In Vivo and In Vitro Evaluation of Urinary Biomarkers in Ischemia/Reperfusion-Induced Kidney Injury

Oxidative stress plays an important role in the pathophysiology of acute kidney injury (AKI). Previously, we reported that vanin-1, which is involved in oxidative stress, is associated with renal tubular injury. This study was aimed to determine whether urinary vanin-1 is a biomarker for the early diagnosis of AKI in two experimental models: in vivo and in vitro. In a rat model of AKI, ischemic AKI was induced in uninephrectomized rats by clamping the left renal artery for 45 min and then reperfusing the kidney. On Day 1 after renal ischemia/reperfusion (I/R), serum creatinine (SCr) in I/R rats was higher than in sham-operated rats, but this did not reach significance. Urinary N-acetyl-β-D-glucosaminidase (NAG) exhibited a significant increase but decreased on Day 2 in I/R rats. In contrast, urinary vanin-1 significantly increased on Day 1 and remained at a significant high level on Day 2 in I/R rats. Renal vanin-1 protein decreased on Days 1 and 3. In line with these findings, immunofluorescence staining demonstrated that vanin-1 was attenuated in the renal proximal tubules of I/R rats. Our in vitro results confirmed that the supernatant from HK-2 cells under hypoxia/reoxygenation included significantly higher levels of vanin-1 as well as KIM-1 and NGAL. In conclusion, our results suggest that urinary vanin-1 might be a potential novel biomarker of AKI induced by I/R.

MicroRNAs as Biomarkers and Therapeutic Targets in Inflammation- and Ischemia-Reperfusion-Related Acute Renal Injury

Acute kidney injury (AKI), caused mainly by ischemia-reperfusion, sepsis, or nephrotoxins (such as contrast medium), is identified by an abrupt decline in kidney function and is associated with high morbidity and mortality. Despite decades of efforts, the pathogenesis of AKI remains poorly understood, and effective therapies are lacking. MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression at the posttranscriptional level to control cell differentiation, development, and homeostasis. Additionally, extracellular miRNAs might mediate cell-cell communication during various physiological and pathological processes. Recently, mounting evidence indicates that miRNAs play a role in the pathogenesis of AKI. Moreover, emerging research suggests that because of their remarkable stability in body fluids, microRNAs can potentially serve as novel diagnostic biomarkers of AKI. Of note, our previous finding that miR-494 is rapidly elevated in urine but not in serum provides insight into the ultimate role of urine miRNAs in AKI. Additionally, exosomal miRNAs derived from stem cells, known as the stem cell secretome, might be a potential innovative therapeutic strategy for AKI. This review aims to provide new data obtained in this field of research. It is hoped that new studies on this topic will not only generate new insights into the pathophysiology of urine miRNAs in AKI but also might lead to the precise management of this fatal disease.

Therapeutic potential of mesenchymal stem cells in acute kidney injury is affected by administration timing

Mesenchymal stem cell (MSC) transplantation is a promising therapy for acute kidney injury; however, the efficacy is limited due to poor survival after transplantation. In this study, we investigated how MSC transplantation timing affected the survival and therapeutic potential of MSCs in the kidney ischemia-reperfusion (I/R) injury model. After kidney I/R injury, the inflammatory process and tissue damage were characterized over 1 week post-I/R, we found that inflammation peaked at 12-24 h post-I/R (h.p.i.), and urine  neutrophil gelatinase-associated lipocalin (NGAL) measurements correlated highly with measures of inflammation. We cultured MSCs with supernatants from I/R injured kidney tissue homogenates collected at different time points and found that kidney homogenates from 12 and 24 h.p.i. were most toxic to MSCs, whereas homogenates from 1 h.p.i. were not as cytotoxic as those from 12 and 24 h.p.i. Compared with MSCs administered at 12, or 24 h.p.i., cells administered immediately after ischemia or 1 h.p.i. yielded the highest renoprotective and anti-inflammatory effects. Our findings indicate that MSC treatment for acute kidney injury is most effective when applied prior to the development of a potent inflammatory microenvironment, and urine NGAL may be helpful for detecting inflammation and selecting MSC transplantation timing in I/R kidney injury.

Dynamics of Urinary Calprotectin after Renal Ischaemia

Background: Urinary calprotectin has been identified as a promising biomarker for acute kidney injury. To date, however, the time-dependent changes of this parameter during acute kidney injury remain elusive. The aim of the present work was to define the time-course of urinary calprotectin secretion after ischaemia/reperfusion-induced kidney injury in comparison to neutrophil gelatinase—associated lipocalin, thereby monitoring the extent of tubular damage in nephron sparing surgery for kidney tumours. Methods: The study population consisted of 42 patients. Thirty-two patients underwent either open or endoscopic nephron sparing surgery for kidney tumours. During the surgery, the renal arterial pedicle was clamped with a median ischaemic time of 13 minutes (interquartile range, 4.5–20.3 minutes) in 26 patients. Ten retro-peritoneoscopic living donor nephrectomy patients and 6 nephron sparing surgery patients in whom the renal artery was not clamped served as controls. Urinary calprotectin and neutrophil gelatinase—associated lipocalin concentrations were repeatedly measured by enzyme-linked immunosorbent assay and assessed according to renal function parameters. Results: Urinary concentrations of calprotectin and neutrophil gelatinase—associated lipocalin increased significantly after ischaemia/reperfusion injury, whereas concentrations remained unchanged after nephron sparing surgery without ischaemia/reperfusion injury and after kidney donation. Calprotectin and neutrophil gelatinase—associated lipocalin levels were significantly increased 2 and 8 hours, respectively, post-ischaemia. Both proteins reached maximal concentrations after 48 hours, followed by a subsequent persistent decrease. Maximal neutrophil gelatinase—associated lipocalin and calprotectin concentrations were 9-fold and 69-fold higher than their respective baseline values. The glomerular filtration rate was only transiently impaired at the first post-operative day after ischaemia/reperfusion injury (p = 0.049). Conclusion: Calprotectin and neutrophil gelatinase—associated lipocalin can be used to monitor clinical and sub-clinical tubular damage after nephron sparing surgery for kidney tumours. Urinary calprotectin concentrations start rising within 2 hours after ischaemia/reperfusion-induced kidney injury.

