Persistent stunning induces myocardial hibernation and protection: flow/function and metabolic mechanisms

Rapamycin and 3-Methyladenine Influence the Apoptosis, Senescence, and Adipogenesis of Human Adipose-Derived Stem Cells by Promoting and Inhibiting Autophagy: An In Vitro and In Vivo Study

OBJECTIVE

We aimed to clarify the changes in apoptosis, proliferation, senescence, and adipogenesis after promoting and inhibiting autophagy in adipose-derived stem cells (ADSCs) by rapamycin and 3-methyladenine in vitro and in vivo.

METHODS

After rapamycin and 3-methyladenine pretreatment, ADSC autophagy was detected by immunofluorescence for LC3, RT-PCR for ATG genes, and western blotting (WB) for the LC3 II/I and p62 proteins. TUNEL staining, PCR of BAX, and WB of Caspase-3 were preformed to assess ADSC apoptosis. The adipogenesis of ADSCs was evaluated by Oil red O staining and PCR of PPAR-γ. CCK8 assays were conducted to detect proliferation. Senescence was tested by Sa-β-gal staining and PCR of the P16/ 19/21 genes. Moreover, the mass and volume retention rate were determined, and perilipin and CD31 staining were performed in vivo.

RESULTS

Rapamycin and 3-methyladenine pretreatment increased and decreased autophagy of ADSCs, respectively, under normal and oxygen-glucose deprivation conditions. Apoptosis and senescence of ADSCs were decreased, and adipogenesis was increased along with the upregulation of autophagy. However, the proliferation of ADSCs was inhibited after either rapamycin or 3-methyladenine pretreatment. In vivo, the volume and mass retention rate and the angiogenesis of the grafts were also improved after rapamycin pretreatment.

CONCLUSIONS

Rapamycin pretreatment reduced apoptosis, delayed senescence, and promoted adipogenesis of ADSCs. These effects were inhibited by 3-methyladenine, indicating that the changes may be mediated by autophagy. Moreover, the survival rate and angiogenesis of the grafts were increased after upregulation of ADSC autophagy in vivo, which may help improve the efficiency of clinical fat transplantation.

NO LEVEL ASSIGNED

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Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

State of the Art: Imaging for Myocardial Viability: A Scientific Statement From the American Heart Association

A substantial proportion of patients with acute myocardial infarction develop clinical heart failure, which remains a common and major healthcare burden. It has been shown that in patients with chronic coronary artery disease, ischemic episodes lead to a global pattern of cardiomyocyte remodeling and dedifferentiation, hallmarked by myolysis, glycogen accumulation, and alteration of structural proteins. These changes, in conjunction with an impaired global coronary reserve, may eventually become irreversible and result in ischemic cardiomyopathy. Moreover, noninvasive imaging of myocardial scar and hibernation can inform the risk of sudden cardiac death. Therefore, it would be intuitive that imaging of myocardial viability is an essential tool for the proper use of invasive treatment strategies and patient prognostication. However, this notion has been challenged by large-scale clinical trials demonstrating that, in the modern era of improved guideline-directed medical therapies, imaging of myocardial viability failed to deliver effective guidance of coronary bypass surgery to a reduction of adverse cardiac outcomes. In addition, current available imaging technologies in this regard are numerous, and they target diverse surrogates of structural or tissue substrates of myocardial viability. In this document, we examine these issues in the current clinical context, collect current evidence of imaging technology by modality, and inform future directions.

Cardiac metabolomic profile of the naked mole-rat-glycogen to the rescue

The African naked mole-rat (Heterocephalus glaber) is unique among mammals, displaying extreme longevity, resistance to cardiovascular disease and an ability to survive long periods of extreme hypoxia. The metabolic adaptations required for resistance to hypoxia are hotly debated and a recent report provides evidence that they are able to switch from glucose to fructose driven glycolysis in the brain. However, other systemic alterations in their metabolism are largely unknown. In the current study, a semi-targeted high resolution ¹H magnetic resonance spectroscopy (MRS) metabolomics investigation was performed on cardiac tissue from the naked mole-rat (NMR) and wild-type C57/BL6 mice to better understand these adaptations. A range of metabolic differences was observed in the NMR including increased lactate, consistent with enhanced rates of glycolysis previously reported, increased glutathione, suggesting increased resistance to oxidative stress and decreased succinate/fumarate ratio suggesting reduced oxidative phosphorylation and ROS production. Surprisingly, the most significant difference was an elevation of glycogen stores and glucose-1-phosphate resulting from glycogen turnover, that were completely absent in the mouse heart and above the levels found in the mouse liver. Thus, we identified a range of metabolic adaptations in the NMR heart that are relevant to their ability to survive extreme environmental pressures and metabolic stress. Our study underscores the plasticity of energetic pathways and the need for compensatory strategies to adapt in response to the physiological and pathological stress including ageing and ischaemic heart pathologies.

Identification of new biophysical markers for pathological ventricular remodelling in tachycardia-induced dilated cardiomyopathy

Our aim was to identify biophysical biomarkers of ventricular remodelling in tachycardia-induced dilated cardiomyopathy (DCM). Our study includes healthy controls (N = 7) and DCM pigs (N = 10). Molecular analysis showed global myocardial metabolic abnormalities, some of them related to myocardial hibernation in failing hearts, supporting the translationality of our model to study cardiac remodelling in dilated cardiomyopathy. Histological analysis showed unorganized and agglomerated collagen accumulation in the dilated ventricles and a higher percentage of fibrosis in the right (RV) than in the left (LV) ventricle (P = .016). The Fourier Transform Infrared Spectroscopy (FTIR) 1st and 2nd indicators, which are markers of the myofiber/collagen ratio, were reduced in dilated hearts, with the 1st indicator reduced by 45% and 53% in the RV and LV, respectively, and the 2nd indicator reduced by 25% in the RV. The 3rd FTIR indicator, a marker of the carbohydrate/lipid ratio, was up-regulated in the right and left dilated ventricles but to a greater extent in the RV (2.60-fold vs 1.61-fold, P = .049). Differential scanning calorimetry (DSC) showed a depression of the freezable water melting point in DCM ventricles - indicating structural changes in the tissue architecture - and lower protein stability. Our results suggest that the 1st, 2nd and 3rd FTIR indicators are useful markers of cardiac remodelling. Moreover, the 2nd and 3rd FITR indicators, which are altered to a greater extent in the right ventricle, are associated with greater fibrosis.

