Peroxidative damage and nephrotoxicity of dichlorovinylcysteine in mice

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

The trichloroethylene metabolite S-(1,2-dichlorovinyl)-L-cysteine induces progressive mitochondrial dysfunction in HTR-8/SVneo trophoblasts

Trichloroethylene is an industrial solvent and common environmental pollutant. Despite efforts to ban trichloroethylene, its availability and usage persist globally, constituting a hazard to human health. Recent studies reported associations between maternal trichloroethylene exposure and increased risk for low birth weight. Despite these associations, the toxicological mechanism underlying trichloroethylene adverse effects on pregnancy remains largely unknown. The trichloroethylene metabolite S-(1,2-dichlorovinyl)-L-cysteine (DCVC) induces mitochondrial-mediated apoptosis in a trophoblast cell line. To gain further understanding of mitochondrial-mediated DCVC placental toxicity, this study investigated the effects of DCVC exposure on mitochondrial function using non-cytolethal concentrations in placental cells. Human trophoblasts, HTR-8/SVneo, were exposed in vitro to a maximum of 20 μM DCVC for up to 12 h. Cell-based oxygen consumption and extracellular acidification assays were used to evaluate key aspects of mitochondrial function. Following 6 h of exposure to 20 μM DCVC, elevated oxygen consumption, mitochondrial proton leak and sustained energy coupling deficiency were observed. Similarly, 12 h of exposure to 20 μM DCVC decreased mitochondrial-dependent basal, ATP-linked and maximum oxygen consumption rates. Using the fluorochrome TMRE, dissipation of mitochondrial membrane potential was detected after a 12-h exposure to 20 μM DCVC, and (±)-α-tocopherol, a known suppressor of lipid peroxidation, attenuated DCVC-stimulated mitochondrial membrane depolarization but failed to rescue oxygen consumption perturbations. Together, these results suggest that DCVC caused progressive mitochondrial dysfunction, resulting in lipid peroxidation-associated mitochondrial membrane depolarization. Our findings contribute to the biological plausibility of DCVC-induced placental impairment and provide new insights into the role of the mitochondria in DCVC-induced toxicity.

Metabolism of Glutathione S-Conjugates: Multiple Pathways

Many potentially toxic electrophilic xenobiotics and some endogenous compounds are detoxified by conversion to the corresponding glutathione S-conjugate, which is metabolized to the N-acetylcysteine S-conjugate (mercapturate) and excreted. Some mercapturate pathway components, however, are toxic. Bioactivation (toxification) may occur when the glutathione S-conjugate (or mercapturate) is converted to a cysteine S-conjugate that undergoes a β-lyase reaction. If the sulfhydryl-containing fragment produced in this reaction is reactive, toxicity may ensue. Some drugs and halogenated workplace/environmental contaminants are bioactivated by this mechanism. On the other hand, cysteine S-conjugate β-lyases occur in nature as a means of generating some biologically useful sulfhydryl-containing compounds.

Trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine induces lipid peroxidation-associated apoptosis via the intrinsic and extrinsic apoptosis pathways in a first-trimester placental cell line

