Chapter 5 Chick Embryo Chorioallantoic Membrane as a Useful Tool to Study Angiogenesis

45S5-Bioglass(®)-based 3D-scaffolds seeded with human adipose tissue-derived stem cells induce in vivo vascularization in the CAM angiogenesis assay

Poor vascularization is the key limitation for long-term acceptance of large three-dimensional (3D) tissue engineering constructs in regenerative medicine. 45S5 Bioglass(®) was investigated given its potential for applications in bone engineering. Since native Bioglass(®) shows insufficient angiogenic properties, we used a collagen coating, to seed human adipose tissue-derived stem cells (hASC) confluently onto 3D 45S5 Bioglass(®)-based scaffolds. To investigate vascularization by semiquantitative analyses, these biofunctionalized scaffolds were then subjected to in vitro human umbilical vein endothelial cells formation assays, and were also investigated in the chorioallantoic membrane (CAM) angiogenesis model, an in vivo angiogenesis assay, which uses the CAM of the hen's egg. In their native, nonbiofunctionalized state, neither Bioglass(®)-based nor biologically inert fibrous polypropylene control scaffolds showed angiogenic properties. However, significant vascularization was induced by hASC-seeded scaffolds (Bioglass(®) and polypropylene) in the CAM angiogenesis assay. Biofunctionalized scaffolds also showed enhanced tube lengths, compared to unmodified scaffolds or constructs seeded with fibroblasts. In case of biologically inert hernia meshes, the quantification of vascular endothelial growth factor secretion as the key angiogenic stimulus strongly correlated to the tube lengths and vessel numbers in all models. This correlation proved the CAM angiogenesis assay to be a suitable semiquantitative tool to characterize angiogenic effects of larger 3D implants. In addition, our results suggest that combinations of suitable scaffold materials, such as 45S5 Bioglass(®), with hASC could be a promising approach for future tissue engineering applications.

Quantitative mass spectrometry-based proteomics in angiogenesis

The process of new blood vessel formation from pre-existing ones is called angiogenesis. Beyond playing a critical role in the physiological development of the vascular system, angiogenesis is a well-recognised hallmark of cancer. Unbiased system-wide approaches are required to complement the current knowledge, and intimately understand the molecular mechanisms regulating this process in physiological and pathological conditions. In this review we describe the cellular and molecular dynamics regulating the physiological growth of vessels and their deregulation in cancer, survey in vitro and in vivo models currently exploited to investigate various aspects of angiogenesis and describe state-of-the-art and most widespread methods and technologies in MS shotgun proteomics. Finally, we focus on current applications of MS to better understand endothelial cell behaviour and propose how modern proteomics can impact on angiogenesis research.

A chorioallantoic membrane model for the determination of anti-angiogenic effects of imatinib

Tumor angiogenesis is of major importance in the growth and metastasis of solid tumors, and the development of anti-angiogenic treatment strategies is thus a relevant option in oncology. The chorioallantoic membrane (CAM) model is a rapid and simple alternative to in vivo studies for the evaluation of anti-angiogenic compounds, thus allowing to reduce animal experiments and, upon establishment of robust and reproducible procedures, to more efficiently and objectively assess the anti-angiogenic efficacy of a given drug. In this paper, we compare two different methods for tumor establishment on a CAM model: (i) a Murine Urothelial Carcinoma (MB49) cell suspension mixed with Matrigel and (ii) an MB49 cell suspension absorbed in Gelfoam gelatin sponges. Based on the applicability of both methods for implant formation, we identify Gelfoam gelatin sponges as superior due to better attachment of the tumors on the membrane surface. For the precise quantitation of tumor xenograft growth and angiogenesis, we furthermore establish in this paper the electronic capturing of the xenografts and the computer-based analysis of the microscopic CAM images in order to determine the number of intersecting vessels and to measure vessel diameters. Beyond its direct effect on tumor cells by inhibiting the tyrosine kinase domain of the abl gene, imatinib has been reported to reduce the Bcr-Abl-mediated secretion of the angiogenesis factor VEGF and hence to interfere with angiogenesis. To test our CAM model for its ability to monitor anti-angiogenic effects, Gelfoam gelatin sponge-based tumor implants were treated by topical application of imatinib at various concentrations. Besides anti-tumor effects, we observed an inhibition of angiogenesis as determined by the number or total diameter of intersecting vessels. We also demonstrate that the calculation of the "blood vessel index" (vessel total diameter/tumor circumference) in our model allows to assess anti-angiogenic effects of imatinib independently of tumor growth inhibition. We conclude that our CAM assay and computer-based analysis represent a useful in vitro technique for the rapid assessment of anti-angiogenic effects of various agents.

