Clear evidence of the carcinogenic potential of anthracene: A 2-year feeding study in rats and mice.

Anthracene is an environmental pollutant and its adverse effects on human health have long been a concern due to its persistence and bioaccumulation properties. However, there is insufficient evidence for its chronic toxicity, especially carcinogenicity, in either humans or experimental animals. In this study, its carcinogenicity and chronic toxicity were investigated in compliance with the OECD test guideline 451 (OECD TG 451) and Good Laboratory Practice Standards. Fifty male and 50 female F344 rats and 50 female BDF1 mice were administrated 0, 8000, 20000, or 50000 ppm anthracene in the diet for 104 weeks, and 50 male BDF1 mice were fed diets containing anthracene at 0, 3200, 8000, or 20000 ppm. Anthracene treatment had no adverse effect on either the survival rate or general condition of the rats or mice during the study period. Body weights were lower or tended to be lower in the anthracene-treated groups than in the control groups. Increased incidence of hepatocellular carcinoma and hepatocellular adenoma was observed in male rats and female mice. Renal cell carcinoma and renal cell adenoma, fibroadenoma in the mammary gland, and uterine endometrial stromal sarcoma were increased in female rats. Transitional cell carcinoma and transitional cell papilloma in the urinary bladder were also increased in male and female rats. In addition, several different pre-neoplastic lesions were increased in the anthracene-treated male and female rats and female mice. These results provide clear evidence that oral administration of anthracene for 104 weeks has a carcinogenic effect in male and female rats and female mice.

Contribution of toxicological pathology to occupational health: lung carcinogenicity of fibrous and particulate substances in rats.

In this review, we focus on the rat pulmonary carcinogenicity of two solid substances, fibrous multi-walled carbon nanotube (MWCNT) and particulate indium tin oxide (ITO). Inhalation exposure to MWNT-7, a type of MWCNTs, and ITO induced lung carcinogenicity in both male and female rats. Toxicity to the alveolar epithelium is induced by macrophages undergoing frustrated phagocytosis or frustrated degradation of engulfed particles (referred to as frustrated macrophages). Melted macrophage contents contribute significantly to development of hyperplasia of the alveolar epithelium, which eventually results in the induction of lung carcinoma. MWNT-7 and ITO induce secondary genotoxicity; consequently, a no-observed-adverse-effect level can be applied to these materials rather than benchmark doses that are used for non-threshold carcinogens. Thus, establishing occupational exposure limit values for MWNT-7 and ITO based on the existence of a carcinogenic threshold is reasonable.

Carcinogenicity and chronic toxicity of acrolein in rats and mice by two-year inhalation study.

The carcinogenicity and chronic toxicity of acrolein was examined by whole body inhalation to groups of 50 F344/DuCrlCrlj rats and 50 B6D2F1/Crlj mice of both sexes for two years. The concentration of acrolein was 0, 0.1, 0.5 or 2 ppm (v/v) for male and female rats; and 0, 0.1, 0.4 or 1.6 ppm for male and female mice. Two-year administration of acrolein induced the squamous cell carcinomas in nasal cavity which is rare tumor in one male and two female rats. In females, rhabdomyoma in nasal cavity was observed in four rats exposed to 2 ppm. In mice, since the survival rate of male and female of mice control group were lowered than 25% in late of the administration periods due to renal lesion and/or amyloid deposition, the mice study was terminated at 93rd week in males, and was terminated at 99th week in females. The incidences of adenomas in nasal cavity were observed in 16 females and significantly increased only in female mice. Thus, acrolein is carcinogenic in two species, i.e. rats and mice. Additionally, non-neoplastic nasal cavity lesions in rats and mice were observed.

Area under the blood concentration-time curve (AUC) of ethylbenzene concentration in rats: relationship to inhalation and oral administration route-dose.

