Effects of natriuretic peptides on load and myocardial function in normal and heart failure dogs

Exploring PKG signaling as a therapeutic avenue for pressure overload, ischemia, and HFpEF

INTRODUCTION

Heart failure (HF) is a complex and heterogeneous syndrome resulting from any diastolic or systolic dysfunction of the cardiac muscle. In addition to comorbid conditions, pressure overload, and myocardial ischemia are associated with cardiac remodeling which manifests as extracellular matrix (ECM) perturbations, impaired cellular responses, and subsequent ventricular dysfunction.

AREAS COVERED

The current review discusses the main aspects of the cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) pathway (cGMP-PKG) pathway modulators and highlights the promising outcomes of its novel pharmacological boosters.

EXPERT OPINION

Among several signaling pathways involved in the pathogenesis of pressure overload, ischemia and HF with preserved ejection fraction (HFpEF) is cGMP-PKG pathway. This pathway plays a pivotal role in the regulation of cardiac contractility, and modulation of cGMP-PKG signaling, contributing to the development of the diseases. Ventricular cardiomyocytes of HF patients and animal models are known to exhibit reduced cGMP levels and disturbed cGMP signaling including hypophosphorylation of PKG downstream targets. However, restoration of cGMP-PKG signaling improves cardiomyocyte function and promotes cardioprotective effects.

Augmentation of Natriuretic Peptide Bioactivity via Combined Inhibition of Neprilysin and Phosphodiesterase-9 in Heart Failure

BACKGROUND

The natriuretic peptides (NPs) are potent natriuretic/diuretic and vasodilatory factors, and augmentation of their levels or signaling via inhibition of the enzymes neprilysin (NEP) and phosphodiesterase 9 (PDE9), respectively, has beneficial actions in heart failure (HF).

OBJECTIVES

The authors investigated dual enhancement of NP bioactivity by combining PDE9 inhibition and NEP inhibition in HF using an ovine model.

METHODS

Eight sheep with pacing-induced HF received on 4 separate days intravenous PDE9 inhibition (PF-04749982), NEP inhibition (SCH-32615), PDE9 inhibition + NEP inhibition (PI+NI), and vehicle control treatment.

RESULTS

Compared with the control treatment, NEP inhibition significantly increased plasma NP concentrations with a corresponding rise in second messenger cyclic guanosine monophosphate (cGMP), whereas PDE9 inhibition increased circulating cGMP with a negligible effect on NP levels. Combined PI+NI elevated plasma NPs to an extent comparable to that seen with NEP inhibition alone but further increased cGMP, resulting in a rise in the cGMP-to-NP ratio. All active treatments reduced mean arterial pressure, left atrial pressure, pulmonary arterial pressure, and peripheral resistance, with combined PI+NI further reducing mean arterial pressure and left atrial pressure relative to either inhibitor separately. Active treatments increased urine volume and sodium, potassium and creatinine excretion, and creatinine clearance, in association with rises in urine cGMP levels. PI+NI induced a significantly greater natriuresis and increase in urinary cGMP relative to either inhibitor singly.

CONCLUSIONS

The present study demonstrates for the first time that combined PI+NI has additional beneficial hemodynamic and renal effects when compared with either PDE9 inhibition or NEP inhibition alone. The superior efficacy of this 2-pronged augmentation of NP bioactivity supports PI+NI as a potential therapeutic strategy for HF.

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Atrial Natriuretic Peptide31-67: A Novel Therapeutic Factor for Cardiovascular Diseases

The characterization of the cardiac hormone atrial natriuretic peptide (ANP_99–126), synthesized and secreted predominantly by atrial myocytes under stimulation by mechanical stretch, has established the heart as an endocrine organ with potent natriuretic, diuretic, and vasodilating actions. Three additional distinct polypeptides resulting from proteolytic cleavage of proANP have been identified in the circulation in humans. The mid-sequence proANP fragment 31–67 (also known as proANP_31–67) has unique potent and prolonged diuretic and natriuretic properties. In this review, we report the main effects of this circulating hormone in different tissues and organs, and its mechanisms of actions. We further highlight recent evidence on the cardiorenal protective actions of chronic supplementation of synthetic proANP_31–67 in preclinical models of cardiorenal disease. Finally, we evaluate the use of proANP_31–67 as a new therapeutic strategy to repair end-organ damage secondary to hypertension, diabetes mellitus, renal diseases, obesity, heart failure, and other morbidities that can lead to impaired cardiac function and structure.

Current trends and future perspectives for heart failure treatment leveraging cGMP modifiers and the practical effector PKG

Cyclic guanosine monophosphate (cGMP), an intracellular second messenger molecule synthesized by guanylated cyclases (GCs), controls various myocardial properties, including cell growth and survival, interstitial fibrosis, endothelial permeability, cardiac contractility, and cardiovascular remodeling. These processes are mediated by the main cGMP effector protein kinase G (PKG) activation of which exerts intrinsic protective responses against the adverse effects of neurohormonal stimulation and pathological cardiac stress. Therapeutic strategies that enhance cGMP levels and PKG activation have been used for heart failure, which can be executed by reducing natriuretic peptide (NP) proteolysis, enhancing cGMP synthesis, or blocking cGMP hydrolysis. Among these, reducing NP clearance with neprilysin inhibitor combined with angiotensin receptor blocker has been shown to greatly improve the prognosis of patients with heart failure with reduced ejection fraction (HFrEF) compared to the prognosis of patients on standard therapy using angiotensin-converting enzyme inhibitors. Moreover, in a recent phase III clinical trial, soluble GC-derived cGMP generation was shown to have potential efficacy in the management of HFrEF. Despite the clinical significance of cGMP/PKG signaling activated by either soluble or particulate GCs in heart failure, the differential signaling events downstream of intracellular cGMP, which are precisely controlled not only by PKG activation but also by the changes in its targeting and compartmentalization depending on the pathophysiology of heart disease, are not yet completely understood. Hitherto, the importance of the latter PKG regulatory mechanisms in developing therapeutic strategies has not been elucidated. Further investigation of redox-based PKG modulation will aid in the successful development of clinical therapies and could also lead to the establishment of improved personalized treatments for patients with heart failure.

Multiplicity of Nitric Oxide and Natriuretic Peptide Signaling in Heart Failure

Heart failure (HF) is a common consequence of several cardiovascular diseases and is understood as a vicious cycle of cardiac and hemodynamic decline. The current inventory of treatments either alleviates the pathophysiological features (eg, cardiac dysfunction, neurohumoral activation, and ventricular remodeling) and/or targets any underlying pathologies (eg, hypertension and myocardial infarction). Yet, since these do not provide a cure, the morbidity and mortality associated with HF remains high. Therefore, the disease constitutes an unmet medical need, and novel therapies are desperately needed. Cyclic guanosine-3',5'-monophosphate (cGMP), synthesized by nitric oxide (NO)- and natriuretic peptide (NP)-responsive guanylyl cyclase (GC) enzymes, exerts numerous protective effects on cardiac contractility, hypertrophy, fibrosis, and apoptosis. Impaired cGMP signaling, which can occur after GC deactivation and the upregulation of cyclic nucleotide-hydrolyzing phosphodiesterases (PDEs), promotes cardiac dysfunction. In this study, we review the role that NO/cGMP and NP/cGMP signaling plays in HF. After considering disease etiology, the physiological effects of cGMP in the heart are discussed. We then assess the evidence from preclinical models and patients that compromised cGMP signaling contributes to the HF phenotype. Finally, the potential of pharmacologically harnessing cardioprotective cGMP to rectify the present paucity of effective HF treatments is examined.

