Natriuretic Peptides and Analytical Barriers

Development of a high-throughput liquid chromatography-tandem mass spectrometry platform for the determination of intact natriuretic peptides in human plasma

We present an innovative, reliable, and antibody-free analytical method to determine multiple intact natriuretic peptides in human plasma. These biomolecules are routinely used to confirm the diagnosis and monitor the evolution of heart failure, so that their determination is essential to improve diagnosis and monitor the efficacy of treatment. However, common immunoassay kits suffer from main limitations due to high cross-reactivity with structurally similar species. In our method, we pre-treated the sample by combining salting-out with ammonium sulfate with microextraction by packed sorbent technique. Analyses were then carried out by ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry. The use of 3-nitrobenzyl alcohol as a supercharger reagent enhanced the ESI ionization and improved the signal-to-noise ratio. The analytical protocol showed good linearity over one order of magnitude, recovery in the range of 94-105 %, and good intra- and inter-day reproducibility (RSD<20 %), and the presence of a matrix effect. Limits of detection were in the range of pg/mL for all peptides (0.2-20 pg/mL). Stability study in plasma samples demonstrated that proper protease inhibitors need to be included in blood collection tubes to avoid peptide degradation. Preliminary analyses on plasma samples from heart failure patients allow the quantification of ANP 1-28 as the most abundant species and the detection of ANP 5-28, BNP 1-32, and BNP 5-32. The method could be used to investigate how cross-reactivity issues among structurally similar species impact determinations by ELISA kits.

NT-proBNP cardiac value in COVID-19: a focus on the paediatric population

NT-proBNP is a peptide related to brain natriuretic peptide, a cardiac biomarker and a member of the natriuretic family of peptides. NT-proBNP has demonstrated its clinical utility in the assessment of a wide spectrum of cardiac manifestations. It is also considered a more precise diagnostic and prognostic cardiac biomarker than brain natriuretic peptide. With the appearance of the Severe Acute Respiratory Syndrome Coronavirus 2 virus and the subsequent COVID-19 pandemic, diagnosis of heart implications began to pose an increasing struggle for the physician. Echocardiography is considered a central means of evaluating cardiac disorders like heart failure, and it is considered a reliable method. However, other diagnostic methods are currently being explored, one of which involves the assessment of NT-proBNP levels. In the literature that involves the adult population, significant positive correlations were drawn between the levels of NT-proBNP and COVID-19 outcomes such as high severity and fatality. In the paediatric population, however, the literature is scarce, and most of the investigations assess NT-proBNP in the context of Multiple Inflammatory Syndrome in Children, where studies have shown that cohorts with this syndrome had elevated levels of NT-proBNP when compared to non-syndromic cohorts. Thus, more large-scale studies on existing COVID-19 data should be carried out in the paediatric population to further understand the prognostic and diagnostic roles of NT-proBNP.

Biomarkers for the Diagnosis of Heart Failure in People with Diabetes: A Consensus Report from Diabetes Technology Society

Diabetes Technology Society assembled a panel of clinician experts in diabetology, cardiology, clinical chemistry, nephrology, and primary care to review the current evidence on biomarker screening of people with diabetes (PWD) for heart failure (HF), who are, by definition, at risk for HF (Stage A HF). This consensus report reviews features of HF in PWD from the perspectives of 1) epidemiology, 2) classification of stages, 3) pathophysiology, 4) biomarkers for diagnosing, 5) biomarker assays, 6) diagnostic accuracy of biomarkers, 7) benefits of biomarker screening, 8) consensus recommendations for biomarker screening, 9) stratification of Stage B HF, 10) echocardiographic screening, 11) management of Stage A and Stage B HF, and 12) future directions. The Diabetes Technology Society panel recommends 1) biomarker screening with one of two circulating natriuretic peptides (B-type natriuretic peptide or N-terminal prohormone of B-type natriuretic peptide), 2) beginning screening five years following diagnosis of type 1 diabetes (T1D) and at the diagnosis of type 2 diabetes (T2D), 3) beginning routine screening no earlier than at age 30 years for T1D (irrespective of age of diagnosis) and at any age for T2D, 4) screening annually, and 5) testing any time of day. The panel also recommends that an abnormal biomarker test defines asymptomatic preclinical HF (Stage B HF). This diagnosis requires follow-up using transthoracic echocardiography for classification into one of four subcategories of Stage B HF, corresponding to risk of progression to symptomatic clinical HF (Stage C HF). These recommendations will allow identification and management of Stage A and Stage B HF in PWD to prevent progression to Stage C HF or advanced HF (Stage D HF).

