Enhanced angiogenesis and growth of collaterals by in vivo administration of recombinant basic fibroblast growth factor in a rabbit model of acute lower limb ischemia: Dose-response effect of basic fibroblast growth factor

[Vascular endothelial factor (VEGF): therapeutic angiogenesis and vasculogenesis in the treatment of cardiovascular disease]

The formation of new blood vessel is essential for a variety of physiological processes like embryogenesis and the female reproduction as well as pathological processes like tumor growth, wound healing and neovascularization of ischemic tissue. Vasculogenesis and angiogenesis are the mechanisms responsible for the development of the blood vessels. While angiogenesis refers to the formation of capillaries from pre-existing vessels in the embryo and adult organism, vasculogenesis, the development of new blood vessels from in situ differentiating endothelial cells, has been previously considered restricted to embryogenesis. Recent investigations, however, show the existence of endothelial progenitor cells (EPCs) in the peripheral blood of the adult and their participation in ongoing neovascularization. Molecular and cell-biological experiments suggest that different cytokines and growth factors have a stimulatory effect on these bone-marrow derived EPCs. Results with GM-CSF (granulocyte macrophage-colony stimulating factor) and VEGF (vascular endothelial growth factor) open a new insight into the clinical use of cytokines and in particular the use of growth factors in gene therapy. The administration via protein or plasmid-DNA for neovascularization seems to enhance both pathways, angiogenesis and vasculogenesis.

Rescue of diabetes-related impairment of angiogenesis by intramuscular gene therapy with adeno-VEGF

Diabetes is a major risk factor for coronary and peripheral artery diseases. Although diabetic patients often present with advanced forms of these diseases, it is not known whether the compensatory mechanisms to vascular ischemia are affected in this condition. Accordingly, we sought to determine whether diabetes could: 1) impair the development of new collateral vessel formation in response to tissue ischemia and 2) inhibit cytokine-induced therapeutic neovascularization. Hindlimb ischemia was created by femoral artery ligation in nonobese diabetic mice (NOD mice, n = 20) and in control C57 mice (n = 20). Hindlimb perfusion was evaluated by serial laser Doppler studies after the surgery. In NOD mice, measurement of the Doppler flow ratio between the ischemic and the normal limb indicated that restoration of perfusion in the ischemic hindlimb was significantly impaired. At day 14 after surgery, Doppler flow ratio in the NOD mice was 0.49+/-0.04 versus 0.73+/-0.06 for the C57 mice (P< or =0.005). This impairment in blood flow recovery persisted throughout the duration of the study with Doppler flow ratio values at day 35 of 0.50+/-0.05 versus 0.90+/-0.07 in the NOD and C57 mice, respectively (P< or =0.001). CD31 immunostaining confirmed the laser Doppler data by showing a significant reduction in capillary density in the NOD mice at 35 days after surgery (302+/-4 capillaries/mm2 versus 782+/-78 in C57 mice (P< or =0.005). The reduction in neovascularization in the NOD mice was the result of a lower level of vascular endothelial growth factor (VEGF) in the ischemic tissues, as assessed by Northern blot, Western blot and immunohistochemistry. The central role of VEGF was confirmed by showing that normal levels of neovascularization (compared with C57) could be achieved in NOD mice that had been supplemented for this growth factor via intramuscular injection of an adenoviral vector encoding for VEGF. We conclude that 1) diabetes impairs endogenous neovascularization of ischemic tissues; 2) the impairment in new blood vessel formation results from reduced expression of VEGF; and 3) cytokine supplementation achieved by intramuscular adeno-VEGF gene transfer restores neovascularization in a mouse model of diabetes.

Expression of messenger ribonucleic acid splice variants for vascular endothelial growth factor in the penis of adult rats and humans

Erectile dysfunction is often associated with problems in vascular perfusion to the erectile components of the penis. In order to better understand the factors that control vascular formation and perfusion in the erectile tissues of the penis, we have begun to characterize the expression of vascular endothelial growth factor (VEGF) in penis tissues. VEGF is one of several polypeptides that have significant angiogenic activity in vitro and in vivo. Extensive characterization of the VEGF gene and its products has shown that several different mature mRNA transcripts exist, originating from alternative splicing of the basic VEGF transcript. These variant transcripts can encode peptides with different biological activities. Penile tissue was obtained from adult rats and from human patients undergoing penile prosthesis implantation. Analysis of the forms of VEGF transcripts was performed using a reverse transcription-polymerase chain reaction technique with primer pairs derived from the first and eighth exon of the VEGF gene. The expression levels of the various isoforms in the rat penis were then quantified using RNase protection assays. Four previously described splice variants of VEGF mRNA (VEGF 120, 144, 164, 188) were detected in rat and human penile tissues. In contrast to what is seen in the rat lung, where the most abundant form of VEGF mRNA is the 188 splice isoform, VEGF 164 is the most abundant transcript detected in the penis. Finally, sequence analysis of numerous VEGF cDNA clones obtained from the rat penis demonstrated the presence of a previously undescribed VEGF splice variant that could give rise to a protein of 110 amino acid residues (VEGF 110, GenBank accession no. AF080594). In summary, a number of VEGF mRNA isoforms are expressed in the rat and human penis, with the splice variant encoding a 164-amino acid protein present in greatest abundance. This study is a prelude to attempts to genetically manipulate VEGF expression in the penis as a therapy for erectile dysfunction.

Age-dependent impairment of angiogenesis

BACKGROUND

The effect of aging on angiogenesis in ischemic vascular disease has not been studied. Accordingly, we investigated the hypothesis that angiogenesis is impaired as a function of age.

METHODS AND RESULTS

Forty days after the resection of 1 femoral artery, collateral vessel development was significantly impaired in old (aged 4 to 5 years; n=7) versus young (aged 6 to 8 months; n=6) New Zealand White (NZW) rabbits on the basis of reduced hindlimb perfusion (ischemic: normal blood pressure ratio=0.58+/-0.05 versus 0.77+/-0.06; P<0.005), reduced number of angiographically visible vessels (angiographic score=0.48+/-0.05 versus 0.70+/-0.05; P<0.01), and lower capillary density in the ischemic limb (130.3+/-5.8/mm2 versus 171.4+/-9.5/mm2; P<0.001). Angiogenesis was also impaired in old (aged 2 years) versus young (aged 12 weeks) mice as shown by reduced hindlimb perfusion (measured by laser Doppler imaging) and lower capillary density (353.0+/-14.3/mm2 versus 713.3+/-63.4/mm2; P<0.01). Impaired angiogenesis in old animals was the result of impaired endothelial function (lower basal NO release and decreased vasodilation in response to acetylcholine) and a lower expression of vascular endothelial growth factor (VEGF) in ischemic tissues (by Northern blot, Western blot, and immunohistochemistry). When recombinant VEGF protein was administered to young and old rabbits, both groups exhibited a significant and similar increase in blood pressure ratio, angiographic score, and capillary density.

CONCLUSIONS

Angiogenesis responsible for collateral development in limb ischemia is impaired with aging; responsible mechanisms include age-related endothelial dysfunction and reduced VEGF expression. Advanced age, however, does not preclude augmentation of collateral vessel development in response to exogenous angiogenic cytokines.

Regulation of new blood vessel growth into ischemic skeletal muscle

PURPOSE

In a rabbit model, transposition of a muscle pedicle flap to an ischemic hind limb has been shown to result in the development of new blood vessels that connect the arterial circulation of the flap to the circulation of the limb. The hypothesis that exogenous recombinant basic fibroblast growth factor (bFGF) would enhance the development of this new blood supply was examined and the regulation of bFGF in this process was investigated.

