Beneficial effects of sampatrilat, a novel vasopeptidase inhibitor, on cardiac remodeling and function of rats with chronic heart failure following left coronary artery ligation

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.

A New Chimeric Natriuretic Peptide, CNAAC, for the Treatment of Left Ventricular Dysfunction after Myocardial Infarction

An innovative natriuretic peptide analog named C_NAA_C (structurally consisting of the C-terminus and ring of ANP and the N-terminus of CNP) that has been shown to exhibit potent vasodilatory, diuretic, and hypotensive effects in our previous study was evaluated for the treatment of left ventricular dysfunction following myocardial infarction. The temporal relaxation effect and metabolic status of C_NAA_C were determined. A myocardial ischemic model was established. Rats were randomly divided into Sham, MI, MI-ANP, MI-CNP, MI-VNP, and MI-C_NAA_C groups. Humoral factors were measured; echocardiography and hemodynamics methods were employed to assess the cardiac function at the fourth week after modeling. The results showed that C_NAA_C had a potent relaxant effect and longer duration of action than ANP, CNP, or VNP. The stability of C_NAA_C in blood was higher than other three NPs. Four weeks of NP administration ameliorated diastolic and systolic dysfunction, the hypertrophic index, myocardial fibrosis, and infarct size; it also restored the abnormal changes in humoral factors. These results demonstrate that C_NAA_C has a potent cardioprotective effect against left ventricular dysfunction after myocardial infarction. The results may lay the foundation for the clinical application of this newly designed NP chimera in the treatment and prevention of heart failure.

Cardioprotection against Heart Failure by Shenfu Injection via TGF-β/Smads Signaling Pathway

Objective

To explore the potential cardioprotective mechanism of Shenfu injection (SFI) against heart failure (HF) by attenuating myocardial fibrosis and cardiac remodeling.

Methods and Results

Four weeks after myocardial infarction (MI), adult male Sprague Dawley rats were randomized for 4-week treatment with Valsartan, SFI, or vehicle. Echocardiography and hemodynamics were applied to evaluate cardiac functions. Myocardia of coronary artery ligated (CAD) rats were observed to investigate changes in cardiac structure and function. Our findings suggest that treatment with SFI could inhibit progression of myocardial fibrosis and attenuate cardiac remodeling. In addition, SFI decreased expression of Smad2 and Smad3, while increasing the expression of Smad7 through regulation of TGF-β/Smads signaling pathway.

Conclusion

Treatment with SFI in Sprague Dawley rats improves ventricular structure and function and reduces cardiac fibrosis by ameliorating TGF-β/Smads signaling pathway after ventricular remodeling.

Combination of drugs acting on the natriuretic system and the renin-angiotensin system in heart failure

Conventional diuretic agents are very effective agents in relieving volume overload and congestive symptoms in chronic heart failure (CHF). However, they are associated with activation of the renin-angiotensin system (RAS) and the sympathetic nervous system and a reduction in glomerular filtration rate, all of which have been associated with adverse outcomes in CHF. Therefore, there is an increasing interest in drugs that target the natriuretic system without neurohormonal activation and deterioration of renal function. In this review, we will discuss the underlying rationale and evidence behind currently pursued strategies that target the natriuretic system. This includes the administration of natriuretic peptides (NPs) and strategies that potentiate the NP system, such as neutral endopeptidase inhibition. We will also highlight some potentially important interactions of these strategies with drugs that target the RAS.

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.

Olmesartan medoxomil reverses glomerulosclerosis in renal tissue induced by myocardial infarction without changes in renal function

The aim of the present study was to investigate the effect of olmesartan medoxomil (OLM) on renal injury in mice with myocardial infarction (MI). A total of 33 male C57/BL/6 mice were divided into a sham surgery group (SHAM group), MI group (MI group) and OLM treatment group (OLM group). Experimental MI models were established in the mice of the MI and OLM groups by coronary artery ligation, and the mice in the OLM group were fed a daily dose of 10 mg/kg OLM for eight weeks. The results showed that MI induced a reduction in cardiac function and an increase in systolic blood pressure. In addition, increased periodic acid-Schiff (PAS) positive staining, combined with increased levels of angiotensin II (Ang II) in the plasma and kidneys, and increased expression levels of renin, angiotensin II type 1 receptor (AT1R) and angiotensinogen (AGT) in the kidney tissues was observed compared with those in the SHAM group. OLM treatment attenuated the injury by reducing the systolic blood pressure and PAS positive staining, and decreasing the expression levels of Ang II, renin, AT1R and AGT in the kidney compared with those in the MI group. It may be concluded that MI activates the intrarenal renin-angiotensin system and leads to glomerulosclerosis, and that OLM protects the kidney by inhibiting the effects of Ang II.

