An evaluation of antioxidant effects on recovery from postischemic acute renal failure

Neutrophils and NADPH Oxidases Are Major Contributors to Mild but Not Severe Ischemic Acute Kidney Injury in Mice

Upregulation of free radical-generating NADPH oxidases (NOX), xanthine oxidoreductase (XOR), and neutrophil infiltration-induced, NOX2-mediated respiratory burst contribute to renal ischemia-reperfusion injury (IRI), but their roles may depend on the severity of IRI. We investigated the role of NOX, XOR, and neutrophils in developing IRI of various severities. C57BL/6 and Mcl-1ΔMyelo neutrophil-deficient mice were used. Oxidases were silenced by RNA interference (RNAi) or pharmacologically inhibited. Kidney function, morphology, immunohistochemistry and mRNA expression were assessed. After reperfusion, the expression of NOX enzymes and XOR increased until 6 h and from 15 h, respectively, while neutrophil infiltration was prominent from 3 h. NOX4 and XOR silencing or pharmacological XOR inhibition did not protect the kidney from IRI. Attenuation of NOX enzyme-induced oxidative stress by apocynin and neutrophil deficiency improved kidney function and ameliorated morphological damage after mild but not moderate/severe IRI. The IR-induced postischemic renal functional impairment (BUN, Lcn-2), tubular necrosis score, inflammation (TNF-α, F4/80), and decreases in the antioxidant enzyme (GPx3) mRNA expression were attenuated by both apocynin and neutrophil deficiency. Inhibition of NOX enzyme-induced oxidative stress or the lack of infiltration by NOX2-expressing neutrophils can attenuate reperfusion injury after mild but not moderate/severe renal IR.

Augmented renal prostacyclin by intrarenal bicistronic cyclo-oxygenase-1/prostacyclin synthase gene transfer attenuates renal ischemia-reperfusion injury

BACKGROUND

We elucidated the protective mechanism of increased prostacyclin (PGI2) derived from adenoviral cyclo-oxygenase (COX)-1/prostacyclin synthase (PGIS) (Adv-COPI) gene transfer in rat kidneys with ischemia-reperfusion (I/R) injury.

METHODS

We tended to augment PGI2 production by intrarenal arterial Adv-COPI administration with renal venous clamping in female Wistar rats. After Adv-COPI transfection, we evaluated the renal COX-1 and PGIS protein expression and PGI2 and prostaglandin E2 (PGE2) levels in the kidney and renal venous plasma. We evaluated the protective effect of PGI2 on hypoxia/reoxygenation-induced tubular cells injury or I/R kidneys by measuring oxidative stress, necrosis, apoptosis, and autophagy in tubules and kidneys and determining renal function, microcirculation, and accumulation of tubular 4-hydroxynonenal in the kidney in vivo.

RESULTS

Adv-COPI treatment selectively augmented COX-1 and PGIS protein expression in the renal proximal and distal tubules and significantly increased PGI2, not PGE2, production in the renal venous plasma and kidney at the baseline level. I/R markedly depressed renal blood flow and increased the production in O2, PGE2, the expression in P47 and Rac-1 expression of two nicotinamide adenine dinucleotide phosphate oxidase subunits, cytosolic cytochrome C release, proapoptotic marker lamin expression, the pathologic appearance of necrosis, apoptosis, and autophagy, and blood urea nitrogen and creatinine levels in the damaged kidneys. Adv-COPI protected distal and proximal tubules against hypoxia/reoxygenation-enhanced oxidative stress and autophagic, apoptotic, and necrotic cell death. Adv-COPI significantly improved renal function by restoring renal blood flow, reducing nicotinamide adenine dinucleotide phosphate oxidase-derived and mitochondria-derived oxidative stress, and necrosis, apoptosis, and autophagy.

CONCLUSIONS

Increased PGI2 by Adv-COPI protects the kidney against I/R-induced oxidative stress, necrosis, apoptosis and autophagy.

Reactive oxygen species and IRF1 stimulate IFNα production by proximal tubules during ischemic AKI

We previously reported that expression of the transcription factor interferon regulatory factor 1 (IRF1) is an early, critical maladaptive signal expressed by renal tubules during murine ischemic acute kidney injury (AKI). We now show that IRF1 mediates signals from reactive oxygen species (ROS) generated during ischemic AKI and that these signals ultimately result in production of α-subtypes of type I interferons (IFNαs). We found that genetic knockout of the common type I IFN receptor (IFNARI-/-) improved kidney function and histology during AKI. There are major differences in the spatial-temporal production of the two major IFN subtypes, IFNβ and IFNαs: IFNβ expression peaks at 4 h, earlier than IFNαs, and continues at the same level at 24 h; expression of IFNαs also increases at 4 h but continues to increase through 24 h. The magnitude of the increase in IFNαs relative to baseline is much greater than that of IFNβ. We show by immunohistology and study of isolated cells that IFNβ is produced by renal leukocytes and IFNαs are produced by renal tubules. IRF1, IFNαs, and IFNARI were found on the same renal tubules during ischemic AKI. Furthermore, we found that ROS induced IFNα expression by renal tubules in vitro. This expression was inhibited by small interfering RNA knockdown of IRF1. Overexpression of IRF1 resulted in the production of IFNαs. Furthermore, we found that IFNα stimulated production of maladaptive proinflammatory CXCL2 by renal tubular cells. Altogether our data support the following autocrine pathway in renal tubular cells: ROS > IRF1 > IFNα > IFNARI > CXCL2.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Pargyline reduces renal damage associated with ischaemia-reperfusion and cyclosporin

BACKGROUND

The slow deterioration of the kidney graft is characterized histologically by interstitial fibrosis and tubular atrophy (IFTA). Immunological and non-immunological stress is the main cause of progression towards IFTA. Our study focused on the non-immunological injuries induced by ischaemia-reperfusion (IR) and cyclosporin (CsA) toxicity, which remain the two stress factors putting a damper on the outcome of the renal graft. Endogenous reactive oxygen species (ROS) are essentially produced by mitochondria, and we have previously shown that the blockage of the mitochondrial enzymes monoamine oxidases (MAOs) prevents H2O2 production in the early reperfusion stage following IR.

METHODS

We used a rat model of IFTA consisting in unilateral nephrectomy followed by IR and daily CsA administration. Four weeks after IR, we analysed renal function, histological alterations and a number of inflammatory and fibrotic genes.

RESULTS

We observed, 28 days after pargyline-mediated blockade of MAO (before or after IR), improved renal function as well as a net decrease in renal inflammation associated to lower IL-1β and TNF-α gene expression. However, significant reduction in apoptosis, necrosis and fibrosis was only observed when pargyline was administrated before IR. This protective effect was associated to decreased expression of TGF-β1, collagen types I, III and IV and also to the normalization of antioxidant (SOD1, catalase) and inflammatory (COX2, LOX5) gene expression.

CONCLUSION

It appears that the blockage of ROS produced by MAO and subsequent cell death might be an effective protective strategy against IFTA progression.

