The cell biology of ischemic renal injury

Functional activation of heat shock factor and hypoxia-inducible factor in the kidney

Renal ischemia is the result of a complex series of events, including decreases in oxygen supply (hypoxia) and the availability of cellular energy (ATP depletion). In this study, the functional activation of two stress-responsive transcription factors, i.e., heat shock factor-1 (HSF-1) and hypoxia-inducible factor-1 (HIF-1), in the kidney was assessed. When rats were subjected to 45 min of renal ischemia, electrophoretic mobility shift assays of kidney nuclear extracts revealed rapid activation of both HIF-1 and HSF. Western blot analyses further demonstrated that this activation resulted in increased expression of the HSF and HIF-1 target genes heat shock protein-72 and heme oxygenase-1, respectively. Whether hypoxia or ATP depletion alone could produce similar activation patterns in vitro was then investigated. Renal epithelial LLC-PK(1) cells were subjected to either ATP depletion (0.1 microM antimycin A and glucose deprivation) or hypoxia (1% O(2)). After ATP depletion, HSF was rapidly activated (within 30 min), whereas HIF-1 was unaffected. In contrast, hypoxia led to the activation of HIF-1 but not HSF. Hypoxic activation of HIF-1 was observed within 30 min and persisted for 4 h, whereas no HSF activation was detected even with prolonged periods of hypoxia. HIF-1 was transcriptionally active in LLC-PK(1) cells, as demonstrated by luciferase reporter gene assays using the vascular endothelial growth factor promoter or a synthetic promoter construct containing three hypoxia-inducible elements. Interestingly, intracellular ATP levels were not affected by hypoxia but were significantly reduced by ATP depletion. These findings suggest that HIF-1 is activated specifically by decreased O(2) concentrations and not by reduced ATP levels alone. In contrast, HSF is activated primarily by metabolic stresses associated with ATP depletion and not by isolated O(2) deprivation. In vivo, the two transcription factors are simultaneously activated during renal ischemia, which might account for observed differences between in vivo and in vitro epithelial cell injury and repair. Selective modulation of either pathway might therefore be of potential interest for modification of the response of the kidney to ischemia, as well as the processes involved in recovery from ischemia.

Loss of cell volume regulation during metabolic inhibition in renal epithelial cells (A6): role of intracellular pH

In renal ischemia, tubular obstruction induced by swelling of epithelial cells might be an important mechanism for reduction of the glomerular filtration rate. We investigated ischemic cell swelling by examining volume regulation of A6 cells during metabolic inhibition (MI) induced by cyanide and 2-deoxyglucose. Changes in cell volume were monitored by recording cell thickness (T(c)). Intracellular pH (pH(c)) measurements were performed with the pH-sensitive probe 5-chloromethyl-fluoresceine diacetate. T(c) measurements showed that MI increases cell volume. Cell swelling during MI is proportional to the rate of Na(+) transport and is not followed by a volume regulatory response. Furthermore, MI prevents the regulatory volume decrease (RVD) elicited by a hyposmotic shock. MI induces a pronounced intracellular acidification that is conserved during a subsequent hypotonic shock. A transient acidification induced by a NH(4)Cl prepulse causes a marked delay of the RVD in response to a hypotonic shock. On the other hand, acute lowering of external pH to 5, simultaneously with the hypotonic shock, allowed the onset of RVD. However, this RVD was completely arrested approximately 10 min after the initiation of the hyposmotic challenge. The inhibition of RVD appears to be related to the pronounced acidification that occurred within this time period. In contrast, when external pH was lowered 20 min before the hyposmotic shock, RVD was absent. These data suggest that internal acidification inhibits cellular volume regulation in A6 cells. Therefore, the intracellular acidification associated with MI might at least partly account for the failure of volume regulation in swollen epithelial cells.

Endothelial dysfunction in ischemic acute renal failure: rescue by transplanted endothelial cells

There is accumulating circumstantial evidence suggesting that endothelial cell dysfunction contributes to the "no-reflow" phenomenon in postischemic kidneys. Here, we demonstrated the vulnerability of in vitro, ex vivo, and in vivo endothelial cells exposed to pathophysiologically relevant insults, such as oxidative and nitrosative stress or ischemia. All of these stimuli compromised the integrity of the endothelial lining. Next, we performed minimally invasive intravital microscopy of blood flow in peritubular capillaries, which provided direct evidence of the existence of the no-reflow phenomenon, attributable, at least in part, to endothelial injury. In an attempt to ameliorate the hemodynamic consequences of lost endothelial integrity, we transplanted endothelial cells or surrogate cells expressing endothelial nitric oxide synthase into rats subjected to renal artery clamping. Implantation of endothelial cells or their surrogates expressing functional endothelial nitric oxide synthase in the renal microvasculature resulted in a dramatic functional protection of ischemic kidneys. These observations strongly suggest that endothelial cell dysfunction is the primary cause of the no-reflow phenomenon, which, when ameliorated, results in prevention of renal injury seen in acute renal failure.

Global analysis of gene expression in renal ischemia-reperfusion in the mouse

Ischemia-induced acute renal failure (ARF) is a relatively common disorder with major morbidity and mortality. To study global gene expression during ARF, 6-week-old C57BL/6 male mice underwent 30 min of bilateral renal ischemia followed by reperfusion [I/R] or sham operation. Oligonucleotide microarrays [Affymetrix] with approximately 10,000 genes, 6,643 of which were present in mouse kidney, were used to analyze mRNA expression for up to 4 days following I/R. Fifty-two genes at day 1 and 40 at day 4 were up-regulated more than 4-fold [400%]. Seventy genes at day 1 and 30 genes at day 4 were down-regulated to under 0.25-fold from baseline [25%]. Real-time quantitative RT-PCR confirmed changes in expression for 8 genes of interest. Most of the induced transcripts are involved in cell structure, extracellular matrix, intracellular calcium binding, and cell division/differentiation. Our data identified several novel genes that may be important in renal repair after ischemia.

Protective effect of glycine on renal injury induced by ischemia-reperfusion in vivo

Although glycine prevents renal tubular cell injury in vitro, its effect in vivo is not clear. The purpose of this study was to investigate whether a bolus injection of glycine given before reperfusion plus continuous dietary supplementation afterward would reduce renal injury caused by ischemia-reperfusion. Female Sprague-Dawley rats received a semisynthetic powdered diet containing 5% glycine and 15% casein (glycine group) or 20% casein (control group). Two days later, renal ischemia was produced by cross-clamping the left renal vessels for 15 min, followed by reperfusion. The right kidney was removed before reperfusion. The postischemic glomerular filtration rate (GFR) showed that renal function was less impaired and recovered more quickly in rats receiving glycine. For example, at day 7, GFR in controls (0.31 +/- 0.03 ml x min(-1) x 100 g(-1)) was about one-half that of glycine-treated rats (0.61 +/- 0.06 ml x min(-1) x 100 g(-1), P < 0.05). Furthermore, tubular injury and cast formation observed in controls was minimized by glycine (pathology score, 3.2 +/- 0.4 vs. 1.0 +/- 0.4, P < 0.05). Urinary lactate dehydrogenase (LDH) concentration was elevated by ischemia-reperfusion in the control group (260 +/- 22 U/l), but values were significantly lower by about fourfold (60 +/- 30 U/l) in glycine-fed rats. Similarly, free radical production in urine was significantly lower in glycine-treated animals. Importantly, on postischemic day 1, binding of pimonidazole, an in vivo hypoxia marker, was increased in the outer medulla in controls; however, this phenomenon was prevented by glycine. Two weeks later, mild leukocyte infiltration and interstitial fibrosis were still observed in controls, but not in kidneys from glycine-treated rats. In conclusion, these results indicate that administration of glycine indeed reduces mild ischemia-reperfusion injury in the kidney in vivo, in part by decreasing initial damage and preventing chronic hypoxia.

