Pregnancy-Associated Plasma Protein A and Its Endogenous Inhibitor, the Proform of Eosinophil Major Basic Protein (proMBP), Are Related to Complex Stenosis Morphology in Patients With Stable Angina Pectoris

Biomarkers of atherosclerotic plaque instability and rupture

Basic research over the last two decades has identified a large number of molecules pertinent to the atherosclerotic process, which have clearly improved our understanding of the underlying pathology. It is now well established that inflammation represents a major feature which is present in the vessel wall throughout all stages of the disease until the final pathophysiologic steps, representing plaque destabilization and eventually plaque rupture. Several cells typical for the atherosclerotic plaque, like monocyte-derived macrophages and T-lymphocytes are able to produce and secrete such mediator molecules, like cytokines, chemokines, growth-factors, enzymes, and disintegrins, which lead to activation of endothelial cells, proliferation of smooth muscle cells, lesion progression, and finally to the weakening of a vulnerable plaque by matrix degradation of its fibrous cap. Today, many of these molecules involved can be measured systemically by sensitive assays, and elevated concentrations in the circulation have been shown to be associated with future cardiovascular events. Determination of several of these molecules carries important prognostic information, independent of traditional risk factors, and may turn out to be useful in improving risk stratification. However, for most of these biomarkers the clinical utility has not yet been established.

The potential role of antiplatelet agents in modulating inflammatory markers in atherothrombosis

Atherothrombosis is the process that links atherosclerotic lesion development with unpredictable and life-threatening ischemic vascular events such as angina, myocardial infarction, transient ischemic attack, and stroke. Atherothrombosis is triggered when an unstable atherosclerotic lesion is ruptured, leading to platelet activation and thrombus formation. Inflammatory mediators are responsible for lesion instability leading to rupture, and in recent years atherothrombosis and its underlying condition of atherosclerosis have come to be recognized as manifestations of inflammatory disease. Inflammatory mediators may therefore serve as early markers of atherothrombosis. Measurement of early markers may be used to predict future ischemic events and improve risk stratification in patients following diagnosis of atherothrombotic disease. In addition, detection of such markers may help to optimize the use of current therapies to manage atherothrombosis. Molecules that may serve as early markers of atherothrombotic disease include C-reactive protein, CD40 ligand, myeloperoxidase, pregnancy-associated plasma protein and plasminogen activator inhibitor-1. Early indications are that levels of these markers are influenced by therapies currently in use in the treatment of atherothrombotic conditions, including antiplatelet agents. Ongoing studies will provide further insight into routine assessment of inflammatory markers as a guide to the management of patients with atherothrombosis.

Current status of risk stratification methods in acute coronary syndromes

Distinguishing which patients with chest pain are at high risk versus which are at low risk remains an important clinical problem despite modern risk stratification strategies. Current approaches often over-utilize hospital resources, yet still miss a significant number of true acute coronary syndromes (ACS). This review focuses on important developments in risk stratification in ACS from 2004 through 2005. Risk models have been developed that use readily available patient characteristics, and head to head comparisons of the various models have been performed to guide clinicians in selecting between the different options. The most powerful models now include measurement of renal function, which has emerged as an important marker of risk. In addition to cardiac troponins, B-type natriuretic peptide (BNP) clearly augments risk prediction, and in the past year serial BNP measurement after discharge has shown promise as a simple way to monitor patient risk following ACS. Newer biomarkers are on the horizon but have not yet established their clinical value. Finally, advances in coronary CT angiography and bedside echocardiography offer hope that noninvasive imaging may play a more important role in early risk stratification in the near future.

Immunofluorometric Point-of-Care Assays for the Detection of Acute Coronary Syndrome-Related Noncomplexed Pregnancy-Associated Plasma Protein A

Background: We recently reported that the pregnancy-associated plasma protein A (PAPP-A) form specifically related to acute coronary syndromes (ACS) is not complexed with the proform of eosinophil major basic protein (proMBP). The aim of this study was to develop rapid point-of-care immunoassays for the measurement of the noncomplexed PAPP-A.

Methods: We developed immunofluorometric noncompetitive dry-reagent assays for total PAPP-A with 2 PAPP-A subunit-specific monoclonal antibodies and for PAPP-A/proMBP complex with 1 PAPP-A subunit-specific antibody and 1 proMBP subunit-specific antibody. The concentration of noncomplexed PAPP-A was determined as the difference of the results obtained with the 2 assays.

