronectin in PAI-1-positive ovarian cancer cells, followed by the inhibition of extracellular signal-regulated kinase and focal adhesion kinase phosphorylation through dissociation of the PAI-urokinase receptor complex from integrin αVβ3. IMD-4482 caused G0/G1 cell arrest and inhibited the proliferation of PAI-1-positive ovarian cancer cells. In the xenograft model, IMD-4482 significantly inhibited peritoneal dissemination with the reduction of PAI-1 expression and the inhibition of focal adhesion kinase phosphorylation. Collectively, the functional inhibition of PAI-1 significantly inhibited ovarian cancer progression, and targeting PAI-1 may be a potential therapeutic strategy in ovarian cancer.

Associations between homocysteine metabolism related SNPs and carotid intima-media thickness: a Chinese sib pair study

Carotid intima-media thickness (CIMT) is a good surrogate for atherosclerosis. Hyperhomocysteinemia is an independent risk factor for cardiovascular diseases. We aim to investigate the relationships between homocysteine (Hcy) related biochemical indexes and CIMT, the associations between Hcy related SNPs and CIMT, as well as the potential gene–gene interactions. The present study recruited full siblings (186 eligible families with 424 individuals) with no history of cardiovascular events from a rural area of Beijing. We examined CIMT, intima-media thickness for common carotid artery (CCA-IMT) and carotid bifurcation, tested plasma levels for Hcy, vitamin B6 (VB6), vitamin B12 (VB12) and folic acid (FA), and genotyped 9 SNPs on MTHFR, MTR, MTRR, BHMT, SHMT1, CBS genes. Associations between SNPs and biochemical indexes and CIMT indexes were analyzed using family-based association test analysis. We used multi-level mixed-effects regression model to verify SNP-CIMT associations and to explore the potential gene–gene interactions. VB6, VB12 and FA were negatively correlated with CIMT indexes (p < 0.05). rs2851391 T allele was associated with decreased plasma VB12 levels (p = 0.036). In FABT, CBS rs2851391 was significantly associated with CCA-IMT (p = 0.021) and CIMT (p = 0.019). In multi-level mixed-effects regression model, CBS rs2851391 was positively significantly associated with CCA-IMT (Coef = 0.032, se = 0.009, raw p < 0.001) after Bonferoni correction (corrected α = 0.0056). Gene–gene interactions were found between CBS rs2851391 and BHMT rs10037045 for CCA-IMT (p = 0.011), as well as between CBS rs2851391 and MTR rs1805087 for CCA-IMT (p = 0.007) and CIMT (p = 0.022). Significant associations are found between Hcy metabolism related genetic polymorphisms, biochemical indexes and CIMT indexes. There are complex interactions between genetic polymorphisms for CCA-IMT and CIMT.

Hypofibrinolysis in diabetes: a therapeutic target for the reduction of cardiovascular risk

An enhanced thrombotic environment and premature atherosclerosis are key factors for the increased cardiovascular risk in diabetes. The occlusive vascular thrombus, formed secondary to interactions between platelets and coagulation proteins, is composed of a skeleton of fibrin fibres with cellular elements embedded in this network. Diabetes is characterised by quantitative and qualitative changes in coagulation proteins, which collectively increase resistance to fibrinolysis, consequently augmenting thrombosis risk. Current long-term therapies to prevent arterial occlusion in diabetes are focussed on anti-platelet agents, a strategy that fails to address the contribution of coagulation proteins to the enhanced thrombotic milieu. Moreover, antiplatelet treatment is associated with bleeding complications, particularly with newer agents and more aggressive combination therapies, questioning the safety of this approach. Therefore, to safely control thrombosis risk in diabetes, an alternative approach is required with the fibrin network representing a credible therapeutic target. In the current review, we address diabetes-specific mechanistic pathways responsible for hypofibrinolysis including the role of clot structure, defects in the fibrinolytic system and increased incorporation of anti-fibrinolytic proteins into the clot. Future anti-thrombotic therapeutic options are discussed with special emphasis on the potential advantages of modulating incorporation of the anti-fibrinolytic proteins into fibrin networks. This latter approach carries theoretical advantages, including specificity for diabetes, ability to target a particular protein with a possible favourable risk of bleeding. The development of alternative treatment strategies to better control residual thrombosis risk in diabetes will help to reduce vascular events, which remain the main cause of mortality in this condition.

