Immunoreactivity and guanosine 3',5'-cyclic monophosphate activating actions of various molecular forms of human B-type natriuretic peptide

Sex-based differences in metabolic protection by the ANP genetic variant rs5068 in the general population

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are produced in the heart and secreted into the circulation. As hormones, both peptides activate the guanylyl cyclase receptor A (GC-A), playing a role in blood pressure (BP) regulation. A significant role for ANP and BNP includes favorable actions in metabolic homeostasis. Sex-based high prevalence of risk factors for cardiovascular disease in males compared with females is well established, but sex-based differences on cardiometabolic protection have not been investigated in relation to ANP (NPPA) and BNP (NPPB) gene variants. We included 1,146 subjects in the general population from Olmsted County, Minnesota. Subjects were genotyped for the ANP gene variant rs5068 and BNP gene variant rs198389. Cardiometabolic parameters and medical records were reviewed. In the presence of the minor allele of rs5068, diastolic BP, creatinine, body mass index (BMI), waist measurement, insulin, and prevalence of obesity and metabolic syndrome were lower, whereas HDL was higher in males with only trends observed in females. We observed no associations of the minor allele with echocardiographic parameters in either males or females. Regarding rs198389 genotype, the minor allele was not associated with any BP, metabolic, renal, or echocardiographic parameters in either sex. In the general community, the minor allele of the ANP gene variant rs5068 is associated with a favorable metabolic phenotype in males. No associations were observed with the BNP gene variant rs198389. These studies support a protective role of the ANP pathway on metabolic function and underscore the importance of sex in relationship to natriuretic peptide responses.NEW & NOTEWORTHY Males are characterized by lower ANP and BNP with greater prevalence of cardiometabolic disease. The ANP genetic variant rs5068 was associated with less metabolic dysfunction in males, whereas no metabolic profile was related to the BNP genetic variant rs198389 in the general population. ANP may play a more biological role in metabolic homeostasis compared with BNP in the general population with greater physiological metabolic actions in males compared with females.

Proteoforms and their expanding role in laboratory medicine

The term “proteoforms” describes the range of different structures of a protein product of a single gene, including variations in amino acid sequence and post-translational modifications. This diversity in protein structure contributes to the biological complexity observed in living organisms. As the concentration of a particular proteoform may increase or decrease in abnormal physiological states, proteoforms have long been used in medicine as biomarkers of health and disease. Notably, the analytical approaches used to analyze proteoforms have evolved considerably over the years. While ligand binding methods continue to play a large role in proteoform measurement in the clinical laboratory, unanticipated or unknown post-translational modifications and sequence variants can upend even extensively tested and vetted assays that have successfully made it through the medical regulatory process. As an alternate approach, mass spectrometry—with its high molecular selectivity—has become an essential tool in detection, characterization, and quantification of proteoforms in biological fluids and tissues. This review explores the analytical techniques used for proteoform detection and quantification, with an emphasis on mass spectrometry and its various applications in clinical research and patient care including, revealing new biomarker targets, helping improve the design of contemporary ligand binding in vitro diagnostics, and as mass spectrometric laboratory developed tests used in routine patient care.

NT-proBNP/BNP ratio for prognostication in European Caucasian patients enrolled in a heart failure prevention programme

Aims

Guidelines support the role of B‐type natriuretic peptide (BNP) and amino‐terminal pro‐BNP (NT‐proBNP) for risk stratification of patients in programmes to prevent heart failure (HF). Although biologically formed in a 1:1 ratio, the ratio of NT‐proBNP to BNP exhibits wide inter‐individual variability. A report on an Asian population suggests that molar NT‐proBNP/BNP ratio is associated with incident HF. This study aims to determine whether routine, simultaneous evaluation of both BNP and NT‐proBNP is warranted in a European, Caucasian population.

Methods and Results

We determined BNP and NT‐proBNP levels for 782 Stage A/B HF patients in the STOP‐HF programme. The clinical, echocardiographic, and biochemical associates of molar NT‐proBNP/BNP ratio were analysed. The primary endpoint was the adjusted association of baseline molar NT‐proBNP/BNP ratio with new‐onset HF and/or progression of left ventricular dysfunction (LVD). We estimated the C‐statistic, integrated discrimination improvement, and the category‐free net reclassification improvement metric for the addition of molar NT‐proBNP/BNP ratio to adjusted models. The median age was 66.6 years [interquartile range (IQR) 59.5–73.1], 371 (47.4%) were female, and median molar NT‐proBNP/BNP ratio was 1.91 (IQR 1.37–2.93). Estimated glomerular filtration rate, systolic blood pressure, left ventricular mass index, and heart rate were associated with NT‐proBNP/BNP ratio in a linear regression model (all P < 0.05). Over a median follow‐up period of 5 years (IQR 3.4–6.8), 247 (31.5%) patients developed HF or progression of LVD. Log‐transformed NT‐proBNP/BNP ratio is inversely associated with HF and LVD risk when adjusted for age, gender, diabetes, hypertension, vascular disease, obesity, heart rate, number of years of follow‐up, estimated glomerular filtration rate, and baseline NT‐proBNP (odds ratio 0.71, 95% confidence interval 0.55–0.91; P = 0.008). However, molar NT‐proBNP/BNP ratio did not increase the C‐statistic (Δ −0.01) and net reclassification improvement (0.0035) for prediction of HF and LVD compared with NT‐proBNP or BNP alone. Substitution of NT‐proBNP for BNP in the multivariable model eliminated the association with HF and LVD risk.

Conclusions

This study characterized, for the first time in a Caucasian Stage A/B HF population, the relationship between NT‐proBNP/BNP ratio and biological factors and demonstrated an inverse relationship with the future development of HF and LVD. However, this study does not support routine simultaneous BNP and NT‐proBNP measurement in HF prevention programmes amongst European, Caucasian patients.

Therapeutic Progress and Knowledge Basis on the Natriuretic Peptide System in Heart Failure

Notwithstanding substantial improvements in diagnosis and treatment, Heart Failure (HF) remains a major disease burden with high prevalence and poor outcomes worldwide. Natriuretic Peptides (NPs) modulate whole cardiovascular system and exhibit multiple cardio-protective effects, including the counteraction of the Renin-Angiotensin-Aldosterone System (RAAS) and Sympathetic Nervous System (SNS), promotion of vasodilatation and natriuresis, and inhibition of hypertrophy and fibrosis. Novel pharmacological therapies based on NPs may achieve a valuable shift in managing patients with HF from inhibiting RAAS and SNS to a reversal of neurohormonal imbalance. Enhancing NP bioavailability through exogenous NP administration and inhibiting Neutral Endopeptidase (NEP) denotes valuable therapeutic strategies for HF. On the one hand, NEP-resistant NPs may be more specific as therapeutic choices in patients with HF. On the other hand, NEP Inhibitors (NEPIs) combined with RAAS inhibitors have proved to exert beneficial effects and reduce adverse events in patients with HF. Highly effective and potentially safe Angiotensin Receptor Blocker Neprilysin Inhibitors (ARNIs) have been developed after the failure of NEPIs and Vasopeptidase Inhibitors (VPIs) due to lacking efficacy and safety. Therapeutic progress and knowledge basis on the NP system in HF are summarized in the current review.

