Endothelial dysfunction in acute renal failure: role of circulating and tissue endothelin-1

Synergistic effect of renalase and chronic kidney disease on endothelin-1 in patients with coronary artery disease ‒ a cross-sectional study

Endothelin-1 (ET-1) is associated with endothelial dysfunction and vasoconstriction. Increased circulating ET-1 levels are associated with long-term cardiovascular mortality. Renalase, released from kidney, metabolizes catecholamines and regulates blood pressure. An increase in circulating renalase levels has been reported in patients with chronic kidney disease (CKD) and is associated with coronary artery disease (CAD). We hypothesized the existence of a synergistic effect of serum renalase levels and CKD on ET-1 levels in patients with CAD. We evaluated 342 non-diabetic patients with established CAD. ET-1 and renalase levels were measured in all patients after an overnight fast. Patients with CKD had higher ET-1 (1.95 ± 0.77 vs. 1.62 ± 0.76 pg/ml, P < 0.001) and renalase levels (46.8 ± 17.1 vs. 33.9 ± 9.9 ng/ml, P < 0.001) than patients without CKD. Patients with both CKD and high renalase levels (>the median of 36.2 ng/ml) exhibited the highest serum ET-1 (P value for the trend <0.001). According to multivariate linear regression analysis, the combination of high serum renalase levels with CKD was a significant risk factor for increased serum ET-1 levels (regression coefficient = 0.297, 95% confidence interval = 0.063‒0.531, P = 0.013). In conclusion, our data suggest a synergistic effect of high serum renalase levels and CKD on increases in ET-1 levels in patients with established CAD.

Cyclosporine A induces endothelin-converting enzyme-1: Studies in vivo and in vitro

AIM

Cyclosporine A (CsA) induces renal vasoconstriction and hypoxia and enhances the expression of endothelin-1 (ET-1) pro-hormone (pre-pro-ET-1), plausibly leading to a feed-forward loop of renal vasoconstriction, hypoxia and enhanced synthesis of the potent vasoconstrictor ET-1. Endothelin-converting enzyme (ECE)-1 cleaves big endothelin to generate endothelin (ET)-1 and is upregulated by hypoxia via hypoxia-inducible factor (HIF). We hypothesized that in addition to the direct induction of ET-1 synthesis, CsA might also intensify renal ECE-1 expression, thus contributing to enhanced ET-1 synthesis following CsA.

METHODS

CsA was administered to Sprague Dawley rats (120 mg/kg/SC) for 4 days, and renal HIF and ECE-1 expression were assessed with Western blots and immunostaining. Human umbilical vein endothelial cells (HUVEC) and proximal tubular cell line (HK-2) were subjected to CsA, and ECE-1 induction was evaluated using real-time mRNA PCR and Western blots.

RESULTS

Cyclosporine A intensified renal parenchymal ECE-1 expression in the rat kidney, particularly in distal nephron segments, along with renal hypoxia (detected by pimonidazole adducts) and HIF expression, in line with our recent observations showing episodic hypoxia in mice subjected to CsA. Furthermore, in cultured normoxic HUVEC and HK-2 cells, CsA dose-dependently induced both pre-pro-ET-1 and ECE-1 mRNA and protein expression, with enhanced ET-1 generation.

CONCLUSION

CsA induces ECE-1 via both hypoxic and non-hypoxic pathways. ECE-1 may contribute to increased renal ET-1 generation following CsA, participating in a feed-forward loop of renal parenchymal hypoxia and ET synthesis.

Purtscher-like retinopathy associated with squamous cell carcinoma of the cervix

PURPOSE

To describe a previously unreported case of Purtscher-like retinopathy secondary to severe acute renal failure associated with squamous cell carcinoma of the cervix.

METHODS

This is a case report.

RESULTS

A 31-year-old female presented with a week history of acute abdominal pain, vomiting and severe renal failure followed by a sudden onset of bilateral visual loss. Vision was hand movement in either eye with central scotoma. Ophthalmic examination demonstrated bilateral retinal thickening and whitening with intraretinal hemorrhages localized to the peripapillary area, consistent with the diagnosis of Purtscher-like retinopathy. Further systemic examination revealed bilateral hydronephrosis secondary to underlying undiagnosed cervical carcinoma. Patient was treated with a short course of high-dose steroids. At 2 months, patient vision remained poor despite the resolution of retinal edema and hemorrhages.

CONCLUSIONS

This case serves as the first report of Purtscher-like retinopathy secondary to acute renal failure associated with cervical carcinoma, expanding the list of causes of Purtscher's or Purtscher-like retinopathies. In the presence of significant uremia and absence of previously known association, the authors postulate that the sudden surge of uremia causes increase of endothelin-1 (a potent vasoconstrictor), resulting in downstream endothelin-induced vasculopathy with subsequent occlusion of the pre-capillary arteriolar network.

