Postinfarction Left Ventricular Remodeling Research Articles

A catheter based chronic porcine model of post-infarct dilated heart failure

Objectives. New surgical treatments for post-infarct antero-septal myocardial akinesia have been developed but evaluation of their mode of function is hampered by absence of suitable large animal heart failure models. We aimed to develop and evaluate a human compatible model for chronic post-infarct left ventricular (LV) remodeling. Design. Fourteen female 50 kg pigs underwent catheter-based coronary artery occlusion (one hour) distal to the first LAD diagonal. Eight weight- and age-matched healthy animals served as controls. LV geometry and function were assessed after 6 weeks with cardiovascular MRI. Results. All animals recovered from interventions. Three animals died during follow-up. All intervention animals had antero-septal akinetic infarcts (mean 26.5% of LV myocardium). Intervention animals had significantly increased end-diastolic and end-systolic volumes, and decreased stroke volume, ejection fraction and cardiac output. Detailed functional analysis showed significant systolic- and diastolic-dysfunction in intervention animals. Conclusions. We have established a feasible model of post-infarct LV remodeling, which accurately simulates human pathogenesis and pathophysiology. The model may be suitable for evaluation of novel surgical alleviations for heart failure.

Does a selective non-peptide angiotensin II type 2 receptor agonist reduce post-infarction left ventricular remodeling?

Does a selective non-peptide angiotensin II type 2 receptor agonist reduce post-infarction left ventricular remodeling?

Very Mild Hypothermia During Ischemia and Reperfusion Improves Postinfarction Ventricular Remodeling

Mild hypothermia (< 4 degrees C) improves myocardial salvage after infarct reperfusion in animals and in early clinical studies. In this experiment the effect of mild hypothermia during ischemia and early reperfusion on long-term postinfarction left ventricular (LV) remodeling was assessed in an ovine infarct model. In the initial phase of the experiment the effect of progressive degrees of hypothermia on infarct size was quantified. Thirty-eight male sheep were subjected to 1 hour of ischemia using a standardized anteroapical infarct followed by 3 hours of reperfusion. Temperature was maintained at either 39.5 degrees C (n = 11), 38.5 degrees C (n = 7), 37.5 degrees C (n = 7), 36.5 degrees C (n = 7), or 35.5 degrees C (n = 6) for the entire period of ischemia and reperfusion. The area at risk (AR) and infarct size as a percentage of AR (I/AR) were determined with a double staining and planimetry technique. In the second phase of the study, chronic post-infarction remodeling was assessed in animals with nonreperfused infarcts (n = 6), 1 hour of ischemia followed by reperfusion at 39.5 degrees C (n = 6) and 1 hour of ischemia followed by reperfusion at 37.5 degrees C (n = 6). Remodeling was determined at 8 weeks after infarction using echocardiography. The I/AR in the 39.5 degrees C, 38.5 degrees C, 37.5 degrees C, 36.5 degrees C, and the 35.5 degrees C groups was 71.8 +/- 3.0%, 63.1 +/- 1.9%, 49.4 +/- 1.4%, 38.7 +/- 1.4%, and 21.7 +/- 2.2%, respectively (p < 0.05 between all groups). In the chronic study LV end systolic volume at 8 weeks after infarction was 81 +/- 8 mL in the nonreperfused group, 57 +/- 4 mL in the 39.5 degrees C reperfusion group, and 41 +/- 3 mL in the 37.5 degrees C reperfusion group (p < 0.05 for between group differences). Subtle degrees of hypothermia can significantly improve immediate myocardial salvage and long-term LV remodeling after infarct reperfusion.

β-Catenin downregulation attenuates ischemic cardiac remodeling through enhanced resident precursor cell differentiation

