Border Zone Myocardium Research Articles

Pharmacological inhibition of RUNX1 reduces infarct size after acute myocardial infarction in rats and underlying mechanism revealed by proteomics implicates repressed cathepsin levels

Myocardial infarction (MI) results in prolonged ischemia and the subsequent cell death leads to heart failure which is linked to increased deaths or hospitalizations. New therapeutic targets are urgently needed to prevent cell death and reduce infarct size among patients with MI. Runt-related transcription factor-1 (RUNX1) is a master-regulator transcription factor intensively studied in the hematopoietic field. Recent evidence showed that RUNX1 has a critical role in cardiomyocytes post-MI. The increased RUNX1 expression in the border zone of the infarct heart contributes to decreased cardiac contractile function and can be therapeutically targeted to protect against adverse cardiac remodelling. This study sought to investigate whether pharmacological inhibition of RUNX1 function has an impact on infarct size following MI. In this work we demonstrate that inhibiting RUNX1 with a small molecule inhibitor (Ro5-3335) reduces infarct size in an in vivo rat model of acute MI. Proteomics study using data-independent acquisition method identified increased cathepsin levels in the border zone myocardium following MI, whereas heart samples treated by RUNX1 inhibitor present decreased cathepsin levels. Cathepsins are lysosomal proteases which have been shown to orchestrate multiple cell death pathways. Our data illustrate that inhibition of RUNX1 leads to reduced infarct size which is associated with the suppression of cathepsin expression. This study demonstrates that pharmacologically antagonizing RUNX1 reduces infarct size in a rat model of acute MI and unveils a link between RUNX1 and cathepsin-mediated cell death, suggesting that RUNX1 is a novel therapeutic target that could be exploited clinically to limit infarct size after an acute MI.

Infliximab Limits Injury in Myocardial Infarction.

The purpose of this study was to investigate a therapeutic approach targeting the inflammatory response and consequent remodeling from ischemic myocardial injury. Coronary thrombus aspirates were collected from patients at the time of ST-segment-elevation myocardial infarction and subjected to array-based proteome analysis. Clinically indistinguishable at myocardial infarction (MI), patients were stratified into vulnerable and resilient on the basis of 1-year left ventricular ejection fraction and death. Network analysis from coronary aspirates revealed prioritization of tumor necrosis factor-α signaling in patients with worse clinical outcomes. Infliximab, a tumor necrosis factor-α inhibitor, was infused intravenously at reperfusion in a porcine MI model to assess whether infliximab-mediated immune modulation impacts post-MI injury. At 3 days after MI (n=7), infliximab infusion increased proregenerative M2 macrophages in the myocardial border zone as quantified by immunofluorescence (24.1%±23.3% in infliximab versus 9.29%±8.7% in sham; P<0.01). Concomitantly, immunoassays of coronary sinus samples quantified lower troponin I levels (41.72±7.34 pg/mL versus 58.11±10.75 pg/mL; P<0.05) and secreted protein analysis revealed upregulation of injury-modifying interleukin-2, -4, -10, -12, and -18 cytokines in the infliximab-treated cohort. At 4 weeks (n=12), infliximab treatment resulted in significant protective influence, improving left ventricular ejection fraction (53.9%±5.4% versus 36.2%±5.3%; P<0.001) and reducing scar size (8.31%±10.9% versus 17.41%±12.5%; P<0.05). Profiling of coronary thrombus aspirates in patients with ST-segment-elevation MI revealed highest association for tumor necrosis factor-α in injury risk. Infliximab-mediated immune modulation offers an actionable pathway to alter MI-induced inflammatory response, preserving contractility and limiting adverse structural remodeling.

Lipomatous Metaplasia Is Associated With Ventricular Tachycardia Recurrence Following Ablation in Patients With Nonischemic Cardiomyopathy

BackgroundVentricular tachycardia (VT) recurrence rates remain high following ablation among patients with nonischemic cardiomyopathy (NICM). ObjectivesThis study sought to define the prevalence of lipomatous metaplasia (LM) in patients with NICM and VT and its association with postablation VT recurrence. MethodsFrom patients who had ablation of left ventricular VT, we retrospectively identified 113 consecutive NICM patients with preprocedural contrast-enhanced cardiac computed tomography (CECT), from which LM was segmented. Nested within this cohort were 62 patients that prospectively underwent CECT and cardiac magnetic resonance from which myocardial border zone and dense late gadolinium enhancement (LGE) were segmented. A control arm of 30 NICM patients without VT with CECT was identified. ResultsLM was identified among 57% of control patients without VT vs 83% of patients without VT recurrence and 100% of patients with VT recurrence following ablation. In multivariable analyses, LM extent was the only independent predictor of VT recurrence, with an adjusted HR per 1-g LM increase of 1.1 (P < 0.001). Patients with LM extent ≥2.5 g had 4.9-fold higher hazard of VT recurrence than those with LM <2.5 g (P < 0.001). In the nested cohort with 32 VT recurrences, LM extent was independently associated with VT recurrence after adjustment for border zone and LGE extent (HR per 1 g increase: 1.1; P = 0.036). ConclusionsMyocardial LM is prevalent in patients with NICM of a variety of etiologies, and its extent is associated with postablation VT recurrence independent of the degree of fibrosis.

