Interventional magnetic resonance imaging for guiding gene and cell transfer in the heart

Genetic maneuvers to ameliorate ventricular function in heart failure: therapeutic potential and future implications

Gene therapy to treat heart failure has evolved into a growing field of investigation yielding remarkable results in preclinical models. Whether these results will persist in clinical trials remains to be seen. However, researchers still face a number of obstacles that need to be overcome before this treatment can be employed effectively. Efforts are required to identify better vectors with minimal side effects and maximal efficiency and durability. There is also a need to develop less invasive and more effective techniques to deliver these vectors. This review will discuss different methods to achieve these goals, the various pathologic mechanisms that have been targeted so far and those with strong potential for use in the future.

MRI roadmap-guided transendocardial delivery of exon-skipping recombinant adeno-associated virus restores dystrophin expression in a canine model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) cardiomyopathy patients currently have no therapeutic options. We evaluated catheter-based transendocardial delivery of a recombinant adeno-associated virus (rAAV) expressing a small nuclear U7 RNA (U7smOPT) complementary to specific cis-acting splicing signals. Eliminating specific exons restores the open reading frame resulting in translation of truncated dystrophin protein. To test this approach in a clinically relevant DMD model, golden retriever muscular dystrophy (GRMD) dogs received serotype 6 rAAV-U7smOPT via the intracoronary or transendocardial route. Transendocardial injections were administered with an injection-tipped catheter and fluoroscopic guidance using X-ray fused with magnetic resonance imaging (XFM) roadmaps. Three months after treatment, tissues were analyzed for DNA, RNA, dystrophin protein, and histology. Whereas intracoronary delivery did not result in effective transduction, transendocardial injections, XFM guidance, enabled 30±10 non-overlapping injections per animal. Vector DNA was detectable in all samples tested and ranged from <1 to >3000 vector genome copies per cell. RNA analysis, western blot analysis, and immunohistology demonstrated extensive expression of skipped RNA and dystrophin protein in the treated myocardium. Left ventricular function remained unchanged over a 3-month follow-up. These results demonstrated that effective transendocardial delivery of rAAV-U7smOPT was achieved using XFM. This approach restores an open reading frame for dystrophin in affected dogs and has potential clinical utility.

Interventional cardiovascular magnetic resonance imaging: a new opportunity for image-guided interventions

Cardiovascular magnetic resonance (CMR) combines excellent soft-tissue contrast, multiplanar views, and dynamic imaging of cardiac function without ionizing radiation exposure. Interventional cardiovascular magnetic resonance (iCMR) leverages these features to enhance conventional interventional procedures or to enable novel ones. Although still awaiting clinical deployment, this young field has tremendous potential. We survey promising clinical applications for iCMR. Next, we discuss the technologies that allow CMR-guided interventions and, finally, what still needs to be done to bring them to the clinic.

Molecular imaging: a primer for interventionalists and imagers

The characterization of human diseases by their underlying molecular and genomic aberrations has been the hallmark of molecular medicine. From this, molecular imaging has emerged as a potentially revolutionary discipline that aims to visually characterize normal and pathologic processes at the cellular and molecular levels within the milieu of living organisms. Molecular imaging holds promise to provide earlier and more precise disease diagnosis, improved disease characterization, and timely assessment of therapeutic response. This primer is intended to provide a broad overview of molecular imaging with specific focus on future clinical applications relevant to interventional radiology.

Interventional cardiovascular magnetic resonance: still tantalizing

The often touted advantages of MR guidance remain largely unrealized for cardiovascular interventional procedures in patients. Many procedures have been simulated in animal models. We argue these opportunities for clinical interventional MR will be met in the near future. This paper reviews technical and clinical considerations and offers advice on how to implement a clinical-grade interventional cardiovascular MR (iCMR) laboratory. We caution that this reflects our personal view of the "state of the art."

Pilot Trial on Determinants of Progenitor Cell Recruitment to the Infarcted Human Myocardium

Background— Clinical trials indicate a beneficial effect of intracoronary infusion of progenitor cells on myocardial function in patients with ischemic heart disease. The extent and potential determinants of proangiogenic progenitor cell homing into the damaged myocardium after intracoronary infusion and the underlying mechanisms are still unknown.

