Urinary Endothelin-1 Research Articles

Urinary endothelin-1 in chronic kidney disease and as a marker of disease activity in lupus nephritis

Chronic inflammation contributes to the development and progression of chronic kidney disease (CKD). Identifying renal inflammation early is important. There are currently no specific markers of renal inflammation. Endothelin-1 (ET-1) is implicated in the pathogenesis of CKD. Thus, we investigated the impact of progressive renal dysfunction and renal inflammation on plasma and urinary ET-1 concentrations. In a prospective study, plasma and urinary ET-1 were measured in 132 subjects with CKD stages 1 to 5, and fractional excretion of ET-1 (FeET-1) was calculated. FeET-1, serum C-reactive protein (CRP), urinary ET-1:creatinine ratio, and urinary albumin:creatinine ratio were also measured in 29 healthy volunteers, 85 subjects with different degrees of inflammatory renal disease but normal renal function, and in 10 subjects with rheumatoid arthritis without renal involvement (RA). In subjects with nephritis associated with systemic lupus erythematosus (SLE), measurements were done before and after 6 mo of treatment. In subjects with CKD, plasma ET-1 increased linearly as renal function declined, whereas FeET-1 rose exponentially. In subjects with normal renal function, FeET-1 and urinary ET-1:creatinine ratio were higher in SLE subjects than in other groups (7.7 +/- 2.7%, 10.0 +/- 3.0 pg/mumol, both P < 0.001), and correlated with CRP, and significantly higher than in RA subjects (both P < 0.01) with similar CRP concentrations. In SLE patients, following treatment, FeET-1 fell to 3.6 +/- 1.4% (P < 0.01). Renal ET-1 production increases as renal function declines. In subjects with SLE, urinary ET-1 may be a useful measure of renal inflammatory disease activity while measured renal function is still normal.

Effect of nicorandil on proteinuria in well controlled hypertensive patients

Proteinuria is an important risk factor for cardiovascular and renal morbidity and mortality. The effect of nicorandil on proteinuria in hypertensive patients well controlled by antihypertensive agents containing a low dose of valsartan has not been studied. A total of 136 proteinuric (300-3000 mg/day), valsartan-treated hypertensive patients with blood pressure less than 140/90 mmHg were randomized into three groups to receive placebo, isosorbide dinitrate (30 mg/day), or nicorandil (15 mg/day) for 6 months. The average dose of valsartan given to the patients was similar in the three groups. Creatinine clearance remained stable throughout the study in the three groups. Nicorandil, but not isosorbide dinitrate, significantly reduced proteinuria by 44% after 6 months (P < 0.0001). Urinary endothelin-1 levels significantly decreased after administration of nicorandil (P = 0.002), whereas placebo and isosorbide dinitrate had no effect. Urinary excretion of endothelin-1 was significantly correlated with improvement in urinary protein excretion in nicorandil-treated patients (r = 0.69, P < 0.0001). The urinary excretion of retinol-binding protein decreased after nicorandil administration, probably reflecting an improvement in tubular function. In contrast, the urinary excretion of immunoglobulin G did not change significantly throughout the study in the three groups. Multivariate analysis revealed that proteinuria was only significantly correlated with the use of nicorandil (model adjusted r = 0.35, P < 0.0001). The addition of nicorandil to treatment for patients with well controlled hypertension may have an additive effect on reducing proteinuria independent of hemodynamics and nitric oxide effects, possibly through inhibiting renal endothelin-1 synthesis and improving tubular function.

Rosiglitazone decreases blood pressure and renal injury in a female mouse model of systemic lupus erythematosus

