Multi-Organ Carcinogenicity of 3,3′-Dimethoxybenzidine Dihydrochloride Given in Drinking Water to F344/N Rats

3,3′-Dimethoxybenzidine dihydrochloride (DMOB) was evaluated for chronic toxicity and carcinogenicity because benzidine, a structurally related chemical, is a known human carcinogen, and because of potential human exposure during production of bisazobiphenyl dyes. Previous carcinogenicity studies of DMOB were considered to be inadequate. Toxicology and carcinogenesis studies were conducted by administering 0,80,170, or 330 ppm DMOB (>97.5% purity) in drinking water to groups of F344/N rats for 21 months. Seventy rats of each sex were used in the control group, 45 in the low-dose, 75 in the mid-dose, and 70 in the high-dose group. Ten rats of each sex in the control and 330 ppm dose groups were evaluated after 9 months. After exposure for 9 months, chemical-related neoplastic effects included liver foci, carcinoma of the preputial gland in one male, carcinoma of the clitoral gland in one female, and carcinoma of the Zymbal gland in two male rats. Although designed for 24 months, these studies were terminated at 21 months because significant numbers of exposed rats died with tumors or were sacrificed in moribund condition. Chemical-related nonneoplastic effects were hematopoietic cell proliferation in the spleen, and cystic and centrilobular degeneration and necrosis of the liver. 3,3′-Dimethoxybenzidine was clearly carcinogenic for male and female F344/N rats. After exposure for up to 21 months, significantly increased incidences of neoplasms were observed in multiple sites: skin, Zymbal gland, preputial and clitoral glands, oral cavity, small and large intestines, liver, brain, mesothelium, mammary gland, and uterus of treated rats.

Carcinogenesis studies of cresols in rats and mice

Cresols, monomethyl derivatives of phenol, are high production chemicals with potential for human exposure. The three isomeric forms of cresol are used individually or in mixtures as disinfectants, preservatives, and solvents or as intermediates in the production of antioxidants, fragrances, herbicides, insecticides, dyes, and explosives. Carcinogenesis studies were conducted in groups of 50 male F344/N rats and 50 female B6C3F1 mice exposed to a 60:40 mixture of m- and p-cresols (m-/p-cresol) in feed. Rats and mice were fed diets containing 0, 1500, 5000, or 15,000 ppm and 0, 1000, 3000, or 10,000 ppm, respectively. Survival of each exposed group was similar to that of their respective control group. Mean body weight gains were depressed in rats exposed to 15,000 ppm and in mice exposed to 3000 ppm and higher. A decrease of 25% over that of controls for the final mean body weight in mice exposed to 10,000 ppm appeared to be associated with lack of palatability of the feed. A marginally increased incidence of renal tubule adenoma was observed in the 15,000-ppm-exposed rats. The increased incidence was not statistically significant, but did exceed the range of historical controls. No increased incidence of hyperplasia of the renal tubules was observed; however, a significantly increased incidence of hyperplasia of the transitional epithelium associated with an increased incidence of nephropathy was observed at the high exposure concentration. The only significantly increased incidence of a neoplastic lesion related to cresol exposure observed in these studies was that of squamous cell papilloma in the forestomach of 10,000-ppm-exposed mice. A definitive association with irritation at the site-of-contact could not be made because of limited evidence of injury to the gastric mucosa at the time of necropsy. However, given the minimal chemical-related neoplastic response in these studies, it was concluded that there was no clear evidence of carcinogenicity in male rats or female mice exposed to the cresol mixture.

Carcinogenesis studies of benzophenone in rats and mice

Benzophenone, an aryl ketone, is used primarily as a photoinitiator and fragrance enhancer. Groups of 50 male and 50 female F344 rats and B6C3 F1 mice were fed diets containing 0, 312, 625, and 1250 ppm benzophenone for 105 weeks. Survival of males exposed to 1250 ppm benzophenone was significantly less than that of controls. There was a positive trend in the incidence of renal tubule adenoma in male rats; these neoplasms were accompanied by significantly increased incidences of renal tubule hyperplasia. Increased incidences of mononuclear cell leukemia were observed in male rats exposed to 312 or 625 ppm benzophenone and in female rats exposed to 625 ppm benzophenone. Liver lesions observed included significantly increased incidences of hepatocytic centrilobular hypertrophy in all exposed groups of rats. In mice, survival of all exposed groups was generally similar to that of the control groups. In male mice, there were significantly increased incidences of hepatocellular adenoma in the 625 and 1250 ppm groups. In female mice, the incidences of hepatocellular adenoma in the 625 and 1250 ppm groups were higher than expected after adjusting for the lower body weights in these groups. The incidences of kidney nephropathy in exposed groups of female mice, as well as the severity of nephropathy in exposed groups of males, were significantly increased. The incidences of metaplasia of the olfactory epithelium were significantly increased in 1250 ppm mice. Rare histiocytic sarcomas were observed in female rats and mice in the 625 and 1250 ppm groups. Under the conditions of these 2-year studies, there was some evidence of carcinogenic activity of benzophenone in male F344/N rats based on increased incidences of renal tubule adenoma. There was equivocal evidence of carcinogenic activity of benzophenone in female F344/N rats based on the marginal increased incidences of mononuclear cell leukemia and histiocytic sarcoma. There was some evidence of carcinogenic activity of benzophenone in male B6C3F(1) mice based on increased incidences of hepatocellular neoplasms, primarily adenoma. There was some evidence of carcinogenic activity of benzophenone in female B6C3F(1) mice based on increased incidences of histiocytic sarcoma; the incidences of hepatocellular adenoma in female B6C3F(1) mice may have been related to benzophenone exposure.

Toxicology and carcinogenesis studies of microencapsulated trans-cinnamaldehyde in rats and mice

trans-Cinnamaldehyde is a widely used natural ingredient that is added to foods and cosmetics as a flavoring and fragrance agent. Male and female F344/N rats and B6C3F(1) mice were exposed to microencapsulated trans-cinnamaldehyde in the feed for three months or two years. All studies included untreated and vehicle control groups. In the three-month studies, rats and mice were given diets containing 4100, 8200, 16,500, or 33,000 ppm trans-cinnamaldehyde. In rats, feed consumption was reduced in all exposed groups. In mice, feed consumption was reduced in the highest dose groups. Body weights of all treated males were less than controls. Body weights were reduced in female rats exposed to 16,500 or 33,000 ppm and female mice exposed to 8200 ppm or greater. All rats survived to the end of the study but some male mice in the highest dose groups died due to inanition from unpalatability of the dosed feed. The incidence of squamous epithelial hyperplasia of the forestomach was significantly increased in rats exposed to 8200 ppm or greater and female mice exposed to 33,000 ppm. In mice, the incidence of olfactory epithelial degeneration of the nasal cavity was significantly increased in males and females exposed to 16,500 ppm and females exposed to 33,000 ppm. In the two-year studies, rats and mice were exposed to 1000, 2100, or 4100 ppm trans-cinnamaldehyde. Body weights were reduced in mice exposed to 2100 ppm and in rats and mice exposed to 4100 ppm. In rats, hippuric acid excretion was dose proportional indicating that absorption, metabolism, and excretion were not saturated. No neoplasms were attributed to trans-cinnamaldehyde in rats or mice. Squamous cell papillomas and carcinomas of the forestomach were observed in male and female mice but the incidences were within the NTP historical control range and were not considered to be related to trans-cinnamaldehyde exposure.

Carcinogenicity of inhaled vanadium pentoxide in F344/N rats and B6C3F1 mice

Vanadium pentoxide (V2O5) is a slightly soluble compound found in airborne particle emissions from metallurgical works and oil and coal burning. Because the carcinogenic potential of V2O5 was not known, F344/N rats and B6C3F1 mice (N=50/sex/species) were exposed to V2O5 at concentrations of 0, 0.5 (rats only), 1, 2, or 4 (mice only) mg/m3, by whole-body inhalation for 2 years. The survival and body weights of rats were minimally affected by exposure to V2O5. The survival and body weights of male mice exposed to 4 mg/m3 and body weights of all exposed groups of female mice were lower than the controls. Alveolar/bronchiolar (A/B) neoplasms occurred in male rats exposed to 0.5 and 2 mg/m3 at incidences exceeding the National Toxicology Program (NTP) historical control ranges. A marginal increase in A/B neoplasms was also observed in female rats exposed to 0.5 mg/m3. Increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar hyperplasia/metaplasia and squamous metaplasia were observed in exposed male and female rats. A/B neoplasms were significantly increased in all groups of exposed mice. As with rats, increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar epithelial hyperplasia were observed in mice exposed to V2O5. Thus, V2O5 exposure was a pulmonary carcinogen in male rats and male and female mice. The marginal tumor response in the lungs of female rats could not be attributed conclusively to exposure to V2O5. These responses were noted at and slightly above the OSHA permissible occupational exposure limit of 0.5 mg/m3 (dust) (National Institute for Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services, Washington, DC, 1997, p. 328).

