Localization of brain and atrial natriuretic peptide in human and porcine heart

Relevance of the assessment of natriuretic peptide plasma concentrations in hypertensive pregnant women

Assessment of the plasma concentrations of natriuretic peptides (NPs) is widely used to diagnose and evaluate the progression of cardiac failure, and their potential as markers of preeclampsia (PE) has been examined in recent years. It has been established that plasma concentrations of NPs do not change in the course of normal pregnancy. However, elevated levels of these peptides may have a prognostic value in patients with PE. This study presents information about the relevance of NPs assessment in the evaluation of physiological pregnancy, as well as in pregnancy complicated with arterial hypertension. The most commonly examined NPs is the N-terminal fragment of the brain natriuretic peptide (NT-proBNP), and it may be prognostic marker of PE and other complications of pregnancy.

Identification and mapping of brain natriuretic peptide in the normal ventricular myocardium of a desert-dwelling mammalian model, the camel (Camelus dromedarius): Immunohistochemical and ultrastructural study

Brain natriuretic peptide (BNP) is mainly produced in the ventricular myocardium, where it is released into the circulation, producing rapid volume decrease by diuresis, natriuresis, and water shift into the extracellular space, and vasodilation. The dromedary camel, a mammalian model of the desert nomads, lives under unfavorable physiological stresses during thirst, starvation, desiccation, and hot climate, thus has a special demand for water homeostasis. The present studies characterized BNP in the ventricular myocardium of healthy camels, immunohistochemically with a specific antibody, and ultrastructurally identified the endocrine property of the cardiomyocytes and Purkinje fibers. The paranuclear, granular, immunoreactive material was not restricted to the cardiomyocytes, as it was also visible in the Purkinje fibers and their associated nerve varicosities. The intensity of immunoreactive BNP showed a transmural gradient from the subepicardium to the myocardium. Intense immunoreactivity was also noted among the perivascular cardiomyocytes. At the electron microscopic level, specific granules were demonstrated in the paranuclear cytosol of cardiomyocytes and Purkinje fibers. The current study provides the first immunohistochemical localization pattern of BNP in the camel myocardium and suggests a relationship between the intense subepicardial BNP-immunoexpression and a possible translocation of the active hormone to the pericardial fluid for further paracrine actions on the heart and its coronaries.

First Identification of Circulating Prepro–A-Type Natriuretic Peptide (PreproANP) Signal Peptide Fragments in Humans: Initial Assessment as Cardiovascular Biomarkers

BACKGROUND

New biomarkers are needed to assist clinical decision making in cardiovascular disease. We have recently shown that signal peptides may represent a novel biomarker target in cardiovascular diseases.

METHODS

We developed a novel immunoassay for the signal peptide of preproANP (ANPsp) and used it to document cardiac tissue levels of ANPsp in explant human hearts (n = 9), circulating venous concentrations of ANPsp in healthy volunteers (n = 65), temporal ANPsp concentrations in patients with ST-elevation myocardial infarction (STEMI) <4 h after chest pain onset (n = 23), and regional plasma ANPsp concentrations in patients undergoing clinically indicated catheterization (n = 10). We analyzed the structure and sequence of circulating ANPsp by tandem mass spectrometry (MS/MS).

RESULTS

ANPsp levels in human heart tissue were 50–1000 times lower than those of ANP/NT-proANP. ANPsp was detectable in control human plasma at concentrations comparable with ANP itself (approximately 20 ng/L). In STEMI patients, plasma concentrations of ANPsp rose to peak values at 5 h after symptom onset, significantly earlier than myoglobin, creatine kinase-MB, and troponin (P < 0.001). There were significant arteriovenous increases in ANPsp concentrations (P < 0.05) across the heart and kidney; arterial and coronary sinus concentrations of ANPsp both negatively correlated with systolic and mean arterial blood pressures (both P < 0.01). MS/MS verified circulating ANPsp to be preproANP(16–25) and preproANP(18–25).

CONCLUSIONS

ANPsp is a novel circulating natriuretic peptide with potential to act as a cardiovascular biomarker. The rapid increase of plasma ANPsp in STEMI and its significant relationship with blood pressure encourage further study of its potential clinical utility.

