Role of renal endopeptidase 24.11 in kinin metabolism in vitro and in vivo

Angiotensin receptor-neprilysin inhibitor improves coronary collateral perfusion

Background

We investigated the pleiotropic effects of an angiotensin receptor-neprilysin inhibitor (ARNi) on collateral-dependent myocardial perfusion in a rat model of coronary arteriogenesis, and performed comprehensive analyses to uncover the underlying molecular mechanisms.

Methods

A rat model of coronary arteriogenesis was established by implanting an inflatable occluder on the left anterior descending coronary artery followed by a 7-day repetitive occlusion procedure (ROP). Coronary collateral perfusion was measured by using a myocardial particle infusion technique. The putative ARNi-induced pro-arteriogenic effects were further investigated and compared with an angiotensin-converting enzyme inhibitor (ACEi). Expression of the membrane receptors and key enzymes in the natriuretic peptide system (NPS), renin-angiotensin-aldosterone system (RAAS) and kallikrein-kinin system (KKS) were analyzed by quantitative polymerase chain reaction (qPCR) and immunoblot assay, respectively. Protein levels of pro-arteriogenic cytokines were measured by enzyme-linked immunosorbent assay, and mitochondrial DNA copy number was assessed by qPCR due to their roles in arteriogenesis. Furthermore, murine heart endothelial cells (MHEC5-T) were treated with a neprilysin inhibitor (NEPi) alone, or in combination with bradykinin receptor antagonists. MHEC5-T proliferation was analyzed by colorimetric assay.

Results

The in vivo study showed that ARNis markedly improved coronary collateral perfusion, regulated the gene expression of KKS, and increased the concentrations of relevant pro-arteriogenic cytokines. The in vitro study demonstrated that NEPis significantly promoted MHEC5-T proliferation, which was diminished by bradykinin receptor antagonists.

Conclusion

ARNis improve coronary collateral perfusion and exert pro-arteriogenic effects via the bradykinin receptor signaling pathway.

Urinary neprilysin for early detection of acute kidney injury after cardiac surgery: A prospective observational study

BACKGROUND

Acute kidney injury (AKI) predicts adverse outcomes after cardiac surgery. The accuracy of using changes in serum creatinine for diagnosis and grading of AKI is limited in the peri-operative cardiac surgical setting and AKI may be underdiagnosed due to haemodilution from cardiopulmonary bypass priming and the need for intra-operative and postoperative volume resuscitation.

OBJECTIVES

To determine whether the urinary biomarker neprilysin can be used as a marker for the early detection of AKI after cardiac surgery.

DESIGN

Prospective, observational cohort study.

SETTING

Austrian tertiary referral centre.

PATIENTS

96 Patients undergoing elective cardiac surgery with cardiopulmonary bypass.

MAIN OUTCOME MEASURES

Differences and discriminatory power of neprilysin levels early after cardiac surgery and on postoperative day 1 between patients with or without AKI, as defined by the Kidney Disease Improving Global Outcomes Group.

RESULTS

AKI was found in 27% (n=26). The median neprilysin levels on postoperative day 1 were significantly higher in the AKI than in the non-AKI group, 4.0 [interquartile range (IQR): 2 to 6.25] vs. 2.0 ng ml [IQR: 1.0 to 4.5], P = 0.0246, respectively. In addition, the median neprilysin levels at the end of surgery were significantly different between both groups, 5.0 [IQR: 2.0 to 9.0] vs. 2.0 ng ml [IQR: 1.0 to 4.0], P = 0.0055, respectively. The discriminatory power of neprilysin for detecting early AKI corresponded to an area under the curve of 0.77 (95% confidence interval, 0.65 to 0.90).

CONCLUSION

Urinary neprilysin has potential as a biomarker for the early detection of AKI after cardiac surgery and has comparable discriminatory power to recently studied AKI biomarkers.

TRIAL REGISTRATION

The trial was registered at ClinicalTrials.gov (NCT03854825, https://clinicaltrials.gov/ct2/show/NCT03854825).

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Increased Stability of Oligopeptidases Immobilized on Gold Nanoparticles

The metallopeptidases thimet oligopeptidase (THOP, EC 3.4.24.25) and neurolysin (NEL, EC 3.4.24.26) are enzymes that belong to the zinc endopeptidase M13 family. Numerous studies suggest that these peptidases participate in the processing of bioactive peptides such as angiotensins and bradykinin. Efforts have been conducted to develop biotechnological tools to make possible the use of both proteases to regulate blood pressure in mice, mainly limited by the low plasmatic stability of the enzymes. In the present study, it was investigated the use of nanotechnology as an efficient strategy for to circumvent the low stability of the proteases. Recombinant THOP and NEL were immobilized in gold nanoparticles (GNPs) synthesized in situ using HEPES and the enzymes as reducing and stabilizing agents. The formation of rTHOP-GNP and rNEL-GNP was characterized by the surface plasmon resonance band, zeta potential and atomic force microscopy. The gain of structural stability and activity of rTHOP and rNEL immobilized on GNPs was demonstrated by assays using fluorogenic substrates. The enzymes were also efficiently immobilized on GNPs fabricated with sodium borohydride. The efficient immobilization of the oligopeptidases in gold nanoparticles with gain of stability may facilitate the use of the enzymes in therapies related to pressure regulation and stroke, and as a tool for studying the physiological and pathological roles of both proteases.

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

Side Chain Cyclized Aromatic Amino Acids: Great Tools as Local Constraints in Peptide and Peptidomimetic Design

Constraining the conformation of flexible peptides is a proven strategy to increase potency, selectivity, and metabolic stability. The focus has mostly been on constraining the backbone dihedral angles; however, the correct orientation of the amino acid side chains (χ-space) that constitute the peptide pharmacophore is equally important. Control of χ-space utilizes conformationally constrained amino acids that favor, disfavor, or exclude the gauche (-), the gauche (+), or the trans conformation. In this review we focus on cyclic aromatic amino acids in which the side chain is connected to the peptide backbone to provide control of χ¹- and χ²-space. The manifold applications for cyclized analogues of the aromatic amino acids Phe, Tyr, Trp, and His within peptide medicinal chemistry are showcased herein with examples of enzyme inhibitors and ligands for G protein-coupled receptors.

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.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

In vitro metabolism of the glucagon-like peptide-1 (GLP-1)-derived metabolites GLP-1(9-36)amide and GLP-1(28-36)amide in mouse and human hepatocytes

Previous studies have revealed that the glucoincretin hormone glucagon-like peptide-1 (GLP-1)(7-36)amide is metabolized by dipeptidyl peptidase-IV (DPP-IV) and neutral endopeptidase 24.11 (NEP) to yield GLP-1(9-36)amide and GLP-1(28-36)amide, respectively, as the principal metabolites. Contrary to the previous notion that GLP-1(7-36)amide metabolites are pharmacologically inactive, recent studies have demonstrated cardioprotective and insulinomimetic effects with both GLP-1(9-36)amide and GLP-1(28-36)amide in animals and humans. In the present work, we examined the metabolic stability of the two GLP-1(7-36)amide metabolites in cryopreserved hepatocytes, which have been used to demonstrate the in vitro insulin-like effects of GLP-1(9-36)amide and GLP-1(28-36)amide on gluconeogenesis. To examine the metabolic stability of the GLP-1(7-36)amide metabolites, a liquid chromatography-tandem mass spectrometry assay was developed for the quantitation of the intact peptides in hepatocyte incubations. GLP-1(9-36)amide and GLP-1(28-36)amide were rapidly metabolized in mouse [GLP-1(9-36)amide: t(1/2) = 52 minutes; GLP-1(28-36)amide: t(1/2) = 13 minutes] and human hepatocytes [GLP-1(9-36)amide: t(1/2) = 180 minutes; GLP-1(28-36)amide: t(1/2) = 24 minutes), yielding a variety of N-terminal cleavage products that were characterized using mass spectrometry. Metabolism at the C terminus was not observed for either peptides. The DPP-IV and NEP inhibitors diprotin A and phosphoramidon, respectively, did not induce resistance in the two peptides toward proteolytic cleavage. Overall, our in vitro findings raise the intriguing possibility that the insulinomimetic effects of GLP-1(9-36)amide and GLP-1(28-36)amide on gluconeogenesis and oxidative stress might be due, at least in part, to the actions of additional downstream metabolites, which are obtained from the enzymatic cleavage of the peptide backbone in the parent compounds.

Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Acute ischemic stroke and traumatic brain injury are a major cause of mortality and morbidity. Due to the paucity of therapies, there is a pressing clinical demand for new treatment options. Successful therapeutic strategies for these conditions must target multiple pathophysiological mechanisms occurring at different stages of brain injury. In this respect, the kallikrein-kinin system is an ideal target linking key pathological hallmarks of ischemic and traumatic brain damage such as edema formation, inflammation, and thrombosis. In particular, the kinin receptors, plasma kallikrein, and coagulation factor XIIa are highly attractive candidates for pharmacological development, as kinin receptor antagonists or inhibitors of plasma kallikrein and coagulation factor XIIa are neuroprotective in animal models of stroke and traumatic brain injury. Nevertheless, conflicting preclinical evaluation as well as limited and inconclusive data from clinical trials suggest caution when transferring observations made in animals into the human situation. This review summarizes current evidence on the pathological significance of the kallikrein-kinin system during ischemic and traumatic brain damage, with a particular focus on experimental data derived from animal models. Experimental findings are also compared with human data if available, and potential therapeutic implications are discussed.

Potentiation of bradykinin effect by angiotensin-converting enzyme inhibition does not correlate with angiotensin-converting enzyme activity in the rat mesenteric arteries

Angiotensin-converting enzyme (kininase II [ACE]) inhibitors are capable of potentiating bradykinin (BK) effects by enhancing the actions of bradykinin on B(2) receptors independent of blocking its inactivation. To investigate further the importance of ACE kininase activity on BK-induced vasodilation, we investigated the effect of inhibiting ACE, as well as other kininases, on both BK metabolism and vasodilator effect in preparations that exhibit increased ACE activity. Mesenteric arterial beds obtained from 1-kidney, 1-clip hypertensive rats presented augmented ACE and angiotensin I converting activities compared with normotensive rats. The isolated and perfused mesenteric beds were exposed to BK for 15 minutes in the absence or in the presence of kininase inhibitors; then, the perfusate was collected for analysis of the products of BK metabolism by high-performance liquid chromatography. BK was metabolized to the fragments BK(1-8), BK(1-7), and BK(1-5), and the recovery of intact BK was reduced by 47% in the hypertensive group. Recovery of BK was increased in both groups in the presence of a kininase I inhibitor and in the hypertensive group by neutral endopeptidase 24.11 inhibitor; however, ACE inhibition did not affect BK metabolism in both groups. In contrast, only the ACE inhibitor potentiated the vasodilator effect of BK in a mesenteric bed preconstricted with phenylephrine; the increase in BK effect, nevertheless, was not greater in arteries from hypertensive rats that presented an increased ACE activity when compared with those in the normotensive group. These data demonstrated that ACE inhibitor-induced potentiation of BK vasodilator effects is not related to their actions on BK degradation.

Pharmacological enhancement of the kallikrein-kinin system promotes anti-fibrotic responses in human mesangial cells

The aim of the present study was to investigate whether pharmacological enhancement of the renal kallikrein-kinin system using the vasopeptidase inhibitor omapatrilat plays a direct role in modulating the fibrotic responses of human mesangial cells to injury. Treatment with 40 micromol/L omapatrilat was able to reduce macrophage-conditioned medium (MPCM)-induced fibronectin levels without affecting mRNA expression. MPCM injury also suppressed kallikrein and low molecular weight kininogen mRNA. Omapatrilat was able to attenuate this suppression. Bradykinin levels in contrast were increased by MPCM and treatment with omapatrilat further augmented levels. Co-incubation with the bradykinin B2 receptor antagonist HOE 140 attenuated the omapatrilat-induced lowering of fibronectin. Moreover, inhibition of cGMP release had a similar effect. Paradoxically, RT-PCR and Southern blotting demonstrated that bradykinin B2 receptor mRNA levels were down regulated in response to omapatrilat. Western blotting supported this data. Supernatant levels of tissue plasminogen activator (tPA), a product of bradykinin stimulation, were decreased by omapatrilat while cell associated tPA levels were increased. Matrix metalloproteinase-9 (MMP-9) mRNA expression was up regulated by omapatrilat treatment, although no difference in active zymogen levels was observed. In conclusion enhancement of kallikrein-kinin system appears to play a direct role in promoting anti-fibrotic responses in MPCM-injured human mesangial cells.

A missing link between a high salt intake and blood pressure increase

It is widely accepted that a high sodium intake triggers blood pressure rise. However, only one-third of the normotensive subjects were reported to show salt-sensitivity in their blood pressure. Many factors have been proposed as causes of salt-sensitive hypertension, but none of them provides a satisfactory explanation. We propose, on the basis of accumulated data, that the reduced activity of the kallikrein-kinin system in the kidney may provide this link. Renal kallikrein is secreted by the distal connecting tubular cells and all kallikrein-kinin system components are distributed along the collecting ducts in the distal nephron. Bradykinin generated is immediately destroyed by carboxypeptidase Y-like exopeptidase and neutral endopeptidase, both quite independent from the kininases in plasma, such as angiotensin converting enzyme. The salt-sensitivity of the blood pressure depends largely upon ethnicity and potassium intake. Interestingly, potassium and ATP-sensitive potassium (K(ATP)) channel blockers accelerate renal kallikrein secretion and suppress blood pressure rises in animal hypertension models. Measurement of urinary kallikrein may become necessary in salt-sensitive normotensive and hypertensive subjects. Furthermore, pharmaceutical development of renal kallikrein releasers, such as K(ATP) channel blockers, and renal kininase inhibitors, such as ebelactone B, may lead to the development of novel antihypertensive drugs.

Vasopeptidase inhibitor restores the balance of vasoactive hormones in progressive nephropathy

BACKGROUND

The mechanism(s) underlying greater renoprotection of combined blockade of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) by vasopeptidase over ACE inhibitors are ill defined. We previously found that progressive renal disease is associated with increased renal synthesis of endothelin-1 (ET-1) in the face of reduced generation of renal nitric oxide (NO) in the remnant kidney model. Here we compared changes in urinary excretion of ET-1 and nitrite/nitrate, markers of renal ET-1, and NO synthesis, respectively, and urinary cGMP, an indirect index of renal atrial natriuretic peptide (ANP) synthesis, after administration of vasopeptidase or ACE inhibitor in rats with renal mass reduction (RMR).