Intracellular Expression of PAI-1 Specific Aptamers Alters Breast Cancer Cell Migration, Invasion and Angiogenesis

Plasminogen activator inhibitor-1 (PAI-1) is elevated in various cancers, where it has been shown to effect cell migration and invasion and angiogenesis. While, PAI-1 is a secreted protein, its intercellular levels are increased in cancer cells. Consequently, intracellular PAI-1 could contribute to cancer progression. While various small molecule inhibitors of PAI-1 are currently being investigated, none specifically target intracellular PAI-1. A class of inhibitors, termed aptamers, has been used effectively in several clinical applications. We previously generated RNA aptamers that target PAI-1 and demonstrated their ability to inhibit extracellular PAI-1. In the current study we explored the effect of these aptamers on intracellular PAI-1. We transiently transfected the PAI-1 specific aptamers into both MDA-MB-231 human breast cancer cells, and human umbilical vein endothelial cells (HUVECs) and studied their effects on cell migration, invasion and angiogenesis. Aptamer expressing MDA-MB-231 cells exhibited a decrease in cell migration and invasion. Additionally, intracellular PAI-1 and urokinase plasminogen activator (uPA) protein levels decreased, while the PAI-1/uPA complex increased. Moreover, a significant decrease in endothelial tube formation in HUVECs transfected with the aptamers was observed. In contrast, conditioned media from aptamer transfected MDA-MB-231 cells displayed a slight pro-angiogenic effect. Collectively, our study shows that expressing functional aptamers inside breast and endothelial cells is feasible and may exhibit therapeutic potential.

Pharmacological Targeting of Plasminogen Activator Inhibitor-1 Decreases Vascular Smooth Muscle Cell Migration and Neointima Formation

OBJECTIVE

Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor that promotes and inhibits cell migration, plays a complex and important role in adverse vascular remodeling. Little is known about the effects of pharmacological PAI-1 inhibitors, an emerging drug class, on migration of vascular smooth muscle cells (SMCs) and endothelial cells (ECs), crucial mediators of vascular remodeling. We investigated the effects of PAI-039 (tiplaxtinin), a specific PAI-1 inhibitor, on SMC and EC migration in vitro and vascular remodeling in vivo.

APPROACH AND RESULTS

PAI-039 inhibited SMC migration through collagen gels, including those supplemented with vitronectin and other extracellular matrix proteins, but did not inhibit migration of PAI-1-deficient SMCs, suggesting that its antimigratory effects were PAI-1-specific and physiologically relevant. However, PAI-039 did not inhibit EC migration. PAI-039 inhibited phosphorylation and nuclear translocation of signal transducers and activators of transcription-1 in SMCs, but had no discernable effect on signal transducer and activator of transcription-1 signaling in ECs. Expression of low-density lipoprotein receptor-related protein 1, a motogenic PAI-1 receptor that activates Janus kinase/signal transducers and activators of transcription-1 signaling, was markedly lower in ECs than in SMCs. Notably, PAI-039 significantly inhibited intimal hyperplasia and inflammation in murine models of adverse vascular remodeling, but did not adversely affect re-endothelialization after endothelium-denuding mechanical vascular injury.

CONCLUSIONS

PAI-039 inhibits SMC migration and intimal hyperplasia, while having no inhibitory effect on ECs, which seems to be because of differences in PAI-1-dependent low-density lipoprotein receptor-related protein 1/Janus kinase/signal transducer and activator of transcription-1 signaling between SMCs and ECs. These findings suggest that PAI-1 may be an important therapeutic target in obstructive vascular diseases characterized by neointimal hyperplasia.

Increased plasminogen activator inhibitor results in a hypofibrinolytic state in adolescents with obesity: in vivo and ex vivo evidence

Obesity in adolescents increases their risk for deep vein thrombosis. The objectives of this study were to determine potential mechanisms for thrombotic risk by investigating the fibrinolytic pathway in a sample of adolescents with and without obesity. Thirty-seven adolescents with obesity and 16 normal weight age-matched controls were recruited. Plasma levels of components of the fibrinolytic system were measured in addition to a Global Haemostasis Potential assay (GHP), which assesses plasma capacity to generate and lyse a fibrin clot. Levels of plasminogen activator inhibitor (PAI) and tissue plasminogen activator (tPA)/PAI complexes were increased in adolescents with obesity when compared to normal weight controls. There was a significant inverse association of increasing PAI with a decrease in plasmin-antiplasmin complexes. The GHP in obese adolescents displayed a hypofibrinolytic response with a markedly increased t_½ clot lysis time, as well as an increase in fibrin clot density as indicated by increased absorbance at maximum peak height. In the obese group, immunodepletion of PAI decreased both t_½ lysis time and absorbance at maximum peak height. We have shown in vivo and ex vivo there is a hypofibrinolytic state in obese adolescents and have established the hypofibrinolytic state is due to increased PAI levels.

