Enhanced Thrombosis in Atherosclerosis-Prone Mice Is Associated With Increased Arterial Expression of Plasminogen Activator Inhibitor-1

Tale of two systems: the intertwining duality of fibrinolysis and lipoprotein metabolism

Fibrinolysis is an enzymatic process that breaks down fibrin clots, while dyslipidemia refers to abnormal levels of lipids and lipoproteins in the blood. Both fibrinolysis and lipoprotein metabolism are critical mechanisms that regulate a myriad of functions in the body, and the imbalance of these mechanisms is linked to the development of pathologic conditions, such as thrombotic complications in atherosclerotic cardiovascular diseases. Accumulated evidence indicates the close relationship between the 2 seemingly distinct and complicated systems-fibrinolysis and lipoprotein metabolism. Observational studies in humans found that dyslipidemia, characterized by increased blood apoB-lipoprotein and decreased high-density lipoprotein, is associated with lower fibrinolytic potential. Genetic variants of some fibrinolytic regulators are associated with blood lipid levels, supporting a causal relationship between these regulators and lipoprotein metabolism. Mechanistic studies have elucidated many pathways that link the fibrinolytic system and lipoprotein metabolism. Moreover, profibrinolytic therapies improve lipid panels toward an overall cardiometabolic healthier phenotype, while some lipid-lowering treatments increase fibrinolytic potential. The complex relationship between lipoprotein and fibrinolysis warrants further research to improve our understanding of the bidirectional regulation between the mediators of fibrinolysis and lipoprotein metabolism.

SERPINE1 mRNA Binding Protein 1 Is Associated with Ischemic Stroke Risk: A Comprehensive Molecular-Genetic and Bioinformatics Analysis of SERBP1 SNPs

The SERBP1 gene is a well-known regulator of SERPINE1 mRNA stability and progesterone signaling. However, the chaperone-like properties of SERBP1 have recently been discovered. The present pilot study investigated whether SERBP1 SNPs are associated with the risk and clinical manifestations of ischemic stroke (IS). DNA samples from 2060 unrelated Russian subjects (869 IS patients and 1191 healthy controls) were genotyped for 5 common SNPs-rs4655707, rs1058074, rs12561767, rs12566098, and rs6702742 SERBP1-using probe-based PCR. The association of SNP rs12566098 with an increased risk of IS (risk allele C; p = 0.001) was observed regardless of gender or physical activity level and was modified by smoking, fruit and vegetable intake, and body mass index. SNP rs1058074 (risk allele C) was associated with an increased risk of IS exclusively in women (p = 0.02), non-smokers (p = 0.003), patients with low physical activity (p = 0.04), patients with low fruit and vegetable consumption (p = 0.04), and BMI ≥25 (p = 0.007). SNPs rs1058074 (p = 0.04), rs12561767 (p = 0.01), rs12566098 (p = 0.02), rs6702742 (p = 0.036), and rs4655707 (p = 0.04) were associated with shortening of activated partial thromboplastin time. Thus, SERBP1 SNPs represent novel genetic markers of IS. Further studies are required to confirm the relationship between SERBP1 polymorphism and IS risk.

Eccentric, but not concentric muscle contraction induce inflammation and impairs fibrinolysis in healthy young men

Different types of muscle contraction can cause different damage to the musculature and differences in inflammatory responses. Acute increases in circulatory inflammation markers can influence the crosstalk between coagulation and fibrinolysis processes, increasing the risk of thrombus formation and detrimental cardiovascular events. The aim of this study was to analyze the effects of concentric and eccentric exercise on hemostasis markers, C-reactive protein (CRP), and the relationship between these variables. Eleven healthy subjects with a mean age of 25.4 ± 2.8, non-smokers, with no history of cardiovascular disease and blood type O, randomly performed an isokinetic exercise protocol consisting of 75 concentric (CP) or eccentric (EP) contractions of knee extension, divided into five sets of 15 repetitions combined with 30-s rest. Blood samples for analysis of FVIII, von Willebrand factor, tissue plasminogen activator (t-PA), plasminogen activator inhibitor type-1 (PAI-1), and CRP were collected pre, post, 24 h, and 48 h after each protocol. Increased levels of CRP at 48 h in EP versus CP (p = 0.002), increased PAI-1 activity 48 h in EP versus CP (p = 0.044), and a reduction in t-PA at 48 h when compared with post-protocol in both protocols (p = 0.001). A correlation was found between CRP and PAI-1 at 48 h of PE (r² = 0.69; p = 0.02). This study showed that both EP and CP increase the clotting process, albeit only the exercise performed eccentrically induces inhibition of fibrinolysis. This is possibly due to the increase in PAI-1 48 h after the protocol, which correlates with the increase in inflammation as demonstrated by the CRP levels.

Adipokines, adiposity, and atherosclerosis

Characterized by a surplus of whole-body adiposity, obesity is strongly associated with the prognosis of atherosclerosis, a hallmark of coronary artery disease (CAD) and the major contributor to cardiovascular disease (CVD) mortality. Adipose tissue serves a primary role as a lipid-storage organ, secreting cytokines known as adipokines that affect whole-body metabolism, inflammation, and endocrine functions. Emerging evidence suggests that adipokines can play important roles in atherosclerosis development, progression, as well as regression. Here, we review the versatile functions of various adipokines in atherosclerosis and divide these respective functions into three major groups: protective, deteriorative, and undefined. The protective adipokines represented here are adiponectin, fibroblast growth factor 21 (FGF-21), C1q tumor necrosis factor-related protein 9 (CTRP9), and progranulin, while the deteriorative adipokines listed include leptin, chemerin, resistin, Interleukin- 6 (IL-6), and more, with additional adipokines that have unclear roles denoted as undefined adipokines. Comprehensively categorizing adipokines in the context of atherosclerosis can help elucidate the various pathways involved and potentially pave novel therapeutic approaches to treat CVDs.

Human umbilical cord mesenchymal stem cell-derived exosomal microRNA-148a-3p inhibits neointimal hyperplasia by targeting Serpine1

BACKGROUND

Restenosis is inevitable when patients undergo percutaneous transluminal angioplasty due to neointimal hyperplasia (NIH). Human umbilical cord mesenchymal stem cell-derived exosomes (hucMSC-Exos) have been studied in the field of cardiovascular diseases. However, the effects and mechanisms of hucMSC-Exos on NIH are unclear. We aimed to investigate whether MSC-Exos regulate vascular smooth muscle cell (VSMC) functions to inhibit NIH and explore the underlying mechanisms.

METHODS

HucMSCs and mouse VSMCs were isolated and characterized by flow cytometry and immunofluorescence. HucMSC-Exos were identified by transmission electron microscopy, nanoparticle tracking analysis and western blots. Exosomes (Exos) were intravenously injected into mice with left common carotid artery ligation, and their effects on NIH were assessed by haematoxylin and eosin (H&E) and immunohistochemistry staining. The effects of hucMSC-Exos on VSMCs were evaluated by Cell Counting Kit-8, scratch wound, Transwell and Western blot assays. MicroRNA sequencing data in the Gene Expression Omnibus and mRNA sequencing results were used to identify potential molecules in hucMSC-Exos and target genes in VSMCs, respectively. We tested the regulatory effect of microRNAs in Exos and target genes in VSMCs using overexpression and knockdown experiments.