Reactive oxygen species generated by renal ischemia and reperfusion trigger protection against subsequent renal ischemia and reperfusion injury in mice

Ischemic preconditioning by a single event of ischemia and reperfusion (SIRPC) dramatically protects renal function against ischemia and reperfusion (I/R) induced several weeks later. We recently reported that reactive oxygen species (ROS) and oxidative stress were sustained in a kidney that had functionally recovered from I/R injury, thus suggesting an association between SIRPC and ROS and oxidative stress. However, the role of ROS in SIRPC remains to be clearly elucidated. To assess the involvement of ROS in SIRPC, mice were subjected to SIRPC (30 min of bilateral renal ischemia and 8 days of reperfusion) and then exposed to I/R injury. Thirty minutes of bilateral renal ischemia in the non-SIRPC mice resulted in a marked increase in plasma creatinine levels 4 and 24 h after reperfusion, which was not observed in the I/R in the SIRPC mice. SIRPC resulted in increases in the levels of kidney superoxide. Administrations of manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin [MnTMPyP; a cell-permeable superoxide dismutase (SOD) mimetic] and N-acetylcysteine (NAc; a ROS scavenger) to SIRPC mice blocked the SIRPC-induced increase in superoxide levels and removed approximately 48-64% of the functional protection of the SIRPC kidney. Additionally, these administrations significantly inhibited I/R-induced increases in superoxide formation, hydrogen peroxide production, and lipid peroxidation, along with the inhibition of I/R-induced reductions in the expression and activity of manganese SOD, copper-zinc SOD, and catalase. Furthermore, administrations of MnTMPyP or NAc inhibited the SIRPC-induced increase in inducible nitric oxide synthase expression but did not inhibit the SIRPC-induced increases in heat shock protein-25 expression. In conclusion, the renoprotection afforded by SIRPC was triggered by ROS generated by SIRPC.

Effects of allopurinol and vitamin E on renal function in patients with cardiac coronary artery bypass grafts

Background:

Acute renal failure is a common complication of cardiac surgery, with oxidants found to play an important role in renal injury. We therefore assessed whether the supplemental antioxidant vitamin E and the inhibitor of xanthine oxidase allopurinol could prevent renal dysfunction after coronary artery bypass graft (CABG) surgery.

Methods:

Of 60 patients with glomerular filtration rate (GFR) < 60 mL/min scheduled to undergo CABG surgery, 30 were randomized to treatment with vitamin E and allopurinol for 3–5 days before surgery and 30 to no treatment. Serum creatinine levels and potassium and creatinine clearances were measured preoperatively and daily until day 5 after surgery.

Results:

The patients consisted of 31 males and 29 females, with a mean age of 63 ± 9 years. After surgery, there were no significant differences in mean serum creatinine (1.2 ± 0.33 vs 1.2 ± 0.4 mg/dL; p = 0.43) concentrations, or creatinine clearance (52 ± 12.8 vs 52 ± 12.8 mL/min; p = 0.9). The frequency of acute renal failure did not differ in treatment group compared with control (16% vs 13%; p = 0.5). Length of stay in the intensive care unit (ICU) was significantly longer in the control than in the treated group (3.9 ± 1.5 vs 2.6 ± 0.7 days; p < 0.001).

Conclusion:

Prophylactic treatment with vitamin E and allopurinol had no renoprotective effects in patients with pre-existing renal failure undergoing CABG surgery. Treatment with these agents, however, reduces the duration of ICU stay.

IRF-1 promotes inflammation early after ischemic acute kidney injury

Acute renal ischemia elicits an inflammatory response that may exacerbate acute kidney injury, but the regulation of the initial signals that recruit leukocytes is not well understood. Here, we found that IFN regulatory factor 1 (IRF-1) was a critical, early proinflammatory signal released during ischemic injury in vitro and in vivo. Within 15 min of reperfusion, proximal tubular cells of the S3 segment produced IRF-1, which is a transcription factor that activates proinflammatory genes. Transgenic knockout of IRF-1 ameliorated the impairment of renal function, morphologic injury, and inflammation after acute ischemia. Bone marrow chimera experiments determined that maximal ischemic injury required IRF-1 expression by both leukocytes and radioresistant renal cells, the latter identified as S3 proximal tubule cells in the outer medulla by in situ hybridization and immunohistochemistry. In vitro, reactive oxygen species, generated during ischemia/reperfusion injury, stimulated expression of IRF-1 in an S3 proximal tubular cell line. Taken together, these data suggest that IRF-1 gene activation by reactive oxygen species is an early signal that promotes inflammation after ischemic renal injury.

Efficacy of the combination of N-acetylcysteine and desferrioxamine in the prevention and treatment of gentamicin-induced acute renal failure in male Wistar rats

BACKGROUND

Oxidative stress and the formation of aminoglycoside-iron complexes through iron-dependent Fenton reaction have been proposed to be the major mechanisms in the development of GM-induced acute renal failure (ARF); however, the efficacy of the combination of N-acetylcysteine (NAC) and desferrioxamine (DFX) in the prevention and the treatment of GM-induced ARF has not previously been investigated.

METHODS

In the prevention protocol, adult male Wistar rats received gentamicin (GM) [70 mg/kg, intraperitoneally (i.p), each 12 h for 7 days], NAC (20 mg/kg, sc, each 8 h for 7 days) and/or DFX (20 mg/kg, sc, at first, fourth and seventh days). In the treatment protocol animals received GM for 7 days. Additionally, animals received NAC and or DFX starting in the fourth day after GM administration. Parameters of renal function had been evaluated 24 h, 4 and 8 days after the beginning of GM administration in the prevention protocol and in Days 5 and 8 in the treatment protocol. At the end of experiment, lipid peroxidation (TBARS assay) and protein oxidation (protein carbonyls levels) formation were evaluated in kidney tissue as oxidative damage parameters.

RESULTS

In the prevention protocol, GM-induced ARF was prevented by the NAC and DFX association. Lipid peroxidation was attenuated by both antioxidant treatments, but the effects of NAC plus DFX were of greater magnitude. In the treatment protocol, plasma markers of renal injury were improved only in the NAC group, despite the similar antioxidant effect of both NAC, DFX and NAC plus DFX.

CONCLUSION

Although the combination of NAC and DFX was more effective in the prevention protocol, the use of NAC alone seemed to be superior to NAC-DFX combination, in the treatment of GM-induced ARF in adult male Wistar rats.

NMDA receptor blocker ameliorates ischemia-reperfusion-induced renal dysfunction in rat kidneys

N-methyl-d-aspartate (NMDA) receptor activated by glutamate/glycine is located in the kidneys. The NMDA receptor subunit NR1 is increased in damaged renal tissue. This study explored the role of NMDA receptors in ischemia-reperfusion-induced renal dysfunction in rats. With Western blot analysis and renal functional assay, NMDA receptor expression was evaluated, as well as its functional role in female Wistar rat kidneys after 45 min of unilateral ischemia followed by 24 h of reperfusion. The effects of intrarenal NMDA receptor agonist and antagonist on renal blood flow (RBF), glomerular filtration rate (GFR), urine volume (UV), sodium (UNaV), and potassium (UKV) excretion were determined. NMDA NR1 was present in the glomeruli, brush-border membrane, and outer medulla but not in the cortex and inner medulla. Homogenous distribution of non-NMDA GluR2/3, sparse kainate KA1, and undetectable group I of metabotropic glutamate receptor were noted in the control kidneys. Ischemia-reperfusion kidneys showed enhanced renal NR1, but not NR2C and GluR2/3 expression, and were associated with decreased GFR/RBF and natriuretic/diuretic responses. Intrarenal NMDA agonists significantly reduced GFR, UV, UNaV, and UKV but had no effect on blood pressure and RBF in sham control and ischemia-reperfusion kidneys. NMDA antagonist d-2-amino-5-phosphonopentanoic acid (D-AP-5) treatment completely abolished NMDA-induced renal dysfunction. D-AP-5 treatment significantly ameliorated ischemia-reperfusion-induced glomerular and tubular dysfunction by restoring decreased GFR, UV, and UNaV levels. Ischemia-reperfusion upregulates renal NMDA NR1 receptor expression, leading to reduced glomerular and tubular function in the kidneys. The NMDA antagonist can ameliorate ischemia-reperfusion-induced renal dysfunction.

