Biodesign of a renal-protective peptide based on alternative splicing of B-type natriuretic peptide

Augmentation of natriuretic peptide (NP) receptor A and B (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) signalling as a therapeutic strategy in heart failure

INTRODUCTION

Heart failure is a complex, debilitating condition and despite advances in treatment, it remains a significant cause of morbidity and mortality worldwide. Therefore, the need for alternative treatment strategies is essential. In this review, we explore the therapeutic strategies of augmenting natriuretic peptide receptors (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) in heart failure.

AREAS COVERED

We aim to provide an overview of the evidence of preclinical and clinical studies on novel heart failure treatment strategies. Papers collected in this review have been filtered and screened following PubMed searches. This includes epigenetics, modulating enzyme activity in natriuretic peptide (NP) synthesis, gene therapy, modulation of downstream signaling by augmenting soluble guanylate cyclase (sGC) and phosphodiesterase (PDE) inhibition, nitrates, c-GMP-dependent protein kinase, synthetic and designer NP and RNA therapy.

EXPERT OPINION

The novel treatment strategies mentioned above have shown great potential, however, large randomized controlled trials are still lacking. The biggest challenge is translating the results seen in preclinical trials into clinical trials. We recommend a multi-disciplinary team approach with cardiologists, geneticist, pharmacologists, bioengineers, researchers, regulators, and patients to improve heart failure outcomes. Future management can involve telemedicine, remote monitoring, and artificial intelligence to optimize patient care.

Natriuretic Peptides: It Is Time for Guided Therapeutic Strategies Based on Their Molecular Mechanisms

Natriuretic peptides (NPs) are the principal expression products of the endocrine function of the heart. They exert several beneficial effects, mostly mediated through guanylate cyclase-A coupled receptors, including natriuresis, diuresis, vasorelaxation, blood volume and blood pressure reduction, and regulation of electrolyte homeostasis. As a result of their biological functions, NPs counterbalance neurohormonal dysregulation in heart failure and other cardiovascular diseases. NPs have been also validated as diagnostic and prognostic biomarkers in cardiovascular diseases such as atrial fibrillation, coronary artery disease, and valvular heart disease, as well as in the presence of left ventricular hypertrophy and severe cardiac remodeling. Serial measurements of their levels may be used to contribute to more accurate risk stratification by identifying patients who are more likely to experience death from cardiovascular causes, heart failure, and cardiac hospitalizations and to guide tailored pharmacological and non-pharmacological strategies with the aim to improve clinical outcomes. On these premises, multiple therapeutic strategies based on the biological properties of NPs have been attempted to develop new targeted cardiovascular therapies. Apart from the introduction of the class of angiotensin receptor/neprilysin inhibitors to the current management of heart failure, novel promising molecules including M-atrial natriuretic peptide (a novel atrial NP-based compound) have been tested for the treatment of human hypertension with promising results. Moreover, different therapeutic strategies based on the molecular mechanisms involved in NP regulation and function are under development for the management of heart failure, hypertension, and other cardiovascular conditions.

Endocrine functions of the heart: from bench to bedside

Heart has a recognized endocrine function as it produces several biologically active substances with hormonal properties. Among these hormones, the natriuretic peptide (NP) system has been extensively characterized and represents a prominent expression of the endocrine function of the heart. Over the years, knowledge about the mechanisms governing their synthesis, secretion, processing, and receptors interaction of NPs has been intensively investigated. Their main physiological endocrine and paracrine effects on cardiovascular and renal systems are mostly mediated through guanylate cyclase-A coupled receptors. The potential role of NPs in the pathophysiology of heart failure and particularly their counterbalancing action opposing the overactivation of renin-angiotensin-aldosterone and sympathetic nervous systems has been described. In addition, NPs are used today as key biomarkers in cardiovascular diseases with both diagnostic and prognostic significance. On these premises, multiple therapeutic strategies based on the biological properties of NPs have been attempted to develop new cardiovascular therapies. Apart from the introduction of the class of angiotensin receptor/neprilysin inhibitors in the current management of heart failure, novel promising molecules, including M-atrial natriuretic peptide (a novel atrial NP-based compound), have been tested for the treatment of human hypertension. The development of new drugs is currently underway, and we are probably only at the dawn of novel NPs-based therapeutic strategies. The present article also provides an updated overview of the regulation of NPs synthesis and secretion by microRNAs and epigenetics as well as interactions of cardiac hormones with other endocrine systems.