Distinct encounter complexes of PAI-1 with plasminogen activators and vitronectin revealed by changes in the conformation and dynamics of the reactive center loop

Plasminogen activator inhibitor-1 (PAI-1) is a biologically important serine protease inhibitor (serpin) that, when overexpressed, is associated with a high risk for cardiovascular disease and cancer metastasis. Several of its ligands, including vitronectin, tissue-type and urokinase-type plasminogen activator (tPA, uPA), affect the fate of PAI-1. Here, we measured changes in the solvent accessibility and dynamics of an important unresolved functional region, the reactive center loop (RCL), upon binding of these ligands. Binding of the catalytically inactive S195A variant of tPA to the RCL causes an increase in fluorescence, indicating greater solvent protection, at its C-terminus, while mobility along the loop remains relatively unchanged. In contrast, a fluorescence increase and large decrease in mobility at the N-terminal RCL is observed upon binding of S195A-uPA to PAI-1. At a site distant from the RCL, binding of vitronectin results in a modest decrease in fluorescence at its proximal end without restricting overall loop dynamics. These results provide the new evidence for ligand effects on RCL conformation and dynamics and differences in the Michaelis complex with plasminogen activators that can be used for the development of more specific inhibitors to PAI-1. This study is also the first to use electron paramagnetic resonance (EPR) spectroscopy to investigate PAI-1 dynamics.

SIGNIFICANCE

Balanced blood homeostasis and controlled cell migration requires coordination between serine proteases, serpins, and cofactors. These ligands form noncovalent complexes, which influence the outcome of protease inhibition and associated physiological processes. This study reveals differences in binding via changes in solvent accessibility and dynamics within these complexes that can be exploited to develop more specific drugs in the treatment of diseases associated with unbalanced serpin activity.

Single fluorescence probes along the reactive center loop reveal site-specific changes during the latency transition of PAI-1

The serine protease inhibitor (serpin), plasminogen activator inhibitor-1 (PAI-1), is an important biomarker for cardiovascular disease and many cancers. It is therefore a desirable target for pharmaceutical intervention. However, to date, no PAI-1 inhibitor has successfully reached clinical trial, indicating the necessity to learn more about the mechanics of the serpin. Although its kinetics of inhibition have been extensively studied, less is known about the latency transition of PAI-1, in which the solvent-exposed reactive center loop (RCL) inserts into its central β-sheet, rendering the inhibitor inactive. This spontaneous transition is concomitant with a large translocation of the RCL, but no change in covalent structure. Here, we conjugated the fluorescent probe, NBD, to single positions along the RCL (P13-P5') to detect changes in solvent exposure that occur during the latency transition. The results support a mousetrap-like RCL-insertion that occurs with a half-life of 1-2 h in accordance with previous reports. Importantly, this study exposes unique transitions during latency that occur with a half-life of ∼5 and 25 min at the P5' and P8 RCL positions, respectively. We hypothesize that the process detected at P5' represents s1C detachment, while that at P8 results from a steric barrier to RCL insertion. Together, these findings provide new insights by characterizing multiple steps in the latency transition.

Nanomedicine as a strategy to fight thrombotic diseases

This review highlights the preclinical and clinical research based on the use of nano- and micro-carriers in thrombolytic drug delivery. Ischemic heart and stroke caused by thrombosis are the main causes of death in the world. Because of their inactivation in the blood, high doses of thrombolytics are administered to patients, increasing the risk of intracranial hemorrhage. Preclinical research conducted with lipid, polymer or magnetic nanoparticles loaded with thrombolytic drugs showed an enhancement of thrombolysis and a reduction of undesirable side effects. Targeted nanocarriers exhibited an increased accumulation into clot. Clinical trials were already conducted with lipid-based microbubbles combined with ultrasound and thrombolytic drug and showed thrombolysis improvement. Future validation of nanosystems is awaited in clinic. This research opens new strategies for the management of thrombotic diseases.

