Renal response to candoxatrilat in patients with heart failure

Hypertension and cardiomyopathy associated with chronic kidney disease: epidemiology, pathogenesis and treatment considerations

Chronic kidney disease (CKD) is a complex condition with a prevalence of 10-15% worldwide. An inverse-graded relationship exists between cardiovascular events and mortality with kidney function which is independent of age, sex, and other risk factors. The proportion of deaths due to heart failure and sudden cardiac death increase with progression of chronic kidney disease with relatively fewer deaths from atheromatous, vasculo-occlusive processes. This phenomenon can largely be explained by the increased prevalence of CKD-associated cardiomyopathy with worsening kidney function. The key features of CKD-associated cardiomyopathy are increased left ventricular mass and left ventricular hypertrophy, diastolic and systolic left ventricular dysfunction, and profound cardiac fibrosis on histology. While these features have predominantly been described in patients with advanced kidney disease on dialysis treatment, patients with only mild to moderate renal impairment already exhibit structural and functional changes consistent with CKD-associated cardiomyopathy. In this review we discuss the key drivers of CKD-associated cardiomyopathy and the key role of hypertension in its pathogenesis. We also evaluate existing, as well as developing therapies in the treatment of CKD-associated cardiomyopathy.

Cardiovascular Outcomes with Sacubitril-Valsartan in Heart Failure: Emerging Clinical Data

One of the defining features of heart failure (HF) is neurohormonal activation. The renin-angiotensin-aldosterone-system (RAAS) and sympathetic nervous system (SNS) cause vasoconstriction and fluid retention and, in response, the secretion of natriuretic peptides (NPs) from volume and pressure-overloaded myocardium promotes vasodilation and diuresis. Inhibition of the RAAS with either angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) has been the cornerstone of medical treatment for HF with a reduced ejection fraction (HFrEF) but, until recently, it was unclear how the beneficial effects of NPs may be augmented in patients with HF. Neprilysin, a metalloproteinase widely distributed throughout the body, plays a role in degrading the gross excess of circulating NPs in patients with HF. Early studies of neprilysin inhibition suggested possible physiological benefits. In 2014, the PARADIGM-HF trial found that sacubitril-valsartan, a combination of the ARB valsartan, and the neprilysin inhibitor sacubitril, was superior to enalapril in patients with HFrEF, reducing the relative risk of cardiovascular (CV) death or first hospitalisation with HF by 20%. Almost half of the patients with HF symptoms have a “preserved” ejection fraction (HFpEF); however, the PARAGON-HF study found that sacubitril-valsartan in patients with LVEF ≥45% had no effect on CV death or first and recurrent hospitalisations with HF compared to valsartan. Guidelines across the world have changed to include sacubitril-valsartan for patients with HFrEF yet, nearly 6 years after PARADIGM-HF, there is still uncertainty as to when and in whom sacubitril-valsartan should be started. Furthermore, there may yet be subsets of patients with HFpEF who might benefit from treatment with sacubitril-valsartan. This review will describe the mechanisms behind the outcome benefit of sacubitril-valsartan in patients with HFrEF and to consider its future role in the management of patients with HF.

New perspectives and future directions in the treatment of heart failure

The management of heart failure has changed significantly over the last 30 years, leading to improvements in the quality of life and outcomes, at least for patients with a substantially reduced left ventricular ejection fraction (HFrEF). This has been made possible by the identification of various pathways leading to the development and progression of heart failure, which have been successfully targeted with effective therapies. Meanwhile, many other potential targets of treatment have been identified, and the list is constantly expanding. In this review, we summarise planned and ongoing trials exploring the potential benefit, or harm, of old and new pharmacological interventions that might offer further improvements in treatment for those with HFrEF and extend success to the treatment of patients with heart failure with preserved left ventricular ejection fraction (HFpEF) and other heart failure phenotypes.

