intraluminal-drug-delivery-to-mouse-arteriovenous-fistula

Intraluminal Drug Delivery to the Mouse Arteriovenous Fistula Endothelium

Delivery of therapeutic agents to enhance arteriovenous fistula (AVF) maturation can be administered either via intraluminal or external routes. The ...

patch-angioplasty-in-the-rat-aorta-or-inferior-vena-cava

Patch Angioplasty in the Rat Aorta or Inferior Vena Cava

Pericardial patches are commonly used in vascular surgery to close vessels. To facilitate studies of the neointimal hyperplasia that forms on the patch, ...

Yale University

First Affiliated Hospital of Zhengzhou University

Basic Medical College of Zhengzhou University

VA Connecticut Healthcare Systems, West Haven, CT

Several models of arteriovenous fistula (AVF) have excellent patency and help in understanding the mechanisms of venous adaptation to the arterial environment. However, these models fail to exhibit either maturation failure or fail to develop stenoses, both of which are critical modes of AVF failure in human patients. We used high-resolution Doppler ultrasound to serially follow mice with AVFs created by direct 25-gauge needle puncture. By day 21, 75% of AVFs dilate, thicken, and increase flow, i.e., mature, and 25% fail due to immediate thrombosis or maturation failure. Mature AVF thicken due to increased amounts of smooth muscle cells. By day 42, 67% of mature AVFs remain patent, but 33% of AVFs fail due to perianastomotic thickening. These results show that the mouse aortocaval model has an easily detectable maturation phase in the first 21 days followed by a potential failure phase in the subsequent 21 days. This model is the first animal model of AVF to show a course that recapitulates aspects of human AVF maturation.

The mouse aortocaval fistula recapitulates human arteriovenous fistula maturation.

The venous limb of arteriovenous fistulae (AVF) adapts to the arterial environment by dilation and wall thickening; however, the temporal regulation of the expression of extracellular matrix (ECM) components in the venous limb of the maturing AVF has not been well characterized. We used a murine model of AVF maturation that recapitulates human AVF maturation to determine the temporal pattern of expression of these ECM components.

Temporal regulation of venous extracellular matrix components during arteriovenous fistula maturation.

Vein bypass is an essential therapy for patients with advanced peripheral and coronary artery disease despite development of neointimal hyperplasia. We have shown that stimulation of the receptor tyrosine kinase ephrin type-B receptor 4 (Eph-B4) with its ligand ephrin-B2 prevents neointimal hyperplasia in murine vein grafts. This study determines whether Eph-B4 in adult human veins is capable of phosphorylation and activation of downstream signaling pathways, as well as functional to release nitric oxide (NO) and prevent neointimal hyperplasia in vitro.

Ephrin type-B receptor 4 activation reduces neointimal hyperplasia in human saphenous vein in vitro.

Pretreatment with antibiotics is commonly performed before surgical implantation of prosthetic materials. We previously showed that pericardial patches are infiltrated by macrophages and arterial stem cells after implantation into an artery. We hypothesized that antibiotic pretreatment would diminish the number of cells infiltrating into the patch, potentially affecting early neointimal formation.

Pretreatment of pericardial patches with antibiotics does not alter patch healing in vivo.

Laminar shear stress (SS) induces an antiproliferative and anti-inflammatory endothelial phenotype and increases Klf2 expression. We altered the diameter of an arteriovenous fistula (AVF) in the mouse model to determine whether increased fistula diameter produces disturbed SS in vivo and if acutely increased disturbed SS results in decreased Klf2 expression. The mouse aortocaval fistula model was performed with 22, 25, or 28 gauge needles to puncture the aorta and the inferior vena cava. Duplex ultrasound was used to examine the AVF and its arterial inflow and venous outflow, and SS was calculated. Arterial samples were examined with western blot, immunohistochemistry, and immunofluorescence analysis for proteins and qPCR for RNA. Mice with larger diameter fistulae had diminished survival but increased AVF patency. Increased SS magnitudes and range of frequencies were directly proportional to the needle diameter in the arterial limb proximal to the fistula but not in the venous limb distal to the fistula, with 22-gauge needles producing the most disturbed SS in vivo. Klf2 mRNA and protein expression was diminished in the artery proximal to the fistula in proportion to increasing SS. Increased fistula diameter produces increased SS magnitude and frequency, consistent with disturbed SS in vivo. Disturbed SS is associated with decreased mRNA and protein expression of Klf2. Disturbed SS and reduced Klf2 expression near the fistula are potential therapeutic targets to improve AVF maturation.

Disturbed shear stress reduces Klf2 expression in arterial-venous fistulae in vivo.

Vein graft adaptation is characterized by loss of expression of the tyrosine kinase receptor Eph-B4, the embryonic determinant of venous identity, without increased expression of its ligand ephrin-B2, the embryonic determinant of arterial identity. Endothelial nitric oxide synthase (eNOS) is an important mediator of vessel remodeling. We hypothesized that the mechanism of action of Eph-B4 during vein graft adaptation might be through regulation of downstream eNOS activity.