The Endocrine Function of the Heart: Physiology and Involvements of Natriuretic Peptides and Cyclic Nucleotide Phosphodiesterases in Heart Failure

Besides pumping, the heart participates in hydro-sodium homeostasis and systemic blood pressure regulation through its endocrine function mainly represented by the large family of natriuretic peptides (NPs), including essentially atrial natriuretic (ANP) and brain natriuretic peptides (BNP). Under normal conditions, these peptides are synthesized in response to atrial cardiomyocyte stretch, increase natriuresis, diuresis, and vascular permeability through binding of the second intracellular messenger’s guanosine 3′,5′-cyclic monophosphate (cGMP) to specific receptors. During heart failure (HF), the beneficial effects of the enhanced cardiac hormones secretion are reduced, in connection with renal resistance to NP. In addition, there is a BNP paradox characterized by a physiological inefficiency of the BNP forms assayed by current methods. In this context, it appears interesting to improve the efficiency of the cardiac natriuretic system by inhibiting cyclic nucleotide phosphodiesterases, responsible for the degradation of cGMP. Recent data support such a therapeutic approach which can improve the quality of life and the prognosis of patients with HF.

Metabolism of atrial and brain natriuretic peptides in the fetoplacental circulation of fetuses with congenital heart diseases

INTRODUCTION

Natriuretic peptides (NPs) play a pivotal role in maintaining fetal circulation; however, little is known about their metabolism. The aim of the present study was to elucidate the metabolism of plasma NPs in the fetoplacental circulation.

METHODS

Plasma NP concentrations in maternal vein and umbilical artery (UA) and vein (UV) samples from fetuses with congenital heart defect (n = 86) or arrhythmia (n = 31) and controls (n = 127) were analyzed.

RESULTS

Levels of plasma atrial NP (ANP) and brain NP (BNP) showed good correlation between UV versus UA samples (p < 0.01). In all three fetus groups, the regression coefficients between UV and UA plasma ANP levels were close to 0.5, while those between UV and UA plasma BNP levels were close to 1. The molecular forms of immunoreactive ANP in UA plasma showed a single peak corresponding to mature ANP, while those of immunoreactive BNP in UA plasma showed two major peaks and several minor peaks corresponding to mature BNP-32 and its partially digested peptides, as well as glycosylated and non-glycosylated BNP precursors (proBNP). No correlation was found between fetuses and mothers in terms of either plasma ANP or BNP levels.

CONCLUSIONS

The mother and fetus independently secrete and metabolize both ANP and BNP. Fetal plasma ANP consists exclusively of the mature form, and the placenta and umbilical vessels are possible major sites of ANP metabolism. In contrast, fetal plasma BNP consists predominantly of the precursor forms, which may contribute to protecting BNP from metabolism in the fetoplacental circulation.

Hydrostatic pressure suppresses fibrotic changes via Akt/GSK-3 signaling in human cardiac fibroblasts

Mechanical stresses play important roles in the process of constructing and modifying heart structure. It has been well established that stretch force acting on cardiac fibroblasts induces fibrosis. However, the effects of compressive force, that is, hydrostatic pressure (HP), have not been well elucidated. We thus evaluated the effects of HP using a pressure‐loading apparatus in human cardiac fibroblasts (HCFs) in vitro. In this study, high HP (200 mmHg) resulted in significant phosphorylation of Akt in HCFs. HP then greatly inhibited glycogen synthase kinase 3 (GSK‐3)α, which acts downstream of the PI3K/Akt pathway. Similarly, HP suppressed mRNA transcription of inflammatory cytokine‐6, collagen I and III, and matrix metalloproteinase 1, compared with an atmospheric pressure condition. Furthermore, HP inhibited collagen matrix production in a three‐dimensional HCF culture. Taken together, high HP suppressed the differentiation of fibroblasts into the myofibroblast phenotype. HP under certain conditions suppressed cardiac fibrosis via Akt/GSK‐3 signaling in HCFs. These results might help to elucidate the pathology of some types of heart disease.

Atrial and brain natriuretic peptides: Hormones secreted from the heart

The natriuretic peptide family consists of three biologically active peptides: atrial natriuretic peptide (ANP), brain (or B-type) natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). Among these, ANP and BNP are secreted by the heart and act as cardiac hormones. Both ANP and BNP preferentially bind to natriuretic peptide receptor-A (NPR-A or guanylyl cyslase-A) and exert similar effects through increases in intracellular cyclic guanosine monophosphate (cGMP) within target tissues. Expression and secretion of ANP and BNP are stimulated by various factors and are regulated via multiple signaling pathways. Human ANP has three molecular forms, α-ANP, β-ANP, and proANP (or γ-ANP), with proANP predominating in healthy atrial tissue. During secretion proANP is proteolytically processed by corin, resulting in secretion of bioactive α-ANP into the peripheral circulation. ProANP and β-ANP are minor forms in the circulation but are increased in patients with heart failure. The human BNP precursor proBNP is proteolytically processed to BNP_1-32 and N-terminal proBNP (NT-proBNP) within ventricular myocytes. Uncleaved proBNP as well as mature BNP_1-32 and NT-proBNP is secreted from the heart, and its secretion is increased in patients with heart failure. Mature BNP, its metabolites including BNP_3-32, BNP_4-32, and BNP_5-32, and proBNP are all detected as immunoreactive-BNP by the current BNP assay system. We recently developed an assay system that specifically detects human proBNP. Using this assay system, we observed that miR30-GALNTs-dependent O-glycosylation in the N-terminal region of proBNP contributes to regulation of the processing and secretion of proBNP from the heart.

Natriuretic Peptide Processing in Patients with and Without Left Ventricular Dysfunction

This study aimed to examine the relationship between corin expression and circulating brain natriuretic peptide in patients with left ventricular (LV) dysfunction.Circulating levels of B-type natriuretic peptide (BNP) can be an indicator of LV dysfunction. The 32-amino-acid BNP is cleaved by corin, a cardiac serine protease, from its108-amino-acid pro-brain natriuretic peptide (proBNP) precursor.This study included 25 patients with idiopathic dilated cardiomyopathy (DCMP) and LV dysfunction and 44 heart transplant recipients with normal LV function who underwent diagnostic left and right heart catheterization. Blood samples were used to determine the ratio of plasma proBNP/BNP levels, and LV endomyocardial biopsies were used to determine the expression of NPPB, which encode BNP and corin, respectively, by quantitative reverse transcription-polymerase chain reaction.Patients with DCMP revealed worse hemodynamic profiles and higher plasma proBNP and BNP levels than those of the transplant recipients. Myocardial NPPB expression was higher and CORIN expression was lower in the DCMP patients than in the transplant recipients. CORIN expression significantly correlated with NPPB expression (r = -0.585; P < 0.001), ejection fraction (EF; r = 0.694; P < 0.01), LV end-diastolic pressure (r = -0.373; P < 0.05), and indexed end-diastolic LV volume (r = -0.452; P < 0.001). In addition, the plasma proBNP/BNP levels inversely correlated with the CORIN expression (r = -0.362; P < 0.005).Decreased myocardial CORIN expression and the corresponding higher levels of circulating unprocessed proBNP in DCMP may partly account for the relative BNP resistance observed in patients with LV dysfunction.

