Angiogenesis — a New Goal in Peripheral Artery Occlusive Disease Therapy

The vasculature is mostly quiescent in the normal adult, with the exception of the growth of new blood vessels during the female reproductive cycle. Recent advances in the knowledge concerning the molecular changes and the identification of genetic events in this vascular quiescence, as well as in vascular growth, has led to an increasing number of studies in which these phenomena are manipulated. Angiogenesis is the growth of new vessels from existing ones. Although new vessel formation is involved in many pathologic situations, like tumour growth, therapeutic angiogenesis has been presented as a novel method for the treatment of ischemic diseases, like peripheral arterial occlusive disease (PAOD).

In experimental studies therapeutic angiogenesis has been produced by recombinant growth-factor protein application as well as by growth factor gene therapy. Most widely studied factors belong to vascular endothelial growth factor (VEGF) or fibroblast growth factor (FGF) families. Studies have also shown that, angiogenic growth factors stimulate endothelial cell migration and accelerate endothelial repair by enhancing post-injury re-endothelization. In clinical studies angiogenic therapy has been evaluated in patients with severe vascular diseases. The results have revealed that therapy is well tolerated as well as safe and that angiogenic therapy has a clear biologic effect. However, controlled studies are still needed to answer the question whether therapeutic angiogenesis offers a real clinical benefit to patients with PAOD.     

Tumor angiogenesis: the pivotal role of vascular endothelial growth factor

Summary There is considerable evidence that vascular endothelial growth factor is involved in the vascularization and growth of primary tumors and in the formation of metastases. The expression of vascular endothelial growth factor depends on activated oncogenes and inactivated tumor-suppressor genes as well as several other factors, e.g., growth factors, hypoxia, and tumor promoters. Substantial expression of vascular endothelial growth factor receptors is mainly restricted to tumor vessels. The causal involvement of this angiogenic factor in the progression of the disease has been successfully evaluated using monoclonal antibodies against vascular endothelial growth factor, dominant negative receptor mutants, and antisense oligonucleotides against the messenger RNA of vascular endothelial growth factor. Thus, the vascular endothelial growth factor-signaling system seems to be an appropriate target for inhibition of tumor angiogenesis and metastasis formation.     

Tumor angiogenesis: molecular facts and therapeutic opportunities

Solid tumors do not grow beyond a size of a few millimetres without supply of nutrients and growth factors by the vascular system. Only when tumors produce angiogenic growth factors new vessels are formed by sprouting of capillaries from the existing vascular system. The tumor can grow and tumor cells reach the circulation through these new and permeable vessels. The vascular endothelial growth factor (VEGF) is the most prominent angiogenic growth factor. VEGF is produced by almost all solid tumors: its receptors are expressed only on vascular endothelial cells and predominantly in vessels in the proximity of the tumor. Therefore, the VEGF/VEGF-receptor system is a target for anti-angiogenic cancer therapy. Experiments show that inhibition of the VEGF-mediated endothelial cell activation interferes with tumor growth and metastases formation. Appropriate therapeutic strategies are currently under clinical investigation.     

Tumor angiogenesis: molecular facts and therapeutic opportunities

Summary. Solid tumors do not grow beyond a size of a few millimetres without supply of nutrients and growth factors by the vascular system. Only when tumors produce angiogenic growth factors new vessels are formed by sprouting of capillaries from the existing vascular system. The tumor can grow and tumor cells reach the circulation through these new and permeable vessels. The vascular endothelial growth factor (VEGF) is the most prominent angiogenic growth factor. VEGF is produced by almost all solid tumors: its receptors are expressed only on vascular endothelial cells and predominantly in vessels in the proximity of the tumor. Therefore, the VEGF/VEGF-receptor system is a target for anti-angiogenic cancer therapy. Experiments show that inhibition of the VEGF-mediated endothelial cell activation interferes with tumor growth and metastases formation. Appropriate therapeutic strategies are currently under clinical investigation.      

