VEGF induces hyperpermeability by a direct action on endothelial cells

Culture insert device with perfusable microchannels enhancesin vitroskin model development and barrier function assessment

The ever-stricter regulations on animal experiments in the field of cosmetic testing have prompted a surge in skin-related research with a special focus on recapitulation of thein vivoskin structurein vitro. In vitrohuman skin models are seen as an important tool for skin research, which in recent years attracted a lot of attention and effort, with researchers moving from the simplest 2-layered models (dermis with epidermis) to models that incorporate other vital skin structures such as hypodermis, vascular structures, and skin appendages. In this study, we designed a microfluidic device with a reverse flange-shaped anchor that allows culturing of anin vitroskin model in a conventional 6-well plate and assessing its barrier function without transferring the skin model to another device or using additional contraptions. Perfusion of the skin model through vascular-like channels improved the morphogenesis of the epidermis compared with skin models cultured under static conditions. This also allowed us to assess the percutaneous penetration of the tested caffeine permeation and vascular absorption, which is one of the key metrics for systemic drug exposure evaluation.

Promising results of a clinical feasibility study: CIRBP as a potential biomarker in pediatric cardiac surgery

Objective

Cold-inducible RNA binding Protein (CIRBP) has been shown to be a potent inflammatory mediator and could serve as a novel biomarker for inflammation. Systemic inflammatory response syndrome (SIRS) and capillary leak syndrome (CLS) are frequent complications after pediatric cardiac surgery increasing morbidity, therefore early diagnosis and therapy is crucial. As CIRBP serum levels have not been analyzed in a pediatric population, we conducted a clinical feasibility establishing a customized magnetic bead panel analyzing CIRBP in pediatric patients undergoing cardiac surgery.

Methods

A prospective hypothesis generating observational clinical study was conducted at the German Heart Center Berlin during a period of 9 months starting in May 2020 (DRKS00020885, https://drks.de/search/de/trial/DRKS00020885). Serum samples were obtained before the cardiac operation, upon arrival at the pediatric intensive care unit, 6 and 24 h after the operation in patients up to 18 years of age with congenital heart disease (CHD). Customized multiplex magnetic bead-based immunoassay panels were developed to analyze CIRBP, Interleukin-1β (IL-1β), Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), Monocyte chemotactic protein 1 (MCP-1), Syndecan-1 (SDC-1), Thrombomodulin (TM), Vascular endothelial growth factor (VEGF-A), Angiopoietin-2 (Ang-2), and Fibroblast growth factor 23 (FGF-23) in 25 µl serum using the Luminex MagPix® system.

Results

19 patients representing a broad range of CHD (10 male patients, median age 2 years, 9 female patients, median age 3 years) were included in the feasibility study. CIRBP was detectable in the whole patient cohort. Relative to individual baseline values, CIRBP concentrations increased 6 h after operation and returned to baseline levels over time. IL-6, IL-8, IL-10, and MCP-1 concentrations were significantly increased after operation and except for MCP-1 concentrations stayed upregulated over time. SDC-1, TM, Ang-2, as well as FGF-23 concentrations were also significantly increased, whereas VEGF-A concentration was significantly decreased after surgery.

Discussion

Using customized magnetic bead panels, we were able to detect CIRBP in a minimal serum volume (25 µl) in all enrolled patients. To our knowledge this is the first clinical study to assess CIRBP serum concentrations in a pediatric population.

Injectable bioactive glass/sodium alginate hydrogel with immunomodulatory and angiogenic properties for enhanced tendon healing

Tendon healing is a complex process involving inflammation, proliferation, and remodeling, eventually achieving a state of hypocellularity and hypovascularity. Currently, few treatments can satisfactorily restore the structure and function of native tendon. Bioactive glass (BG) has been shown to possess immunomodulatory and angiogenic properties. In this study, we investigated whether an injectable hydrogel fabricated of BG and sodium alginate (SA) could be applied to enhance tenogenesis following suture repair of injured tendon. We demonstrated that BG/SA hydrogel significantly accelerated tenogenesis without inducing heterotopic ossification based on histological analysis. The therapeutic effect could attribute to increased angiogenesis and M1 to M2 phenotypic switch of macrophages within 7 days post-surgery. Morphological characterization demonstrated that BG/SA hydrogel partially reverted the pathological changes of Achilles tendon, including increased length and cross-sectional area (CSA). Finally, biomechanical test showed that BG/SA hydrogel significantly improved ultimate load, failure stress, and tensile modulus of the repaired tendon. In conclusion, administration of an injectable BG/SA hydrogel can be a novel and promising therapeutic approach to augment Achilles tendon healing in conjunction with surgical intervention.

Intramuscular Exposure to a Lethal Dose of Ricin Toxin Leads to Endothelial Glycocalyx Shedding and Microvascular Flow Abnormality in Mice and Swine

Ricin toxin isolated from the castor bean (Ricinus communis) is one of the most potent and lethal molecules known. While the pathophysiology and clinical consequences of ricin poisoning by the parenteral route, i.e., intramuscular penetration, have been described recently in various animal models, the preceding mechanism underlying the clinical manifestations of systemic ricin poisoning has not been completely defined. Here, we show that following intramuscular administration, ricin bound preferentially to the vasculature in both mice and swine, leading to coagulopathy and widespread hemorrhages. Increased levels of circulating VEGF and decreased expression of vascular VE-cadherin caused blood vessel impairment, thereby promoting hyperpermeability in various organs. Elevated levels of soluble heparan sulfate, hyaluronic acid and syndecan-1 were measured in blood samples following ricin intoxication, indicating that the vascular glycocalyx of both mice and swine underwent extensive damage. Finally, by using side-stream dark field intravital microscopy imaging, we determined that ricin poisoning leads to microvasculature malfunctioning, as manifested by aberrant blood flow and a significant decrease in the number of diffused microvessels. These findings, which suggest that glycocalyx shedding and microcirculation dysfunction play a major role in the pathology of systemic ricin poisoning, may serve for the formulation of specifically tailored therapies for treating parenteral ricin intoxication.

Heteromeric TRP Channels in Lung Inflammation

Activation of Transient Receptor Potential (TRP) channels can disrupt endothelial barrier function, as their mediated Ca²⁺ influx activates the CaM (calmodulin)/MLCK (myosin light chain kinase)-signaling pathway, and thereby rearranges the cytoskeleton, increases endothelial permeability and thus can facilitate activation of inflammatory cells and formation of pulmonary edema. Interestingly, TRP channel subunits can build heterotetramers, whereas heteromeric TRPC1/4, TRPC3/6 and TRPV1/4 are expressed in the lung endothelium and could be targeted as a protective strategy to reduce endothelial permeability in pulmonary inflammation. An update on TRP heteromers and their role in lung inflammation will be provided with this review.

Plasma P-Selectin Is Inversely Associated with Lung Function and Corticosteroid Responsiveness in Asthma

BACKGROUND

Severe asthma has multiple phenotypes for which biomarkers are still being defined. Plasma P-selectin reports endothelial and/or platelet activation.

OBJECTIVE

To determine if P-selectin is associated with features of asthma in a longitudinal study.

METHODS

Plasmas from 70 adult patients enrolled in the Severe Asthma Research Program (SARP) III at the University of Wisconsin-Madison were analyzed for concentration of P-selectin at several points over the course of 3 years, namely, at baseline (BPS), after intramuscular triamcinolone acetonide (TA) injection, and at 36 months after baseline. Thirty-four participants also came in during acute exacerbation and 6 weeks after exacerbation.

RESULTS

BPS correlated inversely with forced expiratory volume in 1 s (FEV1) and with residual volume/total lung capacity, an indicator of air trapping. BPS was inversely associated with FEV1 change after TA, by regression analysis. FEV1 did not change significantly after TA if BPS was above the median, whereas patients with BPS below the median had significantly increased FEV1 after TA. BPS was higher in and predicted assignment to SARP phenotype cluster 5 ("severe fixed-airflow asthma"). P-selectin was modestly but significantly increased at exacerbation but returned to baseline within 3 years.

CONCLUSIONS

High BPS is associated with airway obstruction, air trapping, the "severe fixed-airflow" cluster, and lack of FEV1 improvement in response to TA injection. P-selectin concentration, which is a stable trait with only modest elevation during exacerbation, may be a useful biomarker for a severe asthma pheno- or endotype characterized by low pulmonary function and lack of corticosteroid responsiveness.

