Myocardial Infarction In Swine Research Articles

Simultaneous Viability Assessment and Invasive Coronary Angiography Using a Therapeutic CT System in Chronic Myocardial Infarction Patients.

In a preclinical study using a swine myocardial infarction (MI) model, a delayed enhancement (DE)-multi-detector computed tomography (MDCT) scan was performed using a hybrid system alongside diagnostic invasive coronary angiography (ICA) without the additional use of a contrast agent, and demonstrated an excellent correlation in the infarct area compared with histopathologic specimens. In the present investigation, we evaluated the feasibility and diagnostic accuracy of a myocardial viability assessment by DE-MDCT using a hybrid system comprising ICA and MDCT alongside diagnostic ICA without the additional use of a contrast agent. We prospectively enrolled 13 patients (median age: 67 years) with a previous MI (>6 months) scheduled to undergo ICA. All patients underwent cardiac magnetic resonance (CMR) imaging before diagnostic ICA. MDCT viability scans were performed concurrently with diagnostic ICA without the use of additional contrast. The total myocardial scar volume per patient and average transmurality per myocardial segment measured by DE-MDCT were compared with those from DE-CMR. The DE volume measured by MDCT showed an excellent correlation with the volume measured by CMR (r=0.986, p<0.0001). The transmurality per segment by MDCT was well-correlated with CMR (r=0.900, p<0.0001); the diagnostic performance of MDCT in differentiating non-viable from viable myocardium using a 50% transmurality criterion was good with a sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 87.5%, 99.5%, 87.5%, 99.5%, and 99.1%, respectively. The feasibility of the DE-MDCT viability assessment acquired simultaneously with conventional ICA was proven in patients with chronic MI using DE-CMR as the reference standard.

Abstract 14766: Acute Impact of Transapical Ventricular Reshaping Device on Dilated Left Ventricle With Functional Mitral Regurgitation in Swine Model

Introduction: Functional mitral regurgitation (FMR) after myocardial infarction (MI) exacerbates morbidity and mortality. Correcting FMR plays a critical role in mitigating or reversing ventricular remodeling in MI patients with FMR. However, the COAPT trial demonstrated that FMR correction yields favorable results in smaller left ventricles (LVs) but not in severely dilated LVs. In this study, we evaluated the efficacy of a transapical device in MI swine model with FMR, which can perform papillary muscle approximation (PMA) and simultaneous reduction of LV volume. Methods: Yorkshire pig (n=15) were used in this study. MI was induced by percutaneous occlusion of the left circumflex artery, which caused LV dilatation and FMR by 3 months. The device was implanted through the LV apex to achieve PMA and LV reshaping until FMR was eliminated (Figure A). The immediate effects of the device implantation on the mitral valve and the LV were assessed using echocardiography and pressure-volume loops. Results: The device implantation decreased inter-papillary muscle distance from 24.5±3.8mm to 16.7±3.8mm (p&lt;0.0001), and significantly reduced FMR. Coaptation length significantly increased from 3.4±0.7mm to 5.5±1.2mm (p&lt;0.0001). End-diastolic volume decreased from 153±48ml to 117±33ml, a 23.5% reduction (p=0.0004). The end-systolic pressure-volume relationship and preload adjusted dP/dt max significantly increased after the device implant, indicating an improvement of LV contractility. There were no differences observed in Tau and end-diastolic pressure-volume relationship, depicting minimal acute impact on diastolic ventricular function after device implantation (Figure B and C). Conclusions: This transapical reshaping device effectively corrects FMR in very enlarged LVs, but also reduces systolic chamber wall stress by reducing the LV volume. An acute improvement in LV systolic function was observed, potentially indicating a therapeutic effect.

Human-umbilical cord matrix mesenchymal cells improved left ventricular contractility independently of infarct size in swine myocardial infarction with reperfusion.