Protective effect of truncated Na+/K+-ATPase β on ischemia/reperfusion-induced renal injury in rats

Renal ischemia/reperfusion(I/R) is an important injury part of ischemic acute renal failure, and it is also the main factor that affects the early functional recovery and the long-term survival of transplanted kidney in renal transplantation. In this study, we cloned and expressed truncated Na+/K+-ATPase β(tNKAβ) and demonstrated that tNKAβ could activate NKA α subunit and induce protective effect on human kidney-2(HK-2) cells via PKCɛ signal pathway. The half maximum effective concentrations (EC₅₀) of tNKAβ were 0.24 µM. Furthermore, the application of EAVSLKPT (PKCɛ inhibitor) could abolish the protective effect of tNKAβ in HK-2 cells subjected to ischemia/reperfusion. To identify the protective effect of tNKAβ against the I/R injury in the kidney, Sprague-Dawley rats were treated with tNKAβ (75 mg/kg) for 2 h before ischemia. The tNKAβ-treated group demonstrated a significant improvement in renal function with a lower serum creatinine and blood urea nitrogen (BUN) levels on postoperative days 1-6. Renal sections obtained from rats of the I/R group showed serious renal injury which included degeneration of tubular structure, tubular dilation, swelling and necrosis, luminal congestion, and muddy brown casts formed by sloughing of severely damaged tubular epithelial cells. However, sections of rats that were administered with tNKAβ 2 h before reperfusion showed marked reduction of the histological features of renal injury compared with kidneys that were subjected to I/R only. In conclusion, the protective effects of tNKAβ against renal I/R injury have been evaluated for the first time, and these protective effects may occur via stimulation of PKCɛ pathways.

Intensive perioperative simvastatin treatment protects from chronic kidney allograft injury

BACKGROUND/AIMS

Ischemia-reperfusion injury (IRI) and innate immune response augment adaptive immunity and may also trigger repair processes that lead to uncontrolled fibrosis and atherosclerosis as seen in chronic allograft injury. Simvastatin has been shown to protect from renal IRI in several experimental studies. The aim of this study was to examine the effect of donor simvastatin pretreatment and early initiation of recipient simvastatin treatment on chronic kidney allograft injury.

METHODS

A rat renal transplantation model was used. Simvastatin was administered perorally for donor (5 mg/kg) and/or for recipient (2 mg/kg) 2 hours before transplantation and/or as daily treatment starting on the first postoperative day (2 mg/kg/day). The study included 5 groups: (1) no simvastatin, (2) donor pretreatment, (3) daily recipient treatment, (4) donor pretreatment + daily recipient treatment and (5) donor pretreatment + recipient pretreatment + daily recipient treatment. The grafts were recovered at day 90 for histopathological and immunohistochemical analysis. Kidney function was followed weekly with serum creatinine, and 24-hour urine protein was measured 60 and 90 days after transplantation.

RESULTS

We found that donor and recipient simvastatin pretreatment combined with daily recipient treatment reduced graft inflammation and chronic allograft injury. Treatment using only statins started after transplantation reduced inflammation to some extent, but did not affect chronic kidney allograft injury. Pretreatment using only donor statins impaired graft function and increased proteinuria.

CONCLUSION

Our data suggest that perioperative recipient statin treatment reduces inflammation and may protect the graft in the long term.

Changes of thioredoxin, oxidative stress markers, inflammation and muscle/renal damage following intensive endurance exercise

Thioredoxin (TRX) is a 12 kDa protein that is induced by oxidative stress, scavenges reactive oxygen species (ROS) and modulates chemotaxis. Furthermore it is thought to play a protective role in renal ischemia/reperfusion injury. Complement 5a (C5a) is a chemotactic factor of neutrophils and is produced after ischemia/reperfusion injury in the kidney. Both TRX and C5a increase after endurance exercise. Therefore, it may be possible that TRX has an association with C5a in renal disorders and/or renal protection caused by endurance exercise. Accordingly, the aim of this study was to investigate relationships among the changes of urine levels of TRX, C5a and acute kidney injury (AKI) caused by ischemia/reperfusion, inflammatory responses, and oxidative stress following intensive endurance exercise. Also, we applied a newly-developed measurement system of neutrophil migratory activity and ROS-production by use of ex vivo hydrogel methodology with an extracellular matrix to investigate the mechanisms of muscle damage. Fourteen male triathletes participated in a duathlon race consisting of 5 km of running, 40 km of cycling and 5 km of running were recruited to the study. Venous blood and urine samples were collected before, immediately following, 1.5 h and 3 h after the race. Plasma, serum and urine were analyzed using enzyme-linked immunosorbent assays, a free radical analytical system, and the ex vivo neutrophil functional measurement system. These data were analyzed by assigning participants to damaged and minor-damage groups by the presence and absence of renal tubular epithelial cells in the urinary sediments. We found strong associations among urinary TRX, C5a, interleukin (IL)-2, IL-4, IL-8, IL-10, interferon (IFN)-γ and monocyte chemotactic protein (MCP)-1. From the data it might be inferred that urinary TRX, MCP-1 and β-N-acetyl-D-glucosaminidase (NAG) were associated with renal tubular injury. Furthermore, TRX may be influenced by levels of IL-10, regulate chemotactic activity of C5a and IL-8, and control inflammatory progress by C5a and IL-8. In the longer duration group (minor-damage group), circulating neutrophil count, plasma concentration of myeloperoxidase (MPO) and serum concentration of myoglobin were markedly increased. In the higher intensity group (damaged group), neutrophil activation and degranulation of MPO might be inhibited, because not only was ROS production observed to be higher, but also antioxidant capacity and antiinflammatory cytokines were increased. Critically, the newlydeveloped ex vivo methodology corroborated the neutrophil activation levels in the two groups of participants.

N-acetyl-beta-glucosaminidase urine activity as a marker of early proximal tubule damage and a predictor of the long-term function of the transplanted kidneys

INTRODUCTION

Ischaemia-reperfusion injury (IRI) is a factor leading to the damages of the transplanted kidney, what affects mainly the proximal tubules. Early monitoring of tubule damage can be an efficient tool to predict the allograft dysfunction. Present in proximal tubules, N-acetyl-beta-glucosaminidase (NAG) is a lysosomal enzyme whose excretion rises as a result of IRI or acute rejection. The aim of this study was to monitor the NAG urine activity to evaluate the early proximal tubule damage, and to try to predict the long-term function of the transplanted kidney.

MATERIAL AND METHODS

The study enrolled 87 Caucasian renal transplant recipients (61.7% males, 38.3% females, mean age 45.56±14.34 years). Urine samples were collected for NAG and creatinine analysis on the 1st day after transplantation, and then in the 3rd and 12th month. Protocol biopsies were performed in the 3rd and 12th month.

RESULTS

A significant positive correlation between NAG urine activity in the 3rd month after transplantation and creatinine concentration on the 14th (p=0.004) and 30th day (p=0.05), in the 3rd month (p=0.009) and after the 1st (p=0.005) and 2nd year (p=0.003) was observed. A statistically significantly higher urinary NAG activity in samples collected in the first 3 days and in the 3rd month after transplantation among patients with DGF (p=0.006 and p=0.03 respectively) was found. There was a significant positive correlation between NAG urine activity in the 3rd month and the grade of tubular atrophy in specimens collected in the 3rd (p=0.03) and 12th (p=0.04) month.

CONCLUSIONS

Monitoring of NAG urine activity is useful in the evaluation of early proximal tubule damage and predicting the long-term function of the transplanted kidneys.

