Hepatotoxicity and carcinogenicity in female Sprague-Dawley rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): A pathology working group reevaluation

Risk assessment for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been based in part on the incidences of liver neoplasms in female Sprague-Dawley (SD) rats reported in a 2-year study conducted by Dow Chemical Corporation and published in 1978. In the years subsequent to the Dow report, the criteria for the diagnosis of proliferative hepatocellular lesions in the rat have been refined based upon ongoing study of these lesions. Because of this, PATHCO, Inc., was requested to conduct an independent review of the liver slides from the Dow TCDD study in order to assess how the current terminology might impact on interpretation of proliferative liver lesions in rats compared to the terminology used in the past. In March 1990, a pathology working group (PWG) was convened to review proliferative lesions in the livers of the female rats. The results of the PWG's evaluation of the microslides indicated a trend in tumor incidence similar to that published in 1978 but with a lower incidence of tumors in the middle and high dose females. Based on the morphologic findings, including the fact that the tumors were predominantly benign and usually associated with lesions of hepatic toxicity, the PWG considered this study to demonstrate a weak oncogenic effect of TCDD in the livers of female SD rats. As a result of its review, the PWG noted that in order to establish a relationship between the toxic hepatitis and the hepatocellular neoplasms, an independent review and grading of the toxic lesions in all female rats would be required. This subsequent review found that in the middle and high dose groups, tumors were observed only in animals with toxicity. In the low dose animals, there was an increase in the incidence and multiplicity of eosinophilic foci and a slight increase in the incidence of hepatotoxicity of a minimal degree of severity compared to controls, but there was no increase in the incidence of hepatocellular neoplasms. There appeared to be a distinct correlation between the presence of overt hepatotoxicity and the development of hepatocellular neoplasms.     

Review of a study reporting an association between 2,4-dichlorophenoxyacetic acid and canine malignant lymphoma: Report of an expert panel

Risk assessment for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been based in part on the incidences of liver neoplasms in female Sprague-Dawley (SD) rats reported in a 2-year study conducted by Dow Chemical Corporation and published in 1978. In the years subsequent to the Dow report, the criteria for the diagnosis of proliferative hepatocellular lesions in the rat have been refined based upon ongoing study of these lesions. Because of this, PATHCO, Inc., was requested to conduct an independent review of the liver slides from the Dow TCDD study in order to assess how the current terminology might impact on interpretation of proliferative liver lesions in rats compared to the terminology used in the past. In March 1990, a pathology working group (PWG) was convened to review proliferative lesions in the livers of the female rats. The results of the PWG's evaluation of the microslides indicated a trend in tumor incidence similar to that published in 1978 but with a lower incidence of tumors in the middle and high dose females. Based on the morphologic findings, including the fact that the tumors were predominantly benign and usually associated with lesions of hepatic toxicity, the PWG considered this study to demonstrate a weak oncogenic effect of TCDD in the livers of female SD rats. As a result of its review, the PWG noted that in order to establish a relationship between the toxic hepatitis and the hepatocellular neoplasms, an independent review and grading of the toxic lesions in all female rats would be required.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic toxicity/carcinogenicity study of trans-anethole in rats

A chronic feeding study was carried out in rats with trans-anethole. The test substance was administered in the diet to groups (n = 26-78) of 312 male and 312 female Sprague-Dawley rats at concentrations of 0, 0.25, 0.5 and 1% for 117-121 wk. The average intakes of trans-anethole varied from 105-550 mg/kg body weight/day. No apparent treatment-related reactions were noted. The only effect was a transient retardation of body-weight gain. No excess mortality was caused by the treatment. No abnormalities related to treatment were seen on necropsy except for reduced adiposity in the highest dose groups. Haematological assessments did not reveal any changes related to treatment. Histological examination revealed certain non-neoplastic and neoplastic lesions common in older rats. The incidence of some hepatic lesions was significantly higher in some treated groups than in controls: altered cell foci (females of the 1% group), nodular hyperplasia (males of the 0.5% group and males and females of the 1% groups), benign tumours (females of the 1% group) and malignant tumours (females of the 1% group). The results are compared with those of previous investigations. The authors of this study stress that the low incidence of hepatocarcinomas is restricted to a single species and sex and to the highest dose tested. This pattern of species, sex and dose dependency strongly suggests that metabolic and pharmacokinetic studies will be helpful in interpreting the significance of the rat tumours with regard to the safe consumption of trans-anethole by man. The changes observed in this chronic feeding study are not thought to be of genetic origin and consequently trans-anethole does not constitute a significant carcinogenic risk to man. Further studies are in progress to substantiate this conclusion.     