METHODS

Twenty-one days after 5/6 nephrectomy, after the onset of hypertension and overt proteinuria, rats were divided in 3 groups (N= 7-8) and given daily by gavage: vehicle, the vasopeptidase inhibitor AVE7688 (3 mg/kg bid), or enalapril (5 mg/kg bid) until day 90. Normal rats (N= 5) served as control rats.

RESULTS

Systolic blood pressure in RMR rats was equally controlled by AVE7688 and enalapril. AVE7688 resulted in a significant antiproteinuric effect, with urinary protein levels being reduced on average by 83% in respect to vehicle (88 +/- 28 vs. 518 +/- 27 mg/day, P < 0.0001). Enalapril achieved a 47% reduction in proteinuria (277 +/- 81 mg/day, P < 0.01 vs. vehicle) to levels that remained higher (P < 0.01), however, than those after AVE7688. Renal function impairment and glomerular and tubular changes were significantly (P < 0.05 vs. vehicle) ameliorated by AVE7688, and partially affected by enalapril. AVE7688 reduced the abnormal urinary excretion of ET-1 of RMR animals (98 +/- 8 vs. vehicle: 302 +/- 50 pg/24 h, P < 0.001) more than enalapril (159 +/- 14 pg/24 h, P < 0.05 vs. AVE7688). Consistently, AVE7688 was more effective than enalapril in augmenting renal synthesis of NO (2487 +/- 267 and 1519 +/- 217 vs. vehicle: 678 +/- 71 nmol/15 h; P < 0.001, AVE7688 vs. vehicle, P < 0.01 AVE7688 vs. enalapril). AVE7688 significantly increased urinary cGMP (78 +/- 6 vs. vehicle 45 +/- 9 nmol/24 h; P < 0.01).

CONCLUSION

The superior renoprotection achieved by AVE7688 over enalapril in progressive renal injury is due to the correction of the altered balance of vasoconstrictor/vasodilator mediators in the kidney.

Neutral endopeptidase expression in mesangial cells

In the kidney, neutral endopeptidase (NEP) is implicated in the metabolism of several peptides involved in blood pressure and sodium homeostasis control, such as the atrial natriuretic peptide, bradykinin and angiotensin I. Due to its physiological importance in the modulation of pressor responses, the presence of NEP in mouse mesangial cells has been investigated, since these cells control glomerular function and are able to synthesise components of the renin-angiotensin system. A NEP-like activity (NEP-like) that cleaves the fluorogenic substrates Abz-BKQ-EDDnp and Abz-DRRL-EDDnp was purified from mesangial cell lysate by ion-exchange, followed by gel filtration chromatography. The enzyme was able to hydrolyse bradykinin at the G4-F5 peptide bond and was inhibited by thiorphan. A pH study established that enzyme activity was maximal at pH 7.5 and the determined K(m) was 4.86 M using Abz-DRRL-EDDnp as substrate. NEP-like was recognised by monoclonal anti-NEP and had a molecular mass of 95 kDa. The purified enzyme was sequenced and showed similarity with human, rat, mouse and rabbit NEPs. We isolated, for the first time, NEP-like from mesangial cells. This enzyme could have an important role in the renal physiology by its action upon different peptides that are able to alter renal haemodynamics.

Dual renin???angiotensin system blockade restores blood pressure???renin dependency in individuals with low renin concentrations

BACKGROUND

The prevailing sodium intake and renin-angiotensin system status influence the blood pressure response to an angiotensin II type 1 (AT1) receptor antagonist or an angiotensin I converting enzyme inhibitor, which is known to be reinforced by a low sodium intake or administration of a diuretic.

OBJECTIVE

To investigate the possibility that combining both drugs might be more effective in conditions of high sodium intake than blocking the renin-angiotensin system in a single step.

METHODS

In a placebo-controlled, four-period crossover study in 12 normotensive volunteers who received a high sodium chloride intake (more than 250 mmol/day for 6 days), the haemodynamic and renin effects of a single oral dose of irbesartan 150 mg combined with fosinopril 20 mg were compared with those of a usual daily dose of fosinopril (20 mg) and a high dose of irbesartan (300 mg).

RESULTS

The changes in blood pressure induced by fosinopril and irbesartan alone were not different from those of placebo, whereas the combination significantly decreased blood pressure. Simultaneously, it increased plasma active renin and prorenin concentrations to a greater extent than did each single-site blocker.

CONCLUSION

In low-renin conditions, combined renin-angiotensin system blockade enables the demonstration of a persistent renin-dependency of the blood pressure. Through its more efficient blockade of the renin-angiotensin system, demonstrated by the increase in renin and prorenin, combined renin-angiotensin system blockade is more effective than doubling the usual dose of an AT1 receptor antagonist. This may offer an alternative strategy for treating patients with a range of renin concentrations, and may potentially increase the cardio- and nephrotective benefits through a more complete blockade of the renin-angiotensin system.

Serine protease inhibitors modulate chemotactic cytokine production by human lung fibroblasts in vitro

Chemotactic chemokines can be released from lung fibroblasts in response to interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. An imbalance between proteases and antiproteases has been observed at inflammatory sites, and, therefore, protease inhibitors might modulate fibroblast release of chemotactic cytokines. To test this hypothesis, serine protease inhibitors (FK-706, alpha(1)-antitrypsin, or N(alpha)-p-tosyl-L-lysine chloromethyl ketone) were evaluated for their capacity to attenuate the release of neutrophil chemotactic activity (NCA) or monocyte chemotactic activity (MCA) from human fetal lung fibroblasts (HFL-1). Similarly, the release of the chemoattractants IL-8, granulocyte colony-stimulating factor, monocyte chemoattractant protein-1, macrophage colony-stimulating factor, and granulocyte/macrophage colony-stimulating factor, from HFL-1, were evaluated in response to IL-1beta and TNF-alpha. NCA, MCA, and chemotactic cytokines were attenuated by FK-706. However, matrix metalloproteinase inhibitors were without effect, and cysteine protease inhibitors only slightly attenuated chemotactic or cytokine release. These data suggest that IL-1beta and TNF-alpha may stimulate lung fibroblasts to release NCA and MCA by a protease-dependent mechanism and that serine protease inhibitors may attenuate the release.

Vasopeptidase inhibition: a double-edged sword?

The enormous benefits of inhibition of ACE demonstrate that manipulation of the metabolism of peptide hormones is a valuable therapeutic strategy for cardiovascular disease. Recent attempts to expand these benefits have combined ACE inhibition with inhibition of other peptidases such as neutral endopeptidase (NEP) in a single molecule, a strategy known as vasopeptidase inhibition. NEP metabolizes natriuretic peptides, and NEP inhibition offers the prospect of combining the benefits of increased natriuretic peptide levels with those of ACE inhibition. However, peptidases such as ACE and NEP have many different substrates, and there are complex interactions between ACE inhibition and NEP inhibition. Both ACE and NEP metabolize the kinin peptides bradykinin and kallidin, and NEP also converts angiotensin (Ang) I to Ang-(1-7) and metabolizes Ang II and endothelin. Addition of NEP inhibition to ACE inhibition potentiates the ACE inhibitor-induced increase in kinin levels, increases Ang II levels, reduces Ang-(1-7) levels, and may increase endothelin levels. These additional consequences of combined ACE/NEP inhibition increase the risk of angioedema and may counteract any benefit of ACE inhibition that depends on reduced Ang II levels and increased Ang-(1-7) levels. Further considerations are that the ratio of ACE and NEP inhibition is fixed for vasopeptidase inhibitors, and there is uncertainty how these drugs should be compared with ACE inhibitors. Vasopeptidase inhibitors will therefore require careful evaluation before they are introduced to patient care.

