Molecular imaging of myocardial infarction

Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery

Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

Crosstalk Between Cardiac Cells and Macrophages Postmyocardial Infarction: Insights from In Vitro Studies

Cardiovascular disease, including myocardial infarction (MI), is the leading cause of death in the western world. Following MI, a large number of cardiomyocytes are lost and inflammatory cells such as monocytes and macrophages migrate into the damaged region to remove dead cells and tissue. These inflammatory cells secrete growth factors to induce degradation of the extracellular matrix in the myocardium and recruit cardiac fibroblasts. However, the contribution of specific macrophage subsets on cardiac cell function and survival in the steady state as well as in the diseased state is not well known. There is an increasing demand for in vitro cardiac disease models to bridge the critical missing link in the existing experimental methods. In this review, studies using in vitro models to examine the interaction between macrophages and cardiac cells, including cardiomyocytes, endothelial cells, and fibroblasts, are summarized to better understand the complex inflammatory cascade post-MI. The current challenges and the future directions of in vitro cardiac models are also discussed. Detailed and more mechanistic insights into macrophages and cardiac cell interactions during the multiphase repair process could potentially revolutionize the development of treatments and diagnostic alternatives. Impact statement The inflammatory cascade postmyocardial infarction (MI) is very complex. In vitro cardiac disease model studies bridge the critical missing link in the existing experimental methods and provide insights, including multicellular interaction post-MI. Detailed and more mechanistic insights into macrophages and cardiac cell interactions during the multiphase repair process could potentially revolutionize in developing treatments and diagnostic alternatives.

Molecular imaging of myocardial necrosis: an updated mini-review

Acute myocardial infarction (AMI) remains the most severe and common cardiac emergency among various ischaemic heart diseases. Both unregulated (necrosis) and regulated (apoptosis, autophagy and necroptosis et al.) forms of cell death can occur during AMI. Non-invasive imaging of cardiomyocyte death represents an attractive approach to acquire insights into the pathophysiology of AMI, track the temporal and spatial evolution of MI, guide therapeutic decision-making, evaluate response to therapeutic intervention and predict prognosis. Although several forms of cell death have been identified during AMI, to date, only apoptosis- and necrosis-detecting probes compatible with currently available tomographic imaging modalities have been successfully developed for non-invasive visualisation of cardiomyocyte death. Myocardial apoptosis imaging has gained more attention because of its potential controllability while less attention has been paid to myocardial necrosis imaging. In our opinion, although cardiomyocyte necrosis is unsalvageable, imaging necrosis can play an important role in early diagnosis, risk stratification, prognostic prediction and guidance in therapeutic decision-making of AMI. In this mini-review, we summarise the updated advances achieved by us and others and discuss the challenges in the development of molecular imaging probes for visualisation of myocardial necrosis.

Feasibility study of a point-of-care positron emission tomography system with interactive imaging capability

PURPOSE

We investigated the feasibility of a novel positron emission tomography (PET) system that provides near real-time feedback to an operator who can interactively scan a patient to optimize image quality. The system should be compact and mobile to support point-of-care (POC) molecular imaging applications. In this study, we present the key technologies required and discuss the potential benefits of such new capability.

METHODS

The core of this novel PET technology includes trackable PET detectors and a fully three-dimensional, fast image reconstruction engine implemented on multiple graphics processing units (GPUs) to support dynamically changing geometry by calculating the system matrix on-the-fly using a tube-of-response approach. With near real-time image reconstruction capability, a POC-PET system may comprise a maneuverable front PET detector and a second detector panel which can be stationary or moved synchronously with the front detector such that both panels face the region-of-interest (ROI) with the detector trajectory contoured around a patient's body. We built a proof-of-concept prototype using two planar detectors each consisting of a photomultiplier tube (PMT) optically coupled to an array of 48 × 48 lutetium-yttrium oxyorthosilicate (LYSO) crystals (1.0 × 1.0 × 10.0 mm³ each). Only 38 × 38 crystals in each arrays can be clearly re-solved and used for coincidence detection. One detector was mounted to a robotic arm which can position it at arbitrary locations, and the other detector was mounted on a rotational stage. A cylindrical phantom (102 mm in diameter, 150 mm long) with nine spherical lesions (8:1 tumor-to-background activity concentration ratio) was imaged from 27 sampling angles. List-mode events were reconstructed to form images without or with time-of-flight (TOF) information. We conducted two Monte Carlo simulations using two POC-PET systems. The first one uses the same phantom and detector setup as our experiment, with the detector coincidence re-solving time (CRT) ranging from 100 to 700 ps full-width-at-half-maximum (FWHM). The second study simulates a body-size phantom (316 × 228 × 160 mm³ ) imaged by a larger POC-PET system that has 4 × 6 modules (32 × 32 LYSO crystals/module, four in axial and six in transaxial directions) in the front panel and 3 × 8 modules (16 × 16 LYSO crystals/module, three in axial and eight in transaxial directions) in the back panel. We also evaluated an interactive scanning strategy by progressively increasing the number of data sets used for image reconstruction. The updated images were analyzed based on the number of data sets and the detector CRT.