Reevaluation of a twenty-four-month chronic toxicity/carcinogenicity study of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the B6C3F1 hybrid mouse

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been widely used as an explosive in U.S. army munitions formulations since World War II. Two-year carcinogenicity studies revealed RDX to be noncarcinogenic in two strains of rats, but a 2-year carcinogenicity study in B6C3F1 mice revealed an increased incidence of hepatocellular neoplasms in females. Based on results of the study in B6C3F1 mice, RDX has been classified as a possible carcinogen. The authors reevaluated the archived histological sections from the B6C3F1 mouse study, using current histopathologic diagnostic criteria and interpretations. The earlier evaluation showed a statistically significant increase in the incidence of hepatocellular adenoma/carcinoma in female mice from the three highest dose groups (7, 35, and 175/100 mg/kg/day). The revaluation yielded a slightly lower incidence at each of the dose levels in female mice. The reduced number of hepatocellular neoplasms was largely due to reclassification of hepatocellular adenomas as foci of cytoplasmic alteration, in compliance with current diagnostic criteria. The reevaluation was reviewed by a pathology working group (PWG), which arrived at a consensus classification of each lesion. Based on the consensus diagnoses of the PWG, only one female group (35 mg/kg/day) showed a significant increase when compared to controls. The incidence of hepatocellular neoplasms for all groups, including the 35 mg/kg/day group, was within the reported incidence range for spontaneous hepatocellular neoplasms in female B6C3F1 mice. The increased incidence of hepatocellular neoplasms in female mice given RDX at 35 mg/kg/day was interpreted as equivocal evidence of a carcinogenic effect.     

Chronic Toxicity and Carcinogenic Evaluation of Diisononyl Phthalate in Rats

Groups of 110 Fischer 344 rats/sex were fed diisononyl phthalate(DINP) at dietary levels of 0, 0.03, 0.3, and 0.6 wt% for periodsup to 2 years. Interim sacrifices of 10 predesignated rats/sexsol;dosewere at 6, 12, and 18 months with surviving animals sacrificedat 24 months. At study termination, survival was in excess of60% for every group. At the mid or high dose, the followingbiological effects were noted: slight decreases in food consumptionand body weight; slight increase in mortality; a dose-relatedincrease in relative organ weights of liver and kidney; andsome slight effects on urinalysis, hematologic, and clinicalchemistry parameters. No peroxisome induction was observed inlivers of treated rats compared with controls. No clear treatment-relatednonneoplastic or neoplastic lesions were found. However, mononuclearcell leukemia (MNCL) and changes known to be associated withan increased incidence of MNCL were seen in the mid-dose andhigh-dose groups. A literature review suggests that MNCL isa common finding in aging F344 rats and that this increasedincidence in rats treated with DINP is not relevant to man.A clear no-observed-effect level was demonstrated for all biologicalend points at a dietary level of 0.03 wt% or approximately 17mgsol;kgsol;day of DINP.     

Lifetime (149-week) oral carcinogenicity study of vinyl chloride in rats

A lifetime (149-wk) oral carcinogenicity study of vinyl chloride monomer (VCM) was carried out. Four groups of Wistar rats were used, each consisting of 100 males and 100 females, except for the high-dose group, which comprised 50 males and 50 females. VCM was administered by incorporating polyvinyl chloride powder with a high content of VCM into the diet. The actual exposure levels of VCM were 0 (control), 0.014, 0.13 and 1.3 mg VCM/kg body weight/day. Detailed histopathological examination was restricted to the liver. In the final stage of the study, the mortality in the high-dose group was slightly higher than in controls. A variety of VCM-related liver lesions was found in the high-dose group. The lesions included increased incidences of liver-cell polymorphism, hepatic cysts, foci of cellular alteration, neoplastic nodules, hepatocellular carcinomas and angiosarcomas. Compared with controls, there were increased incidences of hepatic foci of cellular alteration in females of the mid-dose group and of basophilic foci of hepatocellular alteration in females of both the low- and mid-dose groups. There was no evidence that feeding of VCM affected the incidence of tumours in organs other than the liver. Thus, the present study showed that the feeding of VCM at a level of 1.3 mg/kg body weight/day can induce neoplastic and non-neoplastic changes in the livers of male as well as female rats. The feeding of 0.014 or 0.13 mg VCM/kg body weight/day may result in an increased incidence of (basophilic) foci of cellular alteration in the liver of female rats. It was concluded that 0.13 mg VCM/kg body weight/day is the no-observed-adverse-effect level with respect to the induction of tumours in rats.     

