Splenotoxicity associated with splenic sarcomas in rats fed high doses of D & C Red No. 9 or aniline hydrochloride

A histopathologic review of F344 rat spleens from the National Toxicology Program-National Cancer Institute bioassays of barium salt of 5-chloro-2-(2-hydroxy-1-naphthalenyl)-azo-4-methylbenzenesulfonic acid [(D & C Red No. 9) CAS: 516-00-21] and aniline HCI (CAS: 142-04-1) was conducted to assess splenotoxic changes associated with splenic sarcomas induced by these aromatic amines. Four splenic changes--fatty metamorphosis (FM), splenic fibrosis (FIB), capsule hyperplasia (CH), and hemorrhage--were markedly increased in incidence and severity in males treated with high doses of either D & C Red No. 9 or aniline HCI. Females treated with high doses of either of these compounds showed similar but less severe changes. FIB and FM showed strong group correlations with tumor incidence (r greater than or equal to 0.87). All groups that demonstrated FM also demonstrated splenic sarcomas; groups without the FM lesions did not exhibit splenic tumors. The morphologic similarity of the FIB and CH lesions to the induced splenic sarcomas suggests that these lesions are preneoplastic. Moreover, the treatment-related splenic lesions appear to be precursors of the induced splenic sarcomas. Carcinogenicity studies with serial sacrifices at varying intervals will be required for experimental verification of these conclusions. A schema, based on the findings of the study, suggests a hypothetical pathway for the progression of the treatment-related splenic lesions from onset to tumor formation.     

Alterations in nucleotide pools in rats fed diets deficient in choline, methionine and/or folic acid.

The fidelity of DNA synthesis is critically dependent on the correct balance and availability of the deoxynucleoside triphosphate (dNTP) precursors for the polymerases involved in replication and repair. Since folate-derived one-carbon groups are essential for the de novo synthesis of both purines and pyrimidines, the purpose of the present investigation was to determine whether diet-induced depletion of folates would alter intracellular dNTP pools. Fischer 344 rats were fed one of four semi-purified diets for a period of 8 weeks: (i) supplemented control; (ii) deficient in folic acid; (iii) deficient in methionine and choline; and (iv) deficient in methionine, choline and folic acid. In contrast to natural diets, semi-purified diets are nucleotide-free and consequently lack substrates for salvage pathway synthesis. This omission may place unusual stress on folate-dependent de novo nucleotide synthesis especially under conditions of dietary methyl-donor deficiency. Reversed-phase HPLC analysis of dNTP in spleen cell extracts indicated that both the thymidylate monophosphate and thymidylate triphosphate pools were decreased in spleen cells from the deficient rats consistent with a decrease in folate-dependent de novo synthesis. In addition, purine biosynthesis appeared to be negatively affect by methyl-donor deficiency as evidenced by a reduction in dGTP and dATP pools. These data indicate that deoxynucleotide pool imbalance, well known to produce cytogenetic and mutagenic events in vitro, can also be induced in this in vivo model of diet-induced carcinogenesis.     

Effects of D,L-2-difluoromethylornithine and indomethacin on mammary tumor promotion in rats fed high n-3 and/or n-6 fat diets

Virgin female Sprague-Dawley rats (50 days of age) were administered a single intragastric 10-mg dose of 7,12-dimethylbenz(a)anthracene (DMBA). Twenty-one days later they were placed on diets containing either 20% corn oil (CO), 15% menhaden oil plus 5% corn oil (MO + CO), 20% CO plus 0.5% w/w of the irreversible ornithine decarboxylase inhibitor, D,L-2-difluoromethylornithine (CO + DFMO), 20% CO plus 0.004% w/w of the cyclooxygenase inhibitor indomethacin (CO + INDO), 20% CO + 0.004% INDO + 0.5% DFMO (CO + INDO + DFMO), or 15% MO + 5% CO + 0.5% DFMO (MO + CO + DFMO). The incidence of DMBA-induced mammary tumors was significantly reduced in rats fed diets containing DFMO but not in rats fed the diet containing indomethacin. Incidences of mammary tumors at 16 weeks post-DMBA were 86% in rats fed the CO diet, 83% in rats ingesting the diet containing CO + INDO, 28% in rats fed CO + DFMO, 32% in rats fed diet containing CO + INDO + DFMO, 59% in rats fed the MO + CO diet, and 24% in rats fed the MO + CO + DFMO diet. The average number of tumors and tumor burden per tumor-bearing rat were reduced and tumor latency was increased in all rats fed diets containing DFMO. Body weight gain, but not food intake, of rats fed the 20% fat + 0.5% DFMO diets was significantly less than in rats fed the 20% fat diets. Prostaglandin E and leukotriene (LTB4) syntheses, ODC activity and mammary tumorigenesis were significantly inhibited by feeding the diet containing menhaden oil or by adding 0.5% DFMO to any of the high fat diets. Feeding a 20% CO diet containing 0.004% INDO significantly reduced prostaglandin synthesis and ODC activity and increased LTB4 synthesis of mammary tumors but did not inhibit mammary tumorigenesis. This study suggests that the 5-lipoxygenase product LTB4 may be involved in mammary tumor production. Whereas a decrease in LTB4 appears to be associated with a decrease in tumorigenesis, an increase (as seen in the indomethacin group) was not associated with any change in the tumorigenic response.     

