Vascularization of the Arteriovenous Loop in a Rat Isolation Chamber Model-Quantification of Hypoxia and Evaluation of Its Effects.

Introduction: The aim of this study was to analyze the three-dimensional distribution of hypoxia in the arteriovenous (AV) loop model in rats, by examining the distribution of hypoxia-inducible factor-1 alpha (HIF-1α).

Materials And Methods: AV loops were created from the femoral artery and vein of male Lewis rats and an interpositional graft from the contralateral femoral vein. This AV fistula was embedded in a fibrin-filled isolation chamber and subcutaneously implanted into the thigh.

Three-dimensional mapping of the arteriovenous loop model using two-dimensional histological methods.

Objectives: The aim of this study was to create an analytical tool for the three-dimensional distribution of immunohistochemically stained cells in the arteriovenous (AV) loop model of the femoral vessels of rats that fuses two-dimensional histological slides into stacks.

Methods: A total of 22 AV loops were implanted into male syngeneic Lewis rats by creating an arteriovenous fistula between the femoral artery and vein by interposing a femoral vein graft of the contralateral extremity. This fistula was embedded into an isolation chamber filled with a fibrin matrix.

In vitro cell response to Co-containing 1,393 bioactive glass.

Cobalt ions are known to stimulate angiogenesis via inducing hypoxic conditions and hence are interesting agents to be used in conjunction with bioactive glasses (BGs) in bone tissue engineering approaches. In this work we investigated in vitro cell biocompatibility of Co releasing 1393 BG composition (in wt.%: 53SiO2, 6Na2O, 12K2O, 5MgO, 20CaO, and 4P2O5) derived scaffolds with osteoblast-like cells (MG-63) and human dermal microvascular endothelial cells (hDMECs).

PHDs inhibitor DMOG promotes the vascularization process in the AV loop by HIF-1a up-regulation and the preliminary discussion on its kinetics in rat.

Background: The Arterovenous Loop (AV Loop) model is a vascularization model in tissue engineering research, which is capable of generating a three dimensional in vivo unit with cells as well as the supporting vessels within an isolation chmaber. In our previous studies the AV loop in the isolation chamber was discovered to undergo hypoxia, characterized by Hypoxia Inducible Factor (HIF) up-regulation. The vascularization followed the increase of HIF-α temporally, while it was spatially positively correlated with the HIF-α level, as well.

Combination of BMP2 and MSCs significantly increases bone formation in the rat arterio-venous loop model.

Introduction: In this study the induction of bone formation in an axially vascularized bone matrix using mesenchymal stem cells (MSCs) and application of bone morphogenetic protein 2 (BMP2) was analyzed in the arteriovenous loop (AVL) model.

Materials And Methods: An AVL was created in the medial thigh of 42 rats and placed in a porous titanium chamber filled with a particulated porous hydroxyapatite and beta-tricalcium phosphate matrix and fibrin. In group A the fibrin was loaded with 5×10(6) DiI-stained fibrin gel-immobilized primary MSCs from syngenic Lewis rats, in group B the matrix was loaded with 60 μg/mL BMP2 and in group C both, BMP2 and MSCs were applied at implantation time point.

A novel early precursor cell population from rat bone marrow promotes angiogenesis in vitro.

Background: Some studies demonstrated therapeutic angiogenesis attributable to the effects of endothelial progenitor cells (EPC), others have reported disappointing results. This may be due to the fact that EPC populations used in these contradictory studies were selected and defined by highly variable and differing experimental protocols. Indeed, the isolation and reliable characterization of ex vivo differentiated EPC raises considerable problems due to the fact there is no biomarker currently available to specifically identify EPC exclusively.

Cancer research by means of tissue engineering--is there a rationale?

Tissue engineering (TE) has evoked new hopes for the cure of organ failure and tissue loss by creating functional substitutes in the laboratory. Besides various innovations in the context of Regenerative Medicine (RM), TE also provided new technology platforms to study mechanisms of angiogenesis and tumour cell growth as well as potentially tumour cell spreading in cancer research. Recent advances in stem cell technology--including embryonic and adult stem cells and induced pluripotent stem cells--clearly show the need to better understand all relevant mechanisms to control cell growth when such techniques will be administered to patients.

Myogenic differentiation of mesenchymal stem cells in a newly developed neurotised AV-loop model.

Generation of axially vascularized muscle tissue constitutes a promising new approach to restoration of damaged muscle tissue. Mesenchymal stemcells (MSC), with their ability to be expanded to large cell numbers without losing their differentiation capacity into the myogenic lineage, could offer a promising cell source to generate neomuscle tissue. In vitro experiments showed that cocultures of primary myoblasts and MSC undergo myogenic differentiation by stimulation with bFGF and dexamethasone.

