Elevated proliferation of proximal tubule cells and localization of accumulated alpha 2u-globulin in F344 rats during chronic exposure to unleaded gasoline or 2,2,4-trimethylpentane

Adverse outcome pathway (AOP): α2u-globulin nephropathy and kidney tumors in male rats

The National Research Council's vision of using adverse outcome pathways (AOPs) as a framework to assist with toxicity assessment for regulatory requirements of chemical assessment has continued to gain traction since its release in 2007. The need to expand the AOP knowledge base has gained urgency, with the U.S. Environmental Protection Agency's directive to eliminate reliance on animal toxicity testing by 2035. To meet these needs, our goal was to elucidate the AOP for male-rat-specific kidney cancer. Male-rat-specific kidney tumors occur through the ability of structurally diverse substances to induce α2u-globulin nephropathy (α2u-N), a well-studied mode of action (MoA) not relevant in humans that results in kidney tumor formation in male rats. An accepted AOP may help facilitate the differentiation from other kidney tumors MoAs. Following identification and review of relevant in vitro and in vivo literature, both the MIE and subsequent KEs were identified. Based on the weight of evidence from the various resources, the confidence in this AOP is high. Uses of this AOP include hazard identification, development of in vitro assays to determine if the MoA is through α2u-N and not relevant to humans resulting in decreased use of animals, and regulatory applications.

Streptozotocin induces alpha-2u globulin nephropathy in male rats during diabetic kidney disease

BACKGROUND

Alpha-2u globulin nephropathy mainly shows toxicological pathology only in male rats induced by certain chemicals and drugs, such as levamisole (antiparasitic and anticancer drugs). Streptozotocin (STZ) is also an anticancer-antibiotic agent that has been used for decades to induce a diabetic kidney disease model in rodents. The purpose of this study is to determine if STZ causes alpha-2u globulin nephropathy in male rats during an advanced stage of diabetic kidney disease. Alpha-2u globulin nephropathy, water absorption and filtration capacities (via aquaporin [AQP]-1, - 2, - 4 and - 5) and mitochondrial function (through haloacid dehalogenase-like hydrolase domain-containing protein [HDHD]-3 and NADH-ubiquinone oxidoreductase 75 kDa subunit [NDUFS]-1 proteins) were examined in STZ-induced diabetic Wistar rat model.

RESULTS

More than 80% of severe clinical illness rats induced by STZ injection simultaneously exhibited alpha-2u globulin nephropathy with mitochondrial degeneration and filtration apparatus especially pedicels impairment. They also showed significantly upregulated AQP-1, - 2, - 4 and - 5, HDHD-3 and NDUFS-1 compared with those of the rats without alpha-2u globulin nephropathy.

CONCLUSIONS

STZ-induced alpha-2u globulin nephropathy during diabetic kidney disease in association with deterioration of pedicels, renal tubular damage with adaptation and mitochondrial driven apoptosis.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

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.

Recommendations for the Interpretation of Renal Tubule Proliferative Lesions Occurring in Rat Kidneys with Advanced Chronic Progressive Nephropathy (CPN)

There is little guidance in the literature on the spectrum of proliferative tubule lesions in the kidneys of aging rats affected with spontaneously occurring, chronic progressive nephropathy (CPN), or their interpretation. Through accessing 2-year carcinogenicity studies in male F344 rats held in the Archives of the National Toxicology Program, NIEHS, a large number of cases of advanced CPN have been surveyed histopathologically for proliferative tubule lesions, and an attempt made to provide guidelines for discrimination of lesions common to the CPN process, from those representing precursors of neoplasia. Several proliferative lesions were identified as common in advanced CPN with no apparent evidence supporting a role in renal tubule carcinogenesis. It is recommended that these lesions be viewed generically as CPN tubule profiles, and not recorded separately from the diagnosis of CPN. Criteria were developed to distinguish these CPN-associated lesions from atypical tubule hyperplasia, a precursor of adenoma, both of which were also represented in this survey of advanced CPN.

Invited Review: A Contemporary Overview of Chronic Progressive Nephropathy in the Laboratory Rat, and Its Significance for Human Risk Assessment

CPN (chronic progressive nephropathy) is a spontaneous age-related disease that occurs in high incidence in the strains of rat commonly used in preclinical toxicology studies, exhibiting a male predisposition. Although increasing in incidence and severity with age, evidence indicates that CPN should be regarded as a specific disease entity and not just a manifestation of the aging process. A number of factors, mainly dietary manipulations, have been shown to modify the expression of CPN. Amongst these, restriction of caloric intake is the most effective for inhibiting the disease process. The precise etiology of CPN and the mechanism(s) underlying its pathogenesis remain unknown, but the long-standing assumption that glomerular dysfunction is the primary basis is challenged in the light of contemporary developments in understanding filtration and postglomerular cellular processing of albumin. CPN is not only a degenerative disease, but also has regenerative aspects with a high cell proliferative rate in affected tubules. Accordingly, evidence is emerging that advanced, particularly end-stage CPN, is a risk factor for a marginal increase in the background incidence of renal tubule tumors. Many chemicals are known to exacerbate the severity of CPN to an advanced stage, and this interaction between chemical and CPN can result in a small increase in the incidence of renal adenomas in 2-year carcinogenicity bioassays. Review of the pathological entities associated with chronic renal failure in man emphasizes that this rodent condition has no strict human counterpart. Because CPN is a rodent-specific entity, the finding of a small, statistically significant increase in renal tubule tumors, linked to exacerbation of CPN by a test chemical in a preclinical study for carcinogenicity, can be regarded as having no relevance for extrapolation in human risk assessment.

Transcriptomic alterations induced by Monuron in rat and human renal proximal tubule cells in vitro and comparison to rat renal-cortex in vivo

Monuron (1,1-dimethyl-3-(4-chlorophenyl)urea) is a widely used herbicide in developing countries although concerns have been raised about its toxicity and carcinogenicity.

Safety assessment of isoparaffins as used in cosmetics

The safety of isoparaffins as used in cosmetic products is reviewed in this safety assessment. These ingredients function mostly as solvents and also function as emollients in the 0001% to 90% concentration range. The Cosmetic Ingredient Review (CIR) Expert Panel has reviewed relevant animal and clinical data and concluded that these ingredients are safe in the present practices of use and concentration described in this safety assessment.

