Effect of inhibition of endopeptidase 24.11 on responses to angiotensin II in human volunteers

Targeting Glomerular Hemodynamics for Kidney Protection

The kidney microcirculation is a unique structure as it is composed to 2 capillary beds in series: the glomerular and peritubular capillaries. The glomerular capillary bed is a high-pressure capillary bed, having a 60 mm Hg to 40 mm Hg pressure gradient, capable of producing an ultrafiltrate of plasma quantified as the glomerular filtration rate (GFR), thereby allowing for waste products to be removed and establishing sodium/volume homeostasis. Entering the glomerulus is the afferent arteriole, and the exiting one is the efferent arteriole. The concerted resistance of each of these arterioles is what is known as glomerular hemodynamics and is responsible for increasing or decreasing GFR and renal blood flow. Glomerular hemodynamics play an important role in how homeostasis is achieved. Minute-to-minute fluctuations in the GFR are achieved by constant sensing of distal delivery of sodium and chloride in the specialized cells called macula densa leading to upstream alternation in afferent arteriole resistance altering the pressure gradient for filtration. Specifically, 2 classes of medications (sodium glucose cotransporter-2 inhibitors and renin-angiotensin system blockers) have shown to be effective in long-term kidney health by altering glomerular hemodynamics. This review will discuss how tubuloglomerular feedback is achieved, and how different disease states and pharmacologic agents alter glomerular hemodynamics.

Neprilysin Inhibitors in Heart Failure: The Science, Mechanism of Action, Clinical Studies, and Unanswered Questions

This article provides a contemporary review and a new perspective on the role of neprilysin inhibition in heart failure (HF) in the context of recent clinical trials and addresses potential mechanisms and unanswered questions in certain HF patient populations. Neprilysin is an endopeptidase that cleaves a variety of peptides such as natriuretic peptides, bradykinin, adrenomedullin, substance P, angiotensin I and II, and endothelin. It has a broad role in cardiovascular, renal, pulmonary, gastrointestinal, endocrine, and neurologic functions. The combined angiotensin receptor and neprilysin inhibitor (ARNi) has been developed with an intent to increase vasodilatory natriuretic peptides and prevent counterregulatory activation of the angiotensin system. ARNi therapy is very effective in reducing the risks of death and hospitalization for HF in patients with HF and New York Heart Association functional class II to III symptoms, but studies failed to show any benefits with ARNi when compared with angiotensin-converting enzyme inhibitors or angiotensin receptor blocker in patients with advanced HF with reduced ejection fraction or in patients following myocardial infarction with left ventricular dysfunction but without HF. These raise the questions about whether the enzymatic breakdown of natriuretic peptides may not be a very effective solution in advanced HF patients when there is downstream blunting of the response to natriuretic peptides or among post-myocardial infarction patients in the absence of HF when there may not be a need for increased natriuretic peptide availability. Furthermore, there is a need for additional studies to determine the long-term effects of ARNi on albuminuria, obesity, glycemic control and lipid profile, blood pressure, and cognitive function in patients with HF.

Effects of BNP and Sacubitrilat/Valsartan on Atrial Functional Reserve and Arrhythmogenesis in Human Myocardium

Background

Although the angiotensin receptor-neprilysin inhibitor (ARNI) sacubitril/valsartan started a new era in heart failure (HF) treatment, less is known about the tissue-level effects of the drug on the atrial myocardial functional reserve and arrhythmogenesis.

Methods and Results

Right atrial (RA) biopsies were retrieved from patients (n = 42) undergoing open-heart surgery, and functional experiments were conducted in muscle strips (n = 101). B-type natriuretic peptide (BNP) did not modulate systolic developed force in human myocardium during β-adrenergic stimulation, but it significantly reduced diastolic tension (p < 0.01) and the probability of arrhythmias (p < 0.01). In addition, patient's plasma NTproBNP positively correlated with isoproterenol-induced contractile reserve in atrial tissue in vitro (r = 0.65; p < 0.01). Sacubitrilat+valsartan (Sac/Val) did not show positive inotropic effects on atrial trabeculae function but reduced arrhythmogeneity. Atrial and ventricular biopsies from patients with end-stage HF (n = 10) confirmed that neprilysin (NEP) is equally expressed in human atrial and ventricular myocardium. RA NEP expression correlates positively with RA ejection fraction (EF) (r = 0.806; p < 0.05) and left ventricle (LV) NEP correlates inversely with left atrial (LA) volume (r = −0.691; p < 0.05).

Conclusion

BNP ameliorates diastolic tension during adrenergic stress in human atrial myocardium and may have positive long-term effects on the inotropic reserve. BNP and Sac/Val reduce atrial arrhythmogeneity during adrenergic stress in vitro. Myocardial NEP expression is downregulated with declining myocardial function, suggesting a compensatory mechanism in HF.

The Efficacy and Safety of Sacubitril/Valsartan in Heart Failure Patients: A Review

Heart failure (HF) is one of the leading causes of morbidity and mortality worldwide. Sacubitril/valsartan, an angiotensin receptor-neprilysin inhibitor, has been approved for the treatment of HF. At present, there have been few systematic and detailed reviews discussing the efficacy and safety of sacubitril/valsartan in HF. In this review, we first introduced the pharmacological mechanisms of sacubitril/valsartan, including the reduction in the degradation of natriuretic peptides in the natriuretic peptide system and inhibition of the renin-angiotensin system. Then, we summarized the efficacy of sacubitril/valsartan in HF patients with reduced ejection fraction (HFrEF) or preserved ejection fraction (HFpEF) including the reduction in risks of mortality and hospitalization, reversal of cardiac remodeling, regulation of biomarkers of HF, improvement of the quality of life, antiarrhythmia, improving renal dysfunction and regulation of metabolism. Finally, we discussed the safety and tolerability of sacubitril/valsartan in the treatment of HFrEF or HFpEF. Compared with ACEIs/ARBs or placebo, sacubitril/valsartan showed good safety and tolerability, although the risk of hypotension might be high. In conclusion, the overwhelming majority of studies show that sacubitril/valsartan is effective and safe in the treatment of HFrEF patients but that it has little benefit in HFpEF patients. Sacubitril/valsartan will probably be a promising anti-HF drug in the near future.

Selective Inhibition of the C-Domain of ACE (Angiotensin-Converting Enzyme) Combined With Inhibition of NEP (Neprilysin): A Potential New Therapy for Hypertension

[Figure: see text].

The natriuretic peptide system in heart failure: Diagnostic and therapeutic implications

Natriuretic peptides, which are activated in heart failure, play an important cardioprotective role. The most notable of the cardioprotective natriuretic peptides are atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), which are abundantly expressed and secreted in the atrium and ventricles, respectively, and C-type natriuretic peptide (CNP), which is expressed mainly in the vasculature, central nervous system, and bone. ANP and BNP exhibit antagonistic effects against angiotensin II via diuretic/natriuretic actions, vasodilatory actions, and inhibition of aldosterone secretion, whereas CNP is involved in the regulation of vascular tone and blood pressure, among other roles. ANP and BNP are of particular interest with respect to heart failure, as their levels, most notably BNP and N-terminal proBNP-a cleavage product produced when proBNP is processed to mature BNP-are increased in patients with heart failure. Furthermore, the identification of natriuretic peptides as sensitive markers of cardiac load has driven significant research into their physiological roles in cardiovascular homeostasis and disease, as well as their potential use as both biomarkers and therapeutics. In this review, I discuss the physiological functions of the natriuretic peptide family, with a particular focus on the basic research that has led to our current understanding of its roles in maintaining cardiovascular homeostasis, and the pathophysiological implications for the onset and progression of heart failure. The clinical significance and potential of natriuretic peptides as diagnostic and/or therapeutic agents are also discussed.

