Degradation of human brain natriuretic peptide (BNP) by contact activation of blood coagulation system

EDTA plasma in glass and polyethylene terephthalate tubes is suitable for measurement of B-type natriuretic peptide on the Mindray CL-6000i

AIMS

To explore differences in B-type natriuretic peptide (BNP) concentration and stability and evaluate BNP accuracy in different collection tubes.

METHODS

BNP concentrations in heparin/glass, EDTA/glass, and EDTA/polyethylene terephthalate (PET) tubes were measured on the Mindray CL-6000i at 0.5, 1, 2, and 4 h after collection. Differences were evaluated using Wilcoxon's paired tests and Bland-Altman plots. BNP stability and measurement accuracies were estimated using Kruskal-Wallis H tests and recovery tests.

RESULTS

BNP concentrations in EDTA/glass tubes were 31.4% higher than those in heparin/glass tubes and 3.04% lower than those in EDTA/PET tubes. BNP stability significantly decreased in the heparin/glass tube. BNP remained stable in EDTA/glass and EDTA/PET tubes at room temperature for 4 h. BNP recovery rates in heparin/glass, EDTA/glass, and EDTA/PET tubes were 77.46, 86.04, and 88.23%, respectively.

CONCLUSIONS

Plasma in EDTA/glass and EDTA/PET tubes is suitable for BNP measurement on the Mindray CL-6000i.

Biosensors for the Rapid Detection of Cardiovascular Biomarkers of Vital Interest: Needs, Analysis and Perspectives

We have previously surveyed a panel of 508 physicians from around the world about which biomarkers would be relevant if obtained in a very short time frame, corresponding to emergency situations (life-threatening or not). The biomarkers that emerged from this study were markers of cardiovascular disease: troponin, D-dimers, and brain natriuretic peptide (BNP). Cardiovascular disease is a group of disorders affecting the heart and blood vessels. At the intersection of medicine, basic research and engineering, biosensors that address the need for rapid biological analysis could find a place of choice in the hospital or primary care ecosystem. Rapid, reliable, and inexpensive analysis with a multi-marker approach, including machine learning analysis for patient risk analysis, could meet the demand of medical teams. The objective of this opinion review, proposed by a multidisciplinary team of experts (physicians, biologists, market access experts, and engineers), is to present cases where a rapid biological response is indeed valuable, to provide a short overview of current biosensor technologies for cardiac biomarkers designed for a short result time, and to discuss existing market access issues.

Early B-Type Natriuretic Peptide Change in HFrEF Patients Treated With Sacubitril/Valsartan: A Pooled Analysis of EVALUATE-HF and PROVE-HF

OBJECTIVES

This study assessed changes in B-type natriuretic peptide (BNP) among patients with heart failure with reduced ejection fraction (HFrEF) treated with sacubitril/valsartan (Sac/Val) according to standard prescribing information.

BACKGROUND

Through inhibition of neprilysin, Sac/Val may increase BNP concentrations.

METHODS

In an individual patient analysis from the EVALUATE-HF (Study of Effects of Sacubitril/Valsartan vs. Enalapril on Aortic Stiffness in Patients With Mild to Moderate HF With Reduced Ejection Fraction) (n = 221) and the PROVE-HF (Effects of Sacubitril/Valsartan Therapy on Biomarkers, Myocardial Remodeling and Outcomes) (n = 146) studies, we examined changes in BNP, N-terminal pro-BNP (NT-proBNP), and urinary cyclic guanosine monophosphate (ucGMP) from baseline to week 4 and week 12.

RESULTS

Median (IQRs) concentration of BNP at baseline, week 4, and week 12 were 145 [IQR: 55-329], 136 [IQR: 50-338], and 135 [IQR: 51-299] ng/L, respectively. There was no significant change from baseline to week 4 (0% [-30% to +41%]; P = 0.36) or week 12 (+1% [-36% to +50%]; P = 0.97). By week 12, one-half of the study participants had a BNP decline. There was no association between Sac/Val dose and BNP changes. Change in BNP was directly associated with change in NT-proBNP (rho: = 0.81; P < 0.001), which decreased by -30% (-50% to -8%) and -32% (-54% to -1%) to weeks 4 and 12 (P < 0.001 for both). In contrast, change in BNP was only weakly associated with change in ucGMP (rho: = 0.19; P < 0.001). Increases in ucGMP were observed regardless of whether BNP was decreased (+11% [-34% to +115%]), unchanged (+34% [-15% to +205%]), or increased (+57% [-12% to +14%]).