NTP technical report on the toxicology and carcinogenesis studies of beta-myrcene (CAS No. 123-35-3) in F344/N rats and B6C3F1 mice (Gavage studies)

Beta-myrcene, an acyclic unsubstituted monoterpene, and the essential oils which contain it are used as intermediates in the production of terpene alcohols (geraniol, nerol, and linalool), which, in turn, serve as intermediates in the production of aroma and flavor chemicals. Thus beta-myrcene is used widely in cosmetics, soaps, and detergents and as a flavoring additive in food and beverages. Beta-myrcene is also the major constituent of hop and bay oils, which are used in the manufacture of alcoholic beverages. Beta-myrcene was nominated for study by the National Institute of Environmental Health Sciences based on its high production volume, high level of human exposure, and structural relationship to d-limonene, which induced neoplasms in the kidneys of male rats in association with hyaline droplet nephropathy (NTP, 1990). Male and female F344/N rats and B6C3F1 mice were administered beta-myrcene (greater than 90% pure) by gavage for 3 months or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes. 3-MONTH STUDY IN RATS: Groups of 10 male and 10 female rats were administered 0, 0.25, 0.5, 1, 2, or 4 g beta-myrcene/kg body weight in corn oil by gavage, 5 days per week for 14 weeks. Additional groups of 10 male and 10 female special study rats were administered the same doses for 23 days. All core study rats in the 4 g/kg groups died during the first week of the study except one male that died on day 11. One to three rats in the 1 and 2 g/kg groups and one 0.5 g/kg male died by week 10 of the study. One 2 g/kg female died during the last week of the study. Except for lesion incidence data in groups administered 2 g/kg or less, data from rats that died early were excluded from the analysis and summary tables. Mean body weights were significantly decreased in male rats in the 0.5, 1, and 2 g/kg groups. Special study rats in the 4 g/kg groups died by the end of the first week. Dose-related clinical findings in animals that died early included thinness, lethargy, abnormal breathing, and ruffled fur. Right kidney and liver weights of dosed males and females were generally significantly greater than those of the vehicle controls. In special study rats evaluated on day 23, the incidences and severities of chronic progressive nephropathy (CPN) and renal tubule degeneration were increased in 2 g/kg males. At the end of the 3-month study, the incidences of renal tubule necrosis were significantly increased in all dosed groups of males and females. At 3 months, the incidences of olfactory epithelium degeneration in 2 g/kg males and females were significantly increased, and the severities were increased. The incidences of chronic inflammation in 1 and 2 g/kg males and females were significantly increased. All 2 g/kg males and females had splenic atrophy. In the mesenteric lymph node, significantly increased incidences of atrophy occurred in 2 g/kg males and 1 and 2 g/kg females. Acute inflammation of the forestomach occurred in four 2 g/kg females. The incidences of porphyrin pigmentation in the Harderian gland of males administered 0.5 g/kg or greater were significantly increased. 3-MONTH STUDY IN MICE: Groups of 10 male and 10 female mice were administered 0, 0.25, 0.5, 1, 2, or 4 g beta-myrcene/kg body weight in corn oil by gavage, 5 days per week for 14 weeks. All 4 g/kg male and female mice died during week 1; nine 2 g/kg males and eight 2 g/kg females died by week 4. The mean body weights of 1 g/kg males were significantly less than those of the vehicle controls. Clinical findings in animals that did not survive to the end of the study included thinness, lethargy, and abnormal breathing. The right kidney weights of 1 g/kg females and the liver weights of females administered 0.5 or 1 g/kg were significantly increased. No histopathology changes were observed in mice administered 1 g/kg or less. The 2 and 4 g/kg mice were not evaluated due to early deaths. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were administered 0, 0.25, 0.5, or 1 g beta-myrcene/kg body weight in corn oil by gavage, 5 days per week for 105 weeks. All 1 g/kg male rats died before the end of the study due to renal toxicity. Compared to vehicle controls, the mean body weights of 0.25 and 0.5 g/kg males were slightly greater, and mean body weights of 1 g/kg males and females were at least 8% less than those of vehicle controls after 11 weeks and 13 weeks, respectively. In the standard evaluation of the kidney, the incidence of renal tubule adenoma was significantly increased in 0.5 g/kg male rats, and the combined incidences of renal tubule adenoma or carcinoma were significantly increased in 0.25 and 0.5 g/kg males. In both the extended evaluation and the combined standard and extended evaluations, the incidences of renal tubule adenoma and the combined incidences of renal tubule adenoma or carcinoma were significantly increased in the 0.25 and 0.5 g/kg groups of males. The incidences of renal tubule nephrosis (nephrosis) were markedly increased in all dosed groups of both sexes except in 0.25 g/kg females. The incidences of papillary mineralization in 0.25 and 0.5 g/kg males were significantly increased. Significantly increased incidences of nephropathy occurred in dosed females, and the severity was increased in the 0.5 and 1 g/kg males and females. The incidences of hyperplasia of the transitional epithelium lining the pelvis and overlying the renal papilla were significantly increased in all dosed groups of males and females. In male rats, the incidences of focal suppurative inflammation were significantly increased in the 0.25 and 0.5 g/kg groups. A significantly increased incidence of chronic active inflammation of the nose occurred in 0.5 g/kg males. Also in 0.5 g/kg males, the incidence of chronic active inflammation of the forestomach was increased. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were administered 0, 0.25, 0.5, or 1 g beta-myrcene/kg body weight in corn oil by gavage, 5 days per week for 104 or 105 weeks. Survival of 1 g/kg mice was significantly less than that of the vehicle controls; the cause of the deaths was uncertain. Mean body weights of 1 g/kg males were at least 8% less than those of the vehicle controls between week 8 and week 56. Mean body weights of 0.5 g/kg females were at least 7% less than those of the vehicle controls after week 17, and those of 1 g/kg females were at least 8% less from week 11 to week 96. The incidences of liver neoplasms were significantly increased in 0.25 and/or 0.5 g/kg males and 0.25 g/kg females. Liver neoplasms included hepatocellular adenoma and hepatocellular carcinoma in males and females and hepatoblastoma in males. The incidences of hepatocellular hypertrophy were significantly increased in 0.5 g/kg males and females, as was the incidence of mixed cell focus in 0.5 g/kg females. The incidences of bone marrow atrophy and lymph node follicle atrophy in the spleen were significantly increased in 0.5 g/kg females. In the forestomach, there were significantly increased incidences of inflammation and epithelial hyperplasia in 0.5 g/kg females. GENETIC TOXICOLOGY: beta-myrcene did not show evidence of genotoxicity in assays conducted by the NTP. No mutagenicity was observed in any of several strains of Salmonella typhimurium or Escherichia coli in two independent Ames assays conducted with and without exogenous metabolic activation. In addition, no significant increase in frequency of micronucleated normochromatic erythrocytes, biomarkers of chromosomal damage, was observed in male or female mice administered beta-myrcene for 3 months by gavage. CONCLUSIONS: Under the conditions of these 2-year gavage studies, there was clear evidence of carcinogenic activity of beta-myrcene in male F344/N rats based on increased incidences of renal tubule neoplasms. There was equivocal evidence of carcinogenic activity of beta-myrcene in female F344/N rats based on increased incidences of renal tubule adenoma. There was clear evidence of carcinogenic activity of beta-myrcene in male B6C3F1 mice based on increased incidences of hepatocellular adenoma, hepatocellular carcinoma, and hepatoblastoma. There was equivocal evidence of carcinogenic activity of beta-myrcene in female B6C3F1 mice based on marginally increased incidences of hepatocellular adenoma and carcinoma. Administration of beta-myrcene induced nonneoplastic lesions in the kidney of male and female rats, nose of male rats, and liver of male and female mice. Synonyms: 2-Methyl-6-methylene-2,7-octadiene; 7-methyl-3-methylene-1,6-octadiene; myrcene.     

