A functional role for endogenous atrial natriuretic peptide in a canine model of early left ventricular dysfunction

Discovery, validation, and prodrug design of an ACE2 activator for treating bacterial infection-induced lung inflammation

Exacerbated inflammatory responses can be detrimental and pose fatal threats to the host, as exemplified by the global impact of the COVID-19 pandemic, resulting in millions of fatalities. Developing novel drugs to combat the damaging effects of inflammation is essential for both preventive measures and therapeutic interventions. Accumulating evidence suggests that Angiotensin Converting Enzyme 2 (ACE2) possesses the ability to optimize inflammatory responses. However, the clinical applicability of this potential is limited due to the lack of dependable ACE2 activators. In this study, we conducted a screening of an FDA-approved drug library and successfully identified a novel ACE2 activator, termed H4. The activator demonstrated the capability to mitigate lung inflammation caused by bacterial lung infections, effectively modulating neutrophil infiltration. Importantly, to improve the clinical applicability of the poorly water-soluble H4, we developed a prodrug variant with significantly enhanced water solubility while maintaining a similar level of efficacy as H4 in attenuating inflammatory responses in the lungs of mice exposed to bacterial infections. This finding highlights the potential of formulated H4 as a promising candidate for the treatment and prevention of inflammatory diseases, including lung-related conditions.

A mouse model of inherited choline kinase β-deficiency presents with specific cardiac abnormalities and a predisposition to arrhythmia

The CHKB gene encodes choline kinase β, which catalyzes the first step in the biosynthetic pathway for the major phospholipid phosphatidylcholine. Homozygous loss-of-function variants in human CHKB are associated with a congenital muscular dystrophy. Dilated cardiomyopathy is present in some CHKB patients and can cause heart failure and death. Mechanisms underlying a cardiac phenotype due to decreased CHKB levels are not well characterized. We determined that there is cardiac hypertrophy in Chkb^−/− mice along with a decrease in left ventricle size, internal diameter, and stroke volume compared with wildtype and Chkb^+/− mice. Unlike wildtype mice, 60% of the Chkb^+/− and all Chkb^−/− mice tested displayed arrhythmic events when challenged with isoproterenol. Lipidomic analysis revealed that the major change in lipid level in Chkb^+/− and Chkb^−/− hearts was an increase in the arrhythmogenic lipid acylcarnitine. An increase in acylcarnitine level is also associated with a defect in the ability of mitochondria to use fatty acids for energy and we observed that mitochondria from Chkb^−/− hearts had abnormal cristae and inefficient electron transport chain activity. Atrial natriuretic peptide (ANP) is a hormone produced by the heart that protects against the development of heart failure including ventricular conduction defects. We determined that there was a decrease in expression of ANP, its receptor NPRA, as well as ventricular conduction system markers in Chkb^+/− and Chkb^−/− mice.

Molecular Signaling Mechanisms and Function of Natriuretic Peptide Receptor-A in the Pathophysiology of Cardiovascular Homeostasis

The discovery of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP) and their cognate receptors has greatly increased our knowledge of the control of hypertension and cardiovascular homeostasis. ANP and BNP are potent endogenous hypotensive hormones that elicit natriuretic, diuretic, vasorelaxant, antihypertrophic, antiproliferative, and antiinflammatory effects, largely directed toward the reduction of blood pressure (BP) and cardiovascular diseases (CVDs). The principal receptor involved in the regulatory actions of ANP and BNP is guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which produces the intracellular second messenger cGMP. Cellular, biochemical, molecular, genetic, and clinical studies have facilitated understanding of the functional roles of natriuretic peptides (NPs), as well as the functions of their receptors, and signaling mechanisms in CVDs. Transgenic and gene-targeting (gene-knockout and gene-duplication) strategies have produced genetically altered novel mouse models and have advanced our knowledge of the importance of NPs and their receptors at physiological and pathophysiological levels in both normal and disease states. The current review describes the past and recent research on the cellular, molecular, genetic mechanisms and functional roles of the ANP-BNP/NPRA system in the physiology and pathophysiology of cardiovascular homeostasis as well as clinical and diagnostic markers of cardiac disorders and heart failure. However, the therapeutic potentials of NPs and their receptors for the diagnosis and treatment of cardiovascular diseases, including hypertension, heart failure, and stroke have just begun to be expanded. More in-depth investigations are needed in this field to extend the therapeutic use of NPs and their receptors to treat and prevent CVDs.

Cardiac Versus Renal Response to Volume Expansion in Preclinical Systolic Dysfunction With PDEV Inhibition and BNP

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In preclinical systolic dysfunction, defined as left ventricular systolic dysfunction with no heart failure signs or symptoms, impairment in cardiorenal response to volume expansion may lead to symptomatic heart failure. Rescue of this impaired process in preclinical disease may prevent development of symptomatic heart failure.

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In preclinical systolic dysfunction, inhibition of phosphodiesterase-V in combination with exogenous B-type natriuretic peptide administration results in improved cardiac function but worsened renal function in response to acute volume expansion.

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Future studies are needed to further define the physiological effects and long-term outcomes of phosphodiesterase-V inhibition and exogenous BNP administration. Understanding the cardiorenal effects and outcomes of combination phosphodiesterase-V with exogenous B-type natriuretic peptide may affect the clinical management of patients with preclinical systolic dysfunction and renal dysfunction.

Impaired cardiorenal response to acute saline volume expansion in preclinical systolic dysfunction (PSD) may lead to symptomatic heart failure. The objective was to determine if combination phosphodiesterase-V inhibition and exogenous B-type natriuretic peptide (BNP) administration may enhance cardiorenal response. A randomized double-blinded, placebo-controlled study was conducted in 21 subjects with PSD and renal dysfunction. Pre-treatment with tadalafil and subcutaneous BNP resulted in improved cardiac function, as evidenced by improvement in ejection fraction, left atrial volume index, and left ventricular end-diastolic volume. However, there was reduced renal response with reduction in renal plasma flow, glomerular filtration rate, and urine flow. (Tadalafil and Nesiritide as Therapy in Pre-clinical Heart Failure; NCT01544998)

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

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

Differential Regulation of ANP and BNP in Acute Decompensated Heart Failure: Deficiency of ANP

OBJECTIVES

This study investigated the differential regulation of circulating atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in patients with acute decompensated heart failure (ADHF) and tested the hypothesis that a relative deficiency of ANP exists in a subgroup of patients with ADHF.