The antiangiogenic activity of a soluble fragment of the VEGFR extracellular domain

Vascular endothelial growth factor (VEGF) is a key regulator of pathological angiogenesis and vascular permeability and overexpressed by most solid tumors. VEGF receptor-2 (VEGFR-2 or kinase-insert domain-containing receptor as it is called in human, KDR) is a specific receptor of VEGF with a high binding affinity. A solube recombinant extracellular domain 1-3 of human VEGFR-2 (rKDR1-3) was expressed in Escherichia coli (E. Coli) and purified from the bacterial periplasmic extracts by immobilized metal affinity chromatography and anion exchange chromatography to inhibit the VEGF-induced angiogenesis. A surface plasmon resonance (SPR) technology was adopted to analyze the affinity and kinetics constant between rKDR1-3 and VEGF165. Under the given experimental conditions, the association rate constant Ka was 1.06×10(5)M(-1) S(-1), the dissociation rate Kd was 6.09×10(-3) S(-1), the dissociation constant KD was 5.74×10(-8)M. The effect of rKDR1-3 on VEGF-induced endothelial cell proliferation was studied using MTT assay, scratch-wound healing assay and chorioallantoic membrane (CAM) assay. The results showed that rKDR1-3 could inhibit neovascularization and serve as a useful drug candidate in research, diagnostics and therapy of cancer.

Photoacoustic microscopy: a potential new tool for evaluation of angiogenesis inhibitor

The feasibility of photoacoustic microscopy (PAM) for evaluation of angiogenesis inhibitor was investigated on a chick embryo model in vivo. Different concentrations of the angiogenesis inhibitor, Sunitinib, were applied to the chorioallantoic membrane (CAM) of the chick embryos. Imaging of microvasculature in embryo CAMs was acquired using a laser-scanning PAM system; while the optical microscopy (OM) capturing the microvascular images of the same set of CAMs for comparison served as a gold standard for validating the results from PAM. The microvascular density as a function of applied Sunitinib concentration has been quantified in both PAM and OM images. The results from these two modalities have a good agreement, suggesting that PAM could provide an unbiased quantification of microvascular density for objective evaluation of anti-angiogenesis medication. In comparison with conventional OM which enables only two-dimensional enface imaging, PAM is capable of three-dimensional analysis of microvessels, including not only morphology but also functions, as demonstrated in part by the imaging result on a canine bladder model. The emerging PAM technique shows promise to be used in clinical and preclinical settings for comprehensive and objective evaluation of anti-angiogenesis medications.

Gene transfer to chicks using lentiviral vectors administered via the embryonic chorioallantoic membrane

The lack of affordable techniques for gene transfer in birds has inhibited the advancement of molecular studies in avian species. Here we demonstrate a new approach for introducing genes into chicken somatic tissues by administration of a lentiviral vector, derived from the feline immunodeficiency virus (FIV), into the chorioallantoic membrane (CAM) of chick embryos on embryonic day 11. The FIV-derived vectors carried yellow fluorescent protein (YFP) or recombinant alpha-melanocyte-stimulating hormone (α-MSH) genes, driven by the cytomegalovirus (CMV) promoter. Transgene expression, detected in chicks 2 days after hatch by quantitative real-time PCR, was mostly observed in the liver and spleen. Lower expression levels were also detected in the brain, kidney, heart and breast muscle. Immunofluorescence and flow cytometry analyses confirmed transgene expression in chick tissues at the protein level, demonstrating a transduction efficiency of ∼0.46% of liver cells. Integration of the viral vector into the chicken genome was demonstrated using genomic repetitive (CR1)-PCR amplification. Viability and stability of the transduced cells was confirmed using terminal deoxynucleotidyl transferase (dUTP) nick end labeling (TUNEL) assay, immunostaining with anti-proliferating cell nuclear antigen (anti-PCNA), and detection of transgene expression 51 days post transduction. Our approach led to only 9% drop in hatching efficiency compared to non-injected embryos, and all of the hatched chicks expressed the transgenes. We suggest that the transduction efficiency of FIV vectors combined with the accessibility of the CAM vasculature as a delivery route comprise a new powerful and practical approach for gene delivery into somatic tissues of chickens. Most relevant is the efficient transduction of the liver, which specializes in the production and secretion of proteins, thereby providing an optimal target for prolonged study of secreted hormones and peptides.

