Cellular changes in normal blood capillaries undergoing regression after inhibition of VEGF signaling

p73 is required for endothelial cell differentiation, migration and the formation of vascular networks regulating VEGF and TGFβ signaling

Vasculogenesis, the establishment of the vascular plexus and angiogenesis, branching of new vessels from the preexisting vasculature, involves coordinated endothelial differentiation, proliferation and migration. Disturbances in these coordinated processes may accompany diseases such as cancer. We hypothesized that the p53 family member p73, which regulates cell differentiation in several contexts, may be important in vascular development. We demonstrate that p73 deficiency perturbed vascular development in the mouse retina, decreasing vascular branching, density and stability. Furthermore, p73 deficiency could affect non endothelial cells (ECs) resulting in reduced in vivo proangiogenic milieu. Moreover, p73 functional inhibition, as well as p73 deficiency, hindered vessel sprouting, tubulogenesis and the assembly of vascular structures in mouse embryonic stem cell and induced pluripotent stem cell cultures. Therefore, p73 is necessary for EC biology and vasculogenesis and, in particular, that DNp73 regulates EC migration and tube formation capacity by regulation of expression of pro-angiogenic factors such as transforming growth factor-β and vascular endothelial growth factors. DNp73 expression is upregulated in the tumor environment, resulting in enhanced angiogenic potential of B16-F10 melanoma cells. Our results demonstrate, by the first time, that differential p73-isoform regulation is necessary for physiological vasculogenesis and angiogenesis and DNp73 overexpression becomes a positive advantage for tumor progression due to its pro-angiogenic capacity.

[Dysthyroidism with anti-VEGF treatment, a class effect? about one case report]

Tyrosine-kinase inhibitors are recent therapy used in different neoplastic diseases. Dysthyroidism seems to be a class effect of these drugs with a potentially cross cumulative effect. We describe here the case of a man who first developed dysthyroidism with sunitinib, then a deep and permanent hypothyroidism when axitinib was introduced.

Serum and plasma vascular endothelial growth factor concentrations before and after intravitreal injection of aflibercept or ranibizumab for age-related macular degeneration

PURPOSE

To evaluate serum and plasma vascular endothelial growth factor (VEGF) concentrations in neovascular age-related macular degeneration patients treated bimonthly with an intravitreal injection of aflibercept or ranibizumab.

DESIGN

Prospective, interventional case series.

METHODS

This study includes 17 eyes of 17 patients treated with 2 mg aflibercept (the aflibercept group), 15 eyes of 15 patients treated with 0.5 mg ranibizumab (the ranibizumab group), and 12 patients with cataract (the control group). Serum and plasma VEGF concentrations were quantified using the enzyme-linked immunosorbent assay.

RESULTS

At baseline, mean serum VEGF concentration (in picograms per milliliter) did not differ significantly among the 3 groups (P = .99). In the aflibercept group, it was 28.3 pg/mL at baseline, decreased to below the detectable limit at 1 week (P < .0001), increased to 11.7 pg/mL at 1 month, which was still significantly less than the baseline level (P < .001), and returned to 23.9 pg/mL (P = .35) at 2 months. In the ranibizumab group, there were no significant differences. At baseline, mean plasma VEGF concentration did not differ significantly among the 3 groups (P = .64). In the aflibercept group, it was 16.2 at baseline, decreased to less than the detectable limit at 1 week (P < .01) and at 1 month (P < .05), and returned to 13.6 pg/mL at 2 months (P = .73). In the ranibizumab group, there were no significant differences.

CONCLUSIONS

Aflibercept significantly decreased serum and plasma VEGF concentrations 1 month after injection; however, ranibizumab had no significant effect on either serum or plasma VEGF level.

Aflibercept--a decoy VEGF receptor

Aflibercept (known as ziv-aflibercept in the USA and sold under the trade name Zaltrap®) is a human recombinant fusion protein with antiangiogenic effects that functions as a decoy receptor to bind vascular endothelial growth factors A and B and placental growth factor. Its unique mechanism of action with respect to other agents targeting angiogenesis led investigators to speculate that it may be more ubiquitously efficacious in tumors highly dependent on pathologic angiogenesis for their growth. Despite encouraging preclinical studies in various tumor types, aflibercept has not been proven efficacious in most later-phase clinical studies. In fact, its only currently held US Food and Drug Administration indication is in metastatic colorectal cancer in combination with 5-fluorouracil, leucovorin, and irinotecan for those patients previously treated with an oxaliplatin-containing chemotherapy regimen. Given aflibercept's toxicity profile and cost, further investigation is needed to better understand its mechanism of action and to discover predictive biomarkers for optimization of its appropriate use in treatment of cancer patients.

Phosphoinositide 3-kinase β mediates microvascular endothelial repair of thrombotic microangiopathy

Endothelial PI3Kβ is not required in the quiescent vasculature, but PI3Kβ loss confers sensitivity for thrombotic microangiopathy. PI3Kβ activity is required for endothelial angiogenic differentiation and microvascular repair.

Placental growth factor expression is reversed by antivascular endothelial growth factor therapy under hypoxic conditions

BACKGROUND

Clinical trials have revealed that the antivascular endothelial growth factor (VEGF) therapies are effective in retinopathy of prematurity (ROP). But the low level of VEGF was necessary as a survival signal in healthy conditions, and endogenous placental growth factor (PIGF) is redundant for development. The purpose of this study was to elucidate the PIGF expression under hypoxia as well as the influence of anti-VEGF therapy on PIGF.

METHODS

CoCl2-induced hypoxic human umbilical vein endothelial cells (HUVECs) were used for an in vitro study, and oxygen-induced retinopathy (OIR) mice models were used for an in vivo study. The expression patterns of PIGF under hypoxic conditions and the influence of anti-VEGF therapy on PIGF were evaluated by quantitative reverse transcription-polymerase chain reaction (RTPCR). The retinal avascular areas and neovascularization (NV) areas of anti-VEGF, anti-PIGF and combination treatments were calculated. Retina PIGF concentration was evaluated by ELISA after treatment. The vasoactive effects of exogenous PIGF on HUVECs were investigated by proliferation and migration studies.

RESULTS

PIGF mRNA expression was reduced by hypoxia in OIR mice, in HUVECs under hypoxia and anti-VEGF treatment. However, PIGF expression was reversed by anti-VEGF therapy in the OIR model and in HUVECs under hypoxia. Exogenous PIGF significantly inhibited HUVECs proliferation and migration under normal conditions, but it stimulated cell proliferation and migration under hypoxia. Anti-PIGF treatment was effective for neovascular tufts in OIR mice (P<0.05).

CONCLUSION

The finding that PIGF expression is iatrogenically up-regulated by anti-VEGF therapy provides a consideration to combine it with anti-PIGF therapy.

