Vascular endothelial growth factor (VEGF) induces plasminogen activators and plasminogen activator inhibitor-1 in microvascular endothelial cells

Upregulation of vascular endothelial growth factor by H2O2 in rat heart endothelial cells

Hydrogen peroxide (H2O2) is a reactive oxygen species generated by several metabolic pathways in mammalian cells. Endothelial cells are extremely susceptible to oxidative stress. H2O2 has been reported to increase the permeability in these cells. Using rat heart endothelial cell culture as a model system, we examined the effect of H2O2 on the gene expression of vascular endothelial growth factor (VEGF), a potent mitogen of endothelial cells and a vascular permeability factor. By Northern blot analysis we found that VEGF mRNA responded to H2O2 in a dose-and time-dependent manner. The induction was superinduced by cycloheximide and blocked by actinomycin D. N-Acetylcysteine, a synthetic antioxidant, was able to suppress the induction. H7, a protein kinase C inhibitor, could also block the induction. Electrophoretic mobility shift assay revealed an enhanced binding of transcription factors, AP-1 and NF-kappaB. Immunoblot analysis showed that the amount of secreted VEGF was elevated in the medium 4 h after H2O2 stimulation. Our results demonstrate that VEGF gene expression is upregulated by H2O2 in these endothelial cells.

Ras activation in astrocytomas and neurofibromas

Oncogenic mutations resulting in activated Ras Guanosine Triphosphate (GTP) are prevalent in 30% of all human cancers, but not primary nervous system tumors. Several growth factors/receptors are implicated in the pathogenesis of malignant astrocytomas including epidermal growth factor (EGFR) and platelet derived growth factor (PDGF-R) receptors, plus the highly potent and specific angiogenic vascular endothelial growth factor (VEGF). A significant proportion of these tumors also express a truncated EGFR, which is constitutively activated. Our work demonstrates that the mitogenic signals from both the normal PDGF-R and EGFR and the truncated EGFR activate Ras. Inhibition of Ras by genetic or pharmacological strategies leads to decreased astrocytoma tumorgenic growth in vitro and decreased expression of VEGF. This suggests that these agents may be potentially important as novel anti-proliferative and anti-angiogenic therapies for human malignant astrocytomas. In contrast to astrocytomas, where increased levels of activated Ras GTP results from transmitted signals from activated growth factor receptors, the loss of neurofibromin is postulated to lead to functional up-regulation of the Ras pathway in neurofibromatosis-1(NF-1). We have demonstrated that NF-1 neurofibromas and neurogenic sarcomas, compared to non-NF-1 Schwannomas, have markedly elevated levels of activated Ras GTP. Increased Ras GTP was associated with increased tumor vascularity in the NF-1 neurogenic sarcomas, perhaps related to increased VEGF secretion. The role of Ras inhibitors as potential therapy in this tumor is also under study.

Predictive value of vascular endothelial growth factor (VEGF) in metastasis and prognosis of human colorectal cancer

Vascular endothelial growth factor (VEGF) may affect the phenotype of cancer cells, such as growth velocity and metastatic potential, due to its probable multifunctional property including a mitogenic activity for vascular endothelial cells. The present study was designed to investigate the association of VEGF mRNA expression with progression and metastasis of human colorectal cancer. The level of VEGF mRNA expression was quantified by Northern blot hybridization in tumorous and non-tumorous tissues obtained from 60 primary colorectal cancer patients. The ratio of the former to the latter was defined as the VEGF T/N ratio, and the prognostic significance of this ratio, following surgery, in addition to the relationship to progression and metastatic potential, was evaluated. The value of the VEGF T/N ratio was significantly correlated with the depth of tumour infiltration (P=0.046), the incidence of liver metastasis (P < 0.0001) and lymph node metastasis (P=0.036). Patient prognosis was estimated by the Kaplan-Meier method and the log-rank test. When the VEGF T/N ratio was higher than 4.8 for which the chi2 value of the log-rank test was maximal, the tumour was defined as showing overexpression of VEGF mRNA. Patients with overexpression of VEGF mRNA demonstrated poorer survival than patients without overexpression of VEGF mRNA (P < 0.001). The overall estimated hazard ratio for death in patients with overexpression of VEGF mRNA was 1.94 according to a multivariate analysis (P=0.005). Thus, VEGF is associated with the progression, invasion and metastasis of colorectal cancer, and overexpression of VEGF mRNA in the primary tumour is assumed to be closely correlated with poor prognosis in colorectal cancer patients. Moreover, the VEGF T/N ratio may be used as an independent prognostic marker in colorectal cancer patients.

Control of tumour vascular permeability

Several model tumour systems are now known to display increased vascular permeability compared with normal tissues, permitting their selective targeting using macromolecular drugs. Preliminary clinical observations suggest that this pathology may be reflected in at least some types of human cancer, and this may have important implications in facilitating macromolecular drug treatments, including antibody targeting and delivery of DNA for gene therapy. The enhanced permeability of tumour vasculature is thought to be regulated by tumour-secreted growth factors, with vascular permeability facor (VPF), also known as vascular endothelial growth factor (VEGF), emerging as a particularly likely candidate. VPF/VEGF is known to be an important regulator of tumour-angiogenesis in vivo, and it exerts its endothelium-specific effects via its receptors KDR/Flk-1 and Flt-1 on the endothelial cell membrane. Although the precise mechanism of VEGF's permeabilising action is not yet understood, it is likely to contribute to the enhanced permeability and retention (EPR) effect in tumours which is thought to underlie the anticancer activity of macromolecular drugs.