NTP technical report on the toxicity studies of p-tert-butylcatechol (CAS No. 98-29-3) administered in feed to F344/N rats and B6C3F1 mice

[molecular structure: see text] p-tert-Butylcatechol is used as an antioxidant, stabilizer, and polymerization inhibitor for styrene, butadiene, neoprene, and other olefins and reactive monomers. p-tert-Butylcatechol was nominated by the National Cancer Institute and the U.S. Food and Drug Administration for testing based on reports of its increasing levels of production and use and to compare the toxicity of p-tert-butylcatechol with that of similar antioxidants, butylated hydroxyanisole and butylated hydroxytoluene, which are added to food. Male and female F344/N rats and B6C3F1 mice were exposed to p-tert-butylcatechol (greater than 99% pure) in feed for 15 days or 14 weeks. Genetic toxicology studies were conducted in Salmonella typhimurium, rat bone marrow cells, and mouse peripheral blood erythrocytes. In the 15-day studies, groups of five male and five female rats and mice were fed diets containing 0, 3,125, 6,250, 12,500, 25,000, or 50,000 ppm p-tert-butylcatechol (equivalent to average daily doses of approximately 290 to 2,470 mg p-tert-butylcatechol/kg body weight to rats and 590 to 8,200 mg/kg to mice). All animals in the 50,000 ppm groups were killed moribund on day 8 (rats) or by day 7 (mice). Mean body weights of all groups of rats exposed to 6,250 ppm or greater were significantly less than those of the controls. Mean body weights of male mice exposed to 12,500 or 25,000 ppm and of 25,000 ppm female mice were significantly less than those of the controls. Female rats, male and female mice in the 25,000 ppm groups, and 12,500 ppm male mice lost weight during the studies. Feed consumption by exposed rats generally decreased with increasing exposure concentration; feed consumption by exposed mice was similar to that by the controls. Thymus weights of 25,000 ppm rats and mice were significantly less than those of the controls. Gross findings noted at necropsy included thin carcasses for three male and all female rats in the 12,500 ppm groups and all male and female rats and mice in the 25,000 and 50,000 ppm groups. No exposure-related lesions were observed microscopically. In the 14-week studies, groups of 10 male and 10 female rats and mice were fed diets containing 0, 781, 1,562, 3,125, 6,250, or 12,500 ppm p-tert-butylcatechol (equivalent to average daily doses of approximately 70 to 1,030 mg/kg to rats and 135 to 2,815 mg/kg to mice). All animals survived to the end of the studies. Mean body weights of male rats exposed to 1,562 ppm or greater, female rats exposed to 3,125 ppm or greater, male mice exposed to 12,500 ppm, and female mice exposed to 6,250 or 12,500 ppm were significantly less than those of the controls. Feed consumption by male and female rats in the 6,250 and 12,500 ppm groups at week 1 and the 12,500 ppm groups at week 14 was less than that by the controls; feed consumption by exposed and control mice was similar. An erythrocytosis, indicated by increased hematocrit values, hemoglobin concentrations, and erythrocyte counts, was observed in 6,250 and 12,500 ppm rats on day 4 and in 12,500 ppm rats on day 22. At these time points, a transient hepatic effect was demonstrated by increases in alanine aminotransferase activities and bile salt concentrations in exposed rats. In 12,500 ppm male rats, absolute left cauda epididymis, epididymis, and testis weights were decreased by 15%, 10%, and 9%, respectively, compared to the controls. The number of spermatid heads per testis and epididymal sperm motility of male rats in the 12,500 ppm group were significantly less than those of the controls. The numbers of cycling female rats and females with regular estrous cycles were decreased in the 6,250 and 12,500 ppm groups. Exposed groups of females had significantly fewer estrous cycles than did the controls. Estrous cycle length increased with increasing exposure concentration; female rats in the 6,250 and 12,500 ppm groups had significantly longer cycles and spent more time in diestrus and less time in proestrus, estrus, and metestrus than did the controls. Female mice in the 12,500 ppm group had a significantly longer estrous cycle than did the controls. The incidences of hyperkeratosis of the forestomach epithelium were significantly increased in male and female rats in all exposed groups and in 12,500 ppm female mice. The incidences of hyperplasia of the forestomach epithelium were significantly increased in male and female rats exposed to 3,125 ppm or greater, male mice exposed to 12,500 ppm, and female mice exposed to 6,250 or 12,500 ppm. The severities of the forestomach lesions were minimal to moderate in male rats and minimal to mild in female rats and in mice. All male rats exposed to 6,250 or 12,500 ppm had minimal cytoplasmic alteration in the liver. The absorption, distribution, metabolism, and excretion of p-tert-butylcatechol following intravenous injection, gavage dosing, or dermal application were determined in male F344/N rats and B6C3F1 mice. The absorption of [(14)C]-p-tert-butylcatechol following gavage dosing or dermal application was high. The percent absorption following dermal application increased with increasing dose. Peak concentrations of [(14)C]-p-tert-butylcatechol equivalents in plasma were reached 1 hour after gavage dosing (200 mg/kg) and 2 hours after dermal application (60 mg/kg); no parent compound was detected in the plasma extracts. Regardless of route of administration, p-tert-butylcatechol derived radioactivity was readily excreted in the urine and was markedly nonpersistent in the tissues. p-tert- Butylcatechol was excreted as p-tert-butylcatechol sulfate and other polar metabolites that included predominately sulfate conjugates; it was not excreted as the parent compound. One metabolite was determined to be an O-methyl- ON-sulfate of p-tert-butylcatechol. p-tert-Butylcatechol (10 to 1,000 microg/plate) was not mutagenic in any of several strains of S. typhimurium with or without rat or hamster liver S9. Bone marrow micronucleus tests in which 125 to 500 mg/kg p-tert-butylcatechol was administered three times by intraperitoneal injection to male rats gave negative results. No increases in the frequencies of micronucleated normochromatic erythrocytes were observed in the peripheral blood of male or female mice administered p-tert-butylcatechol in feed for 14 weeks. No significant alteration in the percentage of polychromatic erythrocytes in mouse bone marrow was observed. In summary, the primary toxicity of p-tert-butylcatechol was to the forestomach of rats and mice. In the 14-week study in rats, forestomach toxicity was observed at all exposure concentrations, and the no-observed-adverse-effect level (NOAEL) was not reached for this effect. In the 14-week study in mice, the NOAEL for forestomach toxicity was 1,562 ppm.     

