Widespread human exposure to multifunctional acrylates is of concern, due to their inherent reactivity and irritating properties. Trimethylolpropane triacrylate (TMPTA) and pentaerythritol triacrylate (PETA) are industrially important representatives of multifunctional acrylates. The current studies characterized the toxicity of 3-month topical administration of technical grade TMPTA and PETA in F344/N rats and B6C3F1 mice, and evaluated the carcinogenic potential of TMPTA and PETA in hemizygous Tg.AC (v-Ha-ras) transgenic mice. Administration of 0.75, 1.5, 3, 6, and 12 mg/kg TMPTA and PETA for 3 months resulted in hyperplastic, degenerative, and necrotic lesions, accompanied by chronic inflammation of the skin, with severities generally increasing with dose. Lesions were slightly more severe in rats, when compared with mice, and illustrate the irritant potential of TMPTA and PETA. A similar dosage regimen was used for the 6-month study with Tg.AC mice. Topical application of TMPTA and PETA to Tg.AC mice showed dose-dependent increases in squamous cell papillomas at the site of application, with decreases in the latency of their appearance in mice receiving 3 mg/kg or greater. Papillomas, the reporter phenotype in Tg.AC mice, were accompanied by a few squamous cell carcinomas, along with hyperplastic and inflammatory lesions. Although chronic inflammation might have contributed to the development of the skin lesions, the dose-related nature of the induction of the skin papillomas in Tg.AC mice by TMPTA and PETA may reflect a potential for carcinogenicity.

Tg.AC mice develop epidermal papillomas in response to treatment with dermally applied nongenotoxic and complete carcinogens. The persistent environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a multi-site rodent carcinogen and tumor promoter that induces the formation of papillomas in Tg.AC mice. To examine the dose-response relationship and compare dermal and oral routes of exposure for TCDD-induced skin papillomas, female Tg.AC mice were exposed dermally to average daily doses of 0, 2.1, 7.3, 15, 33, 52, 71, 152, and 326 ng TCDD/kg/day or 0, 75, 321, and 893 ng TCDD/kg body weight by gavage for 26 weeks. The incidence of cutaneous papillomas was increased in a dose-dependent manner, and tumors developed earlier with higher exposure to TCDD regardless of route of administration. Increased incidences of cutaneous squamous cell carcinomas were observed in mice exposed to dermal (> or =52 ng/kg) and oral (893 ng/kg) TCDD. Higher gavage doses than dermal exposure doses were required to induce papillomas and squamous cell carcinomas. Despite a linear correlation between administered dose and terminal skin concentrations, the incidence of tumor formation was lower in the gavage study than in the dermal study with respect to mean terminal skin TCDD concentrations. These studies demonstrate that, although Tg.AC mice are less responsive to TCDD by gavage than by dermal exposure, the induction of skin neoplasms is a response to systemic exposure and not solely a local response at the site of dermal application. Differences in response between the routes of exposure may reflect pharmacokinetic differences in the delivery of TCDD to the skin over the duration of the study.

Methylene blue trihydrate is used widely as a dye and therapeutic agent. Methylene blue was administered by gavage to 30 animals/sex/dose group in a 0.5% aqueous methylcellulose suspension at doses of 0, 25, 50, 100, and 200 mg/kg. Blood samples from 10 animals/sex/dose group were collected at the end of study weeks 1, 6, and 13. Methylene blue treatment resulted in methemoglobin formation and oxidative damage to red blood cells, leading to a regenerative anemia and a variety of tissue and biochemical changes secondary to erythrocyte injury. An early change was a dose-related increase in methemoglobin, where the response of rats and mice was similar in magnitude. Mice appeared to be more sensitive than rats to the formation of Heinz bodies and the development of anemia that was characterized by a decrease in hemoglobin, hematocrit, and erythrocyte count. Splenomegaly was apparent in all treated mice and in the 100 mg/kg (males only) and 200 mg/kg rats at necropsy. There was a dose-related increase in absolute and relative spleen weight for both species. Microscopic examination revealed increased splenic hematopoiesis in all mice treatment groups and in rats at the 50 mg/kg dose level and above. Splenic congestion and bone marrow hyperplasia were also observed in these rat-dose groups. Mice at the higher doses showed hematopoiesis in the liver and accumulation of hemosiderin in Kupffer cells. These gross and microscopic findings are consistent with the development of hemolytic anemia. A dose-related increase in the reticulocyte count during study weeks 6 and 13 suggested a compensatory response to anemia.

