Attenuation of renal ischemia-reperfusion injury in inducible nitric oxide synthase knockout mice

The protective effect of 1400W against ischaemia and reperfusion injury is countered by transient medullary kidney endothelial dysregulation

Renal ischaemia and reperfusion (I/R) is caused by a sudden temporary impairment of the blood flow. I/R is a prevalent cause of acute kidney injury. As nitric oxide generated by inducible nitric oxide synthase (iNOS) has detrimental effects during I/R, the pharmacological blockade of iNOS has been proposed as a potential strategy to prevent I/R injury. The aim of this study was to improve the understanding of 1400W (an iNOS inhibitor) on renal I/R as a pharmacological strategy against kidney disease. BALB/c mice received 30 min of bilateral ischaemia, followed by 48 h or 28 days of reperfusion. Vehicle or 1400W (10 mg/kg) was administered 30 min before inducing ischaemia. We found that after 48 h of reperfusion 1400W decreased the serum creatinine, blood urea nitrogen, neutrophil gelatinase-associated lipocalin and proliferating cell nuclear antigen 3 in the I/R animals. Unexpectedly, we observed mRNA upregulation of genes involved in kidney injury, cell-cycle arrest, inflammation, mesenchymal transition and endothelial activation in the renal medulla of sham animals treated with 1400W. We also explored if 1400W promoted chronic kidney dysfunction 28 days after I/R and did not find significant alterations in renal function, fibrosis, blood pressure or mortality. The results provide evidence that 1400W may have adverse effects in the renal medulla. Importantly, our data point to 1400W-induced endothelial dysfunction, establishing therapeutic limitations for its use. KEY POINTS: Acute kidney injury is a global health problem associated with high morbidity and mortality. The pharmacological blockade of inducible nitric oxide synthase (iNOS) has been proposed as a potential strategy to prevent AKI induced by ischaemia and reperfusion (I/R). Our main finding is that 1400W, a selective and irreversible iNOS inhibitor with low toxicity that is proposed as a therapeutic strategy to prevent kidney I/R injury, produces aberrant gene expression in the medulla associated to tissue injury, cell cycle arrest, inflammation, mesenchymal transition and endothelial activation. The negative effect of 1400W observed in the renal medulla at 48 h from drug administration, is transient as it did not translate into a chronic kidney disease condition.

Accelerated lipid peroxidation in a rat model of gentamicin nephrotoxicity

Kidney disease represents a burden for the health care system worldwide. As the prevalence continues to rise, discovering new biomarkers of early kidney damage has become crucial. Oxidative stress (OS) represents one of the main factors involved in the early stages of many syndromes leading to kidney damage. Therefore, it must be studied in detail. To date, many studies have focused on OS in advanced stages of acute kidney injury (AKI), with great success. The aim of the present study was to ascertain whether even mild renal function impairment can be linked to specific systemic markers of OS and systemic antioxidants in order to pinpoint certain biomarkers for early kidney damage. We used male rats (Rattus norvegicus) in which we induced kidney damage by injecting gentamicin for 7 days. Blood was collected 24 h after the last dose of gentamicin. Urea, creatinine, 3-nitrotyrosine (3-NT), nitric oxide (NO), malondialdehyde (MDA), thiols (TS), total oxidative stress (TOS), and interferon-γ (IFN-γ) were determined. In addition, for the antioxidant status we measured total antioxidant capacity (TAC) and interleukin-10 (IL-10). Our results demonstrated that the rats had mild renal impairment consistent with a pre-AKI stage due to the nephrotoxic effect of gentamicin. However, TOS, MDA and NO were significantly higher in the gentamicin group compared to the control group. In addition, TAC was higher in the control group. Hence, OS markers reach higher levels and may potentially be used as markers of kidney damage even in cases of mild renal function impairment.

The Role of Myeloid Cells in Acute Kidney Injury and Kidney Repair

AKI remains highly prevalent, yet no optimal therapy is available to prevent it or promote recovery after initial insult. Experimental studies have demonstrated that both innate and adaptive immune responses play a central role during AKI. In response to injury, myeloid cells are first recruited and activated on the basis of specific signals from the damaged microenvironment. The subsequent recruitment and activation state of the immune cells depends on the stage of injury and recovery, reflecting a dynamic and diverse spectrum of immunophenotypes. In this review, we highlight our current understanding of the mechanisms by which myeloid cells contribute to injury, repair, and fibrosis after AKI.

An Interplay Between MRTF-A and the Histone Acetyltransferase TIP60 Mediates Hypoxia-Reoxygenation Induced iNOS Transcription in Macrophages

Cardiac ischemia-reperfusion injury (IRI) represents a major pathophysiological event associated with permanent loss of heart function. Several inter-dependent processes contribute to cardiac IRI that include accumulation of reactive oxygen species (ROS), aberrant inflammatory response, and depletion of energy supply. Inducible nitric oxide synthase (iNOS) is a pro-inflammatory mediator and a major catalyst of ROS generation. In the present study we investigated the epigenetic mechanism whereby iNOS transcription is up-regulated in macrophages in the context of cardiac IRI. We report that germline deletion or systemic inhibition of myocardin-related transcription factor A (MRTF-A) in mice attenuated up-regulation of iNOS following cardiac IRI in the heart. In cultured macrophages, depletion or inhibition of MRTF-A suppressed iNOS induction by hypoxia-reoxygenation (HR). In contrast, MRTF-A over-expression potentiated activation of the iNOS promoter by HR. MRTF-A directly binds to the iNOS promoter in response to HR stimulation. MRTF-A binding to the iNOS promoter was synonymous with active histone modifications including trimethylated H3K4, acetylated H3K9, H3K27, and H4K16. Further analysis revealed that MRTF-A interacted with H4K16 acetyltransferase TIP60 to synergistically activate iNOS transcription. TIP60 depletion or inhibition achieved equivalent effects as MRTF-A depletion/inhibition in terms of iNOS repression. Of interest, TIP60 appeared to form a crosstalk with the H3K4 trimethyltransferase complex to promote iNOS trans-activation. In conclusion, we data suggest that the MRTF-A-TIP60 axis may play a critical role in iNOS transcription in macrophages and as such be considered as a potential target for the intervention of cardiac IRI.

Cross organelle stress response disruption promotes gentamicin-induced proteotoxicity

Gentamicin is a nephrotoxic antibiotic that causes acute kidney injury (AKI) primarily by targeting the proximal tubule epithelial cell. The development of an effective therapy for gentamicin-induced renal cell injury is limited by incomplete mechanistic insight. To address this challenge, we propose that RNAi signal pathway screening could identify a unifying mechanism of gentamicin-induced cell injury and suggest a therapeutic strategy to ameliorate it. Computational analysis of RNAi signal screens in gentamicin-exposed human proximal tubule cells suggested the cross-organelle stress response (CORE), the unfolded protein response (UPR), and cell chaperones as key targets of gentamicin-induced injury. To test this hypothesis, we assessed the effect of gentamicin on the CORE, UPR, and cell chaperone function, and tested the therapeutic efficacy of enhancing cell chaperone content. Early gentamicin exposure disrupted the CORE, evidenced by a rise in the ATP:ADP ratio, mitochondrial-specific H2O2 accumulation, Drp-1-mediated mitochondrial fragmentation, and endoplasmic reticulum-mitochondrial dissociation. CORE disruption preceded measurable increases in whole-cell oxidative stress, misfolded protein content, transcriptional UPR activation, and its untoward downstream effects: CHOP expression, PARP cleavage, and cell death. Geranylgeranylacetone, a therapeutic that increases cell chaperone content, prevented mitochondrial H2O2 accumulation, preserved the CORE, reduced the burden of misfolded proteins and CHOP expression, and significantly improved survival in gentamicin-exposed cells. We identify CORE disruption as an early and remediable cause of gentamicin proteotoxicity that precedes downstream UPR activation and cell death. Preserving the CORE significantly improves renal cell survival likely by reducing organelle-specific proteotoxicity during gentamicin exposure.