Proton Pump Inhibitors Are Not Associated With Acute Kidney Injury in Critical Illness

Recent epidemiologic data linking proton pump inhibitor (PPI) use to acute and chronic kidney dysfunction is yet to be validated in other populations, and mechanisms have not been explored. Using a large, well phenotyped inception cohort of 15 063 critically ill patients, we examined the risk of acute kidney injury (AKI), as defined by the Kidney Disease Improving Global Outcomes criteria guidelines, according to prior use of a PPI, histamine-2 receptor antagonist (H₂ RA), or neither. A total of 3725 (24.7%) patients reported PPI use prior to admission, while 905 (6.0%) patients reported H₂ RA use. AKI occurred in 747 (20.0%) and 163 (18.0%) of PPI and H₂ RA users respectively, compared to 1712 (16.2%) of those not taking acid suppressive medications. In unadjusted analysis, PPI and H₂ RA users had a 28% (95%CI 1.17-1.41, P < .001) and 10% (95%CI 0.91-1.30, P = .31) higher risk of AKI compared to those taking neither class of medication. However, in sequential models that included adjustment for demographics, cardiovascular comorbidities, indications for PPI use, and severity of illness, the effect of PPI on the risk of AKI was attenuated, and in the adjusted analysis, PPI was not associated with AKI (OR 1.02; 95%CI 0.91-1.13, P = .73). The presence of sterile pyuria and hypomagnesemia did not modify the association between PPI use and AKI. In summary, after adjustment for demographics, illness severity, and the indication for PPI use, PPI use prior to admission is not associated with critical illness AKI.

Endothelin and the renal microcirculation

Endothelin (ET) is one of the most potent renal vasoconstrictors. Endothelin plays an essential role in the regulation of renal blood flow, glomerular filtration, sodium and water transport, and acid-base balance. ET-1, ET-2, and ET-3 are the three distinct endothelin isoforms comprising the endothelin family. ET-1 is the major physiologically relevant peptide and exerts its biological activity through two G-protein-coupled receptors: ET(A) and ET(B). Both ET(A) and ET(B) are expressed by the renal vasculature. Although ET(A) are expressed mainly by vascular smooth muscle cells, ET(B) are expressed by both renal endothelial and vascular smooth muscle cells. Activation of the endothelin system, or overexpression of downstream endothelin signaling pathways, has been implicated in several pathophysiological conditions including hypertension, acute kidney injury, diabetic nephropathy, and immune nephritis. In this review, we focus on the effects of endothelin on the renal microvasculature, and update recent findings on endothelin in the regulation of renal hemodynamics.

Preventive Role of Endothelin Antagonist on Kidney Ischemia: Reperfusion Injury in Male and Female Rats

Background:

Renal ischemia/reperfusion injury (RIRI) is the most common cause of acute kidney injury. We tested the protective role of endothelin-1 receptor blocker; bosentan (BOS) in animal model of RIRI in two different genders.

Methods:

Male and female Wistar rats were assigned as sham operated (sham), control group (ischemia), and case group (ischemia + BOS) treated with BOS (50 mg/kg) 2 h before bilateral kidney ischemia induced by clamping renal vessels for 45 min followed by 24 h of renal reperfusion.

Results:

The RIRI significantly increased the serum levels of blood urea nitrogen and creatinine in both genders (P < 0.05). These values were significantly decreased by BOS in both genders. In male rats, the serum levels of malondialdehyde in the ischemia + BOS group were decreased significantly when compared with ischemia group (P < 0.05).

Conclusions:

BOS can be used in both genders to attenuate kidney ischemia injury possibly due to its effect in the renal vascular system.

Exercise interventions and peripheral arterial function: implications for cardio-metabolic disease

Physical inactivity is a major risk factor for the development of obesity and other cardiovascular (CV) disease (CVD). Vascular endothelial dysfunction is a key event in the development of CVD and is associated with a sedentary lifestyle in otherwise healthy adults. In addition, vascular endothelial dysfunction may be exacerbated in sedentary individuals who are obese and insulin resistant, since excess body fat is associated with elevated levels of pro-atherogenic inflammatory adipokines and cytokines that reduce the nitric oxide (NO) and other upstream paracrine signaling substances which reduces vascular health. Since blood flow-related shear stress is a major stimulus to NO release from the endothelium, disturbed flow or low shear stress is the likely mechanism by which vascular endothelial function is altered with inactivity. Evidence shows that regular physical exercise has beneficial effects on CVD and the risk factors that promote peripheral arterial function and health. Both aerobic and resistance exercise training are generally believed to improve endothelial function and are commonly recommended for CV health, including the management of obesity, hypertension, and insulin resistance. However, many factors including age, disease status, and race appear to influence these outcomes. Although evidence supporting the health benefits of exercise is compelling, the optimum prescription (volume and intensity) and the exact mechanism underlying the effects of exercise training on arterial function and cardiometabolic risk has yet to be identified. The focus of this review will be on the evidence supporting exercise interventions for peripheral arterial function.

