Chronic Toxicity/Oncogenicity of Dimethylformamide in Rats and Mice Following Inhalation Exposure

The potential chronic toxicity and oncogenicity of dimethylformamide(DMF) was evaluated by exposing male and female rats and miceto 0, 25, 100, or 400 ppm DMF for 6 hr/day, 5 days/week for18 months (mice) or 2 years (rats). Clinical pathology was evaluatedat 3, 6, 12, 18, and 24 (rats only) months. An interim euthanasiafor rats occurred at 12 months and hepatic cell proliferationin rats and mice was examined at 2 weeks, 3 months, and 12 months.No compound-related effects on clinical observations or survivalwere observed. Body weights of rats exposed to 100 (males only)and 400 ppm were reduced. Conversely, body weights were increasedin 400 ppm mice. No hematologic changes were observed in eitherspecies. Serum sorbitol dehydrogenase activity was increasedin rats exposed to 100 or 400 ppm. There were no compound-relatedeffects on the estrous cycle of rats or mice at any concentration.Compound-related morphological changes were observed only inthe liver. In rats, exposure to 100 and 400 ppm produced increasedrelative liver weights, centrilobular hepatocellular hypertrophy,lipofuscin/hemosiderin accumulation in Kupifer cells, and centrilobularsingle cell necrosis (400 ppm only). In mice, increased liverweights (100 ppm males, 400 ppm both sexes), centrilobular hepatocellularhypertrophy, accumulation of lipofuscin/hemosiderin in Kupffercells, and centrilobular single cell necrosis were observedin all exposure groups. These observations occurred in a dose-responsefashion and were minimal at 25 ppm. No increase in hepatic cellproliferation was seen in mice or female rats. Slightly higherproliferation was seen in male rats exposed to 400 ppm at 2weeks and 3 months but not at 12 months. Dimethylformamide wasnot oncogenic under these experimental conditions in eitherthe rat or mouse.     

Rodent carcinogenicity with the thiazolidinedione antidiabetic agent troglitazone.

Carcinogenic potential of the thiazolidinedione antidiabetic troglitazone was assessed in 104-week studies in mice and rats. Mice were given 50, 400, or 800 mg/kg, male rats 100, 400, or 800 mg/kg, and female rats 25, 50, or 200 mg/kg. Vehicle and placebo controls were included. Survival was significantly decreased in both sexes of both species at high doses, but was adequate for valid evaluation of carcinogenicity. Hypertrophy and hyperplasia of brown adipose tissue was observed in both species at all doses, and fatty change and hypocellularity of bone marrow was noted in mice at all doses and in female rats at 50 and 200 mg/kg. Hepatocellular vacuolation was observed in mice at 400 and 800 mg/kg, and centrilobular hepatocellular hypertrophy occurred in rats at > or = 200 mg/kg. Ventricular dilatation, myocardial fibrosis, and atrial myocyte karyomegaly in male rats at 400 and 800 mg/kg and female rats at all doses were morphologically similar to spontaneous lesions, but incidence and severity were increased compared with controls. In mice, the incidence of hemangiosarcoma was increased in females at 400 mg/kg and in both sexes at 800 mg/kg. The incidence of hepatocellular carcinoma was increased in female mice at 800 mg/kg. Troglitazone exposure [AUC((0-24))] at the lowest dose associated with increased tumor incidence in mice was 16 times human therapeutic exposure at 400 mg daily. No tumors of any type were increased in rats at exposures up to 47 times therapeutic exposure.     

Toxicology and carcinogenesis studies of divinylbenzene-HP (Cas No. 1321-74-0) in F344/N rats and B6C3F1 mice (inhalation studies)

Divinylbenzene-HP is used for producing vinyl polymers. Divinylbenzene-HP was nominated for study by the National Cancer Institute because of the potential for worker exposure and the structural similarity of divinylbenzene to styrene, a potential human carcinogen. Male and female F344/N rats and B6C3F1 mice were exposed to divinylbenzene-HP (80%) by inhalation for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: Groups of five male and five female rats were exposed by whole body inhalation to divinylbenzene-HP at target concentrations of 0, 25, 50, 100, 200, or 400 ppm 6 hours plus T90 (12 minutes) per day, 5 days per week for 16 days. All rats survived to the end of the study. Significant decreases in mean body weights occurred in both male and female rats in the 400 ppm groups. Relative kidney weights of 50 ppm or greater males and relative liver weights of 200 and 400 ppm males were significantly greater than those of the chamber controls. A clear serous nasal/eye discharge was observed in groups of males exposed to 100 ppm or greater and females exposed to 50 ppm or greater. Minimal or mild rhinitis occurred in 400 ppm rats of both sexes. 2-WEEK STUDY IN MICE: Groups of five male and five female mice were exposed by whole body inhalation to divinylbenzene-HP at target concentrations of 0, 25, 50, 100, 200, or 400 ppm for 6 hours plus T90 (12 minutes) per day, 5 days per week for 17 days. All 400 ppm males and females died on or before the second day of the study, and two male and two female 200 ppm mice died early. Mean body weights of 100 and 200 ppm males were significantly less than those of the chamber controls. Thymus weights of exposed groups of males were significantly less than those of the chamber controls, and relative liver weights of 100 and 200 ppm males were significantly increased. Kidney and liver weights of exposed groups of females were significantly greater than those of the chamber controls. Mice exposed to 200 and 400 ppm had liver lesions including degeneration, necrosis, hemorrhage or cytomegaly. Renal tubule necrosis and regeneration occurred at 200 ppm. Necrosis or metaplasia of nasal epithelium and glands occurred in the nose in all exposure groups. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed to divinylbenzene-HP at concentrations of 0, 25, 50, 100, 200, or 400 ppm for 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. All rats survived to the end of the study. There were no biologically significant changes in body weight in either sex. Nasal/eye discharge was noted in 400 ppm males and 100 ppm females. Kidney and liver weights of exposed groups of males and of 400 ppm females were generally greater than those of the chamber controls. In addition, the relative weights of the heart and testis were significantly increased in 200 and 400 ppm males. Incidences of degeneration of the olfactory epithelium in 200 and 400 ppm rats and basal cell hyperplasia of the olfactory epithelium in rats exposed to 100 ppm or greater were significantly increased. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed to divinylbenzene-HP at concentrations of 0, 12.5, 25, 50, 100, or 200 ppm for 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. All 200 ppm males and nine 200 ppm females died early. Final mean body weights were significantly lower in males and females exposed to 25, 50, or 100 ppm when compared with chamber controls. Lethargy or hypoactivity was observed in the higher exposure concentration groups. Exposure to divinylbenzene was associated with necrosis of the liver and kidney in 200 ppm males and females dying early. In all exposed groups of male and female mice, there was necrosis of nasal cavity lateral walls, olfactory epithelium, and glands with resultant atrophy of olfactory epithelium and glands in females. A lower number of animals had necrotic or degenerative changes of the upper respiratory tract. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed to divinylbenzene-HP at concentrations of 0, 100, 200, or 400 ppm for 6 hours plus T90 (12 minutes) per day, 5 days per week for up to 105 weeks. Survival of 400 ppm females was significantly less than that of the chamber control group. Survival of all exposed groups of males was similar to that of the chamber control group. Mean body weights of 400 ppm males and females were significantly less than those of the controls during the second half of the study. Renal tubule carcinomas occurred in two of 50 males exposed to 400 ppm in the original kidney sections, an incidence that exceeded the historical control range. In 400 ppm males, the incidence of renal tubule hyperplasia was increased, and the incidence of nephropathy was significantly increased. Following combined analysis of single and step-section data, the incidences of renal tubule adenoma and adenoma or carcinoma (combined) were marginally higher in 200 and 400 ppm males, and the incidence of renal tubule hyperplasia was significantly increased in 400 ppm males. The incidences of malignant glial cell tumors (malignant astrocytoma and oligodendroglioma) in the brain were slightly increased in 100 and 200 ppm males, and the incidence in the 200 ppm group exceeded the historical range for chamber controls. There were increased incidences of degenerative and regenerative changes in the olfactory epithelium in the nose of all exposed groups of rats. The incidence of focal chronic inflammation in the lung of 400 ppm males was significantly greater than in the chamber control group. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed to divinylbenzene-HP at concentrations of 0, 10, 30, or 100 ppm for 6 hours plus T90 (12 minutes) per day, 5 days per week for up to 105 weeks. Survival of all exposed groups of male and female mice was similar to that of the chamber controls. Mean body weights were lower relative to chamber controls in 100 ppm males and in 30 and 100 ppm females. The incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined) in 100 ppm males were greater than chamber control incidences, but the incidences of adenoma or carcinoma (combined) were within the historical control range. The incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined) in all exposed groups of females were generally greater than those of the chamber controls; the incidences were at the upper end or exceeded the historical control ranges. There was a greater incidence and severity of alveolar epithelial hyperplasia in 100 ppm females and a greater severity of this lesion in 30 ppm females, when compared to chamber controls. The incidences and/or severities of atypical bronchiole hyperplasia were significantly increased in all exposed groups of mice. Nonneoplastic nasal lesions occurred in most exposed mice. GENETIC TOXICOLOGY: Divinylbenzene-HP was not mutagenic in any of three independent gene mutation assays using Salmonella typhimurium strains TA97, TA98, TA100, TA1535, or TA1537 or Escherichia coli tester strain WP2 uvrA with or without induced hamster or rat liver enzymes. No increases in the frequencies of micronucleated normochromatic erythrocytes or alterations in the percentages of polychromatic erythrocytes were seen in peripheral blood of male or female B6C3F1 mice exposed to divinylbenzene-HP by inhalation for 3 months. CONCLUSIONS: Under the conditions of this 2-year inhalation study, there was equivocal evidence of carcinogenic activity of divinylbenzene-HP in male F344/N rats based upon the occurrence of carcinomas in the kidney and glial tumors in the brain. There was no evidence of carcinogenic activity in female F344/N rats exposed to 100, 200, or 400 ppm divinylbenzene-HP. There was no evidence of carcinogenic activity in male B6C3F1 mice exposed to 10, 30, or 100 ppm divinylbenzene-HP. There was equivocal evidence of carcinogenic activity of divinylbenzene-HP in female B6C3F1 mice based on the incidences of alveolar/bronchiolar adenoma or carcinoma (combined) in the lung. Exposure to divinylbenzene-HP caused nonneoplastic lesions of the nasal cavity in male and female rats and of the lung and nasal cavity in male and female mice.     

