* Battelle, Toxicology Northwest, Richland, Washington 99352; and
National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709
Received September 25, 2002; accepted January 3, 2003
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ABSTRACT |
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Key Words: decalin (decahydronaphthalene); 2-decalone; decalol; 2u-globulin; hyaline droplet; cell proliferation; hyperplasia; nephropathy; toxicity; carcinogenicity; sex; F344/N.
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INTRODUCTION |
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The most recognized toxicity related to decalin exposure in laboratory animals is 2u-globulin-induced nephropathy in male rats. Decalin is one of a variety of chemicals that induce
2u-globulin accumulation (CIGA) in the male rat kidney (Bruner and Pitts, 1983
; Mao et al., 1998
; Stone et al., 1987
). The synthesis of
2u-globulin is species-, sex-, and age-specific, in that the protein is synthesized in the liver under androgenic control in male rats. Low levels of
2u-globulin are detected in the male rat liver under the stimulus of testosterone at 3540 days, and reach maximum levels by 6080 days. Due to the development of hepatic insensitivity to androgen during aging, hepatic synthesis of
2u-globulin falls gradually after five months of age, and the levels are reduced by more than 90% by 22 months of age in male rats (Hard et al., 1993
; Motwani et al., 1984
; Roy et al., 1983
). Neither
2u-globulin nor its corresponding mRNA is detectable in the livers of sexually intact female rats (Hard et al., 1993
; MacInnes et al., 1986
).
2u-Globulin is filtered by the glomerulus; approximately half the filtrate is normally reabsorbed into kidney proximal tubules, digested in cytoplasmic lysosomes, and reabsorbed back into the circulation. Lehman-McKeeman et al.(1990)
demonstrated in vitro that
2u-globulin forms a complex with CIGA and becomes resistant to lysosomal hydrolysis, leading to its accumulation in tubular epithelium cytoplasm in the form of hyaline droplets. Considerable effort has been invested to establish the mechanistic basis for chemical-induced, male rat-specific nephropathy because of the implications of the potential end result, renal neoplasia, for human risk assessment (Borghoff et al., 1990
, 1991
; Swenberg, 1993
).
Although decalin exposure undoubtedly induces 2u-globulin accumulation, it is not clear which chemical moieties, either decalin alone or its metabolites or both, are responsible for in vivo binding to
2u-globulin. With fusion of two cyclohexane rings, both cis- and trans-decalin may be present in the commercial product (Olson et al., 1986
). Decalin is extensively metabolized in vivo, potentially forming a variety of isomeric metabolites following exposure, such as 2-decalone and isomers of decalols (Longacre, 1987
). When cis- or trans-decalin was administered to female rabbits, 67% (cis) or 53% (trans) of the dose, respectively, was eliminated in urine as decalol glucuronide conjugates (Elliott et al., 1966). In addition to decalols in urine, 2-decalone has been detected in the kidneys of male rats but not females (Elliott et al., 1966; Olson et al., 1986
).
2u-Globulin nephropathy has been observed following short-term exposure to decalin using gavage and inhalation routes (Gaworski et al., 1985
; Saito et al., 1992
). However, there has been no study to determine if chronic exposure to decalin in male rats would result in significant increases in chronic toxicity and more importantly, renal carcinogenicity. Differentiating
2u-globulin-mediated renal tumors in male rats in a chronic study from other possible etiologies is critical for risk assessment because renal tumors induced by
2u-globulin nephropathy are not used in hazard characterization for the human population (Alison et al., 1994
; Borghoff et al., 1996
; Swenberg, 1993
). Chronic exposure to other CIGA such as d-limonene and dichlorobenzene induced a low incidence of renal neoplasia in male rats (Borghoff et al., 1990
; NTP, 1987
, 1988
). Several of these compounds also caused an increase in the severity and/or incidence of chronic progressive nephropathy not only in male rats but also in females, indicating that another mechanism of chronic renal toxicity might be operating in aging rat kidneys (Borghoff et al., 1996
; NTP, 1986
, 1987
; U.S. EPA, 1991
).
Decalin was selected for inhalation toxicity and carcinogenicity studies by the National Institute of Environmental Health Sciences (NIEHS) based on the lack of long-term animal toxicity data, the high potential for consumer exposure, and its structural similarity to naphthalene or tetralin. This report presents findings related to renal toxicity and carcinogenicity following 13-week and two-year studies. The specific objectives were to (1) characterize the subchronic toxicity of decalin in male and female F344 rats, with an emphasis on nephropathy in males; (2) compare the concentrations of decalin, 2-decalone, and 2u-globulin in homogenates prepared from whole kidneys collected from males over 2 to 13 weeks of decalin exposure; and (3) correlate the nephropathy observed in the 13-week study with renal toxicity and carcinogenicity in the two-year study.