CONCLUSIONS

In this pooled analysis of patients with HFrEF with standard indications for Sac/Val treatment, there was no significant overall increase in BNP concentrations, and patients demonstrated increase in ucGMP regardless of the trajectory of BNP change. (Study of Effects of Sacubitril/Valsartan vs. Enalapril on Aortic Stiffness in Patients With Mild to Moderate HF With Reduced Ejection Fraction [EVALUATE-HF]; NCT02874794) (Effects of Sacubitril/Valsartan Therapy on Biomarkers, Myocardial Remodeling and Outcomes [PROVE-HF]; NCT02887183).

BNP and NT-proBNP Interpretation in the Neprilysin Inhibitor Era

PURPOSE OF REVIEW

Describe the mechanisms that may influence change in measured natriuretic peptide levels when using the neprilysin inhibitor sacubitril to treat a patient with heart failure.

RECENT FINDINGS

Prior to the introduction of the neprilysin inhibitor sacubitril as part of a chemical combination with the angiotensin receptor blocker valsartan shown to reduce mortality and heart failure hospitalizations in patients with heart failure with reduced ejection fraction, the natriuretic peptide assays for B-type natriuretic peptide (BNP) and the amino-terminal proBNP (NT-proBNP) assays were shown to have similar diagnostic accuracy to differentiate heart failure from other etiologies of shortness of breath. Sacubitril/valsartan use has been shown to result in a modest and chronic elevation of BNP while reducing levels of NT-prBNP. This review explores the potential impact of these findings on interpreting natriuretic peptide results for diagnosis and prognosis, as well as explore the challenges associated with the heterogeneity of this finding, highlighting the impact of inhibiting neprilysin, a non-specific endopeptidase with multiple target sites within BNP and other proteins. With increased uptake of sacubitril/valsartan expected in patients with heart failure, interpretation of natriuretic peptide assays becomes somewhat more complex, particularly for BNP. However, knowing a baseline steady-state concentration and using the same assay can assist with BNP interpretation for diagnosis and prognosis.

A review on B-type natriuretic peptide monitoring: assays and biosensors

Since its discovery in 1988, B-type natriuretic peptide (BNP) has been recognized as a powerful cardiovascular biomarker for a number of disease states, specifically heart failure. Concurrent with such a discovery, much effort has been allocated to the precise monitoring of physiological BNP levels. Thus, it can be used to guide the therapy of heart failure and determine the patient's stage of disease. Thus, we discuss in this article BNP as a potent biomarker. Subsequently, we will review the progress of biosensing devices as they could be applied to monitor BNP levels as assays, benchtop biosensors and implantable biosensors. The analytical characteristics of commercially available BNP assays are presented. Still emerging as a field, we define four obstacles that present opportunity for the future development of implantable biosensor: foreign body response, sensor renewability, sensitivity and selectivity.

Amino-terminal pro-brain natriuretic peptide: a biomarker for diagnosis, prognosis and management of heart failure

There is a substantial need for a diagnostic tool to aid in the early diagnosis of heart failure and in the recognition of those at risk for its development, as well as in guidance of therapy. Testing for amino-terminal pro-brain natriuretic peptide (NT-proBNP) has been recognized to have utility in the diagnosis, prognosis and management of heart failure. In addition, numerous other applications for NT-proBNP testing are now recognized, such as evaluation of patients with heart disease in the absence of heart failure, as well as the diagnostic and prognostic evaluation of patients with acute coronary syndromes or pulmonary thromboembolism.

[NT-proBNP in practice: from chemistry to medicine]

Since the introduction of routine assay for natriuretic peptides, there are a growing number of clinical applications for those new tests. Numerous studies have defined analytical characteristics and clinical interest of NT-proBNP assay. Originally limited to acute heart failure diagnosis in the emergency room, NT-proBNP assay has now a wide number of applications. This literature review presents the "state of art" of this marker, detailing NT-proBNP physiological recent knowledge and its recognized or investigated clinical applications.