Analysis of the Correlation between the Myocardial Expression of DPP-4 and the Clinical Parameters of Patients with Heart Failure

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used as antidiabetic drugs. We recently reported that DPP-4 inhibition has beneficial effects on heart failure (HF) mice model. Furthermore, we confirmed that myocardial DPP-4 activity was significantly increased in HF mice compared with non-HF mice. The aim of this study was to investigate the level of myocardial CD26 (DPP-4) expression and its association to clinical parameters in HF patients.Endomyocardial biopsy (EMB) specimens (n = 33) were obtained from HF patients who were admitted to Chiba University Hospital from June 2006 to July 2012. EMB specimens were fixed in formaldehyde and stained with Masson's trichrome staining or with anti-CD26 antibody. Patients were divided into the high CD26 density (CD26-H) or low CD26 density groups (CD26-L). DPP-4 density was compared with blood brain natriuretic peptide (BNP) level and echocardiographic parameters at one year after EMB. Although there were no significant differences in echocardiographic parameters between the CD26-H group and CD26-L group, blood BNP levels were higher in the CD26-H group than in the CD26-L group at one year after EMB. Multivariate regression analysis showed that CD26 density was also an independent determinant of blood BNP levels at one year after EMB.The level of myocardial CD26 expression might be a predictive marker of prognosis in patients with HF.

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.

Cutting Edge of Brain Natriuretic Peptide (BNP) Research - The Diversity of BNP Immunoreactivity and Its Clinical Relevance

Brain (or B-type) natriuretic peptide (BNP) is a cardiac hormone produced in the heart and an established biochemical marker for heart failure (HF) because the level in plasma increases in proportion to disease severity. Recently, the diversity of BNP molecular forms in the peripheral circulation, which includes mature BNP (BNP_1-32) and its metabolites (BNP_3-32, BNP_4-32, and BNP_5-32), was demonstrated. Moreover, studies showed that unprocessed BNP prohormone (proBNP) is also secreted from the heart, and its secretion is increased in patients with HF. Interestingly, BNP_1-32, its metabolites, and proBNP are all detected as immunoreactive BNP by the currently available BNP assay system. Current N-terminal proBNP (NT-proBNP) assay systems also can react to both NT-proBNP and proBNP. In addition, the N-terminal region of proBNP and NT-proBNP are often O-glycosylated, which may result in underestimation of total NT-proBNP level, which includes both glycosylated and non-glycosylated NT-proBNP, by the NT-proBNP assay system. More recently, we have shown that miR30-GALNT-dependent O-glycosylation in the N-terminal region of proBNP affects the processing of proBNP and contributes to its secretion from the heart. The level of proBNP relative to BNP (proBNP/BNP ratio) in the coronary sinus is higher in patients with more severe HF. The proBNP/BNP ratio and the deglycosylated NT-proBNP level may be new and clinically useful biomarkers of HF.

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.

Natriuretic Peptides in Heart Failure: Atrial and B-type Natriuretic Peptides

The natriuretic peptides play a vital role in normal physiology and as counter-regulatory hormones in heart failure (HF). Clinical assessment of their levels (for B-type natriuretic peptide [BNP], N-terminal proBNP, and the midregion of N-terminal pro-atrial natriuretic peptide) have become valuable tools in diagnosing patients with HF as well as risk stratifying and guiding therapy. Their roles have further expanded beyond HF to other cardiovascular conditions and for risk stratification in asymptomatic individuals. Understanding the clinical use of these hormones is vital to achieving their full potential.

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.

Synthesis, secretion, function, metabolism and application of natriuretic peptides in heart failure

As a family of hormones with pleiotropic effects, natriuretic peptide (NP) system includes atrial NP (ANP), B-type NP (BNP), C-type NP (CNP), dendroaspis NP and urodilatin, with NP receptor-A (guanylate cyclase-A), NP receptor-B (guanylate cyclase-B) and NP receptor-C (clearance receptor). These peptides are genetically distinct, but structurally and functionally related for regulating circulatory homeostasis in vertebrates. In humans, ANP and BNP are encoded by NP precursor A (NPPA) and NPPB genes on chromosome 1, whereas CNP is encoded by NPPC on chromosome 2. NPs are synthesized and secreted through certain mechanisms by cardiomyocytes, fibroblasts, endotheliocytes, immune cells (neutrophils, T-cells and macrophages) and immature cells (embryonic stem cells, muscle satellite cells and cardiac precursor cells). They are mainly produced by cardiovascular, brain and renal tissues in response to wall stretch and other causes. NPs provide natriuresis, diuresis, vasodilation, antiproliferation, antihypertrophy, antifibrosis and other cardiometabolic protection. NPs represent body's own antihypertensive system, and provide compensatory protection to counterbalance vasoconstrictor-mitogenic-sodium retaining hormones, released by renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS). NPs play central roles in regulation of heart failure (HF), and are inactivated through not only NP receptor-C, but also neutral endopeptidase (NEP), dipeptidyl peptidase-4 and insulin degrading enzyme. Both BNP and N-terminal proBNP are useful biomarkers to not only make the diagnosis and assess the severity of HF, but also guide the therapy and predict the prognosis in patients with HF. Current NP-augmenting strategies include the synthesis of NPs or agonists to increase NP bioactivity and inhibition of NEP to reduce NP breakdown. Nesiritide has been established as an available therapy, and angiotensin receptor blocker NEP inhibitor (ARNI, LCZ696) has obtained extremely encouraging results with decreased morbidity and mortality. Novel pharmacological approaches based on NPs may promote a therapeutic shift from suppressing the RAAS and SNS to re-balancing neuroendocrine dysregulation in patients with HF. The current review discussed the synthesis, secretion, function and metabolism of NPs, and their diagnostic, therapeutic and prognostic values in HF.

Development of a BNP1-32 Immunoassay That Does Not Cross-React with proBNP

BACKGROUND

Plasma B-type natriuretic peptide (BNP) concentration reflects cardiac dysfunction and assists in determining the diagnosis and prognosis of heart failure (HF). Current BNP assays overestimate circulating bioactive BNP1-32 concentrations as they also detect less active BNP metabolites and proBNP. A specific BNP1-32 assay with negligible cross-reactivity to proBNP and/or BNP metabolites may be advantageous.

METHODS

We developed a Luminex-based specific BNP1-32 immunoassay and compared results obtained from 3 other BNP assays (a Luminex-based total-BNP assay, our BNP RIA, and the commercially available Abbott Architect BNP assay) in plasma from 42 patients with HF and 22 healthy controls.

RESULTS

The BNP1-32 assay showed 57% cross-reactivity with BNP2-32, but ≤0.1% cross-reactivity to BNP3-32, other BNP metabolites, and proBNP; its detection limit was 0.35 ng/L; and intra- and interassay CVs were <15%. BNP immunoreactivity increased with HF severity (median concentrations being 0.3, 0.8, 26.2, and 17.3 ng/L in healthy controls and 40.7, 139, 465, and 1778 ng/L in HF patients for the BNP1-32, total-BNP, BNP RIA, and Abbott BNP assays respectively). The fold increase between HF cases with the New York Heart Association (NYHA) class IV was significantly greater with the BNP1-32 assay than the Abbott BNP (P = 0.026) and the BNP RIA (P < 0.0001) but not the total-BNP assay.

CONCLUSIONS

We have developed the first assay that measures BNP1-32 in plasma without interference by proBNP. Analysis of larger patient cohorts is now required to compare the performance of this assay with current less specific assays for the diagnosis or prognosis of HF.

Brain natriuretic peptide and right heart dysfunction after heart transplantation

Heart transplantation (HT) should normalize cardiac endocrine function, but brain natriuretic peptide (BNP) levels remain elevated after HT, even in the absence of left ventricular hemodynamic disturbance or allograft rejection. Right ventricle (RV) abnormalities are common in HT recipients (HTx), as a result of engraftment process, tricuspid insufficiency, and/or repeated inflammation due to iterative endomyocardial biopsies. RV function follow-up is vital for patient management as RV dysfunction is a recognized cause of in-hospital death and is responsible for a worse prognosis. Interestingly, few and controversial data are available concerning the relationship between plasma BNP levels and RV functional impairment in HTx. This suggests that infra-clinical modifications, such as subtle immune system disorders or hypoxic conditions, might influence BNP expression. Nevertheless, due to other altered circulating molecular forms of BNP, a lack of specificity of BNP assays is described in heart failure patients. This phenomenon could exist in HT population and could explain elevated BNP plasmatic levels despite a normal RV function. In clinical practice, intra-individual change in BNP over time, rather than absolute BNP values, might be more helpful in detecting right cardiac dysfunction in HTx.

