Therapeutic angiogenesis: Translating experimental concepts to medically relevant goals

Toward the Clinical Application of Therapeutic Angiogenesis Against Pediatric Ischemic Retinopathy

Therapeutic angiogenesis refers to strategies of inducing angiogenesis to treat diseases involving ischemic conditions. Historically, most attempts and achievements have been related to coronary and peripheral artery diseases. In this review, we propose the clinical application of therapeutic angiogenesis for the treatment of pediatric ischemic retinopathy, including retinopathy of prematurity, familial exudative retinopathy, and NDP-related retinopathy. These diseases are all characterized by the reduction of physiological angiogenesis and the following induction of pathological angiogenesis. Therapeutic angiogenesis, which supplements insufficient physiological angiogenesis, may be a therapeutic approach for ischemic conditions. Various molecules and modalities can be utilized to apply therapeutic angiogenesis for the treatment of ischemic retinopathy, as in coronary and peripheral artery diseases. Experiences with cardiovascular diseases provide a useful reference for the further clinical application of therapeutic angiogenesis in pediatric ischemic retinopathy. Recombinant proteins and gene therapy are powerful tools to deliver angiogenic factors to retinal tissues directly. Furthermore, endothelial progenitor or bone marrow-derived cells can be injected into the vitreous cavity of the eye for therapeutic angiogenesis. Intraocular injections are highly promising for the delivery of therapeutics for therapeutic angiogenesis. We expect that therapeutic angiogenesis will be a breakthrough in the treatment of pediatric ischemic retinopathy.

Isosorbide mononitrate promotes angiogenesis in embryonic development of zebrafish

Coronary heart disease (CHD) is a leading cause of death worldwide, and angiogenesis plays important roles in CHD. Thus, in the present study, the angiogenic efficacy of four common cardiovascular medicines (aspirin, pravastatin, metoprolol and isosorbide mononitrate (ISMN)) was determined by the number and length of zebrafish intersegmental vessels (ISVs) after immersing zebrafish embryos in different medicines. Results showed that ISMN significantly increased the length and number of ISVs. ISMN is a long-acting nitrate ester drug. It has been used as a vasodilator to dilate arteries and veins to reduce the cardiac preload and postload. However, the effect of ISMN on angiogenesis remains unclear. Thus, by in vitro experiments, the angiogenic mechanism of ISMN was evaluated through detecting the viability and proliferation of human umbilical vein endothelial cells (HUVECs) and the expression of angiogenesis-related genes and miRNAs. Results indicated that ISMN could increase the viability and proliferation of HUVECs by decreasing apoptosis, and elevated the expressions of vedf, kdrl, pdgfr in zebrafish embryos. Furthermore, the expressions of miR-126, miR-130a and miR-210 were also regulated in ISMN-treated HUVECs. In conclusion, ISMN could promote angiogenesis in zebrafish embryos and HUVECs, implying ISMN may be a potential therapeutic in treating angiogenesis-related diseases.

Nerve growth factor in metabolic complications and Alzheimer's disease: Physiology and therapeutic potential

As the population ages, obesity and metabolic complications as well as neurological disorders are becoming more prevalent, with huge economic burdens on both societies and families. New therapeutics are urgently needed. Nerve growth factor (NGF), first discovered in 1950s, is a neurotrophic factor involved in regulating cell proliferation, growth, survival, and apoptosis in both central and peripheral nervous systems. NGF and its precursor, proNGF, bind to TrkA and p75 receptors and initiate protein phosphorylation cascades, resulting in changes of cellular functions, and are associated with obesity, diabetes and its complications, and Alzheimer's disease. In this article, we summarize changes in NGF levels in metabolic and neuronal disorders, the signal transduction initiated by NGF and proNGF, the physiological and pathophysiological relevance, and therapeutic potential in treating chronic metabolic diseases and cognitive decline.

MiR-4674 regulates angiogenesis in tissue injury by targeting p38K signaling in endothelial cells

Neoangiogenesis is critical for tissue repair in response to injury such as myocardial ischemia or dermal wound healing. MicroRNAs are small noncoding RNAs and important regulators of angiogenesis under physiological and pathological disease states. Therefore, identification of microRNAs that may restore impaired angiogenesis in response to tissue injury may provide new targets for therapy. Using a microRNA microarray profiling approach, we identified a human-specific microRNA, miR-4674, that was significantly decreased in patients after myocardial tissue injury and had an endothelial cell (EC)-enriched expression pattern. Functionally, overexpression of miR-4674 markedly attenuated EC proliferation, migration, network tube formation, and spheroid sprouting, whereas blockade of miR-4674 had the opposite effects. Transcriptomic profiling, gene set enrichment analyses, bioinformatics, 3'-untranslated region (3'-UTR) reporter and microribonucleoprotein immunoprecipitation (miRNP-IP) assays, and small interfering RNA dependency studies revealed that miR-4674 regulates VEGF stimulated-p38 mitogen-activated protein kinase (MAPK) signaling and targets interleukin 1 receptor-associated kinase 1 (Irak1) and BICD cargo adaptor 2 (Bicd2) in ECs. Furthermore, Irak1 and Bicd2 were necessary for miR-4674-driven EC proliferation and migration. Finally, neutralization of miR-4674 increased angiogenesis, Irak1 and Bicd2 expression, and p38 phosphorylation in human skin organoids as a model of tissue injury. Collectively, targeting miR-4674 may provide a novel therapeutic target for tissue repair in pathological disease states associated with impaired angiogenesis.

