Vascular endothelial growth factor (VEGF) in endocrinology and oncology

Endocrine glands are well vascularized and the structure of their vessels facilitates the exchange of various substances, including hormones. These glands are a frequent experimental model in research on VEGF and angiogenesis. VEGF participates in the pathogenesis of diabetes. Diabetic nephropathy is in essence a microvascular disease that develops as a result of a confluence of hemodynamic and metabolic perturbations. Diabetic retinopathy is the most common microvascular complication of diabetes mellitus and is the leading cause of blindness. In diabetic retinopathy ischemic states and hence tissue hypoxia and angiogenesis takes place. Participation of angiogenesis and VEGF in pathogenesis of neoplastic disease is described in many papers. VEGF protein and mRNA were found in cancers of the thyroid, bronchus, lungs, esophagus, stomach, colon, liver, breast, ovary, uterus, kidney, urinary bladder, in malignant tumors of the brain, bone. In a series of reports connections between the degree of VEGF expression with tumor aggressiveness and prognosis in patients have been reported. Richly vascularized are GEP NET. In neuroendocrine tumors strong expression of VEGF, Flt-1 and KDR in relation to the unchanged surrounding tissues has been demonstrated. Depending on the disease entity or the degree of its severity attempts of application the angiogenic and antiangiogenic therapy are being made. Antiangiogenic therapy (usually regarded as a form of cancer therapy) is based on: inhibitory effects of proangiogenic ligands and their receptors; stimulation or delivery of angiogenesis inhibitors; direct destruction of neoplastic tumor vasculature.     

Vascular endothelial growth factor (VEGF) receptor II-derived peptides inhibit VEGF

Vascular endothelial growth factor (VEGF) directly stimulates endothelial cell proliferation and migration via tyrosine kinase receptors of the split kinase domain family. It mediates vascular growth and angiogenesis in the embryo but also in the adult in a variety of physiological and pathological conditions. The potential binding site of VEGF with its receptor was identified using cellulose-bound overlapping peptides of the extracytosolic part of the human vascular endothelial growth factor receptor II (VEGFR II). Thus, a peptide originating from the third globular domain of the VEGFR II comprising residues 247RTELNVGIDFNWEYP261 was revealed as contiguous sequence stretch, which bound 125I-VEGF165. A systematic replacement with L-amino acids within the peptide representing the putative VEGF-binding site on VEGFR II indicates Asp255 as the hydrophilic key residue for binding. The dimerized peptide (RTELNVGIDFNWEYPAS)2K inhibits VEGF165 binding with an IC50 of 0.5 microM on extracellular VEGFR II fragments and 30 microM on human umbilical vein cells. VEGF165-stimulated autophosphorylation of VEGFR II as well as proliferation and migration of microvascular endothelial cells was inhibited by the monomeric peptide RTELNVGIDFNWEYPASK at a half-maximal concentration of 3-10, 0.1, and 0.1 microM, respectively. We conclude that transduction of the VEGF165 signal can be interrupted with a peptide derived from the third Ig-like domain of VEGFR II by blockade of VEGF165 binding to its receptor.     

Herbal melanin modulates tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6) and vascular endothelial growth factor (VEGF) production.

Recent studies have indicated that cytokines can enhance immunogenicity and promote tumor regression. However, the means for modulating cytokine production are not yet fully investigated. In this study we report the effects of a herbal melanin, extracted from Nigella sativa L., on the production of three cytokines [tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6) and vascular endothelial growth factor (VEGF)], by human monocytes, total peripheral blood mononuclear cells (PBMC) and THP-1 cell line. Cells were treated with variable concentrations of melanin and the expression of TNF-alpha, IL-6 and VEGF mRNA in cell lysates and secretion of proteins in the supernatants were detected by RT-PCR and ELISA. Melanin induced TNF-alpha, IL-6 and VEGF mRNA expression by the monocytes, PBMC and THP-1 cell line. On the protein level, melanin significantly induced TNF-alpha and IL-6 protein production and inhibited VEGF production by monocytes and PBMC. In the THP-1 cell line melanin induced production of all three cytokine proteins. These observations raise the prospects of using N. sativa L. melanin for treatment of diseases associated with imbalanced cytokine production and for enhancing cancer and other immunotherapies.     

