Angiogenesis in arteries: review

Obesity Downregulates MicroRNA-126 Inducing Capillary Rarefaction in Skeletal Muscle: Effects of Aerobic Exercise Training

Background. We investigated the effects of exercise training (ET) on miR-126 levels and skeletal muscle angiogenesis in obese Zucker rats. Results. Zucker rats were randomly assigned to sedentary and swimming-trained groups: lean sedentary (LS) and trained (LTR); obese sedentary (OB) and trained (OBTR). The OB group displayed capillary rarefaction compared with the LS group. In contrast, ET increased the capillary/fiber ratio by 38% in the LTR group and normalized capillary rarefaction in the OBTR group. VEGF, PI3K, and eNOS levels were reduced in the skeletal muscle of the OB group. ET normalized VEGF, PI3K, and eNOS levels in OBTR, contributing to vascular network homeostasis. PI3KR2 inhibits PI3K, a key mediator of the VEGF signaling pathway. Obesity decreased miR-126 and increased PI3KR2 levels compared with the LS group. However, ET normalized miR-126 levels in the OBTR group versus the LS group and decreased expression of PI3KR2. Conclusion. Our findings show that obesity leads to skeletal muscle capillary rarefaction, which is regulated by decreased miR-126 levels and increased PI3KR2. Inversely, ET normalizes miR-126 levels and VEGF signaling and should be considered an important therapeutic strategy for vascular disorders.

Extracellular matrix remodelling in rat endometrium during early pregnancy: the role of fibronectin and laminin

The endometrial extracellular matrix (ECM) remodelling has a crucial role in the establishment of a successful pregnancy. In addition to its basic function such as regulation of cell function, differentiation, migration, proliferation, the substantial alterations in the endometrial ECM may play a specific role in the trophoblast invasion, placentation, cell death and formation of the proper and functional implantation chamber around the embryo. In the present study, immunolocalizations of fibronectin and laminin were determined using avidin-biotin complex-peroxidase in rat implantation sites during 7-10 days of pregnancy. Both proteins were present in the basal membrane of blood vessels and in decidual matrix whereas they were absent or had very weak reactivity in the primary decidual zone on day 7. When placentation has begun, the immunoreactivity of both proteins was increased in the placental bed and in the basal membrane of blood vessels of the mesometrial region. The immunolocalization of both proteins seemed to be decreased in the antimesometrial decidua, however, it was increased in the mesometrial decidual matrix on days 9 and 10. Therefore, it could be suggested laminin and fibronectin demonstrating dynamic expressions in relation with the morphological differentiation of endometrial stroma may play crucial roles in the control of trophoblast adhesion and invasion, in placentation and angiogenesis, in the determination of cell shape and fate thus contributing the endometrial receptivity and a successful pregnancy.

Factors affecting the clearance and biodistribution of polymeric nanoparticles

Nanoparticle (NP) drug delivery systems (5−250 nm) have the potential to improve current disease therapies because of their ability to overcome multiple biological barriers and releasing a therapeutic load in the optimal dosage range. Rapid clearance of circulating nanoparticles during systemic delivery is a critical issue for these systems and has made it necessary to understand the factors affecting particle biodistribution and blood circulation half-life. In this review, we discuss the factors which can influence nanoparticle blood residence time and organ specific accumulation. These factors include interactions with biological barriers and tunable nanoparticle parameters, such as composition, size, core properties, surface modifications (pegylation and surface charge), and finally, targeting ligand functionalization. All these factors have been shown to substantially affect the biodistribution and blood circulation half-life of circulating nanoparticles by reducing the level of nonspecific uptake, delaying opsonization, and increasing the extent of tissue specific accumulation.

Vascular endothelial growth factor and angiogenesis

Angiogenesis is a hallmark of wound healing, the menstrual cycle, cancer, and various ischemic and inflammatory diseases. A rich variety of pro- and antiangiogenic molecules have already been discovered. Vascular endothelial growth factor (VEGF) is an interesting inducer of angiogenesis and lymphangiogenesis, because it is a highly specific mitogen for endothelial cells. Signal transduction involves binding to tyrosine kinase receptors and results in endothelial cell proliferation, migration, and new vessel formation. In this article, the role of VEGF in physiological and pathological processes is reviewed. We also discuss how modulation of VEGF expression creates new therapeutic possibilities and describe recent developments in this field.