Consideration of rat chronic progressive nephropathy in regulatory evaluations for carcinogenicity

Chronic progressive nephropathy (CPN) is a spontaneous renal disease of rats which can be a serious confounder in toxicology studies. It is a progressive disease with known physiological factors that modify disease progression, such as high dietary protein. The weight of evidence supports an absence of a renal counterpart in humans. There is extensive evidence that advanced CPN, particularly end-stage kidney, is a risk factor for development of a background incidence of atypical tubule hyperplasia and renal tubule tumors (RTT). The likely cause underlying this association with tubule neoplasia is the long-term increased tubule cell proliferation that occurs throughout CPN progression. As a variety of chemicals are able to exacerbate CPN, there is a potential for those exacerbating the severity up to and including end-stage kidney to cause a marginal increase in RTT and their precursor lesions. Extensive statistical analysis of National Toxicology Program studies shows a strong correlation between high-grade CPN, especially end-stage CPN, and renal tumor development. CPN as a mode of action (MOA) for rat RTT has received attention from regulatory authorities only recently. In the absence of toxic effects elsewhere, this does not constitute a carcinogenic effect of the chemical but can be addressed through a proposed MOA approach for regulatory purposes to reach a decision that RTT, developing as a result of CPN exacerbation in rats, have no relevance for human risk assessment. Guidelines are proposed for evaluation of exacerbation of CPN and RTT as a valid MOA for a given chemical.

Ninety-Day Toxicity Study of Alpha-Iso-Methylionone in Rats

Alpha-iso-methylionone (AIM), a fragrance ingredient, was evaluated for systemic toxicity in rats. Male and female Sprague Dawley rats were administered 0, 5, 30, or 500 mg/kg/d AIM via gavage for 90 days. Statistically significant changes in blood chemistry parameters (reduced aspartate aminotransferase [AST], and increased cholesterol, creatinine, and total protein) were observed in both sexes at 500 mg/kg/d. There were statistically significant increases in liver and kidney weights in both sexes and in spleen weights in males at 500 mg/kg/d. Adaptive hepatocyte enlargement was observed in both sexes at 500 mg/kg/d. Globular accumulations of eosinophilic material were observed in the renal tubular epithelium in males at ≥30 mg/kg/d. Thyroid and bone marrow histopathological changes were observed in males at 500 mg/kg/d. The no-observed-effect level was 5 mg/kg/d for males and 30 mg/kg/d for females. Based on histopathological changes in the kidney in males, the no-observed-adverse-effect level was 30 mg/kg/d.

Proliferative and nonproliferative lesions of the rat and mouse urinary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Chemically exacerbated chronic progressive nephropathy not associated with renal tubular tumor induction in rats: an evaluation based on 60 carcinogenicity studies by the national toxicology program

Chronic progressive nephropathy (CPN) is a common age-related degenerative-regenerative disease of the kidney that occurs in both sexes of most strains of rats. Recently, claims have been made that enhanced CPN is a mode of action for chemically induced kidney tumors in male rats and that renal tubular tumors (RTTs) induced by chemicals that concomitantly exacerbate CPN are not relevant for human cancer risk assessments. Although CPN is an observable histopathological lesion that may be modified by diet, the etiology of this disease and the mechanisms for its exacerbation by chemicals are unknown, and it fails to meet fundamental principles for defining carcinogenic modes of action and human relevance. Our comprehensive evaluation of possible relationships between exacerbated CPN and induction of RTTs in 58 carcinogenicity studies, conducted by the National Toxicology Program, in male and 11 studies in female F344 rats using 60 chemicals revealed widespread inconsistency in the claimed association. Because the proposed hypothesis lacks evidence of biological plausibility, and due to inconsistent relationships between exacerbated CPN and kidney tumor incidence in carcinogenicity studies in rats, dismissing the human relevance of kidney tumors induced by chemicals that also exacerbate CPN in rats would be wrong.

Chronic progressive nephropathy in male F344 rats in 90-day toxicity studies: its occurrence and association with renal tubule tumors in subsequent 2-year bioassays

The occurrence and severity of spontaneous chronic progressive nephropathy (CPN) in control male F344 rats as well as the frequency of treatment-related CPN exacerbation were histopathologically reevaluated. A series of 43 National Toxicology Program (NTP) 90-day toxicity studies comparing the influence of NIH-07 or NTP-2000 diets was examined. Relationships between the histopathologic findings at 90 days and renal tubule proliferative lesions recorded in subsequent 2-year bioassays for 24 chemicals were statistically analyzed. CPN lesions were observed in 100% of the control male rats regardless of diet, but CPN was more severe in control rats fed NIH-07. Approximately one-third of the 90-day studies demonstrated a treatment-related exacerbation of CPN severity, which was independent of diet. For chemicals that proceeded to 2-year bioassays, all studies with a statistically significant increase in renal tubule tumors (RTT) at 2 years had treatment-related exacerbation of CPN in the 90-day and 2-year studies. These findings indicate that CPN occurs ubiquitously in young male F344 rats and that treatment-related exacerbation of CPN in 90-day studies is a relatively common occurrence, having the potential to be predictive of an increased incidence of RTT in subsequent 2-year bioassays.

Hydroquinone: an evaluation of the human risks from its carcinogenic and mutagenic properties

The toxicology of hydroquinone has been reviewed on a number of previous occasions. This review targets its potential for carcinogenicity and possible modes of carcinogenic action. The evaluation made by IARC (1999) of its carcinogenic risk to humans was that hydroquinone is not classifiable as to its carcinogenicity to humans (Group 3). This evaluation was based on inadequate evidence in humans and limited evidence in experimental animals. The epidemiological information comes from four cohort studies involving occupational exposures. A cohort of lithographers, some of whom had worked with hydroquinone, had an excess of malignant melanoma based on five cases, but only two of the cases had reported exposure to hydroquinone. In a study of photographic processors the number of exposed individuals was uncertain and the numbers of cases of individual cancer sites were small. In view of the statistical power limitations of these studies for individual diagnostic categories of cancers, they are not considered to be informative with regard to the carcinogenicity of hydroquinone. A cohort of workers with definite and lengthy exposure to hydroquinone, during either its manufacture or its use, had low cancer rates compared with two comparison populations; the reason for the lower than expected rates is unclear. In a motion picture film processing cohort there were significant excess malignancies of the respiratory system among workers engaged in developing, where there was exposure to hydroquinone as well as other chemicals. There was no information on tobacco smoking habits and no dose-response relationship. Hydroquinone has been shown reproducibly to induce benign neoplasms in the kidneys of male F344 rats dosed orally either by gavage (25 and 50 mg/kg body weight) or diet (0.8%). The gavage study has been evaluated in considerable detail. This evaluation showed that all renal tubule adenomas and all cases of renal tubule atypical hyperplasia occurred in areas of severe or end-stage chronic progressive nephropathy and that the neoplasms were not otherwise confined to any particular part of the kidney. It is likely that the mode of carcinogenic action of hydroquinone is exacerbation of this natural disease process. Hydroquinone is mutagenic in vitro and in vivo, having caused genotoxicity or chromosomal aberrations in rodent bone-marrow cells. At least a portion, if not all, of the chromosomal effects are caused by interference by hydroquinone or its metabolites with chromosomal segregation, probably due to interaction with mitotic spindle proteins. However, the dose routes used to demonstrate these effects in almost all of the studies in vivo were intraperitoneal or subcutaneous injection, which were considered inappropriate. There were five studies by the oral route. These included a mouse bone-marrow cell micronucleus test in which a weak, marginally positive response was obtained following a single oral dose of 80 mg/kg body weight. The remaining oral route studies all showed no significant effect. They included a mouse bone-marrow cell micronucleus test in which there was no genotoxic activity after exposure to a diet containing 0.8% hydroquinone for 6 days; two (32)P-post-labeling assays, one with targets of Zymbal gland, liver, and spleen in Sprague-Dawley rats, the other with the kidney as target in F344 rats; and the last oral assay was for 8-hydroxydeoxyguanosine adducts in F344 rat kidney DNA. Thus, the evidence (and the database) for any genotoxic effect in vivo is sparse and none has been observed in kidney. While glutathione conjugates could be responsible for the tumor induction, careful histology seems to show that the most actively toxic of several glutathione compounds tested, 2,3,5-triglutathion-S-yl hydroquinone, targets a very specific region of the kidney, the outer stripe of the outer medulla (OSOM), whereas hydroquinone-associated adenomas are more randomly distributed and occur in the cortex as well as the medulla. A nongenotoxic mode of action that involves exacerbation of a spontaneously occurring rodent renal disease, chronic progressive nephropathy (CPN), is proposed and evaluated. This disease is particularly prominent in male rats and the evidence is consistent with an absence of any human counterpart; therefore, the increased incidence of renal tubule adenomas in hydroquinone-dosed male rats is without human consequence.