Natriuretic peptide pathways in heart failure: further therapeutic possibilities

The discovery of the heart as an endocrine organ resulted in a remarkable recognition of the natriuretic peptide system (NPS). Specifically, research has established the production of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) from the heart, which exert pleiotropic cardiovascular, endocrine, renal, and metabolic actions via the particulate guanylyl cyclase A receptor (GC-A) and the second messenger, cGMP. C-type natriuretic peptide (CNP) is produced in the endothelium and kidney and mediates important protective auto/paracrine actions via GC-B and cGMP. These actions, in part, participate in the efficacy of sacubitril/valsartan in heart failure (HF) due to the augmentation of the NPS. Here, we will review important insights into the biology of the NPS, the role of precision medicine, and focus on the phenotypes of human genetic variants of ANP and BNP in the general population and the relevance to HF. We will also provide an update of the existence of NP deficiency states, including in HF, which provide the rationale for further therapeutics for the NPS. Finally, we will review the field of peptide engineering and the development of novel designer NPs for the treatment of HF. Notably, the recent discovery of a first-in-class small molecule GC-A enhancer, which is orally deliverable, will be highlighted. These innovative designer NPs and small molecule possess enhanced and novel properties for the treatment of HF and cardiovascular diseases.

Natriuretic Peptide-Based Novel Therapeutics: Long Journeys of Drug Developments Optimized for Disease States

Simple Summary

Natriuretic peptides are endogenous hormones produced in the heart and vascular endothelium, and they enable cardiorenal protective actions or bone growth via cGMP stimulation through their receptor guanylyl cyclase receptor A or B. To optimize the drug for each disease state, we must consider drug metabolism, delivery systems, and target receptor(s). This review summarizes attempts to develop novel natriuretic peptide-based therapeutics, including novel designer natriuretic peptides and oral drugs to enhance endogenous natriuretic peptides. We introduce some therapeutics that have been successful in clinical practice, as well as the prospective drug developments in the natriuretic peptide system for disease states.

Abstract

The field of natriuretic peptides (NPs) as an endocrine hormone has been developing since 1979. There are three peptides in humans: atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), which bind to the guanylyl cyclase-A (GC-A) receptor (also called natriuretic peptide receptor-A (NPR-A)), and C-type natriuretic peptide (CNP), which binds to the GC-B receptor (also called the NPR-B) and then synthesizes intracellular cGMP. GC-A receptor stimulation has natriuretic, vasodilatory, cardiorenal protective and anti-renin–angiotensin–aldosterone system actions, and GC-B receptor stimulation can suppress myocardial fibrosis and can activate bone growth before epiphyseal plate closure. These physiological effects are useful as therapeutics for some disease states, such as heart failure, hypertension, and dwarfism. To optimize the therapeutics for each disease state, we must consider drug metabolism, delivery systems, and target receptor(s). We review the cardiac NP system; new designer NPs, such as modified/combined NPs and modified peptides that can bind to not only NP receptors but receptors for other systems; and oral drugs that enhance endogenous NP activity. Finally, we discuss prospective drug discoveries and the development of novel NP therapeutics.