Endothelin and the podocyte

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Expression of adrenomedullin 2/intermedin, a possible reno-protective peptide, is decreased in the kidneys of rats with hypertension or renal failure

Adrenomedullin 2/intermedin (AM2/IMD) is a potent vasodilator peptide with organ-protective effects and is abundantly expressed in the kidney. We examined the expression of AM2/IMD in the kidneys of rats with hypertension or chronic renal impairment using quantitative RT-PCR, radioimmunoassay, and immunohistochemistry. Kidneys of 8-wk-old male spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were dissected into inner medulla, outer medulla, cortex, and glomerulus fractions. A rat renal impairment model was prepared by 5/6 nephrectomy in WKY rats. AM2/IMD mRNA levels were the highest in the cortex among four renal portions, and significantly lower in SHR than WKY rats in all renal portions. In the remnant kidneys of 5/6 nephrectomized rats, AM2/IMD mRNA levels were significantly decreased on days 3 and 56, whereas mRNA levels of calcitonin receptor-like receptor, receptor activity-modifying proteins-1 and -2, which form receptor for AM and AM2/IMD, were increased, compared with that in sham-operated rats. AM mRNA levels were decreased on day 3, but increased on day 56, after nephrectomy. Decreased immunoreactive AM2/IMD levels in the remnant kidneys of 5/6 nephrectomized rats on day 56 were confirmed by radioimmunoassay. The renal tubules were immunostained with anti-AM2/IMD antibody, with a decreased AM2/IMD immunostaining found in proximal tubular cells of 5/6 nephrectomized rats compared with sham-operated rats. In conclusion, intrarenal AM2/IMD expression is decreased in SHR and 5/6 nephrectomized rats. Given the organ-protective effects of AM2/IMD, the downregulation of AM2/IMD as an endogenous regulatory peptide may have a role in the progression of renal impairment.

Impaired blood flow in acute kidney injury: pathophysiology and potential efficacy of intrarenal vasodilator therapy

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common complication of hospitalized patients and associated with significant morbidity and mortality. Numerous studies have documented that acute reductions in glomerular filtration rates are associated with significant in-hospital mortality. Moreover, patients progressing to dialysis-dependent AKI can have mortality rates that exceed 60%. The pathophysiology of AKI is unknown, but marked reductions in corticomedullary blood flow leads to significant reductions in glomerular filtration rate during early phases of the disease. The recognition that hypoperfusion of the outer medulla is common to many forms of AKI and contributes to tubular ischemia has led many investigators to re-examine the use of vasodilators to restore blood flow and stabilize renal function.

RECENT FINDINGS

Numerous prospective trials have studied the efficacy of various vasoactive compounds with primarily negative results. However, trial designs that failed to fully examine the dose response of many investigational agents contributed to the development of systemic hypotension, thus offsetting potential benefits of the treatment. Emerging devices that allow for intrarenal administration of drugs have led to the concept of 'targeted renal' prophylaxis and treatment. The rationale is that local renal administration can improve the safety profile of many vasoactive agents. Recent studies confirm that higher doses of fenoldopam or other vasodilators can be administered intrarenally without the development of systemic hypotension.

SUMMARY

Previous trials utilizing vasodilator therapy to stabilize renal function in AKI have given conflicting results. This study will critically review trial design and dose selection used in previous studies of vasodilator therapy in AKI. Lastly, the potential for high-dose therapy using intrarenal drug delivery systems will be discussed.

Acute kidney injury in children

Acute kidney injury (AKI) (previously called acute renal failure) is characterized by a reversible increase in the blood concentration of creatinine and nitrogenous waste products and by the inability of the kidney to regulate fluid and electrolyte homeostasis appropriately. The incidence of AKI in children appears to be increasing, and the etiology of AKI over the past decades has shifted from primary renal disease to multifactorial causes, particularly in hospitalized children. Genetic factors may predispose some children to AKI. Renal injury can be divided into pre-renal failure, intrinsic renal disease including vascular insults, and obstructive uropathies. The pathophysiology of hypoxia/ischemia-induced AKI is not well understood, but significant progress in elucidating the cellular, biochemical and molecular events has been made over the past several years. The history, physical examination, and laboratory studies, including urinalysis and radiographic studies, can establish the likely cause(s) of AKI. Many interventions such as 'renal-dose dopamine' and diuretic therapy have been shown not to alter the course of AKI. The prognosis of AKI is highly dependent on the underlying etiology of the AKI. Children who have suffered AKI from any cause are at risk for late development of kidney disease several years after the initial insult. Therapeutic interventions in AKI have been largely disappointing, likely due to the complex nature of the pathophysiology of AKI, the fact that the serum creatinine concentration is an insensitive measure of kidney function, and because of co-morbid factors in treated patients. Improved understanding of the pathophysiology of AKI, early biomarkers of AKI, and better classification of AKI are needed for the development of successful therapeutic strategies for the treatment of AKI.