We analyzed the effect of conditional, alphaMHC-dependent genetic beta-catenin depletion and stabilization on cardiac remodeling following experimental infarct. beta-Catenin depletion significantly improved 4-week survival and left ventricular (LV) function (fractional shortening: CT(Deltaex3-6): 24 +/- 1.9%; beta-cat(Deltaex3-6): 30.2 +/- 1.6%, P < 0.001). beta-Catenin stabilization had opposite effects. No significant changes in adult cardiomyocyte survival or hypertrophy were observed in either transgenic line. Associated with the functional improvement, LV scar cellularity was altered: beta-catenin-depleted mice showed a marked subendocardial and subepicardial layer of small cTnT(pos) cardiomyocytes associated with increased expression of cardiac lineage markers Tbx5 and GATA4. Using a Cre-dependent lacZ reporter gene, we identified a noncardiomyocyte cell population affected by alphaMHC-driven gene recombination localized to these tissue compartments at baseline. These cells were found to be cardiac progenitor cells since they coexpressed markers of proliferation (Ki67) and the cardiomyocyte lineage (alphaMHC, GATA4, Tbx5) but not cardiac Troponin T (cTnT). The cell population overlaps in part with both the previously described c-kit(pos) and stem cell antigen-1 (Sca-1)(pos) precursor cell population but not with the Islet-1(pos) precursor cell pool. An in vitro coculture assay of highly enriched (>95%) Sca-1(pos) cardiac precursor cells from beta-catenin-depleted mice compared to cells isolated from control littermate demonstrated increased differentiation toward alpha-actin(pos) and cTnT(pos) cardiomyocytes after 10 days (CT(Deltaex3-6): 38.0 +/- 1.0% alpha-actin(pos); beta-cat(Deltaex3-6): 49.9 +/- 2.4% alpha-actin(pos), P < 0.001). We conclude that beta-catenin depletion attenuates postinfarct LV remodeling in part through increased differentiation of GATA4(pos)/Sca-1(pos) resident cardiac progenitor cells.

Abstract 1844: Temporal engraftment and functional outcome of Bone Marrow Derived Multipotent Progenitor cell transplantation (MPC) in a porcine model of postinfarction Left Ventricular (LV) Remodeling

This study compares the short term and long term functional outcomes of bone marrow derived multipotent progenitor cells (MPC) transplantation. In the short term study, the LAD was occluded distal to the 2 nd diagonal branch with PTCA balloon dilatation for 60 minutes (IR, 1 month follow-up) and MPC were delivered through a transarterial catheter, while in the long term study, the coronary artery was occluded with ligation (OCCL, 4 months follow-up). In both IR and OCCL cases, intra-myocardial injection of 50 million LacZ labeled MPC (Cell) was performed in the periscar region with 5 equal injections immediately after myocardial infarction, while in control animals (CONT) saline was injected. The myocardial bioenergetics (P-31 MRS) and LV function (MRI) were followed-up monthly (Table ). MPC transplantation resulted in improvement of ejection fraction in the OCCL study, which persists for 4 months. In the IR study, although the EF was not significantly different between the two groups at 7days postinfarction, Cell induced a significant improvement of EF at week 4 (Table ). The myocardial phosphorylation potential that is reflected by the PCr/ATP ratio was significantly higher in CELL treated group of both studies, which persists during high cardiac workstates secondary to catecholamine stimulation. Although the engraftment was low (less than 0.35%), a small portion of the engrafted cells were found co-staining positive for troponin T and/or N-cadherin suggesting differentiation to myogenic cells. The infarct size was similar between the groups at 10 days. However, the infarct size was significantly reduced at 4 months in the Cell group that was not observed in the CONT. These data demonstrate that MPC transplantation associated improvement in ventricular function and myocardial energetics persists for 4 months follow-up. The beneficial effects are likely caused by cell transplantation induced mobilization and differentiation of endogenous cardiac progenitors. This research has received full or partial funding support from the American Heart Association, AHA Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota &amp; Wisconsin). Improvement in Ejection Fraction after MPC transplantation

Differential Effects of GM-CSF and G-CSF on Infiltration of Dendritic Cells during Early Left Ventricular Remodeling after Myocardial Infarction

