Adenovirus-mediated local expression of human tissue factor pathway inhibitor eliminates shear stress-induced recurrent thrombosis in the injured carotid artery of the rabbit

Pathophysiology of atherothrombosis: Mechanisms of thrombus formation on disrupted atherosclerotic plaques

Atherothrombosis is a leading cause of cardiovascular mortality and morbidity worldwide. The underlying mechanisms of atherothrombosis comprise plaque disruption and subsequent thrombus formation. Arterial thrombi are thought to mainly comprise aggregated platelets as a result of high blood velocity. However, thrombi that develop on disrupted plaques comprise not only aggregated platelets, but also large amounts of fibrin, because plaques contain large amount of tissue factor that activate the coagulation cascade. Since not all thrombi grow large enough to occlude the vascular lumen, the propagation of thrombi is also critical in the onset of adverse vascular events. Various factors such as vascular wall thrombogenicity, local hemorheology, systemic thrombogenicity and fibrinolytic activity modulate thrombus formation and propagation. Although the activation mechanisms of platelets and the coagulation cascade have been intensively investigated, the underlying mechanisms of occlusive thrombus formation on disrupted plaques remain obscure. Pathological findings derived from humans and animal models of human atherothrombosis have uncovered pathophysiological processes during thrombus formation and propagation after plaque disruption, and novel factors have been identified that modulate the activation of platelets and the coagulation cascade. These findings have also provided insights into the development of novel drugs for atherothrombosis.

Thrombus Formation and Propagation in the Onset of Cardiovascular Events

Ischemic cardiovascular disease is a major cause of morbidity and mortality worldwide and thrombus formation on disrupted atherosclerotic plaques is considered to trigger its onset. Although the activation of platelets and coagulation pathways has been investigated intensively, the mechanisms of thrombus formation on disrupted plaques have not been understood in detail. Platelets are thought to play a central role in the formation of arterial thrombus because of rapid flow conditions; however, thrombus that develops on disrupted plaques consistently includes large amounts of fibrin in addition to aggregated platelets. While, thrombus does not always become large enough to completely occlude the vascular lumen, indicating that the propagation of thrombus is also critical for the onset of cardiovascular events. Various factors, such as vascular wall thrombogenicity, altered blood flow and imbalanced blood hemostasis, modulate thrombus formation and propagation on disrupted plaques. Pathological findings derived from humans and experimental animal models of atherothrombosis have identified important factors that affect thrombus formation and propagation, namely platelets, extrinsic and intrinsic coagulation factors, proinflammatory factors, plaque hypoxia and blood flow alteration. These findings might provide insight into the mechanisms of thrombus formation and propagation on disrupted plaques that lead to the onset of cardiovascular events.

Conditional knockout of TFPI-1 in VSMCs of mice accelerates atherosclerosis by enhancing AMOT/YAP pathway

BACKGROUND

Tissue factor pathway inhibitor-1 (TFPI-1) has multiple functions and its precise role and molecular mechanism during the development of atherosclerosis are not clear.

OBJECTIVES

To determine the effect and molecular mechanism of TFPI-1 deficiency in vascular smooth muscle cells (VSMCs) in atherosclerosis in the apolipoprotein E knockout (ApoE^-/-) mouse.

METHODS AND RESULTS

A mouse model with a conditional knockout of TFPI-1 in VSMCs in an atherosclerosis-prone background (ApoE^-/-) was generated. Mice were fed a high fat diet for 18weeks and were then euthanized. Arterial trees and aortas were stained with Sudan IV and were labeled via immunohistochemistry. Cell proliferation and migration of VSMCs in atherosclerotic plaques were assessed. More atherosclerotic lesions and higher levels of proliferation and migration of VSMCs were observed in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/-mice. An interaction between TFPI-1 and angiomotin (AMOT) was identified in human VSMCs by mass spectrometry, immunoprecipitation and co-localization analyses. Signal pathway changes were detected by Western blot analysis, and the expression levels of target genes were determined by real-time PCR. Decreased phosphorylation of AMOT and Yes-associated protein 1 (YAP) in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/- mice resulted in increased expression levels of snail family zinc finger 2 (SLUG) and connective tissue growth factor (CTGF), which are target genes of the Hippo signaling pathway that have been verified as atherosclerosis candidate genes.

CONCLUSION

Deficiency in TFPI-1 in the VSMCs of ApoE^-/- mice accelerated the development of atherosclerosis by promoting the proliferation and migration of VSMCs which may be caused by the decreased phosphorylation of AMOT and YAP.

