The extracellular matrix in normal and diseased myocardium

Toward the development of a polarimetric tool to diagnose the fibrotic human ventricular myocardium

SIGNIFICANCE

Optical polarimetry is an emerging modality that effectively quantifies the bulk optical properties that correlate with the anisotropic structural properties of cardiac tissues. We demonstrate the application of a polarimetric tool for characterizing healthy and fibrotic human myocardial tissues efficiently with a high degree of accuracy.

AIM

The study was aimed to characterize the myocardial tissues from the left ventricle and right ventricle of N  =  7 control and N  =  10 diseased subjects. The diseased subjects were composed of two groups: N  =  7 with rheumatic heart disease (RHD) and N  =  3 with myxomatous valve (MV) disease.

APPROACH

A portable, affordable, and accurate linear polarization-based diagnostic tool is developed to measure the degree of linear polarization (DOLP) of the myocardial tissues while working at a wavelength of 850 nm.

RESULTS

The sensitivity, specificity, and accuracy of the polarimetric tool in distinguishing the control group from the RHD group were found to be 73.33%, 76.92%, and 75%, respectively, and from the MV group were 91.6%, 62.5%, and 80%, respectively, which demonstrates the efficacy of the polarimetric tool to distinguish the healthy myocardial tissues from diseased tissues.

CONCLUSIONS

We have successfully developed a polarimetric tool that can aid cardiologists in characterizing the myocardial tissues in conjunction with endomyocardial biopsy. This work should be followed up with experiments on a large cohort of control and diseased subjects. We intend to create and develop a probe to quantify the DOLP of in vivo heart tissue during surgery.

Possible Treatment of Myocardial Infarct Based on Tissue Engineering Using a Cellularized Solid Collagen Scaffold Functionalized with Arg-Glyc-Asp (RGD) Peptide

Currently, the clinical impact of cell therapy after a myocardial infarction (MI) is limited by low cell engraftment due to low cell retention, cell death in inflammatory and poor angiogenic infarcted areas, secondary migration. Cells interact with their microenvironment through integrin mechanoreceptors that control their survival/apoptosis/differentiation/migration and proliferation. The association of cells with a three-dimensional material may be a way to improve interactions with their integrins, and thus outcomes, especially if preparations are epicardially applied. In this review, we will focus on the rationale for using collagen as a polymer backbone for tissue engineering of a contractile tissue. Contractilities are reported for natural but not synthetic polymers and for naturals only for: collagen/gelatin/decellularized-tissue/fibrin/Matrigel™ and for different material states: hydrogels/gels/solids. To achieve a thick/long-term contractile tissue and for cell transfer, solid porous compliant scaffolds are superior to hydrogels or gels. Classical methods to produce solid scaffolds: electrospinning/freeze-drying/3D-printing/solvent-casting and methods to reinforce and/or maintain scaffold properties by reticulations are reported. We also highlight the possibility of improving integrin interaction between cells and their associated collagen by its functionalizing with the RGD-peptide. Using a contractile patch that can be applied epicardially may be a way of improving ventricular remodeling and limiting secondary cell migration.

Collagen biomaterial for the treatment of myocardial infarction: an update on cardiac tissue engineering and myocardial regeneration

Myocardial infarction (MI) remains one of the leading cause of mortality over the world. However, current treatments are more palliative than curative, which only stall the progression of the disease, but not reverse the disease. While stem cells or bioactive molecules therapy is promising, the limited survival and engraftment of bioactive agent due to a hostile environment is a bottleneck for MI treatment. In order to maximize the utility of stem cells and bioactive molecules for myocardial repair and regeneration, various types of biomaterials have been developed. Among them, collagen-based biomaterial is widely utilized for cardiac tissue engineering and regeneration due to its optimal physical and chemical properties. In this review, we summarize the properties of collagen-based biomaterial. Then, we discuss collagen-based biomaterial currently being applied to treat MI alone, or together with stem cells and/or bioactive molecules. Finally, the delivery system of collagen-based biomaterial will also be discussed.