Modulation of the proteolytic balance plasminogen activator/plasminogen activator inhibitor by enhanced N-myc oncogene expression or application of genistein

The aim of this study was to determine whether enhanced expression of N-myc in a neuroblastoma cell line affects the balance of plasminogen activator/plasminogen activator inhibitor (PA/PAI), a shift towards proteolysis having been observed in other malignant tissues. Two transfected neuroblastoma cell lines with (WAC2 cells) or without (SH-EP007 cells) enhanced expression of the N-myc oncogene were examined by zymography and RNA extraction to determine UPA and PAI enzyme activity and uPA RNA and PAI RNA expression, respectively. The effect of genistein, an inhibitor of tyrosine protein kinase, on uPA/PAI was also investigated. Both the uPA/PAI-1 ratio at mRNA level and the PA/PAI ratio at protein activity level were higher in the more malignant, WAC2 cell line. Genistein attenuated uPA activity and stimulated PAI activity in both cell lines, leading to a decrease in the PA/PAI ratio. This effect was more pronounced in the more malignant, WAC2 cell line.

Autoregulation of angiogenesis by cells of the vessel wall

The cells of the vessel wall can regulate angiogenesis by producing growth factors, proteolytic enzymes, extracellular matrix components, cell adhesion molecules, and vasoactive factors. This property enables preexisting blood vessels to generate new vessels in the absence of exogenous angiogenic stimuli. Vascular autoregulation of angiogenesis can be studied by culturing rat aortic or venous explants in collagen gels under serum-free conditions. In this system, the combined effect of injury and exposure of explants to collagen triggers a self-limited angiogenic response. Interactions among endothelial cells, smooth muscle cells, and fibroblasts play a critical role in the regulation of this process. This chapter reviews the literature on angiogenesis, focusing on the vessel wall as a highly specialized and plastic tissue capable of regenerating itself through autocrine, paracrine, and juxtacrine mechanisms.

Vascular endothelial growth factor B (VEGF-B) binds to VEGF receptor-1 and regulates plasminogen activator activity in endothelial cells

The vascular endothelial growth factor (VEGF) family has recently expanded by the identification and cloning of three additional members, namely VEGF-B, VEGF-C, and VEGF-D. In this study we demonstrate that VEGF-B binds selectively to VEGF receptor-1/Flt-1. This binding can be blocked by excess VEGF, indicating that the interaction sites on the receptor are at least partially overlapping. Mutating the putative VEGF receptor-1/Flt-1 binding determinants Asp63, Asp64, and Glu67 to alanine residues in VEGF-B reduced the affinity to VEGF receptor-1 but did not abolish binding. Mutational analysis of conserved cysteines contributing to VEGF-B dimer formation suggest a structural conservation with VEGF and platelet-derived growth factor. Proteolytic processing of the 60-kDa VEGF-B186 dimer results in a 34-kDa dimer containing the receptor-binding epitopes. The binding of VEGF-B to its receptor on endothelial cells leads to increased expression and activity of urokinase type plasminogen activator and plasminogen activator inhibitor 1, suggesting a role for VEGF-B in the regulation of extracellular matrix degradation, cell adhesion, and migration.

Functions of the VEGF Receptor-1 (FLT-1) in the Vasculature

Vascular endothelial growth factor (VEGF) is a major inducer of angiogenesis and vasculogenesis. Two distinct receptors for VEGF, the tyrosine kinase receptors VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), have been identified. Transfection studies could demonstrate biological activities for the Flk-1/KDR-, but not for the Flt-1-receptor, which led to the hypothesis that Flt-1 is a decoy receptor for VEGF. However, Flt-1 is biologically active in non-endothelial cells, namely monocytes, which exclusively express this receptor. In addition, the Flt-1 ligand placenta growth factor (PlGF), which is unable to bind and activate Flk-1/KDR, elicits activities in both monocytes and endothelial cells. The implications of Flt-1 mediated monocyte transmigration through endothelial monolayers and induction of the procoagulant tissue factor on monocytes for the field of vascular medicine are discussed.

Apposition-Dependent Induction of Plasminogen Activator Inhibitor Type 1 Expression: A Mechanism for Balancing Pericellular Proteolysis During Angiogenesis

Plasminogen-activator inhibitor type I (PAI-1), the primary inhibitor of urinary-type plasminogen activator, is thought to play an important role in the control of stroma invasion by both endothelial and tumor cells. Using an in vitro angiogenesis model of capillary extension through a preformed monolayer, in conjunction with in situ hybridization analysis, we showed that PAI-1 mRNA is specifically induced in cells juxtaposed next to elongating sprouts. To further establish that PAI-1 expression is induced as a consequence of a direct contact with endothelial cells, coculture experiments were performed. PAI-1 mRNA was induced exclusively in fibroblasts (L-cells) contacting endothelial cell (LE-II) colonies. Reporter gene constructs driven by a PAI-1 promoter and stably transfected into L-cells were used to establish that both mouse and rat PAI-1 promoters mediate apposition-dependent regulation. This mode of PAI-1 regulation is not mediated by plasmin, as an identical spatial pattern of expression was detected in cocultures treated with plasmin inhibitors. Because endothelial cells may establish direct contacts with fibroblasts only during angiogenesis, we propose that focal induction of PAI-1 at the site of heterotypic cell contacts provides a mechanism to negate excessive pericellular proteolysis associated with endothelial cell invasion.