Rat and mouse differences in gender-predominant expression of organic anion transporter (Oat1-3; Slc22a6-8) mRNA levels

Organic anion transporters (Oats) mediate the initial step of active renal excretion, specifically substrate uptake into proximal tubule cells. Despite extensive characterization of rat Oats, mouse Oat expression patterns are virtually unknown. This study was designed to identify basal expression patterns of mouse Oat1 (Slc22a6), Oat2 (Slc22a7), and Oat3 (Slc22a8) mRNA, compare these patterns with those in rat, and characterize postnatal development of mouse Oat mRNA. Tissues were collected from adult male and female 129J and C57BL/6 mice, and male and female C57BL/6 mice 0 to 40 days of age. Oat mRNA levels were determined by branched DNA signal amplification. Mouse Oat1 mRNA was primarily expressed in kidney of both strains, with male predominance. Mouse Oat2 mRNA levels were highest in kidney of both strains without gender predominance. In both strains, Oat3 mRNA was highest in kidney, and liver expression was male-predominant. However, only 129J mice had higher Oat3 mRNA levels in female kidney than in male kidney. During postnatal development, both Oat1 and Oat2 mRNA levels began to rise after 25 days of age. Oat3 mRNA levels rose gradually from birth through 40 days of age. Oat2 mRNA increased 30-fold during the first 40 days, whereas Oat1 and Oat3 increased about 2-fold. The most notable species differences in Oat mRNA expression were a lack of Oat2 female predominance in mouse kidney and a less dramatic Oat3 male predominance in mouse liver. With the exception of a significant species difference in Oat2 expression, many similarities were found between rat and mouse Oat mRNA levels.

Chemically induced renal tubule tumors in the laboratory rat and mouse: review of the NCI/NTP database and categorization of renal carcinogens based on mechanistic information

The incidence of renal tubule carcinogenesis in male and female rats or mice with 69 chemicals from the 513 bioassays conducted to date by the NCI/NTP has been collated, the chemicals categorized, and the relationship between carcinogenesis and renal tubule hyperplasia and exacerbation of the spontaneous, age-related rodent disease chronic progressive nephropathy (CPN) examined. Where information on mechanism or mode of action exists, the chemicals have been categorized based on their ability to directly or indirectly interact with renal DNA, or on their activity via epigenetic pathways involving either direct or indirect cytotoxicity with regenerative hyperplasia, or exacerbation of CPN. Nine chemicals were identified as directly interacting with DNA, with six of these producing renal tubule tumors at high incidence in rats of both sexes, and in some cases also in mice. Ochratoxin A was the most potent compound in this group, producing a high tumor incidence at very low doses, often with metastasis. Three chemicals were discussed in the context of indirect DNA damage mediated by an oxidative free radical mechanism, one of these being from the NTP database. A third category included four chemicals that had the potential to cause DNA damage following conjugation with glutathione and subsequent enzymatic activation to a reactive species, usually a thiol-containing entity. Two chemicals were allocated into the category involving a direct cytotoxic action on the renal tubule followed by sustained compensatory cell proliferation, while nine were included in a group where the cell loss and sustained increase in renal tubule cell turnover were dependent on lysosomal accumulation of the male rat-specific protein, alpha2mu-globulin. In a sixth category, morphologic evidence on two chemicals indicated that the renal tumors were a consequence of exacerbated CPN. For the remaining chemicals, there were no pertinent data enabling assignment to a mechanistic category. Accordingly, these chemicals, acting through an as yet unknown mechanism, were grouped as either being associated with an enhancement of CPN (category 7, 16 chemicals), or not associated with enhanced CPN (category 8, 4 chemicals). A ninth category dealt with 11 chemicals that were regarded as producing increases in renal tubule tumors that did not reach statistical significance. A 10th category discussed 6 chemicals that induced renal tumors in mice but not in rats, plus 8 chemicals that produced a low incidence of renal tubule tumors in mice that did not reach statistical significance. As more mechanistic data are generated, some chemicals will inevitably be placed in different groups, particularly those from categories 7 and 8. A large number of chemicals in the series exacerbated CPN, but those in category 7 especially may be candidates for inclusion in category 6 when further information is gleaned from the relevant NTP studies. Also, new data on specific chemicals will probably expand category 5 as cytotoxicity and cell regeneration are identified as obligatory steps in renal carcinogenesis in more cases. Additional confirmatory outcomes arising from this review are that metastases from renal tubule tumors, while encountered with chemicals causing DNA damage, are rare with those acting through an epigenetic pathway, with the exception being fumonisin B1; that male rats and mice are generally more susceptible than female rats and mice to chemical induction of renal tubule tumors; and that a background of atypical tubule hyperplasia is a useful indicator reflecting a chemically associated renal tubule tumor response. With respect to renal tubule tumors and human risk assessment, chemicals in categories 1 and 2, and possibly 3, would currently be judged by linear default methods; chemicals in category 4 (and probably some in category 3) as exhibiting a threshold of activity warranting the benchmark approach; and those in categories 5 and 6 as representing mechanisms that have no relevance for extrapolation to humans.

