Endopeptidase-24.11 and its inhibitors: potential therapeutic agents for edematous disorders and hypertension

New Borane-Protected Derivatives of α-Aminophosphonous Acid as Anti-Osteosarcoma Agents: ADME Analysis and Molecular Modeling, In Vitro Studies on Anti-Cancer Activities, and NEP Inhibition as a Possible Mechanism of Anti-Proliferative Activity

Many organophosphorus compounds (OPs), especially various α-aminophosphonates, exhibit anti-cancer activities. They act, among others, as inhibitors of the proteases implicated in cancerogenesis. Thesetypes of inhibitors weredescribed, e.g., for neutral endopeptidase (NEP) expressed in different cancer cells, including osteosarcoma (OS). The aim of the present study isto evaluate new borane-protected derivatives of phosphonous acid (compounds 1–7) in terms of their drug-likeness properties, anti-osteosarcoma activities in vitro (against HOS and Saos-2 cells), and use as potential NEP inhibitors. The results revealed that all tested compounds exhibited the physicochemical and ADME properties typical for small-molecule drugs. However, compound 4 did not show capability of blood–brain barrier penetration (Lipiński and Veber rules;SwissAdme tool). Moreover, the α-aminophosphonite-boranes (compounds 4–7) exhibited stronger anti-proliferative activity against OS cells than the other phosphonous acid-borane derivatives (compounds 1–3),especially regarding HOS cells (MTT assay). The most promising compounds 4 and 6 induced apoptosis through the activation of caspase 3 and/or cell cycle arrest at the G₂ phase (flow cytometry). Compound 4 inhibited the migration and invasiveness of highly aggressive HOS cells (wound/transwell and BME-coated transwell assays, respectively). Additionally, compound 4 and, to a lesser extent, compound 6 inhibited NEP activity (fluorometric assay). This activity of compound 4 was involved in its anti-proliferative potential (BrdU assay). The present study shows that compound 4 can be considered a potential anti-osteosarcoma agent and a scaffold for the development of new NEP inhibitors.

Natriuretic peptides: new challenges — new solutions

Natriuretic peptides (NPs) are one of the most significant biomarkers, the practical use of which increases, and their diagnostic and prognostic value in patients with various chronic noncommunicable diseases is beyond doubt. Since the discovery of these markers, research has been actively carried out to study the biological and pathophysiological roles of NPs in a wide range of diseases, including hypertension and heart failure (HF). These studies showed that A-type and B-type NPs are hormones secreted by the heart in response to pre- or afterload, which prevent high blood pressure and fluid retention. In addition, C-type NPs are produced by the vascular endothelium and act as a local a  mediator with angioprotective properties. Since the NP system is a natural antagonist of the sympathoadrenal and renin-angiotensinaldosterone systems, it is interesting to study novel strategies to use new drug classes for hypertension. These drugs are neprilysin inhibitors, which destroys NPs; their action is to enhance the synthesis of endogenous peptides. Dual angiotensin receptor and neprilysin inhibition is widespread in clinical practice in patients with heart failure with reduced ejection fraction. Neprilysin inhibition has also been shown to be an effective strategy for hypertensive patients. The article discusses the role and value of NP system in  the dia - gnosis of heart failure and blood pressure regulation, and also considers new promising directions for neprilysin inhibition and activation of endogenous NP synthesis.

 

TaleNeprilysin and Neprilysin inhibition in chronic kidney disease

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is associated with increased risk of progression to end-stage kidney disease and cardiovascular events. There is limited evidence that available treatments have beneficial effects on cardiorenal outcomes in all people with nondiabetic CKD. Neprilysin inhibition (NEPi) is a new therapeutic strategy with potential to improve outcomes for patients with CKD.

RECENT FINDINGS

NEPi enhances the activity of the natriuretic peptide system producing natriuresis, diuresis and inhibition of the renin-angiotensin system and sympathetic nervous system. Sacubitril/valsartan is the first Angiotensin receptor-neprilysin inhibitor (ARNI) to be produced and has been shown to substantially improve cardiovascular outcomes in heart failure and delay progression of kidney disease in this population. Although ARNIs have not shown similar effects on kidney function in the short-to-medium term in people with CKD, they are associated with substantial reductions in cardiac biomarkers and blood pressure in CKD.

SUMMARY

These data suggest that NEPi with an ARNI could benefit patients with CKD by reducing the risk of cardiovascular disease and have the possibility of retarding the progression of CKD (hence delaying the need for renal replacement therapy).

