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Biomedical subjects

R A Zager

Publications and source records attributed to R A Zager.

At least 55 records · Page 3Linked to original sources
PubMed1996

Phospholipase A2: a potentially important determinant of adenosine triphosphate levels during hypoxic-reoxygenation tubular injury.

During the course of O2 deprivation-induced proximal tubular injury, profound alterations in ATP homeostasis exist. This study sought to characterize direct cellular determinants of these abnormalities further. Mouse proximal tubular segments (PTS) were isolated and their adenine nucleotide profiles were determined during hypoxic-reoxygenation injury. The extent of oxidant stress, Ca2+ overload, cytoskeletal disruption, and phospholipase activity were experimentally manipulated by H2O2, Ca2+ ionophore, cytochalasin D, or PLA2 addition, respectively. Hypoxia induced the expected deterioration in adenylate profiles, and a persistent defect in ATP homeostasis was observed during reoxygenation (decreased ATP/ADP ratios and absolute ATP content). H2O2, Ca2+ ionophore, and cytochalasin D had no significant impact on adenylate profiles. However, doses of PLA2 that had no overt effect on normal tubules caused 50 to 75% reductions in both hypoxic and reoxygenation ATP/ADP ratios and absolute ATP content. This effect was completely reproduced by the addition of arachidonic acid (C20:4). No other test fatty acid (C16:0, C18:1, C18:3) reproduced this result. Despite its profound negative impact on hypoxic/reoxygenation ATP concentrations, PLA2 and C20:4 each decreased lethal cell injury (lactate dehydrogenase release), as previously reported. The reductions in ATP and lethal cell injury were not mechanistically linked, because C18:1 and C18:3 reproduced the protective action of C20:4 without altering adenine nucleotide profiles. Ouabain, mannitol, or plasma membrane fatty acid "scavenger" therapy (albumin) did not improve the posthypoxic/PLA2-induced depressions in ATP. The addition of C20:4 caused a modest decrease in posthypoxic tubule oxygen consumption, compared to controls. It was concluded that: (1) PLA2 can be a major determinant of ATP concentrations during both hypoxic and reoxygenation tubular injury; (2) this action is mediated via C20:4 release; (3) a primary defect in mitochondrial ATP production, rather than increased ATP consumption, is likely to be responsible for this action.

Adenosine Diphosphate↗
PubMed1996

Phospholipase A2-induced cytoprotection of proximal tubules: potential determinants and specificity for ATP depletion-mediated injury.

Addition of phospholipase A2 (PLA2) to isolated proximal tubular segments (PTS) has previously been shown to decrease hypoxic cell death without altering ATP concentrations. The study presented here was undertaken to identify determinant(s) of this protection, and to define the spectrum of injuries against which it can operate. PTS were extracted from mouse kidneys and subjected to diverse forms of injury (hypoxia/reoxygenation, antimycin A, Ca2+ ionophore, amphotericin B, FeSO4, and myohemoglobin). In subtoxic doses, addition of PLA2 significantly reduced hypoxic- and antimycin A-induced injury (percentage of lactate dehydrogenase release); however, a dose-dependent exacerbation of all other forms of injury resulted. The ability of PLA2 to mitigate hypoxic injury remained intact despite the inhibition of Na,K-ATPase (ouabain) or the inducement of cytoskeletal disruption (cytochalasin D). However, it was negated by minimally toxic amphotericin B or Ca2+ ionophore doses, indicating its dependence on preserved ionic gradients. Nevertheless, neither lowering/removing buffer Ca2+ or NaCl concentrations, nor hypertonic mannitol addition reproduced the cytoprotective effect of PLA2. PLA2 induced synergistic deacylation in hypoxic tubules, suggesting that unsaturated fatty-acid accumulation might mediate its cytoprotective effect. The fact that the addition of exogenous arachidonate, but not palmitate, to tubules protected against hypoxia, but worsened nonhypoxic forms of injury, supported this hypothesis. Since arachidonate might induce "feedback" inhibition of intracellular PLA2, the ability of an intracellular phospholipase inhibitor (ONO-RS-082; Biomol, Plymouth, PA) to blunt hypoxic damage was tested. This agent fully reproduced the cytoprotective effect of PLA2. It was concluded that: (1) PLA2-induced cytoprotection is relatively specific for ATP depletion injury; (2) it is dependent on, but not explained by, maintenance of NaCl and Ca2+ gradients; (3) it does not require Na,K-ATPase activity or cytoskeletal integrity for its expression; and (4) extracellular PLA2, via arachidonate release, may cause feedback inhibition of intracellular PLA2, thereby protecting critical intracellular targets from attack.

