Zoledronate alters natural progression of tissue-engineered vascular grafts.

Macrophages are a critical driver of neovessel formation in tissue-engineered vascular grafts (TEVGs), but also contribute to graft stenosis, a leading clinical trial complication. Macrophage depletion via liposomal delivery of clodronate, a first-generation bisphosphonate, mitigates stenosis, but simultaneously leads to a complete lack of tissue development in TEVGs. This result and the associated difficulty of utilizing liposomal delivery means that clodronate may not be an ideal means of preventing graft stenosis. Newer generation bisphosphonates, such as zoledronate, may have differential effects on graft development with more facile drug delivery. We sought to examine the effect of zoledronate on TEVG neotissue formation and its potential application for mitigating TEVG stenosis. Thus, mice implanted with TEVGs received zoledronate or no treatment and were monitored by serial ultrasound for graft dilation and stenosis. After two weeks, TEVGs were explanted for histological examination. The overall graft area and remaining graft material (polyglycolic-acid) were higher in the zoledronate treatment group. These effects were associated with a corresponding decrease in macrophage infiltration. In addition, zoledronate affected the deposition of collagen in TEVGs, specifically, total and mature collagen. These differences may be, in part, explained by a depletion of leukocytes within the bone marrow that subsequently led to a decrease in the number of tissue-infiltrating macrophages. TEVGs from zoledronate-treated mice demonstrated a significantly greater degree of smooth muscle cell presence. There was no statistical difference in graft patency between treatment and control groups. While zoledronate led to a decrease in the number of macrophages in the TEVGs, the severity of stenosis appears to have increased significantly. Zoledronate treatment demonstrates that the process of smooth muscle cell-mediated neointimal hyperplasia may occur separately from a macrophage-mediated mechanism.

VEGF and angiopoietins promote inflammatory cell recruitment and mature blood vessel formation in murine sponge/Matrigel model.

A key feature in the induction of pathological angiogenesis is that inflammation precedes and accompanies the formation of neovessels as evidenced by increased vascular permeability and the recruitment of inflammatory cells. Previously, we and other groups have shown that selected growth factors, namely vascular endothelial growth factor (VEGF) and angiopoietins (Ang1 and Ang2) do not only promote angiogenesis, but can also induce inflammatory response. Herein, given a pro-inflammatory environment, we addressed the individual capacity of VEGF and angiopoietins to promote the formation of mature neovessels and to identify the different types of inflammatory cells accompanying the angiogenic process over time. Sterilized polyvinyl alcohol (PVA) sponges soaked in growth factor-depleted Matrigel mixed with PBS, VEGF, Ang1, or Ang2 (200 ng/200 µl) were subcutaneously inserted into anesthetized mice. Sponges were removed at day 4, 7, 14, or 21 post-procedure for histological, immunohistological (IHC), and flow cytometry analyses. As compared to PBS-treated sponges, the three growth factors promoted the recruitment of inflammatory cells, mainly neutrophils and macrophages, and to a lesser extent, T- and B-cells. In addition, they were more potent and more rapid in the recruitment of endothelial cells (ECs) and in the formation and maturation (ensheating of smooth muscle cells around ECs) of neovessels. Thus, the autocrine/paracrine interaction among the different inflammatory cells in combination with VEGF, Ang1, or Ang2 provides a suitable microenvironment for the formation and maturation of blood vessels.

Formation of microvascular networks: role of stromal interactions directing angiogenic growth.

In the adult, angiogenesis leads to an expanded microvascular network as new vessel segments are added to an existing microcirculation. Necessarily, growing neovessels must navigate through tissue stroma as they locate and grow toward other vessel elements. We have a growing body of evidence demonstrating that angiogenic neovessels reciprocally interact with the interstitial matrix of the stroma resulting in directed neovascular growth during angiogenesis. Given the compliance and the viscoelastic properties of collagen, neovessel guidance by the stroma is likely due to compressive strain transverse to the direction of primary tensile forces present during active tissue deformation. Similar stromal strains control the final network topology of the new microcirculation, including the distribution of arterioles, capillaries, and venules. In this case, stromal-derived stimuli must be present during the post-angiogenesis remodeling and maturation phases of neovascularization to have this effect. Interestingly, the preexisting organization of vessels prior to the start of angiogenesis has no lasting influence on the final, new network architecture. Combined, the evidence describes interplay between angiogenic neovessels and stroma that is important in directed neovessel growth and invasion. This dynamic is also likely a mechanism by which global tissue forces influence vascular form and function.