Women with systemic lupus erythematosus (SLE) exhibit a high prevalence of hypertension and renal injury. Rosiglitazone (Rosi), a peroxisome proliferator activator receptor gamma (PPARgamma) agonist, has renal protective and antihypertensive effects. We tested whether Rosi ameliorates hypertension and renal injury in a female mouse model of SLE (NZBWF1). Thirty-week-old SLE and control (NZW/LacJ) mice (n > or = 6/group) were fed Rosi (5 mg.kg(-1).day(-1) in standard chow) or standard chow for 4 wk. SLE mice had increased blood pressure (BP in mmHg) compared with controls (139 +/- 4 vs. 111 +/- 4, P < 0.05). Rosi treatment lowered BP in SLE mice (127 +/- 4, P < 0.05) but not in controls (111 +/- 4). Urinary albumin (mug/mg creatinine) was increased in SLE mice compared with controls (12,396 +/- 6,525 vs. 50 +/- 6) and reduced with Rosi treatment (148 +/- 117). Glomerulosclerosis (% of glomeruli with sclerosis) was reduced in Rosi-treated SLE mice (4.2 +/- 1.6 vs. 0.4 +/- 0.3, P < 0.05). Renal monocyte/macrophage numbers (cell number/1,320 points counted) were reduced in SLE mice treated with Rosi (32.6 +/- 11.0 vs. 10.6 +/- 3.6, P < 0.05) but unchanged in controls (3.7 +/- 1.6 vs. 3.7 +/- 2.0). Renal osteopontin expression, a cytokine-regulating macrophage recruitment, was reduced in Rosi-treated SLE mice. Urinary endothelin (in pg/mg creatinine) was increased in SLE mice compared with controls (1.9 +/- 0.59 vs. 0.6 +/- 0.04, P < 0.05) and reduced in SLE mice treated with Rosi (0.8 +/- 0.11, P < 0.05). PPARgamma protein expression in the renal cortex was significantly lower in SLE mice compared with controls and was unaffected by Rosi. These data suggest that Rosi may be an important therapeutic option for the treatment of SLE hypertension and renal injury.

Urinary Excretion of Endothelin Receptors ETA and ETB in Hypertensive Patients and Normotensive Subjects

Background/Aims: Endothelin (ET)-1 is produced by most renal cell types. Renal tubular and vascular cells express both the ET receptors ET_A and ET_B. Since significant amounts of ET-1 of renal origin were detected in human urine, urinary ET-1 has been used as an index for the capacity of renal ET-1 production. Here, we determine the existence of additional components of the intrarenal ET system, namely the ET_A and ET_B receptor subtypes, in the urine of normal and hypertensive subjects. Methods: ET_A and ET_B receptors were detected in urine samples that were concentrated by TCA precipitation, Speedvac or ProteoSpin™. Results: Analysis of the human urine extracts revealed the existence of approximately 50 and 55 kDa of immunoreactive proteins, corresponding to ET_B and ET_A, respectively, indicating that intact ET_A and ET_B are excreted in the urine of healthy subjects and hypertensive patients. Normotensive and hypertensive subjects had statistically comparable ET_B excretion normalized to creatinine (0.58 ± 0.16 vs. 0.83 ± 0.17 μg/mg creatinine, respectively; p = 0.304). In contrast, ET_A excretion was higher among hypertensive subjects (0.05 ± 0.01 vs. 0.11 ± 0.02 μg/mg creatinine; p = 0.0451). Immunostaining of ET_A and ET_B in the human urinary system revealed expression of both receptors, principally in tubular cells (mainly in medullary collecting ducts) and in the bladder urothelium, and ET_A expression in the peritubular capillaries and arterioles. Urinary ET receptors closely and inversely correlated with indices of urine concentration, suggesting that their shedding is principally affected by urine flow. Conclusion: ET receptors are present in human urine, conceivably originating within the urinary system. Their excretion is principally affected by urinary concentration. It remains to be determined whether urinary ET_A/ET_B is of physiological/pathophysiological relevance.

Pure dietary flavonoids quercetin and (−)-epicatechin augment nitric oxide products and reduce endothelin-1 acutely in healthy men

