Temporal course of pregnancy-associated plasma protein-A in angioplasty-treated ST-elevation myocardial infarction patients and potential significance of concomitant heparin administration

Exploring free pregnancy associated plasma protein a (fPAPP-A) as a biomarker in early pregnancy

Objectives

In combined first trimester screening for Down syndrome, Pregnancy-Associated Plasma Protein A (PAPP-A) is pivotal. PAPP-A tests evaluate total PAPP-A, consisting of the biologically active free PAPP-A (fPAPP-A) and PAPP-A complexed with eosinophil major basic protein's proform (proMBP). While PAPP-A is well-researched, limited understanding persists regarding fPAPP-A's first trimester concentrations and diagnostic utility.

Design

and methods: PAPP-A and fPAPP-A levels were gauged in 602 serum samples at 2-week intervals (gestational weeks 4-14) from 159 women with delivery of a healthy neonate and 80 samples from 37 miscarriages. The final sample at the time of diagnosis from women who miscarried was included in analyses.

Results

During the first trimester, PAPP-A and fPAPP-A levels displayed significant and strong correlation (r = 0.94), with median values doubling weekly. Free PAPP-A constituted only 3.0 % of PAPP-A over gestational weeks. Low fPAPP-A linked to miscarriage (p < 0.001), maternal weight (p < 0.001), and smoking (p = 0.02). For miscarriage prediction fPAPP-A was equal to PAPP-A (area under the receiver operating characteristics curve 0.79 vs. 0.81, p = 0.44).

Conclusions

Investigating fPAPP-A presence and concentration directly in first trimester serum has not been done previously. This study report lower fPAPP-A values than anticipated from prior enzymatic studies of fPAPP-A. fPAPP-A was not superior to PAPP-A as a first trimester biomarker in this dataset.

The pro-atherogenic enzyme PAPP-A is active in eluates from human carotid and femoral atherosclerotic plaques

Background

Pregnancy-associated plasma protein-A (PAPP-A) regulates bioavailability of insulin-like growth factor 1 (IGF1) in various tissues by proteolytic cleavage of a subset of IGF-binding proteins (IGFBPs). Pre-clinical studies have established a role of PAPP-A in atherosclerosis and proposed that targeting the proteolytic activity of PAPP-A has therapeutic value.This study aimed to investigate whether human atherosclerotic plaques contain proteolytically active PAPP-A, a prerequisite for further considering PAPP-A as a therapeutic target in patients.

Methods

We obtained carotid (n = 9) and femoral (n = 11) atherosclerotic plaques from patients undergoing vascular surgery and incubated freshly harvested plaque tissue in culture media for 24 h. Subsequently, conditioned media were assayed for PAPP-A, STC2, IGFBP4, and IGF1 using immunoassays. Enzymatic activity of PAPP-A was assessed by its ability to process recombinant IGFBP4-IGF1 complexes - a specific substrate of PAPP-A - by Western blotting.

Results

PAPP-A and STC2 were detectable in conditioned media from both carotid and femoral plaques, with higher STC2 concentrations in eluates from carotid plaque incubations (p = 0.02). IGFBP4 and IGF1 were undetectable. Conditioned media from all 20 plaques exhibited PAPP-A proteolytic activity. However, no correlation between PAPP-A concentration and its proteolytic activity was observed, whereas the PAPP-A: STC2 molar ratio correlated with PAPP-A activity (R2 = 0.25, p = 0.03).

Conclusion

This study provides evidence for the presence of enzymatically active PAPP-A in atherosclerotic plaques and underscores the need for further investigating potential beneficial effects associated with targeting PAPP-A in atherosclerotic cardiovascular disease.

The Stanniocalcin-PAPP-A-IGFBP-IGF Axis

The pappalysin metalloproteinases, PAPP-A and PAPP-A2, have emerged as highly specific proteolytic enzymes involved in the regulation of insulin-like growth factor (IGF) signaling. The only known pappalysin substrates are a subset of the IGF binding proteins (IGFBPs), which bind IGF-I or IGF-II with high affinity to antagonize receptor binding. Thus, by cleaving IGFBPs, the pappalysins have the potential to increase IGF bioactivity and hence promote IGF signaling. This is relevant both in systemic and local IGF regulation, in normal and several pathophysiological conditions. Stanniocalcin-1 and -2 were recently found to be potent pappalysin inhibitors, thus comprising the missing components of a complete proteolytic system, the stanniocalcin-PAPP-A-IGFBP-IGF axis. Here, we provide the biological context necessary for understanding the properties of this molecular network, and we review biochemical data, animal experiments, clinical data, and genetic data supporting the physiological operation of this branch as an important part of the IGF system. However, although in vivo data clearly illustrate its power, it is a challenge to understand its subtle operation, for example, multiple equilibria and inhibitory kinetics may determine how, where, and when the IGF receptor is stimulated. In addition, literally all of the regulatory proteins have suspected or known activities that are not directly related to IGF signaling. How such activities may integrate with IGF signaling is also important to address in the future.

Risk Assessment after ST-Segment Elevation Myocardial Infarction: Can Biomarkers Improve the Performance of Clinical Variables?

INTRODUCTION

Myocardial infarction with ST-segment elevation (STEMI) is the coronary artery disease associated with the highest risk of morbimortality; however, this risk is heterogeneous, usually being evaluated by clinical scores. Risk assessment is a key factor in personalized clinical management of patients with this disease.

AIM

The aim of this study was to assess whether some new cardiac biomarkers considered alone, combined in a multibiomarker model or in association with clinical variables, improve the short- and long-term risk stratification of STEMI patients.

MATERIALS AND METHODS

This was a retrospective observational study of 253 patients with STEMI. Blood samples were obtained before or during the angiography. The assessed biomarkers were C-terminal fragment of insulin-like growth factor binding protein-4 (CT-IGFBP4), high sensitive cardiac troponin T (hs-cTnT), N-terminal fragment of probrain natriuretic peptide (NT-proBNP), and growth differentiation factor 15 (GDF-15); they reflect different cardiovascular (CV) physiopathological pathways and underlying pathologies. We registered in-hospital and follow-up mortalities and their causes (cardiovascular and all-cause) and major adverse cardiac events (MACE) during a two year follow-up. Discrimination, survival analysis, model calibration, and reclassification of the biomarkers were comprehensively evaluated.