¹H NMR-based metabonomic analysis of the effect of optimized rhubarb aglycone on the plasma and urine metabolic fingerprints of focal cerebral ischemia-reperfusion rats

ETHNOPHARMACOLOGICAL RELEVANCE

The ischemia cerebrovascular disease is one of leading causes of death and long-term disability in modern society. Rhubarb is one of the common traditional Chinese medicine with many effects, and the main pharmacodynamic ingredients are aloe-emodin, rhein, emodin, chrysophanol and physcion. The five components are also known as rhubarb aglycone. Rhubarb aglycone has been confirmed to play a remarkable curative effect on cerebral ischemia, but the mechanism is not clear. In this study, (1)H NMR-based metabonomics approach has been used to investigate the protective effect of the optimized rhubarb aglycone on rats of cerebral ischemia-reperfusion.

MATERIALS AND METHODS

Male Wistar rats were divided into four groups: sham operation group, model group, Nimodipine group and the optimized rhubarb aglycone group. Based on (1)H-NMR spectra of plasma and urine, principal component analyses were performed to identify different metabolic markers and explore the changes of associated biochemical pathways. Behavior research and brain histopathology examinations were also performed.

RESULTS

It was showed that the optimized rhubarb aglycone treatment improved neurological deficits, cerebral infarction and neuronal apoptosis. Principal component analysis scores plots demonstrated that the cluster of model rats was separated from those of sham operation group; rats of the optimized rhubarb aglycone group were classified from model group, but the optimized rhubarb aglycone group closed to the sham operation group. Optimized rhubarb aglycone regulated the associated amino acid, energy and lipid metabolisms disturbed in model rats.

CONCLUSION

Our results suggested that the optimized rhubarb aglycone had protective effect on rats of cerebral ischemia-reperfusion and explored the metabolic regulation mechanism. This work showed that the NMR-based metabonomics approach might be a promising approach to study mechanisms of traditional Chinese medicines.

Evaluation of aqueous extract of Murraya koenigii in unilateral renal ischemia reperfusion injury in rats

AIM

The aqueous extract of leaves of Murraya koenigii was studied for its renoprotective potential against unilateral renal ischemia reperfusion (RIR) injury in male Wistar rats.

MATERIALS AND METHODS

Healthy adult male Wistar rats were divided into five groups (n = 8) and were treated with 200 mg/kg., p.o. of aqueous extract of M. koenigii (AEMK) for 30 days to assess both preventive and curative effects of AEMK. Except Group I, RIR was induced to all the groups by clamping the left renal artery using artery clamp for 1 h followed by reperfusion by removing the clamp. Groups II and III underwent RIR at 30(th) day whereas RIR was induced in Groups IV and V at 1(st) day of treatment schedule. Biochemical parameters (serum creatinine, blood urea nitrogen, serum total protein and serum Na(+)), urinary parameters (urine output, urinary creatinine, urinary urea, urinary total protein, urinary Na(+)), in vivo anti-oxidants, renal myeloperoxidase (MPO) activity and histopathology of kidneys were monitored. Statistical significance was set at P < 0.05.

RESULTS

Rats were treated with AEMK significantly (P < 0.05) restored the serum and urinary parameters with significant (P < 0.05) improvement in endogenous anti-oxidants such as superoxide dismutase, catalase and reduced glutathione and decreased levels of malondialdehyde and renal MPO when compared with the control groups. Histopathological examination also supported the biochemical and urinary tests.

CONCLUSIONS

Aqueous extract of M. koenigii possesses both preventive and curative effects against RIR injury.

Preconditioning with triiodothyronine improves the clinical signs and acute tubular necrosis induced by ischemia/reperfusion in rats

Background

Renal ischemia/reperfusion (I/R) injury is manifested by acute renal failure (ARF) and acute tubular necrosis (ATN). The aim of this study was to evaluate the effectiveness of preconditioning with 3, 3, 5 triiodothyronine (T₃) to prevent I/R renal injury.

Methodology/Principal Findings

The rats were divided into four groups: sham-operated, placebo-treated (SO-P), sham-operated T_3- treated (SO- T₃), I/R-injured placebo-treated (IR-P), and I/R-injured T₃-treated (IR- T₃) groups. At 24 h before ischemia, the animals received a single dose of T₃ (100 μg/kg). Renal function and plasma, urinary, and tissue variables were studied at 4, 24, and 48 h of reperfusion, including biochemical, oxidative stress, and inflammation variables, PARP-1 immunohistochemical expression, and ATN morphology. In comparison to the SO groups, the IR-P groups had higher plasma urea and creatinine levels and greater proteinuria (at all reperfusion times) and also showed: increased oxidative stress-related plasma, urinary, and tissue variables; higher plasma levels of IL6 (proinflammatory cytokine); increased glomerular and tubular nuclear PARP-1 expression; and a greater degree of ATN. The IR-T₃ group showed a marked reduction in all of these variables, especially at 48 h of reperfusion. No significant differences were observed between SO-P and SO-T₃ groups.

Conclusions

This study demonstrates that preconditioning rats with a single dose of T₃ improves the clinical signs and ATN of renal I/R injury. These beneficial effects are accompanied by reductions in oxidative stress, inflammation, and renal PARP-1 expression, indicating that this sequence of factors plays an important role in the ATN induced by I/R injury.

A biphasic response to nitric oxide donation in an ex vivo model of donation after cardiac death renal transplantation

BACKGROUND

Donation after cardiac death (DCD) donors are vital to maximize the organ donor pool. Reperfusion injury (RI) is an important sequela in DCD organs due to warm and cold ischemia. RI manifests clinically as a high incidence of delayed graft function (DGF) and primary non-function (PNF) compared with donation after brain death organs. The importance of nitric oxide (NO) in the generation of reperfusion injury is pivotal.

METHODS

Using an ex vivo porcine model of kidney transplantation the effects of reperfusion with and without NO supplementation on initial renal blood flow and function were compared. Real-time hemodynamic measurements were recorded and biochemical samples taken at set time-points. Molecular markers of reperfusion injury were also measured. Sodium nitroprusside was chosen as the NO donor.

RESULTS

Results showed that NO donation initially improved renal blood flow significantly over controls; at the end of reperfusion this benefit was lost. In addition, there was an improvement in creatinine clearance, fractional excretion of sodium and renal oxygen consumption. There were observed to be higher levels of urinary nitrite/nitrate excretion, but no difference in isoprostane levels.

CONCLUSION

This study represents a good model for the initial reperfusion period in large animal renal transplantation. The improvement in renal blood flow observed in the NO supplemented groups represents NO mediated vasodilatation. Later in reperfusion, accumulation of nitrogenous free radicals impairs renal blood flow. Clinically, NO supplementation during initial reperfusion of DCD kidneys improves renal blood flow but should be considered with caution due to potential deleterious effects of nitrogenous compound accumulation.

