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

Male Patients may be More Vulnerable to Acute Kidney Injury After Colorectal Surgery in an Enhanced Recovery Program: A Propensity Score Matching Analysis

BACKGROUND

Although many reports have shown that enhanced recovery after surgery (ERAS) programs improve the perioperative outcomes of patients undergoing colorectal surgery, the prevalence of early acute kidney injury (AKI) after surgery in such patients requires attention. Protective roles of the female sex in terms of chronic kidney disease and progression of ischemic renal injury have been described in many studies. We thus explored whether a sex difference was evident in terms of postoperative AKI in a colorectal ERAS setting.

METHODS

From January 2017 to August 2019, 453 patients underwent laparoscopic colorectal cancer resection in an enhanced recovery program. Of these, 217 female patients were propensity score (PS)-matched with 236 male patients. Then, 215 patients of either sex were compared in terms of postoperative renal function and complications.

RESULTS

Among the PS-matched patients, the incidence of AKI was significantly higher in male than female patients (24.2% vs. 9.8%, P < 0.001). Male patients also exhibited a greater reduction in the postoperative estimated glomerular filtration rate, compared with female patients. The male sex was associated with an approximately threefold increase in the risk of AKI. The rate of surgical complications was significantly higher in male than female patients.

CONCLUSIONS

Caution must be taken to prevent postoperative AKI in patients (particularly males) participating in colorectal ERAS programs. The mechanism underlying the sex difference remains unclear. Additional studies are required to determine whether male patients require perioperative management that differs from that of females, to prevent postoperative AKI.

Effects of endothelin receptor blockade and COX inhibition on intestinal I/R injury in a rat model: Experimental research

BACKGROUND

Intestinal ischemia is a highly morbid and mortal condition with no specific treatment. The present study aimed to investigate the effects of cyclooxygenase (COX) inhibition synchronized with nitric oxide (NO) release and endothelin (ET) receptor blockade on oxidative stress, inflammation, vasoconstriction, and bacterial translocation which occur during ischemia-reperfusion (I/R) injury in in-vivo rat intestinal I/R model.

MATERIALS AND METHODS

36 male Wistar rats were randomly divided into six groups (n = 6). Superior mesenteric artery blood flow (SMABF) was recorded; SMA was occluded for 30 min; SMABF was re-recorded at the beginning of the reperfusion phase. Rats were sacrificed after the reperfusion period of 60 min. Blood and tissue samples were obtained. Acetylsalicylic acid (ASA), NO-ASA, flurbiprofen (FLUR), and Tezosentan (TS) were administered 15 min after ischemia. Histopathological examination, bacterial translocation, and biochemical analysis were performed in plasma and tissue samples.

RESULTS

SMABF difference, mean Chiu's score and bacterial translocation were increased in the I/R group and decreased in the treatment groups. Plasma LDH, transaminases, intestinal fatty acid-binding protein (I-FABP), TNF-α, ICAM-1, interferon-gamma (IFN-Ɣ) and proinflammatory cytokine panel; tissue lipid peroxidation, MPO, xanthine oxidase (XO), NO, NF-kB levels and the expression of TNF-α were significantly elevated in the I/R group and markedly decreased in the treatment groups. The tissue antioxidant status was decreased in the I/R group and increased in the treatment groups.

CONCLUSION

It is suggested that NO-ASA, TS, and FLUR can be introduced as promising therapeutics to improve intestinal I/R injury.

INSTITUTIONAL PROTOCOL NO

2018-29-05 (Animal Experimentations Ethics Committee, Hacettepe University).

Highly sensitive myosin phosphorylation analysis in the renal afferent arteriole

The regulation of smooth muscle contraction and relaxation involves phosphorylation and dephosphorylation of regulatory proteins, particularly myosin. To elucidate the regulatory mechanisms, analyzing the phosphorylation signal transduction is crucial. Although a pharmacological approach with selective inhibitors is sensitive and a useful technique, it leads to speculation regarding a signaling pathway but does not provide direct evidence of changes at a molecular level. We developed a highly sensitive biochemical technique to analyze phosphorylation by adapting Phos-tag SDS-PAGE. With this technique, we successfully analyzed myosin light chain (LC₂₀) phosphorylation in tiny renal afferent arterioles. In the rat afferent arterioles, endothelin-1 (ET-1) induced diphosphorylation of LC₂₀ at Ser19 and Thr18 as well as monophosphorylation at Ser19 via ET_B receptor activation. Considering that LC₂₀ diphosphorylation can decrease the rate of dephosphorylation and thus relaxation, we concluded that LC₂₀ diphosphorylation contributes, at least in part, to the prolonged contraction induced by ET-1 in the renal afferent arteriole.

Human urine-derived stem cells contribute to the repair of ischemic acute kidney injury in rats

Acute kidney injury (AKI) is a clinical syndrome associated with high rates of morbidity and mortality. It has previously been reported that stem cells may be considered a potential therapeutic strategy for the treatment of AKI. The present study aimed to determine whether administration of urine‑derived stem cells (USCs) to rats with ischemia/reperfusion (I/R)‑induced AKI could improve renal function. USCs were isolated and cultured from 8 healthy men. Subsequently, USCs transduced with green fluorescent protein were mixed with hydrogel and were injected into rats with renal I/R injury. Renal tubular injury, proliferation and apoptosis were detected in the I/R model. Hematoxylin and eosin staining was used to detect the morphological of kidney injury. Immunohistochemistry and TUNEL kits used to evaluate the proliferation and apoptosis of the I/R model. The results demonstrated that USCs could be detected in the tubular epithelial lining of the rats and administration of USCs was able to improve renal function in the I/R model. The USCs‑treated group exhibited significantly reduced serum creatinine and blood urea nitrogen levels, decreased tubular injury score, an increased number of proliferating cells and a decreased number of apoptotic cells. Compared with the control group, the mRNA expression levels of the anti‑inflammatory factors interleukin (IL)‑10 and transforming growth factor‑β1 were significantly upregulated, whereas the expression levels of the proinflammatory factors interferon‑γ and IL‑1β were significantly reduced in the USCs‑treated group. These findings suggested that USCs may promote kidney repair and improve function following ischemic AKI, which may be useful in treating human kidney disease.