Pro-apoptotic BIM is an essential initiator of physiological endothelial cell death independent of regulation by FOXO3

The growth of new blood vessels by angiogenesis is essential for normal development, but can also cause or contribute to the pathology of numerous diseases. Recent studies have shown that BIM, a pro-apoptotic BCL2-family protein, is required for endothelial cell apoptosis in vivo, and can contribute to the anti-angiogenic effect of VEGF-A inhibitors in certain tumor models. Despite its importance, the extent to which BIM is autonomously required for physiological endothelial apoptosis remains unknown and its regulation under such conditions is poorly defined. While the transcription factor FOXO3 has been proposed to induce Bim in response to growth factor withdrawal, evidence for this function is circumstantial. We report that apoptosis was reduced in Bim(-/-) primary endothelial cells, demonstrating a cell-autonomous role for BIM in endothelial death following serum and growth factor withdrawal. In conflict with in vitro studies, BIM-dependent endothelial death in vivo did not require FOXO3. Moreover, endothelial apoptosis proceeded normally in mice lacking FOXO-binding sites in the Bim promoter. Bim mRNA was upregulated in endothelial cells starved of serum and growth factors and this was accompanied by the downregulation of miRNAs of the miR-17∼92 cluster. Bim mRNA levels were also elevated in miR-17∼92(+/-) endothelial cells cultured under steady-state conditions, suggesting that miR-17∼92 cluster miRNAs may contribute to regulating overall Bim mRNA levels in endothelial cells.

Endothelial cell-derived non-canonical Wnt ligands control vascular pruning in angiogenesis

Multiple cell types involved in the regulation of angiogenesis express Wnt ligands. Although β-catenin dependent and independent Wnt signaling pathways have been shown to control angiogenesis, the contribution of individual cell types to activate these downstream pathways in endothelial cells (ECs) during blood vessel formation is still elusive. To investigate the role of ECs in contributing Wnt ligands for regulation of blood vessel formation, we conditionally deleted the Wnt secretion factor Evi in mouse ECs (Evi-ECKO). Evi-ECKO mice showed decreased microvessel density during physiological and pathological angiogenesis in the postnatal retina and in tumors, respectively. The reduced microvessel density resulted from increased vessel regression accompanied by decreased EC survival and proliferation. Concomitantly, survival-related genes were downregulated and cell cycle arrest- and apoptosis-inducing genes were upregulated. EVI silencing in cultured HUVECs showed similar target gene regulation, supporting a mechanism of EC-derived Wnt ligands in controlling EC function. ECs preferentially expressed non-canonical Wnt ligands and canonical target gene expression was unaffected in Evi-ECKO mice. Furthermore, the reduced vascularization of Matrigel plugs in Evi-ECKO mice could be rescued by introduction of non-canonical Wnt5a. Treatment of mouse pups with the non-canonical Wnt inhibitor TNP470 resulted in increased vessel regression accompanied by decreased EC proliferation, thus mimicking the proliferation-dependent Evi-ECKO remodeling phenotype. Taken together, this study identified EC-derived non-canonical Wnt ligands as regulators of EC survival, proliferation and subsequent vascular pruning during developmental and pathological angiogenesis.

Interactions of oxidative stress and neurovascular inflammation in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death in the young age group and leads to persisting neurological impairment in many of its victims. It may result in permanent functional deficits because of both primary and secondary damages. This review addresses the role of oxidative stress in TBI-mediated secondary damages by affecting the function of the vascular unit, changes in blood-brain barrier (BBB) permeability, posttraumatic edema formation, and modulation of various pathophysiological factors such as inflammatory factors and enzymes associated with trauma. Oxidative stress plays a major role in many pathophysiologic changes that occur after TBI. In fact, oxidative stress occurs when there is an impairment or inability to balance antioxidant production with reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels. ROS directly downregulate proteins of tight junctions and indirectly activate matrix metalloproteinases (MMPs) that contribute to open the BBB. Loosening of the vasculature and perivascular unit by oxidative stress-induced activation of MMPs and fluid channel aquaporins promotes vascular or cellular fluid edema, enhances leakiness of the BBB, and leads to progression of neuroinflammation. Likewise, oxidative stress activates directly the inflammatory cytokines and growth factors such as IL-1β, tumor necrosis factor-α (TNF-α), and transforming growth factor-beta (TGF-β) or indirectly by activating MMPs. In another pathway, oxidative stress-induced degradation of endothelial vascular endothelial growth factor receptor-2 (VEGFR-2) by MMPs leads to a subsequent elevation of cellular/serum VEGF level. The decrease in VEGFR-2 with a subsequent increase in VEGF-A level leads to apoptosis and neuroinflammation via the activation of caspase-1/3 and IL-1β release.

Effect of recombinant human VEGF165b protein and bevacizumab on expression of CD34 and cell apoptosis in human gastric carcinoma xenografts in nude mice

AIM: To investigate the effect of recombinant human VEGF₁₆₅b protein (rhVEGF₁₆₅b) and bevacizumab on expression of CD34 and cell apoptosis in human gastric carcinoma xenografts in nude mice.

METHODS: Thirty male nude mice were used to establish the human gastric carcinoma xenograft model. The mice were randomly divided into three groups: a rhVEGF₁₆₅b group (intraperitoneal injection, 10 μg/kg), a bevacizumab group (intraperitoneal injection, 5 mg/kg) and a control group. Tumor growth was detected by measuring tumor volume and weight. The expression of CD34 and apoptosis of tumor cells were detected by immunohistochemistry and TdT-mediated dUTP nick end labeling (TUNEL) assay at weeks 1, 2 and 3, respectively.

RESULTS: Tumor volume and weight at weeks 1 and 2 in the rhVEGF₁₆₅b group (week 1: 0.546 ± 0.132 vs 0.637 ± 0.084, 1.894 ± 0.599 vs 0.46 ± 0.093; week 2: 1.894 ± 0.599 vs 2.238 ± 0.29, 1.537 ± 0.568 vs 2.013 ± 0.833; P < 0.05 for all) and at weeks 1, 2 and 3 in the bevacizumab group (week 1: 0.453 ± 0.119 vs 0.637 ± 0.084, 0.320 ± 0.097 vs 0.460 ± 0.093; week 2: 1.691 ± 0.381 vs 2.238 ± 0.290, 1.168 ± 0.524 vs 2.013 ± 0.833; week 3: 1.709 ± 0.474 vs 4.872 ± 0.594, 1.747 ± 0.557 vs 3.463 ± 0.986, P < 0.05 for all) were significantly smaller than those in the control group. At week 3, tumor volume and weight were significantly larger in the rhVEGF₁₆₅b group than in the bevacizumab group (3.843 ± 1.339 vs 1.709 ± 0.474, 3.066 ± 1.281 vs 1.747 ± 0.557, P < 0.05 for both). Microvascular density (MVD) and apoptosis index (AI) at weeks 1, 2 and 3 in the rhVEGF₁₆₅b group and bevacizumab group were significantly different from those in the control group. MVD and AI also differed significantly between the rhVEGF₁₆₅b group and bevacizumab group.