Renal function and cortical (Na(+)+K(+))-ATPase activity, abundance and distribution after ischaemia-reperfusion in rats

The effects of ischaemic injury and reperfusion on renal function, cortical ATP content, alkaline phosphatase activity and (Na(+)+K(+))-ATPase activity and abundance in cortical homogenates and isolated basolateral and apical membranes were examined. Rats were submitted to 5 or 40 min of right renal artery occlusion and 60 min of reperfusion. Renal function of the ischaemic-reperfused kidney was studied by conventional clearance techniques. Our results show that 1 h of reperfusion after a short period of renal ischaemia (5 min) allows the complete restoration of the biochemical features of cortical cells and functional properties of the injured kidney. A longer period of ischaemia, such as 40 min, followed by 1 h of reperfusion showed functional and biochemical alterations. ATP recovered from 26% after 40 min of ischaemia to 50% of control values after 1 h reperfusion. However, renal function was strongly impaired. Brush border integrity was compromised, as suggested by AP excretion and actin appearance in urine. Although total cortical (Na(+)+K(+))-ATPase activity was not different from controls, its distribution in isolated apical and basolateral membranes was abnormal. Remarkably, we detected an increase in alpha-subunit protein abundance that may suggest that (Na(+)+K(+))-ATPase synthesis is promoted by ischaemia-reperfusion. This increase may play an important role in the pathophysiology of ischaemic acute renal failure.

Pharmacological preconditioning with low-dose cyclosporine or FK506 reduces subsequent ischemia/reperfusion injury in rat kidney

BACKGROUND

Ischemia/reperfusion (I/R) injury in the early posttransplant period is closely associated with delayed recovery of graft function, increased acute rejection, and late allograft dysfunction. Pharmacological preconditioning with low-dose cyclosporine (CsA) or FK506 was performed to induce ischemic tolerance in rat kidney with I/R injury.

METHODS

Low-dose CsA (3 mg/kg, administered i.v.) or FK506 (0.3 mg/kg i.v.) were used to induce ischemic tolerance in Sprague-Dawley rats, and the induction of heat shock protein (hsp) 70 by CsA or FK506 was evaluated overtime. Rats were pretreated with CsA or FK506 6 hr before I/R injury when hsp70 was maximally expressed, and were killed 24 hr later. The effect of pharmacological preconditioning on subsequent I/R injury was evaluated in terms of renal function, histopathology score, assays for apoptosis (DNA fragmentation analysis, TUNEL staining, expressions of pro-apoptotic genes, and caspase activity), and the expression of inflammatory cytokine genes (interleukin-1 and tumor necrosis factor-alpha).

RESULTS

Preconditioning with low-dose CsA or FK506 significantly improved renal function and renal histology, compared to rats with I/R injury. Apoptotic cell death (typical DNA laddering and increased TUNEL-positive cells) in rat kidneys with I/R injury, was decreased by pretreatment with low-dose CsA or FK506. Increased expression of pro-apoptotic genes (Fas, Fas-ligand, caspase 1 and 3) and activated caspases in ischemic rat kidneys were decreased after CsA or FK506 pretreatment.

CONCLUSIONS

Pretreatment with low-dose CsA or FK506 prevents subsequent I/R injury, and this effect may be related to the induction of hsp70. Pretreatment of renal donors with low-dose CsA or FK506 may result in an improvement in immediate posttransplant function.

Renal cortical cholesterol accumulation is an integral component of the systemic stress response

BACKGROUND

Direct tubular injury (such as ischemia or myohemoglobinuria) increases renal cortical cholesterol content. This study explored whether systemic forms of stress (such as heat shock or sepsis) can trigger renal cholesterol accumulation, and if so, whether increased 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR) expression might be involved.

METHODS

Male CD-1 mice were subjected to glycerol-induced myohemoglobinuria (MH), systemic heat shock (HS), or E. coli sepsis. Free cholesterol (FC), cholesteryl esters (CE), and HMGCR (Western blot) levels were assessed 18 hours later. Statin effects on renal cholesterol levels and on the severity of MH-acute renal failure (ARF) were also determined.

RESULTS

Sepsis and HS each induced dramatic FC and CE increments, comparable to those observed with myohemoglobinuria, and without inducing acute tubular necrosis (ATN). Part of the cholesterol increments was localized within plasma membrane (detergent resistant) microdomains (for example, rafts/caveolae). HS and MH each increased renal HMGCR, as well as HS protein (HSP-72) expression. Oxidant stress (Fe) imposed on cultured proximal tubule (HK-2) cells also enhanced HMGCR content. Conversely, sepsis did not raise renal HMGCR or HSP-72 levels. Statin therapy decreased the severity of MH-ARF and renal cholesterol content. However, this appeared to arise from a statin-mediated decrease in glycerol-induced extrarenal tissue damage (myolysis/LDH release).

CONCLUSIONS

Cholesterol appears to be a renal 'acute phase reactant' with tissue levels increasing with either systemic stress (such as, heat shock, sepsis), or direct tissue damage (such as ATN). Increased HMGCR expression can contribute to this result. Mechanisms other than HMGCR induction also can mediate stress-induced cholesterol increments (for example, in the case of sepsis), and statins can mitigate MH-ARF. However, systemic anti-inflammatory effects, rather than a primary renal action, appear more likely to be involved.

Fatty-acid-binding proteins do not protect against induced cytotoxicity in a kidney cell model

Intracellular accumulation of fatty acids (FAs) is a well-described consequence of renal ischaemia and may lead to lethal cell injury. Fatty-acid-binding proteins (FABPs) are small cytosolic proteins with high affinity for FAs. They may protect vital cellular functions by binding to and promoting the metabolism of FAs, thereby reducing their intracellular concentration. In this study we investigated the putative cytoprotective role of FABPs in a Madin-Darby canine kidney (MDCK) cell model for renal damage. We studied the effects of transfection with cDNA encoding heart FABP, adipocyte FABP or liver FABP on cytotoxicity induced by chemical anoxia or FAs. Transfection of MDCK type II cells with these cDNA types caused a 5-20-fold increase in FABP content, but did not change the rate or extent of palmitate uptake. After 1 h of incubation with KCN, all cell types showed reduced viability and cellular ATP content and an intracellular accumulation of non-esterified FAs. High extracellular concentrations of oleate, but not palmitate, caused a markedly decreased cell viability and cellular ATP content. Oleate accumulated in non-esterified form in these cells. Simultaneous addition of glucose ameliorated the damaging effects of KCN or oleate, indicating that glycolytic ATP could substitute for uncoupled oxidative phosphorylation. No significant differences in the effects of chemical anoxia or oleate were observed between non-transfected, mock-transfected and FABP-cDNA-transfected cells. Non-esterified FA accumulation was not reduced in any of the FABP-cDNA-transfected cell lines. In conclusion, our data do not provide evidence for a cytoprotective role of FABP in this kidney cell model.

Ischemia disrupts myosin I beta in renal tubules

In these studies we have examined rat kidneys biochemically and microscopically to determine where myosin I beta is located before, during, and after an acute ischemic injury. Myosin I beta is present in multiple tubule segments including the brush border (BB) of the proximal tubule cell (PTC). Its distribution is severely altered by a 15-min renal artery clamp. Myosin I beta is present in the urine during reflow and is found in the numerous cellular blebs arising from the damaged PTC and other tubules. Two hours of reflow result in a decrease in BB myosin I beta staining and an increase in its cytoplasmic staining. Interestingly, the return of the F-actin in the BB precedes the return of the myosin I beta, suggesting that this myosin I isoform may not play a role in rebuilding the microvilli after an ischemic injury. A nonstructural role for this myosin, such as transport or channel regulation, is supported by its presence in many tubule segments, all of which have transport and channel requirements but do not all contain microvilli.