Lack of an apparent role for endothelin-1 in the prolonged reduction in renal perfusion following severe unilateral ischemia-reperfusion injury in the mouse

Therapeutic approaches to block the progression from acute kidney injury to chronic kidney disease are currently lacking. Endothelin‐1 (ET‐1) is a powerful vasoconstrictor, induced by hypoxia, and previously implicated in renal ischemia‐reperfusion (IR) injury. This study tested the hypothesis that blunting the vascular influence of ET‐1, either through endothelin ET_A receptor blockade (ABT‐627) or vascular endothelial cell deletion of ET‐1 (VEET KO), would improve recovery of renal perfusion and repair of injury following a severe ischemic insult in mice (45 min unilateral renal ischemia). Male C57Bl/6 mice receiving vehicle or ABT‐627 commencing 2 days prior to surgery, and VEET KO mice and wild‐type littermates (WT) underwent 45 min unilateral renal IR surgery followed by 28 days recovery. Renal blood velocity was measured by pulsed‐wave Doppler ultrasound before and after surgery. Renal blood velocity was not significantly different between pairs of groups before surgery. Unilateral IR induced a marked reduction in renal blood velocity of the IR kidney at 24 h postsurgery in all groups, which partially recovered but remained below baseline at 28 days post‐IR. Despite the lack of effect on renal blood velocity, ET_A receptor blockade significantly attenuated the atrophy of the post‐IR kidney, whereas this was not significantly affected by lack of endothelial ET‐1 expression. These data suggest that although blockade of the ET_A receptor is mildly beneficial in preserving renal mass following a severe ischemic insult, this protective effect does not appear to involve improved recovery of renal perfusion.

Cellular and Molecular Mechanisms of AKI

In this article, we review the current evidence for the cellular and molecular mechanisms of AKI, focusing on epithelial cell pathobiology and related cell-cell interactions, using ischemic AKI as a model. Highlighted are the clinical relevance of cellular and molecular targets that have been investigated in experimental models of ischemic AKI and how such models might be improved to optimize translation into successful clinical trials. In particular, development of more context-specific animal models with greater relevance to human AKI is urgently needed. Comorbidities that could alter patient susceptibility to AKI, such as underlying diabetes, aging, obesity, cancer, and CKD, should also be considered in developing these models. Finally, harmonization between academia and industry for more clinically relevant preclinical testing of potential therapeutic targets and better translational clinical trial design is also needed to achieve the goal of developing effective interventions for AKI.

Endothelin and tubulointerstitial renal disease

All components of the endothelin (ET) system are present in renal tubular cells. In this review, we summarize current knowledge about ET and the most common tubular diseases: acute kidney injury (AKI) and polycystic kidney disease. AKI originally was called acute tubular necrosis, pointing to the most prominent morphologic findings. Similarly, cysts in polycystic kidney disease, and especially in autosomal-dominant polycystic kidney disease, are of tubular origin. Preclinical studies have indicated that the ET system and particularly ETA receptors are involved in the pathogenesis of ischemia-reperfusion injury, although these findings have not been translated to clinical studies. The ET system also has been implicated in radiocontrast-dye-induced AKI, however, ET-receptor blockade in a large human study was not successful. The ET system is activated in sepsis models of AKI; the effectiveness of ET blocking agents in preclinical studies is variable depending on the model and the ET-receptor antagonist used. Numerous studies have shown that the ET system plays an important role in the complex pathophysiology associated with cyst formation and disease progression in polycystic kidney disease. However, results from selective targeting of ET-receptor subtypes in animal models of polycystic kidney disease have proved disappointing and do not support clinical trials. These studies have shown that a critical balance between ETA and ETB receptor action is necessary to maintain structure and function in the cystic kidney. In summary, ETs have been implicated in the pathogenesis of several renal tubulointerstitial diseases, however, experimental animal findings have not yet led to use of ET blockers in human beings.

Involvement of myosin regulatory light chain diphosphorylation in sustained vasoconstriction under pathophysiological conditions

Smooth muscle contraction is activated primarily by phosphorylation at Ser19 of the regulatory light chain subunits (LC₂₀) of myosin II, catalysed by Ca²⁺/calmodulin-dependent myosin light chain kinase. Ca²⁺-independent contraction can be induced by inhibition of myosin light chain phosphatase, which correlates with diphosphorylation of LC₂₀ at Ser19 and Thr18, catalysed by integrin-linked kinase (ILK) and zipper-interacting protein kinase (ZIPK). LC₂₀ diphosphorylation at Ser19 and Thr18 has been detected in mammalian vascular smooth muscle tissues in response to specific contractile stimuli (e.g. endothelin-1 stimulation of rat renal afferent arterioles) and in pathophysiological situations associated with hypercontractility (e.g. cerebral vasospasm following subarachnoid hemorrhage). Comparison of the effects of LC₂₀ monophosphorylation at Ser19 and diphosphorylation at Ser19 and Thr18 on contraction and relaxation of Triton-skinned rat caudal arterial smooth muscle revealed that phosphorylation at Thr18 has no effect on steady-state force induced by Ser19 phosphorylation. On the other hand, the rates of dephosphorylation and relaxation are significantly slower following diphosphorylation at Thr18 and Ser19 compared to monophosphorylation at Ser19. We propose that this diphosphorylation mechanism underlies the prolonged contractile response of particular vascular smooth muscle tissues to specific stimuli, e.g. endothelin-1 stimulation of renal afferent arterioles, and the vasospastic behavior observed in pathological conditions such as cerebral vasospasm following subarachnoid hemorrhage and coronary arterial vasospasm. ILK and ZIPK may, therefore, be useful therapeutic targets for the treatment of such conditions.

