Not just angiogenesis--wider roles for the angiopoietins

MFAP4-Mediated Effects in Elastic Fiber Homeostasis, Integrin Signaling and Cancer, and Its Role in Teleost Fish

Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix (ECM) protein belonging to the fibrinogen-related domain superfamily. MFAP4 is highly expressed in elastin-rich tissues such as lung, blood vessels and skin. MFAP4 is involved in organization of the ECM, regulating proper elastic fiber assembly. On the other hand, during pathology MFAP4 actively contributes to disease development and progression due to its interactions with RGD-dependent integrin receptors. Both tissue expression and circulating MFAP4 levels are associated with various disorders, including liver fibrosis and cancer. In other experimental models, such as teleost fish, MFAP4 appears to participate in host defense as a macrophage-specific innate immune molecule. The aim of this review is to summarize the accumulating evidence that indicates the importance of MFAP4 in homeostasis as well as pathological conditions, discuss its known biological functions with special focus on elastic fiber assembly, integrin signaling and cancer, as well as describe the reported functions of non-mammalian MFAP4 in fish. Overall, our work provides a comprehensive overview on the role of MFAP4 in health and disease.

Metastases to the central nervous system: Molecular basis and clinical considerations

BACKGROUND

Metastatic tumors are the most common malignancies of the central nervous system (CNS) in adults. CNS metastases are associated with unfavorable prognosis, high morbidity and mortality. Lung cancer is the most common source of brain metastases, followed by breast cancer and melanoma. Rising incidence is primarily due to improvements in systemic control of primary malignancies, prolonged survival and advances in cancer detection.

PURPOSE

To provide an overview of the metastatic cascade and the role of angiogenesis, neuroinflammation, metabolic adaptations, and clinical details about brain metastases from different primary tumors.

METHODS

A review of the literature on brain metastases was conducted, focusing on the pathophysiology and clinical aspects of the disease. PubMed was used to search for relevant articles published from January 1975 through December 2019 using the keywords brain metabolism, brain metastasis, metastatic cascade, molecular mechanisms, incidence, risk factors, and prognosis. 146 articles met the criteria and were included in this review.

DISCUSSION

Some primary tumors have a higher tendency to metastasize to the CNS. Establishing a suitable metastatic microenvironment is important in maintaining tumor cell growth and survival. Magnetic resonance imaging (MRI) is a widely used tool for diagnosis and treatment monitoring. Available treatments include surgery, radiotherapy, stereotactic radiosurgery, chemotherapy, immunotherapy, and systemic targeted therapies.

CONCLUSIONS

Prevention of metastases to the CNS remains a difficult challenge. Advances in screening of high-risk patients and future development of novel treatments may improve patient outcomes.

Angiogenesis regulation by nanocarriers bearing RNA interference

Since the approval of bevacizumab as anti-angiogenic therapy in 2004 by the FDA, an array of angiogenesis inhibitors have been developed and approved. However, results were disappointing with regard to their therapeutic efficacy. RNA interference approaches offer the possibility of rational design with high specificity, lacking in many current drug treatments for various diseases including cancer. However, in vivo delivery issues still represent a significant obstacle for widespread clinical applications. In the current review, we summarize the advances in the last decade in the field of angiogenesis-targeted RNA interference approaches, with special emphasis on oncology applications. We present pro-angiogenic and anti-angiogenic factors as potential targets, experimental evidence and clinical trials data on angiogenesis regulation by RNA interference. Consequent challenges and opportunities are discussed.

Inhibition of VEGF and Angiopoietin-2 to Reduce Brain Metastases of Breast Cancer Burden

For metastases in the central nervous system, angiogenesis enhances metastatic potential and promotes progression. Primary factors which drive vessel growth are vascular endothelial growth factor (VEGF) and angiopoietin-2. Preclinical models show inhibition of either factor reduces metastases spread and inhibits growth. This work sets out to answer two questions in a preclinical mouse model. First, whether the combined inhibition of VEGF and angiopoietin-2, reduces passive permeability and limits drug uptake into brain metastases; and second, whether this inhibition reduces metastases burden in brain. We observed combinatorial inhibition of VEGF and angiopoietin-2, decreased (p < 0.05) angiogenesis and vascular branching in an aortic ring assay and decreased (p < 0.05) endothelial wound closure times. Using a brain metastases of breast cancer model (induced by intracardiac injections of brain seeking MDA-MB-231Br cells or 4T1Br cells), we observed, similar to VEGF, angiopoetin-2 expression correlates to increased angiogenesis (p < 0.05) and increased lesion permeability. To determine efficacy, animals were administered bevacizumab plus L1-10 (angiopoietin inhibitor) twice per week until neurological symptoms developed. Lesion permeability significantly decreased by ∼50% (p < 0.05) compared to untreated lesions, but remained ∼25% greater (p < 0.0%) than brain. In subsequent experiments, animals were administered similar regimens but sacrificed on day 32. The number of metastatic lesions developed was significantly (p < 0.001) reduced in the bevacizumab group (56%) and combination group (86%). Lesions’ size was reduced in bevacizumab treated lesions (∼67%) and bevacizumab and L1-10 treated lesions (∼78%) developing area < 0.5 mm². In summary, combinatorial inhibition of VEGF and angiopoietin reduces lesion permeability and brain metastatic burden.

Plasma VEGF-related polymorphisms are implied in autoimmune thyroid diseases

Autoimmune thyroid diseases (AITD), including Graves' disease (GD) and Hashimoto thyroiditis (HT), are complex multifactorial diseases. Vascular endothelial growth factor (VEGF) is implicated in various inflammatory diseases, especially autoimmune diseases. Our aim was to elucidate the relationships between plasma VEGF levels and four genome-wide association study-identified single nucleotide polymorphisms (SNPs) related to VEGF with AITD in Tunisian patients. A total of 364 healthy controls and 389 patients with AITD were genotyped for the SNPs rs6921438, rs4416670, rs6993770 and rs10738760. Levels of thyroid hormones and antibodies were quantified simultaneously with plasma VEGF after a period of six months of treatment. We found that the minor alleles of rs10738760 and rs6921438 are associated with the presence of GD. A allele of rs10738760 polymorphism is associated with increased plasma levels of free tri-iodothyronin (FT3) while no relationship was found with circulating VEGF plasma levels after six months of treatment. We also showed that the T allele of rs4416670 polymorphism was associated with increased risk of hyperthyroidism in patients treated for six months, independently of their initial diagnosis. There was no significant association between the SNPs and the risk for HT compared with controls. This study shows that AITD are influenced by 3 SNPs linked to VEGF circulating levels. Whereas rs10738760 appeared specific to GD and FT3 production after six months of treatment, rs6921438 and rs4416670 were implicated in the risk for GD. This study opens new ways to test pharmacogenomics concepts in the future especially in GD in which recurrence prognosis is still challenging.

Presence of sst5TMD4, a truncated splice variant of the somatostatin receptor subtype 5, is associated to features of increased aggressiveness in pancreatic neuroendocrine tumors

Purpose

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare and heterogeneous tumors, and their biological behavior is not well known. We studied the presence and potential functional roles of somatostatin receptors (sst1-5), focusing particularly on the truncated variants (sst5TMD4, sst5TMD5) and on their relationships with the angiogenic system (Ang/Tie-2 and VEGF) in human GEP-NETs.

Experimental Design

We evaluated 42 tumor tissue samples (26 primary/16 metastatic) from 26 patients with GEP-NETs, and 30 non-tumoral tissues (26 from adjacent non-tumor regions and 4 from normal controls) from a single center. Expression of sst1-5, sst5TMD4, sst5TMD5, Ang1-2, Tie-2 and VEGF was analyzed using real-time qPCR, immunofluorescence and immunohistochemistry. Expression levels were associated with tumor characteristics and clinical outcomes. Functional role of sst5TMD4 was analyzed in GEP-NET cell lines.

Results

sst1 exhibited the highest expression in GEP-NET, whilst sst2 was the most frequently observed sst-subtype (90.2%). Expression levels of sst1, sst2, sst3, sst5TMD4, and sst5TMD5 were significantly higher in tumor tissues compared to their adjacent non-tumoral tissue. Lymph-node metastases expressed higher levels of sst5TMD4 than in its corresponding primary tumor tissue. sst5TMD4 was also significantly higher in intestinal tumor tissues from patients with residual disease of intestinal origin compared to those with non-residual disease. Functional assays demonstrated that the presence of sst5TMD4 was associated to enhanced malignant features in GEP-NET cells. Angiogenic markers correlated positively with sst5TMD4, which was confirmed by immunohistochemical/fluorescence studies.