CONCLUSION: Both rhVEGF₁₆₅b and bevacizumab can inhibit the growth of human gastric carcinoma cells possibly by inhibiting angiogenesis and inducing apoptosis, with rhVEGF₁₆₅b having a more significant effect in early stage.

Angiogenesis and the tumor microenvironment: vascular endothelial growth factor and beyond

Our understanding of the dynamic tumor microenvironment (TME) has improved exponentially over the last few decades. In addition to traditional cytotoxic agents, anti-cancer strategies now include numerous molecular-targeted drugs that modulate distinct elements of the TME. Angiogenesis is an underlying promoter of tumor growth, invasion, and metastases. From traditional and emerging angiogenic cytokines and their receptors to novel immune checkpoint inhibitors, regulation of the tumor microenvironment is potentially key in countering tumor progression. In this article, an overview of the architecture of the TME and the orchestration of angiogenesis within the TME is provided. Additionally, traditional and novel angiogenic targets of current interest within the TME are reviewed.

Preliminary safety evaluation of a taurocholate-conjugated low-molecular-weight heparin derivative (LHT7): a potent angiogenesis inhibitor

In our previous studies, taurocholic acid (TA)-conjugated low-molecular-weight heparin derivative (LHT7) has been proven to be a potent anti-angiogenic agent by demonstrated successful blockage capability of vascular endothelial growth factors (VEGF). Preliminary safety evaluations were conducted based on its mechanism of action and chemical behavior. For this purpose, acute toxicity study, and hematological and serological evaluations were carried out. Additionally, in order to evaluate mechanism-related side effects, both blood pressure and the occurrence of proteinuria were measured using a treatment regime of multiple high doses of LHT7 in a biodistribution study. LD50 values for LHT7 in female and male mice were 56.9 and 64.7 mg kg(-1) doses, respectively. There were no vital fluctuations in the serological and hematological parameters, except for the elevated levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) at 100 and 200 mg kg(-1) doses of LHT7, representing vital changes in the liver function. Moreover, the results of mechanism-related studies showed that blood pressure at 50 mg kg(-1) did not change but showed elevated levels of protein in urine. In the biodistribution study, a slight accumulation of LHT7 in the kidney and the liver were observed at the 50 mg kg(-1) repeated dose owing to the presence of bile acid. No fatal damage was observed in this study; most observations were related to the chemical composition or the mechanism of action of the material.

Vascular endothelial growth factor inhibitor-induced hypertension: from pathophysiology to prevention and treatment based on long-acting nitric oxide donors

Hypertension is the most common adverse effect of the inhibitors of vascular endothelial growth factor (VEGF) pathway-based therapy (VEGF pathway inhibitors therapy, VPI therapy) in cancer patients. VPI includes monoclonal antibodies against VEGF, tyrosine kinase inhibitors, VEGF Traps, and so-called aptamers that may become clinically relevant in the future. All of these substances inhibit the VEGF pathway, which in turn causes a decrease in nitric oxide (NO) and an increase in blood pressure, with the consequent development of hypertension and its final events (e.g., myocardial infarction or stroke). To our knowledge, there is no current study on how to provide an optimal therapy for patients on VPI therapy with hypertension. This review summarizes the roles of VEGF and NO in vessel biology, provides an overview of VPI agents, and suggests a potential treatment procedure for patients with VPI-induced hypertension.

Anti-vascular endothelial growth factor therapy for diabetic macular edema

Diabetes mellitus is a serious health problem that affects over 350 million individuals worldwide. Diabetic retinopathy (DR), which is the most common microvascular complication of diabetes, is the leading cause of new cases of blindness in working-aged adults. Diabetic macular edema (DME) is an advanced, vision-limiting complication of DR that affects nearly 30% of patients who have had diabetes for at least 20 years and is responsible for much of the vision loss due to DR. The historic standard of care for DME has been macular laser photocoagulation, which has been shown to stabilize vision and reduce the rate of further vision loss by 50%; however, macular laser leads to significant vision recovery in only 15% of treated patients. Mechanisms contributing to the microvascular damage in DR and DME include the direct toxic effects of hyperglycemia, sustained alterations in cell signaling pathways, and chronic microvascular inflammation with leukocyte-mediated injury. Chronic retinal microvascular damage results in elevation of intraocular levels of vascular endothelial growth factor A (VEGF), a potent, diffusible, endothelial-specific mitogen that mediates many important physiologic processes, including but not limited to the development and permeability of the vasculature. The identification of VEGF as an important pathophysiologic mediator of DME suggested that anti-VEGF therapy delivered to the eye might lead to improved visual outcomes in this disease. To date, four different inhibitors of VEGF, each administered by intraocular injection, have been tested in prospective, randomized phase II or phase III clinical trials in patients with DME. The results from these trials demonstrate that treatment with anti-VEGF agents results in substantially improved visual and anatomic outcomes compared with laser photocoagulation, and avoid the ocular side effects associated with laser treatment. Thus, anti-VEGF therapy has become the preferred treatment option for the management of DME in many patients.

[Treatment of central serous chorioretinopathy: MicroPulse photocoagulation versus bevacizumab]

PURPOSE

The aim of this study was to evaluate the treatment of central serous chorioretinopathy (CSC) with either subthreshold diode-laser MicroPulse (MP) or intravitreal bevacizumab (BCZ) using the Pro Re Nata (PRN) scheme.

METHODS

This comparative, controlled, prospective study over 10 months examined 52 eyes of 52 patients with either (a) treatment with MP at the active leakage site guided by fluorescein angiography (FA) (n=16 eyes), (b) intravitreal injection of 1.25 mg BCZ (n=10 eyes) or (c) passive observation (n=26 eyes). Outcome measures included changes in retinal pigment epithelium (RPE) leakage at FA, central macular thickness (CMT), best corrected visual acuity (BCVA) and 10° macular perimetry.

RESULTS

At the end of the study there was a 12.5 % persistent leakage in the MP group compared to 60 % in the BCZ group and 92 % in the control group. Mean CMT decreased by 94 µm in the MP, 38 µm in the BCZ and did not change in the control group. Mean BCVA improved by six ETDRS letters in the MP, decreased by one letter in the BCZ and by 2 letters in the control group. In the MP group mean perimetric deficit improved by 1.5 decibels and corrected lost variance by 2.6. In the BCZ it improved by 0.6 and by 0.5 in the control group. Retreatment was required in 7 out of 16 eyes of the SDM (43.75 %), and in 5 out of 10 eyes of the BCZ group (50 %).