Methylprednisolone intravenously 1 day after surgery has sustained analgesic and opioid-sparing effects

BACKGROUND

In previous studies on glucocorticoids for postoperative pain, the test drug has been given perioperatively, usually before measurement of baseline pain. In order to evaluate the time course and magnitude of the analgesic effect of a glucocorticoid in well-established postoperative pain, we compared methylprednisolone with ketorolac and placebo, after assessment of baseline pain on the first postoperative day.

METHODS

This was a double-blind, single dose, randomized, parallel comparison of intravenous (i.v.) methylprednisolone 125 mg, ketorolac 30 mg as an active control, and placebo in 75 patients with moderate to severe pain 1 day after orthopaedic surgery. Outcome variables were pain intensity (0-100 VAS), pain relief (0-4 PAR) and rescue opioid consumption.

RESULTS

Methylprednisolone was not significantly different from ketorolac and gave significantly lower pain intensity from 1 h (0-6 h, P < 0.02), and more pain relief 2-6 h after test drugs (P < 0.05) compared with placebo. After 24 h, pain intensity was lower in both active drug groups compared with placebo (methylprednisolone, P < 0.0001; ketorolac, P < 0.007). Number needed to treat (NNT) calculated from patients having more than at least 50% of maximum obtainable total pain relief during the first 6 h (>50%maxTOTPAR(6 h)) was 3.6 for methylprednisolone and 3.1 for ketorolac. Number needed to treat calculated from the percentage reporting at least 50% pain relief for at least 4 h (>50%PAR(4 h)) was 2.8 for both groups. Opioid consumption was significantly reduced for 72 h after methylprednisolone compared with ketorolac (P < 0.02) and placebo (P < 0.003).

CONCLUSION

Methylprednisolone 125 mg i.v. 1 day after surgery gave similar early reduction of pain as i.v. ketorolac 30 mg. Less pain than placebo 24 h after methylprednisolone, and lower opioid consumption for 72 h compared with ketorolac and placebo indicate sustained analgesic effects of methylprednisolone.

Thrombogenesis, atherogenesis and angiogenesis in vascular disease: a new 'vascular triad'

Amongst the components of the pathophysiology of atherosclerosis are the tendency to thrombus formation (i.e., thrombogenesis) and the loss of endothelial cell integrity. The endothelium is also implicated in atherogenesis, as vasa vasorum are present in the adventitia and media at a higher density in atherosclerotic tissue, and that neovascularisation leading to collateral growth bypassing obstruction and/or stenoses provides important alternative routes to feeding distal tissues. The development of these new blood vessels is the process of angiogenesis. The present 'viewpoint' article will explore the relationships between the three processes. There is considerable evidence that atherogenesis and thrombogenesis are intimately linked, but angiogenesis in cardiovascular disease is a recently developed concept. We propose a new 'vascular triad' of these abnormal pathophysiological processes, leading to an alternative view of the pathogenesis of vascular disease. Indeed, we suggest that angiogenesis is an important aspect of the pathophysiology of cardiovascular disease, impacting with both thrombogenesis and atherogenesis, in a new vascular triad (the 'Birmingham vascular triad').

Cellular effects and signalling pathways activated by the anti-coagulant factor, protein S, in vascular cells protein S cellular effects

The anticoagulant factor protein S is a secreted vitamin K-dependent gamma-carboxylated protein that is mainly synthesised in the liver but is also made by endothelial cells and megakaryocytes in culture. In previous studies we have shown that protein S acts as a mitogen for cultured human vascular smooth muscle cells. The synthesis and secretion of protein S by endothelial cells suggests that in addition to its role in the coagulation cascade, protein S may be an important autocrine factor implicated in the pathophysiology of the vascular system. The effects of protein S on hVSMC proliferation, migration and survival are discussed. The activation of the components of the MAP kinase pathway, ERK1/2, JNK/SAPK and p38 is also summarised. Binding and chemical cross-linking experiments provided evidence for the existence of a cell surface protein S receptor(s). By virtue of its many cellular effects, it is suggested here that the anticoagulant factor protein S plays an important role in the pathophysiology of the vasculature.