Urinary hepatocyte growth factor indicates ischemia/reperfusion injury after kidney transplantation

INTRODUCTION

Despite the development of immunosuppressive regimens in kidney transplantation, long-term graft survival rates have not increased significantly. One of the causes of long-term graft loss is ischemia-reperfusion insult. Hepatocyte growth factor (HGF) is a regenerative factor produced in response to injury.

OBJECTIVES

Our aim was to assess the effect of HGF and xanthine oxidase (indicators of ischemia/reperfusion insult) on early and late kidney function.

PATIENTS AND METHODS

In 17 patients, HGF levels in urine and xanthine oxidase activity in blood were examined 1, 7, 14, 30 days, 3 and 6 months after kidney transplantation. We also measured 24-hour diuresis and serum creatinine levels after transplantation.

RESULTS

Urinary HGF levels were highest 1 day after transplantation. During the following week, it rapidly decreased and was maintained at similar levels in the later period. Creatinine at 1 day showed a positive correlation with urinary HGF levels at 1 day and at 3 months (R = 0.54, P <0.05 and R = 0.82, P <0.01, respectively). Creatinine at 7 days positively correlated with HGF levels at 6 months (R = 0.82, P <0.05). HGF levels at 1 day and at 6 months positively correlated with xanthine oxidase activity at 1 day (R = 0.73, P <0.001 and R = 0.77, P <0.02, respectively). A negative correlation was observed between HGF levels at 6 months and diuresis 1 and 7 days after transplantation (R = -0.99, P <0.00 001 and R = -0.77, P <0.05, respectively).

CONCLUSIONS

Urinary HGF is a good marker of perioperative kidney damage and may affect long-term graft function.

Methylprednisolone increases urinary nitrate concentrations and reduces subclinical renal injury during infrarenal aortic ischemia reperfusion

OBJECTIVE

This study tests the hypothesis that methylprednisolone may influence eNOS activity in renal arterial and venous vascular beds and impede subclinical renal injury.

SUMMARY BACKGROUND DATA

Acute renal failure is a major complication of cardiovascular surgery. Renal damage arises in part from excessive vasoconstriction mediated by an imbalance of vasoconstrictive ET-1 and vasodilatory NO produced by eNOS. While methylprednisolone may reduce subclinical renal injury as measured by urinary N-acetyl-beta-D-glucosaminidase (beta-NAG), its effects upon eNOS activity in renal arterial and venous vascular beds, reflected by urinary nitrate levels, is unclear.

METHODS

A porcine model of normotensive, euvolemic infrarenal aortic ischaemia-reperfusion was used. Forty-two pigs underwent a 60-minute laparotomy followed by 150 minutes of infrarenal ischemia and 180 minutes of reperfusion. Animals were randomized to receive methylprednisolone 30 mg/kg or placebo after induction of general anesthesia. Urinary beta-NAG levels were assessed as an index of subclinical renal injury, whereas urinary nitrate was assessed as an indicator of eNOS activity in renal arterial and venous vascular beds.

RESULTS

Methylprednisolone treatment did not influence mean arterial, central venous, or pulmonary artery wedge pressures but suppressed plasma IL-6 levels. After the ischemia-induced rise from preanaesthetic baseline levels, urinary beta-NAG levels declined to significantly lower values in the MP group, indicative of MP renal protection (P < 0.05). Conversely, urinary nitrate levels indicative of vascular e-NOS activity remained significantly and persistently higher in MP-treated animals (P < 0.05).

CONCLUSION

This study, in a porcine model of renal ischaemia-reperfusion injury, shows the benefits of methylprednisolone pretreatment in enhancing urinary nitrate levels indicative of vascular eNOS activity and the reduction of urinary beta-NAG levels, which represent subclinical renal injury.

Single-dose intravenous simvastatin treatment attenuates renal injury in an experimental model of ischemia-reperfusion in the rat

The effect of acute pretreatment with a single dose of simvastatin (1 mg/kg, i.v.; 30 min before ischemia) on renal dysfunction caused by ischemia-reperfusion (I/R) injury in the rat was investigated. I/R injury was induced by clamping both renal vascular pedicles for 45 min, followed by 4 h of reperfusion with saline (2 ml/kg per hour). Simvastatin significantly improved both parameters of glomerular and tubular dysfunction (e.g., creatinine levels and fractional excretion of Na(+), respectively) and especially improved the histological score, compared to control I/R-injured rats treated with saline or 10% DMSO only.

Exosomal Fetuin-A identified by proteomics: a novel urinary biomarker for detecting acute kidney injury

Urinary exosomes containing apical membrane and intracellular fluid are normally secreted into the urine from all nephron segments, and may carry protein markers of renal dysfunction and structural injury. We aimed to discover biomarkers in urinary exosomes to detect acute kidney injury (AKI), which has a high mortality and morbidity. Animals were injected with cisplatin. Urinary exosomes were isolated by differential centrifugation. Protein changes were evaluated by two-dimensional difference in gel electrophoresis and changed proteins were identified by mass spectrometry. The identified candidate biomarkers were validated by Western blotting in individual urine samples from rats subjected to cisplatin injection; bilateral ischemia and reperfusion (I/R); volume depletion; and intensive care unit (ICU) patients with and without AKI. We identified 18 proteins that were increased and nine proteins that were decreased 8 h after cisplatin injection. Most of the candidates could not be validated by Western blotting. However, exosomal Fetuin-A increased 52.5-fold at day 2 (1 day before serum creatinine increase and tubule damage) and remained elevated 51.5-fold at day 5 (peak renal injury) after cisplatin injection. By immunoelectron microscopy and elution studies, Fetuin-A was located inside urinary exosomes. Urinary Fetuin-A was increased 31.6-fold in the early phase (2-8 h) of I/R, but not in prerenal azotemia. Urinary exosomal Fetuin-A also increased in three ICU patients with AKI compared to the patients without AKI. We conclude that (1) proteomic analysis of urinary exosomes can provide biomarker candidates for the diagnosis of AKI and (2) urinary Fetuin-A might be a predictive biomarker of structural renal injury.

Early Proteinuria Is a Strong Indicator of Donor Renal Lesions, Ischemia-Reperfusion Injury and Immunological Aggression

BACKGROUND

Early proteinuria is associated with reduced long-term graft survival. However, the determinants and mechanisms of proteinuria early after transplantation have not been identified.

METHODS

Parameters associated with proteinuria within the first 3 months following transplantation were retrospectively assessed among 484 renal transplant recipients.

RESULTS

Proteinuria was more abundant in patients with a history of two or more rejection episodes (0.42 +/- 0.68 vs 0.18 +/- 0.39 g/d; P = .02). Proteinuria was greater when donor age was 60 or more (OR: 4.43; P = .003), when recipient death was due to cardiovascular causes (OR: 1.98; P = .002), or when cold (OR: 1.77; P = .006) or warm (1.21; P = .09) ischemia times were prolonged.

