Vascular permeability factor accelerates endothelial regrowth following balloon angioplasty

Mechanisms of Endothelial Regeneration and Vascular Repair and Their Application to Regenerative Medicine

Endothelial barrier integrity is required for maintaining vascular homeostasis and fluid balance between the circulation and surrounding tissues and for preventing the development of vascular disease. Despite comprehensive understanding of the molecular mechanisms and signaling pathways that mediate endothelial injury, the regulatory mechanisms responsible for endothelial regeneration and vascular repair are incompletely understood and constitute an emerging area of research. Endogenous and exogenous reparative mechanisms serve to reverse vascular damage and restore endothelial barrier function through regeneration of a functional endothelium and re-engagement of endothelial junctions. In this review, mechanisms that contribute to endothelial regeneration and vascular repair are described. Targeting these mechanisms has the potential to improve outcome in diseases that are characterized by vascular injury, such as atherosclerosis, restenosis, peripheral vascular disease, sepsis, and acute respiratory distress syndrome. Future studies to further improve current understanding of the mechanisms that control endothelial regeneration and vascular repair are also highlighted.

Vascular toxicity associated with anti-angiogenic drugs

Over the past two decades, the treatment of cancer has been revolutionised by the highly successful introduction of novel molecular targeted therapies and immunotherapies, including small-molecule kinase inhibitors and monoclonal antibodies that target angiogenesis by inhibiting vascular endothelial growth factor (VEGF) signaling pathways. Despite their anti-angiogenic and anti-cancer benefits, the use of VEGF inhibitors (VEGFi) and other tyrosine kinase inhibitors (TKIs) has been hampered by potent vascular toxicities especially hypertension and thromboembolism. Molecular processes underlying VEGFi-induced vascular toxicities still remain unclear but inhibition of endothelial NO synthase (eNOS), reduced nitric oxide (NO) production, oxidative stress, activation of the endothelin system, and rarefaction have been implicated. However, the pathophysiological mechanisms still remain elusive and there is an urgent need to better understand exactly how anti-angiogenic drugs cause hypertension and other cardiovascular diseases (CVDs). This is especially important because VEGFi are increasingly being used in combination with other anti-cancer dugs, such as immunotherapies (immune checkpoint inhibitors (ICIs)), other TKIs, drugs that inhibit epigenetic processes (histone deacetylase (HDAC) inhibitor) and poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors, which may themselves induce cardiovascular injury. Here, we discuss vascular toxicities associated with TKIs, especially VEGFi, and provide an up-to-date overview on molecular mechanisms underlying VEGFi-induced vascular toxicity and cardiovascular sequelae. We also review the vascular effects of VEGFi when used in combination with other modern anti-cancer drugs.

Evaluation of Vascular Endothelial Growth Factor and Its Receptors in Human Neointima

OBJECTIVE

The potential contribution of vascular endothelial growth factor (VEGF) in neointima development has been evaluated in numerous animal studies. However, its role remains controversial. Moreover, little is known about neointima formation in humans. In this study we assessed the expression of VEGF-A and its receptors in the human neointima formed within vascular anastomosis.

METHODS

The studied material comprised neointima samples harvested during secondary vascular operations from patients with chronic limb ischemia after aorto-/iliofemoral bypass grafting who developed vascular graft occlusion at 6-18 months after the initial surgical treatment. The control material consisted of segments of femoral arteries without visible macroscopic lesions collected from organ donors. The expression and content of VEGF-A, VEGFR-1 and VEGFR-2 were analyzed with PCR and ELISA methods, respectively.

RESULTS

We observed a significantly increased expression of VEGF-A and VEGFR-2 mRNA in neointima compared to the normal aorta. A significantly higher protein content of VEGF-A and VEGFR-2 in neointima samples compared to the controls was also observed. No significant difference of VEGFR-1 content and VEGFR-1 mRNA expression was found in the studied material.

CONCLUSION

These results indicate a possible involvement of the VEGF-A and VEGFR-2 system in the pathologic process of human neointima formation after vascular interventions.

Important of Angiopoietic System in Evaluation of Endothelial Damage in Children with Crimean-Congo Hemorrhagic Fever

BACKGROUND

Crimean-Congo hemorrhagic fever (CCHF) causes endothelial activation and dysfunction by affecting the endothelium directly or indirectly. In maintaining the vascular integrity, vascular endothelial growth factor (VEGF-A) and its receptor (VEGFR1) and angiopoietin-2 (Ang-2) and its receptor (Tie-2) are very important mediators. For this reason, we aimed at studying the association of Ang-2 and VEGF and their receptors Tie-2 and VEGFR1 with CCHF infection.

METHODS

Thirty one CCHF patients and 31 healthy controls (HC) were included in the study. CCHF patients were classified into 2 groups in terms of disease severity (severe and nonsevere). VEGF-A, VEGFR1, Ang-2 and Tie-2 levels were measured in all groups.

RESULT

Serum levels of Tie-2, Ang-2, VEGF-A and VEGFR1 were significantly increased in CCHF patients compared with the HC. Furthermore, serum Tie-2, Ang-2, VEGF and VEGFR1 levels were found to be significantly higher in the severe group than in the nonsevere and HC groups (P < 0.05 and P < 0.001, respectively). Also, Tie-2, Ang-2, VEGF-A and VEGFR1 levels were significantly higher in the nonsevere group than in the HC group (P < 0.05).

CONCLUSION

Having statistically significant higher Ang-2, Tie-2, VEGF-A and VEGFR1 levels in the severe group when compared with the other groups suggested that VEGF-related Ang-2/Tie-2 system played a critical role in the pathogenesis of the disease, and these markers could be used as the severity criteria.