Toxicology and carcinogenesis study of styrene-acrylonitrile trimer in F344/N rats (perinatal and postnatal feed studies)

Styrene-acrylonitrile trimer (SAN Trimer) is a mixture of isomers formed by the condensation of two moles of acrylonitrile and one mole of styrene and has a molecular weight of 210. The mixture is composed of two structural forms: 4-cyano-1,2,3,4-tetrahydro-a-methyl-1-naphthaleneacetonitrile (THNA, CAS No. 57964-39-3) and 4-cyano-1,2,3,4-tetrahydro-1-naphthalenepropionitrile (THNP, CAS No. 57964-40-6). The THNA form consists of four stereoisomers. [Structure:see text]. The THNP form consists of two stereoisomers. [Structure:see text]. SAN Trimer is a by-product of the production of acrylonitrile styrene plastics and is created in specific manufacturing processes for polymers of acrylonitrile and styrene. In June 1998, due to community concerns about the toxicity of SAN Trimer, it was nominated to the NTP for carcinogenicity testing by a member of Congress. Male and female F344/N rats were exposed to SAN Trimer in feed in perinatal and postnatal studies for 7 weeks, 18 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli, and in rat reticulocytes, leukocytes, liver cells, and brain cells. In vivo comet and micronucleus assays were performed in the juvenile rats. 7-WEEK STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets containing 0, 250, 500, 1,000, 2,000, or 4,000 ppm SAN Trimer (equivalent to average daily doses of approximately 50, 90, 175, 270, or 410 mg SAN Trimer/kg body weight to males and 45, 90, 185, 295, or 430 mg/kg to females) for 2 weeks postweaning; the dams of these rats were fed the same concentrations of SAN Trimer from gestation day 7 until the pups were weaned. One 4,000 ppm male rat died 3 days after weaning; all other rats that started the postweaning phase survived to the end of the study. Mean body weights of 1,000, 2,000, and 4,000 ppm males and 2,000 and 4,000 ppm females were significantly less than those of the controls; weaning mean body weights were reduced in 4,000 ppm males and females and in 2,000 ppm females. Feed consumption by 2,000 and 4,000 ppm males and females was less than that by the control groups. Thinness in 4,000 ppm male rats was the only clinical finding related to SAN Trimer exposure. Nonneoplastic lesions were observed in the brain, thymus, spleen, liver, kidney, and reproductive organs of males and females and were considered due to overt toxicity. 18-WEEK STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets of 0, 100, 200, 400, 800, or 1,600 ppm SAN Trimer (equivalent to average daily doses of 10, 20, 40, 80, or 150 mg/kg to males and females) for 3 months postweaning; the dams of these rats were fed the same concentrations from gestation day 7 until the pups were weaned. All rats survived to the end of the study. Mean body weights of 1,600 ppm males and females exposed to 200 ppm or greater were significantly less than those of the controls. At termination, brown staining of the urogenital fur was observed in females exposed to 200 ppm or greater. The liver weights of all exposed groups of males and the spleen weights of 800 and 1,600 ppm males and 1,600 ppm females were significantly greater than those of the controls. There were no significant differences in sperm parameters of male rats or the estrous cyclicity of female rats administered 400, 800, or 1,600 ppm in the diet when compared to the control groups. No exposure-related histopathologic lesions were observed. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female core study rats were fed diets of 0, 400, 800, or 1,600 ppm SAN Trimer (equivalent to average daily doses of approximately 20, 40, or 75 mg/kg to males and 20, 40, or 85 mg/kg to females) for 2 years. Special study groups of 20 males and 20 females were fed the same exposure concentrations and were evaluated at 27, 52, and 78 weeks for hematology and clinical chemistry or at 26, 51, and 77 weeks for urinalysis. The dams of core and special study rats were fed the same concentrations from gestation day 7 until the pups were weaned. Mean body weights of 1,600 ppm males were less than 90% of the controls after week 1; mean body weights of 800 and 1,600 ppm females were less than 90% of the controls after weeks 41 and 13, respectively. Feed consumption by exposed groups of males and females was generally similar to that by the control groups. Brown staining of the urogenital fur was observed in all exposed groups, and the number of animals affected increased with increasing exposure concentration. Rare neoplasms were present in the central nervous system of male and female rats. In the original evaluation, the 800 and 1,600 ppm groups of male rats each had one astrocytoma and one granular cell tumor in the brain. Also in the brain, one 400 ppm female had a granular cell tumor and one control, one 400 ppm, and one 800 ppm female had a mixed cell glioma. In the spinal cord, one astrocytoma was noted in a 1,600 ppm male in the original evaluation. In the expanded review of the spinal cord, one granular cell tumor was found in a 400 ppm male and one meningioma was found in an 800 ppm female. There were statistically significant increases in the incidence of spinal nerve root degeneration in 1,600 ppm males and the incidences of sciatic nerve degeneration in 800 and 1,600 ppm females. More importantly, there were increases in the severities of both nerve lesions in males and in the severity of spinal nerve root degeneration in females. The incidences of bone marrow hyperplasia were significantly increased in 1,600 ppm males and females and 800 ppm females. Incidences of bone marrow granulomatous inflammation were increased in 1,600 ppm males and 800 and 1,600 ppm females, and the increase in the 800 ppm females was significant. Because this lesion is very rare and did not occur in control animals, it should be considered biologically significant. In the liver, the incidence of eosinophilic focus was significantly increased in 1,600 ppm males and the incidences of mixed cell focus were significantly increased in 400 and 1,600 ppm males. Incidences of mixed cell focus were increased in the liver of all exposed groups of females, and the increase was significant in the 1,600 ppm group. The incidence of transitional epithelial hyperplasia of the urinary bladder in 1,600 ppm females was significantly greater than that in the controls. There were significant decreases in the incidences of pituitary gland pars distalis adenoma in 1,600 ppm males and females, and the incidences in both sexes occurred with negative trends. The incidences of mammary gland fibroadenoma occurred in females with a negative trend, and the incidences in 800 and 1,600 ppm females were significantly less than that in the control group. The incidences of mononuclear cell leukemia in all exposed groups of males and females were significantly less than those in the controls. GENETIC TOXICOLOGY: SAN Trimer (Batch 3) was not mutagenic in Salmonella typhimurium strains TA98 or TA100 or in Escherichia coli strain WP2 uvrA/pKM101 in tests conducted with and without exogenous metabolic activation. In vivo, however, results of a comet assay indicated significantly increased levels of DNA damage in brain cells of male and female juvenile rats following administration of SAN Trimer (Batch 3) by oral gavage. Dose-related increases in DNA damage in liver cells of these rats were also observed, but the increases were smaller than those observed in brain cells and were judged to be equivocal in both males and females. Indications of DNA damage following exposure to SAN Trimer were also seen in leukocytes of male and female rats. Increases in male rats were significant, but in females, observed levels of DNA damage did not correlate with dose. Therefore, the results were judged to be positive in males and equivocal in females. In addition to the positive comet assay results, significant increases in the frequencies of micronucleated reticulocytes were observed in peripheral blood of male and female juvenile rats dosed with SAN Trimer. CONCLUSIONS: Under the conditions of this 2-year feed study preceded by perinatal exposure, there was no evidence of carcinogenic activity of SAN Trimer in male and female F344/N rats given feed containing 400, 800, or 1,600 ppm SAN Trimer. Exposure to SAN Trimer resulted in increased incidences and/or severities of peripheral nerve degeneration in male and female F344/N rats, increased incidences of nonneoplastic lesions of the bone marrow and liver in male and female F344/N rats, and of nonneoplastic urinary bladder lesions in female F344/N rats. The incidences of pituitary gland adenoma and mononuclear cell leukemia in male and female F344/N rats and mammary gland fibroadenoma in female F344/N rats were decreased.     