Bioactive Signaling in Next-Generation Pharmacotherapies for Heart Failure: A Review

Importance

The standard pharmacotherapy for heart failure (HF), particularly HF with reduced ejection fraction (HFrEF), is primarily through the use of receptor antagonists, notably inhibition of the renin-angiotensin system by either angiotensin-converting enzyme inhibition or angiotensin II receptor blockade (ARB). However, the completed Prospective Comparison of ARNI With an ACE-Inhibitor to Determine Impact on Global Mortality and Morbidity in Heart Failure (PARADIGM-HF) trial identified that the use of a single molecule (sacubitril/valsartan), which is an ARB and the neutral endopeptidase inhibitor (NEPi) neprilysin, yielded improved clinical outcomes in HFrEF compared with angiotensin-converting enzyme inhibition alone.

Observations

This review examined specific bioactive signaling pathways that would be potentiated by NEPi and how these would affect key cardiovascular processes relevant to HFrEF. It also addressed potential additive/synergistic effects of ARB. A number of biological signaling pathways that may be potentiated by sacubitril/valsartan were identified, including some novel candidate molecules, which will act in a synergistic manner to favorably alter the natural history of HFrEF.

Conclusions and Relevance

This review identified that activation rather than inhibition of specific receptor pathways provided favorable cardiovascular effects that cannot be achieved by renin-angiotensin system inhibition alone. Thus, an entirely new avenue of translational and clinical research lies ahead in which HF pharmacotherapies will move beyond receptor antagonist strategies.

LCZ696, a promising novel agent in treating hypertension (a meta-analysis of randomized controlled trials)

Background

To determine the effectiveness and safety of LCZ696 for the clinical treatment of hypertension, we performed a meta-analysis of the previous clinical trials.

Methods

Relevant English articles and randomized controlled trials were searched in Pubmed, Embase, EBSCO, Cochrane base and ClinicalTrials.gov. The last search date was July 20th, 2017.

Results

Compared with 20mg olmesartan, 200mg and 400mg LCZ696 outperformed olmesartan in terms of reducing mean sitting systolic blood pressure, mean ambulatory systolic blood pressure, mean sitting diastolic blood pressure and mean ambulatory diastolic blood pressure. Compared with 20mg olmesartan, 200mg and 400mg LCZ696 was better than olmesartan in terms of reducing mean sitting pulse pressure. And these studies showed that 400mg LCZ696 was better than 20mg olmesartan in terms of reducing mean ambulatory pulse pressure, however, there was no significant difference between 200mg LCZ696 and 20mg olmesartan in terms of redducing mean ambulatory pulse pressure. In addition, 200mg and 400mg LCZ696 was better than placebo in terms of reducing blood pressure parameters mentioned above. Compared with placebo or 20 mg olmesartan, LCZ696 showed no superiority in terms of reducing adverse events or serious adverse events.

Conclusions

LCZ696 at 200 mg or 400 mg was better at reducing most of blood pressure parameters than 20 mg olmesartan or placebo. Compared with placebo or 20 mg olmesartan, 200 mg or 400 mg LCZ696 do not result in more adverse events in treating hypertension.

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.

Metabolic actions of natriuretic peptides and therapeutic potential in the metabolic syndrome

Natriuretic peptides (NPs) are a group of peptide-hormones mainly secreted from the heart, signaling via c-GMP coupled receptors. NP are well known for their renal and cardiovascular actions, reducing arterial blood pressure as well as sodium reabsorption. Novel physiological functions have been discovered in recent years, including activation of lipolysis, lipid oxidation, and mitochondrial respiration. Together, these responses promote white adipose tissue browning, increase muscular oxidative capacity, particularly during physical exercise, and protect against diet-induced obesity and insulin resistance. Exaggerated NP release is a common finding in congestive heart failure. In contrast, NP deficiency is observed in obesity and in type-2 diabetes, pointing to an involvement of NP in the pathophysiology of metabolic disease. Based upon these findings, the NP system holds the potential to be amenable to therapeutical intervention against pandemic diseases such as obesity, insulin resistance, and arterial hypertension. Various therapeutic approaches are currently under development. This paper reviews the current knowledge on the metabolic effects of the NP system and discusses potential therapeutic applications.