The Urgent Need to Develop Novel Strategies for the Diagnosis and Treatment of Snakebites

Snakebite envenoming (SBE) is a priority neglected tropical disease, which kills in excess of 100,000 people per year. Additionally, many millions of survivors also suffer through disabilities and long-term health consequences. The only treatment for SBE, antivenom, has a number of major associated problems, not least, adverse reactions and limited availability. This emphasises the necessity for urgent improvements to the management of this disease. Administration of antivenom is too frequently based on symptomatology, which results in wasting crucial time. The majority of SBE-affected regions rely on broad-spectrum polyvalent antivenoms that have a low content of case-specific efficacious immunoglobulins. Research into small molecular therapeutics such as varespladib/methyl-varespladib (PLA2 inhibitors) and batimastat/marimastat (metalloprotease inhibitors) suggest that such adjunctive treatments could be hugely beneficial to victims. Progress into toxin-specific monoclonal antibodies as well as alternative binding scaffolds such as aptamers hold much promise for future treatment strategies. SBE is not implicit during snakebite, due to venom metering. Thus, the delay between bite and symptom presentation is critical and when symptoms appear it may often already be too late to effectively treat SBE. The development of reliable diagnostical tools could therefore initiate a paradigm shift in the treatment of SBE. While the complete eradication of SBE is an impossibility, mitigation is in the pipeline, with new treatments and diagnostics rapidly emerging. Here we critically review the urgent necessity for the development of diagnostic tools and improved therapeutics to mitigate the deaths and disabilities caused by SBE.

Effects of Low-Dose Recombinant Human Brain Natriuretic Peptide on Anterior Myocardial Infarction Complicated by Cardiogenic Shock

Introduction

The mortality due to cardiogenic shock complicating acute myocardial infarction (AMI) is high even in patients with early revascularization. Infusion of low dose recombinant human brain natriuretic peptide (rhBNP) at the time of AMI is well tolerated and could improve cardiac function.

Objective

The objective of this study was to evaluate the hemodynamic effects of rhBNP in AMI patients revascularized by emergency percutaneous coronary intervention (PCI) who developed cardiogenic shock.

Methods

A total of 48 patients with acute ST segment elevation myocardial infarction (STEMI) complicated by cardiogenic shock and whose hemodynamic status was improved following emergency PCI were enrolled. Patients were randomly assigned to rhBNP (n=25) and control (n=23) groups. In addition to standard therapy, study group individuals received rhBNP by continuous infusion at 0.005 µg kg⁻¹ min⁻¹ for 72 hours.

Results

Baseline characteristics, medications, and peak of cardiac troponin I (cTnI) were similar between both groups. rhBNP treatment resulted in consistently improved pulmonary capillary wedge pressure (PCWP) compared to the control group. Respectively, 7 and 9 patients died in experimental and control groups. No drug-related serious adverse events occurred in either group.

Conclusion

When added to standard care in stable patients with cardiogenic shock complicating anterior STEMI, low dose rhBNP improves PCWP and is well tolerated.

Valporic acid enhances the Atrial Natriuretic Peptide (ANP) mediated anti-hypertrophic activity by modulating the Npr1 gene transcription in H9c2 cells in vitro

The present study was aimed to determine whether stimulating Npr1 gene activity using Valporic acid (VA), a small short chain fatty acid molecule can enhance ANP mediated anti-hypertrophic activity in isoproterenol (ISO) - treated H9c2 cells in vitro. H9c2 cells were treated with ISO (10^-5 M) and co-treated with VA (10^-5 M) in the presence and absence of ANP (10^-8M), for 48h. ATRA (10^-5 M) was used as a positive inducer of Npr1 gene transcription. The mRNA expression of Npr1 and PKG-I genes, proto-oncogenes (c-fos, c-jun and c-myc) and hypertrophic markers (ANP, BNP, α-sk and β-MyHC), genes were determined by quantitative PCR (qPCR). The protein profiling of NPR-A, PKG-I and cGMP were evaluated by Western blot, immunofluorescence and ELISA respectively. A marked reduction in the level of expression of Npr1 (3- fold) and PKG-I (2.5-fold) genes and increased expression of proto-oncogenes (p< 0.001, respectively) and hypertrophic marker genes (p<0.001, respectively) were noticed in the ISO-treated H9c2 cells as compared with control cells. In contrast, the VA treated cells showed maximal Npr1 gene expression (3.5-fold) as compared with ATRA treated cells (2 fold), which is well correlated with the intracellular cGMP levels (80% vs 60%) and reduced (2.5-fold) HDAC -1&-2 mRNA expression. Furthermore, VA or ATRA treatment effectively reversed the ISO-induced altered expression of Npr1 and PKG-I genes, proto-oncogenes, and hypertrophic markers genes. Interestingly, the results of the present study suggest that ANP mediated anti-hypertrophic activity was enhanced with either VA (p<0.001) or ATRA (p<0.01) co-treatment. Together, we conclude that VA in combination with ANP can be a novel therapeutical approach for the treatment and management of left ventricular cardiac hypertrophy.

Top-down venomics of the East African green mamba, Dendroaspis angusticeps, and the black mamba, Dendroaspis polylepis, highlight the complexity of their toxin arsenals

We report the characterization, by combination of high-resolution on-line molecular mass and disulfide bond profiling and top-down MS/MS analysis, of the venom proteomes of two congeneric African snake species of medical importance, Dendroaspis angusticeps (green mamba) and D. polylepis (black mamba). Each of these mamba venoms comprised more than two-hundred polypeptides belonging to just a few toxin families. Both venom proteomes are overwhelmingly composed of post-synaptically-acting short- and long-chain neurotoxins that potently inhibit muscle- and neuronal-type nicotinic acetylcholine receptors; muscarinic cardiotoxins; and dendrotoxins, that block some of the Kv1, n-class of K+ channels. However, the identity of the major proteins and their relative abundances exhibit marked interspecific variation. In addition, the greater resolution of the top-down venomic analytical approach revealed previously undetected protein species, isoforms and proteoforms, including the identification and precise location of modified lysine residues in a number of proteins in both venoms, but particularly in green mamba toxins. This comparative top-down venomic analysis unveiled the untapped complexity of Dendroaspis venoms and lays the foundations for rationalizing the notably different potency of green and black mamba lethal arsenals at locus resolution.

SIGNIFICANCE PARAGRAPH

We report the characterization, by combination of high-resolution on-line molecular mass and disulfide bond profiling and top-down MS/MS analysis, of the venom proteomes of two congeneric African snake species of medical importance, Dendroaspis angusticeps (green mamba) and D. polylepis (black mamba). Each of these mamba venoms comprised more than two-hundred polypeptides belonging to just a few toxin families. Both venom proteomes are overwhelmingly composed of post-synaptically-acting short- and long-chain neurotoxins that potently inhibit muscle- and neuronal-type nicotinic acetylcholine receptors; muscarinic cardiotoxins; and dendrotoxins, that block some of the Kv1, n-class of K+ channels. However, the identity of the major proteins and their relative abundances exhibit marked interspecific variation. In addition, the greater resolution of the top-down venomic analytical approach revealed previously undetected protein species, isoforms and proteoforms, including the identification and precise location of modified lysine residues in a number of proteins in both venoms, but particularly in green mamba toxins. This comparative top-down venomic analysis unveiled the untapped complexity of Dendroaspis venoms and lays the foundations for rationalizing the notably different potency of green and black mamba lethal arsenals at locus resolution.

Chronic Peptide Therapy With B-Type Natriuretic Peptide in Patients With Pre-Clinical Diastolic Dysfunction (Stage B Heart Failure)

OBJECTIVES

This study determined whether there is development of tachyphylaxis to enhancement of cardiorenal response to acute volume loading (AVL) with B-type natriuretic peptide (BNP) after 12-week, twice-daily subcutaneous BNP administration in patients with preclinical diastolic dysfunction (PDD).

BACKGROUND

PDD is characterized by normal systolic function and moderate or severe diastolic dysfunction but no symptoms of heart failure (HF). Impairment in cardiorenal endocrine response to stress by AVL exists in PDD and is corrected by acute administration of subcutaneous BNP.

METHODS

A double-blinded, placebo-controlled proof-of-concept study was conducted to compare 12 weeks of twice daily subcutaneous BNP, 10 μg/kg (n = 24), versus placebo (n = 12) in PDD. Subjects underwent 2 study visits, at baseline and after 12 weeks. At each study visit, echocardiography, renal, and neurohumoral assessments were performed before and after intravascular AVL.