Initial In Vitro and In Vivo Evaluation of a Novel CCK2R Targeting Peptide Analog Labeled with Lutetium-177

Targeting of cholecystokinin-2 receptor (CCK2R) expressing tumors using radiolabeled minigastrin (MG) analogs is hampered by rapid digestion of the linear peptide in vivo. In this study, a new MG analog stabilized against enzymatic degradation was investigated in preclinical studies to characterize the metabolites formed in vivo. The new MG analog DOTA-DGlu-Pro-Tyr-Gly-Trp-(N-Me)Nle-Asp-1Nal-NH₂ comprising site-specific amino acid substitutions in position 2, 6 and 8 and different possible metabolites thereof were synthesized. The receptor interaction of the peptide and selected metabolites was evaluated in a CCK2R-expressing cell line. The enzymatic stability of the ¹⁷⁷Lu-labeled peptide analog was evaluated in vitro in different media as well as in BALB/c mice up to 1 h after injection and the metabolites were identified based on radio-HPLC analysis. The new radiopeptide showed a highly increased stability in vivo with >56% intact radiopeptide in the blood of BALB/c mice 1 h after injection. High CCK2R affinity and cell uptake was confirmed only for the intact peptide, whereas enzymatic cleavage within the receptor specific C-terminal amino acid sequence resulted in complete loss of affinity and cell uptake. A favorable biodistribution profile was observed in BALB/c mice with low background activity, preferential renal excretion and prolonged uptake in CCK2R-expressing tissues. The novel stabilized MG analog shows high potential for diagnostic and therapeutic use. The radiometabolites characterized give new insights into the enzymatic degradation in vivo.

Natriuretic peptides and neprilysin inhibition in hypertension and hypertensive organ damage

The family of natriuretic peptides (NPs) discovered in mammalian tissues including cardiac atrium and brain consists of three members, namely, atrial, B- and C-type natriuretic peptides (ANP, BNP, CNP). Since the discovery, basic and clinical studies have been vigorously performed to explore the biological functions and pathophysiological roles of NPs in a wide range of diseases including hypertension and heart failure. These studies revealed that ANP and BNP are hormones secreted from the heart into the blood stream in response to pre- or after-load, counteracting blood pressure (BP) elevation and fluid retention through specific receptors. Meanwhile, CNP was found to be produced by the vascular endothelium, acting as a local mediator potentially serving protective functions for the blood vessels. Because NPs not only exert blood pressure lowering actions but also alleviate hypertensive organ damage, attempts have been made to develop therapeutic agents for hypertension by utilizing this family of NPs. One strategy is to inhibit neprilysin, an enzyme degrading NPs, thereby enhancing the actions of endogenous peptides. Recently, a dual inhibitor of angiotensin receptor-neprilysin was approved for heart failure, and neprilysin inhibition has also been shown to be beneficial in treating patients with hypertension. This review summarizes the roles of NPs in regulating BP, with special references to hypertension and hypertensive organ damage, and discusses the therapeutic implications of neprilysin inhibition.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

Insulin uptake across the luminal membrane of the rat proximal tubule in vivo and in vitro

We visualized insulin uptake in vivo across the apical membrane of the rat proximal tubule (PT) by confocal microscopy; we compared it with in vitro findings in a rat PT cell line (WKPT) using fluorescence microscopy and flow cytometry. Surface tubules were observed in vivo with a 633-nm single laser-illuminated real-time video-rate confocal scanning microscope in upright configuration for optical sectioning below the renal capsule. Fields were selected containing proximal and distal tubules; Cy5-labeled insulin was injected twice (the second time after ∼140 min) into the right jugular vein, and the fluorescence signal (at 650–670 nm) was recorded. Fluorescence was detected almost immediately at the brush-border membrane (BBM) of PT cells only, moving inside cells within 30–40 min. As a measure of insulin uptake, the ratio of the fluorescence signal after the second injection to the first doubled (ratio: 2.11 ± 0.26, mean ± SE, n = 10), indicating a “priming,” or stimulating, effect of insulin on its uptake mechanism at the BBM. This effect did not occur after pretreatment with intravenous lysine (ratio: 1.03 ± 0.07, n = 6; P < 0.01). Cy2- or Cy3-labeled insulin uptake in a PT cell line in vitro was monitored by 488-nm excitation fluorescence microscopy using an inverted microscope. Insulin localized toward the apical membrane of these cells. Semiquantitative analysis of insulin uptake by flow cytometry also demonstrated a priming effect (upregulation) on insulin internalization in the presence of increasing amounts of insulin, as was observed in vivo; moreover, this effect was not seen with, or affected by, the similarly endocytosed ligand β2-glycoprotein.

