Mechanisms mediating cephaloridine inhibition of renal gluconeogenesis

Identification of novel targets of cephaloridine in rabbit renal proximal tubules synthesizing glutamine from alanine

Cephaloridine, which accumulates in the renal proximal tubule, is a model compound used for studying the toxicity of antibiotics towards this nephron segment. Several studies have demonstrated that cephaloridine alters renal intermediary and energy metabolism, but the mechanism by which this compound interferes with renal metabolic pathways remains incompletely understood. In an attempt to improve our knowledge in this field, we have studied the influence of cephaloridine on the synthesis of glutamine, which represents a key metabolic process involving several important enzymatic steps in the rabbit kidney. For this, suspensions of rabbit renal proximal tubules were incubated for 90 and 180 min in the presence of 5 mM alanine, an important glutamine precursor, both in the absence and the presence of 10 mM cephaloridine. Glutamate accumulation and glutamine synthesis were found to be inhibited by cephaloridine after 90 and 180 min of incubation, and cephaloridine accumulation in the renal proximal cells occurred in a time-dependent manner. The renal proximal tubule activities of alanine aminotransferase and glutamate dehydrogenase, which initiates alanine removal and releases the ammonia needed for glutamine synthesis, respectively, were inhibited to a significant degree and in a concentration-dependent manner by cephaloridine concentrations in the range found to accumulate in the renal proximal cells. Citrate synthase and glutamine synthetase activities were also inhibited by cephaloridine, but to a much lesser extent. The above enzymatic activities were not found to be inhibited when they were measured after successive dilutions of renal proximal tubules incubated for 180 min in the presence of 5 mM alanine and 10 mM cephaloridine. When microdissected segments (S1-S3) of rabbit renal proximal tubules were incubated for 180 min with 5 mM alanine with and without 5 and 10 mM cephaloridine, glutamate accumulation and glutamine synthesis were also inhibited in the three renal proximal segments studied; the latter cephaloridine-induced inhibitions observed were concentration-dependent except for glutamine in the S3 segment. These results are consistent with the view that cephaloridine accumulates and is toxic along the entire rabbit renal proximal tubule. They also demonstrate that cephaloridine interferes in a concentration-dependent and reversible manner mainly with alanine aminotransferase and glutamate dehydrogenase, which are therefore newly-identified targets of the toxic effects of cephaloridine in the rabbit renal proximal tubule.

Nonionic contrast media are less nephrotoxic than ionic contrast media to rat renal cortical slices

BACKGROUND

Nephrotoxicity induced by contrast media (CM) is well recognized. Nonionic CM with lower osmolality than that of conventional ionic CM have been developed in an effort to reduce toxicity. However, the nephrotoxic effects of nonionic CM have not been well evaluated. Although our previous experiments using rat renal cortical slices indicated that the direct cellular toxicity of nonionic CM is less than that of ionic CM, it was suggested that the less toxic effects of nonionic CM on the metabolic function of renal epithelial cells were in part attributable to the lower osmolality of nonionic CM. In the present experiment, the direct toxicity of nonionic CM on renal epithelial cells was compared with that of ionic CM under equiosmolar conditions, where the effects of osmotic pressure were excluded.

METHODS

Rat renal cortical slices were incubated with several kinds of CM at 37 degrees C for 120 min. Diatrizoate and iothalamate were employed as ionic CM. Iopamidol and iohexol were employed as nonionic CM. The activities of N-acetyl-beta-D-glucosaminidase (NAG), gamma-glutamyltransferase (GGTP), and lactate dehydrogenase (LDH) released from the renal slices into the incubation buffer were determined in order to evaluate renal epithelial damage caused by CM. Gluconeogenesis, p-aminohippuric (PAH) acid accumulation and ATP content in rat renal slices were determined with a view to examine the inhibitory effects of CM on the metabolic function of renal epithelial cells. The toxic effects of nonionic CM were compared with those of ionic CM under equiosmolar conditions, where mannitol was added to the experimental groups containing nonionic CM in order to exclude the effects of osmotic pressure.