Renal cholesterol accumulation: a durable response after acute and subacute renal insults

Proximal tubular cholesterol levels rise within 18 hours of diverse forms of acute renal tubular injury (eg, myoglobinuria, ischemia/reperfusion, urinary tract obstruction). These increments serve to protect against further bouts of tubular attack (so-called "acquired cytoresistance"). Whether these cholesterol increments are merely transitory, or persist into the maintenance phase of acute renal failure (ARF), has not been previously defined. Furthermore, whether subacute/insidious tubular injury [eg, cyclosporine A (CSA), tacrolimus toxicity], nontubular injury (eg, acute glomerulonephritis), or physiological stress (eg, mild dehydration) impact renal cholesterol homeostasis have not been addressed. This study sought to resolve these issues. Male CD-1 mice were subjected to glycerol-induced ARF. Renal cortical-free cholesterol (FC) and cholesterol ester (CE) levels were determined 3, 5, 7, or 14 days later, and the values contrasted to prevailing blood-urea nitrogen concentrations. The impact of 40 minutes of unilateral renal ischemia plus reflow (3 to 6 days) on mouse cortical FC/CE content was also assessed. Additionally, FC/CE levels were measured in rat renal cortex either 10 days after CSA or tacrolimus therapy, or 48 hours after induction of nephrotoxic serum nephritis. Finally, the impact of overnight dehydration on mouse renal cortical/medullary FC/CE profiles was determined. Compared to sham-treated animals, glycerol, CSA, tacrolimus, ischemia-reperfusion, and nephrotoxic serum each induced dramatic CE +/- FC elevations, rising as much as 10x control values. In the glycerol model, striking correlations (r

CONCLUSIONS

FC/CE accumulation is a hallmark of the maintenance phase of ischemic and nephrotoxic ARF, and can reflect its severity. That cholesterol accumulation can result from glomerular injury and dehydration suggests that it is a generic renal stress response, with potential relevance extending beyond just the phenomenon of acquired cytoresistance.

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Key Words Collapse

MESH Headings

• Acute Kidney Injury/chemically induced
• Acute Kidney Injury/metabolism
• Animals
• Blood Urea Nitrogen
• Cholesterol/metabolism
• Cholesterol Esters/metabolism
• Cyclosporine/toxicity
• Dehydration/physiopathology
• Glomerulonephritis/metabolism
• Glycerol/toxicity
• Ischemia/metabolism
• Kidney/blood supply
• Kidney/metabolism
• Kidney/pathology
• Kidney Cortex/metabolism
• Kidney Medulla/metabolism
• Kidney Tubules/drug effects
• Kidney Tubules/metabolism
• Kidney Tubules/pathology
• Male
• Mice
• Nephritis/metabolism
• Nephritis/pathology
• Rats
• Rats, Sprague-Dawley
• Reperfusion
• Tacrolimus/toxicity

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Grants

• R01 DK038432 NIDDK NIH HHS
• R01 54200 PHS HHS
• R01 DK 37652 NIDDK NIH HHS
• DK38432 NIDDK NIH HHS
• R37 DK038432 NIDDK NIH HHS

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Affiliation(s)

R A Zager Department of Medicine, Fred Hutchinson Cancer Center, University of Washington, 1100 Fairview Ave. N, Rm. D2-190, Seattle, WA 98109, USA.
T Andoh
W M Bennett

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Effects of L-arginine on the kidney levels of malondialdehyde in rats submitted to renal ischaemia-reperfusion

OBJECTIVE

To evaluate the effects of L-arginine, a nitric oxide donor, on kidney levels of malondialdehyde (MDA, a product of cellular lipid peroxidation), serum creatinine levels, and urinary volume in rats undergoing unilateral renal ischaemia-reperfusion.

MATERIALS AND METHODS

Wistar rats (117) were randomly distributed into three experimental groups (of four subgroups each) in which were assessed renal cell-lipid peroxidation (kidney levels of MDA), serum creatinine levels and urinary volume. The rats underwent unilateral nephrectomy followed by contralateral renal ischaemia-reperfusion with or with no pretreatment with L-arginine (200 mg/kg) given intraperitoneally.

RESULTS

Pretreatment with L-arginine caused significantly higher kidney levels of MDA than in the untreated group (P < 0.05). Furthermore, L-arginine given before surgery attenuated the increase in serum creatinine and significantly increased urinary volume in rats subjected to renal ischaemia-reperfusion (P < 0.05).

CONCLUSION

L-arginine tended to be of benefit for renal function during renal ischaemia-reperfusion in rats. Pretreatment with L-arginine (200 mg/kg intraperitoneally) seems to increase the renal damage by increasing kidney levels of MDA.

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

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

PROTEÇÃO FUNCIONAL DO RIM COM LOVASTATINA APÓS ISQUEMIA E REPERFUSÃO RENAL

Introdução - a isquemia renal é causa de graves lesões nesse órgão, estando presente em diferentes situações como em cirurgias renais, vasculares e no transplante renal. Assim, a procura de substâncias protetoras da função renal tem amplo interesse clínico. Neste estudo o objetivo foi o de analisar o efeito da lovastatina na isquemia renal normotérmica seguida da reperfusão.

Reactive oxygen species and acute renal failure

Acute renal failure is commonly due to acute tubular necrosis (ATN), the latter representing an acute, usually reversible loss of renal function incurred from ischemic or nephrotoxic insults occurring singly or in combination. Such insults instigate a number of processes-hemodynamic alterations, aberrant vascular responses, sublethal and lethal cell damage, inflammatory responses, and nephron obstruction-that initiate and maintain ATN. Eventually, reparative and regenerative processes facilitate the resolution of renal injury and the recovery of renal function. Focusing mainly on ischemic ATN, this article reviews evidence indicating that the inordinate or aberrant generation of reactive oxygen species (ROS) may contribute to the initiation and maintenance of ATN. This review also discusses the possibility that ROS may instigate adaptive as well as maladaptive responses in the kidney with ATN, and raises the possibility that ROS may participate in the recovery phase of ATN.

New pharmacologic options for renal preservation

The understanding of the cause and pathophysiology of renal failure has guided the rational development of pharmacologic renoprotective strategies. Although traditionally anesthesiologists have focused on renal hemodynamic derangements, newer information suggests that cellular interactions amplify and perpetuate the insult. Consequently, the potential renoprotective armamentarium not only encompasses the more traditional vasoactive agents but also therapeutic approaches that may modify the cellular response to injury. Although few of these agents have reached the clinical arena, preliminary work suggests that this new approach to renal injury and protection may be promising.

Pathophysiology and management of renal insufficiency in the perioperative and critically ill patient

Acute renal failure remains a common, devastating complication of the postoperative period and in the critically ill patient. The most common cause is the progression of prerenal insufficiency to ATN. Despite improved understanding of the pathogenic mechanisms, including impaired hemodynamic autoregulation, medullary hypoxia, and proximal tubular obstruction and transtubular backleak, the treatment, to date, remains largely supportive. Avoidance by ensuring hemodynamic stability, with provision of adequate renal perfusion, provides the best means for minimizing the complications of this organ dysfunction.

Inhibition of poly(ADP-ribose) polymerase attenuates ischemic renal injury in rats

The enzyme, poly(ADP-ribose) polymerase (PARP), effects repair of DNA after ischemia-reperfusion (I/R) injury to cells in nerve and muscle tissue. However, its activation in severely damaged cells can lead to ATP depletion and death. We show that PARP expression is enhanced in damaged renal proximal tubules beginning at 6-12 h after I/R injury. Intraperitoneal administration of PARP inhibitors, benzamide or 3-amino benzamide, after I/R injury accelerates the recovery of normal renal function, as assessed by monitoring the levels of plasma creatinine and blood urea nitrogen during 6 days postischemia. PARP inhibition leads to increased cell proliferation at 1 day postinjury as assessed by proliferating cell nuclear antigen and improves the histopathological appearance of kidneys examined at 7 days postinjury. Furthermore, inhibition of PARP increases levels of ATP measured at 24 h postischemia compared with those in vehicle-treated animals. Our data indicate that PARP activation is a part of the cascade of molecular events that occurs after I/R injury in the kidney. Although caution is advised, transient inhibition of PARP postischemia may constitute a novel therapy for acute renal failure.