Successive action of meprin A and neprilysin catabolizes B-type natriuretic peptide

Natriuretic peptides such as B-type natriuretic peptide (BNP) are important cardioprotective hormones with essential functions in sodium excretion, water balance and blood pressure regulation. Consequently, the catabolism of these peptides is in the focus of clinical research. In previous studies, we demonstrated that BNP, in contrast to the structurally related atrial and C-type natriuretic peptide, was not hydrolyzed by neprilysin (NEP). Because membrane preparations of several organs of NEP-knockout mice rapidly degrade BNP, the aim of this study was to identify BNP-catabolizing peptidases responsible for this fast clearance. Using kidney membranes of wild-type and NEP-knockout mice, as well as several peptidase inhibitors, we monitored the catabolism of BNP and analyzed its degradation products. We identified meprin A, a multimeric metalloprotease expressed in the brush borders of kidney proximal tubules, to initially truncate mouse BNP in the N terminus to mBNP7-32, a BNP metabolite with conserved biological activity. Consequently, in vivo experiments with the meprin inhibitor actinonin successfully elevated plasma BNP concentration in rats. We further demonstrated that the generation of mBNP7-32 is the prerequisite to catabolize BNP and identified NEP as the peptidase degrading the truncated BNP. Thus, the cooperative, successive action of the 2 transmembranal peptidases meprin A and NEP is crucial for rapid renal BNP inactivation. Therefore, the inhibition of meprin A could be a potent tool for increasing circulating BNP levels.

The endopeptidase inhibitor, candoxatril, and its therapeutic potential in the treatment of chronic cardiac failure in man

Candoxatril (UK-79300) is the orally-active prodrug of candoxatrilat (UK-73967), the active enantiomer of (+/-)candoxatrilat (UK-69578), a potent neutral endopeptidase (NEP) inhibitor. This article describes the rationale behind the use of such a drug in the treatment of chronic heart failure in man. It further describes the pharmacokinetics and pharmacodynamics of candoxatril in normal healthy individuals and in patients with chronic cardiac failure. In addition, we describe the initial results comparing candoxatril with furosemide and captopril in human heart failure.

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.

Omapatrilat: neurohormonal and pharmacodynamic profile when administered with furosemide

Pharmacodynamic effects of combination therapy with omapatrilat and furosemide were evaluated. Two groups of 13 healthy subjects each received furosemide 20 mg dailyfor 15 days coadministered with either placebo on days 6 to 15 or omapatrilat 10 mg on days 6 to 10 and 25 mg on days 11 to 15. In the omapatrilat group, urinary excretion of atrial natriuretic peptide increased, and greater blood pressure reductions were seen compared with placebo. Concomitant omapatrilat treatment did not affect the acute diuresis, natriuresis, and kaliuresis observed with chronic administration of furosemide. Neither effective renal plasma flow nor glomerularfiltration rate changed in either treatment group. No clinically significant safety issues were observed. Daily coadministration of omapatrilat 10 or 25 mg with furosemide 20 mg does not affect the pharmacodynamics offurosemide at steady state.

Vasopeptidase inhibitors, neutral endopeptidase inhibitors, and dual inhibitors of angiotensin-converting enzyme and neutral endopeptidase