Toxicity and carcinogenicity of methyl isobutyl ketone in F344N rats and B6C3F1 mice following 2-year inhalation exposure

Methyl isobutyl ketone (MIBK) is primarily used as a denaturant for rubbing alcohol, as a solvent and in the manufacture of methyl amyl alcohol. Inhalation of vapors is the most likely route of exposure in the work place. In order to evaluate the potential of MIBK to induce toxic and carcinogenic effects following chronic exposure, groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to MIBK at concentrations of 0, 450, 900, or 1800ppm by inhalation, 6h/day, 5 days per week for 2 years. Survival was decreased in male rats at 1800ppm. Body weight gains were decreased in male rats at 900 and 1800ppm and in female mice at 1800ppm. The primary targets of MIBK toxicity and carcinogenicity were the kidney in rats and the liver in mice. In male rats, there was increased mineralization of the renal papilla at all exposure concentrations. The incidence of chronic progressive nephropathy (CPN) was increased at 1800ppm and the severity was increased in all exposed groups. There were also increases in renal tubule hyperplasia at all exposure concentrations, and in adenoma and adenoma or carcinoma (combined) at 1800ppm; these lesions are thought to represent a continuum in the progression of proliferative lesions in renal tubule epithelium. These increases may have resulted from the increased severity of CPN, either through alpha2micro-globulin-dependent or -independent mechanisms. An increase in mononuclear cell leukemia at 1800ppm was an uncertain finding. Adrenal medulla hyperplasia was increased at 1800ppm, and there was a positive trend for increases in benign or malignant pheochromocytomas (combined). In female rats, there were increases in the incidence of CPN in all exposure concentrations and in the severity at 1800ppm, indicating that CPN was increased by mechanisms in addition to those related to alpha2micro-globulin. There were renal mesenchymal tumors, which have not been observed in historical control animals, in two female rats at 1800ppm. The relationship of these tumors to exposure to MIBK was uncertain. Hepatocellular adenomas, and adenoma or carcinoma (combined) were increased in male and female mice exposed to 1800ppm. There were also treatment-related increases in multiple adenomas in both sexes.     

Kidney and Urinary Bladder Lesions in F344/N Rats and B6C3F1 Mice after 13 Weeks of 2,2-Bis(bromomethyl)-1,3-propanediol Administration

Kidney and Urinary Bladder Lesions in F344/N Rats and B6C3F1Mice after 13 Weeks of 2,2-Bis(bromomethyl)-1,3-propanediolAdministration. ELWELL., M. R., DUNNICK, J. K., BROWN, H. R.,AND MONTGOMERY, C. A. (1989). Fundam Appl. Toxicol. 12, 480–490.Thir teen-week toxicity studies of the flame retardant 2,2-bis(bromomethyl)-1,3-propanediol(BMP; dibromoneopentyl glycol; FR-1138; CAS No. 329690-0) wereconducted in male and female F344/N rats and B6C3F1 mice. Thechemical was administered by oral gavage in corn oil 5 daysper week for 13 weeks to rats at doses of 0, 50, 100, 200, 400,and 800 mg/kg and to mice at doses of 0, 25, 50, 100, 200, and400 mg/kg, or in the feed for 13 weeks at concentrations of0, 1250, 2500, 5000, 10,000, and 20,000 ppm for rats and at0, 625, 1250, 2500, 5000, and 10,000 ppm for mice. There wasa dose-related decrease in body weight gain in rats and miceafter chemical administration. Mortality attributed to toxicityof BMP was seen in the gavage study in 2/10 high-dose (800 mg/kg)male rats and 3/10 high-dose (400 mg/kg) male mice; no dose-relatedmortality occurred in the feed study. Minimal degeneration inthe renal papilla was seen in male rats at 800 mg/kg in thegavage study and at doses of 5000 ppm or more in the feed study.This was also present in one female rat at the 20,000 ppm dose.In male mice renal papillary necrosis occurred at 400 mg/kgafter dosing by the gavage route and at 2500, 5000, and 10,000ppm in the dosed-feed study. In female mice papillary necrosisoccurred only at the 10,000 ppm dose in the feed study. Tubularcell regeneration of the renal cortex was also present in miceat the same dose levels at which the papillary necrosis wasobserved. Transitional cell hyperplasia of the urinary bladderwas seen in male rats at 400 and 800 mg/kg and in both sexesof mice at 200 and 400 mg/kg. Hyperplasia of the urinary bladderwas also seen when BMP was administered in the feed at dosesof 20,000 ppm to male rats; at doses of 2500, 5000, and 10,000ppm to male mice; and at doses of 5000 and 10,000 ppm to femalemice. The kidney and urinary bladder are target organs whenBMP is administered by gavage or the dosed-feed route; micewere more sensitive than rats for the development of kidneyand bladder lesions. Male rats and mice were more sensitivethan females for the development of renal papillary degenerationor necrosis.     

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.     

Toxic responses in F344 rats and B6C3F1 mice given roxarsone in their diets for up to 13 weeks

Thirteen-week toxicity studies were conducted in groups of 10 F344 rats and B6C3F1 mice of each sex fed roxarsone at 0, 50, 100, 200, 400, or 800 ppm in the diet. Arsenic levels in blood, urine, kidneys, and liver of rats were measured in additional animals of each sex dosed with 100 or 400 ppm roxarsone. Compound-related mortality occurred in both sexes of rats at 800 ppm and mice at 800 and 400 ppm. Significant body weight gain depression occurred in both sexes of rats at 200, 400, and 800 ppm and mice at 800 ppm. Clinical signs of toxicity (trembling, ataxia, and pale skin) were seen primarily in rats and mice at 800 ppm. Lesions associated with roxarsone administration were noted only in the kidney of rats and were characterized by tubular necrosis and mineralization at the corticomedullary junction. Arsenic levels in urine, blood, liver, and kidneys increased over time and were directly proportional to the level of roxarsone in feed. These levels were greater than 6 times higher in rats than in mice and were about 2 time higher in males than in females. The no-observable-effect level for roxarsone toxicity was estimated at 100 ppm for rats and 200 ppm for mice. No hematology or clinical chemistry effects were found in rats or mice of either sex.     

Toxicology and carcinogenesis studies of tetralin (CAS No. 119-64-2) in F344/N rats and B6C3F1 mice (inhalation studies)