Conclusions

sst5TMD4 is overexpressed in GEP-NETs and is associated to enhanced aggressiveness, suggesting its potential value as biomarker and target in GEP-NETs.

Prognostic value of pro-inflammatory cytokine and pro-angiogenesis factor in differentiating malignant from benign exudative effusion

BACKGROUND AND AIMS

The precise mechanism of pathogenesis in exudation of effusions is uncertain. Released factors in inflammation and malignancy of pleura are related to incremented permeability of the micro-pleural vessels. Angiopoietins (Ang) take part in development of angiogenesis and pleural inflammation. Interleukin-8 (IL-8) influences proliferation and tumor angiogenesis and it is expressed in cancer. The aims of this study were to investigate the relationship between inflammation, angiogenesis and etiologies of exudative effusions, and to evaluate the diagnostic value in differentiating malignant from benign.

METHODS

The study includes 49 pleural fluid (PF) samples. Ang-2 and IL-8 in PF and serum were estimated.

RESULTS

Ten patients were transudative and 39 patients were exudative fluid, subdivided into 16 benign and 23 malignant effusion. Ang-2 and IL-8 either fluid level or ratio were in significantly high in exudative more than in transudative fluid (P = 0.002). Ang-2 and IL-8 in PF were in high level than in serum of exudative and transudative. Ang-2 fluid level and ratio were significantly high in benign exudative effusion (P = 0.01, P = 0.05, respectively), while IL-8 level was significantly high in malignant exudative effusion (P = 0.04). Cut-off points for PF Ang-2 and IL-8 in differentiating malignant from benign exudative were 15.67 ng/mL, 325.54 pg/mL, respectively.

CONCLUSION

Our results support the evidence that angiogenesis and inflammatory pathways are linked, and that inflammation and vascular permeability of pleura constitutes the pathogenic basis of the majority of exudative effusion.

Cross-talk between endothelial and breast cancer cells regulates reciprocal expression of angiogenic factors in vitro

Reciprocal growth factor exchange between endothelial and malignant cells within the tumor microenvironment may directly stimulate neovascularization; however, the role of host vasculature in regulating tumor cell activity is not well understood. While previous studies have examined the angiogenic response of endothelial cells to tumor-secreted factors, few have explored tumor response to endothelial cells. Using an in vitro co-culture system, we investigated the influence of endothelial cells on the angiogenic phenotype of breast cancer cells. Specifically, VEGF, ANG1, and ANG2 gene and protein expression were assessed. When co-cultured with microvascular endothelial cells (HMEC-1), breast cancer cells (MDA-MB-231) significantly increased expression of ANG2 mRNA (20-fold relative to MDA-MB-231 monoculture). Moreover, MDA-MB-231/HMEC-1 co-cultures produced significantly increased levels of ANG2 (up to 580 pg/ml) and VEGF protein (up to 38,400 pg/ml) while ANG1 protein expression was decreased relative to MDA-MB-231 monocultures. Thus, the ratio of ANG1:ANG2 protein, a critical indicator of neovascularization, shifted in favor of ANG2, a phenomenon known to correlate with vessel destabilization and sprouting in vivo. This angiogenic response was not observed in nonmalignant breast epithelial cells (MCF-10A), where absolute protein levels of MCF-10A/HMEC-1 co-cultures were an order of magnitude less than that of the MDA-MB-231/HMEC-1 co-cultures. Results were further verified with a functional angiogenesis assay demonstrating well-defined microvascular endothelial cell (TIME) tube formation when cultured in media collected from MDA-MB-231/HMEC-1 co-cultures. This study demonstrates that the angiogenic activity of malignant mammary epithelial cells is significantly enhanced by the presence of endothelial cells.

Elevated angiopoietin-1 serum levels in patients with Alzheimer's disease

Background. Alzheimer's disease (AD) is the most common cause of dementia in the elderly. AD is characterized by the accumulation of amyloid plaques and neurofibrillary tangles and by massive neuronal loss in the brain. There is epidemiologic and pathologic evidence that AD is associated with vascular risk factors and vascular diseases, contributing to cerebral hypoperfusion with consecutive stimulation of angiogenesis and upregulation of proangiogenic factors such as Angiopoietin-1 (Ang-1). Methods. In the present study, we measured Ang-1 serum levels in 42 patients with AD, 20 patients with mild cognitive impairment (MCI), and in 40 healthy elderly controls by ELISA. Results. We found significantly increased Ang-1 serum levels in patients with AD compared to control subjects (P = 0.003). There was no significant difference between MCI patients and healthy controls (P = 0.553) or between AD and MCI patients (P = 0.054). The degree of cognitive impairment as measured by the mini-mental status examination (MMSE) score was significantly correlated with the Ang-1 serum levels in all patients and healthy controls. Conclusions. We found significantly increased Ang-1 serum levels in AD patients. We could also show an association between Ang-1 serum levels and the cognitive status in all patients and healthy controls. Thus, serum Ang-1 could be a potential candidate for a biomarker panel for AD diagnosis.

Interrelationship and expression profiling of cyclooxygenase and angiogenic factors in Indian patients with multiple myeloma

Multiple myeloma (MM) is classically illustrated by a desynchronized cytokine system with rise in inflammatory cytokines. There are recent reports which emphasized the potential role of angiogenesis in the development of MM. Role of cyclooxygenase 2 (COX-2) is well documented in the pathogenesis of solid tumors, but little is known about its occurrence and function in hematologic neoplasms. Involvement of neoangiogenesis is reported in the progression of MM, and angiopoietins probably contribute to this progression by enhancing neovascularization. Circulatory and mRNA levels of angiogenic factors and cyclooxygenase were determined in 125 subjects (75 MM patients and 50 healthy controls) by using enzyme-linked immunosorbent assay and quantitative PCR. We observed significant increase for angiogenic factors (Ang-1, Ang-2, hepatocyte growth factor, and vascular endothelial growth factor) and cyclooxygenase at circulatory level, as well as at mRNA level, as compared to healthy controls except insignificant increase for Ang-1 at circulatory level. We have also observed the significant positive correlation of all angiogenic factors with cyclooxygenase. The strong association found between angiogenic factors and COX-2 in this study may lead to the development of combination therapeutic strategy to treat MM. Therefore, targeting COX-2 by using its effective inhibitors demonstrating antiangiogenic and antitumor effects could be used as a new therapeutic approach for treatment of MM.

The molecular balance between receptor tyrosine kinases Tie1 and Tie2 is dynamically controlled by VEGF and TNFα and regulates angiopoietin signalling

Angiopoietin-1 (Ang1) signals via the receptor tyrosine kinase Tie2 which exists in complex with the related protein Tie1 at the endothelial cell surface. Tie1 undergoes regulated ectodomain cleavage in response to phorbol esters, vascular endothelial growth factor (VEGF) and tumour necrosis factor-α (TNFα). Recently phorbol esters and VEGF were found also to stimulate ectodomain cleavage of Tie2. Here we investigate for the first time the effects of factors activating ectodomain cleavage on both Tie1 and Tie2 within the same population of cells, and their impact on angiopoietin signalling. We find that phorbol ester and VEGF activated Tie1 cleavage within minutes followed by restoration to control levels by 24 h. However, several hours of PMA and VEGF treatment were needed to elicit a detectable decrease in cellular Tie2, with complete loss seen at 24 h of PMA treatment. TNFα stimulated Tie1 cleavage, and induced a sustained decrease in cellular Tie1 over 24 h whilst increasing cellular Tie2. These differential effects of agonists on Tie1 and Tie2 result in dynamic modulation of the cellular Tie2∶Tie1 ratio. To assess the impact of this on Ang1 signalling cells were stimulated with VEGF and TNFα for differing times and Ang1-induced Tie2 phosphorylation examined. Elevated Tie2∶Tie1, in response to acute VEGF treatment or chronic TNFα, was associated with increased Ang1-activated Tie2 in cells. These data demonstrate cellular levels of Tie1 and Tie2 are differentially regulated by pathophysiologically relevant agonists resulting in dynamic control of the cellular Tie2∶Tie1 balance and modulation of Ang1 signalling. These findings highlight the importance of regulation of signalling at the level of the receptor. Such control may be an important adaptation to allow modulation of cellular signalling responses in systems in which the activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.