Vasopeptidase inhibitors represent a new class of cardiovascular drugs. They function as a combined angiotensin-converting enzyme (ACE) inhibitor and neutral endopeptidase (NEP) inhibitor, the latter of which potentiates the actions of atrial natriuretic peptide (ANP) by minimizing its degradation in the circulation. The consequence of such dual inhibition is a synergistic reduction of vasoconstriction and enhancement of vasodilation, thereby serving to more effectively reduce blood pressure. Furthermore, inhibition of the renin-angiotensin-aldosterone system (RAAS) prevents physiologic compensatory responses in vivo seen with NEP inhibition alone. Vasopeptidase inhibitors have also shown to potentiate bradykinin and adrenomedullin, which additionally contribute to cardiovascular regulation. The most extensively researched and promising agents within the class of VP inhibitors is omapatrilat, a mercaptoacyl derivative of a bicyclic thiazepinone dipeptide. It is a single molecule with equal potency and affinity for ACE and NEP inhibition. Although ACE inhibition tends to more selectively benefit high-renin models of hypertension, vasopeptidase inhibition has been shown to be equally efficacious in low-, normal-, and high-renin models. Contrary to NEP inhibition alone, omapatrilat has also demonstrated the ability to significantly reduce blood pressure in spontaneously hypertensive rats, the equivalent of essential hypertension in humans. Studies also suggest that omapatrilat has cardioprotective properties, especially in the setting of congestive heart failure. More specifically, animal models have demonstrated omapatrilat to be more effective than ACE inhibition alone in remodeling the heart and improving its contractile function. Human studies have documented the efficacy of omapatrilat in the treatment of both hypertension and, to a lesser extent, heart failure. Safety concerns (specifically angioedema) are currently being addressed before the widespread utilization of this promising new agent.

Vasopeptidase inhibitors: a new therapeutic concept in cardiovascular disease?

The cardiovascular system is regulated by hemodynamic and neurohumoral mechanisms. These regulatory systems play a key role in modulating cardiac function, vascular tone, and structure. Although neurohumoral systems are essential in vascular homeostasis, they become maladaptive in disease states such as hypertension, coronary disease, and heart failure. The clinical success of ACE inhibitors has led to efforts to block other humoral systems. Neutral endopeptidase (NEP) is an endothelial cell surface zinc metallopeptidase with similar structure and catalytic site. NEP is the major enzymatic pathway for degradation of natriuretic peptides, a secondary enzymatic pathway for degradation of kinins, and adrenomedullin. The natriuretic peptides can be viewed as endogenous inhibitors of the renin angiotensin system. Inhibition of NEP increases levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) of myocardial cell origin, and C-type natriuretic peptide (CNP) of endothelial cell origin as well as bradykinin and adrenomedullin. By simultaneously inhibiting the renin-angiotensin-aldosterone system and potentiating the natriuretic peptide and kinin systems, vasopeptidase inhibitors reduce vasoconstriction, enhance vasodilation, improve sodium/water balance, and, in turn, decrease peripheral vascular resistance and blood pressure and improve local blood flow. Within the blood vessel wall, this leads to a reduction of vasoconstrictor and proliferative mediators such as angiotensin II and increased local levels of bradykinin (and, in turn, nitric oxide) and natriuretic peptides. Preliminary clinical experiences with vasopeptidase inhibitors are encouraging. Thus, the combined inhibition of ACE and neutral endopeptidase is a new and promising approach to treat patients with hypertension, atherosclerosis, or heart failure.

The clinical, cardiac, renal, arterial and neurohormonal effects of omapatrilat, a vasopeptidase inhibitor, in patients with chronic heart failure

OBJECTIVES

We sought to examine the effects of long-term vasopeptidase inhibition in patients with heart failure.

BACKGROUND

The long-term effects of omapatrilat, an agent that inhibits both neutral endopeptidase and angiotensin-converting enzyme, on clinical status, neurohormonal indexes and left ventricular function in patients with chronic heart failure (CHF) have not been previously documented.

METHODS

Forty-eight patients in New York Heart Association functional class II or III, with left ventricular ejection fraction (LVEF)< or =40% and in sinus rhythm were randomized to a dose-ranging pilot study of omapatrilat for 12 weeks. Measurements were performed at baseline and 12 weeks.

RESULTS

There was an improvement in functional status, as reported by the patient (p<0.001) and physician (p<0.001) at 12 weeks. Dose-dependent improvements in LVEF (p<0.001) and LV end-systolic wall stress (sigma) (p<0.05) were seen, together with a reduction in systolic blood pressure (p<0.05). There was evidence of a natriuretic effect (p<0.001), and total blood volume decreased (p<0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (p<0.01) in the high dose groups, with a reduction in predose plasma brain natriuretic peptide (p<0.001) and epinephrine (p<0.01) levels after 12 weeks of therapy. Omapatrilat was well tolerated.