Angiogenic stem cell delivery platform to augment post-infarction neovasculature and reverse ventricular remodeling

Many cell-based therapies are challenged by the poor localization of introduced cells and the use of biomaterial scaffolds with questionable biocompatibility or bio-functionality. Endothelial progenitor cells (EPCs), a popular cell type used in cell-based therapies due to their robust angiogenic potential, are limited in their therapeutic capacity to develop into mature vasculature. Here, we demonstrate a joint delivery of human-derived endothelial progenitor cells (EPC) and smooth muscle cells (SMC) as a scaffold-free, bi-level cell sheet platform to improve ventricular remodeling and function in an athymic rat model of myocardial infarction. The transplanted bi-level cell sheet on the ischemic heart provides a biomimetic microenvironment and improved cell–cell communication, enhancing cell engraftment and angiogenesis, thereby improving ventricular remodeling. Notably, the increased density of vessel-like structures and upregulation of biological adhesion and vasculature developmental genes, such as Cxcl12 and Notch3, particularly in the ischemic border zone myocardium, were observed following cell sheet transplantation. We provide compelling evidence that this SMC-EPC bi-level cell sheet construct can be a promising therapy to repair ischemic cardiomyopathy.

Tenascin-C aggravates ventricular dilatation and angiotensin-converting enzyme activity after myocardial infarction in mice.

AimsTenascin‐C (TN‐C) is suggested to be detrimental in cardiac remodelling after myocardial infarction (MI). The aim of this study is to reveal the effects of TN‐C on extracellular matrix organization and its haemodynamic influence in an experimental mouse model of MI and in myocardial cell culture during hypoxic conditions.Methods and resultsMyocardial infarction was induced in TN‐C knockout (TN‐C KO) and wild‐type mice. Six weeks later, cardiac function was studied by magnetic resonance imaging and under isolated working heart conditions. Myocardial mRNA levels and immunoreactivity of TN‐C, TIMP‐1, TIMP‐3, and matrix metalloproteinase (MMP)‐9, as well as serum and tissue activities of angiotensin‐converting enzyme (ACE), were determined at 1 and 6 weeks after infarction. Cardiac output and external heart work were higher, while left ventricular wall stress and collagen expression were decreased (P < 0.05) in TN‐C KO mice as compared with age‐matched controls at 6 weeks after infarction. TIMP‐1 expression was down‐regulated at 1 and 6 weeks, and TIMP‐3 expression was up‐regulated at 1 week (P < 0.01) after infarction in knockout mice. MMP‐9 level was lower in TN‐C KO at 6 weeks after infarction (P < 0.05). TIMP‐3/MMP‐9 ratio was higher in knockout mice at 1 and 6 weeks after infarction (P < 0.01). ACE activity in the myocardial border zone (i.e. between scar and free wall) was significantly lower in knockout than in wild‐type mice 1 week after MI (P < 0.05).ConclusionsTenascin‐C expression is induced by hypoxia in association with ACE activity and MMP‐2 and MMP‐9 elevations, thereby promoting left ventricular dilatation after MI.

Delivery of progenitor cells with injectable shear-thinning hydrogel maintains geometry and normalizes strain to stabilize cardiac function after ischemia

