Vascular Endothelial Growth Factor Withdrawal Research Articles

The effect of tetrastarch solution for capillary leak syndrome following allogeneic hematopoietic stem cell transplantation: A report of 2 cases.

Capillary leak syndrome (CLS) is a severe complication of allogeneic hematopoietic stem cell transplantation (HSCT) characterized by weight gain, generalized edema, hypotension, and hypoalbuminemia. The primary pathogenesis is injury of the capillary endothelium resulting in a loss of intravascular fluid into the interstitial space. Treatment is limited to vascular endothelial growth factor withdrawal and systemic corticosteroids. We report two cases with CLS where weight gain, ascites, and hypotension developed after neutrophil engraftment following allogeneic HSCT. We obtained serial electrolytes, blood urea nitrogen, creatinine, and albumin from these patients. Ultrasound with Doppler tracing performed on both patients showed no reversal of portal venous flow. Issues addressed were the restoration of regular hydration by hydroxyethyl starch (HES) solutions, together with systemic corticosteroids and forced diuresis. Tetrastarch was administered 10 and 20 days, respectively. Both patients recovered without sequelae. CLS is a frequent complication after allogeneic HSCT. The effects of HES on CLS merit further consideration and prospective study.

Tumor Angiogenesis: A New Source of Pericytes

Glioblastoma stem cells have been reported to directly contribute to the tumor vasculature by endothelial cell differentiation. Interestingly, a recent study demonstrates that glioblastoma stem cells preferentially differentiate into vascular pericytes to support vasculature function and tumor growth.

Vascular endothelial hyperpermeability induces the clinical symptoms of Clarkson disease (the systemic capillary leak syndrome)

AbstractThe systemic capillary leak syndrome (SCLS) is a rare disorder characterized by transient episodes of hypotensive shock and anasarca thought to arise from reversible microvascular barrier dysfunction. Although the high prevalence of a monoclonal gammopathy of unknown significance in SCLS suggests a pathogenic contribution of endogenous immunoglobulins, the mechanisms of vascular hyperpermeability remain obscure. Herein, we report clinical and molecular findings on 23 patients, the largest SCLS case series to date. Application of episodic SCLS sera, but neither the purified immunoglobulin fraction nor sera obtained from patients during remission, to human microvascular endothelial cells caused vascular endothelial cadherin internalization, disruption of interendothelial junctions, actin stress fiber formation, and increased permeability in complementary functional assays without inducing endothelial apoptosis. Intravenous immunoglobulin, one promising therapy for SCLS, mitigated the permeability effects of episodic sera. Consistent with the presence of endogenous, nonimmunoglobulin, circulating permeability factor(s) constrained to SCLS episodes, we found that vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2), were elevated in episodic SCLS sera but not in remission sera. Ab-based inhibition of Ang2 counteracted permeability induced by episodic SCLS sera. Comparable experiments with anti-VEGF Ab (bevacizumab) yielded less interpretable results, probably because of endothelial toxicity of VEGF withdrawal. Our results support a model of SCLS pathogenesis in which nonimmunoglobulin humoral factors such as VEGF and Ang2 contribute to transient endothelial contraction, suggesting a molecular mechanism for this highly lethal disorder.

Vascular Endothelial Growth Factor and Vascular Homeostasis

Vascular endothelial growth factor (VEGF) is the angiogenic factor promoting and orchestrating most, if not all, processes of neovascularization taking place in the embryo and the adult. VEGF is also required to sustain newly formed vessels and plays additional multiple roles in the maintenance and function of certain mature vascular beds. Correspondingly, perturbations in VEGF signaling may impact organ homeostasis in multiple ways. Here we briefly review potential consequences of VEGF loss of function in adult organs. Different vascular beds display highly variable dependencies on VEGF for survival, and its loss of function may trigger the regression of many VEGF-dependent vasculatures. Normal turnover of blood vessels, in conjunction with the fact that VEGF is indispensable for compensatory angiogenesis to restore adequate perfusion, accounts for progressive vascular rarefaction under conditions of chronic VEGF inhibition of even vasculatures that are not intrinsically dependent on VEGF. Because blood vessels may have paracrine functions other than their traditional role in tissue perfusion, vascular regression resulting from VEGF withdrawal may cause substantial collateral tissue damage. VEGF may also impact tissue homeostasis via acting directly on nonvascular cells expressing cognate receptors. In the particular case of the lung, constitutive abundant expression of VEGF together with the fact that its receptors are distributed on both endothelial and epithelial cells is compatible with multiple homeostatic VEGF functions in the adult lung. Indeed, experimental inhibition of VEGF in the mature lung produces lesions resembling common lung pathologies, including emphysema and respiratory distress syndrome.