Biomarkers in acute lung injury--marking forward progress

This article reviews the state of the art regarding biomarkers for prediction, diagnosis, and prognosis in acute lung injury. Biomarkers and the goals of biomarker research are defined. Progress along 4 general routes is examined. First, the results of wide-ranging existing protein biomarkers are reported. Second, newer biomarkers awaiting or with strong potential for validation are described. Third, progress in the fields of genomics and proteomics is reported. Finally, given the complexity and number of potential biomarkers, the results of combining clinical predictors with protein and other biomarkers to produce better prognostic and diagnostic indices are examined.

Angiopoietin-2: a potential novel diagnostic marker in multiple myeloma

BACKGROUND

Multiple myeloma (MM) was the first hematological malignancy in which a prognostic relevance of bone marrow (BM) angiogenesis was reported. Microenvironment formed by reactive oxygen species, growth factors and chemokines initiates the process of BM angiogenesis. Among the angiopoietins, angiopoietin-1 is involved in vessel stability, whereas angiopoietin-2 is involved in vessel sprouting.

DESIGN AND METHODS

Circulatory levels of angiopoietin-1, angiopoietin-2 and VEGF in 62 MM patients and 50 healthy controls were determined using ELISA.

RESULTS

Significant increase in VEGF and angiopoietin-2 level was observed in patients which correlated positively with the severity of the disease, whereas no alteration was observed in angiopoietin-1 levels.

CONCLUSION

Significant elevation in angiopoietin-2 and VEGF levels and their correlation with severity of the disease indicate their utility as potential tumor markers along with β(2)- microglobulin and might also suggest new therapeutic target for anticancer treatment.

[Angiogenesis in cartilage tumors]

In contrast to normal cartilage, which is avascular, angiogenesis is characteristic of cartilage tumors. In this review, we outline the basic principles of angiogenesis with regard to recent findings on differential morphological and molecular aspects of angiogenesis in cartilage tumors, including enchondromas, conventional chondrosarcomas and dedifferentiated chondrosarcomas. Furthermore, we describe the effects of hypoxia and interleukin-1β on angiogenic signaling in chondrosarcoma cells.

Serum angiopoietin-1 level is increased in patients with Behçet's disease

OBJECTIVE

Angiogenesis may be involved in the pathogenesis of Behçet's disease (BD). Some angiogenic factors such as vascular endothelial growth factor, monocyte chemoattractant protein-1, and endothelin-1 are significantly associated with BD. Here, we investigate whether Angiopoietin contributes to disease activity and clinical manifestations of BD.

METHODS

We recruited 59 consecutive patients with BD and sex- and age-matched 65 healthy control subjects for this study. We reviewed data regarding clinical features, erythrocyte sediment rate (ESR), and C-reactive protein (CRP) at the time of enrollment. Serum angiopoietin-1 and angiopoietin-2 were estimated by enzyme-linked immunosorbent assay. Statistical analyses were performed using the Student t test and Pearson's correlation coefficient analysis.

RESULTS

Levels of serum angiopoietin-1 are significantly increased in BD patients compared to controls (284.5+/-101.2 ng/ml of BD vs 237.1+/-76.4 ng/ml of controls, p=0.012). However, serum angiopoietin-2 levels are similar in both groups (974.2+/-679.3 pg/ml of BD vs 858.3+/-535.3 pg/ml of controls, p=0.562). Serum angiopoietin-1 expression is significantly elevated in patients with skin lesions (p=0.025) and positively correlated with disease duration (r=0.320, p=0.015). ESR levels are closely associated with serum angiopoietin-2 (r=0.306, p=0.018).

CONCLUSION

Angiopoiein-1 expression is enhanced in BD patients compared to controls. This preliminary study identifies that angiopoietin-1 may play an important role in the pathogenesis of BD.

The recognition unit of FIBCD1 organizes into a noncovalently linked tetrameric structure and uses a hydrophobic funnel (S1) for acetyl group recognition

We have recently identified FIBCD1 (Fibrinogen C domain containing 1) as a type II transmembrane endocytic receptor located primarily in the intestinal brush border. The ectodomain of FIBCD1 comprises a coiled coil, a polycationic region, and a C-terminal FReD (fibrinogen-related domain) that assembles into disulfide-linked homotetramers. The FIBCD1-FReD binds Ca(2+) dependently to acetylated structures like chitin, N-acetylated carbohydrates, and amino acids. FReDs are present in diverse innate immune pattern recognition proteins including the ficolins and horseshoe crab TL5A. Here, we use chemical cross-linking, combined with analytical ultracentrifugation and electron microscopy of the negatively stained recombinant FIBCD1-FReD to show that it assembles into noncovalent tetramers in the absence of the coiled coil. We use surface plasmon resonance, carbohydrate binding, and pulldown assays combined with site-directed mutagenesis to define the binding site involved in the interaction of FIBCD1 with acetylated structures. We show that mutations of central residues (A432V and H415G) in the hydrophobic funnel (S1) abolish the binding of FIBCD1 to acetylated bovine serum albumin and chitin. The double mutations (D393N/D395A) at the putative calcium-binding site reduce the ability of FIBCD1 to bind ligands. We conclude that the FReDs of FIBCD1 forms noncovalent tetramers and that the acetyl-binding site of FReDs of FIBCD1 is homologous to that of tachylectin 5A and M-ficolin but not to the FReD of L-ficolin. We suggest that the spatial organization of the FIBCD1-FReDs determine the molecular pattern recognition specificity and subsequent biological functions.

Tie-2 is overexpressed by monocytes in autoimmune thyroid disorders and participates in their recruitment to the thyroid gland

CONTEXT

The angiopoietin/Tie system seems to have an important role in the pathogenesis of inflammatory diseases. Although Tie-2 is mainly expressed by endothelium, it is also detected in monocytes, which participate in the development of angiogenic and inflammatory phenomena.

AIM

The aim was to study the expression and function of Tie-2 and their ligands, angiopoietin-1 (Ang-1) and Ang-2, in thyroid glands and monocytes from patients with autoimmune thyroid disease (AITD).

DESIGN

We studied the expression of Tie-2, Ang-1, and Ang-2 by immunohistochemical techniques in surgical thyroid tissues from 17 patients with Graves' disease, 8 with Hashimoto's thyroiditis, and 3 healthy glands. In addition, we explored the expression and function of Tie-2 in peripheral blood monocytes from 17 patients with Graves' disease, 11 with Hashimoto's thyroiditis, and 14 healthy controls.

RESULTS

We found that the expression of Ang-1, Ang-2, and Tie-2 was up-regulated in thyroid glands from AITD patients. Flow cytometry, immunofluorescence, ELISA, and RT-PCR analyses confirmed the synthesis and release of Ang-1, Ang-2, and Tie-2 by thyroid follicular cells (TFC) from AITD patients. In addition, these patients showed increased levels of Tie-2(+) monocytes in the peripheral blood, which exhibited an enhanced chemotactic response to Ang-2 or autologous TFC.

CONCLUSIONS

Our data suggest that the Ang/Tie-2 system, through the participation of blood vessels, inflammatory cells, and TFC, may have an important role in the recruitment of monocytes to the thyroid gland and the pathogenesis of the tissue damage seen in AITD.

Serum levels of angiogenic molecules in autoimmune thyroid diseases and their correlation with laboratory and clinical features

CONTEXT

Because angiogenesis has a role in the pathogenesis of inflammatory conditions, we studied angiogenesis soluble markers in autoimmune thyroid diseases.

OBJECTIVE

The aim of the study was to measure concentrations of angiopoietins, Tie-2, and vascular endothelial growth factor in sera from autoimmune thyroid disease patients.

DESIGN

Soluble Tie-2 (sTie-2), angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor were quantified by ELISA in sera from 44 untreated Graves' disease (GD) patients, 25 untreated Hashimoto's thyroiditis (HT) patients, 13 non-GD hyperthyroid patients, and 22 age-matched controls. Subgroups of patients with active and non-active Graves' ophthalmopathy (GO) were analyzed. Correlations among these markers and clinical parameters were assessed by bivariate and multivariate analyses.

