Abstract: OBJECTIVES: The aim of this study is to evaluate a catheter-based porcine model for reperfused myocardial infarction and investigate the appropriate location and duration of the occlusion. MATERIAL AND METHODS: A balloon catheter was placed in the left descending coronary artery (LAD) in 78 swine, and used to occlude the LAD. To evaluate this model, left ventricular ejection fraction (LVEF), infarct size, incidence of ventricular fibrillation (VF), and mortality was compared among three groups: 60-min proximal LAD occlusion (60P), 60-min mid LAD occlusion (60M), and 30-min proximal LAD occlusion (30P). RESULTS: In 72 of the 78 pigs, the procedures were successfully completed. Both mortality and incidence of VF were highest in the 60P group (66.7% and 91.7%, respectively). Myocardial infarction was successfully induced in all 72 animals and in situ double-staining with Evans blue dye and 2,3,5-triphenyltetrazolium chloride was performed to delineate area at risk for ischemia and infarcted myocardium. There was no difference in infarct size, expressed as a percentage of the area at risk, between the 60P and 60M groups (49.5% +/- 3.9% vs. 45.4% +/- 13.3%, respectively). Serial changes in LVEF of the 60M group demonstrated that until 14 days after reperfusion, LVEF improved naturally over time (36.4% +/- 6.6% at 24 hr, and 47.3% +/- 10.1% at 14 days). CONCLUSION: This model and methodology could provide a reproducible and consistent infarct size. The current study demonstrated that 60-min mid LAD occlusion can be the most feasible to serve as a porcine reperfused myocardial infarction model.

Abstract: Human embryonic stem (hES) cells are pluripotent stem cells capable of self-renewal and differentiation into virtually all cell types. Thus, they hold tremendous potential as cell sources for regenerative therapies. The concurrent development of accurate, sensitive, and noninvasive technologies capable of monitoring hES cells engraftment in vivo can greatly expedite basic research prior to future clinical translation. In this study, hES cells were stably transduced with a lentiviral vector carrying a novel double-fusion reporter gene that consists of firefly luciferase and enhanced green fluorescence protein (Fluc-eGFP). Reporter gene expression had no adverse effects on cell viability, proliferation, or differentiation to endothelial cells (hESC-ECs). To compare the two popular imaging modalities, hES cells and hESC-ECs were then co-labeled with superparamagnetic iron oxide (SPIO) particles before transplantation into murine hindlimbs. Longitudinal magnetic resonance (MR) imaging showed persistent MR signals in both cell populations that lasted up to 4 weeks. By contrast, bioluminescence imaging indicated divergent signal patterns for hES cells and hESC-ECs. In particular, hESC-ECs showed significant bioluminescence signals at day 2, which decreased progressively over the following 4 weeks, whereas bioluminescence signals from undifferentiated hES cells increased dramatically during the same period. Postmortem histology and immunohistochemistry confirmed teratoma formation after injection of undifferentiated hES cells, but not hESC-ECs. Taken together, we conclude that reporter gene is a better marker for monitoring cell viability, whereas iron particle labeling is a better marker for high-resolution detection of cell location by MR. Furthermore, transplantation of pre-differentiated rather than undifferentiated hES cells would be more suited for avoiding teratoma formation.

Abstract: BACKGROUND: Percutaneous coronary intervention (PCI) continues to revolutionize the treatment of coronary atherosclerosis and technologic advances require a preclinical coronary stenosis model. The purpose of this study was to systematically evaluate a porcine restenosis model of thermal balloon injury compared to stent overstretching. METHODS: To evaluate this injury model, 22 swine were utilized. For the induction of coronary stenoses, the thermal balloon-to-artery ratio was equal to the range of 1.2-1.3 and was placed at a desired location in the coronary arteries, inflated with 2 atm, and heated to 80 degrees C for 80 seconds. Quantitative coronary angiography was analyzed at baseline, immediately postprocedure, and 4 weeks at harvest. Quantitative coronary ultrasound analysis and histopathologic evaluation were also performed at 4 weeks postprocedure. RESULTS: A total of 54 coronary arteries (thermal balloon injury [Thermo]; n = 43, coronary stenting [Stent]; n = 11) from a total of 18 animals were analyzed for this study. At 4 weeks postprocedure, significantly greater coronary stenoses were observed in the Thermo Group versus the Stent Group (minimum lumen diameter: 1.00 % 0.63 mm vs. 1.58 % 0.44 mm; p = 0.009, % diameter stenosis [DS]: 66.2 +/- 21.6% vs. 48.1 +/- 11.4%; p = 0.02). There were significant linear correlations between the balloon-to-artery ratio, post %DS and %DS at 4 weeks (balloon-to-artery ratio; r = 0.538; p = 0.0012, post %DS; r = -0.744; p < 0.0001, respectively). CONCLCUSION: This methodology may provide reproducible and consistent coronary stenoses. This model can be useful fnot only for the evaluation of medical devices, but also for technical training in PCI and development of coronary imaging technologies.

