Dynamics of cardiac wound healing following myocardial infarction: observations in genetically altered mice

125I-labeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (125I-OI5V) imaging visualized augmented sigma-1 receptor expression according to the severity of myocardial ischemia

BACKGROUND

We aimed to explore how the severity of myocardial ischemia affects myocardial sigma-1 receptor (Sig-1R) expression using 125I-labeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (125I-OI5V) imaging.

METHODS AND RESULTS

The left coronary artery was occluded for 30, 20, and 10 minute, to vary the severity of myocardial ischemia, followed by reperfusion. Dual-tracer autoradiography of the left ventricular short-axis slices was performed 3 and 7 days after reperfusion. 125I-OI5V was injected 30 minute before sacrifice and the area at risk (AAR) was evaluated by 99mTc-MIBI. Intense 125I-OI5V uptake was observed in the AAR and was significantly increased with increasing ischemia duration. To evaluate salvaged and nonsalvaged areas (preserved and decreased perfusion areas), triple-tracer autoradiography was performed 3 days after reperfusion. After dual-tracer autoradiography, 201Tl was injected 20 minute post 125I-OI5V injection. On triple-tracer autoradiography, the AAR/normally perfused area 125I-OI5V uptake ratio was positively correlated with the nonsalvaged area/whole left ventricular (LV) area ratio (P < .05). The AAR/normally perfused area 125I-OI5V uptake ratio was negatively correlated with the 201Tl uptake ratio of the AAR to normally perfused areas (P < .05). The comparison of the immunostaining distribution of 125I-OI5V and the macrophage marker CD68 revealed that 125I-OI5V was present mainly in, and immediately adjacent to the macrophage infiltration area.

CONCLUSIONS

Significant 125I-OI5V uptake in the AAR depends on the duration of ischemia and reduced 201Tl uptake; furthermore, 125I-OI5V was found in and around the macrophage infiltrate area. These results indicate that iodine-labeled OI5V is a promising tool for visualizing Sig-1R expression according to the ischemic burden.

Inhibition of ferroptosis alleviates high-power microwave-induced myocardial injury

Background

The use of high-power microwave (HPM) in our daily live is becoming more and more widespread, but the safety has also caused our concern. And ferroptosis is a newly discovered modality that can regulate cell death in recent years. The aim of our study was to demonstrate whether ferroptosis is an important cause of myocardial injury caused by HPM. And whether myocardial injury caused by HPM can be alleviated by inhibiting ferroptosis.

Methods

We verified the extent of myocardial damage by different doses of HPM through in vivo and in vitro assays, respectively. In addition, GPX4 was knocked down and overexpressed in cardiac myocytes to verify the altered sensitivity of cardiac myocytes to HPM. Finally, the therapeutic effect of Fer-1 and tanshinoneIIA on myocardial injury caused by HPM was verified in in vivo and in vitro assays.

Results

We found that cardiac tissue and cardiomyocyte injury in mice gradually increased with increasing HPM dose, while ferroptosis markers were consistent with the injury trend. Gpx4 had an important role in ferroptosis in cardiomyocytes caused by HPM. Finally, tanshinoneIIA and Fer-1 could attenuate the damage of cardiac tissues and cardiomyocytes caused by HPM.

Conclusions

In conclusion, our study found that ferroptosis, a novel mode of cell death, is present in myocardial injury caused by HPM. Moreover, tanshinone, a drug already in clinical use, can significantly reduce myocardial injury caused by HPM, which is promising to provide new therapeutic ideas for myocardial injury caused by HPM.

Cardiac Diffusion Tensor Biomarkers of Chronic Infarction Based on In Vivo Data

In vivo cardiac diffusion tensor imaging (cDTI) data were acquired in swine subjects six to ten weeks post-myocardial infarction (MI) to identify microstructural-based biomarkers of MI. Diffusion tensor invariants, diffusion tensor eigenvalues, and radial diffusivity (RD) are evaluated in the infarct, border, and remote myocardium, and compared with extracellular volume fraction (ECV) and native T1 values. Additionally, to aid the interpretation of the experimental results, the diffusion of water molecules was numerically simulated as a function of ECV. Finally, findings based on in vivo measures were confirmed using higher-resolution and higher signal-to-noise data acquired ex vivo in the same subjects. Mean diffusivity, diffusion tensor eigenvalues, and RD increased in the infarct and border regions compared to remote myocardium, while fractional anisotropy decreased. Secondary (e₂) and tertiary (e₃) eigenvalues increased more significantly than the primary eigenvalue in the infarct and border regions. These findings were confirmed by the diffusion simulations. Although ECV presented the largest increase in infarct and border regions, e₂, e₃, and RD increased the most among non-contrast-based biomarkers. RD is of special interest as it summarizes the changes occurring in the radial direction and may be more robust than e₂ or e₃ alone.

Engineering of Immune Microenvironment for Enhanced Tissue Remodeling

The capability to restore the structure and function of tissues damaged by fatal diseases and trauma is essential for living organisms. Various tissue engineering approaches have been applied in lesions to enhance tissue regeneration after injuries and diseases in living organisms. However, unforeseen immune reactions by the treatments interfere with successful healing and reduce the therapeutic efficacy of the strategies. The immune system is known to play essential roles in the regulation of the microenvironment and recruitment of cells that directly or indirectly participate in tissue remodeling in defects. Accordingly, regenerative immune engineering has emerged as a novel approach toward efficiently inducing regeneration using engineering techniques that modulate the immune system. It is aimed at providing a favorable immune microenvironment based on the controlled balance between pro-inflammation and anti-inflammation. In this review, we introduce recent developments in immune engineering therapeutics based on various cell types and biomaterials. These developments could potentially overcome the therapeutic limitations of tissue remodeling.

SiglecF(HI) Marks Late-Stage Neutrophils of the Infarcted Heart: A Single-Cell Transcriptomic Analysis of Neutrophil Diversification

Background

Neutrophils are thought to be short‐lived first responders to tissue injuries such as myocardial infarction (MI), but little is known about their diversification or dynamics.

Methods and Results

We permanently ligated the left anterior descending coronary arteries of mice and performed single‐cell RNA sequencing and analysis of >28 000 neutrophil transcriptomes isolated from the heart, peripheral blood, and bone marrow of mice on days 1 to 4 after MI or at steady‐state. Unsupervised clustering of cardiac neutrophils revealed 5 major subsets, 3 of which originated in the bone marrow, including a late‐emerging granulocyte expressing SiglecF, a marker classically used to define eosinophils. SiglecF^HI neutrophils represented ≈25% of neutrophils on day 1 and grew to account for >50% of neutrophils by day 4 post‐MI. Validation studies using quantitative polymerase chain reaction of fluorescent‐activated cell sorter sorted Ly6G⁺SiglecF^HI and Ly6G⁺SiglecF^LO neutrophils confirmed the distinct nature of these populations. To confirm that the cells were neutrophils rather than eosinophils, we infarcted GATA‐deficient mice (∆dblGATA) and observed similar quantities of infiltrating Ly6G⁺SiglecF^HI cells despite marked reductions of conventional eosinophils. In contrast to other neutrophil subsets, Ly6G⁺SiglecF^HI neutrophils expressed high levels of Myc‐regulated genes, which are associated with longevity and are consistent with the persistence of this population on day 4 after MI.

Conclusions

Overall, our data provide a spatial and temporal atlas of neutrophil specialization in response to MI and reveal a dynamic proinflammatory cardiac Ly6G⁺SigF⁺(Myc⁺NFϰB⁺) neutrophil that has been overlooked because of negative selection.

