Multiple effects of presumed glutathione depletors on rabbit proximal tubules

The cellular effects of a unique pesticide sulfluramid (N-ethylperfluorooctane sulphonamide) on rabbit renal proximal tubules

The cellular effects of sulfluramid (N-ethylperfluorooctane sulphonamide, NEPFOS) and its major metabolite perfluorooctane sulphonamide (PFOS) were examined using a suspension of rabbit renal proximal tubules as a model. NEPFOS and PFOS were potent stimulators of proximal tubule basal oxygen consumption (QO(2)), with initial effects exhibited at 5-10 mum and maximal effects at 50-200 mum. The increase in basal QO(2) was ouabain insensitive, which suggests that NEPFOS and PFOS may act by uncoupling oxidative phosphorylation. Exposure of tubule suspensions to NEPFOS or PFOS concentrations of 100 mum or higher for 60 min produced tubule death, indicated by an increase in the release of lactate dehydrogenase. The tubule death did not appear to result from alkylation or lipid peroxidation, since glutathione and malondialdehyde levels were unaffected. To determine the mechanism by which NEPFOS and PFOS increased tubule QO(2), the effects of NEPFOS and PFOS on isolated renal cortical mitochondria were examined. NEPFOS (10 mum) and PFOS (5 mum) increased state-4 respiration of mitochondria in the absence of a phosphate acceptor. These results suggest that NEPFOS and PFOS uncouple oxidative phosphorylation and may produce cytotoxicity through this mechanism.

A rapid beta-NADH-linked fluorescence assay for lactate dehydrogenase in cellular death

Lactate dehydrogenase (LDH) release in a common marker of cellular death. Traditionally, the fraction of LDH released has been measured using a NADH-linked UV-Vis spectrophotometric method. The limitation of this method is that samples are usually run serially and thus is time intensive. Therefore, we developed a NADH-linked LDH assay using a fluorescence plate reader that had a correlation of 0.95 with the traditional UV-Vis spectrophotometric method. Using rabbit renal proximal tubule suspensions at a concentration of 1 mg cellular protein/ml of media, the fluorescence assay can determine LDH release in 22 samples in 2 min using 12 microL of cellular homogenates and 150 microL of media. The parallel processing of samples and smaller volumes used in the fluorescence assay results in decreased analysis time and costs.

Proteinases in renal cell death

The role of proteinases in renal proximal tubule (RPT) cellular death was examined using specific inhibitors of proteinases. Rabbit RPT suspensions were incubated with antimycin A for 1 h or tetrafluoroethyl-L-cysteine (TFEC) for 4 h in the absence or presence of the specific cysteine proteinase inhibitor L-trans-epoxysuccinyl-leucylamido (4-guanidino)butane (E-64), the serine proteinase inhibitors N-p-tosyl-L-lysine chloromethyl ketone (TLCK) or 3,4-dichloroisocoumarin (DCS), the serine and cysteine proteinase inhibitors leupeptin or antipain, or the aspartic proteinase inhibitor pepstatin. E-64 and pepstatin decreased lactate dehydrogenase (LDH) release, a marker of cell death, from RPT exposed either to antimycin A or TFEC. TLCK, DCS, leupeptin, or antipain did not decrease antimycin A- or TFEC-induced cell death. Bromohydroquinone- or t-butylhydroperoxide-induced cell death was not decreased by any of the proteinase inhibitors. Loss of lysosomal membrane potential, indicated by neutral red release, occurred prior to the onset of antimycin A-induced cell death. Extensive inhibition of lysosomal cathepsins B and L by E-64 was correlated with cytoprotection. However, E-64 was only protective after some cell death had occurred. These results suggest that lysosomal cysteine and aspartic proteinases, but not serine proteinases, play a role in RPT cell death induced by antimycin A or TFEC. The observation that E-64 was only protective after some cell death had occurred suggests that lysosomal cathepsins are released from dying cells and subsequently attack the remaining viable cells.