Several lines of evidence suggest that the immune activation after myocardial infarction (MI) induces secondary myocardial injury. Although dendritic cells (DC) are potent regulators of immunity, their role in MI is still undetermined. We investigated the effect of DC modulation by CSF on left ventricular (LV) remodeling after MI. MI was induced by ligation of the left coronary artery in male Wistar rats. G-CSF (20 microg/kg/day, MI-G, n = 33), a GM-CSF inducer (romurtide, 200 microg/kg/day, MI-GM, n = 28), or saline (MI-C, n = 55) was administered for 7 days. On day 14, MI-G animals had higher LV max dP/dt and smaller LV dimensions, whereas MI-GM animals had lower LV max dP/dt and larger LV dimensions than did MI-C animals, despite similar infarct size. In MI-C, OX62(+) DC infiltrated the infarcted and border areas, peaking on day 7. Bromodeoxyuridine-positive DC were observed in the border area during convalescence. Infiltration by DC was decreased in MI-G animals and increased in MI-GM animals compared with MI-C (p < 0.05). In the infarcted area, the heat shock protein 70, TLR2 and TLR4, and IFN-gamma expression were reduced in MI-G, but increased in MI-GM in comparison with those in MI-C animals. IL-10 expression was higher in MI-G and lower in MI-GM than in MI-C animals. In conclusion, G-CSF improves and GM-CSF exacerbates early postinfarction LV remodeling in association with modulation of DC infiltration. Suppression of DC-mediated immunity could be a new strategy for the treatment of LV remodeling after MI.

Favourable effects of exercise-based Cardiac Rehabilitation after acute myocardial infarction on left atrial remodeling

Background Left atrial enlargement is an important predictor of cardiovascular outcomes in patients after acute myocardial infarction. While the favourable effect of exercise exercise-based Cardiac Rehabilitation (CR) on postinfarction LV remodeling has been well documented, those on LA remodeling have yet to be defined. This study investigated the effects of CR on LA remodeling in postinfarction patients with moderate left ventricular (LV) dysfunction. Methods Sixty postinfarction patients were randomised randomized into two groups, each composed of 30 patients: group T (LV ejection fraction (EF) 43.7 ± 4.2%, mean ± SD) entered a 6-month CR program, whereas group C (EF 44.7 ± 4.4%, P = ns) did not. Doppler echocardiography and cardiopulmonary exercise test were performed upon enrolment and at 6-month. Results At 6-month, trained patients showed a significant ( P < 0.001) improvement in peak oxygen consumption (ΔVO 2peak = + 5.2 ± 2.1 ml/kg/min) and a reduction in LA (ΔLA V MAX = − 1.9 ± 3.7 ml/m 2) and in LV volumes (ΔLVEDV = − 3.6 ± 4.4 ml/m 2). At 6-month, untrained patients showed LA V MAX (+ 3.6 ± 4.4 ml/m 2, P < 0.001) and LV dilation (+ 4.2 ± 5.1 ml/m 2, P < 0.001; group T vs. C, P < 0.001); whereas no significant changes in VO 2peak were observed. Multiple linear regression analysis showed that age ( β = 0.442, P < 0.001), inclusion in the training group ( β = − 0.599, P < 0.001), E/A ratio ( β = − 0.210, P = 0.038), LVEDV ( β = 0.376, P < 0.001), and LVEF ( β = − 0.279, P = 0.007) are significant predictors of LA remodeling. Conclusions Six-month exercise-based CR in postinfarction patients with mild to moderate LV dysfunction induced a favourable LA remodeling.

A proteomic study of the effects of ramipril on post‐infarction left ventricular remodelling in the rabbit

In this study, we used a proteomic approach to investigate the potential proteins regulated by ramipril in post-infarction left ventricular remodelling in the rabbit. Myocardial infarction (MI) was induced in male New Zealand White rabbits (2.5-3 kg) by ligation of the left anterior descending coronary artery. Two months later, the rabbits were either left untreated (MI group) or were treated daily for one month with 0.1 mg/kg wt of ramipril (ramipril group), then sacrificed. One month of ramipril treatment resulted in a significant improvement in the LV ejection fraction (LVEF) and a decrease in hydroxyproline content. The protein profiles of LV tissue showed that ramipril caused upregulation of glutathione peroxidase, superoxide dismutase (SOD), and heart-type fatty acid binding-protein (h-FABP) and downregulation of HSP27 and cyclophilin A. Ramipril treatment caused an increase in catalase, glutathione peroxidase, and SOD activity in the LV tissue. Oxidized glutathione levels and the GSSG/GSH ratio in the heart tissue were lower in the ramipril group than in the MI group. Ramipril increased antioxidative protein expression and enzyme activity, which could partly explain the role of ramipril in attenuating LV remodelling. In addition, the present study identifies several potential protein targets which may help to explain the mechanism by which ramipril exerts its effect in post-infarction LV remodelling in the rabbit.

