Initial effects of the left ventricular repair by plication may not last long in a rat ischemic cardiomyopathy model

CircMap4k2 Reactivated by Aneurysm Plication Alleviates Residual Cardiac Remodeling After SVR by Enhancing Cardiomyocyte Proliferation in Post-MI Mice

INTRODUCTION

Surgical ventricular reconstruction (SVR) is an alternative therapeutic approach in patients with refractory heart failure (HF), but residual remodeling after SVR limits the improvement of HF. Recently, we reported that SVR may act as an environmental cue to reactivate endogenous proliferation of cardiomyocytes; however, it is unclear whether enhancing endogenous cardiomyocyte regeneration further improves HF after SVR.

OBJECTIVES

We aimed to explore whether circular RNAs (circRNAs) would involved in SVR and their mechanisms.

METHODS

Male C57BL/6 mice were subjected to myocardial infarction (MI) or sham surgery. Four weeks later, MI mice with a large ventricular aneurysm underwent SVR or a second open-chest operation only. Echocardiography and histological analysis were used to evaluate heart function, cardiac remodeling, and myocardial regeneration. Sequencing of circular RNAs, RNA immunoprecipitation, RNA pulldown, and luciferase reporter assay were used to explore the underlying mechanisms.

RESULTS

SVR markedly attenuated cardiac remodeling and induced cardiomyocyte regeneration, as evidenced by positive staining of Ki-67, phospho-histone H3 (pH3), and Aurora B in the plication zone, but significant residual remodeling still existed in comparison with the sham group. Sequencing results showed that SVR altered the expression profile of cardiac circRNAs, and circMap4k2 was identified as the most upregulated one. After characterizing circMap4k2, we noted that overexpression of circMap4k2 significantly promoted proliferation of cardiomyocytes in cultured neonatal rat cardiomyocytes and silencing of circMap4k2 significantly inhibited it; similar results were obtained in SVR-treated MI mice but not in MI mice without SVR treatment. Residual cardiac remodeling after SVR was further attenuated by circMap4k2 overexpression. CircMap4k2 bound with miR-106a-3p and inhibited cardiomyocyte proliferation by targeting a downstream effector of the antizyme inhibitor 1 (Azin1) gene.

CONCLUSIONS

CircMap4k2 acts as an environmental cue and targets the miR-106a-3p/Azin1 pathway to increase cardiac regeneration in the plication zone and attenuate residual remodeling after SVR.

Cardiac-Specific Overexpression of Caveolin-1 in Rats With Ischemic Cardiomyopathy Improves Arrhythmogenicity and Cardiac Remodelling

BACKGROUND

Ischemic cardiomyopathy (ICM) is associated with electrical and structural remodelling, leading to arrhythmias. Caveolin-1 (Cav1) is a membrane protein involved in the pathogenesis of ischemic injury. Cav1 deficiency has been associated with arrhythmogenicity. The current study aimed to determine how Cav1 overexpression inhibits arrhythmias and cardiac remodelling in ICM.

METHODS

ICM was modelled using left anterior descending (LAD) artery ligation for 4 weeks. Cardiac-specific Cav1 overexpression in ICM on arrhythmias, excitation-contraction coupling, and cardiac remodelling were investigated using the intramyocardial injection of an adeno-associated virus serotype 9 (AAV-9) system, carrying a specific sequence expressing Cav1 (AAV^Cav1) under the cardiac troponin T (cTnT) promoter.

RESULTS

Cav1 overexpression decreased susceptibility to arrhythmias by upregulating gap junction connexin 43 (CX43) and reducing spontaneous irregular proarrhythmogenic Ca²⁺ waves in ventricular cardiomyocytes. It also alleviated ischemic injury-induced contractility weakness by improving Ca²⁺ cycling through normalizing Ca²⁺-handling protein levels and improving Ca²⁺ homeostasis. Masson stain and immunoblotting revealed that the deposition of excessive fibrosis was attenuated by Cav1 overexpression, inhibiting the transforming growth factor-β (TGF-β)/Smad2 signalling pathway. Coimmunoprecipitation assays demonstrated that the interaction between Cav1 and cSrc modulated CX43 expression and Ca²⁺-handling protein levels.

CONCLUSIONS

Cardiac-specific overexpression of Cav1 attenuated ventricular arrhythmia, improved Ca²⁺ cycling, and attenuated cardiac remodelling. These effects were attributed to modulation of CX43, normalized Ca²⁺-handling protein levels, improved Ca²⁺ homeostasis, and attenuated cardiac fibrosis.

Effect of early versus late onset mitral regurgitation on left ventricular remodeling in ischemic cardiomyopathy in an animal model

BACKGROUND

Patients who survive a myocardial infarction have progressive cardiac dysfunction and ventricular remodeling. Mitral regurgitation is often diagnosed in these patients, and is a risk factor that portends poor prognosis. Whether such postinfarction mitral regurgitation magnifies adverse left ventricular remodeling is unclear, which was studied in an animal model.

METHODS

Forty-one adult rats were induced with myocardial infarction using left coronary artery ligation and assigned to 3 groups: group 1, myocardial infarction only; group 2, myocardial infarction with severe mitral regurgitation introduced after 4 weeks; and group 3, myocardial infarction with severe mitral regurgitation introduced after 10 weeks. Valve regurgitation was introduced by advancing a transapical ultrasound-guided needle into the mitral valve anterior leaflet. Animals were survived to 20 weeks from the index procedure, with biweekly cardiac ultrasound, and invasive hemodynamics and histology at termination.

RESULTS

At 20 weeks, end diastolic volume was largest in the groups with mitral regurgitation, compared with the group without the valve lesion (group 1, 760.9 ± 124.6 μL; group 2, 958.0 ± 115.1 μL; group 3, 968.3 ± 214.9 μL). Similarly, end systolic volume was larger in groups with regurgitation (group 1, 431.2 ± 152.6 μL; group 2, 533.2 ± 130.8 μL; group 3, 533.1 ± 177.5 μL). In the infarction-only group, left ventricular remodeling was maximal until 6 weeks and plateaued thereafter. In groups with mitral regurgitation, left ventricular remodeling was significantly elevated at the onset of regurgitation and persisted.

CONCLUSIONS

Mitral regurgitation is a potent driver of adverse cardiac remodeling after a myocardial infarction, irrespective of the timing of its onset.

A Modified Surgical Ventricular Reconstruction in Post-infarction Mice Persistently Alleviates Heart Failure and Improves Cardiac Regeneration

Objectives: Large ventricular aneurysm secondary to myocardial infarction (MI) results in severe heart failure (HF) and limits the effectiveness of regeneration therapy, which can be improved by surgical ventricular reconstruction (SVR). However, the conventional SVR procedures do not yield optimal long-term outcome in post-MI rodents. We hypothesized that a modified SVR procedure without aggressive purse string suture would persistently alleviate HF and improve cardiac regeneration in post-MI mice.

Methods: Adult male C57 mice were subjected to MI or sham surgery. Four weeks later, mice with MI underwent SVR or 2nd open-chest operation alone. SVR was performed by plicating the aneurysm with a single diagonal linear suture from the upper left ventricle (LV) to the right side of the apex. Cardiac remodeling, heart function and myocardial regeneration were evaluated.

Results: Three weeks after SVR, the scar area, LV volume, and heart weight/body weight ratio were significantly smaller, while LV ejection fraction, the maximum rising and descending rates of LV pressure, LV contractility and global myocardial strain were significantly higher in SVR group than in SVR-control group. The inhibitory effects of SVR on LV remodeling and HF persisted for at least eight-week. SVR group exhibited improved cardiac regeneration, as reflected by more Ki67-, Aurora B- and PH3-positive cardiomyocytes and a higher vessel density around the plication area of the infarcted LV.

Conclusions: SVR with a single linear suture results in a significant and sustained reduction in LV volume and improvement in both LV systolic and diastolic function as well as cardiac regeneration.

Autophagy during left ventricular redilation after ventriculoplasty: Insights from a rat model of ischemic cardiomyopathy

OBJECTIVES

Myocardial autophagy has been recognized as an important factor in heart failure. It is not known whether changes in ventricular geometry by left ventriculoplasty influence autophagy in ischemic cardiomyopathy. We hypothesized that myocardial autophagy plays an important role in left ventricular (LV) redilation after ventriculoplasty.