RESULTS

A significant difference was generally not found with regard to enzyme release between ionic CM and nonionic CM plus mannitol. The inhibition of gluconeogenesis and PAH accumulation in rat renal slices by nonionic CM with mannitol was less than that by ionic CM. Although the ATP content was reduced by both ionic CM and nonionic CM plus mannitol, there was no significant difference between these two groups.

CONCLUSIONS

The present experiments demonstrated that nonionic CM were less nephrotoxic than ionic CM with regard to the function of renal epithelial cells, including gluconeogenesis and PAH accumulation, under equiosmolar conditions. These differences in nephrotoxicity between ionic and nonionic CM cannot be fully attributable to differences in osmotic pressure.

The influence of lipoic acid on adriamycin induced nephrotoxicity in rats

Adriamycin, which is widely used in the treatment of various neoplastic conditions, exerts toxic effects in several organs. Adriamycin nephrotoxicity has been recently documented in a variety of animal species. The present study was designed to investigate the effect of lipoic acid on the nephrotoxic potential of adriamycin. The study was carried out with adult male albino rats of Wistar strain. Test animals were divided into four groups of six rats each as follows: Group I (control) received only normal saline throughout the course of the experiment. Group II (ADR) received intravenous injections of adriamycin through the tail vein (1 mg kg(-1) body wt day(-1)) once a week for a period of 12 weeks. Group III (LA) received lipoic acid (35 mg kg(-1) body wt day(-1)) intraperitoneally once a week for a period of 12 weeks. Group IV (ADR + LA) received a single injection of lipoic acid intraperitoneally 24 h prior to the administration of adriamycin through the tail vein once a week for a period of 12 weeks. Intravenous injections of adriamycin resulted in decreased activities of the glycolytic enzymes; hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase in the rat renal tissue. The gluconeogenic enzymes, glucose-6-phosphatase and fructose-1,6-diphosphatase, showed a decline in their activities on adriamycin administration. The transmembrane enzymes namely the Na+,K+-ATPase, Ca2+-ATPase, Mg2+-ATPase and the brush-border enzyme alkaline phosphatase also showed a decrease in their activities. This decrease in the activities of ATPases and alkaline phosphatase suggests basolateral and brush-border membrane damage. Decreased activities of the TCA cycle enzymes isocitrate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, suggest a loss in mitochondrial function and integrity. Nephrotoxicity was evident from the increased excretions of N-acetyl-beta-D-glucosaminidase and gamma-glutamyl transferase in the urine of adriamycin administered rats. These biochemical disturbances were effectively counteracted on pre-treatment with lipoic acid, which brought about an increase in the activities of glycolytic enzymes, ATPases and the TCA cycle enzymes. On the other hand, the gluconeogenic enzymes showed a further decrease in their activities on lipoic acid pretreatment. LA pretreatment also restored the activities of the urinary enzymes to normal. These observations shed light on the nephroprotective action of lipoic acid rendered against experimental aminoglycoside toxicity.

Cephaloridine-induced inhibition of cytochrome c oxidase activity in the mitochondria of cultured renal epithelial cells (LLC-PK(1)) as a possible mechanism of its nephrotoxicity

To clarify the mechanism of cephalosporin nephrotoxicity, the effects of cephaloridine (CLD), a nephrotoxic cephalosporin antibiotic, on the mitochondria of the pig kidney proximal tubular epithelial cell line LLC-PK(1) were studied in culture. The activity of cytochrome c oxidase in the mitochondria of LLC-PK(1) cells was significantly decreased from 9 h after addition of 1.0 mM CLD to the cultured cells. These effects were dose-dependent and accompanied with a significant decrease in the ATP content in the cells, followed by marked morphological changes in the mitochondria. These alterations were observed in the treated cells before the increase in lipid peroxidation. The activities of NADH-cytochrome c reductase and succinate dehydrogenase in the mitochondria and NADPH-cytochrome P450 reductase, NADH-cytochrome b(5) reductase, and 7-ethoxycoumarin O-deethylase in the microsomes of the treated cells were not affected. Superoxide anion production by the mitochondria prepared from LLC-PK(1) cells or NADH-cytochrome c reductase was not affected by addition of CLD (1-10 mM), but adriamycin (0.1 mM) or paraquat (0.1 mM) significantly increased the superoxide anion production. These results suggested that the primary action of CLD is inhibition of cytochrome c oxidase activity in the mitochondrial electron transport chain, which decreases intracellular ATP content in renal tubular epithelial cells and that these effects of CLD are followed by increased lipid peroxidation and cellular injury.