Natriuretic peptides and right atrial fibrosis in patients with paroxysmal versus persistent atrial fibrillation

Natriuretic peptides (NPs) are excellent diagnostic and prognostic markers of heart failure, but their roles in atrial fibrillation (AF), particularly of isolated cardiac valvular origin, are unclear. We assessed the mRNA and protein content of pro-atrial natriuretic peptide (pro-ANP) and pro-brain natriuretic peptide (pro-BNP) in right atrial appendages (RAAs) and their N-terminal fragments (nt-proANP and nt-proBNP) in the plasma of 30 patients with paroxysmal AF (PaAF) and 40 patients with persistent AF (PeAF) matched with 34 patients in sinus rhythm (SR) undergoing isolated valvular replacement. To explore the underlying mechanism, fibrosis related examinations were simultaneously carried out in RAAs. Unexpectedly, atrial expression of pro-NPs mRNA was notably augmented in the PaAF subgroup, but not so pronounced in the PeAF subgroup. Atrial content of pro-NPs proteins and plasma nt-proNPs, between which surprisingly strong positive correlations were found (pro-ANP and nt-proANP: r=0.918, p<0.001; pro-BNP and nt-proBNP: r=0.913, p<0.001), were increased analogously in PaAF and PeAF subgroups. We identified significantly increasing gradients of atrial collagen volume fraction (CVF), levels of collagen I and III in the SR, PaAF and PeAF groups, and convincing negative linear correlations between CVF, levels of collagen I and III, and atrial transcripts of pro-NPs. These findings suggest that the discordance between transcripts and protein contents of pro-NPs was possibly due to the more outstanding atrial fibrosis in PeAF, and that circulating nt-proNPs levels could reflect the corresponding atrial pro-NPs contents in this report.

Accuracy of plasma B-type natriuretic peptide to diagnose significant cardiovascular disease in children: the Better Not Pout Children! Study

OBJECTIVES

The purpose of this study was to assess the ability of plasma B-type natriuretic peptide (BNP) to diagnose significant cardiovascular disease (CVD) in the pediatric population.

BACKGROUND

BNP has been shown to be reliable in detecting ventricular dysfunction and heart failure in adults. Timely and accurate identification of significant pediatric heart disease is important but challenging. A simple blood test could aid the front-line physician in this task.

METHODS

Subjects without a history of heart disease with findings possibly attributable to significant CVD in the acute care setting requiring a cardiology consult were enrolled. Clinicians were blinded to the BNP result, and confirmation of disease was made by cardiology consultation.

RESULTS

Subjects were divided into a neonatal (n = 42, 0 to 7 days) and older age group (n = 58, >7 days to 19 years). CVD was present in 74% of neonates and 53% of the older age group. In neonates with disease, median BNP was 526 pg/ml versus 96 pg/ml (p < 0.001) for those without disease. In older children with disease, median BNP was 122 pg/ml versus 22 pg/ml in those without disease (p < 0.001). Subjects with disease from an anatomic defect, a longer hospital stay, or who died had higher BNP. A BNP of 170 pg/ml yielded a sensitivity of 94% and specificity of 73% in the neonatal group and 87% and 70% in the older age group, respectively, using a BNP of 41 pg/ml.

CONCLUSIONS

BNP is a reliable test to diagnose significant structural or functional CVD in children. Optimal cutoff values are different from adult values.

Brain natriuretic peptide and P wave duration in dialysis patients

OBJECTIVES

P wave duration and dispersion, defined as the difference between the maximum and minimum P duration, are regarded as very important non-invasive ECG markers for assessing atrial arrhythmia risk. Plasma brain natriuretic peptide (BNP) level is an independent predictor of recurrence of atrial fibrillation. We compared the effects of hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) on P wave duration, P dispersion, and BNP in end-stage renal disease (ESRD) patients and examined the relationship between BNP levels, P wave duration, and P dispersion.

DESIGN AND METHODS

Age-matched 22 HD patients (mean age 52.3 +/- 14.0 years) and 19 CAPD patients (mean age 46.7 +/- 10.9 years) were studied.

RESULTS

BNP levels were greater in HD patients before the HD session (459.0 +/- 465.1 pg mL(-1)) than in CAPD patients (139.0 +/- 170.1 pg mL(-1)). The maximum and minimum P duration, and P dispersion, were similar for both groups (P > 0.05). Whereas BNP levels were negatively related to minimum P duration (r = -0.518, P = 0.019), BNP levels were positively correlated with systolic blood pressure and diastolic blood pressure (r = 0.672, P = 0.001 and r = 0.497, P = 0.022, respectively) in HD patients.