Exsanguinous metabolic support perfusion--a new strategy to improve graft function after kidney transplantation

BACKGROUND

The compounding damage of warm ischemia (WI) followed by cold preservation is a major barrier in renal transplantation. Although the relative effect of WI is not yet well understood, therapeutic strategies have mostly focused on minimizing the pathology seen upon reperfusion from the cold. Our study was designed to examine the effect of restoration of renal metabolism by warm perfusion on graft survival and to investigate the compounding damage of WI.

METHODS

Using a known critical canine autotransplantation model (1), kidneys were exposed to 30 min WI followed by 24 hr cold storage in Viaspan. They were then either reimplanted directly or first transitioned to 3 hr of warm perfusion with an acellular perfusate before reimplantation. Contralateral kidneys were subjected to 0, 30, or 60 min WI; 24 hr cold storage, and 3 hr warm perfusion.

RESULTS

Transplanted kidneys that were warm perfused before reimplantation had both lower 24 hr posttransplant serum creatinine (median of 3.2 vs. 4.1 mg/dl) and lower peak serum creatinine (median of 4.95 vs. 7.1 mg/dl). Survival rate for warm perfused kidneys was 90% (9/10) vs. 73% (8/11). In the contralateral kidneys, metabolism was affected by the compounding damage of WI. Renal oxygen and glucose consumption diminished significantly, whereas vascular resistance and lactate dehydrogenase-release rose significantly with increasing WI.

CONCLUSIONS

The results demonstrate a reduction of reperfusion damage by an acellular ex vivo restoration of renal metabolism. Furthermore, data from the contralateral kidneys substantiates the relative role of WI on metabolism in renal transplantation.

Changes in free and esterified cholesterol: hallmarks of acute renal tubular injury and acquired cytoresistance

Acute tubular cell injury is accompanied by plasma membrane phospholipid breakdown. Although cholesterol is a dominant membrane lipid which interdigitates with, and impacts, phospholipid homeostasis, its fate during the induction and recovery phases of acute renal failure (ARF) has remained ill defined. The present study was performed to ascertain whether altered cholesterol expression is a hallmark of evolving tubular damage. Using gas chromatographic analysis, free cholesterol (FC) and esterified cholesterol (CE) were quantified in: 1) isolated mouse proximal tubule segments (PTS) after 30 minutes of hypoxic or oxidant (ferrous ammonium sulfate) injury; 2) cultured proximal tubule (HK-2) cells after 4 or 18 hours of either ATP depletion/Ca(2+) ionophore- or ferrous ammonium sulfate-mediated injury; and 3) in renal cortex 18 hours after induction of glycerol-induced myoglobinuric ARF, a time corresponding to the so-called "acquired cytoresistance" state (ie, resistance to further renal damage). Hypoxic and oxidant injury each induced approximately 33% decrements in CE (but not FC) levels in PTS, corresponding with lethal cell injury ( approximately 50 to 60% LDH release). When comparable CE declines were induced in normal PTS by exogenous cholesterol esterase treatment, proportionate lethal cell injury resulted. During models of slowly evolving HK-2 cell injury, progressive CE increments occurred: these were first noted at 4 hours, and reached approximately 600% by 18 hours. In vivo myoglobinuric ARF produced comparable renal cortical CE (and to a lesser extent FC) increments. Renal CE accumulation strikingly correlated with the severity of ARF (eg, blood urea nitrogen versus CE; r, 0.84). Mevastatin blocked cholesterol accumulation in injured HK-2 cells, indicating de novo synthesis was responsible. Acute tubule injury first lowers, then raises, tubule cholesterol content. Based on previous observations that cholesterol has cytoprotectant properties, the present findings have potential relevance for both the induction and maintenance phases of ARF.

Plasma membrane cholesterol: a critical determinant of cellular energetics and tubular resistance to attack

BACKGROUND

Cholesterol is a major component of plasma membranes, forming membrane microdomains ("rafts" or "caveolae") via hydrophobic interactions with sphingolipids. We have recently demonstrated that tubule cholesterol levels rise by 18 hours following diverse forms of injury, and this change helps to protect kidneys from further damage (so-called acquired cytoresistance). The present study was undertaken to better define the effects of membrane cholesterol/microdomains on tubule homeostasis and cell susceptibility to superimposed attack.

METHODS

Plasma membrane cholesterol was perturbed in normal mouse proximal tubular segments with either cholesterol esterase (CE) or cholesterol oxidase (CO). Alternatively, cholesterol-sphingomyelin complexes were altered by sphingomyelinase (SMase) treatment. Changes in cell energetics (ATP/ADP ratios + ouabain), viability [lactate dehydrogenase (LDH) release], phospholipid profiles, and susceptibility to injury (Fe-induced oxidant stress, PLA2, Ca2+ ionophore) were determined. The impacts of selected cytoprotectants were also assessed.

RESULTS

Within 15 minutes, CE and CO each induced approximately 90% ATP/ADP ratio suppressions. These were seen prior to lethal cell injury (LDH release), and it was ouabain resistant (suggesting decreased ATP production, not increased consumption). SMase also depressed ATP without inducing cell death. After 45 minutes, CE and CO each caused marked cytotoxicity (up to 70% LDH release). However, different injury mechanisms were operative since (1) CE, but not CO, toxicity significantly altered cell phospholipid profiles, and (2) 2 mmol/L glycine completely blocked CE- but not CO-mediated cell death. Antioxidants also failed to attenuate CO cytotoxicity. Disturbing cholesterol/microdomains with a sublytic CE dose dramatically increased tubule susceptibility to Fe-mediated oxidative stress and Ca2+ overload, but not PLA2-mediated damage.

CONCLUSION

Intact plasma membrane cholesterol/microdomains are critical for maintaining cell viability both under basal conditions and during superimposed attack. When perturbed, complex injury pathways can be impacted, with potential implications for both the induction of acute tubular damage and the emergence of the postinjury cytoresistance state.

Prediction of early renal graft function by the measurement of donor urinary glutathione S-transferases

BACKGROUND

We have investigated the possibility of urinary alpha- and pi class glutathione S-transferases (GST-a; GST-pi) serving as a valuable parameter to predict early graft function after transplantation.

METHOD

Urinary GST concentrations of 61 donors (DON) and recipients (REC) were analyzed at preoperative, intraoperative, and postoperative periods. We grouped recipients according to the early postoperative graft recovery days.

RESULTS

The donor graft function, represented by the donor urinary GST concentration (GST-pi:17,1+/-12 microg/l mmol creatinine (crea); GST-a:14,3+/-10 microg/mmol crea), sustained a loss in comparison to the healthy controls (GST-a; pi< or =1 microg/mmol crea). According to statistical analysis, the donor GST-pi level showed a strong correlation with graft recovery days-pi (r = 0.84; P<0.001). The early graft function cannot be predicted by means of cold ischemia time (22.8+/-3.4 hr), nor handling time (42.4+/-11.1 min), nor even the intraoperative enzyme concentrations. The GST-pi cut off level (12.55 microg/mmol crea) might predict the possible posttransplant graft dysfunction. The discriminative analysis showed that using only DON GST-pi alone could discriminate well between the groups among all grafts in 68%.

CONCLUSION

Prognosis is poorer if the donor GST-pi concentration is above 12.55 microg/mmol crea. On the basis of the determination of GST-pi concentration in the donor urine, we can predict graft viability before the surgical procedure with a reliability of 68%.

Tubulointerstitial lesions in IgA nephropathy and localization of hepatocyte growth factor

To investigate the relationship between localization of hepatocyte growth factor (HGF) and tubulointerstitial lesions (TILs) in the cortical area of renal biopsy specimens, a clinicopathological study was performed in 55 patients with IgA nephropathy. HGF was detected by an enzyme-antibody method and TILs were assessed semiquantitatively by light microscopy. HGF was observed mainly on epithelial cells in the tubules, but not in the glomeruli. Fourteen patients had biopsies that were positive for HGF. There was a correlation between HGF positivity and histological damage, the TIL grade, and several clinical parameters determined at biopsy. Thus, HGF is related to TILs in IgA nephropathy and may be a factor in the exacerbation of this disease.