Human umbilical cord matrix-mesenchymal stromal cells (hUCM-MSC) have demonstrated beneficial effects in experimental acute myocardial infarction (AMI). Reperfusion injury hampers myocardial recovery in a clinical setting and its management is an unmet need. We investigated the efficacy of intracoronary (IC) delivery of xenogeneic hUCM-MSC as reperfusion-adjuvant therapy in a translational model of AMI in swine. In a placebo-controlled trial, pot-belied pigs were randomly assigned to a sham-control group (vehicle-injection; n = 8), AMI + vehicle (n = 12) or AMI + IC-injection (n = 11) of 5 × 105 hUCM-MSC/Kg, within 30 min of reperfusion. AMI was created percutaneously by balloon occlusion of the mid-LAD. Left-ventricular function was blindly evaluated at 8-weeks by invasive pressure-volume loop analysis (primary endpoint). Mechanistic readouts included histology, strength-length relationship in skinned cardiomyocytes and gene expression analysis by RNA-sequencing. As compared to vehicle, hUCM-MSC enhanced systolic function as shown by higher ejection fraction (65 ± 6% vs. 43 ± 4%; p = 0.0048), cardiac index (4.1 ± 0.4 vs. 3.1 ± 0.2 L/min/m2; p = 0.0378), preload recruitable stroke work (75 ± 13 vs. 36 ± 4 mmHg; p = 0.0256) and end-systolic elastance (2.8 ± 0.7 vs. 2.1 ± 0.4 mmHg*m2/ml; p = 0.0663). Infarct size was non-significantly lower in cell-treated animals (13.7 ± 2.2% vs. 15.9 ± 2.7%; Δ = -2.2%; p = 0.23), as was interstitial fibrosis and cardiomyocyte hypertrophy in the remote myocardium. Sarcomere active tension improved, and genes related to extracellular matrix remodelling (including MMP9, TIMP1 and PAI1), collagen fibril organization and glycosaminoglycan biosynthesis were downregulated in animals treated with hUCM-MSC. Intracoronary transfer of xenogeneic hUCM-MSC shortly after reperfusion improved left-ventricular systolic function, which could not be explained by the observed extent of infarct size reduction alone. Combined contributions of favourable modification of myocardial interstitial fibrosis, matrix remodelling and enhanced cardiomyocyte contractility in the remote myocardium may provide mechanistic insight for the biological effect.

Multi-modality imaging assessment of microbubbles and cerebral emboli in left ventricular pulsed field ablation.

Pulsed field ablation (PFA) may have a superior safety profile compared to other technologies, but it has the potential to cause gaseous microbubbles (MB), which may be associated with cerebral emboli. Limited relative safety data has been published regarding PFA in the left ventricle (LV). Healthy and chronic myocardial infarction (MI) swine underwent PFA (monopolar, biphasic, 25 Amps) in the LV using an irrigated focal catheter under intra-cardiac echocardiography (ICE) guidance for MB monitoring. Two control swine received air MBs through the lumen of the ablation catheter. Swine underwent brain MRI before and after PFA (or control air MB injection). Gross pathology and histology of brains with abnormal MRI findings were performed. Four healthy and 5 chronic MI swine underwent 124 left ventricular PFA applications. No PFA-related MB formation was noted on ICE. Both control swine developed multiple acute emboli in the thalamus and caudate on DWI, ADC, and FLAIR brain MRI images in response to air MB injection. Of the 9 PFA swine, there were no abnormalities on ADC or FLAIR images. There was one hyperintense focus in the left putamen on the DWI trace image, but the absence of ADC or FLAIR affirmation suggested it was artifact. Gross pathology and histopathology of this region did not detect any abnormalities. Focal monopolar biphasic PFA of both healthy and chronically infarcted left ventricular myocardium does not generate any MB or cerebral emboli observable on ICE and brain MRI.

In vivo pulsed-field ablation in healthy vs. chronically infarcted ventricular myocardium: biophysical and histologic characterization.