To dissolve a thrombus, thrombolytic drugs are administered, but they are rapidly inactivated in the blood. High amounts are thus injected to patients with the risk to develop intracranial hemorrhages. Nanocarriers and microbubbles have been tested in preclinical models to deliver thrombolytic drugs. These systems have the advantage to protect the drug from the degradation. In clinical trials, galactose and lipid-based microbubbles associated to ultrasound and thrombolytic drugs showed an enhancement of thrombolysis. Other systems are also expected with new drugs combined or not with endovascular intervention to treat ischemic heart or stroke.

Inhibition of SERPINe1 reduces rhabdoviral infections in zebrafish

While exploring the molecular mechanisms behind the fin hemorrhages that follow zebrafish (Danio rerio) early infection with viral haemorrhagic septicemia virus (VHSV), we discovered that most serpin (serine protease inhibitor) gene transcripts were upregulated, except those of serpine1. Surprisingly, only SERPINe1-derived 14-mer peptide and low molecular weight drugs targeting SERPINe1 (i.e. tannic acid, EGCG, tiplaxtinin) inhibited in vitro infections not only of VHSV, but also of other fish rhabdoviruses such as infectious hematopoietic necrosis virus (IHNV) and spring viremia carp virus (SVCV). While the mechanisms that inhibited rhabdoviral infections remain speculative, these and other results suggested that SERPINEe1-derived peptide specifically targeted viral infectivity rather than virions. Practical applications might be developed from these studies since preliminary evidences showed that tannic acid could be used to reduce VHSV-caused mortalities. These studies are an example of how the identification of host genes targeted by viral infections using microarrays might facilitate the identification of novel prevention drugs in aquaculture and illuminate viral infection mechanisms.

Small Molecule Inhibitors of Plasminogen Activator Inhibitor-1 Elicit Anti-Tumorigenic and Anti-Angiogenic Activity

Numerous studies have shown a paradoxical positive correlation between elevated levels of plasminogen activator inhibitior-1 (PAI-1) in tumors and blood of cancer patients with poor clinical outcome, suggesting that PAI-1 could be a therapeutic target. Here we tested two orally bioavailable small molecule inhibitors of PAI-1 (TM5275 and TM5441) for their efficacy in pre-clinical models of cancer. We demonstrated that these inhibitors decreased cell viability in several human cancer cell lines with an IC₅₀ in the 9.7 to 60.3 μM range and induced intrinsic apoptosis at concentrations of 50 μM. In vivo, oral administration of TM5441 (20 mg/kg daily) to HT1080 and HCT116 xenotransplanted mice increased tumor cell apoptosis and had a significant disruptive effect on the tumor vasculature that was associated with a decrease in tumor growth and an increase in survival that, however, were not statistically significant. Pharmacokinetics studies indicated an average peak plasma concentration of 11.4 μM one hour after oral administration and undetectable levels 23 hours after administration. The effect on tumor vasculature in vivo was further examined in endothelial cells (EC) in vitro and this analysis indicated that both TM5275 and TM5441 inhibited EC branching in a 3D Matrigel assay at concentrations where they had little effect on EC apoptosis. These studies bring novel insight on the activity of PAI-1 inhibitors and provide important information for the future design of inhibitors targeting PAI-1 as therapeutic agents in cancer.

Plasminogen Activator Inhibitor-1 in Cancer: Rationale and Insight for Future Therapeutic Testing

Despite its function as an inhibitor of urokinase and tissue-type plasminogen activator (PA), PA inhibitor-1 (PAI-1) has a paradoxical protumorigenic role in cancer, promoting angiogenesis and tumor cell survival. In this review, we summarize preclinical evidence in support of the protumorigenic function of PAI-1 that has led to the testing of small-molecule PAI-1 inhibitors, initially developed as antithrombotic agents, in animal models of cancer. The review discusses the challenges and the opportunities that lay ahead to the development of efficacious and nontoxic PAI-1 inhibitors as anticancer agents.

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.