DPP-4 inhibition has no acute effect on BNP and its N-terminal pro-hormone measured by commercial immune-assays. A randomized cross-over trial in patients with type 2 diabetes

Background

Use of dipeptidyl peptidase-4 inhibitors (DPP4-i) for the treatment of type 2 diabetes (T2D) has been associated with a possible increase in the risk for heart failure (HF). B-type natriuretic peptide (BNP), which is both a biomarker of HF and a hemodynamically active hormone, is a substrate of DPP-4. We herein tested the acute effects of the DPP-4i linagliptin on BNP and NT-proBNP in a cross-over placebo-controlled trial in patients with T2D with and without chronic kidney disease (CKD).

Methods

B-type natriuretic peptide and NT-proBNP were measured using commercially available clinical-grade immune-assays at baseline and at the end of a 4-day treatment with placebo and linagliptin. Changes from baseline during each treatment arm, as well as placebo-subtracted effects of linagliptin on BNP and NT-proBNP were calculated.

Results

46 patients completed the study, 18 of whom were affected by CKD. Baseline BNP and NT-proBNP levels increased with age, were elevated in CKD patients, and inversely correlated with estimated glomerular filtration rate. No significant change was detected in BNP and NT-proBNP levels after treatment with linagliptin or placebo in patients with or without CKD. Only in CKD patients the placebo-subtracted effect of linagliptin indicated a significant reduction in NT-proBNP levels, but this finding was not statistically robust.

Conclusions

Acute treatment with a DPP-4i exerts no clinically-meaningful effects on BNP and NT-proBNP. As routinely used immunoassays do not discriminate between intact/active and cleaved BNP, these data cannot rule out an effect of DPP-4i on HF pathophysiology.

Trial registration NCT01617824

MiR30-GALNT1/2 Axis-Mediated Glycosylation Contributes to the Increased Secretion of Inactive Human Prohormone for Brain Natriuretic Peptide (proBNP) From Failing Hearts

BACKGROUND

Recent studies have shown that plasma levels of the biologically inactive prohormone for brain natriuretic peptide (proBNP) are increased in patients with heart failure. This can contribute to a reduction in the effectiveness of circulating BNP and exacerbate heart failure progression. The precise mechanisms governing the increase in proBNP remain unclear, however.

METHODS AND RESULTS

We used our recently developed, highly sensitive human proBNP assay system to investigate the mechanisms underlying the increase in plasma proBNP levels. We divided 53 consecutive patients hospitalized with heart failure into 2 groups based on their aortic plasma levels of immunoreactive BNP. Patients with higher levels exhibited more severe heart failure, a higher proportion of proBNP among the immunoreactive BNP forms secreted from failing hearts, and a weaker effect of BNP as estimated from the ratio of plasma cyclic guanosine monophosphate levels to log-transformed plasma BNP levels. Glycosylation at threonines 48 and 71 of human proBNP contributed to the increased secretion of proBNP by attenuating its processing, and GalNAc-transferase (GALNT) 1 and 2 mediated the glycosylation-regulated increase in cardiac human proBNP secretion. Cardiac GALNT1 and 2 expression was suppressed by microRNA (miR)-30, which is abundantly expressed in the myocardium of healthy hearts, but is suppressed in failing hearts.

CONCLUSIONS

We have elucidated a novel miR-30-GALNT1/2 axis whose dysregulation increases the proportion of inactive proBNP secreted by the heart and impairs the compensatory actions of BNP during the progression of heart failure.

Specificity of B-Type Natriuretic Peptide Assays: Cross-Reactivity with Different BNP, NT-proBNP, and proBNP Peptides

BACKGROUND

B-type natriuretic peptides (BNPs) are used clinically to diagnose and monitor heart failure and are present in the circulation as multiple proBNP-derived fragments. We investigated the specificity of BNP immunoassays with glycosylated and nonglycosylated BNP, N-terminal proBNP (NT-proBNP), and proBNP peptides to probe the cross-reactivity of each assay.

METHODS

Nine B-type natriuretic peptides were studied,including synthetic and recombinant BNP (Shionogi, Scios, Mayo), human and synthetic glycosylated and nonglycosylated NT-proBNP (HyTest, Roche Diagnostics), and human glycosylated and nonglycosylated proBNP (HyTest, Scios). Five BNP [Abbott, Abbott POC, Alere, Beckman Coulter, Siemens (Centaur)], 9 NT-proBNP [Ortho-Clinical Diagnostics, Roche, Response, bioMerieux, Siemens (Dimension, Immulite, Stratus CS), Mitsubishi] and 3 research-use-only proBNP immunoassays [Biosite (Alere), Bio-Rad, Goetze] were evaluated. Specificity was assessed by calculating the recovery between baseline and peptide-spiked human plasma pools at target concentrations of 100 ng/L BNP, 300 ng/L proBNP, or 450 ng/L NT-proBNP. All assays were performed in duplicate.

RESULTS

BNP and NT-proBNP assays demonstrated substantial cross-reactivity with proBNP peptides. NT-proBNP assays do not detect glycosylated forms of either NT-proBNP or proBNP. proBNP assays preferentially detect the BNP 1-32 peptide and have minimal cross-reactivity with BNP peptides and glycosylated proBNP.

CONCLUSIONS

BNP or NT-proBNP results are not transferable among the current existing immunoassays owing to their differences in cross-reactivity and ability to detect various glycosylated forms of proBNP-derived fragments. Opportunities remain to standardize and harmonize BNP and NT-proBNP assays, as well as to develop specific proBNP assays, to widen their clinical scope of use.

Unraveling the Molecular Complexity of O-Glycosylated Endogenous (N-Terminal) pro-B-Type Natriuretic Peptide Forms in Blood Plasma of Patients with Severe Heart Failure

BACKGROUND

Currently, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and its physiologically active counterpart, BNP, are most frequently used as biomarkers for diagnosis, prognosis, and disease monitoring of heart failure (HF). Commercial NT-proBNP and BNP immunoassays cross-react to varying degrees with unprocessed proBNP, which is also found in the circulation. ProBNP processing and immunoassay response are related to O-linked glycosylation of NT-proBNP and proBNP. There is a clear and urgent need to identify the glycosylation sites in the endogenously circulating peptides requested by the community to gain further insights into the different naturally occurring forms.

METHODS

The glycosylation sites of (NT-) proBNP (NT-proBNP and/or proBNP) were characterized in leftovers of heparinized plasma samples of severe HF patients (NT-proBNP: >10000 ng/L) by using tandem immunoaffinity purification, sequential exoglycosidase treatment for glycan trimming, β-elimination and Michael addition chemistry, as well as high-resolution nano-flow liquid chromatography electrospray multistage mass spectrometry.

RESULTS

We describe 9 distinct glycosylation sites on circulating (NT-) proBNP in HF patients. Differentially glycosylated variants were detected based on highly accurate mass determination and multistage mass spectrometry. Remarkably, for each of the identified proteolytic glycopeptides, a nonglycosylated form also was detectable.