CONCLUSIONS

MP photocoagulation was superior to intravitreal injections of 1.25 mg BCZ in the treatment of CSC which resulted in enhanced visual acuity and macular perimetry.

Bisphosphonates induce the osteogenic gene expression in co-cultured human endothelial and mesenchymal stem cells

Bisphosphonates (BPs) are known to affect bone homeostasis and also to have anti-angiogenic properties. Because of the intimate relationship between angiogenesis and osteogenesis, this study analysed the effects of Alendronate (AL) and Zoledronate (ZL) in the expression of endothelial and osteogenic genes on interacting endothelial and mesenchymal stem cells, an issue that was not previously addressed. Alendronate and ZL, 10(-12) -10(-6) M, were evaluated in a direct co-culture system of human dermal microvascular endothelial cells (HDMEC) and human bone marrow mesenchymal stem cells (HMSC), over a period of 14 days. Experiments with the respective monocultures were run in parallel. Alendronate and ZL caused an initial dose-dependent stimulation in the cell proliferation in the monocultures and co-cultures, and did not interfere with their cellular organization. In HDMEC monocultures, the expression of the endothelial genes CD31, VE-cadherin and VEGFR2 was down-regulated by AL and ZL. In HMSC monocultures, the BPs inhibited VEGF expression, but up-regulated the expression of the osteogenic genes alkaline phosphatase (ALP), bone morphogenic protein-2 (BMP-2) and osteocalcin (OC) and, to a greater extent, osteoprotegerin (OPG), a negative regulator of the osteoclastic differentiation, and increased ALP activity. In co-cultured HDMEC/HMSC, AL and ZL decreased the expression of endothelial genes but elicited an earlier and sustained overexpression of ALP, BMP-2, OC and OPG, compared with the monocultured cells; they also induced ALP activity. This study showed for the first time that AL and ZL greatly induced the osteogenic gene expression on interacting endothelial and mesenchymal stem cells.

Tyrosine kinase inhibitors induced thyroid dysfunction: a review of its incidence, pathophysiology, clinical relevance, and treatment

Tyrosine kinase inhibitors (TKI) belong to a new class of molecular multitargeted anticancer therapy which targets different growth factor receptors and hence attenuates cancer cell survival and growth. Since their introduction as adjunct treatment for renal cell carcinoma and gastrointestinal stromal tumors (GIST), a number of reports have demonstrated that TKI can induce thyroid dysfunction which was especially more common with sunitinib maleate. Many mechanisms with respect to this adverse effect of tyrosine kinase inhibitors have been proposed including their induction of thyroiditis, capillary regression in the thyroid gland, antithyroid peroxidase antibody production, and their ability to decrease iodine uptake by the thyroid gland. Of interest is the observation that TKI-induced thyroid dysfunction may actually be protective as it was shown to improve overall survival, and it was suggested that it may have a prognostic value. Followup on thyroid function tests while patients are maintained on tyrosine kinase inhibitor is strongly recommended. When thyroid dysfunction occurs, appropriate treatment should be individualized depending on patients symptoms and thyroid stimulating hormone level.

Alveolar oxygen tension and angio-architecture of the distal adult lung

The present study demonstrates the fine structure of pulmonary capillaries first injured and then undergoing growth in response to a change in the ambient alveolar oxygen tension. Breathing a high fraction of inspired oxygen (FiO2 0.75) triggers restriction by endothelial cell injury and effacement leading to segment narrowing and shortening and segment loss as demonstrated by a fall in density. Subsequently, breathing a relatively low fraction (FiO2 0.21) triggers capillary assembly (angiogenesis), which reverses the changes. The data underscore the structural reprogramming (reduction and restoration) of pulmonary capillaries in response to significant shifts in oxygen tension.

Blood flow changes coincide with cellular rearrangements during blood vessel pruning in zebrafish embryos

After the initial formation of a highly branched vascular plexus, blood vessel pruning generates a hierarchically structured network with improved flow characteristics. We report here on the cellular events that occur during the pruning of a defined blood vessel in the eye of developing zebrafish embryos. Time-lapse imaging reveals that the connection of a new blood vessel sprout with a previously perfused multicellular endothelial tube leads to the formation of a branched, Y-shaped structure. Subsequently, endothelial cells in parts of the previously perfused branch rearrange from a multicellular into a unicellular tube, followed by blood vessel detachment. This process is accompanied by endothelial cell death. Finally, we show that differences in blood flow between neighboring vessels are important for the completion of the pruning process. Our data suggest that flow induced changes in tubular architecture ensure proper blood vessel pruning.

Inhibition of placental growth factor improves surgical outcome of glaucoma surgery

Excessive post-operative wound healing with subsequent scarring frequently leads to surgical failure of glaucoma filtration surgery (trabeculectomy). We investigated the hypothesis that placental growth factor (PlGF) plays a role in post-operative scar formation, and that it therefore may be a target for improvement of filtration surgery outcome. ELISA experiments showed that PlGF levels were significantly increased in aqueous humour of glaucoma patients and after VEGF treatment, which may indicate an important contribution of this growth factor to wound healing after trabeculectomy. Using a mouse model of glaucoma filtration surgery, we were able to show that intracameral injection of a previously characterized anti-PlGF antibody (ThromboGenics NV) significantly improved surgical outcome by increasing bleb survival and bleb area. This was associated with a significant reduction in post-operative proliferation, inflammation and angiogenesis during the first post-operative days after surgery, and with a decrease in collagen deposition at later stages. Furthermore, inhibition of PlGF seemed to be more effective than anti-VEGF-R2 treatment in improving surgical outcome, possibly via its additional effect on inflammation. These results render PlGF an appealing target for ocular wound healing and point to potential therapeutic benefits of PlGF inhibition for the prevention of surgical failure.

Thyroid dysfunction and tyrosine kinase inhibitors in renal cell carcinoma

The most recent World Health Organization classification of renal neoplasms encompassed nearly 50 distinctive renal neoplasms. Different histological subtypes have different clinical outcomes and show different responses to therapy. Overall, the incidence of kidney cancer has increased worldwide in the last years. Although the most common type of kidney cancer is localized renal cell carcinoma (RCC), with a 5-year survival rate of 85%, about one third of patients present advanced or metastatic disease at diagnosis, with a 5-year survival rate of only 10%. Multi-targeted receptor tyrosine kinase inhibitors (TKIs, sunitinib and sorafenib), the anti-VEGF MAB bevacizumab in association with interferon-α, and the mTOR inhibitors are now approved for the treatment of mRCC. Recently, the novel agents pazopanib and axitinib have also demonstrated efficacy in mRCC patients. Several recent retrospective and prospective trials have suggested that some of their adverse events, such as hypertension, hypothyroidism, and hand foot syndrome (HFS) may act as potential biomarkers of response and efficacy of treatment. In this review, we analyzed the studies that have suggested a relationship between hypothyroidism onset and a better outcome of mRCC patients treated with TKIs. The biological mechanisms suggesting and explaining this correlation are not well known and different speculative theories have been considered in order to investigate the clinical link between hypothyroidism occurrence and the prolonged therapy with TKIs in solid tumors. Furthermore, the management of this unexplained side effect is very important to maximize the efficacy of therapy in mRCC patients because there is a clear and consistent relationship between drug dose and efficacy of treatment. Certainly, other studies are needed to clarify whether a better outcome is associated with hypothyroidism induced to TKIs in patients with mRCC.