Data on ventricular pulsed-field ablation (PFA) are sparse in the setting of chronic myocardial infarction (MI). The objective of this study was to compare the biophysical and histopathologic characteristics of PFA in healthy and MI swine ventricular myocardium. Myocardial infarction swine (n = 8) underwent coronary balloon occlusion and survived for 30 days. We then performed endocardial unipolar, biphasic PFA of the MI border zone and a dense scar with electroanatomic mapping and using an irrigated contact force (CF)-sensing catheter with the CENTAURI System (Galaxy Medical). Lesion and biophysical characteristics were compared with three controls: MI swine undergoing thermal ablation, MI swine undergoing no ablation, and healthy swine undergoing similar PFA applications that included linear lesion sets. Tissues were systematically assessed by gross pathology utilizing 2,3,5-triphenyl-2H-tetrazolium chloride staining and histologically with haematoxylin and eosin and trichrome. Pulsed-field ablation in healthy myocardium generated well-demarcated ellipsoid lesions (7.2 ± 2.1 mm depth) with contraction band necrosis and myocytolysis. Pulsed-field ablation in MI demonstrated slightly smaller lesions (depth 5.3 ± 1.9 mm, P = 0.0002), and lesions infiltrated into the irregular scar border, resulting in contraction band necrosis and myocytolysis of surviving myocytes and extending to the epicardial border of the scar. Coagulative necrosis was present in 75% of thermal ablation controls but only in 16% of PFA lesions. Linear PFA resulted in contiguous linear lesions with no gaps in gross pathology. Neither CF nor local R-wave amplitude reduction correlated with lesion size. Pulsed-field ablation of a heterogeneous chronic MI scar effectively ablates surviving myocytes within and beyond the scar, demonstrating promise for the clinical ablation of scar-mediated ventricular arrhythmias.

Pocket CLARITY enables distortion-mitigated cardiac microstructural tissue characterization of large-scale specimens.

Molecular phenotyping by imaging of intact tissues has been used to reveal 3D molecular and structural coherence in tissue samples using tissue clearing techniques. However, clearing and imaging of cardiac tissue remains challenging for large-scale (>100 mm3) specimens due to sample distortion. Thus, directly assessing tissue microstructural geometric properties confounded by distortion such as cardiac helicity has been limited. To combat sample distortion, we developed a passive CLARITY technique (Pocket CLARITY) that utilizes a permeable cotton mesh pocket to encapsulate the sample to clear large-scale cardiac swine samples with minimal tissue deformation and protein loss. Combined with light sheet auto-fluorescent and scattering microscopy, Pocket CLARITY enabled the characterization of myocardial microstructural helicity of cardiac tissue from control, heart failure, and myocardial infarction in swine. Pocket CLARITY revealed with high fidelity that transmural microstructural helicity of the heart is significantly depressed in cardiovascular disease (CVD), thereby revealing new insights at the tissue level associated with impaired cardiac function.

Abstract 12020: Overestimation of the Ischemic Area-at-Risk Despite Partial Resolution of Myocardial Edema Twenty-Four Hours After Myocardial Infarction in Swine

