Enhancement of neointima formation with tissue-type plasminogen activator

Oligonucleotide Microarrays Identified Potential Regulatory Genes Related to Early Outward Arterial Remodeling Induced by Tissue Plasminogen Activator

Constrictive vascular remodeling limiting blood flow, as well as compensatory outward remodeling, has been observed in many cardiovascular diseases; however, the underlying mechanisms regulating the remodeling response of the vessels remain unclear. Plasminogen activators (PA) are involved in many of the processes of vascular remodeling. We have shown previously that increased levels of tissue-type PA (tPA) contributes to outward vascular remodeling. To elucidate the mechanisms involved in the induction of outward remodeling we characterized changes in the expression profiles of 8799 genes in injured rat carotid arteries 1 and 4 days after recombinant tPA treatment compared to vehicle. Periadventitial tPA significantly increased lumen size and vessel area, encompassed by the external elastic lamina, at both one and 4 days after treatment. Among 41 differentially expressed known genes 1 day after tPA application, five genes were involved in gene transcription, five genes were related to the regulation of vascular tone [for example, thromboxane A2 receptor (D32080) or non-selective-type endothelin receptor (S65355)], and eight genes were identified as participating in vascular innervation [for example, calpain (D14478) or neural cell adhesion molecule L1 (X59149)]. Four days after injury in tPA-treated arteries, four genes, regulating vascular tone, were differentially expressed. Thus, tPA promotes outward arterial remodeling after injury, at least in part, by regulating expression of genes in the vessel wall related to function of the nervous system and vascular tone.

Fibrinolytic system related to pulmonary arterial pressure and lung function of patients with idiopathic pulmonary fibrosis

OBJECTIVES AND AIMS

To investigate urokinase-(uPA) and tissue-type (tPA) plasminogen activator and plasminogen activator inhibitor type-1 (PAI-1) levels in patients with idiopathic pulmonary fibrosis (IPF) and to determine the relationship between fibrinolytic system and pulmonary arterial pressure and pulmonary function.

METHODS

Seventy-nine patients with IPF were included. Bronchoalveolar lavage fluid (BALF) and blood samples were collected. The concentrations of tPA, uPA and PAI-1 were measured using enzyme-linked immunosorbent assay. Doppler echocardiography was used to detect tricuspid regurgitation pressure gradient (TRPG) to estimate pulmonary arterial pressure.

RESULTS

BALF tPA elevated (P < 0.005), circulatory PAI-1 decreased (P = 0.05) and the ratio of uPA and PAI-1 decreased (P = 0.01) in BALF in IPF patients with pulmonary hypertension (PH) compared to those without PH. Positive linear correlations were found: BALF tPA and TRPG (r = 0.558, P = 0.013); the predicted percentage of diffusion capacity of lung for carbon monoxide adjustments for alveolar volume and BALF uPA (r = 0.319, P = 0.035). Negative linear correlations were as follows: BALF PAI-1 and the predicted percentage of VC_max (r = -0.325, P = 0.020), or total lung capacity (r = -0.312, P = 0.033); circulatory PAI-1 and TRPG (r = -0.697, P = 0.003).

CONCLUSIONS

The change of alveolar fibrolytic system in IPF, especially the uPA reduction and the PAI-1elevation, contributes to the deterioration of lung function. During the lung injury initiating fibrosis, tPA and PAI-1 might be leaked out of the pulmonary capillaries into alveoli, resulting in their elevation in alveoli and reduction in circulation, and finally contributing to the development of PH in IPF.

Gene therapy for the prevention of vein graft disease

Ischemic cardiovascular disease remains the leading cause of death worldwide. Despite advances in the medical management of atherosclerosis over the past several decades, many patients require arterial revascularization to reduce mortality and alleviate ischemic symptoms. Technological advancements have led to dramatic increases in the use of percutaneous and endovascular approaches, yet surgical revascularization (bypass surgery) with autologous vein grafts remains a mainstay of therapy for both coronary and peripheral artery disease. Although bypass surgery is highly efficacious in the short term, long-term outcomes are limited by relatively high failure rates as a result of intimal hyperplasia, which is a common feature of vein graft disease. The supply of native veins is limited, and many individuals require multiple grafts and repeat procedures. The need to prevent vein graft failure has led to great interest in gene therapy approaches to this problem. Bypass grafting presents an ideal opportunity for gene therapy, as surgically harvested vein grafts can be treated with gene delivery vectors ex vivo, thereby maximizing gene delivery while minimizing the potential for systemic toxicity and targeting the pathogenesis of vein graft disease at its onset. Here we will review the pathogenesis of vein graft disease and discuss vector delivery strategies and potential molecular targets for its prevention. We will summarize the preclinical and clinical literature on gene therapy in vein grafting and discuss additional considerations for future therapies to prevent vein graft disease.

