Studies on the mechanism of 4-aminophenol-induced toxicity to renal proximal tubules

MnO2-DNA nanomaterials toward the dual signal detection of P-aminophenol micropollutants

P-Aminophenol (PAP), a potentially toxic and mutagenic compound, is widely distributed in water and soil and has serious side effects on human health. This study presents a convenient, sensitive, and effective dual-signal assay for the detection of PAP in the environment. Two-dimensional manganese dioxide (MnO₂) nanosheets were used as the carrier and quencher for fluorophore-labelled DNA to form a dual-signal nanoprobe, MnO₂-DNA. Based on a specific redox reaction between the MnO₂ nanosheets and target PAP, the corresponding absorption intensity of the product and the fluorescence intensity were both "turn-on" and also exhibited excellent correlation with the concentration of PAP. This strategy not only remarkably simplifies the detection process but also improves the reliability of results due to the dual-signal response, which has promising applications in environmental, clinical, and industrial research fields.

Mapping Adverse Outcome Pathways for Kidney Injury as a Basis for the Development of Mechanism-Based Animal-Sparing Approaches to Assessment of Nephrotoxicity

In line with recent OECD activities on the use of AOPs in developing Integrated Approaches to Testing and Assessment (IATAs), it is expected that systematic mapping of AOPs leading to systemic toxicity may provide a mechanistic framework for the development and implementation of mechanism-based in vitro endpoints. These may form part of an integrated testing strategy to reduce the need for repeated dose toxicity studies. Focusing on kidney and in particular the proximal tubule epithelium as a key target site of chemical-induced injury, the overall aim of this work is to contribute to building a network of AOPs leading to nephrotoxicity. Current mechanistic understanding of kidney injury initiated by 1) inhibition of mitochondrial DNA polymerase γ (mtDNA Polγ), 2) receptor mediated endocytosis and lysosomal overload, and 3) covalent protein binding, which all present fairly well established, common mechanisms by which certain chemicals or drugs may cause nephrotoxicity, is presented and systematically captured in a formal description of AOPs in line with the OECD AOP development programme and in accordance with the harmonized terminology provided by the Collaborative Adverse Outcome Pathway Wiki. The relative level of confidence in the established AOPs is assessed based on evolved Bradford-Hill weight of evidence considerations of biological plausibility, essentiality and empirical support (temporal and dose-response concordance).

Integrated Tear Proteome and Metabolome Reveal Panels of Inflammatory-Related Molecules via Key Regulatory Pathways in Dry Eye Syndrome

Dry eye syndrome (DES) is a growing public health concern with a high global prevalence; however, the fundamental processes involved in its pathogenic mechanisms remain poorly understood. In the present study, we applied nanoscale liquid chromatography and quadrupole time-of-flight tandem mass spectrometry (nanoLC/Q-TOF-MS/MS) and ultraperformance LC/Q-TOF-MS/MS technologies on tear samples obtained from 18 dry eye patients and 19 healthy controls for integrated proteomic and metabolomic analyses. Overall, 1031 tear proteins were detected, while 190 proteins were determined to be significantly expressed in dry eye patients. Further functional analysis suggested that various biological processes were highly expressed and involved in the pathogenesis of DES, especially immune and inflammatory processes. In total, 156 named metabolites were identified, among which 34 were found to be significantly changed in dry eye patients. The results highlighted the key elements, especially inflammatory-related proteins and metabolites that played important roles in the development of DES. Further, the regulatory roles of primary pathways, including complement and coagulation cascades, glycolysis/gluconeogenesis, and amino acid metabolism, were also identified as processes involved in DES. Collectively, our work not only provided insight into the potential biomarkers of DES for diagnostic and prognostic purposes but extended our knowledge of the physiopathology of this syndrome.

Role of Free Radicals and Biotransformation in Trichloronitrobenzene-Induced Nephrotoxicity In Vitro

This study determined the comparative nephrotoxic potential of four trichloronitrobenzenes (TCNBs) (2,3,4-; 2,4,5-; 2,4,6-; and 3,4,5-TCNB) and explored the effects of antioxidants and biotransformation inhibitors on TCNB-induced cytotoxicity in isolated renal cortical cells (IRCC) from male Fischer 344 rats. IRCC were incubated with a TCNB up to 1.0 mM for 15–120 min. Pretreatment with an antioxidant or cytochrome P450 (CYP), flavin monooxygenase (FMO), or peroxidase inhibitor was used in some experiments. Among the four TCNBs, the order of decreasing nephrotoxic potential was approximately 3,4,5- > 2,4,6- > 2,3,4- > 2,4,5-TCNB. The four TCNBs exhibited a similar profile of attenuation of cytotoxicity in response to antioxidant pretreatments. 2,3,4- and 3,4,5-TCNB cytotoxicity was attenuated by most of the biotransformation inhibitors tested, 2,4,5-TCNB cytotoxicity was only inhibited by isoniazid (CYP 2E1 inhibitor), and 2,4,6-TCNB-induced cytotoxicity was inhibited by one CYP inhibitor, one FMO inhibitor, and one peroxidase inhibitor. All of the CYP specific inhibitors tested offered some attenuation of 3,4,5-TCNB cytotoxicity. These results indicate that 3,4,5-TCNB is the most potent nephrotoxicant, free radicals play a role in the TCNB cytotoxicity, and the role of biotransformation in TCNB nephrotoxicity in vitro is variable and dependent on the position of the chloro groups.