CONCLUSIONS

Whereas BNP levels are higher in HD patients when they are at peak-volume status, just before HD, P wave duration and P dispersion were similar for both groups. A negative relationship was detected between BNP levels and minimum P duration in HD patients. Expansion of extra-cellular volume causing myocardial stretching may be the principal cause of increased BNP in HD patients. A functional relationship between BNP and the P wave was not found. Additional studies are needed to evaluate the effect of BNP on the P wave.

B-type natriuretic peptide in heart failure

PURPOSE OF REVIEW

This review focuses on recent literature pertaining to the role of B-type natriuretic peptide (BNP) in heart failure.

RECENT FINDINGS

Heart failure is a common disorder that is associated with significant mortality and morbidity. The diagnosis of heart failure may at times be difficult when using conventional tools. The cardiac natriuretic peptides, particularly BNP, have evolved to be useful biomarkers in heart failure and other cardiovascular disorders. Recent studies have established a close association between plasma BNP and the amino-terminal fragment of the BNP prohormone (NT-proBNP) with the diagnosis of heart failure and independent prediction of mortality and heart failure events. Furthermore, preliminary data from randomized controlled trials suggest that knowledge of BNP and/or NT-proBNP level may optimize the management of patients with heart failure. Exogenous natriuretic peptide in the form of recombinant human BNP (nesiritide) has been shown to improve hemodynamics and dyspnea and is approved in the USA and several other countries for the management of patients with acute decompensated heart failure. The effect of nesiritide on clinical outcome, however, remains unclear.

SUMMARY

When used in the appropriate clinical settings, BNP or NT-proBNP testing is extremely useful in establishing diagnosis and predicting prognosis in heart failure. Nesiritide holds promise in the management of patients with acute decompensated heart failure. Large-scale randomized controlled trials to evaluate BNP/NT-proBNP-guided therapy are currently in progress and studies of the impact of exogenous BNP on clinical outcomes in heart failure are likely to be forthcoming.

Natriuretic peptides in ectopic myocardial tissues originating from mouse embryonic stem cells

In a previous report we described the survival and contractile function of mouse embryonic stem cell-derived cardiomyocytes in the host retroperitoneum. To further understand the nature of embryonic stem cell-derived cardiomyocytes, the study assessed the synthesis of natriuretic peptides in ectopic myocardial tissues of embryonic stem cell origin. Cardiomyocytes formed in embryoid body outgrowths were transplanted into the retroperitoneum of adult nude mice, and the myocardial tissues that developed were characterized by RT-PCR and immunohistochemistry concerning atrial and brain natriuretic peptides (ANP, BNP). In the outgrowths of embryoid bodies in vitro, gene expression of ANP and BNP was detected by RT-PCR and granules positive for the peptides were identified in a few cardiomyocytes by light and electron microscopic immunocytochemistry. Seven days after transplantation the transplants exhibited multidifferentiated teratoma tissues. Developing chamber myocardial tissues positive for cardiac troponin I, cadherin, and connexin 43 were evident in the transplants, which contained ANP-positive cardiomyocytes. Transplants with beating bundles were observed 30 days after transplantation, in which gene expression of both natriuretic peptides was detected. Myocardial tissues with abundant ANP-immunoreactivity, as well as with BNP-immunoreactivity to a lesser extent, were evident in the transplants. Also, myocardial tissues without immunoreactivity for natriuretic peptides were observed. Immunoelectron microscopy showed discernible secretory granules containing ANP and/or BNP in the cardiomyocytes. These results showed that part of the cardiomyocytes in embryonic stem cell-derived ectopic myocardial tissues are capable of producing natriuretic peptides, which suggests that they may be used as an endocrine source for cardiac hormones.