Toxicology and carcinogenesis studies of microencapsulated citral in rats and mice

Citral, a widely used natural ingredient, is added to foods and cosmetics as a flavoring and fragrance agent. Male and female F344/N rats and B6C3F1 mice were exposed to microencapsulated citral in the feed for 14 weeks or two years. All studies included untreated and vehicle control groups. In the 14-week studies, rats and mice were given diets containing 3,900, 7,800, 15,600, or 31,300 ppm citral. In rats, food consumption was reduced in the two highest dose groups. In mice an apparent increase in food consumption was observed, but was due to mice scattering the feed. Body weights of all treated animals were less than controls. All rats and four male mice were killed moribund in the high dose groups. In rats, forestomach and kidney lesions were observed. At the higher doses, lesions observed in the bone marrow, testes, and thymus in rats and in the ovary in mice were considered related to inanition and resultant moribundity. In the two-year studies, rats were exposed to 1,000, 2,000, or 4,000 ppm citral. Body weights were reduced in the 4,000 ppm rats. Mice were exposed to 500, 1,000, or 2,000 ppm citral. Body weights in the 1,000 and 2,000 ppm groups were reduced. No neoplasms were attributed to citral in rats or mice. Malignant lymphoma occurred with a positive trend and was significantly greater than controls in female mice in the 2,000 ppm group. However, the incidences were within the NTP historical control range and could not be clearly related to citral administration.

Tg.AC genetically altered mouse: assay working group overview of available data

In a Government/Industry/Academic partnership to evaluate alternative approaches to carcinogenicity testing, 21 pharmaceutical agents representing a variety of chemical and pharmacological classes and possessing known human and or rodent carcinogenic potential were selected for study in several rodent models. The studies from this partnership project, coordinated by the International Life Sciences Institute, provide additional data to better understand the models' limitations and sensitivity in identifying carcinogens. The results of these alternative model studies were reviewed by members of Assay Working Groups (AWG) composed of scientists from government and industry with expertise in toxicology, genetics, statistics, and pathology. The Tg.AC genetically manipulated mouse was one of the models selected for this project based on previous studies indicating that Tg.AC mice seem to respond to topical application of either mutagenic or nonmutagenic carcinogens with papilloma formation at the site of application. This communication describes the results and AWG interpretations of studies conducted on 14 chemicals administered by the topical and oral (gavage and/or diet) routes to Tg.AC genetically manipulated mice. Cyclosporin A, an immunosuppresant human carcinogen, ethinyl estradiol and diethylstilbestrol (human hormone carcinogens) and clofibrate, an hepatocarcinogenic peroxisome proliferator in rodents, were considered clearly positive in the topical studies. In the oral studies, ethinyl estradiol and diethylstilbestrol were negative, cyclosporin was considered equivocal, and results were not available for the clofibrate study. Of the 3 genotoxic human carcinogens (phenacetin, melphalan, and cyclophosphamide), phenacetin was negative by both the topical and oral routes. Melphalan and cyclophosphamide are, respectively, direct and indirect DNA alkylating agents and topical administration of both caused equivocal responses. With the exception of clofibrate, Tg.AC mice did not exhibit tumor responses to the rodent carcinogens that were putative human noncarcinogens, (di(2-ethylhexyl) phthalate, methapyraline HCl, phenobarbital Na, reserpine, sulfamethoxazole or WY-14643, or the nongenotoxic, noncarcinogen, sulfisoxazole) regardless of route of administration. Based on the observed responses in these studies, it was concluded by the AWG that the Tg.AC model was not overly sensitive and possesses utility as an adjunct to the battery of toxicity studies used to establish human carcinogenic risk.

14-Week toxicity and cell proliferation of methyleugenol administered by gavage to F344 rats and B6C3F1 mice

Methyleugenol, a food flavor and fragrance agent, was tested for toxicity in male and female F344/N rats and B6C3F1 mice. Groups of 10 males and 10 females per sex per species were administered 0, 10, 30, 100, 300 or 1000 mg methyleugenol/kg body weight in 0.5% aqueous methylcellulose by gavage, 5 days per week for 14 weeks. Additional groups of rats and mice of each sex were dosed similarly and used for hematology and clinical chemistry studies. Groups of 10 male and 10 female rats and mice received the vehicle by gavage on the same dosing schedule and served as vehicle controls. For serum gastrin, gastric pH and cell proliferation studies groups of 10 female rats were given 0, 37, 75 or 150 mg/kg, once daily 5 days per week for 30 or 90 days or 300 or 1000 mg/kg for 30 days; male mice were given 0, 9, 18.5, 37, 75, 150 or 300 mg/kg for 30 or 90 days. For the gastrin, pH and cell proliferation studies, groups of 10 female rats and 10 male mice were given the vehicle for 30 or 90 days and served as controls. Methyleugenol administration to rats induced erythrocyte microcytosis and thrombocytosis in male and female rats. It also caused an increase in serum alanine aminotransferase and sorbitol dehydrogenase activities and bile acid concentration, suggesting hepatocellular injury, cholestasis or altered hepatic function. Additionally, methyleugenol induced hypoproteinemia and hypoalbuminemia, evidenced by decreased total protein and albumin concentrations in both male and female rats, suggesting in inefficiency of dietary protein utilization due to methyleugenol-induced toxic effects on the liver and glandular stomach of rats and mice. The increase in gastrin and gastric pH of rats and mice given methyleugenol suggests that gastrin feedback was impaired and resulted in conditions not conducive to protein digestion. In rats, methyleugenol caused an increase in the incidences of hepatocyte cytologic alteration, cytomegaly, Kupffer cell pigmentation, mixed foci of cellular alteration and bile duct hyperplasia of the liver and atrophy and chronic inflammation of the mucosa of the glandular stomach. In mice, it caused an increase in the incidence of cytologic alteration, necrosis, bile duct hyperplasia and subacute inflammation of the liver and atrophy, degeneration, necrosis, edema, mitotic alteration, and cystic glands of the fundic region of the glandular stomach. The increased incidences of adrenal gland cortical hypertrophy and/or cytoplasmic alteration in the submandibular salivary glands, adrenal glands, testis and uterus of rats were considered secondary to the chemical-related effects observed in the liver and glandular stomach. Based on mortality, body weight gain, clinical chemistry and gross and microscopic evaluation of tissues of rats and mice, the no-observed-effect level (NOEL) of methyleugenol for both species was estimated at 10 mg/kg.

Toxicology and carcinogenesis studies of p,p'-dichlorodiphenyl sulfone in rats and mice

p,p'-Dichlorodiphenyl sulfone (DDS) is used as a starting material in the production of polysulfones and polyethersufones, a family of thermoplastics. DDS was studied because of its high production volume and use. In toxicology studies, 10 Fischer 344 rats and 10 B6C3F1 mice/sex/group were fed diets containing 0, 30, 100, 300, 1,000 or 3,000 ppm DDS for 14 weeks. All animals survived until the end of the studies. Mean body weights of groups exposed to 300 ppm or greater were significantly decreased. Liver and kidney in rats and liver in mice were the major target organs of DDS toxicity. Dose-related increases in liver weights and incidences of centrilobular hepatocyte hypertrophy were observed in DDS-exposed groups. Nephropathy was seen in male and female rats only at and above 300 ppm. Neurotoxicity evaluations were negative in DDS-treated animals. Clinical chemistry and hematology parameters were minimally affected. In the 2-year toxicity and carcinogenicity studies, 50 rats and 50 mice/sex/group were fed diets containing 0, 10 (male rats), 30, 100, or 300 ppm DDS for 104 to 105 weeks. Survival of exposed groups was not affected. There were no clinical signs of toxicity related to DDS exposure. Final mean body weights were 2-17% lower in DDS-treated groups. Liver was the only target organ of DDS-induced toxicity. The incidence of centrilobular hepatocyte hypertrophy in mice and rats, and the incidence of bile duct hyperplasia and centrilobular degeneration in female rats was significantly greater than in controls. A no-observed-adverse-effect level (NOAEL) of 30 ppm DDS in the diet (1.5 mg/kg body weight) was established for rats. DDS was not carcinogenic in these studies.