Inhibition of PAI-1 antiproteolytic activity against tPA by RNA aptamers

Plasminogen activator inhibitor-1 (PAI-1; SERPINE1) inhibits the plasminogen activators: tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). Elevated levels of PAI-1 have been correlated with an increased risk for cardiovascular disease. Pharmacologically suppressing PAI-1 might prevent, or successfully treat PAI-1 related vascular diseases. This can potentially be accomplished by using small RNA molecules (aptamers). This study's goal is to develop RNA aptamers to a region of PAI-1 that will prevent the ability of PAI-1 to interact with the plasminogen activators. The aptamers were generated through a systematic evolution of ligands via exponential enrichment approach that ensures the creation of RNA molecules that bind to our target protein, PAI-1. In vitro assays were used to determine the effect of these aptamers on PAI-1's inhibitory activity. Three aptamers that bind to PAI-1 with affinities in the nanomolar range were isolated. The aptamer clones R10-4 and R10-2 inhibited PAI-1's antiproteolytic activity against tPA and disrupted PAI-1's ability to form a stable covalent complex with tPA. Increasing aptamer concentrations correlated positively with an increase in cleaved PAI-1. To the best of our knowledge, this is the first report of RNA molecules that inhibit the antiproteolytic activity of PAI-1.

Novel or expanding current targets in fibrinolysis

Globally the leading cause of long-term disability and mortality stems from cardiovascular diseases, which creates an enormous economic burden. Currently available treatments for intravascular thrombosis consist of a large repertoire of antithrombotic agents targeting coagulation and platelet function. However, the only agents available to enhance fibrinolysis are recombinant or modified forms of plasminogen activators. Their clinical use is limited by low efficacy, life-threatening side-effects (primarily caused by the high systemic dose required) and the inapplicability for prophylactic use. This review provides an update on the latest advances in targeting the antifibrinolytic proteins, plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor, and will highlight novel therapeutic avenues to enhance fibrinolysis.

Mechanisms of thrombosis in obesity

PURPOSE OF REVIEW

Obesity has become a worldwide epidemic that is driving increased morbidity and mortality from thrombotic disorders such as myocardial infarction, stroke, and venous thromboembolism. Effective prevention and treatment of thrombosis in obese patients is limited by an incomplete understanding of the underlying prothrombotic mechanisms and by uncertainties about risks, benefits, and dosing of anticoagulant drugs in this patient population.

RECENT FINDINGS

This review summarizes our current understanding of established and emerging mechanisms contributing to the obesity-induced prothrombotic state. The mechanistic impact of chronic inflammation and impaired fibrinolysis in mediating obesity-associated thrombosis is highlighted. Recent data demonstrating the aberrant expression of adipokines and microRNAs, which appear to function as key modulators of proinflammatory and prothrombotic pathways in obesity, are also reviewed. Finally, some challenges and new approaches to the prevention and management of thrombotic disorders in obese and overweight patients are discussed.

SUMMARY

Obesity-driven chronic inflammation and impaired fibrinolysis appear to be major effector mechanisms of thrombosis in obesity. The proinflammatory and hypofibrinolytic effects of obesity may be exacerbated by dysregulated expression and secretion of adipokines and microRNAs, which further increase the risk of thrombosis and suggest new potential targets for therapy.

Genetic polymorphisms in plasminogen activator inhibitor-1 predict susceptibility to steroid-induced osteonecrosis of the femoral head in Chinese population

Background

Steroid usage has been considered as a leading cause of non-traumatic osteonecrosis of the femoral head (ONFH), which is involved in hypo-fibrinolysis and blood supply interruption. Genetic polymorphisms in plasminogen activator inhibitor-1 (PAI-1) have been demonstrated to be associated with ONFH risk in several populations. However, this relationship has not been established in Chinese population. The aim of this study was to investigate the association of PAI-1 gene polymorphisms with steroid-induced ONFH in a large cohort of Chinese population.

Methods

A case–control study was conducted, which included 94 and 106 unrelated patients after steroid administration recruited from 14 provinces in China, respectively. Two SNPs (rs11178 and rs2227631) within PAI-1 were genotyped using Sequenom MassARRAY system.

Results

rs2227631 SNP was significantly associated with steroid-induced ONFH group in codominant (P = 0.04) and recessive (P = 0.02) models. However, there were no differences found in genotype frequencies of rs11178 SNP between controls and patients with steroid-induced ONFH (all P > 0.05).

Conclusions

Our data offer the convincing evidence for the first time that rs2227631 SNP of PAI-1 may be associated with the risk of steroid-induced ONFH, suggesting that the genetic variations of this gene may play an important role in the disease development.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1569909986109783.