RESULTS

Primary hucMSCs, VSMCs and hucMSC-Exos were isolated and characterized. Administration of hucMSC-Exos suppressed NIH after artery ligation. H&E and immunohistochemistry results showed that hucMSC-Exos decreased the intima and media area and intima/media ratio, increased the contractile phenotype protein SM22a in the media layer and downregulated Serpine1 expression in the carotid artery. Exos were ingested by VSMCs, which inhibited migration and upregulated SM22a expression by suppressing Serpine1 expression in vitro. MiR-148a-3p was enriched in hucMSC-Exos and repressed Serpine1 by targeting its 3' untranslated region. Moreover, exosomal miR-148a-3p suppressed VSMC phenotypic switching and migration by targeting Serpine1.

CONCLUSIONS

We found that hucMSC-Exos inhibited NIH in a mouse carotid artery ligation model and that the inhibitory effects on VSMC phenotypic switching and migration were mediated by delivery of miR-148a-3p to VSMCs to target Serpine1.

Thrombus Structural Composition in Cardiovascular Disease

Thrombosis is a major complication of cardiovascular disease, leading to myocardial infarction, acute ischemic stroke, or venous thromboembolism. Thrombosis occurs when a thrombus forms inside blood vessels disrupting blood flow. Developments in thrombectomy to remove thrombi from vessels have provided new opportunities to study thrombus composition which may help to understand mechanisms of disease and underpin improvements in treatments. We aimed to review thrombus compositions, roles of components in thrombus formation and stability, and methods to investigate thrombi. Also, we summarize studies on thrombus structure obtained from cardiovascular patients and animal models. Thrombi are composed of fibrin, red blood cells, platelets, leukocytes, and neutrophil extracellular traps. These components have been analyzed by several techniques, including scanning electron microscopy, laser scanning confocal microscopy, histochemistry, and immunohistochemistry; however, each technique has advantages and limitations. Thrombi are heterogenous in composition, but overall, thrombi obtained from myocardial infarction are composed of mainly fibrin and other components, including platelets, red blood cells, leukocytes, and cholesterol crystals. Thrombi from patients with acute ischemic stroke are characterized by red blood cell- and platelet-rich regions. Thrombi from patients with venous thromboembolism contain mainly red blood cells and fibrin with some platelets and leukocytes. Thrombus composition from patients with myocardial infarction is influenced by ischemic time. Animal thrombosis models are crucial to gain further mechanistic information about thrombosis and thrombus structure, with thrombi being similar in composition compared with those from patients. Further studies on thrombus composition and function are key to improve treatment and clinical outcome of thrombosis.

Mild hyperlipidemia in mice aggravates platelet responsiveness in thrombus formation and exploration of platelet proteome and lipidome

Hyperlipidemia is a well-established risk factor for cardiovascular diseases. Millions of people worldwide display mildly elevated levels of plasma lipids and cholesterol linked to diet and life-style. While the prothrombotic risk of severe hyperlipidemia has been established, the effects of moderate hyperlipidemia are less clear. Here, we studied platelet activation and arterial thrombus formation in Apoe^-/- and Ldlr^-/- mice fed a normal chow diet, resulting in mildly increased plasma cholesterol. In blood from both knockout mice, collagen-dependent thrombus and fibrin formation under flow were enhanced. These effects did not increase in severe hyperlipidemic blood from aged mice and upon feeding a high-fat diet (Apoe^-/- mice). Bone marrow from wild-type or Ldlr^-/- mice was transplanted into irradiated Ldlr^-/- recipients. Markedly, thrombus formation was enhanced in blood from chimeric mice, suggesting that the hyperlipidemic environment altered the wild-type platelets, rather than the genetic modification. The platelet proteome revealed high similarity between the three genotypes, without clear indication for a common protein-based gain-of-function. The platelet lipidome revealed an altered lipid profile in mildly hyperlipidemic mice. In conclusion, in Apoe^-/- and Ldlr^-/- mice, modest elevation in plasma and platelet cholesterol increased platelet responsiveness in thrombus formation and ensuing fibrin formation, resulting in a prothrombotic phenotype.

Effects of 17β-Estradiol on the Plasminogen Activator System in Vascular Smooth Muscle Cells Treated with Lysophophatidylcholine

Objectives

When administered soon after menopause, hormone therapy can prevent coronary heart diseases in women. To explore the mechanism underlying the cardioprotective actions of estrogen, we investigated the effects of 17β-estradiol (17β-E₂) on the plasminogen activator system using cultured vascular smooth muscle cells (VSMCs).

Methods

VSMCs were isolated from rat aortas. Protein expression of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were evaluated using Western blotting and enzyme-linked immunosorbent assay, respectively. The enzyme activity of PAI-1 in a conditioned medium was assessed via reverse fibrin overlay zymography and that of t-PA was assessed via fibrin overlay zymography. Gene expression was quantified using real-time reverse transcription-polymerase chain reaction.

Results

Following pre-treatment for 24 hours, 17β-E₂ suppressed both protein expression and enzyme activity of PAI-1 stimulated by lysophosphatidylcholine (lysoPC) in a significant and dose-dependent manner at a near physiological concentration. Moreover, 17β-E₂ (10⁻⁷ M) inhibited PAI-1 gene expression, and ICI 182,780—a specific estrogen receptor antagonist—blocked the effects of 17β-E₂ on the PAI-1 protein. 17β-E₂ did not affect t-PA secretion but significantly enhanced free t-PA activity through reduced binding to PAI-1. Furthermore, 17β-E₂ suppressed intracellular reactive oxygen species production and nuclear factor-κB-mediated transcription.

Conclusions

In VSMCs stimulated with lysoPC, 17β-E₂ reduced PAI-1 expression through a non-receptor-mediated mechanism via antioxidant activity as well as a receptor-mediated mechanism; however, it did not alter t-PA secretion. Of note, 17β-E₂ suppressed PAI-1 activity and concurrently enhanced t-PA activity, suggesting a beneficial influence on fibrinolysis.

Breaking the vicious loop between inflammation, oxidative stress and coagulation, a novel anti-thrombus insight of nattokinase by inhibiting LPS-induced inflammation and oxidative stress

Thrombosis is a principle cause of cardiovascular disease, the leading cause of morbidity and mortality worldwide; however, the conventional anti-thrombotic approach often leads to bleeding complications despite extensive clinical management and monitoring. In view of the intense crosstalk between inflammation and coagulation, plus the contributing role of ROS to both inflammation and coagulation, it is highly desirable to develop safer anti-thrombotic agent with preserved anti-inflammatory and anti-oxidative stress activities. Nattokinase (NK) possesses many beneficial effects on cardiovascular system due to its strong thrombolytic and anticoagulant activities. Herein, we demonstrated that NK not only effectively prevented xylene-induced ear oedema in mice, but also remarkably protected against LPS-induced acute kidney injury in mice through restraining inflammation and oxidative stress, a central player in the initiation and progression of inflammation. Fascinatingly, in line with our in vivo data, NK elicited prominent anti-inflammatory activity in RAW264.7 macrophages via suppressing the LPS-induced TLR4 and NOX2 activation, thereby repressing the corresponding ROS production, MAPKs activation, and NF-κB translocation from the cytoplasm to the nucleus, where it mediates the expression of pro-inflammatory mediators, such as TNF-α, IL-6, NO, and PAI-1 in activated macrophage cells. In particular, consistent with the macrophage studies, NK markedly inhibited serum PAI-1 levels induced by LPS, thereby blocking the deposition of fibrin in the glomeruli of endotoxin-treated animals. In summary, we extended the anti-thrombus mechanism of NK by demonstrating the anti-inflammatory and anti-oxidative stress effects of NK in ameliorating LPS-activated macrophage signaling and protecting against LPS-stimulated AKI as well as glomeruler thrombus in mice, opening a comprehensive anti-thrombus strategy by breaking the vicious cycle between inflammation, oxidative stress and thrombosis.

