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At least 19 recordsLinked to original sources
PubMed2006

NTP toxicology and carcinogenesis studies of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) (CAS No. 57465-28-8) in female Harlan Sprague-Dawley rats (Gavage Studies).

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in adipose tissue resulting in chronic lifetime human exposure. Since human exposure to DLCs always occurs as a complex mixture, the Toxic Equivalency Factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD that is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation, because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally-related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 3,3',4,4',5-Pentachlorobiphenyl (PCB 126) was produced commercially before 1977 for the electric industry as a dielectric insulating fluid for transformers and capacitors. Manufacture and use of the chemical was stopped because of increased PCB residues in the environment, but it continues to be released into the environment through the use and disposal of products containing PCBs, as by-products during the manufacture of certain organic chemicals, and during combustion of some waste materials. Bioaccumulation of PCB 126 results in persistent levels in animal and human tissues and the biological responses to PCB 126 are similar to those of TCDD, a known human carcinogen. PCB 126 was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. PCB 126 was included since this is the most potent coplanar PCB that has dioxin-like activities. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report only the results of the PCB 126 study are presented and discussed. Female Harlan Sprague-Dawley rats were administered PCB 126 (99% pure) in corn oil with acetone by gavage for 14, 31, or 53 weeks or 2 years. 2-YEAR STUDY: Groups of 81 female rats were administered 30, 100, 175, 300, 550, or 1,000 ng PCB 126/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 104 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. A group of 28 rats received 10 ng/kg for up to 53 weeks only. Up to 10 rats per group were evaluated at 14, 31, or 53 weeks. A stop-exposure group of 50 female rats was administered 1,000 ng/kg PCB 126 in corn oil:acetone (99:1) by gavage for 30 weeks then the vehicle for the remainder of the study. Mean body weights of 30 and 100 ng/kg rats were similar to those of the vehicle controls during most of the study, mean body weights of 175 and 300 ng/kg rats were less than those of the vehicle controls during year 2 of the study, and mean body weights of 550 ng/kg, 1,000 ng/kg core study, and 1,000 ng/kg stop-exposure rats were less than those of the vehicle controls after week 17. THYROID HORMONE CONCENTRATIONS: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53- week interim evaluations. In the 550 and 1,000 ng/kg rats, total thyroxine (T4) and free T4 were significantly lower than vehicle controls and serum triiodothyronine (T3) and thyroid stimulating hormone (TSH) levels were significantly higher than vehicle controls at the 14-week interim evaluation. Serum T3 was also significantly higher in the 300 ng/kg rats compared to vehicle controls at 14 weeks. At 31 weeks, T3 was significantly higher at doses of 100 ng/kg or greater compared to vehicle controls. TSH levels were higher in 550 and 1,000 ng/kg rats than in vehicle controls. At 53 weeks, significantly lower serum concentrations of total T4 and free T4 were observed compared to vehicle controls in groups administered 175 ng/kg or greater and 30 ng/kg or greater, respectively. Serum T3 levels were significantly higher at doses of 175 ng/kg or greater compared to vehicle controls. No changes in TSH were observed between vehicle controls and dosed rats at 53 weeks. HEPATIC CELL PROLIFERATION DATA: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. The hepatocellular labeling index was significantly higher at doses of 300 ng/kg or greater at 14 weeks and 175 ng/kg or greater at 31 weeks compared to vehicle controls. No statistically significant differences were observed between vehicle controls and PCB 126 dosed rats at 53 weeks. However at 53 weeks, a 5.8-fold increase above the vehicle controls was observed in the 1,000 ng/kg group. CYTOCHROME P450 ENZYME ACTIVITIES: To evaluate the expression of known dioxin-responsive genes, CYP1A1 associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide 4-hydroxylase (A-4-H) activity were evaluated at the 14-, 31-, and 53-week interim evaluations. In addition, CYP2B associated pentoxyresorufin-O-deethylase (PROD) activity was also analysed. Hepatic PROD (CYP2B1) and hepatic and pulmonary EROD (CYP1A1) activity were significantly greater in all dosed groups than in vehicle controls at weeks 14, 31, and 53. Hepatic A-4-H (CYP1A2) activity was significantly greater in the 30, 100, 175, 300, 550, and 1,000 ng/kg groups compared to vehicle controls at weeks 14, 31, and 53. DETERMINATIONS of PCB 126 CONCENTRATIONS IN TISSUES: The tissue disposition of PCB 126 was analyzed in the liver, lung, fat, and blood of all rats in vehicle controls and all dosed groups at the 14-, 31-, and 53-week interim evaluations and in 10 rats per group including vehicle controls at the end of the 2-year study (104 weeks). Detectable concentrations of PCB 126 were observed in the liver, fat, lung, and blood. Measurable concentrations of PCB 126 were present in the liver and fat at weeks 31, 53, and 104. Hepatic and fat concentrations increased with increasing doses of PCB 126. Measurable concentrations of PCB 126 were present in vehicle control lung tissue at 53 and 104 weeks. No PCB 126 was observed in the blood from the vehicle control rats. Lung and blood concentrations tended to increase with increasing doses of PCB 126, with a few exceptions. In the stop-exposure group, PCB 126 concentrations in liver and fat were lower than the levels observed in the 30 ng/kg group. In the stop-exposure group, lung tissue PCB 126 concentrations were equivalent to the levels observed in the 30 ng/kg group. In blood from the stop-exposure group, PCB 126 concentrations were equivalent to the levels observed in the 100 ng/kg group. PATHOLOGY AND STATISTICAL ANALYSES: Absolute and relative liver weights were significantly increased at all time points and correlated with increased incidences of hepatocellular hypertrophy. At 2 years, there were significant treatment-related increases in the incidences of cholangiocarcinoma and hepatocellular adenoma. Three hepatocholangiomas were seen in the 1,000 ng/kg core study group and a single incidence of cholangioma each occurred in the 550 and 1,000 ng/kg core study groups. At 2 years, a significant dose-related increase in hepatic toxicity was observed and was characterized by increased incidences of numerous lesions including hepatocyte hypertrophy, multinucleated hepatocytes, diffuse fatty change, bile duct hyperplasia, bile duct cyst, oval cell hyperplasia, necrosis, pigmentation, inflammation, nodular hyperplasia, portal fibrosis, cholangiofibrosis, and toxic hepatopathy. The incidences of these lesions were generally decreased in the 1,000 ng/kg stop-exposure group compared to the 1,000 ng/kg core study group. The lung weights of 1,000 ng/kg rats were generally significantly increased at weeks 14, 31, and 53. At 2 years, treatment related increases in the incidences of cystic keratinizing epithelioma and squamous cell carcinomas were observed. In addition, dose-related increases in the incidences of bronchiolar metaplasia of the alveolar epithelium and squamous metaplasia were also observed. The incidence of gingival squamous cell carcinoma of the oral mucosa was significantly increased in the 1,000 ng/kg core study group at 2 years. Gingival squamous cell carcinoma, although reduced in incidence as compared to the 1,000 ng/kg core study group, was still present in the 1,000 ng/kg stop-exposure group. At 2 years, adenomas and/or carcinomas were present in the adrenal cortex of most core study groups and in the 1,000 ng/kg stop-exposure group. Dose-related effects on the incidences of adrenal cortex atrophy and cytoplasmic vacuolization were also seen. (ABSTRACT TRUNCATED)

Animals↗
PubMed2006

NTP Toxicology and carcinogenesis studies of bromodichloromethane (CAS No. 75-27-4) in male F344/N rats and female B6C3F1 mice (Drinking Water Studies).

UNLABELLED: Bromodichloromethane is a by-product of the chlorination of drinking water. It is formed by the halogen substitution and oxidation reactions of chlorine with naturally occurring organic matter (e.g., humic or fulvic acids) in water containing bromide. Bromodichloromethane has been shown to be carcinogenic at multiple sites in rats (large intestine and kidney) and in mice (liver and kidney) after administration by gavage in corn oil. To further characterize its dose-response relationships for evaluations of human risk, bromodichloromethane was nominated to the NTP by the United States Environmental Protection Agency for toxicity and carcinogenicity studies in rats and mice by drinking water exposure. Male F344/N rats and female B6C3F1 mice were exposed to bromodichloromethane (greater than 98% pure) in drinking water for 3 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, mouse bone marrow cells, and mouse peripheral blood erythrocytes. 3-WEEK STUDY IN RATS: Groups of 10 male F344/N rats were exposed to target concentrations of 0, 43.7, 87.5, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 12, 20, 38, or 71 mg bromodichloromethane/kg body weight) in drinking water for 3 weeks. All rats survived to the end of the study. The mean body weight gains of 350 and 700 mg/L rats were significantly less than that of the controls. Concentration-related decreases in water consumption were evident during the first week on study. Relative kidney weights of rats in the 175, 350, and 700 mg/L groups were significantly greater than that of the controls. There were no significant chemical-related histopathological changes. 3-WEEK STUDY IN MICE: Groups of 10 female B6C3F1 mice were exposed to target concentrations of 0, 43.7, 87.5, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 10, 16, 29 or 51 mg/kg) in drinking water for 3 weeks. All mice survived to the end of the study. Final mean body weights of the 175, 350, and 700 mg/L mice and mean body weight gains of 350 and 700 mg/L mice were significantly less than those of the controls. These decreases were attributed to decreased water consumption. There were significant concentration-related decreases in water consumption by groups exposed to 87.5 mg/L or greater throughout the study; these decreases were attributed to poor palatability of the dosed water. Relative liver, kidney, and thymus weights of mice in the 350 and 700 mg/L groups were significantly greater than those of the controls. Absolute lung weights of mice in the 350 and 750 mg/L groups were significantly less than that of the controls. There were no significant chemical-related histopathological changes. 2-YEAR STUDY IN RATS: Groups of 50 male F344/N rats were exposed to target concentrations of 0, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 12, or 25 mg/kg) in drinking water for 2 years. Survival of exposed groups was similar to that of the controls. Mean body weights of all exposed groups were generally similar to those of the controls throughout the study. Water consumption by exposed rats was less than that by the controls throughout the study; the decreases were attributed to poor palatability of the dosed water. There were no increased incidences of neoplasms that were attributed to bromodichloromethane. The incidences of chronic inflammation in the liver of the 350 and 700 mg/L groups were significantly greater than that in the controls; however, the biological significance of these increases is uncertain. 2-YEAR STUDY IN MICE: Groups of 50 female B6C3F1 mice were exposed to target concentrations of 0, 175, 350, 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 9, 18, or 36 mg/kg) in drinking water for 2 years. Survival of exposed groups was similar to that of the controls. Mean body weights of all exposed groups were generally less than those of the controls from week 4 through the end of the study. Water consumption by exposed mice was less than that by the controls throughout the study; the decreases were attributed to poor palatability of the dosed water. The incidences of hepatocellular adenoma or carcinoma (combined) occurred with a negative trend, and the incidence in the 700 mg/L group was significantly decreased relative to the control group. The incidence of hemangiosarcoma in all organs was significantly decreased in the 350 mg/L group. GENETIC TOXICOLOGY: The results of in vitro mutagenicity tests with bromodichloromethane were mixed. Bromodichloromethane did not induce mutations in any of several tester strains of Salmonella typhimurium, with or without exogenous metabolic activation (S9 liver enzymes). In contrast to the negative results in Salmonella, tests for mutation induction in mouse lymphoma L5178Y/tk(+/-)cells were positive in the presence of induced rat liver S9; no mutagenic activity occurred in tests conducted without S9. In cytogenetic tests with cultured Chinese hamster ovary cells, bromodichloromethane induced a small increase in sister chromatid exchanges (SCEs) in one of four trials conducted in the presence of induced rat liver S9 enzymes; no significant increase in SCEs occurred without S9, and no induction of chromosomal aberrations occurred in bromodichloromethane-treated Chinese hamster ovary cells with or without S9. Results of in vivo tests for chromosomal damage were negative. No increases in the frequency of micronucleated erythrocytes were seen in bone marrow of male B6C3F1 mice administered bromodichloromethane by intraperitoneal injection for 3 days. In addition, no induction of micronuclei was observed in circulating erythrocytes of female B6C3F1 mice administered up to 700 mg/L bromodichloromethane in drinking water for 3 weeks. CONCLUSIONS: Under the conditions of this 2-year drinking water study, there was no evidence of carcinogenic activity of bromodichloromethane in male F344/N rats exposed to target concentrations of 175, 350, or 700 mg/L. There was no evidence of carcinogenic activity of bromodichloromethane in female B6C3F1 mice exposed to target concentrations of 175, 350, or 700 mg/L.