Lot-to-Lot Variance in Immunoassays-Causes, Consequences, and Solutions

Immunoassays, which have gained popularity in clinical practice and modern biomedical research, play an increasingly important role in quantifying various analytes in biological samples. Despite their high sensitivity and specificity, as well as their ability to analyze multiple samples in a single run, immunoassays are plagued by the problem of lot-to-lot variance (LTLV). LTLV negatively affects assay accuracy, precision, and specificity, leading to considerable uncertainty in reported results. Therefore, maintaining consistency in technical performance over time presents a challenge in reproducing immunoassays. In this article, we share our two-decade-long experience and delve into the reasons for and locations of LTLV, as well as explore methods to mitigate its effects. Our investigation identifies potential contributing factors, including quality fluctuation in critical raw materials and deviations in manufacturing processes. These findings offer valuable insights to developers and researchers working with immunoassays, emphasizing the importance of considering lot-to-lot variance in assay development and application.

ASA Status, NPPA/NPPB Haplotype and Coronary Artery Disease Have an Impact on BNP/NT-proBNP Plasma Levels

Plasma concentrations of natriuretic peptides (NP) contribute to risk stratification and management of patients undergoing non-cardiac surgery. However, genetically determined variability in the levels of these biomarkers has been described previously. In the perioperative setting, genetic contribution to NP plasma level variability has not yet been determined. A cohort of 427 patients presenting for non-cardiac surgery was genotyped for single-nucleotide polymorphisms (SNPs) from the NPPA/NPPB locus. Haplotype population frequencies were estimated and adjusted haplotype trait associations for brain natriuretic peptide (BNP) and amino-terminal pro natriuretic peptide (NT-proBNP) were calculated. Five SNPs were included in the analysis. Compared to the reference haplotype TATAT (rs198358, rs5068, rs632793, rs198389, rs6676300), haplotype CACGC, with an estimated frequency of 4%, showed elevated BNP and NT-proBNP plasma concentrations by 44% and 94%, respectively. Haplotype CGCGC, with an estimated frequency of 9%, lowered NT-proBNP concentrations by 28%. ASA classification status III and IV, as well as coronary artery disease, were the strongest predictors of increased NP plasma levels. Inclusion of genetic information might improve perioperative risk stratification of patients based on adjusted thresholds of NP plasma levels.

Routinely measured cardiac troponin I and N-terminal pro-B-type natriuretic peptide as predictors of mortality in haemodialysis patients

Aims

Cardiac troponin (cTn) and B‐type natriuretic peptide (BNP) are elevated in haemodialysis (HD) patients, and this elevation is associated with HD‐induced myocardial stunning/myocardial strain. However, studies using data from the international Dialysis Outcomes and Practice Patterns Study (DOPPS) have shown that these cardiac biomarkers are measured in <2% of HD patients in real‐world practice. This study aimed to examine whether routinely measured N‐terminal pro‐BNP (NT‐proBNP) and cTnI (contemporary assay) are more appropriate than clinical models for reclassifying the risk of HD patients who have the highest risk of death.

Methods and results

Pre‐dialysis levels of cTnI and NT‐proBNP at study enrolment were measured in 1152 HD patients (Japan DOPPS Phase 5). The patients were prospectively followed for 3 years. Cox regression was used to test the associations of cardiac biomarkers with all‐cause mortality, adjusting for potential confounders. Subgroup analyses were performed to assess potential effect modification of clinical characteristics, such as age, systolic blood pressure, HD vintage, diabetes mellitus, coronary artery disease, and a history of congestive heart failure. At baseline, 337 (29%) patients had elevated cTnI (99th percentile of a healthy population: >0.04 ng/mL) with a median (inter‐quartile range) level of 0.020 (0.005–0.041) ng/mL, and 1140 (99%) patients had elevated NT‐proBNP (cut‐off for heart failure: >125 pg/mL) with a median level of 3658 (1689–9356) pg/mL. There were 167 deaths during a median follow‐up of 2.8 (2.2–2.8) years. Higher levels of both cardiac biomarkers were incrementally associated with mortality after adjustment for potential confounders. Even after adjustment for alternative cardiac biomarkers, the overall P value for the association was <0.01 for both biomarkers. However, the prognostic significance of NT‐proBNP was moderately diminished when cTnI was added to the model. The hazard ratios of mortality for cTnI > 0.04 ng/mL (vs. cTnI < 0.006 ng/mL) and NT‐proBNP > 8000 pg/mL (vs. NT‐proBNP < 2000 pg/mL) were 2.56 (95% confidence interval: 1.37–4.81) and 1.90 (95% confidence interval: 0.95–3.79), respectively. Subgroup analyses showed that the associations of both cardiac biomarkers with mortality were generally consistent between stratified groups.