BACKGROUND

The endocrine heart releases the cardiac hormones ANP and BNP, which play a key role in cardiovascular (CV), renal, and metabolic homeostasis. In heart failure (HF), both plasma ANP and BNP are increased as a compensatory homeostatic response to myocardial overload.

METHODS

ANP and BNP concentrations were measured in a small group of patients with ADHF (n = 112). To support this study's goal, a total of 129 healthy subjects were prospectively recruited to establish contemporary normal values for ANP and BNP. Plasma 3',5'cyclic guanosine monophosphate (cGMP), ejection fraction (EF), and body mass index (BMI) were measured in these subjects.

RESULTS

In cases of ADHF, 74% of patients showed elevated ANP and BNP. Importantly, 26% of patients were characterized as having normal ANP (21% of this subgroup had normal ANP and elevated BNP). Cyclic GMP was lowest in the ADHF group with normal levels of ANP (p < 0.001), whereas BMI and EF were inversely related to ANP levels (p = 0.003).

CONCLUSIONS

Among a subgroup of patients hospitalized with ADHF, the presence of an ANP deficiency is consistent with a differential regulation of ANP and BNP and suggests the existence of a potentially compromised compensatory cardiac endocrine response. These findings have implications for the pathophysiology, diagnostics, and therapeutics of human HF.

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

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

CRRL269: a novel designer and renal-enhancing pGC-A peptide activator

The natriuretic peptides (NPs) B-type NP (BNP) and urodilatin (URO) exert renal protective properties via the particulate guanylyl cyclase A receptor (pGC-A). As a potential renal-enhancing strategy, we engineered a novel designer peptide that we call CRRL269. CRRL269 was investigated in human cell lines and in normal canines to define potential cardiorenal enhancing actions. The mechanism of its cardiorenal selective properties was also investigated. In vitro NP receptor activity was quantified with guanosine 3',5'-cyclic monophosphate generation. In vivo effects were determined in normal canine acute infusion studies. We observed that CRRL269 demonstrated enhanced pGC-A activity in renal compared with nonrenal cell lines. CRRL269 exerted enhanced resistance to neprilysin compared with URO. Importantly, CRRL269 exhibited significant and greater increases in urinary sodium excretion and diuresis, with less blood pressure reduction, than BNP or URO in normal canines. CRRL269 retained potent renin-angiotensin-aldosterone system (RAAS) suppressing properties shared by URO and BNP. Also, CRRL269 exerted less arterial relaxation and higher cAMP cardiomyocytes generation than BNP. CRRL269 possessed superior renal and pGC-A activating properties compared with BNP or URO in vitro. CRRL269 exerted enhanced renal actions while suppressing RAAS in vivo and with less hypotension compared with URO or BNP. Together, our study suggests that CRRL269 is a promising innovative renal-enhancing drug, with favorable protective actions targeting cardiorenal disease states through the pGC-A receptor.

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.

Importance of endogenous compensatory vasoactive peptides in broadening the effects of inhibitors of the renin-angiotensin system for the treatment of heart failure

The magnitude of the clinical benefits produced by inhibitors of the renin-angiotensin system in heart failure has been modest, possibly because of the ability of renin-angiotensin activity to escape from suppression during long-term treatment. Efforts to intensify pharmacological blockade by use of dual inhibitors that interfere with the renin-angiotensin system at multiple sites have not yielded consistent incremental clinical benefits, but have been associated with serious adverse reactions. By contrast, potentiation of endogenous compensatory vasoactive peptides can act to enhance the survival effects of inhibitors of the renin-angiotensin system, as evidenced by trials that have compared angiotensin-converting enzyme inhibitors with drugs that inhibit both the renin-angiotensin system and neprilysin. Several endogenous vasoactive peptides act as adaptive mechanisms, and their augmentation could help to broaden the benefits of renin-angiotensin system inhibitors for patients with heart failure.

The natriuretic peptides system in the pathophysiology of heart failure: from molecular basis to treatment

After its discovery in the early 1980s, the natriuretic peptide (NP) system has been extensively characterized and its potential influence in the development and progression of heart failure (HF) has been investigated. HF is a syndrome characterized by the activation of different neurohormonal systems, predominantly the renin-angiotensin (Ang)-aldosterone system (RAAS) and the sympathetic nervous system (SNS), but also the NP system. Pharmacological interventions have been developed to counteract the neuroendocrine dysregulation, through the down modulation of RAAS with ACE (Ang-converting enzyme) inhibitors, ARBs (Ang receptor blockers) and mineralcorticoid antagonists and of SNS with β-blockers. In the last years, growing attention has been paid to the NP system. In the present review, we have summarized the current knowledge on the NP system, focusing on its role in HF and we provide an overview of the pharmacological attempts to modulate NP in HF: from the negative results of the study with neprilysin (NEP) inhibitors, alone or associated with an ACE inhibitor and vasopeptidase inhibitors, to the most recently and extremely encouraging results obtained with the new pharmacological class of Ang receptor and NEP inhibitor, currently defined ARNI (Ang receptor NEP inhibitor). Indeed, this new class of drugs to manage HF, supported by the recent results and a vast clinical development programme, may prompt a conceptual shift in the treatment of HF, moving from the inhibition of RAAS and SNS to a more integrated target to rebalance neurohormonal dysregulation in HF.

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).

Effect of Breed on Plasma Endothelin-1 Concentration, Plasma Renin Activity, and Serum Cortisol Concentration in Healthy Dogs

BACKGROUND

There are breed differences in several blood variables in healthy dogs.

OBJECTIVE

Investigate breed variation in plasma endothelin-1 (ET-1) concentration, plasma renin activity, and serum cortisol concentration.

ANIMALS

Five-hundred and thirty-one healthy dogs of 9 breeds examined at 5 centers (2-4 breeds/center).

METHODS

Prospective observational study. Circulating concentrations of ET-1 and cortisol, and renin activity, were measured using commercially available assays. Absence of organ-related or systemic disease was ensured by thorough clinical investigations, including blood pressure measurement, echocardiography, ECG, blood and urine analysis.