Novel Immunoassay for Quantification of Brain Natriuretic Peptide and Its Precursor in Human Blood

Background: Brain natriuretic peptide (BNP) is an unstable molecule that can rapidly lose immunologic activity in blood. Conventional sandwich BNP immunoassays use 2 antibodies specific to 2 different epitopes. Larger distances between epitopes are associated with a greater probability of proteolysis sites being located between the antibody-binding sites, and thus such assays have an increased susceptibility to underdetect BNP because of the increased likelihood of proteolytic degradation. The purpose of our study was to develop a sandwich immunoassay for the precise quantification of BNP and BNP precursor (proBNP) in human blood that is not susceptible to proteolysis.

Methods: Mice were immunized with an immune complex consisting of monoclonal antibody (MAb) 24C5 (specific for BNP peptide 11–22) and the entire BNP molecule. The MAb used in our assay (Ab-BNP2) recognizes the immune complex but neither free BNP nor MAb 24C5.

Results: We used MAbs 24C5 and Ab-BNP2 to develop a new type of sandwich BNP assay (the “single-epitope sandwich assay”), which requires only a short BNP fragment (fragment 11–22) for immunodetection. This assay recognizes both BNP and proBNP with the same efficiency and sensitivity and demonstrates both considerably less susceptibility to antigen degradation and greater stability of the measured antigen than conventional sandwich BNP immunoassays.

Conclusions: We have developed this sensitive single-epitope sandwich assay for detecting BNP, proBNP, and their fragments in human blood. This assay appears promising for use in clinical studies to assist in triage, management, and outcomes assessment in heart failure patients.

Influence of sample matrix and storage on BNP measurement on the Bayer Advia Centaur

The assessment and management of congestive heart failure relies increasingly on the measurement of B-type natriuretic peptide (BNP). However, the effective contribution of this biochemical test in the clinical decision making is influenced by reliability of the measure, which also depends on several preanalytical issues. Since there is controversy on the influence of the matrix and the storage conditions on BNP measurement, we compared results of BNP in serum, K2 ethylene diamine tetra-acetic acid (EDTA) plasma and lithium heparin plasma fresh samples and in matching samples stored at -20 and -80 degrees C for 1 week. BNP measured on the Bayer Advia Centaur was systematically underestimated in heparin plasma (-47%) and serum (-62%) when compared to K2 EDTA plasma. According to the established 100 ng/L cutoff value, 25% and 37% of the fresh samples collected in heparin plasma or serum were misclassified from the reference K2 EDTA fresh specimen, respectively. When compared to the fresh specimens, the mean and interindividual bias observed for samples stored at either -20 degrees C or -80 degrees C was, overall, modest for K2 EDTA plasma (-2%) and heparin plasma (+6% and -4%, respectively), though it appeared clinically meaningful in serum (+47% and +28%, respectively). Although we can not rule out that other BNP assays using different antibodies may be not affected from degradation during storage to the same extent, results of our investigation demonstrate that K2 EDTA plasma is the most suitable specimens for BNP testing on fresh and frozen samples stored at either -20 degrees C or -80 degrees C for up to 1 week.

Long-term stability of endogenous B-type natriuretic peptide during storage at −20 °C for later measurement with Biosite Triage assay

OBJECTIVE

To evaluate the long-term stability of B-type natriuretic peptide (BNP) in frozen samples at -20 degrees C.

DESIGN AND METHODS

During a health and nutrition survey of a representative sample of the adult population of Porto, Portugal, blood samples were collected in EDTA tubes. Aliquots of plasma were frozen at -20 degrees C until measurement. Subjects with cardiac structural or functional abnormalities or renal dysfunction were excluded. BNP was assessed using a commercial immunofluorescence assay (Triage BNP Test) as a continuous variable (n=340) and in four subgroups selected according to different storage periods: < or =1 month (n=35), 6-12 months (n=80), 20-24 months (n=18) and > or =36 months (n=21).