[Endothelin-1 production and its involvement in cardiovascular diseases]

Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

Endothelin-1-mediated inflammation in acute renal failure

Acute renal failure presents a serious and life-threatening problem in hospitalized patients. Current therapies address the systemic alterations in renal failure. Cellular changes also occur. These changes affect the glomerular filtration rate and the integrity of the glomerular membrane. ET-1, the most potent vasoconstrictor known, has a negative effect on both the rate of filtration and the integrity of the filtering membrane in renal failure. Using ET-1 antagonists along with the current therapies may prove useful in patients.

Perioperative acute renal failure

PURPOSE OF REVIEW

Recent biochemical evidence increasingly implicates inflammatory mechanisms as precipitants of acute renal failure. In this review, we detail some of these pathways together with potential new therapeutic targets.

RECENT FINDINGS

Neutrophil gelatinase-associated lipocalin appears to be a sensitive, specific and reliable biomarker of renal injury, which may be predictive of renal outcome in the perioperative setting. For estimation of glomerular filtration rate, cystatin C is superior to creatinine. No drug is definitively effective at preventing postoperative renal failure. Clinical trials of fenoldopam and atrial natriuretic peptide are, at best, equivocal. As with pharmacological preconditioning of the heart, volatile anaesthetic agents appear to offer a protective effect to the subsequently ischaemic kidney.

SUMMARY

Although a greatly improved understanding of the pathophysiology of acute renal failure has offered even more therapeutic targets, the maintenance of intravascular euvolaemia and perfusion pressure is most effective at preventing new postoperative acute renal failure. In the future, strategies targeting renal regeneration after injury will use bone marrow-derived stem cells and growth factors such as insulin-like growth factor-1.

Influence of Acute Renal Failure on Coronary Vasoregulation in Dogs

Impaired renal function is associated with an increased risk for cardiovascular events and death, but the pathophysiology is poorly defined. The hypothesis that coronary blood flow regulation and distribution of ventricular blood flow could be compromised during acute renal failure (ARF) was tested. In two separate groups (n = 14 each) of dogs with ARF, (1) coronary autoregulation (pressure-flow relations), vascular reserve (reactive hyperemia), and myocardial blood flow distribution (microspheres) and (2) coronary vessel responses to intracoronary infusion of select endothelium-dependent and -independent vasodilators were evaluated. In addition, coronary pressure-flow relations and vascular reserve after inhibition of nitric oxide and prostaglandin release were evaluated. Under resting conditions, myocardial oxygen consumption increased in dogs with ARF compared with no renal failure (NRF; 11.8 +/- 9.2 versus 5.0 +/- 1.5 ml O(2)/min per 100 g; P = 0.01), and the autoregulatory break point of the coronary pressure-flow relation was shifted to higher diastolic coronary pressures (60 +/- 17 versus 52 +/- 8 mmHg in NRF; P = 0.003); the latter was shifted further rightward after inhibition of both nitric oxide and prostaglandin release. The endocardial/epicardial blood flow ratio was comparable for both groups, suggesting preserved ventricular distribution of blood flow. In dogs with ARF, coronary vascular conductance also was reduced (P = 0.001 versus NRF), but coronary zero-flow pressure was unchanged. Vessel reactivity to each endothelium-dependent/independent compound also was blunted significantly. In conclusion, under resting conditions, coronary vascular tone, reserve, and vessel reactivity are markedly diminished with ARF, suggesting impaired vascular function. Consequently, during ARF, small increases in myocardial oxygen demand would induce subendocardial ischemia as a result of a limited capacity to increase oxygen supply and thereby contribute to higher risk for adverse coronary events and mortality.

Increased endothelin 1 expression in adult-onset minimal change nephropathy with acute renal failure

BACKGROUND

Acute renal failure (ARF) occurs in some adult patients with minimal change nephropathy (MCN). To investigate clinical and pathological factors associated with developing ARF, we compared clinical features and kidney pathological characteristics of endothelin 1 (ET-1) expression in patients with adult-onset MCN with and without ARF.

