Mechanisms of Post-Infarct Left Ventricular Remodeling

Shengmai injection improved doxorubicin-induced cardiomyopathy by alleviating myocardial endoplasmic reticulum stress and caspase-12 dependent apoptosis

BACKGROUND

Apoptosis plays vital roles in the progression of doxorubicin-induced cardiomyopathy (DOX-CM). Endoplasmic reticulum stress (ER stress) could induce specific apoptosis by caspase-12 dependent pathway. Shengmai Injection (SMI), a famous Traditional Chinese Medicine, could alleviate the heart damage via inhibiting myocardial apoptosis. However, it is unknown whether SMI can alleviate ER stress and its specific apoptosis in the setting of DOX-CM.

OBJECTIVE

To explore the effects of SMI on heart function, myocardial ER stress, and apoptosis of DOX-CM rats.

METHODS

Rats with DOX-CM were treated by SMI. Heart function was assessed by echocardiography and brain natriuretic peptide. Myocardial apoptosis was detected by TUNEL assay. ER stress was assessed by detecting the expressions of GRP78 and caspase-12.

RESULTS

At the end of eight-week, compared to control, significant heart dysfunction happened in DOX group. The ratio of apoptotic cardiomyocytes and the expressions of GRP78 and caspase-12 increased significantly (P < 0.05). Compared to DOX group, the apoptotic ratio and the expressions of GRP78 and caspase-12 significantly decreased in DOX + SMI group (P < 0.05), accompanied with improved heart function.

CONCLUSION

SMI could alleviate myocardial ER stress and caspase-12 dependent apoptosis, which subsequently helped to improve the heart function of rats with DOX-CM.

Impact of hypertension on postreperfusion left ventricular recovery in patients with ST-segment elevation myocardial infarction and multivessel coronary artery disease

OBJECTIVE

The aim of this study was to investigate the impact of admission systolic blood pressure (ASBP) and left ventricular (LV) mass on the postreperfusion LV recovery in patients with ST-segment elevation myocardial infarction (STEMI) and concomitant coronary multivessel disease (MVD).

MATERIALS AND METHODS

A retrospective analysis of 12-month postreperfusion LV recovery was performed in 104 patients after primary percutaneous coronary intervention (PPCI). Patients with elevated ASBP (>140mmHg) were assigned to the first group (n=58); with normal ASBP (<140mmHg), to the second group (n=46); with increased myocardial mass index (MMI) (>100g/m(2)), to the third group (n=70); and with normal MMI (<100g/m(2)), to the fourth group (n=34). Severity of MVD was evaluated by the Syntax score. The LV recovery was assessed by evolution of quantitative characteristics of electrocardiography (QRS score, ST score, ECG STEMI stage) and echocardiography (LV ejection fraction, volume and mass indices) registered before and after PPCI, at discharge, and after 1, 6, and 12 months.

RESULTS

There were no significant differences in the baseline QRS and ST scores, ECG STEMI stage, LVEF, MMI, and Syntax score comparing all the patients' groups. The serial ECG criteria showed only a very small impact of ASBP on postreperfusion LV recovery. Only ECG STEMI stage progression was slower in the patients with elevated ASBP. In patients with different MMI, the QRS and ST scores were higher and ECG STEMI stage was lower in patients with increased MMI. LVEF after 1 year was significantly lower in the third group as compared to the fourth group (42.58%±8.25% vs. 46.8%±7.13%, P=0.018).

CONCLUSION

Postreperfusion LV recovery was more related not to ASBP but to the increased LV mass assessed by echocardiography in patients with STEMI and MVD.

Preconditioning of Cardiosphere-Derived Cells With Hypoxia or Prolyl-4-Hydroxylase Inhibitors Increases Stemness and Decreases Reliance on Oxidative Metabolism