For human risk assessment of toxic chemicals, especially volatile organic compounds (VOCs), the Ministry of the Environment, Government of Japan, has called for the interconversion of inhalation-dose and oral-dose data, two common exposure routes. To address this issue, the present study investigated the time-course changes of ethylbenzene (EB) concentrations in the blood of rats during and after 6-hr inhalation exposure to EB (25, 50, 100, and 200 ppm) and after oral administration of EB by a single oral gavage (25, 50, 100, and 200 mg/kg) of EB. The Area Under the blood concentration-time Curve (AUC) at each blood collection time point (0, 30, 60, 120, 180, 360, 420, 540, and 1440 min, after starting exposure) was determined. The inhalation dose of 25 ppm corresponded closely to the oral administration of 25 mg/kg・bw (r value of 0.859), and the inhalation dose of 200 ppm correlated with the oral administration of 100 mg/kg・bw (r value of 0.948). These results suggest that this comparison using the AUC data at each blood collection time point is valuable for understanding the route- and dose-effects of EB. This study will improve risk assessment of human exposure to EB and other VOCs.

Quantitative analysis of mutagenicity and carcinogenicity of 2-amino-3-methylimidazo[4,5-f]quinoline in F344 gpt delta transgenic rats.

Quantitative analysis of the mutagenicity and carcinogenicity of the low doses of genotoxic carcinogens present in food is of pressing concern. The purpose of the present study was to determine the mutagenicity and carcinogenicity of low doses of the dietary genotoxic carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Male F344 gpt delta transgenic rats were fed diets supplemented with 0, 0.1, 1, 10 or 100 ppm IQ for 4 weeks. The frequencies of gpt transgene mutations in the liver were significantly increased in the 10 and 100 ppm groups. In addition, the mutation spectra was altered in the 1, 10 and 100 ppm groups: frequencies of G:C to T:A transversion were significantly increased in groups administered 1, 10 and 100 ppm IQ in a dose-dependent manner, and the frequencies of G:C to A:T transitions, A:T to T:A transversions and A:T to C:G transversions were significantly increased in the 100 ppm group. Increased frequencies of single base pair deletions and Spi- mutants in the liver, and an increase in glutathione S-transferase placental form (GST-P)-positive foci, a preneoplastic lesion of the liver in rats, was also observed in the 100 ppm group. In contrast, neither mutations nor mutation spectra or GST-P-positive foci were statistically altered by administration of IQ at 0.1 ppm. We estimated the point of departure for the mutagenicity and carcinogenicity of IQ using the no-observed-effect level approach and the Benchmark dose approach to characterise the dose-response relationship of low doses of IQ. Our findings demonstrate the existence of no effect levels of IQ for both in vivo mutagenicity and hepatocarcinogenicity. The findings of the present study will facilitate an understanding of the carcinogenic effects of low doses of IQ and help to determine a margin of exposure that may be useful for practical human risk assessment.

In vivo positive mutagenicity of 1,4-dioxane and quantitative analysis of its mutagenicity and carcinogenicity in rats.

1,4-Dioxane is a widely used synthetic industrial chemical and its contamination of drinking water and food is a potential health concern. It induces liver tumors when administered in the drinking water to rats and mice. However, the mode of action (MOA) of the hepatocarcinogenicity of 1,4-dioxane remains unclear. Importantly, it is unknown if 1,4-dioxane is genotoxic, a key consideration for risk assessment. To determine the in vivo mutagenicity of 1,4-dioxane, gpt delta transgenic F344 rats were administered 1,4-dioxane at various doses in the drinking water for 16 weeks. The overall mutation frequency (MF) and A:T- to -G:C transitions and A:T- to -T:A transversions in the gpt transgene were significantly increased by administration of 5000 ppm 1,4-dioxane. A:T- to -T:A transversions were also significantly increased by administration of 1000 ppm 1,4-dioxane. Furthermore, the DNA repair enzyme MGMT was significantly induced at 5000 ppm 1,4-dioxane, implying that extensive genetic damage exceeded the repair capacity of the cells in the liver and consequently led to liver carcinogenesis. No evidence supporting other MOAs, including induction of oxidative stress, cytotoxicity, or nuclear receptor activation, that could contribute to the carcinogenic effects of 1,4-dioxane were found. These findings demonstrate that 1,4-dioxane is a genotoxic hepatocarcinogen and induces hepatocarcinogenesis through a mutagenic MOA in rats. Because our data indicate that 1,4-dioxane is a genotoxic carcinogen, we estimated the point of departure of the mutagenicity and carcinogenicity of 1,4-dioxane using the no-observed effect-level approach and the Benchmark dose approach to characterize its dose-response relationship at low doses.