Abstract: Stem cell therapy may provide an alternative therapeutic option for severe congestive heart failure (CHF). Despite the promise generated by this novel approach, precise in vivo monitoring of the transplanted cells and of subsequent myocardial restoration remains a challenge. The development of a sensitive, noninvasive imaging technology to track stem cells while assessing cardiac function is critical to monitor therapeutic efficacy. In vivo cardiovascular MRI of stem cells is an emerging application to identify, localize, and monitor stem cells while simultaneously evaluating the restoration of the injured myocardium following stem cell therapy. Furthermore, advances in scanner technology, pulse sequence design, and associated hardware have resulted in real-time guidance of catheter-based intervention to deliver cells accurately to the regions of myocardial injury. These capabilities have positioned MRI as the primary comprehensive imaging modality to monitor cell therapy.

Abstract: In vivo MRI of stem cells (SCs) is an emerging application to evaluate the role of cell therapy in restoring the injured myocardium. The high spatial and temporal resolution combined with iron-oxide-based intracellular labeling techniques will provide a sensitive, noninvasive, dual imaging modality for both cells and myocardium. In order to facilitate this novel imaging approach, much effort has been directed towards developing efficient transfection methods. While techniques utilizing poly-L-lysine (PLL), protamine sulfate (PS), and electroporation (ELP) have been proposed, the fundamental biological effects of these methods on mouse embryonic SCs (mESC) have not been investigated systematically. In this study a longitudinal in vitro evaluation of cellular viability, apoptosis, proliferation, and cardiac differentiation of magnetically labeled mESC was conducted. No significant difference was seen in these biological parameters among the three transfection methods. However, cardiac differentiation was most attenuated by ELP, and iron uptake was most effective by PS.

Abstract: BACKGROUND: Treatment of aorto-ostial renal artery stenosis has been associated with a lower procedural success and higher complication and restenosis rate, as compared to nonostial lesions. The design and delivery of currently available stent systems in ostial lesions can result in inaccurate stent positioning and placement leading to stent protrusion into the parent vessel lumen or geographic miss. A novel stent system (SquareOne Inc., Campbell, CA, USA) has been designed specifically for aorto-ostial lesions in the renal artery. This stent system aims to provide both tactile and visual confirmation of the ostium at the aorta, allow for improved accuracy during stent positioning and placement, provide complete scaffolding of the lesion at the aortic junction to the native vessel, and enable future vessel reaccess. METHODS: Stents (n=12) were implanted in both renal arteries of six swine. For histology, two animals were euthanized immediately after stent implantation, and each two animals were then followed up at 2 and 4 weeks, respectively. Intravascular ultrasound (IVUS) studies were performed immediately after stent implantation and at follow-up. RESULTS: Proper stent positioning and implantation was obtained in all animals. Angiographic and IVUS assessments indicated no dissection or thrombus formation. Histology demonstrated good apposition and endothelialization of the stent strut surface. CONCLUSION: The unique flared shape of this novel ostial stent system allows for improved accuracy during stent positioning and placement, as well as complete apposition and coverage/scaffolding of the similarly-shaped luminal ostium. Future studies will determine if this novel stent system fulfills the unmet clinical need in aorto-ostial stenoses.

Abstract: OBJECTIVE: To compare the difference of strut distribution between two clinically available drug-eluting stent platforms (Bx Velocity and Express II stents) using intravascular ultrasound (IVUS). BACKGROUND: Nonuniform strut distribution (NSD) has been shown to be associated with increased intimal hyperplasia after drug-eluting stent implantation. METHODS: IVUS imaging was performed on Bx Velocity (n = 6) and Express II stents (n = 6) after inflation pressures of 10, 16, and 26 atm in a bench test model. Percent NSD was defined as the length of segments with NSD (interstrut angle > 90 degrees) divided by stent length. NSD was also assessed in postprocedure IVUS images in 53 clinical cases (32 Cypher, 21 Taxus) using 3-dimensional IVUS analysis. RESULTS: Frequency of NSD segment and %NSD were lower in Bx Velocity stents than in Express II stents at the inflation pressures of 16 and 26 atm (%NSD: 16 atm, 0% vs. 13.8 +/- 9.4%; p < 0.005; 26 atm, 1.1 +/- 2.6% vs. 19.9 +/- 6.9% p < 0.0001). In postprocedural images from clinical cases, the frequency of NSD segment and %NSD were lower in Cypher stents than in Taxus stents (%NSD: 0.5 +/- 1.6 vs. 6.8 +/- 7.2; p < 0.0001). CONCLUSION: NSD segment was observed less in Bx Velocity stents than in Express II stents.