Case Report: Clinically amyopathic dermatomyositis presenting acutely with isolated facial edema

A 45-year-old Asian man presented with acute-onset periorbital and facial edema associated with pyrexia. Muscle weakness was absent. Initial laboratory investigations showed an inflammatory reaction, while screening for infections was negative. Serum muscle enzyme levels were normal. He was hospitalized and treated empirically with antibiotics and corticosteroids, pending the result of facial skin and muscle biopsy. He showed a good clinical and laboratory response but an attempt to discontinue corticosteroids led to a prompt relapse of facial edema and pyrexia, associated with rising laboratory indices of inflammation. Biopsy findings were typical of dermatomyositis. Reintroduction of corticosteroid treatment resulted in complete clinical and laboratory remission.

Facial edema as the sole clinical manifestation of dermatomyositis is extremely rare. There have been no previous reports of isolated facial edema in the setting of acute, clinically amyopathic dermatomyositis in adults. A high level of suspicion is required to make the diagnosis in the absence of myopathy and the hallmark cutaneous manifestations of the disease (heliotrope rash, Gottron papules).

Sevoflurane protects rat brain endothelial barrier structure and function after hypoxia-reoxygenation injury

Background

After cerebral injury blood-brain barrier disruption significantly impairs brain homeostasis. Volatile anesthetics have been shown to be protective in ischemia-reperfusion injury scenarios. Their impact on brain endothelial cells after hypoxia-reoxygenation (H/R) has not yet been studied in detail.

Methods

Rat brain endothelial cells (RBE4) were exposed to severe hypoxia and reoxygenated in air in the presence or absence of sevoflurane. Changes in dextran permeability and architecture of the cellular junctional proteins ZO-1 and β-catenin were measured. To determine necrosis and apoptosis rate DNA content, LDH release and caspase activity were quantified. The role of vascular endothelial growth factor (VEGF) as an inflammatory mediator increasing vascular permeability was assessed. At the same time, it was evaluated if sevoflurane effects are mediated through VEGF. Results were analyzed by unpaired t-tests or one way-analysis of variance followed by Bonferroni’s correction.

Results

H/R led to a 172% increase in permeability (p<0.001), cell swelling and qualitatively but not quantitatively modified expression of ZO-1, β-catenin and F-actin. In the presence of sevoflurane during reoxygenation, barrier function improved by 96% (p = 0.042) in parallel to a decrease of the cell size and less re-arranged junction proteins and F-actin. Sevoflurane-induced improvement of the barrier function could not be explained on the level of necrosis or apoptosis as they remained unchanged independent of the presence or absence of the volatile anesthetic. Increased expression of VEGF after H/R was attenuated by sevoflurane by 34% (p = 0.004). Barrier protection provided by sevoflurane was similar to the application of a blocking VEGF-antibody. Furthermore, the protective effect of sevoflurane was abolished in the presence of recombinant VEGF.

Conclusions

In H/R-induced rat brain endothelial cell injury sevoflurane maintains endothelial barrier function through downregulation of VEGF, which is a key player not only in mediating injury, but also with regard to the protective effect of sevoflurane.

The Interplay between Inflammation, Coagulation and Endothelial Injury in the Early Phase of Acute Pancreatitis: Clinical Implications

Acute pancreatitis (AP) is an inflammatory disease with varied severity, ranging from mild local inflammation to severe systemic involvement resulting in substantial mortality. Early pathologic events in AP, both local and systemic, are associated with vascular derangements, including endothelial activation and injury, dysregulation of vasomotor tone, increased vascular permeability, increased leukocyte migration to tissues, and activation of coagulation. The purpose of the review was to summarize current evidence regarding the interplay between inflammation, coagulation and endothelial dysfunction in the early phase of AP. Practical aspects were emphasized: (1) we summarized available data on diagnostic usefulness of the markers of endothelial dysfunction and activated coagulation in early prediction of severe AP; (2) we reviewed in detail the results of experimental studies and clinical trials targeting coagulation-inflammation interactions in severe AP. Among laboratory tests, d-dimer and angiopoietin-2 measurements seem the most useful in early prediction of severe AP. Although most clinical trials evaluating anticoagulants in treatment of severe AP did not show benefits, they also did not show significantly increased bleeding risk. Promising results of human trials were published for low molecular weight heparin treatment. Several anticoagulants that proved beneficial in animal experiments are thus worth testing in patients.

Serum Soluble Fms-Like Tyrosine Kinase 1 (sFlt-1) Predicts the Severity of Acute Pancreatitis

Organ failure is the most important determinant of the severity of acute pancreatitis (AP). Soluble fms-like tyrosine kinase 1 (sFlt-1) is positively associated with organ failure in sepsis. Our aim was to evaluate the diagnostic utility of automated sFlt-1 measurements for early prediction of AP severity. Adult patients (66) with AP were recruited, including 46 with mild (MAP), 15 with moderately-severe (MSAP) and 5 with severe AP (SAP). Serum and urine samples were collected twice. Serum sFlt-1 was measured with automated electrochemiluminescence immunoassay. Serum concentrations of sFlt-1 were significantly higher in patients with MSAP and SAP as compared to MAP. SAP patients had the highest concentrations. At 24 and 48 h, sFlt-1 positively correlated with inflammatory markers (leukocyte count, C-reactive protein), kidney function (creatinine, urea, cystatin C, serum and urine neutrophil gelatinase-associated lipocalin, urine albumin/creatinine ratio), D-dimer and angiopoietin-2. sFlt-1 positively correlated with the bedside index of severity in AP (BISAP) score and the duration of hospital stay. Serum sFlt-1 above 139 pg/mL predicted more severe AP (MSAP + SAP). In the early phase of AP, sFlt-1 is positively associated with the severity of AP and predicts organ failure, in particular kidney failure. Serum sFlt-1 may be a practical way to improve early assessment of AP severity.

The Gastrointestinal Circulation: Physiology and Pathophysiology

The gastrointestinal (GI) circulation receives a large fraction of cardiac output and this increases following ingestion of a meal. While blood flow regulation is not the intense phenomenon noted in other vascular beds, the combined responses of blood flow, and capillary oxygen exchange help ensure a level of tissue oxygenation that is commensurate with organ metabolism and function. This is evidenced in the vascular responses of the stomach to increased acid production and in intestine during periods of enhanced nutrient absorption. Complimenting the metabolic vasoregulation is a strong myogenic response that contributes to basal vascular tone and to the responses elicited by changes in intravascular pressure. The GI circulation also contributes to a mucosal defense mechanism that protects against excessive damage to the epithelial lining following ingestion of toxins and/or noxious agents. Profound reductions in GI blood flow are evidenced in certain physiological (strenuous exercise) and pathological (hemorrhage) conditions, while some disease states (e.g., chronic portal hypertension) are associated with a hyperdynamic circulation. The sacrificial nature of GI blood flow is essential for ensuring adequate perfusion of vital organs during periods of whole body stress. The restoration of blood flow (reperfusion) to GI organs following ischemia elicits an exaggerated tissue injury response that reflects the potential of this organ system to generate reactive oxygen species and to mount an inflammatory response. Human and animal studies of inflammatory bowel disease have also revealed a contribution of the vasculature to the initiation and perpetuation of the tissue inflammation and associated injury response.

Giant Cell Arteritis with Facial Edema Presenting with Delayed Jugular Venous Flow

The detection of abnormalities of the cranial arteries on magnetic resonance imaging (MRI) is useful for the diagnosis of giant cell arteritis (GCA). However, reports on the veins of GCA patients are rare. We report the case of an elderly woman with GCA who presented with facial edema. She presented with a one month history of headache and facial edema. After MRI and enhanced computed tomography revealed delayed blood flow in the left jugular vein, a temporal artery biopsy was performed. She was diagnosed with GCA based on the biopsy findings. Following corticosteroid therapy, her symptoms and venous flow improved. The present case indicates that delayed jugular venous flow can occur in GCA patients with facial edema.

