Magnetic resonance mapping demonstrates benefits of VEGF-induced myocardial angiogenesis

Bioactive Glass Stimulates the Secretion of Angiogenic Growth Factors and Angiogenesis in Vitro

Neovascularization of tissue-engineered constructs remains a limiting factor for the engineering of larger tissue constructs. Attempts to stimulate neovascularization, using recombinant protein or gene transfer of angiogenic growth factors, have been proposed; however, these approaches have been associated with problems regarding the delivery and duration of exposure of the growth factor. This study was performed to determine the ability of biologically active glass to stimulate the secretion of angiogenic growth factors from human stromal cells and subsequent angiogenesis. CCD18Co human fibroblasts were cultured on tissue culture surfaces coated with specific quantities of 45S5 Bioglass particles. At 24-, 48-, and 72-h intervals the gene expression of vascular endothelial growth factor (VEGF) and the protein secretion of VEGF and basic fibroblast growth factor (bFGF) from fibroblasts were measured. The effect of conditioned medium collected from Bioglass-stimulated fibroblasts on human dermal microvascular endothelial cells was assessed using in vitro angiogenesis assays. Results showed that surfaces coated with Bioglass produced a significant increase in the secretion of VEGF and bFGF. Conditioned medium from stimulated fibroblasts significantly increased the proliferation of human dermal microvascular endothelial cells and induced a significant increase in the formation of anastomosed networks of human endothelial cell tubules. It is concluded that the ability of 45S5 Bioglass to stimulate the release of angiogenic growth factors and to promote angiogenesis provides a novel alternative approach for stimulating neovascularization of tissue-engineered constructs.

FGF-1: a human growth factor in the induction of neoangiogenesis

Currently available approaches for treating human coronary heart disease aim to relieve symptoms and the risk of myocardial infarction either by reducing myocardial oxygen demand, preventing further disease progression, restoring coronary blood flow pharmacologically or mechanically, or bypassing the stenotic lesions and obstructed coronary artery segments. Gene therapy, especially using angiogenic growth factors, has emerged recently as a potential new treatment for cardiovascular disease. Following extensive experimental research on angiogenic growth factors, the first clinical studies on patients with coronary heart disease and peripheral vascular lesions have been performed. The polypeptides fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) appear to be particularly effective in initiating neovascularisation (neo-angiogenesis) in hypoxic or ischaemic tissues. The first clinical study on patients with coronary heart disease treated by local intramyocardial injection of FGF-1 showed a 3-fold increase of capillary density mediated by the growth factor. Angiogenic therapy of the human myocardium introduces a new modality of treatment for coronary heart disease in terms of regulation of blood vessel growth. Beyond drug therapy, angioplasty and bypass surgery, this new approach may evolve into a fourth principle of treatment of atherosclerotic cardiovascular disease.

The crucial role of vascular permeability factor/vascular endothelial growth factor in angiogenesis: a historical review

Angiogenesis is a biological process by which new capillaries are formed and it occurs in many physiological and pathological conditions. It is controlled by the net balance between molecules that have positive and negative regulatory activity and this concept had led to the notion of the 'angiogenic switch', depending on an increased production of one or more of the positive regulators of angiogenesis. Numerous inducers of angiogenesis have been identified and this review offers a historical account of the relevant literature concerning the discovery of one of the best characterized angiogenic factors, namely vascular endothelial growth factor (VEGF)/vascular permeability factor. Moreover, different strategies, designed to stimulate and to inhibit VEGF production in the context of several potential therapeutical implications, are discussed.

Protein-, gene-, and cell-based therapeutic angiogenesis for the treatment of myocardial ischemia

Therapeutic angiogenesis aims at restoring perfusion to chronically ischemic myocardial territories by using growth factors or cells, without intervening on the epicardial coronary arteries. Despite angiogenesis having received considerable scientific attention over the last decade, it has not yet been shown to provide clinical benefit and is still reserved for patients who have failed conventional therapies. Nevertheless, angiogenesis is a very potent physiologic process involved in the growth and development of every animal and human, and it is likely that its use for therapeutic purposes, once its underlying mechanistic basis is better understood, will one day become an important modality for patients with CAD and other types of organ ischemia. This review summarizes current knowledge in therapeutic angiogenesis research.

Leg ischemia: assessment with MR angiography and spectroscopy

PURPOSE

To prospectively determine reproducibility of magnetic resonance (MR) angiography and MR spectroscopy of deoxymyoglobin in assessment of collateral vessels and tissue perfusion in patients with critical limb ischemia (CLI) and to follow changes in patients undergoing intramuscular vascular endothelial growth factor (pVEGF)-C gene therapy, percutaneous transluminal angioplasty, supervised exercise training, or no therapy.

MATERIALS AND METHODS

Study and gene therapy protocols were approved, and all patients gave written informed consent. To determine repeatability and reproducibility, seven patients underwent MR angiography and five underwent MR spectroscopy. The techniques were used to judge disease progress in 12 other patients with or without therapy: MR angiography to help determine change in visualization of collateral vessels and MR spectroscopy to help assess change in perfusion at proximal and distal calf levels. MR angiographic results were subjectively analyzed by three blinded readers. Intraobserver variability was expressed as 95% confidence interval (CI) (n=7); interobserver variability, as kappa statistic (n=15). Reexamination variability of MR spectroscopy was given as 95% CI for subsequent recovery times, and correlation with disease extent was calculated with Kendall taub rank correlation. Fisher-Yates test was used to correlate changes with pressure measurements and clinical course.

RESULTS

Intraobserver and interobserver concordance was sensitive for detection of collateral vessels. Intraobserver agreement was 85.7% (95% CI: 42.1%, 99.6%). Interobserver agreement was high for small collateral vessels (kappa=0.74, P <.001) and fair for large collateral vessels (kappa=0.36, P=.002). MR spectroscopy was reproducible (95% CI: +/-26 seconds for proximal, +/-21 seconds for distal) and showed a correlation with disease extent (proximal calf, taub=0.84, P <.001; distal calf, taub=0.68, P=.04). Small collateral vessels increased over time (P=.04) but did not correlate with pressure measurements and clinical course. Recovery time correlated with clinical course (proximal calf, P=.03; distal calf, P=.005).

CONCLUSION

MR angiography and MR spectroscopy of deoxymyoglobin can help document changes in visualization of collateral vessels and tissue perfusion in patients with CLI.

Non‐Viral Vectors for Gene Therapy: Clinical Trials in Cardiovascular Disease

The population of patients with end-stage symptomatic coronary and peripheral vascular disease is ever-expanding. Many of these patients no longer have options for mechanical revascularization, and despite maximal medical therapy, they remain physically limited due to angina or critical limb ischemia. The fundamental problem in these patients is insufficient blood supply to muscle due to severely diseased conduit vessels to the target tissue. Therefore, it seems logical that increasing the blood supply to ischemic tissue will relieve symptoms. One potential means to achieving this goal is via therapeutic angiogenesis. The molecular mechanisms behind vascular development are being elucidated, and animal models have shown that mediators of vascular development can be harnessed to produce new capillaries in ischemic tissue. These mediators include cytokines such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). Angiogenic cytokines can be delivered in several forms including recombinant protein or via gene delivery as a naked plasmid or via viral vector. This chapter will describe the clinical trial experience to date with delivery of non-viral gene therapy for therapeutic angiogenesis in humans with disabling myocardial ischemia and peripheral vascular disease.