Conclusions

Routinely measured NT‐proBNP and cTnI levels are strongly associated with mortality among prevalent HD patients. These associations remain robust, even after adjustment for alternative biomarkers, suggesting that cTnI and NT‐proBNP have identical prognostic significance and may reflect different pathological aspects of cardiac abnormalities.

N-terminal pro-B-type natriuretic peptide testing patterns in patients with heart failure with reduced ejection fraction

Aims

The N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) is a commonly used biomarker in heart failure for diagnosis and prognostication. We aimed to determine the prevalence of NT‐proBNP testing, distribution of NT‐proBNP concentrations, and factors associated with receiving an NT‐proBNP test in patients with heart failure with reduced ejection fraction (HFrEF), including the subset with a worsening heart failure event (WHFE).

Methods and results

This was a retrospective cohort study using two US databases: (i) the de‐identified Humana Research Database between January 2015 and December 2018 and (ii) the Veradigm PINNACLE Registry^® between July 2013 and September 2017. We included adult patients with a confirmed diagnosis of HFrEF. In each data source, a subgroup of patients with a WHFE was identified, where a WHFE was defined as a heart failure‐related hospitalization or receipt of intravenous diuretics. Bivariate and multivariate analyses were conducted to assess factors associated with receiving NT‐proBNP testing. In Cohort 1 (n = 249 238), 9.2% of patients with HFrEF and 10.8% of patients with a WHFE received NT‐proBNP testing. When restricted to patients with at least one laboratory claim, 11.3% of patients with HFrEF and 13.2% of those with a WHFE received NT‐proBNP testing. In Cohort 2 (n = 91 444), 2.3% of patients with HFrEF were tested. Median (inter‐quartile range) NT‐proBNP concentrations among patients with HFrEF were 1399 (423–4087) pg/mL in Cohort 1 and 394 (142–688) pg/mL in Cohort 2. Median (inter‐quartile range) NT‐proBNP concentrations in the subset of patients with a WHFE in each cohort were 2209 (740–5894) and 464 (174–783) pg/mL, respectively. In Cohort 1, 13.4% of all HFrEF patients receiving NT‐proBNP testing and 18.9% of patients with a WHFE had NT‐proBNP values >8000 pg/mL; in Cohort 2, these percentages were 1.0% and 2.5%, respectively.

Conclusions

In US clinical practice, NT‐proBNP testing was not frequently performed in patients with HFrEF. NT‐proBNP concentrations varied across data sources and subpopulations within HFrEF.

Determination and stability of N-terminal pro-brain natriuretic peptide in saliva samples for monitoring heart failure

Heart failure (HF) is the main cause of mortality worldwide, particularly in the elderly. N-terminal pro-brain natriuretic peptide (NT-proBNP) is the gold standard biomarker for HF diagnosis and therapy monitoring. It is determined in blood samples by the immunochemical methods generally adopted by most laboratories. Saliva analysis is a powerful tool for clinical applications, mainly due to its non-invasive and less risky sampling. This study describes a validated analytical procedure for NT-proBNP determination in saliva samples using a commercial Enzyme-Linked Immuno-Sorbent Assay. Linearity, matrix effect, sensitivity, recovery and assay-precision were evaluated. The analytical approach showed a linear behaviour of the signal throughout the concentrations tested, with a minimum detectable dose of 1 pg/mL, a satisfactory NT-proBNP recovery (95-110%), and acceptable precision (coefficient of variation ≤ 10%). Short-term (3 weeks) and long-term (5 months) stability of NT-proBNP in saliva samples under the storage conditions most frequently used in clinical laboratories (4, - 20, and - 80 °C) was also investigated and showed that the optimal storage conditions were at - 20 °C for up to 2.5 months. Finally, the method was tested for the determination of NT-proBNP in saliva samples collected from ten hospitalized acute HF patients. Preliminary results indicate a decrease in NT-proBNP in saliva from admission to discharge, thus suggesting that this procedure is an effective saliva-based point-of-care device for HF monitoring.

