NTP toxicology and carcinogenesis studies of decalin (CAS No. 91-17-8) in F344/N rats and B6C3F(1) mice and a toxicology study of decalin in male NBR rats (inhalation studies)

Decalin is used as an industrial solvent for naphthalene, fats, resins, oils, and waxes. It is also used as a substitute for turpentine in lacquers, paints, and varnishes; as a solvent and stabilizer for shoe polishes and floor waxes; and as a constituent of motor fuels and lubricants. Other applications include use as a paint thinner and remover, a patent fuel in stoves, a high-density fuel in submarine-launched cruise missile systems, and in stain removal and cleaning machinery. Decalin was nominated for study by the National Cancer Institute because of its chemical structure, its potential for consumer exposure, and a lack of adequate testing of the chemical. Male and female F344/N rats and B6C3F(1) mice were exposed to decalin (greater than 99% pure) by inhalation for 2 weeks, 3 months, or 2 years. Groups of male NBR rats were exposed to decalin for 2 weeks. Male NBR rats do not produce alpha2u-globulin; the NBR rats were included to study the relationship of alpha2u-globulin and renal lesion induction. Genetic toxicology studies were conducted in Salmonella typhimurium and mouse peripheral blood erythrocytes. 2-WEEK STUDIES IN RATS: Groups of five male and five female F344/N rats and five male NBR rats were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 16 days. All rats survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber controls. Renal toxicity studies were performed in male F344/N and NBR rats. The numbers of labeled cells and the labeling indices in the left kidney of 200 and 400 ppm F344/N male rats were significantly greater than those in the chamber controls. The alpha2u-globulin/soluble protein ratios were significantly increased in all exposed groups of F344/N rats. Liver weights of male F344/N and NBR rats exposed to 100 ppm or greater were significantly increased, as were those of all exposed groups of females. Kidney weights of male F344/N rats exposed to 50 ppm or greater were significantly increased. Exposure-related hyaline droplet accumulation, degeneration and regeneration of renal cortical tubules, and granular casts occurred in the kidney of exposed F344/N male rats. 2-WEEK STUDIES IN MICE: Groups of five male and five female B6C3F(1) mice were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 17 days. All mice survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Liver weights of 200 and 400 ppm males and females and 100 ppm females were significantly increased. 3-MONTH STUDY IN RATS: Groups of 25 male and 20 female F344/N rats were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 2 (five male renal toxicity rats), 6 (10 male and 10 female clinical pathology rats), or 14 (10 core study rats) weeks. All rats survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Urinalysis results indicated that decalin exposure caused increases in urine glucose and protein concentrations and enzyme activities that were consistent with the renal lesions observed microscopically. Renal toxicity studies were performed on rats sacrificed at 2 and 6 weeks and at the end of the study. In kidney tissue examined for cell proliferation, the numbers of PCNA-labeled cells and labeling indices were generally significantly greater than those of the chamber controls in exposed groups of rats at all three time points. Concentrations of alpha2u-globulin in the kidney as well as the alpha2u-globulin/soluble protein ratios were significantly increased at week 2 in all exposed groups and in the 200 and 400 ppm groups at week 6 and at the end of the study. Absolute and/or relative kidney and liver weights of male rats exposed to 50 ppm or greater were increased. Incidences of renal tubule regeneration and granular casts in the medulla of the kidney in exposed male rats were increased, and the severities of hyaline droplets generally increased with increasing exposure concentration. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female B6C3F(1) mice were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 14 weeks. All mice survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Liver weights of 200 and 400 ppm males and females were significantly increased. There was a significant exposure concentration-related decrease in the absolute spermatid head count and a significant decrease in absolute head count of the 400 ppm group compared to the chamber controls. Incidences of centrilobular cytomegaly of the liver were increased in exposed male mice. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female F344/N rats were exposed to 0, 25, 50 (male rats only), 100, or 400 ppm (female rats only) decalin vapor 6 hours per day, 5 days per week for 105 weeks. A group of 20 male rats was exposed to 400 ppm. Survival of exposed groups was similar to that of the chamber control groups. Mean body weights of 400 ppm males were slightly less than those of the chamber controls during the second year of the study. Incidences of renal tubule adenoma and adenoma or carcinoma (combined) and of benign or malignant pheochromocytoma (combined) of the adrenal medulla in 100 and 400 ppm males were significantly increased. There was a significant association between nephropathy severity and adrenal pheochromocytoma incidence. Nonneoplastic lesions related to decalin exposure occurred in the kidney of male rats. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female B6C3F(1) mice were exposed to 0, 25, 100, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 105 weeks. Survival of exposed mice was similar to that of the chamber controls. Mean body weights of exposed groups were generally similar to those of the chamber control groups throughout the study. Increased incidences of hepatocellular neoplasms occurred in 25 and 400 ppm female mice, and the incidences of centrilobular hypertrophy, necrosis, syncytial alteration, and erythrophagocytosis of the liver in 400 ppm males were significantly increased. The incidences of uterine stromal polyp and stromal polyp or stromal sarcoma (combined) occurred with positive trends in female mice. PHARMACOKINETIC MODEL: The rate of metabolism of decalin was the same for males and females in rats and mice. Also in rats and mice, decalin metabolism was saturated at less than 400 ppm. Increased labeling indices in male rats were likely due to changes related to alpha2u-globulin. GENETIC TOXICOLOGY: Decalin was not mutagenic in S. typhimurium strains TA97, TA98, TA100, or TA1535, with or without induced hamster or rat liver S9 enzymes. A small but significant increase in the frequency of micronucleated normochromatic erythrocytes was noted in male mice exposed to decalin for 3 months; however, no induction of micronuclei was observed in female mice. CONCLUSIONS: Under the conditions of these studies, there was clear evidence of carcinogenic activity of decalin in male F344/N rats based on increased incidences of renal tubule neoplasms. The increased incidences of benign or malignant pheochromocytoma (combined) of the adrenal medulla in male rats were also considered to be exposure related. There was no evidence of carcinogenic activity of decalin in female F344/N rats exposed to 25, 100, or 400 ppm. There was no evidence of carcinogenic activity of decalin in male B6C3F(1) mice exposed to 25, 100, or 400 ppm. There was equivocal evidence of carcinogenic activity of decalin in female B6C3F(1) mice based on marginally increased incidences of hepatocellular and uterine neoplasms. Exposure of male rats to decalin resulted in nonneoplastic lesions of the kidney characteristic of alpha2u-globulin accumulation. Nonneoplastic lesions of the liver were observed in male mice exposed to decalin.     