Early activation of bradykinin B2 receptor aggravates reactive oxygen species generation and renal damage in ischemia/reperfusion injury

The kallikrein/kinin system is beneficial in ischemia/reperfusion injury in heart, controversial in brain, but detrimental in lung, liver, and intestine. We examined the role of the kallikrein/kinin system in acute ischemia/reperfusion renal injury induced by 40 min occlusion of the renal artery followed by reperfusion. Rats were infused with tissue kallikrein protein 5 days before (pretreated group) or after (treated group) ischemia. Two days later, the pretreated group exhibited the worst renal dysfunction, followed by the treated group, then the control group. Kallikrein increased tubular necrosis and inflammatory cell infiltration with generation of more tumor necrosis factor-alpha and monocyte chemoattractant protein-1. Reactive oxygen species (ROS), malondialdehyde, and reduced/oxidized glutathione measurement revealed that the oxidative stress was augmented by kallikrein administration in both ischemic and reperfusion phases. The groups with more ROS generation also had more apoptotic renal cells. The deleterious effects of kallikrein on ischemia/reperfusion injury were reversed by cotreatment with bradykinin B2 receptor (B2R) antagonist, but not B1 receptor antagonist, and were not associated with hemodynamic changes. We conclude that early activation of B2R augmented ROS generation in ischemia/reperfusion renal injury, resulting in subsequent apoptosis, inflammation, and tissue damage. This finding suggests the potential application of B2R antagonists in acute ischemic renal disease associated with bradykinin activation.

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 failure secondary to acute tubular necrosis: epidemiology, diagnosis, and management

Acute tubular necrosis (ATN) is a form of acute renal failure (ARF) that is common in hospitalized patients. In critical care units, it accounts for about 76% of cases of ARF. Despite the introduction of hemodialysis > 30 years ago, the mortality rates from ATN in hospitalized and ICU patients are about 37.1% and 78.6%, respectively. The purpose of this review is to discuss briefly the cause, diagnosis, and epidemiology of ARF, and to review in depth the clinical trials performed to date that have examined the influence of growth factors, hormones, antioxidants, diuretics, and dialysis. In particular, the role of the dialysis modality, dialyzer characteristics, and dosing strategies are discussed.

Adenovirus-mediated bcl-2 gene transfer inhibits renal ischemia/reperfusion induced tubular oxidative stress and apoptosis

Ischemia/reperfusion induces oxidative injury to proximal and distal renal tubular cells. We hypothesize that Bcl-2 protein augmentation with adenovirus vector mediated bcl-2 (Adv-bcl-2) gene transfer may improve ischemia/reperfusion induced renal proximal and distal tubular apoptosis through the mitochondrial control of Bax and cytochrome C translocation. Twenty-four hours of Adv-bcl-2 transfection to proximal and distal tubular cells in vitro upregulated Bcl-2/Bax ratio and inhibited hypoxia/reoxygenation induced cytochrome C translocation, O(2) (-) production and tubular apoptosis. Intra-renal arterial Adv-bcl-2 administration with renal venous clamping augmented Bcl-2 protein of rat kidney in vivo in a time-dependent manner. The maximal Bcl-2 protein expression appeared at 7 days after Adv-bcl-2 administration and the primary location of Bcl-2 augmentation was in proximal and distal tubules, but not in glomeruli. With a real-time monitoring O(2) (-) production and apoptosis analysis of rat kidneys, ischemia/reperfusion increased renal O(2) (-) level, potentiated proapoptotic mechanisms, including decrease in Bcl-2/Bax ratio, increases in caspase 3 expression and poly-(ADP-ribose)-polymerase fragments and subsequent proximal and distal tubular apoptosis. However, Adv-bcl-2 administration significantly enhanced Bcl-2/Bax ratio, decreased ischemia/reperfusion induced O(2) (-) amount, inhibited proximal and distal tubular apoptosis and improved renal function. Our results suggest that Adv-bcl-2 gene transfer significantly reduces ischemia/reperfusion induced oxidative injury in the kidney.

The absence of delayed graft function is predicted by the presence of manganese-superoxide dismutase in distal tubules of renal allografts

BACKGROUND

Acute tubular necrosis (ATN) in renal allograft biopsies correlates poorly with delayed graft function (DGF). Factors involved in the pathogenesis of DGF were evaluated in biopsies in an attempt to refine the recognition of DGF.

METHODS

Anti-cubulin and anti-AE-1/AE-3 antibodies identified proximal and distal tubules, respectively. The terminal deoxynucleotide transferase-mediated dUTP nick-end labeling technique and active caspase-3 staining were used to demonstrate apoptosis. Antibodies against superoxide dismutase (SOD) were used as markers of the protective tubular response. Tubular regeneration was evaluated using anti-ki 67 and antivimentin antibodies.

RESULTS

Of a total of 40 biopsies, 9 were associated with DGF. ATN was seen in 16 biopsies; 5 were associated with DGF. The finding of ATN in the biopsy of a graft predicted DGF in only 56% of cases. Absence of distal caspase-3 staining predicted the absence of ATN in 87% of cases. The presence of caspase-3 predicted ATN in 54% of cases. The detection of manganese-SOD in distal tubules predicts the absence of DGF in 76% of the cases.

CONCLUSIONS

The use of immunohistochemical staining on posttransplant renal biopsies improved its predictive value with respect to ATN and DGF: The absence of active caspase-3 in distal tubular epithelium predicts the absence of ATN in 87% of cases, whereas its presence predicts ATN in 54% of cases. The presence of manganese-SOD in distal tubules predicts the absence of DGF in 76% of cases.

Protection of transplant-induced renal ischemia-reperfusion injury with carbon monoxide

Carbon monoxide (CO), a product of heme metabolism by heme oxygenases, is known to impart protection against oxidative stress. We hypothesized that CO would protect ischemia-reperfusion (I/R) injury of transplanted organs, and the efficacy of CO was studied in the rat kidney transplantation model. A Lewis rat kidney graft, preserved in University of Wisconsin solution at 4 degrees C for 24 h, was orthotopically transplanted into syngeneic rats. Recipients were maintained in room air or exposed to CO (250 ppm) in air for 1 h before and 24 h after transplantation. Animals were killed 1, 3, 6, and 24 h after transplantation to assess efficacy of inhaled CO. Rapid upregulation of mRNA for IL-6, IL-1beta, TNF-alpha, ICAM-1, heme oxygenase-1, and inducible nitric oxide synthase was observed within 3 h after transplantation in the control grafts of air-exposed recipients, associating with histopathological evidences of acute tubular necrosis, interstitial hemorrhage, and edema. In contrast, the increase of inflammatory mediators was markedly inhibited in kidney grafts of CO-treated recipients, which correlated with improved renal cortical blood flow. Further detailed morphological analyses revealed that CO preserved the glomerular vascular architecture and podocyte viability with less apoptosis of tubular epithelial cells and less ED1(+) macrophage infiltration. CO inhalation resulted in improved serum creatinine levels and clearance, and animal survival was significantly improved with CO to 60.5 from 25 days in untreated controls. The study demonstrates that exposure of kidney graft recipients to CO at a low concentration can impart significant protective effects against renal I/R injury and improve function of renal grafts.