Secreted Frizzled-Related Protein 2 and Extracellular Volume Fraction in Patients with Heart Failure

Background

Quantification of extracellular volume (ECV) fraction by cardiovascular magnetic resonance (CMR) has emerged as a noninvasive diagnostic tool to assess myocardial fibrosis. Secreted frizzled-related protein 2 (SFRP2) appears to play an important role in cardiac fibrosis. We aimed to evaluate the association between SFRP2 and myocardial fibrosis and the prognostic value of ECV fraction in patients with heart failure (HF).

Methods

In this prospective cohort study, 72 hospitalized adult patients (age ≥ 18 years) with severe decompensated HF were included. CMR measurements and T1 mapping were performed to calculate ECV fraction. Serum SFRP2 level was detected by an enzyme-linked immunosorbent assay kit. All patients were followed up, and the primary outcomes were composite events including all-cause mortality and HF hospitalization.

Results

During the median follow-up of 12 months, 27 (37.5%) patients experienced primary outcome events and had higher levels of N-terminal pro-B-type natriuretic peptide (NT-proBNP), SFRP2, and ECV fraction compared with those without events. In Pearson correlation analysis, levels of SFRP2 (r = 0.33), high-sensitivity C-reactive protein (r = 0.31), and hemoglobin A1c (r = 0.29) were associated with ECV fraction (all P < 0.05); however, in multivariate linear regression analysis, SFRP2 was the only significant factor determined for ECV fraction (r_partial = 0.33, P = 0.02). In multivariate Cox regression analysis, age (each 10 years, hazard ratio (HR) 1.13, 95% confidence interval (CI) 1.04–1.22), ECV fraction (per doubling, HR 1.68, 95% CI 1.03–2.74), and NT-proBNP (per doubling, HR 2.46, 95% CI 1.05–5.76) were independent risk factors for primary outcomes.

Conclusions

Higher ECV fraction is associated with worsened prognosis in HF. SFRP2 is an independent biomarker for myocardial fibrosis. Further studies are needed to explore the potential therapeutic value of SFRP2 in myocardial fibrosis.

The effector cells and cellular mediators of immune system involved in cardiac inflammation and fibrosis after myocardial infarction

The cardiac repair after myocardial infarction (MI) involves two phases, namely, inflammatory response and proliferative response. The former is an inflammatory reaction, evoked by different kinds of pro-inflammatory leukocytes and molecules stimulated by myocardial necrosis, while the latter is a repair process, predominated by a magnitude of anti-inflammatory cells and cytokines, as well as fibroblasts. Cardiac remodeling post-MI is dependent on the balance of individualized intensity of the post-MI inflammation and subsequent cardiac fibrosis. During the past 30 years, enormous studies have focused on investigating immune cells and mediators involved in cardiac inflammation and fibrosis, which are two interacting processes of post-MI cardiac repair. These results contribute to revealing the mechanism of adverse cardiac remodeling after MI and alleviating the impairment of cardiac function. In this study, we will broadly discuss the role of immune cell subpopulation and the involved cytokines and chemokines during cardiac repair post-MI, particular in cardiac inflammation and fibrosis.

Role of Sfrps in cardiovascular disease

Secreted frizzled-related proteins (Sfrps) are a family of secreted proteins that bind extracellularly to Wnt ligands and frizzled receptors. This binding modulates the Wnt signaling cascade, and Sfrps interact with their corresponding receptors. Sfrps are thought to play an important role in the pathological mechanism of cardiac disease such as myocardial infarction, cardiac remodeling, and heart failure. However, the overall role of Sfrps in cardiac disease is unknown. Some members of the Sfrps family modulate cellular apoptosis, angiogenesis, differentiation, the inflammatory process, and cardiac remodeling. In this review, we summarize the evidence of Sfrps association with cardiac disease. We also discuss how multiple mechanisms may underlie Sfrps being involved in such diverse pathologies.

Is There Preclinical and Clinical Value for 19F MRI in Stem Cell Cardiac Regeneration?

Cardiovascular regeneration aims to renew damaged or necrotic tissue and to enhance cardiac functional performance. Despite the hope arisen from the introduction and use of stem cells (SCs) as a novel cardiac regenerative approach, to-this-date, clinical trial findings are still ambivalent despite preclinical successes. Concurrently, noninvasive magnetic resonance imaging (MRI) advances have been based on nanotechnological breakthroughs that have (a) allowed fluorinated nanoparticles and ultrasmall iron oxide single-cell labeling, (b) explored imaging detection sensitivity limits (for preclinical/low-field clinical settings), and (c) accomplished cellular tracking in vivo. Nevertheless, outcomes have been far from ideal. Herein, the recently developed preclinical and clinical 1H and 19F MRI approaches for direct cardiac SC labeling techniques intended for cellular implantation and their potential for tracking these cells in health and infarcted states are summarized. To this extent, the potential preclinical and clinical values of 19F MRI and tracking of SCs for cardiac regeneration in myocardial infarction are questioned and challenged.

In vivo label-free optical monitoring of structural and metabolic remodeling of myocardium following infarction

Cardiac remodeling following myocardial infarction (MI) involves structural and functional alterations in the infarcted and remote viable myocardium that can ultimately lead to heart failure. The underlying mechanisms are not fully understood and, following our previous study of the autofluorescence lifetime and diffuse reflectance signatures of the myocardium in vivo at 16 weeks post MI in rats [Biomed. Opt. Express6(2), 324 (2015)], we here present data obtained at 1, 2 and 4 weeks post myocardial infarction that help follow the temporal progression of these changes. Our results demonstrate that both structural and metabolic changes in the heart can be monitored from the earliest time points following MI using label-free optical readouts, not only in the region of infarction but also in the remote non-infarcted myocardium. Changes in the autofluorescence intensity and lifetime parameters associated with collagen type I autofluorescence were indicative of progressive collagen deposition in tissue that was most pronounced at earlier time points and in the region of infarction. In addition to significant collagen deposition in infarcted and non-infarcted myocardium, we also report changes in the autofluorescence parameters associated with reduced nicotinamide adenine (phosphate) dinucleotide (NAD(P)H) and flavin adenine dinucleotide (FAD), which we associate with metabolic alterations throughout the heart. Parallel measurements of the diffuse reflectance spectra indicated an increased contribution of reduced cytochrome c. Our findings suggest that combining time-resolved spectrofluorometry and diffuse reflectance spectroscopy could provide a useful means to monitor cardiac function in vivo at the time of surgery.

Molecular Imaging in Ischemic Heart Disease

Purpose of Review

The purpose of this paper is to review current and new modalities to image key biological processes in ischemic heart disease and after myocardial infarction non-invasively.

Recent Findings

New imaging targets have been developed to detect and quantify myocardial damage after ischemia. Although positron emission tomography (PET) has been leading the development of new probes in the past, continuous improvements of magnetic resonance imaging (MRI) together with the development of new novel MRI contrast agents opens new research avenues including the combination of both PET and MRI to obtain anatomic, functional, and molecular information simultaneously, which is not possible from a single imaging session.

Summary

This review summarizes the state of art of non-invasive molecular imaging of the myocardium during ischemia and after myocardial infarction using PET and MRI. We also describe the different contrast agents that have been developed to image the different phases of cardiac healing and the biological processes associated with each of those phases. Importantly, here we focus on imaging of inflammation as it is the key biological process that orchestrates clearance of dead cells, tissue remodeling, cardiac repair, and future outcome. We also focus on clinical translation of some of the novel contrast agents that have been tested in patients and discuss the need for larger, multi-center patient studies to fully validate the applicability of new imaging probes.

