Selective matrix metalloproteinase inhibition reduces left ventricular remodeling but does not inhibit angiogenesis after myocardial infarction

Reverse remodeling in heart failure--mechanisms and therapeutic opportunities

Heart failure (HF) involves changes in cardiac structure, myocardial composition, myocyte deformation, and multiple biochemical and molecular alterations that impact heart function and reserve capacity. Collectively, these changes have been referred to as 'cardiac remodeling'. Understanding the components of this process with the goal of stopping or reversing its progression has become a major objective. This concept is often termed 'reverse remodeling', and is successfully achieved by inhibitors of the renin-angiotensin-aldosterone system, β-blockers, and device therapies such as cardiac resynchronization or ventricular assist devices. Not every method of reverse remodeling has long-lasting clinical efficacy. However, thus far, every successful clinical treatment with long-term benefits on the morbidity and mortality of patients with HF reverses remodeling. Reverse remodeling is defined by lower chamber volumes (particularly end-systolic volume) and is often accompanied by improved β-adrenergic and heart-rate responsiveness. At the cellular level, reverse remodeling impacts on myocyte size, function, excitation-contraction coupling, bioenergetics, and a host of molecular pathways that regulate contraction, cell survival, mitochondrial function, oxidative stress, and other features. Here, we review the current evidence for reverse remodeling by existing therapies, and discuss novel approaches that are rapidly moving from preclinical to clinical trials.

Donepezil, anti-Alzheimer's disease drug, prevents cardiac rupture during acute phase of myocardial infarction in mice

BACKGROUND

We have previously demonstrated that the chronic intervention in the cholinergic system by donepezil, an acetylcholinesterase inhibitor, plays a beneficial role in suppressing long-term cardiac remodeling after myocardial infarction (MI). In comparison with such a chronic effect, however, the acute effect of donepezil during an acute phase of MI remains unclear. Noticing recent findings of a cholinergic mechanism for anti-inflammatory actions, we tested the hypothesis that donepezil attenuates an acute inflammatory tissue injury following MI.

METHODS AND RESULTS

In isolated and activated macrophages, donepezil significantly reduced intra- and extracellular matrix metalloproteinase-9 (MMP-9). In mice with MI, despite the comparable values of heart rate and blood pressure, the donepezil-treated group showed a significantly lower incidence of cardiac rupture than the untreated group during the acute phase of MI. Immunohistochemistry revealed that MMP-9 was localized at the infarct area where a large number of inflammatory cells including macrophages infiltrated, and the expression and the enzymatic activity of MMP-9 at the left ventricular infarct area was significantly reduced in the donepezil-treated group.

CONCLUSION

The present study suggests that donepezil inhibits the MMP-9-related acute inflammatory tissue injury in the infarcted myocardium, thereby reduces the risk of left ventricular free wall rupture during the acute phase of MI.

Matrix metalloproteinases as drug targets in ischemia/reperfusion injury

Deficient blood supply (ischemia) is a common consequence of some surgical procedures and certain pathologies. Once blood circulation is re-established (reperfusion), a complex series of events results in recruitment of inflammatory cells, rearrangement of the extracellular matrix and induction of cell death, which lead to organ dysfunction. Although ischemia/reperfusion (I/R) injury is an important cause of death, there is no effective therapy targeting the molecular mechanism of disease progression. Matrix metalloproteinases (MMPs), which are important regulators of many cellular activities, have a central role in disease progression after I/R injury, as suggested by numerous studies using MMP inhibitors or MMP-deficient mice. Here, we review the involvement of MMP activity in the various processes following I/R injury and the therapeutic potential of MMP inhibition.

Tissue inhibitor of metalloproteinase-2 gene delivery ameliorates postinfarction cardiac remodeling

HYPOTHESIS

Adenoviral-mediated (AdV-T2) overexpression of TIMP-2 would blunt ventricular remodeling and improve survival in a murine model of chronic ischemic injury.

METHODS

Male mice (n = 124) aged 10-14 weeks underwent either (1) left coronary artery ligation to induce myocardial infarction (MI group, n = 36), (2) myocardial injection of 6 × 10¹⁰ viral particles of AdV-T2 immediately post-MI (MI + T2 group, n = 30), (3) myocardial injection of 6 × 10¹⁰ viral particles of a control adenovirus (MI + Ct, n = 38), or 4) received no intervention (controls, n = 20). On post-MI day 7, surviving mice (n = 79) underwent echocardiographic, immunohistochemical, and biochemical analysis.

RESULTS

In infarcted animals, the MI + T2 group demonstrated improved survival (p < 0.02), better preservation of developed pressure and ventricular diameter (p < 0.04), and the lowest expression and activity of MMP-2 and MMP-9 (p < 0.04) compared with MI and MI + Ct groups. All infarcted hearts displayed significantly increased inflammatory cell infiltration (p < 0.04 vs. control, MI, or MI + T2), with infiltration highest in the MI + Ct group and lowest in the MI + T2 group (p < 0.04).

CONCLUSIONS

Adenoviral mediated myocardial delivery of the TIMP-2 gene improves post-MI survival and limits adverse remodeling in a murine model of MI.

Plasma TIMP-4 predicts left ventricular remodeling after acute myocardial infarction

BACKGROUND

Alterations in the balance between matrix metalloproteinases and their endogenous tissue inhibitors (TIMPs) are associated with left ventricular (LV) remodeling after acute myocardial infarction (AMI). No relationships have been identified between TIMPs and serial postinfarction change in LV function.

METHODS AND RESULTS

Plasma concentrations of TIMP-1, -2, -4 were measured at baseline (mean 46 h) and at 24 weeks in 100 patients (age 58.9 ± 12 years, 77% male) admitted with AMI and LV dysfunction, with cardiac magnetic resonance imaging at each time point. TIMP-1 concentration was reduced, whereas TIMP-2 and -4 concentrations were elevated at baseline compared with a reference control population. TIMP-1 decreased and TIMP-2 increased significantly over time; there was an incremental trend in TIMP-4 concentration. Baseline TIMP-4 correlated with change in LV end-systolic volume index (∆LVESVI; r = 0.24; P = .023) and change in LV end-diastolic volume index (∆LVEDVI; r = 0.25; P = .015). ∆TIMP-4 also correlated with ∆LVESVI and with ∆LVEDVI, as did ∆TIMP-2. On multivariable analysis, baseline TIMP-4 concentration was an independent predictor of ∆LVESVI.

CONCLUSIONS

Plasma TIMP-4 concentration, measured early after AMI, may assist in the prediction of LV remodeling and therefore in the assessment of prognosis. Further study of the role of the TIMPs in the pathophysiology of postinfarction remodeling is warranted.

Noninvasive monitoring the biology of atherosclerotic plaque development with radiolabeled annexin V and matrix metalloproteinase inhibitor in spontaneous atherosclerotic mice

OBJECTIVES

To compare the ability of (99m)Tc-labeled broad-based matrix metalloproteinase inhibitor (RP805) (MPI) and (99m)Tc-annexin V to identify more advanced atherosclerotic disease in apolipoprotein E-null (apoE(-/-)) mice.

BACKGROUND

Both MMP expression and apoptotic cell death occur in both early and in advanced atherosclerotic plaques.

METHODS

Eight 6-9-week-old apoE(-/-) mice, 10 apoE(-/-) mice at 20 weeks, and 12 apoE(-/-) at 40 weeks were injected with both tracers in alternating sequence separated by 48 h, underwent planar imaging and were killed. Radiotracer uptake was quantified from the scans as percent whole body and from tissue as percent injected dose per gram (%ID/g). Quantitative immunohistopathology of the aorta and carotids for macrophages, MMPs, and caspase was performed.