RESULTS

The proof-of-concept prototype re-solves most of the spherical lesions despite a limited number of coincidence events and incomplete sampling. TOF information reduces artifacts in the reconstructed images. Systems with better timing resolution exhibit improved image quality and reduced artifacts. We observed a reconstruction speed of 0.96 × 10⁶ events/s/iteration for 600 × 600 × 224 voxel rectilinear space using four GPUs. A POC-PET system with significantly higher sensitivity can interactively image a body-size object from four angles in less than 7 min.

CONCLUSIONS

We have developed GPU-based fast image reconstruction capability to support a PET system with arbitrary and dynamically changing geometry. Using TOF PET detectors, we demonstrated the feasibility of a PET system that can provide timely visual feedback to an operator who can scan a patient interactively to support POC imaging applications.

Assessment of the fate of myocardial necrosis by serial myocardial perfusion imaging

BACKGROUND

Myocardial necrosis after myocardial infarction (MI) is common; extent and severity are however variable. The pattern is recognized by myocardial perfusion imaging (MPI) as fixed perfusion defects (FPD). The fate of such FPD is not well appraised. This study addressed this important issue in a large number of patients undergoing serial MPI in relation to type of intervening therapy.

METHODS

Patients with prior MI or MPI-evidence of myocardial necrosis undergoing serial MPI without intervening acute coronary syndromes were included. The fate of necrosis by MPI on per-patient and per-region analysis was analyzed, factoring also the impact of intervening coronary revascularization (CR).

RESULTS

A total of 3691 patients with 25,837 regions were identified, including 1413 (38.3%) subjects with 3358 (13.0%) regions exhibiting necrosis. Serial MPI after 29±21 months confirmed the persistent presence of myocardial necrosis FPD in the vast majority of patients and regions (86%); the consistency was even higher in the presence of moderate or severe necrosis (99%). Neither type nor site of CR significantly impacted on the presence and extent of myocardial necrosis at multivariable analysis.

CONCLUSIONS

The finding of myocardial necrosis by MPI remains highly consistent over time, and is not significantly altered by CR.

Molecular imaging of cardiac remodelling after myocardial infarction

Myocardial infarction and subsequent heart failure is a major health burden associated with significant mortality and morbidity in western societies. The ability of cardiac tissue to recover after myocardial infarction is affected by numerous complex cellular and molecular pathways. Unbalance or failure of these pathways can lead to adverse remodelling of the heart and poor prognosis. Current clinical cardiac imaging modalities assess anatomy, perfusion, function, and viability of the myocardium, yet do not offer any insight into the specific molecular pathways involved in the repair process. Novel imaging techniques allow visualisation of these molecular processes and may have significant diagnostic and prognostic values, which could aid clinical management. Single photon-emission tomography, positron-emission tomography, and magnetic resonance imaging are used to visualise various aspects of these molecular processes. Imaging probes are usually attached to radioisotopes or paramagnetic nanoparticles to specifically target biological processes such as: apoptosis, necrosis, inflammation, angiogenesis, and scar formation. Although the results from preclinical studies are promising, translating this work to a clinical environment in a valuable and cost-effective way is extremely challenging. Extensive evaluation evidence of diagnostic and prognostic values in multi-centre clinical trials is still required.