Endoglin and activin receptor-like kinase 1 heterozygous mice have a distinct pulmonary and hepatic angiogenic profile and response to anti-VEGF treatment

Hereditary hemorrhagic telangiectasia (HHT) is a vascular dysplasia associated with dysregulated angiogenesis and arteriovascular malformations. The disease is caused by mutations in endoglin (ENG; HHT1) or activin receptor-like kinase 1 (ALK1; HHT2) genes, coding for transforming growth factor β (TGF-β) superfamily receptors. Vascular endothelial growth factor (VEGF) has been implicated in HHT and beneficial effects of anti-VEGF treatment were recently reported in HHT patients. To investigate the systemic angiogenic phenotype of Endoglin and Alk1 mutant mice and their response to anti-VEGF therapy, we assessed microvessel density (MVD) in multiple organs after treatment with an antibody to mouse VEGF or vehicle. Lungs were the only organ showing an angiogenic defect, with reduced peripheral MVD and secondary right ventricular hypertrophy (RVH), yet distinctly associated with a fourfold increase in thrombospondin-1 (TSP-1) in Eng (+/-) versus a rise in angiopoietin-2 (Ang-2) in Alk1 (+/-) mice. Anti-VEGF treatment did reduce lung VEGF levels but interestingly, led to an increase in peripheral pulmonary MVD and attenuation of RVH; it also normalized TSP-1 and Ang-2 expression. Hepatic MVD, unaffected in mutant mice, was reduced by anti-VEGF therapy in heterozygous and wild type mice, indicating a liver-specific effect of treatment. Contrast-enhanced micro-ultrasound demonstrated a reduction in hepatic microvascular perfusion after anti-VEGF treatment only in Eng (+/-) mice. Our findings indicate that the mechanisms responsible for the angiogenic imbalance and the response to anti-VEGF therapy differ between Eng and Alk1 heterozygous mice and raise the need for systemic monitoring of anti-angiogenic therapy effects in HHT patients.

Angiogenesis-related pathways in the pathogenesis of ovarian cancer

Ovarian Cancer represents the most fatal type of gynecological malignancies. A number of processes are involved in the pathogenesis of ovarian cancer, especially within the tumor microenvironment. Angiogenesis represents a hallmark phenomenon in cancer, and it is responsible for tumor spread and metastasis in ovarian cancer, among other tumor types, as it leads to new blood vessel formation. In recent years angiogenesis has been given considerable attention in order to identify targets for developing effective anti-tumor therapies. Growth factors have been identified to play key roles in driving angiogenesis and, thus, the formation of new blood vessels that assist in "feeding" cancer. Such molecules include the vascular endothelial growth factor (VEGF), the platelet derived growth factor (PDGF), the fibroblast growth factor (FGF), and the angiopoietin/Tie2 receptor complex. These proteins are key players in complex molecular pathways within the tumor cell and they have been in the spotlight of the development of anti-angiogenic molecules that may act as stand-alone therapeutics, or in concert with standard treatment regimes such as chemotherapy. The pathways involved in angiogenesis and molecules that have been developed in order to combat angiogenesis are described in this paper.

TNF-α decreases VEGF secretion in highly polarized RPE cells but increases it in non-polarized RPE cells related to crosstalk between JNK and NF-κB pathways

Asymmetrical secretion of vascular endothelial growth factor (VEGF) by retinal pigment epithelial (RPE) cells in situ is critical for maintaining the homeostasis of the retina and choroid. VEGF is also involved in the development and progression of age-related macular degeneration (AMD). We studied the effect of tumor necrosis factor-α (TNF-α) on the secretion of VEGF in polarized and non-polarized RPE cells (P-RPE cells and N-RPE cells, respectively) in culture and in situ in rats. A subretinal injection of TNF-α caused a decrease in VEGF expression and choroidal atrophy. Porcine RPE cells were seeded on Transwell™ filters, and their maturation and polarization were confirmed by the asymmetrical VEGF secretion and trans electrical resistance. Exposure to TNF-α decreased the VEGF secretion in P-RPE cells but increased it in N-RPE cells in culture. TNF-α inactivated JNK in P-RPE cells but activated it in N-RPE cells, and TNF-α activated NF-κB in P-RPE cells but not in N-RPE cells. Inhibition of NF-κB activated JNK in both types of RPE cells indicating crosstalk between JNK and NF-κB. TNF-α induced the inhibitory effects of NF-κB on JNK in P-RPE cells because NF-κB is continuously inactivated. In N-RPE cells, however, it was not evident because NF-κB was already activated. The basic activation pattern of JNK and NF-κB and their crosstalk led to opposing responses of RPE cells to TNF-α. These results suggest that VEGF secretion under inflammatory conditions depends on cellular polarization, and the TNF-α-induced VEGF down-regulation may result in choroidal atrophy in polarized physiological RPE cells. TNF-α-induced VEGF up-regulation may cause neovascularization by non-polarized or non-physiological RPE cells.

KRN633, an inhibitor of vascular endothelial growth factor receptor tyrosine kinase, induces intrauterine growth restriction in mice

We previously reported that treatment with KRN633, a vascular endothelial growth factor receptor tyrosine kinase inhibitor, during mid-pregnancy caused intrauterine growth restriction resulting from impairment of blood vessel growth in the labyrinthine zone of the placenta and fetal organs. However, the relative sensitivities of blood vessels in the placenta and fetal organs to vascular endothelial growth factor (VEGF) inhibitors have not been determined. In this study, we aimed to examine the effects of KRN633 on the vasculatures of organs in mother mice and their newborn pups by immunohistochemical analysis. Pregnant mice were treated daily with KRN633 (5 mg/kg) either from embryonic day 13.5 (E13.5) to E17.5 or from E13.5 to the day of delivery. The weights of the pups of KRN633-treated mice were lower than those of the pups of vehicle-treated mothers. However, no significant difference in body weight was observed between the vehicle- and KRN633-treated mice. The vascular development in the organs (the pancreas, kidney, and intestine) and intestinal lymphatic formation of the pups of KRN633-treated mothers was markedly impaired. In contrast, the KRN633 treatment showed no significant effect on the vascular beds in the organs, including the labyrinthine zone of the placenta, of the mother mice. These results suggest that blood vessels in fetal organs are likely to be more sensitive to reduced VEGF signaling than those in the mother. A partial loss of VEGF function during pregnancy could suppress vascular growth in the fetus without affecting the vasculature in the mother mouse, thereby increasing the risk of intrauterine growth restriction.