Contribution of gamma glutamyl transpeptidase to oxidative damage of ischemic rat kidney

BACKGROUND

A variety of mechanisms have been considered in the pathogenesis of the cell damage occurring in the kidney that is undergoing transient ischemia. However, little information is available about the role of oxidative stress in building up the tissue injury in the hypoxic organ during short-term ischemia.

METHODS

After a standard brief period (25 min) of unilateral kidney ischemia in rats, pretreated or not with acivicin (60 micromol/L/kg i.v.), tissue samples from both ischemic and not ischemic kidneys were obtained to measure malondialdehyde (MDA) and glutathione (GSH) content, gamma glutamyl transpeptidase (GGT) activity by spectrophotometry, localization and intensity of enzyme activity, and tissue damage by histochemistry.

RESULTS

GGT activity was found to be increased in both cortical and medullar zones of the ischemic kidneys, where the GSH level was only slightly decreased and the MDA level, in contrast, was markedly increased; in parallel, the cytosolic volume of the proximal tubular (PT) cells showed a significant increment. The animal pretreatment with acivicin, a specific inhibitor of GGT, besides preventing the up-regulation of the enzyme during ischemia, afforded good protection against the observed changes of MDA and GSH tissue levels, as well as of tubular cell volume.

CONCLUSIONS

Ex vivo data supporting a net pro-oxidant effect of up-regulated GGT during short-term ischemia of rat kidney have been obtained. The enzyme stimulation appears to contribute to the renal morphological damage exerted by a brief hypoxic condition at the level of PT cells. The actual impact on kidney function by GGT-dependent oxidative damage during transient ischemia and the potential protective action of GGT inhibitors require subsequent investigation.

Ischemic acute renal failure induces differential expression of small heat shock proteins

AlphaB-crystallin and heat shock protein (hsp) 25 are structurally and functionally related small stress proteins induced by a variety of insults, including heat and ischemia. Cytoprotection by these two hsp is thought to result from molecular chaperoning and/or cytoskeletal stabilization. Because renal ischemia is characterized by disruption of the renal tubular cell actin cytoskeleton, this study was conducted to determine the localization and quantify the expression and phosphorylation of both hsp in renal cortex, isolated glomeruli, outer medulla, and inner medulla of rats after bilateral renal ischemia. Sham-operated kidneys had similarly small amounts of hsp25 and alphaB-crystallin in cortex and glomeruli, with substantially greater amounts of alphaB-crystallin versus hsp25 in outer and inner medulla. Ischemia resulted in significantly increased hsp25 (and hsp70i) but variable alphaB-crystallin levels in cortex and outer medulla, and progressively decreased glomerular hsp25 phosphorylation. In sham-operated kidneys, hsp25 localized to glomeruli, vessels, and collecting ducts, with alphaB-crystallin primarily in medullary thin limbs and collecting ducts. After ischemia, hsp25 accumulated in proximal tubules in cortex and outer medulla, while alphaB-crystallin labeling became nonhomogeneous in outer medulla, and increased in Bowman's capsule. It is concluded that: (1) There is striking differential expression of hsp25 and alphaB-crystallin in various renal compartments; and (2) Renal ischemia results in differential accumulation of hsp25 and alphaB-crystallin, with hsp25 part of a generalized stress response in renal proximal tubular cells, which may play a role in recovery from ischemia-induced actin filament disruption.

Acute renal failure. II. Experimental models of acute renal failure: imperfect but indispensable

Acute renal failure (ARF) due to ischemic or toxic renal injury, a clinical syndrome traditionally referred to as acute tubular necrosis (ATN), is a common disease with a high overall mortality of approximately 50%. Little progress has been made since the advent of dialysis more than 30 years ago in improving this outcome. During this same period, a considerable amount of basic research has been devoted to elucidating the pathophysiology of ATN. The ultimate goal of this research is to facilitate the development of therapeutic interventions that either prevent ARF, ameliorate the severity of tubular injury following an acute ischemic or toxic renal insult, or accelerate the recovery of established ATN. This research endeavor has been highly successful in elucidating many vascular and tubular abnormalities that are likely to be involved in ischemic and toxic ARF. This information has led to impressive advances in the development of a number of different pharmacological interventions that are highly effective in ameliorating the renal dysfunction in animal models of ARF. Although these developments are exciting and promising, enthusiasm of investigators involved in this endeavor has been tempered somewhat by the results of a few recent clinical studies of patients with ATN. These trials, designed to examine the efficacy in humans of some of the interventions effective in animal models of ARF, have resulted in little or no benefit. This is therefore an important time to reevaluate the approaches we have taken over the past three to four decades to develop new and effective treatments for ATN in humans. The major goals of this review are 1) to evaluate the relevance and utility of the experimental models currently available to study ischemic and toxic renal injury, 2) to suggest novel experimental approaches and models that have the potential to provide advantages over methods currently available, 3) to discuss ways of integrating results obtained from different experimental models of acute renal injury and of evaluating the relevance of these findings to ATN in humans, and 4) to discuss the difficulties inherent in clinical studies of ATN and to suggest how studies should be best designed to overcome these problems.

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

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

Plasma membrane phospholipid integrity and orientation during hypoxic and toxic proximal tubular attack

BACKGROUND

Acute cell injury can activate intracellular phospholipase A2 (PLA2) and can inhibit plasma membrane aminophospholipid translocase(s). The latter maintains inner/outer plasma membrane phospholipid (PL) asymmetry. The mechanistic importance of PLA2-mediated PL breakdown and possible PL redistribution ("flip flop") to lethal tubule injury has not been well defined. This study was performed to help clarify these issues.

METHODS

Proximal tubule segments (PTS) from normal CD-1 mice were subjected to either 30 minutes of hypoxia, Ca2+ ionophore (50 microM A23187), or oxidant attack (50 microM Fe). Lethal cell injury [the percentage of lactate dehydrogenase (LDH) release], plasma membrane PL expression [two-dimensional thin layer chromatography (TLC)], and free fatty acid (FFA) levels were then assessed. "Flip flop" was gauged by preferential decrements in phosphatidylserine (PS) versus phosphatidylcholine (PC; PS/PC ratios) in response to extracellular (Naja) PLA2 exposure.

RESULTS

Hypoxia induced approximately 60% LDH release, but no PL losses were observed. FFA increments suggested, at most 3% or less PL hydrolysis. Naja PLA2 reduced PLs in hypoxic tubules, but paradoxically, mild cytoprotection resulted. In contrast to hypoxia, Ca2+ ionophore and Fe each induced significant PL losses (6 to 15%) despite minimal FFA accumulation or cell death (26 to 27% LDH release). Arachidonic acid markedly inhibited PLA2 activity, potentially explaining an inverse correlation (r = -0.91) between tubule FFA accumulation and PL decrements. No evidence for plasma membrane "flip flop" was observed. In vivo ischemia reperfusion and oxidant injury (myohemoglobinuria) induced 0 and 24% cortical PL depletion, respectively, validating these in vitro data.

CONCLUSIONS

(a) Plasma membrane PLs are well preserved during acute hypoxic/ischemic injury, possibly because FFA accumulation (caused by mitochondrial inhibition) creates a negative feedback loop, inhibiting intracellular PLA2. (b) Exogenous PLA2 induces PL losses during hypoxia, but decreased cell injury can result. Together these findings suggest that PL loss may not be essential to hypoxic cell death. (c) Oxidant/Ca2+ overload injury induces early PL losses, perhaps facilitated by ongoing mitochondrial FFA metabolism, and (d) membrane "flip flop" does not appear to be an immediate mediator of acute necrotic tubular cell death.