CONCLUSIONS

The sustained hemodynamic, neurohumoral and renal effects of omapatrilat, together with improved functional status, suggest that vasopeptidase inhibition has potential as a new therapeutic modality for the treatment of CHF.

Short-term effects of ecadotril in dogs with induced congestive heart failure

OBJECTIVE

To evaluate short-term hemodynamic effects of ecadotril in a model of congestive heart failure in dogs.

ANIMALS

6 conscious adult male dogs.

PROCEDURES

Instruments were placed in dogs to measure left ventricular, aortic, and atrial blood pressures. Heart failure was induced by repeated coronary embolization with latex microspheres. Four times, and in random order, dogs were given vehicle or active drug (3, 10, or 30 mg/kg of body weight) orally. Hemodynamic variables, urine flow, and urinary electrolyte excretion were measured before and 30, 90, and 150 minutes, and 10 and 21 hours after drug administration.

RESULTS

Changes in urine flow, heart rate, mean arterial pressure, or peak positive and negative rate of change in ventricular pressure were not apparent. Urinary sodium excretion significantly increased in response to the low and high doses of ecadotril but not in response to the 10 mg/kg dose. Left ventricular end diastolic pressure (LVEDP) consistently decreased in dose- and time-dependent manner. Maximal group-averaged reductions in LVEDP were 5.2, 8.1, and 10 mm Hg for the low, middle, and high doses, respectively. The magnitude of the decrease in LVEDP was not related to cumulative change in urine flow.

CONCLUSIONS AND CLINICAL RELEVANCE

Orally administered ecadotril reduced left ventricular filling pressures in these dogs by a mechanism that does not require a substantial diuretic effect. Ecadotril may be effective for alleviating clinical signs in dogs with left-sided heart failure and may be particularly beneficial for use in dogs that are refractory to traditional diuretic therapy.

Update of ELITE-II, BEST, CHAMP, and IMPRESS clinical trials in heart failure

The ELITE-II, BEST and CHAMP Trials were reported for the first time at the American Heart Association in November 1999. These trials provide valuable new information to guide clinical practice in the management of heart failure and of myocardial infarction, although none mandate a major change from current clinical practice. The IMPRESS trial of the vasopeptidase inhibitor, omapatrilat, indicated a promising new treatment for the management of heart failure.

Enhanced natriuretic response to neutral endopeptidase inhibition in heart-transplant recipients

Heart-transplant recipients (Htx) generally present with body fluid and sodium handling abnormalities and hypertension. To investigate whether neutral endopeptidase inhibition (NEP-I) increases endogenous atrial natriuretic peptide (ANP) and enhances natriuresis and diuresis after heart transplantation, ecadotril was given orally to 8 control subjects and 8 matched Htx, and levels of volume-regulating hormones and renal water, electrolyte, and cyclic guanosine monophosphate (cGMP) excretions were monitored for 210 minutes. Baseline plasma ANP, brain natriuretic peptide (BNP), and cGMP were elevated in Htx, but renin and aldosterone, like urinary parameters, did not differ between groups. NEP-I increased plasma ANP (Htx, 20.6+/-2.3 to 33.2+/-5.9 pmol/L, P<0.01; controls, 7.7+/-1. 2 to 10.6+/-2.6 pmol/L) and cGMP, but not BNP. Renin decreased similarly in both groups, whereas aldosterone decreased significantly only in Htx. Enhanced urinary sodium (1650+/-370% versus 450+/-150%, P=0.01), cGMP, and water excretions were observed in Htx and urinary cGMP positively correlated with natriuresis in 6 of the Htx subjects. Consistent with a normal circadian rhythm of blood pressure, without excluding a possible effect of NEP-I, mean systemic blood pressure increased similarly in both groups at the end of the study (6.9+/-2.0% versus 7.4+/-2.8% in controls and Htx). Thus, systemic hypertension, mild renal impairment, and raised plasma ANP levels are possible contributory factors in the enhanced natriuresis and diuresis with NEP-I in Htx. These results support a physiological role for the cardiac hormone after heart transplantation and suggest that long-term studies may be useful to determine the potential of NEP-I in the treatment of sodium retention and water retention after heart transplantation.