RESULTS

STIE-2 levels were higher in GD or HT patients compared to controls (P < 0.01). In addition, serum Ang-2 concentrations were higher in untreated GD patients compared to controls, HT patients, or non-GD hyperthyroid patients (P < 0.01), and no difference was observed between HT patients and controls. Significant correlations were found between free T(4)/sTie-2 and free T(4)/Ang-2 levels (r = 0.464, P < 0.01; and r = 0.463, P < 0.01, respectively) as well as between sTie-2/anti-TSH receptor antibody (r = 0.527; P < 0.01) and sTie-2/Ang-2 (r = 0.563; P = 0.001). Furthermore, sTie-2 levels were significantly higher in patients with active GO when compared to those with inactive GO (P < 0.05). Interestingly, Ang-2 levels decreased significantly after treatment with antithyroid drugs (P < 0.01).

CONCLUSIONS

Ang-2 and sTie-2 could participate in the pathogenesis of GD and potentially be used as markers of GO activity. Antithyroid drugs affect the angiogenic pattern in GD.

Bench-to-bedside review: Angiopoietin signalling in critical illness - a future target?

Multiple organ dysfunction syndrome (MODS) occurs in response to major insults such as sepsis, severe haemorrhage, trauma, major surgery and pancreatitis. The mortality rate is high despite intensive supportive care. The pathophysiological mechanism underlying MODS are not entirely clear, although several have been proposed. Overwhelming inflammation, immunoparesis, occult oxygen debt and other mechanisms have been investigated, and – despite many unanswered questions – therapies targeting these mechanisms have been developed. Unfortunately, only a few interventions, usually those targeting multiple mechanisms at the same time, have appeared to be beneficial. We clearly need to understand better the mechanisms that underlie MODS. The endothelium certainly plays an active role in MODS. It functions at the intersection of several systems, including inflammation, coagulation, haemodynamics, fluid and electrolyte balance, and cell migration. An important regulator of these systems is the angiopoietin/Tie2 signalling system. In this review we describe this signalling system, giving special attention to what is known about it in critically ill patients and its potential as a target for therapy.

Role of uterine natural killer cells in angiogenesis of human decidua of the first-trimester pregnancy

Decidualization is accompanied by extensive angiogenesis, which is an essential step in the maturation of new blood vessels in mammalian pregnancy. The purpose of this study was to determine a distribution of uNK cells (CD56(+) uNK or CD56(bright) cells) in human decidua of the first-trimester pregnancy, and investigate whether uNK cells in human decidua could express vascular endothelial growth factor (VEGF-A) and/or angiopoietin2 (Ang2). Our immunohistochemical staining results demonstrated that a great amount of uNK (CD56(+)) cells scattered throughout the decidual stroma and near endometrial gland and spiral vessels in human decidua. The protein expression of VEGF-A and Ang2 was detected in decidual stroma cells, capillary endothelial cells and glandular cells in tissue specimens. There was a positive correlation between microvessel density (MVD) and the number of the CD56-positive uNK cells in decidual stroma, and also between the number of the CD56-positive uNK cells and VEGF-A protein expression in the tissue. In addition, we found that uNK cells in human decidua could express VEGF-A mRNA, but not Ang2 mRNA, in isolated uNK cells in human decidua of the first-trimester gestation by combination of LCM and Nested-PCR. Our study indicated that uNK cells, through expressing VEGF-A, may play an important role in the angiogenic response at the time of human decidualization and early placenta development.

Chemotherapy agents and hypertension: a focus on angiogenesis blockade

Two observations highlight the importance of this review. The first observation is that high blood pressure is the most frequent comorbid condition in cancer registries which directly affects the prognosis of the patient. The second observation is that long-term cancer survivors now have a higher risk of cardiovascular disease than of recurrent cancer, and hypertension contributes to this risk. New approaches to cancer chemotherapy disrupt angiogenesis; subjects receiving these agents often have an associated increase in blood pressure. In this article we concentrate on observations published over the past 2 years in this rapidly developing field, outline putative mechanisms and time frames for these prohypertensive effects, and conclude with some management recommendations based on current knowledge.

Downregulation of angiopoietin-1 and Tie2 in chronic hypoxic pulmonary hypertension

BACKGROUND

Angiopoietins, newly discovered vascular-specific growth factors, and vascular endothelial growth factors (VEGF) play distinct and complementary roles in angiogenesis and vascular maturation. However, the exact roles of angiogenic factors in the adult pulmonary vasculature remain unclear.

OBJECTIVE

To elucidate possible roles of angiopoietins and VEGF in the development of hypoxic pulmonary hypertension (PH), changes in the expression of angiogenic factors were examined.

METHODS

The cellular distribution and expression of angiopoietins and their receptor Tie2 and VEGF were investigated by RT-PCR, immunoblot, and immunohistochemical methods in rat lung under normal and hypoxic conditions.

RESULTS

During the development of PH with vascular remodeling characterized by a decrease in vessel density of intrapulmonary arteries, protein expression of angiopoietin-1 (Ang-1), Tie2, and VEGF significantly decreased in the pulmonary arteries, and Tie2 receptor was inactivated in the lung. The expression of angiopoietin-3 (Ang-3), an endogenous antagonist of Ang-1, significantly increased in the intima under hypoxic conditions.

CONCLUSIONS

Since both Ang-1/Tie2 and VEGF promote angiogenesis and vascular survival, and play protective roles in the adaptation of microvascular changes during the onset of PH, the downregulation of both Ang-1/Tie2 and VEGF and upregulation of Ang-3 appear to be associated with vascular rarefaction and the development of hypoxic PH.

Angiopoietin modulation of vascular endothelial growth factor: Effects on retinal endothelial cell permeability

PURPOSE

Vascular permeability is important at many sites, but particularly so in diabetic retinopathy where macular oedema is the major cause of blindness. Angiopoietin-2 (Ang-2) and vascular endothelial growth factor (VEGF) are important factors involved in neovascularization and vascular leakage, but there is little data on their interaction to promote increased vascular permeability.

METHODS

Porcine retinal endothelial cells (PREC) were seeded into permeable inserts and cultured in 24-well plates that permit measurement of permeability using fluorescent dextrans. Cell purity was assessed immunohistochemically. At confluency, PREC were treated with increasing concentrations of VEGF (20-100ng/ml) and Ang-2 (15-75ng/ml). The effect on tight junctions was assessed by visualization with an anti-ZO-1 antibody.

RESULTS

Immunohistochemistry showed high purity of isolated PREC. Permeability of untreated PREC monolayers was low. The increase in permeability in Ang-2 treated cells (25-30% compared with non-treated cells) was less than that for cells treated with VEGF only (20-100% compared with untreated cells). Highest permeability was seen with a combination of Ang-2 and VEGF (100-400% compared with untreated cells). Permeability increased with time after growth factor application. Preliminary ZO-1 immunohistochemistry appeared to demonstrate the presence of tight junctions between untreated PREC, and loss of tight junctions after treatment with VEGF and Ang-2.

CONCLUSIONS

VEGF alone is twice as potent in interrupting tight junctions in an endothelial cell monolayer as Ang-2. However, both growth factors acting together increase permeability three times as much as VEGF alone. Treatments designed to reduce vascular permeability in diabetic macular oedema should consider that crosstalk between growth factors including VEGF and the Ang-2/Tie-2 system can multiply their effects.