Tumor endothelial cell-specific drug delivery system using apelin-conjugated liposomes

Background

A drug delivery system specifically targeting endothelial cells (ECs) in tumors is required to prevent normal blood vessels from being damaged by angiogenesis inhibitors. The purpose of this study was to investigate whether apelin, a ligand for APJ expressed in ECs when angiogenesis is taking place, can be used for targeting drug delivery to ECs in tumors.

Methods and Results

Uptake of apelin via APJ stably expressed in NIH-3T3 cells was investigated using TAMRA (fluorescent probe)-conjugated apelin. Both long and short forms of apelin (apelin 36 and apelin 13) were taken up, the latter more effectively. To improve efficacy of apelin- liposome conjugates, we introduced cysteine, with its sulfhydryl group, to the C terminus of apelin 13, resulting in the generation of apelin 14. In turn, apelin 14 was conjugated to rhodamine-encapsulating liposomes and administered to tumor-bearing mice. In the tumor microenvironment, we confirmed that liposomes were incorporated into the cytoplasm of ECs. In contrast, apelin non-conjugated liposomes were rarely found in the cytoplasm of ECs. Moreover, non-specific uptake of apelin-conjugated liposomes was rarely detected in other normal organs.

Conclusions

ECs in normal organs express little APJ; however, upon hypoxic stimulation, such as in tumors, ECs start to express APJ. The present study suggests that apelin could represent a suitable tool to effectively deliver drugs specifically to ECs within tumors.

Sunitinib as an anti-endometriotic agent

Endometriosis is one of the most frequent diseases in gynecology. Currently available medical therapies for this disease are unsatisfactory. Based on current understanding of the pathogenic mechanisms in endometriosis especially the similarity between this disease and cancer, this study was designed to investigate the efficacy of the anticancer drug sunitinib in treating endometriosis. The effect of sunitinib on regression of endometriotic implants was studied in a rat surgical model. Sunitinib reduced cyst cross sectional area by 78.8% and caused complete cyst disappearance in 50% of the animals. Histologically, extensive fibrosis was detected in sunitinib-treated group with positive reaction in TUNEL assay indicating that apoptosis is a mechanism of action.

Mouse models for studying angiogenesis and lymphangiogenesis in cancer

The formation of new blood vessels (angiogenesis) is required for the growth of most tumors. The tumor microenvironment also induces lymphangiogenic factors that promote metastatic spread. Anti-angiogenic therapy targets the mechanisms behind the growth of the tumor vasculature. During the past two decades, several strategies targeting blood and lymphatic vessels in tumors have been developed. The blocking of vascular endothelial growth factor (VEGF)/VEGF receptor-2 (VEGFR-2) signaling has proven effective for inhibition of tumor angiogenesis and growth, and inhibitors of VEGF-C/VEGFR-3 involved in lymphangiogenesis have recently entered clinical trials. However, thus far anti-angiogenic treatments have been less effective in humans than predicted on the basis of pre-clinical tests in mice. Intrinsic and induced resistance against anti-angiogenesis occurs in patients, and thus far the clinical benefit of the treatments has been limited to modest improvements in overall survival in selected tumor types. Our current knowledge of tumor angiogenesis is based mainly on experiments performed in tumor-transplanted mice, and it has become evident that these models are not representative of human cancer. For an improved understanding, angiogenesis research needs models that better recapitulate the multistep tumorigenesis of human cancers, from the initial genetic insults in single cells to malignant progression in a proper tissue environment. To improve anti-angiogenic therapies in cancer patients, it is necessary to identify additional molecular targets important for tumor angiogenesis, and to get mechanistic insight into their interactions for eventual combinatorial targeting. The recent development of techniques for manipulating the mammalian genome in a precise and predictable manner has opened up new possibilities for the generation of more reliable models of human cancer that are essential for the testing of new therapeutic strategies. In addition, new imaging modalities that permit visualization of the entire mouse tumor vasculature down to the resolution of single capillaries have been developed in pre-clinical models and will likely benefit clinical imaging.

Role of vascular endothelial growth factor in maintenance of pregnancy in mice

It is well known that withdrawal of progesterone from the maternal circulation is a critical stimulus to parturition in rodents, such as rats and mice. However, mechanisms that determine the timing of progesterone withdrawal are not completely understood. In the present study, we examined whether the vascular endothelial growth factor (VEGF) system in the corpus luteum (CL) contributes to the regulation of circulating progesterone levels and acts as a determinant of the timing of parturition in mice. We found that reduction in the expression levels of VEGF and VEGF receptor-2 in the CL precedes the impairment of luteal circulation and a series of events leading to parturition (i.e., reduction of plasma progesterone, enhancement of myometrium contractility, and onset of parturition). Blocking of VEGF signaling by using the inhibitor of VEGFR tyrosine kinase KRN633 at mid-pregnancy caused a similar sequence of events and induced preterm birth. These results suggest that the VEGF system in the CL plays a critical role in maintaining a high level of circulating progesterone, and determining the timing of parturition in mice.

Adipose vascular endothelial growth factor regulates metabolic homeostasis through angiogenesis

Vascular endothelial growth factor A (VEGF) is highly expressed in adipose tissue. Its role, however, has not been fully elucidated. Here, we reveal the metabolic role of adipose-VEGF by studying mice with deletion (VEGF(AdΔ)) or doxycycline-inducible overexpression of a VEGF transgene (VEGF(AdTg)) in the adipose tissue. VEGF(AdΔ) mice have reduced adipose vascular density and show adipose hypoxia, apoptosis, inflammation, and metabolic defects on a high-fat diet. In contrast, induction of VEGF expression in VEGF(AdTg) mice leads to increased adipose vasculature and reduced hypoxia. The latter changes are sufficient to counteract an established compromising effect of high-fat diet on the metabolism, indicating that metabolic misbalance is reversible by adipose vessel density increase. Our data clearly show the essential role of VEGF signaling for adequate adipose function. Besides revealing insights into the molecular mechanisms of obesity-related metabolic diseases, this study points to the therapeutic potential of increased adipose angiogenesis.

Cardiovascular complications associated with novel angiogenesis inhibitors: emerging evidence and evolving perspectives

Novel cancer therapies targeting tumor angiogenesis have revolutionized treatment options in a variety of tumors. Specifically, VEGF signaling pathway (VSP) inhibitors have been introduced into clinical practice at a rapid pace over the last decade. It is becoming increasingly clear that VSP inhibitors can cause cardiovascular toxicities including hypertension, thrombosis, and heart failure. This review highlights these toxicities and proposes several strategies in their prevention and treatment. However, we recognize the dearth of data in this area and advocate a multi-disciplinary approach involving cardiologists and oncologists, as well as clinical and translational studies, in understanding and treating VSP-inhibitor associated toxicities.