Eph-B4 mediates vein graft adaptation by regulation of endothelial nitric oxide synthase.

We hypothesized that delivery of mesenchymal stem cells (MSCs) in a biomimetic collagen scaffold improves wound healing in a diabetic mouse model.

Delivery of mesenchymal stem cells in biomimetic engineered scaffolds promotes healing of diabetic ulcers.

Vascular diseases span diverse pathology, but frequently arise from aberrant signaling attributed to specific membrane-associated molecules, particularly the Eph-ephrin family. Originally recognized as markers of embryonic vessel identity, Eph receptors and their membrane-associated ligands, ephrins, are now known to have a range of vital functions in vascular physiology. Interactions of Ephs with ephrins at cell-to-cell interfaces promote a variety of cellular responses such as repulsion, adhesion, attraction, and migration, and frequently occur during organ development, including vessel formation. Elaborate coordination of Eph- and ephrin-related signaling among different cell populations is required for proper formation of the embryonic vessel network. There is growing evidence supporting the idea that Eph and ephrin proteins also have postnatal interactions with a number of other membrane-associated signal transduction pathways, coordinating translation of environmental signals into cells. This article provides an overview of membrane-bound signaling mechanisms that define vascular identity in both the embryo and the adult, focusing on Eph- and ephrin-related signaling. We also discuss the role and clinical significance of this signaling system in normal organ development, neoplasms, and vascular pathologies.

Membrane-mediated regulation of vascular identity.

Pericardial patches are commonly used during cardiovascular surgery to close blood vessels. In arteries, patches accumulate arterial progenitor cells; we hypothesized that venous patches would accumulate venous progenitor cells, in the absence of arterial pressure. We developed a novel rat inferior vena cava (IVC) venotomy model and repaired it with a pericardial patch. Cells infiltrated the patch to form a thick neointima by day 7; some cells were CD34(+)/VEGFR2(+) and CD31(+)/Eph-B4(+) consistent with development of venous identity in the healing patch. Compared to arterial patches, the venous patches had increased neointimal thickness at day 7 without any pseudoaneurysms. Addition of an arteriovenous fistula (AVF) to increase blood flow on the patch resulted in reduced patch neointimal thickness and proliferation, but neointimal thickness was not reversible with AVF ligation. These results show that rat patch venoplasty is a novel model of aggressive venous neointimal hyperplasia.

Pericardial patch venoplasty heals via attraction of venous progenitor cells.

Prosthetic grafts and patches are commonly used in cardiovascular surgery, however neointimal hyperplasia remains a significant concern, especially under low flow conditions. We hypothesized that delivery of rapamycin from nanoparticles (NP) covalently attached to patches allows sustained site-specific delivery of therapeutic agents targeted to inhibit localized neointimal hyperplasia. NP were covalently linked to pericardial patches using EDC/NHS chemistry and could deliver at least 360 ng rapamycin per patch without detectable rapamycin in serum; nanoparticles were detectable in the liver, kidney and spleen but no other sites within 24 hours. In a rat venous patch angioplasty model, control patches developed robust neointimal hyperplasia on the patch luminal surface characterized by Eph-B4-positive endothelium and underlying SMC and infiltrating cells such as macrophages and leukocytes. Patches delivering rapamycin developed less neointimal hyperplasia, less smooth muscle cell proliferation, and had fewer infiltrating cells but retained endothelialization. NP covalently linked to pericardial patches are a novel composite delivery system that allows sustained site-specific delivery of therapeutics; NP delivering rapamycin inhibit patch neointimal hyperplasia. NP linked to patches may represent a next generation of tissue engineered cardiovascular implants.

Covalent modification of pericardial patches for sustained rapamycin delivery inhibits venous neointimal hyperplasia.

The poor clinical results that are frequently reported for arteriovenous fistulae (AVF) for hemodialysis are typically due to failure of AVF maturation. We hypothesized that early AVF maturation is associated with generation of reactive oxygen species and activation of the HIF-1 pathway, potentially promoting neointimal hyperplasia. We tested this hypothesis using a previously reported mouse AVF model that recapitulates human AVF maturation.

Hualong Bai

Department of Surgery and the Vascular Biology and Therapeutics Program,
Department of Surgery,
Vascular Biology and Therapeutics Program

Yale University

Intraluminal Drug Delivery to the Mouse Arteriovenous Fistula Endothelium

Patch Angioplasty in the Rat Aorta or Inferior Vena Cava

Hualong Bai

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Surgery and the Vascular Biology and Therapeutics Program,Department of Surgery,Vascular Biology and Therapeutics Program

Yale University

Intraluminal Drug Delivery to the Mouse Arteriovenous Fistula Endothelium

Patch Angioplasty in the Rat Aorta or Inferior Vena Cava

Department of Surgery and the Vascular Biology and Therapeutics Program,
Department of Surgery,
Vascular Biology and Therapeutics Program