Comparison of the Efficacy and Safety of Sacubitril/Valsartan versus Ramipril in Patients With ST-Segment Elevation Myocardial Infarction

The role of sacubitril and/or valsartan in patient with heart failure (HF) is established. Whether sacubitril and/or valsartan plays a role in improving outcomes in patients after ST-segment elevation myocardial infarction (STEMI) is unknown. The current study aims to comparing the efficacy and safety of sacubitril and/or valsartan versus ramipril in post-STEMI patients. Patients presenting with STEMI were randomized to receive either sacubitril and/or valsartan or ramipril after primary percutaneous coronary intervention. The main efficacy endpoint was major adverse cardiac events (MACE) at 30 days and 6 months, defined as a composite of cardiac death, myocardial infarction, and HF hospitalizations. Multiple secondary clinical safety and efficacy endpoints were examined. A total of 200 patients were randomized from January 2018 to March 2019, mean age 54.5±10.4, 87% men, 75% presented with anterior wall STEMI. Baseline clinical and echocardiographic characteristics were comparable between groups. The primary endpoint of MACE was similar with sacubitril/valsartan versus ramipril at 30 days (p = 0.18); however, at 6 months, sacubitril/valsartan was associated with significant reduction of MACE (p = 0.005), mainly driven by reduction in HF hospitalizations (18% vs 36%, OR 0.40, 95% 0.22 to 0.75; p = 0.004). At 6 months, LV ejection fraction was higher with sacubitril/valsartan (46.8±12.5% vs 42.09±13.8%; p = 0.012), with improved LV remodelling (LV end diastolic dimension 50.6±3.9 mm vs 53.2±2.7 mm, p = 0.047; and LV end systolic dimension 36.1±3.4 mm versus 39.9±6.3 mm, p = 0.001) compared with ramipril. No difference in other efficacy or safety clinical endpoints was observed. In conclusion, early initiation of sacubitril/valsartan may offer clinical benefit and improvement in myocardial remodelling in post-STEMI patients.

Inhibition of neprilysin with sacubitril without RAS blockage aggravates renal disease in Dahl SS rats

Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 μg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 μg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.

Angiotensin Receptor and Neprylisin Inhibitor: A new drug in pediatric cardiologist's armamentarium

Heart failure due to congenital heart disease and cardiomyopathies is a significant burden in the pediatric population. Pharmacological strategies for the management of pediatric heart failure are largely based on the extrapolation of adult data and Delphi process based on expert opinion. There are differences in the etiology, clinical course, and outcome of pediatric heart failure as compared to adult, thus the results of adult heart failure trials cannot be simply extrapolated to pediatric patients. There have been a lot of newer drugs for adults with heart failure, but there is a void for pediatric population with heart failure due to many reasons. Early results of multi-centric randomized control PANORAMA HF Trial and subsequent Food and Drug Administration approval for Angiotensin Receptor and Neprylisin Inhibitor (Sacubitril / Valsartan) for pediatric patients have tried to fill in this void and paved the way for a newer class of drugs for heart failure with proven benefits in pediatric patients.

Soluble neprilysin and long-term clinical outcomes in patients with coronary artery disease undergoing percutaneous coronary intervention: a retrospective cohort study

Background

Neprilysin has an essential role in regulating fluid balance and vascular resistance, and neprilysin inhibitors have shown beneficial effects in patients with heart failure. However, the potential predictive value of neprilysin levels as a biomarker for cardiovascular risk remains unclear. The aim of this study was to assess the prognostic value of soluble neprilysin (sNEP) levels in patients with ischemic heart disease.

Methods

Neprilysin levels were measured in 694 consecutive patients with coronary artery disease (CAD) undergoing percutaneous coronary intervention (PCI). These patients were classified into two groups according to their serum levels of neprilysin and categorized into the lower neprilysin group (n = 348) and the higher neprilysin group (n = 346). The primary clinical endpoint was all-cause mortality, and the secondary endpoint was a composite of major adverse cardiac events (MACE).

Results

The median sNEP level was 76.0 pg/ml. The median sNEP levels were higher in patients with left ventricular ejection fraction (LVEF) ≥40% (77.6 pg/ml, interquartile range 46.6–141.3) than in those with LVEF < 40% (70.0 pg/ml, interquartile range 47.1–100.6; P = 0.032). Among all patients, each clinical outcome and MACE did not differ significantly according to the groups divided into median, tertile, or quartile of sNEP levels during a median follow-up of 28.4 months. We did not find a significant relationship between sNEP levels and clinical outcomes in multivariate Cox regression analysis. Among patients with LVEF < 40%, an increased sNEP level was associated with a higher rate of all-cause death (adjusted hazard ratio 2.630, 95% confidence interval 1.049–6.595, P = 0.039).

Conclusion

Serum sNEP levels are not associated with long-term mortality or cardiovascular outcomes after PCI in patients with CAD. In the LVEF < 40% group, increased sNEP levels may be associated with a higher risk of all-cause death.

Neutral Endopeptidase (Neprilysin) in Therapy and Diagnostics: Yin and Yang

Neprilysin (NEP) is a zinc-dependent metalloproteinase that exists in organisms in both transmembrane and soluble forms. NEP substrates are involved in regulating the cardiovascular and nervous systems. In this review, we discuss some of the biochemical characteristics and physiological functions of this enzyme with special emphasis on the use of NEP as a therapeutic target. The history and various physiological aspects of applying NEP inhibitors for treating heart failure and attempts to increase NEP activity when treating Alzheimer's disease using gene and cell therapies are described. Another important issue discussed is the role of NEP as a potential marker for predicting the risk of cardiovascular disease complications. The diagnostic and prognostic performance of soluble NEP in various types of heart failure is analyzed and presented. We also discuss the methods and approaches for measuring NEP activity for prognosis and diagnosis, as well as a possible new role of natriuretic peptides (NEP substrates) in cardiovascular diagnostics.

Future pharmacological therapy in hypertension

PURPOSE OF REVIEW

Hypertension (HTN) is a widespread and growing disease, with medication intolerance and side-effect present among many. To address these obstacles novel pharmacotherapy is an active area of drug development. This review seeks to explore future drug therapy for HTN in the preclinical and clinical arenas.