Carcinogenicity of a mutagenic compound from food, 2-amino-3-methyl-9H-pyrido[2, 3-b]indole (MeA{alpha}C), in male F344 rats

Carcinogenicity of 2-amino-3-methyl-9H-pyrido[2,3-b]-indole(MeA     

Toxicology studies of pentaerythritol triacrylate (technical grade) (CAS No. 3524-68-3) in F344/N rats, B6C3F1 mice, and genetically modified (FVB Tg.AC hemizygous) mice (dermal studies)

Pentaerythritol triacrylate is used in the production of ultraviolet-curable inks and coatings, electron beam irradiation- curable coatings, and radiation-cured and photocurable coatings of urethanes and epoxy resins; as a component of photopolymer and flexographic printing inks and plates and photoresists; as an ingredient of acrylic glues, adhesives, and anaerobic sealants; and as a modifier for polyester and fiberglass. It is also used in colloidal dispersions for industrial baked coatings, waterborne and solvent-based alkyds, vinyl/acrylic nonwoven binders, paper and wood impregnates, wire and cable extrusion, polymer-impregnated concrete, and polymer concrete structural composites. Pentaerythritol triacrylate was nominated by the National Cancer Institute for testing based on its high production volume and use, its potential for human exposure, and a lack of adequate testing of the chemical. Male and female F344/N rats and B6C3F(1) mice were administered technical grade pentaerythritol triacrylate (it is reactive and therefore not available as pure pentaerythritol triacrylate) in acetone dermally for 2 weeks or 3 months. Male and female Tg.AC hemizygous mice were administered technical grade pentaerythritol acrylate in acetone for 6 months. Genetic toxicology was evaluated in Salmonella typhimurium and in B6C3F(1) and Tg.AC hemizygous mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: Groups of five male and five female F344/N rats were administered 0, 12.5, 25, 50, 100, or 200 mg pentaerythritol triacrylate/kg body weight in acetone 5 days per week for 17 days. All rats survived to the end of the study; mean body weights of males administered 50 mg/kg or greater and 200 mg/kg females were significantly less than those of the vehicle controls. Irritation at the site of application occurred in all dosed groups except 12.5 mg/kg females. Epidermal hyperplasia, hyperkeratosis, sebaceous gland hyperplasia, ulcer, epidermal degeneration, parakeratosis, chronic active inflammation, and suppurative inflammation occurred at the site of application in most dosed groups of rats. 2-WEEK STUDY IN B6C3F(1) MICE: Groups of five male and five female B6C3F(1) mice were administered 0, 12.5, 25, 50, 100, or 200 mg pentaerythritol triacrylate/kg body weight in acetone 5 days per week for 17 days. All mice survived to the end of the study. The final mean body weight and body weight gain of 25 mg/kg males were significantly greater than those of the vehicle controls, as was the mean body weight gain of 50 mg/kg males. All dosed groups had irritation at the site of application. Thymus weights of males administered 50 mg/kg or greater and 200 mg/kg females were significantly less than those of the vehicle controls. Most dosed groups of mice had epidermal hyperplasia, hyperkeratosis, sebaceous gland hyperplasia, ulcer, epidermal degeneration, parakeratosis, chronic active inflammation, and suppurative inflammation at the site of application. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female F344/N rats were administered 0, 0.75, 1.5, 3, 6, or 12 mg pentaerythritol triacrylate/kg body weight in acetone 5 days per week for 14 weeks. All rats survived to the end of the study. Mean body weights of 12 mg/kg males were significantly less than those of the vehicle controls. Irritation at the site of application occurred in 12 mg/kg rats. Thymus weights of males administered 3 mg/kg or greater were significantly less than those of the vehicle controls. Hematology results indicated that pentaerythritol triacrylate induced a neutrophil count increase that would be consistent with an inflammatory response related to the dermatitis observed histopathologically. Epidermal hyperplasia, hyperkeratosis, epidermal degeneration and necrosis, chronic active inflammation, and sebaceous gland hyperplasia generally occurred at the application site in male and female groups administered 1.5 mg/kg or greater. 