RESULTS

Age- and sex-adjusted BNP values, analyzed as a continuous variable, decreased significantly over time of storage. When we stratified in four intervals of storage time, the median BNP value (25th-75th percentile, p value) was: 22.6 pg/mL (8.9-76.2, reference group) for < or =1 month, 19.8 pg/mL (9.5-48.4, p=0.055) for 6-12 months, 15.3 pg/mL (7.5-35.0, p=0.037) for 20-24 months, and 2.5 pg/mL (2.5-10.5, p<0.001) for > or =36 months.

CONCLUSIONS

BNP is stable at -20 degrees C for 1 year, without protease inhibitors.

The importance of analytical quality specifications for biomarker assays currently used in acute cardiac care

It is very important that cardiac biomarkers on which clinically relevant decisions will rest are measured with highly reliable assays. Adequate studies are needed before new methods can be implemented in the laboratory routine, and only well-documented assays should be considered for clinical use. Therefore, it is critical that, as new biomarkers are proposed, quality specifications are developed. Only after appropriate analytical quality specifications are addressed, the issues pertaining to methodological differences that result in non-harmonized concentration values, and clinical interpretation of biomarker concentrations will be reconciled. Today, the technology to address many analytic problems is at hand, but commitment on the part of manufacturers and their customers in the laboratory and clinical communities is essential. The design control loop is not closed until the finished in vitro diagnostic system is adequately validated to meet the customer needs, including analytical quality specifications. It is essential to determine the attributes and performance characteristics of relevant competitive systems and their degree of acceptance by clinical laboratories in order to demonstrate that user needs are definitely met. The responsibility of defining and implementing these issues must be a shared responsibility among laboratorians, clinicians, industry, and regulatory agencies on an international front. To date, two sets of quality specifications have been published, one for cardiac troponin assays and one for B-type natriuretic peptide assays. Both address analytical factors, such as calibrator characterization, antibody specificity, assay sensitivity and imprecision, and interferents, as well as preanalytical factors, such as sample type and stability. It would be ideal if regulatory agencies, such as FDA in the United States, accept these criteria for premarket approval clearance applications.

Comparison of Abbott AxSYM and Roche Elecsys 2010 for measurement of BNP and NT-proBNP

BACKGROUND

B-type natriuretic peptide (BNP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) are small cardiac hormones released from the heart. They can be used as an important aid to diagnose congestive heart failure (CHF).

METHODS

We compared the performances of the Abbott AxSYM and Roche Elecsys 2010 for the measurement of BNP and NT-proBNP. The first method uses a microparticle enzyme-linked immunoassay, whereas the other uses chemiluminescent immunometric assay.

RESULTS

The CVs using pooled sera ranged from 3.7% to 12.7% for the AxSYM and 0.9% to 2.2% for the Elecsys 2010. The Passing and Bablok regression was Elecsys 2010 NT-proBNP=7.23xAxSYM BNP+2.53. The BNP in EDTA plasma was more stable than in serum. The immunoreactivity difference of NT-proBNP in serum or EDTA plasma was within 10% when stored at 4 degrees Celsius or 25 degrees Celsius for 72 h. Receiver operating characteristic (ROC) curves were different for both assays, and the areas under the curves were 0.704 and 0.841 for the AxSYM and Elecsys 2010 method, respectively.

CONCLUSIONS

Both assays were not entirely specific for heart failure. The precision and stability for NT-proBNP was better than for BNP in serum. It is important to use method-appropriate reference ranges (or cutoff) for the BNP and NT-proBNP, respectively, in the assessment of CHF.

Postmortem pericardial natriuretic peptides as markers of cardiac function in medico-legal autopsies

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in the blood are clinical markers for the diagnosis of cardiac failure. This study was a comprehensive analysis of the postmortem pericardial levels of the natriuretic peptides in serial medico-legal autopsy cases (n=263, within 72 h postmortem) to assess their validity in investigating cardiac function. There was no significant relationship of pericardial ANP or BNP levels with postmortem time or the age of the subjects. The ANP and BNP levels showed negative correlations with the pericardial cardiac troponin T level. The ANP level was significantly elevated in drowning cases. Pericardial BNP and the BNP/ANP ratio were significantly higher for chronic congestive heart disease. However, asphyxiation, sharp instrument injury, hyperthermia, and fatal MA poisoning cases showed lower levels for both markers. These observations suggest that elevations in the postmortem pericardial ANP and BNP may mainly depend on acute atrial overload and subacute or chronic cardiac failure, respectively, and may be reduced by advanced myocardial damage.