Quantification of myocardial infarct area based on TRAFFn relaxation time maps - comparison with cardiovascular magnetic resonance late gadolinium enhancement, T1ρ and T2 in vivo

BACKGROUND

Two days after myocardial infarction (MI), the infarct consists mostly on necrotic tissue, and the myocardium is transformed through granulation tissue to scar in two weeks after the onset of ischemia in mice. In the current work, we determined and optimized cardiovascular magnetic resonance (CMR) methods for the detection of MI size during the scar formation without contrast agents in mice.

METHODS

We characterized MI and remote areas with rotating frame relaxation time mapping including relaxation along fictitious field in nth rotating frame (RAFFn), T1ρ and T2 relaxation time mappings at 1, 3, 7, and 21 days after MI. These results were compared to late gadolinium enhancement (LGE) and Sirius Red-stained histology sections, which were obtained at day 21 after MI.

RESULTS

All relaxation time maps showed significant differences in relaxation time between the MI and remote area. Areas of increased signal intensities after gadolinium injection and areas with increased TRAFF2 relaxation time were highly correlated with the MI area determined from Sirius Red-stained histology sections (LGE: R2 = 0.92, P < 0.01, TRAFF2: R2 = 0.95, P < 0.001). Infarct area determined based on T1ρ relaxation time correlated highly with Sirius Red histology sections (R2 = 0.97, P < 0.01). The smallest overestimation of the LGE-defined MI area was obtained for TRAFF2 (5.6 ± 4.2%) while for T1ρ overestimation percentage was > 9% depending on T1ρ pulse power.

CONCLUSION

T1ρ and TRAFF2 relaxation time maps can be used to determine accurately MI area at various time points in the mouse heart. Determination of MI size based on TRAFF2 relaxation time maps could be performed without contrast agents, unlike LGE, and with lower specific absorption rate compared to on-resonance T1ρ relaxation time mapping.

Advanced Gene Manipulation Methods for Stem Cell Theranostics

In the field of tissue engineering, autologous cell sources are ideal to prevent adverse immune responses; however, stable and reliable cell sources are limited. To acquire more reliable cell sources, the harvesting and differentiation of stem cells from patients is becoming more and more common. To this end, the need to control the fate of these stem cells before transplantation for therapeutic purposes is urgent. Since transcription factors orchestrate all of the gene activities inside of a cell, researchers have developed engineered and synthetic transcription factors to precisely control the fate of stem cells allowing for safer and more effective cell sources. Engineered transcription factors, mutant fusion proteins of naturally occurring proteins, comprise the three main domains of natural transcription factors including DNA binding domains, transcriptional activation domains, and a linker domain. Several key advancements of engineered zinc finger proteins, transcriptional activator-like effectors, and deficient cas9 proteins have revolutionized the field of engineered transcription factors allowing for precise control of gene regulation. Synthetic transcription factors are chemically made transcription factor mimics that use small molecule based moieties to replicate the main functions of natural transcription factors. These include hairpin polyamides, triple helix forming oligonucleotides, and nanoparticle-based methods. Synthetic transcription factors allow for non-viral delivery and greater spatiotemporal control of gene expression. The developments in engineered and synthetic transcription factors have lowered the risk of tumorigenicity and improved differentiation capability of stem cells, as well as facilitated many key discoveries in the fields of cancer and stem cell biology, thus providing a stepping stone to advance regenerative medicine in the clinic for cell replacement therapies.

Correlation between apoptosis and left ventricular remodeling in subacute phase of myocardial ischemia and reperfusion

Background

To investigate whether an apoptotic process demonstrated by ^99mTc-annexin-V (^99mTc-AV) uptake correlates with left ventricular remodeling (LVR) after myocardial infarction, we assessed ^99mTc-AV uptake in rat model of myocardial ischemia and reperfusion.

Methods

The left coronary artery (LCA) of 15 rats was occluded for 20 to 30 min, followed by reperfusion. After 2 weeks, ^99mTc-AV was injected, and then 1 h later, ²⁰¹Tl was injected after reocclusion of the LCA. Dual-tracer autoradiography was performed to assess ^99mTc-AV uptake and the area at risk (AAR) by ²⁰¹Tl defect. ^99mTc-AV uptake ratio was calculated by dividing the count density of the AAR by that of the normally perfused area. In short-axis LV slices, LV cavity dilation index (DI) was calculated by dividing the area of LV cavity by that of the whole LV area. LV wall-thinning ratio (WTR) was calculated by dividing the LV wall thickness in the AAR by that of the normally perfused area.

Results

Significant ^99mTc-AV uptake in the AAR was observed in 10 rats. DI was significantly higher in rats with positive ^99mTc-AV uptake than in rats without uptake. WTR was smaller in rats with positive ^99mTc-AV uptake than in rats without uptake.

Conclusions

The data suggest ^99mTc-AV uptake in injured myocardium might correlate with LVR at 2 weeks after myocardial ischemia and reperfusion.

The role of Wnt regulation in heart development, cardiac repair and disease: A tissue engineering perspective

Wingless-related integration site (Wnt) signaling has proven to be a fundamental mechanism in cardiovascular development as well as disease. Understanding its particular role in heart formation has helped to develop pluripotent stem cell differentiation protocols that produce relatively pure cardiomyocyte populations. The resultant cardiomyocytes have been used to generate heart tissue for pharmaceutical testing, and to study physiological and disease states. Such protocols in combination with induced pluripotent stem cell technology have yielded patient-derived cardiomyocytes that exhibit some of the hallmarks of cardiovascular disease and are therefore being used to model disease states. While FDA approval of new treatments typically requires animal experiments, the burgeoning field of tissue engineering could act as a replacement. This would necessitate the generation of reproducible three-dimensional cardiac tissues in a well-controlled environment, which exhibit native heart properties, such as cellular density, composition, extracellular matrix composition, and structure-function. Such tissues could also enable the further study of Wnt signaling. Furthermore, as Wnt signaling has been found to have a mechanistic role in cardiac pathophysiology, e.g. heart attack, hypertrophy, atherosclerosis, and aortic stenosis, its strategic manipulation could provide a means of generating reproducible and specific, physiological and pathological cardiac models.

Computational modeling of acute myocardial infarction

Myocardial infarction, commonly known as heart attack, is caused by reduced blood supply and damages the heart muscle because of a lack of oxygen. Myocardial infarction initiates a cascade of biochemical and mechanical events. In the early stages, cardiomyocytes death, wall thinning, collagen degradation, and ventricular dilation are the immediate consequences of myocardial infarction. In the later stages, collagenous scar formation in the infarcted zone and hypertrophy of the non-infarcted zone are auto-regulatory mechanisms to partly correct for these events. Here we propose a computational model for the short-term adaptation after myocardial infarction using the continuum theory of multiplicative growth. Our model captures the effects of cell death initiating wall thinning, and collagen degradation initiating ventricular dilation. Our simulations agree well with clinical observations in early myocardial infarction. They represent a first step toward simulating the progression of myocardial infarction with the ultimate goal to predict the propensity toward heart failure as a function of infarct intensity, location, and size.