RECENT FINDINGS

The future of pharmacological therapy in HTN consists of revisiting old pathways to find new targets and exploring wholly new approaches to provide additional avenues of treatment. In this review, we discuss the current status of the most recent drug therapy in HTN. New developments in well trod areas include novel mineralocorticoid antagonists, aldosterone synthase inhibitors, aminopeptidase-A inhibitors, natriuretic peptide receptor agonists, or the counter-regulatory angiotensin converting enzyme 2/angiotensin (Ang) (1-7)/Mas receptor axis. Neprilysin inhibitors popularized for heart failure may also still hold HTN potential. Finally, we examine unique systems in development never before used in HTN such as Na/H exchange inhibitors, vasoactive intestinal peptide agonists, and dopamine beta hydroxylase inhibitors.

SUMMARY

A concise review of future directions of HTN pharmacotherapy.

Effects of neprilysin-renin inhibition in comparison with neprilysin-angiotensin inhibition on the neurohumoral changes in rats with heart failure

Background

The activation of neurohumoral compensatory mechanisms is a common physiological phenomenon in heart failure in order to make up for a failing heart, which will usually have a deteriorating effect on overall health condition. Many medications, such as neprilysin and angiotensin inhibitors, have recently been introduced to remediate neurohumoral changes. This study was conducted to evaluate the efficacy of the sacubitril-aliskiren combination versus the sacubitril-ramipril combination in the treatment of neurohumoral changes in rats with experimentally induced heart failure.

Method

Thirty Wister rats were randomly assigned into five groups each of six rats, the first group was the control group. Intraperitoneal isoprenaline injections of 5 mg/kg/day for 1 week were used to induce experimental models of heart failure in rats of the rest of experimental groups. The second group served as a positive control. Rats in the third, fourth, and fifth groups received oral daily dose of sacubitril 30 mg/kg/day, sacubitril-aliskiren 30,10 mg/kg/day, and sacubitril-ramipril 30/10 mg/kg/day respectively, for 2 weeks.

Results

Induction of heart failure in rats has significantly increased circulating NT-proBNP (980 ± 116.71 pg/ml), MMP9 (15.85 ± 0.57 ng/ml), troponin-I (3.09 ± 0.147 ng/ml), CK-MB (31.55 ± 1.69 ng/ml), renin (736 ± 45.8 pg/ml), urea (52.1 ± 1.57 mg/dl), and creatinine (0.92 ± 0.04 mg/dl). Significant decreases in glomerular filtration rate (7.031 ± 1.6 ml/hr./kg), urine flow (0.2761 ± 0.06 ml/h/kg), total solute excretion (0.11 ± 0.03 meq/m), and mean blood pressure (83.5 ± 2.6 mm hg) were seen in rats with heart failure.

Rats treated with sacubitril combined with aliskiren or ramipril showed a statistically significant reduction of NT-proBNP, MMP9, troponin serum urea, and serum creatinine.

Sacubitril-aliskiren or sacubitril-ramipril administration produced a significant increase in renin plasma level, total solute excretion, urine flow, and glomerular filtration rate.

Conclusion

Sacubitril in combination with aliskiren or with ramipril effectively reduced plasma cardiac biomarkers, such as CK-MB, MMP9, and NT-proBNP, in rats with heart failure. Both combinations showed significant remediation of renal function through increasing GFR, urine flow, and total solute excretion, as well as reducing plasma level of renin. Net results revealed that the sacubitril-aliskiren combination has similar remediating effects on neurohumoral changes compared to the sacubitril-ramipril combination.

Safety of the neprilysin/renin-angiotensin system inhibitor LCZ696

Objectives

The combined neprilysin/rennin-angiotensin system inhibitor sacubitril/valsartan (LCZ696) has shown its superiority over ACEI/ARB therapy. In view of the existing concern of its adverse effects, we aimed to provide evidence of the safety of the new drug.

Results

A total of 6 randomized trials with 11,821 subjects were included in this analysis. No significant differences were found in any adverse effects between LCZ696 and ACEI/ARB or placebo groups. LCZ696 significantly decreased the risks of serious adverse events and death compared with ACEI/ARB. LCZ696 also significantly decrease the risk of discontinuation of treatment for any adverse event no matter compared with ACEI/ARB or a placebo. LCZ696 significantly increased the risk of angioedema and dizziness, while it decreased the risk of renal dysfunction and bronchitis. There was no difference for hypotension, hyperkalemia, cough, upper respiratory tract inflammation, diarrhoea, back pain, nasopharyngitis, headache and influenza between the LCZ696 group and the ACEI/ARB group.

Materials and Methods

A meta-analysis of eligible studies that used LCZ696 in heart failure and hypertension was performed. Embase, PubMed and the Cochrane Library were searched for randomized controlled trials (RCTs) with data on any adverse effects, serious adverse events, discontinuation of treatment for any adverse event, death, angioedema, hypotension, hyperkalemia, and other adverse effects to perform this meta-analysis.

Conclusions

In addition to the beneficial effect of LCZ696 on end point events, the available evidences showed that LCZ696 was associated with less drug-risks than a placebo and ACEI/ARB.

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.

Angiotensin receptor neprilysin inhibitor LCZ696: pharmacology, pharmacokinetics and clinical development

Heart failure still has a significant disease burden with poor outcomes worldwide despite advances in therapy. The standard therapies have been focused on blockade of renin–angiotensin–aldosterone system with angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and mineralocorticoid antagonists and the sympathetic nervous system with β-blockers. The natriuretic peptide system is a potential counter-regulatory system that promotes vasodilatation and natriuresis. Angiotensin receptor neprilysin inhibitors are a new class drug capable of blocking the renin–angiotensin–aldosterone system and enhancing the natriuretic peptide system to improve neurohormonal balance. The success of the PARADIGM-HF trial with LCZ696 and its approval for heart failure treatment is likely to generate a paradigm shift. This review summarises the current knowledge of LCZ696 with a focus on pharmacology, pharmacokinetics and pharmacodynamics, mechanisms of action, clinical efficacy and safety.

Long-term neprilysin inhibition - implications for ARNIs

Neprilysin has a major role in both the generation and degradation of bioactive peptides. LCZ696 (valsartan/sacubitril, Entresto), the first of the new ARNI (dual-acting angiotensin-receptor-neprilysin inhibitor) drug class, contains equimolar amounts of valsartan, an angiotensin-receptor blocker, and sacubitril, a prodrug for the neprilysin inhibitor LBQ657. LCZ696 reduced blood pressure more than valsartan alone in patients with hypertension. In the PARADIGM-HF study, LCZ696 was superior to the angiotensin-converting enzyme inhibitor enalapril for the treatment of heart failure with reduced ejection fraction, and LCZ696 was approved by the FDA for this purpose in 2015. This approval was the first for chronic neprilysin inhibition. The many peptides metabolized by neprilysin suggest many potential consequences of chronic neprilysin inhibitor therapy, both beneficial and adverse. Moreover, LBQ657 might inhibit enzymes other than neprilysin. Chronic neprilysin inhibition might have an effect on angio-oedema, bronchial reactivity, inflammation, and cancer, and might predispose to polyneuropathy. Additionally, inhibition of neprilysin metabolism of amyloid-β peptides might have an effect on Alzheimer disease, age-related macular degeneration, and cerebral amyloid angiopathy. Much of the evidence for possible adverse consequences of chronic neprilysin inhibition comes from studies in animal models, and the relevance of this evidence to humans is unknown. This Review summarizes current knowledge of neprilysin function and possible consequences of chronic neprilysin inhibition that indicate a need for vigilance in the use of neprilysin inhibitor therapy.