Method and Results— Circulating proangiogenic progenitor cells isolated from peripheral blood and cultivated for 3 days were labeled with radioactive indium oxine ( 111 In-oxine). Radiolabeled proangiogenic progenitor cells (7.6±3.0 MBq, mean±SD) were administered to patients with previous myocardial infarction and a revascularized infarct vessel at various stages after infarction (5 days to 17 years). Viability of the infarcted myocardium was determined by 18 F-fluorodeoxyglucose–positron emission tomography and microcirculatory function by intracoronary Doppler measurements. One hour after application of progenitor cells, a mean of 6.9±4.7% (range, 1% to 19%; n=17) of total radioactivity was detected in the heart, which declined to 2±1% after 3 to 4 days. Average activity within the first 24 hours was highest among patients with acute myocardial infarction (≤14 days; 6.3±2.9%; n=8) and progressively decreased in patients treated in an intermediate phase (>14 days to 1 year; 4.5±3.2%; n=4) or a chronic stage (infarct age >1 year; 2.5±1.6%; n=5). Low viability of the infarcted myocardium and reduced coronary flow reserve were significant ( P <0.05) predictors of proangiogenic progenitor cell homing.

Conclusions— In patients after myocardial infarction undergoing intracoronary infusion of 111 In-oxine–labeled proangiogenic progenitor cells, a substantial amount of radioactivity is detected for several days in the heart, indicating homing of progenitor cells to the myocardium. The amount of proangiogenic progenitor cells retained in the heart decreased progressively with time after the acute myocardial infarction. Proangiogenic progenitor cells preferentially home to extensive acute myocardial infarcts characterized by low viability and reduced coronary flow reserve.

Concise review: mesenchymal stromal cells: potential for cardiovascular repair

Cellular therapy for cardiovascular disease heralds an exciting frontier of research. Mesenchymal stromal cells (MSCs) are present in adult tissues, including bone marrow and adipose, from which they can be easily isolated and cultured ex vivo. Although traditional isolation of these cells by plastic adherence results in a heterogeneous composite of mature and immature cell types, MSCs do possess plasticity of differentiation and under appropriate in vitro culture conditions can be modified to adopt cardiomyocyte and vascular cell phenotypic characteristics. In vivo preclinical studies have demonstrated their capacity to facilitate both myocardial repair and neovascularization in models of cardiac injury. The mechanisms underlying these effects appear to be mediated predominantly through indirect paracrine actions, rather than direct regeneration of endogenous cells by transdifferentiation, especially because current transplantation strategies achieve only modest engraftment of cells in the host myocardium. Currently, published clinical trial experience of MSCs as cardiac therapy is limited, and the outcomes of ongoing studies are keenly anticipated. Of relevance to clinical application is the fact that MSCs are relatively immunoprivileged, potentially enabling their allogeneic therapeutic use, although this too requires further investigation. Overall, MSCs are an attractive adult-derived cell population for cardiovascular repair; however, research is still required at both basic and clinical levels to resolve critical areas of uncertainty and to ensure continued development in cell culture engineering and cell transplantation technology.

Stem cell therapy: MRI guidance and monitoring

With the recent advances in magnetic resonance (MR) labeling of cellular therapeutics, it is natural that interventional MRI techniques for targeting would be developed. This review provides an overview of the current methods of stem cell labeling and the challenges that are created with respect to interventional MRI administration. In particular, stem cell therapies will require specialized, MR-compatible devices as well as integration of graphical user interfaces with pulse sequences designed for interactive, real-time delivery in many organs. Specific applications that are being developed will be reviewed as well as strategies for future translation to the clinical realm.

Iron-oxide labeling and outcome of transplanted mesenchymal stem cells in the infarcted myocardium

BACKGROUND

Cell labeling with superparamagnetic iron oxide (SPIO) nanoparticles enables noninvasive MRI and tracking of transplanted stem cells. We sought to determine whether mesenchymal stem cell (MSC) outcome is affected by SPIO labeling in a rat model of myocardial infarction.

METHODS AND RESULTS

Rat MSCs were labeled with SPIO (ferumoxides; Endorem; Guerbet, Villepinte, France). By trypan-blue exclusion assay, almost 100% of the cells remained viable after labeling. Seven days after MI, rats were randomized to injections of 2x10(6) SPIO-labeled MSCs, 2x10(6) unlabeled MSCs, or saline. Labeled cells were visualized in the infarcted myocardium as large black spots by serial MRI studies throughout the 4-week follow-up. The presence of labeled cells was confirmed by iron staining and real-time polymerase chain reaction on postmortem specimens. At 4 weeks after transplantation, the site of cell injection was infiltrated by inflammatory cells. Costaining for iron and ED1 (resident macrophage marker) showed that the iron-positive cells were cardiac macrophages. By real-time polymerase chain reaction, the Y-chromosome-specific SRY DNA of MSCs from male donors was not detected in infarcted hearts of female recipients. Serial echocardiography studies at baseline and 4 weeks after cell transplantation showed that both unlabeled and labeled MSCs attenuated progressive left ventricular dilatation and dysfunction compared with controls.