Cyclic GMP modulating drugs in cardiovascular diseases: Mechanism-based network pharmacology

Mechanism-based therapy centred on the molecular understanding of disease-causing pathways in a given patient is still the exception rather than the rule in medicine, even in cardiology. However, recent successful drug developments centred around the second messenger cyclic guanosine-3′-5′-monophosphate (cGMP), which is regulating a number of cardiovascular disease modulating pathways, are about to provide novel targets for such a personalized cardiovascular therapy. Whether cGMP breakdown is inhibited or cGMP synthesis is stimulated via guanylyl cyclases or their upstream regulators in different cardiovascular disease phenotypes, the outcomes seem to be so far uniformly protective. Thus, a network of cGMP-modulating drugs has evolved that act in a mechanism-based, possibly causal manner in a number of cardiac conditions. What remains a challenge is the detection of cGMPopathy endotypes amongst cardiovascular disease phenotypes. Here, we review the growing clinical relevance of cGMP and provide a glimpse into the future on how drugs interfering with this pathway may change how we treat and diagnose cardiovascular diseases altogether.

Venom natriuretic peptides guide the design of heart failure therapeutics

Heart failure (HF) affects over 26 million people world-wide. It is a syndrome triggered by loss of normal cardiac function due to many acute (eg myocardial infarction) and/or chronic (eg hypertension) causes and characterized by mixed beneficial and deleterious activation of a complex of multifaceted neurohormonal systems the net effect of which frequently is further adverse disruption of pressure-volume homeostasis. Unlike the situation in chronic heart failure, current strategies for treatment of acute heart failure are empirical and lack a strong evidence base. Management includes any of a combination of vasodilators, diuretics and ionotropic agents depending on the hemodynamic profile of the patient. Despite the improvement in the options available to improve outcomes in patients with chronic HF, for several decades little gain has been made in the treatment of the acute decompensated state. Morbidity and mortality rates remain high necessitating new therapeutic agents. The cardiac natriuretic peptides (NPs) are key hormones in pressure-volume homoeostasis. There are three isoforms of mammalian NPs, namely ANP, BNP and CNP. These peptides bind to membrane-bound NP receptors (NPRs) on the heart, vasculature and kidney to lower blood pressure and circulating volume. Intravenous infusion of NPs in HF patients improves hemodynamic status but is associated with occasional severe hypotension. Apart from mammalian NPs, snake venom NPs are an excellent source of pharmacologically distinct ligands that offer the possibility of engineering NPs for therapeutic purposes. Venom NPs have long half-lives, differential NPR activation profiles and varied NPR specificity. The scaffolds of venom NPs encode the molecular information for designing NPs with longer half-lives and improved and differential vascular and renal functions. This review focuses on the structure-function paradigm of mammalian and venom NPs and the different peptide engineering strategies that have been utilized in the design of clinically relevant new NP-analogues.

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.

Natriuretic Peptides in Heart Failure with Preserved Left Ventricular Ejection Fraction: From Molecular Evidences to Clinical Implications

The incidence of heart failure with preserved ejection fraction (HFpEF) is increasing and its challenging diagnosis and management combines clinical, imagistic and biological data. Natriuretic peptides (NPs) are hormones secreted in response to myocardial stretch that, by increasing cyclic guanosine monophosphate (cGMP), counteract myocardial fibrosis and hypertrophy, increase natriuresis and determine vasodilatation. While their role in HFpEF is controversial, most authors focused on b-type natriuretic peptides (BNPs) and agreed that patients may show lower levels. In this setting, newer molecules with an increased specificity, such as middle-region pro-atrial natriuretic peptide (MR-proANP), emerged as promising markers. Augmenting NP levels, either by NP analogs or breakdown inhibition, could offer a new therapeutic target in HFpEF (already approved in their reduced EF counterparts) by increasing the deficient cGMP levels found in patients. Importantly, these peptides also retain their prognostic value. This narrative review focuses on NPs' physiology, diagnosis, therapeutic and prognostic implication in HFpEF.

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.