Personalized Cardiac Computational Models: From Clinical Data to Simulation of Infarct-Related Ventricular Tachycardia

In the chronic stage of myocardial infarction, a significant number of patients develop life-threatening ventricular tachycardias (VT) due to the arrhythmogenic nature of the remodeled myocardium. Radiofrequency ablation (RFA) is a common procedure to isolate reentry pathways across the infarct scar that are responsible for VT. Unfortunately, this strategy show relatively low success rates; up to 50% of patients experience recurrent VT after the procedure. In the last decade, intensive research in the field of computational cardiac electrophysiology (EP) has demonstrated the ability of three-dimensional (3D) cardiac computational models to perform in-silico EP studies. However, the personalization and modeling of certain key components remain challenging, particularly in the case of the infarct border zone (BZ). In this study, we used a clinical dataset from a patient with a history of infarct-related VT to build an image-based 3D ventricular model aimed at computational simulation of cardiac EP, including detailed patient-specific cardiac anatomy and infarct scar geometry. We modeled the BZ in eight different ways by combining the presence or absence of electrical remodeling with four different levels of image-based patchy fibrosis (0, 10, 20, and 30%). A 3D torso model was also constructed to compute the ECG. Patient-specific sinus activation patterns were simulated and validated against the patient's ECG. Subsequently, the pacing protocol used to induce reentrant VTs in the EP laboratory was reproduced in-silico. The clinical VT was induced with different versions of the model and from different pacing points, thus identifying the slow conducting channel responsible for such VT. Finally, the real patient's ECG recorded during VT episodes was used to validate our simulation results and to assess different strategies to model the BZ. Our study showed that reduced conduction velocities and heterogeneity in action potential duration in the BZ are the main factors in promoting reentrant activity. Either electrical remodeling or fibrosis in a degree of at least 30% in the BZ were required to initiate VT. Moreover, this proof-of-concept study confirms the feasibility of developing 3D computational models for cardiac EP able to reproduce cardiac activation in sinus rhythm and during VT, using exclusively non-invasive clinical data.

Quantitative temporal analysis of protein dynamics in cardiac remodeling

Cardiac remodeling (CR) is a complex dynamic process common to many heart diseases. CR is characterized as a temporal progression of global adaptive and maladaptive perturbations. The complex nature of this process clouds a comprehensive understanding of CR, but greater insight into the processes and mechanisms has potential to identify new therapeutic targets. To provide a deeper understanding of this important cardiac process, we applied a new proteomic technique, PALM (Pulse Azidohomoalanine in Mammals), to quantitate the newly-synthesized protein (NSP) changes during the progression of isoproterenol (ISO)-induced CR in the mouse left ventricle. This analysis revealed a complex combination of adaptive and maladaptive alterations at acute and prolonged time points including the identification of proteins not previously associated with CR. We also combined the PALM dataset with our published protein turnover rate dataset to identify putative biochemical mechanisms underlying CR. The novel integration of analyzing NSPs together with their protein turnover rates demonstrated that alterations in specific biological pathways (e.g., inflammation and oxidative stress) are produced by differential regulation of protein synthesis and degradation.

Aging and the cardiac collagen matrix: Novel mediators of fibrotic remodelling

Cardiovascular disease is a leading cause of death worldwide and there is a pressing need for new therapeutic strategies to treat such conditions. The risk of developing cardiovascular disease increases dramatically with age, yet the majority of experimental research is executed using young animals. The cardiac extracellular matrix (ECM), consisting predominantly of fibrillar collagen, preserves myocardial integrity, provides a means of force transmission and supports myocyte geometry. Disruptions to the finely balanced control of collagen synthesis, post-synthetic deposition, post-translational modification and degradation may have detrimental effects on myocardial functionality. It is now well established that the aged heart is characterized by fibrotic remodelling, but the mechanisms responsible for this are incompletely understood. Furthermore, studies using aged animal models suggest that interstitial remodelling with disease may be age-dependent. Thus with the identification of new therapeutic strategies targeting fibrotic remodelling, it may be necessary to consider age-dependent mechanisms. In this review, we discuss remodelling of the cardiac collagen matrix as a function of age, whilst highlighting potential novel mediators of age-dependent fibrotic pathways.

Evaluation of serum prolidase activity in patients with slow coronary flow

INTRODUCTION

Slow coronary flow (SCF) is described as the slow passage of contrast to distal coronaries despite anatomically normal coronary arteries. It has been shown that increased serum prolidase activity (SPA) correlates with collagen turnover. Increased collagen turnover might be associated with the development of atherosclerotic plaques.

AIM

To investigate the relationship between serum prolidase activity and slow coronary flow.

MATERIAL AND METHODS

This cross-sectional study included 40 SCF patients (mean age: 55.0 ±9.5 years, 20 females) and 40 controls (mean age: 53.9 ±8.2 years, 21 females) with normal coronary anatomy and normal coronary flow. The Thrombolysis in Myocardial Infarction (TIMI) frame-count (TFC) method was used for SCF diagnosis. Serum prolidase activity was measured spectrophotometrically, and the relevant parameters were compared between the groups.

RESULTS

There were no statistically significant differences between the SCF and control groups in terms of basic demographic, clinical, and laboratory data. However, the SPA was significantly higher in the SCF group compared to the control (702.7 ±13.8 and 683.9 ±13.2 respectively, p<0.001). Serum prolidase activity was significantly correlated with the mean TFC (r=0.463, p<0.001). The overall findings of this study support the predictive accuracy of the serum prolidase activity in our cohort, with a statistically significant ROC value of 681.3.