Active B-Type Natriuretic Peptide Measured by Mass Spectrometry and Response to Sacubitril/Valsartan

BACKGROUND

B-type natriuretic peptide (BNP) immunoassays (BNP_ia) do not differentiate active and inactive forms. Inactive NT-proBNP is used to track heart failure (HF) during treatment with sacubitril/valsartan, which inhibits BNP degradation. Mass spectrometry (MS) may better assess effects of HF treatment on biologically active BNP1-32.

METHODS AND RESULTS

We developed a MS assay with immediate protease inhibition to quantify BNP1-32 over a linear range, using labeled recombinant BNP standard. In 4 healthy volunteers, BNP1-32 by MS (BNP_MS) increased from below the 5 pg/mL detection limit to 228 pg/mL after nesiritide. In patients with HF, BNP_MS was measured in parallel with BNP and NT-proBNP immunoassays before and during sacubitril/valsartan treatment. BNP_MS was 4.4-fold lower than BNP_ia in patients with HF. Among patients not taking sacubitril/valsartan and without end-stage renal disease, BNP_MS correlated with BNP_ia (r_s = 0.77, P < .001) and NT-proBNP (r_s = 0.74, P < .001). After a median of 8 weeks on sacubitril/valsartan, active BNP_MS levels decreased by 50% (interquartile range -98.3% to 41.7%, n = 22, P = .048) and correlated with NT-proBNP (r_s = 0.64, P < .001), but not with BNP_ia (r_s = 0.46, P = .057).

CONCLUSIONS

Active BNP measured by MS accounts for only a small amount of BNP measured by immunoassays. Although decreased BNP production was anticipated to be masked by inhibition of degradation, levels of active BNP decreased during chronic sacubitril/valsartan treatment.

[Cardiac biomarkers in noncardiac surgery patients : Review of cardiac biomarkers for risk stratification and detection of postoperative adverse cardiac events]

BACKGROUND

Yearly, more than 200 million people worldwide undergo noncardiac surgery of whom about 5% will suffer adverse cardiac events. Therefore, risk stratification and early detection of these events is crucial.

OBJECTIVES

The goal of this review is to summarize the currently available evidence on the role of biomarkers in perioperative cardiac risk assessment. It presents current data of the established biomarkers troponin and brain natriuretic peptide (BNP), and it also reports on new biomarkers that are still under evaluation, e.g. copeptin (a marker of neurohumoral activation) and presepsin (an inflammation marker).

MATERIALS AND METHODS

Narrative review.

RESULTS AND CONCLUSION

According to currently available data, there is a strong association between preoperative troponin or BNP values and postoperative adverse cardiac events and mortality. However, to date, there is only a weak recommendation for routine measurement of these biomarkers even in high-risk patients because the evidence on outcome improvement is still very limited. The evidence on treatment options in case of increased postoperative troponin values is also scarce so that international guidelines come to different conclusions regarding postoperative measurement of toponin. Meanwhile, several new biomarkers are under evaluation.

Analysis of B-type natriuretic peptide impurities using label-free data-independent acquisition mass spectrometry technology

Objectives

Synthetic B-type natriuretic peptide (BNP) is employed in most clinical testing platforms as a raw material of calibrator. Characterization of impurities with structures similar (BNPstrimp compounds) to that of BNP is a reasonable way to decrease clinical measurement errors and improve drug safety.

Methods

A novel quantitative method targeted towards BNPstrimp compounds was developed. First, the peptide samples were separated and identified using ultra-performance liquid chromatography, coupled with high-resolution mass spectrometry (MS). To evaluate biological activity further, BNPstrimp immunoaffinity was investigated using western blot (WB) assays. Second, a quantitative label-free data-independent acquisition (DIA) MS approach was developed, and the internal standard peptide (ISP) was hydrolyzed. Absolute quantification was performed using an isotope dilution MS (ID-MS) approach. Third, method precision was investigated using the C-peptide reference material.