Objective: Accurate delineation of the ischemic area-at-risk (AAR) is essential for precise quantification of tissue salvage following myocardial infarction (MI), but time-dependent changes in tissue composition may influence the AAR when it is measured after reperfusion. Based on evidence that post-MI edema declines 24 hours after reperfusion, we utilized serial contrast-enhanced computed tomography (CT) to determine if this is an optimal timepoint for retrospective assessment of the AAR in swine. Methods: Swine (n=7) were subjected to a 75-minute LAD occlusion, during which an initial CT scan was performed to assess the pre-reperfusion AAR. A second CT scan was performed during re-occlusion of the LAD 24 hours later to determine the post-reperfusion AAR. Echocardiography was performed at baseline as well as 1 hour and 24 hours after reperfusion to assess end-diastolic wall thickness (EDWT) as an index of post-MI edema. Infarct size was quantified via post-mortem TTC staining and expressed relative to pre- vs. post-reperfusion AAR values. Results: Dynamic changes in EDWT were observed throughout the reperfusion period, consistent with marked edema early after reperfusion and a subsequent decline 24 hours later ( Table; top ). Despite partial resolution of edema 24 hours after reperfusion, a significant ~25% increase in the AAR was observed at this timepoint vs. pre-reperfusion values ( Table; bottom ). As a result, infarct size differed significantly if expressed relative to the pre-reperfusion AAR (91.7 ± 9.2 %) vs. the post-reperfusion AAR (70.9 ± 8.3 %, p&lt;0.01). Conclusion: The ischemic AAR is overestimated relative to pre-reperfusion values when measured retrospectively 24 hours after reperfusion, despite partial resolution of myocardial edema at this timepoint. These results illustrate how variability in post-infarction edema may complicate the assessment of relative infarct size and myocardial salvage when the AAR is measured after reperfusion.

The epicardial delivery of cardiosphere derived cells or their extracellular vesicles is safe but of limited value in experimental infarction

The epicardial administration of therapeutics via the pericardial sac offers an attractive route, since it is minimally invasive and carries no risks of coronary embolization. The aim of this study was to assess viability, safety and effectiveness of cardiosphere-derived cells (CDCs), their extracellular vesicles (EVs) or placebo administered via a mini-thoracotomy 72 h after experimental infarction in swine. The epicardial administration was completed successfully in all cases in a surgery time (knife-to-skin) below 30 min. No significant differences between groups were found in cardiac function parameters evaluated using magnetic resonance imaging before therapy and at the end of the study, despite a trend towards improved function in CDC-treated animals. Moreover, infarct size at 10 weeks was smaller in treated animals, albeit not significantly. Arrhythmia inducibility did not differ between groups. Pathological examination showed no differences, nor were there any pericardial adhesions evidenced in any case 10 weeks after surgery. These results show that the epicardial delivery of CDCs or their EVs is safe and technically easy 3 days after experimental myocardial infarction in swine, but it does not appear to have any beneficial effect on cardiac function. Our results do not support clinical translation of these therapies as implemented in this work.

Cardiac reparative therapy with adipose graft transposition procedure reduces slow conduction areas in a chronic myocardial infarction swine model

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Insituto de Salud Carlos III BACKGROUND Cardiac regenerative therapy is a promising treatment for patients with ischemic heart disease, but there are some concerns on the potential increased risk of arrhythmic events following specific cell therapies. Adipose graft transposition procedure (AGTP) is a cardiac reparative therapy consisting in transposing a vascularized adipose flap from the autologous pericardium and placing it over the epicardial scar area and has demonstrated to reduce infarct size and improve the left ventricular ejection fraction in preclinical and human studies. Specific electrophysiological properties of the scar, (i.e. slow conduction velocity (CV)) have been identified as key features of ventricular tachycardia (VT) isthmuses. PURPOSE To assess the effect of the AGTP on VT inducibility and the electrophysiological properties of the post-MI scar with ultra-high density (UHD) mapping. METHODS A left circumflex artery (first marginal branch) MI was induced in 10 Landrace X Large White pigs by delivering 1-3 coils. Two weeks post-MI, all subjects underwent baseline left ventricular endocardial UHD mapping during right ventricular pacing with 64-electrode basket mapping catheter, as well as electrophysiological study (EPS) to test for VT inducibility. Following the mapping, subjects were allocated 1:1 to AGTP or sham group. UHD mapping and EPS were repeated 30 days post-treatment (6 weeks after MI). Voltage and activation maps were analyzed off-line with self-customized Paraview-based software. Voltage cut-offs of 1.5 and 0.5mV (bipolar) defined normal tissue, border zone (BZ) and dense scar, respectively, and 6.7mV for unipolar. Conduction velocity (CV) was determined for every pair of contiguous points and areas of similar CV were quantified for every 0.2m/s steps (for up to 4 m/s). RESULTS There were no differences between groups with regard of dense scar, BZ an low unipolar voltage areas. The AGTP group had a significant reduction of the size of slow CV (&amp;lt;0.2 m/s) areas, compared to the sham group in whom it increased (-4.1 ± 1.7 vs. +2.4 ± 1.6 mm2, p = 0.028)(Figure). There were no differences in the size of other ranges of CV. EPS did not induce VT in any subject at baseline, and only in 1 of the sham group at the follow-up EPS. CONCLUSIONS Cardiac reparative therapy with AGTP of post-MI scar reduced the size of slow conduction areas and could provide a protective effect against arrhythmic events in ischemic heart disease. Abstract Figure.