RESULTS

Median ET-1 concentration was 1.29 (interquartile range [IQR], 0.97-1.82) pg/mL, median cortisol concentration 46.0 (IQR, 29.0-80.8) nmol/L, and median renin activity 0.73 (IQR, 0.48-1.10) ng/mL/h in all dogs. Overall, breed differences were found in ET-1 and cortisol concentrations, and renin activity (P < .0001 for all). Pair-wise comparisons between breeds differed in 67% of comparisons for ET-1, 22% for cortisol, and 19% for renin activity, respectively. Within centers, breed differences were found at 5/5 centers for ET-1, 4/5 centers for cortisol, and 2/5 centers for renin activity. Newfoundlands had highest median ET-1 concentration, 3 times higher than Cavalier King Charles Spaniels, Doberman Pinschers, and Dachshunds. Median renin activity was highest in Dachshunds, twice the median value in Newfoundlands and Boxers. Median cortisol concentration was highest in Finnish Lapphunds, almost 3 times higher than in Boxers.

CONCLUSIONS AND CLINICAL IMPORTANCE

Breed variation might be important to take into consideration when interpreting test results in clinical studies.

Chronic subcutaneous brain natriuretic peptide therapy in asymptomatic systolic heart failure

AIMS

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

METHODS AND RESULTS

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

CONCLUSION

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

Dietary sodium modulation of aldosterone activation and renal function during the progression of experimental heart failure

AIMS

Aldosterone activation is central to the sodium–fluid retention that marks the progression of heart failure (HF). The actions of dietary sodium restriction, a mainstay in HF management, on cardiorenal and neuroendocrine adaptations during the progression of HF are poorly understood. The study aim was to assess the role of dietary sodium during the progression of experimental HF.

METHODS AND RESULTS

Experimental HF was produced in a canine model by rapid right ventricular pacing which evolves from early mild HF to overt, severe HF. Dogs were fed one of three diets: (i) high sodium [250 mEq (5.8 g) per day, n =6]; (ii) standard sodium [58 mEq (1.3 g) per day, n =6]; and (iii) sodium restriction [11 mEq (0.25 g) per day, n =6]. During the 38-day study, haemodynamics, renal function, plasma renin activity (PRA), and aldosterone were measured. Changes in haemodynamics at 38 days were similar in all three groups, as were changes in renal function. Aldosterone activation was demonstrated in all three groups; however, dietary sodium restriction, in contrast to high sodium, resulted in early (10 days) activation of PRA and aldosterone. High sodium demonstrated significant suppression of aldosterone activation over the course of HF progression.

CONCLUSIONS

Excessive dietary sodium restriction particularly in early stage HF results in early aldosterone activation, while normal and excess sodium intake are associated with delayed or suppressed activation. These findings warrant evaluation in humans to determine if dietary sodium manipulation, particularly during early stage HF, may have a significant impact on neuroendocrine disease progression.

Novel vasodilators in heart failure

Heart failure is an important public health problem that is increasing in prevalence throughout the world. Not only is this condition common, but it is associated with significant morbidity and mortality as well as high costs to medical care systems. Vasodilator drugs help unload the heart and may have other effects that could benefit heart failure patients. Consequently, they have emerged as an important therapeutic approach for patients with this condition. Novel vasodilator therapies that are currently in development target new pathways, potentially giving clinicians alternate options for improving outcomes in this vulnerable population. This review focuses on investigational drugs that have the ability to dilate blood vessels amongst their therapeutic properties. These drugs include the natriuretic peptides that activate particulate guanylate cyclase, the novel agent cinaciguat that activates the soluble guanylate cyclase system, and finally a recombinant form of the naturally occurring vasodilating agent relaxin, a hormone that mediates many of the changes that allows the cardiovascular system to successfully adapt to pregnancy.

Natriuretic peptides in developing medaka embryos: implications in cardiac development by loss-of-function studies

Cardiac natriuretic peptides (NPs), atrial NP (ANP) and B-type NP (BNP), and their receptor, guanylyl cyclase (GC)-A have attracted attention of many basic and clinical researchers because of their potent renal and cardiovascular actions. In this study, we used medaka, Oryzias latipes, as a model species to pursue the physiological functions of NPs because it is a suitable model for developmental analyses. Medaka has two ligands, BNP and C-type NP3 (CNP3) (but not ANP), that have greater affinity for the two O. latipes GC-A receptors (OLGC), OLGC7 and OLGC2, respectively. CNP3 is the ancestral molecule of cardiac NPs. Initially, we examined developmental expression of cardiac NP/receptor combinations, BNP/OLGC7 and CNP3/OLGC2, using quantitative real-time PCR and in situ hybridization. BNP and CNP3 mRNA increased at stages 25 (onset of ventricular formation) and 22 (appearance of heart anlage), respectively, whereas both receptor mRNAs increased at as early as stage 12. BNP/OLGC7 transcripts were found in arterial/ventricular tissues and CNP3/OLGC2 transcripts in venous/atrial tissues by in situ hybridization. Thus, BNP and CNP3 can act locally on cardiac myocytes in a paracrine/autocrine fashion. Double knockdown of BNP/OLGC7 genes impaired ventricular development by causing hypoplasia of ventricular myocytes as evidenced by reduced bromodeoxyuridine incorporation. CNP3 knockdown induced hypertrophy of atria and activated the renin-angiotensin system. Collectively, it appears that BNP is important for normal ventricular, whereas CNP3 is important for normal atrial development and performance, a role usually taken by ANP in other vertebrates. The current study provides new insights into the role of cardiac NPs in cardiac development in vertebrates.

Biomarkers in acutely decompensated heart failure with preserved or reduced ejection fraction

BACKGROUND

Acute decompensated heart failure (ADHF) occurs with preserved (heart failure with preserved ejection fraction [HFpEF] ≥50%) or reduced (heart failure with reduced ejection fraction [HFrEF] <50%) ejection fraction. Natriuretic peptide (NP) levels are lower in HFpEF than HFrEF. We hypothesized that lower NP levels in HFpEF may be associated with other differences in biomarkers, specifically, renin-angiotensin-aldosterone system (RAAS) activation, oxidative stress, and a biomarker that reflects collagen synthesis.

METHODS

In this prespecified ancillary analysis of patients with ADHF enrolled in the Diuretic Optimization Strategies Evaluation study, clinical features and N-terminal pro-B-type NP, cystatin C, plasma renin activity, aldosterone, oxidative stress (uric acid), and procollagen type III N-terminal peptide were compared in HFpEF and HFrEF at enrollment and 60-day follow-up.