Inhalation Toxicity of Butylene Oxide

Inhalation Toxicity of Butylene Oxide. Miller, R.R., Quast,J.R., Ayres, J.A. and McKenna, M.J. (1981). Fundam. Appl. Toxicol.1:319–324. Exposure of male and female Fischer 344 ratsand B6C3F1 mice to 0,400,800 or 1600 ppm butylene oxide vapors6 hours per day, 5 days per week, for a total of 9 days duringa 2-week interval revealed a definite species difference insensitivity to these high concentrations of the test material.All mice in the 1600 ppm group were dead prior to the 3rd dayof exposure while all rats exposed to 1600 ppm survived untilscheduled sacrifice with no obvious signs of distress exceptfor a pronounced retardation of growth. Inflammatory and degenerativechanges in the nasal mucosa were detected histopath-ologicallyin rats in the 1600 ppm group. Myeloid hyperpla-sia in the bonemarrow, and elevated mean white blood cell counts for male andfemale rats in the 1600 ppm group may possibly have been relatedto the inflammatory nasal lesions or to generalized stress.A subchronic inhalation toxicity study in which Fischer 344rats and B6C3F1 mice were exposed to 0,75,150 or 600 ppm for13-weeks resulted in no treatment-related mortalities. Slightgrowth retardation, particularly for female rats and mice, wasapparent for animals in the 600 ppm group. Histopathologic examinationsrevealed treatment-related lesions of the nasal mucosa in bothrats and mice in the 600 ppm group. There were no histopathologicobservations in rats or mice in the 75 or 150 ppm groups whichwere considered to be related to exposure to the test material.     

Inhalation toxicology of octamethylcyclotetrasiloxane (D4) following a 3-month nose-only exposure in Fischer 344 rats

Octamethylcyclotetrasiloxane (D4) is a low-molecular-weight cyclic siloxane used primarily in the synthesis of silicone polymers. The objective of the present study was to evaluate the subchronic toxicity of D4 following a 3-month nose-only inhalation exposure. Male and female Fischer 344 rats (20/sex/group) were exposed 6 h/day, 5 days/week for 3 months to vapor concentrations of 0, 35, 122, 488, and 898 ppm D4. Also, an additional 10 per sex in the control and high-exposure groups were allowed a 4-week recovery period to observe reversibility, persistence, or delayed occurrence of any potential adverse effects. Body weights and food consumption were monitored at least twice weekly over the course of exposures. Approximately 18 hours preceding euthanasia, animals were transferred into metabolism cages for urine collection, and were fasted. At necropsy, rats were anesthetized with pentobarbital and euthanized by exsanguination. Blood was collected for hematological and clinical biochemical analyses. Selected organ weights were measured and a complete set of tissues was taken for histopathological examination. A concentration-dependent increase in absolute and relative liver weight (488 to 898 ppm) and a significant decrease in ovarian weight (898 ppm) were observed in female rats. Exposure to D4 via nose-only inhalation (35 to 898 ppm) produced minor alterations in hematological and serum chemistry parameters that were considered either incidental and of little toxicological significance (hematology) or suggestive of metabolic adaptation/alteration (serum chemistry) in response to exposure-related hepatomegaly. There were no histopathological findings noted in the liver. Histopathological evidence indicated the primary target organs following D4 inhalation exposure to be components of the female reproductive tract. Reversible histopathological changes were observed in the ovary (hypoactivity) and vagina (mucification) of female rats in the high-dose group only (898 ppm). Although an increase in the incidence and severity of both macrophage accumulation, interstitial inflammation, and eosinophil infiltration was observed in the lungs of male and female rats exposed to D4, the toxicological significance is uncertain as other inhalation studies at similar concentrations failed to show these effects. In summary, nose-only inhalation of a high concentration of D4 resulted in reversible histopathological changes in the female rat reproductive tract. Lower concentrations did not elicit these same effects.     

Subchronic inhalation study of 1-hexene in Fischer 344 rats.