RESULTS AND DISCUSSION

In total, 55 patients (21.7%) died, 33 in-hospital and 22 during the follow-up, most of them (69.1%) from CV causes; 37 MACE occurred during follow-up. Biomarkers showed good prognostic ability to predict mortality, alone and combined with the multibiomarker model. A predictive clinical model based on age, Killip-Kimball class, estimated glomerular filtration rate (eGFR), and heart rate was derived by multivariate analysis. GDF-15 and NT-proBNP significantly improved risk assessment of the clinical model, as shown by discrimination, calibration, and reclassification of all the end-points except for all-cause mortality. The combination of NT-proBNP and hs-cTnT improved CV mortality prediction.

CONCLUSIONS

GDF-15 and NT-proBNP added value to the usual risk assessment of STEMI patients.

Distinct plasma biomarkers confirm the diagnosis of mastocytosis and identify increased risk of anaphylaxis

BACKGROUND

Mastocytosis encompasses a heterogeneous group of disorders characterized by accumulation of clonal mast cells (MCs) in the skin and/or internal organs. Patients typically present with a broad variety of recurrent mediator-related clinical symptoms, including severe anaphylaxis. However, not all patients with mastocytosis experience anaphylactic reactions.

OBJECTIVE

We sought to identify disease-specific biomarkers in plasma that could be used to predict patients with mastocytosis with increased risk of anaphylaxis.

METHODS

Nineteen patients (≥18 years) and 2 control groups (11 subjects with allergic asthma and 13 healthy volunteers without history of atopy) were recruited. In total, 248 plasma proteins were analyzed by Proximity Extension Assay using Olink Proseek Multiplex panels.

RESULTS

We identified 4 novel proteins, in addition to tryptase, E-selectin, adrenomedullin, T-cell immunoglobulin, and mucin domain 1, and CUB domain-containing protein 1/CD138 to be significantly increased in patients with mastocytosis compared with both patients with asthma and healthy controls. Furthermore, we investigated whether we could discriminate between patients with mastocytosis with or without anaphylaxis. In addition to tryptase, we identified 3 novel proteins, that is, allergin-1, pregnancy-associated plasma protein-A, and galectin-3, with significantly different levels in patients with mastocytosis with anaphylaxis compared with those without anaphylaxis.

CONCLUSIONS

Newly identified proteomic biomarkers may be used to predict patients with mastocytosis with increased risk of anaphylaxis.

Local IGF Bioactivity Associates with High PAPP-A Activity in the Pericardial Cavity of Cardiovascular Disease Patients

OBJECTIVE

Pregnancy-associated plasma protein-A (PAPP-A) has been suggested as a proatherogenic enzyme by its ability to locally increase insulin-like growth factor (IGF) activity through proteolytic cleavage of IGF binding protein-4 (IGFBP-4). Recently, stanniocalcin-2 (STC2) was discovered as an inhibitor of PAPP-A. This study aimed to investigate IGFBP-4, PAPP-A, and STC2 as local regulators of IGF bioactivity in the cardiac microenvironment by comparing levels in the pericardial fluid with those in the circulation of patients with cardiovascular disease.

METHODS

Plasma and pericardial fluid were obtained from 39 patients undergoing elective cardiothoracic surgery, hereof 15 patients with type 2 diabetes. Concentrations of IGF-I, intact and fragmented IGFBP-4, PAPP-A, and STC2 were determined by immunoassays and IGF bioactivity by a cell-based assay.

RESULTS

In pericardial fluid, the concentrations of total IGF-I, intact IGFBP-4, and STC2 were 72 ± 10%, 91 ± 5%, and 40 ± 24% lower than in plasma, while PAPP-A was 15 times more concentrated. The levels of the 2 IGFBP-4 fragments generated by PAPP-A and reflecting PAPP-A activity were elevated by more than 25%. IGF bioactivity was 62 ± 81% higher in the pericardial fluid than plasma. Moreover, pericardial fluid levels of both IGFBP-4 fragments correlated with the concentration of PAPP-A and with the bioactivity of IGF. All protein levels were similar in pericardial fluid from nondiabetic and diabetic subjects.

CONCLUSIONS

PAPP-A increases IGF bioactivity by cleavage of IGFBP-4 in the pericardial cavity of cardiovascular disease patients. This study provides evidence for a distinct local activity of the IGF system, which may promote cardiac dysfunction and coronary atherosclerosis.

PAPP-A and the IGF system in atherosclerosis: what's up, what's down?

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase with a well-established role in releasing bioactive insulin-like growth factor-1 (IGF-1) from IGF-binding protein-2, -4, and -5 by proteolytic processing of these. The IGF system has repeatedly been suggested to be involved in the pathology of atherosclerosis, and both PAPP-A and IGF-1 are proposed biomarkers and therapeutic targets for this disease. Several experimental approaches based on atherosclerosis mouse models have been undertaken to obtain causative and mechanistic insight to the role of these molecules in atherogenesis. However, reports seem conflicting. The literature suggests that PAPP-A is detrimental, while IGF-1 is beneficial. This raises important questions that need to be addressed. Here we summarize the various studies and discuss potential underlying explanations for this seemingly inconsistency with the objective of better understanding complexities and limitations when manipulating the IGF system in mouse models of atherosclerosis. A debate clarifying what's up and what's down is highly warranted going forward with the ultimate goal of improving atherosclerosis therapy by targeting the IGF system.

