Endothelins in the kidney: physiology and pathophysiology

Urinary NGAL is a Potential Biomarker for Early Renal Injury in Insulin Resistant Obese Non-diabetic Children

OBJECTIVE

Neutrophil gelatinase-associated lipocalin (NGAL) is one of the new biomarkers for detecting acute renal injury. There are studies showing the relationship between NGAL and renal injury in obese children. The aim of this study was to investigate whether urinary levels of NGAL, kidney injury molecule-1, and serum cystatin C are increased in insulin resistance (IR) patients before the development of diabetes.

METHODS

Cross-sectional, case-controlled study that included non-diabetic obese children and adolescent patients with IR and a non-diabetic obese control group with no IR, who attended a tertiary center pediatric endocrinology outpatient clinic between 2016-2018. Those with diabetes mellitus and/or known renal disease were excluded. NGAL and creatinine (Cr) levels were evaluated in the morning spot urine from all participants. Serum renal function was evaluated.

RESULTS

Thirty-six control and 63 IR patients were included in the study, of whom 68 (68.7%) were girls. The mean age of all participants was 13.12±2.64 years and no statistically significant difference was found between the two groups in terms of age or gender distribution. Median (range) spot urinary NGAL (u-NGAL) values in the IR group were significantly higher at 26.35 (7.01-108.7) ng/mL than in the control group at 19.5 (3.45-88.14) ng/mL (p=0.018). NGAL/Cr ratio was also significantly higher in the IR group compared to the control group (p=0.018).

CONCLUSION

Obese pediatric patients with IR were shown to have elevated levels of u-NGAL, a marker of renal injury. u-NGAL examination may show early renal injury before development of diabetes.

Rationale and Design of Assessing the Effectiveness of Short-Term Low-Dose Lithium Therapy in Averting Cardiac Surgery-Associated Acute Kidney Injury: A Randomized, Double Blinded, Placebo Controlled Pilot Trial

Background: Burgeoning pre-clinical evidence suggests that therapeutic targeting of glycogen synthase kinase 3β (GSK3β), a convergence point of multiple cellular protective signaling pathways, confers a beneficial effect on acute kidney injury (AKI) in experimental models. However, it remains unknown if GSK3β inhibition likewise mitigates AKI in humans. Cardiac surgery associated acute kidney injury (CSA-AKI) poses a significant challenge for clinicians and currently the only treatment available is general supportive measures. Lithium, an FDA approved mood stabilizer, is the best-known GSK3β inhibitor and has been safely used for over half a century as the first line regimen to treat bipolar affective disorders. This study attempts to examine the effectiveness of short term low dose lithium on CSA-AKI in human patients.

Methods/Design: This is a single center, prospective, randomized, double blinded, placebo controlled pilot study on patients undergoing cardiac surgery with cardiopulmonary bypass. Patients will be randomized to receive a small dose of lithium or placebo treatment for three consecutive days. Renal function will be measured via creatinine as well as novel AKI biomarkers. The primary outcome is incidence of AKI according to Acute Kidney Injury Network (AKIN) criteria, and secondary outcomes include receipt of new dialysis, days on dialysis, days on mechanical ventilation, infections within 1 month of surgery, and death within 90 days of surgery.

Discussion: As a standard selective inhibitor of GSK3β, lithium has been shown to exert a beneficial effect on tissue repair and regeneration upon acute injury in multiple organ systems, including the central nervous system and hematopoietic system. In experimental AKI, lithium at small doses is able to ameliorate AKI and promote kidney repair. Successful completion of this study will help to assess the effectiveness of lithium in CSA-AKI and could potentially pave the way for large-scale randomized trials to thoroughly evaluate the efficacy of this novel regimen for preventing AKI after cardiac surgery.

Trial Registration: This study was registered prospectively on the 17th February 2017 at ClinicalTrials.gov (NCT03056248, https://clinicaltrials.gov/ct2/show/NCT03056248?term=NCT03056248&draw=2&rank=1).

Impact of in vitro embryo culture and transfer on blood pressure regulation in the adolescent lamb

Nutrition during the periconceptional period influences postnatal cardiovascular health. We determined whether in vitro embryo culture and transfer, which are manipulations of the nutritional environment during the periconceptional period, dysregulate postnatal blood pressure and blood pressure regulatory mechanisms. Embryos were either transferred to an intermediate recipient ewe (ET) or cultured in vitro in the absence (IVC) or presence of human serum (IVCHS) and a methyl donor (IVCHS+M) for 6 days. Basal blood pressure was recorded at 19-20 weeks after birth. Mean arterial pressure (MAP) and heart rate (HR) were measured before and after varying doses of phenylephrine (PE). mRNA expression of signaling molecules involved in blood pressure regulation was measured in the renal artery. Basal MAP did not differ between groups. Baroreflex sensitivity, set point, and upper plateau were also maintained in all groups after PE stimulation. Adrenergic receptors alpha-1A (αAR1A), alpha-1B (αAR1B), and angiotensin II receptor type 1 (AT1R) mRNA expression were not different from controls in the renal artery. These results suggest there is no programmed effect of ET or IVC on basal blood pressure or the baroreflex control mechanisms in adolescence, but future studies are required to determine the impact of ET and IVC on these mechanisms later in the life course when developmental programming effects may be unmasked by age.

First-in-Man Demonstration of Direct Endothelin-Mediated Natriuresis and Diuresis

Endothelin (ET) receptor antagonists are potentially novel therapeutic agents in chronic kidney disease and resistant hypertension, but their use is complicated by sodium and water retention. In animal studies, this side effect arises from ETB receptor blockade in the renal tubule. Previous attempts to determine whether this mechanism operates in humans have been confounded by the hemodynamic consequences of ET receptor stimulation/blockade. We aimed to determine the effects of ET signaling on salt transport in the human nephron by administering subpressor doses of the ET-1 precursor, big ET-1. We conducted a 2-phase randomized, double-blind, placebo-controlled crossover study in 10 healthy volunteers. After sodium restriction, subjects received either intravenous placebo or big ET-1, in escalating dose (≤300 pmol/min). This increased plasma concentration and urinary excretion of ET-1. Big ET-1 reduced heart rate (≈8 beats/min) but did not otherwise affect systemic hemodynamics or glomerular filtration rate. Big ET-1 increased the fractional excretion of sodium (from 0.5 to 1.0%). It also increased free water clearance and tended to increase the abundance of the sodium-potassium-chloride cotransporter (NKCC2) in urinary extracellular vesicles. Our protocol induced modest increases in circulating and urinary ET-1. Sodium and water excretion increased in the absence of significant hemodynamic perturbation, supporting a direct action of ET-1 on the renal tubule. Our data also suggest that sodium reabsorption is stimulated by ET-1 in the thick ascending limb and suppressed in the distal renal tubule. Fluid retention associated with ET receptor antagonist therapy may be circumvented by coprescribing potassium-sparing diuretics.

Association of Endothelin-1 rs5370 G>T gene polymorphism with the risk of nephrotic syndrome in children

Background:

Primary nephrotic syndrome (NS) is a common kidney disease in children. Objectives: The present study was aimed to investigate whether rs5370 G>T (lys198Asn) genetic variant of endothelin-1 (ET-1) is involved in the susceptibility to NS.

Patients and Methods:

This case-control study was performed on 138 patients with NS and 150 healthy children. Genomic DNA was extracted from whole blood using salting out method. Polymorphism of the ET-1 rs5370 G>T (lys198Asn) polymorphism detected by T-ARMS-PCR as well as PCR-RFLP method.

Results:

The results showed that the genotype and allelic frequencies of the ET-1 rs5370 G>T variant were not significantly different between cases and controls. Furthermore, subgroup analysis showed that rs5370 G>T variant was not associated with gender of patients. In NS patients the genotype was not associated with cholesterol, triglyceride, total protein and albumin levels.