Ascorbic acid prevents VEGF-induced increases in endothelial barrier permeability

Vascular endothelial growth factor (VEGF) increases endothelial barrier permeability, an effect that may contribute to macular edema in diabetic retinopathy. Since vitamin C, or ascorbic acid, can tighten the endothelial permeability barrier, we examined whether it could prevent the increase in permeability due to VEGF in human umbilical vein endothelial cells (HUVECs). As previously observed, VEGF increased HUVEC permeability to radiolabeled inulin within 60 min in a concentration-dependent manner. Loading the cells with increasing concentrations of ascorbate progressively prevented the leakage caused by 100 ng/ml VEGF, with a significant inhibition at 13 µM and complete inhibition at 50 µM. Loading cells with 100 µM ascorbate also decreased the basal generation of reactive oxygen species and prevented the increase caused by both 100 ng/ml VEGF. VEGF treatment decreased intracellular ascorbate by 25%, thus linking ascorbate oxidation to its prevention of VEGF-induced barrier leakage. The latter was blocked by treating the cells with 60 µM L-NAME (but not D-NAME) as well as by 30 µM sepiapterin, a precursor of tetrahydrobiopterin that is required for proper function of endothelial nitric oxide synthase (eNOS). These findings suggest that VEGF-induced barrier leakage uncouples eNOS. Ascorbate inhibition of the VEGF effect could thus be due either to scavenging superoxide or to peroxynitrite generated by the uncoupled eNOS, or more likely to its ability to recycle tetrahydrobiopterin, thus avoiding enzyme uncoupling in the first place. Ascorbate prevention of VEGF-induced increases in endothelial permeability opens the possibility that its repletion could benefit diabetic macular edema.

Glycocalyx and sepsis-induced alterations in vascular permeability

Endothelial cells line the inner portion of the heart, blood vessels, and lymphatic vessels; a basal membrane of extracellular matrix lines the extraluminal side of endothelial cells. The apical side of endothelial cells is the site for the glycocalyx, which is a complex network of macromolecules, including cell-bound proteoglycans and sialoproteins. Sepsis-associated alterations of this structure may compromise endothelial permeability with associated interstitial fluid shift and generalized edema. Indeed, in sepsis, the glycocalyx acts as a target for inflammatory mediators and leukocytes, and its ubiquitous nature explains the damage of tissues that occurs distant from the original site of infection. Inflammatory-mediated injury to glycocalyx can be responsible for a number of specific clinical effects of sepsis, including acute kidney injury, respiratory failure, and hepatic dysfunction. Moreover, some markers of glycocalyx degradation, such as circulating levels of syndecan or selectins, may be used as markers of endothelial dysfunction and sepsis severity. Although a great deal of experimental evidence shows that alteration of glycocalyx is widely involved in endothelial damage caused by sepsis, therapeutic strategies aiming at preserving its integrity did not significantly improve the outcome of these patients.

Microvascular density and vascular endothelial growth factor and osteopontin expression during the implantation window in a controlled ovarian hyperstimulation rat model

Vascular endothelial growth factor (VEGF) and osteopontin (OPN) are suggested to facilitate angiogenesis and vascular remodeling in endometrial receptivity. Determination of the endometrial microvascular density (MVD) is the commonest method used to indirectly assess the levels of vasculogenesis and angiogenesis; however, the associations among VEGF, OPN and MVD remain unclear. Controlled ovarian hyperstimulation (COH) with the gonadotrophin-releasing hormone agonist-long protocol may impair endometrial receptivity, and Traditional Chinese Medicine (TCM) may exert therapeutic effects to relieve this impairment. The aim of the present study was to investigate the effects of COH on implantation biology and pregnancy outcome, and to explore the potential therapeutic role of the TCM Zi Dan Yin (ZDY). Female Sprague Dawley rats were divided into four groups: Control, COH, ZDY and COH + ZDY. On days 3, 4 and 5 of pregnancy (D3, D4 and D5, respectively), endometrial MVD was measured with cluster of differentiation 34 immunohistochemical detection, and VEGF and OPN protein and mRNA expression was detected through western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. On D10, the average number of implantation sites was observed. Subsequent to conceiving and bearing newborn rats, the number of live births from each group was recorded. COH was shown to have adverse effects on implantation and pregnancy outcome. The MVD was found to be significantly increased in the COH group compared with that in the control, ZDY and COH+ZDY groups. The results of the protein and RT-qPCR analysis of VEGF and OPN revealed the same trend. Conversely, ZDY reversed the changes in endometrial MVD, VEGF and OPN, and was indicated to improve uterine receptivity and pregnancy outcome. No significant difference was observed among the control, ZDY and COH + ZDY groups. In conclusion, since the results for MVD and VEGF and OPN expression were consistent, MVD could be used as an alternative approach to identify the period of receptivity in rats.

Elevations in vascular markers and eosinophils in chronic spontaneous urticarial weals with low-level persistence in uninvolved skin

BACKGROUND

In chronic spontaneous urticaria (CSU) mast cell activation together with inflammatory changes in the skin are well documented and may play an important role in mechanisms of tissue oedema.

OBJECTIVES

To confirm and extend these observations by measuring microvascular markers, leucocytes and mast cell numbers in lesional and uninvolved skin and to compare findings with a control group.

METHODS

Paired biopsies (one from 4-8-h spontaneous weals and one from uninvolved skin) were taken from eight patients with CSU and nine control subjects and studied using immunohistochemistry and confocal microscopy using the lectin Ulex europaeus agglutinin 1 (UEA-1).

RESULTS

Lesional skin in CSU contained significantly more CD31+ endothelial cells; CD31+ blood vessels, neutrophils, eosinophils, basophils and macrophages; and CD3+ T cells than nonlesional skin. Increased vascularity was confirmed by confocal imaging using the lectin UEA-1. Uninvolved skin from CSU contained significantly more CD31+ endothelial cells, CD31+ blood vessels and eosinophils compared with the control subjects. There was a threefold increase in mast cell numbers when CSU was compared with controls but no difference was observed between lesional and uninvolved skin.

CONCLUSIONS

Increased vascular markers together with eosinophil and neutrophil infiltration are features of lesional skin in CSU and might contribute to tissue oedema. Eosinophils and microvascular changes persist in uninvolved skin, which, together with increased mast cells, suggests that nonlesional skin is primed for further wealing.

Dynamics of pulmonary endothelial barrier function in acute inflammation: mechanisms and therapeutic perspectives

The lungs provide a large inner surface to guarantee respiration. In lung alveoli, a delicate membrane formed by endo- and epithelial cells with their fused basal lamina ensures rapid and effective gas exchange between alveolar and vascular compartments while concurrently forming a robust barrier against inhaled particles and microbes. However, upon infectious or sterile inflammatory stimulation, tightly regulated endothelial barrier leakiness is required for leukocyte transmigration. Further, endothelial barrier disruption may result in uncontrolled extravasation of protein-rich fluids. This brief review summarizes some important mechanisms of pulmonary endothelial barrier regulation and disruption, focusing on the role of specific cell populations, coagulation and complement cascades and mediators including angiopoietins, specific sphingolipids, adrenomedullin and reactive oxygen and nitrogen species for the regulation of pulmonary endothelial barrier function. Further, current therapeutic perspectives against development of lung injury are discussed.

The adverse effect of selective cyclooxygenase-2 inhibitor on random skin flap survival in rats

BACKGROUND

Cyclooxygenase-2(COX-2) inhibitors provide desired analgesic effects after injury or surgery, but evidences suggested they also attenuate wound healing. The study is to investigate the effect of COX-2 inhibitor on random skin flap survival.

METHODS

The McFarlane flap model was established in 40 rats and evaluated within two groups, each group gave the same volume of Parecoxib and saline injection for 7 days. The necrotic area of the flap was measured, the specimens of the flap were stained with haematoxylin-eosin(HE) for histologic analysis. Immunohistochemical staining was performed to analyse the level of VEGF and COX-2 .

RESULTS

7 days after operation, the flap necrotic area ratio in study group (66.65 ± 2.81)% was significantly enlarged than that of the control group(48.81 ± 2.33)%(P <0.01). Histological analysis demonstrated angiogenesis with mean vessel density per mm(2) being lower in study group (15.4 ± 4.4) than in control group (27.2 ± 4.1) (P <0.05). To evaluate the expression of COX-2 and VEGF protein in the intermediate area II in the two groups by immunohistochemistry test .The expression of COX-2 in study group was (1022.45 ± 153.1), and in control group was (2638.05 ± 132.2) (P <0.01). The expression of VEGF in the study and control groups were (2779.45 ± 472.0) vs (4938.05 ± 123.6)(P <0.01).In the COX-2 inhibitor group, the expressions of COX-2 and VEGF protein were remarkably down-regulated as compared with the control group.