Animals↗
PubMed2006

NTP technical report on the toxicology and carcinogenesis studies of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (CAS No. 1746-01-6) in female Harlan Sprague-Dawley rats (Gavage Studies).

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized, they accumulate in body tissue, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always involves a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, which is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. TCDD is not manufactured commercially other than for scientific research purposes. The main sources of TCDD releases into the environment are from combustion and incineration; metal smelting, refining, and processing; chemical manufacturing and processing; biological and photochemical processes; and existing reservoir sources that reflect past releases. TCDD (dioxin) was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report, only the TCDD results are presented and discussed. TCDD was included because it is the reference compound for the dioxin TEF methodology. Female Harlan Sprague-Dawley rats were administered TCDD (at least 98% pure) in corn oil:acetone (99:1) by gavage for 14, 31, or 53 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, Drosophila melanogaster, and mouse bone marrow cells. 2-YEAR STUDY: Groups of 81 or 82 female rats were administered 3, 10, 22, 46, or 100 ng TCDD/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 105 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. Up to 10 rats per group were evaluated at 14, 31, or 53 weeks. A stop-exposure group of 50 female rats was administered 100 ng/kg TCDD in corn oil:acetone (99:1) by gavage for 30 weeks and then just the vehicle for the remainder of the study. Survival of dosed groups was similar to that of the vehicle control group. Mean body weights of 100 ng/kg core study and stop-exposure groups were less than those of the vehicle control group after week 13 of the study. Mean body weights of 46 ng/kg rats were less than those of the vehicle controls during year 2 of the study, and those of 22 ng/kg rats were less than those of the vehicle controls the last 10 weeks of the study. THYROID HORMONE CONCENTRATIONS: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53-week interim evaluations. At 14 weeks, there were significant decreases in serum total and free thyroxine (T4) levels and increases in serum total triiodothyronine (T3) and thyroid stimulating hormone (TSH). At 31 weeks, there were significant decreases in serum total and free T4 levels and increases in serum total T3 but no significant effect on TSH. At 53 weeks, there were significant decreases in serum total T4 levels and increases in serum total T3. There were no significant effects on total T4 or TSH levels. HEPATIC CELL PROLIFERATION DATA: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. The hepatocellular labeling index was significantly higher in the 22 ng/kg group compared to vehicle controls at 14 weeks. At the 31-week interim evaluation, the labeling indices in hepatocytes were significantly higher in all dosed groups than in the vehicle controls. At 53 weeks, labeling indices were significantly higher in the 46 and 100 ng/kg groups than in the vehicle controls. CYTOCHROME P450 ENZYME ACTIVITIES: To evaluate the expression of known dioxin-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activity were evaluated at 14, 31, and 53 weeks. In addition, pentoxyresorufin-O-deethylase (PROD) activity was analyzed. Hepatic EROD, PROD, and A4H activities were significantly higher in all dosed groups relative to vehicle controls at the 14-, 31-, and 53-week interim evaluations. Pulmonary EROD was also significantly higher in all dosed groups compared to vehicle controls at 14, 31, and 53 weeks. DETERMINATIONS OF TCDD CONCENTRATIONS IN TISSUES: The tissue disposition of TCDD was analyzed in the liver, lung, fat, and blood of all animals in each group at the 14-, 31-, and 53-week interim evaluations and in 10 animals per group at the end of the 2-year study (105 weeks). The highest concentrations of TCDD were observed in the liver, followed by fat tissue. Liver and fat tissue concentrations of TCDD increased with increasing doses of TCDD. No measurable concentrations of TCDD were observed in blood from vehicle control or treated rats at any of the interim evaluations. Mean levels of TCDD in the liver and fat in the 100 ng/kg group at the end of the 2-year study were 9.3 and 3.2 ng/g, respectively. In liver tissue from the stop-exposure group, TCDD concentrations were slightly higher than those observed in the 3 ng/kg group. In the stop-exposure group, TCDD concentrations in fat were below the limits of quantitation. PATHOLOGY AND STATISTICAL ANALYSES: Absolute and/or relative liver weights were increased at 14, 31, and 53 weeks, with more severe effects occurring in the higher dosed groups. Increased liver weights correlated with increased incidences of hepatocyte hypertrophy at 14, 31, and 53 weeks. Exposure led to a treatment-related increase in hepatic toxicity with a broad spectrum of lesions. Incidences and severities of lesions increased at higher doses and longer durations of exposure. The earliest effects were increased incidences and severities of hepatocyte hypertrophy at 14 weeks. At 2 years, there was a significant increase in toxic hepatopathy characterized by increased incidences of numerous nonneoplastic liver lesions including hepatocyte hypertrophy, multinucleated hepatocytes, altered hepatocellular foci, inflammation, pigmentation, diffuse fatty change, necrosis, portal fibrosis, oval cell hyperplasia, bile duct hyperplasia, bile duct cysts, cholangiofibrosis, and nodular hyperplasia At 2 years, the incidence of hepatocellular adenoma was significantly increased in the 100 ng/kg core study group. Dose-related increased incidences of cholangiocarcinoma were seen in core study rats administered 22 ng/kg or greater. The highest incidence of cholangiocarcinoma was seen in the 100 ng/kg core study group and included a significant number of animals with multiple cholangiocarcinomas. Two cholangiocarcinomas and two hepatocellular adenomas were seen in the 100 ng/kg stop-exposure group. Two hepatocholangiomas were seen in the 100 ng/kg core study group, and one cholangioma was seen in the 100 ng/kg stop-exposure group. In the lung, the incidence of cystic keratinizing epithelioma of the lung was significantly increased at 2 years in the 100 ng/kg core study group. Nonneoplastic effects in the lung included increased incidences of bronchiolar metaplasia. The incidence of gingival squamous cell carcinoma of the oral mucosa was significantly increased in the 100 ng/kg core study group at 2 years and was accompanied by an increased incidence of gingival squamous hyperplasia. At 2 years, the incidence of squamous cell carcinoma of the uterus in the 46 ng/kg group was significantly increased, and there were two squamous cell carcinomas in the 100 ng/kg stop-exposure group. At 2 years, one acinar adenoma and two acinar cell carcinomas of the pancreas were seen in the 100 ng/kg core study group; one acinar carcinoma was seen in the 100 ng/kg stop-exposure group. The incidences of acinar cell adenoma or carcinoma (combined) exceeded the historical vehicle control range. Nonneoplastic effects in the lung included acinar cytoplasmic vacuolization, chronic active inflammation, acinar atrophy, and arterial chronic active inflammation. (ABSTRACT TRUNCATED)

Animals↗
PubMed2006

NTP technical report on the toxicology and carcinogenesis studies of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) (CAS No. 35065-27-1) in female Harlan Sprague-Dawley rats (Gavage studies).