Decrease in VEGF Expression Induces Intussusceptive Vascular Pruning

The concept of vascular pruning, the "cuting-off" of vessels, is gaining importance due to expansion of angio-modulating therapies. The proangiogenic effects of vascular endothelial growth factor (VEGF) are broadly described, but the mechanisms of structural alterations by its downregulation are not known. VEGF(165)-releasing hydrogels were applied onto the chick chorioallantoic membrane on embryonic day 10. The hydrogels, designed to completely degrade within 2 days, caused high-level VEGF presentation followed by abrupt VEGF withdrawal. Application of VEGF resulted in a pronounced angiogenic response within 24 hours. The drastic decrease in level of exogenous VEGF-A within 48 hours was corroborated by enzyme-linked immunosorbent assay. Following this VEGF withdrawal we observed vasculature adaptation by means of intussusception, including intussusceptive vascular pruning. As revealed on vascular casts and serial semithin sections, intussusceptive vascular pruning occurred by emergence of multiple eccentric pillars at bifurcations. Time-lapse in vivo microscopy has confirmed the de novo occurrence of transluminal pillars and their capability to induce pruning. Quantitative evaluation corroborated an extensive activation of intussusception associated with VEGF withdrawal. Diminution of VEGF level induces vascular tree regression by intussusceptive vascular pruning. This observation may allude to the mechanism underlying the "normalization" of tumor vasculature if treated with antiangiogenic drugs. The mechanism described here gives new insights into the understanding of the processes of vasculature regression and hence provides new and potentially viable targets for antiangiogenic and/or angio-modulating therapies during various pathological processes.

Inducible adeno-associated virus vectors promote functional angiogenesis in adult organisms via regulated vascular endothelial growth factor expression

Members of the vascular endothelial growth factor (VEGF) family are among the most promising cytokines to induce neovascularization of ischaemic tissues; however, their unregulated expression often results in major undesired effects. Here, we describe the properties of inducible vectors based on the adeno-associated virus (AAV), allowing precise control of VEGF expression, and exploit these vectors to define the kinetics of the angiogenic response elicited by the factor. Based on a tetracycline-inducible transactivator, we designed an AAV vector system allowing the pharmacological regulation of VEGF production in vivo and tested its efficacy in inducing functional neoangiogenesis in both normoperfused and ischaemic skeletal muscle in mice by a combination of histological, immunofluorescent, and molecular imaging techniques. We observed that a prolonged expression of VEGF was required to determine the formation of stable vessels, able to persist upon withdrawal of the angiogenic stimulus. However, the vessels formed in the presence of continuous VEGF expression consisted mainly of dilated and leaky capillaries. As determined after pinhole scintigraphy, this abnormal vasculature accounted for a significant drop in functional tissue perfusion. In contrast, transient VEGF expression, followed by a period of VEGF withdrawal, allowed maintenance of functional perfusion under resting conditions and during exercise. This VEGF-inducible system was highly effective in improving vascularization and function in a hind-limb ischaemia model. Together, these results clearly indicate that the fine tuning of VEGF expression is required to achieve the formation of a stable vasculature able to sustain functional neovascularization.