RESULTS

Compared with HFrEF (n = 219), HFpEF (n = 81) patients were older, heavier, more commonly female, less treated with RAAS antagonists, but with similar New York Heart Association class, jugular venous pressure, and edema severity. N-terminal pro-B-type NP was lower, and systolic blood pressure and cystatin C were higher in HFpEF. Despite higher systolic blood pressure and less RAAS antagonist use in HFpEF, plasma renin activity and aldosterone levels were similar in HFpEF and HFrEF as were uric acid and procollagen type III N-terminal peptide levels. Changes in biomarker levels from enrollment to 60 days were similar between HFrEF (n = 149) and HFpEF (n = 50).

CONCLUSION

Lower NP levels in decompensated HFpEF occur in association with similar ADHF severity, more impaired vascular and renal function but similar elevation of biomarkers that reflect RAAS activation, oxidative stress, and collagen synthesis as in HFrEF.

Zinc and copper levels in severe heart failure and the effects of atrial fibrillation on the zinc and copper status

Oxidative stress is involved in the pathogenesis of congestive heart failure (CHF). Some trace elements serve as antioxidant defenses. The purpose of this study was to analyze the effect of atrial fibrillation (AF) on zinc (Zn) and copper (Cu) levels in patients with advanced CHF. In this prospective study, serum Zn and Cu levels in 78 patients with clinically advanced CHF, i.e., New York Heart Association (NYHA) functional class III or IV (40 patients with AF and 38 in sinus rhythm) were measured using atomic absorption spectrophotometry. All patients also had a left ventricular ejection fraction (EF) of <35%. We recruited 40 volunteers with nearly the same age and weight as control. They had normal EF. There was no significant difference between patients with AF and those with sinus rhythm regarding serum Zn and Cu levels. However, both groups showed significant hypozincemia (p < 0.000) and a decreased Zn/Cu ratio (p < 0.03) compared with control group. Serum Cu levels were similar in the two groups and did not differ significantly from the control group. In patients with advanced CHF, irrespective of the rhythm, profound hypozincemia, and a decreased Zn/Cu ratio were present, which could be secondary to the activation of the renin-angiotensin-aldosterone system and CHF medications. The results suggest the need for more studies focusing on possible benefits with Zn nutriceutical replacement in patients with advanced CHF.

Impaired natriuretic and renal endocrine response to acute volume expansion in pre-clinical systolic and diastolic dysfunction

OBJECTIVES

We hypothesized an impaired renal endocrine and natriuretic response to volume expansion (VE) in humans with pre-clinical systolic dysfunction (PSD) and pre-clinical diastolic dysfunction (PDD). We further hypothesized that exogenous B-type natriuretic peptide (BNP) could rescue an impaired natriuretic response in PSD and PDD.

BACKGROUND

Recent reports suggest that in early systolic heart failure (HF), there is an impaired natriuretic response to acute VE.

METHODS

PSD was defined as left ventricular ejection fraction <40% without HF symptoms. PDD was defined as ejection fraction >50%, moderate to severe diastolic dysfunction by Doppler criteria, and no HF symptoms. A double-blinded, placebo-controlled, crossover study was employed to determine the renal response to VE (0.25 ml/kg/min of normal saline for 60 min) in the presence and absence of exogenous BNP. Twenty healthy control subjects, 20 PSD subjects, and 18 PDD subjects participated.

RESULTS

In healthy control subjects, urinary cyclic guanosine monophosphate (cGMP) and natriuresis increased after VE. In contrast, among PSD and PDD subjects, there was a paradoxical decrease in urinary cGMP and attenuated natriuresis. Pre-treatment with subcutaneous BNP resulted in similar increases in both urinary cGMP and natriuresis among healthy normal, PSD, and PDD subjects.

CONCLUSIONS

In PSD and PDD, there is impaired renal cGMP activation, which contributes to impaired natriuresis in response to VE. Impaired activation of urinary cGMP and reduced natriuresis may contribute to volume overload and the progression of HF among PSD and PDD subjects. Importantly, the impaired renal excretory response to VE is rescued by exogenous BNP in PSD and PDD.

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.

Brain natriuretic peptide in pulmonary arterial hypertension: biomarker and potential therapeutic agent

B-type natriuretic peptide (BNP) is a member of the natriuretic peptide family, a group of widely distributed, but evolutionarily conserved, polypeptide mediators that exert myriad cardiovascular effects. BNP is a potent vasodilator with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. Circulating levels of BNP correlate with mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) in patients with pulmonary arterial hypertension (PAH). Elevated plasma BNP levels are associated with increased mortality in patients with PAH and a fall in BNP levels after therapy is associated with improved survival. These findings have important clinical implications in that a noninvasive blood test may be used to identify PAH patients at high-risk of decompensation and to guide pulmonary vasodilator therapy. BNP also has several biologic effects that could be beneficial to patients with PAH. However, lack of a convenient method for achieving sustained increases in circulating BNP levels has impeded the development of BNP as a therapy for treating pulmonary hypertension. New technologies that allow transdermal or oral administration of the natriuretic peptides have the potential to greatly accelerate research into therapeutic use of BNP for cor pulmonale and pulmonary vascular diseases. This review will examine the basic science and clinical research that has led to our understanding of the role of BNP in cardiovascular physiology, its use as a biomarker of right ventricular function and its therapeutic potential for managing patients with pulmonary vascular disease.

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.

Distinct roles for renal particulate and soluble guanylyl cyclases in preserving renal function in experimental acute heart failure

Worsening renal function in the setting of human acute heart failure (AHF) predicts poor outcomes, such as rehospitalization and increased mortality. Understanding potential renoprotective mechanisms is warranted. The guanylate cyclase (GC) enzymes and their second messenger cGMP are the target of two important circulating neurohumoral systems with renoprotective properties. Specifically, natriuretic peptides (NP) released from the heart with AHF target particulate GC in the kidney, while the nitric oxide (NO) system is an activator of renal soluble GC. We hypothesized that both systems are essential to preserve renal excretory and hemodynamic function in AHF but with distinct roles. We investigated these roles in three groups of anesthetized dogs (6 each) with AHF induced by rapid ventricular pacing. After a baseline AHF clearance, each group received intrarenal vehicle (control), N(G)-monomethyl-l-arginine (l-NMMA), a competitive NO inhibitor (50 microg.kg(-1).min(-1)) or a specific NP receptor antagonist, HS-142-1 (0.5 mg/kg). We observed that intrarenal l-NMMA decreased renal blood flow (RBF) without significant decreases in glomerular filtration rate (GFR), urinary sodium excretion (UNaV), or urinary cGMP. In contrast, HS-142-1 resulted in a decrease in UNaV and cGMP excretion together with a reduction in GFR and an increase in distal fractional tubular sodium reabsorption. We conclude that in AHF, the NP system plays a role in maintaining sodium excretion and GFR, while the function of NO is in the maintenance of RBF. These studies have both physiological and therapeutic implications warranting further research into cardiorenal interactions in this syndrome of AHF.