Plasma levels of interleukin-12 (IL-12), interleukin-18 (IL-18) and transforming growth factor beta (TGF-beta) in Plasmodium falciparum malaria

The interaction between pro- and anti-inflammatory cytokines such as interleukin 12 (IL-12), interleukin 18 (IL-18) and transforming growth factor beta (TGF-beta) may play an important role in malaria pathogenesis and outcome. IL-18 cooperates with IL-12 in the IFN-gamma production by T, B, and NK cells, and synergizes with IL-12 for IFN-gamma production by Th1 cells. Recently it has been demonstrated that these cytokines modulate the immunoresponse in Plasmodium falciparum malaria. The aim of this study was to measure the plasma levels of IL-12, IL-18 and TGF-beta in 105 African children with various degrees of malaria, and correlate the production of these cytokines with the severity of the disease. IL-12, IL-18 and TGF-beta levels were determined using enzyme-linked immunosorbent assay. The severity of malaria was established by parasitemia, clinical symptoms and haematological parameters. The levels of IL-12, IL-18 and TGF-beta were found to be significantly elevated (15.6 + / - 12.3, 22.7 + / - 13.8 pg/ml and 25.14 + / - 13.22 pg/ml respectively) in all of the children. IL-12 and IL-18 levels were significantly lower (13.2 + / - 5.53 and 21.5 + / - 10 pg/ml pg/ml) in children with severe disease, whereas the level of TGF-beta was higher (28.09 + / - 12.39 pg/ml). In contrast, IL-12 and IL-18 levels were found to be higher (17.32 + / - 7.8 pg/ml and 25.7 + / - 7.6 pg/ml) in patients with mild disease, whereas the level of TGF-beta was lower (20.92 + / - 12.76 pg/ml) compared to the severe malaria group. The correlation between IL-12 and IL-18 demonstrated a progressive relationship up to a value of IL-12 < 25 pg/ml, while IL-18 remained stable at higher levels of IL-12. An inverse correlation was found between IL-12 and TGF-beta up to a value of IL-12 < 30, after which the level of TGF-beta remained stable. This finding suggests that fine mechanisms regulate the interaction between IL-12, IL-18 and TGF-beta in the immune response to Plasmodium falciparum.     

Vascular endothelial growth factor (VEGF) and its receptors in tumor-bearing dogs

The molecular biology of the angiogenic growth factor, vascular endothelial growth factor (VEGF), has been studied in the dog. All major isoforms of VEGF are present in the dog. The amino acid sequences are identical between human and dog in the loop regions that are responsible for receptor binding. Accordingly, the VEGF receptors of dogs and humans are very similar and permit functional exchange of the growth factor. Here we show that canine VEGF activates human endothelial cells to the same extent as human VEGF. Similarly, the two proteins display identical cell binding properties. The VEGF receptor 1 (Flt-1) shows the same alternative splicing in humans and dogs and is overexpressed in the majority of tumors in both species. VEGF occurs also in canine tumors in similar relative quantities as in human malignancies. Based on the literature and our study we suggest that the molecular biology and the function of the VEGF signaling system are virtually identical in humans and canines and in healthy as well as in disease conditions.     

Vascular endothelial growth factor (VEGF) and melanoma. N-acetylcysteine downregulates VEGF production in vitro

Vascular endothelial growth factor (VEGF), the most potent angiogenic factor identified to date, is associated with growth and metastasis of solid tumours, including melanoma. It has been shown in vitro that melanoma cells produce raised concentrations of VEGF. We examined the VEGF concentrations in plasma of 20 patients with primary melanoma, local recurrence and metastatic melanoma. We also studied the inhibiting effect of one antioxidant, N-acetylcysteine, on VEGF production in three human melanoma cell lines. We found elevated levels of VEGF (median 205 pg ml; 95 percent confidence interval, 80-414) in metastatic melanoma, with respect to primary and locally recurrent melanoma (75 pg/ml; 95 percent confidence interval, 35-130). The health control patients had levels of 25 pg/ml (95 percent confidence interval, 10-35). Human melanoma cell lines secreted VEGF in basal conditions (550-963 +/- 125 pg/ml) and N-acetylcysteine (0.5-20 mM) significantly decreased the VEGF production in a dose-dependent manner. VEGF concentrations were found to be raised in patients with primary melanoma, local recurrence, and above all, metastatic melanoma (P=0.008). N-acetylcysteine inhibits VEGF production in three human melanoma cell lines. This antioxidant might have therapeutic applications in metastatic melanoma in combination with other cytotoxic drugs.     