Adenosine Triphosphate↗
PubMed1995

Sphingosine: a mediator of acute renal tubular injury and subsequent cytoresistance.

The goal of this study was to determine whether sphingosine and ceramide, second messengers derived from sphingolipid breakdown, alter kidney proximal tubular cell viability and their adaptive responses to further damage. Adult human kidney proximal tubular (HK-2) cells were cultured for 0-20 hr in the presence or absence of sphingosine, sphingosine metabolites (sphingosine 1-phosphate, dimethylsphingosine), or C2, C8, or C16 ceramide. Acute cell injury was assessed by vital dye exclusion and tetrazolium dye transport. Their subsequent impact on superimposed ATP depletion/Ca2+ ionophore-induced damage was also assessed. Sphingosine (> or = 10 microM), sphingosine 1-phosphate, dimethylsphingosine, and selected ceramides (C2 and C8, but not C16) each induced rapid, dose-dependent cytotoxicity. This occurred in the absence of DNA laddering or morphologic changes of apoptosis, suggesting a necrotic form of cell death. Prolonged exposure (20 hr) to subtoxic sphingosine doses (< or = 7.5 microM) induced substantial cytoresistance to superimposed ATP depletion/Ca2+ ionophore-mediated damage. Conversely, neither short-term sphingosine treatment (< or = 8.5 hr) nor 20-hr exposures to any of the above sphingosine/ceramide derivatives/metabolites or various free fatty acids reproduced this effect. Sphingosine-induced cytoresistance was dissociated from the extent of cytosolic Ca2+ loading (indo-1 fluorescence), indicating a direct increase in cell resistance to attack. We conclude that sphingosine can exert dual effects on proximal renal tubular viability: in high concentrations it induces cell necrosis, whereas in low doses it initiates a cytoresistant state. These results could be reproduced in human foreskin fibroblasts, suggesting broad-based relevance to the area of acute cell injury and repair.

Acute Kidney Injury↗
PubMed1995

Heme protein-induced tubular cytoresistance: expression at the plasma membrane level.

Following experimental rhabdomyolysis, animals become resistant to heme protein-induced acute renal failure (ARF). The goals of this study were to: (a) ascertain whether this resistance, previously documented only in vivo, is expressed directly at the proximal tubular cell level; (b) determine whether heme proteinuria (vs. other consequences of rhabdomyolysis) is its trigger; and (c) ascertain some of its subcellular determinants. Rats were injected with a borderline toxic dose of glycerol and 24 hours later proximal tubular segments (PTS) were isolated for study. Their vulnerability to diverse forms of injury (FeSO4-induced oxidant stress, hypoxia, Ca2+ ionophore, cytochalasin D, PLA2) was compared to that found in normal PTS. Post-glycerol PTS manifested significant resistance to each insult (decreased lactate dehydrogenase +/- N-acetyl-beta-D-glucosaminidase release). Protection against FeSO4 was virtually complete and it was associated with a 50% decrease in membrane lipid peroxidation. No decrease in hydroxyl radical generation was noted during the FeSO4 challenge (salicylate trap assessment), suggesting a primary increase in membrane resistance to attack. That PLA2 addition caused less deacylation, plasma membrane enzyme (alanine aminopeptidase) release, and LDH leakage from post-glycerol versus normal tubules supported this hypothesis. To test whether cytoresistance was specifically triggered by heme proteins (vs. being a non-specific filtered protein effect, or a result of endotoxin cascade activation), rats were injected with purified myoglobin, non-heme containing filterable proteins, or endotoxin. Only myoglobin induced cytoresistance. In vivo heme oxygenase inhibition (tin-protoporphyrin) did not block the emergence of cytoresistance and it was expressed despite Na,K-ATPase inhibition (ouabain) or cytoskeletal disruption (cytochalasin D). In vivo heat shock failed to protect. In conclusion, (1) rhabdomyolysis induces broad based proximal tubular cytoresistance; (2) heme proteinuria is its trigger; and (3) it is most easily explained by a primary increase in plasma membrane resistance to attack.