Doxazosin down-regulates sodium-glucose cotransporter-2 and exerts a renoprotective effect in rat models of acute renal injury

Sodium-glucose cotransporter-2 (SGLT2) is known to be involved in the progression of acute renal injury (ARI) and is regulated by different mediators in the kidneys including extracellular signal-regulated kinase (ERK), hypoxia-inducible factor 1 alpha (HIF1α) and prostaglandin E2 (PGE2). In the present study, we investigated the possible protective effect of doxazosin on renal ischaemia/reperfusion (IR) and glycerol-induced ARI by determining its effect on SGLT2 via modifying ERK-HIF1α pathway and/or PGE2. Rats were divided into control, sham or IR where the rats received the vehicle, doxazosin (8 mg/kg) or the SGLT2 inhibitor, dapagliflozin (10 mg/kg) for 3 days followed by 45 minutes bilateral renal ischaemia then 24 hours reperfusion. Another group of rats received the vehicle, doxazosin or dapagliflozin for three days followed by injection of 50% glycerol (8 mL/kg, IM) or saline. Kidney function tests, systolic blood pressure (SBP), oxidative stress markers (malondialdehyde [MDA] and NADPH oxidase), nitric oxide (NO), inducible nitric oxide synthase (iNOS), HIF1α, ERK phosphorylation and PGE2 levels were determined. Additionally, renal sections were used for immunological expression of SGLT2. ARI rats showed significantly increased SBP; worsened kidney function tests; increased oxidative stress, iNOS, NO, HIF1α levels; and decreased PGE2 and ERK phosphorylation along with up-regulated SGLT2. Doxazosin treatment protected against the kidney damage and attenuated the associated biochemical changes. Doxazosin has a direct renoprotective effect possibly by down-regulating SGLT2.

Oxidative stress as a potential target in acute kidney injury

Background

Acute kidney injury (AKI) is a major problem for health systems being directly related to short and long-term morbidity and mortality. In the last years, the incidence of AKI has been increasing. AKI and chronic kidney disease (CKD) are closely interconnected, with a growing rate of CKD linked to repeated and severe episodes of AKI. AKI and CKD can occur also secondary to imbalanced oxidative stress (OS) reactions, inflammation, and apoptosis. The kidney is particularly sensitive to OS. OS is known as a crucial pathogenetic factor in cellular damage, with a direct role in initiation, development, and progression of AKI. The aim of this review is to focus on the pathogenetic role of OS in AKI in order to gain a better understanding. We exposed the potential relationships between OS and the perturbation of renal function and we also presented the redox-dependent factors that can contribute to early kidney injury. In the last decades, promising advances have been made in understanding the pathophysiology of AKI and its consequences, but more studies are needed in order to develop new therapies that can address OS and oxidative damage in early stages of AKI.

Methods

We searched PubMed for relevant articles published up to May 2019. In this review we incorporated data from different types of studies, including observational and experimental, both in vivo and in vitro, studies that provided information about OS in the pathophysiology of AKI.

Results

The results show that OS plays a major key role in the initiation and development of AKI, providing the chance to find new targets that can be therapeutically addressed.

Discussion

Acute kidney injury represents a major health issue that is still not fully understood. Research in this area still provides new useful data that can help obtain a better management of the patient. OS represents a major focus point in many studies, and a better understanding of its implications in AKI might offer the chance to fight new therapeutic strategies.

Protective effect of piperine in ischemia-reperfusion induced acute kidney injury through inhibition of inflammation and oxidative stress

Background and aim

Renal ischemia-reperfusion is associated with inflammation and oxidative stress. As a major compound in black pepper, piperine has anti-inflammatory and anti-oxidative properties. In present study, the protective effects of oral administration of piperine in renal ischemia-reperfusion (IR) induced acute kidney injuries (AKI) were investigated.

Experimental procedure

Male Wistar rats received piperine (10 or 20 mg/kg.bw) or vehicle for 10 days. The artery and vein of both kidneys were then clamped for 30 min, followed by a 24-h reperfusion period. Concentrations of creatinine and urea-nitrogen in descending aorta blood were measured, and malondialdehyde (MDA) and ferric reducing/antioxidant power (FRAP) levels were measured in kidney tissue to evaluate the oxidative stress. Inflammation was evaluated by measuring the TNF-α and ICAM-1 mRNA expression levels in renal cortical tissue using Real Time PCR method and counting leukocytes infiltration to interstitium. Further measured were tissue damages in H & E stained sections.

Results

Renal IR reduced FRAP, while increasing the plasma concentrations of creatinine and urea-nitrogen, tissue MDA level, TNF-α and ICAM-1 mRNA expressions, leukocyte infiltration and histopathologic injuries. Piperine administration significantly reduced the plasma concentrations of creatinine and urea-nitrogen, expression of pro-inflammatory factors, oxidative stress and renal histopathologic injuries. It is to be noted that 20 mg/kg dose was more effective.

Conclusion

Our results suggest piperine protects the kidney against ischemia-reperfusion induced acute kidney injuries by its anti-inflammatory and anti-oxidative properties.

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Renal ischemia-reperfusion increased the inflammation and oxidative stress parameters.

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Ischemia-reperfusion increased histopathological damages and functional parameters.

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Piperine pretreatment significantly reduced the inflammation and oxidative stress.

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Piperine administration ameliorated renal function and histopathologic damages.

l-NIL prevents the ischemia and reperfusion injury involving TLR-4, GST, clusterin, and NFAT-5 in mice

On renal ischemia-reperfusion (I/R) injury, recruitment of neutrophils during the inflammatory process promotes local generation of oxygen and nitrogen reactive species, which, in turn, are likely to exacerbate tissue damage. The mechanism by which inducible nitric oxide synthase (iNOS) is involved in I/R has not been elucidated. In this work, the selective iNOS inhibitor l- N6-(1-iminoethyl)lysine (l-NIL) and the NOS substrate l-arginine were employed to understand the role of NOS activity on the expression of particular target genes and the oxidative stress elicited after a 30-min of bilateral renal ischemia, followed by 48-h reperfusion in Balb/c mice. The main findings of the present study were that pharmacological inhibition of iNOS with l-NIL during an I/R challenge of mice kidney decreased renal injury, prevented tissue loss of integrity, and improved renal function. Several novel findings regarding the molecular mechanism by which iNOS inhibition led to these protective effects are as follows: 1) a prevention of the I/R-related increase in expression of Toll-like receptor 4 (TLR-4), and its downstream target, IL-1β; 2) reduced oxidative stress following the I/R challenge; noteworthy, this study shows the first evidence of glutathione S-transferase (GST) inactivation following kidney I/R, a phenomenon fully prevented by iNOS inhibition; 3) increased expression of clusterin, a survival autophagy component; and 4) increased expression of nuclear factor of activated T cells 5 (NFAT-5) and its target gene aquaporin-1. In conclusion, prevention of renal damage following I/R by the pharmacological inhibition of iNOS with l-NIL was associated with the inactivation of proinflammatory pathway triggered by TLR-4, oxidative stress, renoprotection (autophagy inactivation), and NFAT-5 signaling pathway.

Protective Role for Antioxidants in Acute Kidney Disease

Acute kidney injury causes significant morbidity and mortality in the community and clinic. Various pathologies, including renal and cardiovascular disease, traumatic injury/rhabdomyolysis, sepsis, and nephrotoxicity, that cause acute kidney injury (AKI), induce general or regional decreases in renal blood flow. The ensuing renal hypoxia and ischemia promotes the formation of reactive oxygen species (ROS) such as superoxide radical anions, peroxides, and hydroxyl radicals, that can oxidatively damage biomolecules and membranes, and affect organelle function and induce renal tubule cell injury, inflammation, and vascular dysfunction. Acute kidney injury is associated with increased oxidative damage, and various endogenous and synthetic antioxidants that mitigate source and derived oxidants are beneficial in cell-based and animal studies. However, the benefit of synthetic antioxidant supplementation in human acute kidney injury and renal disease remains to be realized. The endogenous low-molecular weight, non-proteinaceous antioxidant, ascorbate (vitamin C), is a promising therapeutic in human renal injury in critical illness and nephrotoxicity. Ascorbate may exert significant protection by reducing reactive oxygen species and renal oxidative damage via its antioxidant activity, and/or by its non-antioxidant functions in maintaining hydroxylase and monooxygenase enzymes, and endothelium and vascular function. Ascorbate supplementation may be particularly important in renal injury patients with low vitamin C status.

Histological and Immunohistochemical Basis of the Effect of Aminoguanidine on Renal Changes Associated with Hemorrhagic Shock in a Rat Model

Acute kidney failure is the main cause of death among patients with severe trauma due to massive blood loss and hemorrhagic shock (HS). Renal cell injury is caused by tissue ischemia. Renal ischemia initiates a complex and interconnected chain of events resulting in cell injury and renal cell necrosis. Nitric oxide plays a crucial role in renal function and can be inhibited by aminoguanidine (AG). We studied whether AG can ameliorate pathological renal changes associated with HS syndrome in a rat model and explored the AG protection mechanism. Rats were intraperitoneally injected with heparin sodium and mean arterial blood pressure was monitored. Animals were divided into three groups: control (without hemorrhage), with or without intra-arterially injected AG; HS (blood continuously withdrawn or reinfused to maintain an MABP of 35-40 mmHg); and HS with AG. We found that AG decreased plasma concentrations of urea, creatinine, and nitrates; ameliorated histological changes of HS-induced rats; and decreased the expressions of inducible nitrogen oxide synthase (iNOS), proapoptotic protein (BAX), and vitamin D receptors (VDR). AG ameliorated kidney injury by inhibiting iNOS resulting in decreased BAX and VDR expressions. Therefore, a therapeutic strategy targeting AG may provide new insights into kidney injury during severe shock.