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NK protects against LPS-induced AKI via inhibiting inflammation and oxidative stress.

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NK inhibits LPS-induced TRL4 and NOX2 activation in macrophages.

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NK inhibits inflammation and oxidative stress both in vitro and in vivo.

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NK inhibits LPS-induced PAI-I levels, thereby blocking glomerular thrombus in mice.

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NK may break the vicious loop between inflammation, oxidative stress and coagulation.

How useful are ferric chloride models of arterial thrombosis?

The ferric chloride models of arterial thrombosis are useful tools with which to investigate the cellular and molecular mechanisms that contribute to arterial thrombosis. Recent insights have, however, revealed the complex and multifaceted mechanism by which ferric chloride induces thrombus formation. Here, we discuss the strengths and weaknesses of the ferric chloride models of arterial thrombosis. Particular focus is given to the phenotypes of different knockout mice in the ferric chloride models and how these compare to other models with independent modes of initiation. Further, we discuss the relevance of the ferric chloride models to the human pathology of atherothrombotic disease.

Local Production of Soluble Urokinase Plasminogen Activator Receptor and Plasminogen Activator Inhibitor-1 in the Coronary Circulation Is Associated With Coronary Endothelial Dysfunction in Humans

Background Soluble urokinase plasminogen activator receptor (su PAR ) is a proinflammatory biomarker associated with immune activation and fibrinolysis inhibition. Plasminogen activator inhibitor ( PAI -1) is associated with excessive fibrin accumulation, thrombus formation, and atherosclerosis. The relationship between cross-coronary su PAR and PAI -1 production and endothelial dysfunction remains unknown. Methods and Results Seventy-nine patients (age 53±10 years, 75% women) with angina and normal coronary arteries or mild coronary artery disease (<40% stenosis) on angiogram underwent acetylcholine assessment of epicardial endothelial dysfunction (mid-left anterior descending coronary artery diameter decrease >20% after acetylcholine) and mircovascular endothelial dysfunction (coronary blood flow change <50% after acetylcholine). Simultaneous left main and coronary sinus su PAR and PAI -1 levels were measured in each patient before acetylcholine administration, and cross-coronary su PAR and PAI -1 production rates were calculated. Patients' characteristics, except for age (51±10 versus 57±9, P=0.02), and resting coronary hemodynamics were not significantly different between patients with (26%) versus without (74%) epicardial endothelial dysfunction. Patients' characteristics and resting coronary hemodynamics were not significantly different between those with (62%) and those without (38%) mircovascular endothelial dysfunction. Patients with mircovascular endothelial dysfunction demonstrated local coronary su PAR production versus su PAR extraction in patients with normal microvascular function (median 25.8 [interquartile range 121.6, -23.7] versus -12.7 [52.0, -74.8] ng/min, P=0.03). Patients with epicardial endothelial dysfunction had higher median coronary PAI -1 production rates compared with those with normal epicardial endothelial function (1224.7 [12 940.7, -1915.4] versus -187.4 [4444.7, -4535.8] ng/min, P=0.03). Conclusions su PAR is released in coronary circulation of patients with mircovascular endothelial dysfunction and extracted in those with normal microvascular function. Cross-coronary PAI -1 release is higher in humans with epicardial endothelial dysfunction.

Applications and Limitations of Mouse Models for Understanding Human Atherosclerosis

Most of the biological understanding of mechanisms underlying coronary artery disease (CAD) derives from studies of mouse models. The identification of multiple CAD loci and strong candidate genes in large human genome-wide association studies (GWASs) presented an opportunity to examine the relevance of mouse models for the human disease. We comprehensively reviewed the mouse literature, including 827 literature-derived genes, and compared it to human data. First, we observed striking concordance of risk factors for atherosclerosis in mice and humans. Second, there was highly significant overlap of mouse genes with human genes identified by GWASs. In particular, of the 46 genes with strong association signals in CAD GWASs that were studied in mouse models, all but one exhibited consistent effects on atherosclerosis-related phenotypes. Third, we compared 178 CAD-associated pathways derived from human GWASs with 263 from mouse studies and observed that the majority were consistent between the species.

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.

Acute and persistent platelet and coagulant activities in atherothrombosis

The potential relevance of murine atherothrombosis models for understanding human disease has been debated in the past. Despite this, in the last decade, many thrombosis studies with atherogenic Apoe(-/-) mice have been performed, which provide novel insight into the molecular mechanisms by which platelet and coagulation processes accomplish acute thrombus formation after plaque disruption in vivo. Support for these mechanisms has come from whole blood flow perfusion studies over plaque material in vitro, which are also reviewed in this study. The main plaque-derived triggers for thrombus formation appear to be collagen and tissue factor, next to bioactive mediators such as prostaglandin E2. The atherothrombotic process relies on collagen- and ADP-receptor-induced platelet activation as well as on thrombin/fibrin generation via the extrinsic and intrinsic coagulation pathways. Less is known of the persistent effects of a thrombus on atherosclerosis progression, but evidence suggests roles herein of activated platelets and ongoing thrombin generation.

Biomarkers of kidney injury and klotho in patients with atherosclerotic renovascular disease

BACKGROUND AND OBJECTIVES

Occlusive renovascular disease and hypertension may progress to CKD. Circulating levels of several biomarkers, including fibroblast growth factor (FGF)-23, Klotho, and soluble urokinase plasminogen activator receptor (suPAR), are altered in patients with CKD, but their role in essential hypertension (EH) and renovascular hypertension (RVH) remains unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Levels of FGF-23, Klotho, suPAR, plasminogen activator inhibitor (PAI)-1, tissue factor, and tissue factor pathway inhibitor (TFI) were measured in the inferior vena cava and renal vein of hypertensive patients with atherosclerotic renal artery stenosis (n=12) or age-matched participants with EH (n=12) and relatively preserved renal function. Single-kidney blood flow was measured to calculate renal release of markers. For control, peripheral vein levels were measured in healthy volunteers (HVs; n=12).

RESULTS

FGF-23 levels did not differ among the groups, whereas Klotho levels were lower in participants with RVH and EH than in HVs, and suPAR levels were elevated in patients with RVH compared with HVs and patients with EH (6.1±1.5 versus 4.4±1.9 and 3.2±1.2 ng/ml, P<0.05). PAI-1 levels were higher in patients with RVH than in patients with EH, but tissue factor and TFI levels were not statistically significantly different. After adjustment for GFR, Klotho levels remained decreased in both RVH and EH, and suPAR and PAI-1 levels remained elevated in RVH. eGFR correlated inversely with systemic and renal vein suPAR levels, and directly with systemic Klotho levels.

CONCLUSIONS

Klotho levels are low in hypertensive patients, whereas suPAR and PAI-1 levels are specifically elevated in RVH, correlating with GFR. Klotho, PAI-1, and suPAR may be markers of kidney injury in hypertensive patients.