Gene expression in early ischemic renal injury: clues towards pathogenesis, biomarker discovery, and novel therapeutics

Acute renal failure (ARF) represents a common and serious problem in clinical medicine. Renal ischemia-reperfusion injury (IRI) is the major cause of ARF in the native and transplanted kidney. Several decades of research have provided successful therapeutic approaches in animal models, but translational efforts in humans have yielded disappointing results. The major reasons for this include a lack of early markers for ARF (and hence a delay in initiating therapy), and the multi-factorial nature of the disease. This review focuses on the use of cDNA microarrays to elucidate the molecular genetic mechanisms underlying tubule cell apoptosis, and to identify novel biomarkers for early renal IRI. Also presented is a comparative temporal analysis of cDNA microarray results from mature kidneys following IRI and during normal nephrogenesis. Molecular genetic evidence for the notion that regeneration recapitulates development in the kidney, and that injured tubule cells possess the capacity to de-differentiate to the earliest stages of development, is presented. The implications of these findings to the ability of the kidney to repair itself and potential strategies for accelerating recovery are briefly discussed.

Accumulation of 8-oxoguanine in the cellular DNA and the alteration of the OGG1 expression during ischemia-reperfusion injury in the rat kidney

During ischemia-reperfusion (I/R) injury in the rat kidney, apoptosis was observed in the distal tubules of the cortico-medullary region and outer medulla (OM) while severe necrosis was seen in the proximal straight tubules of the OM. The majority of these changes disappeared within 2 weeks. We examined the contents of 8-oxo-2'-deoxyguanosine (8-oxo-dG), which is a major type of oxidative damage in DNA, in the rat kidney during I/R injury, and also investigated the expression level of the OGG1 gene encoding the 8-oxoguanine DNA glycosylase. High-performance liquid chromatography with an MS/MS analysis of the nuclear DNA revealed an immediate accumulation of 8-oxo-dG in the nuclear DNA prepared from the cortex and OM of the kidney 1h after I/R, and an immunohistochemical analysis demonstrated the immediate accumulation of 8-oxo-dG in the nuclei of renal tubular cells both in the cortex and OM. A delayed increase of cytoplasmic staining with anti-8-oxo-dG was observed only in the cortico-medulla and OM, where the cytoplasmic staining in the proximal tubular cells is higher than in the distal tubular cells. The level of cytoplasmic staining representing 8-oxo-dG in mitochondrial DNA, peaked at 6h after I/R and preceded the necrosis of proximal tubular cells in the OM. An RNase protection assay showed a high level of OGG1 mRNA in the normal kidney, and the level decreased within 3h only in the OM, and increased thereafter 1-7 days of I/R both in the cortex and OM. In situ hybridization showed higher levels of OGG1 mRNA expression in the renal tubules in the OM than in the cortex of the normal kidney, which decreased rapidly within 3h of I/R. Thus, the accumulation of 8-oxo-dG in the mitochondrial DNA rather than in nuclear DNA is likely to be involved in the pathogenic responses such as necrosis of renal tubular cells during I/R injury of the kidney, together with an altered level of OGG1 expression.

Attenuation of ischemia/reperfusion induced MAP kinases by N-acetyl cysteine, sodium nitroprusside and phosphoramidon

Ischemia followed by reperfusion has a number of clinically significant consequences. A number of pathophysiological processes appear to be involved in ischemia/reperfusion (I/R) injury. The mitogen activated protein kinases (MAPK) are integral components of the parallel MAP kinase cascades activated in response to a variety of cellular stress inducing ischemia/ATP depletion and inflammatory cytokines. Many studies suggest that members of the MAP kinase family in particular Jun N-terminal kinase (JNK) are activated in kidney following ischemia/reperfusion of this tissue. The present study underlines the therapeutic potential of the combination of N-acetyl cysteine (NAC), a potent antioxidant, sodium nitroprusside (SNP), a nitric oxide donor and phosphoramidon (P), an endothelin-1 converting enzyme inhibitor in ameliorating the MAPK induced damage during renal ischemia/reperfusion injury. Our previous results showed that 90 min of ischemia followed by reperfusion caused very severe injury and that the untreated animals had 100% mortality after the 3rd day whereas there was improved renal function and 100% survival of animals in the three drug combination treatment group. The present study, mainly on tissue sections, further supports the protection provided by the triple drug therapy. A higher degree of expression of all the three classes of MAPK, i.e. JNK, P38 MAP kinases and P-extracellular signal regulated kinases (ERKs) can be seen in kidneys subjected to ischemia/reperfusion insult. Pretreatment with a combination of N-acetyl cysteine, sodium nitroprusside, and phosphoramidon completely inhibits all three classes of MAPK and ameliorates AP-1 whereas individual or a combination of any two drugs is not as effective.

Regulation of JNK/ERK activation, cell apoptosis, and tissue regeneration by monoamine oxidases after renal ischemia-reperfusion

Reactive oxygen species (ROS) contribute to the ischemia-reperfusion injury. In kidney, the intracellular sources of ROS during ischemia-reperfusion are still unclear. In the present study, we investigated the role of the catecholamine-degrading enzyme monoamine oxidases (MAOs) in hydrogen peroxide (H2O2) generation after reperfusion and their involvement in cell events leading to tissue injury and recovery. In a rat model of renal ischemia-reperfusion, we show concomitant MAO-dependent H2O2 production and lipid peroxidation in the early reperfusion period. Rat pretreatment with the irreversible MAO inhibitor pargyline resulted in the following: i) prevented H2O2 production and lipid peroxidation; ii) decreased tubular cell apoptosis and necrosis, measured by TUNEL staining and histomorphological criteria; and iii) increased tubular cell proliferation as determined by proliferating cell nuclear antigen expression. MAO inhibition also prevented Jun N-terminal kinase phosphorylation and promoted extracellular signal-regulated kinase activation, two mitogen-activated protein kinases described as a part of a "death" and "survival" pathway after ischemia-reperfusion. This work demonstrates the crucial role of MAOs in mediating the production of injurious ROS, which contribute to acute apoptotic and necrotic cell death induced by renal ischemia-reperfusion in vivo. Targeted inhibition of these oxidases could provide a new avenue for therapy to prevent renal damage and promote renal recovery after ischemia-reperfusion.

Utility and limitations of serum creatinine as a measure of renal function in experimental renal ischemia-reperfusion injury

BACKGROUND

Ischemia-reperfusion injury (IRI) is the major cause of delayed graft function in renal allografts. The present study was performed to investigate the validity of serum creatinine (SCr) level as an indicator of postischemic renal dysfunction in mice.

METHODS

Renal IRI or sham surgery was induced in C57BL/6 mice, and SCr level and inulin clearance (Cin) were measured between 24 hr and 7 days after ischemia.

RESULTS

Cin in IRI mice was reduced 75% at 72 hr after ischemia in association with a nearly threefold increase in SCr level. Cin in IRI mice did not recover between 72 hr and 7 days after ischemia, even though SCr level at 7 days was not different between control and IRI mice. In IRI mice, SCr level measured at 24, 48, and 72 hr after ischemia correlated inversely with Cin measured at 72 hr, but not 7 days, after ischemia.

CONCLUSIONS

SCr level in the early postischemic period (24-72 hr) seems to be a valid indicator of early postischemic renal dysfunction, and that renal function remains markedly depressed at 7 days despite suggestion from the SCr value that renal function is improving.

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

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

Positive effect of the induction of p21WAF1/CIP1 on the course of ischemic acute renal failure

BACKGROUND

The p21 protein is found in the nucleus of most cells where it modulates cell cycle activity. At low levels, p21 stabilizes interactions between D cyclins and their cyclin-dependent kinases (cdks), but at high levels after induction by several different stress pathways, it causes cell cycle arrest. The p21 mRNA is induced in murine kidney after several types of acute renal failure, including cisplatin administration, ischemia-reperfusion, and ureteral obstruction. We reported that after cisplatin injection, mice with a p21 gene deletion developed much more severe renal damage than wild-type mice. To dissociate the effects of cisplatin-induced DNA damage and subsequent initiation of DNA damage-dependent cell death pathways from effects of acute renal failure, we have now examined mice after ischemia-reperfusion, a model of renal failure not associated with genotoxin-induced DNA damage early after the injury.