The multifaceted role of the renal microvasculature during acute kidney injury

Pediatric acute kidney injury (AKI) represents a complex disease process for clinicians as it is multifactorial in cause and only limited treatment or preventatives are available. The renal microvasculature has recently been implicated in AKI as a strong therapeutic candidate involved in both injury and recovery. Significant progress has been made in the ability to study the renal microvasculature following ischemic AKI and its role in repair. Advances have also been made in elucidating cell-cell interactions and the molecular mechanisms involved in these interactions. The ability of the kidney to repair post AKI is closely linked to alterations in hypoxia, and these studies are elucidated in this review. Injury to the microvasculature following AKI plays an integral role in mediating the inflammatory response, thereby complicating potential therapeutics. However, recent work with experimental animal models suggests that the endothelium and its cellular and molecular interactions are attractive targets to prevent injury or hasten repair following AKI. Here, we review the cellular and molecular mechanisms of the renal endothelium in AKI, as well as repair and recovery, and potential therapeutics to prevent or ameliorate injury and hasten repair.

Abandon the mouse research ship? Not just yet!

Many preclinical studies in critical care medicine and related disciplines rely on hypothesis-driven research in mice. The underlying premise posits that mice sufficiently emulate numerous pathophysiologic alterations produced by trauma/sepsis and can serve as an experimental platform for answering clinically relevant questions. Recently, the lay press severely criticized the translational relevance of mouse models in critical care medicine. A series of provocative editorials were elicited by a highly publicized research report in the Proceedings of the National Academy of Sciences (PNAS; February 2013), which identified an unrecognized gene expression profile mismatch between human and murine leukocytes following burn/trauma/endotoxemia. Based on their data, the authors concluded that mouse models of trauma/inflammation are unsuitable for studying corresponding human conditions. We believe this conclusion was not justified. In conjunction with resulting negative commentary in the popular press, it can seriously jeopardize future basic research in critical care medicine. We will address some limitations of that PNAS report to provide a framework for discussing its conclusions and attempt to present a balanced summary of strengths/weaknesses of use of mouse models. While many investigators agree that animal research is a central component for improved patient outcomes, it is important to acknowledge known limitations in clinical translation from mouse to man. The scientific community is responsible to discuss valid limitations without overinterpretation. Hopefully, a balanced view of the strengths/weaknesses of using animals for trauma/endotoxemia/critical care research will not result in hasty discount of the clear need for using animals to advance treatment of critically ill patients.

Therapeutic translation in acute kidney injury: the epithelial/endothelial axis

Acute kidney injury (AKI) remains a major clinical event with rising incidence, severity, and cost; it now has a morbidity and mortality exceeding acute myocardial infarction. There is also a documented conversion to and acceleration of chronic kidney disease to end-stage renal disease. The multifactorial nature of AKI etiologies and pathophysiology and the lack of diagnostic techniques have hindered translation of preclinical success. An evolving understanding of epithelial, endothelial, and inflammatory cell interactions and individualization of care will result in the eventual development of effective therapeutic strategies. This review focuses on epithelial and endothelial injury mediators, interactions, and targets for therapy.

Mice with an absent stress response are protected against ischemic renal injury

Inducible heat shock proteins (HSP), regulated by heat shock factor-1 (HSF-1), protect against renal cell injury in vitro. To determine whether HSPs ameliorate ischemic renal injury in vivo, HSF-1functional knock-out mice (HSF-KO) were compared with wild-type mice following bilateral ischemic renal injury. Following injury, the kidneys of wild-type mice had the expected induction of HSP70 and HSP25; a response absent in the kidneys of HSF-KO mice. Baseline serum creatinine was equivalent between strains. Serum creatinines at 24 hours reflow in HSF-KO mice were significantly lower than in the wild-type. Histology showed similar tubule injury in both strains after ischemic renal injury but increased medullary vascular congestion in wild-type compared with HSF-KO mice. Flow-cytometry of mononuclear cells isolated from kidneys showed no difference between strains in the number of CD4⁺ and CD8⁺ T cells in sham operated animals. At 1 hour of reflow, CD4⁺ and CD8⁺ cells were doubled in the kidneys of wild type but not HSF-KO mice. Foxp3⁺ T regulatory cells were significantly more abundant in the kidneys of sham-operated HSF-KO than wild-type mice. Suppression of CD25⁺Foxp3⁺ cells in HSF-KO kidneys with the anti-CD25 antibody PC61 reversed the protection against ischemic renal injury. Thus, HSF-KO mice are protected from ischemic renal injury by a mechanism that depends on an increase in the T regulatory cells in the kidney associated with altered T cell infiltration early in reflow. Hence, stress response activation may contribute to early injury by facilitating T cell infiltration into ischemic kidney.

Adenovirus-mediated eNOS expression augments liver injury after ischemia/reperfusion in mice

Hepatic ischemia/reperfusion (l/R) injury continues to be a critical problem. The role of nitric oxide in liver I/R injury is still controversial. This study examines the effect of endothelial nitric oxide synthase (eNOS) over-expression on hepatic function following I/R. Adenovirus expressing human eNOS (Ad-eNOS) was administered by tail vein injection into C57BL/6 mice. Control mice received either adenovirus expressing LacZ or vehicle only. Sixty minutes of total hepatic ischemia was performed 3 days after adenovirus treatment, and mice were sacrificed after 6 or 24 hrs of reperfusion to assess hepatic injury. eNOS over expression caused increased liver injury as evidenced by elevated AST and ALT levels and decreased hepatic ATP content. While necrosis was not pervasive in any group, TUNEL demonstrated significantly increased apoptosis in Ad-eNOS infected livers. Western blotting demonstrated increased levels of protein nitration and upregulation of the pro-apoptotic proteins bax and p53. Our data suggest that over-expression of eNOS is detrimental in the setting of hepatic I/R.

Endothelium under stress: local and systemic messages

Endothelial responses to stressors are nonuniform and follow the rules of stress-induced hormesis. Responses to the same stressor, depending on its intensity, can range from pro-regenerative to pro-lethal. Exposure to sublethal stressors induces a programmed response that results in stress resistance, whereas a lethal level of a stressor accelerates cell demise. Diverse stressors turn on several default programs within the cells; such programs tend to induce anti-oxidative defenses and anti-inflammatory and pro-survival systems, whereas others tend to switch on pro-apoptotic systems. The response of the kidney endothelium to various forms of acute kidney injury follows these general principles. It is characterized by a proinflammatory pattern that includes up-regulation of different adhesion molecules promoting endothelial-leukocyte interactions, generation of reactive oxygen species, with formation of oxidative and nitrosative stress and mitochondrial damage. Simultaneously, a series of adaptive mechanisms, both local and systemic, are ignited. Stressed endothelial cells broadcast distress signals systemically; these signals can be directed toward the restoration of homeostasis or aggravation of the original insult.

Rosiglitazone affects nitric oxide synthases and improves renal outcome in a rat model of severe ischemia/reperfusion injury

Background. Nitric oxide (NO)-signal transduction plays an important role in renal ischemia/reperfusion (I/R) injury. NO produced by endothelial NO-synthase (eNOS) has protective functions whereas NO from inducible NO-synthase (iNOS) induces impairment. Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor (PPAR)-γ agonist exerted beneficial effects after renal I/R injury, so we investigated whether this might be causally linked with NOS imbalance. Methods. RGZ (5 mg/kg) was administered i.p. to SD-rats (f) subjected to bilateral renal ischemia (60 min). Following 24 h of reperfusion, inulin- and PAH-clearance as well as PAH-net secretion were determined. Morphological alterations were graded by histopathological scoring. Plasma NO_x-production was measured. eNOS and iNOS expression was analyzed by qPCR. Cleaved caspase 3 (CC3) was determined as an apoptosis indicator and ED1 as a marker of macrophage infiltration in renal tissue. Results. RGZ improves renal function after renal I/R injury (PAH-/inulin-clearance, PAH-net secretion) and reduces histomorphological injury. Additionally, RGZ reduces NO_x plasma levels, ED-1 positive cell infiltration and CC3 expression. iNOS-mRNA is reduced whereas eNOS-mRNA is increased by RGZ. Conclusion. RGZ has protective properties after severe renal I/R injury. Alterations of the NO pathway regarding eNOS and iNOS could be an explanation of the underlying mechanism of RGZ protection in renal I/R injury.