SIGNIFICANCE

TFPI-1 has been found to has an anticoagulant activity, induce cell apoptosis and prevent cell proliferation. For the first time, we constructed a line of conditional knockout mice in which the TPFI-1 gene is deleted in VSMCs. We found that TFPI-1 deficiency clearly promoted the development of atherosclerosis when these mice were crossed into an ApoE^-/-background. One notable feature of atherosclerosis is the proliferation and migration of smooth muscle cells. Previous reports involved TFPI-1 do not completely explain the proliferation and migration of VSMCs because heterozygous TF deficient (TF^±) mice bred in an ApoE^-/- background did not show diminished atherosclerosis compared to TF^+/+ mice bred in the same background. Our results first confirmed that TFPI-1 interacts with AMOT, which led to a decrease in the phosphorylation of YAP and further increased the genes expression of the proliferation and migration involved. Our results further confirmed that atherosclerosis was a localized disease.

Toll-like receptor 9 signaling regulates tissue factor and tissue factor pathway inhibitor expression in human endothelial cells and coagulation in mice

Supplemental Digital Content is available in the text.

Objective:

Bacterial DNA (CpG DNA) persists in tissues and blood under pathological conditions that are associated with enhanced intravascular coagulation. Toll-like receptor 9 recognizes CpG DNA and elicits innate and adoptive immunity, yet the impact of CpG DNA on coagulation has not been studied. In this study, we investigated the effects of CpG DNA on the expression and activity of tissue factor, a key initiator of coagulation and tissue factor pathway inhibitor in human coronary artery endothelial cells and on coagulation in mice.

Design:

Controlled in vitro and in vivo studies.

Setting:

University research laboratory.

Subjects:

Cultured human coronary artery endothelial cell, wild-type mice, and TLR9-deficient mice.

Interventions:

Human coronary artery endothelial cell was challenged with CpG DNA, and tissue factor and tissue factor pathway inhibitor expression and activity were assessed. In mice, the effects of CpG DNA on bleeding time and plasma levels of thrombin-antithrombin complexes and tissue factor were measured.

Measurements and Main Results:

We found that CpG DNA, but not eukaryotic DNA, evoked marked nuclear factor-κB-mediated increases in tissue factor expression at both messenger RNA and protein levels, as well as in tissue factor activity. Conversely, CpG DNA significantly reduced tissue factor pathway inhibitor transcription, secretion, and activity. Inhibition of Toll-like receptor 9 with a telomere-derived Toll-like receptor 9 inhibitory oligonucleotide or transient Toll-like receptor 9 knockdown with small interfering RNA attenuated human coronary artery endothelial cell responses to CpG DNA. In wild-type mice, CpG DNA shortened the bleeding time parallel with dramatic increases in plasma thrombin-antithrombin complex and tissue factor levels. Pretreatment with inhibitory oligonucleotide or anti-tissue factor antibody or genetic deletion of TLR9 prevented these changes, whereas depleting monocytes with clodronate resulted in a modest partial inhibition.

Conclusions:

Our findings demonstrate that bacterial DNA through Toll-like receptor 9 shifted the balance of tissue factor and tissue factor pathway inhibitor toward procoagulant phenotype in human coronary artery endothelial cells and activated blood coagulation in mice. Our study identifies Toll-like receptor 9 inhibitory oligonucleotides as potential therapeutic agents for the prevention of coagulation in pathologies where bacterial DNA may abundantly be present.

The extrinsic coagulation cascade and tissue factor pathway inhibitor in macrophages: a potential therapeutic opportunity for atherosclerotic thrombosis

OBJECTIVES

The coagulation protease cascade plays the central requisite role in initiation of arterial atherothrombosis. However, the relative participation of the extrinsic as compared to the intrinsic pathway is incompletely resolved. We have investigated in vivo the relative importance of the extrinsic and intrinsic pathways to define which is more essential to atherothrombosis and therefore the preferable prophylactic therapeutic target. We further addressed which type of plaque associated macrophage population is associated with the thrombotic propensity of atherosclerotic plaques.

METHODS

Both photochemical injury and ferric chloride vascular injury models demonstrated arterial thrombosis formation in ApoE deficient mice. We found that direct interference with the extrinsic pathway, but not the intrinsic pathway, markedly diminished the rate of thrombus formation and occlusion of atherosclerotic carotid arteries following experimental challenge. To explore which plaque macrophage subtype may participate in plaque thrombosis in regard to expression tissue factor pathway inhibitor (TFPI), bone marrow derived macrophages of both M and GM phenotypes expressed tissue factor (TF), but the level of TFPI was much greater in M- type macrophages, which exhibited diminished thrombogenic activity, compared to type GM-macrophages.