Dose-related changes of oxidative stress and cell proliferation in kidneys of male and female F344 rats exposed to potassium bromate

It is still of importance to investigate renal carcinogenesis by potassium bromate (KBrO3), a by-product of water disinfection by ozonation, for assessment of the risk to man. Five female F344 rats in each group were given KBrO3 at a dose of 300 mg/kg by single i.g. intubation or at a dose of 80 mg/kg by single i.p. injection, and were killed 48 h after the administration for measurements of thiobarbituric acid-reactive substances (TBARS) and 8-oxodeoxyguanosine (8-oxodG) levels in the kidney. Both levels in the treated animals were significantly elevated as compared with the control values. In a second experiment, 5 male and female F344 rats in each group were administered KBrO3 at concentrations of 0, 15, 30, 60, 125, 250 and 500 ppm in the drinking water for 4 weeks. KBrO3 in the drinking water did not elevate TBARS in either sex at any of the doses examined, but 8-oxodG formation in both sexes at 250 ppm and above was significantly higher than in the controls. Additionally, the bromodeoxyuridine-labeling index for proximal convoluted tubules was significantly increased at 30 ppm and above in the males, and at 250 ppm and above in the females. Alpha2u-globulin accumulation in the kidneys of male rats was increased with statistical significance at 125 ppm and above. These findings suggest that DNA oxidation induced by KBrO3 may occur independently of lipid peroxidation and more than 250 ppm KBrO3 in the drinking water can exert a carcinogenic effect by way of oxidative stress.

Effects of dibromoacetonitrile on rats following 13-week drinking water exposure

The subchronic toxicity of dibromoacetonitrile (DBAN), a disinfection by-product in drinking water, was studied in the rat. Male (180+/-18 g) and female (152+/-9 g) Sprague-Dawley rats (10 animals per group) were fed DBAN in organic-free distilled water at concentrations of 0.1, 1, 10 and 100 ppm for 13 weeks. Control rats received organic-free distilled water only. Water intakes in the highest dose males and females were reduced by 25 and 32% as compared to the controls, respectively (P<0.05), with no significant reductions in food consumption and body weight gain. The organ to body weight ratio was significantly increased in the highest-dose males and females for kidneys but not for the brain, liver, spleen, thymus and testicles. In the males, decreases were detected in serum uric acid levels at 1 and 100 ppm, and in urinary uric acid at 10 and 100 ppm. Decreased serum protein was detected in the highest-dose males and decreased serum LDH was found in the highest-dose females. Both the white blood cell and lymphocyte counts were significantly elevated in the highest-dose females. A significant increase in hepatic catalase activity was observed only in males starting at 1 ppm, and increased palmitoyl-CoA oxidase (PCO) activity was found in males and females of the highest dose group. In the males, decreased thiobarbituric acid reactive substance (TBARS) level was detected in the liver at 1.0 and 100 ppm groups, while increased TBARS was found in the serum at 100 ppm DBAN. No treatment-related changes were detected in the activities of hepatic benzyloxyresorufin O-dealkylase (BROD), pentoxyresorufin O-dealkylase (PROD) and ethoxresorufin O-deethylase (EROD), and in hepatic UDP-glucuronosyltransferase (UDPGT) and glutathione S-transferases (GST). Although DBAN is a potent inhibitor of hepatic aldehyde dehydrogenase (ALDH) and GST in vitro, there was no evidence of suppression of these enzymes in the treated animals. Mild histological changes were detected in animals receiving the highest dose, consisting of collapsed angularity, increased epithelial height in the thyroid of both sexes, and cytoplasmic vacuolation and nuclear vesiculation in the thyroid of females, increased myeloid to erythroid ratio in the bone marrow of both sexes, and cytoplasmic inclusions in the proximal tubules of male kidneys. In summary, treatment effects occurred predominantly at 100 ppm and included in both sexes: increased kidney weights, histological changes in the thyroid and bone marrow, and increased peroxisomal enzyme activities; and in males: decreased serum and urinary uric acid levels, and indication of oxidative stress. The no-observed-adverse-effect level (NOAEL) was therefore judged to be 10 ppm, equivalent to 1.11 and 1.21 mg/kg/day in the males and females, respectively.

Short-term oral toxicity of gasohol in female rats

The systemic toxicity of gasohol (10% ethanol in gasoline by volume) in female rats following 4-week oral administration was studied. Female Sprague-Dawley rats (198+/-14 g) were divided into four groups of ten animals each. The low- and medium-dose groups received by gavage corn oil containing gasoline/ethanol at 16/1.8 and 160/18 (mg kg(-1) body weight), respectively, for 28 consecutive days. The high-dose animals were administered gasoline/ethanol at 1600/180 mg kg(-1) on the first day and the dose was reduced to 800/90 mg kg(-1) for the rest of the study period. Control animals received corn oil only. Urine was obtained from all rats after weeks 1, 2 and 4 for biochemical analysis. At termination of the study, kidneys of four rats from each group were examined by electron microscopy. Body weight gains, organ weights, tissue and organ histopathology, serum biochemistry, hematology, liver enzymes and biochemistry were determined in the remaining six animals of each group. No treatment-related changes were observed in the following endpoints: body weight gain or relative weights of the brain, lungs, liver, kidneys, spleen and thymus. A significant increase in pentoxyresorufin O-deethylase (PROD) and benzoylresorufin O-dealkylase (BROD) activities was detected in the high-dose animals, whereas ethoxyresorufin O-deethylase (EROD) activity was unchanged. Treatment with gasohol did not produce any significant changes in hematology and serum clinical chemistry parameters. Biomarkers of oxidative stress such as serum and liver thiobarbituric acid reactive substances (TBARS) and liver glutathione also were unaffected by treatments. Urinary ascorbic acid was elevated markedly in the medium- and high-dose groups following the first, second and fourth weeks of treatment. Urine hippuric acid was increased significantly in the high-dose groups. A dose-related increase in urinary aldehydes also was observed in animals after the first, second and fourth week of treatment. Interestingly, a separate 1-week dosing study revealed that the increase in urinary aldehydes was associated with gasoline and not with ethanol treatment. In the high-dose animals slight increases in urinary protein and N-acetylglucosaminidase activity were observed after week 1 but not after week 2 or week 4. No histopathological changes were detected in the liver, kidneys, stomach, brain, lungs or other tissues examined. Electron microscopic examination of the kidneys also did not reveal any abnormalities. It was concluded that short-term oral administration of gasoline/ethanol at 800/90 mg kg(-1) produced a biochemical response in the liver but no adverse effects in the kidneys and lungs. The biological significance of elevated urinary aldehydes at gasoline/ethanol concentrations of 160/18 mg kg(-1) and higher remains to be studied.