ObjectivesThe ventricle undergoes adverse remodeling after myocardial infarction, resulting in abnormal biomechanics and decreased function. We hypothesize that tissue-engineered therapy could minimize postischemic remodeling through mechanical stress reduction and retention of tensile myocardial properties due to improved endothelial progenitor cell retention and intrinsic biomechanical properties of the hyaluronic acid shear-thinning gel. MethodsEndothelial progenitor cells were harvested from adult Wistar rats and resuspended in shear-thinning gel. The constructs were injected at the border zone of ischemic rat myocardium in an acute model of myocardial infarction. Myocardial remodeling, tensile properties, and hemodynamic function were analyzed: control (phosphate-buffered saline), endothelial progenitor cells, shear-thinning gel, and shear-thinning gel + endothelial progenitor cells. Novel high-resolution, high-sensitivity ultrasound with speckle tracking allowed for global strain analysis. Uniaxial testing assessed tensile biomechanical properties. ResultsShear-thinning gel + endothelial progenitor cell injection significantly increased engraftment and retention of the endothelial progenitor cells within the myocardium compared with endothelial progenitor cells alone. With the use of strain echocardiography, a significant improvement in left ventricular ejection fraction was noted in the shear-thinning gel + endothelial progenitor cell cohort compared with control (69.5% ± 10.8% vs 40.1% ± 4.6%, P = .04). A significant normalization of myocardial longitudinal displacement with subsequent stabilization of myocardial velocity with shear-thinning gel + endothelial progenitor cell therapy compared with control was also evident (0.84 + 0.3 cm/s vs 0.11 ± 0.01 cm/s, P = .03). A significantly positive and higher myocardial strain was observed in shear-thinning gel + endothelial progenitor cell (4.5% ± 0.45%) compared with shear-thinning gel (3.7% ± 0.24%), endothelial progenitor cell (3.5% ± 0.97%), and control (8.6% ± 0.3%, P = .05). A resultant reduction in dynamic stiffness was noted in the shear-thinning gel + endothelial progenitor cell cohort. ConclusionsThis novel injectable shear-thinning hyaluronic acid hydrogel demonstrates stabilization of border zone myocardium with reduction in adverse myocardial remodeling and preservation of myocardial biomechanics. The cellular construct provides a normalization of strain measurements and reduces left ventricular dilatation, thus resulting in improvement of left ventricular function.

Label-free Evaluation of Myocardial Infarct in Surgically Excised Ventricular Myocardium by Raman Spectroscopy

Understanding the viability of the ischemic myocardial tissue is a critical issue in determining the appropriate surgical procedure for patients with chronic heart failure after myocardial infarction (MI). Conventional MI evaluation methods are; however, preoperatively performed and/or give an indirect information of myocardial viability such as shape, color, and blood flow. In this study, we realize the evaluation of MI in patients undergoing cardiac surgery by Raman spectroscopy under label-free conditions, which is based on intrinsic molecular constituents related to myocardial viability. We identify key signatures of Raman spectra for the evaluation of myocardial viability by evaluating the infarct border zone myocardium that were excised from five patients under surgical ventricular restoration. We also obtain a prediction model to differentiate the infarcted myocardium from the non-infarcted myocardium by applying partial least squares regression-discriminant analysis (PLS-DA) to the Raman spectra. Our prediction model enables identification of the infarcted tissues and the non-infarcted tissues with sensitivities of 99.98% and 99.92%, respectively. Furthermore, the prediction model of the Raman images of the infarct border zone enabled us to visualize boundaries between these distinct regions. Our novel application of Raman spectroscopy to the human heart would be a useful means for the detection of myocardial viability during surgery.

Effects of hydrogel injection on borderzone contractility post-myocardial infarction.

Injectable hydrogels are a potential therapy for mitigating adverse left ventricular (LV) remodeling after myocardial infarction (MI). Previous studies using magnetic resonance imaging (MRI) have shown that hydrogel treatment improves systolic strain in the borderzone (BZ) region surrounding the infarct. However, the corresponding contractile properties of the BZ myocardium are still unknown. The goal of the current study was to quantify the in vivo contractile properties of the BZ myocardium post-MI in an ovine model treated with an injectable hydrogel. Contractile properties were determined 8 weeks following posterolateral MI by minimizing the difference between in vivo strains and volume calculated from MRI and finite element model predicted strains and volume. This was accomplished by using a combination of MRI, catheterization, finite element modeling, and numerical optimization. Results show contractility in the BZ of animals treated with hydrogel injection was significantly higher than untreated controls. End-systolic (ES) fiber stress was also greatly reduced in the BZ of treated animals. The passive stiffness of the treated infarct region was found to be greater than the untreated control. Additionally, the wall thickness in the infarct and BZ regions was found to be significantly higher in the treated animals. Treatment with hydrogel injection significantly improved BZ function and reduced LV remodeling, via altered MI properties. These changes are linked to a reduction in the ES fiber stress in the BZ myocardium surrounding the infarct. The current results imply that injectable hydrogels could be a viable therapy for maintaining LV function post-MI.

Short term doxycycline treatment induces sustained improvement in myocardial infarction border zone contractility.