Results

Seventeen BNPstrimp compounds were identified in synthetic BNP, and 10 of them were successfully sequenced. The immunoassay results indicated that deaminated, oxidized, and isomerized BNPstrimp compounds exhibited weaker immunoaffinity than intact BNP1-32. The mass fraction of the synthetic solid ISP1-16, quantified by ID-MS, was 853.5 (±17.8) mg/g. Validation results indicated that the developed method was effective and accurate for the quantitation of the well-separated BNP impurities.

Conclusions

The developed approach was easy to perform, and it was suitable for the parallel quantification of low-abundance BNPstrimp compounds when they performed a good separation in liquid chromatography. The quantitative results were comparable and traceable. This approach is a promising tool for BNP product quality and safety assessment.

Pathophysiology and significance of natriuretic peptides in patients with end-stage kidney disease

Natriuretic peptides (NP), especially B type (BNP) and its N-terminal pro-B type natriuretic peptide (NT-proBNP), have long been regarded as biomarkers of volume overload and tools to exclude heart failure in the general population. However, their role in end-stage kidney disease (ESKD) is less certain given that BNP and NT-proBNP are excreted by the kidney and so serum concentrations of NPs are nearly universally elevated compared to controls. Nevertheless, the accumulated evidence suggests thatserum concentrations of NPs in patients with ESKD show moderate or strong positive relationships with underlying heart disease, abnormal cardiac structure or function and mortality. Limited evidence also supports the role of BNP including NT-proBNP, ANP in some studies, rather than CNP or DNP in risk stratification among ESKD patients as well as the utility of BNP samplings pre- and post- hemodialysis. However, studies of the cut-off values of NPs have yielded inconsistent results, such that further large-scale studies are needed to clarify these issues. This review summarizes the pathophysiology and significance of NPs in ESKD patients, especially their potential role as risk stratification biomarkers in clinical management.

Cardiac natriuretic peptides

Investigations into the mixed muscle-secretory phenotype of cardiomyocytes from the atrial appendages of the heart led to the discovery that these cells produce, in a regulated manner, two polypeptide hormones - the natriuretic peptides - referred to as atrial natriuretic factor or atrial natriuretic peptide (ANP) and brain or B-type natriuretic peptide (BNP), thereby demonstrating an endocrine function for the heart. Studies on the gene encoding ANP (NPPA) initiated the field of modern research into gene regulation in the cardiovascular system. Additionally, ANP and BNP were found to be the natural ligands for cell membrane-bound guanylyl cyclase receptors that mediate the effects of natriuretic peptides through the generation of intracellular cGMP, which interacts with specific enzymes and ion channels. Natriuretic peptides have many physiological actions and participate in numerous pathophysiological processes. Important clinical entities associated with natriuretic peptide research include heart failure, obesity and systemic hypertension. Plasma levels of natriuretic peptides have proven to be powerful diagnostic and prognostic biomarkers of heart disease. Development of pharmacological agents that are based on natriuretic peptides is an area of active research, with vast potential benefits for the treatment of cardiovascular disease.

Natriuretic Peptides to Predict Short-Term Mortality in Patients With Sepsis: A Systematic Review and Meta-analysis

Data are conflicting regarding the optimal cutoffs of B-type natriuretic peptide (BNP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) to predict short-term mortality in patients with sepsis. We conducted a comprehensive search of several databases (MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Scopus) for English-language reports of studies evaluating adult patients with sepsis, severe sepsis, and septic shock with BNP/NT-proBNP levels and short-term mortality (intensive care unit, in-hospital, 28-day, or 30-day) published from January 1, 2000, to September 5, 2017. The average values in survivors and nonsurvivors were used to estimate the receiver operating characteristic curve (ROC) using a parametric regression model. Thirty-five observational studies (3508 patients) were included (median age, 51-75 years; 12%-74% males; cumulative mortality, 34.2%). A BNP of 622 pg/mL had the greatest discrimination for mortality (sensitivity, 0.695 [95% CI, 0.659-0.729]; specificity, 0.907 [95% CI, 0.810-1.003]; area under the ROC, 0.766 [95% CI, 0.734-0.797]). An NT-proBNP of 4000 pg/mL had the greatest discrimination for mortality (sensitivity, 0.728 [95% CI, 0.703-0.753]; specificity, 0.789 [95% CI, 0.710-0.867]; area under the ROC, 0.787 [95% CI, 0.766-0.809]). In prespecified subgroup analyses, identified BNP/NT-proBNP cutoffs had higher discrimination if specimens were obtained 24 hours or less after admission, in patients with severe sepsis/septic shock, in patients enrolled after 2010, and in studies performed in the United States and Europe. There was inconsistent adjustment for renal function. In this hypothesis-generating analysis, BNP and NT-proBNP cutoffs of 622 pg/mL and 4000 pg/mL optimally predicted short-term mortality in patients with sepsis. The applicability of these results is limited by the heterogeneity of included patient populations.