Identifying and Managing Hibernating Myocardium: What's New and What Remains Unknown?

PURPOSE OF REVIEW

Hibernation is an important and reversible cause of myocardial dysfunction in ischaemic heart failure.

RECENT FINDINGS

Hibernation is an adaptive process that promotes myocyte survival over maintaining contractile function. It is innate to mammalian physiology, sharing features with physiological hibernation in other species. Advanced imaging methods have reasonable accuracy in identifying hibernating myocardium. Novel superior hybrid methods may provide diagnostic potential. New evidence supports the role of surgical revascularisation in ischaemic heart failure, but the role of viability tests in planning such procedures remains unclear. Research to date has exclusively involved patients with ambulatory heart failure: Investigating the role of hibernation in ADHF is a key avenue for the future. Whilst our understanding of hibernation pathophysiology has improved dramatically, the clinical utility of identifying and targeting hibernation remains unclear.

Guidelines for experimental models of myocardial ischemia and infarction

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models.

Listen to this article’s corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Mitochondrial Transplantation in Myocardial Ischemia and Reperfusion Injury

Ischemic heart disease remains the leading cause of death worldwide. Mitochondria are the power plant of the cardiomyocyte, generating more than 95% of the cardiac ATP. Complex cellular responses to myocardial ischemia converge on mitochondrial malfunction which persists and increases after reperfusion, determining the extent of cellular viability and post-ischemic functional recovery. In a quest to ameliorate various points in pathways from mitochondrial damage to myocardial necrosis, exhaustive pharmacologic and genetic tools have targeted various mediators of ischemia and reperfusion injury and procedural techniques without applicable success. The new concept of replacing damaged mitochondria with healthy mitochondria at the onset of reperfusion by auto-transplantation is emerging not only as potential therapy of myocardial rescue, but as gateway to a deeper understanding of mitochondrial metabolism and function. In this chapter, we explore the mechanisms of mitochondrial dysfunction during ischemia and reperfusion, current developments in the methodology of mitochondrial transplantation, mechanisms of cardioprotection and their clinical implications.

Fabrication of poly(β-cyclodextrin-co-citric acid)/bentonite clay nanocomposite hydrogel: thermal and absorption properties

A β-cyclodextrin (β-CD)/bentonite clay (BNC) nanocomposite hydrogel was prepared through combining in situ intercalative polymerization and melt intercalation methods.

Severity of myocardial fatty acid dysmetabolism induced by coronary spasm does not differ with Thrombolysis in Myocardial Infarction (TIMI) grade during intracoronary acetylcholine provocation tests

Whether additional intracoronary acetylcholine (ACH) injections are required for severe coronary spasm without limited coronary flow in the ACH provocation test remains unclear. We used (123)I-β-methyl-iodophenyl pentadecanoic acid ((123)I-BMIPP) to identify myocardial ischemic memory to compare the severity of myocardial fatty acid dysmetabolism among Thrombolysis in Myocardial Infarction (TIMI) grade flow.Thirteen hypertensive volunteers (mean age, 69.5 years) and 37 patients with VSA (mean age, 62.8 years) were enrolled. The patients with VSA were stratified according to TIMI flow grades of 3 (90% luminal narrowing; n = 12) or TIMI 0-2 (≥ 99% or total occlusion; n = 25) during ACH provocation tests. Two weeks after cardiac catheterization, (123)I-BMIPP myocardial scintigraphic images were obtained at 15 minutes (early) and at 4 hours (delayed) after tracer injection. The heart-to-mediastinum (H/M) ratio and washout rates (WR) were calculated from planar images.The TIMI 3 and TIMI 0-2 groups had significantly lower early and delayed H/M ratios than controls but the difference did not reach significance between the two groups (Early: 2.7 ± 0.5 versus 2.3 ± 0.4 and 2.2 ± 0.3, P = 0.024; Delayed: 2.4 ± 0.4 versus 1.8 ± 0.3 and 1.8 ± 0.3, P = 0.001). The washout rate was greater for TIMI 0-2 than the controls.The severity of myocardial fatty acid dysmetabolism did not differ between TIMI 3 and TIMI 0-2 coronary spasms. Additional ACH might not be required considering safety and the severity of coronary spams with TIMI 3 grade flow.

Calpain system and its involvement in myocardial ischemia and reperfusion injury

Calpains are ubiquitous non-lysosomal Ca²⁺-dependent cysteine proteases also present in myocardial cytosol and mitochondria. Numerous experimental studies reveal an essential role of the calpain system in myocardial injury during ischemia, reperfusion and postischemic structural remodelling. The increasing Ca²⁺-content and Ca²⁺-overload in myocardial cytosol and mitochondria during ischemia and reperfusion causes an activation of calpains. Upon activation they are able to injure the contractile apparatus and impair the energy production by cleaving structural and functional proteins of myocytes and mitochondria. Besides their causal involvement in acute myocardial dysfunction they are also involved in structural remodelling after myocardial infarction by the generation and release of proapoptotic factors from mitochondria. Calpain inhibition can prevent or attenuate myocardial injury during ischemia, reperfusion, and in later stages of myocardial infarction.