Natriuretic Peptides in ESRD

Natriuretic peptides are involved in the regulation of volume homeostasis. Their levels generally are increased in the setting of volume expansion and act on multiple effector systems to cause vasodilation and natriuresis in an effort to return volume status back to normal. In patients with end-stage renal disease, the natriuretic capabilities of these peptides are limited. However, there has been much interest in the potential applicability of measurement of these peptides as a surrogate marker of volume status and in the determination of dry weight. Furthermore, atrial natriuretic peptide and brain natriuretic peptide can serve as markers of left ventricular dysfunction and may have utility in determining cardiac prognosis in patients on long-term dialysis therapy.

Equimolar doses of atrial and brain natriuretic peptides and urodilatin have differential renal actions in overt experimental heart failure

A hallmark of overt congestive heart failure (CHF) is attenuated cGMP production by endogenous atrial natriuretic peptide (ANP) with renal resistance to ANP. ANP and brain natriuretic peptides (BNP) are of myocardial origin, whereas urodilatin (Uro) is thought to be derived from kidney. All three peptides are agonists to the natriuretic peptide-A receptor. Our objective was to compare the cardiorenal and humoral actions of ANP, BNP, and Uro in experimental overt CHF. We determined cardiorenal and humoral actions of 90 min of intravenous equimolar infusion of ANP, BNP, and Uro (2 and 10 pmol.kg-1.min-1) in three separate groups of anesthetized dogs with rapid ventricular pacing-induced overt CHF (240 beats/min for 10 days). BNP resulted in increases in urinary sodium excretion (U(Na)V) (2.2+/-0.7 to 164+/-76 microeq/min, P<0.05) and glomerular filtration rate (GFR) (27+/-4 to 52+/-11 ml/min, P<0.05) that were greater than those with Uro (P<0.05), whereas ANP did not result in increases in U(Na)V or GFR. Increases in plasma cGMP (25+/-2 to 38+/-2 pmol/ml, P<0.05) and urinary cGMP excretion with BNP (1,618+/-151 to 6,124+/-995 pmol/min, P<0.05) were similar to those with Uro; however, there was no change with ANP. Cardiac filling pressures were reduced in all three groups. These studies also support the conclusion that in experimental overt CHF, renal resistance to natriuretic peptides in increasing rank order is BNP<Uro<ANP.

Physiologic consequences of vasopeptidase inhibition in humans: effect of sodium intake

The in vivo inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) were monitored simultaneously by sequentially measuring the urinary excretion of N-Acetyl-Ser-Asp-Lys-Pro and of the atrial natriuretic factor to compare the magnitude and the duration of action of a vasopeptidase inhibitor, omapatrilat, and an ACE inhibitor, fosinopril. Single oral doses of 40 or 80 mg of omapatrilat or 20 mg of fosinopril were administered to 24 normotensive, sodium-depleted or -replete volunteers in a placebo-controlled crossover study. ACE inhibition persisted longer after treatment with omapatrilat than with fosinopril, and there was no major difference between the effects of 40 and 80 mg of omapatrilat. The duration of NEP inhibition by omapatrilat was shorter than that of ACE inhibition. Although omapatrilat effectively inhibited NEP, it had a mild and transient natriuretic effect and did not increase natriuresis more than fosinopril. Omapatrilat induced a decrease in BP and an increase in plasma renin more rapidly and more effectively than fosinopril. The BP and renin effects of omapatrilat persisted despite high sodium intake, which neutralized the effects of fosinopril. The simultaneous inhibition of ACE and NEP may be more effective in reducing BP than the inhibition of ACE alone and less dependent on sodium balance.

Vasopeptidase inhibitors

Vasopeptidase inhibitors are a new class of drugs that have dual inhibitory effects on two key enzymes involved in the metabolism of vasoactive peptides. Essentially, they inhibit angiotensin-converting enzyme (ACE), thereby blocking the generation of angiotensin II (Ang II); at the same time they prevent the breakdown of natriuretic peptides by the enzyme neutral endopeptidase. The combination of reduction of Ang II on a background of increased natriuretic peptide activity has several potential advantages for the treatment of cardiovascular and renal disease and in particular, hypertension and congestive heart failure (CHF). Several vasopeptidase inhibitors, such as sampatrilat, fasidotril, gemopatrilat and omapatrilat (Vanlev, the most clinically developed vasopeptidase inhibitor to date) are under intensive clinical investigation. Recent clinical trials have demonstrated effective antihypertensive activity in hypertension, independent of age, renin and salt status or ethnic origin, and have also highlighted the potential for vasopeptidase inhibition as a new therapeutic modality for the treatment of CHF. Moreover, ongoing research suggests that this new class of drugs may be an important approach, not only for the treatment of hypertension and of conditions associated with overt volume overload but also for ischaemic heart disease.