Solubilized ibuprofen: evaluation of onset, relief, and safety of a novel formulation in the treatment of episodic tension-type headache

OBJECTIVE

To evaluate the relative efficacy of a new solubilized formulation of ibuprofen compared with acetaminophen caplets.

METHODS

This double-blind, randomized, parallel group study evaluated 154 subjects taking a single dose of solubilized ibuprofen, 400 mg; acetaminophen, 1000 mg; or placebo for the relief of episodic tension-type headache. Time to relief was measured using a stopwatch, and overall efficacy was measured using traditional categorical pain and relief scales.

RESULTS

Ibuprofen capsules (liquigel), 400 mg, were significantly faster than both acetaminophen, 1000 mg, and placebo for all time-to-relief measures. Ibuprofen liquigel had a median time to first perceptible pain relief of 39 minutes compared with 47 minutes for acetaminophen and 113 minutes for placebo. For median time to meaningful relief, ibuprofen liquigel had a time of 39 minutes compared with 53 minutes for acetaminophen and more than 180 minutes for placebo (P</=.02 for both measures). In addition, ibuprofen liquigels demonstrated significantly superior overall analgesic efficacy compared with acetaminophen, 1000 mg, for the relief of episodic tension-type headache. Both active treatments had a side effect profile similar to placebo.

CONCLUSIONS

Although several other studies have demonstrated the overall analgesic superiority of ibuprofen to acetaminophen, this study demonstrated that the liquigel formulation also provides a clinically relevant advantage for time to analgesic effects.

Neovascularization in early atherosclerotic lesions of human carotid arteries: its potential contribution to plaque development

Neovascularization is a prominent feature of late-stage atherosclerotic lesions and their complications but is generally regarded as an insignificant, undetectable component of the earliest stages of plaque development, probably because of relatively poor histological techniques. Using an improved vascular staining procedure, we have examined the extent of neovascularization in the earliest plaque lesions. Combined monoclonal antibodies to CD31, CD34, and von Willebrand factor have provided an ultrasensitive technique with which to visualize blood vessels in early atherosclerotic lesions (n = 55) of human carotid arteries obtained through surgical procedures. Capillary-like microvessels were shown in very early atherosclerotic lesions (type II), where they were associated with the distribution of macrophages and a few immature mast cells. Neovascularization was more prominent in type III lesions with vessels of variable size, often providing a focus around which local accumulations of macrophages and apolipoproteins A-I and B were visualized. Thickened type III lesions usually showed an intricate network of microvessels, together with numerous mast cells. These studies have shown neovascularization as a prominent feature of early stages of atherosclerotic plaque development. Whereas distribution of apolipoproteins A-I and B were observed in the very earliest stages of the plaque intima, these lipids, together with macrophages, foam cells, and mast cells, were observed as perivascular accumulations in a proportion of type II and III lesions. Such findings indicate that neovascularization is an important feature of early plaque development and may provide an additional or alternative source of leukocyte and lipid accumulations relative to the arterial lumen.

Local neovascularization and cellular composition within vulnerable regions of atherosclerotic plaques of human carotid arteries

