Urinary neutral endopeptidase 24.11 activity: modulation by chronic salt loading

Plasma Neprilysin Displays No Relevant Association With Neurohumoral Activation in Chronic HFrEF

Background

Neprilysin is a transmembrane endopeptidase involved in the breakdown of a variety of vasoactive peptides and serves as a therapeutic target in heart failure with reduced ejection fraction (HFrEF). This study aimed to investigate the relationship of circulating neprilysin with neurohumoral activation and the impact of plasma neprilysin activity on prognosis in HFrEF.

Methods and Results

A total of 369 chronic HFrEF patients were enrolled prospectively. Plasma neprilysin concentration and activity were determined by a specific ELISA and a fluorometric method. The association between plasma neprilysin and heart failure (HF) severity, neurohumoral activation, ie norepinephrine and absolute renin concentration, as well as all‐cause mortality was assessed. Median plasma neprilysin concentrations and activity levels were 413 pg/mL (interquartile range 0–4111) and 2.36 nmol/mL per minute (interquartile range 1.16–4.59). No correlation could be shown between plasma neprilysin concentrations and activity (r_s=0.09, P=0.088). Plasma neprilysin activity correlated with HF severity reflected by New York Heart Association stage (P=0.003) and tertiles of N‐terminal pro‐B‐type natriuretic peptide (P<0.001), whereas neprilysin concentrations did not (P=0.220; P=0.849). There was no relevant relationship between plasma neprilysin concentrations and activity, with neurohumoral activation reflected by absolute renin concentration (r_s=−0.02, P=0.648; r_s=0.03, P=0.574) or norepinephrine levels (r_s=−0.06, P=0.248; r_s=0.20, P<0.001). Neither circulating neprilysin concentrations nor activity were associated with outcome.

Conclusions

Plasma neprilysin concentrations and activity are not directly related to neurohumoral activation, indicating that neprilysin regulation is either more complex or not correctly mirrored by circulating neprilysin as a biomarker. Circulating neprilysin concentrations and activity were not associated with overall survival, implicating limited prognostic value of plasma neprilysin measurements in HFrEF patients.

Soluble neprilysin: A versatile biomarker for heart failure, cardiovascular diseases and diabetic complications-A systematic review

The potential role of soluble neprilysin (sNEP) as a biomarker has been poorly documented. Hence, the present systematic review emphasizes to explore sNEP as an emerging biomarker for heart failure (HF), cardiovascular diseases, diabetic kidney diseases, and so on. A systematic review was performed using an online database search in PubMed, Science Direct, Scopus, and Cochrane Library. Articles reporting biomarker's performance to diagnose various diseases in human participants were included. The results of the search outcome were 4723 articles. Based on the inclusion criteria of the systematic review, finally, 12 articles fulfilled the selection criteria. In these studies, 8 cohort study, 2 cross-sectional study, 1 case-control, and 1 prospective cohort study were identified. All these studies clearly suggested sNEP as a potential biomarker for diagnosis of various diseases (HF, cardiovascular diseases, diabetic kidney diseases, metabolic syndrome). sNEP may be a potential biomarker for HF, cardiovascular diseases, diabetic kidney disease, and so on.

Serum neprilysin and the risk of death in patients with out-of-hospital cardiac arrest of non-traumatic origin

BACKGROUND

Early risk stratification remains an unmet clinical need in patients with in out-of-hospital cardiac arrest. We hypothesised that soluble neprilysin may represent a promising biomarker in patients with out-of-hospital cardiac arrest of non-traumatic origin and provide new pathobiological insight.

METHODS

This pilot study was a biomarker analysis from the Heidelberg Resuscitation Registry. Serum soluble neprilysin levels on admission were measured in 144 patients with successful return of spontaneous circulation after out-of-hospital cardiac arrest of non-traumatic origin. The primary endpoint was time to all-cause mortality. KM Event Rates are reported. Cox models were adjusted for age, bystander resuscitation, initial ECG rhythm, baseline estimated glomerular filtration rate, baseline lactate, left ventricular function at baseline, and targeted temperature management.