Pathophysiology of ischemic acute kidney injury

Acute kidney injury (AKI) as a consequence of ischemia is a common clinical event leading to unacceptably high morbidity and mortality, development of chronic kidney disease (CKD), and transition from pre-existing CKD to end-stage renal disease. Data indicate a close interaction between the many cell types involved in the pathophysiology of ischemic AKI, which has critical implications for the treatment of this condition. Inflammation seems to be the common factor that links the various cell types involved in this process. In this Review, we describe the interactions between these cells and their response to injury following ischemia. We relate these events to patients who are at high risk of AKI, and highlight the characteristics that might predispose these patients to injury. We also discuss how therapy targeting specific cell types can minimize the initial and subsequent injury following ischemia, thereby limiting the extent of acute changes and, hopefully, long-term structural and functional alterations to the kidney.

Role for endothelial nitric oxide synthase in nitrite-induced protection against renal ischemia-reperfusion injury in mice

Nitrite is protective against renal ischemia/reperfusion injury (IRI); an effect due to its reduction to nitric oxide (NO). In addition to other reductase pathways, endothelial NO synthase (eNOS) may also facilitate nitrite reduction in ischemic environments. We investigated the role of eNOS in sodium nitrite (60 microM, 10 ml/kg applied topically 1 min before reperfusion)-induced protection against renal IRI in C57/BL6 wild-type (WT) and eNOS knockout (eNOS KO) mice subjected to bilateral renal ischemia (30 min) and reperfusion (24h). Markers of renal dysfunction (plasma [creatinine] and [urea]), damage (tubular histology) and inflammation (cell recruitment) were elevated following IRI in WT mice; effects significantly reduced following nitrite treatment. Chemiluminescence analysis of cortical and medullary sections of the kidney demonstrated rapid (within 1 min) distribution of nitrite following application. Whilst IRI caused a significant (albeit substantially reduced compared to WT mice) elevation of markers of renal dysfunction and damage in eNOS KO mice, the beneficial effects of nitrite were absent or reduced, respectively. Moreover, nitrite treatment enhanced renal dysfunction in the form of increased plasma [creatinine] in eNOS KO mice. Confirmation of nitrite reductase activity of eNOS was provided by demonstration of nitrite (100 microM)-derived NO production by kidney homogenates of WT mice, that was significantly reduced by L-NMMA. L-NMMA was without effect using kidney homogenates of eNOS KO mice. These results support a role for eNOS in the pathways activated during renal IRI and also identify eNOS as a nitrite reductase in ischemic conditions; activity which in part underlies the protective effects of nitrite.

IL-18 contributes to renal damage after ischemia-reperfusion

IL-18 is a proinflammatory cytokine produced by macrophages and other cell types present in the kidney during ischemia-reperfusion injury (IRI), but its role in this injury is unknown. Here, compared with wild-type mice, IL-18(-/-) mice subjected to kidney IRI demonstrated better kidney function, less tubular damage, reduced accumulation of neutrophils and macrophages, and decreased expression of proinflammatory molecules that are downstream of IL-18. For determination of the relative contributions of leukocytes and parenchymal cells to IL-18 production and subsequent kidney damage during IRI, bone marrow-chimeric mice were generated. Wild-type mice engrafted with IL-18(-/-) hemopoietic cells showed less kidney dysfunction and tubular damage than IL-18(-/-) mice engrafted with wild-type bone marrow. In vitro, macrophages produced IL-18 mRNA and protein in response to ischemia. These data suggest bone marrow-derived cells are the key contributors to IL-18-mediated effects of renal IRI. Finally, similar to IL-18(-/-) mice, pretreatment of wild-type mice with IL-18-binding protein was renoprotective in this model of IRI. In conclusion, IL-18, derived primarily from cells of bone marrow origin, contributes to the renal damage observed during IRI. IL-18-binding protein may have potential as a renoprotective therapy.

Inhibition of cystathionine-beta-synthase activity during renal ischemia-reperfusion: role of pH and nitric oxide

Our recent study (Prathapasinghe GA, Siow YL, O K. Am J Physiol Renal Physiol 292: F1354-F1363, 2007) indicates that homocysteine (Hcy) plays a detrimental role in ischemia-reperfusion-induced renal injury. Elevation of renal Hcy concentration during ischemia-reperfusion is attributed to reduced activity of cystathionine-beta-synthase (CBS) that catalyzes the rate-limiting step in the transsulfuration pathway for the metabolism of the majority of Hcy in the kidney. However, the mechanisms of impaired CBS activity in the kidney are unknown. The aim of this study was to investigate the effects of pH and nitric oxide (NO) on the CBS activity in the kidney during ischemia-reperfusion. The left kidney of a Sprague-Dawley rat was subjected to ischemia-reperfusion. The CBS activity was significantly reduced in kidneys subjected to ischemia alone (15-60 min) or subjected to ischemia followed by reperfusion for 1-24 h. The pH was markedly reduced in kidneys upon ischemia. Injection of alkaline solution into the kidney partially restored the CBS activity during ischemia. Further analysis revealed that reduction of CBS activity during reperfusion was accompanied by an elevation of NO metabolites (nitrate and nitrite) in the kidney tissue. Injection of a NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), restored the CBS activity in the kidneys subjected to ischemia-reperfusion. Treatment with PTIO could abolish ischemia-reperfusion-induced lipid peroxidation and prevent cell death in the kidney. These results suggested that metabolic acidosis during ischemia and accumulation of NO metabolites during reperfusion contributed, in part, to reduced CBS activity leading to an elevation of renal Hcy levels, which in turn, played a detrimental role in the kidney.

Inhibition of hypoxia inducible factor hydroxylases protects against renal ischemia-reperfusion injury

Acute renal failure resulting from hypoperfusion and hypoxia is a significant clinical problem. Hypoxia activates the heterodimeric transcription factor hypoxia inducible factor (HIF), leading to changes in gene expression that promote tissue adaptation and survival. To determine whether HIF may protect the kidney from ischemia-reperfusion injury, we subjected hif1a(+/-) and hif2a(+/-) mice to renal ischemia-reperfusion injury. Injury was substantially more severe in hif(+/-) than in littermate controls, consistent with a protective role for HIF. Because wild-type mice exhibited submaximal HIF accumulation in response to no-flow ischemia, we tested compounds that might augment the protective HIF response following ischemia-reperfusion in these animals. We found that l-mimosine and dimethyloxalylglycine, two small molecules that activate HIF by inhibiting HIF hydroxylases, protected mouse kidneys from ischemia-reperfusion injury. Therefore, pharmacological activation of HIF may offer an effective strategy to protect the kidney from ischemic injury.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.

Favorable balance of anti-oxidant/pro-oxidant systems and ablated oxidative stress in Brown Norway rats in renal ischemia-reperfusion injury

Oxidative stress is important in the pathogenesis of renal ischemia-reperfusion (IR) injury; however whether imbalances in reactive oxygen production and disposal account for susceptibility to injury is unclear. The purpose of this study was to compare necrosis, apoptosis, and oxidative stress in IR-resistant Brown Norway rats vs. IR-susceptible Sprague-Dawley (SD) rats in an in vivo model of renal IR injury. As superoxide (O (2) (.-) ) interacts with nitric oxide (NO) to form peroxynitrite, inducible NO synthase (iNOS) and nitrotyrosine were also examined. Renal IR was induced in SD and BN rats by bilateral clamping of renal arteries for 45 min followed by reperfusion for 24 h (SD 24 and BN 24, respectively). BN rats were resistant to renal IR injury as evidenced by lower plasma creatinine and decreased acute tubular necrosis. TUNEL staining analysis demonstrated significantly decreased apoptosis in the BN rats vs. SD rats after IR. Following IR, O (2) (.-) levels were also significantly lower in renal tissue of BN rats vs. SD rats (P < 0.05) in conjunction with a preservation of the O (2) (.-) dismutating protein, CuZn superoxide dismutase (CuZn SOD) (P < 0.05). This was accompanied by an overall decrease in 4-hydroxynonenal adducts in the BN but not SD rats after IR. BN rats also displayed lower iNOS expression (P < 0.05) resulting in lower tissue NO levels and decreased nitrotyrosine formation (P < 0.01) following IR. Collectively these results show that the resistance of the BN rat to renal IR injury is associated with a favorable balance of oxidant production vs. oxidant removal.