Combined Angiotensin Receptor Antagonism and Neprilysin Inhibition

Heart failure affects ≈5.7 million people in the United States alone. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, and aldosterone antagonists have improved mortality in patients with heart failure and reduced ejection fraction, but mortality remains high. In July 2015, the US Food and Drug Administration approved the first of a new class of drugs for the treatment of heart failure: Valsartan/sacubitril (formerly known as LCZ696 and currently marketed by Novartis as Entresto) combines the angiotensin receptor blocker valsartan and the neprilysin inhibitor prodrug sacubitril in a 1:1 ratio in a sodium supramolecular complex. Sacubitril is converted by esterases to LBQ657, which inhibits neprilysin, the enzyme responsible for the degradation of the natriuretic peptides and many other vasoactive peptides. Thus, this combined angiotensin receptor antagonist and neprilysin inhibitor addresses 2 of the pathophysiological mechanisms of heart failure: activation of the renin-angiotensin-aldosterone system and decreased sensitivity to natriuretic peptides. In the Prospective Comparison of ARNI With ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure (PARADIGM-HF) trial, valsartan/sacubitril significantly reduced mortality and hospitalization for heart failure, as well as blood pressure, compared with enalapril in patients with heart failure, reduced ejection fraction, and an elevated circulating level of brain natriuretic peptide or N-terminal pro-brain natriuretic peptide. Ongoing clinical trials are evaluating the role of valsartan/sacubitril in the treatment of heart failure with preserved ejection fraction and hypertension. We review here the mechanisms of action of valsartan/sacubitril, the pharmacological properties of the drug, and its efficacy and safety in the treatment of heart failure and hypertension.

Critical Questions about PARADIGM-HF and the Future

Cardiovascular (CV) diseases in general and heart failure (HF) in particular are major contributors to death and morbidity and are also recognized as important drivers of health care expenditure. The PARADIGM-HF trial was a pivotal trial designed to compare the long-term effects of LCZ696 with enalapril in patients with symptomatic HF with reduced ejection fraction (HFrEF). This review article presents an in-depth view of the PARADIGM-HF trial and the implications of the results in the management of patients with HF and is based on peer reviewed manuscripts, editorials, perspectives and opinions written about the PARADIGM-HF trial. The article presents the key safety and efficacy results of the trial with specific emphasis on the clinical implications of these findings. The review highlights the highly statistically significant, 20% reduction in the primary composite endpoint of cardiovascular death or HF hospitalization, and a 16% reduction in the risk of death from any cause. It also provides an overview of the design, clinical findings, limitations and special areas of clinical interest. The review discusses the future of LCZ696 and additional trials that seek to answer questions in other sub-populations of patients with HF. The article reiterates what has been concluded by many experts in the field of HF- the introduction of LCZ696 into routine clinical care, while dependent on the regulatory approvals in various countries as well as acceptance by physicians, payers and patients, will change the treatment landscape for patients with HFrEF.

The neprilysin pathway in heart failure: a review and guide on the use of sacubitril/valsartan

Inhibition of neurohumoural pathways such as the renin angiotensin aldosterone and sympathetic nervous systems is central to the understanding and treatment of heart failure (HF). Conversely, until recently, potentially beneficial augmentation of neurohumoural systems such as the natriuretic peptides has had limited therapeutic success. Administration of synthetic natriuretic peptides has not improved outcomes in acute HF but modulation of the natriuretic system through inhibition of the enzyme that degrades natriuretic (and other vasoactive) peptides, neprilysin, has proven to be successful. After initial failures with neprilysin inhibition alone or dual neprilysin-angiotensin converting enzyme (ACE) inhibition, the Prospective comparison of angiotensin receptor neprilysin inhibitor (ARNI) with ACEI to Determine Impact on Global Mortality and morbidity in Heart Failure trial (PARADIGM-HF) trial demonstrated that morbidity and mortality can be improved with the angiotensin receptor blocker neprilysin inhibitor sacubitril/valsartan (formerly LCZ696). In comparison to the ACE inhibitor enalapril, sacubitril/valsartan reduced the occurrence of the primary end point (cardiovascular death or hospitalisation for HF) by 20% with a 16% reduction in all-cause mortality. These findings suggest that sacubitril/valsartan should replace an ACE inhibitor or angiotensin receptor blocker as the foundation of treatment of symptomatic patients (NYHA II–IV) with HF and a reduced ejection fraction. This review will explore the background to neprilysin inhibition in HF, the results of the PARADIGM-HF trial and offer guidance on how to use sacubitril/valsartan in clinical practice.

Current Understanding of the Compensatory Actions of Cardiac Natriuretic Peptides in Cardiac Failure: A Clinical Perspective

Natriuretic peptides play a crucial role in maintaining cardiovascular homeostasis. Among their properties are vasodilation, natriuresis, diuresis, and inhibition of cardiac remodeling. As heart failure progresses, however, natriuretic peptides fail to compensate. Knowledge of their processing and signaling pathways has guided the development of pharmacological therapies aimed at bolstering their effects. The drugs that have achieved the most clinical success have also stirred the most controversy. Nesiritide, the synthetic B-type natriuretic peptide, yielded significant symptomatic relief and improved haemodynamics but its use was plagued with questions surrounding its possibly harmful impact on renal function. More recently, compounds containing inhibitors of neprilysin, the enzyme responsible for degrading natriuretic peptides, have demonstrated morbidity and mortality benefit, but have also been linked to possible negative side effects. Clearly, potentiating the actions of natriuretic peptides for the benefit of patients is not as simple as just raising their serum concentration. This article reviews the current understanding of the compensatory actions of cardiac natriuretic peptides in heart failure and how this knowledge is revolutionizing heart failure therapy.

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.

Neprilysin inhibition to treat heart failure: a tale of science, serendipity, and second chances

This review describes the role of neprilysin (also known as neutral endopeptidase or enkephalinase) in the degradation of natriuretic and other vasoactive peptides, including bradykinin and adrenomedullin. The initial development of neprilysin inhibitors, then angiotensin converting enzyme-neprilysin inhibitors and, most recently, the angiotensin receptor neprilysin inhibitor (ARNI) LCZ696 (sacubitril valsartan) as an extension of the nurohumoral basis for the treatment of heart failure is also summarised. Finally, the implications of the compelling benefits of LCZ696 compared with enalapril in the Prospective comparison of ARNI with ACEI to Determine Impact on Global Mortality and morbidity in Heart Failure trial (PARADIGM-HF) is discussed.

Effects of neutral endopeptidase (neprilysin) inhibition on the response to other vasoactive peptides in small human resistance arteries: studies with thiorphan and omapatrilat

PURPOSE

New compounds with neprilysin or neutral endopeptidase (NEP) inhibiting activity are under clinical investigation in heart failure and hypertension. We investigated the effect of NEP inhibition on the functional vasomotor responses to a range of vasoactive peptides in human blood vessels.