The objective of this study was to evaluate the toxicity of 1-hexene following repeated inhalation exposures in male and female Fischer 344 rats. Groups of 40 male and 40 female rats were exposed for 6 hours per day, 5 days per week, over a 13-week period. Treatment groups consisted of air-exposed control (0 ppm) and three test groups of 300, 1000, and 3000 ppm 1-hexene. During the treatment period, the rats were observed daily for clinical signs of toxicity; body weights and neuromuscular coordination [females only] were measured at 7-day intervals. After 7 weeks of exposure and at the end of the treatment period, the rats were subject to macroscopic and microscopic pathology, clinical chemistry, hematology, urinalysis, and sperm counts. No mortalities were observed during the course of the study. No clinical signs of toxicity attributable to 1-hexene exposure were observed. Female rats exposed to 3000 ppm had significantly lower body weights compared to control rats from exposure day 5 persisting throughout the treatment period. Male rats exposed to 3000 ppm had slightly but not statistically significant lower body weights in comparison to controls. Male rats exhibited slightly increased absolute and relative testicular weights, and female rats had slightly decreased absolute [but not relative] liver and kidney weights, at 3000 ppm. There were no gross or microscopic morphological findings attributed to treatment. Exposure to 1-hexene did not affect neuromuscular coordination in females as determined using the Rotarod, nor sperm counts in male rats. Several statistically significant effects in hematology, clinical chemistry, and urinalysis evaluations were observed, but were either of small magnitude or did not correlate with histopathological findings, and thus did not appear to be of biological significance. In summary, the no-adverse-effect-level for this study was determined to be 1000 ppm, based on decreased weight gain in female rats, and on slight organ weight changes in both sexes at 3000 ppm.     

Inhalation Toxicity of Phosphine for Fischer 344 Rats and B6C3F1 Mice

Abstract

Because of the potential increased use of phosphine (PH₃) as a fumigant and the lack of adequate toxicity data, short-term inhalation studies were conducted to characterize the toxicity of PH₃ for Fischer 344 (F344) rats and B6C3F1 mice. Male rats and mice were exposed to 0, 1, 5, or 10 ppm PH₃ for up to 4 days, and males and females to 0, 1.25, 2.5, or 5 ppm for 2 wk. In the 4-day study, all rats died by the end of the third exposure to 10 ppm, and all mice were euthanized in moribund condition after the fourth exposure to 10 ppm. Clinical pathology data were obtained only for mice, due to early mortality of rats. There were no significant treatment-related effects in hematological indices in mice exposed to 1 or 5 ppm; at 10 ppm there was a moderate anemia, and leukocyte counts were significantly decreased. There were significant biologically relevant increases in serum activity of alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) and in the concentration of urine nitrogen (UN) at 10 ppm. Flectrophoretic evaluation of hemoglobin from mice exposed to 10 ppm did not reveal any differences in banding patterns from controls. Moribund mice euthanized after 4 exposures to 10 ppm had minimal to mild degeneration and necrosis of the renal tubule epithelium, minimal myocardial degeneration, and minimal to mild subcapsular foci of hemorrhage and necrosis in the liver. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or lungs of rats exposed to 10 ppm for 3–4 days. There were no treatment-related mortalities in rats or mice exposed for 2 weeks. Lung weights of male rats and mice were significantly decreased and heart weights of female rats and mice were significantly increased after 2 wk of exposure to 5 ppm. Slight but statistically significant increases were observed in serum UN in male mice exposed to 5 ppm. There was no microscopic evidence of treatment-related effects in any of the tissues examined from rats or mice exposed to 5 ppm for 2 wk. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or rats exposed to 5 ppm for 2 wk. These studies demonstrated that PH₃ inhalation does not cause a specific target organ toxicity in the B6C3F1 mouse or F344 rat, and that the primary hazard of subchronic inhalation in these species is lethality.     

Alpha 2u-globulin nephropathy and carcinogenicity following exposure to decalin (decahydronaphthalene) in F344/N rats.

Decalin (decahydronaphthalene) is a widely used industrial solvent known to cause male rat-specific alpha2u-globulin nephropathy. In this project, 13-week and two-year inhalation studies of decalin were conducted consecutively in both sexes of F344/N rats. The key objectives were to (1) characterize the 13-week toxicity of decalin in rats, with an emphasis on nephropathy in males; (2) compare the kidney concentrations of decalin, 2-decalone, and alpha2u-globulin in males over 2 to 13 weeks of decalin exposure; and (3) correlate male rat nephropathy observed in the 13-week study with renal carcinogenicity in the two-year study. F344 rats (M/F) were exposed via whole-body inhalation to 0, 25, 50, 100, 200, or 400 ppm decalin for 13 weeks. Urine was collected at weeks 2 and 6 for creatinine and decalol analyses and at week 12 for clinical urinalysis. Right kidneys were collected from male rats at weeks 2 and 6 and from both sexes at week 13, homogenates were prepared using the whole kidney, and these homogenates were analyzed for alpha2u-globulin, decalin, and 2-decalone. Left kidneys were evaluated for histopathology and cell proliferation utilizing a proliferating cell nuclear antigen technique and counting proximal renal tubular epithelial cells to determine cell labeling indices. Necropsies and histopathologic evaluations were performed at week 13. Decalin exposure caused increases in kidney weight, urinalysis parameters (protein, AST, LDH), kidney alpha2u-globulin concentration, and proximal convoluted renal tubular cell proliferation in males. These changes were accompanied by microscopic lesions (accumulation of hyaline droplets in cortical tubules, regeneration of proximal tubular epithelium, and granular casts in medullary tubules) clearly linked to alpha2u-globulin nephropathy. Both decalin and 2-decalone were related to increased alpha2u-globulin in male kidneys. Kidney concentrations of decalin, 2-decalone, and alpha2u-globulin in exposed females were negligible, while females excreted greater amounts of decalol metabolites in urine than males at weeks 2 and 6. There were no exposure-related microscopic lesions in females. For chronic exposure, F344 rats were exposed via whole-body inhalation to 0, 25, 50 (males only), 100, or 400 ppm decalin for two years. Chronic exposure induced a spectrum of nonneoplastic and neoplastic lesions in the renal cortex of males, ranging from regenerative lesions of chronic nephropathy to tubular carcinomas. Incidences of renal tubular adenoma, tubular carcinoma, combined tubular adenomas and carcinomas, cortical tubular hyperplasia, hyaline droplet accumulation, hyperplasia of pelvic epithelium, and mineralization in renal papilla were increased in exposed males compared to controls. There was a clear increase in the mean severity of chronic nephropathy in decalin-exposed males. It was concluded that the carcinogenic effect on the renal cortical epithelium of male rats exposed to decalin was related to increased turnover of this epithelium, resulting from the cytotoxic effects of alpha2u-globulin accumulation in the renal cortical tubular cell cytoplasm.     

