Vascular permeability factor: a tumor-derived polypeptide that induces endothelial cell and monocyte procoagulant activity, and promotes monocyte migration

Antiangiogenic effects of somatostatin analogues

Inhibition of angiogenesis has become a target for antineoplastic therapy and for treatment of retinal neovascularization. The presence of somatostatin receptors on tumour cells and on the proliferating vascular endothelium has led to several in vitro and in vivo studies to investigate the antiproliferative and antiangiogenic effects of somatostatin analogues. Currently available data suggest that somatostatin analogues might inhibit angiogenesis directly through somatostatin receptors present on endothelial cells and also indirectly through the inhibition of growth factor secretion such as IGF-I and vascular endothelial growth factor (VEGF) and reducing monocyte chemotaxis. However, beneficial effects on inhibition of neovascularization have been questioned by some studies. More work is therefore required to firmly establish the role of somatostatin analogues as potential antiangiogenic therapy. The currently available somatostatin analogues have high affinity for somatostatin receptor subtype 2 (sst2) and, to a lesser extent, sst5 and sst3. However, because vascular endothelial cells express several types of somatostatin receptors, it will be important to investigate somatostatin analogues with different receptor subtype affinities, which might increase the spectrum of available therapy for tumours.

Hypoxia-induced pathways in breast cancer

Hypoxia, a common consequence of solid tumor growth in breast cancer and other cancers, serves to propagate a cascade of molecular pathways which include angiogenesis, glycolysis, and alterations in microenvironmental pH. Hypoxia-inducible factors, heterodimeric DNA binding complexes composed of two subunits, provide critical regulation of this response. This review presents a synopsis of the genes induced by hypoxia in the context of breast cancer and discusses how upregulation of HIF-1 activity, and the homologous factor HIF-2, are not only fundamental for the adaptation to hypoxia but also may be critical for tumor progression.

Analysis of coagulation cascade and endothelial cell activation during inhibition of vascular endothelial growth factor/vascular endothelial growth factor receptor pathway in cancer patients

OBJECTIVE

The angiogenesis inhibitor SU5416 is a potent inhibitor of vascular endothelial growth factor (VEGF) receptor-1 and -2. VEGF may be involved in hemostasis by altering the hemostatic properties of endothelial cells. We analyzed the effects of SU5416 on the coagulation cascade and the vessel wall in patients with advanced cancer.

METHODS AND RESULTS

Markers for thrombin generation, activation of the protein C pathway, fibrinolysis, and endothelial cell activation were measured in patients with renal cell carcinoma, soft tissue sarcoma, or melanoma on days 0, 14, and 28 of treatment with SU5416. Three of 17 sampled patients developed a thromboembolic event in the fifth week of treatment. Markers for thrombin generation and fibrinolysis did not show significant changes. We observed a significant increase in endogenous thrombin potential and of parameters reflecting endothelial cell activation (von Willebrand antigen, soluble tissue factor, and soluble E-selectin) in all patients (P< or =0.001). In patients experiencing a thromboembolic event, endogenous thrombin potential, soluble tissue factor, and soluble E-selectin increased to a significantly greater extent (P=0.029, P=0.021, and P=0.007, respectively).

CONCLUSIONS

VEGF is not only a permeability, proliferation, and migration factor, but it is also a maintenance and protection factor for endothelial cells.

Vascular endothelial growth factor (VEGF) is expressed by neoplastic Hodgkin-Reed-Sternberg cells in Hodgkin's disease

Vascular endothelial growth factor (VEGF) is involved in tumour angiogenesis, an important process for the growth and metastatic potential of solid tumours. Numerous studies have demonstrated up-regulation of VEGF at both mRNA and protein level in various tumours and a correlation with advanced stage and prognosis has been demonstrated in some cases. Limited information exists about its role in lymphoid malignancies and in particular, Hodgkin's disease. The present study examined the immunohistochemical expression of VEGF using the monoclonal antibody VG1 in a series of 61 cases of Hodgkin's disease, including both classical Hodgkin's disease and the nodular lymphocyte predominance variant, and correlated these results with microvessel density, using an anti-CD31 monoclonal antibody. In 41 cases (70.6%) of classical Hodgkin's disease and one of the three cases of nodular lymphocyte predominance Hodgkin's disease, the neoplastic Reed-Sternberg and Hodgkin cells expressed VEGF. The staining observed was cytoplasmic, either diffuse or with a focal paranuclear distribution. Macrophages were always positive, while reactive lymphocytes showed occasional positivity. A variable amount of strong extracellular staining was also observed in the tissue stroma and intravascular plasma staining was prominent. There was no statistically significant relationship between VEGF expression and the subtype of Hodgkin's disease or microvessel density. In vitro studies using the Reed-Sternberg cell lines L428 and KM-H2 were also performed in both normoxia and hypoxia and VEGF protein production was assessed by flow cytometry (FACS), immunoassay of cell culture supernatant, and RT-PCR. Analysis by FACS demonstrated a subset of cells in both cell lines reacting with VG1 and analysis of secreted VEGF (pg/ml per 1x10(6) cells) in cell culture supernatant confirmed the normoxic production in both cell lines and significant hypoxic induction (p<0.005). Additionally, both cell lines expressed VEGF mRNA, as demonstrated using the RT-PCR method. In conclusion, neoplastic cells express VEGF in Hodgkin's disease, as is the case in solid tumours, and this expression may be induced by hypoxia. The presence of VEGF in reactive macrophages and in the extracellular matrix might facilitate tumour progression.

Spontaneously formed tumorigenic hybrids of Meth A sarcoma and macrophages grow faster and are better vascularized than the parental tumor

Macrophages and Meth A sarcoma cells spontaneously fuse and give rise to tumorigenic hybrid cell lines with a mixed phenotype. We report here that the hybrid tumors grow faster and have a strikingly better developed vasculature than the parent sarcoma. Thus, electron microscopy and immunohistochemical analysis revealed that in the most active areas of neovascularization, the tumors that emerged from inocula of monoclonal hybrid cell populations had a microvessel density nearly twice that of Meth A tumors after 1 week of growth. Moreover, the proportion of vessels associated with pericytes, detected by staining for smooth muscle alpha-actin, was 3 times higher in the hybrid tumors, attesting to the more advanced differentiation of their vasculature. The collagenous stroma component was also more extensive in the hybrid tumors. Concentration of the angiogenic proteins vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-beta) were significantly higher in supernatants of hybrid cell cultures compared with Meth A cultures. These observations indicate that the growth advantage of the hybrid tumors over the parental sarcoma is due to a higher angiogenic capacity. Because the malignant features of many tumors correlate with angiogenesis and because macrophages are known to be major producers of angiogenic factors, our data open the possibility that the intense neovascularization of highly aggressive cancers in some cases reflects the acquisition of macrophage traits by heterotypic cell fusion.

Angiogenesis, thrombospondin, and ductal carcinoma in situ of the breast

Angiogenesis, the growth of new vessels from existing vasculature, plays an essential role in tumour development. The process involves interaction between a variety of cells, growth factors, and components of the extracellular matrix, regulated by pro-angiogenic and anti-angiogenic factors. This review profiles these factors, outlines the available methods for measuring new vessel formation, and discusses the importance of angiogenesis in breast cancer, with emphasis on ductal carcinoma in situ.