Induction of the fibrinolytic system by cartilage extract mediates its antiangiogenic effect in mouse glioma

Both the antiangiogenic and antitumoral activity of shark cartilage extracts (SCE) have been demonstrated in animal models and clinical trials. Studies reported that SCE induces the expression of tissue plasminogen activator gene (PLAT) in endothelial cells and increases the activity of the protein (t-PA) in vitro. The aim of this study was to demonstrate the crucial role of t-PA induction in the antiangiogenic and antitumor activity of SCE in experimental glioma. This study showed antiangiogenic and antitumoral effects of SCE in three mice glioma models (C6, HGD and GL26). Histological examination suggested perivascular proteolysis and edema as well as important intratumoral necrosis, which artefactually increased the tumor volume at high doses. Thus, the antiangiogenic effect of SCE correlated with the presence of t-PA and angiostatin in degenerating vessels. Functional in vivo experiments were conducted to modulate the plasminogen pathway. No antiangiogenic effect was observed on tumors overexpressing the plasminogen activator inhibitor-1 (PAI-1). Moreover, therapeutical effects were neutralized in mice that were cotreated with ε-aminocaproic acid (EACA, 120 mg/kg p.o.), an inhibitor that blocks the high-affinity lysine binding sites of both plasminogen and plasmin. In contrast, cotreatment with N-acetylcysteine (NAC, 7,5mg/kg i.p.), a sulfhydril donor that reduces plasmin into angiostatin or other antiangiogenic fragments, increased the benefit of SCE on mice survival. In subcutaneous models, NAC prevented the increase in tumor volume caused by high doses of cartilage extract. In conclusion, this study indicates that induction of t-PA by shark cartilage extract plays an essential role in its antiangiogenic activity, but that control of excessive proteolysis by a plasmin reductor could prevent edema and uncover the full benefit of shark cartilage extract in the treatment of intracranial tumors.

Directed Migration of Smooth Muscle Cells to Engineer Plaque-Resistant Vein Grafts

PURPOSE

To test the hypothesis that controlled perivascular release of tissue plasminogen activator (tPA) can generate cleaved extracellular matrix (ECM) chemotactic gradients to guide the migration of vascular smooth muscle cells (SMCs) away from the lumen, thereby limiting neointima formation.

METHODS

This hypothesis was tested in rabbit models in which the perivascular surface of vein bypass grafts was treated with microspheres releasing tPA (MS-tPA), microspheres containing no drug (MS-blank), or phosphate buffered saline (PBS). Vein graft segments harvested after 7 days were then evaluated for elastin content, proliferating SMCs, intima-to-media (I/M) ratio, and inflammation; late impact on neointima formation was also examined.

RESULTS

The 7-day results demonstrated cleaved elastin gradients and proliferating SMCs that assumed a more peripheral distribution in the MS-tPA group than MS-blank and PBS controls (p<0.05). At 28 days, vein grafts treated with MS-tPA showed a mean I/M ratio (0.35+/-0.04) that was 63.5% lower than PBS controls (0.96+/-0.07, p<0.005) and 43.5% lower than MS-blank specimens (0.62+/-0.08, p<0.05).

CONCLUSIONS

Perivascular release of tPA modifies ECM gradients, directionally guides SMC migration away from the lumen, and limits neointima formation.

Effect of tissue plasminogen activator on vascular smooth muscle cells

OBJECTIVE

Engineered overexpression of tissue plasminogen activator (tPA) in vascular cells has been proposed as a means to decrease intravascular thrombosis; however, tPA gene transfer has augmented intimal hyperplasia in vivo in some studies. The purpose of this study was to define in vitro the effect of tPA gene transfer on smooth muscle cells (SMCs).

METHODS

Human SMCs were retrovirally transduced with the tPA gene (SMCs/tPA).

RESULTS

In the absence of plasminogen, no statistical differences in proliferation, migration, and morphology were observed between SMCs/tPA and SMCs. In the presence of plasminogen, many differences became apparent. Matrix metalloproteinase-2 (MMP-2) activation was 10-fold higher in SMCs/tPA than in SMCs. This activation was inhibited by aprotinin, a plasmin inhibitor. Collagen degradation increased sevenfold in SMCs/tPA. SMCs/tPA contracted dramatically in the presence of plasminogen. This cell contraction, indicative of extracellular matrix degradation, was blocked by aprotinin and partially inhibited by MMP inhibitors. SMC/tPA-conditioned medium induced significantly more SMC proliferation. The migration of SMCs/tPA through a porous membrane significantly exceeded untransduced SMCs.

CONCLUSIONS

Over-expression of tPA in SMCs results in increased extracellular matrix degradation and can promote cell proliferation and migration. This effect is mediated via plasmin, which further activates MMP-2.