CONCLUSIONS

Proteinuria early after transplantation was related to pretransplant renal lesions, ischemia-reperfusion, and immunologic injuries.

Polyenylphosphatidylcholine pretreatment ameliorates ischemic acute renal injury in rats

AIM

Polyenylphosphatidycholine has been demonstrated to have antioxidant, cytoprotective and anti-inflammatory effects. Whether polyenylphosphatidycholine pretreatment affects ischemia/reperfusion-induced renal damage in vivo is not known and was investigated here in rats.

METHODS

Forty female Sprague-Dawley rats were divided into three groups. Group 1 (n = 10) was given saline (control, sham operated). Group 2 (n = 15) were given saline, and Group 3 (n = 15) were given polyenylphosphatidycholine (100 mg/day for 10 days prior to experiment). Groups 2 and 3 were subjected to bilateral renal ischemia (60 min) followed by reperfusion (6 h). After the reperfusion period, the rats were sacrificed and kidney tissue superoxide dismutase, glutathione, total nitrite and nitrate, malondialdehyde and myeloperoxidase levels, plasma aspartate aminotransferase, blood urea nitrogen and creatinine concentrations, and nuclear factor kappa beta expression were determined.

RESULTS

Serum levels of aspartate aminotransferase, blood urea nitrogen and creatinine were significantly decreased (P < 0.05) in the treatment group compared to those in the ischemic group. There were significant differences between treatment and ischemic groups regarding the tissue superoxide dismutase, glutathione, total nitrite and nitrate, malondialdehyde, and myeloperoxidase levels (P < 0.05). In addition, polyenylphosphatidycholine pretreatment reduced nuclear factor kappa beta expression in ischemic kidney tissue. Kidneys obtained from rats pretreated with polyenylphosphatidycholine demonstrated marked reduction of the histological features of renal injury compared to kidneys obtained from Group 2 rats, including a little vacuolization, pyknosis and necrosis.

CONCLUSIONS

Polyenylphosphatidycholine pretreatment provided significant protection against ischemia/reperfusion injury to the kidney. This treatment could be therapeutic in kidney transplantation and other conditions associated with ischemia/reperfusion injury to the kidney.

Early prediction of acute renal injury using urinary proteomics

AIMS

The lack of early biomarkers for acute renal failure (ARF) has crippled our ability to launch potentially effective therapeutic measures. We tested the hypothesis that urinary proteomics could identify novel early biomarker patterns for ischemic renal injury.

METHODS

Sixty patients undergoing cardiopulmonary bypass (CPB) were enrolled. Urine samples obtained at 2 and 6 h post CPB were analyzed by Surface-Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF-MS). The primary outcome variable was ARF, defined as a 50% or greater increase in serum creatinine.

RESULTS

Fifteen patients (25%) developed ARF 2-3 days after CPB. SELDI-TOF-MS analysis of urine from the ARF group at baseline versus at 2 and 6 h post-CPB consistently showed a marked and statistically significant enhancement of protein biomarkers with m/z of 6.4, 28.5, 43 and 66 kDa. The same biomarkers were enhanced when comparing control versus ARF groups at 2 and 6 h post-CPB. The sensitivity and specificity of the 28.5-, 43- and 66-kDa biomarkers for the prediction of ARF at 2 h following CPB was 100%. The receiver operating characteristic curves revealed an area under the curve of 0.98.

CONCLUSION

SELDI-TOF-MS is a novel, non-invasive, sensitive, highly predictive, reproducible, rapid method for the prediction of acute renal injury following CPB.

[Determination of urinary NAG to detect renal ischemia-reperfusion injury and the protective effect of Allopurinol]

We analysed the effect of ischemia-reperfusion injury to renal parenchyma after unilateral renal artery clamping using urinary N-acetyl-beta-D-glucosaminidase (NAG) that is a sensitive parameter of early renal tubular injury. In the study 60 mongrel dogs were divided into 3 groups: in the 1st group the left renal artery was clamped for 45 minutes, in the 2nd group Allopurinol was administered before the clamping, the 3rd was the control group, where only laparotomy and closure of the abdomen was performed. Urinary NAG activity referring to urinary creatinine (NAG index) was determined before the operation, at the beginning of the reperfusion, in the 60th and 120th minute of the reperfusion then 1, 2, 3 and 5 days after the operation. The highest NAG indices relating to injury of the proximal tubuli were found at the beginning of the reperfusion, in the 60th and 120th minutes of the reperfusion, then NAG returned to preoperative level in each group. Significantly higher NAG indices were found in the ischemia-reperfusion group compared to the group with Allopurinol pretreatment. Renal ischemia-reperfusion injury and the protective effect of Allopurinol could be detected by lysosomal NAG enzyme. The injury of the tubular function was reversible so it could be a change in tubular function.

Patients with critical ischemia of the lower limb are at risk of developing kidney dysfunction

BACKGROUND

The aim of this study is to establish a relationship between critical ischemia of the lower limb and kidney dysfunction.

MATERIALS AND METHODS

At rest, urine samples were collected from three groups: group A, 16 patients with critical ischemia; group B, 22 patients with stable intermittent claudication; and group C, 12 normal individuals. Urinary N-acetyle-beta-D-glucosaminidase (NAG) enzyme was measured using spectrophotometer. Microalbuminuria was measured by radioimmunoassay.

RESULTS

There was a significant difference in the NAG activity between groups A and B, P = 0.001. Also, between group A and C, P = 0.01. There was no significant difference between groups B and C, P = 0.13. Microalbuminuria was not significantly different among the three groups: A versus B, P = 0.27; A versus C, P = 0.22; B versus C, P = 0.11.

CONCLUSIONS

Elevated levels of NAG enzyme in patients with critical ischemia of the lower limb suggest that they are at greater risk of developing kidney dysfunction. This could be caused by the release of more free radicals into the systemic circulation.

Early detection of cysteine rich protein 61 (CYR61, CCN1) in urine following renal ischemic reperfusion injury

BACKGROUND

Acute renal failure (ARF) has a high morbidity and mortality. Many therapies have worked in animals but were unsuccessful in clinical trials. The inability to diagnose ARF early may have impaired the success of these trials.

METHOD

We screened a subtraction library to search for potential disease markers that would be induced rapidly after renal injury. Mice and rats were subjected to 30 to 40 minutes of bilateral ischemia.

RESULTS

mRNA for Cyr61, a secreted growth factor-inducible immediate early gene, was markedly up-regulated at two hours in the kidney but not other organs following renal ischemia. In situ hybridization studies suggested Cyr61 was synthesized in the proximal straight tubule. Cyr61 protein was analyzed by capture with heparin beads followed by Western blotting. Induction of Cyr61 protein could be detected in the kidney within one hour, peaked at four to eight hours, and remained elevated for at least 24 hours following ischemia. Cyr61 protein was detected in urine at three to six hours and peaked at six to nine hours after renal injury. Cyr61 was not detected after volume depletion, which is often difficult to differentiate from ARF.