Vitronectin-binding PAI-1 protects against the development of cardiac fibrosis through interaction with fibroblasts

Plasminogen activator inhibitor-1 (PAI-1) promotes or abates fibrotic processes occurring in different organs. Binding of PAI-1 to vitronectin, an extracellular matrix component, may inhibit vitronectin-integrin complex-mediated cellular responses in pathophysiological conditions. To investigate the importance of plasmin suppression vs vitronectin-binding pathways of PAI-1 in cardiac fibrosis, we studied uninephrectomized mice fed a high salt diet and infused with angiotensin II (Ang II) together with different PAI-1 variants, including PAI-1AK (AK) that inhibits plasminogen activators but does not bind vitronectin, PAI-1RR (RR) that binds vitronectin but does not have protease inhibitory effects or control PAI-1 (CPAI), the control mutant that has similar molecular backbone and half-life as AK and RR while retaining all functions of native PAI-1. Compared with RR and CPAI, non-vitronectin-binding AK significantly increased expression of cardiac fibroblast marker, periostin (Ang+AK 8.40±3.55 vs Ang+RR 2.23±0.44 and Ang+CPAI 2.33±0.12% positive area, both P<0.05) and cardiac fibrosis (Ang+AK 1.79±0.26% vs Ang+RR 0.91±0.18% and Ang+CPAI 0.81±0.12% fibrotic area, both P<0.05), as well as Col1 mRNA (Ang+AK 12.81±1.84 vs Ang+RR 4.04±1.06 and Ang+CPAI 5.23±1.21 fold increase, both P<0.05). To elucidate mechanisms underlying the protective effects of vitronectin-binding PAI-1 against fibrosis, fibroblasts from normal adult human ventricles were stimulated with Ang and different PAI-1 variants. Protease inhibitory AK and CPAI increased supernatant fibronectin, while decreasing plasminogen activator/plasmin activities and matrix metalloproteinase. RR and CPAI variants significantly reduced fibroblast expression of integrin β3, vitronectin level in the supernatant and fibroblast adhesion to vitronectin compared with the non-vitronectin-binding AK. Further, RR and CPAI preserved apoptotic, decreased anti-apoptotic and proliferative activities in fibroblasts. Thus, PAI-1 promotes or protects against development of cardiac fibrosis differentially through the protease inhibitory pathway or through its binding to vitronectin.

Proinflammatory, immunomodulating, and prothrombotic properties of anemia and red blood cell transfusions

For many years, the traditional treatment for hospitalized patients in the United States who have developed anemia, whether associated with medical illness, surgical procedures or trauma, has been red blood cell transfusion, despite the absence of supporting data in many patient populations. Emerging evidence suggests that transfusions may, in fact, be associated with risk beyond commonly held concerns of microbial transmission and acute antigen-antibody reactions. The following overview represents a biological paradigm for understanding the relationship between medical illness, surgical procedures, inflammatory states, anemia, red blood cell transfusion and immunothrombotic phenomena among hospitalized patients.

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

INTRODUCTION

Plasminogen activator inhibitor-1 (PAI-1), the serine protease inhibitor (serpin), binds to and inhibits the plasminogen activators-tissue-type plasminogen activator (tPA) and the urokinase-type plasminogen activator (uPA). This results in both a decrease in plasmin production and a decrease in the dissolution of fibrin clots. Elevated levels of PAI-1 are correlated with an increased risk for cardiovascular disease and have been linked to obesity and metabolic syndrome. Consequently, the pharmacological suppression of PAI-1 might prevent or treat vascular disease.

AREAS COVERED

This article provides an overview of the patenting activity on PAI-1 inhibitors. Patents filed by pharmaceutical companies or individual research groups are described, and the biological and biochemical evaluation of the inhibitors, including in vitro and in vivo studies, is discussed. An overview of patents pertaining to using these inhibitors for treating various diseases is also included.

EXPERT OPINION

Although there is still no PAI-1 inhibitor being evaluated in a clinical setting or approved for human therapy, research in this field has progressed, and promising new compounds have been designed. Most research has focused on improving the pharmacological profile of these compounds, which will hopefully allow them to proceed to clinical studies. Despite the need for further testing and research, the potential use of PAI-1 inhibitors for treating cardiovascular disease appears quite promising.

Adipokines and thrombosis

1. Obesity is a major risk factor for cardiovascular disease. An increased body mass index (BMI) is associated with venous thromboembolism, myocardial infarction, stroke and stent thrombosis after percutaneous interventions. Studies in mouse models of obesity and induced arterial or venous thrombosis have provided insights into the mechanisms involved. 2. In addition to elevated circulating levels of fibrinogen, factor VII and plasminogen activator inhibitor (PAI)-1, changes in platelet biology and function may underlie the increased (athero) thrombotic risk in obesity. These include elevated platelet counts, an increase in mean platelet volume, an increased platelet aggregatory response to agonists and a reversible resistance to the anti-aggregatory effects of nitric oxide and prostacyclin I(2) . 3. Specific adipokines mediate the prothrombotic state in obesity. Of these, leptin enhances both arterial and venous thrombosis by promoting platelet adhesion, activation and aggregation. Leptin also induces tissue factor expression by human neutrophils and other cells. C-Reactive protein enhances the formation of monocyte-platelet aggregates and also promotes P-selectin expression and platelet adhesion to endothelial cells. Further, the adipose tissue is a significant source of tissue factor and PAI-1. Conversely, the circulating levels of adiponectin, a hormone that exerts vasculoprotective, anti-atherosclerotic and antithrombotic effects, are reduced in obese individuals. 4. A better understanding of the interactions of the adipose tissue with circulating and vascular cells and the dissection of the mechanisms linking adipokines to arterial and venous thrombosis may identify obese individuals at particularly high cardiovascular risk and indicate promising vasculoprotective and therapeutic targets.

Impact of lysophosphatidylcholine on the plasminogen activator system in cultured vascular smooth muscle cells

The balance between tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) regulates fibrinolysis. PAI-1 expression increases in atherosclerotic arteries and vascular smooth muscle cells (VSMCs) are one of major constituents of atheroma. We investigated the impact of lysophosphatidylcholine (lysoPC), an active component of oxidized low-density lipoprotein, on the plasminogen activator system of the rat VSMCs. The lysoPC stimulated the protein and gene expressions of PAI-1 but did not affect the protein expression of t-PA. Fibrin overlay zymography revealed that lysoPC increased the activity of PAI-1 in the conditioned media, while concurrently decreasing that of free t-PA. Vitamin E inhibited the lysoPC-induced PAI-1 expression. Further, lysoPC increased the intracellular reactive oxygen species (ROS) formation. Caffeic acid phenethyl ester, an inhibitor of NF-κB, blocked this lysoPC effect. Indeed, lysoPC induced the NF-κB-mediated transcriptional activity as measured by luciferase reporter assay. In addition, genistein, an inhibitor of protein-tyrosine kinase (PTK), diminished the lysoPC effect, while 7,12-dimethylbenz[a]anthracene, a stimulator of PTK, stimulated PAI-1 production. In conclusion, lysoPC does not affect t-PA expression but induces PAI-1 expression in the VSMC by mediating NF-κB and the genistein-sensitive PTK signaling pathways via oxidative stress. Importantly, lysoPC stimulates the enzyme activity of PAI-1 and suppresses that of t-PA.

Sources of tissue factor that contribute to thrombosis after rupture of an atherosclerotic plaque

Hyperlipidemia leads to the formation of oxidized LDL (oxLDL), vessel dysfunction, atherosclerotic disease, and ultimately to plaque rupture and thrombosis. OxLDL induces tissue factor (TF) expression in various cell types, including monocytes and macrophages. High levels of TF are present in atherosclerotic plaques and this represents that major source of TF that triggers thrombosis after plaque rupture. In addition, increased levels of "circulating TF" are observed in hyperlipidemic animals and patients. This is due to induced TF expression in monocytes and release of monocyte-derived, TF(+) microparticles, which represents a minor source of TF that likely contributes to thrombosis after plaques rupture. This review will summarize the connections between hyperlipidemia and TF expression within atherosclerotic plaques and circulating monocytes, as well as its inhibition by statins.