Inhibitors of renal chloride transport do not block toxicant-induced chloride influx in the proximal tubule

We have previously demonstrated that chloride influx occurs during the late stages of mitochondrial inhibitor-induced renal proximal tubule (RPT) cell injury. The purpose of this study was to determine if chloride influx is a common pathway in toxicant-induced cell injury and if inhibitors of renal chloride transport block the chloride influx. Chloride influx occurred in the late stages of RPT cell injury induced by the diverse toxicants mercuric chloride, t-butyl hydroperoxide, bromohydroquinone, and tetrafluoroethyl-L-cysteine. Specific inhibitors of known renal chloride transport did not prevent antimycin A-induced chloride influx. Toxicant-induced chloride influx occurred prior to cell swelling and decreasing the extracellular chloride concentration diminished toxicant-induced cell death. Thus, chloride influx is a common pathway in the late stages of toxic cell injury and does not occur through known mechanisms of renal chloride transport. Further, we propose that toxicant-induced chloride influx is mediated by a novel receptor related to the neuronal strychnine-sensitive glycine receptor and that chloride influx is a key step in cell swelling and lysis.

A putative cytoprotective receptor in the kidney: relation to the neuronal strychnine-sensitive glycine receptor

The neutral amino acid glycine has been demonstrated to prevent cell death in numerous cell types exposed to a variety of toxic insults. Recently, the central nervous system (CNS) glycine antagonist strychnine was demonstrated to bind specifically to the plasma membrane of renal proximal tubules (RPT) and mimic glycine cytoprotection. Further, it has been demonstrated in RPT that glycine and strychnine block chloride influx in the late stages of cell injury. The aim of this study was to determine if the RPT cytoprotective site is related to neuronal glycine receptors. Only antagonists to the CNS strychnine-sensitive glycine receptor (strychnine, brucine), and not antagonists to the glycine modulatory site of the NMDA receptor (DCQX, 7-CKA, HA-966) or the GABAA receptor (bicuculline methiodide, picrotoxin), prevented mitochondrial inhibitor (antimycin A)-induced RPT cell death. Using immunoblot analysis, proteins corresponding to the 58 kDa beta-subunit of the strychnine-sensitive glycine receptor and the associated protein gephyrin were identified in rabbit kidney cortical membrane fractions and RPT. No protein corresponding to the 48 kDa alpha-subunit was identified. Thus, glycine and strychnine may exert their cytoprotective effects via a putative plasma membrane receptor that is related to the strychnine-sensitive glycine receptor found in the CNS.

Decreasing glycolysis increases sensitivity to mitochondrial inhibition in primary cultures of renal proximal tubule cells

We have previously shown that shaking the culture plates (SHAKE) of rabbit renal proximal tubule cells (RPTC) to maintain adequate aeration increased aerobic metabolism and decreased the induction of glycolysis compared to RPTC cultured under standard conditions (STILL). However, glycolysis in SHAKE RPTC remained elevated compared to glycolysis in proximal tubules in vivo. In the present study the contribution of culture medium sugar composition and concentration to glycolytic metabolism was assessed in RPTC. SHAKE and STILL RPTC cultured in 5 mM glucose contained lactate levels equivalent to the respective SHAKE and STILL RPTC cultured in standard culture medium which contains 17.5 mM glucose. Similarly, the activity of lactate dehydrogenase was unchanged by lowering the medium glucose concentration. Substituting 5 mM galactose for 5 mM glucose in the culture medium significantly reduced the lactate content of both SHAKE and STILL RPTC but had no effect on lactate dehydrogenase activity. Cell growth was equivalent under all culture conditions. Sensitivity to mitochondrial inhibition was determined for each culture condition by measuring cell death after exposure to the respiratory inhibitor antimycin A. The results showed a hierarchy of sensitivity to antimycin A (5 mM galactose SHAKE > 5 mM glucose SHAKE > 17.5 mM glucose SHAKE = 17.5 mM glucose STILL), which was generally inversely correlated with the level of glycolysis as measured by lactate content (17.5 mM glucose STILL > 17.5 mM glucose SHAKE = 5 mM glucose SHAKE > 5 mM galactose SHAKE).