Long-term effects of a PPAR-gamma agonist, pioglitazone, on neointimal hyperplasia and endothelial regrowth in insulin resistant rats

OBJECTIVE

Insulin resistance is an independent risk factor for cardiovascular disease. PPAR-gamma agonists like pioglitazone decrease insulin resistance and have been shown to reduce neointimal hyperplasia in the short-term. However long-term studies on endothelial regrowth and neointimal hyperplasia have not been done.

METHODS AND RESULTS

We used hyperinsulinemic, normoglycemic Zucker fatty rats. Rats were treated with either 10 mg/kg body wt. pioglitazone or placebo till the end of the experiment. Rats underwent carotid angioplasty at age 12-14 weeks, 1 week after treatment was begun. In one set of experiments rats were sacrificed at 6 months and neointimal hyperplasia and VEGF expression was assessed. In another set of experiments rats were sacrificed at 3 and 6 months. Endothelial regrowth was determined. The rats were all normoglycemic and hyperinsulinemic. Pioglitazone treated rats had a significantly lesser degree of neointimal hyperplasia than control rats. Treated rats also had decreased VEGF expression. Endothelial regrowth was decreased in the treated rats at 6 months.

CONCLUSION

We conclude that although pioglitazone decreases neointimal hyperplasia even at 6 months, it retards endothelial regrowth, which could predispose the denuded vessel to thrombotic events. This may be modulated by a suppression of VEGF expression.

Fluid shear stress modulates cell migration induced by sphingosine 1-phosphate and vascular endothelial growth factor

The rational design of drug delivery systems requires the ability to predict the environment-specific responses of target cells to the delivered drug. Here we describe the in vitro effects of fluid shear stress, vascular endothelial growth factor (VEGF), and sphingosine 1-phosphate (S1P) on the migration of human umbilical vein endothelial cells (HUVEC). Endothelial cell migration into a scrape wound was enhanced in S1P- or VEGF-stimulated HUVEC by the addition of fluid shear stress. In both cases, scrape wound closure rates were near a maximal value that was not exceeded when cells were exposed to all three factors. We also found that cell migration into a scrape wound due to S1P stimulation was correlated with the S1P1 mRNA concentration, in systems where cell migration was not already near maximal. The present work represents our initial steps toward predicting cell migration based upon the activation state of the receptors and enzymes involved in the chemokinetic response. These results also illustrate the importance of context-dependent analysis of cell signaling cascades.

Acute VEGF effect on solute permeability of mammalian microvessels in vivo

To investigate the effect of vascular endothelial growth factor (VEGF) on solute permeability of mammalian microvessels, we measured the apparent permeability (P) of various-sized solutes on the postcapillary venules of rat mesentery in vivo. Exposure to 1 nM VEGF transiently increased P from a mean of 1.4 (+/-0.11 SE, n = 17) to a peak of 2.8 (+/-0.28 SE) x 10(-5) cm/s, a 2.4-fold increase for small solute sodium fluorescein (Stokes radius 0.45 nm), from a mean of 0.44 (+/-0.05 SE, n = 16) to a peak of 1.5 (+/-0.19 SE) x 10(-)5 cm/s, a 3.6-fold increase for intermediate-sized solute alpha-lactalbumin (Stokes radius 2.01 nm), from a mean of 0.049 (+/-0.0032 SE, n = 16) to a peak of 0.36 (+/-0.032 SE) x 10(-5) cm/s, a 7.9-fold increase for large solute bovine serum albumin (Stokes radius 3.55 nm), within 30 s. In approximately 2 min, all increased P returned to the baseline values. The response pattern of P to VEGF and the ratios of the peak to control values for rat mesenteric microvessels are similar to those of frog mesenteric microvessels [Am. J. Physiol.: Heart Circ. Physiol. 284 (2003) H2124]. Instead of considerable heterogeneity in the frog mesenteric microvessels, the acute response to 1 nM VEGF is homogeneous in the rat mesenteric microvessels.

Vascular Endothelial Growth Factor Regulates Reendothelialization and Neointima Formation in a Mouse Model of Arterial Injury

Background— The rate of reendothelialization is critical in neointima formation after arterial injury. Vascular endothelial growth factor (VEGF), a potent endothelial mitogen, has been advocated for accelerating endothelial repair and preventing intimal hyperplasia after percutaneous coronary interventions. However, the precise mechanism of action of VEGF treatment and the physiologic role of endogenous VEGF after arterial injury are not well described. To better understand the role of VEGF in arterial repair, we overexpressed both VEGF and a soluble, chimeric VEGF receptor (VEGF-trap), which binds free VEGF with high affinity, in a mouse model of arterial injury.

Methods and Results— Four groups of C57BL/6 mice underwent denuding endothelial injury 1 day after systemic injection of recombinant adenovirus expressing (1) VEGF, (2) VEGF-trap, (3) VEGF plus VEGF-trap, or (4) control adenovirus. Circulating levels of adenovirus-encoded proteins were significantly elevated after gene transfer. VEGF overexpression accelerated reendothelialization and increased luminal endothelial cell proliferation 2 weeks after arterial injury ( P <0.05), resulting in decreased neointima formation at 4 weeks compared with control ( P <0.01). Cotreatment with VEGF-trap completely sequestered free VEGF and abrogated the beneficial effect of VEGF overexpression. Interestingly, sequestration of endogenous VEGF by VEGF-trap overexpression alone also led to delayed reendothelialization at 2 weeks ( P <0.01) and increased neointima formation at 4 weeks ( P <0.01).