Endothelial cells and magnesium: implications in atherosclerosis

There is no doubt that the functional and structural integrity of the endothelium is critical in maintaining vascular homoeostasis and in preventing atherosclerosis. In the light of epidemiological and experimental studies, magnesium deficiency is emerging as an inducer of endothelial dysfunction. In particular, data on the effects of low extracellular magnesium on cultured endothelial cells reinforce the idea that correcting magnesium homoeostasis might be a helpful and inexpensive intervention to prevent and treat endothelial dysfunction and, consequently, atherosclerosis.

Effect of the factor Xa inhibitor rivaroxaban on arterial thrombosis in wild-type and apolipoprotein E-deficient mice

Rivaroxaban is a potent and specific direct inhibitor of coagulation factor Xa. Recent studies have highlighted its effectiveness in the prevention of venous thrombosis and embolic stroke due to atrial fibrillation. To evaluate the antithrombotic effects of rivaroxaban in an in vivo model of arterial thrombosis, photochemical vascular injury was induced in wild-type mice by intravenous rose bengal (50 mg/kg body weight [BW]) followed by illumination of the left common carotid artery using a 543 nm helium-neon laser beam. Rivaroxaban, injected concomitantly with rose bengal at doses of 1.0, 1.5, 2.0, or 3.0 mg/kg BW, dose-dependently prolonged the times to first thrombotic occlusion and stable thrombosis. Quantitative analysis of carotid flow curves revealed higher blood volumes passing through the injured artery with increasing rivaroxaban doses (P<0.01 and P<0.001 vs. vehicle for 2.0 and 3.0 mg/kg , respectively), suggesting a dose-dependent effect on vascular patency. Consistently, a significantly higher proportion of mice that received 2.0 and 3.0 mg/kg rivaroxaban exhibited patent carotid arteries at the end of the flow monitoring period compared to vehicle alone (P<0.05 and P<0.001, respectively). Histological analysis showed complete thrombotic arterial occlusion in vehicle-treated mice compared to less thrombotic material in mice injected with 3.0 mg/kg rivaroxaban (P<0.05). Rivaroxaban also prolonged the time to cessation of tail bleeding in a dose-dependent manner, starting at 1.5 mg/kg. Similar findings were obtained in apolipoprotein E-knockout mice. Rivaroxaban may exert beneficial effects by preventing arterial thrombosis and vascular occlusion after endothelial injury.

Involvement of NADPH oxidase in up-regulation of plasminogen activator inhibitor-1 and heat shock factor-1 in mouse embryo fibroblasts induced by oxidized LDL and in apolipoprotein E-deficient mice

The present study demonstrated that oxidized LDL (oLDL) increased the generation of superoxide and hydrogen peroxide (H(2)O(2)), the abundances of NADPH oxidase (NOX)4, NOX2, p22-phox and lectin-like oLDL receptor-1 (LOX-1) in wild-type or heat shock factor-1 (HSF1)-deficient mouse embryo fibroblasts (MEF). LOX-1 antibody inhibited LDL or oLDL-induced expression of NOX components in MEF. Abundance of HSF1 or plasminogen activator inhibitor-1 (PAI-1) was increased by oLDL in wild-type, but not in HSF1-deficient MEF. Diphenyleneiodonium or siRNA for NOX or p22-phox inhibited oLDL-induced increases of HSF1, PAI-1 and H(2)O(2) in MEF. Increased NOX4, NOX2, LOX1, HSF1 and PAI-1 were detected in aortae and hearts of apolipoprotein E-knockout (apoE-KO) mice compared to controls, which were associated with increased serum cholesterol or plasma PAI-1. The results suggest that NOX is required for oLDL-induced HSF1 or PAI-1 expression in MEF, which was supported by the up-regulation of NOX, LOX-1, HSF1 and PAI-1 in apoE-KO mice.

Vascular smooth muscle Jak2 deletion prevents angiotensin II-mediated neointima formation following injury in mice

The in vitro treatment of vascular smooth muscle cells (VSMC) with angiotensin II (Ang II) causes Janus kinase 2 (Jak2) to interact with the Ang II type 1 receptor (AT(1)-R) resulting in enhanced cell growth. However, the role that Jak2 plays in AT(1)-R-mediated vascular cell growth and remodeling in vivo is less clear. We hypothesized that in vivo, Jak2 plays a rate-limiting role in Ang II-mediated neointima formation following vascular injury. Using the Cre-loxP system, we conditionally ablated Jak2 from the VSMC of mice. We found that these mice are protected from Ang II-mediated neointima formation following iron chloride-induced vascular injury. In addition, the VSMC Jak2 null mice were protected from injury-induced vascular fibrosis and the pathological loss of the contractile marker, smooth muscle α-actin. Finally, when compared to controls, the VSMC Jak2 null mice exhibited significantly less Ang II-induced VSMC proliferation and migration in vitro and in vivo and more apoptosis. These results suggest that Jak2 plays a central role in the causation of Ang II-induced neointima formation following vascular injury and may provide a novel target for the prevention of neointima formation.

COX-1(+/-)COX-2(-/-) genotype in mice is associated with shortened time to carotid artery occlusion through increased PAI-1

BACKGROUND

We found a high incidence of thrombotic deaths in COX-1(+/-)COX-2(-/-) mice and sought to define the mechanism of these events. The cyclooxygenase products thromboxane A(2) and prostacyclin are important in the regulation of coagulation but their role in fibrinolysis is largely unexplored. PAI-1 blocks fibrinolysis by inhibiting plasminogen activator.

AIM

Our objective was to explain the mechanism of increased thrombosis associated with the COX-1(+/-)COX-2(-/-) genotype.

METHODS

Carotid artery occlusion times were measured after photochemical injury. PAI-1 levels were measured in the plasma by ELISA. PAI-1 levels in the aorta were measured by RT-PCR and Western blotting. Urinary metabolites of Thromboxane A(2) and prostacyclin were measured by ELISA.

RESULTS

The COX-1(+/-)COX-2(-/-) genotype is associated with a decreased time to occlusion in the carotid artery thrombosis model (30 ± 5 minutes vs 60 ± minutes in wild type, p<.001). The COX-1(-/-)COX-2(+/+), COX-1(+/-)COX-2(+/-) and COX-1(+/-)COX-2(+/+) all had occlusion times similar to wild type. COX-1(+/+)COX-2(-/-) had a prolonged occlusion time. COX-1(+/-)COX-2(-/-) had increased PAI-1 levels in the plasma and aorta and with a prolonged euglobulin lysis time (37.4 ± 10.2 hours vs 15.6 ± 9.8 hours in wild type, p<.004). The decreased time to occlusion in the COX-1(+/-)COX2(-/-) mice was normalized by an inhibitory antibody to PAI-1 whereas the antibody had no effect on the time to occlusion in wild type mice.

CONCLUSION

The COX-1(+/-)COX-2(-/-) genotype is associated with a shortened time to occlusion in the carotid thrombosis model and the shortened time to occlusion is mediated through increased PAI-1 levels resulting in decreased fibrinolysis.

Use of mouse models to study plasminogen activator inhibitor-1

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

Regulation of platelet function by class B scavenger receptors in hyperlipidemia

Platelets constitutively express class B scavenger receptors CD36 and SR-BI, 2 closely related pattern recognition receptors best known for their roles in lipoprotein and lipid metabolism. The biological role of scavenger receptors in platelets is poorly understood. However, in vitro and in vivo data suggest that class B scavenger receptors modulate platelet function and contribute significantly to thrombosis by sensing pathological or physiological ligands, inducing prothrombotic signaling, and increasing platelet reactivity. Platelet CD36 recognizes a novel family of endogenous oxidized choline phospholipids that accumulate in plasma of hyperlipidemic mice and in plasma of subjects with low high-density lipoprotein levels. This interaction leads to the activation of specific signaling pathways and promotes platelet activation and thrombosis. Platelet SR-BI, on the other hand, plays a critical role in the induction of platelet hyperreactivity and accelerated thrombosis under conditions associated with increased platelet cholesterol content. Intriguingly, oxidized high-density lipoprotein, an SR-BI ligand, can suppress platelet function. These recent findings demonstrate that platelet class B scavenger receptors play roles in thrombosis in dyslipidemia and may contribute to acute cardiovascular events in vivo in hypercholesterolemia.