Decreased contractility in the non-ischemic border zone surrounding a MI is in part due to degradation of cardiomyocyte sarcomeric components by intracellular matrix metalloproteinase-2 (MMP-2). We recently reported that MMP-2 levels were increased in the border zone after a MI and that treatment with doxycycline for two weeks after MI was associated with normalization of MMP-2 levels and improvement in ex-vivo contractile protein developed force in the myocardial border zone. The purpose of the current study was to determine if there is a sustained effect of short term treatment with doxycycline (Dox) on border zone function in a large animal model of antero-apical myocardial infarction (MI). Antero-apical MI was created in 14 sheep. Seven sheep received doxycycline 0.8 mg/kg/hr IV for two weeks. Cardiac MRI was performed two weeks before, and then two and six weeks after MI. Two sheep died prior to MRI at six weeks from surgical/anesthesia-related causes. The remaining 12 sheep completed the protocol. Doxycycline induced a sustained reduction in intracellular MMP-2 by Western blot (3649±643 MI+Dox vs 9236±114 MI relative intensity; p = 0.0009), an improvement in ex-vivo contractility (65.3±2.0 MI+Dox vs 39.7±0.8 MI mN/mm2; p<0.0001) and an increase in ventricular wall thickness at end-systole 1.0 cm from the infarct edge (12.4±0.6 MI+Dox vs 10.0±0.5 MI mm; p = 0.0095). Administration of doxycycline for a limited two week period is associated with a sustained improvement in ex-vivo contractility and an increase in wall thickness at end-systole in the border zone six weeks after MI. These findings were associated with a reduction in intracellular MMP-2 activity.

Quantitative Proteomics and Immunohistochemistry Reveal Insights into Cellular and Molecular Processes in the Infarct Border Zone One Month after Myocardial Infarction.

Postinfarction remodeling and expansion of the peri-infarct border zone (BZ) directly correlate with mortality following myocardial infarction (MI); however, the cellular and molecular mechanisms underlying remodeling processes in the BZ remain unclear. Herein, we utilized a label-free quantitative proteomics approach in combination with immunohistochemical analyses to gain a better understanding of processes contributing to postinfarction remodeling of the peri-infarct BZ in a swine model of MI with reperfusion. Our analysis uncovered a significant down-regulation of proteins involved in energy metabolism, indicating impaired myocardial energetics and possibly mitochondrial dysfunction, in the peri-scar BZ. An increase in endothelial and vascular smooth muscles cells, as well as up-regulation of proteins implicated in vascular endothelial growth factor (VEGF) signaling and marked changes in the expression of extracellular matrix and subendothelial basement membrane proteins, is indicative of active angiogenesis in the infarct BZ. A pronounced increase in macrophages in the peri-infarct BZ was also observed, and proteomic analysis uncovered evidence of persistent inflammation in this tissue. Additional evidence suggested an increase in cellular proliferation that, concomitant with increased nestin expression, indicates potential turnover of endogenous stem cells in the BZ. A marked up-regulation of pro-apoptotic proteins, as well as the down-regulation of proteins important for adaptation to mechanical, metabolic, and oxidative stress, likely contributes to increased apoptosis in the peri-infarct BZ. The cellular processes and molecular pathways identified herein may have clinical utility for therapeutic intervention aimed at limiting remodeling and expansion of the BZ myocardium and preventing the development of heart failure post-MI.

Improving Delivery of a Biomaterial Payload in Myocardial Infarction

Survival after an acute coronary syndrome has greatly improved because of advances in thrombolytic therapy, stabilization of the culprit lesion such as with coronary stents, and the use of pharmacological approaches to prevent recurrent thrombotic and arrhythmic events. Despite these approaches, however, myocardial injury culminating in myocardial infarction (MI) continues to be an all too common sequela. The MI region is a highly heterogeneous structure that contains several cell types, such as residual cardiac myocytes, inflammatory cells of different lineages, proliferating and transdifferentiating fibroblasts, and extracellular matrix proteins and signaling molecules. Although canonical thought was that the MI region was a rather static, fibrotic structure, it is now clear that this is a dynamic and ever-evolving entity with changes in geometry, biophysical properties, and cellular/extracellular composition. The time course and extent of these post-MI processes have been generically termed post-MI remodeling and is recognized as a milestone event for the initiation and progression to left ventricular (LV) dilation and dysfunction. One ubiquitous feature of post-MI remodeling is a progressive thinning and dyskinesia of the MI region, which is because of the summation of several factors: a loss of cardiac myocytes and thus functional myocardium, continuous turnover and instability of the extracellular matrix, and significant shifts in stress–strain patterns within this region throughout the cardiac cycle. Specifically, significant heterogeneity arises in the stress–strain patterns both within and surrounding the MI region and in turn can contribute to a feed-forward process of continuous activation of bioactive molecules and extracellular matrix instability. These biomechanical changes result in continued MI thinning and recruitment of border zone myocardium into the MI region, which is defined as MI expansion. As the MI expansion process continues in an inexorable fashion, the degree of heterogeneity in stress–strain relations are exacerbated, bulging of the MI region becomes evident by …

31P NMR 2D Mapping of Creatine Kinase Forward Flux Rate in Hearts with Postinfarction Left Ventricular Remodeling in Response to Cell Therapy.