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MATERIALS AND METHODS |
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Animals.
Male and female F344 rats were obtained from Taconic (Germantown, NY) at 4 weeks of age and quarantined for 10 to 14 days before study. They were randomized, assigned to groups using body weight as a blocking variable, and housed in individual wire-mesh units in exposure chambers (Hazleton 2000, Lab Products, Inc., Harford System Division; Aberdeen, MD). Chamber environmental conditions (temperature, 75 ± 3°F; relative humidity, 55 ± 15%; airflow, 15 ± 2 cfm) were monitored at
4-h cycles for 24 h/day and maintained within acceptable ranges through the studies. Water and food (NTP-2000, Zeigler Bros., Inc., Gardners, PA) were available ad libitum, except food was withheld during exposures and urine collection. A 12-h light/dark cycle (light started at 0600 h) was maintained throughout the studies.
Experimental Design
13-Week inhalation study.
Rats (6 weeks old; total 20 rats/sex/group) were exposed via whole-body inhalation to 0, 25, 50, 100, 200, or 400 ppm decalin for 6 h plus T90/day (T90
12 min), five days/week (exclusive of weekends and holidays) for up to 13 weeks. Animals were observed at least twice daily for moribundity and mortality, and their individual body weights and clinical signs were recorded weekly and at terminal sacrifice. At weeks 2 and 6 (five/sex/group) and week 12 (10/sex/group), rats were placed in metabolism cages (Lab Products Inc., Maywood, NJ) for 16-h urine collection immediately following exposure. Urine samples collected at weeks 2 and 6 were analyzed for volume, creatinine, and decalol isomers. Urine samples collected at week 12 were analyzed for the following analytes using Roche Cobas Fara methodologies: creatinine (Larson, 1972
), protein (Silverman and Christenson, 1994
), lactate dehydrogenase (LDH; Gay et al., 1968
), aspartate aminotransferase (AST; Moss and Henderson, 1994
), and N-acetyl-glucosaminidase (NAG; Yakata, 1983
). Following urine collections at weeks 2 and 6, male rats were euthanized and kidneys were collected (five males/group). A complete necropsy was performed on both sexes at terminal sacrifice (week 13; 10/sex/group), selected organs (kidney, liver, thymus, testis, heart, and lungs) were collected and weighed.
Homogenates prepared using the right kidney from male rats at weeks 2, 6, and 13 were subsequently analyzed for 2u-globulin, decalin, and 2-decalone. Homogenates prepared from the right kidney from female rats at week 13 were analyzed for decalin and 2-decalone. Left kidneys from both sexes were fixed in 10% neutral buffered formalin, processed, and stained with hematoxylin and eosin (H&E) for histopathologic evaluation. Left kidneys from male rats were also stained with Mallory-Heidenhain (MH) for protein evaluation and with anti-proliferating cell nuclear antigen (anti-PCNA) for determination of cell proliferation indices.
Complete histopathologic evaluations were performed on all controls and 400-ppm rats. Target organs and gross lesions were examined in lower exposure groups until adverse effects were not observed. Kidneys from male rats were evaluated microscopically for all exposure groups.
Two-year inhalation study.
Rats (6 weeks old) were exposed via whole-body inhalation to 0, 25, 50, 100, or 400 ppm decalin for males (50/group, except 20 males at 400 ppm) and at 0, 25, 100, or 400 ppm for females (50/group) for 6 h plus T90/day (T90
12 min), 5 days/week (exclusive of weekends and holidays) for two years.
Note that in selecting these exposure concentrations for male rats, pathology findings from the 13-week inhalation study suggested that kidney lesions in male rats exposed to 400 ppm would be too severe, and that significant body weight loss and mortality would likely occur in male rats at this concentration during the two-year study. However, the feed for these studies was the relatively low-protein NTP 2000 diet (14% protein), and it was of interest to determine whether less severe male kidney lesions might be observed with this low-protein diet. Accordingly, the high exposure concentration for male rats in the chronic study was set at 100 ppm while the high exposure concentration remained at 400 ppm for female rats (50 rats/exposure/sex). An additional group of 20 male rats was exposed to 400 ppm to evaluate the effects of the low protein diet on the severity of kidney lesions. It was also necessary to include some males with the female rats exposed to 400 ppm to promote estrus cycling. Because male and female rats were housed in the same 400 ppm chamber as mice during a concurrently run two-year study, space limitations precluded using a greater number of male rats at this concentration.