RESULTS AND CONCLUSIONS

Our works support the hypothesis that the TF-initiated and direct extrinsic pathway provides the more significant contribution to arterial plaque thrombogenesis. Activation of the TF driven extrinsic pathway can be influenced by differing colony-stimulating factor influenced macrophage TFPI-1 expression. These results advance our understanding of atherothrombosis and identify potential therapeutic targets associated with the extrinsic pathway and with macrophages populating arterial atherosclerotic plaques.

The role of tissue factor pathway inhibitor in atherosclerosis and arterial thrombosis

Tissue factor pathway inhibitor (TFPI) is the main inhibitor of tissue factor (TF)-mediated coagulation. In atherosclerotic plaques TFPI co-localizes with TF, where it is believed to play an important role in attenuating TF activity. Findings in animal models such as TFPI knockout models and gene transfer models are consistent on the role of TFPI in arterial thrombosis as they reveal an active role for TFPI in attenuating arterial thrombus formation. In addition, ample experimental evidence exists indicating that TFPI has inhibitory effects on both smooth muscle cell migration and proliferation, both which are recognized as important pathological features in atherosclerosis development. Nonetheless, the clinical relevance of these antithrombotic and atheroprotective effects remains unclear. Paradoxically, the majority of clinical studies find increased instead of decreased TFPI antigen and activity levels in atherothrombotic disease, particularly in atherosclerosis and coronary artery disease (CAD). Increased TFPI levels in cardiovascular disease might result from complex interactions with established cardiovascular risk factors, such as hypercholesterolemia, diabetes and smoking. Moreover, it is postulated that increased TFPI levels reflect either the amount of endothelial perturbation and platelet activation, or a compensatory mechanism for the increased procoagulant state observed in cardiovascular disease. In all, the prognostic value of plasma TFPI in cardiovascular disease remains to be established. The current review focuses on TFPI in clinical studies of asymptomatic and symptomatic atherosclerosis, coronary artery disease and ischemic stroke, and discusses potential atheroprotective actions of TFPI.

Impact of the tissue factor pathway inhibitor gene on apoptosis in human vascular smooth muscle cells

Tissue factor pathway inhibitor (TFPI) plays a vitally important role in the blood coagulation pathway. Recent studies indicated that TFPI induces apoptosis in vascular smooth-muscle cells (VSMCs) in animals. The present study investigated whether the TFPI gene could also induce apoptosis in human vascular smooth-muscle cells (hVSMCs). Such cells were isolated from human umbilical arteries and subsequently transfected with pIRES-TFPI plasmid (2 μg/mL). MTT assaying and cell counting were applied to measure cell viability and proliferation, RT-PCR was utilized to analyze TFPI gene expression in the cells. Apoptosis was analyzed by fluorescence activated cell sorting (FACS). Several key proteins involved in apoptosis were examined through Western blotting. It was shown that TFPI gene transfer led to its increased cellular expression, with a subsequent reduction in hVSMC proliferation. Further investigation demonstrated that TFPI gene expression resulted in lesser amounts of procaspase-3, procaspase-8 and procascase-9, and an increased release of mitochondrial cytochrome c (cyt-c) into cytoplasm, thereby implying the involvement of both extrinsic and intrinsic pathways in TFPI gene-induced apoptosis in hVSMCs.

Delivery of TFPI-2 using ultrasound with a microbubble agent (SonoVue) inhibits intimal hyperplasia after balloon injury in a rabbit carotid artery model

Here we report a new, simple and efficient method by using ultrasound and a microbubble agent (SonoVue) for delivering a gene to balloon-injured carotid arteries for restenosis prophylaxis. The tissue factor pathway inhibitor-2 (TFPI-2) has been shown to inhibit the postinjury intimae hyperplasia in atherosclerotic vessels. New Zealand white rabbits were divided into 4 groups with 14 in each, a treatment control for balloon injury, a gene vehicle control, a gene delivery of TFPI-2 without using ultrasound and a gene delivery of TFPI-2 using ultrasound. After four weeks, the injured artery neointimal proliferation was significantly lower in the TFPI-2 group with ultrasound than the control groups (p < 0.01) according to the measurement of the mean luminal diameters by B-mode ultrasonography. The ratio of intimal/media area and the stenosis rate in the gene delivery facilitated by ultrasound were significantly lower than those of the nonultrasound gene delivering method (p < 0.01).

