Molecular Distinction of Circulating Pregnancy-Associated Plasma Protein A in Myocardial Infarction and Pregnancy

PAPP-A-Specific IGFBP-4 Proteolysis in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

The insulin-like growth factors IGF-I and IGF-II-as well as their binding proteins (IGFBPs), which regulate their bioavailability-are involved in many pathological and physiological processes in cardiac tissue. Pregnancy-associated plasma protein A (PAPP-A) is a metalloprotease that preferentially cleaves IGFBP-4, releasing IGF and activating its biological activity. Previous studies have shown that PAPP-A-specific IGFBP-4 proteolysis is involved in the pathogenesis of cardiovascular diseases, such as ischemia, heart failure, and acute coronary syndrome. However, it remains unclear whether PAPP-A-specific IGFBP-4 proteolysis participates in human normal cardiomyocytes. Here, we report PAPP-A-specific IGFBP-4 proteolysis occurring in human cardiomyocytes derived from two independent induced pluripotent cell lines (hiPSC-CMs), detected both on the cell surface and in the cell secretome. PAPP-A was measured by fluoroimmune analysis (FIA) in a conditioned medium of hiPSC-CMs and was detected in concentrations of up to 4.3 ± 1.33 ng/mL and 3.8 ± 1.1 ng/mL. The level of PAPP-A-specific IGFBP-4 proteolysis was determined as the concentration of NT-IGFBP-4 proteolytic fragments using FIA for a proteolytic neo-epitope-specific assay. We showed that PAPP-A-specific IGFBP-4 proteolysis is IGF-dependent and inhibited by EDTA and 1,10-phenanthroline. Therefore, it may be concluded that PAPP-A-specific IGFBP-4 proteolysis functions in human normal cardiomyocytes, and hiPSC-CMs contain membrane-bound and secreted forms of proteolytically active PAPP-A.

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.

Pregnancy Associated Plasma Protein-A as a Cardiovascular Risk Marker in Patients with Stable Coronary Heart Disease During 10 Years Follow-Up-A CLARICOR Trial Sub-Study

Elevated pregnancy-associated plasma protein A (PAPP-A) is associated with mortality in acute coronary syndromes. Few studies have assessed PAPP-A in stable coronary artery disease (CAD) and results are conflicting. We assessed the 10-year prognostic relevance of PAPP-A levels in stable CAD. The CLARICOR trial was a randomized controlled clinical trial including outpatients with stable CAD, randomized to clarithromycin versus placebo. The placebo group constituted our discovery cohort (n = 1.996) and the clarithromycin group the replication cohort (n = 1.975). The composite primary outcome was first occurrence of cardiovascular event or death. In the discovery cohort, incidence rates (IR) for the composite outcome were higher in those with elevated PAPP-A (IR 12.72, 95% Confidence Interval (CI) 11.0-14.7 events/100 years) compared to lower PAPP-A (IR 8.78, 8.25-9.34), with comparable results in the replication cohort. Elevated PAPP-A was associated with increased risk of the composite outcome in both cohorts (discovery Hazard Ratio (HR) 1.45, 95% CI 1.24-1.70; replication HR 1.29, 95% CI 1.10-1.52). In models adjusted for established risk factors, these trends were attenuated. Elevated PAPP-A was associated with higher all-cause mortality in both cohorts. We conclude that elevated PAPP-A levels are associated with increased long-term mortality in stable CAD, but do not improve long-term prediction of death or cardiovascular events when added to established predictors.

Direct Immunoassay for Free Pregnancy-Associated Plasma Protein A (PAPP-A)

Background

Pregnancy-associated plasma protein A (PAPP-A), especially in its noncomplexed form (fPAPP-A), is linked to vulnerable atherosclerotic plaques and risk of cardiac events. An assay for sensitive detection of fPAPP-A has been lacking. Our aim was to develop and validate a direct fPAPP-A assay to meet this need.

Methods

Monoclonal antibodies binding exclusively fPAPP-A were produced by immunizing mice with recombinant PAPP-A. In the optimized immunoassay, we used an fPAPP-A–specific capture antibody together with a lanthanide-chelate–labeled monoclonal antibody recognizing all PAPP-A forms. The assay was evaluated with CLSI guidelines and compared to a 2-assay subtractive fPAPP-A approach. Clinical performance was assessed with acute coronary syndrome patients.