Animals were observed at least twice daily for moribundity and mortality and their individual body weights and clinical signs were recorded monthly through week 89, and every two weeks thereafter until terminal sacrifice. Complete necropsy and histopathological evaluations were done on all animals.
Generation and monitoring of decalin exposure.
Decalin was pumped through a preheater into the top of a heated glass column filled with glass beads. Heated nitrogen entered the column from below, assisting vaporization while transporting the decalin vapor to the chambers in heated lines to prevent condensation. Decalin exposure concentrations were monitored every 24 min during the exposure by on-line GC/FID (Hewlett-Packard [HP]-5890). The peaks for the cis- and trans-isomers were integrated separately, which showed no fractionation of decalin composition. The sum of the cis and trans peak areas was used to calculate the concentration of decalin for each determination. Calibration of the on-line monitor was achieved by quantitative determination of decalin in exposure chamber samples collected with adsorbent gas sampling tubes (ORBO 101; Supelco, Bellfonte, PA). The actual exposure concentrations for both 13-week and two-year studies were maintained within 5% of the target exposure concentrations.
Renal cell proliferation.
The antibody of proliferating cell nuclear antigen (PCNA; PC-10 clone) was obtained from DAKO (Carpenteria, CA). Sections of left kidneys and duodenum (as a positive control for cell proliferation), stained with anti-PCNA, were qualitatively (duodenum) and quantitatively (kidneys) assessed for proliferation labeling. Using a 20x objective and a 10 x 10 mm optical micrometer, 2000 proximal tubule nuclei in the cortex were counted from kidney sections and numbers of labeled and total (S-phase labeled and unlabeled) nuclei were recorded. Proximal tubules were counted from the lysosomal segment of the proximal convoluted tubule, referred as the P2 segment in the cortex of the kidney. The lysosomal segment of the straight segment of the proximal tubule was not counted. Identification of cells in the S-phase was based on cellular distribution and intensity of the reaction product. Proximal tubule nuclei with uniform deep red to black nuclear staining were recorded as positive for PCNA expression and counted as labeled. Cells in the G1 (those cells with minimal nuclear staining) and G2 (speckled nuclear and cytoplasmic staining) were not counted as labeled.
This method is consistent with the method of Foley et al.(1991). Selection of the counting sites was done using the method of Larson et al.(1994)
: Starting at the second field in from the outer edge of the cortex at one pole of the kidney and moving from pole to pole across the cortex, all identifiable proximal tubular cell nuclei in every other field were counted until a total of
2000 proximal tubule nuclei were counted. If <2000 were obtained when the opposite pole of the kidney was reached, the grid was moved toward the convex surface of the kidney and counting was resumed using the same method as described above. The labeling index was calculated by dividing the number of labeled nuclei by the total nuclei, expressed as a percent.
Diagnosis of proliferative lesions in kidney.
In the kidney, hyperplasia, adenoma, and carcinoma are thought to represent a continuum in the progression of proliferative lesions of the renal tubule epithelium. Hyperplasias were generally focal lesions characterized by increased numbers of tubule epithelial cells forming multiple layers that partially or totally filled the tubule lumen and usually caused dilatation of the tubule. Adenomas were generally discrete expansile masses that were larger than hyperplasias (greater than the diameter of five tubules) and had a more complex structure. Carcinomas were less discrete and larger than adenomas with hemorrhage, necrosis, local invasion, and/or metastasis to distant sites (Hard et al., 1995).
Analyses of 2u-Globulin, Decalin, and 2-Decalone in Kidney
2u-Globulin.
Supernatants prepared from kidney homogenates were analyzed for 2u-globulin by competitive indirect ELISA (Borghoff et al., 1992
), using ascites fluid containing anti-
2u-globulin monoclonal antibody, which was kindly provided by Dr. Susan J. Borghoff (CIIT Center for Health Research, Research Triangle Park, NC).
Decalin.
Kidney concentrations of cis- and trans-decalin were determined following cyclohexane extraction of kidney homogenates (100 mg) spiked with (cis + trans)-decalin-d18 (Aldrich Chemical Co.), using a mass selective detector interfaced to a gas chromatograph. Temperature programming (50 to 300°C) was used to conduct separations on a fused-silica capillary column (DB-5MS; 30-m x 0.25-mm ID; film thickness, 0.25-µm; J&W Scientific, Folsom, CA) with helium as the carrier gas. Selected ion mass chromatograms were obtained by monitoring characteristic ions for cis- and trans-decalin (m/z 138) and trans-decalin-d18 (m/z 156). Concentrations for total decalin isomers (cis and trans) were used for statistics and reporting.
