Cory Swingen

Safety and Feasibility of Autologous Myoblast Transplantation in Patients With Ischemic Cardiomyopathy Four-Year Follow-Up

Background—Successful autologous skeletal myoblast transplantation into infarcted myocardium in a variety of animal models has demonstrated improvement in cardiac function. We evaluated the safety and feasibility of transplanting autologous myoblasts into infarcted myocardium of patients undergoing concurrent coronary artery bypass grafting (CABG) or left ventricular assist device (LVAD) implantation. In addition, we sought to gain preliminary information on graft survival and any associated changes in cardiac function. Methods and Results—Thirty patients with a history of ischemic cardiomyopathy participated in a phase I, nonrandomized, multicenter pilot study of autologous skeletal myoblast transplantation concurrent with CABG or LVAD implantation. Twenty-four patients with a history of previous myocardial infarction and a left ventricular ejection fraction <40% were enrolled in the CABG arm. In a second arm, 6 patients underwent LVAD implantation as a bridge to heart transplantation, and patients donated their explanted native hearts for testing at the time of heart transplantation. Myoblasts were successfully transplanted in all patients without any acute injection-related complications or significant long-term, unexpected adverse events. Follow-up positron emission tomography scans showed new areas of glucose uptake within the infarct scar in CABG patients. Echocardiography measured an average change in left ventricular ejection fraction from 28% to 35% at 1 year and of 36% at 2 years. Histological evaluation in 4 of 6 patients who underwent heart transplantation documented survival and engraftment of the skeletal myoblasts within the infarcted myocardium. Conclusions—These results demonstrate the survival, feasibility, and safety of autologous myoblast transplantation and suggest that this modality offers a potential therapeutic treatment for end-stage heart disease.

Myocardial blood flow quantification with MRI by model-independent deconvolution

Magnetic resonance (MR) imaging during the first pass of an injected contrast agent has been used to assess myocardial perfusion, but the quantification of blood flow has been generally judged as too complex for its clinical application. This study demonstrates the feasibility of applying model-independent deconvolution to the measured tissue residue curves to quantify myocardial perfusion. Model-independent approaches only require minimal user interaction or expertise in modeling. Monte Carlo simulations were performed with contrast-to-noise ratios typical of MR myocardial perfusion studies to determine the accuracy of the resulting blood flow estimates. With a B-spline representation of the tissue impulse response and Tikhonov regularization, the bias of blood flow estimates obtained by model-independent deconvolution was less than 1% in all cases for peak contrast to noise ratios in the range from 15:1 to 20:1. The relative dispersion of blood flow estimates in Monte Carlo simulations was less than 7%. Comparison of MR blood flow estimates against measurements with radio-isotope labeled microspheres indicated excellent linear correlation (R2 = 0.995, slope: 0.96, intercept: 0.06). It can be concluded from these studies that the application of myocardial blood flow quantification with MRI can be performed with model-independent methods, and this should support a more widespread use of blood flow quantification in the clinical environment.

Bioenergetic and Functional Consequences of Bone Marrow–Derived Multipotent Progenitor Cell Transplantation in Hearts With Postinfarction Left Ventricular Remodeling