Intrapericardial administration of cardiosphere derived cells or their extracellular vesicles early after experimental myocardial infarction in swine: safe, easy but of limited effectiveness

Intrapericardial administration of cardiosphere derived cells or their extracellular vesicles early after experimental myocardial infarction in swine: safe, easy but of limited effectiveness

From the Literature

From the Literature

Abstract 13381: hiPSC of CIITA and B2M KO Derived Cardiac Cells Engineered 3D Spheroid Transplantation Induce Tachycardia in Myocardial Infarction in Swine

Introduction: Human induced pluripotent stem cells (hiPSCs) are among one the most significant discoveries in life sciences. As a promising —biological drug for cell therapy, multiple lineages of iPSC-derived cardiac cells have been administered in human clinical trials in multiple important organ systems. The potential immunogenicity of hiPSC-derived cardiac cells continues to be one of the concerns in large animal models. Methods: In the present study, WT hiPSCs were generated by transfecting male human cardiac fibroblasts with Sendai viruses coding for OCT4, SOX2, KLF4, and C-MYC.Then hiPSCs carrying knockout mutations for both HLA Class I and Class II (HLAI/II-KOhiPSC) were generated via CRISPR/Cas9 gene-editing technology (Mattapally et al, 2018). hiPSCs were differentiated into cardiomyocytes (CM) endothelial cells (ECs) and spheroid cultured was performed as previously described (Mattapally et al, 2018). We evaluated spheroid transplantation and its potency for myocardial repair in the Swine. Programmed stimulation was used to determine the arrhythmogenic outcome. Results: To determine the engraftment efficacy of HLAI/II KO compared to WT Spheroid, a swine study was performed. After LAD ligation in swine, 800μm spheroid was injected into the border zone of the left ventricle. After transplantation, cell engraftment was monitored by Q-PCR. At week 4, there was a significant difference between the 2 groups. Animal groups included: MI hearts treated with 500 WT Spheroid injection (MI+WT Spheroid, n=5), MI hearts treated with 500 KO Spheroid injection (n=6), MI only hearts (n=6); the fourth group of animals underwent sham surgery (Sham, n=6). Arrhythmia was studied by programmed electrical stimulations (PES) and conduction velocities measured with electrode mapping, and the engraftment rate by calculation of quantitative polymerase chain reaction measurements of expression of the human Y chromosome. Engraftment of iPSC-CMs was found in both treatment groups; however, a significantly higher engraftment rate was found in KO Spheroid. The spheroid treatment is associated with significant changes in arrhythmogenicity. Conclusion: Our study established the improved graft but associated with arrhythmogenicity.