Marrow angiogenesis-associated factors as prognostic biomarkers in patients with acute myelogenous leukaemia

Bone marrow (BM) neoangiogenesis plays an important role in acute myelogenous leukaemia (AML), and depends on the interplay of members of the vascular endothelial growth factor (VEGF) and angiopoietin (Ang) families. We determined the marrow levels of seven molecules associated with angiogenesis in 52 AML patients before chemotherapy and 20 healthy controls: VEGF-A, VEGF/PlGF, VEGF-C, VEGF-D, Ang-1, Ang-2, and Tie-2. All the molecules were quantified using enzyme-linked immunosorbent assay (ELISA). Comparing to normal controls, the marrow levels of VEGF/PlGF, Ang-2, and Tie-2 were significantly higher, and those of VEGF-C and Ang-1 were significantly lower in the AML patients (P<0.001). A total of 31 patients were further subjected to survival analysis. Patients with lower Tie-2 (<26 ng ml⁻¹) and Ang-2 levels (<4500 pg ml⁻¹) displayed a survival advantage (P=0.037 and 0.042, respectively), same as patients with higher VEGF/PlGF (⩾1 pg ml⁻¹) and VEGF-D levels (⩾350 pg ml⁻¹) (P=0.020 and 0.016, respectively). An angio-index ((Ang-2 × Tie-2)/(VEGF/PlGF × VEGF-D)) was established and multivariate Cox regression analysis revealed that patients with higher angio-index values (⩾50) displayed poor prognosis (hazard ratio 5.91, 95% confidence interval 1.99–17.56; P=0.001). The angio-index is closely associated with the clinical outcome of AML patients and may be valuable in disease prognosis.

Angiopoietin-1 production in islets improves islet engraftment and protects islets from cytokine-induced apoptosis

Successful islet transplantation depends on the infusion of sufficiently large quantities of islets, but only a small fraction of implanted islets become engrafted. The underlying mechanisms remain elusive. To probe the mechanism of islet revascularization, we determined the effect of angiopoietin-1 (Ang-1), a proangiogenic and antiapoptotic factor, on the survival, function, and revascularization of transplanted islets using a syngeneic model. Islets were transduced with adenoviruses expressing Ang-1 or control LacZ, followed by transplantation under the renal capsule. Diabetic mice receiving a marginal mass of 150 islets pretransduced with Ang-1 vector exhibited near normoglycemia posttransplantation. In contrast, diabetic mice receiving an equivalent islet mass pretransduced with control vector remained hyperglycemic. At 30 days posttransplantation, mice were killed and islet grafts retrieved for immunohistochemistry. Islet grafts with elevated Ang-1 production retained significantly increased microvascular density, improved glucose profiles, and increased glucose-stimulated insulin release. Cultured islets expressing Ang-1 displayed improved viability and enhanced glucose-stimulated insulin secretion in the presence of cytokines. In contrast, control islets exhibited increased apoptosis and diminished glucose-stimulated insulin release in response to cytokine treatment. These results indicate that Ang-1 confers a cytoprotective effect on islets, enhancing islet engraftment and preserving functional islet mass in transplants.

Angiopoietin-2 is increased in severe sepsis: correlation with inflammatory mediators

OBJECTIVE

Angiopoietin (Ang)-2 is an endothelium-specific growth factor, regulated by proinflammatory stimuli, that destabilizes vascular endothelium and increases vascular leakage; consequently, Ang-2 may contribute to sepsis pathophysiology. We have studied 1) serum Ang-2 levels in critically-ill patients and investigated potential relationships with inflammatory mediators and indices of disease severity and 2) the effect of sepsis-related inflammatory mediators on Ang-2 production by lung endothelium in vitro.

DESIGN

Prospective clinical study followed by cell culture studies.

SETTING

General intensive care unit and research laboratory of a university hospital.

SUBJECTS

Human and bovine lung microvascular endothelial cells and 61 patients (32 men). Patients were grouped according to their septic stage as having: no systemic inflammatory response syndrome (n = 6), systemic inflammatory response syndrome (n = 8), sepsis (n = 16), severe sepsis (n = 18), and septic shock (n = 13).

INTERVENTIONS

Cells were exposed to lipopolysaccharide, tumor necrosis factor-alpha, and interleukin-6.

MEASUREMENTS AND MAIN RESULTS

Patients' serum Ang-2 levels were significantly increased in severe sepsis as compared with patients with no systemic inflammatory response syndrome or sepsis (p < .05 by analysis of variance). Positive linear relationships were observed with: serum tumor necrosis factor-alpha (rs = 0.654, p < .001), serum interleukin-6 (rs = 0.464, p < .001), Acute Physiology and Chronic Health Evaluation II score (rs = 0.387, p < .001), and Sequential Organ Failure Assessment score (rs = 0.428, p < .001). Multiple regression analysis revealed that serum Ang-2 is mostly related to serum tumor necrosis factor-alpha and severe sepsis. Treatment of human lung microvascular endothelial cells with all mediators resulted in a concentration-dependent Ang-2 reduction. Treatment of bovine lung microvascular endothelial cells with lipopolysaccharide and tumor necrosis factor-alpha increased Ang-2 release, and interleukin-6 reduced basal Ang-2 levels.

CONCLUSIONS

First, patients' serum Ang-2 levels are increased during severe sepsis and associated with disease severity. The strong relationship of serum Ang-2 with serum tumor necrosis factor-alpha suggests that the latter may participate in the regulation of Ang-2 production in sepsis. Second, inflammatory mediators reduce Ang-2 release from human lung microvascular endothelial cells, implying that this vascular bed may not be the source of increased Ang-2 in human sepsis.

Immunohistochemical detection of platelet-derived endothelial cell growth factor/thymidine phosphorylase and angiopoietins in ameloblastic tumors

BACKGROUND

To evaluate the roles of angiogenic factors in the development and progression of odontogenic tumors, expression of platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) and of angiopoietins in ameloblastic tumors as well as in tooth germs.

METHODS

Tissue specimens of 11 tooth germs, 44 ameloblastomas, and five malignant ameloblastic tumors were examined immunohistochemically with the use of antibodies against PD-ECGF/TP and angiopoietin-1 and -2.

RESULTS

Immunohistochemical reactivity for PD-ECGF/TP was detected in mesenchymal cells in tooth germs and stromal cells in ameloblastic tumors, and the level of immunoreactivity for PD-ECGF/TP was significantly higher in ameloblastomas than in tooth germs. Granular cell ameloblastomas showed PD-ECGF/TP reactivity in granular neoplastic cells as well as in stromal cells. Immunoreactivity for angiopoietin-1 and -2 was detected predominantly in odontogenic epithelial cells near the basement membrane in tooth germs and in benign and malignant ameloblastic tumors. Malignant ameloblastic tumors had decreased angiopoietin-1 reactivity and ameloblastic carcinomas had increased angiopoietin-2 reactivity as compared with the respective levels in tooth germs and ameloblastomas. Immunohistochemical reactivity for angiopoietin-2 was slightly higher in follicular ameloblastomas than in plexiform ameloblastomas.

CONCLUSION

Expression of PD-ECGF/TP and angiopoietin-1 and -2 in tooth germs and ameloblastic tumors suggests that these angiogenic factors participate in tooth development and odontogenic tumor progression by regulating angiogenesis. Altered expression of PD-ECGF/TP and angiopoietins in ameloblastic tumors may be involved in oncogenesis, malignant potential, and tumor cell differentiation.

Angiogenesis - understanding the mathematical challenge

Biological mathematics is based on the development of mathematical descriptions of biological systems and behaviour. We are interested in developing mathematical models of capillary sprouting, and have adopted a novel approach to our modelling, in that the mathematics is based on the biochemistry underpinning cell behaviour. By considering the crucial steps of the angiogenic process, and through an understanding of the biochemistry involved, we successfully developed a preliminary model of angiogenesis. More importantly, our approach is applicable to many other areas of biological research. As mathematics remains a mystery to the majority of life scientists, we have aimed to describe our mathematical modelling strategy in biological terms. The assumptions and simplifications that form the basis of the modelling are explained, pinpointing the manner in which the different biological processes are linked via the mathematics. Examples of simulations using the mathematical model are shown, highlighting the success of our approach.

Regulation of Ang2 release by PTEN/PI3-kinase/Akt in lung microvascular endothelial cells

Angiopoietin-2 (Ang2) is a Tie-2 ligand that destabilizes vascular structures, allowing for neovascularization or vessel regression depending on local vascular endothelial cell growth factor (VEGF) concentrations. Although various stimuli have been shown to affect Ang2 expression, information on the underlying mechanisms involved in Ang2 production in endothelial cells (EC) is just beginning to emerge. In the present study, we have used adenovirus-mediated gene transfer and pharmacological inhibitors to examine the role of the PTEN/PI3-K/Akt pathway on Ang2 release. Inhibition of PI3-kinase with wortmannin led to a stimulation of basal Ang2 release in EC, while overexpression of an active form of Akt reduced Ang2. In addition, adenovirus-mediated gene transfer of the phosphatase PTEN stimulated Ang2 release. Incubation of the cells with Ang1, an agent that activates the PI3-K/Akt pathway in EC, reduced Ang2 release. This effect of Ang1 could be prevented by wortmannin and LY-294002 pretreatment. Similarly, in VEGF-treated EC the increase in Ang2 production observed was greater in the presence of a PI3-K inhibitor. Our observations that PTEN acts as a positive modulator of Ang2 release, while activation of the PI3-K/Akt pathway downregulates Ang2, reveal an additional mechanism through which the PTEN/PI3-K/Akt pathway could affect the angiogenic process.