Trichloroethylene (TCE), a prevalent environmental contaminant, is a potent renal and hepatic toxicant through metabolites such as S-(1, 2-dichlorovinyl)-l-cysteine (DCVC). However, effects of TCE on other target organs such as the placenta have been minimally explored. Because elevated apoptosis and lipid peroxidation in placenta have been observed in pregnancy morbidities involving poor placentation, we evaluated the effects of DCVC exposure on apoptosis and lipid peroxidation in a human extravillous trophoblast cell line, HTR-8/SVneo. We exposed the cells in vitro to 10-100μM DCVC for various time points up to 24h. Following exposure, we measured apoptosis using flow cytometry, caspase activity using luminescence assays, gene expression using qRT-PCR, and lipid peroxidation using a malondialdehyde quantification assay. DCVC significantly increased apoptosis in time- and concentration-dependent manners (p<0.05). DCVC also significantly stimulated caspase 3, 7, 8 and 9 activities after 12h (p<0.05), suggesting that DCVC stimulates the activation of both the intrinsic and extrinsic apoptotic signaling pathways simultaneously. Pre-treatment with the tBID inhibitor Bl-6C9 partially reduced DCVC-stimulated caspase 3 and 7 activity, signifying crosstalk between the two pathways. Additionally, DCVC treatment increased lipid peroxidation in a concentration-dependent manner. Co-treatment with the antioxidant peroxyl radical scavenger (±)-α-tocopherol attenuated caspase 3 and 7 activity, suggesting that lipid peroxidation mediates DCVC-induced apoptosis in extravillous trophoblasts. Our findings suggest that DCVC-induced apoptosis and lipid peroxidation in extravillous trophoblasts could contribute to poor placentation if similar effects occur in vivo in response to TCE exposure, indicating that further studies into this mechanism are warranted.

Nephrotoxic effect of subchronic exposure to S-(1,2-dichlorovinyl)-L-cysteine in mice

The effect of subchronic exposure of S-(1,2-dichlorovinyl)-L-cysteine (DCVC), an active metabolite of trichloroethylene (TCE), was investigated in mice, as a part of mechanistic assessment of renal toxicity of TCE. To examine the subchronic effects of DCVC on kidney function, Balb/c male mice were administered DCVC orally and intraperitoneally once a week for 13 weeks at 1, 10 and 30 mg/kg (Main Study) and for 8 weeks at 30 mg/kg (PCR Study). At the terminal sacrifice, mice orally and intraperitoneally administered with 10 and 30 mg/kg showed significantly lower kidney weight and significantly higher blood urea nitrogen levels than the control group. Pathological examination revealed that a dose of 30 mg/kg delivered by both routes resulted in renal tubular degeneration characterized by tubular necrosis and interstitial fibrosis, and in degradation of the cortex. Degenerative changes were accompanied by the increased expression of tumor necrosis factor-α, interleukin-6 and cyclooxygenase-2 mRNAs in the kidney of mice treated with 30 mg/kg for 8 weeks. These pathohistological observations mostly corresponded to those in short-term toxicity studies on DCVC. DCVC might be a direct cause of renal toxicity, which is suggested from the aggravation in these symptoms with the dose increase.

Enzymes Involved in Processing Glutathione Conjugates

Many potentially toxic electrophiles react with glutathione to form glutathione S-conjugates in reactions catalyzed or enhanced by glutathione S-transferases. The glutathione S-conjugate is sequentially converted to the cysteinylglycine-, cysteine- and N-acetyl-cysteine S-conjugate (mercapturate). The mercapturate is generally more polar and water soluble than the parent electrophile and is readily excreted. Excretion of the mercapturate represents a detoxication mechanism. Some endogenous compounds, such as leukotrienes, prostaglandin (PG) A2, 15-deoxy-Δ^12,14-PGJ₂, and hydroxynonenal can also be metabolized to mercapturates and excreted. On occasion, however, formation of glutathione S- and cysteine S-conjugates are bioactivation events as the metabolites are mutagenic and/or cytotoxic. When the cysteine S-conjugate contains a strong electron-withdrawing group attached at the sulfur, it may be converted by cysteine S-conjugate β-lyases to pyruvate, ammonium and the original electrophile modified to contain an –SH group. If this modified electrophile is highly reactive then the enzymes of the mercapturate pathway together with the cysteine S-conjugate β-lyases constitute a bioactivation pathway. Some endogenous halogenated environmental contaminants and drugs are bioactivated by this mechanism. Recent studies suggest that coupling of enzymes of the mercapturate pathway to cysteine S-conjugate β-lyases may be more common in nature and more widespread in the metabolism of electrophilic xenobiotics than previously realized.

