Changes in urinary excretion of endothelin-1-like immunoreactivity before and after unilateral nephrectomy in humans. Comparison with other urinary parameters and unilateral adrenalectomy

MicroRNAs as markers to monitor endothelin-1 signalling and potential treatment in renal disease: Carcinoma - proteinuric damage - toxicity

This review highlights new developments in miRNA as diagnostic and surveillance tools in diseases damaging the renal proximal tubule mediated by endothelin in the field of renal carcinoma, proteinuric kidney disease and tubulotoxicity. A new mechanism in the miRNA regulation of proteins leads to the binding of the miRNA directly to the DNA with premature transcriptional termination and hence the formation of truncated protein isoforms (Mxi2, Vim3). These isoforms are mediated through miRNA15a or miRNA 498, respectively. ET-1 can activate a cytoplasmic complex consisting of NF-κB p65, MAPK p38α, and PKCα. Consequently, PKCα does not transmigrate into the nucleus, which leads to the loss of suppression of a primiRNA15a, maturation of this miRNA in the cytoplasm, tubular secretion and detectability in the urine. This mechanism has been shown in renal cell carcinoma and in proteinuric disease as a biomarker for the activation of the signalling pathway. Similarly, ET-1 induced miRNA 498 transmigrates into the nucleus to form the truncated protein Vim3, which is a biomarker for the benign renal cell tumour, oncocytoma. In tubulotoxicity, ET-1 induced miRNa133a down-regulating multiple-drug-resistant related protein-2, relevant for proteinuric and cisplatin/cyclosporine A toxicity. Current advantages and limitations of miRNAs as urinary biomarkers are discussed.

Urinary endothelin-1-like immunoreactivity excretion in Wilms' tumor survivors

BACKGROUND

We evaluated urinary endothelin (ET)-1-like Immunoreactivity (uET-1 L) excretion in Wilms tumor (WT) survivors and investigated its relationships with glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Glomerular hemodynamics were also assessed by Gomez formulae.

METHODS

Seventeen WT survivors underwent renal sequential scintigraphy for residual kidney function determination including ERPF and GFR. Forty-five healthy individuals were selected as the control group. uET-1 L was measured by radioimmunoassay from the 24-h urine collection.

RESULTS

In WT survivors, uET-1 L excretion was significantly higher than in controls. Significant correlations were found between uET-1 L and ERPF and GFR. Cluster analysis, applied on uET-1 L, identified two different patient groups. Between them, GFR and ERPF were significantly different. No significant difference existed between the two clusters for age and sex, elapsed time from nephrectomy, treatment, or nephrectomy side. Applying Gomez formulae, significant difference was found for afferent and total renal resistance.

CONCLUSIONS

According to our results, uET-1 L seems to be a marker of glomerular injury in patients with renal mass loss revealing renal overload condition. The uET-1 L role in renal damage progression and hemodynamic glomerular worsening in nephrectomized patients should be proven by prospective long-term follow-up studies, even for potential ET-1 receptor antagonist therapeutic use.

Urinary endothelin-1 excretion according to morpho-functional damage lateralization in reflux nephropathy

BACKGROUND

Reflux nephropathy (RN) is a pathophysiological human model of reduced nephron reserve, due to loss of renal mass, but little information exists about the role of urinary endothelin-1 (uET-1) in this disease. The aim of this study was to assess the presence of uET-1-like-immunoreactivity (uET-1L) in RN patients, particularly if lateralized renal damage existed.

METHODS

Thirty patients with vescico-ureteral reflux (VUR) and consequent RN, were studied. The presence of VUR was established by voiding cysto-urethrography. RN was assessed and graded by 99mTc-dimercapto-succinic acid scan (DMSA). Renal plasma flow (ERPF) was evaluated by (123)I-Hippuran renal sequential scintigraphy, and glomerular filtration rate (GFR) by creatinine clearance. Forty-five healthy subjects were selected as a control group. uET-1L excretion, in both affected and control groups, was assayed.

RESULTS

Mann-Whitney U test showed a significant difference between control and patient groups in both GFR and uET-1L. A good correlation between DMSA grading, single kidney clearance and VUR grade was shown. A significant relationship was also shown between uET-1L and both ERPF and GFR. Patients with RN were divided into two subgroups according to functional damage lateralization. Between the two groups, a significant difference was found only for uET-1L when GFR was applied as a covariate in ANCOVA analysis.

CONCLUSION

Our preliminary results confirmed the increase of urinary ET-1L excretion in RN, especially when renal functional injury was lateralized.