Results

The limits of detection and quantitation were 0.4 mIU/L and 1.3 mIU/L, respectively, and the assay was linear up to 1000 mIU/L (R2 = 0.999). Both serum and heparin plasma were suitable matrices, and the complexed form of PAPP-A caused no significant interference. Correlation between the developed assay and the 2-assay approach was fair (Pearson's r = 0.819). Median concentration in healthy individuals was 1.0 mIU/L. fPAPP-A concentration was higher in patients who had myocardial infarction or died during the 1-year follow-up period than in those who did not (1.13 mIU/L vs 0.82 mIU/L, P = 0.008, model adjusted with age and sex). fPAPP-A measured with this direct assay predicted this end point as well as (follow-up 1 year) or better (30 days) than the 2-assay fPAPP-A alone or in combination with cTnI.

Conclusions

The new assay enables sensitive and reliable measurement of low cardiac-related fPAPP-A concentrations from blood samples.

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.

The utility of pregnancy-associated plasma protein A for determination of prognosis in a cohort of patients with coronary artery disease

Background: Pregnancy-associated plasma protein-A (PAPP-A) is discussed as a biomarker representing unstable plaques in coronary artery disease (CAD). Methods: In this study 927 patients with CAD (534 with stable angina and 393 with acute coronary syndrome [ACS]) and 217 patients without CAD and measured PAPP-A levels were included. Follow-up for a median of 5 years was documented. Results: Rising quartiles of PAPP-A concentration had a higher cardiovascular mortality in the overall cohort of patients with CAD (p = 0.002) and the cohort with ACS (p = 0.01). Patients with suspected ACS below the LOD for troponin I but elevated PAPP-A levels had an increased cardiovascular mortality. A cut-off of 11.4 IU/l identified patients with a higher mortality during follow-up. Conclusion: Rising PAPP-A levels are prognostic in patients with CAD. PAPP-A levels were especially predictive in ACS patients with troponin below 10% CV of the 99th percentile for cardiovascular mortality.

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.

Elevated serum free pregnancy-associated plasma protein-A independently predicts mortality in haemodialysis patients but is not associated with recurrent haemodialysis-induced ischaemic myocardial injury

BACKGROUND/AIMS

Pregnancy-associated plasma protein-A (PAPP-A) is a putative marker of atheroma instability and ischaemic myocardial stress prior to necrosis. Total PAPP-A (tPAPP-A) levels in acute coronary syndromes predict adverse outcomes. However, free PAPP-A (fPAPP-A) predominates in the circulation. Ischaemic haemodialysis (HD)-induced cardiac injury (myocardial stunning) is common and is associated with markers of myocardial necrosis, inflammation, cardiovascular events and mortality. Coronary plaque instability in pathophysiology of HD-induced myocardial stunning has not been studied. We aimed to investigate the relationship of fPAPP-A with stunning and mortality.

METHODS

130 prevalent patients from two HD centres (Finland and UK) were studied. Pre-HD free, complexed and total PAPP-A were measured by immunoassay. A subset of 62 patients underwent echocardiography to assess HD-induced myocardial stunning. The mean duration of follow-up was 407 ± 98 days.

RESULTS

fPAPP-A was elevated (median: 3.45 mIU/l) and correlated with dialysis vintage (r = 0.391, p < 0.001), cardiac troponin T (cTnT; r = 0.29, p = 0.001) and cardiac troponin I (cTnI; r = 0.22, p = 0.01). PAPP-A was not related to stunning. Dialysis vintage and cTnT independently predicted Ln fPAPP-A (model R = 0.463). fPAPP-A, cTnT and age independently predicted death (Nagelkerke R(2) = 0.362).

CONCLUSIONS

fPAPP-A, a novel predictor of HD-related mortality, demonstrates better prognostic power than tPAPP-A. Coronary plaque instability may contribute to sub-lethal myocardial injury, but may not be critical in pathogenesis of HD-induced ischaemic cardiac injury.

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.