Results: The assays were linear from 0.5 to 300 mIU/L. The analytical detection limit and functional detection limit (CV <20%) were 0.18 mIU/L and 0.27 mIU/L for total PAPP-A assay and 0.23 mIU/L and 0.70 mIU/L for PAPP-A/proMBP assay, respectively. The total assay imprecisions were <10%, and recoveries were 88%–107% for both assays. The mean difference (95% limits of agreement) between the new total PAPP-A assay and a previously reported total PAPP-A assay was −3.2% (−45.7% to 39.3%; n = 546; P = 0.0019). In serum samples from 159 non-ACS individuals, median concentrations (interquartile range) were 2.42 (1.14) mIU/L for total PAPP-A, 2.20 (1.18) mIU/L for PAPP-A/proMBP, and 0.18 (0.63) mIU/L for noncomplexed PAPP-A. Total PAPP-A and PAPP-A/proMBP, but not noncomplexed PAPP-A, correlated with age (r = 0.290, P = 0.0002; r = 0.230, P = 0.0035; r = 0.075, P = 0.3483, respectively).

Conclusions: The new assays described revealed that noncomplexed PAPP-A is found only in negligible amounts in non-ACS samples.

Plasma adiponectin levels are associated with coronary lesion complexity in men with coronary artery disease

OBJECTIVES

We sought to assess whether plasma adiponectin levels correlate with angiographic coronary lesion complexity in patients with coronary artery disease (CAD).

BACKGROUND

Metabolic disorders, including diabetes mellitus and metabolic syndrome, are important risk factors for acute cardiovascular events, and adiponectin is a key molecule of metabolic disorders, with anti-atherogenic properties. Low plasma adiponectin levels are associated with CAD and future incidence of myocardial infarction. The involvement of adiponectin in coronary plaque vulnerability, which may be reflected by angiographic complex lesions, remains to be elucidated.

METHODS

We measured plasma adiponectin levels in 207 men (152 with stable CAD and 55 with acute coronary syndromes [ACS]). Coronary lesions were classified as of simple or complex appearance.

RESULTS

Plasma adiponectin levels were significantly lower in stable CAD patients with complex coronary lesions (n = 60) than in those with simple lesions (n = 92) (4.14 [range 2.95 to 6.02] vs. 5.27 [range 3.67 to 8.12] microg/ml, p = 0.006). Multiple logistic regression analysis demonstrated that adiponectin level was independently associated with complex lesions (odds ratio 0.514, 95% confidence interval 0.278 to 0.951; p = 0.034). Polytomous logistic regression revealed that adiponectin correlated independently with both single and multiple complex lesions. Among patients with ACS, who had lower adiponectin levels than stable CAD patients, those with multiple complex lesions had significantly lower adiponectin than those with a single complex lesion (3.26 [range 2.26 to 4.46] vs. 4.21 [range 3.36 to 5.41] microg/ml, p = 0.032).

CONCLUSIONS

Plasma adiponectin levels are significantly associated with coronary lesion complexity in men with CAD. Low adiponectin levels may contribute to coronary plaque vulnerability.

Pregnancy-associated plasma protein A: a biomarker in acute ST-elevation myocardial infarction (STEMI)

BACKGROUND

Elevated circulating levels of pregnancy-associated plasma protein A (PAPP-A), a novel marker of atherosclerotic plaque instability, are associated with increased risk of future cardiac events in patients with acute coronary syndromes (ACS). However, little is known of the kinetics or clinical significance of circulating PAPP-A after plaque rupture in acute ST-elevation myocardial infarction (STEMI).

AIM

To evaluate the 48-hour release of pregnancy-associated plasma protein A (PAPP-A) and its association with 12-month outcome in patients with acute ST-elevation myocardial infarction (STEMI).

METHODS

Sixty-two consecutive STEMI patients were included (40 men and 22 women, median age 67.5 years (range 34-84)), of whom 54 (87.1%) received reperfusion therapy. PAPP-A was measured at admission and 6-12, 24 and 48 hours thereafter. In 14 patients, samples were obtained also at 1, 2 and 4 hours.

RESULTS

There was an early peak of circulating PAPP-A during the first 12 hours from symptom onset, followed by rapid normalization. A second, late PAPP-A elevation was noticed in 20/62 patients (32.3%). Admission PAPP-A >10.0 mIU/L (highest tertile) was associated (P = 0.049) with increased 12-month risk of cardiovascular death or non-fatal myocardial infarction. Moreover, the combination of failed early reperfusion together with late PAPP-A elevation was strongly (7/13 versus 10/49 patients, P = 0.016) associated with adverse outcome. Admission PAPP-A did not correlate with admission C-reactive protein or cardiac troponin I.

CONCLUSIONS

PAPP-A is elevated early in STEMI and then declines rapidly, a pattern consistent with release from the ruptured plaque. The variability of PAPP-A kinetics at 48 hours reflects the success of reperfusion. This study also shows that PAPP-A may have prognostic value in STEMI.