An improved immunohistochemical method has been used to assess neovascularization within the vulnerable 'shoulder' regions of atherosclerotic plaques from carotid arteries. A combination of monoclonal antibodies (CD31, CD34, +/- von Willebrand factor) was shown to be far more effective than conventional techniques in demonstrating extensive vascularizations within the 'shoulder' and cap regions of late-stage plaques. Such sites were shown to be microfocal, often appearing as a plexus of both large and small vessels which occupied a significant proportion of the 'shoulder' area. These regions of marked neovascularization were commonly associated with accumulations of macrophages, mast cells, and T-cells, indicative of local inflammatory reactions. The matrix components elastin and collagen type VI showed variable distributions which suggested extensive tissue remodelling, whereas collagen type IV was recognized as a basement membrane protein of most blood vessels, as well as being associated with 'stellate' smooth muscle cells. Evidence of local microvascular damage within the shoulder regions of some specimens was demonstrated by extravascular red blood cells, macrophages containing haemosiderin, and perivascular fibrin deposition. These local haemorrhages derived from microvessels beneath the lining of the arterial lumen are a further indication of how the microfocal vascularization of the plaque 'shoulder' might contribute to further complications of inflammation and plaque destabilization in late-stage disease.

Lipoprotein (a) induces angiogenesis on the chick embryo chorioallantoic membrane

BACKGROUND

Both lipoprotein (a) [Lp(a)] and angiogenesis have been shown to be associated with initiation and progression of atherosclerotic plaque. Lp(a) and two neutralizing anti-Lp(a) antibodies were investigated for their capacity to affect the vasoproliferative processes of the chick embryo chorioallantoic membrane (CAM), a useful model for such an investigation.

METHODS

Gelatin sponges loaded with Lp(a) alone or together with anti-Lp(a) antibodies, or with vehicle alone, phosphate-buffered saline (PBS), were implanted in vivo onto the CAM at incubation day 8. Four days later, sponges and the adjacent CAM tissues were assessed for the extent of angiogenesis in terms of microvessel counts.

RESULTS

Lp(a)-loaded sponges gave significantly higher counts than those loaded with the LP(a)-anti-Lp(a) antibodies complex, which overlapped those treated with PBS. The angiogenic response was similar to that obtained with basic fibroblast growth factor, a well known angiogenic molecule.

CONCLUSION

These data suggest that Lp(a) is capable of inducing angiogenesis in vivo, which might account for its ability to enhance and support atherosclerosis.

Influence of vascular load on plasma endothelin-1, cytokines and catecholamine levels in essential hypertensives

In vitro studies demonstrated a relationship between ET-1 and basic Fibroblast Growth Factor (bFGF), and of bFGF with Platelet Derived Growth Factor (PDGF). The present study was carried out to investigate in vivo the behaviour after vascular stress of circulating ET-1, bFGF and PDGF, and catecholamines, and their relationship. In 12 healthy normotensives (NTs) and 15 essential hypertensives (Ehs) venous blood samples to determine circulating ET-1, bFGF and PDGF, and catecholamine (EPI and NE) levels were drawn before and at the third minute of a handgrip test. Blood pressures (BP) and heart rate were automatically recorded before starting, and at 1, 2, and 3 minutes during the test. The NTs showed, in basal condition, lower values than the EHs of all the examined parameters; later, the handgrip test induced significant increases in circulating levels of ET-1, bFGF and catecholamine. In the EHs at the third minute of the exercise significant increases in plasma ET-1 (p < 0.002), bFGF (p < 0.006), and EPI and NE (p < 0.0005) levels were observed. Systolic and diastolic BP significantly increased after handgrip test in NTs and EHs. Plasma ET-1 correlated with bFGF both before (p < 0.01) and at the acme (p < 0.05) of the isometric exercise. Our results show that in EHs plasma ET-1 and bFGF correlate each other, indicating that in human hypertension a linkage between ET-1 and bFGF exists.

Neovascularization in atherectomy specimens from patients with unstable angina: implications for pathogenesis of unstable angina

Although neovascularization has been noted in atherosclerotic plaque, the presence of neovascularization has not been correlated with clinical syndromes. This study examined the relation between neovascularization in atherosclerotic plaque removed during directional coronary atherectomy and clinical status in 28 patients. Neovascularization was determined by immunohistochemistry with endothelial cell-specific monoclonal antibodies and was found in nine (50%) of 18 specimens from patients with unstable angina and in only one (10%) of 10 specimens from patients with stable angina (p < 0.05). There was no significant relation between neovascularization and other clinical factors (age, sex, race, hypertension, diabetes, tobacco use, hypercholesterolemia, positive family history of coronary artery disease, history of myocardial infarction, or stenosis severity). These results suggest that neovoscularization may play a role in the pathogenesis of unstable angina.

