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Chronic fibrosis caused by acute myocardial infarction (MI) leads to increased morbidity and mortality due to cardiac dysfunction. We have developed a therapeutic materials strategy that aims to mitigate myocardial fibrosis by utilizing injectable polymeric microstructures to mechanically alter the microenvironment. Polymeric microstructures were fabricated using photolithographic techniques and studied in a three-dimensional culture model of the fibrotic environment and by direct injection into the infarct zone of adult rats. Here, we show dose-dependent down-regulation of expression of genes associated with the mechanical fibrotic response in the presence of microstructures. Injection of this microstructured material into the infarct zone decreased levels of collagen and TGF-β, increased elastin deposition and vascularization in the infarcted region, and improved functional outcomes after six weeks. Our results demonstrate the efficacy of these discrete anti-fibrotic microstructures and suggest a potential therapeutic materials approach for combatting pathologic fibrosis., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background and Objectives: Clinical trials of bone-marrow (BM)-derived cells for therapy after acute myocardial infarct (MI) have been controversial. The most commonly used cells for these trials have been mononuclear cells (MNC), obtained by fractionation of BM cells (BMCs) via different protocols. In this study, we performed a head-to-head comparison of: 1) whole BMC; 2) fractionated BM (fBM) using the commonly used Ficoll protocol; 3) the extract derived from the fBM (fBM extract) versus 4) saline (HBSS) control for treatment of acute MI., Methods: In total, 155 male C57BL/6J (10-12-week old) mice were included. Echocardiography was performed at baseline and 2 days after permanent ligation of the left anterior descending artery to induce MI. Echocardiography and histology were employed to measure outcome at 28 days post-MI., Results: Whole BMC therapy improved left ventricular ejection fraction (LVEF) post-MI, but fBM or fBM extract was not beneficial compared to control (change of LVEF of 4.9% ±4.6% (P = 0.02), -0.4% ±5.8% (P = 0.86), -2.0% ±6.2% (P = 0.97) versus -1.4% ±5.3%, respectively). The histological infarct size or numbers of arterioles or capillaries at infarct or border zone did not differ between the groups., Conclusions: Clinical studies should be performed to test whether whole BMC therapy translates into better outcome also after human MI.

Background: Endogenous cardiac progenitor cells are a promising option for cell-therapy for myocardial infarction (MI). However, obtaining adequate numbers of cardiac progenitors after MI remains a challenge. Cardiospheres (CSs) have been proposed to have cardiac regenerative properties; however, their cellular composition and how they may be influenced by the tissue milieu remains unclear., Methodology/principal Finding: Using "middle aged" mice as CSs donors, we found that acute MI induced a dramatic increase in the number of CSs in a mouse model of MI, and this increase was attenuated back to baseline over time. We also observed that CSs from post-MI hearts engrafted in ischemic myocardium induced angiogenesis and restored cardiac function. To determine the role of Sca-1(+)CD45(-) cells within CSs, we cloned these from single cell isolates. Expression of Islet-1 (Isl1) in Sca-1(+)CD45(-) cells from CSs was 3-fold higher than in whole CSs. Cloned Sca-1(+)CD45(-) cells had the ability to differentiate into cardiomyocytes, endothelial cells and smooth muscle cells in vitro. We also observed that cloned cells engrafted in ischemic myocardium induced angiogenesis, differentiated into endothelial and smooth muscle cells and improved cardiac function in post-MI hearts., Conclusions/significance: These studies demonstrate that cloned Sca-1(+)CD45(-) cells derived from CSs from infarcted "middle aged" hearts are enriched for second heart field (i.e., Isl-1(+)) precursors that give rise to both myocardial and vascular tissues, and may be an appropriate source of progenitor cells for autologous cell-therapy post-MI.

Objective: The endogenous role of the VEGF family member vascular endothelial growth factor-B (VEGF-B) in pathological angiogenesis remains unclear., Methods and Results: We studied the role of VEGF-B in various models of pathological angiogenesis using mice lacking VEGF-B (VEGF-B(-/-)) or overexpressing VEGF-B(167). After occlusion of the left coronary artery, VEGF-B deficiency impaired vessel growth in the ischemic myocardium whereas, in wild-type mice, VEGF-B(167) overexpression enhanced revascularization of the infarct and ischemic border zone. By contrast, VEGF-B deficiency did not affect vessel growth in the wounded skin, hypoxic lung, ischemic retina, or ischemic limb. Moreover, VEGF-B(167) overexpression failed to enhance vascular growth in the skin or ischemic limb., Conclusions: VEGF-B appears to have a relatively restricted angiogenic activity in the ischemic heart. These insights might offer novel therapeutic opportunities.