METHODS

Four weeks after ligation of the left anterior descending artery, ventriculoplasty or sham operation was performed. The animals were euthanized at 2 days (early) or 28 days (late) after the second operation. Ventricular autophagy was evaluated by protein expression of microtubule-associated protein light chain 3 II, an autophagosome marker. Cardiomyocyte area was assessed by histologic examination. LV function was evaluated by echocardiography. To examine the implications of autophagy, an autophagy inhibitor (3-methyladenine) was injected intraperitoneally for 3 weeks before sacrifice.

RESULTS

The LV was reduced in size early and redilated late after ventriculoplasty. LV systolic function was improved early and later worsened after ventriculoplasty. Light chain 3 II expression decreased early after ventriculoplasty and increased in the late period. Myocyte area increased from the early to late stage after ventriculoplasty. Autophagic inhibition exaggerated the increased myocyte hypertrophy and LV redilation.

CONCLUSIONS

In a rat model of myocardial infarction, autophagy decreased early after ventriculoplasty and increased again during LV redilation. These results provide new insights into the mechanism underlying the late failure of ventriculoplasty.

Dexmedetomidine Exerted Anti-arrhythmic Effects in Rat With Ischemic Cardiomyopathy via Upregulation of Connexin 43 and Reduction of Fibrosis and Inflammation

Background

Persistent myocardial ischemia post-myocardial infarction can lead to fatal ventricular arrhythmias such as ventricular tachycardia and fibrillation, both of which carry high mortality rates. Dexmedetomidine (Dex) is a highly selective α2-agonist used in surgery for congenital cardiac disease because of its antiarrhythmic properties. Dex has previously been reported to prevent or terminate various arrhythmias. The purpose of the present study was to determine the anti-arrhythmic properties of Dex in the context of ischemic cardiomyopathy (ICM) after myocardial infarction.

Methods and Results

We randomly allocated 48 rats with ICM, created by persistent ligation of the left anterior descending artery for 4 weeks, into six groups: Sham (n = 8), Sham + BML (n = 8), ICM (n = 8), ICM + BML (n = 8), ICM + Dex (n = 8), and ICM + Dex + BML (n = 8). Treatments started after ICM was confirmed (the day after echocardiographic measurement) and continued for 4 weeks (inject intraperitoneally, daily). Dex inhibited the generation of collagens, cytokines, and other inflammatory mediators in rats with ICM via the suppression of NF-κB activation and increased the distribution of connexin 43 (Cx43) via phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK). Dex reduced the occurrence of spontaneous ventricular arrhythmias (ventricular premature beat or ventricular tachycardia), decreased the inducibility quotient of ventricular arrhythmias induced by PES, and partly improved cardiac contraction. The AMPK antagonist BML-275 dihydrochloride (BML) partly weakened the cardioprotective effect of Dex.

Conclusion

Dex conferred anti-arrhythmic effects in the context of ICM via upregulation of Cx43 and suppression of inflammation and fibrosis. The anti-arrhythmic and anti-inflammatory properties of Dex may be mediated by phosphorylation of AMPK and subsequent suppression of NF-κB activation.

Notoginsenoside R1 for Organs Ischemia/Reperfusion Injury: A Preclinical Systematic Review

Notoginsenoside R1 (NGR1) exerts pharmacological actions for a variety of diseases such as myocardial infarction, ischemic stroke, acute renal injury, and intestinal injury. Here, we conducted a preclinical systematic review of NGR1 for ischemia reperfusion (I/R) injury. Eight databases were searched from their inception to February 23rd, 2019; Review Manager 5.3 was applied for data analysis. CAMARADES 10-item checklist and cell 10-item checklist were used to evaluate the methodological quality. Twenty-five studies with 304 animals and 124 cells were selected. Scores of the risk of bias in animal studies ranged from 3 to 8, and the cell studies ranged from 3 to 5. NGR1 had significant effects on decreasing myocardial infarct size in myocardial I/R injury, decreasing cerebral infarction volume and neurologic deficit score in cerebral I/R injury, decreasing serum creatinine in renal I/R injury, and decreasing Park/Chiu score in intestinal I/R injury compared with controls (all P < 0.05 or P < 0.01). The multiple organ protection of NGR1 after I/R injury is mainly through the mechanisms of antioxidant, anti-apoptosis, and anti-inflammatory, promoting angiogenesis and improving energy metabolism. The findings showed the organ protection effect of NGR1 after I/R injury, and NGR1 can potentially become a novel drug candidate for ischemic diseases. Further translation studies are needed.

Basic fibroblast growth factor attenuates left-ventricular remodeling following surgical ventricular restoration in a rat ischemic cardiomyopathy model

OBJECTIVE

Although surgical ventricular restoration for ischemic cardiomyopathy is expected as an alternative or bridge to heart transplantation, post-operative remodeling of left ventricle (LV) needs to be addressed. This study aimed to examine the effect of basic fibroblast growth factor (bFGF), which induces angiogenesis and tissue regeneration in ischemic myocardium, to prevent remodeling after surgical ventricular restoration (SVR) using a rat ischemic cardiomyopathy model.

METHODS

Four weeks after coronary artery ligation, rats were divided into two groups: rats treated with SVR alone (SVR; n = 21), and rats treated with SVR and local sustained release of bFGF using gelatin hydrogel sheet (SVR + bFGF; n = 22). Cardiac function was assessed by serial echocardiography and cardiac catheterization. Cardiac tissue sections were histologically examined for vascular density and fibrosis.

RESULTS

Higher systolic function and lower LV end-diastolic pressure (LVEDP) were observed in rats treated with SVR + bFGF (SVR vs SVR + bFGF; Ees: 0.22 ± 0.11 vs 0.33 ± 0.22 mmHg/μL, p = 0.0328; LVEDP: 12.7 ± 7.0 vs 8.5 ± 4.3 mmHg, p = 0.0230). LV area tended to be lower in rats treated with SVR + bFGF compared to rats treated with SVR alone (left-ventricular end-diastolic area: 0.66 ± 0.07 vs 0.62 ± 0.07 cm², p = 0.071). Vascular density tended to be higher in rats treated with SVR + bFGF than those without bFGF (23.3 ± 8.1 vs 28.8 ± 9.5/mm², p = 0.0509).

CONCLUSIONS

BFGF induced angiogenesis and attenuated remodeling after SVR which secured the efficacy of SVR in a rat ischemic cardiomyopathy model.

Folic Acid Derived Hydrogel Enhances the Survival and Promotes Therapeutic Efficacy of iPS Cells for Acute Myocardial Infarction

Stem cell therapy has obtained extensive consensus to be an effective method for post myocardial infarction (MI) intervention. Induced pluripotent stem (iPS) cells, which are able to differentiate into multiple cell types, have the potential to generate cardiovascular lineage cells for myocardial repair after ischemic damage, but their poor retention rate significantly hinders the therapeutic efficacy. In the present study, we developed a supramolecular hydrogel which is formed by the self-assembly of folic acid (FA)-modified peptide via a biocompatible method (glutathione reduction) and suitable for cell encapsulation and transplantation. The iPS cells labeled with CM-Dil were transplanted into the MI hearts of mice with or without FA hydrogel encapsulation. The results corroborated that the FA hydrogel significantly improved the retention and survival of iPS cells in MI hearts post injection, leading to augmentation of the therapeutic efficacy of iPS cells including better cardiac function and much less adverse heart remodeling, by subsequent differentiation toward cardiac cells and stimulation of neovascularization. This study reported a novel supramolecular hydrogel based on FA-peptides capable of improving the therapeutic capacity of iPS cells, which held big potential in the treatment of MI.

Alteration of Cholinergic Anti-Inflammatory Pathway in Rat With Ischemic Cardiomyopathy-Modified Electrophysiological Function of Heart

BACKGROUND

With chronic ischemia after myocardial infarction, the resulting scar tissue result in electrical and structural remodeling vulnerable to an arrhythmogenic substrate. The cholinergic anti-inflammatory pathway elicited by vagal nerve via α7 nicotinic acetylcholine receptors (α7-nAChR) can modulate local and systemic inflammatory responses. Here, we aimed to clarify a novel mechanism for the antiarrhythmogenic properties of vagal nerve during the ischemic cardiomyopathy (ICM).