Mineralocorticoid escape by the kidney but not the heart in experimental asymptomatic left ventricular dysfunction

Unlike healthy subjects, overt congestive heart failure cannot "escape" the sodium- and water-retaining actions of mineralocorticoid excess. It is undefined whether escape occurs in asymptomatic left ventricular dysfunction (ALVD), which is characterized by preserved sodium homeostasis, natriuretic peptide activation, and normal circulating aldosterone. We hypothesized that, in ALVD, mineralocorticoid excess with exogenous deoxycorticosterone acetate (DOCA) would overwhelm renal compensatory mechanisms, resulting in sodium and water retention, and promote renal and cardiac collagen deposition. ALVD was induced in 2 groups (N=5 each) of dogs by tachypacing at 180 bpm. Urine was collected daily and blood drawn at baseline and days 2, 5, 8, and 11. One group served as control (ALVD), and the other received DOCA (ALVD+DOCA) starting at day 2 of pacing. Urine flow and sodium excretion were unchanged in the ALVD group. In ALVD+DOCA, urine flow and sodium excretion decreased on the first 2 days DOCA was given but normalized starting day 4. Urine flow and urinary cGMP excretion increased in ALVD+DOCA after DOCA escape. Plasma atrial natriuretic peptide, B-type natriuretic peptide, and cGMP increased equally in both groups. There were no differences in cardiorenal and hemodynamic parameters in an acute study on day 11. Although renal collagen area fraction was similar, left ventricular collagen area fraction in ALVD+DOCA was significantly higher than in ALVD (3.3+/-0.4% versus 2.0+/-0.2%; P=0.012). We conclude that ALVD can escape the sodium- and water-retaining effects of mineralocorticoid excess. Despite renal escape, increased left ventricular collagen deposition suggests that the heart but not the kidney failed to escape the tissue effects of DOCA.

Maximizing the renal cyclic 3'-5'-guanosine monophosphate system with type V phosphodiesterase inhibition and exogenous natriuretic peptide: a novel strategy to improve renal function in experimental overt heart failure

Type V phosphodiesterase (PDE V) metabolizes cyclic guanosine monophosphate (cGMP) and is abundant in the kidney and vasculature and was found recently in the heart. Sildenafil is a PDE V inhibitor that is used clinically for erectile dysfunction. Brain natriuretic peptide (BNP) is a cardiac peptide with vasodilating, lusitropic, and natriuretic properties that are mediated via cGMP. It was hypothesized that chronic inhibition of PDE V (PDE VI) will enhance the renal actions of exogenous BNP by potentiating the renal cGMP. The cardiorenal and humoral function was determined at baseline in two groups of dogs with pacing-induced overt chronic heart failure (CHF; 240 bpm for 10 d): Group 1 (n = 6) received Sildenafil 50 mg orally three times daily during the 10 d of pacing, and group 2 (n = 5) received no PDE V inhibitor. The response to acute subcutaneous BNP (5 microg/kg) administration also was compared in both groups on day 11. The GFR was assessed by inulin clearance (P < 0.05). There was no improvement of renal function in group 1 after 10 d of PDE VI as compared with group 2, despite having higher cardiac output (P < 0.05). Group 1 had significantly higher plasma (44 +/- 2 versus 21 +/- 3 pmol/ml; P < 0.05) and urinary cGMP (4219 +/- 900 versus 1954 +/- 300 pmol/min; P < 0.05) as compared with group 2. With acute subcutaneous BNP administration, group 1 had a natriuretic and diuretic response that was associated with an increase in GFR (30 +/- 6 to 45 +/- 6 ml/min; P < 0.05) and that was not observed in group 2 (25 +/- 6 to 29 +/- 4 ml/min). Plasma BNP increased to a similar extent in both groups with subcutaneous BNP. In contrast, group 1 had a much greater urinary cGMP excretion (4219 +/- 900 to 8600 +/- 1600 pmol/min; P < 0.05) as compared with group 2 (1954 +/- 300 to 3580 +/- 351 pmol/min; P < 0.05). In experimental overt CHF, chronic administration of PDE V inhibitor did not enhance renal function despite an improvement in cardiac output. However, chronic PDE VI significantly enhanced the renal hemodynamic and excretory responses to exogenous BNP. This study supports a role for PDE V as contributing to renal maladaptation in a model of experimental overt CHF and the strategy of maximizing the renal cGMP system by combined PDE VI and natriuretic peptides in CHF to improve renal function.

Natriuretic peptides in patients with atrial fibrillation and advanced chronic heart failure: determinants and prognostic value of (NT-)ANP and (NT-pro)BNP

AIMS

To study the determinants of natriuretic peptides in advanced chronic heart failure (CHF) patients with and without atrial fibrillation (AF) and to evaluate the prognostic value of natriuretic peptides in AF compared with sinus rhythm patients with advanced CHF.

METHODS AND RESULTS

The study group comprised 354 advanced CHF patients [all New York Heart Association (NYHA) III/IV], including 76 AF patients. AF patients were older (70+/-7 vs. 67+/-8; P=0.01), and non-ischaemic CHF was more common (42 vs. 19%; P=0.002) than in sinus rhythm patients, but left-ventricular ejection fraction was comparable (0.23+/-0.08 vs. 0.24+/-0.07; P=ns). At baseline, (NT-)ANP and NT-proBNP levels were significantly higher in AF patients, compared with those in sinus rhythm. By multivariate regression analysis, AF was identified as independent determinant of (NT-)ANP, but not of (NT-pro)BNP levels. After a mean follow-up of 3.2+/-0.9 (range 0.4-5.4) years, cardiovascular mortality was comparable (55 vs. 47%; P=ns). In both groups, AF and sinus rhythm, NT-proBNP [AF: adjusted HR 5.8 (1.3-25.4), P=0.02; sinus rhythm: adjusted HR 3.1 (1.7-5.7), P<0.001] was an independent risk indicator of cardiovascular mortality.