Reproducible ion-current-based approach for 24-plex comparison of the tissue proteomes of hibernating versus normal myocardium in swine models

Hibernating myocardium is an adaptive response to repetitive myocardial ischemia that is clinically common, but the mechanism of adaptation is poorly understood. Here we compared the proteomes of hibernating versus normal myocardium in a porcine model with 24 biological replicates. Using the ion-current-based proteomic strategy optimized in this study to expand upon previous proteomic work, we identified differentially expressed proteins in new molecular pathways of cardiovascular interest. The methodological strategy includes efficient extraction with detergent cocktail; precipitation/digestion procedure with high, quantitative peptide recovery; reproducible nano-LC/MS analysis on a long, heated column packed with small particles; and quantification based on ion-current peak areas. Under the optimized conditions, high efficiency and reproducibility were achieved for each step, which enabled a reliable comparison of 24 the myocardial samples. To achieve confident discovery of differentially regulated proteins in hibernating myocardium, we used highly stringent criteria to define “quantifiable proteins”. These included the filtering criteria of low peptide FDR and S/N > 10 for peptide ion currents, and each protein was quantified independently from ≥2 distinct peptides. For a broad methodological validation, the quantitative results were compared with a parallel, well-validated 2D-DIGE analysis of the same model. Excellent agreement between the two orthogonal methods was observed (R = 0.74), and the ion-current-based method quantified almost one order of magnitude more proteins. In hibernating myocardium, 225 significantly altered proteins were discovered with a low false-discovery rate (∼3%). These proteins are involved in biological processes including metabolism, apoptosis, stress response, contraction, cytoskeleton, transcription, and translation. This provides compelling evidence that hibernating myocardium adapts to chronic ischemia. The major metabolic mechanisms include a down-regulation of mitochondrial respiration and an increase in glycolysis. Meanwhile, cardioprotective and cytoskeletal proteins are increased, while cardiomyocyte contractile proteins are reduced. These intrinsic adaptations to regional ischemia maintain long-term cardiomyocyte viability at the expense of contractile function.

Myocardial viability and microvascular obstruction: role of cardiac magnetic resonance imaging

Established coronary artery disease has a prevalence of 7% in adult Americans, accounting for 16 million people. As morbidity and mortality rates have risen, research efforts to identify the pathophysiologic mechanisms of systolic dysfunction have risen in parallel. The current goal is to develop new therapeutic strategies with the potential to reverse systolic dysfunction in patients with established coronary artery disease. Cardiac magnetic resonance imaging has gained a key role in cardio vascular medicine. We will comment on the potential pivotal role of cardiac magnetic resonance imaging for the assessment of myocardial viability, including hibernating and stunned myocardium and microvascular obstruction.

Hibernating myocardium in heart failure

Ischemic left ventricular systolic dysfunction may result from myocardial necrosis or from hypocontractile areas of viable myocardium. In some cases, recovery of contractility may occur on revascularization--this reversibly dysfunctional tissue is commonly referred to as hibernating myocardium. Observational data suggest that revascularization of patients with ischemic left ventricular systolic dysfunction and known viable myocardium provides a survival benefit over medical therapy. Identification of viable, dysfunctional myocardium may be especially worthwhile in deciding which patients with ischemic left ventricular systolic dysfunction will benefit from revascularization procedures. Randomized, prospective trials evaluating this are currently ongoing. This review will provide an overview of the complex pathophysiology of viable, dysfunctional myocardium, and will discuss outcomes after revascularization. Of the techniques used to determine the presence of hibernating myocardium, functional methods such as stress echocardiography and cardiac magnetic resonance appear more specific, but less sensitive, than the nuclear modalities, which assess perfusion and metabolic activity. Currently, the availability of all methods is variable.

Chronic hibernating myocardium in sheep can occur without degenerating events and is reversed after revascularization

INTRODUCTION

Our goal was to show that blunting of myocardial flow reserve is mainly involved in adaptive chronic myocardial hibernation without apparent cardiomyocyte degeneration.

METHODS AND RESULTS

Sheep chronically instrumented with critical multivessel stenosis and/or percutaneous transluminal coronary angioplasty (PTCA)-induced revascularization were allowed to run and feed in the open for 2 and 5 months, respectively. Regional myocardial blood flow (MBF) with colored microspheres, regional and global left ventricular function and dimensions (2D echocardiography), and myocardial structure were studied. In sheep with a critical stenosis, a progressive increase in left ventricular end-diastolic and end-systolic cavity area and a decrease in fractional area change were found. Fraction of wall thickness decreased in all left ventricular wall segments. MBF was slightly but not significantly decreased at rest at 2 months. Morphological quantification revealed a rather small but significant increase in diffusely distributed connective tissue, cardiomyocyte hypertrophy, and presence of viable myocardium of which almost 30 % of the myocytes showed depletion of sarcomeres and accumulation of glycogen. The extent of myolysis in the transmural layer correlated with the degree of left ventricular dilation. Structural degeneration of cardiomyocytes was not observed. Balloon dilatation (PTCA) of one of the coronary artery stenoses at 10 weeks revealed recovery of fraction of wall thickness and near normalization of global subcellular structure at 20 weeks.

CONCLUSION

These data indicate that chronic reduction of coronary reserve by itself can induce ischemic cardiomyopathy characterized by left ventricular dilatation, depressed regional and global function, adaptive chronic myocardial hibernation, reactive fibrosis and cardiomyocyte hypertrophy in the absence of obvious degenerative phenomena.

SUMMARY

Reduction of myocardial flow reserve due to chronic coronary artery stenosis in sheep induces adaptive myocardial hibernation without involvement of degenerative phenomena.