METHODS

The patient population consisted of 53 patients consecutively diagnosed with adult-onset MCN during a 10-year period. Based on creatinine clearance, 25 patients were assigned to the ARF group and 28 patients were assigned to the non-ARF group.

RESULTS

Clinical data show that the ARF group had a higher blood pressure, higher serum cholesterol level, and lower serum albumin level than the non-ARF group. Pathological data showed more severe foot-process effacement, interstitial edema, and flattened tubular epithelium in the same group. Greater ET-1 expression was detected in vessels, tubules, and glomeruli of the ARF compared with non-ARF group. The ARF group experienced a lower steroid response rate. However, there was no significant difference in stability of remission to steroid treatment in patients who achieved a remission.

CONCLUSION

ARF associated with enhanced kidney ET-1 expression is a reversible complication of MCN that occurs frequently in patients with apparently expanded extracellular fluid. Presumptively, ARF may develop as an amplification of the underlying pathogenesis of MCN involved in enhanced ET-1 expression, which may be superimposed by a transient episode of circulatory insufficiency during diuretic treatment.

Endothelin activation and postoperative renal failure after human liver transplantation

Renal failure is an established risk factor for impaired patient outcome after orthotopic liver transplantation (OLT). As the endothelin pathway is known to be involved in the development of acute renal failure (ARF), we designed a study to clarify its role in ARF following OLT. Twenty consecutive patients with intact kidney function scheduled for their first OLT were prospectively studied. Plasma big endothelin-1 (ET-1) levels were measured before surgery, after graft reperfusion, and on the first and second postoperative day. According to postoperative glomerular filtration rate (GFR), patients were assigned to the acute renal dysfunction group (ARDF) and the non-ARDF group. Each patient's GFR was estimated according to the 4-variable formula used in the modification of diet in renal disease before surgery, daily within the first postoperative week, and at 1, 3, 12, and 24 months after surgery. Postoperative mean big ET-1 levels correlated significantly with the maximum percent decrease of GFR within 3 days after OLT (P < 0.01). The proportion of patients who developed ARDF was significantly correlated to mean postoperative big ET-1 quartiles (P < 0.01). In the ARDF group, the percent decrease of GFR within 24 months was significantly higher (P < 0.05) as compared to the non-ARDF group. In conclusion, patients who develop ARDF immediately after OLT do not fully recover to baseline regarding long-term kidney function. Short-term GFR was significantly correlated with postoperative big ET-1 plasma levels, suggesting renal dysfunction is mediated by the activated endothelin system.

Asymmetrical dimethylarginine plasma concentrations are related to basal nitric oxide release but not endothelium-dependent vasodilation of resistance arteries in peritoneal dialysis patients

Vascular dysfunction in chronic renal failure may be linked to reduced nitric oxide (NO) bioactivity and increased circulating concentrations of the endogenous NO synthase inhibitor asymmetrical dimethyl L-arginine (ADMA). The association between ADMA and basal endothelial NO release and endothelium-dependent vasodilation in resistance arteries of chronic renal failure patients is unknown. Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine, the endothelium-independent vasodilator nitroglycerine, and the endothelium-dependent vasoconstrictor N(G)-monomethyl-L-arginine (L-NMMA) were assessed in 37 peritoneal dialysis patients. L-arginine and ADMA plasma concentrations were measured by HPLC. ADMA (mean +/- SEM: 0.68 +/- 0.02 micromol/L) was associated with basal forearm blood flow (r = -0.33; P < 0.05) and L-NMMA induced vasoconstriction (r = -0.55; P < 0.0005), but not with dilator effects of acetylcholine or nitroglycerine. L-arginine (68 +/- 3 micromol/L) tended to correlate with acetylcholine-induced vasodilation (r = 0.32; P = 0.05) but was not associated with other parameters. ADMA is related to basal but not to acetylcholine-stimulated NO bioactivity in patients on peritoneal dialysis. Impaired endothelium-dependent vasodilation found in chronic renal failure is not explained by elevated circulating NO synthase inhibitors in renal failure.

Endothelin receptor blockade during hypothermic perfusion preservation mitigates the adverse effect of preretrieval warm ischemic injury on posttransplant glomerular filtration rate

BACKGROUND

Preretrieval warm ischemic injury predisposes to both short-term and long-term dysfunction of cadaveric renal allografts. We previously reported that the excretion of the vasoactive peptide, endothelin (ET), is significantly increased during hypothermic perfusion preservation (HPP) of kidneys subjected to preretrieval warm ischemia compared with nonischemic controls. As such, the purpose of this study was to determine if endothelin receptor (ET-R) blockade during HPP would improve glomerular filtration rate (GFR) of kidneys subjected to preretrieval warm ischemia when measured in situ at 2 weeks after transplantation (Tx).