Endothelin-1, but not angiotensin II, induces afferent arteriolar myosin diphosphorylation as a potential contributor to prolonged vasoconstriction

Bolus administration of endothelin-1 elicits long-lasting renal afferent arteriolar vasoconstriction, in contrast to transient constriction induced by angiotensin II. Vasoconstriction is generally evoked by myosin regulatory light chain (LC20) phosphorylation at Ser19 by myosin light chain kinase (MLCK), which is enhanced by Rho-associated kinase (ROCK)-mediated inhibition of myosin light chain phosphatase (MLCP). LC20 can be diphosphorylated at Ser19 and Thr18, resulting in reduced rates of dephosphorylation and relaxation. Here we tested whether LC20 diphosphorylation contributes to sustained endothelin-1 but not transient angiotensin II-induced vasoconstriction. Endothelin-1 treatment of isolated arterioles elicited a concentration- and time-dependent increase in LC20 diphosphorylation at Thr18 and Ser19. Inhibition of MLCK or ROCK reduced endothelin-1-evoked LC20 mono- and diphosphorylation. Pretreatment with an ETB but not an ETA receptor antagonist abolished LC20 diphosphorylation, and an ETB receptor agonist induced LC20 diphosphorylation. In contrast, angiotensin II caused phosphorylation exclusively at Ser19. Thus, endothelin-1 and angiotensin II induce afferent arteriolar constriction via LC20 phosphorylation at Ser19 due to calcium activation of MLCK and ROCK-mediated inhibition of MLCP. Endothelin-1, but not angiotensin II, induces phosphorylation of LC20 at Thr18. This could contribute to the prolonged vasoconstrictor response to endothelin-1.

Online feedback-controlled renal constant infusion clearances in rats

Constant infusion clearance techniques using exogenous renal markers are considered the gold standard for assessing the glomerular filtration rate. Here we describe a constant infusion clearance method in rats allowing the real-time monitoring of steady-state conditions using an automated closed-loop approach based on the transcutaneous measurement of the renal marker FITC-sinistrin. In order to optimize parameters to reach steady-state conditions as fast as possible, a Matlab-based simulation tool was established. Based on this, a real-time feedback-regulated approach for constant infusion clearance monitoring was developed. This was validated by determining hourly FITC-sinistrin plasma concentrations and the glomerular filtration rate in healthy and unilaterally nephrectomized rats. The transcutaneously assessed FITC-sinistrin fluorescence signal was found to reflect the plasma concentration. Our method allows the precise determination of the onset of steady-state marker concentration. Moreover, the steady state can be monitored and controlled in real time for several hours. This procedure is simple to perform since no urine samples and only one blood sample are required. Thus, we developed a real-time feedback-based system for optimal regulation and monitoring of a constant infusion clearance technique.

RGS4, a GTPase activator, improves renal function in ischemia-reperfusion injury

Acute kidney dysfunction after ischemia-reperfusion injury (IRI) may be a consequence of persistent intrarenal vasoconstriction. Regulators of G-protein signaling (RGSs) are GTPase activators of heterotrimeric G proteins that can regulate vascular tone. RGS4 is expressed in vascular smooth muscle cells in the kidney; however, its protein levels are low in many tissues due to N-end rule-mediated polyubiquitination and proteasomal degradation. Here, we define the role of RGS4 using a mouse model of IRI comparing wild-type (WT) with RGS4-knockout mice. These knockout mice were highly sensitized to the development of renal dysfunction following injury exhibiting reduced renal blood flow as measured by laser-Doppler flowmetry. The kidneys from knockout mice had increased renal vasoconstriction in response to endothelin-1 infusion ex vivo. The intrinsic renal activity of RGS4 was measured following syngeneic kidney transplantation, a model of cold renal IRI. The kidneys transplanted between knockout and WT mice had significantly reduced reperfusion blood flow and increased renal cell death. WT mice administered MG-132 (a proteasomal inhibitor of the N-end rule pathway) resulted in increased renal RGS4 protein and in an inhibition of renal dysfunction after IRI in WT but not in knockout mice. Thus, RGS4 antagonizes the development of renal dysfunction in response to IRI.

Tezosentan, a novel endothelin receptor antagonist, markedly reduces rat hepatic ischemia and reperfusion injury in three different models

This study investigated the effects of dual endothelin (ET) receptor blockade in rat models of liver ischemia and reperfusion injury (IRI). Three models of IRI were used: (1) in vivo total hepatic warm ischemia with portal shunting for 60 minutes with control (saline) and treatment groups (15 mg/kg tezosentan intravenously prior to reperfusion), (2) ex vivo hepatic perfusion after 24 hours of cold storage in University of Wisconsin solution with control and treatment groups (10 mg/kg tezosentan in the perfusate), and (3) syngeneic liver transplantation (LT) after 24 hours of cold storage in University of Wisconsin solution with control and treatment groups (10 mg/kg tezosentan intravenously prior to reperfusion). Tezosentan treatment significantly improved serum transaminase and histology after IRI in all 3 models. This correlated with reduced vascular resistance, improved bile production, and an improved oxygen extraction ratio. Treatment led to a reduction in neutrophil infiltration and interleukin-1 beta and macrophage inflammatory protein 2 production. A reduction in endothelial cell injury as measured by purine nucleoside phosphorylase was seen. Survival after LT was significantly increased with tezosentan treatment (90% versus 50%). In conclusion, this is the first investigation to examine dual receptor ET blockade in 3 models of hepatic IRI and the first to use the parenterally administered agent tezosentan. The results demonstrate that in both warm and cold IRI tezosentan administration improves sinusoidal hemodynamics and is associated with improved tissue oxygenation and reduced endothelial cell damage. In addition, reduced tissue inflammation, injury, and leukocyte chemotactic signaling were seen. These results provide compelling data for the further investigation of the use of tezosentan in hepatic IRI.

Tezosentan reduces the renal injury induced by abdominal aortic ischemia-reperfusion in rats

BACKGROUND

Renal injury induced by aortic ischemia-reperfusion (IR) is an important factor in the development of postoperative acute renal failure following abdominal aortic surgery. Endothelin (ET) is involved in the development of renal injury induced by aortic IR and tezosentan (R0 61-0612) is a specific ET receptor antagonist. The aim of this study was to examine the effect of tezosentan on renal injury induced by abdominal aortic IR in rats.

MATERIAL AND METHODS

Twenty-four Wistar-Albino rats were randomized into three groups (eight per group). Control group underwent laparotomy and dissection of the infrarenal abdominal aorta (IAA) without occlusion. The aortic IR group underwent laparotomy and clamping of the IAA for 120 min followed by 120 min of reperfusion. Aortic IR + tezosentan group underwent same aortic IR periods, and received a bolus intravenous injection of 10 mg/kg tezosentan before ischemia plus continuous intravenous infusion of 1 mg/kg/h tezosentan during 120 min ischemia and 120 min reperfusion. At the end of the experiment, blood and kidney tissue specimens were obtained for biochemical analysis. Histological evaluation of the rat kidney tissues was also done.