METHODS

The right common iliac artery was ligated in 12 male New Zealand white rabbits. An abdominal wall muscle flap based on the left inferior epigastric artery was transposed to the right thigh. bFGF in phosphate-buffered saline (PBS) at 3 ng/h (n = 6), or PBS alone (n = 6), was infused for 7 days via mini-osmotic pumps with an infusion catheter positioned at the flap-muscle interface. The flap-muscle interface was immunostained with anti-alpha-actin antibody to determine blood vessel density (number of vessels/mm) and with anti-bFGF antibody to evaluate bFGF distribution. RNA was isolated from these sections, and polymerase chain reaction (PCR) was used to examine endogenous bFGF messenger RNA (mRNA) expression.

RESULTS

Blood vessel density was significantly increased in animals receiving exogenous bFGF (22. 0 +/- 10.6 vessels/mm vs. 10.7 +/- 8.8 vessels/mm, P =.009). In the controls, neovessels were arranged in clusters with endogenous bFGF concentrated around these clusters. In bFGF-treated animals, vessels were diffusely scattered throughout the flap-limb interface, corresponding to the distribution pattern of infused bFGF. There was no difference in bFGF mRNA expression between the control and the bFGF-treated groups.

CONCLUSION

Exogenous bFGF infusion significantly augmented new blood vessel development at the flap-limb interface. Endogenous bFGF was up-regulated around the newly developed microvessels in control animals, and vessel growth correlated with the diffuse distribution of exogenous bFGF, implicating bFGF as an important factor in angiogenesis. Exogenous bFGF did not affect bFGF mRNA expression, suggesting that the regulation of bFGF is not under autocrine control.

The vascular endothelial growth factor mRNA contains an internal ribosome entry site

Vascular endothelial growth factor (VEGF), an essential regulator of angiogenesis during early development as well as during the growth of solid tumours, bears an unusually large 5' untranslated region (5'-UTR) in the mRNA of over 1000 nucleotides. We found that the VEGF 5'-UTR, despite being GC-rich and containing an upstream short open reading frame, promotes efficient translation of a luciferase reporter. The VEGF 5'-UTR also allowed translation of luciferase from a dicistronic mRNA when placed between the two cistrons, demonstrating that it contains an internal ribosome entry site. Deletion analysis indicated that the IRES resides towards the 3' end of the 5'-UTR.

Basic fibroblast growth factor stimulates angiogenesis in the hindlimb of hyperglycemic rats

Angiogenic growth factors including basic fibroblast growth factor (bFGF) have therapeutic value for chronic ischemia in nondiabetic animals. However, angiogenic therapy for chronic ischemia in a background of diabetes remains unexplored. In the present study, we evaluated the effects of exogenous bFGF on angiogenesis in streptozotocin-induced diabetic rats with ischemic and nonischemic limbs. We produced ischemia of the left lower limb by excising the superficial femoral artery. At 2 weeks, the rats received an intramuscular injection of vehicle (group A), 0.3 microg bFGF/day (group B), or 1 microg bFGF/day (group C), daily for 2 weeks. At 4 weeks, we assessed limb angiogenesis by skeletal muscle capillary density (cap/mm2) and capillary per muscle fiber ratio (cap/F) counts. Group C had significantly higher mean levels compared to group A for calf capillary density (P < 0.0024) and capillary per muscle fiber ratio in both thigh (P < 0.0015) and calf (P < 0.0001). There was a trend toward increased mean capillary per muscle fiber ratio with increasing dose. This trend was significant in the calf (P < 0.0015) and just missed statistical significance in the thigh. There was a similar trend in calf capillary density. We conclude that exogenous bFGF enhances angiogenesis and, possibly, collateral circulation in ischemic limbs of diabetic rats.

Therapeutic angiogenesis with basic fibroblast growth factor: technique and early results

BACKGROUND

Patients not amenable to complete myocardial revascularization by conventional methods present a difficult clinical problem. Here we present the early results and technical considerations of the administration of basic fibroblast growth factor for the induction of collateral growth using heparin-alginate slow-release devices in patients undergoing coronary artery bypass grafting.

METHODS

Eight patients were enrolled. Patients were candidates if they had at least one graftable obstructed coronary artery and at least one major arterial distribution not amenable to revascularization, a serum creatinine level less than 3 mg/dL, ejection fraction greater than 0.20, and estimated operative mortality of less than 25%. During conventional coronary artery bypass grafting, 10 heparin-alginate devices, each containing either 1 microg or 10 microg of basic fibroblast growth factor, were implanted in the epicardial fat in multiple regions of the unrevascularizable territory and also in the distal distribution of a grafted or patent artery.

RESULTS

There was no mortality and no evidence of renal, hematologic, or hepatic toxicity during follow-up. Three months after the operation, all patients remain free of angina. Seven patients were examined with stress perfusion scans. Three patients had clear enhancement of perfusion to the unrevascularized myocardium, 1 patient had a new fixed defect, and 3 had minimal overall change but had evidence of new small, fixed perfusion defects. Seven patients had improved or similar myocardial contractile function (ejection fraction at 3-month follow-up = 0.53 +/- 0.22 versus 0.47 +/- 0.14 preoperatively). One patient suffered a perioperative myocardial infarction in the area of basic fibroblast growth factor administration.

CONCLUSIONS

This preliminary study demonstrates the safety and technical feasibility of therapeutic angiogenesis with basic fibroblast growth factor delivered by heparin-alginate slow-release devices. Further studies examining the safety, clinical efficacy, and long-term results are ongoing.

Exercise training enhances basic fibroblast growth factor-induced collateral blood flow

This study evaluated whether daily exercise would enhance the peripheral collateral vessel development found in response to exogenous basic fibroblast growth factor (bFGF) infusion. After bilateral femoral occlusion, male Sprague-Dawley rats (approximately 325 g) received intra-arterial infusions of either bFGF (1 microg/day; n = 15) or carrier solution (n = 13) via osmotic pumps for 2 wk. Subgroups of each treatment were kept sedentary (cage activity) or trained by walking at 20 m/min at 15% grade, two times a day, 5 days/wk for 4 wk. Training markedly increased citrate synthase activity in the active muscle (P < 0.001). Muscle function and blood flows (85Sr microsphere) were evaluated using an isolated hindquarter perfused at 100 mmHg via the abdominal aorta. The significant increase in blood flow to the entire hindlimb in the sedentary animals, caused by bFGF infusion (P < 0.05), was further increased (P < 0.01) in the bFGF-trained group. The quantitatively largest increases in blood flows were observed in the collateral-dependent tissues of the distal hindlimb. Blood flows to the entire calf muscle group increased approximately 140% in carrier-trained (P < 0.001), approximately 180% in bFGF sedentary (P < 0.001), and approximately 240% in the bFGF-trained (P < 0.001) groups compared with the carrier sedentary group. The increases in collateral blood flow were functionally important, as improvements in calf muscle performance correlated with measured blood flows. Our results demonstrate that exogenous bFGF administration in combination with a moderate-intensity exercise program greatly increases collateral-dependent blood flow and improves muscle performance. That physical activity enriched the bFGF response is consistent with the hypothesis that hemodynamic factors are important contributors to collateral vessel enlargement.