Utilizing a fast 31P magnetic resonance spectroscopy (MRS) 2-dimensional chemical shift imaging (2D-CSI) method, this study examined the heterogeneity of creatine kinase (CK) forward flux rate of hearts with postinfarction left ventricular (LV) remodeling. Immunosuppressed Yorkshire pigs were assigned to 4 groups: 1) A sham-operated normal group (SHAM, n = 6); 2) A 60 minutes distal left anterior descending coronary artery ligation and reperfusion (MI, n = 6); 3) Open patch group; ligation injury plus open fibrin patch over the site of injury (Patch, n = 6); and 4) Cell group, hiPSCs-cardiomyocytes, -endothelial cells, and -smooth muscle cells (2 million, each) were injected into the injured myocardium pass through a fibrin patch (Cell+Patch, n = 5). At 4 weeks, the creatine phosphate (PCr)/ATP ratio, CK forward flux rate (Flux PCr→ATP), and k constant of CK forward flux rate (kPCr→ATP) were severely decreased at border zone myocardium (BZ) adjacent to MI. Cell treatment results in significantly increase of PCr/ATP ratio and improve the value of kPCr→ATP and Flux PCr→ATP in BZ myocardium. Moreover, the BZ myocardial CK total activity and protein expression of CK mitochondria isozyme and CK myocardial isozyme were significantly reduced, but recovered in response to cell treatment. Thus, cell therapy results in improvement of BZ bioenergetic abnormality in hearts with postinfarction LV remodeling, which is accompanied by significantly improvements in BZ CK activity and CK isozyme expression. The fast 2D 31P MR CSI mapping can reliably measure the heterogeneity of bioenergetics in hearts with post infarction LV remodeling.

Transplantation of Wharton’s Jelly Mesenchymal Stem Cells to Improve Cardiac Function in Myocardial Infarction Rats

Background: Myocardial infarction (MI) is a fatal disease that is increasing in incidence. The worst sequelae of MI include myocardial fibrosis and deterioration of pumping function that can lead to irreversible heart failure. This study aims to compare the therapeutic effect of undifferentiated versus TGF-β2–stimulated Wharton’s jelly mesenchymal stem cells (WJ-MSCs) in MI rats. Results: Left anterior descending (LAD) artery ligation-induced myocardial infarct rats were used to evaluate changes in left ventricular function and fibrosis following injection of PBS or 1.6 × 106 undifferentiated or TGF-β2–stimulated WJ-MSCs into the border zone myocardium. Electrocardiograph, echocardiogram, serum cardiac Troponin I level, Masson’s Trichrome staining, immunohistochemistry were used to analyze the therapeutic effects. We found that transplantation of both undifferentiated and TGF-β2 stimulated WJ-MSCs decreased serum Cardiac Troponin I levels, improved fractional shortening, ameliorated ejection fraction changes, and decreased the area of myocardial fibrosis. Moreover, some of the transplanted human WJ-MSCs survived in the myocardium. Conclusions: Transplantation of either undifferentiated or TGF-β2 stimulated WJ-MSCs improved left ventricular function after MI and increased survival. The effects were most marked using undifferentiated WJ-MSCs. These results indicate WJMSCs as a potential stem cell source for use in myocardial infarct therapy.

Abstract 18952: A Novel Engineered Neuregulin-hydrogel System Regenerates Mammalian Heart Muscle and Enhances Ventricular Function in a Preclinical Ovine Model of Ischemic Cardiomyopathy