Cardiovascular magnetic resonance imaging to assess myocardial fibrosis in valvular heart disease

The left ventricular (LV) remodeling process associated with significant valvular heart disease (VHD) is characterized by an increase of myocardial interstitial space with deposition of collagen and loss of myofibers. These changes occur before LV systolic function deteriorates or the patient develops symptoms. Cardiovascular magnetic resonance (CMR) permits assessment of reactive fibrosis, with the use of T1 mapping techniques, and replacement fibrosis, with the use of late gadolinium contrast enhancement. In addition, functional consequences of these structural changes can be evaluated with myocardial tagging and feature tracking CMR, which assess the active deformation (strain) of the LV myocardium. Several studies have demonstrated that CMR techniques may be more sensitive than the conventional measures (LV ejection fraction or LV dimensions) to detect these structural and functional changes in patients with severe left-sided VHD and have shown that myocardial fibrosis may not be reversible after valve surgery. More important, the presence of myocardial fibrosis has been associated with lesser improvement in clinical symptoms and recovery of LV systolic function. Whether assessment of myocardial fibrosis may better select the patients with severe left-sided VHD who may benefit from surgery in terms of LV function and clinical symptoms improvement needs to be demonstrated in prospective studies. The present review article summarizes the current status of CMR techniques to assess myocardial fibrosis and appraises the current evidence on the use of these techniques for risk stratification of patients with severe aortic stenosis or regurgitation and mitral regurgitation.

Intermittent pacing therapy favorably modulates infarct remodeling

Despite early revascularization, remodeling and dysfunction of the left ventricle (LV) after acute myocardial infarction (AMI) remain important therapeutic targets. Intermittent pacing therapy (IPT) of the LV can limit infarct size, when applied during early reperfusion. However, the effects of IPT on post-AMI LV remodeling and infarct healing are unknown. We therefore investigated the effects of IPT on global LV remodeling and infarct geometry in swine with a 3-day old AMI. For this purpose, fifteen pigs underwent 2 h ligation of the left circumflex coronary artery followed by reperfusion. An epicardial pacing lead was implanted in the peri-infarct zone. After three days, global LV remodeling and infarct geometry were assessed using magnetic resonance imaging (MRI). Animals were stratified into MI control and IPT groups. Thirty-five days post-AMI, follow-up MRI was obtained and myofibroblast content, markers of extracellular matrix (ECM) turnover and Wnt/frizzled signaling in infarct and non-infarct control tissue were studied. Results showed that IPT had no significant effect on global LV remodeling, function or infarct mass, but modulated infarct healing. In MI control pigs, infarct mass reduction was principally due to a 26.2 ± 4.4% reduction in infarct thickness (P ≤ 0.05), whereas in IPT pigs it was mainly due to a 35.7 ± 4.5% decrease in the number of infarct segments (P ≤ 0.05), with no significant change in infarct thickness. Myofibroblast content of the infarct zone was higher in IPT (10.9 ± 2.1%) compared to MI control (5.4 ± 1.6%; P ≤ 0.05). Higher myofibroblast presence did not coincide with alterations in expression of genes involved in ECM turnover or Wnt/frizzled signaling at 5 weeks follow-up. Taken together, IPT limited infarct expansion and altered infarct composition, showing that IPT influences remodeling of the infarct zone, likely by increasing regional myofibroblast content.

Molecular Imaging of Angiogenesis in Cardiac Regeneration

PURPOSE OF REVIEW

Myocardial infarction (MI) leading to heart failure displays an important cause of death worldwide. Adequate restoration of blood flow to prevent this transition is a crucial factor to improve long-term morbidity and mortality. Novel regenerative therapies have been thoroughly investigated within the past decades.

RECENT FINDINGS

Increased angiogenesis in infarcted myocardium has shown beneficial effects on the prognosis of MI; therefore, the proangiogenic capacity of currently tested treatments is of specific interest. Molecular imaging to visualize formation of new blood vessels in vivo displays a promising option to monitor proangiogenic effects of regenerative substances.

SUMMARY

Based on encouraging results in preclinical models, molecular angiogenesis imaging has recently been applied in a small set of patients. This article reviews recent literature on noninvasive in vivo molecular imaging of angiogenesis after MI as an integral part of cardiac regeneration.