Basic fibroblast growth factor increased regional myocardial blood flow and limited infarct size of acutely infarcted myocardium in dogs

Basic fibroblast growth factor (bFGF), a growth factor potent in promoting angiogenesis, has been shown to reduce infarct size in experimentally induced acute myocardial infarction. However, the effect of bFGF on regional myocardial blood flow (Qm) in the acutely infarcted myocardium has not been well clarified. In 20 open-chest dogs, the left anterior descending (LAD) coronary artery was occluded and animals were maintained in this condition for 4 weeks. In eight of these dogs, bFGF (300 microg) was injected into the myocardium supplied by the LAD and the artery was ligated (bFGF group), and in the other 12 dogs, saline was injected (control group). Nonradioactive colored microspheres were used to measure Qm. The amount of viable myocardium as percent of visual field in the microscope and the extent of fibrosis scored histologically from 0 to 5 in the infarcted area 4 weeks after occlusion were measured. In the outer layer, the Qm values immediately after and 4 weeks after occlusion were 26 +/- 2% and 70 +/- 6%, respectively, in the control group, and 46 +/- 5% and 121 +/- 13%, respectively, in the bFGF group. The Qm at both times in the bFGF group was significantly higher than the corresponding control group values (p < 0.01). The Qm at 4 weeks in the inner and the middle layers also significantly increased in the bFGF group. There was more viable myocardium (control vs bFGF group; 41 +/- 5 vs 61 +/- 7%, p < 0.05) and less fibrosis (3.1 +/- 0.2 vs 2.0 +/- 0.4, p < 0.01) at the outer layer in the bFGF group. It was found that bFGF caused a marked increase in Qm, an increase of viable myocardium, and a decrease of fibrosis in the infarcted myocardium in dogs.

Controlled delivery of vascular endothelial growth factor promotes neovascularization and maintains limb function in a rabbit model of ischemia

PURPOSE

Vascular endothelial growth factor (VEGF) modulates new blood vessel development and growth and has been suggested as a potential therapeutic agent that could alleviate debilitating claudication in patients. The objective of this study was to determine whether controlled, local delivery of a low dose of VEGF from an osmotic pump could promote neovascularization, limb perfusion, and functional improvements in the hind limbs of rabbits rendered partially ischemic by surgery. The effects of VEGF were compared with those of the vasodilator nitroglycerin (NTG) and to saline administered similarly.

METHODS

Thirty rabbits were randomly assigned to either VEGF (n = 10), NTG (n = 10), or saline (n = 10) treatment groups. Partial ischemia was induced in each left hind limb by surgical ligation of the common and superficial femoral arteries, leaving the internal iliac artery intact. The right limb of each animal served as a nonischemic control. Immediately after vessel ligations, a 28-day osmotic pump was implanted to deliver VEGF (0.22 microg/kg/day), NTG (17.8 microg/kg/day), or saline solution into the common iliac artery just proximal to the ligation site. Comparative vascularity between ischemic and nonischemic limbs within treatment groups and between groups was evaluated by (1) capillary counts from representative fields of hematoxylin and eosin stained muscle tissue taken from hind limbs at day 40; (2) digitized arteriograms of ischemic legs at day 40, which were used to quantify the complexity of vascular branching (fractal dimension index) and the total extent of vascularization (vascular density index); (3) measuring capillary refill times in ischemic limbs; and (4) observations of functional and trophic changes in ischemic limbs. Statistical differences between treatment groups were evaluated by one-way ANOVA.

RESULTS

Complexity of vascular branching and vascular density were significantly greater (p < 0.001) in VEGF-treated ischemic limbs compared with NTG- and saline-treated ischemic limbs. By postoperation day 14, all VEGF-treated ischemic limbs had restored capillary refill (p < 0.001), new hair growth, and greatly improved limb function and appearance. Saline-treated limbs exhibited ischemic changes, with poor capillary refill and negligible limb function. Capillary refill in NTG-treated ischemic limbs did not differ significantly from saline-treated limbs. Ischemic VEGF-treated limbs had significantly more capillaries compared with both ischemic and nonischemic limbs in saline-treated animals (p < 0.05). Ischemic NTG-treated limbs also had significantly more capillaries compared with ischemic limbs in saline-treated animals (p < 0.05). Because of high variability, however, capillary counts in VEGF-treated ischemic limbs did not differ significantly from those of contralateral nonischemic limbs, or from capillary counts in either ischemic or nonischemic limbs of NTG-treated rabbits.

CONCLUSIONS

Controlled release of microgram quantities of VEGF significantly enhanced neovascularization and vascular perfusion in ischemic limbs compared with controls in this rabbit model of partial ischemia. In addition, VEGF-treated ischemic limbs demonstrated near-normal function and appearance, whereas NTG- and saline-treated ischemic controls remained noticeably impaired. This novel approach of VEGF delivery may prove clinically useful either alone or combined with revascularization procedures.

Positive and negative regulation of angiogenesis: from cell biology to the clinic

Virtually every subspecialty in medicine in one way or another deals with angiogenesis-associated physiological or pathological processes and, without exception, every organ system in the body has many diseases in which angiogenesis is an important component. This in itself makes the study of angiogenesis mandatory, in both basic science and clinical settings. Yet the study of angiogenesis does not require this justification. As a biological process it is extraordinarily rich, touching on virtually every aspect of modern cell biology, making it almost impossible for molecular biologists, biochemists and morphologists to ignore. Considerable therapeutic benefit can now be obtained through positive or negative manipulation of the angiogenic process, and this is due in large part to the rapid transfer to the clinical setting of knowledge acquired through a cell biological approach.

Therapeutic angiogenesis: a new frontier for vascular therapy

Angiogenic cytokines constitute a potentially novel form of therapy for patients with cardiovascular disease. The feasibility of using recombinant formulations of angiogenic growth factors to expedite and/or augment collateral artery development in animal models of myocardial and hindlimb ischemia--'therapeutic angiogenesis'--has now been well established. These studies have suggested that two angiogenic growth factors in particular--basic fibroblast growth factor and vascular endothelial growth factor--are sufficiently potent to merit further investigation. More recently, experiments performed in our laboratory have indicated that, in the case of vascular endothelial growth factor--a secreted protein--similar results may be achieved by percutaneous arterial gene transfer. Further laboratory and clinical studies may yield promising insights into the fundamental basis for native as well as therapeutic angiogenesis, and at the same time more explicitly define the manner in which therapeutic angiogenesis may be successfully incorporated into clinical practice.

Constitutive expression of phVEGF165 after intramuscular gene transfer promotes collateral vessel development in patients with critical limb ischemia

BACKGROUND

Preclinical studies have indicated that angiogenic growth factors can stimulate the development of collateral arteries, a concept called "therapeutic angiogenesis." The objectives of this phase 1 clinical trial were (1) to document the safety and feasibility of intramuscular gene transfer by use of naked plasmid DNA encoding an endothelial cell mitogen and (2) to analyze potential therapeutic benefits in patients with critical limb ischemia.

METHODS AND RESULTS

Gene transfer was performed in 10 limbs of 9 patients with nonhealing ischemic ulcers (n=7/10) and/or rest pain (n=10/10) due to peripheral arterial disease. A total dose of 4000 microg of naked plasmid DNA encoding the 165-amino-acid isoform of human vascular endothelial growth factor (phVEGF165) was injected directly into the muscles of the ischemic limb. Gene expression was documented by a transient increase in serum levels of VEGF monitored by ELISA. The ankle-brachial index improved significantly (0.33+/-0.05 to 0.48+/-0.03, P=.02); newly visible collateral blood vessels were directly documented by contrast angiography in 7 limbs; and magnetic resonance angiography showed qualitative evidence of improved distal flow in 8 limbs. Ischemic ulcers healed or markedly improved in 4 of 7 limbs, including successful limb salvage in 3 patients recommended for below-knee amputation. Tissue specimens obtained from an amputee 10 weeks after gene therapy showed foci of proliferating endothelial cells by immunohistochemistry. PCR and Southern blot analyses indicated persistence of small amounts of plasmid DNA. Complications were limited to transient lower-extremity edema in 6 patients, consistent with VEGF enhancement of vascular permeability.

CONCLUSIONS

These findings may be cautiously interpreted to indicate that intramuscular injection of naked plasmid DNA achieves constitutive overexpression of VEGF sufficient to induce therapeutic angiogenesis in selected patients with critical limb ischemia.

