A novel urokinase receptor-targeted inhibitor for plasmin and matrix metalloproteinases suppresses vein graft disease

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

The Role of Immunomodulation in Vein Graft Remodeling and Failure

Obstructive arterial disease is a major cause of morbidity and mortality in the developed world. Venous bypass graft surgery is one of the most frequently used revascularization strategies despite its considerable short and long time failure rate. Due to vessel wall remodeling, inflammation, intimal hyperplasia, and accelerated atherosclerosis, vein grafts may (ultimately) fail to revascularize tissues downstream to occlusive atherosclerotic lesions. In the past decades, little has changed in the prevention of vein graft failure (VGF) although new insights in the role of innate and adaptive immunity in VGF have emerged. In this review, we discuss the pathophysiological mechanisms underlying the development of VGF, emphasizing the role of immune response and associated factors related to VG remodeling and failure. Moreover, we discuss potential therapeutic options that can improve patency based on data from both preclinical studies and the latest clinical trials. This review contributes to the insights in the role of immunomodulation in vein graft failure in humans. We describe the effects of immune cells and related factors in early (thrombosis), intermediate (inward remodeling and intimal hyperplasia), and late (intimal hyperplasia and accelerated atherosclerosis) failure based on both preclinical (mouse) models and clinical data.

Therapeutics targeting the fibrinolytic system

The function of the fibrinolytic system was first identified to dissolve fibrin to maintain vascular patency. Connections between the fibrinolytic system and many other physiological and pathological processes have been well established. Dysregulation of the fibrinolytic system is closely associated with multiple pathological conditions, including thrombosis, inflammation, cancer progression, and neuropathies. Thus, molecules in the fibrinolytic system are potent therapeutic and diagnostic targets. This review summarizes the currently used agents targeting this system and the development of novel therapeutic strategies in experimental studies. Future directions for the development of modulators of the fibrinolytic system are also discussed.

The fibrinolytic system was originally identified to dissolve blood clots, and is shown to have important roles in other pathological processes, including cancer progression, inflammation, and thrombosis. Molecules or therapeutics targeting fibrinolytic system have been successfully used in the clinical treatments of cancer and thrombotic diseases. The clinical studies and experimental models targeting fibrinolytic system are reviewed by Haili Lin at Sanming First Hosipital, Mingdong Huang at Fuzhou University in China, and Peng Xu at A*STAR in Singapore to demonstrate fibrinolytic system as novel therapeutic targets. As an example, the inhibition of fibrinolytic system protein can be used to suppress cancer prolifieration and metastasis. This review also discusses the potential therapeutic effects of inhibitiors of fibrinolytic system on inflammatory disorders.

A Rabbit Model of Durable Transgene Expression in Jugular Vein to Common Carotid Artery Interposition Grafts

Vein graft bypass surgery is a common treatment for occlusive arterial disease; however, long-term success is limited by graft failure due to thrombosis, intimal hyperplasia, and atherosclerosis. The goal of this article is to demonstrate a method for placing bilateral venous interposition grafts in a rabbit, then transducing the grafts with a gene transfer vector that achieves durable transgene expression. The method allows the investigation of the biological roles of genes and their protein products in normal vein graft homeostasis. It also allows the testing of transgenes for the activities that could prevent vein graft failure, e.g., whether the expression of a transgene prevents the neointimal growth, reduces the vascular inflammation, or reduces atherosclerosis in rabbits fed with a high-fat diet. During an initial survival surgery, the segments of right and left external jugular vein are excised and placed bilaterally as reversed end-to-side common carotid artery interposition grafts. During a second survival surgery, performed 28 days later, each of the grafts is isolated from the circulation with vascular clips and the lumens are filled (via an arteriotomy) with a solution containing a helper-dependent adenoviral (HDAd) vector. After a 20-min incubation, the vector solution is aspirated, the arteriotomy is repaired, and flow is restored. The veins are harvested at time points dictated by individual experimental protocols. The 28-day delay between the graft placement and the transduction is necessary to ensure the adaptation of the vein graft to the arterial circulation. This adaptation avoids rapid loss of transgene expression that occurs in vein grafts transduced before or immediately after grafting. The method is unique in its ability to achieve durable, stable transgene expression in grafted veins. Compared to other large animal vein graft models, rabbits have advantages of low cost and easy handling. Compared to rodent vein graft models, rabbits have larger and easier-to-manipulate blood vessels that provide abundant tissue for analysis.