An in vitro model of renal proximal tubule cell regeneration

The ability of renal cells to regenerate is critical for the recovery of renal function following injury. Research on the recovery of renal function has been limited by the lack of in vitro models of renal repair. The goal of this study was to develop an in vitro model of renal proximal tubule cell (RPTC) injury and regeneration using primary cultures of rabbit RPTC. Renal proximal tubules were isolated and cultured in hormonally defined DME/F-12 medium at 37 degrees C under 95% air/5% CO2. RPTC were grown to confluency, made quiescent by the removal of insulin and hydrocortisone from the medium for 24-48 hr, and treated with the nephrotoxicant, 1,2-dichlorovinyl-L-cysteine (DCVC). DCVC (100 microM for 2 hr, n = 3-6) resulted in cell injury and the release of nonviable cells from the plate at 24 hr (55% +/- 6% confluency, mean +/- SEM) and 48 hr (37% +/- 7% confluency). Cell monolayers began to regenerate 96 hr after exposure (57% +/- 9% confluency) and continued to regenerate reaching 76% +/- 8% and 84% +/- 1% confluency by 6 and 8 days postexposure. Control cells maintained confluency throughout the experiment. Thus, an in vitro primary cell culture model has been developed in which the cell monolayer regenerates after nephrotoxicant-induced injury. This model may be useful in the study of mechanisms of renal cell injury and repair.

A novel low-affinity strychnine binding site on renal proximal tubules: role in toxic cell death

Previous studies have shown that the neuronal glycine receptor antagonist, strychnine, mimics the cytoprotective effects of glycine in renal proximal tubules (RPT) (1). The goal of this study was to identify and characterize the site of action of strychnine. 3H-Strychnine bound to RPT in a saturable and reversible manner, and was displaced by unlabelled strychnine (IC50 = 0.87 mM and a Bmax = 57 nmol/mg protein). However, strychnine binding was not inhibited by glycine or related cytoprotective amino acids. Furthermore, the neurotoxicants bicuculline and norharmane, which share the cytoprotective properties of strychnine, inhibited 3H-strychnine binding. These data support the existence of a novel low-affinity strychnine binding site on the RPT plasma membrane that prevents toxic cell death.

Cytoprotection by inhibition of chloride channels: the mechanism of action of glycine and strychnine

Previous studies have demonstrated that strychnine mimics the cytoprotective effects of glycine (1) and that strychnine binds specifically to renal proximal tubules (RPT) at cytoprotective concentrations (2). The goal of this study was to determine a mechanism by which strychnine and glycine are cytoprotective. Antimycin A (0.1 microM) caused chloride influx subsequent to mitochondrial inhibition and prior to the release of lactate dehydrogenase (LDH) activity (a marker of cell death/lysis). The addition of strychnine or glycine prevented the chloride influx and LDH release. The chloride channel inhibitors ethacrynic acid, furosemide, anthracene-9-carboxylic acid, DIDS, and SITS decreased LDH release in RPT exposed to antimycin A with a rank order of potency of DIDS > ethacrynic acid = furosemide = anthracene-9-carboxylic acid > SITS. These data, in conjunction with the preceeding paper, indicate a critical role for chloride influx in cell death/lysis; support the existence of a novel strychnine binding site on the plasma membrane of RPT that is coupled to a chloride channel; and suggest that glycine and strychnine are cytoprotective through their inhibition of chloride influx.

Role of glutathione for cisplatin nephrotoxicity in young and adult rats

Investigations were done in 10- and 55-day-old Wistar rats. Glutathione (GSH) level in kidney was decreased by 8 mmol buthionine sulfoximine (BSO)/100 g BW. There was no effect on the renal function and nephrotoxicity of cisplatin (0.6 mg CP/100 g BW) in adult rats. In young rats BSO treatment was followed by nephrotoxic effects. Pt concentration remained unaffected by BSO in young and adult rats. GSH concentration in kidney was increased by 100 mg acetyl-cysteine (accys)/100 g BW. CP nephrotoxicity was lower in young as well as in adult ac-cys-treated rats. Pt levels in renal tissue were significantly decreased in rats from both age groups. From our results we conclude that the beneficial effect of high GSH concentration in renal tissue on CP nephrotoxicity is the result of decreased Pt concentration in kidney.

Glutathione depletion and rabbit renal medulla 6-ketoPGF1 alpha and TxB2: levels in vivo and following homogenate incubation in vitro

1. The effect of glutathione (GSH) depletion on rabbit renal medullary homogenate 6-ketoPGF1 alpha and TxB2 synthesizing capability was investigated. 2. GSH depletion in vivo with diethyl maleate (DEM) produced higher (P less than 0.05) 6-ketoPGF1 alpha and TxB2 renal medullary levels compared to controls. Homogenization and incubation lowered (P less than 0.05) GSH such that there were no differences in GSH between treatments after 5 min of incubation. By 30 min, GSH was lower (P less than 0.05) and 6-ketoPGF1 alpha higher (P less than 0.05) in homogenates from controls in comparison to those from DEM-treated rabbits. 3. The results indicate GSH depletion increased 6-ketoPGF1 alpha levels in rabbit renal medulla in vivo but subsequent GSH catabolism prevented assessing the effect of this GSH depletion on prostanoid synthesizing capability.