CONCLUSIONS

Our results directly demonstrate for the first time a rather complex distribution of the endogenously circulating glycoforms by mass spectrometric analysis in HF patients, and show 9 glycosites in human (NT-) proBNP. This information may also have an impact on commercial immunoassays applying antibodies specific for the central region of (NT-) proBNP, which detect mostly nonglycosylated forms.

Natriuretic Peptides and Analytical Barriers

BACKGROUND

The natriuretic peptide system is an endocrine, autocrine and paracrine system that plays an important role in the maintenance of cardiovascular homeostasis. Biomarkers based on these peptides are important diagnostic and prognostic tools for myocardial function.

CONTENT

Although natriuretic peptides were discovered more than 2 decades ago, their intricate and complex biology is associated with important questions not yet elucidated. The diversity of circulating forms of natriuretic peptides, the distinct expression of these forms in particular patients, and the heterogeneity of heart failure forms, along with specific assay-related and preanalytic issues, cause assays to be poorly harmonized.

SUMMARY

This review presents the relevant issues related to the biology of natriuretic peptides and differences between assays with immediate implications for clinical practice.

Chronic subcutaneous brain natriuretic peptide therapy in asymptomatic systolic heart failure

AIMS

We have previously reported that asymptomatic systolic heart failure (HF) is characterized by an impaired renal response to volume expansion due to lack of activation of urinary cGMP which is corrected by subcutaneous (SQ) BNP. In the current study, we sought to define the cardiorenal response to intravascular volume expansion after 12 weeks of SQ BNP therapy.

METHODS AND RESULTS

We utilized a double-blinded, placebo-controlled study to compare 12 weeks of twice-daily SQ BNP 10 µg/kg (n = 22) or placebo (n = 12) in asymptomatic systolic HF. Subjects underwent two study visits: baseline and after 12 weeks of therapy. At each study visit, echocardiography, renal, and neurohumoral assessments were performed before and after intravascular volume expansion. The primary endpoint was change in urinary sodium excretion in response to volume expansion at 12 weeks, and we observed a greater increase in urinary sodium excretion [166 (77, 290) vs. 15 (-39, 72) mEq/min; P = 0.02] with SQ BNP treatment vs. placebo. Secondary endpoints included change in urine flow and glomerular filtration rate (GFR) in response to volume expansion at 12 weeks. We observed a significant increase in urine flow (P < 0.01) and trend for differential response in GFR (P = 0.08) with SQ BNP treatment vs. placebo.

CONCLUSION

Among patients with asymptomatic systolic HF, twice-daily SQ BNP therapy improved the cardiorenal response to volume expansion at 12-week follow-up. Further studies are warranted to determine if these beneficial physiological observations with chronic natriuretic peptide administration translate into a delay in the progression to symptomatic HF.

Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma

Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.

Regulated inositol-requiring protein 1-dependent decay as a mechanism of corin RNA and protein deficiency in advanced human systolic heart failure

Background

The compensatory actions of the endogenous natriuretic peptide system require adequate processing of natriuretic peptide pro‐hormones into biologically active, carboxyl‐terminal fragments. Natriuretic peptide pro‐peptide processing is accomplished by corin, a transmembrane serine protease expressed by cardiomyocytes. Brain natriuretic peptide (BNP) processing is inadequate in advanced heart failure and is independently associated with adverse outcomes; however, the molecular mechanisms causing impaired BNP processing are not understood. We hypothesized that the development of endoplasmic reticulum stress in cardiomyocytes in advanced heart failure triggers inositol‐requiring protein 1 (IRE1)‐dependent corin mRNA decay, which would favor a molecular substrate favoring impaired natriuretic peptide pro‐peptide processing.

Methods and Results

Two independent samples of hearts obtained from patients with advanced heart failure at transplant demonstrated that corin RNA was reduced as Atrial natriuretic peptide (ANP)/BNP RNA increased. Increases in spliced X‐box protein 1, a marker for IRE1‐endoribonuclease activity, were associated with decreased corin RNA. Moreover, ≈50% of the hearts demonstrated significant reductions in corin RNA and protein as compared to the nonfailing control sample. In vitro experiments demonstrated that induction of endoplasmic reticulum stress in cultured cardiomyocytes with thapsigargin activated IRE1's endoribonuclease activity and time‐dependent reductions in corin mRNA. In HL‐1 cells, overexpression of IRE1 activated IRE1 endoribonuclease activity and caused corin mRNA decay, whereas IRE1‐RNA interference with shRNA attenuated corin mRNA decay after induction of endoplasmic reticulum stress with thapsigargin. Pre‐treatment of cells with Actinomycin D to inhibit transcription did not alter the magnitude or time course of thapsigargin‐induced corin mRNA decline, supporting the hypothesis that this was the result of IRE1‐mediated corin mRNA degradation.

Conclusions

These data support the hypothesis that endoplasmic reticulum stress‐mediated, IRE1‐dependent targeted corin mRNA decay is a mechanism leading to corin mRNA resulting in corresponding corin protein deficiency may contribute to the pathophysiology of impaired natriuretic peptide pro‐hormone processing in humans processing in humans with advanced systolic heart failure.

Rationale and therapeutic opportunities for natriuretic peptide system augmentation in heart failure

The natriuretic peptide system (NPS) is intimately involved in cardiorenal homeostasis in health, and dysregulation of the NPS plays an important role in the pathophysiology of heart failure (HF). Indeed, the diuretic, vasorelaxation, beneficial remodeling, and potent neurohumoral inhibition of the NPS support the therapeutic development of chronic augmentation of the NPS in symptomatic HF. Further, chronic augmentation of the protective NPS and in early stages of HF may ultimately prevent the progression of HF and reduced subsequent morbidity and mortality. In the current manuscript, we review the rationale for as well as previous and current efforts aimed at chronic therapeutic augmentation of the NPS in HF.

B-type Natriuretic Peptide circulating forms: Analytical and bioactivity issues

B-type Natriuretic Peptide (BNP), A-type and C-type Natriuretic Peptides (ANP and CNP) comprise a family of peptides that retain a common ring structure and conserved amino acid sequences. All are present in the heart, but only BNP and ANP are regarded as primarily cardiac secretory products. BNP and ANP, acting through a guanylyl cyclase receptor, increase sodium and water excretion by the kidney, induce vasodilation, reduce blood pressure, counteract the bioactivity of the renin-angiotensin-aldosterone and sympathetic nervous systems and possess anti-hypertrophic and anti-fibrotic properties. BNP is synthesised in cardiomyocytes first as the precursor peptide preproBNP. Removal of the signal peptide from preproBNP produces proBNP which is cleaved to produce the biologically active carboxy-terminal BNP peptide and the inactive N-terminal fragment, NT-proBNP. BNP, NT-proBNP, proBNP and the C-terminal portion of the BNP signal peptide have been detected in human plasma as well as multiple sub-forms including truncated forms of BNP and NT-proBNP, as well as variable glycosylation of NT-proBNP and proBNP. The origin of these circulating forms, their potential bioactivity and their detection by current analytical methods are presented in this review.

Regulated inositol-requiring protein 1-dependent decay as a mechanism of corin RNA and protein deficiency in advanced human systolic heart failure

BACKGROUND

The compensatory actions of the endogenous natriuretic peptide system require adequate processing of natriuretic peptide pro‐hormones into biologically active, carboxyl‐terminal fragments. Natriuretic peptide pro‐peptide processing is accomplished by corin, a transmembrane serine protease expressed by cardiomyocytes. Brain natriuretic peptide (BNP) processing is inadequate in advanced heart failure and is independently associated with adverse outcomes; however, the molecular mechanisms causing impaired BNP processing are not understood. We hypothesized that the development of endoplasmic reticulum stress in cardiomyocytes in advanced heart failure triggers inositol‐requiring protein 1 (IRE1)‐dependent corin mRNA decay, which would favor a molecular substrate favoring impaired natriuretic peptide pro‐peptide processing.