Plasma CCN2 is independently related to subsequent need for abdominal aorta aneurysm repair

The objective of this study was to determine if plasma CCN2 is associated with abdominal aorta aneurysm (AAA), and future need for AAA repair, and further to assess the potential clinical value of CCN2 in predicting disease outcome. CCN2 was quantified in plasma samples obtained from a cohort of 679 men aged 65-74 at initial ultrasound screening for AAA in the Viborg Vascular (VIVA) screening trial. Plasma CCN2 was correlated with need for future surgical repair in the whole study population (HR = 1.457 (1.081-1.962), p = .013) and in the AAA group alone (HR = 1.431 (1.064-1.926), p = .018), yet the predictive value (CCN2 > 0 and <0 of 0.52 and 0.55, respectively) disqualified its use in clinically relevant AAA repair prediction. In conclusion, CCN2 is independently related to subsequent need for AAA repair, but has negligible predictive power for clinical use.

IGFBP-4 and PAPP-A in normal physiology and disease

Insulin-like growth factor (IGF) binding protein-4 (IGFBP-4) is a modulator of the IGF system, exerting both inhibitory and stimulatory effects on IGF-induced cellular growth. IGFBP-4 is the principal substrate for the enzyme pregnancy-associated plasma protein-A (PAPP-A). Through IGF-dependent cleavage of IGFBP-4 in the vicinity of the IGF receptor, PAPP-A is able to increase IGF bioavailability and stimulate IGF-mediated growth. Recently, the stanniocalcins (STCs) were identified as novel inhibitors of PAPP-A proteolytic activity, hereby adding additional members to the seemingly endless list of proteins belonging to the IGF family. Our understanding of these proteins has advanced throughout recent years, and there is evidence to suggest that the role of IGFBP-4 and PAPP-A in defining the relationship between total IGF and IGF bioactivity can be linked to a number of pathological conditions. This review provides an overview of the experimental and clinical findings on the IGFBP-4/PAPP-A/STC axis as a regulator of IGF activity and examines the conundrum surrounding extrapolation of circulating concentrations to tissue action of these proteins. The primary focus will be on the biological significance of IGFBP-4 and PAPP-A in normal physiology and in pathophysiology with emphasis on metabolic disorders, cardiovascular diseases, and cancer. Finally, the review assesses current new trajectories of IGFBP-4 and PAPP-A research.

Prognostic value of the Stanniocalcin-2/PAPP-A/IGFBP-4 axis in ST-segment elevation myocardial infarction

Objective

The aim of the present study was to evaluate the prognostic value of the Stanniocalcin-2/PAPP-A/IGFBP-4 axis in patients with ST-segment elevation myocardial infarction (STEMI).

Methods

Observational cohort study performed in 1085 consecutive STEMI patients treated with early reperfusion between February 2011 and August 2014. Stanniocalcin-2, PAPP-A, and IGFBP-4 were measured using state-of-the art immunoassays. The primary outcome was the composite endpoint of all-cause mortality and readmission due to heart failure (HF).

Results

Median follow-up was 3.3 years (IQR 1.0–3.7), during which 176 patients (16.2%) presented a composite endpoint. Multivariable cox regression analysis revealed that Stanniocalcin-2 (HR 2.06; 95% CI 1.13–3.75; p = 0.018), IGFBP-4 (HR 1.73; 95% CI 1.14–2.64; p = 0.010), Killip–Kimball class III–IV (HR 1.40; 95% CI 1.13–1.74; p = 0.002), NT-ProBNP (HR 1.21; 95% CI 1.07–1.37; p = 0.002), age (HR 1.06; 95% CI 1.04–1.08; p < 0.001) and left ventricular ejection fraction (HR 0.97; 95% CI 0.95–0.98; p < 0.001) were independent predictors of the composite endpoint. A model containing Stanniocalcin-2 and IGFBP-4 on top of clinical variables significantly improved C-index discrimination (p = 0.036). Stanniocalcin-2 was also identified as independent predictor of all-cause mortality (HR 2.23; 95% CI 1.16–4.29; p = 0.017) and readmission due to HF (HR 3.42; 95% CI 1.22–9.60; p = 0.020).

Conclusions

In STEMI patients, Stanniocalcin-2 and IGFBP-4 emerged as independent predictors of all-cause death and readmission due to HF. The Stanniocalcin-2/PAPP-A/IGFBP-4 axis exhibits a significant role in STEMI risk stratification.

Current IGFBP-Related Biomarker Research in Cardiovascular Disease-We Need More Structural and Functional Information in Clinical Studies

Cardiovascular diseases are the leading cause of death around the world and the insulin-like growth factor (IGF)-system has multiple functions for the pathological conditions of atherosclerosis. IGF binding proteins (IGFBPs) are widely investigated as biomarkers for pathological disorders, including those of the heart. At the tissue level, IGFBP-1 to -6 decrease bioactivity of IGF-I and -II due to their high affinity IGF-binding sites. By contrast, in the circulation, the IGFBPs increase biological half-life of the IGFs and may therefore be regarded as positive regulators of IGF-effects. The IGFBPs may also exert IGF-independent functions inside or outside the cell. Importantly, the circulating IGFBP-concentrations are regulated by trophic, metabolic, and reproductive hormones. In a multitude of studies of healthy subjects and patients with coronary heart diseases, various significant associations between circulating IGFBP-levels and defined parameters have been reported. However, the complex hormonal and conditional control of IGFBPs may explain the lack of clear associations between IGFBPs and parameters of cardiac failure in broader studies including larger populations. Furthermore, the IGFBPs are subject to posttranslational modifications and proteolytic degradation by proteases, upon which the IGFs are released. In this review, we emphasize that, with the exception of IGFBP-4 and in sharp contrast to the preclinical studies, virtually all clinical studies do not have structural or functional information on their biomarker. The use of analytical systems with no discriminatory potential toward intact vs. fragmented IGFBPs represents a major issue in IGFBP-related biomarker research and an important focus point for the future. Overall, measurements of selected IGFBPs or more complex IGFBP-signatures of the family of IGFBPs have potential to identify pathophysiological alterations in the heart or patients with high cardiovascular risk, particularly if defined cohorts are to be assessed. However, a more thorough understanding of the dynamic IGF-IGFBP system as well as its proteases and protease inhibitors in both normal physiology and in cardiovascular diseases is necessary.