2-Decalone.
Kidney concentrations of cis- and trans-2-decalone (authentic standards for each isomer were purchased from Aldrich Chemical Co.) were determined following cyclohexane extraction of kidney homogenates spiked with 2-decalone-1,1,3,3-d4 (synthesized by Dr. John Cashman; Seattle Biomedical Research Institute, Seattle, WA) using GC/MS. Temperature programming (70 to 250°C) was used to conduct separations on a fused silica capillary column (DB-1701; 30-m x 0.25-mm ID; film thickness, 0.25 µm; J&W Scientific), with helium as the carrier gas. Selected ion mass chromatograms were obtained by monitoring characteristic ions for cis- and trans-2-decalone (m/z 152) and 2-decalone-d4 (m/z 156). Concentrations for total 2-decalone isomers (cis and trans) were used for statistics and reporting.
Analysis of decalol isomers in urine.
Urine samples (10 µl) were added to 0.2 M acetate buffer (100 µl; pH 5.4) containing an internal standard (1,2,3,4-tetrahydro-1-naphthol; Aldrich Chemical Co.) and incubated overnight at 37°C with
10 µl ß-glucuronidase/arylsulfatase (Boehringer Mannheim, GmbH, Germany). Samples were extracted with cyclohexane and the eight possible decalol isomers were analyzed using GC/MS. Temperature programming (70 to 250°C) was used to conduct separations on a fused silica capillary column (DB-Wax; 30-m x 0.25-mm ID; film thickness 0.25 µm; J&W Scientific), with helium as the carrier gas. Selected ion mass chromatograms were obtained by monitoring characteristic ions for the eight decalol (m/z 136) isomers and 1,2,3,4-tetrahydro-1-naphthol (m/z 130). Six urinary decalol isomers were identified as trans,cis-1-decalol, trans,trans-1-decalol, trans,trans-2-decalol, trans,cis-2-decalol, cis,cis-2-decalol, and cis,cis-1-decalol (standards synthesized by Dr. John Cashman [Seattle Biomedical Research Institute], except cis,cis-1-decalol [Aldrich Chemical Co.]). No standards for cis,trans-1-decalol and cis,trans-2-decalol were available for isomer identification. Concentrations for total decalol isomers (all eight isomers) were used for statistics and reporting.
Statistics.
The Toxicology Data Management System (TDMS, supplied by NIEHS, Research Triangle Park, NC) was used to collect data and to perform statistical analyses for toxicology and pathology data. A modified Dunnetts t-test using the Xybion Path/Tox System (Cedar Knolls, NJ) was used to compare exposed and control groups with respect to body and organ weights, and organ:body weight ratios. ANOVA using Statistical Analysis System software (SAS Institute, Inc., Cary, NC) was used to compare treated and control groups with respect to cell proliferation, 2u-globulin, decalin, 2-decalone, and total decalol concentrations, and clinical urinalysis measurements. Difference was considered statistically significant at p
0.05.
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RESULTS |
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Histopathology, week 13, complete necropsy for both sexes.
No exposure-related lesions were observed in female rats. Lesions related to decalin exposure were observed in the kidneys of the male rats.
Number and size of hyaline droplets in male kidneys were related to exposure concentration; however it was difficult to differentiate the amounts among the 100-, 200-, and 400-ppm groups. The 50-ppm group had fewer droplets than rats exposed to 100 ppm and higher, and kidneys from the 25-ppm group were very difficult to differentiate from control kidneys on blinded evaluation based on the presence of hyaline droplets, even with the aid of the MH stain. Although not diagnosed separately, there was microscopic evidence of minimal proximal tubular degeneration accompanying hyaline droplet accumulation in some males exposed to higher concentrations. This lesion was characterized by swollen, granular, and disrupted cytoplasm, pyknosis, karyorrhexis, and sloughing of cellular contents into the tubular lumen. Foci of regenerating proximal tubules were present in only decalin-exposed rats. Males exposed to concentrations of 100 ppm or higher had regenerative lesions of similar severity, while those exposed to 50 or 25 ppm had fewer foci of regenerative tubules. Occasional granular casts filled dilated tubules in the outer zone of the renal medulla. Although minimal to mild, granular casts were easily detected and more clearly related to exposure concentration than the other lesions observed.