CLINICAL RELEVANCE

TPA has been clinically used as a thrombolytic agent in the treatment of acute thrombotic disorders. Transferring the tPA gene into vascular cells as a strategy of gene therapy has been proposed to enhance fibrinolytic capability and therefore inhibit thrombosis and restenosis after vascular interventions. The mechanism(s) by which tPA affects SMC proliferation and vascular remodeling has not been thoroughly characterized. This study unveils the relationship between thrombolytic activity and intimal hyperplasia by showing how the elevated expression of tPA affects the vascular remodeling. This study underscores that the overexpression of an enzyme thought beneficial to blood flow can potentially compromise blood flow by altering the biology of the cell engineered to express it. The results are important to the rational engineering of bioactive grafts with better patency. A new strategy to enhance the thrombolytic ability of a vascular surface without inducing excessive neointimal hyperplasia is proposed.

Neointimal hyperplasia on a cell-seeded polytetrafluoroethylene graft is promoted by transfer of tissue plasminogen activator gene and inhibited by transfer of nitric oxide synthase gene

OBJECTIVE

The objective of this study was to examine the effect of tissue plasminogen activator (tPA) and endothelial nitric oxide synthase (eNOS) on thrombosis and neointimal hyperplasia on a polytetrafluoroethylene (PTFE) graft seeded with smooth muscle cells (SMCs).

METHODS

SMCs retrovirally transduced with tPA and eNOS genes were seeded on PTFE grafts and then implanted into the infrarenal rabbit aorta. Thrombosis and neointimal hyperplasia on the grafts were examined after 30 and 100 days of implantation.

RESULTS

At 30 days of implantation, thrombus was observed on the luminal surface of both unseeded and SMC seeded control grafts, whereas grafts seeded with SMCs secreting tPA were nearly free of thrombus. At 100 days, the neointima on grafts seeded with tPA transduced SMCs was significantly thicker (925 +/- 150 microm, n = 5) than neointima on the other grafts (range, 132 to 374 microm; P < .001). Neointima thickness on grafts seeded with eNOS transduced SMCs (154 +/- 27 microm) was similar to that of unseeded grafts (132 +/- 16 microm, P > .05); both were thinner than those on grafts seeded with SMCs transduced with only lacZ gene (287 +/- 35 microm). The ratio of seeded cells in the neointima was significantly higher on SMC/tPA grafts (46% +/- 8%) than SMC/NOS grafts (21% +/- 6%, P < .05), indicating tPA transduced cells proliferated more than eNOS transduced cells.

CONCLUSIONS

Engineered tPA expression in seeded SMCs causes significantly more neointimal hyperplasia, despite the favorable inhibition of luminal thrombus. eNOS expression in the seeded cells inhibits neointimal hyperplasia.

The effect of anticoagulation with subcutaneously delivered polyethylene glycol conjugated hirudin and recombinant tissue plasminogen activator on recurrent stenosis in the rabbit double-balloon injury model

Myointimal hyperplasia is the condition usually responsible for recurrent stenosis (restenosis) after endarterectomy, bypass grafting and angioplasty. Its cause is still not known. The present study examined whether inhibition of thrombin by tissue plasminogen activator (r-TPA) or polyethylene glycol recombinant hirudin (PEG-hirudin) could reduce restenosis in an animal model. Restenosis was induced in 20 cholesterol-fed rabbits. The right carotid artery underwent a double-balloon injury while left carotid artery acted as a control. Recombinant tissue plasminogen activator (1 mg kg(-1) s.c.) and PEG-hirudin (0.7 mg kg(-1) s.c.) were given subcutaneously with normal saline acting as a control. Blood levels of PEG-hirudin were measured by both ELISA and an Ecarin (activity) assay. Vessel dimensions were measured in histological sections, obtained from perfusion-fixed tissue, using computerised planimetry. The model reproduced many of the histological changes found in human restenosis, such as intramural thrombus, rupture of the elastic lamina, macrophage infiltration and smooth muscle migration. Reinjury caused an almost three-fold reduction in the area of the lumen (median 0.25 mm(2)) compared with uninjured vessels (median 0.72 mm(2)). The mean plasma levels of PEG-hirudin and r-tPA achieved were 291 ng/ml (S.E.M. 28 ng/ml) and 34 IU/ml (S.E.M. 12 IU/ml), respectively. PEG-hirudin significantly inhibited the effect of balloon injury on luminal area compared with saline-treated controls (0.21 versus 0.44 mm(2), respectively, P<0.05). Recombinant tPA also had a similar inhibitory affect, but this did not reach statistical significance (0.16 versus 0.44 mm(2), respectively, P>0.05). The magnitude of luminal narrowing was significantly reduced by subcutaneous injection of PEG-hirudin. Further studies are required to determine whether this effect can be enhanced by other antithrombins or improved methods of delivery.

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.