Physiological Implications of Myocardial Scar Structure

Once myocardium dies during a heart attack, it is replaced by scar tissue over the course of several weeks. The size, location, composition, structure, and mechanical properties of the healing scar are all critical determinants of the fate of patients who survive the initial infarction. While the central importance of scar structure in determining pump function and remodeling has long been recognized, it has proven remarkably difficult to design therapies that improve heart function or limit remodeling by modifying scar structure. Many exciting new therapies are under development, but predicting their long-term effects requires a detailed understanding of how infarct scar forms, how its properties impact left ventricular function and remodeling, and how changes in scar structure and properties feed back to affect not only heart mechanics but also electrical conduction, reflex hemodynamic compensations, and the ongoing process of scar formation itself. In this article, we outline the scar formation process following a myocardial infarction, discuss interpretation of standard measures of heart function in the setting of a healing infarct, then present implications of infarct scar geometry and structure for both mechanical and electrical function of the heart and summarize experiences to date with therapeutic interventions that aim to modify scar geometry and structure. One important conclusion that emerges from the studies reviewed here is that computational modeling is an essential tool for integrating the wealth of information required to understand this complex system and predict the impact of novel therapies on scar healing, heart function, and remodeling following myocardial infarction.

Dronedarone does not affect infarct volume as assessed by magnetic resonance imaging in a porcine model of myocardial infarction

Dronedarone has been demonstrated to be harmful in patients with recent decompensated heart failure. Furthermore, a PALLAS study reported that dronedarone therapy increases mortality rates in patients with permanent atrial fibrillation. Although a pathophysiological explanation for these finding remains to be elucidated, the long term effects of dronedarone on myocardial structure and stability have been suggested. The aim of the present study was to determine whether dronedarone therapy affects left ventricular (LV) function in a chronic model of myocardial infarction (MI). An anterior MI was induced in 16 pigs. Of these animals, eight pigs were then treated with dronedarone for 1 week prior to, and 4 weeks following MI, the remaining pigs served as controls. LV angiography was performed 4 weeks after MI to determine the LV ejection fraction (LVEF). A post‑mortem magnetic resonance imaging scan of the LV was then performed on the two groups (n=6) to determine the volume and size of the induced MI. Dronedarone therapy did not affect systemic and intracardiac hemodynamic parameters or LVEF during the follow‑up assessment. Of note, dronedarone had no negative effect on the total infarct volume and size and did not induce lethal proarrhythmic effects following the induced anterior MI. Therefore, the results suggested that dronedarone did not increase the volume or size of induced anterior MI and did not affect LV performance. Thus, dronedarone therapy was observed to be safe in a porcine model of anterior MI.

Intraoperative systemic infusion of lidocaine reduces postoperative pain after lumbar surgery: a double-blinded, randomized, placebo-controlled clinical trial

BACKGROUND CONTEXT

Analgesic effect of lidocaine infusion on postoperative pain.

PURPOSE

The aim of this study was to evaluate the analgesic effect of lidocaine infusion on postoperative pain after lumbar microdiscectomy.

STUDY DESIGN

This study used a prospective, randomized, double-blinded, and placebo-controlled clinical trial.

PATIENT SAMPLE

Fifty-one patients participated in this randomized, double-blinded study.

OUTCOME MEASURES

The primary outcome was the visual analog scale (VAS) (0-100 mm) pain score at 4 hours after surgery. The secondary outcomes were the VAS pain score at 2, 8, 12, 24, and 48 hours after surgery, the frequency with which patients pushed the button (FPB) of the patient-controlled analgesia system, and the fentanyl consumption at 2, 4, 8, 12, 24, and 48 hours after surgery. Other outcomes were satisfaction scores regarding pain control and the overall recovery process, incidence of postoperative nausea and vomiting (PONV), and length of hospital stay (HS).

METHODS

Preoperatively and throughout the surgery, Group L received intravenous lidocaine infusion (a 1.5-mg/kg bolus followed by a 2-mg/kg/h infusion until the end of the surgical procedure) and Group C received normal saline infusion as a placebo.

RESULTS

The VAS scores and fentanyl consumption were significantly lower in Group L compared with Group C except at 48 h after surgery (p<.05). Total fentanyl consumption, total FPB, length of HS, and satisfaction scores were also significantly lower in Group L compared with Group C (p<.05).

CONCLUSIONS

Intraoperative systemic infusion of lidocaine decreases pain perception during microdiscectomy, thus reducing the consumption of opioid and the severity of postoperative pain. This effect contributes to reduce the length of HS.

Foxp3+ CD4+ T cells improve healing after myocardial infarction by modulating monocyte/macrophage differentiation

RATIONALE

An exaggerated or persistent inflammatory activation after myocardial infarction (MI) leads to maladaptive healing and subsequent remodeling of the left ventricle. Foxp3(+) CD4(+) regulatory T cells (Treg cells) contribute to inflammation resolution. Therefore, Treg cells might influence cardiac healing post-MI.

OBJECTIVE

Our aim was to study the functional role of Treg cells in wound healing post-MI in a mouse model of permanent left coronary artery ligation.

METHODS AND RESULTS

Using a model of genetic Treg-cell ablation (Foxp3(DTR) mice), we depleted the Treg-cell compartment before MI induction, resulting in aggravated cardiac inflammation and deteriorated clinical outcome. Mechanistically, Treg-cell depletion was associated with M1-like macrophage polarization, characterized by decreased expression of inflammation-resolving and healing-promoting factors. The phenotype of exacerbated cardiac inflammation and outcome in Treg-cell-ablated mice could be confirmed in a mouse model of anti-CD25 monoclonal antibody-mediated depletion. In contrast, therapeutic Treg-cell activation by superagonistic anti-CD28 monoclonal antibody administration 2 days after MI led to improved healing and survival. Compared with control animals, CD28-SA-treated mice showed increased collagen de novo expression within the scar, correlating with decreased rates of left ventricular ruptures. Therapeutic Treg-cell activation induced an M2-like macrophage differentiation within the healing myocardium, associated with myofibroblast activation and increased expression of monocyte/macrophage-derived proteins fostering wound healing.

CONCLUSIONS

Our data indicate that Treg cells beneficially influence wound healing after MI by modulating monocyte/macrophage differentiation. Moreover, therapeutic activation of Treg cells constitutes a novel approach to improve healing post-MI.

Thrombomodulin's lectin-like domain reduces myocardial damage by interfering with HMGB1-mediated TLR2 signalling

AIMS

Thrombomodulin (TM), via its lectin-like domain (LLD), exhibits anti-inflammatory properties partly by sequestering the pro-inflammatory cytokine, high-mobility group box 1 (HMGB1). Since myocardial damage after ischaemia and reperfusion is mediated by inflammation, we evaluated the cardioprotective effects of the LLD of TM. Using an in vivo mouse model of transient ischaemia and in vitro models of cardiomyocyte hypoxia, we assessed the ability of the LLD to suppress HMGB1-mediated activation of the receptors, receptor for advanced glycation endproducts (RAGEs) and Toll-like receptors (TLRs) 2 and 4.

METHODS AND RESULTS

Thirty-minute myocardial ischaemia was induced in isoflurane-anaesthetized mice followed by 24 h of reperfusion in wild-type (WT) mice, in mice lacking the LLD of TM (TM(LeD/LeD) mice), and in WT with systemic overexpression of the LLD of TM induced by hydrodynamic transfection. Infarct size, HMGB1 protein, and apoptotic cells were significantly increased in TM(LeD/LeD) mice when compared with WT. Neonatal rat cardiomyocytes transfected with TLR2-, TLR4-, and RAGE-siRNA were exposed to hypoxia (0.8% O2) and reoxygenation (21% O2). HMGB1 augmented hypoxia-induced apoptosis in TLR2- but not in RAGE- or TLR4-suppressed cells. Administration of HMGB1- and TLR2-blocking antibodies in TM(LeD/LeD) mice prior to myocardial ischaemia diminished apoptosis. Therapeutic systemic gene therapy using the LLD reduced the infarct size and HMGB1 protein levels 24 h after reperfusion.