RESULTS

Among those with PDD, there was a statistically significant improvement in diastolic function after 12 weeks of BNP, as measured by a decrease in the Doppler E/e' ratio (where E is early mitral inflow velocity and e' is mitral annulus early diastolic motion) (p = 0.004) and improvement of diastolic dysfunction grade (p = 0.008). After 12 weeks, there was statistically significantly greater sodium excretion, urine flow, and urinary cyclic guanosine monophosphate excretion to AVL (all p < 0.001), as well as a trend toward greater glomerular filtration rate (p = 0.050) in the BNP group as compared to the placebo group.

CONCLUSIONS

In subjects with PDD, chronic BNP administration resulted in sustained improvement in diastolic function without development of tachyphylaxis to the enhancement of cardiorenal response to volume expansion with BNP. (Human Brain Natriuretic Peptide [BNP] [or Nesiritide] to Help Heart, Kidney and Humoral Function; NCT00405548).

Effects of human atrial natriuretic peptide on myocardial performance and energetics in heart failure due to previous myocardial infarction

BACKGROUND

Human atrial natriuretic peptide (hANP) and spontaneous nitric oxide (NO) donor share cyclic guanosine monophosphate (cGMP) as a second messenger, but their effect on myocardium may differ. We compared the effect of hANP and sodium nitroprusside (SNP) on left ventricular (LV) mechano-energetics in heart failure (HF).

METHODS

Ten patients with HF due to previous myocardial infarction (LV ejection fraction: 45±3%) were instrumented with conductance and coronary sinus thermodilution catheters. LV contractility (Ees: slope of end-systolic pressure-volume relation) and the ratio of LV stroke work (SW) to myocardial oxygen consumption (SW/MVO2=mechanical efficiency) were measured in response to intravenous infusion of ANP (0.05 μg/kg/min) or SNP (0.3 μg/kg/min) to lower blood pressure by at least 10 mmHg, and changes in plasma cGMP.

RESULTS

SNP had no effect on Ees, SW, or MVO2, thus SW/MVO2 remained unchanged (40.54±5.84% to 36.59±5.72%, p=0.25). ANP increased Ees, and decreased MVO2 with preserved SW, resulting in improved SW/MVO2 (40.49±6.35% to 50.30±7.96%, p=0.0073). Infusion of ANP (10.42-34.95 pmol/ml, p=0.0003) increased cGMP levels, whereas infusion of SNP had no effect (10.42-12.23 pmol/ml, p=0.75).

CONCLUSIONS

Compared to SNP, the ANP-dependent increase in cGMP may ameliorate myocardial inotropy and energetics in HF.

Microdomain switch of cGMP-regulated phosphodiesterases leads to ANP-induced augmentation of β-adrenoceptor-stimulated contractility in early cardiac hypertrophy

RATIONALE

Cyclic nucleotides are second messengers that regulate cardiomyocyte function through compartmentalized signaling in discrete subcellular microdomains. However, the role of different microdomains and their changes in cardiac disease are not well understood.

OBJECTIVE

To directly visualize alterations in β-adrenergic receptor-associated cAMP and cGMP microdomain signaling in early cardiac disease.

METHODS AND RESULTS

Unexpectedly, measurements of cell shortening revealed augmented β-adrenergic receptor-stimulated cardiomyocyte contractility by atrial natriuretic peptide/cGMP signaling in early cardiac hypertrophy after transverse aortic constriction, which was in sharp contrast to well-documented β-adrenergic and natriuretic peptide signaling desensitization during chronic disease. Real-time cAMP analysis in β1- and β2-adrenergic receptor-associated membrane microdomains using a novel membrane-targeted Förster resonance energy transfer-based biosensor transgenically expressed in mice revealed that this unexpected atrial natriuretic peptide effect is brought about by spatial redistribution of cGMP-sensitive phosphodiesterases 2 and 3 between both receptor compartments. Functionally, this led to a significant shift in cGMP/cAMP cross-talk and, in particular, to cGMP-driven augmentation of contractility in vitro and in vivo.

CONCLUSIONS

Redistribution of cGMP-regulated phosphodiesterases and functional reorganization of receptor-associated microdomains occurs in early cardiac hypertrophy, affects cGMP-mediated contractility, and might represent a previously not recognized therapeutically relevant compensatory mechanism to sustain normal heart function.

Suppression of neutrophil superoxide generation by BNP is attenuated in acute heart failure: a case for 'BNP resistance'

AIMS

The release of the B-type natriuretic peptide (BNP) is increased in heart failure (HF), a condition associated with oxidative stress. BNP is known to exert anti-inflammatory effects including suppression of neutrophil superoxide (O2(-)) release. However, BNP-based restoration of homeostasis in HF is inadequate, and the equivocal clinical benefit of a recombinant BNP, nesiritide, raises the possibility of attenuated response to BNP. We therefore tested the hypothesis that BNP-induced suppression of neutrophil O2(-) generation is impaired in patients with acute HF.

METHODS AND RESULTS

We have recently characterized suppression of neutrophil O2(-) generation (PMA- or fMLP-stimulated neutrophil burst) by BNP as a measure of its physiological activity. In the present study, BNP response was compared in neutrophils of healthy subjects (n = 29) and HF patients (n = 45). Effects of BNP on fMLP-induced phosphorylation of the NAD(P)H oxidase subunit p47phox were also evaluated. In acute HF patients, the suppressing effect of BNP (1 µmol/L) on O2(-) generation was attenuated relative to that in healthy subjects (P < 0.05 for both PMA and fMLP). Analogously, BNP inhibited p47phox phosphorylation in healthy subjects but not in HF patients (P < 0.05). However, O2(-)-suppressing effects of the cell-permeable cGMP analogue (8-pCPT-cGMP) were preserved in acute HF. Conventional HF treatment for 5 weeks partially restored neutrophil BNP responsiveness (n = 25, P < 0.05), despite no significant decrease in plasma NT-proBNP levels.

CONCLUSIONS

BNP inhibits neutrophil O2(-) generation by suppressing NAD(P)H oxidase assembly. This effect is impaired in acute HF patients, with partial recovery during treatment.

Natriuretic peptides in the management of solid organ transplantation associated acute kidney injury: a systematic review and meta-analysis

Randomized controlled trials involving natriuretic peptide administration in solid organ transplantation setting have shown inconsistent effects for renal endpoints. We conducted a systematic review and meta-analysis of these trials to ascertain the role of natriuretic peptides in the management of solid organ transplantation associated acute kidney injury (AKI). MEDLINE, EMBASE, and Google scholar were searched independently by two authors for randomized trials evaluating renal effects of natriuretic peptides in solid organ transplantation settings. Two reviewers independently assessed the studies for eligibility and extracted the relevant data. The pooled estimate showed that natriuretic peptide administration is associated with a reduction in AKI requiring dialysis (odds ratio = 0.50 [0.26–0.97]), a statistically nonsignificant trend toward improvement in posttransplant creatinine clearance (weighted mean difference = 5.5 mL/min, [−1.3 to 12.2 mL/min]), and reduction in renal replacement requirement duration (weighted mean difference −44.0 hours, [−60.5 to −27.5 hours]). There were no mortality events and no adverse events related to natriuretic peptides. In conclusion, administration of natriuretic peptides in solid organ transplantation may be associated with significant improvements in renal outcomes. These observations need to be confirmed in an adequately powered, prospective multicenter study.

Novel protein therapeutics for systolic heart failure: chronic subcutaneous B-type natriuretic peptide

OBJECTIVES

The purpose of the present study was to translate our laboratory investigations to establish safety and efficacy of 8 weeks of chronic SC B-type natriuretic peptide (BNP) administration in human Stage C heart failure (HF).

BACKGROUND

B-Type natriuretic peptide is a cardiac hormone with vasodilating, natriuretic, renin-angiotensin inhibiting, and lusitropic properties. We have previously demonstrated that chronic cardiac hormone replacement with subcutaneous (SC) administration of BNP in experimental HF resulted in improved cardiovascular function.

METHODS

We performed a randomized double-blind placebo-controlled proof of concept study comparing 8 weeks of SC BNP (10 μg/kg bid) (n = 20) with placebo (n = 20) in patients with ejection fraction <35% and New York Heart Association functional class II to III HF. Primary outcomes were left ventricular (LV) volumes and LV mass determined by cardiac magnetic resonance imaging. Secondary outcomes include LV filling pressure by Doppler echo, humoral function, and renal function.