Genetic predisposition to heart failure

This review describes the numerous and complex molecular systems that are either known players or candidates in heart failure(HF). All systems whose genetic background has been investigated to date in HF are listed and discussed. Discussion also includes functional notes and known genetic polymorphisms already investigated in HF or candidates that have not yet been investigated. Despite substantial research on HF, relatively few coordinated studies have been conducted that assign precise risk to specific genetic polymorphisms. Identification of risk associated with genetic variations and subsequent translation of genetic knowledge into clinical practice will likely progress only in cases of large coordinated studies based on identical standards. The potential result will be a more accurate definition of HF identified as an evolving complex of cardiovascular diseases.

Clinical applications of B-type natriuretic peptides

Diagnostic, prognostic and therapeutic applications of B-type natriuretic peptides (NPs) will probably become part of routine management of heart failure within five years. Cardiac release of NPs rises with increasing cardiac dysfunction. Their secretion and plasma levels respond to intracardiac distending pressures, with other modulating influences including age, sex, renal function and other aspects of neurohormonal status. Single and serial plasma NP measurements, particularly of B-type and N-terminal pro-B-type NP, show promise in diagnosis of heart failure, risk stratification in those with known heart disease, and in adjustment of anti-failure therapy. Recombinant B-type NP is an effective parenteral treatment in decompensated heart failure. These applications of B-type NPs require confirmation before they become established in routine management of heart failure.

Expression of brain natriuretic peptide in the rat heart studies during heart growth and in relation to sympathectomy

Brain natriuretic peptide (BNP) might be of importance during heart development and is described to be increasingly expressed in congestive heart failure and to affect the progress of this condition. However, details in the normal expression of BNP are still unclear in various parts of the adult and growing heart, including the conduction system. In this study, we investigated the expression of BNP in relation to that of atrial natriuretic peptide (ANP) in the growing as well as in the adult rat heart. The effects of chemical sympathectomy in adult rats were also examined. Contrary to previous BNP immunohistochemical studies, the BNP antiserum was preabsorbed with an excess of ANP before staining to abolish the crossreactivity with ANP. There was a pronounced BNP immunoreaction in the auricles, the trabeculated ventricular walls, and the peripheral parts of the conduction system at 0-1 days postnatally. The degree of immunoreaction gradually decreased with increasing age. A similar developmental pattern was seen concerning ANP expression, but the magnitude of the latter clearly exceeded that for BNP. Immunoreaction for BNP was never detected in the atrioventricular (AV) node and AV bundle at any stage. In contrast to the situation for ANP previously observed, no obvious changes in BNP immunoreaction patterns were observed in response to sympathectomy. This is the first study to thoroughly demonstrate the expression of BNP in the various regions of the rat heart during growth and in the normal and sympathectomized adult stage. The observations are related to possible functions of natriuretic peptides in the growing and adult heart.

B-type natriuretic peptide in cardiovascular disease

Natriuretic peptide hormones, a family of vasoactive peptides with many favourable physiological properties, have emerged as important candidates for development of diagnostic tools and therapeutic agents in cardiovascular disease. The rapid incorporation into clinical practice of bioassays to measure natriuretic peptide concentrations, and drugs that augment the biological actions of this system, show the potential for translational research to improve patient care. Here, we focus on the physiology of the natriuretic peptide system, measurement of circulating concentrations of B-type natriuretic peptide (BNP) and the N-terminal fragment of its prohormone (N-terminal BNP) to diagnose heart failure and left ventricular dysfunction, measurement of BNP and N-terminal BNP to assess prognosis in patients with cardiac abnormalities, and use of recombinant human BNP (nesiritide) and vasopeptidase inhibitors to treat heart failure.

Ventricular expression of atrial natriuretic peptide in chronic chagasic cardiomyopathy is not induced by myocarditis

BACKGROUND

The ventricles of the normal heart are virtually devoid of atrial natriuretic peptide (ANP). Although ANP occurs in ventricles submitted to elevated wall stress, it is not clear whether ANP expression is affected by myocarditis. We investigated the immunohistochemical expression of ANP in chronic chagasic cardiomyopathy, an inflammatory cardiomyopathy caused by infection with the protozoan Trypanosoma cruzi.

METHODS

Necropsy samples from the left and right ventricles of 16 patients exhibiting chronic chagasic cardiomyopathy were evaluated for myocarditis, fibrosis, T. cruzi parasites and ANP immunoreactivity. The diameters of 50 myocytes per sample were measured.