RESULTS

At 6 weeks, mice showed no tracer uptake in the chest or neck and had minimal lesion. At 20 weeks, uptake of annexin V as %ID was borderline higher than MPI (1.10 ± .48% vs .77 ± .31%, P = .09), between 20 and 40 weeks aortic lesion area increased from 37.4 ± 12.0% to 46.2 ± 7.4% and at 40 weeks MPI was significantly greater than annexin V uptake (1.11 ± .66% vs .70 ± .16%, P = .05). On histology there were greater increases in % MMP-2 and -9 than % caspase positive cells. Carotid uptake of MPI was greater than annexin V at both 20 and 40 weeks (1.25 ± .48% vs .78 ± .25%, P = .02 and 3.70 ± 1.45% vs 2.25 ± .66%, P = .005). The carotid lesion area at 40 weeks was 74 ± 9% with greater % cells positive for MMP's than caspase. %ID/g annexin V correlated significantly with % macrophages and with caspase-3 positive cells and %ID/g MPI correlated significantly with % macrophages and with MMP-2 and -9 positive cells.

CONCLUSIONS

In apoE(-/-) mice, MMP expression is greater than apoptosis as the disease progresses and MPI may be a better imaging agent for more advanced disease.

Induction of cardiac angiogenesis requires killer cell lectin-like receptor 1 and α4β7 integrin expression by NK cells

Recent findings indicate that NK cells are involved in cardiac repair following myocardial infarction. The aim of this study is to investigate the role NK cells in infarct angiogenesis and cardiac remodeling. In normal C57BL/6 mice, myelomonocytic inflammatory cells invaded infarcted heart within 24 h followed by a lymphoid/NK cell infiltrate by day 6, accompanied by substantial expression of IL-2, TNF-α, and CCL2. In contrast, NOD SCID mice had virtually no lymphoid cells infiltrating the heart and did not upregulate IL-2 levels. In vitro and in vivo, IL-2-activated NK cells promoted TNF-α-stimulated endothelial cell proliferation, enhanced angiogenesis and reduced fibrosis within the infarcted myocardium. Adoptive transfer of IL-2-activated NK cells to NOD SCID mice improved post-myocardial infarction angiogenesis. RNA silencing technology and neutralizing Abs demonstrated that this process involved α4β7 integrin/VCAM-1 and killer cell lectin-like receptor 1/N-cadherin-specific binding. In this study, we show that IL-2-activated NK cells reduce myocardial collagen deposition along with an increase in neovascularization following acute cardiac ischemia through specific interaction with endothelial cells. These data define a potential role of activated NK cells in cardiac angiogenesis and open new perspectives for the treatment of ischemic diseases.

ACE inhibitors in cardiac surgery: current studies and controversies

Major complications associated with cardiac surgery are still common and carry great prognostic significance. Current medical interventions to prevent these cardiovascular complications include antiplatelet therapy, statins, β-blockers and angiotensin-converting enzyme (ACE) inhibitors. Both experimental studies and clinical trials have shown that ACE inhibitors hold promise as cardiovascular protective agents for cardiac surgery patients. Several lines of evidence support this hypothesis. First, long-term use of ACE inhibitors has been well established to provide cardiovascular protection and reduce ischemic events and complications, independent of their effect on heart function and blood pressure. Second, early ACE inhibitor therapy has been demonstrated to produce remarkable survival and heart function benefits in patients with acute myocardial infarction. Third, ACE blockage can prevent or delay the development or progression of renal disease at all stages, from subclinical microalbuminuria to end-stage renal disease. Nevertheless, perioperative studies of the effects of ACE inhibitors remain few and inconclusive. Results from recent clinical trials and observational studies are conflicting and raise more questions than answers. Further studies, both retrospective and larger-scale prospective studies, are critically needed to examine whether ACE inhibitors reduce mortality and major complications in patients undergoing cardiac surgery.

Proteomic analysis identifies in vivo candidate matrix metalloproteinase-9 substrates in the left ventricle post-myocardial infarction

Matrix metalloproteinase-9 (MMP-9) deletion has been shown to improve remodeling of the left ventricle post-myocardial infarction (MI), but the mechanisms to explain this improvement have not been fully elucidated. MMP-9 has a broad range of in vitro substrates, but relevant in vivo substrates are incompletely defined. Accordingly, we evaluated the infarct regions of wild-type (wt) and MMP-9 null (null) mice using a proteomic strategy. Wt and null groups showed similar infarct sizes (48+/-3 in wt and 45+/-3% in null), indicating that both groups received an equal injury stimulus. Left ventricle infarct tissue was homogenized and analyzed by 2-DE and MS. Of 31 spot intensity differences, the intensities of 9 spots were higher and 22 spots were lower in null mice compared to wt (all p<0.05). Several extracellular matrix proteins were identified in these spots by MS, including fibronectin, tenascin-C, thrombospondin-1, and laminin. Fibronectin was observed on the gels at a lower than expected molecular weight in the wt group, which suggested substrate cleavage, and the lower molecular weight spot was observed at lower intensity in the MMP-9 null group, which suggested cleavage by MMP-9. Immunoblotting confirmed the presence of fibronectin cleavage products in the wt samples and lower levels in the absence of MMP-9. In conclusion, examining infarct tissue from wt and MMP-9 null mice by proteomic analysis provides a powerful and unique method to identify in vivo candidate MMP substrates.

Periostin advances atherosclerotic and rheumatic cardiac valve degeneration by inducing angiogenesis and MMP production in humans and rodents

Valvular heart disease (VHD) is the term given to any disease process involving one or more of the heart valves. The condition can be congenital or acquired, for example as a result of atherosclerosis or rheumatic fever. Despite its clinical importance, the molecular mechanisms underlying VHD remain unknown. We investigated the pathophysiologic role and molecular mechanism of periostin, a protein that plays critical roles in cardiac valve development, in degenerative VHD. Unexpectedly, we found that periostin levels were drastically increased in infiltrated inflammatory cells and myofibroblasts in areas of angiogenesis in human atherosclerotic and rheumatic VHD, whereas periostin was localized to the subendothelial layer in normal valves. The expression patterns of periostin and chondromodulin I, an angioinhibitory factor that maintains cardiac valvular function, were mutually exclusive. In WT mice, a high-fat diet markedly increased aortic valve thickening, annular fibrosis, and MMP-2 and MMP-13 expression levels, concomitant with increased periostin expression; these changes were attenuated in periostin-knockout mice. In vitro and ex vivo studies revealed that periostin promoted tube formation and mobilization of ECs. Furthermore, periostin prominently increased MMP secretion from cultured valvular interstitial cells, ECs, and macrophages in a cell type-specific manner. These findings indicate that, in contrast to chondromodulin I, periostin plays an essential role in the progression of cardiac valve complex degeneration by inducing angiogenesis and MMP production.

Spatiotemporal induction of matrix metalloproteinase-9 transcription after discrete myocardial injury

Radiofrequency (RF) ablation of the myocardium causes discrete sites of injury. RF scars can expand, altering the extracellular matrix (ECM) structure and the continuity of the electrical syncytium of the adjacent myocardium. Matrix metalloproteinases (MMPs), such as MMP-9, contribute to ECM remodeling. However, whether and to what degree transcriptional induction of MMP-9 occurs after myocardial RF injury and the association with electrical conduction patterns after RF injury remains unexplored. This study examined MMP-9 gene promoter (M9PROM) activation after myocardial RF injury using mice in which the M9PROM was fused to a β-galactosidase (β-gal) reporter. RF lesions (0.5-mm probe, 80°C, 30 s) were created on the left ventricular (LV) epicardium of M9PROM mice (n=62) and terminally studied at 1 h, 1 d, 3 d, 7 d, 14 d, and 28 d after RF injury. M9PROM activation was localized through β-gal staining. The RF scar area and the area of β-gal staining were measured and normalized to LV area (planimetry). RF scar size increased from 1 h post-RF-injury values by 7 d and remained higher at 28 d. M9PROM activation became evident at 3 d and peaked at 7 d. Electrical conduction was measured (potentiometric dye mapping) at 7 d after RF injury. Heterogeneities in action potentials and electrical impulse propagation coincident with M9PROM activation were observed after RF injury. For example, conduction proximal to the RF site was slower than that in the remote myocardium (0.15±0.02 vs. 0.83±0.08 mm/ms, P<0.05). Thus, a unique spatiotemporal pattern of MMP-9 transcriptional activation occurred after discrete myocardial injury, which was associated with the development of electrical heterogeneity. Therefore, these findings suggest that changes in a key determinant of extracellular matrix remodeling, in addition to changes in myocardial structure, can contribute to arrhythmogenesis around the region of myocardial injury.