RESULTS

In total, 90 (62.5%) patients died over a follow-up of at least 30 days. Soluble neprilysin correlated weakly with high-sensitivity troponin T (r=0.18, P=0.032) but did not correlate significantly with estimated glomerular filtration rate (r=-0.12) or lactate (r=0.11). Patients with elevated soluble neprilysin levels on admission were at significantly higher risk of all-cause mortality (Q4 69.1% vs. Q1 48.4%). After multivariable adjustment, soluble neprilysin in the top quartile (Q4) was significantly associated with all-cause mortality (Q4 vs. Q1: adjusted hazard ratio 2.48 (1.20-5.12)). In an adjusted multimarker model including high-sensitivity troponin T and high-sensitivity C-reactive protein, soluble neprilysin and high-sensitivity troponin T remained independently associated with all-cause mortality (soluble neprilysin: adjusted hazard ratio 2.27 (1.08-4.78); high-sensitivity troponin T: adjusted hazard ratio 3.40 (1.63-7.09)).

CONCLUSION

Soluble neprilysin, measured as early as on hospital admission, was independently associated with all-cause mortality in patients with out-of-hospital cardiac arrest of non-traumatic origin and may prove to be useful in the estimation of risk in these patients.

Urinary Proteome Analysis Identified Neprilysin and VCAM as Proteins Involved in Diabetic Nephropathy

Urinary proteome was analyzed and quantified by tandem mass tag (TMT) labeling followed by bioinformatics analysis to study diabetic nephropathy (DN) pathophysiology and to identify biomarkers of a clinical outcome. We included type 2 diabetic normotensive non-obese males with (n = 9) and without (n = 11) incipient DN (microalbuminuria). Sample collection included blood and urine at baseline (control and DN basal) and, in DN patients, after 3 months of losartan treatment (DN treated). Urinary proteome analysis identified 166 differentially abundant proteins between controls and DN patients, 27 comparing DN-treated and DN-basal patients, and 182 between DN-treated patients and controls. The mathematical modeling analysis predicted 80 key proteins involved in DN pathophysiology and 15 in losartan effect, a total of 95 proteins. Out of these 95, 7 are involved in both processes. VCAM-1 and neprilysin stand out of these 7 for being differentially expressed in the urinary proteome. We observed an increase of VCAM-1 urine levels in DN-basal patients compared to diabetic controls and an increase of urinary neprilysin in DN-treated patients with persistent albuminuria; the latter was confirmed by ELISA. Our results point to neprilysin and VCAM-1 as potential candidates in DN pathology and treatment.

Biochemistry, Therapeutics, and Biomarker Implications of Neprilysin in Cardiorenal Disease

BACKGROUND

Neprilysin (NEP) is a membrane-bound neutral endopeptidase that degrades a variety of bioactive peptides. The substrates include natriuretic peptides (NPs), which are important regulating mediators for cardiovascular and renal biology. Inhibition of NEP activity and exogenous NP administration thus have emerged as potential therapeutic strategies for treating cardiorenal diseases. More recently, B-type natriuretic peptide (BNP) or N-terminal-proBNP (NT-proBNP), 3'-5' cyclic guanosine monophosphate (cGMP), and soluble NEP as biomarkers have also been investigated in heart failure (HF) trials and their predictive value are beginning to be recognized.

CONTENT

The biological functions of NEP and NPs are discussed. Enhancing NPs through NEP inhibition combined with renin-angiotensin-aldosterone system (RAAS) antagonism has proved to be successful in HF treatment, although future surveillance studies will be required. Direct NP enhancement through peptide delivery may have fewer potentially hazardous effects compared to NEP inhibition. Strategies of combined inhibition on NEP with other cardiorenal pathophysiological pathways are promising. Finally, monitoring BNP/NT-proBNP/cGMP concentrations during NEP inhibition treatment may provide supplemental benefits to conventional biomarkers, and the identification of soluble NEP as a novel biomarker for HF needs further investigation.