Hepatocyte growth factor induces tubulogenesis of primary renal proximal tubular epithelial cells

Hepatocyte growth factor (HGF)-induced tubulogenesis has been demonstrated with renal epithelial cell lines grown in collagen gels but not with primary cultured renal proximal tubular epithelial cells (RPTEs). We show that HGF selectively induces proliferation and branching morphogenesis of primary cultured rat RPTEs. Additional growth factors including fibroblast growth factor (FGF)-1, epidermal growth factor (EGF), FGF-7, or insulin-like growth factor-1 (IGF-1) did not selectively induce tubulogenesis. However, when administered in combination, these factors initiated branching morphogenesis comparable to HGF alone and greatly augmented HGF-induced proliferation and branching. Microscopic analysis revealed that branching RPTEs were undergoing tubulogenesis and formed a polarized epithelium. TGF-beta1 blocked HGF- or growth factor cocktail (GFC; HGF, FGF-1, EGF, IGF-1)-induced proliferation and branching morphogenesis. Adding TGF-beta1 after GFC-induced tubulogenesis had occurred caused a progressive regression of the tubular structures, a response associated with an increase in apoptosis of the RPTEs. Primary cultured RPTEs are capable of undergoing HGF-induced tubulogenesis. Unlike cell lines, combinations of growth factors differentially augment the response.

Role of fatty acid beta-oxidation and calcium-independent phospholipase A2 in ischemic acute renal failure

Membrane phospholipolysis during ischemic cell injury is accompanied by the activation of a novel calcium-independent phospholipase A2 in the proximal tubule. Long-chain fatty acid metabolic products produced by phospholipase A2 activation accumulate during ischemia as a result of the inhibition of fatty acid beta-oxidation on the mitochondria and peroxisomes. Altogether, lysophospholipids, long-chain acyl carnitines, and long-chain acyl coenzyme A inhibit proximal tubule Na+K(+)-ATPase. Metabolic regulation of the gene expression of fatty acid beta-oxidation enzymes during ischemic acute renal failure may represent a novel therapeutic maneuver to enhance the recovery of kidney function during ischemia.

Transmembrane proteins in the tight junction barrier

Three types of transmembrane proteins have been identified within the tight junction, but it remains to be determined how they provide the molecular basis for regulating the paracellular permeability for water, solutes, and immune cells. Several of these proteins localize specifically within the continuous cell-to-cell contacts of the tight junction. One of these, occludin, is a cell adhesion molecule that has been demonstrated to influence ion and solute permeability. The claudins are a family of four-membrane spanning proteins; unexpectedly, other members of this family have already been characterized without recognizing their relationship to tight junctions. Junction adhesion molecule, the most recently identified tight junction component, is a member of the Ig superfamily and influences the paracellular transmigration of immune cells. A plaque of cytoplasmic proteins under the junction may be responsible for scaffolding the transmembrane proteins, creating a link to the perijunctional actin cytoskeleton and transducing regulatory signals that control the paracellular barrier.

Rho controls actin cytoskeletal assembly in renal epithelial cells during ATP depletion and recovery

Actin cytoskeletal disruption is a hallmark of ischemic injury and ATP depletion in a number of cell types, including renal epithelial cells. We manipulated Rho GTPase signaling by transfection and microinjection in LLC-PK proximal tubule epithelial cells and observed actin cytoskeletal organization following ATP depletion or recovery by confocal microscopy and quantitative image analysis. ATP depletion resulted in disruption of stress fibers, cortical F-actin, and apical actin bundles. Constitutively active RhoV14 prevented disruption of stress fibers and cortical F-actin during ATP depletion and enhanced the rate of stress fiber reassembly during recovery. Conversely, the Rho inhibitor C3 or dominant negative RhoN19 prevented recovery of F-actin assemblies upon repletion. Actin bundles in the apical microvilli and cytosolic F-actin were not affected by Rho signaling. Assembly of vinculin and paxillin into focal adhesions was disrupted by ATP depletion, and constitutively active RhoV14, although protecting stress fibers from disassembly, did not prevent dispersion of vinculin and paxillin, resulting in uncoupling of stress fiber and focal adhesion assembly. We propose that ATP depletion causes Rho inactivation during ischemia and that recovery of normal cellular architecture and function requires Rho.

The effects of thromboxane synthase inhibition on reperfusion injury and endothelin-1,2 levels in allograft kidney transplantation in rats

Thromboxane A2 is a proaggregative vasoconstrictor that is synthesized and released in reperfusion injury. We aimed to investigate the effects of thromboxane synthase inhibitor, UK 38485, on endothelin-1,2 (ET) response of the renal endothelium and lipid peroxidation and protein oxidation in the early period of kidney transplantation. Four groups (n=8 in group IV and n=10 in the others) [corrected] of Sprague-Dawley rats were designed as Group I (sham nephrectomy), Group II (autotransplantation), Group III (allotransplantation) and Group IV (allotransplantation group in which the allografts were perfused with UK 38485. All subjects underwent right nephrectomy after transplantation. The grafts were flushed with 4 ml of ice-cold Ringer's lactate and in Group IV 10 microg of UK 38485 was added into the solution for each kidney. In allotransplantation groups, the kidneys were harvested from allogeneic white Wistar albino rats. The kidney grafts were allowed 120 min of reperfusion after 40 min of cold ischemic period. ET-1,2 plasma concentrations in the renal vein blood and diene conjugates (DC), hydroxyalkanals (HAA), hydroxyalkenals (HAE) and malondialdehyde (MDA) levels as the products of lipid peroxidation, protein carbonyls and protein sulfhydryls as the indicators of protein oxidation were analyzed in kidney tissue. Plasma ET-1,2 concentrations increased significantly in Group II and Group III (P<0.01) when compared to Group I but decreased in Group IV in comparison with Group III (P<0.05). DC, HAA, HAE and MDA levels increased in Groups II and III (P<0.001). Significant protein oxidation occurred only in Group III (P<0.01). Perfusion of the allografts with UK 38485 prevented lipid peroxidation and protein oxidation in Group IV. Histopathological changes were mild in the last group. We concluded that, in kidney transplantation, local administration of UK 38485 has cytopreservative effects on the allografts and this effect can be related to ET-1,2 concentrations.

Ablating the ischemia-reperfusion injury in non-heart-beating donor kidneys

BACKGROUND

The objective of this study was to determine if allopurinol (AL) and/or trifluoperazine (TFP) added to the Belzer machine preservation solution (MPS) improves the function of non-heart-beating donor (NHBD) canine kidneys.

METHODS

Anesthetized canines underwent bilateral dissection of the renal vessels, obtaining baseline flow. After removing one kidney (heart-beating donor [HBD]), the dog was exsanguinated. After remaining in situ for 120 min (30-min warm ischemia time, 90-min cold ischemia time), the second kidney was removed (NHBD), flushed, biopsied, and weighed. The kidneys were machine-perfused separately for 20 hr, and pressure, flow, and resistance were measured serially. The kidneys were randomly assigned to a perfusate group (G): G1=MPS, G2=MPS+TFP, G3=MPS+AL, and G4=MPS+TFP+AL. Kidneys were implanted separately into a single recipient dog. Flow, resistance, and urine output were measured serially for 4 hr. Blood and urine samples and kidney biopsies were then obtained. All measurements were standardized to 100 g of kidney weight.

RESULTS

HBD kidneys functioned better than NHBD kidneys in all groups, as expected. Although perfusate G1 was the most effective solution for HBD kidneys, the TFP additive (perfusate G2) more effectively reversed the vasospastic effects of ischemia/reperfusion for NHBD than the MPS solution (G1) with or without other additives. In HBD kidneys, the addition of AL resulted in the best creatinine clearance; however, AL was less effective than MPS alone in NHBD kidneys. TFP+AL together were completely ineffective in preserving renal function, regardless of whether the kidneys were from HBD or NHBD.

CONCLUSIONS

MPS+TFP more effectively protected renal function against reperfusion injury in the NHBD than MPS alone, AL, or AL+TFP. AL exerts a salutary effect on creatinine clearance in HBD but not in the NHBD. The TFP and AL combination should not be used together with the MPS in machine preservation of kidneys.