Pregnancy-associated plasma protein A associates with cardiovascular events in diabetic hemodialysis patients

OBJECTIVE

Pregnancy-associated plasma protein A (PAPP-A) has prognostic impact in pregnancy and acute coronary syndrome. Patients with chronic kidney disease have an excessive cardiovascular risk. In an effort to identify novel risk factors for cardiovascular disease, we investigated the relationship of PAPP-A with specific outcomes in diabetic patients undergoing dialysis.

METHODS

PAPP-A was measured in 1098 diabetic hemodialysis patients, who participated in the German Diabetes and Dialysis Study and followed-up for a median of 4 years. By Cox regression analysis, we assessed the association of baseline levels of PAPP-A with all-cause mortality, combined cardiovascular events and the specific outcomes of sudden death, stroke, myocardial infarction and infectious mortality.

RESULTS

Patients had a mean age of 66 ± 8 years (54% male) and median PAPP-A concentration of 17 mIU/L (IQR 13.4-20.9 mIU/L). Per standard deviation increase in PAPP-A the adjusted risk of sudden cardiac death increased by 23% (HR 1.23, 95%CI 1.12-1.36). Categorical analyses showed that the patients in the 4(th) PAPP-A quartile had an adjusted 2.6 fold increased risk of sudden death and 2.8 fold increased risk of stroke as compared to the patients in the 1st quartile. Similarly, the risk of combined cardiovascular events was significantly elevated by the factor 1.5 in patients of the 4(th) quartile. Additionally, PAPP-A levels were associated with infectious deaths and all-cause mortality.

CONCLUSIONS

PAPP-A is associated with sudden death, stroke and infectious complications in diabetic dialysis patients. PAPP-A may be useful for risk assessment and monitoring in populations at high risk of cardiovascular events.

Pregnancy-associated plasma protein A (PAPP-A) and preeclampsia

Pregnancy-associated plasma protein A (PAPP-A) is a key regulator of insulin-like growth factor bioavailability essential for normal fetal development. In maternal blood, this protein increases with gestational age and then rapidly decreases after delivery. It is routinely used for Down syndrome screening in the first trimester of pregnancy, and its decrease compared to a normal pregnancy indicates an increased risk for both chromosomal anomalies and adverse pregnancy outcomes. It belongs to a group of biomarkers that predict later preeclampsia development, primarily early onset preeclampsia; however, it should be combined with a Doppler ultrasonography of the uterine artery (pulsatile index) and other biochemical and maternal factors to achieve a higher detection rate with an acceptable false positivity rate. Some studies have demonstrated an even more pronounced decrease of PAPP-A in the early second trimester of pregnancy in women who subsequently develop preeclampsia compared with women who do not develop preeclampsia. Conversely, during the last trimester of pregnancy, its concentration increases even more in patients with preeclampsia than in patients without. It is also detectable at very low levels in nonpregnant individuals, and a higher concentration indicates an adverse effect in patients with acute coronary syndromes or stable atherosclerotic disease and in patients with end-stage renal disease who are being treated with hemodialysis.

Integrative computational and experimental approaches to establish a post-myocardial infarction knowledge map

Vast research efforts have been devoted to providing clinical diagnostic markers of myocardial infarction (MI), leading to over one million abstracts associated with “MI” and “Cardiovascular Diseases” in PubMed. Accumulation of the research results imposed a challenge to integrate and interpret these results. To address this problem and better understand how the left ventricle (LV) remodels post-MI at both the molecular and cellular levels, we propose here an integrative framework that couples computational methods and experimental data. We selected an initial set of MI-related proteins from published human studies and constructed an MI-specific protein-protein-interaction network (MIPIN). Structural and functional analysis of the MIPIN showed that the post-MI LV exhibited increased representation of proteins involved in transcriptional activity, inflammatory response, and extracellular matrix (ECM) remodeling. Known plasma or serum expression changes of the MIPIN proteins in patients with MI were acquired by data mining of the PubMed and UniProt knowledgebase, and served as a training set to predict unlabeled MIPIN protein changes post-MI. The predictions were validated with published results in PubMed, suggesting prognosticative capability of the MIPIN. Further, we established the first knowledge map related to the post-MI response, providing a major step towards enhancing our understanding of molecular interactions specific to MI and linking the molecular interaction, cellular responses, and biological processes to quantify LV remodeling.