N-terminal fragment of cardiac myosin binding protein-C triggers pro-inflammatory responses in vitro

Myocardial infarction (MI) leads to loss and degradation of contractile cardiac tissue followed by sterile inflammation of the myocardium through activation and recruitment of innate and adaptive cells of the immune system. Recently, it was shown that cardiac myosin binding protein-C (cMyBP-C), a protein of the cardiac sarcomere, is degraded following MI, releasing a predominant N-terminal 40-kDa fragment (C0C1f) into myocardial tissue and the systemic circulation. We hypothesized that early release of C0C1f contributes to the initiation of inflammation and plays a key role in recruitment and activation of immune cells. Therefore, we investigated the role of C0C1f on macrophage/monocyte activation using both mouse bone marrow-derived macrophages and human monocytes. Here we demonstrate that C0C1f leads to macrophage/monocyte activation in vitro. Furthermore, C0C1f induces strong upregulation of pro-inflammatory cytokines (interleukin-6 (IL-6), tumor necrosis factor α (TNFα), and interleukin-1β (IL-1β)) in cultured murine macrophages and human monocytes, resulting in a pro-inflammatory phenotype. We identified the toll-like receptor 4 (TLR4), toll-like receptor 2 (TLR2), and Advanced Glycosylation End Product-Specific Receptor (RAGE) as potential receptors for C0C1f whose activation leads to mobilization of the NFκB signaling pathway, a central mediator of the pro-inflammatory signaling cascade. Thus, C0C1f appears to be a key player in the initiation of inflammatory processes and might also play an important role upon MI.

Novel Radioligands for Cyclic Nucleotide Phosphodiesterase Imaging with Positron Emission Tomography: An Update on Developments Since 2012

Cyclic nucleotide phosphodiesterases (PDEs) are a class of intracellular enzymes that inactivate the secondary messenger molecules, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Thus, PDEs regulate the signaling cascades mediated by these cyclic nucleotides and affect fundamental intracellular processes. Pharmacological inhibition of PDE activity is a promising strategy for treatment of several diseases. However, the role of the different PDEs in related pathologies is not completely clarified yet. PDE-specific radioligands enable non-invasive visualization and quantification of these enzymes by positron emission tomography (PET) in vivo and provide an important translational tool for elucidation of the relationship between altered expression of PDEs and pathophysiological effects as well as (pre-)clinical evaluation of novel PDE inhibitors developed as therapeutics. Herein we present an overview of novel PDE radioligands for PET published since 2012.

Discovery of Radioiodinated Monomeric Anthraquinones as a Novel Class of Necrosis Avid Agents for Early Imaging of Necrotic Myocardium

Assessment of myocardial viability is deemed necessary to aid in clinical decision making whether to recommend revascularization therapy for patients with myocardial infarction (MI). Dianthraquinones such as hypericin (Hyp) selectively accumulate in necrotic myocardium, but were unsuitable for early imaging after administration to assess myocardial viability. Since dianthraquinones can be composed by coupling two molecules of monomeric anthraquinone and the active center can be found by splitting chemical structure, we propose that monomeric anthraquinones may be effective functional groups for necrosis targetability. In this study, eight radioiodinated monomeric anthraquinones were evaluated as novel necrosis avid agents (NAAs) for imaging of necrotic myocardium. All (131)I-anthraquinones showed high affinity to necrotic tissues and (131)I-rhein emerged as the most promising compound. Infarcts were visualized on SPECT/CT images at 6 h after injection of (131)I-rhein, which was earlier than that with (131)I-Hyp. Moreover, (131)I-rhein showed satisfactory heart-to-blood, heart-to-liver and heart-to-lung ratios for obtaining images of good diagnostic quality. (131)I-rhein was a more promising "hot spot imaging" tracer for earlier visualization of necrotic myocardium than (131)I-Hyp, which supported further development of radiopharmaceuticals based on rhein for SPECT/CT ((123)I and (99m)Tc) or PET/CT imaging ((18)F and (124)I) of myocardial necrosis.

Synthesis and Preclinical Evaluation of Radioiodinated Hypericin Dicarboxylic Acid as a Necrosis Avid Agent in Rat Models of Induced Hepatic, Muscular, and Myocardial Necroses