Recent advances in molecular mechanisms of nephrotoxicity

Numerous drugs and endogenous compounds are efficiently excreted from the renal proximal tubule via two carrier-mediated pathways, that are organic anion and organic cation transport systems. Since most nephrotoxicants are taken up into renal target cells for further actions, these transport systems seem to be an early event for nephrotoxicity. Recent advances in nephrotoxicity are molecular cloning of several transporters related to important toxic compounds in the kidney. An organic cation transporter 1 (OCT1) was cloned in 1994. On the other hand, we recently isolated a complementary DNA that encodes an organic anion transporter 1 (OAT1) as an anion/dicarboxylate exchanger of the basolateral membrane of proximal tubule. Transepithelial secretion of organic anion consists of an influx of anionic substrates into the cell through the basolateral membrane and their efflux to the urine across the apical membrane. OAT1 displays a remarkably wide substrate specificity, including endogenous substrates, a variety of drugs with different structures and natural toxins. We further isolated homologs of OAT series such as liver-specific OAT2 and kidney-, liver- and brain-expressing OAT3. Because the amino acid sequence of OAT1 shows 38% identity to OCT1, a newly defined 'multispecific organic ion transporter superfamily' will provide potential tools to assess mechanisms of many nephrotoxicants including drugs and xenobiotics, and contribute also in understanding more precisely nephrotoxic mechanisms of chemicals.

A study of the nephrotoxicity of three cephalosporins in rabbits using 1H NMR spectroscopy

Male New Zealand White rabbits received a single intravenous injection of 125 mg/kg cephaloridine, 500 mg/kg cefoperazone or 1000 mg/kg cephalothin. Histological examination of kidneys at 48 h post-dose confirmed the presence of bilateral necrosis of the proximal convoluted tubules in the cephaloridine-treated animals. 1H-NMR urinalysis of cephaloridine-treated rabbits detected drug-related resonances, decreased hippurate and increased glucose at 0-24 h post-dose accompanied by elevated levels of lactate, glycine, citrate, glutamine/glutamate and alanine at 24-48 h post-dose. No histopathological changes were observed following administration of cefoperazone or cephalothin. 1H-NMR spectra of urine collected from these animals showed drug-related resonances and decreased hippurate levels at 0-24 h post-dose, and increased glucose levels at 24-48 h post-dose. Analysis of urine by conventional clinical-chemistry failed to reveal any statistically significant differences between the treatment groups. Under the conditions of this study, the nephrotoxic effects of cephaloridine and the minimal effects of cefoperazone and cephalothin could be clearly distinguished by 1H-NMR urinalysis but not by conventional urinalysis.

Toxicity of cephalosporins to fatty acid metabolism in rabbit renal cortical mitochondria

Cephaloglycin (Cgl) and cephaloridine (Cld) are acutely toxic to the proximal renal tubule, in part because of their cellular uptake by a contraluminal anionic secretory carrier and in part through their intracellular attack on the mitochondrial transport and oxidation of tricarboxylic acid (TCA) cycle anionic substrates. Preliminary studies with Cgl have provided evidence of a role of fatty acid (FA) metabolism in its nephrotoxicity, and work with Cld has shown it to be a potent inhibitor of renal tubular cell and mitochondrial carnitine (Carn) transport. Studies were therefore done to examine the effects of Cgl and Cld on the mitochondrial metabolism of butyrate, the anion of a short-chain FA that does not require the Carn shuttle to enter the inner matrix, and the effects of Cgl on the metabolism of palmitoylcarnitine (PCarn), the Carn conjugate of a long-chain FA that does enter the mitochondrion by the Carn shuttle. The following was found: (1) Cgl reduced the oxidation and uptake of butyrate after in vitro (2000 micrograms/mL, immediate effect) and after in vivo (300 mg/kg body weight, 1 hr before killing) exposure; (2) Cld caused milder in vitro toxicity, and no significant in vivo toxicity, to mitochondrial butyrate metabolism; (3) like Cld, Cgl reduced PCarn-mediated respiration after in vivo exposure, but, unlike Cld, it did not inhibit respiration with PCarn in vitro; (4) the Carn carrier was stimulated slightly by in vitro Cgl but was unaffected by in vivo Cgl; (5) in vivo Cgl had no effect on mitochondrial free Carn or long-chain acylCarn concentrations in the in situ kidney; (6) Cgl increased the excretion of Carn minimally compared with the effect of Cld; and (7) cephalexin, a nontoxic cephalosporin, caused mild reductions of respiration with butyrate and PCarn during in vitro exposure, but stimulated respiration with both substrates after in vivo exposure.