3-MONTH STUDY IN B6C3F(1) MICE: Groups of 10 male and 10 female B6C3F(1) mice were administered 0, 0.75, 1.5, 3, 6, or 12 mg pentaerythritol triacrylate/kg body weight in acetone 5 days per week for 14 weeks. One female vehicle control mouse was sacrificed during the first week of the study due to ataxia and one 1.5 mg/kg female died during week 8. Mean body weights of dosed groups were similar to those of the vehicle control groups. Irritation at the site of application occurred in the 6 and 12 mg/kg male groups. Hematology results indicated an increased neutrophil count consistent with an inflammatory response related to the dermatitis observed histopathologically. There also was a minimal decrease in the erythron (hematocrit, hemoglobin concentration, and erythrocyte count) likely secondary to the inflammatory skin process. Males and females administered 1.5 mg/kg or greater generally had increased incidences of epidermal hyperplasia, degeneration, and necrosis; dermal chronic active inflammation, sebaceous gland hyperplasia, and hyperkeratosis at the site of application. 6-MONTH STUDY IN Tg.AC HEMIZYGOUS MICE: Groups of 15 male and 15 female Tg.AC hemizygous mice were administered 0, 0.75, 1.5, 3, 6, or 12 mg pentaerythritol triacrylate per kg body weight in acetone 5 days per week for 27 weeks. Additional groups of 15 male and 15 female mice maintained as positive controls received dermal applications of 1.25 mug 12-O-tetradecanoylphorbol-13-acetate per 100 mL acetone 3 days per week for 28 weeks. Survival of all dosed groups of mice was similar to that of the vehicle controls. With the exception of the 3 mg/kg group, body weights of male mice were less than those of the vehicle controls during the last 3 to 6 weeks of the study. Females administered 3 mg/kg had generally reduced body weights during the last month of the study. Treatment-related clinical findings included papillomas at the site of application in males and females receiving 3 mg/kg or more; papillomas were also observed in one 1.5 mg/kg male. Heart and liver weights of 12 mg/kg males were significantly greater than those of the vehicle controls. Lung weights of 6 and 12 mg/kg males and females were significantly decreased, as were thymus weights of 6 and 12 mg/kg females. Squamous cell neoplasms at the site of application were associated with dermal application of pentaerythritol triacrylate. At 6 months, all 3 and 6 mg/kg males had squamous cell papilloma at the site of application, and the incidences of this neoplasm were significantly increased in males and females receiving 3 mg/kg or more. Squamous cell carcinomas at the site of application occurred in two 3 mg/kg males, three 12 mg/kg males, and one 12 mg/kg female. Nonneoplastic lesions noted at the site of application in dosed mice included hyperkeratosis, chronic active inflammation, and epidermal hyperplasia. Incidences of hematopoietic cell proliferation were increased in various organs, including the liver of 12 mg/kg females, the spleen of 6 and 12 mg/kg males and females, and the mandibular lymph node of 12 mg/kg females. A hematopoietic disorder (myelodysplasia) occurred in 12 mg/kg males. GENETIC TOXICOLOGY: Pentaerythritol triacrylate was not mutagenic in several strains of S. typhimurium, with or without hamster or rat liver S9 activation enzymes. No increase in the frequency of micronucleated erythrocytes was observed in peripheral blood samples from B6C3F(1) mice treated with pentaerythritol triacrylate by skin painting for 3 months. In contrast, similar treatment of female Tg.AC hemizygous mice for 6 months induced a significant increase in micronucleated erythrocytes; the increase in micronuclei seen in male Tg.AC hemizygous mice was judged to be equivocal. CONTACT HYPERSENSITIVITY STUDIES: Studies were conducted with female BALB/c mice to evaluate the potential for pentaerythritol triacrylate to induce contact hypersensitization. In an irritancy study in which formulations of pentaerythritol triacrylate (approximately 10% or 45% pure) in acetone were applied to the ear, the maximal nonirritating concentration was 0.1% and the minimal irritating concentration was 0.25% for both mixtures. A mouse ear swelling test yielded negative results for pentaerythritol triacrylate as a potential contact sensitizer using the 10% mixture and positive results with the 45% mixture. Positive responses were seen in local lymph node assays at concentrations of 0.05%, 0.1%, and 0.25% pentaerythritol triacrylate when the approximately 10% pentaerythritol triacrylate mixture was used and at a concentration of 0.25% pentaerythritol triacrylate when the approximately 45% pentaerythritol triacrylate mixture was used. CONCLUSIONS: Male and female Tg.AC hemizygous mice dosed with pentaerythritol triacrylate for 6 months had significantly increased incidences of squamous cell papillomas of the skin at the site of dermal application. Treatment-related squamous cell carcinomas occurred at the site of application in male mice. Nonneoplastic lesions noted at the site of application included hyperkeratosis, chronic active inflammation, and epidermal hyperplasia. A hematopoietic disorder (myelodysplasia) occurred in dosed male mice.     