CONCLUSION

The LLD of TM suppresses HMGB1-induced and TLR2-mediated myocardial reperfusion injury and apoptosis in vitro and in vivo.

Direct cardiomyocyte reprogramming: a new direction for cardiovascular regenerative medicine

The past few years have seen unexpected new developments in direct cardiomyocyte reprogramming. Direct cardiomyocyte reprogramming potentially offers an entirely novel approach to cardiovascular regenerative medicine by converting cardiac fibroblasts into functional cardiomyocytes in situ. There is much to be learned, however, about the mechanisms of direct reprogramming in order that the process can be made more efficient. Early efforts have suggested that this new technology can be technically challenging. Moreover, new methods of inducing heart reprogramming will need to be developed before this approach can be translated to the bedside. Despite this, direct cardiomyocyte reprogramming may lead to new therapeutic options for sufferers of heart disease.

Ecto-5′-Nucleotidase on Immune Cells Protects From Adverse Cardiac Remodeling

Rationale:

Ecto-5′-nucleotidase (CD73) on immune cells is emerging as a critical pathway and therapeutic target in cardiovascular and autoimmune disorders.

Objective:

Here, we investigated the role of CD73 in postinfarction inflammation, cardiac repair, and remodeling in mice after reperfused myocardial infarction (50-minute ischemia).

Methods and Results:

We found that compared with control mice (1) cardiac function in CD73 −/− mice more severely declined after infarction (systolic failure with enhanced myocardial edema formation) as determined by MRI and was associated with the persistence of cardiac immune cell subsets, (2) cardiac adenosine release was augmented 7 days after ischemia/reperfusion in control mice but reduced by 90% in CD73 mutants, (3) impaired healing involves M1-driven immune response with increased tumor necrosis factor-α and interleukin-17, as well as decreased transforming growth factor-β and interleukin-10, and (4) CD73 −/− mice displayed infarct expansion accompanied by an immature replacement scar and diffuse ventricular fibrosis. Studies on mice after bone marrow transplantation revealed that CD73 present on immune cells is a major determinant promoting cardiac healing.

Conclusions:

These results, together with the upregulation of CD73 on immune cells after ischemia/reperfusion, demonstrate the crucial role of purinergic signaling during cardiac healing and provide groundwork for novel anti-inflammatory strategies in treating adverse cardiac remodeling.

Passive targeting of lipid-based nanoparticles to mouse cardiac ischemia-reperfusion injury

Reperfusion therapy is commonly applied after a myocardial infarction. Reperfusion, however, causes secondary damage. An emerging approach for treatment of ischemia-reperfusion (IR) injury involves the delivery of therapeutic nanoparticles to the myocardium to promote cell survival and constructively influence scar formation and myocardial remodeling. The aim of this study was to provide detailed understanding of the in vivo accumulation and distribution kinetics of lipid-based nanoparticles (micelles and liposomes) in a mouse model of acute and chronic IR injury. Both micelles and liposomes contained paramagnetic and fluorescent lipids and could therefore be visualized with magnetic resonance imaging (MRI) and confocal laser scanning microscopy (CLSM). In acute IR injury both types of nanoparticles accumulated massively and specifically in the infarcted myocardium as revealed by MRI and CLSM. Micelles displayed faster accumulation kinetics, probably owing to their smaller size. Liposomes occasionally co-localized with vessels and inflammatory cells. In chronic IR injury only minor accumulation of micelles was observed with MRI. Nevertheless, CLSM revealed specific accumulation of both micelles and liposomes in the infarct area 3 h after administration. Owing to their specific accumulation in the infarcted myocardium, lipid-based micelles and liposomes are promising vehicles for (visualization of) drug delivery in myocardial infarction.

Microvascular repair: post-angiogenesis vascular dynamics

Vascular compromise and the accompanying perfusion deficits cause or complicate a large array of disease conditions and treatment failures. This has prompted the exploration of therapeutic strategies to repair or regenerate vasculatures, thereby establishing more competent microcirculatory beds. Growing evidence indicates that an increase in vessel numbers within a tissue does not necessarily promote an increase in tissue perfusion. Effective regeneration of a microcirculation entails the integration of new stable microvessel segments into the network via neovascularization. Beginning with angiogenesis, neovascularization entails an integrated series of vascular activities leading to the formation of a new mature microcirculation, and includes vascular guidance and inosculation, vessel maturation, pruning, AV specification, network patterning, structural adaptation, intussusception, and microvascular stabilization. While the generation of new vessel segments is necessary to expand a network, without the concomitant neovessel remodeling and adaptation processes intrinsic to microvascular network formation, these additional vessel segments give rise to a dysfunctional microcirculation. While many of the mechanisms regulating angiogenesis have been detailed, a thorough understanding of the mechanisms driving post-angiogenesis activities specific to neovascularization has yet to be fully realized, but is necessary to develop effective therapeutic strategies for repairing compromised microcirculations as a means to treat disease.

CXC chemokine KC fails to induce neutrophil infiltration and neoangiogenesis in a mouse model of myocardial infarction

BACKGROUND

Chemokines and neutrophils, known as important players in the inflammatory cascade, also contribute to heart tissue recovery and scar formation after myocardial infarction (MI). The objective of this study was to determine the importance of ELR-containing CXC chemokine KC in neutrophil infiltration and neoangiogenesis, in a mouse model of chronic MI.

METHODS AND RESULTS

MI was induced in mice divided in four groups: control (untreated), anti-KC "later" (anti-KC antibody injections started 4 days after MI and then delivered every 72 hours for 3 weeks, to inhibit angiogenesis), anti-KC "earlier" (anti-KC antibody injections 1 day before and 1 day after MI, to block neutrophil infiltration), anti-KC (anti-KC antibody injections 1 day before and 1 day after MI, and then every 72 hours for 3 weeks). The efficiency of the anti-KC treatment was determined by the measurement of KC serum concentration and immunofluorescence staining, in each of the four groups. Surprisingly, we did not find any difference in neutrophil infiltration in the infarcted area between untreated and treated animals. Moreover, the heart function, infarct size, and neoangiogenesis were not different between the four groups. As expected, a comparable anti-CXCR2 treatment of mice before and after MI was able to significantly reduce neutrophil infiltration into the infarcted area and angiogenesis, but also to reduce the infarction size after long or "later" treatment.

CONCLUSIONS

The major finding of our study is that KC, a potent neutrophil chemoattractant and an established angiogenic factor, failed to interfere in the post-infarction inflammatory response, in wound healing and scar formation after MI. Therefore, these aspects need to be carefully taken into account when devising therapeutic strategies for myocardial infarction and ischemic cardiomyopathy.