Methyleugenol (MEG) was tested for toxicity/carcinogenicity in a 2-yr carcinogenesis bioassay because of its widespread use in a variety of foods, beverages, and cosmetics as well as its structural resemblance to the known carcinogen safrole. F344/N rats and B6C3F(1) mice (50 animals/sex/dose group) were given MEG suspended in 0.5% methylcellulose by gavage at doses of 37, 75, or 150 mg/kg/day for 2 yr. Control groups (60 rats/sex and 50 mice/sex) received only the vehicle. A stop-exposure group of 60 rats/sex received 300 mg/kg/day by gavage for 53 weeks followed by the vehicle only for the remaining 52 weeks of the study. A special study group (10 animals/sex/species/dose group) were used for toxicokinetic studies. All male rats given 150 and 300 mg/kg/day died before the end of the study; survival of female rats given 150 mg/kg/day and all treated female mice was decreased. Mean body weights of treated male and female rats and mice were decreased when compared to control. Area under the curve results indicated that greater than dose proportional increases in plasma MEG occurred for male 150 and 300 mg/kg/day group rats (6 and 12 month) and male 150 mg/kg/day mice (12 month). Target organs included the liver, glandular stomach, forestomach (female rats) and kidney, mammary gland, and subcutaneous tissue (male rats). Liver neoplasms occurred in all dose groups of rats and mice and included hepatoadenoma, hepatocarcinoma, hepatocholangioma (rats only), hepatocholangiocarcinoma, and hepatoblastoma (mice only). Nonneoplastic liver lesions included eosinophilic and mixed cell foci (rats only), hypertrophy, oval cell hyperplasia, cystic degeneration (rats only), and bile duct hyperplasia. Mice also exhibited necrosis, hematopoietic cell proliferation, and hemosiderin pigmentation. Glandular stomach lesions in rats and mice included benign and malignant neuroendocrine tumors, neuroendocrine cell hyperplasia, and atrophy and in mice included glandular ectasia/chronic active inflammation. In female rats, the forestomach showed a positive trend in the incidences of squamous cell papilloma or carcinoma (combined). Male rats also exhibited kidney (renal tubule hyperplasia, nephropathy, and adenomacarcinoma), mammary gland (fibroadenoma), and subcutaneous tissue (fibroma, fibrosarcoma) lesions. Male rats also exhibited malignant mesotheliomas and splenic fibrosis. These data demonstrate that MEG is a multisite, multispecies carcinogen.

Pentachlorophenol (PCP) has been used as an herbicide, algaecide, defoliant, wood preservative, germicide, fungicide, and molluscicide. A 28-day toxicity study of PCP in F344/N rats of both sexes was conducted to select dose levels for a carcinogenicity study. Groups of 10 male and 10 female rats were given 0, 200, 400, 800, 1600, or 3200 ppm PCP in feed for 28 days. The incidences of minimal to mild hepatocyte degeneration in males and females exposed to 400 ppm or greater and the incidences of centrilobular hepatocyte hypertrophy in the 3200-ppm groups were increased. For carcinogenicity studies, groups of 50 male and 50 female F344/N rats were fed diets containing 200, 400, or 600 PCP for 2 years. A stop-exposure group of 60 male and 60 female rats received 1000 ppm of PCP in feed for 52 weeks and control feed thereafter for the remainder of the 2-year studies; 10 male and 10 female rats were evaluated at 7 months. Survival of 600-ppm males was significantly greater than that of the controls; survival of all other exposed groups was similar to that of the control groups. Mean body weights of the 400- and 600-ppm groups were generally less than those of the controls throughout the studies. There was no evidence of carcinogenic activity of PCP in male or female rats fed diets containing 200, 400, or 600 ppm for 2 years. Stop-exposure study males and females regained a transitory body weight reduction by the end of the 2 year study, and males had better survival than the controls. At a 7-month interim evaluation, the incidences of centrilobular hypertrophy in stop-exposure males and females exceeded those in the controls. At 2 years, malignant mesothelioma originating from the tunica vaginalis was present in 9 1000-ppm males and 1 control male (p = 0.014). Nasal squamous cell carcinomas were present in five 1000-ppm males and 1 control male. This incidence was not significantly increased but exceeded the historical control range (0-4%). Based on the increased incidences of mesotheliomas and nasal tumors, there was some evidence of carcinogenic activity of PCP in male rats given a diet containing 1000 ppm for 1 year followed by control diet for 1 year. There was no evidence of PCP carcinogenic activity in stop-exposure female rats.