Effects of high glucose on vascular endothelial growth factor expression in vascular smooth muscle cells

Vascular endothelial growth factor (VEGF), in addition oto its growth-promoting effects on endothelial cells, can also increase vascular permeability and monocyte migration. It has therefore been implicated in the pathogenic neovascularization associated with diabetic retinopathy and atherosclerosis. However, the factors regulating VEGF expression in the vascular wall are not fully understood. In this study, we examined the regulation of VEGF expression in vascular smooth muscle cells (VSMC) by hyperglycemia as well as by angiotensin II (ANG II). We also examined whether the 12-lipoxygenase (12-LO) product 12-hydroxyeicosatetraenoic acid (12-HETE) can alter VEGF expression, since 12-LO products of arachidonic acid have angiogenic properties, and ANG II as well as high glucose (HG, 25 mM) can increase 12-LO activity and expression in VSMC. Studies were carried out in human (HSMC) or porcine VSMC (PSMC), which were cultured for at least two passages under normal glucose (NG, 5.5 mM) or HG conditions. HG culture alone increased the expression of VEGF mRNA and protein in both HSMC and PSMC. Furthermore, ANG II treatment significantly induced VEGF mRNA and protein expression only in VSMC cultured in HG and not NG. In addition, 12-HETE significantly increased VEGF mRNA and protein expression in HSMC cultured in NG as well as in HG. Cells cultured in HG also secreted significantly greater amounts of VEGF into the culture medium. These results suggest that elevated VEGF production under HG conditions may play a role in the accelerated vascular disease observed in diabetes.

An in vitro model of human dental pulp repair

Pulp tissue responds to dentin injury by laying down reactionary dentin secreted by existing odontoblasts or reparative dentin elaborated by odontoblast-like cells that differentiated from precursor cells in the absence of inner dental epithelium and basement membrane. Furthermore, growth factors or active dentin matrix components are fundamental signals involved in odontoblast differentiation. In vitro, dental pulp cells cultured under various conditions are able to express typical markers of differentiation, but no culture system can re-create pulp response to dentin drilling. This paper reports the behavior of thick slices from human teeth drilled immediately after extraction and cultured from 3 days to 1 month. Results show that the damaged pulp beneath the cavity is able to develop, in vitro, some typical aspects correlated to tissue healing, evidenced by cell proliferation (BrdU-positive cells), neovascularization (positive with antitype-IV collagen antibodies), and the presence of functional (3H proline-positive) cuboidal cells close to the injured area. After 30 days of culture, elongated spindle-shaped cells can be seen aligned along the edges of the relevant dentin walls, whereas sound functional odontoblasts are well-preserved beneath healthy areas. This tissue recovery leads us to believe that such a culture model will be a useful system for testing factors regulating pulp repair.

Morphology and distribution of microglial cells in the young and adult mouse cerebellum

The morphology and distribution of microglial cells were studied in the normal cerebellum of young and adult mice using the histochemical demonstration of nucleoside diphosphatase as a specific microglial marker. Our results showed that microglial cells were present in all cerebellular lobules of both young and adult mice, but their distribution and morphology were not homogeneous throughout the cerebellum. Heterogeneity in microglial cell distribution was exclusively related to their location in the different histological layers, and no significant differences were found either between the different cerebellar lobules or between young and adult mice. Microglial density was higher in the cerebellar nuclei than in the cortex; within the cortex, the molecular layer was less densely populated by microglial cells than the granular layer and the white matter. The morphological study revealed that microglial cells were ramified in all cerebellar lobules of both young and adult mice but showed different sizes and ramification patterns as a function of their specific location in the different histological layers. Several typologies of microglial cells were described on the basis of observations in both horizontal and coronal sections. The specific layer-related pattern of microglial distribution and morphology in mouse cerebellum strongly suggests a physical and functional adaptation of these cells to the characteristics of their microenvironment.