UNLABELLED: DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized, they accumulate in body tissue, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always involves a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, which is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 2,2',4,4',5,5'-Hexachlorobiphenyl (PCB 153) was produced as a component of some commercial PCB mixtures before 1977 for the electric industry as a dielectric insulating fluid for transformers and capacitors. Manufacture and use of the chemical was stopped due to increased PCB residues in the environment, but it continues to be released into the environment through the use and disposal of products containing PCBs, as by-products during the manufacture of certain organic chemicals, and during the combustion and biodegradation of some waste materials. Bioaccumulation of PCB 153 results in persistent levels in animal and human tissues. PCB 153 was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. PCB 153 was included since it is present at the highest PCB concentrations in human samples on a molar basis. PCB 153 was also included in a mixture study with PCB 126, since previous studies have demonstrated interactions between PCB 153 and DLCs on pharmacokinetic and biological effects. While one of the aims of this study was a comparative analysis of effects seen with PCB 126 and the mixture of PCB 126 and PCB 153, in this Technical Report only the results of the present study of PCB 153 are presented and discussed. 2-YEAR STUDY: Female Harlan Sprague-Dawley rats were administered PCB 153 (greater than 99% pure) in corn oil:acetone (99:1) by gavage for 14, 31, or 53 weeks or 2 years. Groups of 80 (3,000 microg PCB 153/kg body weight), 81 (100, 300, and 1,000 microg/kg), or 82 (10 microg/kg) female rats received PCB 153 in corn oil:acetone (99:1) by gavage at doses of 10, 100, 300, 1,000, or 3,000 microg/kg 5 days per week for up to 105 weeks; a group of 81 female rats received the corn oil:acetone (99:1) vehicle alone. A stop-exposure group of 50 female rats was administered 3,000 microg/kg for 30 weeks and then the vehicle for the remainder of the study. Dose selection for the PCB 153 study was based on the range of PCB 153 doses used in the mixture study of PCB 126 and PCB 153 (10 to 3,000 microg/kg). Survival of dosed groups was similar to that of the vehicle control group. Mean body weights of 3,000 microg/kg core study rats were less than those of the vehicle controls after week 69 of the study. Thyroid Hormone Concentrations: Serum total thyroxine (T4), free T4, and total triiodothyronine (T3) concentrations in the 3,000 microg/kg group were significantly lower than those in the vehicle controls at the 14-week interim evaluation. At the 31-week interim evaluation, no significant differences were observed in serum total T4, free T4, T3, or thyroid stimulating hormone concentrations. At the 53-week interim evaluation, serum total T4 and free T4 concentrations in the 3,000 microg/kg group were significantly lower than in the vehicle controls. Hepatic Cell Proliferation Data: No significant differences in hepatocellular labeling index were observed between the vehicle control and dosed groups at any of the interim evaluations. Cytochrome P450 Enzyme Activities Hepatic pentoxyresorufin-O-deethylase activities were highly and significantly elevated relative to the vehicle control groups. Maximum increases over controls at 14, 31, and 53 weeks were 136-, 140-, and 40-fold, respectively. Hepatic 7-ethoxyresorufin-O-deethylase (EROD) and acetanilide-4-hydroxylase (A4H) activities were significantly elevated over controls at 14 and 31 weeks; increases were less than twofold. At 14 weeks, EROD activities in the lung were dose-dependently reduced compared to vehicle controls. Determinations of PCB 153 Concentrations in Tissues: In the fat from vehicle controls, detectable levels of PCB 153 were observed at 14, 31, and 53 weeks and at the end of the 2-year study. Fat concentrations of PCB 153 increased with increasing doses of PCB 153 and tended to increase with the longer exposure durations. In the fat of the 3,000 microg/kg stop-exposure group, PCB 153 concentrations were between the levels observed in the 300 and 1,000 microg/kg groups. In the liver of vehicle controls, no measurable concentrations of PCB 153 were observed at any time point. In dosed groups, hepatic concentrations of PCB 153 increased with increasing dose and longer exposure duration. Measurable concentrations of PCB 153 were observed in the lungs of vehicle control rats at 31 and 53 weeks and at 2 years. At all time points, PCB 153 lung and blood concentrations increased with increasing dose, and blood concentrations increased with duration of exposure. In liver, lung, and blood of rats from the 3,000 microg/kg stop-exposure group, PCB 153 concentrations were slightly above or below the levels observed in the 1,000 microg/kg group. Organ Weights: Absolute liver weights of 1,000 microg/kg rats and absolute and relative liver weights of 3,000 microg/kg rats were significantly greater than those of vehicle controls at week 14. At week 31, relative liver weights of 1,000 microg/kg rats and absolute and relative liver weights of 3,000 microg/kg rats were significantly greater than those of vehicle controls. At week 53, absolute and relative liver weights were significantly greater in rats administered 100 microg/kg or greater compared to vehicle controls. Absolute kidney weights of all exposed groups and the relative kidney weight of 3,000 microg/kg rats were significantly increased at week 53. Pathology and Statistical Analyses: The incidences of hepatocyte hypertrophy were significantly increased in the 1,000 and 3,000 microg/kg groups at 14 weeks and in all groups administered 300 microg/kg or greater at 31 and 53 weeks. At 2 years, the incidences of hepatocyte hypertrophy were significantly increased in all dosed groups. The incidences of diffuse fatty change in the 300 microg/kg or greater groups and bile duct hyperplasia of the liver in 300 microg/kg and 3,000 microg/kg (core and stop-exposure) groups were significantly increased. The incidences of oval cell hyperplasia and pigmentation of the liver were significantly increased in the 3,000 microg/kg core study group. At 2 years, two cholangiomas were seen in the 1,000 microg/kg group and two cholangiomas were seen in the 3,000 microg/kg stop-exposure group. A single hepatocellular adenoma was observed in the 3,000 microg/kg core study group. At 53 weeks, sporadic incidences of minimal to mild follicular cell hypertrophy of the thyroid gland occurred in all groups (except 10 microg/kg). At 2 years, the incidences of minimal to mild follicular cell hypertrophy were significantly increased in the 300 microg/kg and 3,000 microg/kg (core and stop-exposure) groups. At 2 years, significantly increased incidences of chronic active inflammation in the ovary and oviduct occurred in the 1,000 and 3,000 microg/kg core study groups. Incidences of suppurative inflammation of the uterus in the 1,000 microg/kg group and chronic active inflammation in the 3,000 microg/kg core study group were significantly greater than those in the vehicle control group. CONCLUSIONS: Under the conditions of this 2-year gavage study there was equivocal evidence of carcinogenic activity of PCB 153 in female Harlan Sprague-Dawley rats based on the occurrences of cholangioma of the liver. PCB 153 administration caused increased incidences of nonneoplastic lesions of the liver, thyroid gland, ovary, oviduct, and uterus in female rats.

Adenoma, Bile Duct↗
PubMed2006

Toxicology and carcinogenesis studies of transplacental AZT (Cas No. 30516-87-1) in Swiss (CD-1®) mice (in utero studies).

UNLABELLED: 3'-Azido-3'-deoxythymidine (AZT) is the most widely used and evaluated chemotherapeutic agent for the treatment of persons with acquired immune deficiency syndrome (AIDS) and persons seropositive for human immunodeficiency virus (HIV). The study in this report was conducted to obtain information on AZT transplacental carcinogenicity at doses that were lower than those used in previous NCI studies and analogous to therapeutic doses. Male and female Swiss (CD-1(R)) mice were exposed to AZT (greater than 99% pure) during all of gestation. Genetic toxicology studies were conducted in mouse peripheral blood erythrocytes. Groups of 22, 28, 34, or 46 female mice (F(0) generation) were administered AZT in 0.5% methylcellulose by gavage at doses of 50, 100, 200, or 300 mg AZT/kg body weight 7 days per week for 29 to 39 days (day of delivery). A vehicle control group of 22 female mice received methylcellulose alone. Each female group was divided into two groups with dosing started 1 week apart in order to facilitate cohabitation, mating, and delivery. Groups of six, six, seven, nine, or twelve undosed male mice were cohabited with the vehicle control and 50, 100, 200, and 300 mg/kg dosed females, respectively, on study days 9 to 13 and then discarded. Pups (F(1) generation) were culled (0, 50, and 100 mg/kg groups) to yield a maximum of five pups/sex per litter on postnatal day 4; no more than four pups/sex per litter were used in the study. On postnatal day 25, all surviving 200 and 300 mg/kg pups were placed on study. After culling and randomization to cage groups, the 0, 50, 100, 200, and 300 mg/kg groups consisted of 50, 50, 50, 37, and 32 male pups and 50, 50, 50, 40, and 42 female pups, respectively. Decreased litter size and fertility rates were observed in the 200 and 300 mg/kg F0 dams. Survival of all exposed groups of F(1) mice was similar to that of the vehicle controls. Mean body weights of 200 mg/kg males were generally less than those of the vehicle controls after week 29. Mean body weights of 300 mg/kg males were less during the first year of the study, but these mice recovered and body weights were generally similar to those of the vehicle controls at the end of the study. The incidences of alveolar/bronchiolar carcinoma and of adenoma or carcinoma (combined) in 200 and 300 mg/kg males were significantly greater than those in the vehicle controls. The incidences of histiocytic cellular infiltration of the lung in 200 and 300 mg/kg males were significantly increased. GENETIC TOXICOLOGY: The NTP conducted a number of studies of the genetic toxicity of AZT, independent of this transplacental carcinogenicity study. In these genetic toxicity studies, AZT (50, 75, 100, or 150 mg/kg) administered to pregnant Swiss (CD-1(R)) dams, beginning prior to conception and continuing throughout gestation and lactation, induced high levels of micronucleated polychromatic erythrocytes (PCEs) in pups sampled on postnatal days 1 and 4. Direct gavage treatment of these transplacentally and lactationally exposed pups, beginning on postnatal day 4, resulted in further increases in the frequencies of micronucleated PCEs on postnatal days 8 and 21. The percentage of PCEs among erythrocytes in pups was significantly elevated over normal adult levels, indicating a high rate of erythropoiesis in neonatal mice. The percentage of PCEs was decreased in all pups exposed to AZT, consistent with treatment-related bone marrow toxicity. CONCLUSIONS: Under the conditions of this study, there was clear evidence of carcinogenic activity in F(1) male mice exposed transplacentally to AZT based on increased incidences of alveolar/bronchiolar neoplasms. There was no evidence of carcinogenic activity in F(1) female mice exposed transplacentally to AZT at 50, 100, 200, or 300 mg/kg. Reproductive toxicity in the form of decreased litter size and fertility rates was observed in dams in the 200 and 300 mg AZT/kg dose groups.

Animals↗
PubMed2006

Toxicology and carcinogenesis studies of 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (Cas No. 57117-31-4) in female Harlan Sprague-Dawley rats (gavage studies).