Morphogenesis of decalin-induced renal alterations in the male rat

Adult male Fischer 344 rats were killed after 5, 12, 19 or 31 days' 'occupational' (6 hr/day, 5 days/wk), 'semi-continuous' (22 hr/day, 5 days/wk) or 'continuous' (22 hr/day, 7 days/wk) exposure to 125 ppm decalin vapour. Control rats were exposed to filtered air. Kidney sections were evaluated to determine the nature and time-course of development of decalin-induced lesions. The development of renal lesions was characterized by a specific sequence of light microscopically evident alterations. The extent of the alterations was dependent on time and exposure regimen. Severe exacerbation of the spontaneous protein accumulation (hyaline droplets) routinely observed in the kidneys of control male rats was present in kidneys of all decalin-exposed animals at day 5, and was considered to be the primary morphological alteration associated with decalin exposure. The following sequelae of the hyaline droplet response were observed: the variable occurrence of light microscopically evident proximal convoluted tubule (PCT) epithelial cell degeneration/necrosis, presumably a reflection of cellular injury associated with excessive protein accumulation; the occurrence of granular casts at the junction of the inner and outer bands of the outer zone of the medulla secondary to PCT epithelial cell injury; chronic nephrosis, occurring secondary to tubular obstruction by granular casts. This triad of lesions (hyaline droplet accumulation, granular cast formation and chronic nephrosis) lends specificity to the decalin response and establishes a potential mechanistic relationship with other chemicals that induce these effects.     

Inhalation Developmental Toxicity Study of Propylene Oxide in Fischer 344 Rats

The developmental toxicity potential of propylene oxide (PO)was evaluated in Fischer 344 rats following inhalation exposure.Four groups of 25 mated female rats were exposed to 0, 100,300, and 500 ppm of PO for 6 hr per day on Gestation Days 6through 15, inclusive. Cesarean sections were performed on allfemales on Gestation Day 20 and the fetuses removed for morphologicalevaluation. Exposure to propylene oxide did not adversely affectsurvival, appearance, or behavior at any of the exposure levelstested. Maternal body weight gain and food consumption werereduced significantly among the females at the 500 ppm levelduring the exposure period. No exposure-related effects werenoted with respect to maternal water consumption, organ weights,cesarean section, or fetal morphological observations with thesole exception of increased frequency of seventh cervical ribsin fetuses at the maternally toxic exposure level of 500 ppm.In summation, the no-observable-adverse-effect level (NOAEL)of propylene oxide. when administered to Fischer 344 rats viawhole-body inhalation exposure, was considered to be 300 ppm.     

Carcinogenic and toxicologic effects of inhaled ethylene oxide and propylene oxide in F344 rats

The chronic inhalation toxicity and carcinogenicity of ethylene oxide (EO) and propylene oxide (PO) were evaluated in a 2-year inhalation bioassay. Five groups of male weanling Fischer 344 rats, 80 per group, were exposed at 0 ppm (shared control; filtered air), 50 ppm EO, 100 ppm EO, 100 ppm PO, or 300 ppm PO (7 hr/day, 5 days/week) for 104 weeks. Body weights from rats exposed to EO and PO at all exposure concentrations were significantly reduced compared to controls. A statistically significant increase in mortality was observed in all groups of exposed rats compared to controls. Skeletal muscle atrophy in the absence of any sciatic nerve neuropathology was found in rats exposed at 100 ppm EO and 300 ppm PO. Statistically significant associations between EO exposure and an increased incidence of the following rat neoplasms were observed: mononuclear cell leukemia, peritoneal mesothelioma, and mixed cell brain glioma. Among rats exposed to PO there was a dose-dependent increase in the incidence of complex epithelial hyperplasia in the nasal passages, and two adenomas were detected in the nasal passages of rats exposed at 300 ppm PO. The incidence of adrenal pheochromocytomas was elevated in both PO exposure groups, but not in a dose-related manner. All rat groups were affected by an outbreak of Mycoplasma pulmonis infection which occurred about 16 months into the study. This infection alone and in combination with the epoxide exposures affected the survival of rats in this study, and influenced the development of the proliferative lesions in the nasal mucosa of the PO-exposed rats. No treatment-related changes in any clinical chemistry or urinalysis indices were detected. PO exposure did not increase the incidence of the three neoplasms associated with EO exposure; however, adrenal pheochromocytomas and proliferative lesions of the nasal cavity were increased in rats exposed to PO.     