Inflammation in Vein Graft Disease

Bypass surgery is one of the most frequently used strategies to revascularize tissues downstream occlusive atherosclerotic lesions. For venous bypass surgery the great saphenous vein is the most commonly used vessel. Unfortunately, graft efficacy is low due to the development of vascular inflammation, intimal hyperplasia and accelerated atherosclerosis. Moreover, failure of grafts leads to significant adverse outcomes and even mortality. The last couple of decades not much has changed in the treatment of vein graft disease (VGD). However, insight is the cellular and molecular mechanisms of VGD has increased. In this review, we discuss the latest insights on VGD and the role of inflammation in this. We discuss vein graft pathophysiology including hemodynamic changes, the role of vessel wall constitutions and vascular remodeling. We show that profound systemic and local inflammatory responses, including inflammation of the perivascular fat, involve both the innate and adaptive immune system.

Vein graft failure: from pathophysiology to clinical outcomes

Occlusive arterial disease is a leading cause of morbidity and mortality worldwide. Aside from balloon angioplasty, bypass graft surgery is the most commonly performed revascularization technique for occlusive arterial disease. Coronary artery bypass graft surgery is performed in patients with left main coronary artery disease and three-vessel coronary disease, whereas peripheral artery bypass graft surgery is used to treat patients with late-stage peripheral artery occlusive disease. The great saphenous veins are commonly used conduits for surgical revascularization; however, they are associated with a high failure rate. Therefore, preservation of vein graft patency is essential for long-term surgical success. With the exception of 'no-touch' techniques and lipid-lowering and antiplatelet (aspirin) therapy, no intervention has hitherto unequivocally proven to be clinically effective in preventing vein graft failure. In this Review, we describe both preclinical and clinical studies evaluating the pathophysiology underlying vein graft failure, and the latest therapeutic options to improve patency for both coronary and peripheral grafts.

Synergistic effect of a tissue kallikrein 1 and tissue inhibitor of matrix metalloproteinase 1 co‑expression vector on the proliferation of rat vascular smooth muscle cells

Tissue kallikrein 1 (TK1) and tissue inhibitor of matrix metalloproteinase 1 (TIMP1) are important in inhibiting vascular smooth muscle cell (VSMC) proliferation and improving vascular remodeling, respectively. It was hypothesized that a combination of TK1 and TIMP1 genes, mediated by an adenovirus vector could augment or act in synergy to enhance the inhibitory effects. The promoter, mCMV carrying hTIMP1 cDNA was subcloned into pDC316-hTK1 to construct a recombinant plasmid carrying hTK1 and hTIMP1 genes. Subsequently, the double gene plasmid and adenovirus backbone plasmid were packaged into HEK293A cells. Gene transcription and protein expression were examined, respectively using reverse transcription-quantitative polymerase chain reaction (PCR) and western blotting assays. VSMC proliferation was assessed using cell counting and methyl-thiazolyl-tetrazoliuin methods. The constructed plasmid containing hTK1 and hTIMP1 genes was correctly identified by means of PCR, double digestion and sequencing analysis. The co-expression vector, Ad-hTK1-hTIMP1 was successfully constructed and packaged into HEK293A cells. When VSMCs were transfected with the co-expression vector, the mRNA transcription and protein expression of hTK1 and hTIMP1 exhibited abundant expression in a concentration-dependent and time-dependent manner, independently. In conclusion, the co-expression vector synergistically inhibited the cell growth and proliferation induced by platelet-derived growth factor-BB compared with the single gene vector.