Surgical removal of submacular choroidal neovessels in children: Outcome and literature review.

PURPOSE: To report on the outcome of surgical submacular choroidal neovascular membrane (CNV) removal in children and to perform a comprehensive review of literature concerning this intervention in children. METHODS: In this retrospective, noncomparative, interventional case series, we included 8 eyes of 7 consecutive children with subfoveal choroidal neovascularization treated by pars plana vitrectomy (PPV) and CNV removal. Main outcome measures were visual acuity and complications. RESULTS: Mean age at surgery was 8.6 ± 5.2 years (range: 2-16). Two out of 8 eyes were idiopathic. Corrected-distance visual acuity (CDVA) improved from 1.01 ± 0.45logMAR (range:0.3-1.5) at presentation to 0.60 ± 0.37 (range:0-1) at last follow-up (p = 0.03). Mean follow-up was 3.9 ± 3.9 years. Six eyes received at least one intravitreal injection of bevacizumab prior to surgery. Recurrence occurred in one eye with Best's disease.Literature review revealed a total of 42 cases with the most frequent etiologies being Presumed ocular histoplasmosis syndrome (POHS) and idiopathic CNV. Considering all cases together, mean CDVA improved from 1.00 ± 0.37logMAR to 0.52 ± 0.42 (p < 0.01). CNV recurrence occurred in 11 eyes (22.0%), 7 of which had an inflammatory etiology. Other complications included pigment epithelium tear, atrophy and retinal tear. CONCLUSION: Surgical removal of CNV is a viable, effective and safe option in children with persistent submacular neovascular membranes.

The Evaluation of Neovessel Angiogenesis Behavior at Tissue Interfaces.

Angiogenesis, the formation of new vessel elements from existing vessels, is important in homeostasis and tissue repair. Dysfunctional angiogenesis can contribute to numerous pathologies, including cancer, ischemia, and chronic wounds. In many instances, growing vessels must navigate along or across tissue-associated boundaries and interfaces tissue interfaces. To understand this dynamic, we developed a new model for studying angiogenesis at tissue interfaces utilizing intact microvessel fragments isolated from adipose tissue. Isolated microvessels retain their native structural and cellular complexity. When embedded in a 3D matrix, microvessels, sprout, grow, and connect to form a neovasculature. Here, we discuss and describe methodology for one application of our microvessel-based angiogenesis model, studying neovessel behavior at tissue interfaces.

In vivo development of tissue engineered vascular grafts: a fluid-solid-growth model.

Methods of tissue engineering continue to advance, and multiple clinical trials are underway evaluating tissue engineered vascular grafts (TEVGs). Whereas initial concerns focused on suture retention and burst pressure, there is now a pressing need to design grafts to have optimal performance, including an ability to grow and remodel in response to changing hemodynamic loads. Toward this end, there is similarly a need for computational methods that can describe and predict the evolution of TEVG geometry, composition, and material properties while accounting for changes in hemodynamics. Although the ultimate goal is a fluid-solid-growth (FSG) model incorporating fully 3D growth and remodeling and 3D hemodynamics, lower fidelity models having high computational efficiency promise to play important roles, especially in the design of candidate grafts. We introduce here an efficient FSG model of in vivo development of a TEVG based on two simplifying concepts: mechanobiologically equilibrated growth and remodeling of the graft and an embedded control volume analysis of the hemodynamics. Illustrative simulations for a model Fontan conduit reveal the utility of this approach, which promises to be particularly useful in initial design considerations involving formal methods of optimization which otherwise add considerably to the computational expense.

Influence of γ-Radiation on Mechanical Stability to Cyclic Loads Tubular Elastic Matrix of the Aorta.

