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

Protective effects of adipose-derived stem cells against testicular injury induced after ischemia-reperfusion by regulating autophagy

The damaged organ may experience severe pathological alterations as a result of tissue ischemia-reperfusion (I/R). The study of stem cell-based repair therapies is actively being conducted, and the outcomes and therapeutic potential of these cells are both promising. Autophagy checks protein homeostasis by breaking down huge damaged proteins or organelles. The study's objective was to assess how ADSCs impact the autophagic process after testicular ischemia/reperfusion. In our investigation, 30 male rats were divided into five groups: control, ADSC, ischemia, I/R, and I/R + ADSC (n = 6). Hematoxylin-eosin (HE) was used to stain the testes, and histological changes were assessed. The immunoexpression of androgen receptor (AR), Beclin1, protein light chain 3B (LC3B), and p62 were examined. The seminiferous epithelium in the testis from the ischemia and I/R groups revealed significant degeneration with disorganized morphology, damaged spermatogenic cells, and interstitial space congestion, according to HE stain results. Johnsen's score were significantly better in I/R + ADSC group than in ischemia and I/R groups. We demonstrated that in rat testes from the I/R groups, immunostaining of Beclin 1 (p = 0.042) and LC3B (p = 0.011) were raised, and p62 (p = 0.047) and AR (p = 0.049) were decreased. Ischemia and I/R promoted testicular autophagy, therefore we can conclude that ADSCs prevent excessive autophagy. Additionally, these results show that the use of ADSCs cures testicular injury and dysfunction associated with I/R injury in rats even a little.

The role of non-protein-coding RNAs in ischemic acute kidney injury

Acute kidney injury (AKI) is a condition characterized by a rapid decline in kidney function within a span of 48 hours. It is influenced by various factors including inflammation, oxidative stress, excessive calcium levels within cells, activation of the renin-angiotensin system, and dysfunction in microcirculation. Ischemia-reperfusion injury (IRI) is recognized as a major cause of AKI; however, the precise mechanisms behind this process are not yet fully understood and effective treatments are still needed. To enhance the accuracy of diagnosing AKI during its early stages, the utilization of innovative markers is crucial. Numerous studies suggest that certain noncoding RNAs (ncRNAs), such as long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), play a central role in regulating gene expression and protein synthesis. These ncRNAs are closely associated with the development and recovery of AKI and have been detected in both kidney tissue and bodily fluids. Furthermore, specific ncRNAs may serve as diagnostic markers and potential targets for therapeutic interventions in AKI. This review aims to summarize the functional roles and changes observed in noncoding RNAs during ischemic AKI, as well as explore their therapeutic potential.

Study of the Role of the Tyrosine Kinase Receptor MerTK in the Development of Kidney Ischemia-Reperfusion Injury in RCS Rats

Renal ischaemia reperfusion (I/R) triggers a cascade of events including oxidative stress, apoptotic body and microparticle (MP) formation as well as an acute inflammatory process that may contribute to organ failure. Macrophages are recruited to phagocytose cell debris and MPs. The tyrosine kinase receptor MerTK is a major player in the phagocytosis process. Experimental models of renal I/R events are of major importance for identifying I/R key players and for elaborating novel therapeutical approaches. A major aim of our study was to investigate possible involvement of MerTK in renal I/R. We performed our study on both natural mutant rats for MerTK (referred to as RCS) and on wild type rats referred to as WT. I/R was established by of bilateral clamping of the renal pedicles for 30' followed by three days of reperfusion. Plasma samples were analysed for creatinine, aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), kidney injury molecule -1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL) levels and for MPs. Kidney tissue damage and CD68-positive cell requirement were analysed by histochemistry. monocyte chemoattractant protein-1 (MCP-1), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS), and histone 3A (H3A) levels in kidney tissue lysates were analysed by western blotting. The phagocytic activity of blood-isolated monocytes collected from RCS or WT towards annexin-V positive bodies derived from cultured renal cell was assessed by fluorescence-activated single cell sorting (FACS) and confocal microscopy analyses. The renal I/R model for RCS rat described for the first time here paves the way for further investigations of MerTK-dependent events in renal tissue injury and repair mechanisms.

The Role and Mechanism of Histone Deacetylases in Acute Kidney Injury

Acute kidney injury (AKI) is a common clinical complication with an incidence of up to 8-18% in hospitalized patients. AKI is also a complication of COVID-19 patients and is associated with an increased risk of death. In recent years, numerous studies have suggested that epigenetic regulation is critically involved in the pathophysiological process and prognosis of AKI. Histone acetylation, one of the epigenetic regulations, is negatively regulated by histone deacetylases (HDACs). Increasing evidence indicates that HDACs play an important role in the pathophysiological development of AKI by regulation of apoptosis, inflammation, oxidative stress, fibrosis, cell survival, autophagy, ATP production, and mitochondrial biogenesis (MB). In this review, we summarize and discuss the role and mechanism of HDACs in the pathogenesis of AKI.

NOX1 Inhibition Attenuates Kidney Ischemia-Reperfusion Injury via Inhibition of ROS-Mediated ERK Signaling

The protective effects of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) 1 inhibition against kidney ischemia-reperfusion injury (IRI) remain uncertain. The bilateral kidney pedicles of C57BL/6 mice were clamped for 30 min to induce IRI. Madin–Darby Canine Kidney (MDCK) cells were incubated with H₂O₂ (1.4 mM) for 1 h to induce oxidative stress. ML171, a selective NOX1 inhibitor, and siRNA against NOX1 were treated to inhibit NOX1. NOX expression, oxidative stress, apoptosis assay, and mitogen-activated protein kinase (MAPK) pathway were evaluated. The kidney function deteriorated and the production of reactive oxygen species (ROS), including intracellular H₂O₂ production, increased due to IRI, whereas IRI-mediated kidney dysfunction and ROS generation were significantly attenuated by ML171. H₂O₂ evoked the changes in oxidative stress enzymes such as SOD2 and GPX in MDCK cells, which was mitigated by ML171. Treatment with ML171 and transfection with siRNA against NOX1 decreased the upregulation of NOX1 and NOX4 induced by H₂O₂ in MDCK cells. ML171 decreased caspase-3 activity, the Bcl-2/Bax ratio, and TUNEL-positive tubule cells in IRI mice and H₂O₂-treated MDCK cells. Among the MAPK pathways, ML171 affected ERK signaling by ERK phosphorylation in kidney tissues and tubular cells. NOX1-selective inhibition attenuated kidney IRI via inhibition of ROS-mediated ERK signaling.

Sanqi Oral Solution Ameliorates Renal Ischemia/Reperfusion Injury via Reducing Apoptosis and Enhancing Autophagy: Involvement of ERK/mTOR Pathways

Ischemia-reperfusion (I/R) induced acute kidney injury (AKI) is a significant health problem with high morbidity and mortality, yet prophylaxis strategies and effective drugs are limited. Sanqi oral solution (SQ) is a formulated medicine widely used in clinical settings to treat various renal diseases via enriching qi and activating blood circulation while its role on I/R-AKI remains unclear. Herein, by establishing rat I/R-AKI models, we intended to investigate the effect of SQ on the prevention of I/R-AKI and explore its underlying mechanisms. We demonstrated that SQ treatment significantly attenuated renal dysfunction of I/R-AKI, alleviated histological damages, inhibited renal apoptosis, and enhanced autophagy. Further investigation proved that SQ could significantly inhibit the activation of ERK and mTOR signaling pathways. Moreover, its renoprotective effect can be abolished by autophagy inhibitor 3-methyladenine (3-MA). Collectively, our results suggest that SQ exerts renoprotective effects on renal I/R injury via reducing apoptosis and enhancing autophagy, which are associated with regulating ERK/mTOR pathways.