Heart attack, known medically as myocardial infarction, often occurs as a result of partial shortage of blood supply to a portion of the heart, leading to the death of heart muscle cells. Following myocardial infarction, complications might arise, including arrhythmia, myocardial rupture, left ventricular dysfunction, and heart failure. Although myocardial infarction can be quickly diagnosed using a various number of tests, including blood tests and electrocardiography, there have been no available prognostic tests to predict the long-term outcome in response to myocardial infarction. Here, we present a framework to analyze how the left ventricle responds to myocardial infarction by combining protein interactome and experimental results retrieved from published human studies. The framework organized current understanding of molecular interactions specific to myocardial infarction, cellular responses, and biological processes to quantify left ventricular remodeling process. Specifically, our knowledge map showed that transcriptional activity, inflammatory response, and extracellular matrix remodeling are the main functional themes post myocardial infarction. In addition, text analytics of relevant abstracts revealed differentiated protein expressions in plasma or serum expressions from patients with myocardial infarction. Using this data, we predicted expression levels of other proteins following myocardial infarction.

Association between serum pregnancy-associated plasma protein-A and bicarbonate in hemodialysis patients

BACKGROUND

Acidosis is associated with protein-energy malnutrition, inflammation, and bone disease, and low bicarbonate levels have been implicated in higher mortality rates in chronic kidney disease. Recently, the concentration of serum pregnancy-associated plasma protein-A (PAPP-A) has become accepted as a prognostic marker in hemodialysis patients. This study determined the relationship between PAPP-A and bicarbonate levels in these patients.

METHODS

The study enrolled 65 hemodialysis patients (41 males, 24 females) and 26 control subjects (11 males, 15 females). Serum PAPP-A, intact parathormone (iPTH), calcium, phosphorus (P), and bicarbonate levels were measured. Correlations between PAPP-A and bicarbonate, iPTH, calcium, and phosphorus were evaluated.

RESULTS

Median PAPP-A levels were significantly higher in hemodialysis patients [15.1 (<0.03-158.8) ng/ml] than in control subjects [6.6 (<0.03-16.4) ng/ml] (P < 0.05). There were statistically significant correlations between serum PAPP-A and bicarbonate, iPTH, and P in hemodialysis patients but not in control subjects.

CONCLUSION

Elevation of serum PAPP-A has been found in hemodialysis patients and its significant correlation with bicarbonate suggests that it may be a prognostic factor.

Analysis of pregnancy-associated plasma protein A production in human adult cardiac progenitor cells

IGF-binding proteins (IGFBPs) and their proteases regulate IGFs bioavailability in multiple tissues. Pregnancy-associated plasma protein A (PAPP-A) is a protease acting by cleaving IGFBP2, 4, and 5, regulating local bioavailability of IGFs. We have previously shown that IGFs and IGFBPs are produced by human adult cardiac progenitor cells (haCPCs) and that IGF-1 exerts paracrine therapeutic effects in cardiac cell therapy with CPCs. Using immunofluorescence and enzyme immunoassays, we firstly report that PAPP-A is produced and secreted in surprisingly high amounts by haCPCs. In particular, the homodimeric, enzymatically active, PAPP-A is secreted in relevant concentrations in haCPC-conditioned media, while the enzymatically inactive PAPPA/proMBP complex is not detectable in the same media. Furthermore, we show that both homodimeric PAPP-A and proMBP can be detected as cell associated, suggesting that the previously described complex formation at the cell surface does not occur easily, thus positively affecting IGF signalling. Therefore, our results strongly support the importance of PAPP-A for the IGFs/IGFBPs/PAPP-A axis in CPCs biology.

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.

Pathophysiological roles and clinical importance of biomarkers in acute coronary syndrome

Early diagnosis of acute coronary syndrome (ACS) is important to guide appropriate therapy at a time when it is most likely to be of value. Accurate prognostic and risk stratification will facilitate high-risk patients to have early advanced diagnostic investigations and early appropriate interventions in a cost-effective and efficient manner, while those patients at low risk of ACS complications do not need such costly diagnostic tests and unnecessary hospital admission. Recent investigations have demonstrated that elevation of biomarkers upstream from acute-phase biomarkers, biomarkers of plaque destabilization and rupture, biomarkers of myocardial ischemia, necrosis, and dysfunction may provide an earlier assessment of patient risk and identify patients with higher risk of having an adverse event. This review provides an overview of the pathophysiology and clinical characteristics of several well-established biomarkers as well as emerging biomarkers that may have potential clinical utility in patients with ACS. Such emerging biomarkers hold promise and need to be more thoroughly evaluated before utilization in routine clinical practice.