Doses in rodent cancer studies: sorting fact from fiction

The belief that rodent cancer bioassays predict for human cancers is a fundamental public health precept based on sound biological principles. Nonetheless, it is appropriate to periodically debate this point as scientific understanding of cancer causation advances. This presentation addresses one of the many factors that determines the predictive value of rodent tumor bioassay results for human health. This is the issue of dose. Examination of several recent National Toxicology Program (NTP) studies demonstrates that the applied dose often far overestimates the actual effective dose, or maximum blood concentration attained in a rodent, when compared with similar relationships in humans. Further examination of the NTP database on rodent toxicity and carcinogenicity studies revealed summary information on factors that were pivotal in prechronic studies for selecting doses for chronic studies. Contrary to popular belief, target organ toxicity was a determining factor in only about half of the studies. The typically minimal nature of the lesions which limit doses for chronic studies is described for several common target sites. Taken together, these facts paint a far different picture than the common public perception of the "massive" doses used in chronic rodent studies and suggest that, in some cases, dose limitations are actually so severe as to limit the sensitivity of a chronic bioassay to detect a carcinogenic effect.

Effects of glutaraldehyde in a 2-year inhalation study in rats and mice

Whole-body inhalation toxicology and carcinogenicity studies were performed with the widely used fixative and cold-sterilant glutaraldehyde. Groups of 50 male and female F344/N rats and B6C3F(1) mice were exposed to glutaraldehyde (rats: 0, 250, 500, or 750 ppb; mice: 0, 62.5, 125, or 250 ppb) 6 h/day, 5 days/week, for 104 weeks. Survival of 500- and 750-ppb female rats was less than that of controls. Mean body weights of all exposed groups of male rats, 500- and 750-ppb female rats, and 250-ppb female mice were generally less than those of controls. No exposure-related neoplastic lesions were observed in either rats or mice. Non-neoplastic lesions were limited primarily to the most anterior region of the nasal cavity. In rats, hyperplasia and inflammation of the squamous epithelium; hyperplasia, goblet cell hyperplasia, inflammation, and squamous metaplasia of the respiratory epithelium; and hyaline degeneration of the olfactory epithelium were observed. In mice, the nasal lesions were qualitatively similar to those in rats. Squamous metaplasia of the respiratory epithelium was observed in both sexes of mice while female mice also had inflammation and hyaline degeneration of the respiratory epithelium. In contrast to the nasal carcinogen formaldehyde, no neoplastic lesions were observed after inhalation exposure to glutaraldehyde. However, exposure to glutaraldehyde resulted in considerable non-neoplastic lesions in the noses of rats and mice.

Toxicity of 3,3',4,4'-tetrachloroazoxybenzene in rats and mice

The toxicity of 3,3',4,4'-tetrachloroazoxybenzene (TCAOB) was evaluated in 13-week gavage studies in male and female F344/N rats and B6C3F1 mice. In addition to histopathology, evaluations included clinical chemistry, hematology, thyroid hormone analyses, and effects on sperm morphology and estrous cycle length. Groups of 10 rats and 10 mice of each sex were exposed to TCAOB at dose levels of 0, 0.1, 1, 3, 10, or 30 mg/kg 5 days a week for 13 weeks. In the rat studies, the major effects included death in the 30 mg TCAOB/kg dose group; at lower exposure levels, a decrease in body weight gain, a decrease in thymus weight, an increase in liver weight, an increase in hematopoietic cell proliferation in the spleen and liver, a responsive anemia, a decrease in platelet counts, a chronic active inflammation of the vasculature in the lung, an increase in cardiomyopathy, hyperplasia of the forestomach, and a marked decrease in circulating thyroxine concentrations were observed. In male rats a decrease in sperm motility in the epididymides was observed. In addition, in female rats an increase in lung, spleen, kidney, and heart weights and nephropathy was observed. Furthermore, the estrous cycle length was increased. In the mouse studies, the major effects for males and females included a decrease in thymus weights, an increase in liver and kidney weights, centrilobular hypertrophy in the liver, hematopoietic cell proliferation, hyperplasia of the forestomach, and dilatation of hair follicles. The spectrum of effects in both rats and mice after exposure to TCAOB indicates that dioxin-like effects occur in addition to effects that have not been observed with dioxin-like compounds. No no-observed-adverse-effect level was reached in male or female rats or mice.

Inhalation toxicity and carcinogenicity studies of cobalt sulfate

Cobalt sulfate is a water-soluble cobalt salt with a variety of industrial and agricultural uses. Several cobalt compounds have induced sarcomas at injection sites in animals, and reports have suggested that exposure to cobalt-containing materials may cause lung cancer in humans. The present studies were done because no adequate rodent carcinogenicity studies had been performed with a soluble cobalt salt using a route relevant to occupational exposures. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to aerosols containing 0, 0.3, 1.0, or 3.0 mg/m3 cobalt sulfate hexahydrate, 6 h/day, 5 days/week, for 104 weeks. Survival and body weights of exposed rats and mice were generally unaffected by the exposures. In rats, proteinosis, alveolar epithelial metaplasia, granulomatous alveolar inflammation, and interstitial fibrosis were observed in the lung in all exposed groups. Nonneoplastic lesions of the nose and larynx were also attributed to exposure to all concentrations of cobalt sulfate. In 3.0 mg/m3 male rats and in female rats exposed to 1.0 or 3.0 mg/m3, the incidences of alveolar/bronchiolar neoplasms were increased over those in the control groups. Lung tumors occurred with significant positive trends in both sexes. The incidences of adrenal pheochromocytoma in 1.0 mg/m3 male rats and in 3.0 mg/m3 female rats were increased. Nonneoplastic lesions of the respiratory tract were less severe in mice than in rats. In mice, alveolar/bronchiolar neoplasms in 3.0 mg/m3 males and females were greater than those in the controls, and lung tumors occurred with significantly positive trends. Male mice had liver lesions consistent with a Helicobacter hepaticus infection. Incidences of liver hemangiosarcomas were increased in exposed groups of male mice; however, because of the infection, no conclusion could be reached concerning an association between liver hemangiosarcomas and cobalt sulfate. In summary, exposure to cobalt sulfate by inhalation resulted in increased incidence of alveolar/bronchiolar neoplasms and a spectrum of inflammatory, fibrotic, and proliferative lesions in the respiratory tracts of male and female rats and mice. Adrenal pheochromocytomas were increased in female rats, and possibly in male rats.

Toxicity of 3,3',4,4'-tetrachloroazobenzene in rats and mice

The toxicity of 3,3',4,4'-tetrachloroazobenzene (TCAB) was evaluated in 13-week gavage studies in male and female F344/N rats and B6C3F1 mice. In addition to histopathology, evaluations included clinical chemistry, hematology, thyroid hormone analyses, and reproductive parameters. Groups of 10 rats and 10 mice of each sex were exposed to TCAB at dose levels of 0, 0.1, 1, 3, 10, or 30 mg/kg for 5 days a week for 13 weeks. In the rat studies, the major effects for both males and females included a 10% decrease in terminal body weight at 30 mg/kg/day, an increase in hematopoietic cell proliferation in the spleen at 10 and 30 mg/kg/day, and a responsive anemia at 10 and 30 mg/kg/day. A 15 to 30% decrease in platelet counts and a 20 to 40% decrease in thymus weights was observed at 10 and 30 mg/kg/day. An increase in liver weight up to 15% was found at 3 mg/kg/day and higher doses in males and at 10 and 30 mg/kg/day in females, respectively. An increase in spleen weights up to 15% was observed at 10 and 30 mg/kg/day in males and at 30 mg/kg/day in females. A marked decrease in circulating total thyroxine (TT4) was found in both males and females at all dose levels tested. TT4 could hardly be detected at 10 and 30 mg TCAB/kg/day. In addition, hyperplasia of the forestomach was increased at 3 mg/kg/day and higher doses in males and at 30 mg/kg/day in females. In the mouse studies, an increase in liver and spleen weight was observed up to approximately 25% in both males and females at 10 and 30 mg/kg/day. Hyperplasia of the forestomach was observed at 1 mg/kg/day and higher doses in both males and females. In males, a 30% decrease in thymus weights at 30 mg/kg/day and a 60% decrease in epididymal sperm density at 3 and 30 mg/kg/day was observed. Also in males, centrilobular hypertrophy of hepatocytes and an increase in hematopoietic cell proliferation in the spleen was observed at 3 mg/kg/day and higher doses. Based on the current study and information in the literature, TCAB has dioxin-like properties. Comparison of the effects of TCAB in the present study and in the literature to those with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) indicates that TCAB is from two to six orders of magnitude less potent than TCDD depending on the end point.

Toxicology and carcinogenesis studies of pentachlorophenol in rats

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.