Adeno-associated viral vector delivers cardiac-specific and hypoxia-inducible VEGF expression in ischemic mouse hearts

It has been shown that the adeno-associated virus (AAV) vector can deliver the VEGF gene efficiently into the ischemic mouse myocardium. However, the AAV genomes can be found in extracardiac organs after intramyocardial injection. To limit unwanted VEGF expression in organs other than the heart, we tested the use of the cardiac myosin light chain 2v (MLC-2v) promoter and the hypoxia-response element to mediate cardiac-specific and hypoxia-inducible VEGF expression. An AAV vector, MLCVEGF, with 250 bp of the MLC-2v promoter and nine copies of the hypoxia-response element driving VEGF expression, was constructed. Gene expression was studied in vitro by infection of rat cardiomyocytes, rat skeletal myocytes, and mouse fibroblasts with the vector and in vivo by direct injection of the vector into normal and ischemic mouse hearts. With MLCVEGF infection, VEGF expression was higher in cardiomyocytes than the other two cell lines and was hypoxiainducible. VEGF expression was also higher in ischemic hearts than in normal hearts. No VEGF expression was detectable in organs with detectable MLCVEGF vectors other than the heart. MLCVEGF-injected ischemic hearts had more capillaries and small vessels around the injection site, smaller infarct size, and better cardiac function than the negative controls. Hence, MLCVEGF can mediate cardiac-specific and hypoxia-inducible VEGF expression, neoangiogenesis, infarct-size reduction, and cardiac functional improvement.

Vascular Endothelial Growth Factor-Induced Nitric Oxide- and PGI2-Dependent Relaxation in Human Internal Mammary Arteries

The role of the vascular endothelial growth factors (VEGF) receptors (KDR and Flt-1) and their characteristics in VEGF-induced vasodilation in human vessels is unclear. This study investigated the in vitro vasorelaxant effects of KDR-selective (KDR-SM) and Flt-1-selective mutants (Flt-1-SM) in the human internal mammary artery (IMA). IMA segments (n = 183) taken from 48 patients were studied in organ baths. The cumulative concentration (-12 to -8 log10M)-relaxation curves were established for VEGF, KDR-SM, Flt-1-SM, and placenta growth factor (PlGF) in the absence or presence of indomethacin (INDO, 7 microM), N-nitro-L-arginine (L-NNA, 300 microM), L-NNA + oxyhemoglobin (HbO, 20 microM), or INDO + L-NNA + HbO. The VEGF-induced relaxation was abolished in endothelium-denuded IMA. In the endothelium-intact vessel rings, VEGF (63.2 +/- 3.9%) induced significantly more (P < 0.001) relaxation than Flt-1-SM (28.5 +/- 4.3%, 95% CI 18.1-51.3%), and PlGF (26.0 +/- 4.7%, 95% CI 17.6-56.8%). The maximal relaxation induced by KDR-SM (53.0 +/- 4.0%) was only slightly less than that by VEGF (P = 0.075) but significantly more than that by Flt-1-SM (P = 0.001, 95% CI 7.8-41.1%). Pretreatment of INDO or L-NNA + HbO significantly (P < 0.001) inhibited the relaxation by VEGF (21.2 +/- 3.9% or 23.3 +/- 4.3%) and KDR-SM (9.8 +/- 8.2% or 10.1 +/- 17.8%). INDO + L-NNA + HbO completely inhibited the relaxation by VEGF, KDR-SM, or Flt-1-SM. KDR may be the dominant receptor in mediating the VEGF-mediated relaxation, which is regulated by both PGI2 and nitric oxide but probably not by endothelium-derived hyperpolarizing factor, in the human IMA. This study gives insight into the characteristics of the VEGF-mediated vasodilation and provides a scientific basis for potential clinical application of VEGF/KDR-SM in ischemic heart disease.

Molecular evaluation of endothelial progenitor cells in patients with ischemic limbs: therapeutic effect by stem cell transplantation

OBJECTIVE

Although some patients with limb ischemia have recently undergone therapeutic angiogenesis by cell transplantation, their angiogenic potential has not been well characterized. It is also important to evaluate endothelial progenitor cell (EPC) contents in different stem cell sources to choose the best material for therapeutic angiogenesis.

METHODS AND RESULTS

We quantitated the mRNA expression of EPC-specific molecules (eg, Flk-1, Flt-1, CD133, VE-cadherin, etc) in bone marrow-derived or peripheral blood-derived mononuclear cells obtained from patients with ischemic limbs, using real-time reverse-transcription polymerase chain reaction technique. The mRNA expression level of EPC markers was significantly lower in the patients than in healthy controls, which was consistent with results of flow cytometric analysis. However, the implantation of autologous bone marrow mononuclear cells increased the circulating EPCs in the peripheral blood of patients. We furthermore revealed the different expression pattern of EPC markers in possible sources for stem cell transplantation, including normal bone marrow, peripheral blood obtained from recombinant granulocyte colony-stimulating factor-treated donor, and umbilical cord blood.

CONCLUSIONS

Patients with peripheral obstructive arterial diseases may have lower angiogenic potential because of decreased expression of EPC specific molecules in their marrow and blood. Therapeutic angiogenesis by transplantation of autologous marrow mononuclear cells increased circulating EPCs in the patients and improved ischemic symptoms.

Aspirin decreases vascular endothelial growth factor release during myocardial ischemia

BACKGROUND

Vascular Endothelial Growth Factor (VEGF) is an important angiogenesis factor involved in pathophysiology of cardiovascular diseases. Controlling this factor's level in the serum might have significant prognostic outcomes.

METHODS

Twenty-four patients undergoing coronary artery bypass grafting were prospectively categorized into two groups according to aspirin administration before surgery. Vascular Endothelial Growth Factor levels were compared and correlated and adjusted with platelets count between two groups in the serum, before and after the surgery. Serum creatine kinase (CK) levels were determined before and after the operation in parallel to other clinical data.

RESULTS

Vascular Endothelial Growth Factor levels were significantly lower in patients of the aspirin group compared to those of the non-aspirin group; 94+/-61 vs. 241+/-118 pg/ml, p=0.0003, respectively, this-despite an absence of difference in the platelet count between the groups. These titers decreased postoperatively in both groups, 94+/-61 to 10+/-9 pg/ml, p=0.001 in aspirin group and from 241+/-118 to 84+/-54 pg/ml, p=0.001 in control group. Serum creatine kinase levels were higher in the non-aspirin group, 214+/-83 u/l compared to 70+/-32 u/l in the aspirin group. Creatine kinase levels increased significantly postoperatively in both groups; however, the aspirin group had a significantly lower creatine kinase levels compared to non-aspirin group, 107+/-51 vs. 401+/-127 u/l, respectively, p=<0.0001. A significant correlation was seen between VEGF levels and platelets count in both groups, r=0.5.

CONCLUSIONS

Aspirin treated patients have lower Vascular Endothelial Growth Factor titer levels in the perioperative course. This difference between the aspirin and the non-aspirin group is not accounted for by the platelets count.

Time delay for arrival of MR contrast agent in collateral-dependent myocardium

An analysis of the kinetics of myocardial contrast enhancement is an important component of myocardial perfusion studies. The contrast enhancement can be modeled by a linear time-invariant system, and the myocardial impulse response, calculated by deconvolution of the measured tissue response with an arterial input, gives a direct estimate of myocardial blood flow. In this paper, we analyze the effects of delays in the contrast enhancement, that occur in collateral-dependent myocardium, where the tracer reaches the tissue region only through branches from other coronary arteries that form natural bypass vessels. We investigate how the delayed arrival of tracer alters the myocardial impulse response. Model-independent deconvolution is applied to determine the lag between arterial input and tissue enhancement. Experimental data in a porcine model of collateral development indicate that the delayed arrival of an injected tracer, measured at rest, is a useful marker to identify collateral-dependent myocardium, and predict its flow capacitance.

Therapeutic angiogenesis in chronically ischemic porcine myocardium: comparative effects of bFGF and VEGF

BACKGROUND

Both vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) have been used in preclinical studies to induce new blood vessel growth in ischemic cardiac muscle with promising results. However, clinical trials have been much less convincing and further work is needed. This study expands on prior work by comparing the long-term proangiogenic effects of direct intramyocardial (IM) injection of bFGF, as well as IM and intravenous (IV) VEGF in a porcine model of chronic hibernating myocardium.

