A possible molecular basis of natriuresis during ischemic-reperfusion injury in the kidney

Elevations in sweat sodium concentration following ischemia-reperfusion injury during passive heat stress

Renal ischemia-reperfusion (I/R) injury results in damage to the renal tubules and causes impairments in sodium [Na+] reabsorption. Given the inability to conduct mechanistic renal I/R injury studies in vivo in humans, eccrine sweat glands have been proposed as a surrogate model given the anatomical and physiological similarities. We tested the hypothesis that sweat Na+ concentration is elevated following I/R injury during passive heat stress. We also tested the hypothesis that I/R injury during heat stress will impair cutaneous microvascular function. Fifteen young healthy adults completed ∼160 min of passive heat stress using a water-perfused suit (50°C). At 60 min of whole body heating, one upper arm was occluded for 20 min followed by a 20-min reperfusion. Sweat was collected from each forearm via an absorbent patch pre- and post-I/R. Following the 20-min reperfusion, cutaneous microvascular function was measured via local heating protocol. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux/mean arterial pressure and normalized to CVC during local heating to 44°C. Na+ concentration was log-transformed and data were reported as a mean change from pre-I/R (95% confidence interval). Changes in sweat sodium concentration from pre-I/R differed between arms post-I/R (experimental arm: +0.97 [+0.67 - 1.27] [LOG] Na+; control arm: +0.68 [+0.38 - 0.99] [LOG] Na+; P < 0.01). However, CVC during the local heating was not different between the experimental (80 ± 10%max) and control arms (78 ± 10%max; P = 0.59). In support of our hypothesis, Na+ concentration was elevated following I/R injury, but likely not accompanied by alterations in cutaneous microvascular function.NEW & NOTEWORTHY In the present study, we have demonstrated that sweat sodium concentration is elevated following ischemia-reperfusion injury during passive heat stress. This does not appear to be mediated by reductions in cutaneous microvascular function or active sweat glands, but may be related to alterations in local sweating responses during heat stress. This study demonstrates a potential use of eccrine sweat glands to understand sodium handling following ischemia-reperfusion injury, particularly given the challenges of in vivo studies of renal ischemia-reperfusion injury in humans.

Hypernatremia in brain-dead patients

OBJECTIVES

Hypernatremia often occurs in patients with brain death. This study summarizes its characteristics.

METHODS

We recorded 57 patient's highest blood sodium value, as well as daily NT-proBNP, blood creatinine, and urine output. Further, we analyzed the time of the first rise in blood sodium, and the relationship between NT-proBNP, serum creatinine, urine output, and serum sodium.

RESULTS

There was no hyponatremia in these patients, and only seven of the 53 patients registered blood sodium between 137 and 150 mmol/L. We found that blood sodium started to rise at 36.0 (28.5-52.3) h, reaching the highest value in 79.0 (54.0-126.0) h. Urine volume and creatinine have no correlation with serum sodium level, while NT-proBNP has a significant correlation with serum sodium level.

CONCLUSION

It is necessary to conduct volume assessments and urine electrolyte testing on patients with brain death. BNP has a protective effect on water and electrolytes to prevent hypernatremia.

Protective Role of Sarpogrelate in Combination with Bromocriptine and Cabergoline for Treatment of Diabetes in Alloxan-induced Diabetic Rats

BACKGROUND

Although dopamine D2 receptor agonists, bromocriptine and cabergoline, are notable medications in the treatment of Parkinsonism, hyperprolactinemia, and hyperglycemia, there is an identified relationship between the utilization of D2-like R agonists and the progress of myocardial injury, especially in the early phase of therapy.

OBJECTIVE

This investigation aimed to examine the potential activity of sarpogrelate (a 5-hydroxytryptamine 2A [5-HT2A] receptor blocker) in reducing myocardial injury prompted by extended haul utilization of D2 receptor agonists in a model of diabetic rats.

METHODS

In the in vivo studies, both bromocriptine and cabergoline were managed independently and combined with sarpogrelate for about a month in diabetic nephropathy rats. Blood glucose level and other myocardial biochemical parameters were estimated. The probable mechanism for insulin secretagogue action was evaluated through in vitro isolated islets study. Sodium/potassium-adenosine triphosphatase activity was assayed in an isolated microsomal fraction of the renal cortex. Isolated perfused rat hearts were treated with different doses of dopamine before and after being subjected to the tested drugs, dose response of heart rate, and heart contractility were recorded.

RESULTS

Bromocriptine and cabergoline created a significant reduction in blood glucose level without any action on insulin secretagogues. Bromocriptine prevented the loss of sodium/potassium-adenosine triphosphatase activity in the cortex of an ischemic kidney. Treatment of bromocriptine or cabergoline with sarpogrelate altogether decreased the levels of the elevated myocardial biomarkers in serum. Administration of different doses of dopamine in presence of bromocriptine or capergoline resulted in significantly rising in the heart rate percentage comparing to dopamine alone. A mix of bromocriptine or cabergoline with sarpogrelate diminished both heart rate and contractility, respectively.

CONCLUSIONS

The examination demonstrated that the combined use of sarpogrelate with bromocriptine or cabergoline decreased the potential adverse effects of these 2 drugs on myocardial tissues.

Mass Spectrometric Analysis of Urine from COVID-19 Patients for Detection of SARS-CoV-2 Viral Antigen and to Study Host Response

SARS-CoV-2 infection has become a major public health burden and affects many organs including lungs, kidneys, the liver, and the brain. Although the virus is readily detected and diagnosed using nasopharyngeal swabs by reverse transcriptase polymerase chain reaction (RT-PCR), detection of its presence in body fluids is fraught with difficulties. A number of published studies have failed to detect viral RNA by RT-PCR methods in urine. Although microbial identification in clinical microbiology using mass spectrometry is undertaken after culture, here we undertook a mass spectrometry-based approach that employed an enrichment step to capture and detect SARS-CoV-2 nucleocapsid protein directly from urine of COVID-19 patients without any culture. We detected SARS-CoV-2 nucleocapsid protein-derived peptides from 13 out of 39 urine samples. Further, a subset of COVID-19 positive and COVID-19 negative urine samples validated by mass spectrometry were used for the quantitative proteomics analysis. Proteins with increased abundance in urine of SARS-CoV-2 positive individuals were enriched in the acute phase response, regulation of complement system, and immune response. Notably, a number of renal proteins such as podocin (NPHS2), an amino acid transporter (SLC36A2), and sodium/glucose cotransporter 5 (SLC5A10), which are intimately involved in normal kidney function, were decreased in the urine of COVID-19 patients. Overall, the detection of viral antigens in urine using mass spectrometry and alterations of the urinary proteome could provide insights into understanding the pathogenesis of COVID-19.

Renal ischemia-reperfusion leads to hypertension and changes in proximal tubule Na+ transport and renin-angiotensin-aldosterone system: Role of NADPH oxidase

Acute renal injury (AKI) is a risk factor for the development of hypertension, which involves oxidative stress, changes in Na⁺ handling, and the intrarenal renin-angiotensin-aldosterone system (RAAS) as underlying mechanisms. We investigated in rats whether renal ischemia-reperfusion (IR) leads to changes in the proximal tubule ATP-dependent Na⁺ transport and the intrarenal content of RAAS components, as well as the role of NADPH oxidase. Rats weighing 300-350 g were submitted to AKI by bilateral IR (n = 25). After IR injury, the animals were followed up for 4 weeks. One part (n = 7) received daily treatment with the NADPH oxidase inhibitor apocynin (100 mg/kg, drinking water), while another part (n = 9) received apocynin 24 h before and after IR. One group was submitted to sham surgery (n = 8). Four weeks after IR, the rats presented elevated systolic blood pressure, as well as increased lipid peroxidation, NADPH oxidase activity, (Na⁺+K⁺)ATPase activity, and upregulation of type 1 angiotensin II receptor in the renal cortex. On the other hand, there was a decrease in Na⁺-ATPase activity and downregulation of the isoforms 1 and 2 of the angiotensin-converting enzyme, type 2 angiotensin II receptor, and of the α and ε isoforms of protein kinase C. Most of these alterations was prevented by both apocynin treatment protocols. Thus, we conclude that AKI-induced by IR may induce changes in proximal tubule ATPases and RAAS components compatible with renal Na⁺ retention and hypertension. These data also indicate that the NADPH oxidase represents a key factor in the origin of these alterations.

Structural and Functional Alterations of the Peritoneum after Prolonged Exposure to Dialysis Solutions: Role of Aminoguanidine

Objective

The effect of long-term use of high glucose dialysate on peritoneal structure and function, and its relation with accumulation of advanced glycosylation end-product (AGE) in the peritoneum was investigated in this study.

Methods

Dialysates with 4.25% glucose were injected into the peritoneal cavity of normal rats for 12 weeks without (PD, n = 7) and with (1 g/L, PD+AG, n = 7) aminoguanidine in their drinking water. Rats not having intraperitoneal (IP) injection served as control ( n = 9). After 12 weeks of IP injection, a 2-hour peritoneal equilibration test (PET) was performed using 30 mL 4.25% glucose dialysate. Intraperitoneal volume (IPV), dialysate-to-plasma urea ratio at 2 hours (D2/P2), the ratio of dialysate glucose at 2 hours to initial dialysate glucose (D2/D0), and the peritoneal fluid absorption rate (Qa) were evaluated. After the PET, samples of the parietal peritoneum were taken for hematoxylin and eosin (H&E) staining and immunohistochemical staining for AGE.