Angiogenic potential of perivascularly delivered aFGF in a porcine model of chronic myocardial ischemia

A number of heparin-binding growth factors, including basic (bFGF) and acidic (aFGF) fibroblast growth factors have been shown to promote angiogenesis in vivo. In this study, we employed a sustained-release polymer extravascular delivery system to evaluate the angiogenic efficacy of a novel form of genetically modified aFGF in the setting of chronic myocardial ischemia. Fifteen Yorkshire pigs subjected to Ameroid occluder placement on the left circumflex (LCX) artery were treated with perivascularly administered aFGF in ethylene vinyl acetate (EVAc) polymer (10 micrograms, n = 7) or EVAc alone (controls, n = 8). Seven to nine weeks later, after coronary angiography to document Ameroid-induced coronary occlusion, all animals underwent studies of coronary flow and global and regional left ventricular function. Microsphere-determined coronary flow in the Ameroid-compromised territory was significantly increased in aFGF-treated compared with control animals, and this improvement in perfusion was maintained during ventricular pacing. Left ventricular function studies demonstrated improved global and regional function in aFGF-treated animals. We conclude that local perivascular delivery of genetically modified aFGF results in significant improvement in myocardial flow and regional and global left ventricular function.

Induction of neoangiogenesis in ischemic myocardium by human growth factors: first clinical results of a new treatment of coronary heart disease

BACKGROUND

The present article is a report of our animal experiments and also of the first clinical results of a new treatment for coronary heart disease using the human growth factor FGF-I (basic fibroblast growth factor) to induce neoangiogenesis in the ischemic myocardium.

METHODS AND RESULTS

FGF-I was obtained from strains of Escherichia coli by genetic engineering, then isolated and highly purified. Several series of animal experiments demonstrated the apathogenic action and neoangiogenic potency of this factor. After successful conclusion of the animal experiments, it was used clinically for the first time. FGF-I (0.01 mg/kg body weight) was injected close to the vessels after the completion of internal mammary artery (IMA)/left anterior descending coronary artery (LAD) anastomosis in 20 patients with three-vessel coronary disease. All the patients had additional peripheral stenoses of the LAD or one of its diagonal branches. Twelve weeks later, the IMA bypasses were selectively imaged by intra-arterial digital subtraction angiography and quantitatively evaluated. In all the animal experiments, the development of new vessels in the ischemic myocardium could be demonstrated angiographically. The formation of capillaries could also be demonstrated in humans and was found in all cases around the site of injection. A capillary network sprouting from the proximal part of the coronary artery could be shown to have bypassed the stenoses and rejoined the distal parts of the vessel.

CONCLUSIONS

We believe that the use of FGF-I for myocardial revascularization is in principle a new concept and that it may be particularly suitable for patients with additional peripheral stenoses that cannot be revascularized surgically.

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.

Adenovirus-mediated expression of the secreted form of basic fibroblast growth factor (FGF-2) induces cellular proliferation and angiogenesis in vivo

Blood supply through collateral arteries is of critical importance in occlusive arterial diseases such as coronary atherosclerosis. Induction of angiogenic growth factor within either the narrowing arteries or jeopardized myocardium may promote angiogenesis in vivo, leading to salvage of ischemic myocardium. We constructed a replication-defective adenovirus (AdCAsFGF-2) coding for human basic fibroblast growth factor (FGF)-2 that is modified, so that its secretion will be facilitated, by tagging a signal sequence derived from FGF-4. A large quantity of FGF-2 was detected in both the cell lysate and culture medium of COS cells infected with AdCAsFGF-2, indicating that FGF-2 was secreted at least partly from the infected cells. The conditioned medium from the infected COS cells stimulated DNA synthesis in and induced cellular proliferation of arterial smooth muscle cells. These effects were eliminated by adenovirus-mediated overexpression of a dominant-negative truncated FGF-receptor type 1. Implantation of a gel of basement membrane proteins containing fibroblasts infected with AdCAsFGF-2 into the ventral subcutaneous space of mice induced extensive cellular proliferation and the formation of functional arterioles. Cells surrounding the vessels were positively immunostained with antibodies recognizing either smooth muscle-specific alpha-actin or factor VIII antigen as a marker for endothelium. These results suggest that AdCAsFGF-2 may be useful for delivering functional FGF-2 into tissues and may lead to therapeutic angiogenesis in vivo.

Extent of myocardial collateralization: determination with three-dimensional elastic-subtraction spiral CT

RATIONALE AND OBJECTIVES

This study was undertaken to develop a standard that can be used to assess new high-resolution collateral zone imaging methods.

MATERIALS AND METHODS

The authors performed ex vivo helical CT in seven pig hearts after microsphere studies of blood flow and coronary angiography. They compared the zones of collateralization depicted at CT and at microsphere studies.

RESULTS

The extent of the collateral zone at CT, computed by using elastic subtraction, correlated well with the coronary blood flow distribution determined with microsphere analysis (r = .95). The root-mean-square error was 6.5%, which indicates good agreement.

CONCLUSION

Accurate assessment of collateralization extent has become an important goal because of the discovery of agents that stimulate the growth of coronary collateral vessels. The precision of elastic-subtraction CT and its validation with respect to the blood flow distribution at microsphere analysis indicate that elastic-subtraction CT can serve as a standard for the measurement of collateralization extent.

Tie2 expression and phosphorylation in angiogenic and quiescent adult tissues

Angiogenesis, the process of new vessels sprouting from the existing vasculature, is a critical process during early development. However, angiogenesis rarely occurs in the adult, except in response to cyclic hormonal stimulation in the ovary and uterus, in response to injury, and in response to pathological conditions such as tumorigenesis and diabetes mellitus. Tie2 (also known as Tek) is a novel endothelium-specific receptor tyrosine kinase, which has been demonstrated to be essential for the development of the embryonic vasculature; Tie2 knockout mice die by embryonic day 10.5 with specific defects in the formation of microvessels. Tie2 is downregulated later in embryogenesis, and its function in the adult has been relatively unexplored. To gain insight into the potential functions of Tie2 in the adult vasculature, Tie2 expression was examined in adult tissues undergoing angiogenesis and in quiescent tissues. Tie2 expression was localized by immunohistochemistry to the endothelium of neovessels in rat tissues undergoing angiogenesis during hormonally stimulated follicular maturation and uterine development and in healing skin wounds. Immunoprecipitation and RNase protection assay demonstrated upregulation of Tie2 protein and mRNA in rat and mouse skin wounds, respectively. Moreover, Tie2 immunoprecipitated from skin wounds was tyrosine-phosphorylated, indicating active downstream signaling. Surprisingly, Tie2 was also expressed in the entire spectrum of the quiescent vasculature (arteries, veins, and capillaries) in a wide range of adult tissues, and Tie2 immunoprecipitated from quiescent adult tissues was also tyrosine-phosphorylated. Together, these results suggest a dual function for Tie2 in adult tissues involving both angiogenesis and vascular maintenance.

Therapeutic angiogenesis: a comparative study of the angiogenic potential of acidic fibroblast growth factor and heparin

PURPOSE

Acidic fibroblast growth factor (aFGF) is a potent mitogen for vascular and other mesenchymal cells in vitro that can induce angiogenesis in vivo. Although heparin has no mitogenic potential of its own, it is an important aFGF cofactor in vitro and may also be capable of stimulating angiogenesis. Because the development of a collateral vasculature in response to ischemia appears to be dependent on angiogenesis, we compared the abilities of aFGF with or without heparin and heparin alone to accelerate angiogenesis in a rat hind limb ischemia model.