RESULTS

ANP was present in myocytes of the subendocardial region in 13/16 (81.3%) left and 10/16 (62.5%) right ventricular samples (P=0.25). Myocytes present in the inflammatory foci, near the infiltrating inflammatory cells but distant from the subendocardial region, did not express ANP. Trypanosoma cruzi parasites exhibited intense immunoreactivity for ANP. The mean myocyte diameter and the incidence of myocarditis, fibrosis, and T. cruzi parasites was similar between the left and right ventricular samples. No statistical differences were found between the ANP-positive and ANP-negative cases.

CONCLUSIONS

In chronic chagasic cardiomyopathy, both ventricles exhibit hypertrophy, fibrosis and ANP in the subendocardial region. The inflammatory infiltrate does not induce ANP expression in the myocytes. Regional stress but not myocarditis itself, is probably responsible for ventricular ANP expression in myocarditis.

Natriuretic peptides in relation to the cardiac innervation and conduction system

During the past two decades, the heart has been known to undergo endocrine action, harbouring peptides with hormonal activities. These, termed "atrial natriuretic peptide (ANP)," "brain natriuretic peptide (BNP)," and "C-type natriuretic peptide (CNP)," are polypeptides mainly produced in the cardiac myocardium, where they are released into the circulation, producing profound hypotensive effects due to their diuretic, natriuretic, and vascular dilatory properties. It is, furthermore, well established that cardiac disorders such as congestive heart failure and different forms of cardiomyopathy are combined with increased expression of ANP and BNP, leading to elevated levels of these peptides in the plasma. Besides the occurrence of natriuretic peptides (NPs) in the ordinary myocardium, the presence of ANP in the cardiac conduction system has been described. There is also evidence of ANP gene expression in nervous tissue such as the nodose ganglion and the superior cervical ganglion of the rat, ganglia known to be involved in the neuronal regulation of the heart. Furthermore, in the mammalian heart, ANP appears to affect the cardiac autonomic nervous system by sympathoinhibitory and vagoexcitatory actions. This article provides an overview of the relationship between the cardiac conduction system, the cardiac innervation and NPs in the mammalian heart and provides data for the concept that ANP is also involved in neuronal cardiac regulation.

Chamber-dependent expression of brain natriuretic peptide and its mRNA in normal and diabetic pig heart

Brain natriuretic peptide (BNP) is produced in cardiac myocytes, and increased secretion is closely associated with cardiac dysfunction. However, several fundamental aspects of BNP expression in the myocardium have not yet been resolved. In the present study, we report the presence of a precursor BNP mRNA transcript and a mature BNP mRNA transcript in normal porcine hearts. In normal pigs, the amount of precursor BNP mRNA was similar in atrial and ventricular myocardium, whereas the mature BNP transcript was 10- to 50-fold more abundant in atrial than in ventricular myocardium. Quantitation of proBNP in normal porcine hearts by radioimmunoassay disclosed abundant proBNP in the atria, whereas proBNP was undetectable in the ventricles. Laser confocal microscopy revealed proBNP in secretory granules of atrial but not in the ventricular myocardium of normal pigs. Mild streptozotocin-induced diabetes doubled the expression of BNP mRNA in porcine atrial myocardium (P=0.03), but was without effect on BNP mRNA in the ventricular myocardium. The data suggest that BNP mRNA processing and proBNP storage differ between the atrial and ventricular myocardium. The results also imply that diabetes increases cardiac BNP expression in a chamber-dependent manner.

Histamine release induced by dendroaspis natriuretic peptide from rat mast cells

Dendroaspis natriuretic peptide (DNP), recently isolated from the venom of the green Mamba snake Dendroaspis angusticeps, is a 38 amino acid peptide containing a 17 amino acid disulfide ring structure similar to that of the natriuretic peptide family. The natriuretic peptide family is known to induce histamine release from human and rat mast cells, but there are no published data concerning the effects of DNP on histamine release from mast cells. The purpose of this study is to investigate whether DNP induces the histamine release from rat peritoneal mast cells (RMPCs) and to determine the mechanism of DNP-induced histamine release from RPMCs. After treatment of RPMC with DNP, mast cell degranulation was observed, and calcium uptake and histamine release were measured. DNP released the histamine, induced the mast cell degranulation, and increased the calcium uptake of RPMCs, in a dose-dependent manner. The results indicate that DNP can increase Ca-uptake and induce histamine release.