Proteomics of S-(1, 2-dichlorovinyl)-L-cysteine-induced acute renal failure and autoprotection in mice

Previous studies (Vaidya VS, Shankar K, Lock EA, Bucci TJ, Mehendale HM. Toxicol Sci 74: 215-227, 2003; Korrapati MC, Lock EA, Mehendale HM. Am J Physiol Renal Physiol 289: F175-F185, 2005; Korrapati MC, Chilakapati J, Lock EA, Latendresse JR, Warbritton A, Mehendale HM. Am J Physiol Renal Physiol 291: F439-F455, 2006) demonstrated that renal repair stimulated by a low dose of S-(1,2-dichlorovinyl)l-cysteine (DCVC; 15 mg/kg i.p.) 72 h before administration of a normally lethal dose (75 mg/kg i.p.) protects mice from acute renal failure (ARF) and death (autoprotection). The present study identified the proteins indicative of DCVC-induced ARF and autoprotection in male Swiss Webster mice. Renal dysfunction and injury were assessed by plasma creatinine and histopathology, respectively. Whole-kidney homogenates were run on two-dimensional gel electrophoresis gels, and the expression of 18 common proteins was maximally changed (> or =10-fold) in all the treatment groups and they were conclusively identified by liquid chromatography tandem mass spectrometry. These proteins were mildly downregulated after low dose alone and in autoprotected mice in contrast to severe downregulation with high dose alone. Glucose-regulated protein 75 and proteasome alpha-subunit type 1 were further investigated by immunohistochemistry for their localization in the kidneys of all the groups. These proteins were substantially higher in the proximal convoluted tubular epithelial cells in the low-dose and autoprotected groups compared with high-dose alone group. Proteins involved in energetics were downregulated in all the three groups of mice, leading to a compromise in cellular energy. However, energy is recovered completely in low-dose and autoprotected mice. This study provides the first report on proteomics of DCVC-induced ARF and autoprotection in mice and reflects the application of proteomics in mechanistic studies as well as biomarker development in a variety of toxicological paradigms.

Role of small heat shock protein HSP25 in radioresistance and glutathione-redox cycle

Expression of heat shock proteins (HSPs) has been shown to protect mammalian cells exposed to a variety of stress stimuli. Among various HSPs, small HSPs from diverse species were shown to protect cells against oxidative stress. Here, we show that the overexpression of the mouse small hsp gene, hsp25, provides protection against ionizing radiation. Our results demonstrate that the radiation survival of the L929 cells stably transfected with hsp25 was enhanced compared with that of the parental or vector transfected control, L25#1 cells. Our results also demonstrate that the radiation-induced apoptosis was reduced in HSP25 overexpressors. A detailed analysis of glutathione composition of those clones that overexpressed HSP25 revealed the increases of the glutathione pool, which primarily resulted from the increase of reduced glutathione. Our data suggest that higher content of GSH in HSP25 overexpressors was because of a faster reduction of oxidized glutathione (GSSG) to GSH rather than an increased de novo synthesis of GSH. The activities of glutathione reductase (GRd) and glutathione peroxidase (GPx) were greater in HSP25 overexpressors but the activity of gamma-glutamylcysteine synthetase was similar between the transfectants and the control cells. Consistent with our view, a steady state ratio of the GSH/GSSG was greater in the transfectants in comparison with the control L25#1 cells. A difference in the relative ratio became more significant after exposure to the ionizing radiation. To our knowledge, this study provides the first experimental evidence in support of the hypothesis that small HSP plays a key role in radioresistance by modulating the metabolism of glutathione. Based on the results obtained from the current investigation, we propose that HSP25 helps facilitate the glutathione-redox cycle and therefore, enhances glutathione utilization and maintains the cellular glutathione pool in favor of the reduced states.