Tetralin is used as an industrial solvent primarily for naphthalene, fats, resins, oils, and waxes; as a solvent and stabilizer for shoe polishes and floor waxes; as a solvent for pesticides, rubber, asphalt, and aromatic hydrocarbons (e.g., anthracene); as a dye solvent carrier in the textile industry; as a substitute for turpentine in lacquers, paints, and varnishes; in paint thinners and as a paint remover; in alkali-resistant lacquers for cleaning printing ink from rollers and type; as a constituent of motor fuels and lubricants; for the removal of naphthalene in gas distribution systems; and as an insecticide for clothes moths. Tetralin was nominated by the National Cancer Institute for carcinogenicity and disposition studies because of its structure, high production volume, and high potential for worker and consumer exposure. Male and female F344/N rats and B6C3F1 mice were exposed to tetralin (at least 97% pure) by inhalation for 2 weeks, 3 months, or 2 years; male NCI Black Reiter (NBR) rats were exposed to tetralin by inhalation for 2 weeks. Male NBR rats do not produce 2u-globulin; the NBR rats were included to study the relationship of 2u-globulin and renal lesion induction. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: Groups of five male (F344/N and NBR) and five female (F344/N) rats were exposed to tetralin at air concentrations of 0, 7.5, 15, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 12 exposures. All rats survived to the end of the studies. The final mean body weight of female rats exposed to 120 ppm and mean body weight gains of female rats exposed to 30 ppm or greater were significantly less than those of the chamber controls. Final mean body weights of exposed groups of male NBR rats and mean body weight gains of all exposed groups of male rats were significantly less than those of the chamber controls. Dark-stained urine was observed in all 120 ppm rats. Squinting, weeping, or matted fur around the eyes were noted in the majority of F344/N rats exposed to 120 ppm. The 2u-globulin concentrations in the kidney of male F344/N rats were significantly greater in all exposed groups than in the chamber control group. The absolute kidney weight of 60 ppm females and the relative kidney weights of male F344/N rats exposed to 30 ppm or greater and female rats exposed to 15 ppm or greater were significantly increased. The absolute liver weight of 120 ppm NBR male rats and the relative liver weights of male and female rats exposed to 60 or 120 ppm were significantly increased. In the nose, the incidences of mononuclear cell cellular infiltration were generally significantly increased in all exposed groups of rats, and incidences of olfactory epithelium degeneration and glandular hypertrophy occurred in all male F344/N rats exposed to 120 ppm. 2-WEEK STUDY IN MICE: Groups of five male and five female mice were exposed to tetralin at air concentrations of 0, 7.5, 15, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 13 exposures. All mice survived to the end of the study. Mean body weights of male and female mice were similar to those of the chamber controls. Dark-stained urine was observed in most of the exposed mice. The absolute and relative liver weights of 60 and 120 ppm males and 30 and 120 ppm females and the relative liver weights of 60 ppm females were significantly greater than those of the chamber controls. In the nose, the incidences of olfactory epithelium atrophy were significantly increased in 60 and 120 ppm males and females. Glandular dilatation occurred in all 120 ppm females, and glandular hyperplasia occurred in all 120 ppm males and females. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed to tetralin at air concentrations of 0, 7.5, 15, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. The same exposure concentrations were given to additional groups of 10 male and 10 female clinical pathology study rats for up to 6 weeks and five male renal toxicity rats for 2 weeks. All rats survived to the end of the study. During the first 4 weeks of exposure, dark-stained urine was observed in the catch pans of rats exposed to 30, 60, or 120 ppm. Tetralin induced a minimal decrease in the erythron in both sexes that resulted in a hematopoietic response. Tetralin increased urine aspartate aminotransferase and urine lactate dehydrogenase activities (males and females) and glucose/creatinine ratio (males), suggestive of renal injury. The absolute kidney weights of 60 and 120 ppm females and the relative kidney weights of males and females exposed to 15 ppm or greater were significantly greater than those of the chamber controls. Concentrations of 2u-globulin in the kidney of exposed male rats were generally greater than those of the chamber controls at all time points and greater at 6 and 14 weeks than at 2 weeks. There were significantly increased incidences of olfactory epithelium necrosis in rats exposed to 30 ppm or greater and of olfactory epithelium regeneration in 60 and 120 ppm rats. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed to tetralin at air concentrations of 0, 7.5, 15, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. All mice survived to the end of the study. Mean body weights of 120 ppm males were significantly less than those of the chamber controls. Dark-stained urine was observed in the catch pans of mice exposed to 30, 60, or 120 ppm during the first month of the study. Tetralin induced a minimal decrease in the erythron in both sexes that resulted in a hematopoietic response. The relative liver weights of 120 ppm males and 30 ppm or greater females were significantly greater than those of the chamber controls. Incidences of olfactory epithelium metaplasia in 60 and 120 ppm males and females, respiratory epithelium hyaline droplet accumulation in 120 ppm males and 60 and 120 ppm females, cytoplasmic eosinophilic granules within the transitional epithelium lining the urinary bladder in all exposed groups of males and females, and ovarian atrophy and uterine atrophy in 60 and 120 ppm females were significantly increased. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed to tetralin at air concentrations of 0, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 105 weeks. Additional groups of five male and five female rats were exposed to the same concentrations for 12 months. Survival of all exposed groups of rats was similar to that of the chamber controls. Mean body weights of 120 ppm females were 6% less than those of the chamber controls after week 29. Dark-stained urine was observed in all exposed groups of rats. Creatinine-adjusted levels of all urinary metabolites increased with increasing exposure concentration in males and females. In the standard evaluation of the kidney, there were slightly increased incidences of cortical renal tubule adenoma in male rats. In the combined analysis of single and step sections, the incidence of cortical renal tubule adenoma was significantly increased in the 120 ppm group. In the combined analysis, there was also a significantly increased incidence of renal tubule hyperplasia in the 120 ppm group. In 120 ppm males in the standard evaluation, the severity of chronic nephropathy was increased and the incidence of transitional epithelial hyperplasia in the renal pelvis was significantly increased. Three hepatocellular adenomas occurred in 120 ppm females, and one hepatocellular carcinoma each was observed in the 60 and 120 ppm groups. The incidences of uterine stromal polyp and endometrium hyperplasia were significantly increased in 120 ppm females. Incidences of interstitial cell adenoma and germinal epithelium atrophy of the testis in 30 and 120 ppm males were significantly greater than those in the chamber controls. The incidences of olfactory epithelium degeneration, metaplasia, basal cell hyperplasia, suppurative inflammation, and mineralization (except 30 ppm females) in the nose were significantly increased in all exposed groups of rats. The incidences of glandular dilatation were significantly increased in 120 ppm males and all exposed groups of females. The incidences of respiratory epithelium chronic inflammation were significantly increased in males exposed to 60 or 120 ppm and all exposed groups of females. The incidences of lens cataract in 120 ppm females were significantly increased. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed to tetralin at air concentrations of 0, 30, 60, or 120 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 105 weeks. Additional groups of five male and five female mice were exposed to the same concentrations for 12 months. Survival of 60 and 120 ppm female mice was significantly greater than that of the chamber controls. The mean body weights of all exposed groups of male and female mice were similar to those of the chamber controls by the end of the study. Dark-stained urine was observed in all exposed groups of male mice and in females exposed to 60 or 120 ppm. Creatinine-adjusted levels of all urinary metabolites increased with increasing exposure concentration in males and females. The incidence of hemangiosarcoma of the spleen was increased in 120 ppm females and exceeded the historical control range for inhalation studies. The incidences of olfactory epithelium atrophy, respiratory metaplasia, glandular hyperplasia, and suppurative inflammation in exposed groups of mice were significantly greater than those in the chamber controls. Transitional epithelium cytoplasmic eosinophilic granules were present in the urinary bladder of all exposed mice. (ABSTRACT TRUNCATED)     

Toxicology and carcinogenesis studies of p,p'-dichlorophenyl sulfone (CAS No. 80-07-9) in F344/N rats and B6C3F1 mice (feed studies)

p,pN-Dichlorodiphenyl sulfone is used as a starting material in the production of polysulfones and polyethersulfones and as a component in reactive dyes in the textile industry; it is also a by-product of pesticide production. p,pN-Dichlorodiphenyl sulfone was nominated for study by the National Cancer Institute because of its history of high production and use, the prospect of increased production and use, and the absence of adequate toxicity testing. Male and female F344/N rats and B6C3F1 mice were exposed top,pN-dichlorodiphenyl sulfone (greater than 99% pure)in feed for 14 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium,cultured Chinese hamster ovary cells, and mouse bone marrow. 14-WEEK STUDY IN RATS: Groups of 10 male and 10 female F344/N rats were fed diets containing 0, 30, 100, 300, 1,000, or 3,000 ppm p,pN-dichlorodiphenyl sulfone (equivalent to average daily doses of approximately 2, 6, 19, 65, or 200 mgp,pN-dichlorodiphenyl sulfone/kg body weight) for 14 weeks. All rats survived until the end of the study. Mean body weights of groups exposed to 300 ppm or greater were significantly less than those of the controls. Liver weights of groups exposed to 100 ppm or greater and kidney weights of 1,000 and 3,000 ppm male rats were significantly greater than those of the controls. Centrilobular hepatocyte hypertrophy of the liver was observed in most male rats exposed to 100 ppm or greater and in all female rats exposed to 300 ppm or greater, and the severities were increased in 300 ppm males and 1,000 and 3,000 ppm males and females. The incidences of nephropathy in 1,000 and 3,000 ppm female rats were significantly increased. Dose-related increases in severity of nephropathy were observed in male rats. 14-WEEK STUDY IN MICE: Groups of 10 male and 10 female B6C3F1 mice were fed diets containing 0, 30, 100, 300, 1,000, or 3,000 ppm p,pN-dichlorodiphenyl sulfone (equivalent to average daily doses of approximately 3.5, 15, 50, 165,or 480 mg/kg) for 14 weeks. All mice survived until the end of the study. Mean body weights of groups exposed to 300 ppm or greater were significantly less than those of the controls. Liver weights of groups exposed to 300 ppm or greater were significantly increased. Centrilobular hypertrophy of the liver was observed in most males exposed to 100 ppm or greater and in all females exposed to 1,000 or 3,000 ppm, and the severities generally increased with increasing exposure concentration. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were fed diets containing 0, 10 (males), 30, 100, or 300 (females) ppm p,pN-dichlorodiphenyl sulfone for 105 weeks. Dietary concentrations of 10, 30, and 100 ppm resulted in average daily doses of approximately 0.5, 1.5, and 5.0 mg/kg to males. Dietary concentrations of 30, 100,and 300 ppm resulted in average daily doses of approximately 1.6, 5.4, and 17 mg/kg to females. Additional groups of 10 male and 10 female rats were fed the same p,pN-dichlorodiphenyl sulfone-containing diets for 18 months and bled for plasma determinations of p,pN-dichlorodiphenyl sulfone at approximately 2 weeks and 3, 12, and 18 months. Survival of all exposed groups of male and female rats was similar to that of the control groups. Mean body weights of 30 and 100 ppm males were generally less than those of the controls during the latter part of the study, and mean body weights of 100 and 300 ppm female rats were less from weeks 30 and 18,respectively. Feed consumption by the exposed groups was similar to that by the controls throughout the study. The incidences of centrilobular hepatocyte hypertrophy in 100 ppm male and 100 and 300 ppm female rats were significantly greater than those in the controls. The incidences of bile duct hyperplasia and centrilobular degeneration were also significantly increased in 100 and 300 ppm females. No neoplasms were related to chemical exposure. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were fed diets containing 0, 30, 100, or 300 ppm p,pN-dichlorodiphenyl sulfone for 105 to 106 weeks. Dietary concentrations of 30, 100, and 300 ppm delivered average daily doses of approximately 4, 13, and 40 mg/kg to males and approximately 3, 10, and 33 mg/kg to females. Additional groups of 10 male and 10 female mice were fed the same p,pN-dichlorodiphenyl sulfone-containing diets for up to 12 months;three mice in each group were bled for plasma determinations of p,pN-dichloro-diphenyl sulfone at approximately 2 weeks or 3 or 12 months. Survival of all exposed groups of male and female mice was similar to that of the control groups. Mean body weights of 300 ppm mice were less than those of the controls throughout most of the study. Feed consumption by the exposed groups was similar to that by the controls throughout the study. The incidences of centrilobular hepatocyte hypertrophy in all exposed groups of male mice and in 100 and 300 ppm females were significantly greater than those in the controls. The incidence of eosinophilic foci in 300 ppm females was significantly increased. No neoplasms were related to chemical exposure. PHARMACOKINETICS OF p,pN-DICHLORODIPHENYL SULFONE: p,pN-Dichlorodiphenyl sulfone is rapidly absorbed from the gut and metabolized by a saturable process. Although some p,pN-dichlorodiphenyl sulfone is eliminated unchanged in feces and urine, most of the elimination is via metabolism. Mathematical modeling of the toxicokinetics supports the view that p,pN-dichlorodiphenyl sulfone induces enzymes involved in its metabolism. GENETIC TOXICOLOGY: p,pN-Dichlorodiphenyl sulfone was not mutagenic in any of several strains of Salmonella typhimurium, with or without metabolic activation enzymes (S9). Results of the sister chromatid exchange test in cultured Chinese hamster ovary cells were judged to be negative in the presence of S9 and equivocal in the absence of S9, but no induction of chromosomal aberrations was noted, with or without S9. In contrast to the in vitro results, positive results were obtained in an acute in vivo mouse bone marrow micronucleus assay with p,pN-dichlorodiphenyl sulfone administered by intraperitoneal injection three times over a dose range of 200 to 800 mg/kg. CONCLUSIONS: Under the conditions of these 2-year feed studies, there was no evidence of carcinogenic activity* of p,pN-dichlorodiphenyl sulfone in male F344/N rats exposed to 10, 30, or 100 ppm or in female F344/N rats exposed to 30, 100, or 300 ppm. There was no evidence of carcinogenic activity of p,pN-dichlorodiphenyl sulfone in male or female B6C3F1 mice exposed to 30,100, or 300 ppm. Exposure to p,pN-dichlorodiphenyl sulfone for 2 years caused increased incidences of nonneoplastic lesions of the liver in male and female rats and mice.     