Age-related cell proliferation and apoptosis in the kidney of male Fischer 344 rats with observations on a spontaneous tubular cell adenoma

Cell proliferation rate and apoptosis were examined in archival kidneys from young, middle-aged, and old male F344 rats. Immunohistochemical expression of proliferating cell nuclear antigen (PCNA) and apoptosis were quantified in the same cell populations of the proximal tubule epithelium. A total of 79 kidneys from 40 rats were examined. There was a progressive increase in cell proliferation rates in rats from 4 and 6-10 months of age. In 23-month-old rats, proliferative activity appeared to be reduced. No age-related variations in apoptotic indices were found. One of the 16 rats aged 23 months had a tubular cell adenoma. In the tumor-affected kidney, cell proliferation rate was dramatically higher than in the contralateral kidney as well as in all the other kidneys examined. This high proliferative activity was not balanced by variation in cell death.

Assessment in rats of the reproductive toxicity of gasoline from a gasoline vapor recovery unit

Gasoline (CAS 86290-81-5) is one of the world's largest volume commercial products. Although numerous toxicology studies have been conducted, the potential for reproductive toxicity has not been directly assessed. Accordingly, a two-generation reproductive toxicity study in rats was conducted to provide base data for hazard assessment and risk characterization. The test material, vapor recovery unit gasoline (68514-15-8), is the volatile fraction of formulated gasoline and the material with which humans are most likely to come in contact. The study was of standard design. Exposures were by inhalation at target concentrations of 5000, 10 000, and 20 000 mg/m(3). The highest exposure concentration was approximately 50% of the lower explosive limit and several orders of magnitude above anticipated exposure during refueling. There were no treatment-related clinical or systemic effects in the parental animals, and no microscopic changes other than hyaline droplet nephropathy in the kidneys of the male rats. None of the reproductive parameters were affected, and there were no deleterious effects on offspring survival and growth. The potential for endocrine modulation was also assessed by analysis of sperm count and quality as well as time to onset of developmental landmarks. No toxicologically important differences were found. Therefore, the NOAEL for reproductive toxicity in this study was > or =20 000 mg/m(3). The only systemic effects, in the kidneys of the male rats, were consistent with an alpha-2 u-globulin-mediated process. This is a male rat-specific effect and not relevant to human health risk assessment.

Molecular evidence of complex tissue- and sex-specific mRNA expression of the rat alpha(2u)-globulin multigene family

alpha(2u)-Globulin is well known to be a rat protein encoded by a highly homologous multigene family with more than twenty members. We report here the cloning and identification of major alpha(2u)-globulin mRNA species expressed in various tissues. Initially, eight individual clones (PGCL1-8) were obtained from a male preputial gland cDNA library. Data base analysis with BLAST demonstrated six mRNAs to be novel, all clones being characterized by highly conserved sequence motifs as lipocalins. All cDNAs contained an open reading frame of 543 nucleotides and encode 181 amino acid proteins showing 92.5-98.7% and 87.3-98.3% nucleic and amino acid identity, respectively. Denaturing gradient gel electrophoresis (DGGE) with sequence analysis showed that PGCL4 is a major member in the female mammary gland, and in the submaxillary and lachrymal glands of both sexes, while the counterpart in male liver and the coagulate glands was found to be PGCL1. Numbers of cDNA species including PGCL1 and PGCL4 were found in preputial glands, no sex-related difference being observed. These results directly demonstrate complex tissue- and sex-specific expression of alpha(2u)-globulins in terms of mRNA species, providing useful information for understanding regulation of the alpha(2u)-globulin multigene family.

A physiological model for ligand-induced accumulation of alpha 2u globulin in male rat kidney: roles of protein synthesis and lysosomal degradation in the renal dosimetry of 2,4,4-trimethyl-2-pentanol

A physiologically based pharmacokinetic (PBPK) model was constructed for the disposition of 2,4,4-trimethyl-2-pentanol (TMP-2-OH) in male rats and its induction of accumulation of renal alpha2u-globulin (alpha2u). The model included diffusion-restricted delivery of TMP-2-OH to compartments representing liver, lung, fat, kidney, GI tract, aggregated rapidly perfused tissues, and aggregated slowly perfused tissues. Metabolism by oxidation and glucuronidation was included for liver and kidneys. Rates of hepatic alpha2u production and resorption by renal proximal tubules were taken from the literature. Degradation of liganded alpha2u by renal lysosomal cathepsins was modeled with a Km value corresponding to the measured 30% reduction in proteolytic efficiency and with free and bound forms of alpha2u competing for access to the enzymes. Increased pinocytotic uptake of alpha2u into the kidney induces cathepsin activity. A model that ascribed renal alpha2u accumulation solely to reduced lysosomal proteolysis failed to reproduce the observed accumulation. The model could reproduce experimental observations if a transient increase in hepatic synthesis of alpha2u, stimulated by the presence of liganded alpha2u in the blood, and accelerated secretion of the protein from the liver were assumed. This model reproduces time course data of blood and kidney TMP-2-OH and renal alpha2u concentrations, suggesting that renal accumulation of alpha2u is not simply a consequence of reduced proteolytic degradation but may also involve a transient increase in hepatic alpha2u production. The model predicts increased delivery of TMP-2-OH to the kidney and consequent increased renal production of potentially toxic TMP-2-OH metabolites than would be the case if no alpha2u were present. Induced lysosomal activity and increased production of toxic metabolites may both contribute to the nephrotoxicity observed in male rats exposed to an alpha2u ligand or its precursor.

Quantitation of alpha2u-globulin in rat kidney cytosol by capillary electrophoresis

The renal accumulation of alpha2u-globulin has been implicated in the tumorigenicity of many nongenotoxic chemicals to the kidney of the male rat. Several chemicals inducing renal tumors in the male rat were shown to bind to alpha2u-globulin. This binding impairs the renal degradation of alpha2u-globulin, resulting in lysosomal overload, cell death, increased cell proliferation, and, presumably, renal tumor formation. To support the role of alpha2u-globulin accumulation in the renal toxicity of a chemical, a demonstration of the accumulation of this protein in the kidney of the male rat is one prerequisite. Monoclonal antibodies to alpha2u-globulin are available for quantifying alpha2u-globulin content; however, the procedure is time-consuming and complicated. We developed a method for the quantitation of alpha2u-globulin in renal cytosol using capillary electrophoresis. Renal cytosol fractions were analyzed by capillary electrophoresis as protein-SDS complexes. Using alpha2u-globulin purified from urine of male rats, the limit of detection was 10 microg/ml sample in routine analyses. Excellent run to run reproducibility in migration time (CV </= 4%) and peak areas corresponding to alpha2u-globulin (CV </= 3%) after normalization to the internal standard was observed. Significant increases in renal alpha2u-globulin content (up to 85% of total protein content) compared to controls (approx 15%) were observed in kidney cytosol of rats treated with alpha2u-globulin nephropathy-inducing agents such as trimethylpentane or the alkylphosphonates dimethyl methylphosphonate and diethyl ethylphosphonate, but not in kidney cytosol of male rats treated with tris-(2-chloroethyl)phosphate or the nephrotoxic agent hexachlorobutadiene. A good correlation of the alpha2u-globulin contents determined by capillary electrophoresis and immunoblotting with an alpha2u-globulin-specific antibody (r2 = 0.997) was obtained. Capillary electrophoresis provides a simple, rapid, and highly reproducible quantitation of alpha2u-globulin accumulation for renal tumorigens and may assist in the risk assessment process for these chemicals.