Background: Dietary flavonoids may improve endothelial function and ultimately lead to beneficial cardiovascular effects.Objective: The objective was to assess whether pure dietary flavonoids can modulate nitric oxide and endothelin-1 production and thereby improve endothelial function.Design: A randomized, placebo-controlled, crossover trial in 12 healthy men was conducted to compare the acute effects of the oral administration of 200 mg quercetin, (−)-epicatechin, or epigallocatechin gallate on nitric oxide, endothelin-1, and oxidative stress after nitric oxide production was assessed via the measurement of plasma S-nitrosothiols and plasma and urinary nitrite and nitrate concentrations. The effects on oxidative stress were assessed by measuring plasma and urinary F2-isoprostanes. Plasma and urinary concentrations of quercetin, (−)-epicatechin, and epigallocatechin gallate were measured to establish the absorption of these flavonoids.Results: Relative to water (control), quercetin and (−)-epicatechin resulted in a significant increase in plasma S-nitrosothiols, plasma nitrite, and urinary nitrate concentrations (P < 0.05), but not in plasma nitrate or urinary nitrite. Epigallocatechin gallate did not alter any of the measures of nitric oxide production. Quercetin and (−)-epicatechin resulted in a significant reduction in plasma endothelin-1 concentration (P < 0.05), but only quercetin significantly decreased the urinary endothelin-1 concentration. None of the 3 treatments significantly changed plasma or urinary F2-isoprostane concentrations. Significant increases in the circulating concentrations of the 3 flavonoids were observed (P < 0.05) after the corresponding treatment.Conclusions: Dietary flavonoids, such as quercetin and (−)-epicatechin, can augment nitric oxide status and reduce endothelin-1 concentrations and may thereby improve endothelial function.

Endothelin 1 levels in relation to clinical presentation and outcome of Henoch Schonlein purpura

BackgroundHenoch Schonlein purpura (HSP) is a common vasculitis of small vessels whereas endothelin-1 (ET-1) is usually reported elevated in vasculities and systematic inflammation. The aim of the present study was to investigate whether ET-1 levels are correlated with the clinical presentation and the outcome of HSP.MethodsThe study sample consisted of thirty consecutive patients with HSP. An equal number of healthy patients of similar age and the same gender were served as controls. The patients' age range was 2–12.6 years with a mean ± SD = 6.3 ± 3 years. All patients had a physical examination with a renal, and an overall clinical score. Blood and urinary biochemistry, immunology investigation, a skin biopsy and ET-1 measurements in blood and urine samples were made at presentation, 1 month later and 1 year after the appearance of HSP. The controls underwent the same investigation with the exception of skin biopsy.ResultsET-1 levels in plasma and urine did not differ between patients and controls at three distinct time points. Furthermore the ET-1 were not correlated with the clinical score and renal involvement was independent from the ET-1 measurements. However, the urinary ET-1 levels were a significant predictor of the duration of the acute phase of HSP (HR = 0.98, p = 0.032, CI0.96–0.99). The ET-1 levels did not correlate with the duration of renal involvement.ConclusionUrinary ET-1 levels are a useful marker for the duration of the acute phase of HSP but not for the length of renal involvement.

Interleukin-1β, but not interleukin-6, enhances renal and systemic endothelin production in vivo

The inflammatory cytokines IL-1beta and IL-6 have been shown to stimulate production of endothelin-1 (ET-1) by several cell types in vitro, but their effects on renal ET-1 production in vivo are not known. To test whether IL-1beta and IL-6 stimulate renal ET-1 production and release in vivo, urine was collected from male C57BL/6 mice over 24-h periods at baseline and on days 7 and 14 of a 14-day subcutaneous infusion of IL-1beta (10 ng/h), IL-6 (16 ng/h), or vehicle. By day 14, plasma ET-1 was significantly increased by IL-1beta infusion (1.7 +/- 0.1 vs. 0.8 +/- 0.1 pg/ml for vehicle, P < 0.001). Compared with vehicle infusion, IL-1beta infusion induced significant increases in urinary ET-1 excretion rate and urine flow but did not affect conscious mean arterial pressure (telemetry). IL-1beta infusion significantly increased renal cortical and medullary IL-1beta content (ELISA) and prepro-ET-1 mRNA expression (quantitative real-time PCR). In contrast, 14 days of IL-6 infusion had no significant effect on plasma ET-1 or urinary ET-1 excretion rate. To determine whether IL-1beta stimulates ET-1 release via activation of NF-kappaB, inner medullary collecting duct (IMCD-3) cells were incubated for 24 h with IL-1beta, and ET-1 release and NF-kappaB activation were measured (ELISA). IL-1beta activated NF-kappaB and increased ET-1 release in a concentration-dependent manner. The effect of IL-1beta on ET-1 release could be partially inhibited by pretreatment of IMCD-3 cells with an inhibitor of NF-kappaB activation (BAY 11-7082). These results indicate that IL-1beta stimulates renal and systemic ET-1 production in vivo, providing further evidence that ET-1 participates in inflammatory responses.