Acetylglucosaminidase↗
PubMed1995

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.

Acute Kidney Injury↗
PubMed1995

Iron, heme oxygenase, and glutathione: effects on myohemoglobinuric proximal tubular injury.

UNLABELLED: This study assessed the impacts of iron, heme oxygenase (HO), hydroxyl radical (.OH), and glutathione (GSH) on the initiation phase of myohemoglobinuric proximal tubular injury using a novel model system. Rhabdomyolysis was induced in rats by glycerol injection and four hours later proximal tubular segments (PTS) were isolated. They were incubated for 0 to 90 minutes either in the presence or absence of an iron chelator (deferoxamine; DFO), .OH scavengers, an .OH trapping agent (salicylate; to gauge .OH production), GSH, or catalase. In selected experiments, an HO inhibitor (Sn protoporphyrin) was given at the time of glycerol injection to assess HO's acute effects on the evolving injury. Cell death and lipid peroxidation were quantified by % LDH release and malondialdehyde (MDA) generation, respectively. PTS from normal rats served as controls. Post-glycerol PTS manifested progressive LDH release (47 +/- 2%) and 20-fold MDA increments during the incubations, whereas only 11 +/- 1% LDH release and no MDA generation was observed in the normal PTS. DFO completely prevented both parameters of glycerol-induced injury. HO inhibition exerted an acute protective effect, despite previous in vivo data suggesting that HO is a cytoprotectant. Neither .OH scavengers nor catalase mitigated post-glycerol injury, the latter correlating with reduced, not increased, .OH production. GSH slightly decreased LDH release while causing a paradoxical threefold MDA increment. The latter was iron dependent (blocked by DFO), was expressed in normal PTS, and it could be reproduced by equimolar cysteine. That GSH increased iron-dependent lipid peroxidation in a cell free system (exogenous phosphatidylcholine) indicated that GSH metabolism to cysteine was not a requirement for this reaction. IN CONCLUSION: (1) chelatable iron can fully account for heme protein-triggered proximal tubular injury; (2) HO contributes to this injury, presumably by causing iron release; (3) the heme-induced injury appears to be mediated by non-.OH oxidizing intermediates; (4) GSH can exert both anti- and pro-oxidant effects; and (5) i.m. glycerol injection, followed by proximal tubular isolation, represents a new and highly useful model for studying direct determinants of heme protein cytotoxicity.

Animals↗
PubMed1995

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.

Adenine Nucleotides↗
PubMed1995

Protein synthesis inhibition induces cytoresistance in cultured human proximal tubular (HK-2) cells.