Objective: The clinical efficacy of neuregulin (NRG), a ligand of the Her family receptors, is hindered by off-target exposure and requisite daily systemic infusions. We recently encapsulated NRG in a hydrogel (HG) for targeted and sustained myocardial delivery; beneficial results in a murine model of ischemic cardiomyopathy were clear. Here, we evaluate NRG-HG’s translational potential for myocardial regeneration and functional improvement in the clinical realm using a preclinical ovine model of ischemic cardiomyopathy. Methods: Male Dorset sheep (n=30) underwent baseline cardiac assessment with MRI and pressure-volume (PV) catheterization. Myocardial infarction (MI) was induced by ligating the 2 nd and 3 rd diagonal artery branches, and sheep were randomized to receive myocardial borderzone injection of 1mL saline, HG alone, NRG alone, or NRG-HG. Eight weeks post-infarction, repeat hemodynamic assessment was performed followed by tissue acquisition. A subset underwent sacrifice at 1 week for molecular analyses. Results: Analysis of myocardial borderzone 1-week post-infarction revealed NRG-HG augmented phosphorylated ErbB4, ErbB2, ERK, and histone h3 compared with all other groups. This marker activation suggests receptor activation, downstream signaling, and cardiac cell-cycle entry. At 8 weeks, NRG-HG significantly reduced scar size and augmented ventricular function (Table). There was no evidence of off-target NRG at 1 and 8 weeks, and no evidence of gel embolization or neurologic insult (by brain MRI) from intramyocardial hydrogel delivery. Conclusion: Targeted and sustained intramyocardial delivery of NRG with an engineered hydrogel platform triggers regeneration of mammalian heart muscle and augments ventricular function in a large animal model of ischemic cardiomyopathy. This novel, engineered delivery system realizes the true potential of NRG and its translation to clinical regenerative therapeutics.

Abstract 17861: Injectable Shear-thinning Hydrogels to Deliver Endothelial Progenitor Cells, Reduce Ventricular Strain, and Dynamic Stiffness to Stabilize Cardiac Function Following Ischemic Injury

The ventricle undergoes adverse remodeling, post-infarction. We developed an injectable shear-thinning hyaluronic acid hydrogel(STG) and endothelial progenitor cell construct(STG-EPC) to enhance vasculogenesis(shown previously) and mechanically stabilize the infarcted myocardium. We hypothesize that this tissue-engineered therapy will minimize adverse remodeling and maintain myocardial tensile properties in a clinically translatable therapy. EPCs(DiLDL+ VEGFR2+ CD34+) were harvested from adult Wistar Rats and suspended in STG. STG-EPC constructs were circumferentially injected at the borderzone of ischemic rat myocardium, following LAD ligation. Engraftment and retention were assessed by near infrared cellular tag. Myocardial remodeling, tensile properties, and hemodynamic function were analyzed in 4 groups: control(PBS), EPC injection(EPC), STG injection(STG), and STG-EPC construct(STG-EPC). High-resolution ultrasound with speckle tracking (VSI Vevo 2100) allowed analysis of regional epicardial and endocardial strain. Uniaxial testing assessed tensile strength. STG-EPC injection significantly increased engraftment, migration, and retention of the EPCs one-week post implant compared to EPC (0.7 vs 0.4 RFU, p=0.02). Using strain echocardiography a significant increase in left ventricular function was noted in the STG-EPC cohort. Strain echocardiography examination revealed a significant retention of myocardial longitudinal displacement with subsequent stabilization of myocardial velocity with STG-EPC therapy. A reduction in dynamic stiffness was noted in the STG-EPC cohort.(Table) This novel injectable shear-thinning hyaluronic acid hydrogel seeded with EPCs demonstrates stabilization of borderzone myocardium with reduction in adverse myocardial remodeling and preservation of myocardial biomechanics. There is a markedly increased retention of delivered stem cells with this tissue engineered therapy.

A Tissue-Engineered Chondrocyte Cell Sheet Induces Extracellular Matrix Modification to Enhance Ventricular Biomechanics and Attenuate Myocardial Stiffness in Ischemic Cardiomyopathy.

There exists a substantial body of work describing cardiac support devices to mechanically support the left ventricle (LV); however, these devices lack biological effects. To remedy this, we implemented a cell sheet engineering approach utilizing chondrocytes, which in their natural environment produce a relatively elastic extracellular matrix (ECM) for a cushioning effect. Therefore, we hypothesized that a chondrocyte cell sheet applied to infarcted and borderzone myocardium will biologically enhance the ventricular ECM and increase elasticity to augment cardiac function in a model of ischemic cardiomyopathy (ICM). Primary articular cartilage chondrocytes of Wistar rats were isolated and cultured on temperature-responsive culture dishes to generate cell sheets. A rodent ICM model was created by ligating the left anterior descending coronary artery. Rats were divided into two groups: cell sheet transplantation (1.0 × 10(7) cells/dish) and no treatment. The cell sheet was placed onto the surface of the heart covering the infarct and borderzone areas. At 4 weeks following treatment, the decreased fibrotic extension and increased elastic microfiber networks in the infarct and borderzone areas correlated with this technology's potential to stimulate ECM formation. The enhanced ventricular elasticity was further confirmed by the axial stretch test, which revealed that the cell sheet tended to attenuate tensile modulus, a parameter of stiffness. This translated to increased wall thickness in the infarct area, decreased LV volume, wall stress, mass, and improvement of LV function. Thus, the chondrocyte cell sheet strengthens the ventricular biomechanical properties by inducing the formation of elastic microfiber networks in ICM, resulting in attenuated myocardial stiffness and improved myocardial function.