METHODS

Daily subcutaneous injections of saline solution (1 ml), heparin (0.05 mg), or human recombinant aFGF with or without heparin (1 microgram aFGF, 0.05 mg heparin) were administered into the hind limb region distal to the point of unilateral femoral artery ligation in the rat for the 10 days immediately after vascular occlusion. Angiogenicity was determined by histologic assessment of treatment outcomes.

RESULTS

Histologic assessment of the number of vessels per microscopic field 10 days after vascular ligation in the fibrofatty tissues distal to the ligation point had the following results: saline solution, 10 +/- 4 vessels; heparin, 13 +/- 4 vessels (p < 0.05 vs saline solution); aFGF, 26 +/- 8 vessels; and aFGF/heparin 36 +/- 8 vessels (aFGF, aFGF/ heparin, p < 0.001 vs saline solution). Similar increases in vascularization were also noted in the skeletal muscle tissues distal to the vascular ligation point. Immunohistochemical analysis for the presence of proliferating cell nuclear antigen, a marker for mitogenic activity, demonstrated corresponding increases in proliferating cell nuclear antigen labeling for each of the treatment groups, expressed as a percentage of total vascular cell nuclei, as follows: saline solution, 7% +/- 2%; heparin, 21% +/- 8% (p < 0.05 vs saline solution); aFGF, 67% +/- 9%; and aFGF/heparin, 83% +/- 5% (aFGF, aFGF/heparin, p < 0.001 vs saline solution).

CONCLUSIONS

The increased vascularization and mitogenic activity demonstrated by these respective studies suggest that angiogenesis is significantly accelerated by the administration of heparin alone and is accelerated to a greater extent by the administration of aFGF with or without heparin. The aFGF/heparin regimen may represent an optimal means of augmenting collateral vessel growth to relieve ischemia in the clinical setting.

Inhibitory effects of hypercholesterolemia and ox-LDL on angiogenesis-like endothelial growth in rabbit aortic explants. Essential role of basic fibroblast growth factor

Hypercholesterolemic (HC) rabbits exhibit suppressed compensatory vascular growth after restriction of arterial supply. However, neovascularization is commonly found in atheromas containing inflammatory cells. We used an in vitro model to determine the effects of hypercholesterolemia on angiogenesis in the absence or presence of inflammatory cells. HC rabbit aortic explants (1 mm2) with or without (n = 90 each) lesion-forming inflammatory cells were cultured in a collagen matrix with serum-free medium. Explant-derived endothelial cell growth was organized into capillary-like microtubes (CLM) that could be videomicroscopically quantified. CLM growth from lesion-free HC explants was significantly reduced to 13 +/- 4% of the value in explants (n = 90) from normocholesterolemic (NC, n = 15) rabbits (P < .001). In contrast, in lesion-containing HC explants, the matrix was invaded by foam cells, and CLM growth was not inhibited. Immunoassayable basic fibroblast growth factor (bFGF, in pg/mL) in the culture medium was significantly lower in lesion-free HC (< 5) than NC explants (11 +/- 2, P < .01) or HC explants with lesions (14 +/- 3). In addition, CLM growth was reduced in NC explants incubated with oxidized LDL (ox-LDL, 50-100 micrograms/mL). Exogenous bFGF (10 ng/mL) reversed the inhibitory effects of hypercholesterolemia and ox-LDL, whereas bFGF-neutralizing antibody (10 micrograms/mL) abolished CLM growth in all groups. In cultured rabbit aortic endothelial cells, ox-LDL reduced DNA synthesis, but this inhibition was reversed by bFGF. We conclude that hypercholesterolemia and ox-LDL inhibit angiogenesis like endothelial growth because of a suppressed availability of endogenous bFGF. Retained responsiveness to exogenous bFGF suggests that inducing bFGF expression at targeted sites may improve collateral growth in hyperlipidemic arterial disease.

Manipulating angiogenesis. From basic science to the bedside

Considerable progress has been made recently in understanding the molecular mechanisms of angiogenesis, which like most other biological processes is the result of subtle and often complex interactions between molecules that have regulatory (eg, cytokines and their receptors) and effector (eg, extracellular matrix, integrins, and proteases) functions. The title of this review was chosen to reflect a recent trend in which knowledge acquired through a molecular/cell biological approach is being rapidly transferred to the clinical setting. As a result, by manipulating angiogenesis either positively or negatively, considerable therapeutic benefit can now be envisaged in physiological and pathological settings in which neovascularization is a prominent component.

Isolation of putative progenitor endothelial cells for angiogenesis

Putative endothelial cell (EC) progenitors or angioblasts were isolated from human peripheral blood by magnetic bead selection on the basis of cell surface antigen expression. In vitro, these cells differentiated into ECs. In animal models of ischemia, heterologous, homologous, and autologous EC progenitors incorporated into sites of active angiogenesis. These findings suggest that EC progenitors may be useful for augmenting collateral vessel growth to ischemic tissues (therapeutic angiogenesis) and for delivering anti- or pro-angiogenic agents, respectively, to sites of pathologic or utilitarian angiogenesis.

Gene therapy and vascular disease: potential applications in vascular surgery

Advances in molecular biology have generated methods that are used to enhance diagnosis and treatment of a variety of human diseases. More recently modification of gene expression in cells by gene transfer has been introduced as a new therapeutic modality. The targeting of vascular cells with this method is appealing not only for anatomical reasons, but also because endovascular techniques provide access to the vasculature and makes site-specific delivery possible. Over the past few years, gene transfer has been widely used to explore the pathophysiology of vascular diseases in experimental models and available data suggests that this method may eventually become a therapeutic alternative for vascular disorders such as restenosis, graft failure, and critical ischaemia. In the following we discuss the methodology of gene transfer, its tentative use in vascular diseases related to vascular surgery, and the problems associated with this new technology.

Induction of angiogenesis by lidocaine and basic fibroblast growth factor: a model for in vivo retroviral-mediated gene therapy

A strategy of direct, in vivo retroviral-mediated gene therapy targeting capillary endothelial cells must provide an environment of active angiogenesis. Both lidocaine and basic fibroblast growth factor (bFGF) promote angiogenesis, but the angiogenic response invoked by these substances in normal skeletal muscle has not been fully characterized. We sought to characterize these agents' angiogenic effects in anterior tibialis muscles of male Sprague-Dawley rats. An injection of either 1% lidocaine with 1:100,000 epinephrine or alternate-day injections of bFGF (0.025 or 0.25 microgram) with or without heparin were tested (n = 6 muscles/condition). Rats were sacrificed 4, 7, 10, or 12 days later and muscles were evaluated histologically to determine the number of proliferating cells using 5-bromo-2'-deoxycytidine (BrdC) and evaluated for capillary density using Griffonia simplicifolia I (GSI) lectin. At all time points, lidocaine produced at least 20-fold greater capillary density and cellular proliferation than PBS control (P < 0.0001). Injections of high-dosage bFGF produced more than fivefold greater capillary density than control injections at 7 and 10 days (P < 0.001), and more than twofold greater proliferation at 4, 7, and 12 days (P < 0.001). Capillary density returned to control levels 12 days following bFGF administration, whereas it remained well above control levels for 12 days after lidocaine administration. To confirm that lidocaine can be utilized in gene therapy strategies targeting vascular endothelium and skeletal muscle fibers, concentrated pLJ retrovirus containing cDNA for the heat-stable human placental alkaline phosphatase (hpAP) marker gene was infused into the rat hindlimb vasculature 4 days post-lidocaine administration. Rats receiving pLJhpAP retrovirus demonstrated significant hpAP transgene expression in endothelial cells and myocytes 21 days after the lidocaine injection (n = 6 muscles). In contrast, controls receiving pLJhpAP infusion without prior lidocaine administration failed to demonstrate any hpAP transgene expression. Lidocaine treatment evokes a substantially higher proliferative response than bFGF and, importantly, a durable angiogenic response in skeletal muscle. Thus, lidocaine is an ideal agent to induce angiogenesis in preparation for direct in vivo retroviral-mediated gene therapy targeting vascular endothelium.