Characterization of Acetaminophen Toxicity in Human Kidney HK-2 Cells

Acetaminophen (APAP) overdose causes liver injury, but in some cases it is associated also with renal impairment. While several studies exist in relation to acetaminophen nephrotoxicity, no reports have been published describing intracellular changes related to APAP nephrotoxicity in vitro. Because proximal tubular cells are considered to constitute a secondary site of drug-induced injury after hepatocytes, our study's aim was to estimate the toxicity in the human HK-2 cell line. We used a range of APAP concentrations (1-10 mM) to examine toxicity in the cells (1-48 h). We evaluated cell viability using the WST-1 and LDH tests. Cells impairment was also determined by monitoring ROS production, glutathione levels. We proved that HK-2 cells are able to metabolize acetaminophen. We observed moderate impairment of cells already after 1 h of treatment based on a finding of increased ROS production and decreased cell viability. After 24 h, the results showed significant cellular impairment at all tested concentrations except for 1 mM APAP, but no glutathione depletion was found. We conclude that HK-2 cells are susceptible to acetaminophen toxicity but, unlike hepatocytes, it might be not linked to glutathione depletion.

The role of biotransformation and oxidative stress in 3,5-dichloroaniline (3,5-DCA) induced nephrotoxicity in isolated renal cortical cells from male Fischer 344 rats

Among the mono- and dichloroanilines, 3,5-dichloroaniline (3,5-DCA) is the most potent nephrotoxicant in vivo and in vitro. However, the role of renal biotransformation in 3,5-DCA induced nephrotoxicity is unknown. The current study was designed to determine the in vitro nephrotoxic potential of 3,5-DCA in isolated renal cortical cells (IRCC) obtained from male Fischer 344 rats, and the role of renal bioactivation and oxidative stress in 3,5-DCA nephrotoxicity. IRCC (∼ 4 million cells/ml) from male rats were exposed to 3,5-DCA (0-1.0mM) for up to 120 min. In IRCC, 3,5-DCA was cytotoxic at 1.0mM by 60 min as evidenced by the increased release of lactate dehydrogenase (LDH), but 120 min was required for 3,5-DCA 0.5mM to increase LDH release. In subsequent studies, IRCC were exposed to a pretreatment (antioxidant or enzyme inhibitor) prior to exposure to 3,5-DCA (1.0mM) for 90 min. Cytotoxicity induced by 3,5-DCA was attenuated by pretreatment with inhibitors of flavin-containing monooxygenase (FMO; methimazole, N-octylamine), cytochrome P450 (CYP; piperonyl butoxide, metyrapone), or peroxidase (indomethacin, mercaptosuccinate) enzymes. Use of more selective CYP inhibitors suggested that the CYP 2C family contributed to 3,5-DCA bioactivation. Antioxidants (glutathione, N-acetyl-l-cysteine, α-tocopherol, ascorbate, pyruvate) also attenuated 3,5-DCA nephrotoxicity, but oxidized glutathione levels and the oxidized/reduced glutathione ratios were not increased. These results indicate that 3,5-DCA may be activated via several renal enzyme systems to toxic metabolites, and that free radicals, but not oxidative stress, contribute to 3,5-DCA induced nephrotoxicity in vitro.

HPTLC Method for the Determination of Paracetamol, Pseudoephedrine and Loratidine in Tablets and Human Plasma

A sensitive, accurate and selective high performance thin layer chromatography (HPTLC) method was developed and validated for the simultaneous determination of paracetamol (PAR), its toxic impurity 4-aminophenol (4-AP), pseudoephedrine HCl (PSH) and loratidine (LOR). The proposed chromatographic method has been developed using HPTLC aluminum plates precoated with silica gel 60 F254 using acetone-hexane-ammonia (4:5:0.1, by volume) as a developing system followed by densitometric measurement at 254 nm for PAR, 4-AP and LOR, while PSH was scanned at 208 nm. System suitability testing parameters were calculated to ascertain the quality performance of the developed chromatographic method. The method was validated with respect to USP guidelines regarding accuracy, precision and specificity. The method was successfully applied for the determination of PAR, PSH and LOR in ATSHI(®) tablets. The three drugs were also determined in plasma by applying the proposed method in the ranges of 0.5-6 µg/band, 1.6-12 µg/band and 0.4-2 µg/band for PAR, PSH and LOR, respectively. The results obtained by the proposed method were compared with those obtained by a reported HPLC method, and there was no significance difference between both methods regarding accuracy and precision.

3,4,5-Trichloroaniline nephrotoxicity in vitro: potential role of free radicals and renal biotransformation

Chloroanilines are widely used in the manufacture of drugs, pesticides and industrial intermediates. Among the trichloroanilines, 3,4,5-trichloroaniline (TCA) is the most potent nephrotoxicant in vivo. The purpose of this study was to examine the nephrotoxic potential of TCA in vitro and to determine if renal biotransformation and/or free radicals contributed to TCA cytotoxicity using isolated renal cortical cells (IRCC) from male Fischer 344 rats as the animal model. IRCC (~4 million cells/mL; 3 mL) were incubated with TCA (0, 0.1, 0.25, 0.5 or 1.0 mM) for 60–120 min. In some experiments, IRCC were pretreated with an antioxidant or a cytochrome P450 (CYP), flavin monooxygenase (FMO), cyclooxygenase or peroxidase inhibitor prior to incubation with dimethyl sulfoxide (control) or TCA (0.5 mM) for 120 min. At 60 min, TCA did not induce cytotoxicity, but induced cytotoxicity as early as 90 min with 0.5 mM or higher TCA and at 120 min with 0.1 mM or higher TCA, as evidenced by increased lactate dehydrogenase (LDH) release. Pretreatment with the CYP inhibitor piperonyl butoxide, the cyclooxygenase inhibitor indomethacin or the peroxidase inhibitor mercaptosuccinate attenuated TCA cytotoxicity, while pretreatment with FMO inhibitors or the CYP inhibitor metyrapone had no effect on TCA nephrotoxicity. Pretreatment with an antioxidant (α-tocopherol, glutathione, ascorbate or N-acetyl-l-cysteine) also reduced or completely blocked TCA cytotoxicity. These results indicate that TCA is directly nephrotoxic to IRCC in a time and concentration dependent manner. Bioactivation of TCA to toxic metabolites by CYP, cyclooxygenase and/or peroxidase contributes to the mechanism of TCA nephrotoxicity. Lastly, free radicals play a role in TCA cytotoxicity, although the exact nature of the origin of these radicals remains to be determined.