Subchronic Inhalation Study of 1-Hexene in Fischer 344 Rats

ABSTRACT

The objective of this study was to evaluate the toxicity of 1-hexene following repeated inhalation exposures in male and female Fischer 344 rats. Groups of 40 male and 40 female rats were exposed for 6 hours per day, 5 days per week, over a 13-week period. Treatment groups consisted of air-exposed control (0 ppm) and three test groups of 300, 1000, and 3000 ppm 1-hexene. During the treatment period, the rats were observed daily for clinical signs of toxicity; body weights and neuromuscular coordination [females only] were measured at 7-day intervals. After 7 weeks of exposure and at the end of the treatment period, the rats were subject to macroscopic and microscopic pathology, clinical chemistry, hematology, urinalysis, and sperm counts. No mortalities were observed during the course of the study. No clinical signs of toxicity attributable to 1-hexene exposure were observed. Female rats exposed to 3000 ppm had significantly lower body weights compared to control rats from exposure day 5 persisting throughout the treatment period. Male rats exposed to 3000 ppm had slightly but not statistically significant lower body weights in comparison to controls. Male rats exhibited slightly increased absolute and relative testicular weights, and female rats had slightly decreased absolute [but not relative] liver and kidney weights, at 3000 ppm. There were no gross or microscopic morphological findings attributed to treatment. Exposure to 1-hexene did not affect neuromuscular coordination in females as determined using the Rotarod®, nor sperm counts in male rats. Several statistically significant effects in hematology, clinical chemistry, and urinalysis evaluations were observed, but were either of small magnitude or did not correlate with histopathological findings, and thus did not appear to be of biological significance. In summary, the no-adverse-effect-level for this study was determined to be 1000 ppm, based on decreased weight gain in female rats, and on slight organ weight changes in both sexes at 3000 ppm.     

Studies of acute nephrotoxic potential of trichloroethylene in Fischer 344 rats

Group of male Fischer 344 rats, after pretreatment with phenobarbital (80 mg/kg, ip, 3 d), were treated ip in corn oil with 0, 5.5, 11.0, and 22.0 mmol trichloroethylene (TRI) per kg body weight. Urines were collected 24 h after the treatment and the animals were then sacrificed. The nephrotoxicity of TRI was then studied by measuring certain biochemical parameters characteristic of renal injury and its in vivo metabolism by quantitating the TRI principal urinary metabolites. Treatment of rats with TRI up to 11 mmol/kg did not influence any of the measured biochemical parameters of nephrotoxicity. On the other hand, significant increases in the urinary level of N-acetyl-beta-glucose-D-aminidase (NAG) and glucose as well as serum urea nitrogen were observed at 24 h only at the highest dose level (22 mmol/kg) or TRI. Urinary excretions of both trichloroethanol and trichloroacetic acid reached an apparent saturation at the highest dose level of TRI. In inhalation studies, urinary levels of gamma-glutamyltranspeptidase, NAG, glucose, proteins, and serum urea nitrogen were significantly increased at 24 h when rats were exposed to either 1000 or 2000 ppm TRI for 6 h. The capacity of renal cortical slices to accumulate p-aminohippurate was significantly reduced 24 h after the exposure to 22 mmol TRI/kg (ip), or to 1000 or 2000 ppm TRI. These results have demonstrated that TRI exerts its acute nephrotoxic potential at a very high dose level and produces nephrotoxic insult at the proximal tubular and possibly glomerular regions of the rat kidney, whether exposed by inhalation or by an ip route. These data further indicate an involvement of a capacity-limited metabolism in the expression of acute nephrotoxicity due to TRI in Fischer 344 rats.     

Decalin-induced nephrotoxicity: light and electron microscopic examination of the effects of oral dosing on the development of kidney lesions in the rat

Male and female Fischer 344 rats were given decalin by oral gavage for 5 or 12 consecutive days in order to determine whether oral dosing would result in light microscopically evident renal effects that were comparable to those that have been observed after inhalation exposure. Decalin (in corn oil vehicle) was administered at doses of 0, 0.1, 0.5, 1.0 or 2.0 g/kg body weight to male rats, and 0, 1.0, 1.5, 1.75 or 2.0 g/kg to female rats. Biopsies of the kidneys of selected control and high-dose male rats were taken for examination by electron microscopy. Sections of kidneys from all control and treated rats were examined by light microscopy. The kidneys of all male control rats contained minimal levels of hyaline droplets within the cytoplasm of proximal convoluted tubule (PCT) epithelial cells. Decalin-induced alterations in the kidneys of male rats included an exacerbation of the hyaline droplet/globule levels found in controls and the formation of granular casts in the outer zone of the renal medulla. The exacerbated formation of hyaline droplets was characterized light microscopically by a marked dose-related increase in the number and size of individual droplets/globules and ultrastructurally by a marked increase in the size range of, and the presence of crystalline inclusions in, the PCT epithelial cell phagolysosomal populations. No other ultrastructural alterations occurred that differentiated treated male rats from control males. The formation of granular casts was dose and time related, occurring in 60% of male rats given 0.5 g decalin/kg for 12 days and in 100% of those given 1.0 g decalin/kg for 12 days. Light microscopy revealed no differences between the kidneys of control and decalin-treated female rats, and no hyaline droplets or granular casts were observed in the kidneys of any female rat killed after 5 or 12 days. These results were in agreement with those of inhalation studies and provide additional evidence that the formation of hyaline droplets in response to exposure to volatile hydrocarbons may be unique to the male rat.     