METHODS

Wild-type and p21(-/-) mice were made ischemic by clamping both renal hila for 30 or 50 minutes. At various times after reflow, mortality and parameters of renal function and morphology were quantified. Also, the nuclear proteins p21 and proliferating cell nuclear antigen (PCNA) were localized in kidney sections by immunohistochemistry.

RESULTS

Kidney function was more impaired and mortality increased significantly in p21(-/-) mice as compared with p21(+/+) mice. We found more cell cycle activity, indicated by increased number of mitotic cells and nuclear PCNA-positive cells, in kidney of p21(-/-) mice.

CONCLUSIONS

In this study, p21(-/-) mice were more susceptible to ischemia-induced acute renal failure, with similarly elevated levels of parameters of cell cycle activity. We propose that the increased and inappropriate cell cycle activity in kidney cells is responsible for the increased kidney impairment and mortality.

Regulation of renal tubular cell apoptosis and proliferation after ischemic injury to a solitary kidney

The time course and regulation of apoptosis and cellular regeneration after 30 minutes of acute ischemic injury to a single kidney was elucidated in rats at five time points over 20 weeks. The fraction of apoptotic cells was most prominent at 1 day after the insult in the distal tubule (8% +/- 4% vs 0% +/- 0%, acute renal failure [ARF] vs sham, respectively) and was still elevated at 7 days (2% +/- 2% vs 0% +/- 0%). At that time, the whole kidney mRNA expression of the apoptosis inhibitory genes bcl-xL and bcl-2, as well as that of the apoptosis promotor bax, was significantly reduced. Immunohistochemistry of kidney specimen showed suppression of bcl-2 in the distal tubule but up-regulation in the proximal tubule, whereas bax protein was more strongly expressed in the distal tubule. Cellular proliferation started at day 1 and continued over the following 20 weeks, leading to severe tubular dilation and kidney failure. These data indicate that differential regulation of bcl-2 family members contributes to the early apoptotic clearance of lethally injured tubular epithelial cells after ischemic injury to a solitary kidney.

De novo demonstration and co-localization of free-radical production and apoptosis formation in rat kidney subjected to ischemia/reperfusion

Ischemia-induced oxidative damage to the reperfused kidney was examined. A modified chemiluminescence method, an in situ nitro blue tetrazolium perfusion technique, and a DNA fragmentation/apoptosis-related protein assay were adapted for demonstration de novo and co-localization of reactive oxygen species (ROS) production and apoptosis formation in rat kidneys subjected to ischemia/reperfusion injury. The results showed that prolonged ischemia potentiated proapoptotic mechanisms, including increases in the Bax/Bcl-2 ratio, CPP32 expression, and poly-(ADP-ribose)-polymerase fragments, and subsequently resulted in severe apoptosis, including increases in DNA fragmentation and apoptotic cell number in renal proximal tubules (PT) and distal tubules (DT) in a time-dependent manner. The increased level of ROS detected on the renal surface was correlated with that in blood and was intensified by a prolonged interval of ischemia. The main source of ROS synthesis was the PT epithelial cells. The ROS and apoptotic nuclei detected in the PT cells can be ameliorated by superoxide dismutase (SOD) treatment before reperfusion. However, the apoptotic nuclei remained in DT in the SOD-treated rats, indicating that formation of apoptosis in DT was not influenced by the small amounts of ROS produced. In PT and DT cell cultures, significant increases in apoptotic cells and ROS were evident in PT cells after hypoxia/reoxygenation insult. Furthermore, the oxidative damage in PT, but not in DT, can be alleviated by ROS scavengers SOD and hexa(sulfobutyl)fullerene, confirming that PT are vulnerable to ROS. These results lead us to conclude that ROS produced in significant amounts in PT epithelium under ischemia/reperfusion or hypoxia/reoxygenation conditions may be responsible for the apoptotic death of these cells.

Relationship between expression of Bcl-2 genes and growth factors in ischemic acute renal failure in the rat

The promotion of cell survival and regeneration in acute renal failure (ARF) is important for restitution of renal function. This study analyzes the temporal and spatial relationship between expression of pro- and anti-apoptotic members of the Bcl-2 gene family (Bcl-2, Bcl-X(L), Bax) and epidermal growth factor (EGF), insulin-like growth factor- (IGF-1), and transforming growth factor-beta (TGF-beta), growth factors that are thought to be reparative in ARF. A rat model of ischemic ARF involving 30 min of bilateral renal artery occlusion followed by reperfusion for 0 to 14 d was used. Apoptosis and mitosis were quantified and qualitative assessment was made of other cellular damage including necrosis and loss of cellular adhesion. Locality and level of expression of the Bcl-2 and growth factor proteins were determined using immunohistochemistry. Apoptosis peaked between 4 and 14 d postischemia in both proximal and distal tubules. Mitosis peaked at 2 d in proximal tubules and 4 to 14 d in the distal tubules. A spatio-temporal relationship was observed between anti-apoptotic Bcl-2 gene family members and growth factors after ischemia-reperfusion. In control kidneys, expression of Bcl-2, Bcl-X(L) was low in epithelium of distal tubules, Bax had low-to-moderate expression in the proximal tubule and had low expression in the distal tubule, EGF and IGF-1 had low-to-moderate expression in the distal tubule, and TGF-beta had low expression in the proximal tubule. In contrast, within 24 h of reperfusion, distal tubules showed a marked increase in expression of Bcl-2 and a moderate increase in Bcl-X(L) and Bax. Proximal tubules showed a marked increase in Bax expression and a moderate increase in Bcl-X(L). Twenty-four hours after expression of the Bcl-2 proteins was increased, IGF-1 and EGF protein levels were increased in the distal tubule, similar to the Bcl-2 anti-apoptotic proteins, and were also detected in the adjacent proximal tubules, suggestive of paracrine action in these tubules. TGF-beta expression was moderately increased in regenerating proximal tubules, but no relationship was seen with the pattern of expression of the Bcl-2 genes. An explanation of these results is that the distal tubule is adaptively resistant to ischemic injury via promotion of survival by anti-apoptotic Bcl-2 genes, and its survival allows expression of growth factors critical not only to the maintenance and regeneration of its own cell population (autocrine action), but also to the adjacent ischemia-sensitive proximal tubular cells (paracrine action).