Conclusions— VEGF overexpression accelerated endothelial repair and inhibited neointima formation after arterial injury. Conversely, sequestration of exogenous and/or endogenous VEGF by VEGF-trap delayed reendothelialization and significantly increased neointima size. This demonstrates the therapeutic potential of VEGF but also emphasizes the important physiologic role of endogenous VEGF in vascular repair.

Role of the endothelium in modulating neointimal formation: vasculoprotective approaches to attenuate restenosis after percutaneous coronary interventions

Restenosis at the site of an endoluminal procedure remains a significant problem in the practice of interventional cardiology. We present current data on intimal hyperplasia, which identify the major role of endothelial cells (ECs) in the development of restenosis. Considering endothelial denudation as one of the most important mechanisms contributing to restenosis, we focus more attention on methods of accelerating restoration of endothelial continuity. Prevention of restenosis may be achieved by promoting endothelial regeneration through the use of growth factors, EC seeding, vessel reconstruction with autologous EC/fibrin matrix, and the use of estrogen-loaded stents and stents designed to capture progenitor ECs.

Plasma angiopoietin-1, angiopoietin-2, and angiopoietin receptor tie-2 levels in congestive heart failure

OBJECTIVES

The goal of this research was to test the hypothesis that plasma angiopoietin (Ang-1), its soluble receptor tie-2, and Ang-2 levels would be abnormal in patients with acute and chronic congestive heart failure (CHF) when compared with healthy controls.

BACKGROUND

Increased plasma vascular endothelial growth factor (VEGF) in CHF is suggestive of excess angiogenesis-possibly driven by tissue hypoxia. However, other growth factors also have a major role in angiogenesis, such as those of the angiopoietin family (e.g., Ang-1, which exerts its activity via its receptor, tie-2, and Ang-2).

METHODS

We recruited 39 patients with acute CHF (mean age 67 +/- 10 years), 40 patients with chronic CHF (mean age 63 +/- 9 years), and 17 healthy controls (mean age 67 +/- 7 years), all in sinus rhythm. Citrated plasma was analyzed for Ang-1, Ang-2, tie-2, and VEGF by enzyme-linked immunosorbent assay.

RESULTS

Angiopoietin-2 (p < 0.001), tie-2 (p < 0.05), and VEGF (p < 0.05) levels were all higher in acute CHF compared with controls. The Ang-2 levels were higher in acute CHF compared with chronic CHF (p < 0.001), but there were no significant differences in Ang-1 levels between the groups. The principal significant correlations were between Ang-2 and tie-2 (Spearman, r = 0.407; p < 0.0001) and between Ang-2 and ejection fraction (r = -0.241, p = 0.043). Although only marginally raised, levels of VEGF correlated with both Ang-2 (r = 0.468, p < 0.001) and tie-2 (r = 0.569, p < 0.001).

CONCLUSIONS

We have demonstrated abnormal levels of Ang-2 and tie-2, but normal Ang-1, in both CHF patients. These abnormalities may, alongside VEGF, indicate a role for these angiogenic factors in the pathophysiology of CHF.

Angiopoietin/tie-2 as mediators of angiogenesis: a role in congestive heart failure?

Angiogenic factors, in particular vascular endothelial growth factor (VEGF) and the angiopoietins, Ang-1 and -2, have recently generated significant interest, especially in oncology. The process of angiogenesis is also thought to occur in response to ischaemic conditions, which lie at the core of cardiovascular disease states such as coronary artery disease and congestive heart failure. However, current data do not conclusively show evidence of angiogenesis per se in these conditions, despite (for example) the presence of high levels of VEGF and Ang-2. High levels of these angiogenic factors in heart disease also have not translated into clinically significant new vessel formation, as in accelerated cancer growth or proliferative retinopathy. Indeed, we would hypothesize that these angiogenic markers--especially the angiopoietins--do not necessarily translate into new vessel formation in congestive heart failure (CHF), but may well reflect disturbances of endothelial integrity in CHF.

Bone marrow monocyte lineage cells adhere on injured endothelium in a monocyte chemoattractant protein-1-dependent manner and accelerate reendothelialization as endothelial progenitor cells

Peripheral blood (PB)-derived CD14+ monocytes were shown to transdifferentiate into endothelial cell (EC) lineage cells and contribute to neovascularization. We investigated whether bone marrow (BM)- or PB-derived CD34-/CD14+ cells are involved in reendothelialization after carotid balloon injury. Although neither hematopoietic nor mesenchymal stem cells were included in human BM-derived CD34-/CD14+ monocyte lineage cells (BM-MLCs), they expressed EC-specific markers (Tie2, CD31, VE-cadherin, and endoglin) to an extent identical to mature ECs. When BM-MLCs were cultured with vascular endothelial growth factors, hematopoietic markers were drastically decreased and new EC-specific markers (Flk and CD34) were induced. BM-MLCs were intra-arterially transplanted into balloon-injured arteries of athymic nude rats. When BM-MLCs were activated by monocyte chemoattractant protein-1 (MCP-1) in vivo or in vitro, they adhered onto injured endothelium, differentiated into EC-like cells by losing hematopoietic markers, and inhibited neointimal hyperplasia. Ability to prevent neointimal hyperplasia was more efficient than that of BM-derived CD34+ cells. MCP-dependent adhesion was not observed in PB-derived CD34-/CD14+ monocytes. Regenerated endothelium exhibited a cobblestone appearance, blocked extravasation of dye, and induced NO-dependent vasorelaxation. Basal adhesive activities on HUVECs under laminar flow and beta1-integrin expression (basal and active forms) were significantly increased in BM-MLCs compared with PB-derived monocytes. MCP-1 markedly enhanced adhesive activity of BM-MLCs (2.8-fold) on HUVECs by activating beta1-integrin conformation. Thus, BM-MLCs can function as EC progenitors that are more potent than CD34+ cells and acquire the ability to adhere on injured endothelium in a MCP-1-dependent manner, leading to reendothelialization associated with inhibition of intimal hyperplasia. This will open a novel window to MCP-1-mediated biological actions and vascular regeneration strategies by cell therapy.