RESULTS

Biochemical analysis showed that aortic IR significantly increased (P < 0.05 versus control) while tezosentan significantly decreased (P < 0.05 versus aortic IR) the tissue levels of malondialdehyde, superoxide dismutase, catalase and myeloperoxidase. Histological analyses showed that aortic IR significantly increased (P < 0.05 versus control) while tezosentan significantly decreased (P < 0.05 versus aortic IR) focal glomerular necrosis, dilatation of Bowman's capsule, degeneration of tubular epithelium, necrosis in tubular epithelium and tubular dilatation in the renal tissue samples.

CONCLUSION

The results of this study indicate that tezosentan reduces renal injury induced by aortic IR in rats. We think that tezosentan exerted this beneficial effect via reducing oxidative stress and lipid peroxidation, inhibition of leukocyte infiltration into renal tissue and acting cytoprotective on renal tubular cells after aortic IR.

Lack of renal improvement with nonselective endothelin antagonism with tezosentan in type 2 hepatorenal syndrome

Renal vasoconstriction is a key factor in the development of hepatorenal syndrome (HRS) and may be secondary to increased activities of endothelin-1, a potent renal vasoconstrictor. To assess the effects of tezosentan, a nonselective endothelin receptor antagonist, on renal function in patients with type 2 HRS, six male patients, 56.3 +/- 2.5 years old, with cirrhosis and type 2 HRS were treated with tezosentan; ascending doses of 0.3, 1.0, and 3.0 mg/hour, each for 24 hours, were used for the initial 2 patients, but a constant dose of 0.3 mg/hour for up to 7 days was used for the remaining 4 patients. The glomerular filtration rate, renal plasma flow, 24-hour urinary volume, mean arterial pressure (MAP), heart rate, tezosentan levels, and vasoactive hormones were measured daily. Albumin was given as required. The study was stopped early because of concerns about the safety of tezosentan in type 2 HRS. Five patients discontinued the study early; one stopped within 4 hours because of systemic hypotension (MAP < 70 mm Hg), and 4 patients stopped at approximately 4 days because of concerns about worsening renal function (serum creatinine increased from 180 +/- 21 to 222 +/- 58 micromol/L, P > 0.05) and decreasing urine volume (P = 0.03) but without a significant change in MAP. The plasma tezosentan concentrations were 79 +/- 34 ng/mL at a steady state during infusion at 0.3 mg/hour. The plasma endothelin-1 concentrations increased from 2.7 +/- 0.3 pg/mL at the baseline to 19.1 +/- 7.3 pg/mL (P < 0.05).

CONCLUSION

An endothelin receptor blockade potentially can cause a deterioration in renal function in patients with cirrhosis and type 2 HRS. Caution should be taken in future studies using endothelin receptor antagonists in these patients.

Pharmacologic treatment of acute kidney injury: why drugs haven't worked and what is on the horizon

Current strategies to limit the extent of injury in acute renal failure are based on extensive studies that identified cellular and molecular mechanisms of acute kidney injury. Despite successes in various animal models, translation to human studies has failed or studies are inconclusive. This review describes past failures and barriers to successful clinical trials. It also focuses on promising preclinical studies using novel compounds that currently are in or close to human investigation. Implementation of previous or novel compounds in well-designed clinical trials provides hope for the successful treatment of this devastating disorder.

Pathophysiological role of platelets in acute experimental pancreatitis: influence of endothelin A receptor blockade

The potential pathophysiological role of platelet-endothelium interactions was investigated during ischemia/reperfusion (I/R), and the effect of a selective endothelin(A) receptor antagonist (ET(A)-RA) was evaluated in an acute pancreatitis model. Acute pancreatitis was induced by warm ischemia (60 min) in Wistar rats, and its effects with and without antagonist treatment were investigated. Equivalent sham-operated animals were also studied. Microcirculatory changes were assessed by in vivo microscopy, and serum levels for lipase/amylase and histological specimens were investigated. Capillary constriction to 83.7 +/- 6.7% of sham-operated diameters was observed after 60 min of ischemia. A capillary density of 56.8 +/- 9.3% of the sham-operated group (396.3 +/- 15.8 mm(-1)) was measured after reperfusion. Stagnant leukocytes (329.5 +/- 30.4%) and platelets (337.5 +/- 32.3%) increased in postcapillary venules (P < 0.05). Administration of the ET(A)-RA significantly reduced I/R injury. Capillary diameters were maintained (101.4 +/- 4.5%), and capillary density was improved to 73.3 +/- 7.6% of sham-operated animals (P < 0.05). Stagnant leukocytes (152.3 +/- 10.6%) and platelets (207.1 +/- 19.8%) in sinusoids and postcapillary venules were reduced (P < 0.05). The extent of acute pancreatitis was reduced in the therapy group as indicated by serum lipase/amylase values and histological tissue damage (P < 0.05). Thus, ET(A)-RA therapy was effective in reducing I/R-induced pancreatitis in this experimental model.

Role of endothelin and endothelin receptor antagonists in renal disease

Endothelin (ET)-1 is a potent vasoconstrictor peptide with pro-inflammatory, mitogenic, and pro-fibrotic properties that is closely involved in both normal renal physiology and pathology. ET-1 exerts a wide variety of biological effects, including constriction of cortical and medullary vessels, mesangial cell contraction, stimulation of extracellular matrix production, and inhibition of sodium and water reabsorption along the collecting duct, effects that are primarily mediated in an autocrine/paracrine manner. Increasing evidence indicates that the ET system is involved in an array of renal disorders. These comprise chronic proteinuric states associated with progressive glomerular and tubulointerstitial fibrosis, including diabetic and hypertensive nephropathy, glomerulonephritis and others. In addition, ET-1 is causally linked to renal disorders characterized by increased renal vascular resistance, including acute ischaemic renal failure, calcineurin inhibitor toxicity, endotoxaemia, hepatorenal syndrome and others. Furthermore, derangement of the ET system may be involved in conditions associated with inappropriate sodium and water retention; for example, in congestive heart failure and hepatic cirrhosis. Both selective and non-selective ET receptor antagonist have been developed and tested in animal models with promising results. As key events in progressive renal injury like inflammation and fibrosis are mediated via both ET(A) and ET(B) receptors, while constrictor effects are primarily transduced by ET(A) receptors, dual ET receptor blockade may be superior over selective ET(A) antagonism. Several compounds have been developed with remarkable effects in several models of acute and progressive renal injury. Thus, clinical studies are required to assess whether these results can be confirmed in humans, hopefully leading to novel and effective therapeutic options with few side effects.