Growth factors for therapeutic angiogenesis in hypercholesterolemic erectile dysfunction

The past decade has seen an explosion of new information on the physiology of penile erection, and pathophysiology of erectile dysfunction （ED）. Hypercholesterolemia is a chronic condition that can lead to degeneration in the vasculature bed and can result in ED if the penile vasculature is involved. Angiogenesis is the growth of new blood vessels from preexisting vasculature. Therapeutic angiogenesis seeks to harness the mechanisms of vascular growth to treat disorders of inadequate tissue perfusion, such as coronary artery disease and ED. There have been tremendous changes in the field of therapeutic angiogenesis over the past decade, and there is much promise for the future. Initial preclinical work with cytokine growth factor delivery resulted in a great deal of enthusiasm for the treatment of ischemic heart and/or peripheral vascular disease, though clinical studies have not achieved similar success. With an increased understanding of the complex mechanisms involved in angiogenesis, novel therapies which target multiple different angiogenic pathways are also being developed and tested. The penis is a convenient tissue target for gene therapy because of its external location and accessibility, the ubiquity of endothelial lined spaces, and low level of blood flow, especially in the flaccid state. Therapeutic angiogenesis is an exciting field that continues to evolve. This review will focus on the development of growth factors for hypercholesterolemic ED, the use of various growth factors for ED therapy, their routes of delivery, and the results in animal studies.     

A targeted approach for antiangiogenic therapy of metastatic human colon cancer

The realization that the growth and spread of tumors are dependent on angiogenesis has created new avenues of research designed to help us to better understand cancer biology and to facilitate the development of new therapeutic strategies. However, the process of angiogenesis consists of multiple sequential and interdependent steps with a myriad of positive and negative regulators of angiogenesis being involved. The survival of tumors and thus their metastases are dependent on the balance of endogenous angiogenic and antiangiogenic factors such that the outcome favors increased angiogenesis. Several growth factors have been identified that regulate angiogenesis in colon cancer; the most important of these is vascular endothelial growth factor. In addition, specific integrins such as alphavbeta3 and alpha5beta1 mediate endothelial cell survival and have been shown to be overexpressed on the endothelium of colon cancer. These angiogenic mediators thus serve as targets for therapy of metastatic colon cancer and have shown promise in preclinical trials.     

Vascular growth factors and angiogenesis in cardiac surgery

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 administration of angiogenic growth factors has been demonstrated in animal models of chronic myocardial ischemia. Recently, preliminary clinical trials using growth factor proteins or genes encoding these angiogenic factors have demonstrated clinical and other objective evidence of relevant angiogenesis. A recent study reported beneficial long-term effects of therapeutic angiogenesis using fibroblast growth factor (FGF)-2 protein in terms of freedom from angina and perfusion on single-photon emission computed tomographic imaging. Thus, therapeutic angiogenesis has the potential to extend treatment options to patients who are not optimal candidates for conventional methods of myocardial revascularization. However, endogenous antiangiogenic influences, intrinsic lack of response of patients with severe endothelial dysfunction, and other limitations will need to be overcome before angiogenesis becomes a standard therapy for the treatment of patients with severe coronary disease.     

血管内皮生长因子与治疗性血管生成研究进展

血管内皮生长因子(vascular endothelial growtll factor,VEGF)是内皮细胞特异的有丝分裂原,有促进内皮细胞增生、增强血管通透性、加速新血管形成的作用.血管生成是一个具有重要生理、病理意义的过程.在人体的创伤愈合、炎症反应、器官再生过程以及肿瘤生长转移、血管增生性疾病中,血管生成有重要作用.治疗性血管生成是指利用成血管诱导因子或内皮祖细胞,模拟体内血管生成机制,促进新生血管形成,改善侧支循环.本文就VEGF和治疗性血管生成研究进展做一综述.     

Up-regulation of vascular endothelial growth factor mRNA and angiogenesis after transmyocardial laser revascularization.