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Increased expression of renal neutral endopeptidase in severe heart failure

The enzyme neutral endopeptidase (NEP; EC 3.4.24.11) cleaves several vasoactive peptides such as the atrial natriuretic peptide (ANP). ANP is a hormone of cardiac origin with diuretic and natriuretic actions. Despite elevated circulating levels of ANP, congestive heart failure (CHF) is characterized by progressive sodium and water retention. In order to elucidate the loss of natriuretic and diuretic properties of ANP in CHF we analyzed activity, protein concentrations, mRNA and immunostaining of NEP in kidneys of different models of severe CHF in the rat.CHF was induced by either aortocaval shunt, aortic banding or myocardial infarction in the rat. All models were defined by increased left ventricular end-diastolic pressure and decreased contractility. The diminished effectiveness of ANP was reflected by reduced cGMP/ANP ratio in animals with shunt or infarction. Renal NEP activity was increased in rats with aortocaval shunt (203 +/- 7%, p < 0.001), aortic banding (184 +/- 11%, p < 0.001) and infarction (149 +/- 10%, p < 0.005). Western blot analysis revealed a significant increase in renal NEP protein content in two models of CHF (shunt: 214 +/- 57%, p < 0.05; infarction: 310 +/- 53 %, p < 0.01). The elevated protein expression was paralleled by a threefold increase in renal NEP-mRNA level in the infarction model. The increased renal NEP protein expression and activity may lead to enhanced degradation of ANP and may contribute to the decreased renal response to ANP in heart failure. Thus, the capacity to counteract sodium and water retention, would be diminished. The increased renal NEP activity may therefore be a hitherto unknown factor in the progression of CHF.

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.

Soluble metalloendopeptidases and neuroendocrine signaling

Peptidases play a vital and often highly specific role in the physiological and pathological generation and termination of peptide hormone signals. The thermolysin-like family of metalloendopeptidases involved in the extracellular processing of neuroendocrine and cardiovascular peptides are of particular significance, reflecting both their specificity for particular peptide substrates and their utility as therapeutic targets. Although the functions of the membrane-bound members of this family, such as angiotensin-converting enzyme and neutral endopeptidase, are well established, a role for the predominantly soluble family members in peptide metabolism is only just emerging. This review will focus on the biochemistry, cell biology, and physiology of the soluble metalloendopeptidases EC 3.4.24.15 (thimet oligopeptidase) and EC 3.4.24.16 (neurolysin), as well as presenting evidence that both peptidases play an important role in such diverse functions as reproduction, nociception, and cardiovascular homeostasis.

Effects of losartan and benazepril on abnormal circadian blood pressure rhythm and target organ damage in SHRSP

The effects of chronic treatment with losartan, an angiotensin II type 1 (AT1) receptor antagonist, and benazepril, an angiotensin converting enzyme (ACE) inhibitor, on target-organ damage and abnormal circadian blood pressure (BP) rhythm were compared in stroke-prone spontaneously hypertensive rats (SHRSP). Losartan and benazepril were given by intraperitoneal infusion for 3 weeks after 17 weeks of age to minimize any influence of their different pharmacokinetic properties. BP was continuously monitored by telemetrical method before treatment and at the end of the observation period. The left ventricular (LV) weight, 24-hour urinary albumin excretion (UalbV) and morphological changes in the kidney were observed. Losartan and benazepril (1, 3 and 10 mg/day) reduced BP and LV weight in a dose-dependent manner with good correlation between the effects. Losartan significantly improved UalbV in a dose-dependent manner, whereas benazepril was effective at only 10 mg/day. Renal morphological analysis showed that reduction of glomerulosclerosis and collagen fiber thickness was related to the effect on UalbV, but not to the antihypertensive effects. Losartan improved the shifted circadian BP rhythm towards the active phase in a dose-dependent manner, whereas the improvement caused by 1 and 3 mg/day of benazepril was less effective than the same dosage of losartan. These results suggest that both losartan and benazepril can reduce cardiac hypertrophy showing good correlation with their antihypertensive effects, but losartan, especially at a low dose, alleviates renal damage more effectively than benazepril, with its effect correlating well with improvement of the abnormal circadian BP rhythm in SHRSP. Thus, the protective effect against hypertensive target organ damage of the AT1 receptor antagonist seems to be more effective than that of ACE inhibitor.

Differential actions of vasopeptidase inhibition versus angiotensin-converting enzyme inhibition on diuretic therapy in experimental congestive heart failure

BACKGROUND

Omapatrilat (OMA), a vasopeptidase inhibitor, simultaneously inhibits angiotensin-converting enzyme (ACE) and neutral endopeptidase, which degrades vasodilatory factors (eg, ADM) and natriuretic peptides. Based on the beneficial cardiorenal and humoral properties of the natriuretic peptides, we hypothesized that an acute vasopeptidase inhibitor with or without diuretic would result in more favorable cardiorenal and hormonal actions than ACE inhibition plus diuretic (ACEI+D) in congestive heart failure.

METHODS AND RESULTS

We compared the actions of OMA alone and with diuretic (OMA+D) to ACEI+D in a model of pacing-induced congestive heart failure. OMA+D decreased pulmonary arterial and pulmonary capillary wedge pressures to a greater level than OMA alone or ACEI+D. Glomerular filtration rate was lower with ACEI+D than with either OMA group. Plasma renin activity and aldosterone immediately increased with ACEI+D, whereas OMA+D resulted in higher plasma renin activity and a delayed increase in aldosterone. OMA alone did not increase plasma renin activity and aldosterone, but resulted in a sustained increase in plasma adrenomedullin, with higher urinary atrial natriuretic peptide, adrenomedullin, and cGMP excretions than with ACEI+D.

CONCLUSIONS

Acute administration of OMA with or without diuretic results in more favorable cardiorenal and humoral responses in experimental congestive heart failure than does ACEI+D. There is no acute activation of renin and aldosterone with OMA alone such as occurs with ACEI+D and OMA+D. Thus, OMA with or without a diuretic possesses beneficial cardiorenal and humoral actions comparable to those observed with ACEI+D that can be explained by potentiation of natriuretic peptides.

Neutral endopeptidase knockout induces hyperalgesia in a model of visceral pain, an effect related to bradykinin and nitric oxide

Neutral endopeptidase (EC3.4.24.11, NEP, enkephalinase) is a zinc-metalloendopeptidase, cleaving a variety of substrates like enkephalins, substance P, and bradykinin. In the brain, NEP is a key enzyme in the degradation of enkephalins. Pharmacological inhibition of NEP-activity causes analgesia resulting from enhanced extracellular enkephalin concentrations. Recently, transgenic mice lacking the enzyme NEP have been developed (Lu, 1995). The present study was designed to investigate the nociceptive behavior of these NEP-knockout mice. Interestingly, NEP-deficient mice did not respond with decreased pain perception, but exhibited hyperalgesia in the hot-plate jump, warm-water tail-withdrawal, and mostnotablyin theacetic-acid writhing test. Inhibition of aminopeptidase N by bestatin reduced writhing in both strains, whereas NEP-inhibition by thiorphan reduced writhing selectively in wild-type mice. Naloxone increased writhing in wild-type but not in knockouts, whereas the bradykinin B2-receptor antagonist HOE140 reduced writhing selectively in NEP-knockouts. Similarly, the nitric oxide synthase inhibitor L-NAME reduced writhing in NEP-knockouts. These results indicate that genetic elimination of NEP, in contrast to pharmacological inhibition, leads to bradykinin-induced hyperalgesia instead of enkephalin-mediated analgesia. Nitric oxide (NO) is suggested to be involved in this process.