CONCLUSIONS

Our study showed that SPA was increased in SCF patients. The activity of this enzyme was significantly correlated with the mean TFC.

Animal Models and "Omics" Technologies for Identification of Novel Biomarkers and Drug Targets to Prevent Heart Failure

It is now accepted that heart failure (HF) is a complex multifunctional disease rather than simply a hemodynamic dysfunction. Despite its complexity, stressed cardiomyocytes often follow conserved patterns of structural remodelling in order to adapt, survive, and regenerate. When cardiac adaptations cannot cope with mechanical, ischemic, and metabolic loads efficiently or become chronically activated, as, for example, after infection, then the ongoing structural remodelling and dedifferentiation often lead to compromised pump function and patient death. It is, therefore, of major importance to understand key events in the progression from a compensatory left ventricular (LV) systolic dysfunction to a decompensatory LV systolic dysfunction and HF. To achieve this, various animal models in combination with an “omics” toolbox can be used. These approaches will ultimately lead to the identification of an arsenal of biomarkers and therapeutic targets which have the potential to shape the medicine of the future.

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.

Long-term organ cultures of newt hearts

Adult newts regenerate their hearts after injury by initiating proliferation of cardiac muscle and non-muscle cells. Mechanistic studies in vivo to analyze heart regeneration are challenging due to the long reproduction cycle of newts and the complexity of the genome. Culture of primary newt cells might offer alternative experimental approaches, but monolayers of newt cardiomyocytes and slice cultures of newt hearts show extensive morphological changes during cultivation. Hence, we developed a protocol to culture intact newt hearts in vitro, avoiding major morphological changes of explanted organs during a 5-week cultivation. The model provides improved accessibility and allows manipulation of cultured organs by small molecules and viral vectors. We found that dedifferentiation and S-phase entry of cardiomyocytes, which are hallmarks of cardiac regeneration in vivo, can be recapitulated in cultured hearts in vitro. We reason that long-term organ cultures of newts are a versatile tool for mechanistic studies on organ regeneration.

Type I collagen degradation during tissue repair: comparison of mechanisms following fracture and acute coronary syndromes

There is turnover of type I collagen during tissue repair. The degradation of type I collagen by matrix metalloproteinases (MMPs) is reflected by serum ICTP and that by cathepsins by CTX-I. There is evidence for increases in ICTP after acute coronary syndromes (ACS) and in CTX-I during fracture repair. The involvement of the MMP pathway in fracture repair and cathepsins after myocardial infarction is unclear. We studied 74 men; 22 were admitted to the hospital on the day of their ACS (ST or non-ST elevation myocardial infarction) (mean age 56 years, range 39 to 82) and 9 attended hospital on the day of their tibial shaft fracture (mean age 33 years, range 21 to 79); we had 43 age-matched controls (mean age 54 years, range 20 to 82). Subjects with ACS and tibial shaft fracture were followed up for up to one year; control subjects were used to establish a reference interval. We measured serum ICTP by ELISA (reference interval 1.1 to 17.6 ng/mL) and CTX-I by chemiluminescence (reference interval 0.094 to 0.991 ng/mL). After ACS, the mean ICTP increased from 5.41 to 6.60 ng/mL within one day of admission (p<0.05); the mean CTX-I increased from 0.263 to 0.414 ng/mL (p<0.05). In two cases, the CTX increased to above the reference interval. After tibial shaft fracture, the mean ICTP increased from 5.51 to maximum of 8.71 ng/mL within 28 days of admission (p<0.01); the mean CTX increased from 0.200 to 0.374 ng/mL (p<0.001). In four cases, the CTX increased to above the reference interval. We conclude that the MMP and cathepsin pathways are both implicated in tissue repair in the bone and heart. This may have clinical implications; drugs that block either pathway (TIMPs, cathepsin K inhibitors) may affect the repair of both tissues.

