Inhalation Oncogenicity Bioassay in Rats and Mice with Vinyl Fluoride

The purpose of this study was to assess the oncogenic potentialof vinyl fluoride in rats and mice when administered by inhalation.Male and female rats and mice were exposed to 0, 25, 250, or2500 ppm vinyl fluoride 6 hr per day, 5 days per week, for 2years (rats) or 18 months (mice). Slight body weight gain decrementswere noted in groups of vinyl fluoride-exposed rats and mice.No significant clinical signs of toxicity were noted other thanan increase in the incidence of palpable masses in the regionof the mammary gland in female mice exposed to vinyl fluoride.Survival was decreased in male rats and mice of the 250 and2500 ppm groups and female rats and mice of all vinyl fluoride-exposedgroups compared to controls. Urinary fluoride excretion, anindicator of vinyl fluoride metabolism, increased with concentrationand time although the dose relationship appeared to plateauat concentrations 250 ppm. Gross observations made at necropsyof rats supported histological observations of hepatic hemangiosarcoma,hepatocellular adenoma and carcinoma, hepatic foci of clearcell and basophilic alteration, hepatic sinusoidal dilatation,metastatic lung tumors, and Zymbal's gland tumors. Hepatic hemangiosarcomawas the sentinel lesion in rats. Gross observations made atnecropsy of mice supported histological observations of bronchioloalveolaradenoma and hyperplasia, hepatic hemangiosarcoma and hepatocellularhyperplasia with angiectasis and peliosis, and mammary glandadenocarcinoma and hyperplasia. Bronchioloalveolar adenoma appearedto be the sentinel lesion in mice. The spectrum of vinyl fluoride-inducedtumors is similar to that induced by other monohaloethylenesin rats and mice. Under the conditions of this study, vinylfluoride was carcinogenic in male and female rats and mice atconcentrations greater than or equal to 25 ppm.     

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     

Chronic ethanol intake and reduction of lung tumours from urethane in strain A mice

Combinations of ethanol and urethane were added to the drinking-water of female strain A/Ph mice for 12 wk, at the end of which the animals were killed. Urethane concentrations were 0, 200, 500 and 1000 ppm and ethanol concentrations, 0, 5, 10 and 20% (v/v). All possible combinations of these urethane and ethanol concentrations were tested. Urethane induced primary lung adenomas in all treated mice in a dose-dependent manner. An average of 71 +/- 15 tumours/mouse were found, when the animals were killed, after treatment with 1000 ppm urethane for 12 wk. Ethanol alone did not alter the background incidence of tumours and produced only marginal hepatotoxicity. The tumour yields induced by urethane treatment were greatly reduced by simultaneous treatment with ethanol. The effect of ethanol was independent of urethane dose. When the concentrations of ethanol in the drinking-water were 20 and 10% the incidences of lung adenomas induced by urethane were reduced by about two-thirds and one-half, respectively. The effect of 5% ethanol, if any, was not statistically significant.     

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 studies of acrylamide (CASRN 79-06-1) in F344/N rats and B6C3F1 mice (feed and drinking water studies)