Effects of Ischemia-Reperfusion on Tubular Cell Membrane Transporters and Consequences in Kidney Transplantation

Ischemia-reperfusion (IR)-induced acute kidney injury (IRI) is an inevitable event in kidney transplantation. It is a complex pathophysiological process associated with numerous structural and metabolic changes that have a profound influence on the early and the late function of the transplanted kidney. Proximal tubular cells are particularly sensitive to IRI. These cells are involved in renal and whole-body homeostasis, detoxification processes and drugs elimination by a transporter-dependent, transcellular transport system involving Solute Carriers (SLCs) and ATP Binding Cassettes (ABCs) transporters. Numerous studies conducted mainly in animal models suggested that IRI causes decreased expression and activity of some major tubular transporters. This could favor uremic toxins accumulation and renal metabolic alterations or impact the pharmacokinetic/toxicity of drugs used in transplantation. It is of particular importance to understand the underlying mechanisms and effects of IR on tubular transporters in order to improve the mechanistic understanding of IRI pathophysiology, identify biomarkers of graft function or promote the design and development of novel and effective therapies. Modulation of transporters’ activity could thus be a new therapeutic opportunity to attenuate kidney injury during IR.

Cell-specific image-guided transcriptomics identifies complex injuries caused by ischemic acute kidney injury in mice

The kidney's inherent complexity has made identifying cell-specific pathways challenging, particularly when temporally associating them with the dynamic pathophysiology of acute kidney injury (AKI). Here, we combine renal cell-specific luciferase reporter mice using a chemoselective luciferin to guide the acquisition of cell-specific transcriptional changes in C57BL/6 background mice. Hydrogen peroxide generation, a common mechanism of tissue damage, was tracked using a peroxy-caged-luciferin to identify optimum time points for immunoprecipitation of labeled ribosomes for RNA-sequencing. Together, these tools revealed a profound impact of AKI on mitochondrial pathways in the collecting duct. In fact, targeting the mitochondria with an antioxidant, ameliorated not only hydrogen peroxide generation, but also significantly reduced oxidative stress and the expression of the AKI biomarker, LCN2. This integrative approach of coupling physiological imaging with transcriptomics and drug testing revealed how the collecting duct responds to AKI and opens new venues for cell-specific predictive monitoring and treatment.

Zinc Supplementation and Ischemia Pre-conditioning in Renal Ischemia/Reperfusion Injury

Backgrounds

Renal ischemia/reperfusion (RIR) is a major cause of kidney dysfunction in clinic. The main objective of this study was to investigate the effect of pre-conditioning ischemia (IPC) and zinc (Zn) supplementation on renal RIR injury.

Methods

A total of 63 unilateral nephrectomised male and female Wistar rats were divided into five groups. Group 1 (ShOPR): Rats as sham-operated group were subjected to surgical procedure without RIR. Group 2 (Isch): Rats underwent RIR (left kidney ischemia for 30 min followed by 48 h reperfusion). Group 3 (Zn+Isch): Rats were treated as group 2 but they received Zn sulphate (30 mg/kg) 1 h before induction of RIR. Group 4 (IPC+Isch): Rats were treated as group 2 but they underwent 1 min of ischemia followed by 3 min reperfusion as IPC, which was repeated for three times before induction of RIR. Group 5 (Zn+IPC+Isch): Rats were subjected to receive both Zn sulphate and IPC before induction of RIR. Urine samples were collected in the last 6 h of reperfusion, and finally biochemical and histological measurements were performed.

Results

The serum level of creatinine (Cr), normalised kidney weight (KW) and kidney tissue damage score (KTDS) increased by RIR alone significantly (P < 0.05). These parameters were attenuated statistically by Zn supplementation (P < 0.05). However, IPC alone or co-treatment of Zn and IPC did not improve the biochemical and histological markers altered by RIR injury.

Conclusion

Zn supplementation had a protective role against RIR while such protective effect was not observed by IPC alone or by co-treatment of Zn and IPC.

Acute Kidney Injury Following Cardiothoracic Surgery

This article reviews acute kidney injury following cardiothoracic surgery, addressing the full spectrum of the perioperative environment including preoperative, intraoperative, and postoperative factors for acute kidney injury. Topics discussed include pathophysiology, risk prediction scoring, diagnosis, prevention, treatment, and new directions for research.

Comparison of Intermittent Versus Continuous Ischemia During Laparoscopic Partial Nephrectomy in a Porcine Model

Renal ischemic time is one of the most variable risk factors in partial nephrectomy (PN). Our purpose was to investigate if intermittent ischemia could decrease renal impairment in the process of PN in porcine model and explore the feasibility of this surgical procedure in nephrectomy. A kidney ischemia-reperfusion injury model was successfully established in six pigs under laparoscopic surgery. One kidney of each pig was continuously ischemic, and intermittent ischemia was administered to the kidney of another side. Laparoscopic renal artery occlusion was applied to each kidney for 120 minutes. Intermittent ischemia was 15/3 minutes of cycles (ischemia for 15 minutes and reperfusion for 3 minutes). Microdialysis technique, immunohistochemistry, and histopathology were used to evaluate the extent of renal function injures. The concentration of glycerol in intermittently ischemic group was significantly lower than that in continuously ischemic group (F = 19.06, p = 0.001). NGAL and BCL-2 immunostaining of the renal tubular epithelial cell in the intermittent ischemia kidneys was significantly reduced compared with that in the continuously ischemic kidneys (F = 5.51, p = 0.041; F = 13.53, p = 0.004). Our study has shown that intermittent ischemia is a possibly effective and practicable surgical process for reducing renal ischemic damage in porcine model nephrectomy.

Does Resveratrol Play a Role in Decreasing the Inflammation Associated with Contrast Induced Nephropathy in Rat Model?

Contrast is widely used in invasive image examinations such as computed tomography (CT) and angiography; however, the risk of contrast-induced nephropathy (CIN) is high. The aim of this study was to investigate the protective effect of resveratrol in a rat model of CIN. Sprague-Dawley rats were divided into four groups: the control group (0.9% saline infusion only); resveratrol group (RSV, resveratrol, 30 mg/kg); contrast media group (CIN); and resveratrol + contrast media group (RCIN, resveratrol 30 mg/kg 60 min before CIN). CIN was induced via an intravenous injection of a single dose of indomethacin (10 mg/kg), one dose of N-nitro-L-arginine methyl ester (10 mg/kg), and a single dose of contrast medium iopromide (2 g/kg). Blood urea nitrogen, creatinine, and neutrophil gelatinase-associated lipocalin (NGAL) were higher in the CIN group compared to the other groups. Histopathological tubule injury scores were also higher in the CIN group compared to the other groups (p < 0.01). NLPR3 in kidney tissue were higher in the CIN group compared to the other groups; however, these results were improved by resveratrol in the RCIN group compared with the CIN group. The expressions of IL-1β and the percentage of apoptotic cells were higher in the CIN group than in the control and RSV groups, but they were lower in the RCIN group than in the CIN group. The expression of cleaved caspase-3 was higher in the CIN group than in the control and RSV groups, but lower in the RCIN group than in the CIN group. Resveratrol treatment attenuated both injury processes and apoptosis and inhibited the inflammasome pathway in this rat CIN model.