Role of peroxynitrite on cytoskeleton alterations and apoptosis in renal ischemia-reperfusion

During renal ischemia-reperfusion (I/R) injury, apoptosis has been reported as a very important contributor to final kidney damage. The determinant role of cytoskeleton derangement in the development of apoptosis has been previously reported, but a clear description of the different mechanisms involved in this process has not been yet provided. The aim of our study was to know the role of peroxynitrite as an inductor of cytoskeleton derangement and apoptosis during renal I/R. Based on a rat kidney I/R model, using experiments in which both the actin cytoskeleton and peroxynitrite generation were pharmacologically manipulated, results indicate that the peroxynitrite produced during the I/R-derived oxidative stress state is able to provoke cytoskeleton derangement and apoptosis development. Thus control of peroxynitrite generation during I/R could be an effective tool for the improvement of cytoskeleton damage and reduction of apoptosis incidence in renal I/R injury.

Nitric oxide differentially regulates renal ATP-binding cassette transporters during endotoxemia

Nitric oxide (NO) is an important regulator of renal transport processes. In the present study, we investigated the role of NO, produced by inducible NO synthase (iNOS), in the regulation of renal ATP-binding cassette (ABC) transporters in vivo during endotoxemia. Wistar–Hannover rats were injected with lipopolysaccharide (LPS⁺) alone or in combination with the iNOS inhibitor, aminoguanidine. Controls received detoxified LPS (LPS⁻). After LPS⁺, proximal tubular damage and a reduction in renal function were observed. Furthermore, iNOS mRNA and protein, and the amount of NO metabolites in plasma and urine, increased compared to the LPS⁻ group. Coadministration with aminoguanidine resulted in an attenuation of iNOS induction and reduction of renal damage. Gene expression of 20 ABC transporters was determined. After LPS⁺, a clear up-regulation in Abca1, Abcb1/P-glycoprotein (P-gp), Abcb11/bile salt export pump (Bsep), and Abcc2/multidrug resistance protein (Mrp2) was found, whereas Abcc8 was down-regulated. Up-regulation of Abcc2/Mrp2 was accompanied by enhanced calcein excretion. Aminoguanidine attenuated the effects on transporter expression. Our data indicate that NO, produced locally by renal iNOS, regulates the expression of ABC transporters in vivo. Furthermore, we showed, for the first time, expression and subcellular localization of Abcb11/Bsep in rat kidney.

Effects of sodium nitrite on ischemia-reperfusion injury in the rat kidney

Reactive oxygen and nitrogen species play a key role in the pathophysiology of renal ischemia-reperfusion (I/R) injury. Recent studies have shown that nitrite (NO2−) serves as an endogenous source of nitric oxide (NO), particularly in the presence of hypoxia and acidosis. Nanomolar concentrations of NO2−reduce injury following I/R in the liver and heart in vivo. The purpose of this study was to evaluate the role of NO2−in renal I/R injury. Male Sprague-Dawley rats underwent a unilateral nephrectomy followed by 45 min of ischemia of the contralateral kidney or sham surgery under isoflurane anesthesia. Animals received normal saline, sodium NO2−, or sodium nitrate (NO3−; 1.2 nmol/g body wt ip) at 22.5 min after induction of ischemia or 15 min before ischemia. A separate set of animals received saline, NO2−, or NO3−(0.12, 1.2, or 12 nmol/g body wt iv) 45 min before ischemia. Serum creatinine and blood urea nitrogen were increased following I/R injury but were not significantly different among treatment groups at 24 and 48 h after acute renal injury. Interestingly, NO3−administration appeared to worsen renal injury. Histological scoring for loss of brush border, tubular necrosis, and red blood cell extravasation showed no significant differences among the treatment groups. The results indicate that, contrary to the protective effects of NO2−in I/R injury of the liver and heart, NO2−does not provide protection in renal I/R injury and suggest a unique metabolism of NO2−in the kidney.

Renal ischemia and reperfusion activates the eIF 2 alpha kinase PERK

Inhibition of protein synthesis occurs in the post-ischemic reperfused kidney but the molecular mechanism of renal translation arrest is unknown. Several pathways have been identified whereby cell stress inhibits translation initiation via phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF 2 alpha, phospho-form eIF 2 alpha(P)]. Here, we report a 20-fold increase in eIF 2 alpha(P) in kidney homogenates following 10 min of cardiac arrest-induced ischemia and 10 min reperfusion. Using immunohistochemistry, we observed eIF 2 alpha(P) in tubular epithelial cells in both cortex and medulla, where the greatest eIF 2 alpha(P) staining was found in epithelial cells of the so-called watershed area at the corticomedullary junction. We further show that increased eIF 2 alpha(P) is accompanied by activation of the PKR-like endoplasmic reticulum eIF 2 alpha kinase (PERK). These observations indicate that renal ischemia and reperfusion induce stress to the endoplasmic reticulum and activate the unfolded protein response in renal epithelial cells. As the unfolded protein response can result alternatively in a pro-survival or pro-apoptotic outcome, the present study demonstrates an new additional mechanism involved in cell damage and/or repair in ischemic and reperfused kidney.

Nitric oxide induces apoptosis in renal tubular epithelial cells through activation of caspase-8

The susceptibility or resistance of tubular epithelial cells (TEC) to apoptosis is pivotal to the long-term maintenance of kidney function following episodes of inflammation, such as graft rejection. TEC apoptosis can occur with ischemia as well as with proinflammatory cytokines and nitric oxide (NO), produced by infiltrating mononuclear cells. TEC can also produce abundant amounts of NO during inflammation but the role and regulation of NO-induced injury of TEC are not well understood. Apoptosis in TEC in vitro was determined by FACS analysis with annexin-V and propidium iodide staining. NO in culture supernatants was measured by Greiss reagent, and protein expression of inducible NO synthetase (NOS2/iNOS) and caspase-8 was examined by Western blot analysis. Here, we showed that murine TEC produced abundant amounts of NO in response to proinflammatory cytokines (IFN-gamma/TNF-alpha) through upregulation of NOS2, and inhibition of endogenous NO production by l-NMMA reduced TEC apoptosis in cytokine-stimulated cultures. Addition of exogenous NO (sodium nitroprusside) induced TEC apoptosis as well as caspase-8 activation in a dose-dependent manner. The key role of caspase-8 in NO-induced TEC apoptosis was demonstrated by that NO-induced TEC apoptosis can be blocked by caspase-8 inhibition using z-IETD-fmk, caspase-8 silencing with shRNA or by overexpressing the endogenous caspase-8 inhibitor c-FLIP (cellular Flice-inhibitory protein). In conclusion, endogenous NO from NOS2 activity as well as exogenous NO can contribute to renal injury through apoptosis of TEC. Activation of caspase-8 plays a central role in NO-induced apoptosis and caspase-8 inhibition may be an important therapeutic target during renal inflammation.

Nitric oxide synthase distribution and expression with ischemic preconditioning of the rat liver

This study was undertaken to identify nitric oxide synthase (NOS) isoforms responsible for the generation of cytoprotective NO during liver ischemic preconditioning (IPC). Sprague-Dawley rats were subjected to 45 min lobar ischemia followed by 2 h reperfusion. L-arginine or Nomega-nitro-L-arginine methyl ester (L-NAME) was administered to stimulate or block NO synthesis. Study groups (n=6) had 1) sham laparotomy, 2) ischemia reperfusion (IR), 3) IPC with 5 min ischemia and 10 min reperfusion before IR, 4) L-arginine before IR, or 5) L-NAME + IPC before IR. Liver function tests, nitrite + nitrate (NOx) and plasma amino acids were analyzed. The endothelial cell and inducible isoforms of NOS (eNOS and iNOS) were identified using immunohistochemistry and Western blotting. Both IPC and L-arginine treatment increased NOx (P<0.05) and improved serum liver enzymes (P<0.05) when compared with IR. These effects were prevented by L-NAME. Hepatic vein NOx was significantly higher than circulating NOx. iNOS expression was absent within the groups. The preconditioned livers were associated with up-regulation of eNOS expression and also increased L-arginine levels. The effects of L-arginine administration were similar to those evident following IPC. Thus, cytoprotective NO generation during IPC of the liver was a result of increased eNOS expression and increased L-arginine substrate availability.

Reperfusion injury in skeletal muscle is reduced in inducible nitric oxide synthase knockout mice

Inducible nitric oxide synthase (iNOS) participates in many pathological events, and selective inhibition of iNOS has been shown to reduce ischemia-reperfusion (I/R) injury in different tissues. To further confirm its role in this injury process, I/R injury was observed in denervated cremaster muscles of iNOS-deficient (iNOS−/−) and wild-type mice. After 3-h ischemia and 90-min reperfusion, blood flow in reperfused muscle was 80 ± 8.5% (mean ± SE) of baseline at 10-min reperfusion and completely returned to the preischemia baseline after 20 min in iNOS−/− mice. In contrast, blood flow was 32 ± 7.4% at 10 min and increased to 60 ± 20% of the baseline level at 90 min in wild-type mice ( P < 0.001 vs. iNOS−/− mice at all time points). The increased muscle blood flow in iNOS−/− mice was associated with significantly less vasospasm in all three sizes of arterial vessel size categories. The weight ratio to the contralateral muscle not subjected to I/R was greater in wild-type mice (173 ± 11%) than in iNOS−/− mice (117 ± 3%; P < 0.01). Inflammation and neutrophil extravasation were also more severe in wild-type mice. Western blot analysis demonstrated an absence of iNOS protein band in iNOS−/− mice and upregulation of iNOS protein expression in wild-type mice. Our results confirm the importance of iNOS in I/R injury. Upregulated iNOS exacerbates I/R injury and appears to be a therapeutic target in protection of tissues against this type of injury.