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in human tissues, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always involves a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, which is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 2,3,4,7,8-Pentachlorodibenzofuran (PeCDF) is not manufactured commercially other than for scientific research purposes. The main sources of PeCDF releases into the environment are from combustion and incineration sources. PeCDF was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report only the results of the present PeCDF study are presented and discussed. Female Harlan Sprague-Dawley rats were administered PeCDF (at least 97% pure) in corn oil:acetone (99:1) by gavage for 14, 31, or 53 weeks or 2 years. 2-YEAR STUDY: Groups of 81 female rats were administered 6, 20, 44, 92, or 200 ng PeCDF/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 105 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. Up to 10 rats per group were evaluated at 14, 31, and 53 weeks. A stop-exposure group was administered 200 ng/kg PeCDF in corn oil:acetone (99:1) by gavage for 30 weeks and then the vehicle for the remainder of the study. The PeCDF in this study was at least 97% pure. Survival of dosed groups was similar to that of the vehicle control group. Mean body weights of the 200 ng/kg core and stop-exposure groups were less than those of the vehicle controls during year 2 of the study. Thyroid Hormone Concentrations: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53-week interim evaluations. There were significant decreases in total serum thyroxine (T(4)) levels at the 14-week interim evaluation. There were no significant differences observed in serum free T(4), total triiodothyronine (T(3)), or thyroid stimulating hormone (TSH) at 14 weeks. At both 31 and 53 weeks, there were treatment-related decreases in free and total T(4) concentrations and increases in serum T(3) levels. Serum TSH levels in dosed groups at 31 and 53 weeks were not significantly different than in the vehicle controls. Hepatic Cell Proliferation Data: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine (BrdU) was conducted at the 14-, 31-, and 53-week interim evaluations. At 14 and 53 weeks, hepatocyte BrdU-labeling indices were significantly higher in the 200 ng/kg groups compared to time-matched vehicle controls. No significant differences were observed between the dosed groups and vehicle controls at 31 weeks. Cytochrome P450 Enzyme Activities: To evaluate the expression of known dioxin-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activity were evaluated at the 14-, 31-, and 53-week interim evaluations. Hepatic EROD and A4H activities were significantly higher in all groups administered PeCDF relative to the vehicle controls at all three interim evaluations. Pulmonary EROD was also significantly higher in all dosed groups compared to vehicle controls at 14, 31, and 53 weeks. Determinations of PeCDF Concentrations in Tissues: The tissue disposition of PeCDF was analyzed in the liver, lung, fat, and blood of all animals at the 14-, 31-, and 53-week interim evaluations, and in 10 animals per group at the end of the 2-year study (105 weeks). In the liver of vehicle controls, PeCDF concentrations were detectable at 105 weeks. Measurable concentrations of PeCDF were not detected in fat or lung from vehicle control rats at any of the interim evaluations or at 105 weeks. Hepatic and fat concentrations were higher in groups with increasing doses of PeCDF, demonstrating a dose-related increase in tissue burden of PeCDF at each time point. No measurable concentrations of PeCDF were detected in the lungs of vehicle controls or any of the dosed groups at 14 weeks or in the lungs of the vehicle control group at 31, 53, and 105 weeks, or the 6 ng/kg group at 31 and 53 weeks. In groups with measurable levels, PeCDF concentrations were higher with respect to increasing doses. Mean levels of PeCDF in the liver, fat, lung, and blood in the 200 ng/kg group at the end of the 2-year study were 500 ng/g, 7.75 ng/g, 0.28 ng/g and 0.04 ng/mL, respectively. Negligible PeCDF concentrations were observed in blood of the 200 ng/kg group at 53 weeks and the 92 and 200 ng/kg groups at 105 weeks. In liver and fat from the stop-exposure group, the PeCDF concentrations were between the levels observed in the 6 and 20 ng/kg groups. In the stop-exposure group, PeCDF concentration in lung was comparable to levels observed in the 6 ng/kg group. No measurable concentrations were observed in blood from the stop-exposure group. Pathology and Statistical Analyses: There were dose-dependent increases in both absolute and relative liver weights at 4, 31, and 53 weeks, and these tended to correlate with increased incidences of hepatocellular hypertrophy. In the liver at 14 weeks, the only significant effect was an increase in the incidences of hepatocellular hypertrophy. At 53 weeks, there were significant increases in the incidences of hepatocellular hypertrophy and pigmentation. At 2 years, there were significant dose-dependent trends for increased incidences of hepatocellular adenoma and cholangiocarcinoma of the liver. A significant dose-dependent increase in hepatic toxicity was observed and was characterized by increased incidences of numerous nonneoplastic lesions including hepatocellular hypertrophy, multinucleated hepatocytes, oval cell hyperplasia, diffuse fatty change, pigmentation, nodular hyperplasia, eosinophilic foci, hepatocellular necrosis, bile duct hyperplasia, bile duct fibrosis, cholangiofibrosis, and toxic hepatopathy. At 2 years, three gingival squamous cell carcinomas of the oral mucosa were seen in the 200 ng/kg core and stop-exposure groups, two occurred in the 6 ng/kg group, and one occurred in each of the vehicle control, 20 ng/kg, and 92 ng/kg groups. Gingival squamous hyperplasia occurred in all groups including the vehicle controls, with increasing incidences in groups administered 44 ng/kg or greater. The incidence of carcinoma of the uterus was marginally increased in the 92 ng/kg group at 2 years. Increased incidences of chronic active inflammation of the uterus were observed in all dosed groups, and the incidence in the 200 ng/kg stop-exposure group was greater than those in the vehicle control and 200 ng/kg core study groups. Increased incidences of squamous metaplasia of the uterus occurred in all dosed groups. In the 200 ng/kg stop-exposure group, the incidence of squamous metaplasia was significantly greater than that in the vehicle controls, but was lower than that in the 200 ng/kg core study group. At 14-weeks, lung weights were significantly increased in the 200 ng/kg group compared to the vehicle controls. A single occurrence of a multiple cystic keratinizing epithelioma of the lung was observed in the 200 ng/kg core study group. There were increases in the incidences of bronchiolar metaplasia of the alveolar epithelium and sporadic incidences of squamous metaplasia. One pancreatic acinar adenoma and one pancreatic acinar carcinoma were each observed in the 92 ng/kg group and in the 200 ng/kg stop-exposure group at 2 years. Significantly increased incidences of acinar cytoplasmic vacuolization and arterial chronic active inflammation and increased severity of chronic active inflammation were observed in the 200 ng/kg core study group. Numerous nonneoplastic effects were seen in other organs including thyroid follicular cell hypertrophy, thymic atrophy, adrenal cortex cystic degeneration, nephropathy, cardiomyopathy, and squamous hyperplasia of the forestomach.

Animals↗
PubMed2006

Toxicology and carcinogenesis studies of a binary mixture of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) (Cas No. 57465-28-8) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) (CAS No. 35065-27-1) in female Harlan Sprague-Dawley rats (gavage studies).

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bio-concentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in body tissues, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always occurs as a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 2-YEAR STUDY: The 2-year study of a binary mixture of PCB 126 and PCB 153 was designed to assess the carcinogenicity of a constant ratio mixture of PCB 126 and PCB 153. In addition, varying ratio mixture groups were used to assess the impact of increasing PCB 153 on the carcinogenicity of PCB 126. Dose groups were divided into two study arms (Figure 1). TCDD equivalent (TEQ) doses are based on the PCB 126 doses after adjustment for the PCB 126 TEF of 0.1. Groups of 81 (Groups 2, 3, 5, and 7) or 80 (Groups 4 and 6) female rats received a mixture of PCB 126 and PCB 153 in corn oil:acetone (99:1) by gavage 5 days per week for up to 105 weeks; a group of 81 female rats received the corn oil:acetone (99:1) vehicle only and served as the vehicle control (Group 1). Up to 10 rats per group were evaluated at 14, 31, and 53 weeks. Survival of all dosed groups was similar to that of the vehicle controls. The mean body weights of Groups 4 and 5 were generally less than those of the vehicle controls after week 25. The mean body weights of Group 6 were less after week 12, and those of Group 7 were less after week 8. Thyroid Hormone Concentrations: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31-, and 53-week interim evaluations. In the constant ratio groups, serum total thyroxine (T(4)) and free T(4) generally showed a treatment-related decrease relative to controls. Serum total triiodothyronine (T(3)) exhibited a treatment-related increase at the 14-, 31-, and 53-week interim evaluations, but serum thyroid stimulating hormone (TSH) levels were increased at the 14-week time point only. In the varying ratio groups, the decrease in total and free T(4) was more pronounced in those groups dosed with the increasing proportion of PCB 153 at the 31- and 53-week time points. Hepatic Cell Proliferation Data: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. At 31 and 53 weeks, a significant increase in the hepatocellular labeling index occurred in Group 7. In the varying ratio groups, the labeling index at the 53-week interim time point was significantly higher in Group 6, which had the highest proportion of PCB 153 compared to the other varying ratio groups. Cytochrome P450 Enzyme Activities: To evaluate the expression of known PCB 126-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activities were evaluated at the 14-, 31-, and 53-week interim evaluations. In addition, PCB 153-inducible CYP2B-associated 7-pent-oxyresorufin-O-dealkylase (PROD) activity was analyzed. In the constant ratio Groups 2, 3, 5, and 7, hepatic and pulmonary EROD (CYP1A1) activities, hepatic A4H (CYP1A2) activities, and hepatic PROD (CYP2B) activities were significantly greater in all dosed groups compared to the vehicle controls at weeks 14, 31, and 53. In the varying ratio groups, hepatic EROD, A4H, and PROD activities at 14 weeks were higher in groups receiving a greater proportion of PCB 153 in the PCB mixture. At 31 and 53 weeks, hepatic CYP1A1 and CYP1A2 enzyme activities in Group 6 were generally lower than in Groups 4 and 5. Determinations of PCB 126 and PCB 153 Concentrations in Tissues: Concentrations of PCB 126 and PCB 153 were determined in fat, liver, lung, and blood at the 14-, 31-, and 53-week interim evaluations and at the end of the 2-year study (105 weeks). PCB 126 was not detectable in vehicle control animals, but increased with increasing dose of PCB 126 and duration of exposure; the highest concentrations were found in liver and fat, and lower levels were seen in lung and blood. Increasing the proportion of PCB 153 in the mixture relative to PCB 126 led to a general decrease in the amount of PCB 126 in liver and lung at the later time points, whereas in fat and blood, there was generally either no effect of PCB 153 on the disposition of PCB 126, or there was an increase in the amount of PCB 126 in the tissue. In vehicle control animals, PCB 153 was detectable in the fat at all time points, in the lung at all time points except 53 weeks, and in the liver and blood at 2 years. PCB 153 was measurable in all examined tissues of treated animals, with the highest concentrations found in fat at the end of the 2-year study in groups administered the highest doses of PCB 153. Pathology and Statistical Analyses -- Constant Ratio Mixture of PCB 126 and PCB 153: At 14, 31, and 53 weeks, the absolute and relative liver weights of all dosed groups were generally greater than those of the vehicle controls. Exposure to the PCB mixture led to significant toxicity in the liver. At 14 weeks, the incidences of several nonneoplastic liver lesions were increased compared to the vehicle controls including hepatocyte hypertrophy, pigmentation, multinucleated hepatocytes, and diffuse fatty change. The spectrum and severity of effects increased with dose and duration of exposure. At the end of the 2-year study, there were significantly increased incidences and severities of toxic hepatopathy characterized by hepatocyte hypertrophy, multinucleated hepatocytes, pigmentation, diffuse and focal fatty change, eosinophilic focus, nodular hyperplasia, cholangiofibrosis, oval cell hyperplasia, bile duct cysts, bile duct hyperplasia, necrosis, and portal fibrosis. Significantly increased incidences of hepatocellular adenoma, cholangiocarcinoma, and hepatocholangioma were observed in the study. In addition, two animals in the highest dose group had hepatocellular carcinoma. The incidences of these lesions generally exceeded the historical vehicle control ranges. At 2 years, a significantly increased incidence of cystic keratinizing epithelioma of the lung was observed in Group 7. In addition, single occurrences of squamous cell carcinoma were seen in the top two dose groups. Nonneoplastic effects whose incidences were increased in the lung included bronchiolar metaplasia of the alveolar epithelium and squamous metaplasia. Significantly increased incidences of squamous cell carcinoma (gingival) of the oral mucosa were seen at the end of the 2-year study and were accompanied by increased incidences of gingival squamous hyperplasia. In the pancreas at 53 weeks, the incidence of acinar cytoplasmic vacuolization was significantly increased in the highest dose group. At 2 years, increased incidences of acinar atrophy and acinar cytoplasmic vacuolization were seen in addition to pancreatic acinar neoplasms in dosed groups. In Groups 5 and 7, these incidences exceeded the historical vehicle control ranges. In the uterus at 2 years, there was a marginal increase in the incidence of squamous cell carcinoma in Group 5. Numerous nonneoplastic effects were seen in other organs at the interim time points including atrophy of the thymus and follicular cell hypertrophy of the thyroid gland. These responses were also affected by administration of the mixture of PCB 126 and PCB 153 at the end of the 2-year study and were accompanied by additional nonneoplastic responses in numerous organs including atrophy of the adrenal cortex and cortical hyperplasia, severity of nephropathy, and incidences of pigmentation of the kidney. Other nonneoplastic lesions that were treatment related were forestomach hyperplasia, hyperplasia of the nasal respiratory epithelium, metaplasia of the olfactory epithelium, and ectasia of the mandibular lymph node. Varying Ratio Mixture of PCB 126 and PCB 153: An effect of increasing the proportion of PCB 153 in the PCB mixture was seen in several tissues, most notably in the liver. Treatment-related nonneoplastic effects seen across the varying ratio groups were generally the same as those seen in the constant ratio groups. In general there was a positive effect of PCB 153 in the mixture on the incidences and severities of these lesions with higher incidences and higher severities being seen in Group 6, which had the highest proportion of PCB 153. (ABSTRACT TRUNCATED).