Tissue factor in cardiovascular disease pathophysiology and pharmacological intervention

Tissue factor (TF) is the major trigger of the coagulation cascade and thereby crucially involved in the maintenance of vascular hemostasis. By binding factor VIIa, the resulting TF:VIIa complex activates the coagulation factors IX and X ultimately leading to fibrin and clot formation. In the vessel wall, TF expression and activity is detectable in vascular smooth muscle cells and fibroblasts and, at a much lower level, in endothelial cells and can be induced by various stimuli including cytokines. In addition, TF is found in the bloodstream in circulating cells such as monocytes, in TF containing microparticles, and as a soluble splicing isoform. Besides its well-known extracellular role as a trigger of coagulation, TF also functions as a transmembrane receptor, and TF-dependent intracellular signaling events regulate the expression of genes involved in cellular responses such as proliferation and migration. TF indeed appears to be involved in the pathogenesis of neointima formation and tumor growth, and increased levels of TF have been detected in patients with cardiovascular risk factors or coronary artery disease as well as in those with cancer. Therefore, pharmacological or genetic inhibition of TF may be an attractive target for the treatment of cardiovascular disease and cancer. Different strategies for inhibition of TF have been developed such as inhibition of TF synthesis and blockade of TF action. Clinical applications of such strategies need to be tested in appropriate trials, in particular for evaluating the advantages of targeted versus systemic delivery of the inhibitors.

Tissue factor: beyond coagulation in the cardiovascular system

TF (tissue factor) is the main trigger of the coagulation cascade; by binding Factor VIIa it activates Factor IX and Factor X, thereby resulting in fibrin formation. Various stimuli, such as cytokines, growth factors and biogenic amines, induce TF expression and activity in vascular cells. Downstream targets of these mediators include diverse signalling molecules such as MAPKs (mitogen-activated protein kinases), PI3K (phosphoinositide 3-kinase) and PKC (protein kinase C). In addition, TF can be detected in the bloodstream, known as circulating or blood-borne TF. Many cardiovascular risk factors, such as hypertension, diabetes, dyslipidaemia and smoking, are associated with increased expression of TF. Furthermore, in patients presenting with acute coronary syndromes, elevated levels of circulating TF are found. Apart from its role in thrombosis, TF has pro-atherogenic properties, as it is involved in neointima formation by inducing vascular smooth muscle cell migration. As inhibition of TF action appears to be an attractive target for the treatment of cardiovascular disease, therapeutic strategies are under investigation to specifically interfere with the action of TF or, alternatively, promote the effects of TFPI (TF pathway inhibitor).

Porphyromonas gingivalis infection and prothrombotic effects in human aortic smooth muscle cells

INTRODUCTION

Accumulating evidence has demonstrated an association between periodontal infectious agents, such as Porphyromonas gingivalis, and vascular disease. Tissue factor (TF) and its specific tissue factor pathway inhibitor (TFPI) are produced by vascular cells and are important regulators of the coagulation cascade.

MATERIALS AND METHODS

To assess the role of P. gingivalis in atherothrombosis, we infected primary human aortic smooth muscle cells (HASMC) with either P. gingivalis 381, its non-invasive mutant DPG3, or heat-killed P. gingivalis 381. Levels and activity of TF and TFPI were measured 8 and 24 hours after infection in cell extracts and cell culture supernatants.

RESULTS

P. gingivalis 381 did not affect total TF antigen or TF activity in HASMC, but it significantly suppressed TFPI levels and activity compared to uninfected control cells, and those infected with the non-invasive mutant strain or the heat-killed bacteria. Further, P. gingivalis' LPS (up to a concentration of 5 microg/ml) failed to induce prothrombotic effects in HASMC, suggesting a significant role for the ability of whole viable bacteria to invade this cell type.

CONCLUSION

These data demonstrate for the first time that infection with a periodontal pathogen induces a prothrombotic response in HASMC.

Impact of Adenovirus-mediated Local Expression of Human Tissue Factor Pathway Inhibitor on Vascular Smooth Muscular Cell Proliferation and Apoptosis in the Stent-implanted Femoral Artery of the Rabbit

This study examined the effect of gene transfer of local tissue factor pathway inhibitor (TFPI) on vascular smooth muscle cells (VSMCs) in stent-implanted arteries. Rabbit femoral arteries were balloon-injured, stent-implanted and infected with the replication-defective recombinant adenovirus-mediated TFPI gene (Ad-TFPI) or the β-galactosidase gene (Ad- LacZ), or treated with saline solution. Expression of TFPI at the site of the stent was confirmed after 3 days using reverse transcription-polymerase chain reaction (RT-PCR). After 7 days, proliferating cells were visualized by immunostaining with antibodies to proliferating cell nuclear antigen (PCNA) and apoptotic cells were detected using the terminal deoxynucleotidyl mediated nick end labelling (TUNEL) technique. Cell proliferation was significantly decreased and apoptosis significantly increased in the media in the Ad-TFPI group compared with the other two groups. In conclusion, Ad-TFPI gene transfer can significantly suppress VSMC proliferation and induce its apoptosis in the media at the site of an implanted stent and may have potential for the treatment of instent re-stenosis.