Acute renal failure: definitions, diagnosis, pathogenesis, and therapy

Acute renal failure (ARF), characterized by sudden loss of the ability of the kidneys to excrete wastes, concentrate urine, conserve electrolytes, and maintain fluid balance, is a frequent clinical problem, particularly in the intensive care unit, where it is associated with a mortality of between 50% and 80%. In this review, the epidemiology and pathophysiology of ARF are discussed, including the vascular, tubular, and inflammatory perturbations. The clinical evaluation of ARF and implications for potential future therapies to decrease the high mortality are described.

COX-2 and iNOS in opioid-induced delayed cardioprotection in the intact rat

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) have been previously implicated in the late phase of cardioprotection associated with opioid-induced and ischemic preconditioning (IPC) in conscious rabbits and COX-2 in isolated rat hearts pretreated with an exogenous delta opioid agonist. However, it is not know if both iNOS and COX-2 mediate the late phase of cardioprotection induced by opioids in the intact blood-perfused rat. Therefore, we investigated the role of COX-2 and iNOS in the delayed phase of protection mediated by delta opioid receptor activation. Rats were pretreated 24 hours prior to an occlusion/reperfusion protocol with the selective non-peptide delta opioid agonists, BW373U86 (BW) and SNC-121 (SNC). NS-398, a selective COX-2 inhibitor was administered after the 24-hour recovery period just prior to index ischemia. The selective iNOS inhibitors, S-methylthiourea (SMT) and aminoguanidine (AG), were administered in conjunction with opioid pretreatment or were also given 24 hours after opioid administration just prior to index ischemia. COX-2 inhibition by NS-398 given 24 hours after opioid administration attenuated the protective effects of both BW and SNC (46 +/- 6 vs. 13 +/- 3 and 51 +/- 5 vs. 29 +/- 2, p < 0.001, respectively). Similarly, inhibition of iNOS following 24 hours of treatment with opioids also attenuated the protective effects of BW and SNC. However, the delayed protective effects of the opioids were not attenuated by pretreatment with the iNOS inhibitors 24 hours prior to the infarct protocol. These results suggest that both COX-2 and iNOS are mediators of delayed protection induced by non-peptide delta opioid agonists. It appears that the trigger effect is not dependent on the activity of iNOS or COX-2 but the late phase of cardioprotection is dependent on the upregulation of these enzymes.

The story so far: Molecular regulation of the heme oxygenase-1 gene in renal injury

Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, the latter of which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Two major isoforms of the HO enzyme have been described: an inducible isoform, HO-1, and a constitutively expressed isoform, HO-2. A third isoform, HO-3, closely related to HO-2, has also been described. Several stimuli implicated in the pathogenesis of renal injury, such as heme, nitric oxide, growth factors, angiotensin II, cytokines, and nephrotoxins, induce HO-1. Induction of HO-1 occurs as an adaptive and beneficial response to these stimuli, as demonstrated by studies in renal and non-renal disease states. This review will focus on the molecular regulation of the HO-1 gene in renal injury and will highlight the interspecies differences, predominantly between the rodent and human HO-1 genes.

Arginine Immunonutrition in Critically Ill Patients: A Clinical Dilemma

Commercial enteral nutritional formulas for enhancement of the immune system are widely used in critical care. Immunonutrition with arginine can enhance inflammatory and immunologic responses in animal models and in humans. Although clinical improvements in surgical patients have been reported, benefits in critically ill patients with systemic inflammatory response syndrome, sepsis, or organ failure are less clear. Recent meta-analyses on the use of immunonutrition with arginine in critically ill and surgical patients revealed methodological weaknesses in most published studies. Specifically, a meta-analysis indicated that critically ill patients with preexisting severe sepsis may have an increased mortality rate when fed an immunonutritional enteral formula that contains arginine. These findings brought about confusion and controversy over the use of immunonutritional formulas in subsets of critically ill patients. A review of the literature on the function of arginine, its effect on the immune system, its roles in immunonutrition and in the clinical outcomes of critically ill patients, and the implications for nursing practice indicated that the benefits of immunonutrition with arginine in critically ill patients are unproven and warrant further study. Until more information is available, nutritional support should focus primarily on preventing nutritional deficiencies rather than on immunomodulation.

Induction of LOX-1 and iNOS expressions by ischemia-reperfusion of rat kidney and the opposing effect of L-arginine

Lectin-like oxidized low-density lipoprotein receptor (LOX-1) is a newly identified endothelial cell surface major receptor for oxidatively modified low-density lipoprotein. Progression of arthrosclerosis in the donor organ after organ transplantation is a major problem. We hypothesized that ischemia-reperfusion induces LOX-1. After 1 h ischemia of bilateral kidneys plus 3, 6, or 12 h reperfusion, we first revealed that LOX-1 mRNA expression was increased in renal cortex and medulla at 6 h after reperfusion, which was decreased by L-arginine supplement. Plasma nitric oxide (NO) end-product nitrite plus nitrate and inducible nitric oxide synthase (NOS) expression were increased after reperfusion of 6 h. However, NOS substrate L-arginine did not augment but markedly decreased plasma NO end product, because L-arginine supplement suppressed inducible NOS expression in kidney. We hypothesized that available L-arginine is depleted by ischemia-reperfusion, leading to inducible NOS induction. Ischemia decreased L-arginine levels in kidney and L-arginine supplement increased NO end products in renal cortex in the earliest phase of reperfusion. These results disclosed for the first time that a deficiency in L-arginine by ischemia reperfusion causes uncoupling of constitutive NOS, which induces inducible NOS and LOX-1, implying why L-arginine is effective for stroke or transplantation in preventing atherosclerotic progress.

Interaction among nitric oxide, reactive oxygen species, and antioxidants during endotoxemia-related acute renal failure

Acute renal failure (ARF) during sepsis is associated with increased nitric oxide (NO) and oxygen radicals, including superoxide (O(2)(-)). Because O(2)(-) reacts with NO in a rapid manner, it plays an important role in modulating NO levels. Therefore, scavenging of O(2)(-) by superoxide dismutase (SOD) may be critical for preserving NO bioavailability. In mice, substantial renal extracellular SOD (EC-SOD) expression implies its important role in scavenging O(2)(-) in the kidney. We hypothesized that during endotoxemic ARF, EC-SOD is decreased in the kidney, resulting in increased O(2)(-) and thus decreased vascular NO bioavailability with resultant renal vasoconstriction and ARF. In the present study, normotensive endotoxemic ARF was induced in mice using lipopolysaccharide (LPS; 5 mg/kg ip). Sixteen hours after LPS, glomerular filtration rate (GFR; 50 +/- 16 vs. 229 +/- 21 microl/min, n = 8, P < 0.01) and renal blood flow (RBF; 0.61 +/- 0.10 vs. 0.86 +/- 0.05 ml/min, n = 8, P < 0.05) were subsequently decreased. EC-SOD mRNA and protein expression in endotoxemic kidneys were decreased at 16 h compared with controls. A catalytic antioxidant, metalloporphyrin, reversed the deleterious effects of endotoxemia on renal function as GFR (182 +/- 40 vs. 50 +/- 16 microl/min, n = 6, P < 0.01) and RBF (1.08 +/- 0.10 vs. 0.61 +/- 0.10 ml/min, n = 6, P < 0.05) were preserved. Similar results were obtained with tempol, a chemically dissimilar antioxidant. Specific inhibition of inducible nitric oxide synthase (iNOS), l-N(6)-(1-iminoethyl)-lysine, reversed the renal protective effect on GFR and RBF observed with antioxidant treatment during endotoxemia. In summary, renal EC-SOD expression is decreased during endotoxemia. Antioxidant therapy preserved GFR and RBF during endotoxemia. The reversal of this protective effect by inhibition of iNOS suggests the importance of the bioavailability of NO for preservation of renal function during early endotoxemia.

Role of endogenous nitric oxide in unilateral ureteropelvic junction obstruction in children

BACKGROUND

Obstructive nephropathy leads to tubulointerstitial fibrosis and loss of renal function. Nitric oxide has been shown to have antifibrotic properties. We examined nitric oxide synthase (NOS) activity and expression in kidneys from children who underwent surgery release of unilateral ureteropelvic junction (UPJ) obstruction in relation to clinical and histologic parameters.