Decreased level of vascular endothelial growth factor in bronchoalveolar lavage fluid of normal smokers and patients with pulmonary fibrosis

Vascular endothelial growth factor (VEGF) plays multifunctional roles in both the development of vasculature and the maintenance of vascular function. A decrease in VEGF reduces angiogenesis and induces apoptosis of vascular endothelial cells. Inhibition of the VEGF receptor causes endothelial cell apoptosis and emphysema. We postulated that VEGF concentrations might be reduced in patients with chronic lung diseases. The level of VEGF was evaluated by enzyme-liked immunosorbent assay in bronchoalveolar lavage fluid (BALF) from normal smokers, nonsmoking volunteers, idiopathic pulmonary fibrosis, pulmonary fibrosis associated with a connective tissue disease, and sarcoidosis. The isoforms of VEGF in BALF were determined by high-performance liquid chromatography. VEGF in nonsmoking volunteers was detectable at a high concentration. In contrast, VEGF in most of the normal smokers was below the detectable limit. The VEGF found in nonsmoking volunteers BALF was VEGF165. VEGF was significantly decreased in idiopathic pulmonary fibrosis, pulmonary fibrosis associated with a connective tissue disease, and sarcoidosis compared with nonsmoking volunteers. The smoking patients showed a further decrease in VEGF. These data suggest that the decrease in VEGF in smokers and patients with chronic lung diseases may reduce angiogenesis and induce apoptosis of vascular endothelial cells.

Vascular growth factors and lymphangiogenesis

Blood and lymphatic vessels develop in a parallel, but independent manner, and together form the circulatory system allowing the passage of fluid and delivering molecules within the body. Although the lymphatic vessels were discovered already 300 years ago, at the same time as the blood circulation was described, the lymphatic system has remained relatively neglected until recently. This is in part due to the difficulties in recognizing these vessels in tissues because of a lack of specific markers. Over the past few years, several molecules expressed specifically in the lymphatic endothelial cells have been characterized, and knowledge about the lymphatic system has started to accumulate again. The vascular endothelial growth factor (VEGF) family of growth factors and receptors is involved in the development and growth of the vascular endothelial system. Two of its family members, VEGF-C and VEGF-D, regulate the lymphatic endothelial cells via their receptor VEGFR-3. With the aid of these molecules, lymphatic endothelial cells can be isolated and cultured, allowing detailed studies of the molecular properties of these cells. Also the role of the lymphatic endothelium in immune responses and certain pathological conditions can be studied in more detail, as the blood and lymphatic vessels seem to be involved in many diseases in a coordinated manner. Discoveries made so far will be helpful in the diagnosis of certain vascular tumors, in the design of specific treatments for lymphedema, and in the prevention of metastatic tumor spread via the lymphatic system.

Plasma vascular endothelial growth factor in sleep apnea syndrome: effects of nasal continuous positive air pressure treatment

Sleep apnea syndrome is associated with recurrent episodic hypoxia during sleep, which has been implicated in the development of cardiovascular morbidity. Hypoxia is the major stimulus of vascular endothelial growth factor (VEGF), which is a potent angiogenic cytokine. In the present article we describe the results of three experiments in which plasma concentrations of VEGF were measured in patients with sleep apnea. In Experiment 1, apnea-hypopnea index was found to be a significant independent predictor of morning VEGF concentrations in 85 male subjects investigated in the sleep laboratory, of whom 47 had an apnea-hypopnea index greater than 20. In Experiment 2, VEGF concentrations measured hourly during the sleep period were found to be significantly higher in a group of five sleep apnea patients compared with six age-similar snorers and six normal young adults (129.1 +/- 43.4 versus 74.6 +/- 11.5 and 32.5 +/- 12.8 pg/ml, respectively [p < 0.007]). In Experiment 3, VEGF concentrations were compared in patients with sleep apnea before and 1 year after nasal continuous positive airway pressure treatment. A significant decrease in VEGF concentrations was found only in patients in whom nocturnal hypoxia improved after treatment (57.1 +/- 62.5 versus 39.6 +/- 46.9 pg/ml, p < 0.01). There was no comparable improvement in patients who did not accept treatment (53.9 +/- 23.6 versus 54.0 +/- 21.5 pg/ml, ns). These results raise the possibility that VEGF may contribute to the long-term adaptation of sleep apnea syndrome to recurrent nocturnal hypoxia.

Vascular endothelial growth factor enhances cardiac allograft arteriosclerosis

BACKGROUND

Cardiac allograft arteriosclerosis is a complex process of alloimmune response, chronic inflammation, and smooth muscle cell proliferation that includes cross talk between cytokines and growth factors.

METHODS AND RESULTS

Our results in rat cardiac allografts established alloimmune response as an alternative stimulus capable of inducing vascular endothelial growth factor (VEGF) mRNA and protein expression in cardiomyocytes and graft-infiltrating mononuclear inflammatory cells, which suggests that these cells may function as a source of VEGF to the cells of coronary arteries. Linear regression analysis of these allografts with different stages of arteriosclerotic lesions revealed a strong correlation between intragraft VEGF protein expression and the development of intimal thickening, whereas blockade of signaling downstream of VEGF receptor significantly reduced arteriosclerotic lesions. In addition, in cholesterol-fed rabbits, intracoronary perfusion of cardiac allografts with a clinical-grade adenoviral vector that encoded mouse VEGF(164) enhanced the formation of arteriosclerotic lesions, possibly secondary to increased intragraft influx of macrophages and neovascularization in the intimal lesions.

CONCLUSIONS

Our findings suggest a positive regulatory role between VEGF and coronary arteriosclerotic lesion formation in the allograft cytokine microenvironment.

Vascular endothelial growth factor (VEGF)-induced angiogenesis in herniated disc resorption

Intervertebral disc herniation is a major cause of low back pain and sciatica. Spontaneous resorption of herniated disc (HD) is frrequently detected by magnetic resonance imaging (MRI). Marked infiltration by macrophages and neo-vascularization are observed upon histogical examination of HD. In addition, enhanced MRI studies suggest that HD resorption occurs more frequently in those completely exposed to the epidural space and that this correlates with their degree of vascularization. We have postulated that the angiogenic factor, vascular endothelial growth factor (VEGF), may be implicated in the neo-vascularization of HD tissues. Here we demonstrate that VEGF and its receptors VEGFR-1 and VEGFR-2 are expressed in human surgical samples of HD. Using a co-culture system comprised of murine peritoneal macrophages and intervertebral disc tissue as a model of the acute phase of HD developed previously, an increase in macrophage VEGF protein and mRNA expression was observed upon exposure to disc tissue. Tumor necrosis factor alpha (TNF-alpha) was required for this induction of VEGF. Use of a novel angiogenesis assay revealed that addition of the conditioned media from the co-culture system resulted in an increase of vascular tubule formation. This effect was strongly inhibited by anti-VEGF antibody, but augmented by recombinant VEGF. We conclude that VEGF induction, under the co-culture conditions tested can result in neo-vascularization of intervertebral disc tissue and may thus play a role in the resorption of HD.

Role of monocytes and macrophages in adult angiogenesis: a light at the tunnel's end

In spite of sustained efforts, there are still gaps in our understanding of angiogenesis as it takes place in vivo. Older observations and a number of recent developments strongly involve the blood mononuclear cell population, collectively known as monocytes (MC), in the normal and pathological adult angiogenesis. An emerging paradigm should eventually incorporate the established biochemical cross talk between MC and their descendents, tissular macrophages (Mph), and the endothelial cells (EC); additionally, it should account for both the intercellular cooperation at the morphological level and the phenotypic overlap between the two cell populations. This focused review puts together the pieces of this puzzle in such a way as to suggest an alternative angiogenic model applicable to adult animals, and particularly to pathological conditions. A working hypothesis is put forward, which is centered on the preformation of capillary lumen as a "tunnel" drilled by penetrating MC/Mph. The tunnels may be colonized in a later stage by sprouts, circulating progenitor endothelial cells (CPEC) or transdifferentiated EC. Thus, MC/Mph are suggested to be included among the targets of therapeutic manipulation of angiogenesis.