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

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.

Atrial natriuretic peptide augments the variability of sympathetic nerve activity in human heart failure

OBJECTIVES

Activation of the sympathetic nervous system, decreased heart rate variability (HRV), and loss of modulation of muscle sympathetic nerve activity (MSNA) within the low frequency (LF, 0.05-0.15 Hz) range are three adverse features of advanced congestive heart failure (CHF). In healthy men, atrial natriuretic peptide (ANP) infusion attenuates reflex increases in MSNA and reduces LF components of HRV spectral power. Sympathoinhibitory actions have also been documented in CHF, but effects on the variability of MSNA and HRV have not been described.

DESIGN AND METHODS

Heart rate and MSNA were recorded in 10 men (aged 39 +/- 3 years, mean +/- SE) with dilated cardiomyopathy (mean EF 20 +/- 4%) treated with angiotensin converting enzyme (ACE) inhibitors. Subjects received i.v. ANP (50 microg bolus then 50 ng/kg/min) and nitroglycerin (NTG, 8 mg/min) as a hemodynamic control. Signals at baseline, and 13-20 min into each infusion were submitted to spectral analysis.

RESULTS

ANP had no effect on HRV, but increased MSNA LF (from 7.9 +/- 1.5 to 12.1 +/- 2.6 U2; P< 0.02) and total spectral power (from 47.9 +/- 5.4 to 61.9 +/- 6.8 U2; P < 0.05). NTG had no effect on the variability of MSNA or HRV.

CONCLUSIONS

In CHF patients receiving ACE inhibitors, ANP (i) does not suppress HRV and (ii) enhances the modulation of MSNA, particularly within the LF range. This latter action is not observed with NTG. These findings suggest beneficial actions of exogenous ANP on neurogenic circulatory control.

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.

A double-blind, placebo-controlled study to assess tolerability, pharmacokinetics and preliminary pharmacodynamics of single escalating doses of Z13752A, a novel dual inhibitor of the metalloproteases ACE and NEP, in healthy volunteers

AIMS

The objective of this study was to evaluate the tolerability of a novel dual ACE-NEP inhibitor, Z13752A, after the oral administration of rising single doses in healthy volunteers. This study was also a preliminarily investigation of Z13752A pharmacodynamics (PD) and pharmacokinetics (PK).

METHODS

In this randomized, placebo-controlled, sequential study, two alternating panels of eight healthy male volunteers each (six subjects receiving the active treatment + two subjects receiving placebo) were treated with increasing oral doses of Z13752A: 10, 50, 200, and 600 mg were given to panel I and 20, 100, 400 and 800 mg were given to panel II. The study was double-blind relative to placebo or active treatment, and was open with respect to the dose levels. The same volunteer received placebo only once.

RESULTS

Single oral doses of Z13752A, as high as 800 mg, were well tolerated. Only six mild-to-moderate adverse events mainly headache, were reported and appeared to be of little clinical relevance. After administration of 200, 400, 600 and 800 mg of Z13752A, a nonsignificant fall in diastolic blood pressure was detected, in both the standing and supine position. After single oral doses of Z13752A, ACE inhibition appeared to be significant at all the doses tested, linearly correlated with the dose and was almost complete at doses > or = 100-200 mg. NEP inhibition was indicated by elevation of ANP and cGMP plasma concentrations in almost all subjects. In the 200-800 mg dose range, Z13752A produced a 50-100% increase of plasma cGMP levels and a 50-80% elevation in urinary cGMP concentrations. Detectable plasma levels of Z13752A were found in all the treated subjects. Z13752A was well and rapidly absorbed, with peak concentrations reached approximately 2.5 h after administration. The mean apparent elimination half-life from plasma was approximately 12 h. The pharmacokinetics of Z13752A after single oral doses were characterized by low intersubject variability and appeared to be dose-independent.

CONCLUSIONS

Z13752A showed a good single dose tolerability profile at doses up to 800 mg. The pharmacokinetic data indicate that Z13752A administered orally is rapidly absorbed and available to the systemic circulation in humans. The relatively slow clearance indicates that a once-a-day dose regimen could be considered for Z13752A.