Angiogenic efficacy of Heparin on chick chorioallantoic membrane

Heparin is an anticoagulant agent known to have diverse effects on angiogenesis with some reports suggesting that it can induce angiogenesis while a few have indicated of its inhibitory property. Cancer patients treated for venous thromboembolism with low molecular heparin had a better survival than the unfractionated heparin (UFH). Heparin is known to interact with various angiogenic growth factors based on its sulfation modifications within the glycosaminoglycan chains. Therefore it is important to study the mechanism of action of heparin of different molecular weight to understand its angiogenic property. In this concern, we examined the angiogenic response of higher molecular weight Heparin (15 kDa) of different concentrations using late CAM assay. Growth of blood vessels in terms of their length and size was measured and thickness of the CAM was calculated morphometrically. The observed increase in the thickness of the CAM is suggestive of the formation of capillary like structures at the treated region. Analysis of the diffusion pattern showed internalized action of heparin that could affect gene expression leading to proliferation of endothelial cells. Angiogenesis refers to formation of new blood vessels from the existing ones and occurrence of new blood vessels at the treated area strongly confirms that heparin of 15 kDa molecular weight has the ability to induce angiogenesis on CAM vascular bed in a dose dependent manner. The results demonstrate the affinity of heparin to induce angiogenesis and provide a novel mechanism by which heparin could be used in therapeutics such as in wound healing process.

Real-time visualization and quantitation of vascular permeability in vivo: implications for drug delivery

The leaky, heterogeneous vasculature of human tumors prevents the even distribution of systemic drugs within cancer tissues. However, techniques for studying vascular delivery systems in vivo often require complex mammalian models and time-consuming, surgical protocols. The developing chicken embryo is a well-established model for human cancer that is easily accessible for tumor imaging. To assess this model for the in vivo analysis of tumor permeability, human tumors were grown on the chorioallantoic membrane (CAM), a thin vascular membrane which overlays the growing chick embryo. The real-time movement of small fluorescent dextrans through the tumor vasculature and surrounding tissues were used to measure vascular leak within tumor xenografts. Dextran extravasation within tumor sites was selectively enhanced an interleukin-2 (IL-2) peptide fragment or vascular endothelial growth factor (VEGF). VEGF treatment increased vascular leak in the tumor core relative to surrounding normal tissue and increased doxorubicin uptake in human tumor xenografts. This new system easily visualizes vascular permeability changes in vivo and suggests that vascular permeability may be manipulated to improve chemotherapeutic targeting to tumors.

Chicken chorioallantoic membrane angiogenesis model

The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane which serves as a gas exchange surface and its function is supported by a dense capillary network. Because of its extensive vascularization and easy accessibility, the CAM has been broadly used to study the morphofunctional aspects of the angiogenesis process in vivo and to investigate the efficacy and mechanisms of action of proangiogenic and antiangiogenic natural and synthetic molecules. The CAM has long been a favored system for the study of tumor angiogenesis and metastasis, because at this stage the chick immunocompetence system is not fully developed and the conditions for rejection have not been established. The CAM may also be used to verify the ability to inhibit the growth of capillaries by implanting tumors onto the CAM and by comparing tumor growth and vascularization with or without the administration of an antiangiogenic molecule. Other studies using the tumor cells/CAM model have focused on the invasion of the chorionic epithelium and the blood vessels by tumor cells. The cells invade the epithelium and the mesenchymal connective tissue below, where they are found in the form of a dense bed of blood vessels, which is a target for intravasation.