Rapamycin induces autophagy to alleviate acute kidney injury following cerebral ischemia and reperfusion via the mTORC1/ATG13/ULK1 signaling pathway

Acute kidney injury (AKI) is a clinically common and severe complication of ischemia-reperfusion (I/R), associated with high morbidity and mortality rates, and prolonged hospitalization. Rapamycin is a type of macrolide, primarily used for anti-rejection therapy following organ transplantation and the treatment of autoimmune diseases. Rapamycin has been identified to exert a protective effect against AKI induced by renal I/R as an autophagy inducer. However, whether rapamycin preconditioning may relieve AKI following cerebral I/R (CIR) remains to be fully elucidated. The purpose of the present study was to investigate the effects of CIR on the renal system of rats and the role of rapamycin in AKI following CIR. In the present study, a CIR model was established in Sprague-Dawley rats via a 90-min period of middle cerebral artery occlusion and 24 h reperfusion, and pretreatment with an intraperitoneal injection of rapamycin (dosage: 1 mg/kg; 0.5 h) prior to CIR. The levels of serum creatinine and blood urea nitrogen (BUN), and the expression of inflammation-, apoptosis- and autophagy-associated markers were subsequently measured. In addition to certain histopathological alterations to the kidney, it was identified that CIR significantly increased the levels of serum creatinine, BUN, tumor necrosis factor-α and interleukin-1β, and significantly induced apoptosis and autophagy. It was observed that rapamycin induced autophagy through the mammalian target of rapamycin complex 1/autophagy-related 13/unc-51 like autophagy activating kinase 1 signaling pathway, and that rapamycin pre-treatment significantly improved renal function and alleviated renal tissue inflammation and cell apoptosis in rats following CIR. In conclusion, the results suggested that rapamycin may alleviate AKI following CIR via the induction of autophagy.

Renal hypoxia in kidney disease: Cause or consequence?

Tissue hypoxia has been proposed as an important factor in the pathophysiology of both chronic kidney disease (CKD) and acute kidney injury (AKI), initiating and propagating a vicious cycle of tubular injury, vascular rarefaction, and fibrosis and thus exacerbation of hypoxia. Here, we critically evaluate this proposition by systematically reviewing the literature relevant to the following six questions: (i) Is kidney disease always associated with tissue hypoxia? (ii) Does tissue hypoxia drive signalling cascades that lead to tissue damage and dysfunction? (iii) Does tissue hypoxia per se lead to kidney disease? (iv) Does tissue hypoxia precede pathology? (v) Does tissue hypoxia colocalize with pathology? (vi) Does prevention of tissue hypoxia prevent kidney disease? We conclude that tissue hypoxia is a common feature of both AKI and CKD. Furthermore, at least under in vitro conditions, renal tissue hypoxia drives signalling cascades that lead to tissue damage and dysfunction. Tissue hypoxia itself can lead to renal pathology, independent of other known risk factors for kidney disease. There is also some evidence that tissue hypoxia precedes renal pathology, at least in some forms of kidney disease. However, we have made relatively little progress in determining the spatial relationships between tissue hypoxia and pathological processes (i.e. colocalization) or whether therapies targeted to reduce tissue hypoxia can prevent or delay the progression of renal disease. Thus, the hypothesis that tissue hypoxia is a "common pathway" to both AKI and CKD still remains to be adequately tested.

Ischemia/reperfusion-associated tubular cells injury in renal transplantation: Can metabolomics inform about mechanisms and help identify new therapeutic targets?

Tubular cells are central targets of ischemia-reperfusion (I/R) injury in kidney transplantation. Inflammation and metabolic disturbances occurring within these cells are deleterious by themselves but also favor secondary events, such as activation of immune response. It is critical to have an in depth understanding of the mechanisms governing tubular cells response to I/R if one wants to define pertinent biomarkers or to elaborate targeted therapeutic interventions. As oxidative damage was shown to be central in the patho-physiological mechanisms, the impact of I/R on proximal tubular cells metabolism has been widely studied, contrary to its effects on expression and activity of membrane transporters of the proximal tubular cells. Yet, temporal modulation of transporters over ischemia and reperfusion periods appears to play a central role, not only in the induction of cells injury but also in graft function recovery. Metabolomics in cell models or diverse biofluids has the potential to provide large pictures of biochemical consequences of I/R. Metabolomic studies conducted in experimental models of I/R or in transplanted patients indeed retrieved metabolites belonging to the pathways known to be particularly affected. Interestingly, they also revealed that metabolic disturbances and transporters activities are in very close mutual interplay. As well as helping to select diagnostic biomarkers, such analyses could also contribute to identify new pharmacological targets and to set up innovative nephroprotective strategies for the future. Even if various therapeutic approaches have been evaluated for a long time to prevent or treat I/R injuries, metabolomics has helped identifying new ones, those related to membrane transporters seeming to be of particular interest. However, considering the very complex and multifactorial effects of I/R in the context of kidney transplantation, all tracks must be followed if one wants to prevent or limit its deleterious consequences.

Risk factors of long-term postoperative renal function after partial nephrectomy in a solitary kidney

The effect of warm ischemia time (WIT) on longterm renal function after partial nephrectomy remains controversial. In this retrospectively cohort study, 75 solitary kidney patients were included and the effects of warm ischemia time, preoperative renal function and resected normal parenchyma volume on long-term renal function were evaluated. Multivariable analysis showed that the preoperative renal function baseline was significantly associated with renal function 12 months postoperation (P=0.01), adjusting for age and comorbidities factors. Meanwhile, perioperative acute renal failure (ARF) events significantly affected postoperative renal function at postoperative time points of 12 months (P=0.001) and 60 months (P=0.03), as well as renal function change at postoperative 12 months (P<0.01). Warm ischemia time and resected normal parenchyma volume were not risk factors for long-term postoperative renal function, while the latter was significantly associated with renal function change (P=0.03 at 12 months, P<0.01 at 36 and 60 months).

In conclusion, the quality of preoperative kidney primarily determines long-term postoperative renal function, while the quantity of preserved functional parenchyma volume was the main determinant for long-term kidney recovery. ARF was an independent risk factor while WIT was indirectly associated with postoperative renal function by causing perioperative ARF.

miR-17-92 ameliorates renal ischemia reperfusion injury

There is limited information on the role of miR-17-92 in renal tubular pathophysiology. Therefore, the present study was performed to determine whether miR-17-92 plays a role in ischemia-reperfusion injury (IRI)-induced acute kidney injury. We originally demonstrated that miR-17-92 is up-regulated following IRI in vivo. To explore the roles of miR-17-92 in the IRI process, we first generated a renal proximal tubule-specific miR-17-92 deletion (PT-miR-17-92^-/-) knockout mouse model with Cre driven by the Kap promoter. We found that PT-deficient miR-17-92 mice had more severe renal dysfunction and renal structures than their littermates. Compared with sham-operated mice, both wide-type (WT) mice and PT-miR-17-92^-/- mice showed increased serum levels of creatinine and urea. However, the levels of serum urea and creatinine in PT-miR-17-92^-/- mice after the IRI operation were significantly higher than the levels in WT mice. In addition, PT-miR-17-92^-/- mice showed higher levels of serum potassium and phosphonium after the IRI operation. Histological analysis revealed that PT-miR-17-92^-/- mice had substantial histopathologic changes, such as tubular dilation and tubular necrosis. Overexpression of miR-17-92 could partially reverse the side-effects of IRI on the proximal tubules in vivo. Furthermore, we employed a quantitative proteomic strategy and identified 16 proteins as potential targets of miR-17-92. Taken together, our findings suggested that miR-17-92 may ameliorates IRI-induced acute kidney injury. Our results indicate that pharmacologic modulation of these miRNAs may have therapeutic potential for acute kidney injury.