HO-1 modified mesenchymal stem cells modulate MMPs/TIMPs system and adverse remodeling in infarcted myocardium

The present study was to determine the effects of the heme oxygenase-1 (HO-1) modified mesenchymal stem cells (MSCs) transplantation into acute MI hearts on normalizing the ratio of MMPs/TIMPs and remodeling in infarcted myocardium. HO-1 was transfected into cultured MSCs using an adenoviral vector. 1 x 10(6) Ad-HO-1-transfected MSCs (HO-1-MSCs) or Ad-Null-transfected MSCs (Null-MSCs) or PBS was respectively injected into rat hearts 1 h intramyocardially after myocardial infarction. The cardiac performance was significantly improved and left ventricular dilatation was significantly attenuated in HO-1-MSCs transplanted hearts. Moreover, a significant increase in microvessel density was observed in HO-1-MSCs transplanted hearts. TIMP2,3 expression in HO-1-MSCs transplanted hearts was significantly increased, and MMP2,9 expression in HO-1-MSCs transplanted hearts was significantly lower than Null-MSCs transplanted and PBS-treated hearts. TIMP1 expression did not vary significantly. Null-MSCs transplantation did not decrease the expression of MMP2,9 significantly compared with PBS-treated hearts. The ratio of TIMP2 to MMP2, and TIMP3 to MMP9 in cell-grafted hearts was increased significantly. HO-1-MSCs transplantation normalize the ratio of MMPs/TIMPs, contributing to the reversion of myocardial extracellular remodeling.

Advances in radionuclide molecular imaging in myocardial biology

Molecular imaging is a new and evolving field that employs a targeted approach to noninvasively assess biologic processes in vivo. By assessing key elements in specific cellular processes prior to irreversible end-organ damage, molecular tools will allow for earlier detection and intervention, improving management and outcomes associated with cardiovascular diseases. The goal of those working to expand this field is not just to provide diagnostic and prognostic information, but rather to guide an individual's pharmacological, cell-based, or genetic therapeutic regimen. This article will review molecular imaging tools in the context of our current understanding of biological processes of the myocardium, including angiogenesis, ventricular remodeling, inflammation, and apoptosis. The focus will be on radiotracer-based molecular imaging modalities with an emphasis on clinical application. Though this field is still in its infancy and may not be fully ready for widespread use, molecular imaging of myocardial biology has begun to show promise of clinical utility in acute and chronic ischemia, acute myocardial infarction, congestive heart failure, as well as in more global inflammatory and immune-mediated responses in the heart-like myocarditis and allogeneic cardiac transplant rejection. With continued research and development, molecular imaging promises to be an important tool for the optimization of cardiovascular care.

Emerging concepts in cardiac matrix biologyThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

The cardiac extracellular matrix, far from being merely a static support structure for the heart, is now recognized to play central roles in cardiac development, morphology, and cell signaling. Recent studies have better shaped our understanding of the tremendous complexity of this active and dynamic network. By activating intracellular signal cascades, the matrix transduces myocardial physical forces into responses by myocytes and fibroblasts, affecting their function and behavior. In turn, cardiac fibroblasts and myocytes play active roles in remodeling the matrix. Coupled with the ability of the matrix to act as a dynamic reservoir for growth factors and cytokines, this interplay between the support structure and embedded cells has the potential to exert dramatic effects on cardiac structure and function. One of the clearest examples of this occurs when cell–matrix interactions are altered inappropriately, contributing to pathological fibrosis and heart failure. This review will examine some of the recent concepts that have emerged regarding exactly how the cardiac matrix mediates these effects, how our collective vision of the matrix has changed as a result, and the current state of attempts to pharmacologically treat fibrosis.

Effects of myosin heavy chain manipulation in experimental heart failure

The myosin heavy chain (MHC) isoforms, alpha- and beta-MHC, are expressed in developmental- and chamber-specific patterns. Healthy human ventricle contains approximately 2-10% alpha-MHC and these levels are reduced even further in the failing ventricle. While down-regulation of alpha-MHC in failing myocardium is considered compensatory, we previously demonstrated that persistent transgenic (TG) alpha-MHC expression in the cardiomyocytes is cardioprotective in rabbits with tachycardia-induced cardiomyopathy (TIC). We sought to determine if this benefit extends to other types of experimental heart failure and focused on two models relevant to human heart failure: myocardial infarction (MI) and left ventricular pressure overload. TG and nontransgenic rabbits underwent either coronary artery ligation at 8 months or aortic banding at 10 days of age. The effects of alpha-MHC expression were assessed at molecular, histological and organ levels. In the MI experiments, we unexpectedly found modest functional advantages to alpha-MHC expression. In contrast, despite subtle benefits in TG rabbits subjected to aortic banding, cardiac function was minimally affected. We conclude that the benefits of persistent alpha-MHC expression depend upon the mechanism of heart failure. Importantly, in none of the scenarios studied did we find any detrimental effects associated with persistent alpha-MHC expression. Thus manipulation of MHC composition may be beneficial in certain types of heart failure and does not appear to compromise heart function in others. Future considerations of myosin isoform manipulation as a therapeutic strategy should consider the underlying etiology of cardiac dysfunction.

TIMPs and cardiac remodeling: 'Embracing the MMP-independent-side of the family'

Unraveling the biological role of tissue inhibitors of metalloproteinases (TIMPs) during cardiac remodeling and the progression of heart failure has proven to be an enormous challenge. Remodeling of the cardiac extracellular matrix (ECM), regulated by matrix metalloproteinases (MMPs) and their endogenous inhibitors, TIMPs, is a well-established paradigm in cardiac health and disease. Originally, TIMPs were thought to function exclusively as endogenous inhibitors of MMP activity, thereby fine-tuning MMP-mediated ECM degradation and numerous related processes. However, during the last two decades, the concept of MMP-independent TIMP-mediated receptor signaling and regulation of cell fate has emerged. Although our current knowledge is still limited, in this review, we highlight some of the novel data, illustrating the MMP-independent biological properties of the four TIMP family members. Moreover, we discuss how these cell-specific insights may contribute to the process of cardiac remodeling, disease and failure. Finally, we identify where additional research is needed that will codetermine the possible future of TIMPs as therapeutic targets.