Structural mechanisms of acute VEGF effect on microvessel permeability

To investigate the ultrastructural mechanisms of acute microvessel hyperpermeability by vascular endothelial growth factor (VEGF), we combined a mathematical model (J Biomech Eng 116: 502-513, 1994) with experimental data of the effect of VEGF on microvessel hydraulic conductivity (L(p)) and permeability of various-sized solutes. We examined the effect of VEGF on microvessel permeability to a small solute (sodium fluorescein, Stokes radius 0.45 nm), an intermediate solute (alpha-lactalbumin, Stokes radius 2.01 nm), and a large solute [albumin (BSA), Stokes radius 3.5 nm]. Exposure to 1 nM VEGF transiently increased apparent permeability to 2.3, 3.3, and 6.2 times their baseline values for sodium fluorescein, alpha-lactalbumin, and BSA, respectively, within 30 s, and all returned to control within 2 min. On the basis of L(p) (DO Bates and FE Curry. Am J Physiol Heart Circ Physiol 271: H2520-H2528, 1996) and permeability data, the prediction from the model suggested that the most likely structural changes in the interendothelial cleft induced by VEGF would be a approximately 2.5-fold increase in its opening width and partial degradation of the surface glycocalyx.

Optimal dosing of intravascular low-power red laser light as an adjunct to coronary stent implantation: insights from a porcine coronary stent model

BACKGROUND

It is believed that restenosis following coronary interventions is the result of endothelial denudation that leads to thrombus formation, vascular remodeling, and smooth muscle cell proliferation. Low-power red laser light (LPRLL) irradiation enhances endothelial cell growth in vitro and in vivo, and reduces restenosis in animal models. The present study investigated the optimal dose of intravascular LPRLL therapy in the prevention of in-stent stenosis in a porcine coronary stent model.

METHODS AND RESULTS

Selected right coronary artery segments were pretreated with a LPRLL balloon, delivering a dose of 0 mW during 1 min (group 1, n = 10), 50 mW during 1 min (group II, n = 10), or 100 mW during 1 min (group III, n = 10) before stenting. Quantitative coronary analysis of the stented vessel was performed before stenting, immediately after stenting, and at 6 weeks follow-up. The pigs were sacrificed, and histologic and morphometric analyses were conducted. At 6 weeks, minimal luminal stent diameter was significantly narrower in the control group compared to the 50-mW dose group (p < 0.05). These results were confirmed by morphometric analysis. Neointimal area was also significantly decreased in the 50-mW dose group.

CONCLUSIONS

Intravascular LPRLL contributes to reduction of angiographic in-stent restenosis and neointimal hyperplasia in this animal model. The optimal dose using the LPRLL balloon system seems to be approximately 5 mW delivered during 1 min.

Low-power helium: neon laser irradiation enhances production of vascular endothelial growth factor and promotes growth of endothelial cells in vitro

BACKGROUND AND OBJECTIVE

Numerous reports suggest that low-power laser irradiation (LPLI) is capable of affecting cellular processes in the absence of significant thermal effect. The objective of the present study was to determine the effect of LPLI on secretion of vascular endothelial growth factor (VEGF) and proliferation of human endothelial cells (EC) in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Cell cultures were irradiated with single different doses of LPLI (Laser irradiance from 0.10 to 6.3 J/cm(2)) by using a He:Ne continuous wave laser (632 nm). VEGF secretion by smooth muscle cells (SMC) and fibroblasts was quantified by sandwich enzyme immunoassay technique. The endothelial cell proliferation was measured by Alamar Blue assay. VEGF and transforming growth factor beta (TGF-beta) expression by cardiomyocytes was studied by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

We observed that (1) LPLI of vascular and cardiac cells results in a statistically significant increase of VEGF secretion in culture (1.6-fold for SMC and fibroblasts and 7-fold for cardiomyocytes) and is dose dependent (maximal effect was observed with LPLI irradiance of 0.5 J/cm(2) for SMC, 2.1 J/cm(2) for fibroblasts and 1.05 J/cm(2) for cardiomyocytes). (2) Significant stimulation of endothelial cell growth was obtained with LPLI-treated conditioned medium of SMC (maximal increase was observed with LPLI conditioned medium with irradiance of 1.05 J/cm(2) for SMC and 2.1 J/cm(2) for fibroblasts.

CONCLUSIONS

Our studies demonstrate that low-power laser irradiation increases production of VEGF by SMC, fibroblasts, and cardiac myocytes and stimulates EC growth in culture. These data may have significant importance leading to the establishment of new methods for endoluminal postangioplasty vascular repair and myocardial photoangiogenesis.

Construction and biological characterization of an HB-GAM/FGF-1 chimera for vascular tissue engineering

OBJECTIVE

Cardiovascular tissue engineering approaches to vessel wall restoration have focused on the potent but relatively nonspecific and heparin-dependent mesenchymal cell mitogen fibroblast growth factor 1 (FGF-1). We hypothesized that linking FGF-1 to a sequence likely to bind to cell surface receptors relatively more abundant on endothelial cells (ECs) might induce a relative greater EC bioavailability of the FGF-1. We constructed a heparin-binding growth-associated molecule (HB-GAM)/FGF-1 chimera by linking full-length human HB-GAM to the amino-terminus of human FGF-1beta (21-154) and tested its activities on smooth muscle cells (SMCs) and ECs.