4-Amino-2-chlorophenol: Comparative in vitro nephrotoxicity and mechanisms of bioactivation

Chlorinated anilines are nephrotoxicants both in vivo and in vitro. The mechanism of chloroaniline nephrotoxicity may occur via more than one mechanism, but aminochlorophenol metabolites appear to contribute to the adverse in vivo effects. The purpose of this study was to compare the nephrotoxic potential of 4-aminophenol (4-AP), 4-amino-2-chlorophenol (4-A2CP), 4-amino-3-chlorophenol (4-A3CP) and 4-amino-2,6-dichlorophenol (4-A2,6DCP) using isolated renal cortical cells (IRCC) from male Fischer 344 rats as the model and to explore renal bioactivation mechanisms for 4-A2CP. For these studies, IRCC (∼4×10(6)cells/ml) were incubated with an aminophenol (0.5 or 1.0mM) or vehicle for 60min at 37°C with shaking. In some experiments, cells were pretreated with an antioxidant or cytochrome P450 (CYP), flavin-containing monooxygenase (FMO), peroxidase or cyclooxygenase inhibitor prior to 4-A2CP (1.0mM). Lactate dehydrogenase (LDH) release served as a measure of cytotoxicity. The order of decreasing nephrotoxic potential in IRCC was 4-A2,6-DCP>4-A2CP>4-AP>4-A3CP. The cytotoxicity induced by 4-A2CP was reduced by pretreatment with the peroxidase inhibitor mercaptosuccinic acid, and some antioxidants (ascorbate, glutathione, N-acetyl-l-cysteine) but not by others (α-tocopherol, DPPD). In addition, pretreatment with the iron chelator deferoxamine, several CYP inhibitors (except for the general CYP inhibitor piperonyl butoxide), FMO inhibitors or indomethacin (a cyclooxygenase inhibitor) failed to attenuate 4-A2CP cytotoxicity. These results demonstrate that the number and ring position of chloro groups can influence the nephrotoxic potential of 4-aminochlorophenols. In addition, 4-A2CP may be bioactivated by cyclooxygenase and peroxidases, and free radicals appear to play a role in 4-A2CP cytotoxicity.

In vitro nephrotoxicity induced by propanil

Propanil is a postemergence herbicide used primarily in rice and wheat production in the United States. The reported toxicities for propanil exposure include methemoglobinemia, immunotoxicity, and nephrotoxicity. A major metabolite of propanil, 3,4-dichloroaniline (3,4-DCA), has been shown to be a nephrotoxicant in vivo and in vitro, but the nephrotoxic potential of propanil has not been examined in detail. The purpose of this study was to determine the nephrotoxic potential of propanil using an in vitro kidney model, determine whether in vitro propanil nephrotoxicity is due to metabolites arising from propanil hydrolysis, and examine mechanistic aspects of propanil nephrotoxicity in vitro. Propanil, 3,4-DCA, propionic acid (0.1-5.0 mM), or vehicle was incubated for 15-120 min with isolated renal cortical cells (IRCC; approximately 4 million cells/mL) obtained from untreated male Fischer 344 rats. Cytotoxicity was determined by measuring lactate dehydrogenase release from IRCC. In 120-min incubations, propanil induced cytotoxicity at concentrations >0.5 mM. At 1.0 mM, propanil induced cytotoxicity following 60- or 120-min exposure. Cytotoxicity was observed with 3,4-DCA (2.0 mM) at 60 and 120 min, while propionic acid (5.0 mM) induced cytotoxicity at 60 min. In IRCC pretreated with an antioxidant, cytochrome P450(CYP) inhibitor, flavin adenine dinucleotide monooxygenase activity modulator, or cyclooxygenase inhibitor before propanil exposure (1.0 mM; 120 min), only piperonyl butoxide (0.1 mM), a CYP inhibitor, pretreatment decreased propanil cytotoxicity. These results demonstrate that propanil is an in vitro nephrotoxicant in IRCC. Propanil nephrotoxicity is not primarily due to metabolites resulting from hydrolysis of propanil, but a metabolite resulting from propanil oxidation may contribute to propanil cytotoxicity.

Contribution of reactive oxygen species to para-aminophenol toxicity in LLC-PK1 cells

para-aminophenol (PAP) causes nephrotoxicity by biochemical mechanisms that have not been fully elucidated. PAP can undergo enzymatic or non-enzymatic oxidation to form reactive intermediates. Using modulators of reactive oxygen species (ROS), the role of ROS in PAP toxicity in LLC-PK(1) cells was investigated. ROS formation was determined using a fluorescein derivative and viability using alamarBlue. Following treatment of cells with PAP, ROS formation occurred prior to loss of cell viability. Several modulators of ROS were used to identify the pathways involved in PAP toxicity. Viability was improved with catalase treatment, while viability was decreased when cells were treated with superoxide dismutase (SOD). Both catalase and SOD exert their effects outside of cells in the incubation medium, since there was no evidence of uptake of these enzymes in LLC-PK(1) cells. In cell-free incubations, hydrogen peroxide (H(2)O(2)) was produced when 0.5 mM PAP was included in the incubation medium. Further, SOD greatly increased and catalase greatly decreased H(2)O(2) production in these cell-free incubations. These data suggest that H(2)O(2) formed in the incubation medium contributes to loss of viability following PAP treatment. When cells were coincubated with 0.5 mM PAP and tiron, pyruvate, bathocuproine, 1, 10-phenanthroline, or dimethylthiourea (DMTU), ROS formation was decreased. However, there was minimal improvement in cell viability. Paradoxically, DMTU exacerbated PAP-induced loss of viability. These data suggest that ROS are generated in cells exposed to PAP but these species are not the predominant cause of cellular injury.