Educational Recommendations on Selected Analytical and Clinical Aspects of Natriuretic Peptides with a Focus on Heart Failure: A Report from the IFCC Committee on Clinical Applications of Cardiac Bio-Markers

The IFCC Committee on Clinical Applications of Cardiac Bio-Markers (C-CB) has directives and initiatives focused on providing evidence-based educational resources to aid and improve understanding around key analytical and clinical aspects of cardiac biomarkers used in clinical practice and the research setting. As a task force, we have previously published position statements and recommendations focused on use and analytical aspects of high-sensitivity cardiac troponin assays. The current educational document is the first from the C-CB highlighting important biochemical, analytical, and clinical aspects as they relate to the natriuretic peptides (NPs), including B-type natriuretic peptide (BNP) and N-terminal pro–B-type natriuretic peptide (NT-proBNP), with a focus on heart failure.

The role of N-terminal pro-B-type natriuretic peptide in prognostic evaluation of heart failure

Heart failure (HF) is a growing challenge in the Asia Pacific region. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a well-established tool for diagnosis of HF; however, it is relatively underutilized in predicting adverse outcomes in HF. Multiple studies have demonstrated the prognostic role of NT-proBNP in HF. A single value of NT-proBNP >5000 pg/mL predicts a worse outcome in hospitalized patients with HF with reduced ejection fraction (HFrEF). In stable outpatients with HFrEF, NT-proBNP > 1000 pg/mL predicts a poorer prognosis. NT-proBNP provides the same prognostic information in patients with HF with preserved ejection fraction (HFpEF) as in those with HFrEF. An expert panel composed of cardiologists mainly from Asia Pacific region was convened to discuss the utility of NT-proBNP in HF prognostication. This article summarizes available scientific evidence and consensus recommendations from the meeting.

Natriuretic peptides in human heart: Novel insight into their molecular forms, functions, and diagnostic use

Among the three natriuretic peptides, atrial/A-type natriuretic peptide (ANP) and brain/B-type natriuretic peptide (BNP) are primarily produced by, and secreted from, heart tissue. They maintain cardiovascular homeostasis by binding to natriuretic peptide receptor-A. Since plasma ANP and BNP concentrations, as well as expression, are elevated in response to increased body fluid volume and pressure load on the heart wall, these peptides are widely utilized as diagnostic biomarkers for evaluating heart failure. Regardless of their high utility, differences in their molecular forms between healthy and diseased subjects and how these relate to pathophysiology have not well been examined. Recent studies have shown that the circulating molecular forms of ANP and BNP are not uniform; bioactive α-ANP is the major ANP form, whereas the weakly active proBNP is the major BNP form. The relative ratios of the different molecular forms are altered under different pathophysiological conditions. These facts indicate that detailed measurements of each form may provide useful information on the pathophysiological state of heart tissue. Here, we revisit the relationship between the molecular forms of, and pathophysiological alterations in, human ANP and BNP and discuss the possible utility of the measurement of each of the molecular forms. The third peptide, C-type natriuretic peptide, activates natriuretic peptide receptor-B, but little is known about its production and function in the heart because of its extremely low levels. However, through recent studies, its role in the heart is gradually becoming clear. Here, we summarize its molecular forms, assay systems, and functions in the heart.