METHODS AND RESULTS

Left anterior descending artery of adult male Sprague-Dawley rats was ligated for 4 weeks to develop ICM. Western blot revealed that eliciting the cholinergic anti-inflammatory pathway by nicotine treatment showed a significant reduction in the amounts of collagens, cytokines, and other inflammatory mediators in the left ventricular infarcted border zone via inhibited NF-κB activation, whereas it increased the phosphorylated connexin 43. Vagotomy inhibited the anti-inflammatory, anti-fibrosis, and anti-arrhythmogenic effect of nicotine administration. And immunohistochemistry confirmed that the nicotine administration-induced increase of connexin 43 was located in intercellular junctions. Furthermore nicotine treatment suppressed NF-κB activation in lipopolysaccharide-stimulated RAW264.7 cells, and α-bungarotoxin (an α7-nAChR selective antagonist) partly inhibited the nicotine-treatment effect. In addition, 4-week nicotine administration slightly improved the cardiac function, increased cardiac parasympathetic tone, decreased the prolonged QTc, and decreased the arrhythmia score of programmed electric stimulation-induced ventricular arrhythmia.

CONCLUSIONS

Eliciting the cholinergic anti-inflammatory pathway exerts anti-arrhythmogenic effects against ICM-induced ventricular arrhythmia accompanied by downregulation of cytokines, downgenerating of collagens, decrease in sympathetic/parasympathetic ratio, and prevention of the loss of phosphorylated connexin 43 during ICM. Our findings may suggest a promising therapy for the generation of ICM-induced ventricular arrhythmia by eliciting the cholinergic anti-inflammatory pathway.

A combined cellular and surgical ventricular reconstruction therapeutic approach produces attenuation of remodeling in infarcted rats

BACKGROUND

Left ventricular reconstruction (LVR) has been shown to provide transient benefits to the LV structure and function of infarcted hearts; however, long-term results have been disappointing as LVR-induced benefits are typically not sustained. We hypothesized that administration of cardiosphere-derived cells (CDCs), which promote myocardial repair and regeneration, may result in long-term preservation of the beneficial effects of LVR in ischemic cardiomyopathy.

METHODS

Wistar Kyoto rats underwent myocardial infarction (MI) and two weeks later were randomized into 3 groups: in Group 1 (n=9), LVR was performed by plication of the infarcted apex and CDCs were injected in the infarct border zone (IBZ); group 2 animals (n=9) underwent LVR and received vehicle solution in the IBZ; and Group 3 animals (n=10) were injected with vehicle solution in the IBZ without undergoing LVR. Echocardiograms were performed at baseline, 4 days post-apex plication, and at 3 months post-MI.

RESULTS

At baseline, all animal groups had a comparable LVEF, LV end-diastolic volume (EDV) and LV end-systolic volume (ESV). Four days post-LV apex plication, Group 1 and Group 2 animals exhibited comparable significant improvement in EF and comparable significant reduction in LVEDV and LVESV. Three months post-MI, Group 1 animals had a decreased LVEDV, decreased LVESV, less impaired CS, increased peak systolic torsion and increased EF compared to animals in Groups 2 and 3.

CONCLUSION

In infarcted rat hearts, intramyocardial delivery of CDCs in conjunction with LVR resulted in significant and sustained amelioration of LV remodeling and improvement in LV function compared to LVR alone.

Efficient long-term survival of cell grafts after myocardial infarction with thick viable cardiac tissue entirely from pluripotent stem cells

Poor engraftment of cells after transplantation to the heart is a common and unresolved problem in the cardiac cell therapies. We previously generated cardiovascular cell sheets entirely from pluripotent stem cells with cardiomyocytes, endothelial cells and vascular mural cells. Though sheet transplantation showed a better engraftment and improved cardiac function after myocardial infarction, stacking limitation (up to 3 sheets) by hypoxia hampered larger structure formation and long-term survival of the grafts. Here we report an efficient method to overcome the stacking limitation. Insertion of gelatin hydrogel microspheres (GHMs) between each cardiovascular cell sheet broke the viable limitation via appropriate spacing and fluid impregnation with GHMs. Fifteen sheets with GHMs (15-GHM construct; >1 mm thickness) were stacked within several hours and viable after 1 week in vitro. Transplantation of 5-GHM constructs (≈2 × 10(6) of total cells) to a rat myocardial infarction model showed rapid and sustained functional improvements. The grafts were efficiently engrafted as multiple layered cardiovascular cells accompanied by functional capillary networks. Large engrafted cardiac tissues (0.8 mm thickness with 40 cell layers) successfully survived 3 months after TX. We developed an efficient method to generate thicker viable tissue structures and achieve long-term survival of the cell graft to the heart.

Establishment of a chronic left ventricular aneurysm model in rabbit

OBJECTIVES

To establish a cost-effective and reproducible procedure for induction of chronic left ventricular aneurysm (LVA) in rabbits.

METHODS

Acute myocardial infarction (AMI) was induced in 35 rabbits via concomitant ligation of the left anterior descending (LAD) coronary artery and the circumflex (Cx) branch at the middle portion. Development of AMI was confirmed by ST segment elevation and akinesis of the occluded area. Echocardiography, pathological evaluation, and agar intra-chamber casting were utilized to validate the formation of LVA four weeks after the surgery. Left ventricular end systolic pressure (LVESP) and diastolic pressure (LVEDP) were measured before, immediately after and four weeks after ligation. Dimensions of the ventricular chamber, thickness of the interventricular septum (IVS) and the left ventricular posterior wall (LVPW) left ventricular end diastolic volume (LVEDV), systolic volume (LVESV), and ejection fraction (EF) were recorded by echocardiogram.

RESULTS

Thirty one (88.6%) rabbits survived myocardial infarction and 26 of them developed aneurysm (83.9%). The mean area of aneurysm was 33.4% ± 2.4% of the left ventricle. LVEF markedly decreased after LVA formation, whereas LVEDV, LVESV and the thickness of IVS as well as the dimension of ventricular chamber from apex to mitral valve annulus significantly increased. LVESP immediately dropped after ligation and recovered to a small extent after LVA formation. LVEDP progressively increased after ligation till LVA formation. Areas in the LV that underwent fibrosis included the apex, anterior wall and lateral wall but not IVS. Agar intra-chamber cast showed that the bulging of LV wall was prominent in the area of aneurysm.

CONCLUSIONS

Ligation of LAD and Cx at the middle portion could induce development of LVA at a mean area ratio of 33.4% ± 2.4% which involves the apex, anterior wall and lateral wall of the left ventricle.

Effects of hepatocyte growth factor in myocarditis rats induced by immunization with porcine cardiac myosin

OBJECTIVES

Myocarditis is considered one of the major causes of dilated cardiomyopathy. Hepatocyte growth factor (HGF) has pleiotropic activities that promote tissue regeneration and facilitate functional improvement of injured tissue. We investigated whether the epicardial sustained-release of HGF, using gelatin hydrogel sheets, improves cardiac function in a chronic myocarditis rat model.

METHODS

Six weeks after Lewis rats were immunized with porcine cardiac myosin to establish autoimmune myocarditis, HGF- or normal saline (NS)-incorporated gelatin hydrogel sheets were applied to the epicardium (G-HGF and G-NS, respectively). At either 2 or 4 weeks after treatment, these were compared with the Control myocarditis group. Cardiac function was evaluated by echocardiography and cardiac catheterization. Development of fibrosis was determined by histological study and expression of transforming growth factor-β1 (TGF-β1). Bax and Bcl-2 levels were measured to evaluate apoptotic activity.