METHODS

Small human resistance arteries from patients with coronary artery disease and preserved left ventricular systolic function were studied. Thiorphan (a NEP inhibitor) was compared with captopril (an ACE inhibitor) and omapatrilat (a dual NEP-ACE inhibitor) with regard to their effects on the response of human arteries to key vasoactive peptides.

RESULTS

As expected, both captopril and omapatrilat (but not thiorphan) inhibited the vasoconstrictor effect of angiotensin I (maximal response [SEM]: 27 ± 8% vehicle, 6 ± 2% captopril, 39 ± 10% thiorphan, 8 ± 7% omapatrilat, P < 0.05). Thiorphan, captopril, and omapatrilat all enhanced the vasodilator response to bradykinin (all P < 0.01). Omapatrilat markedly augmented the vasodilator action of adrenomedullin (P < 0.05), whilst thiorphan and captopril did not. None of the three inhibitors studied affected the vasodilator action of c-type natriuretic peptide, calcitonin gene-related peptide, vasoactive intestinal polypeptide or substance P.

CONCLUSIONS

NEP inhibition with thiorphan modestly augmented the vasodilator action of bradykinin, but did not potentiate the response to adrenomedullin; dual ACE and NEP inhibition with omapatrilat, as expected, markedly augmented the response to bradykinin and also potentiated the effect of adrenomedullin. Thiorphan weakly enhanced the vasoconstrictor response to angiotensin I. Neither omapatrilat nor thiorphan had any effect on the action of a range of other vasoactive peptides including CNP.

Natriuretic and renoprotective effect of chronic oral neutral endopeptidase inhibition in acute renal failure

Neutral endopeptidase (NEP: EC 3.4.24.11) is involved in the degradation of peptides such as atrial natriuretic peptide, angiotensin II (AngII), and endothelin-1 (ET-1). In this study we propose that NEP inhibition provides protection in glycerol-induced acute renal failure (ARF). Renal vascular responses were evaluated in ARF rats where ARF was induced by injecting 50% glycerol in candoxatril, a NEP inhibitor (30 mg/kg, orally; for 3 weeks) pretreated rats. AngII and U46619 (a TxA2 mimetic) vasoconstriction was increased (2- to 4-fold) in ARF while ET-1 vasoconstriction was surprisingly reduced (23+/-3%; p<0.05). In ARF, candoxatril paradoxically enhanced ET-1 response (60+/-20%; p<0.05) but reduced AngII vasoconstriction (51+/-11%; p<0.05) without affecting U46619 response. However, candoxatril treatment was without effect on plasma ET-1 and TxB2 levels in ARF. Candoxatril reduced plasma AngII by 34+/-4% (p<0.05) in ARF which was approximately 3.5-fold higher compared to control. Candoxatril doubled the nitrite excretion in control but was without effect on proteinuria or nitrite excretion in ARF. Candoxatril enhanced Na+ and creatinine excretion in ARF by 73+/-9% and 33+/-2%, respectively. These results suggest that NEP inhibition may confer protection in glycerol-induced ARF by stimulating renal function but without a consistent effect on renal production and renal vascular responses to endogenous vasoconstrictors.

Chronic endopeptidase inhibition in DOCA-salt hypertension: mechanism of cardiovascular protection

These studies examined the interactions of neutral endopeptidase (NEP), endothelin-1 (ET-1), and nitric oxide (NO) in deoxycorticosterone acetate (DOCA)-induced hypertension. Male Sprague-Dawley rats (n = 35) were uninephrectomized (UNx) or uninephrectomized and treated with DOCA (25 mg pellet implanted subcutaneously). Candoxatril (30 mg/kg day(-1)), a NEP inhibitor, was given orally for 3 weeks in UNx or DOCA rats. Sham nephrectomized rats (SHAM) served as controls. Except SHAM, all other groups received 1% NaCl in drinking water ad libitum. Measurements were taken of systolic blood pressure (SBP), left ventricle (LV), and aortic weight (AW), plasma ET-1, and urinary excretion of nitrite and Na+. Whole body vascular hypertrophy and morphometric analysis of histological sections of the heart were also determined. In DOCA rats, SBP increased from 113 +/- 5 to 170 +/- 5 mmHg without significant changes in body weight (BW). Candoxatril reduced the increase in SBP to 135 +/- 9 mmHg (P < 0.05), abolished the increased LV wall thickness (P < 0.05), and increased the reduced LV lumen diameter (P < 0.05) in DOCA-salt rats. Candoxatril also reduced plasma ET-1 by 88 +/- 9% and 89 +/- 17% (P < 0.05) in UNx and DOCA rats, respectively, and elicited increases in urinary excretion of nitrite. These effects were accompanied by a marked increase in urinary excretion of Na+ (U(Na)V) (P < 0.05) and a blunting of the proteinuria (32 +/- 5%; P < 0.05) in DOCA rats. We conclude that endopeptidase inhibition in DOCA-salt hypertension reduced the increase in blood pressure and the attendant tissue hypertrophy and renal injury. These effects suggest a correlation between endopeptidase-related reduction in ET-1 production and protection in DOCA-salt hypertension.

The renin-angiotensin and the kallikrein-kinin systems

The renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) each encompasses a large number of molecules, with several participating in both systems. The RAS generates a family of bioactive angiotensin peptides with varying biological activities. These include angiotensin-(1-8) (Ang II), angiotensin-(2-8) (Ang III), angiotensin-(3-8) (Ang IV), and angiotensin-(1-7) [Ang-(1-7)]. Ang II and Ang III act on type 1 (AT(1)) and type 2 (AT(2)) angiotensin receptors, whereas, Ang IV and Ang-(1-7) act on their own receptors. The KKS also generates a family of bioactive peptides with varying biological activities. These include hydroxylated and non-hydroxylated bradykinin and kallidin peptides and their carboxypeptidase metabolites des-Arg(9)-bradykinin and des-Arg(10)-kallidin. Whereas bradykinin and kallidin act mainly via the type 2 bradykinin (B(2)) receptor, des-Arg(9)-bradykinin and des-Arg(10)-kallidin act mainly via the type 1 bradykinin (B(1)) receptor. The AT(1) receptor forms heterodimers with the AT(2) and B(2) receptors and there is cross talk between the AT(1) and epidermal growth factor receptors. The B(2) receptor also interacts with angiotensin converting enzyme and nitric oxide synthase. Both angiotensin and kinin peptides are metabolised by many different peptidases that are important determinants of the activities of the RAS and KKS, and several of which participate in both systems.

The therapeutic effect of natriuretic peptides in heart failure; differential regulation of endothelial and inducible nitric oxide synthases

The abnormal regulation of nitric oxide synthase activity represents an underlying feature of heart failure. Increased peripheral vascular resistance, and decreased renal function may be in part related to impaired endothelium-dependent nitric oxide (NO) synthesis. Paradoxically, the chronic production of NO by inducible nitric oxide synthase (iNOS) in heart failure exerts deleterious effects on ventricular contractility, and circulatory function. Consequently, pharmacologically improving endothelium-dependent NO synthesis and the concomitant inhibition of iNOS activity would be therapeutically advantageous. Interestingly, natriuretic peptides have been shown to differentially regulate endothelial NOS (eNOS) and iNOS activity. Moreover, in both patients and animal models of heart failure, pharmacologically increasing plasma natriuretic peptide levels ameliorated vascular tone, renal function, and ventricular contractility. Based on these observations, the following review will explore whether the therapeutic benefit of the natriuretic peptide system in heart failure may occur in part via the amelioration of endothelium-dependent NO synthesis, and the concomitant inhibition of cytokine-mediated iNOS expression.