Infection with a periodontal pathogen induces procoagulant effects in human aortic endothelial cells

BACKGROUND

Multiple studies have demonstrated a link between periodontal infections and vascular disease. Porphyromonas gingivalis, a major periodontal pathogen, has been shown to adhere to and invade endothelial cells.

OBJECTIVE

In order to dissect mechanisms underlying these observations, we assessed the role of P. gingivalis infection in modulating properties of endothelial cells linked to atherothrombosis.

METHODS

Primary human aortic endothelial cells (HAEC) were infected with either P. gingivalis 381 or its non-invasive fimbriae-deficient mutant, DPG3. Markers of coagulation and thrombosis were assessed 8 h and 18 h postinfection in cell lysates and supernatants.

RESULTS

Infection with P. gingivalis 381 significantly enhanced tissue factor expression and activity, and suppressed levels of tissue factor pathway inhibitor. Furthermore, P. gingivalis infection decreased levels and activity of tissue plasminogen activator, and enhanced plasminogen activator inhibitor-1 antigen and activity. Consistent with an important role for bacterial adhesion/invasion in this setting, infection with DPG3 failed to induce procoagulant properties in HAEC. Most of the above effects of P. gingivalis 381 were more apparent at the later time point (18 h postinfection). This suggests that P. gingivalis infection, rather than having an immediate and direct effect, might activate pathways that, in turn, trigger endothelial procoagulant mechanisms.

CONCLUSIONS

Taken together these data demonstrate for the first time that infection with a periodontal pathogen induces procoagulant responses in HAEC.

Gene therapy of the ischemic lower limb--Therapeutic angiogenesis

The limitations of surgical revascularisation and pharmacological treatment in peripheral arterial occlusive disease (PAOD) are well recognized. Therapeutic options for critical leg ischemia are consequently limited to percutaneous transluminal angioplasty (PTA) or surgical revascularisation. Unfortunately, many patients with critical leg ischemia are poor candidates for either procedure. Therapeutic angiogenesis is a novel promising tool to treat these patients. Experimental and clinical and trials of gene transfer for therapeutic angiogenesis have already shown some clinical efficacy. This review is focused on gene transfer techniques in preclinical and clinical therapeutic angiogenesis, angiogenic growth factors, vectors, delivery methods and routes. The results of clinical and experimental studies, safety and side effects of gene therapy, and the perspectives of future research are also discussed.

Intratracheal gene transfer of tissue factor pathway inhibitor attenuates pulmonary fibrosis

Activation of the coagulation system and increased expression of tissue factor (TF) in pulmonary fibrosis associated with acute and chronic lung injury have been previously documented. In the present study, we evaluated the effect of TF inhibition with intratracheal gene transfer of tissue factor pathway inhibitor (TFPI), a potent and highly specific endogenous inhibitor of TF-dependent coagulation activation, in a rat model of bleomycin-induced lung fibrosis. Significant lung fibrotic changes as assessed by histologic findings and hydroxyproline content, and increased procoagulant activity and thrombin generation in bronchoalveolar lavage fluid were detected in rats after intratracheal injection of bleomycin. Intratracheal administration of an adenovirus vector expressing TFPI significantly decreased bleomycin-induced procoagulant and thrombin generation resulting in a strong inhibition of pulmonary fibrosis. TFPI-overexpression in the lung was associated with a significant reduction in gene expression of the connective tissue growth factor, a potent profibrotic growth factor. This is the first report showing that direct inhibition of TF-mediated coagulation activation abrogates bleomycin-induced pulmonary fibrosis.

Gene Therapy for Cardiovascular Disease

The last decade has seen substantial advances in the development of gene therapy strategies and vector technology for the treatment of a diverse number of diseases, with a view to translating the successes observed in animal models into the clinic. Perhaps the overwhelming drive for the increase in vascular gene transfer studies is the current lack of successful long-term pharmacological treatments for complex cardiovascular diseases. The increase in cardiovascular disease to epidemic proportions has also led many to conclude that drug therapy may have reached a plateau in its efficacy and that gene therapy may represent a realistic solution to a long-term problem. Here, we discuss gene delivery approaches and target diseases.

Prolonged procoagulant activity on overstretch-injured coronary arteries in pigs

This study was designed to assess the time course and nature of the vascular procoagulant response after 1.5-fold balloon overstretch injury of the coronary arteries in pigs. Arteries were excised for chromogenic assay of bound factor (F)Xa and thrombin at 24 h, 3 days, 1 week, or 2 weeks after injury. FXa at the site of injury remained elevated for 1 week (4.9 +/- 5.9 microg cm(-2), n = 10), compared with non-injured control arteries (0.4 +/- 0.2 microg cm(-2), n = 18, P = 0.00025), while thrombin was increased only at 24 h. Tissue factor protein was abundant in non-injured coronaries (10 +/- 6 ng microg(-1) total protein, n = 9) and levels were unchanged by injury (13 +/- 11 ng microg(-1), n = 6) or 24-h administration of tissue factor pathway inhibitor (16 +/- 6 ng microg(-1), n = 6). Persistent tissue factor-mediated procoagulant activity may explain the need for prolonged anticoagulation to attenuate neointimal formation after balloon-induced coronary injury.