Direct intramuscular gene transfer of naked DNA encoding vascular endothelial growth factor augments collateral development and tissue perfusion

BACKGROUND

Striated muscle has been shown to be capable of taking up and expressing foreign genes transferred in the form of naked plasmid DNA, although typically with a low level of gene expression. In the case of genes that encode secreted proteins, however, low transfection efficiency may not preclude bio-activity of the secreted gene product. Accordingly, we investigated the hypothesis that intramuscular (IM) gene therapy with naked plasmid DNA encoding vascular endothelial growth factor (VEGF) could augment collateral development and tissue perfusion in an animal model of hindlimb ischemia.

METHODS AND RESULTS

Ten days after ischemia was induced in one rabbit hindlimb, 500 micrograms of phVEGF165, or the reporter gene LacZ, was injected IM into the ischemic hindlimb muscles. Thirty days later, angiographically recognizable collateral vessels and histologically identifiable capillaries were increased in VEGF transfectants compared with controls. This augmented vascularity improved perfusion to the ischemic limb, documented by a superior calf blood pressure ratio for phVEGF165 (0.85 +/- 0.05) versus controls (0.64 +/- 0.05, P < .01), improved blood flow in the ischemic limb (measured with an intra-arterial Doppler wire) at rest (phVEGF165 = 21.3 +/- 3.9 mL/min, control = 14.6 +/- 1.6 mL/min, P < .01) and after a vasodilator (phVEGF165 = 54.2 +/- 12.0 mL/min, control = 37.3 +/- 8.9 mL/min, P < .01) and increased microspheres in the adductor (phVEGF165 = 4.3 +/- 1.6 mL.min-1.100 g of tissue-1, control = 2.9 +/- 1.2 mL.min-1.100 g of tissue-1, P < .05) and gastrocnemius (phVEGF165 = 3.9 +/- 1.0 mL.min-1.100 g of tissue-1, control = 2.8 +/- 1.4 mL.min-1.100 g of tissue-1, P < .05) muscles of the ischemic limb.

CONCLUSIONS

Ischemic skeletal muscle represents a promising target for gene therapy with naked plasmid DNA. IM transfection of genes encoding angiogenic cytokines, particularly those that are naturally secreted by intact cells, may constitute an alternative treatment strategy for patients with extensive peripheral vascular disease in whom the use of intravascular catheter-based gene transfer is compromised and/or prohibited.

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.

Basic fibroblast growth factor increases collateral blood flow in rats with femoral arterial ligation

The potential for exogenous infusion of basic fibroblast growth factor (bFGF) to increase collateral blood flow to dependent tissue was quantified in adult male rats with peripheral arterial insufficiency. Occlusion of the femoral artery at a proximal site did not infringe on resting blood flow to the distal hindlimb muscle, but did remove the blood flow reserve. Blood flow to the hindlimb muscles was measured with radiolabeled microspheres using an isolated hindlimb preparation perfused in the descending aorta (Krebs-Henseleit bicarbonate, 5% albumin medium containing red blood cells [40% hematocrit]) at 100 mm Hg. Calf muscle blood flow changed modestly (approximately equal to 50%) with infusion of only the carrier (heparin/saline), increased markedly over the first 2 weeks of bFGF infusion (1 microgram/d into the femoral artery), but did not change further with infusion for 4 weeks. Waiting 2 weeks after 1 week of bFGF infusion did not further increase the intermediate improvement in blood flow. The improved collateral blood flow and increased muscle capillary density likely contributed to the enhanced muscle performance observed during nerve stimulation in situ. X-ray films of arterial casts identified an expansion of upper thigh vessels that likely served as collaterals. In animals with peripheral arterial insufficiency, short-term exogenous infusion of bFGF is effective at inducing vascular expansion that is sufficient to improve the flow reserve of dependent distal tissue and enhance muscle function. This raises the expectation that a similar response in patients with peripheral arterial insufficiency would significantly improve morbidity, including the symptoms of intermittent claudication.

The effect of basic fibroblast growth factor on the blood flow and morphologic features of a latissimus dorsi cardiomyoplasty

Previous studies designed to determine whether latissimus cardiomyoplasty could be used to revascularize ischemic myocardium showed that after operation the latissimus was ischemic and had severely deteriorated. This study was undertaken to determine whether basic fibroblast growth factor, a potent angiogenic peptide, would improve the vascularity of the latissimus and enhance collateral formation between the muscle of the cardiomyoplasty and ischemic myocardium. In goats, myocardial ischemia was induced with an ameroid constrictor and cardiomyoplasty performed. The latissimus was continuously stimulated electrically at 2 Hz for 6 weeks and given four weekly bolus injections of human recombinant basic fibroblast growth factor (80 micrograms infused into the left subclavian artery). In eight animals, rates of regional blood flow were measured and both the heart and latissimus were evaluated histochemically. The latissimus blood flow rate was 0.114 +/- 0.029 ml/gm per minute, which was three times greater than that of historical controls (chronically stimulated latissimus cardiomyoplasty without basic fibroblast growth factor treatment; 0.042 +/- 0.007 ml/gm per minute, p < 0.05). Associated with the improved blood flow, there was significantly less evidence of skeletal muscle fiber dropout and muscle fibrosis in the animals treated with basic fibroblast growth factor. Latissimus-derived collateral flow to ischemic myocardium developed in five of the eight goats and averaged 0.288 +/- 0.075 ml/gm per minute. This flow was 42.8% +/- 15.7% (n = 5) of the flow required by normal myocardium (which was 0.728 +/- 0.095 ml/gm per minute). This value for latissimus-derived collateral blood flow was almost twice that of the historical controls (24.0% +/- 3.9%), but the increase did not achieve statistical significance (p = 0.08). These results hold the promise that basic fibroblast growth factor treatment might enhance the formation of extramyocardial collaterals to the heart and improve skeletal muscle function.

Basic fibroblast growth factor increases regional cerebral blood flow and reduces infarct size after experimental ischemia in a rat model

BACKGROUND AND PURPOSE

The aim of this study was to ascertain whether basic fibroblast growth factors (bFGF) caused reduction in size of cerebral infarcts in Sprague-Dawley rats with experimental ischemia.

METHODS

In the first experiment we induced permanent occlusion of the left middle cerebral artery (MCA). Within 5 minutes after MCA occlusion, we infused bFGF (100 ng in 0.1 mL of saline) in the bFGF-treated group (n = 14) and 0.1 mL of saline alone in the control group (n = 7) into the common carotid artery ipsilateral to MCA occlusion. We harvested the brains 24 hours after MCA occlusion and determined infarct size planimetrically as a percentage of hemisphere size. In the second experiment cerebral blood flow (CBF) was continuously measured for 120 minutes after MCA occlusion in the bFGF-treated group (n = 9) and in the control group (n = 8) with the use of laser-Doppler flowmetry.

RESULTS

Infarct size in the bFGF-treated group decreased significantly in comparison with that in the control group (repeated-measures ANOVA, P < .0001). CBF in the transitional areas between the MCA and the anterior cerebral artery significantly increased in the bFGF-treated group in comparison with that in the control group (repeated-measures ANOVA, P < .005). An approximate 58% decrease in infarct size and a 40% increase in regional CBF were seen on bFGF treatment.

CONCLUSIONS

The present study suggested that intracarotid administration of bFGF (100 ng) can reduce infarct size after MCA occlusion. It was speculated that the increased CBF in the penumbral areas of MCA may contribute to contraction of infarct size.