Role of the natriuretic peptides in the cardiorenal and humoral actions of omapatrilat: insights from experimental heart failure

Vasopeptidase (VP) inhibitors are novel molecules that co-inhibit neutral endopeptidase 24.11 (NEP), which degrades natriuretic peptides and angiotensin-converting enzyme (ACE). We review the biology of the natriuretic peptide system and a recent study of the role for the natriuretic peptide system in the mechanism of action of omapatrilat (the most clinically advanced VP inhibitor). This study compared the cardiorenal and humoral actions of omapatrilat with those of ACE inhibition. The actions of omapatrilat were further defined in the presence and absence of a natriuretic peptide receptor antagonist. This investigation provided insight into a unique new pharmacologic agent that has beneficial renal actions in experimental mild heart failure that exceed those seen with ACE inhibition alone and that are linked to the natriuretic peptide system.

Determination of bradykinin in rat urine by coupled-column high pressure liquid chromatography with precolumn derivatization with a water-soluble fluorogenic reagent

Bradykinin (BK) in rat urine was determined by coupled-column HPLC with precolumn fluorogenic derivatization with a water-soluble reagent, 3-(7-fluoro-2,1,3-benzoxadiazole-4-sulfonamido)benzenesulfonic acid (m-BS-ABD-F). The derivatization of BK with m-BS-ABD-F was completed at 70 degrees C for 100 min and gave only a single peak of BK derivative in addition to the peaks of the blank. The hydrophilicity of the derivatization reagent effectively prevented the adsorption of BK during the sample pretreatment and improved the recovery of BK. Good linearity was shown between the amount of BK spiked in urine (0-10 pmol) and the peak area of the BK derivatives (correlation coefficients >0.999), and the detection limits of the BK derivative were 35 fmol (S/N = 3). The precisions (cv, %) of intra- and interday assay were not more than 5.5% and the accuracies were in the range of 95.3-111% (1 and 5 pmol of BK in urine, n = 3). Although the peak regarded as that of the BK derivative rapidly decreased after incubation at 37 degrees C, addition of urinary kininase inhibitors to the urine samples drastically suppressed the decrease of this peak, confirming that the identified peak was that of the BK derivative. The urinary kinin excretion in male SD rats (9-11 weeks old) determined by the present method was 56.0 +/- 22.1 pg/min/kg (mean +/- SE, n = 5).

Vasopeptidase inhibition affords greater renoprotection than angiotensin-converting enzyme inhibition alone

The renoprotective efficacy of the vasopeptidase inhibitor omapatrilat (OMA) was compared with that of enalapril (ENA) in male Munich-Wistar rats subjected to 5/6 nephrectomy. ENA and OMA administered beginning on day 2 after surgery were equally effective in normalizing systolic BP (SBP) and preventing glomerulosclerosis (GS) for 12 wk. Micropuncture studies of rats performed using a similar treatment protocol demonstrated greater reduction of glomerular capillary hydraulic pressure with OMA than with ENA, at similar mean arterial pressures. To investigate whether these glomerular hemodynamic differences might be associated with differences in chronic renoprotective efficacy, additional rats were included in a protocol in which treatment was delayed until 4 wk after surgery (after the onset of hypertension and proteinuria) and continued for a longer period. Both treatments normalized SBP, but OMA resulted in more sustained reduction of proteinuria than did ENA. At week 20, OMA- and ENA-treated rats exhibited less GS than did untreated (control) rats at week 12, but only the difference in control versus OMA values was statistically significant [GS scores: control (12 wk), 36 +/- 4%; ENA (20 wk), 22 +/- 6%; OMA (20 wk), 14 +/- 2%]. The remaining ENA-treated rats were euthanized at 32 wk because of rapidly increasing proteinuria, whereas the remaining OMA-treated rats demonstrated a substantially slower increase in proteinuria until euthanasia at 50 wk. At this extremely late time point, OMA-treated rats exhibited GS scores similar to those of ENA-treated rats at 32 wk and control rats at 12 wk [GS scores: ENA (32 wk), 34 +/- 5%; OMA (50 wk), 38 +/- 8%]. It is concluded that, in this model, OMA affords greater long-term renoprotection than ENA when doses are adjusted to yield equivalent control of SBP.

Endogenous natriuretic peptides participate in renal and humoral actions of acute vasopeptidase inhibition in experimental mild heart failure

Mild heart failure is characterized by increases in atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in the absence of activation of the renin-angiotensin-aldosterone system (RAAS). Vasopeptidase (VP) inhibitors are novel molecules that coinhibit neutral endopeptidase 24.11, which degrades the natriuretic peptides (NPs) and ACE. In a well-characterized canine model of mild heart failure produced by ventricular pacing at 180 bpm for 10 days, we defined the renal and humoral actions of acute VP inhibition with omapatrilat (OMA, n=6) and acute ACE inhibition (n=5) alone with fosinoprilat. We also sought to determine whether the NPs participate in the renal actions of acute VP inhibition by the administration of OMA together with an intrarenal administration of the NP receptor antagonist HS-142-1 (n=5). OMA resulted in a greater natriuretic response than did ACE inhibition in association with increases in plasma cGMP, ANP, BNP, urinary cGMP, urinary ANP excretion, and glomerular filtration rate (P<0.05 for OMA versus ACE inhibition). Plasma renin activity was increased only in the group subjected to ACE inhibition. Administration of intrarenal HS-142-1 attenuated the renal properties of OMA in association with a decrease in urinary cGMP excretion despite similar increases in plasma ANP and BNP. This study provides new insight into a unique new pharmacological agent that has beneficial renal actions in experimental mild heart failure beyond the actions that are observed with ACE inhibition alone and that are linked to the NP system.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Vascular catabolism of bradykinin in the isolated perfused rat kidney

Kinins in the circulation are rapidly metabolized by several different peptidases. The purpose of this study was to evaluate the contribution of membrane-bound peptidases to kinin metabolism in the renal circulation. Experiments were performed in vitro, in isolated rat kidneys perfused at a constant flow rate (8 ml/min) with Tyrode's solution. The effects of peptidase inhibitors were evaluated on the functional vasodilator response caused by bradykinin (30 nM) or [Tyr(Me)(8)]bradykinin (10 nM) via activation of bradykinin B2 receptors in kidneys precontracted with prostaglandin F2alpha. Angiotensin converting enzyme inhibitors, enalaprilat (3 microM), ramiprilat (1 microM) or lisinopril (1 microM), increased the bradykinin-induced renal vasodilation by 40% or more. Inhibitors of neutral endopeptidase (thiorphan or phosphoramidon, 10 microM), basic carboxypeptidase (DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid or MGTPA, 10 microM) and aminopeptidase P (apstatin, 20 microM) however did not enhance the renal vasodilator response elicited by kinins, whatever tested alone or in the presence of lisinopril. These findings indicate that angiotensin converting enzyme is the major peptidase whose inhibition potentiates the renal bradykinin B2 receptor mediated vasodilator response of kinins. The relative contribution in this potentiation of inhibition of kinin inactivation and of cross-talk of angiotensin converting enzyme with bradykinin B2 receptor remains however to be clarified.