Cardiosphere-derived cells (CDCs), which can be isolated from heart explants, are a promising candidate cell source for infarcted myocardium regeneration. However, current protocols used to expand CDCs require at least 1 month in vitro to obtain sufficient cells for transplantation. We report that CDC culture can be optimized by preconditioning the cells under hypoxia (2% oxygen), which may reflect the physiological oxygen level of the stem cell niche. Under hypoxia, the CDC proliferation rate increased by 1.4-fold, generating 6 × 10(6) CDCs with higher expression of cardiac stem cell and pluripotency gene markers compared to normoxia. Furthermore, telomerase (TERT), cytokines/ligands involved in stem cell trafficking (SDF/CXCR-4), erythropoiesis (EPO), and angiogenesis (VEGF) were increased under hypoxia. Hypoxic preconditioning was mimicked by treatment with two types of hypoxia-inducible factor (HIF) prolyl-4-hydroxylase inhibitors (PHDIs): dimethyloxaloylglycine (DMOG) and 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetic acid (BIC). Despite the difference in specificity, both PHDIs significantly increased c-Kit expression and activated HIF, EPO, and CXCR-4. Furthermore, treatment with PHDIs for 24 h increased cell proliferation. Notably, all hypoxic and PHDI-preconditioned CDCs had decreased oxygen consumption and increased glycolytic metabolism. In conclusion, cells cultured under hypoxia could have potentially enhanced therapeutic potential, which can be mimicked, in part, by PHDIs.

The effect of antisense to NF-κB in an albumin microsphere formulation on the progression of left-ventricular remodeling associated with chronic volume overload in rats

BACKGROUND

Increased NF-κB levels play a crucial role in the pathophysiology of heart failure and are known to cause ventricular remodeling. Antisense therapy can be used for blocking the expression of NF-κB and subsequently avoiding heart failure. However, as with most biotechnology products, molecular instability and overall cost are often the major issues and concerns limiting the advancement of most antisense drugs to the market. Therefore, a cost-efficient biodegradable sustained release particle drug delivery system to transport and target NF-kB antisense to its intended site of action would be ideal.

PURPOSE

To evaluate the in vivo performance of a sustained release spray-dried albumin microsphere formulation for effective delivery and treatment of left ventricular remodeling with antisense to NF-κB.

METHODS

Albumin-based microspheres encapsulating antisense to NF-kB were prepared by spray drying and studied in a rat model to treat congestive heart failure.

RESULTS

The NF-κB activation and TNF-α release seen in treated animals were significantly lower than control animals. Ventricular remodeling was controlled in animals with antisense-treated AV fistulas as ΔV0-25 and ΔV0 were significantly lower compared to animals with untreated AV fistulas.

CONCLUSION

This treatment was successful in curbing ventricular remodeling by suppressing NF-κB activation.

Angiotensin type 2 receptor stimulation ameliorates left ventricular fibrosis and dysfunction via regulation of tissue inhibitor of matrix metalloproteinase 1/matrix metalloproteinase 9 axis and transforming growth factor β1 in the rat heart

Left ventricular (LV) remodeling is the main reason for the development of progressive cardiac dysfunction after myocardial infarction (MI). This study investigated whether stimulation of the angiotensin type 2 receptor is able to ameliorate post-MI cardiac remodeling and what the underlying mechanisms may be. MI was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with the angiotensin type 2 receptor agonist compound 21 (0.03 mg/kg) was started 6 hours post-MI and continued for 6 weeks. Hemodynamic parameters were measured by echocardiography and intracardiac catheter. Effects on proteolysis were studied in heart tissue and primary cardiac fibroblasts. Compound 21 significantly improved systolic and diastolic functions, resulting in improved ejection fraction (71.2±4.7% versus 53.4±7.0%; P<0.001), fractional shortening (P<0.05), LV internal dimension in systole (P<0.05), LV end-diastolic pressure (16.9±1.2 versus 22.1±1.4 mm Hg; P<0.05), ratio of early (E) to late (A) ventricular filling velocities, and maximum and minimum rate of LV pressure rise (P<0.05). Compound 21 improved arterial stiffness parameters and reduced collagen content in peri-infarct myocardium. Tissue inhibitor of matrix metalloproteinase 1 was strongly upregulated, whereas matrix metalloproteinases 2 and 9 and transforming growth factor β1 were diminished in LV of treated animals. In cardiac fibroblasts, compound 21 initially induced tissue inhibitor of matrix metalloproteinase 1 expression followed by attenuated matrix metalloproteinase 9 and transforming growth factor β1 secretion. In conclusion, angiotensin type 2 receptor stimulation improves cardiac function and prevents cardiac remodeling in the late stage after MI, suggesting that angiotensin type 2 receptor agonists may be considered a future pharmacological approach for the improvement of post-MI cardiac dysfunction.