Kidney decalin concentrations.
In exposed females, kidney decalin concentrations increased 12 times between 25 and 400 ppm decalin at week 13 (Table 5
). Kidney decalin concentrations from the 200- and 400-ppm groups were statistically higher than those of the lower exposure groups. Overall kidney decalin concentrations in females were substantially (
40-fold) lower than those in males within the same exposure group.
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Urinary excretion of decalol isomers.
Urine volumes collected 16 h postexposure were not significantly different with regard to sex or exposure concentration (data not shown). Urinary creatinine concentrations were not affected by exposure concentration, but were significantly different as a function of sex and time, revealing that older animals excreted more creatinine, and that males had higher creatinine levels than females at later sampling times (Table 7). These trends in creatinine were expected, as body masses of animals increased over the period of
10 weeks and was more marked in males than females.
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Two-Year Inhalation Study
In-life observations.
All exposed male groups exhibited slightly lower two-year survival (4047%) relative to controls (56%), except the 400-ppm group (70%). In females, only the 400-ppm group had slightly lower survival (56%) compared to controls (64%). Although differences in the mean body weights of surviving animals were generally minimal between the exposed and control groups in either sex, the 400-ppm male group had consistently lower body weights (3 to 7%) than controls, starting
week 33 on study (data not shown). There were no significant clinical signs, in either sex, associated with decalin exposure throughout the study.
Histopathology.
Chronic inhalation exposure to decalin induced a spectrum of nonneoplastic and neoplastic lesions in the renal cortex of male rats, ranging from an increase in the severity of the regenerative lesions of chronic nephropathy to tubular carcinomas (Table 8). Incidences of renal tubule adenoma and adenoma or carcinoma (combined) were significantly increased in males exposed to 50 ppm or greater. Incidences of adenoma and adenoma or carcinoma (combined) in all exposed groups of males exceeded the historical ranges in controls (all routes of exposure) given the NTP-2000 diet (NIEHS, 2002
). The incidences of carcinoma were also increased in exposed males and although these increases were not statistically significant, the incidences exceeded the historical control range. Two renal tubular cell carcinomas metastasized to the lung; one in a male rat exposed to 100 ppm and one in a male rat exposed to 25 ppm. There were no increased incidences of renal tumors in females that were related to exposure to decalin. There were no statistically significant increases in incidences of tumors of nonrenal tissues in either male or female rats that could be related to exposure to decalin.
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The incidence and severity of mineralization of the renal papilla were also increased in all exposed groups of males and the severity and incidence increased with exposure concentration. The mineral was present in tubules within the papilla and, in many instances, the profiles of the mineral were elongate (linear mineralization), which is characteristic of mineralization associated with 2u-globulin-induced nephropathy. The incidence of hyperplasia of transitional epithelium lining of the renal pelvis was significantly increased in all exposed groups of males. This change was generally mild and was characterized by increased thickness, often with papillary projections of the transitional epithelium lining the renal pelvis.
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DISCUSSION |
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PCNA expression is greatly dependent on the cell cycle and that PCNA expression is increased and peaked at the time of S-phase where the PCNA production is greatest (Foley et al., 1991). Cell proliferation labeling indices were elevated for all decalin-exposed male rats, supporting evidence of an increase in renal cellular proliferation following exposure.
As anticipated, the progression of histopathological lesions observed in the cortical region in male kidneys generally correlated well with changes in kidney 2u-globulin concentrations measured in the homogenates prepared from the kidney. Relatively milder lesions at week 2 were associated with
2u-globulin concentration substantially lower than those observed at week 13. The finding that females tended to eliminate more decalin, in the form of urinary decalols, than males was probably due to a substantially lower level of
2u-globulin (Dill et al., 2003
). Low levels of decalin in female kidney homogenates likely reflect a passive tissue partitioning of decalin from blood. However, it is not known if other sex differences such as the rate or extent of decalin metabolism could also contribute to higher urinary excretion in females (Longacre, 1987
). In addition to increases in kidney
2u-globulin concentration in male rat kidney homogenates between weeks 2 and 6, concentrations of decalin and 2-decalone also increased. Accumulations of both decalin and 2-decalone, in a similar molar ratio to
2u-globulin at all exposure concentrations, supported the hypothesis that both the parent and the metabolite bind to
2u-globulin, thereby leading to the accumulation of the protein in male kidneys.