Toxicology studies of trimethylolpropane triacrylate (technical grade) (CAS No. 15625-89-5) in F344/N rats, B6C3F1 mice, and genetically modified (FVB Tg.AC hemizygous) mice (dermal studies)

Trimethylolpropane triacrylate is a multifunctional monomer with a wide range of industrial applications. It is used in the production of ultraviolet-curable inks, electron beam irradiation-curable coatings, and polymers and resins; as a component of photopolymer and flexographic printing plates and photoresists; and as an ingredient in acrylic glues and anaerobic sealants. The chemical is also used in paper and wood impregnates, wire and cable extrusion, polymer-impregnated concrete, and polymer concrete structural composites. Trimethylolpropane triacrylate was nominated by the National Cancer Institute for testing due to its high production volume and use, 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 administered technical grade trimethylolpropane triacrylate (it is reactive and therefore not available as pure trimethylolpropane triacrylate) in acetone dermally for 2 weeks or 3 months. Male and female Tg.AC hemizygous mice were administered technical grade trimethylolpropane triacrylate in acetone for 6 months. Genetic toxicology studies were conducted in B6C3F(1) and Tg.AC hemizygous mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: Groups of five male and five female F344/N rats were administered 0, 12.5, 25, 50, 100, or 200 mg trimethylolpropane triacrylate/kg body weight in acetone 5 days per week for 16 days. All rats survived to the end of the study, and mean body weights of dosed groups were similar to those of the vehicle controls. Dosed rats had irritation at the site of application; this clinical finding was most commonly seen in rats administered 50 mg/kg or greater. Male and female rats had epidermal hyperplasia, hyperkeratosis, sebaceous gland hyperplasia, inflammation of the epidermis and dermis, ulceration, epidermal degeneration, and parakeratosis at the site of application. 2-WEEK STUDY IN B6C3F(1) MICE: Groups of five male and five female B6C3F(1) mice were administered 0, 12.5, 25, 50, 100, or 200 mg trimethylolpropane triacrylate/kg body weight in acetone 5 days per week for 16 days. All mice survived to the end of the study. The final mean body weight gain of 200 mg/kg males was less than that of the vehicle controls; 100 and 200 mg/kg females had significantly increased final mean body weights. Irritation at the site of application occurred in all dosed males, all 100 and 200 mg/kg females, and one 50 mg/kg female. Thymus weights of males administered 50 mg/kg or greater were significantly decreased. Dosed male and female mice had epidermal hyperplasia, hyperkeratosis, chronic active inflammation of the dermis, sebaceous gland hyperplasia, ulcer, epidermal degeneration, parakeratosis, and/or suppurative inflammation of the epidermis at the site of application. Atrophy of the thymus occurred in 100 and 200 mg/kg male mice. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female F344/N rats were administered 0, 0.75, 1.5, 3, 6, or 12 mg trimethylolpropane triacrylate/kg body weight in acetone 5 days per week for 14 weeks. All rats survived to the end of the study, and mean body weights of dosed groups were similar to those of the vehicle controls. Irritation at the site of application was noted in five males and all females administered 12 mg/kg. Hematology results indicated that trimethylolpropane triacrylate at the doses selected induced a neutrophil count increase at 12 mg/kg that would be consistent with an inflammatory response related to the dermatitis observed histopathologically. Thymus weights of 12 mg/kg males and 0.75 and 12 mg/kg females were decreased. Incidences of epidermal hyperplasia, degeneration, and necrosis (females only); chronic active inflammation of the dermis, hyperkeratosis, and sebaceous gland hyperplasia were generally increased at the site of application in 1.5 mg/kg or greater males and in 3 mg/kg or greater females. 3-MONTH STUDY IN B6C3F(1) MICE: Groups of 10 male and 10 female B6C3F(1) mice were administered 0, 0.75, 1.5, 3, 6, or 12 mg trimethylolpropane triacrylate/kg body weight in acetone 5 days per week for 14 weeks. All animals survived to the end of the study; mean body weights of dosed groups were similar to those of the vehicle controls. Irritation at the site of application occurred in male and female mice administered 12 mg/kg. Hematology results indicated that trimethylolpropane triacrylate induced a neutrophil count increase at 12 mg/kg that would be consistent with an inflammatory response related to the dermatitis observed histopathologically. Increased incidences of several nonneoplastic lesions occurred at the site of application in 3 mg/kg and greater males and females, including hyperplasia of the epidermis, hyperkeratosis, epidermal degeneration (except 3 mg/kg females) and necrosis, chronic active inflammation of the dermis, and sebaceous gland hyperplasia. Epidermal suppurative inflammation and necrosis and dermal fibrosis occurred in 12 mg/kg males and females. 6-MONTH STUDY IN Tg.AC HEMIZYGOUS MICE: Groups of 15 male and 15 female Tg.AC hemizygous mice were administered 0, 0.75, 1.5, 3, 6, or 12 mg trimethylolpropane triacrylate/kg body weight in acetone 5 days per week for 28 weeks. Additional groups of 15 male and 15 female mice maintained as positive controls received dermal applications of 1.25 microg 12-O-tetradecanoylphorbol-13-acetate per 100 mL acetone 3 days per week for 28 weeks; the dosing volume was held constant at 100 microL. Survival and mean body weights of dosed groups were similar to those of the vehicle controls throughout the study. Treatment-related clinical findings included papillomas at the site of application in 3 mg/kg and greater males and 6 and 12 mg/kg females. The heart weights of males and females administered 12 mg/kg and the kidney and lung weights of 12 mg/kg females were significantly increased. The lung weights of 6 and 12 mg/kg males and females were decreased. Squamous cell neoplasms at the site of application were associated with dermal application of trimethylolpropane triacrylate. At 6 months, the incidences of squamous cell papilloma were significantly increased in 6 and 12 mg/kg males and females. One female in each of the 1.5, 6, and 12 mg/kg groups also had squamous cell carcinoma. The incidence of squamous cell papilloma of the forestomach in 12 mg/kg females was significantly greater than that in the vehicle control group. Nonneoplastic skin lesions at the site of application in dosed mice included epidermal hyperplasia, hyperkeratosis, and chronic active inflammation. A hematopoietic disorder (myelodysplasia) also occurred in some 12 mg/kg males and females. GENETIC TOXICOLOGY: No increase in the frequency of micronucleated erythrocytes was observed in peripheral blood samples from male or female B6C3F(1) mice treated with trimethlylolpropane triacrylate by skin painting for 3 months. Similarly, no increase in micronucleus frequency was seen in male or female Tg.AC hemizygous mice administered trimethylolpropane triacrylate by skin painting for 6 months. CONTACT HYPERSENSITIVITY STUDIES: Studies were conducted with female BALB/c mice to evaluate the potential for trimethylolpropane triacrylate to induce contact hypersensitization. In an irritancy study in which the chemical, in acetone, was applied to the ear, the maximal nonirritating and minimal irritating doses were 0.1% and 0.25% trimethylolpropane triacrylate. No significant differences in the percentage of ear swelling occurred between trimethylolpropane triacrylate-sensitized and -challenged mice and background controls at 24 or 48 hours after dosing. The local lymph node assay indicated no significant increase in lymph node cell proliferation in mice administered trimethylolpropane triacrylate compared to that in the vehicle controls. Testing for sensitizing potential using the mouse ear swelling test and local lymph node assay failed to indicate trimethylolpropane triacrylate as a potential contact sensitizer. CONCLUSIONS: Male and female Tg.AC hemizygous mice dosed with trimethylolpropane triacrylate for 6 months had significantly increased incidences and multiplicity of papillomas of the skin at the site of dermal application. Treatment-related squamous cell carcinomas occurred at the site of application in dosed female mice. Increased incidences of forestomach squamous cell papilloma in female mice may have been related to chemical administration. Increased incidences of minimal to moderate (mostly mild) hyperplasia of the epidermis, hyperkeratosis, and chronic active inflammation also occurred at the site of application. A hematopoietic disorder (myelodysplasia) also occurred in exposed male and female mice.     