Stable, covalent attachment of laminin to microposts improves the contractility of mouse neonatal cardiomyocytes

The mechanical output of contracting cardiomyocytes, the muscle cells of the heart, relates to healthy and disease states of the heart. Culturing cardiomyocytes on arrays of elastomeric microposts can enable inexpensive and high-throughput studies of heart disease at the single-cell level. However, cardiomyocytes weakly adhere to these microposts, which limits the possibility of using biomechanical assays of single cardiomyocytes to study heart disease. We hypothesized that a stable covalent attachment of laminin to the surface of microposts improves cardiomyocyte contractility. We cultured cells on polydimethylsiloxane microposts with laminin covalently bonded with the organosilanes 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane with glutaraldehyde. We measured displacement of microposts induced by the contractility of mouse neonatal cardiomyocytes, which attach better than mature cardiomyocytes to substrates. We observed time-dependent changes in contractile parameters such as micropost deformation, contractility rates, contraction and relaxation speeds, and the times of contractions. These parameters were affected by the density of laminin on microposts and by the stability of laminin binding to micropost surfaces. Organosilane-mediated binding resulted in higher laminin surface density and laminin binding stability. 3-glycidoxypropyltrimethoxysilane provided the highest laminin density but did not provide stable protein binding with time. Higher surface protein binding stability and strength were observed with 3-aminopropyltriethoxysilane with glutaraldehyde. In cultured cardiomyocytes, contractility rate, contraction speeds, and contraction time increased with higher laminin stability. Given these variations in contractile function, we conclude that binding of laminin to microposts via 3-aminopropyltriethoxysilane with glutaraldehyde improves contractility observed by an increase in beating rate and contraction speed as it occurs during the postnatal maturation of cardiomyocytes. This approach is promising for future studies to mimic in vivo tissue environments.

Electrospun PLGA fibers incorporated with functionalized biomolecules for cardiac tissue engineering

Structural similarity of electrospun fibers (ESFs) to the native extracellular matrix provides great potential for the application of biofunctional ESFs in tissue engineering. This study aimed to synthesize biofunctionalized poly (L-lactide-co-glycolide) (PLGA) ESFs for investigating the potential for cardiac tissue engineering application. We developed a simple but novel strategy to incorporate adhesive peptides in PLGA ESFs. Two adhesive peptides derived from laminin, YIGSR, and RGD, were covalently conjugated to poly-L-lysine, and then mingled with PLGA solution for electrospinning. Peptides were uniformly distributed on the surface and in the interior of ESFs. PLGA ESFs incorporated with YIGSR or RGD or adsorbed with laminin significantly enhanced the adhesion of cardiomyocytes isolated from neonatal rats. Furthermore, the cells were found to adhere better on ESFs compared with flat substrates after 7 days of culture. Immunofluorescent staining of F-actin, vinculin, a-actinin, and N-cadherin indicated that cardiomyocytes adhered and formed striated α-actinin better on the laminin-coated ESFs and the YIGSR-incorporated ESFs compared with the RGD-incorporated ESFs. The expression of α-myosin heavy chain and β-tubulin on the YIGSR-incorporated ESFs was significantly higher compared with the expression level on PLGA and RGD-incorporated samples. Furthermore, the contraction of cardiomyocytes was faster and lasted longer on the laminin-coated ESFs and YIGSR-incorporated ESFs. The results suggest that aligned YIGSR-incorporated PLGA ESFs is a better candidate for the formation of cardiac patches. This study demonstrated the potential of using peptide-incorporated ESFs as designable-scaffold platform for tissue engineering.

Using proteomics to uncover extracellular matrix interactions during cardiac remodeling

The left ventricle (LV) responds to a myocardial infarction with an orchestrated sequence of events that result in fundamental changes to both the structure and function of the myocardium. This collection of responses is termed as LV remodeling. Myocardial ischemia resulting in necrosis is the initiating event that culminates in the formation of an extracellular matrix (ECM) rich infarct scar that replaces necrotic myocytes. While the cardiomyocyte is the major cell type that responds to ischemia, infiltrating leukocytes and cardiac fibroblasts coordinate the subsequent wound healing response. The matrix metalloproteinase family of enzymes regulates the inflammatory and ECM responses that modulate scar formation. Matridomics is the proteomic evaluation focused on ECM, while degradomics is the proteomic evaluation of proteases as well as their inhibitors and substrates. This review will summarize the use of proteomics to better understand matrix metalloproteinase roles in post myocardial infarction LV remodeling.

Reconstitution of the myocardium in regenerating newt hearts is preceded by transient deposition of extracellular matrix components

Adult newts efficiently regenerate the heart after injury in a process that involves proliferation of cardiac muscle and nonmuscle cells and repatterning of the myocardium. To analyze the processes that underlie heart regeneration in newts, we characterized the structural changes in the myocardium that allow regeneration after mechanical injury. We found that cardiomyocytes in the damaged ventricle mainly die by necrosis and are removed during the first week after injury, paving the way for the extension of thin myocardial trabeculae, which initially contain only very few cardiomyocytes. During the following 200 days, these thin trabeculae fill up with new cardiomyocytes until the myocardium is fully reconstituted. Interestingly, reconstruction of the newly formed trabeculated network is accompanied by transient deposition of extracellular matrix (ECM) components such as collagen III. We conclude that the ECM is a critical guidance cue for outgrowing and branching trabeculae to reconstruct the trabeculated network, which represents a hallmark of uninjured cardiac tissue in newts.