Mechanistic aspects of 4-amino-2,6-dichlorophenol-induced in vitro nephrotoxicity

4-Amino-2,6-dichlorophenol (ADCP) is a potent acute nephrotoxicant in vivo inducing prominent renal corticomedullary necrosis. In vitro, ADCP exposure increases lactate dehydrogenase (LDH) release from rat renal cortical slices at 0.05 mM or greater. The purpose of this study was to examine the ability of antioxidants, cytochrome P450 (CYP) and flavin adenine dinucleotide monooxygenase (FMO) activity modulators, indomethacin, glutathione and inhibitors of glutathione conjugate metabolism to attenuate ADCP cytotoxicity in vitro. Renal cortical slices prepared from untreated male Fischer 344 rats (N=4/group) were preincubated at 37 degrees C under a 100% oxygen atmosphere with an inhibitor or vehicle for 5-30 min. ADCP (0.05-0.5mM) or vehicle was added and incubations continued for 120 min. At the end of the incubation period, LDH release was measured as an index of nephrotoxicity. ADCP cytotoxicity was partially attenuated by ascorbate (1.0 or 2.0mM), but not by N,N'-diphenyl-p-phenylenediamine (DPPD), alpha-tocopherol or deferoxamine. Inhibitors of CYP (metyrapone, piperonyl butoxide and isoniazid) and FMO activity modulators (methimazole, N-octylamine) had no effect on ADCP cytotoxicity. Indomethacin or glutathione 1.0mM completely and partially blocked ADCP 0.1 and 0.5mM cytotoxicity, respectively. N-acetylcysteine, AOAA (an inhibitor of cysteine conjugate beta-lyase) and probenecid (an organic anion transport inhibitor), but not AT-125 (an inhibitor of gamma-glutamyl transferase), partially attenuated ADCP 0.1mM cytotoxicity. Overall, these results suggest that reactive metabolites may be produced from ADCP primarily via a co-oxidation-mediated mechanism. The difference in the ability of ascorbate and glutathione to attenuate ADCP-induced cytotoxicity in vitro in kidney cells could indicate that alkylation via the reactive benzoquinoneimine metabolite might be responsible for cytotoxicity rather than a free radical-mediated mechanism.

Generation of Quinoneimine Intermediates in the Bioactivation of 3-(N-Phenylamino)alanine (PAA) by Human Liver Microsomes: A Potential Link Between Eosinophilia-Myalgia Syndrome and Toxic Oil Syndrome

Eosinophilia-myalgia syndrome (EMS) was an intoxication episode that occurred in the US in 1989 and affected 1,500 people. EMS was associated with the ingestion of manufactured L-tryptophan, and 3-(N-phenylamino)alanine (PAA) was identified as one of the contaminants present in the L-tryptophan batches responsible for intoxication. In previous studies (Martínez-Cabot et al., Chem Res. Toxicol., in press), we have shown that the incubation of 3-(N-phenylamino)propane-1,2-diol (PAP), a toxic biomarker of the oil batches that caused Toxic Oil Syndrome in Spain, with human liver microsomes generates a reactive quinoneimine intermediate. The structural similarity between PAA and PAP led Mayeno and co-workers (Mayeno et al. (1995) Chem. Res. Toxicol. 8, 911-916) to hypothesize that both xenobiotics could be linked to a common etiologic agent. We thus set about to study the bioactivation of PAA by human liver microsomes. Under these conditions, PAA is converted to its 4'-hydroxy derivative, an unstable intermediate that is rapidly transformed into the final metabolites 4-aminophenol and formylglycine, which were identified in the incubations by GC/MS using the H2(18)O-labeled medium. We also provide evidence that 4-aminophenol and formylglycine are formed from a quinoneimine intermediate via a pathway similar to that demonstrated for PAP bioactivation. This quinoneimine, in the absence of nucleophiles in the incubation medium, could isomerize to give the corresponding imine, which could undergo hydrolysis to yield the aforementioned final products. These findings establish that EMS and TOS are linked by a common toxic metabolite (4-aminophenol) and that they may be further linked by the concomitant release of potentially hazardous carbonyl species.

Inactivation of lactate dehydrogenase by several chemicals: implications for in vitro toxicology studies

Lactate dehydrogenase (LDH) release is frequently used as an end-point for cytotoxicity studies. We have been unable to measure LDH release during studies using para-aminophenol (PAP) in LLC-PK(1) cells. When LLC-PK(1) cells were incubated with either PAP (0-10 mM) or menadione (0-1000 microM), viability was markedly reduced when assessed by alamar Blue or total LDH activity but not by release of LDH into the incubation medium. In addition, we incubated cells with PAP or menadione and compared LDH activity using two different assays. Both assays confirmed our observation of decreased LDH activity in cell lysates without corresponding increases in LDH activity in incubation media. Using purified LDH and 10 mM PAP, we found that PAP produced loss of LDH activity that was inversely proportional to the amount of LDH initially added. In additional experiments, we incubated 0.5 units of LDH for 1 h with varying concentrations of PAP, menadione, hydrogen peroxide (H(2)O(2)) or cisplatin. All four chemicals produced concentration-dependent decreases in LDH activity. In previous experiments, inclusion of antioxidants such as reduced glutathione (GSH) and ascorbate protected cells from PAP toxicity. GSH (1 mM) preserved LDH activity in the presence of toxicants while ascorbate (1 mM) only prevented LDH loss induced by PAP. These studies suggest that LDH that is released into the incubation medium is susceptible to degradation when reactive chemicals are present.