Qualitative and quantitative approaches in the dose-response assessment of genotoxic carcinogens.

Qualitative and quantitative approaches are important issues in field of carcinogenic risk assessment of the genotoxic carcinogens. Herein, we provide quantitative data on low-dose hepatocarcinogenicity studies for three genotoxic hepatocarcinogens: 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and N-nitrosodiethylamine (DEN). Hepatocarcinogenicity was examined by quantitative analysis of glutathione S-transferase placental form (GST-P) positive foci, which are the preneoplastic lesions in rat hepatocarcinogenesis and the endpoint carcinogenic marker in the rat liver medium-term carcinogenicity bioassay. We also examined DNA damage and gene mutations which occurred through the initiation stage of carcinogenesis. For the establishment of points of departure (PoD) from which the cancer-related risk can be estimated, we analyzed the above events by quantitative no-observed-effect level and benchmark dose approaches. MeIQx at low doses induced formation of DNA-MeIQx adducts; somewhat higher doses caused elevation of 8-hydroxy-2'-deoxyquanosine levels; at still higher doses gene mutations occurred; and the highest dose induced formation of GST-P positive foci. These data indicate that early genotoxic events in the pathway to carcinogenesis showed the expected trend of lower PoDs for earlier events in the carcinogenic process. Similarly, only the highest dose of IQ caused an increase in the number of GST-P positive foci in the liver, while IQ-DNA adduct formation was observed with low doses. Moreover, treatment with DEN at low doses had no effect on development of GST-P positive foci in the liver. These data on PoDs for the markers contribute to understand whether genotoxic carcinogens have a threshold for their carcinogenicity. The most appropriate approach to use in low dose-response assessment must be approved on the basis of scientific judgment.

Lung carcinogenicity of inhaled multi-walled carbon nanotube in rats.

BACKGROUND: Multi-walled carbon nanotubes (MWCNTs) constitute one of the most promising types of nanomaterials in industry today. With their increasing use, the potential toxicity and carcinogenicity of MWCNT needs to be evaluated in bioassay studies using rodents. Since humans are mainly exposed to MWCNT by inhalation, we performed a 104-week carcinogenicity study using whole-body inhalation exposure chambers with a fibrous straight type of MWCNT at concentrations of 0, 0.02, 0.2, and 2 mg/m3 using male and female F344 rats. RESULTS: Lung carcinomas, mainly bronchiolo-alveolar carcinoma, and combined carcinomas and adenomas were significantly increased in males exposed to 0.2 and 2 mg/m3 MWNT-7 and in females exposed to 2 mg/m3 MWNT-7 compared to the clean air control group. However, no development of pleural mesothelioma was observed. Concentration-dependent toxic effects in the lung such as epithelial hyperplasia, granulomatous change, localized fibrosis, and alteration in BALF parameters were found in MWNT-7 treatment groups of both sexes. There were no MWNT-7-specific macroscopic findings in the other organs, including the pleura and peritoneum. Absolute and relative lung weights were significantly elevated in male rats exposed to 0.2 and 2 mg/m3 MWNT-7 and in all exposed female groups. The lung burdens of MWNT-7 were clearly increased in a concentration-dependent as well as a duration-dependent manner. CONCLUSION: There is clear evidence that MWNT-7 is carcinogenic to the lungs of male and female F344 rats, however no plural mesothelioma was observed.

Carcinogenicity and chronic toxicity of hydrazine monohydrate in rats and mice by two-year drinking water treatment.

The carcinogenicity and chronic toxicity of hydrazine monohydrate was examined by administrating hydrazine monohydrate in drinking water to groups of 50 F344/DuCrj rats and 50 Crj:BDF1 mice of both sexes for two years. The drinking water concentration of hydrazine monohydrate was 0, 20, 40 or 80 ppm (wt/wt) for male and female rats and male mice; and 0, 40, 80 or 160 ppm for female mice. Survival rates of each group of males and females rats and mice were similar to the respective controls, except female rats administered 80 ppm. Two-year administration of hydrazine monohydrate produced an increase in the incidences of hepatocellular adenomas and carcinomas in rats of both sexes along with hepatic foci. In mice, the incidences of hepatocellular adenomas and carcinomas were increased in females, and significantly increased incidences of hepatocellular adenomas in females administered 160 ppm were observed. Thus, hydrazine monohydrate is carcinogenic in two species, rats and mice. Additionally, non-neoplastic renal lesions in rats and mice and non-neoplastic nasal lesions in mice were observed.