Improvement in collagen metabolism after 12 weeks' cardiac resynchronization therapy in patients with ischaemic cardiomyopathy

OBJECTIVES

To investigate the effects of cardiac resynchronization therapy (CRT) on collagen metabolism biomarkers and their relationship to cardiac function, in patients with ischaemic cardiomyopathy (ICM).

METHODS

Serum levels of matrix metalloproteinase (MMP)-9, tissue inhibitor of MMP-9 (TIMP-1), carboxyterminal propeptide of type I procollagen (PICP) and carboxyterminal telopeptide of type I collagen (ICTP) were quantified before and after 12 weeks' treatment, in patients with ICM receiving CRT and standard medical therapy (CRT group) or standard medical therapy alone (non-CRT group), and in controls. Cardiac function was measured echocardiographically.

RESULTS

MMP-9, TIMP-1, ICTP and the MMP-9/TIMP-1 ratio were significantly higher, and the PICP/ICTP ratio significantly lower, in patients with ICM (n = 27) compared with controls (n = 20). After 12 weeks' treatment, MMP-9, TIMP-1, ICTP and the MMP-9/TIMP-1 ratio were significantly higher, and the PICP/ICTP ratio significantly lower, in the non-CRT group (n = 15) compared with the CRT group (n = 12). The PICP/ICTP ratio correlated positively with TIMP-1 and negatively with MMP-9. The early/atrial ratio and left ventricular ejection fraction correlated positively and negatively, respectively, with the MMP-9/TIMP-1 ratio. Echocardiographic measurements of cardiac function were significantly worse in patients with ICM compared with controls and improved significantly after treatment in the CRT group.

CONCLUSIONS

In ICM, collagen degradation biomarkers were elevated and correlated positively with cardiac function. CRT partially reversed the deterioration in collagen metabolism and enhanced cardiac function.

Evidence of altered biochemical composition in the hearts of adult intrauterine growth-restricted rats

PURPOSE

Epidemiological studies clearly link intrauterine growth restriction with increased risk of cardiac disease in adulthood. The mechanisms leading to this increased risk are poorly understood; remodeling of the myocardium is implicated. The aim was to determine the effect of early life growth restriction on the biochemical composition of the left ventricular myocardium in adult rats.

METHODS

Wistar Kyoto dams were fed either a low protein diet (LPD; 8.7 % casein) or normal protein diet (NPD; 20 % casein) during pregnancy and lactation; from weaning, the offspring were fed normal rat chow. At 18 weeks of age, the biochemical composition of the hearts of NPD control (n = 9) and LPD intrauterine growth-restricted (n = 7) offspring was analyzed using Fourier Transform Infrared (FTIR) micro-spectroscopy.

RESULTS

Body weights at postnatal day 4 were significantly lower and remained lower throughout the experimental period in the LPD offspring compared to controls. FTIR analysis of the infrared absorption spectra across the whole "fingerprint" region (1,800-950 cm(-1)) demonstrated wider variation in absorbance intensity in the LPD group compared to controls. In particular, there were marked differences detected in the protein (1,540 cm(-1)), lipid (1,455 and 1,388 cm(-1)), proteoglycan (1,228 cm(-1)) and carbohydrate (1,038 cm(-1)) bands, indicating increased lipid, proteoglycan and carbohydrate content in the growth-restricted myocardium.

CONCLUSION

In conclusion, changes in the biochemical composition of the myocardium provide a likely mechanism for the increased vulnerability to cardiovascular disease in offspring that were growth restricted in early life.

Biomaterial strategies for alleviation of myocardial infarction

World Health Organization estimated that heart failure initiated by coronary artery disease and myocardial infarction (MI) leads to 29 per cent of deaths worldwide. Heart failure is one of the leading causes of death in industrialized countries and is expected to become a global epidemic within the twenty-first century. MI, the main cause of heart failure, leads to a loss of cardiac tissue impairment of left ventricular function. The damaged left ventricle undergoes progressive ‘remodelling’ and chamber dilation, with myocyte slippage and fibroblast proliferation. Repair of diseased myocardium with in vitro-engineered cardiac muscle patch/injectable biopolymers with cells may become a viable option for heart failure patients. These events reflect an apparent lack of effective intrinsic mechanism for myocardial repair and regeneration. Motivated by the desire to develop minimally invasive procedures, the last 10 years observed growing efforts to develop injectable biomaterials with and without cells to treat cardiac failure. Biomaterials evaluated include alginate, fibrin, collagen, chitosan, self-assembling peptides, biopolymers and a range of synthetic hydrogels. The ultimate goal in therapeutic cardiac tissue engineering is to generate biocompatible, non-immunogenic heart muscle with morphological and functional properties similar to natural myocardium to repair MI. This review summarizes the properties of biomaterial substrates having sufficient mechanical stability, which stimulates the native collagen fibril structure for differentiating pluripotent stem cells and mesenchymal stem cells into cardiomyocytes for cardiac tissue engineering.