CONCLUSION

Selective COX-2 inhibitor had adverse effect on random skin flap survival. Suppression of neovascularization induced by low level of VEGF was supposed to be the biological mechanism.

Markers of vascular perturbation correlate with airway structural change in asthma

RATIONALE

Air trapping and ventilation defects on imaging are characteristics of asthma. Airway wall thickening occurs in asthma and is associated with increased bronchial vascularity and vascular permeability. Vascular endothelial cell products have not been explored as a surrogate to mark structural airway changes in asthma.

OBJECTIVES

Determine whether reporters of vascular endothelial cell perturbation correlate with airway imaging metrics in patients with asthma of varying severity.

METHODS

Plasma from Severe Asthma Research Program subjects was analyzed by ELISAs for soluble von Willebrand factor mature protein (VWF:Ag) and propeptide (VWFpp), P-selectin, and platelet factor 4. Additional subjects were analyzed over 48 hours after whole-lung antigen challenge. We calculated ventilation defect volume by hyperpolarized helium-3 magnetic resonance imaging and areas of low signal density by multidetector computed tomography (less than -856 Hounsfield units [HU] at functional residual capacity and -950 HU at total lung capacity [TLC]).

MEASUREMENTS AND MAIN RESULTS

VWFpp and VWFpp/Ag ratio correlated with and predicted greater percentage defect volume on hyperpolarized helium-3 magnetic resonance imaging. P-selectin correlated with and predicted greater area of low density on chest multidetector computed tomography less than -950 HU at TLC. Platelet factor 4 did not correlate. Following whole-lung antigen challenge, variation in VWFpp, VWFpp/Ag, and P-selectin among time-points was less than that among subjects, indicating stability and repeatability of the measurements.

CONCLUSIONS

Plasma VWFpp and P-selectin may be useful as surrogates of functional and structural defects that are evident on imaging. The results raise important questions about why VWFpp and P-selectin are associated specifically with different imaging abnormalities.

Role of vascular and lymphatic endothelial cells in hantavirus pulmonary syndrome suggests targeted therapeutic approaches

BACKGROUND

Hantaviruses in the Americas cause a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). Hantaviruses nonlytically infect microvascular and lymphatic endothelial cells and cause dramatic changes in barrier functions without disrupting the endothelium. Hantaviruses cause changes in the function of infected endothelial cells that normally regulate fluid barrier functions. The endothelium of arteries, veins, and lymphatic vessels are unique and central to the function of vast pulmonary capillary beds that regulate pulmonary fluid accumulation.

RESULTS

We have found that HPS-causing hantaviruses alter vascular barrier functions of microvascular and lymphatic endothelial cells by altering receptor and signaling pathway responses that serve to permit fluid tissue influx and clear tissue edema. Infection of the endothelium provides several mechanisms for hantaviruses to cause acute pulmonary edema, as well as potential therapeutic targets for reducing the severity of HPS disease.

CONCLUSIONS

Here we discuss interactions of HPS-causing hantaviruses with the endothelium, roles for unique lymphatic endothelial responses in HPS, and therapeutic targeting of the endothelium as a means of reducing the severity of HPS disease.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

Improvement of a long random skin flap survival by application of vascular endothelial growth factor in various ways of local administration in a rat model

Background:

Vascular endothelial growth factor (VEGF) is a heparin-binding glycoprotein which plays a significant role in angiogenesis and vascular permeability. The effect of various ways of local administration of VEGF on random skin flap survival was studied, using flaps with a relatively high length (L) to width (W) ratio (5:1).

Materials and Methods:

An 1.5 × 7.5 cm dorsal skin flap with the pedicle orientated, centered, and remaining attached between the lower angles of the scapulae was elevated in 45 Wistar rats in different phases, depending on the group. Rats were divided in five groups of nine. In group A, injections of saline were administered, in equally divided spaces, into flap's fascia and transposed to a created skin defect. In group B, injections of VEGF were applied subdermally, in equally divided spaces, within the limits of a predesigned flap, a week prior to flap dissection and transposition. In group C, injections of VEGF were applied into a recipient bed's fascia just before flap raising and transposition. In group D, injections of VEGF were applied subdermally, only in the distal third of the flap and then the flap was transposed to a recipient area. Finally, in group E, injections of VEGF were applied in the flap intrafascially and in equally divided spaces and then again, the flap was transposed to a recipient area. A week after final flap raising and positioning, rats were euthanatised and flaps were excised. Specimens were photographed, measured, put in formalin 10% and were sent for histological and image analysis.

Results:

Mean flap survival percentage was 35.4% in group A, and 33.7% in group B. In groups C and D, the mean survival area was 56.3% and 80.4%, respectively. In group E, the mean flap survival percentage was 28.3%. Histological analysis demonstrated increased angiogenesis in groups C and D.

Conclusions:

VEGF application improved skin flap survival when injected subdermally in the distal third of a random skin flap or into the fascia of a recipient area even though the length-to-width ratio was high.

The Role of the Endothelium in HPS Pathogenesis and Potential Therapeutic Approaches

American hantaviruses cause a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). Hantaviruses nonlytically infect endothelial cells and cause dramatic changes in barrier functions of the endothelium without disrupting the endothelium. Instead hantaviruses cause changes in the function of infected endothelial cells that normally regulate fluid barrier functions of capillaries. The endothelium of arteries, veins, and lymphatic vessels is unique and central to the function of vast pulmonary capillary beds, which regulate pulmonary fluid accumulation. The endothelium maintains vascular barrier functions through a complex series of redundant receptors and signaling pathways that serve to both permit fluid and immune cell efflux into tissues and restrict tissue edema. Infection of the endothelium provides several mechanisms for hantaviruses to alter capillary permeability but also defines potential therapeutic targets for regulating acute pulmonary edema and HPS disease. Here we discuss interactions of HPS causing hantaviruses with the endothelium, potential endothelial cell-directed permeability mechanisms, and therapeutic targeting of the endothelium as a means of reducing the severity of HPS disease.

Microvascular transport and tumor cell adhesion in the microcirculation

One critical step in tumor metastasis is tumor cell adhesion to the endothelium forming the microvessel wall. Understanding this step may lead to new therapeutic concepts for tumor metastasis. Vascular endothelium forming the microvessel wall and the glycocalyx layer at its surface are the principal barriers to, and regulators of the material exchange between circulating blood and body tissues. The cleft between adjacent ECs (interendothelial cleft) is the principal pathway for water and solutes transport through the microvessel wall in health. It is also suggested to be the pathway for high molecular weight plasma proteins, leukocytes and tumor cells across microvessel walls in disease. Thus the first part of the review introduced the mathematical models for water and solutes transport through the interendothelial cleft. These models, combined with the experimental results from in vivo animal studies and electron microscopic observations, are used to evaluate the role of the endothelial surface glycocalyx, the junction strand geometry in the interendothelial cleft, and the surrounding extracellular matrix and tissue cells, as the determinants of microvascular transport. The second part of the review demonstrated how the microvascular permeability, hydrodynamic factors, microvascular geometry and cell adhesion molecules affect tumor cell adhesion in the microcirculation.

An unexpected tail of VEGF and PlGF in pre-eclampsia

PET (pre-eclamptic toxaemia), characterized by pregnancy-related hypertension and proteinuria, due to widespread endothelial dysfunction, is a primary cause of maternal morbidity. Altered circulating factors, particularly the VEGF (vascular endothelial growth factor) family of proteins and their receptors, are thought to be key contributors to this disease. Plasma from patients with PET induces numerous cellular and physiological changes in endothelial cells, indicating the presence of a circulating imbalance of the normal plasma constituents. These have been narrowed down to macromolecules of the VEGF family of proteins and receptors. It has been shown that responses of endothelial cells in intact vessels to plasma from patients with pre-eclampsia is VEGF-dependent. It has recently been shown that this may be specific to the VEGF₁₆₅b isoform, and blocked by addition of recombinant human PlGF (placental growth factor). Taken together with results that show that sVEGFR1 (soluble VEGF receptor 1) levels are insufficient to bind VEGF-A in human plasma from patients with pre-eclampsia, and that other circulating macromolecules bind, but do not inactivate, VEGF-A, this suggests that novel hypotheses involving altered bioavailability of VEGF isoforms resulting from reduced or bound PlGF, or increased sVEGFR1 increasing biological activity of circulating plasma, could be tested. This suggests that knowing how to alter the balance of VEGF family members could prevent endothelial activation, and potentially some symptoms, of pre-eclampsia.