Results

The IPV and D2/D0glucose were significantly lower and Qaand D2/P2urea significantly higher in the PD group than in the control group. Aminoguanidine reversed in part the changes in IPV and D2/P2urea in the PD group; it had no effect on Qaand D2/D0glucose. The H&E staining showed a linear mesothelial lining with negligible cells and capillaries in the narrow submesothelial space in the control group. Mesothelial denudation and submesothelial infiltration of monocytes and capillary formation were observed in the PD group. Mesothelial denudation was relatively intact in the PD+AG group compared with the PD group. Submesothelial monocyte infiltration and capillary formation in the PD+AG group were not as prominent as in the PD group. Positive AGE staining was found in the submesothelial space, vascular walls, and endomysium in the PD group, while it was markedly attenuated in PD+AG group and negligible in the control group.

Conclusion

Long-term use of high glucose solutions induced peritoneal AGE accumulation and mesothelial denudation, and increased peritoneal permeability and peritoneal fluid absorption rate. Inhibition of peritoneal AGE accumulation prevented those functional and structural damages to the peritoneum.

Fluid and Solute Transport using Different Sodium Concentrations in Peritoneal Dialysis Solutions

Background

Fluid and sodium balance is important for the success of long-term peritoneal dialysis. Convective transport is the major determinant for sodium removal during peritoneal dialysis using conventional dialysis solutions. However, recent studies showed that lower sodium concentration in dialysate could significantly increase sodium removal by increasing the diffusion gradient, thereby increasing diffusive transport. In the present study, we investigated the influence of the sodium concentration gradient on the diffusive transport coefficient, KBD for sodium.

Methods

A 4-hour dwell study was done in Sprague–Dawley rats using 25 mL 5% glucose (NS), 5% glucose + 0.3% NaCl (LS), 5% glucose + 0.6% NaCl (MS), or 5% glucose + 0.9% NaCl (HS), with frequent dialysate and blood sampling. Radiolabeled human albumin (RISA) was added to the solution as an intraperitoneal volume marker. The peritoneal fluid and sodium transport characteristics were evaluated.

Results

Significant ultrafiltration (both net ultrafiltration and transcapillary ultrafiltration) was observed in each group despite the osmolality of the 5% glucose solution being slightly lower than the plasma osmolality. There was no difference in peritoneal fluid absorption rate and direct lymphatic absorption among the four groups. With the sieving coefficient for sodium set to 0.55, a significantly higher KBD for sodium was found in the NS compared to the HS group. The KBD for sodium was 0.21 ± 0.01, 0.20 ± 0.01, 0.17 ± 0.01, and 0.09 ± 0.01 mL/min for the NS, LS, MS, and HS groups, respectively. The KBD values for glucose were significantly lower in the NS and LS groups compared to the MS and HS groups.

Conclusions

Our results suggest that ( 1 ) sodium concentration may affect peritoneal sodium KBD — as the sodium concentration gradient increased, the KBD decreased; ( 2 ) 5% glucose solution could induce significant peritoneal ultrafiltration in normal rats despite its initial hypo-osmotic nature, this was due to the significantly lower glucose transport rate than sodium transport rate; and ( 3 ) a lower dialysate sodium concentration may decrease peritoneal glucose absorption.

Effect of renal ischemia on urinary excretion of lithium in rats

Lithium, administered to patients with bipolar disorders, is mainly excreted in the urine, and tubular reabsorption is involved. This study characterized the renal excretion of lithium in rats subjected to renal ischemia for 60 min or 90 min. After intravenous injection of lithium chloride at 25 mg/kg, the pharmacokinetic parameters of lithium were determined. In sham-operated rats, the renal clearance of lithium was calculated to be 1.49 ml/min/kg, and its ratio to creatinine clearance (fractional excretion) was 43.4%. Renal ischemia inhibited the renal excretion of lithium, and did not affect its fractional excretion. The urinary pH of rats with renal ischemia for 90 min was significantly higher than those of the other groups, and the linear regression with the fractional excretion of lithium in rats with renal ischemia showed a moderate correlation (r = 0.650, p = 0.00193). This study demonstrated the effect of renal ischemia on the renal excretion of lithium in rats. It was suggested that not only glomerular filtration but also the reabsorption of lithium was impaired by renal ischemia.

Vasopressin analog terlipressin attenuates kidney injury in hemorrhagic shock

Background

In hemorrhagic shock (HS), volume replacement with crystalloid solution can restore the hemodynamic status and decrease mortality. However, it can also lead to tissue edema and pulmonary congestion, as well as increasing vascular permeability. Here, we analyzed the effects that resuscitation with lactated Ringer's solution (LRS) or administration of the vasopressin analog terlipressin has on renal function in a porcine model of HS.

Methods

Using pressure-controlled bleeding, we induced pigs to HS, maintaining mean arterial pressure (MAP) at 40 mm Hg for 30 min. Animals were divided into 4 groups: sham (anesthesia only); shock-only (HS induction); shock+LRS (HS induction and subsequent resuscitation with LRS at 3 times the volume of blood removed); and shock+Terli (HS induction and subsequent bolus administration of 2 mg of terlipressin). Parameters were evaluated at baseline, then at 30, 60, and 120 min after treatment (T30, T60, and T120, respectively). Animals were euthanized at T60 or T120.

Results

Both treatments restored MAP to baseline values. At T30 and T60, creatinine clearance was highest in shock+LRS pigs, whereas it was highest in shock+Terli pigs at T120. Both treatments initially induced hyponatremia, although urinary excretion of all ions was higher in shock+LRS pigs at T30. Both treatments restored Na-K-2Cl cotransporter expression, whereas only terlipressin restored aquaporin 2 expression. Both treatments also prevented HS-induced acute tubular necrosis. Expression of the vasopressin receptors V1a and V2 was highest in shock-only pigs. At T120, V1a expression was lowest in shock+LRS pigs.

Discussion

Terlipressin might be useful for preventing HS-induced acute kidney injury.

Tubular Transport in Acute Kidney Injury: Relevance for Diagnosis, Prognosis and Intervention

The clinical diagnosis and recovery of acute kidney injury (AKI) are mainly based on the rapid decline of glomerular filtration rate (GFR) and its subsequent recovery. The factors that determine kidney recovery and reduce the risk of subsequent progression to chronic kidney disease (CKD), however, are poorly understood. Thus, there is a need to better define the magnitude and time pattern of changes in kidney function during AKI and its recovery that go beyond GFR. Tubular transport regulates body homeostasis and the associated transport work is a primary determinant of the kidneys' energy needs. The tubular system is at the center of the pathophysiology of AKI and its recovery. In particular, proximal tubules and thick ascending limbs have been proposed to act as sensors, effectors and injury recipients of AKI stimuli. Surprisingly little attention has been given to aspects of tubular transport function in AKI and the relevance for kidney recovery. This review aims to outline changes in tubular transport function in AKI, discusses their potential consequences and relevance for the diagnosis and prognosis of AKI and its recovery, including changes in GFR, and poses the question whether tubular transport provides an opportunity for intervention to rest the tubular system, which may have consequences for the progression to CKD. © 2016 S. Karger AG, Basel.

Epithelial transport during septic acute kidney injury

A goal for scientists studying septic acute kidney injury (AKI) should be to formulate a conceptual model of disease that is able to coherently reconcile the molecular and inflammatory consequences of sepsis with impaired epithelial tubular function, diminished glomerular filtration rate (GFR) and ultimately kidney failure. Recent evidence has shed light on how sepsis modulates the tubular regulation of ion, glucose, urea and water transport and acid-base homeostasis in the kidney. The present review summarizes recent discoveries on changes in epithelial transport under septic and endotoxemic conditions as well as the mechanisms that link inflammation with impaired tubular membrane transport. This paper also proposes that the tubular dysfunction that is mediated by inflammation in sepsis ultimately leads to increased sodium and chloride delivery to the distal tubule and macula densa, contributing to tubuloglomerular feedback and impaired GFR. We feel that this conceptual model resolves many of the physiologic and clinical paradoxes that septic AKI presents to practicing researchers and clinicians.

Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction

The Na+/H+ exchanger-3 (NHE3) belongs to the mammalian NHE protein family and catalyzes the electro-neutral exchange of extracellular sodium for intracellular proton across cellular membranes. Its transport function is of essential importance for the maintenance of the body's salt and water homeostasis as well as acid-base balance. Indeed, NHE3 activity is finely regulated by a variety of stimuli, both acutely and chronically, and its transport function is fundamental for a multiplicity of severe and world-wide infection-pathological conditions. This review aims to provide a concise overview of NHE3 physiology and discusses the role of NHE3 in clinical conditions of prominent importance, specifically in hypertension, diabetic nephropathy, heart failure, acute kidney injury, and diarrhea. Study of NHE3 function in models of these diseases has contributed to the deciphering of mechanisms that control the delicate ion balance disrupted in these disorders. The majority of the findings indicate that NHE3 transport function is activated before the onset of hypertension and inhibited thereafter; NHE3 transport function is also upregulated in diabetic nephropathy and heart failure, while it is reported to be downregulated in acute kidney injury and in diarrhea. The molecular mechanisms activated during these pathological conditions to regulate NHE3 transport function are examined with the aim of linking NHE3 dysfunction to the analyzed clinical disorders.