Direct lysosomal uptake of alpha 2-microglobulin contributes to chemically induced nephropathy

BACKGROUND

An abnormal accumulation of alpha 2-microglobulin (alpha 2 mu) in kidney lysosomes of male rats has been described in the nephropathy resulting from exposure to a variety of chemicals. The increment in lysosomal levels of alpha 2 mu cannot be explained by a decrease in its proteolytic susceptibility. Because a portion of alpha 2 mu resides in the cytosol of kidney cells, we decided to analyze whether this cytosolic form also contributes to the abnormal lysosomal accumulation of alpha 2 mu after exposure to chemicals.

METHODS

Intact kidney lysosomes were isolated from untreated or 2,2,4-trimethylpentane (TMP) treated rats, and their ability to take up alpha 2 mu was compared.

RESULTS

alpha 2 mu can be directly transported into isolated lysosomes in the presence of the heat shock cognate protein of 73 kDa (hsc73). alpha 2 mu specifically binds to a lysosomal membrane glycoprotein of 96 kDa, previously identified as the receptor for the hsc73-mediated lysosomal pathway of protein degradation. In rats exposed to TMP, the specific lysosomal transport of alpha 2 mu increases, as well as the ability of lysosomes to directly transport other substrates for this pathway. The increased lysosomal transport is mainly due to an increase in the levels of the receptor protein in the lysosomal membrane.

CONCLUSIONS

The hsc73-mediated lysosomal pathway contributes to the normal degradation of alpha 2 mu in rat kidney and liver, and the activity of this pathway is increased after exposure to TMP. Our results suggest that the chemically induced accumulation of cytosolic alpha 2 mu in lysosomes is mediated by an increased rate of direct uptake into lysosomes.

Analysis of alpha2u-globulin in rat urine and kidneys by liquid chromatography-electrospray ionization mass spectrometry

A quantitative method was developed for determination of alpha2u-globulin in urine and kidney samples collected from male rats using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS). Samples prepared from urine and kidney homogenates using size exclusion filters were subject to reversed-phase liquid chromatography and the effluent passed into an electrospray ionization source. Quantitative analysis using external standard calibration was based upon selected ion monitoring of protonated molecular ions by the mass spectrometer. Linear calibration curves were developed over the range of approximately 4. 6-370 microg of alpha2u-globulin/microL for spiked urine standards and over the range of approximately 4.6-550 microg of alpha2u-globulin/microL for spiked kidney standards. The precision (relative standard deviation) for repeated injection (using urine samples) and intra-assay precision (using both urine and kidney samples) were within +/-10.4% and +/-13.2%, respectively. Using spiked urine standards, inter-assay precision, intra-assay accuracy, and inter-assay accuracy were within +/-20%, +/-20%, and +/-15%, respectively. Using spiked kidney standards, intra-assay accuracy was within +/-15%. The limits of detection (LOD) for the determination of alpha2u-globulin in urine and kidney samples were approximately 0.41 pg/nL (1.0 fmol injected) and 25 pg/nL ( approximately 13 fmol injected), respectively. The limits of quantitation (LOQ) for determination of alpha2u-globulin in urine and kidney samples were calculated as 1.4 pg/nL (3.7 fmol injected) and 83 pg/nL (45 fmol injected), respectively. Applicability of the LC-ESI/MS method was demonstrated by determination of alpha2u-globulin in both urine and kidney samples collected from male Fischer 344/N rats dosed intravenously with cis-Decalin at concentrations of 0, 2.5, 5.0, 10, and 20 mg/kg. A dose-dependent relationship was found between the amount of cis-Decalin administered and alpha2u-globulin accumulation in kidney samples, whereas no significant change in the urinary levels of alpha2u-globulin occurred. These observations are consistent with excessive accumulation of alpha2u-globulin occurring in protein droplets in renal proximal tubule epithelial cells as a result of decreased catabolic activity due to formation of ligand-protein complexs with Decalin and its metabolite(s). This report demonstrates that LC-ESI/MS may be routinely applied for quantitative analysis of alpha2u-globulin in rat urine and kidney samples to address alpha2u-globulin accumulation and its role in the development of nephrotoxicity associated with chemical exposures.

Mechanisms of chemically induced renal carcinogenesis in the laboratory rodent

Laboratory studies with classical renal carcinogens in the rat and mouse, as well as research investigation with some of the chemicals proving positive for the kidney in National Toxicology Program carcinogenicity bioassays, have demonstrated the existence of a range of diverse mechanisms underlying rodent kidney carcinogenesis. The classical carcinogens used as experimental models for studying renal tumor pathogenesis, such as the nitrosamines, are genotoxic and interact directly with DNA, forming DNA adducts with mutagenic potential. In contrast, potassium bromate and ferric nitrilotriacetate (Fe-NTA), also effective renal carcinogens, appear to cause indirect damage to DNA mediated by oxidative stress. A number of nongenotoxic chemicals are associated with epigenetic renal tumor induction in rodents, and the activity of these tends to involve prolonged stimulation of cell proliferation throughout the duration of exposure. This mode of action reflects a sustained regenerative response, either due to direct chemical toxicity to the tubule cells, as with chloroform, or to indirect cytotoxicity associated with lysosomal overload, as in alpha2u-globulin accumulation in male rats resulting from the administration of such chemicals as d-limonene and tetrachloroethylene. The histopathologic nature of hydroquinone renal carcinogenesis suggests that an additional epigenetic pathway to renal tubule tumor formation in rats may be through chemical-mediated exacerbation of, and interaction with, the age-related spontaneous renal disease, chronic progressive nephropathy. These various mechanistic pathways have implications for the nature of the induced cancer process with respect to tumor incidence, latency, malignancy, and sex predisposition.