Pregnancy associated plasma protein-A as a prognostic biomarker of all-cause mortality and cardiovascular events in patients presenting with chest pain: a systematic review

AIM

Novel biomarkers have been proposed for identification of patients at greater risk of future adverse events among those presenting with chest pain. In this review, we aim to elucidate the ability of pregnancy associated plasma protein-A (PAPP-A) to predict mortality and other cardiovascular events in this patient population.

METHODS

A literature search of the electronic databases Medline, Scopus, Cochrane Library and ClinicalTrials.gov was performed in order to identify studies investigating the utility of PAPP-A to predict mortality and adverse cardiovascular events in patients with chest pain.

RESULTS

Eight studies met our inclusion criteria. Five of these studies pertained to patients with confirmed ischemic chest pain, while the rest included patients presenting with chest pain possibly due to acute coronary syndrome, irrespectively of the underlying cause. Although the results for long-term events were inconclusive in both groups of patients, higher PAPP-A concentrations were found to be a significant predictor of short-term adverse events in patients with confirmed ischemic chest pain.

CONCLUSIONS

PAPP-A appears to be a potentially useful biomarker for short-term risk stratification of patients presenting with chest pain of ischemic origin. However, there is an eminent need for more standardized clinical studies investigating the prognostic value of this biomarker.

Novel Risk Stratification Assays for Acute Coronary Syndrome

PURPOSE OF REVIEW

Since identification of aspartate aminotransferase as the first cardiac biomarker in the 1950s, there have been a number of new markers used for myocardial damage detection over the decades. There have also been several generations of troponin assays, each with progressively increasing sensitivity for troponin detection. Accordingly, the "standard of care" for myocardial damage detection continues to change. The purpose of this paper is to review the clinical utility, biological mechanisms, and predictive value of these various biomarkers in contemporary clinical studies.

RECENT FINDINGS

As of this writing, a fifth "next" generation troponin assay has now been cleared by the US Food and Drug Administration for clinical use in the USA for subjects presenting with suspected acute coronary syndromes. Use of these high-sensitivity assays has allowed for earlier detection of myocardial damage as well as greater negative predictive value for infarction after only one or two serial measurements. Recent algorithms utilizing these assays have allowed for more rapid rule-out of myocardial infarction in emergency department settings. In this review, we discuss novel assays available for the risk assessment of subjects presenting with chest pain, including both the "next generation" cardiac troponin assays as well as other novel biomarkers. We review the biological mechanisms for these markers, and explore the positive and negative predictive value of the assays in clinical studies, where reported. We also discuss the potential use of these new markers within the context of future clinical care in the modern era of higher sensitivity troponin testing. Finally, we discuss advances in new platforms (e.g., mass spectrometry) that historically have not been considered for rapid in vitro diagnostic capabilities, but that are taking a larger role in clinical diagnostics, and whose prognostic value and power promise to usher in new markers with potential for future clinical utility in acute coronary syndrome.

Insulin-Like Growth Factor Binding Protein 4 Fragments Provide Incremental Prognostic Information on Cardiovascular Events in Patients With ST-Segment Elevation Myocardial Infarction

BACKGROUND

Fragments of insulin-like growth factor binding protein 4 (IGFBP-4) are potential new biomarkers for cardiac risk assessment. The fragments are generated on specific cleavage by pregnancy-associated plasma protein-A, which exerts proatherogenic activity. This study investigated the prognostic value of IGFBP-4 fragments in patients with ST-segment elevation myocardial infarction.

METHODS AND RESULTS

We prospectively included 656 patients with ST-segment elevation myocardial infarction treated with percutaneous coronary intervention from September 2006 to December 2008. Blood samples were drawn before percutaneous coronary intervention, and levels of intact IGFBP-4 and N-terminal and C-terminal IGFBP-4 fragments were measured by specific assays. End points were 5-year all-cause and cardiovascular mortality and the combined end point of major adverse cardiac events. Prognostic potential was evaluated on top of a clinical model in terms of discrimination, calibration, and reclassification analysis. During follow-up, 166 patients experienced a major adverse cardiac event and 136 patients died, of whom 69 died from cardiovascular causes. Both IGFBP-4 fragments were associated with all end points (P<0.001). After multivariable adjustments, both N-terminal and C-terminal IGFBP-4 fragment levels remained associated with all end points, including cardiovascular mortality with hazard ratios per doubling in protein concentration of 2.54 (95% CI 1.59-4.07; P<0.001) and 2.07 (95% CI 1.41-3.04; P<0.001), respectively. Incorporation of IGFBP-4 fragments into a clinical model with 15 risk factors improved C-statistics and model calibration and provided incremental prognostic contribution, as assessed by net reclassification improvement and integrated discrimination improvement.

CONCLUSIONS

IGFBP-4 fragments are associated with increased risk of all-cause mortality, cardiovascular mortality, and major adverse cardiac events in patients with ST-segment elevation myocardial infarction.

PAPP-A, IGFBP-4 and IGF-II are secreted by human adipose tissue cultures in a depot-specific manner

OBJECTIVE

Adipose tissue secretes pregnancy-associated plasma protein-A (PAPP-A), which may increase local IGF action through cleavage of IGF-binding protein-4 (IGFBP-4). We tested whether this mechanism was operational in human visceral and subcutaneous adipose tissue (i.e. VAT and SAT).

DESIGN

Explants of VAT and SAT from 26 obese subjects (hereof 17 women, BMI 39.5 (37.2; 42.8) kg/m² (median (25%; 75% confidence interval) and SAT from eight lean, age-matched women (BMI 23.6 (22.4; 24.9) kg/m²) were incubated with or without GH (100 µg/L) and the media were harvested.

METHODS

Media were assessed for concentrations of PAPP-A, intact and PAPP-A-cleaved IGFBP-4, IGF-I and IGF-II, and IGF-I receptor (IGF-IR) activation by bioassay.