Plasminogen activator inhibitor-1 (PAI-1): a key factor linking fibrinolysis and age-related subclinical and clinical conditions

INTRODUCTION

The close relationship existing between aging and thrombosis has growingly been studied in this last decade. The age-related development of a prothrombotic imbalance in the fibrinolysis homeostasis has been hypothesized as the basis of this increased cardiovascular and cerebrovascular risk. Fibrinolysis is the result of the interactions among multiple plasminogen activators and inhibitors constituting the enzymatic cascade, and ultimately leading to the degradation of fibrin. The plasminogen activator system plays a key role in a wide range of physiological and pathological processes.

METHODS

Narrative review.

RESULTS

Plasminogen activator inhibitor-1 (PAI-1) is a member of the superfamily of serine-protease inhibitors (or serpins), and the principal inhibitor of both the tissue-type and the urokinase-type plasminogen activator, the two plasminogen activators able to activate plasminogen. Current evidence describing the central role played by PAI-1 in a number of age-related subclinical (i.e., inflammation, atherosclerosis, insulin resistance) and clinical (i.e., obesity, comorbidities, Werner syndrome) conditions is presented.

CONCLUSIONS

Despite some controversial and unclear issues, PAI-1 represents an extremely promising marker that may become a biological parameter to be progressively considered in the prognostic evaluation, in the disease monitoring, and as treatment target of age-related conditions in the future.

Scavenger receptor BI modulates platelet reactivity and thrombosis in dyslipidemia

Hypercholesterolemia is associated with increased platelet sensitivity to agonists and a prothrombotic phenotype. Mechanisms of platelet hypersensitivity are poorly understood; however, increased platelet cholesterol levels associated with hypercholesterolemia were proposed as leading to hypersensitivity. Scavenger receptor class B type I (SR-BI) in the liver controls plasma high-density lipoprotein (HDL) levels, and SR-BI-deficient mice display a profound dyslipoproteinemia. SR-BI is also expressed on platelets, and recent studies have suggested a role for SR-BI in platelet function; however, its role in hemostasis is unknown. Our present studies demonstrated that non-bone marrow-derived SR-BI deficiency and the dyslipidemia associated with it lead to platelet hyperreactivity that was mechanistically linked to increased platelet cholesterol content. Platelet-specific deficiency of SR-BI, on the other hand, was associated with resistance to hyperreactivity induced by increased platelet cholesterol content. Intravital thrombosis studies demonstrated that platelet SR-BI deficiency protected mice from prothrombotic phenotype in 2 types of dyslipidemia associated with increased platelet cholesterol content. These novel findings demonstrate that SR-BI plays dual roles in thrombosis and may contribute to acute cardiovascular events in vivo in hypercholesterolemia.

Diabetes is a proinflammatory state: a translational perspective

The diabetic state confers an increased propensity to accelerated atherogenesis. Inflammation is pivotal in atherosclerosis; in addition to the established risk factors, inflammation appears to play a pivotal role in diabetes and its complications. Evidence for increased inflammation includes: increased levels of plasma C-reactive protein, the prototypic marker of inflammation; increased levels of plasminogen-activator inhibitor; increased monocyte superoxide and proinflammatory cytokine release (IL-1, IL-6 and TNF-alpha); increased monocyte adhesion to endothelium; increased NF-kappaB activity; and increased Toll-like receptor 2 and 4 expression and activity in diabetes. Thus, it appears that both Type 1 and Type 2 diabetes are proinflammatory states and that these could contribute to increased diabetic vasculopathies.

Type 2 scavenger receptor CD36 in platelet activation: the role of hyperlipemia and oxidative stress

Platelet hyper-reactivity and a systemic prothrombotic state are associated with atherosclerosis and other inflammatory conditions. CD36, a member of the Type 2 scavenger receptor family, is a multiligand pattern recognition receptor that recognizes specific oxidized phospholipids, molecules expressed on microbial pathogens, apoptotic cells, and cell-derived microparticles. Recent studies have demonstrated that CD36 binding to oxidized LDL or microparticles activates a specific signaling pathway that induces platelet activation. This pathway is activated in vivo in the setting of hyperlipidemia and oxidant stress. Genetic deletion of CD36 protects mice from pathological thrombosis associated with hyperlipidemia without any apparent effect on normal hemostasis. Targeting CD36 or its signaling pathway could potentially lead to the development of novel antithrombotic therapies for patients with atheroinflammatory disorders.

Platelet dense-granule secretion plays a critical role in thrombosis and subsequent vascular remodeling in atherosclerotic mice

BACKGROUND

Platelet aggregation plays a critical role in myocardial infarction and stroke; however, the role of platelet secretion in atherosclerotic vascular disease is poorly understood. Therefore, we examined the hypothesis that platelet dense-granule secretion modulates thrombosis, inflammation, and atherosclerotic vascular remodeling after injury.

METHODS AND RESULTS

Functional deletion of the Hermansky-Pudlak syndrome 3 gene (HPS3(-/-)) markedly reduces platelet dense-granule secretion. HPS3(-/-) mice have normal platelet counts, platelet morphology, and alpha-granule number, as well as maximal secretion of the alpha-granule marker P-selectin; however, their capacity to form platelet-leukocyte aggregates is significantly reduced (P<0.05). To examine the role of platelet dense-granule secretion in these processes, atherosclerosis-prone mice with combined genetic deficiency of apolipoprotein E and HPS3 (ApoE(-/-), HPS3(-/-)) were compared with congenic, atherosclerosis-prone mice with normal platelet secretion (ApoE(-/-), HPS3(+/+)). After 16 to 18 weeks on a high-fat diet, both groups of mice had similar fasting cholesterol levels and body weight. Carotid arteries of ApoE(-/-), HPS3(+/+) mice thrombosed rapidly after FeCl(3) injury, but ApoE(-/-), HPS3(-/-) mice were completely resistant to thrombotic arterial occlusion (P<0.01). Three weeks after injury, neointimal hyperplasia (from alpha-smooth muscle actin-positive cells) was significantly less (P<0.001) in arteries from ApoE(-/-), HPS3(-/-) mice. In ApoE(-/-), HPS3(-/-) mice, there were also pronounced reductions in arterial inflammation, as indicated by a 74% decrease in CD45-positive leukocytes (P<0.01) and a 73% decrease in Mac-3-positive macrophages (P<0.05).

CONCLUSIONS

In atherosclerotic mice, reduced platelet dense-granule secretion is associated with marked protection against the development of arterial thrombosis, inflammation, and neointimal hyperplasia after vascular injury.