Myocardial infarction (MI) leads to substantial morbidity and mortality around the world. Accurate assessment of myocardial viability is essential to assist therapies and improve patient outcomes. (131)I-hypericin dicarboxylic acid ((131)I-HDA) was synthesized and evaluated as a potential diagnostic agent for earlier assessment of myocardium viability compared to its preceding counterpart (131)I-hypericin ((131)I-Hyp) with strong hydrophobic property, long plasma half-life, and high uptake in mononuclear phagocyte system (MPS). Herein, HDA was synthesized and characterized, and self-aggregation constant Kα was analyzed by spectrophotometry. Plasma half-life was determined in healthy rats by γ-counting. (131)I-HDA and (131)I-Hyp were prepared with iodogen as oxidant. In vitro necrosis avidity of (131)I-HDA and (131)I-Hyp was evaluated in necrotic cells induced by hyperthermia. Biodistribution was determined in rat models of induced necrosis using γ-counting, autoradiography, and histopathology. Earlier imaging of necrotic myocardium to assess myocardial viability was performed in rat models of reperfused myocardium infarction using single photon emission computed tomography/computed tomography (SPECT/CT). As a result, the self-aggregation constant Kα of HDA was lower than that of Hyp (105602 vs 194644, p < 0.01). (131)I-HDA displayed a shorter blood half-life compared with (131)I-Hyp (9.21 vs 31.20 h, p < 0.01). The necrotic-viable ratio in cells was higher with (131)I-HDA relative to that with (131)I-Hyp (5.48 vs 4.63, p < 0.05). (131)I-HDA showed a higher necrotic-viable myocardium ratio (7.32 vs 3.20, p < 0.01), necrotic myocardium-blood ratio (3.34 vs 1.74, p < 0.05), and necrotic myocardium-lung ratio (3.09 vs 0.61, p < 0.01) compared with (131)I-Hyp. (131)I-HDA achieved imaging of necrotic myocardium at 6 h postinjection (p.i.) with SPECT/CT, earlier than what (131)I-Hyp did. Therefore, (131)I-HDA may serve as a promising necrosis-avid diagnostic agent for earlier imaging of necrotic myocardium compared with (131)I-Hyp. This may support further development of radiopharmaceuticals ((123)I and (99m)Tc) based on HDA for SPECT/CT of necrotic myocardium.

Exploring diagnostic potentials of radioiodinated sennidin A in rat model of reperfused myocardial infarction

Non-invasive "hot spot imaging" and localization of necrotic tissue may be helpful for definitive diagnosis of myocardial viability, which is essential for clinical management of ischemic heart disease. We labeled Sennidin A (SA), a naturally occurring median dianthrone compound, with (131)I and evaluated (131)I SA as a potential necrosis-avid diagnostic tracer agent in rat model of reperfused myocardial infarction. Magnetic resonance imaging (MRI) was performed to determine the location and dimension of infarction. (131)I-SA was evaluated in rat model of 24-hour old reperfused myocardial infarction using single-photon emission computed tomography/computed tomography (SPECT/CT), biodistribution, triphenyltetrazolium chloride (TTC) histochemical staining, serial sectional autoradiography and microscopy. Gamma counting revealed high uptake and prolonged retention of (131)I SA in necrotic myocardium and fast clearance from non-targeted tissues. On SPECT/CT images, myocardial infarction was persistently visualized as well-defined hotspots over 24h, which was confirmed by perfect matches of images from post-mortem TTC staining and autoradiography. Radioactivity concentration in infarcted myocardium was over 9 times higher than that of the normal myocardium at 24h. With favorable hydrophilicity and stability, radioiodinated SA may serve as a necrosis-avid diagnostic agent for assessment of myocardial viability.

Assessment of Myocardial Remodeling Using an Elastin/Tropoelastin Specific Agent with High Field Magnetic Resonance Imaging (MRI)

Background

Well-defined inflammation, proliferation, and maturation phases orchestrate the remodeling of the injured myocardium after myocardial infarction (MI) by controlling the formation of new extracellular matrix. The extracellular matrix consists mainly of collagen but also fractions of elastin. It is thought that elastin is responsible for maintaining elastic properties of the myocardium, thus reducing the risk of premature rupture. An elastin/tropoelastin–specific contrast agent (Gd-ESMA) was used to image tropoelastin and mature elastin fibers for in vivo assessment of extracellular matrix remodeling post-MI.

Methods and Results

Gd-ESMA enhancement was studied in a mouse model of myocardial infarction using a 7 T MRI scanner and results were compared to those achieved after injection of a nonspecific control contrast agent, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). In the infarcted tissue, Gd-ESMA uptake (measured as R1 relaxation rate) steadily increased from day 3 to day 21 as a result of the synthesis of elastin/tropoelastin. R1 values were in good agreement with histological findings. A similar R1 behavior was observed in the remote myocardium. No mature cross-linked elastin was found at any time point. In contrast, Gd-DTPA uptake was only observed in the infarct with no changes in R1 values between 3 and 21 days post-MI.