Activation of peripheral blood mononuclear cells and extracellular matrix and inflammatory gene profile in acute myocardial infarction

Inflammation and ECM (extracellular matrix) remodelling play important roles in LV (left ventricular) remodelling following acute MI (myocardial infarction). Previous studies show elevated plasma MMP (matrix metalloproteinase) levels in patients with acute MI, but their sources are not clear. The recruitment of mononuclear cells into the infarcted myocardium is critical for inflammatory responses, but their exact roles in LV remodelling have not been fully investigated, as it is difficult to isolate and study the function of regional inflammatory cells. To address these questions, we isolated PBMCs (peripheral blood mononuclear cells) from blood samples of patients with acute MI or stable angina, or healthy controls (n=14, 8 and 12 respectively). PBMCs were cultured for 24 h and the MMP9 level in the culture medium was measured by gelatin zymography, and MMP9 gene expression was measured by real-time PCR. Two superarrays (ECM and adhesion molecules, and common cytokines; 84 genes included in each array) were employed to screen gene expression profiles by PBMCs in five patients with acute MI and five controls. We found that MMP9 expression by PBMCs at both the mRNA and protein levels was increased 2-fold (both P<0.05) in patients with acute MI compared with the two control groups. Notably, MMP2 was not expressed by PBMCs. Superarray screening revealed that PBMCs not only expressed MMPs, TIMPs (tissue inhibitors of metalloproteinases) and matrix proteins, but also served as an important source of cell adhesion molecules, inflammatory cytokines and growth factors. A total of 42 genes were differentially expressed in patients with acute MI compared with controls. Expression of selected genes was confirmed by real-time PCR. In conclusion, PBMCs constitute a key cellular source for elevated plasma MMP9, but not for MMP2. PBMCs also contribute to systemic and regional inflammation and matrix remodelling in acute MI.

Treatment with spironolactone for 24 weeks decreases the level of matrix metalloproteinases and improves cardiac function in patients with chronic heart failure of ischemic etiology

BACKGROUND

The myocardial extracellular matrix is believed to be central to the remodelling that takes place following myocardial infarction. The contribution of markers of collagen metabolism to this process remains less well understood. The present study examined the contribution of some of the markers of collagen metabolism in cardiac remodelling, as well as the effect of spironolactone on the remodelling process.

OBJECTIVES

To investigate the pathological contribution of markers of collagen metabolism, including matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), type I collagen carboxyterminal telopeptide (ICTP) and procollagen type I carboxyterminal propeptide (PICP), in cardiac remodelling following ischemic cardiomyopathy, and to examine the pharmacoregulatory effects of spironolactone on collagen metabolism.

METHOD

Eighty-six consecutive patients (62 men and 24 women) with chronic heart failure of ischemic etiology (patient group) and 25 age-matched controls were enrolled in the study. The subjects in the patient group were randomly assigned into a spironolactone or nonspironolactone group. Plasma levels of MMP-9, TIMP-1, ICTP and PICP were measured using ELISA and radioimmunoassay techniques. Furthermore, left ventricular diastolic diameter and ejection fraction were assessed using two-dimensional and Doppler echocardiography.

RESULTS

The plasma concentrations of MMP-9, TIMP-1 and the MMP-9 to TIMP-1 ratio, as well as ICTP, were significantly increased in the patient group. The PICP to ICTP ratio in the patient group was significantly lower than that in the age-matched control subjects. After a follow-up period of 24 weeks, the PICP to ICTP ratio increased, and MMP-9, TIMP-1 and the MMP-9 to TIMP-1 ratio decreased in the spironolactone subgroup.

CONCLUSIONS

Biomarkers of collagen degradation were elevated and correlated with depressed heart function; spironolactone may partially reverse the dysregulation in collagen metabolism.