Signaling and functions of angiopoietin-1 in vascular protection

Angiopoietin-1 (Ang1) has powerful vascular protective effects: suppressing plasma leakage, inhibiting vascular inflammation, and preventing endothelial death. Preclinical studies indicate that Ang1 may be therapeutically useful in a number of situations, including treatment of edema, endotoxemia, and transplant arteriosclerosis. However, the ligand has also been implicated in vessel remodeling, induction of angiogenesis and pulmonary hypertension, indicating that strategies to minimize any deleterious effects while optimizing vessel protection are likely to be needed. This review surveys the published data on vascular protective effects of Ang1 and highlights the therapeutic potential of this ligand, as well as possible limitations to its use. We also consider the data on Ang1 receptors and speculate on how to maximize therapeutic benefit by targeting the Tie receptors.

Angiopoietin-2 levels are elevated in exudative pleural effusions

OBJECTIVE

To examine the pleural fluid (PF) and serum levels of angiopoietin (Ang)-1, Ang-2, and vascular endothelial growth factor (VEGF) in patients with pleural effusions (PEs).

METHODS

One hundred fifteen patients, 16 with transudative PEs due to heart failure and 99 with exudative PEs (malignant, 40; para-pneumonic, 24; tuberculous, 13; miscellaneous etiologies, 22) were included in the study. PF and serum levels of the growth factors were measured using enzyme-linked immunosorbent assay.

RESULTS

PF Ang-2 and VEGF levels but not Ang-1 levels were higher (p < 0.001) in exudates than in transudates. PF Ang-2 levels were higher in tuberculous PEs than in PEs of any other etiology and were lower in heart failure PEs than in PEs of any other etiology. The highest PF VEGF levels were observed in patients with malignant and parapneumonic PEs. The lowest PF VEGF levels were observed in patients with transudates. In PEs, Ang-2 levels correlate with VEGF levels (p < 0.001), RBC count (p = 0.002), nucleated cell count (p < 0.001), total protein levels (p < 0.001), and lactate dehydrogenase levels (p < 0.001). PF Ang-1 levels were lower than serum Ang-1 levels both in patients with exudates (p < 0.001) and in those with transudates (p = 0.001). PF Ang-2 levels were higher than serum Ang-2 levels both in patients with exudates (p < 0.001) and in those with transudates (p = 0.045). PF VEGF levels were higher than serum VEGF levels in patients with malignant PEs (p < 0.001) and parapneumonic PEs (p = 0.003), but lower than serum VEGF levels in heart failure PEs (p < 0.001). In patients with tuberculous PEs and exudative PEs of miscellaneous etiology, PF and serum VEGF levels did not differ significantly.

CONCLUSION

Ang-2 levels but not Ang-1 levels are elevated in exudative PEs, and they correlate with levels of VEGF and markers of pleural inflammation. It is thus possible that Ang-2 along with VEGF participate in pleural inflammation and the pathogenesis of exudative PEs.

Mutant Tie2 causing venous malformation signals through Shc

Tie2 is a receptor tyrosine kinase expressed predominantly in endothelial cells. A missense mutation in the intracellular domain of Tie2 resulting in an arginine to tryptophan substitution causes an inherited form of vascular dysmorphogenesis, venous malformation (VM). The signalling pathways activated by mutant Tie2 and responsible for formation and maintenance of the abnormal vessels in VM are not known. In this study, we have sought to define these pathways by identifying phosphoproteins interacting with mutant Tie2 expressed in endothelial cells. We find R849W Tie2 is constitutively active in endothelium and recruits and phosphorylates a 52 kDa protein. This protein is identified as p52 ShcA. We show endothelial cells expressing VM-mutant Tie2 are protected from cell death and expression of dominant-negative ShcA inhibits the anti-apoptotic activity of the mutant receptor. Suppression of this pro-survival signalling could be a therapeutic option for inducing regression of lesional vessels.

Differential expression of VEGF-A and angiopoietins in cartilage tumors and regulation by interleukin-1β

BACKGROUND

Vascular endothelial growth factor (VEGF)-A and angiopoietin (Ang)-1 and Ang-2 are key factors in angiogenic signaling. In this study the expression of these factors was identified in cartilage tumors. As interleukin (IL)-1beta has been found to be an indispensable factor in angiogenic signaling, we further analyzed the effect of IL-1beta on the expression of VEGF-A, Ang-1, and Ang-2 using a previously established cell culture model.

METHODS

Surgical specimens of enchondromas, conventional chondrosarcomas, and dedifferentiated chondrosarcomas were obtained from 72 patients. VEGF-A, Ang-1, and Ang-2 mRNA expression was detected by conventional and quantitative reverse transcription polymerase chain reaction (PCR). VEGF-A expression was also detected by immunohistochemistry or Western blot.

RESULTS

Differential expression of VEGF-A, Ang-1, and Ang-2 was clearly demonstrated in cartilage tumors. VEGF-A expression was positively correlated with the tumor type. Higher VEGF-A expression levels were detected in conventional chondrosarcomas Grades II and III (using a 3-tier grading system) than in dedifferentiated chondrosarcomas (P < .05). A typical pattern of VEGF-A isoforms was identified, including VEGF(121), VEGF(145), VEGF(165), and VEGF(189). Ang-1 presented as a low-level transcript with slightly elevated levels in chondrosarcomas (P < .05). Highly variable Ang-2 expression levels were detected in solitary cases of conventional chondrosarcomas. IL-1beta regulated VEGF-A and Ang-1 expressions in a dose-dependent manner. Whereas low IL-1beta concentrations increased VEGF-A and Ang-1 transcription, high IL-1beta concentrations had the opposite effect. IL-1beta did not activate Ang-2 expression.

CONCLUSIONS

Angiogenic signaling in cartilage tumors is variable and at least partly regulable by IL-1beta. The findings are of therapeutic relevance, either as a desired effect or a side effect in medical treatment.

Adipocyte-derived angiopoietin-1 supports neurite outgrowth and synaptogenesis of sensory neurons

Sensory and sympathetic innervation of the white fat tissue (WAT) contributes to lipolysis. In addition, both fiber types adapt in density to weight gain and loss. Because these findings are indicative for a tight control of nerve fiber plasticity by adipokines, we tested whether adipocytes control neurite growth of sensory neurons through angiopoietin-1 (Ang-1). We further considered initial hints that Ang-1-induced neuritogenesis involves transactivation of the high-affinity nerve growth factor (NGF) receptor trkA. Coculturing dorsal root ganglion (DRG) cells with 3T3-L1 adipocytes supported neurite outgrowth. These neurotrophic effects were associated with the increased expression of Ang-1 (presumably in adipocytes) as well as of trkA. The effects were abolished upon inactivating Ang-1 in culture with selective antibodies. Likewise, neurite outgrowth was impaired in the presence of inactivating NGF antibodies as well as upon inhibition of the NGF high-affinity trkA receptor with the antagonist K252a, indicating a tight cooperation of Ang-1 and NGF in the control of neuritogenesis. DRG-adipipocyte cocultures were further used to establish whether sensory neurons would form synaptic contacts with adipocytes. Electron microscopy demonstrated that cultured sensory neurons develop predominantly neuroneuronal synapses but seem to affect adipocytes by synapses en passant. Comparably to the case for neuritogenesis, expression of the presynaptic protein synaptophysin as well of the postsynaptic protein PSD-95 correlated with Ang-1 levels in culture. It is concluded that adipocyte-secreted Ang-1 supports neurite outgrowth, which is involved in synaptogenesis. The novel function of Ang-1 appears to play a physiological role in WAT plasticity.