Inhalation carcinogenicity of dichloromethane in rats and mice.

The carcinogenicity of inhaled dichloromethane (DCM) was examined by exposing groups of 50 F344/DuCrj rats and 50 Crj: BDF1 mice of both sexes to 0, 1000, 2000, or 4000 ppm (w/w) DCM-containing aerosol for 2 years. Inhalation of DCM resulted in increased incidences of subcutis fibromas, mammary gland fibroadenoma, and peritoneum mesotheliomas in male rats; mammary gland fibroadenomas in female rats; and bronchiolar-alveolar adenomas and carcinomas in the lung and hepatocellular adenomas and carcinomas in male and female mice. These results clearly indicate that inhaled DCM is carcinogenic in F344/DuCrj (SPF) rats and Crj: BDF1 (SPF) mice.

Estimation of chloroform inhalation dose by other routes based on the relationship of area under the blood concentration-time curve (AUC)-inhalation dose to chloroform distribution in the blood of rats.

The present study investigated the time-course changes of concentration of chloroform (CHCl3) in the blood during and after exposure of male rats to CHCl3 by inhalation. Increasing the dose of CHCl3 in the inhalation exposed groups caused a commensurate increase in the concentration of CHCl3 in the blood and the area under the blood concentration-time curve (AUC). There was good correlation (r = 0.988) between the inhalation dose and the AUC/kg body weight. Based on the AUC/kg body weight-inhalation dose curve and the AUC/kg body weight after oral administration, inhalation equivalent doses of orally administered CHCl3 were calculated. Calculation of inhalation equivalent doses allows the body burden due to CHCl3 by inhalation exposure and oral exposure to be directly compared. This type of comparison facilitates risk assessment in humans exposed to CHCl3 by different routes. Our results indicate that when calculating inhalation equivalent doses of CHCl3, it is critical to include the AUC from the exposure period in addition to the AUC after the end of the exposure period. Thus, studies which measure the concentration of volatile organic compounds in the blood during the inhalation exposure period are crucial. The data reported here makes an important contribution to the physiologically based pharmacokinetic (PBPK) database of CHCl3 in rodents.

Inhalation exposure to 1,2-dichloropropane: Distribution of blood and tissue concentrations of 1,2-dichloropropane in rats during and after exposure.

The present investigation was undertaken to determine the distribution and accumulation of 1,2-dichloropropane (DCP) in the blood, lung, liver, kidney, and abdominal fat of rats during and after inhalation exposure. Male rats were exposed to 80 or 500 ppm (v/v) DCP vapor for 360 min and the concentrations of DCP in the blood and tissues during the inhalation exposure period and after the end of the exposure period were measured. DCP accumulation in the abdominal fat was much greater than that in the blood and other tissues. Eighteen hours after the end of inhalation exposure, DCP could still be detected in the abdominal fat in the 80-ppm group, and in the blood, liver, kidney, and abdominal fat in the 500-ppm group. Our results are valuable data pertaining to the pharmacokinetics of DCP and to human health risk assessment of exposure to DCP vapor by inhalation.

Subchronic toxicity and carcinogenicity studies of 1,2-dichloropropane inhalation to mice.

The subchronic toxicity and carcinogenicity of 1,2-dichloropropane (DCP) in male and female B6D2F1 mice exposed to DCP by inhalation for 13 weeks or for 2 years was investigated. The DCP concentrations used were 50, 100, 200, 300 or 400 ppm (v/v) in the 13-week study, and 32, 80 or 200 ppm (v/v) in the 2-year study. Thirteen weeks inhalation exposure of mice to DCP caused death in the mice exposed to 300 ppm and above, and was found to induce hemolytic anemia and lesions of the liver, forestomach and heart. Two years exposure to DCP significantly increased the combined incidence of bronchiolo-alveolar adenomas and carcinomas in females and marginally increased the incidence of Harderian gland adenomas in males. As non-neoplastic lesion, atrophy and respiratory metaplasia in the olfactory epithelium, and respiratory metaplasia in the submucosal gland of the nasal cavity were increased. Thus, two years inhalation exposure to DCP is carcinogenic in female mice and there is a marginal evidence of carcinogenicity in males.