METHODS

Primary canine carotid SMCs and jugular vein ECs were plated in 96-well plates in media containing 10% fetal bovine serum and grown to approximately 80% confluence. After being growth arrested in serum-free media for 24 hours, the cells were exposed to concentration ranges of cytokines and heparin, and proliferation was measured with tritiated-thymidine incorporation. Twenty percent fetal bovine serum was used as positive control, and phosphate-buffered saline was used as negative control.

RESULTS

In the presence of heparin the HB-GAM/FGF-1 chimera stimulated less SMC proliferation than did the wild-type FGF-1 with a median effective dose of approximately 0.3 nmol versus approximately 0.1 nmol (P <.001). By contrast, the chimera retained full stimulating activity on EC proliferation with a median effective dose of 0.06 nmol for both cytokines. Unlike the wild-type protein, the chimera possessed heparin-independent activity. In the absence of heparin, the chimera induced dose-dependent EC and SMC proliferation at 0.06 nmol or more compared with the wild-type FGF-1, which stimulated minimal DNA synthesis at 6.0-nmol concentrations.

CONCLUSIONS

The HB-GAM/FGF-1 chimera displays significantly greater and uniquely heparin-independent mitogenic activity for both cell types, and in the presence of heparin it displays a significantly greater EC specificity.

Endoluminal reconstruction of the arterial wall with endothelial cell/glue matrix reduces restenosis in an atherosclerotic rabbit

OBJECTIVES

The objectives of this study were 1) to improve the attachment of reimplanted endothelial cells (EC) using a fibrin glue, and 2) to assess the impact of endothelial reseeding on restenosis eight weeks after balloon angioplasty.

BACKGROUND

A possible mechanism contributing to restenosis after balloon angioplasty is the loss of the EC lining. Previous attempts to reseed EC had little effect due to rapid loss of the seeded cells.

METHODS

Twelve atherosclerotic rabbits were subjected to angioplasty of iliac arteries and reseeding procedure. One iliac artery was subjected to EC/glue reconstruction and a contralateral site to EC seeding without glue. The animals were sacrificed after 4 h. In another series 12 rabbits were treated in the same fashion and were restudied at eight weeks. Additionally, in 10 animals one iliac was subjected to glue treatment, and another served as control.

RESULTS

Histological examination demonstrated the ability of this method to reattach the EC/glue matrix circumferentially to 68.0 +/- 6.7% of the arterial wall in comparison with 13.5 +/- 3.9% reattachment after EC seeding. Morphometry at eight weeks showed that the lumen area was significantly greater in the EC/glue group (1.23 +/- 0.35 mm2) than in the EC seeding alone (0.65 +/- 0.02 mm2) and 0.72 +/- 0.41 mm2 in the glue group. This was principally accounted for by the statistically significant differences in the intimal area (0.76 +/- 0.18 mm vs. 1.25 +/-0.26 mm2 and 1.01 +/- 0.53 mm2, respectively).

CONCLUSIONS

The attachment of EC after angioplasty can be greatly improved with fibrin glue matrix. The near 70% endothelial coverage achieved by this method resulted in a significant reduction of restenosis in atherosclerotic rabbit.

Interaction between human monocytes and vascular smooth muscle cells induces vascular endothelial growth factor expression

The objective of this study was to investigate whether synthesis of vascular endothelial growth factor (VEGF), a major mitogen for vascular endothelial cells, was induced by a cell-to-cell interaction between monocytes and vascular smooth muscle cells (VSMCs). Human VSMCs and THP-1 cells (human monocytoid cell) were cocultured. VEGF levels in the coculture medium were determined by enzyme-linked immunosorbent assay. Northern blot analysis of VEGF mRNA was performed using a specific cDNA probe. Immunohistochemistry was performed to determine which types of cell produce VEGF. Adding THP-1 cells to VSMCs for 24 h increased VEGF levels of the culture media, 8- and 10-fold relative to those of THP-1 cells and VSMCs alone, respectively. Northern blot analysis showed that VEGF mRNA expression was induced in the cocultured cells and peaked after 12 h. Immunohistochemistry disclosed that both types of cell in the coculture produced VEGF. Separate coculture experiments revealed that both direct contact and a soluble factor(s) contributed to VEGF production. Neutralizing anti-interleukin (IL)-6 antibody inhibited VEGF production by the coculture of THP-1 cells and VSMCs. A cell-to-cell interaction between monocytes and VSMCs induced VEGF synthesis in both types of cell. An IL-6 mediated mechanism is at least partially involved in VEGF production by the cocultures. Local VEGF production induced by a monocyte-VSMC interaction may play an important role in atherosclerosis and vascular remodeling.

Intravascular low-power red laser light as an adjunct to coronary stent implantation: initial clinical experience

Low-power red laser light (LPRLL) irradiation enhances endothelial cell growth in vitro and in vivo and reduces restenosis in animal models. The present study reports the preliminary clinical experience in our center. Eighty-one patients were treated with LPRLL, 30 mW/1 min, for in-stent restenosis (n = 27), elective stenting for recurrent restenosis (n = 16), and stenting for treatment of a suboptimal PTCA result (n = 38). All interventions were successful and no major adverse events due to LPRLL therapy were observed. At follow-up, 12 patients (14.8%) underwent an early control coronarogram due to target vessel restenosis. At 6 months, another 20 patients showed a significant restenosis of the target vessel. Preliminary clinical evaluation demonstrates that LPRLL is feasible and safe. The preliminary results suggest that LPRLL results in a decrease of in-stent restenosis when used during primary stenting.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