Pathways for angiotensin-(1---7) metabolism in pulmonary and renal tissues

Two of the primary sites of actions for angiotensin (ANG)-(1---7) are the vasculature and the kidney. Because little information exists concerning the metabolism of ANG-(1---7) in these tissues, we investigated the hydrolysis of the peptide in rat lung and renal brush-border membrane (BBM) preparations. Radiolabeled ANG-(1---7) was hydrolyzed primarily to ANG-(1---5) by pulmonary membranes. The ANG-converting enzyme (ACE) inhibitor lisinopril abolished the generation of ANG-(1---5), as well as that of smaller metabolites. Kinetic studies of the hydrolysis of ANG-(1---7) to ANG-(1---5) by somatic (pulmonary) and germinal (testes) forms of rat ACE yielded similar values, suggesting that the COOH-domain is responsible for the hydrolysis of ANG-(1---7). Pulmonary metabolism of ANG-(1---5) yielded ANG-(3---5) and was independent of ACE but may involve peptidyl or dipeptidyl aminopeptidases. In renal cortex BBM, ANG-(1---7) was rapidly hydrolyzed to mono- and dipeptide fragments and ANG-(1---4). Aminopeptidase (AP) inhibition attenuated the hydrolysis of ANG-(1---7) and increased ANG-(1---4) formation. Combined treatment with AP and neprilysin (Nep) inhibitors abolished ANG-(1---4) formation and preserved ANG-(1---7). ACE inhibition had no effect on the rate of hydrolysis or the metabolites formed in the BBM. In conclusion, ACE was the major enzymatic activity responsible for the metabolism of ANG-(1---7) in the lung, which is consistent with the ability of ACE inhibitors to increase the half-life of circulating ANG-(1---7) and raise endogenous levels of the peptide. An alternate pathway of metabolism was revealed in the renal cortex, where increased AP and Nep activities, relative to ACE activity, promote conversion of ANG-(1---7) to ANG-(1---4) and smaller fragments.

In vivo transfer of antisense oligonucleotide against urinary kininase blunts deoxycorticosterone acetate-salt hypertension in rats

We have previously reported that the renal kallikrein-kinin system suppressed the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Kinins were degraded in the kidney mainly by carboxypeptidase Y (CPY)-like kininase. Blockade of renal kinin degradation may reduce hypertension in the developmental stage. We constructed an antisense oligonucleotide against rat CPY homologue (5'-CAT-CTC-TGC-TTC-CTT-GTG-TC-3', AS) and its randomized control oligonucleotide (5'-TCC-TTC-CTG-CTT-GAG-TTC-CT-3', RC), and prepared an HVJ-liposome complex that prolongs and increases the effectiveness of the antisense oligonucleotide. Antisense oligonucleotide was transfected (25 nmole rat(-1), in terms of nucleotide) into the kidney from the renal artery. Blood pressure was measured through a catheter inserted into the abdominal aorta. Mean blood pressure (MBP) in DOCA-salt treated (for 2 weeks) Sprague Dawley strain rats was 130+/-3 mmHg (n=11), and was reduced significantly (P<0.05) more by AS transfection (122+/-4 mmHg, n=6) than by RC treatment (137+/-6 mmHg, n=5) 4 days after the transfection. This reduction in MBP was accompanied by increased urinary sodium excretion (AS, 8.4+/-1.5 mmole day(-1); RC, 4.6+/-0.5 mmole day(-1), P<0.05) and a reduction in urinary CPY-like kininase activity. Ebelactone B (5 mg kg(-1), twice a day, p.o.), an inhibitor for urinary CPY-like kininase, also reduced MBP and induced natriuresis to the same degree as AS. Lisinopril, an inhibitor for angiotensin converting enzyme (ACE) failed to reduce the elevated MBP. These results suggest that CPY-like kininase may have more contribution than ACE to degrade kinin in the kidney, and that knockdown of CPY-like kininase in the kidney may partly prevent rat DOCA-salt hypertension.

Human neutral brush border endopeptidase EC 3.4.24.11 in urine, its isolation, characterisation and activity in renal diseases

Human neutral brush border endopeptidase (NEP) was purified from the urine of patients suffering from acute toxic tubulointerstitial nephropathy. An enzyme preparation with specific activity of 102 Ug(-1) protein was obtained. The urinary activities of neutral endopeptidase and alanine aminopeptidase were measured in patients with renal disease and in 30 control patients, resulting in a reference range from 0.1 to 0.7 Ug(-1) creatinine and 1.4-14.1 Ug(-1) creatinine, respectively. Urine enzyme activities were highest in patients with acute tubulotoxic renal diseases. Neutral endopeptidase and alanine aminopeptidase activities were found to be 6.5- and 10-fold higher than the upper value of the reference range, respectively. Smaller increases in the rate of excretion of these enzymes (2.5- and 3.5-fold), respectively, were observed in patients suffering from acute tubular insufficiency and even lower increases, 2- and 1.5-fold, respectively, were observed in patients with chronic renal diseases. In diabetics and kidney transplant patients the enzyme excretion rates were within the reference range. Assay of both transmembrane metalloproteinases in urine may prove valuable in serving as markers for renal toxicity. Together with beta-NAG these enzymes could be employed as differentiation markers between acute and chronic tubular insufficiency.

Molecular cloning and biochemical characterization of a new mouse testis soluble-zinc-metallopeptidase of the neprilysin family

Because of their roles in controlling the activity of several bio-active peptides, members of the neprilysin family of zinc metallopeptidases have been identified as putative targets for the design of therapeutic agents. Presently, six members have been reported, these are: neprilysin, endothelin-converting enzyme (ECE)-1 and ECE-2, the Kell blood group protein, PHEX (product of the phosphate-regulating gene with homologies to endopeptidase on the X chromosome) and X-converting enzyme (XCE). In order to identify new members of this important family of peptidases, we designed a reverse transcriptase-PCR strategy based on conserved amino acid sequences of neprilysin, ECE-1 and PHEX. We now report the cloning from mouse testis of a novel neprilysin-like peptidase that we called NL1. NL1 is a glycoprotein that, among the members of the family, shows the strongest sequence identity with neprilysin. However, in contrast with neprilysin and other members of the family which are type II integral membrane proteins, NL1 was secreted when expressed in cultured mammalian cells, likely due to cleavage by a subtilisin-like convertase at a furin-like site located 22 amino acid residues in the C-terminus of the transmembrane domain. The recombinant enzyme exhibited neprilysin-like peptidase activity and was efficiently inhibited by phosphoramidon and thiorphan, two inhibitors of neprilysin. Northern blot analysis and in situ hybridization showed that NL1 mRNA was found predominantly in testis, specifically in round and elongated spermatids. This distribution of NL1 mRNA suggests that it could be involved in sperm formation or other processes related to fertility.