Within the total molar amount, there was a higher amount of 2-decalone than decalin at lower exposure concentrations (i.e., 100 ppm), but the relative amount of decalin increased with exposure concentration (i.e.,
200 ppm). Several possible explanations might account for this observation. Metabolism of decalin to 2-decalone could be saturated at high exposure concentrations, leaving more decalin available for
2u-globulin binding. In a single inhalation study, the area under the blood decalin concentration curve increased supra-proportionally to the exposure concentration at
100 ppm (Dill et al., 2003
). A lesser amount of decalin metabolized at saturating high exposure concentrations would result in relatively less 2-decalone being generated and thus competing for
2u-globulin binding. Although the actual binding affinities of decalin and 2-decalone to
2u-globulin were not measured, a higher amount of decalin would leave less free
2u-globulin for 2-decalone binding. Additionally, it is possible that formation of decalin-
2u-globulin complexes might delay the metabolism of decalin to 2-decalone. A combination of these different processes likely occurred with the net result that the relative quantity of the 2-decalone in the male kidneys decreased while that of decalin increased with increasing exposure concentration, but their combined molar amount was overall equivalent to that for
2u-globulin.
Exposure to decalin at concentrations up to 400 ppm for two years did not result in significant in-life toxicity in males. A higher two-year survival of 400-ppm male rats compared to the other exposed or control males was likely associated with slightly but consistently lower mean body weights of the 400-ppm group. The association of low body weights with increased survival in laboratory animals has been recognized in the literature (Haseman et al., 1989). It appears that decalin exposure caused lower body weight gain, which contributed to the slightly higher survival for the 400-ppm group but the exposure-related pathological changes in kidneys did not increase moribundity or mortality during two years of exposure. However, it is noteworthy that the 400-ppm groups had a smaller number of animals used (20) compared to 50 males/exposure at other exposure concentrations. This might have increased the degree of uncertainty in the survival rate of the 400-ppm group.
Chronic exposure to decalin induced a spectrum of neoplastic and nonneoplastic lesions in male kidneys, ranging from an increase in the severity of the regenerative lesions of chronic nephropathy to malignant renal tumors. The combined incidence of renal tubular carcinomas and adenomas in males was 1/50, 3/50, 7/49, 12/50, and 6/20 for the 0-, 25-, 50-, 100-, and 400-ppm groups, respectively. The combined incidence of these two tumor types in historical controls of male F344 rats fed NTP-2000 diet in NIEHS two-year studies is 3/906 (NIEHS, 2002). The increase in renal tumor incidence, coupled with the incidence of cortical tubular hyperplasia and the increased severity of chronic nephropathy in exposed males, clearly indicates a detrimental effect of chronic exposure to decalin on male kidneys. Linear mineralization of renal papillary epithelium and hyperplasia of transitional epithelium lining the renal pelvis were also clearly related to decalin exposure. This spectrum of lesions is characteristic of renal toxicity and carcinogenesis related to the chronic accumulation of
2u-globulin in cortical tubular epithelium (Hard et al., 1993
). Hyaline droplets, although present in a relatively low incidence, were observed in cortical tubular epithelium of some males necropsied relatively early in this two-year study. Granular casts in the renal medulla were rarely observed in the chronic males. This lack of granular casts and hyaline droplets in male rats chronically exposed to CIGA was reported previously (Hard et al., 1993
), and was considered to be related to the spontaneous decrease in
2u-globulin levels in aging rats.
In summary, decalin inhalation exposure from 25 to 400 ppm for up to 13 weeks clearly induced male rat-specific 2u-globulin nephropathy. Both decalin and 2-decalone accumulated in the male kidneys but not in female rat kidneys along with
2u-globulin, suggesting that one or both of these compounds may bind to the protein. Following a two-year exposure, a spectrum of nonneoplastic and neoplastic urinary tract lesions involving the renal cortex was present in exposed male rats. It is concluded that the nonneoplastic lesions caused by chronic exposure to decalin were related to the carcinogenic effect on the renal cortical epithelium in male rats. This effect was considered to be related to excessive
2u-globulin bound to decalin or its metabolite in the cytoplasm of cortical tubular epithelial cells, resulting in cytotoxicity and increased renal cortical epithelium cell turnover.
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ACKNOWLEDGMENTS |
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NOTES |
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1 To whom correspondence should be addressed at Battelle, Toxicology Northwest, MS K4-16, P.O. Box 999, Richland, WA 99352. Fax: (509) 375-3649. E-mail: dillj{at}battelle.org.
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