RESULTS

Eight weeks of chronic SC BNP resulted in a greater reduction of LV systolic and diastolic volume index and LV mass index as compared with placebo. There was a significantly greater improvement of Minnesota Living with Heart Failure score, LV filling pressure as demonstrated by the reductions of E/e' ratio, and decrease in left atrial volume index as compared with placebo. Glomerular filtration rate was preserved with SC BNP, as was the ability to activate plasma 3',5'-cyclic guanosine monophosphate (p < 0.05 vs. placebo).

CONCLUSIONS

In this pilot proof of concept study, chronic protein therapy with SC BNP improved LV remodeling, LV filling pressure, and Minnesota Living with Heart Failure score in patients with stable systolic HF on optimal therapy. Renin-angiotensin was suppressed, and glomerular filtration rate was preserved. Subcutaneous BNP represents a novel, safe, and efficacious protein therapeutic strategy in human HF. Further studies are warranted to determine whether these physiologic observations can be translated into improved clinical outcomes and ultimately delay the progression of HF. (Cardiac Hormone Replacement With BNP in Heart Failure: A Novel Therapeutic Strategy; NCT00252187).

Sildenafil and B-type natriuretic peptide acutely phosphorylate titin and improve diastolic distensibility in vivo

BACKGROUND

In vitro studies suggest that phosphorylation of titin reduces myocyte/myofiber stiffness. Titin can be phosphorylated by cGMP-activated protein kinase. Intracellular cGMP production is stimulated by B-type natriuretic peptide (BNP) and degraded by phosphodiesterases, including phosphodiesterase-5A. We hypothesized that a phosphodiesterase-5A inhibitor (sildenafil) alone or in combination with BNP would increase left ventricular diastolic distensibility by phosphorylating titin.

METHODS AND RESULTS

Eight elderly dogs with experimental hypertension and 4 young normal dogs underwent measurement of the end-diastolic pressure-volume relationship during caval occlusion at baseline, after sildenafil, and BNP infusion. To assess diastolic distensibility independently of load/extrinsic forces, the end-diastolic volume at a common end-diastolic pressure on the sequential end-diastolic pressure-volume relationships was measured (left ventricular capacitance). In a separate group of dogs (n=7 old hypertensive and 7 young normal), serial full-thickness left ventricular biopsies were harvested from the beating heart during identical infusions to measure myofilament protein phosphorylation. Plasma cGMP increased with sildenafil and further with BNP (7.31±2.37 to 26.9±10.3 to 70.3±8.1 pmol/mL; P<0.001). Left ventricular diastolic capacitance increased with sildenafil and further with BNP (51.4±16.9 to 53.7±16.8 to 60.0±19.4 mL; P<0.001). Changes were similar in old hypertensive and young normal dogs. There were no effects on phosphorylation of troponin I, troponin T, phospholamban, or myosin light chain-1 or -2. Titin phosphorylation increased with sildenafil and BNP, whereas titin-based cardiomyocyte stiffness decreased.

CONCLUSION

Short-term cGMP-enhancing treatment with sildenafil and BNP improves left ventricular diastolic distensibility in vivo, in part by phosphorylating titin.

Dipeptidyl peptidase IV inhibition improves cardiorenal function in overpacing-induced heart failure

AIMS

Recent studies indicate that brain natriuretic peptide (BNP(1-32)) may be truncated into BNP(3-32) by dipeptidyl peptidase IV (DPP4) and that BNP(3-32) has reduced biological activities compared with BNP(1-32). We investigated if DPP4 contributes to the cardiorenal alterations and to the attenuated response to BNP seen in heart failure.

METHODS AND RESULTS

Haemodynamic and renal assessment was performed in 12 pigs at baseline, 4 weeks after pacing-induced heart failure, and during BNP infusion. They were randomized to either placebo or treatment with a DPP4 inhibitor, sitagliptin. After 4 weeks of pacing, heart rate was reduced compared with baseline in the sitagliptin group (60 ± 2 vs. 95 ± 16 b.p.m., P < 0.01), and an increase in stroke volume was observed in the sitagliptin group compared with placebo (+24 ± 6% vs. -17 ± 7%, P < 0.01). Glomerular filtration rate declined at week 4 compared with baseline in the placebo group (1.3 ± 0.4 vs. 2.3 ± 0.3 mL/kg/min, P < 0.01) but remained preserved in the sitagliptin group [1.8 ± 0.2 vs. 2.0 ± 0.3 mL/kg/min, P = NS (non-significant)]. In the sitagliptin group, BNP infusion improved end-systolic elastance (68 ± 5 vs. 31 ± 4 mmHg/kg/mL, P < 0.05), ventricular-arterial coupling, and mechanical efficiency. Compared with controls (n = 6), myocardial gene expression of BNP, interleukin-6, Na(+)-Ca(2+) exchanger, and calmodulin was up-regulated in the placebo group, but not in the sitagliptin group.

CONCLUSION

In pacing-induced heart failure, DPP4 inhibition preserves the glomerular filtration rate, modulates stroke volume and heart rate, and potentiates the positive inotropic effect of exogenous BNP at no energy expense.

Diabetic neuropathy and heart failure: role of neuropeptides

Cardiovascular autonomic neuropathy (CAN), in which patients present with damage of autonomic nerve fibres, is one of the most common complications of diabetes. CAN leads to abnormalities in heart rate and vascular dynamics, which are features of diabetic heart failure. Dysregulated neurohormonal activation, an outcome of diabetic neuropathy, has a significant pathophysiological role in diabetes-associated cardiovascular disease. Key players in neurohormonal activation include cardioprotective neuropeptides and their receptors, such as substance P (SP), neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). These neuropeptides are released from the peripheral or autonomic nervous system and have vasoactive properties. They are further implicated in cardiomyocyte hypertrophy, calcium homeostasis, ischaemia-induced angiogenesis, protein kinase C signalling and the renin-angiotensin-aldosterone system. Therefore, dysregulation of the expression of neuropeptides or activation of the neuropeptide signalling pathways can negatively affect cardiac homeostasis. Targeting neuropeptides and their signalling pathways might thus serve as new therapeutic interventions in the treatment of heart failure associated with diabetes. This review discusses how neuropeptide dysregulation in diabetes might affect cardiac functions that contribute to the development of heart failure.

Association of genetic variation in the natriuretic peptide system with cardiovascular outcomes

Polymorphisms within individual natriuretic peptide genes have been associated with risk factors for cardiovascular disease, but their association with clinical outcomes was previously unknown. This study aimed to investigate the association between genetic variants in key genes of the natriuretic peptide system with cardiovascular outcomes in patients with coronary artery disease. Coronary disease patients (n=1810) were genotyped for polymorphisms within NPPA, NPPB, NPPC, NPR1 and NPR2. Clinical history, natriuretic peptide concentrations, echocardiography, all-cause mortality and cardiovascular hospital readmissions were recorded over a median 2.8 years. Minor alleles of NPPA rs5068, rs5065 and rs198358 were associated with less history of hypertension; minor alleles of NPPA rs5068 and rs198358 was also associated with higher circulating natriuretic peptide levels (p=0.003 to p=0.04). Minor alleles of NPPB rs198388, rs198389, and rs632793 were associated with higher circulating BNP and NT-proBNP (p=0.001 to p=0.03), and reduced E/E(1) (p=0.011), or LVESVI (p=0.001) and LVEDVI (p=0.004). Within NPPC, both rs11079028 and rs479651 were associated with higher NT-proBNP and CNP (p=0.01 to p=0.03), and rs479651 was associated with lower LVESVI (p=0.008) and LVEDVI (p=0.018). NPR2 rs10758325 was associated with smaller LVMI (p<0.02). A reduced rate of cardiovascular readmission was observed for minor alleles of NPPA rs5065 (p<0.0001), NPPB rs632793 (p<0.0001), rs198388 (p<0.0001), rs198389 (p<0.0001), and NPR2 rs10758325 (p<0.0001). There were no associations with all-cause mortality. In established cardiovascular disease, natriuretic peptide system polymorphisms were associated with natriuretic peptide levels, hypertension, echocardiographic indices and the incidence of hospital readmission for cardiovascular events.