RESULTS

At both points, fractional shortening and end-systolic elastance were higher in the G-HGF group than in the Control and G-NS groups (P < 0.01). Fractional shortening at 2 weeks of each group were as follows: 31.0 ± 0.9%, 24.8 ± 2.7% and 48.6 ± 2.6% (Control, G-NS and G-HGF, respectively). The ratio of the fibrotic area of the myocardium was lower in the G-HGF group than in the Control and G-NS groups at 2 weeks (G-HGF, 8.8 ± 0.9%; Control, 17.5 ± 0.2%; G-NS, 15.6 ± 0.7%; P < 0.01). The ratio at 4 weeks was lower in the G-HGF group than in the G-NS group (10.9 ± 1.4% vs 18.5 ± 1.3%; P < 0.01). The mRNA expression of TGF-β1 in the G-HGF group was lower than in the Control group at 2 weeks (0.6 ± 0.1 vs 1.1 ± 0.2) and lower than that in the G-NS group at 4 weeks (0.7 ± 0.1 vs 1.3 ± 0.2). The Bax-to-Bcl-2 ratios at both points were lower in the G-HGF group than in the Control group.

CONCLUSIONS

Sustained-released HGF markedly improves cardiac function in chronic myocarditis rats. The antifibrotic and antiapoptotic actions of HGF may contribute to the improvement. HGF-incorporated gelatin hydrogel sheet can be a new therapeutic modality for myocarditis.

Pluripotent stem cell-engineered cell sheets reassembled with defined cardiovascular populations ameliorate reduction in infarct heart function through cardiomyocyte-mediated neovascularization

Although stem cell therapy is a promising strategy for cardiac restoration, the heterogeneity of transplanted cells has been hampering the precise understanding of the cellular and molecular mechanisms. Previously, we established a cardiovascular cell differentiation system from mouse pluripotent stem cells, in which cardiomyocytes (CMs), endothelial cells (ECs), and mural cells (MCs) can be systematically induced and purified. Combining this with cell sheet technology, we generated cardiac tissue sheets reassembled with defined cardiovascular populations. Here, we show the potentials and mechanisms of cardiac tissue sheet transplantation in cardiac function after myocardial infarction (MI). Transplantation of the cardiac tissue sheet to a rat MI model showed significant and sustained improvement of systolic function accompanied by neovascularization. Reduction of the infarct wall thinning and fibrotic length indicated the attenuation of left ventricular remodeling. Cell tracing with species-specific fluorescent in situ hybridization after transplantation revealed a relatively early loss of transplanted cells and an increase in endogenous neovascularization in the proximity of the graft, suggesting an indirect angiogenic effect of cardiac tissue sheets rather than direct CM contributions. We prospectively dissected the functional mechanisms with cell type-controlled sheet analyses. Sheet CMs were the main source of vascular endothelial growth factor. Transplantation of sheets lacking CMs resulted in the disappearance of neovascularization and subsequent functional improvement, indicating that the beneficial effects of the sheet were achieved by sheet CMs. ECs and MCs enhanced the sheet functions and structural integration. Supplying CMs to ischemic regions with cellular interaction could be a strategic key in future cardiac cell therapy.

Aged human cells rejuvenated by cytokine enhancement of biomaterials for surgical ventricular restoration

OBJECTIVES

This study investigated whether cytokine enhancement of a biodegradable patch could restore cardiac function after surgical ventricular restoration (SVR) even when seeded with cells from old donors.

BACKGROUND

SVR can partially restore heart size and improve function late after an extensive anterior myocardial infarction. However, 2 limitations include the stiff synthetic patch used and the limited healing of the infarct scar in aged patients.

METHODS

We covalently immobilized 2 proangiogenic cytokines (vascular endothelial growth factor and basic fibroblast growth factor) onto porous collagen scaffolds. We seeded human mesenchymal stromal cells from young (50.0 ± 8.0 years, N = 4) or old (74.5 ± 7.4 years, N = 4) donors into the scaffolds, with or without growth factors. The patches were characterized and used for SVR in a rat model of myocardial infarction. Cardiac function was assessed.

RESULTS

In vitro results showed that cells from old donors grew slower in the scaffolds. However, the presence of cytokines modulated the aging-related p16 gene and enhanced cell proliferation, converting the old cell phenotype to a young phenotype. In vivo studies showed that 28 days after SVR, patches seeded with cells from old donors did not induce functional recovery as well as patches seeded with young cells. However, cytokine-enhanced patches seeded with old cells exhibited preserved patch area, prolonged cell survival, and augmented angiogenesis, and rats implanted with these patches had better cardiac function. The patch became an elastic tissue, and the old cells were rejuvenated.

CONCLUSIONS

This sustained-release, cytokine-conjugated system provides a promising platform for engineering myocardial tissue for aged patients with heart failure.

Myoblast sheet can prevent the impairment of cardiac diastolic function and late remodeling after left ventricular restoration in ischemic cardiomyopathy

BACKGROUND

Impairment of diastolic function and late remodeling are concerns after left ventricular restoration (LVR) for ischemic cardiomyopathy. This study aims to evaluate the effects of combined surgery of myoblast sheets (MS) implantation and LVR.

METHODS

Rat myocardial infarction model was established 2 weeks after left anterior descending artery ligation. They were divided into three groups: sham operation (n=15; group sham), LVR by plicating the infracted area (n=15; group LVR), and MS implantation with LVR (n=15; group LVR+MS).

RESULTS

Serial echocardiographic study revealed significant LV redilatation and decrease of ejection fraction 4 weeks after LVR in group LVR. MS implantation combined with LVR prevented those later deteriorations of LV function in group LVR+MS. Four weeks after the operation, a hemodynamic assessment using a pressure-volume loop showed significantly preserved diastolic function in group LVR+MS; end-diastolic pressure (LVR vs. LVR+MS: 9.0±6.6 mm Hg vs. 2.0±1.0 mm Hg, P<0.05), end-diastolic pressure-volume relationship (LVR vs. LVR+MS 42±23 vs. 13±6, P<0.05). Histological examination revealed cellular hypertrophy and LV fibrosis were significantly less and vascular density was significantly higher in group LVR+MS than in the other two groups. Reverse transcription polymerase chain reaction demonstrated significantly suppressed expression of transforming growth factor-beta, Smad2, and reversion-inducing cysteine-rich protein with Kazal motifs in group LVR+MS.

CONCLUSIONS

MS implantation decreased cardiac fibrosis by suppressing the profibrotic gene expression and attenuated the impairment of diastolic function and the late remodeling after LVR. It is suggesting that MS implantation may improve long-term outcome of LVR for ischemic heart disease.

Proteomic analysis of mitochondria reveals a metabolic switch from fatty acid oxidation to glycolysis in the failing heart

This work characterizes the mitochondrial proteomic profile in the failing heart and elucidates the molecular basis of mitochondria in heart failure. Heart failure was induced in rats by myocardial infarction, and mitochondria were isolated from hearts by differential centrifugation. Using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry, a system biology approach was employed to investigate differences in mitochondrial proteins between normal and failing hearts. Mass spectrometry identified 27 proteins differentially expressed that involved in energy metabolism. Among those, the up-regulated proteins included tricarboxylic acid cycle enzymes and pyruvate dehydrogenase complex subunits while the down-regulated proteins were involved in fatty acid oxidation and the OXPHOS complex. These results suggest a substantial metabolic switch from free fatty acid oxidation to glycolysis in heart failure and provide molecular evidence for alterations in the structural and functional parameters of mitochondria that may contribute to cardiac dysfunction during ischemic injury.

Controlled release of matrix metalloproteinase 1 with or without skeletal myoblasts transplantation improves cardiac function of rat hearts with chronic myocardial infarction

Skeletal myoblast transplantation has been applied clinically for severe ischemic cardiomyopathy. Matrix metalloproteinase 1 (MMP-1) reduces fibrosis and prevents the progress of heart failure. We hypothesized that MMP-1 administration to the infarct area enhances the efficacy of skeletal myoblast transplantation. The controlled release of MMP-1 improved cardiac functions of rats with chronic myocardiac infarction with or without transplantation of skeletal myoblasts. Improvement in cardiac function and small fibrotic area inside the infarcted area were observed compared with those of myoblast transplantation. In conclusion, controlled release of MMP-1 was effective in cardioprotection in postmyocardial infarction although the combination with cell transplantation showed the similar effect.