Pharmacological Closure of Patent Ductus Arteriosus: Effects on Pulse Pressure and on Endothelin-1 and Vasopressin Excretion

Widened pulse pressure is a classic sign of significant left-to-right shunting patent ductus arteriosus (PDA), but little evidence supports this statement in the early life of premature infants with respiratory distress syndrome (RDS) needing nonsteroidal anti-inflammatory drugs (NSAIDs), the pharmacological treatment for PDA. Pulse pressure and urinary endothelin-1 (ET-1) and arginine vasopressin (AVP) vasoactive factors involved in the transitional circulation were measured before and after the NSAIDs treatment of 46 RDS premature infants receiving either ibuprofen (n = 22) or indomethacin (n = 24), with 28 responders and 18 nonresponders to the first NSAIDs course. We found that following pharmacological PDA closure, systolic and diastolic blood pressure significantly increased, maintaining a stable pulse pressure. However, when pharmacological closure failed, the trend (nonsignificant) was for a more consistent increase in systolic than in diastolic blood pressure, which determined a statistically significant widening pulse pressure. In addition, urinary ET-1 excretion rates decreased significantly after PDA closure, whereas persistent more aggressive pharmacological therapy failed. Urinary AVP excretion rates decreased insignificantly after therapy, uninfluenced by the efficacy of the drugs. We concluded that widened pulse pressure is a clinical sign of failed PDA pharmacological closure in RDS premature infants. ET-1 levels remain elevated when NSAIDs fail to interrupt left-to-right PDA shunting that complicates recovery from RDS.

Endothelin-1 levels and albuminuria in patients with type 2 diabetes mellitus

Aim To evaluate the relationship of plasma endothelin-1 (ET-1) levels, a marker of endothelial dysfunction, and urinary albumin excretion in patients with type 2 diabetes mellitus (DM). Methods Cross-sectional study was conducted in 279 patients (132 males, mean age: 58.7 ± 11.0 years, mean DM duration: 11.3 ± 8.1 years). Urinary albumin excretion, ET-1, and insulin were measured. Insulin sensitivity was estimated by homeostasis model assessment (HOMA-ir) index. Results ET-1 was associated with urinary albumin excretion after controlling for age, gender, body mass index, blood pressure, HbA1c test, and total cholesterol ( R = 0.436; adjusted R 2 = 0.190, P < 0.01). Furthermore, there was a progressive increase in plasma ET-1 levels from patients with normoalbuminuria ( n = 187, 0.92 ± 0.50 pg/ml), microalbuminuria ( n = 68, 1.13 ± 0.52 pg/ml) to macroalbuminuria ( n = 24, 1.93 ± 1.10 pg/ml, P < 0.01). Conclusion There is an independent association of plasma ET-1 levels with urinary albumin excretion. In addition, plasma ET-1 levels started to increase in the normal values of urinary albumin excretion suggesting that in patients with type 2 DM endothelial dysfunction is already present, in urinary albumin excretion values considered normal.

Urinary endothelin-1-like immunoreactivity excretion in the newborn period.

Urinary endothelin-1-like immunoreactivity (ET-1-LI) excretion was determined in 31 neonates, six sick infants with renal dysfunction secondary to neonatal asphyxia and 25 healthy infants, during the first week of life to clarify its evolutional change and the origin of the urinary ET-1-LI in the newborn period. Urinary ET-1-LI concentrations in the healthy infants maintained the same level during the first week of life (n = 35, 36 +/- 22 pg/mg creatinine, mean +/- SD). There was no difference in urinary ET-1-LI excretion in infants between 30 and 41 weeks of gestation. Urinary ET-1-LI concentrations in the sick infants were significantly elevated through the first week of life when compared with those of healthy infants. Fractional excretion of sodium and endothelin clearance were more elevated in the sick infants than in the healthy infants. A good correlation was observed between urinary ET-1-LI concentrations and urinary N-acetyl-beta-D-glucosaminidase index (r = 0.72, p < 0.01). These results suggest that the origin of urinary endothelin-1 may be the renal tissue and that ET-1 may be a nonspecific marker of renal injury in neonates.