METHODS

Mini-swine with proximal 90% left circumflex (LCx) coronary stenosis subtending chronically ischemic, viable (hibernating) myocardium by positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were randomized to IM bFGF (n = 5), IM VEGF(165) (n = 5), IV VEGF(165) (n = 5), IM vehicle (n = 5), or sham redo-thoracotomy (n = 4). The bFGF protein was administered in a total dose of 1.35 microg divided into 30 IM injections. IM VEGF(165) protein was administered in a total dose of 15 microg/kg divided into 30 injections; IV VEGF(165) was given at a dose of 50 ng. kg(-1). min(-1) for 200 minutes at three 72-hour intervals (30 microg/kg total dose). After 3 and 6 months the PET and DSE studies were repeated, and the animals were sacrificed for tissue vascular density and angiogenic protein analysis.

RESULTS

Myocardial blood flow (MBF) by PET was significantly improved 3 months posttreatment in the IM bFGF and IM VEGF(165) groups, differences that were sustained at 6 months. There was no significant increase in MBF 3-months posttreatment in the IV VEGF(165) group; however, at 6 months MBF was significantly improved. No change in MBF was seen in the IM vehicle or sham groups. Regional wall motion at rest and peak stress in the LCx region demonstrated small but statistically significant improvements by 6 months in the IM bFGF and IV VEGF(165) groups only; no improvement was seen in the IM VEGF(165), IM vehicle, or sham groups. Quantitative vascular density was significantly increased in the LCx regions of all treatment groups (IM bFGF, IM VEGF(165), IV VEGF(165)) 6-months postoperatively. No significant increase in LCx region myocardial bFGF or VEGF protein levels was seen in the treated animals at 6 months.

CONCLUSIONS

The IM bFGF, IM VEGF(165), and IV VEGF(165) all improve regional perfusion and vascular density 6-months posttherapy in the animal model utilized. Functional improvements were less consistent. Both bFGF and VEGF(165) may be useful therapies for improving regional perfusion in chronically ischemic myocardium, although combination therapy with additional growth factors or cellular therapies may be necessary if concomitant improvements in function are to be seen.

Structural, functional, and molecular MR imaging of the microvasculature

Magnetic resonance imaging (MRI) is widely applied for functional imaging of the microcirculation and for functional and structural studies of the microvasculature. The interest in the capabilities of MRI in noninvasively monitoring changes in vascular structure and function expanded over the past years, with specific efforts directed toward the development of novel imaging methods for quantification of angiogenesis. Molecular imaging approaches hold promise for further expansion of the ability to characterize the microvasculature. Exciting applications for MRI are emerging in the study of the biology of microvessels and in the evaluation of potential pharmaceutical modulators of vascular function and development, and preclinical MRI tools can serve for the design of mechanism-of-action-based noninvasive clinical methods for monitoring response to therapy. The aim of this review is to provide a current snapshot of recent developments in this rapidly evolving field.

Novel therapeutic strategy to treat brain ischemia: overexpression of hepatocyte growth factor gene reduced ischemic injury without cerebral edema in rat model

BACKGROUND

Although cerebral occlusive disease leads to cerebral ischemic events, an effective treatment has not yet been established. An ideal therapeutic approach to treat ischemia might have both aspects of enhancement of collateral formation and prevention of neuronal death. Hepatocyte growth factor (HGF) is a potent angiogenic factor that also acts as a neurotrophic factor. Thus, in this study, we examined the therapeutic effects of HGF on brain injury in a rat permanent middle cerebral artery occlusion model.

METHODS AND RESULTS

Gene transfer into the brain was performed by injection of human HGF gene with hemagglutinating virus of Japan-envelope vector into the cerebrospinal fluid via the cisterna magna. Overexpression of the HGF gene resulted in a significant decrease in the infarcted brain area as assessed by triphenyltetrazolium chloride staining, whereas rats transfected with control vector exhibited a wide area of brain death after 24 hours of ischemia. Consistently, the decrease in neurological deficit was significantly attenuated in rats transfected with the HGF gene at 24 hours after the ischemic event. Stimulation of angiogenesis was also detected in rats transfected with the HGF gene compared with controls. Of importance, no cerebral edema or destruction of the blood-brain barrier was observed in rats transfected with the HGF gene.

CONCLUSIONS

Overall, the present study demonstrated that overexpression of the HGF gene attenuated brain ischemic injury in a rat model, without cerebral edema, through angiogenic and neuroprotective actions. In particular, the reduction of brain injury by HGF may provide a new therapeutic option to treat cerebrovascular disease.

Vascular endothelial growth factor (VEGF) in seizures: a double-edged sword

Vascular endothelial growth factor (VEGF) is a vascular growth factor which induces angiogenesis (the development of new blood vessels), vascular permeability, and inflammation. In brain, receptors for VEGF have been localized to vascular endothelium, neurons, and glia. VEGF is upregulated after hypoxic injury to the brain, which can occur during cerebral ischemia or high-altitude edema, and has been implicated in the blood-brain barrier breakdown associated with these conditions. Given its recently-described role as an inflammatory mediator, VEGF could also contribute to the inflammatory responses observed in cerebral ischemia. After seizures, blood-brain barrier breakdown and inflammation is also observed in brain, albeit on a lower scale than that observed after stroke. Recent evidence has suggested a role for inflammation in seizure disorders. We have described striking increases in VEGF protein in both neurons and glia after pilocarpine-induced status epilepticus in the brain. Increases in VEGF could contribute to the blood-brain barrier breakdown and inflammation observed after seizures. However, VEGF has also been shown to be neuroprotective across several experimental paradigms, and hence could potentially protect vulnerable cells from damage associated with seizures. Therefore, the role of VEGF after seizures could be either protective or destructive. Although only further research will determine the exact nature of VEGF's role after seizures, preliminary data indicate that VEGF plays a protective role after seizures.

Time-of-flight quantitative measurements of blood flow in mouse hindlimbs

PURPOSE

To evaluate the feasibility of using time-of-flight (TOF) imaging to directly measure hindlimb blood flow in a mouse model of peripheral vascular disease.

MATERIALS AND METHODS

Four tubes were imaged simultaneously (diameters = 0.39 mm, 0.59 mm, and two at 1.46 mm) with a 1.0 mM copper sulfate solution for 19 flow velocities. In vivo measurements were performed in the hindlimbs of three mouse strains-C57BL/6 (N = 5), BALB/c (N = 5), and 129S2/Sv (N = 5)-three weeks after femoral artery ligation with a calibration standard.

RESULTS

The flow phantom showed that the intensity was linear (r2 = 0.92) over the pertinent blood flow velocities in the mouse hindlimbs. Measurements of the blood flow in the distal hindlimbs in different strains of mice (combination of both the venous and arterial flows) were obtained 21 days after right-sided femoral artery occlusion. The results showed that under similar conditions of anesthesia and temperature, SV129 mice on the nonligated side had the highest flows (0.50 +/- 0.07 mL/minute), followed by C57BL/6 (0.28 +/- 0.04 mL/minute) and BALB/c (0.23 +/- 0.05 mL/minute), P < 0.02. The ligated side measurements (SV129, 0.31 +/- 0.05 mL/minute (P = 0.02); C57BL/6, 0.21 +/- 0.02 mL/minute (P = 0.13); and BALB/c, 0.12 +/- 0.02 mL/minute (P= 0.06)) showed a trend in BALB/c and C57BL/6 and significant differences in SV129 for incomplete recovery three weeks after surgery, compared to the nonligated side.

CONCLUSION

Two-dimensional TOF imaging permits quantitative in vivo measurements of hindlimb blood flow in a mouse model of peripheral vascular disease without the need of contrast injection, offering advantages of serial imaging not limited by tissue penetration.