Surgical ventricular reconstruction in mice: elucidating potential targets for combined molecular/surgical intervention

OBJECTIVES

We hypothesize that persistent alterations in molecular signaling may drive recurrent pathologic remodeling even after the reduction of mechanical stress achieved via surgical ventricular reconstruction. We developed a murine model of surgical ventricular reconstruction that would facilitate molecular analysis of the postreconstruction myocardium and allow future exploitation of genetic models.

METHODS

C57/B6 mice underwent coronary artery ligation. For surgical ventricular reconstruction at 4 weeks after myocardial infarction, a purse-string suture (7-0 polypropylene) achieved at least partial exclusion of the apical aneurysm. Serial echocardiography was correlated to measurements of apoptosis and to Western blot analysis of key signaling cascades.

RESULTS

An immediate 21.7% +/- 2.6% improvement in fractional shortening was seen in the remaining myocardium after surgical ventricular reconstruction. Reduction in left ventricular volume and improved function persisted at 1 week, but recurrent dilatation at 4 weeks (left ventricular end-diastolic volume of 63.5 +/- 2.5 vs 42.1 +/- 5.4 microL immediately after reconstruction; P < .05) was associated with a loss of functional improvement (fractional shortening 41.2% +/- 2% vs 46% +/- 0.9%; P < .01). At 1 week after surgical ventricular reconstruction, there was a transient reduction in myocardial apoptosis. A steady reduction in cardioprotective myocardial Akt activation, however, was not affected by ventricular reconstruction.

CONCLUSION

This murine model recapitulates both the immediate benefits of surgical ventricular reconstruction and the longer-term recurrence of dilated cardiomyopathy seen previously in some animal models and human studies. Early analysis has begun to implicate persistent signaling changes in the postinfarction myocardium that may be responsible for recurrent dilatation after surgical ventricular reconstruction and that may become targets for combined surgical and molecular interventions.

Paradoxical mineralocorticoid receptor activation and left ventricular diastolic dysfunction under high oxidative stress conditions

BACKGROUND

Salt status plays a pivotal role in angiotensin-II-induced organ damage by regulating reactive oxygen species status, and it is reported that reactive oxygen species activate mineralocorticoid receptors.

METHOD

To clarify the role of reactive oxygen species-related mineralocorticoid receptor activation in angiotensin-II-induced cardiac dysfunction, we examined the effect of the following: salt status; an MR antagonist, eplerenone; and an antioxidant, tempol in angiotensin-II-loaded Sprague-Dawley rats.

RESULTS

Angiotensin-II/salt-loading elevated blood pressure, and neither eplerenone nor tempol antagonized the rise in blood pressure significantly. Left ventricular diastolic function was monitored by measuring peak velocity of a mitral early inflow (E), the ratio of mitral early inflow to atrial contraction related flow (E/A), deceleration time of mitral early inflow and -dP/dt, the time constant (T), and filling pressure (left ventricular end-diastolic pressure) by echocardiography or cardiac catheterization. Despite the suppressed serum aldosterone, left ventricular diastolic function was deteriorated with angiotensin II/high salt, but not affected by angiotensin II/low salt. However, angiotensin-II/salt-induced cardiac dysfunction was restored by eplerenone and tempol. Nicotinamide adenine dinucleotide phosphateoxidase-derived superoxide formation was greater in the hearts of the angiotensin II/high-salt rats than of the angiotensin II/low-salt rats. The expression of the Na(+) -H(+) exchanger isoform 1, a target of mineralocorticoid receptor activation, was significantly increased in the angiotensin II/high-salt group. Both tempol and eplerenone inhibited the angiotensin-II/salt-induced upregulation of Na(+) -H(+) exchanger isoform 1.

CONCLUSION

These findings demonstrate that mineralocorticoid receptor activation by oxidative stress can cause left ventricular diastolic dysfunction in a rat model of mild hypertension.

Endoventricular patch plasty for dyskinetic anteroapical left ventricular aneurysm increases systolic circumferential shortening in sheep

OBJECTIVE

Endoventricular patch plasty (Dor procedure) has gained favor as a surgical treatment for heart failure associated with large anteroapical myocardial infarction. We tested the hypotheses that the Dor procedure increases systolic circumferential shortening and longitudinal shortening in noninfarcted left ventricular regions in sheep.

METHODS

In 6 male Dorsett sheep, the left anterior descending coronary artery and its second diagonal branch were ligated 40% of the distance from the apex to the base. Sixteen weeks after myocardial infarction, a Dor procedure was performed with a Dacron patch that was 50% of the infarct neck dimension. Two weeks before and 2 and 6 weeks after the Dor procedure, animals underwent magnetic resonance imaging with tissue tagging in multiple short-axis and long-axis slices. Fully three-dimensional strain analyses were performed. All 6 end-systolic strain components were compared in regions 1 cm, 2 cm, 3 cm, and 4 cm below the valves, as well as in the anterior, posterior, and lateral left ventricular walls and the interventricular septum.

RESULTS

Circumferential shortening increased from before the Dor procedure to 6 weeks after repair in nearly every left ventricular region (13/16). The greatest regional change in circumferential shortening was found in the equatorial region or 2 cm below the base and in the posterior wall (from 9.0% to 18.4%; P < .0001). Longitudinal shortening increased 2 weeks after the Dor procedure but then returned near baseline by 6 weeks after the Dor procedure.

CONCLUSION

The Dor procedure significantly increases systolic circumferential shortening in nearly all noninfarcted left ventricular regions in sheep.

Beneficial effects of carvedilol as a concomitant therapy to angiotensin-converting enzyme inhibitor in patients with ischemic left ventricular systolic dysfunction

Studies are scant on the effects of short-term carvedilol treatment as an adjuvant to angiotensin-converting enzyme (ACE) inhibitor in patients with left ventricular (LV) systolic dysfunction. The objective of this study was to find the effects of short-term treatment of carvedilol on patients with ischemic LV systolic dysfunction (defined as LV ejection fraction (LVEF) ≤30% on 2D echocardiography) undergoing coronary artery bypass surgery (CABG). There were 74 patients that received ACE inhibitor without any β-blocker (control) and 67 patients that received carvedilol in addition to ACE inhibitor following CABG (carvedilol group). After 1 month of drug administration following CABG, the control group was found to have significantly greater percent improvement in LVEF (29.1% ± 5.39%) as compared with the carvedilol group (15.3% ± 4.89%). However, after 3 and 6 months, LVEF levels were found to be significantly greater in the carvedilol group as compared with the control group. Further, at 6 months of drug administration, LV end systolic diameter was significantly less in the carvedilol group (39.11 ± 1.10 mm) as compared with the control group (43.49 ± 1.39 mm). Thus, carvedilol produces beneficial effect on short-term administration in terms of LV contractility when given along with ACE inhibtior as compared with ACE inhibitor therapy alone.

An experimental rabbit model for off-pump left ventricular reconstruction following left ventricular aneurysm

BACKGROUND

Cardiac electromechanical remodeling following left ventricular reconstruction (LVR) surgery is not fully understood. Further development of an animal model will facilitate investigations in this area. In the present study, we aimed to establish a novel LVR procedure without the use of cardiopulmonary bypass in a rabbit left ventricular (LV) aneurysm model.

METHODS

LV aneurysm was created in 6 rabbits by ligation of the distal left coronary artery. More than a month later, LVR aneurysm surgery was performed off-pump using a purse-string suture around the aneurysm. Cardiac dimensions and function were evaluated using echocardiographic techniques perioperatively and 4 weeks after LVR surgery. Six structurally normal hearts were used as controls.

RESULTS

LVR surgery was successfully performed in all 6 rabbits. Both LV end-diastolic volume (LVEDV, 4.6 +/- 0.9 to 3.3 +/- 0.6 mL; P < .01) and LV end-systolic volume (LVESV, 2.5 +/- 0.6 to 1.5 +/- 0.2 mL, P < .01) were decreased immediately postsurgery versus presurgery, and LV ejection fraction (LVEF) was increased (44.5 +/- 5.3 to 55.6 +/- 4.8%, P < .001). For comparison, in normal rabbits (n = 6), LVEDV, LVESV and LVEF were 3.1 +/- 0.7 mL, 1.2 +/- 0.5 mL, and 64.5 +/- 8.8%, respectively. During follow-up, one rabbit died 3 weeks after surgery from an unknown cause. In the remaining 5 animals, improvements of LVEDV (3.7+/- 0.4 mL, P < .05), LVESV (1.7 +/- 0. 3 mL, P < .01), and LVEF (53.1 +/- 2.8%, P < .01) were maintained versus presurgery values for more than 4 weeks after LVR.