Protective effect of SM-19712, a novel and potent endothelin converting enzyme inhibitor, on ischemic acute renal failure in rats

Effects of SM-19712 (4-chloro-N-[[(4-cyano-3-methyl- 1-1-phenyl- 1H-pyrazol-5-yl)amino]carbonyl] benzenesulfonamide, monosodium salt), a novel endothelin converting enzyme (ECE) inhibitor, on ischemic acute renal failure (ARF) in rats were examined in comparison with those of phosphoramidon, a conventional ECE inhibitor. ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function in ARF rats markedly decreased at 24 h after reperfusion. Intravenous bolus injection of SM-19712 (3, 10, 30 mg/kg) prior to the occlusion attenuated dose-dependently the ischemia/reperfusion-induced renal dysfunction. Histopathological examination of the kidney of ARF rats revealed severe renal damages such as tubular necrosis, proteinaceous casts in tubuli and medullary congestion, all of which were dose-dependently attenuated by SM-19712. Protective effects of phosphoramidon (10 mg/kg) on ARF-induced functional and tissue damages were less potent than that of the same dose of SM-19712. Endothelin-1 (ET-1) content in the kidney after the ischemia/reperfusion was significantly increased, being the maximum level at 6 h after reperfusion, and this elevation was completely suppressed by the higher dose of SM-19712. Our findings support the view that renal ET-1 plays an important role in the development of ischemia/reperfusion-induced renal injury. SM-19712 may be useful in the treatment of ischemic ARF.

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.

New classes of antihypertensive drugs: therapeutic potentials

A number of new classes of antihypertensive drugs have become available in the recent years which appear to hold therapeutic potential for better management of hypertension. Losartan, an angiotensin II receptor antagonist, does not produce cough which is classically seen with ACE inhibitors. Fenoldopam, a dopamine D1-receptor agonist, has a rapid and short duration of action and is ideally suited by intravenous infusion for quick control of BP in hypertensive emergencies. Kentaserin, a serotonin (5-HT2A) receptor antagonist, has a long duration of action and can be given once daily. It has the added benefit of having antiplatelet effect. Monatepil, a dual alpha-receptor and calcium channel blocker, has potent antihypertensive effect, lowers serum cholesterol and also has antiatherosclerotic effect. Dual ACE and endopeptidase inhibitor, such as alatriopril, has a "broad spectrum" antihypertensive effect and may be effective in majority of hypertensive patients. Many other classes of antihypertensive drugs are still in the investigative stage, and their therapeutic potentials and safety need to be ascertained in long-term controlled clinical trials.

Dual inhibition of neutral endopeptidase and angiotensin-converting enzyme in rats with hypertension and diabetes mellitus

It has been suggested that combined inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) may lower blood pressure more effectively than either treatment alone, independent of the degree of salt and volume status or the activity of the renin-angiotensin system. The effects of NEP inhibition in hypertension associated with diabetes mellitus are largely unknown. We therefore compared ACE inhibition, NEP inhibition, and dual NEP/ACE inhibition in diabetic hypertensive rats. Spontaneously hypertensive rats (SHR) aged 9 to 10 weeks were injected with either streptozotocin (45 mg/kg) or citrate buffer and randomized to receive either the ACE inhibitor captopril (25 mg/kg BID), the NEP inhibitor SCH 42495 (30 mg/kg BID), the dual NEP/ACE inhibitor S 21402 (25 or 50 mg/kg BID), or vehicle by gavage for 4 weeks. A group of diabetic SHR was also allocated to receive the combination of SCH 42495 (30 mg/kg BID) and captopril (25 mg/kg BID). The degree of renal NEP inhibition was determined by autoradiography, and plasma renin activity (PRA) was determined by radioimmunoassay. In diabetic SHR, the dual NEP/ACE inhibitor (50 mg/kg BID), as well as the combination of the NEP inhibitor and the ACE inhibitor, reduced systolic blood pressure more effectively than the ACE inhibitor (P<0.001) or the NEP inhibitor (P<0.001) alone. In nondiabetic SHR, the dual NEP/ACE inhibitor and the ACE inhibitor were equally effective, while the NEP inhibitor had only slight blood pressure lowering effects. Relative heart weight decreased in parallel to the changes in blood pressure. Renal NEP was clearly inhibited (70% to 92%; P<0.001) by both the NEP inhibitor and the dual NEP/ACE inhibitor. Both the ACE inhibitor and the dual NEP/ACE inhibitor increased PRA, but the stimulating effect of dual NEP/ACE inhibition on PRA was less than that observed with ACE inhibition alone (P<0.05). Albuminuria in diabetic SHR was lower during treatment with both the dual NEP/ACE inhibitor (50 mg/kg BID) and the combination of NEP inhibition and ACE inhibition compared with vehicle treatment (P<0.05). In conclusion, the present study shows that hypertension in SHR with streptozotocin-induced diabetes is modulated by natriuretic peptides and thus is sensitive to NEP inhibition. The increased efficacy of dual NEP/ACE inhibition on blood pressure in diabetic SHR, compared with ACE or NEP inhibition alone, suggests that this therapeutic approach may prove beneficial in the treatment of hypertension associated with diabetes mellitus and other forms of volume-dependent hypertension.