Tumor-associated macrophages in breast cancer

Neoplastic cells form only one part of a complex network of cell types that make up a breast tumor. The normal cell types that make up the nonneoplastic components of tumors include fibroblasts, endothelium, and inflammatory cells, such as tumor associated macrophages (TAMs). TAMs have the potential to carry out both anti- and protumor activities In their antitumor role TAMs can present tumor antigens to cytotoxic T-cells and are capable of being directly cytotoxic to neoplastic cells. Conversely, TAMs are also able to promote tumor growth directly by secreting breast tumor mitogens, such as epidermal growth factor, and indirectly by stimulating tumor angiogenesis and metastasis. Recent studies have indicated that in breast cancers the protumor role of TAMs is dominant, and that TAMs may be executing a "wound healing" type of process in response to stimuli found in the tumor microenvironment, such as hypoxia. As such, TAMs may provide opportunities for future therapeutic interventions.

Developmental control of blood cell migration by the Drosophila VEGF pathway

We show that a vascular endothelial growth factor (VEGF) pathway controls embryonic migrations of blood cells (hemocytes) in Drosophila. The VEGF receptor homolog is expressed in hemocytes, and three VEGF homologs are expressed along hemocyte migration routes. A receptor mutation arrests progression of blood cell movement. Mutations in Vegf17E or Vegf27Cb have no effect, but simultaneous inactivation of all three Vegf genes phenocopied the receptor mutant, and ectopic expression of Vegf27Cb redirected migration. Genetic experiments indicate that the VEGF pathway functions independently of pathways governing hemocyte homing on apoptotic cells. The results suggest that the Drosophila VEGF pathway guides developmental migrations of blood cells, and we speculate that the ancestral function of VEGF pathways was to guide blood cell movement.

The role of tumour-associated macrophages in tumour progression: implications for new anticancer therapies

The role of macrophages in tumour growth and development is complex and multifaceted. Whilst there is limited evidence that tumour-associated macrophages (TAMs) can be directly tumouricidal and stimulate the anti-tumour activity of T cells, there is now contrasting evidence that tumour cells are able to block or evade the activity of TAMs at the tumour site. In some cases, tumour-derived molecules even redirect TAM activities to promote tumour survival and growth. Indeed, evidence has emerged for a symbiotic relationship between tumour cells and TAMs, in which tumour cells attract TAMs and sustain their survival, with TAMs then responding to micro-environmental factors in tumours such as hypoxia (low oxygen tension) by producing important mitogens as well as various growth factors and enzymes that stimulate tumour angiogenesis. This review presents evidence for the number and/or distribution of TAMs being linked to prognosis in different types of human malignancy. It also outlines the range of pro- and anti-tumour functions performed by TAMs, and the novel therapies recently devised using TAMs to stimulate host immune responses or deliver therapeutic gene constructs to solid tumours.

Adenovirus vector-mediated transfer of the vascular endothelial growth factor cDNA to healing abdominal fascia enhances vascularity and bursting strength in mice with normal and impaired wound healing

BACKGROUND

We hypothesized that adenovirus-mediated transfer of the vascular endothelial growth factor (VEGF121) complementary DNA (cDNA) to murine laparotomy fascial wounds would enhance vascularity and bursting strength.

METHODS

Microfibrillar collagen sponges saturated with adenovirus (Ad) vectors encoding for the human VEGF121 cDNA (Ad(CU)VEGF121.1), a control marker gene (Ad beta gal, AdLuc) or no transgene (AdNull) were sutured to fascial edges during laparotomy closure in normal mice and mice treated with dexamethasone. Endpoints addressed included transgene expression in the fascia and surrounding tissue, the number of blood vessels in the healing wound determined using immunostaining, and wound bursting strength using a calibrated tensinometer.

RESULTS

Transgene expression was detected readily in the fascial edges, but only marginally detectable in neighboring tissues. In normal mice and mice treated with dexamethasone, no differences were observed at 7 days. Strikingly, however, 21 days after wound closure/therapy, significantly more blood vessels were present in the wounds that received the VEGF121 vector compared with controls (normal: AdNull: 4.2 +/- 1.8; Ad(CU)VEGF121.1: 11.2 +/- 1.2; P <.05; dexamethasone: AdNull: 1.4 +/- 0.8; Ad(CU)VEGF121.1: 5.4 +/- 1.2; P <.05), and bursting strength was significantly higher in VEGF121-treated wounds (normal: AdNull: 665 +/- 68 mN/mm; Ad(CU)VEGF121.1: 956 +/- 82 mN/mm; P <.0005; dexamethasone: AdNull: 234 +/- 111 mN/mm; Ad(CU)VEGF121.1: 592 +/- 121 mN/mm; P <.03).

CONCLUSIONS

Adenovirus-mediated gene transfer to healing fascial wounds is achieved readily using a microfibrillar collagen sponge, with transfer of the human VEGF121 cDNA significantly enhancing wound vascularity and bursting strength in normal mice, as well as in mice treated with dexamethasone.

Retinal vascular endothelial growth factor induces intercellular adhesion molecule-1 and endothelial nitric oxide synthase expression and initiates early diabetic retinal leukocyte adhesion in vivo

Leukocyte adhesion to the diabetic retinal vasculature results in early blood-retinal barrier breakdown, capillary nonperfusion, and endothelial cell injury and death. Previous work has shown that intercellular adhesion molecule-1 (ICAM-1) and CD18 are required for these processes. However the relevant in vivo stimuli for ICAM-1 and CD18 expression in diabetes remain unknown. The current study investigated the causal role of endogenous vascular endothelial growth factor (VEGF) and nitric oxide in initiating these events. Diabetes was induced in Long-Evans rats with streptozotocin, resulting in a two- to threefold increase in retinal leukocyte adhesion. Confirmed diabetic animals were treated with a highly specific VEGF-neutralizing Flt-Fc construct (VEGF TrapA(40)). Retinal ICAM-1 mRNA levels in VEGF TrapA(40)-treated diabetic animals were reduced by 83.5% compared to diabetic controls (n = 5, P < 0.0001). VEGF TrapA(40) also potently suppressed diabetic leukocyte adhesion in retinal arterioles (47%, n = 11, P < 0.0001), venules (36%, n = 11, P < 0.0005), and capillaries (36%, n = 11, P < 0.001). The expression of endothelial nitric oxide synthase (eNOS), a downstream mediator of VEGF activity, was increased in diabetic retina, and was potently suppressed with VEGF TrapA(40) treatment (n = 8, P < 0.005). Further, VEGF TrapA(40) reduced the diabetes-related nitric oxide increases in the retinae of diabetic animals. The inhibition of eNOS with N-omega-nitro-L-arginine methyl ester also potently reduced retinal leukocyte adhesion. Although neutrophil CD11a, CD11b, and CD18 levels were increased in 1-week diabetic animals, VEGF TrapA(40) did not alter the expression of these integrin adhesion molecules. Taken together, these data demonstrate that VEGF induces retinal ICAM-1 and eNOS expression and initiates early diabetic retinal leukocyte adhesion in vivo. The inhibition of VEGF bioactivity may prove useful in the treatment of the early diabetic retinopathy.