Diagnostic and prognostic value of angiogenesis-modulating genes in malignant thyroid neoplasms

BACKGROUND

Angiogenesis is an essential biologic event in the pathogenesis of human malignancies. We postulated that expression analysis of genes that modulate angiogenesis would identify differentially expressed genes that would help to distinguish benign from malignant thyroid neoplasms and serve as markers of aggressive differentiated thyroid cancer.

METHODS

A complementary DNA (cDNA) array with 96 genes that modulate angiogenesis was used to identify differentially expressed genes (2-fold higher or lower) in malignant versus benign thyroid neoplasms. Real-time quantitative polymerase chain reaction was used to confirm cDNA array expression data in 123 patients (4 normal thyroid, 26 hyperplastic nodules, 27 follicular adenomas, 23 follicular cancers, 18 follicular variant of papillary cancers, 25 papillary cancers).

RESULTS

Twenty-two genes were upregulated in malignant thyroid neoplasms by cDNA array analysis, but only 13 genes had higher messenger RNA (mRNA) expression levels in malignant than in benign thyroid neoplasms by real-time quantitative polymerase chain reaction (P < or = .04). Of the 13 differentially expressed genes, the combined use of angiopoietin 2 (ANGPT2) and tissue inhibitor of metalloproteinase 1 (TIMP1) mRNA expression levels was best for distinguishing malignant from benign thyroid neoplasms, with a sensitivity of 90%, specificity of 85%, positive predictive value of 75%, and negative predictive value of 94%. Epidermal growth factor receptor and ephrin B2 mRNA expression was elevated in higher TNM stage neoplasms and in patients with high-risk AMES (Age, distant Metastasis, Extrathyroidal invasion, and tumor Size) differentiated thyroid cancers (P < or = .005).

CONCLUSIONS

Angiopoietin 2 and tissue inhibitor of metalloproteinase 1 are diagnostic markers of malignant thyroid nodules and could improve the diagnostic accuracy of FNA biopsy. Epidermal growth factor receptor and ephrin B2 are markers of aggressive differentiated thyroid cancer.

Angiopoietin-2 stimulates migration of endothelial progenitors and their interaction with endothelium

The factors controlling recruitment of endogenous and transplanted endothelial progenitor cells (EPC) to areas of neovascularization are largely unknown. In this study, we have examined the possibility that EPC migration and adhesion could be regulated by angiopoietin-2 (Ang2), a soluble ligand expressed by endothelial cells at sites of vessel remodelling and angiogenesis. We show for the first time that Ang2 causes a marked stimulation of EPC migration. This was specific for EPC as the ligand failed to affect endothelial cell migration. Ang2-stimulated EPC migration was inhibited by soluble Tie2 ectodomain. Furthermore, the ligand stimulated adhesion between EPC and endothelial monolayers.

Abnormal angiopoietins 1&2, angiopoietin receptor Tie-2 and vascular endothelial growth factor levels in hypertension: relationship to target organ damage [a sub-study of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT)]

BACKGROUND

The increased risk of target organ damage (TOD) in hypertension may be related to a prothrombotic or hypercoagulable state, with abnormalities in platelet activation. Altered angiogenesis, possibly related to increased plasma vascular endothelial growth factor (VEGF) is also a feature of hypertension. We hypothesized a link between altered angiogenesis and TOD in hypertension. Accordingly, the angiogenic growth factors VEGF, angiopoietin 1 and 2 (Ang 1 & 2) and soluble angiopoietin receptor Tie-2 in plasma and in platelets were assessed in terms of the presence or absence of hypertensive TOD.

METHODS

We studied 199 patients (75% men; mean age 68 years) with hypertension. Of these, 125 had evidence of hypertensive TOD (stroke, previous myocardial infarction, angina, left ventricular hypertrophy and mild renal failure). Patients were compared with 74 healthy normotensive controls (69% men; mean age 68 years). Plasma VEGF, Ang 1 & 2 and Tie-2, and total platelet levels of VEGF and Ang-1 (obtained by lysing a known number of platelets with 0.5% Tween) were measured by an enzyme-linked immunosorbent assay.

RESULTS

Hypertensive patients had higher levels of plasma VEGF, Ang-1, Ang-2, Tie-2 and platelet VEGF (all P<or=0.01), but not platelet Ang-1, when compared with normotensive controls. Patients with TOD had higher levels of platelet VEGF and Ang-1 (both P<0.001), and plasma Ang-1 (P<0.001). Amongst the hypertensives, plasma levels of VEGF correlated significantly with Ang-1, Ang-2, Tie-2 and platelet VEGF, whilst platelet VEGF correlated strongly with plasma levels of VEGF and Ang-1 (all P<0.05).

CONCLUSION

Patients with hypertension have evidence of changes in plasma angiogenic growth factors that correlate with the platelet levels of these molecules. Platelets may be involved in the abnormal angiogenesis seen in hypertension.

Increased angiopoietin2 expression is associated with endothelial apoptosis and blood-brain barrier breakdown

Normal intracerebral and pial vessels show constitutive expression of angiopoietin (Ang) 1 in endothelium while weak Ang2 immunoreactivity is present in occasional vessels. In the early phase postinjury, blood-brain barrier (BBB) breakdown at the lesion site is associated with decreased endothelial Ang1 and increased Ang2 expression, raising the possibility that Ang2 may have a role in early BBB breakdown. In order to determine whether Ang2 can cause BBB breakdown, the effect of recombinant Ang2 on cerebrovascular permeability to horseradish peroxidase (HRP) was studied in normal rat cortex. As hypothesized, Ang2 produced significant BBB breakdown to HRP as compared with vehicle-injected control rats. Since Ang2 is reported to have proapoptotic activity, the possibility that Ang2 may be associated with endothelial apoptosis was investigated in the rat cortical cold injury model over a period of 6 h to 6 days postinjury. Perilesion and pial vessels showed evidence of endothelial apoptosis as demonstrated by active Caspase-3 localization and TUNEL staining. Dual labeling for Ang proteins and active Caspase-3 demonstrated endothelial colocalization of Ang2 with active caspase-3. These data suggest that following injury, Ang2 may play a role in BBB breakdown of perilesional vessels, and it may also be a factor in endothelial cell apoptosis that occurs at days 1 and 2 following the injury.

The dynamic roles of angiopoietins in tumor angiogenesis

Angiopoietin (Ang)-1 and -2, and mouse Ang-3/human Ang-4 are ligands of the receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie)-2. It is well established that the Ang–Tie-2 pathway is involved in tumor angiogenesis. However, the exact effects of angiopoietins on tumor angiogenesis are under debate. Experimental and clinical studies have demonstrated that increased expression of Ang-1 and -2 promotes or inhibits tumor angiogenesis, and correlates with a reduced or extended survival time of patients, and with a declined or improved clinical outcome. In general, these studies suggest that Ang-1 is a proangiogenic factor that promotes endothelial cell survival and tumor angiogenesis, especially in the presence of vascular endothelial growth factor; whereas Ang-2 destabilizes vasculature that leads to the initiation of angiogenesis or apoptosis of endothelial cells/vessel regression in the presence or absence of vascular endothelial growth factor, respectively, and that the cell-surface tethered Ang-3 displays antiangiogenic activity. Together, these results suggest that the Ang–Tie-2 functional axis is an attractive target for antiangiogenesis-based cancer therapy.

Gene expression analysis of Tek/Tie2 signaling

The elaboration of the vasculature during embryonic development involves restructuring of the early vessels into a more complex vascular network. Of particular importance to this vascular remodeling process is the requirement of the Tek/Tie2 receptor tyrosine kinase. Mouse gene-targeting studies have shown that the Tie2-deficient embryos succumb to embryonic death at midgestation due to insufficient sprouting and remodeling of the primary capillary plexus. To identify the underlying genetic mechanisms regulating the process of vascular remodeling, transcriptomes modulated by Tie2 signaling were analyzed utilizing serial analysis of gene expression (SAGE). Two libraries were constructed and sequenced using embryonic day 8.5 yolk sac tissues from Tie2 wild-type and the Tie2-null littermates. After tag extraction, 45,689 and 45,275 SAGE tags were obtained for the Tie2 wild-type and Tie2-null libraries, respectively, yielding a total of 21,376 distinct tags. Close to 62% of the tags were uniquely annotated, whereas 10% of the total tags were unknown. Using semiquantitative PCR, the differential expression of eight genes was confirmed that included Elk3, an important angiogenic switch gene which was upregulated in the absence of Tie2 signaling. The results of this study provide valuable insight into the potential association between Tie2 signaling and other known angiogenic pathways as well as genes that might have novel functions in vascular remodeling.