Methyl tert-butyl ether causes alpha2u-globulin nephropathy and enhanced renal cell proliferation in male Fischer-344 rats

Methyl tert-butyl ether (MTBE), a fuel additive blended into unleaded gasoline to decrease carbon monoxide emissions, induces renal tumors in male, but not female, rats exposed by inhalation to > or =3000 ppm MTBE. A number of chemicals that induce male rat-specific renal tumors also cause a syndrome unique to male rats referred to as alpha2u-globulin nephropathy (alpha2u-N). The objective of the present study was to determine if MTBE induces an alpha2u-N and renal cell proliferation in male F-344 rats. Male and female F-344 rats were exposed to MTBE vapors of 0, 413, 1516, or 3013 ppm for 6 hr/day for 10 consecutive days. Significant proximal tubule necrosis and protein droplet accumulation were observed in kidneys from male rats exposed to 1516 and 3013 ppm MTBE. Significantly greater labeling indices were observed in all groups of MTBE-exposed male rats. alpha2u-Globulin immunoreactivity was present in and confined to protein droplets in male rat kidney. A mild dose-related increase in alpha2u concentration in the kidney, as measured by an enzyme-linked immunosorbent assay, was observed in male rats exposed to MTBE, with a statistically significant increase in alpha2u concentration in male rats exposed to 3013 ppm MTBE. There was a strong positive correlation (r = 0.994) with exposure concentration between cell proliferation and alpha2u concentration in male rat kidney. No significant differences were observed in female rats for any of these responses. Further analysis of kidney cytosol failed to demonstrate the accumulation of any protein besides alpha2u in MTBE-exposed male rat kidney. These findings demonstrate that MTBE causes a mild induction of alpha2u-N and enhanced renal cell proliferation in male, but not female, F-344 rats, suggesting a role for alpha2u-N in renal tumorigenesis.

1,3,5-Trinitrobenzene-induced alpha-2u-globulin nephropathy

Male and female Fischer-344 (F-344) and male NCI-Black-Reiter (NBR) rats were dosed with 0, 35.5, or 71 mg 1,3,5-trinitrobenzene (TNB)/kg/day for 10 days. Male F-344 rats were dosed with TNB (0 and 35.5 mg/kg) for 20 and 30 days. Hematoxylin and eosin and Mallory-Heidenhain stains and alpha-2u-globulin and proliferating cell nuclear antigen immunohistochemical stains were performed on kidney sections. All treated male F-344 rats exhibited dose-related accumulation of hyaline droplets containing alpha-2u-globulin in proximal tubules. The kidney weights were significantly increased in male and female rats treated with TNB. Significant increases in cell proliferation in proximal tubules were observed in male F-344 rats. Renal changes observed in TNB-treated rats appeared identical to those from other chemicals that induce alpha-2u-globulin nephropathy in male rats. No hyaline droplet accumulation was found in female F-344 and male NBR rats at any doses. We can conclude that TNB induces dose-related exacerbation of hyaline droplets containing alpha-2u-globulin in male rat kidney and subsequent cell proliferation.

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.

Short-term inhalation toxicity of methanol, gasoline, and methanol/gasoline in the rat

Four- to five-week-old male and female Sprague Dawley rats were exposed to vapors of methanol (2500 ppm), gasoline (3200 ppm), and methanol/gasoline (2500/3200 ppm, 570/3200 ppm) six hours per day, five days per week for four weeks. Control animals were exposed to filtered room air only. Depression in body weight gain and reduced food consumption were observed in male rats, and increased relative liver weight was detected in rats of both sexes exposed to gasoline or methanol/gasoline mixtures. Rats of both sexes exposed to methanol/gasoline mixtures had increased relative kidney weight and females exposed to gasoline and methanol/gasoline mixtures had increased kidney weight. Decreased serum glucose and cholesterol were detected in male rats exposed to gasoline and methanol/gasoline mixtures. Decreased hemoglobin was observed in females inhaling vapors of gasoline and methanol/gasoline at 570/3200 ppm. Urine from rats inhaling gasoline or methanol/gasoline mixtures had up to a fourfold increase in hippuric acid, a biomarker of exposure to the toluene constituent of gasoline, and up to a sixfold elevation in ascorbic acid, a noninvasive biomarker of hepatic response. Hepatic mixed-function oxidase (aniline hydroxylase, aminopyrine N-demethylase and ethoxyresorufin O-deethylase) activities and UDP-glucuronosyltransferase activity were elevated in rats exposed to gasoline and methanol/gasoline mixtures. Histopathological changes were confined to very mild changes in the nasal passages and in the uterus, where decreased incidence or absence of mucosal and myometrial eosinophilia was observed in females inhaling gasoline and methanol/gasoline at 570/3200 ppm. It was concluded that gasoline was largely responsible for the adverse effects, the most significant of which included depression in weight gain in the males, increased liver weight and hepatic microsomal enzyme activities in both sexes, and suppression of uterine eosinophilia. No apparent interactive effects between methanol and gasoline were observed.

Induced regenerative cell proliferation in livers and kidneys of male F-344 rats given chloroform in corn oil by gavage or ad libitum in drinking water

These studies were designed to establish the dose response relationships for the induction of cytolethality and regenerative cell proliferation in the liver and kidneys of male F-344 rats given chloroform by gavage or in drinking water. Rats were administered oral doses of 0, 10, 34, 90 or 180 mg/kg/day chloroform dissolved in corn oil by gavage for 4 days or for 5 days/week for 3 weeks. A second group of rats was given chloroform ad libitum in the drinking water at concentrations of 0, 60, 200, 400, 900 or 1800 ppm for 4 days or 3 weeks. Bromodeoxyuridine (BrdU) was administered via an implanted osmotic pump 3.5 days prior to necropsy to label cells in S-phase. Cells having incorporated BrdU were visualized in tissue sections immunohistochemically and the labelling index (LI) evaluated as the percentage of S-phase cells. Rats treated with 90 or 180 mg/kg/day by gavage for 4 days had mild to moderate degeneration of renal proximal tubules and centrilobular hepatocytes. These alterations were absent or slight after 3 weeks of treatment. LI were increased in the kidney cortex only in the rats treated with 180 mg/kg/day for 4 days. A dose-dependent increase in LI was seen in rat liver after 4 days of treatment with 90 and 180 mg/kg/day by gavage, but the LI remained elevated after 3 weeks of treatment only at the 180 mg/kg/day dose. When chloroform was administered in the drinking water, no microscopic alterations were seen in the kidneys after 4 days of treatment. As a general observation, rats treated for 3 weeks with 200 ppm chloroform and greater had slightly increased numbers of focal areas of regenerating renal proximal tubular epithelium and cell proliferation than were noted in the controls, but no clear dose response relationship was evident. However, the overall renal LI was not increased at any dose or time point. Similarly, only mild hepatocyte vacuolation was observed in rats given 1800 ppm chloroform in the water for 3 weeks with no increase in the hepatic LI at any time point, even though the rats were consuming chloroform at a rate of 106 mg/kg/day at the 1800 ppm drinking water concentration. These data indicate more severe hepatic and renal toxicity when chloroform is administered by gavage than in the drinking water and a different pattern of regenerative proliferation in the kidney.(ABSTRACT TRUNCATED AT 400 WORDS)