GM-CSF: a strong arteriogenic factor acting by amplification of monocyte function

We investigated the role of the colony stimulating factor for monocytes (GM-CSF) to test the hypothesis whether prolongation of the monocyte's life cycle will support arteriogenesis (rapid growth of preexisting collateral arteries). This appeared logical in view of our discovery that circulating monocytes play an important part in the positive remodeling of small preexisting arterioles into arteries to compensate for arterial occlusions (arteriogenesis) and especially following our findings that MCP-1 markedly increases the speed of arteriogenesis. The continuous infusion of GM-CSF for 7 days into the proximal stump of the acutely occluded femoral artery of rabbits by osmotic minipump produced indeed a marked arteriogenic response as demonstrated by an increase (2-fold) in number and size of collateral arteries on postmortem angiograms and by the increase of maximal blood flow during vasodilation measured in vivo by blood pump perfusion of the hindquarter (5-fold). When GM-CSF and MCP-1 were simultaneously infused the effects on arteriogenesis were additive on angiograms as well as on conductance. GM-CSF was also able to widen the time window of MCP-1 activity: MCP-1 treatment alone was ineffective when given after the third week following occlusion. When administered together with GM-CSF about 80% of normal maximal conductance of the artery that was replaced by collaterals were achieved, a result that was not reached before by any other experimental treatment. Experiments with cells isolated from treated animals showed that monocyte apoptosis was markedly reduced. In addition we hypothesize that GM-CSF may aid in releasing pluripotent monocyte (stem-) cells from the bone marrow into the circulation. In contrast to MCP-1, GM-CSF showed no activity on monocyte transmigration through- and also no influence on monocyte adhesion to cultured endothelial cells. In conclusion we have discovered a new function of the hemopoietic stem cell factor GM-CSF, which is also a powerful arteriogenic peptide that acts via prolongation of the life cycle of monocytes/macrophages.

Monoclonal antibodies to vascular endothelial growth factor (VEGF) and the VEGF receptor, FLT-1, inhibit the growth of C6 glioma in a mouse xenograft

Monoclonal antibodies raised to peptide sequences of vascular endothelial growth factor (VEGF) and the VEGF receptor, FLT-1, inhibited the growth of C6 tumors growing subcutaneously in nude mice. Immunohistochemical analysis demonstrated antibody targeting of blood vessels, tumor cells, and macrophages. A control antibody demonstrated no growth inhibition or tumor uptake. An antibody to FLT- I impaired microvascular maturation and diminished the accumulation of tumor infiltrating macrophages. The antibodies demonstrated affinity for microvasculature and tumor cells in immunohistochemistry of human glioblastoma multiforme. Targeting VEGF and its receptors has potential in the treatment of tumors of the central nervous system. FLT-1 presents an attractive target due to its presence on multiple cell types.

Role of ischemia and of hypoxia-inducible genes in arteriogenesis after femoral artery occlusion in the rabbit

Vascular endothelial growth factor (VEGF) is known to play an important role in angiogenesis. Its place in collateral artery growth (arteriogenesis), however, is still debated. In the present study, we analyzed the expression of VEGF and its receptors (Flk-1 and Flt-1) in a rabbit model of collateral artery growth after femoral artery occlusion. Hypoxia presents the most important stimulus for VEGF expression. We therefore also investigated the expression level of distinct hypoxia-inducible genes (HIF-1alpha, LDH A) and determined metabolic intermediates indicative for ischemia (ATP, creatine phosphate, and their catabolites). We found that arteriogenesis was not associated with an increased expression of VEGF or the mentioned hypoxia-inducible genes. Furthermore, the high-energy phosphates and their catabolites were entirely within normal limits. Despite the absence of an increased expression of VEGF and its receptors, collateral vessels increased their diameter by a factor of 10. The speed of collateral development could be increased by infusion of the chemoattractant monocyte chemotactic protein-1 but not by infusion of a 30 times higher concentration of VEGF. From these data, we conclude that under nonischemic conditions, arteriogenesis is neither associated with nor inducible by increased levels of VEGF and that VEGF is not a natural agent to induce arteriogenesis in vivo.

Update on tumor cell procoagulant factors

Tumor cells produce tissue factor, cancer procoagulant, plasminogen activators and other factors that interact with the coagulation system, the fibrinolytic system and vascular or blood cells such that they can upset the normal homeostasis and balance between activation and inhibition of the coagulation and fibrinolytic systems. These activities play a role in tumor cell growth and metastasis, vascular wall function, and hemostasis. Proteases and their inhibitors are intimately involved in all aspects of the hemostatic, cell proliferation and cellular signalling systems. This review provides a brief examination of recent observations in this complex interaction of cellular and hemostatic factors.

Blood-retinal barrier breakdown in experimental coronavirus retinopathy: association with viral antigen, inflammation, and VEGF in sensitive and resistant strains

Intraocular coronavirus inoculation results in a biphasic retinal disease in susceptible mice (BALB/c) characterized by an acute inflammatory response, followed by retinal degeneration associated with autoimmune reactivity. Resistant mice (CD-1), when similarly inoculated, only develop the early phase of the disease. Blood-retinal barrier (BRB) breakdown occurs in the early phase in both strains, coincident with the onset of inflammation. As the inflammation subsides, the extent of retinal vascular leakage is decreased, indicating that BRB breakdown in experimental coronavirus retinopathy (ECOR) is primarily due to inflammation rather than to retinal cell destruction. Vascular endothelial growth factor (VEGF) is upregulated only in susceptible mice during the secondary (retinal degeneration) phase.

An inhibitory role of the phosphatidylinositol 3-kinase-signaling pathway in vascular endothelial growth factor-induced tissue factor expression

Vascular endothelial growth factor (VEGF) is not only essential for vasculogenesis and angiogenesis but is also capable of inducing tissue factor, the prime initiator of coagulation, in endothelial cells. In this study we have analyzed the VEGF-elicited pathways involved in the induction of tissue factor in human umbilical cord vein endothelial cells. Using specific low molecular weight inhibitors we could demonstrate a crucial role of the p38 and Erk-1/2 mitogen-activated protein (MAP) kinases. In contrast, treatment with wortmannin or LY294002, inhibitors of phosphatidylinositol 3 (PI3)-kinase, resulted in a strong enhancement of the VEGF-induced tissue factor production, indicating a negative regulatory role of the PI3-kinase on tissue factor-inducing pathways. Accordingly, transduction with constitutively active Akt led to a reduction of VEGF-induced tissue factor production. Western blot analyses using antibodies specific for phosphorylated p38 showed an enhanced activation of this MAP kinase in human umbilical cord vein endothelial cells when stimulated with VEGF in the presence of wortmannin in comparison to either agent alone. Thus, the negative regulation of the PI3-kinase pathway on endothelial tissue factor activity can be explained at least in part by a suppression of this MAP kinase-signaling pathway. This is the first demonstration of a reciprocal relationship between procoagulant activity and the PI3-kinase-Akt signaling pathway, and it reveals a novel mechanism by which tissue factor expression can be controlled in endothelial cells.

Significant correlation of monocyte chemoattractant protein-1 expression with neovascularization and progression of breast carcinoma

BACKGROUND

Macrophages often infiltrate into solid tumor tissues. Tumor-associated macrophages (TAMs) are known to play a crucial role in tumor progression. Monocyte chemoattractant protein-1 (MCP-1) is one of the major chemokines capable of inducing chemotactic migration of monocytes.

METHODS

With the objective of investigating the clinical significance of MCP-1, the authors analyzed the expression of MCP-1 and of some other molecules by immunohistochemistry in 230 samples of primary breast carcinoma tissue. MCP-1 staining was performed using an anti-MCP-1 monoclonal antibody, and it was assessed by grading the percentage of stained cells.

RESULTS

It was found that 117 breast tumor specimens (51%) had intensive staining in tumor cells. The expression of MCP-1 in tumor cells had a significant correlation with the expression of thymidine phosphorylase and membrane type 1-matrix metalloproteinase. In addition, MCP-1 expression tended to be associated with the accumulation of TAMs, which were counted by CD68 staining, and with microvessel density. MCP-1 expression in TAMs was correlated significantly with the histologic vessel invasion of tumor cells.

CONCLUSIONS

The results of this study suggest that MCP-1 may play key roles in macrophage recruitment, in the expression of angiogenic factors, and in the activation of matrix metalloproteinases in patients with breast carcinoma.