Carcinogenicity and Toxicity of Inhaled Nitrobenzene in B6C3F1 Mice and F344 and CD Rats

The potential carcinogenicity and toxicity of inhaled nitrobenzenewere evaluated following chronic (2-year) exposure in mice andrats. Male and female B6C3F1 mice were exposed to 0, 5, 25,or 50 ppm nitrobenzene, while male and female F344 rats andmale CD rats were exposed to 0, 1, 5, or 25 ppm nitrobenzene.All exposures were for 6 hr/day, 5 days/week excluding holidays,for a total of 505 days over 2 years. Survival was not adverselyaffected by nitrobenzene exposure, and only mild exposure-relateddecreases in body weights (<10% of control) were occasionallynoted. Nitrobenaene exposure resulted in increased incidenceof neoplasia in male B6C3F1 mice (pulmonary alveolar/bronchiolarand thyroid follicular cell neoplasms), female B6C3FI mice (mammarygland neoplasms), male F344 rats (hepatocellular and renal neoplasms),female F344 rats (endometrial stromal neoplasms), and male CDrats (hepatocellu lar neoplasms). In addition, there were marginalincreases in the incidence of hepatocellular neoplasia in femaleB6C3F1 mice and thyroid follicular neoplasia in male F344 rats.Groups of nitrobenzene-exposed mice and rats with increasedincidence of renal and thyroid neoplasia also had increasedincidences of hyperplasia in these tissues. Toxicity resultingfrom chronic inhalation of nitrobenzene was manifested by methemoglobinemia,anemia, and adaptive or degenerative changes in the nose, liver,and testis. The results indicate that inhaled nitrobenzene iscarcinogenic and toxic in mice and rats, and that the spectrumof these responses in animals is dependent on species, sex,and genetic background.     

The FEMA GRAS assessment of trans-anethole used as a flavouring substance. Flavour and Extract Manufacturer's Association.

This publication is the fourth in a series of safety evaluations performed by the Expert Panel of the Flavour and Extract Manufacturers' Association (FEMA). In 1993, the Panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavouring substances under conditions of intended use. In this review, scientific data relevant to the safety evaluation of trans-anethole (i.e. 4-methoxypropenylbenzene) as a flavouring substance is critically evaluated by the FEMA Expert Panel. The evaluation uses a mechanism-based approach in which production of the hepatotoxic metabolite anethole epoxide (AE) is used to interpret the pathological changes observed in different species and sexes of laboratory rodents in chronic and subchronic dietary studies. Female Sprague Dawley rats metabolize more trans-anethole to AE than mice or humans and, therefore, are the most conservative model for evaluating the potential for AE-induced hepatotoxicity in humans exposed to trans-anethole from use as a flavouring substance. At low levels of exposure, trans-anethole is efficiently detoxicated in rodents and humans primarily by O-demethylation and omega-oxidation, respectively, while epoxidation is only a minor pathway. At high dose levels in rats, particularly females, a metabolic shift occurs resulting in increased epoxidation and formation of AE. Lower activity of the "fast" acting detoxication enzyme epoxide hydrolase in the female is associated with more pronounced hepatotoxicity compared to that in the male. The continuous intake of high dose levels of trans-anethole (i.e. cumulative exposure) has been shown in dietary studies to induce a continuum of cytotoxicity, cell necrosis and cell proliferation. In chronic dietary studies in rats, hepatotoxicity was observed when the estimated daily hepatic production of AE exceeded 30 mg AE/kg body weight. In female rats, chronic hepatotoxicity and a low incidence of liver tumours were reported at a dietary intake of 550 mg trans-anethole/kg body weight/day. Under these conditions, daily hepatic production of AE exceeded 120 mg/kg body weight. Additionally, neither trans-anethole nor AE show any evidence of genotoxicity. Therefore, the weight of evidence supports the conclusion that hepatocarcinogenic effects in the female rat occur via a non-genotoxic mechanism and are secondary to hepatotoxicity caused by continuous exposure to high hepatocellular concentrations of AE. trans-Anethole was reaffirmed as GRAS (GRASr) based on (1) its low level of flavour intake (54 microg/kg body weight/day); (2) its metabolic detoxication pathway in humans at levels of exposure from use as a flavouring substance; (3) the lack of mutagenic or genotoxic potential; (4) the NOAEL of 120 mg trans-anethole/kg body weight/day in the female rat reported in a 2 + -year study which produces a level of AE (i.e. 22 mg AE/kg body weight/day) at least 10,000 times the level (0.002 mg AE/kg body weight day) produced from the intake of trans-anethole from use as a flavouring substance; and (5) the conclusion that a slight increase in the incidence of hepatocellular tumours in the high dose group (550 mg trans-anethole/kg body weight/day) of female rats was the only significant neoplastic finding in a 2+ -year dietary study. This finding is concluded to be secondary to hepatotoxicity induced by high hepatocellular concentrations of AE generated under conditions of the study. Because trans-anethole undergoes efficient metabolic detoxication in humans at low levels of exposure, the neoplastic effects in rats associated with dose-dependent hepatotoxicity are not indicative of any significant risk to human health from the use of trans-anethole as a flavouring substance.     