NTP technical report on the toxicity studies of 2- and 4-Methylimidazole (CAS No. 693-98-1 and 822-36-6) administered in feed to F344/N rats and B6C3F1 mice

[Structure-see text] 2-Methylimidazole and 4-methylimidazole are intermediate/starting materials or components in the manufacture of pharmaceuticals, photographic and photothermographic chemicals, dyes and pigments, agricultural chemicals, and rubber; these chemicals have been identified as undesirable by-products in several foods and have been detected in mainstream and sidestream tobacco smoke. The National Cancer Institute nominated 2- and 4-methylimidazole as candidates for toxicity and carcinogenicity studies. Toxicity studies were carried out in male and female F344/N rats and B6C3F1 mice. Animals were exposed to 2- or 4-methylimidazole in feed for 15 days or 14 weeks; clinical pathology studies were conducted in the 14-week studies on days 8, 29, and 86 and at week 14. Genetic toxicity studies were conducted in Salmonella typhimurium, rat and mouse bone marrow, and mouse peripheral blood. Groups of five male and five female rats and mice were fed diets containing 0, 1,200, 3,300, or 10,000 ppm 2-methylimidazole (equivalent to average daily doses of approximately 115, 290, or 770 mg 2-methylimidazole/ kg body weight to rats; 220, 640, or 2,100 mg/kg to male mice; 300, 800, or 2,400 to female mice) for 15 days. Groups of five male and five female rats and mice were fed diets containing 0, 300, 800, or 2,500 ppm 4-methylimidazole (equivalent to average daily doses of approximately 30, 80, or 220 mg/kg for rats and 65, 170, or 500 mg/kg for mice) for 15 days. In the 15-day 2-methylimidazole studies, all animals survived to the end of the studies. The mean body weights of 10,000 ppm male rats and female mice were significantly less than those of the controls. Feed consumption by 10,000 ppm male and female rats was reduced. Enlarged thyroid glands were observed in 3,300 and 10,000 ppm male and female rats. The incidences of diffuse hyperplasia of follicular cells of the thyroid gland in 3,300 and 10,000 ppm male and female rats and pars distalis hypertrophy of the pituitary gland in 3,300 and 10,000 ppm males and 10,000 ppm females were increased compared to the controls. In all exposed groups of male and female mice, the incidences and severities of follicular cell hypertrophy of the thyroid gland and the severities of hematopoietic cell proliferation of the spleen generally increased with increasing exposure concentration. In the 4-methylimidazole studies, all animals survived to the end of the studies, and there were no significant differences in mean body weights, clinical findings, organ weights, or gross or microscopic lesions between exposed and control groups. Groups of 10 male and 10 female rats and mice were fed diets containing 0, 625, 1,250, 2,500, 5,000, or 10,000 ppm 2- or 4-methylimidazole (equivalent to average daily doses of approximately 40, 80, 160, 300, or 560 mg/kg 2- or 4-methylimidazole to rats; and 100, 165, 360, 780, or 1,740 mg/kg 2-methylimidazole or 100, 240, 440, 915, or 1,840 mg/kg 4-methylimidazole to male mice; and 90, 190, 400, 800, or 1,860 mg/kg 2-methylimidazole or 110, 240, 540, 1,130, or 3,180 mg/kg 4-methylimidazole to females) for 14 weeks. All animals survived to the end of the 14-week 2-methylimidazole studies. Compared to the controls, the mean body weights were significantly decreased in groups of male rats and mice exposed to 2,500 ppm or greater and in 5,000 and 10,000 ppm female rats and mice. In rats, 2-methylimidazole induced a transient erythrocytosis in females and a minimal, exposure concentration-related, microcytic, normochromic, nonresponsive anemia. 2-Methylimidazole increased thyroid-stimulating hormone concentrations and decreased thyroxine and triiodothyronine concentrations of male and female rats in an exposure concentration-related manner. 2-Methylimidazole induced a mild to moderate, exposure concentration-related, macrocytic, hyperchromic, responsive anemia in mice. Triiodothyronine concentrations were increased in exposed male and female mice, and thyroxine concentrations were decreased in exposed females. Relative to the control groups, clinical chemistry evaluations on day 29 and at week 14 identified decreases in alanine aminotransferase concentrations and total protein and albumin concentrations of rats. In the 2-methylimidazole studies, absolute spleen weights were significantly increased in all exposed groups of male rats. The heart and liver weights were increased in all exposed groups of male mice, as were the spleen weights of female mice exposed