A comprehensive chronic toxicity and carcinogenicity study was conducted on a series of Aroclors (1016, 1242, 1254, and 1260). Each Aroclor was assessed at multiple dietary concentrations, ranging from 25 to 200 ppm, for 24 months in male and female Sprague–Dawley rats. Liver toxicity was indicated by elevated serum enzyme activity (AST, ALT, and GGT), elevated serum cholesterol concentration, decreases in hematologic parameters (RBC, Hb, and Hct), hepatocellular hypertrophy, an increased incidence of altered hepatocellular foci, and an increased incidence of hepatocellular neoplasms (primarily adenomas). Liver toxicity was distinctly more severe in females than in males. The incidence of hepatocellular neoplasms was highly sex-dependent (females ⪢ males), differed between Aroclor mixtures and, for females, increased with dose and followed the general incidence pattern of Aroclor 1254 > Aroclor 1260 ≈ Aroclor 1242 > Aroclor 1016. A significant response (p< 0.05) in males was seen only for the high dose of Aroclor 1260. A small increase in the incidence of thyroid gland follicular cell adenomas was noted in males for Aroclors 1242, 1254, and 1260, with the incidence being uniform across dose groups and Aroclor mixtures. For females, increased survival relative to controls was observed for all Aroclor treatment groups. A significantly decreased trend in the incidence of mammary gland neoplasms compared to control was also noted for females receiving Aroclors 1242, 1254, and 1260.

The US National Toxicology Program (NTP) has conducted toxicity and carcinogenicity studies with sodium fluoride administered in the drinking water to F344/N rats and B6C3F1 mice. The drinking water concentrations used in the 2-year studies were 0, 25, 100, or 175 ppm sodium fluoride (equivalent to 0, 11, 45 or 79 ppm fluoride). Survival and weight gains of rats and mice were not affected by fluoride treatment. Animals receiving sodium fluoride developed effects typical of dental fluorosis, and female rats given 175 ppm had increased osteosclerosis. There were no increases in neoplasms in female rats or in male or female mice that were attributed to sodium fluoride administration. There was equivocal evidence of carcinogenic activity of sodium fluoride in male rats based on the occurrence of a small number of osteosarcomas in treated animals.

Toxicology and carcinogenicity studies of N-methylolacrylamide were conducted by administering the chemical by gavage in water to both sexes of F344/N rats and B6C3F1 mice 5 times per week for 16 d, 13 wk, or 2 yr. In 16-d studies, rats receiving doses of 200 mg/kg or higher and mice receiving 400 mg/kg died. In 13-wk studies, all rats given 100 mg/kg or higher doses died. Rats receiving 50 mg/kg or higher doses developed hindlimb ataxia progressing to paralysis. In neurobehavioral assessments, decreased forelimb and hindlimb grip strength occurred in rats at doses as low as 12.5 mg/kg. Landing footspread was also increased in dosed rats compared to controls. Axon filament and myelin sheath degeneration in the spinal cord and/or peripheral nerves occurred in rats receiving doses of 25 mg/kg or higher. Necrosis in the granular cell layer of the cerebellum was seen in rats given 200 mg/kg. Mice receiving 200 mg/kg in 13-wk studies died. Decreased grip strength was noted in mice at doses as low as 25 mg/kg, and rotarod performance was also affected by N-methylolacrylamide administration, but no neuropathology was seen microscopically. Testicular weights were decreased at doses as low as 12.5 mg/kg, and hepatocellular necrosis, thymic lymphocyte necrosis, and hemorrhage, necrosis, and mineralization of the zona reticularis of the adrenal gland were seen in mice that died (200 mg/kg). In 2-yr studies, survival and weight gains in male and female rats receiving doses of 6 or 12 mg/kg/d were minimally affected. No biologically important clinical signs or neoplastic or nonneoplastic lesions were attributed to N-methylolacrylamide administration to rats, suggesting that higher doses could have been tolerated. In mice, survival was not different between dosed and control groups (0, 25, or 50 mg/kg/d). Body weights were higher by as much as 25% in dosed compared to control groups. No compound-related clinical signs were observed, but increases in neoplasms of the harderian gland, liver, and lung were clearly related to chemical administration in both sexes of mice. Benign granulosa-cell neoplasms of the ovary were also increased in dosed female mice.