Inhalation toxicology and carcinogenesis studies of propylene glycol mono-t-butyl ether in rats and mice

Propylene glycol mono-t-butyl ether (PGMBE) is used as a solvent in a variety of commercial applications. Male and female F344/N rats and B6C3F(1) mice were exposed to PGMBE by whole-body inhalation for 2 or 14 weeks (0, 75, 150, 300, 600, or 1200 ppm) or 2 years (0, 75, 300, or 1200 ppm); male NBR rats were exposed for 2 weeks. The kidney and the liver were targets of PGMBE toxicity in rats. Renal lesions suggestive of alpha(2u)-globulin nephropathy were observed in male F344/N, in the 2 and 14-week studies, no kidney lesions were seen in NBR rats. In the 2-year study, male rats displayed exposure-related nonneoplastic lesions in the kidney, and may have shown marginal increases in tubular neoplasms. In the liver, the incidences of hepatocellular adenomas occurred with a positive trend in male rats, and may have been related to PGMBE exposure. In mice of both sexes, the major target of PGMBE toxicity was the liver. In the 2-week study, liver weights and in the 14-week study, liver weights and the incidences of centrilobular hypertrophy were increased. In the 2-year study, the incidences of exposure-related hepatocellular adenoma, adenoma or carcinoma combined, and hepatoblastoma occurred with a positive trend, and were significantly increased in 1200 ppm groups. In summary, exposure to PGMBE resulted in nonneoplastic lesions of the kidney characteristic of alpha(2u)-globulin nephropathy, and may have increased renal tubular neoplasms in male rats. Exposure to PGMBE also produced increases in hepatic tumors in male and female mice.     

Spontaneous renal tumors in two rats from a thirteen week rodent feeding study with grain from molecular stacked trait lepidopteran and coleopteran resistant (DP-ØØ4114-3) maize

A thirteen week feeding study was conducted by feeding young adult male and female Sprague Dawley [Crl:CD®(SD)] rats diets containing grain from genetically modified (GM) DP-ØØ4114-3 maize that was either untreated (4114) or treated in the field with glufosinate ammonium (4114GLU). Control rats were fed diets containing the same concentration of near isogenic, non-GM maize grain (091) or one of three types of commercially available non-GM maize grain. At the end of the in-life phase, renal tubule tumors were reported in two male rats consuming diets containing 4114 maize grain. An expert panel of pathologists was convened as a Pathology Working Group (PWG) to review coded kidney histology sections from control (091) and treated (4114 and 4114GLU) male rats. The objectives were for the panel to characterize the histopathologic findings and to interpret their relationship to consumption of the indicated diet. The PWG concluded unanimously that the kidney tumors were characteristic of amphophilic-vacuolar (AV) tumors and AV atypical tubular hyperplasia which represent a distinctive phenotype that has been reported to occur sporadically in young Sprague Dawley Rats. The PWG determined that the neoplasms and atypical tubular hyperplasias were multicentric and bilateral which typifies tumors of familial origin. Degenerative/regenerative or cytotoxic changes consistent with nephrotoxicity leading to tumor induction were not observed in these rats and thus supports the conclusion that tumors were unrelated to consumption of the test diet. It was the unanimous opinion of the PWG that the proliferative renal tubule cell lesions were spontaneous and not related to consumption of diets containing 4114 maize grain.     

Carcinogenicity of toxaphene: a review.

Toxaphene is highly carcinogenic in rats and mice. Toxaphene induced malignant neoplasms of the liver in rats. Neoplasms at all sites, as well as malignant neoplasms, were increased in male and female rats ingesting toxaphene. Sarcomas were found more often in male rats and carcinomas in female rats. Neoplasms of the endocrine organs were also increased in male and female toxaphene-treated rats. The incidence of neoplasms of the reproductive system was increased in female rats, as was the incidence of mammary gland neoplasms in male rats. Toxic changes in male rats given toxaphene included interstitial fibrosis of the kidney and atrophy of the testes. Toxaphene induced malignant neoplasms of the liver in male and female mice. The incidence of malignant neoplasms at all sites was also increased. In addition to hepatic neoplasms, male mice had leukemia or lymphosarcoma and females had sarcomas of the uterus.     

