Serological evidence of altered collagen homeostasis reflects early ventricular remodeling following acute myocardial infarction

Extracellular Matrix in Ischemic Heart Disease, Part 4/4: JACC Focus Seminar

Myocardial ischemia and infarction, both in the acute and chronic phases, are associated with cardiomyocyte loss and dramatic changes in the cardiac extracellular matrix (ECM). It has long been appreciated that these changes in the cardiac ECM result in altered mechanical properties of ischemic or infarcted myocardial segments. However, a growing body of evidence now clearly demonstrates that these alterations of the ECM not only affect the structural properties of the ischemic and post-infarct heart, but they also play a crucial and sometimes direct role in mediating a range of biological pathways, including the orchestration of inflammatory and reparative processes, as well as the pathogenesis of adverse remodeling. This final part of a 4-part JACC Focus Seminar reviews the evidence on the role of the ECM in relation to the ischemic and infarcted heart, as well as its contribution to cardiac dysfunction and adverse clinical outcomes.

Matrix Metalloproteinases in Myocardial Infarction and Heart Failure

Cardiovascular disease is the leading cause of death, accounting for 600,000 deaths each year in the United States. In addition, heart failure accounts for 37% of health care spending. Matrix metalloproteinases (MMPs) increase after myocardial infarction (MI) and correlate with left ventricular dysfunction in heart failure patients. MMPs regulate the remodeling process by facilitating extracellular matrix turnover and inflammatory signaling. Due to the critical role MMPs play during cardiac remodeling, there is a need to better understand the pathophysiological mechanism of MMPs, including the biological function of the downstream products of MMP proteolysis. Future studies developing new therapeutic targets that inhibit specific MMP actions to limit the development of heart failure post-MI are warranted. This chapter focuses on the role of MMPs post-MI, the efficiency of MMPs as biomarkers for MI or heart failure, and the future of MMPs and their cleavage products as targets for prevention of post-MI heart failure.

Changes in the myocardial interstitium and contribution to the progression of heart failure

The myocardial interstitium is highly organized and orchestrated, whereby small disruptions in composition, spatial relationships, or content lead to altered myocardial systolic and/or diastolic performance. These changes in extracellular matrix structure and function are important in the progression to heart failure in pressure overload hypertrophy, dilated cardiomyopathy, and ischemic heart disease. The myocardial interstitium is not a passive entity, but rather a complex and dynamic microenvironment that represents an important structural and signaling system within the myocardium.

Time course of early changes in plasma markers of collagen turnover following percutaneous transluminal coronary angioplasty

INTRODUCTION

Marked changes occur in the collagen framework of the heart following acute ischemia, which is associated with adverse ventricular remodelling. Plasma markers of collagen turnover are useful in the assessment of remodelling and have predictive value, but their exact temporal dynamics following ischemia are unclear.

OBJECTIVE

To characterize the early temporal dynamics of plasma markers of collagen turnover in a human model of coronary artery occlusion.

METHODS

Fourteen patients undergoing elective percutaneous coronary intervention (PCI) to a single coronary artery were recruited in addition to a control group of eight patients undergoing elective diagnostic coronary arteriography. Sequential assessment of plasma levels of procollagen type I carboxyterminal propeptide and C-telopeptide for type I collagen (CITP) as markers of synthesis and degradation, respectively, was performed over a 16 h period.

RESULTS

The ischemic burden in the PCI group was high, with 13 of the 14 patients demonstrating transient ST segment shift or positive troponin. Mean plasma levels of CITP on admission were 3.1 ng⁄mL and 3.0 ng⁄mL in the PCI and control groups, respectively (P value nonsignificant). There was a sequential increase in plasma CITP following PCI, peaking at 4.7 ng⁄mL at 16 h (P<0.01), with no change in the control group. There were no significant changes in plasma levels of procollagen type I carboxyterminal propeptide in either group.

CONCLUSIONS

Plasma levels of CITP demonstrated early temporal dynamics of collagen degradation following transient coronary artery occlusion supporting the use of plasma markers of collagen turnover as an early tool in the assessment of the remodelling process following myocardial ischemia.