Animals↗
PubMed2006

NTP-CERHR monograph on the potential human reproductive and developmental effects of styrene.

The National Toxicology Program (NTP) Center for the Evaluation of Risks to Human Reproduction (CERHR) conducted an evaluation of the potential for styrene to cause adverse effects on reproduction and development in humans. Styrene was selected for evaluation because of (1) public concern about styrene exposure and (2) recently available exposure studies. Styrene (ethenylbenzene; CAS RN: 100-42-5) is a high production volume chemical (a million pounds or more produced each year) and is used in the production of polystyrene resins and as a co-polymer with acrylonitrile and 1,3-butadiene. Styrene is found in items such as foam cups, dental fillings, matrices for ion exchange filters, construction materials, and boats. It is also used in protective coatings, reinforced glass fiber, agricultural products, and as a food additive. The Food and Drug Administration regulates styrene for use as a synthetic flavoring substance and as a component of polymers in contact with dry food, and also regulates the amount of residual styrene monomer allowed in polystyrene intended for use in contact with food. The public can be exposed to styrene by ingesting food or drink that has been in contact with styrene polymers or through inhalation of polluted air and cigarette smoke. The results of this evaluation on styrene are published in a NTP-CERHR monograph that includes: (1) the NTP Brief, (2) the Expert Panel Report on the Reproductive and Developmental Toxicity of Styrene, and (3) public comments received on the expert panel report. The NTP reached its conclusion of negligible concern for adverse developmental and reproductive effects resulting from styrene exposures in humans based on information presented in the NTP-CERHR Expert Panel Report on the Reproductive and Developmental Toxicity of Styrene and the public comments on that report. This conclusion is based on estimated exposures in both the general population and in people whose occupation involves styrene exposure. The expert panel estimated styrene exposure in the general U.S. population to be less than 0.3 microg/kg body weight/day in nonsmokers and 3.51 and 2.86 microg/kg body weight/day in smokers ages 12-19 years and 20-70 years, respectively. Average occupational exposures are estimated to range from 1,400-52,000 microg/kg body weight/day. Studies in humans show no evidence that occupational exposures or exposure of the general population to styrene adversely affect reproduction or development. Further, data from experimental animal studies show no adverse reproductive or developmental effects at styrene doses far above human exposure levels. The NTP will transmit the NTP-CERHR monograph on styrene to federal and state agencies, interested parties, and the public and it will be available in electronic PDF format on the CERHR web site http://cerhr.niehs.nih.gov and in printed text or CD-ROM from the CERHR: M.D. Shelby, Ph.D., Director, CERHR, NIEHS, P.O. Box 12233, MD EC-32, Research Triangle Park, NC 27709, 919-541-3455 [phone], 919-316-4511 [fax], shelby@niehs.nih.gov [email].

Animals↗
PubMed2005

NTP toxicology and carcinogenesis studies of decalin (CAS No. 91-17-8) in F344/N rats and B6C3F(1) mice and a toxicology study of decalin in male NBR rats (inhalation studies).

Decalin is used as an industrial solvent for naphthalene, fats, resins, oils, and waxes. It is also used as a substitute for turpentine in lacquers, paints, and varnishes; as a solvent and stabilizer for shoe polishes and floor waxes; and as a constituent of motor fuels and lubricants. Other applications include use as a paint thinner and remover, a patent fuel in stoves, a high-density fuel in submarine-launched cruise missile systems, and in stain removal and cleaning machinery. Decalin was nominated for study by the National Cancer Institute because of its chemical structure, its potential for consumer exposure, and a lack of adequate testing of the chemical. Male and female F344/N rats and B6C3F(1) mice were exposed to decalin (greater than 99% pure) by inhalation for 2 weeks, 3 months, or 2 years. Groups of male NBR rats were exposed to decalin for 2 weeks. Male NBR rats do not produce alpha2u-globulin; the NBR rats were included to study the relationship of alpha2u-globulin and renal lesion induction. Genetic toxicology studies were conducted in Salmonella typhimurium and mouse peripheral blood erythrocytes. 2-WEEK STUDIES IN RATS: Groups of five male and five female F344/N rats and five male NBR rats were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 16 days. All rats survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber controls. Renal toxicity studies were performed in male F344/N and NBR rats. The numbers of labeled cells and the labeling indices in the left kidney of 200 and 400 ppm F344/N male rats were significantly greater than those in the chamber controls. The alpha2u-globulin/soluble protein ratios were significantly increased in all exposed groups of F344/N rats. Liver weights of male F344/N and NBR rats exposed to 100 ppm or greater were significantly increased, as were those of all exposed groups of females. Kidney weights of male F344/N rats exposed to 50 ppm or greater were significantly increased. Exposure-related hyaline droplet accumulation, degeneration and regeneration of renal cortical tubules, and granular casts occurred in the kidney of exposed F344/N male rats. 2-WEEK STUDIES IN MICE: Groups of five male and five female B6C3F(1) mice were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 17 days. All mice survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Liver weights of 200 and 400 ppm males and females and 100 ppm females were significantly increased. 3-MONTH STUDY IN RATS: Groups of 25 male and 20 female F344/N rats were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 2 (five male renal toxicity rats), 6 (10 male and 10 female clinical pathology rats), or 14 (10 core study rats) weeks. All rats survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Urinalysis results indicated that decalin exposure caused increases in urine glucose and protein concentrations and enzyme activities that were consistent with the renal lesions observed microscopically. Renal toxicity studies were performed on rats sacrificed at 2 and 6 weeks and at the end of the study. In kidney tissue examined for cell proliferation, the numbers of PCNA-labeled cells and labeling indices were generally significantly greater than those of the chamber controls in exposed groups of rats at all three time points. Concentrations of alpha2u-globulin in the kidney as well as the alpha2u-globulin/soluble protein ratios were significantly increased at week 2 in all exposed groups and in the 200 and 400 ppm groups at week 6 and at the end of the study. Absolute and/or relative kidney and liver weights of male rats exposed to 50 ppm or greater were increased. Incidences of renal tubule regeneration and granular casts in the medulla of the kidney in exposed male rats were increased, and the severities of hyaline droplets generally increased with increasing exposure concentration. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female B6C3F(1) mice were exposed to 0, 25, 50, 100, 200, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 14 weeks. All mice survived to the end of the study, and mean body weights of exposed groups were similar to those of the chamber control groups. Liver weights of 200 and 400 ppm males and females were significantly increased. There was a significant exposure concentration-related decrease in the absolute spermatid head count and a significant decrease in absolute head count of the 400 ppm group compared to the chamber controls. Incidences of centrilobular cytomegaly of the liver were increased in exposed male mice. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female F344/N rats were exposed to 0, 25, 50 (male rats only), 100, or 400 ppm (female rats only) decalin vapor 6 hours per day, 5 days per week for 105 weeks. A group of 20 male rats was exposed to 400 ppm. Survival of exposed groups was similar to that of the chamber control groups. Mean body weights of 400 ppm males were slightly less than those of the chamber controls during the second year of the study. Incidences of renal tubule adenoma and adenoma or carcinoma (combined) and of benign or malignant pheochromocytoma (combined) of the adrenal medulla in 100 and 400 ppm males were significantly increased. There was a significant association between nephropathy severity and adrenal pheochromocytoma incidence. Nonneoplastic lesions related to decalin exposure occurred in the kidney of male rats. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female B6C3F(1) mice were exposed to 0, 25, 100, or 400 ppm decalin vapor 6 hours per day, 5 days per week for 105 weeks. Survival of exposed mice was similar to that of the chamber controls. Mean body weights of exposed groups were generally similar to those of the chamber control groups throughout the study. Increased incidences of hepatocellular neoplasms occurred in 25 and 400 ppm female mice, and the incidences of centrilobular hypertrophy, necrosis, syncytial alteration, and erythrophagocytosis of the liver in 400 ppm males were significantly increased. The incidences of uterine stromal polyp and stromal polyp or stromal sarcoma (combined) occurred with positive trends in female mice. PHARMACOKINETIC MODEL: The rate of metabolism of decalin was the same for males and females in rats and mice. Also in rats and mice, decalin metabolism was saturated at less than 400 ppm. Increased labeling indices in male rats were likely due to changes related to alpha2u-globulin. GENETIC TOXICOLOGY: Decalin was not mutagenic in S. typhimurium strains TA97, TA98, TA100, or TA1535, with or without induced hamster or rat liver S9 enzymes. A small but significant increase in the frequency of micronucleated normochromatic erythrocytes was noted in male mice exposed to decalin for 3 months; however, no induction of micronuclei was observed in female mice. CONCLUSIONS: Under the conditions of these studies, there was clear evidence of carcinogenic activity of decalin in male F344/N rats based on increased incidences of renal tubule neoplasms. The increased incidences of benign or malignant pheochromocytoma (combined) of the adrenal medulla in male rats were also considered to be exposure related. There was no evidence of carcinogenic activity of decalin in female F344/N rats exposed to 25, 100, or 400 ppm. There was no evidence of carcinogenic activity of decalin in male B6C3F(1) mice exposed to 25, 100, or 400 ppm. There was equivocal evidence of carcinogenic activity of decalin in female B6C3F(1) mice based on marginally increased incidences of hepatocellular and uterine neoplasms. Exposure of male rats to decalin resulted in nonneoplastic lesions of the kidney characteristic of alpha2u-globulin accumulation. Nonneoplastic lesions of the liver were observed in male mice exposed to decalin.

Administration, Inhalation↗
PubMed2005

Toxicology and carcinogenesis studies of malachite green chloride and leucomalachite green. (CAS NOS. 569-64-2 and 129-73-7) in F344/N rats and B6C3F1 mice (feed studies).