Research on renal endothelin in proteinuric nephropathies dictates novel strategies to prevent progression

Proteinuria is one of the major risk factors for renal disease progression in patients with chronic nephropathies. Studies in disease models have helped to delineate mechanisms leading to renal structural damage as a result of persistent dysfunction of the glomerular barrier to proteins, even when the primary immune or non-immune insult to the kidney has ceased. From these preclinical studies, a role for endothelin in proteinuric chronic renal diseases has been suggested, thus providing the rationale for novel therapeutic approaches with endothelin receptor antagonists to maximize renoprotection so far achieved with blockade of the renin-angiotensin system by angiotensin-converting enzyme inhibition or angiotensin II receptor antagonism. Trials are needed to explore this potential area of clinical interest.

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.

Understanding the nature of renal disease progression

Animal and human proteinuric glomerulopathies evolve to terminal renal failure by a process leading to progressive parenchymal damage, which appears to be relatively independent of the initial insult. Despite the fact that the mechanism(s) leading to renal disease progression has been only partially clarified, several studies have found that the amount of urinary proteins (taken to reflect the degree of protein trafficking through the glomerular capillary) correlated with the tendency of a given disease to progress more than the underlying renal pathology. On the other hand, dietary protein restriction and ACE inhibitors were capable of limiting the progressive decline in GFR to the extent that they could effectively lower the urinary protein excretion rate. A constant feature of proteinuric nephritis is also the concomitant presence of tubulointerstitial inflammation. So far it was not clear if this is a reaction to the ischemic obliteration of peritubular capillaries that follows glomerular obsolescence or whether albumin and other proteins that accumulated in the urinary space are indeed instrumental for the formation of the interstitial inflammatory reaction. In recent years several studies have convincingly documented that excessive and sustained protein trafficking could have an intrinsic renal toxicity. Here we have reviewed the abundant evidence in the literature that the process of reabsorption of filtered proteins activates the proximal tubular epithelium. Biochemical events associated with tubular cell activation in response to protein stress include up-regulation of inflammatory and vasoactive genes such as MCP-1 and endothelins. The corresponding molecules formed in an excessive amount by renal tubuli are secreted toward the basolateral compartment of the cell and give rise to an inflammatory reaction that in most forms of glomerulonephritis consistently precede renal scarring.

Endothelins in the normal and diseased kidney

Endothelin-1 (ET-1) is a 21-amino acid peptide that potently modulates renal function. ET-1 is produced by, and binds to, most renal cell types. ET-1 exerts a wide range of biologic effects in the kidney, including constriction of most renal vessels, mesangial cell contraction, inhibition of sodium and water reabsorption by the nephron, enhancement of glomerular cell proliferation, and stimulation of extracellular matrix accumulation. ET-1 functions primarily as an autocrine or paracrine factor; its renal effects must be viewed in the context of its local production and actions. This is particularly important when comparing ET-1 biology in the nephron, where it promotes relative hypotension through increased salt and water excretion, with ET-1 effects in the vasculature, where it promotes relative hypertension through vasoconstriction. Numerous studies indicate that ET-1 is involved in the pathogenesis of a broad spectrum of renal diseases. These include those characterized by excessive renal vascular resistance, such as ischemic renal failure, cyclosporine (CyA) nephrotoxicity, radiocontrast nephropathy, endotoxemia, rhabdomyolysis, acute liver rejection, and others. ET-1 appears to play a role in cell proliferation in the setting of inflammatory glomerulonephritides. The peptide also may mediate, at least in part, excessive extracellular matrix accumulation and fibrosis occurring in chronic renal failure, diabetes mellitus, and other disorders. Deranged ET-1 production in the nephron may cause inappropriate sodium and water retention, thereby contributing to the development and/or maintenance of hypertension. Finally, impaired renal clearance of ET-1 may cause hypertension in patients with end-stage renal disease. Many ET-1 antagonists have been developed; however, their clinical usefulness has not yet been determined. Despite this, these agents hold great promise for the treatment of renal diseases; it is hoped that the next decade will witness their introduction into clinical practice.

Measurement and clinical significance of endothelin in neonatal urine

The present study was undertaken to figure out the source of urinary endothelin (ET) and the clinical significance of its possible variations. Urinary ET levels were measured by radioimmunoassay (RIA) in 17 healthy newborns and 20 asphyxiated neonates on days 1, 3, 7 after birth. Plasma ET concentrations of healthy premature infants on day 7 and urinary ET levels in 10 healthy children were also observed at the same time. Results showed that: (1) Urinary ET levels and ET excretion rates were higher than plasma ET in preterm infants on days 7 after birth; (2) Both in preterm and full term infants, urinary ET concentrations fell from the 1st day to the 7th day after birth, ET excretion rates elevated markedly at the end of the 1st week, and they were significantly higher than that of children; (3) Urinary ET levels of asphyxiated group on days 1 and 3 were much higher than those of healthy neonates, and positively correlated with the severity of the illness and urinary NAG. We conclude that: (1) urinary ET mainly comes from the production in renal cells; (2) ET levels in healthy neonatal urine reflect the maturity of kidney; (3) measurement of urinary ET levels in asphyxiated neonates is helpful to judge the degree and to evaluate the prognosis of renal injury.