Conclusions:

In conclusion, our findings indicate that ET-1 rs5370 G>T is not associated with NS. Further studies with larger sample sizes and different ethnicities are required to validate our findings.

AKI associated with cardiac surgery

Approximately 18% of patients undergoing cardiac surgery experience AKI (on the basis of modern standardized definitions of AKI), and approximately 2%-6% will require hemodialysis. The development of AKI after cardiac surgery portends poor short- and long-term prognoses, with those developing RIFLE failure or AKI Network stage III having an almost 2-fold increase in the risk of death. AKI is caused by a variety of factors, including nephrotoxins, hypoxia, mechanical trauma, inflammation, cardiopulmonary bypass, and hemodynamic instability, and it may be affected by the clinician's choice of fluids and vasoactive agents as well as the transfusion strategy used. The risk of AKI may be ameliorated by avoidance of nephrotoxins, achievement of adequate glucose control preoperatively, and use of goal-directed therapy hemodynamic strategies. Remote ischemic preconditioning is an exciting future strategy, but more work is needed before widespread implementation. Unfortunately, there are no pharmacologic agents known to reduce the risk of AKI or treat established AKI.

Cardiac surgery-associated acute kidney injury

Cardiac surgery-associated acute kidney injury (AKI) is a major health problem that is extremely common and has a significant effect on cardiac surgical outcomes. AKI occurs in nearly 30 % of patients undergoing cardiac surgery, with about 1-2 % of these ultimately requiring dialysis. The development of AKI predicts a significant increase in morbidity and mortality independent of other risk factors. The pathogenetic mechanisms associated with cardiac surgery-associated AKI include several biochemical pathways, of which the most important are hemodynamic, inflammatory and nephrotoxic factors. Risk factors for AKI have been identified in several models, and these facilitate physicians to prognosticate and develop a strategy for tackling patients predisposed to developing renal dysfunction. Effective therapy of the condition is still suboptimal, and hence the accent has always been on risk factor modification. Thus, strategies for reducing preoperative anemia, perioperative blood transfusions and surgical re-explorations may be effective in attenuating the incidence and severity of this complication.

Renal and systemic effects of endothelin-1 in diabetic-hypertensive rats

The Cohen-Rosenthal Diabetic Hypertensive rat (CRDH) is a unique animal model in which genetic hypertension and diabetes developed after crossbreeding of Cohen diabetic rats sensitive substrain (CDR) and spontaneously hypertensive rats (SHR). The present study examined: 1) The acute effects of ET-1 on the systemic and renal hemodynamics in CRDH rats, CDR, and SHR; 2) The expression of ET-1 and its receptors in the renal tissue of CRDH rats. Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized SHR rats resulted in a significant immediate depressor response (mean arterial pressure (MAP) decreased from 165 ± 3 to 124 ± 12 mmHg, p < 0.0001) followed by a minor hypertensive phase (MAP increased to 170 ± 2 mmHg). Simultaneously, the administration of ET-1 caused a significant decrease in renal blood flow (RBF) from 5.8 ± 0.9 ml/min to 3.2 ± 0.5 ml/min (p = 0.026). These responses were blunted in CRDH rats and CDR. Analysis of intra-renal blood flow by laser-Doppler in CRDH rats revealed that ET-1 injection caused a decrease in cortical blood flow (Δ = -12 ± 2.9%). However, in contrast to its well-known renal medullary vasodilatory effect, ET-1 produced a significant decline in the medulla blood flow (Δ = -17.5 ± 3.4%) (p = 0.0125). These findings suggest that CDR and CRDH rats have reduced sensitivity to vascular and renal action of ET-1. Furthermore, in the CRDH rats, the expected ET-1-induced medullary vasodilatation was abolished and even reversed into prolonged vasoconstriction.

Podocyte dysfunction in aging--related glomerulosclerosis

We review podocyte molecular structure and function, consider the underlying mechanisms related to podocyte dysfunction and propose that podocyte dysfunction be considered in the evaluation and management of age-associated glomerulosclerosis. With aging, progressive sympathetic activation, increased intrarenal renin-angiotensin system (RAS) activity, endothelin system and oxidative stress and reduced nitric oxide (NO)-availability can damage podocytes. Apoptosis and proliferation are the principal podocyte changes following injury with the latter leading to sclerosis and loss of nephrons. Podocyte loss can be evaluated by either determining their average number in biopsed glomeruli or by estimating podocyte number or their associated molecules in urine sediment. Podocyturia may be considered a marker of active glomerular disease. Preliminary data suggest that antiadrenergic drugs, angiotensin converting enzyme (ACE) inhibitors, RAS blocking drugs, endothelin system inhibitors and reduced oxidative stress can protect podocytes. Thus podocytes appear to play an important role in the pathogenesis, evaluation and therapy of age related glomerulosclerosis.

Effects of allopurinol and vitamin E on renal function in patients with cardiac coronary artery bypass grafts

Background:

Acute renal failure is a common complication of cardiac surgery, with oxidants found to play an important role in renal injury. We therefore assessed whether the supplemental antioxidant vitamin E and the inhibitor of xanthine oxidase allopurinol could prevent renal dysfunction after coronary artery bypass graft (CABG) surgery.

Methods:

Of 60 patients with glomerular filtration rate (GFR) < 60 mL/min scheduled to undergo CABG surgery, 30 were randomized to treatment with vitamin E and allopurinol for 3–5 days before surgery and 30 to no treatment. Serum creatinine levels and potassium and creatinine clearances were measured preoperatively and daily until day 5 after surgery.

Results:

The patients consisted of 31 males and 29 females, with a mean age of 63 ± 9 years. After surgery, there were no significant differences in mean serum creatinine (1.2 ± 0.33 vs 1.2 ± 0.4 mg/dL; p = 0.43) concentrations, or creatinine clearance (52 ± 12.8 vs 52 ± 12.8 mL/min; p = 0.9). The frequency of acute renal failure did not differ in treatment group compared with control (16% vs 13%; p = 0.5). Length of stay in the intensive care unit (ICU) was significantly longer in the control than in the treated group (3.9 ± 1.5 vs 2.6 ± 0.7 days; p < 0.001).

Conclusion:

Prophylactic treatment with vitamin E and allopurinol had no renoprotective effects in patients with pre-existing renal failure undergoing CABG surgery. Treatment with these agents, however, reduces the duration of ICU stay.

Deficiency in Six2 during prenatal development is associated with reduced nephron number, chronic renal failure, and hypertension in Br/+ adult mice

The Br/+ mutant mouse displays decreased embryological expression of the homeobox transcription factor Six2, resulting in hertitable renal hypoplasia. The purpose of this study was to characterize the renal physiological consequences of embryonic haploinsuffiency of Six2 by analyzing renal morphology and function in the adult Br heterozygous mutant. Adult Br/+ kidneys weighed 50% less than those from wild-type mice and displayed glomerulopathy. Stereological analysis of renal glomeruli showed that Br/+ kidneys had an average of 88% fewer glomeruli than +/+ kidneys, whereas individual glomeruli in Br/+ mice maintained an average volume increase of 180% compared with normal nephrons. Immunostaining revealed increased levels of endothelin-1 (ET-1), endothelin receptors A (ET(A)) and B (ET(B)), and Na-K-ATPase were present in the dilated renal tubules of mutant mice. Physiological features of chronic renal failure (CRF) including elevated mean arterial pressure, increased plasma creatinine, and dilute urine excretion were measured in Br/+ mutant mice. Electron microscopy of the Br/+ glomeruli revealed pathological alterations such as hypercellularity, extracellular matrix accumulation, and a thick irregular glomerular basement membrane. These results indicate that adult Br/+ mice suffer from CRF associated with reduced nephron number and renal hypoplasia, as well as glomerulopathy. Defects are associated with embryological deficiencies of Six2, suggesting that proper levels of this protein during nephrogenesis are critical for normal glomerular development and adult renal function.