After sublethal injury, proximal tubular cells acquire resistance to further attack. This study evaluated whether this could be a possible consequence of decreased protein synthesis, a potential correlate of cell damage. To this end, cultured human proximal tubular cells (HK-2) were subjected to 0-24 h of protein synthesis inhibition (> 98%), either by adding protein synthesis inhibitors [cycloheximide (CH) or verrucarin A] or by inducing sublethal ATP depletion (antimycin A + 2-deoxyglucose). After 24 h of these treatments, significant resistance to Ca2+ ionophore/ATP depletion-induced attack was noted (assessed by vital dye exclusion, compared with normal cells). That < or = 6 h of protein synthesis inhibition caused no cytoresistance implied the importance of evolving protein depletion rather than nonspecific drug effects or protein synthesis inhibition per se. CH plus ATP depletion did not induce additive benefits, suggesting a common mechanism. Cytoresistance was dissociated from the extent of free Ca2+ loading and ATP depletion but was associated with a decrease in membrane deacylation. CH removal promptly restored protein synthesis and cytoresistance was lost; conversely, ATP recovery did not restore protein synthesis and cytoresistance persisted. The emergence of cytoresistance correlated with the disappearance/dephosphorylation of an unidentified 130-kDa tyrosine-phosphorylated protein/protein complex (denoted pp-130). The functional significance of this change was suggested by the fact that tyrosine phosphatase inhibition with orthovanadate maintained pp-130 expression and prevented the cytoresistant state. We conclude that protein synthesis inhibition in HK-2 cells can induce a cytoresistant state. Suppression in phospholipase activity and altered tyrosine phosphorylation events may have functional significance in this regard.

Adenosine Triphosphate↗
PubMed1995

Marked enzymuria after bone marrow transplantation: a correlate of veno-occlusive disease-induced "hepatorenal syndrome".

During the first month after bone marrow transplantation, approximately 15% of patients develop acute renal failure (ARF). This usually occurs in the setting of hepatic veno-occlusive disease (VOD). Prior clinical data have suggested that this form of ARF has a hemodynamic basis, analogous to the hepatorenal syndrome (HRS). If so, then proximal tubular injury would not be expected. To directly test this hypothesis, enzymuria (N-acetyl-beta-D-glucosaminidase [NAG]) was quantitated in the following groups of patients within the first 35 days after BMT: (1) VOD+ARF (serum creatinine level > 1.5 mg/dL; N = 10); (2) VOD with relatively normal renal function (serum creatinine level < 1.5 mg/dL; N = 11); and (3) patients without hepatic or renal complications (BMT controls; N = 12). For comparison, NAG was also quantitated in the following groups of non-BMT patients: (1) toxic/ischemic acute tubular necrosis (ATN) (N = 10); (2) jaundice without azotemia (N = 5); and (3) HRS (N = 6). Urine samples from eight healthy subjects established normal NAG concentrations (2.5 +/- 0.5 microU/mg urinary creatinine; mean +/- SE). All non-BMT patients with ATN had markedly elevated NAG levels (61 +/- 12; P < 0.001), validating the test as a marker of tubular damage. NAG concentrations were significantly elevated in all of the control BMT patients (24 +/- 3; P < 0.01), and the presence of VOD was associated with further striking increments (approximately 50 times normal). However, the degree of enzymuria was virtually identical for VOD patients with (125 +/- 27) and without (122 +/- 17) ARF. Jaundice in a non-BMT setting was associated with only mild NAG elevations (11 +/- 2). However, striking enzymuria was noted in all HRS patients (61 +/- 20), equaling the levels seen with ATN. The following conclusions were derived: (1) subclinical tubular injury, as defined by enzymuria, appears to be ubiquitous after BMT; (2) VOD dramatically increases the extent of enzymuria; (3) the degree of enzymuria in VOD patients is not correlated with renal dysfunction, implying that the associated ARF has a large hemodynamic component; and (4) HRS and ATN manifest comparable degrees of enzymuria, suggesting that substantial tubular damage exists in both of these forms of ARF.

Acetylglucosaminidase↗
PubMed1995

Postischemic proximal tubular resistance to oxidant stress and Ca2+ ionophore-induced attack. Implications for reperfusion injury.