Acute effects of intravenous nesiritide on cardiac contractility in heart failure

BACKGROUND

Although nesiritide is a potent vasodilator, studies using myocytes and isolated muscle strips have shown that recombinant B-type natriuretic peptide (BNP; nesiritide) decreases contractility. We sought to determine whether nesiritide decreases contractility in heart failure patients.

METHODS AND RESULTS

Twenty-five heart failure patients underwent left heart catheterization (using a pressure-volume conductance catheter) and echocardiography at baseline and after a 2 mcg/kg bolus and 30-minute nesiritide infusion (0.01 mcg.kg.min). From invasive and noninvasive measurements, left ventricular (LV) systolic function indices were calculated, including ejection fraction, end-systolic elastance (E(es); single-beat invasive and noninvasive methods) and preload-recruitable stroke work (PRSW; noninvasive, single-beat method). The mean age was 60 +/- 11 years, 48% were male, 56% had coronary disease, and 64% had hypertension. Although nesiritide did not change LV ejection fraction, it did decrease contractility on pressure-volume analysis. Noninvasive E(es) decreased from 2.6 +/- 1.6 to 2.0 +/- 1.4 mm Hg/mL (P = .02). For those with reduced ejection fraction, E(es) decreased by invasive (P = .006) and noninvasive (P = .02) methods. PRSW decreased from 76 +/- 37 to 62 +/- 28 g/cm(2) (P = .003). On tissue Doppler imaging, nesiritide reduced the systolic annular tissue velocity of the mitral annulus from 8.0 +/- 1.9 to 6.9 +/- 1.3 cm/s (P = .04).

CONCLUSIONS

Nesiritide infusion acutely decreases derived measures of contractility and systolic function in patients with chronic heart failure.

A sandwich ELISA for assessment of pharmacokinetics of HSA-(BNP)2 fusion protein in mouse plasma

Brain natriuretic peptide (BNP) is a circulating hormone of cardiac origin that plays an important role in the regulation of intravascular blood volume and vascular tone. HSA-(BNP)(2), derived from the joining of human BNP to the C-terminus of human serum albumin (HSA), has been developed to prolong the BNP pharmacodynamic action. For the analysis of pharmacokinetics of the new drug, a novel sandwich enzyme-linked immunosorbent assay (ELISA) was established and validated to quantify HSA-(BNP)(2) fusion protein in mouse plasma. The ELISA method was calibrated with 1:10 and 1:100 dilutions of blank mouse plasma spiked with HSA-(BNP)(2) standard and validated with respect to parallelism, precision (intra- and inter-assay variation), accuracy (recovery), specificity and stability. The practical working range was estimated to be 31.2-2000ng/ml with the limit of detection was 7.8ng/ml. Recoveries ranged from 80.5 to 108.4%, while the intra- and inter-assay precisions were <2.73% and <4.32%, respectively. The terminal half-life of HSA-(BNP)(2) was 2.14h, which had extended more than 40 times compared to 3.1min half-life of BNP monomer in mouse.

Atrial natriuretic peptide regulates Ca channel in early developmental cardiomyocytes

Background

Cardiomyocytes derived from murine embryonic stem (ES) cells possess various membrane currents and signaling cascades link to that of embryonic hearts. The role of atrial natriuretic peptide (ANP) in regulation of membrane potentials and Ca²⁺ currents has not been investigated in developmental cardiomyocytes.

Methodology/Principal Findings

We investigated the role of ANP in regulating L-type Ca²⁺ channel current (I_CaL) in different developmental stages of cardiomyocytes derived from ES cells. ANP decreased the frequency of action potentials (APs) in early developmental stage (EDS) cardiomyocytes, embryonic bodies (EB) as well as whole embryo hearts. ANP exerted an inhibitory effect on basal I_CaL in about 70% EDS cardiomyocytes tested but only in about 30% late developmental stage (LDS) cells. However, after stimulation of I_CaL by isoproterenol (ISO) in LDS cells, ANP inhibited the response in about 70% cells. The depression of I_CaL induced by ANP was not affected by either Nω, Nitro-L-Arginine methyl ester (L-NAME), a nitric oxide synthetase (NOS) inhibitor, or KT5823, a cGMP-dependent protein kinase (PKG) selective inhibitor, in either EDS and LDS cells; whereas depression of I_CaL by ANP was entirely abolished by erythro-9-(2-Hydroxy-3-nonyl) adenine (EHNA), a selective inhibitor of type 2 phosphodiesterase(PDE2) in most cells tested.

Conclusion/Significances

Taken together, these results indicate that ANP induced depression of action potentials and I_CaL is due to activation of particulate guanylyl cyclase (GC), cGMP production and cGMP-activation of PDE2 mediated depression of adenosine 3′, 5′–cyclic monophophate (cAMP)–cAMP-dependent protein kinase (PKA) in early cardiomyogenesis.

Low-dose nesiritide in human anterior myocardial infarction suppresses aldosterone and preserves ventricular function and structure: a proof of concept study

BACKGROUND

B-type natriuretic peptide (BNP, nesiritide) has anti-fibrotic, anti-hypertrophic, anti-inflammatory, vasodilating, lusitropic and aldosterone-inhibiting properties but conventional doses of BNP cause hypotension, limiting its use in heart failure.

OBJECTIVE

To determine whether infusion of low-dose BNP within 24 h of successful reperfusion for anterior acute myocardial infarction (AMI) would prevent adverse left ventricular (LV) remodelling and suppress aldosterone.

METHODS

A translational proof-of-concept study was carried out to determine tolerability and biological activity of intravenous BNP at 0.003 and 0.006 microg/kg/min, without bolus started within 24 h of successful reperfusion for anterior AMI. 24 patients with first anterior wall ST elevation AMI and successful revascularisation were randomly assigned to receive 0.003 (n = 12) or 0.006 (n = 12) microg/kg/min of IV BNP for 72 h in addition to standard care during hospitalisation for anterior AMI.

RESULTS

Baseline characteristics, drugs and peak cardiac biomarkers for myocardial damage were similar between both groups. Infusion of BNP at 0.006 microg/kg/min resulted in greater biological activity than infusion at 0.003 microg/kg/min as measured by higher mean (SEM) plasma cGMP levels (8.6 (1) vs 5.5 (1) pmol/ml, p<0.05) and suppression of plasma aldosterone (8.0 (2) to 4.6 (1) ng/dl, p<0.05), which was not seen in the 0.003 microg/kg/min group. LV ejection fraction (LVEF) improved significantly from baseline to 1 month (40 (4)% to 54 (5)%, p<0.05) in the 0.006 group but not in the 0.003 group. Infusion of BNP at 0.006 microg/kg/min was associated with a decrease of LV end-systolic volume index (61 (9) to 43 (8) ml/m(2), p<0.05) at 1 month, which was not seen in the 0.003 group. No drug-related serious adverse events occurred in either group.

CONCLUSIONS

72 h infusion of low BNP at the time of anterior AMI is well tolerated and biologically active. Patients treated with low-dose BNP had improved LVEF and smaller LV end-systolic volume at 1 month.

Modulation of cGMP in heart failure: a new therapeutic paradigm

Heart failure (HF) is a common disease that continues to be associated with high morbidity and mortality warranting novel therapeutic strategies. Cyclic guanosine monophosphate (cGMP) is the second messenger of several important signaling pathways based on distinct guanylate cyclases (GCs) in the cardiovascular system. Both the nitric oxide/soluble GC (NO/sGC) as well as the natriuretic peptide/GC-A (NP/GC-A) systems are disordered in HF, providing a rationale for their therapeutic augmentation. Soluble GC activation with conventional nitrovasodilators has been used for more than a century but is associated with cGMP-independent actions and the development of tolerance, actions which novel NO-independent sGC activators now in clinical development lack. Activation of GC-A by administration of naturally occurring or designer natriuretic peptides is an emerging field, as is the inhibition of enzymes that degrade endogenous NPs. Finally, inhibition of cGMP-degrading phosphodiesterases, particularly phosphodiesterase 5 provides an additional strategy to augment cGMP-signaling.