The physiological significance of a coronary stenosis differentially affects contractility and mitochondrial function in viable chronically dysfunctional myocardium

The reversibility of viable dysfunctional myocardium after revascularization is variable and the reasons for this are unknown. Using 2D-DIGE, we tested the hypothesis that this could reflect the extent of molecular remodeling of myocardial tissue in the absence of infarction. Swine with a progressive left anterior descending (LAD) stenosis were studied 2 months (n = 18) or 3 months (n = 22) post-instrumentation. Coronary flow reserve (vasodilated/rest) was severely reduced at 2 months (LAD 2.6 ± 0.4 versus 5.1 ± 0.4 in normal, p < 0.05) and became critically impaired after 3 months (LAD 1.1 ± 0.2, p < 0.05 vs. 2 months). Despite progression in stenosis severity, reductions in wall thickening at 2 months (LAD 37 ± 4% vs. remote 86 ± 9%, p < 0.05) were unchanged at 3 months (LAD 32 ± 3%, p = ns). Contractile dysfunction was primarily related to reductions (LAD/normal) in contractile proteins which were not affected by stenosis severity (e.g., troponin T, 2 months 0.82 ± 0.03 vs. 0.74 ± 0.03 at 3 months, p-ns). In contrast, mitochondrial function and proteins were normal at 2 months but declined with progression to a critical stenosis (state 3 respiration at 3 months 145 ± 13 vs. 216 ± 5 ng-atoms O2 mg(-1) min(-1) at 2 months, p < 0.05). In a similar fashion, increases in stress (e.g., αB-crystalline 2.13 ± 0.2 vs. 1.17 ± 0.13 at 2 months, p < 0.05) and cytoskeletal proteins (e.g., desmin 1.63 ± 0.12 vs. 1.24 ± 0.10 at 2 months, p < 0.05) only developed with more advanced remodeling from a critical stenosis. We conclude that similar degrees of chronic contractile dysfunction can have diverse intrinsic molecular adaptations to ischemia. This spectrum of adaptations may underlie variability in the time course and extent of reversibility in viable chronically dysfunctional myocardium after revascularization.

Integrative proteomic and microRNA analysis of primary human coronary artery endothelial cells exposed to low-dose gamma radiation

High doses of ionising radiation significantly increase the risk of cardiovascular disease (CVD), the vascular endothelium representing one of the main targets. Whether radiation doses lower than 500 mGy induce cardiovascular damage is controversial. The aim of this study was to investigate radiation-induced expression changes on protein and microRNA (miRNA) level in primary human coronary artery endothelial cells after a single 200 mGy radiation dose (Co-60). Using a multiplex gel-based proteomics technology (2D-DIGE), we identified 28 deregulated proteins showing more than ±1.5-fold expression change in comparison with non-exposed cells. A great majority of the proteins showed up-regulation. Bioinformatics analysis indicated "cellular assembly and organisation, cellular function and maintenance and molecular transport" as the most significant radiation-responsive network. Caspase-3, a central regulator of this network, was confirmed to be up-regulated using immunoblotting. We also analysed radiation-induced alterations in the level of six miRNAs known to play a role either in CVD or in radiation response. The expression of miR-21 and miR-146b showed significant radiation-induced deregulation. Using miRNA target prediction, three proteins found differentially expressed in this study were identified as putative candidates for miR-21 regulation. A negative correlation was observed between miR-21 levels and the predicted target proteins, desmoglein 1, phosphoglucomutase and target of Myb protein. This study shows for the first time that a low-dose exposure has a significant impact on miRNA expression that is directly related to protein expression alterations. The data presented here may facilitate the discovery of low-dose biomarkers of radiation-induced cardiovascular damage.

Metabolomic analysis of two different models of delayed preconditioning

Recently we described an ischemic preconditioning induced by repetitive coronary stenosis, which is induced by 6 episodes of non-lethal ischemia over 3 days, and which also resembles the hibernating myocardium phenotype. When compared with traditional second window of ischemic preconditioning using cDNA microarrays, many genes which differed in the repetitive coronary stenosis appeared targeted to metabolism. Accordingly, the goal of this study was to provide a more in depth analysis of changes in metabolism in the different models of delayed preconditioning, i.e., second window and repetitive coronary stenosis. This was accomplished using a metabolomic approach based on liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques. Myocardial samples from the ischemic section of porcine hearts subjected to both models of late preconditioning were compared against sham controls. Interestingly, although both models involve delayed preconditioning, their metabolic signatures were radically different; of the total number of metabolites that changed in both models (135 metabolites) only 7 changed in both models, and significantly more, p<0.01, were altered in the repetitive coronary stenosis (40%) than in the second window (8.1%). The most significant changes observed were in energy metabolism, e.g., phosphocreatine was increased 4 fold and creatine kinase activity increased by 27.2%, a pattern opposite from heart failure, suggesting that the repetitive coronary stenosis and potentially hibernating myocardium have enhanced stress resistance capabilities. The improved energy metabolism could also be a key mechanism contributing to the cardioprotection observed in the repetitive coronary stenosis and in hibernating myocardium. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Correlation between left ventricular global and regional longitudinal systolic strain and impaired microcirculation in patients with acute myocardial infarction

OBJECTIVES

We investigated the correlation between left ventricular global and regional longitudinal systolic strain (GLS and LRS) and coronary flow reserve (CFR) assessed by transthoracic echocardiography (TTE) in patients with a recent acute myocardial infarction (AMI). Furthermore, we investigated if LRS and GLS imaging is superior to conventional measures of left ventricle (LV) function.

METHODS

In a consecutive population of first time AMI patients, who underwent successful revascularization, we performed comprehensive TTE. GLS and LRS were obtained from the three standard apical views. Assessment of CFR by TTE was performed in a modified apical view using color Doppler guidance.