Sex differences and the role of sex steroids in renal injury

PURPOSE

There is growing evidence that significant sex differences exist in the response of the kidney to injury. In this review we explored the cumulative clinical knowledge and experimental evidence of this phenomenon.

MATERIALS AND METHODS

The current clinical evidence of increased male susceptibility to acute and chronic renal injury, and experimental data elucidating potential mechanisms of this phenomenon were reviewed.

RESULTS

Renal damage induced by nephron reduction, patient age and renal ischemia is tolerated differently by the sexes. Sex differences in disease susceptibility have historically been attributed to the protective effects of estrogen but recent evidence suggests that male hormones also have an important role in these differences. Vascular mediators, such as endothelin, nitric oxide and angiotensin II, appear to be influenced by sex and sex steroids. Additionally, inflammatory mediators, such as transforming growth factor-beta1, tumor necrosis factor-alpha and p38 mitogen activating protein kinase, similarly show differential expression and activity based on sex and the presence of sex steroids. These mediators have a significant impact on the kidney response to inflammation and injury.

CONCLUSIONS

Greater understanding of the specific role of sex steroids in renal injury may provide new therapeutic strategies to protect against inflammatory injury and renal damage in the future.

Distribution of endothelin receptor subtypes ETA and ETB in the rat kidney

The endothelin (ET) receptor system is markedly involved in the regulation of renal function under both physiological and pathophysiological conditions. The present study determined the detailed cellular localization of both ET receptor subtypes, ET(A) and ET(B), in the vascular and tubular system of the rat kidney by immunofluorescence microscopy. In the vascular system we observed both ET(A) and ET(B) receptors in the media of interlobular arteries and afferent and efferent arterioles. In interlobar and arcuate arteries, only ET(A) receptors were present on vascular smooth muscle cells. ET(B) receptor immunoreactivity was sparse on endothelial cells of renal arteries, whereas there was strong labeling of peritubular and glomerular capillaries as well as vasa recta endothelium. ET(A) receptors were evident on glomerular mesangial cells and pericytes of descending vasa recta bundles. In the renal tubular system, ET(B) receptors were located in epithelial cells of proximal tubules and inner medullary collecting ducts, whereas ET(A) receptors were found in distal tubules and cortical collecting ducts. Distribution of ET(A) and ET(B) receptors in the vascular and tubular system of the rat kidney reported in the present study supports the concept that both ET receptor subtypes cooperate in mediating renal cortical vasoconstriction but exert differential and partially antagonistic effects on renal medullary function.

Continuous infusion of oxalate by minipumps induces calcium oxalate nephrocalcinosis

It is hypothesized that oxalate plays an active role in calcium oxalate (CaOx) nephrocalcinosis and oxalate driven nephrolithiasis by interacting with the kidney. We developed an adjustable, nonprecursor, continuous infusion model of hyperoxaluria and CaOx nephrocalcinosis to investigate this hypothesis. Minipumps containing PBS or KOx (60-360 micromol/day; n = 5-7/dose) were implanted subcutaneously in male Sprague-Dawley rats on D0 and D6. Rats were killed on D13. Oxalate excretion and CaOx crystalluria were monitored by 20+4 h urine collections. Localization and content of intrarenal crystals were determined on frozen sections using polarization and microFTIR. Oxalate excretion was significantly elevated in all KOx rats (P < or = 0.005). CaOx crystalluria was most persistent in the 240-360 micromol/day KOx rats, but even 60 micromol/day KOx rats showed sporadic crystalluria. One hundred percent of KOx rats had CaOx nephrocalcinosis as confirmed by microFTIR. Most crystals were localized to the lumens of the corticomedullary collecting ducts. A few crystals are localized just under the papillar urothelium. The minipump model is the first model of hyperoxaluria to provide continuous infusion of oxalate. It permits control of the levels of hyperoxaluria, crystalluria and CaOx nephrocalcinosis. The level of sustained hyperoxaluria and CaOx nephrocalcinosis induced by treatment with 360 micromol/day KOx for 13D models the conditions frequently observed in jejunoileal bypass patients. Adjustments in the length of treatment and level of hyperoxaluria may allow this model to also be used to study the oxalate driven CaOx-nephrolithiasis common in patients with hyperoxaluria due to other causes.

Inhibition of nitric oxide synthase reduces renal ischemia/reperfusion injury

BACKGROUND

The role of nitric oxide (NO) production because of inducible nitric oxide synthase (iNOS) in the pathogenesis of renal ischemia/reperfusion (I/R) injury is unclear. In this study the roles of both iNOS and NO were characterized in a rat model of renal I/R injury. In addition, the effect of iNOS inhibition on renal function was evaluated.

METHODS

Sprague-Dawley rats underwent 45 min of left renal ischemia and contralateral nephrectomy followed by various periods of reperfusion and renal function analysis [plasma creatinine, fractional excretion of sodium (FENa), creatinine clearance (CrCl), and measurement of plasma and urine NO levels]. In addition, the effect of treatment with 1400W, a highly selective iNOS inhibitor, was evaluated.

RESULTS

Renal dysfunction peaked at 48 h after reperfusion and immunohistochemistry studies revealed iNOS expression in the vasculature (3 h) and renal tubules (48 h) after reperfusion. Renal function improved significantly in treated animals compared to controls [creatinine of 1.1 v. 1.9 mg/dl (P < 0.05) and CrCl of 0.54 v. 0.31 ml/min (P < 0.05), respectively]. In addition, FENa was decreased by 50%, plasma NO levels were significantly lower (32.7 v. 45.7 micromol/L, P < 0.01), and deposition of nitrotyosine in the tubules of treated rats was less than in control animals.

CONCLUSIONS

These data support the hypothesis that iNOS and NO are involved in the pathogenesis of renal I/R injury and suggests that use of iNOS inhibitors may be a valuable therapeutic strategy clinical situations where renal I/R may be prevalent.