Distribution of blood and tissue concentrations in rats by inhalation exposure to 1,2-dichloroethane.

The compound 1,2-dichloroethane (DCE) is a ubiquitous environmental contaminant. The primary route of exposure of humans to DCE is inhalation of its vapor. The present investigation was undertaken to determine the distribution and accumulation of DCE in the blood, lung, liver, brain, kidney and abdominal fat of rats during and after inhalation exposure. Male rats were exposed to 160 ppm (v/v) of DCE vapor for 360 min and the concentrations of DCE in the blood and tissues during the inhalation exposure period and after the end of the exposure period were measured. DCE accumulation in the abdominal fat was much greater than that in the blood and other tissues. The information we obtained in this study is useful basic data pertaining to the pharmacokinetics of DCE and DCE-mediated carcinogenicity: Our results suggest that one of the factors involved in the induction of peritoneal tumors in rats exposed to DCE vapor by inhalation is DCE accumulation in the abdominal fat.

Multi-organ carcinogenicity by inhalation exposure to 2-Bromopropane in rats.

OBJECTIVE: The purpose of this study was to investigate the carcinogenicity of 2-bromopropane (2-BP) in rats. METHODS: Male and female F344 rats were exposed by whole body inhalation to 2-BP vapor at concentrations of 0, 67, 200, and 600 ppm for 6 h/day, 5 days/week for 2 years. RESULTS: All rats of both sexes exposed to 600 ppm died or became moribund within 85 weeks. Death/moribundity was caused by 2-BP induced tumors. In males, significantly increased tumors were malignant Zymbal's gland tumors; sebaceous adenoma and basal cell carcinoma of the skin/appendage; adenocarcinoma of the small/large intestine; follicular cell adenoma of the thyroid; fibroma of the subcutis, and malignant lymphoma of the lymph node. In addition, an increased trend in tumor incidence was found in the preputial gland, lung, forestomach, pancreas islet, brain, and spleen. In females, significantly increased tumors were adenocarcinoma and fibroadenoma of the mammary gland, squamous cell papilloma of the vagina, and large granular lymphocytic leukemia of the spleen. In addition, an increased trend in tumor incidence was found in Zymbal's gland, the clitoral gland, skin, large intestine, pancreas islet, uterus, and subcutis. Particularly, malignant Zymbal's gland tumors were induced even in males exposed to the lowest concentration, 67 ppm. CONCLUSION: Two-year inhalation exposure to 2-BP resulted in multi-organ carcinogenicity in rats. Based on sufficient evidence of carcinogenicity in this study, 2-BP has the potential to be a human carcinogen.

Carcinogenicity and chronic toxicity of butyl methacrylate in rats and mice by a two-year inhalation study.

We conducted a two-year inhalation study of butyl methacrylate using F344/DuCrlCrlj rats and B6D2F1/Crl mice. Rats were exposed to 0, 30, 125 and 500 ppm (v/v) and mice were exposed to 0, 8, 30 and 125 ppm (v/v) using whole-body inhalation chambers. Non-neoplastic lesions developed in the nasal cavities of both rats and mice, but neoplastic lesions were not found. There was also a positive trend in the incidence of large granular lymphocytic (LGL) leukemia in the spleen of male rats. No changes were observed in female rats. Overall, there is some evidence of carcinogenicity in male rats, but there is no evidence of carcinogenicity in female rats. In male mice, there was a positive trend by Peto's test in the incidence of hepatocellular adenomas, and the incidence of hepatocellular adenomas and hepatocellular carcinomas combined was significantly increased compared to the controls by Fisher's exact test in the 30 ppm exposed male group. In female mice, the incidence of hemangiosarcoma in all organs combined showed a positive trend by Peto's test. Therefore, there is some evidence of carcinogenicity in male mice, and there is equivocal evidence of carcinogenicity in female mice.

Carcinogenicity of ortho-phenylenediamine dihydrochloride in rats and mice by two-year drinking water treatment.