Isoflurane alters proximal tubular cell susceptibility to toxic and hypoxic forms of attack

BACKGROUND

Fluorinated anesthetics can profoundly alter plasma membrane structure and function, potentially impacting cell injury responses. Because major surgery often precipitates acute renal failure, this study assessed whether the most commonly used fluorinated anesthetic, isoflurane, alters tubular cell responses to toxic and hypoxic attack.

METHODS

Mouse proximal tubule segments were incubated under control conditions or with a clinically relevant isoflurane dose. Cell viability (lactate dehydrogenase release), deacylation (fatty acid, such as C20:4 levels), and adenosine triphosphate (ATP) concentrations were assessed under one or more of the following conditions: (a) exogenous phospholipase A2 (PLA2) or C20:4 addition, (b) Ca2+ overload (A23187 ionophore), (c) increased metabolic work (Na ionophore), and (d) hypoxia- or antimycin A-induced attack. Isoflurane's effect on NBD phosphatidylserine uptake (an index of plasma membrane aminophospholipid translocase activity) was also assessed.

RESULTS

Isoflurane alone caused trivial deacylation and no lactate dehydrogenase release. However, it strikingly sensitized to both PLA2- and A23187-induced deacylation and cell death. Isoflurane also exacerbated C20:4's direct membrane lytic effect. Under conditions of mild ATP depletion (Na ionophore-induced increased ATP consumption; PLA2-induced mitochondrial suppression), isoflurane provoked moderate/severe ATP reductions and cell death. Conversely, under conditions of maximal ATP depletion (hypoxia, antimycin), isoflurane conferred a modest cytoprotective effect. Isoflurane blocked aminophospholipid translocase activity, which normally maintains plasma membrane lipid asymmetry (that is, preventing its "flip flop").

CONCLUSIONS

Isoflurane profoundly and differentially affects tubular cell responses to toxic and hypoxic attack. Direct drug-induced alterations in lipid trafficking/plasma membrane orientation and in cell energy production are likely involved. Although the in vivo relevance of these findings remains unknown, they have potential implications for intraoperative renal tubular cell structure/function and how cells may respond to superimposed attack.

Protection from renal ischemia-reperfusion injury by the 2-methylaminochroman U83836E

BACKGROUND

In a prior study the 21-aminosteroid (lazaroid) U74389F provided in vivo protection from oxidative stress when used as a preventive therapy in ischemia-reperfusion injury in the kidney. As the cell membrane is the principal site for lipoperoxidation, in the current study the very lipophilic 2-methylaminochroman U83836E, a recently developed lazaroid, was administered to rats at 3 mg/kg before renal ischemia-reperfusion. In addition to the biochemical parameters, the renal function and the histological appearance were carefully evaluated.

METHODS

Glutathione, adenine nucleotides and lipid peroxidation products were determined in kidneys reperfused for 2 and 24 hours after 90 minutes of ischemia. Renal function was assessed by plasma creatinine, and renal injury by histological examination.

RESULTS

Reperfusion-induced glutathione oxidation, expressed as an oxidized-to-total glutathione ratio, was significantly attenuated both after 2 and 24 hours of reperfusion by treatment with U83836E. Adenosine triphosphate (ATP) was still significantly depleted after 24 hours in the control group, while at the same time treated animals had already recovered to baseline values. Lipid peroxidation products were significantly lower in lazaroid-groups both after 2 and 24 hours of reperfusion. Renal function after 24 hours of reperfusion was notably better in the treated rats. Histological examination confirmed the protective action of the drug. After 24 hours the control group showed large areas of parenchymal hemorrhage and necrosis with dilated tubules and blood vessel thrombosis, while treated animals showed small necrotic areas with a background of mild interstitial inflammatory cells.

CONCLUSIONS

Our results suggest that there is a protective effect of U83836E in ischemia-reperfusion injury, in that tissue damage due to oxidative stress is reduced, thus ameliorating renal function impairment.

Difference in H2O2 toxicity between intact renal tubules and cultured proximal tubular cells

The present study was undertaken to examine the response to H2O2 and t-butylhydroperoxide (t-BHP) in various in vitro model systems of renal proximal tubules: rabbit renal cortical slices, freshly isolated rabbit proximal tubules, rabbit primary cultured proximal tubular cells, and opossum kidney (OK) cells. t-BHP increased lactate dehydrogenase release and lipid peroxidation in a concentration-dependent manner over the concentration range of 0.2 to 3 mM in cortical slices, whereas H2O2 caused a similar concentration-dependent increase in both parameters at 5-100 mM. The sensitivity of isolated tubules to both peroxides was similar to that of cortical slices. In primary cultured cells and OK cells, however, the cytotoxicity of H2O2 was identical to that of t-BHP. The cytotoxicity of t-BHP was not different among all the systems examined. The specific activity of catalase in cortical slices was similar to that of isolated tubules, but it was much higher than that of primary cultured cells or opossum kidney cells. Glutathione (GSH) peroxidase activity was not different among all the systems examined. The expression of catalase mRNA in cortical slices and isolated tubules was higher than that in primary cultured cells, whereas those of superoxide dismutase, glutathione peroxidase, or beta-actin were not different among the systems. These results indicate that intact proximal tubules are more resistant to H2O2 than are cultured proximal tubular cells, and the resistance is due to a higher specific activity of catalase resulting from the increased expression of its mRNA.

Impairment of cellular redox status and membrane protein activities in kidneys from rats with ischemic acute renal failure

Cellular redox status and membrane protein activities were analyzed in kidneys from rats with ischemic acute renal failure (ARF). ARF was induced by clamping the left renal artery for 50 min. A parallel group of control animals was processed. In the ischemic group urea plasma levels were statistically increased as compared with the control group. Studies employing whole kidney homogenates revealed that ischemia produces an increment in lipid peroxidation levels and a reduction in glutathione concentration and in superoxide dismutase and glutathione peroxidase activities. Since lipid peroxidation may alter the function of membrane proteins we determined succinate cytochrome c reductase (SuccR), sodium-potassium ATPase (Na-K-ATPase), glucose-6-phosphatase (G-6-Pase) and alkaline phosphatase (ALP) activities in whole renal homogenates. Only G-6-Pase and ALP activities were modified by ischemia. Since ALP is a brush border membrane (BBM) enzyme and BBM is one of the main target structures in ARF, we assessed some parameters of BBM functionality. ALP, gamma-glutamyl transferase (gamma-GT) and 5'-nucleotidase (5'-NT) showed diminished activities in BBM from ischemic kidneys. Ischemia also modified the Vmax of paraaminohippuric acid (PAH) uptake without altering Km. An increment of lipid peroxidation and membrane fluidity in BBM was observed after the treatment. Total membrane proteins and protein recoveries in BBM were similar in both experimental groups. Sialic acid and sulfhydryl levels were similar in BBM from ischemic kidney and control ones. In summary, ARF induced by renal artery clamping for 50 min takes place with a significant increase in urea plasma levels. A decrease in the antioxidant defense system is detected. This induces lipid peroxidation in whole renal tissue, which may justify the diminished activities of some membrane enzymes such as G-6-Pase and ALP. A specific analysis of BBM function reveals a significant increment of lipid peroxidation which may be the cause of an increased membrane fluidity. This latter parameter might be, at least in part, responsible for the damaged function of apical ALP, 5'-NT, gamma-GT and PAH carrier.