Vascular endothelial growth factor improves functional outcome and decreases secondary degeneration in experimental spinal cord contusion injury

Spinal cord injury leads to acute local ischemia, which may contribute to secondary degeneration. Hypoxia stimulates angiogenesis through a cascade of events, involving angiogenesis stimulatory substances, such as vascular endothelial growth factor (VEGF). To test the importance of angiogenesis for functional outcome and wound healing in spinal cord injury VEGF165 (proangiogenic), Ringer's (control) or angiostatin (antiangiogenic) were delivered locally immediately after a contusion injury produced using the NYU impactor and a 25 mm weight-drop. Rats treated with VEGF showed significantly improved behavior up to 6 weeks after injury compared with control animals, while angiostatin treatment lead to no statistically significant changes in behavior outcome. Furthermore, VEGF-treated animals had an increased amount of spared tissue in the lesion center and a higher blood vessel density in parts of the wound area compared with controls. These effects were unlikely to be due to increased cell proliferation as determined by bromo-deoxy-uridine-labeling. Moreover, VEGF treatment led to decreased levels of apoptosis, as revealed by TUNEL assays. In situ hybridization demonstrated presence of mRNA for VEGF receptors Flt-1, fetal liver kinase-1, neuropilin-1 and -2 in several important cellular compartments of the spinal cord. The different experiments indicate that beneficial effects seen by acute VEGF delivery was attributable to protection/repair of blood vessels, decreased apoptosis and possibly also by other additional effects on glial cells or certain neuron populations.

Arteriogenesis Induced by Intramyocardial Vascular Endothelial Growth Factor 165 Gene Transfer in Chronically Ischemic Pigs

Exogenous vascular endothelial growth factor (VEGF) improves tissue perfusion in large animals and humans with chronic myocardial ischemia. Because tissue perfusion is mainly dependent on the arteriolar tree, we hypothesized that the neovascularizing effect of VEGF should include arteriogenesis, an effect not as yet described in large mammalian models of myocardial ischemia. In the present study we investigated the effect of intramyocardial plasmid-mediated human VEGF(165) gene transfer (pVEGF(165)) on the proliferation of vessels with smooth muscle in a pig model of myocardial ischemia. In addition, we assessed the effect of treatment on capillary growth, myocardial perfusion, myocardial function and collateralization. Three weeks after positioning of an Ameroid constrictor (Research Instruments SW, Escondido, CA) in the left circumflex artery, pigs underwent basal perfusion (single-photon emission computed tomography [SPECT] with (99m)Tc-sestamibi) and regional function (echocardiography) studies at rest and under dobutamine stress, and were then randomly assigned to receive transepicardial injection of pVEGF(165) 3.8 mg (n = 8) or placebo (empty plasmid, n = 8). All experimental steps and data analysis were done in a blinded fashion. Five weeks later, pVEGF(165)-treated pigs showed a significantly higher density of small (8-50 microm in diameter) vessels with smooth muscle, higher density of capillaries, and improved myocardial perfusion. These results indicate an arteriogenic effect of VEGF in a large mammalian model of myocardial ischemia and encourage the use of VEGF to promote arteriolar growth in patients with severe coronary artery disease.

Gene therapy for cardiovascular angiogenesis

Atherosclerosis and endothelial dysfunction are responsible for the pathophysiologic basis of the spectrum of cardiovascular disorders including ischaemic heart disease (IHD), the leading cause of morbidity and mortality in the US. There have been major advances, including the use of pharmacotherapy, coronary and peripheral percutaneous transluminal interventions (PTI), coronary and peripheral bypass surgery and primary/secondary prevention measures. There are, however, multiple unmet needs: IHD refractory to medical therapy and unsuitable for revascularisation; critical limb ischaemia unsuitable for PTI or surgery; restenosis; ischaemic/diabetic neuropathy and heart failure. Cardiovascular gene therapy (GT) with vascular endothelial growth factor (VEGF) has yielded improved perfusion and reduced ischaemia in preclinical models of IHD. Several preclinical studies and Phase I and II clinical trials have shown the safety and therapeutic potential of GT in the treatment of IHD, peripheral arterial disease (PAD), restenosis, and ischaemic and diabetic neuropathy, pointing to the need for Phase III clinical trials.

High-resolution three-dimensional MR angiography of rodent tumors: morphologic characterization of intratumoral vasculature

PURPOSE

To evaluate high-resolution three-dimensional MR angiography (MRA) for the visualization and morphologic characterization of intratumoral vasculature.

MATERIALS AND METHODS

Two subcutaneous rodent tumor models (human skin carcinoma HaCaT-ras-A-5RT3 grown in nude mice and rat prostate carcinoma R3327-AT1 grown in Copenhagen rats) were examined with a clinical 1.5 T MR-system. For MRA a dedicated high-resolution three-dimensional gradient echo pulse sequence with a voxel size of 166 x 206 x 320 microm(3) was performed after injection of Gadomer-17. The image analysis included a correlation of intratumoral vessels with histology. Signal intensity measurements were performed in the vena cava, the tumor underlying muscle, and in various regions of the tumor. Signal-to-noise-ratios (SNR) and contrast-to-noise-ratios (CNR) were calculated from this measurement.

RESULTS

High-resolution MRA allowed a clear distinction of intratumoral blood vessels. The mouse tumor model tended to be strongly vascularized with several intratumoral blood vessels clearly displayed by MRA. When correlated with histology, these intratumoral blood vessels had a size in the range of 300 to 400 microm. In contrast, rat tumors had only sparse capillary intratumoral blood vessels that could only be demonstrated by histology. In both tumor models, dilated blood vessels were observed in the subcutaneous tissue near the tumor. In general, areas with a strong contrast enhancement correlated with viable, well vascularized tumor regions, whereas non-enhancing tumor areas correlated with tumor necrosis or hypoxic areas.

CONCLUSION

High-resolution three-dimensional MRA allows the visualization of intratumoral vasculature in rodent models. With minimal hardware and software modifications, high-resolution MRA could be performed on a clinical 1.5 T MRI scanner. Morphologic characterization of intratumoral blood vessels could add important insights into the process of tumor angiogenesis.

Angiogenic protein therapy

Therapeutic angiogenesis, in the form of growth factor protein administration or gene therapy, has emerged as a new method of treatment for patients with severe, inoperable coronary artery disease. Improved myocardial perfusion and function after the administration of angiogenic growth factors has been demonstrated in animal models of chronic myocardial ischemia. A recent clinical study reported beneficial long-term effects of therapeutic angiogenesis using FGF-2 protein in terms of freedom from angina and myocardial perfusion on nuclear imaging and suggested that protein angiogenic therapy has the potential to extend treatment options to patients who are not optimal candidates for conventional methods of myocardial revascularization. The ultimate role that angiogenesis will play in the treatment of ischemic heart disease will, however, be determined from adequately powered, randomized, double-blind, placebo-controlled trials. It is likely that endogenous antiangiogenic influences, intrinsic lack of response of patients with severe endothelial dysfunction, and other limitations will have to be overcome before angiogenesis becomes standard therapy for the treatment of coronary artery disease.

Hepatocyte growth factor and vascular endothelial growth factor in ischaemic heart disease

BACKGROUND

Hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) are endothelial cell-specific growth factors, but the production of these growth factors in cardiomyocytes has also been demonstrated. However, there have been no reports focusing their attention on the changes in these growth factors after coronary intervention. We investigated the time-course changes of the serum VEGF and HGF levels in angina pectoris (AP) and acute myocardial infarction (AMI).

METHODS

The serum HGF and VEGF levels were measured in 60 patients with AP, in 62 patients with AMI (AP, before heparin administration, and at 24 and 48 hours, and one week after intervention; AMI, before heparin, and at 48 and 72 hours, and one, two, three and four weeks) and in 56 patients with neurocirculatory asthenia as controls. We defined the patients with remodelling who showed an increase in left ventricular end-diastolic volume index (LVEDVI) in the sub-acute phase of AMI.