Gq-dependent signaling upregulates COX2 in glomerular podocytes

Accumulating evidence suggests that upregulation of cyclooxygenase 2 (COX2) in glomerular podocytes promotes podocyte injury. Because Gq signaling activates calcineurin and calcineurin-dependent mechanisms are known to mediate COX2 expression, this study investigated the role of Gqalpha in promoting COX2 expression in podocytes. A constitutively active Gq alpha subunit tagged with the TAT HIV protein sequence was introduced into an immortalized podocyte cell line by protein transduction. This stimulated inositol trisphosphate production, activated an nuclear factor of activated T cells-responsive reporter construct, and enhanced levels of both COX2 mRNA and protein compared with cells treated with a Gq protein lacking the TAT sequence. Induction of COX2 was associated with increased prostaglandin E(2) production and podocyte death, both of which were attenuated by selective COX2 inhibition. In vivo, levels of COX2 mRNA and protein were significantly enhanced in podocytes from transgenic mice that expressed podocyte-targeted constitutively active Gqalpha compared with nontransgenic littermates. These data suggest that Gq-dependent signaling cascades stimulate calcineurin and, in turn, upregulate COX2 mRNA and protein, increase eicosanoid production, and cause podocyte injury.

Beneficial effects of the Rho kinase inhibitor Y27632 in murine puromycin aminonucleoside nephrosis

BACKGROUND AND AIMS

Rho kinase (ROCK) inhibition reduces systemic blood pressure (BP) and decreases renal damage in animal models of kidney disease. The aim of this study was to determine if ROCK inhibition might have beneficial effects in glomerular disease processes that are independent of systemic BP.

METHODS

We investigated the effects of the ROCK inhibitor Y27632 and hydralazine in murine puromycin aminonucleoside (PAN) nephrosis.

RESULTS

Treatment with either Y27632 or hydralazine similarly reduced systolic BP compared to vehicle-treated controls. Seven days after treatment with PAN, albuminuria, proteinuria and effacement of podocyte foot processes were significantly reduced in Y27632- and hydralazine-treated mice compared to vehicle-treated animals. Treatment with PAN significantly reduced expression of the podocyte proteins nephrin and Neph1, and the loss of glomerular nephrin was attenuated by treatment with Y27632 but not by treatment with hydralazine. In cultured podocytes, PAN potently activated both Rho and ROCK, and PAN-induced ROCK activation was prevented by Y27632.

CONCLUSIONS

The ROCK inhibitor Y27632 attenuated glomerular nephrin loss in murine PAN nephrosis independent of its effects on systemic BP.

Preparation of a protected phosphoramidon precursor via an H-Phosphonate coupling strategy

The preparation of a phosphoramidon precursor is described using a phosphorus(III) coupling protocol.

Endothelin receptor antagonists

Endothelin receptor antagonists (ERAs) have been developed to block the effects of endothelin-1 (ET-1) in a variety of cardiovascular conditions. ET-1 is a powerful vasoconstrictor with mitogenic or co-mitogenic properties, which acts through the stimulation of 2 subtypes of receptors [endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) receptors]. Endogenous ET-1 is involved in a variety of conditions including systemic and pulmonary hypertension (PH), congestive heart failure (CHF), vascular remodeling (restenosis, atherosclerosis), renal failure, cancer, and cerebrovascular disease. The first dual ETA/ETB receptor blocker, bosentan, has already been approved by the Food and Drug Administration for the treatment of pulmonary arterial hypertension (PAH). Trials of endothelin receptor antagonists in heart failure have been completed with mixed results so far. Studies are ongoing on the effects of selective ETA antagonists or dual ETA/ETB antagonists in lung fibrosis, cancer, and subarachnoid hemorrhage. While non-peptidic ET-1 receptor antagonists suitable for oral intake with excellent bioavailability have become available, proven efficacy is limited to pulmonary hypertension, but it is possible that these agents might find a place in the treatment of several cardiovascular and non-cardiovascular diseases in the coming future.

Insulin resistance, hyperinsulinemia, and renal injury: mechanisms and implications

Most of the basic components of the metabolic syndrome, namely type 2 diabetes mellitus, hypertension, obesity, or low high-density lipoprotein cholesterol levels, apart from being major risk factors for cardiovascular disease have been also associated with an increased risk of chronic kidney disease. However, several epidemiologic studies conducted over the past years suggest that the central component of the syndrome, insulin resistance, as well as compensatory hyperinsulinemia are independently associated with an increased prevalence of chronic kidney disease. In addition, background studies support the existence of several pathways linking insulin resistance and hyperinsulinemia with kidney damage. Insulin per se promotes the proliferation of renal cells and stimulates the production of other important growth factors such as insulin-like growth factor-1 and transforming growth factor beta. Insulin also upregulates the expression of angiotensin II type 1 receptor in mesangial cells, thus enhancing the deleterious effects of angiotensin II in the kidney, and stimulates production and renal action of endothelin-1. Moreover, insulin resistance and hyperinsulinemia are associated with decreased endothelial production of nitric oxide and increased oxidative stress which have been also implicated in the progression of diabetic nephropathy. This review analyzes the above and other potential mechanisms, through which insulin resistance and hyperinsulinemia can contribute to renal injury.

Galphaq-dependent signaling cascades stimulate water-seeking behavior

We used the mouse nephrin promoter to express a constitutively active Galphaq [Galphaq(Q>L)] transgene in mice. As previously reported, the transgene was expressed in kidney, pancreas, and brain, and the kidney phenotype was characterized by albuminuria and reduced nephron mass. Additional studies revealed a second phenotype characterized by polyuria and polydipsia. The polyuric phenotype was not caused by abnormal glucose metabolism or hypercalcemia but was accompanied by reduced urinary concentrating ability. Additional studies found that 1) water restriction was associated with an appropriate increase in serum vasopressin levels in transgenic (TG) mice; 2) the urinary concentrating defect was not corrected by administration of desamino-d-arginine vasopressin (DDAVP); and 3) papillary length was similar in TG and non-TG mice. To examine the renal response to DDAVP at the molecular level, we monitored aquaporin 2 (AQP2) and vasopressin V2 receptor (V2R) mRNA levels in mouse kidney. Consistent with the known effects of vasopressin, administration of DDAVP caused a decrease in V2R mRNA levels and an increase in AQP2 mRNA levels in both TG and non-TG animals, suggesting an appropriate renal response to DDAVP in the TG mice. To determine whether the urine concentrating abnormality was the result of primary polydipsia, water intake by TG mice was restricted to the amount ingested by non-TG animals. After 5 days, urinary concentrating ability was similar in TG mice and non-TG littermate controls. These data are consistent with the notion that expression of the Galphaq(Q>L) transgene in the brain induced primary polydipsia in the TG mice.

Activation of Gαq-Coupled Signaling Pathways in Glomerular Podocytes Promotes Renal Injury

The glomerular podocyte plays a key role in maintaining the integrity of the glomerular filtration barrier. This function may be regulated by activation of cell surface G protein-coupled receptors (GPCR). Studies suggest that podocytes express GPCR that are implicated in the pathogenesis of glomerular diseases. Common to these GPCR systems is activation of phospholipase C through the Gq alpha-subunit (Galpha q). For investigating the role of Galpha q-coupled signaling pathways in promoting renal injury in podocytes, a constitutively active Galpha q subunit (Galpha qQ > L) was expressed in glomerular podocytes using the mouse nephrin promoter. Transgenic (TG) mice demonstrated albuminuria as well as a decrease in both kidney mass and nephron number. By light microscopy, a portion of the TG mice had glomerular abnormalities, including focal to diffuse hypercellularity and segmental sclerosis. Consistent with injury-promoting effects of Galpha qQ > L, there was a significant reduction in podocalyxin mRNA as well as nephrin mRNA and protein levels in glomeruli from TG mice compared with non-TG controls. Expression of the transgene also seemed to increase susceptibility to glomerular injury, because treatment with puromycin aminonucleoside enhanced proteinuria in TG mice compared with non-TG littermate controls (4.2 +/- 1.0 [TG] versus 1.6 +/- 0.3 [non-TG] mg/24 h; P = 0.0161). Thus, activation of Galpha q in glomerular podocytes caused alterations in glomerular histomorphology, albuminuria, decreased nephron mass, and reduced glomerular expression of both nephrin and podocalyxin as well as enhanced susceptibility to glomerular damage induced by puromycin aminonucleoside. It is speculated that Galpha q-coupled signaling cascades may be important effector pathways mediating renal injury.