Examination of serum pregnancy-associated plasma protein A clinical value in acute coronary syndrome prediction and monitoring

INTRODUCTION

Chronic vascular inflammatory process promotes and intensifies all atherogenic events. The aim of this research was to estimate the clinical value of pregnancy-associated plasma protein A (PAPP-A) measurement associated with plaque destabilization and rupture in prediction and monitoring of acute coronary syndromes (ACS) as well as to assess the predictive value of this biomarker in comparison to traditional myocardial infarction (MI) risk markers.

MATERIAL AND METHODS

The study included 119 patients in 2 investigated groups and one control group. PAPP-A assay was performed using manual ELISA kit, DRG. All other parameters were determined using automatic analyzers: Olympus and Dade Behring.

RESULTS

A statistically significant difference between PAPP-A concentration median value was found in the investigated group MI individuals' serum and control group individuals' serum (11.42 ng/ml and 7.22 ng/ml respectively, p = 0.003). PAPP-A assay had the highest specificity (83.3%) and sensitivity (53.8%), and therefore the highest clinical value. In patients with clinically and laboratory confirmed MI we proved that PAPP-A serum level is a clinically useful biomarker in ACS prediction, better than C-reactive protein (hsCRP) and fibrinogen (FBG) level.

CONCLUSIONS

The highest diagnostic efficiency for ACS prediction was proved for simultaneous panel assays consisting of 2-3 parameters (PAPP-A - hsCRP, PAPP-A - FBG, PAPP-A - hsCRP - FBG), while PAPP-A itself does not show characteristics necessary for it to be used as a biomarker for MI dynamic monitoring. It is possible that prothrombotic component is mainly responsible for repeated major adverse cardiac events, more than inflammatory process.

First Trimester Maternal Serum Screening Using Biochemical Markers PAPP-A and Free β-hCG for Down Syndrome, Patau Syndrome and Edward Syndrome

The first trimester screening programme offers a noninvasive option for the early detection of aneuploidy pregnancies. This screening is done by a combination of two biochemical markers i.e. serum free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein A (PAPP-A), maternal age and fetal nuchal translucency (NT) thickness at 11 + 0-13 + 6 weeks of gestation. A beneficial consequence of screening is the early diagnosis or trisomies 21, 18 and 13. At 11 + 0-13 + 6 weeks, the relative prevalence of trisomies 18 and 13 to trisomy 21 are found to be one to three and one to seven, respectively. All three trisomies are associated with increased maternal age, increased fetal NT and decreased PAPP-A, but in trisomy 21 serum free β-hCG is increased whereas in trisomies 18 and 13 free β-hCG is decreased.

PAPP-A in cardiac and non-cardiac conditions

Pregnancy-associated plasma protein-A (PAPP-A), a newly discovered member of insulin like growth factors (IGFs) axis, has been reported to be a biomarker in both cardiac and non-cardiac conditions. PAPP-A mainly acts as a protease cleaving IGF inhibitors - IGF binding proteins (IGFBPs), thereby setting free IGFs. In cardiac conditions, PAPP-A plays an important role in progressive atherosclerosis. As a biomarker, PAPP-A is not only sensitive, specific and early for diagnosis of acute coronary syndrome, but also an independent risk factor for all-cause mortality or combined cardiovascular events. In non-cardiac conditions, PAPP-A is a new anti-aging target. PAPP-A knock out (KO) mice have a prolonged lifespan than the wild type. In addition, PAPP-A is also a biomarker associated with malignant cancer and end stage renal disease.