Catheter-mediated vascular endothelial growth factor gene transfer to human coronary arteries after angioplasty

Blood vessels are among the easiest targets for gene therapy. However, no data are available about the safety and feasibility of intracoronary gene transfer in humans. We studied the safety and efficacy of catheter-mediated vascular endothelial growth factor (VEGF) plasmid/liposome (P/L) gene transfer in human coronary arteries after percutaneous translumenal coronary angioplasty (PTCA) in a randomized, double-blinded, placebo-controlled study. The optimized angioplasty/gene delivery method was previously shown to lead to detectable VEGF gene expression in human peripheral arteries as analyzed from amputated leg samples. Gene transfer to coronary arteries was done with a perfusion-infusion catheter, using 1000 microg of VEGF or beta-galactosidase plasmid complexed with 1000 microl of DOTMA:DOPE liposomes. Ten patients received VEGF P/L, three patients received beta-galactosidase P/L, and two patients received Ringer lactate. Gene transfer to coronary arteries was feasible and well tolerated. Except for a slight increase in serum C-reative protein in all study groups, no adverse effects or abnormalities in laboratory parameters were detected. No VEGF plasmid or recombinant VEGF protein was present in the systemic circulation after the gene transfer. In control angiography 6 months later, no differences were detected in the degree of coronary stenosis between treatment and control groups. We conclude that catheter-mediated intracoronary gene transfer performed after angioplasty is safe and well tolerated and potentially applicable for the prevention of restenosis and myocardial ischemia.

Vascular endothelial growth factor attenuates trauma-induced injury in rats

Endothelial dysfunction and loss of nitric oxide (NO) is an integral part of the initiation and maintenance of the inflammatory process such as that occurring in traumatic shock, and is considered responsible for much of the trauma induced microvascular injury. We investigated the effects of a vascular endothelial growth factor (VEGF) in a rat model of traumatic shock. Pentobarbital-anaesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension and a 93% mortality rate with a mean survival time of 108+/-10 min in 14 rats. Accompanying these effects was a significant degree of endothelial dysfunction and a markedly elevated intestinal myeloperoxidase (MPO) activity. Treatment with 125 microg kg(-1) VEGF administered intravenously 18 h pre-trauma, increased survival rate to 67% (P<0.01), and prolonged survival time to 252+/-24 min in 12 rats (P<0.01). VEGF also significantly preserved the endothelium-dependent relaxation to ACh indicating a preservation of endothelium-derived NO. Our results indicate that endothelial dysfunction with its accompanying loss of NO plays an important role in tissue injury associated with trauma, and that preservation of NO is beneficial in traumatic shock. The mechanisms of the protective effect of VEGF in trauma involves preservation of eNOS function and diminished neutrophil accumulation resulting in reduced neutrophil-mediated tissue injury. British Journal of Pharmacology (2000) 129, 71 - 76

[Pathophysiologic significance of growth factors and new therapeutic concepts in cardiovascular disease]

Peptide growth factors such as PDGF, FGF, VEGF, and TGF-beta play a critical role in the pathogenesis of cardiovascular diseases. In addition to their pathophysiological role in atherosclerosis and myocardial remodeling, growth factors also promote beneficial effects such as stimulation of angiogenesis and formation of collateral vessels in ischemic tissue. This review focuses on the mechanisms of action and signal relay cascades of peptide growth factors, and summarizes novel therapeutic approaches in cardiovascular medicine. These approaches include both inhibition of growth factors in order to suppress pathogenic processes, and stimulation of growth factors to promote their beneficial effects.

Apolipoprotein(a), a link between atherosclerosis and tumor angiogenesis

Lipoprotein (a) [Lp(a)] is a LDL-like particle with one apolipoprotein(a) [apo(a)] covalently bound to apolipoprotein B, the structural protein of Low Density Lipoprotein (LDL). Lewis Lung Carcinoma (LL/2) cells exhibited delayed growth and reduced angiogenesis in apo(a) transgenic mice, expressing a recombinant apo(a) [r-apo(a)] with 18 kringle 4 repeats. The mean microvessel density of subcutaneous LL/2 tumors from apo(a) transgenic mice was significantly lower than that of tumors from control wild type mice. CHO cells secreting a truncated apo(a) protein with only six kringle 4 repeats did not exhibit delayed tumor growth nor did it impair angiogenesis. These data point to an unappreciated role of human apo(a) in angiogenesis and cancer biology. As angiogenesis is necessary for reendothelialization following vascular injury, suppression of angiogenesis by apo(a) may also contribute to the atherogenicity of apo(a). The differences between the truncated apo(a) and r-apo(a) are consistent with the higher atherogenicity of higher molecular weight isoforms.

Photoremodeling of arterial wall reduces restenosis after balloon angioplasty in an atherosclerotic rabbit model

OBJECTIVES

This study evaluated the long-term impact of endoluminal low power red laser light (LPRLL) on restenosis in an atherosclerotic rabbit model.

BACKGROUND

Despite widespread application of balloon angioplasty for treatment of coronary artery disease, restenosis limits its clinical benefits. Restenosis is a complex process and may be partly attributed to the inability of the vascular endothelium to regenerate and cover the denuded area at the site of arterial injury. We previously demonstrated that LPRLL stimulates endothelial cell proliferation in vitro and contributes to rapid endothelial regeneration after balloon injury in nonatherosclerotic rabbits.

METHODS

Rabbit abdominal aortas (n = 12) were treated in separate zones with balloon dilation and balloon dilation plus laser illumination. Endoluminal laser therapy was performed using a laser-balloon catheter delivering a single dose of 10 mW for 3 min from a helium-neon laser (632 nm). Angiography was performed before and after treatment and was repeated 8 weeks before harvesting the aortas.