Acrylamide, a water-soluble α,β-unsaturated amide, is a contaminant in baked and fried starchy foods, including french fries, potato chips, and bread, as a result of Maillard reactions involving asparagine and reducing sugars. Additional sources of acrylamide exposure include cigarettes, laboratory procedures involving polyacrylamide gels, and various occupations (e.g, monomer production and polymerization processes). Acrylamide is carcinogenic in experimental animals. To obtain data for developing quantitative risk assessments for dietary exposures to acrylamide, the Food and Drug Administration nominated acrylamide for an in-depth toxicological evaluation by the National Toxicology Program. As part of this evaluation, male and female B6C3F1/Nctr (C57BL/6N x C3H/HeN MTV-) mice and male and female F344/N Nctr rats were exposed to acrylamide (at least 99.4% pure) in drinking water for 2 years. 2-WEEK STUDY IN RATS: Groups of four male and four female F344/N rats were administered 0, 0.14, 0.35, 0.70, 1.41, 3.52, or 7.03 mM acrylamide in the drinking water (0, 10, 25, 50, 100, 250, or 500 ppm acrylamide) or 0.0, 7.4, 18.5, 37, 74, 185, or 370 mg acrylamide per kg diet for 14 days. One male rat administered 7.03 mM acrylamide in the drinking water died on day 14. Male and female rats receiving 7.03 mM acrylamide weighed 56% and 64% of controls, respectively. Male and female rats fed 370 mg acrylamide per kg diet weighed 74% and 83% of controls, respectively. Female rats receiving 3.52 mM acrylamide in drinking water and male rats fed 185 mg acrylamide per kg diet weighed 85% and 89% of controls, respectively. Rats receiving 7.03 mM acrylamide in drinking water or 370 mg acrylamide per kg diet exhibited hind-leg paralysis on day 14. Mild to moderate dilatation of the urinary bladder was observed in all rats given 370 mg acrylamide per kg diet, and in three of four male rats and all four female rats given 7.03 mM acrylamide in drinking water, and in one of four male rats given 3.52 mM acrylamide in drinking water. Mild to moderate degeneration of the germinal epithelium in the seminiferous tubules of the testes was noted microscopically in all male rats given 7.03 mM acrylamide in drinking water and in two of four male rats fed 370 mg acrylamide per kg diet. 2-WEEK STUDY IN MICE: Groups of four male and four female B6C3F1 mice were administered 0, 0.14, 0.35, 0.70, 1.41, 3.52, or 7.03 mM acrylamide in the drinking water (0, 10, 25, 50, 100, 250, or 500 ppm acrylamide) or 0.0, 7.4, 18.5, 37, 74, 185, or 370 mg acrylamide per kg diet for 14 days. None of the mice administered 7.03 mM acrylamide in the drinking water survived the 14-day study. Mice administered 7.03 mM acrylamide in the drinking water showed marked decreases in body weight (greater than 25% compared to control mice) after seven days of treatment, and two of the mice displayed hind leg paralysis. No significant adverse effects were observed in mice administered 3.52 mM acrylamide in the drinking water for 14 days. Female B6C3F1 mice given 370 mg acrylamide per kg diet for 14 days showed a modest decrease (11%) in body weight. No other significant adverse effects were observed in mice administered any dose of acrylamide in the diet. 3-MONTH STUDY IN RATS: Groups of eight male and eight female F344/N rats were administered 0.0, 0.14, 0.35, 0.70, 1.41, or 3.52 mM acrylamide in the drinking water (0, 10, 25, 50, 100, or 250 ppm acrylamide) or 0.0, 7.4, 18.5, 37, 74, or 185 mg acrylamide per kg diet for 13 weeks. After 13 weeks, male and female rats administered 3.52 mM acrylamide weighed 73% and 71% of the control rats, respectively. Male and female rats fed 185 mg acrylamide per kg diet for 13 weeks weighed 86% and 82% of the control rats, respectively. Hind-leg paralysis was observed in all rats administered 3.52 mM acrylamide in the drinking water or 185 mg acrylamide per kg diet. Four of eight female rats administered 1.41 mM acrylamide also displayed hind-leg paralysis. Radiculoneuropathy (a degenerative lesion) involving the sciatic nerve and lumbar spinal cord was observed in all male and female rats administered 3.52 mM acrylamide or 185 mg acrylamide per kg diet. A low incidence of radiculoneuropathy was also noted in female rats fed 74 mg acrylamide per kg diet. The neuronal degenerative changes were accompanied, at times, by atrophy in skeletal muscle of the hind-limb and luminal dilation of the urinary bladder. All rats treated with 3.52 mM acrylamide displayed increased hemosiderin pigment in their spleens and hyperplasia of red blood cell precursors in their bone marrow. Two of eight male rats fed 185 mg acrylamide per kg diet also had increased hemosiderin pigment in their spleens. Degeneration of the germ cells in the testes was observed in all male rats given 1.41 or 3.52 mM acrylamide, or 185 mg acrylamide per kg diet. A lower incidence of this lesion was also detected in all other doses of acrylamide in the diet. 3-MONTH STUDY IN MICE: Groups of eight male and eight female B6C3F1 mice were administered 0, 0.14, 0.35, 0.70, 1.41, or 3.52 mM acrylamide in the drinking water (0, 10, 25, 50, 100, or 250 ppm acrylamide) or 0.0, 18.5, 37, 74, 185, or 370 mg acrylamide per kg diet. After 13 weeks, the male and female mice given 3.52 mM acrylamide weighed 86% and 94% of their respective control mice; male mice administered 1.41 mM acrylamide weighed 91% of the control male mice; and male and female mice fed 370 mg acrylamide per kg diet weighed 87% and 81% of their respective control groups. Hind-limb paralysis was observed in all mice administered 3.52 mM acrylamide or 370 mg acrylamide per kg diet. Radiculoneuropathy involving the sciatic nerve, lumbar spinal cord, or both was observed in all male and female mice administered 3.52 mM acrylamide. Radiculoneuropathy, involving primarily the sciatic nerve, was also noted in one of eight female mice fed 185 mg acrylamide per kg diet and in mice fed 370 mg acrylamide per kg diet. The neuronal degenerative changes were accompanied, at times, by atrophy in skeletal muscle of the hind-limb and luminal dilation of the urinary bladder. Degeneration of the germ cells in the testes was observed in six of eight male mice given 3.52 mM acrylamide and seven of seven mice fed 370 mg acrylamide per kg diet. 2 YEAR STUDY IN RATS: Groups of 48 male and 48 female F344/N rats were administered acrylamide in the drinking water ad libitum for 2 years. Concentrations of 0.0875, 0.175, 0.35, and 0.70 mM acrylamide (6.25, 12.5, 25, and 50 ppm acrylamide) resulted in an average daily consumption of approximately 0.33, 0.66, 1.32, and 2.71 mg acrylamide per kg body weight in male F344/N rats and 0.44, 0.88, 1.84, and 4.02 mg acrylamide per kg body weight in female F344/N rats. Acrylamide had no effect upon the survival of male F344/N rats. Female F344/N rats administered 0.175, 0.35, or 0.70 mM acrylamide had decreased survival compared to control female F344/N rats. Acrylamide caused significant dose-related decreasing trends in body weight in F344/N rats. At the end of the 2 year period, male and female F344/N rats administered 0.70 mM acrylamide weighed 86% and 85% of their respective control groups. Feed consumption was generally not affected by acrylamide; water consumption in female F344/N rats was increased at later time points. In male F344/N rats, the incidence of epididymis malignant mesothelioma, combined epididymis or testicular tunica malignant mesothelioma, heart malignant incidences of schwannoma, pancreatic islets adenoma, thyroid gland follicular cell carcinoma, and combined thyroid gland follicular cell adenoma or carcinoma was increased significantly in the 0.70 mM acrylamide group. In female F344/N rats, the incidence of clitoral gland carcinoma was increased significantly in the 0.0875, 0.175, and 0.70 mM acrylamide groups. The incidence of mammary gland fibroadenoma was increased significantly at 0.175, 0.35, and 0.70 mM acrylamide. Significant increases in neoplasm incidences were also observed in oral mucosa squamous cell papilloma, combined oral mucosa or tongue squamous cell papilloma or carcinoma, combined skin fibroma, fibrosarcoma, or sarcoma, and combined thyroid gland follicular cell adenoma or carcinoma at 0.70 mM acrylamide. 2-YEAR STUDY IN MICE: Groups of 48 male and 48 female B6C3F1 mice were administered acrylamide in the drinking water ad libitum for 2 years. Concentrations of 0.0875, 0.175, 0.35, and 0.70 mM acrylamide (6.25, 12.5, 25, and 50 ppm acrylamide) resulted in average daily consumption of approximately 1.04, 2.20, 4.11, and 8.93 mg acrylamide per kg body weight in male B6C3F1 mice and 1.10, 2.23, 4.65, and 9.96 mg acrylamide per kg body weight in female B6C3F1 mice. Acrylamide caused dose-related decreasing trends in survival in B6C3F1 mice, with the survival being significantly decreased in male B6C3F1 mice administered 0.70 mM acrylamide and female B6C3F1 mice given 0.35 and 0.70 mM acrylamide. Acrylamide caused only sporadic changes in body weight in B6C3F1 mice, with the magnitude of the change never exceeding 6% of the respective control body weight. Food and water consumption was generally not affected by acrylamide, except for an increased consumption by female B6C3F1 mice in the 0.70 mM acrylamide group toward the end of the study. In male B6C3F1 mice, the incidence of harderian gland adenoma and combined harderian gland adenoma or adenocarcinoma was increased significantly in all acrylamide dose groups. The incidence of lung alveolar/bronchiolar adenoma and combined lung alveolar/bronchiolar adenoma or carcinoma was increased significantly at 0.175 and 0.70 mM acrylamide, and the incidence of stomach (forestomach) squamous cell papilloma and combined stomach (forestomach) squamous cell papilloma or carcinoma was increased significantly at 0.35 and 0.70 mM acrylamide. (ABSTRACT TRUNCATED)     

Toxicology and carcinogenesis studies of o-nitrotoluene sulfone (CAS no. 88-72-2) in F344/N rats and B6C3F(1) mice (feed studies)