Effects of the novel dual inhibitor of neutral endopeptidase and angiotensin-converting enzyme, CGS 30440, on blood pressure and cardiac hypertrophy in spontaneously hypertensive rats

This study examined the long-term effects of CGS 30440 on blood pressure, heart rate, cardiac hypertrophy, and urinary parameters in conscious spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. Initial studies with CGS 30440 produced dose-related reductions in mean arterial pressure, with a dose of 30 mg/kg/day of CGS 30440 producing a maximal sustained response of 40 mm Hg. CGS 30440 significantly inhibited plasma angiotensin-converting enzyme (ACE) activity by 82% in WKY rats. In SHRs, lung ACE and renal neutral endopeptidase (NEP) were inhibited by >60 and >90%, respectively. Urinary cyclic guanosine monophosphate (cGMP) excretion was significantly increased by CGS 30440 in SHRs but was unaltered in WKY rats. One hour after the final dose of an 8-week regimen, blood pressure was 122 +/- 4 and 189 +/- 5 mm Hg in CGS 30440-treated (30 mg/kg/day) and vehicle-treated SHRs, respectively. Heart-rate responses were not different between treatment groups. Left ventricular hypertrophy (LV weight/body weight ratio) was reduced significantly in SHRs to 2.45 +/- 0.08 mg/g at 10 mg/kg/day and 2.26 +/- 0.07 mg/g at 30 mg/kg/day versus 2.91 +/- 0.09 mg/g in rats receiving only vehicle. These results demonstrate that CGS 30440 is a potent, orally active antihypertensive agent with a long duration of action. The cardiac hypertrophy of established hypertension in the SHRs was attenuated by CGS 30440. Thus CGS 30440, an orally active prodrug, has been shown to be a novel antihypertensive agent with dual ACE/NEP inhibitory activity in SHRs.

Characterization and stimuli for production of pericardial fluid atrial natriuretic peptide in dogs

Recently high immunoreactive atrial natriuretic peptide (ir-ANP) levels have been found in the pericardial fluid of patients undergoing cardiac surgery. The present study was designed to characterize pericardial fluid ANP in anesthetized dogs. Pericardial fluid ir-ANP levels were 3.4-fold higher than plasma levels and the molecular form, revealed by high performance liquid chromatography, was indistinguishable from ANP[99-126]. Elimination of [125I]ANP was 5-fold slower in the pericardial space than in plasma. Activity of the major ANP degrading enzyme, neutral endopeptidase (NEP, EC 3.4.24.11), was 15-times higher in the pericardial fluid than in plasma. Right atrial balloon distension and rapid right ventricular pacing induced maximally 2.3-fold and 1.5-fold increases of pericardial fluid ir-ANP, respectively. Pericardial fluid ir-ANP concentrations and right atrial pressure values showed significant correlation during the stimuli. Our present results show that high concentrations of ir-ANP can be found in the dog pericardial fluid even under unstimulated conditions. Slow elimination of ANP from the pericardial fluid compartment may contribute to the high peptide levels. However this slow elimination cannot be attributed to a lower NEP activity. High basal levels of ANP in the pericardial fluid could be further increased by atrial balloon stretch and rapid ventricular pacing. The increase of pericardial fluid ir-ANP appeared to be a stretch-dependent response. ANP released into the pericardial fluid may be involved in the regulation of cardiac function and coronary vascular tone.

Acute reversal of cyclosporine nephrotoxicity by neutral endopeptidase inhibition in stable renal transplant recipients

BACKGROUND

Atrial natriuretic peptide and cyclosporine have opposing effects on renal hemodynamics and excretory function.

METHODS

Twelve male stable cyclosporine-treated renal transplant recipients received a single 100-mg i.v. dose of the neutral endopeptidase EC 24.11 inhibitor candoxatrilat in a double-blind, placebo-controlled cross-over study. Each study day consisted of 2 hr of baseline and 7 hr of postdose evaluation.