Characterization of inhaled alpha-methylstyrene vapor toxicity for B6C3F1 mice and F344 rats.

alpha-Methylstyrene (AMS) is a chemical intermediate used in the synthesis of specialty polymers and copolymers. Inhalation studies of AMS were conducted because of the lack of toxicity data and the structural similarity of AMS to styrene, a toxic and potentially carcinogenic chemical. Male and female B6C3F1 mice were exposed to 0, 600, 800, or 1000 ppm AMS 6 h/day, 5 days/week, for 12 days. After 1 exposure, 21% (5/24) of female mice were found dead in the 1000-ppm group, 56% (10/18) in the 800-ppm group, and 6% (1/18) in the 600-ppm concentration group. After 12 exposures, relative liver weights were significantly increased and relative spleen weights were significantly decreased in both male and female mice at all concentrations. No microscopic treatment-related lesions were observed. A decrease in hepatic glutathione (GSH) was associated with AMS exposure for 1 and 5 days. Male and female F344 rats were exposed to 0, 600 or 1000 ppm AMS for 12 days. No mortality or sedation occurred in AMS-exposed rats. Relative liver weights were significantly increased in both males and females after 12 exposures to 600 or 1000 ppm. An increased hyaline droplet accumulation was detected in male rats in both concentration groups; no significant microscopic lesions were observed in other tissues examined. Exposure of male and female F344 rats and male NBR rats to 0, 125, 250 or 500 ppm AMS, 6 h/day for 9 days resulted in increased accumulation of hyaline droplets in the renal tubules of male F344 rats in the 250 and 500 ppm concentration groups. Although AMS and styrene are structurally very similar, AMS was considerably less toxic for mice and more toxic for male rats than styrene.     

Theophylline-induced mesenteric periarteritis in F344/N rats

The toxicity and carcinogenic potential of theophylline (an alkaloid bronchodilator drug) was investigated in male and female F344/N rats in 16-day, 14-week, and 2-year gavage and feeding studies. In 16-day studies, rats were fed diets containing 0, 500, 1000, 2000, 4000, and 8000 ppm of theophylline or given 0, 12.5 (twice daily), 25 (once daily), 50 (once daily), 50 (twice daily), 100 (once daily), 200 (once daily), 200 (twice daily), and 400 (once daily) mg theophylline/kg body weight in corn oil by gavage. In 14-week studies, rats were fed diets containing 0, 1000, 2000, and 4000 ppm theophylline or given 0, 37.5, 75, and 150 mg/kg body weight theophylline in corn oil by gavage. In 2-year gavage studies, rats were given 0, 7.5, 25, and 75 mg/kg body weight in corn oil. In 16-day gavage studies, treatment-related periarteritis occurred in arteries of the pancreas and adjacent to the mesenteric lymph nodes of early death male and female rats given 400 mg/kg once daily. In the 14-week studies, treatment-related periarteritis occurred at similar sites and in male rats exposed to 75 and 150 mg/kg, and in all exposed female rats (gavage studies), in females exposed to 1000 ppm, and in both sexes exposed to 2000 and 4000 ppm (feeding studies). In the 2-year study, chronic periarteritis was significantly increased only in the males receiving 75 mg/kg of theophylline. The adventitia, media and intima of medium- and large-sized mesenteric arteries were involved. Similar to other vasodilator chemicals, the pathogenesis of theophylline-induced vascular lesions may be a consequence of hemodynamic changes induced in the vascular wall. Received: 11 May 1998 / Accepted: 6 July 1998     

Respiratory tract lesions in F344/N rats and B6C3F1 mice after inhalation exposure to 1,2-epoxybutane

1,2-Epoxybutane, a short-chain epoxide used as a stabilizer in chlorinated hydrocarbon solvents, was administered by inhalation exposure as a vapor 6 h/day, 5 day/week, for 24 months at exposure concentrations of 0, 200 or 400 ppm to F344/N rats and 0, 50, or 100 ppm to B6C3F1 mice. Survival of all groups of rats was 50% or greater until week 98 but was reduced in exposed groups by the end of the study. Survival in male mice was comparable among groups. Survival in female mice was greater than 50% until week 86, but was then reduced in the high-exposure group of mice. Exposure-related inflammatory, degenerative, and proliferative lesions occurred in the nasal cavity of both rats and mice. Seven papillary adenomas occurred in the nasal passages of high-exposure male rats and 2 in the nasal passages of high-exposure female rats. Alveolar/bronchiolar adenoma or carcinoma (combined) occurred with increased incidence in exposed male rats relative to controls. No exposure-related neoplastic lesions were seen in mice. After inhalation exposure, 1,2-epoxybutane was carcinogenic in rodents as were other epoxides or related compounds including propylene oxide, 1,3-butadiene, and ethylene oxide. The site of carcinogenic activity was considered to be related to length of the carbon chain.     

Toxicity and carcinogenicity studies of 4-methylimidazole in F344/N rats and B6C3F1 mice

4-Methylimidazole (4MI) is used in the manufacture of pharmaceuticals, photographic chemicals, dyes and pigments, cleaning and agricultural chemicals, and rubber. It has been identified as a by-product of fermentation in foods and has been detected in mainstream and side stream tobacco smoke. 4MI was studied because of its high potential for human exposure. Groups of 50 male and 50 female F344/N rats were fed diets containing 0-, 625-, 1,250-, or 2,500 ppm 4MI (males) or 0-, 1,250-, 2,500-, or 5,000 ppm 4MI (females) for 106 weeks. Based on the food consumption the calculated average daily doses were approximately 30, 55, or 115 mg 4MI/kg body weight to males and 60, 120, or 250 mg 4MI/kg to females. Survival of all exposed groups of males and females was similar to that of the control groups. The mean body weights of males in the 1,250- and 2,500 ppm groups and females in the 2,500- and 5,000 ppm groups were less than those of the control groups throughout the study. Feed consumption by 5,000 ppm females was less than that by the controls. Clonic seizures, excitability, hyperactivity, and impaired gait were observed primarily in 2,500- and 5,000 ppm females. The incidence of mononuclear cell leukemia in the 5,000 ppm females was significantly greater than that in the controls. The incidences of hepatic histiocytosis, chronic inflammation, and focal fatty change were significantly increased in all exposed groups of male and female rats. The incidences of hepatocellular eosinophilic and mixed cell foci were significantly increased in 2,500 ppm males and 5,000 ppm females. Groups of 50 male and 50 female B6C3F1 mice were fed diets containing 0-, 312-, 625-, or 1,250 ppm 4MI for 106 weeks. Based on the food consumption the calculated average daily doses were approximately 40, 80, or 170 mg 4MI/kg body weight to males and females. Survival of all exposed groups of males and females was similar to that of the control groups. Mean body weights of males and females in the 1,250 ppm groups and that in the 312- and 625 ppm females were less than those of the control groups. Feed consumption by exposed groups of male and female mice was similar to that by the controls. The incidences of alveolar/bronchiolar adenoma in all exposed groups of females, alveolar/bronchiolar carcinoma in 1,250 ppm males, and alveolar/bronchiolar adenoma or carcinoma (combined) in 1,250 ppm males and 625- and 1,250 ppm females were significantly greater than those in the control groups. The incidence of alveolar epithelial hyperplasia was significantly increased in the 1,250 ppm females. 4MI is carcinogenic inducing alveolar/bronchiolar adenoma and carcinoma in male and female mice. 4MI may also induce mononuclear cell leukemia in female rats. An erratum to this article can be found at     