Pretransplant Pregnancy-Associated Plasma Protein-A as a Predictor of Chronic Allograft Nephropathy and Posttransplant Cardiovascular Events

BACKGROUND

Cardiovascular disease and chronic allograft nephropathy (CAN) are two of the main complications observed in patients after renal transplantation. Both appear to be manifestations of the same process, in which inflammation plays a determinate role. Pregnancy-associated plasma protein A (PAPP-A) has been shown to be a marker of acute coronary syndrome and cardiovascular pathology. The objective of this study was to demonstrate whether or not serum concentration of pretransplant PAPP-A is a marker of CAN and a predictor of posttransplant cardiovascular events.

METHODS

In all, 178 renal transplants (65% males; 53+/-12 years of age) followed up over the course of 49.3+/-33.6 months were used in this study. During the follow-up period, 19 patients developed CAN (diagnosed by renal biopsy) and 27 patients had a cardiovascular event. Previous to transplantation, the following were determined: ultrasensitive C-reactive protein (CRP) (nephelometry); interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) (immunofluorimetric automatized method), and ultrasensitive PAPP-A (ELISA).

RESULTS

A positive correlation was found between PAPP-A and the inflammatory markers (PAPP-A vs. CRP, r=0.218; P=0.004; PAPP-A vs. IL-6, r=0.235; P<0.001; PAPP-A vs. TNF-alpha, r=0.372; P<0.001). The multiple regression analysis showed PAPP-A (relative risk [RR]: 6.4; 95% confidence interval [CI]:1.24-33.11; P=0.027) and CRP (RR: 6.05; 95% CI:1.21-29.74; P=0.028) to be predictors of posttransplant cardiovascular events and PAPP-A (RR: 4.27; 95% CI: 1.03-17.60; P=0.044) and TNF-alpha (RR: 5.6; 95% CI: 1.43-21.83; P=0.013) to be predictors of CAN.

CONCLUSIONS

PAPP-A correlated with the inflammatory markers studied (CRP, IL-6 and TNF-alpha). Pretransplant serum concentration of PAPP-A is a predictor of posttransplant cardiovascular events and CAN.

Relationship among pregnancy associated plasma protein-A levels, clinical characteristics, and coronary artery disease extent in patients with chronic stable angina pectoris

AIMS

To assess, in chronic stable angina (CSA) patients, the relationship among clinical characteristics and cardiovascular risk factors, extent of coronary artery disease (CAD), and pregnancy-associated plasma protein-A (PAPP-A) levels.

METHODS AND RESULTS

We studied 643 CSA patients (63+/-10 years, 482 men) undergoing diagnostic coronary angiography; 97 with angiographically normal coronary arteries or <50% stenosis, 127 with single vessel disease (VD), and 419 with multi-VD. Patients' age, gender, cardiovascular risk factors, body mass index, history of previous myocardial infarction, angina class, left ventricular ejection fraction (LVEF), and treatment were assessed at study entry. PAPP-A levels (mIU/L) were higher in men than in women (6.2+/-2.4 vs. 5.2+/-1.8; P<0.001) and in hypertensive vs. normotensive patients (6.4+/-2.8 vs. 5.8+/-2.1; P=0.01). PAPP-A correlated directly with age (r=0.19, P<0.001) and inversely with LVEF (r=-0.11, P=0.01). Patients with multivessel disease (VD) had higher PAPP-A levels (6.45+/-2.58) than those with single-VD (5.49+/-1.54, P<0.001) or normal coronaries (4.62+/-1.17, P<0.001). Male gender, age, history of a previous MI, hypercholesterolaemia, and PAPP-A levels were independent predictors for the presence of CAD.

CONCLUSION

In CSA patients PAPP-A levels correlate with age, male gender, hypertension, and CAD extent. In the present study, PAPP-A was an independent predictor for the presence and extent of CAD.

Plasma levels of oxidized-low-density lipoproteins are higher in patients with unstable angina and correlated with angiographic coronary complex plaques

OBJECTIVES

To measure circulating levels of oxidized-low-density lipoproteins (ox-LDL) in patients with stable and unstable angina and controls, and to investigate their correlation with the extent of coronary artery disease (CAD) and the presence of complex plaques at coronary angiography.

METHODS AND RESULTS

Circulating ox-LDL were assessed, using ELISA, in patients with unstable angina (UA, n=26), stable angina (SA, n=29) and in controls (C, n=27). All patients underwent coronary angiography. The extent of CAD was evaluated using a quantitative score, while the presence of complex, vulnerable plaques was angiographically assessed. Ox-LDL were higher in UA patients than in SA patients and in C subjects, and in SA patients than in C subjects (C, 45.6+/-12.8 U/L; SA, 58.8+/-11.0 U/L; UA, 73.7+/-13.6 U/L; p<0.001). No correlation was found with the extent of atherosclerotic disease in the coronary tree. Patients with angiographic complex lesions showed significantly higher levels of ox-LDL (68.4+/-13.9 U/L versus 55.2+/-16.4 U/L, p<0.001). Multiple regression analysis showed that ox-LDL were independent predictors of the presence of complex plaques (p<0.023).