Mesenchymal stem cells improve wound healing in vivo via early activation of matrix metalloproteinase-9 and vascular endothelial growth factor

We investigated the effects of mesenchymal stem cells (MSCs) on wound healing using a three-dimensional (3D) collagen gel scaffold. Three circular full-thickness skin defects were created on the back of Sprague-Dawley rats. One site was covered with a 3D collagen gel containing 2 × 10(6) MSCs (MSCs+/3D collagen+). Another site was replaced with a 3D collagen gel without MSCs and the third site was left empty. The wound size was significantly reduced in the MSCs+/3D collagen+ sites. MSCs+/3D collagen+ sites exhibited the most neovascularization. FISH showed that Y-chromosome possessing cells were found within the dermis of MSCs+/3D collagen+ sites. Gelatin zymography revealed that the most intense expression of MMP-9 was detected early in the MSCs+/3D collagen+ sites. Our results indicate that MSCs upregulate the early expression of MMP-9 which induces the early mobilization of VEGF. Thus, MSCs appear to accelerate significantly wound healing via early activation of MMP-9 and VEGF.

Activation of beta1 integrins on blood eosinophils by P-selectin

Activation of β(1) integrins of blood eosinophils, assessed by mAb N29, correlates inversely with FEV(1) in two paradigms for studying control of human asthma. We asked whether P-selectin causes eosinophil β(1) integrin activation and results in increased adhesivity. By dual-label flow cytometry, eosinophils with high levels of surface-associated P-selectin had higher reactivity with the activation-sensitive anti-β(1) mAbs N29, 8E3, and 9EG7 than eosinophils with no or with a low-level of surface-associated P-selectin. Among patients with nonsevere asthma, surface P-selectin correlated with N29, 8E3, and 9EG7 signals. By immunofluorescence microscopy, surface-associated P-selectin was present in patches on eosinophils, some of which stained for the platelet marker thrombospondin-1. Activated β(1) and P-selectin partially colocalized on eosinophils. Soluble P-selectin added to whole blood enhanced activation of eosinophil β(1), but not β(2), integrins. In contrast, IL-5 activated eosinophil β(2), but not β(1), integrins. Eosinophils that did not attach to vascular cell adhesion molecule-1 (VCAM-1) in a static adhesion assay had a lower N29 signal than the original population. Soluble P-selectin added to whole blood enhanced eosinophil adhesion to VCAM-1. These findings are compatible with a scenario whereby P-selectin, on eosinophil-associated activated platelets or acquired from plasma or from prior interactions with endothelial cells or platelets, activates eosinophil α(4)β(1) integrin and stimulates eosinophils to adhere to VCAM-1 and move to the airway in asthma.

Arterial and venous thrombosis in cancer patients

The most frequent ultimate cause of death is myocardial arrest. In many cases this is due to myocardial hypoxia, generally arising from failure of the coronary macro- and microcirculation to deliver enough oxygenated red cells to the cardiomyocytes. The principle reason for this is occlusive thrombosis, either by isolated circulating thrombi, or by rupture of upstream plaque. However, an additionally serious pathology causing potentially fatal stress to the heart is extra-cardiac disease, such as pulmonary hypertension. A primary cause of the latter is pulmonary embolus, considered to be a venous thromboembolism. Whilst the thrombotic scenario has for decades been the dominating paradigm in cardiovascular disease, these issues have, until recently, been infrequently considered in cancer. However, there is now a developing view that cancer is also a thrombotic disease, and notably a disease predominantly of the venous circulation, manifesting as deep vein thrombosis and pulmonary embolism. Indeed, for many, a venous thromboembolism is one of the first symptoms of a developing cancer. Furthermore, many of the standard chemotherapies in cancer are prothrombotic. Accordingly, thromboprophylaxis in cancer with heparins or oral anticoagulation (such as Warfarin), especially in high risk groups (such as those who are immobile and on high dose chemotherapy), may be an important therapy. The objective of this communication is to summarise current views on the epidemiology and pathophysiology of arterial and venous thrombosis in cancer.

New advancements and developments in treatment of renal cell carcinoma: focus on pazopanib

With the recent approval of pazopanib, an oral multitargeted tyrosine kinase inhibitor which potently targets vascular endothelial growth factor receptors 1–3, platelet-derived growth factor, and c-kit, six agents are now available for use in the management of metastatic renal cell carcinoma (RCC). Pazopanib has shown improved progression-free survival compared with placebo in treatment-naïve or cytokine-treated patients with metastatic RCC in large Phase II and Phase III clinical trials. Pazopanib has demonstrated a tolerable side effect profile and is currently being compared with sunitinib in a Phase III noninferiority trial. In this review, the outcomes of the clinical testing of pazopanib are discussed, as well as a perspective on the placement of pazopanib among other approved agents.

Vascular endothelial growth factors and vascular permeability

Vascular endothelial growth factors (VEGFs) are key regulators of permeability. The principal evidence behind how they increase vascular permeability in vivo and in vitro and the consequences of that increase are addressed here. Detailed analysis of the published literature has shown that in vivo and in vitro VEGF-mediated permeability differs in its time course, but has common involvement of many specific signalling pathways, in particular VEGF receptor-2 activation, calcium influx through transient receptor potential channels, activation of phospholipase C gamma and downstream activation of nitric oxide synthase. Pathways downstream of endothelial nitric oxide synthase appear to involve the guanylyl cyclase-mediated activation of the Rho–Rac pathway and subsequent involvement of junctional signalling proteins such as vascular endothelial cadherin and the tight junctional proteins zona occludens and occludin linked to the actin cytoskeleton. The signalling appears to be co-ordinated through spatial organization of the cascade into a signalplex, and arguments for why this may be important are considered. Many proteins have been identified to be involved in the regulation of vascular permeability by VEGF, but still the mechanisms through which these are thought to interact to control permeability are dependent on the experimental system, and a synthesis of existing data reveals that in intact vessels the co-ordination of the pathways is still not understood.

Synchronized changes in serum vascular endothelial growth factor during the clinical course of chronic systemic capillary leak syndrome

Systemic capillary leak syndrome (SCLS) is a rare disease characterized by leakage of plasma from blood vessels into the interstitial space due to increased capillary permeability. We describe a 24-year-old man who was hospitalized with systemic edema, hypoalbuminemia, and disseminated intravascular coagulation. After extensive investigative procedures, he was diagnosed with chronic SCLS and made a gradual recovery after starting on prednisolone, terbutaline, and theophylline. We measured the patient's serum vascular endothelial growth factor (VEGF) over time and found a relationship between serum VEGF and the clinical course.

The association between vascular endothelial growth factor levels and clinically evident peripheral edema in dogs with systemic inflammatory response syndrome

OBJECTIVE

To determine the relationship between plasma vascular endothelial growth factor (VEGF) levels, severity of illness, and edema formation in critically ill dogs.

DESIGN

Prospective, observational, descriptive, clinical study.

SETTING

University Teaching Hospital.

ANIMALS

Twenty-eight dogs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Physical examination and multifrequency bioimpedance (MFBIA) measurements were performed daily on 28 critically ill dogs with evidence of severe inflammatory disease and compared with the corresponding plasma VEGF levels. The change in VEGF values and the relationship between MFBIA measurements and clinical evidence of edema were also examined. Eighteen dogs had a positive VEGF level, 12 dogs had clinical evidence of edema, and 7 dogs had both a positive VEGF level and clinical evidence of edema. There was no statistically significant correlation between VEGF levels and the presence of edema on physical examination (P=0.2). VEGF values were also evaluated with respect to WBC count, survival prediction index, presence of known sepsis, change in extracellular water, and outcome. No statistical relationship could be identified between VEGF levels in the blood of dogs with inflammatory disease and their survival prediction index (P=0.1), the WBC count (P=0.2), or presence of sepsis (P=0.2). Dogs with a VEGF level >70 pg/mL (n=3) were less likely to survive (P=0.04). Because of high variability within and between animals, conclusions regarding changes in MFBIA could not be made, suggesting that this technology requires further refinement and investigation in critically ill dogs.