Background— The present study examined whether transplantation of adherent bone marrow-derived stem cells, termed pMultistem, induces neovascularization and cardiomyocyte regeneration that stabilizes bioenergetic and contractile function in the infarct zone and border zone (BZ) after coronary artery occlusion. Methods and Results— Permanent left anterior descending artery occlusion in swine caused left ventricular remodeling with a decrease of ejection fraction from 55±5.6% to 30±5.4% (magnetic resonance imaging). Four weeks after left anterior descending artery occlusion, BZ myocardium demonstrated profound bioenergetic abnormalities, with a marked decrease in subendocardial phosphocreatine/ATP (31P magnetic resonance spectroscopy; 1.06±0.30 in infarcted hearts [n=9] versus 1.90±0.15 in normal hearts [n=8; P<0.01]). This abnormality was significantly improved by transplantation of allogeneic pMultistem cells (subendocardial phosphocreatine/ATP to 1.34±0.29; n=7; P<0.05). The BZ protein expression of creatine kinase-mt and creatine kinase-m isoforms was significantly reduced in infarcted hearts but recovered significantly in response to cell transplantation. MRI demonstrated that the infarct zone systolic thickening fraction improved significantly from systolic “bulging” in untreated animals with myocardial infarction to active thickening (19.7±9.8%, P<0.01), whereas the left ventricular ejection fraction improved to 42.0±6.5% (P<0.05 versus myocardial infarction). Only 0.35±0.05% donor cells could be detected 4 weeks after left anterior descending artery ligation, independent of cell transplantation with or without immunosuppression with cyclosporine A (with cyclosporine A, n=6; no cyclosporine A, n=7). The fraction of grafted cells that acquired an endothelial or cardiomyocyte phenotype was 3% and ≈2%, respectively. Patchy spared myocytes in the infarct zone were found only in pMultistem transplanted hearts. Vascular density was significantly higher in both BZ and infarct zone of cell-treated hearts than in untreated myocardial infarction hearts (P<0.05). Conclusions— Thus, allogeneic pMultistem improved BZ energetics, regional contractile performance, and global left ventricular ejection fraction. These improvements may have resulted from paracrine effects that include increased vascular density in the BZ and spared myocytes in the infarct zone.

Analysis of myocardial perfusion MRI

Rapid MR imaging (MRI) during the first pass of an injected tracer is used to assess myocardial perfusion with a spatial resolution of 2–3 mm, and to detect any regional impairments of myocardial blood flow (MBF) that may lead to ischemia. The spatial resolution is sufficient to detect flow reductions that are limited to the subendocardial layer. The capacity of the coronary system to increase MBF severalfold in response to vasodilation can be quantified by analysis of the myocardial contrast enhancement. The myocardial perfusion reserve (MPR) is a useful concept for quantifying the vasodilator response. The perfusion reserve can be estimated from the ratio of MBFs during vasodilation and at baseline, in units identical to those used for invasive measurements with labeled microspheres, or from dimensionless flow indices normalized by their value for autoregulated flow at rest. The perfusion reserve can be reduced as a result of a blunted hyperemic response and/or an abnormal resting blood flow. The absolute quantification of MBF removes uncertainties in the evaluation of the vasodilator response, and can be achieved without the use of complex tracer kinetic models; therefore, its application to clinical studies is feasible. J. Magn. Reson. Imaging 2004;19:758–770.

Cardiac Repair in a Porcine Model of Acute Myocardial Infarction with Human Induced Pluripotent Stem Cell-Derived Cardiovascular Cells

Human induced pluripotent stem cells (hiPSCs) hold promise for myocardial repair following injury, but preclinical studies in large animal models are required to determine optimal cell preparation and delivery strategies to maximize functional benefits and to evaluate safety. Here, we utilized a porcine model of acute myocardial infarction (MI) to investigate the functional impact of intramyocardial transplantation of hiPSC-derived cardiomyocytes, endothelial cells, and smooth muscle cells, in combination with a 3D fibrin patch loaded with insulin growth factor (IGF)-encapsulated microspheres. hiPSC-derived cardiomyocytes integrated into host myocardium and generated organized sarcomeric structures, and endothelial and smooth muscle cells contributed to host vasculature. Trilineage cell transplantation significantly improved left ventricular function, myocardial metabolism, and arteriole density, while reducing infarct size, ventricular wall stress, and apoptosis without inducing ventricular arrhythmias. These findings in a large animal MI model highlight the potential of utilizing hiPSC-derived cells for cardiac repair.