Effect of intensive vs standard statin therapy on endothelial progenitor cells and left ventricular function in patients with acute myocardial infarction: Statins for regeneration after acute myocardial infarction and PCI (STRAP) trial

Background Intensive statin therapy can lower the risk of recurrence of major cardiac events in patients with acute coronary syndromes. This could be related to the ability of statins to increase levels of Endothelial Progenitor Cells (EPCs), which were demonstrated to be favorably associated with a better prognosis and post-infarction left ventricular remodeling in patients with ischemic heart disease. Aim of the study First, to evaluate, in a randomized clinical trial, the effect of an intensive vs a standard treatment with statins on EPC mobilization in patients undergoing a successful primary or rescue percutaneous coronary intervention; secondary, to evaluate whether left ventricular remodeling could be influenced by statin therapy through EPC mobilization. Methods Forty ST-segment elevation myocardial infarction (STEMI) patients undergoing a successful primary or rescue PCI were randomized to receive atorvastatin 80 mg immediately after the admission (Intensive Treatment, IT) or atorvastatin 20 mg from the day of the discharge (Standard Treatment, ST). CD34+/KDR+ EPC count by flow cytometry and left ventricular function by 2-D Echo were measured on admission, at discharge and at 4 months follow up. Results We found that EPC count was similar in the two groups of patients both on admission and at discharge. At follow up, however, EPC count was higher in patients randomized to IT compared to patients randomized to ST (7.59 ± 7.30 vs 3.04 ± 3.93, p = 0.04). However, LV volumes, ejection fraction and wall motion score index were similar in both groups. Conclusions An intensive statin treatment after primary or rescue PCI is associated with a higher EPC count at follow up as compared to standard treatment. This beneficial effect did not translate in an improvement of LV function.

Relationships between regional myocardial wall stress and bioenergetics in hearts with left ventricular hypertrophy

This study utilized porcine models of postinfarction left ventricular (LV) remodeling [myocardial infarction (MI); n = 8] and concentric LV hypertrophy secondary to aortic banding (AoB; n = 8) to examine the relationships between regional myocardial contractile function (tagged MRI), wall stress (MRI and LV pressure), and bioenergetics ((31)P-magnetic resonance spectroscopy). Physiological assessments were conducted at a 4-wk time point after MI or AoB surgery. Comparisons were made with size-matched normal animals (normal; n = 8). Both MI and AoB instigated significant LV hypertrophy. Ejection fraction was not significantly altered in the AoB group, but significantly decreased in the MI group (P < 0.01 vs. normal and AoB). Systolic and diastolic wall stresses were approximately two times greater than normal in the infarct region and border zone. Wall stress in the AoB group was not significantly different from that in normal hearts. The infarct border zone demonstrated profound bioenergetic abnormalities, especially in the subendocardium, where the ratio of PCr/ATP decreased from 1.98 +/- 0.16 (normal) to 1.06 +/- 0.30 (MI; P < 0.01). The systolic radial thickening fraction and the circumferential shortening fraction in the anterior wall were severely reduced (MI, P < 0.01 vs. normal). The radial thickening fraction and circumferential shortening fraction in the AoB group were not significantly different from normal. The severely elevated wall stress in the infarct border zone was associated with a significant increase in chemical energy demand and abnormal myocardial energy metabolism. Such severe metabolic perturbations cannot support normal cardiac function, which may explain the observed regional contractile abnormalities in the infarct border zone.

Age-related differences in postinfarct left ventricular rupture and remodeling

Cardiac rupture is more prevalent in elderly patients with first onset of acute myocardial infarct (MI), but the mechanism remains unexplored. We investigated the differences in the incidence of cardiac rupture and early left ventricular (LV) remodeling following coronary artery ligation between old (12-mo) and young (3-mo) C57Bl/6 male mice and explored responsible mechanisms. The incidence of rupture within 1 wk after MI was significantly higher in old than in young mice (40.7 vs. 18.3%, P = 0.013) despite a similar infarct size in both age groups. Old mice dying of rupture had more severe infarct expansion than young counterparts. Echocardiography and catheterization at day 7 revealed more profound LV chamber dilatation and dysfunction as well as higher blood pressures in aged mice. At day 3 after MI immediately before the peak of rupture occurrence, we observed significantly higher content of type I and III collagen, a greater density of macrophage and neutrophil, and markedly enhanced mRNA expression of inflammatory cytokines in the infarcted myocardium in old than in young mice. Furthermore, a more dramatic increment of matrix metalloproteinase (MMP)-9 activity was found in old than in young infarcted hearts, in keeping with enhanced inflammatory response. Collectively, these results revealed that old mice had a higher risk of post-MI cardiac rupture despite a higher level of collagen content and cross-linking. Enhanced inflammatory response and subsequent increase in MMP-9 activity together with higher blood pressure are important factors responsible for the higher risk of cardiac rupture and more severe LV remodeling in the aged heart following acute MI.