SUMMARY

In this review, the biology of NEP is summarized, with a focus on NP regulation. The degradation of NPs by NEP provides the rationale for NEP inhibition as a strategy for cardiorenal disease treatment. We also describe the current therapeutic strategies of NEP inhibition and NP therapeutics in cardiorenal diseases. Moreover, the discovery of its circulating form, soluble NEP, as a biomarker is also discussed.

Genetic homogeneity but IgG subclass-dependent clinical variability of alloimmune membranous nephropathy with anti-neutral endopeptidase antibodies

Alloimmune antenatal membranous nephropathy (MN) during pregnancy results from antibodies produced by a neutral endopeptidase (NEP)-deficient mother. Here we report two recent cases that provide clues to the severity of renal disease. Mothers of the two children had circulating antibodies against NEP showing the characteristic species-dependent pattern by immunofluorescence on kidney slices. A German mother produced predominantly anti-NEP IgG4 accompanied by a low amount of IgG1. Her child recovered renal function within a few weeks. In sharp contrast, an Italian mother mainly produced complement-fixing anti-NEP IgG1, which also inhibits NEP enzymatic activity, whereas anti-NEP IgG4 has a weak inhibitory potency. Her child was dialyzed for several weeks. A kidney biopsy performed at 12 days of age showed MN, ischemic glomeruli, and arteriolar and tubular lesions. A second biopsy performed at 12 weeks of age showed aggravation with an increased number of collapsed capillary tufts. Both mothers were homozygous for the truncating deletion mutation 466delC and were thus NEP deficient. The 466delC mutation, identified in three previously described families, suggests a founder effect. Because of the potential severity of alloimmune antenatal MN, it is essential to identify families at risk by the detection of anti-NEP antibodies and NEP antigen in urine. On the basis of the five families identified to date, we propose an algorithm for the diagnosis of the disease and the prevention of complications.

Temporal changes in neutral endopeptidase/CD10 immunoexpression in the cyclic and early pregnant canine endometrium

CD10 is a multifunctional transmembrane neutral endopeptidase (NEP) that is considered to be a reliable marker of ectopic human endometrial stroma. Available information on NEP/CD10 protein expression in animal endometria is scarce. This study focused on the immunolocalization of NEP/CD10 in the canine uterus and on its temporal changes during the estrous cycle and early pregnancy (Days 11 to 23 post-LH surge) in healthy females. NEP/CD10 expression was found in the canine endometrial stroma in all stages of the estrous cycle, showing cyclic differences both in intensity and in distribution pattern. A small population of negative stromal cells in subsurface position was also observed. This population shared some morphological characteristics with the human predecidual cells, which became positive in progesterone-associated stages of the cycle. In addition, positive immunolabeling was also observed in canine myometrial stroma. In early pregnancy, the basal glandular epithelia and the syncytium cords remained negative to this marker contrasting with the trophoblast and the lacunar epithelium. A weak to moderate intensity of immunolabeling was observed in the decidual cells, whereas stromal immunolabeling was more intense at the delimitation of the syncytium cords. In conclusion, CD10 is consistently expressed in the canine endometrial stroma and myometrium but not in the endometrial epithelia. The characteristic pattern seen in early pregnancy also suggests a role for this molecule in the process of embryo invasion at implantation.

Endogenous cardiotonic steroids and differential patterns of sodium pump inhibition in NaCl-loaded salt-sensitive and normotensive rats

BACKGROUND

Endogenous sodium pump inhibitors promote sodium excretion in normotensives and contribute to vasoconstriction in NaCl-sensitive hypertension. Marinobufagenin (MBG), an endogenous bufadienolide inhibitor of alpha-1 sodium pump, contributes to hypertension in Dahl salt-sensitive rats (DS). We hypothesized that in NaCl-loaded DS and normotensive Sprague-Dawley rats (S-D), MBG would elicit different patterns of sodium pump inhibition.

METHODS

We compared systolic blood pressure (SBP), renal sodium excretion, activity of the sodium pump in aorta and renal medulla, and levels of MBG, atrial natriuretic peptide (ANP), and cyclic guanosine monophosphate (cGMP) in salt-loaded DS and S-D (20% NaCl, 2.5 ml/kg, intraperitoneally).