Embryonic cardiomyocyte, but not autologous stem cell transplantation, restricts infarct expansion, enhances ventricular function, and improves long-term survival

AIMS

Controversy exists in regard to the beneficial effects of transplanting cardiac or somatic progenitor cells upon myocardial injury. We have therefore investigated the functional short- and long-term consequences after intramyocardial transplantation of these cell types in a murine lesion model.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in mice (n = 75), followed by the intramyocardial injection of 1-2×10(5) luciferase- and GFP-expressing embryonic cardiomyocytes (eCMs), skeletal myoblasts (SMs), mesenchymal stem cells (MSCs) or medium into the infarct. Non-treated healthy mice (n = 6) served as controls. Bioluminescence and fluorescence imaging confirmed the engraftment and survival of the cells up to seven weeks postoperatively. After two weeks MRI was performed, which showed that infarct volume was significantly decreased by eCMs only (14.8±2.2% MI+eCM vs. 26.7±1.6% MI). Left ventricular dilation was significantly decreased by transplantation of any cell type, but most efficiently by eCMs. Moreover, eCM treatment increased the ejection fraction and cardiac output significantly to 33.4±2.2% and 22.3±1.2 ml/min. In addition, this cell type exclusively and significantly increased the end-systolic wall thickness in the infarct center and borders and raised the wall thickening in the infarct borders. Repetitive echocardiography examinations at later time points confirmed that these beneficial effects were accompanied by better survival rates.

CONCLUSION

Cellular cardiomyoplasty employing contractile and electrically coupling embryonic cardiomyocytes (eCMs) into ischemic myocardium provoked significantly smaller infarcts with less adverse remodeling and improved cardiac function and long-term survival compared to transplantation of somatic cells (SMs and MSCs), thereby proving that a cardiomyocyte phenotype is important to restore myocardial function.

14C-Methionine uptake as a potential marker of inflammatory processes after myocardial ischemia and reperfusion

A relationship between l-[methyl-(11)C]methionine ((11)C-methionine) uptake and angiogenesis has been suggested in gliomas. However, methionine uptake in myocardial ischemia and reperfusion has received little attention. We investigated the serial changes and mechanisms of (14)C-methionine uptake in a rat model of myocardial ischemia and reperfusion.

METHODS

The left coronary artery was occluded for 30 min, followed by reperfusion for 1-28 d. At the time of the study, (14)C-methionine (0.74 MBq) and (201)Tl (14.8 MBq) were injected intravenously at 20 and 10 min before sacrifice, respectively. One minute before sacrifice, the left coronary artery was reoccluded, and (99m)Tc-hexakis-2-methoxyisobutylisonitrile (150-180 MBq) was injected to verify the area at risk. Histologic sections of the heart were immunohistochemically analyzed using anti-CD68, anti-smooth-muscle α-actin (SMA), and antitroponin I and compared with the autoradiography findings.

RESULTS

Both (14)C-methionine (uptake ratio, 0.71 ± 0.13) and (201)Tl uptake were reduced in the area at risk at 1 d after reperfusion. However, 3 d after reperfusion, an increased (14)C-methionine uptake (1.79 ± 0.23) was observed corresponding to the area of still-reduced (201)Tl uptake, and the (14)C-methionine uptake gradually declined until 28 d. The increased (14)C-methionine uptake area at 3 and 7 d corresponded well to the macrophage infiltrations demonstrated by positive CD68 staining. Anti-SMA staining appeared at 7 d, after which CD68 staining was gradually replaced by the SMA staining, suggesting that methionine uptake in the early phase after ischemia and reperfusion might reflect inflammatory activity.

CONCLUSION

(14)C-methionine accumulated in the infarcted area, and its uptake corresponded closely to macrophage infiltration at 3-7 d after reperfusion. Methionine imaging may be useful for inflammatory imaging early after myocardial infarction.

Cardiac wound healing post-myocardial infarction: a novel method to target extracellular matrix remodeling in the left ventricle

Myocardial infarction (MI) is a leading cause of death worldwide. Permanent ligation of the left anterior descending coronary artery (LAD) is a commonly used surgical model to study post-MI effects in mice. LAD occlusion induces a robust wound healing response that includes extracellular matrix (ECM) remodeling. This chapter provides a detailed guide on the surgical procedure to permanently ligate the LAD. Additionally, we describe a prototype method to enrich cardiac tissue for ECM, which allows one to focus on ECM remodeling in the left ventricle following surgically induced MI in mice.

Thrombospondin-4, tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14: novel extracellular matrix modulating factors in cardiac remodelling

Cardiac remodelling is defined as changes in the size, shape, and function of the heart, which are most commonly caused by hypertension-induced left ventricular hypertrophy and myocardial infarction. Both neurohumoral and inflammatory factors have critical roles in the regulation of cardiac remodelling. A characteristic feature of cardiac remodelling is modification of the extracellular matrix (ECM), often manifested by fibrosis, a process that has vital consequences for the structure and function of the myocardium. In addition to established modulators of the ECM, the matricellular protein thrombospondin-4 (TSP-4) as well as the tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 has been recently shown to modulate cardiac ECM. TSP-4 null mice develop pronounced cardiac hypertrophy and fibrosis with defects in collagen maturation in response to pressure overload. TWEAK and Fn14 belong to the tumour necrosis factor superfamily of proinflammatory cytokines. Recently it was shown that elevated levels of circulating TWEAK via Fn14 critically affect the cardiac ECM, characterized by increasing fibrosis and cardiomyocyte hypertrophy in mice. Here we review the literature concerning the role of matricellular proteins and inflammation in cardiac ECM remodelling, with a special focus on TSP-4, TWEAK, and its receptor Fn14.

Activation of natural killer T cells ameliorates postinfarct cardiac remodeling and failure in mice

RATIONALE

Chronic inflammation in the myocardium is involved in the development of left ventricular (LV) remodeling and failure after myocardial infarction (MI). Invariant natural killer T (iNKT) cells have been shown to produce inflammatory cytokines and orchestrate tissue inflammation. However, no previous studies have determined the pathophysiological role of iNKT cells in post-MI LV remodeling.

OBJECTIVE

The purpose of this study was to examine whether the activation of iNKT cells might affect the development of LV remodeling and failure.

METHODS AND RESULTS

After creation of MI, mice received the injection of either α-galactosylceramide (αGC; n=27), the activator of iNKT cells, or phosphate-buffered saline (n=31) 1 and 4 days after surgery, and were followed during 28 days. Survival rate was significantly higher in MI+αGC than MI+PBS (59% versus 32%, P<0.05). LV cavity dilatation and dysfunction were significantly attenuated in MI+αGC, despite comparable infarct size, accompanied by a decrease in myocyte hypertrophy, interstitial fibrosis, and apoptosis. The infiltration of iNKT cells were increased during early phase in noninfarcted LV from MI and αGC further enhanced them. It also enhanced LV interleukin (IL)-10 gene expression at 7 days, which persisted until 28 days. AntienIL-10 receptor antibody abrogated these protective effects of αGC on MI remodeling. The administration of αGC into iNKT cell-deficient Jα18(-/-) mice had no such effects, suggesting that αGC was a specific activator of iNKT cells.

CONCLUSIONS

iNKT cells play a protective role against post-MI LV remodeling and failure through the enhanced expression of cardioprotective cytokines such as IL-10.