Matrix metalloproteinases in atherosclerosis: role of nitric oxide, hydrogen sulfide, homocysteine, and polymorphisms

Atherosclerosis is an inflammatory process that involves activation of matrix metalloproteinases (MMPs); MMPs degrade collagen and allow for smooth-muscle cell migration within a vessel. Moreover, this begets an accumulation of other cellular material, resulting in occlusion of the vessel and ischemic events to tissues in need of nutrients. Homocysteine has been shown to activate MMPs via an increase in oxidative stress and acting as a signaling molecule on receptors like the peroxisome proliferator activated receptor-γ and N-methyl-D-aspartate receptor. Nitric oxide has been shown to be beneficial in some cases of deactivating MMPs. However, in other cases, it has been shown to be harmful. Further studies are warranted on the scenarios that are beneficial versus destructive. Hydrogen sulfide (H₂S) has been shown to decrease MMP activities in all cases in the literature by acting as an antioxidant and vasodilator. Various MMP-knockout and gene-silencing models have been used to determine the function of the many different MMPs. This has allowed us to discern the role that each MMP has in promoting or alleviating pathological conditions. Furthermore, there has been some study into the MMP polymorphisms that exist in the population. The purpose of this review is to examine the role of MMPs and their polymorphisms on the development of atherosclerosis, with emphasis placed on pathways that involve nitric oxide, hydrogen sulfide, and homocysteine.

A novel tumor targeting drug carrier for optical imaging and therapy

Human serum albumin (HSA), a naturally abundant protein in blood plasma and tissue fluids, has an extraordinary ligand-binding capacity and is advocated as a drug carrier to facilitate drug delivery. To render it tumor targeting specificity, we generated a recombinant HSA fused with the amino-terminal fragment (ATF) of urokinase, allowing the fusion protein to bind to urokinase receptor (uPAR), which is shown to have a high expression level in many tumors, but not in normal tissues. To test the efficacy of this bifunctional protein (ATF-HSA), a hydrophobic photosensitizer (mono-substituted β-carboxy phthalocyanine zinc, CPZ) was chosen as a cytotoxic agent. A dilution-incubation-purification (DIP) strategy was developed to load the ATF-HSA with this CPZ, forming a 1:1 molecular complex (ATF-HSA:CPZ). We demonstrated that CPZ was indeed embedded inside ATF-HSA at the fatty acid binding site 1 (FA1) of HSA, giving a hydrodynamic radius of 7.5 nm, close to HSA's (6.5 nm). ATF-HSA:CPZ showed high stability and remarkable optical and photophysical properties in aqueous solution. In addition, the molecular complex ATF-HSA:CPZ can bind to recombinant uPAR in vitro and uPAR on tumor cell surfaces, and was efficient in photodynamic killing of tumor cells. The tumor-killing potency of this molecular complex was further demonstrated in a tumor-bearing mouse model at a dose of 0.080 μmol / kg, or 0.050 mg CPZ / kg of mouse body weight. Using fluorescent molecular tomography (FMT), ATF-HSA:CPZ was shown to accumulate specifically in tumors, and importantly, such tumor retention was higher than that of HSA:CPZ. Together, these results indicate that ATF-HSA:CPZ is not only an efficient tumor-specific cytotoxic agent, but also an useful tumor-specific imaging probe. This bifunctional protein ATF-HSA can also be used as a drug carrier for other types of cytotoxic or imaging agents to render them specificity for uPAR-expressing tumors.

TLR accessory molecule RP105 (CD180) is involved in post-interventional vascular remodeling and soluble RP105 modulates neointima formation

Background

RP105 (CD180) is TLR4 homologue lacking the intracellular TLR4 signaling domain and acts a TLR accessory molecule and physiological inhibitor of TLR4-signaling. The role of RP105 in vascular remodeling, in particular post-interventional remodeling is unknown.

Methods and Results

TLR4 and RP105 are expressed on vascular smooth muscle cells (VSMC) as well as in the media of murine femoral artery segments as detected by qPCR and immunohistochemistry. Furthermore, the response to the TLR4 ligand LPS was stronger in VSMC from RP105^−/− mice resulting in a higher proliferation rate. In RP105^−/− mice femoral artery cuff placement resulted in an increase in neointima formation as compared to WT mice (4982±974 µm² vs.1947±278 µm²,p = 0.0014). Local LPS application augmented neointima formation in both groups, but in RP105^−/− mice this effect was more pronounced (10316±1243 µm² vs.4208±555 µm²,p = 0.0002), suggesting a functional role for RP105. For additional functional studies, the extracellular domain of murine RP105 was expressed with or without its adaptor protein MD1 and purified. SEC-MALSanalysis showed a functional 2∶2 homodimer formation of the RP105-MD1 complex. This protein complex was able to block the TLR4 response in whole blood ex-vivo. In vivo gene transfer of plasmid vectors encoding the extracellular part of RP105 and its adaptor protein MD1 were performed to initiate a stable endogenous soluble protein production. Expression of soluble RP105-MD1 resulted in a significant reduction in neointima formation in hypercholesterolemic mice (2500±573 vs.6581±1894 µm²,p<0.05), whereas expression of the single factors RP105 or MD1 had no effect.