Short term interactions with long term consequences: modulation of chimeric vessels by neural progenitors

Vessels are a critical and necessary component of most tissues, and there has been substantial research investigating vessel formation and stabilization. Several groups have investigated coculturing endothelial cells with a second cell type to promote formation and stabilization of vessels. Some have noted that long-term vessels derived from implanted cocultures are often chimeric consisting of both host and donor cells. The questions arise as to whether the coculture cell might impact the chimeric nature of the microvessels and can modulate the density of donor cells over time. If long-term engineered microvessels are primarily of host origin, any impairment of the host's angiogenic ability has significant implications for the long-term success of the implant. If one can modulate the host versus donor response, one may be able to overcome a host's angiogenic impairment. Furthermore, if one can modulate the donor contribution, one may be able to engineer microvascular networks to deliver molecules a patient lacks systemically for long times. To investigate the impact of the cocultured cell on the host versus donor contributions of endothelial cells in engineered microvascular networks, we varied the ratio of the neural progenitors to endothelial cells in subcutaneously implanted poly(ethylene glycol)/poly-L-lysine hydrogels. We found that the coculture of neural progenitors with endothelial cells led to the formation of chimeric host-donor vessels, and the ratio of neural progenitors has a significant impact on the long term residence of donor endothelial cells in engineered microvascular networks in vivo even though the neural progenitors are only present transiently in the system. We attribute this to the short term paracrine signaling between the two cell types. This suggests that one can modulate the host versus donor contributions using short-term paracrine signaling which has broad implications for the application of engineered microvascular networks and cellular therapy more broadly.

Renoprotective effects of hepatocyte growth factor in the stenotic kidney

Renal microvascular (MV) damage and loss contribute to the progression of renal injury in renal artery stenosis (RAS). Hepatocyte growth factor (HGF) is a powerful angiogenic and antifibrotic cytokine that we showed to be decreased in the stenotic kidney. We hypothesized that renal HGF therapy will improve renal function mainly by protecting the renal microcirculation. Unilateral RAS was induced in 15 pigs. Six weeks later, single-kidney RBF and GFR were quantified in vivo using multidetector computed tomography (CT). Then, intrarenal rh-HGF or vehicle was randomly administered into the stenotic kidney (RAS, n = 8; RAS+HGF, n = 7). Pigs were observed for 4 additional weeks before CT studies were repeated. Renal MV density was quantified by 3D micro-CT ex vivo and histology, and expression of angiogenic and inflammatory factors, apoptosis, and fibrosis was determined. HGF therapy improved RBF and GFR compared with vehicle-treated pigs. This was accompanied by improved renal expression of angiogenic cytokines (VEGF, p-Akt) and tissue-healing promoters (SDF-1, CXCR4, MMP-9), reduced MV remodeling, apoptosis, and fibrosis, and attenuated renal inflammation. However, HGF therapy did not improve renal MV density, which was similarly reduced in RAS and RAS+HGF compared with controls. Using a clinically relevant animal model of RAS, we showed novel therapeutic effects of a targeted renal intervention. Our results show distinct actions on the existing renal microcirculation and promising renoprotective effects of HGF therapy in RAS. Furthermore, these effects imply plasticity of the stenotic kidney to recuperate its function and underscore the importance of MV integrity in the progression of renal injury in RAS.

Role of fibroblast growth factor signaling in vascular formation and maintenance: orchestrating signaling networks as an integrated system

The vascular system has begun to be perceived as a dynamic organ actively controlling a wide variety of physiological processes. The structural and functional integrity of blood vessels, regulated by signaling activities finely modulating cell-cell and cell-matrix interactions, is crucial for vessel physiology, as well as basic functionality of the tissue. Throughout the process of new vessel formation, while blood vessels are actively reorganized and remodeled with migration and proliferation of vascular cells, maintenance of vascular barrier function is essentially important. These conflicting properties, i.e., dynamic cellular mobilization and maintenance of barrier integrity, are simultaneously achieved through the interaction of highly organized signaling networks governing coordinated cell-cell interplay. Recent evidence suggests that the fibroblast growth factor (FGF) system plays a regulatory role in several physiological conditions in the vascular system. In this article, we will attempt to summarize current knowledge in order to understand the mechanism of this coordination and evaluate the pivotal role of FGF signaling in integrating a diverse range of signaling events in vascular growth and maintenance.

A reversal in the vascularity of metastatic liver tumors from colorectal cancer after the cessation of chemotherapy plus bevacizumab: contrast-enhanced ultrasonography and histological examination

OBJECTIVE

To assess the effect of chemotherapy plus bevacizumab on tumor vessels, as well as the reversibility of this effect, using contrast-enhanced ultrasonography (CEUS) and histology in patients with metastatic liver tumors derived from colorectal cancer.

METHODS

The study included 12 patients who received chemotherapy plus bevacizumab, experienced a reduction in tumor vascularity as demonstrated by CEUS and consequently underwent liver resection. CEUS was performed before and after four courses of chemotherapy and before surgery. The numbers of microvessels highlighted by anti-CD34 antibodies in the viable tumor tissue were counted to quantify the microvessel density (MVD). As a control, 12 surgical specimens from 12 patients who had not received chemotherapy were examined.

RESULTS

A reversal of tumor vascularity was observed in 10 of 12 patients. In two patients, the vascularity remained reduced. The MVD in the treatment group was significantly lower than that observed in the group without treatment.

CONCLUSION

The data suggest that the tumor vessels regenerated substantially, although the effect of chemotherapy plus bevacizumab remained weak for approximately 6 weeks after the cessation of treatment. Therefore, future research must determine whether bevacizumab should be used prior to surgery.

Emerging role of multikinase inhibitors for refractory thyroid cancer

Thyroid cancer incidence continues to increase, remaining the most common endocrine malignancy. The need for effective systemic therapies combined with high incidence of driver mutations and overexpression of molecular pathways make refractory thyroid cancer an ideal candidate for treatment with novel agents. Multikinase inhibitors have caused a paradigm shift in the treatment of patients with advanced iodine-refractory thyroid cancer. These agents have shown to be the most effective systemic therapy for this disease not only causing prolonged responses but also improving survival. The activity of these agents inhibiting several pathways simultaneously, such as rearranged during transfection protooncogene, mitogen-activated protein kinase, and angiogenesis, can probably explain the effectiveness in controlling the progression of this malignancy. Several of these agents are currently on clinical studies in patients with differentiated and medullary thyroid cancer and most of them are showing promising clinical activity. With the approval of vandetanib for the treatment of medullary thyroid cancer, a new era in the management of this disease has begun. The molecular rationale for the use of these drugs for thyroid cancer is discussed as well as their promising clinical results.