Gene therapy in cardiovascular disease. Current status

Cardiovascular disease is the leading cause of mortality and morbidity in developed countries. Most conventional therapy is often inefficacious and tends to treat the symptoms rather than the underlying causes of the disorder. Gene therapy offers a novel approach for prevention and treatment of cardiovascular diseases. Technical advances in viral vector systems and the development of fusigenic liposome vectors have been crucial to the development of effective gene therapy strategies directed at the vasculature and myocardium in animal models. Gene transfer techniques are being evaluated as potential treatment alternatives for both genetic (familial hypercholesterolemia) and acquired occlusive vascular diseases (atherosclerosis, restenosis, arterial thrombosis) as well as for cardiac disorders including heart failure, myocardial ischemia, graft coronary arteriosclerosis and hypertension. Continued technologic advances in vector systems and promising results in human and animal gene transfer studies make the use of gene therapy a promising strategy for the treatment of cardiovascular disorders.

Role of tissue factor pathway inhibitor in the regulation of tissue factor-dependent blood coagulation

Tissue factor pathway inhibitor (TFPI) is a multivalent, Kunitz-type plasma proteinase inhibitor that modulates tissue factor-dependent coagulation in vivo. TFPI possesses a peculiar two-step mechanism of action; it directly inhibits activated factor X and subsequently produces feedback inhibition of the factor VIIa/tissue factor catalytic complex in a factor Xa-dependent fashion. TFPI biochemistry and physiology have been extensively studied during the last decade. Its pathophysiologic role in thrombotic disorders has, however, only recently started to be unraveled. In particular, circulating plasma TFPI levels have been found to modulate the activity of the tissue factor-dependent coagulation cascade. In animal models, neutralization of circulating TFPI activity results in restoration of intravascular thrombus formation previously abolished by aspirin. In patients with acute myocardial infarction, TFPI plasma levels measured in blood samples obtained from the coronary sinus were significantly lower than those measured in blood obtained from the ascending aorta, indicating acute consumption of TFPI within the coronary circulation of patients with intracoronary thrombosis. Finally, recent data indicate that transfection of the arterial wall with the gene coding for TFPI is an effective therapeutic intervention to prevent intravascular thrombus formation. Taken together, these observations underline the pathophysiologic importance of TFPI in regulating the procoagulant activity of tissue factor and open new potential therapeutic approaches for the treatment of thrombotic disorders.

Long-term inhibition of nitric oxide synthesis increases arterial thrombogenecity in rat carotid artery

Reduced activity of endothelial nitric oxide (NO) may be involved in thrombus formation on atherosclerotic plaques, a major cause of acute coronary syndrome. However, mechanisms of such increase in arterial thrombogenecity have not been fully understood. We previously reported that long-term inhibition of NO synthesis by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) causes hypertension and activates vascular tissue angiotensin-converting enzyme (ACE) activity. We used this model to investigate the mechanism by which long-term impairment of NO activity increases arterial thrombogenecity. We observed cyclic flow variations (CFVs), a reliable marker of platelet thrombi, after the production of stenosis of the carotid artery in rats treated with L-NAME for 4 wk. The thrombin antagonist argatroban suppressed the CFVs. The CFVs were detected in rats receiving L-NAME plus hydralazine but not in rats receiving L-NAME plus an ACE inhibitor (imidapril). Treatment with the ACE inhibitor imidapril, but not with hydralazine, prevented L-NAME-induced increases in carotid arterial ACE activity and attenuated tissue factor expression. These results suggest that long-term inhibition of endothelial NO synthesis may increase arterial thrombogenecity at least in part through angiotensin II-induced induction of tissue factor and the resultant thrombin generation. These data provide a new insight as to how endothelial NO exhibits antithrombogenic properties of the endothelium.