Monocyte-directed RNAi targeting CCR2 improves infarct healing in atherosclerosis-prone mice

BACKGROUND

Exaggerated and prolonged inflammation after myocardial infarction (MI) accelerates left ventricular remodeling. Inflammatory pathways may present a therapeutic target to prevent post-MI heart failure. However, the appropriate magnitude and timing of interventions are largely unknown, in part because noninvasive monitoring tools are lacking. Here, we used nanoparticle-facilitated silencing of CCR2, the chemokine receptor that governs inflammatory Ly-6C(high) monocyte subset traffic, to reduce infarct inflammation in apolipoprotein E-deficient (apoE(-/-)) mice after MI. We used dual-target positron emission tomography/magnetic resonance imaging of transglutaminase factor XIII (FXIII) and myeloperoxidase (MPO) activity to monitor how monocyte subset-targeted RNAi altered infarct inflammation and healing.

METHODS AND RESULTS

Flow cytometry, gene expression analysis, and histology revealed reduced monocyte numbers and enhanced resolution of inflammation in infarcted hearts of apoE(-/-) mice that were treated with nanoparticle-encapsulated siRNA. To follow extracellular matrix cross-linking noninvasively, we developed a fluorine-18-labeled positron emission tomography agent ((18)F-FXIII). Recruitment of MPO-rich inflammatory leukocytes was imaged with a molecular magnetic resonance imaging sensor of MPO activity (MPO-Gd). Positron emission tomography/magnetic resonance imaging detected anti-inflammatory effects of intravenous nanoparticle-facilitated siRNA therapy (75% decrease of MPO-Gd signal; P<0.05), whereas (18)F-FXIII positron emission tomography reflected unimpeded matrix cross-linking in the infarct. Silencing of CCR2 during the first week after MI improved ejection fraction on day 21 after MI from 29% to 35% (P<0.05).

CONCLUSION

CCR2-targeted RNAi reduced recruitment of Ly-6C(high) monocytes, attenuated infarct inflammation, and curbed post-MI left ventricular remodeling.

Short-term mechanical unloading with left ventricular assist devices after acute myocardial infarction conserves calcium cycling and improves heart function

OBJECTIVES

This study sought to demonstrate that short-term cardiac unloading with a left ventricular (LV) assist device (LVAD) after acute myocardial infarction (MI) can conserve calcium cycling and improve heart function.

BACKGROUND

Heart failure secondary to MI remains a major source of morbidity and mortality. Alterations in calcium cycling are linked to cardiac dysfunction in the failing heart.

METHODS

Adult Dorsett hybrid sheep underwent acute MI and were mechanically unloaded with an axial-flow LVAD (Impella 5.0) for 2 weeks (n = 6). Six sheep with MI only and 4 sham sheep were used as controls. All animals were followed for 12 weeks post-MI. Regional strains in the LV were measured by sonomicrometry. Major calcium-handling proteins (CHPs), including sarco-/endoplasmic reticulum calcium ATPase-2α (SERCA-2α), Na(+)-Ca(2+) exchanger-1, and phospholamban, and Ca(2+)-ATPase activity were investigated. The electrophysiological calcium cycling in single isolated cardiomyocytes was measured with the patch-clamp technique. The related ultrastructures were studied with electron microscopy.

RESULTS

LVAD unloading alleviated LV dilation and improved global cardiac function and regional contractility compared with the MI group. The regional myocardial strain (stretch) was minimized during the unloading period and even attenuated compared with the MI group at 12 weeks. Impaired calcium cycling was evident in the adjacent noninfarcted zone in the MI group, whereas CHP expression was normalized and Ca(2+)-ATPase activity was preserved in the LVAD unloading group. The electrophysiological calcium cycling was also conserved, and the ultrastructural damage was ameliorated in the unloaded animals.

CONCLUSIONS

Short-term LVAD unloading may conserve calcium cycling and improve heart function during the post-infarct period.

Long-term left ventricular remodelling in rat model of nonreperfused myocardial infarction: sequential MR imaging using a 3T clinical scanner

Purpose. To evaluate whether 3T clinical MRI with a small-animal coil and gradient-echo (GE) sequence could be used to characterize long-term left ventricular remodelling (LVR) following nonreperfused myocardial infarction (MI) using semi-automatic segmentation software (SASS) in a rat model. Materials and Methods. 5 healthy rats were used to validate left ventricular mass (LVM) measured by MRI with postmortem values. 5 sham and 7 infarcted rats were scanned at 2 and 4 weeks after surgery to allow for functional and structural analysis of the heart. Measurements included ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), and LVM. Changes in different regions of the heart were quantified using wall thickness analyses. Results. LVM validation in healthy rats demonstrated high correlation between MR and postmortem values. Functional assessment at 4 weeks after MI revealed considerable reduction in EF, increases in ESV, EDV, and LVM, and contractile dysfunction in infarcted and noninfarcted regions. Conclusion. Clinical 3T MRI with a small animal coil and GE sequence generated images in a rat heart with adequate signal-to-noise ratio (SNR) for successful semiautomatic segmentation to accurately and rapidly evaluate long-term LVR after MI.