Toxicity and carcinogenicity of nitrofurazone in F344/N rats and B6C3F1 mice

Toxicology and carcinogenesis studies were conducted by feeding diets containing nitrofurazone (99% pure) to groups of F344/N rats and B6C3F1 mice for 14 days, 13 wk or 2 yr. In the 14-day studies, in which doses ranged from 630 to 10,000 ppm, nitrofurazone was more toxic to mice than to rats. Accordingly, in the 13-wk studies, doses for rats ranged from 150 to 2500 ppm and for mice from 70 to 1250 ppm. At the higher doses, convulsive seizures and gonadal hypoplasia were observed in both species. Evidence of toxicity in rats also included degenerative arthropathy. For the 2-yr studies, rats were exposed to 0, 310 or 620 ppm nitrofurazone and the survival of male rats given 620 ppm was lower than that of controls (33/50, 30/50 and 20/50 in the control, 310- and 620-ppm groups, respectively). Nitrofurazone administration increased the incidences of mammary gland fibroadenomas in female rats (8/49, 36/50 and 36/50 in the control, 310- and 620-ppm groups, respectively). In male rats it was associated with a marginal increase in sebaceous gland adenomas and trichoepitheliomas of the skin, mesotheliomas of the tunica vaginalis, and tumours of the perputial gland. Nitrofurazone caused testicular degeneration (atrophy of germinal epithelium and aspermatogenesis) in rats, and degeneration of vertebral and knee articular cartilage in rats of both sexes. In mice, dietary concentrations of nitrofurazone for the 2-yr studies were 0, 150 or 310 ppm. In mice of each sex, nitrofurazone administration induced stimulus-sensitive convulsive seizures, primarily during the first year of study. In male mice, there was no evidence of any chemically-related carcinogenic effects, but there was a treatment-related decrease in survival (39/50, 31/50 and 27/50 in the control, 150- and 310-ppm groups, respectively). In female mice nitrofurazone induced ovarian lesions with increased incidences of benign mixed tumours (0/47, 17/50 and 20/50 in control, low- and high-dose groups, respectively) and granulosa cell tumours (1/47, 4/50 and 9/50 in control, low- and high-dose groups, respectively).     

Encephalopathy in rats and nephropathy in rats and mice after subchronic oral exposure to benzaldehyde

Male and female Fischer 344 rats and B6C3F1 mice were treated daily (5 days/wk) with benzaldehyde by gavage either in 12 doses of 0 (vehicle control), 100 (rats only), 200, 400, 800, 1600 or (for mice only) 3200 mg/kg body weight/day (followed by 2 days' observation without treatment), or for 90 days in doses of 0, 50, 100, 200, 400 or 800 mg/kg/day (rats) or 0, 75, 150, 300, 600 or 1200 mg/kg/day (mice). In the acute studies, benzaldehyde induced deaths and decreased body-weight gain in both sexes of rats given 800 or 1600 mg/kg/day and caused deaths in both sexes of mice given 1600 or 3200 mg/kg/day. In the 90-day studies, deaths occurred in both sexes of rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Body-weight gain was depressed in male rats on 800 mg/kg/day, in male mice on 600 mg/kg/day and in female mice on 1200 mg/kg/day. Necrotic and degenerative lesions were seen in the cerebellar and hippocampal regions of the brain in both sexes of rats given 800 mg/kg/day, but not in mice. Renal tubular necrosis occurred in male and female rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Mild epithelial hyperplasia or hyperkeratosis of the forestomach was seen in male and female rats on 800 mg/kg/day. In this limited study, the no-observed-toxic-effect doses of benzaldehyde administered by gavage were 400 mg/kg/day in male and female rats, 300 mg/kg/day in male mice and 600-1200 mg/kg/day in female mice.     

Toxicology and carcinogenesis studies of fumonisin B1 (cas no. 116355-83-0) in F344/N rats and B6C3F1 mice (feed studies)

[formula: see text] Fumonisin B1 is a mycotoxin produced by the fungus Fusarium moniliforme, one of the major species found in corn. There are no known commercial or medical uses of fumonisin B1. Fumonisin B1 was nominated by the FDA Center for Food Safety and Applied Nutrition for study because of its occurrence in corn and corn-based products in the United States and its toxicity in field exposure of horses and pigs. Male and female F344/N Nctr BR rats and B6C3F1/Nctr BR (C57BL/6N x C3H/HeN MTV-) mice were exposed to fumonisin B1 (92% pure) in feed for 28 days or (greater than 96% pure) for 2 years. 28-DAY STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets containing 0, 99, 163, 234, or 484 ppm fumonisin B1 for 28 days. There were no exposure-related deaths in rats. The mean body weights of the 484 ppm groups were significantly less (-16%) than those of the controls. Dietary concentrations of 99, 163, 234, and 484 ppm fumonisin B1 resulted in average daily doses of 12, 20, 28, and 56 mg fumonisin B1/kg body weight for males and females. Additional groups of male and female rats were exposed to the same concentrations of fumonisin B1 for 28 days for clinical pathology studies. The concentrations of creatinine, cholesterol, triglycerides, and total bile acids, as well as activities of the enzymes alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, and gamma-glutamyltransferase, were generally significantly greater in the 484 ppm groups than in the control groups at all time points, indicating hyperlipidemia and a hepatic effect. Fumonisin B1 is an inhibitor of ceramide synthase, resulting in an interruption of de novo sphingolipid synthesis. This enzyme inhibition results in increased levels of sphinganine (or increased sphinganine:sphingosine ratio) in tissues and urine. Urinary sphinganine was increased in groups of males exposed to 163 ppm or greater, while urinary sphinganine was increased in all exposed groups of females. The kidney weights, relative to body weight, of all exposed groups of rats were less than those of the control groups, decreasing by approximately 11% in the females and 20% in the males. Apoptosis and degeneration of the kidney were observed in all exposed males and in most females exposed to 163 ppm or greater. The incidences of minimal to mild apoptosis, degeneration, and mitotic alteration of the liver were significantly increased in 234 and 484 ppm males and in females exposed to 163 ppm or greater. The incidences of bile duct hyperplasia were significantly increased in males and females in the 484 ppm groups. In the core study, male rats in all exposed groups and females exposed to 163 ppm or greater had significantly increased percentages of hepatocytes in one or more proliferative (non-G0) states. 28-DAY STUDY IN MICE: Groups of 12 male and 12 female mice were fed diets containing 0, 99, 163, 234, or 484 ppm fumonisin B1 for 28 days. There were no exposure-related deaths in mice. The mean body weights of the 484 ppm groups of males were significantly less than those of the controls. Feed consumption by males exposed to 484 ppm was less than that by the controls; dietary concentrations of 99, 163, 234, and 484 ppm fumonisin B1 resulted in average daily doses of approximately 19, 31, 44, and 93 mg/kg for males and 24, 41, 62, and 105 mg/kg for females. Additional groups of male and female mice were exposed to the same concentrations of fumonisin B1 for 28 days for clinical pathology studies. Cholesterol and total bile acid concentrations and alanine aminotransferase and alkaline phosphatase activities were increased at 484 ppm, indicating hyperlipidemia and a hepatic effect. Urinary sphinganine concentrations and sphinganine/sphingosine ratios were increased in 484 ppm male mice. In 484 ppm males and all exposed groups of females, the incidences of hepatocellular necrosis, diffuse periportal hypertrophy, and diffuse centrilobular hyperplasia, as well as hyperplasia of the bile canaliculi and Kupffer cells, were generally significantly greater than those in the controls. Core study males exposed to 99, 163, or 234 ppm had significantly increased incidences of hepatocellular cytoplasmic alteration. Hepatocytes of 484 ppm male mice and all exposed groups of female mice were induced into proliferative (non-G0) states. 2-YEAR STUDY IN RATS: Groups of 48 male and 48 female rats (40 for 5 ppm groups) were fed diets containing 0, 5, 15, 50, or 150 ppm fumonisin B1 (males) or 0, 5, 15, 50, or 100 ppm fumonisin B1 (females) (equivalent to average daily doses of approximately 0.25, 0.76, 2.5, or 7.5 mg/kg to males and 0.31, 0.91, 3.0, or 6.1 mg/kg to females) for 105 weeks. Additional groups of four male and four female rats were exposed to the same concentrations as the core study animals and were evaluated at 6, 10, 14 or 26 weeks. Survival, Body Weights, and Feed Consumption Survival, mean body weights, and feed consumption of exposed male and female rats were generally similar to the controls throughout the study. Clinical Pathology Findings Sphinganine/sphingosine ratios were increased in the urine of 15, 50 and 150 ppm males and 50 and 100 ppm females exposed to fumonisin B1 for up to 26 weeks. The sphinganine/sphingosine ratios were also increased in kidney tissue of 50 and 150 ppm males (85- and 119-fold) and 50 and 100 ppm females (7.8- and 22-fold) at 2 years. Cell Proliferation Analyses Renal tubule epithelial cell proliferation was increased in 50 and 150 ppm male rats exposed to fumonisin B1 for up to 26 weeks. Renal tubule epithelial cell proliferation was marginally increased in 100 ppm females. Organ Weights and Pathology Findings Kidney weights of 50 and 150 ppm males were less than those of the controls at 6, 10, 14, and 26 weeks and at 2 years. Kidney weights of 100 ppm females were less than those of the controls at 26 weeks, and kidney weights of 15, 50, and 100 ppm females were less than those of the controls at 2 years. At 2 years, there was a significant increase in the incidences of renal tubule adenoma from none in the groups receiving 15 ppm or less to five of 48 in 150 ppm males. Renal tubule carcinomas were not present in male rats receiving 15 ppm or less and occurred in seven of 48 and 10 of 48 male rats in the 50 and 150 ppm groups, respectively. Incidences of apoptosis of the renal tubule epithelium were generally significantly increased in males exposed to 15 ppm or greater for up to 26 weeks. The incidences of focal renal tubule epithelial hyperplasia were significantly increased in 50 and 150 ppm males at 2 years. 2-YEAR STUDY IN MICE: Groups of 48 male and 48 female mice were fed diets containing 0, 5, 15, 80, or 150 ppm (males) or 0, 5, 15, 50, or 80 ppm (females) fumonisin B1 (equivalent to average daily doses of approximately 0.6, 1.7, 9.7, or 17.1 mg/kg to males or 0.7, 2.1, 7.1, or 12.4 mg/kg to females) for 105 weeks. Additional groups of four male and four female mice were exposed to the same concentrations as the core study animals and were evaluated at 3, 7, 9, or 24 weeks. Survival, Body Weights, and Feed Consumption Survival of males and females in the 15 ppm groups and of 5 ppm females was significantly greater and survival of 80 ppm males and females was significantly less than that of the control groups. Mean body weights and feed consumption of exposed mice were generally similar to the controls. Organ Weights and Pathology Findings Liver weights, relative to body weight, were increased 1.3- and 2.9-fold in 50 and 80 ppm females at 2 years. At 2 years, the incidences of hepatocellular adenoma in 50 and 80 ppm females were significantly greater than those in the controls and occurred with a positive trend. Similarly, the incidences of hepatocellular carcinoma increased from none in the groups receiving 0, 5, or 15 ppm fumonisin B1 to 10 of 47 females at 50 ppm and nine of 45 females at 80 ppm. The incidences of hepatocellular hypertrophy were significantly increased in 15, 80, and 150 ppm males and in 50 and 80 ppm females at 2 years. The incidences of hepatocellular apoptosis were significantly increased in 50 and 80 ppm females at 2 years. CONCLUSIONS: Under the conditions of these 2-year feed studies, there was clear evidence of carcinogenic activity of fumonisin B1 in male F344/N rats based on the increased incidences of renal tubule neoplasms. There was no evidence of carcinogenic activity of fumonisin B1 in female F344/N rats exposed to 5, 15, 50, or 100 ppm. There was no evidence of carcinogenic activity of fumonisin B1 in male B6C3F1 mice exposed to 5, 15, 80, or 150 ppm. There was clear evidence of carcinogenic activity of fumonisin B1 in female B6C3F1 mice based on the increased incidences of hepatocellular neoplasms. The sphinganine/sphingosine ratios were increased in the urine and the kidney tissue of rats receiving diets containing fumonisin B1. There was evidence of apoptosis and increased cell proliferation of the renal tubule epithelium in exposed rats, particularly in those groups of males that developed renal tubule neoplasms. Increased incidences of hyperplasia of the renal tubule epithelium also occurred in these groups of male rats. In mice exposed to the higher concentrations of fumonisin B1, males and females had increased incidences of hepatocellular hypertrophy and females had increased incidences of hepatocellular apoptosis.     