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

Repairing cardiac tissue after myocardial infarction (MI) is one of the most challenging goals in tissue engineering. Following ischemic injury, significant matrix remodeling and the formation of avascular scar tissue significantly impairs cell engraftment and survival in the damaged myocardium. This limits the efficacy of cell replacement therapies, demanding strategies that reduce pathological scarring to create a suitable microenvironment for healthy tissue regeneration. Here, we demonstrate the successful fabrication of discrete hyaluronic acid (HA)-based microrods to provide local biochemical and biomechanical signals to reprogram cells and attenuate cardiac fibrosis. HA microrods were produced in a range of physiological stiffness and shown to degrade in the presence of hyaluronidase. Additionally, we show that fibroblasts interact with these microrods in vitro, leading to significant changes in proliferation, collagen expression and other markers of a myofibroblast phenotype. When injected into the myocardium of an adult rat MI model, HA microrods prevented left ventricular wall thinning and improved cardiac function at 6 weeks post infarct.

Background: Endogenous cardiac progenitor cells are a promising option for cell-therapy for myocardial infarction (MI). However, obtaining adequate numbers of cardiac progenitors after MI remains a challenge. Cardiospheres (CSs) have been proposed to have cardiac regenerative properties; however, their cellular composition and how they may be influenced by the tissue milieu remains unclear. Methodology/Principal Finding: Using ''middle aged'' mice as CSs donors, we found that acute MI induced a dramatic increase in the number of CSs in a mouse model of MI, and this increase was attenuated back to baseline over time. We also observed that CSs from post-MI hearts engrafted in ischemic myocardium induced angiogenesis and restored cardiac function. To determine the role of Sca-1+CD45- cells within CSs, we cloned these from single cell isolates. Expression of Islet- 1 (Isl1) in Sca-1+CD45- cells from CSs was 3-fold higher than in whole CSs. Cloned Sca-1+CD45- cells had the ability to differentiate into cardiomyocytes, endothelial cells and smooth muscle cells in vitro. We also observed that cloned cells engrafted in ischemic myocardium induced angiogenesis, differentiated into endothelial and smooth muscle cells and improved cardiac function in post-MI hearts. Conclusions/Significance: These studies demonstrate that cloned Sca-1+CD45- cells derived from CSs from infarcted ''middle aged'' hearts are enriched for second heart field (i.e., Isl-1+) precursors that give rise to both myocardial and vascular tissues, and may be an appropriate source of progenitor cells for autologous cell-therapy post-MI. [ABSTRACT FROM AUTHOR]

Objectives: Various approaches to myocardial reconstruction have been developed for the treatment of congestive heart failure resulting from ischemic cardiomyopathy. Methods: In this study we determined whether in situ application of polymers could reshape left ventricular geometry in a chronic rodent model of ischemic cardiomyopathy. Results: We demonstrate that alginate and fibrin can augment left ventricular wall thickness, resulting in reconstruction of left ventricular geometry and improvement of cardiac function. Echocardiographic results at 5 weeks after injection of alginate demonstrated persistent improvement of left ventricular fractional shortening and prevention of a continued enlargement of left ventricular dimensions, whereas fibrin glue demonstrated no progression of left ventricular negative remodeling. There was increased arteriogenesis in both the alginate and fibrin glue groups compared with that seen in the phosphate-buffered saline control group. Infarct size was significantly reduced in the fibrin group (P < .05), and there was a trend toward a smaller myocardial infarction in the alginate group. Conclusion: Intramyocardially injected polymers can be used to reshape the aneurysmal left ventricle and might therefore be an approach for myocardial reconstruction and a potential option in treating chronic heart failure in human subjects. [Copyright &y& Elsevier]

The aim of this study was to determine the feasibility and accuracy of wall motion score index (WMSI) and myocardial performance index (MPI) for measuring regional and global left ventricular (LV) function with use of high-resolution echocardiography after myocardial infarction (Ml) in mice. In 48 mice, myocardial infarction was induced by ligation in the middle of the left anterior descending coronary artery. Echocardiography was performed under anesthesia at baseline and 1 mo after MI. WMSI was analyzed by a 16-segment model on short-axis views, and wall motion was scored as 1 for normal, 2 for hypokinetic, 3 for akinetic, 4 for dyskinetic, and 5 for aneurysmal. WMSI was calculated as the sum of scores divided by the total number of segments. MPI was calculated on the basis of isovolumetric contraction time (IVCT), isovolumetric relaxation time (IVRT), and ejection time (ET): MPI = (IVCT + IVRT)/ET. We measured LV ejection fraction (LVEF), end-systolic and end-diastolic volumes (ESV and EDV), fractional shortening (FS), and infarct size (IS). LVEF at 4 wk after MI was reduced at 32.8 ± 9.0%. Linear correlation analyses showed that WMSI (1.6 ± 0.3) correlated with LVEF (r = -0.84, P < 0.0005), FS (r = -0.43, P = 0.003), and IS (34.3 ± 15.3%, r = 0.86, P < 0.0005). MPI (0.67 ± 0.09) correlated with LVEF (r = -0.67, P < 0.0005) and IS (r = 0.72, P < 0.0005). MPI also correlated with mitral inflow velocity (r = -0.68, P < 0.0005) and deceleration time (r = -0.42, P = 0.003). Stepwise regression analysis revealed that WMSI was independently associated with IS. IS, FS, mitral inflow velocity, and deceleration time were independent determinants of MPI. In conclusion, echocardiographic assessments of WMSI and MPI in mice are feasible and correlate strongly with two-dimensional measurement of LV function and IS. These novel parameters provide additional noninvasive assessment of regional and global LV function in mice after MI. [ABSTRACT FROM AUTHOR]