CONCLUSIONS

Cgl has essentially the same patterns of in vitro and in vivo toxicity against mitochondrial butyrate uptake and oxidation that both Cgl and Cld have against TCA-cycle substrates. Cld has little or no in vivo toxicity to mitochondrial butyrate metabolism, whereas in vivo Cgl is as toxic as Cld to respiration with PCarn. The greater overall in vivo toxicity of Cgl to mitochondrial FA metabolism, with lower cortical concentrations and AUCs than those of Cld, supports earlier evidence that Cld is less toxic than Cgl at the molecular level.

Renal cell type specificity of cephalosporin-induced cytotoxicity in suspensions of isolated proximal tubular and distal tubular cells

We have developed an in vitro model for investigation of nephron heterogeneity and cell type-specific patterns of renal injury. To further validate our model and to study biochemical mechanisms of cephalosporin-induced injury, cytotoxicity of three cephalosporins was studied in freshly isolated proximal tubular (PT) and distal tubular (DT) cells from rat kidney. The three cephalosporins [cephaloridine (CPH), cephalexin (CXN), cephalothin (CTN)] were chosen because they exhibit varying degrees of nephrotoxicity in vivo and contain different functional groups. CPH produced greater amounts of lactate dehydrogenase release from PT cells than either CXN or CTN, indicating greater toxicity of CPH, which agrees with in vivo observations. DT cells were not affected by any of the cephalosporins. Thus, the cephem ring is sufficient to produce PT cell injury but the presence of other functional groups modifies toxicity. SKF-525A and alpha-tocopherol protected PT cells from both CPH and CTN, suggesting involvement of cytochrome P-450 metabolism and oxidative stress. Both PT and DT cells exhibited transport of CPH or CXN and transport of CPH into PT cells was inhibitable by probenecid, consistent with action of a specific carrier. Transport alone, therefore, cannot account for the cell type specificity pattern in vitro. Effects on intracellular glutathione status, malondaldehyde formation, and uncoupler-stimulated respiration were also investigated, and these generally correlated with cell type specificity patterns but not always with degree of cytotoxicity. These results validate further the isolated PT and DT cells as in vitro models to study cell type-specific renal injury and show a role for oxidative stress, cytochrome P-450 bioactivation, and mitochondrial dysfunction in cephalosporin-induced PT cell injury.

Effects of KW-3902, a novel adenosine A1-receptor antagonist, on cephaloridine-induced acute renal failure in rats

We investigated the possible renal protective effects of KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine), a selective and potent adenosine A1-receptor antagonist, against cephaloridine (CER)-induced acute renal failure (ARF) in rats. ARF was induced by intravenous injection of CER at a dose of 600 mg/kg body weight. KW-3902 at doses higher than 0.01 mg/kg (p.o.) dose-dependently attenuated the decrease of creatinine clearance and the increase of proteinuria in rats with CER-induced ARF. In contrast, furosemide and trichlormethiazide (TCM) increased urinary protein and aggravated the serum parameters. These results suggest that KW-3902 has some advantages over furosemide and TCM when used in combination with CER. In the diuretic study in the rats with established ARF induced by CER, KW-3902, furosemide and TCM caused a significant increase in sodium excretion, whereas acetazolamide was ineffective. These results suggest that the proximal tubule is functionally damaged in rats with CER-induced ARF, in accord with the histological observation demonstrating the degeneration of the proximal tubule. From the fact that KW-3902 induces diuretic action even in CER-induced ARF, it is suggested that KW-3902 acts, directly or indirectly, on the proximal tubule or other tubular sites in the kidney, resulting in the diuretic effect.