Hepatic and Renal Assessment of Acute Exposure to Inhaled Epichlorohydrin: Toxicological Evaluation and Exposure Modeling

Abstract

To examine the hepatic and renal effects of acute exposure to inhaled epichlorohydrin (ECH), male F344 rats were exposed either to 0 or 100 ppm ECH by inhalation for 4 h. Hepatic and renal toxicity were assessed at the termination of exposure and on days 1, 2, and 3 postexposure. Exposure to inhaled ECH caused no histopathological evidence of hepatic or renal toxicity and had no effect on serum indicators of hepatic toxicity, or hepatic cytochrome P-450 and glutathione concentrations. Exposure to inhaled ECH resulted in an increase in relative kidney weight in rats that were either 65 ± 2 days old or 73 ± 2 days old on the day of inhalation exposure (young adult rats) but not in rats that were 96 ± 2 days old on the day of inhalation exposure (adult rats), and a decrease in absolute and relative liver weight in adult rats but not young adult rats. Blood urea nitrogen/creatinine (BUN/CREAT) was decreased in young adult rats on day 0, and BUN was slightly increased in adult rats on days I, 2 and 3. These observations indicate that acute exposure to 100 ppm ECH did not produce consistent alterations in indicators of hepatic and renal toxicity. Ambient impact assessment modeling (AIAM), a methodology for estimation of exposure over short time periods and comparison of these predicted ambient concentration levels to short-term toxicological threshold values, was conducted for three typical industrial sources of ECH pollution. The results of these analyses illustrated the interdependence of toxicological evaluation and exposure modeling in short-term non-cancer risk assessment and demonstrated the usefulness of AIAM in prioritizing chemicals for additional toxicological evaluation.     

Evaluation of propargyl alcohol toxicity and carcinogenicity in F344/N rats and B6C3F1/N mice following whole-body inhalation exposure

Propargyl alcohol (PA) is a high production volume chemical used in synthesis of many industrial chemicals and agricultural products. Despite the potential for prolonged or accidental exposure to PA in industrial settings, the toxicity potential of PA was not well characterized. To address the knowledge gaps relevant to the toxicity profile of PA, the National Toxicology Program (NTP) conducted 2-week, 14-week and 2-year studies in male and female F344/N rats and B6C3F1/N mice. For the 2-week inhalation study, the rats and mice were exposed to 0, 31.3, 62.5, 125, 250 or 500 ppm. Significant mortality was observed in both rats and mice exposed to ≥125 ppm of PA. The major target organ of toxicity in both mice and rats was the liver with exposure-related histopathological changes (250 and 500 ppm). Based on the decreased survival in the 2-week study, the rats and mice were exposed to 0, 4, 8, 16, 32 or 64 ppm of PA in the 14-week study. No treatment-related mortality was observed. Mean body weights of male (≥8 ppm) and female mice (32 and 64 ppm) were significantly decreased (7–16%). Histopathological changes were noted in the nasal cavity, and included suppurative inflammation, squamous metaplasia, hyaline droplet accumulation, olfactory epithelium atrophy, and necrosis. In the 2-year inhalation studies, the rats were exposed to 0, 16, 32 and 64 ppm of PA and the mice were exposed to 0, 8, 16 and 32 ppm of PA. Survival of male rats was significantly reduced (32 and 64 ppm). Mean body weights of 64 ppm male rats were significantly decreased relative to the controls. Both mice and rats showed a spectrum of non-neoplastic changes in the nose. Increased neoplastic incidences of nasal respiratory/transitional epithelial adenoma were observed in both rats and mice. The incidence of mononuclear cell leukemia was significantly increased in male rats and was considered to be treatment-related. In conclusion, the key findings from this study indicated that the nose was the primary target organ of toxicity for PA. Long term inhalation exposure to PA led to nonneoplastic changes in the nose, and increased incidences of respiratory/transitional epithelial adenomas in both mice and rats. Increased incidences of harderian gland adenoma may also have been related to exposure to PA in male mice.     

Subacute (28-day) toxicity of furfural in Fischer 344 rats: a comparison of the oral and inhalation route.

The subacute oral and inhalation toxicity of furfural vapour was studied in Fischer 344 rats to investigate whether route-to-route extrapolation could be employed to derive the limit value for inhalation exposure from oral toxicity data. Groups of 5 rats per sex were treated by gavage daily for 28 days at dose levels of 6-192 mg/kg bw/day, or exposed by inhalation to concentrations of 20-1280 mg/m3 (6 h/day, 5 days/week) or 160-1280 mg/m3 (3 h/day, 5 days/week) for 28 days. Controls received vehicle (corn oil) or were exposed to clean air. Daily oral treatment with the highest dose of furfural (initially 192 mg/kg bw/day, later reduced to 144 mg/kg bw/day and finally to 120 mg/kg bw/day) resulted in mortality, and in increases in absolute and relative kidney and liver weight in surviving females of this group. Exposure of rats by inhalation for 6 h/day, 5 days/week for 28 days induced mortality at concentrations of 640 mg/m3 and above within 1-8 days. At 640 mg/m3 (3 h/day) and at 320 mg/m3 (3 and 6 h/day) and below, however, exposure was tolerated without serious clinical effects. In contrast, histopathological nasal changes were seen even at the lowest concentration of 20 mg/m3. With increasing exposure concentration, the nasal effects increased in incidence and severity and also expanded from the anterior part to the posterior part, including the olfactory epithelium. It was concluded that the no-observed-adverse-effect level (NOAEL) for oral toxicity was 96 mg/kg bw/day. The NOAEL for systemic inhalation toxicity was comparable, i.e. 92 mg/kg bw/day (corresponding to 320 mg/m3 (6 h/day) or 640 mg/m3 (3 h/day)) assuming 100% absorption. The presence of the histopathological nasal changes at the lowest tested concentration of 20 mg/m3 (corresponding to 6 mg/kg bw/day) proves that for locally acting substances like furfural extrapolation from the oral to the inhalation route is not valid.     