A fibrin patch-based enhanced delivery of human embryonic stem cell-derived vascular cell transplantation in a porcine model of postinfarction left ventricular remodeling

It is unknown how to use human embryonic stem cell (hESC) to effectively treat hearts with postinfarction left ventricular (LV) remodeling. Using a porcine model of postinfarction LV remodeling, this study examined the functional improvement of enhanced delivery of combined transplantation of hESC‐derived endothelial cells (ECs) and hESC‐derived smooth muscle cells (SMCs) with a fibrin three‐dimensional (3D) porous scaffold biomatrix. To facilitate tracking the transplanted cells, the hESCs were genetically modified to stably express green fluorescent protein and luciferase (GFP/Luc). Myocardial infarction (MI) was created by ligating the first diagonal coronary artery for 60 minutes followed by reperfusion. Two million each of GFP/Luc hESC‐derived ECs and SMCs were seeded in the 3D porous biomatrix patch and applied to the region of ischemia/reperfusion for cell group (MI+P+C, n = 6), whereas biomatrix without cell (MI+P, n = 5), or saline only (MI, n = 5) were applied to control group hearts with same coronary artery ligation. Functional outcome (1 and 4 weeks follow‐up) of stem cell transplantation was assessed by cardiac magnetic resonance imaging. The transplantation of hESC‐derived vascular cells resulted in significant LV functional improvement. Significant engraftment of hESC‐derived cells was confirmed by both in vivo and ex vivo bioluminescent imaging. The mechanism underlying the functional beneficial effects of cardiac progenitor transplantation is attributed to the increased neovascularization. These findings demonstrate a promising therapeutic potential of using these hESC‐derived vascular cell types and the mode of patch delivery. STEM CELLS 2011;29:367–375

Circadian Dependence of Infarct Size and Left Ventricular Function After ST Elevation Myocardial Infarction

Rationale: In rodents, infarct size after ischemia/reperfusion exhibits a circadian dependence on the time of coronary occlusion. It is not known if a similar circadian dependence of infarct size occurs in humans. Objective: To determine if humans exhibit a circadian dependence of infarct size in the setting of ST elevation myocardial infarction (STEMI). Methods and Results: A retrospective analysis of 1031 patients with STEMI referred for primary percutaneous coronary intervention with known ischemic times between 1 and 6 hours identified 165 patients with occluded arteries on presentation without evidence of preinfarction angina or collateral blood flow. Both ischemic duration and angiographic area at risk were not dependent on time of infarct onset. We observed that the extent of infarct size measured by creatine kinase release was significantly associated with time of day onset of infarction (P<0.0001). The greatest myocardial injury occurred at 1:00 AM onset of ischemia and 5:00 AM onset of reperfusion, with the peak creatine kinase measured at the peak of the curve being 82% higher than that recorded at the trough. Similarly, left ventricular ejection fraction measured within 2 days of infarction was also dependent on time of onset of STEMI with the absolute left ventricular ejection fraction at peak >7% higher than at trough (43% vs 51%; P<0.03). These findings were supported by a subgroup of patients (n=45) who underwent cardiac MRI measurements of infarct size and area-at-risk measurements. Conclusions: The results of this study demonstrate for the first time in humans that myocardial infarct size and left ventricular function after STEMI have a circadian dependence on the time of day onset of ischemia.

Functional Consequences of Human Induced Pluripotent Stem Cell Therapy Myocardial ATP Turnover Rate in the In Vivo Swine Heart With Postinfarction Remodeling

Background— The use of cells derived from human induced pluripotent stem cells as cellular therapy for myocardial injury has yet to be examined in a large-animal model. Methods and Results— Immunosuppressed Yorkshire pigs were assigned to 1 of 3 groups: A myocardial infarction group (MI group; distal left anterior descending coronary artery ligation and reperfusion; n=13); a cell-treatment group (MI with 4×106 vascular cells derived from human induced pluripotent stem cells administered via a fibrin patch; n=14); and a normal group (n=15). At 4 weeks, left ventricular structural and functional abnormalities were less pronounced in hearts in the cell-treated group than in MI hearts (P<0.05), and these improvements were accompanied by declines in scar size (10.4±1.6% versus 8.3±1.1%, MI versus cell-treatment group, P<0.05). The cell-treated group displayed a significant increase in vascular density and blood flow (0.83±0.11 and 1.05±0.13 mL·min−1·g−1, MI versus cell-treatment group, P<0.05) in the periscar border zone (BZ), which was accompanied by improvements in systolic thickening fractions (infarct zone, −10±7% versus 5±5%; BZ, 7±4% versus 23±6%; P<0.05). Transplantation of vascular cells derived from human induced pluripotent stem cells stimulated c-kit+ cell recruitment to BZ and the rate of bromodeoxyuridine incorporation in both c-kit+ cells and cardiomyocytes (P<0.05). Using a magnetic resonance spectroscopic saturation transfer technique, we found that the rate of ATP hydrolysis in BZ of MI hearts was severely reduced, and the severity of this reduction was linearly related to the severity of the elevations of wall stresses (r=0.82, P<0.05). This decline in BZ ATP utilization was markedly attenuated in the cell-treatment group. Conclusions— Transplantation of vascular cells derived from human induced pluripotent stem cells mobilized endogenous progenitor cells into the BZ, attenuated regional wall stress, stimulated neovascularization, and improved BZ perfusion, which in turn resulted in marked increases in BZ contractile function and ATP turnover rate.