CONCLUSION

In advanced CHF patients, AF affects (NT-)ANP levels, but not (NT-pro)BNP levels. NT-proBNP is an independent determinant of prognosis in advanced CHF, irrespective of the rhythm, AF, or sinus rhythm.

Effects of omapatrilat on cardiac nerve sprouting and structural remodeling in experimental congestive heart failure

BACKGROUND

Congestive heart failure (CHF) results in decreased cardiac sympathetic innervation.

OBJECTIVES

The purpose of this study was to test the hypothesis that therapy with the vasopeptidase inhibitor omapatrilat (OMA) attenuates cardiac neuronal remodeling in CHF.

METHODS

We induced CHF in dogs with rapid ventricular pacing for 5 weeks with (CHF+OMA group, n = 8) or without (CHF group, n = 10) concomitant OMA treatment (10 mg/kg twice daily). Cardiac catheterization and echocardiography were performed to determine cardiac structure and hemodynamic parameters. Myocardial nerve density was determined by immunocytochemical staining with anti-growth associated protein 43 (GAP43) and anti-tyrosine hydroxylase (TH) antibodies. Seven normal dogs were used as histologic controls.

RESULTS

In the CHF group, ascites developed in 3 dogs and 4 dogs died, compared with no ascites or death in the CHF+OMA group (P = .07). In the 6 CHF dogs that survived, all had atrial fibrosis, severely depressed left ventricular systolic function, and increased atrial and ventricular chamber size. OMA treatment decreased the atrial and ventricular chamber sizes and the degree of atrial fibrosis. Most CHF dogs showed severe myocardial denervation, although some showed normal or abnormally high nerve counts. OMA treatment prevented heterogeneous reduction of nerve density. The left ventricular TH-positive nerve densities were 128 +/- 170 microm(2)/mm(2), 261 +/- 185 microm(2)/mm(2), and 503 +/- 328 microm(2)/mm(2) (P < .05), and the atrial GAP43-positive nerve densities were 1,683 +/- 1,365 microm(2)/mm(2), 305 +/- 368 microm(2)/mm(2), and 1,278 +/- 1,479 microm(2)/mm(2) (P < .05) for the control, CHF, and CHF+OMA groups, respectively.

CONCLUSION

CHF results in heterogeneous cardiac denervation. Long-term OMA treatment prevented the reduction of nerve density and promoted beneficial cardiac structural remodeling.

Bioenergetic protection of failing atrial and ventricular myocardium by vasopeptidase inhibitor omapatrilat

Deficient bioenergetic signaling contributes to myocardial dysfunction and electrical instability in both atrial and ventricular cardiac chambers. Yet, approaches capable to prevent metabolic distress are only partially established. Here, in a canine model of tachycardia-induced congestive heart failure, we compared atrial and ventricular bioenergetics and tested the efficacy of metabolic rescue with the vasopeptidase inhibitor omapatrilat. Despite intrinsic differences in energy metabolism, failing atria and ventricles demonstrated profound bioenergetic deficiency with reduced ATP and creatine phosphate levels and compromised adenylate kinase and creatine kinase catalysis. Depressed phosphotransfer enzyme activities correlated with reduced tissue ATP levels, whereas creatine phosphate inversely related with atrial and ventricular load. Chronic treatment with omapatrilat maintained myocardial ATP, the high-energy currency, and protected adenylate and creatine kinase phosphotransfer capacity. Omapatrilat-induced bioenergetic protection was associated with maintained atrial and ventricular structural integrity, albeit without full recovery of the creatine phosphate pool. Thus therapy with omapatrilat demonstrates the benefit in protecting phosphotransfer enzyme activities and in preventing impairment of atrial and ventricular bioenergetics in heart failure.

Corin gene minor allele defined by 2 missense mutations is common in blacks and associated with high blood pressure and hypertension

BACKGROUND

The natriuretic peptide system contributes to blood pressure regulation. Atrial and brain natriuretic peptides are cleaved into smaller biologically active molecules by corin, a transmembrane serine protease expressed in cardiomyocytes.

METHOD AND RESULTS

This genotype-phenotype genetic association study included replication samples and genomic control to correct for population stratification. Sequencing of the human corin gene identified 2 nonsynonymous, nonconservative single nucleotide polymorphisms (Q568P and T555I) in near-complete linkage disequilibrium, thus describing a single minor I555 (P568) corin gene allele. This allele was present in the heterozygote state in &12% of blacks but was extremely rare in whites (<0.5% were homozygous for the minor allele). In our primary population sample, the Dallas Heart Study, after adjustment for potential confounders, including population stratification, the corin I555 (P568) allele remained independently associated with increased risk for prevalent hypertension (odds ratio, 1.63; 95% CI, 1.11 to 2.38; P=0.013). The corin I555 (P568) allele also was associated with higher systolic blood pressure in subjects not using antihypertensive medication in unadjusted (133.7+/-20.7 versus 129.4+/-17.4 mm Hg; P=0.029) and adjusted (132.5+/-1.6 versus 128.9+/-0.6 mm Hg; P=0.029) analyses. The independent association of the minor corin allele with increased risk for prevalent hypertension was confirmed in the Multi-Ethnic Study of Atherosclerosis (odds ratio, 1.50; 95% CI, 1.09 to 2.06; P=0.014). In addition, the association of the minor corin I555 (P568) allele with higher systolic blood pressure was confirmed in adjusted analysis in the Chicago Genetics of Hypertension Study (125.8+/-1.9 versus 121.4+/-0.7 mm Hg; P=0.03).

CONCLUSIONS

The corin I555 (P568) allele is common in blacks and is associated with higher blood pressure and an increased risk for prevalent hypertension.

Natriuretic and antialdosterone actions of chronic oral NEP inhibition during progressive congestive heart failure

BACKGROUND

Neutral endopeptidase (NEP) degrades atrial natriuretic peptide (ANP) that via cyclic guanosine monophosphate (cGMP) is natriuretic and aldosterone-inhibiting. We hypothesized that chronic oral NEP inhibition (NEPI), initiated in early experimental congestive heart failure (CHF), would delay onset of decreases in sodium excretion during the progression of CHF and, in the severe phase, suppress aldosterone activation and reduce the magnitude of sodium retention. We also hypothesized that chronic NEPI during progressive CHF (PCHF) would improve the natriuretic response to acute volume expansion.