CONCLUSIONS

At 4 weeks after transplantation of SPIO-labeled MSCs, the transplanted cells are not present in the scar and the enhanced MRI signals arise from cardiac macrophages that engulfed the SPIO nanoparticles. However, both labeled and unlabeled cells attenuate left ventricular dilatation and dysfunction after myocardial infarction.

Use of a genetically engineered protein for the design of a multivalent MRI contrast agent

The majority of clinically used contrast agents (CAs) for magnetic resonance imaging have low relaxivities and thus require high concentrations for signal enhancement. Research has turned to multivalent, macromolecular CAs to increase CA efficiency. However, previously developed macromolecular CAs do not provide high relaxivities, have limited biocompatibility, and/or do not have a structure that is readily modifiable to tailor to particular applications. We report a new family of multivalent, biomacromolecular, genetically engineered protein polymer-based CAs; the protein backbone contains evenly spaced lysines that are derivatized with gadolinium (Gd(III)) chelators. The protein's length and repeating amino acid sequence are genetically specified. We reproducibly obtained conjugates with an average of 8-9 Gd(III) chelators per protein. These multivalent CAs reproducibly provide a high relaxivity of 7.3 mM (-1) s (-1) per Gd(III) and 62.6 mM (-1) s (-1) per molecule. Furthermore, they can be incorporated into biomaterial hydrogels via chemical cross-linking of the remaining free lysines, and provide a dramatic contrast enhancement. Thus, these protein polymer CAs could be a useful tool for following the evolution of tissue engineering scaffolds.

Cardiac repair--fact or fancy?

Patients with ischemic cardiomyopathy have a poor prognosis despite all pharmacological, interventional and surgical treatment modalities currently applied. Heart transplantation remains the ideal treatment for this group of patients but the scarcity of donors hinders its widespread application. The autologous transplantation of stem cells (SCs) for cardiac repair is emerging as a new therapy for patients with myocardial dysfunction early after an acute infarction or ischemic cardiomyopathy. The rationale of this novel method is the enhancement of the repair mechanisms achieved by tissue-specific and circulating stem/progenitor cells. SCs assist naturally occurring myocardial repair by contributing to increased myocardial perfusion and contractile performance especially in the setting of acute myocardial infarction (AMI), but also in patients with chronic ischemic heart failure and advanced, diffuse coronary artery disease. The exact mechanism of their action has not been fully elucidated. Few studies continue to suggest a formation of few new contractile tissue. The majority if investigators believe that these cells do not persist long in the myocardium but that they secrete vascular growth and other cardioprotective factors.

Tracking stem cells in vivo

Stem cells have been targeted to many organ systems specifically to replace scarred organs and to rejuvenate diseased organs. Even though our understanding of the versatility of stem cells is slowly unraveling, tracking these cells as they enter the body has become a very important field of study. In this chapter, we review various modalities for imaging stem cells and assess the advantages and shortcomings of each technique.

Molecular Imaging: A Primer for Interventionalists and Imagers

The characterization of human diseases by their underlying molecular and genomic aberrations has been the hallmark of molecular medicine. From this, molecular imaging has emerged as a potentially revolutionary discipline that aims to visually characterize normal and pathologic processes at the cellular and molecular levels within the milieu of living organisms. Molecular imaging holds promise to provide earlier and more precise disease diagnosis, improved disease characterization, and timely assessment of therapeutic response. This primer is intended to provide a broad overview of molecular imaging with specific focus on future clinical applications relevant to interventional radiology.

Effect of Matrix Metalloproteinase Inhibition by Doxycycline on Myocardial Healing and Remodeling after Myocardial Infarction