CONCLUSIONS

A relationship between VEGF and clinically evident increased vascular permeability was not found in this study. Dogs with markedly elevated VEGF levels may be more likely to die, but further studies are needed to determine the diagnostic and prognostic value of VEGF in critically ill dogs.

Brain angiogenesis in developmental and pathological processes: mechanism and therapeutic intervention in brain tumors

Formation of new blood vessels is required for the growth and metastasis of all solid tumors. New blood vessels are established in tumors mainly through angiogenesis. Brain tumors in particular are highly angiogenic. Therefore, interventions designed to prevent angiogenesis may be effective at controlling brain tumors. Indeed, many recent findings from preclinical and clinical studies of antiangiogenic therapy for brain tumors have shown that it is a promising approach to managing this deadly disease, especially when combined with other cytotoxic treatments. In this minireview, we summarize the basic characteristics of brain tumor angiogenesis and the role of known angiogenic factors in regulating this angiogenesis, which may be targets of antiangiogenic therapy. We also discuss the current status of antiangiogenic therapy for brain tumors, the suggested mechanisms of this therapy and the limitations of this strategy.

Genetic delivery of bevacizumab to suppress vascular endothelial growth factor-induced high-permeability pulmonary edema

High-permeability pulmonary edema causing acute respiratory distress syndrome is associated with high mortality. Using a model of intratracheal adenovirus (Ad)-mediated overexpression of human vascular endothelial growth factor (VEGF)-A(165) in mouse lung to induce alveolar permeability and consequent pulmonary edema, we hypothesized that systemic administration of a second adenoviral vector expressing an anti-VEGF antibody (AdalphaVEGFAb) would protect the lung from pulmonary edema. Pulmonary edema was induced in mice by intratracheal administration of AdVEGFA165. To evaluate anti-VEGF antibody therapy, the mice were treated intravenously with AdalphaVEGFAb, an adenoviral vector encoding the light and heavy chains of an anti-human VEGF antibody with the bevacizumab (Avastin) antigen-binding site. Lung VEGF-A(165) and phosphorylated VEGF receptor (VEGFR)-2 levels, histology, lung wet-to-dry weight ratios, and bronchoalveolar lavage fluid (BALF) levels of total protein were assessed. Administration of AdalphaVEGFAb to mice decreased AdVEGFA165-induced levels of human VEGF-A(165) and phosphorylated VEGFR-2 in the lung. Histological analysis of AdalphaVEGFAb-treated mice demonstrated a reduction of edema fluid in the lung tissue that correlated with a reduction of lung wet-to-dry ratios and BALF total protein levels. Importantly, administration of AdalphaVEGFAb 48 hr after induction of pulmonary edema with AdVEGFA165 was effective in suppressing pulmonary edema. Administration of an adenoviral vector encoding an anti-VEGF antibody that is the equivalent of bevacizumab effectively suppresses VEGF-A(165)-induced high-permeability pulmonary edema, suggesting that anti-VEGF antibody therapy may represent a novel therapy for high-permeability pulmonary edema.

Regulation of vascular permeability by sphingosine 1-phosphate

A significant and sustained increase in vascular permeability is a hallmark of acute inflammatory diseases such as acute lung injury (ALI) and sepsis and is an essential component of tumor metastasis, angiogenesis, and atherosclerosis. Sphingosine 1-phosphate (S1P), an endogenous bioactive lipid produced in many cell types, regulates endothelial barrier function by activation of its G-protein coupled receptor S1P(1). S1P enhances vascular barrier function through a series of profound events initiated by S1P(1) ligation with subsequent downstream activation of the Rho family of small GTPases, cytoskeletal reorganization, adherens junction and tight junction assembly, and focal adhesion formation. Furthermore, recent studies have identified transactivation of S1P(1) signaling by other barrier-enhancing agents as a common mechanism for promoting endothelial barrier function. This review summarizes the state of our current knowledge about the mechanisms through which the S1P/S1P(1) axis reduces vascular permeability, which remains an area of active investigation that will hopefully produce novel therapeutic agents in the near future.

Hantaviruses direct endothelial cell permeability by sensitizing cells to the vascular permeability factor VEGF, while angiopoietin 1 and sphingosine 1-phosphate inhibit hantavirus-directed permeability

Hantaviruses infect human endothelial cells and cause two vascular permeability-based diseases: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Hantavirus infection alone does not permeabilize endothelial cell monolayers. However, pathogenic hantaviruses inhibit the function of alphav beta3 integrins on endothelial cells, and hemorrhagic disease and vascular permeability deficits are consequences of dysfunctional beta3 integrins that normally regulate permeabilizing vascular endothelial growth factor (VEGF) responses. Here we show that pathogenic Hantaan, Andes, and New York-1 hantaviruses dramatically enhance the permeability of endothelial cells in response to VEGF, while the nonpathogenic hantaviruses Prospect Hill and Tula have no effect on endothelial cell permeability. Pathogenic hantaviruses directed endothelial cell permeability 2 to 3 days postinfection, coincident with pathogenic hantavirus inhibition of alphav beta3 integrin functions, and hantavirus-directed permeability was inhibited by antibodies to VEGF receptor 2 (VEGFR2). These studies demonstrate that pathogenic hantaviruses, similar to alphav beta3 integrin-deficient cells, specifically enhance VEGF-directed permeabilizing responses. Using the hantavirus permeability assay we further demonstrate that the endothelial-cell-specific growth factor angiopoietin 1 (Ang-1) and the platelet-derived lipid mediator sphingosine 1-phosphate (S1P) inhibit hantavirus directed endothelial cell permeability at physiologic concentrations. These results demonstrate the utility of a hantavirus permeability assay and rationalize the testing of Ang-1, S1P, and antibodies to VEGFR2 as potential hantavirus therapeutics. The central importance of beta3 integrins and VEGF responses in vascular leak and hemorrhagic disease further suggest that altering beta3 or VEGF responses may be a common feature of additional viral hemorrhagic diseases. As a result, our findings provide a potential mechanism for vascular leakage after infection by pathogenic hantaviruses and the means to inhibit hantavirus-directed endothelial cell permeability that may be applicable to additional vascular leak syndromes.

Biological Aspects and Binding Strategies of Vascular Endothelial Growth Factor in Renal Cell Carcinoma

Vascular endothelial growth factor (VEGF) is a key mediator in the pathogenesis of renal cell carcinoma (RCC). VEGF is up-regulated in clear cell RCC as a result of loss of the von Hippel-Lindau tumor suppressor gene and subsequent activation of the hypoxia response pathway. VEGF expression drives the migration and proliferation of endothelial cells to support the extensive angiogenesis in RCC. Strategies have been developed to bind and neutralize VEGF and have been investigated in RCC with promising results. Bevacizumab, a VEGF ligand-binding antibody, has shown prolonged time-to-progression versus placebo in treatment-refractory RCC patients and is being investigated currently in multiple RCC settings. VEGF-Trap is also a VEGF binding molecule with ongoing investigation in RCC.

Induction of three-dimensional assembly and increase in apoptosis of human endothelial cells by simulated microgravity: impact of vascular endothelial growth factor

Endothelial cells play a crucial role in the pathogenesis of many diseases and are highly sensitive to low gravity conditions. Using a three-dimensional random positioning machine (clinostat) we investigated effects of simulated weightlessness on the human EA.hy926 cell line (4, 12, 24, 48 and 72 h) and addressed the impact of exposure to VEGF (10 ng/ml). Simulated microgravity resulted in an increase in extracellular matrix proteins (ECMP) and altered cytoskeletal components such as microtubules (alpha-tubulin) and intermediate filaments (cytokeratin). Within the initial 4 h, both simulated microgravity and VEGF, alone, enhanced the expression of ECMP (collagen type I, fibronectin, osteopontin, laminin) and flk-1 protein. Synergistic effects between microgravity and VEGF were not seen. After 12 h, microgravity further enhanced all proteins mentioned above. Moreover, clinorotated endothelial cells showed morphological and biochemical signs of apoptosis after 4 h, which were further increased after 72 h. VEGF significantly attenuated apoptosis as demonstrated by DAPI staining, TUNEL flow cytometry and electron microscopy. Caspase-3, Bax, Fas, and 85-kDa apoptosis-related cleavage fragments were clearly reduced by VEGF. After 72 h, most surviving endothelial cells had assembled to three-dimensional tubular structures. Simulated weightlessness induced apoptosis and increased the amount of ECMP. VEGF develops a cell-protective influence on endothelial cells exposed to simulated microgravity.