Fractional urinary excretion of endothelin-1 is reduced by acute ETB receptor blockade

Evidence suggests that urinary excretion of endothelin-1 (ET-1) reflects renal ET-1 production and is independent of systemic ET-1 activity. The influence of ET receptors on urinary ET-1 excretion has not been studied in humans, yet peritubular ETB receptors are abundant within the kidney. We have studied the effects of acute ETA and ETB receptor blockade with BQ-123 and BQ-788, respectively, on urinary ET-1 excretion in a randomized, placebo-controlled, double-blind study in 16 subjects with a wide range of GFRs (15-152 ml/min). Plasma ET-1 concentrations (pET-1) and urinary ET-1 excretion rate (uET-1) at baseline correlated inversely with GFR (R2 = 0.18 and 0.36, respectively, P < 0.01). However, changes in pET-1 after ET receptor antagonism were not related to changes in uET-1 (R2 = 0.007, P = 0.18). pET-1 increased only after BQ-788, alone or in combination with BQ-123, consistent with ETB receptor-mediated clearance of ET-1 from the circulation. uET-1 was reduced only after BQ-788 alone [-4.7 pg/min (SD 5.5), P < 0.01]. Because BQ-788 also reduced GFR, fractional excretion of ET-1 (FeET-1) was calculated. FeET-1 fell after BQ-788 alone [-41% (SD 26%), P < 0.01] or in combination with BQ-123 [-40% (SD 29%), P < 0.01]. FeET-1 was not altered by placebo or BQ-123 alone. In conclusion, urinary ET-1 excretion does not appear to relate to the pool of plasma ET-1. Because of the short duration of this study, it is unlikely that ET receptor blockade had significant effects on renal ET-1 production. Therefore, the reduction in FeET-1 after ETB blockade appears to indicate that renal excretion of ET-1 is at least partly facilitated by ETB receptor activation.

Diagnosis of Ureteropelvic Junction Obstruction in Children: Role of Endothelin-1 in Voided Urine

To examine the role of voided urine endothelin-1 (ET-1) in the diagnosis and follow-up of children with ureteropelvic junction obstruction. The study included 35 children with unilateral ureteropelvic junction obstruction who underwent pyeloplasty and 30 control children, including 10 healthy children, 10 with vesicoureteral reflux, and 10 with renal stones. Voided urine samples were obtained from the children in the study group before surgery and from the renal pelvis by needle aspiration during pyeloplasty. Bladder urine samples were also collected from the study group 1, 2, 3, 6, 9, and 12 months postoperatively. Bladder urine samples were also collected from all 30 control children. ET-1 was measured in the urine samples collected from the study and control groups. The preoperative ET-1 level in the voided urine of the study group was significantly greater than its level in each of the three control groups. For the whole study group, a cutoff value of 3 fmol/mg creatinine gave a sensitivity of 74.3%, a specificity of 90%, and an overall accuracy of 81.5%. In 8 children (1 year old or younger), a cutoff value of 4 fmol/mg creatinine gave a sensitivity and specificity of 100%. Compared with the preoperative value, ET-1 had decreased significantly at 12 months after pyeloplasty. The ET-1 level in voided urine is a useful marker that could be used as a noninvasive tool for the diagnosis and long-term follow-up of children with ureteropelvic junction obstruction.

Dietary protein induces endothelin-mediated kidney injury through enhanced intrinsic acid production