The antiangiogenic activity of rPAI-1(23) inhibits vasa vasorum and growth of atherosclerotic plaque

Plaque vascularity has been implicated in its growth and stability. However, there is a paucity of information regarding the origin of plaque vasculature and the role of vasa vasorum in plaque growth. To inhibit growth of vasa vasorum in atherogenic mice and assess its effect on plaque growth, we used a truncated plasminogen activator inhibitor (PAI)-1 protein, rPAI-1(23), that has significant antiangiogenic activity. Female LDLR(-/-)ApoB-48-deficient mice fed Paigen's diet without cholate for 20 weeks received rPAI-1(23) treatment (n=21) for the last 6 weeks. Plaque size and vasa vasorum density were compared to 2 controls: mice fed Paigen's diet and treated with saline for the last 6 weeks (n=16) and mice fed Paigen's diet until the onset of treatment (n=14). The rPAI-1(23) treatment significantly reduced plaque area and plaque cholesterol in the descending aorta and plaque area in the innominate artery. Measurements of reconstructed confocal microscopy images of vasa vasorum demonstrate that rPAI-1(23) treatment decreased vasa vasorum area and length, which was supported by microCT images. Confocal images provide evidence for vascularized plaque in the saline-treated group but not in rPAI-1(23)-treated mice. The increased vessel density in saline-treated mice is attributable, in part, to upregulated fibroblast growth factor-2 expression, which is inhibited by rPAI-1(23). In conclusion, rPAI-1(23) inhibits growth of vasa vasorum, as well as vessels within the adjacent plaque and vessel wall, through inhibition of fibroblast growth factor-2, leading to reduced plaque growth in atherogenic female LDLR(-/-)ApoB-48-deficient mice.

WRN polymorphisms affect expression levels of plasminogen activator inhibitor type 1 in cultured fibroblasts

BACKGROUND

Recessive mutations in WRN gene eliminate WRN protein function (helicase) and cause Werner syndrome. One of the most important clinical features of Werner syndrome patients are the premature onset and accelerated atherosclerosis process. Studies carried out on polymorphic WRN locus have shown that the alleles 1367R and 1074L confer protection for cardiovascular disease. Given that the levels of plasminogen activator inhibitor type 1 (PAI-1) were found to be significantly increased in Werner syndrome patients, is quiet possible that PAI-1 expression could be under regulation of WRN helicase. Therefore the purpose of this work was to evaluate the role of WRN polymorphism in modulating the expression of PAI-1.

METHODS

In order to accomplish our aim, an array of primary cultured fibroblasts from normal adult donors was genotyped for polymorphisms of both the WRN and PAI-1 loci. In addition, steady state levels of WRN and PAI-1 were measured by semi-quantitative RT-PCR assays in such cultures. To search for the potential relationship between the lack of WRN protein and PAI-1 expression, heterozygous cultures of fibroblasts (1367RC/1074LF; WRN genotype) were treated with a molecule of interference RNA against WRN messenger RNA (mRNA).

RESULTS

We found that, carriers of 1367R and 1074L alleles of WRN shown to have low amounts of PAI-1 in plasma (7.56 +/- 5.02), as compared with carriers of 1367C and 1074F alleles (16.09 +/- 6.03). Moreover, fibroblasts from carriers with these alleles had low expression levels of PAI-1 mRNA. The treatment of heterozygous primary fibroblast cultures (1367RC/1074LF; WRN genotype) with iRNA against WRN mRNA caused PAI-1 overexpression. Treatment with normal PAI-1 inducers (TGFbeta, TNFalpha, or insulin) in these cultures and from those with genotypes 1367CC/1074FF and 1367RR/1074FL resulted in a genotype-dependent PAI-1 expression level.

CONCLUSION

Our results suggest that polymorphisms in the WRN gene might have a significant role regulating PAI-1 levels in healthy individuals and "normal states" as well as acute or chronic stress, obesity, aging, acute inflammation, among others, where characteristic high levels of insulin, TNF alpha and TGFbeta, could favor PAI-1 high levels in carriers with polymorphic variants (C and F alleles), beyond the levels reached by carriers with other alleles (R and L alleles).

Platelet CD36 links hyperlipidemia, oxidant stress and a prothrombotic phenotype

Dyslipidemia is associated with a prothrombotic phenotype; however, the mechanisms responsible for enhanced platelet reactivity remain unclear. Proatherosclerotic lipid abnormalities are associated with both enhanced oxidant stress and the generation of biologically active oxidized lipids, including potential ligands for the scavenger receptor CD36, a major platelet glycoprotein. Using multiple mouse in vivo thrombosis models, we now demonstrate that genetic deletion of Cd36 protects mice from hyperlipidemia-associated enhanced platelet reactivity and the accompanying prothrombotic phenotype. Structurally defined oxidized choline glycerophospholipids that serve as high-affinity ligands for CD36 were at markedly increased levels in the plasma of hyperlipidemic mice and in the plasma of humans with low HDL levels, were able to bind platelets via CD36 and, at pathophysiological levels, promoted platelet activation via CD36. Thus, interactions of platelet CD36 with specific endogenous oxidized lipids play a crucial role in the well-known clinical associations between dyslipidemia, oxidant stress and a prothrombotic phenotype.

Expression of the leptin receptor in different types of vascular lesions

Clinical and experimental evidence suggests that the adipokine leptin may be important for the development of cardiovascular complications associated with obesity, possibly through interaction with its receptor on vascular cells. In the present study, we systematically analysed expression of the leptin receptor in normal and diseased vascular specimens using immunohistochemistry, immunofluorescence and quantitative real time-PCR. In particular, human atherosclerotic plaques as well as experimental vascular lesions induced in hypercholesterolemic mice and minipigs, respectively, were examined. Our results demonstrate the presence of the leptin receptor in normal vessel wall segments as well as neointimal or atherosclerotic lesions. In the latter, ObR expressing cells were predominantly localised on the luminal border and within the subintima, and coexpression of von Willebrand factor, VEGF receptor-2 or VE cadherin identified them as endothelial cells. Moreover, CD14-positive monocytes/macrophages were strongly positive for the leptin receptor. In contrast, only few ObR-expressing smooth muscle cells could be detected in human atherosclerotic plaques. The findings of the present study thus support a possible action of leptin on the cardiovascular system by demonstrating expression of the leptin receptor in different types of vascular lesions.

Murine models of vascular thrombosis (Eitzman series)

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

Vascular Functions of the Plasminogen Activation System

The plasminogen activator (PA) system, which controls the formation and activity of plasmin, plays a key role in modulating hemostasis, thrombosis, and several other biological processes. While a great deal is known about the function of the PA system, it remains a focus of intensive investigation, and the list of biological pathways and human diseases that are modulated by normal and pathologic function of its components continues to lengthen. Because of remarkable advances in molecular genetics, the laboratory mouse has become the most useful animal system to study the normal and pathologic functions of the PA system. The purpose of this review is to summarize studies that have used genetically modified mice to examine the functions of the PA system in hemostasis and thrombosis, intimal hyperplasia after vascular injury, and atherosclerosis. Particular emphasis is placed on the vascular functions of PA inhibitor-1, a key regulator of the PA system, and the multiple variables that appear to account for the complex role of PA inhibitor-1 in regulating vascular remodeling. Lastly, the strengths and limitations of using mice to model human vascular disease processes are discussed.

Systemic hypothermia increases PAI-1 expression and accelerates microvascular thrombus formation in endotoxemic mice

Introduction

Hypothermia during sepsis significantly impairs patient outcome in clinical practice. Severe sepsis is closely linked to activation of the coagulation system, resulting in microthrombosis and subsequent organ failure. Herein, we studied whether systemic hypothermia accelerates microvascular thrombus formation during lipopolysacharide (LPS)-induced endotoxemia in vivo, and characterized the low temperature-induced endothelial and platelet dysfunctions.

Methods

Ferric-chloride induced microvascular thrombus formation was analyzed in cremaster muscles of hypothermic endotoxemic mice. Flow cytometry, ELISA and immunohistochemistry were used to evaluate the effect of hypothermia on endothelial and platelet function.