Key questions and answers about pregnancy-associated plasma protein-A

Twenty-five years after it was identified as a circulating protein of unknown function derived from the placenta, pregnancy-associated plasma protein-A (PAPP-A) was discovered to be a novel zinc metalloproteinase expressed by a variety of cell types. Great progress has been made in understanding the biology of PAPP-A and its regulation during recent years, especially in regard to physiological and pathophysiological inflammatory injury responses. However, much remains to be learned about this complex protein and its potential clinical implications outside pregnancy. In this article we address some of the outstanding questions about PAPP-A, in particular about its newly emerging role in the insulin-like growth factor (IGF) system.

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.

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.

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.

Present and Future Biochemical Markers for Detection of Acute Coronary Syndrome

The use of biochemical markers in the diagnosis and management of patients with acute coronary syndrome has increased continually in recent decades. The development of highly sensitive and cardiac-specific troponin assays has changed the view on diagnosis of myocardial infarction and also extended the role of biochemical markers of necrosis into risk stratification and guidance for treatment. The consensus definition of myocardial infarction places increased emphasis on cardiac marker testing, with cardiac troponin replacing creatine kinase MB as the "gold standard" for diagnosis of myocardial infarction. Along with advances in the use of more cardiac-specific markers of myocardial necrosis, biochemical markers that are involved in the progression of atherosclerotic plaques to the vulnerable state or that signal the presence of vulnerable plaques have recently been identified. These markers have variable abilities to predict the risk of an individual for acute coronary syndrome. The aim of this review is to provide an overview of the well-established markers of myocardial necrosis, with a special focus on cardiac troponin I, together with a summary of some of the potential future markers of inflammation, plaque instability, and ischemia.

Pregnancy-associated plasma protein-A (PAPP-A) and cardiovascular risk

The search for markers to improve risk prediction for individuals at risk of developing serious cardiovascular events is ongoing. New markers of coronary artery disease progression have been identified in recent years, among which, circulating levels of pregnancy-associated plasma protein-A (PAPP-A) offer an interesting profile. PAPP-A may play a role in the development of atherosclerotic lesions and represent also a marker of atheromatous plaque instability and extent of cardiovascular disease. PAPP-A has been shown to be a marker of adverse outcome in both acute coronary syndrome and stable coronary disease patients. The present article reviews currently available evidence supporting a role for PAPP-A as a marker of cardiovascular risk and discusses some of the pitfalls that may limit its use in clinical practice.

Pregnancy-associated plasma protein-A elevation in patients with acute coronary syndrome and subsequent atorvastatin therapy

Pregnancy-associated plasma protein-A (PAPP-A) was associated with atherosclerotic plaque vulnerability, whereas statin therapy was associated with increased plaque stability. Eighty-six patients presenting with clinical indications (non-ST-elevation myocardial infarction, unstable angina, and stable angina) for invasive coronary angiography and subsequent verified coronary artery disease (CAD) were randomly assigned in a double-blind manner to atorvastatin 10 or 80 mg/day. PAPP-A, high-sensitivity C-reactive protein (hs-CRP), and lipids were measured at baseline (before statin therapy) and at 1 and 6 months. PAPP-A was significantly increased in 35 patients with acute coronary syndrome (ACS) compared with 51 patients with stable CAD (p <0.001). Patients randomly assigned to atorvastatin 10 mg did not show a significant decrease in PAPP-A from baseline at 1 or 6 months. Patients treated with atorvastatin 80 mg showed a significant decrease at 1 month compared with baseline, but not at 6 months. hs-CRP was not significantly different between the ACS and stable CAD groups. Patients receiving atorvastatin 10 mg showed no hs-CRP decrease at 1 or 6 months, whereas it significantly decreased in the 80-mg group at 6 months, but not at 1 month. In conclusion, PAPP-A significantly increased in patients with ACS compared with those with stable coronary disease. High-dose atorvastatin significantly decreased PAPP-A at 1 month and hs-CRP at 6 months in patients with verified CAD. Low-dose atorvastatin did not produce this effect.

Quantification of Proteolytically Active Pregnancy-Associated Plasma Protein-A with an Assay Based on Quenched Fluorescence

Background: Maternal serum concentrations of pregnancy-associated plasma protein-A (PAPP-A, pappalysin-1, EC 3.4.24.79) are used to predict the occurrence of Down syndrome. In pregnancy, PAPP-A primarily circulates as a covalent 2:2 complex with the proform of eosinophil major basic protein (proMBP), which inhibits the proteolytic activity of PAPP-A. At term, however, ∼1% of PAPP-A exists as an active, uncomplexed dimer with proteolytic activity directed specifically toward insulin-like growth factor binding protein (IGFBP)-4 and IGFBP-5. No assays have been developed that allow quantification of PAPP-A proteolytic activity.