RESULTS

Hepatocyte growth factor levels in the AP and AMI were significantly higher than that in the control (p<0.0001). The AMI level was also significantly higher than AP (p<0.001). In the AMI and AP, HGF peaked at 48 hours. Vascular endothelial growth factor level in the AMI was significantly higher than that in the control and AP (p<0.0001). In the AMI, VEGF peaked at two weeks. There was a significant positive correlation between the peak VEGF and LVEDVI in the sub-acute phase of AMI (p=0.0089, r=0.436). Peak VEGF in the remodelling (+) group was significantly higher than that in the remodelling (-) group (p<0.001). In the AP, VEGF was unchanged.

CONCLUSION

While both myocardial and vascular damage contribute to an increase in HGF level, vascular damage is not associated with the increase in VEGF. Vascular endothelial growth factor might be related to left ventricular remodelling in the sub-acute phase of myocardial infarction.

Spatial heterogeneity in VEGF-induced vasodilation: VEGF dilates microvessels but not epicardial and systemic arteries and veins

This study was designed to investigate the site of vascular endothelial growth factor (VEGF)-induced vasodilation in the systemic and coronary vasculature. Intracoronary infusion of VEGF in Yorkshire pigs resulted in a significant drop in the mean arterial blood pressure, with a decline in the left ventricular left end-diastolic pressure, and no change in the heart rate. Coronary blood flow increase after intracoronary infusion of 10 mg VEGF (2.63 +/- 0.49x) was comparable to that seen after 40 mg of intracoronary adenosine (2.5 +/- 0.53x, p = 0.67) and was significantly higher then after 200 mg of intracoronary nitroglycerine (1.9 +/- 0.12x, p = 0.0005). At the same time, intracoronary VEGF did not result in a significant increase in coronary cross-sectional area determined using intravascular ultrasound. In vitro, VEGF produced dose-dependent relaxation of myocardial and systemic arterioles and venules (arterioles: 60-100 mm and venules: 120-200 mm in internal diameter) that was partially inhibited by L-NNA, but had no effect on epicardial coronary arteries, systemic arteries, or veins. Both VEGF receptors (flt-1 and flk-1) were identified on endothelial cells of epicardial arteries and veins. We conclude that this spatial heterogeneity of VEGF vasomotor effects cannot be explained by the absence VEGF receptors and suggests differential patterns of signal transduction in the vascular tree.

In vivo mapping of fractional plasma volume (fpv) and endothelial transfer coefficient (Kps) in solid tumors using a macromolecular contrast agent: correlation with histology and ultrastructure

Contrast-enhanced MRI, immunostaining and electron microscopy were used to detect areas of intense angiogenesis in experimental tumors. This work was also aimed at evaluating the possible effect of the surrounding tissues on tumor microvasculature and at studying the penetration of macromolecules in avascular areas. Human colon carcinoma cells were implanted in subcutaneous tissue of nude mice. Dynamic T(1)-weigthed 3D pulse sequences were acquired before and after administration of Gd-DTPA-albumin to obtain parametric maps of fractional plasma volume (fpv) and transendothelial permeability (Kps). The maps suggested that tumor can be subdivided into 4 zones located in the peripheral rim (zones I-II) or in the core (zones III-IV) of the tumor itself. Significant differences (p<0.001) were found in the values of Kps and fpv of zones I-II with respect to zones III-IV. In the peripheral rim, permeability was significantly higher (p<0.01) in the muscle-peripheral region (zone I) with respect to the skin-peripheral region (zone II). In areas with high Kps, histological and ultrastructural examination revealed clusters of newly formed vessels and signs of intense permeability. Numerous vascular vesicular organs were visible in these areas. In the tumoral core, analysis of the microcirculatory parameters revealed regions with mild permeability (zone III) and regions with negligible permeability (zone IV). These 2 zones were discriminated by the average value of Kps (p<0.05), while their fpv was not significantly different. Upon histological examination, the tumoral core exhibited necrotic areas; CD31 immunocytochemistry exhibited that it was diffusely hypovascularized with large avascular areas. Upon ultrastructural examination, capillaries were rarely visible and exhibited signs of endothelial cell damage. The results suggest that segmentation based on microvascular parameters detects in vivo zones characterized by immunocytochemical and ultrastructural aspects of intense angiogenesis. The finding that a certain amount of contrast agent penetrates in the tumoral core suggests that high oncotic and hydrostatic pressure only partially hinders the penetration of macromolecules.

The VIVA trial: Vascular endothelial growth factor in Ischemia for Vascular Angiogenesis

BACKGROUND

Recombinant human vascular endothelial growth factor protein (rhVEGF) stimulates angiogenesis in animal models and was well tolerated in Phase I clinical trials. VIVA (Vascular endothelial growth factor in Ischemia for Vascular Angiogenesis) is a double-blind, placebo-controlled trial designed to evaluate the safety and efficacy of intracoronary and intravenous infusions of rhVEGF.

METHODS AND RESULTS

A total of 178 patients with stable exertional angina, unsuitable for standard revascularization, were randomized to receive placebo, low-dose rhVEGF (17 ng x kg(-1) x min(-1)), or high-dose rhVEGF (50 ng x kg(-1) x min(-1)) by intracoronary infusion on day 0, followed by intravenous infusions on days 3, 6, and 9. Exercise treadmill tests, angina class, and quality of life assessments were performed at baseline, day 60, and day 120. Myocardial perfusion imaging was performed at baseline and day 60. At day 60, the change in exercise treadmill test (ETT) time from baseline was not different between groups (placebo, +48 seconds; low dose, +30 seconds; high dose, +30 seconds). Angina class and quality of life were significantly improved within each group, with no difference between groups. By day 120, placebo-treated patients demonstrated reduced benefit in all three measures, with no significant difference compared with low-dose rhVEGF. In contrast, high-dose rhVEGF resulted in significant improvement in angina class (P=0.05) and nonsignificant trends in ETT time (P=0.15) and angina frequency (P=0.09) as compared with placebo.

CONCLUSIONS

rhVEGF seems to be safe and well tolerated. rhVEGF offered no improvement beyond placebo in all measurements by day 60. By day 120, high-dose rhVEGF resulted in significant improvement in angina and favorable trends in ETT time and angina frequency.

MR imaging of myocardial perfusion and viability

CMR is a rapidly developing new modality with applications in clinical cardiology for detection and assessment of myocardial ischemia and viability. CMR perfusion results for the detection of ischemia in comparison with stress echocardiography and scintigraphic techniques are reasonable, but all the studies reported to date have been conduced in selected patients. Larger studies in patient populations reflecting a broader spectrum of disease are necessary before perfusion CMR can be envisaged as a clinically reliable and robust diagnostic tool. Other CMR techniques provide a variety of novel methods of obtaining information on postischemic viability. Signs of viability that can be observed by CMR are the absence of late gadolinium-based contrast enhancement in a myocardial region involved in a recent infarct, any sign of wall thickening at rest (which is detectable with high accuracy by CMR), wall thickening after stimulation by low-dose dobutamine, and preserved wall thickness. Conversely, myocardial necrosis is characterized by signal enhancement of the infarct area after injection of Gd-DTPA, reduced wall thickness in chronic infarcts, and absence of a contractile reserve during dobutamine stimulation. Dobutamine CMR and late enhancement contrast-enhanced CMR predict contractile improvement after revascularization.

Angiogenesis of the heart

Despite continued advances in the prevention and treatment of coronary artery disease, there are still a large number of patients who are not candidates for the conventional revascularization techniques of balloon angioplasty and stenting, or coronary artery bypass grafting (CABG). Therapeutic angiogenesis, in the form of the administration of growth factor protein or gene therapy, has emerged as a promising new method of treatment for patients with coronary artery disease. The goal of this strategy is to promote the development of supplemental blood conduits that will act as endogenous bypass vessels. New vessel formation occurs through the processes of angiogenesis, vasculogenesis, and arteriogenesis, under the control of growth factors such as those that belong to the vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and angiopoeitin (Ang) families of molecules. Preclinical studies have suggested that such an approach is both feasible and effective; however many questions remain to be answered. This review will address the elements of pharmacologic revascularization, focusing on gene and protein-based therapy. The important growth factors, the vector (for gene therapy), routes of delivery, the desired therapeutic effect, and quantifiable clinical end points for trials of angiogenesis will all be addressed.