The aim of conducting this study was to assess the clinical relevance of matrix metalloproteinase (MMP) inhibition by doxycycline, an effective MMP inhibitor, in a rat model of extensive myocardial infarction (MI) and left ventricular (LV) dysfunction. Rats (n = 22) were subjected to extensive anterior MI. Doxycycline (25 mg SC, daily) or saline (control) injections were started for nine days thereafter. The effect of doxycycline on MMP activity in the infarcted and remote myocardium was measured by zymography, in another subgroup (n = 8), nine days after MI. Echocardiography and magnetic resonance imaging (MRI) studies were performed at one and thirty days after MI to assess LV remodeling and function. After 4 weeks, hearts were fixed, and subjected to morphometric and histological analysis. Compared with control, doxycycline treatment attenuated MMP-9 and -2 activity in both infarcted and remote myocardium. Serial echocardiography studies showed that doxycycline failed to attenuate scar thinning, LV dilatation and dysfunction. MRI study showed that doxycycline impaired LV compensatory hypertrophy. Furthermore, compared with control, doxycycline reduced vessel density (/mm(2) +/- SEM) in the infarcted myocardium (84 +/- 16 vs. 46 +/- 9/mm(2), respectively; p < 0.05). Our work suggest that effective MMPs' inhibition in the infarcted and remote myocardium by doxycycline does not prevent LV remodeling and dysfunction but impairs angiogenesis and compensatory LV hypertrophy. Our findings caution against aggressive, non-selective inhibition of MMPs in the early healing phase after MI.

Cardiovascular interventional MR imaging: a new road for therapy and repair in the heart

Over the last 5 years, interventional MR imaging has been fertile ground for research. Real-time MR imaging, combined with recent advances in other MR imaging modalities such as perfusion imaging and intravascular imaging, has opened up new paths for cardiac therapy. The recent reports on cardiac stem cell therapy guided and monitored by MR imaging suggest that we are already seeing the establishment of an important role for cardiac MR imaging in cardiac restoration. The collaborative effort from a multidisciplinary team of basic biologists, engineers, and clinicians will refine stem cell incubation and labeling for MR-guided transcatheter endomyocardial injections, and this in turn may facilitate new studies in humans. Several groups have demonstrated in animal studies the feasibility of MR-guided catheter interventions for the treatment of congenital heart disease and arrythmia therapy. Hence, applications in humans remain the challenge for the next years. Although there have been first reports of cardiac catheterizations in humans by combined use of x-ray fluoroscopy and MR imaging, there are no reports in the literature suggesting that active tracking methods by MR imaging have been applied to humans. Safety issues (namely, heating of catheters and wires) hamper clinical use, particularly in infants and children. Current reports are promising that these limitations will be overcome in the near future and will eventually reduce x-ray usage during catheterization. In its current state, cardiac MR imaging offers a unique opportunity to investigate new therapeutic strategies for the treatment of congenital and acquired heart disease.

MR-guided interventional procedures: a review

Magnetic resonance imaging (MRI) has emerged as a potential guidance tool for a variety of procedures. Diagnostic and therapeutic procedures using either open surgical or percutaneous access are performed. They span from simple lesion targeting and biopsy to complex applications requiring multiple tasks performed simultaneously or in rapid succession. These tasks include instrument guidance and therapy monitoring as well as procedural follow-up. The interventional use of MRI (IMRI) is increasing steadily. This article reviews the prerequisites, systems, and clinical interventional procedures of IMRI.

Closed-chest cell injections into mouse myocardium guided by high-resolution echocardiography

The mouse is an important model for the development of therapeutic stem cell/bone marrow cell implantation to treat ischemic myocardium. However, its small heart size hampers accurate implantation into the left ventricular (LV) wall. Precise injections have required surgical visualization of the heart, which is subject to complications and is impractical for delayed or repeated injections. Furthermore, the thickness of the myocardium is comparable to the length of a needle bevel, so surgical exposure does not prevent inadvertent injection into the LV cavity. We describe the use of high-resolution echocardiography to guide nonsurgical injections accurately into the mouse myocardial wall. We optimized this system by using a mixture of ultrasound contrast and fluorescent microspheres injected into the myocardium, which enabled us to interpret the ultrasound image of the needle during injection. Quantitative dye injection studies demonstrated that guided closed-chest injections and open-chest injections deliver comparable amounts of injectate to the myocardium. We successfully used this system in a mouse myocardial infarction model to target the injection of labeled cells to a region adjacent to the infarct. Intentional injection of tracer into the LV cavity resulted in a small accumulation in the myocardium, suggesting that non-guided cell injections into mouse hearts may appear to be successful even if the majority of the injectate is lost in the chamber. The use of this system will allow more precise cellular implantation into the mouse myocardium by accurately guiding injections to desired locations, confirming successful implantation of cells, in a clinically relevant time frame.

Myocardial gene and cell delivery

Although we now have the tools to introduce vectors and stem cells into specific myocardial locations, these devices are yet to be matched by comparable advances in molecular virology, cell biology, and our understanding of the pathophysiology of ischaemic heart disease