Innovative Therapeutics: Designer Natriuretic Peptides

Endogenous natriuretic peptides serve as potent activators of particulate guanylyl cyclase receptors and the second messenger cGMP. Natriuretic peptides are essential in maintenance of volume homeostasis, and can be of myocardial, renal and endothelial origin. Advances in peptide engineering have permitted the ability to pursue highly innovative drug discovery strategies. This has resulted in designer natriuretic peptides that go beyond native peptides in efficacy, specificity, and resistance to enzymatic degradation. Together with recent improvements in peptide delivery systems, which have improved bioavailability, further advances in this field have been made. Therefore, designer natriuretic peptides with pleotropic actions together with strategies of chronic delivery have provided an unparalleled opportunity for the treatment of cardiovascular disease. In this review, we report the conceptual framework of peptide engineering of the natriuretic peptides that resulted in designer peptides for cardiovascular disease. We specifically provide an update on those currently in clinical trials for heart failure and hypertension, which include Cenderitide, ANX042 and ZD100.

B-type natriuretic peptide and acute heart failure: Fluid homeostasis, biomarker and therapeutics

Natriuretic peptides are a family of peptides with similar structures, but are genetically distinct with diverse actions in cardiovascular, renal and fluid homeostasis. The family consists of an atrial natriuretic peptide (ANP) and a brain natriuretic peptide (BNP) of myocardial cell origin, a C-type natriuretic peptide (CNP) of endothelial origin, and a urodilatin (Uro) which is processed from a prohormone ANP in the kidney. Nesiritide, a human recombinant BNP, was approved by the Federal Drug Administration (FDA) for the management of acute heart failure (AHF) in 2001. Human recombinant ANP (Carperitide) was approved for the same clinical indication in Japan in 1995, and human recombinant Urodilatin (Ularitide) is currently undergoing phase III clinical trial (TRUE AHF). This review will provide an update on important issues regarding the role of BNP in fluid hemostasis as a biomarker and therapeutics in AHF.

Alternative Splicing in CKD

Alternative splicing (AS) has emerged in the postgenomic era as one of the main drivers of proteome diversity, with ≥94% of multiexon genes alternatively spliced in humans. AS is therefore one of the main control mechanisms for cell phenotype, and is a process deregulated in disease. Numerous reports describe pathogenic mutations in splice factors, splice sites, or regulatory sequences. Additionally, compared with the physiologic state, disease often associates with an abnormal proportion of splice isoforms (or novel isoforms), without an apparent driver mutation. It is therefore essential to study how AS is regulated in physiology, how it contributes to pathogenesis, and whether we can manipulate faulty splicing for therapeutic advantage. Although the disease most commonly linked to deregulation of AS in several genes is cancer, many reports detail pathogenic splice variants in diseases ranging from neuromuscular disorders to diabetes or cardiomyopathies. A plethora of splice variants have been implicated in CKDs as well. In this review, we describe examples of these CKD-associated splice variants and ideas on how to manipulate them for therapeutic benefit.

Focus on renal congestion in heart failure

Hospitalizations due to heart failure are increasing steadily despite advances in medicine. Patients hospitalized for worsening heart failure have high mortality in hospital and within the months following discharge. Kidney dysfunction is associated with adverse outcomes in heart failure patients. Recent evidence suggests that both deterioration in kidney function and renal congestion are important prognostic factors in heart failure. Kidney congestion in heart failure results from low cardiac output (forward failure), tubuloglomerular feedback, increased intra-abdominal pressure or increased venous pressure. Regardless of the cause, renal congestion is associated with increased morbidity and mortality in heart failure. The impact on outcomes of renal decongestion strategies that do not compromise renal function should be explored in heart failure. These studies require novel diagnostic markers that identify early renal damage and renal congestion and allow monitoring of treatment responses in order to avoid severe worsening of renal function. In addition, there is an unmet need regarding evidence-based therapeutic management of renal congestion and worsening renal function. In the present review, we summarize the mechanisms, diagnosis, outcomes, prognostic markers and treatment options of renal congestion in heart failure.