Clusterin protects against oxidative stress in vitro through aggregative and nonaggregative properties

Perturbations of cell interactions, an early event in acute renal injury, have important pathophysiologic consequences. We hypothesized that promotion of cell interactions protects cells from injury. To test this hypothesis, a single cell suspension of LLC-PK1 cells (porcine proximal tubular cell line) treated with albumin (control) was compared to cells aggregated with fibrinogen or purified human clusterin (aggregation graded 0 to 4). Following aggregation, the cells were injured with 1.5 mM hydrogen peroxide (H2O2) for three hours. Cell aggregation induced by clusterin but not fibrinogen protected against oxidant injury by H2O2. Complete abrogation of cytotoxicity occurred at a clusterin concentration of 2.5 micrograms/ml, which resulted in an aggregation score of 1. In the absence of aggregation, clusterin at concentrations of 20 and 50 micrograms/ml, but not lower doses, partially protected against injury induced by H2O2. Cell aggregation induced by both clusterin and fibrinogen partially protected against endogenously generated oxidant stress induced by incubating LLC-PK1 cells with aminotriazole and 1-chloro-2,4-dinitrobenzene (CDNB). In conclusion, clusterin protects against models of oxidant stress in vitro, whether generated by exogenously administered hydrogen peroxide, or from endogenously produced peroxide, and such protective effects can accrue from aggregative and nonaggregative properties of clusterin.

Identification of gene family of caspases in rat kidney and altered expression in ischemia-reperfusion injury

In the present study, we demonstrate that rat kidney contains caspase activity that was markedly inhibited by specific peptide inhibitors of caspases but not by inhibitors of Ser, Cys, Asp, or metalloproteinases. Using primers based on the nucleotide sequence of known members of Ced-3/interleukin-1 beta-converting enzyme (ICE) family from human origin, we have identified by reverse-transcription (RT) polymerase chain reaction (PCR) analyses that rat kidney transcribes the genes for caspase-1 (ICE), caspase-2 (Nedd2), caspase-3 (CPP32), and caspase-6 (Mch2). RT-PCR products, when subcloned and sequenced, provided full-length cDNAs for ICE (1,209 bp) and CPP32 (786 bp) and partial cDNA products for Mch2 (561 bp) and Nedd2 (811 bp). The sequence analysis of the caspase cDNAs showed conserved catalytic site QACRG as well as Asp cleavage site. Rat kidneys subjected to ischemia-reperfusion injury revealed differential expression of caspases with marked increase in CPP32 and ICE mRNA and proteins during reperfusion, transient increase in Nedd2 mRNA and proteins during ischemia and the early period of reperfusion, and little change in Mch2 expression during the ischemia or reperfusion period. The altered expression suggests that caspases may act in concert in a cascade and may play an important role in ischemic acute renal failure.

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.

Low environmental pH is responsible for the induction of nitric-oxide synthase in macrophages. Evidence for involvement of nuclear factor-kappaB activation

Stimulation of macrophages with endotoxin and/or cytokines is responsible for the expression of the inducible isoform of nitric oxide synthase (iNOS). Because macrophages are exposed to low pH within the microenvironment of inflammatory lesions, the potential role of acidic pH as an additional regulator of iNOS was investigated. Substitution of the culture medium of rat peritoneal macrophages at pH 7.4 with medium at pH 7.0 up-regulated iNOS activity, as reflected by a 2.5-fold increase in nitrite accumulation. The increase in iNOS activity was associated with a similar increase in iNOS mRNA expression that reflected an increase in iNOS mRNA synthesis rather than stability. Low environmental pH-induced iNOS gene transcription involved the activation of nuclear factor-kappaB (NF-kappaB) transcription factor since exposure of macrophages to low environmental pH both increased NF-kappaB binding activity in the nucleus and enhanced NF-kappaB-driven reporter gene expression. In addition, treatment of macrophages with pyrrolidine dithiocarbamate or n-acetyl-leucinyl-leucinyl-norleucinal, two drugs preventing NF-kappaB translocation to the nucleus, canceled low pH-induced nitrite accumulation. The overall mechanism required the synthesis of tumor necrosis factor alpha (TNFalpha). Indeed, 1) elevated TNFalpha bioactivity was observed in the medium of macrophages exposed to pH 7.0, and 2) incubation of macrophages with a neutralizing anti-TNFalpha antibody impaired both NF-kappaB activation and nitrite accumulation in response to acid challenge. In summary, exposure of macrophages to acidic microenvironment in inflammatory lesions leads to the up-regulation of iNOS activity through the activation of NF-kappaB.

Graded ATP depletion can cause necrosis or apoptosis of cultured mouse proximal tubular cells

The mechanisms of cell death induced by ATP depletion were studied in primary cultures of mouse proximal tubular (MPT) cells. Graded ATP depletion, ranging in severity from approximately 2 to 70% of control levels, was induced by incubating cells with either antimycin or 2-deoxyglucose, with varying concentrations of dextrose. We found that cells subjected to ATP depletion below approximately 15% of control died uniformly of necrosis. In contrast, cells subjected to ATP depletion between approximately 25 and 70% of control all died by apoptosis. The rapidity of cell death was proportional to the severity of reduction of cell ATP content and was independent of the mechanism of cell death. Renal growth factors, epidermal growth factor (EGF) and high-dose insulin, did not ameliorate apoptotic cell death induced by ATP depletion. We conclude that ATP depletion can cause either necrosis or apoptosis in MPT cells. Furthermore, we have identified a narrow range of ATP depletion (approximately 15 to 25% of control) representing a threshold that determines whether cells die by necrosis or apoptosis.

Purinergic receptors mediate cell proliferation and enhanced recovery from renal ischemia by adenosine triphosphate

Kidney dysfunction after ischemia can be improved by either limiting the initial injury or by enhancing the subsequent proliferative repair process. Adenosine triphosphate (ATP) favorably affects kidney function when it is given shortly after ischemia. We tested whether ATP promotes the proliferative repair response. Rats were subjected to occlusion of the left renal artery for 40 minutes and received an infusion of ATP, 12.5 micromol intravenously over 30 minutes, beginning at reperfusion. Control animals received saline solution or the hydroxyl radical scavenger dimethylthiourea (DMTU). Despite comparable functional protection by DMTU and ATP, only ATP specifically increased DNA synthesis (renal incorporation of tritiated thymidine) to an extent greater than that produced by ischemia alone. In other animals, ribonucleic acid was extracted from kidneys for Northern analysis. Expression of the proto-oncogenes c-fos and c-jun was enhanced in ATP-treated animals as compared with controls. Expression of a histone protein gene (H2b) and thymidine kinase was increased by ischemia but was not additionally affected by ATP. In vitro studies of primary cultures of renal proximal tubule epithelial cells confirmed the ability of ATP to stimulate cellular proliferation as a consequence of stimulation of purinergic P2 receptors, possibly of the P2x subclass. In summary, ATP given after ischemia increased new DNA synthesis and augmented expression of genes critical to cellular proliferation. These beneficial effects were not merely a consequence of limiting initial cellular damage, and they suggest a novel mechanism of action for ATP and other purinergic receptor agonists in renal ischemia.

Heat-shock protein 25 induction and redistribution during actin reorganization after renal ischemia

The small heat-shock proteins appear to have a regulatory role in actin dynamics. Since cytoskeletal disruption is integral to ischemic renal injury, we evaluated expression and intracellular distribution of heat-shock protein 25 (HSP-25) in rat renal cortex after 45 min of renal ischemia. HSP-25 was constitutively expressed and induced by ischemia with peak levels reached by 6 h reflow. Ischemia caused a shift of HSP-25 from the detergent-soluble into the insoluble cytoskeletal fraction. By 2 h reflow, the majority of HSP-25 had redistributed into the soluble fraction. HSP-25 was predominantly localized in a subapical distribution in control proximal tubules, a pattern intermediate between deoxyribonuclease (DNase)-reactive and filamentous actin. After ischemia, HSP-25 dispersed through the cytoplasm with small punctate accumulations similar to DNase-reactive actin. During later reflow, all three proteins were found in coarse intracytoplasmic accumulations; however, HSP-25 and DNase-reactive actin were in separate accumulations. HSP-25 and microfilamentous actin staining returned to the subapical domain. Thus the temporal and spatial patterns of HSP-25 induction and distribution suggest specific interactions between HSP-25 and actin during the early postischemic reorganization of the cytoskeleton. HSP-25 may have additional roles distinct from actin dynamics later in the course of postischemic recovery.