CONCLUSIONS

Ox-LDL levels are higher in unstable patients and correlate with the presence of angiographically documented complex plaques. Ox-LDL might be markers of destabilization of CAD.

Pregnancy-associated plasma protein-A levels in patients with acute coronary syndromes: comparison with markers of systemic inflammation, platelet activation, and myocardial necrosis

OBJECTIVES

The goal of this study was to determine the predictive value of pregnancy-associated plasma protein-A (PAPP-A) in patients with acute coronary syndromes (ACS).

BACKGROUND

Pregnancy-associated plasma protein-A is a zinc-binding matrix metalloproteinase abundantly expressed in eroded and ruptured plaques and may serve as a marker of plaque destabilization.

METHODS

In 547 patients with angiographically validated ACS and in a heterogeneous emergency room population of 644 patients with acute chest pain, respectively, PAPP-A as well as markers of myocardial necrosis (troponin T [TnT]), ischemia (vascular endothelial growth factor [VEGF]), inflammation (high-sensitivity C-reactive protein [hsCRP]), anti-inflammatory activity (interleukin [IL]-10), and platelet activation (soluble CD40 ligand [sCD40L]) were determined. Patients were followed for the occurrence of death or myocardial infarction.

RESULTS

In patients with ACS, elevated PAPP-A levels (>12.6 mIU/l) indicated an increased risk (odds ratio 2.44 [95% confidence interval (CI) 1.43 to 4.15]; p = 0.001). When the analysis was restricted to TnT-negative patients, PAPP-A still identified a subgroup of high-risk patients (odds ratio [OR] 2.72 [95% confidence interval (CI) 1.25 to 5.89]; p = 0.009). In a multivariable model, PAPP-A (OR 2.01; p = 0.015), sCD40L (OR 2.37; p = 0.003), IL-10 (OR 0.43; p = 0.003), and VEGF (OR 2.19; p = 0.018) were independent predictors. Prospective validation in patients with chest pain confirmed that PAPP-A levels reliably identify high-risk patients (adjusted OR 2.32 [95% CI 1.32 to 4.26]; p = 0.008). Patients negative for all three markers (TnT, sCD40L, and PAPP-A) were at very low cardiac risk (30 days: 3.0% event rate; no death).

CONCLUSIONS

The PAPP-A level as a marker of plaque instability is a strong independent predictor of cardiovascular events in patients with ACS. Simultaneous determination of biomarkers with distinct pathophysiological profiles appears to remarkably improve risk stratification in patients with ACS.

Biomarkers of cardiac disease

The challenge of medical practice today is to identify individuals who are at risk of developing disease, determine the severity of the disease and distinguish the responders from the nonresponders to therapy (individualized medicine). Advances in molecular genetics and biology have shifted the paradigm for identification of markers from large-scale epidemiologic studies to studies on genomic- and proteomic-based techniques. Consequently, a large number of biologic markers, referred to as biomarkers, are being identified and validated to serve for risk stratification, prognostication and individualization of therapy. Identification of biomarkers for cardiovascular diseases could also provide insight into the pathogenesis of the phenotype, which is fundamental for the development of specific therapies. The list of biomarkers for cardiovascular disease is expanding rapidly. Nonetheless, the field is in the early stages of evolution and large-scale clinical studies are required to validate the utility of newly identified biomarkers in diagnosis, risk stratification and treatment of cardiovascular diseases. Selected biomarkers for coronary atherosclerosis, acute coronary syndromes and heart failure are discussed in this review.

CDC/AHA Workshop on Markers of Inflammation and Cardiovascular Disease

Inflammation is a recognized key component of acute coronary syndromes. Such pathogenetic achievement has led to the use of inflammatory cells and proteins as prognostic markers in these syndromes. A number of markers have been proposed, including proinflammatory cytokines such as interleukin-6, interleukin-1RA, and tumor necrosis factor-α, adhesion molecules such as intracellular adhesion molecule-1 and vascular adhesion molecule-1 and markers of cell activation. Although all are of scientific interest, the clinical use of these markers is limited by their high cost, low availability, and unfavorable biological profile. Conversely, common markers of inflammation such as C-reactive protein (CRP), the prototypic acute phase protein, and to a lesser extent fibrinogen, have been proven to be reliable and important markers of risk in ischemic heart disease. CRP, in particular, has been found to be associated with short- and long-term prognosis in acute coronary syndromes, including ST-elevation myocardial infarction, and in stable angina, and to predict the risk of restenosis and major events, including death, after revascularization procedures. CRP has been consistently found to be independent from other risk factors and to have an incremental value beyond the common risk factors and biochemical markers of risk, including troponin. Whether CRP also should be used as a guide to therapy is still a matter of discussion that deserves further, properly designed studies.