Glomerular loss after arteriovenous and arterial clamping for renal warm ischemia in a swine model

PURPOSE:

To evaluate the glomerular loss after arteriovenous or arterial warm ischemia in a swine model.

METHODS:

Twenty four pigs were divided into Group Sham (submitted to all surgical steps except the renal ischemia), Group AV (submitted to 30 minutes of warm ischemia by arteriovenous clamping of left kidney vessels), and Group A (submitted to 30 minutes of ischemia by arterial clamping). Right kidneys were used as controls. Weigh, volume, cortical volume, glomerular volumetric density (Vv[Glom]), volume-weighted glomerular volume (VWGV), and the total number of glomeruli were measured for each organ.

RESULTS:

Group AV showed a 24.5% reduction in its left kidney Vv[Glom] and a 25.4% reduction in the VWGV, when compared to the right kidney. Reductions were also observed when compared to kidneys of sham group. There was a reduction of 19.2% in the total number of glomeruli in AV kidneys. No difference was observed in any parameters analyzed on the left kidneys from group A.

CONCLUSIONS:

Renal warm ischemia of 30 minutes by arterial clamping did not caused significant glomerular damage, but arteriovenous clamping caused significant glomerular loss in a swine model. Clamping only the renal artery should be considered to minimize renal injury after partial nephrectomies.

Protective effects of taurine against renal ischemia/reperfusion injury in rats by inhibition of gelatinases, MMP-2 and MMP-9, and p38 mitogen-activated protein kinase signaling

Dysregulated expression of matrix metalloproteinases (MMPs) is closely associated with the pathogenesis of renal ischemia/reperfusion injury (I/R). The production of excessive reactive oxygen species (ROS) causes tissue damage. Increased ROS production causes activation of p38 mitogen-activated protein kinase (MAPK) signaling, which participates in gene regulation of MMPs, especially MMP-2 and MMP-9 (gelatinases). Taurine (2-aminoethanesulfonic acid) in mammalian cells functions in bile acid conjugation, maintenance of calcium homeostasis, osmoregulation, membrane stabilization, and antioxidation, antiinflammatory, and antiapoptotic action. We investigated the effects of taurine and the possible role of p38 MAPK signaling on regulation of MMP-2 and MMP-9 in a renal I/R injury model in rats. Rats were divided into three groups: sham, I/R, and I/R + taurine treated. After a right nephrectomy, I/R was induced by clamping the left renal pedicle for 1 h followed by 6 h reperfusion. Taurine was administered 45 min prior to induction of ischemia. Renal function was assessed by serum creatinine and blood urea nitrogen (BUN) levels. Tubule injury and structural changes were evaluated by light microscopy. Malondialdehyde (MDA) levels were analyzed by high performance liquid chromatography (HPLC). Superoxide dismutase (SOD) activity levels were measured using a colorimetric kit. mRNA expression of MMP-2 and MMP-9 was determined by real-time polymerase chain reaction. MMP-2 and MMP-9 activities were measured using a fluorimetric kit. Phosphorylated p38 (p-p38) and total p38 MAPK protein expressions were evaluated by western blot. Taurine pretreatment significantly attenuated renal dysfunction and histologic damage, such as renal tubule dilation and loss of brush borders. The pretreatment also decreased the MDA level and attenuated the reduction of SOD activity in the kidney during I/R. Taurine pretreatment also decreased significantly both MMP-2 and MMP-9 mRNA expression and MMP-9 activity induced by I/R. In addition, the activity of p38 MAPK signaling was down-regulated significantly by taurine administration. Inhibition of MMP-2 and MMP-9 expression and MMP-9 activity caused by taurine may be associated with suppression of p38 MAPK activation during I/R induced renal injury in rats. Therefore, taurine administration may prove to be a strategy for attenuating renal I/R injury.

Independent Risk Factors and 2-Year Outcomes of Acute Kidney Injury after Surgery for Congenital Heart Disease

BACKGROUND

Data are limited regarding risk factors for acute kidney injury (AKI) following cardiac surgery in children with congenital heart disease (CHD). This observational study was performed to examine temporal trends in AKI incidence according to the Pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease (pRIFLE) criteria, identify independent risk factors for AKI after cardiac surgery, and examine associations between AKI and long-term mortality.

METHODS

We retrospectively evaluated 418 patients (259 males, 159 females; median age, 5 months) who underwent cardiac surgery for CHD between April 2007 and August 2013. Patients were followed up for 2 years. AKI was defined according to the pRIFLE criteria as ≥25% decrease in estimated creatinine clearance.

RESULTS

AKI developed postoperatively in 104 cases (24.9%). Approximately 80% belonged to the "Risk" category according to the pRIFLE criteria, and only 21 cases (5%) required renal replacement therapy (peritoneal dialysis in all cases). Multivariate analysis revealed 3 independent risk factors for onset of AKI: young age (<1 year), surgery in Risk Adjustment in Congenital Heart Surgery (RACHS-1) category ≥4, and long cardiopulmonary bypass (CPB) time (≥90 min). Twenty-three patients (22%) with AKI died during the 2-year follow-up. In multivariate cox hazard regression analysis, the most significant contributor to risk of mortality was AKI.

CONCLUSIONS

Postoperative AKI was strongly associated with young age, high RACHS-1 category, and prolonged CPB time. In addition, mortality rate was higher in patients who survived after recovery from AKI than in those without AKI, even among the lower pRIFLE categories.

Use of Xenopus Frogs to Study Renal Development/Repair

The Xenopus genus includes several members of aquatic frogs native to Africa but is perhaps best known for the species Xenopus laevis and Xenopus tropicalis. These species were popularized as model organisms from as early as the 1800s and have been instrumental in expanding several biological fields including cell biology, environmental toxicology, regenerative biology, and developmental biology. In fact, much of what we know about the formation and maturation of the vertebrate renal system has been acquired by examining the intricate genetic and morphological patterns that epitomize nephrogenesis in Xenopus. From these numerous reports, we have learned that the process of kidney development is as unique among organs as it is conserved among vertebrates. While development of most organs involves increases in size at a single location, development of the kidney occurs through a series of three increasingly complex nephric structures that are temporally distinct from one another and which occupy discrete spatial locales within the body. These three renal systems all serve to provide homeostatic, osmoregulatory, and excretory functions in animals. Importantly, the kidneys in amphibians, such as Xenopus, are less complex and more easily accessed than those in mammals, and thus tadpoles and frogs provide useful models for understanding our own kidney development. Several descriptive and mechanistic studies conducted with the Xenopus model system have allowed us to elucidate the cellular and molecular mediators of renal patterning and have also laid the foundation for our current understanding of kidney repair mechanisms in vertebrates. While some species-specific responses to renal injury have been observed, we still recognize the advantage of the Xenopus system due to its distinctive similarity to mammalian wound healing, reparative, and regenerative responses. In addition, the first evidence of renal regeneration in an amphibian system was recently demonstrated in Xenopus laevis. As genetic and molecular tools continue to advance, our appreciation for and utilization of this amphibian model organism can only intensify and will certainly provide ample opportunities to further our understanding of renal development and repair.

