In vivo nanoparticle assessment of pathological endothelium predicts the development of inflow stenosis in murine arteriovenous fistula

The rodent models of arteriovenous fistula

Arteriovenous fistulas (AVFs) have long been used as dialysis access in patients with end-stage renal disease; however, their maturation and long-term patency still fall short of clinical needs. Rodent models are irreplaceable to facilitate the study of mechanisms and provide reliable insights into clinical problems. The ideal rodent AVF model recapitulates the major features and pathology of human disease as closely as possible, and pre-induction of the uremic milieu is an important addition to AVF failure studies. Herein, we review different surgical methods used so far to create AVF in rodents, including surgical suturing, needle puncture, and the cuff technique. We also summarize commonly used evaluations after AVF placement. The aim was to provide recent advances and ideas for better selection and induction of rodent AVF models. At the same time, further improvements in the models and a deeper understanding of AVF failure mechanisms are expected.

Relationship between vascular cell adhesion molecule-1 (VCAM-1), soluble receptor for advanced glycation end products (sRAGE) and functional hemodynamic parameters of arteriovenous fistula

BACKGROUND

The preferred vascular access for hemodialysis is represented by arteriovenous fistula (AVF) due to fewer complications and more prolonged survival. Considerable efforts have been made to identify biomarkers associated with AVF dysfunction, but results are conflicting. Vascular cell adhesion molecule (VCAM-1) and advanced glycation end products are involved in atherogenesis, vascular calcification, peripheral artery disease, and neointimal hyperplasia in renal and non-renal patients. The objective of this study was to evaluate whether there is an association between VCAM-1, soluble receptor for advanced glycation end products (sRAGE), NcarboxymethylLysine (CML), and arteriovenous fistula dysfunction (AVF).

METHODS

VCAM-1, sRAGE, and CML were performed using the ELISA technique in 88 HD patients. Ultrasound assessment of AVF reports brachial artery blood flow (Qa), brachial resistivity index (RI), presence of calcification, and the diameter. AVF dysfunction was defined as a brachial artery Qa ⩽ 500 ml/min or RI ⩾ 0.5.

RESULTS

The median level of VCAM-1 [2676.5(2206.8-4203.9) versus 2613.2(1885.7-3161.8), p 0.026] was significantly higher in patients with AVF dysfunction compared to the rest of the patients. sRAGE and CML were higher in this group but without statistical significance. In patients with AVF dysfunction, significant positive correlations were found between VCAM-1and sRAGE (r = 0.417, p = 0.001), RI (r = 0.313, p = 0.046), dialysis vintage (r = 0.540, p < 0.001), AVF vintage (r = 0.336, p = 0.032), intima-media thickness (r = 0.423, p = 0.006) and C-reactive protein (r = 0.315, p = 0.045). VCAM-1 correlated inversely with cholesterol (r = -0.312, p = 0.047), triglycerides (r = -0.358, p = 0.021), body mass index (r = -0.388, p = 0.012). In multivariate regression analysis, VCAM-1 (p = 0.013) and sRAGE (p = 0.01) remained significant predictors of RI and Qa. Logistic regression disclosed calcification, VCAM-1, as risks factors for AVF dysfunction.

CONCLUSION

The results we obtained showed that patients with AVF dysfunction had a significantly higher level of VCAM-l. A positive correlation between VCAM-1 and sRAGE was identified in this group.

Atorvastatin Reduces In Vivo Fibrin Deposition and Macrophage Accumulation, and Improves Primary Patency Duration and Maturation of Murine Arteriovenous Fistula

BACKGROUND

Arteriovenous fistulas placed surgically for dialysis vascular access have a high primary failure rate resulting from excessive inward remodeling, medial fibrosis, and thrombosis. No clinically established pharmacologic or perisurgical therapies currently address this unmet need. Statins' induction of multiple anti-inflammatory and antithrombotic effects suggests that these drugs might reduce arteriovenous fistula failure. Yet, the in vivo physiologic and molecular effects of statins on fistula patency and maturation remain poorly understood.

METHODS

We randomized 108 C57Bl/6J mice to receive daily atorvastatin 1.14 mg/kg or PBS (control) starting 7 days before end-to-side carotid artery-jugular vein fistula creation and for up to 42 days after fistula creation. We then assessed longitudinally the effects of statin therapy on primary murine fistula patency and maturation. We concomitantly analyzed the in vivo arteriovenous fistula thrombogenic and inflammatory macrophage response to statin therapy, using the fibrin-targeted, near-infrared fluorescence molecular imaging agent FTP11-CyAm7 and dextranated, macrophage-avid nanoparticles CLIO-VT680.

RESULTS

In vivo molecular-structural imaging demonstrated that atorvastatin significantly reduced fibrin deposition at day 7 and macrophage accumulation at days 7 and 14, findings supported by histopathologic and gene-expression analyses. Structurally, atorvastatin promoted favorable venous limb outward remodeling, preserved arteriovenous fistula blood flow, and prolonged primary arteriovenous fistula patency through day 42 (P<0.05 versus control for all measures).

CONCLUSIONS

These findings provide new in vivo evidence that statins improve experimental arteriovenous fistula patency and maturation, indicating that additional clinical evaluation of statin therapy in patients on dialysis undergoing arteriovenous fistula placement is warranted.