Analytical barriers in clinical B-type natriuretic peptide measurement and the promising analytical methods based on mass spectrometry technology

B-type natriuretic peptide (BNP) is a circulating biomarker that is mainly applied in heart failure (HF) diagnosis and to monitor disease progression. Because some identical amino acid sequences occur in the precursor and metabolites of BNP, undesirable cross-reactions are common in immunoassays. This review first summarizes current analytical methods, such as immunoassay- and mass spectrometry (MS)-based approaches, including the accuracy of measurement and the inconsistency of the results. Second, the review presents some promising approaches to resolve the current barriers in clinical BNP measurement, such as how to decrease cross-reactions and increase the measurement consistency. Specific approaches include research on novel BNP assays with higher-specificity chemical antibodies, the development of International System of Units (SI)-traceable reference materials, and the development of structure characterization methods based on state-of-the-art ambient and ion mobility MS technologies. The factors that could affect MS analysis are also discussed, such as biological sample cleanup and peptide ionization efficiency. The purpose of this review is to explore and identify the main problems in BNP clinical measurement and to present three types of approaches to resolve these problems, namely, materials, methods and instruments. Although novel approaches are proposed here, in practice, it is worth noting that the BNP-related peptides including unprocessed proBNP were all measured in clinical BNP assays. Therefore, approaches that aimed to measure a specific BNP or proBNP might be an effective way for the standardization of a particular BNP form measurement, instead of the standardization of “total” immunoreactive BNP assays in clinical at present.

Diagnostic concordance between NT-proBNP and BNP for suspected heart failure

OBJECTIVES

BNP and NT-proBNP are viewed as comparable in their ability to diagnose and monitor HF in clinical guidelines. However, no recent large-scale study has directly established diagnostic concordance between BNP and NT-proBNP. This study sought to assess diagnostic concordance of BNP and NT-proBNP for ruling in and ruling out heart failure (HF).

METHODS

Simultaneous BNP and NT-proBNP testing was performed on 2729 patient samples with routinely ordered BNP testing. Hospital location, age, sex, creatinine, BNP and NT-proBNP were also recorded. Recommended cutoffs for BNP and NT-proBNP for ruling in and out HF were used for assessing diagnostic concordance and correlation.

RESULTS

In the ED setting, concordance between BNP and NT-proBNP was 0.695 (95% CI, 0.668-0.723) by weighted kappa using the recommended cutoffs for the acute setting. In non-ED patients, the concordance was 0.642 (95% CI, 0.580-0.705) using non-acute setting cutoffs. In the ED setting, patients with eGFR <60 mL/min/1.73m² had lower overall concordance (0.626; 95% CI 0.580-0.672) compared to those with eGFR >60 mL/min/1.73m² (0.707, 95% CI 0.669-0.744). Patients with an eGFR <15 mL/min/1.73m² had a much higher ratio of NT-proBNP to BNP than patients with eGFR >60 mL/min/1.73m² (17.0 vs. 4.7, P < .001). Linear regression revealed an r² of 0.52 in the ED setting and 0.49 in the non-ED setting between BNP and NT-proBNP. For 368 patients with multiple measurements of natriuretic peptides, 19.7% of paired temporal measurements had an increase in one peptide and a decrease in the other.

CONCLUSION

The current cutoffs for diagnosing HF for NT-proBNP and BNP have relatively low diagnostic concordance and correlation, particularly among patients with chronic kidney disease.

Brain Natriuretic Peptide and Its Biochemical, Analytical, and Clinical Issues in Heart Failure: A Narrative Review

Heart failure (HF) is a primary cause of morbidity and mortality worldwide. As the most widely studied and commonly applied natriuretic peptide (NP), B-type natriuretic peptide (BNP) has the effects of diuresis, natriuresis, vasodilation, anti-hypertrophy, and anti-fibrosis and it inhibits the renin-angiotensin-aldosterone and sympathetic nervous systems to maintain cardiorenal homeostasis and counteract the effects of HF. Both BNP and N-terminal pro B-type natriuretic peptide (NT-proBNP) are applied as diagnostic, managing, and prognostic tools for HF. However, due to the complexity of BNP system, the diversity of BNP forms and the heterogeneity of HF status, there are biochemical, analytical, and clinical issues on BNP not fully understood. Current immunoassays cross-react to varying degrees with pro B-type natriuretic peptide (proBNP), NT-proBNP and various BNP forms and cannot effectively differentiate between these forms. Moreover, current immunoassays have different results and may not accurately reflect cardiac function. It is essential to design assays that can recognize specific forms of BNP, NT-proBNP, and proBNP to obtain more clinical information. Not only the processing of proBNP (corin/furin) and BNP (neprilysin), but also the effects of glycosylation on proBNP processing and BNP assays, should be targeted in future studies to enhance their diagnostic, therapeutic, and prognostic values.