Paracrine angiogenic loop between head-and-neck squamous-cell carcinomas and macrophages

Angiogenesis, an essential step in the development of neoplasia, is a complex process that involves the interaction of tumor cells with stromal cells. Tumor-associated macrophages (TAMs) can participate in the induction of tumor angiogenesis and are thought to be of prognostic value in some neoplasms. We have investigated how macrophages contribute to angiogenesis in head-and-neck squamous-cell carcinoma (HNSCC) and have found that tumor cells attract monocytes and activate them to secrete angiogenic factors. The attraction of macrophages was due to the secretion of monocyte chemotactic protein-1 and TGF-beta1 by tumor cells, while tumor production of TGF-beta1 was responsible for activating macrophages. In addition, activated macrophages produced cytokines that acted in a paracrine fashion by secreting both TNF-alpha and IL-1, which in turn stimulated tumor cells to secrete increased levels of IL-8 and VEGF. These data demonstrate that TAMs play an important role in the in vivo induction of angiogenesis in HNSCC and suggest that anti-angiogenic therapies for HNSCC and perhaps other neoplasms must include strategies that will block the ability of tumor cells to recruit macrophages into the tumor micro-environment.

Budesonide reduces vascular endothelial growth factor secretion and expression in airway (Calu-1) and alveolar (A549) epithelial cells

Vascular endothelial growth factor (VEGF), a cytokine expressed in the respiratory epithelial cells, induces vascular hyperpermeability and edema, symptoms that are alleviated by budesonide, an anti-asthma corticosteroid. However, modulation of VEGF levels by budesonide in the respiratory epithelium has not been studied. In this study, we investigated the mechanisms of VEGF secretion using brefeldin A and monensin in human airway (Calu-1) and alveolar (A549) epithelial cells, and further determined whether budesonide inhibits VEGF secretion and mRNA expression through a glucocorticoid receptor-mediated mechanism. In both cell types, VEGF secretion was inhibited by brefeldin A and monensin, suggesting vesicular transport of VEGF through endoplasmic reticulum (ER)-golgi pathway. At concentrations devoid of cytotoxicity, budesonide reduced VEGF secretion and VEGF mRNA expression in both cell types and these effects were inhibited by mifepristone (RU 486), a glucocorticoid receptor antagonist, suggesting that budesonide reduces VEGF secretion and expression through its glucocorticoid receptor-mediated action. Also, budesonide-mediated inhibition of VEGF mRNA was time- and protein synthesis-dependent. Thus, budesonide may be of potential value in treating disorders of the respiratory tract that are associated with VEGF elevation.

Extensive in vivo angiogenesis following controlled release of human vascular endothelial cell growth factor: implications for tissue engineering and wound healing

Vascular endothelial cell growth factor (VEGF) has strong stimulating effects on vascularization. Though very potent, VEGF is rapidly degraded due to its short half-life and when administrated by uncontrolled and nonspecific methods; however, its systemic administration in large doses can cause harmful side effects. Controlled release technology would allow delivering desired levels of bioactive VEGF within extended periods and permit examination of the in vivo effects of the compound in a broader way. The objective of this study was to determine the in vitro release behavior of VEGF from calcium alginate microspheres and the potency of this controlled release system in promoting localized neovascularization at the subcutaneous site of the rat model. In vitro release of human VEGF165 (2 and 4 microg/cm3 microsphere) was studied for 3 weeks under static conditions at 25 degrees C, and daily hormone release was measured using a competitive enzyme immunoassay. Following an uncontrolled release within the first 4 days, a quite constant zero-order VEGF release of 50 to 90 and 70 to 120 ng/day was achieved from 2 and 4 microg/cm3 polymer loaded microspheres respectively. In vivo angiogenesis was studied for a period of 8 weeks and evaluated using immunoperoidase staining and histopathological measurements. In vivo studies with rats (n = 24) showed a considerable level of capillary network formation at the epigastric groin fascia of VEGF microsphere-implanted rats starting from the first week. The most extensive neovascularization was observed in the group with 3 week postimplanted 4 microg VEGF containing microspheres; this level of vascularization was quite similar after 8 weeks. While the control group showed no evidence of angiogenesis, the difference in VEGF-induced neovascularization is statistically significant (p < 0.03). Immunostaining of the specimens showed a strong relationship between the release of human VEGF and neovascularization. The controlled VEGF release system described here promotes vigorous angiogenesis and has applicability for tissue engineering and wound healing studies.

Molecular basis for the relationship between thrombosis and cancer

Cancer patients are highly susceptible to thromboembolic complications, which some have estimated accounts for a significant percentage of the morbidity and mortality of the disease. Not all of the mechanisms for the production of the hypercoagulable state characteristic of cancer are entirely understood. Those that are known seem to interdigitate the biology of cancer with the major regulatory pathways that mediate blood coagulation, platelet-vessel wall interaction, fibrinolysis and inflammatory cytokine production. In other words, the events responsible for thrombosis in cancer appears to be a result of an over exuberant host response in an attempt to delimit tumor growth. In this brief review, therefore, we attempt to put into the context of tumor growth, angiogenesis and metastasis the current information about the pathogenesis of venous thromboembolism (VTE).

Effect of human recombinant vascular endothelial growth factor165 on progression of atherosclerotic plaque

OBJECTIVES

This study was designed to evaluate the impact of recombinant human vascular endothelial growth factor165 (rhVEGF) on atherosclerotic plaque progression.

BACKGROUND

Therapeutic angiogenesis represents a promising treatment for ischemic diseases. However, angiogenesis may impact atherosclerosis.

METHODS

Albumin or rhVEGF was administered by a single intramuscular injection (2 microg/kg body weight) to New Zealand White rabbits fed with a 0.25% cholesterol diet beginning three weeks before therapy. Subsets of rabbits from each group underwent perfusion-fixation and harvesting of the thoracic aorta for morphometric and immunohistochemical analyses at 7 or 21 days.

RESULTS

The mean plaque area was 15.75+/-2.28% and 22.00+/-3.24% with VEGF and 0.67+/-0.22% and 1.17+/-0.34% with albumin at 7 and 21 days, respectively. The plaque circumference was 13.00+/-2.58% and 23.75+/-2.86% with VEGF and 2.50+/-0.65% and 6.25+/-1.88% with albumin at 7 and 21 days, respectively. The maximal plaque thickness was 0.11+/-0.002 and 0.15+/-0.007 mm with VEGF and 0.04+/-0.009 and 0.07+/-0.003 mm with albumin at 7 and 21 days, respectively. The endothelial density (reported as percent total plaque area) was 31.75+/-4.42% and 63.00+/-8.45% with VEGF and 7.75+/-1.65% and 12.75+/-1.93% with albumin at 7 and 21 days, respectively. The macrophage density was 4.5+/-0.86 and 19.25+/-1.54 with VEGF and 4.26+/-0.75 and 6.00+/-1.08 with albumin at 7 and 21 days, respectively.

CONCLUSIONS

Recombinant human VEGF increases the rate and degree of atherosclerotic plaque formation in the thoracic aorta in a cholesterol-fed rabbit model.