Atheroma Susceptible to Thrombosis Exhibit Impaired Endothelial Permeability In Vivo as Assessed by Nanoparticle-Based Fluorescence Molecular Imaging

BACKGROUND

The role of local alterations in endothelial functional integrity in atherosclerosis remains incompletely understood. This study used nanoparticle-enhanced optical molecular imaging to probe in vivo mechanisms involving impaired endothelial barrier function in experimental atherothrombosis.

METHODS AND RESULTS

Atherosclerosis was induced in rabbits (n=31) using aortic balloon injury and high-cholesterol diet. Rabbits received ultrasmall superparamagnetic iron oxide nanoparticles (CLIO) derivatized with a near-infrared fluorophore (CyAm7) 24 hours before near-infrared fluorescence imaging. Rabbits were then either euthanized (n=9) or underwent a pharmacological triggering protocol to induce thrombosis (n=22). CLIO-CyAm7 nanoparticles accumulated in areas of atheroma (P<0.05 versus reference areas). On near-infrared fluorescence microscopy, CLIO-CyAm7 primarily deposited in the superficial intima within plaque macrophages, endothelial cells, and smooth muscle cells. Nanoparticle-positive areas further exhibited impaired endothelial barrier function as illuminated by Evans blue leakage. Deeper nanoparticle deposition occurred in areas of plaque neovascularization. In rabbits subject to pharmacological triggering, plaques that thrombosed exhibited significantly higher CLIO-CyAm7 accumulation compared with nonthrombosed plaques (P<0.05). In thrombosed plaques, nanoparticles accumulated preferentially at the plaque-thrombus interface. Intravascular 2-dimensional near-infrared fluorescence imaging detected nanoparticles in human coronary artery-sized atheroma in vivo (P<0.05 versus reference segments).

CONCLUSIONS

Plaques that exhibit impaired in vivo endothelial permeability in cell-rich areas are susceptible to subsequent thrombosis. Molecular imaging of nanoparticle deposition may help to identify biologically high-risk atheroma.

Patient-Specific, Multi-Scale Modeling of Neointimal Hyperplasia in Vein Grafts

Neointimal hyperplasia is amongst the major causes of failure of bypass grafts. The disease progression varies from patient to patient due to a range of different factors. In this paper, a mathematical model will be used to understand neointimal hyperplasia in individual patients, combining information from biological experiments and patient-specific data to analyze some aspects of the disease, particularly with regard to mechanical stimuli due to shear stresses on the vessel wall. By combining a biochemical model of cell growth and a patient-specific computational fluid dynamics analysis of blood flow in the lumen, remodeling of the blood vessel is studied by means of a novel computational framework. The framework was used to analyze two vein graft bypasses from one patient: a femoro-popliteal and a femoro-distal bypass. The remodeling of the vessel wall and analysis of the flow for each case was then compared to clinical data and discussed as a potential tool for a better understanding of the disease. Simulation results from this first computational approach showed an overall agreement on the locations of hyperplasia in these patients and demonstrated the potential of using new integrative modeling tools to understand disease progression.

Imaging the pharmacology of nanomaterials by intravital microscopy: Toward understanding their biological behavior

Therapeutic nanoparticles (NPs) can deliver cytotoxic chemotherapeutics and other drugs more safely and efficiently to patients; furthermore, selective delivery to target tissues can theoretically be accomplished actively through coating NPs with molecular ligands, and passively through exploiting physiological "enhanced permeability and retention" features. However, clinical trial results have been mixed in showing improved efficacy with drug nanoencapsulation, largely due to heterogeneous NP accumulation at target sites across patients. Thus, a clear need exists to better understand why many NP strategies fail in vivo and not result in significantly improved tumor uptake or therapeutic response. Multicolor in vivo confocal fluorescence imaging (intravital microscopy; IVM) enables integrated pharmacokinetic and pharmacodynamic (PK/PD) measurement at the single-cell level, and has helped answer key questions regarding the biological mechanisms of in vivo NP behavior. This review summarizes progress to date and also describes useful technical strategies for successful IVM experimentation.

Assessing Large-Vessel Endothelial Permeability Using Near-Infrared Fluorescence Imaging—Brief Report

Objective—

Loss of endothelial barrier function in arterial blood vessels is characteristic of vascular pathologies, including atherosclerosis. Here, we present a near-infrared fluorescence (NIRF) imaging methodology for quantifying endothelial permeability and macromolecular uptake in large arteries in the mouse and evaluate its applicability for studying mechanisms of vascular inflammation.

Approach and Results—

To validate the NIRF methodology, macrovascular inflammation was induced in C57bl/6 mice by local tumor necrosis factor-α stimulation of the carotid artery or in apolipoprotein E–deficient mice by Western diet for 4 weeks. Evans blue dye, serving as plasma protein marker and fluorescent in the near-infrared spectrum, was given intravenously at different doses. Carotids and aorta were excised, and Evans blue dye fluorescence was assessed through whole vessel scan in an infrared imaging system. NIRF correlated to extraction–absorbance methodology for Evans blue dye quantification and was superior at discriminating plasma protein accumulation in tumor necrosis factor-α–stimulated carotids. NIRF allowed for focal quantification of increased arterial wall Evans blue dye uptake in apolipoprotein E–deficient mice. Importantly, NIRF left vessels intact for subsequent histological analysis or quantification of leukocyte subpopulations by flow cytometry.

Conclusions—

The described NIRF methodology provides a sensitive and rapid tool to locate and quantify macromolecular uptake in the wall of arterial blood vessels in vascular pathologies in mice.