BACKGROUND: The severity of "reperfusion injury" is dependent on the extent to which the involved pathways are activated and on the degree of tissue susceptibility to them. This study was undertaken to ascertain whether preexistent ischemic proximal tubular damage (ischemic "pre-conditioning") significantly alters the expression of two purported mediators of reperfusion damage: oxidant stress and cytosolic Ca2+ loading. EXPERIMENTAL DESIGN: Male Sprague-Dawley rats underwent 35 minutes of bilateral renal arterial occlusion. Fifteen minutes or 24 hours later, the kidneys were removed, proximal tubular segments (PTS) were isolated, and their susceptibility to oxidant stress (H2O2 or FeSO4) and to cytosolic Ca2+ loading (Ca2+ ionophore, A23187) was determined. Results were contrasted to those obtained with normal PTS. Cell injury was quantified by percentage of cellular lactate dehydrogenase released. Lipid peroxidation was gauged by PTS malondialdehyde (MDA) concentrations. As an index of endogenous antioxidant defenses, PTS catalase and superoxide dismutase activities were determined. Vulnerability to lipid peroxidation is highly dependent on phospholipid unsaturated fatty content, so PTS fatty acid concentrations also were assessed. RESULTS: Although PTS harvested at 15 minutes postischemia manifested sublethal injury (increased lactate dehydrogenase release under control conditions), no increased vulnerability to the oxidant insults or to the Ca2+ ionophore was noted. By 24 hours of reflow, cytoresistance to each of the insults had developed. Postischemic PTS demonstrated no increase in basal MDA concentrations (indicating a lack of in vivo lipid peroxidation), and when challenged with H2O2 or FeSO4, significantly less MDA generation developed (vs. the normal PTS). This resistance to lipid peroxidation was not associated with increased superoxide dismutase/catalase levels or altered PTS fatty acid content. CONCLUSIONS: Sublethal ischemic proximal tubular injury does not directly predispose to oxidant stress or cytosolic Ca2+ loading, and by 24 hours postischemia, increased resistance to these insults develops. Decreased membrane susceptibility to lipid peroxidation may contribute to this result.

Animals↗
PubMed1994

Post-ischemic acute renal failure protects proximal tubules from O2 deprivation injury, possibly by inducing uremia.

Rats within the early maintenance phase of post-ischemic acute renal failure (ARF) can resist additional ischemic insults. This study assessed whether this protection exists directly at the tubular cell level, and if so, whether it is a consequence of prior cell injury (for example, due to heat-shock protein synthesis; HSP), or if it arises in response to reductions in functional renal mass and/or the uremic environment. Rats were subjected to either 15 or 35 minutes of unilateral or bilateral renal ischemia, and after 15 minutes to 24 hours of reflow, proximal tubular segments (PTS) were isolated for study. Their viability following oxygenation and hypoxic/reoxygenation injury (H/R) was tested (LDH release). The influence of uremia/reduced renal mass was determined by studying PTS extracted 24 hours after 1 1/2 nephrectomy, and by determining whether PTS exposure to a "uremic milieu" (urine addition) blocks H/R damage. HSP effects were gauged by correlating renal cortical HSP-70 expression with degrees of in vitro protection, and by ascertaining whether in vivo hyperthermia (42 degrees C; 15 min) mitigates subsequent PTS H/R damage. Results were compared with those obtained from normal PTS. The in vivo experimental protocols did not substantially alter PTS isolation or their viability during oxygenation. Fifteen minutes of ischemia induced neither azotemia nor PTS cytoprotection. In contrast, 35 minutes of ischemia conferred marked protection against subsequent H/R, but only when azotemia was permitted to develop (protection seen after 24 hr, but not at 4 hr of reflow; protection abrogated by retention of 1 normal kidney). Renal failure in the absence of tubular necrosis (1 1/2 uninephrectomy) protected PTS from H/R damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1994

HK-2: an immortalized proximal tubule epithelial cell line from normal adult human kidney.