Angiogenesis in acute promyelocytic leukemia: induction by vascular endothelial growth factor and inhibition by all-trans retinoic acid

Recent studies indicate that angiogenesis is important in the pathogenesis of leukemias, apart from its well-established role in solid tumors. In this study, the possible role of angiogenesis in acute promyelocytic leukemia (APL) was explored. Bone marrow trephine biopsies from patients with APL showed significantly increased microvessel density and hot spot density compared with normal control bone marrow biopsies. To identify the mediators of angiogenesis in APL, quantitative and functional assays were performed using the NB4 APL cell line as a model system. Conditioned media (CM) from the NB4 cells strongly stimulated endothelial cell migration. CM from the NB4 cells contained high levels of vascular endothelial growth factor (VEGF) but not basic fibroblast growth factor (bFGF). Most important, the addition of neutralizing VEGF antibodies completely inhibited the ability of NB4 CM to stimulate endothelial cell migration, suggesting that APL angiogenesis is mediated by VEGF. The effect of all-trans retinoic acid (ATRA) on APL angiogenesis was then studied. ATRA therapy resulted in a decrease in bone marrow microvessel density and hot spot density. CM from ATRA-treated APL cells did not stimulate endothelial cell migration. Finally, quantitative assays showed that ATRA treatment resulted in the abrogation of VEGF production by the NB4 cells. These results show that there is increased angiogenesis and VEGF production in APL and that ATRA therapy inhibits VEGF production and suppresses angiogenesis. The addition of specific antiangiogenic agents to differentiation therapy or chemotherapy should be explored. (Blood. 2001;97:3919-3924)

Signaling mechanisms mediating vascular protective actions of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is essential for angiogenesis in health and pathophysiology, and it is currently a major focus for drug targeting in the development of treatments for diverse human diseases. Recently, we proposed that VEGF could also play a role as a vascular protective factor in the adult vasculature and in disease. In this model, vascular protection is defined as a VEGF-induced enhancement of endothelial functions that mediate the inhibition of vascular smooth muscle cell proliferation, enhanced endothelial cell survival, suppression of thrombosis, and anti-inflammatory effects. A feature of this model is that protective effects of VEGF are essentially independent of angiogenesis or endothelial cell proliferation. VEGF-dependent cell survival and VEGF-induced synthesis of nitric oxide and prostacyclin are likely to be key mediators of a vascular protective effect. Vascular protection should help to improve insight into the underlying mechanisms of cardiovascular actions of VEGF and prove valuable for developing novel therapeutic approaches to cardiovascular disease.

Granulomatous tissue formation of shikon and shikonin by air pouch method

"The extract of shikon" (SK) and shikonin play important roles in the development of granulomatous tissue formation. To reveal the augmenting effect of SK or shikonin on vascular endothelial growth factor (VEGF) production and neovascularization, we investigated murine granulomatous tissue induced by SK and shikonin, comparing them to pouches in which trehalose 6,6'-dimycolate (TDM) was injected. The development of granulomatous tissue formation was evaluated by the wet weight of pouch walls. At day 5 and 7 after SK and shikonin injection, prominent granulomatous tissue formation was detected. Histological observations on the development of granulomatous tissue showed that the pouch was formed in the submuscular connective tissue and necrotic tissue directly facing the cavity and granulomatous tissue developed in the connective tissue. At day 1, VEGF-positive neutrophils accumulated in the pouch wall. Granulomatous tissue formation and neovascularization by injection of SK or shikonin was not more prominent than TDM. However, the present results indicate that SK and shikonin induce neovascularization in granulomatous tissue.

Coagulation and cancer: implications for diagnosis and management

Coagulation disorders are a common problem in neoplastic patients and many factors contribute to increase the risk of thromboembolic events in these patients. An hypercoagulable state is induced by malignant cells interacting directly with hemostatic system and activating the coagulation cascade. More sensitive tests to assess an hypercoagulable state in cancer patients have been developed; even though these tests are always altered in cancer patients, none of them possess a clinical significance in terms of predictive value for the occurence of thromboembolism and disease prognosis in the individual patient. The most frequent thromboembolic complications in cancer patients are deep vein thrombosis of the lower extremities and pulmonary embolism; therefore, disseminated intravascular coagulation, thrombotic thrombocytopenic purpura or haemolytic uremic syndrome are special manifestations of neoplastic disease. Diagnosis of idiopathic deep vein thrombosis, in the absence of other risk factors, could indicate the presence of occult malignant disease; however, the need for an extensive work-up to detect malignancy is still controversial. Neoplastic patients showing a thromboembolic event should be treated with unfractioned heparin or, alternatively, with low molecular weight heparins. In order to prevent recurrence, the administration of heparin should be associated and followed by an oral anticoagulant drug. In recent years new approaches in anti-aggregation therapy have been studied, such as COX-inhibitors, cicaprost and ReoPro; further studies are needed to determine the usefulness of these molecules in treatment of malignancies.

Vascular endothelial growth factor secreted by replicating hepatocytes induces sinusoidal endothelial cell proliferation during regeneration after partial hepatectomy in rats

BACKGROUND

The aim of this study was to investigate regulatory mechanisms of sinusoidal endothelial cell (SEC) proliferation after hepatectomy in rats.

METHODS

We investigated expressions of vascular endothelial cell growth factor (VEGF) and its receptors, flt-1 and KDR/flk-1, in regenerating liver after 70% hepatectomy. Proliferation of both hepatocytes and SECs was also monitored by evaluating the proliferating cell nuclear antigen (PCNA) labeling index. Furthermore, VEGF production by cultured hepatocytes isolated at different times after hepatectomy was measured in vitro.

RESULTS

The expression of VEGF mRNA was increased markedly between 48 and 72 h after hepatectomy, and thereafter decreasing gradually. The immunohistochemical staining revealed that expression of VEGF started to increase 24 h after hepatectomy, with a peak at 72 h, and the majority of the VEGF-positive cells were hepatocytes located in periportal areas. Meanwhile, expression of flt-1 and KDR/flk-1 was observed along the sinusoids even before hepatectomy, but was increased between 72 and 120 h. Furthermore, VEGF production by cultured hepatocytes isolated 72 h after hepatectomy was significantly increased. The PCNA labeling index of the SECs exhibited a delayed and slower regenerative response in comparison to the hepatocytes, reaching a peak at 72 h.

CONCLUSIONS

These data strongly suggest that VEGF secreted by proliferating hepatocytes may represent an important stimulator of SEC proliferation.

Vascular endothelial growth factor enhances atherosclerotic plaque progression

Vascular endothelial growth factor (VEGF) can promote angiogenesis but may also exert certain effects to alter the rate of atherosclerotic plaque development. To evaluate this potential impact on plaque progression, we treated cholesterol-fed mice doubly deficient in apolipoprotein E/apolipoprotein B100 with low doses of VEGF (2 microg/kg) or albumin. VEGF significantly increased macrophage levels in bone marrow and peripheral blood and increased plaque area 5-, 14- and 4-fold compared with controls at weeks 1, 2 and 3, respectively. Plaque macrophage and endothelial cell content also increased disproportionately over controls. In order to confirm that the VEGF-mediated plaque progression was not species-specific, the experiment was repeated in cholesterol-fed rabbits at the three-week timepoint, which showed comparable increases in plaque progression.

Hemoglobin enhances tissue factor expression on human malignant cells

Tissue Factor (TF) is a transmembrane glycoprotein that complexes with factor VII/activated factor VII to initiate blood coagulation. TF may be expressed on the surface of various cells including monocytes and endothelial cells. Over-expression of TF in human tumor cell lines promotes metastasis. We recently showed that hemoglobin (Hb) forms a specific complex with TF purified from human malignant melanoma cells and enhances its procoagulant activity (PCA). To further study this interaction, we examined the effect of Hb on the expression of TF on human malignant (TF+) cells and KG1 myeloid leukemia (TF-) cells. Human melanoma A375 and J82 bladder carcinoma cells, which express TF at moderate and relatively high levels, respectively, were incubated with varying concentrations (0-1.5 mg/ml) of Hb. After washing, cells were analyzed for Hb binding and TF expression using flow cytometry and confocal microscopy. Hb bound to the cells in a concentration-dependent manner, and increased both TF expression and PCA. The human A375 malignant melanoma cells incubated with Hb (1 mg/ml) expressed up to six times more TF antigen than cells without Hb. This increase in TF expression and PCA of intact cells incubated with Hb was significantly inhibited by cycloheximide at a concentration of 10 microg/ml (P < 0.01). An increase in total cellular TF antigen content was demonstrated by specific immunoassay. In contrast, Hb (5 mg/ml) did not induce TF expression and PCA on KG1 cells as determined by flow cytometry and TF (FXAA) activity. We conclude that Hb specifically binds to TF-bearing malignant cells and increases their PCA. This effect seems to be at least partly due to de novo synthesis of TF and increased surface expression. However, the exact mechanism by which Hb binds and upregulates TF expression remains to be determined.