Evolution of natriuretic peptide biomarkers in heart failure: Implications for clinical care and clinical trials

Natriuretic peptides (NPs) are recommended by international guidelines to exclude non-heart failure causes of acute dyspnea and to assess prognosis. NPs are commonly used as an entry criterion for clinical trials, to minimize enrollment of misdiagnosed patients, or to ensure enrollment of a sufficiently at-risk population. NP values used to select trial populations to date have been inconsistent across studies. Future trials should consider using standardized thresholds for NP levels, with protocol-specified adaptations appropriate for the specific study and patient population to account for factors that can influence the NP level. NPs have been used as an endpoint for proof-of-concept or phase 2 clinical trials, although it is important to remember that positive results in early phase studies may be unstable due to small numbers and the play of chance, and they are not always reproducible in phase 3 trials. Likewise, failure to reduce NP in phase 2 may not necessarily indicate that a drug will be ineffective on clinical outcomes in phase 3. NP guided therapy has been intensively studied, but the clinical outcome benefits of this approach remain uncertain. Neprilysin inhibitors have stimulated further exploration of the NP system and how it influences, and is potentially influenced by, heart failure therapies. This paper discusses the utility of NPs in the current clinical research and practice environment and addresses areas in need of further research from the perspectives of academic clinical trialists, clinicians, biostatisticians, regulators, and pharmaceutical industry scientists who participated in the 13th Global Cardiovascular Clinical Trialists Forum.

New issues on measurement of B-type natriuretic peptides

The measurement of the active hormone of B-type natriuretic peptide (BNP) system actually has several analytical limitations and difficulties in clinical interpretations compared to that of inactive peptide N-terminal proBNP (NT-proBNP) because of the different biochemical and pathophysiological characteristics of two peptides and quality specifications of commercial immunoassay methods used for their measurement. Because of the better analytical characteristics of NT-proBNP immunoassays and the easier pathophysiological and clinical interpretations of variations of NT-proBNP levels in patients with heart failure (HF), some authors claimed to measure the inactive peptide NT-proBNP instead of the active hormone BNP for management of HF patients. The measurement of the active peptide hormone BNP gives different, but complementary, pathophysiological and clinical information compared to inactive NT-proBNP. In particular, the setup of new more sensitive and specific assays for the biologically active peptide BNP1-32 should give better accurate information on circulating natriuretic activity. In conclusion, at present time, clinicians should accurately consider both the clinical setting of patients and the analytical characteristics of BNP and NT-proBNP immunoassays in order to correctly interpret the variations of natriuretic peptides measured by commercially available laboratory methods, especially in patients treated with the new drug class of angiotensin receptor-neprilysin inhibitors.

A candidate liquid chromatography mass spectrometry reference method for the quantification of the cardiac marker 1-32 B-type natriuretic peptide

BACKGROUND

B-type natriuretic peptide (BNP) is a 32 amino acid cardiac hormone routinely measured by immunoassays to diagnose heart failure. While it is reported that immunoassay results can vary up to 45%, no attempt of standardization and/or harmonization through the development of certified reference materials (CRMs) or reference measurement procedures (RMPs) has yet been carried out.

METHODS

B-type natriuretic peptide primary calibrator was quantified traceably to the International System of Units (SI) by both amino acid analysis and tryptic digestion. A method for the stabilization of BNP in plasma followed by protein precipitation, solid phase extraction (SPE) and liquid chromatography (LC) mass spectrometry (MS) was then developed and validated for the quantification of BNP at clinically relevant concentrations (15-150 fmol/g).

RESULTS

The candidate reference method was applied to the quantification of BNP in a number of samples from the UK NEQAS Cardiac Markers Scheme to demonstrate its applicability to generate reference values and to preliminary evaluate the commutability of a potential CRM. The results from the reference method were consistently lower than the immunoassay results and discrepancy between the immunoassays was observed confirming previous data.

CONCLUSIONS

The application of the liquid chromatography-mass spectrometry (LC-MS) method to the UK NEQAS samples and the correlation of the results with the immunoassay results shows the potential of the method to support external quality assessment schemes, to improve understanding of the bias of the assays and to establish RMPs for BNP measurements. Furthermore, the method has the potential to be multiplexed for monitoring circulating truncated forms of BNP.