Use of the mouse aortic ring assay to study angiogenesis

Here we provide a protocol for quantitative three-dimensional ex vivo mouse aortic ring angiogenesis assays, in which developing microvessels undergo many key features of angiogenesis over a timescale similar to that observed in vivo. The aortic ring assay allows analysis of cellular proliferation, migration, tube formation, microvessel branching, perivascular recruitment and remodeling-all without the need for cellular dissociation-thus providing a more complete picture of angiogenic processes compared with traditional cell-based assays. Our protocol can be applied to aortic rings from embryonic stage E18 through to adulthood and can incorporate genetic manipulation, treatment with growth factors, drugs or siRNA. This robust assay allows assessment of the salient steps in angiogenesis and quantification of the developing microvessels, and it can be used to identify new modulators of angiogenesis. The assay takes 6-14 d to complete, depending on the age of the mice, treatments applied and whether immunostaining is performed.

Gc protein-derived macrophage-activating factor (GcMAF) stimulates cAMP formation in human mononuclear cells and inhibits angiogenesis in chick embryo chorionallantoic membrane assay

The effects of Gc protein-derived macrophage-activating factor (GcMAF) have been studied in cancer and other conditions where angiogenesis is deregulated. In this study, we demonstrate for the first time that the mitogenic response of human peripheral blood mononuclear cells (PBMCs) to GcMAF was associated with 3'-5'-cyclic adenosine monophosphate (cAMP) formation. The effect was dose dependent, and maximal stimulation was achieved using 0.1 ng/ml. Heparin inhibited the stimulatory effect of GcMAF on PBMCs. In addition, we demonstrate that GcMAF (1 ng/ml) inhibited prostaglandin E(1)- and human breast cancer cell-stimulated angiogenesis in chick embryo chorionallantoic membrane (CAM) assay. Finally, we tested different GcMAF preparations on CAM, and the assay proved to be a reliable, reproducible and inexpensive method to determine the relative potencies of different preparations and their stability; we observed that storage at room temperature for 15 days decreased GcMAF potency by about 50%. These data could prove useful for upcoming clinical trials on GcMAF.

Paracrine stimulation of endothelial cell motility and angiogenesis by platelet-derived deoxyribose-1-phosphate

OBJECTIVE

Micromolar concentrations of the proangiogenic metabolite deoxyribose-1-phosphate (dRP) were detected in platelet supernatants by mass spectrometry. In this study, we assessed whether the release of dRP by platelets stimulates endothelial cell migration and angiogenesis.

METHODS AND RESULTS

Protein-free supernatants from thrombin-stimulated platelets increased human umbilical vein endothelial cell migratory activity in transmigration and monolayer repair assays. This phenomenon was ablated by genetic silencing of dRP-generating uridine phosphorylase (UP) and thymidine phosphorylase (TP) or pharmacological inhibition of UP and restored by exogenous dRP. The stimulation of endothelial cell migration by platelet-derived dRP correlated with upregulation of integrin β(3), which was induced in a reactive oxygen species-dependent manner, and was mediated by the activity of the integrin heterodimer α(v)β(3). The physiological relevance of dRP release by platelets was confirmed in a chick chorioallantoic membrane assay, where the presence of this metabolite in platelet supernatants strongly induced capillary formation.

CONCLUSIONS

Platelet-derived dRP stimulates endothelial cell migration by upregulating integrin β(3) in a reactive oxygen species-dependent manner. As demonstrated by our in vivo experiments, this novel paracrine regulatory pathway is likely to play an important role in the stimulation of angiogenesis by platelets.

Gene signatures in wound tissue as evidenced by molecular profiling in the chick embryo model

BACKGROUND

Modern functional genomic approaches may help to better understand the molecular events involved in tissue morphogenesis and to identify molecular signatures and pathways. We have recently applied transcriptomic profiling to evidence molecular signatures in the development of the normal chicken chorioallantoic membrane (CAM) and in tumor engrafted on the CAM. We have now extended our studies by performing a transcriptome analysis in the "wound model" of the chicken CAM, which is another relevant model of tissue morphogenesis.

