Species differences in renal gamma-glutamyl transpeptidase activity do not correlate with susceptibility to 2-bromo-(diglutathion-S-yl)-hydroquinone nephrotoxicity

Mechanisms of Rodent Renal Carcinogenesis Revisited

The important renal tumors that can be induced by exposure of rats to chemical carcinogens are renal tubule tumors (RTTs) derived from tubule epithelium; renal pelvic carcinoma derived from the urothelial lining of the pelvis; renal mesenchymal tumors (RMTs) derived from the interstitial connective tissue; and nephroblastoma derived from the metanephric primordia. However, almost all of our knowledge concerning mechanisms of renal carcinogenesis in the rodent pertains to the adenomas and carcinomas originating from renal tubule epithelium. Currently, nine mechanistic pathways can be identified in either the rat or mouse following chemical exposure. These include direct DNA reactivity, indirect DNA reactivity through free radical formation, multiphase bioactivation involving glutathione conjugation, mitotic disruption, sustained cell proliferation from direct cytotoxicity, sustained cell proliferation by disruption of a physiologic process (alpha 2u-globulin nephropathy), exaggerated pharmacologic response, species-dominant metabolic pathway, and chemical exacerbation of chronic progressive nephropathy. Spontaneous occurrence of RTTs in the rat will be included since one example is a confounder for interpreting kidney tumor results in chemical carcinogenicity studies in rats.

Sex-related differences in renal toxicodynamics in rodents

INTRODUCTION

An issue yet to be addressed, in the investigation of the xenobiotic toxicity, is a detailed characterization of the sex differences in toxicological responses. The 'sex issue' is particularly significant in nephrotoxicology as the kidney is a relevant target organ for xenobiotics and few studies have approached this subject in the past. There is a strong need to improve our understanding regarding the influence of sex in toxicology, given their increased requirement to establish the limits of exposure to chemicals in the environment and at work.

AREAS COVERED

In this review, the authors provide the reader with the current knowledge of sex differences in kidney toxicity for rats and mice. To make the review easier to consult, these studies have been organized according to the class of xenobiotic.

EXPERT OPINION

From the analysis of the present knowledge emerges a dramatic need for information on sex differences in xenobiotics toxicity. Although animals are reasonably good predictors of adverse renal effects in patients, there is need to identify alternative methods (e.g. in vitro/ex vivo) to better study sex differences in organ toxicity.

Role of SAM-dependent thiol methylation in the renal toxicity of several solvents in mice

The role of S-adenosylmethionine (SAM)-dependent thiol methylation in the nephrotoxicity of seven industrial solvents was studied in mice. The seven following solvents were utilized: bromobenzene (BB), styrene (STY), tetrachloroethylene (TTCE), trichloroethylene (TCE), 1,1-dichloroethylene (DCE), 1,2-dichloroethane (DCA) and hexachlorobutadiene (HCB). The experimental model comprised mice pretreated with periodate oxidized adenosine (ADOX) (100 micromol kg(-1) i.p.) 30 min before injection of solvents. In the first 4 h after ADOX treatment, the SAM levels were about fourfold higher than controls for the liver and kidney. The S-adenosylhomocysteine (SAH) levels were increased by factors of 11 and 14 and the SAM/SAH ratios were decreased by factors of 3 and 10 for the liver and kidney, respectively. These results show that ADOX treatment probably induces an inhibition of methyltransferase SAM-dependent in the liver and kidney and thus decreases the methylation capabilities. A single oral administration of BB (500 or 800 mg kg(-1)), TTCE (3500 or 4000 mg kg(-1)), TCE (3000 or 3500 mg kg(-1)) or STY (400 or 600 mg kg(-1)) did not induce renal toxicity, evaluated by the percentage of damaged tubules compared to controls. On the other hand, the three solvents DCE, HCB and DCA were nephrotoxic and the percentage of damaged tubules observed for each solvent was significantly different from the value of <1.8% for controls: 19% and 40% for DCE (130 and 200 mg kg(-1)), 50% and 46% for HCB (80 and 100 mg kg(-1)) and 5.1% and 7.6% for DCA (1000 and 1500 mg kg(-1)). The ADOX treatment in the mice did not modify the renal toxicity of the seven solvents. Thus, their renal toxicity, when it existed, was probably independent of the SAM-dependent thiolmethyltransferase activity in the mice. The results of this study are discussed from two viewpoints. The first concerns the general considerations on inhibition of thiol methyltransferase activities in mice and the second is related to the different solvents that are evoked individually.

