Topological analysis of the vasculature of angiopoietin-expressing tumours through scale-space tracing

This work describes the topological analysis of the vasculature of tumours. The analysis is performed with a scale-space technique, which traces the centrelines of vessels as topological ridges of the image intensities and then obtains a series of measurements, which are used to compare the vasculatures. Besides the measurements directly associated with the centrelines, the scales obtained allow the estimation of width andthusareacoveredwithvessels. Tumours of SW1222 human colorectal carcinoma xenografts were observed when growing in dorsal skin-fold window chambers in mice. Three variants of the tumours expressing either endogenous levels of angiopoietins (WT) or over-expressing either angiopoietin-1 (Ang-1) or angiopoietin-2 (Ang-2) were assessed with/without vascular targeted therapy. The scale-space technique was able to discriminate between the vasculatures of the three different tumour types prior to treatment. Results also suggested that over-expression of Ang-2 was associated with susceptibility of the tumour vasculature to the vascular disrupting agent, combretastatin A4 phosphate (CA4P). Substantiation of this finding would point to the potential of tumour Ang-2 expression as a predictive bio-marker for response to CA4P

Angiopoietin-1 induces sprouting angiogenesis in vitro

Sprouting of new capillaries from pre-existing blood vessels is a hallmark of angiogenesis during embryonic development and solid tumor growth [1]. In addition to the vascular endothelial growth factor (VEGF) and its receptors, the Tie receptors and their newly identified ligands, the angiopoietins, have been implicated in the control of blood vessel formation [2,3]. Although 'knockouts' of the gene encoding the Tie2 receptor, or its activating ligand angiopoietin-1 (Ang1), result in embryonic lethality in mice due to an absence of remodeling and sprouting of blood vessels [4,5], biological activity in vitro has not yet been described for this receptor-ligand system. In an assay in which a monolayer of endothelial cells were cultured on microcarrier beads and embedded in three-dimensional fibrin gels, recombinant Ang1 (0.5-10 nM) induced the formation of capillary sprouts in a dose-dependent manner that was completely inhibited by soluble Tie2 receptor extracellular domains. In contrast with VEGF, which also induced sprouting of capillaries, Ang1 was only very weakly mitogenic for endothelial cells. Suboptimal concentrations of VEGF and Ang1 acted synergistically to induce sprout formation. Thus, the biological activity of Ang1 in vitro is consistent with the specific phenotype of mice deficient in Tie2 or Ang1. The data suggest that, like in other developmental systems, blood vessel formation requires a hierarchy of master-control genes in which VEGF and angiopoietins, along with their receptors, are amongst the most important regulators

Angiopoietins assemble distinct Tie2 signalling complexes in endothelial cell-cell and cell-matrix contacts

The receptor tyrosine kinase Tie2, and its activating ligand Angiopoietin-1 (Ang1), are required for vascular remodelling and vessel integrity, whereas Ang2 may counteract these functions. However, it is not known how Tie2 transduces these different signals. Here, we show that Ang1 induces unique Tie2 complexes in mobile and confluent endothelial cells. Matrix-bound Ang1 induced cell adhesion, motility and Tie2 activation in cell-matrix contacts that became translocated to the trailing edge in migrating endothelial cells. In contrast, in contacting cells Ang1 induced Tie2 translocation to cell-cell contacts and the formation of homotypic Tie2-Tie2 trans-associated complexes that included the vascular endothelial phosphotyrosine phosphatase, leading to inhibition of paracellular permeability. Distinct signalling proteins were preferentially activated by Tie2 in the cell-matrix and cell-cell contacts, where Ang2 inhibited Ang1-induced Tie2 activation. This novel type of cellular microenvironment-dependent receptor tyrosine kinase activation may explain some of the effects of angiopoietins in angiogenesis and vessel stabilization

Expression of growth mediators in the gingival crevicular fluid of patients with aggressive periodontitis undergoing periodontal surgery

Objectives: To describe changes in growth factor mediators in the gingival crevicular fluid (GCF) of patients with aggressive periodontitis (AgP) undergoing regenerative (GTR) and access flap (AF) surgery. Materials and methods: This was a 12-month, single-blind, split-mouth RCT involving 18 AgP patients with a bilateral intrabony defect which was treated with GTR or AF. GCF was collected prior to surgery and at subsequent follow-up visits from 3 days to 12 months post-operatively, and the levels of angiopoietin-1 (Ang-1), vascular-endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), bone morphogenetic protein-2 (BMP-2), osteoprotegerin (OPG), tissue inhibitor of metalloproteinase 1 (TIMP-1), keratinocyte growth factor (KGF) and platelet-derived growth factor-AB (PDGF-AB) were measured. At baseline, 6 and 12 months post-surgery, periodontal clinical parameters were evaluated. ANOVA was applied to test for differences in the amount of mediators (p < 0.05). Results: Higher amounts of BMP-2 and OPG and a higher area under the curve (AUC) of KGF at the GTR versus AF sites were observed. The maximum change in the amount of KGF correlated significantly with periodontal clinical parameters at the GTR sites at 6 and 12 months. The AUC over 30 days of the amount of Ang-1, VEGF and KGF significantly correlated with periodontal clinical parameters at the AF sites at 6 months. Conclusions: AF and GTR differentially affected the profile of the growth mediators in GCF, and significant correlations between certain GCF mediators and periodontal clinical outcomes were identified. Clinical relevance: GCF components represent attractive prognostic markers for periodontal tissues undergoing repair or regeneration. However, the available evidence is not robust enough to suggest the use of a specific marker, and future adequately powered studies are warranted to identify the most relevant mediators that could be applied in clinical practice