Current approaches toward chemical mixture studies at the National Institute of Environmental Health Sciences and the U.S. National Toxicology Program

The National Institute of Environmental Health Sciences (NIEHS) has several new initiatives involving chemical mixtures and has recognized the need to develop new experimental approaches to enhance our efforts in this area. Responding to recent increases in nominations of complex occupational exposures for toxicologic assessment by the U.S. National Toxicology Program, the NIEHS and the National Institute for Occupational Safety and Health have begun a program to characterize exposures through field studies, identify biomarkers of exposure in workers, and recreate relevant mixed exposures in a laboratory setting. A second initiative with the National Center for Environmental Health/Centers for Disease Control and Prevention will examine blood samples from the U.S. National Health and Nutrition Examination Survey population surveys for selected endocrine-disrupting agents and for common patterns of persistent xenobiotics, providing critical information for the design of animal studies to assess risks of relevant chemical mixtures to humans. New toxicology testing methods (lower cost, faster) will enhance our ability to study chemical mixtures (e.g., dioxin and dioxinlike chemicals, combination AIDS therapies). Ongoing method development efforts involve in vitro functional toxicology assays, screens for estrogenic activity, and carcinogenesis studies in transgenic mice. A major scientific initiative with mixtures involves studies of individual and mixtures of dioxin and dioxinlike chemicals to determine if toxic equivalence factors predict carcinogenic potency in traditional and transgenic bioassays. Complementing these studies is an increased emphasis on physiologically based pharmacokinetic modeling, an activity central to the proper interpretation of chemical mixture studies.

Update on national toxicology program (NTP) assays with genetically altered or "transgenic" mice

The NTP is evaluating several lines of genetically altered mice for possible use in identifying and assessing carcinogens. The NIEHS/NTP programs and progress in this area were recently reviewed by the NTP Board of Scientific Counselors (BSC). A number of comments and concerns were raised. This commentary summarizes and responds to the BSC review and offers some thoughts on future directions for this line of research as well as possible ways genetically altered mice might be integrated into a comprehensive testing strategy.

Impact of Helicobacter hepaticus infection in B6C3F1 mice from twelve National Toxicology Program two-year carcinogenesis studies

Male and female B6C3F1 mice from 12 National Toxicology Program (NTP) 2-yr carcinogenesis studies were found to be infected with Helicobacter hepaticus. Many of the male mice from 9 of these studies had an associated hepatitis (affected studies). Helicobacter hepaticus has been reported to be associated with an increased incidence of hepatitis and hepatocellular neoplasms in the A/JCr male mouse. We attempted to determine if the data from the Helicobacter-affected NTP B6C3F1 mouse studies were compromised and unsuitable for cancer hazard identification. The incidences of neoplasms of the liver (both hepatocellular and hemangiosarcoma) but not of other organs in control male B6C3F1 mice were increased in affected studies as compared with control males from unaffected studies. The increased incidence of hepatocellular neoplasms was observed in those males exhibiting H. hepaticus-associated hepatitis. Other observations further differentiated control male mice from affected and unaffected studies. H-ras codon 61 CAA to AAA mutations were less common in liver neoplasms from males from affected studies as compared with historical and study controls. In addition, increases in cell proliferation rates and apoptosis were observed in the livers of male mice with H. hepaticus-associated hepatitis. These data support the hypothesis that the increased incidence of liver neoplasms is associated with H. hepaticus and that hepatitis may be important in the pathogenesis. Therefore, interpretation of carcinogenic effects in the liver of B6C3F1 mice may be confounded if there is H. hepaticus-associated hepatitis.

Selective inhibition of cytochrome P450 2E1 in vivo and in vitro with trans-1,2-dichloroethylene

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1, on the catalytic activities and total content of hepatic P450 was determined in vivo and in vitro. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 h postdosing, and total P450 content and the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, P450 2E1, and P450 3A were determined. The lowest dose of DCE that yielded maximal inactivation of P450 2E1 was found to be 100 mg/kg. Significant decreases in total content of P450 or the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, and P450 3A were not observed during the 24 h following administration of DCE (100 mg/kg ip), but P450 2E1 activity was diminished about 65% at 2 and 5 h after DCE treatment and returned to control levels at 24 h. Additionally, there was little or no significant effect on the activities of hepatic cytosolic alcohol dehydrogenase or mitochondrial or microsomal aldehyde dehydrogenases 5 h postdosing. DCE showed the same selectivity for P450 inactivation in vitro, and P450 2E1 activity was inhibited by >80% without affecting the other isozymes. However, DCE (5 mM) also proved to be a good competitive inhibitor of the probe activities of P450 1A2 and P450 2C6. The in vivo inhibition of P450 2E1 was accompanied by decreases in the levels of the immunoreactive protein, and an additional immunoreactive band appeared at ca. 30 kDa in the Western blot of microsomes from DCE-treated rats, possibly arising from proteolytic degradation of P450 2E1 protein after covalent modification by the inhibitor. DCE is an effective, relatively nontoxic inhibitor of P450 2E1 in vivo and in vitro that has greater selectivity than other agents currently used.

The National Toxicology Program evaluation of genetically altered mice as predictive models for identifying carcinogens

National Institute of Environmental Health Sciences researchers are exploring the utility of genetically altered mice to study mechanisms of carcinogenesis. Two of these mouse models, the Tg.AC (carrier of an activated mouse H-ras oncogene) and the p53+/- (heterozygous for the wild-type tumor suppressor gene Trp53), have genetic alterations that appear to hasten their expression of chemically induced tumors. These 2 models have been proposed as a basis for new strategies for identifying chemical carcinogens and for assessing risk. The National Toxicology Program (NTP) is conducting a series of studies with these 2 genetically altered strains to further examine their strengths and weaknesses for identification of documented rodent and human carcinogens. In this first evaluation, candidates for study were drawn from the NTP historical database of 2-yr rodent carcinogenicity studies and the open literature (primarily for drugs). Results with this first set of 11 chemicals tested in genetically altered mice, compared with previous findings in the traditional 2-yr rodent assays and literature on human tumor findings, appear to support the premise advanced by Tennant et al that these models have the potential to serve as more rapid and less expensive test systems to identify carcinogens.

Pharmacodynamic responses of F344 rats to the mouse hepatocarcinogen oxazepam in a 90-day feed study

Oxazepam (Serax) is a widely used benzodiazepine anxiolytic agent and a metabolite of other benzodiazepines such as Valium and Librium. Chronic feeding studies indicated that oxazepam is an hepatocarcinogen in B6C3F1 mice but did not increase hepatic tumors in F344 rats. The present study was performed to compare the hepatic responses of rats with our previous findings in mice to explore the reason(s) for the dramatic differences in tumor response between the two species. Male F344 rats (10 per dose-time group) received diets containing oxazepam at 0, 25, 125, 2500, and 5000 ppm. Hepatocyte labeling indices were measured immunohistochemically by PCNA and BrDU during the last 7 days before sacrifices after 15, 30, 45, and 90 days of dosing. Serum oxazepam was determined by reverse phase HPLC. Results indicated that oxazepam induced significant liver weight increases in a dose-related fashion by 15 days, which remained elevated for the entire study. No important clinical chemistry or pathology changes were noted except those related to hypertrophy. Cell proliferation was significantly increased in a dose-related manner by the 15- and 30-day timepoint in the 2500 and 5000 ppm groups. The most significant finding in the present study of oxazepam was plasma levels of the parent compound. Plasma levels in rats were dramatically lower than in B6C3F1 mice exposed to oxazepam in studies conducted earlier at the same dose levels. These results suggest that the early responses of rats and mice to oxazepam, such as cell proliferation and clinical chemistry parameters, are similar. Our previous studies demonstrated that oxazepam metabolites are excreted in the urine of rats, similar to humans, whereas mice excrete oxazepam metabolites in bile allowing enterohepatic recirculation, which results in high plasma levels of oxazepam. These data indicate that the rat excretes oxazepam kinetically (rate and route) similar to humans, but the mouse produces metabolites similar to humans.