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

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

Peptidic tools applied to redirect alternative splicing events

Peptides are versatile and attractive biomolecules that can be applied to modulate genetic mechanisms like alternative splicing. In this process, a single transcript yields different mature RNAs leading to the production of protein isoforms with diverse or even antagonistic functions. During splicing events, errors can be caused either by mutations present in the genome or by defects or imbalances in regulatory protein factors. In any case, defects in alternative splicing have been related to several genetic diseases including muscular dystrophy, Alzheimer's disease and cancer from almost every origin. One of the most effective approaches to redirect alternative splicing events has been to attach cell-penetrating peptides to oligonucleotides that can modulate a single splicing event and restore correct gene expression. Here, we summarize how natural existing and bioengineered peptides have been applied over the last few years to regulate alternative splicing and genetic expression. Under different genetic and cellular backgrounds, peptides have been shown to function as potent vehicles for splice correction, and their therapeutic benefits have reached clinical trials and patenting stages, emphasizing the use of regulatory peptides as an exciting therapeutic tool for the treatment of different genetic diseases.

Cell surface protein disulfide isomerase regulates natriuretic peptide generation of cyclic guanosine monophosphate

Rationale

The family of natriuretic peptides (NPs), including atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), exert important and diverse actions for cardiovascular and renal homeostasis. The autocrine and paracrine functions of the NPs are primarily mediated through the cellular membrane bound guanylyl cyclase-linked receptors GC-A (NPR-A) and GC-B (NPR-B). As the ligands and receptors each contain disulfide bonds, a regulatory role for the cell surface protein disulfide isomerase (PDI) was investigated.

Objective

We utilized complementary in vitro and in vivo models to determine the potential role of PDI in regulating the ability of the NPs to generate its second messenger, cyclic guanosine monophosphate.

Methods and Results

Inhibition of PDI attenuated the ability of ANP, BNP and CNP to generate cGMP in human mesangial cells (HMCs), human umbilical vein endothelial cells (HUVECs), and human aortic smooth muscle cells (HASMCs), each of which were shown to express PDI. In LLC-PK1 cells, where PDI expression was undetectable by immunoblotting, PDI inhibition had a minimal effect on cGMP generation. Addition of PDI to cultured LLC-PK1 cells increased intracellular cGMP generation mediated by ANP. Inhibition of PDI in vivo attenuated NP-mediated generation of cGMP by ANP. Surface Plasmon Resonance demonstrated modest and differential binding of the natriuretic peptides with immobilized PDI in a cell free system. However, PDI was shown to co-localize on the surface of cells with GC-A and GC-B by co-immunoprecpitation and immunohistochemistry.

Conclusion

These data demonstrate for the first time that cell surface PDI expression and function regulate the capacity of natriuretic peptides to generate cGMP through interaction with their receptors.

B-Type Natriuretic Peptide Forms within the Heart, Coronary Sinus, and Peripheral Circulation in Humans: Evidence for Degradation before Secretion

BACKGROUND

The B-type natriuretic peptides (BNP and N-terminal pro-BNP) are secreted by the heart and, in the case of BNP, serve to maintain circulatory homeostasis through renal and vascular actions and oppose many effects of the renin-angiotensin system. Recent evidence suggests that in patients with severe heart failure, circulating immunoreactive BNP is made up mainly of metabolites that may have reduced bioactivity. We hypothesized that BNP may be degraded before it even leaves the heart.

METHODS

Peripheral venous plasma plus atrial and ventricular tissue, obtained from explanted hearts at the time of transplantation, were collected from 3 patients with end-stage heart failure. In a separate study, plasma was collected from the coronary sinus and femoral artery of 3 separate patients undergoing cardiac catheterization. Plasma C18 reverse-phase extracts were separated on reverse-phase HPLC, and the collected fractions were subjected to RIAs with highly specific antisera directed to the amino- and carboxy-terminal ends of BNP(1–32).