Vascular changes in mouse tumors following endothelial cell targeted therapy

Vascular endothelial growth factor (VEGF) is an important mitogen and survival signal for endothelial cells. Withdrawal of VEGF can lead to vascular changes and tumor stasis. However, the degree of response to VEGF targeted therapy is tumor dependent and little is known regarding what factors determine sensitivity to VEGF withdrawal measured by tumor progression. We analyzed the vasculature within mmtv-Her2 driven mammary tumors, which show varying degree of response to anti-VEGF therapy. Interestingly, responsiveness measured by tumor progression appears to correlate with vascular morphology and density in the tumor cohort prior to treatment. Vascular marker analysis revealed that inhibiting VEGF leads to a change in vascular molecular profile independent of tumor progression. Furthermore, targeting a tumor vascular ECM factor EGFL7 in combination with anti-VEGF enhances the vascular response. We conclude that VEGF withdrawal changes the molecular characteristics of endothelial cells, and targeting other vascular factors may enhance the vascular response.

The Role of Vascular Endothelial Growth Factor in Langerhans Cell Histiocytosis

In angiogenesis, new blood vessels are generated from pre-existing ones. It plays a major role in tumor growth and metastasis. The main pro-angiogenic factor is the vascular endothelial growth factor (VEGF). VEGF displays high specificity for vascular endothelial cells and also elicits a pronounced angiogenic response in a variety of in vivo models. VEGF withdrawal has been shown to result in regression of vasculature in tumors. The pathogenic and the angiogenic processes of Langerhans cell histiocytosis (LCH) are not yet clear. The purpose of this study was to investigate the extent of the angiogenic response in LCH tumors. The authors examined tissue sections from LCH patients with single lesion (5 patients) or multisystem disease (5 patients). The preparations were examined by using monoclonal anti-VEGF antibody, CD34, and factor VIII-like antigen. VEGF was expressed in 70% of the cases examined. All the multisystem lesions were positive, as were two of the five single-lesion tumors. LCH cells expressed VEGF. The blood vessel density was significantly higher within the lesion than in normal margins. The findings that VEGF was expressed in LCH cells and that all multisystem lesions were VEGF producers raise the possibility of using anti-angiogenic drugs to treat these patients. Further studies to explore the role of angiogenesis in LCH are warranted.

Regulated Angiogenesis and Vascular Regression in Mice Overexpressing Vascular Endothelial Growth Factor in Airways

Angiogenesis and vascular remodeling occurs in many inflammatory diseases, including asthma. In this study, we determined the time course and reversibility of the angiogenesis and vascular remodeling produced by vascular endothelial growth factor (VEGF) in a tet-on inducible transgenic system driven by the CC10 promoter in airway epithelium. One day after switching on VEGF expression, endothelial sprouts arose from venules, grew toward the epithelium, and were abundant by 3 to 5 days. Vessel density reached twice baseline by 7 days. Many new vessels were significantly larger than normal, were fenestrated, and penetrated the epithelium. Despite their mature appearance at 7 days suggested by their pericyte coat and basement membrane, the new vessels started to regress within 3 days when VEGF was switched off, showing stasis and luminal occlusion, influx of inflammatory cells, and retraction and apoptosis of endothelial cells and pericytes. Vessel density returned to normal within 28 days after VEGF withdrawal. Our study showed the dynamic nature of airway angiogenesis and regression. Blood vessels can respond to VEGF by sprouting angiogenesis within a few days, but regress more slowly after VEGF withdrawal, and leave a historical record of their previous extent in the form of empty basement membrane sleeves.

Selective ablation of immature blood vessels in established human tumors follows vascular endothelial growth factor withdrawal.

Features that distinguish tumor vasculatures from normal blood vessels are sought to enable the destruction of preformed tumor vessels. We show that blood vessels in both a xenografted tumor and primary human tumors contain a sizable fraction of immature blood vessels that have not yet recruited periendothelial cells. These immature vessels are selectively obliterated as a consequence of vascular endothelial growth factor (VEGF) withdrawal. In a xenografted glioma, the selective vulnerability of immature vessels to VEGF loss was demonstrated by downregulating VEGF transgene expression using a tetracycline-regulated expression system. In human prostate cancer, the constitutive production of VEGF by the glandular epithelium was suppressed as a consequence of androgen-ablation therapy. VEGF loss led, in turn, to selective apoptosis of endothelial cells in vessels devoid of periendothelial cells. These results suggest that the unique dependence on VEGF of blood vessels lacking periendothelial cells can be exploited to reduce an existing tumor vasculature.