Vascular endothelial growth factor (VEGF) - part 1: in physiology and pathophysiology

Angiogenesis is an important component of many physiological processes, such as the female sexual cycle, placenta formation, the processes of growth and differentiation of tissues, and reparative processes including wound healing, fracture repair, and liver regeneration. The formation of new blood vessels during angiogenesis and vasculogenesis allows the growth and functioning of multicellular organisms. Pathological angiogenesis most commonly occurs in ischaemic, inflammatory and neoplastic diseases. Conditions in the pathogenesis of which angiogenesis plays an important role are sometimes labelled angiogenic diseases. To date, a number of pro-and anti-angiogenic factors have been defined. VEGF is the only specific mitogen for endothelial cells. It stimulates their growth and inhibits apoptosis, increases vascular permeability in many tissues, promotes vasculogenesis and angiogenesis. VEGF signalling activity in relation to the cell is dependent on having its specific membrane receptors (Flt-1, KDR, Flt-4). Angiogenesis plays a protective role in ischaemic heart disease and myocardial infarction. Angiogenesis extends life for patients after a stroke. Most of the facts about physiological angiogenesis are derived from studies into liver regeneration as a result of an acute injury or partial hepatectomy. Pathological hepatic angiogenesis occurs in the course of inflammation, fibrosis, hypoxia, and during tumourogenesis. There is interesting data relating to liver steatosis and obesity.     

Vascular endothelial growth factor (VEGF) - part 2: in endocrinology and oncology

Endocrine glands are well vascularised and the structure of their vessels facilitates the exchange of various substances, including hormones. These glands are a frequent experimental model in research on VEGF and angiogenesis. VEGF participates in the pathogenesis of diabetes. Diabetic nephropathy is in essence a microvascular disease that develops as a result of a confluence of haemodynamic and metabolic perturbations. Diabetic retinopathy is the commonest microvascular complication of diabetes mellitus and is the leading cause of blindness. In diabetic retinopathy, ischaemic states, and hence tissue hypoxia and angiogenesis, take place. The participation of angiogenesis and VEGF in the pathogenesis of neoplastic disease has been described in many papers. VEGF protein and mRNA have been found in cancers of the thyroid, bronchus, lungs, oesophagus, stomach, colon, liver, breast, ovary, uterus, kidney, and urinary bladder, and in malignant tumours of the brain and bone. There have been many reports of the connections between the degree of VEGF expression and tumour aggression and prognosis in patients. Richly vascularised are GEP NET. In neuroendocrine tumours, strong expression of VEGF, Flt-1 and KDR in relation to the unchanged surrounding tissues has been demonstrated. Depending on the disease entity or the degree of its severity, attempts to apply angiogenic and antiangiogenic therapy have being made. Antiangiogenic therapy (usually regarded as a form of cancer therapy) is based on: 1. inhibitory effects of proangiogenic ligands and their receptors; 2. stimulation or delivery of angiogenesis inhibitors; and 3. direct destruction of neoplastic tumour vasculature.     

Vascular endothelial growth factor (VEGF), a survival factor for tumour cells: implications for anti-angiogenic therapy

Angiogenesis is central to both the growth and metastasis of solid tumours. Anti-angiogenic strategies result in blood vessel regression accompanied by tumour cell apoptosis. Radiotherapy and many chemotherapeutic agents kill tumours by inducing apoptotic cell death. We propose that, in addition to its role as an angiogenic factor, vascular endothelial growth factor (VEGF) can act as a survival factor for tumour cells protecting them from apoptosis. Thus anti-angiogenics, in particular those directed against VEGF, have multiple anti-tumour effects. We suggest that anti-VEGF strategies prevent vessel growth and block a tumour cell survival factor, VEGF, rendering tumour cells more sensitive to chemotherapy and radiotherapy. In addition, as chemotherapy and radiotherapy have been shown to increase VEGF expression, anti-VEGF strategies may overcome therapy- induced tumour cell resistance.     