BACKGROUND: Malachite green chloride is a dye used to prevent fungus infections in commercial fisheries. Leucomalachite green is formed from malachite green and remains in the tissues of exposed fish. We studied the effects of malachite green on female rats and female mice, and the effects of leucomalachite green on male and female rats and female mice, to identify potential toxic or cancer-related hazards to humans. METHODS: For each study we mixed the dye into the feed of rats and mice. The doses of malachite green chloride given were 100, 300, or 600 parts per million (ppm) for female rats and 100, 225, or 450 ppm for female mice. Doses of leucomalachite green were 91, 272, or 543 ppm for male and female rats and 91, 204, or 408 ppm for female mice. There were 48 animals in each dose group. Control animals received the same feed with no chemical added. The study lasted for two years. Tissues from more than 40 sites were examined for every animal. RESULTS: Rats, but not mice, exposed to malachite green chloride or leucomalachite green weighed less on average than the control animals. In rats exposed to the dyes, there were very slight increases in a few types of tumors: cancers of the thyroid gland, liver, and mammary gland in females exposed to malachite green chloride; of the thyroid gland and testes in males exposed to leucomalachite green; and of the thyroid gland and liver of females exposed to leucomalachite green. We saw no increase in cancers in female mice given malachite green chloride, but there was an increase in liver tumors in female mice given to leucomalachite green. CONCLUSIONS: We conclude that tumors of the thyroid gland, liver, or mammary gland in female rats might have been caused by malachite green chloride, but the malachite green chloride did not cause cancer in female mice. We conclude that leucomalachite green might have caused cancers of the thyroid gland in male and female rats, and of the testes in male rats and liver in female rats. Leucomalachite green caused an increase in cancer of the liver in female mice.

Administration, Oral↗
PubMed2005

NTP-CERHR monograph on the potential human reproductive and developmental effects of acrylamide.

Acrylamide, used in the manufacture of polyacrylamide and grouting agents, is produced during the cooking of foods. Workplace exposure to acrylamide can occur through the dermal and inhalation routes. The objectives of this study were to evaluate the metabolism of acrylamide in humans following oral administration, to compare hemoglobin adduct formation on oral and dermal administration, to measure hormone levels, and to monitor the safety of acrylamide in people exposed under controlled conditions. Prior to conducting exposures in humans, a low-dose study was conducted in rats administered 3 mg/kg 1,2,3-¹³C₃acrylamide by gavage. The study protocol was reviewed and approved by Institute Review Boards both at RTI which performed the sample analysis, and the clinical research center conducting the study. 1,2,3-¹³C₃Acrylamide (AM) was administered in an aqueous solution orally (single dose of 0.5, 1.0,or 3.0 mg/kg) or dermally (3 daily doses of 3.0 mg/kg) to sterile male volunteers. Urine samples (3 mg/kg oral dose) were analyzed for AM metabolites using 13C NMR spectroscopy. Approximately 86 % of the urinary metabolites were derived from GSH conjugation, and excreted as N-acetyl-S-(3-amino-3-oxopropyl)cysteine and its S-oxide.Glycidamide, glycer amide, and low levels of N-acetyl-S-(3-amino-2-hydroxy-3-oxopropyl)cysteine were detected in urine. On oral administration, a linear dose response was observed for N-(2-carbamoylethyl)valine (AAVal) and N-(2-carbamoyl-2-hydroxyethyl)valine (GAVal) in hemoglobin. Dermal administration resulted in lower levels of AAVal and GAVal. This study indicated that humans metabolize acrylamide via glycidamide to a lesser extent than rodents, and dermal uptake was approximately 5%of that observed with oral uptake. Acrylamide is used in the manufacture of water- soluble polymers (European Union,2002). These polymers are then used for wastewater and sludge treatment, paper manufacture, soil stabilization, mining and many other uses (European Union, 2002).Acrylamide is also a chemical intermediate in the manufacture of other monomeric chemicals and used for grouting and preparation of laboratory gels for electrophoresis.Human exposure through these applications is very small (European Union, 2002).Previously, it has been postulated that dermal absorption was the major route of human exposure to acrylamide (European Union, 2002). The magnitude of this dermal absorption is highly relevant as one of the uses of acrylamide based polymers is in the formulation of skin creams (European Union, 2002). Estimates of dermal absorption based on in vitro and rodent studies have ranged from 3% to 100 (European Union,2002). Recently, exposure to acrylamide in a variety of cooked foods has been described(Rosen and Hellen as, 2002; Tareke et al., 2002). Human exposure via this route is substantial, with estimated exposures as high as 70 μg per day proposed (Tareke et al.,2002). Acrylamide is metabolized by two main pathways: glutathione conjugation (Dixit et al.,1982; Edwards, 1975; Hashimoto and Aldridge, 1970; Miller et al., 1982; Sumner et al.,1992), and oxidation to glycidamide (Calleman et al., 1990; Sumner et al., 1992). The metabolism of acrylamide in vivo results in the formation of a number of metabolites.These metabolism of acrylamide in vivo has been investigated by administration of 1,2,3-13C3 acrylamide to rodents, with the detection and quantitation of metabolites by 13 CNMR spectroscopy (Sumner et al., 1999; Sumner et al., 1992; Sumner et al., 2003). The oxidation reaction to glycidamide is catalyzed by cytochrome P450 2E1 in rodents(Sumner et al., 1999). Both acrylamide and glycidamide react with hemoglobin producing a stable adduct which can be measured as an indicator of exposure.Correlations have been made with hemoglobin adducts and neurotoxicity, but there has been no systematic standardization of hemoglobin adducts with dose. Glycidamide is weakly mutagenic in the Salmonella test (Hashimoto and Tanii, 1985). It can react with DNA in vitro to produce a guanine derivative N7-(2-carbamoyl-2-hydroxyethyl)guanine(Gamboa da Costa et al., 2003; Segerback et al., 1995). In vivo, administration of acrylamide to rats and mice produces low levels of N7-(2-carbamoyl-2-hydroxyethyl)guanine (Gamboa da Costa et al., 2003; Segerback et al., 1995).Acrylamide induces a characteristic peripheral neurotoxicity in animals and man(Spencer and Schaumburg, 1974a, b, 1975). This toxicity manifests itself as a distal to proximal loss of nerve function and dying back of cells. Acrylamide also effects rodent reproduction, namely smaller litter size. At elevated acrylamide doses other reproductive effects are seen, likely as a consequence of the neurotoxicity. Acrylamide is carcinogenic in drinking water studies in laboratory rats (Friedman et al.,1995; Johnson et al., 1986). In male rats, it induces tumors of the tunica vaginalis testes and the thyroid, while in females, it induces mammary fibroadenomas and thyroid tumors(Friedman et al., 1995). The mechanism for this tumorigenicity is unclear, although interaction with the dopamine receptor has been postulated as well as genotoxicity (Tyland Friedman, 2003). If the mechanism were genotoxicity, then conversion of acrylamide to glycidamide is directly proportional to carcinogenic activity.Understanding the mechanism of tumorigenicity is important, since conventional risk assessment techniques place the order of magnitude of the risk at approximately 10-3 with exposures of 70 μg/ day.The relative contributions of acrylamide and glycidamide in the mode of action of acrylamide are the subject of debate and current research. Understanding the conversion of acrylamide to glycidamide and differences that may occur between species, exposure route, and dose are important considerations in assessing the risk of the possible effects of acrylamide exposures in the diet, in consumer products, and in the workplace.The primary objectives of this study were to evaluate the conversion of acrylamide to glycidamide in people exposed to acrylamide, and to evaluate the extent of uptake following dermal administration. This was conducted by administering a low dose of 13C labeled acrylamide to volunteers orally or dermally, and by measuring urinary metabolites or hemoglobin adducts derived from the glycidamide pathway and comparing them to metabolites and hemoglobin adducts derived from acrylamide directly. More specifically, we intended to evaluate urinary metabolites and hemoglobin adducts, and to measure hormone levels after exposure to a known dose of acrylamide. As a secondary and no less important objective, we intended to monitor the safety of acrylamide in people exposed under controlled conditions.

Acrylamide↗
PubMed2005

NTP-CERHR monograph on the potential human reproductive and developmental effects of amphetamines.

The National Toxicology Program (NTP) Center for the Evaluation of Risks to Human Reproduction (CERHR) conducted an evaluation of the potential for amphetamines to cause adverse effects on reproduction and development in humans. Amphetamines evaluated were D- and D,L-amphetamine and methamphetamine. Amphetamine is approved by the U.S. Food and Drug Administration for the treatment of attention deficit hyperactivity disorder (ADHD) in persons over 3 years of age and narcolepsy; methamphetamine is approved for the treatment of ADHD in persons 6 years of age and older and for short-term treatment of obesity. Amphetamines were selected for evaluation because of 1) widespread usage in children, 2) availability of developmental studies in children and experimental animals, and 3) public concern about the effect of this stimulant on child development. The results of this evaluation on amphetamines are published in an NTP-CERHR monograph which includes: 1) the NTP Brief, 2) the Expert Panel Report on the Reproductive and Developmental Toxicity of Methylphenidate, and 3) public comments received on the Expert Panel Report. As stated in the NTP Brief, the NTP reached the following conclusions regarding the possible effects of exposure to methylphenidate on human development and reproduction. First, there is some concern for developmental effects, specifically for potential neurobehavioral alterations, from prenatal amphetamine exposure in humans both in therapeutic and non-therapeutic settings. After prenatal exposure to therapeutic doses of amphetamine, rat pups demonstrated neurobehavioral alterations. Data from human and animal studies were judged insufficient for an evaluation of the effect of amphetamine exposure on growth and other related developmental effects. Second, there is concern for methamphetamine-induced adverse developmental effects, specifically on growth and neurobehavioral development, in therapeutic and non-therapeutic settings. This conclusion is based on evidence from studies in experimental animals that prenatal and postnatal exposures to methamphetamine produce neurobehavioral alterations, small litter size, and low birth weight. Results from studies in humans suggest that methamphetamine may cause low birth weight and shortened gestation, but study confounders such as possible multiple drug usage prevent a definite conclusion. NTP-CERHR monographs are transmitted to federal and state agencies, interested parties, and the public and are available in electronic PDF format on the CERHR web site (http://cerhr.niehs.nih.gov) and in printed text or CD-ROM from the CERHR (National Institute of Environmental Health Sciences, P.O. Box 12233, MD EC-32, Research Triangle Park, NC; fax: 919-316-4511).

Amphetamine↗
PubMed2005

NTP technical report on the toxicology and carcinogenesis studies of anthraquinone (CAS No. 84-65-1) in F344/N rats and B6C3F1 mice (Feed Studies).