Toll-Like Receptor 4 Mediates Maladaptive Left Ventricular Remodeling and Impairs Cardiac Function After Myocardial Infarction

Left ventricular (LV) remodeling leads to congestive heart failure and is a main determinant of morbidity and mortality following myocardial infarction. Therapeutic options to prevent LV remodeling are limited, which necessitates the exploration of alternative therapeutic targets. Toll-like receptors (TLRs) serve as pattern recognition receptors within the innate immune system. Activation of TLR4 results in an inflammatory response and is involved in extracellular matrix degradation, both key processes of LV remodeling following myocardial infarction. To establish the role of TLR4 in postinfarct LV remodeling, myocardial infarction was induced in wild-type BALB/c mice and TLR4-defective C3H-Tlr4(LPS-d) mice. Without affecting infarct size, TLR4 defectiveness reduced the extent of LV remodeling (end-diastolic volume: 103.7+/-6.8 microL versus 128.5+/-5.7 microL; P<0.01) and preserved systolic function (ejection fraction: 28.2+/-3.1% versus 16.6+/-1.3%; P<0.01), as assessed by MRI. In the noninfarcted area, interstitial fibrosis, and myocardial hypertrophy were reduced in C3H-Tlr4(LPS-d) mice. In the infarcted area, however, collagen density was increased, which was accompanied by fewer macrophages, reduced inflammation regulating cytokine expression levels (interleukin [IL]-1alpha, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, tumor necrosis factor-alpha, interferon-gamma, granulocyte/macrophage colony-stimulating factor), and reduced matrix metalloproteinase-2 (4684+/-515 versus 7573+/-611; P=0.002) and matrix metalloproteinase-9 activity (76.0+/-14.3 versus 168.0+/-36.2; P=0.027). These data provide direct evidence for a causal role of TLR4 in postinfarct maladaptive LV remodeling, probably via inflammatory cytokine production and matrix degradation. TLR4 may therefore constitute a novel target in the treatment of ischemic heart failure.

The Transforming Growth Factor-β/Smad3 Pathway

Myocardial infarction (MI) is followed by a well-described sequence of events known as postinfarction ventricular remodeling, a process that involves both the infarct scar itself and the residual surviving myocardium.1 The net results of infarct remodeling are changes in chamber size, function, and geometry. Furthermore, the remodeled ventricle becomes a substrate for both heart failure and sudden cardiac death. The elements of post-MI remodeling include infarct expansion, neurohormonal activation, myocardial hypertrophy, myocardial fibrosis, and cellular apoptosis. Article p 2127 These are linked physiological responses that attempt to compensate for the sudden decrease in contractility resulting from acute myocardial cell death.2 Infarct expansion is the thinning of the infarcted segment from slippage and stretching of myocytes and cell rupture. It is highly influenced by hemodynamic loading conditions.3 The prototypic pathways that participate in post-MI remodeling include the autonomic nervous system and renin-angiotensin-aldosterone system, which may be an attempt to maintain blood pressure and cardiac output.4 Over time, however, elevated adrenergic activity may lead to further myocardial cell loss from apoptosis,5 and both adrenergic and renin-angiotensin-aldosterone system upregulation have an adverse impact on cardiac hemodynamics. Myocardial hypertrophy, fibrosis, and apoptosis are primarily seen in the noninfarcted regions of the heart, particularly within the peri-infarct zones.2,6–8 Hypertrophy occurs in response to the increased workload for the surviving myocardiocytes, especially under suboptimal hemodynamic conditions. Myocardial hypertrophy, fibrosis, and apoptosis in the noninfarcted regions are believed to result, in part, from the neurohormonal activation of the sympathetic nervous system, renin-angiotensin-aldosterone system and cytokine cascades. The effect of these processes is to further compound the myocardial damage sustained during the initial acute injury. The end result of these remodeling responses is global ventricular dilatation, which is a significant predictor of dysfunction and future mortality.9 Understanding the components of remodeling …