Oxidized LDL regulates vascular endothelial growth factor expression in human macrophages and endothelial cells through activation of peroxisome proliferator-activated receptor-gamma

Vascular endothelial growth factor (VEGF) has been recognized as an angiogenic factor that induces endothelial proliferation and vascular permeability. Recent studies have also suggested that VEGF can promote macrophage migration, which is critical for atherosclerosis. We have reported that VEGF is remarkably expressed in activated macrophages, endothelial cells, and smooth muscle cells within human coronary atherosclerotic lesions, and we have proposed the significance of VEGF in the progression of atherosclerosis. To clarify the mechanism of VEGF expression in atherosclerotic lesions, we examined the regulation of VEGF expression by oxidized low density lipoprotein (Ox-LDL), which is abundant in atherosclerotic arterial walls. A recent report has revealed that peroxisome proliferator-activated receptor-gamma (PPARgamma) is expressed not only in adipocytes but also in monocytes/macrophages and has suggested that PPARgamma may have a role in the differentiation of monocytes/macrophages. Furthermore, 9- and 13-hydroxy-(S)-10,12-octadecadienoic acid (9- and 13-HODE, respectively), the components of Ox-LDL, may be PPARgamma ligands. Therefore, we investigated the involvement of PPARgamma in the regulation of VEGF by Ox-LDL. PPARgamma expression was detected in human monocyte/macrophage cell lines, human acute monocytic leukemia (THP-1) cells, and human coronary artery endothelial cells (HCAECs). Ox-LDL (10 to 50 microg/mL) upregulated VEGF secretion from THP-1 dose-dependently. VEGF mRNA expression in HCAECs was also upregulated by Ox-LDL. The mRNA expression of VEGF in THP-1 cells and HCAECs was also augmented by PPARgamma activators, troglitazone (TRO), and 15-deoxy-(12,14)-prostaglandin J(2) (PGJ2). In contrast, VEGF expression in another monocyte/macrophage cell line, human histiocytic lymphoma cells (U937), which lacks PPARgamma expression, was not augmented by TRO or PGJ2. We established the U937 cell line, which permanently expresses PPARgamma (U937T). TRO and Ox-LDL augmented VEGF expression in U937T. In addition, VEGF production by THP-1 cells was significantly increased by exposure to 9-HODE and 13-HODE. In conclusion, Ox-LDL upregulates VEGF expression in macrophages and endothelial cells, at least in part, through the activation of PPARgamma.

The splice variants of vascular endothelial growth factor (VEGF) and their receptors

Vascular endothelial growth factor (VEGF) is a secreted mitogen highly specific for cultured endothelial cells. In vivo VEGF induces microvascular permeability and plays a central role in both angiogenesis and vasculogenesis. VEGF is a promising target for therapeutic intervention in certain pathological conditions that are angiogenesis dependent, most notably the neovascularisation of growing tumours. Through alternative mRNA splicing, a single gene gives rise to several distinct isoforms of VEGF, which differ in their expression patterns as well as their biochemical and biological properties. Two VEGF receptor tyrosine kinases (VEGFRs) have been identified, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1). VEGFR-2 seems to mediate almost all observed endothelial cell responses to VEGF, whereas roles for VEGFR-1 are more elusive. VEGFR-1 might act predominantly as a ligand-binding molecule, sequestering VEGF from VEGFR-2 signalling. Several isoform-specific VEGF receptors exist that modulate VEGF activity. Neuropilin-1 acts as a co-receptor for VEGF(165), enhancing its binding to VEGFR-2 and its bioactivity. Heparan sulphate proteoglycans (HSPGs), as well as binding certain VEGF isoforms, interact with both VEGFR-1 and VEGFR-2. HSPGs have a wide variety of functions, such as the ability to partially restore lost function to damaged VEGF(165) and thereby prolonging its biological activity.

Vascular endothelial growth factor KDR receptor signaling potentiates tumor necrosis factor-induced tissue factor expression in endothelial cells

Vascular endothelial growth factor (VEGF) and tumor necrosis factor-alpha (TNF-alpha) have been shown to synergistically increase tissue factor (TF) expression in endothelial cells; however, the role of the VEGF receptors (KDR, Flt-1, and neuropilin) in this process is unclear. Here we report that VEGF binding to the KDR receptor is necessary and sufficient for the potentiation of TNF-induced TF expression in human umbilical vein endothelial cells. TF expression was evaluated by Western blot analysis and fluorescence-activated cell sorting. In the absence of TNF-alpha, wild-type VEGF- or KDR receptor-selective variants induced an approximate 7-fold increase in total TF expression. Treatment with TNF alone produced an approximate 110-fold increase in total TF expression, whereas coincubation of TNF-alpha with wild-type VEGF- or KDR-selective variants resulted in an approximate 250-fold increase in TF expression. VEGF lacking the heparin binding domain was also able to potentiate TF expression, indicating that heparin-sulfate proteoglycan or neuropilin binding is not required for TF up-regulation. Neither placental growth factor nor an Flt-1-selective variant was capable of inducing TF expression in the presence or absence of TNF. Inhibition of protein-tyrosine kinase or protein kinase C activity significantly blocked the TNF/VEGF potentiation of TF up-regulation, whereas phorbol 12-myristate 13-acetate, a protein kinase C activator, increased TF expression. These data demonstrate that KDR receptor signaling governs both VEGF-induced TF expression and the potentiation of TNF-induced up-regulation of TF.

Pathogenesis of Thrombosis in Patients with Malignancy

Cancer cells can contribute to activation of the clotting system by their capacity to produce and release procoagulant/fibrinolytic substances and inflammatory cytokines, and by their interaction with host cells (endothelial, monocytes, platelets, and neutrophils). Moreover, anticancer drugs (chemotherapy/hormone therapy) may greatly affect the risk of thromboembolic complications in cancer patients by similar mechanisms, eg, through the release of procoagulants by tumor cells, through endothelial damage, or stimulation of tissue factor production by host cells. The interactions between cancer/metastatic processes and thrombosis have been reviewed here from the pathogenetic viewpoint. We hope that better knowledge of these pathogenetic pathways will lead to the development of more targeted strategies to prevent thromboembolism in cancer patients.

The biology and tumour-related properties of monocyte tissue factor

Tissue factor (TF, coagulation factor III, CD142) is not only the main physiological initiator of normal blood coagulation, but is also important in the natural history of solid malignancies in that it potentiates metastasis and angiogenesis and mediates outside-in signalling. TF is expressed constitutively by many tissues which are not in contact with blood and by other cells upon injury or activation; the latter include endothelial cells, tissue macrophages, and peripheral blood monocytes. It can exist encrypted and unavailable functionally in the plasma membrane and the appearance of functional TF may be due to synthesis and/or de-encryption. Inflammatory cells often express TF and act to induce its production or de-encryption by other cells locally and, apparently, at remote sites. Inappropriate expression of TF by endothelial cells, macrophages or monocytes is thought to be an important trigger of coagulation in various pathological conditions. Several studies have shown that measurements of monocyte TF (mTF) may provide clinically significant information, particularly in patients with malignant and inflammatory diseases.