The link between met-enkephalin-induced down-regulation of APN activity and the release of superoxide anion

We have previously shown that methionine-enkephalin (MENK) differentially alters the production of superoxide anion (O(2)(-)) from neutrophils of different donors. This effect could be due to variable activity of proteolytic enzymes involved in the degradation of this neuropeptide. In this study, we investigated the possible association between the effect of MENK on O(2)(-)release and the two neutrophil associated hydrolytic enzymes that participate in enkephalin degradation; aminopeptidase N (APN) and neutral endopeptidase (NEP). We have demonstrated that APN but not NEP activity was down-regulated by MENK. This might be due to internalization, since APN down-regulation was observed only with intact neutrophils and not with the respective membranes. Preincubation of neutrophils with inhibitory anti CD13 MoAb (WM15) abbrogated the suppressive effect of MENK (10(-12), 10(-10)and 10(-8)M). These facts, show that in the periphery (as well as the brain) the dominant role in MENK hydrolysis can be attributed to APN. Also, they further support the idea of the link between the membrane associated CD13 and binding of the ligand to the opioid receptor.

Effects of a neutral endoprotease enzyme inhibitor, thiorphan, on hemodynamics and renal excretory function in four models of experimental hypertension

Thiorphan, a neutral endoprotease (NEP) enzyme inhibitor, has been shown to enhance the effects of atrial natriuretic peptide (ANP) in vivo. In this study, we examined the effects of an intravenous (iv) infusion of thiorphan on cardiovascular hemodynamics and excretion of urine volume (UV), sodium (U(Na)V) and potassium (UKV) in four different models of experimental hypertension, namely: 1) SHR, 2) two-kidney, one clip (2K1C),3) one-kidney, 1 clip (1K1C) and. 4) 70% reduced renal mass-salt (RRM-S) hypertensive rats. SHR has normal plasma renin activity, 2K1C is renin dependent, and 1K1C and RRM-S are low renin volume dependent models of hypertension. Rats were divided into experimental and control groups. Under inactin (120 mg/kg, body weight) anesthesia, rats were instrumented to record blood pressure and dP/dt (Millar catheter) and urine was collected through a suprapubic urinary bladder catheter. Experimental animals received an iv infusion of thiorphan, 0.5 mg/kg/min for 120 minutes. Control animals received vehicle only. In some animals, vascular smooth muscle cell membrane potentials (Em) was measured in vivo. In another series of experiments, using the identical protocol, cardiac output was recorded. The thiorphan infusion produced a similar progressive decrease in blood pressure in all models of hypertension. Cardiac output did not change relative to vehicle infused control animals. Thus pressure decreased because of a decrease in total peripheral resistance. The contractility index (dP/dt/P, where P = left ventricular pressure) did not change but vascular smooth muscle cells in tail arteries hyperpolarized in all four models. In spite of a significant decrease in blood pressure, thiorphan infusion either increased or produced no change in urinary volume (UV) and sodium (U(Na)V) excretion. These data show that thiorphan, an NEP inhibitor, decreases the blood pressure of hypertensive rats due to a decrease in total peripheral resistance, perhaps by hyperpolarizing vascular smooth muscle cells. These effects are independent of the mechanism of the hypertension. Increased UV and U(Na)V in the face of decreased pressure suggests a direct renal effect.

Inhibition of kinin degradation on the luminal side of renal tubules reduces high blood pressure in deoxycorticosterone acetate salt-treated rats

1. To determine whether the antihypertensive response in deoxycorticosterone acetate (DOCA) salt-treated rats was mediated by kinins on the luminal side of renal tubules or in the circulation, selective urinary kininase inhibitors were administered to normal Brown Norway Kitasato (BN-Ki) rats and kininogen-deficient Brown Norway Katholiek (BN-Ka) rats. 2. Kinins were degraded by neutral endopeptidase (NEP) and carboxypeptidase Y-like kininase (CPY) in urine, but were inactivated mainly by angiotensin-converting enzyme (ACE) in the plasma. 3. Ebelactone B inhibited CPY, while poststatin inhibited CPY and NEP. 4. Daily administration of poststatin (5 mg/kg per day, s.c.) for 3 days reduced blood pressure (BP) in DOCA salt-treated BN-Ki rats, but not in BN-Ka rats. 5. Ebelactone B (5 mg/kg per day, s.c.) also reduced BP in BN-Ki rats, which was accompanied by increased urinary sodium excretion, but had no effect on BP in BN-Ka rats. 6. Lisinopril (5 mg/kg per day, s.c.) had no effect on BP in either rat strain. 7. Arterial kinin levels in BN-Ki rats increased significantly (2.2-4.6 pg/mL) with captopril (10 mg/kg, s.c.). However, arterial kinin levels that induced hypotension following the infusion of bradykinin (1000 ng/kg per min, i.v.) were 110-fold higher than endogenous arterial kinin levels attained following captopril. 8. These results suggest that inhibition of kinin degradation on the luminal side of the renal tubules may effectively attenuate hypertension.

Renal response to acute neutral endopeptidase inhibition in mild and severe experimental heart failure

BACKGROUND

Neutral endopeptidase 24.11 (NEP) is a metalloprotease that is localized in the greatest abundance in the kidney and degrades natriuretic peptides, such as atrial natriuretic peptide (ANP). Mild congestive heart failure (CHF) is characterized by increases in circulating ANP without activation of the renin-angiotensin-aldosterone system (RAAS) or sodium retention. In contrast, severe CHF is characterized by sodium retention and coactivation of both ANP and the RAAS.

METHODS AND RESULTS

We defined the acute cardiorenal actions of the NEP inhibitor candoxatrilat (8 microg. kg(-1). min(-1)) in 4 groups of anesthetized dogs (normal, n=8; mild CHF, n=6; severe CHF, n=5; and severe CHF with chronic AT(1) receptor antagonism, n=5). Mild CHF was produced by rapid ventricular pacing at 180 bpm for 10 days and severe CHF at 245 bpm for 10 days. In mild CHF, urinary sodium excretion and glomerular filtration rate were greatest in response to acute NEP inhibition compared with the response in either control animals or those with severe CHF. Furthermore, an increase in glomerular filtration rate was observed only in mild CHF in association with increases in renal blood flow and decreases in renal vascular resistance and distal tubular sodium reabsorption. Urinary ANP and cGMP excretion, markers for renal biological actions of ANP, were greatest in mild CHF. The renal actions observed in mild CHF were attenuated in severe CHF and not restored by chronic AT(1) receptor antagonism.

CONCLUSIONS

The results of the present study demonstrate that acute NEP inhibition in mild CHF results in marked increases in renal hemodynamics and sodium excretion that exceed that observed in control animals and severe CHF. These studies underscore the potential therapeutic role for NEP inhibition to enhance renal function in mild CHF, an important phase of CHF that is marked by selective activation of endogenous ANP in the absence of an activated RAAS.

Functional, biochemical, and molecular investigations of renal kallikrein-kinin system in diabetic rats

A reduction of renal kallikrein has been found in non-insulin-treated diabetic individuals, suggesting that an impaired renal kallikrein-kinin system (KKS) contributes to the development of diabetic nephropathy. We analyzed relevant components of the renal KKS in non-insulin-treated streptozotocin (STZ)-induced diabetic rats. Twelve weeks after a single injection of STZ, rats were normotensive and displayed hyperglycemia, polyuria, proteinuria, and reduced glomerular filtration rate. Blood bradykinin (BK) levels and prekallikrein activity were significantly increased compared with controls. Renal kallikrein activity was reduced by 70%, whereas urinary BK levels were increased up to threefold. Renal kininases were decreased as indicated by a 3-fold reduction in renal angiotensin-converting enzyme activity and a 1.8-fold reduction in renal expression of neutral endopeptidase 24.11. Renal cortical expression of kininogen and B2 receptors was enhanced to 1.4 and 1. 8-fold, respectively. Our data suggest that increased urinary BK levels found in severely hyperglycemic STZ-diabetic rats are related to increased filtration of components of the plasma KKS and/or renal kininogen synthesis in combination with decreased renal kinin-degrading activity. Thus, despite reduced renal kallikrein synthesis, renal KKS is activated in the advanced stage of diabetic nephropathy.