© 1998 by The American Society of Hematology.

Apposition-Dependent Induction of Plasminogen Activator Inhibitor Type 1 Expression: A Mechanism for Balancing Pericellular Proteolysis During Angiogenesis

Plasminogen-activator inhibitor type I (PAI-1), the primary inhibitor of urinary-type plasminogen activator, is thought to play an important role in the control of stroma invasion by both endothelial and tumor cells. Using an in vitro angiogenesis model of capillary extension through a preformed monolayer, in conjunction with in situ hybridization analysis, we showed that PAI-1 mRNA is specifically induced in cells juxtaposed next to elongating sprouts. To further establish that PAI-1 expression is induced as a consequence of a direct contact with endothelial cells, coculture experiments were performed. PAI-1 mRNA was induced exclusively in fibroblasts (L-cells) contacting endothelial cell (LE-II) colonies. Reporter gene constructs driven by a PAI-1 promoter and stably transfected into L-cells were used to establish that both mouse and rat PAI-1 promoters mediate apposition-dependent regulation. This mode of PAI-1 regulation is not mediated by plasmin, as an identical spatial pattern of expression was detected in cocultures treated with plasmin inhibitors. Because endothelial cells may establish direct contacts with fibroblasts only during angiogenesis, we propose that focal induction of PAI-1 at the site of heterotypic cell contacts provides a mechanism to negate excessive pericellular proteolysis associated with endothelial cell invasion.

© 1998 by The American Society of Hematology.

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.

Regulation of vascular endothelial growth factor receptor-2 (Flk-1) expression in vascular endothelial cells

We have previously reported the existence of a synergistic interaction between vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in the induction of angiogenesis in vitro. Here we demonstrate that bFGF increases VEGF receptor-2 (VEGFR-2/Flk-1) expression: mRNA levels were increased by 4.5- to 8.0-fold and total protein by 2.0- to 3.5-fold, in bovine microvascular endothelial (BME), aortic endothelial (BAE), and transformed fetal aortic (GM7373) endothelial cells. VEGF itself did not affect VEGFR-2 expression, and neither bFGF nor VEGF altered expression of FGF receptor-1. We also show that synergism occurs at the level of proliferation when this is measured in a three-dimensional but not in a conventional two-dimensional assay. Differences in the level of VEGFR-2 expression were also observed when cells were grown on or within collagen gels under different conditions: mRNA levels were lowest under sparse conditions, increased 20- to 26-fold at confluence, and increased even further (57-fold) when cells were cultured in suspension in three-dimensional collagen gels. Finally, a synergistic increase was seen in the level of expression of urokinase and urokinase receptor mRNAs when cells were exposed to bFGF and VEGF for 4 days. These findings demonstrate that the level of VEGFR-2 expression can be modulated by environmental factors including cytokines and the geometry of the culture conditions and provide some insight into the mechanisms of synergism between bFGF and VEGF in the induction of angiogenesis in vitro.

A plasticity window for blood vessel remodelling is defined by pericyte coverage of the preformed endothelial network and is regulated by PDGF-B and VEGF

Little is known about how the initial endothelial plexus is remodelled into a mature and functioning vascular network. Studying postnatal remodelling of the retina vasculature, we show that a critical step in vascular maturation, namely pericyte recruitment, proceeds by outmigration of cells positive for (alpha)-smooth muscle actin from arterioles and that coverage of primary and smaller branches lags many days behind formation of the endothelial plexus. The transient existence of a pericyte-free endothelial plexus coincides temporally and spatially with the process of hyperoxia-induced vascular pruning, which is a mechanism for fine tuning of vascular density according to available oxygen. Acquisition of a pericyte coating marks the end of this plasticity window. To substantiate that association with pericytes stabilizes the vasculature, endothelial-pericyte associations were disrupted by intraocular injection of PDGF-BB. Ectopic PDGF-BB caused the detachment of PDGF-beta receptor-positive pericytes from newly coated vessels, presumably through interference with endogenous cues, but had no effect on mature vessels. Disruption of endothelial-pericyte associations resulted in excessive regression of vascular loops and abnormal remodelling. Conversely, intraocular injection of VEGF accelerated pericyte coverage of the preformed endothelial plexus, thereby revealing a novel function of this pleiotropic angiogenic growth factor. These findings also provide a cellular basis for clinical observations that vascular regression in premature neonates subjected to oxygen therapy [i.e. in retinopathy of prematurity] drops precipitously upon maturation of retina vessels and a mechanistic explanation to our previous findings that VEGF can rescue immature vessels from hyperoxia-induced regression.

Increased serum levels of vascular endothelial growth factor in patients with inflammatory bowel disease

BACKGROUND

Vascular endothelial growth factor (VEGF) is a potent angiogenic, vascular permeability-enhancing, and calcium-dependent enzyme-modulating cytokine with overexpression in various pathologic disorders, including granulomatous inflammation, tissue repair, delayed hypersensitivity reactions, rheumatoid arthritis, and tissue ischemia. The present study investigates the role of VEGF in chronic inflammatory bowel disease.