Vascular endothelial growth factor (VEGF) induces remodeling and enhances TH2-mediated sensitization and inflammation in the lung

Exaggerated levels of VEGF (vascular endothelial growth factor) are present in persons with asthma, but the role(s) of VEGF in normal and asthmatic lungs has not been defined. We generated lung-targeted VEGF(165) transgenic mice and evaluated the role of VEGF in T-helper type 2 cell (T(H)2)-mediated inflammation. In these mice, VEGF induced, through IL-13-dependent and -independent pathways, an asthma-like phenotype with inflammation, parenchymal and vascular remodeling, edema, mucus metaplasia, myocyte hyperplasia and airway hyper-responsiveness. VEGF also enhanced respiratory antigen sensitization and T(H)2 inflammation and increased the number of activated DC2 dendritic cells. In antigen-induced inflammation, VEGF was produced by epithelial cells and preferentially by T(H)2 versus T(H)1 cells. In this setting, it had a critical role in T(H)2 inflammation, cytokine production and physiologic dysregulation. Thus, VEGF is a mediator of vascular and extravascular remodeling and inflammation that enhances antigen sensitization and is crucial in adaptive T(H)2 inflammation. VEGF regulation may be therapeutic in asthma and other T(H)2 disorders.     

Vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and soluble interleukin-2 receptor (sIL-2R) concentrations in peripheral blood as markers of pituitary tumours

Vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and soluble interleukin-2 receptor (sIL-2R) are important cytokines. They are secreted by normal pituitary glands and those with all types of adenomas and may be involved in pituitary tissue growth. The peripheral blood concentrations of VEGF, bFGF and sIL-2R in nineteen patients (17-70 years) with pituitary tumours and ten healthy subjects (23-34 years) were studied. Hypersecretion of prolactin (five cases), human growth hormone (four cases), and thyroid stimulating hormone (one case) was recorded in some patients, and the remaining subjects were diagnosed as having nonfunctional pituitary tumours. Increased peripheral blood plasma levels of VEGF (310.82 +/- 59.17 pg/ml) compared with controls (40.32 +/- 11.80 pg/ml; p < 0.01), as well as bFGF (87.27 +/- 7.58 pg/ml) versus controls (11.14 +/- 2.43 pg/ml; p < 0.001) were recorded. The levels of sIL-2R did not differ between the pituitary tumour patients (4,490.58 +/- 581.50 pg/ml) and control subjects (3,617.01 +/- 1,397.18 pg/ml; p > 0.05). The concentrations of VEGF and bFGF in the peripheral blood are useful additional markers of the presence of tumours.     

Vascular endothelial growth factor (VEGF) isoform regulation of early forebrain development

This work was designed to determine the role of the vascular endothelial growth factor A (VEGF) isoforms during early neuroepithelial development in the mammalian central nervous system (CNS), specifically in the forebrain. An emerging model of interdependence between neural and vascular systems includes VEGF, with its dual roles as a potent angiogenesis factor and neural regulator. Although a number of studies have implicated VEGF in CNS development, little is known about the role that the different VEGF isoforms play in early neurogenesis. We used a mouse model of disrupted VEGF isoform expression that eliminates the predominant brain isoform, VEGF164, and expresses only the diffusible form, VEGF120. We tested the hypothesis that VEGF164 plays a key role in controlling neural precursor populations in developing cortex. We used microarray analysis to compare gene expression differences between wild type and VEGF120 mice at E9.5, the primitive stem cell stage of the neuroepithelium. We quantified changes in PHH3-positive nuclei, neural stem cell markers (Pax6 and nestin) and the Tbr2-positive intermediate progenitors at E11.5 when the neural precursor population is expanding rapidly. Absence of VEGF164 (and VEGF188) leads to reduced proliferation without an apparent effect on the number of Tbr2-positive cells. There is a corresponding reduction in the number of mitotic spindles that are oriented parallel to the ventricular surface relative to those with a vertical or oblique angle. These results support a role for the VEGF isoforms in supporting the neural precursor population of the early neuroepithelium.     