METHODS

The left kidney was retrieved from 300-g Lewis rats after in situ cold perfusion and transplanted after 2 hr of HPP. A 30-min period of preretrieval warm ischemia was induced. Kidneys were divided into four groups: nonischemic controls (n=9), ischemic (isch) kidneys not receiving ET-R blockade during HPP (n=7), isch kidneys receiving the ETA receptor antagonist (n=7), and isch kidneys receiving the ETA/B receptor antagonist (n=8). ET-R blockade was induced by adding the ETA, A-147627, or the ETA/B, A-182086, receptor antagonist (Abbott Laboratories, Abbott Park, IL) directly to the preservation solution (5x10-6M). The kidneys were then isografted into genetically identical Lewis rats and GFR, determined by measurement of urinary iohexol clearance, measured 2 weeks after Tx.

RESULTS

Two-week GFRs (mL/min) for each of the study cohorts are as follows: nonischemic controls, 1.18+/-0.11; ischemic (isch) only, 0.57+/-0.08 (P< or =0.05 vs. nonischemic controls); isch + ETA blockade, 0.95+/-0.15 (P< or =0.05 vs. isch only); isch + ETA/B blockade, 0.90+/-0.08 (P< or =0.05 vs. isch only).

CONCLUSION

Addition of an ETA, A-147627, or an ETA/B, A-182086, receptor antagonist to preservation solution used during HPP of kidneys subjected to preretrieval warm ischemia resulted in a normalization of GFR measured 2 weeks after Tx. The data provide a basis for further investigation of the impact of ET-R blockade on both the short- and long-term adverse effects of preretrieval warm ischemic injury in cadaveric renal Tx.

Acute renal failure

Acute renal failure is characterized by an increase in the blood concentration of creatinine and nitrogenous waste products and by the inability of the kidney to appropriately regulate fluid and electrolyte homeostasis. There are many different causes of acute renal failure in children, including prerenal disease, intrinsic renal failure, which includes ischemic hypoxic insults, and obstructive uropathy. This review will focus on hypoxic/ischemic acute renal failure, the most common causes of hospital acquired acute renal failure in children. This review will briefly discuss the epidemiology and incidence of acute renal failure in pediatric patients and review new insights into the pathogenesis of acute renal failure. including hemodynamic alterations induced by alterations in nitric oxide and endothelin metabolism, the role of the inflammatory response, and alteration in polarity in the acute renal failure. The therapy of acute renal failure has changed substantially during the past few years. Controlled trials (in adults) to test the efficacy of "renal dose" dopamine have shown that it is ineffective, and hemofiltration has become increasingly popular as a choice of therapy for acute renal failure.

Acute renal failure in children: aetiology and management

This review evaluates the various causes and management of acute renal failure (ARF) in children. ARF is defined as an abrupt decline in the renal regulation of water, electrolytes and acid-base balance, and continues to be an important factor contributing to the morbidity and mortality of critically ill infants and children. The common causes of ARF in children include acute tubular necrosis secondary to various causes (including congestive heart failure and sepsis), haemolytic uremic syndrome, and glomerulonephritis and urinary tract obstruction. Ischaemia, toxins (including drugs) as well as primary parenchymal disease, have to be considered and ARF can also be a complication of systemic disease. The basic principles of management are avoidance of life-threatening complications, maintenance of fluid and electrolyte balance, and nutritional support. Only a few patients require specific management of the underlying disorder, although it is important to diagnose these conditions. Knowledge about the use of drugs for the prevention of ARF is scarce. Mannitol, low-dose dopamine, calcium channel antagonists, atrial natriuretic peptide and albumin have been evaluated and, where possible, meta-analyses are cited. Mannitol treatment appears to be warranted prophylactically after paediatric renal transplantation. Albumin infusion can reverse prerenal ARF in children with nephritic syndrome. For treatment of the complications of hyperkalaemia and volume overload, salbutamol, insulin and glucose infusion and diuretics such as furosemide and sodium bicarbonate, are discussed. All of the major dialysis modalities (peritoneal dialysis, haemodialysis and continuous haemofiltration) can be used to provide equivalent solute clearance and ultrafiltration. The indication for, and the choice of the modality depend on the patient requirements and on local resources, and should involve the care of a paediatric nephrologist. Peritoneal dialysis requires minimal equipment and infrastructure, is easy to perform and remains the favoured modality of renal replacement therapy in children. However, continuous haemofiltration is an excellent alternative to peritoneal dialysis in patients with ARF and severe fluid overload. Dialysis remains the most important tool to bridge the time needed for recovery of renal function. There is increasing evidence that more intense use of dialysis may improve the overall prognosis.