CONCLUSIONS

Off-pump LVR of rabbit LV aneurysm is an effective and less invasive surgery that resulted in sustained improvement in cardiac function with no gross intraoperative or postoperative mortality. This may be a useful model for investigations of electromechanical remodeling following LVR.

Effects of cardiac patches engineered with bone marrow-derived mononuclear cells and PGCL scaffolds in a rat myocardial infarction model

Little is known about the cardioprotective effects against heart failure (HF), the effects on differentiation of bone marrow-derived mononuclear cell (BMMNC), and the biocompatibility of BMMNC-seeded biodegradable poly-glycolide-co-caprolactone (PGCL) scaffolds in a myocardial infarction (MI) animal model. This study hypothesized that implantation of a BMMNC-seeded PGCL scaffold into the epicardial surface in a rat MI model would be biocompatible, induce BMMNC migration into infarcted myocardium, and effectively improve left ventricular (LV) systolic dysfunction. One week after the implantation of a BMMNC-seeded PGCL scaffold, BMMMC showed migration into the epicardial region. Four weeks after implantation, augmented neovascularization was observed in infarcted areas and in infarct border zones. Some BMMNCs exhibited the presence of alpha-MHC and troponin I, markers of differentiation into cardiomyocytes. In echocardiographic examinations, BMMNC-seeded PGCL scaffold and non-cell-seeded simple PGCL scaffold groups effectively reduced progressive LV dilatation and preserved LV systolic function as compared to control rat MI groups. Thus, BMMNC-seeded PGCL scaffolding influences BMMNC migration, differentiation to cardiomyocytes, and induction of neovascularization, ultimately effectively lessening LV remodeling and progressive LV systolic dysfunction. PGCL scaffolding can be considered as an effective treatment alternative in MI-induced advanced HF.

Chymase inhibition prevents cardiac fibrosis and dysfunction after myocardial infarction in rats

Human chymase activates not only angiotensin II but also transforming growth factor-beta, a major stimulator of myocardial fibrosis, while rat chymase activates transforming growth factor-beta, but not angiotensin II. To clarify the role of chymase-dependent transforming growth factor-beta activation, we evaluated whether chymase inhibition prevents cardiac fibrosis and cardiac dysfunction after myocardial infarction in rats. Myocardial infarction was induced by ligation of the left anterior descending coronary artery. One day after the ligation, rats were randomized into 2 groups: 1) a chymase-treated group that received 10 mg/kg per day of the chymase inhibitor NK3201 orally for 4 weeks; and 2) a vehicle group of non-treated rats with myocardial infarction. We also included a control group who underwent sham-operation and no treatment. Four weeks after ligation, echocardiography revealed that chymase inhibitor treatment reduced the akinetic area and increased fractional area change but did not significantly change left ventricular end-diastolic area. Chymase inhibition significantly reduced left ventricular end-diastolic pressure, increased the maximal end-systolic pressure-volume relationship and decreased the time constant of left ventricular relaxation. Chymase activity in the non-infarcted myocardium was significantly increased in the vehicle group, but it was significantly reduced by chymase inhibitor treatment. The fibrotic area in the cardiac tissues and the mRNA levels of collagen I and collagen III were also significantly lower in the chymase inhibitor-treated group than in the vehicle group. Therefore, the pathway forming chymase-dependent transforming growth factor-beta may play an important role in myocardial fibrosis and cardiac dysfunction rather than left ventricular dilatation after myocardial infarction.

A novel method for safe and accurate left anterior descending coronary artery ligation for research in rats

BACKGROUND

Left anterior descending artery (LAD) ligation has been commonly used in rats to induce left ventricular infarction for research purposes. However, LAD ligation is a very difficult procedure with high mortality rate in rats. We have developed a safe method of LAD ligation in rats with low mortality.

METHODS

Thirty-six Sprague-Dawley male rats weighing 300-350 g were selected for LAD ligation for the induction of ischemic cardiomyopathy. The surgery was performed under general anesthesia. Left-sided thoracotomy was performed by cutting the fifth and sixth ribs. The pericardium was opened, and the heart exteriorized with a cardiac holder consisting of a plastic loop (1.5x2 cm). The LAD was localized 1-2 mm below the junction of pulmonary conus and the left atrial appendage. A 5.0 silk suture was used to ligate the LAD from the left border of the pulmonary conus to the right border of the left atrial appendage. The heart was returned back to the chest and the chest wall closed with presutured lopes of 4.0 silk.

RESULTS

Mid-LAD ligation was successful in all rats, with less than 5% mortality. The entire surgery was performed in less than 15 min. This method is simple and can be learned in a short period of time. Rats survived the procedure with induction of congestive heart failure for up to 3 weeks of follow-up.

CONCLUSIONS

Using our method, LAD ligation can safely be performed in rats 1-2 mm below the junction of the pulmonary conus and the left atrial appendage, with a very low mortality rate.

Left Ventricular Reconstruction Brings Benefit for Patients With Ischemic Cardiomyopathy

BACKGROUND

Optimal treatment strategies for some patients with ischemic cardiomyopathy can be unclear. We compared the outcome for patients treated with revascularization only or with additional ventricular reconstruction.

METHODS AND RESULTS

We compared 74 consecutive patients with an ejection fraction <35% and a left end-systolic volume index >80 mL/m(2). All patients underwent revasularization but some received only revascularization (group 1) and some were randomized into a group that received additional ventricular reconstruction (group 2). Preoperative and postoperative ejection fraction, end-systolic volume, mitral regurgitation, mortality, heart failure (HF) symptoms, and recurrence were compared between groups. There was 1 postoperative death in group 2 (P =. 58). Preoperative ejection fraction between the groups was similar (P =. 19) but it differed significantly postoperatively (P < .001). HF class (New York Heart Association) decreased more in group 2 (group 2, 2.3 +/- 0.4 versus group 1, 1.4 +/- 0.4; P < .001). Incidence of HF recurrence and rehospitalization was significantly less in group 2 (P = .028). The postoperative development of higher-grade mitral regurgitation was greater in group 1 (147 +/- 32 mL/m(2) versus 119 +/- 25 mL/m(2), P = .024).

CONCLUSION

The outcome at midterm of coronary artery surgery alone in patients with a preoperative large left ventricle was inferior compared with the outcome achieved with additional ventricular restoration.

High rate of right ventricular infarction after ligation of mid left anterior descending artery in rats

BACKGROUND

The left anterior descending artery (LAD) supplies the left ventricle in humans. LAD ligation has been commonly used in rats to induce left ventricular (LV) infarction for research purposes. However, the myocardial supply territories of LAD are not well established in rats. We measured the infarction zone in rats after ligation of the mid-LAD.

METHODS

Twenty-four male Sprague-Dawley rats weighing 300-350 g were selected for LAD ligation for the induction of ischemic cardiomyopathy. The surgery was performed under full anesthesia. Left-sided thoracotomy was performed through cuts in the fifth and sixth ribs. Ligation of the LAD was performed 1 to 2 mm distal to a line between the left border of the pulmonary conus and the right border of the left atrial appendage. LAD was ligated after the first diagonal and septal branches. After 24 h, the hearts were removed and stained with Tetrazolium Tetrachloride (TTC) for the detection of infracted areas.

RESULTS

Ligation of LAD induces 85% infarction of the right anterior free wall and anterior right ventricular septum and induces 100% infarction of the anterior free wall of the left ventricle and anterior septum. Infarction after LAD ligation extends all the way to the distal of the ligation site down to the apex of the heart.

CONCLUSIONS

Mid-LAD ligation after the first septal and diagonal branches causes substantial right ventricular infarction in addition to LV infarct in rats. Therefore, the hemodynamic effect of right ventricle infarct should be considered in research involving LAD ligation in rats.