A significant drawback of the rigid synthetic vascular prostheses used in the clinic is the mechanical mismatch between the implant and the prosthetic vessel. When placing prostheses with radial elasticity, in which this deficiency is compensated, the integration of the graft occurs more favorably, so that signs of cell differentiation appear in the prosthesis capsule, which contributes to the restoration of vascular tone and the possibility of vasomotor reactions. Aortic prostheses fabricated by electrospinning from a blend of copolymers of vinylidene fluoride with hexafluoropropylene (VDF/HFP) had a biomechanical behavior comparable to the native aorta. In the present study, to ensure mechanical stability in the conditions of a living organism, the fabricated blood vessel prostheses (BVP) were cross-linked with γ-radiation. An optimal absorbed dose of 0.3 MGy was determined. The obtained samples were implanted into the infrarenal aorta of laboratory animals-Landrace pigs. Histological studies have shown that the connective capsule that forms around the prosthesis has signs of high tissue organization. This is evidenced by the cells of the fibroblast series located in layers oriented along and across the prosthesis, similar to the orientation of cells in a biological arterial vessel.

Quantifying Vascular Density in Tissue Engineered Constructs Using Machine Learning.

Given the considerable research efforts in understanding and manipulating the vasculature in tissue health and function, making effective measurements of vascular density is critical for a variety of biomedical applications. However, because the vasculature is a heterogeneous collection of vessel segments, arranged in a complex three-dimensional architecture, which is dynamic in form and function, it is difficult to effectively measure. Here, we developed a semi-automated method that leverages machine learning to identify and quantify vascular metrics in an angiogenesis model imaged with different modalities. This software, BioSegment, is designed to make high throughput vascular density measurements of fluorescent or phase contrast images. Furthermore, the rapidity of assessments makes it an ideal tool for incorporation in tissue manufacturing workflows, where engineered tissue constructs may require frequent monitoring, to ensure that vascular growth benchmarks are met.

[Multimodal imaging in atypical choroidal nevus]. / Imagerie multimodale d'un nævus choroïdien atypique.

Choroidal nevi are frequent, asymptomatic, usually easy-to-diagnose lesions. They can cause macular syndrome in patients with choridal degeneration or neovascularization. In doubtful cases, the combination of different diagnostic means, such as clinical examination, ultrasound, fluorescein angiography and indocyanine green (ICG) can help to correct the diagnosis. We here report the case of a female patient with atypical choroidal lesion, in whom multimodal imaging allowed to retain the diagnosis of achromic choroidal nevus complicated by choroidal neovascularization.

Stromal Cells Promote Neovascular Invasion Across Tissue Interfaces.

Vascular connectivity between adjacent vessel beds within and between tissue compartments is essential to any successful neovascularization process. To establish new connections, growing neovessels must locate other vascular elements during angiogenesis, often crossing matrix and other tissue-associated boundaries and interfaces. How growing neovessels traverse any tissue interface, whether part of the native tissue structure or secondary to a regenerative procedure (e.g., an implant), is not known. In this study, we developed an experimental model of angiogenesis wherein growing neovessels must interact with a 3D interstitial collagen matrix interface that separates two distinct tissue compartments. Using this model, we determined that matrix interfaces act as a barrier to neovessel growth, deflecting growing neovessels parallel to the interface. Computational modeling of the neovessel/matrix biomechanical interactions at the interface demonstrated that differences in collagen fibril density near and at the interface are the likely mechanism of deflection, while fibril alignment guides deflected neovessels along the interface. Interestingly, stromal cells facilitated neovessel interface crossing during angiogenesis via a vascular endothelial growth factor (VEGF)-A dependent process. However, ubiquitous addition of VEGF-A in the absence of stromal cells did not promote interface invasion. Therefore, our findings demonstrate that vascularization of a tissue via angiogenesis involves stromal cells providing positional cues to the growing neovasculature and provides insight into how a microvasculature is organized within a tissue.

Differential outcomes of venous and arterial tissue engineered vascular grafts highlight the importance of coupling long-term implantation studies with computational modeling.