S3226, a novel NHE3 inhibitor, attenuates ischemia-induced acute renal failure in rats

BACKGROUND

Acute renal failure (ARF) remains a major problem in clinical nephrology characterized by sudden loss of the kidney function due to ischemia, trauma, and/or nephrotoxic drugs. The current therapy of ARF is symptomatic with mortality rates exceeding 50%. The aim of this study was to investigate the effects of an intravenous infusion of S3226 (3-[2-(3-guanidino-2-methyl-3-oxopropenyl)-5-methyl-phenyl]-N-isopropylidene-2-methyl-acrylamide dihydrochloride), a selective Na+/H+ exchange subtype 3 (NHE3) blocker, in ischemia-induced ARF in rats. In a second series of experiments cytosolic pH (pHi) changes in the kidney during ARF were continuously measured by means of nuclear magnetic resonance spectroscopy (MRS).

METHODS

ARF was induced by bilateral occlusion of renal arteries for 40 minutes in three groups of anaesthetized Wistar rats. Control rats (N = 12) were infused with saline (6.25 mL/kg over 30 min) before occlusion and the compound groups (each N = 12) were infused with S3226 at a dose of 20 mg/kg over 30 minutes either before initiation of ischemia or immediately after release of clamps. Plasma creatinine (PCr), creatinine clearance (CCr), urine volume, sodium, and potassium excretion were determined up to seven days after release of clamps. In the second series of experiments in anaesthetized rats the left kidney was exposed by flank incision and fixed in a non-magnetic device. An inflatable cuff was positioned around the pedicle to induce ischemia without removing animals from the magnet. A double-tuned 1H-31P home-built surface coil was placed above the exposed kidney for the detection of pHi.

RESULTS

At day 1 after ischemia CCr in the control group was significantly lower as compared to S3226-treated animals (control 0.30 +/- 0.05 vs. before 0.90 +/- 0.26 and reperfusion 0.83 +/- 0.15 mL/min/kg, respectively). PCr increased from 18 +/- 0.1 micromol/L before occlusion to 245 +/- 7 micromol/L in the control. The increase in PCr was significantly lower in the S3226 treated groups on days 1, 2, and 3 post-infusion. Fractional sodium excretion decreased significantly from 8.17% in the control to 1.42% and 1.88% in the treated groups. Renal pHi was significantly decreased by 0.15 units versus control during reperfusion. Histological examination of the kidneys on day 7 revealed pronounced reduction of tubular necrosis, dilatation, protein casts and cellular infiltration.

CONCLUSIONS

These results demonstrate that an intravenous administration of S3226 acutely improves GFR and kidney function and structure in both treated groups. In addition, in a separate set of studies S3226 significantly decreased post-occlusion renal pHi values. Thus, the inhibition of NHE3 with S3226 may be beneficial in treatment of ischemic ARF.

Amelioration of post-ischaemic renal injury by contralateral uninephrectomy: a role of endothelin-1

BACKGROUND

Previous studies showed that unilateral renal damage is attenuated by prior contralateral uninephrectomy (Nx) in ischaemia-induced acute renal failure (ARF). Since renal ischaemia increases endothelin-1 (ET-1) production in the kidney, we examined whether the alteration of renal ET-1 content may contribute to the nephrectomy-induced attenuation of renal injury.

METHODS

Ischaemic renal injury was provoked by 60-min left renal artery occlusion (RAO). Removal of the right kidney was performed just before RAO in the Nx group. Forty-eight hours after release of the clamp, renal ET-1 content was measured in both non-nephrectomized and unilaterally nephrectomized rats. We also examined the effects of a selective ET(A) receptor (FR139317) and monoclonal ET antibody (AwETN40) on the RAO-induced changes in renal haemodynamics at 2 and 48 h after RAO respectively.

RESULTS

The plasma concentration of ET-1 did not change in the two groups of ARF rats, but the cortical content of ET-1 increased to a lesser extent in Nx animals after ischaemia. Prior removal of the right kidney significantly facilitated the percentage recovery of left renal blood flow (RBF) during the first 2 h after release of the clamp. The percentage recovery of inulin clearance (Cin) by the kidney was also significantly better in Nx than sham-Nx rats at 48 h after RAO. Continuous administration of FR139317 (50 mg/kg/day) using osmotic minipumps for 3 days significantly attenuated exogenous ET-1-induced decrease in Cin and RBF. Infusion of FR139317 restored the decrease in RBF to control values during first 2 h in sham-Nx rats. However, FR139317 and AwETN40 did not ameliorate the RAO-induced decline of Cin in sham-Nx or Nx rats at 2 and 48 h after ischaemia respectively.