Acute kidney injury associated with cardiac surgery

Acute renal failure (ARF) occurs in up to 30% of patients who undergo cardiac surgery, with dialysis being required in approximately 1% of all patients. The development of ARF is associated with substantial morbidity and mortality independent of all other factors. The pathogenesis of ARF involves multiple pathways. Hemodynamic, inflammatory, and nephrotoxic factors are involved and overlap each other in leading to kidney injury. Clinical studies have identified risk factors for ARF that can be used to determine effectively the risk for ARF in patients who undergo bypass surgery. These high-risk patients then can be targeted for renal protective strategies. Thus far, no single strategy has demonstrated conclusively its ability to prevent renal injury after bypass surgery. Several compounds such as atrial natriuretic peptide and N-acetylcysteine have shown promise, but large-scale trials are needed.

Peroxisome proliferator-activated receptor-alpha activation reduces salt-dependent hypertension during chronic endothelin B receptor blockade

Endothelin B (ETB) receptor stimulation inhibits sodium transport in a similar fashion as 20-HETE. Clofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonist, increases protein expression of cytochrome P450 4A (CYP4A), which is responsible for 20-HETE synthesis in the kidney. Experiments were designed to determine whether clofibrate reduces hypertension associated with chronic ETB receptor blockade. Male Sprague-Dawley rats received either normal-salt (0.8% NaCl) or high-salt (8% NaCl) diet for 10 days. Female rats were fed a high-salt (8% NaCl) diet for 10 days. During the last 7 days, rats of both sexes were divided into 3 treatment groups: (1) clofibrate in drinking water (80 mg per day), (2) ETB receptor antagonist A-192621 in food (10 mg/kg per day), or (3) clofibrate and A-192621. During ETB receptor blockade, clofibrate had no effect on mean arterial pressure (MAP) under normal salt conditions. In contrast, clofibrate significantly inhibited the increase in MAP produced by A-192621 in rats fed a high-salt diet (34+/-3 versus 19+/-4 mm Hg; P <0.05). Similar results were observed in female rats administered A-192621 and fed a high-salt diet. ETB receptor blockade significantly decreased CYP4A protein expression in the renal cortex of rats on high salt. Clofibrate significantly increased renal cortical and medullary CYP4A protein expression in A-192621-treated male rats on high salt. Therefore, chronic PPAR-alpha agonist treatment reduces salt-dependent hypertension produced by ETB receptor blockade in male and female Sprague-Dawley rats. This suggests a possible relationship between ETB receptor activation and the maintenance of CYP4A protein expression in the kidney of rats fed a high-salt diet.

Ursodeoxycholic acid reduces increased circulating endothelin 2 in primary biliary cirrhosis

BACKGROUND

Endothelins and nitric oxide regulate sinusoidal blood flow and the perfusion of the peribiliary vascular plexus.

AIMS

To study the serum and hepatic vein concentration of ET-1, ET-2, ET-3 and nitric oxide in patients with primary biliary cirrhosis and the effect of ursodeoxycholic acid treatment.

METHODS

Endothelins and nitrites/nitrates were measured in serum and hepatic vein blood in primary biliary cirrhosis and viral cirrhotic patients prior and after ursodeoxycholic acid therapy and in serum in controls. Endothelins were measured with commercial enzyme-linked immunosorbent assays and nitrites/nitrates with a modification of Griess reaction.

RESULTS

The ET-1 and ET-3 levels were similar in patients and controls. Primary biliary cirrhosis patients had the highest serum ET-2 (P < 0.001) compared with other groups. Nitrites/nitrates was increased in primary biliary cirrhosis (P < 0.05) compared with normal. ET-2 and nitric oxide were similar in all primary biliary cirrhosis stages. Ursodeoxycholic acid significantly decreased ET-2 in all stages (I and II: P < 0.05 and III and IV: P < 0.01) and increased nitric oxide (P < 0.05) in early primary biliary cirrhosis. Hepatic vein ET-1 and ET-3 were higher in viral cirrhosis patients, but only in primary biliary cirrhosis a significant difference for ET-1 and ET-3 between hepatic and peripheral veins was found.

CONCLUSIONS

Increased ET-2 is an early defect in primary biliary cirrhosis that is significantly reduced by the ursodeoxycholic acid treatment. The possibility of a more generalized endothelial cell dysfunction in primary biliary cirrhosis requires further investigation.

Pathophysiology of ischaemic acute renal failure

This chapter summarizes the pathophysiology of ischaemic acute renal failure from both the experimental and clinical points of view. Traditionally, the abrupt fall in glomerular filtration rate (GFR) is thought to be due to an interplay of haemodynamic and tubular abnormalities. The intrarenal haemodynamic alterations include renal vasoconstriction, leukocyte-endothelium interactions and loss of blood flow and GFR autoregulation. During recent years it has become evident that pronounced outer medulary ischaemia makes an important contribution. In severe and prolonged ischaemia, the tubular epithelial cells can undergo either sublethal or lethal cell damage. Cell death occurs by necrosis and apoptosis. The different mechanisms of post-ischaemic cell damage are discussed. The post-ischaemic kidney also shows a dramatic capacity for recovery. During this recovery phase some of the damaged cells undergo de-differentiation--which is an important step in regeneration of the tubular epithelium. Recent evidence points to the possibility that infiltration of the kidney with bone-marrow-derived stem cells contributes to the repair process. The molecular mechanisms and the effect of growth factors are summarized.

Influence of acute selective endothelin-receptor-A blockade on renal hemodynamics in a rat model of chronic allograft rejection

We have recently demonstrated up-regulation of renal endothelin (ET) synthesis in a rat model of chronic renal allograft rejection. Treatment with a selective ET-A receptor antagonist improved survival and reduced functional and morphological kidney damage. However, the underlying mechanisms have not yet been elucidated, as ET exhibits both hemodynamic and inflammatory properties. Therefore, in the present study we investigated acute hemodynamic effects of the selective ET-A receptor antagonist LU 302146 (LU) on chronic renal allograft rejection in rats. Experiments were performed in the Fisher-to-Lewis model of chronic renal allograft rejection. Lewis-to-Lewis isografts served as controls. After 2, 12, and 24 weeks, hemodynamic measurements were performed on anesthetized animals. Measurement of mean arterial pressure (MAP) was performed via a catheter in the femoral artery. Renal blood flow (RBF) was measured by an ultrasonic flow probe placed around the renal transplant artery. Medulla blood flow (MBF) and cortex blood flow (CBF) were determined with laser Doppler probes. Hemodynamic response upon intravenous bolus injection of LU (50 mg/kg) was investigated. The application of LU was followed by a decline in MAP that reached statistical significance only in isografts (ISOs) after 12 weeks and allografts (ALLOs) after 24 weeks. RBF slightly decreased in all groups; however, without reaching statistical significance. MBF showed a small increase in ALLO12 and ALLO24 whereas CBF slightly decreased in all groups. Acute ET-A receptor blockade does not induce important hemodynamic effects in kidneys undergoing chronic rejection. The lack of response to ET-A receptor blockade suggests that the beneficial effect of ET receptor antagonists in this model is likely to be due to improvement of renal morphology.