Resveratrol improves renal microcirculation, protects the tubular epithelium, and prolongs survival in a mouse model of sepsis-induced acute kidney injury

The mortality rate of patients who develop acute kidney injury during sepsis nearly doubles. The effectiveness of therapy is hampered because it is usually initiated only after the onset of symptoms. As renal microvascular failure during sepsis is correlated with the generation of reactive nitrogen species, the therapeutic potential of resveratrol, a polyphenol vasodilator that is also capable of scavenging reactive nitrogen species, was investigated using the cecal ligation and puncture (CLP) murine model of sepsis-induced acute kidney injury. Resveratrol when given at 5.5 h following CLP reversed the decline in cortical capillary perfusion, assessed by intravital microscopy, at 6 h in a dose-dependent manner. Resveratrol produced the greatest improvement in capillary perfusion and increased renal blood flow and the glomerular filtration rate without raising systemic pressure. A single dose at 6 h after CLP was unable to improve renal microcirculation assessed at 18 h; however, a second dose at 12 h significantly improved microcirculation and decreased the levels of reactive nitrogen species in tubules, while improving renal function. Moreover, resveratrol given at 6, 12, and 18 h significantly improved survival. Hence, resveratrol may have a dual mechanism of action to restore the renal microcirculation and scavenge reactive nitrogen species, thus protecting the tubular epithelium even when administered after the onset of sepsis.

The reduction of Na/H exchanger-3 protein and transcript expression in acute ischemia-reperfusion injury is mediated by extractable tissue factor(s)

Ischemic renal injury is a formidable clinical problem, the pathophysiology of which is incompletely understood. As the Na/H exchanger-3 (NHE3) mediates the bulk of apical sodium transport and a significant fraction of oxygen consumption in the proximal tubule, we examined mechanisms by which ischemia-reperfusion affects the expression of NHE3. Ischemia-reperfusion dramatically decreased NHE3 protein and mRNA (immunohistochemistry, immunoblot, and RNA blot) in rat kidney cortex and medulla. The decrease in NHE3 protein was uniform throughout all tubules, including those appearing morphologically intact. In the kidney cortex, a decrease in NHE3 surface protein preceded that of NHE3 total protein and mRNA. Kidney homogenates from rats exposed to mild renal ischemia-reduced cell surface NHE3 protein expression in opossum kidney cells in vitro, whereas homogenates from animals with moderate-to-severe ischemia reduced both total NHE3 protein and mRNA. The decrease in total NHE3 protein was dependent on the proteasomal degradation associated with NHE3 ubiquitylation measured by coimmunoprecipitation. The transferable factor(s) from the ischemic homogenate that reduce NHE3 expression were found to be heat sensitive and to be associated with a lipid-enriched fraction, and did not include regulatory RNAs. Thus, transferable factor(s) mediate the ischemia-reperfusion injury-induced decrease in NHE3 of the kidney.

Male susceptibility to hepatic damage in acute uremia in rats

OBJECTIVE

To evaluate the role of gender in hepatic oxidative stress response and production of inflammatory cytokines in acute uremia after bilateral nephrectomy. Published studies indicate that the severity of tissue damage in kidney, brain, or heart injury may differ according to gender. We recently demonstrated that acute renal failure after kidney injury or bilateral nephrectomy activates oxidative stress and causes damage to the liver.

METHODS

Male and female rats were subjected to bilateral nephrectomy and euthanized four hours later. Serum and liver tissues were collected and analyzed. To ascertain the role of testosterone and estrogen in hepatic oxidative stress, castration was carried out 15 days before bilateral nephrectomy. In some groups, animals were administrated 17-β-estradiol or vehicle for 2 weeks before bilateral nephrectomy.

RESULTS

Hepatic oxidative stress was significantly pronounced in male rats as determined by increase in malondialdehyde (MDA) levels and decrease in total glutathione (GSH) contents. An increase in proinflammatory cytokine concentration was seen in male rats, whereas the antiinflammatory cytokine level was more elevated in females. Castration reduced hepatic oxidative stress and proinflammatory cytokine concentration, whereas exogenous estradiol after castration did not have an additional effect on these parameters.

CONCLUSIONS

There is a gender difference with regard to the severity of hepatic oxidative stress and inflammatory response in acute uremia after bilateral nephrectomy, with female rats displaying significant protection relative to male rats. We suggest that sex hormones could play an important role in the severity of remote tissue damage in acute kidney failure.

Oxygen tension correlates with regional blood flow in obstructed rat kidney

As renal tissue oxygen tension (P(O(2))) is determined by the balance between oxygen supply and consumption, direct tissue P(O(2)) measurements are essential when evaluating the presence of hypoxia. The present study aimed at evaluating invasively and continuously the renal medullary and cortical tissue P(O(2)) by novel fibre-optic probes in rats subjected to acute unilateral ureteral obstruction (AUUO). In parallel, regional blood flow measurements were obtained by MRI to investigate the relationship between regional blood flow and tissue oxygen tension. The abundance of transport proteins was determined by immunoblotting. In the obstructed kidney, AUUO caused a prompt decrease in medullary tissue P(O(2)) to 60% of baseline level whereas cortical tissue P(O(2)) was unchanged. By contrast, tissue P(O(2)) slightly increased in the non-obstructed kidney. These changes developed during the first 30 min after AUUO and persisted for the 3 h observation period. Medullary blood flow declined 1.5-2 h after induction of AUUO to 61% of baseline level in the obstructed kidney. By contrast, cortical blood flow increased to 108% of baseline level in the non-obstructed kidney. Finally, the abundance of phosphorylated aquaporin 2 decreased significantly in the obstructed kidney medulla, but increased in the obstructed kidney cortex. The Na(+)/K(+)-ATPase abundance increased in the obstructed kidney medulla whereas the Na(+)/K(+)/2Cl(-) co-transporter abundance remained unchanged in the obstructed kidney. In conclusion, measurements of regional blood flow reflect tissue P(O(2)) changes during AUUO suggesting that reduced regional blood flow is a predictor of local hypoxia. Furthermore, the abundance of major transport protein is independent of tissue P(O(2)).

Ischemic and non-ischemic acute kidney injury cause hepatic damage

Recent studies have documented that remote organs are affected by ischemic injury to the kidney. Here we studied whether the liver also suffers damage during induction of renal ischemia-reperfusion in rats and compared this to bilateral nephrectomy. Hepatic levels of tumor necrosis factor-alpha increased significantly after 6 and 24 h of renal ischemia or nephrectomy. Malondialdehyde, an index of lipid peroxidation, increased while total glutathione was decreased in the liver in both the renal ischemia and nephrectomy groups, suggesting activation of oxidative stress. Expression of liver spermine-spermidine acetyl transferase, an enzyme upregulated in early phases of hepatic injury was significantly increased 6 h after either kidney ischemia or nephrectomy. Apoptosis was increased in hepatocytes 24 h after nephrectomy. We also found histological evidence of hepatocyte injury following both ischemia and bilateral nephrectomy. Infusion of reduced glutathione, before the induction of renal ischemia, significantly improved liver architecture and was associated with a reduction in hepatic malondialdehyde and serum alanine transaminase levels. Our study shows that acute kidney ischemia or renal failure activates oxidative stress and promotes inflammation, apoptosis, and tissue damage in hepatocytes.

Oat5 and NaDC1 protein abundance in kidney and urine after renal ischemic reperfusion injury

The aim of this study was to evaluate the abundance of the organic anion transporter 5 (Oat5) and the sodium-dicarboxylate cotransporter 1 (NaDC1) in kidney and urine after renal ischemic reperfusion injury. Renal injury was induced in male Wistar rats by occlusion of both renal pedicles for 0 (Group Sham), 5 (Group I5R60), or 60 (Group I60R60) min. The studies were performed after 60 min of reperfusion. The expression of Oat5 and NaDC1 was evaluated by IHC and Western blotting. Oat5 and NaDC1 abundance and alkaline phosphatase activity (AP) were assayed in urine. A decreased expression in renal homogenates and apical membranes and an increase in urinary excretion of Oat5 and NaDC1 were observed in I60R60 rats, as well as alterations of other widely used parameters for renal dysfunction and injury (plasma creatinine, urinary AP activity, kidney weight, histological lesions). In contrast, in the I5R60 group, only an increase in urinary excretion of Oat5 and mild histopathological damage was detected. This is the first study on Oat5 and NaDC1 detection in urine. These results suggest that urinary excretion of Oat5 might be an early indicator of renal dysfunction, which is useful for detection of even minor alterations in renal structural and functional integrity.