Evaluation of a new model of hind limb ischemia in rabbits

OBJECTIVE

Various animal models of critical limb ischemia have been developed in the past. However, there is no animal model that can undergo endovascular treatment, while providing reproducible true critical limb ischemia with arterial ulcers and rest pain. We evaluated the efficacy of a new model of rabbit hindlimb ischemia created through a percutaneous approach using embolization with calibrated particles.

METHODS

Through a percutaneous transauricular artery approach and selective catheterization of the superficial femoral artery, embolization of distal limb vessels was performed using a mixture of 300- to 500-μm calibrated microparticles (Embosphere, Merit Medical, Salt Lake City, Utah), saline solution, and iodine contrast. Clinical and ultrasound imaging-based blood flow evaluation was performed before embolization and during follow-up. Histologic evaluation was performed at humane killing 14 days after the procedure.

RESULTS

The model was successfully created in 10 rabbits (10 limbs). One rabbit died of sudden death at 8 days after the procedure. The nine surviving rabbits developed hind ulcers. All rabbits had a higher pain score in the follow-up compared to baseline value (P < .0001). Blood flow in the saphenous artery decreased significantly after the procedure and later at 14 days follow-up (baseline value 63.4 ± 31.3 μL per cardiac cycle vs 32.0 ± 28.4 μL per cardiac cycle postprocedure [P = .0013] and 32.0 ± 28.4 μL per cardiac cycle at 14 days [P = .0015]). Pathology showed signs of severe limb ischemia in all rabbits with subacute and chronic injury patterns.

CONCLUSIONS

A rabbit hind limb ischemia model created by percutaneous transauricular distal femoral artery embolization with calibrated particles may overcome some of the limitations of existing animal models. As such, this model could prove useful for assessing therapies designed to improve arterial perfusion and collateral growth.

Cardiomyocyte and Vascular Smooth Muscle-Independent 11β-Hydroxysteroid Dehydrogenase 1 Amplifies Infarct Expansion, Hypertrophy, and the Development of Heart Failure After Myocardial Infarction in Male Mice

Global deficiency of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), an enzyme that regenerates glucocorticoids within cells, promotes angiogenesis, and reduces acute infarct expansion after myocardial infarction (MI), suggesting that 11β-HSD1 activity has an adverse influence on wound healing in the heart after MI. The present study investigated whether 11β-HSD1 deficiency could prevent the development of heart failure after MI and examined whether 11β-HSD1 deficiency in cardiomyocytes and vascular smooth muscle cells confers this protection. Male mice with global deficiency in 11β-HSD1, or with Hsd11b1 disruption in cardiac and vascular smooth muscle (via SM22α-Cre recombinase), underwent coronary artery ligation for induction of MI. Acute injury was equivalent in all groups. However, by 8 weeks after induction of MI, relative to C57Bl/6 wild type, globally 11β-HSD1-deficient mice had reduced infarct size (34.7 ± 2.1% left ventricle [LV] vs 44.0 ± 3.3% LV, P = .02), improved function (ejection fraction, 33.5 ± 2.5% vs 24.7 ± 2.5%, P = .03) and reduced ventricular dilation (LV end-diastolic volume, 0.17 ± 0.01 vs 0.21 ± 0.01 mL, P = .01). This was accompanied by a reduction in hypertrophy, pulmonary edema, and in the expression of genes encoding atrial natriuretic peptide and β-myosin heavy chain. None of these outcomes, nor promotion of periinfarct angiogenesis during infarct repair, were recapitulated when 11β-HSD1 deficiency was restricted to cardiac and vascular smooth muscle. 11β-HSD1 expressed in cells other than cardiomyocytes or vascular smooth muscle limits angiogenesis and promotes infarct expansion with adverse ventricular remodeling after MI. Early pharmacological inhibition of 11β-HSD1 may offer a new therapeutic approach to prevent heart failure associated with ischemic heart disease.

miRNAs in post-ischaemic angiogenesis and vascular remodelling

miRNAs are highly conserved non-coding RNA molecules that negatively control gene expression by binding to target mRNAs promoting their degradation. A multitude of miRNAs have been reported to be involved in angiogenesis and vascular remodelling. In the present review, we aim to describe the effect of miRNAs in post-ischaemic repair. First, we describe the miRNAs reported in ischaemic diseases and in angiogenesis. Then we examine their capacity to modulate the behaviour of stem and progenitor cells which could be utilized for vascular repair. And finally we discuss the potential of miRNAs as new clinical biomarkers and therapeutic targets.