BACKGROUND: Angiogenesis has been proposed as a potential mechanism whereby transmyocardial laser revascularization (TMLR) has provided clinical relief of angina. Experimental work has found histologic evidence supporting this, as well as an improved response when angiogenic growth factors have been added to TMLR. The purpose of this study was to demonstrate that the molecular response to TMLR was an increase in the production of endogenous vascular endothelial growth factor to promote angiogenesis. METHODS: Ameroid constrictors were placed on the proximal circumflex artery in 12 domestic pigs. After a chronic ischemic zone was established the animals were randomly divided into two groups. In the TMLR group the ischemic zone was treated with carbon dioxide laser. In the control group the ischemic zone was untreated. Six weeks later the animals were sacrificed, and sections from the ischemic zone and the nonischemic zone were submitted for immunohistochemical, histologic, and molecular analysis. Messenger RNA was obtained from northern blot analysis after being probed with vascular endothelial growth factor. RESULTS: There was a twofold increase in the vascular endothelial growth factor messenger RNA in the ischemic zone of the TMLR group compared with the control group. Additionally, there was a threefold increase in the number of new blood vessels in the ischemic zone of the TMLR group compared with the control group. CONCLUSIONS: Transmyocardial laser revascularization promotes angiogenesis by upregulation of vascular endothelial growth factor. The resulting angiogenesis could be the principle mechanism for the clinical efficacy of TMLR.     

Differential effects of vascular growth factors on arterial and venous angiogenesis

OBJECTIVE: Angiogenesis, the development of new blood vessels, has become an area of increased interest for both scientific and clinical application purposes. Proangiogenic agents, such as vascular endothelial growth factor (VEGF) and naltrexone, have been shown to effectively induce new blood vessel growth. Other growth factors, such as the endogenous opioid growth factor (OGF; [Met(5)]-enkephalin) and retinoic acid, are inhibitors of angiogenesis. The differential effects on veins and arteries, however, by any vascular growth factor, have not previously been investigated. METHODS: The chick chorioallantoic membrane (CAM) assay was used for the in vivo quantitation of angiogenesis. After 3 days of incubation, fertilized chick embryos were explanted, and a 3.2-mm methylcellulose disk containing either the known angiogenic stimulators VEGF (0.2 microg, 1.0 microg) or naltrexone (0.1 microg, 5.0 microg), or the angiogenic inhibitors OGF (1.0 microg, 5.0 microg) or retinoic acid (1.0 microg) was placed onto the CAM surface. An equal volume of distilled water served as a control. After 2 days of growth, the CAM arteries and veins were identified, and images were obtained with a digital camera. Quantitative analysis of angiogenesis was performed on a 100-mm(2) area surrounding the applied disk, and the number and length of the veins and arteries were measured. RESULTS: The angiogenic stimulators VEGF and naltrexone markedly increased both the total number and length of all blood vessels as compared with control values. The mean length of blood vessels decreased, suggesting the induction of new vessel growth. VEGF and naltrexone proportionately increased vein and arterial angiogenesis, maintaining artery/vein ratios for vessel number and length that were unchanged compared with controls. The angiogenic inhibitors, OGF and retinoic acid, notably decreased the total number and length of blood vessels in the CAM preparations. However, these compounds had a disproportionately greater inhibitory effect on arterial angiogenesis as reflected in decreased artery/vein ratios for vessel number and length. CONCLUSIONS: The angiogenic stimulators VEGF and naltrexone induce development of veins and arteries in a proportional manner. In contrast, the angiogenic inhibitors OGF and retinoic acid demonstrated a greater inhibitory effect on arterial as compared with venous angiogenesis. Such differential effects on angiogenesis may be important in both defining mechanisms of action and designing therapeutic interventions.     

Therapeutic angiogenesis in peripheral arterial disease: can biotechnology produce an effective collateral circulation?