Renal activation of trichloroethene and S-(1,2-dichlorovinyl)-L-cysteine and cell proliferative responses in the kidneys of F344 rats and B6C3F1 mice

Covalent binding of reactive intermediates formed by renal beta-lyase activation of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) has been suggested to be responsible for the greater renal sensitivity of rats than mice to the carcinogenic effects of chronic treatment with trichloroethene (TRI). Previous work demonstrated that the activation of DCVC results in acid-labile adducts to protein that can be distinguished from adducts formed by other pathways of TRI metabolism. By analyzing acid-labile adduct formation, the relationship between DCVC formation and activation from TRI and increases in rates of cell division in the kidneys of male F344 rats and B6C3F1 mice could be investigated. The delivered dose of DCVC from an oral dose of 1000 mg/kg TRI was approximately six times greater in rats than mice. However, renal activation of DCVC in mice was approximately 12 times greater than in rats. Therefore, the overall activation of TRI was about two times greater in mice than rats. Induction of cell replication in liver and kidney following doses of 1, 5, or 25 mg/kg DCVC or 1000 mg/kg TRI was also measured through the use of miniosmotic pumps that delivered BrdU subcutaneously for 3 d. Acid-labile adduct formation from DCVC and TRI displayed a consistent relationship with increased cell replication in mice and between mice and rats. Both cell replication and acid-labile adduct formation in rats given 25 mg/kg DCVC were approximately equal to that observed in mice given 1 mg/kg. Increased cell replication was not observed in rats receiving 1 or 5 mg/kg DCVC or 1000 mg/kg TRI, nor were there histological signs of nephrotoxicity. Thus, net activation of TRI by the cysteine S-conjugate pathway was found to be greater in mice than rats and these findings appeared related to differences in cell proliferative responses of the kidneys of the two species. Based on these data, it would appear that other factors must contribute to the greater sensitivity of the rat to the induction of renal carcinogenesis by TRI.

S-(1,2-dichlorovinyl)-L-cysteine-induced nephrotoxicity in the New Zealand white rabbit: characterization of proteinuria and examination of the potential role of oxidative injury

S-(1,2-dichlorovinyl)-L-cysteine (DCVC)-induced nephrotoxicity in vivo was investigated in New Zealand White rabbits. A primary emphasis in these studies was further characterization of DCVC-induced nephrotoxicity using a variety of serum and urinary analytes, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Additionally, the role of oxidative injury was assessed to address the dichotomy between reports indicating that such a mechanism is important in vivo and those indicating that such mechanisms do not contribute substantially to the mechanism of effects observed in vitro. Urine was collected prior to and at 8 and 24 hr after iv administration of DCVC. Serum was collected 15 min prior to and 24 hr after DCVC administration. Rabbits were euthanized 24 hr post-DCVC administration, and kidneys were fixed in formalin and further processed for light microscopic examination. DCVC (10 mg/kg, iv) induced a 45-50-fold increase in total urinary protein excretion, a 10-15-fold increase in urinary N-acetyl-beta-D-glucosaminidase concentration, plus a marked glucosuria by 24 hr postadministration. Additionally, DCVC increased serum creatinine levels by about 2-fold, with a trend toward increased blood urea nitrogen. SDS-PAGE analysis of rabbit urine confirmed the clinical finding of marked proteinuria in DCVC-treated animals, which in contrast to previously reported data was due to the presence of both low and high molecular weight proteins. Antioxidants had no significant effect on DCVC-dependent renal injury, nor was there evidence for DCVC-induced lipid peroxidation, as measured by either thiobarbituric acid-reactive substances or a commercial assay for malondialdehyde and hydroxalkenals.(ABSTRACT TRUNCATED AT 250 WORDS)

Early cellular events couple covalent binding of reactive metabolites to cell killing by nephrotoxic cysteine conjugates