Dietary protein as casein (CAS) augments intrinsic acid production, induces endothelin-mediated kidney acidification, and promotes kidney injury. We tested the hypothesis that dietary CAS induces endothelin-mediated kidney injury through augmented intrinsic acid production. Munich-Wistar rats ate minimum electrolyte diets from age 8 to 96 weeks with 50 or 20% protein as either acid-inducing CAS or non-acid-inducing SOY. Urine net acid excretion and distal nephron net HCO3 reabsorption by in vivo microperfusion (Net J(HCO3)) were higher in 50 than 20% CAS but not 50 and 20% SOY. At 96 weeks, 50% compared the 20% CAS had higher urine endothelin-1 excretion (U(ET-1)V) and a higher index of tubulo-interstitial injury (TII) at pathology (2.25+/-0.21 vs 1.25+/-0.13 U, P<0.03), but each parameter was similar in 50 and 20% SOY. CAS (50%) eating NaHCO3 to reduce intrinsic acid production had lower Net J(HCO3), lower U(ET-1)V, and less TII. By contrast, 50% SOY eating dietary acid as (NH4)2SO4 had higher Net J(HCO3), higher U(ET-1)V, and more TII. Endothelin A/B but not A receptor antagonism reduced Net J(HCO3) in 50% CAS and 50% SOY+(NH4)2SO4 animals. By contrast, endothelin A but not A/B receptor antagonism reduced TII in each group. The data support that increased intake of acid-inducing dietary protein induces endothelin B-receptor-mediated increased Net J(HCO3) and endothelin A-receptor-mediated TII through augmented intrinsic acid production.

DIETARY PROTEIN INDUCES REMNANT KIDNEY INJURY BY INCREASED INTRINSIC ACID PRODUCTION MEDIATED THROUGH ENDOTHELIN RECEPTORS.

Purpose We tested the hypothesis that acid-producing dietary protein induces endothelin-mediated parenchymal injury in the 5/6 nephrectomized rat by increasing intrinsic acid production. Methods Munich-Wistar rats underwent surgical 5/6 nephrectomy (Nx) and were studied 12 weeks after eating diets with either acid-producing protein (casein) or non-acid-producing protein (soy). Intrinsic acid production in the casein group was reduced by added Ca ++ citrate with Ca ++ phosphate as a control. Intrinsic acid production in the soy group was increased by added (NH 4 ) 2 SO 4 with Na 2 SO 4 as a control. Both casein-eating Nx and soy + (NH 4 ) 2 SO 4 -eating Nx received either the oral endothelin A/B receptor antagonist bosentan or the oral endothelin A antagonist darunsentan. Distal nephron Net HCO 3 reabsorption (Net J HCO3 ) was measured at 4 weeks by in vivo microperfusion. Urine endothelin 1 excretion (U ET-1 V), urine albumin excretion (U alb V), kidney glomerulosclerosis (GS), and tubulointerstitial injury (TII) were measured at 12 weeks. Results (1) Casein-eating Nx versus soy-eating Nx had higher U ET-1 V (315 ± 52 vs 78 ± 13 fmol/d, p alb V (180 ± 22 vs 74 ± 10 mg/d, p p p ++ citrate versus Ca ++ phosphate had lower U ET-1 V (89 ± 22 vs 341 ± 56 fmol/d, p alb V (105 ± 11 vs 177 ± 20 mg/d, p p p 4 ) 2 SO 4 versus Na 2 SO 4 had higher U ET-1 V (350 ± 40 vs 211 ± 26 fmol/d, p alb V (145 ± 16 vs 86 ± 10 mg/d, p p p HCO3 in acid-ingesting groups. By contrast, the endothelin A but not endothelin A/B antagonist reduced U alb V and TII in acid-ingesting groups. Conclusions Acid-producing dietary protein induces endothelin B-mediated increased acidification and endothelin A-mediated TII in the 5/6 nephrectomized rat through increased intrinsic acid production.

Antihypertensive and Renal Protective Effects of Renin-Angiotensin System Blockade in Uremic Rats Treated With Erythropoietin