Tumor induction in F344/N rats and B6C3F1 mice following inhalation exposure to ethylbenzene

Carcinogenesis studies of ethylbenzene were conducted because of its extensive use as a solvent and because it is structurally similar to the known carcinogen benzene. Groups of 50 male and 50 female Fischer rats and B6C3F1 mice were exposed to ethylbenzene by inhalation at 0, 75, 250, and 750 ppm 6 h per day, 5 days per week, for 2 years. The dose levels were selected based on the results of 13-week studies. In the 750 ppm group of male and female rats, body weights were slightly lower and incidences of renal hyperplasia and tubular neoplasms were significantly increased compared with controls. Incidence of testicular tumors was also significantly increased in male rats. Survival and body weights of the exposed groups of male and female mice and controls were comparable. Incidences of alveolar epithelium metaplasia, alveolar/bronchiolar adenoma, and hepatocyte hypertrophy and necrosis were significantly increased in the 750 ppm male mice and incidences of liver eosinophilic foci and hepatocellular neoplasms were significantly increased in the 750 ppm female mice compared with controls. Ethylbenzene is carcinogenic inducing neoplasms in kidneys and testes in Fischer rats and in lungs in male and liver in female B6C3F1 mice.     

Toxicology and carcinogenesis studies of diethylamine (CAS No. 109-89-7) in F344/N rats and B6C3F1 mice (inhalation studies)

Diethylamine is used mainly as a chemical intermediate to produce the corrosion inhibitor N,N-diethylethanolamine and a lesser amount is used to produce pesticides and insect repellants and in rubber processing. Diethylamine was nominated for study by the National Institute of Environmental Health Sciences based upon its high production volume and ubiquitous natural occurrence in trace amounts and because of the lack of chronic toxicity and carcinogenicity data on the chemical. Male and female F344/N rats and B6C3F1 mice were exposed to diethylamine (approximately 99.9% pure) by inhalation for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in bacterial mutagenicity tester strains and mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: Groups of five male and five female rats were exposed to diethylamine vapor at concentrations of 0, 31, 62.5, 125, 250, or 500 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 16 days. All rats survived to the end of the study. The mean body weights of 250 and 500 ppm males and females and 125 ppm males were significantly less than those of the chamber controls. Clinical findings included lethargy, nasal/eye discharge, abnormal breathing, thinness, eye abnormalities, and discolored urine. The thymus weights of males exposed to 125 ppm or greater and females exposed to 500 ppm were significantly less than those of the chamber controls. Focal eye lesions were noted at necropsy in four males and three females exposed to 500 ppm and one male exposed to 250 ppm. Crusty noses were observed in most 500 ppm males and females and in two 250 ppm males. Suppurative inflammation, necrosis of the turbinates (except in one 125 ppm female), and squamous metaplasia of the respiratory epithelium of the nose were present in all rats exposed to 125 ppm or greater. Ulcer of the respiratory epithelium and atrophy of the olfactory epithelium occurred in all rats exposed to 250 or 500 ppm, and ulcer of the nasopharyngeal duct was present in all 500 ppm rats. Suppurative inflammation of the cornea was present in most rats exposed to 500 ppm. 2-WEEK STUDY IN MICE: Groups of five male and five female mice were exposed to diethylamine vapor at concentrations of 0, 31, 62.5, 125, 250, or 500 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 17 days. Two males and three females exposed to 500 ppm died during the first week of the study. The mean body weights of males and females exposed to 125 ppm or greater were significantly less than those of the chamber controls. Males and females exposed to 250 or 500 ppm lost weight during the study. Lethargy, abnormal breathing, and thinness were observed in most mice exposed to 250 or 500 ppm. Eye irritation and discharge, nasal discharge, and low fecal and urine output were noted in 500 ppm mice. Thymus weights of 250 and 500 ppm males and 125 ppm or greater females were significantly less than those of the chamber controls. Suppurative inflammation of the nose occurred in all males exposed to 250 or 500 ppm and all females exposed to 125 ppm or greater, and most males exposed to 125 ppm. Turbinate necrosis occurred in all exposed mice except one 31 ppm female. Squamous metaplasia of the respiratory epithelium and olfactory epithelial atrophy were seen in mice exposed to 125 ppm or greater. In the lung, the incidence of minimal chronic active inflammation of mainstem bronchi was significantly increased in 500 ppm males. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed to diethylamine vapor at concentrations of 0, 8, 16, 32, 62, or 125 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. All rats survived to the end of the study. Mean body weights of all exposed groups were similar to those of the chamber control groups. There were significant exposure concentration-related decreases in sperm motility in 32, 62, and 125 ppm males; there were no significant differences in the lengths of estrous cycles between chamber control and exposed groups of females. Exposure-related nasal lesions were seen primarily in rats exposed to 62 or 125 ppm. These lesions included turbinate necrosis, suppurative inflammation, respiratory epithelial hyperplasia, squamous metaplasia of the respiratory epithelium, and olfactory epithelial atrophy. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed to diethylamine vapor at concentrations of 0, 8, 16, 32, 62, or 125 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 14 weeks. All mice survived to the end of the study. The mean body weights of 125 ppm males and females were significantly less than those of the chamber controls. There were significant exposure concentration-related decreases in sperm motility in males exposed to 32, 62, or 125 ppm; the estrous cycle of 125 ppm females was significantly longer than that of the chamber controls but only by half a day. Histopathologic changes were noted primarily in the nasal cavity and involved both the respiratory and olfactory epithelium of males and females principally in the 62 or 125 ppm groups. These lesions included suppurative inflammation, squamous metaplasia of the respiratory epithelium, olfactory epithelial atrophy, and necrosis of the turbinates. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed to diethylamine vapor at concentrations of 0, 31, 62.5, or 125 ppm, 6 hours plus T90 (15 minutes) per day, 5 days per week for 105 weeks. Survival of exposed groups of rats was similar to that of the chamber control groups. Mean body weights of males and females exposed to 125 ppm were less than those of the chamber controls after week 57. Increased incidences of eye abnormality occurred in exposed males and females. A spectrum of nonneoplastic lesions was observed in the respiratory and olfactory epithelium of the nose in exposed rats. The lesions included suppurative inflammation, ulceration of the respiratory epithelium, hyaline droplet accumulation in the glands of the respiratory epithelium, necrosis of the turbinates, squamous metaplasia of the respiratory epithelium, hyperplasia of the respiratory epithelium, atrophy of the olfactory epithelium, hyaline droplet accumulation in the respiratory and olfactory epithelium, basal cell hyperplasia of the olfactory epithelium, respiratory metaplasia of the olfactory epithelium, and goblet cell hyperplasia. The incidence of chronic inflammation of the pleura was significantly increased in 125 ppm females. The incidences of histiocytic cellular infiltration of the alveolus of the lung were significantly increased in all exposed groups of females and the incidence of chronic inflammation was significantly increased in 125 ppm females. In 125 ppm males, the incidence of suppurative inflammation of the cornea was significantly increased. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed to diethylamine vapor at concentrations of 0, 16, 31, or 62.5 ppm, 6 hours plus T90 (15 minutes) per day, 5 days per week for 105 weeks. Survival of exposed groups of mice was similar to that of the chamber control groups. Mean body weights of males and females were similar to those of the chamber controls. Eye abnormality was observed in greater incidence in exposed groups of males than in the chamber controls, and torso/ventral ulcer/abscess was observed in six 62.5 ppm males compared to none in the chamber controls. A similar spectrum of nonneoplastic lesions was seen in the nose of exposed mice as was seen in rats. GENETIC TOXICOLOGY: Diethylamine was not mutagenic in either of two independent bacterial mutagenicity assays, each conducted with and without exogenous metabolic activation enzymes. Bacterial strains tested included Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 and Escherichia coli strain WP2 uvrA/pKM101. In addition to the negative results in the two bacterial assays, no significant increases in the frequencies of micronucleated erythrocytes were seen in peripheral blood of male or female B6C3F1 mice from the 3-month study. CONCLUSIONS: Under the conditions of these 2-year inhalation studies, there was no evidence of carcinogenic activity of diethylamine in male or female F344/N rats exposed to 31, 62.5, or 125 ppm. There was no evidence of carcinogenic activity of diethylamine in male or female B6C3F1 mice exposed to 16, 31, or 62.5 ppm. Exposure to diethylamine resulted in increased incidences of nonneoplastic lesions of the nose in male and female rats and mice, of the cornea in male rats, and of the pleura and lung in female rats.     