Chronic toxicity/carcinogenicity studies of gentian violet in Fischer 344 rats: two-generation exposure

A chronic feeding study was carried out in the F1a generation of dosed Fischer 344 rats of both sexes with gentian violet (GV). The test substance was administered in the diet to 570 male and 570 female rats at dose levels of 0 (control), 100, 300 and 600 ppm for 24 months. Rats were killed and necropsied after 12, 18 and 24 months of continuous dosing. Measurements of body weights, food consumption (and dose rate) and mortality and the results of histopathological examination were analysed statistically. Male and female rats fed 600 ppm GV for 24 months showed a decrease in body weights. Average food consumption based on g food/kg average body weight was essentially equal in all groups. Mortality at the end of the study (24 months) was approximately 33% in the controls for both males and females and approximately 66% in females of the high-dose group and 48 and 39% in males of the mid- and high-dose groups, respectively. All dose-related neoplastic pathology was noted at the final necropsy. Following 24 months of dosing, there was a significant difference from the controls in the incidence of follicular cell adenocarcinoma of the thyroid gland for both males (600 ppm GV) and females (300 and 600 ppm GV). Although the incidences were very low, statistical analysis showed a significant difference from the controls for hepatocellular adenomas in the mid-dose group of the females and the mid- and high-dose groups of the males. A dose-time-related incidence of mononuclear cell leukaemia was also noted in the females. There was high background incidence of the leukaemia. Several non-neoplastic dose-related lesions were observed in both males and females, principally in the 18- and 24-month necropsies. Almost all of these lesions were focal changes in the liver, many of which were probably related to the mononuclear cell leukaemia.     

The subchronic oral toxicity of ethane, 1,2-bis(pentabromophenyl) (Saytex 8010) in rats

Ethane, 1,2-bis(pentabromophenyl) (EBP; CAS no. 8452-53-9) dose levels of 0, 100, 320 and 1000 mg/kg/day administered to rats by gavage in corn oil for 90 consecutive days produced no compound-related clinical signs of systemic toxicity, ocular lesions, or alterations in urinalysis, clinical chemistry, and hematology values in the treated or recovery groups. No biologically or toxicologically significant differences were observed in body weights, body weight gains, and food consumption. Statistically significant differences were found between control and high-dose animals in mean absolute or relative liver weights. Histomorphological evaluation showed in male rats low-grade liver changes consisting of minimal to slight hepatocellular vacuolation (high-dose males) and minimal to slight centrilobular hepatocytomegaly (high- and possibly mid-dose males). These changes had resolved by the end of the 28-day recovery period. No treatment-related changes were found in the livers of female rats. No treatment-related histomorphologic changes were present in any of the other tissues examined in either sex, except for evidence of aspirated test article in individual rats. The 90-day EBP no-adverse-effect level in the rat was > or = 1000 mg/kg/day, and was consistent with that of the preceding 28-day study (no-effect level > or = 1250 mg/kg/day). EBP's lack of toxicity is likely related to poor bioavailability due to its high molecular weight and low solubility.     

Inhalation toxicity of dimethyl piperidinone

A mixture of 1,3-dimethyl-2-piperidinone and 1,5-dimethyl-2-piperidinone (DMPD) (approximately 63-37 parts by weight) was tested for its inhalation toxicity in rats following 90-day repeated exposures. Male and female rats were exposed whole-body to either 0, 51, 230, or 310 mg/m(3) DMPD for 6 h/day, 5 days/weak for 90 days. Clinical signs, growth, clinical pathology, tissue pathology, neurobehavior, neuropathology, and semen quality were evaluated. No compound-related adverse effects were noted in clinical signs, body weights, food consumption, clinical laboratory evaluations, neurobehavioral evaluations, neuropathology, or sperm counts. Laryngeal changes consisting of minimal squamous epithelial hyperplasia and degeneration/necrosis of the cartilage were present in male and female rats exposed to 310 mg/m(3) both immediately following exposure and after the 1-month recovery period Male rats exposed to DMPD had increased relative kidney weights, increased formation of hyaline droplets and granular casts, and increased incidence of chronic progressive nephropathy. These kidney effects are consistent with increased accumulation of the urinary protein alpha(2 mu)-globulin, which has been well essential for several xenobiotics. The subsequent increased incidence of progressive nephropathy was specific to male rats with the alpha(2 mu) syndrome. Male and female rats exposed to 230 or 310 mg/m(3) had centrilobular hepatocellular hypertrophy, and male rats exposed to 310 mg/m(3) had increased relative liver weights. These liver changes were reversible following the recovery period and were considered not to represent adverse toxicological effects of treatment. Since the male rat-specific renal findings do not connote adversity for man and are net considered relevant to human hazard assessment, the no-observed-effect level in male and female rats was 230 mg/m(3), based on the microscopic changes in the larynx exposed to 310 mg/m(3).     