Exercise-induced rhabdomyolysis mechanisms and prevention: A literature review

Exercise-induced rhabdomyolysis (exRML), a pathophysiological condition of skeletal muscle cell damage that may cause acute renal failure and in some cases death. Increased Ca²⁺ level in cells along with functional degradation of cell signaling system and cell matrix have been suggested as the major pathological mechanisms associated with exRML. The onset of exRML may be exhibited in athletes as well as in general population. Previous studies have reported that possible causes of exRML were associated with excessive eccentric contractions in high temperature, abnormal electrolytes balance, and nutritional deficiencies possible genetic defects. However, the underlying mechanisms of exRML have not been clearly established among health professionals or sports medicine personnel. Therefore, we reviewed the possible mechanisms and correlated prevention of exRML, while providing useful and practical information for the athlete and general exercising population.

The Role of Extracellular Adenosine Triphosphate in Ischemic Organ Injury

OBJECTIVES

Ischemic tissue injury contributes to significant morbidity and mortality and is implicated in a range of pathologic conditions, including but not limited to myocardial infarction, ischemic stroke, and acute kidney injury. The associated reperfusion phase is responsible for the activation of the innate and adaptive immune system, further accentuating inflammation. Adenosine triphosphate molecule has been implicated in various ischemic conditions, including stroke and myocardial infarction.

STUDY SELECTION

Adenosine triphosphate is a well-defined intracellular energy transfer and is commonly referred to as the body's "energy currency." However, Laboratory studies have demonstrated that extracellular adenosine triphosphate has the ability to initiate inflammation and is therefore referred to as a damage-associated molecular pattern. Purinergic receptors-dependent signaling, proinflammatory cytokine release, increased Ca influx into cells, and subsequent apoptosis have been shown to form a common underlying extracellular adenosine triphosphate molecular mechanism in ischemic organ injury.

CONCLUSIONS

In this review, we aim to discuss the molecular mechanisms behind adenosine triphosphate-mediated ischemic tissue injury and evaluate the role of extracellular adenosine triphosphate in ischemic injury in specific organs, in order to provide a greater understanding of the pathophysiology of this complex process. We also appraise potential future therapeutic strategies to limit damage in various organs, including the heart, brain, kidneys, and lungs.

ABT-719 for the Prevention of Acute Kidney Injury in Patients Undergoing High-Risk Cardiac Surgery: A Randomized Phase 2b Clinical Trial

Background

Patients undergoing cardiac surgeries with cardiopulmonary bypass (on‐pump) have a high risk for acute kidney injury (AKI). We tested ABT‐719, a novel α‐melanocyte‐stimulating hormone analog, for prevention of AKI in postoperative cardiac surgery patients.

Methods and Results

This phase 2b randomized, double‐blind, placebo‐controlled trial included adult patients with stable renal function undergoing high‐risk on‐pump cardiac surgery in the United States and Denmark. Participants received placebo (n=61) or cumulative ABT‐719 doses of 800 (n=59), 1600 (n=61), or 2100 μg/kg (n=59). Primary outcome was development of AKI based on Acute Kidney Injury Network (AKIN) criteria, measured utilizing preoperative creatinine value and maximum value within 48 hours and urine output within the first 42 hours postsurgery. Secondary outcomes included incidence of AKI based on maximal changes from baseline in novel AKI biomarkers over a 72‐hour period after clamp release and length of intensive care unit stays through 90 days postsurgery. A total of 65.5%, 62.7%, and 69.6% of patients in the 800‐, 1600‐, and 2100‐μg/kg groups, respectively, developed AKI (stages 1, 2, and 3 combined) versus 65.5% in the placebo group (for each pair‐wise comparison with placebo, P=0.966, 0.815, and 0.605, respectively). Adverse events occurred at a similar rate in all treatment groups.

Conclusions

ABT‐719 treatment did not lower AKI incidence using AKIN criteria, influence the elevations of novel biomarkers, or change 90‐day outcomes in patients after cardiac surgery.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01777165.

Peptidyl arginine deiminase-4-deficient mice are protected against kidney and liver injury after renal ischemia and reperfusion

We previously demonstrated that renal peptidyl arginine deiminase-4 (PAD4) is induced after renal ischemia and reperfusion (I/R) injury and exacerbates acute kidney injury (AKI) by increasing the renal tubular inflammatory response. Here, we tested whether genetic ablation of PAD4 attenuates renal injury and inflammation after I/R in mice. After renal I/R, PAD4 wild-type mice develop severe AKI with large increases in plasma creatinine, neutrophil infiltration, as well as significant renal tubular necrosis, apoptosis, and proinflammatory cytokine generation. In contrast, PAD4-deficient mice are protected against ischemic AKI with reduced real tubular neutrophil infiltration, renal tubular necrosis, and apoptosis. In addition, hepatic injury and inflammation observed in PAD4 wild-type mice after renal I/R are significantly attenuated in PAD4-deficient mice. We also show that increased renal tubular PAD4 expression after renal I/R is associated with translocation of PAD4 from the nucleus to the cytosol. Consistent with PAD4 cytosolic translocation, we show increased renal tubular cytosolic peptidyl-citrullination after ischemic AKI. Mechanistically, recombinant PAD4 treatment increased nuclear translocation of NF-κB in cultured human as well as murine proximal tubule cells that is inhibited by a PAD4 inhibitor (2-chloroamidine). Taken together, our studies further support the hypothesis that renal tubular PAD4 plays a critical role in renal I/R injury by increasing the renal tubular inflammatory response and neutrophil infiltration after renal I/R perhaps by interacting with the proinflammatory transcription factor NF-κB in the cytosol and promoting its nuclear translocation.

Impact of Different Initial Epinephrine Treatment Time Points on the Early Postresuscitative Hemodynamic Status of Children With Traumatic Out-of-hospital Cardiac Arrest

The postresuscitative hemodynamic status of children with traumatic out-of-hospital cardiac arrest (OHCA) might be impacted by the early administration of epinephrine, but this topic has not been well addressed. The aim of this study was to analyze the early postresuscitative hemodynamics, survival, and neurologic outcome according to different time points of first epinephrine treatment among children with traumatic OHCA.Information on 388 children who presented to the emergency departments of 3 medical centers and who were treated with epinephrine for traumatic OHCA during the study period (2003-2012) was retrospectively collected. The early postresuscitative hemodynamic features (cardiac functions, end-organ perfusion, and consciousness), survival, and neurologic outcome according to different time points of first epinephrine treatment (early: <15, intermediate: 15-30, and late: >30 minutes after collapse) were analyzed.Among 165 children who achieved sustained return of spontaneous circulation, 38 children (9.8%) survived to discharge and 12 children (3.1%) had good neurologic outcomes. Early epinephrine increased the postresuscitative heart rate and blood pressure in the first 30 minutes, but ultimately impaired end-organ perfusion (decreased urine output and initial creatinine clearance) (all P < 0.05). Early epinephrine treatment increased the chance of achieving sustained return of spontaneous circulation, but did not increase the rates of survival and good neurologic outcome.Early epinephrine temporarily increased heart rate and blood pressure in the first 30 minutes of the postresuscitative period, but impaired end-organ perfusion. Most importantly, the rates of survival and good neurologic outcome were not significantly increased by early epinephrine administration.

NephroCheck data compared to serum creatinine in various clinical settings

BACKGROUND

Acute kidney injury is frequently observed at the intensive care unit, after surgery, and after toxic drug administration. A rise in serum creatinine and a fall in urine output are consequences of much earlier injury to the most sensitive part of tubular cells located at the proximal tubule. The aim of the present study was to investigate the course of two cell-cycle arrest urinary biomarkers compared to serum creatinine in four clinical settings: ischemic reperfusion injury, cardiac failure, severe acute kidney injury, and chemotherapy-induced kidney injury.