METHODS

Thirty-one patients with Crohn's disease, 15 patients with ulcerative colitis, and 9 healthy volunteers were studied. VEGF serum levels were measured with a solid-phase enzyme-linked immunosorbent assay.

RESULTS

Significantly increased VEGF serum levels were observed in both active Crohn's disease and active ulcerative colitis when compared with healthy controls. Patients with active Crohn's disease and active ulcerative colitis showed significantly higher VEGF serum levels than patients with quiescent disease. No difference was observed between inactive disease and healthy controls. In addition, strongly increased VEGF serum levels were found in patients with Crohn's disease with fistulas in the absence of clinical, endoscopic, histologic, and laboratory findings of disease activity.

CONCLUSIONS

Significantly increased VEGF serum levels were observed in patients with active Crohn's disease and ulcerative colitis, which suggests that VEGF has an important role in chronic inflammatory bowel disease. Its possible association with fistulas has yet to be determined.

In oesophageal squamous cell carcinoma vascular endothelial growth factor is associated with p53 mutation, advanced stage and poor prognosis

Vascular endothelial growth factor (VEGF) affects malignant tumours by promoting angiogenesis. The tumour-suppressor gene p53 has been thought to regulate VEGF. We investigated the effect of VEGF on oesophageal carcinoma and the connection between VEGF and p53. One hundred and nine resected oesophageal squamous cell carcinomas were examined. VEGF expression was analysed by immunohistochemical staining. Sixty-five tumours (59.6%, 65 out of 109) were classified as VEGF positive. A significant correlation was found between the VEGF expression and both the depth of invasion (P = 0.0001) and lymph node metastasis (P < 0.0001). With regard to p53, we compared the expression of VEGF with the mutation of p53, examined using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and direct sequencing in tumour samples obtained from 36 patients who we have reported previously. The VEGF expression was significantly correlated to p53 mutation (P = 0.0291). To evaluate the angiogenesis, microvascular density (MVD) was counted, and endothelial cells were stained immunohistochemically using anti-CD34 monoclonal antibody against 29 cases with invasion limited to the submucosal layer. The average MVD had a tendency to correlate to VEGF expression (P = 0.1626). The prognoses of patients with VEGF-positive primary tumours were significantly worse than for those with VEGF-negative primary tumours (P = 0.0077). We have assumed that VEGF contributes to aggressive characteristics in oesophageal carcinomas and that VEGF expression might be affected by p53 status.

Vascular permeability factor/vascular endothelial growth factor and vascular stroma formation in neoplasia. Insights from in situ hybridization studies

The formation of vascular stroma plays an important role in the pathophysiology of malignancy. We describe the use of in situ hybridization in our laboratory as a tool to study the role of vascular permeability factor/vascular endothelial growth factor in the angiogenesis associated with malignancy.

The endothelial receptor tyrosine kinase tie-1 is upregulated by hypoxia and vascular endothelial growth factor

The receptor tyrosine kinase tie-1 is essential for angiogenesis where it appears to have a role in vessel maturation. Here we have examined the effects of hypoxia and vascular endothelial growth factor (VEGF) on the level of tie-1 protein expressed in bovine aortic endothelial cells. Both hypoxia (2% O2) and VEGF were found to increase tie-1 in a time-dependent manner. Hypoxic induction was direct and effects of hypoxia and VEGF were not additive. Experiments with actinomycin D indicate that these activators regulate tie-1 at the transcriptional level.

Upregulation of vascular endothelial growth factor by angiotensin II in rat heart endothelial cells

Vascular endothelial growth factor (VEGF) is a potent mitogen for endothelial cells and a vascular permeability factor. In this study we found that the addition of angiotensin II (AII) to rat heart endothelial cells induced VEGF mRNA production. VEGF mRNA levels reached a plateau within 2 h after the addition of AII and decreased after 4 h. The induction was superinduced by cycloheximide and blocked by actinomycin D. Losartan, an AT1 receptor antagonist, abolished the induction of VEGF mRNA by AII, whereas PD 123319, an AT2 receptor antagonist, had no effect on VEGF mRNA induction. H7, a protein kinase C inhibitor, blocked the induction. RT-PCR experiments showed two mRNA species (VEGF 120 and VEGF 164) in these cells and both species were stimulated by AII. Transient transfection experiment showed that VEGF promoter activity was increased 2.2-fold upon AII stimulation. Electrophoretic mobility shift assay revealed an enhanced binding of transcription factors AP-1 and NF-kappa B. Immunoblot analysis showed that the amount of secreted VEGF was elevated in the medium 8 h after AII stimulation. Our results demonstrate for the first time that the upregulation of VEGF by AII may play a significant role in AII-induced hyperpermeability.

Growth factor-mediated angiogenesis in the malignant progression of glial tumors: a review

BACKGROUND

We review the role of peptide growth factors in angiogenesis and progression of low grade glial tumors to higher grade glioblastoma multiforme (GBM).

METHODS

Vascular pathology is a key feature of glioblastoma multiforme characterized by hypervascularity, vascular permeability, and hypercoagulability.

RESULTS

Vascular endothelial growth factor (VEGF) can mediate all of these effects, but by itself does not promote malignant growth. Epidermal growth factor (EGF), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and transforming growth factor beta (TGF-beta) are implicated in the angiogenesis of a number of tumors including those of glial origin.