RESULTS

The study population consisted of 183 patients (51 females) with a median age of 63 [54;70] years. Eighty-nine (49%) patients had a non-ST elevation myocardial infarction and 94 (51%) patients had a ST elevation myocardial infarction. The GLS was -15.2 [-19.3;-10.1]% in the total population of 183 patients. Total wall motion score index (WMSI) in the population was 1.19 [1;1.5]. Eighty-five patients suffered from culprit lesion in left anterior descending artery (LAD). The CFR in these patients was 1.86 [1.36;2.35] and the GLS was -14.3 [-18.9; -9.8]%. A significant difference was observed in the LRS in LAD territory in culprit LAD infarction patients with a CFR ≤ 2 (-9.6 [-13.77;-6.44]) compared with the LRS in LAD territory in culprit LAD infarction patients with a CFR > 2 (-19.33 [-21.1;-16.5]), P < 0.0001. We found no significant difference between WMSI in LAD territory in culprit LAD infarction patients with a CFR ≤ 2 (1.56 [1.06;2.23]) compared with WMSI in LAD territory in culprit LAD infarction patients with a CFR > 2 (1.37 [1.03;2.11]); P = 0.18. The same pattern was observed in both circumflex coronary artery (CX) and right coronary artery (RCA) territories. In the total population, we found a strong correlation between CFR and GLS (r = -0.85, P < 0.0001). This was also seen in the multivariate regression model adjusting for possible confounders including WMSI (P < 0.001).

CONCLUSION

In this study, we have shown a close association between myocardial deformation in patients with a recent AMI and the degree of diminished microcirculation. We found that both GLS and LRS correlated with CFR. We conclude that GLS and LRS are significantly better tools to assess impaired CFR and LV function after a recent AMI, than conventional echocardiographic measurements.

Myocardial perfusion and contraction in acute ischemia and chronic ischemic heart disease

A large body of evidence has demonstrated that there is a close coupling between regional myocardial perfusion and contractile function. When ischemia is mild, this can result in the development of a new balance between supply and energy utilization that allows the heart to adapt for a period of hours over which myocardial viability can be maintained, a phenomenon known as "short-term hibernation". Upon reperfusion after reversible ischemia, regional myocardial function remains depressed. The "stunned myocardium" recovers spontaneously over a period of hours to days. The situation in myocardium subjected to chronic repetitive ischemia is more complex. Chronic dysfunction can initially reflect repetitive stunning with insufficient time for the heart to recover between episodes of spontaneous ischemia. As the frequency and/or severity of ischemia increases, the heart undergoes a series of adaptations which downregulate metabolism to maintain myocyte viability at the expense of contractile function. The resulting "hibernating myocardium" develops regional myocyte cellular hypertrophy as a compensatory response to ischemia-induced apoptosis along with a series of molecular adaptations that while regional, are similar to global changes found in advanced heart failure. As a result, flow-function relations become independently affected by tissue remodeling and interventions that stimulate myocyte regeneration. Similarly, chronic vascular remodeling may alter flow regulation in a fashion that increases myocardial vulnerability to ischemia. Here we review our current understanding of myocardial flow-function relations during acute ischemia in normal myocardium and highlight newly identified complexities in their interpretation in viable chronically dysfunctional myocardium with myocyte cellular and molecular remodeling. This article is part of a Special Issue entitled "Coronary Blood Flow".

An isolated perfused pig heart model for the development, validation and translation of novel cardiovascular magnetic resonance techniques

BACKGROUND

Novel cardiovascular magnetic resonance (CMR) techniques and imaging biomarkers are often validated in small animal models or empirically in patients. Direct translation of small animal CMR protocols to humans is rarely possible, while validation in humans is often difficult, slow and occasionally not possible due to ethical considerations. The aim of this study is to overcome these limitations by introducing an MR-compatible, free beating, blood-perfused, isolated pig heart model for the development of novel CMR methodology.

METHODS

6 hearts were perfused outside of the MR environment to establish preparation stability. Coronary perfusion pressure (CPP), coronary blood flow (CBF), left ventricular pressure (LVP), arterial blood gas and electrolyte composition were monitored over 4 hours. Further hearts were perfused within 3T (n = 3) and 1.5T (n = 3) clinical MR scanners, and characterised using functional (CINE), perfusion and late gadolinium enhancement (LGE) imaging. Perfusion imaging was performed globally and selectively for the right (RCA) and left coronary artery (LCA). In one heart the RCA perfusion territory was determined and compared to infarct size after coronary occlusion.

RESULTS

All physiological parameters measured remained stable and within normal ranges. The model proved amenable to CMR at both field strengths using typical clinical acquisitions. There was good agreement between the RCA perfusion territory measured by selective first pass perfusion and LGE after coronary occlusion (37% versus 36% of the LV respectively).

CONCLUSIONS

This flexible model allows imaging of cardiac function in a controllable, beating, human-sized heart using clinical MR systems. It should aid further development, validation and clinical translation of novel CMR methodologies, and imaging sequences.

Molecular mechanisms mediating preconditioning following chronic ischemia differ from those in classical second window

A major difference between experimental ischemic preconditioning (IPC), induced by brief ischemic episodes, and the clinical situation is that patients generally have repetitive episodes of ischemia. We used a swine model to examine differences in genes regulated by classical second-window IPC (SWOP) [two 10-min episodes of coronary artery occlusion (CAO) followed by 24 h reperfusion] compared with repetitive CAO/reperfusion (RCO), i.e., two 10-min CAO 12 h apart, and to repetitive coronary stenosis (RCS), six episodes of 90 min coronary stenosis 12 h apart (n = 5/group). All three models reduced infarct size by 60-85%, which was mediated by nitric oxide in SWOP but not in the other two models. We employed microarray analyses to discover additional molecular pathways intrinsic to models of repetitive ischemia and different from classical SWOP. There was an 85% homology in gene response between the RCO and RCS models, whereas SWOP was qualitatively different. Both RCO and RCS, but not SWOP, showed downregulation of genes encoding proteins involved in oxidative metabolism and upregulation of genes involved in protein synthesis, unfolded protein response, autophagy, heat shock response, protein secretion, and an activation of the NF-kappaB signaling pathway. Therefore, the regulated genes mediating IPC with repetitive ischemia differ radically from SWOP both quantitatively and qualitatively, showing that a repetitive pattern of ischemia, rather than the difference between no-flow vs. low-flow ischemia, dictates the genomic response of the heart. These findings illustrate new cardioprotective mechanisms developed by repetitive IPC, which are potentially more relevant to patients with chronic ischemic heart disease, who are subjected to repetitive episodes of ischemia.