Short- and long-term A3 adenosine receptor activation inhibits the Na+/H+ exchanger NHE3 activity and expression in opossum kidney cells

The renal function of the A(3) adenosine receptor (A3AR) is poorly characterized. In this study, we report that the A3AR-selective agonist, 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purine-9-yl]-1-deoxy-N-methyl-b-D-ribofuranuronamide (2-Cl-IBMECA) regulates the Na+/H+ exchanger-3 (NHE3) in a dose- and time-dependent fashion. In opossum kidney (OK) cells, 2-Cl-IBMECA at high (10(-6) M) and low (10(-8) M) dose inhibits NHE3 by a multiphasic time course with an acute phase of NHE3 inhibition from 15 min to 1 h, followed by a chronic phase of NHE3 inhibition from 24 to 48 h. Pre-incubation with either the selective A3AR-antagonist MRS1523 (10(-7) M) or the protein kinase C inhibitor, Calphostin C (10(-8) M) completely blocked 10(-6) M 2-Cl-IBMECA-induced acute (15 min) and chronic (24 h) phases of NHE3 inhibition. In contrast, the acute inhibitory phase (15 min) of 10(-8) M 2-Cl-IBMECA was completely prevented only when Calphostin C (10(-8) M) was added in conjunction with the protein kinase A inhibitor, H89 (10(-7) M). Acute (15 or 30 min depending on the A3AR-agonist concentration) A3AR-dependent inhibition of NHE3 activity was accompanied by decrease in cell surface NHE3 protein with no change in total NHE3 antigen. Chronic (24 h) A3AR-mediated down-regulation of NHE3 was associated with reduction of surface NHE3, decreased total NHE3 protein (70%) and a paradoxical rise of NHE3 RNA (40%). In summary, these results indicate that A3AR directly regulates NHE3 at multiple levels in a complex pattern. A3AR-dependent short- and long-term inhibition of NHE3 may be a fundamental mechanism of net sodium and fluid balance.

Effects of ischemia-reperfusion injury on renal ammonia metabolism and the collecting duct

Acute renal injury induces metabolic acidosis, but its specific effects on the collecting duct, the primary site for urinary ammonia secretion, the primary component of net acid excretion, are incompletely understood. We induced ischemia-reperfusion (I/R) acute renal injury in Sprague-Dawley rats by clamping the renal pedicles bilaterally for 30 min followed by reperfusion for 6 h. Control rats underwent sham surgery without renal pedicle clamping. I/R injury decreased urinary ammonia excretion significantly but did not persistently alter urine volume, Na+, K+, or bicarbonate excretion. Histological examination demonstrated cellular damage in the outer and inner medullary collecting duct, as well as in the proximal tubule and the thick ascending limb of the loop of Henle. A subset of collecting duct cells were damaged and/or detached from the basement membrane; these cells were present predominantly in the outer medulla and were less frequent in the inner medulla. Immunohistochemistry identified that the damaged/detached cells were A-type intercalated cells, not principal cells. Both TdT-mediated dUTP nick-end labeling (TUNEL) staining and transmission electron microscopic examination demonstrated apoptosis but not necrosis. However, immunoreactivity for caspase-3 was observed in the proximal tubule, but not in collecting duct intercalated cells, suggesting that mechanism(s) of collecting duct intercalated cell apoptosis differ from those operative in the proximal tubule. We conclude that I/R injury decreases renal ammonia excretion and is associated with intercalated cell-specific detachment and apoptosis in the outer and inner medullary collecting duct. These effects likely contribute to the metabolic acidosis frequently observed in acute renal injury.

Influence of warm ischemia time on peripheral-type benzodiazepine receptor: a new aspect of the role of mitochondria

The peripheral benzodiazepine receptor (PBR) is located mainly in the outer mitochondrial membrane and many functions are associated directly or indirectly with the PBR. We have studied the influence of different durations of warm ischemia (WI) on renal function, tissue damage and PBR expression in a Large Whitepig model. After a midline incision, the renal pedicle was clamped for 10 (WI10), 30 (WI30), 45 (WI45), 60 (WI60) or 90 min (WI90), and blood and renal tissue samples were collected between 1 day and 2 weeks after reperfusion for assessment of renal function. Metabolite excretion associated with renal ischemia reperfusion injury such as trimethylamine-N-oxide (TMAO) was quantified in blood by magnetic resonance spectroscopy. PBR mRNA and protein expression were determined in renal tissue. TMAO levels rose progressively and significantly with increasing duration of WI. PBR mRNA expression was upregulated between 3 h and 1 day after reperfusion in WI30, WI45 and WI60. Its upregulation was noted 3 days after reperfusion in WI90. At day 14, PBR transcript expression was not different from basal level in any group. PBR protein followed the same pattern. These findings suggest a new role for PBR which could be a major target in the regeneration process during ischemia reperfusion.

Regulation of renal sodium transporters during severe inflammation

Sepsis-associated acute renal failure is characterized by decreased GFR and tubular dysfunction. The pathogenesis of endotoxemic tubular dysfunction with failure in urine concentration and increased fractional sodium excretion is poorly understood. This study investigated the regulation of renal sodium transporters during severe inflammation in vivo and in vitro. Injection of high-dosage LPS reduced BP and GFR, increased fractional sodium excretion, and strongly decreased the expression of Na(+)/H(+)-exchanger, renal outer medullary potassium channel, Na(+)-K(+)-2Cl(-) co-transporter, epithelial sodium channel, and Na(+)/K(+)-ATPase in mice. Also, injection of TNF-alpha, IL-1beta, or IFN-gamma decreased renal function and expression of renal sodium transporters. LPS-induced downregulation of sodium transporters was not affected in cytokine-knockout mice. However, supplementary glucocorticoid treatment, which inhibited LPS-induced increase of tissue cytokine concentrations, attenuated LPS-induced renal dysfunction and downregulation of tubular sodium transporters. Injection of low-dosage LPS increased renal tissue cytokines and downregulated renal sodium transporters without arterial hypotension. In vitro, in cortical collecting duct cells, cytokines also decreased expression of renal outer medullary potassium channel, epithelial sodium channel, and Na(+)/K(+)-ATPase. Renal hypoperfusion by renal artery clipping did not influence renal sodium transporter expression, in contrast to renal ischemia-reperfusion injury, which depressed transporter expression. These findings demonstrate downregulation of renal sodium transporters that likely accounts for tubular dysfunction during inflammation. These data suggest that alteration of renal sodium transporters during LPS-induced acute renal failure is mediated by cytokines rather than renal ischemia. However, in a complex in vivo model of severe inflammation, the possible presence and influence of renal hypoperfusion and reperfusion on the expression of renal sodium transporters cannot be completely excluded.

Post-conditioning by a short administration of desflurane reduced renal reperfusion injury after differing of ischaemia times in rats

BACKGROUND

'Anaesthetic post-conditioning', that is administration of anaesthetics during early reperfusion, is known to have positive effects on several organs. For the kidney, however, the effects of post-conditioning by volatile anaesthetics are not well researched. We examined renal function and morphology after post-conditioning by desflurane.

METHODS

Anaesthetized rats were subjected to 30 or 45 min of renal ischaemia 14 days after contralateral nephrectomy. Post-conditioning was achieved by administration of 1 MAC desflurane (6.7 vol%) for 15 min during early reperfusion (all groups n=8). Cystatin C (CyC), creatinine clearance (Cl(Cr)) and fractional sodium excretion (FE(Na)) were measured in the awake rats over 3 days. Cell damage was graded from 1 to 4 in histological sections. Functional variables [mean (SD)] were compared statistically by a one-way anova followed by Bonferroni's multiple comparison test and histological scores (median and range) by Kruskal-Wallis test followed by Dunn's multiple comparison test.

RESULTS

Pre-ischaemia function did not differ between the groups, but was markedly reduced after ischaemia. After 30 min ischaemia, the area under the curve (AUC) for Cl(Cr) was smaller in the desflurane than in the control group [21.5 (5.0) vs 31.6 (5.1) ml min(-1) h, P<0.05]. After 45 min desflurane reduced the AUC compared with the control group for both CyC [15 (4) vs 21 (3) mg litre(-1) h] and FE(Na) [1054 (221) vs 1570 (572)% h, both P<0.05). Morphological differences were greater between the 30 min groups [control: 2.75 (2.0-3.5) vs desflurane: 1.5 (1.0-2.5); P<0.05] than between the 45 min groups [control: 3.5 (3.0-4.0) vs desflurane: 3.0 (1.5-4.0)].

CONCLUSION

Desflurane post-conditioning protects renal function and tissue. This protection was greater after the short episode than after the long episode of ischaemia.