The extracellular matrix as a modulator of the inflammatory and reparative response following myocardial infarction

The dynamic alterations in the cardiac extracellular matrix following myocardial infarction not only determine the mechanical properties of the infarcted heart, but also directly modulate the inflammatory and reparative response. During the inflammatory phase of healing, rapid activation of Matrix Metalloproteinases (MMP) causes degradation of the cardiac extracellular matrix. Matrix fragments exert potent pro-inflammatory actions, while MMPs process cytokines and chemokines altering their biological activity. In addition, vascular hyperpermeability results in extravasation of fibronectin and fibrinogen leading to formation of a plasma-derived provisional matrix that serves as a scaffold for leukocyte infiltration. Clearance of the infarct from dead cells and matrix debris is essential for resolution of inflammation and marks the transition to the proliferative phase. The fibrin-based provisional matrix is lysed and cellular fibronectin is secreted. ED-A fibronectin, mechanical tension and Transforming Growth Factor (TGF)-beta are essential for modulation of fibroblasts into myofibroblasts, the main collagen-secreting cells in the wound. The matricellular proteins thrombospondin-1 and -2, osteopontin, tenascin-C, periostin, and secreted protein acidic and rich in cysteine (SPARC) are induced in the infarct regulating cellular interactions and promoting matrix organization. As the infarct matures, matrix cross-linking results in formation of a dense collagen-based scar. At this stage, shielding of fibroblasts from external mechanical tension by the mature matrix network may promote deactivation and cellular quiescence. The components of the extracellular matrix do not passively follow the pathologic alterations of the infarcted heart but critically modulate inflammatory and reparative pathways by transducing signals that affect cell survival, phenotype and gene expression.

Extracellular matrix remodeling during the progression of volume overload-induced heart failure

Volume overload-induced heart failure results in progressive left ventricular remodeling characterized by chamber dilation, eccentric cardiac myocyte hypertrophy and changes in extracellular matrix (ECM) remodeling changes. The ECM matrix scaffold is an important determinant of the structural integrity of the myocardium and actively participates in force transmission across the LV wall. In response to this hemodynamic overload, the ECM undergoes a distinct pattern of remodeling that differs from pressure overload. Once thought to be a static entity, the ECM is now regarded to be a highly adaptive structure that is dynamically regulated by mechanical stress, neurohormonal activation, inflammation and oxidative stress, that result in alterations in collagen and other matrix components and a net change in matrix metalloproteinase (MMP) expression and activation. These changes dictate overall ECM turnover during volume overload hear failure progression. This review will discuss the cellular and molecular mechanisms that dictate the temporal patterns of ECM remodeling during heart disease progression.

New molecular imaging targets to characterize myocardial biology

Molecular imaging represents a targeted approach to noninvasively assess biologic (both physiologic and pathologic) processes in vivo. Ideally the goal of molecular imaging is not just to provide diagnostic and prognostic information based on identification of the molecular events associated with a pathologic process but rather to guide individually tailored pharmacologic, cell-based, or genetic therapeutic regimens. This article reviews the recent advances in myocardial molecular imaging in the context of the cardiovascular processes of angiogenesis, apoptosis, inflammation, and ventricular remodeling. The focus is on radiotracer-based single photon emission computed tomography and positron emission tomography molecular imaging approaches.

IL-10 inhibits inflammation and attenuates left ventricular remodeling after myocardial infarction via activation of STAT3 and suppression of HuR

Persistent inflammatory response has adverse effects on left ventricular (LV) function and remodeling following acute myocardial infarction. We hypothesized that suppression of inflammation with interleukin (IL)-10 treatment attenuates LV dysfunction and remodeling after acute myocardial infarction. After the induction of acute myocardial infarction, mice were treated with either saline or recombinant IL-10, and inflammatory response and LV functional and structural remodeling changes were evaluated. IL-10 significantly suppressed infiltration of inflammatory cells and expression of proinflammatory cytokines in the myocardium. These changes were associated with IL-10-mediated inhibition of p38 mitogen-activated protein kinase activation and repression of the cytokine mRNA-stabilizing protein HuR. IL-10 treatment significantly improved LV functions, reduced infarct size, and attenuated infarct wall thinning. Myocardial infarction-induced increase in matrix metalloproteinase (MMP)-9 expression and activity was associated with increased fibrosis, whereas IL-10 treatment reduced both MMP-9 activity and fibrosis. Small interfering RNA knockdown of HuR mimicked IL-10-mediated reduction in MMP-9 expression and activity in NIH3T3 cells. Moreover, IL-10 treatment significantly increased capillary density in the infarcted myocardium which was associated with enhanced STAT3 phosphorylation. Taken together, our studies demonstrate that IL-10 suppresses inflammatory response and contributes to improved LV function and remodeling by inhibiting fibrosis via suppression of HuR/MMP-9 and by enhancing capillary density through activation of STAT3.

Potential novel pharmacological therapies for myocardial remodelling

Left ventricular (LV) remodelling remains an important treatment target in patients after myocardial infarction (MI) and chronic heart failure (CHF). Accumulating evidence has supported the concept that beneficial effects of current pharmacological treatment strategies to improve the prognosis in these patients, such as angiotensin-converting enzyme (ACE) inhibition, angiotensin type 1 receptor blocker therapy, and beta-blocker therapy, are related, at least in part, to their effects on LV remodelling and dysfunction. However, despite modern reperfusion therapy after MI and optimized treatment of patients with CHF, LV remodelling is observed in a substantial proportion of patients and is associated with an adverse clinical outcome. These observations call for novel therapeutic strategies to prevent or even reverse cardiac remodelling. Recent insights from experimental studies have provided new targets for interventions to prevent or reverse LV remodelling, i.e. reduced endothelial nitric oxide (NO) synthase-derived NO availability, activation of cardiac and leukocyte-dependent oxidant stress pathways, inflammatory pathway activation, matrix-metalloproteinase activation, or stem cell transfer and delivery of novel paracrine factors. An important challenge in translating these observations from preclinical studies into clinical treatment strategies relates to the fact that clinical studies are designed on top of established pharmacological therapy, whereas most experimental studies have tested novel interventions without concomitant drug regimens such as ACE inhibitors or beta-blockers. Therefore, animal studies may overestimate the effect of potential novel treatment strategies on LV remodelling and dysfunction, since established pharmacological therapies may act, in part, via identical or similar signalling pathways. Nevertheless, preclinical studies provide essential information for identifying potential novel targets, and their potential drawbacks, and are required for developing novel clinical treatment strategies to prevent or reverse LV remodelling and dysfunction.

Plasma tissue inhibitor of metalloproteinase-1 and matrix metalloproteinase-9: novel indicators of left ventricular remodelling and prognosis after acute myocardial infarction

AIMS

Matrix metalloproteinase (MMP) activity is central to the development of left ventricular (LV) remodelling and dysfunction after acute myocardial infarction (AMI). We assessed the relationships with LV structure and function and outcome, of tissue inhibitors of metalloproteinase-1 (TIMP-1) and MMP-9, and compared with N-terminal pro-B-type natriuretic peptide (NTproBNP).

METHODS AND RESULTS

We studied 404 patients with AMI. Primary outcome measures were the associations of TIMP-1, MMP-9, and NTproBNP with death or heart failure, and with LV dimensions, function and remodelling (ΔLVEDV, change in LV end-diastolic volume between discharge and follow-up). Cut-off concentrations for prediction of death or heart failure were identified from receiver operator characteristic (ROC) curves. In multivariable analysis, TIMP-1 and NTproBNP had predictive value for LV ejection fraction pre-discharge (TIMP-1 P = 0.023; N-BNP P = 0.007) and at follow-up (TIMP-1 P = 0.001; N-BNP P = 0.003). MMP-9, TIMP-1, and NTproBNP correlated directly with LV volumes. MMP-9 (P = 0.005) and TIMP-1 (P = 0.036), but not NTproBNP, correlated with ΔLVEDV. For the combined endpoint of death or heart failure the area under the ROC curve was 0.640 for MMP-9, 0.799 for NTproBNP and 0.811 for TIMP-1. Patients with TIMP-1 > 135 ng/mL (P < 0.001) or NTproBNP >1472 fmol/mL (P < 0.001) had increased risk of endpoint. Consideration of both NTproBNP and TIMP-1 further improved risk stratification.

CONCLUSION

TIMP-1 and MMP-9 correlate with echocardiographic parameters of LV dysfunction and remodelling after AMI and may identify patients at risk of subsequent LV remodelling and adverse prognosis.