Cephaloridine-induced nephrotoxicity in the Fischer 344 rat: proton NMR spectroscopic studies of urine and plasma in relation to conventional clinical chemical and histopathological assessments of nephronal damage

The acute toxicological effects of the nephrotoxic antibiotic cephaloridine (CPH, 0-1500 mg/kg) in male Fischer 344 (F344) rats, have been investigated over 48 h using clinical chemistry, histopathology and proton nuclear magnetic resonance (1H NMR) spectroscopy of urine and plasma. High field (400 and 600 MHz)1H NMR urinalysis revealed increased excretion of lactic acid, acetoacetate, alanine, valine, lysine, glutamine and glutamate and a severe, time-dependent glycosuria. A major change observed in urine of CPH-treated animals was the dose-dependent increase in HB which may relate to altered energy metabolism. CPH also caused dose-dependent decreases in the urinary excretion of hippurate, allantoin and protein (conventional assay). This abnormal metabolic profile is consistent with a functional defect in the S1/S2 regions of the proximal tubule, and was confirmed by histology post mortem. Functional changes observed included elevations in blood urea nitrogen (BUN) and urine flow rate (UFR) and dose-related decreases in urine osmolality. Spin-echo 1H NMR spectroscopic analysis of lyophilised plasma, reconstituted with 2H2O revealed an abnormal phase modulation of the methyl signal from free alanine and it is postulated that this is due to the release of transaminases from damaged tissue which via a reversible conversion to pyruvate, cause variable deuteration of alanine at the alpha-CH position. This observation suggests that 1H NMR spectral patterns are also dependent on the level of plasma transaminases and this may provide a novel indicator of tissue damage.

Comparative studies of in vitro renal cephaloridine toxicity between normoglycemic and diabetic rats

This study investigated if the attenuation in cephaloridine toxicity associated with streptozotocin (STZ)-induced diabetes can be attributed to a direct cellular effect. Comparative studies examined the direct toxicity of cephaloridine 14 days after (35 mg kg-1, i.p.) STZ or vehicle injection of male Fischer 344 (F344) rats. In vitro cephaloridine toxicity was assessed by measuring lipid peroxidation, renal gluconeogenesis and organic ion accumulation in renal cortical slices. The in vitro toxicity of cephaloridine was reduced in the diabetic group since lipid peroxidation was not increased following a 120-min exposure to cephaloridine. This was in contrast to a concentration- and time-dependent increase in lipid peroxidation in renal tissue derived from normoglycemic animals pre-incubated with 0-5 mM cephaloridine. Renal gluconeogenesis was inhibited in a concentration-dependent manner in the normoglycemic group following a 15-90-min exposure to 0-5 mM cephaloridine. Pyruvate-stimulated gluconeogenesis was diminished in the diabetic group only after a 90-min preincubation. Renal cortical slice accumulation of p-aminohippurate (PAH) and tetraethylammonium (TEA) was decreased in the normoglycemic group. Accumulation of TEA, but not PAH, was decreased (P less than 0.05) in the diabetic group. These results indicate that in vitro cephaloridine toxicity was attenuated by STZ-induced diabetes.