Contrast-enhanced MRI of murine myocardial infarction - part I

The use of contrast agents has added considerable value to the existing cardiac MRI toolbox that can be used to study murine myocardial infarction, as it enables detailed in vivo visualization of the molecular and cellular processes that occur in the infarcted and remote tissue. A variety of non-targeted and targeted contrast agents to study myocardial infarction are available and under development. Manganese, which acts as a calcium analogue, can be used to assess cell viability. Traditionally, low-molecular-weight Gd-containing contrast agents are employed to measure infarct size in a late gadolinium enhancement experiment. Gd-based blood-pool agents are used to study the vascular status of the myocardium. The use of targeted contrast agents facilitates more detailed imaging of pathophysiological processes in the acute and chronic infarct. Cell death was visualized by contrast agents functionalized with annexin A5 that binds specifically to phosphatidylserine accessible on dying cells and with an agent that binds to the exposed DNA of dead cells. Inflammation in the myocardium was depicted by contrast agents that target cell adhesion molecules expressed on activated endothelium, by contrast agents that are phagocytosed by inflammatory cells, and by using a probe that targets enzymes excreted by inflammatory cells. Cardiac remodeling processes were visualized with a contrast agent that binds to angiogenic vasculature and with an MR probe that specifically binds to collagen in the fibrotic myocardium. These recent advances in murine contrast-enhanced cardiac MRI have made a substantial contribution to the visualization of the pathophysiology of myocardial infarction, cardiac remodeling processes and the progression to heart failure, which helps to design new treatments. This review discusses the advances and challenges in the development and application of MRI contrast agents to study murine myocardial infarction.

Matrix production and remodeling capacity of cardiomyocyte progenitor cells during in vitro differentiation

Cell-based therapy has emerged as a treatment modality for myocardial repair. Especially cardiac resident stem cells are considered a potential cell source since they are able to differentiate into cardiomyocytes and have improved heart function after injury in a preclinical model for myocardial infarction. To avoid or repair myocardial damage it is important not only to replace the lost cardiomyocytes, but also to remodel and replace the scar tissue by "healthy" extracellular matrix (ECM). Interestingly, the role of cardiac stem cells in this facet of cardiac repair is largely unknown. Therefore, we investigated the expression and production of ECM proteins, matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) in human cardiomyocyte progenitor cells (CMPCs) undergoing differentiation towards the cardiomyogenic lineage. Our data suggest that CMPCs have the capacity to synthesize and modulate their own matrix environment, especially during differentiation towards the cardiomyogenic lineage. While undifferentiated CMPCs expressed collagen I, III, IV and fibronectin, but no elastin, during the process of differentiation the expression of collagen I, III, IV and fibronectin increased and interestingly also elastin expression was induced. Furthermore, undifferentiated CMPCs express MMP-1 -2 and -9 and upon differentiation the expression of MMP-1 decreased, while the expression of MMP-2 and MMP-9, although the latter only in the early stage of differentiation, increased. Additionally, the expression of TIMP-1, -2 and -4 was induced during differentiation. This study provides new insights into the matrix production and remodeling capacity of human CMPCs, with potential beneficial effects for the treatment of cardiac injury.

Distribution of lipid-based nanoparticles to infarcted myocardium with potential application for MRI-monitored drug delivery

Adverse cardiac remodeling after myocardial infarction ultimately causes heart failure. To stimulate reparative processes in the infarct, efficient delivery and retention of therapeutic agents is desired. This might be achieved by encapsulation of drugs in nanoparticles. The goal of this study was to characterize the distribution pattern of differently sized long-circulating lipid-based nanoparticles, namely micelles (~15 nm) and liposomes (~100 nm), in a mouse model of myocardial infarction (MI). MI was induced in mice (n=38) by permanent occlusion of the left coronary artery. Nanoparticle accumulation following intravenous administration was examined one day and one week after surgery, representing the acute and chronic phase of MI, respectively. In vivo magnetic resonance imaging of paramagnetic lipids in the micelles and liposomes was employed to monitor the trafficking of nanoparticles to the infarcted myocardium. Ex vivo high-resolution fluorescence microscopy of fluorescent lipids was used to determine the exact location of the nanoparticles in the myocardium. In both acute and chronic MI, micelles permeated the entire infarct area, which renders them very suited for the local delivery of cardioprotective or anti-remodeling drugs. Liposomes displayed slower and more restricted extravasation from the vasculature and are therefore an attractive vehicle for the delivery of pro-angiogenic drugs. Importantly, the ability to non-invasively visualize both micelles and liposomes with MRI creates a versatile approach for the development of effective cardioprotective therapeutic interventions.

Decreased fibrocyte number is associated with atherosclerotic plaque instability in man

AIMS

Plaque rupture partly results from inadequate collagen synthesis due to lower smooth muscle cell numbers in fibrous caps. Fibrocytes are bone-marrow-derived circulating mesenchymal progenitors and have recently been identified in fibrous caps. This study hypothesized that reduced fibrocyte numbers would be associated with plaque instability.

METHODS AND RESULTS

Patients with acute myocardial infarction (MI) (n = 22), stable angina (SA) (n = 20), or healthy controls (n = 22) were recruited. Circulating fibrocytes (CD45(+)/CD34(+)/collagen I(+)) were measured by flow cytometry. Peripheral blood mononuclear cells (PBMCs) were isolated from blood and cultured for 2 weeks, and fibrocytes were quantified by morphology (spindle-shaped) and flow cytometry (CD45(+)/collagen I(+)). Another set of PBMCs was stimulated with macrophage colony-stimulating factor (M-CSF) for 72 h and the expression of several macrophage markers was measured by flow cytometry. Acute MI patients had decreased circulating fibrocyte numbers compared with healthy controls or SA patients. Following 2 weeks' culture, both the number of spindle-shaped fibrocytes counted under the microscope and the percentage of fibrocytes of the remaining adherent cells in culture measured by flow cytometry were reduced in acute MI patients. Expression of macrophage markers CD68, CD36, and EMR in M-CSF-stimulated PBMCs was enhanced in acute MI patients compared with the other two groups. SA patients with previous MI had decreased circulating fibrocyte numbers and a lower yield of fibrocytes from PBMCs than those without previous MI.

CONCLUSIONS

This is the first report of decreased fibrocyte numbers in patients with MI. Reduced fibrocytes and preferential differentiation of PBMCs into macrophages may contribute to plaque instability.

Low oxygen tension positively influences cardiomyocyte progenitor cell function

Previously we observed that cardiomyocyte progenitor cells (hCMPCs) isolated from the human heart differentiate spontaneously into cardiomyocytes and vascular cells when transplanted after myocardial infarction (MI) in the ischemic heart. After MI, deprivation of oxygen is the first major change in the cardiac environment. How cells handle hypoxia is highly cell type dependent. The effect of hypoxia on cardiac stem or progenitor cells remains to be elucidated. Here, we show for the first time that short- and long-term hypoxia have different effects on hCMPCs. Short-term hypoxia increased the migratory and invasive capacities of hCMPCs likely via mesenchymal transformation. Although long-term exposure to low oxygen levels did not induce differentiation of hCMPCs into mature cardiomyocytes or endothelial cells, it did increase their proliferation, stimulated the secretome of the cells which was shifted to a more anti-inflammatory profile and dampened the migration by altering matrix metalloproteinase (MMP) modulators. Interestingly, hypoxia greatly induced the expression of the extracellular matrix modulator thrombospondin-2 (TSP-2). Knockdown of TSP-2 resulted in increased proliferation, migration and MMP activity. In conclusion, short exposure to hypoxia increases migratory and invasive capacities of hCMPCs and prolonged exposure induces proliferation, an angiogenic secretion profile and dampens migration, likely controlled by TSP-2.