Inhibitory profiles of captopril on matrix metalloproteinase-9 activity

To investigate the inhibitory profiles of angiotensin-converting enzyme (ACE) inhibitors on matrix metalloproteinase-9 (MMP-9) activity, the inhibitory activity and molecular interaction of captopril on human MMP-9 were studied. Plasma MMP-9 and ACE activities in samples from patient with acute myocardial infarction were similarly inhibited by captopril. Molecular models showed that captopril directly bound to the MMP-9 active center. Compared with the other ACE inhibitors, the compact structure of captopril seemed to make the inhibitory profiles on the MMP-9 active site.

Serum matrix metalloproteinase-3 as a novel marker for risk stratification of patients with nonischemic dilated cardiomyopathy

BACKGROUND

Selective induction of myocardial matrix metalloproteinases (MMPs) has been reported to occur in human nonischemic dilated cardiomyopathy (DCM). We aimed to evaluate the utility of serum MMPs for risk stratification of patients with DCM.

METHODS AND RESULTS

We measured serum levels of MMP-2, MMP-3, and MMP-9 using enzyme-linked immunosorbent assay in 71 patients with mild to moderate DCM (left ventricular ejection fraction = 28.3 +/- 11.5%). The primary end point was the composite incidence of cardiac death and hospitalizations for worsening heart failure. During the follow-up period (mean, 28 +/- 16 months), 19 patients had major cardiac events with sudden cardiac death in 6 cases and hospitalizations for worsening heart failure in 13 cases. Multivariate analysis revealed that MMP-3 and B-type natriuretic peptide were significant independent predictors of cardiac events in patients with DCM (hazard ratio 1.41, P = .012; hazard ratio 2.72, P = .048, respectively). According to the Kaplan-Meier analyses of cumulative cardiac event-free rates of the two groups that were based on the median levels of MMPs, the differences in the cardiac event-free curves were significant only for MMP-3 (P = .009). Moreover, patients with elevations of both MMP-3 and B-type natriuretic peptide were found to have the poorest prognosis.

CONCLUSION

Our results may address the utility of serum MMP-3 for risk stratification of patients with DCM.

Circulating stromelysin-1 (MMP-3): a novel predictor of LV dysfunction, remodelling and all-cause mortality after acute myocardial infarction

INTRODUCTION

Changes to cardiac matrix are central to ventricular remodelling after acute MI and matrix metalloproteinase expression is implicated in this process. We investigated the temporal profile of MMP-3 and its relationship to LV dysfunction and prognosis following AMI.

METHODS

We studied 382 patients with AMI. Plasma MMP-3 was measured at 0-12, 12-24 h and for subsequent 24 h periods during admission. LV function (LVEF) was assessed by echocardiography pre-discharge and at a median of 148 days and clinical endpoints at a median of 313 days.

RESULTS

MMP-3 peaked prior to discharge thus pre-discharge levels were used in analyses. MMP-3 was associated with patient age (p<0.001), creatinine (p<0.001) and was higher in males (p<0.001) and hypertensives (p<0.001). MMP-3 inversely correlated with LVEF at follow-up (p=0.043), was higher in subjects with LVEF <40% (p=0.017) and in subjects with increasing EDV (p=0.017) or ESV (p=0.007) compared to those in whom volumes fell between visits. In the 58 patients reaching the endpoint of death or heart failure, MMP-3 was higher (p<0.001). On Kaplan-Meier analysis, subjects with levels above optimum cut off identified via ROC curves were more likely to suffer a clinical event (p=0.037).

CONCLUSION

MMP-3 is associated with left ventricular dysfunction, adverse left ventricular remodelling and prognosis after AMI.

Effects of chronic therapy with cardiac contractility modulation electrical signals on cytoskeletal proteins and matrix metalloproteinases in dogs with heart failure

OBJECTIVES

Therapy with cardiac contractility modulation (CCM) electrical signals delivered to left ventricular (LV) muscle during the absolute refractory period improves LV systolic and diastolic function in dogs with heart failure (HF). This study examined the effects of CCM therapy on mRNA and protein expression of cytoskeletal proteins, matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) in the LV myocardium of dogs with HF.

METHODS

HF was produced in 14 dogs by coronary microembolizations. Dogs were randomized to 3 months of CCM therapy (n = 7) or to sham-operated controls (n = 7). LV tissue from 6 normal (NL) dogs was used for comparison. mRNA expression was measured using reverse-transcriptase polymerase chain reaction and protein expression using Western blots.

RESULTS

Compared with NL dogs, controls showed upregulation of mRNA and protein expression of the cytoskeletal proteins tubulin and fibronectin and MMP-1, MMP-2 and MMP-9, and downregulation of the cytoskeletal protein titin. Normalized expression of all these genes and proteins was seen after CCM therapy. No differences in expression of TIMP-1 and TIMP-2 were observed among groups.

CONCLUSIONS

CCM therapy normalizes expression of key cytoskeletal proteins and MMPs and may partly explain the improvement in LV function seen in HF following CCM therapy.

Efferent vagal nerve stimulation induces tissue inhibitor of metalloproteinase-1 in myocardial ischemia-reperfusion injury in rabbit

Vagal nerve stimulation has been suggested to ameliorate left ventricular (LV) remodeling in heart failure. However, it is not known whether and to what degree vagal nerve stimulation affects matrix metalloproteinase (MMP) and tissue inhibitor of MMP (TIMP) in myocardium, which are known to play crucial roles in LV remodeling. We therefore investigated the effects of electrical stimulation of efferent vagal nerve on myocardial expression and activation of MMPs and TIMPs in a rabbit model of myocardial ischemia-reperfusion (I/R) injury. Anesthetized rabbits were subjected to 60 min of left coronary artery occlusion and 180 min of reperfusion with (I/R-VS, n = 8) or without vagal nerve stimulation (I/R, n = 7). Rabbits not subjected to coronary occlusion with (VS, n = 7) or without vagal stimulation (sham, n = 7) were used as controls. Total MMP-9 protein increased significantly after left coronary artery occlusion in I/R-VS and I/R to a similar degree compared with VS and sham values. Endogenous active MMP-9 protein level was significantly lower in I/R-VS compared with I/R. TIMP-1 mRNA expression was significantly increased in I/R-VS compared with the I/R, VS, and sham groups. TIMP-1 protein was significantly increased in I/R-VS and VS compared with the I/R and sham groups. Cardiac microdialysis technique demonstrated that topical perfusion of acetylcholine increased dialysate TIMP-1 protein level, which was suppressed by coperfusion of atropine. Immunohistochemistry demonstrated a strong expression of TIMP-1 protein in cardiomyocytes around the dialysis probe used to perfuse acetylcholine. In conclusion, in a rabbit model of myocardial I/R injury, vagal nerve stimulation induced TIMP-1 expression in cardiomyocytes and reduced active MMP-9.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

Significance of matrix metalloproteinase-9 in cardiac dysfunction during the very acute phase after myocardial infarction in hamsters

Matrix metalloproteinase-9 activity is dramatically increased during the acute phase after myocardial infarction. However, the relationship between matrix metalloproteinase-9 activity and cardiac dysfunction is unclear. In 1-day post-myocardial infarction hamsters, matrix metalloproteinase-9 activity was significantly increased, while matrix metalloproteinase-2 activity was not increased. A selective matrix metalloproteinase inhibitor, [2S,4S]-N-Hydroxy-5-ethoxymethyloxy-2-methyl-4-[4-phenoxybenzoyl] aminopentanamide (ONO-4817), significantly suppressed matrix metalloproteinase-9 activity 1 day after myocardial infarction. ONO-4817 also significantly prevented the development of cardiac dysfunction and left-ventricular dilatation. Matrix metalloproteinase-9 might play a crucial role in cardiac dysfunction and left-ventricular dilatation during the very acute phase after myocardial infarction.