The physiological processes of angiogenesis, vasculogenesis and arteriogenesis contribute to the growth of collateral vessels in response to obstructive arterial disease causing lower limb or myocardial ischaemia, but in clinical practice the endogenous angiogenic response is often suboptimal or impaired, e.g. by factors such as ageing, diabetes or drug therapies. Therapeutic angiogenesis is an application of biotechnology to stimulate new vessel formation via local administration of pro-angiogenic growth factors in the form of recombinant protein or gene therapy, or by implantation of endothelial progenitor cells that will synthesize multiple angiogenic cytokines. Numerous experimental and clinical studies have sought to establish 'proof of concept' for therapeutic angiogenesis in PAD and myocardial ischaemia using different treatment modalities, but the results have been inconsistent. This review summarises the mechanisms of angiogenesis and the results of recent trials evaluating the efficacy and safety of different gene therapy, recombinant protein and cellular-based treatment approaches to enhance collateral vessel formation.     

New insights in synovial angiogenesis

Angiogenesis is the formation of new capillaries from pre-existing vessels. A number of soluble and cell-bound factors may stimulate neovascularization. The perpetuation of angiogenesis involving numerous soluble and cell surface-bound mediators has been associated with rheumatoid arthritis (RA). These angiogenic mediators, among others, include growth factors, primarily vascular endothelial growth factor (VEGF) and hypoxia-inducible factors (HIFs), as well as pro-inflammatory cytokines, various chemokines, cell adhesion molecules, proteases and others. Among the several potential angiogenesis inhibitors, targeting of VEGF, HIF-1, angiopoietin and the α_Vβ₃ integrin, as well as some endogenous or synthetic compounds including angiostatin, endostatin, paclitaxel, fumagillin analogues, 2-methoxyestradiol and thalidomide seems to be promising for the management of synovial inflammation and angiogenesis. A complete review of antiangiogenic drugs used in animal models of arthritis or human RA is available in a table.     

Clinical significance of angiogenesis in gastrointestinal cancers: a target for novel prognostic and therapeutic approaches

OBJECTIVE: To review the current data on the prognostic and therapeutic implications of tumor angiogenesis in gastrointestinal cancers. SUMMARY BACKGROUND DATA: Numerous studies have evaluated the prognostic value of tumor angiogenesis and the potential role of antiangiogenic therapy in various gastrointestinal cancers. METHODS: A Medline literature search was conducted using "angiogenesis" or the names of various angiogenic factors in combination with the names of gastrointestinal cancers as the key words. RESULTS: Several studies have demonstrated a significant prognostic impact of tumor microvessel density and tumor expression of angiogenic factors, in particular vascular endothelial growth factor (VEGF), in various gastrointestinal cancers. A few studies have suggested that circulating VEGF might be a useful prognostic marker. However, results were not consistent across all studies and were limited by the retrospective nature of most studies. Antiangiogenic therapy has been shown to be effective against all common gastrointestinal cancers in preclinical studies, but currently there are few clinical data with regard to antiangiogenic therapy in gastrointestinal cancers. CONCLUSIONS: There is mounting evidence to suggest that assessment of tumor angiogenesis might provide a novel approach of prognostication in patients with gastrointestinal cancers. However, current results from retrospective studies need to be validated by prospective studies. Antiangiogenic therapy is a promising strategy of cancer treatment that might be particularly useful in combination therapy for unresectable cancers or as an adjuvant therapy for resectable tumors.     

Relaxin induces vascular endothelial growth factor expression and angiogenesis selectively at wound sites

Relaxin is a reproductive hormone that has historically been characterized as being responsible for pubic ligament loosening and cervical ripening. Recently, relaxin has been associated with neovascularization of the endometrial lining of the uterus, potentially via specific induction of vascular endothelial growth factor. Previously conducted clinical studies using partially purified porcine relaxin have described relaxin's ability to stimulate the healing of ischemic wounds, suggesting that relaxin may also have angiogenic effects at sites of ischemic wound healing. In the present study, relaxin's angiogenic effects in the context of wound repair were tested in rodent models of angiogenesis and wound healing. Relaxin showed an ability to stimulate new blood vessel formation, particularly at ischemic wound sites, and to induce both vascular endothelial growth factor and basic fibroblast growth factor specifically in cells, presumably including macrophages, collected from wound sites. Resident macrophages collected from nonwound sites, such as the lung, did not show altered expression of these cytokines following relaxin administration. Because angiogenic wound cells are frequently macrophages, THP-1 cells, a cell line of monocyte lineage that binds relaxin specifically, were tested for and shown to induce vascular endothelial growth factor and basic fibroblast growth factor in response to relaxin. In conclusion, relaxin may be useful in the treatment of ischemic wounds by stimulating angiogenesis via the induction of vascular endothelial growth factor and basic fibroblast growth factor in wound macrophages.     