CONCLUSIONS

These growth factors are suggested to play a role in autocrine and/or paracrine mediated tumorogenesis of astrocytic tumors. VEGF secretion might be the product of induction by physiologic concentrations of other growth factors with VEGF being the common pathway of neovascularization and progression to GBM.

Thrombomodulin-dependent anticoagulant activity is regulated by vascular endothelial growth factor

Thrombomodulin (TM) is a cell-surface receptor that plays a critical role in endothelial cell anticoagulant activity through its cofactor role in the thrombin-catalyzed activation of human protein C. In this study, we examined the effect of vascular endothelial growth factor (VEGF), a potent angiogenic factor, on surface anticoagulant activity and thrombomodulin expression. We show that thrombin-dependent activation of human protein C, measured on the endothelial cell surface, increased from 50 to 80% following exposure of cells to VEGF for 24 h. The effect was concentration dependent with the half-maximal stimulatory effect at approximately 100 pM. This increase in thrombin-dependent aPC generation correlated with a proportional and concentration-dependent increase in the level of cell-surface TM antigen. Both the total cellular TM antigen and the total cellular TM mRNA levels increased approximately 2.5-fold in VEGF-treated cells suggesting that most if not all of the regulation was at the message level. We further show that VEGF blocked IL-1 beta-induced suppression of both TM surface antigen and mRNA and was similarly capable of antagonizing the down-regulation of TM by TGF-beta and from cell activation by LPS. Our data suggest that VEGF regulation of TM may contribute to mechanisms that would maintain local hemostasis during angiogenesis and revascularization and could play a role in minimizing loss of vessel anticoagulant function during inflammatory processes.

VEGF and tPA co-expressed in malignant glioma

Neovascularisation and migration of tumour cells are two features of highly malignant glioma. Vascular endothelial growth factor (VEGF) and tissue plasminogen activator (tPA) seem to be of importance in the process of malignancy. In the present study a topographical co-expression of tPA mRNA and VEGF mRNA (VEGF121 and VEGF165 isoforms) was demonstrated in the tumour edge of a rat malignant glioma, using in situ hybridisation. No signs of co-expression was seen in the normal brain tissue. In the normal brain the forms of VEGF mainly expressed were VEGF121, VEGF165, and VEGF189. Further studies are required to show whether VEGF and tPA are produced by the same tumour cells and to elucidate the role of this co-expression.

TGF beta-1 regulation of VEGF production by breast cancer cells

BACKGROUND

Angiogenesis is essential for tumor growth and metastasis. Vascular endothelial growth factor (VEGF) is the most potent angiogenic factor identified to date. TGF beta-1 acts as an indirect angiogenic agent.

METHODS

VEGF and TGF beta-1 were measured in the serum of breast cancer patients and age-matched controls and in tumor tissue of cancer patients by ELISA. VEGF protein and mRNA expression by breast tumor cell lines were examined, and the effect of TGF beta-1 on VEGF production in these cells was assessed.

RESULTS

VEGF levels were significantly higher (P = .03) in the serum of patients with breast cancer compared to age-matched controls. A positive correlation was found between serum (r = 0.539) and tumor tissue (r = 0.688) levels of VEGF and TGF beta-1. Metastatic MDA-MB-231 breast cancer cells produce more VEGF than do the primary BT474 cells. TGF beta-1 significantly (P < .05) increased production of VEGF.

CONCLUSIONS

Breast cancer cells constitutively produce VEGF protein and mRNA. There is a relationship between VEGF and TGF beta-1 levels in breast cancer patients, and TGF beta-1 regulates VEGF expression by breast cancer cells.

Growth/differentiation factor-5 induces angiogenesis in vivo

Bone morphogenetic proteins (BMPs) are multifunctional cytokines, which induce bone and cartilage formation and exert various other effects on many tissues. Since angiogenesis is involved in the bone formation process, certain members in the BMP family may induce angiogenesis. We examined the in vivo angiogenic activity of BMP family members, i.e., growth/differentiation factor (GDF)-5 and BMP-2. GDF-5 induced angiogenesis in both chick chorioallantoic membrane and rabbit cornea assays. In contrast, BMP-2 did not induce angiogenesis. In order to elucidate the mechanism of angiogenesis, we examined the effects of GDF-5 on cultured bovine aortic endothelial cells (BECs). GDF-5 induced plasminogen activator activity and accelerated the migration of BECs in a chemotactic fashion, which may contribute to the process of angiogenesis in vivo. These results suggest that GDF-5 is one of the molecules which induce angiogenesis in the bone formation process.

[Transmyocardial laser revascularization--an innovative pathophysiologic concept]