Matrix metalloproteinases in cardiovascular disease

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that are regulated by inflammatory signals to mediate changes in extracellular matrix. Members of the MMP family share sequence homology, act on interstitial protein substrates, acutely participate in inflammatory processes and chronically mediate tissue remodelling. MMPs are important in vascular remodelling, not only in the overall vasculature architecture but also, more importantly, in the advancing atherosclerotic plaque. MMP activation modifies the architecture of the plaque and may directly participate in the process of plaque rupture. MMPs also participate in cardiac remodelling following myocardial infarction and development of dilated cardiomyopathy. Soluble MMPs are now potential biomarkers in delineating cardiovascular risk for plaque rupture and coronary risk. They also constitute innovative direct or indirect targets to modify cardiovascular tissue remodelling in atherosclerosis and heart failure.

TIMP-3 deficiency accelerates cardiac remodeling after myocardial infarction

The activity of TIMP-3, a natural tissue inhibitor of matrix metalloproteinases (MMPs), is decreased in the failing heart. This study evaluated the response to coronary ligation of cardiac structure, function, and matrix remodeling in wild-type (WT) mice, and those deficient in TIMP-3 (timp-3(-/-)). The coronary artery was ligated in timp-3(-/-) and age-matched WT mice. At various time points over the following 28-day period, left ventricular structure and function (by echocardiography, pressure-volume measurements and morphometry), MMP levels and activity, blood vessel density, cell proliferation, apoptosis, matrix structure, and inflammatory cytokine levels were assessed in both groups. After ligation, mortality was significantly greater in timp-3(-/-) than in WT mice. Morphometry and echocardiography demonstrated no difference in heart size or function prior to ligation; however, the progression of left ventricular systolic dysfunction was accelerated in timp-3(-/-) mice at 7, 14 and 28 days after infarction compared to WT controls. Left ventricular dilatation, gelatinase MMP activity, and TNF-alpha levels were significantly greater in timp-3(-/-) than in WT mice at different times after ligation. By histological evaluation, timp-3(-/-) mice exhibited significantly increased blood vessel density, cell proliferation, and apoptosis in the infarct area, and reduced collagen content in the viable remote myocardium compared to WT mice at 7 and 14 days after ligation. TIMP-3 deficiency accelerated maladaptive cardiac remodeling after a myocardial infarction by promoting matrix degradation and inflammatory cytokine expression. This study supports further investigations to determine whether such remodeling could be reduced by augmenting TIMP-3 expression in the infarcted myocardium.

Mechanisms of Post-Infarct Left Ventricular Remodeling

Heart failure secondary to myocardial infarction (MI) remains a major source of morbidity and mortality. Long-term outcome after MI can be largely be defined in terms of its impact on the size and shape of the left ventricle (i.e., LV remodeling). Three major mechanisms contribute to LV remodeling: 1) early infarct expansion, 2) subsequent infarct extension into adjacent noninfarcted myocardium, and 3) late hypertrophy in the remote LV. Future developments in preventing post-MI heart failure will depend not only on identifying drugs targeting each of these individual mechanisms, but also on diagnostic techniques capable of assessing efficacy against each mechanism.

Effects of autologous stem cells on immunohistochemical patterns and gene expression of metalloproteinases and their tissue inhibitors in doxorubicin cardiomyopathy in a rabbit model

This study aims to investigate the expression of metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in chronic doxorubicin cardiomyopathy in a rabbit model and to evaluate the effects of bone marrow-derived mesenchymal stem cell (MSC) transplantation in this disease. Thirty-nine 3-month-old New Zealand rabbits were divided into 4 groups: group 1 (n = 9) was the untreated control. Groups 2-4 were treated with 6 weeks of doxorubicin (3 mg/kg). Group 2 (n = 6) received no further treatment. In group 3 (n = 9), animals were treated with culture medium (CM) alone. In group 4 (n = 15), autologous MSCs (1.5-2.0 x 10(6)/ml) were injected in the left ventricular (LV) wall. Hearts were stained with HE and picrosirius red. MMP-1, -2, -3 and -9 and TIMP-2 and -3 were detected immunohistochemically. The mRNA levels were determined by real-time polymerase chain reaction. The results confirmed that doxorubicin treatment resulted in minimal myocardial fibrosis and showed that expression of MMPs increased and TIMP-3 decreased. The injection procedure resulted in increased myocardial fibrosis in groups 3 and 4. After MSC injection, MMP-1, MMP-2, and TIMP-3 expression was higher than that in group 2. CM injection led to more fibrosis, elevated TIMP-3, but diminished MMP-1 and MMP-2 expression compared with MSC injection. The mRNA levels of MMPs and TIMPs were not significantly different among all groups. In conclusion, chronic doxorubicin cardiomyopathy was characterized by increased MMP and decreased TIMP-3 expression. MSCs injection into the LV resulted in marked differences of collagen content and MMP/TIMP expression in the whole heart, although significant numbers of living MSCs were not detected after 4 weeks.

Molecular mechanism of imidapril for cardiovascular protection via inhibition of MMP-9

To investigate the inhibitory specificity of angiotensin converting enzyme (ACE) inhibitors to matrix metalloproteinase (MMP)-9, we predicted molecular interactions between an ACE inhibitor imidapril and MMP-9 active site based on recent X-ray structural analyses. Two binding modes differing in the orientation of imidapril on the active site were identified, and its hydrophobic group appeared to preferentially interact with the S1 site compared with the S1' site. Compared with the lisinopril-MMP-9 model in our previous study, imidapril was stabilized effectively on the active site with less of molecular distortions. We also measured ACE and MMP-9 inhibitory activities of imidapril and lisinopril after myocardial infarction. Imidapril had a stronger inhibitory activity against MMP-9 than lisinopril. These findings show that imidapril inhibits MMP-9 directly like lisinopril and its hydrophobic interactions with the S1 site of MMP-9 would be important for enhancing inhibitory activity.

Differences in inflammation, MMP activation and collagen damage account for gender difference in murine cardiac rupture following myocardial infarction

Cardiac rupture remains a fatal complication of acute myocardial infarction (MI) with its mechanism partially understood. We hypothesized that damage to the collagen matrix of infarcted myocardium is the central mechanism of rupture and therefore responsible for the difference in the incidence of rupture between genders. We examined left ventricular (LV) remodeling during the acute phase post-MI in 129sv mice. Following induction of MI, we monitored rupture events and assessed the extent of LV remodeling by echocardiography. Muscle tensile strength, content of insoluble and soluble collagen, expression and activity of matrix metalloproteinases (MMPs) and density of inflammatory cells were determined in the infarcted and non-infarcted myocardium. We then tested the effects of MMP inhibition on rupture. Compared to female mice, males with MI displayed greater extent of LV remodeling, reduced muscle tensile strength, loss of insoluble collagen, local inflammatory response and MMP-9 activation, changes associated with a 3 times higher incidence of rupture than in females. MMP-9 expression by circulating blood mononuclear cells was also increased in male mice with acute MI. Treatment of male mice with an MMP inhibitor reduced MMP activity and halved rupture incidence. Our findings demonstrate that the differences in the severity of inflammation, MMP activation and damage to collagen matrix account for gender difference in cardiac rupture. Our study illustrates the breakdown of fibril collagen as a central mechanism of cardiac rupture.

Inhibition of matrix metalloproteinase-9 activity by lisinopril after myocardial infarction in hamsters

We measured angiotensin-converting enzyme and matrix metalloproteinase-9 activities after myocardial infarction in hamsters and compared the effects of an angiotensin-converting enzyme inhibitor lisinopril with those of an angiotensin receptor blocker candesartan cilexetil after myocardial infarction. Angiotensin-converting enzyme activity was significantly increased 3 and 7 days, but not 1 day after myocardial infarction. Matrix metalloproteinase-9 activity was significantly increased 1 day after myocardial infarction. Lisinopril significantly inhibited both angiotensin-converting enzyme and matrix metalloproteinase-9 activities, but candesartan cilexetil did not. Angiotensin-converting enzyme inhibitors might directly inhibit matrix metalloproteinase-9 activity.