to 2,500 ppm or greater. Spermatid heads per testis and mean spermatid count were significantly decreased in 10,000 ppm male rats. The estrous cycle of 10,000 ppm female rats was significantly increased. Gross pathology observations included enlarged thyroid glands, small uteri, and mottled spleen in 5,000 and 10,000 ppm mice. The incidences of diffuse follicular cell hyperplasia of the thyroid gland were significantly increased in male rats exposed to 1,250 ppm or greater and female rats exposed to 2,500 ppm or greater. The incidence of testicular degeneration was significantly increased in 10,000 ppm male rats, and two males in the 10,000 ppm group had follicular cell adenoma of the thyroid gland. In mice, there were generally significant increases in the incidences of follicular cell hypertrophy of the thyroid gland, hematopoietic cell proliferation of the spleen, and hemosiderin pigmentation of the renal tubule in males exposed to 1,250 ppm or greater and females exposed to 2,500 ppm or greater. In the 14-week 4-methylimidazole studies, one 10,000 ppm male mouse was found dead during week 4, and seven 10,000 ppm female mice were found dead during weeks 1 and 2. Mean body weights were significantly less than those of the controls for male rats exposed to 2,500 ppm or greater, 5,000 and 10,000 ppm female rats, male mice exposed to 1,250 ppm or greater, and all exposed groups of female mice. Reduced feed consumption was observed in 5,000 and 10,000 ppm male and female rats. Clinical findings included nasal/eye discharge, ruffled fur, thinness, ataxia, and abnormal breathing in rats, and ruffled fur and dull coats in female mice. On days 29 and 82, functional observations in 5,000 and 10,000 ppm rats included labored or increased respiration, mild tremors, walking on tiptoes, hunched posture, piloerection, crouching over, impaired coordination of movement, ataxia, and pupillary constriction. 4-Methylimidazole induced a transient erythrocytosis and a minimal, exposure concentration-related, microcytic, normochromic, nonresponsive anemia in male and female rats. Clinical chemistry evaluations generally showed a cholestatic effect in exposed male and female rats. At week 14, there was a significant decrease in total protein and albumin concentrations of female rats exposed to 5,000 or 10,000 ppm. In mice, 4-methylimidazole induced a macrocytic, hyperchromic, responsive anemia and, particularly in males, increases in triiododthyronine concentrations and transient decreases in thyroxine concentrations. In the 4-methylimidazole studies, the liver weights of male rats exposed to 2,500 ppm or greater were significantly increased; spleen weights of female rats exposed to 2,500 ppm or greater were decreased. The absolute liver weight was decreased in 10,000 ppm male mice, and relative weights were significantly increased in all exposed groups of mice. In female mice, there was a significant decrease in the absolute weights and increase in the relative weights of the heart, right kidney, and liver in groups exposed to 2,500 ppm or greater. The epididymal spermatozoal concentration was significantly increased in 5,000 ppm male rats. Gross pathology observations included pale livers in male rats exposed to 2,500 ppm or greater and small testes and uteri in 10,000 ppm male and female rats. Microscopic analysis identified significantly increased incidences of cytoplasmic hepatocyte vacuolization of the liver of male rats exposed to 2,500 ppm or greater and 10,000 ppm female rats, hypospermia of the epididymis in 10,000 ppm male rats, atrophy and inflammation of the prostate gland in 10,000 ppm male rats, and degeneration of the testes in 5,000 and 10,000 ppm male rats. 2-Methylimidazole and 4-methylimidazole were negative in the S. typhimurium mutation assay when tested in strains TA97, TA98, TA100, and TA1535, with and without S9 activation enzymes. Testing of 2-methylimidazole in vivo for induction of chromosomal damage, as measured by micronucleated erythrocyte frequency, produced mixed results. When administered by intraperitoneal injection three times at 24-hour intervals, 2-methylimidazole produced negative results in bone marrow micronucleus tests in rats and mice. However, in the 14-week study of 2-methylimidazole, a significant exposure-related increase in the frequency of micronucleated normochromatic erythrocytes was noted in peripheral blood of male and female mice. In vivo, 4-methylimidazole produced uniformly negative results in three-injection bone marrow micronucleus tests in rats and mice and in 14-week peripheral blood micronucleus tests in male and female mice.     