RESULTS

After administration of candoxatrilat, plasma atrial natriuretic factor rose from 12.8+/-1.6 (mean +/- SEM) to 44.1+/-6.8 pmol/L (P<0.001) in association with a threefold increase in urine cGMP excretion (573+/-195 pmol/min baseline to 1823+/-545 pmol/ min; P<0.001), marked natriuresis (207+/-34 micromol/min baseline to 416+/-62 micromol/min; P<0.001), fractional sodium excretion (3.3+/-0.5% baseline to 5.6+/-0.7%; P<0.01), and diuresis (3.4+/-0.5 ml/min baseline to 7.4+/-1 ml/min; P<0.001). All parameters remained elevated above baseline for the remaining 7-hr study period. In response to candoxatrilat, the glomerular filtration rate rose by 19% (P=0.01), renal plasma flow by 7% (P=0.04), renal blood flow by 13% (P=0.03) in association with an increase in filtration fraction from 24+/-2% to 28+/-2% (P=0.002) and small fall in renal vascular resistance from 0.38+/-0.04 to 0.30+/-0.04 mmHg x min x 1.73 m2 x ml(-1) (P=0.02). There was a fall in plasma angiotensin II without a change in plasma renin concentration or plasma aldosterone. Median urinary albumin excretion increased after candoxatrilat administration from 48 (3-131) to 114 (32-641) microg/min (P<0.01).

CONCLUSIONS

Acute neutral endopeptidase inhibition with candoxatrilat appears to reverse the adverse renal hemodynamic and renal excretory effects of cyclosporine in stable renal transplant recipients.

Dual metalloprotease inhibitors: mercaptoacetyl-based fused heterocyclic dipeptide mimetics as inhibitors of angiotensin-converting enzyme and neutral endopeptidase

A series of 7,6- and 7,5-fused bicyclic thiazepinones and oxazepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. These compounds are potent inhibitors of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) both in vitro and in vivo. Compound 1a, a 7,6-fused bicyclic thiazepinone, demonstrated excellent blood pressure lowering in a variety of animal models characterized by various levels of plasma renin activity and significantly potentiated urinary sodium, ANP, and cGMP excretion in a cynomolgus monkey assay. On the basis of its potency and duration of action, compound 1a (BMS-186716) was advanced into clinical development for the treatment of hypertension and congestive heart failure.

Comparison of candoxatril and atrial natriuretic factor in healthy men. Effects on hemodynamics, sympathetic activity, heart rate variability, and endothelin

The purpose of these experiments was to compare the effects of endopeptidase inhibition with oral candoxatril on systemic and forearm hemodynamics and muscle sympathetic nerve activity with responses to a low-dose atrial natriuretic factor infusion. Eleven healthy men received at random on three separate days either intravenous saline, natriuretic factor (1.6 pmol/kg per minute) plus saline, or oral candoxatril (200 mg) plus saline. Measurements were made at baseline and 30, 60, and 90 minutes after interventions. Atrial natriuretic factor lowered diastolic pressure (P < .01), central venous pressure (P < .001), forearm blood flow (P < .05), and forearm vascular compliance (P < .05) but had no effect on systolic pressure, heart rate or its variability, stroke volume, sympathetic nerve activity, plasma norepinephrine, or endothelin-1. Plasma epinephrine increased (P < .01). Candoxatril lowered central venous pressure (P < .001) and increased systolic pressure (from 116 +/- 6 to 120 +/- 7 mm Hg; P < .05), endothelin (from 4.6 +/- 1.1 to 6.8 +/- 3.2 pmol/L; P < .02), and epinephrine (P < .05), without affecting any other variables. Candoxatril and atrial natriuretic factor lowered central venous pressure in healthy men without causing a reflex increase in sympathetic nerve activity or norepinephrine, yet epinephrine rose. This suggests that both interventions may specifically inhibit sympathetic nerve traffic to muscle at physiological plasma atrial natriuretic factor concentrations. However, whereas the peptide lowered blood pressure, candoxatril increased systolic pressure. These contrasting hemodynamic responses may be related to differences in plasma atrial natriuretic peptide concentration and to altered endothelin metabolism by candoxatril.