Toxicity and carcinogenicity studies of oxazepam in the Fischer 344 rat

Oxazepam and related benzodiazepines are used in the treatment of anxiety. Carcinogenicity studies of oxazepam were performed with the F344 rat because of marked differences in tumor responses observed in NTP studies with B6C3F1 and Swiss-Webster mice compared to the results of Sprague-Dawley rat studies submitted to the FDA by a manufacturer to support registration of the drug. Groups of 50 male and 50 female F344/N rats were fed diets containing 0, 625, 2500, or 5000 ppm oxazepam for up to 105 weeks. A stop-exposure group of 50 males and 50 females received 10,000 ppm oxazepam in diet for 26 weeks, after which animals received control diet. All 5000- and 10, 000-ppm stop-exposure males died before the end of the study. Survival of 2500-ppm males and females was lower than that of controls. Body weight gains of 2500- and 5000-ppm males and females were less than those of controls. Male rats exposed to 2500 ppm had an increased incidence of renal tubule adenoma and hyperplasia. In addition, the incidences of renal tubule adenoma and hyperplasia were increased in the 10,000-ppm stop-exposure group. The incidences of nephropathy in exposed females were greater than those in controls, and the severity of nephropathy increased in exposed males. Epithelial hyperplasia and chronic inflammation of the nonglandular stomach were increased in males given 2500 and 5000 ppm and the incidence of ulcers of the nonglandular stomach in 2500-ppm males was also greater than that in controls. In males exposed to 5000 ppm, mineralization of the glandular stomach and erosion of the duodenum were observed. In females exposed to 2500 ppm, the incidences of epithelial hyperplasia, chronic inflammation, and ulcers of the nonglandular stomach and the incidence of erosion in the glandular stomach were increased. The incidences of centrilobular hepatocyte hypertrophy in males and females given 2500 and 5000 ppm were greater than those in controls. In summary, there was equivocal evidence of carcinogenicity in males based on increased renal tubule adenomas in groups which also had significantly enhanced nephropathy. There was no evidence of carcinogenicity of oxazepam in females given a diet containing 625, 2500, or 5000 ppm for 2 years or 10,000 ppm for 6 months.

Do endogenous volatile organic chemicals measured in breath reflect and maintain CYP2E1 levels in vivo?

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1 (CYP2E1), on the composition and quantity of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with hepatic P450 activity and content. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 hr postdosing with DCE (100 mg/kg ip), and total P450 content and the activity of CYP2E1 was determined. Breath was collected from parallel groups of rats predose and at several intervals that encompassed the time points for rats euthanized for microsome preparation. Over 100 breath components were identified by GC/MS and quantitated by GC/FID. The overall change in the profile of breath VOCs resulting from administration of DCE was striking. An increase of approximately 1000% was measured in the mass of non-DCE-derived VOCs exhaled 4-6 hr after dosing, but there was no increase in hepatic lipid peroxidation. In addition to hexane, short-chain methyl ketones were particularly affected, and percentage increases in response to inhibition were inversely related to chain length, with acetone and 2-butanone > 2-pentanone >> 2-hexanone > 2-heptanone. There were no statistically significant decreases in total content of P450, but the activity of CYP2E1 was diminished about 65% at 2 and 5 hr after DCE treatment. However, 24 hr after inhibitor administration the total mass of VOCs expired was only marginally elevated above baseline and CYP2E1 activity was not significantly different from that of untreated rats. The compounds most markedly increased upon inhibition of CYP2E1 are also excellent inducers of that isozyme, and this finding is consistent with the hypothesis that these chemicals are important to the normal homeostasis of CYP2E1. The increase in breath components observed following inhibition of CYP2E1 suggests that VOCs in breath can reflect the activity of that isozyme in vivo.

Workshop overview. National Toxicology Program Studies: principles of dose selection and applications to mechanistic based risk assessment

A workshop entitled "NTP Studies: Principles of Dose Selection and Applications to Mechanistic Based Risk Assessment" was held at the 34th Annual Meeting of the Society of Toxicology in Baltimore, Maryland. The purpose of the workshop was to provide an overview of factors currently considered important in the selection of doses for NTP studies, to describe some of the confounding factors that can result from the indiscriminate use of bioassay data in quantitative risk assessment, and to suggest ways in which information from mechanistic studies or studies of biomarkers of exposure or effect might be used to better advantage in risk assessment.

Thirteen-week inhalation toxicity of 2- and 4-chloronitrobenzene in F344/N rats and B6C3F1 mice

Toxicity studies were performed by exposing F344/N rats and B6C3F1 mice to 2- and 4-chloronitrobenzene (CNB) by whole-body inhalation 6 hr/day, 5 days/week, for 13 weeks. Animals were evaluated for clinical chemistry (rats), hematology (rats), histopathology, and body/organ weights. Exposure concentrations were 0, 1.1, 2.3, 4.5, 9, and 18 ppm for 2-CNB and 0, 1.5, 3, 6, 12, and 24 ppm for 4-CNB. All rats in the 2-CNB study survived until the end of the study. Two male mice in the 18-ppm group in the 2-CNB study, however, died during Week 12; no deaths attributable to 4-CNB exposure occurred in rats or mice. In both studies, the mean body weight gains of exposed animals were similar to those of the respective controls. In rats, inhalation exposure to 2- or 4-CNB resulted in methemoglobinemia leading to a regenerative anemia and a variety of tissue changes secondary to the oxidative erythrocyte injury. In the 2-CNB study, methemoglobinemia resulted in a normocytic, normochromic, responsive anemia, whereas with 4-CNB, the methemoglobinemia was more severe and resulted in a macrocytic, hyperchromic, responsive anemia. Alterations of erythrocyte morphology were observed in both studies; changes included Heinz bodies, poikilocytes, and polychromasia. In rats, both isomers caused increases in serum activities of alanine aminotransferase and sorbitol dehydrogenase and increased bile acid concentrations. Microscopic liver changes included hemosiderin deposition in Kupffer cells (rats and mice exposed to 4-CNB), hepatocytomegaly (mice), and cytoplasmic basophilia (rats). Hepatocellular necrosis and chronic inflammation observed in mice were rather specific to the 2-CNB isomer, as only slight evidence of focal necrosis in the liver was observed in mice exposed to 4-CNB. Splenic lesions included hemosiderin accumulation capsular fibrosis, and increased hematopoietic cell proliferation. Increased bone marrow hemosiderin and hematopoietic cell proliferation and kidney tubule hemosiderin deposition were also observed. Other findings, attributed to chemical exposure but not to the hematotoxicity, were described. Lesions included hyaline droplet nephropathy and degeneration of the testis in male rats exposed to 4-CNB, inflammation of the harderian gland in rats exposed to 4-CNB, hyperplasia of the nasal cavity epithelium in rats exposed to 2-CNB, and hyperplasia of the forestomach epithelium in mice exposed to 4-CNB; these lesions have not been described previously in studies with these chemicals. Based on the exposure concentrations evaluated, A no-observed-adverse-effect level (NOAEL) for histopathological injury in mice was 4.5 ppm for 2-chloronitrobenzene and 6 ppm for 4-chloronitrobenzene; a NOAEL was not determined for rats.

Toxicity and carcinogenicity of delta 9-tetrahydrocannabinol in Fischer rats and B6C3F1 mice

delta 9-Tetrahydrocannabinol (delta 9-THC) was studied for potential carcinogenicity in rodents because it is the principal psychoactive ingredient in marihuana and it has potential medicinal uses. delta 9-THC in corn oil was administered by gavage to groups of male and female Fischer rats and B6C3F1 mice at 0, 5, 15, 50, 150, or 500 mg/kg, 5 days a week for 13 weeks and for 13-week plus a 9-week recovery period, and to groups of rats at 0, 12.5, or 50 mg/kg and mice at 0, 125, 250, or 500 mg/kg, 5 times a week for 2 years. In all studies, mean body weights of dosed male and female rats and mice were lower than controls but feed consumptions were similar. Convulsions and hyperactivity were observed in dosed rats and mice; the onset and frequency were dose related. Serum FSH and LH levels in all dosed male rats and corticosterone levels in 25 mg/kg female rats were significantly higher than controls at 15 months in the 2-year studies. delta 9-THC administration for 13 weeks induced testicular atrophy and uterine and ovarian hypoplasia; the lesions persisted in a 9-week recovery period. In the 2-year studies, survival of dosed rats was higher than controls; that of mice was similar to controls. Incidences of testicular interstitial cell, pancreas and pituitary gland adenomas in male rats, mammary gland fibroadenoma and uterus stromal polyp in female rats, and hepatocellular adenoma/carcinoma in male and female mice were reduced in a dose-related manner. Decreased tumor incidences may be at least in part due to reduced body weights of dosed animals. Incidences of thyroid gland follicular cell hyperplasia were increased in all dosed groups of male and female mice, and follicular cell adenomas were significantly increased in the 125 mg/kg group of males, but there was no evidence of a dose-related trend in proliferative lesions of the thyroid. There was no evidence that delta 9-THC was carcinogenic in rats or mice.

Early changes in sex hormones are not evident in mice exposed to the uterine carcinogens chloroethane or bromoethane

Chloroethane and bromoethane have been shown to cause a marked uterine tumor response in B6C3F1 mice exposed for 2 years. These chemicals are nearly unique in this regard among the nearly 400 chemicals studied by the National Toxicology Program, and the reasons for this carcinogenic activity are unclear. The possible relationship of changes in blood concentrations of sex hormones to this response was evaluated by examining the estrous cycle of mice prior to and during a 21-day exposure to concentrations of the haloethanes which resulted in the tumorigenic response in the 2-year studies. Serum concentrations of estradiol and progesterone were determined at the termination of the exposures and compared to exposure group and stage of the estrous cycle. No consistent patterns of change were found in estrous cyclicity or in blood concentrations of sex hormones. Thus, the findings suggest that early changes in circulating sex hormones are not important contributing factors in the uterine neoplasia caused by these chemicals.