METHODS

In a novel canine model that progresses over 38 days from early to moderate and finally severe CHF, we defined the actions of chronic NEPI (candoxatril, 10 mg/kg, orally, twice a day) upon cardiorenal and neurohumoral function as well as the clinical well being of treated and untreated dogs in CHF.

RESULTS

From baseline through the moderate phase of CHF, NEPI maintained sodium excretion. In contrast, in moderate CHF, sodium excretion was reduced compared to the early phase in the controls. In severe CHF, sodium excretion was higher with NEPI compared to control. Chronic NEPI also resulted in lower plasma aldosterone as compared to controls. In severe CHF, the natriuretic response to acute saline volume expansion was enhanced with oral NEPI as compared to control.

CONCLUSION

This study supports the conclusion that chronic oral NEPI delays the onset of reduction in sodium excretion during the transition from early to severe CHF in this model of PCHF. This therapeutic strategy also improved the natriuretic response to acute volume expansion in severe CHF while enhancing ANP and suppressing aldosterone activation. Thus, these studies demonstrated a selective renal and adrenal action of chronic NEPI in heart failure indicating a therapeutic potential.

Natriuretic peptides as prognostic and diagnostic markers in Chagas' disease

Atrial natriuretic factor (ANF) is a hormone secreted predominantly from atrial myocardium in response to changes in wall tension. Chagas' disease is caused by the parasite Trypanosom cruzi (T. cruzi), the heart being one of the most affected organs, resulting in myocarditis and chronic cardiomyopathy. The inflammatory response of the myocardium may be the result of factors such as ischemia, direct parasite invasion, and autoimmune mechanisms. In this review, we discuss the current knowledge about ANF in Chagas' disease and describe our findings in studying: (1) the development of chagasic cardiomyophathy in T. cruzi-infected rats and its relationship with plasma ANF levels; (2) the evolution of plasma ANF in chagasic patients in different stages (asymptomatic, with conduction defects and with chronic heart failure [CHF]); and (3) the possible usefulness of plasma ANF as a prognostic factor of development of myocardial compromise and survival. In rats, the elevated ANF levels found could mirror the inflammatory response of myocardial cells to acute T. cruzi infection and of progressive failure of cardiac function in the chronic infection. In patients, plasma ANF could be a sensitive marker capable of detecting gradual impairments in cardiac function and poor survival in CHF patients and of myocardiopathy development in the asymptomatic state.

Mechanisms of neurohormonal activation in chronic congestive heart failure: pathophysiology and therapeutic implications

Patients with chronic congestive heart failure have a sequential and incessant activation of those neurohormonal systems, which control body fluids, cardiac output and systemic blood pressure. Neurohormonal activation is initially selective and regional. Generalized activation is a late event in the natural history of congestive heart failure. Although the ultimate stimulus responsible for the activation of these neurohormonal systems is unknown, a decreased cardiac output and diminished effective blood volume have been proposed as the responsible mechanisms. However, extensive clinical and experimental research suggest that cardiac remodeling and loading of low-pressure cardiac receptors with sympathetic afferents could be the triggering events followed by unloading of high-pressure carotid receptors by decreased cardiac output and diminished effective blood volume.

Recent advances in natriuretic peptides in congestive heart failure

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted by the heart and play important roles in the compensation of congestive heart failure with their vasodilating, natriuretic, antiproliferative, lusitropic and neurohumoral-modulating properties. Based on these beneficial properties, exogenous BNP was developed as a new treatment for congestive heart failure and approved in the US for acute decompensated heart failure. New therapeutic strategies for heart failure that are currently being investigated include chronic subcutaneous BNP administration and intermittent BNP infusions. Furthermore, strategies combining exogenous BNP with an inhibitor of the BNP-degrading enzyme neutral endopeptidase could contribute to maximising the actions of BNP and reduce the amount of exogenous BNP needed.

The natriuretic peptides and their role in disorders of right heart dysfunction and pulmonary hypertension

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are increased in conditions with cardiac ventricular volume and pressure overload. The general physiological and potential therapeutic roles of natriuretic peptides in respiratory disease, right ventricular (RV) dysfunction, and pulmonary arterial hypertension (PAH) are reviewed. BNP levels can be used to differentiate between dyspneic patients with a pure respiratory defect and those with RV dysfunction. BNP levels also correlate with mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) in patients with PAH (atrial septal defect, chronic thromboembolic disease, and scleroderma). BNP is a predictor of mortality in patients with primary pulmonary hypertension (PPH). These are important clinical implications in that a noninvasive blood test may be used to identify high-risk patients for more invasive procedures such as cardiac catheterization. BNP or NT-proBNP measurements may also be used to guide therapy (e.g., pulmonary vasorelaxants) in PAH since upregulation of the natriuretic peptide pathway has been shown to reduce cardiac hypertrophy and PAH. Additionally, there may be therapeutic potential via recombinant BNP or neutral endopeptidase inhibitors in RV dysfunction and PAH.

Cardiorenal syndrome in decompensated heart failure: Prognostic and therapeutic implications

Various lines of evidence implicate impaired renal function as an important prognostic indicator in patients with congestive heart failure (CHF). Conventional diuretics may aggravate renal dysfunction and can result in neurohumoral activation. Evolving new therapeutic strategies that enhance renal function include administration of B-type natriuretic peptide, adenosine and vasopressin antagonists, and ultrafiltration methods. Prospective studies are needed to evaluate whether these new renal-enhancing strategies will improve patient outcome in CHF.

Implications of the natriuretic peptide system in the pathogenesis of heart failure: diagnostic and therapeutic importance

The natriuretic peptide family consists of at least 3 structurally similar peptides: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). Under normal conditions, ANP is synthesized by the atrium and released in response to atrial stretch. This peptide plays an important role in sodium and water homeostasis and is involved in cardiovascular function. In contrast, BNP is synthesized primarily by the ventricles, and its circulatory concentrations are significantly elevated in profound congestive heart failure (CHF). While both plasma levels of ANP and BNP have been found to be increased in patients with various heart diseases, the elevation in circulatory BNP correlates better than ANP with the severity of CHF. Therefore, plasma BNP has been suggested (and lately used) to aid in the accurate diagnosis of heart failure in patients admitted to the emergency room with symptoms of decompensated heart failure. Furthermore, circulatory BNP has been utilized as a prognostic marker in CHF as well as a hormone guide in the evaluation of the efficacy of the conventional treatment of this disease state. In light of the cardiovascular and renal effects of BNP, which most likely exceed those of ANP, the former has been used as a therapeutic agent for the treatment of patients with acute severe CHF. Intravenous infusion of BNP into patients with sustained ventricular dysfunction causes a balanced arterial and venous vasodilatation that has been shown to result in rapid reduction in ventricular filling pressure and reversal of heart failure symptoms, such as dyspnea and acute hemodynamic abnormalities. Thus, the goal of this article is to review the physiology and pathophysiology of natriuretic peptides and the potential use of their circulating levels for diagnosis and treatment of heart failure.