The carcinogenicity of ortho-phenylenediamine (o-PD) was examined by administrating o-phenylenediamine dihydrochloride (o-PD2HCl) in dinking water to groups of 50 F344/DuCrj rats and 50 Crj:BDF1 mice of both sexes for 2 years. The drinking water concentration of o-PD2HCl was 0, 500, 1,000 or 2,000 ppm (wt/wt) for male rats; 0, 250, 500 or 1,000 ppm for female rats; 0, 500, 1,000 or 2,000 ppm for male mice; and 0, 1,000, 2,000 or 4,000 ppm for female mice. Two-year administration of o-PD2HCl produced a dose-dependent increase in the incidences of hepatocellular adenomas and carcinomas in rats of both sexes and in female mice, and hepatocellular adenomas in male mice. In mice, the incidences of hepatocellular adenomas were increased at the lowest dose used in both males and females. Metastasis from hepatocellular carcinomas of rats occurred predominantly in the lung. Incidences of transitional cell papillomas and carcinomas in the urinary bladder were noted in male rats administered 2,000 ppm, together with an increased incidence of papillary and/or nodular hyperplasia of transitional epithelium. In mice, the incidence of papillary adenomas in the gall bladder, which is rare in mice, was increased in both males and females administered 2,000 ppm. Thus, o-PD is carcinogenic in two species, i.e., rats and mice of both sexes.

2,4-Dichloro-1-nitrobenzene exerts carcinogenicities in both rats and mice by two years feeding.

Carcinogenicity and chronic toxicity of 2,4-dichloro-1-nitrobenzene (2,4-DCNB) were examined by dietary administration to F344/DuCrj rats and Crj:BDF(1) mice of both sexes for 2 years. Dietary administration commenced when the animals were 6 weeks old. The dietary concentration of 2,4-DCNB was 0 (control), 750, 1,500 and 3,000 ppm (w/w) for male and female rats; 0, 750, 1,500 and 3,000 ppm for male mice; and 0, 1,500, 3,000 and 6,000 ppm for female mice. In rats, there was a dose-dependent and significant induction of renal cell adenomas and carcinomas in both sexes and of preputial glands adenomas in males. In all the 2,4-DCNB-fed groups of both sexes, the incidence of atypical tubular hyperplasia, a pre-neoplastic lesion in the kidney, in the proximal tubule was significantly increased. In mice, there was a dose-dependent and significant induction of hepatocellular adenomas, hepatocellular carcinomas, hepatoblastomas and peritoneal hemangiosarcomas in both sexes. The incidence of acidophilic hepatocellular foci was also significantly increased in female mice. Thus, clear evidence of carcinogenic activity of 2,4-DCNB by 2-year feeding was demonstrated in both rats and mice.

Inhalation carcinogenicity and toxicity of 1,2-dichloropropane in rats.

The toxicity and carcinogenicity of 1,2-dichloropropane (DCP) were examined by inhalation exposure of male and female F344 rats to DCP for either 13 wk or 2 years. In the 13-wk study, the DCP concentrations used were 125, 250, 500, 1000, or 2000 ppm (v/v), and in the 2-year study the DCP concentrations were 80, 200, or 500 ppm (v/v). Thirteen-week exposure to DCP induced hyperplasia in the respiratory epithelium and atrophy of the olfactory epithelium at 125 ppm and above. At the higher levels of exposure, hemolytic anemia and lesions of liver and adrenal gland were observed. Two-year exposure to DCP significantly increased incidences of papilloma in the nasal cavity of male and female rats exposed to 500 ppm DCP. In addition, three cases of esthesioneuroepithelioma were observed in the DCP-exposed male rats. Total nasal tumors increased in a concentration-dependent manner. Hyperplasia of the transitional epithelium and squamous cell hyperplasia, both of which were morphologically different from the hyperplasia of the respiratory epithelium observed in the 13-wk exposure study, occurred in a concentration-dependent manner; these lesions are considered to be preneoplastic lesions. Atrophy of the olfactory epithelium, inflammation of the respiratory epithelium, and squamous cell metaplasia were also seen in the 2-year study. These results demonstrate that DCP is a nasal carcinogen in rats. Lifetime cancer risks for humans exposed to DCP in the ambient air and work environment were quantitatively estimated, using both nonthreshold and threshold approaches, with the data obtained from the 2-year study.