Glutathione-dependent bioactivation of haloalkenes

Several halogenated alkenes are nephrotoxic in rodents. A mechanism for the organ-specific toxicity of these compounds to the kidney has been elucidated. The mechanism involves hepatic glutathione conjugation to dihaloalkenyl or 1,1-difluoroalkyl glutathione S-conjugates, which are cleaved by gamma-glutamyltransferase and dipeptidases to cysteine S-conjugates. Haloalkene-derived cysteine S-conjugates may have four fates in the organism: (a) They may be substrates for renal cysteine conjugate beta-lyases, which cleave them to form reactive intermediates identified as thioketenes (chloroalkene-derived S-conjugates), thionoacyl halides (fluoroalkene-derived S-conjugates not containing bromide), thiiranes, and thiolactones (fluoroalkene-derived S-conjugates containing bromine); (b) cysteine S-conjugates may be N-acetylated to excretable mercapturic acids; (c) they may undergo transamination or oxidation to the corresponding 3-mercaptopyruvic acid S-conjugate; (d) finally, oxidation of the sulfur atom in halovinyl cysteine S-conjugates and corresponding mercapturic acids forms Michael acceptors and may also represent a bioactivation reaction. The formation of reactive intermediates by cysteine conjugate beta-lyase may play a role in the target-organ toxicity and in the possible renal tumorigenicity of several chlorinated olefins widely used in many chemical processes.

DNA damage, gadd153 expression, and cytotoxicity in plateau-phase renal proximal tubular epithelial cells treated with a quinol thioether

2-Bromo-bis-(glutathion-S-yl)hydroquinone [2-Br-bis-(GSyl)HQ] causes DNA single-strand breaks (SSB), causes growth arrest, induces the expression of gadd153 (a gene inducible by growth arrest and DNA damage), and decreases histone H2B mRNA in log-phase renal proximal tubular epithelial cells (LLC-PK1). Renal epithelial cells in vivo normally exhibit a low mitotic index, therefore experiments in both plateau- and log-phase cells are necessary for a comprehensive understanding of the stress response to 2-Br-bis-(GSyl)HQ. In the present article we demonstrate that not all features of the stress response in log-phase cells are reproduced in plateau-phase cells. Thus, although 2-Br-bis-(GSyl)HQ causes concentration and time-dependent increases in DNA SSB, and increases the expression of gadd153, histone H2B mRNA levels are unaltered in plateau-phase cells. The relationship between reactive oxygen species, DNA damage, gene expression, and cytotoxicity was also investigated. Our findings suggest that (i) 2-Br-bis-(GSyl)HQ-mediated DNA damage in LLC-PK1 cells is mediated by the generation of H2O2; (ii) DNA damage, either directly or indirectly, contributes to cell death; and (iii) DNA damage, either directly or indirectly, provides the initial signal for gadd153 expression. In addition, DNA repair is rapid in LLC-PK1 cells, and the DNA-repair inhibitors 1-beta-D-arabinofuranosylcytosine and hydroxyurea have no effect on the amount of DNA SSB. Although the addition of 3-aminobenzamide following 2-Br-bis-(GSyl)HQ exposure has no effect on the removal of DNA SSB, it causes a slight but significant increase in gadd153 expression and cell viability, indicating that activation of poly(ADP-ribose)polymerase may exacerbate toxicity. Finally, aurintricarboxylic acid did not prevent DNA SSB or cytotoxicity in 2-Br-bis-(GSyl) HQ-treated LLC-PK1 cells, implying that activation of endonucleases does not play a role in these processes.

Biotransformation and membrane transport in nephrotoxicity

The kidney is a frequent target organ for toxic effects of xenobiotics. In recent years, the molecular mechanisms responsible for the selective renal toxicity of many nephrotoxic xenobiotics have been elucidated. Accumulation by renal transport mechanisms, and thus aspects of renal physiology, plays an important role in the renal toxicity of some antibiotics, metals, and agents binding to low molecular weight proteins such as alpha(2u)-globulin. The accumulation by active transport of metabolites formed in other organs is involved in the kidney-specific toxicity of certain polyhaloalkanes, polyhaloalkenes, hydroquinones, and aminophenols. Other xenobiotics are selectively metabolized to reactive electrophiles by enzymes expressed in the kidney. This review summarizes the present knowledge on the mechanistic basis of target organ selectivity of these compounds.