RESULTS

In obese subjects, VAT media contained higher concentrations than SAT of PAPP-A (4.4-fold) and both PAPP-A-generated IGFBP-4 fragments (C-terminal: 3.3-fold, N-terminal: 1.5-fold) (all P < 0.0005). Intact IGFBP-4 levels were similar in SAT and VAT. VAT media contained elevated IGF-II (1.4-fold; P < 0.005), but similar IGF-I concentrations compared with SAT. Still, VAT media contained a 1.8-fold increased ability to stimulate the IGF-IR (P < 0.005). IGF-I protein concentration and IGF-IR activation increased more in VAT media than SAT media following GH stimulation (both P < 0.05). At baseline, SAT media protein levels from lean and obese women were similar, with the exception of PAPP-A being 1.8-fold elevated in VAT media (P < 0.05). GH induced a similar increase in IGF-I media levels in SAT from obese and lean women.

CONCLUSION

Human adipose tissue cultures secrete enzymatically active PAPP-A, IGFBP-4 and IGF-II in a depot-specific manner, suggesting differential regulation of IGF activity. Further, IGF-II appears to be more prominent than IGF-I. Finally, VAT appears more GH responsive than SAT.

Myocardial and Peripheral Ischemia Causes an Increase in Circulating Pregnancy-Associated Plasma Protein-A in Non-atherosclerotic, Non-heparinized Pigs

The usefulness of circulating pregnancy-associated plasma protein-A (PAPP-A) as a biomarker for acute coronary syndrome (ACS) is widely debated. We used the pig as a model to assess PAPP-A dynamics in the setting of myocardial ischemia. Induction of myocardial ischemia by ligation of the left anterior descending (LAD) coronary artery caused a systemic rise in PAPP-A. However, the ischemic myocardium was excluded as the source of PAPP-A. Interestingly, induction of ischemia in peripheral tissues by ligation of the left femoral artery caused a systemic rise in PAPP-A originating from the left hind limb. This is the first study to demonstrate PAPP-A elevations in the absence of atherosclerosis or heparin during myocardial ischemia. Our findings thus add to the current discussion of the usefulness of PAPP-A as a biomarker for ACS.

Pregnancy-associated plasma protein-A and the vulnerable plaque

For more than a decade, pregnancy-associated plasma protein-A (PAPP-A) has been examined for its relation to acute coronary syndrome (ACS) and the vulnerable plaque. This review summarizes the current knowledge of plasma PAPP-A in relation to nonpregnant individuals focusing on patients with ACS, discusses its use as a possible biomarker for diagnosis and prognosis in ACS, briefly describes the challenges in different assay technologies and describes the effect of heparin administration on PAPP-A concentrations in plasma.

Characterization of endogenously circulating IGFBP-4 fragments-Novel biomarkers for cardiac risk assessment

BACKGROUND

Recent findings show that circulating N- and C-terminal fragments of IGF-binding protein-4 (NT-IGFBP-4 and CT-IGFBP-4) can be utilized as biomarkers for cardiac risk assessment in acute coronary syndrome (ACS) patients. The fragments are thought to be the products of pregnancy-associated plasma protein A (PAPP-A)-dependent proteolysis. Two immunoassays for the measurement of IGFBP-4 fragments have been proposed. However, properties of the endogenous IGFBP-4 fragments that could influence the performance of the immunoassays were still not investigated.

METHODS

NT- and CT-IGFBP-4 were extracted from pooled ACS plasma using affinity purification, and their concentrations were measured using sandwich immunoassays utilizing antibodies specific to their proteolytic neo-epitopes or internal epitopes. The extracted fragments were characterized by Western blots (WB) and mass-spectrometry. ACS plasma samples were analyzed by size exclusion chromatography (SEC).

RESULTS

Immunoassays utilizing the neo-epitope-specific and the internal epitope-specific antibodies measured equal concentrations of the analyte in the endogenous IGFBP-4 fragments preparations. Only the 18 kDa NT-IGFBP-4 and 14 kDa CT-IGFBP-4 were detected in the WB analysis. Using mass-spectrometry, peaks corresponding to intact non-truncated and non-modified NT-IGFBP-4 (14626 Da) and CT-IGFBP-4 (11346 Da) were observed. The absence of complexed forms of IGFBP-4 in patients' plasma was demonstrated using SEC.

CONCLUSIONS

Endogenous NT- and CT-IGFBP-4 from ACS patients' plasma correspond to the PAPP-A-derived IGFBP-4 fragments and do not undergo any truncation, modification, or complex formation in the patients' blood. Because of the demonstrated intact state of the circulating IGFBP-4 fragments, the neo-epitope-specific immunoassays perform reliably, allowing further clinical validation of these novel biomarkers.

The effect of heparin on pregnancy associated plasma protein-A concentration in healthy, non-pregnant individuals

OBJECTIVES

The objective of this study was to determine the differences in pregnancy associated plasma protein-A (PAPP-A) concentrations in heparin naive and heparin treated healthy men and non-pregnant women, to find a possible difference in different age groups, and to determine the response in PAPP-A concentration to repeated injections of unfractionated heparin.

DESIGN AND METHODS

Twenty-five healthy, non-pregnant volunteers divided into five groups (determined by gender and age) received 5000 IU unfractionated heparin intravenously. Five young men received an additional 5000 IU after 90 and 180 min. Blood samples to determine PAPP-A concentration and APTT were drawn at different time points.

RESULTS

Injection of heparin elicited increase in and rapid normalization of PAPP-A concentrations in all subjects. The group of 20-30-year-old never-pregnant women had lower responses than the individuals of the four other groups. The difference was not significant (p > 0.05). Repeated injections of heparin caused additional peaks in PAPP-A concentration of about the same sizes as the first peak. We observed an increase in time to normalization of PAPP-A concentration (from 75-90 min to 90-150 min) and APTT levels with repeated injections.

CONCLUSIONS

We observed a rapid normalization of PAPP-A. Our result has a great similarity to the half-life of unfractionated heparin. This result combined with the finding of equally sized peaks in PAPP-A concentration, and that all of this was found in healthy, non-pregnant individuals, suggests that heparin might compete for a binding-site on PAPP-A or with PAPP-A itself for a common receptor in healthy arterial vessels.