Effects of the vasopeptidase inhibitor, omapatrilat, in 723 patients with coronary heart disease

INTRODUCTION

Among individuals with a history of myocardial infarction (MI), higher levels of blood pressure (BP) are associated with increased long-term risks of death from coronary heart disease. Treatment with a BP-lowering regimen, based on omapatrilat may result in greater clinical benefits than treatment with a regimen based on a regular angiotensin-converting enzyme (ACE) inhibitor because of more favourable effects on the renin-angiotensin-aldosterone system.

METHODS

Seven hundred and twenty-three clinically stable patients with a history of MI or unstable angina, and a mean entry BP of 134/77 mmHg, were randomised to six months treatment with omapatrilat 40 mg, omapatrilat 20 mg, or matching placebo.

RESULTS

After six months, mean BP levels (systolic/diastolic) in the omapatrilat 40 mg group were reduced by 4.3/2.9 mmHg (95% confidence interval 1.3 to 7.2/1.2 to 4.6). Mean BP levels in the omapatrilat 20 mg group were reduced by 4.6/1.0 mmHg (1.6 to 7.6/ 0.7 to 2.6) in comparison with the placebo group. Both doses of omapatrilat also produced significant decreases in plasma ACE activity and significant increases in levels of plasma renin activity, atrial natriuretic peptide, endothelin and homocysteine (p<0.05 for all). Premature discontinuations were more frequent with omapatrilat than with placebo (p<0.001 for 20 mg and 40 mg).

CONCLUSIONS

Omapatrilat produced changes in BP, neurohormone and biochemical parameters that were similar for the two doses. The long-term clinical implications of the observed effects are uncertain and a large-scale randomised trial would be required to reliably establish the effects of omapatrilat on the risks of major vascular disease events among patients with coronary heart disease.

A review of vasopeptidase inhibitors: a new modality in the treatment of hypertension and chronic heart failure

Vasopeptidase inhibitors are a group of agents capable of inhibiting neutral endopeptidase and angiotensin-converting enzymes, which leads to potentiation of natriuretic peptide actions and suppression of the renin-angiotensin-aldosterone system. With this distinctively characteristic mechanism, these agents have emerged as a new drug class for management of hypertension and heart failure. Several vasopeptidase inhibitors are under clinical investigation. Omapatrilat is the most studied agent in this class. Clinical studies of omapatrilat in hypertension have consistently shown the agent's effectiveness in a variety of patient populations. In patients with heart failure, omapatrilat significantly improved neurohormonal and hemodynamic status. Long-term effects of omapatrilat in patients with heart failure recently were compared with those of conventional therapy in a large phase II trial. Results of the study appear promising. Large clinical trials are ongoing, and additional information regarding safety and efficacy from these studies may help define the place in therapy for this agent.

Effects of omapatrilat on pharmacodynamic biomarkers of neutral endopeptidase and Angiotensin-converting enzyme activity in humans

Vasopeptidase inhibition is a new concept in blood pressure management. A single molecule simultaneously inhibits two enzymes that regulate cardiovascular function: neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE)[1]. Development of vasopeptidase inhibitors stemmed from the need for new and more efficacious antihypertensive agents that not only reduce blood pressure but also treat hypertension as part of a larger syndrome involving endothelial dysfunction [2]. By inhibiting NEP and ACE, vasopeptidase inhibitors enhance the natriuretic peptide and kallikrein-kinin systems and inhibit the renin-angiotensin-aldosterone system. This article outlines the pharmacodynamic effects of the vasopeptidase inhibitor omapatrilat on biomarkers of NEP and ACE activity in humans.

Vasopeptidase inhibitors

Vasopeptidase inhibitors are a new class of cardiovascular drug that simultaneously inhibit both neutral endopeptidase and angiotensin-converting enzyme (ACE). They increase the availability of peptides that have vasodilatory and other vascular effects; they also inhibit production of angiotensin II. In animal models vasopeptidase inhibitors decrease blood pressure in low, medium, and high renin forms of hypertension, and they also appear to confer benefits in models of heart failure and ischaemic heart disease. Studies in human hypertension show that these agents are effective in decreasing blood pressure regardless of race or age. Experience with omapatrilat, the most clinically advanced of these drugs, has shown it to be more effective than currently available ACE inhibitors or other widely used antihypertensive agents. Studies with omapatrilat in congestive heart failure have shown beneficial effects on haemodynamics and symptoms. The vasopeptidase inhibitors appear to have safety profiles similar to ACE inhibitors, though the frequency of side-effects such as angio-oedema and cough remains to be established. Large trials with clinical endpoints, some already in progress, are needed to establish the place of this class of drug beside that of established therapies in conditions such as hypertension, heart failure, ischaemic heart disease, and nephropathy.

Effects of the vasopeptidase inhibitor omapatrilat on cardiac endogenous kinins in rats with acute myocardial infarction

The purposes of this study were to evaluate and to compare the effects of simultaneous angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) inhibition by the vasopeptidase inhibitor omapatrilat (1 mg. kg(-1). day(-1)) with those of the selective ACE inhibitor enalapril (1 mg. kg(-1). day(-1)) on survival, cardiac hemodynamics, and bradykinin (BK) and des-Arg(9)-BK levels in cardiac tissues 24 h after myocardial infarction (MI) in rats. The effect of the co-administration of both B(1) and B(2) kinin receptor antagonists (2.5 mg. kg(-1). day(-1) each) with metallopeptidase inhibitors was also evaluated. The pharmacological treatments were infused subcutaneously using micro-osmotic pumps for 5 days starting 4 days before the ligation of the left coronary artery. Immunoreactive kinins were quantified by highly sensitive and specific competitive enzyme immunoassays. The post-MI mortality of untreated rats with a large MI was high; 74% of rats dying prior to the hemodynamic study. Mortality in the other MI groups was not significantly different from that of the untreated MI rats. Cardiac BK levels were not significantly different in the MI vehicle-treated group compared with the sham-operated rats. Both omapatrilat and enalapril treatments of MI rats significantly increased cardiac BK concentrations compared with the sham-operated group (P < 0.05). However, cardiac BK levels were significantly increased only in the MI omapatrilat-treated rats compared with the MI vehicle-treated group (P < 0.01). Cardiac des-Arg(9)-BK concentrations were not significantly modified by MI, and MI with omapatrilat or enalapril treatment compared with the sham-operated group. The co-administration of both kinin receptor antagonists with MI omapatrilat- and enalapril-treated rats had no significant effect on cardiac BK and des-Arg(9)-BK levels. Thus, the significant increase of cardiac BK concentrations by omapatrilat could be related to a biochemical or a cardiac hemodynamic parameter on early (24 h) post-MI state.