Conclusions

We demonstrate the feasibility of in vivo imaging of extracellular matrix remodeling post-MI using a tropoelastin/elastin binding MR contrast agent, Gd-ESMA. We found that tropoelastin is the main contributor to the increased MRI signal at late stages of MI where its augmentation in areas of infarction was in good agreement with the R1 increase.

Circulating NOS3 modulates left ventricular remodeling following reperfused myocardial infarction

Purpose

Nitric oxide (NO) is constitutively produced and released from the endothelium and several blood cell types by the isoform 3 of the NO synthase (NOS3). We have shown that NO protects against myocardial ischemia/reperfusion (I/R) injury and that depletion of circulating NOS3 increases within 24h of ischemia/reperfusion the size of myocardial infarction (MI) in chimeric mice devoid of circulating NOS3. In the current study we hypothesized that circulating NOS3 also affects remodeling of the left ventricle following reperfused MI.

Methods

To analyze the role of circulating NOS3 we transplanted bone marrow of NOS3^−/− and wild type (WT) mice into WT mice, producing chimerae expressing NOS3 only in vascular endothelium (BC−/EC+) or in both, blood cells and vascular endothelium (BC+/EC+). Both groups underwent 60 min of coronary occlusion in a closed-chest model of reperfused MI. During the 3 weeks post MI, structural and functional LV remodeling was serially assessed (24h, 4d, 1w, 2w and 3w) by echocardiography. At 72 hours post MI, gene expression of several extracellular matrix (ECM) modifying molecules was determined by quantitative RT-PCR analysis. At 3 weeks post MI, hemodynamics were obtained by pressure catheter, scar size and collagen content were quantified post mortem by Gomori’s One-step trichrome staining.

Results

Three weeks post MI, LV end-systolic (53.2±5.9μl;***p≤0.001;n = 5) and end-diastolic volumes (82.7±5.6μl;*p<0.05;n = 5) were significantly increased in BC−/EC+, along with decreased LV developed pressure (67.5±1.8mmHg;n = 18;***p≤0.001) and increased scar size/left ventricle (19.5±1.5%;n = 13;**p≤0.01) compared to BC+/EC+ (ESV:35.6±2.2μl; EDV:69.1±2.6μl n = 8; LVDP:83.2±3.2mmHg;n = 24;scar size/LV13.8±0.7%;n = 16). Myocardial scar of BC−/EC+ was characterized by increased total collagen content (20.2±0.8%;n = 13;***p≤0.001) compared to BC+/EC+ (15.9±0.5;n = 16), and increased collagen type I and III subtypes.

Conclusion

Circulating NOS3 ameliorates maladaptive left ventricular remodeling following reperfused myocardial infarction.

Sialyltransferase7A, a Klf4-responsive gene, promotes cardiomyocyte apoptosis during myocardial infarction

Myocardial infarction (MI) is one major cause of heart failure through its induction of cardiomyocyte death. However, the molecular mechanisms associated with MI-induced cardiomyocyte apoptosis in the context of sialylation of heart are not yet understood. In this study, we found that sialyltransferase7A (Siat7A), one of the members of sialyltransferase family, was significantly increased in the ischemic myocardium, as well as in the human cardiomyocyte cell line AC16 under hypoxic condition. The Sialyl-Tn antigen (Neu5Acα2-6GalNAc-O-Ser/Thr) synthesized by Siat7A also increased in the AC16 cardiomyocytes following hypoxic stimulus. Increased Siat7A promoted cardiomyocyte apoptosis. The knockdown of Siat7A expression reduced cardiomyocyte apoptosis in both of vivo and vitro. Furthermore, the decreased extracellular signal-regulated kinase ERK1 and ERK2 (ERK1/2) activity was involved in the Siat7A-induced cardiomyocyte apoptosis. Notably, we showed that Krüppel-like factor 4 (Klf4), one of the transcription factors, specifically bound to the Siat7A promoter by ChIP assays. Deletion and mutagenesis analysis identified that Klf4 could transactivate the Siat7A promoter region (nt -655 to -636 bp). The upregulated Siat7A expression, which was paralleled by the increased Klf4 in the ischemic myocardium, contributed to cardiomyocyte apoptosis. Our study suggests Siat7A could be a valuable target for developing treatments for MI patients.