Reply to “Letter to the editor: Infarct size measurements are critically important when comparing interventions affecting ventricular remodeling”

Reply to “Letter to the editor: Infarct size measurements are critically important when comparing interventions affecting ventricular remodeling”

Abstract 1395: Role of High Mobility Group Box 1 Protein in Post-Infarction Healing Process and Left Ventricular Remodeling

Background: The appropriate infarct healing process is prerequisite for preventing left ventricular (LV) remodeling after myocardial infarction (MI). High mobility group box1 protein (HMGB1) is derived from necrotic cells and activated macrophages and involved in tissue repair as immunostimulatory signal. However, the role of HMGB1 in post-MI LV remodeling is unknown. Methods and Results: We examined 35 patients with first ST-elevated acute MI. Peak serum HMGB1 level, determined by serial measurements (q. 6h), did not differ in age, sex, coronary risk factors and infarct site. Its peak level was markedly higher in patients with adverse in-hospital clinical outcomes, including pump failure, cardiac rupture, LV aneurysm and cardiac death, compared with those without (all p&lt;0.05). Then we performed experimental study using rat MI model, induced by permanent left coronary ligation. Anti-HMGB1 antibodies (1 mg/day, MI/antiH, n=20) or control antibodies (MI/C, n=20) were injected subcutaneously every 24 hours for 7 days. Sham-operated rats served as controls (n=10). Quantitative RT-PCR and immunoblotting showed that HMGB1 expression was increased in the infarcted area peaking at day 3 in MI/C compared with sham (p&lt;0.05). Its expression was localized in myocytes and inflammatory cells by immunohistochemistry. The mRNA level of TNF-α (−48%, p=0.03) and IL1-β (−44%, p=0.02) and the number of infiltrated macrophages (p=0.04) in the infarcted area were markedly reduced at day 3 in MI/antiH compared with MI/C. Echocardiographic and hemodynamic studies at day 7 showed increased LV end-diastolic dimension (p=0.03), LVEDP (p=0.03), and decreased LV max dP/dt (p=0.01) in MI/antiH compared with MI/C. Histologically, scar thinning in the infarcted area (0.53±0.23 vs 0.68±0.21 mm, p=0.02) and hypertrophy in the non-infarcted myocardium (2.01±0.23 vs 1.63±0.21 mm, p=0.03) were more prominent in MI/antiH compared with MI/C at day 14. Conclusions: Elevation of serum HMGB1 level is associated with adverse clinical outcomes in patients with acute MI. However, blockade of HMGB1 in rat MI model aggravated early LV remodeling through impaired infarct healing and advanced scar thinning, suggesting an essential role of HMGB1 in the appropriate repairing process after MI.

Abstract 865: Gata-4 Is An Angiogenic Survival Factor Of The Infarcted Heart

Recent data suggest that the cardiac-restricted transcription factor GATA-4 is an anti-apoptotic factor required for adaptive responses as well as a key regulator of hypertrophy and hypertrophy-associated genes in the heart. As a leading cause of chronic heart failure, reversal of post-infarction left ventricular remodeling represents an important target for therapeutic interventions. Here we studied the role of GATA-4 as a mediator of post-infarction remodeling. Rats were subjected to experimental myocardial infarction (MI) by ligating the left anterior descending coronary artery (LAD). Ligation of the LAD decreased the DNA binding activity of GATA-4 by 69 % at day 1 after MI (P&lt;0.001, n=7– 8) as assessed by gel mobility shift assays. At 2 weeks the GATA-4 DNA binding was significantly upregulated (2.4-fold, P&lt;0.05, n=7), and returned to baseline at 4 weeks. To determine the functional role of GATA-4, rats underwent LAD ligation followed by peri-infarct intramyocardial delivery of adenoviral vector expressing GATA-4. Hearts treated with the GATA-4 gene transfer exhibited significantly increased ejection fraction (58±5% vs. 38±3% in LacZ-treated control animals with MI, P&lt;0.001, n=8 –9) and fractional shortening (28±3% vs. 16±1%, P&lt;0.001, n=8 –9) 2 weeks after MI. Accordingly, the infarct size was significantly reduced (26±4% vs. 45±4%, P&lt;0.01, n=8 –9). To determine the cardioprotective mechanisms of GATA-4, the number of cardiac stem cells, apoptotic cardiomyocytes and capillaries were assessed. The number of capillaries (59±4/field vs. 48±3/field, P&lt;0.051, n=7– 8) and c-kit positive stem cells (13±5 cells vs. 4±2 cells, P&lt;0.05, n=7– 8) were increased in GATA-4 treated hearts, and a tendency to decreased apoptosis was observed in TUNEL-stained histological sections. These results indicate that the reversal of reduced GATA-4 activity prevents adverse post-infarction remodeling through increased angiogenesis, recruitment of cardiac stem cells and anti-apoptosis. GATA-4-based gene transfer may represent a novel, efficient therapeutic approach for heart failure.