RESULTS

To induce granulation tissue (GT) formation, we performed wounding of the chicken CAM and compared gene expression to normal CAM at the same stage of development. Matched control samples from the same individual were used. We observed a total of 282 genes up-regulated and 44 genes down-regulated assuming a false-discovery rate at 5% and a fold change > 2. Furthermore, bioinformatics analysis lead to the identification of several categories that are associated to organismal injury, tissue morphology, cellular movement, inflammatory disease, development and immune system. Endothelial cell data filtering leads to the identification of several new genes with an endothelial cell signature.

CONCLUSIONS

The chick chorioallantoic wound model allows the identification of gene signatures and pathways involved in GT formation and neoangiogenesis. This may constitute a fertile ground for further studies.

The chick chorioallantoic membrane: a model of molecular, structural, and functional adaptation to transepithelial ion transport and barrier function during embryonic development

The chick chorioallantoic membrane is a very simple extraembryonic membrane which serves multiple functions during embryo development; it is the site of exchange of respiratory gases, calcium transport from the eggshell, acid-base homeostasis in the embryo, and ion and H(2)O reabsorption from the allantoic fluid. All these functions are accomplished by its epithelia, the chorionic and the allantoic epithelium, by differentiation of a wide range of structural and molecular peculiarities which make them highly specialized, ion transporting epithelia. Studying the different aspects of such a developmental strategy emphasizes the functional potential of the epithelium and offers an excellent model system to gain insights into questions partly still unresolved.

The Chick Embryo Chorioallantoic Membrane as an In Vivo Assay to Study Antiangiogenesis

Antiangiogenesis, e.g., inhibition of blood vessel growth, is being investigated as a way to prevent the growth of tumors and other angiogenesis-dependent diseases. Pharmacological inhibition interferes with the angiogenic cascade or the immature neovasculature with synthetic or semi-synthetic substances, endogenous inhibitors or biological antagonists.The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane, which serves as a gas exchange surface and its function is supported by a dense capillary network. Because its extensive vascularization and easy accessibility, CAM has been used to study morphofunctional aspects of the angiogenesis process in vivo and to study the efficacy and mechanism of action of pro- and anti-angiogenic molecules. The fields of application of CAM in the study of antiangiogenesis, including our personal experience, are illustrated in this review article.

Omentum-derived stromal cells improve myocardial regeneration in pig post-infarcted heart through a potent paracrine mechanism

Cell-based therapy could be a valid option to treat myocardial infarct (MI). Adipose-derived stromal cells (ADStCs) have demonstrated tissue regenerative potential including cardiomyogenesis. Omentum is an extremely rich source of visceral fat and its accumulation seems to correlate with cardiovascular diseases. We investigated the capacity of human fat Omentum-derived StCs (FOStCs) to affect heart function upon acute infarct in pigs induced by permanent ligation of the anterior interventricular artery (IVA). We demonstrated for the first time that the local injection of 50x10(6) of FOStCs ameliorates the functional parameters of post-infarct heart. Most importantly, histology of FOStCs treated hearts demonstrated a substantial improvement of cardiomyogenesis. In culture, FOStCs produced an impressive number and amount of angiogenic factors and cytokines. Moreover, the conditioned medium of FOStCs (FOStCs-CM) stimulates in vitro cardiac endothelial cells (ECs) proliferation and vascular morphogenesis and inhibits monocytes, EC activation and cardiomyocyte apoptosis. Since FOStCs in vivo did not trans-differentiate into cardiomyocyte-like cells, we conclude that FOStCs efficacy was presumably mediated by a potent paracrine mechanism involving molecules that concomitantly improved angiogenesis, reduced inflammation and prevented cardiomyocytes death. Our results highlight for the first time the important role that human FOStCs may have in cardiac regeneration.