A servo-controlled canine model of stable severe ischemic left ventricular failure

Reversible left ventricular failure was produced in conscious dogs by compromise of the coronary circulation. In animals with prior left anterior descending coronary artery occlusion, mean left atrial pressure (LAP) was incorporated into an automatic feedback control system used to inflate a balloon cuff on the circumflex (Cfx) coronary artery. The system could produce stable increases in LAP to 15-20 mm Hg. The dominating system transfer function was the ratio of LAP to balloon volume (BV), which was characterized by a fixed delay (5 s), with LAP/BV = (8e(-jomegatau ))/(0.02 + jomega). The system was stabilized by a phase lead network to reduce oscillations of LAP. A total of seven experiments were conducted in three dogs, and testing of inotropic agents was possible in three experiments under stable conditions with the pump off after an hour or more of operation. Problems encountered were 0.003-0.008 Hz oscillations in LAP in three experiments, which could usually be controlled by reducing the system gain. Late stage ventricular fibrillation occurred in all three animals, but defibrillation was easily accomplished after deflating the Cfx balloon. This system produces reversible left ventricular failure solely due to ischemia, thus closely simulating clinical heart failure due to coronary insufficiency.

Role of glycogen synthase kinase-3beta in cardioprotection

Limitation of infarct size by ischemic/pharmacological pre- and postconditioning involves activation of a complex set of cell-signaling pathways. Multiple lines of evidence implicate the mitochondrial permeability transition pore (mPTP) as a key end effector of ischemic/pharmacological pre- and postconditioning. Increasing the ROS threshold for mPTP induction enhances the resistance of cardiomyocytes to oxidant stress and results in infarct size reduction. Here, we survey and synthesize the present knowledge about the role of glycogen synthase kinase (GSK)-3beta in cardioprotection, including pre- and postconditioning. Activation of a wide spectrum of cardioprotective signaling pathways is associated with phosphorylation and inhibition of a discrete pool of GSK-3beta relevant to mitochondrial signaling. Therefore, GSK-3beta has emerged as the integration point of many of these pathways and plays a central role in transferring protective signals downstream to target(s) that act at or in proximity to the mPTP. Bcl-2 family proteins and mPTP-regulatory elements, such as adenine nucleotide translocator and cyclophilin D (possibly voltage-dependent anion channel), may be the functional downstream target(s) of GSK-3beta. Gaining a better understanding of these interactions to control and prevent mPTP induction when appropriate will enable us to decrease the negative impact of the reperfusion-induced ROS burst on the fate of mitochondria and perhaps allow us to limit propagation of damage throughout and between cells and consequently, to better limit infarct size.

Inhibition of oxygen sensors as a therapeutic strategy for ischaemic and inflammatory disease

Cells in the human body need oxygen to function and survive, and severe deprivation of oxygen, as occurs in ischaemic heart disease and stroke, is a major cause of mortality. Nevertheless, other organisms, such as the fossorial mole rat or diving seals, have acquired the ability to survive in conditions of limited oxygen supply. Hypoxia tolerance also allows the heart to survive chronic oxygen shortage, and ischaemic preconditioning protects tissues against lethal hypoxia. The recent discovery of a new family of oxygen sensors--including prolyl hydroxylase domain-containing proteins 1-3 (PHD1-3)--has yielded exciting novel insights into how cells sense oxygen and keep oxygen supply and consumption in balance. Advances in understanding of the role of these oxygen sensors in hypoxia tolerance, ischaemic preconditioning and inflammation are creating new opportunities for pharmacological interventions for ischaemic and inflammatory diseases.

Repetitive ischemia by coronary stenosis induces a novel window of ischemic preconditioning

BACKGROUND

The hypothesis of the present study was that molecular mechanisms differ markedly when mediating ischemic preconditioning induced by repetitive episodes of ischemia versus classic first- or second-window preconditioning.

METHODS AND RESULTS

To test this, chronically instrumented conscious pigs were subjected to either repetitive coronary stenosis (RCS) or a traditional protocol of second-window ischemic preconditioning (SWIPC). Lethal ischemia, induced by 60 minutes of coronary artery occlusion followed by reperfusion, resulted in an infarct size/area at risk of 6+/-3% after RCS and 16+/-3% after SWIPC (both groups P<0.05, less than shams 42+/-4%). Two molecular signatures of SWIPC, the increased expression of the inducible isoform of nitric oxide synthase and the translocation of protein kinase Cepsilon to the plasma membrane, were observed with SWIPC but not with RCS. Confirming this, pretreatment with a nitric oxide synthase inhibitor prevented the protection conferred by SWIPC but not by RCS. Microarray analysis revealed a qualitatively different genomic profile of cardioprotection between ischemic preconditioning induced by RCS and that induced by SWIPC. The number of genes significantly regulated was greater in RCS (5739) than in SWIPC (2394) animals. Of the 5739 genes regulated in RCS, only 31% were also regulated in SWIPC. Broad categories of genes induced by RCS but not SWIPC included those involved in autophagy, endoplasmic reticulum stress, and mitochondrial oxidative metabolism. The upregulation of these pathways was confirmed by Western blotting.

CONCLUSIONS

RCS induces cardioprotection against lethal myocardial ischemia that is at least as powerful as traditional ischemic preconditioning but is mediated through radically different mechanisms.

Metabolic reserve of the heart: the forgotten link between contraction and coronary flow

Myocardial energy substrate metabolism entails a complex system of enzyme catalyzed reactions, in which the heart efficiently converts chemical to mechanical energy. The system is highly regulated and responsive to changes in workload as well as in substrate and hormone supply to the heart. Akin to the terms "contractile reserve" and "coronary flow reserve" we propose the term "metabolic reserve" to reflect the heart's capacity to respond to increases in workload. The heart's metabolic response to inotropic stimulation involves the ability to increase oxidative metabolism over a wide range, by activating the oxidation of glycogen and carbohydrate substrates. Here we review the known biochemical mechanisms responsible for those changes. Specifically, we explore the notion that disturbances in the metabolic reserve result in contractile dysfunction of the stressed heart.