RESULTS

ProBNP, BNP(1–32), and 2 major BNP metabolites were present in atrial and ventricular tissue, where BNP(1–32) represented 45% and 70% of total processed BNP, respectively. Neither BNP(1–32) nor the 2 metabolites were detected in peripheral venous plasma. Nor was BNP(1–32) detected in matching coronary sinus and femoral artery plasma from the 3 patients undergoing cardiac catheterization.

CONCLUSIONS

BNP(1–32) is partly degraded within the hearts of patients with end-stage heart failure, and even in patients with relatively well-preserved left ventricular systolic function, only BNP metabolites enter the systemic circulation.

Investigation of cenderitide controlled release platforms for potential local treatment of cardiovascular pathology

In this work, we focused on the development and investigation of controlled release matrices for a novel cardiotherapeutic peptide, cenderitide (CD-NP) that has shown to be useful for control of ventricular remodeling. To circumvent the hydrophilicity disparity between CD-NP and hydrophobic polymer matrix, a cosolvent system (water/dichloromethane) was selected for investigation. The effect of emulsification conditions, addition of poly(ethylene glycol) (PEG) and its copolymer on the release mechanism and profile were investigated. To verify the retention of bioactivity of entrapped CD-NP in different formulations, the generation of 3',5' cyclic guanosine monophospate (cGMP) and the inhibition of human cardiac fibroblast (HCF) were evaluated. The results showed that neat poly(ε-caprolactone) matrices carried out via two distinct emulsification conditions had either an unacceptably high burst or incomplete release of CD-NP; and the addition of PEG and its copolymer obtained intermediate profiles. Our confocal laser scanning microscopy and surface morphological investigations showed that the copolymer excipient was superior in playing stabilizer role by colocalizing and redistributing peptide throughout the matrix, making the release less sensitive to emulsification conditions. Furthermore, the released CD-NP is able to generate the cGMP and inhibit the HCF proliferation. Our investigations showed that CD-NP-loaded platforms can be a feasible option to provide sustained antifibrotic moderation of fibrotic scar formation and be potentially used to alleviate the adverse effects of cardiac remodeling.

The alternative heart: impact of alternative splicing in heart disease

Alternative splicing is the main driver of protein diversity and allows the production of different proteins from each gene in the genome. Changes in exon exclusion, intron retention or the use of alternative splice sites can alter protein structure, localisation, regulation and function. In the heart, alternative splicing of sarcomeric genes, ion channels and cell signalling proteins can lead to cardiomyopathies, arrhythmias and other pathologies. Also, a number of inherited conditions and heart-related diseases develop as a result of mutations affecting splicing. Here, we review the impact that changes in alternative splicing have on individual genes and on whole biological processes associated with heart disease. We also discuss promising therapeutic tools based on the manipulation of alternative splicing.

The relevance of congestion in the cardio-renal syndrome

Worsening renal function (WRF) during the treatment of acute decompensated heart failure (ADHF) occurs in up to a third of patients and is associated with worse survival. Venous congestion is increasingly being recognized as a key player associated with WRF in ADHF. Understanding the hemodynamic effects of venous congestion and the interplay between venous congestion and other pathophysiological factors such as raised abdominal pressure, endothelial cell activation, anemia/ iron deficiency, sympathetic overactivity, and stimulation of the renin-angiotensin-aldosterone system will help in devising effective management strategies. Early recognition of venous congestion through novel techniques such as bioimpedance measurements and remote monitoring of volume status combined with customized diuretic regimens may prevent venous congestion and perhaps avoid significant WRF.

A novel bioassay for the activity determination of therapeutic human brain natriuretic peptide (BNP)

Background

Recombinant human brain natriuretic peptide (rhBNP) is an important peptide-based therapeutic drug indicated for the treatment of acute heart failure. Accurate determination of the potency of therapeutic rhBNP is crucial for the safety and efficacy of the drug. The current bioassay involves use of rabbit aortic strips, with experiments being complicated and time-consuming and markedly variable in results. Animal-less methods with better precision and accuracy should be explored. We have therefore developed an alternative cell-based assay, which relies on the ability of BNP to induce cGMP production in HEK293 cells expressing BNP receptor guanylyl cyclase-A.