Induction of angiogenesis by smooth muscle cell-derived factor: possible role in neovascularization in atherosclerotic plaque

The development of atherosclerotic plaque is associated with neovascularization in the thickened intima and media of vascular walls. Neovascularization may have a role in the progression of atherosclerotic plaque as well as in the development of intraplaque hemorrhage. However, the mechanism and stimulus for neovascularization in atherosclerotic plaque are unknown. We postulated that smooth muscle cells (SMCs), a major cellular component in the vascular wall, might contribute to the induction of neovascularization in atherosclerotic plaque through the secretion of an angiogenic factor. We observed that endothelial cells (ECs) cultured on collagen gel with SMC-conditioned medium became spindle shaped, invaded the underlying collagen gel, and organized a capillary-like branching cord structure in the collagen gel. The conditioned medium also stimulated EC proliferation and increased the EC-associated plasminogen activator activity. The angiogenic factor in SMC-conditioned medium was retained in a heparin-Sepharose column and eluted with 0.9 M NaCl. Neutralizing anti-vascular endothelial growth factor (VEGF) antibody attenuated the angiogenic activity in the conditioned medium, including the induction of morphologic changes in ECs, mitogenic activity, and increased plasminogen activator activity associated with ECs. Immunoblotting analysis confirmed the secretion of VEGF from SMCs. These observations indicate that SMC may be responsible for the neovascularization in atherosclerotic plaque through the secretion of VEGF.

Nitric oxide mediates cytotoxicity and basic fibroblast growth factor release in cultured vascular smooth muscle cells. A possible mechanism of neovascularization in atherosclerotic plaques

To define the pathophysiological role of nitric oxide (NO) released from vascular smooth muscle cells (VSMC), we examined whether NO released from VSMC induces cytotoxicity in VSMC themselves and adjacent endothelial cells (EC) using a coculture system. Prolonged incubation with interleukin-1 (IL-1) induced large amounts of NO release and cytotoxicity in VSMC. NG-Monomethyl-L-arginine, an inhibitor of NO synthesis, inhibited both NO release and cytotoxicity induced by IL-1. In contrast, DNA synthesis in cocultured EC was not inhibited but rather stimulated by prolonged incubation with IL-1 or sodium nitroprusside (SNP), a NO donor. However, IL-1 and SNP did not stimulate but inhibited DNA synthesis in EC alone. On the other hand, conditioned medium from VSMC incubated for a long period with IL-1 or SNP stimulated DNA synthesis in EC alone. Furthermore, the concentration of basic fibroblast growth factor in the conditioned medium was increased and correlated with the degree of cytotoxicity in VSMC. These results indicate that NO released from VSMC induces VSMC death, which results in release of basic fibroblast growth factor, which then stimulates adjacent EC proliferation. Thus, NO released from VSMC may participate in the mechanism of neovascularization in atherosclerotic plaques.

Induction of vascular endothelial growth factor gene expression by interleukin-1 beta in rat aortic smooth muscle cells

Vascular endothelial growth factor (VEGF) is a potent and specific mitogen for vascular endothelial cells and promotes neovascularization in vivo. To determine whether interleukin-1 beta (IL-1 beta), which is present in atherosclerotic lesions, induces VEGF gene expression in vascular smooth muscle cells, we performed RNA blot analysis on rat aortic smooth muscle cells (RASMC) with a rat VEGF cDNA probe. IL-1 beta increased VEGF mRNA levels in RASMC in a time- and dose-dependent manner. As little as 0.1 ng/ml IL-1 beta increased VEGF mRNA levels by 2-fold and 10 ng/ml IL-1 beta increased VEGF mRNA by 4-fold. We also measured the half-life of VEGF mRNA and performed nuclear run-on experiments before and after addition of IL-1 beta to see if IL-1 beta increased VEGF mRNA levels by stabilizing the mRNA or by increasing its rate of transcription. The normal, 2-h half-life of VEGF mRNA in RASMC was lengthened to 3.2 h (60%) by IL-1 beta, and IL-1 beta increased the rate of VEGF gene transcription by 2.1-fold. In immunoblot experiments with an antibody specific for VEGF, we found that IL-1 beta increased VEGF protein levels in RASMC by 3.3-fold. Together these data indicate that IL-1 beta induces VEGF gene expression in smooth muscle cells. This IL-1 beta-induced expression of VEGF may accelerate the progression of atherosclerotic lesions by promoting the development of new blood vessels.