MAPK activation determines renal epithelial cell survival during oxidative injury

Ischemia/reperfusion (I/R) injury induces both functional and morphological changes in the kidney. Necrosis, predominantly of the proximal tubule (PT), is the hallmark of this model of renal injury, whereas cells of the distal nephron survive, apparently intact. We examined whether differences in cellular outcome of the various regions of the nephron may be due to segmental variation in the activation of the mitogen-activated protein kinases (MAPKs) in response to I/R injury. Whereas c-Jun N-terminal kinase (JNK) is activated in both the cortex and inner stripe of the outer medulla, the extracellular regulated kinase (ERK) pathway is activated only in the inner stripe in which thick ascending limb (TAL) cells predominate. These studies are consistent with the notion that ERK activation is essential for survival. To test this hypothesis directly, we studied an in vitro system in which manipulation of these pathways and their effects on cellular survival could be examined. Oxidant injury was induced in mouse PT and TAL cells in culture by the catabolism of hypoxanthine by xanthine oxidase. PT cells were found to be more sensitive than TAL cells to oxidative stress as assessed by cell counting, light microscopy, propidium iodide uptake, and fluorescence-activated cell sorting (FACS) analysis. Immunoprecipitation/kinase analysis revealed that JNK activation occurred in both cell types, whereas ERK activation occurred only in TAL cells. We then examined the effect of PD-098059, a MAP kinase kinase (MEK)-1 inhibitor of the ERK pathway, on PT and TAL survival. In TAL cells, ERK inhibition reduced cell survival nearly fourfold (P < 0.001) after oxidant exposure. In PT cells, activation of the ERK pathway by insulin-like growth factor I (IGF-I) increased survival by threefold (P < 0.001), and this IGF-I-enhanced cell survival was inhibited by PD-098059. These results indicate that cell survival in the kidney after ischemia may be dependent on ERK activation, suggesting that this pathway may be a target for therapeutic treatment in I/R injury.

Contrast medium- and mannitol-induced apoptosis in heart and kidney of SHR rats

The induction of apoptosis by contrast media (CM) and mannitol (M) was investigated in the hearts and kidneys of 12-mo-old male SHR rats. Ten groups of 3 SHR rats received a dose of 5 ml/kg of one of the following: Hypaque (H)-30, H-60, H-76, Omnipaque (O)-140, O-350, mannitol (M)-4%, M-9%, M-19%, M-27%, or saline (S). DNA fragmentation was detected using the terminal deoxynucleotidyl transferase-mediated [TdT] dUTP nick-end labeling (TUNEL) method, and the morphology characteristics of apoptosis were confirmed in cardiac and renal cells. The immunoreactivities of Bcl-2, Bax, and p53 were assessed immunohistochemically in the kidneys. Apoptosis occurred in cardiac myocytes and renal tubular and glomerular cells as well as in vascular endothelial and smooth muscle cells of the heart and kidneys. The high frequency of apoptosis correlated significantly with the increase in the osmolality of the H, O, and M. The increased Bax, the increased p53, and the decreased Bcl-2 immunoreactivities were detected in H- or O-treated, but not in M-treated, rats. These findings suggest that CM and M activate cardiac and renal apoptosis by different mechanisms and that the apoptotic process may be implicated in acute heart and renal damage.

Bcl-2 genes and growth factors in the pathology of ischaemic acute renal failure

For the past decade, an attempt has been made by many research groups to define the roles of the growing number of Bcl-2 gene family proteins in the apoptotic process. The Bcl-2 family consists of pro-apoptotic (or cell death) and anti-apoptotic (or cell survival) genes and it is the balance in expression between these gene lineages that may determine the death or survival of a cell. The majority of studies have analysed the role/s of the Bcl-2 genes in cancer development. Equally important is their role in normal tissue development, homeostasis and non-cancer disease states. Bcl-2 is crucial for normal development in the kidney, with a deficiency in Bcl-2 producing such malformation that renal failure and death result. As a corollary, its role in renal disease states in the adult has been sought. Ischaemia is one of the most common causes of both acute and chronic renal failure. The section of the kidney that is most susceptible to ischaemic damage is the outer zone of the outer medulla. Within this zone the proximal tubules are most sensitive and often die by necrosis or desquamate. In the distal nephron, apoptosis is the more common form of cell death. Recent results from our laboratory have indicated that ischaemia-induced acute renal failure is associated with up-regulation of two anti-apoptotic Bcl-2 proteins (Bcl-2 and Bcl-XL) in the damaged distal tubule and occasional up-regulation of Bax in the proximal tubule. The distal tubule is a known reservoir for several growth factors important to renal growth and repair, such as insulin-like growth factor-1 (IGF-1) and epidermal growth factor (EGF). One of the likely possibilities for the anti-cell death action of the Bcl-2 genes is that the protected distal cells may be able to produce growth factors that have a further reparative or protective role via an autocrine mechanism in the distal segment and a paracrine mechanism in the proximal cells. Both EGF and IGF-1 are also up-regulated in the surviving distal tubules and are detected in the surviving proximal tubules, where these growth factors are not usually synthesized. As a result, we have been using in vitro methods to test: (i) the relative sensitivities of renal distal and proximal epithelial cell populations to injury caused by mechanisms known to act in ischaemia-reperfusion; (ii) whether a Bcl-2 anti-apoptotic mechanism acts in these cells; and (iii) whether an autocrine and/or paracrine growth factor mechanism is initiated. The following review discusses the background to these studies as well as some of our preliminary results.

Effects of radical scavengers and antioxidant on ischemic acute renal failure in rabbits

This study was undertaken to determine whether reactive oxygen species (ROS) are involved in the pathogenesis of ischemic acute renal failure (IARF) in rabbits. Renal ischemia was induced by clamping bilateral renal arteries for 60 min. Animals were pretreated with combination of xanthine oxidase inhibitor (allopurinol), hydrogen peroxide scavenger (catalase), and hydroxyl radical scavenger (sodium benzoate). Serum creatinine level significantly increased 24 h after ischemia and remained higher to 72 h. Ischemia caused a reduction of GFR and an increase of FENa. Such changes were significantly attenuated by scavenger pretreatment. The uptake of p-aminohippurate in cortical slices and microsomal Na(+)-K(+)-ATPase activity were depressed in kidneys subjected to 72 h of reflow following ischemia, indicating impairment of tubular transport function, which were significantly attenuated by scavenger treatment. Renal blood flow 72 h after reflow was markedly reduced and it was restored by scavenger pretreatment. When animals were pretreated with a potent antioxidant DPPD, lipid peroxidation in cortex and medulla was significantly inhibited. However, ischemia-induced impairment of renal function was not attenuated by pretreatment of the antioxidant. These results suggest that radical scavengers may exert a protective effect against ischemia acute renal failure by other actions rather than ROS scavenging. Thus, the data do not support involvement of ROS in IARF in rabbits.

The role of oxygen free radicals in cisplatin-induced acute renal failure in rats

We examined the role of oxygen free radicals in cisplatin-induced acute renal failure (ARF). The intravenous injection of cisplatin (5 mg/kg body weight) induced an increase in serum creatinine and tubular damage in the outer stripe of the outer medulla in rats. The renal content of malondialdehyde (MDA) transiently increased. Treatment with the free radical scavengers dimethylthiourea (DMTU) or lecithinized superoxide dismutase (L-SOD) attenuated the increase in serum creatinine. The beneficial effect of DMTU, a hydroxyl radical scavenger, was associated with less accumulation of MDA, less tubular damage, and enhanced expression of proliferating cell nuclear antigen (PCNA) in the damaged tubular cells, but not with improvement of reduced renal blood flow (RBF). On the other hand, the beneficial effect of L-SOD, a superoxide anion scavenger, was associated with preservation of RBF and increased urinary guanosine 3',5'-cyclic monophosphate excretion but not with modification of tubular damage or PCNA expression. These results suggest that (1) cisplatin-induced nephrotoxicity was associated with lipid peroxidation, (2) the hydroxyl radical scavenger prevented ARF through both attenuation of tubular damage and enhanced regenerative response of the damaged tubular cells, and (3) the superoxide anion scavenger did the same through preservation of RBF. It follows that oxygen free radicals may play an important role in cisplatin-induced ARF by reducing RBF and inducing tubular damage.