Neutrophils and mononuclear cells express vascular endothelial growth factor in acute Kawasaki disease: its possible role in progression of coronary artery lesions

Kawasaki disease (KD) is a syndrome of systemic vasculitis of unknown etiology that is complicated by coronary artery lesions (CAL), leading occasionally to cardiac ischemic sequelae. To examine whether vascular endothelial growth factor (VEGF) is responsible for CAL in KD, we determined serum VEGF levels by ELISA and peripheral blood mononuclear cell (PBMC) and neutrophil VEGF expression by immunoblot analysis. Significantly increased levels of VEGF were demonstrated in acute KD as well as in other vasculitis syndromes (p < 0.0001). In the 10 KD patients with CAL, serum VEGF levels were maximal approximately 2 wk post-onset when CAL generally develops and were significantly higher than in 20 patients without CAL (mean, 474 and 241 pg/mL, respectively; p = 0.00015). During the same period, immunoblot analysis revealed maximal VEGF expression in PBMC, corresponding to serum VEGF levels in most patients and being particularly marked in patients with CAL (p < 0.01). Neutrophils expressed VEGF only in the early stage of acute KD and declined rapidly in the majority of KD patients regardless of the presence of CAL, showing a strikingly different expression pattern than that for PBMC. Predominant VEGF expression by PBMC was also demonstrated in patients with other vasculitis syndromes and only faintly in normal controls. The results suggest that VEGF is generated dynamically in KD, presumably reflecting its disease activity. Neutrophil-derived VEGF may play a role in regulating early vascular responses, whereas PBMC-derived VEGF may contribute to later vascular injury and remodeling.

Specificity, diversity, and convergence in VEGF and TNF-alpha signaling events leading to tissue factor up-regulation via EGR-1 in endothelial cells

Tissue factor (TF) has been shown to be up-regulated in endothelial cells by the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) as well as by the main angiogenic factor VEGF. Since both stimuli induce the transcription factor EGR-1, which is critically involved in TF gene regulation, we used EGR-1-dependent TF induction as a model to identify potential cross-talks between the various signal transduction cascades initiated by VEGF and TNF-alpha. The data show that at the MAP kinase level, VEGF mainly activates ERK1/2 and p38 MAP kinases in human endothelial cells. TNF-alpha is able to activate all three MAP kinase cascades as well as the classical inflammatory IkappaB/NFkappaB pathway. Furthermore, the MEK/ERK module of MAP kinases appears to act as the convergence point of VEGF- and TNF-alpha-initiated signaling cascades, which lead to the activation of EGR-1 and subsequent TF expression, whereas the upstream signals are distinct. We found that induction of TF by VEGF via EGR-1 is strongly PKC dependent. The TNF-alpha-initiated MEK/ERK cascade connected to EGR-1 and TF expression is clearly less sensitive to PKC inhibition. TNF-alpha-mediated activation of MEK/ERK and EGR-1 can be blocked by adenoviral expression of a dominant negative mutant of IKK2, whereas the VEGF signaling pathway is unaffected. Thus, our data demonstrate a new link between the classical inflammatory IKK/IkappaB and the MEK/ERK cascades triggered by TNF-alpha. The additional finding that EGF induces ERK and EGR-1 in a PKC-independent manner and that this signal is not sufficient to up-regulate TF emphasizes the importance of a VEGF-specific signaling pattern for the induction of TF.

Egr-1, a master switch coordinating upregulation of divergent gene families underlying ischemic stress

Activation of the zinc-finger transcription factor early growth response (Egr)-1, initially linked to developmental processes, is shown here to function as a master switch activated by ischemia to trigger expression of pivotal regulators of inflammation, coagulation and vascular hyperpermeability. Chemokine, adhesion receptor, procoagulant and permeability-related genes are coordinately upregulated by rapid ischemia-mediated activation of Egr-1. Deletion of the gene encoding Egr-1 strikingly diminished expression of these mediators of vascular injury in a murine model of lung ischemia/reperfusion, and enhanced animal survival and organ function. Rapid activation of Egr-1 in response to oxygen deprivation primes the vasculature for dysfunction manifest during reperfusion. These studies define a central and unifying role for Egr-1 activation in the pathogenesis of ischemic tissue damage.

Improved perfusion after subcritical ischemia in muscle flaps treated with vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), a potent endothelial mitogen, is secreted in ischemic tissue and plays a pivotal role in angiogenesis. We studied whether VEGF administered to a rat muscle flap at the time of ischemia induction would increase microcirculatory flow to the flap. The cremaster muscle flap was isolated on its neurovascular pedicle. Ischemia was induced by clamping the vascular pedicle, and 0.2 ml of either VEGF (0.1 microg) or vehicle (phosphate-buffered saline) was immediately infused into the muscle. After 4 or 6 hours, the clamps were released, and the cremaster was placed in a pocket in the medial thigh for 24 hours. The muscle was then dissected, and microcirculatory measurements were made under intravital microscopy. Six animals were used in each of the four groups. All flaps exposed to 6 hours of ischemia, the duration considered to be critical ischemia, had no significant microcirculatory flow, regardless of treatment with VEGF. In the 4-hour ischemia group, or subcritical ischemia group, red blood cell velocity in arterioles was 14 mm/sec in muscles treated with VEGF and 9 mm/sec in controls (p = 0.02), and capillary flow was 7 per high-power field in muscles treated with VEGF versus 2 per high-power field in controls (p = 0.0005). Thus, VEGF did not alter microcirculatory flow in a muscle flap exposed to critical ischemia, but it did enhance flow to a flap exposed to subcritical ischemia.

Immunohistochemical analysis of endothelial-monocyte-activating polypeptide-II expression in vivo

Endothelial-monocyte activating polypeptide (EMAP)-II is a novel molecule with cytokine-like pro-inflammatory properties, inducing procoagulant activity on the surface of endothelial cells and monocyte/macrophages in vitro, as well as up-regulating E- and P-selectin expression. EMAP-II is chemotactic for monocytes/macrophages and neutrophils, and stimulates myeloperoxidase release from neutrophils. Injection of EMAP-II into the mouse footpad induces an acute inflammatory response, although some regression occurs in response to direct injection of EMAP-II into murine tumors. Very little is known about the expression of EMAP-II in normal tissues of mice or humans, or about its function in vivo. We developed polyclonal antibodies against EMAP-II using recombinant protein produced in Escherichia coli, and used these antibodies to carry out an immunohistochemical study of the occurrence and distribution of EMAP-II in human tissues. The distribution of EMAP-II protein is relatively restricted, occurring primarily in endocrine organs, in cells of neuroendocrine origin, but also in tissues with high turnover. EMAP-II is strongly expressed in secretory epithelial cells of the thyroid, pancreas, adrenal and salivary glands, among others, as well as in neurons and subsets of monocytes/macrophages. It is also found in the epithelium of the small and large intestines. We conclude that EMAP-II expression is usually, but not always, associated with tissues that display high turnover and high levels of protein synthesis.

Angiogenesis and placental growth in normal and compromised pregnancies

Research on the subject of pre-eclampsia has revolved around placental growth and angiogenesis, as both are central to the aetiology of the disease. Vascular angiogenic growth factor (VEGF) is elevated in pre-eclampsia and correlates with the severity of disease. Its actions in vitro mimic the actions of plasma from women with pre-eclampsia. This chapter examines the available evidence that implicates VEGF in the maternal systemic effects seen in pre-eclampsia, and discusses how an understanding of this growth factor could lead to diagnostic and therapeutic options. Oxygenation status is the unifying concept that surrounds the discussion of placental growth and angiogenesis. The concept that 'hypoxia' is too simplistic a notion to describe pre-eclampsia is discussed. Maldevelopment of the angiogenic process can be assessed by Doppler ultrasound. The future may see a role for magnetic resonance imaging in the identification of poorly perfused placenta.