Carcinogenesis studies of benzophenone in rats and mice.

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

The effects of dietary butylated hydroxytoluene on liver and colon tumor development in mice

Male and female C3H mice were fed a diet containing 0.5% or 0.05% of the antioxidant butylated hydroxytoluene (BHT). After 10 months, male but not female animals had a significantly increased incidence of liver tumors compared to animals kept on a BHT-free control diet. In a second experiment, male BALB/c mice were treated subcutaneously with the carcinogens dimethylhydrazine (DMH) or intrarectally with methylnitrosourea (MNU). A diet containing 0.5% BHT significantly increased the incidence of colon tumors in DMH treated animals but had no effect in mice given MNU. It is concluded that the effect of BHT on tumor development depends on strain and target organ examined and possibly also on the chemical carcinogen used.     

Toxicity and carcinogenicity of riddelliine in rats and mice

These investigations of riddelliine analyzed potential carcinogenesis and the utility of the female-rat/male-mouse design in bioassays and dose-response. Groups of 50 Fischer rats and B6C3F1 mice were gavage-administered riddelliine 5 days per week for 105 weeks. The dose levels for male rats were 0 or 1.0 mg/kg body weight; female rats 0, 0.01, 0.033, 0.1, 0.33, or 1.0 mg/kg; male mice 0, 0.1, 0.3, or 1.0, 3.0 mg/kg; and female mice 0 or 3.0 mg/kg. The dose groups were purposely designed to evaluate the dose-response relationship only in female rats and male mice. In rats, liver hemangiosarcoma, hepatocellular adenoma, and mononuclear cell leukemia were significantly increased in the 1.0 mg/kg male and female dose groups. Non-neoplastic lesions occurred in the liver and kidney of male and female rats. In mice, hemangiosarcomas increased significantly in the liver of males in the 3.0 mg/kg dose group. Alveolar/bronchiolar neoplasms in the 3.0 mg/kg dose group of female mice were significantly increased. Hepatocellular neoplasms were significantly decreased in the 1.0 mg/kg dose group of male and 3.0 mg/kg dose groups of male and female mice. Non-neoplastic lesions occurred in the liver and kidney of male and female, and lung and arteries of female mice. These studies demonstrate toxicity and carcinogenicity of riddelliine in rats and mice, and a dose-response relationship in female rats and male mice under the experimental conditions employed.     

Inhalation toxicity and carcinogenicity studies of cobalt sulfate.

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

Chronic toxicity and carcinogenicity to the urinary bladder of sodium saccharin in the in utero-exposed rat

In utero-exposed Charles River CD strain rats, the offspring of parents treated from weaning through mating, gestation and lactation, were fed sodium saccharin chronically at dietary levels of 0, 0.01, 0.1, 1.0, 5.0, and 7.5%. Calcium cyclamate was fed as a reference compound at a level of 5.0%. Groups of 48 male and 48 female weanlings were placed on the same regimen as their parents. The study was continued until the number of survivors in a group fell to 20% with the last survivors being killed approximately 28 months after the first weanlings were selected for the chronic study. Serial sacrifices were performed at 14 and 18 months. Treatment-related effects were not observed in hematological values, organ weights, and survival. Average weaning weights were decreased in litters from parents receiving 5.0 and 7.5% sodium saccharin and 5.0% calcium cyclamate. Some of the initial weaning weight depression was overcome, but the rats on these dose levels had lower average body weights throughout the study. The incidence and types of neoplasms and nonneoplastic lesions, other than urinary bladder neoplasms and hyperplasia, were typical of the aged rat and were not treatment related. A significantly increased incidence of urinary bladder hyperplasia occurred in female rats that received 7.5% sodium saccharin, but the lesion was not morphologically precancerous. A significantly increased incidence of urinary bladder neoplasms occurred in the males fed 7.5% sodium saccharin. A total of 11 bladder neoplasms was observed in rats on study longer than 18 months; nine in the 7.5% saccharin group and one each in the control and 5.0% saccharin groups. There were nine neoplasms in males and two in females. Histologically, six of the neoplasms were classified as benign and five as malignant. All the malignant neoplasms occurred in the 7.5% saccharin group. The occurrence of the urinary bladder neoplasms could not be related to such predisposing factors as gross calculi, parasites, or hyperplasia.