RESULTS

NaCl loading produced sustained elevations in renal MBG excretion in both DS (2.41 +/- 0.24 vs. 0.79 +/- 0.08 pmol/h/kg, P < 0.01) and S-D (1.97 +/- 0.37 vs. 0.60 +/- 0.07 pmol/h/kg, P < 0.01) vs. that at baseline (n = 10 for each group). In NaCl-loaded DS, SBP rose by 18 mm Hg (P < 0.01) and aortic sodium pump was inhibited by 22% (P < 0.05 vs. control), while in S-D, SBP and activity of aortic sodium pump did not change. NaCl-loaded S-D excreted twice as much sodium as DS; in S-D, renal sodium pump was inhibited by 24% vs. 14% inhibition in DS (P < 0.05). NaCl loading elicited increases in plasma ANP and in renal cGMP excretion in S-D but not in DS.

CONCLUSIONS

Our present observations demonstrate that in NaCl-loaded S-D and DS, a comparable MBG response is associated with preferential inhibition of the sodium pump in the kidney and in vascular smooth muscle, respectively, resulting in an adaptive natriuresis in S-D but sodium retention and pressor response in DS.

Vasopeptidase inhibition and Ang-(1-7) in the spontaneously hypertensive rat

BACKGROUND

Omapatrilat, a new vasopeptidase inhibitor, inhibits the activity of angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP). Because these two enzymes participate in the degradation of the vasodilator and natriuretic peptide, angiotensin-(1-7) [Ang-(1-7)], we assessed whether omapatrilat treatment is associated with changes in the plasma and urinary excretion rates of the angiotensins.

METHODS

We investigated in spontaneously hypertensive rats (SHR) (0.24 kg body weight) the effect of omapatrilat on plasma and urinary concentrations of angiotensin (Ang) I, Ang II and Ang-(1-7) during 17 days of administration of either the drug (N = 15, 100 micromol/kg/day) or vehicle (N = 14) in the drinking water. Hemodynamic and renal excretory function studies were associated with histological examination of the expression of Ang-(1-7) in the kidneys of both vehicle and omapatrilat-treated SHRs.

RESULTS

Omapatrilat induced a sustained lowering of systolic blood pressure (-68 mm Hg) without changes in cardiac rate. The mild positive water balance produced by omapatrilat did not cause natriuresis or kaliuresis, although it was associated with a significant decrease in urine osmolality. Blood pressure normalization was accompanied by increases in plasma Ang I (2969%), Ang II (57%), and Ang-(1-7) (163%) levels, paralleling pronounced increases in urinary excretion rates of Ang I and Ang-(1-7) but not Ang II. Detection of Ang-(1-7) immunostaining in the kidneys of five other SHR exposed either to vehicle (N = 3) or omapatrilat (N = 2) ascertained the source of the Ang-(1-7) found in the urine. Intense Ang-(1-7) staining, more pronounced in omapatrilat-treated SHR, was found in renal proximal tubules throughout the outer and inner regions of the renal cortex and the thick ascending loop of Henle, whereas no Ang-(1-7)-positive immunostaining was found in glomeruli and distal tubules.

CONCLUSIONS

Omapatrilat antihypertensive effects caused significant activation of the renin-angiotensin system associated with increases in urinary excretion rates of Ang I and Ang-(1-7). Combined studies of Ang-(1-7) metabolism in urine and immunohistochemical studies in the kidney revealed the existence of an intrarenal source, which may account for the pronounced increase in the excretion rate of the vasodilator heptapeptide. These findings provide further evidence for a contribution of Ang-(1-7) to the regulation of renal function and blood pressure.

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.

Endothelin-1 inactivating peptidase in the human kidney and urine

OBJECTIVE

Recently, an apparently novel, specific endothelin-1 inactivating metalloendopeptidase (ET-1 peptidase) has been isolated from the rat kidney. In this study we attempted to determine whether the same or a similar peptidase is present in the human kidney, and whether the enzyme is excreted into the urine. The urinary ET-1 peptidase could serve as an indirect index of the renal endothelin system, both in physiology and pathophysiology.