Vascular endothelial growth factor (VEGF)-C synergizes with basic fibroblast growth factor and VEGF in the induction of angiogenesis in vitro and alters endothelial cell extracellular proteolytic activity

Vascular endothelial growth factor-C (VEGF-C) is a recently characterized member of the VEGF family of angiogenic polypeptides. We demonstrate here that VEGF-C is angiogenic in vitro when added to bovine aortic or lymphatic endothelial (BAE and BLE) cells but has little or no effect on bovine microvascular endothelial (BME) cells. As reported previously for VEGF, VEGF-C and basic fibroblast growth factor (bFGF) induced a synergistic in vitro angiogenic response in all three cells lines. Unexpectedly, VEGF and VEGF-C also synergized in the in vitro angiogenic response when assessed on BAE cells. Characterization of VEGF receptor (VEGFR) expression revealed that BME, BAE, and BLE cell lines express VEGFR-1 and -2, whereas of the three cell lines assessed, only BAE cells express VEGFR-3. We also demonstrate that VEGF-C increases plasminogen activator (PA) activity in the three bovine endothelial cell lines and that this is accompanied by a concomitant increase in PA inhibitor-1. Addition of α₂-antiplasmin to BME cells co-treated with bFGF and VEGF-C partially inhibited collagen gel invasion. These results demonstrate, first, that by acting in concert with bFGF or VEGF, VEGF-C has a potent synergistic effect on the induction of angiogenesis in vitro and, second, that like VEGF and bFGF, VEGF-C is capable of altering endothelial cell extracellular proteolytic activity. These observations also highlight the notion of context, i.e., that the activity of an angiogenesis-regulating cytokine depends on the presence and concentration of other cytokines in the pericellular environment of the responding endothelial cell. J. Cell. Physiol. 177:439–452, 1998. © 1998 Wiley-Liss, Inc.     

Glycoproteome profiling of transforming growth factor-beta (TGFbeta) signaling: nonglycosylated cell death-inducing DFF-like effector A inhibits TGFbeta1-dependent apoptosis

Transforming growth factor-beta (TGFbeta) is a potent regulator of cell growth, differentiation, and apoptosis. TGFbeta binds to specific serine/threonine kinase receptors, which leads to activation of Smad-dependent and Smad-independent signaling pathways. O-Glycosylation is a dynamic PTM which has been observed in many regulatory proteins, but has not been studied in the context of TGFbeta signaling. To explore the effect of TGFbeta1 on protein O-glycosylation in human breast epithelial cells, we performed analyses of proteins which were affinity purified with Helix pomatia agglutinin (HPA). HPA lectin allowed enrichment of proteins containing GalNAc and GlcNAc linked to serine and threonine residues. Using 2-DE and MALDI-TOF-MS, we identified 21 HPA-precipitated proteins, which were affected by treatment of cells with TGFbeta1. Among these proteins, regulators of cell survival, apoptosis, trafficking, and RNA processing were identified. We found that TGFbeta1 inhibited the appearance of cell death-inducing DFF-like effector A (CIDE-A) in 2-D gels with HPA-precipitated proteins. CIDE-A is a cell death activator which promotes DNA fragmentation. We observed that TGFbeta1 did not affect expression of CIDE-A, but inhibited its glycosylation. We found that deglycosylation of CIDE-A correlated with enhanced nuclear export of the protein, and that high level of nonglycosylated CIDE-A inhibited TGFbeta1-dependent cell death. Thus, inhibition of the glycosylation of CIDE-A may be a mechanism to protect cells from apoptosis.     

Relationship between circulating interleukin-10 (IL-10) with interleukin-6 (IL-6) type cytokines (IL-6, interleukin-11 (IL-11), oncostatin M (OSM)) and soluble interleukin-6 (IL-6) receptor (sIL-6R) in patients with multiple myeloma