METHODS

A recently developed bedside test known as NephroCheck measures two urinary parameters: insulin-like growth factor binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinase-2 (TIMP-2). The test is based on a sandwich immunoassay technique. The final test output, labeled AKIRisk, is shown as a numeric result.

RESULTS

This report revealed that [IGFBP7] · [TIMP-2] in urine rise rapidly prior to any change in serum creatinine. A unique feature of all four clinical settings is that a rapid decline predicts the recovery of kidney function. Besides, a subclinical kidney injury might be detected by the test.

CONCLUSION

This bedside test detects biomarkers of renal injury. A rapid decline in AKIRisk was associated with the restoration of kidney function, whereas a prolonged high AKIRisk score was associated with end-stage renal disease. However, the dynamics seem to differ, depending on the cause and the extent of injury. Further studies will be needed to clarify the issue.

Acute Kidney Injury in Cardiac Surgery and Cardiac Intensive Care

Acute kidney injury (AKI) is a serious postoperative complication following cardiac surgery. Despite the incidence of AKI requiring temporary renal replacement therapy being low, it is nonetheless associated with high morbidity and mortality. Therefore, preventing AKI associated with cardiac surgery can dramatically improve outcomes in these patients. The pathogenesis of AKI is multifactorial and many attempts to prevent or treat renal injury have been met with limited success. In this article, we will discuss the incidence and risk factors for cardiac surgery associated AKI, including the pathophysiology, potential biomarkers of injury, and treatment modalities.

Ameliorative Effect of Recombinant Human Erythropoietin and Ischemic Preconditioning on Renal Ischemia Reperfusion Injury in Rats

BACKGROUND

Ischemia-reperfusion (IR) injury is one of the most common causes of renal dysfunction. There is increasing evidence about the role of the reactive oxygen species (ROS) in these injuries and endogenous antioxidants seem to have an important role in decreasing the renal tissue injury.

OBJECTIVES

The aim of this study was to compare the effect of recombinant human erythropoietin (EPO) and ischemic preconditioning (IPC) on renal IR injury.

MATERIALS AND METHODS

Twenty four male Wistar rats were allocated into four experimental groups: sham-operated, IR, EPO + IR, and IPC + IR. Rats were underwent 50 minutes bilateral ischemia followed by 24 hours reperfusion. Erythropoietin (5000 IU/kg, i.p) was administered 30 minutes before onset of ischemia. Ischemic preconditioning was performed by three cycles of 3 minutes ischemia followed by 3 minutes reperfusion. Plasma concentrations of urea and creatinine were measured. Kidney samples were taken for reactive oxidative species (ROS) measurement including superoxide dismutase (SOD) activity, glutathione (GSH) contents, and malondialdehyde (MDA) levels.

RESULTS

Compared to the sham group, IR led to renal dysfunction as evidenced by significantly higher plasma urea and creatinine. Treatment with EPO or IPC decreased urea, creatinine, and renal MDA levels and increased SOD activity and GSH contents in the kidney.

CONCLUSIONS

Pretreatment with EPO and application of IPC significantly ameliorated the renal injury induced by bilateral renal IR. However, both treatments attenuated renal dysfunction and oxidative stress in kidney tissues. There were no significant differences between pretreatment with EPO or application of IPC.

Induced Pluripotent Stem Cell-Derived Conditioned Medium Attenuates Acute Kidney Injury by Downregulating the Oxidative Stress-Related Pathway in Ischemia-Reperfusion Rats

Teratoma-like formation addresses a critical safety concern for the potential utility of induced pluripotent stem cells (iPSCs). Therefore, therapy utilizing iPSC-derived conditioned medium (iPSC-CM) for acute kidney injury (AKI) has attracted substantial interest. A recent study showed that iPSC-CM effectively alleviated ventilator-induced lung injury in rats. It prompts us to assess the therapeutic effects of iPSC-CM on ischemic AKI. First, we assessed the changes in renal function and tubular cell apoptosis by intraperitoneal administration of iPSC-CM to ischemia-reperfusion (I/R) rats. Second, we explored the oxidative stress-related pathway in the apoptosis of renal tubular cells subjected to hypoxia-reoxygenation (H/R). Administration of iPSC-CM significantly improved renal function and protected tubular cells against apoptosis in rats with I/R-AKI, and the optimal effect was observed at the 50-fold concentrated iPSC-CM. iPSC-CM also mitigated the H/R-induced apoptosis of NRK-52E cells in vitro. Reactive oxygen species (ROS) production was augmented in kidneys following I/R and in NRK-52E cells subjected to H/R. Meanwhile, expressions of phosphorylated p38 MAPK, TNF-α, and cleaved caspase 3 and NF-κB activity were consistently increased in vivo and in vitro. Following administration of iPSC-CM, ROS production was abolished, and inflammatory cytokine expression was significantly suppressed. Annexin V-propidium iodide flow cytometry and in situ TUNEL assay further showed that iPSC-CM markedly attenuated H/R- or I/R-induced tubular cell apoptosis. Intriguingly, treatment with iPSC-CM significantly improved the survival of rats with I/R-induced AKI. iPSC-CM represents a favorable source of stem cell-based therapy and may serve as a potential therapeutic strategy for kidney repair in ischemic AKI.

Renal ischemia/reperfusion injury; from pathophysiology to treatment

Ischemia/reperfusion injury (IRI) is caused by a sudden temporary impairment of the blood flow to the particular organ. IRI usually is associated with a robust inflammatory and oxidative stress response to hypoxia and reperfusion which disturbs the organ function. Renal IR induced acute kidney injury (AKI) contributes to high morbidity and mortality rate in a wide range of injuries. Although the pathophysiology of IRI is not completely understood, several important mechanisms resulting in kidney failure have been mentioned. In ischemic kidney and subsequent of re-oxygenation, generation of reactive oxygen species (ROS) at reperfusion phase initiates a cascade of deleterious cellular responses leading to inflammation, cell death, and acute kidney failure. Better understanding of the cellular pathophysiological mechanisms underlying kidney injury will hopefully result in the design of more targeted therapies to prevent and treatment the injury. In this review, we summarize some important potential mechanisms and therapeutic approaches in renal IRI.

Intraoperative High-Dose Dexamethasone and Severe AKI after Cardiac Surgery

Administration of prophylactic glucocorticoids has been suggested as a strategy to reduce postoperative AKI and other adverse events after cardiac surgery requiring cardiopulmonary bypass. In this post hoc analysis of a large placebo-controlled randomized trial of dexamethasone in 4465 adult patients undergoing cardiac surgery, we examined severe AKI, defined as use of RRT, as a primary outcome. Secondary outcomes were doubling of serum creatinine level or AKI-RRT, as well as AKI-RRT or in-hospital mortality (RRT/death). The primary outcome occurred in ten patients (0.4%) in the dexamethasone group and in 23 patients (1.0%) in the placebo group (relative risk, 0.44; 95% confidence interval, 0.19 to 0.96). In stratified analyses, the strongest signal for potential benefit of dexamethasone was in patients with an eGFR<15 ml/min per 1.73 m(2). In conclusion, compared with placebo, intraoperative dexamethasone appeared to reduce the incidence of severe AKI after cardiac surgery in those with advanced CKD.