In patients with coronary artery disease where standard revascularization procedures are not appropriate, transmyocardial laser revascularization (TMLR) represents an innovative technique which is currently validated worldwide. Initially, it has been assumed that myocardial perfusion of ischemic regions could be instantly improved by inducing TMLR channels, which, however, might not be confirmed in ongoing studies. Indeed, the gain in O2 diffusion surface obtained by 20 patent TMLR channels is only 6 cm2 which accounts for just 0.01% of the total capillary surface (47000 cm2) of the myocardium. Instead, a chronic structural remodeling of myocardial regions, adjacent to TMLR channels and mediated by TMLR-induced expression of vascular endothelial growth factor (VEGF), may occur leading to neocapillarization of ischemic myocardium irrespective of the long-term patency of TMLR channels and, thereby, would improve myocardial perfusion (Figure 1). Six weeks following TMLR in the pig, patent TMLR channels were not observed. Instead, a marked degree of reparative fibrosis was found at the site of TMLR-treated myocardial regions (Figure 2). It is, however, not known, whether ischemic conditions would affect chronic channel patency. TMLR combined with intramyocardial administration of 0.5 microgram VEGF between the laser-induced channels resulted in few patent channels (Figure 3). The apparently low efficacy of VEGF applied as protein could be attributed to degradation of VEGF by local peptidases. In addition to VEGF, other growth factors and the interaction of endothelial cells and the extracellular matrix need to be considered. Of particular relevance appears alpha v beta 3-integrin which is needed for adhesion of endothelial cells to extracellular matrix components and is, therefore, required for neocapillarization. Among various other growth factors associated with neoangiogenesis, TGF-beta 1 and PDGF-BB are involved in the formation of extracellular matrix anchoring newly formed vessels. Thus, the expression of VEGF and alpha V beta 3-integrin in myocardial regions surrounding TMLR channels appears to be of major importance for the development of neoangiogenesis within the ischemic myocardium. Whether concomitant therapeutical strategies, i. e., gene transfer leading to over-expression of VEGF, will optimize the TMLR procedure by improving neoangiogenesis remains to be elucidated in future experimental studies.

Reciprocal relation between VEGF and NO in the regulation of endothelial integrity

Balloon angioplasty disrupts the protective endothelial lining of the arterial wall, rendering arteries susceptible to thrombosis and intimal thickening. We show here that vascular endothelial growth factor (VEGF), an endothelial cell mitogen, is upregulated in medial smooth muscle cells of the arterial wall in response to balloon injury. Both protein kinase C (PKC) and tyrosine kinase pp60src mediate augmented VEGF expression. In contrast, nitric oxide (NO) donors inhibit PKC-induced VEGF upregulation by interfering with binding of the transcription factor activator protein-1 (AP-1) to the VEGF promoter. Inhibition of VEGF promoter activation suggests that NO secreted by a restored endothelium functions as the negative feedback mechanism that downregulates VEGF expression to basal levels. Administration of a neutralizing VEGF antibody impaired reendothelialization following balloon injury performed in vivo. These findings establish a reciprocal relation between VEGF and NO in the endogenous regulation of endothelial integrity following arterial injury.

Expression of vascular endothelial growth factor and its receptors in pilocytic astrocytoma

Vascular endothelial growth factor (VEGF), a potent angiogenic and vascular permeability factor, is important in the angiogenesis of glioblastoma. A major difference between pilocytic astrocytoma, a grade I tumor, and the grade II fibrillary astrocytoma is the vascular proliferation, highly vascularized stroma, and great propensity for cyst formation in the former. In order to explore factors regulating such angiogenesis and cyst formation in pilocytic astrocytoma, we examined expression of VEGF and its receptors (KDR and Flt-1) using in situ hybridization. In all 14 cases a high level of VEGF transcripts could be demonstrated. These were found in specific regions, namely, in the tumor cyst wall, in areas of hyaline cystic degeneration, in stellate reticulated astrocytes around microcysts in the biphasic compact and loose areas, and in tumor cells with degenerative pleomorphic multicoated nuclei. KDR and Flt-1 were expressed in the tumor vasculature, with particularly high levels seen in coiled young proliferating vessels, especially those in the cyst wall. Given the known angiogenic and vascular permeability activities of VEGF, we propose that VEGF plays an important role in molding the characteristic morphologic features of this tumor, namely, the formation of cysts, microcystic pattern, hyaline cystic degeneration, hyaline vessels, and vascular proliferation. Mechanisms that block the VEGF pathway could constitute a potential therapeutic strategy for the treatment of this tumor.

Vascular endothelial growth factor increases endothelin-converting enzyme expression in vascular endothelial cells

Endothelin-converting enzyme-1 (ECE-1) is a key enzyme in endothelin processing. Although it has been revealed that ECE-1 expression increases in vascular wall after balloon injury in vivo experimental models, the regulation of ECE-1 expression in vitro remains undefined. In this study, we demonstrated that the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF) increased ECE-1 expression in cultured bovine aortic endothelial cells (BAEC). Northern blot analysis revealed that VEGF increased ECE-1 mRNA expression in 12-24 hours by 2-fold in BAEC, and this effect was dose-dependent. VEGF also increased ECE-1 protein expression detected by immunoblotting in 36 hours in BAEC. Therefore, VEGF increased ECE-1 expression in BAEC, which suggests that ECE-1 induction by VEGF may be involved in endothelin-system upregulation under pathological conditions such as neointimal formation and atherosclerosis.