Abstract 16836: Quantitative Speckle Tracking Strain Analysis of Border and Remote Left Ventricular Regions After an Infero-Lateral Myocardial Infarction in a Chronic Swine Model

Introduction: A myocardial infarction (MI) imposes a significant pathological load on the viable myocardium, leading to an acutely adaptive response and chronically maladaptive remodeling. In patients with an inferolateral MI, the mechanical load on the remote regions is significant, and thus the resulting ventricular remodeling is extensive and often leading to congestive heart failure. In this study, we used 3D echocardiography combined with speckle tracking strain to quantify the myocardial strains of the remote and border zone in an inferolateral MI swine. Hypothesis: An inferolateral MI imposes significant changes in myocardial strains is not only the border zone but also the remote regions. Methods: Six swine were induced with an inferolateral MI by ethanol injection. The animals were survived to 10 weeks post-infarction. Nine healthy swine were used as controls. Both animal groups underwent cardiac echocardiography with Siemens, by tunneling of a transesophageal probe into the thoracic cavity for direct placement onto the left atrium, such that the entire left heart was imaged. Strain analysis was performed with eSie LV analysis (Figure A). Results: EF was significantly lower than the control group (43.0±8.2% vs 52.2±5.2%, p=0.0190). EDV and ESV in the MI group were greater compared to the control group (127.8±32.0 ml vs 81.9±19.2 ml, p=0.0040, and 74.5±28.6 ml vs 38.5±6.8 ml, p=0.0027, respectively) indicative of remodeling. Circumferential end-systolic strains of basal- and mid-inferolateral wall in the MI group were significantly reduced compared to the control group (24.1±20.0% vs 48.0±18.6%, p=0.0339 and 10.5±11.4% vs 27.8±12.8%, p=0.0186, respectively). Similarly, longitudinal strain in mid-inferolateral wall in the MI group was significantly reduced (-7.8±5.8% vs -16.3±12.8%, p=0.0120) (Figure B, C). Conclusion: Reduction in both circumferential and longitudinal strains were observed in the border zone, but not in the remote zone.

Erratum for the Research Article: "Exosomes secreted by hiPSC-derived cardiac cells improve recovery from myocardial infarction in swine" by L. Gao, L. Wang, Y. Wei, P. Krishnamurthy, G. P. Walcott, P. Menasché, J. Zhang.

In the Research Article “Exosomes secreted by hiPSC-derived cardiac cells improve recovery from myocardial infarction in swine,” the images displayed in Fig. 4A lower right panel and fig. S7C of the Supplementary Materials were incorrect. The legends for the figures were correct as written and remain unchanged. The online PDF and HTML (full text) of main text and the Supplementary Materials have been updated with the corrected figure panels.

Exosomes secreted by hiPSC-derived cardiac cells improve recovery from myocardial infarction in swine.

Cell therapy treatment of myocardial infarction (MI) is mediated, in part, by exosomes secreted from transplanted cells. Thus, we compared the efficacy of treatment with a mixture of cardiomyocytes (CMs; 10 million), endothelial cells (ECs; 5 million), and smooth muscle cells (SMCs; 5 million) derived from human induced pluripotent stem cells (hiPSCs), or with exosomes extracted from the three cell types, in pigs after MI. Female pigs received sham surgery; infarction without treatment (MI group); or infarction and treatment with hiPSC-CMs, hiPSC-ECs, and hiPSC-SMCs (MI + Cell group); with homogenized fragments from the same dose of cells administered to the MI + Cell group (MI + Fra group); or with exosomes (7.5 mg) extracted from a 2:1:1 mixture of hiPSC-CMs:hiPSC-ECs:hiPSC-SMCs (MI + Exo group). Cells and exosomes were injected into the injured myocardium. In vitro, exosomes promoted EC tube formation and microvessel sprouting from mouse aortic rings and protected hiPSC-CMs by reducing apoptosis, maintaining intracellular calcium homeostasis, and increasing adenosine 5'-triphosphate. In vivo, measurements of left ventricular ejection fraction, wall stress, myocardial bioenergetics, cardiac hypertrophy, scar size, cell apoptosis, and angiogenesis in the infarcted region were better in the MI + Cell, MI + Fra, and MI + Exo groups than in the MI group 4 weeks after infarction. The frequencies of arrhythmic events in animals from the MI, MI + Cell, and MI + Exo groups were similar. Thus, exosomes secreted by hiPSC-derived cardiac cells improved myocardial recovery without increasing the frequency of arrhythmogenic complications and may provide an acellular therapeutic option for myocardial injury.