Addition of the nephrotoxic cysteine conjugate, S-(1,2-dichlorovinyl)-L-cysteine (DCVC), to the LLC-PK1 line of renal epithelial cells leads to covalent binding of reactive intermediates followed by thiol depletion, lipid peroxidation, and cell death (Chen et al., 1990, J. Biol. Chem., 265:21603-21611). The present study was designed to determine if increased intracellular free calcium might play a role in this pathway of DCVC-induced toxicity by comparing the temporal relationships among increased intracellular free calcium, lipid peroxidation, and cytotoxicity. Intracellular free calcium increased 1 hr after DCVC treatment, long before LDH release occurred. The elevation of intracellular free calcium and cytotoxicity was prevented by inhibiting DCVC metabolism with AOA. The cell-permeable chelators, Quin-2AM and EGTA-AM, prevented the toxicity. Pretreatment of cells with a nontoxic concentration of ionomycin increased intracellular free calcium and potentiated DCVC-induced LDH release. However, the antioxidant, DPPD, which blocks lipid peroxidation and toxicity, did not affect the increase in intracellular free calcium, whereas buffering intracellular calcium with Quin-2AM or EGTA-AM blocked both lipid peroxidation and toxicity without preventing the depletion of nonprotein sulfhydryls by DCVC. Ruthenium red, an inhibitor of mitochondrial calcium uptake, also blocked cell death. We hypothesize that covalent binding of the reactive fragment from DCVC metabolism leads to deregulation of intracellular calcium homeostasis and elevation of intracellular free calcium. Increased intracellular free calcium may in turn be coupled to mitochondrial damage and the accumulation of endogenous oxidants which cause lipid peroxidation and cell death.

Inhibition of S-(1,2-dichlorovinyl)-L-cysteine-induced lipid peroxidation by antioxidants in rabbit renal cortical slices: dissociation of lipid peroxidation and toxicity

Precision-cut, rabbit renal slices were used to examine the effects of three novel antioxidants (U-74006, U-74500, and U-78517) on S-(1,2-dichlorovinyl)-L-cysteine (DCVC)-induced lipid peroxidation and toxicity. Slices exposed to DCVC showed a dose- and time-dependent increase in lipid peroxidation (TBARS) and a decrease in cellular viability, as evidenced by the loss of intracellular potassium, during the course of a 3 hour incubation. Subsequent studies employed DCVC concentrations of 100 microM. Microemulsion formulations of U-78517, U-74500, and U-74006 (100 microM) inhibited DCVC-induced lipid peroxidation by 100 +/-, 50 +/-, and < 5% (not significant), respectively. However, none of these antioxidants had a significant effect on DCVC-dependent cytotoxicity, as indicated by intracellular potassium release. The effects of U-78517, the most potent of the three antioxidants, were similar to those observed with two model antioxidants, diphenyl-p-phenylenediamine (DPPD) and the iron chelator, deferoxamine. Aminooxyacetic (AOAA), an inhibitor of renal cysteine conjugate beta-lyase, had only a minimal effect on DCVC-induced lipid peroxidation, and no effect on toxicity. These data represent the first report of DCVC-induced lipid peroxidation in rabbit renal cortical slices, a system which has been widely used to investigate mechanisms of nephrotoxicity, including that induced by DCVC. Our results demonstrate that DCVC-induced lipid peroxidation in renal slices can be inhibited by a variety of antioxidant compounds operating by different mechanisms. Because inhibition of lipid peroxidation had minimal effect on DCVC-dependent cytotoxicity, the data suggest that DCVC-induced lipid peroxidation is not a major mechanism in the cytotoxicity induced by this compound.

Events that precede and that follow S-(1,2-dichlorovinyl)-L-cysteine-induced release of mitochondrial Ca2+ and their association with cytotoxicity to renal cells