Arterial baroreflex dysfunction impairs ischemia-induced angiogenesis

Background

Endothelium‐derived acetylcholine (eACh) plays an important role in the regulation of vascular actions in response to hypoxia, whereas arterial baroreflex (ABR) dysfunction impairs the eACh system. We investigated the effects of ABR dysfunction on ischemia‐induced angiogenesis in animal models of hindlimb ischemia with a special focus on eACh/nicotinic ACh receptor (nAChR) signaling activation.

Methods and Results

Male Sprague‐Dawley rats were randomly assigned to 1 of 3 groups that received (1) sham operation (control group), (2) sinoaortic denervation (SAD)‐induced ABR dysfunction (SAD group), or (3) SAD rats on diet with an acetylcholinesterase inhibitor pyridostigmine (30 mg/kg per day, SAD+Pyr group). After 4 weeks of the SAD intervention, unilateral limb ischemia was surgically induced in all animals. At postoperative day 14, SAD rats exhibited impaired angiogenic action (skin temperature and capillary density) and decreased angiogenic factor expressions (vascular endothelial growth factor [VEGF] and hypoxic inducible factor [HIF]‐1α) in ischemic muscles. These changes were restored by acetylcholinesterase inhibition. Rats with ABR dysfunction had lower eACh levels than did control rats, and this effect was recovered in SAD+Pyr rats. In α7‐nAChR knockout mice, pyridostigmine improved ischemia‐induced angiogenic responses and increased the levels of VEGF and HIF‐1α. Moreover, nicotinic receptor blocker inhibited VEGF expression and VEGF receptor 2 phosphorylation (p‐VEGFR2) induced by ACh analog.

Conclusions

Thus, ABR dysfunction appears to impair ischemia‐induced angiogenesis through the reduction of eACh/α7‐nAChR‐dependent and ‐independent HIF‐1α/VEGF‐VEGFR2 signaling activation.

Pronerve growth factor induces angiogenesis via activation of TrkA: possible role in proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is the leading cause of blindness in working age Americans. We demonstrated that diabetes disturbs the homeostasis of nerve growth factor (NGF) resulting in accumulation of its precursor proNGF. Increases in proNGF were positively correlated with progression of diabetic retinopathy, having the highest level in ocular fluids from PDR patients compared to nondiabetic patients. Here, we attempted to evaluate the contribution and the possible mechanism of proNGF to PDR. The angiogenic response of aqueous humor samples from PDR patients was examined in human retinal endothelial cells in the presence or absence of anti-proNGF antibody. Additional cultures were treated with mutant-proNGF in the presence of specific pharmacological inhibitors of TrkA and p75(NTR) receptors. PDR-aqueous humor samples exerted significant angiogenic response including cell proliferation, migration, and alignment into tube-like structures. These effects were significantly reduced by anti-proNGF antibody but not by IgG. Treatment of retinal endothelial cells with mutant-proNGF activated phosphorylation of TrkA and p38MAPK; however, it did not alter p75(NTR) expression. Inhibition of TrkA but not p75(NTR) significantly reduced mutant-proNGF-induced cell proliferation, cell migration, and tube formation. Taken together, these results provide evidence that proNGF can contribute to PDR at least in part via activation of TrkA.

MicroRNAs in Postischemic Vascular Repair

The term angiogenesis describes the growth of endothelial sprouts from preexisting postcapillary venules. More recently, this term has been used to generally indicate the growth and remodeling process of the primitive vascular network into a complex network during development. In adulthood, angiogenesis is activated as a reparative process during wound healing and following ischemia, and it plays a key role in tumor growth and metastasis as well as in inflammatory diseases and diabetic retinopathy. MicroRNAs (miRNAs) are endogenous, small, noncoding RNAs that negatively control gene expression of target mRNAs. In this paper, we aim at describing the role of miRNAs in postischemic angiogenesis. First, we will describe the regulation and the expression of miRNAs in endothelial cells. Then, we will analyze the role of miRNAs in postischemic vascular repair. Finally, we will discuss the role of circulating miRNAs as potential biomarkers in ischemic diseases.