Carcinogenicity studies of oxazepam in mice

Oxazepam is a benzodiazepine widely used as a sedative-hypnotic and antianxiety drug. In chronic studies, groups of 60 male and 60 female Swiss-Webster (SW) or B6C3F1 mice received oxazepam in feed at concentrations of 0,2500, or 5000 ppm. Additional groups of 60 male and female B6C3F1 mice received 125 ppm in feed to allow for study of mice with serum concentrations of oxazepam similar to those achieved in humans taking a therapeutic dose. At 57 weeks, treatment-related mortality of exposed SW mice caused the study to be terminated. Enhanced systemic amyloidosis contributing to heart failure was considered the principal cause of death. Hepatocellular adenomas and carcinomas were increased in exposed SW mice. Survival of B6C3F1 mice receiving 2500 and 5000 ppm oxazepam was also lower than that of controls. Early deaths were due to increased incidences of hepatoblastoma and hepatocellular carcinoma, and nearly all mice receiving 2500 or 5000 ppm developed hepatocellular neoplasia. An increase in follicular cell hyperplasia of the thyroid gland occurred in all exposed groups of B6C3F1 mice, and thyroid gland follicular cell adenoma was increased in exposed females. Further studies of the capacity of oxazepam to induce liver cell mitogenesis and an evaluation of the frequency of activated H- and K-ras oncogenes in the liver tumors of B6C3F1 mice has shown that many of the neoplastic and nonneoplastic responses of mice to oxazepam resemble those observed with phenobarbital.

Toxicity and carcinogenicity of riddelliine following 13 weeks of treatment to rats and mice

Toxicity studies of riddelliine, a member of a class of pyrrolizidine alkaloids, were conducted because riddelliine has been found to contaminate human food sources. Groups of male and female Fischer rats were administered riddelliine by gavage in phosphate buffer at doses up to 10 mg/kg, and B6C3F1 mice at doses up to 25 mg/kg, five times a week. The animals were necropsied after 13 weeks of treatment or after a 7 or 14 week recovery period. Body weight gains were inversely related to dose in both rats and mice. Body weight of the 1.0 and 3.3 mg/kg female rats and 10.0 and 25.0 mg/kg mice remained depressed during the 14 week recovery period. At 13 weeks, significant findings included dose-related hepatopathy and intravascular macrophage accumulation in rats and hepatocytomegaly in mice. During the 14 week recovery period these lesions persisted and hepatic foci of cellular alteration in male rats and bile duct proliferation in female rats and male and female mice increased in severity. In the 10 mg/kg group of female rats adenomas of the liver occurred in two of ten at 13 weeks and in one of five at the 14 week recovery period. In separate studies, the frequency of micronucleated erythrocytes in peripheral blood was increased in male mice administered a single dose (150 mg/kg) of riddelliine. Increases in unscheduled DNA and S-phase syntheses were detected in primary hepatocytes from rats and mice treated with riddelliine at doses up to 25.0 mg/kg for 5 or 30 days. In mating trials in rats and mice, pup weights from treated dams at birth and during suckling were lower than controls. Thus, riddelliine is genotoxic and carcinogenic and may cross the placenta and/or be found in milk, causing developmental toxicity in rodents.

Low frequency of H-ras mutations in hepatocellular adenomas and carcinomas and in hepatoblastomas from B6C3F1 mice exposed to oxazepam in the diet

Oxazepam has been the subject of recent toxicological and carcinogenesis studies because it is a commonly prescribed tranquilizer and has been shown to cause tumors in rodents. In this study, male and female B6C3F1 mice received 0, 125, 2500 or 5000 p.p.m. oxazepam in the diet for up to 2 years. Hepatocellular adenomas and carcinomas, as well as hepatoblastomas, which developed in these mice, were examined for the presence of activated ras proto-oncogenes. DNA was isolated from 20 or more tumors from each exposure group and analyzed by oligonucleotide hybridization, single-stranded conformation polymorphism analysis and direct sequencing of PCR-amplified H-ras gene fragments for codon 61 mutations. Thirteen of 37 (35%) hepatocellular adenomas and carcinomas from the 125 p.p.m. exposure group had mutations in codon 61, while mutations were detected in only 2 of 25 or 8% of the liver tumors from the 2500 p.p.m. exposure group and none of the 22 tumors from the 5000 p.p.m. group. This compares to 63% of 126 historical control liver tumors and 55% of 20 liver tumors from unexposed B6C3F1 mice in this study. In addition, 12 hepatoblastomas from the two high dose groups were examined for H-ras mutations at codon 61, but none were detected. No tumor DNAs from any of the exposure groups tested had mutations in codons 12, 13 or 117 of the H-ras gene or codons 12 or 13 of the K-ras gene, the other known hotspots for ras activation in mouse liver tumors. These results, together with those from the National Toxicology Program study showing no evidence of cytotoxicity or genotoxicity by oxazepam, suggest that oxazepam preferentially promotes cells that have activating lesions other than ras.

Comparative toxicities of o-, m-, and p-nitrotoluene in 13-week feed studies in F344 rats and B6C3F1 mice

Nitrotoluenes are high-production-volume chemicals used in the synthesis of agricultural chemicals and in various dyes. Because of differences in the metabolism of the three isomers and their capabilities to bind to DNA, comparative toxicity studies of o-, m-, and p-nitrotoluene were conducted in F344 rats and B6C3F1 mice. o-, m-, or p-Nitrotoluene was administered in the feed to male and female rats and mice at doses ranging from 625 to 10,000 ppm for 13 weeks. These doses delivered approximately 40 to 700 mg/kg body wt/day for rats and 100 to 1700 mg/kg/day for mice. There were no treatment-related effects on survival in any of the studies. Decreased body weights relative to controls occurred in dosed rats and mice in all studies at the higher dose levels and were most pronounced in rats receiving o-nitrotoluene. Mesotheliomas of the tunica vaginalis were observed in 3 of 10 male rats receiving o-nitrotoluene at 5000 ppm, and mesothelial cell hyperplasia was observed in 2 of 10 male rats receiving o-nitrotoluene at 10,000 ppm. Kidney toxicity was observed in male rats receiving o-, m-, or p-nitrotoluene and included hyaline droplet nephropathy and an associated increase in the renal concentration of alpha 2U-globulin. Evidence of liver toxicity in the male rats receiving o-nitrotoluene included hepatocyte vacuolization, oval cell hyperplasia, and increased serum bile acids, sorbitol dehydrogenase, and alanine aminotransferase. Although there was no histopathologic evidence of hepatic toxicity in male or female rats given the m- or p-isomers or in female rats given the o-isomer, treatment-related hepatic effects were detected in these groups, as measured by an increase in the relative liver weights and by elevations in serum bile acids and liver-specific enzymes. The spleens of treated male and female rats had a mild increase in hematopoiesis, hemosiderin deposition, and/or congestion. These splenic changes were slightly more prominent in rats administered the o- and p-isomers. Administration of o-, m-, or p-nitrotoluene impaired testicular function in the rat, as shown by testicular degeneration and reduction in the density, motility, and number of sperm cells. Administration of each isomer to rats caused increases in the length of the estrus cycle. The only histopathologic evidence for treatment-related toxicity in mice in the 13-week studies occurred in animals receiving the o-nitrotoluene isomer where the chemical caused degeneration and metaplasia of the olfactory epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicity of diethanolamine. 1. Drinking water and topical application exposures in F344 rats

Toxicology studies of diethanolamine were conducted in male and female F344 rats for 13 weeks' duration to characterize and compare effects of exposure in the drinking water with those caused by topical application. Doses of diethanolamine ranged from 160 to 5000 ppm in the drinking water study (equivalent to daily doses of 25-440 mg kg-1 in males and 15-240 mg kg-1 in females) and from 32 to 500 mg kg-1 in the topical application study. Dose-dependent toxic effects due to exposure to diethanolamine included hematological changes (a poorly regenerative, microcytic anemia), as well as toxic responses in the kidney (increased weight, tubular necrosis, decreased renal function, and/or tubular mineralization), brain and spinal cord (demyelination), testis (degeneration of the seminiferous tubules) and skin (site of application: ulceration, inflammation, hyperkeratosis and acanthosis). A no-observed-adverse-effect level was not achieved for hematological changes, nephropathy or hyperkeratosis of the skin. Differences in dose-response between the drinking water and topical application exposures were attributed largely to the limited dermal absorption of this chemical.