Single administration toxicokinetic studies of decalin (decahydronaphthalene) in rats and mice.

Decalin (decahydronaphthalene) is an industrial solvent known to cause alpha2u-globulin nephropathy in male rats. Studies were conducted using decalin (mixture of cis and trans isomers) to (1) characterize systemic elimination of decalin in rats and mice and (2) evaluate disposition of decalin, its metabolites, and kidney alpha2u-globulin in young and old rats of both sexes following a single 6-h whole-body inhalation exposure at up to 400 ppm decalin. Additionally, a separate group of young male F344/N rats were administered either cis- or trans-decalin iv at doses up to 20 mg/kg to assess disposition of each isomer, its metabolites, and kidney alpha2u-globulin. Decalin was eliminated from blood in a dose-dependent manner, regardless of sex, age, or species. C0 and AUC infinity increased supra-proportionally with exposure concentration. Mice were more efficient in eliminating decalin than rats at lower exposure concentrations, but nonlinear elimination kinetics were more noticeable at 400 ppm. Sex differences in blood decalin elimination were observed in rats; females had a consistently higher AUC infinity at all exposure concentrations. There was a dose-dependent increase in kidney decalin, decalone, and alpha2u-globulin in male rats exposed to decalin. Kidney alpha2u-globulin and decalone concentrations in old male rats were substantially lower than those in young males, but were similar to those observed in all (young and old) females. Compared to old males and all females, young male rats had significantly lower urinary decalol concentrations, but higher kidney decalin, decalone, and alpha2u-globulin concentrations. Administration of decalin to male rats as either the cis or trans isomer revealed that more cis -decalone is produced per unit dose as compared to trans-decalone, and that more trans-decalin accumulated in the kidney (as alpha2u-globulin-ligand complexes) compared to cis-decalin. These patterns of isomer-specific metabolism were also reflected in the cis/trans ratios of decalin in blood, as well as urinary decalol metabolites. The ratio of alpha2u-globulin to the total amount of decalin plus decalone measured in the male rat kidney was approximately 1.0. Therefore, alpha2u-globulin was a key factor in the accumulation of decalin and decalone in kidneys of young male rats, decalin and decalone were practically absent in all females and in old males.     

Comparative Toxicity of Arsine Gas in B6C3F1 Mice, Fischer 344 Rats, and Syrian Golden Hamsters: System Organ Studies and Comparison of Clinical Indices of Exposure

Comparative Toxicity of Arsine Gas in B6C3F₁ Mice, Fischer 344Rats, and Syrian Golden Hamsters: System Organ Studies and Comparisonof Clinical Indices of Exposure. BLAIR, P. C, THOMPSON, M. B.,MORRISSEY, R. E., MOORMAN, M. P., SLOANE, R. A., AND FOWLER,B. a. (1990). Fundam. Appl. Toxicol. 14, 776–787. In orderto examine possible species differences in response to arsineexposure, multiple inhalation studies consisting of acute (1-day),subacute (14- and 28-day), and subchronic (90-day) exposuresto this agent were conducted using three different species ofrodents. Evaluations of hematopoietic organs and alterationsin the heme biosynthetic pathway were the focus of these studies.Species used were B6C3F₁ mice (exposed 1, 14, or 90 days), Fischer344 rats (exposed 14, 28, or 90 days), and Syrian Golden hamsters(exposed 28 days). All arsine exposures were at concentrationsof 0.5, 2.5, or 5.0 ppm except for 90-day studies, in whichconcentrations were lowered to 0.025, 0.5, or 2.5 ppm. No changesin body weight gain were observed in either sex of mice or hamsters.The only decrease in body weight gain occurred in male ratsexposed to 5.0 ppm arsine for 28 days. Significant exposure-relatedincreases in relative spleen weights occurred in both sexesof mice and rats in the 0.5 (except 14-day female rats), 2.5,and 5.0 ppm exposure groups from all studies and in hamstersin the 2.5 and 5.0 ppm exposure groups. Generally, increasesin relative liver weight occurred in fewer exposure groups andwere of a lesser magnitude than increases in spleen weight.Other parameters affected included decreased packed cell volumes(mice, rats, and hamsters), hematol-ogy profiles (rats), andan increase in 6-aminolevulinic acid dehydratase activity inall species. Arsenic content was measured in livers of ratsafter 90 days of exposure. Concentrations increased in relationto atmospheric concentrations of arsine. Histopathological changesincluded increased hemosiderosis and extramedullary hematopoiesisin spleen and intracanalicular bile stasis (mice only) in liver.Additionally, bone marrow hyperplasia was observed in rats.Effects on other organs were not observed, suggesting that thehematopoietic system is the primary target for arsine. In conclusion,we have determined that the effects of arsine exposure uponmice, rats, and hamsters are similar. Most importantly, eventhough no effects on the hematopoietic system were observedfollowing a single exposure to 0.5 ppm arsine which is 10 timesthe Threshold Limit Value (TLV) set by the American Conferenceof Governmental Industrial Hygienists, repeated exposure to0.025 ppm (one-half the TLV) caused a significant anemia inrats.     