Conclusion

RP105 is a potent inhibitor of post-interventional neointima formation.

Role of hemodynamic forces in the ex vivo arterialization of human saphenous veins

BACKGROUND

Human saphenous vein grafts are one of the salvage bypass conduits when endovascular procedures are not feasible or fail. Understanding the remodeling process that venous grafts undergo during exposure to arterial conditions is crucial to improve their patency, which is often compromised by intimal hyperplasia. The precise role of hemodynamic forces such as shear stress and arterial pressure in this remodeling is not fully characterized. The aim of this study was to determine the involvement of arterial shear stress and pressure on vein wall remodeling and to unravel the underlying molecular mechanisms.

METHODS

An ex vivo vein support system was modified for chronic (up to 1 week), pulsatile perfusion of human saphenous veins under controlled conditions that permitted the separate control of arterial shear stress and different arterial pressure (7 mm Hg or 70 mm Hg).

RESULTS

Veins perfused for 7 days under high pressure (70 mm Hg) underwent significant development of a neointima compared with veins exposed to low pressure (7 mm Hg). These structural changes were associated with altered expression of several molecular markers. Exposure to an arterial shear stress under low pressure increased the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 at the transcript, protein, and activity levels. This increase was enhanced by high pressure, which also increased TIMP-2 protein expression despite decreased levels of the cognate transcript. In contrast, the expression of plasminogen activator inhibitor-1 increased with shear stress but was not modified by pressure. Levels of the venous marker Eph-B4 were decreased under arterial shear stress, and levels of the arterial marker Ephrin-B2 were downregulated under high-pressure conditions.

CONCLUSIONS

This model is a valuable tool to identify the role of hemodynamic forces and to decipher the molecular mechanisms leading to failure of human saphenous vein grafts. Under ex vivo conditions, arterial perfusion is sufficient to activate the remodeling of human veins, a change that is associated with the loss of specific vein markers. Elevation of pressure generates intimal hyperplasia, even though veins do not acquire arterial markers.

CLINICAL RELEVANCE

The pathological remodeling of the venous wall, which leads to stenosis and ultimately graft failure, is the main limiting factor of human saphenous vein graft bypass. This remodeling is due to the hemodynamic adaptation of the vein to the arterial environment and cannot be prevented by conventional therapy. To develop a more targeted therapy, a better understanding of the molecular mechanisms involved in intimal hyperplasia is essential, which requires the development of ex vivo models of chronic perfusion of human veins.

Plaque rupture complications in murine atherosclerotic vein grafts can be prevented by TIMP-1 overexpression

The current study describes the incidence and phenotype of plaque rupture complications in murine vein grafts. Since matrix metalloproteinases (MMPs) are highly involved in atherosclerotic plaque vulnerability and plaque rupture, we hypothesized that this model can be validated by overexpression of the MMP inhibitor TIMP-1. First we studied 47 vein grafts in hypercholesterolemic ApoE3*Leiden mice for the incidence of plaque complications. In 79% of these grafts, extensive lesions with plaque rupture complications like dissections, intraplaque hemorrhages or erosions with intramural thrombi were found. Next, in vivo Near-InfraRed-Fluorescence imaging demonstrated that electroporation mediated TIMP-1-overexpression reduced local MMP activity in vein grafts by 73% (p<0.01). This led to a 40% reduction in lesion-size after 28d (p = 0.01) and a more stable lesion phenotype with significant more smooth muscle cells (135%), collagen (47%) and significant less macrophages (44%) and fibrin (55%) than controls. More importantly, lesions in the TIMP-1 group showed a 90% reduction of plaque complications (10/18 of control mice showed plaque complications versus 1/18 in TIMP-1 treated mice). Murine vein grafts are a relevant spontaneous model to study plaque stability and subsequent hemorrhagic complications, resulting in plaque instability. Moreover, inhibition of MMPs by TIMP-1-overexpression resulted in decreased plaque progression, increased stabilization and decreased plaque rupture complications in murine vein grafts.