Early responses of the liver of B6C3F1 mice to the hepatocarcinogen oxazepam

Oxazepam has recently been shown to induce hepatocarcinogenicity in B6C3F1 mice. Due to the widespread human exposure to this anxiolytic compound and other structurally similar benzodiazepines, we conducted toxicity and cell proliferation studies on oxazepam to determine possible mechanisms whereby this nonmutagenic chemical may have exerted a carcinogenic effect. Male B6C3F1 mice (10 per dose-time group) received diets containing oxazepam at 0, 25, 125, 2500, and 5000 ppm. Mice were treated for 15, 30, 45, or 90 days, at which time they were evaluated for feed consumption, liver/body weight ratios, clinical pathology, serum oxazepam levels, and histopathology of the liver. During the final 7 days before sacrifice, the mice were exposed to BrDU via osmotic minipump to quantify hepatocellular replicative DNA synthesis. Few effects were observed resulting from chronic exposure to oxazepam other than statistically significant, dose-related increases in liver/body weight ratios. Replicative DNA synthesis was significantly increased in a dose-related manner at the 15-day time point in the 125, 2500, and 5000 ppm dose groups, and attained levels of four- to five-fold above control levels which returned to control levels by 30 days. The lack of significant toxicity, sustained increased liver/body weight ratios, and the rapid and transient induction of replicative DNA synthesis are similar to the effects reported for exposure to another widely used therapeutic agent shown to be a nongenotoxic carcinogen, phenobarbital.

Toxicity of diethanolamine. 2. Drinking water and topical application exposures in B6C3F1 mice

Toxicology studies of diethanolamine were conducted in male and female B6C3F1 mice to characterize and compare effects of exposure in the drinking water with those caused by topical application and to compare responses in mice to those observed in rats. Each study consisted of five dose groups plus controls and the size of each group was 10 animals per sex. Doses of diethanolamine ranged from 630 to 10,000 ppm in the drinking water study (approximately equivalent to daily doses of 100-1700 mg kg-1 in males and 140-1100 mg kg-1 in females) and from 80 to 1250 mg kg-1 in the topical application study. Exposure to diethanolamine caused dose-dependent toxic effects in the liver (hepatocellular cytological alterations and necrosis), kidney (nephropathy and tubular epithelial necrosis in males), heart (cardiac myocyte degeneration) and skin (site of application: ulceration, inflammation, hyperkeratosis, and acanthosis). Cytological alterations in the liver consisted of multiple hepatocyte changes, including enlarged cells that were frequently multinucleated, increased nuclear pleomorphism, increased eosinophilia and disruption of hepatic cords. A no-observed-adverse-effect level (NOAEL) was not achieved for hepatocellular cytological alterations or for acanthosis in the skin.

Comparative carcinogenicity of polybrominated biphenyls with or without perinatal exposure in rats and mice

Chronic toxicity and carcinogenicity studies of a polybrominated biphenyl mixture (PBB) were conducted in F344/N rats and B6C3F1 mice of each sex. The major objective of the study was to determine if exposure to PBB during the perinatal period, in addition to conventional exposure of animals for 2 years, enhances the sensitivity of the bioassay to identify the carcinogenic potential of this chemical. The studies were designed to determine the toxic and carcinogenic effects of dietary PBB in rats and mice receiving (i) perinatal exposure up to 8 weeks of age followed by control diet for 2 years, (ii) exposure for 2 years beginning at the age of 8 weeks, and (iii) combined perinatal/adult exposure to PBB (perinatal exposure to 8 weeks of age followed by adult exposure for 2 years). During the perinatal period, rats were exposed to PBB at dose levels ranging from 1 to 10 ppm and adult exposure concentrations ranged from 3 to 30 ppm in the diet. In the mice, the dose levels ranged from 3 to 30 ppm in both perinatal and adult exposure portions of the chronic studies. A total of eight dose groups (including controls) were used with 60 animals in each group. Liver was the major target organ of PBB toxicity. Perinatal exposure alone (through dietary administration of 10 ppm PBB to the dams) had no effect on the incidences of neoplasms in female F344/N rats, but in male rats, perinatal exposure was associated with a marginally increased incidence of hepatocellular adenomas that may have been related to chemical administration. In male and female B6C3F1 mice, perinatal exposure to 30 ppm PBB resulted in significantly increased incidences of hepatocellular neoplasms. In adult-only dietary exposure studies, PBB was carcinogenic in male and female F344/N rats and male and female B6C3F1 mice based on increased incidences of hepatocellular neoplasms. Combined perinatal and adult dietary exposure to PBB confirmed the findings of the adult-only exposures for the increased incidences of hepatocellular neoplasms in rats and mice. In male rats, there were no enhancing effects of combined perinatal and adult exposure. However, perinatal exposure enhanced the susceptibility of female rats receiving adult exposure of 10 or 30 ppm to the induction of liver neoplasms. For male and female rats, a combined analysis of the incidences of leukemia in the adult-only, perinatal-only, and combined perinatal and adult exposure groups revealed an apparent association between increasing incidences of mononuclear cell leukemia and exposure to PBB.(ABSTRACT TRUNCATED AT 400 WORDS)

Subchronic toxicity of cupric sulfate administered in drinking water and feed to rats and mice

The effects of acute poisoning by cupric sulfate in a number of species are well known; however, the effects of chronic low-level ingestion of cupric sulfate are less well characterized. Because exposure of humans to cupric sulfate may occur through drinking water, food, soil, or ambient air, subchronic toxicity studies were conducted in male and female F344/N rats and B6C3F1 mice by the drinking water (2-week exposure) and dosed feed (2- and 13-week exposure) routes. Animals were evaluated for histopathology, clinical pathology, reproductive toxicity, and tissue metal accumulation, and target organs were examined by a variety of special stains and by electron microscopy to characterize the observed lesions. In drinking water, cupric sulfate concentrations of 300 to 100 ppm produced no ill effects, whereas concentrations of 3000 to 30,000 ppm were lethal to rats and mice within 2 weeks. In feed, cupric sulfate concentrations of 4000 to 16,000 ppm caused significant reductions in body weight gain in both species in the 2- and 13-week studies. Hyperplasia and hyperkeratosis of the limiting ridge of the forestomach were present in both species in the 2- and 13-week studies. Rats in the dosed feed studies had a dose-related increase in inflammation in the liver and changes in clinical chemistry parameters which were indicative of hepatocellular damage and cholestasis. Histologic changes in the kidneys of rats consisted of a dose-related increase in the number and size of eosinophilic protein droplets in the epithelial cytoplasm and the lumina of the proximal convoluted tubules. Droplets were larger and more numerous in males than in females. Urinalysis results were suggestive of renal tubular epithelial damage. Iron staining of spleens from treated animals indicated a marked depletion of iron stores in both male and female rats, but not in mice, while hematologic and clinical chemistry alterations in rats in the 13-week study, along with histologic changes in bone in the 2-week dosed feed study, were indicative of a microcytic anemia. Cupric sulfate produced no adverse effects on any of the reproductive parameters measured in rats or mice of either sex. These results indicate that cupric sulfate at high exposure levels is a hepatic and renal toxicant, as well as an inducer of anemia in rodents, with rats more sensitive than mice following subchronic exposure.

Comparative carcinogenicity of 5,5-diphenylhydantoin with or without perinatal exposure in rats and mice

Chronic toxicity and carcinogenicity studies of 5,5-diphenylhydantoin (DPH), were conducted in F344/N rats and B6C3F1 mice of each sex. The major objective of the study was to determine if incorporating exposure to DPH during the perinatal period, in addition to conventional exposure of animals for 2 years, enhances the sensitivity of the bioassay to identify the carcinogenic potential of chemical. The studies were designed to determine the toxic and carcinogenic effects of dietary DPH in rats and mice receiving; (1) the perinatal administration including exposure of maternal animals prior to breeding, through gestation, lactation, weaning, and continued dietary exposure of offspring to the age of 8 weeks followed by control diet for 2 years, (2) exposure for 2 years beginning at the age of 8 weeks, and (3) of combined perinatal/adult exposure to DPH (perinatal exposure to 8 weeks of age followed by the adult exposure for 2 years). During the perinatal period, rats were exposed to DPH at dose levels ranging from 63 to 630 ppm and adult exposure concentrations ranged from 240 to 2400 ppm in diet. In the mice, the perinatal exposure ranged from 21 to 210 ppm in both males and females. In the adult exposure portion of the mouse studies, the dietary levels ranged from 30 to 300 ppm in males and 60 to 600 ppm in females. A total of eight dose groups (including controls) were used with 60 animals in each group. The only effect of perinatal exposure alone on tumor rate was a marginal increase in the incidence of hepatocellular neoplasms in female mice. The adult exposure to DPH significantly increased the incidence of hepatocellular neoplasms in female mice. There were also marginal increases in the incidence of liver tumors in male rats exposed to high DPH dietary concentrations during the adult-only regimen. Combined perinatal and adult dietary exposure to 5,5-diphenylhydantoin confirmed the findings for the increased incidences of hepatocellular neoplasms in male rats and female mice, although combined exposure did not enhance these effects. However, in male mice, perinatal and adult exposure resulted in an increase in the incidence of hepatocellular neoplasms that was not seen when dietary exposure was limited to the adult period only.