Effect of glutathione depletion on tissue and plasma prostacyclin and thromboxane in rats

Experiments were designed to determine the effects of glutathione (GSH) depletion with L-buthionine sulfoximine (BSO) or diethyl maleate (DEM) on tissue and plasma prostacyclin (6-keto-PGF1 alpha) and thromboxane (TxB2) levels in male Sprague-Dawley rats. Despite depleting hepatic GSH to as much as 34% of control, BSO at various levels (0.4, 0.8 and 1.2 g/kg body wt) had no effect on hepatic, renal, pulmonary or cardiac tissue levels of 6-keto-PGF1 alpha and TxB2 or circulating levels of 6-keto-PGF1 alpha in portal or arterial plasma. When rats were pretreated with 3-methylcholanthrene (3-MC) to induce cytochrome P450, BSO (0.8 g/kg body wt) also had no effect on tissue or plasma prostanoid levels with the exception of a slight, but significant, increase in hepatic 6-keto-PGF1 alpha in non-induced rats. In contrast, depletions of hepatic, renal and pulmonary tissue GSH by DEM (1 mL/kg body wt) to 12, 50 and 30% of control, respectively, were associated with elevations of 6-keto-PGF1 alpha in these tissues and in plasma obtained by right ventricular heart puncture. Pretreatment of rats with 3-MC had no significant effect on tissue GSH or prostanoid levels in controls or DEM-treated rats but plasma levels of 6-keto-PGF1 alpha were lower in comparison to non-induced rats. DEM with or without 3-MC pretreatment was associated with increased TxB2 in renal tissue, whereas DEM elevated TxB2 only in pulmonary tissue from non-induced rats. It appears that factors besides GSH depletion may be required to raise plasma and/or tissue 6-keto-PGF1 alpha levels in vivo.

The neurotoxicants strychnine and bicuculline protect renal proximal tubules from mitochondrial inhibitor-induced cell death

Glycine-induced cytoprotection of renal proximal tubules exposed to chemical- or hypoxic/anoxic-induced cell death is shared by a few amino acid agonists of the neuronal strychnine-sensitive glycine receptor. The goal of this study was to determine if antagonists of the strychnine-sensitive glycine receptor attenuated the cytoprotective effects of glycine. Strychnine did not antagonize the cytoprotective effects of glycine in proximal tubules exposed to antimycin A. In contrast, strychnine was cytoprotective, was equipotent as glycine (EC50 = 0.4 mM), and the combination of strychnine and glycine was additive. Likewise, bicuculline and norharmane were cytoprotective but 20-50% less potent than glycine. These results suggest that glycine and strychnine act as a common site to produce proximal tubule cytoprotection, but this site does not share the same potency and agonist/antagonist properties as the neuronal strychnine-sensitive glycine receptor.

Effect of glutathione manipulation on prostaglandin synthesis in renal medullary homogenates

1. The effect of glutathione (GSH) manipulation on arachidonic acid (AA) metabolism in renal medullary (RM) homogenates was investigated. 2. Diethyl maleate (DEM) depleted GSH initially by 50% (P less than 0.05) and produced a general suppression (P less than 0.05) of all PGs with the exception of TXB2. GSH was further depleted during homogenization and a 30-min incubation period (P less than 0.01). 3. Adding glutathione monoethyl ester (GSH-MEE) (0, 0.8, 1.6 or 3.2 mmol/ml) to RM homogenates increased GSH (P less than 0.01) and decreased RM homogenates' PGs-synthesizing capability (P less than 0.05), with the exception of PGE2 and TXB2 at the highest concentration. 4. The results indicate that homogenization has a significant impact (P less than 0.05) on GSH concentration of the media and alterations in GSH concentration affect the profile and quantity of AA metabolites in renal medullary homogenates.