CONCLUSIONS

The secreted, cysteine-rich, heparin binding protein Cyr61 is rapidly induced in proximal straight tubules following renal ischemia, and excreted in the urine where it might serve as an early biomarker of renal injury.

Monocyte chemoattractant protein-1 expression correlates with monocyte infiltration in the post-ischemic kidney

Chemokines play a prominent role in the acute inflammatory response in several models of kidney disease. We reported that monocyte chemotactic peptide-1 (MCP-1) mRNA is increased by ischemia-reperfusion injury. In this report, we examined the effects of ischemia-reperfusion injury on the kinetics and location of MCP-1 protein expression, the excretion of MCP- 1 protein in the urine and on the infiltration of mononuclear cells in the kidney. Pair-fed Sprague-Dawley rats underwent bilateral renal ischemia (50 min) or sham ischemia and placed in metabolic cages for daily urine collections. Kidneys were harvested at d. 1, 3, 7, and 10 after ischemia-reperfusion (I-R) or sham-ischemia (S-I). Kidney MCP-1 mRNA levels were increased on d. I and 3 post-ischemia. Kidney MCP-1 protein levels were increased in the I-R group on d. 1 and 3. MCP-1 expression occurred predominantly in the distal tubule segments by immunohistology. There was an increase in monocytes/macrophages infiltration in the I-R group, compared to the S-I or controls by d. 1. Urinary MCP-1 excretion increased 3-fold in the I-R group, and remained elevated above the S-I group and baseline levels, on d. 3 through d. 8. Kidney MCP-1 mRNA levels, protein levels and urinary MCP-1 excretion rates are increased by ischemia-reperfusion injury. The areas of increase in MCP-1 chemoattractant expression correlates with an increase in monocyte infiltration in the kidney. Although its pathophysiologic role remains to be determined, MCP-1 may participate in, and be a biomarker for, the mononuclear inflammatory processes that occur after ischemia-induced acute renal failure.

Resveratrol, a component of wine and grapes, in the prevention of kidney disease

Ischemia is an inciting factor in 50% of incidences of acute renal failure, and it increases the risk of organ rejection after renal transplantation. We have previously demonstrated that resveratrol (RSV) reduces ischemia-reperfusion (I/R) injury of rat kidney both by antioxidant and anti-inflammatory mechanisms. However, a clear morphological demonstration of this activity has not been made. To answer this question we have performed a new set of experiments following the experimental protocol reported below to investigate the effects of I/R injury and RSV pretreatment on kidney morphology by computerized morphometric analysis. Both renal arteries were clamped for 40 minutes in 40 male Wistar rats (b.w. 220 +/- 20 g); 20 rats were pretreated with RSV 1 microM e.v. 40 minutes before clamping. All animals were reperfused for 24 hours and then sacrificed. Histological examination showed tissue conservation in treated rats. I/R-induced glomerular collapse (as revealed by mean glomerular volume and glomerular shape factor) was significantly reduced by RSV pretreatment. Capillary tuft/Bowman's capsule area ratio was enhanced in the I/R group suggesting tubular hypertension. RSV pre-treatments significantly reduced this parameter to the control value. The number of platelet clots in the capillary tuft and tubular necrosis were also reduced by RSV versus I/R group. L-NAME administration worsened both functional and structural damage. Finally, cGMP urinary levels were markedly reduced from 12.1 +/- 8.4 nmol/day to 0.10 +/- 0.10 nmol/day in the I/R group. RSV provided cGMP (5.01 +/- 1.5 nmol/day, P < 0.05). As expected, L-NAME administration significantly reduced cGMP in urine (0.71 +/- 0.6 nmol/day). The present study confirms the protective effect of RSV pretreatment in I/R injury of rat kidney and suggests multiple mechanisms of action.

Protective effect of alpha-lipoic acid against ischaemic acute renal failure in rats

1. In the present study, we investigated whether treatment with alpha-lipoic acid (LA), a powerful and universal anti-oxidant, has renal protective effects in rats with ischaemic acute renal failure (ARF). 2. Ischaemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Blood urea nitrogen (BUN), plasma concentrations of creatinine (Pcr) and urinary osmolality (Uosm) were measured for the assessment of renal dysfunction. Creatinine clearance (Ccr) and fractional excretion of Na+ (FENa) were used as indicators of glomerular and tubular function, respectively. 3. Renal function in ARF rats decreased markedly 24 h after reperfusion. Intraperitoneal injection of LA at a dose of 10 mg/kg before the occlusion tended to attenuate the deterioration of renal function. A higher dose of LA (100 mg/kg) significantly (P < 0.01) attenuated the ischaemia/reperfusion-induced increases in BUN (19.1 +/- 0.7 vs 7.2 +/- 0.7 mmol/L before and after treatment, respectively), Pcr (290 +/- 36 vs 78.1 +/- 4.2 micromol/L before and after treatment, respectively) and FENa (1.39 +/- 0.3 vs 0.33 +/- 0.09% before and after treatment, respectively). Treatment with 100 mg/kg LA significantly (P < 0.01) increased Ccr (0.70 +/- 0.13 vs 2.98 +/- 0.27 mL/min per kg before and after treatment, respectively) and Uosm (474 +/- 39 vs 1096 +/- 80 mOsmol/kg before and after treatment, respectively). 4. Histopathological examination of the kidney of ARF rats revealed severe lesions. Tubular necrosis (P < 0.01), proteinaceous casts in tubuli (P < 0.01) and medullary congestion (P < 0.05) were significantly suppressed by the higher dose of LA. 5. A marked increase in endothelin (ET)-1 content in the kidney after ischaemia/reperfusion was evident in ARF rats (0.43 +/- 0.02 ng/g tissue) compared with findings in sham- operated rats (0.20 +/- 0.01 ng/g tissue). Significant attenuation (P < 0.01) of this increase occurred in ARF rats treated with the higher dose of LA (0.24 +/- 0.03 ng/g tissue). 6. These results suggest that administration of LA to rats prior to development of ischaemic ARF prevents renal dysfunction and tissue injury, possibly through the suppression of overproduction of ET-1 in the postischaemic kidney.