Methodology/Principal Findings

An alternative assay based on the measurement of BNP-induced cGMP production was developed. Specifically, the bioassay employs cells engineered to express BNP receptor guanylyl cyclase-A (GCA). Upon rhBNP stimulation, the levels of the second messager cGMP in these cells drastically increased and subsequently secreted into culture supernatants. The quantity of cGMP, which corresponds to the rhBNP activity, was determined using a competitive ELISA developed by us. Compared with the traditional assay, the novel cell-based assay demonstrated better reproducibility and precision.

Conclusion/Significance

The optimized cell-based assay is much simpler, more rapid and precise compared with the traditional assay using animal tissues. To our knowledge, this is the first report on a novel and viable alternative assay for rhBNP potency analysis.

Novel natriuretic peptides: new compounds and new approaches

The natriuretic peptides (NPs) are a group of structurally similar yet genetically distinct peptides that have diverse actions in cardiovascular, renal, and endocrine homeostasis. Since the discovery of atrial natriuretic peptide in 1981, the diagnostic, prognostic, and therapeutic significance of NPs have been studied extensively in relation to heart failure. Indeed, it now is understood that a hallmark of heart failure is the activation of the cardiac endocrine system, in particular the natriuretic peptide family including atrial natriuretic peptide and B-type natriuretic peptide. Currently, the only approved therapeutic application for NPs is the intravenous treatment of acute decompensated heart failure. However, in recent years there has been considerable research aimed at creating novel NPs and administering them via novel routes. This review focuses on the novel NPs that have been created and on novel approaches for their administration.

B-type natriuretic peptides: looking to the future

Whereas the role of the cardiac natriuretic peptides, ANP and BNP, in some aspects of physiology and pathophysiology is clear, their potential in diagnosis, prognosis, and therapeutics in many clinical disorders remains uncertain. We predict that circulating levels of these peptides will find increasing diagnostic utility in patients presenting with dyspnoea, in guiding the complex pharmacotherapy in heart failure, and may likewise be useful in guiding the management of patients on chronic maintenance renal dialysis. We predict also that levels of these peptides will be of practical use as prognostic indicators in 'at-risk' populations (such as those with diabetes, coronary heart disease, hypertension, thalassaemia, etc.) but probably not in the general population. It appears likely that administration of these peptides will find a place in the therapeutics of acute myocardial infarction, but this is less clear for heart failure. We describe the presence of a segment of the signal peptide for BNP within the circulation and discuss its potential clinical utility.

Biochemistry of the human B-type natriuretic peptide precursor and molecular aspects of its processing

B-type Natriuretic Peptide (BNP) is a circulating hormone primarily produced by the myocardium in response to volume overload and increased filling pressure. BNP acts to increase natriuresis and to decrease cardiac load and blood pressure. The appearance of active BNP hormone in the bloodstream is preceded by the proteolytic cleavage of its precursor, proBNP. The products of proBNP processing, BNP and the N-terminal fragment of proBNP (NT-proBNP), have been extensively shown to be powerful biomarkers of heart failure (HF) and risk assessments for cardiovascular complications. In contrast to the clinical utility of proBNP-derived peptides, knowledge of posttranslational proBNP maturation and molecular aspects of its processing are far from being completely comprehended. A clear understanding of proBNP processing mechanisms in normal and diseased states appears to be required to improve our understanding of HF development and the clinical significance of both proBNP and proBNP-derived peptides. The aim of the present review is to summarize the available data in the field of human proBNP maturation and processing and to discuss potential clinical implications.