METHODS AND RESULTS

Two independent samples of hearts obtained from patients with advanced heart failure at transplant demonstrated that corin RNA was reduced as Atrial natriuretic peptide (ANP)/BNP RNA increased. Increases in spliced X‐box protein 1, a marker for IRE1‐endoribonuclease activity, were associated with decreased corin RNA. Moreover, ≈50% of the hearts demonstrated significant reductions in corin RNA and protein as compared to the nonfailing control sample. In vitro experiments demonstrated that induction of endoplasmic reticulum stress in cultured cardiomyocytes with thapsigargin activated IRE1's endoribonuclease activity and time‐dependent reductions in corin mRNA. In HL‐1 cells, overexpression of IRE1 activated IRE1 endoribonuclease activity and caused corin mRNA decay, whereas IRE1‐RNA interference with shRNA attenuated corin mRNA decay after induction of endoplasmic reticulum stress with thapsigargin. Pre‐treatment of cells with Actinomycin D to inhibit transcription did not alter the magnitude or time course of thapsigargin‐induced corin mRNA decline, supporting the hypothesis that this was the result of IRE1‐mediated corin mRNA degradation.

CONCLUSIONS

These data support the hypothesis that endoplasmic reticulum stress‐mediated, IRE1‐dependent targeted corin mRNA decay is a mechanism leading to corin mRNA resulting in corresponding corin protein deficiency may contribute to the pathophysiology of impaired natriuretic peptide pro‐hormone processing in humans processing in humans with advanced systolic heart failure.

Pro-B-type natriuretic peptide-1-108 processing and degradation in human heart failure

BACKGROUND

We have reported that pro-B-type natriuretic peptide (BNP)-1-108 circulates and is processed to mature BNP1-32 in human blood. Building on these findings, we sought to determine whether proBNP1-108 processed forms in normal circulation are biologically active and stimulate cGMP, and whether proBNP1-108 processing and activity are altered in human heart failure (HF) compared with normal. Because BNP1-32 is deficient whereas proBNP1-108 is abundant in HF, we hypothesize that proBNP1-108 processing and degradation are impaired in HF patients ex vivo.

METHODS AND RESULTS

We measured circulating molecular forms, including BNP1-32, proBNP1-108, and N-terminal-proBNP, and all were significantly higher in patients with HF when compared with that in normals. Fresh serum samples from normals or patients with HF were incubated with or without exogenous nonglycosylated proBNP1-108 tagged with 6 C-terminal Histidines to facilitate peptide isolation. His-tag proBNP1-108 was efficiently processed into BNP1-32/3-32 at 5 minutes in normal serum, persisted for 15 minutes, then disappeared. Delayed processing of proBNP1-108 was observed in HF samples, and the degradation pattern differed depending on left ventricular function. The 5-minute processed forms from both normal and HF serums were active and generated cGMP via guanylyl cyclase-A receptors; however, the 180-minute samples were not active. The proBNP1-108 processing enzyme corin and BNP-degrading enzyme dipeptidyl peptidase-4 were reduced in HF versus normal, perhaps contributing to differential BNP metabolism in HF.

CONCLUSIONS

Exogenous proBNP1-108 is processed into active BNP1-32 and ultimately degraded in normal circulation. The processing and degradation of BNP molecular forms were altered but complete in HF, which may contribute to the pathophysiology of HF.

Dipeptidyl-peptidase 4 inhibition: linking metabolic control to cardiovascular protection

Dipeptidyl peptidases 4 (DPP4) inhibitors are a new class of oral anti-hyperglycemic drugs for the treatment of type 2 diabetes (T2DM). They are also called "incretins" because they act by inhibiting the degradation of endogenous incretin hormones, in particular GLP-1, that mediates their main metabolic effects. DPP4 is an ubiquitous protease that regulates not only glucose and lipid metabolism, but also exhibits several systemic effects at different site levels. DPP4 inhibition improves endothelial function, reduces the pro-oxidative and the pro-inflammatory state, and exerts renal effects. These actions are mediated by different DPP4 ligands, such as cytokines, growth factors, neuotransmitters etc. Clinical and experimental studies have demonstrated that DPP4 inhibitors are efficient in protecting cardiac, renal and vascular systems, through antiatherosclerotic and vasculoprotective mechanisms. For these reasons DDP4 inhibitors are thought to be "cardiovascular protective" as well as anti-diabetic drugs. Clinical trials aimed to demonstrate the efficacy of DPP4 inhibitors in reducing cardiovascular events, independent of their anti-hyperglycemic action, are ongoing. These trials will also give necessary information on their safety.

Secretion of prohormone of B-type natriuretic peptide, proBNP1-108, is increased in heart failure

OBJECTIVES

Using a novel, specific assay for proBNP(1-108), this study tested the hypotheses that proBNP(1-108) is secreted by both nonfailing and failing human hearts and that proBNP(1-108) secretion is increased in failing hearts.

BACKGROUND

The prohormone of B-type natriuretic peptide (proBNP(1-108)) is a 108-amino acid peptide produced primarily by the heart and cleaved into biologically active BNP(1-32) and the biologically inactive NT-proBNP(1-76). It is unknown to what extent increased cardiac proBNP1-108 secretion compared to reduced peripheral processing is responsible for elevated proBNP(1-108) levels in patients with heart failure (HF) compared to subjects without HF.

METHODS

The transcardiac gradient of proBNP(1-108) was determined by collecting arterial blood and blood from the coronary sinus (CS). Samples from subjects without overt heart disease (n = 9) were collected during cardiac catheterization after coronary artery disease had been excluded. Samples from HF patients (n = 21) were collected during implantation of a biventricular pacemaker. ProBNP(1-108) was measured with a new assay. Values are medians (25th/75th percentiles).

RESULTS

The gradient of proBNP(1-108) across the nonfailing hearts was 8 (2/20) ng/l (aorta: 15 [1/25] ng/l; CS: 24 [8/41] ng/l; p = 0.018). The transcardiac gradient of proBNP(1-108) in the failing hearts was 326 (96/482) ng/l (arterial: 381 [201/586] ng/l; CS: 709 [408/1,087] ng/l; p<0.001). The transcardiac gradient was greater in failing than nonfailing hearts (p = 0.001).

CONCLUSIONS

ProBNP(1-108) is secreted by nonfailing and failing human hearts, but more so in the latter. It remains to be established where peripheral processing of proBNP(1-108) occurs and how this is affected by disease.

Direct immunochemiluminescent assay for proBNP and total BNP in human plasma proBNP and total BNP levels in normal and heart failure

Background

Recent studies have shown that in addition to brain (or B-type) natriuretic peptide (BNP) and the N-terminal proBNP fragment, levels of intact proBNP are also increased in heart failure. Moreover, present BNP immunoassays also measure proBNP, as the anti-BNP antibody cross-reacts with proBNP. It is important to know the exact levels of proBNP in heart failure, because elevation of the low-activity proBNP may be associated with the development of heart failure.