Iron- and ascorbic acid-induced lipid peroxidation in renal microsomes isolated from rats treated with platinum compounds

Renal microsomes isolated on day 3 from cisplatin (CDDP, single i.p. injection, 4 or 6 mg/kg)-treated rats were monitored for their susceptibility to lipid peroxidation as compared with microsomes from rats treated with carboplatin (CBDCA, 30 mg/kg), transplatin (TDDP, 6 mg/kg) or CDDP hydrolysis products (4 or 6 mg/kg) or from control animals. Cephaloridine (1 g/kg daily for 4 days, i.p. injection) was used as a positive control. The effect of CDDP on renal microsomal glucose-6-phosphatase activity was investigated in vivo and in vitro. Following treatment with CDDP and CDDP hydrolysis products vs CBDCA and TDDP treatment, microsomes revealed an enhanced susceptibility to lipid peroxidation in a Fe2+ and/or ascorbic acid stimulation system. Increased lipid peroxidation, expressed as an increase in malondialdehyde (MDA) generation, paralleled the alterations in body and kidney weight and the elevations of plasma creatinine and blood urea nitrogen concentrations. Injection of the antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD, 0.5 g/kg, i.p.) at 24 h prior to CDDP treatment abolished the increased vulnerability of renal microsomes to lipid peroxidation. In vivo, only CDDP hydrolysis products exhibited a significant inhibitory effect on renal glucose-6-phosphatase activity. In vitro, rat renal and hepatic microsomal glucose-6-phosphatase activity was decreased by CDDP both time- and concentration-dependently. Nephrotoxicity induced by CDDP and CDDP hydrolysis products might be attributable to iron-dependent lipid peroxidation and microsomes might represent target organelles on a subcellular level.

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.

Thienamycin nephrotoxicity. Mitochondrial injury and oxidative effects of imipenem in the rabbit kidney

The nephrotoxic cephalosoprins cephaloridine and cephaloglycin both produce mitochondrial respiratory toxicity in renal cortex. Recent work has provided evidence that this respiratory toxicity is caused by acylation and inactivation of mitochondrial anionic substrate transporters. While cephaloridine also causes significant lipid peroxidative injury in cortical mitochondria and microsomes, cephaloglycin causes little or no oxidative damage under identical conditions. The recently released thienamycin antibiotic, imipenem, like the toxic cephalosporins, produces acute proximal tubular necrosis which can be prevented completely by prior administration of probenecid. The ability of imipenem to block mitochondrial substrate uptake and respiration and produce oxidative changes has not been examined. We therefore evaluated the effects of imipenem in rabbit renal cortex on the following: (1) mitochondrial function [respiration with and uptake of succinate, and uptake of ADP]; and (2) evidence of oxidative change [depletion of reduced glutathione (GSH), production of oxidized glutathione (GSSG), and production of lipid peroxidative injury, as reflected in microsomal conjugated dienes (CDs)]. The mitochondrial effects of 300 mg/kg body wt of imipenem, given i.v. 1 and 2 hr before killing the animals, were comparable to those of the nephrotoxic cephalosporins. There was significant reduction of respiration with, and unidirectional uptake of, succinate at both times, while mitochondrial ADP transport was comparatively unaffected. Imipenem also depleted GSH and increased GSSG and CDs at 1 hr. These effects, however, were considerably smaller than those of a comparably nephrotoxic dose of cephaloridine, and this evidence of oxidative stress had resolved by 2 hr. We conclude that imipenem and the nephrotoxic cephalosporins have similar effects on mitochondrial substrate uptake and respiration, but differ significantly in their production of oxidative injury.

Oxidative and mitochondrial toxic effects of cephalosporin antibiotics in the kidney. A comparative study of cephaloridine and cephaloglycin

Cephaloridine and cephaloglycin are the two most nephrotoxic cephalosporins released for human use. Cephaloridine has been shown to produce both oxidative and mitochondrial respiratory injury in renal cortex in patterns of dose (or concentration) and time that are consistent with pathogenicity. Cephaloglycin also produces respiratory toxicity, and recent studies have provided evidence that this injury results from an inactivation of mitochondrial anionic substrate transporters. The abilities of cephaloglycin to produce oxidative changes and cephaloridine to block mitochondrial substrate uptake have not been examined yet. We therefore compared these two cephalosporins with one another and with cephalexin, which is not nephrotoxic, in the production of the following: (1) several components of oxidative stress or damage [depletion of reduced glutathione (GSH) and production of oxidized glutathione (GSSG) in renal cortex, inhibition of glutathione reductase in vitro, and production of the lipid peroxidation products malondialdehyde (MDA) and conjugated dienes (CDs) in renal cortex]; and (2) renal cortical mitochondrial toxicity [to both respiration with, and the transport of, succinate]. Cephaloridine depleted GSH and elevated GSSG in renal cortex, inhibited glutathione reductase, and increased both MDA in whole cortex and CDs in cortical microsomes and mitochondria. While cephaloglycin depleted GSH at least as much as did cephaloridine, it produced one-fifth as much GSSG and had little or no effect on glutathione reductase activity or on cortical MDA or microsomal CDs; cephaloglycin caused a transient small increase of mitochondrial CDs. Cephalexin produced no oxidative changes except for a slight increase of mitochondrial CDs comparable to that produced by cephaloglycin. Both cephaloridine and cephaloglycin, but not cephalexin, decreased the unidirectional uptake of, and respiration with, succinate in cortical mitochondria. We conclude that cephaloridine and cephaloglycin are both toxic to mitochondrial substrate uptake and respiration, but differ significantly in their generation of products of oxidation.