Studies assessing mechanisms of proximal tubular cell (PTC) physiology and pathophysiology increasingly utilize cell culture systems to avoid the complexity of whole organ/whole animal experiments. However, no well-differentiated PTC line derived from adult human kidney currently exists. Therefore, the goal of this research was to establish such a line by transduction with human papilloma virus (HPV 16) E6/E7 genes. A primary PTC culture from normal adult human renal cortex was exposed to a recombinant retrovirus containing the HPV 16 E6/E7 genes, resulting in a cell line designated HK-2 (human kidney-2) which has grown continuously in serum free media for more than one year. HK-2 cell growth is epidermal growth factor dependent and the cells retain a phenotype indicative of well-differentiated PTCs (positive for alkaline phosphatase, gamma glutamyltranspeptidase, leucine aminopeptidase, acid phosphatase, cytokeratin, alpha 3 beta 1 integrin, fibronectin; negative for factor VIII-related antigen, 6.19 antigen and CALLA endopeptidase). Furthermore, HK-2 cells retain functional characteristics of proximal tubular epithelium (Na+ dependent/phlorizin sensitive sugar transport; adenylate cyclase responsiveness to parathyroid, but not to antidiuretic, hormone). The E6/E7 genes are present in the HK-2 genome, as determined by PCR. To assess its potential usefulness as a tool for studying injury and repair, HK-2 cells were exposed to a toxic concentration of H2O2 +/- iron chelation (deferoxamine) or hydroxyl radical scavenger (Na benzoate) therapy. Only the former blocked H2O2 cytotoxicity, reproducing results previously obtained with freshly isolated rat proximal tubular segments. In conclusion, an immortalized adult human PTC line has been established by transduction with HPV 16 E6/E7 genes. It appears to be well-differentiated on the basis of its histochemical, immune cytochemical, and functional characteristics, and it can reproduce experimental results obtained with freshly isolated PTCs. Thus, this new PTC line could have substantial research application.

Adult↗
PubMed1994

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

Xanthine oxidase (XO) activity and hydroxyl radical (.OH) formation are widely proposed mediators of renal reperfusion injury, potentially altering the severity of, and recovery from, postischemic acute renal failure. The goal of this study was to ascertain whether combination XO inhibitor (oxypurinol) and .OH scavenger (Na benzoate) therapy, given at the time of renal ischemia, alters the extent of: (1) tubular necrosis and filtration failure; (2) DNA fragmentation/apoptosis (assessed in situ by terminal deoxynucleotidyl transferase reactivity); (3) early tubular regenerative responses (proliferating cell nuclear antigen expression; (3H)thymidine incorporation); and (4) the rate and/or degree of functional and morphologic repair. The effects of XO inhibition, .OH scavengers, and "catalytic" iron (FeSO4) on human proximal tubular cell proliferation in vitro were also assessed with a newly established cell line (HK-2). Male Sprague-Dawley rats were subjected to 35 min of bilateral renal arterial occlusion with or without oxypurinol/benzoate therapy. These agents did not alter the extent of tubular necrosis or filtration failure, proliferating cell nuclear antigen expression or thymidine incorporation, or the rate/extent of renal functional/morphologic repair. DNA fragmentation did not precede tubular necrosis, and it was unaffected by antioxidant therapy. By 5 days postischemia, both treatment groups demonstrated regenerating epithelial fronds that protruded into the lumina. These structures contained terminal deoxynucleotidyl transferase-reactive, but morphologically intact, cells, suggesting the presence of apoptosis. Oxypurinol and .OH scavengers (benzoate; dimethylthiourea) suppressed in vitro tubular cell proliferation; conversely, catalytic Fe had a growth-stimulatory effect. These results suggest that: (1) XO inhibition/.OH scavenger therapy has no discernible net effect on postischemic acute renal failure; (2) DNA fragmentation does not precede tubular necrosis, suggesting that it is not a primary mediator of ischemic cell death; and (3) antioxidants can be antiproliferative for human tubular cells, possibly mitigating their potential beneficial effects.