Regulatory Effects of Soluble Growth Factors on Choriocapillaris Endothelial Growth and Survival

The effects of soluble growth factors on regulating the survival and growth of choriocapillaris endothelial (CCE) cells were investigated in vitro. CCE cells were cultured in a serum-free medium in the presence or absence of various soluble growth factors. Cell growth and cell viability were assessed by counting viable cells. Results showed that acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) significantly stimulated CCE growth in a dose-dependent manner. Platelet-derived growth factor BB (PDGF, 0.4–10 ng/ml), insulin-like growth factor (IGF, 0.4–10 ng/ml) or insulin (0.4–10 µg/ml) alone did not affect the growth of CCE cells. In the presence of insulin (10 µg/ml), however, PDGF stimulated CCE growth in a dose-dependent manner. By contrast, transforming growth factor β1 (TGF-β1) induced CCE death in the absence of other growth factors and inhibited the CCE growth induced by aFGF, bFGF or VEGF. When CCE cells had been cultured in media containing aFGF, bFGF, VEGF or the combination of PDGF and insulin for 48 h, withdrawal of aFGF, bFGF or VEGF, but not PDGF, from the media resulted in CCE death. The CCE death induced by either an introduction of TGF-β1 or withdrawal of aFGF, bFGF or VEGF was defined as apoptosis based on morphologic characteristics (condensation and fragmentation of nuclei, shrinkage of cells in size) and DNA fragmentation in multiples of approximately 180 base pairs. Phorbol 12-myristate 13-acetate (PMA, 2 or 5 nM) protected CCE cells against apoptosis induced by the introduction of TGF-β1 and withdrawal of aFGF, bFGF or VEGF, while H7 (50 µM), but not HA1004 (50 µM), abrogated the protective effect of PMA on CCE apoptosis. However, cycloheximide (0.1 µM), a protein synthesis inhibitor, was only effective to protect CCE cells from apoptosis induced by aFGF, bFGF or VEGF withdrawal, but not that induced by the introduction of TGF-β1. Moreover, cycloheximide and a low concentration of PMA (2 nM) showed an additive effect on protecting CCE cells from apoptosis as the result of a growth factor withdrawal. These data may suggest that some growth factors, such as aFGF, bFGF, VEGF and TGF-β1, play a more critical role than the others, such as PDGF and IGF, in the regulation of CCE growth and survival. CCE apoptosis as a result of withdrawal of a survival factor or of receiving a death factor such as TGF-β1 may involve different mechanisms, which merits further study.

Conditional switching of vascular endothelial growth factor (VEGF) expression in tumors: induction of endothelial cell shedding and regression of hemangioblastoma-like vessels by VEGF withdrawal.

We have recently shown that VEGF functions as a survival factor for newly formed vessels during developmental neovascularization, but is not required for maintenance of mature vessels. Reasoning that expanding tumors contain a significant fraction of newly formed and remodeling vessels, we examined whether abrupt withdrawal of VEGF will result in regression of preformed tumor vessels. Using a tetracycline-regulated VEGF expression system in xenografted C6 glioma cells, we showed that shutting off VEGF production leads to detachment of endothelial cells from the walls of preformed vessels and their subsequent death by apoptosis. Vascular collapse then leads to hemorrhages and extensive tumor necrosis. These results suggest that enforced withdrawal of vascular survival factors can be applied to target preformed tumor vasculature in established tumors. The system was also used to examine phenotypes resulting from over-expression of VEGF. When expression of the transfected VEGF cDNA was continuously "on," tumors became hyper-vascularized with abnormally large vessels, presumably arising from excessive fusions. Tumors were significantly less necrotic, suggesting that necrosis in these tumors is the result of insufficient angiogenesis.