METHODS

Kidney specimens were obtained from part of nephrectomized kidneys unaffected by any neoplastic process from six adult patients. The enzyme was purified using differential centrifugation, detergent solubilization of the membrane proteins, ultrafiltration and nondenaturing gel electrophoresis. The enzyme activity assays were performed at pH 5.5 and 37 degrees C in the presence of increasing concentrations of unlabelled peptides and inhibitors using a fixed amount of [125I]ET-1 as substrate. The degradation extent was quantified with trichloroacetic acid precipitation and high performance liquid chromatography. The degrading activity of ET-1 was determined in urine samples from adult patients with hypertension, children with chronic renal failure and those with stable renal allograft

RESULTS

ET-1 peptidase from the human kidney displays characteristics close to that of the rat ET-1 peptidase we have recently described (J. Hypertens 1994; 12:1155-1162). The enzyme, a membrane-bound metalloendopeptidase, exhibits low electro- phoretical mobility on nondenaturing gel (Rf 0.08); it is an apparently heterologous structure comprising three enzymatically inactive subunits, it has a pH optimum at 5.5, a nanomolar range affinity to the ET-1 (KM 180 nmol/l) that is hydrolysed to two main degradation products, and a 10-100-fold lower affinity to big ET-1 (KM 11.5 micromol/l), endothelin 11 21 fragment (KM 15.3 micromol/l), endothelin antagonist Trp-Leu-Asp-Ile-Ile-Trp (KM 3.1 micromol/I), gastrin (KM 2.2 micromol/l) and cholecystokinin (KM 4.0 micromol/l). Substance P, neuropeptide Y, atrial natriuretic peptide, bradykinin, angiotensin II and enkephalin were poor substrates for the enzyme. The most powerful inhibitors of the ET-1 peptidase included thiorphan (IC50 0.28 nmol/l), phosphoramidon (IC50 0.55 nmol/l), phenanthroline (IC50 11.5 micromol/l), cyclosporin (IC50 400 micromol/l), phosphate (IC50 1.2 mmol/l), citrate (IC50 0.6 mmol/l) and aniline naphthalene sulphonic acid (IC50 0.25 mmol/l). Our data suggest that three ET-1 degrading peptidases with optimal activity at pH 4.5, 5.5 and 7.0, respectively, are excreted into the urine. The enzyme with a pH optimum 4.5 is of lysosomal origin whereas the two other enzymes correspond by their pH optima to the renal ET-1 peptidase and neutral endopeptidase. We have found statistically significant increases (P < 0.001) in the activity of both lysosomal and ET-1 peptidase in the urine in patients with hypertension and in children with chronic renal failure compared with healthy subjects or children with stable renal allograft

CONCLUSIONS

Human kidney contains an acidic, highly specific endothelin-1 inactivating metalloendopeptidase that may have a key role in the regulation of concentrations of renal and circulating endothelins. The enzyme is excreted into the urine where its activity seems to be increased in patients with hypertension and chronic renal failure; it may potentially serve as an indirect index of the renal endothelin system.

Urinary thiamine excretion in the rat: effects of furosemide, other diuretics, and volume load

Long-term furosemide therapy is associated with increased urinary loss of thiamine. To examine the mechanism of furosemide-induced urinary thiamine loss, we measured urinary excretion of thiamine in rats in response to increasing doses of furosemide, acetazolamide, chlorothiazide, amiloride, mannitol, and extracellular fluid (ECF) volume loading by saline infusion. All animals were in normal thiamine balance as reflected by a thiamine pyrophosphate effect (TPPE) of 2.25% +/- 0.60% (mean +/- SEM), and all had normal renal function. Urinary flow increased in response to diuretic administration in a dose-dependent manner, reaching (mean) peak urinary flow rates of 283 to 402 microL/min. Fractional excretion of sodium (FE(Na)) exhibited the same pattern, reaching peak values of 12.3% to 23.2%. Urinary thiamine excretion increased in proportion to the incremental doses of diuretic agents, reaching (mean) maximal values of 7.44 to 9.34 pmol/min, with no significant difference (P = .11) between the various diuretics tested nor in response to saline loading. None of the diuretics tested differed in the effect on thiamine excretion, which was clearly flow dependent and only partially related to fractional sodium excretion. Urinary flow rate, being the single significant predictor, explained 78% (R2 = 0.78) of the variability in thiamine excretion rates. These findings indicate that urinary thiamine loss is caused by a nonspecific, flow-dependent mechanism common to all of the diuretics tested.