Evolution of renal function and Na+, K +-ATPase expression during ischaemia-reperfusion injury in rat kidney

The aim of the present work was to study the effects of an unilateral ischaemic-reperfusion injury on Na+, K+-ATPase activity, alpha1 and beta1 subunits protein and mRNA abundance and ATP content in cortical and medullary tissues from postischaemic and contralateral kidneys. Right renal artery was clamped for 40 min followed by 24 and 48 h of reperfusion. Postischaemic and contralateral renal function was studied cannulating the ureter of each kidney. Postischaemic kidneys after 24 (IR24) and 48 (IR48) hours of reperfusion presented a significant dysfunction. Na+, K+-ATPase alpha1 subunit abundance increased in IR24 and IR48 cortical tissue and beta1 subunit decreased in IR48. In IR24 medullary tissue, alpha1 abundance increased and returned to control values in IR48 while beta1 abundance was decreased in both periods. Forty minutes of ischaemia without reperfusion (I40) promoted an increment in alpha1 mRNA in cortex and medulla that normalised after 24 h of reperfusion. beta1 mRNA was decreased in IR24 medullas. No changes were observed in contralateral kidneys. This work provides evidences that after an ischaemic insult alpha1 and beta1 protein subunit abundance and mRNA levels are independently regulated. After ischaemic-reperfusion injury, cortical and medullary tissue showed a different pattern of response. Although ATP and Na+, K+-ATPase activity returned to control values, postischemic kidney showed an abnormal function after 48 h of reflow.

Na+/H+ exchangers: physiology and link to hypertension and organ ischemia

PURPOSE OF REVIEW

Na/H exchangers (NHEs) are ubiquitous proteins with a very wide array of physiological functions, and they are summarized in this paper in view of the most recent advances. Hypertension and organ ischemia are two disease states of paramount importance in which NHEs have been implicated. The involvement of NHEs in the pathophysiology of these disorders is incompletely understood. This paper reviews the principal findings and current hypotheses linking NHE dysfunction to hypertension and ischemia.

RECENT FINDINGS

With the advent of large-scale sequencing projects and powerful in-silico analyses, we have come to know what is most likely the entire mammalian NHE gene family. Recent advances have detailed the roles of NHE proteins, exploring new functions such as anchoring, scaffolding and pH regulation of intracellular compartments. Studies of NHEs in disease models, even though not conclusive to date, have contributed new evidence on the interplay of ion transporters and the delicate ion balances that may become disrupted.

SUMMARY

This paper provides the interested reader with a concise overview of NHE physiology, and aims to address the implication of NHEs in the pathophysiology of hypertension and organ ischemia in light of the most recent literature.

The ATP levels in kidneys and blood are mainly decreased by acute ingestion of tullidora (Karwinskia humboldtiana)

Our previous acute toxicity studies with Karwinskia humboldtiana (Kh) in rats showed renal hemodynamic changes with a marked increase in the fractional excretion of sodium and morphological damage. To analyse the effects of Kh or 'tullidora' on energetic metabolism, a single dose of an oral preparation from the seed fruits was given to Wistar rats (1.25 g/kg). In tullidora-treated rats there was 8% mortality. ATP concentrations in renal tissue decreased significantly (control: 53.85+/-3.34, tullidora 38.28+/-5.31 micromol/g fresh tissue, P<0.05). Total blood (54.8+/-0.96, tullidora: 40.2+/-1.55 micromol/dL, P<0.01) and haemoglobin-ATP concentrations (3.69+/-0.12, tullidora: 2.56+/-0.11 micromol/g, P<0.01) were also significantly diminished. Moreover, the total protein in renal cortex from tullidora-treated rats decreased as compared to control group (control: 71.43+/-2.88, tullidora: 55.20+/-4.06 mg/g fresh tissue, P<0.05). In contrast, Na+-K+-ATPase activity in tullidora-treated animals was not different from control rats. These findings might partially explain the acute effects and mortality observed in the Kh treated rats.

Magnesium Supplementation Combined with N-Acetylcysteine Protects against Postischemic Acute Renal Failure

Magnesium is a potent vasodilator whose effects have not been evaluated in renal ischemia. The antioxidant properties of N-acetylcysteine (NAC) partially protect animals from ischemic/reperfusion injury. This study was designed to evaluate magnesium supplementation, alone or combined with NAC, on ischemic acute renal failure. Rats were maintained on normal diets, supplemented or not with MgCl(2).6H(2)O (1% in drinking water) for 23 d, and some rats received NAC (440 mg/kg body wt) on days 20 to 23. On day 21, ischemia was induced by clamping both renal arteries for 30 min. Five groups were studied: Normal, ischemia, ischemia+magnesium, ischemia+NAC, and ischemia+magnesium+NAC. GFR (inulin clearance), renal blood flow (RBF), FEH(2)O, and FENa were determined. Serum magnesium was decreased in ischemia-only rats. Magnesium prevented postischemia GFR and RBF decreases but did not protect against tubular damage. However, NAC completely restored the tubular damage induced by ischemia/reperfusion. Semiquantitative immunoblotting showed that NAC prevented the decreased expression of Na-K-2Cl co-transporter and aquaporin 2 after renal ischemia/reperfusion. Untreated rats with acute renal failure demonstrated markedly decreased endothelial nitric oxide synthase expression. Significantly, treatment with NAC, magnesium, or both completely inhibited downregulation of endothelial nitric oxide synthase. The tubular necrosis scores were lower in rats that were treated with NAC alone or with the magnesium-NAC combination. Magnesium prevented postischemia GFR and RBF decreases but did not protect against tubular damage. The NAC protected tubules from ischemia, decreased infiltrating macrophages/lymphocytes, and had a mild protective effect on GFR. In ischemic/reperfusion injury, renal function benefits more from the magnesium-NAC combination than from magnesium alone.

Acute rejection after rat renal transplantation leads to downregulation of NA+ and water channels in the collecting duct

Renal transplantation is associated with alterations of tubular functions and of the renin-angiotensin-aldosterone system. The underlying cellular and molecular mechanisms are unclear. We used an allogeneic rat renal transplantation model of acute rejection with and without immunosuppression by cyclosporine A (CsA) and a syngeneic model as control. Uninephrectomized Lewis or Lewis-Brown-Norway (LBN) rats received a kidney from LBN-rats. Renal transporters and receptors were analyzed by immunohistochemistry, semiquantitative RT-PCR and Western-blot analysis. Intracellular Na(+) was analyzed microfluorimetrically in isolated cortical collecting ducts. mRNA expression and function of the epithelial Na(+)-channel (ENaC) and mRNA and protein expression of the water-channel AQP2 were downregulated in transplanted kidneys undergoing rejection. Expression of the serum- and glucocorticoid-kinase (Sgk1) was decreased and that of the ubiquitin-protein ligase Nedd4-2 was increased. These changes were absent under CsA-therapy and in syngeneic model. Expression and function of the Na(+)-K(+)-ATPase, expression of the secretory K(+)-channel and of the mineralocorticoid receptor remained unchanged. Reduced ENaC function is likely due to decreased Sgk1- and increased Nedd4-2 mRNA expression leading to reduced ENaC expression in the membrane. These acute downregulations of ENaC and AQP2 may be triggered to reduce energy consumption in the distal nephron to protect the kidney immediately after transplantation.

Regulation of the renal sodium-dependent phosphate cotransporter NaPi2 (Npt2) in acute renal failure due to ischemia and reperfusion

BACKGROUND

Acute renal failure (ARF) is associated with hyperphosphatemia and decreased urinary phosphate excretion. The present study was undertaken to characterize the effects of ARF due to ischemia and reperfusion on renal phosphate transport and on gene and protein expression of type IIa NaPi cotransporter (Npt2) the physiologically most relevant renal sodium-dependent phosphate cotransporter.

METHODS

The following groups of rats with intact parathyroid glands were studied: (1) sham operated (sham); (2) after 1 h ischemia by bilateral renal artery clamping (I), and after 1 h ischemia and reperfusion of 1 h (I + R 1 h); (3) 24 h (I + R 24 h); (4) 48 h (I + R 48 h), and (5) 72 h (I + R 72 h) duration. The effect of ARF on Npt2 mRNA and protein expression was also examined after parathyroidectomy (PTX) of 2 and 4 days' duration.

RESULTS

Ischemia and reperfusion were associated with increases in plasma creatinine, hyperphosphatemia, and with decreased tubular phosphate reabsorption. Npt2 mRNA was significantly downregulated in the cortex, maximal at 24 and 48 h of reperfusion. The degree of Npt2 mRNA downregulation was not affected by PTX of 2-4 days' duration. The abundance of Npt2 protein in proximal tubular apical brush border membrane was markedly decreased after reperfusion. Npt2 protein, however, was more abundant in PTX animals than in those with intact parathyroids and a similar degree of renal insufficiency. The immunohistochemical analysis of proximal tubular apical brush border membrane showed a progressive decrease of Npt2 protein labeling after ischemia and reperfusion, with progressive regeneration after 72 h.

CONCLUSION

These results suggest that downregulation of Npt2 protein may contribute to the decreased tubular reabsorption of phosphate in acute ischemic renal failure and hyperphosphatemia.