A review of methods for assessment of coronary microvascular disease in both clinical and experimental settings

Obstructive disease of the large coronary arteries is the prominent cause for angina pectoris. However, angina may also occur in the absence of significant coronary atherosclerosis or coronary artery spasm, especially in women. Myocardial ischaemia in these patients is often associated with abnormalities of the coronary microcirculation and may thus represent a manifestation of coronary microvascular disease (CMD). Elucidation of the role of the microvasculature in the genesis of myocardial ischaemia and cardiac damage-in the presence or absence of obstructive coronary atherosclerosis-will certainly result in more rational diagnostic and therapeutic interventions for patients with ischaemic heart disease. Specifically targeted research based on improved assessment modalities is needed to improve the diagnosis of CMD and to translate current molecular, cellular, and physiological knowledge into new therapeutic options.

Persistent Regional Downregulation in Mitochondrial Enzymes and Upregulation of Stress Proteins in Swine With Chronic Hibernating Myocardium

Hibernating myocardium is accompanied by a downregulation in energy utilization that prevents the immediate development of ischemia during stress at the expense of an attenuated level of regional contractile function. We used a discovery based proteomic approach to identify novel regional molecular adaptations responsible for this phenomenon in subendocardial samples from swine instrumented with a chronic LAD stenosis. After 3 months (n=8), hibernating myocardium was present as reflected by reduced resting LAD flow (0.75±0.14 versus 1.19±0.14 mL · min −1 · g −1 in remote) and wall thickening (1.93±0.46 mm versus 5.46±0.41 mm in remote, P <0.05). Regionally altered proteins were quantified with 2D Differential-in-Gel Electrophoresis (2D-DIGE) using normal myocardium as a reference with identification of candidates using MALDI-TOF mass spectrometry. Hibernating myocardium developed a significant downregulation of many mitochondrial proteins and an upregulation of stress proteins. Of particular note, the major entry points to oxidative metabolism (eg, pyruvate dehydrogenase complex and Acyl-CoA dehydrogenase) and enzymes involved in electron transport (eg, complexes I, III, and V) were reduced ( P <0.05). Multiple subunits within an enzyme complex frequently showed a concordant downregulation in abundance leading to an amplification of their cumulative effects on activity (eg, “total” LAD PDC activity was 21.9±3.1 versus 42.8±1.9 mU, P <0.05). After 5-months (n=10), changes in mitochondrial and stress proteins persisted whereas cytoskeletal proteins (eg, desmin and vimentin) normalized. These data indicate that the proteomic phenotype of hibernating myocardium is dynamic and has similarities to global changes in energy substrate metabolism and function in the advanced failing heart. These proteomic changes may limit oxidative injury and apoptosis and impact functional recovery after revascularization.

Cardioprotection in stunned and hibernating myocardium

Although myocardial ischemia was once thought to result in irreversible cellular damage, it is now demonstrated that in cardiac tissue, submitted to the stress of oxygen and substrate deprivation, endogenous mechanisms of cell survival may be activated. These molecular mechanisms result in physiological conditions of adaptation to ischemia, known as myocardial stunning and hibernation. These conditions result from a switch in gene and protein expression, which sustains cardiac cell survival in a context of oxygen deprivation and during the stress of reperfusion. The pattern of cell survival elicited by ischemia in myocardial stunning or hibernation results in the activation of cytoprotective mechanisms that will protect the heart against further ischemic damage, a condition referred to as ischemic preconditioning. The basic mechanisms underlying stunning and hibernation are still a matter of intense research, which includes the discovery and characterization of novel survival genes not described in the heart before, or the unraveling of new cellular processes, such as autophagy. Understanding how the molecular adaptation of the cardiac myocyte during stress sustains its survival in these conditions therefore might help defining novel mechanisms of endogenous myocardial salvage, in order to expand the conditions of maintained cellular viability and functional salvage of the ischemic myocardium.

Metabolic imaging using SPECT

INTRODUCTION

In normal condition, the heart obtains more than two-thirds of its energy from the oxidative metabolism of long chain fatty acids, although a wide variety of substrates such as glucose, lactate, ketone bodies and amino acids are also utilised. In ischaemic myocardium, on the other hand, oxidative metabolism of free fatty acid is suppressed and anaerobic glucose metabolism plays a major role in residual oxidative metabolism. Therefore, metabolic imaging can be an important technique for the assessment of various cardiac diseases and conditions.

MATERIALS AND METHODS

In SPECT, several iodinated fatty acid traces have been introduced and studied. Of these, (123)I-labelled 15-(p-iodophenyl)3-R, S-methylpentadecanoic acid (BMIPP) has been the most commonly used tracer in clinical studies, especially in some of the European countries and Japan.

RESULTS AND DISCUSSION

In this review article, several fatty acid tracers for SPECT are characterised, and the mechanism of uptake and clinical utility of BMIPP are discussed in detail.

Pathophysiology of cardiogenic shock complicating acute myocardial infarction

Cardiogenic shock is a rapidly progressive, often fatal complication of acute myocardial infarction. A vicious circle of ischemia, decreased cardiac output and reinfarction progress to left ventricular failure and death. The fundamental pathophysiology of this cascade and other mechanisms beyond the classic paradigm of ischemia and dysfunction are discussed in detail.