Altered renal response to acute volume expansion in transgenic rats harboring the human tissue kallikrein gene

The renal response to acute volume expansion was investigated in transgenic (TGR) rats harboring the human tissue kallikrein gene. After a primer injection of 0.9% NaCl (3 ml/100 g, i.v), Sprague-Dawley (SD) or TGR rats received a continuous infusion of 0.9% NaCl (15 microl/100 g/min, i.a.) through a catheter placed into the carotid artery. Acute volume expansion was produced by a second injection of 0.9% NaCl (2 ml/100 g, i.v.) 65 min after the first injection. Plasma vasopressin (AVP) and atrial natriuretic peptide (ANP) concentration was measured before and within 10 min of volume expansion. TGR animals presented a blunted response to acute volume expansion evidenced by an attenuated increase in total and fractional water and sodium excretion. Before or after volume expansion, plasma AVP and ANP did not differ between SD and TGR. Pre-treatment with the BK-B2 antagonist HOE-140 (7.5 microg/100 g. i.a) partially improved the renal response of TGRs and severely blunted the response in SD rats. These data show that TGR (hKLK1) rats have an impaired renal response to acute volume expansion that can not be accounted for by changes in the release of AVP or ANP.

The role and assessment of ventricular peptides in heart failure

Although heart failure may be diagnosed readily in its advanced stages, it may be difficult to diagnose clinically in its early stages.Thus, there is a critical need for an inexpensive, simple, rapid,and objective test for heart failure. This article discusses the role and assessment of ventricular natriuretic peptides and related pep-tides in heart failure.

The effect of class-specific protease inhibitors on the stabilization of B-type natriuretic peptide in human plasma

BACKGROUND

B-type natriuretic peptide (BNP) is a cardiac hormone that regulates hemodynamic equilibrium. In the circulation, its activity is controlled by proteolytic factors. Accurate measurement of BNP in a patient's plasma may be affected by degradation due to proteolysis.

OBJECTIVE

We report on the identification and performance of classes of protease inhibitors that stabilize BNP in plasma.

DESIGN AND METHODS

Using the Bayer ADVIA Centaur BNP assay, we measured the effect of arginine, serine and/or specific kallikrein protease inhibitors (PIs) on exogenous spiked or endogenous BNP in patient plasma.

RESULTS

Compared to controls without inhibitor, all PIs were capable, to varying degrees, of retarding the rate of proteolytic degradation. The kallikrein-specific inhibitor, D-Phe-Phe-Arg-chloromethylketone (PPACK II) was most effective as a single constituent and was able to eliminate BNP degradation in patient samples for up to 6-10 days when stored at 2-8 degrees C.

CONCLUSIONS

The stability of BNP was markedly increased in the presence of kallikrein-specific PPACK II and a broad spectrum of serine PIs. Use of these compounds offers a simple method of extending sample handling and storage of plasma samples containing BNP.

Molecular forms of human brain natriuretic peptide in plasma

BACKGROUND

Brain natriuretic peptide (BNP) is a vasoreactive peptide hormone, which is synthesized and secreted mainly from the heart ventricles.

METHODS

Molecular forms of immunoreactive human brain natriuretic peptide (BNP) were examined. Chemically synthesized human BNP was added to whole blood samples from a healthy volunteer. The immunoreactive peptide was recovered by immunoaffinity chromatography followed by reversed-phase HPLC (RP-HPLC). Molecular form of immunoreactive BNP in plasma from heart failure patients was also examined.

RESULTS

Sequential analysis and amino acid analysis of the peptide revealed that two amino acid residues were deleted from the amino terminus of BNP. When roughly classified according to molecular weight (MW), two forms of BNP (high-MW BNP and low-MW BNP) were observed. The estimated MW of high-MW BNP (36 kDa) was three times that of pro-BNP (12 kDa).

CONCLUSIONS

Analysis of low-MW BNP by RP-HPLC revealed that a small amount of BNP 1-32 or des-SerPro-BNP (BNP 3-32) was contained in plasma from heart failure patients.