Effects of a dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240, on endocrine and renal functions in healthy volunteers

OBJECTIVE

To investigate the endocrine and renal effects of the dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240.

DESIGN

A randomized, placebo-controlled, crossover study was performed in 12 healthy volunteers.

METHODS

MDL 100,240 was administered intravenously over 20 min at single doses of 6.25 and 25 mg in subjects with a sodium intake of 280 (n = 6) or 80 (n = 6) mmol/day. Measurements were taken of supine and standing blood pressure, plasma angiotensin converting enzyme activity, angiotensin II, atrial natriuretic peptide, urinary atrial natriuretic peptide and cyclic GMP excretion, effective renal plasma flow and the glomerular filtration rate as p-aminohippurate and inulin clearances, electrolytes and segmental tubular function by endogenous lithium clearance.

RESULTS

Supine systolic blood pressure was consistently decreased by MDL 100,240, particularly after the high dose and during the low-salt intake. Diastolic blood pressure and heart rate did not change. Plasma angiotensin converting enzyme activity decreased rapidly and dose-dependently. In both the high- and the low-salt treatment groups, plasma angiotensin II levels fell and renin activity rose accordingly, while plasma atrial natriuretic peptide levels remained unchanged. In contrast, urinary atrial natriuretic peptide excretion increased dose-dependently under both diets, as did urinary cyclic GMP excretion. Effective renal plasma flow and the glomerular filtration rate did not change. The urinary flow rate increased markedly during the first 2 h following administration of either dose of MDL 100,240 (P < 0.001) and, similarly, sodium excretion tended to increase from 0 to 4 h after the dose (P = 0.07). Potassium excretion remained stable. Proximal and distal fractional sodium reabsorption were not significantly altered by the treatment. Uric acid excretion was increased. The safety and clinical tolerance of MDL 100,240 were good.

CONCLUSIONS

The increased fall in blood pressure in normal volunteers together with the preservation of renal hemodynamics and the increased urinary volume, atrial natriuretic peptide and cyclic GMP excretion distinguish MDL 100,240 as a double-enzyme inhibitor from inhibitors of the angiotensin converting enzyme alone. The differences appear to be due, at least in part, to increased renal exposure to atrial natriuretic peptide following neutral endopeptidase blockade.

Novel neuropeptides in the pathophysiology of heart failure: adrenomedullin and endothelin-1

The clinical success of neurohumoral manipulation by ACE inhibitors and beta blockers in heart failure has led to new therapeutic approaches. New neurohumoral factors are now viewed as offering the potential for treatment interventions. Not only do we consider blocking the production of deleterious hormones, but also, more recently, consideration has been given to augmenting the actions of factors with potentially beneficial actions. Hopefully such manipulation of ADM and ET-1 can result in further improvement in the well-being of heart failure patients.

Diuretic treatment and diuretic resistance in heart failure

Diuretic therapy decreases capillary wedge pressure and improves New York Heart Association (NYHA) functional class both in acute and chronic heart failure. In advanced symptomatic heart failure, loop diuretics are generally necessary to improve symptoms of congestion. Diuretic resistance in the edematous patient has been defined as a clinical state in which diuretic response is diminished or lost before the therapeutic goal of relief from edema has been reached. The major causes of diuretic resistance are functional renal failure (prerenal azotemia), hyponatremia, altered diuretic pharmacokinetics, and sodium retention caused by counterregulatory mechanisms intended to reestablish the effective arterial blood volume. Therapeutic approaches to combat diuretic resistance include restriction of fluid and sodium intake, use of angiotensin-converting-enzyme (ACE) inhibitors, changes in route (oral, intravenous) and timing (single dose, multiple doses, continuous infusion) of diuretic therapy, and use of diuretic combinations.