[structure: see text] o-Nitrotoluene is used to synthesize agricultural and rubber chemicals, azo and sulfur dyes, and dyes for cotton, wool, silk, leather, and paper. o-Nitrotoluene was nominated for study by NIOSH and the NTP based on its considerable human exposure as well as the absence of long-term studies of carcinogenicity in rodents. Male and female F344/N rats and B6C3F1 mice were exposed to o-nitrotoluene (greater than 99% pure) in feed for 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, rat and mouse bone marrow cells, and mouse peripheral blood erythrocytes. 2-YEAR STUDY IN RATS: In the core study, groups of 60 male and 60 female rats were fed diets containing 625, 1,250, or 2,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 25, 50, or 90 mg o-nitrotoluene/kg body weight to males and 30, 60, or 100 mg/kg to females) for 105 weeks. In a 3-month stop-exposure study, groups of 70 male rats were fed diets containing 2,000 or 5,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 125 or 315 mg/kg) for 13 weeks followed by undosed feed for the remainder of the study. A group of 70 male rats receiving undosed feed served as a control group for both male rat studies; 60 female rats receiving undosed feed were the control group for the female core study. Ten control males and 10 males from each stop-exposure group were sacrificed at 3 months. Survival, Body Weights, and Feed Consumption: All 2,000 ppm core study, all 5,000 ppm stop-exposure, and all but three core study 1,250 ppm male rats died before the end of the studies. Survival of 625 ppm core study and 2,000 ppm stop-exposure males and of 2,000 ppm females was significantly less than that of the controls. Mean body weights of all exposed groups of males except the 625 ppm group were generally less than those of the controls throughout the study. Mean body weights of 2,000 ppm females were less than those of the controls during year 2 of the study. Feed consumption by exposed groups of rats was similar to that by the controls. Biomarkers of Exposure: Three urinary metabolites were followed during the study as biomarkers of exposure. The ratios of o-nitrobenzoic acid to creatinine and of o-nitrobenzylmercapturic acid to creatinine determined at 2 weeks and at 3, 12, and 18 months were linearly related to exposure concentration in males and females. The ratio of o-aminobenzoic acid to creatinine was not related to exposure concentration. Pathology Findings: The incidences of malignant mesothelioma in male rats occurred with positive trends in both the core and stop-exposure studies and were significantly greater in exposed groups than in the controls. Incidences of subcutaneous skin neoplasms (fibroma, fibrosarcoma, and lipoma) were increased in exposed groups of males, while the incidences of fibroma or fibrosarcoma (combined) were increased in exposed females. In all exposed groups of males and females except 2,000 ppm core study males, the incidences of mammary gland fibroadenoma were significantly increased. The incidences of mammary gland hyperplasia were significantly increased in 625 and 1,250 ppm females. Increased incidences of mesothelioma, skin neoplasms, and mammary gland fibroadenoma in the stop-exposure males indicated that 3 months of dosing were sufficient to produce a carcinogenic effect. Liver weights of 5,000 ppm stop-exposure males were significantly greater than those of the controls at 3 months. The incidences of hepatocellular adenoma in 2,000 ppm core study males and females and of hepatocellular adenoma or carcinoma (combined) in 2,000 ppm core study and 5,000 ppm stop-exposure males were significantly increased. Cholangiocarcinoma occurred in three 5,000 ppm stop-exposure males, and a single hepatocholangiocarcinoma occurred in a 625 ppm male and in a 2,000 ppm core study male. Nonneoplastic lesions of the liver included eosinophilic, mixed cell, and clear cell foci in exposed groups of males and females and mixed cell infiltrate in exposed males and basophilic focus in exposed females. The incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined) were significantly increased in 5,000 ppm stop-exposure males, as were alveolar/bronchiolar hyperplasia in most exposed groups of males and females. The incidences of hematopoietic cell proliferation of the spleen and of hyperplasia of the mandibular lymph node (females) and bone marrow were increased in exposed groups of males at 3 months and/or 2 years and in exposed groups of females at 2 years. The incidences of mononuclear cell leukemia were significantly decreased in all groups of males exposed to 1,250 ppm or greater and in all exposed groups of females; the incidence of testicular interstitial cell adenoma was significantly decreased in 5,000 ppm stop-exposure males. 2-YEAR STUDY IN MICE: Groups of 60 male and 60 female mice were fed diets containing 0, 1,250, 2,500, or 5,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 165, 360, or 700 mg/kg to males and 150, 320, or 710 mg/kg to females) for 105 weeks. Survival, Body Weights, and Feed Consumption: All 2,500 and 5,000 ppm males died before the end of the study. Survival of 1,250 ppm males and 5,000 ppm females was significantly less than that of the controls. Mean body weights of exposed males and 5,000 ppm females were generally less than those of the controls throughout the study, and those of 2,500 ppm females were less during the second year of the study. Feed consumption by 5,000 ppm males was less than that by the controls. Biomarkers of Exposure: Three urinary metabolites were followed during the study as biomarkers of exposure. The ratios of o-nitrobenzoic acid to creatinine determined at 2 weeks and at 3, 12, and 18 months were linearly related to exposure concentration in males and females. The concentrations of o-nitrobenzylmercapturic acid and o-aminobenzoic acid were below the limit of quantitation at most time points. Pathology Findings: The incidences of hemangiosarcoma in all exposed groups of males and in 5,000 ppm females were significantly greater than those in the controls. Large intestine (cecum) carcinomas were observed in all exposed groups except 5,000 ppm males. The incidences of hepatocellular neoplasms were significantly increased in 2,500 and 5,000 ppm females. Nonneoplastic liver lesions including eosinophilic and basophilic foci and minimal to mild necrosis were enhanced in exposed males and females. Also present were focal hepatocyte syncytial alteration in exposed males and hepatocyte necrosis and focal hepatocyte cytoplasmic vacuolization in 5,000 ppm females. Renal tubule pigmentation occurred more frequently in exposed groups of males and in 5,000 ppm females than in the controls. Olfactory epithelial degeneration occurred in every male and female mouse exposed to 2,500 or 5,000 ppm, and the severity of this lesion increased with increasing exposure concentration. GENETIC TOXICOLOGY: o-Nitrotoluene was not mutagenic in any of several strains of S. typhimurium, with or without metabolic activation enzymes (S9). Sister chromatid exchanges were significantly increased in cultured Chinese hamster ovary cells following exposure to o-nitrotoluene in the presence of S9; an equivocal response was seen without S9. o-Nitrotoluene did not induce chromosomal aberrations in cultured Chinese hamster ovary cells, with or without S9. o-Nitrotoluene did not induce a significant increase in the frequency of micronuclei in bone marrow polychromatic erythrocytes of male rats or male mice when administered by intraperitoneal injection. Results of a peripheral blood micronucleus test were equivocal for male mice and negative for female mice administered o-nitrotoluene in feed for 13 weeks. CONCLUSIONS: Under the conditions of these studies, there was clear evidence of carcinogenic activity* of o-nitrotoluene in male rats based on increased incidences of malignant mesothelioma, subcutaneous skin neoplasms, mammary gland fibroadenoma, and liver neoplasms. The increased incidences of lung neoplasms in male rats were also considered to be exposure related. There was clear evidence of carcinogenic activity of o-nitrotoluene in female rats based on increased incidences of subcutaneous skin neoplasms and mammary gland fibroadenoma. The increased incidence of hepatocellular adenoma in female rats was also considered to be exposure related. There was clear evidence of carcinogenic activity of -o-nitrotoluene in male and female mice based on increased incidences of hemangiosarcoma, carcinoma of the large intestine (cecum), and hepatocellular neoplasms (females only). Exposure to o--nitrotoluene caused increased incidences of nonneoplastic lesions of the mammary gland (females only), liver, bone marrow, spleen, lung, and mandibular lymph node (females only) in male and female rats and of the liver, kidney, and nose in male and female mice. Decreased incidences of mononuclear cell leukemia occurred in exposed groups of rats; the incidence of testicular interstitial cell adenoma was decreased in exposed male rats. [tables: see text]     