Synergistic effect of vascular endothelial growth factor and basic fibroblast growth factor on angiogenesis in vivo

BACKGROUND

Recent studies have suggested that vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) may have synergistic effects on the induction of angiogenesis in vitro. Therefore, we investigated the hypothesis that the simultaneous administration of VEGF and bFGF, each having been previously shown to independently enhance collateral development in an animal model of hind limb ischemia, could have a synergistic effect in vivo.

METHODS AND RESULTS

Ten days after surgical induction of unilateral hind limb ischemia, New Zealand White rabbits were randomized to receive either VEGF 500 micrograms alone (n = 6), bFGF 10 micrograms alone (n = 7), VEGF 500 micrograms, immediately followed by 10 micrograms bFGF (n = 7), or vehicle only (control animals, n = 8) in each case administered intra-arterially via a catheter in the internal iliac artery of the ischemic limb. BP ratio (BPR, ischemic/healthy limb) at day 10 for the VEGF+bFGF group was 0.82 +/- 0.01, much superior (P < .0005) to that of either the VEGF group (0.52 +/- 0.02) or the bFGF group (0.57 +/- 0.02). This outcome persisted at day 30: BPR in the VEGF+bFGF group (0.91 +/- 0.02) exceeded that of the control group (0.49 +/- 0.05, P < .0001), the VEGF group (0.65 +/- 0.03, P < .0005), or the bFGF group (0.66 +/- 0.03, P < .0005). Serial angiography demonstrated a progressive increase in luminal diameter of the stem collateral artery and the number of opacified collaterals in the thigh of the ischemic limbs in all groups. Stem artery diameter with VEGF+bFGF (1.34 +/- 0.07 mm) on day 30 was significantly (P < .05) greater than with either VEGF (1.09 +/- 0.09) or bFGF (1.18 +/- 0.06) alone. Capillary density was significantly greater (P < .05) in VEGF+bFGF animals (275 +/- 20 mm2) compared with VEGF (201 +/- 8) or bFGF (209 +/- 15).

CONCLUSIONS

Combined administration of VEGF and bFGF stimulates significantly greater and more rapid augmentation of collateral circulation, resulting in superior hemodynamic improvement compared with either VEGF or bFGF alone. This synergism of two angiogenic mitogens with different target cell specificities may have important implications for the treatment of severe arterial insufficiency in patients whose disease is not amenable to direct revascularization.

Synergistic effect of basic fibroblast growth factor and methylprednisolone on neurological function after experimental spinal cord injury

The authors evaluated the effects of exogenous basic fibroblast growth factor (bFGF) in combination with intravenous methylprednisolone on neurological function and cord angiogenesis in a model of spinal cord injury. Cord injury was produced by extradural clip compression through a T-1 laminectomy. Rats were randomized to one of six groups. Group A was given sham laminectomy without cord injury or treatment. The remaining animals were divided into five groups: untreated injury (Group B); injury treated with methylprednisolone (Group C); combined methylprednisolone and 1 microgram bFGF administered locally at the site of injury (Group D); methylprednisolone and 3 micrograms bFGF (Group E); or methylprednisolone and 3 micrograms heated bFGF (Group F). Groups C through F received treatment 1 hour after cord injury. At 1, 2, 3, and 4 weeks after surgery, neurological function of hindlimbs was assessed by blinded observers using an established multiple test method (toe spread, reflexes to extension, pain, and pressure as well as inclined plane and swim test) with tests graded and results expressed as a combined behavioral score. Animals were killed to study spinal cord angiogenesis in cord samples (2-mm sections proximal and distal to the injury site) by capillary density determination. Behavioral scores over time showed a significant difference among Groups B, C, D, E, and F (p = 0.0044), with Groups E and B maintaining highest and lowest scores, respectively. There was a linear dose effect of bFGF over time (p = 0.0187). At 4 weeks, scores showed a difference among the five groups (p = 0.006), with Group E showing higher scores than any other treatment group (for example, vs. group F: p = 0.035). There was a significant difference among the groups in gray matter capillary density counts: proximal (p = 0.0192) and distal (p = 0.024), whereas white matter capillary counts were similar across treatment groups. These results show: 1) possible synergism exists between methylprednisolone and bFGF, such that combinations of these drugs significantly enhance neurological recovery, 2) bFGF exhibits a dose-response effect in function but not in capillary density, and 3) heated, inactivated bFGF is not therapeutically effective.

Intrapericardial basic fibroblast growth factor induces myocardial angiogenesis in a rabbit model of chronic ischemia

The objective of this study was to determine whether basic fibroblast growth factor (bFGF), a known angiogenic factor, can promote new vessel growth when infused within the pericardial space in a model of chronic myocardial ischemia. Intravenous angiotensin II (AII) was infused to induce left ventricular hypertrophy and concomitant ischemia in New Zealand white rabbits. Basic FGF was infused into the intrapericardial space with an osmotic pump. Animals were assigned to one of four groups: group 1 received intrapericardial bFGF and intravenous AII, group 2 received intrapericardial bFGF and intravenous saline solution, group 3 received intrapericardial albumin and intravenous AII, and group 4 received intravenous AII only. Epicardial angiogenesis was graded histologically on a scale of 0 to 2. Animals receiving intravenous administration of AII displayed left ventricular hypertrophy that disproportionately affected the interventricular septum with a wall thickness of 5.62 +/- 1.00 mm versus 3.98 +/- 0.61 mm in the AII group and the saline solution control group, respectively (p < 0.005). A highly localized angiogenic effect of bFGF was observed. The mean angiogenesis scores were 1.9, 1.4, 1.3, and 0.2 (p < 0.001) with an angiogenesis score of 2 (marked increase in vascularity) noted in 86%, 40%, 43%, and 0% of hearts in groups 1 through 4, respectively. We conclude that intrapericardial bFGF enhances new epicardial small-vessel growth in a rabbit model; furthermore this effect is enhanced in the presence of left ventricular hypertrophy.

Ischaemia-induced expression of bFGF in normal skeletal muscle: a potential paracrine mechanism for mediating angiogenesis in ischaemic skeletal muscle

To test the hypothesis that induction of endogenous bFGF can lead to angiogenesis in ischaemic skeletal muscle, we studied the expression of bFGF after transposition of a well-vascularized muscle flap onto an ischaemic hindlimb in the rabbit. The results indicated a marked induction of bFGF mRNA throughout the myoblasts of the well-perfused muscle flap but not the myoblasts of the ischaemic muscle. bFGF protein was detected in the muscle flap, particularly in the myoblasts located closest to a newly formed, adjacent interface, and in the interface itself. In contrast, bFGF expression was not induced after transposition of a well-perfused muscle flap onto healthy muscle tissue. These data provide evidence that the juxtaposition of ischaemic skeletal muscle with healthy mesenchymal tissue triggers an increased expression of bFGF in the myoblasts of the well-perfused muscle. This paracrine induction of bFGF, in turn, leads to increased angiogenesis and regeneration of the ischaemic skeletal muscle.

Site-specific therapeutic angiogenesis after systemic administration of vascular endothelial growth factor

PURPOSE

Recent experimental studies have established the feasibility of therapeutic angiogenesis; in all cases, this has been achieved with local administration of angiogenic growth factors. This study was designed to investigate the hypothesis that systemic administration of an angiogenic growth factor specifically mitogenic for endothelial cells--vascular endothelial growth factor (VEGF)--could augment collateral vessel development in a rabbit ischemic hindlimb model.

METHODS

Ten days after the ligation of the external iliac artery and excision of the common and superficial femoral arteries in one limb of New Zealand white rabbits, heparin (800 IU, n = 13), VEGF (1 mg, n = 3; 5 mg, n = 5), heparin (800 IU) + VEGF (1 mg, n = 5; 5 mg, n = 7), or saline solution (n = 8) was injected as a single bolus in a marginal ear vein. Collateral vessel formation and limb perfusion were assessed 10 and 30 days after treatment.