Vascular permeability factor/vascular endothelial growth factor inhibits anchorage-disruption-induced apoptosis in microvessel endothelial cells by inducing scaffold formation

Survival and proliferation of endothelial cells requires both growth factors and an appropriate extracellular matrix to which cells can attach. In the absence of either, endothelial cells rapidly undergo apoptosis. Thus, when human microvascular endothelial cells (HDMEC) are plated on a hydrophobic surface such as untreated polystyrene, they rapidly undergo apoptosis and die. The present study demonstrates that vascular permeability factor/vascular endothelial growth factor (VPF/VEGF), an endothelial cell-selective cytokine, inhibits apoptosis of HDMEC cultured on untreated polystyrene and induces these cells to adhere, spread, and proliferate. VPF/VEGF-induced HDMEC adhesion was time-dependent, required de novo protein synthesis, and was inhibited by a soluble RGD peptide but not by an inhibitor of collagen synthesis. Under the conditions of these experiments, VPF/VEGF downregulated expression of collagen IV and fibronectin but did not change collagen I mRNA levels. VPF/VEGF-induced HDMEC adhesion was inhibited by antibodies to alpha(v)beta5 and vitronectin but not by antibodies to alpha(v)beta3. Other endothelial growth factors and cytokines such as bFGF, HGF, and TGFbeta did not reproduce the VPF/VEGF effect. We suggest that VPF/VEGF induces endothelial cells to deposit a scaffolding (likely involving vitronectin) that allows them to attach to and proliferate on an otherwise nonsupportive surface (hydrophobic polystyrene) and in this manner serves as both a survival factor and a growth factor.

Urokinase-type plasminogen activator overexpression enhances the invasive capacity of endothelial cells

Fetal bovine aortic endothelial GM 7373 cells were transfected with a viral expression vector harboring the human urokinase-type plasminogen activator (uPA) gene. The stable transfectant clone uPA-R5 overexpressed and secreted human uPA as shown by Northern blot analysis, immunoprecipitation of metabolically labeled proteins, plasmin chromogenic assays, and SDS-PAGE zymography of cell extracts and conditioned media. The uPA-R5 cells were analyzed for their invasive capacity in vitro in the Matrigel chemoinvasion assay in the presence of serine- or metalloprotease inhibitors. uPA overexpression enhanced the invasive capacity of GM 7373 cells through a mechanism which differs from that mediated by metalloproteases. Endothelial cell uPA transfectants may represent an useful experimental model to investigate the role of uPA in angiogenesis and angioproliferative diseases.

Design, synthesis, and biological activity of anti-angiogenic hypoxic cell radiosensitizer haloacetylcarbamoyl-2-nitroimidazoles

We designed, synthesized, and evaluated haloacetylcarbamoyl-2-nitroimidazoles, including chloro (KIN-1800, TX-1835, and TX-1836) and bromo derivatives (TX-1844, TX-1845, and TX-1846), as potential hypoxic cell radiosensitizers with antiangiogenic activities. To establish biological function owing to the haloacetylcarbamoyl group in the side-chain, we compared their in vitro radiosensitizing activities with those of their parent 2-nitroimidazoles without haloacetylcarbamoyl groups: misonidazole (MISO), TX-1831, and TX-1832, respectively. Both tert-butoxy substituted derivatives. TX-1835 and TX-1845, were more potent radiosensitizers than TX-1831. The p-tert-butylphenoxy-substituted derivatives, TX-1836 and TX-1846, and the methoxysubstituted derivatives, KIN-1800 and TX-1844, were stronger radiosensitizers than TX-1832 and MISO. We examined the anti-angiogenic activities of these 2-nitroimidazole derivatives containing haloacetylcarbamoyl group by the rat lung endothelial (RLE) cell proliferation assay and chick embryo chorioallantoic membrane (chick CAM) angiogenesis assay and showed that haloacetylcarbamoyl-2-nitroimidazoles were more potent angiogenic inhibitors than the corresponding desacetylcarbamoyl-2-nitroimidazoles. The in vivo chick CAM angiogenesis assay showed that the strong bromoacetylcarbamoyl-2-nitroimidazole radiosensitizers, such as TX-1845 and TX-1846, were the strongest angiogenic inhibitors among them. We concluded that the bromoacetylcarbamoyl-2-nitroimidazole radiosensitizers, such as TX-1845 and TX-1846, are promising as anti-angiogenic hypoxic cell radiosensitizers.

Isolation of putative progenitor endothelial cells for angiogenesis

Putative endothelial cell (EC) progenitors or angioblasts were isolated from human peripheral blood by magnetic bead selection on the basis of cell surface antigen expression. In vitro, these cells differentiated into ECs. In animal models of ischemia, heterologous, homologous, and autologous EC progenitors incorporated into sites of active angiogenesis. These findings suggest that EC progenitors may be useful for augmenting collateral vessel growth to ischemic tissues (therapeutic angiogenesis) and for delivering anti- or pro-angiogenic agents, respectively, to sites of pathologic or utilitarian angiogenesis.

Endothelial and macrophage upregulation of urokinase receptor expression in human renal cell carcinoma

The binding of urokinase-type plasminogen activator (u-PA) to a specific cell surface receptor (uPA-R) has been shown to enhance plasminogen activation, a process involved in extracellular matrix degradation and cell migration during angiogenesis and tumor growth. We investigated the expression of u-PA and uPA-R in renal cell carcinomas (n = 11). By immunohistochemistry using monoclonal and polyclonal anti-uPA-R antibodies, we found that tumoral capillary endothelial cells (von Willebrand factor and CD31 positive cells) overexpressed uPA-R, whereas vascular endothelial cells of the normal human kidney do not. In addition, tumor-associated macrophages (CD68-positive cells) strongly expressed uPA-R. In contrast, few tumoral cells and stromal fibroblasts expressed uPA-R. By in situ hybridization using a cDNA S35-labeled probe specific for uPA-R, we confirmed the local expression of uPA-R messenger RNA. We also detected the induction of u-PA in tumoral capillary endothelial cells and in tumor-associated macrophages. In two cases, tumoral cells themselves were also stained by anti-u-PA antibodies in focal areas. Finally tissue-type plasminogen activator (t-PA) was also overexpressed by tumoral capillary endothelial cells as compared with endothelial cells of normal human kidney vessels. These findings indicate an active invasive phenotype of endothelial cells in renal cell carcinoma and suggest a role for the plasminogen activation system in tumoral angiogenesis and invasion.