Methodology/Principal Findings

We therefore established a two-step immunochemiluminescent assay for total BNP (BNP+proBNP) and proBNP using monoclonal antibodies and glycosylated proBNP as a standard. The assay enables measurement of plasma total BNP and proBNP within only 7 h, without prior extraction of the plasma. The detection limit was 0.4 pmol/L for a 50-µl plasma sample. Within-run CVs ranged from 5.2%–8.0% in proBNP assay and from 7.0%–8.4% in total BNP assay, and between-run CVs ranged from 5.3–7.4% in proBNP assay and from 2.9%–9.5% in total BNP assay, respectively. The dilution curves for plasma samples showed good linearity (correlation coefficients = 0.998–1.00), and analytical recovery was 90–101%. The mean total BNP and proBNP in plasma from 116 healthy subjects were 1.4±1.2 pM and 1.0±0.7 pM, respectively, and were 80±129 pM and 42±70 pM in 32 heart failure patients. Plasma proBNP levels significantly correlate with age in normal subjects.

Conclusions/Significance

Our immunochemiluminescent assay is sufficiently rapid and precise for routine determination of total BNP and proBNP in human plasma.

BNP molecular forms and processing by the cardiac serine protease corin

The cardiac hormone, B-type natriuretic peptide (BNP), is one of human natriuretic peptides which possesses cardiorenal protective actions and is used as a therapeutic and a biomarker for heart failure (HF). Its prohormone, proBNP1_108, is processed by the proNPs convertases, corin or furin, to inactive NT-proBNP1_76 and active BNP1-32. Paradoxically, circulating NT-proBNP and BNP are elevated in HF leading to the use of BNP as a sensitive and predictive marker of HF. This paradox may be explained by the "nonspecific" nature of conventional assays and/or a relative deficiency state of "active BNP" as characterized by an increase in inactive proBNP_108 and a decrease in active BNP1-32. Therefore, understanding the regulation of proBNP1_108 processing and the role of the convertase corin may be important in understanding the physiology of HF. Corin is expressed in heart and kidney and may play an important role in regulating blood pressure and remodeling of the heart. The processing of proBNP1_108 by corin may be controlled by O-linked glycosylation of proBNP1-108. A potential impairment of proBNP1lo8 processing in HF may be linked to dysregulation of the convertase corin, which may offer therapeutic opportunities to control proBNPlo0s processing and its activation in HF.

Human hypertension is characterized by a lack of activation of the antihypertensive cardiac hormones ANP and BNP

OBJECTIVES

This study sought to investigate plasma levels of circulating cardiac natriuretic peptides, atrial natriuretic peptide (ANP) and B-type or brain natriuretic peptide (BNP), in the general community, focusing on their relative differences in worsening human hypertension.

BACKGROUND

Although ANP and BNP are well-characterized regulators of blood pressure in humans, little is known at the population level about their relationship with hypertension. The authors hypothesized that hypertension is associated with a lack of activation of these hormones or their molecular precursors.

METHODS

The study cohort (N = 2,082, age >45 years) was derived from a random sample from Rochester, Minnesota, and each subject had a medical history, clinical examination, and assessment of different plasma forms of ANP and BNP. Patients were stratified by blood pressure. Multivariable linear regression was used to assess differences in natriuretic peptide levels in worsening hypertension.

RESULTS

Compared to normotensive, BNP(1-32) and N-terminal proBNP(1-76) (NT-proBNP(1-76)) were significantly decreased in pre-hypertension (p < 0.05), with BNP(1-32) significantly decreased in stage 1 as well (p < 0.05). Although proBNP(1-108) remained unchanged, the processed form was significantly increased only in stage 2 hypertension (p < 0.05). ANP(1-28) remained unchanged, while NT-ANP(1-98) was reduced in pre-hypertension (p < 0.05).

CONCLUSIONS

The authors demonstrated the existence of an impaired production and/or release of proBNP(1-108) along with a concomitant reduction of BNP(1-32) and NT-proBNP(1-76) in the early stages of hypertension, with a significant elevation only in stage 2 hypertension. Importantly, they simultaneously demonstrated a lack of compensatory ANP elevation in advanced hypertension.

Differential expression of the pro-natriuretic peptide convertases corin and furin in experimental heart failure and atrial fibrosis

In heart failure (HF), the cardiac hormone natriuretic peptides (NPs) atrial (ANP), B-type (BNP), and C-type (CNP) play a key role to protect cardiac remodeling. The proprotein convertases corin and furin process their respective pro-NPs into active NPs. Here we define in a canine model of HF furin and corin gene and protein expression in normal and failing left atrium (LA) or ventricle (LV) testing the hypothesis that the NP proproteins convertases production is altered in experimental HF. Experimental canine HF was produced by rapid right ventricular pacing for 10 days. NPs, furin, and corin mRNA expression were determined by quantitative RT-PCR. Protein concentration or expression was determined by immunostaining, radioimmunoassay, or Western blot. Furin and corin proteins were present in normal canine LA and LV myocardium and vasculature and in smooth muscle cells. In normal canines, expression of NPs was dominant in the atrium compared with the ventricle. In experimental early stage HF characterized with marked atrial fibrosis, ANP, BNP, and CNP mRNA, and protein concentrations were higher in HF LA but not HF LV compared with normals. In LA, corin mRNA and protein expressions in HF were lower, whereas furin mRNA and protein expressions were higher than normals. NPs and furin expressions were augmented in the atrium in experimental early stage HF and, conversely, corin mRNA and protein expressions were decreased with atrial remodeling. Selective changes of these NP convertases may have significance in the regulation of pro-NP processing and atrial remodeling in early stage HF.

NT-ProBNP levels in saliva and its clinical relevance to heart failure

Background

Current blood based diagnostic assays to detect heart failure (HF) have large intra-individual and inter-individual variations which have made it difficult to determine whether the changes in the analyte levels reflect an actual change in disease activity. Human saliva mirrors the body’s health and well being and ∼20% of proteins that are present in blood are also found in saliva. Saliva has numerous advantages over blood as a diagnostic fluid which allows for a non-invasive, simple, and safe sample collection. The aim of our study was to develop an immunoassay to detect NT-proBNP in saliva and to determine if there is a correlation with blood levels.

Methods

Saliva samples were collected from healthy volunteers (n = 40) who had no underlying heart conditions and HF patients (n = 45) at rest. Samples were stored at −80°C until analysis. A customised homogeneous sandwich AlphaLISA^(R) immunoassay was used to quantify NT-proBNP levels in saliva.

Results

Our NT-proBNP immunoassay was validated against a commercial Roche assay on plasma samples collected from HF patients (n = 37) and the correlation was r² = 0.78 (p<0.01, y = 1.705× +1910.8). The median salivary NT-proBNP levels in the healthy and HF participants were <16 pg/mL and 76.8 pg/mL, respectively. The salivary NT-proBNP immunoassay showed a clinical sensitivity of 82.2% and specificity of 100%, positive predictive value of 100% and negative predictive value of 83.3%, with an overall diagnostic accuracy of 90.6%.

Conclusion

We have firstly demonstrated that NT-proBNP can be detected in saliva and that the levels were higher in heart failure patients compared with healthy control subjects. Further studies will be needed to demonstrate the clinical relevance of salivary NT-proBNP in unselected, previously undiagnosed populations.