New therapeutics that antagonize endothelin: promises and frustrations

The discovery of endothelin--a highly potent endogenous vasoconstrictor - in 1988 has led to considerable efforts to develop antagonists of endothelin receptors that could have therapeutic potential in disorders including hypertension, heart failure and renal diseases. However, in general, the results of trials in humans have not mirrored the highly promising effects in animal disease models. Here, we discuss preclinical and clinical results with endothelin antagonists, and consider possible approaches to fully realizing the potential of endothelin antagonism.

Effect of glycerol on endothelium-derived factors in the vasculature of the rabbit kidney

1. In the present study, endothelium-derived relaxing factor (EDRF/nitric oxide (NO)), conversion of big endothelin (ET)-1 to endothelin-1 (ET-1) and the role of reactive oxygen species were investigated in kidneys isolated from glycerol (GLY)-pretreated rabbits. 2. Acetylcholine (ACh)-induced vasodilation that is due to the release of EDRF/NO is significantly decreased, whereas big ET-1-induced vasoconstriction was increased in kidneys isolated from GLY-pretreated rabbits. 3. Pretreatment of rabbits with the xanthine oxidase inhibitor allopurinol and the NO precursor L-arginine reversed the inhibition of ACh-induced vasodilation due to GLY and protects the kidney vasculature. 4. Big ET-1, but not ET-1, responses were found to be significantly increased in kidneys isolated from GLY-pretreated rabbits. This increase is attributed to the higher conversion rate of big ET-1 to ET-1 because the ET-converting enzyme (ECE) inhibitor phosphoramidon, at a concentration of 10(-6) mol/L, causes an inhibition in the response to big ET-1 by 52.6% in normal kidneys, whereas this inhibition with the same concentration of phosphoramidon was found to be significantly decreased in kidneys isolated from GLY-pretreated rabbits. 5. The non-selective NO synthase inhibitor N(G)-nitro-L- arginine methyl ester (L-NAME) caused a significant potentiation in the vasoconstrictor response to ET-1 in normal isolated perfused rabbit kidneys. However, L-NAME did not alter the responses to ET-1 in GLY-pretreated kidneys. 6. These results indicate that accumulation of reactive oxygen species causes an inhibition in NO bioavailability. Increased conversion of big ET-1 to ET-1 may also contribute to the mechanism of vascular damage due to GLY.

Endothelin receptor antagonists and cardiovascular diseases of aging

Our understanding of the role of the endothelin system in human cardiovascular physiology and pathophysiology has evolved very rapidly since the initial description of its constituent parts in 1988. Endothelin-1 (ET-1) is the predominant endothelin isoform in the human cardiovascular system and has potent vasoconstrictor, mitogenic and antinatriuretic properties which have implicated it in the pathophysiology of a number of cardiovascular diseases. The effects of ET-1 have been shown to be mediated by 2 principal endothelin receptor subtypes: ET(A) and ET(B). The development of a range of peptidic and nonpeptidic endothelin receptor antagonists represents an exciting breakthrough in human cardiovascular therapeutics. Two main classes of endothelin receptor antagonist have been developed for possible human therapeutic use: ET(A)-selective and nonselective antagonists. Extensive laboratory and clinical research with these agents has highlighted their promise in various cardiovascular diseases. Randomised, placebo-controlled clinical trials have yielded very encouraging results in patients with hypertension and chronic heart failure with more preliminary data suggesting a possible role in the treatment and prevention of atherosclerosis and stroke. Much more research is needed, however, before endothelin receptor antagonists can be considered for clinical use.

Endothelin is a potent inhibitor of matrix metalloproteinase-2 secretion and activation in rat mesangial cells

We examined the effects of endothelin (ET) on the activity of matrix metalloproteinase-2 (MMP-2) in cultured MCs. Addition of the ET(A) receptor antagonists or neutralizing anti-endothelin antibody into MC cultures markedly augmented the secretion and activation of MMP-2. On the contrary, addition of the exogenous ET-1 into MC culture significantly inhibited the synthesis of MMP-2 in both basal and cytokines (tumor necrosis factor-alpha and interferon-gamma) plus lipopolysaccharide-stimulated conditions. Furthermore, pretreatment of cells with exogenous ET-1 obviously prevented cytochalasin D-elicited activation of MMP-2, an effect that was completely abolished by ET(A) receptor antagonist, FR139317. In addition, ET-1 was found to be able to suppress the expression of membrane type-1 MMP (MT1-MMP) and promote the conversion of tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) from cell associated form to secreted form. The addition of recombinant TIMP-2 into the culture abrogated dose-dependently the cytochalasin D-elicited activation of MMP-2. These results suggest that ET is a potent inhibitor of MMP-2 secretion and activation in MCs. These novel findings may help us understand the subtle regulation of the synthesis and activation of MMP-2 in MCs. It also provides us with further insight into the pathophysiological mechanisms involving ET in the regulation of matrix turnover in glomerulus.

Endothelins: vasoactive modulators of renal function in health and disease

Vasoactive autocoids with directly opposing actions on the renal vasculature, glomerular function, and in salt and water homeostasis have been demonstrated in the kidney. In the renal cortex, endothelin (ET)-1 and angiotensin-II cause vasoconstriction, decreasing renal blood flow, and glomerular filtration rate, whereas bradykinin and atrial natriuretic peptide cause vasodilation and increase glomerular capillary permeability. ET-1 causes vasoconstriction of the afferent and efferent arteries and outer medullary descending vasa recta, thereby decreasing vasa recta and papillary blood flow, while bradykinin has the opposite effect. ET-1 stimulates cell proliferation, increasing the expression of several genes, including collagenase, prostaglandin endoperoxidase synthase, and platelet-derived growth factor. ET-1 promotes natriuresis via the ET-B receptor, causing down-regulation of the epithelial Na(+) channel in the renal tubule. Thus, ETs affect three major aspects of renal physiology: vascular and mesangial tone, Na(+) and water excretion, and cell proliferation and matrix formation.

Therapeutic administration of an endothelin-A receptor antagonist after acute ischemic renal failure dose-dependently improves recovery of renal function

Endothelin (ET) is known to reduce glomerular filtration rate and renal blood flow and is a possible mediator of acute renal failure (ARF). We recently demonstrated that the administration of a very high dose of the ET(A)-receptor antagonist LU 135252 (LU) accelerates recovery from postischemic acute renal failure by an improvement of renal perfusion in a rat model. The aim of this study was to investigate whether this effect of LU is dose dependent. ARF was induced in rats by clamping both renal arteries. Serum creatinine was measured and endogenous creatinine clearance and fractional sodium excretion were calculated up to 4 days after acute ischemia. Rats were treated either with the selective ET(A)-receptor antagonist LU or with vehicle only after reperfusion. LU in doses of 0.5, 1, or 5 mg/kg per day was infused via a femoral vein using an osmotic minipump. Serum creatinine was increased approximately eightfold after induction of ARF. Creatinine clearance decreased from 4.35 +/- 0.26 ml/min before acute renal failure to 0.15 +/- 0.02, 0.54 +/- 0.1, and 1.49 +/- 0.19 ml/min on days 1, 2, and 4 after ischemia (p < 0.05). Fractional sodium excretion increased from baseline 0.77 +/- 0.05% to 7.5 +/- 1.21 % on day 1 and 8.53 +/- 1.34% on day 2 (p < 0.05). Treatment with LU improved kidney function dose relatedly. There was no significant change in creatinine clearance, but compared with controls, with doses of 0.5 mg/kg per day and 1 mg/kg per day (0.28 +/- 0.1, 0.88 +/- 0.22, and 1.93 +/- 0.24 ml/min on days 1, 2, and 4), we noted a significant increase under 5 mg/kg per day (day 1: 0.62 +/- 0.17 ml/min; day 2: 1.38 +/- 0.26 ml/min; and day 4: 2.45 +/- 0.21 ml/min; p < 0.05). Fractional sodium excretion decreased dose-relatedly to a maximally 2.48 +/- 0.58% on day 1 and 2.25 +/- 0.71 % on day 2 after treatment with the highest dose when compared with untreated control rats (p < 0.05). Our data support the hypothesis that ET plays a major role in ARF. It can be concluded from these results that recovery from ischemic ARF is significantly and dose-dependently enhanced by treatment with a selective ET(A)-receptor antagonist.