Stem Cells for Myocardial Repair With Use of a Transarterial Catheter

Background— Using a swine model of postinfarction left ventricle (LV) remodeling, we investigated marrow-derived, multipotent progenitor cell (MPC) transplantation into hearts with acute myocardial infarction (AMI) via a novel transarterial catheter. Methods and Results— The left anterior descending coronary artery was balloon-occluded after percutaneous transluminal angiography to generate AMI (60-minute no-flow ischemia). The transarterial catheter was then placed in the same coronary artery, and either 50×106 MPCs (cell group, n=6) or saline (control, n=6) was injected into the border zone (BZ) myocardium. LV function was assessed by magnetic resonance imaging before AMI and at 1 and 4 weeks after AMI, whereas myocardial energy metabolism was assessed by 31P-magnetic resonance spectroscopy at week 4. One week after AMI, the ejection fraction was significantly reduced in both groups from a baseline of ≈50% to 31.3±3.9% (cell group) and 33.3±3.1% (control). However, at week 4, the cell group had a significant recovery in ejection fraction. The functional improvements were accompanied by a significant improvement in myocardial bioenergetics. Histologic data demonstrated a 0.55% cell engraftment rate 4 weeks after MPC transplantation. Only 2% of engrafted cells were costaining positive for cardiogenic markers. Vascular density in the BZ was increased in the cell group. Conditioned medium from cultured MPCs contained high levels of vascular endothelial growth factor, which was increased in response to hypoxia. MPCs cocultured with cardiomyocytes inhibited changes in cardiomyocyte mitochondrial membrane potential and cytochrome c release induced by tumor necrosis factor-&agr;. Conclusions— Thus, a paracrine effect may contribute significantly to the observed therapeutic effects of MPC transplantation.

Evaluation of a New Method for Automated Detection of Left Ventricular Boundaries in Time Series of Magnetic Resonance Images Using an Active Appearance Motion Model

The purpose of this study was the evaluation of a computer algorithm for the automated detection of endocardial and epicardial boundaries of the left ventricle in time series of short-axis magnetic resonance images based on an Active Appearance Motion Model (AAMM). In 20 short-axis MR examinations, manual contours were defined in multiple temporal frames (from end-diastole to end-systole) in multiple slices from base to apex. Using a leave-one-out procedure, the image data and contours were used to build 20 different AAMMs giving a statistical description of the ventricular shape, gray value appearance, and cardiac motion patterns in the training set. Automated contour detection was performed by iteratively deforming the AAMM within statistically allowed limits until an optimal match was found between the deformed AAMM and the underlying image data of the left-out subject. Global ventricular function results derived from automatically detected contours were compared with results obtained from manually traced boundaries. The AAMM contour detection method was successful in 17 of 20 studies. The three failures were excluded from further statistical analysis. Automated contour detection resulted in small, but statistically nonsignificant, underestimations of ventricular volumes and mass: differences for end-diastolic volume were 0.3%+/-12.0%, for end-systolic volume 2.0%+/-23.4% and for left ventricular myocardial mass 0.73%+/-14.9% (mean+/-SD). An excellent agreement was observed in the ejection fraction: difference of 0.1%+/-6.7%. In conclusion, the presented fully automated contour detection method provides assessment of quantitative global function that is comparable to manual analysis.