Methods: We developed a sensitive and specific immunocapture assay for PAPP-A activity based on intramolecular quenched fluorescence. We used a 26-residue synthetic peptide derived from IGFBP-4 in which specific positions on each side of the PAPP-A cleavage site were substituted with 3-nitrotyrosine and o-aminobenzoic acid.

Results: The assay detected the activity of recombinant PAPP-A as well as PAPP-A in serum samples from pregnant women. The limit of detection (mean signal of blank plus 3 SD) of the active PAPP-A subunit was 13 pmol/L, and the intra- and interassay CVs were &lt;10% and &lt;15%, respectively. Interestingly, the fraction of active PAPP-A decreased gradually from week 7 to week 19 of pregnancy.

Conclusions: This method allows the measurement of PAPP-A enzymatic activity and because of its specificity it is relevant to the study of the biological function of PAPP-A. The method may also be useful in the diagnosis of pregnancy disorders.

Pregnancy associated plasma protein-A and risk stratification of patients presenting with chest pain in the emergency department

BACKGROUND

The aim of this study was to evaluate the clinical utility of serum pregnancy associated plasma protein-A (PAPP-A) levels in assisting triage of an intermediate to high-risk patient presenting with chest pain in the Emergency Department and no definite evidence of an acute coronary syndrome.

METHODS

Serum levels of PAPP-A were measured in 59 patients presenting with chest pain to the Emergency Department. The patients were independently grouped according to the presence of acute coronary syndromes or the absence thereof.

RESULTS

In a multivariate model that corrected for age, sex, type of chest pain, number of risk factors, history of coronary artery disease, troponin levels, and non-specific ECG changes, PAPP-A levels were still predictive of a final diagnosis of acute coronary syndrome in patients presenting with chest pain to the Emergency Department (Odds Ratio, 2.093; 95th confidence intervals, 1.037-4.224; p=0.039).

CONCLUSIONS

Elevated serum PAPP-A levels were predictive of a diagnosis of acute coronary syndrome in intermediate- to high-risk patients presenting to the Emergency Department with chest pain and no definite evidence of an acute coronary syndrome. Thus, serum PAPP-A may be valuable as an adjunct, minimally invasive marker to improve risk stratification in chest pain patients.

Measurement and clinical significance of circulating PAPP-A in ACS patients

BACKGROUND

The rupture of coronary atherosclerotic plaque and subsequent thrombus formation are major events underlying acute coronary syndromes (ACS). Pregnancy associated plasma protein A (PAPP-A), a biomarker of plaque rupture, has been studied in patients with ACS. This review aimed to provide an overview of clinical utility of PAPP-A in ACS patients and analytical issues adhering to immunological PAPP-A measurement.

METHODS

The literature relating to PAPP-A in ACS, the molecular structure and immunodetection of PAPP-A was reviewed. PubMed was used to search the relevant articles published from 1974 to 2006.

RESULTS

Higher PAPP-A concentrations have been found in patients with ACS than in patients with stable angina and subjects without coronary artery disease. Elevated PAPP-A concentrations have also been shown to associate with adverse cardiac events in ACS patients. The prognostic value of PAPP-A appears to be independent of cardiac troponins. Noteworthy, the PAPP-A form that accounts for increase in ACS is uncomplexed with the proform of eosinophil major basic protein (proMBP). However, PAPP-A assays applied in clinical studies published thus far detect total PAPP-A. Consequently, the clinical value may be non-optimal when total PAPP-A is measured in ACS patients. In addition, the clinical value can also be affected by the analytical factors that exert an effect on the performance of PAPP-A assays.

CONCLUSIONS

PAPP-A appears to be a very promising biomarker useful in the clinical management of ACS patients. However, more prospective and interventional studies with carefully established immunoassays are required to validate its clinical utility.