Previous studies showed that S-(1,2-dichlorovinyl)-L-cysteine perturbs intracellular Ca2+ homeostasis [Vamvakas et al., Mol Pharmacol 38: 455-461, 1990]. The objective of the present study was to investigate the cellular events that precede and that follow S-(1,2-dichlorovinyl)-L-cysteine-induced mitochondrial Ca2+ release. In incubations with isolated kidney mitochondria, S-(1,2-dichlorovinyl)-L-cysteine-induced Ca2+ efflux is preceded by increased oxidation of mitochondrial pyridine nucleotides and is prevented by ATP, an inhibitor of the hydrolysis of pyridine nucleotides, and by meta-iodobenzylguanidine, an acceptor of ADP-ribose moieties. In LLC-PK1 cells, elevation in the cytosolic Ca2+ concentration is followed by a several-fold increase in DNA double-strand breaks which is attributed to the activation of Ca2+- and Mg(2+)-dependent endonucleases. The formation of DNA double-strand breaks is followed by increased poly(ADP-ribosylation) of nuclear proteins. S-(1,2-Dichlorovinyl)-L-cysteine-induced cytotoxicity in LLC-PK1 cells is blocked by chelation of cytosolic Ca2+ with Quin-2, by inhibition of DNA fragmentation with aurintricarboxylic acid and by inhibition of increased poly(ADP-ribosyl)transferase activity by 3-aminobenzamide. These findings indicate that S-(1,2-dichlorovinyl)-L-cysteine bioactivation in renal cells may initiate the following cascade of events: increased oxidation and hydrolysis of mitochondrial pyridine nucleotides resulting in the modification of mitochondrial membrane proteins by pyridine nucleotide-derived ADP-ribose moieties, followed by Ca2+ release. Elevated Ca2+ concentrations may activate Ca(2+)-dependent endonucleases, which leads to DNA fragmentation followed by increased poly(ADP-ribosylation) of nuclear proteins and, finally, cytotoxicity.

Inhibition of iodoacetamide and t-butylhydroperoxide toxicity in LLC-PK1 cells by antioxidants: a role for lipid peroxidation in alkylation induced cytotoxicity

Previously we reported that thiol depletion and lipid peroxidation were associated with the cytotoxicity of nephrotoxic cysteine S-conjugates, a group of toxins which kill LLC-PK1 cells after metabolic activation and covalent binding. To determine if this is a general mechanism of cytotoxicity in these cells, we compared the effect of antioxidants, an iron chelator, and a thiol reducing agent on the toxicity of an alkylating agent, iodoacetamide (IDAM), and an organic peroxidant, t-butylhydroperoxide (TBHP). IDAM or TBHP toxicity was concentration (0.01 to 1.0 mM) and time (1 to 6 h) dependent. Both toxins caused lipid peroxidation which occurred prior to cell death as determined by leakage of lactate dehydrogenase (LDH). The alkylating agent IDAM bound to cellular macromolecules and depleted cellular non-protein thiols almost completely by 1 h, while LDH release occurred first at 2 to 3 h. The toxicity of IDAM and TBHP was inhibited by the antioxidants DPPD, BHA, BHQ, PGA, and BHT and the iron chelator deferoxamine. However, DPPD blocked TBHP- and IDAM-induced lipid peroxidation and toxicity without affecting binding and depletion of cellular nonprotein thiols. Furthermore, the thiol reducing agent dithiothreitol was able to block lipid peroxidation and toxicity. Therefore it is possible that with an alkylating agent, depletion of cellular nonprotein thiols cooperates with covalent binding and contributes to lipid peroxidation and cell death. There appear to be common elements in the toxicity of alkylating agents and organic peroxidants in LLC-PK1 cells.

Bioactivation of xenobiotics by formation of toxic glutathione conjugates

Evidence has been accumulating that several classes of compounds are converted by glutathione conjugate formation to toxic metabolites. The aim of this review is to summarize the current knowledge on the biosynthesis and toxicity of glutathione S-conjugates derived from halogenated alkanes, halogenated alkenes, and hydroquinones and quinones. Different types of toxic glutathione conjugates have been identified and will be discussed in detail: (i) conjugates which are transformed to electrophilic sulfur mustards, (ii) conjugates which are converted to toxic metabolites in an enzyme-catalyzed multistep mechanism, (iii) conjugates which serve as a transport form for toxic quinones and (iv) reversible glutathione conjugate formation and release of the toxic agent in cell types with lower glutathione concentrations. The kidney is the main, with some compounds the exclusive, target organ for compounds metabolized by pathways (i) to (iii). Selective toxicity to the kidney is easily explained due to the capability of the kidney to accumulate intermediates formed by processing of S-conjugates and to bioactivate these intermediates to toxic metabolites. The influences of other factors participating in the renal susceptibility are discussed.