Dynamic MRI reveals that the magnitude of the ischemia-related enhancement in skeletal muscle is age-dependent

This study was designed to evaluate the influence of age on the dynamic contrast-enhanced MRI of ischemic tissue. A well-established model of peripheral arterial insufficiency (i.e., the rat hindlimb ischemia after removal of femoral artery) in different age groups (i.e., young, presenescent, and senescent rats) was studied. The analysis of the MR signal demonstrated a marked accumulation of a contrast agent (Gd-DTPA) in the ischemic leg (ischemia-related enhancement, IRE). IRE was an age-related event: 4-month-old rats showed a strong IRE while 12-month-old rats and 20-month old rats showed a significantly reduced IRE in comparison to young animals. Histological analysis of the ischemic muscles revealed that there was no evidence of significant necrosis of the muscle tissue but only a weak interstitial fibrosis; CD31-immunostaining revealed a preserved microcirculatory bed.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Vascular growth factors for coronary angiogenesis

Coronary artery disease not amendable to conventional revascularization poses a significant medical problem. Advances in the understanding of blood vessel growth have given rise to efforts to develop novel therapeutic approaches for these "no-option" patients. Therapeutic angiogenesis makes use of the administration of angiogenic growth factor protein or gene to promote the development of endogenous collateral vessels in ischemic myocardium. Among the growth factors that play a role in blood vessel growth and development, vascular endothelial growth factors (VEGFs) and fibroblast growth factors have been the most extensively studied. Various methods of delivery have been used to enhance localization and persistence. Preliminary animal experiments have been promising with evidence of capillary formation at the target myocardium after growth factor administration. Initial phase I and II clinical trials have been undertaken. Preliminary information on efficacy is beginning to become available, raising hopes and questions about the future direction and potential success of therapeutic angiogenesis as a clinical approach to the treatment of myocardial ischemia. Although the initial clinical results are encouraging, real efficacy has still to be proven and the potential side-effects of these potent angiogenic growth factors remain a concern. Large-scale, randomized, and placebo-controlled studies will be required to demonstrate the true clinical benefit of this novel therapeutic treatment for ischemic heart disease.

Lack of alpha2-antiplasmin promotes pulmonary heart failure via overrelease of VEGF after acute myocardial infarction

Identification of a novel therapy for prevention of sudden death by ischemic cardiac infarction is an area of intensive investigation. We here report that the mortality due to an experimental acute myocardial infarction (AMI) was markedly increased in mice deficient in alpha2-antiplasmin (alpha2-AP(-/-) mice) but not in mice deficient in other components acting in fibrinolysis (tissue-type PA, urokinase type PA, or plasminogen activator inhibitor-1) even if the infarct area in alpha2-AP(-/-) mice was not different from those in the other mice. Echocardiography showed in alpha2-AP(-/-) mice after AMI an overload of the right ventricle and that pulmonary permeability was increased. According to the experiments using explanted myocytes and vascular smooth muscle cells, it was found that the amount of secreted vascular endothelial cell growth factor (VEGF) in alpha2-AP(-/-) mice was markedly increased compared with that in wild-type mice. Finally, an injection of an anti-VEGF antibody decreased the mortality after AMI in alpha2-AP(-/-) mice. Plasmin cleaves extracellular matrix-bound VEGF to release a diffusible proteolytic fragment and is inactivated mainly by alpha2-AP. Therefore, lack of alpha2-AP could markedly result in overrelease of VEGF by the continuous activation of plasmin because of AMI and could result in an acute cor pulmonale. Our results provide new aspects on the role of alpha2-AP and VEGF in the pathogenesis of cardiac events.

VEGF enhances functional improvement of postinfarcted hearts by transplantation of ESC-differentiated cells

Despite considerable advances in medicine, the incidence of heart failure remains high in patients after myocardial infarction (MI). This study investigated the effects of engrafted early-differentiated cells (EDCs) from mouse embryonic stem cells, with or without transfection of vascular endothelial growth factor (VEGF) cDNA (phVEGF(165)), on cardiac function in postinfarcted mice. EDCs were transfected with green fluorescent protein (GFP) cDNA and transplanted into infarcted myocardium. Compared with the MI mice receiving cell-free medium, cardiac function was significantly improved in the MI mice 6 wk after transplantation of EDCs. Moreover, improvement of heart function was significantly greater in the mice implanted with EDCs overexpressing VEGF (EDCs-VEGF) than with EDCs alone. Frozen sections of infarcted myocardium with EDCs or EDCs-VEGF transplantation showed GFP-positive tissue. The area with positive immunostaining for cardiac troponin I and alpha-myosin heavy chain was larger in injured myocardium with EDCs or EDCs-VEGF transplantation than with medium injection. Transplantation of EDCs or EDCs-VEGF significantly increased the number of blood vessels in the MI area. However, the density of capillaries was significantly higher in the EDCs-VEGF animals than in the EDC mice. Double staining for GFP and connexin-43 was positive in injured myocardium with EDC transplantation. Our data demonstrate that engrafted EDCs or EDCs-VEGF regenerated cardiac tissue and significantly improved cardiac function in postinfarcted hearts. The novel EDCs-VEGF synergistic approach may have an important impact on future cell therapy for patients experiencing MI or heart failure.

Adeno-associated viral vector-mediated hypoxia response element-regulated gene expression in mouse ischemic heart model

Intramyocardial injection of genes encoding angiogenic factors could provide a useful approach for the treatment of ischemic heart disease. However, uncontrolled expression of angiogenic factors in vivo may cause some unwanted side effects, such as hemangioma formation, retinopathy, and arthritis. It may also induce occult tumor growth and artherosclerotic plaque progression. Because hypoxia-inducible factor 1 is up-regulated in a variety of hypoxic conditions and it regulates gene expression by binding to a cis-acting hypoxia-responsive element (HRE), we propose to use HRE, found in the 3' end of the erythropoietin gene to control gene expression in ischemic myocardium. A concatemer of nine copies of the consensus sequence of HRE isolated from the erythropoietin enhancer was used to mediate hypoxia induction. We constructed two adeno-associated viral vectors in which LacZ and vascular endothelial growth factor (VEGF) expressions were controlled by this HRE concatemer and a minimal simian virus 40 promoter. Both LacZ and VEGF expression were induced by hypoxia and/or anoxia in several cell lines transduced with these vectors. The functions of these vectors in ischemic myocardium were tested by injecting them into normal and ischemic mouse myocardium created by occlusion of the left anterior descending coronary artery. The expression of LacZ gene was induced eight times and of VEGF 20 times in ischemic myocardium compared with normal myocardium after the viral vector transduction. Hence, HRE is a good candidate for the control of angiogenic factor gene expression in ischemic myocardium.

Dynamic contrast-enhanced magnetic resonance imaging of the sarcopenic muscle

BACKGROUND: Studies about capillarity of the aged muscle provided conflicting results and no data are currently available about the magnetic resonance imaging (MRI) in vivo characteristics of the microvascular bed in aged rats. We have studied age-related modifications of the skeletal muscle by in vivo T2-relaxometry and dynamic contrast-enhanced magnetic resonance imaging (CE-MRI) at high field intensity (4.7 T). The aim of the work was to test the hypothesis that the ageing process involves microvessels in skeletal muscle. METHODS: The study was performed in 4-month-old (n = 6) and 20-month-old (n = 6) rats. RESULTS: At MRI examination, the relaxation time T2 of the gastrocnemius muscle showed no significant difference between these two groups. The kinetic of contrast penetration in the tissue showed that in 4-month-old rats the enhancement values of the signal intensity at different time-points were significantly higher than those found in senescent rats. CONCLUSION: The reported finding suggests that there is a modification of the microcirculatory function in skeletal muscle of aged rats. This work also demonstrates that CE-MRI allows for an in vivo quantification of the multiple biological processes involving the skeletal muscle during aging. Therefore, CE-MRI could represent a further tool for the follow up of tissue modification and therapeutic intervention both in patients with sarcopenia and in experimental models of this pathology.