Demonstration of a temporal relationship between ethyl acrylate-induced forestomach cell proliferation and carcinogenicity

Ethyl acrylate (EA) is a known forestomach carcinogen in both rats and mice. Recent work in this laboratory indicated that carcinogenic doses of EA administered by gavage for 13 wk resulted in a sustained increase in forestomach epithelial hyperplasia as long as exposure to EA continued. However, hyperplasia regressed and no forestomach neoplasms were seen after a 19-mo recovery period. Current studies were designed to further investigate the time required for sustained hyperplasia to lead to neoplasia as well as the organ specificity of EA-induced cell proliferation/hyperplasia vs carcinogenicity. EA was administered at 200 mg/kg (po) to male Fischer-344 rats, 5 days/wk. Squamous cell proliferation/hyperplasia was observed in the forestomach of all rats that received EA for 6 or 12 mo. Treatment of rats with EA for 12 mo followed by 2 mo of recovery resulted in the development of forestomach papillomas in 2 of 5 treated rats. Furthermore, animals treated for 12 mo and allowed 9 mo of recovery exhibited an increase in forestomach squamous cell carcinomas and papillomas at a combined incidence of 4 in 13. In contrast, animals treated with EA for 6 mo and allowed 2 or 15 mo of recovery exhibited a time-dependent regression of cell proliferation and did not develop forestomach neoplasms. No significant elevation in liver cell proliferation or neoplasia was seen at any time in any of the rats included in the present study, further confirming the organ specificity in the relationship between EA-induced cell proliferation and carcinogenicity. In conclusion, EA resulted in increased cell proliferation in the target organ of carcinogenicity (forestomach) but not in nontarget organs such as the liver. This work indicates that cell proliferation, sustained for a sufficient period of time, results in the development of neoplasia despite cessation of chemical administration. Furthermore, a temporal relationship exists between EA-induced epithelial cell proliferation and forestomach carcinogenicity.

Occupational hydrocarbon exposure and chronic nephropathy

This review aims at discussing the questions raised by the hydrocarbon-related chronic nephropathy and its possible consequence, the hydrocarbon-related chronic renal failure. It has been attempted to adopt the point of view of the clinician. Therefore, the most important part of the review is devoted to a presentation and an analysis of the available data on humans. The main features of the available studies on human subjects are presented, their conclusions discussed in the light of the possible methodological flaws, and practical conclusions drawn. After a discussion of the main difficulties encountered for selecting the suitable exposure indicator, the studies are discussed in order of decreasing quality of the study design (cohort, case-control, cross-sectional studies, and the case reports). It is concluded that a great deal of controversies about chronic hydrocarbon-related nephropathy is explained by differences in the study design and that hydrocarbon-induced nephropathy is probably more than a mere hypothesis, although a causal relationship has not yet been proven. Finally, some practical consequences for dealing with a hydrocarbon-exposed patient diagnosed with a kidney disease and the need for further research are discussed.

Risk assessment of d-limonene: an example of male rat-specific renal tumorigens

The naturally occurring food constituent d-limonene has been found to cause tumors at high doses only in the kidney of the male rat in association with the development of hyaline droplet nephropathy. In contrast, neither kidney tumors nor the associated nephropathy have been found in female rats or mice at much higher doses. Adult male rats produce large quantities of a specific low-molecular-weight protein in the liver, which is known as alpha 2U-globulin (alpha 2U-g). With administration of sufficient doses of d-limonene to male rats, this protein has been found to accumulate excessively in the P2 segment cells of renal proximal tubules, resulting in hyaline droplet formation as a manifestation of protein overload. Hyaline droplet accumulation is the first stage in a unique sequence of nephropathic lesions (also known as alpha 2U-g nephropathy), including granular casts in the outer medulla and linear mineralization in the papilla. The mechanism underlying protein accumulation appears to be the reversible binding of chemical to alpha 2U-g with subsequent prolongation of its half-life in the tubule cell. In the case of d-limonene, the minor metabolite d-limonene-1,2-oxide has been shown to be the primary chemical species that binds reversibly to alpha 2U-g, impeding the normal process of lysosomal proteinase degradation of alpha 2U-g. The ensuing nephropathy is associated with a sustained increase in compensatory renal tubule cell proliferation, which provides the putative mechanistic link with renal tumor formation possibly through tumor promotion of spontaneously initiated cells or enhanced spontaneous mutagenesis. This proposed mechanism has been supported by additional information, including negative genotoxicity tests for d-limonene and its oxide metabolites, experimentally verified tumor promotion, and enhanced cell proliferation primarily in P2 segment tubule cells in male F344 rats, but no such effects in the alpha 2U-g-deficient NBR rat. The mechanism of d-limonene tumor development does not appear to be possible in humans since neither the quantity nor the type of protein that binds d-limonene or d-limonene-1,2-oxide is present. The deduction that the renal tumors induced in male rats are not relevant to human carcinogenicity in the hazard evaluation step of risk assessment completes the evaluation of human risk for d-limonene. Consequently, it can be concluded that d-limonene does not pose any carcinogenic or nephrotoxic risk to humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Interpretation of male rat renal tubule tumors

Based on an analysis of recent scientific studies, a Technical Panel of the U.S. Environmental Protection Agency's (EPA) Risk Assessment Forum recently advised EPA risk assessors against using information on certain male rat renal tubule tumors to assess human risk under conditions specified in a new Forum report. Risk assessment approaches generally assume that chemicals producing tumors in laboratory animals are a potential cancer hazard to humans. For most chemicals, including classical rodent kidney carcinogens such as N-ethyl-N-hydroxyethylnitrosamine, this extrapolation remains appropriate. Some chemicals, however, induce accumulation of alpha 2u-globulin (alpha 2u-g), a low molecular weight protein, in the male rat kidney. The alpha 2u-g accumulation initiates a sequence of events that appears to lead to renal tubule tumor formation. Female rats and other laboratory mammals administered the same chemicals do not accumulate low molecular weight protein in the kidney, and they do not develop renal tubule tumors. Because humans appear to be more like other laboratory animals than like the male rat, in this special situation, the male rat is not a good model for assessing human risk. The Forum report stresses the need for full scrutiny of a substantial set of data to determine when it is reasonable to presume that renal tumors in male rats are linked to a process involving alpha 2u-g accumulation and to select appropriate procedures for estimating human risks under such circumstances.