Insights into natriuretic peptides in heart failure: an update

Natriuretic peptides (NPs) secreted by the heart in response to volume overload are pleiotropic molecules with vasodilating, diuretic, natriuretic, antiproliferative, and antifibrotic actions. Functioning of the NP system is altered in congestive heart failure (CHF), suggesting that support of the NP system might be beneficial in treatment of acute and chronic CHF. Several approaches alone or in combination with other pharmacologic therapies have been shown to enhance function of the NP system: direct administration of native and designer NPs, inhibition of degradation of NPs and their second messenger (cyclic guanosine monophosphate ), and stimulation of cGMP generation. Despite increasing numbers of studies using NPs in therapy of acute and chronic CHF, several controversies regarding safety, efficacy, and dosing of NPs need to be addressed. Moreover, further research is warranted to identify the stages and etiologies of CHF that may profit from NP therapy.

Clinical utility of serum N-terminal pro-B-type natriuretic peptide concentration for identifying cardiac disease in dogs and assessing disease severity

OBJECTIVE

To determine whether serum N-terminal pro-B-type natriuretic (NT-proBNP) concentration could be used to identify cardiac disease in dogs and to assess disease severity in affected dogs.

DESIGN

Cross-sectional study.

ANIMALS

119 dogs with mitral valve disease, 18 dogs with dilated cardiomyopathy, and 40 healthy control dogs.

PROCEDURES

Serum NT-proBNP concentration was measured with an ELISA validated for use in dogs. Results of physical examination, thoracic radiography, echocardiography, and serum biochemical analyses were recorded for dogs with cardiac disease.

RESULTS

Serum NT-proBNP concentration was significantly higher in dogs with cardiac disease than in control dogs, and a serum NT-proBNP concentration > 445 pmol/L could be used to discriminate dogs with cardiac disease from control dogs with a sensitivity of 83.2% and specificity of 90.0%. In dogs with cardiac disease, serum NT-proBNP concentration was correlated with heart rate, respiratory rate, echocardiographic heart size, and renal function. For dogs with cardiac disease, serum NT-proBNP concentration could be used to discriminate dogs with and without radiographic evidence of cardiomegaly and dogs with and without congestive heart failure.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that serum NT-proBNP concentration may be a useful adjunct clinical test for diagnosing cardiac disease in dogs and assessing the severity of disease in dogs with cardiac disease.

Low dose nesiritide and the preservation of renal function in patients with renal dysfunction undergoing cardiopulmonary-bypass surgery: a double-blind placebo-controlled pilot study

BACKGROUND

Renal insufficiency is associated with increased morbidity and mortality after cardiopulmonary bypass cardiac surgery. B-type natriuretic peptide is a cardiac hormone that enhances glomerular filtration rate and inhibits aldosterone. Cystatin has been shown to be a better endogenous marker of renal function than creatinine.

METHODS AND RESULTS

We performed a double-blinded placebo-controlled proof of concept pilot study in patients (n=40) with renal insufficiency preoperatively (defined as an estimated creatinine clearance of <60 mL/min determined by the Cockroft-Gault formula), undergoing cardiopulmonary bypass cardiac surgery. Patients were randomized to placebo (n=20) or i.v. low dose nesiritide (n=20; 0.005 microg/Kg/min) for 24 hours started after the induction of anesthesia and before cardiopulmonary bypass. Patients in the nesiritide group had an increase of plasma B-type natriuretic peptide and its second messenger cGMP with a decrease in plasma cystatin levels at the end of the 24-hour infusion. These changes were not observed in the placebo group. There was a significant activation of aldosterone in the placebo group at the end of the 24-hour infusion, but not in the nesiritide group. At 48 and 72 hours, there was a decrease in estimated creatinine clearance and an increase in plasma cystatin as compared with end of the 24-hour infusion in the placebo group. In contrast, renal function was preserved in the nesiritide group with no significant change in estimated creatinine clearance and a trend for plasma cystatin to increase as compared with end of the 24-hour infusion.

CONCLUSION

This proof of concept pilot study supports the conclusion that perioperative administration of low dose nesiritide is biologically active and decreases plasma cystatin in patients with renal insufficiency undergoing cardiopulmonary bypass cardiac surgery. Further studies are warranted to determine whether these physiological observations can be translated into improved clinical outcomes.

Natriuretic peptide receptor B signaling in the cardiovascular system: protection from cardiac hypertrophy

Natriuretic peptides (NP) represent a family of structurally homologous but genetically distinct peptide hormones involved in regulation of fluid and electrolyte balance, blood pressure, fat metabolism, cell proliferation, and long bone growth. Recent work suggests a role for natriuretic peptide receptor B (NPR-B) signaling in regulation of cardiac growth by either a direct effect on cardiomyocytes or by modulation of other signaling pathways including the autonomic nervous system. The research links NPR-B for the first time to a cardiac phenotype in vivo and underlines the importance of the NP in the cardiovascular system. This manuscript will focus on the role of NPR-B and its ligand C-type natriuretic peptide in cardiovascular physiology and disease and will evaluate these new findings in the context of the known function of this receptor, with a perspective on how future research might further elucidate NPR-B function.

Acute Phosphodiesterase 5 Inhibition Mimics Hemodynamic Effects of B-Type Natriuretic Peptide and Potentiates B-Type Natriuretic Peptide Effects in Failing But Not Normal Canine Heart

OBJECTIVES

The aim of this work was to test whether acute phosphodiesterase 5 (PDE5) inhibition via sildenafil (SIL) mimics and/or potentiates cardiorenal effects of exogenous natriuretic peptide (NP) infusion.

BACKGROUND

Heart failure (HF) is often accompanied by elevated NP secretion yet blunted responsiveness. Such NP resistance may, in part, relate to increased cyclic guanosine monophosphate (cGMP) catabolism by PDE5.

METHODS

Dogs (n = 7) were studied before and after tachypacing-induced HF. Animals received 30-min infusion of B-type natriuretic peptide (BNP) (2 mug/kg bolus, 0.02 mug/kg/min), and on a separate day SIL (1 mg/kg, intravenous), followed by BNP (SIL + BNP). Phosphodiesterase 5 activity was measured in lung, vasculature, and kidney.

RESULTS

At baseline (non-failing), BNP lowered central venous, pulmonary capillary wedge, diastolic, mean pulmonary artery, and mean arterial pressure. Sildenafil had no effects, and SIL + BNP was similar to BNP alone. In contrast, SIL lowered these pressures similarly to BNP in dogs with HF, and SIL + BNP was additive in further reducing pulmonary pressures over BNP alone. Plasma cGMP/plasma BNP ratio was markedly reduced with HF, indicating NP resistance. Sildenafil plus BNP increased this ratio in HF, but had no effect in non-failing animals. Sildenafil had no independent diuretic/natriuretic effects nor did it enhance BNP effects under baseline or HF conditions. In HF, PDE5 activity was significantly increased in the systemic and pulmonary vasculature and in the kidney.

CONCLUSIONS

The PDE5 activity in systemic and pulmonary vasculature increases in HF rendering hemodynamic responses to PDE5 inhibition identical to those from BNP infusion. Natriuretic peptide desensitization in HF relates, in part, to increased PDE5 activity, supporting a therapeutic role for PDE5 inhibition.

AlbuBNP, a recombinant B-type natriuretic peptide and human serum albumin fusion hormone, as a long-term therapy of congestive heart failure

PURPOSE

B-type natriuretic peptide (BNP) has been in clinical use for the treatment of decompensated congestive heart failure. However, BNP has a very short half-life in circulation, which limits its application to acute CHF and requires continuous i.v. infusion. To provide superior pharmacological benefits of BNP to other stages of chronic congestive heart failure and to eliminate problems associated with drug delivery via continuous i.v. infusion, we have designed and evaluated AlbuBNP, a long-acting form of BNP by recombinant fusion to human serum albumin for use in chronic congestive heart failure, post-acute follow-up, and postmyocardial infarction.

METHODS

Human BNP (1-32) was seamlessly fused to mature human serum albumin at N-terminus to create AlbuBNP. The bioactivities of AlbuBNP were evaluated by natriuretic peptide receptor-A mediated cGMP activation assay, hemodynamic responses, and plasma cGMP elevation. The pharmacokinetic properties were determined after single i.v. or s.c. bolus injection in C57/BL6 mice.