KDR (VEGF receptor 2) is the major mediator for the hypotensive effect of VEGF

Vascular endothelial growth factor (VEGF) exerts vasodilation-induced hypotension as a major side effect for treatment of ischemic diseases. VEGF has 2 receptor tyrosine kinases, KDR and Flt-1. Little is known about which receptor mediates VEGF-induced hypotension. To elucidate the role of each receptor in mediating hypotension, KDR-selective and Flt-1-selective mutants were used for in vitro and in vivo studies. The KDR-selective mutant induced vascular endothelial cell proliferation comparable to VEGF, whereas the Flt-1- selective mutant had no effect on proliferation. Intravenous injection of KDR-selective mutant, Flt-selective mutant, or VEGF caused a dose-related decrease in mean arterial pressure in conscious rats. The hypotensive response to KDR-selective mutant was significantly less than that to VEGF (P<0.01) but was greater than that to Flt-selective mutant (P<0.01). Similarly, VEGF and KDR-selective mutant induced more potent vasorelaxation than Flt-selective mutant or placenta growth factor that binds Flt-1 only (P<0.01), and the vasorelaxation to KDR-selective mutant was not significantly different at low concentrations but less than that to VEGF at high concentrations. The results indicate that the vasodilation and hypotensive effect of VEGF may involve both receptors, but KDR is the predominant receptor mediating this effect. Because KDR-selective mutant induced proliferation and angiogenesis similar to VEGF but was associated with 36% attenuation in hypotension, the data suggest that the KDR-selective mutant may represent an alternative treatment for ischemic diseases.

Gene transfer of hepatocyte growth factor to subarachnoid space in cerebral hypoperfusion model

Although cerebral hypoperfusion caused by cerebral occlusive disease leads to cerebral ischemic events, an effective treatment has not yet been established. Recently, a novel therapeutic strategy for ischemic disease using angiogenic growth factors to expedite and/or augment collateral artery development has been proposed. Therapeutic angiogenesis might be useful for the treatment of cerebral occlusive disease. Hepatocyte growth factor (HGF) is a potent angiogenic factor, in addition to vascular endothelial growth factor (VEGF), whereas in the nervous system HGF also acts as neurotrophic factor. Therefore, we hypothesized that gene transfer of these angiogenic growth factors could induce angiogenesis, thus providing an effective therapy for cerebral hypoperfusion or stroke. In this study, we employed a highly efficient gene transfer method, the viral envelop (Hemagglutinating Virus of Japan [HVJ]-liposome) method, because we previously documented that beta-galactosidase gene could be transfected into the brain by the HVJ-liposome method. Indeed, we confirmed wide distribution of transgene expression using beta-galactosidase via injection into the subarachnoid space. Of importance, transfection of HGF or VEGF gene into the subarachnoid space 7 days before occlusion induced angiogenesis on the brain surface as assessed by alkaline phosphatase staining (P<0.01). In addition, significant improvement of cerebral blood flow (CBF) was observed by laser Doppler imaging (LDI) 7 days after occlusion (P<0.01). Unexpectedly, transfection of HGF or VEGF gene into the subarachnoid space immediately after occlusion of the bilateral carotid arteries also induced angiogenesis on the brain surface and had a significant protective effect on the impairment of CBF by carotid occlusion (P<0.01). Interestingly, coinjection of recombinant HGF with HGF gene transfer revealed a further increase in CBF (P<0.01). Here, we demonstrated successful therapeutic angiogenesis using HGF or VEGF gene transfer into the subarachnoid space to improve cerebral hypoperfusion, thus providing a new therapeutic strategy for cerebral ischemic disease.

Increased proliferation of endothelial cells with overexpression of soluble TNF-alpha receptor I gene

Vascular endothelial growth factor (VEGF) can overcome a potential anti-angiogenic effect of TNF-alpha by inhibiting endothelial apoptosis induced by this cytokine. Soluble TNF-alpha receptor I (sTNFRI) is an extracellular domain of TNFRI and antagonizes the activity of TNF-alpha. Here we report that sTNFRI is able to stimulate the growth of endothelial cells not by antagonizing TNF-alpha. Exogenously added recombinant human sTNFRI stimulated significantly more cell growth of human umbilical venous endothelial cells (HUVEC) with a low dose (50-200 pg/ml) compared with smooth muscle cells. In contrast, monoclonal antibody against TNF-alpha did not stimulate growth of human HUVEC. The sTNFRI expression plasmid (pcDNA3.1 plasmid) was introduced into the cell culture using OPTI-MEM, lipofectin and transferrin. Growth of HUVEC transfected with sTNFRI vector also increased significantly compared with those transfected with control vector. HUVEC transfected with sTNFRI vector increased the extracellular domain of TNFRI mRNA levels, but did not affect the intracellular domain of TNFRI mRNA levels. Accumulation of sTNFRI significantly increased in conditioned medium from HUVEC transfected with sTNFRI vector compared with those transfected with control vector. HUVEC transfected with sTNFRI vector not only increased sTNFRI but also prevented shedding of sTNFRI from TNFRI. The TNF-alpha -induced internucleosomic fragmentation was also significantly prevented in HUVEC transfected with sTNFRI vector compared with those transfected with control vector. These results suggest that instead of growth factors such as VEGF, local transfection of the sTNFRI gene may have potential therapeutic value in vascular diseases in which TNF-alpha is also usually highly expressed.

VEGF gene delivery for treatment of ischemic cardiovascular disease

There are increasing numbers of patients with ischemic myocardial disease not amenable to traditional methods of revascularization. These patients may benefit from new research into the use of naturally occurring angiogenic compounds, such as vascular endothelial growth factor (VEGF) for re-establishing blood flow into regions of hibernating myocardium. Animal studies and human clinical trials evaluating VEGF demonstrate increases in myocardial perfusion after treatment, with some patients reporting improvement in anginal symptoms. Further research into the ideal form of VEGF therapy (protein, plasmid, or adenoviral) and delivery method (intracoronary, intramyocardial, or epicardial) seems justified.

Intraventricular infusion of vascular endothelial growth factor promotes cerebral angiogenesis with minimal brain edema

OBJECTIVE

Therapeutic cerebral angiogenesis, i.e., using angiogenic factors to enhance collateral vessel formation within the central nervous system, is a potential method for cerebral revascularization. Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen that also increases capillary permeability, particularly in ischemic tissue. The purpose of this study was to assess the angiogenic and capillary permeability effects of chronic intraventricular infusion of exogenous VEGF in nonischemic brain tissue, because many patients with impaired cerebrovascular reserve do not exhibit chronic cerebral ischemia.

METHODS

Recombinant human VEGF(165) was infused into the right lateral ventricle of rats at a rate of 1 microl/h for 7 days, at concentrations of 1 to 25 microg/ml, with osmotic minipumps. Control animals received vehicle only. Vessels were identified in laminin immunohistochemical analyses. Capillary permeability and brain edema were assessed with Evans blue extravasation, [(3)H]inulin permeability, and brain water content measurements.

RESULTS

Vessel density was dose-dependently increased by VEGF(165) infusions, with significant increases occurring in animals treated with 5 or 25 microg/ml, compared with control animals (P h 0.01). Significant enlargement of the lateral ventricles was observed for the highest-dose group but not for animals treated with other doses. Capillary permeability was assessed in animals treated with a dose of 5 microg/ml. An increase in capillary permeability in the diencephalon was identified with Evans blue extravasation and [(3)H]inulin permeability assessments; however, the brain water content was not significantly increased.

CONCLUSION

Chronic intraventricular infusions of VEGF(165) increased vascular density in a dose-dependent manner. There seems to be a therapeutic window, because infusion of VEGF(165) at a concentration of 5 microg/ml resulted in a significant increase in vessel density with minimal associated brain edema and no ventriculomegaly.