CONCLUSIONS

Contralateral uninephrectomy prior to ischaemia-induced ARF attenuated the increase in cortical ET-1 content and subsequent renal response to ischaemic injury. This beneficial effect of unilateral nephrectomy, however, was not mediated through well-preserved RBF due to reduced intrarenal ET-1 action.

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.

Endothelial dysfunction and xanthine oxidoreductase activity in rats with human renin and angiotensinogen genes

We examined whether xanthine oxidoreductase (XOR), a hypoxia-inducible enzyme capable of generating reactive oxygen species, is involved in the onset of angiotensin (Ang) II-induced vascular dysfunction in double-transgenic rats (dTGR) harboring human renin and human angiotensinogen genes. In 7-week-old hypertensive dTGR, the endothelium-mediated relaxation of noradrenaline (NA)-precontracted renal arterial rings to acetylcholine (ACh) in vitro was markedly impaired compared with Sprague Dawley rats. Preincubation with superoxide dismutase (SOD) improved the endothelium-dependent vascular relaxation, indicating that in dTGR, endothelial dysfunction is associated with increased superoxide formation. Preincubation with the XOR inhibitor oxypurinol also improved endothelium-dependent vascular relaxation. The endothelium-independent relaxation to sodium nitroprusside was similar in both strains. In dTGR, serum 8-isoprostaglandin F(2alpha), a vasoconstrictor and antinatriuretic arachidonic acid metabolite produced by oxidative stress, was increased by 100%, and the activity of XOR in the kidney was increased by 40%. Urinary nitrate plus nitrite (NO(x)) excretion, a marker of total body NO generation, was decreased by 85%. Contractile responses of renal arteries to Ang II, endothelin-1 (ET-1), and NA were decreased in dTGR, suggesting hypertension-associated generalized changes in the vascular function rather than a receptor-specific desensitization. Valsartan (30 mg/kg PO for 3 weeks) normalized blood pressure, endothelial dysfunction, and the contractile responses to ET-1 and NA. Valsartan also normalized serum 8-isoprostaglandin F(2alpha) levels, renal XOR activity, and, to a degree, NO(x) excretion. Thus, overproduction of Ang II in dTGR induces pronounced endothelial dysfunction, whereas the sensitivity of vascular smooth muscle cells to nitric oxide is unaltered. Ang II-induced endothelial dysfunction is associated with increased oxidative stress and vascular xanthine oxidase activity.

Cell biology and molecular mechanisms of injury in ischemic acute renal failure

The pathogenesis of acute renal failure has been attributed to persistent vasoconstriction and leukocyte-endothelial interactions, resulting in inflammation and compromise of local blood flow to the outer medulla, the loss of tubular epithelial cell polarity with multiple functional sequelae, necrosis or apoptosis of epithelial cells, and the de-differentiation, migration and proliferation of surviving cells. In this paper, the authors present their views of pathophysiology of ischemic acute renal failure.

Regulatory peptides and their antagonists in nephropathies

Many peptides influence renal function and structure in physiological and pathophysiological situations. Bioactive peptides that regulate renal function and structure encompass various substances including vasopeptides, growth factors, cytokines and peptide hormones. We highlight some novel concepts indicating that the vasoactive peptides angiotensin II and endothelin-1 play a major role in the progression of renal disease. These effects may be amplified by reduced concentration of counteracting natriuretic peptides. In addition, recent evidence suggests that peptides such as leptin, previously not considered to exert any renal effects, may be involved in renal pathophysiology under certain conditions. One of the most imperative tasks in nephrology is to develop innovative strategies to slow the progression of chronic renal disease. Interference with the renal action of bioactive peptides will certainly be part of this strategy.

Angiotensin converting enzyme inhibitors and vascular protection in hypertension

Strategically located between the circulating blood and the vascular smooth muscle, endothelial cells release numerous vasoactive substances regulating the function of vascular smooth muscle and circulating blood cells. Endothelium-derived vasodilators include prostacyclin, nitric oxide and endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin, nitric oxide exerts potent antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by vasoconstrictors, such as angiotensin II and endothelin (ET)-1, both of which exert prothrombotic and growth-promoting properties. In hypertension, elevated blood pressure causes vascular disease by inducing endothelial dysfunction. Hence, modern therapeutic strategies in human hypertension focus on preserving or restoring endothelial integrity. Beyond inhibiting the renin-angiotensin system, angiotensin-converting enzyme (ACE) inhibitors diminish the inactivation of bradykinin, thus leading to an augmentation of nitric oxide release. In addition, the compounds stabilize the B2-receptor, and reduce oxidative stress and tissue ET-1 levels. In patients with coronary artery disease, chronic ACE inhibition improves endothelial function. Further clinical studies are already under way which will prove whether these beneficial vascular effects of ACE inhibitors on endothelial dysfunction result in a clinical benefit for patients with hypertension.