METHODS

NOS activity and the expression of NOS isoforms measured at the mRNA level by reverse transcription-polymerase chain reaction (RT-PCR) assay were determined in tissue obtained by biopsy from obstructed kidneys of 18 children at the time of pyeloplasty. Tissue from kidneys removed because of various malignancies were issued as control.

RESULTS

A significant increase in calcium/calmodulin-independent NOS activity (iNOS) and iNOS mRNA expression was found in the medulla of obstructed kidneys. Calcium/calmodulin-dependent NOS activity (cNOS) and endothelial (eNOS) mRNA, by contrast, were increased in the cortex from obstructed kidneys. A role of tumor necrosis factor-alpha (TNF-alpha) on enhanced iNOS was suggested by the finding of increased urine levels in obstructed pelvis. Increased interstitium macrophage number, by immunolabeling of CD68, was related to the delay in obstruction release and to decreased glomerular filtration rate (GFR) at surgery. A positive linear relationship was found between cNOS activity in cortex and creatinine clearance. The degree of interstitial fibrosis correlated negatively with cNOS activity in cortex.

CONCLUSION

In kidneys from children with UPJ obstruction an increased activity and expression of iNOS in medulla and cNOS-dependent eNOS in cortex were demonstrated. A role of cNOS in modulating GFR and interstitial fibrosis can be suggested. Prolonged UPJ obstruction would lead to a worsened prognosis on renal injury.

The effects of the nitric oxide donor molsidomine prevent in warm ischemia-reperfusion injury of the rat renal--a functional and histophatological study

Aim of this experimental study is to verify the protective effect of molsidomine on the renal function and structural modifications in the ischemia-reperfusion rat kidney. Sixty-eight male Sprague-Dawley rats, which were right nephrectomized and occluded left renal artery for 60 minutes were used. Group I (n = 10) Sham-Operated animals, which only underwent right nephrectomy. Group II (n = 20) Untreated ischemic rats, which underwent left renal ischemia by occlusion of the renal artery for 60 minutes before blood flow was restored. Group III (n = 18) Molsidomine treated ischemic rats, Group IV (n = 20) L-NAME (N(G)-nitro-L-arginine methyl ester) treated ischemic rats. Serum creatinine and blood urea nitrogen (BUN) were measured daily and biopsies were obtained from the remaining left kidneys. At seventh day, 55% and 50% of the rats remained alive at the G-II and G-IV respectively. Molsidomine treated rats (G-III) were alive and healthy at day 7. The serum creatinine and BUN levels were significantly higher in G-II and G-IV when compared with the sham-operated group (G-I). G-III rats showed a rapid return to the normal serum creatinine and BUN values on postoperative days 1, 2, 3 and 4. The obtained values in G-II were significantly lower in comparison to the values of G-II and G-IV. The most severe damage (grade 3 to 4) was determined in the kidneys of rats from GII or GIV. The degree of renal tubular damage in GIII was evaluated as grade 1 or 2 tubular damage according to Jablonkski's scale. Our findings suggested that the administration of molsidomine may vanquish the pernicious effects of warm ischemia on kidney structure and function.

alpha-Melanocyte-simulating hormone and interleukin-10 do not protect the kidney against mercuric chloride-induced injury

The anti-inflammatory cytokines alpha-melanocyte-stimulating hormone (MSH) and interleukin (IL)-10 inhibit acute renal failure (ARF) after ischemia or cisplatin administration; however, these agents have not been tested in a pure nephrotoxic model of ARF. Therefore, we examined the effects of alpha-MSH and IL-10 in HgCl(2)-induced ARF. Mice were injected subcutaneously with HgCl(2) and then given vehicle, alpha-MSH, or IL-10 by intravenous injection. Animals were killed to study serum creatinine, histology, and myeloperoxidase activity. Treatment with either alpha-MSH or IL-10 did not alter the increase in serum creatinine, tubular damage, or leukocyte accumulation at 48 h after HgCl(2) injection. Because alpha-MSH and IL-10 are active in other injury models that involve leukocytes, we studied the time course of tubular damage and leukocyte accumulation to investigate whether leukocytes caused the tubular damage or accumulated in response to the tubular damage. Tubular damage was present in the outer stripe 12 h after HgCl(2) injection. In contrast, the number of leukocytes and renal myleoperoxidase activity were normal at 12 h but were significantly increased at 24 and 48 h after injection. We conclude that neither alpha-MSH nor IL-10 altered the course of HgCl(2)-induced renal injury. Because the tubular damage preceded leukocyte infiltration, the delayed leukocyte accumulation may play a role in the removal of necrotic tissue and/or tissue repair in HgCl(2)-induced ARF.

Injury in renal ischemia-reperfusion is independent from immunoglobulins and T lymphocytes

Ischemia-reperfusion injury (IRI) is a complex and incompletely understood process involving a cascade of events that culminates in apoptotic and/or necrotic cell death. Natural IgM antibodies and complement have been implicated in the pathogenesis of IRI in a variety of organ systems as have T lymphocytes in renal IRI. To investigate the role of Ig and T lymphocytes in renal IRI, recombination-activating gene (RAG)-1-deficient mice were studied. RAG-1(-/-) mice were not protected from acute renal failure induced by 27.5 min of bilateral renal ischemia and subsequent reperfusion [serum urea nitrogen levels 30 h after reperfusion, 155.2 +/- 5.6 and 152.8 +/- 11.4 mg/dl in RAG-1(-/-) and wild-type mice, respectively; n = 13 each]. Histological examination showed acute tubular necrosis and neutrophilic infiltration with no significant differences between groups. In contrast with other organ systems, Igs were not found in kidneys at time points ranging from 1 min to 30 h after ischemia. Thus Igs and mature T lymphocytes do not appear to play a significant role in the pathogenesis of IRI in the kidney.

Interleukin-10 inhibits ischemic and cisplatin-induced acute renal injury

BACKGROUND

Acute renal failure (ARF) is caused by ischemic and nephrotoxic insults acting alone or in combination. Anti-inflammatory agents have been shown to decrease renal ischemia-reperfusion and cisplatin-induced injury and leukocyte infiltration. Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine that inhibits inflammatory and cytotoxic pathways implicated in acute renal injury. Therefore, we sought to determine if IL-10 inhibits acute renal injury.

METHODS

The effects of IL-10 were studied in mice following cisplatin administration and bilateral renal ischemia-reperfusion, in a rat model of renal transplantation, and in cultured mouse cortical tubule cells.

RESULTS

IL-10 significantly decreased renal injury following cisplatin administration and following renal ischemia/reperfusion. Delay of IL-10 treatment for one hour after cisplatin also significantly inhibited renal damage. IL-10 and alpha-melanocyte stimulating hormone (alpha-MSH) increased recovery following transplantation of a kidney subjected to warm ischemia. To explore the mechanism of action of IL-10, its effects were measured on mediators of leukocyte trafficking and inducible nitric oxide synthase (NOS-II). IL-10 inhibited cisplatin and ischemia-induced increases in mRNA for tumor necrosis factor-alpha (TNF-alpha), intercellular adhesion molecule-1 (ICAM-1), and NOS-II. IL-10 also inhibited staining for markers of apoptosis and cell cycle activity following cisplatin administration, and nitric oxide production in cultured mouse cortical tubules.

CONCLUSIONS

IL-10 protects against renal ischemic and cisplatin-induced injury. IL-10 may act, in part, by inhibiting the maladaptive activation of genes that cause leukocyte activation and adhesion, and induction of iNOS.

Oxidative and nitrosative stress in acute renal ischemia

Generation of reactive oxygen species and nitric oxide in hypoxia-reperfusion injury may form a cytotoxic metabolite, peroxynitrite, which is capable of causing lipid peroxidation and DNA damage. This study was designed to examine the contribution of oxidative and nitrosative stress to the renal damage in ischemic acute renal failure (iARF). iARF was initiated in rats by 45-min renal artery clamping. This resulted in lipid peroxidation, DNA damage, and nitrotyrosine modification confirmed both by Western and immunohistochemical analyses. Three groups of animals were randomly treated with an inhibitor of inducible nitric oxide synthase (NOS), L-N(6)-(1-iminoethyl)lysine (L-Nil), cell-permeable lecithinized superoxide dismutase (SOD), or both. Each treatment resulted in amelioration of renal dysfunction, as well as reduced nitrotyrosine formation, lipid peroxidation, and DNA damage, thus suggesting that peroxynitrite rather than superoxide anion is responsible for lipid peroxidation and DNA damage. Therefore, in a separate series of experiments, a scavenger of peroxynitrite, ebselen, was administered before the reperfusion period. This treatment resulted in a comparable degree of amelioration of iARF. In conclusion, the present study provides the first attempt to elucidate the role of peroxynitrite in initiation of the cascade of lipid peroxidation and DNA damage to ischemic kidneys. The results demonstrate that L-Nil, lecithinized SOD, and ebselen treatments improve renal function due to their suppression of peroxynitrite production or its scavenging, consequently preventing lipid peroxidation and oxidative DNA damage.