RESULTS

Animals in both VEGF-treated groups had a significantly higher (p < 0.01) increase in calf blood pressure ratio at day 10 (control, 0.44 +/- 0.02; heparin, 0.47 +/- 0.02; VEGF, 0.60 +/- 0.01; heparin+VEGF, 0.61 +/- 0.02) and day 30 (control, 0.49 +/- 0.05; heparin, 0.48 +/- 0.02; VEGF, 0.70 +/- 0.03; heparin+VEGF, 0.73 +/- 0.03). Both VEGF-treated groups had a significantly higher (p < 0.05) angiographic score at day 30 (control, 0.28 +/- 0.01; heparin, 0.28 +/- 0.01; VEGF, 0.37 +/- 0.01; heparin+VEGF, 0.38 +/- 0.02). Maximum flow reserve at day 30 in the ischemic limb was higher (p < 0.05) in VEGF-treated rabbits (control, 1.87 +/- 0.07; heparin, 1.92 +/- 0.08; VEGF, 2.42 +/- 0.16; heparin+VEGF, 2.33 +/- 0.12). Capillary density was higher (p < 0.01) in the ischemic muscles of VEGF-treated rabbits (control, 156 +/- 10/mm2; heparin, 178 +/- 8/mm2; VEGF, 230 +/- 10/mm2; heparin+VEGF, 233 +/- 8/mm2).

CONCLUSIONS

This series of in vivo experiments demonstrates that intravenous administration of VEGF, with or without heparin, results in both anatomic and physiologic evidence of enhanced collateral vessel formation in the rabbit ischemic hindlimb. Single-bolus systemic administration of VEGF may be a feasible therapeutic strategy in patients with lower-extremity ischemia.

Enhanced revascularisation after angiogenic stimulation in a rabbit model of bilateral limb ischaemia

OBJECTIVE

We previously demonstrated stimulation of collateral vessel formation in a rabbit model of unilateral limb ischaemia after administration of endothelial cell growth factor (ECGF). To distinguish clearly the effects of ischaemia alone from those of ischaemia combined with angiogenic stimulation in the same animal, a model of bilateral hindlimb ischaemia was used to evaluate further the angiogenic effect of ECGF.

DESIGN

Ischaemia was produced in both hindlimbs of 11 rabbits by femoral artery excision. Beginning 10 days later, ECGF (8 mg in 3 ml of saline) was injected in one hindlimb while 3 ml of saline alone was injected in the other every other day for a total of five doses.

OUTCOME MEASURES

Calf systolic blood pressure was measured in both limbs on postoperative days, 10, 30, and 50. On day 50, collateral formation was quantitated angiographically, and muscle samples were obtained for quantitation of capillary density and histologic studies.

RESULTS

The mean calf systolic blood pressure in the both hindlimbs was similar on day 10 (36.9 +/- 2.3 versus 38.1 +/- 2.9 mmHg) but was significantly higher in the ECGF-treated limb on day 30 (68.9 +/- 3.1 versus 45.0 +/- 2.9 mmHg) and day 50 (83.0 +/- 3.0 versus 57.0 +/- 1.7; p < 0.0001 for both comparisons). On day 50, collateral vessels were significantly more numerous in the ECGF-treated limb (17.2 +/- 1.6 versus 11.0 +/- 0.8; p < 0.0006), as were capillaries (225.9 +/- 11.4 versus 159.6 +/- 12.9 per mm2; p < 0.002).

CONCLUSION

Local administration of ECGF enhanced collateral development leading to significantly improved perfusion in the treated as compared with the untreated limb in the same animal. Exogenous administration of an angiogenic mitogen can upregulate the normal collateral response to ischaemia and may be useful in treating severe limb ischaemia.

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

Surgically induced angiogenesis to compensate for hemodynamic cerebral ischemia

BACKGROUND AND PURPOSE

The ischemic brain may stimulate angiogenesis to compensate for impaired circulation. We examined the conditions promoting such angiogenesis to provide the basis for surgical treatment.

METHODS

The degree of cerebral hemodynamic stress was studied in patients with moyamoya disease using the stable xenon-enhanced computed tomographic acetazolamide tolerance test and positron emission tomography. Patients were subjected to surgery in which scalp arteries were placed on the cerebral cortex without vessel-to-vessel anastomosis. Formation of the newly vascularized collateral network connecting the implanted artery to cortical arteries was assessed angiographically 12 to 17 months after surgery.

RESULTS

Preoperative average resting cerebral blood flow for cortex that developed revascularization of cortical arteries was not significantly different from that for cortex that did not. However, cortex that developed revascularization had an average preoperative increase of blood flow by acetazolamide treatment of -3.29 +/- 4.6 mL/min per 100 cm3 (n = 20), which was significantly less (P = .0034) than that of cortex that did not show revascularization (20.7 +/- 4.3 mL/min per 100 cm3; n = 9). Good revascularization developed when the cortex showed increase of blood flow by acetazolamide treatment of less than 0 (steal phenomenon). Preoperative positron emission tomography data indicated that revascularization developed when the cortex was under "misery perfusion." Postoperative hemodynamics were ameliorated by revascularization.

CONCLUSIONS

Angiogenesis to connect the implanted scalp arteries to the cerebral cortical arteries was selectively initiated when ischemia of hemodynamic origin existed.

The development and enhancement of the collateral circulation in an animal model of lower limb ischaemia

In an animal model of hind limb ischemia we documented the levels of endogenous basic fibroblast growth factor (bFGF) in control and ischaemic hind limbs, and evaluated the response to the administration of exogenous recombinant bFGF and heparin. Variations in this model were tested for their ability to alter the development of the collateral circulation. Recovery after acute arterial occlusion was significantly delayed by immediate bilateral mirror-image arterial ligations, when compared with either unilateral arterial ligation or delayed contralateral ligations performed after 2 months. If the major veins were also occluded all limbs developed gangrene, tissue loss and a marked delay in the recovery of blood flow, while none of the animals with unilateral arterial ligations developed gangrene. This indicates that the recovery in blood flow during the acute phase in this model is dependent on collateral vessels from the contralateral iliac artery and that major venous occlusion impedes the development of collateral vessels. Lumbar sympathectomy did not alter the recovery of blood flow after arterial occlusion, suggesting that collateral blood flow is not significantly influenced by autonomic neural supply. Following arterial occlusion there was a ten-fold increase in the levels of endogenous bFGF in all ischaemic muscle groups. Intramuscular implantation of bFGF in heparin-sepharose pellets at the time of arterial ligation markedly enhanced the blood flow for 3 weeks compared with untreated ischaemic limbs. A further increment in blood flow occurred if an additional dose of bFGF was administered 4 weeks after ligation.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of PDGF-BB on the development of the collateral circulation after acute arterial occlusion

The survival of tissues in the presence of arterial occlusion is critically dependent on the development of collateral blood vessels. Identification of the biochemical mediators and their mechanism of action is fundamental to an understanding of the evolution of the collateral circulation. The ability of PDGF-BB to promote this was evaluated in an animal model of hind limb ischaemia. In order to obtain significant quantities of this mitogen for use in our animal model, human recombinant PDGF-BB was expressed in a Chinese Hamster Ovary (CHO) cell line. The transfected CHO cells produced 544 micrograms/l of PDGF-BB in serum free medium (SFM). The 30 kDa form of PDGF-BB was purified to homogeneity as judged by silver staining and amino-acid sequencing. Purified PDGF-BB was shown to be bioactive by a cell proliferation assay. The exogenous administration of PDGF-BB enhanced the recovery of blood flow after acute arterial occlusion. The results suggest that PDGF-BB may have therapeutic value in promoting collateral development following arterial occlusion.