Tempol Protects against Ischemic Acute Renal Failure by Inhibiting Renal Noradrenaline Overflow and Endothelin-1 Overproduction

The effects of tempol, a superoxide dismutase mimetic, on ischemia/reperfusion-induced acute renal failure (ARF), noradrenaline (NA) overflow and endothelin-1 (ET-1) overproduction in rats were examined. Ischemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal functional parameters such as blood urea nitrogen, plasma creatinine concentration, and fractional excretion of sodium, NA concentrations in renal venous plasma, and renal ET-1 contents were determined. Renal function in ARF rats markedly decreased at 1 d after reperfusion. Pre-ischemic treatment with tempol (10, 100 mg/kg, i.v.) dose-dependently attenuated the ischemia/reperfusion-induced renal dysfunction. Histopathological examination of the kidney of ARF rats revealed severe renal damages, such as tubular necrosis, proteinaceous casts in tubuli and medullary congestion, which were also significantly suppressed by the tempol treatment. There was a significant increase in NA concentrations in renal venous plasma after the ischemia/reperfusion, and this increase was markedly suppressed by the treatment with tempol. In addition, tempol treatment significantly attenuated the increment of ET-1 content in the kidney exposed to the ischemia/reperfusion. These findings suggest that tempol improves the post-ischemic renal injury by inhibiting the neural activity of renal sympathetic nerve and ET-1 overproduction.

Expanded criteria donor grafts for deceased donor liver transplantation under the MELD system: a decision analysis

Expanded criteria donor (ECD) liver grafts have a higher likelihood of primary graft failure (PGF) compared with standard criteria donor (SCD) grafts. Given a choice between an available ECD graft versus waiting for an SCD graft that may not always become available, what should liver transplant candidates do? The study's aim was to estimate 1-year survival comparing immediate ECD liver grafting with waiting for an SCD organ. Using UNOS data, published literature estimates, and expert opinion, we constructed a Markov decision analytic model to estimate survival while waiting for an SCD transplant and survival with immediate ECD transplant. Sensitivity analyses were performed by varying model parameters individually and simultaneously with a second-order Monte Carlo simulation. For all patients with MELD scores >20, survival was higher with immediate ECD transplant despite the additional increased risk for PGF. Survival was better with an immediate ECD transplant unless the probability of PGF exceeded 23%, 72%, and 88% for recipients with MELD scores of 11-20, 21-25, and 26-30 respectively. For patients with MELD scores >30, the survival benefit with the immediate ECD strategy persisted at even higher rates of PGF. In conclusion, our results suggest that, despite the higher risk for PGF, transplantation with an available ECD graft should be preferred over waiting for an SCD organ for patients with advanced MELD scores. At less advanced MELD scores, the survival benefit depends on the risk of PGF associated with the ECD organ.

Tezosentan, a combined parenteral endothelin receptor antagonist, produces pulmonary vasodilation in lambs with acute and chronic pulmonary hypertension

OBJECTIVE

To investigate the hemodynamic effects of tezosentan in the intact lamb both at rest and during acute and chronic pulmonary hypertension.

DESIGN

Prospective, randomized experimental study.

SETTING

University-based research laboratory.

SUBJECTS

Lambs with and without pulmonary hypertension.

INTERVENTIONS

Six newborn lambs were instrumented to measure vascular pressures and left pulmonary blood flow. The hemodynamic effects of tezosentan (0.5, 1.0, 5.0 mg/kg, intravenously) were studied at rest and during U46619-induced pulmonary hypertension. Following in utero placement of an aortopulmonary vascular graft, nine additional lambs with increased pulmonary blood flow and chronic pulmonary hypertension (shunt) were also studied at 1 wk (n = 5) and 8 wks (n = 4) of age.

MEASUREMENTS AND MAIN RESULTS

At rest, tezosentan had no significant effect on any of the variables. During acute U46619-induced pulmonary hypertension, tezosentan caused a dose-dependent decrease in pulmonary arterial pressure (from 5.9% +/- 4.7 to 16.0% +/- 10.7; p < .05) and pulmonary vascular resistance (from 6.2% +/- 8.0 to 21% +/- 8.8; p < .05). Mean systemic arterial pressure was unchanged. In 1- and 8-wk-old shunt lambs with increased pulmonary blood flow, tezosentan (1 mg/kg) produced potent nonselective pulmonary vasodilation.

CONCLUSIONS

Tezosentan, a combined endothelin receptor antagonist optimized for parenteral use, induces potent selective pulmonary vasodilation during acute U46619-induced pulmonary hypertension and potent nonselective vasodilation in chronic pulmonary hypertension secondary to increased pulmonary blood flow. In general, the hemodynamic effects of bolus doses of tezosentan occurred within 60 secs of administration and lasted approximately 5-10 mins. The hemodynamic profile of intravenous tezosentan may make it a useful adjunct therapy for acute pulmonary hypertensive disorders and warrants further study.

Tezosentan in the Treatment of Acute Heart Failure

OBJECTIVE

To evaluate the pharmacology, pharmacokinetics, clinical efficacy, and tolerability of tezosentan, a new intravenous endothelin (ET)-1 receptor antagonist.

DATA SOURCES

Literature was identified through a MEDLINE search (1990-June 2003) using the search terms endothelin-1, heart failure, RITZ, and tezosentan. References listed in articles and abstracts from scientific meetings were also used.

STUDY SELECTION AND DATA EXTRACTION

English-language literature reporting controlled animal and human clinical studies was reviewed to evaluate the pharmacology, pharmacokinetics, therapeutic use, and adverse effects of tezosentan. Clinical trials selected for inclusion were limited to those with human subjects and included data from animal studies if human data were not available.

DATA SYNTHESIS

Tezosentan is a dual ET-1 receptor antagonist that has demonstrated efficacy in improving cardiac index and reducing pulmonary capillary wedge pressure in patients with acute, decompensated heart failure. Following infusion, tezosentan's plasma concentration approaches steady-state within the first 6 hours, with a relatively small volume of distribution (17 L) and clearance (39 L/h) that are dose independent. Tezosentan is excreted almost entirely unchanged via the bile (>95%), with the rest (<5%) excreted in the urine. Elimination can be explained by a biphasic profile that has a rapid elimination phase (half-life 6 min) followed by a slow phase (half-life 3 h) that accounts for distribution from tissues. The adverse event profile is significant for a higher incidence of headaches, nausea, and hypotension compared with placebo.