Borderzone Contractile Dysfunction Is Transiently Attenuated and Left Ventricular Structural Remodeling Is Markedly Reduced Following Reperfused Myocardial Infarction in Inducible Nitric Oxide Synthase Knockout Mice

We sought to determine the effect of inducible nitric oxide synthase (iNOS) expression on regional contractile function and left ventricular (LV) remodeling after reperfused myocardial infarction (MI). Inducible nitric oxide synthase is known to contribute to global LV dysfunction after a large MI, but the mechanisms underlying this dysfunction remain unclear. We used immunohistochemistry to investigate the distribution of iNOS expression in wild-type (WT) and iNOS knockout (KO) mice early (day 1) and late (day 28) after reperfused MI. We also used serial cardiac magnetic resonance imaging at baseline and at 1, 7, and 28 days after MI to assess LV volumes, ejection fraction (EF), regional circumferential strain (E(cc)), and day 1 infarct size. At baseline, LV volumes and EF were similar between groups. Day 1 infarct size was also similar between groups. Immunohistochemistry revealed that iNOS expression was abundant throughout the heart in WT mice on day 1 after MI, particularly near the infarct borderzone. On day 7 after MI, E(cc) in KO mice was significantly improved in some borderzone sectors compared with WT. The LV volumes were significantly lower in KO mice at days 7 and 28 compared with WT. The EF on days 7 and 28 was significantly higher in KO mice compared with WT. The circumferential extent of wall thinning was also significantly reduced in KO versus WT mice at days 7 and 28. Expression of iNOS contributes importantly to post-infarction contractile dysfunction and subsequent LV remodeling, suggesting new strategies to combat heart failure resulting from large MI.

Controlled Release of Stromal Cell–Derived Factor-1alphaIn SituIncreases C-kit+Cell Homing to the Infarcted Heart

Stromal-derived factor 1alpha (SDF-1alpha) is a key stem cell homing factor that is crucial for mobilization of stem cells from bone marrow to peripheral blood and subsequent engraftment to the tissue of diseased organs. It has been reported that SDF-1alpha is transiently over-expressed in ischemic myocardium. Therefore, there may be a limited time window after acute myocardial infarction (AMI) during which stem cells are recruited to injured myocardium for repair. This study aimed at investigating whether controlled release of SDF-1alpha via a novel conjugated poly(ethylene glycol) (PEG) (PEGylated) fibrin patch at the infarct site would increase the rate of stem cell recruitment and offer potential therapeutic benefits. Recombinant mouse SDF-1alpha was covalently bound to the PEGylated fibrinogen as evidenced by immunoprecipitation and western blotting. The PEGylated fibrinogen, bound with recombinant mouse SDF-1alpha, was mixed with thrombin to form the PEGylated fibrin patch. The release kinetics of SDF-1alpha were detected in vitro using enzyme-linked immunosorbent assay. Using a mouse AMI model produced by a ligature on the left anterior descending coronary artery, a PEGylated fibrin patch bound with SDF-1alpha (100 ng) was placed on the surface of the infarct area of the left ventricle. Infarct size, left ventricular (LV) function, and the percentage of sca-1(+)/c-kit(+) cells within the infarct area were measured at days 7, 14, and 28 after AMI. In vitro results showed that SDF-1alpha was successfully bound to the PEGylated fibrin patch and can be released from the patch constantly for up to 10 days. Two weeks after infarction, the myocardial recruitment of c-kit(+) cells was significantly higher in the group treated with the SDF-1alpha PEGylated fibrin patch (n = 9) than in the AMI control group (n = 10) (p < 0.05; 11.20 +/- 1.71% vs. 4.22 +/- 0.96%, respectively). At day 28 post-AMI, unlike the control group, the group with the SDF-1alpha-releasing patch maintained stable release of SDF-1alpha concurrent with additional stem cell homing. Moreover, LV function was significantly better than in the control group. These data demonstrate that the PEGylated fibrin patch based SDF-1alpha delivery can improve the rate of c-kit(+) cell homing and improve LV function in hearts with postinfarction LV remodeling.