Differences in enzymatic and mechanical isolated rabbit renal proximal tubules: comparison in long-term incubation

Suspensions of renal proximal tubules (RPT) are the in vitro model for many biochemical and physiologic investigations. Inasmuch as there are numerous procedures for tubule isolation and the more commonly used enzymatic procedures may disrupt the basement membrane, there is a need for information comparing the influence of various isolation methods on RPT viability and function in long-term suspension. Rabbit RPT isolated a) enzymatically (ENZ) by in vitro collagenase digestion and Percoll size and density purification, and b) mechanically (MECH) by in vitro iron oxide perfusion and purification by sieving and magnetic removal of glomeruli were compared for viability, morphology, and functional stability during long-term suspension. RPT isolated by ENZ and MECH methods had excellent viability (less than 15% lactate dehydrogenase release), limited lipid peroxidation (less than 0.2 nmol MDA.mg protein-1), and stable nystatin-stimulated oxygen consumption (QO2) (38 and 36 nmol O2.mg protein-1.min-1) throughout 24 h of incubation. Basal QO2 was higher in ENZ than MECH tubules (27 and 19 nmol O2.mg protein-1.min-1, respectively), and was unchanged over 24 h in each preparation. The higher basal QO2 in ENZ tubules was ouabain-sensitive, suggesting an increased rate of Na+,K(+)-ATPase activity in these tubules. Total glutathione content (oxidized + reduced) in ENZ and MECH tubules increased over the 24-h incubation from 8 to 18 nmol.mg protein-1. gamma-Glutamyltranspeptidase (GGT) activity of the RPT homogenates was equivalent in both preparations and stable over time. The ratio of suspension GGT activity to homogenate GGT activity doubled (0.4 to 0.8) during the incubation period. MECH tubules retained their tubule structure during 24 h of incubation whereas the ENZ tubules had a striking loss of tubular morphology over time. These results show that ENZ- and MECH-isolated renal proximal tubule suspensions exhibit similar biochemical properties in long-term incubations but differ in ouabain-sensitive QO2 and the retention of tubular morphology. The loss of tubular morphology and the increase in the rate of Na+,K(+)-ATPase activity in ENZ tubules may be secondary to the disruption of the tubular basement membrane.

Effects of glutathione depletion, chelation and diuresis on iron nitrilotriacetate-induced lipid peroxidation in rats and mice

1. Rats and mice dosed with iron nitrilotriacetate (FeNTA) i.p. (2-12 mg Fe/kg) showed evidence of lipid peroxidation as indicated by increased exhalation of ethane and increased malondialdehyde formation in liver and kidney. 2. Buthionine sulphoximine (BSO) administered i.p. to rats and mice decreased the total glutathione (GSH) content of liver and kidney. When the rodents were pretreated i.p. with BSO prior to injection of FeNTA the increases in ethane exhalation, and in liver and kidney malondialdehyde production, were greater than with FeNTA alone, and the total GSH of liver and kidney were decreased. 3. Diuresis produced by i.p. administration of furosemide to mice substantially decreased the ethane exhalation resulting from FeNTA administration, had a lowering effect on kidney MDA, but had no significant effect on liver MDA production. 4. Similarly, desferrioxamine beta-mesylate administered i.p. to mice markedly decreased the ethane exhalation and kidney MDA production resulting from FeNTA administration.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.

Improved use of buthionine sulfoximine to prevent cisplatin nephrotoxicity in rats

Male Sprague Dawley rats were treated with buthionine sulfoximine (BSO) and cisplatin in different doses and schedules to optimize the chemoprotective effect of BSO against cisplatin nephrotoxicity. BSO at 4 mmol/kg, administered s.c. 2 h prior to cisplatin, resulted in normal blood urea nitrogen (BUN) levels in rats treated with 3 or 4 mg/kg cisplatin, and modestly, but significantly reduced the toxicity of cisplatin at 5 mg/kg. Administration of BSO (4 mmol/kg) at intervals ranging from 0 to 16 h prior to cisplatin (5 mg/kg) resulted in a significant reduction in BUN values. A BSO dose as low as 0.04 mmol/kg was found to be as effective as 4 mmol/kg against nephrotoxicity associated with cisplatin at 4 mg/kg. Repetitive injections of BSO (1 mmol/kg every 12 h, four times, beginning 2 h prior to cisplatin) significantly inhibited elevations of BUN associated with higher-dose cisplatin (6 mg/kg), whereas a single BSO injection of 4 mmol/kg was ineffective. The degree and duration of renal glutathione depletion was related to the dose of BSO. Renal glutathione content following 4 mmol/kg BSO was 38% of control at 2 h and 40% at 24 h; following 0.04 mg/kg, glutathione was 47% at 2 h and almost 100% at 24 h. Simultaneous in vitro administration of BSO did not inactivate cisplatin cytotoxicity as measured by the colony-forming ability of MBT-2 cells in soft agar. These data indicate that repeated injections of BSO, beginning prior to cisplatin administration, would improve the nephroprotective effect without compromising the chemotherapeutic efficacy of cisplatin. It is suggested that the ability of BSO to reduce cisplatin nephrotoxicity may not correlate with the degree of renal glutathione depletion and that the mechanism of action is unlikely to involve direct inactivation of cisplatin.