Effects of novel semiselective matrix metalloproteinase inhibitors on ex vivo cardiac structure-function

The purpose of this study was to evaluate the ability of novel semiselective matrix metalloproteinase inhibitors (MMPI) to protect myocardial structure-function in the setting of ischemia-reperfusion injury. For this purpose, an isolated rat model of myocardial stunning and infarction was used. Isolated hearts were subjected to 20-30 minutes of global no-flow ischemia and 30-minute reperfusion. Myocardial performance was assessed as the product of the heart rate and left ventricular developed pressure (rate-pressure product, RPP). Coronary flow rates, ventricular weights, indicators of muscle (troponin I), and fibrillar collagen damage (collagen opalation) were measured. Four MMPI were tested: 2 non-hydroxamate, semiselective inhibitors (PY-2 and 1,2-HOPO-2) and 2 broad-spectrum inhibitors (PD166793 and CGS27023A). The non-hydroxamate, semiselective inhibitors were shown to be nontoxic in cocultures of cardiac cells. Results indicate that semiselective inhibitors (in particular 1,2-HOPO-2) yield improved cardiac performance (approximately 23% higher RPP vs. controls) and coronary flow rates (approximately 22%), reducing muscle (approximately 25%) and fibrillar collagen damage (approximately 60%). Evidence suggests the involvement of matrix metalloproteinase-2 in these actions. Interestingly, broad-spectrum inhibitors only show modest improvement (approximately 8% higher RPP vs. controls) without affecting the other measured parameters. In conclusion, semiselective MMPI can act as cardioprotectors in isolated perfused rat hearts. Protection is observed in all structural components of the myocardium translating into improved contractile function. Based on these findings, non-hydroxamate, semiselective MMPI warrant further studies as to their ability to protect ischemic myocardium in the in vivo setting.

Extracellular matrix profiles in the progression to heart failure. European Young Physiologists Symposium Keynote Lecture-Bratislava 2007

The myocardial extracellular matrix (ECM), which preserves the geometry and integrity of the myocardium, is a dynamic structure whose component proteins are maintained by a finely controlled homeostatic balance between deposition and degradation. One of the key targets in cardiology is the elucidation of the molecular mechanisms which mediate pathological remodelling of this matrix causing the transition from compensatory hypertrophy to congestive decompensated heart failure. In response to injury or increased workload, cardiac remodelling including myocyte hypertrophy, develops as the heart attempts to compensate for increased wall stresses. Persistence of these stresses over extended time periods leads to disruption of ECM homeostasis resulting in irreversible maladaptive cardiac remodelling, ventricular dilatation and finally heart failure. ECM remodelling is regulated by the matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs). Clinical studies and experimental models of cardiac disease states have reported alterations in the balance between the MMPs and TIMPs in the failing heart and crucially at intermediate time points in the progression to failure. This article reviews the recent clinical, genetic and experimental approaches employed to compare ECM, MMP and TIMP profiles in healthy, compensated and failing hearts and identifies common themes in the perturbation of ECM homeostasis in the transition to heart failure.

Enhanced expression of fibrillin-1, a constituent of the myocardial extracellular matrix in fibrosis

Fibrillin-1 localization in the myocardium and the modulation of its expression in cardiac fibrosis were examined. In normal rat hearts, fibrillin-1 was abundant throughout the myocardium as thin fibers that crossed over the perimysium and around arteries. After cardiac fibrosis was induced in rats by either 14-day ANG II infusion or 21-day DOCA-salt treatment [a high endothelin-1 (ET-1) model], fibrillin-1 immunostaining was stronger in the interstitium (2.8-fold and 4.4-fold increases, respectively, in each model), extended between myocytes, and accumulated in microscopic scars and in the perivascular area of both ventricles. mRNA analysis confirmed its enhanced ventricular expression in both groups of rats (2.5-fold and 6.6-fold increments, respectively, in each model). In 1B normotensive and 2C hypertensive transgenic mice, two lines expressing an ANG II fusion protein in cardiac myocytes, strong fibrillin-1 immunoreactivity was observed in the interstitium and around arteries (3.7-fold and 7-fold increases, respectively). ANG II and transforming growth factor-beta1 enhanced fibrillin-1 synthesis by cardiac fibroblasts. Some fibrillin-1 fragments interacted with RGD-dependent integrins, including alpha(8)beta(1)-integrin, of cardiac fibroblasts but not necessarily through the RGD motif. Our findings illustrate that fibrillin-1 is an important constituent of the myocardium. In vitro and in vivo evidence suggests that ANG II can directly induce fibrillin-1 expression in cardiac fibroblasts. This protein can thus contribute to reactive and reparative processes.

Myocardial function in severe aortic stenosis before and after aortic valve replacement: A Doppler tissue imaging study

BACKGROUND

The aim of the study was to assess the value of Pulsed-wave Doppler tissue imaging (DTI) in assessing diastolic and systolic function in patients with severe aortic value stenosis.