Plasma matrix metalloproteinase-9 and left ventricular remodelling after acute myocardial infarction in man: a prospective cohort study

AIM

To describe temporal profiles of plasma matrix metalloproteinases (MMP-2 and MMP-9), and their relationship with echocardiographic (Echo) parameters of left ventricular (LV) function and remodelling, after acute myocardial infarction (AMI) in man.

METHODS AND RESULTS

Plasma MMP-2 and MMP-9 were assayed at intervals (0-12, 12-24, 24-48, 48-72, 72-96, and > 96 h) in 91 patients with AMI (ST-elevation/non-ST-elevation 77/24; 73% male; 40% anterior site) and on a single occasion in 172 age- and sex-matched control subjects with stable coronary artery disease. Echo assessment of LV volumes, LV ejection fraction (LVEF), and wall motion index score were assessed before discharge and at follow-up (median 176, range 138-262 days) for patients and on a single occassion in controls. Plasma MMP-2 was similar at all times after AMI, elevated when compared with control (P = 0.005-0.001) and unrelated to LV function or volume during index admission or at follow-up. Maximal MMP-9 was seen at 0-12 h and was elevated when compared with control (P = 0.002) followed by fall to a plateau. Both maximal and plateau MMP-9 concentration correlated with white blood cell (WBC, P = 0.023 to < 0.001) and neutrophil count (P = 0.014 to < 0.001). Maximal MMP-9 had independent predictive value for lower LVEF (P = 0.004) during admission and for greater change in LV end-diastolic volume between admission and follow-up (R = 0.3, P = 0.016). In contrast, higher plateau levels of MMP-9 were associated with relative preservation of LV function (increasing LVEF, P = 0.002; decreasing WMIS, P = 0.009) and less change in end-systolic volume and end-diastolic volumes after discharge (P = 0.001 and 0.024, respectively).

CONCLUSION

Both MMP-9 and MMP-2 are elevated following AMI. The biphasic profile of plasma MMP-9 is related to LV remodelling and function following AMI in man. Higher early levels of MMP-9 associate with the extent of LV remodelling and circulating WBC levels. In contrast, higher plateau levels later after AMI are associated with relative preservation of LV function. Temporal profile, rather than absolute magnitude, of MMP-9 activity appears to be important for LV remodelling after AMI.

Selective spatiotemporal induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 transcription after myocardial infarction

Myocardial remodeling after myocardial infarction (MI) is associated with increased levels of the matrix metalloproteinases (MMPs). Levels of two MMP species, MMP-2 and MMP-9, are increased after MI, and transgenic deletion of these MMPs attenuates post-MI left ventricular (LV) remodeling. This study characterized the spatiotemporal patterns of gene promoter induction for MMP-2 and MMP-9 after MI. MI was induced in transgenic mice in which the MMP-2 or MMP-9 promoter sequence was fused to the β-galactosidase reporter, and reporter level was assayed up to 28 days after MI. Myocardial localization with respect to cellular sources of MMP-2 and MMP-9 promoter induction was examined. After MI, LV diameter increased by 70% ( P < 0.05), consistent with LV remodeling. β-Galactosidase staining in MMP-2 reporter mice was increased by 1 day after MI and increased further to 64 ± 6% of LV epicardial area by 7 days after MI ( P < 0.05). MMP-2 promoter activation occurred in fibroblasts and myofibroblasts in the MI region. In MMP-9 reporter mice, promoter induction was detected after 3 days and peaked at 7 days after MI (53 ± 6%, P < 0.05) and was colocalized with inflammatory cells at the peri-infarct region. Although MMP-2 promoter activation was similarly distributed in the MI and border regions, activation of the MMP-9 promoter was highest at the border between the MI and remote regions. These unique findings visually demonstrated that activation of the MMP-2 and MMP-9 gene promoters occurs in a distinct spatial relation with reference to the MI region and changes in a characteristic time-dependent manner after MI.

Spatial disruption and enhanced degradation of collagen with the transition from compensated ventricular hypertrophy to symptomatic congestive heart failure

The cardiac extracellular matrix (ECM) maintains the structural and mechanical integrity of the myocardium. We determined the alterations in the composition of the ECM coincident with the transition from compensated left ventricular (LV) hypertrophy (LVH) to symptomatic congestive heart failure (CHF) and the mechanisms underlying such changes. Heart failure was induced in ferrets by aortic banding. Myocardial collagen content was assessed by HPLC and histological analysis. Matrix metalloproteinase (MMP) activity and tissue inhibitor of metalloproteinase (TIMP) expression were evaluated using gelatin zymography and Western blotting, respectively. LV free wall thickness increased by 29% in asymptomatic LVH and was associated with a 20% increase in interstitial fibrosis (P < 0.05). CHF was coincident with increased plasma angiotensin II levels (149 +/- 48, 40 +/- 19, and 5.6 +/- 1 pg/ml for CHF, LVH, and sham, respectively; P < 0.01, CHF vs. sham and LVH), ventricular dilatation (LV internal diameter = 15 +/- 0.4 vs. 9 +/- 0.1 mm, P < 0.05), increased active MMP-9 (3.0- and 2.2-fold increase over sham and LVH, respectively, n = 5-10 animals per group, P < 0.01), and reduced myocardial total collagen content (3.5 +/- 0.4, 2.6 +/- 0.3, and 2.2 +/- 0.3% in sham, LVH, and CHF, respectively, P < 0.05). In CHF the distribution of collagen was markedly altered, becoming punctate in nature. No difference in MMP-2 activity, TIMP-1, TIMP-2, TIMP-3, or TIMP-4 expression, or collagen cross-linking was found at any time. The present work demonstrates structural reorganization and loss of collagen from cardiac ECM during the transition to decompensated CHF. The enhanced MMP-9 activity coincident with the transition to CHF provides potential therapeutic opportunities for managing the progression from asymptomatic LVH to symptomatic CHF.

FGF1/p38 MAP kinase inhibitor therapy induces cardiomyocyte mitosis, reduces scarring, and rescues function after myocardial infarction

Mammalian cardiomyocytes have limited proliferation potential, and acutely injured mammalian hearts do not regenerate adequately. Instead, injured myocardium develops fibrosis and scarring. Here we show that FGF1/p38 MAP kinase inhibitor treatment after acute myocardial injury in 8- to 10-week-old rats increases cardiomyocyte mitosis. At 3 months after injury, 4 weeks of FGF1/p38 MAP kinase inhibitor therapy results in reduced scarring and wall thinning, with markedly improved cardiac function. In contrast, p38 MAP kinase inhibition alone fails to rescue heart function despite increased cardiomyocyte mitosis. FGF1 improves angiogenesis, possibly contributing to the survival of newly generated cardiomyocytes. Our data indicate that FGF1 and p38 MAP kinase, proteins involved in cardiomyocyte proliferation and angiogenesis during development, may be delivered therapeutically to enhance cardiac regeneration.

Effects of Selective Matrix Metalloproteinase Inhibitor (PG-116800) to Prevent Ventricular Remodeling After Myocardial Infarction

OBJECTIVES

We sought to determine whether matrix metalloproteinase (MMP) inhibitor, PG-116800, reduced left ventricular (LV) remodeling after myocardial infarction (MI).

BACKGROUND

PG-116800 is an oral MMP inhibitor with significant antiremodeling effects in animal models of MI and ischemic heart failure.