RESULTS

Quantitative angiographic analysis demonstrated no differences in the minimal lumen diameter (MLD) between the two zones before treatment; an increase in the MLD in both zones after balloon angioplasty and a significant versus slight reduction of the MLD in the balloon treatment versus balloon plus laser zones at 8 weeks. Histologic examination showed a very high level of myointimal hyperplasia in the balloon treatment zones but a minimal level in the LPRLL-treated zones. Morphometric analysis revealed a statistically significant difference in the lumen area, intimal area and intima/media ratio between the balloon versus balloon plus laser treatment sites.

CONCLUSIONS

Our experimental data indicate that endoluminal irradiation with LPRLL prevents restenosis after balloon angioplasty in an atherosclerotic rabbit model.

Vascular endothelial growth factor (VEGF) expression during arterial repair in the pig

OBJECTIVES

Vascular endothelial growth factor (VEGF) is reported to be a potent and specific mitogen for endothelial cells (EC) and an inducer of angiogenesis in vivo. Originally called vascular permeability factor (VPF), VEGF also increases permeability of microvessels to circulating macromolecules. The aim of this study was to examine whether the VEGF gene was expressed in porcine arteries following denudation of EC.

DESIGN

Experimental animal model with mechanical injury to large arteries.

METHODS

The right iliac artery of juvenile pigs was de-endothelialised using an inflated balloon catheter. At a number of time-points after injury, these arteries were harvested together with uninjured contralateral arteries. Sections of arteries were used for RNA analysis by Northern blots and for protein localisation studies by immunohistochemistry.

RESULTS

Two VEGF transcripts (2.0 kb, 4.5 kb) were markedly elevated in pig arteries soon after injury. Newly synthesised VEGF protein was located in smooth muscle cells (SMC) throughout the media of injured arteries.

CONCLUSIONS

The elevated expression of VEGF by SMC in denuded porcine arteries is evidence that this cytokine plays a role in the injury response of large arteries. Since several biological activities have been identified for VEGF, the function of this cytokine in the arterial repair process remains to be determined.

Modulation of growth factor action: implications for the treatment of cardiovascular diseases

Peptide growth factors are involved in fundamental cellular processes relevant for cardiovascular physiology and pathology, namely, atherogenesis and angiogenesis. The modulation of growth factor-related signals represents a novel strategy for the treatment of cardiac and vascular disease. Experimental modulation of growth factor action has already provided a better understanding of cardiovascular biology and pathophysiology. In turn, the development of specific and powerful molecular tools is setting the stage for the exploration of their clinical potentials. Current strategies include the use of recombinant proteins, specific inhibitors of protein-protein interactions, tyrosine kinase inhibitors, the generation and application of dominant-negative molecules, the development of antisense strategies, and a variety of different gene transfer approaches. Parallel avenues of research are heading toward the same goal, the specific suppression of potent pathogenic stimuli that induce and promote atherogenesis or the augmentation of beneficial ones such as induction of therapeutic angiogenesis. The successful application of one of these strategies seems to be in reach and will certainly be a milestone in molecular medicine.

VEGF gene transfer reduces intimal thickening via increased production of nitric oxide in carotid arteries

Thickening of the arterial intima and smooth muscle cell (SMC) proliferation remain major problems after vascular surgery and other types of vascular manipulations. We studied the effect of endothelial cell (EC)-specific vascular endothelial growth factor (VEGF) gene transfer on the thickening of the intima using a silicone collar inserted around carotid arteries that acted both as the agent that caused intimal SMC growth and as a reservoir for the transfected gene. The model preserved EC integrity and permitted direct extravascular gene transfer without any intravascular manipulation. Compared to beta-galactosidase (lacZ)-transfected control arteries, plasmid/liposome-mediated VEGF gene transfer significantly reduced intimal thickening 1 week after the gene transfer. Administration to the experimental animals of the nitric oxide (NO) synthase inhibitor L-NAME abolished the difference in intimal thickening between VEGF and lacZ-transfected arteries. Furthermore, VEGF caused NO release from cultured human umbilical vein EC. It is concluded that extravascular VEGF gene transfer attenuates intimal growth and could be useful for the prevention of intimal thickening during vascular surgery. Our results further suggest that VEGF may reduce SMC proliferation via a mechanism that involves VEGF-induced NO production from the endothelium.

Vascular permeability factor/vascular endothelial growth factor: a multifunctional angiogenic cytokine

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the endothelial cells lining nearby microvessels to proliferate, to migrate and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular endothelial cells hyperpermeable so that they spill plasma proteins into the extravascular space, leading to profound alterations in the extracellular matrix that favor angiogenesis. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of endothelial cell division and new blood vessel formation. It would seem, therefore, that tumors have made use of fundamental pathways that developed in multicellular organisms for purposes of tissue defense, renewal and repair. VPF/VEGF, therefore, has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important--perhaps essential--elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in sub-toxic concentrations that are more than sufficient to induce angiogenesis (Connolly et al., 1989a). Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating VPF/VEGF expression. In fact, there are already clear example of this. A number of putative angiogenic factors including small molecules (e.g. prostaglandins, adenosine) as well as many cytokines (e.g. TGF-alpha, bFGF, TGF-beta, TNF-alpha, KGF, PDGF) have all been shown to upregulate VPF/VEGF expression. Further studies that elucidate the crosstalk among various angiogenic factors are likely to contribute significantly to a better understanding of the mechanisms by which new blood vessels are formed in health and in disease.