Abstract: Nanocrystals with advanced magnetic or optical properties have been actively pursued for potential biological applications, including integrated imaging, diagnosis and therapy. Among various magnetic nanocrystals, FeCo has superior magnetic properties, but it has yet to be explored owing to the problems of easy oxidation and potential toxicity. Previously, FeCo nanocrystals with multilayered graphitic carbon, pyrolytic carbon or inert metals have been obtained, but not in the single-shelled, discrete, chemically functionalized and water-soluble forms desired for biological applications. Here, we present a scalable chemical vapour deposition method to synthesize FeCo/single-graphitic-shell nanocrystals that are soluble and stable in water solutions. We explore the multiple functionalities of these core-shell materials by characterizing the magnetic properties of the FeCo core and near-infrared optical absorbance of the single-layered graphitic shell. The nanocrystals exhibit ultra-high saturation magnetization, r1 and r2 relaxivities and high optical absorbance in the near-infrared region. Mesenchymal stem cells are able to internalize these nanoparticles, showing high negative-contrast enhancement in magnetic-resonance imaging (MRI). Preliminary in vivo experiments achieve long-lasting positive-contrast enhancement for vascular MRI in rabbits. These results point to the potential of using these nanocrystals for integrated diagnosis and therapeutic (photothermal-ablation) applications.

Abstract: BACKGROUND: Recently, indirect magnetic resonance lymphangiography with gadolinium (Gd) has been demonstrated to offer the potential for safe, high-resolution visualization of the lymphatic vessels, in addition to the lymph nodes. In this study, the potential utility of indirect Gd contrast magnetic resonance imaging of lymphatic vascular function was investigated in the murine tail. Functional imaging of healthy mice is contrasted with the findings in experimentally-induced lymphatic vascular insufficiency. METHODS: Postsurgical lymphedema was experimentally created in the murine tail. Normal and lymphedematous mouse tails were imaged following direct subcutaneous administration of Gadolinium-DTPA, 0.1 mmol/kg. Images were obtained in axial and coronal planes with a T1-weighted spin echo inversion-recovery sequence. RESULTS: In the normal tail, both of the bilateral major collecting lymphatics were clearly visualized as the Gd tracer was cleared from the interstitial compartment. In contrast, the Gd tracer accumulated at the prior surgical site in the lymphedematous tail. Quantitative assessment of Gd clearance demonstrates that accumulation of Gd correlates with the impedance to lymph flow proximal to the site of surgical lymphatic ablation. CONCLUSION: Magnetic resonance is a feasible and reliable method to be applied to quantitative functional imaging of the lymphatic vasculature in experimental models of lymphedema.

Abstract: OBJECTIVES: The purpose of this study is to compare the stent strut distribution between Cypher and Taxus stents by using optical coherence tomography (OCT) in a phantom model. BACKGROUND: Previous studies demonstrated that the distribution of stent struts might affect amount of neointima proliferation after drug-eluting stent (DES) implantation. METHODS: We developed experimental models made of silicon tubing angled at 0 degrees, 30 degrees, and 60 degrees. Testing was performed on two types of stents, Cypher and Taxus, which represent current FDA-approved DES. After deployment, OCT was performed and measurements were obtained as follows at two cross sections; maximum and minimum numbers of visualized stent strut sites: (1) number of visualized stent struts; (2) angle between stent struts (interstrut angle); (3) mean interstrut angle; (4) the delta mean angle was defined as the margin between each value of the interstrut angle and mean interstrut angle. RESULTS: In the Cypher stent, both the interstrut angle and the delta mean angle were significantly better than all other stents evaluated (all comparisons between stents; p < 0.05, respectively). CONCLUSIONS: The present study found that the stent strut distribution of two stents, Cypher and Taxus, which represent current FDA-approved drug-eluting systems, were significantly different and suggested that the Cypher stent maintained a more regular strut distribution despite expansion in various anatomical situations, and therefore would provide the most regular and predictable drug delivery.