CONCLUSIONS

Phase II and III clinical trials have rendered mixed results for the efficacy and tolerability of tezosentan. A dose optimization trial yet to be published and an ongoing Phase III registration study will provide valuable data regarding the efficacy and tolerability benefits, as well as the morbidity and mortality, of tezosentan. Until then, tezosentan's role in the treatment of patients with acute heart failure will remain unclear.

A novel and selective Na+/Ca2+ exchange inhibitor, SEA0400, improves ischemia/reperfusion-induced renal injury

We evaluated the effects of SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline), a novel and selective Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure. Ischemic acute renal failure in rats was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after the contralateral nephrectomy. SEA0400 administration (0.3, 1 and 3 mg/kg, i.v.) before ischemia dose-dependently attenuated the ischemia/reperfusion-induced renal dysfunction and histological damage such as tubular necrosis. SEA0400 pretreatment at the higher dose suppressed the increment of renal endothelin-1 content after reperfusion. The ischemia/reperfusion-induced renal dysfunction was also overcome by post-ischemia treatment with SEA0400 at 3 mg/kg, i.v. In in vitro study, SEA0400 (0.2 and 1 microM) protected cultured porcine tubular cells (LLC-PK1) from hypoxia/reoxygenation-induced cell injury. These findings support the view that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by endothelin-1 overproduction, plays an important role in the pathogenesis of ischemia/reperfusion-induced renal injury. The possibility exists that a selective Na+/Ca2+ exchange inhibitor such as SEA0400 is useful as effective therapeutic agent against ischemic acute renal failure in humans.

Intravenous vasodilator therapy in congestive heart failure

The prevalence of congestive heart failure (CHF) is increasing in the US and worldwide, partly because patients are living longer. Treatment of CHF is mostly on an outpatient basis, but inpatient care is required for decompensated CHF, acute CHF or poor response to outpatient treatment. Control of symptoms is usually achieved by diuresis. Intravenous (IV) vasodilators are an important adjunct to the inpatient treatment of CHF. They work mainly by reducing the afterload on the myocardium although preload reduction also occurs. After clinical stabilisation, the goal is to switch to a maintenance oral regimen to be continued as outpatient therapy. The range of IV vasodilators available for inpatient treatment of CHF includes nitrates, phosphodiesterase inhibitors, dobutamine, morphine, ACE inhibitors, B-type natriuretic peptides and endothelin receptor antagonists. As each agent may have a different mechanism or site of action, each agent may affect preload, contractility or afterload to a different extent and it may be desirable to choose one over the other in a particular clinical setting. Examples of standard therapy include dobutamine, milrinone and nitroglycerin. Nesiritide, a B-type natriuretic peptide, is a newer vasodilator and US FDA approved for use in acute CHF. However, most studies with this agent have been in small numbers of patients with anecdotal findings. Larger studies are warranted to pinpoint the efficacy and adverse effects of this agent. It is primarily used to reduce the acuity of decompensated CHF on admission to hospital.Endothelin receptor antagonists show promise in the management of acute CHF, but continue to be investigational. Long-term data on their efficacy and safety are limited. None of the endothelin receptor antagonists are FDA approved for use in patients with CHF.

Endothelin(A) receptor blockade reduces ischemia/reperfusion injury in pig pancreas transplantation

OBJECTIVE

The effect of prophylactic administration of a selective endothelin(A) receptor antagonist (ET(A)-RA) on ischemia/reperfusion injury in an experimental model of graft pancreatitis after pancreas transplantation was evaluated.

SUMMARY BACKGROUND DATA

It is well established that endothelin-1 (ET-1), a powerful vasoconstrictor, plays an important role in the development of pancreatitis. Recent studies have shown a beneficial effect of endothelin receptor antagonists in the therapy for experimental pancreatitis.

METHODS

Relevant ischemia/reperfusion injury was induced in pig pancreas transplants after 6 hours hypothermic preservation in University of Wisconsin solution. The recipients were randomized into 2 groups: control pigs received isotonic saline and the treated group received the selective ET(A)-RA BSF 208075 at the beginning of reperfusion. On postoperative days 2 and 5, animals were relaparotomized to obtain tissue specimens. Blood monitoring included lipase, amylase, C-reactive protein, trypsinogen-activation peptide, thiobarbituric acid-reacting substances, and ET-1. Partial oxygen tension (p(ti)O(2)) was measured by a Clarke-type electrode and blood flow by laser doppler. A semiquantitative score index was used for assessment of histologic injury and for immunohistochemical analysis of ET-1 and ET(A) receptor expression. Tissue mRNA levels of prepro ET-1, ET(A) receptor, pro-interleukin (IL)-6, and pro-IL-1beta were quantified using TaqMan real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Prophylactic treatment with ET(A)-RA significantly reduced the severity of graft pancreatitis evidenced by C-reactive protein. The finding of transient capillary perfusion at the beginning of reperfusion supports the application of the ET(A)-RA during this period. The dramatic increase of plasma ET-1 in the therapy group is a clear evidence of effective receptor blockade. Mean trypsinogen-activation peptide levels from the portal venous effluent, but not mean systemic plasma TAP values were significantly lower in the treated group. Analysis of p(ti)O(2) and blood flow revealed a significant improvement of capillary perfusion and blood flow in the treated group and was associated with relevant reduction of tissue injury. Intrapancreatic ET-1 and IL-6 mRNA expression and ET-1 protein levels were significantly lower in the therapy group as compared with the control group. In contrast, ET(A) mRNA showed a marked up-regulation by ET(A) receptor blockade.

CONCLUSION

Application of a ET(A)-RA reduces ischemia/reperfusion induced graft pancreatitis in a pig transplantation model by improving microcirculation and reducing tissue injury.

The utility of marginal donors in liver transplantation

The shortage of organs has led centers to expand their criteria for the acceptance of marginal donors. The combination of multiple marginal factors seems to be additive on graft injury. In this review, the utility of various marginal donors in patients requiring liver transplantation will be described, including older donors, steatotic livers, non-heart-beating donors, donors with viral hepatitis, and donors with malignancies. The pathophysiology of the marginal donor will be discussed, along with strategies for minimizing the ischemia reperfusion injury experienced by these organs. Finally, new strategies for improving the function of the marginal/expanded donor liver will be reviewed.