Oxidative and nitrosative stress in acute renal ischemia

First Published July 12, 2001; 10.1152/ajprenal.0071.2001.—Generation of reactive oxygen species and nitric oxide in hypoxia-reperfusion injury may form a cytotoxic metabolite, peroxynitrite, which is capable of causing lipid peroxidation and DNA damage. This study was designed to examine the contribution of oxidative and nitrosative stress to the renal damage in ischemic acute renal failure (iARF). iARF was initiated in rats by 45-min renal artery clamping. This resulted in lipid peroxidation, DNA damage, and nitrotyrosine modification confirmed both by Western and immunohistochemical analyses. Three groups of animals were randomly treated with an inhibitor of inducible nitric oxide synthase (NOS),l- N 6-(1-iminoethyl)lysine (l-Nil), cell-permeable lecithinized superoxide dismutase (SOD), or both. Each treatment resulted in amelioration of renal dysfunction, as well as reduced nitrotyrosine formation, lipid peroxidation, and DNA damage, thus suggesting that peroxynitrite rather than superoxide anion is responsible for lipid peroxidation and DNA damage. Therefore, in a separate series of experiments, a scavenger of peroxynitrite, ebselen, was administered before the reperfusion period. This treatment resulted in a comparable degree of amelioration of iARF. In conclusion, the present study provides the first attempt to elucidate the role of peroxynitrite in initiation of the cascade of lipid peroxidation and DNA damage to ischemic kidneys. The results demonstrate that l-Nil , lecithinized SOD, and ebselen treatments improve renal function due to their suppression of peroxynitrite production or its scavenging, consequently preventing lipid peroxidation and oxidative DNA damage.

TGF-beta(1) modulates NOS expression and phosphorylation of Akt/PKB in rat myocytes exposed to hypoxia-reoxygenation

Myocardial hypoxia-reoxygenation (H-R) is associated with upregulation of inducible nitric oxide synthase (iNOS), decrease in endothelial NOS (eNOS), and increase in protein kinase B (PKB). Previous work also shows that transforming growth factor-beta(1) (TGF-beta(1)) can attenuate myocardial injury induced by H-R. We examined the modulation of NOS and PKB expression in response to H-R by TGF- beta(1). Myocytes from Sprague-Dawley rat hearts were cultured and exposed to hypoxia (95% N(2)-5% CO(2), PO(2) ~30 mmHg) for 24 h and reoxygenation (95% air-5% CO(2)) for 3 h. Myocytes were then examined for lactate dehydrogenase (LDH) release, iNOS activity (conversion of L-[(3)H]arginine to L-[(3)H]citrulline), iNOS and eNOS expression, and PKB phosphorylation. H-R alone resulted in myocyte injury, upregulation of iNOS activity and expression, decrease in eNOS expression, and increase in PKB phosphorylation (all P < 0.05 vs. cells cultured in normoxic conditions). Treatment of myocytes with TGF-beta(1) (1 ng/ml) resulted in a reduction in LDH release, attenuation of the alterations in NOS expression (both iNOS and eNOS), and PKB phosphorylation in response to H-R (all P < 0.05 vs. H-R alone). These observations suggest that TGF-beta(1) decreases H-R injury and attenuates alterations in NOS and PKB phosphorylation in myocytes exposed to H-R.

Effect of mycophenolate mofetil on nitric oxide production and inducible nitric oxide synthase gene expression during renal ischaemia-reperfusion injury

BACKGROUND

Recent animal data suggest that inducible nitric oxide synthase (iNOS) derived nitric oxide (NO) plays an important role in the pathogenesis of renal ischaemia-reperfusion injury (IRI) and that inhibition of iNOS ameliorates IRI. Mycophenolate mofetil (MMF), a lymphocyte selective anti-proliferative agent, has been shown to inhibit NO production in vitro. The aim of this study is to evaluate the effect of MMF on NO production and iNOS gene expression in vivo during renal IRI.

METHODS

Renal IRI was induced by clamping the left renal pedicle of male BALB/c mice for 30 min, followed by 15 min of reperfusion. The mice received placebo or MMF at 40, 80 or 120 mg/kg/day by oral gavage for 5 days before the operation. Sham-operated mice served as the operation control. The amount of NO produced and the level of iNOS gene expression in the kidney tissue during IRI was assessed by spin trapping electron paramagnetic resonance (EPR) spectroscopy and semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) respectively.

RESULTS

In the sham-operated kidneys, only low levels of NO and iNOS mRNA were detected. In mice with renal IRI, the amount of NO detected was significantly increased, which was reduced in a dose dependent fashion by pre-treatment with MMF. Pre-treatment with MMF also substantially reduced iNOS gene expression in the kidney tissue.

CONCLUSIONS

We conclude that pre-treatment with MMF inhibits the production of NO and the induction of iNOS gene expression in the kidney during IRI. These results suggest that MMF might have the potential to ameliorate renal IRI.

Cardioprotective actions of endogenous IL-10 are independent of iNOS

Myocardial ischemia-reperfusion (I/R) is a well-known stimulus for acute inflammatory responses that promote cell death and impair pump function. Interleukin-10 (IL-10) is an endogenous, potent anti-inflammatory cytokine. Recently, it has been proposed that IL-10 inhibits inducible nitric oxide synthase (iNOS) activity after myocardial I/R and consequently exerts cardioprotective effects. However, whether this actually occurs remains unclear. To test this hypothesis, we utilized iNOS-deficient (-/-), IL-10 -/-, and IL-10/iNOS -/- mice to examine the potential mechanism of IL-10-mediated cardioprotection after myocardial I/R. Wild-type, iNOS -/-, IL-10 -/-, and IL-10/iNOS -/- mice were subjected to in vivo myocardial ischemia (30 min) and reperfusion (24 h). Deficiency of iNOS alone did not significantly alter the extent of myocardial necrosis compared with wild-type mice. We found that deficiency of IL-10 resulted in a significantly (P < 0.05) larger infarct size than that in wild-type hearts. Interestingly, deficiency of both IL-10 and iNOS yielded significantly (P < 0.01) larger myocardial infarct sizes compared with wild-type animals. Histological examination of myocardial tissue samples revealed augmented neutrophil infiltration into the I/R myocardium of IL-10 -/- and IL-10/iNOS -/- mice compared with hearts of wild-type mice. These results demonstrate that 1) deficiency of endogenous IL-10 exacerbates myocardial injury after I/R; 2) the cardioprotective effects of IL-10 are not dependent on the presence or absence of iNOS; and 3) deficiency of IL-10 enhances the infiltration of neutrophils into the myocardium after I/R.

Mechanisms underlying induction of heme oxygenase-1 by nitric oxide in renal tubular epithelial cells

We examined whether nitric oxide-generating agents influence expression of heme oxygenase-1 (HO-1) in renal proximal tubular epithelial cells, LLC-PK(1) cells, and the mechanisms underlying any such effects. In sublytic amounts, the nitric oxide donor sodium nitroprusside induced HO-1 mRNA and protein and HO activity in a dose-dependent and time-dependent fashion; this induction was specific for nitric oxide since the nitric oxide scavenger carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide significantly reduced such induction. The induction of HO activity by sodium nitroprusside, or by another nitric oxide donor, spermine NONOate, was markedly reduced by the iron chelator deferoxamine. Two different thiol-containing agents, N-acetylcysteine and dithiothreitol, blunted such induction of HO by nitric oxide. Downstream products of nitric oxide, such as peroxynitrite or cGMP, were not involved in inducing HO. In higher concentrations (millimolar amounts), sodium nitroprusside induced appreciable cytotoxicity as assessed by lactate dehydrogenase (LDH) release and lipid peroxidation, and both of these effects were markedly reduced by deferoxamine. Inhibition of HO did not affect the cytotoxic effects (measured by LDH release) of sodium nitroprusside. We thus provide the novel description of the induction of HO-1 in renal proximal tubular epithelial cells exposed to nitric oxide donors and provide the first demonstration in kidney-derived cells for the involvement of a redox-based mechanism in such expression. We also demonstrate that, in LLC-PK(1) cells exposed to nitric oxide donors, chelatable iron is involved in eliciting the HO-1 response observed at lower concentrations of these donors, and in mediating the cytotoxic effects of these donors when present in higher concentrations.