Urinary thymidine glycol as a biomarker for oxidative stress after kidney transplantation

Reactive oxygen species are generated during ischemia-reperfusion tissue injury. Oxidation of thymidine by hydroxyl radicals (HO*) causes formation of 5,6-dihydroxy-5,6-dihydrothymidine (thymidine glycol). Thymidine glycol excreted in urine can be used as a biomarker of oxidative DNA damage. The aim of this study was to investigate the oxidative DNA damage in patients showing immediate allograft function after kidney transplantation, and to find out whether this damage correlates with glomerular and tubular lesions. Time dependent changes in urinary excretion rates of thymidine glycol, but also of total protein, albumin, low molecular weight (alpha1-microglobulin, beta2-microglobulin) and high molecular weight proteins (transferrin, IgG, alpha2-macroglobulin) were analyzed quantitatively and by polyacrylamide-gel electrophoresis in six patients. Urinary thymidine glycol was determined by a fluorimetric assay in combination with affinity chromatography and HPLC. After kidney transplantation the urinary excretion rate of thymidine glycol increased gradually reaching a maximum within the first 48 hours (16.56+/-11.3 nmol/m mol creatinine, ref. 4.3+/-0.97). Severe proteinuria with an excretion rate of up to 7.2 g/mmol creatinine was observed and declined within the first 24 hours of allograft function (0.35+/-0.26 g/mmol creatinine). The gel-electrophoretic pattern showed a nonselective glomerular and tubular proteinuria. The initial nonselective glomerular proteinuria disappeared within 48 hours, changing to a mild selective glomerular proteinuria. In this period (12-48 hours) higher levels of thymidine glycol excretion were observed, when compared to the initial posttransplant phase (13.66+/-9.76 vs. 4.31+/-3.61 nmol/mmol creatinine; p<0.05). An increased excretion of thymidine glycol is seen after kidney transplantation and is explained by the ischemia-reperfusion induced oxidative DNA damage in the kidney. In the second phase higher levels of excretion were observed parallel to the change from a nonselective to a selective glomerular and tubular proteinuria. An explanation may be sought in the repair process of DNA in the glomerular and tubular epithelial cells, appearing simultaneously with functional recovery.

Noninvasive monitoring of citrate, acetate, lactate, and renal medullary osmolyte excretion in urine as biomarkers of exposure to ischemic reperfusion injury

Injury during the transplant process affects the alloantigen-dependent factors and the alloantigen-independent processes of "chronic" rejection. Consequently, the determination of reliable parameters for the assessment of ischemic damage is essential for the prediction of renal changes after ischemia/reperfusion injury. The aim of this study was to assess the ability of (1)H NMR spectroscopy to predict the early graft dysfunction in an ischemia/reperfusion model after preservation in two standard preservation solutions, Euro-Collins (EC) and University of Wisconsin (UW). The second aim was to specify the role of the UW solution in preventing renal medullary injury. Urine and plasma samples from three experimental groups were examined during 2 weeks: control group (n = 5), EC group (cold flushed and 48-h cold storage of kidney in EC and autotransplantation, n = 12), and UW group (cold flushed and 48-h cold storage of kidney in UW and autotransplantation; n = 12). We also examined these kidneys 30-40 min after implantation and on the sacrifice day. Creatinine clearance was significantly reduced in the EC group during the second week. Fractional excretion of sodium and urine N-acetyl-beta-d-glucosaminidase activity were improved but not significantly different in the preserved groups. Urinary concentrations of the alpha-class glutathione S-transferase were significantly greater in the EC group during the first week after transplantation. The most relevant resonances for evaluating renal function after transplantation determined by (1)H NMR spectroscopy were those arising from citrate, dimethylamine (DMA), lactate, and acetate in urine and trimethylamine-N-oxide (TMAO) in urine and plasma. These findings suggest that graft dysfunction is associated with damage to the renal medulla determined by TMAO release in urine and plasma associated with DMA and acetate excretion. Citrate is also a urinary marker that can discriminate kidneys with a favorable evolution. Our results suggest that (1)H NMR spectroscopy is an efficient technique for detecting ischemic damage when accurate and precise data on graft injury is required. In addition, this study outlines the specific impact of the UW solution against injury to the renal medulla.

Trimetazidine reduces renal dysfunction by limiting the cold ischemia/reperfusion injury in autotransplanted pig kidneys

Ischemia/reperfusion injury leads to delayed graft function, which is a major problem in kidney transplantation. This study investigated the effects of adding trimetazidine (TMZ) to the perfusate of cold-stored kidneys on the function of reperfused autotransplanted pig kidney. The left kidney was removed and cold-flushed with Euro-Collins (EC), or University of Wisconsin (UW) solutions with or without 10(-6)M TMZ and stored for 48 h at 4 degrees C. The kidneys were then autotransplanted and the contralateral kidneys were removed. Several parameters were analyzed over the 14 d after transplantation. The survival rate was 57% in pigs transplanted with kidneys cold-flushed with UW and 43% for those flushed with EC solution; it was 100% for pigs having kidneys cold-flushed with TMZ-supplemented UW and EC solutions. The functions of the transplanted kidneys were also better preserved after cold flush with TMZ-supplemented solutions than with TMZ-free solutions. Creatinine clearance was higher and the urinary excretion of trimethylamine-N-oxide and dimethylamine, used as markers of renal medulla injury, were 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 and peritubular inflammation and the numbers of infiltrating mononuclear CD45+and CD3+ T cells. These results indicate that the tissue damage due to ischemia/reperfusion injury may be prevented, at least in part, by adding TMZ to preservation solutions.

Determination of urinary thymidine glycol using affinity chromatography, HPLC and post-column reaction detection: a biomarker of oxidative DNA damage upon kidney transplantation

Reactive oxygen species are generated during ischaemia-reperfusion of tissue. Oxidation of thymidine by hydroxyl radicals (HO) leads to the formation of 5,6-dihydroxy-5,6-dihydrothymidine (thymidine glycol). Thymidine glycol is excreted in urine and can be used as biomarker of oxidative DNA damage. Time dependent changes in urinary excretion rates of thymidine glycol were determined in six patients after kidney transplantation and in six healthy controls. A new analytical method was developed involving affinity chromatography and subsequent reverse-phase high-performance liquid chromatography (RP-HPLC) with a post-column chemical reaction detector and endpoint fluorescence detection. The detection limit of this fluorimetric assay was 1.6 ng thymidine glycol per ml urine, which corresponds to about half of the physiological excretion level in healthy control persons. After kidney transplantation the urinary excretion rate of thymidine glycol increased gradually reaching a maximum around 48 h. The excretion rate remained elevated until the end of the observation period of 10 days. Severe proteinuria with an excretion rate of up to 7.2 g of total protein per mmol creatinine was also observed immediately after transplantation and declined within the first 24 h of allograft function (0.35+/-0.26 g/mmol creatinine). The protein excretion pattern, based on separation of urinary proteins on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), as well as excretion of individual biomarker proteins, indicated nonselective glomerular and tubular damage. The increased excretion of thymidine glycol after kidney transplantation may be explained by ischaemia-reperfusion induced oxidative DNA damage of the transplanted kidney.