Toxicology and carcinogenesis studies of 1-bromopropane (CAS No. 106-94-5) in F344/N rats and B6C3F1 mice (inhalation studies)

In the early to mid 1990s, 1-bromopropane was used primarily as an intermediate in the production of pesticides, quaternary ammonium compounds, flavors and fragrances, pharmaceuticals, and other chemicals in well-controlled, closed processes. In the mid to late 1990s, it was introduced as a less toxic replacement for methylene chloride in emissive applications such as vapor and immersion degreasing operations and critical cleaning of electronics and metals. 1-Bromopropane was also introduced as a nonflammable, nontoxic, fast-drying, and inexpensive solvent for adhesive resins, and has been marketed as a replacement for ozone depleting refrigerants. 1-Bromopropane was nominated for study by the Occupational Safety and Health Administration based on the potential for widespread occupational and environmental exposure and a lack of toxicity and carcinogenicity data. Male and female F344/N rats and B6C3F1 mice were exposed to 1-bromopropane (99% or greater pure) by inhalation for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli and mouse peripheral blood. 2-WEEK STUDY IN RATS: Groups of five male and five female rats were exposed to 1-bromopropane vapor at concentrations of 0, 125, 250, 500, 1,000, or 2,000 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 except one 500 ppm male. Mean body weights of 2,000 ppm rats were significantly less than those of the chamber controls. The absolute kidney weight of 1,000 ppm males, relative kidney weights of all exposed groups of males, and absolute and relative kidney weights of all exposed groups of females were significantly increased. The absolute and relative liver weights of 1,000 ppm males, relative liver weights of 500 and 2,000 ppm males, and absolute and relative liver weights of 500 ppm or greater females were significantly increased. Nasal lesions included suppurative inflammation in males exposed to 500 ppm or greater, respiratory epithelial necrosis in 1,000 and 2,000 ppm males, and respiratory epithelial regeneration in 1,000 and 2,000 ppm females. 2-WEEK STUDY IN MICE: Groups of five male and five female mice were exposed to 1-bromopropane vapor at concentrations of 0, 125, 250, 500, 1,000, or 2,000 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 17 days. All 2,000 ppm males, two 2,000 ppm females, four 500 ppm males, one 1,000 ppm male, and one 1,000 ppm female died early. The mean body weight gain of 1,000 ppm males was significantly less than that of the chamber controls. Abnormal breathing, lethargy, and eye discharge were observed primarily during week 1 in groups exposed to 500 ppm or greater. Liver weights of 1,000 ppm males and of females exposed to 500 ppm or greater were significantly increased. Kidney weights of 1,000 and 2,000 ppm females were significantly increased. Microscopic lesions related to 1-bromopropane exposure occurred in the lung, liver, and nose of males and females and were primarily seen in mice exposed to 500 ppm or greater. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were exposed to 1-bromopropane vapor at concentrations of 0, 62.5, 125, 250, 500, or 1,000 ppm, 6 hours plus T90 (10 minutes) 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. Mean body weights of 1,000 ppm males were significantly less than those of the chamber controls. The increases in sorbitol dehydrogenase activities in 500 ppm males and 1,000 ppm males and females were consistent with the histopathologic evidence of mild hepatotoxicity caused by 1-bromopropane. Liver weights of males exposed to 250 ppm or greater and of females exposed to 125 ppm or greater were significantly increased. Spleen and kidney weights of 1,000 ppm females were significantly increased. Exposure concentration-related decreases of 28% in sperm motility and 37% in sperm counts were seen in the 1,000 ppm group of male rats. Female rats in all three exposure groups evaluated exhibited altered estrous cycles, spending significantly more time in extended estrus and less time in extended diestrus. The incidences of cytoplasmic vacuolization of the liver were significantly increased in males exposed to 250 ppm or greater and in females exposed to 500 ppm or greater. Hepatocyte degeneration was also observed in 1,000 ppm females. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were exposed to 1-bromopropane vapor at concentrations of 0, 62.5, 125, 250, or 500 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 14 weeks. One 250 ppm male and four males and five females in the 500 ppm groups died early. Mean body weights of exposed groups were similar to those of the chamber controls. Lethargy was observed in males and females exposed to 500 ppm, and abnormal breathing was observed in moribund mice. The kidney, liver, and lung weights of 500 ppm females were significantly greater than those of the chamber controls. The kidney weights of 500 ppm males were significantly decreased. Sperm counts in the 500 ppm group of male mice were 28% less than that in the chamber controls. Female mice exhibited altered estrous cycles, with females in the 500 ppm group spending significantly more time in extended diestrus and those in the 250 ppm group spending significantly more time in extended estrus compared to the chamber controls. Nonneoplastic lesions were observed in the nose, larynx, trachea, lung, and liver of 500 ppm males and females and in the adrenal cortex of 500 ppm females. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were exposed to 1-bromopropane vapor at concentrations of 0, 125, 250, or 500 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 105 weeks. Survival of 500 ppm males was significantly less than that of the chamber control group. Mean body weights of exposed groups were similar to those of the chamber controls. Increased incidences of macroscopic, soft, pale-yellow to green, variably sized nodules were seen predominantly in the nose and skin of exposed rats. The number of animals with multiple masses was increased in the 500 ppm groups. In most cases, these lesions were microscopically shown to be suppurative inflammation, many with Splendore-Hoeppli material. The incidence of adenoma of the large intestine (colon or rectum) was significantly greater in 500 ppm females than in the chamber control group. The incidence of adenoma of the large intestine in 250 ppm males exceeded the historical control ranges for inhalation studies and all routes. The incidences of keratoacanthoma, basal cell adenoma, basal cell carcinoma, or squamous cell carcinoma (combined) were significantly greater in all exposed groups of males than in the chamber control group and exceeded the historical control range for inhalation studies. The incidences of keratoacanthoma and of keratoacanthoma or squamous cell carcinoma (combined) in 250 and 500 ppm males were also significantly increased and exceeded the historical control ranges for inhalation studies. In 500 ppm females, the incidence of squamous cell papilloma, keratoacanthoma, basal cell adenoma, or basal cell carcinoma (combined) exceeded the historical control range for inhalation studies. The incidence of malignant mesothelioma was significantly greater in 500 ppm males than in the chamber control group. The incidences of pancreatic islet adenoma in all exposed groups of males and of pancreatic islet adenoma or carcinoma (combined) in 125 and 250 ppm males were significantly increased. Treatment-related nonneoplastic lesions were observed in the respiratory system of exposed male and female rats. In the nose, the incidences of suppurative chronic inflammation, chronic active inflammation, glandular hyperplasia, respiratory epithelial hyperplasia (females), and respiratory metaplasia of the olfactory epithelium (females) were increased in all exposed groups. In the larynx, the incidences of chronic active inflammation and squamous metaplasia (except 125 ppm females) were increased in all exposed groups, and the incidences of suppurative chronic inflammation were increased in the 500 ppm groups. Also, chronic inflammation of the lung was observed in the 500 ppm females. In the trachea, there were increased incidences of chronic active inflammation in all exposed groups of females and 500 ppm males, and the incidence of epithelial hyperplasia was increased in 500 ppm females. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were exposed to 1-bromopropane vapor at concentrations of 0, 62.5, 125, or 250 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 105 weeks. Survival of exposed groups was similar to that of the chamber controls. Mean body weights of all exposed groups were similar to those of the chamber controls throughout the study. In the females, there were increased incidences of alveolar/bronchiolar adenoma, alveolar/bronchiolar carcinoma, and alveolar/bronchiolar adenoma or carcinoma (combined); the incidences of alveolar/bronchiolar adenoma or carcinoma (combined) were significantly increased in all exposed groups of females. There were significantly increased incidences of cytoplasmic vacuolization of the bronchiolar epithelium in all exposed male groups and regeneration of the bronchiolar epithelium in all exposed groups of males and females. In the nose, there were significantly increased incidences of cytoplasmic vacuolization of the respiratory epithelium in all exposed groups of males and in 125 and 250 ppm females. There were significantly increased incidences of respiratory epithelial hyperplasia in all exposed female groups and in 62.5 and 250 ppm males. (ABSTRACT TRUNCATED)     