A novel atrial natriuretic peptide based therapeutic in experimental angiotensin II mediated acute hypertension

M-atrial natriuretic peptide (ANP; M-ANP) is a novel next generation 40 amino acid peptide based on ANP, which is highly resistant to enzymatic degradation and has greater and more sustained beneficial actions compared with ANP. The current study was designed to advance our understanding of the therapeutic potential of M-ANP in a canine model of acute angiotensin II-induced hypertension with elevated cardiac filling pressures and aldosterone activation. We compare M-ANP with vehicle and equimolar human B-type natriuretic peptide, which possesses the most potent in vivo actions of the native natriuretic peptides. M-ANP significantly lowered mean arterial pressure and systemic vascular resistance. Importantly, despite a reduction in blood pressure, renal function was enhanced with significant increases in renal blood flow, glomerular filtration rate, diuresis, and natriuresis after M-ANP infusion. Although angiotensin II induced an acute increase in pulmonary capillary wedge pressure, M-ANP significantly lowered pulmonary capillary wedge pressure, pulmonary artery pressure, and right atrial pressure. Further, M-ANP significantly suppressed angiotensin II-induced activation of aldosterone. These cardiovascular and renal enhancing actions of M-ANP were accompanied by significant increases in plasma and urinary cGMP, the second messenger molecule of the natriuretic peptide system. When compared with human B-type natriuretic peptide, M-ANP had comparable cardiovascular actions but resulted in a greater natriuretic effect. These results suggest that M-ANP, which is more potent than ANP in normal canines, has potent blood pressure lowering and renal enhancing properties and may, therefore, serve as an ANP based therapeutic for acute hypertension.

Exon-skipping brain natriuretic peptide variant is overexpressed in failing myocardium and attenuates brain natriuretic peptide production in vitro

Brain natriuretic peptide/natriuretic peptide precursor B (NPPB) is one of the most studied genes in relation to heart failure (HF) conditions. However, it is still unclear as to whether alternative splicing could create NPPB mRNA variants, which may be expressed in normal and diseased myocardium. We aimed to identify and characterize a novel alternatively spliced variant of porcine and human NPPB resulting from exon 2 skipping (designated as ΔE2-NPPB). A variety of conventional molecular, biochemical and immunochemical methods were used to examine the expression and functional consequences of ΔE2-NPPB in vitro and in vivo. The pig ΔE2-NPPB mRNA is effectively translated into stable protein in cell-based assays but, in contrast to normally spliced NPPB, the ΔE2-NPPB protein is not secreted into the media. Co-transfection assays demonstrate that ΔE2-NPPB attenuates production and secretion of normally spliced NPPB, suggesting a negative feedback loop of NPPB signaling through generation of ΔE2-NPPB. The inhibitory effects of ΔE2-NPPB on the expression of NPPB are associated with sequence elements residing in exon 3 of ΔE2-NPPB. In piglets, ΔE2-NPPB gene expression is downregulated in both ventricles after birth, but it is markedly re-activated in the postnatal myocardium in experimental diastolic heart failure. In addition, we demonstrate that the exon-skipped NPPB variants are expressed in the postnatal and adult human myocardium and upregulated at end-stage HF due to dilated cardiomyopathy. Our work uncovers an important role of alternative exon skipping in the regulation of NPPB gene expression, thereby pinpointing a putative new mechanism for post-transcriptional regulation of NPPB production and secretion.

Early intervention in acute kidney injury

The prevalence of acute kidney injury (AKI) in the US is increasing, which can be attributed in part to the aging population and the pandemic of obesity, diabetes and hypertension. Individuals over the age of 70 years constitute 7% of the US population, but account for 36-70% of AKI cases. Presently, major efforts are underway to enable the early detection of AKI by use of various innovative biomarkers, thereby facilitating early intervention. Now is the time, therefore, to consider potential interventions to attenuate or prevent AKI. Several randomized studies have failed to alter the course of AKI, but these studies have been complicated by extrarenal consequences, which could have obscured the potential intrarenal benefit of the agent. Thus, agents that have exclusive effects on renal hemodynamics and tubular function, or the intrarenal infusion of short-acting agents that do not have systemic effects, need to be considered in future studies for the prevention of AKI.