Diverse effects of vascular endothelial growth factor on human pulmonary endothelial barrier and migration

Increased endothelial permeability is involved in the pathogenesis of many cardiovascular and pulmonary diseases. Vascular endothelial growth factor (VEGF) is a permeability-increasing cytokine. At the same time, VEGF is known to have a beneficial effect on endothelial cells (EC), increasing their survival. Pulmonary endothelium, particularly, may be exposed to higher VEGF concentrations, since the VEGF level is the higher in the lungs than in any other organ. The purpose of this work was to evaluate the effects of VEGF on barrier function and motility of cultured human pulmonary EC. Using transendothelial resistance measurements as an indicator of permeability, we found that 10 ng/ml VEGF significantly improved barrier properties of cultured human pulmonary artery EC (118.6+/-0.6% compared with 100% control, P<0.001). In contrast, challenge with 100 ng/ml VEGF decreased endothelial barrier (71.6+/-1.0% compared with 100% control, P<0.001) and caused disruption of adherens junctions. VEGF at both concentrations increased cellular migration; however, 10 ng/ml VEGF had a significantly stronger effect. VEGF caused a dose-dependent increase in intracellular Ca2+ concentration; however, phosphorylation of myosin light chain was detectably elevated only after treatment with 100 ng/ml. In contrast, 10 ng/ml but not 100 ng/ml VEGF caused a significant increase in intracellular cAMP (known barrier-protective stimulus) compared with nonstimulated cells (1,096+/-157 and 610+/-86 fmol/mg, respectively; P<0.024). Y576-specific phosphorylation of focal adhesion kinase was also stimulated by 10 ng/ml VEGF. Our data suggest that, depending on its concentration, VEGF may cause diverse effects on pulmonary endothelial permeability via different signaling pathways.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Vascular endothelial growth factor and related molecules in acute lung injury

VEGFs and their receptors have been implicated in the regulation of vascular permeability in many organ systems, including the lung. Increased permeability and interstitial and pulmonary edema are prominent features of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Extrapolating data from other organ systems and animal experiments have suggested that overexpression of VEGF functions primarily as proinjurious molecules in the lung. Recent data, from animal models as well as from patients with ARDS, have shown decreased levels of VEGF in the lung. The role of VEGF and related molecules in ALI/ARDS is, therefore, controversial: what has become clear is that there are many unique features in the regulation of pulmonary vascular permeability and in VEGF expression in the lung. In this review, we explore a growing body of literature looking at the expression and function of VEGF and related molecules in different models of ALI and in patients with ALI/ARDS. Novel evidence points to a potential role of VEGF in promoting repair of the alveolar-capillary membrane during recovery from ALI/ARDS. Understanding the role of VEGF in this disease process is crucial for developing new therapeutic strategies for ALI/ARDS.

Tumor necrosis factor-alpha-dependent expression of phosphodiesterase 2: role in endothelial hyperpermeability

The pleiotropic cytokine tumor necrosis factor-alpha (TNF-alpha) and thrombin lead to increased endothelial permeability in sepsis. Numerous studies demonstrated the significance of intracellular cyclic nucleotides for the maintenance of endothelial barrier function. Actions of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are terminated by distinct cyclic nucleotide phosphodiesterases (PDEs). We hypothesized that TNF-alpha could regulate PDE activity in endothelial cells, thereby impairing endothelial barrier function. In cultured human umbilical vein endothelial cells (HUVECs), we found a dramatic increase of PDE2 activity following TNF-alpha stimulation, while PDE3 and PDE4 activities remained unchanged. Significant PDE activities other than PDE2, PDE3, and PDE4 were not detected. TNF-alpha increased PDE2 expression in a p38 mitogen-activated protein kinase (MAPK)-dependent manner. Endothelial barrier function was investigated in HUVECs and in isolated mice lungs. Selective PDE2 up-regulation sensitized HUVECs toward the permeability-increasing agent thrombin. In isolated mice lungs, we demonstrated that PDE2 inhibition was effective in preventing thrombin-induced lung edema, as shown with a reduction in both lung wet-to-dry ratio and albumin flux from the vascular to bronchoalveolar compartment. Our findings suggest that TNF-alpha-mediated up-regulation of PDE2 may destabilize endothelial barrier function in sepsis. Inhibition of PDE2 is therefore of potential therapeutic interest in sepsis and acute respiratory distress syndrome (ARDS).

Vascular endothelium growth factor, surgical delay, and skin flap survival

OBJECTIVE

Cytokines may be a mechanism by which surgical delay can increase flap survival. We previously found that preoperative vascular endothelium growth factor (VEGF) administration in the rat transverse rectus abdominis myocutaneous (TRAM) flap could improve skin paddle survival. In this study, we used partial elevation of the rat TRAM flap as a surgical delay to assess endogenous cytokine expression and tissue survival comparable to undelayed TRAM flaps.

METHODS

In Part I, TRAM flaps underwent surgical delay procedures; 7 days later, the flaps were completely elevated and reinset. At the same time, other flaps were raised and reinset without delay. Skin paddle survival in both groups was evaluated at 7 days. In Part II, skin biopsies from TRAM zones I to IV were taken at the time of delay and at intervals of 12, 24, 48, and 72 hours. Specimens were assessed for selected cytokine gene expression by reverse transcription-polymerase chain reaction analysis (TR-PCR).

RESULTS

Surgical delay significantly (P < 0.001) increased skin paddle survival in the delayed TRAM flaps (16.14 +/- 1.53 cm, 81.9%) compared with undelayed flaps (7.68 +/- 3.16 cm, 40.9%). TGF-beta and PDGF expressions were not changed by surgical delay, but basic fibroblast growth factor (bFGF) and VEGF expressions increased significantly (P < 0.05 and P < 0.01) after delay.

CONCLUSIONS

In the rat TRAM model, surgical delay resulted in increased VEGF expression and increased skin paddle survival. These results correlate with previous studies showing the preoperative injection of VEGF increases skin paddle survival. VEGF may be an important element in the delay phenomenon and may be an agent for pharmacological delay.

VEGF-mediated endothelial P-selectin translocation: role of VEGF receptors and endogenous PAF synthesis

The acute increase in vascular permeability produced by vascular endothelial growth factor (VEGF-A(165)) requires activation of endothelial Flk-1 receptors (VEGFR-2) and stimulation of platelet-activating factor (PAF) synthesis. Like PAF, VEGF-A(165) promotes translocation of P-selectin to the endothelial cell (EC) surface. However, the mechanisms involved remain unknown. By treating human umbilical vein endothelial cells (HUVECs) with VEGF analogs, we show that activation of VEGFR-1 or VEGFR-2 or both induced a rapid and transient translocation of endothelial P-selectin and neutrophil adhesion to activated ECs. The effects mediated by VEGF-A(165) and VEGF-A(121) (VEGFR-1/VEGFR-2 agonists) were blocked by a selective VEGFR-2 inhibitor, SU1498. VEGF-A(165) was twice as potent as VEGF-A(121), which can be explained by the binding capacity of VEGF-A(165) to its coreceptor neuropilin-1 (NRP-1). Indeed, treatment with NRP-1 antagonist (GST-Ex7) reduced the effect of VEGF-A(165) to the levels observed upon stimulation with VEGF-A(121). Finally, the use of selective PAF receptor antagonists reduced VEGF-A(165)-mediated P-selectin translocation. Together, these data show that maximal P-selectin translocation and subsequent neutrophil adhesion was mediated by VEGF-A(165) on the activation of VEGFR-2/NRP-1 complex and required PAF synthesis.

Marked increase in vascular endothelial growth factor concentrations during Escherichia coli endotoxin-induced acute inflammation in humans

BACKGROUND

Bacterial endotoxins can induce the synthesis and release of vascular endothelial growth factor (VEGF), which may alter vascular permeability and cause vascular leakage.