Angiogenesis as a biologic and prognostic indicator in human breast carcinoma

In this review we describe angiogenesis pathways involved in the development of breast carcinoma. Different assessment techniques for angiogenesis and their optimisation are discussed. Angiogenesis is an important factor for prognosis and will be increasingly important in therapeutic decisions.

Vascular permeability factor/vascular endothelial growth factor: a multifunctional angiogenic cytokine

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the endothelial cells lining nearby microvessels to proliferate, to migrate and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular endothelial cells hyperpermeable so that they spill plasma proteins into the extravascular space, leading to profound alterations in the extracellular matrix that favor angiogenesis. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of endothelial cell division and new blood vessel formation. It would seem, therefore, that tumors have made use of fundamental pathways that developed in multicellular organisms for purposes of tissue defense, renewal and repair. VPF/VEGF, therefore, has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important--perhaps essential--elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in sub-toxic concentrations that are more than sufficient to induce angiogenesis (Connolly et al., 1989a). Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating VPF/VEGF expression. In fact, there are already clear example of this. A number of putative angiogenic factors including small molecules (e.g. prostaglandins, adenosine) as well as many cytokines (e.g. TGF-alpha, bFGF, TGF-beta, TNF-alpha, KGF, PDGF) have all been shown to upregulate VPF/VEGF expression. Further studies that elucidate the crosstalk among various angiogenic factors are likely to contribute significantly to a better understanding of the mechanisms by which new blood vessels are formed in health and in disease.

Regulation of angiogenesis in malignant gliomas

Gliomas are highly resistant to conventional therapeutic measures, requiring the development of novel treatments. Since gliomas are particularly vascular tumors, one approach involves treatments directed at inhibiting angiogenic mechanisms. Although multiple factors contribute to the ultimate vascularization of any tumor, some are especially relevant to gliomas. Early experimental work directed at inhibiting angiogenic pathways has shown promise toward achieving control of tumor growth. This article focuses on the evidence that angiogenesis and related vascular cell responses play important roles in glioma biology, and reviews those biochemical pathways known through experimentation to be involved in the vascular response to gliomas. Finally, contemporary vessel-targeted approaches that have been used to inhibit glioma growth are discussed.

Markers of tumor angiogenesis: clinical applications in prognosis and anti-angiogenic therapy

Numerous studies in many tumor types have demonstrated that quantitation by microvessel as a measure of angiogenesis is a powerful prognostic tool. However, the ability to exploit tumor angiogenesis as a prognostic marker is limited by the methods currently used for capillary identification and quantitation. This report critically evaluates all aspects of the techniques and their associated problems used for assessing tumor angiogenesis in tissue sections including the area of tumor assessed, the vascular parameter measured, the method of quantitation, the stratification of patients and the practical utility of computer image analysis systems. The potential of angiogenic factors assays, proteolytic enzymes, and cell adhesion molecules as surrogate endpoints for quantifying tumor angiogenesis are discussed and other methods for quantifying tumor angiogenesis are described. The potential clinical applications of these angiogenic markers in prognosis, stratification for adjuvant treatments (both cytotoxic and anti-angiogenic/vascular targeting) and other aspects of patient management is also discussed, particularly design of phase I and II trials.

Platelet-derived growth factor and vascular endothelial growth factor expression in disc herniation tissue: and immunohistochemical study

Angiogenesis is essential in tissue growth and regeneration. There are several factors that are able to stimulate vascular endothelial cell growth, including platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). Disc herniation tissue (DHT) contains vascular ingrowth, which promotes granulation tissue formation. In this study we observed 50 disc herniations for PDGF and VEGF immunoreactivity. PDGF immunopositivity was detected in 38 samples (78%). In 28 samples (56%) there were PDGF immunopositive capillaries, PDGF immunopositive disc cells were detected in 19 samples (38%) and PDGF immunopositive fibroblasts in 6 DHT samples (12%). VEGF immunopositive capillaries were identified in 44 DHT samples (88%). For neither growth factor was immunopositivity dependent on preoperative radicular pain duration. In extrusions (n = 25) VEGF immunopositive capillaries were detected in 23 samples (92%) and PDGF immunopositivity in 21 samples (84%). PDGF immunopositivity was more commonly associated with capillaries than with nuclei of disc cells. In sequesters (n = 20) VEGF immunopositive capillaries were identified in all samples and PDGF immunopositivity in 16 (80%). As in extrusions, PDGF immunoreaction was more prevalent in capillaries than in disc cells. Patient age did not relate to VEGF expression. In all age groups it was higher than 80%. Thus capillaries in disc herniation tissue are evidently newly formed and our results demonstrate that PDGF and VEGF participate in the neovascularization process. The presence of PDGF in fibroblasts and in disc cells suggests that this growth factor regulates the function of these cells, possibly the proliferation of the cells and the production of extracellular matrix components.