Modulation of quinol/quinone-thioether toxicity by intramolecular detoxication

A variety of cytotoxic, mutagenic, and carcinogenic conjugates of GSH require processing by enzymes of the mercapturic acid pathway to produce toxicity. However, metabolism of quinone-thioethers by gamma-GT can result in either activation or detoxication. For example, inhibition of gamma-GT completely protects against the nephrotoxicity caused by 2-bromo-bis-(glutathion-S-yl)hydroquinone and 2,3,5-tris-(glutathion-S-ly)hydroquinone, whereas the same protocol potentiates the nephrotoxicity of 2,5-dichloro-3-(glutathion-S-yl)hydroquinone and 2,5,6-trichloro-3-(glutathion-S-yl)hydroquinone. Which of these two scenarios occur as a consequence of metabolism by gamma-GT appears to be determined by the relative rate at which the product is transported into cells and/or interacts with cellular constituents, and the rate which the product undergoes intramolecular detoxication (cyclization) to a 1,4-benzothiazine. The same reaction may also explain why the mercapturic acid metabolite of menadione is nephrotoxic following systemic administration, whereas the GSH conjugate is without activity. Species differences exist in susceptibility to both 2-bromo-bis-(glutathion-S-ly)hydroquinone and 2,3,5-tris(glutathion-S-ly)hydroquinone induced nephrotoxicity. In this case, however, susceptibility does not correlate with renal gamma-GT activity, but rather to differences in the rate at which the corresponding cysteine and N-acetylcysteine conjugates undergo N-acetylation/N-deacetylation cycling. Thus the guinea pig--which is the only other rodent species (in addition to the rat), that is susceptible to 2-bromo-bis-(glutathion-S-ly)hydroquinone and 2,3,5-tris-(glutathion-S-ly)hydroquinone mediated nephrotoxicity--expresses the lowest activity of renal gamma-GT but exhibits the highest N-deacetylation:N-acetylation ratio. Differences in kinetics of these two reactions therefore contribute to species susceptibility. The toxicity of quinol/quinone thioethers is dependent upon a number of physiological, biochemical, and electrochemical factors. The rates at which quinol-thioethers undergo oxidation, with the concomitant generation of reactive oxygen species (IV, Fig. 1), macromolecular arylation (V, Fig. 1), intramolecular cyclization (VI, Fig. 1), and acetylation-deacetylation cycling (III, Fig. 1) is dependent upon the substrate in question. All these factors will contribute to the cell, tissue, and species susceptibility of this interesting class of GSH conjugates.

Quinone-thioether-mediated nephrotoxicity

It is clear that quinone-thioethers possess a variety of biological and toxicological activity [5]. The ubiquitous nature of quinones and the high concentrations of GSH within cells virtually guarantees that humans will be exposed to the potential adverse effects of the resulting quinone-thioethers. The generation of a biologically reactive intermediate is usually the initial and necessary step that eventually results in cell death, tissue necrosis, and/or tumor formation. The various mechanisms in which reactive intermediates interact with cellular constituents and trigger events that lead to cell death or cell transformation, are only now becoming unravelled. Knowledge of the disposition of quinone-thioethers will therefore be an important prerequisite to understanding their mechanism of action. Studies on the occurrence and biological and toxicological activity of quinone-thioethers therefore will be an important area for future research.

Urinary enzyme excretion as a parameter for detection of acute renal damage mediated by N-(3,5-dichlorophenyl)succinimide (NDPS) in Fischer 344 rats

The kidney has been identified as the specific target organ for in vivo exposure to an agricultural fungicide, N-(3,5-dichlorophenyl)succinimide (NDPS). The goal of this study was to determine if urinary protein and enzyme excretion were sensitive, non-invasive markers for NDPS-induced renal damage. The proximal tubular enzymes that were monitored were the brush-border enzyme alkaline phosphatase (ALP) and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase (NAG). Male Fischer 344 (F344) rats were injected intraperitoneally (i.p.) with 0.2 or 1.0 mmol kg-1 NDPS. Control animals were injected i.p. with sesame oil (2.5 ml kg-1). Urine was collected on ice 0-3, 3-6 and 6-24 h after NDPS or vehicle injection. Urinary protein and urinary NAG excretion levels were elevated (P < 0.05) above the control levels 0-3 h after treatment with 0.2 mmol kg-1 NDPS. Urinary protein and enzyme excretion was comparable between 0.2 mmol kg-1 NDPS-treated and control groups for all other time periods. Administration of a marked nephrotoxicant dose (1.0 mmol kg-1) was associated with elevated levels of urinary protein, NAG and ALP beginning 0-3 h after treatment when compared to the control group or to respective baseline values. It was concluded from these studies that measurement of urinary protein as well as the release of ALP and NAG were sensitive markers of renal damage produced by NDPS.