Tumour angiogenesis

The progressive emergence of a close relationship between the formation of blood vessels in the vicinity of tumour cells and the development and spreading of tumours, strongly suggests that angiogenesis might be a prerequisite for tumour development. Angiogenesis starts and develops in response to two sets of extracellular signals: soluble angiogenic factors and extracellular matrix. Different experimental models have been used to study angiogenesis in vivo, but they have numerous limitations. Three-dimensional culture systems reconstitute normal interactions between endothelial cells and the surrounding extracellular matrix. Numerous parameters including angiogenic growth factors and cytokines, cell-to-cell interactions and cell-to-extracellular matrix adhesion influence the growth and differentiation of endothelial cells in vitro as well as in vivo. Angiogenesis plays a major role not only in tumour growth but also in metastasis development. Mechanisms of switching to angiogenic phenotype have been recently described and onset of angiogenic activity is now recognized as another discrete step in tumorigenesis. Tumour cells can induce b-FGF expression and exportation, VEGF and VEGF receptor expression and inactivation of the cancer suppressor gene encoding for a fragment of thrombospondin. A controlled net proteolytic balance produced by tumour cells or endothelial cells is required to favour migration and invasion of endothelial cells and angiogenesis. The hypothesis that assessment of tumour angiogenesis might predict tumour aggressiveness in human cancer has recently gained support from several clinical studies. This has been shown for cutaneous melanoma, breast carcinoma, and non-small-cell lung cancer by quantitation of microvessels in human biopsies using von Willebrand factor or CD3 antigen labelling with specific antibodies. However, more specific and sensitive markers are needed to improve this approach for predicting tumour aggressiveness. Folkman proposed twenty years ago that inhibition of angiogenesis might represent a suitable complementary strategy for the treatment of various forms of cancer. Since then numerous angiostatic compounds have been identified but very few of them fit the required criteria of a potential drug. Fumagillin and particularly its synthetic analogue AGM 1470 might be developed for use in humans in the near future.

Large-vessel endothelium switches to a microvascular phenotype during angiogenesis in collagen gel culture of rat aorta

The purpose of this study was to investigate the vasoformative behavior in vitro of the native intimal endothelium of the rat aorta. To visualize the intimal surface directly, thoracic aortas were everted using a procedure that sequestered adventitial cells and possible remnant microvessels of periaortic soft tissues inside the aortic tube. Everted aortas embedded in collagen gel and cultured under serum-free conditions generated branching microvessels by a process of sprouting from the aortic intima. The newly formed microvessels originated from patches of activated intimal endothelial cells, which had survived the mechanical damage of the eversion procedure. Activated endothelial cells crawled over each other and engaged in lumen formation forming bilayers or multilayers of cells which became the source of sprouting histotypic microvessels. The endothelium of the newly formed microvessels was positive for factor VIII-related antigen and was partially surrounded by periendothelial cells which expressed alpha-smooth muscle actin. The results of this study indicate that the intimal endothelium of the rat aorta has considerable functional plasticity and can switch to a vasoformative phenotype in response to changes in the surrounding extracellular matrix environment.

Assays for angiogenesis: a review

Accurate, reliable quantitation of the neovascular (angiogenic) response, both in vitro and in vivo, is an essential requirement for the study of new blood vessel growth. Over many years, ingenious ways have been developed for measuring this process, and they have contributed much to our present understanding of the vasculogenesis and angiogenesis that accompany normal embryonic development, lactation and wound healing, as well as tumor growth and a variety of other disease states ranging from diabetic retinopathy to autoimmune vasculitis. In this review we describe and evaluate the methodology and specific features of some of the most frequently used of these assays.