Endopeptidases (kininases) are able to hydrolyze kinins in tubular fluid along the rat nephron

The activities of serine endopeptidase, prolyl endopeptidase and neutral endopeptidase were determined in tubular fluid collected from several portions of the rat nephron as well as in urine. The enzyme activities were measured by HPLC using bradykinin (BK) as substrate. Free residual peptides of BK obtained by the action of these enzymes on the locally produced BK were also determined. The endopeptidase activities were found to be present throughout the nephron. Equimolar fragments of BK were detected in the early proximal tubule (Arg(1)-Pro(7), Phe(8)-Arg(9), Arg(1)-Gly(4), Phe(5)-Arg(9), and BK), late proximal tubule (Arg(1)-Phe(5), Arg(1)-Pro(7), Gly(4)-Pro(7), Gly(4)-Arg(9), and BK), late distal tubule (Arg(1)-Gly(4), Phe(5)-Arg(9), Arg(1)-Phe(5), Ser(6)-Arg(9), Gly(4)-Arg(9), BK, and [des-Arg(9)]BK) and urine (Phe(8)-Arg(9), Phe(5)-Arg(9), Arg(1)-Phe(5), Ser(6)-Arg(9), Arg(1)-Pro(7), Gly(4)-Pro(7), Gly(4)-Arg(9), BK, and [des-Arg(9)]BK). Our data suggest that the endopeptidases and exopeptidases are secreted by the nephron. Early proximal tubules secrete angiotensin converting enzyme and neutral endopeptidase, differing from late distal tubules that produce prolyl endopeptidase, serine endopeptidase, carboxypeptidase, and also neutral endopeptidase. All enzymes detected along the rat nephron were found in the urine. The existence of endopeptidases and carboxypeptidase in the distal nephron may have a potential physiological role in the inactivation of the kinins formed by kallikrein in the kidney and also in the inactivation of additional peptides other than BK.

Activation of the kallikrein kinin system in interstitial cystitis

PURPOSE

We investigated whether the kallikrein kinin system is activated in interstitial cystitis by measuring urinary excretion rates of kinin peptides, active and total kallikrein, and the kininase neutral endopeptidase in women with interstitial cystitis. We compared these excretion rates to a control group of women with stress incontinence and normal bladder function.

MATERIALS AND METHODS

Catheter urine was collected from subjects during a water diuresis (approximately 10 ml. per minute) before and after distention of the bladder with 100 ml. water. The contribution of the bladder wall to urinary kinins was assessed by measuring the change in kinin levels after 2 minutes of bladder stasis before and after distention.

RESULTS

Absolute bradykinin and kallidin excretion rates were similar in women with interstitial cystitis and control subjects. Two minutes of bladder stasis after bladder distention increased urinary bradykinin (p = 0.02) but not kallidin excretion rates. Active and total kallikrein excretion rates were similar in patients with interstitial cystitis and control subjects. Neutral endopeptidase excretion rates were reduced in the initial urine collection from subjects with interstitial cystitis but were similar in both groups during later collection periods.

CONCLUSIONS

These data provide evidence for increased bradykinin levels in the bladder wall of subjects with interstitial cystitis, which may be due in part to reduced neutral endopeptidase levels. These increased bradykinin levels may participate in the pathogenesis and symptomatology of interstitial cystitis.

Effects of aminopeptidase P inhibition on kinin-mediated vasodepressor responses

We studied in anesthetized rats whether aminopeptidase P (AMP) may be involved in bradykinin (BK) metabolism and responses. For this we inhibited AMP with the specific inhibitor apstatin (Aps). Studies were done with Aps alone or together with the angiotensin-converting enzyme inhibitor lisinopril (Lis). Aps increased the vasodepressor response to an intravenous bolus of BK (400 ng/kg): vehicle, -3.0 +/- 0.7 mmHg; Aps, -7.8 +/- 0.7 mmHg (P < 0.01 vs. vehicle); Lis, -23.8 +/- 1.8 mmHg; Aps + Lis, -37.5 +/- 1.9 mmHg (P < 0.01 vs. Lis). Aps did not affect the vasodepressor response to BK given into the descending aorta. Plasma BK increased only in Aps + Lis-treated rats (in pg/ml): control, 48.0 +/- 1.4; Lis, 57.5 +/- 7.6; Aps + Lis, 121. 8 +/- 30.6 (P < 0.05 vs. control or Lis), whereas in rats infused with BK (400 ng. kg-1. min-1 for 5 min), Aps increased plasma BK (in pg/ml): control, 51.9 +/- 2.5; Aps, 83.5 +/- 20.5; Lis, 725 +/- 225; Aps + Lis, 1,668 +/- 318 (P < 0.05, Aps vs. control and Lis vs. Aps + Lis). In rats with aortic coarctation hypertension, the acute antihypertensive effects of Aps plus Lis were greater than Lis alone (P < 0.01). Hoe-140, a BK B2-receptor antagonist, abolished the difference. We concluded that in the rat AMP contributes to regulation of BK metabolism and responses.

Kallidin- and bradykinin-degrading pathways in human heart: degradation of kallidin by aminopeptidase M-like activity and bradykinin by neutral endopeptidase

BACKGROUND

Since kinins kallidin (KD) and bradykinin (BK) appear to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of kinin-degrading enzymes should potentiate such effects. Indeed, it is believed that this mechanism is partly responsible for the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors. In the heart, enzymes other than ACE may contribute to local degradation of kinins. The purpose of this study was to investigate which enzymes are responsible for the degradation of KD and BK in human heart tissue.

METHODS AND RESULTS

Cardiac membranes were prepared from the left ventricles of normal (n=5) and failing (n=10) hearts. The patients had end-stage congestive heart failure as the result of coronary heart disease or idiopathic dilated cardiomyopathy. Heart tissue was incubated with KD or BK in the presence or absence of enzyme inhibitors. We found no difference in the enzymes responsible for kinin metabolism or their activities between normal and failing hearts. Thus KD was mostly converted into BK by the aminopeptidase M-like activity. When BK was used as substrate, it was converted into an inactive metabolite BK-(1-7) mostly (80% to 90%) by the neutral endopeptidase (NEP) activity, with ACE unexpectedly playing only a minor role. The low enzymatic activity of ACE in the cardiac membranes, compared with that of NEP, was not due to chronic ACE inhibitor therapy, because the cardiac ACE activities of patients, whether receiving ACE inhibitors or not, and of normal subjects were all equal.

CONCLUSIONS

The present in vitro study shows that in human cardiac membranes, the most critical step in kinin metabolism, that is, inactivation of BK, appears to be mediated mostly by NEP. This observation suggests a role for NEP in the local control of BK concentration in heart tissue. Thus inhibition of cardiac NEP activity could be cardioprotective by elevating the local concentration of BK in the heart.