Invited Commentary

By using a combination of magnetic resonance imaging (MRI), catheterization, computational modeling, and numeric optimization, McGarvey and his colleagues responsible for this paper serially quantified the in vivo material properties and fiber orientation of infarcted myocardium over a 12-week period in a porcine model of myocardial infarction (MI) [1McGarvey J.R. Mojsejenko D. Dorsey S.M. et al.Temporal changes in infarct material properties: an in vivo assessment using magnetic resonance imaging and finite element simulations.Ann Thorac Surg. 2015; 100: 582-590Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar]. This is an elegant work that utilizes a well-established animal model and a multidisciplinary approach. Specifically, properties were determined by minimizing the difference between in vivo strains and volume calculated through MRI and the finite element model predicted strains and volume. These novel findings in the in vivo model are consistent with previously described ex vivo biaxial studies of infarct material properties and the circumferential change of collagen orientation in the infarcts. It would be quite helpful to use the postmortem left ventricle (LV) specimens harvested at the end of the 12-week experiment to assess the altered microstructure of the LV tissues for tissue stiffness, collagen deposition, and myofiber orientation. Hopefully, the in vitro study on the tissue microstructure will correlate with or further confirm the in vivo findings of the current study. It will also be imperative to serially quantify the in vivo material properties of remote and border-zone myocardium during the remodeling period. The current study definitely represents a significant advance in that the multiple approaches employed allow for the serial assessment of an individual infarct in vivo overtime. These diagnostic techniques may be used in the future to accurately assess the potential therapeutic efficacy of LV restraint devices, biomaterials, stem cells, and other new medications on the infarct material properties during the remodeling period in vivo overtime. Obviously, these novel approaches may be applied to quantify the in vivo material properties and fiber orientation of infarcted myocardium in patients with LV remodeling. Clinically, patients often suffer from multiple coronary artery occlusions with a more complicated MI. It can be assumed that the LV remodeling developed in patients with MI will be more complicated than that of the animal models with either left anterior descending artery (anteroapical infarcts) or left circumflex artery occlusion (posterolateral infarcts). Taken together, the current study supports the notion that the inhibition of infarct expansion is an important therapeutic target in the prevention of adverse LV remodeling after MI. The application of a multidisciplinary approach, such as a combination of MRI and computational cardiac modeling for assessing LV remodeling, is still in its infancy in cardiac surgery. It continues to be a challenge for cardiac surgeons to use the multiple diagnostic tools to improve efficiency in assessing the development of LV remodeling after MI and therapeutic efficacy in vivo overtime. This challenge would best be met through improved multidisciplinary collaboration and cooperation from other specialists, including those specializing in computational modeling, MRI, ultrasound, bioengineering, pathology, cardiology, and basic research. Temporal Changes in Infarct Material Properties: An In Vivo Assessment Using Magnetic Resonance Imaging and Finite Element SimulationsThe Annals of Thoracic SurgeryVol. 100Issue 2PreviewInfarct expansion initiates and sustains adverse left ventricular (LV) remodeling after myocardial infarction (MI) and is influenced by temporal changes in infarct material properties. Data from ex vivo biaxial extension testing support this hypothesis; however, infarct material properties have never been measured in vivo. The goal of the current study was to serially quantify the in vivo material properties and fiber orientation of infarcted myocardium over a 12-week period in a porcine model of MI. Full-Text PDF

Myofilament dysfunction contributes to impaired myocardial contraction in the infarct border zone.

After myocardial infarction, a poorly contracting nonischemic border zone forms adjacent to the infarct. The cause of border zone dysfunction is unclear. The goal of this study was to determine the myofilament mechanisms involved in postinfarction border zone dysfunction. Two weeks after anteroapical infarction of sheep hearts, we studied in vitro isometric and isotonic contractions of demembranated myocardium from the infarct border zone and a zone remote from the infarct. Maximal force development (Fmax) of the border zone myocardium was reduced by 31 ± 2% versus the remote zone myocardium (n = 6/group, P < 0.0001). Decreased border zone Fmax was not due to a reduced content of contractile material, as assessed histologically, and from myosin content. Furthermore, decreased border zone Fmax did not involve altered cross-bridge kinetics, as assessed by muscle shortening velocity and force development kinetics. Decreased border zone Fmax was associated with decreased cross-bridge formation, as assessed from muscle stiffness in the absence of ATP where cross-bridge formation should be maximized (rigor stiffness was reduced 34 ± 6%, n = 5, P = 0.011 vs. the remote zone). Furthermore, the border zone myocardium had significantly reduced phosphorylation of myosin essential light chain (ELC; 41 ± 10%, n = 4, P < 0.05). However, for animals treated with doxycycline, an inhibitor of matrix metalloproteinases, rigor stiffness and ELC phosphorylation were not reduced in the border zone myocardium, suggesting that doxycycline had a protective effect. In conclusion, myofilament dysfunction contributes to postinfarction border zone dysfunction, myofilament dysfunction involves impaired cross-bridge formation and decreased ELC phosphorylation, and matrix metalloproteinase inhibition may be beneficial for limiting postinfarct border zone dysfunction.