Electrospinning is commonly used to generate polymeric scaffolds for tissue engineering. Using this approach, we developed a small-diameter tissue engineered vascular graft (TEVG) composed of poly-ε-caprolactone-co-l-lactic acid (PCLA) fibers and longitudinally assessed its performance within both the venous and arterial circulations of immunodeficient (SCID/bg) mice. Based on in vitro analysis demonstrating complete loss of graft strength by 12 weeks, we evaluated neovessel formation in vivo over 6-, 12- and 24-week periods. Mid-term observations indicated physiologic graft function, characterized by 100% patency and luminal matching with adjoining native vessel in both the venous and arterial circulations. An active and robust remodeling process was characterized by a confluent endothelial cell monolayer, macrophage infiltrate, and extracellular matrix deposition and remodeling. Long-term follow-up of venous TEVGs at 24 weeks revealed viable neovessel formation beyond graft degradation when implanted in this high flow, low-pressure environment. Arterial TEVGs experienced catastrophic graft failure due to aneurysmal dilatation and rupture after 14 weeks. Scaffold parameters such as porosity, fiber diameter, and degradation rate informed a previously described computational model of vascular growth and remodeling, and simulations predicted the gross differential performance of the venous and arterial TEVGs over the 24-week time course. Taken together, these results highlight the requirement for in vivo implantation studies to extend past the critical time period of polymer degradation, the importance of differential neotissue deposition relative to the mechanical (pressure) environment, and further support the utility of predictive modeling in the design, use, and evaluation of TEVGs in vivo. STATEMENT OF SIGNIFICANCE: Herein, we apply a biodegradable electrospun vascular graft to the arterial and venous circulations of the mouse and follow recipients beyond the point of polymer degradation. While venous implants formed viable neovessels, arterial grafts experienced catastrophic rupture due to aneurysmal dilation. We then inform a previously developed computational model of tissue engineered vascular graft growth and remodeling with parameters specific to the electrospun scaffolds utilized in this study. Remarkably, model simulations predict the differential performance of the venous and arterial constructs over 24 weeks. We conclude that computational simulations should inform the rational selection of scaffold parameters to fabricate tissue engineered vascular grafts that must be followed in vivo over time courses extending beyond polymer degradation.

Immuno-driven and Mechano-mediated Neotissue Formation in Tissue Engineered Vascular Grafts.

In vivo development of a neovessel from an implanted biodegradable polymeric scaffold depends on a delicate balance between polymer degradation and native matrix deposition. Studies in mice suggest that this balance is dictated by immuno-driven and mechanotransduction-mediated processes, with neotissue increasingly balancing the hemodynamically induced loads as the polymer degrades. Computational models of neovessel development can help delineate relative time-dependent contributions of the immunobiological and mechanobiological processes that determine graft success or failure. In this paper, we compare computational results informed by long-term studies of neovessel development in immuno-compromised and immuno-competent mice. Simulations suggest that an early exuberant inflammatory response can limit subsequent mechano-sensing by synthetic intramural cells and thereby attenuate the desired long-term mechano-mediated production of matrix. Simulations also highlight key inflammatory differences in the two mouse models, which allow grafts in the immuno-compromised mouse to better match the biomechanical properties of the native vessel. Finally, the predicted inflammatory time courses revealed critical periods of graft remodeling. We submit that computational modeling can help uncover mechanisms of observed neovessel development and improve the design of the scaffold or its clinical use.

[Anti-VEGF therapy for juxtafoveolar choroidal neovessels in people with high myopia: about a case]. / Le traitement anti-VEGF des néovaisseaux choroïdiens juxta-fovéolaires du fort myope: à propos d'une observation.

Choroidal neovessels are a threatening complication of high myopia, accounting for 5 to 10% of cases. They require immediate treatment because of their poor prognosis. Anti-VEGF intravitreal injections are currently a new therapeutic alternative far exceeding photodynamic therapy (PDT). Nevertheless, anti-VEGF treatment algorithm for this type of neovessels remains a matter of discussion among the authors. The purpose of this study was to highlight the difficulties in managing these neovessels and to discuss the Anti-VEGF therapeutic regimen to follow.

Accelerated atherogenesis in completely ligated common carotid artery of apolipoprotein E-deficient mice.