Acute Kidney Injury↗
PubMed1994

An evaluation of renal tubular DNA laddering in response to oxygen deprivation and oxidant injury.

It has recently been suggested that endonuclease activation and/or apoptosis, possibly triggered by oxidant stress, are important pathogenetic mechanisms in oxygen deprivation/reoxygenation-induced proximal tubular cell death. To explore this possibility, DNA "laddering," a characteristic feature of these processes, was sought in: (1) postischemic rat kidneys (25- or 40-min arterial clamping; 0, 1, 4, 8, 24, and 48 h and 6 days reflow); (2) posthypoxic isolate rat proximal tubular segments and (3) cultured human kidney proximal tubular cells (HK-2) subjected either to energy depletion plus Ca2+ overload (antimycin A plus 2-deoxyglucose plus Ca2+ ionophore A23187), or to H2O2-induced cell death. DNA was subsequently extracted, electrophoresed through agarose gels, and visualized with ethidium bromide or Southern blotting. To maximize ladder detection, DNA samples were also end-labeled with 32P dideoxyadenosine triphosphate with terminal deoxynucleotidyl transferase (tdt), followed by electrophoresis. None of the postischemic DNA samples demonstrated any laddering by either ethidium bromide staining or Southern analysis (apoptotic lymphocyte DNA was a positive control). However, trace laddering was apparent by the tat technique, commencing at 1 h of reflow, peaking at 24 h, and resolving slowly thereafter. This finding correlated with the morphologic expression of tubular necrosis, not apoptosis. Hypoxia/reoxygenation caused proximal tubular segment death (44 to 64%), and HK-2 cells were slowly killed by both the H2O2 and the energy depletion/Ca(2+)-loading protocols. However, neither protocol induced ethidium bromide- or tdt-detectable DNA laddering. It was concluded that: (1) minimal DNA laddering develops postischemia, and this change is reliably detected only by the tdt method; (2) it correlates with the morphologic expression of tubular necrosis, not apoptosis; and (3) in vitro oxidative- and energy depletion-mediated proximal tubular cell death can be dissociated from DNA ladder formation.

Animals↗
PubMed1993

Phospholipase A2 activity can protect renal tubules from oxygen deprivation injury.

During hypoxic or ischemic renal tubular injury, phospholipase A2 (PLA2) induces membrane deacylation, causing fatty acid accumulation and phospholipid breakdown. Because these changes can compromise cellular integrity, PLA2 activity has been widely proposed as a critical mediator of hypoxic renal tubular injury and, hence, of ischemic acute renal failure. To explore this hypothesis, isolated rat proximal tubules were subjected to continuous oxygenation or to hypoxic injury with or without exogenous PLA2 addition (porcine or bovine pancreatic PLA2; bee or snake venom PLA2). Cell death was quantified by lactic dehydrogenase (LDH) release. Pancreatic PLA2 (0.4 unit/ml) caused no LDH release under oxygenated conditions, and it dramatically attenuated hypoxic cell death (e.g., no PLA2, 55 +/- 3% LDH release; porcine pancreatic PLA2, 22 +/- 1% LDH release; P < 0.001). Bee and snake venom PLA2 (0.4 unit/ml) were directly toxic to tubules under oxygenated conditions, and this injury was additive with that induced by hypoxia. However, when these venoms were serially diluted (removing their overt toxicity), they, too, mitigated hypoxic cell death (LDH release with PLA2, 33 +/- 2%; without PLA2, 60 +/- 1% LDH release; P < 0.001). PLA2-mediated cytoprotection was Ca2+ dependent (negated by Ca2+ chelation), and it was expressed despite worsening hypoxia-associated membrane deacylation/fatty acid accumulation (12 times) and ATP depletion. These results indicate that PLA2 activity can exert both beneficial and deleterious effects on O2-deprived renal tubules, the net result of which can be a salvaging of cells from hypoxic cell death.

Adenine Nucleotides↗