A bioengineered hydrogel system enables targeted and sustained intramyocardial delivery of neuregulin, activating the cardiomyocyte cell cycle and enhancing ventricular function in a murine model of ischemic cardiomyopathy.

Neuregulin-1β (NRG) is a member of the epidermal growth factor family possessing a critical role in cardiomyocyte development and proliferation. Systemic administration of NRG demonstrated efficacy in cardiomyopathy animal models, leading to clinical trials using daily NRG infusions. This approach is hindered by requiring daily infusions and off-target exposure. Therefore, this study aimed to encapsulate NRG in a hydrogel to be directly delivered to the myocardium, accomplishing sustained localized NRG delivery. NRG was encapsulated in hydrogel, and release over 14 days was confirmed by ELISA in vitro. Sprague-Dawley rats were used for cardiomyocyte isolation. Cells were stimulated by PBS, NRG, hydrogel, or NRG-hydrogel (NRG-HG) and evaluated for proliferation. Cardiomyocytes demonstrated EdU (5-ethynyl-2'-deoxyuridine) and phosphorylated histone H3 positivity in the NRG-HG group only. For in vivo studies, 2-month-old mice (n=60) underwent left anterior descending coronary artery ligation and were randomized to the 4 treatment groups mentioned. Only NRG-HG-treated mice demonstrated phosphorylated histone H3 and Ki67 positivity along with decreased caspase-3 activity compared with all controls. NRG was detected in myocardium 6 days after injection without evidence of off-target exposure in NRG-HG animals. At 2 weeks, the NRG-HG group exhibited enhanced left ventricular ejection fraction, decreased left ventricular area, and augmented borderzone thickness. Targeted and sustained delivery of NRG directly to the myocardial borderzone augments cardiomyocyte mitotic activity, decreases apoptosis, and greatly enhances left ventricular function in a model of ischemic cardiomyopathy. This novel approach to NRG administration avoids off-target exposure and represents a clinically translatable strategy in myocardial regenerative therapeutics.

Minimally invasive delivery of a novel direct epicardial assist device in a porcine heart failure model.

Despite advances in design, modern ventricular assist device placement involves median sternotomy and cardiopulmonary bypass and is associated with infectious/embolic complications. In this study, we examine the feasibility and function of a novel minimally invasive, non-blood-contacting epicardial assist device in a porcine ischemic cardiomyopathy model. Feasibility was first tested in an ex vivo thoracoscopic trainer box with slaughterhouse hearts. Five male Yorkshire swine underwent selective ligation of the circumflex artery to create a posterolateral infarct Twelve weeks after infarct, all animals underwent left minithoracotomy. A custom inflatable bladder was positioned over the epicardial surface of the infarct and firmly secured to the surrounding border zone myocardium with polypropylene mesh and minimally invasive mesh tacks. An external gas pulsation system actively inflated and deflated the bladder in synchrony with the cardiac cycle. All animals then underwent cardiac magnetic resonance imaging to assess ventricular function. All subjects successfully underwent off-pump placement of the epicardial assist device via minithoracotomy. Ejection fraction significantly improved from 29.1% ± 4.8% to 39.6% ± 4.23% (P < 0.001) when compared with pretreatment. End-systolic volume decreased (76.6 ± 13.3 mL vs 62.4 ± 12.0 mL, P < 0.001) and stroke volume increased (28.6 ± 3.4 mL vs 37.9 ± 3.1 mL, P < 0.05) when assisted. No change was noted in end-diastolic volume (105.1 ± 11.4 vs 100.3 ± 12.7). On postmortem examination, mesh fixation and device position were excellent in all cases. No adverse events were encountered. Directed epicardial assistance improves ventricular function in a porcine ischemic cardiomyopathy model and may provide a safe alternative to currently available ventricular assist device therapies. Further, the technique used for device positioning and fixation suggests that an entirely thoracoscopic approach is possible.