Carcinogenicity of malachite green chloride and leucomalachite green in B6C3F1 mice and F344 rats.

Malachite green is a triphenylmethane dye used in the fish industry as an anti-fungal agent. Leucomalachite green is formed by the metabolic reduction of malachite green and persists in the tissues of exposed fish. In this study, we examined the carcinogenicity of malachite green chloride and leucomalachite green. Female F344 rats (48 per group) were fed diets containing 0, 100, 300, or 600 ppm malachite green chloride for 104 weeks, at which time the extent of tumorigenesis was assessed. Additional groups of 48 female and 48 male F344 rats were fed diets containing 0, 91, 272, or 543 ppm leucomalachite green for 104 weeks. Groups of 48 female B6C3F1 mice were fed diets containing 0, 100, 225, or 450 ppm malachite green chloride or 0, 91, 204, or 408 ppm leucomalachite green for 104 weeks. For each of the exposures, food consumption in the treatment groups was similar to the controls. Rats fed malachite green chloride or leucomalachite green had dose-dependent reductions in body weight; in mice, there were no consistent effects upon body weights with either compound. Female rats exposed to malachite green chloride had increased incidences of thyroid gland follicular cell adenoma or carcinoma and hepatocellular adenoma, and a dose-related increasing trend in mammary gland carcinoma. Female rats fed malachite green chloride and female and male rats fed leucomalachite green had a dose-related decreasing trend in the incidence of mononuclear cell leukemia. In male rats fed leucomalachite green there was a decreasing trend in pituitary gland adenoma and an increasing trend in interstitial cell adenoma of the testis. There were no treatment-related neoplasms in female B6C3F1 mice fed malachite green chloride. Female mice fed leucomalachite green had a dose-related increasing trend in the incidence of hepatocellular adenoma or carcinoma, with the incidence being significant in the highest dose group.     

Toxicology and carcinogenesis studies of 4-methylimidazole (Cas No. 822-36-6) in F344/N rats and B6C3F1 mice (feed studies)

4-Methylimidazole 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 sidestream tobacco smoke. 4-Methylimidazole was nominated by the National Cancer Institute for a long-term study because of the high potential for human exposure. Male and female F344/N rats and B6C3F1 mice were exposed to 4-methylimidazole (99.5% pure) in feed for 2 years. Fifteen-day and 14-week toxicity studies of 4-methylimidazole in F344/N rats and B6C3F1 mice are reported in NTP Toxicity Report No. 67. Genetic toxicology studies were conducted in Salmonella typhimurium, rat and mouse bone marrow cells, and mouse peripheral blood. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were fed diets containing 0, 625, 1,250, or 2,500 ppm 4-methylimidazole (males) or 0, 1,250, 2,500, or 5,000 ppm 4-methylimidazole (females) (equivalent to average daily doses of approximately 30, 55, or 115 mg 4-methylimidazole/kg body weight to males and 60, 120, or 260 mg/kg to females) for 106 weeks. Survival of all exposed groups of male and female rats was similar to that of the control groups. 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; mean body weights of 1,250 ppm females were less after week 41. 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 5,000 ppm females was significantly greater than that in the controls, and the incidence exceeded the historical range in feed study controls. The incidences of hepatic histiocytosis, chronic inflammation, and focal fatty change were generally significantly increased in all exposed groups of male and female rats. The incidences of hepatocellular eosinophilic and mixed cell focus were significantly increased in 2,500 ppm males and 5,000 ppm females. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were fed diets containing 0, 312, 625, or 1,250 ppm 4-methylimidazole (equivalent to average daily doses of approximately 40, 80, and 170 mg 4-methylimidazole/kg body weight to males and females) for 106 weeks. Survival of all exposed groups of male and female mice was similar to that of the control groups. Mean body weights of males and females in the 1,250 ppm groups were less than those of the control groups after weeks 17 and 12, respectively. Mean body weights of 312 and 625 ppm females were less after weeks 85 and 65, respectively. Feed consumption by exposed groups of male and female mice was generally 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 epithelium hyperplasia was significantly increased in 1,250 ppm females. GENETIC TOXICOLOGY: 4-Methylimidazole was not mutagenic in the S. typhimurium mutation assay when tested in strains TA97, TA98, TA100, and TA1535, with and without hamster or rat liver metabolic activation enzymes. No consistent or significant increases in the frequencies of micronucleated erythrocytes were seen in the bone marrow of male rats or mice treated with 4-methylimidazole by intraperitoneal injection, or in peripheral blood samples from male and female mice administered the compound in dosed feed for 14 weeks. CONCLUSIONS: Under the conditions of these 2-year studies, there was no evidence of carcinogenic activity of 4-methylimidazole in male F344/N rats exposed to 625, 1,250, or 2,500 ppm. There was equivocal evidence of carcinogenic activity of 4-methylimidazole in female F344/N rats based on increased incidences of mononuclear cell leukemia. There was clear evidence of carcinogenic activity of 4-methylimidazole in male and female B6C3F1 mice based on increased incidences of alveolar/bronchiolar neoplasms. Exposure to 4-methylimidazole resulted in nonneoplastic lesions in the liver of male and female rats and the lung of female mice and in clinical findings of neurotoxicity in female rats.     