Immediate Functional Effects of Left Ventricular Reduction: A Doppler Echocardiographic Study in the Rat

BACKGROUND

Immediate functional effects of left ventricle reduction (LVR) are not yet fully defined. Those effects have been studied in the experimental model of myocardial infarction scar plication (MISP) in the rat.

METHODS AND RESULTS

A Doppler echocardiogram was performed immediately before and after MISP in 20 rats with infarction of the left ventricle (LV) larger than 40%. LV diastolic volume reduction (475 +/- 114 versus 185 +/- 65 muL) was accompanied by heart rate decrease (230 +/- 25 versus 166 +/- 27 beats/min) and increase of ejection fraction (37 +/- 7 versus 67 +/- 12%), fractional shortening (18 +/- 3 versus 46 +/- 8%) and posterior wall shortening velocity (1.50 +/- 0.62 versus 2.01 +/- 0.46 cm/s). LV diastolic volume/stroke volume slope was steeper after LVR, suggesting enhancement of the Frank-Starling mechanism. Restrictive pattern of left atrial emptying was alleviated after LVR (E wave: 101 +/- 15 versus 66 +/- 14 cm/s; E/A ratio: 6.8 +/- 2.9 versus 5.0 +/- 2.2; E wave deceleration time: 36 +/- 6 versus 51 +/- 10 msec) even though left atrial diameter (0.69 +/- 0.07 versus 0.66 +/- 0.06 cm) and A wave (18.0 +/- 9.4 versus 15.8 +/- 7.8 cm/s) did not vary. Additionally, a pulmonary flow profile suggesting pulmonary hypertension was observed in 12 of 17 animals before, and in only 3 after, LVR.

CONCLUSION

LVR favors cardiac function not only by reducing afterload. The present data are in consonance with previous suggestions that the Frank-Starling mechanism is enhanced after MISP and, in addition to LV ejection function improvement, the unprecedented facilitation of left atrial emptying after LVR was particularly noteworthy. Even though LVR restricts ventricular distensibility, atrial emptying can be facilitated, probably on account of LV ejection improvement.

Left ventricular volume and function after endoventricular patch plasty for dyskinetic anteroapical left ventricular aneurysm in sheep

OBJECTIVE

Endoventricular patch plasty (the Dor procedure) has gained favor as a surgical treatment for heart failure associated with large anteroapical myocardial infarction. We tested the hypothesis that the Dor procedure reduces left ventricular volume, increases end-systolic elastance, decreases diastolic compliance, and maintains left ventricular function.

METHODS

In 6 male Dorsett sheep, the left anterior descending coronary artery and its second diagonal branch were ligated 40% of the distance from apex to base. Sixteen weeks after myocardial infarction, a Dor procedure was performed with a Dacron patch that was 50% of the infarct neck dimension. Absolute left ventricular volume was measured with magnetic resonance imaging, and left ventricular pressure and relative left ventricular volume changes during pharmacologic preload reduction were measured with a volume conductance catheter 2 weeks before and 2 and 6 weeks after the Dor procedure. End-systolic elastance, diastolic compliance, and Starling relationships were calculated from the resultant left ventricular pressure/volume loops.

RESULTS

Two weeks after the Dor procedure, the left ventricular volume at end systole and end diastole was significantly reduced, and there was no redilation at 6 weeks. Six weeks after the Dor procedure, the ejection fraction was significantly increased. Although stroke volume increased slightly at 6 weeks, the change was not significant. The slopes of end-systolic elastance, diastolic compliance, and Starling relationships were unchanged at 2 and 6 weeks.

CONCLUSIONS

The Dor procedure significantly reduces left ventricular volume. Unlike linear repair, left ventricular volume changes seem stable. The ejection fraction is improved, and left ventricular function (stroke volume and the Starling relationship) is maintained.

Cardiac remodeling and failure: from molecules to man (Part III)

Given the lack of a unified theory of heart failure, future research efforts will be required to unify and synthesize our current understanding of the multiple mechanisms that control remodeling in the failing heart. Matrix remodeling and the associated activation of inflammatory cytokines and MMPs have emerged as key pathways in the development of heart failure. As such, attempts to understand the integrated control of ECM homeostasis with the bioactivation of inflammatory cytokines may be of particular relevance to the development of effective anti-remodeling approaches. Notably, the implantation of isolated populations of cells in failing myocardium has a profound and consistent anti-remodeling effect that limits the progression to CHF. These observations were consistently identified in numerous studies using diverse experimental animal models and varied cell types. Accordingly, multicenter clinical trials are underway, and the preliminary data in patients with CHF are encouraging. Despite the enormous promise of cell transplantation to restore and regenerate failing myocardium, the mechanisms underlying these profound biological effects are not understood. An improved understanding of the myocardial response to cell implantation, particularly on parameters of matrix remodeling, may help unify our current understanding of the progression of heart failure and optimize the development of this technique for its evolving therapeutic use. The following review outlines recent advances in medical and surgical approaches to control the remodeling process that underlies the progression of heart failure.

Heterotopic transplantation of the failing rat heart as a model of left ventricular mechanical unloading toward recovery

The left ventricular assist device (LVAD) is usually used in patients with end-stage heart failure as a bridge to transplantation. Recently, some studies have reported functional recovery with the use of an LVAD, although the mechanisms responsible for recovery are not fully understood. We investigated the functional recovery of the infarcted, failing rat heart in response to mechanical unloading after heterotopic transplantation. Heart failure was induced in Lewis rats by ligating the left anterior descending artery. After 4 weeks, the infarcted hearts were harvested and heterotopically transplanted. The transplanted infarcted heart was removed after 2 weeks of unloading and examined for hypertrophy and fibrosis, as well as for mRNA levels encoding for brain natriuretic peptide, sarco(endo)plasmic reticulum Ca(2+)-ATPase2a (SERCA2a), and beta1- and beta2-adrenergic receptors. Normal and infarcted rats without transplantation served as control animals. The infarcted heart was hypertrophied as evidenced by an increase in heart weight and myocyte diameter. After unloading the infarcted heart for 2 weeks, there was a decrease in heart weight and myocyte diameter. However, the percentage of myocardial fibrosis increased after unloading. The mRNA expression of brain natriuretic peptide and the beta2-adrenergic receptor significantly improved after mechanical unloading. The levels of SERCA2a mRNA tended to increase after unloading. In conclusion, unloading the failing, infarcted heart can help normalize left ventricular hypertrophy and cardiac gene expression. This unloading model appears to partially mimic the conditions of hemodynamic support with an LVAD in heart failure patients and potentially offers insights into the mechanisms of functional recovery.

Improved left ventricular aneurysm repair with bioengineered vascular smooth muscle grafts

BACKGROUND

Recurrent ventricular dilatation can occur after surgical repair of a left ventricular (LV) aneurysm. Use of an autologous bioengineered muscle graft to replace resected scar tissue may prevent recurrent dilatation and improve cardiac function.

METHODS

Vascular smooth muscle cells (SMCs, 5 x 10(6) cells) from rat aortas were seeded onto synthetic PCLA (sponge polymer of epsilon-caprolactone-co-L-lactide reinforced with knitted poly-L-lactide fabric) patches and cultured for 2 weeks to allow tissue formation. Syngenic rats underwent proximal left coronary artery ligation to create a transmural myocardial scar. Four weeks after coronary ligation, cell-seeded patches (n=15) or unseeded patches (n=12) were used for a modified endoventricular circular patch plasty (EVCPP) repair of the infarct area. Ligated controls (n=14) and nonligated normal rats (n=10) had sham surgeries without EVCPP. Cardiac function was assessed by echocardiography and isolated Langendorff heart perfusion. Graft histology and morphology was also assessed.

RESULTS

After 8 weeks in vivo, seeded patches were thicker (P<0.05) and smaller in area (P<0.003) than unseeded patches. Only seeded patches had prominent elastic tissue formation (P<0.001) in association with SMCs. LV systolic function by echocardiography was improved in the seeded group compared with both unseeded (P<0.002) and control groups (P<0.0001). LV volumes in both patch repair groups were comparable but were significantly smaller (P<0.05) than controls. LV distensibility tended toward improvement in the seeded group as compared with unseeded hearts, but the difference did not achieve statistical significance (P=0.06).