Regional cardiac expression and concentration of natriuretic peptides in patients with severe chronic heart failure

The purpose of this study was to examine the regional cardiac mRNA expression and concentration of brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) in relation to the circulating peptide concentrations in patients with chronic heart failure (CHF). The myocardial mRNA levels and peptide concentrations of BNP and ANP were analysed in seven different regions of the heart from patients undergoing cardiac transplantation. Autopsy samples from individuals without known cardiovascular disease were used as controls. The plasma levels of natriuretic peptides and their N-terminal propeptides, Nt-proBNP and Nt-proANP, were measured in the CHF patients and healthy volunteers. In the autopsy specimens, the atrial regions appeared to contain the highest peptide levels for BNP as well as ANP, the atrioventricular ratio being 12-262 and 72-637-fold, respectively. In the CHF patients there was a relative shift towards the ventricle for BNP, reducing the atrioventricular ratio to 6-16-fold. The circulating concentrations of BNP/Nt-proBNP in the CHF patients correlated closely to the BNP mRNA expression in most myocardial regions including the left ventricle (r = 0.72, P < 0.001). For circulating concentrations of ANP/Nt-proANP, such correlation were limited to the left atrium free wall (r = .66, P < 0.002). Thus, of the two natriuretic peptides, BNP/Nt-proBNP may be a better reflector of left ventricular overload.

A new, fast and reliable radioimmunoassay of brain natriuretic peptide in human plasma. Reference values in healthy subjects and in patients with different diseases

A new, fast and reliable radioimmunoassay for measurement of brain natriuretic peptide (BNP) in human plasma has been developed and its application is reported in healthy subjects and in patients with congestive heart failure, chronic renal failure, liver cirrhosis and essential hypertension. The antibody was raised in rabbits, the tracer was made by the iodogen method and polyethylene glycol was used for separation of free and bound tracer. BNP was extracted from plasma using Sep-Pak C18 cartridges. The recovery of unlabelled BNP added to plasma was 77.5 +/- 6.2% (mean +/- SD). The detection limit in plasma was 0.55 pmol l-1. No cross-reactivity existed with the natriuretic peptides ANP, CNP or urodilatin. In 124 healthy subjects the mean BNP was 1.8 +/- 1.0 pmol l-1 (SD), range 0.6-5.5. BNP increased slightly with age, was higher in women than men and had no circadian rhythm. In eight patients with congestive heart failure the median BNP level was 30.5 pmol l-1, range 3.9-65.3. In 14 patients with chronic renal failure the median BNP level was 50.5 pmol l-1, range 10.9-219.8 before dialysis, and 38.0 pmol l-1, range 9.4-180.0 immediately following dialysis. In 25 patients with liver cirrhosis the median BNP value was 7.8 pmol l-1, range 1.2-43.1. There was no difference between patients with or without ascites. In 18 medically treated patients with essential hypertension the median BNP level was 5.0 pmol l-1, range 1.2-45.5 pmol l-1.

Natriuretic peptide immunoreactivity in nerve structures and Purkinje fibres of human, pig and sheep hearts

Atrial natriuretic peptide is a well-described peptide in cardiac Purkinje fibres and has been shown to interfere with the autonomic regulation in the heart of various species, including man. Recently, we detected immunoreactivity for the peptide in intracardial ganglionic cells and nerve fibre varicosities of bovine hearts, by the use of a modified immunostaining technique that induced an improved detection of natriuretic peptides. These findings raised the question as to whether natriuretic peptides are detectable in these tissues in man and other species. The conduction system from human, pig and sheep hearts was dissected processed with antisera against atrial natriuretic peptide and the closely related brain natriuretic peptide. Immunostaining for the brain natriuretic peptide was detected in some Purkinje fibres in all of these species. Interestingly, in pig, sheep and human hearts, some ganglionic cells and nerve fibres showed atrial natriuretic peptide immunoreactivity, particularly in the soma of human ganglionic cells. This is the first study showing immunoreactivity for the atrial natriuretic peptide in nerve structures and for the brain natriuretic peptide in Purkinje fibres of the human heart. The results give a morphological correlate for the documented effects of atrial natriuretic peptide on the heart autonomic nervous system and for the presumable effects of brain natriuretic peptide in the conduction system of man.