A computational approach to the study of the binding mode of dual ACE/NEP inhibitors

Combined blockade of the renin-angiotensin-aldosterone system (RAAS) is an attractive therapeutic strategy for the treatment of cardiovascular diseases. Vasopeptidase inhibitors are a group of compounds capable of inhibiting more than one enzyme, which leads to potentiation of natriuretic peptide actions and suppression of the RAAS. In this study, molecular modeling has been used to elucidate key structural features that govern the binding and/or selectivity of a single compound toward the zinc catalytic sites of the N- and C-domains of the angiotensin-converting enzyme (ACE) and the neutral endopeptidase (NEP). Eleven dual inhibitors were categorized in three classes, according to their zinc binding groups. Analysis of their docked conformers revealed the molecular environment of the catalytic sites and the specific interactions between the inhibitors and amino acid residues that are important for selectivity and cooperativity. In addition, inhibitors were predicted to bind to the C-domain of the ACE with greater affinity than the N-domain, with an average difference in the free energy of binding approximately 2-3 kcal mol(-1). Residues that were identified to actively participate in the binding and stabilizing of the enzyme-inhibitor complexes were analyzed in a consensus way for both the ACE and the NEP. These atomic-level insights into enzyme-ligand binding can be used to drive new structure-based drug design processes in the quest for more selective and effective vasopeptidase inhibitors.

Towards triple vasopeptidase inhibitors for the treatment of cardiovascular diseases

Cardiovascular diseases (CDs) are among the most encountered pathologies in western countries; with obesity reaching pandemic proportions, they are soon to become a worldwide problem. High blood pressure is the main risk factor for CDs, and its tight control is an imperative for the treatment of complications such as renal diseases, heart failure, and atherosclerosis. Blood homeostasis and vascular tone are regulated through at least 3 major closely interrelated pathways in which zinc metallopeptidases modulate the concentration of vasoactive mediators. Those extensively studied vasopeptidases were therefore rapidly targeted with specific inhibitors in order to control the levels of vasoconstrictors [angiotensin II (AII) and endothelin-1 (ET-1)] and vasodilators [bradykinin (BK) and atrial natriuretic peptide (ANP)], thereby controlling blood pressure. The first class of inhibitors to be developed were against angiotensin-converting enzyme (ACE), recently followed by dual inhibitors of ACE/neprylisin (NEP), NEP/endothelin-converting enzyme (ECE), and finally triple ACE/NEP/ECE inhibitors. The dual and triple inhibitors are defined as vasopeptidase inhibitors (VPI). In addition to their ability to effectively lower blood pressure in hypertensive patients, drugs targeting these enzymes also displayed antiinflammatory and antifibrotic activities. The major point emerging from recent studies undertaken to improve the management of CDs is that the combined action of different therapeutic strategies (ie, simultaneous modulation of several neurohumoral mediators) shows better results than conservative therapeutic approaches. In this review, we historically present the advances made in the comprehension of the different mechanisms of blood pressure regulation and some of the drugs that arose from this understanding.