Toxicology and carcinogenesis studies of alpha-methylstyrene (Cas No. 98-83-9) in F344/N rats and B6C3F1 mice (inhalation studies)

alpha-Methylstyrene is used in the production of acrylonitrile-butadiene-styrene resins and copolymers, which improve the impact and heat-resistant properties of polymers, specialty grades of plastics, rubber, and protective coatings. alpha-Methylstyrene also moderates polymerization rates and improves product clarity in coatings and resins. Low molecular weight liquid polymers are used as plasticizers in paints, waxes, adhesives, and plastics. alpha-Methylstyrene was nominated by the U.S. Environmental Protection Agency for toxicologic evaluation and genotoxicity studies based on its high production volume and limited information available on its toxicity. Male and female F344/N rats and B6C3F1 mice were exposed to alpha-methylstyrene (99.5% pure) by inhalation for 3 months or 2 years. Inhalation studies were conducted because the primary route of human exposure is via inhalation. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, and mouse peripheral blood erythrocytes. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed by whole-body inhalation to alpha-methylstyrene at concentrations of 0, 75, 150, 300, 600, or 1,000 ppm for 6 hours per day, 5 days per week for 14 weeks. Additional clinical pathology groups of 10 male and 10 female rats were exposed to the same concentrations for 23 days. All rats survived to the end of the study, and mean body weights of all exposed groups were similar to those of the chamber controls. Kidney weights were significantly increased in 1,000 ppm males and 600 and 1,000 ppm females. Statistically significant increases in liver weights occurred in 150 ppm or greater males and 600 and 1,000 ppm females. The incidences of renal hyaline droplet accumulation were similar between exposed groups and chamber control groups, but the severity of hyaline droplet accumulation in 600 and 1,000 ppm males was greater than in chamber controls. Consistent with the hyaline droplet accumulation, an exposure-related increase in alpha2μ-globulin was detected in the kidneys of males exposed to alpha-methylstyrene. Morphologic changes were not detected in the liver. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed by whole-body inhalation to alpha-methylstyrene at concentrations of 0, 75, 150, 300, 600, or 1,000 ppm for 6 hours per day, 5 days per week for 14 weeks. Two female mice in the 1,000 ppm group died before exposure on day 3. Final mean body weights of 600 and 1,000 ppm males and 75, 300, and 1,000 ppm females were significantly less than those of the chamber controls; final mean body weight gains of mice exposed to 300 ppm or greater were also significantly less. Moderate to severe sedation (males only) and ataxia were observed in 1,000 ppm mice. The absolute liver weights of 600 and 1,000 ppm females and the relative liver weights of 300, 600, and 1,000 ppm males and females were significantly increased. The estrous cycle lengths of 600 and 1,000 ppm female mice were significantly longer than that of the chamber controls. Minimal to mild centrilobular hypertrophy was present in the livers of male and female mice exposed to 600 or 1,000 ppm alpha-methylstyrene. The incidences of exposure-related nasal lesions, including atrophy and hyperplasia of Bowman's glands and atrophy and metaplasia of the olfactory epithelium, were significantly increased in all exposed groups of males and females. The incidences of hyaline degeneration, characterized by the accumulation of eosinophilic globules in the cytoplasm of the respiratory epithelium, were significantly increased in females exposed to 150 ppm or greater. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed by whole body inhalation to alpha-methylstyrene at concentrations of 0, 100, 300, or 1,000 ppm for 6 hours per day, 5 days per week, except holidays, for 105 weeks. Survival rates of exposed male and female rats were similar to those of the chamber controls. The mean body weights of 1,000 ppm males and females were less than those of the chamber control groups during year 2 of the study. Two 1,000 ppm males and one 300 ppm male had renal tubule carcinomas, and one 300 ppm male had a renal tubule adenoma. Because of the neoplasms observed in 300 and 1,000 ppm males at the end of the 2-year study and the finding of alpha2μ-globulin accumulation in the kidneys at 3 months, which is often associated with kidney neoplasms, additional step sections of kidney were prepared; additional males with focal hyperplasia or adenoma were identified. The incidences of renal tubule adenoma and carcinoma (combined) in the 1,000 ppm males were significantly greater than those in the chamber controls when the single and step sections were combined. The incidence of mineralization of the renal papilla was significantly increased in 1,000 ppm males. The incidence of mononuclear cell leukemia in 1,000 ppm males was significantly increased compared to the chamber controls. In the nose, the incidences of basal cell hyperplasia were significantly increased in all exposed groups of males and females, and the incidences of degeneration of the olfactory epithelium were increased in 1,000 ppm males and females and 300 ppm females. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed by whole body inhalation to alpha-methylstyrene at concentrations of 0, 100, 300, or 600 ppm for 6 hours per day, 5 days per week, except holidays, for 105 weeks. Survival of all exposed male and female mice was similar to that of the chamber control groups. Mean body weights of 600 ppm males were less than those of the chamber control group throughout the study, and those of 600 ppm females were less after week 13. The mean body weights of 300 ppm males and females were less than those of the chamber controls during much of the study, but these groups recovered by the end of the study. The incidences of hepatocellular adenoma or carcinoma (combined) were significantly increased in the 100 and 600 ppm males and in all exposed groups of females. The incidences of hepatocellular adenoma were significantly increased in all exposed groups of females, and the incidences in all exposed groups of males and females exceeded the historical range for chamber controls. The incidences of hepatocellular carcinoma and eosinophilic foci of the liver were significantly increased in 600 ppm females. The incidences of olfactory epithelial metaplasia and hyperplasia of the glands overlying the olfactory epithelium were significantly increased in all exposed groups of males and females. In addition, atrophy of the olfactory epithelium was significantly increased in 300 and 600 ppm males. The incidence and severity of nephropathy were increased in 600 ppm females compared to chamber controls. Epithelial hyperplasia of the forestomach also was present in male mice. GENETIC TOXICOLOGY: alpha-Methylstyrene was not mutagenic in four strains of Salmonella typhimurium, with or without rat or hamster liver metabolic activation enzymes (S9). alpha-Methylstyrene did not induce chromosomal aberrations in cultured Chinese hamster ovary cells, with or without S9 activation, but did significantly increase the frequency of sister chromatid exchanges in cultures exposed in the presence of S9. In vivo, no significant increases in the frequencies of micronucleated erythrocytes were seen in blood samples of male mice obtained at the conclusion of the 3-month study. However, in female mice from the 3-month study, a significant increase in micronucleated erythrocytes was observed in the 1,000 ppm group. CONCLUSIONS: Under the conditions of this 2-year inhalation study, there was some evidence of carcinogenic activity of alpha-methylstyrene in male F344/N rats based on increased incidences of renal tubule adenomas and carcinomas (combined). The increased incidence of mononuclear cell leukemia in 1,000 ppm male F344/N rats may have been related to alpha-methylstyrene exposure. There was no evidence of carcinogenic activity of alpha-methylstyrene in female F344/N rats exposed to 100, 300, or 1,000 ppm. There was equivocal evidence of carcinogenic activity of alpha-methylstyrene in male B6C3F1 mice based on marginally increased incidences of hepatocellular adenoma or carcinoma (combined). There was clear evidence of carcinogenic activity of alpha-methylstyrene in female B6C3F1 mice based on increased incidences of hepatocellular adenomas and carcinomas. Exposure of rats to alpha-methylstyrene resulted in kidney toxicity, which in males exhibited some features of alpha2μ-globulin nephropathy. Exposure to alpha-methylstyrene resulted in nonneoplastic lesions of the nose in male and female rats and mice and of the liver and kidney in female mice.