Plasma and urinary endothelin-1 in focal segmental glomerulosclerosis

The kidney is an important site of endothelin-1 (ET-1) production and is particularly susceptible to ET-1 action. Infusion of ET-1 in rats induces both functional and morphological alterations in the kidneys. Increased plasma level of ET-1 has been reported in patients with chronic renal failure. However, there are still no reports on the plasma and urinary ET-1 levels in patients with focal segmental glomerulosclerosis (FSGS). In the present study, we have measured the plasma concentration and urinary excretion rate of ET-1 in 15 patients with nephrotic syndrome due to FSGS, and observed the serial changes of plasma and urinary ET-1 in nephrotic rats with FSGS, induced by repeated injection with puromycin aminonucleoside (PAN). ET-1 was measured with radioimmunoassay. The results showed that plasma ET-1 concentration in FSGS patients was significantly higher than in normal controls (P < 0.05), and that urinary ET-1 excretion rate was also significantly higher in FSGS patients than in normal controls (P < 0.01). In FSGS patients, the plasma and urinary ET-1 was significantly correlated (P < 0.05), and the urinary ET-1 excretion rate was significantly correlated with the amount of proteinuria (P < 0.05) and the glomerular sclerosing score (P < 0.01). In the ten rats with PAN-induced FSGS, serial examination showed a significant increase in plasma ET-1 after 8 weeks of injections, while the urinary ET-1 excretion rate showed a biphasic increase that showed a peak after 4 to 6 weeks. The same changes in plasma and urinary ET-1 levels were not observed in control rats injected with normal saline at the same frequency. Our results suggest that ET-1 may be involved in the pathogenesis of FSGS in both humans and rats.

The role of endothelins and their receptors in heart failure

Endothelin (ET) is a peptide composed of 21 amino acids, derived from a larger precursor, the big-endothelin, by action of the endothelin-converting enzyme (ECE) family; three isoforms of endothelin, named ET-1, ET-2 and ET-3, have been identified. Endothelin-1 is generated mainly by vascular endothelial cells and exerts various important biological actions, mediated by two receptor subtypes, ET-A and ET-B, belonging to the G protein-coupled family that have been identified in various human tissues such as the cardiac tissue. Endothelin-1 is a potent vasoconstrictive agent, has inotropic and mitogenic actions, modulates salt and water homeostasis and plays an important role in the maintenance of vascular tone and blood pressure in healthy subjects. Endothelin-1, as well as ET-A and ECE-1, also has an important role in cardiovascular development, as observed by the variety of abnormalities related to neural crest-derived tissues in mouse embryos deficient of a member of the ET-1/ECE-1/ET-A pathway. Various evidence indicates that endogenous endothelin-1 may contribute to the pathophysiology of conditions associated with sustained vasoconstriction, such as heart failure. In heart failure, elevated circulating levels of both endothelin-1 and big-endothelin-1 are observed; in failing hearts an activation of the endothelin system is found: tissue level of ET-1 is increased with respect to non-failing hearts as well as receptor density, due mainly to an upregulation of the ET-A subtype, the prevalent receptor subclass in cardiac tissue. Finally, studies in both humans and animal models of cardiovascular disease show that inhibition of the endothelin function (anti-endothelin strategy) is associated with an improvement of haemodynamic conditions; these observations indicate that endothelin receptor antagonists or endothelin-converting enzyme inhibitors may constitute a novel and potentially important class of agents for the treatment of this disease.

Pneumoperitoneum upregulates preproendothelin-1 messenger RNA

BACKGROUND

Laparoscopic pneumoperitoneum has been shown to decrease glomerular filtration rate (GFR) and urine volume (UV). Endothelin-1 (ET-1), a potent renal vasoconstrictor, has been implicated. The purpose of this study was to determine renal function, ET-1 gene expression, and peptide localization in kidneys subjected to CO2 pneumoperitoneum.

METHODS

Experiments were performed in three groups of anesthetized Sprague-Dawley rats in which GFR and UV were measured before, during, and after insufflation. In the first group (n = 8), pneumoperitoneum (10 mmHg) was established for 30 min. The second group (n = 4) underwent a sham operation without pneumoperitoneum. In the final group (n = 4), kidneys were obtained from normal control animals without any prior surgical instrumentation. PreproET-1 (ppET-1) mRNA levels were measured by reverse transcription-polymerase chain reaction (RT-PCR). The ET-1 peptide was localized within kidneys by immunohistochemistry (IHC).

RESULTS

Pneumoperitoneum caused a significant (p < 0.05) 87% decrease in GFR and a 79% decrease in UV from baseline, with a return to baseline values after desufflation. RT-PCR showed a significant (p < 0.05) increase in expression of ppET-1 mRNA in the laparoscopic group; it was 3.52 +/- 0.33 densitometric units (DU), as compared to 0.35 +/- 0.06 DU and 0.57 +/- 0.12 DU in the control and sham groups, respectively. IHC showed enhanced expression of the ET-1 peptide in the vascular endothelium and proximal tubular cells of the laparoscopic group compared to the control and sham groups.

CONCLUSION

Pneumoperitoneum induces ET-1 gene and peptide upregulation in the kidney. Expression of ET-1 is increased in the renal vasculature and proximal tubular cells. The elevation of ET-1 and its localization may account for some of the renal dysfunction observed during pneumoperitoneum. This suggests that antagonism of ET-1 may be beneficial in patients with renal impairment undergoing prolonged laparoscopic procedures or in protecting allograft function during and after living donor nephrectomy.

The use of the endothelin receptor antagonist, tezosentan, before or after renal ischemia protects renal function

BACKGROUND

Utilization of organs subjected to ischemia/reperfusion (I/R) injury could expand the donor pool. Endothelin (ET) is implicated in renal I/R injury. Therefore, our study compared the effectiveness of pre- and postischemic administration of the ET receptor antagonist, Tezosentan, in preserving renal function.

METHODS

In a rat model, a kidney was subjected to 45 min of ischemia along with a contralateral nephrectomy. After 24 hr of reperfusion, renal function was assessed by serum creatinine (Scr), inulin clearance (glomerular filtration rate; GFR), and histology. ET-1 peptide expression was localized using immunohistochemistry. Three groups were studied: I/R untreated (n=17), I/R pretreated (n=11), and I/R posttreated (n=13) with Tezosentan (15 mg/kg, i.v.).

RESULTS

Tezosentan significantly decreased (P<0.05) the rise in Scr from I/R injury (2.0+/-0.4 mg/dl, before and 2.9+/-0.4 mg/dl, after treatment) compared with untreated animals (4.2+/-0.4 mg/dl). GFR was significantly increased (P<0.05) from 0.13+/-0.03 ml/min (untreated animals) to 0.74+/-0.16 and 0.47+/-0.14 ml/min (pre- and posttreated animals). Untreated animals had significant cortical acute tubular necrosis, which was almost completely prevented by pretreatment with Tezosentan and markedly reduced by posttreatment. Increased ET-1 peptide expression was noted in the renal vasculature and in the cortical tubular epithelium of kidneys exposed to I/R.

CONCLUSIONS

The purpose of this study was to optimize the function of kidneys exposed to I/R injury. Pretreatment as well as posttreatment with Tezosentan successfully decreased Scr, increased GFR, and maintained renal architecture in kidneys after ischemia. Therefore, ET receptor antagonists may be useful to preserve renal function in the transplantation setting.