Results

Control animals at 37°C revealed complete occlusion of arterioles and venules after 759 ± 115 s and 744 ± 112 s, respectively. Endotoxemia significantly (p < 0.05) accelerated arteriolar and venular occlusion in 37°C animals (255 ± 35 s and 238 ± 58 s, respectively). This was associated with an increase of circulating endothelial activation markers, agonist-induced platelet reactivity, and endothelial P-selectin and plasminogen activator inhibitor (PAI)-1 expression. Systemic hypothermia of 34°C revealed a slight but not significant reduction of arteriolar (224 ± 35 s) and venular (183 ± 35 s) occlusion times. Cooling of the endotoxemic animals to 31°C core body temperature, however, resulted in a further acceleration of microvascular thrombus formation, in particular in arterioles (127 ± 29 s, p < 0.05 versus 37°C endotoxemic animals). Of interest, hypothermia did not affect endothelial receptor expression and platelet reactivity, but increased endothelial PAI-1 expression and, in particular, soluble PAI-1 antigen (sPAI-Ag) plasma levels.

Conclusion

LPS-induced endotoxemia accelerates microvascular thrombus formation in vivo, most probably by generalized endothelial activation and increased platelet reactivity. Systemic hypothermia further enhances microthrombosis in endotoxemia. This effect is associated with increased endothelial PAI-1 expression and sPAI-Ag in the systemic circulation rather than further endothelial activation or modulation of platelet reactivity.

Carbon Monoxide-Induced Early Thrombolysis Contributes to Heme Oxygenase-1-Mediated Inhibition of Neointimal Growth after Vascular Injury in Hypercholesterolemic Mice

Arterial thrombosis is a critical event in the pathogenesis of lesion development. In this study, we evaluated the effect of heme oxygenase-1 (HO-1), a stress-inducible enzyme with vasoprotective functions, on arterial thrombosis following vascular mechanical injury. The carotid arteries of apoE-deficient mice were subjected to angioplasty with a modified beaded-needle. Arterial thrombosis occurred at 12 h after injury. Treatment of the injured vessels with an adenovirus bearing HO-1 gene (Adv-HO-1) (1 x 10(8) pfu), but not saline or empty adenovirus (Adv), immediately after angioplasty resulted in earlier thrombolysis and restoration of blood flow detected at 24 h. Immunohistochemistry revealed that the arterial plasminogen activator inhibitor-1 (PAI-1) expression was markedly reduced in Adv-HO-1-treated injured arteries as compared to control counterparts. The thrombolytic effect was also observed by exposing animals with existing arterial thrombosis to carbon monoxide (CO) (250 ppm, 2 h), a byproduct derived from heme degradation by HO-1. In parallel with less fibrin(ogen) deposition, the macrophage infiltration, monocyte chemoattractant protein-1 expression and neointimal formation assessed at 2 weeks after angioplasty were substantially reduced in injured arteries treated with Adv-HO-1. These results support a role of early thrombolysis induced by CO in HO-1-mediated protection against intimal hyperplasia after vascular injury.

Plasminogen Activator Inhibitor-1 From Bone Marrow–Derived Cells Suppresses Neointimal Formation After Vascular Injury in Mice

Objective— To investigate the ability of bone marrow (BM)–derived cells to modulate neointimal growth after injury by expressing plasminogen activator inhibitor-1 (PAI-1).

Methods and Results— We performed BM transplantation (BMT) in lethally irradiated wild-type (WT) and PAI-1−/− mice. Three weeks after carotid injury with ferric chloride, analysis of Y-chromosome DNA expression in the vessel wall of female hosts revealed that 20.8±6.0% of the cells in the neointima and 37.6±5.7% of those in the media were of BM origin. Lack of PAI-1 in either the host or the donor cells did not affect recruitment of BM-derived cells into sites of vascular injury. The neointima consisted predominantly of smooth muscle cells, and a proportion of these cells expressed PAI-1. Overall, lack of PAI-1 was associated with enhanced neointimal formation. However, importantly, BMT WT→PAI-1−/− mice exhibited reduced neointimal area ( P =0.05) and luminal stenosis ( P =0.04) compared with BMT PAI-1−/−→PAI-1−/− mice. Although PAI-1–expressing cells were shown to be present in BMT WT→PAI-1−/− lesions, these mice did not exhibit detectable levels of the inhibitor in the circulation, suggesting that local production of PAI-1 by cells in the neointima and media was sufficient to reduce luminal stenosis.

Conclusions— PAI-1 from BM-derived cells appears capable of suppressing neointimal growth after vascular injury.

C-peptide exerts antithrombotic effects that are repressed by insulin in normal and diabetic mice

AIMS/HYPOTHESIS

Diabetic macro- and microangiopathy are associated with a high risk of vascular complications. The diabetic patient exhibits a pathological coagulation state, with an increased synthesis of coagulation factors and plasminogen activator inhibitor 1 (PAI-1) as well as an enhanced aggregation of platelets. Previous studies have shown that C-peptide can reduce leucocyte-endothelial cell interaction and improve microvascular blood flow in patients with type 1 diabetes. In the present study, we examined in vivo whether C-peptide is able to reduce platelet activation and through that microvascular thrombus formation.

MATERIALS AND METHODS

In the microvessels of cremaster muscle preparations taken from normal and diabetic mice, ferric chloride-induced thrombus formation was analysed using intravital fluorescence microscopy.

RESULTS

I.V. administration of C-peptide in high dose (70 nmol/kg), but not in low dose (7 nmol/kg), caused a significant delay in arteriolar and venular thrombus growth in normal and diabetic mice. This effect was repressed by cremaster muscle superfusion with insulin (100 microU/ml) in diabetic animals, but particularly in normal animals. In parallel, immunohistochemistry demonstrated a higher number of PAI-1-expressing vessels in cremaster muscle tissue from control animals and from animals treated with C-peptide and insulin compared with tissue from animals with C-peptide treatment application alone.

CONCLUSIONS/INTERPRETATION

We conclude that C-peptide possesses antithrombotic actions in vivo. A causal role of PAI-1 in this scenario needs to be further addressed. However, the reversal of C-peptide action by insulin may invalidate the use of this peptide as a treatment option to improve rheology and microcirculation in diabetic patients.

Transendothelial migration of ferric ion in FeCl3 injured murine common carotid artery

INTRODUCTION/OBJECTIVES

Adventitial application of FeCl(3) causes endothelial injury, platelet aggregation, and a rapid onset of thrombus formation. The transmigration pathway of the ferric ion has not been definitively identified. Using a combination of TEM and X-ray elemental analysis, this study aims to elucidate the endothelial pathway of ferric ion migration in carotid artery.

METHODS AND RESULTS

Vascular injury was induced by placing a Whatman #1 filter paper strip saturated with 10% FeCl(3) over the common carotid artery in male C57BL/6 mice for 3 min. After rinsing in saline, the mice were terminated at 10 or 30 min. The FeCL(3) exposed segments of the common carotid artery were dissected, and processed for TEM. Thrombus formation was observed in all cases. Endothelial and smooth muscle injuries were observed in segments of the vessel in direct contact with the oxidant. The endothelial injury ranged from minimal damage to total denudation. The basal endothelial surface adjacent to the internal elastic lamina showed accumulation of electron opaque vesicles. The membrane enclosed particles transmigrated across the endothelium and exocytosed into the lumen. The nature of the particles shown by STEM/EDS was rich in ferric ion. Elemental analysis also showed that some ferric oxide aggregates formed near the developing thrombus in the vascular lumen.

CONCLUSION

Our results showed the ferric ion permeated the endothelial basal lamina before entering the arterial lumen via endocytic-exocytic pathway. This study provides an ultrastructural framework for future analysis of the adluminal and luminal injuries in this model.