NTP report on the toxicology studies of dicyclohexylcarbodiimide (CAS No. 538-75-0) in F344/N rats, B6C3F 1 mice, and genetically modified (FVB Tg.AC hemizygous) mice and carcinogenicity study of dicyclohexylcarbodiimide in genetically modified [B6.129-Trp53 tm1Brd (N5) haploinsufficient] mice (dermal studies)

Dicyclohexylcarbodiimide is used in industry as a stabilizing agent, coupling agent, and condensing agent. Its widespread use during protein synthesis in the recombinant DNA industry and in the synthesis of polypeptides in the chemical and pharmaceutical industries provides an increasing potential for low-level human exposure. Dicyclohexylcarbodiimide was nominated for study by The National Cancer Institute as a key representative of the carbodiimide chemical class because of its acute toxicity and the absence of data on potential health effects. Male and female F344/N rats and B6C3F 1 mice were administered dicyclohexylcarbodiimide (greater than 98% pure) dermally for 3 or 13 weeks. Female Tg.AC hemizygous and p53 haploinsufficient mice were administered dicyclohexylcarbodiimide dermally for 20 or 27 weeks, respectively. Genetic toxicology studies were conducted in Salmonella typhimurium, male F344/N rat bone marrow cells, and B6C3F 1 mouse peripheral blood erythrocytes. 3-WEEK STUDY IN F344/N RATS Groups of five male and five female rats were dermally administered 0.3 mL ethanol containing 0, 0.6, 1.8, 5.1, 15, or 45 mg dicyclohexylcarbodiimide, 5 days per week for 3 weeks. All males and females in the 15 and 45 mg groups, four 5.1 mg males, and all 5.1 mg females died before the end of the study. Of the surviving groups, final mean body weights were similar to those of the vehicle controls, although the one surviving 5.1 mg male rat lost weight during the study. Histopathologic examination of rats dosed with 5.1 mg dicyclohexylcarbodiimide or less revealed treatment-related lesions of the skin at the site of application including epidermal hyperplasia, epidermal necrosis, or chronic active inflammation in the dermis. 3-WEEK STUDY IN B6C3F 1 MICE Groups of five male and five female mice were dermally administered 0.1 mL of ethanol containing 0, 0.2, 0.6, 1.7, 5, or 15 mg dicyclohexylcarbodiimide, 5 days per week for 3 weeks. One 0.6 mg female mouse and all mice in the 1.7, 5, and 15 mg groups died before the end of the study. Final mean body weights of the 0.6 mg groups were significantly less than those of the vehicle controls, and animals in these groups generally lost weight during the study. Histopathologic examination of mice dosed with 1.7 mg dicyclohexylcarbodiimide or less revealed treatment-related lesions of the skin at the site of application including epidermal hyperplasia, epidermal necrosis, and acute or chronic active dermal inflammation. 13-WEEK STUDY IN F344/N RATS Groups of 10 male and 10 female core study rats were dermally administered 0, 0.75, 1.5, 3, 6, or 12 mg dicyclohexylcarbodiimide/kg body weight in ethanol, 5 days per week for 13 weeks; groups of 10 male and 10 female clinical pathology study rats were administered the same doses for 22 days. All 12 mg/kg male and female core study rats died or were found moribund and sacrificed prior to day 45. Final mean body weight and body weight gain of 6 mg/kg males were significantly less than those of the vehicle controls. The predominant clinical pathology changes suggest a secondary, treatment-related inflammatory leukogram and minimal decreased erythron of chronic inflammation that would be consistent with necrosis and chronic active inflammation of the skin. Significantly increased incidences of skin lesions at the site of application included epidermal hyperplasia in 3 mg/kg or greater males and 1.5 mg/kg or greater females, chronic active inflammation in 6 and 12 mg/kg males and 1.5 mg/kg or greater females, and epidermal necrosis in 12 mg/kg males. The incidences and severities of epidermal hyperplasia increased in a dose-related manner in both sexes of rats 13-WEEK STUDY IN B6C3F 1 MICE Groups of 10 male and 10 female mice were dermally administered 0, 1.5, 3, 6, 12, or 24 mg dicyclohexylcarbodiimide/kg body weight in ethanol, 5 days per week for 13 weeks. All 24 mg/kg male and female mice died or were found moribund and sacrificed prior to day 16. Final mean body weights of 6 and 12 mg/kg males and mean body weight gains of 6 and 12 mg/kg males and females were significantly less than those of the vehicle controls. The predominant clinical pathology changes suggest a secondary, treatment-related inflammatory leukogram and minimal decreased erythron of chronic inflammation that would be consistent with necrosis and chronic active inflammation of the skin. Dermal administration of dicyclohexylcarbodiimide significantly decreased the weight of the epididymis in 6 and 12 mg/kg males and significantly decreased epididymal spermatozoal motility in 6 mg/kg males. Significantly increased incidences of skin lesions at the site of application included epidermal hyperplasia in all dosed groups except those administered 24 mg/kg, chronic active inflammation in all dosed groups except 1.5 mg/kg females, and epidermal necrosis in 24 mg/kg males and females. 20-WEEK STUDY IN FEMALE TG.AC HEMIZYGOUS MICE Groups of 10 female Tg.AC hemizygous mice were dermally administered 0, 0.75, 1.5, 3, 6, or 12 mg dicyclohexylcarbodiimide/kg body weight in ethanol, 5 days per week for up to 20 weeks. Due to the severity of skin lesions observed in 12 mg/kg animals, the application of dicyclohexylcarbodiimide was discontinued after eight dermal applications in this group. There were no deaths considered related to dicyclohexylcarbodiimide administration, although 13 animals died or were sacrificed moribund prior to the end of the study: three each from the vehicle control and 0.75 mg/kg groups, four from the 3 mg/kg group, two from the 6 mg/kg group, and one from the 12 mg/kg group. Overall, the survival was within the range known for the Tg.AC hemizygous mouse. Mean body weights of dosed groups of mice were similar to those of the vehicle controls. At the site of application, the incidences of squamous cell papilloma were increased in a dose-related manner. The incidences of chronic active inflammation of the dermis and epidermal hyperplasia were significantly increased in mice administered 3 or 6 mg/kg. 27-WEEK STUDY IN FEMALE p53 HAPLOINSUFFICIENT MICE Groups of 15 female mice were dermally administered 0, 0.75, 1.5, 3, 6, or 12 mg dicyclohexylcarbodiimide/kg body weight in ethanol, 5 days per week for up to 27 weeks. Dosing of the 6 and 12 mg/kg groups was discontinued after 11 and 8 days, respectively, because of the severity of skin lesions at the site of application. Twelve animals died or were sacrificed moribund prior to the end of the study: three from the 3 mg/kg group, one from the 6 mg/kg group, and eight from the 12 mg/kg group. Mean body weights of dosed groups of mice were similar to those of the vehicle controls. No neoplasms were attributed to administration of dicyclohexylcarbodiimide. At the site of application, the incidences of focal epidermal hyperplasia were significantly increased in 1.5, 3, and 12 mg/kg mice, the incidences of focal chronic active inflammation of the dermis were increased in groups administered 3 or 12 mg/kg, and the incidences of focal ulcer and focal chronic active inflammation of the subcutaneous tissue were increased in the 12 mg/kg group. GENETIC TOXICOLOGY Dicyclohexylcarbodiimide was not mutagenic in Salmonella typhimurium strains TA97, TA98, TA100, or TA1535, with or without rat or hamster liver S9 activation enzymes. In vivo, there was a small but significant increase in the frequency of micronucleated normochromatic erythrocytes in male and female B6C3F 1 mice after 13 weeks of dermal exposure to dicyclohexylcarbodiimide. Negative results were obtained, however, in an acute three-injection micronucleus study in bone marrow of male F344/N rats. CONCLUSIONS Under the conditions of this 27-week dermal study, there was no evidence of carcinogenic activity* of dicyclohexylcarbodiimide in female p53 haploinsufficient mice administered 0.75, 1.5, 3, 6, or 12 mg/kg in ethanol. Female Tg.AC hemizygous mice dermally dosed with dicyclohexylcarbodiimide for 20 weeks had significantly increased incidences of squamous cell papilloma of the skin at the site of application. Nonneoplastic lesions noted at the site of application included chronic active inflammation and epidermal hyperplasia in female p53 haploinsufficient mice and female Tg.AC hemizygous mice.