Variable renal atrial natriuretic factor gene expression in hypertension

We have previously established the existence of atrial natriuretic factor (ANF) gene expression within the renal parenchyma. Neither the role nor the regulation of this extracardiac source of ANF is clearly defined. To determine whether renal ANF gene expression, similar to cardiac expression, is linked to the activity of the renin-angiotensin system (RAS), we compared renal ANF gene expression in rats after suprarenal aortic banding, a hypertension model associated with activation of RAS, and in the deoxycorticosterone acetate (DOCA)-salt model, which is characterized by depression of RAS. Renal ANF mRNA was measured with a quantitative competitive reverse transcription polymerase chain reaction method. DOCA-salt hypertension significantly reduced the expression of renal ANF. In contrast, aortic banding significantly increased renal ANF expression. In both cases, ANF gene expression in the heart increased. Ramipril treatment at 10 micrograms/kg of aortic-banded rats, a treatment that specifically affects local RAS but maintains hypertension, normalized renal ANF mRNA levels. Altogether, these results suggest that renal ANF gene expression is modulated by local RAS and is independent of circulating RAS and hypertension per se. The marked decrease of renal ANF mRNA in DOCA-salt hypertension suggests a pathogenic role for renal ANF gene downregulation by decreasing the sodium excretory mechanism mediated by the local expression of ANF acting on receptors found in the inner medullary collecting ducts. In aortic banding, renal ANF gene expression upregulation suggests a local compensatory function consistent with the consensus role of natriuretic peptides in the modulation of RAS, thus ameliorating the sodium-retaining effects of renal underperfusion.

Tissue-specific regulation of renal and cardiac atrial natriuretic factor gene expression in deoxycorticosterone acetate-salt rats

Atrial natriuretic factor (ANF) is expressed in several noncardiac tissues where it may have an autocrine or paracrine function. Such function may be expected of locally synthesized ANF in the renal parenchyma. Previous investigations of the existence of ANF mRNA in the renal parenchyma have yielded conflicting results. The investigations reported here were designed to detect and measure ANF mRNA in normal rats and in rats subjected to a deoxycorticosterone acetate (DOCA)-salt treatment schedule known to strongly activate cardiac ANF gene expression. The expression of the renal ANF gene was measured using a newly developed quantitative competitive reverse transcription-polymerase chain reaction (QC-RT-PCR). This method uses an internal competitor that serves as an internal standard and makes the procedure independent of measurement relative to housekeeping genes. It was found that renal ANF mRNA levels were 10(7) times lower than those found in left or right atria, but immunoreactive (ir) renal ANF concentration by specific radioimmunoassay was 10(4) times lower than that of atrial irANF levels. Reverse-phase high-performance liquid chromatography analysis revealed that more than 99% of renal irANF is processed ANF(99-126). This finding suggests that most of the irANF measured in kidney extracts likely originates from atrial sources. Left atrial ANF mRNA levels after 1 week of DOCA-salt treatment was significantly higher than that of control rats ([21.06+/-2.99] x 10(-l5) mol/microg total RNAversus [8.59 +/-1.26] x 10(-5) mol/microg total RNA, P<.05). However, renal ANF mRNA levels in DOCA-salt rats were significantly decreased compared with those of control rats ([1.64+/-0.34] x 10(-22) mol/microg total RNA versus [3.96+/-0.61]x 10(-22) mol/microg total RNA, P<.05). These results indicate that (1) renal ANF mRNA can be consistently and specifically demonstrated after reverse transcription and PCR amplification; (2) renal and cardiac ANF synthesis are regulated in a tissue-specific, opposite manner during DOCA-salt treatment; and (3) the finding that renal ANF mRNA is downregulated by DOCA-salt treatment together with previous findings suggest the need for further investigation into the role of renal ANF mRNA downregulation in the pathogenetic mechanism that leads to volume expansion and hypertension after chronic DOCA-salt treatment.