Effect of intravitreal bevacizumab on retrobulbar blood flow in injected and uninjected fellow eyes of patients with neovascular age-related macular degeneration

BACKGROUND

To determine the effect of intravitreal administration of bevacizumab (1.25 mg/0.05 mL) on retrobulbar circulation of the injected and the fellow (uninjected) eyes in patients with neovascular age-related macular degeneration.

METHODS

In this prospective study, the retrobulbar hemodynamics of 43 patients with neovascular age-related macular degeneration was examined by color Doppler ultrasonography. Peak systolic velocity, end-diastolic velocity, and resistive index values in the central retinal artery and short posterior ciliary artery in both injected and uninjected fellow eyes were measured at baseline and 7 days after a single intravitreal injection of bevacizumab.

RESULTS

At baseline, the peak systolic velocity, end-diastolic velocity, and the resistive index in the central retinal artery and short posterior ciliary artery of the injected eye were not significantly different compared with the fellow uninjected eye (P > 0.05 for all). However, intravitreal bevacizumab induced a significant reduction in the peak systolic velocity and end-diastolic velocity and a significant rise in the resistive index of the central retinal artery and short posterior ciliary artery of the injected eye (P ≤ 0.006 for all). Peak systolic velocity and end-diastolic velocity decreased in the central retinal artery (P = 0.023 and P = 0.030) and the short posterior ciliary artery (P = 0.001 and P < 0.000) in the uninjected eye while the resistive index did not significantly change in central retinal artery (P = 0.114) and short posterior ciliary artery (P = 0.082) of the fellow eyes.

CONCLUSION

Intravitreal injection of bevacizumab significantly affects ocular hemodynamic parameters of both the injected and the uninjected fellow eyes with neovascular age-related macular degeneration.

Differential drug class-specific metastatic effects following treatment with a panel of angiogenesis inhibitors

Inhibiting angiogenesis has become an important therapeutic strategy for cancer treatment but, like other current targeted therapies, benefits experienced for late-stage cancers can be curtailed by inherent refractoriness or by acquired drug resistance, requiring a need for better mechanistic understanding of such effects. Numerous preclinical studies have demonstrated that VEGF pathway inhibitors suppress primary tumour growth and metastasis. However, it has been recently reported that short-term VEGF and VEGFR inhibition can paradoxically accelerate tumour invasiveness and metastasis in certain models. Here we comprehensively compare the effects of both antibody and small molecule receptor tyrosine kinase (RTK) inhibitors targeting the VEGF-VEGFR pathway, using short-term therapy in various mouse models of metastasis. Our findings demonstrate that antibody inhibition of VEGF pathway molecules does not promote metastasis, in contrast to selected small molecule RTK inhibitors at elevated-therapeutic drug dosages. In particular, a multi-targeted RTK inhibitor, sunitinib, which most profoundly potentiated metastasis, also increased lung vascular permeability and promoted tumour cell extravasation. Mechanistically, sunitinib, but not anti-VEGF treatment, attenuated endothelial barrier function in culture and caused a global inhibition of protein tyrosine phosphorylation, including molecules important for maintaining endothelial cell-cell junctions. Together these findings indicate that, rather than a specific consequence of inhibiting the VEGF signalling pathway, pharmacological inhibitors of the VEGF pathway can have dose- and drug class-dependent side-effects on the host vasculature. These findings also advocate for the continued identification of mechanisms of resistance to anti-angiogenics and for therapy development to overcome it.

Pericytes promote selective vessel regression to regulate vascular patterning

Blood vessel networks form in a 2-step process of sprouting angiogenesis followed by selective branch regression and stabilization of remaining vessels. Pericytes are known to function in stabilizing blood vessels, but their role in vascular sprouting and selective vessel regression is poorly understood. The endosialin (CD248) receptor is expressed by pericytes associated with newly forming but not stable quiescent vessels. In the present study, we used the Endosialin(-/-) mouse as a means to uncover novel roles for pericytes during the process of vascular network formation. We demonstrate in a postnatal retina model that Endosialin(-/-) mice have normal vascular sprouting but are defective in selective vessel regression, leading to increased vessel density. Examination of the Endosialin(-/-) mouse tumor vasculature revealed an equivalent phenotype, indicating that pericytes perform a hitherto unidentified function to promote vessel destabilization and regression in vivo in both physiologic and pathologic angiogenesis. Mechanistically, Endosialin(-/-) mice have no defect in pericyte recruitment. Rather, endosialin binding to an endothelial associated, but not a pericyte associated, basement membrane component induces endothelial cell apoptosis and detachment. The results of the present study advance our understanding of pericyte biology and pericyte/endothelial cell cooperation during vascular patterning and have implications for the design of both pro- and antiangiogenic therapies.

The mechanisms of cerebral vascular dysfunction and neuroinflammation by MMP-mediated degradation of VEGFR-2 in alcohol ingestion

OBJECTIVE

Blood-brain barrier (BBB) dysfunction caused by activation of matrix metalloproteinases (MMPs) is a pathological feature in vascular/neurological disease. We describe the mechanisms of BBB dysfunction and neuroinflammation as a result of MMP-3/9 activation and disruption of vascular endothelial growth factor (VEGF)-A/VEGFR-2 interaction, impairing effective angiogenesis.

METHODS AND RESULTS

We investigate the hypothesis in human brain endothelial cells and animal model of chronic alcohol ingestion. Proteome array analysis, zymography, immunofluorescence, and Western blotting techniques detected the activation, expression, and levels of MMP-3 and MMP-9. We found that degradation of VEGFR-2 and BBB proteins, for example, occludin, claudin-5, and ZO-1 by MMP-3/9, causes rupture of capillary endothelium and BBB leakiness. Impairment of BBB integrity was demonstrated by increased permeability of dye tracers and Fluo-3/calcein-AM-labeled monocyte adhesion or infiltration and decrease in transendothelial electric resistance. Alcohol-induced degradation of endothelial VEGFR-2 by MMP-3/9 led to a subsequent elevation of cellular/serum VEGF-A level. The decrease in VEGFR-2 with subsequent increase in VEGF-A level led to apoptosis and neuroinflammation via the activation of caspase-1 and IL-1β release. The use of MMPs, VEGFR-2, and caspase-1 inhibitors helped to dissect the underlying mechanisms.

CONCLUSIONS

Alcohol-induced MMPs activation is a key mechanism for dysfunction of BBB via degradation of VEGFR-2 protein and activation of caspase-1 or IL-1β release. Targeting VEGF-induced MMP-3/9 activation can be a novel preventive approach to vascular inflammatory disease in alcohol abuse.