2-Bromohydroquinone-induced toxicity to rabbit renal proximal tubules: the role of biotransformation, glutathione, and covalent binding

2-Bromohydroquinone (BHQ) is a model toxic hydroquinone and plays an important role in bromobenzene-induced nephrotoxicity. Proximal tubules isolated to contain decreased glutathione (GSH) levels were at least twice as sensitive to the GSH depleting effects of BHQ and BHQ-induced mitochondrial dysfunction as were tubules with "normal" (i.e., in vivo) GSH content. The decrease in tubular GSH content resulted from BHQ-GSH conjugate formation. A mono-GSH conjugate (2-bromo-3-(glutathion-S-yl)hydroquinone) and a di-GSH conjugate (2-bromo-3,5- or 6-(diglutathion-S-yl)hydroquinone) were identified. In addition, a glucuronide conjugate was identified (2-bromo-1- or 4-O-glucuronylhydroquinone). BHQ-GSH conjugates were not responsible for BHQ-induced toxicity since (1) tubules with normal levels of GSH were more resistant to BHQ-induced toxicity even though they formed more BHQ-GSH conjugates than tubules with decreased GSH levels and (2) inhibition of gamma-glutamyltranspeptidase did not prevent BHQ-induced toxicity. BHQ-equivalents bound covalently to tubular protein in a concentration-, time-, and temperature-dependent manner with the majority of the binding (61%) occurring during the first 15 min after exposure to 0.2 mM BHQ. Tubules pretreated with GSH underwent less BHQ-protein alkylation and mitochondrial dysfunction, and the amount of BHQ recovered and BHQ-di-GSH conjugate formed increased. These data suggest that BHQ is biotransformed to a reactive intermediate (2-bromoquinone and/or 2-bromosemiquinone) and that this intermediate can react with GSH to form BHQ-GSH conjugates and/or bind covalently to tubular protein which may result in mitochondrial dysfunction and tubular death.

2-Bromohydroquinone-induced toxicity to rabbit renal proximal tubules: evidence against oxidative stress

2-Bromohydroquinone (BHQ) plays an important role in bromobenzene-induced nephrotoxicity and is a model toxic hydroquinone. Since BHQ has a quinone nucleus and various quinones have been shown to produce cytotoxicity via oxidative stress, the goal of this study was to determine whether BHQ produced cytotoxicity in a suspension of rabbit renal proximal tubules via oxidative stress. t-Butyl hydroperoxide (TBHP), an agent known to produce cytotoxicity via oxidative stress in this preparation, was used as a positive control. BHQ decreased tubular glutathione disulfide content whether glutathione reductase was inhibited or not. Inhibition of glutathione reductase did not result in the potentiation of BHQ-induced mitochondrial dysfunction or cell death. In contrast, TBHP increased tubular glutathione disulfide content. TBHP-induced increases in glutathione disulfide content, mitochondrial dysfunction, and cell death were potentiated when glutathione reductase was inhibited. Unlike TBHP, BHQ did not initiate lipid peroxidation nor was the antioxidant butylated hydroxytoluene protective. However, BHQ and TBHP both increased sodium cyanide-insensitive oxygen consumption. These results suggest that BHQ may undergo "redox cycling," but BHQ-induced mitochondrial dysfunction and cell death are not due to oxidative stress.