Correcting anemia with recombinant human erythropoietin (rhEPO) in chronic renal failure has been associated with an increased blood pressure (BP), which may accelerate the decline in renal function. This has been attributed, in part, to the activation of the renin-angiotensin system. The present study was designed to investigate the protective effect of the angiotensin II-receptor blocker losartan compared with the angiotensin-converting enzyme inhibitor captopril and conventional triple therapy (TRx) in uremic rats receiving rhEPO therapy. Renal failure was induced by renal mass ablation followed by a 3-week stabilization period. Uremic rats were then divided into five groups with similar systolic BP: vehicle; rhEPO (100 U/kg, subcutaneously, three times per week); rhEPO + losartan (20 mg/kg/d); rhEPO + captopril (20 mg/kg/d); and rhEPO + TRx (reserpine 5 mg/L, hydralazine 80 mg/L, hydrochlorothiazide 20 mg/L). Systolic BP as well as blood and renal parameters were assessed before and after a 3-week treatment period. Renal histology was evaluated at the end of the study. The uremic rats developed hypertension, anemia, proteinuria, and increased urinary endothelin-1 (ET-1) excretion. The rhEPO corrected the anemia but aggravated the hypertension (P < .01), glomerular sclerosis, tubular atrophy, and interstitial fibrosis. Treatment with losartan, captopril, and the TRx prevented the rhEPO-induced increased in systolic BP. The TRx was less effective in preventing histologic injuries despite similar systolic BP reduction. Blockade of the renin-angiotensin system is highly effective in preventing both hypertension and renal histologic damage in rhEPO-treated uremic rats and this benefit seems to extend beyond the antihypertensive effect.

Collecting duct-specific knockout of the endothelin B receptor causes hypertension and sodium retention

Collecting duct (CD)-derived endothelin-1 (ET-1) inhibits renal Na reabsorption and its deficiency increases blood pressure (BP). The role of CD endothelin B (ETB) receptors in mediating these effects is unknown. CD-specific knockout of the ETB receptor was achieved using an aquaporin-2 promoter-Cre recombinase transgene and the loxP-flanked ETB receptor gene (CD ETB KO). Systolic BP in mice with CD-specific knockout of the ETB receptor, ETA receptor (CD ETA KO) and ET-1 (CD ET-1 KO), and their respective controls were compared during normal- and high-salt diet. On a normal-sodium diet, CD ETB KO mice had elevated BP, which increased further during high salt feeding. However, the degree of hypertension in CD ETB KO mice and the further increase in BP during salt feeding were lower than that of CD ET-1 KO mice, whereas CD ETA KO mice were normotensive. CD ETB KO mice had impaired sodium excretion following acute sodium loading. Aldosterone and plasma renin activity were decreased in CD ETB KO mice on normal- and high-sodium diets, while plasma and urinary ET-1 levels did not differ from controls. In conclusion, the CD ETB receptor partially mediates the antihypertensive and natriuretic effects of ET-1. CD ETA and ETB receptors do not fully account for the antihypertensive and natriuretic effects of CD-derived ET-1, suggesting paracrine effects of this peptide.

Interleukin‐6 does not contribute to the increase in renal endothelin production stimulated by high salt intake

High salt intake stimulates production of certain inflammatory cytokines and enhances renal endothelin-1 (ET-1) production, as indicated by increased urinary ET-1 excretion. Whether cytokines participate in the signaling cascade to increase ET-1 production during high salt intake is unknown. As interleukin-6 (IL-6) stimulates ET-1 production by cultured cells, we hypothesized that the increase in urinary ET-1 excretion in response to high salt intake would be attenuated in IL-6 −/− mice. After a 24-hour baseline urine collection (normal 0.8% NaCl chow), wild type (WT) and IL-6 −/− mice received either normal NaCl (NS) or 4% NaCl (HS) chow for 2 weeks. Urine was collected for 24 hours at the end of each week. Baseline urinary ET-1 excretion rates, urine flows and Na+ excretion rates were not significantly different between the four groups. Urine ET-1 excretion rate was significantly increased (P < 0.01) in mice that received 4% NaCl chow for 2 weeks compared to mice on normal NaCl chow, but this effect did not differ significantly between WT and IL-6 −/− mice (% change vs baseline: 40 ± 12% WT HS, 49 ± 17% IL-6 −/− HS, 7 ± 11% WT NS, −6 ± 23% IL-6 −/− NS). Urine flow and Na+ excretion rate were also significantly increased (P < 0.001 and P = 0.0001 respectively) in mice receiving 4% NaCl chow compared to mice receiving normal NaCl chow, but these effects were similar in both genotypes. Thus IL-6 does not participate in the increase in renal ET-1 production stimulated by high salt intake.