Mesenchymal stem cell transplantation improves regional cardiac remodeling following ovine infarction

Progressive cardiac remodeling, including the myopathic process in the adjacent zone following myocardial infarction (MI), contributes greatly to the development of cardiac failure. Cardiomyoplasty using bone marrow-derived mesenchymal stem cells (MSCs) has been demonstrated to protect cardiomyocytes and/or repair damaged myocardium, leading to improved cardiac performance, but the therapeutic effects on cardiac remodeling are still under investigation. Here, we tested the hypothesis that MSCs could improve the pathological remodeling of the adjacent myocardium abutting the infarct. Allogeneic ovine MSCs were transplanted into the adjacent zone by intracardiac injection 4 hours after infarction. Results showed that remodeling and contractile strain alteration were reduced in the adjacent zone of the MSC-treated group. Cardiomyocyte hypertrophy was significantly attenuated with the normalization of the hypertrophy-related signaling proteins phosphatidylinositol 3-kinase α (PI3Kα), PI3Kγ, extracellular signal-regulated kinase (ERK), and phosphorylated ERK (p-ERK) in the adjacent zone of the MSC-treated group versus the MI-alone group. Moreover, the imbalance of the calcium-handling proteins sarcoplasmic reticulum Ca(2+) adenosine triphosphatase (SERCA2a), phospholamban (PLB), and sodium/calcium exchanger type 1 (NCX-1) induced by MI was prevented by MSC transplantation, and more strikingly, the activity of SERCA2a and uptake of calcium were improved. In addition, the upregulation of the proapoptotic protein Bcl-xL/Bcl-2-associated death promoter (BAD) was normalized, as was phospho-Akt expression; there was less fibrosis, as revealed by staining for collagen; and the apoptosis of cardiomyocytes was significantly inhibited in the adjacent zone by MSC transplantation. Collectively, these data demonstrate that MSC implantation improved the remodeling in the region adjacent to the infarct after cardiac infarction in the ovine infarction model.

Serial ultrasound evaluation of intramyocardial strain after reperfused myocardial infarction reveals that remote zone dyssynchrony develops in concert with left ventricular remodeling

This study noninvasively evaluated the development of left ventricular (LV) dyssynchrony following reperfused myocardial infarction (MI) in mice using an ultrasonic speckle-tracking method. Eight C57BL/6J mice were assessed by high-resolution echocardiography at baseline and at eight time-points following MI. Images were acquired at 1mm elevational intervals encompassing the entire LV to determine chamber volumes and radial strain. Receiver-operating characteristic (ROC) analysis of regional radial strain was used to segment the three-dimensional (3-D) LV into infarct, adjacent and remote zones. This in vivo segmentation was correlated to histologic infarct size (R = 0.89, p < 0.01) in a short-axis, slice-by-slice comparison. The onset of dyssynchrony during LV remodeling was assessed by standard deviation of time to peak radial strain in the infarct, adjacent and remote zones. It was discovered that the form of LV dyssynchrony that develops in the remote zone late after MI does so in concert with the progression of LV remodeling (R = 0.70, p < 0.05).

Proteomic analysis of myocardial tissue from the border zone during early stage post-infarct remodelling in rats

AIMS

Long-term outcome of patients after myocardial infarction (MI) largely depends on the extent of post-infarct remodelling. To explore the molecular mechanism of remodelling, comparative proteomic analysis was undertaken to identify differential myocardial proteome profiles expressed in the border zone of the post-MI heart.

METHODS AND RESULTS

Two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry were used to identify the differential protein profiles expressed in the border zone at specific time points (Days 0, 1, 4, and 10 post-infarction) in a permanent rat MI model. We identified 96 differential protein spots, corresponding to 69 proteins. Cluster analysis exhibited five main temporal expression patterns corresponding to the three phases of early stage remodelling. The alteration in expression was supported by reverse transcription-polymerase chain reaction, western blotting, and immunohistochemical analysis of three selected proteins. Bioinformatics analysis revealed that the proteins in each pattern were functionally related to specific cell processes in remodelling, such as ischaemia, inflammation, and proliferation.