Prevention of coronary in-stent restenosis and vein graft failure: does vascular gene therapy have a role?

Coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI), including stent insertion, are established therapies in both acute coronary syndromes (ACS) and symptomatic chronic coronary artery disease refractory to pharmacological therapy. These continually advancing treatments remain limited by failure of conduit grafts in CABG and by restenosis or thrombosis of stented vessel segments in PCI caused by neointimal hyperplasia, impaired endothelialisation and accelerated atherosclerosis. While pharmacological and technological advancements have improved patient outcomes following both procedures, when grafts or stents fail these result in significant health burdens. In this review we discuss the pathophysiology of vein graft disease and in-stent restenosis, gene therapy vector development and design, and translation from pre-clinical animal models through human clinical trials. We identify the key issues that are currently preventing vascular gene therapy from interfacing with clinical use and introduce the areas of research attempting to overcome these.

Vein graft failure: current clinical practice and potential for gene therapeutics

Autologous saphenous vein is commonly used as a conduit to bypass atherosclerotic lesions in coronary and femoral arteries. Despite the wide use of arterial conduits, which are less susceptible to complications and failure, as alternative conduits, the saphenous vein will continue to be used in coronary artery bypass grafting until acceptable alternative approaches are evaluated. Hence, preservation of vein graft patency is essential for the long-term success. Gene therapy is attractive in this setting as an ex-vivo technology to genetically manipulate the conduit before grafting. The use of safe and efficient vectors for delivery is a necessity as well as a strategy to improve patency in the long term. Here, we review the current clinical practice, the pathogenesis of bypass graft failure and adenovirus-mediated gene therapy strategies designed to improve late vein graft failure by modulation of smooth muscle cells in the vein wall.

The urokinase system in the pathogenesis of atherosclerosis

Atherogenesis refers to the development of atheromatous plaques in the inner lining of the arteries. These atherosclerotic lesions are characterized by accumulation of monocyte-derived macrophage-foam cells loaded with cholesterol, which eventually undergo apoptotic death, leading finally to formation of the necrotic core of the plaque. Atheroma formation also involves the recruitment of smooth muscle cells (SMC) from the media into the intima, where they proliferate and form the neointima in a process called "remodeling". Cells in the advanced atherosclerotic plaques express high levels of the serine protease urokinase-type plasminogen activator (uPA) and its receptor (uPAR). uPA is a multi-functional multi-domain protein that is not only a regulator of fibrinolysis, but it is also associated with several acute and chronic pathologic conditions. uPA mediate the extracellular matrix (ECM) degradation, and plays a pivotal role in cell adhesion, migration and proliferation, during tissue remodeling. On cell surface uPA binds to the high affinity urokinase receptor, providing a strictly localized proteolysis of ECM proteins. The uPA/uPAR complex also activates intracellular signaling, thus regulating cellular function. An imbalance in the uPA/uPAR system leads to dis-orders in tissue structure and function. This review summarizes recent progress in understanding the role and mechanisms of the uPA/uPAR system in atherogenesis.

Restenosis after PCI. Part 1: pathophysiology and risk factors

Restenosis is a complex disease for which the pathophysiological mechanisms have not yet been fully elucidated, but are thought to include inflammation, proliferation, and matrix remodeling. Over the years, many predictive clinical, biological, (epi)genetic, lesion-related, and procedural risk factors for restenosis have been identified. These factors are not only useful in risk stratification of patients, they also contribute to our understanding of this condition. Furthermore, these factors provide evidence on which to base treatment tailored to the individual and aid in the development of novel therapeutic modalities. In this Review, we will evaluate the available evidence on the pathophysiological mechanisms of restenosis and provide an overview of the various risk factors, together with the possible clinical application of this knowledge.