BACKGROUND: Anthraquinone is used to make dyes and paper and as a bird repellant. We studied anthraquinone to determine if it caused cancer in rats or mice. METHODS: We fed groups of 50 male and female rats feed containing 469, 938, 1,875, or 3,750 parts per million (ppm) anthraquinone for 2 years. Similar groups of male and female mice received feed containing 833, 2,500, or 7,500 ppm anthraquinone. Groups of 50 male and female rats and mice receiving undosed feed served as the control groups. Tissues from more than 40 sites were examined for every animal. RESULTS: In each group, the group receiving the highest dose of anthraquinone weighed less than its control group. Male and female rats given anthraquinone had higher rates of tumors of the kidney and urinary bladder. Liver tumors also were increased in female rats and slightly increased in male rats. In male and female mice given anthraquinone, the rates of liver tumors were greatly increased, and a few of these animals developed thyroid gland tumors. CONCLUSIONS: We conclude that anthraquinone caused cancer of the kidney and urinary bladder in male and female rats and of the liver in female rats. The occurrence of some liver tumors in male rats may have been related to anthraquinone exposure. We conclude that anthraquinone caused liver cancer in male and female mice, and thyroid gland tumors in mice may have been related to anthraquinone.

Animals↗
PubMed2005

Toxicology and carcinogenesis studies of sodium chlorate (Cas No. 7775-09-9) in F344/N rats and B6C3F1 mice (drinking water studies).

BACKGROUND: Sodium chlorate occurs when drinking water is disinfected by chlorine dioxide. We studied the effects of sodium chlorate in rats and mice to identify potential toxic or carcinogenic hazards to humans. METHODS: We gave groups of male and female rats drinking water containing 125, 1,000, or 2,000 milligrams (mg) of sodium chlorate per liter (L) of water for two years. Male and female mice received 500, 1,000, or 2,000 mg/L. Other groups of animals received plain tap water and served as the control groups. At the end of the study, tissues from more than 40 sites were examined for every animal. RESULTS: Male and female rats receiving sodium chlorate had higher rates of follicular cell hypertrophy of the thyroid gland, and the groups receiving 2,000 mg/L had higher rates of thyroid gland cancer, compared with the control groups. Female mice exposed to sodium chlorate had a few pancreatic islet cell tumors. CONCLUSIONS: We conclude that sodium chlorate caused some thyroid gland neoplasms in male and female rats. The pancreatic islet cell tumors in female mice may have been related to sodium chlorate exposure.

Administration, Oral↗
PubMed2005

NTP carcinogenesis studies of 2,2-bis(bromomethyl)-1,3-propanediol, nitromethane, and 1,2,3-trichloropropane (cas nos. 3296-90-0, 75-52-5, and 96-18-4) in guppies (Poecilia reticulata) and medaka (Oryzias latipes) (Waterborne Studies).

The NTP chose to initiate studies in fish as an exploration of alternate or additional models for examining chemical toxicity and carcinogenicity. The use of small fish species in carcinogenicity testing offered potential advantages as a bioassay test system, including significant savings in cost and time over rodent studies. Large numbers of small fish could be easily maintained in a limited area. The two species chosen for study were guppy (Poecilia reticulata) and medaka (Oryzias latipes), both of which are hardy, easily maintained, and have a low occurrence of background lesions. The three chemicals chosen for study in fish had already been studied by the NTP in rodents, permitting a comparison of results between the two models. Two of the chemicals used (2,2-bis(bromomethyl)-1,3-propanediol and 1,2,3-trichloropropane) were mutagenic and multisite carcinogens in rats and mice. The third chemical, nitromethane, was nonmutagenic with a more modest carcinogenic response in rodents. Male and female guppies and medaka were exposed to 2,2-bis(bromomethyl)- 1,3-propanediol (greater than 99% pure), nitromethane, (greater than 99% pure), or 1,2,3-trichloropropane (99% pure) in aquaria water for up to 16 months. OVERALL STUDY DESIGN: Groups of approximately 220 guppies (two replicates of 110) were maintained in aquaria water containing nominal concentrations of 0, 24, 60, or 150 mg/L 2,2-bis(bromomethyl)-1,3-propanediol; 0, 10, 30, or 70 mg/L nitromethane; or 0, 4.5, 9.0, or 18.0 mg/L 1,2,3-trichloropropane. Groups of approximately 340 medaka (two replicates of 170) were maintained in aquaria water containing 0, 24, 60, or 150 mg/L 2,2-bis(bromomethyl)-1,3-propanediol; 0, 10, 20, or 40 mg/L nitromethane; or 0, 4.5, 9.0, or 18.0 mg/L 1,2,3-trichloropropane. The overall study durations were 16 months for all guppy studies, 14 months for 2,2-bis(bromomethyl)-1,3-propanediol-exposed medaka, and 13 months for nitromethane- and 1,2,3-trichloropropane-exposed medaka. Ten guppies and 10 medaka from each group replicate were sacrificed at 9 months for histopathologic analysis. Approximately one third of the remaining fish from each group were placed in chemical-free water at 9 months and constituted a stop-exposure study component. The remainder of the fish were exposed for the duration of the study and constituted the core study component. A stop-exposure component was added to determine if stopping the exposure at 9 months and transferring to chemical-free aquaria might allow for better survival and tumor development. The sex of guppies and medaka was determined at histopathologic analysis. 2,2-BIS(BROMOMETHYL)-1,3-PROPANEDIOL - 16-MONTH STUDY IN GUPPIES: 2,2-Bis(bromomethyl)-1,3-propanediol was chronically toxic to guppies in the 60 and 150 mg/L core and stop-exposure groups. Due to mortality, exposure of core study animals in the 150 mg/L group was terminated on day 443, after approximately 64 weeks on study, and fish were maintained in 2,2-bis(bromomethyl)- 1,3-propanediol-free water in the exposure system until the end of the study at 69 weeks. Nominal exposure concentrations of 24, 60, and 150 mg/L provided actual aquaria water exposure concentrations of 20.0, 53.5, and 139.0 mg/L 2,2-bis(bromomethyl)- 1,3-propanediol, respectively. There were no treatment-related differences between the control and exposed groups in body weights or lengths. At 9 months, hepatocellular adenomas occurred in one 24 mg/L male and in one 150 mg/L male. In the core study, the incidence of hepatocellular adenoma or carcinoma (combined) in 150 mg/L males was greater than that in the controls; multiple adenomas occurred in two 150 mg/L males and in one 150 mg/L female. Cholangioma occurred in a small number of exposed males and females. In the stop-exposure study, incidences of hepatocellular adenoma (including multiple) and of hepatocellular carcinoma were greater in 150 mg/L males than in controls. One cholangioma and one cholangiocarcinoma occurred in the 150 mg/L female group. 14-MONTH STUDY IN MEDAKA: Exposure to 2,2-bis(bromomethyl)-1,3-propanediol did not result in any significant reduction in survival, although the mortality of fish was somewhat greater in the 60 and 150 mg/L core study groups than in the control and 24 mg/L groups. After reallocation, mortality of medaka in the 60 and 150 mg/L core groups was slightly increased over the corresponding stop-exposure groups. Nominal exposure concentrations of 24, 60, and 150 mg/L provided actual exposure concentrations of 19.4, 56.9, and 137.8 mg/L 2,2-bis(bromomethyl)- 1,3-propanediol, respectively. Core study animals in the 60 and 150 mg/L groups were significantly larger, in both body length and weight, than control group fish. In the core study, the incidence of hepatocellular adenoma or carcinoma (combined) was increased in 150 mg/L males. Cholangiocarcinomas occurred in a few exposed males and females, with all but one occurring in 150 mg/L fish. One cholangioma occurred in a 150 mg/L female, and one occurred in a control female. In the stop-exposure study, incidences of hepatocellular adenoma or carcinoma (combined) were marginally increased in the 150 mg/L group of males and in the 60 and 150 mg/L groups of females as compared with controls. Cholangiocarcinoma occurred in one male and one female in the 150 mg/L groups and in one control female. NITROMETHANE - 16-MONTH STUDY IN GUPPIES: Although the cause of death could not be confirmed in many cases, mortality in the 70 mg/L groups appeared to indicate that this level of nitromethane exposure was chronically toxic. This is confirmed by the similar survival rate of guppies from all treatments following removal from treatment aquaria and placement in stop-exposure. Due to the high mortality of fish in the 70 mg/L core study groups, these fish were removed from treatment (day 396) and fixed for histological analyses after approximately 57 weeks on study. The controls and other exposed groups were sacrificed at 70 weeks. Nominal exposure concentrations of 10, 30, and 70 mg/L provided actual exposure concentrations of 9.9, 28.7, and 66.4 mg/L nitromethane, respectively. There were no treatment-related differences between the control and exposed groups in body lengths or weights. 13-MONTH STUDY IN MEDAKA: Nitromethane in the aquaria supported a substantial microfaunal growth which, without frequent cleaning, affected water quality and treatment concentrations. To maintain acceptable water quality and treatment concentrations potentially affected by the rapid microfaunal growth, the study aquaria were brushed once and siphoned three times each day. Due to this frequent activity, a number of fish probably died due to mechanical injury. Unfortunately, the cause of death could not be confirmed in many cases; the mortality from this activity is believed to have been approximately uniform among treatments and should not have affected the comparison of survival between treatments. Based on mortality in this study and the previous life-span evaluation, the life phase of this study was terminated approximately 13.5 months after hatching. Nominal exposure concentrations of 10, 20, and 40 mg/L resulted in actual exposure concentrations of 9.3, 20.8, and 41.7 mg/L nitromethane, respectively. No differences between control and exposed groups were found in body lengths or weights at the 9-month interim evaluation. Due to mortality, unequal numbers of fish were distributed among the core study and stop-exposure aquaria at 9 months. Differences in lengths and weights were found at 13 months. The biological significance of this finding is unknown. At 9 months, a single cholangiocarcinoma occurred in a 40 mg/L male. Hepatocellular adenomas occurred in two 20 mg/L males and in one 40 mg/L female. In the core study, one cholangioma occurred in a 20 mg/L male, and cholangiocarcinomas were seen in a few exposed males, but none occurred in control males. 1,2,3-TRICHLOROPROPANE - 16-MONTH STUDY IN GUPPIES: The survival of exposed guppies was less than that of the control group at 9 months. Reduced survival was evident at 6 months in the 18.0 mg/L groups and at 7 months in the 4.5 and 9.0 mg/L groups. Survival was significantly reduced in the 18.0 mg/L core study group within 1 month of the 9-month interim evaluation, and mortality in this group was 42.6% between 9 months and study termination. Nominal exposure concentrations of 4.5, 9.0, and 18.0 mg/L resulted in actual exposure concentrations of 4.4, 8.8, and 18.2 mg/L 1,2,3-trichloropropane, respectively. Guppies in the 18.0 mg/L core study group were significantly longer and weighed more than the controls. Fish in the 18.0 mg/L stop-exposure group also weighed more than the controls. Mortality of fish during the study resulted in unequal numbers of individuals distributed to core study and stop-exposure aquaria at 9 months. This appears to have influenced the length and weight of fish measured at study termination (i.e., the smaller tank population allowed the fish to grow more). Observed differences in weight and length between controls and 18.0 mg/L fish was most likely an artifact of the reduced numbers of fish in the 18.0 mg/L aquaria. At 9 months, multiple hepatocellular adenomas occurred in one 4.5 mg/L male, and one hepatocellular adenoma occurred in a control male. In the core study, increased incidences of cholangiocellular (bile duct) and hepatocellular neoplasms occurred in exposed groups of males and females. Cholangioma and cholangiocarcinoma were seen in several exposed males and females. In the stop-exposure study, increased incidences of hepatocellular neoplasms occurred in 18.0 mg/L males and increased incidences of cholangiocellular (bile duct) neoplasms occurred in 18.0 mg/L females. (ABSTRACT TRUNCATED)

Animal Feed↗
PubMed2004

NTP technical report on the toxicology and carcinogenesis studies of propylene glycol mono-t-butyl ether (CAS No. 57018-52-7) in F344/N rats and B6C3F1 mice and a toxicology study of propylene glycol mono-t-butyl ether in male NBR rats (inhalation studies).