CONCLUSIONS

Surgical repair with muscle-cell seeded grafts reduced abnormal chamber distensibility and improved LV function after myocardial infarction as compared with unseeded grafts. Bioengineered muscle grafts may be superior to synthetic materials for the surgical repair of LV scar.

Effects of two inhibitors of renin-angiotensin system on attenuation of postoperative remodeling after left ventricular aneurysm repair in rats

We reported that the initial beneficial effects of left ventricular repair (LVR) surgery for LV aneurysm after myocardial infarction (MI) did not persist because of postoperative LV remodeling in a rat model. The renin-angiotensin system (RAS) plays an important role in postinfarction LV remodeling. Inhibition of RAS may be useful to preserve LV function by preventing remodeling. We studied the effects of two inhibitors of RAS in an attempt to improve the operative results of LVR. LV aneurysms were created in rats after ligating the left anterior descending artery. These rats underwent LVR by plicating the LV aneurysm and were treated by three methods: no treatment, treatment with angiotensin-converting enzyme inhibitor (ACE-I) (lisinopril 10 mg/kg per day), and treatment with angiotensin II receptor blocker (ARB) (candesartan 5 mg/kg per day). One week after LVR, echocardiography revealed smaller LV size and better LV motion than before surgery. Four weeks after LVR, LV size returned to the preoperative value in the untreated group, but not as much in the treated groups. Cardiac catheterization revealed lower LV end-diastolic pressure and higher E-max in the treated groups. There was no difference between ACE-I and ARB groups except for systolic blood pressure. LVR decreased LV size and improved systolic function only in the early phase. Adjuvant therapy of ACE-I or ARB-attenuated LV remodeling and maintained LV function at the same level after LVR. This probably indicates that tissue RAS is associated with postoperative remodeling. Concomitant use of RAS inhibitors may make LVR a longer-lasting procedure for LV aneurysm.

Restoration and regeneration of failing myocardium with cell transplantation and tissue engineering

Cell transplantation and the creation of bioengineered cardiovascular tissues are novel biologic approaches to restore and regenerate failing myocardium. These rapidly evolving therapies may complement and enhance other mechanical and surgical interventions for patients with congestive heart failure, providing cardiac surgeons with a wider range of treatments for patients at risk of congestive heart failure. Proof-of-concept studies have been performed in several experimental animal models of human cardiovascular disease, such as myocardial infarction and dilated cardiomyopathy. Although the exact mechanisms are unclear, cell transplantation restores cardiac function and limits ventricular dilatation. Clinical cell transplantation has been performed in a limited number of patients with encouraging preliminary results. In contrast, bioengineered muscle grafting is largely experimental but offers the promise of myocardial regeneration by replacing irreversibly damaged myocardium with healthy autologous tissue to facilitate more extensive ventricular remodeling surgery.

Importance of preserving the apex and plication of the base in left ventricular volume reduction surgery

OBJECTIVE

Volume reduction surgery for dilated cardiomyopathy has not yielded predictable outcomes. The purpose of this study was to clarify the efficacy of modified volume reduction surgery in preserving the left ventricular apex and reducing the left ventricular diameter at the base to maintain fiber continuity.

METHODS

Heart failure was induced with propranolol in 12 dogs, and the animals were randomized into 2 groups. In one group the left ventricular wall was plicated between the 2 papillary muscles from the middle to the apex (apex-sacrificing volume reduction surgery, group A, n = 6), and in the other group plication was done from the base to the middle (apex-sparing volume reduction surgery, group B, n = 6). Left ventricular function was then compared between the groups by using echocardiography and sonomicrometry crystals.

RESULTS

After volume reduction surgery, the fractional area change at the base in group B was greater than that in group A (40% +/- 3% vs 27% +/- 4%, P =.003). Cardiac output in group B was better than that in group A (2.5 +/- 0.2 vs 1.8 +/- 0.2 L/min, P =.023). Left ventricular end-diastolic pressure in group A was higher than that in group B (16 +/- 2 vs 8 +/- 1 mm Hg, P =.001). Fractional shortening in the long axis, as assessed by means of sonomicrometry, was better in group B than in group A.

CONCLUSIONS

Apex-sparing volume reduction surgery capable of maintaining left ventricular fiber continuity provided better left ventricular function in both the systolic and diastolic phases than apex-sacrificing volume reduction surgery in the acute heart failure model. This modification might improve the results of left ventricular volume reduction surgery.

Cardiomyocyte transplantation does not reverse cardiac remodeling in rats with chronic myocardial infarction

BACKGROUND

Several reports have documented the potential benefits of cell transplantation as an alternative to cardiac transplantation. This study was designed to investigate whether cardiomyocyte transplantation is effective in rats with chronic myocardial infarction.

METHODS

Syngeneic Lewis rats were used in this study. Chronic myocardial infarction was induced in rats by ligating the left anterior descending artery. Four weeks later, after left ventricular (LV) dysfunction with akinetic regions was confirmed by echocardiography, the rats were randomized into two groups: a group that received fetal cardiomyocyte transplantation (TX group; n = 11); and a group that received an intramyocardial injection of culture medium only (control group; n = 12).

RESULTS

Four weeks after treatment, the TX group had smaller end-systolic dimension (LVDs) (7.5 +/- 0.9 vs 8.9 +/- 0.8 mm, p < 0.01) and better fractional shortening (FS) (26.2 +/- 5.9 vs 17.7% +/- 5.1%, p < 0.01) than the control group. However, there were no differences in LV end-diastolic dimension, LVDs, and FS between baseline and post-treatment values in the TX group. In addition, plasma levels of atrial natriuretic peptide were not significantly different between the two groups 4 weeks after treatment. In microscopic examination, small amounts of transplanted cardiomyocytes were found only in the periinfarct area, not in the center of scar area, and a thicker ventricular wall in the infarct area was detected in the TX group.

CONCLUSIONS

Fetal cardiomyocyte transplantation prevented, but did not reverse, cardiac remodeling that was accompanied with heart failure in myocardial infarction rats. Further investigation is warranted for optimal clinical application to the failing heart.

Prevascularization with gelatin microspheres containing basic fibroblast growth factor enhances the benefits of cardiomyocyte transplantation

OBJECTIVE

The effects of cell transplantation on the ischemic failing heart have already been documented. However, the area in and around infarct regions is not a good environment for cells to survive in because they are exposed to poor conditions in which certain requirements cannot be adequately supplied. We therefore designed a study to investigate the efficacy of prevascularization in ischemic regions before cell transplantation.

METHODS

Rats with myocardial infarction were randomized into 4 groups: 11 rats received a culture medium injection to the left ventricular wall (control group), 11 received fetal cardiomyocyte transplantation (TX group), 11 received gelatin hydrogel microspheres incorporating basic fibroblast growth factor (FGF group), and 11 received basic fibroblast growth factor pretreatment sequentially, followed by cardiomyocyte transplantation (FGF-TX group). Four weeks later, left ventricular function was assessed by means of echocardiography and cardiac catheterization.

RESULTS

In the FGF and FGF-TX groups neovascularization was found in the scar tissue 1 week later. The TX, FGF, and FGF-TX groups showed better fractional shortening than the control group (TX, FGF, FGF-TX, and control: 28% +/- 4.4%, 24% +/- 8.6%, 27% +/- 7.3%, and 17% +/- 4.6%, respectively; P <.01). Left ventricular maximum time-varying elastance was higher in the FGF-TX group than in the TX and FGF groups (FGF-TX, TX, and FGF: 0.52 +/- 0.23, 0.30 +/- 0.08, and 0.27 +/- 0.20 mm Hg/microL, respectively; P <.01). Histologically, more transplanted cells survived in the FGF-TX group than in the TX group.

CONCLUSIONS

Prevascularization with basic fibroblast growth factor-incorporated microspheres enhances the benefits of cardiomyocyte transplantation. We expect that this system will contribute to regeneration medicine through its extensive application to other growth factors.