An inhalation toxicity study of chlorine in Fischer 344 rats following 30 days of exposure.

A subacute study was completed in groups of 10 male and 10 female Fischer 344 rats exposed to air (controls), 1, 3, or 9 ppm chlorine for 6 hr/day, 5 days/week, for 6 weeks. Concentration related decreases in body weight gain were seen at all exposure concentrations in females and at 3 and 9 ppm in males. Additionally, three females at 9 ppm died before the end of Day 30 of exposure. Urinalysis, hematology, and clinical chemistry evaluations were completed on the surviving animals. The urine specific gravity was elevated at all exposure concentrations in the females and at 3 and 9 ppm in the males. The hematocrit and white blood cell count were increased in the females exposed to 9 ppm. Elevations in alkaline phosphatase activity, blood urea nitrogen, γ-glutamyl transpeptidase, and serum glutamic-pyruvic transaminase occurred at 9 ppm; alkaline phosphatase was elevated at 3 ppm in rats of both sexes. Widespread evidence of inflammation was seen throughout the respiratory tract with hyperplasia and hypertrophy of epithelial cells of the respiratory bronchioles, alveolar ducts, and alveoli of male and female rats exposed to 9 ppm. Changes in male rats at 3 or 1 ppm consisted of focal inflammation of the nasal turbinates and a slight to moderate inflammatory reaction around the respiratory bronchioles and alveolar ducts. Increased eosinophilic cytoplasmic homogeneity and decreased granularity of the epithelial cells of the proximal convoluted tubules were seen in the kidneys of male rats exposed to 9 ppm. The livers of rats of both sexes at 9 or 3 ppm had an increased hepato-cellular cytoplasmic vacuolation. These data indicated that repeated exposure of Fischer 344 rats to chlorine resulted in pulmonary effects at all levels of chlorine used, and hepatic and renal effects at 9 and 3 ppm.     

Effect of inhaled dimethylselenide in the Fischer 344 male rat.

In this project, a total of 60 adult Fischer 344 male rats were exposed to dimethylselenide (DMSe) vapor at 1607, 4499, or 8034 ppm for 1 h (20 rats/group). In addition, 26 unexposed rats were used as controls. The exposed rats were observed frequently during the 7 d following exposure and appeared normal. The animals were sacrificed at either 1 or 7 d after inhalation and the major tissues were grossly examined and weighed. Selenium levels were found to be elevated only in the lung at d 1. At d 1, significant changes in organ weights were an increase in the lung weight at exposure levels of 1607 and 8034 ppm of DMSe and in liver weight at 4499 and 8034 ppm. At d 1, significant changes in the lung were an increase in protein at 1607 and 8034 ppm of DMSe, and an increase in RNA and a reduction in DNA at 4499 ppm DMSe. The only change in the liver was a reduction in DNA at 4499 ppm. At 7 d, the protein content and RNA content of spleen were increased. Lung, liver, kidney, spleen, thymus, lymph nodes, pancreas, and adrenal gland were examined microscopically and found to be normal. All of these observed responses were minor and did not severely impact the health of the rats. Overall, the data indicate that the inhalation of DMSe for 1 h has relatively low toxicity in rats even at high concentrations.     

Carcinogenicity and Toxicity of Inhaled Nitrobenzene in B6C3F1 Mice and F344 and CD Rats

The potential carcinogenicity and toxicity of inhaled nitrobenzenewere evaluated following chronic (2-year) exposure in mice andrats. Male and female B6C3F1 mice were exposed to 0, 5, 25,or 50 ppm nitrobenzene, while male and female F344 rats andmale CD rats were exposed to 0, 1, 5, or 25 ppm nitrobenzene.All exposures were for 6 hr/day, 5 days/week excluding holidays,for a total of 505 days over 2 years. Survival was not adverselyaffected by nitrobenzene exposure, and only mild exposure-relateddecreases in body weights (<10% of control) were occasionallynoted. Nitrobenaene exposure resulted in increased incidenceof neoplasia in male B6C3F1 mice (pulmonary alveolar/bronchiolarand thyroid follicular cell neoplasms), female B6C3FI mice (mammarygland neoplasms), male F344 rats (hepatocellular and renal neoplasms),female F344 rats (endometrial stromal neoplasms), and male CDrats (hepatocellu lar neoplasms). In addition, there were marginalincreases in the incidence of hepatocellular neoplasia in femaleB6C3F1 mice and thyroid follicular neoplasia in male F344 rats.Groups of nitrobenzene-exposed mice and rats with increasedincidence of renal and thyroid neoplasia also had increasedincidences of hyperplasia in these tissues. Toxicity resultingfrom chronic inhalation of nitrobenzene was manifested by methemoglobinemia,anemia, and adaptive or degenerative changes in the nose, liver,and testis. The results indicate that inhaled nitrobenzene iscarcinogenic and toxic in mice and rats, and that the spectrumof these responses in animals is dependent on species, sex,and genetic background.