The influence of allopurinol on kidney haemodynamic and excretory responses to renal ischaemia in anaesthetized rats

1. This study examined the impact of allopurinol on the renal functional responses to a 30 min period of ischaemia in anaesthetized rats. 2. Immediately on reperfusion, blood pressure rose transiently, while renal blood flow remained stable throughout at control values. Glomerular filtration rate was decreased by some 90% over the first and 80% over the sixth hour (P<0.001). 3. Allopurinol, 50 or 100 mg kg-1, had no effect on the blood pressure or renal blood flow responses over the 6 h reperfusion period but glomerular filtration decreased by 60% initially, and to less than 30% of basal at 6 h. 4. Urine flow and absolute sodium excretion increased 2 - 3 fold in the first 2 h but decreased thereafter. Fractional sodium excretion was 30 times higher for the first 2 h but decreased reaching some 10 fold higher at 6 h. In the presence of allopurinol, urine flow and absolute sodium excretion increased by 5 - 6 fold in the first 2 h, and fell by half by 6 h which was greater than in the vehicle group (P<0.01). Fractional sodium excretion increased 20 fold in the allopurinol animals in the first 2 h period, but fell at a faster rate (P<0.01) than in untreated rats. 5. Potassium excretion decreased (P<0.05) by one half for the 6 h reperfusion period but in the allopurinol animals it was minimally altered. 6. Allopurinol largely ameliorated the decrease in kidney haemodynamic and excretory function following an ischeamic period for the initial few hours of reperfusion.

Indices of oxidative stress in urine of patients undergoing coronary artery bypass grafting

Indices of oxidative stress in urine were measured in twenty patients undergoing elective coronary artery bypass grafting. Hypoxanthine, xanthine and uric acid were measured in urine, as markers of ischaemia together with malondialdehyde, which is a marker for lipid peroxidation. To correct for renal dysfunction during coronary artery bypass grafting the creatinine concentration was measured in urine and plasma. The creatinine concentration in plasma increases significantly during surgery, from 84 +/- 23 mumol/l to 133 +/- 52 mumol/l, whereas the creatinine concentration in urine decreases significantly, from 8.29 +/- 4.45 mmol/l to 2.70 +/- 1.01 mmol/l, during reperfusion. For reasons of comparison, the values of the observed measurements in urine are expressed per mol creatinine. The hypoxanthine and xanthine excretions both increase significantly, from 15.0 +/- 7.3 and 10.9 +/- 5.7 mmol/mol creatinine, respectively, after induction of anaesthesia to a maximum of 33.1 +/- 16.7 and 17.4 +/- 11.1 mmol/mol creatinine, respectively, during reperfusion. The malondialdehyde excretion increases significantly, from 1.38 +/- 0.80 mmol/mol creatinine after induction of anaesthesia to a maximum of 3.87 +/- 1.87 mmol/mol creatinine during reperfusion. The purines and malondialdehyde in urine (expressed as a ratio of creatinine), increase during coronary artery bypass grafting as a consequence of oxygen mediated tissue injury.

[The effect of electrostimulation with the Rebox apparatus on ischemic renal injury in rats]

BACKGROUND

With developing transplantation programmes the problem of protection against ischaemic renal damage had become important. The results of experimental pharmacological protection of the kidneys are not quite conclusive. The objective of the presented paper was to assess the effect of electrostimulation by means of a Rebox apparatus (generator of direct rectangular impulses at a frequency of 1 to 10 kHz), on the development of ischaemic damage of the renal parenchyma induced experimentally in rats.

METHODS AND RESULTS

The experiments were made on Wistar strains rats (n = 15) which were subjected to dextrolateral nephrectomy and the left renal artery was closed by a clamp which was released in the tested and the control group after 30 minutes. In the rebox group electrostimulation with the Rebox apparatus was implemented immediately after release of the clamp. In rats which were in metabolic cages the following parameters were assessed: diuresis, period of survival, endogenous creatinine clearance, plasma creatinine level, urea level and excretion, as well as sodium and potassium urinary excretion. No significant difference in the survival time of the rats was found nor in the plasma levels of creatinine, urea and urinary excretion of potassium and urea between the control and the Rebox group. In the Rebox group, as compared with the control group, a significantly higher diuresis was found 22.8 vs 5.6 (p < 0.001) and natriuresis 0.44 vs 0.11 (p < 0.01).

CONCLUSIONS

Electrostimulation by rebox currents in rats increases significantly the diuresis and natriuresis of the solitary kidney exposed to 30-minute ischaemia but has no impact on other parameters. The mechanism of action is not quite clear, apparently the reabsorption of sodium in the proximal tubule is inhibited.

Effect of oxygen tension on activity of antioxidant enzymes and on renal function of the postischemic reperfused rat kidney

The aim of the present study was to examine the effect of exposing animals to 100% oxygen instead of room air on renal function and endogenous antioxidant enzymes of the postischemic reperfused rat kidney. Superoxide dismutase (SOD), catalase and glutathione peroxidase (GPX) were determined in the homogenate of the left kidney after 45 min of ischemia, caused by clamping the left renal artery, 10 and 90 min after reperfusion while the animals breathed room air or 100% O2. The right kidney served as a control. The possible influence of trapped blood in the clamped kidney was also investigated by the use of a correction factor based on the Hb concentration in the homogenate. The results indicate that such correction is necessary as the blood adds significant antioxidant activity. The activities of all 3 enzymes after 45 min of ischemia decreased significantly in the left (ischemic) compared to the right (control) kidney, to 64% of the control levels for catalase, 58% for SOD and 49% for GPX. After 10 min of reflow, a further decrease in the activities of catalase (to 49%) and of GPX (to 29%) was found. SOD activity, however, increased to 64%. After 90 min of reperfusion, restoration toward normal levels was noticed (SOD activity increased to 70%, catalase to 76% and GPX to 58%). Breathing 100% O2 resulted in a significant decrease in all enzyme activities (to 38.6% for catalase, 45% for SOD and to 27.4% for GPX). This inactivation can be explained by increased reactive oxygen species (ROS) activity during hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of nitric oxide in the oxidant stress during ischemia/reperfusion injury of the liver

The potential role of nitric oxide (NO) and its reaction product with superoxide, peroxynitrite, was investigated in a model of hepatic ischemia-reperfusion injury in male Fischer rats in vivo. Pretreatment with the NO synthase inhibitor nitro-L-arginine (10 mg/kg) did neither affect the post-ischemic oxidant stress and liver injury during the initial reperfusion phase nor the subsequent infiltration of neutrophils into the liver and the later, neutrophil-induced injury phase. Furthermore, no evidence was found for a postischemic increase of the urinary excretion of nitrite, a stable oxidation metabolite of NO. In contrast, the administration of Salmonella enteritidis endotoxin (1 mg/kg) induced a significant diuresis in Fischer rats and an 800-fold enhancement of the urinary nitrite excretion. Nitro-L-arginine pretreatment inhibited the endotoxin-induced nitrite formation by 97%. Hepatic cGMP levels, as index of NO formation in the liver, were only increased significantly after endotoxin administration but not after ischemia and reperfusion. Our results provide no evidence for any enhanced generation of NO or peroxynitrite either systemically or locally during reperfusion and therefore it is unlikely that any of these metabolites are involved in the oxidant stress and liver injury during reperfusion after hepatic ischemia.