RESULTS

AlbuBNP had approxiamtely the same maximal bioactivity as BNP to activate cGMP in the in vitro NPRA/cGMP assay. The EC50s were 28.4+/-1.2 and 0.46+/-1.1 nM for AlbuBNP and BNP, respectively. In spontaneously hypertensive rats, AlbuBNP lowered both systolic and diastolic blood pressure, having sustainable mean arterial pressure reduction for more than 2 days. Six nmol/kg AlbuBNP i.v. bolus in mice increased plasma cGMP level 5.6-fold over the baseline. The elimination half-life in mice was dramatically increased from 3 min for BNP to 12-19 h for AlbuBNP.

CONCLUSIONS

AlbuBNP is bioactive and has desired pharmacokinetic properties for long-term use. It has the potential to be further developed as a new therapeutic option for chronic, acute, and post-acute CHF to alleviate symptoms, improve clinical status, and slow the disease progression by sustained drug exposure via infrequent simple subcutaneous injections.

Equimolar doses of atrial and brain natriuretic peptides and urodilatin have differential renal actions in overt experimental heart failure

A hallmark of overt congestive heart failure (CHF) is attenuated cGMP production by endogenous atrial natriuretic peptide (ANP) with renal resistance to ANP. ANP and brain natriuretic peptides (BNP) are of myocardial origin, whereas urodilatin (Uro) is thought to be derived from kidney. All three peptides are agonists to the natriuretic peptide-A receptor. Our objective was to compare the cardiorenal and humoral actions of ANP, BNP, and Uro in experimental overt CHF. We determined cardiorenal and humoral actions of 90 min of intravenous equimolar infusion of ANP, BNP, and Uro (2 and 10 pmol.kg-1.min-1) in three separate groups of anesthetized dogs with rapid ventricular pacing-induced overt CHF (240 beats/min for 10 days). BNP resulted in increases in urinary sodium excretion (U(Na)V) (2.2+/-0.7 to 164+/-76 microeq/min, P<0.05) and glomerular filtration rate (GFR) (27+/-4 to 52+/-11 ml/min, P<0.05) that were greater than those with Uro (P<0.05), whereas ANP did not result in increases in U(Na)V or GFR. Increases in plasma cGMP (25+/-2 to 38+/-2 pmol/ml, P<0.05) and urinary cGMP excretion with BNP (1,618+/-151 to 6,124+/-995 pmol/min, P<0.05) were similar to those with Uro; however, there was no change with ANP. Cardiac filling pressures were reduced in all three groups. These studies also support the conclusion that in experimental overt CHF, renal resistance to natriuretic peptides in increasing rank order is BNP<Uro<ANP.

Atrial natriuretic peptide, B-type natriuretic peptide, and serum collagen markers after acute myocardial infarction

Experimental data suggest that atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) act locally as antifibrotic factors in heart. We investigated the interrelationships of natriuretic peptides and collagen markers in 93 patients receiving thrombolytic treatment for their first acute myocardial infarction (AMI). Collagen formation following AMI, evaluated as serum levels of amino terminal propeptide of type III procollagen, correlated with NH2-terminal proANP ( r = 0.45, P < 0.001), BNP ( r = 0.55, P < 0.001) and NH2-terminal proBNP ( r = 0.50, P < 0.01) on day 4 after thrombolysis. Levels of intact amino terminal propeptide of type I procollagen decreased by 34% ( P < 0.001), and levels of carboxy terminal cross-linked telopeptide of type I collagen (ICTP) increased by 65% ( P < 0.001). ICTP levels correlated with NH2-terminal proBNP ( r = 0.25, P < 0.05) and BNP ( r = 0.28, P < 0.05) on day 4. Our results suggest that ANP and BNP may act as regulators of collagen scar formation and left ventricular remodeling after AMI in humans. Furthermore, degradation of type I collagen is increased after AMI and may be regulated by BNP.

Hemodynamic and humoral effects of vasopeptidase inhibition in canine hypertension

Vasopeptidase inhibitors are potent new antihypertensive agents. The dual inhibition of ACE and neutral endopeptidase may result in synergistic humoral effects with unique hemodynamic actions. We investigated the hemodynamic and neurohumoral effects of vasopeptidase inhibition in conscious dogs made hypertensive by bilateral renal wrapping and subsequently instrumented for long-term assessment of left ventricular pressure and volume (n=8). Intravenous vasopeptidase inhibition (omapatrilat, 30 micromol/kg over 10 minutes) reduced peak left ventricular pressure (171+/-6 versus 130+/-6 mm Hg immediately after infusion, P<0.01) through arterial vasodilation (arterial elastance, 9.8+/-0.8 to 5.8+/-1.6 mm Hg/mL, P<0.01) and preload reduction (left ventricular end-diastolic volume, 51.1+/-6.8 to 46.0+/-6.9 mL, P<0.01). At 60 minutes, preload decreased further (40.5+/-5.9 mL, P<0.01 versus baseline). Vasopeptidase inhibition increased plasma levels of adrenomedullin (41.2+/-9.6 versus 72.3+/-15 pg/mL, P<0.01), whereas levels of the natriuretic peptides and cGMP were unchanged. Similar hemodynamic and humoral effects were observed with long-term therapy. Neither an equimolar dose of an ACE inhibitor (fosinopril) nor exogenous adrenomedullin had as potent of a hypotensive effect, and neither reduced preload. In summary, the potent short-term and long-term hypotensive effects of vasopeptidase inhibition were prominently mediated by preload reduction, an effect not reproduced by ACE inhibition nor adrenomedullin augmentation and not associated with enhanced natriuretic peptide levels. Combined arterial vasodilation and preload reduction may confer additional potency as well as unique cardioprotective effects. Synergistic effects on humoral and probably endothelial vasodilatory factors appear to be important in mediating the unique hemodynamic profile of vasopeptidase inhibition in this form of experimental hypertension.

Intravenous adrenomedullin in myocardial function and energy metabolism in patients after myocardial infarction

This study investigated the effects of adrenomedullin on left ventricular myocardial contraction and relaxation, coronary blood flow, and myocardial oxygen consumption in comparison with those of atrial natriuretic peptide (ANP). Fourteen patients who had had myocardial infarctions were randomly assigned to receive IV infusion of adrenomedullin (0.05 microg/kg/min) or ANP (0.05 microg/kg/min). Both adrenomedullin and ANP significantly decreased left ventricular systolic pressure (-17 mm Hg, -13 mm Hg, respectively, both p < 0.05). The increase in cardiac index by adrenomedullin (+31%) was significantly greater than that by ANP (+16%). Adrenomedullin significantly increased an index of myocardial contractility, Emax (2.5 +/- 0.3 mm Hg-3.7 +/- 0.3 mm Hg/ml, p < 0.05) and shortened an index of myocardial relaxation, Tau (52 +/- 5 ms-48 +/- 4 ms, p < 0.05). In contrast, ANP did not significantly alter either parameter. In addition, adrenomedullin, but not ANP, significantly increased coronary sinus blood flow (73 +/- 10 ml/min-86 +/- 10 ml/min, p < 0.05). Adrenomedullin did not increase myocardial oxygen consumption. Unlike ANP, IV administration of adrenomedullin enhanced left ventricular myocardial contraction and improved left ventricular relaxation without increasing myocardial oxygen consumption in patients who had had a myocardial infarction.