Inhalation toxicity of 1,6-hexanediamine dihydrochloride in F344/N rats and B6C3F1 mice

1,6-Hexanediamine (HDA) is a high production volume chemical which is used as an intermediate in the synthesis of paints, resins, inks, and textiles and as a corrosion inhibitor in lubricants. Two- and 13-week studies of the toxicity of the dihydrochloride salt of HDA (HDDC) were conducted in male and female Fischer 344/N rats and B6C3F1 mice using whole-body inhalation exposure. Both species were evaluated for histopathologic and reproductive effects, and rats were examined for clinical chemistry and hematologic changes. In the 2-week inhalation studies, animals were exposed to 10-800 mg HDDC/m3, 6 hr per day. All rats, all female mice, and two of five male mice in the high-exposure group died before the end of the study. Surviving mice in this group had a dose-dependent depression in body weight gain. Clinical signs were primarily related to upper respiratory tract irritation and included dyspnea and nasal discharge in both species. Treatment-related histopathologic lesions included inflammation and necrosis of the laryngeal epithelium of both species and the tracheal epithelium of mice, as well as focal inflammation and ulceration of the respiratory and olfactory nasal mucosa. In the 13-week inhalation studies, animals were exposed to HDDC at concentrations of 1.6-160 mg/m3 for 6 hr per day, 5 days per week. In addition to the base study groups, a supplemental group of rats at each exposure level was included to assess the effect of HDDC on reproduction. No treatment-related changes in organ weights or organ-to-body-weight ratios occurred in rats, and no treatment-related clinical signs or gross lesions were seen in either species. Chemical-related microscopic lesions were limited to the upper respiratory tract (larynx and nasal passages) in the two highest exposure groups and were similar in both species. These lesions included minimal to mild focal erosion, ulceration, inflammation, and hyperplasia of the laryngeal epithelium, in addition to degeneration of the olfactory and respiratory nasal epithelium. HDDC caused no significant changes in sperm morphology or vaginal cytology and no significant adverse effects on reproduction in rats or mice. Hematologic and clinical chemistry changes in rats were minor and sporadic and were not accompanied by related histologic findings. HDDC did not increase the frequency of micronucleated erythrocytes in mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of microencapsulation for toxicology studies. III. Bioavailability of microencapsulated cinnamaldehyde

The bioavailability of microencapsulated cinnamaldehyde (CNMA) was investigated in male F344 rats. Rats were gavaged with CNMA in corn oil using either microencapsulated or the neat chemical at doses of 50, 250, and 500 mg/kg. No differences between the two formulations at any of the doses were found in either CNMA blood concentration profiles or in the rate of urinary hippuric acid excretion. Both formulations showed a low bioavailability (< 20%) at 250 and 500 mg/kg. Regardless of the formulation used, oral gavage of CNMA significantly increased the urinary excretion of hippuric acid. About 75% of the dose of CNMA was metabolized to hippuric acid and recovered in the urine. The total amount of hippuric acid recovered in a 50-hr urinary collection correlated well with the CNMA dose. The data suggest that there was complete release of CNMA from the microcapsules and that microencapsulation of CNMA does not affect its bioavailability or its metabolism. Since CNMA microcapsules are stable in rodent diet, the microencapsulation of CNMA, and perhaps other labile chemicals, will prevent degradation and facilitate the testing of such compounds in toxicology studies.

Toxicokinetics of cinnamaldehyde in F344 rats

The toxicokinetic profile of cinnamaldehyde (CNMA) was investigated in Fischer 344 rats. CNMA was found to be unstable in blood. After iv administration, a large fraction of CNMA was immediately oxidized to cinnamic acid. The biological half-life of CNMA after iv administration was found to be 1.7 hr. After administration by gavage of CNMA at 250 or 500 mg/kg body weight using corn oil as vehicle, the maximum blood concentrations of CNMA were in the order of 1 microgram/ml. These low blood concentrations were maintained over a 24-hr period after a dose of 500 mg/kg, which is relatively long considering the short (1.7 hr) biological half-life of CNMA. The estimated oral bioavailability of CNMA was less than 20% for both the 250 and 500 mg/kg doses. No CNMA was present in blood at any time in rats dosed with 50 mg CNMA/kg body weight. Only a small amount of the administered CNMA was excreted in rat urine as free cinnamic acid or beta-glucuronide-conjugated cinnamic acid. The majority of CNMA administered orally was excreted in urine as hippuric acid within 24 hr. The maximum excretion rate occurred at 8 hr after gavage. Hippuric acid recovered in 50-hr urine samples was found to be directly proportional to the oral dose of CNMA.

Quantitation of cinnamaldehyde and cinnamic acid in blood by HPLC

A rapid and sensitive high performance liquid chromatographic (HPLC) method is described for the quantitation of cinnamaldehyde (CNMA) in rat blood at concentrations of 0.1-100 micrograms/mL. One of the metabolites of CNMA, cinnamic acid, can also be quantified simultaneously. CNMA is unstable in rat blood, probably because of rapid oxidation to cinnamic acid by enzymatic catalysis and nonenzymatic Schiff base formation with free amine groups of blood proteins. The disappearance of CNMA from rat blood follows first-order reaction kinetics with a half-life of 9 min at room temperature. The current analysis method involves the addition of an agent that will prevent CNMA degradation by denaturing protein and competitively blocking nucleophilic addition reactions, resulting in the nearly complete recovery of CNMA from blood. Recovery of cinnamic acid was approximately 80% at concentrations of 1-10 micrograms/mL.

Results and conclusions of the National Toxicology Program's rodent carcinogenicity studies with sodium fluoride

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.

Inhalation of tetranitromethane causes nasal passage irritation and pulmonary carcinogenesis in rodents

Fischer 344 rats and B6C3F1 mice were exposed for 2 years to vapors of tetranitromethane at concentrations below (0.5 ppm) and slightly above (2 or 5 ppm) the current U.S. recommended occupational exposure limit. Under the conditions of exposure of 6 h/day, 5 days/week, tetranitromethane was found to cause mild irritation and hyperplastic lesions in the nasal passages, but not nasal cavity neoplasms were observed. In contrast, nearly all animals exposed to the higher TNM concentrations, and the majority of animals exposed to the lower concentrations developed alveolar/bronchiolar adenoma or carcinoma; squamous cell neoplasms of the lung also occurred in exposed rats. The extent of the lung tumor response, and the low concentrations of tetranitromethane required for this response, are unprecedented in National Toxicology Program (NTP) studies.

Toxicity and carcinogenicity studies of nalidixic acid in rodents

Toxicity and carcinogenicity studies of nalidixic acid, an antimicrobial agent used to treat bacterial infections of the urinary tract, were conducted in F344/N rats and B6C3F1 mice of each sex for 13 weeks or 2 years. In the 13-week studies, nalidixic acid was administered at dietary concentrations ranging from 1,000 to 16,000 ppm. Body weights of both rats and mice were reduced in the groups receiving diet containing 8,000 and 16,000 ppm, and feed consumption of rats in the highest treatment groups was approximately two-thirds that of controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in either species. Two-year studies were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 rats and mice/sex/group. The average daily feed consumption was slightly reduced compared to control groups and resulted in approximate daily doses of 82 or 175 mg nalidixic acid/kg for low dose and high dose rats, and 220 or 475 mg/kg for low dose and high dose mice. Mean body weights of dosed rats and mice were lower than those of controls, except for groups of low dose female rats and male mice. The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly increased compared to those in controls; responses in low dose groups were similar to those in high dose groups. There were decreased incidences of leukemia and mammary gland neoplasms in dosed female rats and of pituitary gland neoplasms in dosed male rats. Subcutaneous tissue fibrosarcomas were marginally increased in dosed male mice. There were no increased incidences of neoplasms in dosed female mice. Under the conditions of these studies, the dietary administration of nalidixic acid was carcinogenic for rats, causing preputial gland or clitoral gland neoplasms in males and females, respectively. The association of subcutaneous neoplasms with administration of nalidixic acid to male mice was equivocal.