Autophagy activation attenuates renal ischemia-reperfusion injury in rats

Ischemia-reperfusion (I/R) injury is a leading cause of acute kidney injury (AKI), which is a common clinical complication but lacks effective therapies. This study investigated the role of autophagy in renal I/R injury and explored potential mechanisms in an established rat renal I/R injury model. Forty male Wistar rats were randomly divided into four groups: Sham, I/R, I/R pretreated with 3-methyladenine (3-MA, autophagy inhibitor), or I/R pretreated with rapamycin (autophagy activator). All rats were subjected to clamping of the left renal pedicle for 45 min after right nephrectomy, followed by 24 h of reperfusion. The Sham group underwent the surgical procedure without ischemia. 3-MA and rapamycin were injected 15 min before ischemia. Renal function was indicated by blood urea nitrogen and serum creatinine. Tissue samples from the kidneys were scored histopathologically. Autophagy was indicated by light chain 3 (LC3), Beclin-1, and p62 levels and the number of autophagic vacuoles. Apoptosis was evaluated by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method and expression of caspase-3. Autophagy was activated after renal I/R injury. Inhibition of autophagy by 3-MA before I/R aggravated renal injury, with worsened renal function, higher renal tissue injury scores, and more tubular apoptosis. In contrast, rapamycin pretreatment ameliorated renal injury, with improved renal function, lower renal tissue injury scores, and inhibited apoptosis based on fewer TUNEL-positive cells and lower caspase-3 expression. Our results demonstrate that autophagy could be activated during I/R injury and play a protective role in renal I/R injury. The mechanisms were involved in the regulation of several autophagy and apoptosis-related genes. Furthermore, autophagy activator may be a promising therapy for I/R injury and AKI in the future.

Renal endothelial dysfunction in acute kidney ischemia reperfusion injury

Acute kidney injury is associated with alterations in vascular tone that contribute to an overall reduction in GFR. Studies in animal models indicate that ischemia triggers alterations in endothelial function that contribute significantly to the overall degree and severity of a kidney injury. Putative mediators of vasoconstriction that may contribute to the initial loss of renal blood flow and GFR are highlighted. In addition, there is discussion of how intrinsic damage to the endothelium impairs homeostatic responses in vascular tone as well as promotes leukocyte adhesion and exacerbating the reduction in renal blood flow. The timing of potential therapies in animal models as they relate to the evolution of AKI, as well as the limitations of such approaches in the clinical setting are discussed. Finally, we discuss how acute kidney injury induces permanent alterations in renal vascular structure. We posit that the cause of the sustained impairment in kidney capillary density results from impaired endothelial growth responses and suggest that this limitation is a primary contributing feature underlying progression of chronic kidney disease.

Fighting against kidney diseases with small interfering RNA: opportunities and challenges

The significant improvements in siRNA therapy have been achieved, which have great potential applications in humans. The kidney is a comparatively easy target organ of siRNA therapy due to its unique structural and functional characteristics. Here, we reviewed recent achievements in siRNA design, delivery and application with focuses on kidney diseases, in particular kidney transplant-related injuries. In addition, the strategy for increasing serum stability and immune tolerance of siRNA was also discussed. At last, the future challenges of siRNA therapy including organ/tissue/cell-specific delivery and time-controlled silence, as well as selecting therapeutic targets, were addressed as well.

Oat1/3 restoration protects against renal damage after ischemic AKI

Expression of proximal tubular organic anion transporters Oat1 and Oat3 is reduced by PGE2 after renal ischemia and reperfusion (I/R) injury. We hypothesized that impaired expression of Oat1/3 is decisively involved in the deterioration of renal function after I/R injury. Therefore, we administered probenecid, which blocks proximal tubular indomethacin uptake, to abolish the indomethacin-mediated restoration of Oat1/3 regulation and its effect on renal functional and morphological outcome. Ischemic acute kidney injury (iAKI) was induced in rats by bilateral clamping of renal arteries for 45 min with 24-h follow-up. Low-dose indomethacin (1 mg/kg) was given intraperitoneally (ip) at the end of ischemia. Probenecid (50 mg/kg) was administered ip 20 min later. Indomethacin restored the expression of Oat1/3, PAH net secretion, and PGE2 clearance. Additionally, indomethacin improved kidney function as measured by glomerular filtration rate (GFR), renal perfusion as determined by corrected PAH clearance, and morphology, whereas it reduced renal cortical apoptosis and nitric oxide production. Notably, indomethacin did not affect inflammation parameters in the kidneys (e.g., monocyte chemoattractant protein-1, ED1+ cells). On the other hand, probenecid blocked the indomethacin-induced restoration of Oat1/3 and moreover abrogated all beneficial effects. Our study indicates that the beneficial effect of low-dose indomethacin in iAKI is not due to its anti-inflammatory potency, but in contrast to its restoration of Oat1/3 expression and/or general renal function. Inhibition of proximal tubular indomethacin uptake abrogates the beneficial effect of indomethacin by resetting the PGE2-mediated Oat1/3 impairment, thus reestablishing renal damage. This provides evidence for a mechanistic effect of Oat1/3 in a new model of the induction of renal damage after iAKI.

AKI associated with cardiac surgery

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

Acute kidney injury after cardiac surgery: is minocycline protective?

BACKGROUND AND OBJECTIVES

Acute kidney injury (AKI) after cardiac bypass surgery (CABG) is common and carries a significant association with morbidity and mortality. Since minocycline therapy attenuates kidney injury in animal models of AKI, we tested its effects in patients undergoing CABG.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

This is a randomized, double-blinded, placebo-controlled, multi-center study. We screened high risk patients who were scheduled to undergo CABG in two medical centers between Jan 2008 and June 2011. 40 patients were randomized and 19 patients in each group completed the study. Minocycline prophylaxis was given twice daily, at least for four doses prior to CABG. Primary outcome was defined as AKI [0.3 mg/dl increase in creatinine (Cr)] within 5 days after surgery. Daily serum Cr for 5 days, various clinical and hemodynamic measures and length of stay were recorded.

RESULTS

The two groups had similar baseline and intra-operative characteristics. The primary outcome occurred in 52.6% of patients in the minocycline group as compared to 36.8% of patients in the placebo group (p = 0.51). Peak Cr was 1.6 ± 0.7 vs. 1.5 ± 0.7 mg/dl (p = 0.45) in minocycline and placebo groups, respectively. Death at 30 days occurred in 0 vs. 10.5% in the minocycline and placebo groups, respectively (p = 0.48). There were no differences in post-operative length of stay, and cardiovascular events between the two groups. There was a trend towards lower diastolic pulmonary artery pressure [16.8 ± 4.7 vs. 20.7 ± 6.6 mmHg (p = 0.059)] and central venous pressure [11.8 ± 4.3 vs. 14.6 ± 5.6 mmHg (p = 0.13)] in the minocycline group compared to placebo on the first day after surgery.

CONCLUSIONS

Minocycline did not protect against AKI post-CABG.

Changes in renal medulla gene expression in a pre-clinical model of post cardiopulmonary bypass acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common and serious complication of cardiac surgery using cardiopulmonary bypass (CPB). The pathogenesis is poorly understood and the study of AKI in rodent models has not led to improvements in clinical outcomes. We sought to determine the changes in renal medullary gene expression in a novel and clinically relevant porcine model of CPB-induced AKI.