Gene transfer therapy in vascular diseases

Somatic gene therapy of vascular diseases is a promising new field in modern medicine. Recent advancements in gene transfer technology have greatly evolved our understanding of the pathophysiologic role of candidate disease genes. With this knowledge, the expression of selective gene products provides the means to test the therapeutic use of gene therapy in a multitude of medical conditions. In addition, with the completion of genome sequencing programs, gene transfer can be used also to study the biologic function of novel genes in vivo. Novel genes are delivered to targeted tissue via several different vehicles. These vectors include adenoviruses, retroviruses, plasmids, plasmid/liposomes, and oligonucleotides. However, each one of these vectors has inherent limitations. Further investigations into developing delivery systems that not only allow for efficient, targeted gene transfer, but also are stable and nonimmunogenic, will optimize the clinical application of gene therapy in vascular diseases. This review further discusses the available mode of gene delivery and examines six major areas in vascular gene therapy, namely prevention of restenosis, thrombosis, hypertension, atherosclerosis, peripheral vascular disease in congestive heart failure, and ischemia. Although we highlight some of the recent advances in the use of gene therapy in treating vascular disease discovered primarily during the past two years, many excellent studies published during that period are not included in this review due to space limitations. The following is a selective review of practical uses of gene transfer therapy in vascular diseases. This review primarily covers work performed in the last 2 years. For earlier work, the reader may refer to several excellent review articles. For instance, Belalcazer et al. (6) reviewed general aspects of somatic gene therapy and the different vehicles used for the delivery of therapeutic genes. Gene therapy in restenosis and stimulation of angiogenesis in the cardiac muscle are discussed in reviews by several investigators (13,26,57,74,83). In another review, Meyerson et al. (43) discuss advances in gene therapy for vascular proliferative disorders and chronic peripheral and cardiac ischemia.

Gene therapy for acute diseases

The use of gene transfer systems to study cell function makes it apparent that overexpression of a transgene can restore or improve the function of a protein and positively influence cell function in a predetermined manner for purposes of counterbalancing cellular pathophysiology. The ability of some gene transfer vehicles to produce transgene product within hours of delivery positions gene transfer as a unique pharmaceutical administration system that can quickly affect production of biologic response modifiers in a highly compartmentalized fashion. This approach can be expected to overcome many of the adverse effects and high costs of systemic delivery of recombinant pharmaceuticals. This review highlights recent advances toward development of gene therapies for acute illnesses with particular emphasis on preclinical models of disease. In this context, a growing body of data suggests that gene therapies for polygenic and non-genetic diseases such as asthma, cardiogenic and non-cardiogenic pulmonary edema, stroke, subarachnoid hemorrhage, seizures, acute myocardial infarction, endovascular thrombosis, and infections may someday be options for the treatment of patients.

Tissue factor pathway inhibitor: an update of potential implications in the treatment of cardiovascular disorders

Tissue factor (TF) plays a crucial role in the pathogenesis of thrombotic, vascular and inflammatory disorders. Thus, the inhibition of this membrane protein provides a unique therapeutic approach for prophylaxis and/or treatment of various diseases. Tissue factor pathway inhibitor (TFPI), the only endogenous inhibitor of the TF/Factor VIIa (FVIIa) complex, has recently been characterised biochemically and pharmacologically. Studies in patients demonstrated that both TF and TFPI may be indicators for the course and the outcome of cardiovascular and other diseases. Based on experimental and clinical data, TFPI might become an important drug for several clinical indications. TFPI is expected to inhibit the development of post-injury intimal hyperplasia and thrombotic occlusion in atherosclerotic vessels as well as to be effective in acute coronary syndromes, such as unstable angina and myocardial infarction. Of special interest is the inhibition of TF-mediated processes in sepsis and disseminated intravascular coagulation (DIC), which are associated with the activation of various inflammatory pathways as well as of the coagulation system. A Phase II trial of the efficacy of TFPI in patients with severe sepsis showed a mortality reduction in TFPI- compared to placebo-treated patients and an improvement of organ dysfunctions. TFPI can be administered exogenously in high doses to suppress TF-mediated effects, alternatively high amounts of TFPI can be released from intravascular stores by other drugs, such as heparin and low molecular weight heparins (LMWH). Using this method high concentrations of the inhibitor are provided at sites of tissue damage and ongoing thrombosis. At present, clinical studies with TFPI are rather limited so that the clinical potential of the drug cannot be assessed properly. However, TFPI and its variants are expected to undergo further development and to find indications in various clinical states.

Expression of exogenous tissue factor pathway inhibitor in vivo suppresses thrombus formation in injured rabbit carotid arteries

OBJECTIVES

The aim of the present study was to test the hypothesis that retrovirus-mediated in vivo tissue factor pathway inhibitor (TFPI) gene transfer to the arterial wall would efficiently inhibit thrombosis without causing significant changes in systemic hemostatic variables.

BACKGROUND

Acute coronary syndromes (unstable angina and acute myocardial infarction) are usually caused by atherosclerotic plaque rupture, with consequent activation of the coagulation cascade and circulating platelets. Tissue factor (TF) exposure represents an early event in this pathophysiologic sequence, leading to activation of the extrinsic coagulation pathway and thrombin formation. Tissue factor pathway inhibitor is a naturally occurring inhibitor of the extrinsic pathway.