Pregnancy-associated plasma protein-A (PAPP-A): a local regulator of IGF bioavailability through cleavage of IGFBPs

Pregnancy-associated plasma protein-A (PAPP-A) was originally isolated in 1974, as one of four proteins of placental origin found in high concentrations in the blood of pregnant women. In the early 1990s several laboratories reported novel protease activity against insulin-like growth factor binding protein-4 (IGFBP-4) in media conditioned by several cell types. This activity was unique, as it appeared to require the presence of IGF to cleave IGFBP-4. In 1999, this IGF-dependent IGFBP-4 protease activity was isolated from human fibroblast conditioned media and identified as PAPP-A. Subsequently, PAPP-A was shown to be expressed by a variety of cell types, and thus no longer could be considered to be just "pregnancy-associated". This review will describe what is currently known about the structure of PAPP-A and about its function as an IGFBP protease, with a focus on new insights obtained through study of a PAPP-A knock-out mouse model and on potential clinical applications.

Surface association of pregnancy-associated plasma protein-A accounts for its colocalization with activated macrophages

Intense immunostaining for pregnancy-associated plasma protein-A (PAPP-A), a newly characterized metalloproteinase in the insulin-like growth factor system, colocalizes with activated macrophages in human atherosclerotic plaque. To determine macrophage regulation of PAPP-A expression, we developed two models of human macrophages with basal and activated phenotypes. THP-1 cells and peripheral blood monocytes could be differentiated into macrophages and activated upon specific treatment regimens with phorbol myristate acetate, macrophage colony-stimulating factor, and interleukin-1β. Activation was assessed by cell secretion of tumor necrosis factor-α, which increased 30- to 100-fold with activation. Activated macrophages also secreted matrix metalloproteinase-9. However, no PAPP-A mRNA or PAPP-A antigen could be detected in these cells under any condition. Upon incubation with recombinant PAPP-A, we found that activated macrophages bound and internalized more PAPP-A than unactivated macrophages or monocytes. Internalization accounted for at least 50% of macrophage-associated PAPP-A, as assessed in studies with cytochalasin B. Membrane-bound PAPP-A retained protease activity, whereas internalized PAPP-A had little or no activity. Similar experiments carried out with a mutated variant of PAPP-A, which retains functionality as a protease but is unable to bind surface-associated glycosaminoglycan, showed no macrophage association or internalization. Absence of PAPP-A expression was confirmed in activated macrophages isolated from a hypercholesterolemic rabbit model of atherosclerosis. We therefore conclude that PAPP-A is not synthesized in, but rather is bound and internalized by, macrophages. Our findings likely account for the observed intense immunostaining for PAPP-A colocalizing with activated macrophages and may have physiological significance in the development of vulnerable plaque.

The effect of primary percutaneous coronary intervention as compared to tenecteplase on myeloperoxidase, pregnancy-associated plasma protein A, soluble fibrin and D-dimer in acute myocardial infarction

INTRODUCTION

Acute coronary reperfusion is accomplished pharmacologically with intravenous thrombolytic therapy or mechanically with primary percutaneous coronary intervention (PCI).

METHODS

We have determined the immediate effects of the main coronary reperfusion procedures on the plasma concentrations of myeloperoxidase (MPO), pregnancy-associated plasma protein A (PAPP-A), fibrin monomer (FM) and D-dimer (DD). We studied a total of 38 patients admitted for ST-segment elevation infarct (STEMI). 18 patients were given thrombolytic therapy with tenecteplase and 20 were treated with primary PCI.

RESULTS

The plasma concentrations of PAPP-A increased by a factor of six to eight times (p<0.001) following both reperfusion therapies. No significant increase was observed for MPO by either procedure. DD and FM concentrations both increased significantly following thrombolytic therapy, p=0.000, whereas only minor increases, although statistically significant for FM (p=0.013), were noted after PCI. DD and FM were highly correlated prior to the two treatment regimens (R=0.91), and were still highly correlated after PCI (R=0.94) and thrombolytic therapy (R=0.86). No correlation was demonstrated between PAPP-A and markers of activated coagulation.

CONCLUSIONS

This is the first report of a significant rise in the plasma concentration of PAPP-A after PCI as compared to thrombolytic treatment (p=0.002) and may indicate a greater impact of PCI than that of thrombolytic therapy on target coronary plaques.

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 &lt;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 &lt;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.