Comparison of a vasopeptidase inhibitor with neutral endopeptidase and angiotensin-converting enzyme inhibitors on bradykinin metabolism in the rat coronary bed

The in vitro effects of omapatrilat, a dual vasopeptidase inhibitor that simultaneously inhibits neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), on exogenous bradykinin metabolism after a single passage through the coronary bed were compared with that of a NEP inhibitor (retrothiorphan, 25 nM), an ACE inhibitor (enalaprilat, 130 nM), and omapatrilat (25 nM). Bradykinin and inhibitors were infused into isolated Langendorff rat hearts perfused at 1 ml/min followed by reperfusion at 10 ml/min. Residual bradykinin was quantified in the coronary effluent by enzyme-linked immunosorbent assay to calculate bradykinin recovery and its kinetic parameters (Vmax/Km). Bradykinin degradation rate at 1 ml/min was 4.56 +/- 0.39 1/min per gram without inhibitors and was significantly reduced to 2.57 +/- 0.19 1/min per gram in the presence of enalaprilat, to 2.97 +/- 0.38 1/min per gram with retrothiorphan, to 1.82 +/- 0.17 1/min per gram with both enalaprilat and retrothiorphan, and to 1.14 +/- 0.35 1/min per gram with omapatrilat. In a second set of experiments, the effect of a 14-day treatment of rats with either ACE inhibitors (enalapril, quinapril, and ramipril), a NEP inhibitor (candoxatril), or omapatrilat on exogenous bradykinin metabolism was studied in Langendorff perfused hearts isolated from these long-term treated rats. In untreated rats, bradykinin degradation at a coronary perfusion of 1 ml/min was 4.35 +/- 0.41 1/min per gram. This value was reduced by 30% for the NEP inhibitor, by 50% for all ACE inhibitors, and by 75% for omapatrilat. All inhibitors administered either short term or long term significantly reduced bradykinin degradation during a single passage through the coronary bed. However, omapatrilat administration resulted in the greatest protection from bradykinin breakdown than ACE or NEP inhibitors alone.

Practical implications of current natriuretic peptide research

Since the original discovery of atrial natriuretic peptide (ANP) nearly 20 years ago and the subsequent realisation of the existence of a family of natriuretic peptides, there has been considerable progress in the elucidation of the physiological and pathophysiological significance of these peptides. This review has examined two potentially important practical aspects arising from natriuretic peptide research - the significance of measurement of plasma levels of ANP and of brain natriuretic peptide BNP for cardiovascular disease and the therapeutic potential of targeting the natriuretic peptide system. Several situations where the measurement of plasma ANP and BNP may be of benefit in the overall assessment and prognosis of cardiac disease have been discussed. The measurement of plasma levels of these peptides appears to have limited value as a specific diagnostic tool and is unlikely to replace well-established procedures to assess cardiac function. Nevertheless, given the strong negative predictive value, the value of the measurement of plasma natriuretic peptides particularly BNPs, in people with suspected heart disease, rests on the evidence that a normal value indicates a low risk of cardiac impairment. Moreover, a consistently elevated plasma level of BNP after myocardial infarction is associated with a distinctly poor prognosis. In turn, this may help to select those with high plasma levels for subsequent detailed investigation of cardiac dysfunction. This may be an important option, especially where the facilities for the more invasive cardiological procedures are not available. Intriguingly, recent research also suggests the possibility that plasma levels of natriuretic peptides may have an important role in guiding more effective therapy for heart failure. The potent cardiovascular and renal effects of ANP and BNP provide an important therapeutic potential for hypertension and for conditions associated with volume overload. A number of approaches which have been used to enhance endogenous activity of these peptides have been highlighted. The use of the native peptides ANP and BNP may well be valuable in some circumstances, such as in critically ill individuals with congestive heart failure or renal failure. However, the limitations of the use of peptides, especially for long-term treatment, are obvious. In view of this, considerable effort has been devoted to the development of orally active agents to enhance endogenous natriuretic peptides by inhibition of breakdown by neutral endopeptidase. This research has led to the development of vasopeptidase inhibitors - dual inhibitors of both endopeptidase and angiotensin-converting enzyme - to enhance endogenous natriuretic peptide function on a background of reduced angiotensin II activity. The broad spectrum of action and the potentially important target-organ protection of these inhibitors offer potential benefits which may well go beyond existing treatment of hypertension and of conditions associated with overt volume overload.

Vasopeptidase inhibition: a new direction in cardiovascular treatment

The development of new antihypertensive agents is becoming even more important. We need better blood pressure control and also agents that treat hypertension as a disease of the vascular endothelium. Recently, it has been shown that blocking the renin-angiotensin system with angiotensin converting enzyme (ACE) inhibitors reduces blood pressure and decreases the incidence of vascular disease. Another peptide system, the natriuretic peptide system, has also been shown to be important in blood pressure control and volume homeostasis. Because ACE and neutral endopeptidase, the enzyme responsible for the degradation of the natriuretic peptides, are both zinc metalloproteases, new pharmaceuticals that inhibit both enzymes have been developed. The first of these, omapatrilat, has been shown to be an effective antihypertensive agent and to have great potential for treating congestive heart failure.

The effects of Z13752A, a combined ACE/NEP inhibitor, on responses to coronary artery occlusion; a primary protective role for bradykinin

The effects on the responses to coronary artery occlusion of a combined ACE/NEP inhibitor (Z13752A) were examined in anaesthetized dogs. A 1 h infusion of Z13752A (128 microgram kg(-1) min(-1) intravenously) decreased arterial blood pressure (by 11+/-3%; P<0. 05) and increased coronary blood flow (by 12+/-4%, P<0.05). There were no other significant haemodynamic changes. Z13752A inhibited both NEP and ACE enzymes both in dog plasma and in tissue (lung ACE; kidney NEP). Pressor responses to angiotensin I in vivo were inhibited and systemic vasodilator responses to bradykinin were potentiated. When the left anterior descending coronary artery was occluded for 25 min, Z13752A markedly reduced the severity of the resultant ventricular arrhythmias. No ventricular fibrillation (VF) occurred (compared to 7/16 in the controls; P<0.05), and ventricular tachycardia (VT) was reduced (VT in 2/9 dogs treated with Z13752A cp. 16/16 of controls; episodes of VT 0.2+/-0.1 c.p. 10.7+/-3.3; P<0. 05). Reperfusion of the ischaemic myocardium led to VF in all control dogs but occurred less frequently in dogs given Z13752A (survival from the combined ischaemia-reperfusion insult 67% c.p. 0% in controls; P<0.05). Z13752A reduced two other indices of ischaemia severity; epicardial ST-segment elevation and inhomogeneity of electrical activation. These protective effects of Z13752A during ischaemia and reperfusion were abolished by the administration of icatibant (0.3 mg kg(-1), i.v.) a selective antagonist of bradykinin at B(2) receptors; the ischaemic changes in dogs given both icatibant and Z13752A were similar to those in the controls. We conclude that this ACE/NEP inhibitor is effective at reducing the consequences of coronary artery occlusion in this canine model and that this protection is primarily due to potentiation of released bradykinin. British Journal of Pharmacology (2000) 129, 671 - 680