Exaggerated hypotensive effect of vascular endothelial growth factor in spontaneously hypertensive rats

Vascular endothelial growth factor (VEGF) induces hypotension in normotensive subjects, which is considered to be a major side effect for treatment of ischemic diseases. However, the hypotensive effect of VEGF has not been investigated in the setting of hypertension. This study determined effects of VEGF on hemodynamics, pharmacokinetics, and release of NO and prostaglandin I2 (PGI2) in vivo and on vasorelaxation of mesentery artery rings in vitro in spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto rats (WKY). Intravenous infusion of VEGF for 2 hours produced a dose-related decrease in arterial pressure, which was enhanced in conscious SHR compared with WKY (P<0.01), and an increase in heart rate in WKY but not in SHR. In response to similar doses of VEGF, compared with WKY, SHR had a higher plasma VEGF level and lower VEGF clearance (P<0.01). Circulating NO and PGI2 levels after VEGF administration were not increased in SHR versus WKY, and VEGF-induced vasorelaxation was blunted in SHR versus WKY in vitro, suggesting endothelial dysfunction in SHR. One-week VEGF infusion also caused greater hypotension (P<0.05) in the absence of tachycardia in SHR compared with WKY controls. Thus, despite blunted vasorelaxation in vitro because of endothelial dysfunction, SHR exhibited exaggerated hypotension without tachycardia in response to VEGF, which was independent of NO and PGI2. The exaggerated hypotensive response to VEGF in SHR may be owing to impaired baroreflex function and reduced VEGF clearance. The data may also suggest that more caution should be taken when VEGF is administered in patients with hypertension.

Pharmacological treatment of coronary artery disease with recombinant fibroblast growth factor-2: double-blind, randomized, controlled clinical trial

BACKGROUND

Single-bolus intracoronary administration of fibroblast growth factor-2 (FGF2) improved symptoms and myocardial function in a phase I, open-label trial in patients with coronary artery disease. We conducted the FGF Initiating RevaScularization Trial (FIRST) to evaluate further the efficacy and safety of recombinant FGF2 (rFGF2).

METHODS AND RESULTS

FIRST is a multicenter, randomized, double-blind, placebo-controlled trial of a single intracoronary infusion of rFGF2 at 0, 0.3, 3, or 30 microg/kg (n=337 patients). Efficacy was evaluated at 90 and 180 days by exercise tolerance test, myocardial nuclear perfusion imaging, Seattle Angina Questionnaire, and Short-Form 36 questionnaire. Exercise tolerance was increased at 90 days in all groups and was not significantly different between placebo and FGF-treated groups. rFGF2 reduced angina symptoms as measured by the angina frequency score of the Seattle Angina Questionnaire (overall P=0.035) and the physical component summary scale of the Short-Form 36 (pairwise P=0.033, all FGF groups versus placebo). These differences were more pronounced in highly symptomatic patients (baseline angina frequency score < or =40 or Canadian Cardiovascular Society score of III or IV). None of the differences were significant at 180 days because of continued improvement in the placebo group. Adverse events were similar across all groups, except for hypotension, which occurred with higher frequency in the 30-microg/kg rFGF2 group.

CONCLUSIONS

A single intracoronary infusion of rFGF2 does not improve exercise tolerance or myocardial perfusion but does show trends toward symptomatic improvement at 90 (but not 180) days.

Coronary collateral size, flow capacity, and growth: estimates from the angiogram in patients with obstructive coronary disease

BACKGROUND

Stimulation of coronary collateral growth has potential clinical value, yet techniques to assess such growth in patients are limited.

METHODS AND RESULTS

A cineangiographic approach to classify the dominant collaterals and to quantify their lumen caliber and flow capacity was developed and validated. For measurement of 0.4- to 1.5-mm-diameter phantoms, mean error ranged from -0.01 to +0.02 mm. To illustrate the utility of such a method, 52 collateral pathways were measured in 13 patients with 17 occluded arteries before and after 10 years of intensive lipid therapy. The mean variance, final sigma, of 9 separate measurements of each collateral was +/-0.101 mm. At pretreatment, collateral diameter averaged 0.50+/-0.11 mm (SD) (range, 0.3 to 1.4 mm) without tapering or central narrowing. Over 10 years, mean increase in diameter was +16% (P=0.028); in area, +64% (P=0.015); and in estimated flow capacity, +214% (P=0.009). Certain lipoprotein characteristics tended to predict collateral growth. Patients for whom angina disappeared during 10 years had a greater increase in flow capacity than those for whom it persisted (+331% versus 4%; P=0.05).

CONCLUSIONS

Coronary collateral diameter can be estimated with a precision of 0.10 mm. Flow capacity of the network is well approximated by measurement of the 2 or 3 largest connections serving an occluded artery. Initial studies with this method show that disappearance of angina is significantly associated with growth in collateral flow capacity. Collateral growth tends to associate with lipid therapy and with certain in-treatment lipid measures.

Magnetic resonance imaging demonstrates improved regional systolic wall motion and thickening and myocardial perfusion of myocardial territories treated by laser myocardial revascularization

OBJECTIVES

This study was designed to investigate the use of magnetic resonance (MR) functional and perfusion imaging to evaluate laser myocardial revascularization (LMR).

BACKGROUND

Most clinical studies of LMR have shown improvements in angina class and exercise capacity, with minimal or absent improvements in myocardial perfusion and function.

METHODS

Fifteen patients who underwent percutaneous Biosense-guided holmium:yttrium aluminum garnet LMR to areas of viable but ischemic myocardium were followed clinically and underwent functional and perfusion MRI at baseline, 30 days and 6 months.

RESULTS

The mean age was 64 +/- 11 years; four patients were women. The ejection fraction was 47.4 +/- 14.0%. Angina class at baseline was 3.4 +/- 0.6 and improved to 2.5 +/- 1.4 at six months (p = 0.054). Exercise time at baseline was 298 +/- 97 s and increased to 350 +/- 95 s at 30 days and 365 +/- 79 s at six months, p = 0.04. There were no significant changes in nuclear perfusion scans. Although MR determined that resting radial motion and thickening of the target wall were significantly less than normal at baseline (p < 0.001), they improved significantly during follow-up (wall thickening: baseline, 30.6 +/- 11.7%; day 30, 41.2 +/- 13.3% and day 180, 44.2 +/- 11.9%, p = 0.01). The size of the underperfused myocardial area was 14.5 +/- 5.4% at baseline and was reduced to 6.3 +/- 2.8% at 30 days and 7.7 +/- 3.7% at 6 months (p < 0.001).

CONCLUSIONS

This small phase I, open-label, uncontrolled study of MR functional and perfusion imaging in patients undergoing Biosense-guided LMR suggests a beneficial effect of this treatment strategy on myocardial function and perfusion. The efficacy of Biosense-guided LMR is being evaluated in a large phase II, randomized, blinded placebo-controlled trial with an MRI substudy (DIRECT).

Potentiation of angiogenic response by ischemic and hypoxic preconditioning of the heart

This review is intended to discuss the newly discovered role of preconditioning which should make it an attractive therapeutic stimulus for repairing the injured myocardium. We recently found that apart from rendering the myocardium tolerant to ischemic reperfusion injury, preconditioning also potentiates angiogenesis. Our study demonstrated for the first time that both ischemic and hypoxic preconditioning triggered myocardial angiogenesis at the capillary and arteriolar levels which nicely corroborated with the improved myocardial contractile function. Hypoxic preconditioning resulted in the stimulation of VEGF, the most potent angiogenic factor known to date. In concert, endothelial cell specific tyrosine kinase receptors, Tie 1, Tie 2 and Flt-1 and Flk-1 were also significantly enhanced in the preconditioned myocardium. The redox-regulated transcription factor NF kappa B was found to play an essential role in the preconditioning regulation of angiogenesis.