Objective: Myocardial regeneration based on stem cell transplantation has emerged as a potential therapeutic approach toward replacing myocardial scar with functioning contractile tissue after myocardial infarction (MI). Considerable interest has focused on bone marrow cells (BMCs) and endothelial progenitor cells (EPCs) because they appear successful in attenuating remodeling following acute MI. However, preclinical experiments toward this goal have been limited to treatment within hours of an MI, in contrast to human trials, in which cell treatment has been performed several days later after patient stabilization and autologous cell harvesting. We sought to compare the therapeutic effects of different types of putative stem and progenitor cells in a mouse model of MI using a novel closed-chest echo-guided injection approach to deliver cells 3 days after infarction.Methods: MI was surgically induced in adult male mice by performing a mid-LAD ligation. Closed-chest echo-guided injection of cells (5 x 105 in 5 ul or saline control (HBSS) into myocardium at the peri-infarct border zone was performed at day 3 post-MI in the following groups (n=8/group): mouse BMCs (mBMCs) into C57BL/6 mice, human BMCs into immunodeficient SCID mice, mBMCs into SCID, human EPCs into SCID, and HBSS into both C57BL/6 and SCID as controls. Echocardiography was accomplished in a blinded manner with a Vevo 660 system (VisualSonics, Toronto) at baseline, 2 days post-MI (before injection), and at day 28 post-MI.Results: Left ventricular ejection fraction (LVEF) was uniformly reduced from 57.2+/-4.0% to 38.4+/-3.7% (p<0.0001) after MI in all groups. Mice injected with mBMCs showed the best effect with significant improvement in global LVEF (37.8+/-2.3% vs 44.4+/-6.3%, p=0.03), and in regional wall motion index in the infarct area (1.79+/-0.21 vs 1.4+/-0.29, p=0.02) at day 28, and there was a tendency toward less dilation of cardiac dimensions compared with that before injection. The global systolic function of the treatment group injected with mBMCs was significantly better preserved than that of its corresponding control group (44.4+/-6.3% vs 31.1+/-10.4%, p<0.0005). Human EPC injection showed a non-significant trend toward improvement of LVEF and less LV dilation, while the LVEF of its corresponding control group continued to decrease, resulting in a significant difference between the EPC group and its controls at day 28 (41.5 +/-4.3 vs 32.1+/-6.3, p<0.0005).Conclusions: Unfractionated mouse bone marrow cells attenuated ventricular remodeling and partially preserved LV function when delivered several days after surgically-induced MI. However, injection of different cell types affects LV function to varying extents. The percutaneous echo-guided injection approach made it possible to assess therapeutic cell implantation at a clinically relevant time after MI in a mouse model.Molecular Therapy (2006) 13, S175–S175; doi: 10.1016/j.ymthe.2006.08.521 [ABSTRACT FROM AUTHOR]

Objectives: In this study, we determined whether fibrin glue improves cell transplant retention and survival, reduces infarct expansion, and induces neovasculature formation.Background: Current efforts in restoring the myocardium after myocardial infarction (MI) include the delivery of viable cells to replace necrotic cardiomyocytes. Cellular transplantation techniques are, however, limited by transplanted cell retention and survival within the ischemic tissue.Methods: The left coronary artery of rats was occluded for 17 min followed by reperfusion. One week later, bovine serum albumin (BSA), fibrin glue, skeletal myoblasts in BSA, or skeletal myoblasts in fibrin glue were injected into the infarcted area of the left ventricle. The animals were euthanized five weeks after injection, and their hearts were excised, fresh frozen, and sectioned for histology and immunohistochemistry.Results: After five weeks, the mean area covered by skeletal myoblasts in fibrin glue was significantly greater than the area covered by myoblasts injected in BSA. Myoblasts within the infarct were often concentrated around arterioles. The infarct scar size and myoblasts in the fibrin group were significantly smaller than those in the control and BSA groups. Fibrin glue also significantly increased the arteriole density in the infarct scar as compared with the control group.Conclusions: This study indicates that fibrin glue increases cell transplant survival, decreases infarct size, and increases blood flow to ischemic myocardium. Therefore, fibrin glue may have potential as a biomaterial scaffold to improve cellular cardiomyoplasty treat and MIs. [Copyright &y& Elsevier]