We investigated the serum concentration of the interleukin-10 (IL-10), along with cytokines of interleukin-6 (IL-6) family (IL-6, IL-11 and oncostatin M - OSM), as well as soluble receptor for IL-6 (sIL-6R), in 121 patients with multiple myeloma (MM) and 28 healthy subjects. We studied the interactions between IL-10 and other cytokines, and the receptor. The correlation between IL-10 and some clinical and laboratory parameters associated with the disease activity were also analysed. The IL-10 was detectable in all patients with multiple myeloma and in all controls. The IL-10 concentration was significantly increased in myeloma patients compared with healthy persons (mean - 7.09 and 2.1 pg/ml, respectively) (p = 0.008). The level of IL-10 correlated positively with the advanced stage of disease estimated according to the Salmon and Durie classification (I versus III stage - p = 0.03). Higher values of IL-10 were found in patients with the light chain disease, hypercalcaemia, and correlated with the elevated concentrations of C-reactive protein (CRP). IL-6 was detected in 117 of the 121 patients and in all controls. The concentration of IL-6 was statistically increased in MM patients compared with control group (mean - 16.06 and 4.49 pg/ml, respectively) (p = 0.01). We found a positive correlation between IL-10 and IL-6 serum levels in MM patients. The relationship, expressed as Spearman's rank sum coefficient (rho = 0.249, p = 0.006) was significant. IL-11 was detected in 26 of the 121 MM patients and in 3 of the 28 healthy subjects at the mean concentration of 1.2 and 0.6 pg/ml respectively (p > 0.05). OSM was at detectable levels in 51 of the 121 patients and in only 4 of the 28 controls (mean - 3.84 and 0.1 pg/ml, p = 0. 002). The correlation between IL-10 and IL-11 levels in MM patients was not significant, but there was a strong statistical correlation between IL-10 and OSM concentrations (rho= 0.327, p = 0.0002). The serum concentration of sIL-6R was measurable in all patients and all controls (mean - 66.00 and 39.57 ng/ml respectively), but the difference between these groups was not significant. We found significant, positive correlation between the levels of IL-10 and sIL-6R (rho= 0.233, p = 0.01). In conclusion, we state that the serum concentrations of IL-10, IL-6, OSM and sIL-6R in MM patients may be a useful markers for the evaluation of the disease activity.     

Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) expression during induced luteolysis in the bovine corpus luteum

Angiogenic factors, like vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), and their receptors, are strongly regulated during the development of bovine corpus luteum (CL). The aim of this study was to investigate real-time changes of these factors in luteal tissue of cows (n = 4-5 per group) in the mid-luteal phase (day 8-12) after intramuscular injection of the PGF2alpha-analog Cloprostenol. Before (control) and 2, 4, 12, 48, and 64 hr after prostaglandin (PG) injection, CL were collected by transvaginal ovariectomy. RT-PCR for VEGF, VEGF-receptor type 1 (VEGF-R1), VEGF-R2, acidic FGF (FGF-1), basic FGF (FGF-2), and FGF-receptor (FGF-R) was performed. Additionally, the protein concentration for VEGF was determined. The mRNA expression of VEGF and its two receptors (VEGF-R1 and -R2) was significantly downregulated during structural luteolysis (after 12 hr). VEGF protein concentration already significantly declined 2 hr after PGF2alpha. Surprisingly FGF-1 and FGF-2 were significantly and maximally upregulated during functional luteolysis (until 12 hr). Furthermore, FGF-R mRNA was significantly upregulated at 2 hr after PGF2alpha, when compared with the control group. During structural luteolysis, the expression of FGFs and their receptors was not significantly different from control, except FGF-2 mRNA, which was downregulated at 64 hr. We conclude that the cessation of VEGF-support for the CL plays a role during structural luteolysis, whereas FGFs seem to have a major impact on functional luteolysis. The possible role of these growth factors could be a transient counter-regulation of luteolysis, but also an involvement in preventing inflammatory reactions during luteal regression.     

Vascular endothelial growth factor (VEGF) stimulates monocyte migration through endothelial monolayers via increased integrin expression

Monocytes play an important role in collateral vessel formation (arteriogenesis) by attaching to activated endothelium and by invading the walls of innate collateral vessels where they produce growth factors. Previous studies have demonstrated that this process can be promoted by several chemokines and growth factors. In this study we examined the interaction between monocytes and endothelium under stimulation of the angiogenic agent vascular endothelial growth factor (VEGF). We report here the novel finding that VEGF stimulates the expression of the alphaL-, alphaM- and beta2-integrin monomers. In functional assays and by using neutralizing antibodies it was shown that VEGF stimulates adhesion of monocytes to human umbilical vein endothelial cells (HUVEC), and increased transmigration through endothelial monolayers is dependent on interaction of monocyte beta2-integrins with its endothelial counter ligand ICAM-1. Based on these in vitro data we hypothesize that the positive effect of VEGF on arteriogenesis may involve monocyte activation.