Role of NO and cytochrome P-450-derived eicosanoids in ET-1-induced changes in intrarenal hemodynamics in rats

Endothelin-1 (ET-1) produces potent renal effects that we have previously shown to be dependent on cytochrome P-450 (CYP450) metabolites of aracidonic acid (24) This study evaluated the role of these metabolites in the effects produced by ET-1 on renal blood flow (RBF), cortical blood flow (CBF), medullary blood flow (MBF), and mean arterial blood pressure (MBP). ET-1 (20-200 pmol/kg) increased MBP, renal vascular resistance (RVR), and MBF but reduced CBF and RBF in a dose-dependent manner. The decreases in CBF and RBF, and increases in MBP and RVR were blunted by BMS-182874, an ET(A) receptor antagonist or BQ-788, an ET(B) receptor antagonist. Similarly, indomethacin, an inhibitor of cyclooxygenase activity, or 12,12-dibromododecenoic acid (DBDD), a CYP450-dependent inhibitor of production of 20-hydroxyeicosatetraenoic acid (20-HETE), blunted these effects. ET-3 elicited dose-related reduction in CBF and increase in MBF. Indomethacin accentuated the reduction in CBF and attenuated the increase in MBF, as did DBDD. ET-1-induced increase in MBF was attenuated by BQ-788, N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, indomethacin, or DBDD. DBDD inhibited the hemodynamic effects of L-NAME. Miconazole, the inhibitor of CYP450-dependent epoxygenase activity, was without effect. These results indicate that hemodynamic changes produced by ET-1 are mediated by vasoconstrictor prostanoids and/or prostanoid-like substances, possibly, 20-HETE via activation of ET(A) and ET(B) receptors. However, the increase in MBF is mediated by vasodilator prostanoids or by NO via ET(B) receptor activation.

Pathophysiology and management of renal insufficiency in the perioperative and critically ill patient

Acute renal failure remains a common, devastating complication of the postoperative period and in the critically ill patient. The most common cause is the progression of prerenal insufficiency to ATN. Despite improved understanding of the pathogenic mechanisms, including impaired hemodynamic autoregulation, medullary hypoxia, and proximal tubular obstruction and transtubular backleak, the treatment, to date, remains largely supportive. Avoidance by ensuring hemodynamic stability, with provision of adequate renal perfusion, provides the best means for minimizing the complications of this organ dysfunction.

Increased renal medullary endothelin-1 synthesis in prehypertensive DOCA- and salt-treated rats

To investigate the role of renal endothelin-1 (ET-1) synthesis in water-sodium homeostasis, we measured mRNA expressions, protein levels, enzyme activity, and receptor binding of the renal ET-1 system in a DOCA- and salt-treated rat model. Male Wistar rats were divided into control and DOCA- and salt-treated (DOCA-Salt) groups. The DOCA-Salt group received 25 mg/kg body wt DOCA and was maintained on 1% NaCl drinking water. Rats were killed on days 1, 2, 4, and 10 of the experiment. Urinary ET-1-like immunoreactivity significantly increased from the second day in the DOCA-Salt group and correlated well with the urinary sodium excretion rate (r = 0.81, P < 0.001). Renal endothelin-converting enzyme (ECE) activity, ET-1, and ECE-1 mRNA expressions were significantly increased in the renal medullary area of DOCA-Salt rats. In situ hybridization and immunohistochemical studies showed that the increase in ET-1 synthesis was mainly localized in the inner medullary collecting ducts. The maximum binding of endothelin B receptor also increased from the second day in the renal medulla of the DOCA-Salt group. Our results suggest that renal medullary synthesized ET-1 may be a natriuretic factor and may participate in the intrarenal regulation of water and salt homeostasis in prehypertensive DOCA-and salt-treated rats.

The renoprotective potential of endothelin receptor antagonists

The endothelin system has been identified as having a substantial role in renal failure, both acute and chronic. Beside its well characterised haemodynamic effects, its mitogenic and pro-fibrotic properties have gained increased interest in the pathophysiology of chronic renal failure. This review outlines the role of endothelin in the pathogenesis of various renal diseases with a special focus on the potential of blocking this system with endothelin receptor antagonists. So far, most data were derived from animal models, but they provide strong evidence that endothelin receptor antagonists may represent a powerful therapeutic strategy in ameliorating the course of acute and chronic renal failure.

Diuretic effect of hypoxia, hypocapnia, and hyperpnea in humans: relation to hormones and O(2) chemosensitivity

We studied the contributions of hypoxemia, hypocapnia, and hyperpnea to the acute hypoxic diuretic response (HDR) in humans and evaluated the role of peripheral O(2) chemosensitivity and renal hormones in HDR. Thirteen healthy male subjects (age 19-38 yr) were examined after sodium equilibration (intake: 120 mmol/day) during 90 min of normoxia (NO), poikilocapnic hypoxia (PH), and isocapnic hypoxia (IH) (days 1-3, random order, double blind), as well as normoxic voluntary hyperpnea (HP; day 4), matching ventilation during IH. O(2) saturation during PH and IH was kept equal to a mean level measured between 30 and 90 min of breathing 12% O(2) in a pretest. Urine flow during PH and IH (1.81 +/- 0.92 and 1.94 +/- 1.03 ml/min, respectively) but not during HP (1.64 +/- 0.96 ml/min) significantly exceeded that during NO (control, 1.38 +/- 0.71 ml/min). Urine flow increases vs. each test day's baseline were significant with PH, IH, and HP. Differences in glomerular filtration rate, fractional sodium clearance, urodilatin, systemic blood pressure, or leg venous compliance were excluded as factors of HDR. However, slight increases in plasma and urinary endothelin-1 and epinephrine with PH and IH could play a role. In conclusion, the early HDR in humans is mainly due to hypoxia and hypocapnia. It occurs without natriuresis and is unrelated to O(2) chemosensitivity (hypoxic ventilatory response).

Different roles of two types of endothelin receptors in partial ablation-induced chronic renal failure in rats

Recent work has drawn attention to endothelin as a likely contributor to renal pathogenesis. To elucidate the mechanism of progressive renal disease, we investigated the mRNA expression of endothelin and endothelin receptors, and the effect of endothelin ET(A), and/or ET(B) receptor antagonists on disease progression in the remnant kidney model. Proteinuria progressively increased in rats subjected to 5/6 nephrectomy (Nx) after 8 weeks (from 25+/-3 to 221+/-28 microg min(-1) kg(-1)). Creatinine clearance (Ccr) after renal ablation gradually decreased by 8 weeks (from 5.04+/-0.42 to 2. 68+/-0.26 ml min(-1) kg(-1)). Together with maximal proteinuria and decreased renal function, there was an increase in cortical mRNA expression of prepro endothelin-1 and endothelin ET(A) receptor expression, but a decrease in endothelin ET(B) receptor expression and in urinary excretion of endothelin-1. Administration (1-3 mg/day) of S-0139, (+)-disodium 27-[(E)-3-[2-[(E)-3-carboxylatoacryloylamino]-5-hydroxyphenyl]a crylay loxy]-3-oxoolean-12-en-28-oate, an endothelin ET(A) receptor-specific antagonist, had a beneficial effect on the evolution of the disease, preventing the appearance of intense proteinuria (113+/-11) and decreased Ccr (3.97+/-0.33). High blood pressure was observed in rats with 5/6 Nx and was decreased by S-0139 administration. To examine whether treatment modalities that decrease endothelin ET(B) receptor signaling have a deleterious effect on the kidney remnant, the effect of 97-618, an endothelin ET(B) receptor-specific antagonist, 4-tert-butyl-N-[5-(2-methoxyphenoxy)-6-(4-oxobutoxy)pyromidine+ ++-4-yl]b enzenesulfonamide, was also examined on the action of S-0139. Concomitant administration of S-0139 and 97-618 reversed the beneficial effect of S-0139 alone in the remnant kidney on proteinuria and renal functional impairment. These findings indicate that endothelin participates in the pathogenesis of proteinuria and glomerular injury and that an endothelin ET(A) receptor-specific antagonist could be useful in the treatment of some forms of human nephritis. The loss of endothelin ET(B) receptor seems to be important in the progression of renal disease.