Altered sphingomyelinase and ceramide expression in the setting of ischemic and nephrotoxic acute renal failure

Diverse physical and chemical stimuli can activate sphingomyelinases (SMases), resulting in sphingomyelin (SM) hydrolysis with ceramide release. Since ceramide can profoundly impact a host of homeostatic mechanisms, the concept of a "SM (or SMase) signaling pathway" has emerged. We recently documented that ceramide levels fall abruptly during renal ischemia, and then rebound to twice normal values during early reperfusion (30 to 90 min) Therefore, the present study assessed whether these ceramide changes are paralleled, and hence potentially mediated, by comparable changes in SMase activity. Mice were subjected to 45 minutes of renal ischemia +/- 30 minutes, 90 minutes, or 24 hours of reperfusion. Renal cortices (or isolated proximal tubules) were then assayed for SMase activity (acidic, neutral forms). To characterize whether early post-ischemic ceramide increments are a relatively persistent event, ceramide was assayed following a 24-hour reperfusion period. Finally, to assess whether the observed perturbations were unique to post-ischemic injury, SMase and ceramide were quantified in the setting of glycerol-induced myohemoglobinuria and anti-glomerular basement membrane (alpha GBM) antibody-induced acute renal failure (ARF). Ischemia induced abrupt declines (approximately 50%) in both acidic and neutral SMase activities, and these persisted in an unremitting fashion throughout 24 hours of reperfusion. Nevertheless, increased ceramide expression (2x normal) resulted. Myohemoglobinuria also suppressed acidic/neutral SMases, and again, "paradoxical" ceramide increments were observed. Finally, alpha GBM nephritis increased ceramide levels, but in this instance, a correlate was increased SMase activity. These results suggest that: (1) ceramide is an acute renal "stress rectant" increasing in response to diverse renal insults; (2) this response may occur independently of the classic SM pathway, since the ceramide increments can seemingly be dissociated from increased SMase activity; and (3) given the well documented impact of ceramide and the SM(ase) pathway on apoptosis, cell proliferation, differentiation, and tissue inflammation, the present results have potentially broad ranging implications for the induction and evolution of diverse forms of ARF.

Effects of integrins on proliferation and apoptosis of renal epithelial cells after acute injury

We sought to determine the importance of integrins for recovery after acute tubular injury and to investigate the signal transduction pathways for integrin effects on cell cycle regulation involving proliferation and apoptosis. Primary cultures of rat renal proximal tubule epithelial cells were exposed to a superoxide-generating system to induce injury in the absence of overt necrosis. Integrin function was antagonized by the integrin recognition sequence tetrapeptide Gly-Arg-Gly-Asp (GRGD) or monoclonal antibody to beta 1-integrin. Injured cells had reduced thymidine uptake compared with normal cells. The presence of GRGD during recovery from injury caused a further 44% reduction in DNA synthesis but did not affect DNA synthesis in normal cells. Injured cells had an increased proportion of apoptosis that was further accentuated by exposed to GRGD during recovery. Integrin antagonism also stimulated apoptosis in uninjured cells. To investigate signal transduction mechanisms for this effect of integrins, inhibitors and activators of protein tyrosine kinase (PTK) and protein kinase C (PKC) were evaluated. Activation of PKC stimulated cellular proliferation, whereas inhibitors of PKC and PTK had no significant effect. Genistein, a PTK inhibitor, induced apoptosis in normal cells, mimicking the effect of integrin inhibition. On the other hand, PMA, an activator of PKC, prevented cells from becoming apoptotic when exposed to injury plus GRGD. The phosphorylation status of intracellular proteins was evaluated by immunoblotting with antiphosphotyrosine antibody. A similar pattern of decreased phosphorylation was observed after either integrin inhibition, injury, both, or PTK inhibition. These findings suggest that kinase cascades are involved in the effects of integrins on renal epithelial cell proliferation and apoptosis. After injury, an interaction between cells and the extracellular matrix is required for cells to proliferate and contribute to repair rather than to enter an apoptotic pathway.

What does cell death have to do with aging?

When Lockshin and Zakeri discussed the relevance of apoptosis to aging 7 years ago, the common view was that apoptosis would have primarily a negative impact on aging by destroying essential and often irreplaceable cells. That view has now changed to one that acknowledges that there are two general ways in which apoptosis can play a role in aging: (1) elimination of damaged and presumably dysfunctional cells (e.g., fibroblasts, hepatocytes), which can then be replaced by cell proliferation, thereby maintaining homeostasis, and (2) elimination of essential post-mitotic cells (e.g., neurons, cardiac myocytes), which cannot be replaced, thereby leading to pathology. Evidence exists in two systems (fibroblasts and thymocytes/lymphocytes) that there are age-related decreases in the potential for apoptosis, although the molecular bases for the decreases in these two systems appear to differ. Upon becoming senescent, fibroblasts lose the ability to down-regulate expression of the bcl-2 gene in response to an apoptotic signal; thus, apoptosis is blocked even though an initiating signal has been received. In contrast, thymocytes/lymphocytes lack the ability to initiate the signal because of down-regulation of the cell surface receptor Fas. There is limited information available for other tissue types, and nothing is known about why and how age-related changes occur. An interesting observation is that the frequency of up-regulation of the bcl-2 gene as a result of chromosome translocation in otherwise normal B cells increases with age; the functional consequences of this phenomenon during aging are not known. The role of apoptosis in regulating cell number is also a promising area of research. The studies on liver damage and neoplastic lesions suggest an extremely important role for apoptosis in controlling cancer. This may be particularly important in the prostate where hypertrophy and/or cancer are a virtual certainty with ever-increasing age. It is not known whether the ability to undergo apoptosis declines in the prostate with increasing age, but it appears possible that it may, thus explaining the loss of control over cell number in this tissue. A particularly important area of research is whether apoptosis plays a role in the changing balance between bone formation and resorption observed during osteoporosis. Monica Driscoll has already pointed out that, "regulation and execution of cell death is an absolutely critical process that interfaces with nearly every aspect of life. Future investigation of the links of cell death to cellular aging and the aging of organisms should be an exciting enterprise." The results currently available do suggest that apoptosis is a process that may be important in aging, at least in some tissues, and the mechanism of its regulation, in particular, needs to be understood. Several tumor suppressor gene and oncogene products are involved in signal transduction associated with apoptosis, but it remains to be shown which of these, if any, are actually involved in "on-off" switches for apoptosis. Where great progress has been made is in understanding the events occurring after binding of either Fas ligand or tumor necrosis factor to their respective receptors. However, one area about which little is known is the identity of the signals that initiate this process in response to intracellular damage. Through continuing research on cell death mechanisms, funded by the NIA, we hope to provide answers to such fundamental questions as: 1. Are there age-related changes in apoptosis, and what role, if any, do these have in the aging process? 2. If age-related changes in apoptosis do occur, what molecular mechanisms are altered to produce these changes? 3. Can approaches be developed to improve the detection and elimination of damaged cells in vivo in tissues where cell replacement is possible? 4. Can death of damaged cells be attenuated or delayed in nonrenewable tissues, and, if so, is it advantageous to the org

Acute renal failure and proximal tubule lesions after trichosanthin injection in rats

The structural basis of the recently recognized renal impairment after infusion of trichosanthin (TCS), a type I ribosome inactivating protein, is uncertain, but functionally it appears to be related to a lesion in the renal tubules. In this study, renal dysfunction in experimental rats was induced by a single dose of TCS. Creatinine clearance and tubular proteinuria were used to assess renal function. Light microscopy and ultrastructure of the kidneys were examined and apoptosis in proximal tubules was evaluated by the in situ TdT-mediated nick end labeling technique. TCS-treated rats demonstrated a significant dose-dependent decrease in creatinine clearance together with a mild degree of low-molecular-weight proteinuria. The proximal convoluted tubule was the site of lesions showing individual tubular cell death, which was more abundant in rats receiving high doses of TCS. Apoptotic cell death, together with heterophagosomes and large residual bodies, was observed. DNA fragmentation was confirmed by the in situ technique. There was also a dose-dependent density of apoptotic cells. Other portions of the nephron were spared, and it was not accompanied by any inflammatory infiltrate. In conclusion, these findings are consistent with TCS-induced proximal tubular toxicity resulting in reduction of glomerular filtration rate and tubular proteinuria. The extent of injury is dosage dependent. Both necrotic cell death and apoptosis participated in the loss of cells from the proximal tubules. Such toxicity may be mediated through intracellular events induced by trichosanthin.