RESULTS

Adult pigs (n = 12 per group) were randomised to undergo sham procedure, or 2.5 hours CPB. AKI was determined using biochemical (Cr51 EDTA clearance, CrCl, urinary IL-18 release) and histological measures. Transcriptomic analyses were performed on renal medulla biopsies obtained 24 hours post intervention or from sham group. Microarray results were validated with real-time polymerase chain reaction and Western Blotting.Of the transcripts examined, 66 were identified as differentially expressed in CPB versus Sham pig's kidney samples, with 19 (29%) upregulated and 47 (71%) down-regulated. Out of the upregulated and downregulated transcripts 4 and 16 respectively were expression sequence tags (EST). The regulated genes clustered into three classes; Immune response, Cell adhesion/extracellular matrix and metabolic process. Upregulated genes included Factor V, SLC16A3 and CKMT2 whereas downregulated genes included GST, CPE, MMP7 and SELL.

CONCLUSION

Post CPB AKI, as defined by clinical criteria, is characterised by molecular changes in renal medulla that are associated with both injury and survival programmes. Our observations highlight the value of large animal models in AKI research and provide insights into the failure of findings in rodent models to translate into clinical progress.

Acute kidney injury induced by various pneumoperitoneum pressures in a rabbit model of mild and severe hydronephrosis

OBJECTIVE

Increased pneumoperitoneum pressure during laparoscopic surgery can result in acute kidney injury. We aimed to clarify whether intraabdominal pressure tolerance is modified in various degrees of unilateral kidney hydronephrosis in rabbits.

METHODS

A total 90 rabbits were randomly allocated to three groups (group PN, PM and PS, i.e. rabbits with no, mild and severe hydronephrosis, respectively, subjected to intraabdominal pressures). Rabbits in group PM (n=30) and group PS (n=30) underwent a surgical procedure inducing a mild or severe left hydronephrosis. Rabbits in all groups were then allocated to 5 subgroups. Then, they were subjected to intraabdominal pressures of 0, 6, 9, 12, and 15 mm Hg, respectively. Acute kidney injury was assessed by measuring serum creatinine (Scr), blood urea nitrogen (BUN), tubular cell apoptosis, kidney injury molecule-1 (KIM-1) and cysteine-rich 61 (Cyr-61/CCN1) expression.

RESULTS

Acute kidney injury with increased tubular apoptosis and KIM-1 and Cyr-61 expression occurred when intraabdominal pressure reached 15, 15 and 9 mm Hg in PN, PM and PS groups, respectively. The Scr and BUN levels were similar in all groups.

CONCLUSIONS

In rabbits, kidneys with severe hydronephrosis were more likely to suffer acute injury when they were exposed to pneumoperitoneal pressure.

The role of mast cells in ischemia and reperfusion injury

INTRODUCTION

Ischemia and reperfusion (IR) injury is a challenging clinical problem that is triggered by ischemia in an organ followed by subsequent restoration of the blood supply. The effects of mast cell (MC) in IR injury are not totally clear.

MATERIALS AND METHODS

We review the body of literature on the role of MCs in IR injury based on an unrestricted Pubmed search for the descriptors "mast cell", "ischemia" and "reperfusion injury", as well as discuss implications for treatment and future directions.

RESULTS

Shortly after IR, chemicals released by MC can trigger vasoactive substance formation, tissue leakage, upregulation of adhesive molecules followed by leukocyte recruitment and infiltration, and pronecrotic pathway activation, among other physiologic changes. In the long term, MCs may influence tissue remodeling and repair as well as blood restoration after IR. Consistent with these findings, methods and drugs that target MCs have been shown to attenuate IR injury.

CONCLUSION

It has been demonstrated that MCs play a role in IR injury, but the mechanisms are complex and need to be further studied.

Kidney regeneration: common themes from the embryo to the adult

The vertebrate kidney has an inherent ability to regenerate following acute damage. Successful regeneration of the injured kidney requires the rapid replacement of damaged tubular epithelial cells and reconstitution of normal tubular function. Identifying the cells that participate in the regeneration process as well as the molecular mechanisms involved may reveal therapeutic targets for the treatment of kidney disease. Renal regeneration is associated with the expression of genetic pathways that are necessary for kidney organogenesis, suggesting that the regenerating tubular epithelium may be "reprogrammed" to a less-differentiated, progenitor state. This review will highlight data from various vertebrate models supporting the hypothesis that nephrogenic genes are reactivated as part of the process of kidney regeneration following acute kidney injury (AKI). Emphasis will be placed on the reactivation of developmental pathways and how our understanding of the resulting regeneration process may be enhanced by lessons learned in the embryonic kidney.

Kidney injury molecule-1 expression is closely associated with renal allograft damage

The aim of our study was to investigate the expression of kidney injury molecule-1 (KIM-1) in renal allograft biopsy samples and assess the clinical significance of its use as a biomarker for tissue damage. A total of 69 renal allograft biopsy samples from 17 patients with normal serum creatinine and 52 cases of increased serum creatinine were collected. They were divided into different groups according to the Banff 2007 diagnostic criteria. KIM-1 expression was detected by immunohistochemical methods and the association of KIM-1 and blood biochemical indexes was analyzed. KIM-1 expression increased as Banff 2007 classification grade increased and was positively correlated with tubular inflammation severity in the acute T-cell rejection group. Moreover, KIM-1 expression was strongly positive in the chronic active antibody-mediated rejection group. Interestingly, KIM-1 was weakly positive in the normal group without obvious acute rejection and injury of immunosuppressant toxicity. In this group, 27.3% (3/11) of the cases with normal serum creatinine level showed weakly positive KIM-1 expression in their renal tissues. KIM-1 expression level is positively correlated with renal allograft damage and tubular cell injury. KIM-1 is expressed in tubular epithelial cells before blood biochemical indexes become elevated and morphological changes occur. KIM-1 expression is an early, sensitive, and specific biomarker to determine renal tubular epithelial cell injury in renal allograft tissue.

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf-2-dependent genes by ischaemic pre-conditioning and post-conditioning: new adaptive endogenous protective responses against renal ischaemia/reperfusion injury

AIM

To investigate the impact of ischaemic pre-conditioning (Ipre) and post-conditioning (Ipost) on expression of nuclear factor erythroid 2-related factor 2 (Nrf2) gene and its dependent genes, haem oxygenase-1 (HO-1) and NADPH-quinone oxidoreductase-1 (NQO-1); inflammatory cytokines TNF-α, IL1β and ICAM-1; and apoptotic markers such as caspase-3 in renal ischaemia/reperfusion (I/R) injury.

METHODS

One hundred and fifty male Sprague Dawley rats were classified into five groups (each consisted of 30 rats): sham, control (I/R), Ipre + I/R, Ipre without I/R and Ipost + I/R. Serum creatinine and blood urea nitrogen (BUN) were measured at 2, 24 and 48 h after ischaemia. In kidney tissues, mRNA of Nrf2, HO-1, NQO-1, TNF-α, IL-1β and ICAM-1 and immunohistochemical expression of Nrf2 and caspase-3 were assessed.

RESULTS

Serum creatinine and BUN improved significantly in Pre + I/R group; however, they did not show any significant improvement in Post + I/R group. Also, Ipre-I/R group showed non-significant change in serum creatinine and BUN. The expression of Nrf2, HO-1 and NQO-1 is increased significantly in Pre + I/R and Pre - I/R groups, while the enhancement in Post + I/R group was non-significant. Moreover, the expression of proinflammatory cytokines (TNF-α, IL-1 and ICAM-1) and apoptotic (caspase-3) markers showed high significant attenuation in Pre + I/R group, but slight significant attenuation in Pre + I/R group.

CONCLUSION

The renoprotective action of Ipre might include early activation and enhanced expression of Nrf2 gene and its dependent antioxidant genes, HO-1 and NOQ1, as endogenous adaptive renoprotective genes, as well as reduction in TNF-α, IL-1β, ICAM-1 and caspase-3.