Inhibition of kidney neutral endopeptidase after administration of the neutral endopeptidase inhibitor candoxatril: quantitation by autoradiography

Inhibition of neutral endopeptidase (NEP) in the kidney was studied ex vivo after oral administration of candoxatril (UK79300), an NEP inhibitor, to rats to study the time course and dose response by quantitative in vitro autoradiography by using the NEP inhibitor 125I-SCH47896 as a radioligand. In control rats, high NEP binding was demonstrated in the deep proximal tubule. After oral administration of candoxatril (10 mg/kg), kidney NEP binding was rapidly decreased and recovered gradually over a period of 24 h. The inhibition was maximal at 1 h (13.3 +/- 2.5% of control). Increasing doses of candoxatril administered to rats produced progressive inhibition of NEP binding in the kidney. A dose of 100 mg/kg inhibited kidney NEP binding to 2.6 +/- 0.2% of the control value at 1 h after administration. Candoxatrilat (UK73967), an active metabolite of candoxatril, given intravenously inhibited kidney NEP binding also in a time- and dose-dependent manner. This inhibition of NEP activity at the tissue level may be important in the actions of NEP inhibitors.

New hormonal blockade strategies in cardiovascular disease

The circulation is controlled by overlapping haemodynamic, structural and neurohumoral mechanisms. Many hormonal vasoactive substances, mostly derived from endothelial cells, are also growth regulators. Although neurohormonal systems are involved in normal physiological compensatory responses they often become maladaptive in conditions such as congestive heart failure. The success of blocking the renin angiotensin system by angiotensin converting enzyme (ACE) inhibitors has led to efforts to block other hormonal systems. Neutral endopeptidase (NEP), the major enzymatic pathway for degradation of natriuretic peptides, has a similar catalytic site to ACE. This has led to compounds that simultaneously inhibit both enzymes. Such dual ACE/NEP inhibitors show promise in experimental hypertension and heart failure. Similar dual NEP/ECE (endothelin converting enzyme) inhibitors are becoming available. The hormone vasopressin has dual actions on the vasculature and the kidney via specific membrane receptors. Specific orally active vasopressin receptor antagonists have been developed and their therapeutic potential in hypertension, heart failure and oedematous states are being explored.

Renal effects of concurrent E-24.11 and ACE inhibition in the aorto-venocaval fistula rat

1. The present studies compare the early renal response to (a) an endopeptidase-24.11 (E-24.11) inhibitor (candoxatrilat) (b) an angiotensin-converting enzyme (ACE) inhibitor (lisinopril) and (c) the combination of endopeptidase-24.11 and ACE inhibition in the rat A-V fistula model of chronic volume overload. 2. Candoxatrilat (3 and 10 mg kg-1) i.v. produced a prompt 3 fold increase in urinary sodium and cyclic GMP excretion without affecting significantly blood pressure or glomerular filtration rate (GFR). 3. Lisinopril (0.03 mg kg-1) alone inhibited the pressor response to angiotensin I but had no significant effect on urinary sodium excretion or blood pressure. 4. Lisinopril (0.03 mg kg-1) attenuated significantly the early natriuretic response to candoxatrilat (3 mg kg-1) and the associated rise in urinary cyclic GMP, but sodium excretion eventually reached levels associated with acute E-24.11 inhibition. 5. Doses of the dual E-24.11/ACE inhibitor, sampatrilat, that inhibited the pressor response to angiotensin I reduced mean arterial blood pressure and produced a delayed natriuresis and rise in urinary cyclic GMP excretion when compared to candoxatrilat alone. 6. Concurrent administration of an ACE inhibitor reduces the early renal response to E-24.11 inhibition in the A-V fistula rat, an effect attributable to the hypotensive action of this combination.