The endothelin receptor antagonist TAK-044 in the treatment of reperfusion injury in organ transplantation

Ischaemia and reperfusion are complex interrelated events that involve the vascular endothelium. The endothelium produces endothelin (ET), the most potent vasoconstrictor identified to date. During ischaemia, endothelial transcription of ET is increased, leading to strong and sustained vasoconstriction. Ischaemia and reperfusion are indispensable parts of solid organ transplantation. Various experimental data discussed in this review show an efficacy of the mixed ET(A/B) antagonist TAK-044 in the treatment of reperfusion injury. The overall safety and tolerability of TAK-044 in humans seems to be excellent. Large clinical randomised trials on the use of TAK-044 in the treatment of reperfusion injury in different clinical situations are missing, nevertheless, the future for ET antagonists is promising.

Recovery of Na-glucose cotransport activity after renal ischemia is impaired in mice lacking vimentin

Vimentin, an intermediate filament protein mainly expressed in mesenchyma-derived cells, is reexpressed in renal tubular epithelial cells under many pathological conditions, characterized by intense cell proliferation. Whether vimentin reexpression is only a marker of cell dedifferentiation or is instrumental in the maintenance of cell structure and/or function is still unknown. Here, we used vimentin knockout mice ( Vim−/−) and an experimental model of acute renal injury (30-min bilateral renal ischemia) to explore the role of vimentin. Bilateral renal ischemia induced an initial phase of acute tubular necrosis that did not require vimentin and was similar, in terms of morphological and functional changes, in Vim+/+and Vim−/−mice. However, vimentin was essential to favor Na-glucose cotransporter 1 localization to brush-border membranes and to restore Na-glucose cotransport activity in regenerating tubular cells. We show that the effect of vimentin inactivation is specific and results in persistent glucosuria. We propose that vimentin is part of a structural network that favors carrier localization to plasma membranes to restore transport activity in injured kidneys.

Dopamine D2-like receptor agonist bromocriptine protects against ischemia/reperfusion injury in rat kidney

BACKGROUND

Dopamine, via activation of D1-like and D2-like receptors, plays an important role in the regulation of renal sodium excretion. Recently, we demonstrated that dopamine D2-like receptor agonist (bromocriptine) stimulates p44/42 mitogen-activated protein kinases (MAPKs) and Na+,K(+)ATPase (NKA) activity in proximal tubular epithelial cells. Since both these parameters are compromised in ischemia/reperfusion (I/R) injury to the kidney, we investigated whether bromocriptine protects against the injury.

METHODS

In this study we used unilateral rat model of renal I/R injury. The Sprague-Dawley rats were divided into vehicle and bromocriptine groups. The vehicle and bromocriptine group was treated with vehicle and bromocriptine (500 microg/kg intravenously), respectively, 15 minutes before the induction of unilateral ischemia followed by 24- or 48-hour reperfusion. At the end of 24 or 48 hours the animals were sacrificed to collect control and ischemic kidney cortices, in which necrosis, apoptosis, NKA activity, NKA alpha1 subunit expression, and p44/42 MAPK phosphorylation were measured.

RESULTS

We found extensive necrosis, apoptosis, and decreased NKA activity (with no change in alpha1 subunit) in the ischemic kidney cortex compared to the nonischemic cortex from the vehicle-treated rats as early as 24 hours post-reperfusion. In contrast, I/R injury-induced necrotic, apoptotic, and decrease in NKA activity were absent in the outer cortex of bromocriptine-treated rats after 24 or 48 hours. Interestingly, we detected significantly higher phosphorylation of p44/42 MAPKs in control and ischemic kidneys of bromocriptine-treated rats compared to those of vehicle-treated rats.

CONCLUSION

Therefore, bromocriptine, a D1-like receptor agonist, may protect against I/R injury to proximal tubules of the kidney, via p44/42 MAPK activation.

Can the outcome of older donor kidneys in transplantation be predicted? An analysis of existing scoring systems

The use of older cadaveric donors in kidney transplantation is increasing. The transplant outcome of the single older kidney is generally inferior prompting some to recommend dual kidney transplantation. The ability to predict the outcome of the solitary marginal kidney becomes clinically important. Such insight might allow for better allocation strategies that would minimize poorer outcomes while permitting optimal rationalization of this scarce resource. A retrospective, single center review of 79 single kidney transplants from 50 donors aged > or =55 yr was performed. We tested the validity of published scoring strategies to predict subsequent recipient kidney function. Receiver operating characteristic curve analysis was used to quantify the donor strategies separating good and poor outcomes based upon recipient creatinine clearance (CrCl) <30 mL/min. Two pre-transplant donor assessment strategies, Nyberg score and donor CrCl (dCrCl) were found to predict subsequent kidney function in recipients. When Nyberg variables (cold ischemia time, donor diabetes and hypertension status, incremental donor age >55 yr and cause of death) in conjunction with the dCrCl were considered, they were no better than dCrCl alone. Although dCrCl had a reasonable negative predictive ability, the positive predictive value was <50%. Our analysis suggests that a dCrCl of > or =70 mL/min is a better discriminator of subsequent kidney function outcomes than a dCrCl of 90 mL/min as recommended by the Dual Transplant Registry.

Urinary measurement of Na+/H+ exchanger isoform 3 (NHE3) protein as new marker of tubule injury in critically ill patients with ARF

BACKGROUND

It has been shown that apical sodium transporters of the renal tubule can be detected by immunoblotting of urine membrane fraction from rats. We raised the hypothesis that protein levels of the Na+/H+ exchanger isoform 3 (NHE3), the most abundant apical sodium transporter in renal tubule, should be increased in urine of patients presenting with acute renal failure (ARF) with severe tubular cell damage and thus might be a noninvasive marker of acute tubular necrosis (ATN).

METHODS

Sixty-eight patients admitted to the intensive care unit were studied prospectively (54 patients with ARF, 14 controls without renal dysfunction). Patients with ARF were divided into 3 subgroups as follows: prerenal azotemia, ATN, and intrinsic ARF other than ATN. Urinary NHE3 protein abundance was estimated from semiquantitative immunoblots of urine membrane fraction samples collected from patients. The amount of urinary NHE3 was compared with the fractional excretion of sodium (FeNa) and urinary retinol-binding protein (RBP).

RESULTS

NHE3 was not detected in urine from controls. Levels of urinary NHE3 normalized to urinary creatinine level were increased in patients with prerenal azotemia and 6 times as much in patients with ATN, without overlap (ATN, 0.78 +/- 0.36; prerenal azotemia, 0.12 +/- 0.08; P < 0.001). Conversely, urinary NHE3 protein was not detected in patients with intrinsic ARF other than ATN. Normalized NHE3 level correlated positively with serum creatinine level in patients with tubular injury (R2 = 0.305; P = 0.0003). Values for FeNa and normalized urinary RBP did not discriminate ATN from intrinsic ARF other than ATN and prerenal azotemia, respectively.

CONCLUSION

In patients with ARF, urinary NHE3 abundance might be a novel noninvasive marker of renal tubule damage, helping to differentiate prerenal azotemia, ATN, and intrinsic ARF other than ATN.

Expression of SSAT, a novel biomarker of tubular cell damage, increases in kidney ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is the major cause of acute renal failure in native and allograft kidneys. Identifying the molecules and pathways involved in the pathophysiology of renal IRI will yield valuable new diagnostic and therapeutic information. To identify differentially regulated genes in renal IRI, RNA from rat kidneys subjected to an established renal IRI protocol (bilateral occlusion of renal pedicles for 30 min followed by reperfusion) and time-matched kidneys from sham-operated animals was subjected to suppression subtractive hybridization. The level of spermidine/spermine N(1)-acetyltransferase (SSAT) mRNA, an essential enzyme for the catabolism of polyamines, increased in renal IRI. SSAT expression was found throughout normal kidney tubules, as detected by nephron segment RT-PCR. Northern blots demonstrated that the mRNA levels of SSAT are increased by greater than threefold in the renal cortex and by fivefold in the renal medulla at 12 h and returned to baseline at 48 h after ischemia. The increase in SSAT mRNA was paralleled by an increase in SSAT protein levels as determined by Western blot analysis. The concentration of putrescine in the kidney increased by approximately 4- and approximately 7.5-fold at 12 and 24 h of reperfusion, respectively, consistent with increased functional activity of SSAT. To assess the specificity of SSAT for tubular injury, a model of acute renal failure from Na(+) depletion (without tubular injury) was studied; SSAT mRNA levels remained unchanged in rats subjected to Na(+) depletion. To distinguish SSAT increases from the effects of tubular injury vs. uremic toxins, SSAT was increased in cis-platinum-treated animals before the onset of renal failure. The expression of SSAT mRNA and protein increased by approximately 3.5- and >10-fold, respectively, in renal tubule epithelial cells subjected to ATP depletion and metabolic poisoning (an in vitro model of kidney IRI). Our results suggest that SSAT is likely a new marker of tubular cell injury that distinguishes acute prerenal from intrarenal failure.

Acute renal failure leads to dysregulation of lung salt and water channels

BACKGROUND

Renal ischemia/reperfusion (I/R) injury and the acute respiratory distress syndrome (ARDS) frequently coexist in the intensive care setting, and this combination is associated with a high mortality. Recent experimental data demonstrate that renal I/R injury leads to an increase in pulmonary vascular permeability, similar to that observed in ARDS. However, the effects of renal I/R injury on alveolar fluid clearance-of potential importance in the setting of increased permeability-are unknown. We investigated the effects of renal I/R injury on pulmonary epithelial sodium channel (ENaC), Na,K-ATPase and aquaporin expression as a first step in addressing this question.