Time-dependent effect of p-aminophenol (PAP) toxicity in renal slices and development of oxidative stress

p-Aminophenol (PAP), a metabolite of acetaminophen, is nephrotoxic. This study investigated PAP-mediated changes as a function of time that occur prior to loss of membrane integrity. Experiments further evaluated the development of oxidative stress by PAP. Renal slices from male Fischer 344 (F344) rats (N = 4-6) were exposed to 0.1, 0.25, and 0.5 mM PAP for 15-120 min under oxygen and constant shaking at 37 degrees C. Pyruvate-stimulated gluconeogenesis, adenine nucleotide levels, and total glutathione (GSH) levels were diminished in a concentration- and time-dependent manner prior to detection of a rise in lactate dehydrogenase (LDH) leakage. Glutathione disulfide (GSSG) levels were increased by PAP suggesting the induction of oxidative stress. Western blot analysis confirmed a rise in 4-hydroxynonenal (4-HNE)-adducted proteins in tissues exposed to 0.1 and 0.25 mM PAP for 90 min. The appearance of 4-HNE-adducted proteins at the 0.1 mM concentration of PAP occurred prior to development of increased LDH leakage. Pretreatment with 1 mM glutathione (GSH) for 30 min only partially reduced PAP toxicity as LDH values were less severely depleted relative to tissues not pretreated with GSH. In contrast, pretreatment for 15 min with 2 mM ascorbic acid completely protected against PAP toxicity. Further studies showed that ascorbic acid pretreatment prevented PAP-mediated depletion of GSH. In summary, PAP rapidly depletes GSH and adenine nucleotides and inhibits gluconeogenesis prior to a rise in LDH leakage. PAP induces oxidative stress as indicated by an increase in GSSG and 4-HNE-adducted proteins. Ascorbic acid pretreatment prevents PAP toxicity by maintaining GSH status.

Pyruvate reduces 4-aminophenol in vitro toxicity

Pyruvate has been observed to reduce the nephrotoxicity of some agents by maintaining glutathione status and preventing lipid peroxidation. This study examined the mechanism for pyruvate protection of p-aminophenol (PAP) nephrotoxicity. Renal cortical slices from male Fischer 344 rats were incubated for 30-120 min with 0, 0.1, 0.25 or 0.5 mM PAP in oxygenated Krebs buffer containing 0 or 10 mM pyruvate or glucose (1.28 or 5.5 mM). LDH leakage was increased above control by 0.25 and 0.5 mM PAP beginning at 60 min and by 0.1 mM PAP at 120 min. Pyruvate prevented an increase in LDH leakage at 60- and 120-min exposure to 0.1 and 0.25 mM PAP. Pyruvate also prevented a decline in ATP levels. Glucose (1.28 and 5.5 mM) provided less protection than pyruvate from PAP toxicity. Total glutathione levels were diminished by 0.1 and 0.25 mM PAP within 60 and 30 min, respectively. Pyruvate prevented the decline in glutathione by 0.1 mM PAP at both time periods and at 30 min for 0.25 mM PAP. Pyruvate reduced the magnitude of glutathione depletion by 0.25 mM PAP following a 60-min incubation. Glutathione disulfide (GSSG) levels in renal slices were increased at 60 min by exposure to 0.25 mM PAP, while pyruvate prevented increased GSSG levels by PAP. Pyruvate also reduced the extent of 4-hydroxynonenal (4-HNE)-adducted proteins present after a 90-min incubation with PAP. These results indicate that pyruvate provided protection for PAP toxicity by providing an energy substrate and reducing oxidative stress.

Comparison of para-aminophenol cytotoxicity in rat renal epithelial cells and hepatocytes

Several chemicals, including para-aminophenol (PAP), produce kidney damage in the absence of hepatic damage. Selective nephrotoxicity may be related to the ability of the kidney to reabsorb filtered water, thereby raising the intraluminal concentration of toxicants and exposing tubular epithelial cells to higher concentrations than would be present in other tissues. The present experiments tested the hypothesis that hepatocytes and renal epithelial cells exposed to equivalent concentrations of PAP would be equally susceptible to toxicity. Hepatocytes and renal epithelial cells were prepared by collagenase digestion of tissues obtained from female Sprague-Dawley rats. Toxicity was monitored using trypan blue exclusion, oxygen consumption and ATP content. We measured the rate of PAP clearance and formation of PAP-glutathione conjugate by HPLC. We found that renal epithelial cells accumulated trypan blue and showed declines in oxygen consumption and ATP content at significantly lower concentrations of PAP and at earlier time points than hepatocytes. The half-life of PAP in hepatocyte incubations was significantly shorter (0.71+/-0.07 h) than in renal epithelial cell incubations (1.33+/-0.23 h), suggesting that renal epithelial cells were exposed to PAP for longer time periods than hepatocytes. Renal epithelial cells formed significantly less glutathione conjugates of PAP (PAP-SG) than did hepatocytes, consistent with less efficient detoxification of reactive PAP intermediates by renal epithelial cells. Finally, hepatocytes contained significant more reduced glutathione (NPSH) than did renal epithelial cells, possibly explaining the enhanced formation of PAP-SG by this cell population. In conclusion, our data indicates that renal epithelial cells are intrinsically more susceptible to PAP cytotoxicity than are hepatocytes. This enhanced cytotoxicity may be due to longer exposure to PAP and/or reduced detoxification of reactive intermediates due to lower concentrations of reduced NPSH in renal epithelial cells than in hepatocytes.