Cardiovascular magnetic resonance in ischemic heart disease

Ischemic heart disease is the major cause of death in developed countries. Recently, cardiovascular magnetic resonance (CMR) has appeared as a powerful technique for diagnosis and prognosis of ischemia, as well as for postischemic therapy follow-up. The objective of this chapter is to provide an overview of the role of CMR in assessing ischemic myocardium. It reviews the most recent studies in this field and includes CMR parameters that are already well established in the clinical setting as well as promising or emerging parameters in clinical use.

Multifunctional MR monitoring of the healing process after myocardial infarction

Healing of the myocardium after infarction comprises a variety of local adaptive processes which contribute to the functional outcome after the insult. Therefore, we aimed to establish a setting for concomitant assessment of regional alterations in contractile function, morphology, and immunological state to gain prognostic information on cardiac recovery after infarction. For this, mice were subjected to myocardial ischemia/reperfusion (I/R) and monitored for 28 days by cine MRI, T2 mapping, late gadolinium enhancement (LGE), and (19)F MRI. T2 values were calculated from gated multi-echo sequences. (19)F-loaded nanoparticles were injected intravenously for labelling circulating monocytes and making them detectable by (19)F MRI. In-house developed software was used for regional analysis of cine loops, T2 maps, LGE, and (19)F images to correlate local wall movement, tissue damage as well as monocyte recruitment over up to 200 sectors covering the left ventricle. This enabled us to evaluate simultaneously zonal cardiac necrosis, oedema, and inflammation patterns together with sectional fractional shortening (FS) and global myocardial function. Oedema, indicated by a rise in T2, showed a slightly better correlation with FS than LGE. Regional T2 values increased from 19 ms to above 30 ms after I/R. In the course of the healing process oedema resolved within 28 days, while myocardial function recovered. Infiltrating monocytes could be quantitatively tracked by (19)F MRI, as validated by flow cytometry. Furthermore, (19)F MRI proved to yield valuable insight on the outcome of myocardial infarction in a transgenic mouse model. In conclusion, our approach permits a comprehensive surveillance of key processes involved in myocardial healing providing independent and complementary information for individual prognosis.

A theoretical timeline for myocardial infarction: immunohistochemical evaluation and western blot quantification for Interleukin-15 and Monocyte chemotactic protein-1 as very early markers

BACKGROUND

Experimental and human studies have demonstrated that innate immune mechanisms and consequent inflammatory reaction play a critical role in cardiac response to ischemic injury. Thus, the detection of immuno-inflammatory and cellular phenomena accompanying cardiac alterations during the early inflammatory phase of myocardial infarction (MI) may be an excellent diagnostic tool. Current knowledge of the chronology of the responses of myocardial tissue following the occurrence of ischemic insult, as well as the existence of numerous studies aiming to identify reliable markers in dating MI, induced us to investigate the myocardial specimens of MI fatal cases in order to better define the age of MI.

METHODS

We performed an immunohistochemical study and a Western blot analysis to evaluate detectable morphological changes in myocardial specimens of fatal MI cases and to quantify the effects of cardiac expression of inflammatory mediators (CD15, IL-1β, IL-6, TNF-α, IL-15, IL-8, MCP-1, ICAM-1, CD18, tryptase) and structural and functional cardiac proteins.

RESULTS

We observed a biphasic course of MCP-1: it was strongly expressed in the very early phase (0-4 hrs), to diminish in the early period (after 6-8 hrs). Again, our choice of IL-15 is explained by the synergism with neutrophilic granulocytes (CD15) and our study shows the potential for striking cytokine synergy in promoting fast, local neutrophil response in damaged tissues. A progressively stronger immunoreaction for the CD15 antibody was visible in the areas where the margination of circulating inflammatory cells was detectable, up to very strong expression in the oldest ones (>12 hours). Further, the induction of CD15, IL-15, MCP-1 expression levels was quantified by Western blot analysis. The results were as follows: IL-15/β-actin 0.80, CD15/β-actin 0.30, and MCP-1/β-actin 0.60, matching perfectly with the results of immunohistochemistry. Control hearts from traumatic death cases did not show any immunoreactivity to the pro-inflammatory markers, neither were there any reactions in Western blot analysis.

CONCLUSIONS

Essential markers (i.e. IL-15, MCP-1) are suitable indicators of myocardial response to ischemic insult involving very early phase reaction (inflammatory response and cytokine release). In the very near future, proteomics may help clinicians and pathologists to better understand mechanisms relating to cardiac repair and remodeling and provide targets for future therapies.