Cardioprotective actions of peptide hormones in myocardial ischemia

The myocardium represents a major source of several families of peptide hormones under normal physiological conditions and the plasma concentrations of many of these "cardiac peptides" (or related pro-peptide fragments) are substantially augmented in many cardiac disease states. In addition to well-characterised endocrine functions of several of the cardiac peptides, pleiotropic functions within the myocardium and the coronary vasculature represent a significant aspect of their actions in health and disease. Here, we focus specifically on the cardioprotective roles of four major peptide families in myocardial ischemia and reperfusion: adrenomedullin, kinins, natriuretic peptides and the urocortins. The patterns of early release of all these peptides are consistent with roles as autacoid cardioprotective mediators. Clinical and experimental research indicates the early release and upregulation of many of these peptides by acute ischemia and there is a convincing body of evidence showing that exogenously administered adrenomedullin, bradykinin, ANP, BNP, CNP and urocortins are all markedly protective against experimental myocardial ischemia-reperfusion injury through a conserved series of cytoprotective signal transduction pathways. Intriguingly, all the peptides examined so far have the potential to salvage against infarction when administered specifically during early reperfusion. Thus, the myocardial secretion of peptide hormones likely represents an early protective response to ischemia. Further work is required to explore the potential therapeutic manipulation of these peptides in acute coronary syndromes and their promise as biomarkers of acute myocardial ischemia.

Angiotensin I-converting enzyme-dependent and neutral endopeptidase-dependent generation and degradation of angiotensin II contrarily modulate noradrenaline release: implications for vasopeptidase-inhibitor therapy?

OBJECTIVES

Vasopeptidase inhibitors inhibit neutral endopeptidase (NEP) and angiotensin I-converting enzyme (ACE). Since angiotensin (ANG) II availability is decreased by ACE inhibition but is increased by NEP inhibition, we evaluated the influence of the vasopeptidase inhibitor omapatrilat on ANG II-dependent noradrenaline (NA) release.

DESIGN

The functional relevance of ACE-dependent and NEP-dependent generation and degradation of ANG II on NA overflow was determined in pithed rats by applications of ANG I (0.1-100 microg/kg) or ANG II (0.01-10 microg/kg) after single injections of ramipril (1 mg/kg), the NEP inhibitor candoxatril (100 mg/kg), or the vasopeptidase inhibitor omapatrilat (30 mg/kg).

RESULTS

Blood pressure was equipotently decreased by ramipril and omapatrilat, but not by candoxatril. NA overflow was increased after ANG I infusions in controls (EC50 = 9.0 microg/kgANG I, Emax = 5680 pg/ml), but almost completely suppressed by ramipril and omapatrilat. Candoxatril decreased EC50 (4.1 microg/kg) and increased Emax (7259 pg/ml). NA overflow after ANG II infusions was enhanced by candoxatril or omapatrilat. Ex vivo ACE activity was extensively inhibited by ramipril or omapatrilat, whereas ex vivo NEP activity was reduced by omapatrilat and candoxatril only. In vitro, omapatrilat inhibited NEP and ACE with similar potencies (IC50 NEP/IC50 ACE = 0.4).

CONCLUSIONS

Vasopeptidase inhibitors influence ANG II-related NA release depending on their ability to modulate the availability of ANG II via ACE or NEP. After acute application, the vasopeptidase inhibitor suppresses NA release in response to ANG I due to a predominant reduction of ANG II formation. These results indicate that the ratio of ACE-inhibitory and NEP-inhibitory potencies of vasopeptidase inhibitors may be relevant for sympathetic activation in chronic therapy.

Cardiac and renal effects of omapatrilat, a vasopeptidase inhibitor, in rats with experimental congestive heart failure

Omapatrilat (OMP) is a novel mixed inhibitor of angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP), the enzyme that metabolizes natriuretic peptides. Congestive heart failure (CHF) is characterized by excessive sodium retention, attributed to both an excessive effect of angiotensin II and diminished responsiveness to natriuretic peptides. In this study, we examined the acute and chronic renal and cardiac effects of OMP in rats with compensated [urinary sodium excretion (UNaV) > 1,200 microeq/day] and decompensated (UNaV < 100 microeq/day) CHF, induced by a surgical aortocaval fistula (ACF). Bolus injection of OMP (10 mg/kg) to sham controls produced significant diuretic and natriuretic responses [UNaV increased from 0.67 +/- 0.19 to 3.27 +/- 1.35 microeq/min, P < 0.05; fractional sodium excretion (FENa) increased from 0.23 +/- 0.06 to 0.95 +/- 0.34%, P < 0.01] despite a significant decline in blood pressure (BP). Rats with compensated CHF displayed blunted diuresis and natriuresis to this dose of OMP but a significant decrease in BP. However, in rats with decompensated CHF, OMP induced significant natriuresis (FENa increased from 0.18 +/- 0.15 to 0.82 +/- 0.26%, P < 0.05) despite a further decrease in BP (from 90 +/- 9 to 71 +/- 6 mmHg, P < 0.01). Two weeks after ACF, the heart/body weight ratio was significantly greater in rats with CHF than controls (0.51 +/- 0.026 vs. 0.30 +/- 0.004%, P < 0.0001), and UNaV was significantly lower. Immediate or late (1 or 6 days after ACF) OMP treatment in the drinking water (140 mg/l) reduced cardiac hypertrophy to 0.41-0.43% (P < 0.01) and induced natriuresis. These results suggest that OMP improves both sodium balance and cardiac remodeling and might be advantageous to ACE inhibitors for the treatment of decompensated CHF.