Myoglobin inhibits proliferation of cultured human proximal tubular (HK-2) cells

Following nephrotoxic injury, renal repair is dependent on tubular regeneration. In the case of myoglobinuric acute renal failure (ARF), persistence of myoglobin within tubular cells, or sublethal injury sustained at the height of exposure to it, might retard this process. To test this hypothesis, a human proximal tubular cell line (HK-2) was cultured for 24 hours in the absence or presence of clinically relevant myoglobin concentrations (0.5, 1, 2, 4 mg/ml). Immediately following myoglobin removal, lethal cell injury (vital dye uptake), lipid peroxidation, and DNA damage (alkaline unwinding assay) were assessed. The extent of cell proliferation was estimated over the next four days by a tetrazolium based (MTT) assay and by determining total intracellular LDH. Myoglobin's effects on protein and DNA synthesis were also assessed (35S-methionine and bromodeoxyuridine incorporation, respectively). Myoglobin induced dose-dependent lipid peroxidation (malondialdehyde generation) and cell death (up to 80% vital dye uptake with the 4 mg/ml challenge). Although 1 mg/ml myoglobin caused no cell death, it induced nearly complete growth arrest. This lasted for approximately three days following myoglobin removal from the media. Neither of two control proteins (albumin; lysozyme) nor a second nephrotoxin (gentamicin; 1 mg/ml) reproduced this effect. The 1 mg/ml myoglobin challenge caused an 80 to 90% depression in protein and DNA synthesis. It also induced significant DNA damage, as assessed by the alkaline unwinding assay (P < 0.01). Iron chelation therapy (deferoxamine) mitigated myoglobin-induced cell killing. However, its addition following myoglobin loading worsened HK-2 outgrowth by exerting a direct anti-proliferative effect. These results indicate that: (1) sublethal myoglobin toxicity can induce transient proximal tubular cell growth arrest, potentially slowing recovery from ARF; (2) this effect correlates with, and could result from, heme-induced DNA damage and a blockade in DNA/protein synthesis; and (3) deferoxamine can inhibit proximal tubular cell proliferation. This possibility needs to be considered in designing clinical trials with DFO for myohemoglobinuric ARF.

Role of thromboxane A2 and prostacyclin in uninephrectomy-induced attenuation of ischemic renal injury

Contralateral uninephrectomy attenuates unilateral renal ischemic injury. The present work was performed to elucidate whether the beneficial effect of uninephrectomy was mediated through the modification of the actions of thromboxane A2 (TxA2) or prostacyclin. Unilateral ischemic injury was provoked by a 60-minute left renal artery occlusion in right nephrectomized (Nx) and in sham-nephrectomized (Sham-Nx) rats. Inulin clearance (CIn) of left kidney 48 hours after ischemia was significantly higher in the Nx group than in the Sham-Nx group (0.11 +/- 0.07 vs. 0.00 +/- 0.00 ml/min/kidney, P < 0.05). Ischemia-induced tubular necrosis was also less in Nx animals. Proliferating cell nuclear antigen (PCNA) staining, a marker for cell proliferation, was found more markedly in Nx rats than in Sham-Nx animals. Forty-eight hours after ischemia, renal cortical TxB2 content was greater in Sham-Nx rats than in Nx rats (29.5 +/- 4.4 vs. 18.3 +/- 1.7 pg/mg protein, P < 0.05). No significant difference was found in the intrarenal content of 6-keto prostaglandin F1 alpha between two ischemia groups. A thromboxane synthetase inhibitor, OKY-046 (100 mg/kg/day, i.p.), significantly increased CIn 48 hours after ischemia (0.00 +/- 0.00 vs. 0.17 +/- 0.09 ml/min/kidney, P < 0.05) and attenuated ischemic tubular damage in Sham-Nx rats but not in Nx animals. Under OKY-046 treatment, no significant difference was found in postischemic CIn and ischemic tubular damage between the Nx and Sham-Nx groups. OKY-046 also increased PCNA expression in the cortex and outer stripe in Sham-Nx animals. These data suggest that less production of intrarenal TxB2 plays an important role for the uninephrectomy-induced attenuation of ischemic renal damage and for the facilitation of tubular recovery.

Rapid DNA fragmentation from hypoxia along the thick ascending limb of rat kidneys

Extensive DNA fragmentation, a marker for programmed cell death, was selectively and rapidly induced by hypoxia in the thick ascending limbs of rat kidneys. In isolated perfused kidneys, DNA breaks were present in medullary tubules as early as after 10 minutes of local hypoxia and were prevented by reduction of metabolic work. In a model of radiocontrast-induced acute renal failure, DNA breaks were detected selectively along thick ascending limbs as early as 15 minutes following insult, preceding overt morphological damage. Hypoxia induces rapid DNA fragmentation along thick ascending limbs, where programmed cell death could play an important role in nephron injury and kidney failure.

Obstruction of proximal tubules initiates cytoresistance against hypoxic damage

Following acute tubular necrosis (ATN), cytoresistance to further renal injury results. However, the initiating events and the subcellular determinants of this phenomenon have not been defined. Since tubular obstruction is a consequence of ATN, this study evaluated whether it alters tubular susceptibility to hypoxic damage. Extrarenal obstruction (ureteral ligation in rats) was used for this purpose to dissociate obstructive effects from those of ATN. Twenty-four hours following ureteral ligation or sham surgery, cortical proximal tubular segments (PTS) were isolated and subjected to hypoxic (15 or 30 min)/reoxygenation injury. Since oxidant stress, cell Ca2+ overload, and PLA2 attack are purported mediators of hypoxic/reoxygenation injury, degrees of FeS04, Ca2+ ionophore, and phospholipase A2-induced PTS damage also were assessed. The cell injury (% LDH release) which resulted from each of the above was consistently less in PTS obtained from obstructed kidneys. This cytoresistance: (a) did not require prior uremia to develop (seen with unilateral obstruction); (b) it did not appear to correlate with a tubular proliferative response (assessed by proliferating cell nuclear antigen expression); (c) it was uninfluenced by early tubular repair (unchanged by 24 hrs of obstruction release); and (d) it occurred without increased heat shock protein (HSP-70) or antioxidant enzyme (superoxide dismutase, catalase) expression. Total adenylate pools were higher in obstructed versus control PTS during injury; however, this appeared to be a correlate of the protection, rather than a mediator of it. In contrast, obstructed tubules manifested a primary increase in plasma membrane resistance to PLA2 attack (approximately 3-fold less lysophosphatidylcholine and free fatty acid generation in obstructed vs. control PTS during incubation with exogenous PLA2). In sum, these results indicate that: (1) tubular obstruction protects PTS from injury, suggesting that its development during ATN may initiate cytoresistance; and (2) this cytoresistance appears to be mediated, at least in part, by a direct increase in plasma membrane resistance to PLA2 and potentially other forms (such as, oxidant stress, cytosolic Ca2+ loading) of attack.