Endothelin up-regulation and localization following renal ischemia and reperfusion

BACKGROUND

Endothelin (ET), a potent vasoconstrictor, is known to play a role in ischemic acute renal failure. Although preproET-1 (ppET-1) mRNA is known to be up-regulated following ischemia/reperfusion injury, it has not been determined which component of the injury (ischemia or reperfusion) leads to initial gene up-regulation. Likewise, although ET-1 peptide expression has been localized in the normal kidney, its expression pattern in the ischemic kidney has not been determined. Therefore, the purpose of this study was twofold: (a) to determine whether ischemia alone or ischemia plus reperfusion is required for the up-regulation of ppET-1 mRNA to occur, and (b) to localize ET-1 peptide expression following ischemia in the rat kidney to clarify better the role of ET in the pathophysiology of ischemia-induced acute renal failure.

METHODS

Male Lewis rats underwent clamping of the right renal vascular pedicle for either 30 minutes of ischemia (group 1), 60 minutes of ischemia (group 2), 30 minutes of ischemia followed by 30 minutes of reperfusion (group 3), or 60 minutes of ischemia followed by three hours of reperfusion (group 4). The contralateral kidney acted as a control. ppET-1 mRNA up-regulation and ET-1 peptide expression were examined using the reverse transcription-polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Reverse transcription-polymerase chain reaction yielded a control (nonischemic) value of 0.6 +/- 0.2 densitometric units (DU) of ppET-1 mRNA in the kidney. Group 1 levels (30 min of ischemia alone) were 1.8 +/- 0.4 DU, a threefold increase (P < 0.05). Group 2 levels (60 min of ischemia alone) increased almost six times above baseline, 3.5 +/- 0.2 DU (P < 0.01), whereas both group 3 and group 4 (ischemia plus reperfusion) did not experience any further significant increases in mRNA levels (1.9 +/- 0.4 DU and 2.8 +/- 0.6 DU, respectively) beyond levels in group 1 or 2 animals subjected to similar ischemic periods. ET-1 peptide expression in the ischemic kidneys was significantly increased over controls and was clearly localized to the endothelium of the peritubular capillary network of the kidney.

CONCLUSIONS

Initial ET-1 gene up-regulation in the kidney occurs secondary to ischemia, but reperfusion most likely contributes to sustaining this up-regulation. The marked increase of ET-1 in the peritubular capillary network suggests that ET-induced vasoconstriction may have a pathophysiological role in ischemic acute tubular necrosis.

Novel neuropeptides in the pathophysiology of heart failure: adrenomedullin and endothelin-1

The clinical success of neurohumoral manipulation by ACE inhibitors and beta blockers in heart failure has led to new therapeutic approaches. New neurohumoral factors are now viewed as offering the potential for treatment interventions. Not only do we consider blocking the production of deleterious hormones, but also, more recently, consideration has been given to augmenting the actions of factors with potentially beneficial actions. Hopefully such manipulation of ADM and ET-1 can result in further improvement in the well-being of heart failure patients.

Elevated neointimal endothelin-1 in transplantation-associated arteriosclerosis of renal allograft recipients

BACKGROUND

Chronic renal allograft rejection is characterized histologically by transplantation-associated arteriosclerosis and glomerulosclerosis (Tx-AA and Tx-AGS). Recent studies in animal models implicate the mitogenic and pressor actions of endothelin-1 (ET-1) in Tx-AA. In humans, however, a link between elevated ET-1 secretion and Tx-AA or Tx-AGS remains unclear. In this study we analyzed expression of ET-1 in the vasculature of renal transplant patients with chronic or acute rejection and in normal controls.

METHODS

Renal vascular and glomerular ET-1 was assessed by immunohistochemistry in 12 patients with clinically and histologically defined chronic rejection, in 11 patients with acute rejection, and in 5 normal kidneys. ET-1 staining was also correlated with various clinical parameters and with a morphometric index of neointima formation. ET-1 secretion was measured by ELISA in cultured human vascular cell types treated with T cell- and macrophage-associated cytokines.

RESULTS

We found that renal allografts with chronic rejection and Tx-AA expressed 6.1-fold more ET-1 in the vasculature relative to allografts with acute rejection or to normal kidneys (P < 0.01). In Tx-AA, ET-1 was detected predominantly in the neointima, which contained mostly endothelial cells and smooth muscle cells. A strong positive correlation (r = 0.82, P < 0.01) was observed between vascular ET-1 peptide expression and hypertension in patients with chronic rejection. We also showed that macrophage-associated cytokines, but not T cell-associated cytokines, stimulated ET-1 secretion in human endothelial cells, vascular smooth muscle and mesangial cells.

CONCLUSIONS

These results demonstrate that elevated ET-1 in the neointima is associated with Tx-AA and chronic rejection. In addition, these results point to an important role for endothelial dysfunction in chronic renal allograft rejection.

Improvement of postischemic acute renal failure with the novel orally active endothelin-A receptor antagonist LU 135252 in the rat

The endothelin (ET) system may play an important role in the pathogenesis of acute renal failure (ARF). We hypothesize that the course of ARF in an ischemia-reperfusion model will be markedly attenuated by the orally active ET(A)-receptor antagonist LU 135252 (LU) because of an improvement of renal perfusion. ARF was induced in rats by clamping both renal arteries for 60 min. The study was divided into two parts. In part 1, Rats received LU orally (100 mg/kg/day) starting 1 h after induction of ARF for 14 days. Cr(s), Cl(cr) and FE(na) were measured on days 1, 6, 9, and 14 after ARF. Cr(s) was lower in the treatment group on days 1 [1.3 +/- 0.31 mg/dl (n = 9) vs. 2.7 +/- 0.46 mg/dl (n = 10); p < 0.05] and 6 [0.5 +/- 0.1 mg/dl (n = 9) vs. 1.0 +/- 0.2 mg/dl (n = 9); p < 0.05], and Cl(cr) was higher on day 1 [0.9 +/- 0.17 ml/min (n = 9) vs. 0.2 +/- 0.1 ml/min (n = 8); p < 0.05] and 6 [1.8 +/- 0.29 ml/min (n = 9) vs. 1.0 +/- 0.21 ml/min (n = 9); p < 0.05] compared with vehicle. Additionally, FE(na) was lower in treated rats on day 1 [1 +/- 0.4% (n = 9) vs. 8 +/- 3% (n = 8); p < 0.051 compared with vehicle. In part 2, ARF was induced as described. Treated animals received 10 mg/kg LU on days 0, 1, 3, 6, 9, and 14 after ARF as an i.v. bolus injection. RBF, cortex blood flow (CBF), and medulla blood flow (MBF) were measured after application of LU on the same days: LU induced an increase in RBF (day 1: 14 +/- 5.3%, n = 6, p = 0.04; day 3: 15 +/- 2.8%, n = 8; p = 0.0008; day 6: 21 +/- 5.8%, n = 6, p = 0.02; day 9: 13 +/- 4%, n = 6; p = 0.03) and CBF (day 1: 8 +/- 2.2%, n = 7, p = 0.03; day 3: 7 +/- 2.5%, n = 7; p = 0.05; day 6: 18 +/- 4.8%, n = 6, p = 0.04; day 9: 10 +/- 2.5%, n = 6; p = 0.008) up to the first 9 days. MBF did increase on days 1 (9 +/- 3.1%, n = 6; p = 0.04) and 6 (13 +/- 3.6%, n = 6; p = 0.03). Our data confirm the hypothesis that ET plays a major role in the genesis of ARF associated with ischemia-reperfusion.