Induction of brain natriuretic peptide and monocyte chemotactic protein-1 gene expression by oxidized low-density lipoprotein: relevance to ischemic heart failure

Brain natriuretic peptide (BNP) and monocyte chemotactic protein-1 (MCP-1) are biomarkers of heart failure (HF). The aim of the present study was to determine the role of oxidized low-density lipoprotein (Ox-LDL) in the induction of these biomarkers and the signaling pathways involved in vitro. Incubation of HL-1 cardiomyocytes and human myocytes with Ox-LDL induced the expression of BNP and MCP-1 genes, while native LDL had no effect. When peroxides associated with Ox-LDL were reduced to hydroxides, the ability to induce BNP and MCP-1 gene expression was abolished. Furthermore, exposure of HL-1 cells to ischemic conditions alone had no effect on BNP gene expression, while ischemia followed by reperfusion resulted in increased expression of BNP gene. Inhibitors of ERK and JNK inhibited the induction of BNP. Signaling array results suggested that the induction of both MAPK and NF-κB pathways is involved in the induction of BNP by Ox-LDL. These results suggest that Ox-LDL or peroxidized lipids formed in oxidatively stressed myocytes during ischemia-reperfusion injury may play a role in the induction of BNP and MCP-1.

Guanylyl cyclase (GC)-A and GC-B activities in ventricles and cardiomyocytes from failed and non-failed human hearts: GC-A is inactive in the failed cardiomyocyte

Cardiomyocytes release atrial natriuretic peptide (ANP) and B-type natriuretic peptide to stimulate processes that compensate for the failing heart by activating guanylyl cyclase (GC)-A. C-type natriuretic peptide is also elevated in the failing heart and inhibits cardiac remodeling by activating the homologous receptor, GC-B. We previously reported that GC-A is the most active membrane GC in normal mouse ventricles while GC-B is the most active membrane GC in failing ventricles due to increased GC-B and decreased GC-A activities. Here, we examined ANP and CNP-specific GC activity in membranes obtained from non-failing and failing human left ventricles and in membranes from matched cardiomyocyte-enriched pellet preparations. Similar to our findings in the murine study, we found that CNP-dependent GC activity was about half of the ANP-dependent GC activity in the non-failing ventricular and was increased in the failing ventricle. ANP and CNP increased GC activity 9- and 5-fold in non-failing ventricles, respectively. In contrast to the mouse study, in failing human ventricles, ANP-dependent activity was unchanged compared to non-failing values whereas CNP-dependent activity increased 35% (p=0.005). Compared with ventricular membranes, basal GC activity was reduced an order of magnitude in membranes derived from myocyte-enriched pellets from non-failing ventricles. ANP increased GC activity 2.4-fold but CNP only increased GC activity 1.3-fold. In contrast, neither ANP nor CNP increased GC activity in equivalent preparations from failing ventricles. We conclude that: 1) GC-B activity is increased in non-myocytes from failing human ventricles, possibly as a result of increased fibrosis, 2) human ventricular cardiomyocytes express low levels of GC-A and much lower levels or possibly no GC-B, and 3) GC-A in cardiomyocytes from failing human hearts is refractory to ANP stimulation.

Biomarkers of left ventricular hypertrophy and remodeling in blacks

Left ventricular (LV) hypertrophy, a marker for adverse cardiovascular events, is more common in blacks than in non-Hispanic whites. Mechanisms leading to LV hypertrophy and mediating its clinical sequelae in blacks are not fully understood. We investigated the associations of 39 candidate biomarkers in distinct biological pathways with LV mass and geometry in blacks. Participants included 1193 blacks (63±9 years of age; 72% women; 78% hypertensive) belonging to hypertensive sibships. LV mass was measured by transthoracic echocardiography and indexed to height.(2.7) LV geometry was categorized as normal, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy. Generalized estimating equations were used to assess associations of the 39 biomarkers with LV mass index after adjustment for age, sex, and conventional risk factors. After adjustment for potential confounders, log-transformed levels of the following biomarkers were independently associated with LV mass index: N-terminal pro-brain natriuretic peptide (β±SE=0.07±0.01 pg/mL; P<0.0001), mid-regional pro-atrial natriuretic peptide (β±SE=0.08±0.02 pmol/L; P<0.0001), mid-regional pro-adrenomedullin (β±SE=0.09±0.03 nmol/L; P=0.0006), C-terminal pro-endothelin (β± SE=0.05±0.02 pmol/L; P=0.0009), and osteoprotegerin (β±SE=0.07±0.02 pg/mL; P=0.0005) (β is for 1 log increase in biomarker level). The associations of these biomarkers with LV mass index were mainly due to their association with eccentric hypertrophy. Higher circulating levels of natriuretic peptides, adrenomedullin, endothelin, and osteoprotegerin were associated with increased LV mass index, providing insights into the pathophysiology of LV hypertrophy in blacks.

Designer natriuretic peptides: a vision for the future of heart failure therapeutics

Despite recent pharmacological advances in heart failure therapy, mortality from acute decompensated heart failure remains high. Conventional therapies are often insufficient to address the complex interplay between structural, functional, neurohumoral, and renal mechanisms involved in the heart failure syndrome. The natriuretic peptide system, however, offers a unique pleiotropic strategy which could bridge this gap in heart failure therapy. Exogenous administration of native A-type and B-type natriuretic peptides has been met with both success and limitations, and despite the limitations, remains a worthwhile endeavor. Alternatively, synthetic modification to create “designer” chimeric peptides holds the possibility to extend both the application and therapeutic benefits possible with a natriuretic peptide based approach. Herein we describe the development of natriuretic peptide based heart failure therapies, including the design, rationale, and preliminary studies of the novel chimeric peptides CD-NP and CU-NP.

ProBNP(1-108) is resistant to degradation and activates guanylyl cyclase-A with reduced potency

BACKGROUND

B-type natriuretic peptide (BNP) compensates for the failing heart and is synthesized as a 108-residue prohormone that is cleaved to a 32-residue C-terminal maximally active peptide. During heart failure, serum concentrations of proBNP(1-108) exceed concentrations of BNP(1-32). The aim of this study was to determine why the proBNP(1-108)/BNP(1-32) ratio increases and whether proBNP(1-108) is bioactive.

METHODS

Using cGMP elevation and (125)I-ANP binding assays, we measured binding and activation of individual human natriuretic peptide receptor populations by recombinant human proBNP(1-108) and human synthetic BNP(1-32). Using receptor bioassays, we measured degradation of recombinant proBNP(1-108) and BNP(1-32) by human kidney membranes.

RESULTS

ProBNP(1-108) stimulated guanylyl cyclase-A (GC-A) to near-maximum activities but was 13-fold less potent than BNP(1-32). ProBNP(1-108) bound human GC-A 35-fold less tightly than BNP(1-32). Neither proBNP(1-108) nor BNP(1-32) activated GC-B. The natriuretic peptide clearance receptor bound proBNP(1-108) 3-fold less tightly than BNP(1-32). The half time for degradation of proBNP(1-108) by human kidney membranes was 2.7-fold longer than for BNP(1-32), and the time required for complete degradation was 6-fold longer. BNP(1-32) and proBNP(1-108) were best fitted by first- and second-order exponential decay models, respectively.

CONCLUSIONS

ProBNP(1-108) activates GC-A with reduced potency and is resistant to degradation. Reduced degradation of proBNP(1-108) may contribute to the increased ratio of serum proBNP(1-108) to BNP(1-32) observed in patients with congestive heart failure.

Systems biology and heart failure: concepts, methods, and potential research applications

Dramatic advances in molecular biology dominated twentieth century biomedical science and delineated the function of individual genes and molecules in exquisite detail. However, biological processes cannot be fully understood based on the properties of individual genes and molecules alone, since these elements act in concert to enable the specific functions that make for living cells and organisms. The discipline of systems biology provides a novel conceptual framework for understanding biological phenomenon. Systems biology synthesizes information concerning the interactions of genes and molecules and allows characterization of the supramolecular networks and functional modules that represent the most essential aspects of cell organization and physiology.