METHODS

Thirty-five patients with aortic stenosis (AS) (valve orifice < or = 1 cm 2 , mean age 71.8 +/- 6.2) and 35 comparable healthy subjects were studied. All subjects performed conventional 2-dimensional Doppler echocardiography and DTI at mitral annulus level. Patients with AS were divided into 2 groups: 16 patients who presented initial signs of HF and a depressed left ventricular systolic function (AS I) (EF: 35%-50%) and 19 patients were asymptomatic and had normal left ventricular systolic function (EF > 50%) (ASII). The 16 symptomatic AS patients underwent surgical aortic valve replacement and were examined after 1 year.

RESULTS

DTI was able to detect abnormalities of systolic and diastolic function in AS: the significantly lower peak S velocity in AS I than in AS II and in controls, both at septum and lateral wall level; the significantly lower peak E velocity in AS I than in AS II and in controls both at septum and lateral wall level; the significantly higher peak A velocity in AS I than in AS II and in controls both at septum and lateral wall level; the significant lower E/A ratio in AS I than in AS II and in controls both at septum and lateral wall level.

CONCLUSION

We found a significant inverse correlation between DTI lateral S velocity, DTI peak E velocity, lateral DTI E/A ratio, and AS peak and mean gradient. According to the results of this study we can affirm that DTI parameters surely had an important physiopathological impact in the knowledge of myocardial function in patients with severe aortic stenosis.

Severe Aortic Stenosis and Myocardial Function

Background— The aim of this study was to assess the myocardial reflectivity pattern in severe aortic valve stenosis through the use of integrated backscatter (IBS) analysis. Patients with aortic stenosis (AS) were carefully selected in the Department of Cardiology.

Methods and Results— Thirty-five subjects (AS: valve orifice ≤1 cm 2 ; 12 female; mean age, 71.8±6.2 years) and 25 healthy subjects were studied. All subjects of the study had conventional 2D-Doppler echocardiography and IBS. Backscatter signal was sampled at the septum and posterior wall levels. Patients with AS were divided into 2 groups: 16 patients with initial signs of congestive heart failure and a depressed left ventricular systolic function (DSF) (ejection fraction [EF] range, 35% to 50%) and 19 asymptomatic patients with normal left ventricular systolic function (NSF) (EF >50%). Myocardial echo intensity (pericardium related) was significantly higher at the septum and posterior wall levels in DSF than in NSF and in control subjects. IBS variation, as an expression of variation of the signal, appeared to be significantly lower in AS with DSF than in NSF and in control subjects, at both the septum and posterior wall levels. Patients with DSF underwent aortic valve replacement, and, during surgical intervention, a septal myocardial biopsy was made for evaluation of myocardium/fibrosis ratio. Abnormally increased echo intensity was detected in left ventricular pressure overload by severe aortic stenosis and correlated with increase of myocardial collagen content (operating biopsy).

Conclusions— One year after aortic valve replacement, we observed a significant reduction of left ventricular mass, and, only if pericardial indexed IBS value (reduction of interstitial fibrosis) decreased, it was possible to observe an improvement of EF and of IBS variation.

Progression from compensated hypertrophy to failure in the pressure-overloaded human heart: structural deterioration and compensatory mechanisms

BACKGROUND

The progression of compensated hypertrophy to heart failure (HF) is still debated. We investigated patients with isolated valvular aortic stenosis and differing degrees of left ventricular (LV) systolic dysfunction to test the hypothesis that structural remodeling, as well as cell death, contributes to the transition to HF.

METHODS AND RESULTS

Structural alterations were studied in LV myectomies from 3 groups of patients (group 1: ejection fraction [EF] >50%, n=12; group 2: EF 30% to 50%, n=12; group 3: EF <30%, n=10) undergoing aortic valve replacement. Control patients were patients with mitral valve stenosis but normal LV (n=6). Myocyte hypertrophy was accompanied by increased nuclear DNA and Sc-35 (splicing factor) content. ACE and TGF-beta1 were upregulated correlating with fibrosis, which increased 2.3-, 2.2-, and 3.2-fold over control in the 3 groups. Myocyte degeneration increased 10, 22, and 32 times over control. A significant correlation exists between EF and myocyte degeneration or fibrosis. Ubiquitin-related autophagic cell death was 0.5 per thousand in control and group 1, 1.05 in group 2, and 6.05 per thousand in group 3. Death by oncosis was 0 per thousand in control, 3 per thousand in group 1, and increased to 5 per thousand (groups 2 and 3). Apoptosis was not detectable in control and group 3, but it was present at 0.02 per thousand in group 1 and 0.01 per thousand in group 2. Cardiomyocyte mitosis was never observed.

CONCLUSIONS

These structure-function correlations confirm the hypothesis that transition to HF occurs by fibrosis and myocyte degeneration partially compensated by hypertrophy involving DNA synthesis and transcription. Cell loss, mainly by autophagy and oncosis, contributes significantly to the progression of LV systolic dysfunction.