Characterization of 2-amino-4,5-dichlorophenol (2A45CP) in vitro toxicity in renal cortical slices from male Fischer 344 rats

2-Amino-4,5-dichlorophenol (2A45CP) is a major, aromatic ring hydroxylated metabolite of the renal toxicant, 3,4-dichloroaniline. 3,4-Dichloroaniline is nephrotoxic with primary damage located to the proximal tubules. The purpose of this study was to first characterize the in vitro toxicity of 2A45CP in renal cortical slices. Second, the effect of antioxidants and sulfhydryl containing agents on the severity of 2A45CP toxicity was explored since part of the mechanism of toxicity for aminophenols may involve redox cycling. Renal tissue was isolated from male Fischer 344 rats (190--220 g). Renal slices were rinsed three times for 3 min each in 5-ml Krebs buffer. Tissues were then incubated for 90--120 min with varying concentrations of 2A45CP between 0 and 0.5 mM. In a separate series of experiments, the slices (50--100 mg) were preincubated for 30 min with 1 mM dithiothreitol (DTT), 1 mM glutathione (GSH) or 2 mM ascorbic acid prior to exposure to 0, 0.05, 0.1 or 0.25 mM 2A45CP. 2A45CP produced a concentration and time dependent increase in LDH leakage from renal cortical slices. Total glutathione levels were diminished by 0.5 mM 2A45CP within 30 min. Renal slices incubated for 60 and 120 min with 0.05 and 0.1 mM 2A45CP had lower malondialdehyde levels than control. Pretreatment with DTT did not alter 2A45CP toxicity. Pretreatment of renal cortical slices with GSH or ascorbic acid reduced 2A45CP toxicity. These findings indicate that 2A45CP is directly toxic to renal cortical slices and that cytotoxicity is at least partially mediated by a reactive intermediate.

3,4-Dichlorophenylhydroxylamine cytotoxicity in renal cortical slices from Fischer 344 rats

3,4-Dichlorophenylhydroxylamine (3,4-CPHA) is the N-hydroxyl metabolite of 3,4-dichloroaniline. 3,4-Dichloroaniline is a breakdown product of the herbicide Propanil. Previous work has shown that 3,4-dichloroaniline is acutely toxic to the kidney and bladder. The purpose of this study was to examine the in vitro toxicity of 3,4-dichlorophenylhydroxylamine. Renal cortical slices were prepared from male Fischer 344 rats (190-250 g) and were incubated with 0-0.5 mM 3,4-CPHA for 30-120 min under oxygen and constant shaking. 3,4-CPHA produced a concentration and time dependent alteration in lactate dehydrogenase (LDH) leakage, organic ion accumulation and pyruvate stimulated gluconeogenesis. Glutathione levels were diminished within 60 min below control values by 0.1 and 0.5 mM 3,4-CPHA. A 30 min pretreatment with 0.1 mM deferoxamine did not alter 3,4-CPHA toxicity. Alterations in pyruvate stimulated gluconeogenesis and LDH leakage were comparable between vehicle and deferoxamine pretreated tissues. Other studies examined the effect of (1 mM) glutathione, 2 mM ascorbic acid and 1 mM dithiothreitol (DTT) on toxicity. Pretreatment for 30 min with vehicle or 1 mM DTT induced comparable changes in LDH leakage and pyruvate stimulated gluconeogenesis. Pretreatment for 30 min with 1 mM glutathione or 2 mM ascorbic acid reduced 3,4-CPHA toxicity. LDH leakage was not elevated as markedly in renal slices pretreated with glutathione relative to slices pretreated with vehicle. These results indicate that 3,4-CPHA toxicity is through an iron independent mechanism. 3,4-CPHA cytotoxicity was reduced by pretreatment with glutathione or ascorbic acid suggesting formation of a reactive intermediate.

Lipoxygenase-mediated biotransformation of p-aminophenol in the presence of glutathione: possible conjugate formation

This study tested a hypothesis that soybean lipoxygenase (SLO), a model enzyme, may be capable of generating a glutathione (GSH) conjugate(s) from p-aminophenol (PAP). Horseradish peroxidase was employed as a positive control. GSH depletion or an increase in the absorption at 327 nm with time due to GS-PAP formation was used to quantitate the reaction. The rate of GS-PAP formation was dependent on the incubation time and the amount of SLO and exhibited Km values of 0.44 and 0.71 mM for PAP and H2O2, respectively. Classical inhibitors of lipoxygenase and free radical scavengers markedly decreased the rate of GS-PAP formation in a concentration-dependent manner. PAP-dependent GSH depletion from the reaction medium occurred at a rate of 2.37 +/- 0.18 micromol/min/mg protein. Collectively, the results suggest that lipoxygenase pathway may be involved in the enzymatic formation of GSH conjugate(s) from PAP.

2-Amino-5-chlorophenol toxicity in renal cortical slices from Fischer 344 rats: effect of antioxidants and sulfhydryl agents

2-Amino-5-chlorophenol is nephrotoxic through an unidentified mechanism. This study examined the in vitro toxicity of 2-amino-5-chlorophenol in renal cortical slices from Fischer 344 rats and specifically assessed induction of lipid peroxidation and depletion of renal glutathione. Renal cortical slices exposed to 0, 0.25, 0.5, and 1 mM 2-amino-5-chlorophenol exhibited a concentration- and time-dependent increase in lactate dehydrogenase (LDH) leakage. Pyruvate-directed gluconeogenesis was diminished in a concentration-dependent manner following a 90-min incubation with 0, 0.25, 0.5, and 1 mM 2-amino-5-chlorophenol. Lipid peroxidation was induced within 60 min by 1 mM 2-amino-5-chlorophenol in renal slices relative to control tissue. Total glutathione (GSH) levels were decreased below control values within 30 min of exposure to 0.5 and 1 mM 2-amino-5-chlorophenol. These results indicated that GSH levels were decreased prior to the appearance of increased LDH leakage and diminished membrane integrity. 2-Amino-5-chlorophenol toxicity was increased in renal slices isolated from animals pretreated with buthionine sulfoximine (BSO, 890 mg/kg ip). Pretreatment of renal slices with the phenolic antioxidant N,N'-diphenyl-1, 4-phenylenediamine (DPPD, 50 microM) or the iron chelator deferoxamine did not reduce 2-amino-5-chlorophenol cytotoxicity. These results suggest that 2-amino-5-chlorophenol toxicity was not mediated through an iron-dependent mechanism. 2-Amino-5-chlorophenol cytotoxicity was reduced by a 15-min pre-incubation with 2 mM ascorbate or a 30-min preincubation with the thiol-containing agents GSH (1 mM) or dithiothreitol (1 mM, DTT). Pretreatment with GSH, DTT, or ascorbate reduced LDH leakage and lipid peroxide generation induced by 2-amino-5-chlorophenol. These results suggest that 2-amino-5-chlorophenol cytotoxicity involved free radical generation through an iron-independent mechanism. Toxicity was reduced by the presence of the antioxidant ascorbate or by addition of glutathione.