A-type and B-type natriuretic peptides in cardiac surgical procedures

This study was performed to determine the secretion pattern and prognostic value of A-type (ANP) and B-type (BNP) natriuretic peptide in patients undergoing cardiac surgical procedures. We measured ANP and BNP in patients undergoing coronary artery bypass grafting (CABG) with (n = 28) or without (n = 32) ventricular dysfunction and in patients undergoing mitral (n = 21) or aortic (n = 24) valve replacement, respectively. Postoperative mortality was recorded up to 730 days after operation. ANP, but not BNP, concentrations were closely associated with volume reloading of the heart after aortic cross-clamp in all patients. The secretion pattern of BNP during surgery was much less uniform. BNP, but not ANP, concentrations correlated with aortic cross-clamp time (r(2) = 0.32; P = 0.006) and postoperative troponin I concentrations (r(2) = 0.22; P = 0.0009) in bypass patients, and preoperative BNP increases were associated with a more frequent postoperative (2-yr) mortality in these patients. Markedly increased preoperative BNP concentrations in mitral (3-fold) and aortic (14-fold) valve disease patients did not further increase during cardiopulmonary surgery. The data suggest that ANP is primarily influenced by intravascular volume reloading of the heart after cross-clamp, whereas the secretion of BNP is related to other factors, such as duration of ischemia and long-term left ventricular pressure and/or excessive intravascular volume. BNP, but not ANP, was shown to be a mortality risk predictor in patients undergoing CABG.

IMPLICATIONS

A-type natriuretic peptide is primarily influenced by volume reloading of the heart after cross-clamp, whereas the secretion of B-type natriuretic peptide (BNP) is related to the duration of ischemia and long-term left ventricular pressure and/or volume overload. Preoperative BNP, but not postoperative BNP, concentrations predict long-term outcome after coronary artery bypass grafting.

Mechanisms of renal hyporesponsiveness to ANP in heart failure

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

Revisiting salt and water retention: new diuretics, aquaretics, and natriuretics

Diuretics continue to be a mainstay in patients with CHF. Conventional diuretic therapy is associated, however, with potentially deleterious neurohumoral activation and renal impairment. It is not known to what extent these neurohumoral effects are offset by concurrent therapy with ACE-I, beta-blockers, and other agents. In the past, there was no alternative to conventional diuretic therapy, so their potential for adverse outcome in the long term could not be assessed. Enhancement of the natriuretic peptide system could provide us with a better strategy to treat sodium and water retention. In a unique way, the natriuretic peptides combine several of the beneficial actions of the other diuretics, but without the associated cost. Natriuretic peptides, like conventional diuretics, are natriuretic and diuretic. There are important differences, however. First, unlike conventional diuretics, NPs do not activate RAAS. Activation of this system is associated with progression of CHF. Second, NPs inhibit the sympathetic nervous system, the activation of which is associated with heart failure progression, myocyte necrosis and apoptosis, and arrhythmias. Third, unlike conventional diuretics that lead to a decrease in GFR by reflex mechanisms. NPs maintain or even improve GFR. We now appreciate that some "old" drugs may be beneficial to CHF patients in a new way, as is the case with spironolactone. The survival benefit of this aldosterone antagonist is clear: its usefulness, however, may be more a result of both its antifibrotic actions in addition to its tradional role as a potassium-sparing and natriuretic agent. It is hoped that the SARAs will provide the same survival benefit, but with fewer of the sex-steroid side effects. In addition, AVP-receptor antagonists may become useful tools in the treatment of patients with hyponatremia. Likewise, the A1 AR antagonists may find a role in the CHF armamentarium by providing good diuresis and natriuresis while at the same time maintaining GFR through inhibition of TGF. Many questions remain unanswered, and studies are needed to demonstrate that the positive results seen in basic research translate into improved morbidity and mortality.

Changes in concentrations of neuroendocrine hormones and catecholamines in dogs with myocardial failure induced by rapid ventricular pacing

OBJECTIVE

To describe neuroendocrine responses that develop in dogs subjected to prolonged periods of ventricular pacing.

ANIMALS

14 adult male hound-type dogs.

PROCEDURE

Samples were obtained and neuroendocrine responses measured before (baseline) and after 3 periods of ventricular pacing. A pacemaker was used to induce heart rates of 180, 200, and 220 beats/min (BPM). Each heart rate was maintained for 3 weeks before increasing to the next rate. Atrial natriuretic peptide, antidiuretic hormone, aldosterone, norepinephrine, epinephrine, and dopamine concentrations and plasma renin activity were measured. Severity of left ventricular compromise was estimated.

RESULTS

Shortening fraction decreased significantly with increasing heart rates (mean +/- SE, 35.5 +/- 1.4, 25.0 +/- 1.4, 19.5 +/- 1.9, and 12.2 +/- 2.3 for baseline, 180 BPM, 200 BPM, and 220 BPM, respectively). Atrial natriuretic peptide concentrations increased significantly at 180 BPM (44.1 +/- 3.0 pg/mL) and 200 BPM (54.8 +/- 5.5 pg/mL), compared with baseline concentration (36.8 +/- 2.6 pg/mL). Dopamine concentration increased significantly at 200 BPM (70.4 +/- 10.4 pg/mL), compared with baseline concentration (44.2 73 pg/mL). Norepinephrine concentrations increased significantly from baseline concentration (451 +/- 46.2 pg/mL) to 678 +/- 69.8, 856 +/- 99.6, and 1,003 +/- 2676 pg/mL at 180, 200, and 220 BPM, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Dogs subjected to ventricular pacing for 9 weeks developed neuroendocrine responses similar to those that develop in humans with more chronic heart failure and, except for epinephrine concentrations, similar to those for dogs subjected to ventricular pacing for < 6 weeks.