Complete ligation of the common carotid artery near its bifurcation induces neointimal formation due to smooth muscle cell proliferation in normolipidemic wild-type mice, but it was unknown what would happen to hyperlipidemic apolipoprotein E-deficient (Apoe-/-) mice. Examination of these mice revealed rapid development of atherosclerotic lesions in completely ligated carotid arteries within 4 weeks. Mice were fed a Western diet, starting 1 week before ligation, or a chow diet. Foam cell lesions formed as early as 1 week after ligation in mice fed the Western diet and 2 weeks in mice fed the chow diet. Fibrous lesions comprised of foam cells and smooth muscle cells and more advance lesions containing neovessels occurred at 2 and 4 weeks after ligation, respectively, in the Western diet group. Lesions were larger and more advanced in the Western diet group than the chow group. Neutrophil infiltration was observed in growing intimal lesions in both diet groups, while CD8+ T cells were found in lesions of chow-fed mice. This study demonstrates that Apoe-/- mice develop the entire spectrum of atherosclerosis in ligated carotid arteries in an accelerated manner and this model could be a valuable tool for investigating the development and therapy of atherosclerosis.

Endoscopic surgery to chronic subdural hematoma with neovessel septation: technical notes and literature review.

OBJECTIVE AND IMPORTANCE: We report Septated Chronic Subdural Hematoma (sCSDH) cases with the neovessel in the hematoma cavity, and evaluate surgical effect of the neuroendoscope-assisted neovessel coagulation for these sCSDH patients. CLINICAL PRESENTATION: Four patients suffered from sCSDH with different clinical symptoms. Magnetic resonance imaging (MRI) was applied to differentiate the neovessel from the bridge vein and septa fibra. Endoscopic surgeries were performed after their admission. TECHNIQUE: Through the small bone window, we used suction to clean the surgical field so that the neovessels can be exposed, which is thought to be the one of recurrence factors for the sCSDH, then we coagulated and cut them under the neuroendoscope. Case examples are described here to illustrate the technique. CONCLUSION: This report illustrates that the neovessel is one of recurrence factors of sCSDH and has special characteristics showed on MRI. Through this technique with the guidance of MRI the recurrence rate of sCSDH can be reduced.

A change in inflammatory footprint precedes plaque instability: a systematic evaluation of cellular aspects of the adaptive immune response in human atherosclerosis.

BACKGROUND: Experimental studies characterize adaptive immune response as a critical factor in the progression and complications of atherosclerosis. Yet, it is unclear whether these observations translate to the human situation. This study systematically evaluates cellular components of the adaptive immune response in a biobank of human aortas covering the full spectrum of atherosclerotic disease. METHODS AND RESULTS: A systematic analysis was performed on 114 well-characterized perirenal aortic specimens with immunostaining for T-cell subsets (CD3/4/8/45RA/45RO/FoxP3) and the Th1/non-Th1/Th17 ratio (CD4(+)T-bet(+)/CD4(+)T-bet(-)/CD4(+)/interleukin-17(+) double staining). CD20 and CD138 were used to identify B cells and plasma cells, while B-cell maturation was evaluated by AID/CD21 staining and expression of lymphoid homeostatic CXCL13. Scattered CD4 and CD8 cells with a T memory subtype were found in normal aorta and early, nonprogressive lesions. The total number of T cells increases in progressive atherosclerotic lesions (≈1:5 CD4/CD8 T-cell ratio). A further increase in medial and adventitial T cells is found upon progression to vulnerable lesions.This critical stage is further hallmarked by de novo formation of adventitial lymphoidlike structures containing B cells and plasma cells, a process accompanied by transient expression of CXCL13. A dramatic reduction of T-cell subsets, disappearance of lymphoid structures, and loss of CXCL13 expression characterize postruptured lesions. FoxP3 and Th17 T cells were minimally present throughout the atherosclerotic process. CONCLUSIONS: Transient CXCL13 expression, restricted presence of B cells in human atherosclerosis, along with formation of nonfunctional extranodal lymphoid structures in the phase preceding plaque rupture, indicates a "critical" change in the inflammatory footprint before and during plaque destabilization.