The role of glutathione in p-aminophenol-induced nephrotoxicity in the mouse

p-Aminophenol (PAP) produces nephrotoxicity in rats through a mechanism presumably involving oxidation and conjugation with glutathione (GSH). Recently it was found that PAP also causes nephrotoxicity in mice as evidenced by elevated blood urea nitrogen (BUN) and serum creatinine levels. The objective of this study was to further investigate the mechanism and elucidate the role of GSH in PAP-induced nephrotoxicity in the mouse. Male C57BL/6 mice injected i.p. with various doses of PAP were sacrificed at 12 hr for measurement of BUN and serum creatinine levels and determination of the extent of renal cortical nonprotein sulfhydryl (NPSH) and GSH depletion. PAP depleted renal cortical NPSH content in a dose- and time-dependent manner. Depletion of NPSH in mouse kidney did not occur at PAP doses below 600 mg/kg. Buthionine sulfoximine, an inhibitor of GSH synthesis, decreased nephrotoxicity. Ascorbate, a reducing agent, prevented PAP-induced nephrotoxicity and attenuated renal cortical NPSH depletion. However, acivicin and aminooxyacetic acid, inhibitors of gamma-glutamyltranspeptidase and beta-lyase, respectively, did not prevent toxicity in the mouse. Piperonyl butoxide, an inhibitor of cytochrome P-450 enzymes, enhanced nephrotoxicity and renal cysteine depletion but not GSH depletion. The results suggest that PAP-induced nephrotoxicity in the mouse may involve oxidation and formation of a GSH conjugate.

4-Amino-2,6-dichlorophenol nephrotoxicity in the Fischer 344 rat: protection by ascorbic acid, AT-125, and aminooxyacetic acid

A halogenated derivative of 4-aminophenol, 4-amino-2, 6-dichlorophenol (ADCP), is a potent nephrotoxicant and a weak hepatotoxicant in Fischer 344 rats. Although the mechanism of ADCP nephrotoxicity is unknown, ADCP could undergo oxidation to a reactive intermediate, such as a 4-amino-2,6-dichlorophenoxy radical or 2,6-dichloro-1,4-benzoquinoneimine, which can generate additional free radicals and/or covalently bind to cellular proteins. The toxic process might also be mediated by glutathione (GSH) conjugates of ADCP, as suggested for the mechanism of 4-aminophenol nephrotoxicity. In this study, the effects of modulators of oxidation and GSH conjugation-related metabolism or transport on ADCP-induced nephrotoxicity were examined. In one set of experiments, male Fischer 344 rats (four/group) were intraperitoneally (ip) administered ADCP (0.38 mmol/kg) only or coadministered an antioxidant, ascorbic acid (1.14 mmol/kg, ip) with ADCP. Administration of ascorbic acid markedly reduced both functional nephrotoxicity and morphological changes induced by ADCP. Administration of a gamma-glutamyltransferase (GGT) inhibitor, l-(alphaS, 5S)-alpha-amino-3-chloro-4,5-dihydroxy-5-isoxazoleacetic acid (10 mg/kg, ip), or a cysteine conjugate beta-lyase inhibitor, aminooxyacetic acid (0.5 mmol/kg, ip), 1 hr before ADCP (0.38 mmol/kg) challenge partially protected rats against ADCP nephrotoxicity. In contrast, administration of an organic anion transport inhibitor, probenecid (140 mg/kg, ip), 30 min before ADCP had little effect on ADCP nephrotoxicity. The GSH depletor, buthionine sulfoximine (890 mg/kg, ip), was given 2 hr prior to ADCP and only minimal protection was noted. In addition, the nonprotein sulfhydryl (NPSH) contents in renal cortex and liver were determined at 2 hr following the administration of ADCP only or ascorbic acid/ADCP. Ascorbic acid afforded complete prevention of the depletion of NPSH in the kidney and liver caused by ADCP administration and also prevented the elevation of renal glutathione disulfide content induced by ADCP. The results indicate that oxidation of ADCP appears to be essential to ADCP nephrotoxicity and that GSH or GSH-derived conjugates of ADCP may be partly responsible for the nephrotoxic effects of ADCP via a GGT-mediated mechanism.

Cisplatin-induced changes in adenine nucleotides in rat kidney slices: amelioration by tiopronin and procaine

The adenine nucleotides (ATP, ADP and AMP) in rat renal cortical slices exposed in-vitro to cisplatin, an anticancer drug, were determined by HPLC. Cisplatin had no effect on total adenine nucleotides in the slices but caused a time- and concentration-dependent decrease in ATP levels with a concomitant increase in ADP and AMP levels. The decrease in ATP and increases in ADP and AMP concentrations became statistically significant after incubation with cisplatin (2 mM) for 90 min or after cisplatin (1 mM) for 120 min. Both tiopronin, a sulphydryl-containing drug, and procaine, an antioxidant, protected against cisplatin-induced changes in the adenine nucleotides. The results indicate a cisplatin-induced defect in cellular energetics that occurs at a relatively late stage in the process of toxicity to the slices in this in-vitro model. Cisplatin-induced depletion of ATP in the slices might result from an increase in catabolism of ATP to ADP and AMP. Maintenance of the normal concentration of ATP in the slices might be involved in the protection afforded by tiopronin and procaine against cisplatin-induced nephrotoxicity.