Interstitial changes after reperfused myocardial infarction in swine: morphometric and genetic analysis

BackgroundFollowing myocardial infarction (MI), we aimed to characterize morphometric and genetic changes in extracellular matrix (ECM) components from ischemia onset until late phases after coronary reperfusion in necrotic and salvaged myocardium.ResultsSwine were divided into one control (n = 5) and three MI groups: 90-min of ischemia without reperfusion, or followed by 1-week or 1-month reperfusion (n = 5 per group). In samples from the necrotic and salvaged areas, ECM components were morphometrically quantified and mRNA levels of factors involved in ECM remodeling were evaluated. After 90-min of ischemia, fibronectin, laminin, and elastic fibers content as well as upregulated mRNA expression of tissue inhibitors of metalloproteinases (TIMP)1, TIMP2, TIMP3 and connective tissue growth factor increased in the necrotic and salvaged myocardium. In both reperfused MI groups, collagen-I, collagen-III, elastic fibers, glycosaminoglycans, laminin, and fibronectin levels heightened in the necrotic but not the salvaged myocardium. Moreover, mRNA expression of TIMP1, TIMP2 and TIMP3, as well as metalloproteinase-2 and metalloproteinase-9 heightened in the necrotic but not in the salvaged myocardium.ConclusionsMatrix remodeling starts after ischemia onset in both necrotic and salvaged myocardium. Even if ECM composition from the salvaged myocardium was altered after severe ischemia, ECM makes a full recovery to normal composition after reperfusion. Therefore, rapid coronary reperfusion is essential not only to save cardiomyocytes but also to preserve matrix, thus avoiding impaired left ventricular remodeling.

Injectable collagen scaffold promotes swine myocardial infarction recovery by long-term local retention of transplanted human umbilical cord mesenchymal stem cells.

Stem cell therapy is an attractive approach for recovery from myocardial infarction (MI) but faces the challenges of rapid diffusion and poor survival after transplantation. Here we developed an injectable collagen scaffold to promote the long-term retention of transplanted cells in chronic MI. Forty-five minipigs underwent left anterior descending artery (LAD) ligation and were equally divided into three groups 2 months later (collagen scaffold loading with human umbilical mesenchymal stem cell (hUMSC) group, hUMSC group, and placebo group (only phosphate-buffered saline (PBS) injection)). Immunofluorescence staining indicated that the retention of transplanted cells was promoted by the collagen scaffold. Echocardiography and cardiac magnetic resonance imaging (CMR) showed much higher left ventricular ejection fraction (LVEF) and lower infarct size percentage in the collagen/hUMSC group than in the hUMSC and placebo groups at 12 months after treatment. There were also higher densities of vWf-, α-sma-, and cTnT-positive cells in the infarct border zone in the collagen/cell group, as revealed by immunohistochemical analysis, suggesting better angiogenesis and more cardiomyocyte survival after MI. Thus, the injectable collagen scaffold was safe and effective on a large animal myocardial model, which is beneficial for constructing a favorable microenvironment for applying stem cells in clinical MI.

Production of Swine Myocardial Infarction and Ischemic Heart Failure Models Using a Three-Dimensional Bioprinted Occluder