MATERIALS AND METHODS

The effect of acute systemic inflammation on VEGF concentration was measured in healthy males after an intravenous bolus infusion of Escherichia coli endotoxin (lipopolysaccharide, LPS, 20 IU kg-1) in a double-blind, placebo-controlled parallel group study. LPS administration was followed by an infusion of lepirudin (bolus 0.1 mg kg-1, continuous infusion of 0.1 mg kg-1 h-1, n = 12) or saline (n = 12).

RESULTS

Plasma VEGF increased from a mean of 15.1 pg mL-1 to 74.6 pg mL-1 5 h after LPS (P < 0.003). Body temperature, pulse rate, leukcytes, prothrombin fragment 1 + 2 (F1 + 2) and lactoferrin increased and platelets decreased after LPS (P < 0.05). The LPS-induced increase in VEGF was paralleled by the neutrophil cell degranulation marker lactoferrin but not by F1 + 2, and was not affected by lepirudin, which blunted F1 + 2 formation (P < 0.05).

CONCLUSIONS

Inflammation-induced activation of leukcytes rather than platelets plays a role in the marked increase in VEGF, which cannot be abrogated by antithrombotic therapy.

p38 MAP kinase--a molecular switch between VEGF-induced angiogenesis and vascular hyperpermeability

Vascular endothelial growth factor (VEGF) is not only essential for vasculogenesis and angiogenesis but also is a potent inducer of vascular permeability. Although a dissection of the molecular pathways between angiogenesis- and vascular permeability-inducing properties would be desirable for the development of angiogenic and anti-angiogenic therapies, such mechanisms have not been identified yet. Here we provide evidence for a role of the p38 MAPK as the signaling molecule that separates these two processes. Inhibition of p38 MAPK activity enhances VEGF-induced angiogenesis in vitro and in vivo, a finding that was accompanied by prolonged Erk1/2 MAPK activation, increased endothelial survival, and plasminogen activation. Conversely, the same inhibitors abrogate VEGF-induced vascular permeability in vitro and in vivo. These dualistic properties of p38 MAPK are relevant not only for therapeutic angiogenesis but also for reducing edema formation and enhancing tissue repair in ischemic diseases.

Rosiglitazone and pulmonary oedema: an acute dose-dependent effect on human endothelial cell permeability

AIMS/HYPOTHESIS

Peripheral and pulmonary oedema has emerged as the most common drug-related side effect of rosiglitazone in clinical practice, but the underlying mechanisms are not clear. Fluid retention and changes in vascular tone could contribute to oedema formation, but the interpretation of clinical and in vivo studies is particularly difficult and the direct effects of thiazolidinediones on endothelial barrier function have not been previously reported.

METHODS

Human pulmonary artery endothelial cells were seeded and grown on 0.4 microm collagen-coated filters to form a tight monolayer (transendothelial electrical resistance 9-11 ohms.cm(-2) after 2-3 days). Transendothelial albumin flux (expressed as the percentage clearance of albumin relative to control) was measured using Evans blue-labelled albumin after exposure to rosiglitazone 1-100 micromol/l for 1 h to 48 h, and after removal of drug from the monolayer.

RESULTS

Incubation of pulmonary artery endothelial cells with rosiglitazone for 4 h produced immediate concentration-dependent increases in transendothelial albumin flux: e.g., relative to control (100%), 113%+/-13% (1 micromol/l), 215%+/-37% (10 micromol/l, p=0.01) and 461%+/-96% (100 micromol/l, p=0.002) (n=12). There was no effect after 1 h. The acute hyperpermeability response to rosiglitazone, maximal after 4 h, was fully reversible after washing the monolayer. After incubation for 24 to 48 h the effect of rosiglitazone on pulmonary endothelial permeability tended to subside: e.g., 210%+/-59% (24 h) for rosiglitazone 100 micromol/l (p=0.06).

CONCLUSION/INTERPRETATION

Exposure to high-therapeutic concentrations of rosiglitazone causes a reversible fourfold increase in pulmonary endothelial permeability which could be clinically relevant especially at higher doses and at times of peak plasma drug concentration.

Regulation of vascular permeability by vascular endothelial growth factors

Increased vascular permeability is one of the first stages in both physiological and pathological angiogenesis-the generation of new blood vessels from preexisting vasculature. Although this has been hypothesised to be true in physiological angiogenesis, it is clearly a mark of blood vessel growth in disease. Normal, healthy blood vessel growth (physiological angiogenesis) occurs throughout development as well as during tissue repair and growth in adult tissues. Angiogenesis is also seen in a wide variety of diseases, which include all the major causes of mortality in the West-heart disease, cancer, stroke, vascular disease, and diabetes. Much of this angiogenesis is significantly different from normal blood vessel growth and is termed pathological angiogenesis. Angiogenesis is regulated by vascular growth factors, the most notable being the vascular endothelial growth factor family of proteins (VEGF). These act on specific receptors in the vascular system to stimulate new vessel growth by a number of mechanisms. VEGFs also directly stimulate increased vascular permeability to water and large molecular weight proteins and vasodilatation. These two effects result in a large flux of water and macromolecules from the vasculature to the interstitium, often resulting in oedema. This review will outline the mechanisms by which VEGFs do this and discuss some of the difficulties in interpreting data from VEGF studies due to the conflicting and synergistic effects of these actions.

The hypercoagulable state of malignancy: pathogenesis and current debate

A hypercoagulable or prothrombotic state of malignancy occurs due to the ability of tumor cells to activate the coagulation system. It has been estimated that hypercoagulation accounts for a significant percentage of mortality and morbidity in cancer patients. Prothrombotic factors in cancer include the ability of tumor cells to produce and secrete procoagulant/fibrinolytic substances and inflammatory cytokines, and the physical interaction between tumor cell and blood (monocytes, platelets, neutrophils) or vascular cells. Other mechanisms of thrombus promotion in malignancy include nonspecific factors such as the generation of acute phase reactants and necrosis (i.e., inflammation), abnormal protein metabolism (i.e., paraproteinemia), and hemodynamic compromise (i.e., stasis). In addition, anticancer therapy (i.e., surgery/chemotherapy/hormone therapy) may significantly increase the risk of thromboembolic events by similar mechanisms, e.g., procoagulant release, endothelial damage, or stimulation of tissue factor production by host cells. However, not all of the mechanisms for the production of a hypercoagulable state of cancer are entirely understood. In this review, we attempt to describe what is currently accepted about the pathophysiology of the hypercoagulable state of cancer. We also discuss whether or not to screen patients with idiopathic deep venous thrombosis for an underlying malignancy, and whether this would be beneficial to patients. It is hoped that a better understanding of these mechanisms will ultimately lead to the development of more targeted treatment to prevent thromboembolic complications in cancer patients. It is also hoped that antithrombotic strategies may also have a positive effect on the process of tumor growth and dissemination.

Regulation of microvascular permeability by vascular endothelial growth factors

Generation of new blood vessels from pre-existing vasculature (angiogenesis) is accompanied in almost all states by increased vascular permeability. This is true in physiological as well as pathological angiogenesis, but is more marked during disease states. Physiological angiogenesis occurs during tissue growth and repair in adult tissues, as well as during development. Pathological angiogenesis is seen in a wide variety of diseases, which include all the major causes of mortality in the west: heart disease, cancer, stroke, vascular disease and diabetes. Angiogenesis is regulated by vascular growth factors, particularly the vascular endothelial growth factor family of proteins (VEGF). These act on two specific receptors in the vascular system (VEGF-R1 and 2) to stimulate new vessel growth. VEGFs also directly stimulate increased vascular permeability to water and large-molecular-weight proteins. We have shown that VEGFs increase vascular permeability in mesenteric microvessels by stimulation of tyrosine auto-phosphorylation of VEGF-R2 on endothelial cells, and subsequent activation of phospholipase C (PLC). This in turn causes increased production of diacylglycerol (DAG) that results in influx of calcium across the plasma membrane through store-independent cation channels. We have proposed that this influx is through DAG-mediated TRP channels. It is not known how this results in increased vascular permeability in endothelial cells in vivo. It has been shown, however, that VEGF can stimulate formation of a variety of pathways through the endothelial cell, including transcellular gaps, vesiculovacuolar organelle formation, and fenestrations. A hypothesis is outlined that suggests that these all may be part of the same process.