Indirect targeting of IGF receptor signaling in vivo by substrate-selective inhibition of PAPP-A proteolytic activity

The insulin-like growth factor (IGF) signaling pathway is involved in certain human cancers, and the feasibility of directly targeting the IGF receptor has been actively investigated. However, recent evidence from clinical trials suggests that this approach can be problematic. We have developed an alternative strategy to indirectly inhibit the IGF signaling by targeting the metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). PAPP-A associated with the cell surface cleaves IGF binding protein-4 (IGFBP-4), when IGF is bound to IGFBP-4, and thereby increases IGF bioavailability for receptor activation in an autocrine/paracrine manner. We hypothesized that inhibition of PAPP-A would suppress excessive local IGF signaling in tissues where this is caused by increased PAPP-A proteolytic activity. To test this hypothesis, we developed an inhibitory monoclonal antibody, mAb 1/41, which targets a unique substrate-binding exosite of PAPP-A. This inhibitor selectively and specifically inhibits proteolytic cleavage of IGFBP-4 with an inhibitory constant (Ki) of 135 pM. In addition, it inhibited intracellular signaling of the IGF receptor (AKT phosphorylation) in monolayers of A549 cells, an IGF-responsive lung cancer-derived cell line found to express high levels of PAPP-A. We further showed that mAb 1/41 is effective towards PAPP-A bound to cell surfaces, and that it is capable of inhibiting PAPP-A activity in vivo. Using a murine xenograft model of A549 cells, we demonstrated that mAb 1/41 administered intraperitoneally significantly inhibited tumor growth. Analysis of xenograft tumor tissue recovered from treated mice showed penetration of mAb 1/41, reduced IGFBP-4 proteolysis, and reduced AKT phosphorylation. Our study provides proof of concept that IGF signaling can be selectively reduced by targeting a regulatory proteinase that functions extracellularly, upstream of the IGF receptor. PAPP-A targeting thus represents an alternative therapeutic strategy for inhibiting IGF receptor signaling.

PAPP-A and IGFBP-4 fragment levels in patients with ST-elevation myocardial infarction treated with heparin and PCI

OBJECTIVES

Circulating levels of pregnancy-associated plasma protein-A (PAPP-A) predict outcome in patients with acute coronary syndrome (ACS). Unfortunately, administration of heparin to patients with ACS increases circulating PAPP-A, probably by a detachment of PAPP-A from cell surfaces, inducing a considerable bias when using PAPP-A as a biomarker. It remains unknown whether PAPP-A-derived N- and C-terminal fragments of insulin-like growth factor binding protein-4 (NT-IGFBP-4/CT-IGFBP-4) are acutely affected by the increase in PAPP-A.

METHODS

We prospectively included 78 patients with ST-segment elevation myocardial infarction (STEMI) treated with percutaneous coronary intervention (PCI). Prior to PCI, patients were injected with 10,000IU of unfractionated heparin (UFH). Blood samples were collected immediately before PCI, but after UFH-injection, immediately after PCI and on day 1 and day 2. Plasma IGFBP-4, CT-IGFBP-4 and NT-IGFBP-4 levels were determined by specific, novel immunoassays, and PAPP-A and IGF-I by commercial immunoassays.

RESULTS

Plasma PAPP-A was strongly elevated upon STEMI, UFH-administration and PCI with mean concentrations (95%-confidence interval) pre-PCI, post-PCI, day 1, and day 2 of 13.0 (11.2;15.2), 14.8 (13.1;16.8), 1.03 (0.90;1.18), and 1.08 (0.92;1.28) μg/L, respectively (p<0.0001). Pre-PCI concentrations of IGFBP-4, CT-IGFBP-4 and NT-IGFBP-4 were 154 (142;166), 53 (47;60) and 136 (122;150) μg/L, and levels were unaltered post-PCI. Concentrations increased on day 1 by 63 (43;87)%, 69 (36;110)%, and 47 (21;79)%, respectively (p<0.0001), i.e. at a time point when PAPP-A levels had normalized.

CONCLUSION

Plasma IGFBP-4-fragment levels are not acutely altered in patients with STEMI treated with UFH and PCI. Thus, they possess potentials as prognostic markers in ACS patients.

Lipocalin-type prostaglandin D synthase is not a biomarker of atherosclerotic manifestations

OBJECTIVE

Over the last decades Lipocalin-type prostaglandin D synthase (L-PGDS), Osteoprotegerin (OPG), Osteopontin (OPN) and Pregnancy associated plasma protein A (PAPP-A) have been reported to be associated with coronary artery disease, and L-PGDS has been proposed as a potential new diagnostic tool in the setting of stable coronary artery disease. We set out to investigate if measurement of concentrations of these biomarkers could be used to differentiate between four groups of individuals with different atherosclerotic manifestations.

METHODS

A total of 120 individuals from four equal gender- and age-matched groups were studied: (i) no previous cardiovascular disease (CVD) and no coronary calcifications [CAC-negative group], (ii) no previous CVD but evidence of severe coronary calcifications [CAC-positive group], (iii) acute coronary syndrome [ACS-group], and (iv) clinical stable patients with CVD, who were referred for cardiovascular surgery [CVD-group]. Concentrations of L-PGDS, OPG, OPN and PAPP-A were analyzed and compared between the four groups.

RESULTS

We did not find any significant differences in L-PGDS concentrations between the four groups (p = 0.32). OPG concentrations differed significantly (p = 0.003), with the highest concentration observed in ACS patients. Considering OPN (p = 0.12) and PAPP-A (p = 0.53) their concentrations between groups did not differ significantly.

CONCLUSION

The main message from this study is the observation that L-PGDS based on a single blood test appears to be less valuable than previously proposed in identification of patients with coronary artery disease. However, ACS patients have higher OPG concentrations than patients with different manifestations of stable atherosclerosis. Neither OPN nor PAPP-A concentrations differed between groups.