METHODS

In an international, randomized, double-blind, placebo-controlled study, 253 patients with first ST-segment elevation MI and ejection fraction between 15% and 40% were enrolled 48+/- 24 h after MI and treated with placebo or PG-116800 for 90 days. Major efficacy end points were changes in LV volumes as determined by serial echocardiography, and clinical and safety outcomes were also collected.

RESULTS

In total, 203 patients (80%) completed 90 days of treatment and had evaluable baseline and 90-day echocardiograms. The proportion of patients with anterior MI (78% vs. 81%) and primary percutaneous coronary intervention (90% vs. 91%) along with baseline LV ejection fraction (35.5% vs. 36.8%) did not differ between PG-116800-treated and placebo-treated patients. There was no difference in the change in LV end-diastolic volume index from days 0 to 90 with PG-116800 versus placebo (5.09 +/- 1.45 ml/m(2) vs. 5.48 +/- 1.41 ml/m2, p = 0.42). Changes in LV diastolic volume, LV systolic volume, LV ejection fraction, sphericity index, plus rates of death or reinfarction were not significantly improved with PG-116800. PG-116800 was well tolerated; however, there was increased incidence of arthralgia and joint stiffness without significant increase in overall musculoskeletal adverse events (21% vs. 15%, p = 0.33).

CONCLUSIONS

Matrix metalloproteinase inhibition with PG-116800 failed to reduce LV remodeling or improve clinical outcomes after MI.

Pharmacologic inhibition of mast cell degranulation prevents left ventricular remodeling induced by chronic volume overload in rats

BACKGROUND

Left ventricular (LV) hypertrophy and dilation are important compensatory responses to chronic volume overload; however, the mechanisms responsible for this LV remodeling have not been well characterized. Previous observations that the number of myocardial mast cells are increased in congestive heart failure (CHF) suggested the hypothesis that mast cells might be involved in the ventricular remodeling induced by a chronic volume overload.

METHODS AND RESULTS

Accordingly, the intent of this study was to determine the contribution of mast cells to LV remodeling, dysfunction, and morbidity/mortality secondary to CHF in the infrarenal aortocaval fistula model of sustained volume overload. To this end, LV end-diastolic pressure, size, and function (ie, isovolumetric pressure-volume relations in the blood-perfused isolated heart) were assessed in both nedocromil sodium treated and untreated rats at 8 weeks after fistula and compared with age-matched controls. Nedocromil, a mast cell-stabilizing drug, effectively prevented the LV dilation and decreased contractility seen in the untreated fistula group in a dose-dependent fashion, resulting in a significant reduction in the incidence of morbidity/mortality from CHF.

CONCLUSION

The ability of mast cell stabilization to prevent ventricular dilation induced by chronic volume overload identifies a key role for mast cells in the regulation of myocardial remodeling.

Circulating biomarkers of extracellular matrix remodeling and risk of atherosclerotic events

PURPOSE OF REVIEW

Disturbances of the synthesis and breakdown of the extracellular matrix of arterial walls have emerged as key features of the atherosclerotic process. Altered levels of circulating extracellular matrix markers have frequently been observed in relation to manifestations of atherosclerotic disease and its risk factors.

RECENT FINDINGS

Research has been focused on the matrix-degrading metalloproteinases, their tissue inhibitors, and procollagen peptides. The most promising matrix metalloproteinase is matrix metalloproteinase-9, which has been observed to predict rapid coronary artery narrowing, ischemic heart disease incidence, abdominal aortic aneurysm expansion, worse outcome in stroke patients, and cardiovascular death. The use of tissue inhibitors of metalloproteinases for prognostication is uncertain thus far. The procollagen marker with most prognostic potential is the marker for type III collagen turnover rate, the N-terminal propeptide PIIINP, higher levels of which predict an adverse outcome after a myocardial infarction and in chronic heart failure, and portend abdominal aortic aneurysm expansion and risk of rupture. Also, the marker for type I collagen synthesis, the C-terminal propeptide PICP, predicts adverse outcomes following myocardial infarction and in chronic heart failure. Extracellular matrix remodeling is also a promising therapeutic target, being favorably affected by several conventional cardiovascular drugs and select dietary interventions. Synthetic matrix metalloproteinase inhibitors are also under development.

SUMMARY

Circulating matrix markers have emerged as candidate biomarkers for predicting risk of subsequent atherosclerotic events. Future large longitudinal observational and intervention studies will determine the role of matrix biomarkers in diagnosis and prognostication, and as targets for intervention in cardiovascular diseases.

Selective Targeting of Matrix Metalloproteinase Inhibition in Post-Infarction Myocardial Remodeling

BACKGROUND

A cause-effect relationship has been established between MMP activation and left ventricular (LV) remodeling following myocardial infarction. The goal of the present study was to examine a selective MMP inhibitor (sMMPi) strategy that effectively spared MMP-1, -3, and -7 with effect to regional and global left ventricular remodeling in a pig model of myocardial infarction.

METHODS AND RESULTS

Pigs instrumented with coronary snares and radiopaque markers within the area at risk were randomized to myocardial infarction-only (n = 10) or sMMPi (PGE-530742, 1 mg/kg TID) begun 3 days prior to myocardial infarction. Ten weight-matched noninstrumented pigs served as reference controls. Left ventricular end-diastolic volume in the myocardial infarction-only group was increased from baseline (81 +/- 3 mL versus 55 +/- 4 mL, respectively, P < 0.05) but was attenuated with sMMPi (67 +/- 3 mL, P < 0.05). Fractional area of shortening of marker area was decreased in the myocardial infarction-only group (change from baseline -63 +/- 10%, P < 0.05) but this effect was attenuated with sMMPi (-28 +/- 14%, P < 0.05), indicative of less dyskinesis of the infarct region with sMMPi. Wall stress was reduced within both the septal and posterior wall regions with sMMPi. Myocardial MMP-2 activity was decreased in both remote and border areas of sMMPi-treated samples compared with myocardial infarction-only values, consistent with pharmacologic MMP inhibition.

CONCLUSIONS

Selective MMP inhibition favorably affected regional myocardial geometry and decreased left ventricular dilation post-myocardial infarction. This study suggests that a strategy of selective MMP inhibition of a limited array of MMPs may be an achievable goal in preventing pathologic left ventricular remodeling post-myocardial infarction.

Effect of Matrix Metalloproteinase Inhibition by Doxycycline on Myocardial Healing and Remodeling after Myocardial Infarction

The aim of conducting this study was to assess the clinical relevance of matrix metalloproteinase (MMP) inhibition by doxycycline, an effective MMP inhibitor, in a rat model of extensive myocardial infarction (MI) and left ventricular (LV) dysfunction. Rats (n = 22) were subjected to extensive anterior MI. Doxycycline (25 mg SC, daily) or saline (control) injections were started for nine days thereafter. The effect of doxycycline on MMP activity in the infarcted and remote myocardium was measured by zymography, in another subgroup (n = 8), nine days after MI. Echocardiography and magnetic resonance imaging (MRI) studies were performed at one and thirty days after MI to assess LV remodeling and function. After 4 weeks, hearts were fixed, and subjected to morphometric and histological analysis. Compared with control, doxycycline treatment attenuated MMP-9 and -2 activity in both infarcted and remote myocardium. Serial echocardiography studies showed that doxycycline failed to attenuate scar thinning, LV dilatation and dysfunction. MRI study showed that doxycycline impaired LV compensatory hypertrophy. Furthermore, compared with control, doxycycline reduced vessel density (/mm(2) +/- SEM) in the infarcted myocardium (84 +/- 16 vs. 46 +/- 9/mm(2), respectively; p < 0.05). Our work suggest that effective MMPs' inhibition in the infarcted and remote myocardium by doxycycline does not prevent LV remodeling and dysfunction but impairs angiogenesis and compensatory LV hypertrophy. Our findings caution against aggressive, non-selective inhibition of MMPs in the early healing phase after MI.