Endothelin-receptor blockade mitigates the adverse effect of preretrieval warm ischemia on posttransplantation renal function in rats

BACKGROUND

Ischemia-reperfusion injury has been established as a nonimmunologic risk factor for the development of chronic graft nephropathy after renal transplantation. This objective of this study was to determine if oral administration of an endothelin-1 receptor (ET-R) antagonist over a 2-month period after renal transplantation would mitigate long-term dysfunction associated with 30 min of preretrieval warm ischemia (pre-WI).

METHODS

The left kidney was retrieved from 250-g Lewis rats. Recipients underwent left nephrectomy and isografting using standard techniques. Animals were divided into three groups: nonischemic controls (no pre-WI, n=8); ischemic controls (pre-WI only, n=6); and pre-WI kidneys in which recipients received the ET(A/B) receptor antagonist, A182086, daily (30 mg/kg/day) (pre-WI/ET-R antagonist, n=6). Isograft glomerular filtration rate (GFR) was measured at 2 months.

RESULTS

Measurement of GFR (mL/min) were as follows: no pre-WI, 2.1+/-0.26; pre-WI only, 1.24+/-0.14 (P<0.05 vs. no pre-WI); and pre-WI/ET-R antagonist, 2.3+/-0.45 (P<0.05 vs. pre-WI only and P=NS vs. no pre-WI).

CONCLUSIONS

Chronic administration of a nonselective ET-R antagonist given after the ischemic insult, mitigated the decline in GFR at 2 months. These observations provide an experimental rationale for further investigation of the potential long-term protective effect of nonselective ET-R blockade versus ischemia-reperfusion injury in the clinical setting.

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.

Will endothelin receptor antagonists have a role in heart failure?

Mixed ET(A/B) and selective ET(A) receptor antagonists showed promising hemodynamic and symptomatic improvements in patients with heart failure. Randomized, clinical trials to investigate the effects of ET receptor antagonists on survival in patients with heart failure still need to be conducted. Also, the effects of selective ET(A) and mixed ET(A/B) receptor antagonists on the clinical outcome of patients with CHF will have to be assessed.

Endothelin A receptor blockade reduces hepatic ischemia/reperfusion injury after warm ischemia in a pig model

It is well established that endothelin-1 (ET-1) is a very potent mediator of vasoconstriction that leads to microcirculatory disturbances. The aim of the study was to evaluate the effect of a selective endothelin A receptor antagonist on severe ischemia/reperfusion injury in a pig model. Fourteen pigs were subjected to 120 minutes of complete vascular exclusion of the liver with a passive bypass. The animals were randomized into two groups: a control group, which was given isotonic saline solution, and a therapy group, which received the selective endothelin A receptor antagonist BSF 208075 at the beginning of reperfusion. On postoperative days 4 and 7, animals were relaparotomized to obtain tissue specimens. Blood monitoring included aspartate aminotransferase (AST), alanine aminotransferase (ALT), glutamate dehydrogenase (GLDH), alkaline phosphatase, and ET-1. Partial oxygen tension (p(ti)O(2)) was measured by a Clarke-type electrode and blood flow by laser Doppler. A semiquantitative scoring index was used for assessment of histologic injury and for immunohistochemical analysis of ET-1. Treatment with the endothelin A receptor antagonist significantly reduced the severity of the ischemia/reperfusion injury, as evidenced by lower levels of AST, ALT, and GLDH. The dramatic increase in plasma ET-1 in the therapy group is clear evidence of effective receptor blockade. Analysis of p(ti)O(2) and blood flow revealed a significant improvement in capillary perfusion and blood flow in the treated group and was associated with relevant reduction of tissue injury. In summary, in the control group we observed serious microcirculatory disturbances and severe histologic damage in the liver after reperfusion. Treatment with a selective endothelin A receptor antagonist attenuated the ischemia/reperfusion injury in a porcine model of severe ischemia/reperfusion, as demonstrated by improved microcirculation, a reduction in histologic damage, and an decrease in liver enzymes.

Attenuation of ischemia/reperfusion-induced renal injury in mice deficient in Na+/Ca2+ exchanger

Using Na+/Ca2+ exchanger (NCX1)-deficient mice, the pathophysiological role of Ca2+ overload via the reverse mode of NCX1 in ischemia/reperfusion-induced renal injury was investigated. Because NCX1(-/-) homozygous mice die of heart failure before birth, we used NCX1(+/-) heterozygous mice. NCX1 protein in the kidney of heterozygous mice decreased to about half of that of wild-type mice. Expression of NCX1 protein in the tubular epithelial cells and Ca2+ influx via NCX1 in renal tubules were markedly attenuated in the heterozygous mice. Ischemia/reperfusion-induced renal dysfunction in heterozygous mice was significantly attenuated compared with cases in wild-type mice. Histological renal damage such as tubular necrosis and proteinaceous casts in tubuli in heterozygous mice were much less than that in wild-type mice. Ca2+ deposition in necrotic tubular epithelium was observed more markedly in wild-type than in heterozygous mice. Increases in renal endothelin-1 content were greater in wild-type than in heterozygous mice, and this reflected the difference in immunohistochemical endothelin-1 localization in necrotic tubular epithelium. When the preischemic treatment with KB-R7943 was performed, the renal functional parameters of both NCX1(+/+) and NCX1(+/-) acute renal failure mice were improved to the same level. These findings strongly support the view that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by renal endothelin-1 overproduction, plays an important role in the pathogenesis of ischemia/reperfusion-induced renal injury.

Renal ischemia--reperfusion injury: an inescapable event affecting kidney transplantation outcome

Ischemia--reperfusion (I-R) injury has been shown to be a common cause of late and irreversible complications during a variety of standard medical and surgical procedures. The pathogenesis of events which follow the I-R involves both injured endothelium and activated leukocytes and their interaction. In kidney transplantation, an I-R injury occurs in situations such as graft harvesting, cold storage and surgery. Clinical consequences of I-R injury have been considered to be delayed graft function and acute rejection in the short term and chronic rejection late after transplantation. Here we focused on current knowledge of pathophysiology of renal I-R injury in kidney transplantation and on possibilities of experimental therapy.