Clinical differences between total PAPP-A and measurements specific for the products of free PAPP-A activity in patients with stable cardiovascular disease

OBJECTIVES

We have previously reported that increases in total pregnancy-associated plasma protein-A (PAPP-A) which are thought to be indicative of vulnerable plaques and thus poor outcomes predict outcomes in patients with stable coronary artery disease. We hypothesized that the determination of CT- and NT-fragments of insulin-like growth factor binding protein 4 (CT- and NT-IGFBP4) which should be indicative of free PAPP-A would result in better performance.

METHODS

In 229 stable cardiovascular patients with indication for heart catheterization after performance of a stress test and an echocardiogram, CT- and NT-IGFBP4 were measured. Their values were investigated in relation to clinical characteristics, findings of noninvasive investigations, laboratory data and coronary angiography as well as to outcomes after a follow-up of 1094±307days.

RESULTS

CT-IGFBP4 values were independently predicted by patients with B-type (p=0.0069) or complex coronary lesions (p=0.0445). B-type and vulnerable coronary lesions were independently predicted by levels of CT-IGFBP4≥a cutoff of 31.55ng/mL derived from ROC analysis (p=0.0090 and 0.0480). NT-IGFBP4 was not predictive of coronary characteristics. Both IGFBP4 fragments were strongly dependent on age and renal function and were not predictive of outcomes.

CONCLUSION

Despite the relation of CT-IGFBP4 to a more severe coronary artery disease, CT- and NT-IGFBP4, in contrast to our report based on total PAPP-A, failed to predict any long-term outcomes in patients with stable cardiovascular disease. Further knowledge about the interaction of the PAPP-A-insulin-like growth factor system is needed to explain values of IGFBP4 fragments in these patients.

N-terminal and C-terminal fragments of IGFBP-4 as novel biomarkers for short-term risk assessment of major adverse cardiac events in patients presenting with ischemia

OBJECTIVES

Pregnancy Associated Plasma Protein A (PAPP-A)-derived N- and C-terminal fragments of IGF-binding protein-4 (NT- and CT-IGFBP-4) released from vulnerable atherosclerotic plaques are proposed to be used for cardiovascular risk assessment.

DESIGN AND METHODS

NT- and CT-IGFBP-4 were measured by novel immunoassays in EDTA-plasma of 180 patients admitted to the emergency department with symptoms of myocardial ischemia but without ST-segment elevation. Six-month incidence of major adverse cardiac events (MACE), including myocardial infarction, cardiac death, percutaneous coronary interventions, and coronary artery bypass grafting was recorded.

RESULTS

Sixteen patients met the endpoint. NT- and CT-IGFBP-4 were strong predictors of MACE: area under ROC curve (AUC) 0.856 and 0.809, respectively. NT-IGFBP-4 concentrations≥214μg/L and CT-IGFBP-4 concentrations≥124μg/L were associated with increased risk of future MACE: adjusted hazard ratio 13.79 and 7.93, respectively.

CONCLUSIONS

IGFBP-4 fragments can be utilized as biomarkers for MACE prediction in patients with suspected myocardial ischemia.

Established and novel biomarkers in ST-elevation myocardial infarction

Cardiac biomarkers assist in the diagnosis of and risk stratification in acute coronary syndromes. In ST-elevation myocardial infarction (STEMI), rapid diagnosis and initiation of reperfusion via primary percutaneous coronary intervention or fibrinolysis is often based on the clinical history and presenting ECG, but measurement of biomarkers in the early and/or late phases of STEMI may allow the selection of patients who are at increased or decreased risk of subsequent complications. Although the measurement of only three biomarkers (troponin, natriuretic peptides and C-reactive protein) are currently included in practice guidelines, more than 20 other novel cardiac biomarkers have been proposed to provide improved risk stratification after a STEMI.

A timely diagnosis of myocardial infarction

The diagnosis of acute myocardial infarction currently rests on the measurement of troponin, a biomarker of myocardial necrosis. Unfortunately, the current generation troponin assays detect troponin only 6-9 h after symptom onset. This can lead to a delay in diagnosis and also excessive resource utilization when triaging patients who, ultimately, have noncardiac causes of acute chest pain. For these reasons, there has been extensive research interest in biomarkers that can detect and rule out myocardial infarction early after symptom onset. These include markers of myocardial injury, such as myoglobin, heart-type fatty acid binding protein, glycogen phosphorylase BB; hemostatic markers, such as D-dimer; and finally, inflammatory markers, such as matrix metalloproteinase 9. Recently, highly sensitive troponin assays have reported an early sensitivity for myocardial infarction of greater than 95%, although at a cost of reduced specificity. The optimal strategy with which to use these novel biomarkers and highly sensitive troponins has yet to be determined, and interpretation of their results in light of thorough clinical assessment remains essential.

Free vs Total Pregnancy-Associated Plasma Protein A (PAPP-A) as a Predictor of 1-Year Outcome in Patients Presenting with Non–ST-Elevation Acute Coronary Syndrome

Background: The free fraction of pregnancy-associated plasma protein A (FPAPP-A) was found to be the PAPP-A form released to the circulation in acute coronary syndrome (ACS). We estimated the prognostic value of FPAPP-A vs total PAPP-A (TPAPP-A) concentrations in forecasting death and nonfatal myocardial infarction (combined endpoint) in patients with non–ST-elevation ACS.

Methods: We recruited 267 patients hospitalized for symptoms consistent with non–ST-elevation ACS and followed them for 12 months. FPAPP-A, TPAPP-A, C-reactive protein (CRP), and cardiac troponin I (cTnI) were measured at admission; cTnI was also measured at 6–12 h and 24 h. Because of the recently shown interaction between PAPP-A and heparin, we excluded patients treated with any heparin preparations before the admission blood sampling.