Hormonal and renal responses to neutral endopeptidase inhibition in normal humans on a low and on a high sodium intake

Hormonal and renal effects of candoxatril, a neutral endopeptidase 24.11 inhibitor, were investigated in eight subjects equilibrated on a low sodium diet (10 mmol sodium per day) and a high sodium (350 mmol per day) diet. After candoxatril treatment, plasma ANP increased to a maximum at 2-4 h and declined to baseline within 24 h. The increases were relatively greater on the high sodium diet, which was also associated with increases in urinary sodium, with highest values at 4h. On the low sodium diet, the magnitude of the changes was significantly lower (24 h cumulative sodium excretion was 11.4 +/- 5.5 mmol on the low sodium diet and 73.1 +/- 25.6 mmol on the high sodium diet; P < 0.01). There were no significant effects on urinary potassium excretion, creatinine clearance or haematocrit. After candoxatril treatment there were reductions in PRA, especially on the low sodium diet. On either diet there were no effects on systemic blood pressure. These results demonstrate that dietary sodium intake is an important determinant of the renal and hormonal responses to neutral endopeptidase inhibition.

Potentiation of natriuretic peptides by neutral endopeptidase inhibitors

1. Inhibitors of neutral endopeptidase (NEP) EC 3.4.24.11 were developed to regulate endogenous levels of the natriuretic and vasodilatory hormone atrial natriuretic peptide (ANP). The selective NEP inhibitor SQ 28603 enhanced the increases in plasma ANP and urinary excretion of ANP, cyclic GMP and sodium stimulated by infusion of human ANP in conscious monkeys. SQ 28603 also potentiated the renal and depressor responses to rat brain natriuretic peptide (BNP) in conscious spontaneously hypertensive rats (SHR) and human BNP in conscious monkeys. Therefore, selective NEP inhibitors protected both natriuretic peptides from degradation in vivo and enhanced their biological activities. 2. Selective NEP inhibitors lowered blood pressure in conscious DOCA/salt hypertensive rats and SHR with antihypertensive activity similar to that of exogenous ANP. Furthermore, simultaneous treatment with an angiotensin converting enzyme (ACE) inhibitor enhanced the depressor activity of the NEP inhibitor in SHR. 3. SQ 28603 stimulated urinary excretion of cyclic GMP and sodium in a dose-related manner in conscious dogs with tachycardia-induced heart failure. Addition of the ACE inhibitor captopril significantly reduced blood pressure and systemic vascular resistance while sustaining sodium excretion and increasing cardiac output, glomerular filtration rate and renal blood flow. Therefore, combined NEP and ACE inhibition produced a unique haemodynamic and renal profile in dogs with pacing-induced heart failure. 4. The novel dual metalloprotease inhibitor BMS-182657 potentiated the renal responses to exogenous ANP and suppressed the pressor response to angiotensin I in conscious monkeys, indicating in vivo inhibition of both NEP and ACE.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of, and a putative role for, the cell-surface neutral metallo-endopeptidases during mammalian craniofacial development

Endopeptidase-24.11 (neutral endopeptidase, neprilysin, ‘enkephalinase’, EC 3.4.24.11) and endopeptidase-24.18 (endopeptidase-2, meprin, EC 3.4.24.18) are cell-surface zinc-dependent metallo-endopeptidases able to cleave a variety of bioactive peptides including growth factors. We report the first study of the cellular and tissue distribution of both enzymes and of the mRNA for NEP during embryonic development in the rat. Endopeptidase-24.11 protein was first detected at E10 in the lining of the gut and, at E12, the enzyme was present on the notochord, medial and lateral nasal processes, otocyst, mesonephros, heart and neuroepithelium. In contrast, at this time endopeptidase-24.18 was present only on the apical surface of the neuroepithelial cells. By E14 and E16, NEP was also detected in a wide range of craniofacial structures, notably the palatal mesenchyme, the choroid plexus, tongue and perichondrium. The distribution of endopeptidase-24.18 at these stages was restricted to the inner ear, the nasal conchae, and ependymal layer of the brain ventricles and the choroid plexus. Although endopeptidase-24.11 had been detectable in the craniofacial vasculature at E12 and E14, this was no longer apparent at E16. Significantly, the distribution of endopeptidase-24.11 mRNA closely matched the immunolocalization of the protein at all stages investigated. In order to explore the functional role of these enzymes, inhibition studies were carried out using two selective inhibitors of endopeptidase-24.11, phosphoramidon and thiorphan. E9.5 and E10.5 embryos exposed to either inhibitor displayed a characteristic, asymmetric abnormality consisting of a spherical swelling, possibly associated with a haematoma, predominantly on the left side of the prosencephalon, and the severity of this defect appeared to be a dose-dependent phenomenon. This study suggests that these enzymes play previously unrecognized roles during mammalian embryonic development.