Relation of high concentrations of plasma carboxy-terminal telopeptide of collagen type I with outcome in acute myocardial infarction

Acute myocardial infarction (AMI) is associated with matrix metalloproteinase activation. The plasma concentrations of carboxy-terminal telopeptide of collagen type I (CITP) reflect collagen type I degradation due to matrix metalloproteinase activation. We assessed the role of CITP as an early marker of outcome in AMI. Plasma CITP was measured 72 hours after hospital admission in 432 patients presenting with AMI. The 2 composite end points of the study (death, resuscitated cardiac arrest, recurrent AMI or ischemia, and heart failure or stroke; and death, resuscitated cardiac arrest, or heart failure) and mortality were assessed at 1 year in 4 patient groups stratified by the CITP quartiles. Patients with ST-segment elevation MI represented 75.7% of the population. In-hospital percutaneous coronary intervention was performed in 70.4% of the patients. The mean left ventricular ejection fraction was 53.9 +/- 12.5%. At 1 year of follow-up, high levels of CITP were associated with the occurrence of both composite end points and mortality (p <0.01 for all). Stepwise logistic regression analysis identified CITP as an independent predictor of both composite end points (odds ratio 2.14, 95% confidence interval 1.34 to 3.42, p = 0.001; and odds ratio 3.19, 95% confidence interval 1.50 to 6.81, p = 0.003), along with the Killip class and brain natriuretic peptide levels. In conclusion, high hospital levels of CITP, a marker of collagen degradation and ventricular remodeling, are associated with late mortality and other serious clinical events after AMI.

Extracellular matrix turnover and signaling during cardiac remodeling following MI: causes and consequences

The concept that extracellular matrix (ECM) turnover occurs during cardiac remodeling is a well-accepted paradigm. To date, a multitude of studies document that remodeling is accompanied by increases in the synthesis and deposition of ECM components as well as increases in extracellular proteases, especially matrix metalloproteinases (MMPs), which break down ECM components. Further, soluble ECM fragments generated from enzymatic action serve to stimulate cell behavior and have been proposed as candidate plasma biomarkers of cardiac remodeling. This review briefly summarizes our current knowledge base on cardiac ECM turnover following myocardial infarction (MI), but more importantly extends discussion by defining avenues that remain to be explored to drive the ECM remodeling field forward. Specifically, this review will discuss cause and effect roles for the ECM changes observed following MI and the potential role of the ECM changes that may serve as trigger points to regulate remodeling. While the pattern of remodeling following MI is qualitatively similar but quantitatively different from various types of injury, the basic theme in remodeling is repeated. Therefore, while we use the MI model as the prototype injury model, the themes discussed here are also relevant to cardiac remodeling due to other types of injury.

Macrophage roles following myocardial infarction

Following myocardial infarction (MI), circulating blood monocytes respond to chemotactic factors, migrate into the infarcted myocardium, and differentiate into macrophages. At the injury site, macrophages remove necrotic cardiac myocytes and apoptotic neutrophils; secrete cytokines, chemokines, and growth factors; and modulate phases of the angiogenic response. As such, the macrophage is a primary responder cell type that is involved in the regulation of post-MI wound healing at multiple levels. This review summarizes what is currently known about macrophage functions post-MI and borrows literature from other injury and inflammatory models to speculate on additional roles. Basic science and clinical avenues that remain to be explored are also discussed.

Serological evidence of early remodeling in high-risk non-ST elevation acute coronary syndromes

INTRODUCTION

Non-ST elevation acute coronary syndrome (ACS) represents a spectrum of risk, with electrocardiographic (ECG) changes and a positive troponin being associated with higher morbidity and mortality. Ischaemia produces alterations in the collagenous component of the heart, even in the absence of myocyte necrosis. Collagen turnover can be assessed biochemically with C-propeptide for type I collagen (PICP) and C-telopeptide for type I collagen (CITP) being markers of collagen synthesis and degradation respectively. Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) is a marker of inhibition of degradation.

METHODS

Fifty-two patients with non-ST elevation acute ACS were recruited and dichotomised into high- and low-risk groups based on ECG and troponin level. Sequential measurements of plasma PICP, CITP and TIMP-1 were performed over a 48 hour period.

RESULTS

Twenty were classified as low-risk (negative troponin and normal ECG) and 32 as high-risk. PICP was within the normal range at all time points in both groups. However, admission CITP was higher in the high-risk group (3.7 vs. 2.6 ng/ml, p<0.001) and, unlike the low-risk group, demonstrated a further rise over 48 h. Similarly, mean TIMP-1 displayed a sequential change over time in the high-risk group only, and admission level was higher compared to the low-risk group (302 vs. 221 ng/ml, p<0.01).

DISCUSSION

There is serological evidence of time-dependent altered collagen metabolism in high-risk ACS, which is not present in the low-risk group. This may reflect a degree of remodeling and may aid risk stratification of patients presenting with non-ST elevation ACS.