Endothelin Receptors in the Kidney of Patients with Proteinuric and Non-Proteinuric Nephropathies

Background. Endothelin-1 (ET-1), which acts via the specific receptors ET-A and ET-B, has been implicated in the development of renal scarring. The activation of the endothelin system was observed in experimental models of glomerular diseases and was attributed to the toxic action of proteinuria on the tubular epithelial cells. The aim of this study was to investigate whether the endothelin system in the kidney is altered in glomerular diseases and possibly related to proteinuria. Methods. Thirty-seven patients with different types of glomerulonephritis and 14 controls were included. Patients presented either nephrotic syndrome (n=25) or mild proteinuria (<1g/24h, n=12). The expression of ET-A and ET-B receptors in the renal tissue was examined immunohistochemically. At the time of biopsy, urinary ET-1 was determined. Results. Both receptors were mainly localized within tubular epithelial cells, and their expression was significantly higher in patients with glomerulonephritis compared to controls. The expression of ET-B was higher in nephrotic compared to non-nephrotic patients, while no difference was observed in the expression of ET-A receptors. A significant positive correlation of the degree of proteinuria with the excreted ET-1 (r= 0.487, p<0.05) and the extent of immunostaining for ET-B receptors (r=0.420, p<0.05) was observed. The expression of ET-B receptors and the excretion of ET-1 decreased significantly in patients with remission of nephrotic syndrome after therapy. Conclusion. This study provides evidence that the endothelin system is activated in human glomerular disease, confirming data from experimental studies. Proteinuria seems to be related to the activation of endothelin system, though further investigation is necessary to clarify this issue.

Association between endothelin-1 and collagen deposition in db/ db diabetic mouse kidneys

Endothelin-1 has been implicated in diabetic kidney injury, but there are few firm data establishing the temporal and spatial expression of kidney endothelin-1 in diabetes. We performed an immunohistochemical and histopathological analysis to determine endothelin-1 peptide expression in the kidneys of diabetic db/ db mice and non-diabetic db/ m controls. Diabetic mice were studied at 8 weeks, before histological damage is evident, and again at 16 weeks, when significant glomerular injury has occurred. Urinary endothelin-1 was 6.2- and 3.6-fold higher in 8- and 16-week diabetic mice compared to age-matched controls ( P < 0.01 db/ db vs. db/ m). Compared to non-diabetic kidneys, immunoreactive endothelin-1 was first elevated 2.5-fold ( P = 0.02) in the tubulointerstitial compartment at 8-week and remained high (3.8-fold, P < 0.01) at 16 weeks. In contrast, glomerular endothelin-1 was elevated 3.2-fold ( P = 0.03) only in 16-week diabetic mice. Glomerular and tubulointerstitial endothelin-1 were unchanged in 8- and 16-week non-diabetic mice. Elevated endothelin-1 in diabetic mice associated temporally and spatially with collagen deposition, especially in the tubulointerstitial compartment. The localization of kidney endothelin-1 is consistent with a role for this peptide in renal fibrogenesis. These results also highlight the potential role of ET-1 in the pathogenesis of early tubulointerstitial changes in diabetes.

Urinary endothelin-1 as a marker of renal damage in sickle cell disease

Sickle cell disease (SCD) affects the kidney by acute mechanisms as well as by insidious renal medullary/papillary necrosis, resulting in tubular defects, which increase the risk of dehydration and subsequent sickle crisis. Hypoxia has been reported to stimulate endothelin-1 (ET-1) synthesis by endothelial cells and also in the renal tubule. This case-control study measured ET-1 in urine as a marker of its renal synthesis in asymptomatic SCD patients. Baseline plasma and urinary ET-1 levels were measured and followed during a water deprivation study and a subsequent administration of desmopressin. Urine and plasma levels of ET-1 were elevated in patients with SCD, compared with carefully matched African-French and African controls, and urine ET-1 excretion was associated with a marked urine-concentrating defect. Moreover, urinary ET-1 output was correlated with microalbuminuria in SCD patients. ET-1 is known to antagonize the tubular effects of vasopressin and to promote renal scarring; increased renal production of ET-1 could produce nephrogenic diabetes insipidus and dehydration in SCD patients through a combination of fibrosis and functional resistance to vasopressin. This study provides a rationale for trials with endothelin receptor antagonists in sickle cell disease nephropathy.