Return to the fetal gene program protects the stressed heart: a strong hypothesis

A common feature of the hemodynamically or metabolically stressed heart is the return to a pattern of fetal metabolism. A hallmark of fetal metabolism is the predominance of carbohydrates as substrates for energy provision in a relatively hypoxic environment. When the normal heart is exposed to an oxygen rich environment after birth, energy substrate metabolism is rapidly switched to oxidation of fatty acids. This switch goes along with the expression of "adult" isoforms of metabolic enzymes and other proteins. However, the heart retains the ability to return to the "fetal" gene program. Specifically, the fetal gene program is predominant in a variety of pathophysiologic conditions including hypoxia, ischemia, hypertrophy, and atrophy. A common feature of all of these conditions is extensive remodeling, a decrease in the rate of aerobic metabolism in the cardiomyocyte, and an increase in cardiac efficiency. The adaptation is associated with a whole program of cell survival under stress. The adaptive mechanisms are prominently developed in hibernating myocardium, but they are also a feature of the failing heart muscle. We propose that in failing heart muscle at a certain point the fetal gene program is no longer sufficient to support cardiac structure and function. The exact mechanisms underlying the transition from adaptation to cardiomyocyte dysfunction are still not completely understood.

Cardioprotection by adenosine A2A agonists in a canine model of myocardial stunning produced by multiple episodes of transient ischemia

We sought to determine whether administration of a very low, nonvasodilating dose of a highly selective adenosine A(2A) receptor agonist (ATL-193 or ATL-146e) would be cardioprotective in a canine model of myocardial stunning produced by multiple episodes of transient ischemia. Twenty-four anesthetized open-chest dogs underwent either 4 (n=12) or 10 cycles (n=12) of 5-min left anterior descending coronary artery (LAD) occlusions interspersed by 5 or 10 min of reperfusion. Left ventricular thickening was measured from baseline through 180 min after the last occlusion-reperfusion cycle. Regional flow was measured with microspheres. In 12 of 24 dogs, A(2A) receptor agonist was infused intravenously beginning 2 min prior to the first occlusion and continuing throughout reperfusion at a dose below that which produces vasodilatation (0.01 microg x kg(-1) x min(-1)). Myocardial flow was similar between control and A(2A) receptor agonist-treated animals, confirming the absence of A(2) receptor agonist-induced vasodilatation. During occlusion, there was severe dyskinesis with marked LAD zone thinning in all animals. After 180 min of reperfusion following the last cycle, significantly greater recovery of LAD zone thickening was observed in A(2A) receptor agonist-treated vs. control animals in both the 4-cycle (91 +/- 7 vs. 56 +/- 12%, respectively; P<0.05) and the 10-cycle (65 +/- 9 vs. 8 +/- 16%, respectively; P<0.05) occlusion groups. The striking amount of functional recovery observed with administration of low, nonvasodilating doses of adenosine A(2A) agonist ATL-193 or ATL-146e supports their further evaluation for the attenuation of postischemic stunning in the clinical setting.

Reduced force generating capacity in myocytes from chronically ischemic, hibernating myocardium

The contractile dysfunction of the hibernating myocardium in situ results from local environmental factors, but also from intrinsic cellular remodelling that may determine reversibility. Previous studies have suggested defects in myofilament Ca2+ responsiveness. We prepared single myocytes from control (CTRL, n(pigs)=7) and from hibernating myocardium (HIB, n(pigs)=8), removed the membranes and measured isometric force development during direct activation of the myofilaments. One- and 2-dimensional polyacrylamide gel electrophoresis and specific phosphoprotein immunoblotting were performed on tissue homogenates from matched samples. Cellular ultrastructure was evaluated using electron microscopy. Normalized for cross-sectional area, passive force was not different but maximal isometric force was significantly reduced in myocytes from HIB (11.6+/-1.5 kN/m2 versus 18.7+/-1.6 kN/m2 in CTRL, P<0.05). Ca2+ sensitivity and steepness of the normalized force-pCa relationship were not different, and neither was the rate of force redevelopment (K(tr)). No alterations were observed in isoform expression, phosphorylation or degradation of specific myofibrillar proteins. However, in HIB samples the total protein volume density was decreased by 23% (P<0.05). Histology showed glycogen accumulation and electron microscopy confirmed a reduction in myofilament density from 69.9+/-1.9% in CTRL to 57.1+/-0.9% of cell volume in HIB (P<0.05). In conclusion, decreased potential for force development in the hibernating myocardium is related to a reduction of myofibrillar protein per cell volume unit with replacement by glycogen and mitochondria. These changes may contribute to slow functional recovery on revascularization.

Reduction in postsystolic wall thickening during late preconditioning

Brief coronary artery occlusion (CAO) and reperfusion induce myocardial stunning and late preconditioning. Postsystolic wall thickening (PSWT) also develops with CAO and reperfusion. However, the time course of PSWT during stunning and the regional function pattern of the preconditioned myocardium remain unknown. The goal of this study was to investigate the evolution of PSWT during myocardial stunning and its modifications during late preconditioning. Dogs were chronically instrumented to measure (sonomicrometry) systolic wall thickening (SWT), PSWT, total wall thickening (TWT = SWT + PSWT), and maximal rate of thickening (dWT/d tmax). Two 10-min CAO (circumflex artery) were performed 24 h apart ( day 0 and day 1, n = 7). At day 0, CAO decreased SWT and increased PSWT. During the first hours of the subsequent stunning, evolution of PSWT was symmetrical to that of SWT. At day 1, baseline SWT was similar to day 0, but PSWT was reduced (−66%), while dWT/d tmax and SWT/TWT ratio increased (+48 and +14%, respectively). After CAO at day 1, stunning was reduced, indicating late preconditioning. Simultaneously vs. day 0, PSWT was significantly reduced, and dWT/d tmax as well as SWT/TWT ratio were increased, i.e., a greater part of TWT was devoted to ejection. Similar decrease in PSWT was observed with a nonischemic preconditioning stimulus (rapid ventricular pacing, n = 4). In conclusion, a major contractile adaptation occurs during late preconditioning, i.e., the rate of wall thickening is enhanced and PWST is almost abolished. These phenotype adaptations represent potential approaches for characterizing stunning and late preconditioning with repetitive ischemia in humans.