Toxicology and carcinogenesis studies of androstenedione (CAS No. 63-05-8) in F344/N rats and B6C3F1 mice (gavage studies)

Androstenedione is an androgen steroid that is normally synthesized within men and women and may be metabolized to a more potent androgen or estrogen hormone. It was nominated to the National Toxicology Program for study due to concern for adverse health effects associated with its chronic use as a dietary supplement by athletes (prior to the banning of its over the counter sales). In order to evaluate its subchronic and chronic toxicity, male and female F344/N rats and B6C3F1 mice were administered androstenedione (98% pure) by gavage for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, rat bone marrow cells, and mouse peripheral blood erythrocytes. 2-WEEK STUDY IN RATS: groups of five male and five female rats were administered 0, 1, 5, 10, 20, or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for 12 days. All rats survived to the end of the study, and the mean body weights of dosed groups were similar to those of the vehicle control groups. The development of cytoplasmic vacuoles within centrilobular hepatocytes in male rats was the only treatment-related effect observed. 2-WEEK STUDY IN MICE: groups of five male and five female mice were administered 0, 1, 5, 10, 20, or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for 12 days. One vehicle control female, one 20 mg/kg female, and one 50 mg/kg female died early due to gavage accidents. There were no significant chemical-related histopathological or mean body weight changes. 3-MONTH STUDY IN RATS: groups of 10 male and 10 female core study rats were administered 0, 1, 5, 10, 20, or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for 14 weeks; additional groups of 10 male and 10 female clinical pathology study rats received the same doses for 23 days. All rats survived to the end of the study. The mean body weights of the 20 mg/kg female group was significantly greater than those of the vehicle control group and there was significant increased weight gain in the 1, 20, and 50 mg/kg female groups. Female thymus weights were significantly increased in the 20 and 50 mg/kg groups, which may be related to the increase in mean body weight. The numbers of sperm per mg cauda epididymis in the 10, 20, and 50 mg/kg male groups and the total number of sperm per cauda epididymis in 50 mg/kg males were significantly less than those of the vehicle controls. No treatment-related histological lesions were observed in males or females. 3-MONTH STUDY IN MICE: groups of 10 male and 10 female mice were administered 0, 1, 5, 10, 20, or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for 14 weeks. Except for one 10 mg/kg female that died early due to a dosing accident, all mice survived to the end of the study. The mean body weights of dosed groups were similar to those of the vehicle control groups. The number of spermatids per mg testis and the total number of spermatids per testis in 20 mg/kg males were significantly greater than those of the vehicle controls. Sperm motility in 50 mg/kg males was significantly lower than that in the vehicle controls. The incidences of x-zone atrophy of the adrenal cortex, an androgen-sensitive endpoint, were significantly increased in females administered 5 mg/kg or greater. There were also significant decreases in the incidences of x-zone cytoplasmic vacuolization in 20 and 50 mg/kg females. The incidences of bone marrow hyperplasia were significantly increased in 5 and 50 mg/kg males. 2-YEAR STUDY IN RATS: groups of 50 male and 50 female rats were administered 0, 10, 20, or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for at least 104 weeks. Survival of 10 mg/kg males was significantly greater than that of the vehicle controls. The mean body weights of 20 and 50 mg/kg females were greater than those of the vehicle controls after weeks 17 and 9, respectively. The incidences of mononuclear cell leukemia were significantly increased in 20 and 50 mg/kg females and significantly decreased in 20 and 50 mg/kg males. Incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined) were significantly increased in 20 mg/kg males. The incidence of testicular interstitial cell adenoma (including bilateral) was significantly decreased in 50 mg/kg males. In females, the incidences of mammary gland fibroadenoma were significantly decreased in the 20 and 50 mg/kg groups, the incidences of mammary gland hyperplasia were significantly decreased in all dosed groups, and the incidences of mammary gland cyst were significantly decreased in the 10 and 50 mg/kg groups. In the liver of males, the incidences of basophilic focus in all dosed groups, the incidence of clear cell focus in the 20 mg/kg group, and the incidence of eosinophilic focus in the 50 mg/kg group were significantly increased. The incidences of pancreatic islet hyperplasia and atrophy of the exocrine pancreas were significantly increased in 50 mg/kg females. 2-YEAR STUDY IN MICE: groups of 50 male and 50 female mice were administered 0, 2 (females only), 10, 20 (males only), or 50 mg androstenedione/kg body weight in a 0.5% aqueous methylcellulose solution by gavage, 5 days per week for at least 104 weeks. Survival of dosed groups was similar to that of the vehicle control groups. Mean body weights of 10 and 50 mg/kg females were generally less than those of the vehicle controls after weeks 81 and 17, respectively. The incidences of hepatocellular adenoma in males and females were significantly increased in the 50 mg/kg groups. In females, the incidences of hepatocellular carcinoma were significantly increased in all dosed groups. Incidences of hepatocellular adenoma or carcinoma (combined) in males and females were significantly increased in the 50 mg/kg groups. Incidences of hepatoblastoma were marginally increased in dosed males. Incidences of multiple hepatocellular adenomas and carcinomas were significantly increased in 10 and 50 mg/kg males, and there was an increased incidence of multiple hepatocellular adenomas in 50 mg/kg females. The incidence of eosinophilic focus was significantly increased in 50 mg/kg males, and the incidences of mixed cell focus and cytoplasmic vacuolization were significantly increased in 50 mg/kg females. There was a marginally increased incidence of pancreatic islet adenoma in 50 mg/kg males and in 10 and 50 mg/kg females, with an earlier day of first incidence in males. The incidences of clitoral gland hyperplasia and clitoral gland duct dilatation were significantly increased in 10 and 50 mg/kg females. The incidence of glomerular metaplasia of the kidney was significantly increased in 50 mg/kg females, and the incidences of cytoplasmic alteration of the submandibular salivary gland were significantly increased in all dosed female groups. The increased incidences of cytoplasmic alteration of the submandibular salivary gland and glomerular metaplasia of the kidney in female mice indicated a masculinizing effect from androstenedione treatment. In 50 mg/kg females, the incidence of malignant lymphoma was significantly decreased. GENETIC TOXICOLOGY: androstenedione was not mutagenic in either of two independent bacterial mutation assays conducted with and without exogenous metabolic activation. No significant increases in the frequencies of micronucleated polychromatic erythrocytes, indicators of chromosomal damage, were observed in bone marrow of male rats administered androstenedione by gavage once daily for 3 consecutive days. Results of a peripheral blood erythrocyte micronucleus test in mice, in which androstenedione was administered by gavage for 3 months, were negative in males but judged to be equivocal in females due to a small increase (twofold over background) in micronucleated normochromatic erythrocytes observed at the highest dose administered (50 mg/kg). CONCLUSIONS: under the conditions of these 2-year gavage studies, there was equivocal evidence of carcinogenic activity of androstenedione in male F344/N rats based on increased incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined). There was equivocal evidence of carcinogenic activity of androstenedione in female F344/N rats based on increased incidences of mononuclear cell leukemia. There was clear evidence of carcinogenic activity of androstenedione in male B6C3F1 mice based on increased incidences of multiple hepatocellular adenoma and hepatocellular carcinoma and increased incidence of hepatoblastoma. There was clear evidence of carcinogenic activity of androstenedione in female B6C3F1 mice based on increased incidences of hepatocellular adenoma and hepatocellular carcinoma. Increased incidences of pancreatic islet adenoma in male and female mice were also considered chemical related. Androstenedione administration caused increased incidences in nonneoplastic lesions of the liver in male and female rats and mice; pancreatic islets and exocrine pancreas of female rats; and clitoral gland, kidney, and submandibular salivary gland of female mice. Decreases in the incidences of testicular interstitial cell adenoma in male rats, mammary gland fibroadenoma, cysts, and hyperplasia in female rats, and malignant lymphoma in female mice were considered related to androstenedione administration. Synonyms: Andro; androst-4-ene-3,17-dione; 4-androstene-3,17-dione; delta-4-androstene-3,17-dione; delta-4-androstenedione; 3,17-dioxoandrost-4-ene; 17-ketotestosterone; SKF 2170 Trade names: Androtex, Fecundin.     