Actions of a novel synthetic natriuretic peptide on hemodynamics and ventricular function in the dog

Dendroaspis natriuretic peptide (DNP) is a recently discovered peptide with structural similarity to known natriuretic peptides. DNP has been shown to possess potent renal actions. Our objectives were to define the acute hemodynamic actions of DNP in normal anesthetized dogs and the acute effects of DNP on left ventricular (LV) function in conscious chronically instrumented dogs. In anesthetized dogs, DNP, but not placebo, decreased mean arterial pressure (141 +/- 6 to 109 +/- 7 mmHg, P < 0.05) and pulmonary capillary wedge pressure (5.8 +/- 0.3 to 3.4 +/- 0.2 mmHg, P < 0.05). Cardiac output decreased and systemic vascular resistance increased with DNP and placebo. DNP-like immunoreactivity and guanosine 3',5'-cyclic monophosphate concentration increased without changes in other natriuretic peptides. In conscious dogs, DNP decreased LV end-systolic pressure (120 +/- 7 to 102 +/- 6 mmHg, P < 0.05) and volume (32 +/- 6 to 28 +/- 6 ml, P < 0.05) and LV end-diastolic volume (38 +/- 5 to 31 +/- 4 ml, P < 0.05) but not arterial elastance. LV end-systolic elastance increased (6.1 +/- 0.7 to 7.4 +/- 0.6 mmHg/ml, P < 0.05), and Tau decreased (31 +/- 2 to 27 +/- 1 ms, P < 0.05). The effects on hemodynamics, LV function, and second messenger generation suggest synthetic DNP may have a role as a cardiac unloading and lusitropic peptide.

Effects of avertin versus xylazine-ketamine anesthesia on cardiac function in normal mice

Anesthetic regimens commonly administered during studies that assess cardiac structure and function in mice are xylazine-ketamine (XK) and avertin (AV). While it is known that XK anesthesia produces more bradycardia in the mouse, the effects of XK and AV on cardiac function have not been compared. We anesthetized normal adult male Swiss Webster mice with XK or AV. Transthoracic echocardiography and closed-chest cardiac catheterization were performed to assess heart rate (HR), left ventricular (LV) dimensions at end diastole and end systole (LVDd and LVDs, respectively), fractional shortening (FS), LV end-diastolic pressure (LVEDP), the time constant of isovolumic relaxation (tau), and the first derivatives of LV pressure rise and fall (dP/dt(max) and dP/dt(min), respectively). During echocardiography, HR was lower in XK than AV mice (250 +/- 14 beats/min in XK vs. 453 +/- 24 beats/min in AV, P < 0.05). Preload was increased in XK mice (LVDd: 4.1 +/- 0.08 mm in XK vs. 3.8 +/- 0.09 mm in AV, P < 0.05). FS, a load-dependent index of systolic function, was increased in XK mice (45 +/- 1.2% in XK vs. 40 +/- 0.8% in AV, P < 0.05). At LV catheterization, the difference in HR with AV (453 +/- 24 beats/min) and XK (342 +/- 30 beats/min, P < 0.05) anesthesia was more variable, and no significant differences in systolic or diastolic function were seen in the group as a whole. However, in XK mice with HR <300 beats/min, LVEDP was increased (28 +/- 5 vs. 6.2 +/- 2 mmHg in mice with HR >300 beats/min, P < 0.05), whereas systolic (LV dP/dt(max): 4,402 +/- 798 vs. 8,250 +/- 415 mmHg/s in mice with HR >300 beats/min, P < 0.05) and diastolic (tau: 23 +/- 2 vs. 14 +/- 1 ms in mice with HR >300 beats/min, P < 0.05) function were impaired. Compared with AV, XK produces profound bradycardia with effects on loading conditions and ventricular function. The disparate findings at echocardiography and LV catheterization underscore the importance of comprehensive assessment of LV function in the mouse.

Differential effects of natriuretic peptides and NO on LV function in heart failure and normal dogs

beta-Adrenergic hyporesponsiveness in congestive heart failure (CHF) is mediated, in part, by nitric oxide (NO). NO and brain natriuretic peptide (BNP) share cGMP as a second messenger. Left ventricular (LV) function and inotropic response to intravenous dobutamine (Dob) were assessed during sequential intracoronary infusion of saline, HS-142-1 (a BNP receptor antagonist), and HS-142-1 + N(G)-monomethyl-L-arginine (L-NMMA) in anesthetized dogs with CHF due to rapid pacing and in normal dogs during intracoronary infusion of saline, exogenous BNP, and sodium nitroprusside (SNP). In CHF dogs, intracoronary HS-142-1 did not alter the inotropic response to Dob [percent change in first derivative of LV pressure (% Delta dP/dt) 47 +/- 4% saline vs. 54 +/- 7% HS-142-1, P = not significant]. Addition of intracoronary L-NMMA to HS-142-1 enhanced the response to Dob (% Delta dP/dt 73 +/- 8% L-NMMA + HS-142-1, P < 0.05 vs. H142-1). In normal dogs, intracoronary SNP blunted the inotropic response to Dob (% Delta dP/dt 93 +/- 6% saline vs. 71 +/- 5% SNP, P < 0.05), whereas intracoronary BNP had no effect. In CHF dogs, the time constant of LV pressure decay during isovolumic relaxation increased with intracoronary HS-142-1 (48 +/- 4 ms saline vs. 58 +/- 5 ms HS-142-1, P < 0.05) and further increased with intracoronary L-NMMA (56 +/- 6 ms HS-142-1 vs. 66 +/- 7 ms L-NMMA + HS-142-1, P < 0.05). Endogenous BNP and NO preserve diastolic function in CHF, whereas NO but not BNP inhibits beta-adrenergic responsiveness.

Nesiritide (hBNP): a new class of therapeutic peptide for the treatment of decompensated congestive heart failure

Natriuretic peptides are a family of endogenous peptide hormones with vasodilating, natriuretic, diuretic, and lusitropic properties. Administration of pharmacologic doses of exogenous natriuretic peptides may provide therapeutic benefit in patients with chronic heart failure. In controlled clinical trials, short-term administration of nesiritide (human brain natriuretic peptide) to patients with heart failure is associated with improved resting hemodynamics, modest increases in sodium excretion, evidence of suppression of neurohormonal activation, and improvements in symptoms of heart failure. Additional trials to determine the clinical efficacy and safety of nesiritide are warranted. (c)2001 by CHF, Inc.

Diastolic heart failure in the community

Although it is now widely recognized that isolated diastolic dysfunction can lead to the classic signs and symptoms of congestive heart failure (CHF), this disease process is poorly understood and remains of great interest and concern to cardiovascular disease specialists, as well as to primary care physicians. Recent epidemiologic data have suggested that diastolic heart failure is predominantly a disease of the elderly, the fastest growing segment of our population. Diagnosis is often difficult in this subgroup of patients due to the presence of confounding comorbidities. However, early identification in community-based practices and timely intervention is important due to the significant disability and death that results from this progressive disease process. The poor prognosis of CHF patients with systolic dysfunction is shared by those with isolated diastolic heart failure and preserved systolic function. Further studies of the prevalence, clinical characteristics, and natural history of patients with diastolic dysfunction are needed. This review focuses on the emerging data regarding the prevalence and natural history of diastolic heart failure in the community.

The role of coenzyme Q10 in the pathophysiology and therapy of experimental congestive heart failure in the dog

BACKGROUND

Coenzyme Q10 (CoQ10) is essential for ATP generation and has antioxidant properties. Decreased CoQ10 levels have been reported in human heart failure (CHF), but it remains unclear if this is a conserved feature of CHF. The objective of the study was to determine if tachycardia-induced CHF in the dog is associated with reduced CoQ10 levels. Furthermore, it was hypothesized that CoQ10 supplementation may improve CHF severity by preventing CoQ10 deficiency (if present) or via antioxidant effects.

METHODS AND RESULTS

Serum and myocardial levels of CoQ10 were examined in normal dogs (n = 6), dogs with CHF (control, n = 5), and dogs with CHF treated with CoQ10 (CoQ10; 10 mg/kg/day, n = 5). Serum CoQ10 levels did not change with CHF in control dogs, and myocardial levels were similar to those of normal dogs. CoQ10 therapy increased serum but not myocardial levels of CoQ10. In early CHF, CoQ10-treated dogs had lower filling pressures, and, in severe CHF, CoQ10-treated dogs had less hypertrophy as compared with untreated dogs. Other indices of CHF severity were similar in control and CoQ10-treated dogs.

CONCLUSION

These data indicate that CoQ10 deficiency is not present in this model of CHF. Although dramatic effects on hemodynamics were not observed, CoQ10 supplementation did appear to attenuate the hypertrophic response associated with CHF. Key words: enzymes, cardiomyopathy, hormones, antioxidant.