N-(3,5-dichlorophenyl)succinimide nephrotoxicity: evidence against the formation of nephrotoxic glutathione or cysteine conjugates

The agricultural fungicide N-(3,5-dichlorophenyl)succinimide (NDPS) induces nephrotoxicity via one or more metabolites. Previous studies suggested that glutathione is important for mediating NDPS-induced nephropathy. The purpose of this study was to examine the possibility that a glutathione or cysteine conjugate of NDPS or an NDPS metabolite might be the penultimate or ultimate nephrotoxic species. In one set of experiments, male Fischer 344 rats were administered intraperitoneally (i.p.) NDPS (0.4 or 1.0 mmol/kg) 1 h after pretreatment with the gamma glutamyltranspeptidase inhibitor AT-125 (acivicin) (10 mg/kg, i.p.) and renal function was monitored at 24 and 48 h. In general, AT-125 pretreatment had few effects on NDPS-induced nephropathy. In a second set of experiments, rats were treated i.p. or orally (p.o.) with a putative glutathione (S-(2-(N-(3,5-dichlorophenyl)succinimidyl)glutathione (NDPSG), a cysteine (S-(2-(N-(3,5-dichlorophenyl)succinimidyl)cysteine (NDPSC) (as the methyl ester) or N-acetylcysteine (S-(2-(N-(3,5-dichlorophenyl)succinimidyl)-N-acetylcysteine (NDPSN) conjugate of NDPS (0.2, 0.4 or 1.0 mmol/kg) or vehicle and renal function was monitored at 24 and 48 h. An intramolecular cyclization product of NDPSC, 5-carbomethoxy-2-(N-(3,5-dichlorophenyl)carbamoylmethyl)-1,4-th iazane-3-one (NDCTO) was also examined for nephrotoxic potential. None of the compounds produced toxicologically important changes in renal function or morphology. The in vitro ability of the conjugates to alter organic ion accumulation by cortical slices was also examined. All of the conjugates tested caused a reduction in p-aminohippurate (PAH) accumulation at a conjugate bath concentration of 10(-4) M, but none of the conjugates reduced tetraethylammonium (TEA) uptake. In a third experiment, the ability of the cysteine conjugate beta-lyase inhibitor aminooxyacetic acid (AOAA) (0.5 mmol/kg, i.p.) to alter the nephrotoxicity induced by two NDPS metabolites, N-(3,5-dichlorophenyl)-2-hydroxysuccinimide (NDHS) or N-(3,5-dichlorophenyl)-2-hydroxysuccinamic acid (NDHSA) (0.2 mmol/kg, i.p.), was examined. AOAA pretreatment had no effect on NDHS- or NDHSA-induced nephrotoxicity. These results do not support a role for a glutathione or cysteine conjugate of NDPS or and NDPS metabolite as being the penultimate or ultimate nephrotoxic species.

Nephrotoxicity of halogenated alkenyl cysteine-S-conjugates

In 1916 a relationship was postulated between the occurrence of aplastic anaemia in cattle and the soy bean meal that they had been fed, which had been extracted with trichloroethylene. The toxic compound was later identified as S-(1,2-dichlorovinyl)-L-cysteine (DCV-Cys). In addition to effects on the hemopoietic system it also produced nephrotoxicity in calves. In rats only renal tubular necrosis was found. Further research demonstrated that other halogenated hydrocarbons produced similar nephrotoxicity. The haloalkenyl cysteine-S-conjugates (Cys-S-conjugates) have extensively been studied; this has provided new insight into the biochemical processes that lead to nephrotoxicity. It has been shown that a combination of transport processes and specific metabolic pathways, resulting in reactive intermediates that bind to cellular macromolecules, makes the kidney vulnerable to the noxious effects of the haloalkenyl Cys-S-conjugates. The first part of this review gives a brief overview of the bioactivation of the haloalkenes; in the second part the present knowledge of the underlying mechanisms of cytotoxicity will be outlined.