Intracellular distribution and depletion of glutathione in rabbit renal proximal tubules

The intracellular compartmentation of glutathione (GSH) in rabbit renal proximal tubules under various conditions was examined using the digitonin fractionation technique. Tubules with GSH contents similar to those found in vivo (13.4 +/- 0.8 nmol . mg protein-1) and with decreasing amounts of GSH had an apparently constant mitochondrial GSH pool of 1.9 +/- 0.1 nmol . mg protein-1. This renal mitochondrial GSH pool is similar in size to that of hepatic mitochondria and represents 10 to 15 percent of the total cellular GSH. Using phorone and diethyl maleate to decrease tubular GSH concentrations, the cytosolic GSH pool could be depleted without affecting the mitochondrial GSH pool. Depletion of the cytosolic GSH pool and decreases in the mitochondrial pool of up to 42 percent were not associated with mitochondrial dysfunction nor loss of tubular viability.

Mitochondrial toxicity of 2-bromohydroquinone in rabbit renal proximal tubules

2-Bromohydroquinone (BHQ) is a nephrotoxic metabolite of bromobenzene and a model toxic hydroquinone. The primary goal of these studies was to determine whether BHQ produces toxicity in rabbit renal proximal tubules by inhibiting mitochondrial function. BHQ induces a specific sequence of cellular events. Initially there was decrease in tubular glutathione content followed by a decrease in nystatin-stimulated ouabain-sensitive respiration. A decrease in cell viability, as measured by a decrease in lactate dehydrogenase retention, was late event. Associated with the decrease in respiration was a decrease in intracellular ATP content. Probing of mitochondrial function in the tubule revealed that BHQ did inhibit mitochondrial function in a somewhat selective manner. State 3 respiration was inhibited prior to changes in the rate of electron flow through cytochrome c-cytochrome oxidase. It is postulated that BHQ may initially inhibit state 3 respiration by inhibiting the adenine nucleotide translocator and/or the F1-ATPase.

A mechanism of S-(1,2,3,4,4-pentachloro-1,3-butadienyl)-L-cysteine toxicity to rabbit renal proximal tubules

S-(1,2,3,4,4-Pentachloro-1,3-butadienyl)-L-cysteine (PCBC) has been identified as the penultimate compound responsible for hexachlorobutadiene-induced nephrotoxicity. The primary goal of these studies was to determine the mechanism of PCBC-induced toxicity in rabbit renal proximal tubules by examining the early changes in tubular physiology. PCBC (20-500 microM) induced a specific sequence of toxic events. Following 15 min of exposure, 200 microM PCBC increased basal (25%) and ouabain-insensitive (78%) respiration. This was followed by a decrease in basal (46%), nystatin-stimulated (54%), and ouabain-insensitive (21%) respiration and a decrease in glutathione content (79%). Finally, there was a decrease in cell viability as measured by a decrease in LDH retention at 60 min. Direct probing of mitochondrial function revealed that the initial increase in respiration resulted from the uncoupling of oxidative phosphorylation, while the late changes in respiration appeared to result from gross mitochondrial damage characterized by inhibited state 3 respiration, inhibited cytochrome c-cytochrome oxidase, and inhibited electron transport. Studies utilizing tubules with decreased glutathione content revealed that glutathione plays little if any role in the early events of PCBC-induced toxicity. These results suggest that PCBC-induced mitochondrial dysfunction may initiate the renal proximal tubule injury.

Inhibition of cisplatin-induced nephrotoxicity in rats by buthionine sulfoximine, a glutathione synthesis inhibitor

DL-Buthionine-(S,R)-sulfoximine (BSO), a glutathione-depleting agent, was found to diminish the nephrotoxic effect of cisplatin (cis-diamminedichloroplatinum). Pretreatment of rats with BSO (4 mmol/kg s.c.) 2 h prior to cisplatin, either as a single dose of 5 mg/kg or at a daily dose of 2.5 mg/kg for 3 consecutive days, resulted in diminished elevations of plasma BUN concentration and decreased cisplatin-induced inhibition of renal gamma-glutamylcysteine synthetase and gamma-glutamyl transpeptidase activity measured 6 days following treatment. Administration of BSO prior to cisplatin at 7.5 mg/kg did not significantly alter the effect of cisplatin on either BUN concentration or enzyme activity. The influence of BSO pretreatment on the antitumor activity of cisplatin was studied using implantation of a murine bladder cancer (MBT-2) in C3H mice. Pretreatment of mice with BSO (5 mmol/kg) did not influence cisplatin antitumor efficacy.