METHODS

Sprague Dawley rats were subjected to four protocols: (1) surgery for bilateral I/R injury, (2) sham surgery, (3) surgery for unilateral I/R injury, or (4) bilateral nephrectomy. Lung tissue was examined for Na channel, Na,K-ATPase, aquaporin-1, and aquaporin-5 expression. Northern and Western blots were performed.

RESULTS

Renal I/R injury and bilateral nephrectomy both led to marked down-regulation of pulmonary ENaC, Na,K-ATPase and aquaporin-5 but not aquaporin-1 compared to sham surgery. These changes were not influenced by the animals' volume status. In contrast, unilateral I/R with an intact contralateral kidney did not lead to down-regulation of channel down-regulation.

CONCLUSIONS

Ischemic acute renal failure leads to down regulation of pulmonary ENaC, Na,K-ATPase and aquaporin-5, but not aquaporin-1. Since bilateral nephrectomy but not single kidney I/R injury also leads to lung changes, these changes are likely mediated by systemic effects of acute renal failure (ARF), such as "uremic toxins," rather than reperfusion products. These changes may modulate lung dysfunction, susceptibility to lung injury, or both.

Modulation of peripheral-type benzodiazepine receptor levels in a reperfusion injury pig kidney-graft model

BACKGROUND

Ischemia-reperfusion injury is associated with an increased risk of acute rejection, delayed graft function, or chronic graft dysfunction. Mitochondria play a central role in this process.

METHODS

Using an autotransplantation pig kidney model, both early (40 min and 7 days) and late (2-16 weeks) changes in renal function and morphology were determined after different periods of cold ischemia in University of Wisconsin or Euro-Collins solutions. We have also investigated the expression of the peripheral-type benzodiazepine receptor (PBR), which is also critical in maintaining outer mitochondrial membrane stability.

RESULTS

Function of the kidneys was better preserved after 1 hr and 24 hr than after 48 hr and 72 hr in Euro-Collins and University of Wisconsin solutions. Medulla injury was reduced in 1 hr-preserved and 24 hr-preserved groups. PBR was found to be present in epithelial cells of the deep cortical and outer medulla in both normal human and well-preserved pig kidneys. PBR expression was modulated by ischemia-reperfusion injury and the concurrent tubular injury and repair processes.

CONCLUSION

This study indicates that PBR expression correlates with the quality of kidney preservation and might serve as an index of kidney and mitochondria viability. Moreover, these data suggest that PBR might be involved in membrane biogenesis during reperfusion. In addition, considering the identical localization of PBR in human and pig kidneys, these findings could have a direct application in human clinical settings of kidney pathology.

Contrast-associated nephropathy

Contrast-associated nephropathy (CaN) has become a major cause of iatrogenic acute renal failure, especially with the increasing use of radiographic contrast media in both diagnostic and interventional procedures. CaN is the third most common cause of iatrogenic acute renal failure, and is associated with increased morbidity and in-hospital mortality. CaN typically presents as an acute rise in serum creatinine levels, usually within 48 hours after exposure to contrast media. Renal medullary ischemia secondary to contrast-induced vasoconstriction is now believed to be the most likely cause of CaN, although direct renal tubular cytotoxicity does appear to play a role. The occurrence of CaN is directly related to the number of coexisting clinical risk factors. Among the many risk factors, preexisting renal impairment, the presence of diabetes mellitus and the volume of the contrast agent administered are the most important. The most effective means of reducing the incidence of CaN is through prevention, by first identifying the risk factors and then attempting to correct for them before the administration of contrast material. Although the earliest and most well-tested preventive measure, namely intravenous hydration, continues to be the most effective way to prevent CaN, recent studies have provided many new preventive modalities. The growing use of these new agents, such as acetylcysteine, endothelin blockers, and most recently fenoldopam, has increased the options available for the prevention of CaN.

Polyethylene glycol reduces early and long-term cold ischemia-reperfusion and renal medulla injury

Ischemia-reperfusion injury (IRI) after transplantation is a major cause of delayed graft function, which has a negative impact on early and late graft function and improve acute rejection. We have previously shown that polyethylene glycol (PEG) and particularly PEG 20M has a protective effect against cold ischemia and reperfusion injury in an isolated perfused pig and rat kidney model. We extended those observations to investigate the role of PEG using different doses (30g or 50g/l) added (ICPEG30 or ICPEG50) or not (IC) to a simplified preservation solution to reduce IRI after prolonged cold storage (48-h) of pig kidneys when compared with Euro-Collins and University of Wisconsin solutions. The study of renal function and medulla injury was performed with biochemical methods and proton NMR spectroscopy. Histological and inflammatory cell studies were performed after reperfusion (30-40 min) and on days 7 and 14 and weeks 4, 8, and 12. Peripheral-type benzodiazepine receptor (PBR), a mitochondrial protein involved in cholesterol homeostasis, was also studied. The results demonstrated that ICPEG30 improved renal function and reduced medulla injury. ICPEG30 also improved tubular function and strongly protect mitochondrial integrity. Post-IRI inflammation was strongly reduced in this group, particularly lymphocytes TCD4(+), PBR expression was influenced by IRI in the early period and during the development of chronic dysfunction. This study clearly shows that PEG has a beneficial effect in renal preservation and suggests a role of PBR as a marker IRI and repair processes.

Effects of fenoldopam, a dopamine D-1 agonist, and clevidipine, a calcium channel antagonist, in acute renal failure in anesthetized rats

The present studies were conducted to: a) comparatively evaluate the effects of clevidipine, a new dihydropyridine calcium antagonist, and fenoldopam, a dopamine (D-1) receptor agonist on basal renal function, and b) to determine the efficacy of these agents in protecting renal function in an experimental model of ischemia/reperfusion (I/R) induced acute renal failure in rats. Infusions of either clevidipine or fenoldopam (5.0 nmol/kg(-1) min(-1) i.v. for 60 min) produced significant increases in urine flow (UV), urinary sodium excretion (UNaV), and fractional excretion of sodium (FENa) in inactin anesthetized rats. Unlike clevidipine, fenoldopam also produced significant increases in renal blood flow (RBF) and urinary potassium excretion (UKV). In a separate series, unilateral renal failure was induced in anesthetized rats by occluding the left renal artery for 40 min followed by reperfusion. In this model, there was a 70-75% reduction in the GFR that was paradoxically associated with several fold increases in UV, UNaV, and FENa in the vehicle treated group. In two separate groups, infusions of neither clevidipine nor fenoldopam (5.0 nmol/kg(-1) min(-1)) for 60 min beginning 10 min before reperfusion, improved filtration fraction. However, clevidipine treatment markedly improved tubular function in that loss of sodium and water were significantly attenuated and UV and UNaV were restored towards basal levels. In contrast, in the fenoldopam group, tubular function was further deteriorated as evidenced by exacerbated losses of sodium and water. These observations suggest that whereas both clevidipine and fenoldopam were potent natriuretic agents, only the calcium antagonist was effective in preserving renal function in the present experimental model of ischemic renal failure.

Regulation of ROMK and channel-inducing factor (CHIF) in acute renal failure due to ischemic reperfusion injury

BACKGROUND

Acute renal failure caused by ischemia followed by reperfusion is often associated with severe hyperkalemia. The present study was undertaken to characterize the effects of renal ischemia and reperfusion on plasma potassium (K) and on the gene expression of channel-inducing factor (CHIF), a putative K channel regulator, and of ROMK, the distal nephron secretory K channel.

METHODS

The following groups of rats were studied: (1) sham operated (sham); (2) after one hour of ischemia by bilateral renal artery clamping (I), and after one hour of ischemia; (3) one hour of reperfusion (I-R 1 h); (4) 24 hours of reperfusion (I-R 24 h); (5) 48 hours of reperfusion (I-R 48 h); and (6) 72 hours reperfusion (I-R 72 h). The expression of CHIF and ROMK was examined by Northern blot hybridization in renal cortex, medulla, and papilla and in the colon. The abundance of ROMK protein was determined in the renal cortex and medulla by immunoblotting.

RESULTS

Maximal plasma creatinine and potassium levels after ischemia and reperfusion were 470 +/- 16 micromol/L, P < 0.0001 versus sham, and 9.65 +/- 0.33 mmol/L, P < 0.0001 versus sham, respectively. The expression of CHIF was significantly down-regulated in the medulla and papilla, with a maximal decrease of 80% at 48 to 72 hours. In contrast, a most significant increase in CHIF mRNA expression (250% of baseline) was noted in the colon after 24 to 48 hours of reperfusion. ROMK expression was reduced in the cortex and was completely abolished in the medulla at 48 to 72 hours of reperfusion. Ischemia and reperfusion injury significantly decreased ROMK protein abundance to 10% of control in the medullary fractions.

CONCLUSIONS

These results suggest that down-regulation of renal CHIF and ROMK may contribute at least partly to the hyperkalemia of acute renal failure after ischemia and reperfusion, while CHIF up-regulation in the colon may act as a compensatory mechanism of maintaining K balance via increased K secretion.