New aspects on efficient anticoagulation and antiplatelet strategies in sheep.

Background: After addressing fundamental questions in preclinical models in vitro or in small animals in vivo, the translation into large animal models has become a prerequisite before transferring new findings to human medicine. Especially in cardiovascular, orthopaedic and reconstructive surgery, the sheep is an important in vivo model for testing innovative therapies or medical devices prior to clinical application. For a wide variety of sheep model based research projects, an optimal anticoagulation and antiplatelet therapy is mandatory.

Severe soft tissue infection caused by a non-beta-hemolytic Streptococcus pyogenes strain harboring a premature stop mutation in the sagC gene.

We recovered a non-beta-hemolytic Streptococcus pyogenes strain from a severe soft tissue infection. In this isolate, we detected a premature stop codon within the sagC gene of the streptolysin S (SLS) biosynthetic operon. Reintroduction of full-length sagC gene on a plasmid vector restored the beta-hemolytic phenotype to our clinical isolate, indicating that the point mutation in sagC accounted for loss of hemolytic activity.

Guanylate-binding protein 1 expression from embryonal endothelial progenitor cells reduces blood vessel density and cellular apoptosis in an axially vascularised tissue-engineered construct.

Background: Guanylate binding protein-1 (GBP-1) is a large GTPase which is actively secreted by endothelial cells. It is a marker and intracellular inhibitor of endothelial cell proliferation, migration, and invasion. We previously demonstrated that stable expression of GBP-1 in murine endothelial progenitor cells (EPC) induces their premature differentiation and decreases their migration capacity in vitro and in vivo.

Composition of fibrin glues significantly influences axial vascularization and degradation in isolation chamber model.

In this study, different fibrin sealants with varying concentrations of the fibrin components were evaluated in terms of matrix degradation and vascularization in the arteriovenous loop (AVL) model of the rat. An AVL was placed in a Teflon isolation chamber filled with 500 μl fibrin gel. The matrix was composed of commercially available fibrin gels, namely Beriplast (Behring GmbH, Marburg, Germany) (group A), Evicel (Omrix Biopharmaceuticals S.

Three-dimensional vascularization of electrospun PCL/collagen-blend nanofibrous scaffolds in vivo.

Nanofiber scaffolds have proven their various advantages for tissue engineering and have been analyzed extensively. However, to date the three-dimensional pattern of vascularization inside nanofibrous scaffolds is unknown. This study introduces a novel method to visualize and quantify vascularization of electrospun nanofibrous PCL/collagen scaffolds in 3D in vivo.

Engineering axially vascularized bone in the sheep arteriovenous-loop model.

Treatment of complex bone defects in which vascular supply is insufficient is still a challenge. To overcome the limitations from autologous grafts, a sheep model has been established recently, which is characterized by the development of an independent axial vascularization of a bioartificial construct, permitting microsurgical transplantation. To engineer independently axially vascularized bone tissue in the sheep arteriovenous (AV)-loop model, mesenchymal stem cells (MSCs), without and in combination with recombinant human bone morphogenetic protein-2 (rhBMP-2), were harvested and directly autotransplanted in combination with β-tricalcium phosphate-hydroxyapatite (β-TCP-HA) granules into sheep in this study.

Combination of extrinsic and intrinsic pathways significantly accelerates axial vascularization of bioartificial tissues.

Background: In this study, the authors present a modification of the arteriovenous loop model that combines extrinsic and intrinsic vascularization modes to enhance vascularization of bioartificial matrices.

Methods: An arteriovenous loop was created in the medial thighs of 24 rats. The loop was placed in a newly developed titanium chamber, which was fabricated with an electron beam melting facility, and was embedded in a hydroxyapatite/β-tricalcium phosphate/fibrin matrix.

[Report of the consensus workshop on microsurgical training at the 32nd annual meeting of the german-speaking group for microsurgery of the peripheral nerves and vessels in Basel 2010].

After the foundation of a trinational task force to develop quality criteria for a training and educational system in microsurgery at the annual conference of the German-speaking group for microsurgery of the nerves and vessels (DAM) in Erlangen 2009, at the 2010 conference in Basel, a modular educational system was approved and criteria for a basic course were discussed. Before the next annual conference in 2011 these aspects should be clarified and defined in a spring meet-ing.

Hyaluronan-based heparin-incorporated hydrogels for generation of axially vascularized bioartificial bone tissues: in vitro and in vivo evaluation in a PLDLLA-TCP-PCL-composite system.