Cisplatin-induced lipid peroxidation and decrease of gluconeogenesis in rat kidney cortex: different effects of antioxidants and radical scavengers

The present in vitro study was performed to investigate the effect of the nephrotoxic anticancer agent cisplatin (CP) on lipid peroxidation, on pyruvate-stimulated gluconeogenesis and on p-aminohippurate (PAH) accumulation in rat renal cortical slices. In addition, the inhibitory effects of the antioxidants and radical scavengers N,N'-diphenyl-p-phenylenediamine (DPPD), (+)-cyanidanol-3 or alpha-tocopherol on CP-induced lipid peroxidation and CP-induced decrease of gluconeogenesis and the inhibitory effect of DPPD on CP-induced decrease of PAH accumulation were evaluated. Slices were incubated in a CP-containing medium for different periods of time (7.5-300 min) and at different concentrations (0.025-1.5 mg/ml). Lipid peroxidation was monitored by measuring the production of malondialdehyde (MDA). Accumulation of PAH was expressed as slice to medium concentration ratio. Pyruvate-stimulated gluconeogenesis, measured as glucose production, was determined after a subsequent 60- or 15-min incubation in a pyruvate-containing, CP-free medium. CP led to a time- and concentration-dependent increase in MDA production, a time- and concentration-dependent decrease of pyruvate-stimulated gluconeogenesis and a time-dependent decrease of PAH accumulation in renal cortical slices. Decrease of gluconeogenesis preceded MDA production and decrease of PAH accumulation. Antioxidants reduced CP-induced MDA production and CP-induced decrease of accumulation of PAH, but did not reverse CP-induced decrease of gluconeogenesis. This might indicate, that the generation of free radicals and subsequent lipid peroxidation may play a role, at least in part, in inducing CP nephrotoxicity. There could be more than one mechanism of CP-induced nephrotoxicity, since decrease of gluconeogenesis preceded MDA production and decrease of PAH accumulation and could not be inhibited by antioxidants and radical scavengers.

Biochemical mechanisms of cephaloridine nephrotoxicity

Large doses of the cephalosporin antibiotic, cephaloridine, produce acute proximal tubular necrosis in humans and in laboratory animals. Cephaloridine is actively transported into the proximal tubular cell by an organic anion transport system while transport across the lumenal membrane into tubular fluid appears restricted. High intracellular concentrations of cephaloridine are attained in the proximal tubular cell which are critical to the development of nephrotoxicity. There is substantial evidence indicating that oxidative stress plays a major role in cephaloridine nephrotoxicity. Cephaloridine depletes reduced glutathione, increases oxidized glutathione and induces lipid peroxidation in renal cortical tissue. The molecular mechanisms mediating cephaloridine-induced oxidative stress are not well understood. Inhibition in gluconeogenesis is a relatively early biochemical effect of cephaloridine and is independent of lipid peroxidation. Furthermore, cephaloridine inhibits gluconeogenesis in both target (kidney) and non-target (liver) organs of cephaloridine toxicity. Since glucose is not a major fuel of proximal tubular cells, it is unlikely that cephaloridine-induced tubular necrosis is mediated by the effects of this drug on glucose synthesis.