Results: During the follow-up, 57 (21.3%) patients met the endpoint (22 deaths and 35 nonfatal myocardial infarctions). According to FPAPP-A (&lt;1.27, 1.27–1.74, &gt;1.74 mIU/L) and TPAPP-A (&lt;1.98, 1.98–2.99, &gt;2.99 mIU/L) tertiles, this endpoint was met by 12 (13.5%), 18 (20.2%), 27 (30.3%) (P = 0.02), and 17 (19.1%), 17 (19.1%), 23 (25.8%) (P = 0.54) patients, respectively. After adjusting for age, sex, diabetes, previous myocardial infarction, and ischemic electrocardiogram (ECG) findings, FPAPP-A &gt;1.74 mIU/L [risk ratio (RR) 2.0; 95% CI 1.0–4.1, P = 0.053), increased cTnI, and CRP ≥2.0 mg/L were independent predictors of an endpoint. The prognostic performance of TPAPP-A was inferior to that of FPAPP-A.

Conclusions: FPAPP-A seems to be superior as a prognostic marker compared to TPAPP-A, giving independent and additive prognostic information when measured at the time of admission in patients hospitalized for non–ST-elevation ACS.

Pregnancy-associated plasma protein-A, a marker for outcome in patients suspected for acute coronary syndrome

OBJECTIVES

To examine if pregnancy-associated plasma protein-A (PAPP-A) in patients with chest pain, could identify patients at risk for death or myocardial infarction.

DESIGN AND METHODS

Patients admitted with chest pain and both normal ECG and normal biomarkers were evaluated by serial measurement of PAPP-A. Main outcome measures were mortality and non-fatal myocardial infarction.

RESULTS

Median age of patients included (415) was 67years and 43% were women. The risk of death or non-fatal myocardial infarction after 3 months was 15% in the highest quartile of circulating PAPP-A compared with 3% in the lowest quartile (relative risk 3.7, p<0.01). Corresponding numbers after 1 year were 24% and 10% (relative risk 2.4, p=0.01).

CONCLUSION

In patients admitted with chest pain and both normal ECG and normal biomarkers PAPP-A seems to be valuable for predicting patients at high risk of death or non-fatal myocardial infarction.

The activity of pregnancy-associated plasma protein A (PAPP-A) as expressed by immunohistochemistry in atherothrombotic plaques obtained by aspiration thrombectomy in patients presenting with a ST-elevation myocardial infarction: a brief communication

Background

The expression of pregnancy-associated plasma protein A (PAPP-A) was identified by immunohistochemistry (IHC) in culprit atherothrombotic plaque specimens harvested from patients admitted with ST-segment elevation myocardial infarction (STEMI).

Methods

The atherothrombotic samples were collected from a consecutive cohort consisting of 20 individuals admitted with STEMI to Stavanger University Hospital, Norway, from 2005-2006, presenting angiographically with an acute thrombotic occlusion of a coronary artery characterized by TIMI flow 0. The atherothrombotic plaques were obtained by aspiration thrombectomy during percutaneous coronary intervention within 12 hours from the onset of symptoms and prepared for IHC analysis.

Results

In the IHC analysis staining for PAPP-A occurred in the extracellular matrix of the plaques and no evidence of staining for PAPP-A was found in the thrombi.

Conclusion

Our results indicate that in vivo PAPP-A is strongly expressed in atherothrombotic plaques harvested from patients admitted with STEMI, as documented by IHC.

Trial registration

biobankregisteret@fhi.no1846

Intravenous administration of low molecular weight and unfractionated heparin elicits a rapid increase in serum pregnancy-associated plasma protein A

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A) has been suggested as a useful diagnostic and prognostic marker in acute coronary syndromes. Because low molecular weight heparin (LMWH) and unfractionated heparin (UFH) are commonly used in these cases, we analyzed the effects of intravenous administration of these heparins on serum PAPP-A concentrations.

METHODS

Serum concentrations of total and free PAPP-A were analyzed in 14 patients on chronic hemodialysis and in 10 coronary angiography patients. Ten of the dialysis patients received standard LMWH anticoagulation at the start of dialysis, and 4 were treated with a heparin-free method. Two of the patients on heparin-free hemodialysis received a reduced LMWH bolus 2 h after the start of dialysis. All angiography patients received UFH at the start of the procedure, and 1 patient received 2 extra boluses of UFH. Serum PAPP-A concentrations were analyzed before and during the dialysis session and during the coronary angiography examination.

RESULTS

A rapid increase in total PAPP-A (median, 25-fold) was seen in all patients within 5 min of administration for both LMWH and UFH boluses. This response was due to an increase in free PAPP-A in the serum. PAPP-A did not increase significantly in the patients who underwent heparin-free hemodialysis. Repeated heparin boluses induced a new PAPP-A release. In vitro addition of heparins to samples of whole blood did not increase PAPP-A concentrations.

CONCLUSIONS

Intravenous administration of heparin induces an intense and rapid increase in free PAPP-A in the serum. We recommend that this effect be considered when PAPP-A is assessed as a biomarker in acute coronary syndromes.

PAPP-A as a marker of increased long-term risk in patients with chest pain

OBJECTIVES

Long-term risk stratification in patients presenting with acute coronary syndromes (ACS) is possible by measuring cardiac troponin (cTn). The present study examined whether PAPP-A measured in an emergency department (ED) chest pain population in association with conventional and novel high sensitivity cTn (hs-cTnI) assays can predict long-term mortality.

METHODS

In 320 patients with cTn measurements the earliest heparinized plasma PAPP-A concentration after presentation was used for risk stratification for death by Kaplan-Meier and Cox analyses. Subgroup analyses using the earliest PAPP-A concentrations were also performed in a cohort of subjects with presentation cTnI < or = 99th percentile but with significantly changing cardiac troponin concentrations as measured by the AccuTnI assay and the hs-cTnI assay (n=45 and 120 subjects, respectively).

RESULTS

Subjects with PAPP-A concentrations in the highest tertile were at higher risk for death (HR > 2.00; p < or = 0.05 at 2 years) even after adjusting for cTnI at presentation. In the cohort with cTnI < or = 99th percentile but with changing hs-cTnI concentrations, subjects in the top PAPP-A tertile had a higher probability for death (p=0.02).

CONCLUSION

Early measurement of PAPP-A may identify chest pain patients at higher risk for long-term death. Additional prospective ACS studies are required to fully elucidate PAPP-A's role.