Smart matrices are required in bone tissue-engineered grafts that provide an optimal environment for cells and retain osteo-inductive factors for sustained biological activity. We hypothesized that a slow-degrading heparin-incorporated hyaluronan (HA) hydrogel can preserve BMP-2; while an arterio-venous (A-V) loop can support axial vascularization to provide nutrition for a bio-artificial bone graft. HA was evaluated for osteoblast growth and BMP-2 release.

De novo generation of an axially vascularized processed bovine cancellous-bone substitute in the sheep arteriovenous-loop model.

Background/aims: The aim of this study was to generate an axially vascularized bone substitute. The arteriovenous (AV)-loop approach in a large-animal model was applied in order to induce axial vascularization in a clinically approved processed bovine cancellous bone (PBCB) matrix of significant volume with primary mechanical stability and to assess the course of increasing axial vascularization.

Methods: PBCB constructs were implanted into 13 merino sheep together with a microsurgically created AV loop in an isolation chamber.

Endothelial progenitor cells are integrated in newly formed capillaries and alter adjacent fibrovascular tissue after subcutaneous implantation in a fibrin matrix.

Vascularization of bioartificial matrices is crucial for successful tissue engineering. Endothelial progenitor cells (EPC) have shown vascularization potential in ischemic conditions and may also support blood vessel formation in tissue-engineered matrices. The aim of our study was to investigate the impact of a well-characterized murine embryonal EPC line (T17b-EPC) on vascularization and fibrovascular granulation tissue formation after suspension in a fibrine matrix followed by subcutaneous implantation in a separation chamber in rats.

Myogenic differentiation of mesenchymal stem cells co-cultured with primary myoblasts.

TE (tissue engineering) of skeletal muscle is a promising method to reconstruct loss of muscle tissue. This study evaluates MSCs (mesenchymal stem cells) as new cell source for this application. As a new approach to differentiate the MSCs towards the myogenic lineage, co-cultivation with primary myoblasts has been developed and the myogenic potential of GFP (green fluorescent protein)-transduced rat MSC co-cultured with primary rat myoblasts was assessed by ICC (immunocytochemistry).

Role of guanylate binding protein-1 in vascular defects associated with chronic inflammatory diseases.

Rheumatic autoimmune disorders are characterized by a sustained pro-inflammatory microenvironment associated with impaired function of endothelial progenitor cells (EPC) and concomitant vascular defects. Guanylate binding protein-1 (GBP-1) is a marker and intracellular regulator of the inhibition of proliferation, migration and invasion of endothelial cells induced by several pro-inflammatory cytokines. In addition, GBP-1 is actively secreted by endothelial cells.

Directly auto-transplanted mesenchymal stem cells induce bone formation in a ceramic bone substitute in an ectopic sheep model.

Bone tissue engineering approaches increasingly focus on the use of mesenchymal stem cells (MSC). In most animal transplantation models MSC are isolated and expanded before auto cell transplantation which might be critical for clinical application in the future. Hence this study compares the potential of directly auto-transplanted versus in vitro expanded MSC with or without bone morphogenetic protein-2 (BMP-2) to induce bone formation in a large volume ceramic bone substitute in the sheep model.

Automatic quantitative micro-computed tomography evaluation of angiogenesis in an axially vascularized tissue-engineered bone construct.

Introduction: We invented an automatic observer-independent quantitative method to analyze vascularization using micro-computed tomography (CT) along with three-dimensional (3D) reconstruction in a tissue engineering model.

Materials And Methods: An arteriovenous loop was created in the medial thigh of 30 rats and was placed in a particulated porous hydroxyapatite and beta-tricalcium phosphate matrix, filled with fibrin (10 mg/mL fibrinogen and 2 IU/mL thrombin) without (group A) or with (group B) application of fibrin-gel-immobilized angiogenetic growth factors vascular endothelial growth factor (VEGF¹⁶⁵) and basic fibroblast growth factor (bFGF). The explantation intervals were 2, 4, and 8 weeks.

Development of a regulatable oncolytic herpes simplex virus type 1 recombinant virus for tumor therapy.

Oncolytic viruses are genetically modified viruses that preferentially replicate in host cancer cells, leading to the production of new viruses and, ultimately, cell death. Currently, no oncolytic viruses that are able to kill only tumor cells while leaving normal cells intact are available. Using T-REx (Invitrogen, Carlsbad, CA) gene switch technology and a self-cleaving ribozyme, we have constructed a novel oncolytic HSV-1 recombinant, KTR27, whose replication can be tightly controlled and regulated by tetracycline in a dose-dependent manner.