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.     

Lack of modifying effects of eugenol on development of lung proliferative lesions induced by urethane in transgenic mice carrying the human prototype c-Ha-ras gene

To investigate the modifying effects of eugenol (EUG), a component of cigarette smoke, on lung carcinogenesis, male and female transgenic mice carrying the human prototype c-Ha-ras gene (rasH2 mice) were given a single intraperitoneal injection of 250 mg/kg urethane (UR) or saline, followed by a diet containing 6,000 ppm EUG or basal diet for 26 weeks. Their non-transgenic CB6F1 littermates (non-Tg mice) were also treated in the same manner. In both male and female rasH2 mice, alveolar/bronchiolar hyperplasias, adenomas and carcinomas were observed in all UR-treated groups. However, there were no significant intergroup differences in the incidences and multiplicities of these lesions between the UR alone and UR + EUG groups. In non-Tg mice, alveolar/bronchiolar hyperplasias, adenomas or carcinomas were sporadically observed in UR-treated groups of both sexes, with no significant differences in the incidences and multiplicities between the UR alone and UR + EUG groups. There were no intergroup differences between them in the PCNA-positive ratios of adenomas or carcinomas and the areas of adenomas or carcinomas to the whole lung area examined. The present results suggest that the EUG treatment does not exert modifying effects on lung carcinogenesis induced by UR in both male and female rasH2 mice and non-Tg mice.     

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

Androstenedione was marketed as a dietary supplement to increase muscle mass during training. Due to concern over long-term use, the NTP evaluated the subchronic and chronic toxicity and carcinogenicity of androstenedione in male and female F344/N rats and B6C3F1 mice. In subchronic studies, dose limiting effects were not observed. A chronic (2-year) exposure by gavage at 10, 20, or 50 mg/kg in rats and male mice, and 2, 10, or 50 mg/kg in female mice (50 mg/kg, maximum feasible dose) was conducted. Increased incidences of lung alveolar/bronchiolar adenoma and carcinoma occurred in the 20 mg/kg male rats and increases in mononuclear cell leukemia occurred in the 20 and 50 mg/kg female rats, which may have been related to androstenedione administration. In male and female mice, androstenedione was carcinogenic based upon a significant increase in hepatocellular tumors. A marginal increase in pancreatic islet cell adenomas in male (50 mg/kg) and female (2, 10, 50 mg/kg) mice was considered to be related to androstenedione administration. Interestingly, incidences of male rat Leydig cell adenomas and female rat mammary gland fibroadenomas decreased. In conclusion, androstenedione was determined to be carcinogenic in male and female mice, and may have been carcinogenic in rats.     

Spontaneous neoplasms in B6C3F1 mice.

Spontaneous neoplasms in untreated B6C3F1 mice (200 males and 200 females) used as controls in 4 carcinogenicity studies were evaluated and tabulated. The most common neoplasms in male mice were hepatocellular adenomas/carcinomas (24.5%) followed by alveolar-bronchiolar adenomas/carcinomas (10.0%), lymphoreticular neoplasms (7.0%) [malignant lymphomas mixed (4.5%), histiocytic sarcomas (3.5%)], harderian gland adenoma (6.5%), and hemangiomas/hemangiosarcomas (5.5%). In the females, the most frequently occurring neoplasms were lymphoreticular neoplasms (22.0%) [malignant lymphoma mixed (10.0%), malignant lymphoma lymphocytic (6.5%), histiocytic sarcomas (5.5%)] followed by pituitary adenomas (15.5%), alveolar-bronchial adenomas/carcinomas (11.5%), hepatocellular adenomas/carcinomas (7.0%), harderian gland adenomas, uterine stromal polyps (2.5%), and hemangiomas/hemangiosarcoma (2.0%). The incidence of tumors in various other organs was found to be low.     

Application of the margin of exposure (MoE) approach to substances in food that are genotoxic and carcinogenic: Example: Ethyl carbamate (CAS 51-79-6)

Ethyl carbamate is mutagenic and produces DNA-adducts in vivo, and is carcinogenic in rodent bioassays. Dose-response modelling of the data for alveolar and bronchiolar adenoma or carcinoma in male and female mice combined gave a BMDL₁₀ of 0.25 mg/kg-bw/day. The dietary exposure from consumption of foods and non-alcoholic beverage was estimated to be 1 μg/person/day (15 ng/kg-bw/day), while the exposure of a high-percentile consumer of alcoholic beverages was estimated to be 5 μg/person per day (80 ng/kg-bw/day). The corresponding calculated MOEs were 16600 and 3125, respectively.     

Toxicology and carcinogenesis studies of milk thistle extract (CAS No. 84604-20-6) in F344/N rats and B6C3F1 mice (Feed Studies)