Proximal tubular injury in Chinese herbs nephropathy: monitoring by neutral endopeptidase enzymuria

Neutral endopeptidase (NEP) is a 94 kDa ectoenzyme of the proximal tubule brush border, physiologically released into the urine with apical membrane fragments. As proximal tubular atrophy was a histological hallmark of Chinese herbs nephropathy (CHN), this study firstly determined renal excretion of NEP in healthy control subjects (N = 31), in patients with CHN (N = 26) and in women having consumed Chinese herbs and whose renal function was normal but running the risk of developing CHN (N = 27). Another patient group consisted of female patients with glomerular diseases (N = 12). At the same time, measurements of urinary microproteins (Clara cell protein, retinol binding protein, beta 2-microglobulin and alpha 1-microglobulin) were performed, as indicators of tubular dysfunction. Cell damage was estimated by the excretion of N-acetyl-beta-D-glucosaminidase (NAG). In the control group, the physiological NEP enzymuria was 43.1 micrograms/24 hr (geometric mean). In CHN patients, levels of urinary NEP were significantly decreased in those with moderate renal failure (26.7 micrograms/24 hr; N = 21; P < 0.05) and almost abolished in end-stage renal failure patients (4.35 micrograms/24 hr; N = 5; P < 0.05). In patients at risk as well as in patients with glomerular diseases, urinary NEP levels were not statistically different from those observed in control subjects (40.68 micrograms/24 hr and 48.5 micrograms/24 hr, respectively). Several degrees of tubular dysfunction and injury were noted in patients groups, as attested by increased urinary microproteins and NAG excretions. Considering the data from control and CHN patients, NEP enzymuria positively correlated with individual creatinine clearance values (r = 0.76; P = 0.0001) and negatively correlated with urinary microproteins levels (r = -0.55; P = 0.00001). Finally, NEP was regularly quantitated in the urine of 6 CHN patients for a period ranging from six months to two years and in 19 patients at risk during two years, respectively. In the first group, renal function progressively deteriorated in 3 patients, leading them to renal replacement therapy after 38 to 115 weeks. Stable parameters were observed in the remaining 3 patients. A direct correlation between creatinine clearance and NEP excretion was found longitudinally in each case. In the second group, no significant change of urinary NEP levels was observed (45.9 micrograms/24 hr), in parallel with stable renal function. Taken together, these results indicate that, in CHN patients, NEP enzymuria provides a rapid and noninvasive determination of the degree of structural impairment affecting the proximal tubular population and further reflecting the severity of the renal disease. The interest of this urinary marker in monitoring the progression of other tubulointerstitial diseases remains to be assessed.

Angiotensin-converting enzyme and enkephalinase in human breast cyst fluid

Palpable breast cysts with an apocrine epithelial lining (type 1) are reported to be associated with a higher risk of developing breast cancer. The composition of breast cyst fluid (BCF) might include those factors involved in this increased risk. In this study peptidase activities that were active against the substrate [125I]metenkephalin-Arg-Phe were detected in BCF. The products were identified by reversed phase high-performance liquid chromatography (HPLC) as [125I]Tyr-Gly-Gly and [125I]Met-enkephalin. This proteolysis was not inhibited by PCMB, pepstatin A, leupeptin or aprotinin but was by EDTA, showing that the activity was due to metalloproteases. The production of [125I]Try-Gly-Gly was inhibited by phosphoramidon and thiorphan, whereas that of [125I]met-enkephalin was inhibited by captopril and Bothrops jararaca peptide, indicating that these activities are enkephalinase and angiotensin-converting enzyme (ACE) respectively. A fluorometric assay for ACE demonstrated that ACE levels are significantly higher in type 2 BCF than in type 1 BCF (30.8 vs 6.1 nmol hr-1 10 microliters-1, P < 0.001). As the increased risk of cancer is linked to type 1 cysts it is possible that higher levels of peptidase in type 2 BCF reflect a protective environment in the breast in which mitogenic peptide growth factors are neutralised by proteolysis.