Toxicology of quinone-thioethers

Cytotoxicity associated with exposure to quinones has generally been attributed to either redox cycling, and the subsequent development of "oxidative stress," and/or to their interaction with cellular nucleophiles, such as protein and non-protein sulfhydryls. Glutathione (GSH) is the major non-protein sulfhydryl present in cells, and conjugation of potentially toxic electrophiles with GSH is usually associated with detoxication and excretion. However, this review discusses the biological (re)activity of quinone-thioethers. For example, quinone-thioethers are (1) capable of redox cycling (2) substrates for, and inhibitors of, a variety of enzymes (3) methemoglobinemic (4) potent nephrotoxicants (5) DNA reactive and (6) may contribute to quinone-mediated carcinogenicity and neurotoxicity. The ubiquitous nature of quinones, and the high intracellular concentrations of GSH, ensures that cells and tissues will be exposed to quinone-thioethers. The toxicological importance of quinone-thioethers in quinone-mediated toxicities therefore deserves further attention.

Nephrotoxicity of 2-bromo-(cystein-S-yl) hydroquinone and 2-bromo-(N-acetyl-L-cystein-S-yl) hydroquinone thioethers

The in vivo toxicity of isomeric cystein-S-yl and N-acetylcystein-S-yl conjugates of 2-bromohydroquinone was determined in male Sprague-Dawley rats. 2-Bromo-(dicystein-S-yl)hydroquinone [2-Br-(diCYS)HQ] and 2-bromo-(di-N-acetyl-L-cystein-S-yl)hydroquinone [2-Br-(diNAC)HQ] were considerably more nephrotoxic than their corresponding monosubstituted thioethers and 2-Br-(diCYS)HQ was more nephrotoxic than 2-Br-(diNAC)HQ. 2-Br-(diCYS)HQ caused elevations in blood urea nitrogen (BUN) concentrations and increases in the urinary excretion of glucose, lactate dehydrogenase (LDH), and gamma-glutamyl transpeptidase (gamma-GT) at a dose of 25 mumol/kg (iv). In contrast, 2-Br-(diNAC)HQ caused significant elevations in BUN at 100 mumol/kg and glucosuria and enzymuria at 50 mumol/kg. 2-Br-3-(CYS)HQ and 2-Br-5&6-(CYS)HQ caused increases in the biochemical indices of nephrotoxicity at doses between 50 and 150 mumol/kg whereas 2-Br-5-(NAC)HQ and 2-Br-6-(NAC)HQ required doses of 150-200 mumol/kg to cause smaller, though significant increases in urinary glucose, gamma-GT, and LDH excretion. The histological alterations caused by each thioether were qualitatively similar; only differences in the extent of the renal proximal tubular damage were observed. The initial lesion appears to involve the cells of the medullary ray and the S3M within the outer stripe of the outer medulla. The in vivo nephrotoxicity of 2-Br-(DiCYS)HQ, 2-Br-(diNAC)HQ, and the most potent monosubstituted thioethers, 2-Br-5&6-(CYS)HQ and 2-Br-6-(NAC)HQ, was investigated further. Pretreatment of animals with aminooxyacetic acid, an inhibitor of cysteine conjugate beta-lyase (beta-lyase), had no effect on the toxicity of 2-Br-(diCYS)HQ, partially inhibited the toxicity of 2-Br-5&6-(CYS)HQ, and almost completely protected against the toxicity of both 2-Br-6-(NAC)HQ and 2-Br-(diNAC)HQ. Thus, the nephrotoxicity of 2-Br-5&6-(CYS)HQ, 2-Br-6-(NAC)HQ, and 2-Br-(diNAC)HQ may be mediated, in part, via their processing by beta-lyase. Pretreatment of animals with probenecid, an inhibitor of renal organic anion transport, completely protected against the toxicity of 2-Br-(diNAC)HQ but had no effect on the toxicity of the other thioethers.