Cardiac biomarkers in the intensive care unit

Cardiac biomarkers (CB) were first developed for assisting the diagnosis of cardiac events, especially acute myocardial infarction. The discoveries of other CB, the better understanding of cardiac disease process and the advancement in detection technology has pushed the applications of CB beyond the 'diagnosis' boundary. Not only the measurements of CB are more sensitive, the applications have now covered staging of cardiac disease, timing of cardiac events and prognostication. Further, CB have made their way to the intensive care setting where their uses are not just confined to cardiac related areas. With the better understanding of the CB properties, CB can now help detecting various acute processes such as pulmonary embolism, sepsis-related myocardial depression, acute heart failure, renal failure and acute lung injury. This article discusses the properties and the uses of common CB, with special reference to the intensive care setting. The potential utility of "multimarkers" approach and microRNA as the future CB are also briefly discussed.

Activation of CD4+ T lymphocytes improves wound healing and survival after experimental myocardial infarction in mice

BACKGROUND

The role of adaptive immunity, especially CD4(+) T-helper cells, has not yet been systematically investigated in wound healing and remodeling after myocardial infarction (MI). Therefore, we studied whether CD4(+) T cells become activated and influence wound healing after experimental MI in mice.

METHODS AND RESULTS

When we compared sham versus MI in wild-type (WT) mice, T-cell receptor-dependent activation of both conventional Foxp3(-) and regulatory Foxp3(+) CD4(+) T cells could be demonstrated in heart-draining lymph nodes within the first week after MI. Concomitantly, we found infiltration of CD4(+) T cells in infarcted myocardium. To study the role of CD4(+) T cells in wound healing and remodeling, CD4(+) T-cell-deficient mice (CD4 knockout [KO], MHCII(Δ/Δ)) and T-cell receptor-transgenic OT-II mice recognizing an irrelevant ovalbumin-derived peptide were studied. Serial echocardiography up to day 56 after MI revealed increased left ventricular dilation in CD4 KO compared with WT mice. Within the infarcted myocardium, CD4 KO mice displayed higher total numbers of leukocytes and proinflammatory monocytes (18.3±3.0 10(4)/mg WT versus 75.7±17.0 10(4)/mg CD4 KO, P<0.05). MHCII(Δ/Δ) and OT-II mice displayed significantly greater mortality (21% WT versus 48% OT-II, P<0.05, and WT 22% versus 52% MHCII(Δ/Δ), P<0.05) and myocardial rupture rates than WT mice. Collagen matrix formation in the infarct zone was severely disturbed in CD4 KO and MHCII(Δ/Δ) mice, as well as in OT-II mice.

CONCLUSIONS

The present study provides the first evidence that CD4(+) T cells become activated after MI, presumably driven by recognition of cardiac autoantigens, and facilitate wound healing of the myocardium.

The Wnt/Frizzled pathway as a therapeutic target for cardiac hypertrophy: where do we stand?

Cardiac hypertrophy is an enlargement of the heart muscle in response to wall stress. This hypertrophic response often leads to heart failure. In recent years, several studies have shown the involvement of Wnt signalling in hypertrophic growth. In this review, the role of Wnt signalling and the possibilities for therapeutic interventions are discussed. In healthy adult heart tissue, Wnt signalling is very low. However, under pathological condition such as hypertension, Wnt signalling is activated. In recent years, it has become clear that both β-catenin-dependent signalling and β-catenin-independent signalling are involved in hypertrophic growth. Several studies, both in vitro and in vivo, have shown that genetic interventions in Wnt signalling at different levels resulted in an attenuated or diminished hypertrophic response. Therefore, inhibition of Wnt signalling could provide a new therapeutic strategy for cardiac hypertrophy, but further research on the Wnts and Frizzleds involved in the different forms of cardiac hypertrophy will be needed to achieve this goal.

A collagen α2(I) mutation impairs healing after experimental myocardial infarction

Collagen breakdown and de novo synthesis are important processes during early wound healing after myocardial infarction (MI). We tested the hypothesis that collagen I, the main constituent of the extracellular matrix, affects wound healing after MI. The osteogenesis imperfecta mouse (OIM), lacking procollagen-α2(I) expression, represents a model of the type III form of the disease in humans. Homozygous (OIM/OIM), heterozygous (OIM/WT), and wild-type (WT/WT) mice were subjected to a permanent myocardial infarction protocol or sham surgery. Baseline functional and geometrical parameters determined by echocardiography did not differ between genotypes. After MI but not after sham surgery, OIM/OIM animals exhibited significantly increased mortality, due to early ventricular rupture between day 3 and 7. Echocardiography at day 1 demonstrated increased left ventricular dilation in OIM/OIM animals. Less collagen I mRNA within the infarct area was found in OIM/OIM animals. At 2 days after MI, MMP-9 expression in the infarct border zone was higher in OIM/OIM than in WT/WT animals. Increased granulocyte infiltration into the infarct border zone occurred in OIM/OIM animals. Neither granulocyte depletion nor MMP inhibition reduced mortality in OIM/OIM animals. In this murine model, deficiency of collagen I leads to a myocardial wound-healing defect. Both structural alterations within pre-existing collagen matrix and impaired collagen de novo expression contribute to a high rate of early myocardial rupture after MI.

Interleukin-2 enhances angiogenesis and preserves cardiac function following myocardial infarction

We previously demonstrated that injection of IL-2-activated natural killer (NK) cells contribute to vascular remodeling via a4b7 integrin and killer cell lectin-like receptor (KLRG) 1 and promote cardiac repair following myocardial infarction (MI). The aim of the present study is to test the hypothesis that injection of recombinant human interleukin (rhIL)-2 improves angiogenesis and preserves heart function after MI. A single IV injection of rhIL-2 two days following MI improved by 27.7% the left ventricular (LV) fractional shortening of immune competent (C57Bl6) mice, but had no effect on cardiac function of immune-deficient (NOD-SCID IL2Rγnull) mice. Immunohistochemical analysis of C57Bl6 cross sections of heart revealed that collagen deposition was reduced by 23.1% and that capillary density was enhanced in the scar area and the border zone of the infarct respectively by 22.4% and 33.6% following rhIL-2 injection. In addition, rhIL-2 enhanced 1.6-fold the in vivo endothelial cell proliferation index and 1.8-fold the number of NK cell infiltrating the infarcted heart, but had no effect on the number of cardiac CD4 and CD8 cells. In vitro, rhIL-2 activated NK cells enhanced cardiac endothelial cell proliferation by 17.2%. Here we show that a single IV injection of rhIL-2 positively impacted cardiac function by improving angiogenesis through a process involving NK cells.

Large animal models for cardiac stem cell therapies

Cardiovascular disease is the leading cause of death in developed countries and is one of the leading causes of disease burden in developing countries. Therapies have markedly increased survival in several categories of patients, nonetheless mortality still remains high. For this reason high hopes are associated with recent developments in stem cell biology and regenerative medicine that promise to replace damaged or lost cardiac muscle with healthy tissue, and thus to dramatically improve the quality of life and survival in patients with various cardiomyopathies. Much of our insight into the molecular and cellular basis of cardiovascular biology comes from small animal models, particularly mice. However, significant differences exist with regard to several cardiac characteristics when mice are compared with humans. For this reason, large animal models like dog, sheep and pig have a well established role in cardiac research. A distinct characteristic of cardiac stem cells is that they can either be endogenous or derive from outside the heart itself; they can originate as the natural course of their differentiation programme (e.g., embryonic stem cells) or can be the result of specific inductive conditions (e.g., mesenchymal stem cells). In this review we will summarize the current knowledge on the kind of heart-related stem cells currently available in large animal species and their relevance to human studies as pre-clinical models.