Relation of ANP and BNP to their N-terminal fragments in fetal circulation: evidence for enhanced neutral endopeptidase activity and resistance of BNP to neutral endopeptidase in the fetus

OBJECTIVES

To investigate the role of neutral endopeptidase in the turnover of atrial (ANP) and brain (BNP) natriuretic peptides and their N-terminal fragments in human fetal circulation.

DESIGN

Retrospective case-control study.

SETTING

Department of Obstetrics and Gynaecology, University of Leipzig, Germany.

SAMPLE

Nine control pregnancies and nine pregnancies with rhesus isoimmunisation before and after intravascular transfusion.

METHODS

Natriuretic peptides and N-terminal fragments in maternal and fetal blood were measured by radio-immunoassay. Neutral endopeptidase activity was determined by HPLC.

MAIN OUTCOME MEASURES

Maternal and fetal plasma concentrations of ANP, NT-proANP, BNP, NT-proBNP as well as neutral endopeptidase activity. Ratios between mature peptide and N-terminal fragment. Feto-maternal ratio.

RESULTS

Plasma NT-proANP concentrations are 11.7 times higher in fetal than in maternal circulation. The ANP concentration is only 1.8 times higher, probably due to doubled neutral endopeptidase activity. In contrast, both NT-proBNP and BNP are doubled in fetal plasma. Fetuses with Rh isoimmunisation had significantly higher NT-proBNP but not NT-proANP and neutral endopeptidase activity than controls. An additional volume load by intravascular transfusion did not influence N-terminal fragments or neutral endopeptidase activity.

CONCLUSIONS

Our study is the first to determine NT-pro natriuretic peptide concentrations and neutral endopeptidase activity in human fetuses. The results show that increased fetal neutral endopeptidase activity shifts the ANP/NT-proANP but not the BNP/NT-proBNP ratio and that the shifted BNP/NT-proBNP ratio in fetuses with Rh isoimmunisation does not involve increased neutral endopeptidase activity. These findings point to a BNP degradation that is not dependent on neutral endopeptidase.

Vasopeptidase inhibitors: will they have a role in clinical practice?

The human cardiovascular system is regulated by haemodynamic, neurohumoral and structural mechanisms. The endothelium and the neurohumoral system play a key role in modulating both vascular tone and structure by producing vasoactive substances, and in the modulation of blood cell adhesion. Although the neurohormonal systems are essential in vascular homeostasis, they become maladaptive in conditions such as hypertension, coronary disease and heart failure. The clinical success of blocking the renin-angiotensin system by angiotensin converting enzyme (ACE)-inhibitors and the sympathetic nerve system by beta-blockers demonstrates the importance of neurohumoral blockade. The inadequate effect of angiotensin converting enzyme (ACE) or neutral endopeptidase (NEP) inhibitor monotherapy seen in some patients treated for hypertension or congestive heart failure, and the promising effect seen after their combination, led to the development of drugs that simultaneously inhibit both enzyme systems. Neutral endopeptidase, like ACE, is an endothelial cell surface zinc metallopeptidase with similar structure and catalytic site to ACE. NEP is the major enzymatic pathway for degradation of natriuretic peptides. The natriuretic peptide system can be viewed as the endogenous inhibitor of the renin angiotensin system. The dual metalloprotease inhibitors of ACE and NEP, called vasopeptidase inhibitors therefore represent a new and attractive therapeutic strategy for the treatment of cardiovascular disease. The ability to add incremental benefit over already proven therapy, with an acceptable side-effect profile however, is questionable in this new class of agents.