Inorganic nitrite and chronic tissue ischaemia: a novel therapeutic modality for peripheral vascular diseases

Ischaemic tissue damage represents the ultimate form of tissue pathophysiology due to cardiovascular disease, which is the leading cause of morbidity and mortality across the globe. A significant amount of basic research and clinical investigation has been focused on identifying cellular and molecular pathways to alleviate tissue damage and dysfunction due to ischaemia and subsequent reperfusion. Over many years, the gaseous molecule nitric oxide (NO) has emerged as an important regulator of cardiovascular health as well as protector against tissue ischaemia and reperfusion injury. However, clinical translation of NO therapy for these pathophysiological conditions has not been realized for various reasons. Work from our laboratory and several others suggests that a new form of NO-associated therapy may be possible through the use of nitrite anion (sodium nitrite), a prodrug which can be reduced to NO in ischaemic tissues. In this manner, nitrite anion serves as a highly selective NO donor in ischaemic tissues without substantially altering otherwise normal tissue. This surprising and novel discovery has reinvigorated hopes for effectively restoring NO bioavailability in vulnerable tissues while continuing to reveal the complexity of NO biology and metabolism within the cardiovascular system. However, some concerns may exist regarding the effect of nitrite on carcinogenesis. This review highlights the emergence of nitrite anion as a selective NO prodrug for ischaemic tissue disorders and discusses the potential therapeutic utility of this agent for peripheral vascular disease.

Therapeutic angiogenesis by implantation of a capillary structure constituted of human adipose tissue microvascular endothelial cells

OBJECTIVE

We previously reported a novel technology for the engineering of a capillary network using an optical lithographic technique. To apply this technology to the therapy of ischemic diseases, we tested human omental microvascular endothelial cells (HOMECs) as an autologous cell source and decellularized human amniotic membranes (DC-AMs) as a pathogen-free and low immunogenic transplantation scaffold.

METHODS AND RESULTS

Human umbilical vein endothelial cells were aligned on a patterned glass substrate and formed a capillary structure when transferred onto an amniotic membrane (AM). In contrast, HOMECs were scattered and did not form a capillary structure on AMs. Treatment of HOMECs with sphingosine 1-phosphate (S1P) inhibited HOMEC migration and enabled HOMEC formation of a capillary structure on AMs. Using quantitative RT-PCR and Western blot analyses, we demonstrated that the main S1P receptor in HOMECs is S1P(2), which is lacking in human umbilical vein endothelial cells, and that inhibition of cell migration by S1P is mediated through an S1P(2)-Rho-Rho-associated kinase signaling pathway. Implantation of capillaries engineered on DC-AMs into a hindlimb ischemic nude mouse model significantly increased blood perfusion compared with controls.

CONCLUSIONS

A capillary network consisting of HOMECs on DC-AMs can be engineered ex vivo using printing technology and S1P treatment. This method for regeneration of a capillary network may have therapeutic potential for ischemic diseases.

Notch signalling in ischaemia-induced angiogenesis

Notch signalling represents a key pathway essential for normal vascular development. Recently, great attention has been focused on the implication of Notch pathway components in postnatal angiogenesis and regenerative medicine. This paper critically reviews the most recent findings supporting the role of Notch in ischaemia-induced neovascularization. Notch signalling reportedly regulates several steps of the reparative process occurring in ischaemic tissues, including sprouting angiogenesis, vessel maturation, interaction of vascular cells with recruited leucocytes and skeletal myocyte regeneration. Further characterization of Notch interaction with other signalling pathways might help identify novel targets for therapeutic angiogenesis.

How can cardiac MR imaging help guide development of gene therapy for treatment of coronary heart disease?

Jacquier et al have shown with magnetic resonance (MR) imaging that therapy with direct intracardiac injection of vascular endothelial growth factor gene (VEGF) improves myocardial function in a model of myocardial infarction in swine. Jacquier and colleagues used MR imaging to measure left ventricular (LV) function and strain and showed that animals treated with gene therapy had stable ejection fraction whereas control animals deteriorated.

[Angiogenesis. Possibilities for therapeutic intervention in rheumatic diseases]

In contrast to vasculogenesis, angiogenesis is defined as the formation of new vessels from preexisting ones. Physiologically, this multistep process occurs in adults during the reproductive cycle and during pregnancy, pathophysiologically it can be found in wound healing, inflammation and carcinogenesis. The underlying mechanisms are vasodilatation and increasing permeability, destabilization of vessel walls and degradation of extracellular matrix, followed by the proliferation and migration of endothelial cells. Migrated endothelial cells form vascular tubes at sites of ischemia and these tubes are finally stabilized by pericytes and smooth muscle cells. This process is controlled by a complex interaction of angiogenic and angiostatic factors. In contrast to carcinogenesis, the role of angiogenesis for the pathogenesis and therapy of rheumatic diseases is less understood. Two examples for pathologically disturbed angiogenesis, rheumatoid arthritis and systemic sclerosis, are discussed in this review with respect to therapeutic options.