Symptomatic systolic ventricular failure

Over the past 20 to 30 years there have been significant advances in the management of heart failure related to improved understanding of pathophysiology, better methods of assessment, and improved drug treatments. The aims of treatment have broadened, with increased emphasis on earlier intervention. Clinical research activity in this area has been considerable, increasingly allowing an evidence-based approach to management. Most earlier trials of treatment were relatively short-term, small-group studies with various clinical end points, including severity of symptoms, exercise performance, and left ventricular function assessment; however, increasingly a higher standard of evidence has been required, including a provision of reliable, large-scale mortality trial data. This has been further encouraged, if not mandated, by the relatively recent appreciation that some agents may demonstrate dissociation of treatment effects, possibly dose related, with improved short-term outcomes but adverse effects on survival with prolonged treatment. The general principles of management of congestive heart failure encompass patient evaluation and confirmation of the diagnosis, consideration, and correction of underlying remediable causes and precipitating factors, pharmacological treatment, patient education and counseling, and planned follow-up, as summarized in recently published guidelines. This review focuses primarily on the available randomized controlled clinical trial evidence related to the pharmacological treatment of the clinical congestive heart failure syndrome. Other aspects of management, such as patient education, counseling, and planned follow-up, should be regarded as complementary to pharmacological treatment and important to ensure compliance and optimal long-term outcomes.

Metabolism of bradykinin by the rat coronary vascular bed

OBJECTIVE

To study the metabolism of bradykinin (BK) after a single passage through the coronary bed in isolated Langendorff rat hearts.

METHODS

BK was infused into the aortic flow line to obtain a final concentration of 10 nM, and the coronary, effluent was collected to quantify BK and des-Arg9-BK by competitive enzyme immunoassay. The nature of immunoreactive material was confirmed by immunograms after HPLC separation. The experiments were performed with hearts perfused at either one of the following coronary flow rates: 1, 5 or 10 ml/min.

RESULTS

BK recovery without inhibitors was 86.3 +/- 2.9, 60.8 +/- 6.3, and 29.6 +/- 6.8% at 10, 5, and 1 ml/min, respectively. The Vmax/Km ratios at these coronary flow rates were 2.19 +/- 0.72, 4.81 +/- 0.64, and 2.59 +/- 0.33 min-1 g-1), respectively. The angiotensin-converting enzyme (ACE) inhibitor, enalaprilat (130 nM), reduced BK degradation at all flow rates. Inhibition of neutral endopeptidase with retrothiorphan (25 nM) had no effect on BK degradation. However, the combined treatment with enalapril and retrothiorphan reduced BK degradation to lower values than enalaprilat alone. The effect of enzyme inhibitors on BK recovery was inversely related to coronary flow: inhibiting BK degradation markedly increased BK recovery at 1 ml/min, but had no effect at 10 ml/min. The kininase I metabolite of BK, des-Arg9-BK, could not be detected under these experimental conditions.

CONCLUSIONS

ACE is the major enzyme responsible for BK degradation during a single passage through the coronary bed. Neutral endopeptidase contributes to BK degradation only when ACE activity is impaired. The effect of enzyme inhibitors on the coronary concentration of BK is highly dependent on coronary flow rate.

Effects of MDL 100,240, a dual inhibitor of angiotensin-converting enzyme and neutral endopeptidase on the vasopressor response to exogenous angiotensin I and angiotensin II challenges in healthy volunteers

MDL 100,240, a dual inhibitor of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), was administered intravenously to two panels of four healthy males in a four-period, dose-increasing (0, 1.56, 6.25, and 25 mg, and 0, 3.13, 12.5, and 50 mg, respectively) double-blind, placebo-controlled study. Plasma ACE activity and blood-pressure response to exogenous angiotensin I and angiotensin II i.v. challenges and safety and tolerance were assessed over a 24-h period. MDL 100,240 induced a rapid, dose-related, and sustained inhibition of ACE (>70% over 24 h at doses > or =12.5 mg). The time integral of ACE inhibition was related to the dose but with near-maximal values already attained at doses > or =12.5 mg. Systolic and diastolic blood-pressure responses to exogenous angiotensin I challenges were inhibited in a dose-dependent fashion, whereas the effects of angiotensin II remained unaffected. Mean supine blood pressure decreased transiently (3 h) at doses > or =3.125 mg and < or =24 h with the 25- and 50-mg doses, but not significantly. MDL 100,240 was well tolerated. In healthy subjects, MDL 100,240 exerts a dose-dependent and long-lasting ACE-blocking activity, also expressed by the inhibition of the pressor responses to exogenous angiotensin I challenges. The baroreceptor reflex, assessed by the response to exogenous angiotensin II challenge, remains unaltered.

Comparative effects of the dual metallopeptidase inhibitor, MDL 100,240 and of enalaprilat on regional and on cardiac haemodynamics in conscious, hypertensive, transgenic ((mRen-2)27) rats

1. Heterozygous, male, hypertensive, transgenic ((mRen-2)27) rats (350-450 g) were instrumented for the measurement of regional or cardiac haemodynamics (n = 16, in both groups). Animals were given continuous i.v. infusions of the angiotensin-converting enzyme inhibitor, enalaprilat, or the dual metallopeptidase inhibitor, MDL 100,240 (both at 3 mg kg-1, 3 mg kg-1 h-1; n = 8 for regional and cardiac haemodynamics), for 32 h. Twenty four hours after the onset of infusion of enalaprilat or MDL 100,240, the bradykinin (B2)-receptor antagonist, Hoe 140 (1 mg kg-1, i.v.), was given and measurements were continued for a further 8 h, to assess any possible involvement of bradykinin. 2. Over the first 8 h of infusion, both enalaprilat and MDL 100,240 had significant antihypertensive effects, accompanied by similar regional vasodilatations. However, the blood pressure lowering effect of MDL 100,240 (-54 +/- 9 mmHg) was greater than that of enalaprilat (-38 +/- 4 mmHg), because the former caused a significantly greater reduction in cardiac index. 3. Between 8-24 h after the onset of infusion, there was a reduction in the effect of enalaprilat on blood pressure, because cardiac index rose, with no further increase in total peripheral conductance. In contrast, the antihypertensive effect of MDL 100,240 persisted, in spite of a recovery in cardiac index, because there was further vasodilatation, particularly in the mesenteric and hindquarters vascular beds. 4. There were no apparent haemodynamic changes associated with the injection of Hoe 140, and over the following 8 h, the difference between the haemodynamic effects of enalaprilat and MDL 100,240 persisted; there was little evidence of suppression of the effects of either drug. 5. These results are more consistent with the antihypertensive effects of enalaprilat or MDL 100,240 in transgenic ((mRen-2)27) rats being due to suppression of angiotensin II production, than due to inhibition of bradykinin degradation. The additional effects of MDL 100,240 may be accounted for by inhibition of the degradation of natriuretic peptides reducing cardiac output, initially, and decreasing vascular tone, subsequently. Alternatively, the additional increase in vascular conductance following treatment with MDL 100,240 may represent an autoregulatory response to the reduced pressure.