Urinary endothelin-1 excretion is enhanced by low-dose infusion of brain natriuretic peptide in normal humans

To evaluate the functional relationship between cardiac natriuretic peptides and endothelin-1 within the human kidney, we studied the effects exerted by infusion of brain natriuretic peptide on urinary endothelin-1 excretion. We studied twice in a single-blind manner five normal volunteers who received a constant infusion of 5% dextrose (250 mL/h) or human brain natriuretic peptide-32 at a dose of 4 pmol/kg per minute. Blood samples were drawn at intervals for measurement of hematocrit and concentrations of creatinine, electrolytes, brain natriuretic peptide, and endothelin-1. Urine was collected an intervals for measurement of flow rate and concentrations of creatinine, sodium, cGMP, and endothelin-1. Blood pressure and heart rate were measured every 15 minutes. Placebo administration did not change blood pressure, heart rate, or any of the other parameters measured in plasma and urine. As expected, brain natriuretic peptide infusion caused significant increases in its own plasma levels (basal versus peak levels [mean +/- SD], 1.45 +/- 0.20 versus 50.5 +/- 6.0 pmol/L, P < .01), in urinary cGMP (0.75 +/- 0.16 versus 1.92 +/- 0.81 fmol/min, P < .05), and in urinary sodium excretion (140.0 +/- 38.7 versus 624.2 +/- 181.6 mumol/min, P < .01). In addition, it caused an increase in urinary endothelin-1 excretion (4.32 +/- 2.11 versus 19.67 +/- 9.52 fmol/min, P < .05), without modifying plasma endothelin-1, blood pressure, heart rate, creatinine clearance, and urinary flow rate. Our data indicate that brain natriuretic peptide, at plasma levels comparable to those observed in patients with heart failure, causes a significant increase in urinary but not plasma endothelin-1, thus demonstrating a functional link between cardiac natriuretic peptides and renal release of endothelin-1.

Endothelin is a key modulator of progressive renal injury: experimental data and novel therapeutic strategies

1. Glomerulosclerosis and tubulointerstitial damage are common histological abnormalities of many renal diseases that progress to end-stage renal failure. 2. In some models of renal damage, glomerulosclerosis seems to be associated with increased glomerular capillary pressure. 3. Due to the positive correlation of glomerulosclerosis and proteinuria in both experimental models and in humans, abnormal permeability to macromolecules has also been considered a possible determinant of glomerulosclerosis. 4. Abnormally filtered macromolecules have an intrinsic toxicity to the kidney due to protein over-reabsorption, possibly leading to tubulointerstitial damage. 5. Endothelin-1 (ET-1) is a vasoconstrictor peptide that induces mitogenesis and the accumulation of matrix proteins by mesangial cells. 6. Evidence is available that ET-1 plays a role in progressive renal disease in different experimental models, including renal mass reduction, lupus nephritis, streptozotocin-induced diabetes and puromycin-induced nephrosis.

Proximal tubular cell synthesis and secretion of endothelin-1 on challenge with albumin and other proteins

Abnormal traffic of proteins through the glomerular capillary has an intrinsic renal toxicity possibly linked to the subsequent process of over-reabsorption by proximal tubular cells. We investigated in vitro the effect of different protein concentrations on proximal tubular cell endothelin-1 (ET-1) synthesis. Rabbit proximal tubular RC.SV1 cell line was grown to confluence in serum-free hormonally defined medium. Cells were incubated for 6 and 24 hours with serum-free medium containing bovine serum albumin (BSA, 0.1 to 10 mg/mL). ET-1, a locally released hormone that stimulates cell proliferation and promotes extracellular matrix protein synthesis, was measured in cell supernatant by radioimmunoassay. BSA induced a significant dose-dependent increase in proximal tubular cell ET-1 synthesis. BSA and fatty acid-free BSA stimulated tubular ET-1 synthesis and release to a comparable extent, indicating that the lipid component of the molecule is not involved in the observed phenomenon. Experiments in which tubular cells grown on filters in bicameral systems were incubated with BSA (10 mg/mL) showed that ET-1 release was predominantly basolateral. The stimulatory effect on tubular ET-1 synthesis and release was not specific to albumin but was shared by immunoglobulin (Ig) G and transferrin. Exposure of proximal tubular cells for 6 and 24 hours to both proteins (1 and 10 mg/mL) resulted in a dose-dependent increase in ET-1 synthesis. These data suggest that overexposure of proximal tubular cells to proteins, as it occurs in vivo in proteinuric renal diseases, may promote excessive tubular synthesis of ET-1, which is mostly secreted toward the interstitial compartment.(ABSTRACT TRUNCATED AT 250 WORDS)