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.     

Therapeutic angiogenesis for coronary artery disease

Therapeutic angiogenesis may be a realistic approach in treating ischemic heart disease. VEGF is a major angiogenic factor involved in physiological as well as pathological angiogenesis. The ability of VEGF to promote angiogenesis in animal and clinical studies has been studied extensively. However, it is becoming clear that VEGF alone may not be sufficient to effectively complete the angiogenesis process. The use of more than one growth factor may be more pertinent in creating a sustainable angiogenic effect with clinically significant outcome. The challenge is to find complementary partners in angiogenesis to better affect the outcome of the process. To this end, we have been studying the effects of other angiogenic factors such as angiopoietin-1 (Ang-1) in a chronic ischemic porcine model. Single intramyocardial introduction of adenovirus-mediated gene transfer of Ang-1 into the left ventricle free wall has been found to enhance angiogenesis by augmenting the formation of new capillaries that manifested in improved total blood flow in the myocardium. A combined therapeutic angiogenesis study involving VEGF and Ang-1 is currently underway. Due to their unique complementary properties, it is expected that the combination will not merely enhance angiogenesis but will also lead to healthy and mature vascular network in the ischemic myocardium.     

Angiogenesis and gliomas: current issues and development of surrogate markers

Despite significant improvements, current therapies have yet to cure infiltrative gliomas. Glioma progression is strongly dependent on the development of a new vascular network that occurs primarily by angiogenesis. Hypoxia and genetic anomalies within a glioma trigger the angiogenic switch, thus upregulating angiogenic factors and downregulating antiangiogenic factors. The main factors indicative of angiogenesis are now well known, and more recently, differences based on grade and subtype have been reported. New data also indicate a potential role for postnatal vasculogenesis with bone marrow endothelial progenitors in addition to angiogenesis in tumor vascular development. All of these factors may have therapeutic implications. Antiangiogenic therapies are presently being developed; more than 80 trials are ongoing. Initial results indicate that epidermal growth factor receptor inhibitors, anti-metalloproteases, and thalidomide do not demonstrate strong anti-tumor activity. Thus, antiangiogenic agents combined with conventional therapies and second-generation antiangiogenic drugs for targeting multiple molecular pathways are presently being tested. Clinical experience also demonstrates the failure of conventional imaging to monitor these new approaches accurately. New advances in the design of surrogate markers for angiogenesis have been reported for both magnetic resonance and molecular imaging techniques. This article summarizes the mechanisms of the angiogenic switch based on tumor grade and subtype, reviews completed and ongoing clinical trials, and details the present and the future of surrogate markers for angiogenesis in gliomas.     

The Mammary Gland Vasculature Revisited

Concomitant with the extensive growth and differentiation of the mammary epithelium during pregnancy and lactation, and epithelial involution after weaning, the vasculature of the mammary gland undergoes repeated cycles of expansion and regression. Vascular expansion is effected by sprouting angiogenesis, intussusception and conceivably also vasculogenesis. The capacity of the epithelial cells to stimulate vascular growth and differentiation is dependent on the constellation of systemic and local hormones and growth factors as well as the changing demands for oxygenation and nutrient supply. This results in the release of angiogenic factors which stimulate endothelial cell growth and regulate vascular architecture. In contrast to the angiogenic phase of the mammary gland cycle, little is known about the control of vascular regression although this would possibly offer new insights into therapeutic possibilities against breast cancer. In this review we summarize knowledge regarding the mechanisms regulating the vasculature of the mammary gland and delineate the importance of the vasculature in the attainment of organ function. In addition, we discuss the angiogenic mechanisms observed during mammary carcinogenesis and their consequences for breast cancer therapy.