Milk thistle extracts have been used as medicinal herbs in the treatment of liver cirrhosis, chronic hepatitis (liver inflammation), and gallbladder disorders. Treatment claims also include lowering cholesterol levels; reducing insulin resistance; reducing the growth of cancer cells in breast, cervical, and prostate gland cancers; and antiviral activity. Other reported uses of milk thistle in folk medicine include as a treatment for malarial fever, bronchitis, gallstones, jaundice, peritonitis, uterine congestion, varicose veins, and as a milk production stimulant for nursing mothers. The roots soaked in water overnight are used in food, and the despined leaves are added to salads. Roasted milk thistle fruit has been used as a coffee substitute. Milk thistle extract was nominated for study by the National Institute of Environmental Health Sciences because it is one of the most widely used herbs in the United States. Male and female F344/N rats and B6C3F1 mice were exposed to an ethanol/water extract of milk thistle fruit (milk thistle extract) containing approximately 65% silymarin in feed for 3 months or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli and mouse peripheral blood erythrocytes. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were fed diets containing 0, 3,125, 6,250, 12,500, 25,000, or 50,000 ppm milk thistle extract (equivalent to average daily doses of approximately 260, 525, 1,050, 2,180, or 4,500 mg milk thistle extract/kilogram body weight to males and 260, 510, 1,050, 2,150, or 4,550 mg/kg to females) for 14 weeks. All rats survived to the end of the study. Mean body weights of exposed groups were within 10% of those of the controls. Feed consumption by exposed and control groups was similar. The sperm motility in 12,500, 25,000, and 50,000 ppm males was decreased by 5%, 11%, and 9%, respectively, relative to that of the controls; the total number of spermatid heads per testis decreased by 11%, 21%, and 9% in 12,500, 25,000, and 50,000 ppm males. No significant differences in estrous cyclicity were observed between exposed and control groups of female rats. No exposure-related histopathologic lesions were observed. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were fed diets containing 0, 3,125, 6,250, 12,500, 25,000, or 50,000 ppm milk thistle extract (equivalent to average daily doses of approximately 640, 1,340, 2,500, 5,280, or 11,620 mg/kg to males and 580, 1,180, 2,335, 4,800, or 9,680 mg/kg to females) for 14 weeks. All mice survived to the end of the study. Mean body weights and feed consumption of all exposed groups were similar to those of the controls. Absolute and relative thymus weights were significantly decreased in 25,000 and 50,000 ppm males. No significant differences were observed between exposed and control groups, for sperm parameters of male mice, for estrous cyclicity of female mice, or for reproductive organ weights of male or female mice, when mice were administered milk thistle extract in feed at 12,500, 25,000, or 50,000 ppm. No exposure-related histopathologic lesions were observed. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were fed diets containing 0, 12,500, 25,000, or 50,000 ppm milk thistle extract (equivalent to average daily doses of approximately 570, 1,180, or 2,520 mg/kg to males and 630, 1,300, or 2,750 mg/kg to females) for 105 to 106 weeks. Exposure to milk thistle extract had no effect on survival of male or female rats. Mean body weights of all exposed groups were similar to those of the controls throughout the study. Feed consumption by exposed groups of males and females was generally similar to that by the controls throughout the study. Significantly decreased incidences of mammary gland fibroadenoma, adenoma, or carcinoma (combined) occurred in females exposed to 25,000 or 50,000 ppm. Significantly increased incidences of clear cell and mixed cell focus of the liver occurred in 25,000 and 50,000 ppm females. The incidences of bile duct hyperplasia were significantly decreased in 50,000 ppm males and in all exposed groups of females, and the incidence of mixed inflammatory cell infiltration was significantly decreased in 50,000 ppm males. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were fed diets containing 0, 12,500, 25,000, or 50,000 ppm milk thistle extract (equivalent to average daily doses of approximately 1,610, 3,530, or 7,770 mg/kg to males and 1,500, 3,175, or 7,180 mg/kg to females) for 105 to 106 weeks. Exposure to milk thistle extract had no effect on survival of male or female mice. The mean body weights of the 25,000 ppm groups were less than those of controls after week 25; mean body weights of 50,000 ppm groups were less than those of controls after week 12. Feed consumption by exposed groups of males and females was generally similar to that by the controls throughout the study. Significantly decreased incidences of hepatocellular adenoma and hepatocellular carcinoma occurred in 50,000 ppm males, and decreased incidences of hepatocellular adenoma or carcinoma (combined) occurred in 25,000 and 50,000 ppm males. GENETIC TOXICOLOGY: Five milk thistle extracts were tested independently in bacterial mutagenicity studies using a variety of S. typhimurium tester strains and one E. coli strain. Results were negative in three of the five studies, with and without exogenous metabolic activation. In two studies, milk thistle extract was mutagenic in S. typhimurium strain TA98 in the presence of exogenous metabolic activation enzymes. Silymarin, a major constituent of milk thistle extract, was positive in S. typhimurium strains TA98 and TA100, when testing occurred in the presence of exogenous metabolic activation enzymes. Silybin, another component of milk thistle extract, was negative in a S. typhimurium gene mutation assay, with and without liver S9 activation enzymes. Administration of milk thistle extract in feed for 3 months did not increase the frequencies of micronucleated normochromatic erythrocytes, an indication of chromosomal abnormalities, in the peripheral blood of male or female B6C3F1 mice. CONCLUSIONS: Under the conditions of these 2-year feed studies, there was no evidence of carcinogenic activity of milk thistle extract in male or female F344/N rats or B6C3F1 mice exposed to 12,500, 25,000, or 50,000 ppm. Exposure to milk thistle extract resulted in increased incidences of clear cell and mixed cell foci in the liver of female rats and decreases in body weights of exposed groups of male and female mice. Decreased incidences of mammary gland neoplasms occurred in exposed groups of female rats, and decreased incidences of hepatocellular neoplasms occurred in exposed groups of male mice.     

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.     

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

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

Harderian gland tumours in mice

A survey of the occurrence of harderian gland tumours in Charles River CD-1 mice (Caesarian derived) showed a relatively higher incidence of harderian gland adenomas in males (5%) in comparison with females (2%) among 3302 untreated control mice from two-year carcinogenicity studies. This sex difference did not apply to the incidence of harderian gland carcinomas. Porphyrin pigment was observed in some of the tumours. Metastasis of the harderian gland carcinoma was seen in lymph node and lung, and in one case the thymus and liver was also affected. Vacuolation, due to fat was seen as helpful diagnostic feature.     

Carcinogenicity Studies of Oxazepam in Mice

Oxazepam is a benzodiazepine widely used as a sedative-hypnoticand antianxiety drug. In chronic studies, groups of 60 maleand 60 female Swiss-Webster (SW) or B6C3F₁ mice received oxazepamin feed at concentrations of 0, 2500, or 5000 ppm. Additionalgroups of 60 male and female B6C3F, mice received 125 ppm infeed to allow for study of mice with serum concentrations ofoxazepam similar to those achieved in humans taking a therapeuticdose. At 57 weeks, treatment-related mortality of exposed SWmice caused the study to be terminated. Enhanced systemic amyloidosiscontributing to heart failure was considered the principal causeof death. Hepatocellular adenomas and carcinomas were increasedin exposed SW mice. Survival of B6C3F₁ mice receiving 2500 and5000 ppm oxazepam was also lower than that of controls. Earlydeaths were due to increased incidences of hepatoblastoma andhepatocellular carcinoma, and nearly all mice receiving 2500or 5000 ppm developed hepatocellular neoplasia. An increasein follicular cell hyperplasia of the thyroid gland occurredin all exposed groups of B6C3F₁ mice, and thyroid gland follicularcell adenoma was increased in exposed females. Further studiesof the capacity of oxazepam to induce liver cell mitogenesisand an evaluation of the frequency of activated H- and K-rasoncogenes in the liver tumors of B6C3F₁ mice has shown thatmany of the neoplastic and nonneoplastic responses of mice tooxazepam resemble those observed with phenobarbital.