BACKGROUND: Propylene glycol mono-t-butyl ether is used as a solvent in all-purpose cleaners, inks, and nail polish lacquers. We studied the effects of propylene glycol mono-t-butyl ether on male and female rats to identify potential toxic or cancer-related hazards to humans. METHODS: We exposed groups of male and female rats and mice to air containing vapors of propylene glycol mono-t-butyl ether at concentrations of 75, 300, or 1,200 parts per million (ppm) for 6 hours per day, 5 days a week for 2 years. Untreated control animals were housed in similar exposure chambers but without chemical exposure for comparison. Tissues from more than 40 sites were examined for every animal. RESULTS: Rats receiving 1,200 ppm propylene glycol mono-t-butyl ether weighed less on average than the control animals. Tumors were seen in the liver and kidney of a few male rats exposed to propylene glycol mono-t-butyl ether. No increases in the numbers of tumors were seen in female rats. In male and female mice there were large increases in the numbers of liver tumors compared with the control animals. CONCLUSIONS: We conclude that propylene glycol mono-t-butyl ether caused cancer in the liver of male and female mice. Propylene glycol mono-t-butyl ether did not cause cancer in female rats, and its effect on the liver and kidney of male rats was considered uncertain.

Administration, Inhalation↗
PubMed2004

NTP toxicology and carcinogenesis studies of trans-cinnamaldehyde (CAS No. 14371-10-9) in F344/N rats and B6C3F1 mice (feed studies).

UNLABELLED: Cinnamaldehyde is used in foods, beverages, medical products, perfumes, cosmetics, soaps, detergents, creams, and lotions. Cinnamaldehyde has been used as a filtering agent and a rubber reinforcing agent and is used as a brightener in electroplating processes, as an animal repellent, as an insect attractant, and as an antifungal agent. trans-cinnamaldehyde was nominated for study by the Food and Drug Administration based on its widespread use as a flavor and fragrance ingredient and its structural similarity to cinnamyl anthranilate and 3,4,5-trimethoxy cinnamaldehyde, two known rodent carcinogens. Male and female F344/N rats and B6C3F1 mice were exposed to trans-cinnamaldehyde (at least 95% pure) in feed for 3 months or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, Drosophila melanogaster, and mouse peripheral blood erythrocytes. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female F344/N rats were fed diets containing 4,100, 8,200, 16,500, or 33,000 ppm microencapsulated trans-cinnamaldehyde (equivalent to average daily doses of approximately 275, 625, 1,300, or 4,000 mg trans-cinnamaldehyde/kg body weight to males and 300, 570, 1,090, or 3,100 mg/kg to females) for 3 months. Additional groups of 10 male and 10 female rats received untreated feed (untreated controls) or feed containing placebo microcapsules (vehicle controls). All rats survived to the end of the study. Mean body weights of all exposed groups of males and 16,500 and 33,000 ppm females were significantly less than those of the vehicle controls, and 33,000 ppm males lost weight during the study. Feed consumption by exposed groups of males and females was less than that by the vehicle controls throughout the study. Clinical chemistry results of these studies indicated that trans-cinnamaldehyde administration, at the doses selected, induced an increase in serum bile acid concentration that suggests a hepatic effect in both male and female rats. Gross lesions observed at necropsy included multifocal to diffuse white nodules of the forestomach mucosa in 8,200 ppm or greater males and females. Increased incidences of nonneoplastic lesions of the forestomach included squamous epithelial hyperplasia in 8,200 ppm or greater males and females and chronic active inflammation in 33,000 ppm males and 16,500 and 33,000 ppm females. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female B6C3F1 mice were fed diets containing 4,100, 8,200, 16,500, or 33,000 ppm microencapsulated trans-cinnamaldehyde (equivalent to average daily doses of approximately 650, 1,320, 2,550, and 5,475 mg/kg to males and 625, 1,380, 2,680, and 5,200 mg/kg to females) for 3 months. Additional groups of 10 male and 10 female mice received untreated feed (untreated controls) or feed containing placebo microcapsules (vehicle controls). One vehicle control male, one 4,100 ppm male, and one 33,000 ppm male died during the first week of the study due to inanition that resulted from difficulty with the feeder. Five 16,500 ppm and eight 33,000 ppm male mice died during weeks 2 and 3 due to unpalatability of the dosed feed. Mean body weights of all exposed groups of males and of females exposed to 8,200 ppm or greater were significantly less than those of the vehicle controls. Feed consumption by 16,500 and 33,000 ppm mice was less than that by the vehicle controls during weeks 1 and 2. The incidence of squamous epithelial hyperplasia of the forestomach mucosa in 33,000 ppm females was significantly increased, and olfactory epithelial degeneration of the nasal cavity occurred in 16,500 and 33,000 ppm males and females. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female F344/N rats were fed diets containing 1,000, 2,100, or 4,100 ppm microencapsulated trans-cinnamaldehyde for 2 years. Additional groups of 50 male and 50 female rats received untreated feed (untreated controls) or feed containing placebo microcapsules (vehicle controls). Dietary concentrations of 1,000, 2,100, or 4,100 ppm delivered average daily doses of approximately 50, 100, or 200 mg/kg to males and females. Survival of 4,100 ppm males was greater than that of the vehicle controls. Mean body weights of 4,100 ppm males and females were generally less than those of the vehicle controls throughout the study. Feed consumption by 2,100 and 4,100 ppm males and 4,100 ppm females was less than that by the vehicle controls at the beginning and end of the study. There were no neoplasms or nonneoplastic lesions that were attributed to exposure to trans-cinnamaldehyde. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female B6C3F1 mice were fed diets containing 1,000, 2,100, or 4,100 ppm microencapsulated trans-cinnamaldehyde for 2 years. Additional groups of 50 male and 50 female mice received untreated feed (untreated controls) or feed containing placebo microcapsules (vehicle controls). Dietary concentrations of 1,000, 2,100, or 4,100 ppm delivered average daily doses of approximately 125, 270, or 550 mg/kg to males and females. Survival of males in the 2,100 ppm group was less than that of the vehicle control group. Mean body weights of 2,100 and 4,100 ppm males and females were generally less than those of the vehicle controls throughout the study, and mean body weights of 1,000 ppm males were less after week 74. Feed consumption by exposed mice was similar to that by the vehicle controls. The incidences of olfactory epithelial pigmentation in 4,100 ppm males and in 2,100 and 4,100 females were significantly greater than those in vehicle controls. There were no neoplasms that were attributed to exposure to trans-cinnamaldehyde. GENETIC TOXICOLOGY: trans-cinnamaldehyde was mutagenic in S. typhimurium strain TA100 in the presence of induced mouse liver S9 activation enzymes only. All other strain and activation combinations, including the standard rat and hamster derived liver S9 fractions yielded negative results. trans-cinnamaldehyde induced sister chromatid exchanges in Chinese hamster ovary cells with and without induced rat liver S9 activation. No significant increase in the frequency of chromosomal aberrations occurred in Chinese hamster ovary cells cultured with trans-cinnamaldehyde, with or without induced rat liver S9. In tests for induction of germ cell genetic damage in male Drosophila melanogaster, trans-cinnamaldehyde induced a significant increase in the frequency of sex-linked recessive lethal mutations when administered by abdominal injection; however, no induction of reciprocal translocations occurred in germ cells of treated males. No increase in the frequency of micronucleated erythrocytes was observed in peripheral blood of male or female mice administered trans-cinnamaldehyde in dosed feed for 3 months. CONCLUSIONS: Under the conditions of this 2-year feed study, there was no evidence of carcinogenic activity of transcinnamaldehyde in male or female F344/N rats exposed to 1,000, 2,100, or 4,100 ppm. There was no evidence of carcinogenic activity of trans-cinnamaldehyde in male or female B6C3F1 mice exposed to 1,000, 2,100, or 4,100 ppm. Exposure to trans-cinnamaldehyde resulted in olfactory epithelial pigmentation in male and female mice.

Acrolein↗
PubMed2004

Toxicology and carcinogensis studies of 2-methylimidazole (Cas No. 693-98-1) in B6C3F1 mice (feed studies).

BACKGROUND: 2-methylimidazole is used to make many other chemicals for drugs, photography, dyes, rubber, and agriculture. We studied the effects of 2-methylimidazole on male and female rats and mice to identify potential toxic or cancer-related hazards to humans. METHODS: We studied the effects of 2-methylimidazole by mixing it in the feed of rats and mice for 2 years. The doses given were 300, 1,000, or 3,000 parts per million (ppm) 2-methylimidazole (equivalent to 0.03%, 0.1%, or 0.3%) for male rats; 1,000, 2,500, or 5,000 ppm for female rats; and 625, 1,250, or 2,500 ppm for male and female mice. There were 50 animals in each exposure group. Control animals received the same feed with no chemical added. Tissues from more than 40 sites were examined for every animal. RESULTS: For both male and female rats and mice, the groups receiving the highest amounts of 2-methylimidazole weighed less on average than the control animals. Male and female rats and male mice receiving 2-methylimidazole had higher rates of thyroid gland cancers than did the untreated control animals. The rates of liver tumors were greater in male and female mice receiving 2-methylimidazole and also slightly increased in male and female rats receiving 2-methylimidazole. CONCLUSIONS: We concluded that 2-methylimidazole caused increased rates of cancer of the thyroid gland and liver in rats and mice.

Administration, Oral↗