METHODS

In the present study, the gene coding for rabbit TFPI was inserted in a retroviral vector under control of a tetracycline-inducible promoter. Replication-defective, infectious, recombinant retroviruses were used to transfect rabbit carotid arteries with either TFPI or a reporter gene--green fluorescent protein (GFP).

RESULTS

Retroviral-mediated arterial gene transfer of TFPI resulted in potent inhibition of intravascular thrombus formation in stenotic and injured rabbit carotid arteries, whereas transfection of the contralateral carotid artery with GFP had no effect on thrombosis. No significant changes in systemic hemostatic variables (prothrombin time and partial thromboplastin time) were observed when thrombosis was inhibited.

CONCLUSIONS

These data suggest that retroviral-mediated transfection of the arterial wall with TFPI might represent an attractive approach for the treatment of thrombotic disorders.

Local gene transfer of tissue factor pathway inhibitor regulates intimal hyperplasia in atherosclerotic arteries

Tissue factor (TF), the initiator of blood coagulation and thrombosis, is up-regulated after vascular injury and in atherosclerotic states. Systemic administration of recombinant TF pathway inhibitor (TFPI) has been reported to decrease intimal hyperplasia after vascular injury and also to suppress systemic mechanisms of blood coagulation and thrombosis. Here we report that, in heritable hyperlipidemic Watanabe rabbits, adenoviral gene transfer of TFPI to balloon-injured atherosclerotic arteries reduced the extent of intimal hyperplasia by 43% (P < 0.05) compared with a control vector used at identical titer (1 x 10(10) plaque-forming units/ml). Platelet aggregation and coagulation studies performed 7 days after local gene transfer of TFPI failed to show any impairment in systemic hemostasis. At time of sacrifice, 4 weeks after vascular injury, the 10 Ad-TFPI treated carotid arteries were free of thrombi, whereas two control-treated arteries were occluded (P, not significant). These findings suggest that TFPI overexpressed in atherosclerotic arteries can regulate hyperplastic response to injury in the absence of changes in the hemostatic system, establishing a role for local TF regulation as target for gene transfer-based antirestenosis therapies.

The future of gene therapy for stroke

New diagnostic and treatment strategies are being developed for stroke. Gene therapy has several potential advantages over classical pharmacologic therapy. Direct administration of DNA into the brain offers the advantage of producing high concentrations of therapeutic agents in a relatively localized environment. Gene transfer also provides longer duration of effect than traditional drug therapy. Recent studies indicate that gene transfer can produce functional proteins in brain parenchyma and cerebral blood vessels after stroke. In animal models, gene transfer may reduce effects of cerebral ischemia or subarachnoid hemorrhage. This review summarizes some current methods of gene transfer to the brain and recent progress that may lead to gene therapy for stroke.

Pressurization facilitates adenovirus-mediated gene transfer into vein graft

We investigated whether application of non-distending hydrostatic pressure facilitates gene transfer into vein grafts. An external jugular vein was placed in a chamber with 100 microl adenovirus solution at a titer of 10(10) pfu/ml and was pressurized to up to 8 atm above ambient pressure for 10 min. Histochemical analysis demonstrated a positive transgene expression in all layers of the vessel wall. Gene transfer with 8 atm pressurization resulted in an approximately 50 times higher transgene expression than that without pressurization. Under 8 atm pressurization, the efficiency of gene transfer reached a plateau at 7.5 min. The application of hydrostatic pressure may improve the effectiveness of intraoperative genetic engineering of vein grafts.

Cardiovascular gene therapy

Vascular gene transfer potentially offers new treatments for cardiovascular diseases. It can be used to overexpress therapeutically important proteins and correct genetic defects, and to test experimentally the effects of various genes in a local vascular compartment. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers have improved blood flow and collateral development in ischaemic limb and myocardium. Promising therapeutic effects have been obtained in animal models of restenosis or vein-graft thickening with the transfer of genes coding for VEGF, nitric-oxide synthase, thymidine kinase, retinoblastoma, growth arrest homoeobox, tissue inhibitor of metalloproteinases, cyclin or cyclin-dependent kinase inhibitors, fas ligand and hirudin, and antisense oligonucleotides against transcription factors or cell-cycle regulatory proteins. First experiences of VEGF gene transfer and decoy oligonucleotides in human beings have been reported. However, further developments in gene-transfer vectors, gene-delivery techniques and identification of effective treatment genes will be required before the full therapeutic potential of gene therapy in cardiovascular disease can be assessed.