Enhancement of embryonic stem cell differentiation promoted by avian chorioallantoic membranes

Avian chorioallantoic membrane (CAM) has been used as a model to explore angiogenesis and to study the microvasculature of transplanted tissues. Because CAM provides a vascular bed, cells can be implanted, and their development can be monitored and modified. We used the CAM model to study the differentiation process of embryoid bodies (EBs) derived from mouse embryonic stem cells (ESCs) influenced by the CAM vascular bed. After EBs were incubated in CAM for 5 days, they underwent further differentiation and became tissue masses (TMs) of different morphologies from those that grew outside CAM. Immunohistochemical analysis of TMs demonstrated tissue-specific markers such as neurofilament light, CD34, collagen IV, cardiac myosin heavy chain (MHC), and cardiotin. Differentiated mouse blood vessels stained with anti-CD31 were found within the TMs, as well as blood vessels stained positive for QH1 and QCPN, markers for quail endothelial cells and perinuclear quail antigen, respectively. Quail erythrocytes inside mouse blood vessels suggested a connection between existing quail vessels and blood vessels growing inside the TMs as a result of EB differentiation. Therefore, CAM could be a suitable model to trigger and study the differentiation of EBs in close interaction with surrogate quail blood vessels.

Chick ex ovo culture and ex ovo CAM assay: how it really works

Chicken eggs in the early phase of breeding are between in vitro and in vivo systems and provide a vascular test environment not only to study angiogenesis but also to study tumorigenesis. After the chick chorioallantoic membrane (CAM) has developed, its blood vessel network can be easily accessed, manipulated and observed and therefore provides an optimal setting for angiogenesis assays. Since the lymphoid system is not fully developed until late stages of incubation, the chick embryo serves as a naturally immunodeficient host capable of sustaining grafted tissues and cells without species-specific restrictions. In addition to nurturing developing allo- and xenografts, the CAM blood vessel network provides a uniquely supportive environment for tumor cell intravasation, dissemination, and vascular arrest and a repository where arrested cells extravasate to form micro metastatic foci. For experimental purposes, in most of the recent studies the CAM was exposed by cutting a window through the egg shell and experiments were carried out in ovo, resulting in significant limitations in the accessibility of the CAM and possibilities for observation and photo documentation of effects. When shell-less cultures of the chick embryo were used(1-4), no experimental details were provided and, if published at all, the survival rates of these cultures were low. We refined the method of ex ovo culture of chick embryos significantly by introducing a rationally controlled extrusion of the egg content. These ex ovo cultures enhance the accessibility of the CAM and chick embryo, enabling easy in vivo documentation of effects and facilitating experimental manipulation of the embryo. This allows the successful application to a large number of scientific questions: (1) As an improved angiogenesis assay(5,6), (2) an experimental set up for facilitated injections in the vitreous of the chick embryo eye(7-9), (3) as a test environment for dissemination and intravasation of dispersed tumor cells from established cell lines inoculated on the CAM(10-12), (4) as an improved sustaining system for successful transplantation and culture of limb buds of chicken and mice(13) as well as (5) for grafting, propagation, and re-grafting of solid primary tumor tissue obtained from biopsies on the surface of the CAM(14). In this video article we describe the establishment of a refined chick ex ovo culture and CAM assay with survival rates over 50%. Besides we provide a step by step demonstration of the successful application of the ex ovo culture for a large number of scientific applications.

Anti-angiogenic properties of calcium trifluoroacetate

Endothelial cell proliferation and the formation of new vessels are strictly regulated by angiogenic factors (e.g., VEGF) that induce the activation of signal transduction pathways controlled by calcium dynamics. Using in vitro and in vivo experiments, we investigated the effect of calcium trifluoroacetate (CaTFAc), a complex, poorly dissociated salt that is characterized by its low toxicity, on angiogenesis. In vitro, CaTFAc inhibited VEGF-induced effects on endothelial cell proliferation. In two in vivo models of angiogenesis, a Matrigel plug in mice and a chick embryo chorioallantoic membrane, CaTFAc inhibited the VEGF-induced formation of new vessels. The exact mechanism of action is still under investigation, but in vitro experiments demonstrate that CaTFAc induced a reversible increase in the levels of intracellular calcium under basal conditions and prevented calcium signaling induced by VEGF. These results are the first to suggest that CaTFAc may be useful for the treatment of diseases caused by enhanced angiogenesis.