Functional and bioenergetic modulations in the infarct border zone following autologous mesenchymal stem cell transplantation

Preclinical and clinical studies have demonstrated that stem cell transplantation can improve the left ventricular (LV) contractile performance, yet the underlying mechanisms remain unknown. We examined whether mesenchymal stem cell (MSC) transplantation-induced beneficial effects are secondary to paracrine-associated improvements in LV contractile performance, wall stress, and myocardial bioenergetics in hearts with postinfarction LV remodeling. Myocardial contractile function and bioenergetics were compared 4 wk after acute myocardial infarction in normal pigs (n = 6), untreated pigs with myocardial infarction (MI group; n = 6), and pigs receiving autologous MSC transplantation (MI + MSC group; n = 5). A distal occlusion of the left anterior descending coronary artery instigated significant myocardial hypertrophy. Ejection fraction decreased from 55.3 +/- 3.1% (normal) to 30.4 +/- 2.3% (MI group; P < 0.01) and to 45.4 +/- 3.1% (MI + MSC group; P < 0.01 vs. MI). Hearts in the MI group developed severe contractile dyskinesis in the infarct zone and border zone (BZ). MSC transplantation significantly improved contractile performance from dyskinesis to active contraction (P < 0.01 vs. MI). BZ systolic wall stress was severely increased in MI hearts but significantly improved after MSC transplantation (P < 0.01 vs. MI). The BZ demonstrated profound bioenergetic abnormalities in MI pigs; this was significantly improved after MSC transplantation (P < 0.01 vs. MI). Patchy spared myocytes were found in the infarct zone of hearts receiving MSC transplantation but not in control hearts. These data demonstrate that MSC transplantation into the BZ causes significant improvements in myocardial contractile performance and reduction in wall stress, which ultimately results in significant bioenergetic improvements. Low cell engraftment indicates that MSCs did not provide a structural contribution to the damaged heart and that the observed beneficial effects likely resulted from paracrine repair mechanisms.

Time course of changes in the expression of DHPR, RyR2, and SERCA2 after myocardial infarction in the rat left ventricle

Postinfarction left ventricular remodeling leads to the functional decline of the left ventricle (LV). Since dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum (SR) Ca(2+)-ATPase2 (SERCA2a) play a major role in the contractility of the heart, the aim of our study was to evaluate the time course of changes in the expression of these proteins 1 day, 2 weeks and 4 weeks after myocardial infarction (MI). Myocardial infarction was produced by ligation of left anterior descending coronary artery of the rat. Transthoracic echocardiography was performed to characterize structural and functional changes after MI. To evaluate protein mRNA levels and the relative amount of proteins, real-time quantitative RT-PCR and Western blotting were used. LV ejection fraction and fractional shortening decreased significantly during the 4-week follow-up period (P < 0.001). Typical features of LV remodeling after MI were seen, with a decrease in anterior wall thickness (P < 0.001) and dilatation of the LV (P < 0.001). Expression of DHPR and RyR(2) mRNAs decreased and Serca2a mRNA tended to decrease 1 day after MI (P < 0.001, P < 0.01 and P = 0.06, respectively), followed by recovery of the expression during the next 4 weeks. In the infarcted hearts the quantities of SERCA2 proteins in the LV were significantly decreased at the time of 4 weeks. In conclusion, MI was associated with transient decrease in the expression of the DHPR and RyR(2) mRNAs and a reduced quantity of SERCA2 proteins in the LV. Since they have a key role in the contraction of the heart, changes in the expression of these proteins may be important regulators of LV systolic function after MI.