Role of Fibrinogen-Like Protein 2 Prothrombinase/Fibroleukin in Experimental and Human Allograft Rejection

Immune coagulation is a major contributor to the pathogenesis of xenograft rejection, viral-induced hepatocellular injury and cytokine-induced fetal loss syndrome. In this study, we investigated the contribution of the novel gene product, fibrinogen-like protein 2 (fgl2) prothrombinase, in mediating immune injury in experimental and human acute allograft rejection. Using a mouse heterotopic cardiac transplant model, mouse fgl2(mfgl2)/fibroleukin mRNA transcripts and protein were highly expressed in macrophages, CD4- and CD8-positive T lymphocytes, and endothelial cells in rejecting cardiac allografts in association with deposits of fibrin. Although mfgl2-deficient mice rejected allografts at similar rates to littermate controls, survival of grafts from mfgl2-deficient mice were prolonged and deposition of intravascular fibrin was diminished. Treatment of wild-type mice with a neutralizing anti-fgl2 Ab ameliorated histological evidence for allorejection and intravascular fibrin deposition, and resulted in an increase in graft survival. To address further the relevance of fgl2 in acute allograft rejection, we examined kidney biopsies from patients who had undergone renal transplantation. Human fgl2 mRNA transcripts and protein were markedly expressed mainly in renal tubule cells, infiltrating lymphoid cells including macrophages, CD8(+) T cells, mature B cells (plasma cells), and endothelial cells. Dual staining showed fibrin deposition was localized mainly to blood vessels, in the glomerulus and interstitium and the lumen of tubules, and occurred in association with human fgl2 expression. These data collectively suggest that fgl2 accounts for the fibrin deposition seen in both experimental and human allograft rejection and provide a rationale for targeting fgl2 as adjunctive therapy to treat allograft rejection.

Local delivery of angiopoietin-2 into the preovulatory follicle terminates the menstrual cycle in rhesus monkeys

The angiopoietin (ANGPT)-receptor (TEK) system plays a crucial role in blood vessel formation and stability. Because the endogenous agonist ANGPT1, antagonist ANGPT2, and TEK are expressed in the primate ovary, experiments were designed to investigate their role at a critical time during tissue remodeling/ angiogenesis in the menstrual cycle (i.e., at midcycle during maturation, ovulation, and luteinization of the dominant follicle). Either vehicle, 20 microg of ANGPT1, 2 microg of ANGPT2 (low-dose), or 20 microg of ANGPT2 (high-dose) was injected directly into the preovulatory follicle of monkeys around the day (-1 to 0) of the midcycle estradiol (E2)/LH peak. Ovaries were evaluated on Day 3 postinjection for follicle rupture, and serum samples were analyzed for levels of E2 and progesterone. Similar to controls, ANGPT1 treatment was followed by ovulation, and elevated progesterone levels during the luteal phase. In contrast, high-dose ANGPT2 treatment prevented follicle rupture, and progesterone levels never rose above baseline in the subsequent 12 days. However, an E2 peak typically occurred 12 days postinjection. Laparoscopy detected a preovulatory follicle on the contralateral (noninjected) ovary. Progesterone levels subsequently increased above baseline in these animals. Thus, exogenous ANGPT2 disrupted maturation of the preovulatory follicle, preventing its ovulation and conversion into the corpus luteum. ANGPT antagonism eliminated the dominant structure, thereby resetting the ovarian cycle, with selection and maturation of the next preovulatory follicle occurring in a timely manner. The data are consistent with a critical role of the ANGPT-TIE1/TEK system in the ovary, notably at the late stages of follicle maturation during the menstrual cycle.

Protective role of angiopoietin-1 in endotoxic shock

BACKGROUND

Angiopoietin-1 (Ang1) plays an essential role in embryonic vasculature development, protects the adult peripheral vasculature from leakage, and has antiinflammatory properties. Because endotoxin-induced shock is a condition with microvascular leakage resulting from inflammation, we examined the potential therapeutic benefit of Ang1 in a murine model of lipopolysaccharide (LPS)-induced endotoxic shock.

METHODS AND RESULTS

To induce endotoxic shock, LPS was injected intraperitoneally into C57BL/6 mice. Half of the mice received an intravenous application of 1.0x10(9) plaque-forming units of an adenoviral construct expressing human Ang1 (AdhAng1); in the other half an identical vector expressing green fluorescent protein (AdGFP) was injected as a control. In the AdhAng1-treated mice, hepatic transfection and high expression of circulating Ang1 protein were observed. Whereas in LPS-treated control mice, hemodynamic function was severely depressed 12 hours after LPS injection (decrease of blood pressure from 91+/-3 to 49+/-7 mm Hg, dP/dt(max) from 7284+/-550 to 2699+/-233 mm Hg/s, cardiac output from 11.3+/-1.2 to 2.8+/-0.8 mL/min; P<0.0005), in LPS-treated AdhAng1 mice blood pressure fell only to 76+/-3 mm Hg, dP/dt(max) to 5091+/-489 mm Hg/s, and cardiac output to 6.7+/-1.4 mL/min (P<0.05). This resistance to LPS-induced hemodynamic changes was reflected by an improved Kaplan-Meier survival rate of the AdhAng1 mice. Histological analysis revealed that lung injury after LPS injection was markedly attenuated in AdhAng1 mice. In addition, LPS-induced increase in lung water content and pulmonary myeloperoxidase activity was significantly reduced. Furthermore, LPS-induced increases in the expression level of vascular cell adhesion molecule-1, intracellular adhesion molecule-1, and E-selectin protein in the lungs were markedly lower in AdhAng1 mice than in control mice. Finally, in the mice overexpressing Ang1, pulmonary endothelial NO synthase (eNOS) expression and activity remained preserved after LPS challenge, providing evidence that the beneficial effect of Ang1 in endotoxic shock is mediated by eNOS-derived NO.

CONCLUSIONS

Our study demonstrates an improved mortality rate in mice with endotoxic shock pretreated with an adenoviral construct encoding Ang1. The enhanced survival rate induced by Ang1 was accompanied by an improvement in hemodynamic function, reduced lung injury, a lower expression of inflammatory adhesion molecules, and preserved eNOS activity in the lung tissue. Ang1 may therefore have utility as an adjunctive agent for the treatment of septic shock condition.

A mathematical model of tumour angiogenesis, regulated by vascular endothelial growth factor and the angiopoietins

Angiogenesis--the growth of new blood vessels from existing ones--is a prerequisite for the growth of solid tumours beyond a diameter of approximately 2 mm. In recent years, the angiopoietins have emerged as important regulators of angiogenesis. They mediate a delicate balance between vascular quiescence, regression and new growth, but their mechanism of action is not fully understood. This work attempts to provide a mathematical description of the role of the angiopoietins in angiogenesis. The model is formulated within the framework of reinforced random walks, which allows easy transition between the continuum (macroscopic) and discrete (microscopic) forms. Model predictions are in qualitative agreement with experimental observations, and may have implications for anti-cancer therapies based on the prevention of angiogenesis.

Antiangiogenic gene therapy of cancer: recent developments

With the role of angiogenesis in tumor growth and progression firmly established, considerable effort has been directed to antiangiogenic therapy as a new modality to treat human cancers. Antiangiogenic agents have recently received much widespread attention but strategies for their optimal use are still being developed. Gene therapy represents an attractive alternative to recombinant protein administration for several reasons. This review evaluates the potential advantages of gene transfer for antiangiogenic cancer therapy and describes preclinical gene transfer work with endogenous angiogenesis inhibitors demonstrating the feasibility of effectively suppressing and even eradicating tumors in animal models. Additionally, we describe the advantages and disadvantages of currently available gene transfer vectors and update novel developments in this field. In conclusion, gene therapy holds great promise in advancing antiangiogenesis as an effective cancer therapy and will undoubtedly be evaluated in human clinical trials in the near future.