Objectives: Clinical reproducibility of large animal models is important for developing new therapies for myocardial infarction (MI) and ischemic heart failure (IHF). This study aimed to induce MI and IHF in a swine model by using 3D bioprinted occluders to interrupt intravascular blood flow permanently. Methods: The 3D bioprinted occluder was placed in the proximal left anterior descending artery using a guide wire and a balloon catheter. Echocardiography was performed at the baseline, post MI (day 7-14), and at 28 days follow-up after the placement of the occluder to evaluate cardiac function. Quantitative coronary angiography was performed at baseline, post MI (immediately after the procedure) and at 42 days follow-up. Histopathology confirmed the deformation of the heart tissue and hypoxic damage.Results: Luminal diameter distal to the 3D bioprinted occluder was significantly reduced from the baseline to 42 days follow-up and left ventricular (LV) ejection fraction gradually decreased from the baseline to 28 days follow-up after the induction of MI. Tetrazolium staining showed firm and white area of the infarction in the LV apex and LV anterior wall. Hematoxylin and eosin stained section samples showed loss of normal architecture and morphology of myocytes in the LV myocardium. In addition, HIF-1 alpha was expressed in the ischemic myocardium area by immunohistochemistry staining. Conclusions: The customized occluder via 3D bioprinting technology could induce a stable, consistent and reproducible swine MI and IHF model.

Early reductive stress and late onset overexpression of antioxidant enzymes in experimental myocardial infarction

Reductive stress is defined as a pathophysiological situation in which the cell becomes more reduced than in the normal, resting state. It represents a disturbance in the redox state that is harmful to biological systems. Our aim was to study the occurrence of reductive stress in the early phases of experimental myocardial infarction and to determine the mechanisms leading to such stress using a swine model. During the ischemic period, we found a decrease in the oxidized to reduced glutathione ratio (GSSG/GSH) (0.7–0.3), in the lactate to pyruvate ratio (42.7–132.4), in protein glutathionylation (111.8–96.1), and in p38 phosphorylation (0.9–0.4). This was accompanied by a significant increase in the expression of Thioredoxin (TXN) (0.6–1.9) and peroxiredoxin (PRDX6) (0.6–1.6) in different left ventricle areas. After reperfusion, there was a massive increase in oxidative damage markers including lipid peroxidation (0.2–0.4), protein carbonylation (144.9–462.8), and glutathionylation (111.8–176.8). Concomitantly, we found an activation of nuclear factor erythroid 2-related factor 2 (Nrf2) (1.2–6.1) and of a set of antioxidant enzymes including TXN, PRDX6, glutathione peroxidase (GPX1), glutathione reductase (GSR), and glucose 6 phosphate dehydrogenase (G6PD). We describe an early reductive, followed by a late onset oxidative stress (1 week and 1 month after reperfusion) in a swine myocardial infarction model. The occurrence of an early reductive phase may explain the lack of effectiveness of antioxidant therapies when administered in the early phases after reperfusion of ischemic hearts.

Magnetic resonance microscopy and correlative histopathology of the infarcted heart

Delayed enhancement cardiovascular magnetic resonance (MR) is the gold-standard for non-invasive assessment after myocardial infarction (MI). MR microscopy (MRM) provides a level of detail comparable to the macro objective of light microscopy. We used MRM and correlative histopathology to identify infarct and remote tissue in contrast agent-free multi-sequence MRM in swine MI hearts. One control group (n = 3 swine) and two experimental MI groups were formed: 90 min of ischemia followed by 1 week (acute MI = 6 swine) or 1 month (chronic MI = 5 swine) reperfusion. Representative samples of each heart were analysed by contrast agent-free multi-sequence (T1-weighting, T2-weighting, T2*-weighting, T2-mapping, and T2*-mapping). MRM was performed in a 14-Tesla vertical axis imager (Bruker-AVANCE 600 system). Images from MRM and the corresponding histopathological stained samples revealed differences in signal intensities between infarct and remote areas in both MI groups (p-value < 0.001). The multivariable models allowed us to precisely classify regions of interest (acute MI: specificity 92% and sensitivity 80%; chronic MI: specificity 100% and sensitivity 98%). Probabilistic maps based on MRM images clearly delineated the infarcted regions. As a proof of concept, these results illustrate the potential of MRM with correlative histopathology as a platform for exploring novel contrast agent-free MR biomarkers after MI.