Expression of VEGF receptors in arteries after endothelial injury and lack of increased endothelial regrowth in response to VEGF

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific factor with angiogenic effects in vivo and mitogenic effects in vitro. Administration of VEGF has been reported to stimulate endothelial growth in denuded arteries and new blood vessel formation in models of induced tissue ischemia. In the present study, expression of VEGF and its receptors flk-l and flt-l was determined in injured aortas and carotid arteries of rats and mice. Neither VEGF nor flk-l mRNA was detectable in vascular cells. mRNA levels for flt-l were dramatically upregulated at the leading edge of a growing endothelial monolayer in vivo; however, these cells did not demonstrate increased replication after VEGF infusion. Furthermore, all doses and treatment protocols of VEGF failed to promote reendothelialization in denuded arteries. At sites of flt-l expression, VEGF increased permeability. These areas revealed a loss of endothelial contacts at the ultrastructural level. These findings suggest that VEGF is not a direct mitogen for large-vessel endothelium in vivo and that VEGF may play a role in abolishing contact inhibition, which may be a prerequisite for endothelial proliferation.

Functional upregulation of the vascular endothelial growth factor receptor KDR by hypoxia

BACKGROUND

Vascular endothelial growth factor (VEGF) is a specific endothelial mitogen and chemoattractant that has been shown to be useful for inducing therapeutic angiogenesis in ischemic myocardium and found to stimulate mitogenicity and chemotaxis of endothelial cells through the receptor tyrosine kinase KDR. Although VEGF expression is upregulated by hypoxic stimuli, regulation of KDR remained unknown under these conditions.

METHODS AND RESULTS

With the use of human umbilical vein endothelial cells and transfected porcine aortic endothelial cells, KDR protein was found to be upregulated under hypoxic conditions (2% O2) in both cell types. This process of KDR upregulation was found to be reversible, was maximal after 24 hours of hypoxia, and was regulated on a posttranscriptional level. Furthermore, the susceptibility for VEGF-induced mitogenicity was enhanced under hypoxic conditions as shown by [3H]-thymidine incorporation assay. The activated state of increased VEGF function in hypoxic endothelial cells was associated with elevated tyrosine phosphorylation of KDR as demonstrated by anti-phosphotyrosine blot.

CONCLUSIONS

These data indicate that hypoxia stimulates VEGF-dependent signaling not only by upregulation of VEGF ligand but also by functional upregulation of a specific signaling receptor. Therefore, these data provide evidence that the endothelium plays an active role in hypoxia-induced angiogenesis.

Vascular endothelial growth factor and heparin in a biologic glue promotes human aortic endothelial cell proliferation with aortic smooth muscle cell inhibition

BACKGROUND

Incomplete luminal endothelialization may contribute to small diameter vascular graft failure. Vascular endothelial growth factor (VEGF) can be used to stimulate endothelialization without provoking smooth muscle cell (SMC) proliferation. Heparin and VEGF in a fibrin glue (FG) were investigated for their ability to promote selective human aortic endothelial cell (HAEC) proliferation and human aortic smooth muscle cell (HASMC) inhibition.

METHODS

HAECs and HASMCs were seeded on FG containing VEGF (2.5, 10, 30, 100 ng/ml) or VEGF and heparin (5, 50, 500 units/ml). Proliferation assays were performed with tritiated thymidine on days 1 and 3. Results were analyzed by ANOVA, with p < or = 0.05 significant.

RESULTS

HAEC proliferation on FG with 10, 30, and 100 ng/ml VEGF was significantly greater than FG alone at days 1 and 3. The addition of 50 units/ml heparin to VEGF significantly increased HAEC proliferation to greater than FG with VEGF alone at day 1. Human aortic SMC proliferation was not stimulated by the addition of VEGF. The addition of 5, 50, and 500 units/ml heparin significantly inhibited HASMC proliferation regardless of VEGF concentration.

DISCUSSION

VEGF at 10 ng/ml combined with heparin at 50 units/ml exhibited maximal stimulation of HAECs with inhibition of HASMCs. VEGF and heparin in a biologic glue may improve patency by selectively promoting HAEC proliferation without HASMC growth on synthetic vascular bypass grafts.

Assignment of the vascular endothelial growth factor gene to human chromosome 6p21.3

BACKGROUND

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific growth factor and a regulator of physiological and pathological angiogenesis. Four different proteins are produced by alternative splicing of a unique transcript generated from a single-copy gene. Knowledge of the chromosomal location of the VEGF gene would help in determining a linkage to any known human congenital syndrome and/or to known chromosomal rearrangements in tumors.

METHODS AND RESULTS

A human chromosome mapping panel was used to assign the VEGF gene to human chromosomes by polymerase chain reaction using VEGF-specific oligonucleotide primers. Amplified DNA fragments were fractionated on a 1% agarose gel. A single band of the expected size was obtained only from the DNA of those hybrid cell lines that contained the human chromosome 6. Three YAC clones containing the VEGF gene were obtained by screening the ICI Diagnostics library. In situ hybridization was then used to locate the VEGF gene in the 6p21.3 region.

CONCLUSIONS

The location of the VEGF gene in the 6p21.3 region is a potential starting point for a linkage study. In addition, the isolation of YAC clones containing the VEGF gene will contribute to the construction of the physical map of this chromosomal region.

Enhancing expression of recombinant proteins in mammalian cells using the herpesvirus VP16 transactivator

The herpesvirus VP16 transactivator has become a useful tool for facilitating the production of recombinant proteins in cultured mammalian cells. Not only does it afford the rapid isolation of stable high-level producer cell lines, but also VP16-expressing cells have been found to rival COS cells in their ability to express proteins transiently. Some of the most interesting developments have been the expression of heterodimeric receptors and soluble forms of membrane proteins.