Effect of ischemia-reperfusion on the renal brush-border membrane sodium-dependent phosphate cotransporter NaPi-2

To understand the mechanisms underlying ischemia-reperfusion-induced renal proximal tubule damage, we analyzed the expression of the Na+-dependent phosphate (Na+/Pi) cotransporter NaPi-2 in brush border membranes (BBM) isolated from rats which had been subjected to 30 min renal ischemia and 60 min reperfusion. Na+/Pi cotransport activities of the BBM vesicles were also determined. Ischemia caused a significant decrease (about 40%, P < 0.05) in all forms of NaPi-2 in the BBM, despite a significant increase (31 ± 3%, P < 0.05) in the Na+/Pi cotransport activity. After reperfusion, both NaPi-2 expression and Na+/Pi cotransport activity returned to control levels. In contrast with Na+/Pi cotransport, ischemia significantly decreased Na+-dependent glucose cotransport but did not affect Na+-dependent proline cotransport. Reperfusion caused further decreases in both Na+/glucose (by 60%) and Na+/proline (by 33%) cotransport. Levels of NaPi-2 were more reduced in the BBM than in cortex homogenates, suggesting a relocalization of NaPi-2 as a result of ischemia. After reperfusion, NaPi-2 levels returned to control values in both BBM and homogenates. These data indicate that the NaPi-2 protein and BBM Na+/Pi cotransport activity respond uniquely to reversible renal ischemia and reperfusion, and thus may play an important role in maintaining and restoring the structure and function of the proximal tubule.Key words: kidney, ischemia, reperfusion, phosphate, transport.

Changes in expression of sodium cotransporters and aquaporin-2 during ischemia-reperfusion injury in rabbit kidney

Ischemic renal injury is associated with defects in transport functions of the proximal tubules and urinary concentration ability. To determine whether alterations in expression of various transporter genes contribute to an impairment in renal functions, the expression of various solute transport genes was analyzed in renal cortex and medulla of rabbits with ischemic acute renal failure. Rabbits were subjected to 60 min of renal pedicle clamping followed by 24, 48, or 72 h of reperfusion. Urine volume and glomerular filtration rate were markedly decreased, which were accompanied by an increase in serum creatinine level and fraction Na+ excretion. Glucosuria and phosphaturia were evident during reperfusion periods. These alterations in renal functions were persisted to 72 h after reperfusion. The Na+-dependent uptakes of glucose and phosphate by brush border membrane vesicles were inhibited by 24 h of reperfusion. mRNA levels for Na+-glucose, Na+-phosphate, and Na+-succinate cotransporter analyzed by RT-PCR were not changed by 60 min of ischemia alone, but were significantly reduced by 24 h of reperfusion. mRNA levels for apical Na+-K+-2Cl- cotransporter, NaCl cotransporter, and turea transporter in the medulla were not changed during reperfusion. Protein levels for AQP2 in the medulla, but not AQP1 in the cortex, analyzed by Western blot were significantly reduced at 24 h after reperfusion. These results suggest that reductions in expression of Na+-cotransporter genes in the proximal tubules may be important factors in the impairment in Na+-dependent reabsorption of solutes and that decrease in AQP2 protein may be involved in defect in urinary concentration ability in rabbits with ischemic acute renal failure.

Endothelin: what does the radiologist need to know?

Endothelin (ET) is a potent endogenous vasoconstrictor peptide. It has been implicated in various pathological states since its discovery in 1988. The cardiovascular system and the kidneys are important sites for the action of this peptide. Two types of ET receptor, ETA and ETB, govern the biological effects of ET. Drugs that can prevent the endogenous synthesis of ET or block its binding to receptors may offer important therapeutic impact to patients with congestive heart failure, pulmonary hypertension and acute renal failure. Areas of particular interest to the radiologist include the role of ET in mediating some of the side effects of contrast media, particularly contrast medium nephropathy, and the involvement of ET in the pathogenesis of restenosis following angioplasty. This review outlines the basic biology of this important mediator and its role in health and disease.

Ontogeny of Na+/H+ antiporter activity in rat proximal convoluted tubules

Neonates have a lower serum bicarbonate level than adults, which is caused by a lower renal threshold for bicarbonate. Eighty percent of bicarbonate reabsorption occurs in the proximal tubule, in which proton secretion is predominantly mediated by a luminal Na+/H+ antiporter. Previous studies have demonstrated that there is a maturational increase in apical membrane rabbit proximal convoluted tubule Na+/H+ antiporter activity. However, in rat brush border membrane vesicles, Na+/H+ activity was higher in neonates than that in adult rats. To examine the maturation of Na+/H+ antiporter activity in rat proximal convoluted tubules, we perfused rat proximal convoluted tubules in vitro. Na+/H+ antiporter activity was assayed as the proton secretory rate on luminal sodium removal. Na+/H+ antiporter activity was 121.2 +/- 18.4 pmol/mm x min in neonatal and 451.8 +/- 40.6 pmol/mm x min in adult proximal convoluted tubules (p < 0.001). We next examined whether the increase in Na+/H+ antiporter activity was associated with changes in renal cortical NHE3 mRNA and brush border membrane NHE3 protein abundance. Adult renal cortical NHE3 mRNA abundance was 10-fold greater than that in 1-d-old neonates (p < 0.001). There was a comparable developmental increase in renal brush border membrane vesicle NHE3 protein abundance (p < 0.001). In summary, this study demonstrates that there is a maturational increase in rat apical membrane Na+/H+ antiporter activity, renal cortical NHE3 mRNA, and brush border membrane vesicle NHE3 protein abundance.

Influence of cold-storage conditions on renal function of autotransplanted large pig kidneys

BACKGROUND

The consequences of ischemia/reperfusion injury (IRI) on delayed graft function (DGF) and graft survival for kidney recipients remain a matter of debate. Several strategies have been proposed to reduce IRI. We have shown that adding the anti-ischemic drug trimetazidine (TMZ) to different preservation solutions had beneficial effects on the function of reperfused rat and pig kidneys.

METHODS

We analyzed the renal parameters of reperfused, autotransplanted large pigs following transplantation. The left kidneys were first removed and cold flushed with Euro-Collins (EC) and University of Wisconsin (UW) solutions (with or without 10-6 mol/L TMZ) and were stored for 48 hours at 4 degrees C. The kidney was then autotransplanted, and the contralateral kidneys were removed. Creatinine clearance, natriuresis, proteinuria, the degree of interstitial fibrosis, the number of CD4, CD8, and macrophage-positive cells, and the amount of vascular cell adhesion molecule-1 were analyzed on kidney biopsies taken at 2, 4 to 5, and 10 to 12 weeks after surgery.

RESULTS

The functions of the transplanted kidneys were better preserved after cold flushing with TMZ-supplemented solutions than with TMZ-free solutions. Creatinine clearance was higher, and proteinuria was lower in animals transplanted with kidneys cold flushed with TMZ-supplemented solutions than with TMZ-free solutions. The cytoprotective action of TMZ also reduced interstitial fibrosis and the numbers of infiltrating CD4- and CD8-positive cells.

CONCLUSION

These results indicate that the condition of cold preservation may influence long-term kidney graft functions and suggest that, to a certain extent, TMZ reduces the degree of interstitial fibrosis.

Decreased abundance of major Na(+) transporters in kidneys of rats with ischemia-induced acute renal failure

Ischemia-induced acute renal failure (ARF) is known to be associated with significant impairment of tubular Na reabsorption. We examined whether temporary bilateral renal ischemia (30, 40, or 60 min) and reperfusion (1-5 days) affect the abundance of several renal Na transporters and urinary Na excretion (U(Na)V) in rats. In rats with mild ARF (30 min), immunoblotting revealed that proximal tubule type 3 Na(+)/H(+) exchanger (NHE-3) and type II Na-P(i) cotransporter (NaPi-II) were significantly decreased to 28 +/- 6 and 14 +/- 6% of sham levels, respectively, at day 1. Moreover, Na(+)-K(+)-ATPase levels were also significantly decreased (51 +/- 11%), whereas there was no significant decrease in type 1 bumetanide-sensitive cotransporter (BSC-1) and thiazide-sensitive cotransporter (TSC) levels. Consistent with reduced Na transporter abundance, fractional urinary Na excretion (FE(Na)) was significantly increased in mild ARF (30 min) and U(Na)V was unchanged, despite a marked reduction in glomerular filtration rate. Na transporter levels and renal Na handling were normalized within 5 days. Severe ischemic injury (60 min) resulted in a marked decrease in the abundance of Na(+)-K(+)-ATPase, NHE-3, NaPi-II, BSC-1, and TSC at both days 1 and 5. Consistent with this, FE(Na) was significantly increased at days 1 and 5. Intravenous K-melanocyte-stimulated hormone treatment partially prevented the ischemia-induced downregulation of renal Na transporters and reduced the high FE(Na) to control levels. We conclude that reduced levels of Na transporters along the nephron may play a critical role in the impairment of tubular Na reabsorption, and hence increased Na excretion, in ischemia-induced ARF.