Nephrotoxicity of 4-amino-2-chlorophenol and 2-amino-4-chlorophenol in the Fischer 344 rat

Aminophenols and halogenated anilines induce nephrotoxicity and mild hepatotoxicity in rats. In this study, the in vivo and in vitro nephrotoxic potential of 4-amino-2-chlorophenol and 2-amino-4-chlorophenol, monochlorinated aminophenols and potential metabolites of 3-chloroaniline, was evaluated. Hepatotoxicity of both compounds was also examined in vivo. Male Fischer 344 rats (four/group) were administered 4-amino-2-chlorophenol hydrochloride (0.4, 0.8 or 1.0 mmol/kg), 2-amino-4-chlorophenol hydrochloride (0.4, 0.8 or 1.2 mmol/kg) or vehicle intraperitoneally (i.p.) and renal and hepatic function monitored for 48 h. Administration of 4-amino-2-chlorophenol (0.8 mmol/kg) induced nephrotoxicity, while only minor changes in kidney function were observed following administration of 0.4 mmol/kg of 4-amino-2-chlorophenol or 0.8 mmol/kg of 2-amino-4-chlorophenol. Increasing the dose of 4-amino-2-chlorophenol to 1.0 mmol/kg or 2-amino-4-chlorophenol to 1.2 mmol/kg resulted in lethality. Nephrotoxicity induced by 4-amino-2-chlorophenol was characterized by diuresis, increased proteinuria, glucosuria, hematuria, elevated blood urea nitrogen (BUN) concentration and kidney weight, and marked proximal tubular damage, while 2-amino-4-chlorophenol induced milder effects on renal function and transient oliguria instead of diuresis. No hepatotoxicity was observed with either compound at any dose tested. In the in vitro studies, the direct effects of 4-amino-2-chlorophenol or 2-amino-4-chlorophenol on organic ion accumulation, pyruvate-stimulated gluconeogenesis and lactate dehydrogenase (LDH) leakage were determined using renal cortical slices. 4-Amino-2-chlorophenol and 2-amino-4-chlorophenol were almost equally effective in inhibiting organic anion or cation uptake and gluconeogenesis or increasing LDH leakage, although small differences in the minimum effective concentrations were present (minimum effective concentration, 0.01-0.5 mM range). These results demonstrate that 4-amino-2-chlorophenol is a more potent nephrotoxicant than 2-amino-4-chlorophenol in vivo. The results also indicate that the addition of a chloride group to aminophenols enhances renal toxicity.

Nephrotoxic potential of 2-amino-5-chlorophenol and 4-amino-3-chlorophenol in Fischer 344 rats: comparisons with 2- and 4-chloroaniline and 2- and 4-aminophenol

Nephrotoxicity occurs following intraperitoneal (i.p.) administration of 2-chloroaniline or 4-chloroaniline hydrochloride to Fischer 344 rats, but the nephrotoxicant chemical species and mechanism of nephrotoxicity are unknown. The purpose of this study was to evaluate the in vivo and in vitro nephrotoxic potential of 2-amino-5-chlorophenol and 4-amino-3-chlorophenol, metabolites of 4-chloroaniline and 2-chloroaniline. A comparison was also made between the nephrotoxic potential of the aminochlorophenols and the corresponding aminophenols to examine the effect of adding a chloride group on the nephrotoxic potential of the animophenols. Male Fischer 344 rats (4/group) were given an i.p. injection of a chloroaniline or aminochlorophenol hydrochloride (1.5 mmol/kg), and aminophenol (1.0 or 1.5 mmol/kg), or vehicle, and renal function monitored at 24 and 48 h. Both aminochlorophenols induced smaller and fewer renal effects that the parent chloroanilenes in vivo. Also, 4-aminophenol was markedly more potent as a nephrotoxicant that 4-amino-3-chlorophenol, while 2-aminophenol and 2-amino-5-chlorophenol induced only mild change in renal function. In vitro, the phenolic compounds reduce p-aminohippurate accumulation by renal cortical slices at bath concentrations of 0.01 mM, while a bath concentration of 0.50 mM or greater was required for the chloroanilines. However, all compounds reduced tetraethylammonium accumulation at bath concentrations of 0.1-0.5 mM or greater. These results indicate that extrarenally-produced aminochlorophenol metabolites do not contribute to the mechanism of chloroaniline nephrotoxicity. Also, the reduced nephrotoxic potential of 4-amino-3-chlorophenol compared to 4-aminophenol could result from an altered ability of the aminochlorophenol to redox cycle or form conjugates.

Nephrotoxicity of 4-amino-3-S-glutathionylphenol and its modulation by metabolism or transport inhibitors

The nephrotoxicity of 4-amino-3-S-glutathionylphenol (PAP-GSH), a known metabolite of 4-amino-phenol (PAP), was determined in male Fischer 344 rats. Administration of a single dose of 40 or 60 mumol kg-1 caused a marked elevation in blood urea nitrogen and an increase in the urinary excretion of glucose, protein and gamma-glutamyltransferase (GGT). These changes were associated with histological alterations in the proximal tubule, where at the lower dose the lesion was restricted to the S3 region of the proximal tubule in the medullary rays, while at the higher dose the lesion extended to affect the S3 region in both the medullary rays and the outer stripe of the outer medulla. Studies with [35S]-PAP-GSH at 40 mumol kg-1 showed selective retention of radioactivity in the kidney, relative to other organs 24 h after dosing and that some radioactivity was covalently bound to renal proteins. Pretreatment of animals with probenecid, an inhibitor of renal organic anion transport, or aminooxyacetic acid, an inhibitor of cysteine conjugate beta-lyase, had little or no effect on the toxicity. In contrast, pretreatment of animals with acivicin, an inhibitor of gamma-glutamyltransferase, or co-administration of PAP-GSH with ascorbic acid almost completely protected against the nephrotoxicity. This protection was associated with a decreased concentration of radioactivity from [35S]-PAP-GSH in the kidneys and a decrease in the amount covalently bound to renal protein. Thus, the nephrotoxicity of PAP-GSH may be mediated by oxidation and further processing of the glutathione conjugate via gamma-glutamyltransferase.