CONCLUSION

A differential myocardial proteome profile was identified in the border zone during early stage post-infarct remodelling. Bioinformatics analysis indicated a possible role of these proteins in remodelling. Proteomics data provided the basis for further functional study of these proteins and for identifying potential molecular targets with therapeutic anti-remodelling effects.

Angiotensin-converting enzyme inhibition prevents the release of monocytes from their splenic reservoir in mice with myocardial infarction

RATIONALE

Monocytes recruited to ischemic myocardium originate from a reservoir in the spleen, and the release from their splenic niche relies on angiotensin (Ang) II signaling.

OBJECTIVE

Because monocytes are centrally involved in tissue repair after ischemia, we hypothesized that early angiotensin-converting enzyme (ACE) inhibitor therapy impacts healing after myocardial infarction partly via effects on monocyte traffic.

METHODS AND RESULTS

In a mouse model of permanent coronary ligation, enalapril arrested the release of monocytes from the splenic reservoir and consequently reduced their recruitment into the healing infarct by 45%, as quantified by flow cytometry of digested infarcts. Time-lapse intravital microscopy revealed that enalapril reduces monocyte motility in the spleen. In vitro migration assays and Western blotting showed that this was caused by reduced signaling through the Ang II type 1 receptor. We then studied the long-term consequences of blocked splenic monocyte release in atherosclerotic apolipoprotein (apo)E(-/-) mice, in which infarct healing is impaired because of excessive inflammation in the cardiac wound. Enalapril improved histologic healing biomarkers and reduced inflammation in infarcts measured by FMT-CT (fluorescence molecular tomography in conjunction with x-ray computed tomography) of proteolytic activity. ACE inhibition improved MRI-derived ejection fraction by 14% on day 21, despite initially comparable infarct size. In apoE(-/-) mice, ischemia/reperfusion injury resulted in larger infarct size and enhanced monocyte recruitment and was reversible by enalapril treatment. Splenectomy reproduced antiinflammatory effects of enalapril.

CONCLUSION

This study suggests that benefits of early ACE inhibition after myocardial infarction can partially be attributed to its potent antiinflammatory impact on the splenic monocyte reservoir.

The metamorphosis of myocardial infarction following coronary recanalization

The "metamorphosis" of acute myocardial infarction (AMI) in terms of pathological features and complications in the reperfusion era is herein discussed. Typically, the AMI following coronary artery recanalization is characterized by frequent subendocardial location, since a prompt coronary lumen recanalization is able to prevent the transmural progression of myocardial necrosis from the endocardium towards the epicardium. Transmural AMI may develop when recanalization occurs late (>6 hours) or is not effective (persistent coronary occlusion). Moreover, reperfused AMI frequently appears reddish because of interstitial haemorrhage, which is thought to be caused by vascular cell damage with leakage of blood out of the injured vessels. Hemorrhage occurs always within the area of necrosis and it is significantly related to the infarct size and to the coronary occlusion time. At histology, typical features of reperfused AMI consist of contraction band necrosis and interstitial hemorrhage. Moreover, a more pronounced inflammatory cellular response is visible within the necrotic area when comparing reperfused with non-reperfused AMI. Reperfusion after prolonged coronary occlusion is also associated with secondary impairment of microcirculatory flow ("no-reflow" phenomenon), that is due to endothelial swelling, luminal obstruction and external compression but may also be aggravated by distal embolization. Finally, the reperfused AMI with its typical subendocardial, non-transmural location, is characterized by a lower incidence of expansive remodelling and related complications, in terms of cardiogenic shock, myocardial rupture, aneurysm and pseudoaneurysm formation and thromboembolism. Moreover, pericardial involvement is a rare occurrence. Unfavorable mechanical consequences of intramyocardial haemorrhage could consist in increased myocardial stiffness, propensity to wall rupture and delayed healing process. However, prospective in vivo large-scale studies in patients with reperfused AMI are needed to assess the prognostic value of hemorrhagic AMI in terms of morbidity and mortality. The knowledge and correct interpretation of these findings at post-mortem by the general and forensic pathologists is of great importance, to provide useful information to the clinicians.